Sae Final Sp01

2000-2001 FORMULA SAE RACECAR2000-2001 FORMULA SAE RACECAR

EE290/291 & ME272/273 SENIOR DESIGN PROJECTS EE290/291 & ME272/273 SENIOR DESIGN PROJECTS BY EE TEAM 1 & ME TEAM 15BY EE TEAM 1 & ME TEAM 15

SUSPENSION, STEERING, AND ENGINE CONTROL SUSPENSION, STEERING, AND ENGINE CONTROL SYSTEM DESIGN FINAL REPORTSYSTEM DESIGN FINAL REPORT

Team Members: Andy Bilmanis, ME Robert Hotaling, EE Jason Mangual, CMPE Michael McGee, EE Nnamdi Okam, EE Greg Pineau, ME Justin Pribanic, ME

Advisors:Professor John Ayers, Ph.D.: [email protected] Jim Cowart, Ph.D.: [email protected]

SAE Collegiate Design Series: http://www.sae.org/students/formula.htmUConn Racing Team: http://www.engr.uconn.edu/~ucracing

ME Due Date: May 7, 2001EE Due Date: May 9, 2001

http://www.engr.uconn.edu/~ucracing

http://www.sae.org/students/formula.htm

mailto:[email protected]

mailto:[email protected]

Glossary

Ackerman’s Principal – While turning, the outer tire follows a larger radius than

the inner tire. To account for this the control arm must connect to the upright

along an imaginary line that connects the spindle and the center of the rear axis

Autocross – A competition for automobiles that tests driving skill and speed.

Bump Steer – Toe-in/out of a tire caused by its vertical displacement

Caster Angle – Caster is a line from ball joint to ball joint seen from the side view

Camber – The tilting of the tires about the horizontal axis perpendicular to the

direction of rotation

Center of Gravity – Location where force would be if the mass of the vehicle was

lumped

Chicanes – S–turn in a race track

Coil-on-plug system – Ignition firing scheme where an individual coil is used for

each cylinder

Droop – Negative displacement of the wheel

Five-link suspension – A suspension system with four points of attachment to the

frame

Four-link suspension – A suspension system with five points of attachment to the

frame

Front Roll Center – Point that the front of the vehicle desires to roll about,

determined by front suspension geometry

Jacking – When the tires skip as the vehicle turns

Jounce – Positive displacement of the wheel

Kingpin inclination – An imaginary line drawn from the center of the top ball joint

to the center of the lower ball joint, looking at the suspension from the front of the

car

LED – light emitting diode

McPherson struts – Suspension type where the shock is one of the suspension

arms

Proto-board – An experimental device for prototyping electronic circuits

2000-2001 Formula SAE Racecar

2

Rim spacing – Distance from centerline to the bolt on the rim

Roll Axis – The imaginary line that connects the front and the rear roll centers,

about which the body will rotate or roll

Rear Roll Center – Point that the rear of the vehicle desires to roll about,

determined by front suspension geometry

RPM (revolutions per minute) – Rate of revolution of a motor

Scrub radius – The distance between the two points created by the inter-section

of the wheel centerline (centerline of tire patch) and the steering axis with the

ground plane

Short-Long arm (SLA) – Suspension type using unequal length arms for top and

bottom

Solid axle – No independent suspension

Spindle – Connects The Wheel to the A-Arms, allows the tire to rotate

Steering rack – Rack & Pinion system that transmits steering wheel turn into tire

turn

Tire patch – Area of tire touching the ground

Toe-in/out – Toe-in is when the front of the tires angle in towards each other and

toe-out is when they angle away from each other

Torsen – Torque-Sensing (Gleason differential that biases torque)

Track – Distance between the outside edges of the tires when viewing the car

from the front

Trailing Arms – Independent suspension that is pivoted ninety degrees

TTL (Transistor-Transistor Logic) – A common semiconductor technology for

building discrete digital logic integrated circuits where the voltage swing is 0-5V

Uprights – Centerpiece of suspension, connect steering, shocks, A-arms, and

tires together

Waste Spark – Ignition firing scheme where two companion cylinders are fired

using one ignition coil

Wheelbase – Distance between the front and rear tire centers


3

Nomenclature

- stress (lbs/in2)

P - force (lbs)

A - area (in2)

M - moment (lbin)

I - moment of inertia (in4)

c - distance from force (in)

- critical force (lbs)

E - modulus of elasticity (lbs/in)

L – length (in)

r – radius (in)

psi – pounds per square inch (lbs/in2)


4

Abstract

This report describes two combined design projects that are to be

implemented through inter-disciplinary teamwork as components of the 2000-

2001 Formula SAE vehicle being built by the Formula SAE Chapter at the

University of Connecticut. The design project is motivated by the Formula SAE

student competition, and is funded by sponsorship support and the Electrical and

Computer Engineering Department. The first project to be discussed is designed

through a mechanical engineering senior design project while the second project

is the interdisciplinary senior design project between one Mechanical, one

Electrical and Computer Engineering, and three Electrical Engineering Students.

The Formula SAE car suspension design incorporates features that are

designed to make the car’s handling predictable as well as adjustable. The

adaptability of the car extends to meet the needs of different sized drivers, driver

preference, and varying track conditions. The goal of the suspension design is to

maintain the maximum accelerations in the lateral, positive, and negative

directions that can be achieved while competing during the Formula SAE

challenge. Some existing components are re-used, such as the rear five link

suspension arms, and the drive train so these will constrain several design

aspects. Similarly, the steering is designed to minimize bump steer while reusing

existing components such as the steering rack, uprights, rim spacers, and

spindles.

The engine control system for the Formula SAE racecar will offer a high

performance engine control system. It was specifically designed for a Honda F1

600cc motorcycle engine. The system provides electronic control of the fuel

injection and ignition system. The system uses feedback from the engine

combined with pre-programmed information to deliver metered fuel to the

cylinders, and ignition spark to the cylinders at the optimum time for peak engine

performance. This system is competitive in both performance and price with the

current complete fuel injection systems available from various manufacturers.


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TABLE OF CONTENTSGlossary.............................................................................................................................2Nomenclature.....................................................................................................................4Abstract..............................................................................................................................5Introduction........................................................................................................................8

Background..................................................................................................................10Market Research..........................................................................................................13

Discussion........................................................................................................................14Suspension Design......................................................................................................14

Static weight.............................................................................................................24Lateral load transfer due to lateral acceleration.......................................................25Longitudinal weight transfer due to negative acceleration........................................26Maximum loads achieved.........................................................................................27Maximum Tractive Forces........................................................................................27Factor of Safety Development..................................................................................28Design Overview......................................................................................................29Safety Considerations..............................................................................................39Manufacturing considerations...................................................................................39Modifications.............................................................................................................40

Engine Intake Design...................................................................................................41Motivation.................................................................................................................41Engine Considerations.............................................................................................41Powerplant Selection................................................................................................42Additional Engine Decisions.....................................................................................44EFI Requirements.....................................................................................................45Pulse Width Determination.......................................................................................48Valve Train Timing....................................................................................................52Engine Intake Manifold Design.................................................................................52Testing......................................................................................................................59

Engine Control Design.................................................................................................61Fuel Injection............................................................................................................61Engine Control System.............................................................................................62Engine Control Overview..........................................................................................65Crankshaft Sensor (Variable Reluctance Sensor)....................................................65Variable Reluctance Sensor (VRS) Interface Circuit................................................66MAP Sensor..............................................................................................................67Manifold Absolute Pressure (MAP) Sensor Circuit...................................................68Rich/Lean Adjustment Circuit...................................................................................69Ambient Air and Throttle Position sensors...............................................................70Driver Circuits...........................................................................................................70Fuel Injector Driver Circuit........................................................................................71Ignition System.........................................................................................................71Ignition Coil Driver Circuit.........................................................................................72Cylinder Compression Detector................................................................................74Microcontroller..........................................................................................................76

Implementation.............................................................................................................80Patent Opportunities....................................................................................................82

Budget..............................................................................................................................83Suspension...................................................................................................................83Engine Intake...............................................................................................................84Engine Control..............................................................................................................85


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Timeline...........................................................................................................................87Conclusion.......................................................................................................................88References.......................................................................................................................90Acknowledgements..........................................................................................................91Appendix..........................................................................................................................92

Appendix A – Figure List..............................................................................................92Appendix B – Timeline.................................................................................................93Appendix C – Tire Data................................................................................................94Appendix D – Valve Timing..........................................................................................95Appendix E – String Model...........................................................................................96Appendix F – Microcontroller.......................................................................................97

Port Schema.............................................................................................................97Microcontroller Code................................................................................................98

Appendix G – PCBoards Circuit Layout.....................................................................107Appendix H – RC Compression Damping..................................................................108Appendix H – RC Compression Damping..................................................................108Appendix I – RC Rebound Damping..........................................................................109Appendix J – Simulations of Cylinder Compression Detector....................................110Appendix K – Thank you to all of our Sponsors.........................................................111


7

Introduction

The objective of the Formula SAE competition is to design, build, and

compete with a prototype car that is of high performance in acceleration, braking,

and handling. The car was built assuming that a manufacturing firm could

produce the winning design at a rate of four cars per day in a limited production

run costing less than $30,000 for a prototype vehicle. Our project goal was to

create a competitive car that outperforms previous designs in the areas of engine

performance and suspension dynamics through interdisciplinary teamwork

between Mechanical, Electrical, and Computer Engineers.

The objective of our suspension system design was to maintain the

maximum traction during lateral, forward, and rearward accelerations while

responding to body roll and small vertical wheel movements. The force

generated by cornering, accelerating, and braking, or any combination of

cornering-accelerating and cornering-braking were directed to the vehicle’s

center of mass. Three planes represented by the SAE standard define the

center of mass of the vehicle. These planes are illustrated in Figure 1 below.

Figure 1 – Vehicle Coordinates


8

This coordinate system is used throughout the car’s design. However, this

coordinate system is local to front and rear suspension systems with the front

suspension and steering combined.

One way to build a successful first year car is to study the winning

competitors. Ideas were first generated during a visit to the May 2000

competition in Pontiac Michigan. Research continued through Internet sources

and enabled us to obtain a good idea of what features current winning designs

include. Winning designs such as Texas A&M produced brainstorming sessions

to develop an improved suspension design for the 2001 FSAE car. Creativity

and “thinking out of the box” are great tools when constructing preliminary

designs. Input from sources such as faculty, car clubs, classmates and friends

also supplied us with many ideas and solutions.

Since time was limited the team had to focus on basic implementations

rather than design ideals. Thus, the team met time deadlines and the projected

budget. It was our responsibility as Formula SAE car club members to fund

much of the project independently of our senior design projects. This underlying

factor was considered throughout the design process and limited us to reusing

components from previous years in some situations. The final design was a

combination of design constraints, creativity and communication.

The Engine Control System designed by the EE/CMPE and ME teams is

an electronic fuel injection and ignition system. The electronic fuel injection

system delivers fuel to the engine’s intake manifold, and the ignition system

delivers spark to each cylinder at the appropriate time. Both of these systems

must be controlled so that they will vary as needed with different temperature,

engine speed and load conditions. This process is accomplished using various

sensors, feedback to a microprocessor, and computer code in the

microprocessor.

Gasoline engines that are currently in use incorporate a variety of different

fuel injection systems. Virtually all automobiles use electronic fuel injection

systems to deliver fuel to the cylinders. Three common types of electronic fuel

injection (EFI) systems used today are throttle body injection (TBI), multi-port fuel


9

injection (MFI) and sequential fuel injection (SFI) systems. Throttle body

injection systems deliver all of the fuel for the engine at the same point at the

intake manifold inlet through one large fuel injector. This is somewhat like a

hybrid between fuel injection and a carburetor.

The most common types of fuel injection systems today are multi-port fuel

injection and sequential fuel injection. These are both systems where the fuel is

delivered to each individual cylinder by using separate fuel injectors for all the

cylinders. These injectors are located in the intake manifold runners in close

proximity to each individual cylinder. In multi-port fuel injection, the injectors are

actuated in groups (also known as bank firing). In sequential fuel injection, the

injectors are actuated individually just before each cylinder’s combustion stroke.

For sequential fuel injection, the engine stroke position must be known. This is

usually accomplished through the use of a camshaft position sensor. If bank

firing is used, there is no need for a camshaft position sensor to give an

indication of the engine’s stroke position. Sequential Fuel injection offers the

lowest exhaust emissions and the most efficient use of fuel, so it is usually

preferred over multi-port fuel injection by automobile manufacturers.

Background

In May 2001, the Society of Automotive Engineers (SAE) will be hosting

an annual student design competition for colleges and universities across the

country. The competition consists of developing and racing formula style

automobiles according to SAE specifications. The components of this project will

be used on the Uconn SAE Chapter’s car for this year’s competition.

This joint project, between both the Mechanical and Electrical and

Computer Engineering departments of Uconn, is to design and build certain

aspects of the racecar. The Mechanical students are focusing on two different

aspects the suspension and the engine. The components that the Electrical and

Computer Engineering students are responsible for are fuel injection and ignition

systems. The reason for designing the fuel injection system comes from the fact


10

that the Original equipment manufacturer (OEM) carburetor system on the

engine will not supply adequate fuel for hard cornering portions of the

competition. The ignition system design is a logical extension of the fuel injection

system design. Since both systems rely on the same parameters, the design of

an ignition system that will allow control of the spark timing and increase engine

performance can be made without a significant loss in time and resources.

Although the senior design project at the University of Connecticut only

concentrates on a few aspects of the vehicle, it is necessary to refer to the

overall competition. The references to the competition were included in order to

explain the requirements of a competitive car and how the project affected the

overall performance of the car. The objective of the Formula SAE competition

restated from page 8 of the rulebook is:

To conceive, design, fabricate, and compete with small formula-style

racing cars. The restrictions on the car frame and engine are limited so

that the knowledge, creativity, and imagination of the students are

challenged. The cars are built with a team effort over a period of about

one year and are taken to the annual competition for judging and

comparison with approximately 100 other vehicles from colleges and

universities throughout the world. The end result is a great experience for

young engineers in a meaningful engineering project as well as the

opportunity of working in a dedicated team effort.

For the purpose of the competition, the students assumed that a

manufacturing firm has engaged them to produce a prototype car for evaluation

as a production item. The intended sales market is the nonprofessional weekend

autocross racer. Therefore, the car should have very high performance in terms

of its acceleration, braking, and handling qualities. The car should also be low in

cost, easy to maintain, and reliable. In addition, the car’s marketability is

enhanced by other factors such as aesthetics, comfort and use of common parts.

The manufacturing firm is planning to produce four cars per day for a limited

production run and the prototype vehicle should cost below $30,000. The


11

challenge is to design and fabricate a prototype car that best meets these goals

and intents.

Each design will be compared and judged with other competing designs to

determine the best overall car. The cars will be judged both statically and

dynamically. Each car must be inspected before being permitted to enter any

aspect of the competition to ensure safety. The static events include

Presentation, Engineering design, and cost and manufacturing analysis.

Dynamic events are judged in areas of acceleration, skid-pad, autocross, fuel

economy, and endurance events. The combined total of both static and dynamic

events is 1000 points.

The desired dynamics of the vehicle can be summed up by two objectives.

The first objective is to maintain maximum lateral, positive, and negative

accelerations in a specified range of operating conditions. The second is to

produce a reliable engine management system that out performs other methods

of aspiration, spark, and fuel delivery. While the two objectives correspond to the

competition, each is designated as separate senior design projects.


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Market Research

Although there are several commercial fuel injection systems available,

none of the complete systems fit our needs. They were either too expensive or

did not provide all of the controls the engine needed. A search of prices was

done on www.rancefi.com and www.sdsefi.com. Table 1 below summarizes the

models we researched.

Product Manufacturer Cost Description/Comments74022A – Accel Closed Loop Auto/RV Computer and Harness Kit

Accel $880 The 74022A is a general conversion kit made to replace a carburetor. Therefore, it does not include ignition or timing system control.

EM-3 F Simple Digital Systems (SDS)

$1134 - $1300

Provides fuel injection and crank triggered, distributor-less ignition control on 4 and 6 cylinder engines.

E6K Haltech $1495 Provides fuel injection and ignition timing. Includes a one bar manifold air pressure (MAP) sensor, a 3-wire O2 sensor, a throttle position sensor (TPS), air and temperature sensors, software and cables.

Figure 2 – Various Commercially Available Fuel Injection/Ignition Systems

According to cost, the best low-end solution is the Accel 74022A closed

loop injection controller for 4, 6, 8, and 12 cylinder engines that are 600cc or

higher. This system allows for re-programmability of fuel injection and costs

$880, but does not include ignition control. A more advanced commercially

available solution is the Haltech E6K. This device is programmable and provides

multiple feedbacks and more engine control, but at a much higher price. There

are additional solutions at different costs between these two extremes.


13

http://www.sdsefi.com/

http://www.rancefi.com/

Discussion

Suspension Design

The autocross course is constructed of several components that are

typically found in formula racing: straight-aways, slaloms, constant radius turns,

hairpin turns, chicanes, multiple turns, and varying radius turns. The course is on

an asphalt parking lot surface generally termed “asphalt lake” in Michigan. The

length of one lap of the course is roughly ½ mile where several laps will be taken.

The straight-aways will be no longer than 200 feet with hairpins at either end, or

no longer than 150 feet with wide turns on the end. The minimum track width will

be 11.5 feet, constant turns 75 to 148 feet diameter, hairpin turns no less than 23

feet outside diameter, and slalom cones will have a spacing of 25 to 40 feet.

These dimensions directly correspond to maximum accelerations developed

while competing. From previous races, it is stated that these dimensions suggest

average speeds between 25 to 30 mph. Maximum speeds are also suggested to

be as high as 65 mph. Using this information, the forces generated were

determined and used to design the suspension geometry and components and

steering mechanism.

There exist many types of suspension systems today with differing

advantages and disadvantages. Choosing which system best suited our project

involved a number of factors, from which we selected an SLA (short-long arm)

set-up. The first factor was in our application where, in this type of autocross

race, the SLA design is very popular and suits the track conditions well. Another

factor involved our ability to ease budget constraints by reusing old car parts. As

an example, we reused the front uprights in a four-link SLA setup, with the rack

and pinion steering system. We chose the rack and pinion steering system since

it was the most common for an SLA setup and it kept us within budget. Some of

the other types of suspension systems considered include McPherson struts,

solid axle, and trailing arm.

There are seven different geometric configurations possible for a front

SLA suspension system. In order to narrow down our choices, we tested wheel


14

displacement verses both camber and roll center. We decided that these two

characteristics were the most important factors since they are essential in the

handling of the car. After reviewing our results, we were able to narrow our

system down to three possibilities. In the following table (Figure 3), all seven

SLA geometries are illustrated. The geometric setup shown third is the

suspension system that we are using.

Suspension Set-Up Wheel Displacement

Camber Roll Center

None

Negative

Positive

Always Negative

Always Positive

Always Positive

Positive Majority of

the Displacements

Always Negative

Negative Majority

of the

Displacements

Figure 3 – Suspension Setup Types


15

One of the most difficult parts of designing a suspension system is

compromising. There is no optimum suspension for all conditions; therefore, for

every improvement there is a sacrifice. The key is to decide what is most

important for your particular application. In our case, we had to account for a

race on a smooth track that contains many tight turns but can be subject to a

variety of weather conditions.

To fulfill our goal of maintaining the largest accelerations possible, we

examined the many components of a suspension design (the definitions of these

terms are conveniently defined during the discussion). The first heavily debated

design component examined was the roll axis, a line that connects the front and

rear roll centers, around which the car body rotates when lateral forces are

applied. The roll center is defined as the effective center that the body will

appear to rotate about. For roll centers with small radii, one could image a box

suspended by two short strings at two corners suspended as something of a

pendulum. The longer the string, the larger the pendulum, and the more minute

the angular displacements the box will achieve. As shown below, the body roll

Theta 1 is greater than Theta 2 with a longer roll center located below ground

level.

Figure 4 – Roll Center Location


16

Ground

Theta 1Theta 2

Theta 1 > Theta 2

L,rc2

L,rc1

Car Body

One of our sponsors, Altair Engineering, provided the team kinematic

software for the fall and spring semesters. The software is considered kinematic

because suspension geometry changes through wheel displacement. Much of

the geometry mentioned was calculated using this software and then verified by

a string calculator (see Appendix C). However, the software does not analyze

the dynamic response associated with a mass-spring-damper system, and is

used purely as an efficient tool to generate geometrical changes with wheel

displacement in all the specific geometrical areas considered in the design.

In order to understand the importance of the roll axis of a vehicle, the

dynamics had to be first examined. Essentially, the roll of the vehicle is a result

of the moment formed by the distance of the CG (center of gravity) from the roll

axis. The three factors that affect the roll axis of the vehicle are the front and

rear roll centers, and the CG. When a car goes into a turn, a lateral force is

exerted at its center of gravity. If the roll center is below the CG, a moment is

formed and the car appears to lean during the turn.

One of the difficulties involved with roll center selection is that it changes

with wheel displacement. One approach is to choose the region in which you

want to keep the roll center within for all displacements. The three basic regions

for the roll center location are the same height as the CG, below the ground, and

between the ground and the CG. It is usually not desirable to have your roll

center change between regions since this makes handling less predictable.

Another method is to design a suspension in which the roll center stays constant,

such as using parallel links, but this involves sacrificing other aspects of

handling.

At first analysis, it appeared the best arrangement would be to have the

CG and both roll centers on the same plane. This would create no moment and

would result in no body roll during cornering, but there were a few problems

involved. The first was that “jacking” could develop on high velocity turns.

“Jacking” happens when the tires skip around the turn, which is not desirable

since contact with the ground is not maintained and the ability to fulfill the

maximum lateral acceleration fails. The second problem involves the tune-ability


17

of the system. A problem with no roll is that the shocks are not being

compressed very much, and thus, the absorption of corning forces through the

suspension has been limited. A car with some degree of body roll can be

adjusted via spring rates of the shocks and anti-roll bar, but a car with no roll

cannot. Due to the number of factors affecting handling, it is desirable to be able

to adjust the system as needed.

The resultant moment must be investigated if the roll center is located

below the CG. If the roll center is too far below the generated moment, it will be

very large, causing the inner tires to lift off the ground. This is highly undesirable

since the result will be loss of both power and control. Our car will have a CG

approximately 11 inches above the ground. This has been determined by using

a geometric approach with the existing vehicle, and the following equation.

weightvehicletotal

differenceweightWheelbaseCGofHeight

*sin* 1

Using this equation, we decided that the moment for any roll center below the

ground would be too great. We then decided on a roll center between the ground

and the CG of the car. The following graph (see Figure 5) shows the range of roll

center heights for our car.

Figure 5 – Graph of Roll Center Height vs. Wheel Displacement

Our main controlling factor of the roll axis was the front suspension

geometry. The front is critical since that is where the steering is taking place.

The only sufficient geometries are those that incorporate both positive steering

and handling aspects. We can only change the rear suspension to a limited


18

extent since the rear wheels must be powered by an existing drive train. One

major suspension limitation was that we decided to reuse the old spindles. This

choice was made for two basic reasons. One, we found the setup suitable and

two, to simply keep cost down.

Camber is a very important feature in controlling the handling of a vehicle

during turning. Camber is defined as the tilting of the tires about the horizontal

axis perpendicular to the direction of rotation. Camber is adjusted by two

methods: static and dynamic camber. Static camber is gained through small

adjustments to the control arm lengths. Dynamic camber is determined by the

suspensions geometry through the path of a vertically deflected tire. This tilting

action can be used as a valuable handling characteristic. It also can be a very

negative characteristic if it is not properly studied and implemented.

Figure 6 – Demonstration of Negative and Positive Camber

A small amount of negative camber is desirable in a turn, as determined

through a tire manufacturer’s data. Specific tire data can be difficult to achieve

but a variety of tire types were available (see Appendix A). However, the

geometry must be such that the camber is zero for straight driving. If camber

exists even when the car is not turning, the tire patch area is reduced and

maximum possible traction is not attained. This also leads to uneven tire wear

results. The desirable aspect of camber is that it can be used to increase tire

patch area when the vehicle experiences body roll. To achieve this effect,

camber must be positive when wheel displacement is negative (wheel droop),

and negative when wheel displacement is positive (jounce).


19

Below is a graph for our suspension system. It achieves slightly more

than a degree of camber per inch of displacement. Comparing this slope to the

tire data in Appendix A, the results support that an increase in lateral force can

be achieved.

Figure 7 – Graph of Camber vs. Wheel Displacement

Many complications are added to the suspension geometry where the

steering control arms and rack are located. One of the biggest effects it can

cause is “toe-in/out”, commonly known as “bump steer”. “Toe-in” is when the

front of the tires angle in towards each other, and “toe-out” is when they angle

away from each other. It is undesirable to have the tires independently steer the

vehicle when the vehicle hits bump. This characteristic complicates tuning the

vehicle by adding responses that are unpredictable to the driver. Both kinds of

toe are a result of the position of the steering linkages. Since we are using an

existing steering rack, its position has several constraints. To steer the vehicle,

the control arms must be a distance from the axis about which the tire turns

specifically the king pin inclination (KPI) to induce a moment, thus turning the car.

As the figure below demonstrates, the kingpin inclination affects scrub radius,

which is pre-determined by re-using the vertical uprights.


20

Figure 8 – Scrub Radius

Bump steer is a very difficult characteristic to accommodate. In a majority

of geometries tested, the amount of bump steer cannot be zero for all wheel

displacements. Therefore, we designed our suspension system with a minimal

amount of Toe-In/Toe-Out by placing the rack where the pivots for inner and

outer tie rod match the control arm pivot axis. In previous car designs, there has

been as much as 5.5 degrees of toe-out over a 3-inch wheel displacement. Our

results were a considerable improvement since our design has less than a 0.4-

degree angle over 4-inch wheel displacement. This amount will not noticeably

affect the handling of the vehicle.

Figure 9 – Toe-In/Out vs. Wheel Displacement


21

Another aspect that must be considered is the caster angle. Viewing from

the side, caster angle is the angle between the steering axis and the vertical

plane. The combination of the caster angle and kingpin inclination greatly affects

the handling of the car. Both are very important since they influence the steering

forces during lateral acceleration and the self-centering effect of the steering. As

with Toe, it is desirable to minimize both the caster angle and the kingpin angle

for all wheel displacements. The combination of the two has a large effect on the

rate of camber change during wheel displacement.

The final design uses pneumatic trail to provide steering center effect at

higher speeds. Pneumatic trail differs from the mechanical trail defined by the

KPI and caster angle by specific tire characteristics. Pneumatic trail is a result of

the tire patch area shape. The patch area roughly forms a triangle, thus

providing a wedge effect with the ground and provides a horizontal centering

force. Both types of trails act as weather vanes to the steering wheel but have

varying effects at over a given range of speed. Mechanical trail is dominant at

low speeds while pneumatic trail at high speeds. Skid warning is also maintained

by minimizing mechanical trail, and since the effect of pneumatic trail is non-

linear with vehicle speed, the driver will be able to sense when there is a

significant decrease in pneumatic trail. This provides an important source of

driver feedback at higher speeds, and the vehicle will exhibit under steer and feel

“loose”.

Figure 10 – Graph of Caster Angle vs. Wheel Displacement


22

Figure 11 – Graph of Kingpin Angle vs. Wheel Displacement

Steering arm geometry is another important factor of vehicle control on

driver response. A major focus of our system was to incorporate Ackerman’s

principal, where the control arm must connect to the spindle along an imaginary

line that connects the spindle and the center of the rear axis. This supports the

fact that the outer tire has a larger turning radius than the inner tire. Our control

arm will connect in front of the spindle, and therefore, must be set into the wheel.

For this reason, as mentioned above, the bump steer cannot be reduced to zero

with the existing wheel offset.

Figure 12 – Diagram of Ackerman’s Principle

These parameters are coupled so that changing one aspect will change

any combination of geometries, the key to designing the suspension, as

mentioned before, is to compromise. The following data has been chosen as the

suspension parameters:


23

Wheel base=65” Front: 4-Link, SLA, non-parallel double A-arms Track=50” Roll center height=1.8-6.5” Camber=-2.7->2.5°, Toe-in=-.36->.08° No caster KPI=3Rear: Five-Link, SLA, non-parallel double A-arms Track=51” Roll center height=4.8-8” Camber=-2->2° No casterPredicted Center of gravity height=11” Estimated weight distribution 50/50 True Ackerman steering angle Ground static ground clearance of 2.5” Spring rate=350lbf/in Damping Coefficients of selected Fox Vanilla RC damper: Adjustable

compression between 0-8.75lbf*s/in, Adjustable rebound between 0-87.5lbf*s/in.

Static weight

The load transfer calculations use the following parameters (see Figure

13) to model the forces generated. The static forces are calculated using a driver

weight of 175 lbs, vehicle weight of 520 lbs estimated from previous vehicles,

front-to-rear weight distribution 50/50, and left-to-right weight distribution 50/50.

The static roll centers are geometrically determined using a string computer then

checked using SuspensionGen software. The height of the CG is estimated from

the average of the moment of inertias of major components.

Height of CG Wheel Base (WB)11 65

Front Track – 50Rear Track – 51.6

Weight Driver (WD) Front Static Roll Center175 4Weight Vehicle (WV) Rear Static Roll Center520 6Total Vehicle Weight (TVW) = WD + WV


24

695Front Bias Positive Acceleration0.5 1.5Rear Bias Negative Acceleration0.5 1.5Left Bias Lateral Acceleration0.5 1.5Right Bias0.5

Figure 13 – Acceleration Data used for Calculations

Lateral load transfer due to lateral acceleration

The lateral forces generated act through the center of gravity and are

summed as a torque, or moment, to determine the vertical force on a tire. The

moments are summed about the roll center axis when roll centers are determined

at a static height. The two moments are summed to find Ftire and then split front

to rear by multiplying by the bias ratio. The lateral acceleration has been set to a

high value of 1.5 times the force of gravity, 1.5 g’s. This number is used as a

safety factor since the car will not encounter more than 1.2 g’s of force.

Figure 14 – Graph of Relevant Forces

Front Rear


25

L1 = Lcg – Lrc,f = 6 L3 = Lcg – Lrc,r = 4 L5 = 11L2 = front track/2 = 25 L4 = rear track/2 = 25.8 L6 = WB*front bias =

32.5F1 = a1*(Fz,sfl + Fz,sfr) = 521.25

F2 = a1*(Fz,srl + Fz,srr) = 521.25

L7 = WB*rear bias = 32.5

Ft = (F1*L1 + F2*L3)/(L2 + L4) = 102.6082677Figure 15 – Vertical Tire Force Calculation

Fz, Lateral Acceleration Loads, steady stateFront, 1 tire = 51.30413Rear, 1 tire = 51.30413

Figure 16 – Lateral Acceleration Loads

Longitudinal weight transfer due to negative acceleration

The rear-to-front weight transfer due to braking is a sum of moments

about the y-axis and is defined by the intersection of the x-coordinate of the CG

projected on the ground.

Figure 17 – Tire Force Schematic

Fz, Longitudinal weight transfer, negative acceleration, steady stateFront = 264.6346 Front Left =

132.3173Front Right = 132.3173

Rear = -264.635 Rear Left = -132.317 Rear Right = -132.317

Figure 18 – Longitudinal Weight Transfer


26

Maximum loads achieved

The maximum vertical loads that could be reached correspond to the

combined forces of negative and lateral accelerations with the static weight of the

vehicle.

Fz, Maximum achievable loads; lateral + negative accelerations

static + lateral + negativeFront Left = 357.3714 Front Right = 357.3714Rear Left = 92.73683 Rear Right = 92.73683

Figure 19 – Maximum Achievable Loads

Maximum Tractive Forces

The traction generated by a tire (Fx,y) is a function of vertical force

exerted on a tire and the coefficient of friction () between the tire and ground.

The coefficient of friction is a function of many variables including velocity,

temperature, and tire wear. Wet, dry, and/or sandy surface conditions also serve

as variables. The coefficient is estimated to be high at 1.5 so that the x and y

components of the forces developed are high, since these forces will be used

when determining component materials and dimensions as an added margin of

safety.

Figure 20 – Schematic of tire with axes


27

Horizontal tire force, Fx,y (lbs)Fy: Cornering = u*(static + lateral acceleration loads)Front Left = 337.5812 Front Right = 337.5812Rear Left = 337.5812 Rear Right = 337.5812Fx,y: Cornering & braking=u*(static + lateral + negative acceleration loads)Front Left = 536.0572 Front Right = 536.05716Rear Left = 139.1052 Rear Right = 139.10524Fx: Braking = u*(static + negative acceleration loads)Front Left = 459.101 Front Right = 459.10096Rear Left = 62.14904 Rear Right = 62.149038

Figure 21 – Horizontal Tire Force

Factor of Safety Development

To determine the factor of safety we will assume worst-case scenarios for

the loading of each component. Specifically the vehicle is under hard braking

and hits a pothole or cone. This example exhibits a realistic case for a high

performance vehicle and parking lot track condition. The following is part of the

analysis of the design of a front pushrod element.

The following forces are developed in the push-rod member during full

spring compression and max damping setting on the Fox Racing shock:

F=n*(k*x + c*velocity) where k is the spring constant, x is displacement, c is the

damping coefficient, and n is the rocker ratio. The damping force is obtained

through the manufacturer’s supply of damper dyno charts found in appendixes H

& I and the spring rate is 350 lb/in with maximum x displacement of two inches.

To use a worst case scenario we will assume the vehicle bottoms out, that is max

displacement of two inches is achieved, the damping is set at max 12 clicks

closed, and the rocker ratio is three.

The pushrod is under buckling in a pin-pin configuration, thus using Bernoulli-

Euler technique:

(1)


28

Using this method with an aluminum ¾” diameter pushrod member 14”

long will result in a factor of safety of four. For this worst-case scenario

prediction, we are able to find a factor of safety by dividing the maximum

load/static load to essentially get a factor of safety for each member. Where the

factor of safety was less than three, the member was re-designed until this

criterion was met.

Design Overview

A-Arm Force Calculations

In order to compute the thickness necessary for each arm, the maximum

forces had to be computed. After the forces were found, we used the largest one

to calculate the diameter needed. A factor of safety of three was used. The

relationship between the force in the arm and its area is as follows:

(2)

The area can then be used to compute the needed diameter. The forces were

found using standard static analysis equations. The four defining equations are

as follows:

(3)

(4)

(5)

(6)

They state that the sum of the forces in x, y, and z directions must be

zero. The last equation states that the sum of the moments about any point in

the system must be equal to zero. The figure below shows the forces involved

and their relationship to each other.


29

Figures 22a & 22b – Force Schematic & Truss Design

According to the force equations, we determined that the maximum force

in any arm of the A-arms was 900 lbs. Our computations were completed using

just a basic A-Arm with no truss braces. Therefore, when we discuss the

maximum force in any of the arms, we mean the two major arms of the A-Arm.

The truss design seen in Figure 22b was incorporated to cut down on the

moments acting on the arm. Since that force was the maximum attained for any

member, we used it for all calculations. This insured that all members would be

able to handle the maximum possible force encountered. Using the maximum

forces, the diameter needed for the A-arms was then calculated. The A-arms

were treated as a pin-pin beam, since they are connected with ball joints on each

end. Ball joints do not act against moments, similar to the behavior of a pin.

The Bernoulli-Euler buckling criterion is defined as equation 1, where I is

the moment of inertia. For a round member:

4

2

1rI

(7)

Using equation 2, we determined the thickness needed for each type of material

that we had considered. Also shown is the weight of an arm of the needed

diameter. The results are shown in the figure below (see Figure 23) for the 14-

inch arm. The results are based on a maximum force of 900 lbs and a factor of


30

safety of 3. Therefore, the force calculated for a pin-pin beam is less than 2700

lbs of force.

Material Modulus of Elasticity

Diameter Weight

Aluminum 10.3E6 psi 0.63886 in 0.45326 lbsAZ91 6.5E6 psi 0.71679 in 0.37286 lbsSteel 30E6 psi 0.489032 in 0.7468 lbs

Figure 23 – Material Properities for a 14 inch pin-pin beam

One of the critical factors we used to determine the best material was the

strength to weight ratio of each material. We computed this by dividing the

amount of force in the member by the weight required to hold that load. This

determined that AZ91 alloy magnesium is the best of the three materials. In the

end, other factors weighed into the decision of what material to use and AZ91

was not selected for the steering arms or the push rods. Further detail on this

topic is discussed in the steering arm and push rod sections. AZ91 was selected

for the front and rear uprights as well as the A-Arms.


31

Front Uprights

Figure 24 – Front Uprights

The front uprights are based on the design of the previous car. They are

made of AZ91 magnesium to cut down on the weight of the vehicle. We modified

the design heavily to incorporate a more adjustable steering arm. The uprights

are the centerpieces of the suspension system; they transfer the forces from the

tire to the A-arms. Their geometry is very important to the handling

characteristics of the car.

Magnesium was used for the uprights since they are a part that is cast to

the specific form that is needed. Casting was an excellent option since the

uprights are not a simple shape that can be easily machined. They also can be


32

Upper A-arm

Steering Arm

Front Upright

Push Rod

Lower A-Arm

cast very close to the exact shape needed. This leads to minimal machining

which saves both cost and time.

Rear Uprights

Figure 25 – Rear Uprights

We are reusing the previous cars rear upright design for our car. We

chose to do this was since we are reusing the rear differential of the old car. The

differential used severely limits the options for rear suspension design. The

upright must only travel within the range that the drive shafts can handle. The

suspension characteristics of the rear end were modified, but this was done in

other ways. Although the uprights are the same the mounting points on the body

are different which leads to a different geometrical configuration. We did this to


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Rear Upright

Push Rod

Upper A-Arm

Drive Shaft

Lower A-Arm

Suspension Link

customize the handling characteristics, as we wanted them. Magnesium was

used for the same reasons discussed in the front upright section.

Rockers

Figure 26 – Rockers

The rocker design is a prototype rather than a final model. The final

model will be based on the dynamic vehicle testing to optimize the wheel to

shock travel ratio that can be changed from 1.3:3 to 3:1.8 in .5 increments. The

design permits the use of a single two-inch travel spring and damper unit to

perform in a spring rate range of 150 lb/in to 583 lb/in while retaining the required

two inches of wheel travel.

This variable system is a design common to some teams and combines

manufacturing time savings with material cost savings by using only one rocker

to do the same work as six individually cast rockers.


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Rocker

Shock

SupportBrace

Push Rod

Push rods

Figure 27 – Push Rods

The pushrods are the member that transmits the vertical force of the tire to

the spring/damper unit. As a result this member is subject to buckling loads in a

pin-pin configuration. The calculations and results of the pin-pin calculations

were shown previously.

If weight was the only factor we considered then we would have used

AZ91 for the push rods. We ended up using aluminum push rods for a number of

reasons. A major reason is the availability of materials. Aluminum is readily

available, but magnesium would have to be cast to a specific length. The

availability factor also leads us to aluminum since we want components that can

easily be repaired or replaced at the race. Repairs are very difficult with

magnesium since it is not a weldable metal. Aluminum allowed us more

versatility since we could make new arms quickly. We wanted to be able to


35

Push Rod

change the rod lengths if needed to adjust the system. Aluminum is much less

expensive than magnesium.

The push rod design is based on keeping the system highly adjustable.

The push rod is a rod with a left-handed thread on one side and a right-handed

thread on the other. With this setup twisting one way enlarges the length of the

rod and twisting the other decreases the length. A nut is tightened on each end

to prevent it from adjusting while racing due to vibrations. The steering arms are

designed with this same setup.

Steering Arms

Figure 28 – Steering Arms

Like the pushrods, the steering arms are loaded to buckle in the pin-pin

configuration as well. The force developed in this configuration is tabulated in

the A-Arm force calculations section. The diameter on the rod is calculated using

modulus of aluminum and required length of 12”.


36

Steering Arm

Ideal Ackermans Steering

Process Controls (Troubleshooting):

Process controls are the events that can be attributed to some malfunction

or undesirable handling effect. For example, if the nose of the vehicle dives

during braking, the cause of this problem could be attributed, but not limited to,

low front damping, too soft spring rate, or high center of gravity. The process

sheet is divided into front and rear suspension, steering components, and

possible solutions to the problems listed. The method behind the sheet is to limit

total time wasted during competition trying to tune the car to the current track

conditions, or analyzing a problem.

Stiff Movement

Probable Cause: High spring rate

Possible Solution: Reduce spring pre-load, adjust rocker ratio, and replace

spring with different spring rates

High Friction

Possible Solution: Re-grease rocker and damper bushings, inspect links

for stiff rod-ends, verify misalignment angle to be less than 11, re-torque

rocker bolts to 20 ft-lbs and verify rocker clearance for .050” clearance

High Compression Damping

Readjust damping with 12 click knob one or two clicks lighter

Nose Dive

Probable Cause: Light front spring rate

Possible Solution: Adjust pre-load, replace springs with higher rate, adjust

rocker ratio

Light Front Damping

Possible Solution: Adjust damping compression with incremental knob


37

High Center of Gravity

Possible Solution: None; may be more prominent with excessively large

drivers

Front Brakes Over-Biased

Possible Solution: Adjust bias proportioning valve

Rear Steer

Probable Cause: Differential torque bias

Possible Solution: The Torsen differential bias can be adjusted with

different shims, otherwise a common behavior with torque-sensing

differentials

Probable Cause: Improper rear alignment

Possible Solution: Calibrate using caster/camber and toe-in/out device

Vehicle Pulls to One Side

Probable Cause: Torque bias in differential, see rear steer

Over/Under steer

Probable Cause: Ackerman angle

Possible Solution: Increase the Ackerman steering angle if the vehicle

under-steers, decrease for over-steer

Excessive Steering Force

Probable Cause: Binding rack

Possible Solution: Re-grease rack and inspect for component wear

Probable Cause: Rod-end misalignment

Possible Solution: Verify that misalignment angle does not exceed 11


38

Steering Arm to Short

Possible Solution: Recalculate equivalent Ackerman angle and

manufacture new are with greater length

Improper Rack Ratio

Possible Solution: Re-cut new rack and pinion or replace rack with lower

ratio

Safety Considerations

The suspension system of a vehicle is critical to the safety of the occupant

or occupants of that vehicle. In our case this is a very important issue since our

vehicle is very small and is capable of large accelerations and decelerations.

The vehicle safety issues are minimized by the SAE rules. The rules have many

requirements and restrictions to make the vehicle as safe as possible.

One critical aspect of this project is the factor of safety used. The

appropriate factor of safety can be determined by three different methods. The

most detailed method would be to conduct a full detailed study of the situation

using modeling and equations. Another method is to used “Back of the envelope

calculations”, which are best done with worst case scenario numbers used. The

final method is to use standard practice values. This is common since it only

requires a little research and the values found usually have been tested to

confirm their validity. We used this method combined with “Back of the envelope

calculations” to verify the validity. The standard factor of safety for the formula

SAE suspensions systems is three.

Manufacturing considerations

The use of magnesium for some of the suspension components is also a

safety consideration due to its low ignition temperature. The safety issue is more

with machining rather than the actual use on the car. A good analogy of this is

the danger of throwing a match on sawdust compared with throwing a match on


39

a log. There is just not enough heat to ignite the solid body and this is the case

with the magnesium also. The solution to machining magnesium safely is quite

simply to work at low feed rates, low tool rpm’s, and use sharp tools. In addition

to these steps one should monitor the temperature of the part during machining.

If the part is getting too hot to touch for more than a moment then a break should

be taken to give the part time to cool. If a fire were to break out water must not

be used to extinguish this, in fact water will usually make it worst. A powder that

is specially formulated to extinguish magnesium fires must be thrown on it.

Modifications

We had only a few major modifications of the design of our system. The

modifications were for various reasons, which include safety, aesthetics,

interference issues, and ease of manufacture. The design of the front uprights

was modified in order to increase the turning ability of the car. Material was

removed from the top of the upright where the oversteer stops and steering

mounts were going to be. The stops were placed directly on the rack. The

steering mounts are located on the side of the upright so they don’t interfere with

the turning of the tire.

The height of the steering rack was modified to allow for more room for the

driver. At the original location, the driver would have difficulty getting his feet into

the vehicle. We added two inches changing the clearance from 7 to 9 inches.

Luckily this change only modified the suspension dynamics minimally. In fact,

none of the changes are large enough to be noticeable to the performance of the

car.


40

Engine Intake Design

Motivation

The reason that a fuel injection system was needed for our vehicle was

that the carburetors for motorcycles are not designed to take lateral forces. If the

motorcycle carburetor was used in our car, as hard turns were performed the

lateral forces in the turn would cause the fuel to spill from the carburetors and the

engine would be starved. This system is sufficient in motorcycle applications

since when a motorcycle turns, it leans such that lateral forces are transmitted in

the vertical plane of the bike. Therefore the lateral acceleration experienced in a

four-wheeled car is a vertical acceleration on a motorcycle with respect to the

position of the engine. The SAE rules also require that all fluids, such as fuel,

need to be contained, therefore the spilling of fuel is illegal.

In the early stages of brainstorming ideas came up to solve this. Engine

positioning was considered as a solution to the problem. However this still poses

the same problem when the car experiences hard accelerations and braking.

Another possible solution was to use an automotive carburetor, but it would be

difficult to find a carburetor that would be suitably sized for our engine. The use

of a fuel injection system was the best option for our situation.

Engine Considerations

The engines that are used in a Formula SAE race car are 4-stroke piston

engines with no more than 610cc of displacement. Most teams use mid-size

motorcycle engines because of their compatibility with the SAE rules. However

other engines can be used, as long as they meet the SAE requirements. Teams

may choose to supercharge or turbo-charge their engines. The only other major

restriction is the fuel type; SAE allows the use of 94 and 100 octane Sunoco

gasoline or M85 (methanol) fuel. These are the major constraints that are

considered when designing the drive train.


41

The engine group’s responsibilities are to decide on a suitable engine and

the controls that will operate it. These controls will be used to reliably run the

engine, while also increasing its performance. Some of these controls will be

new designs and others will be changes to existing equipment. The major

controls that are needed to run the engine are a fuel injection system and the

integration of an ignition system to work with the fuel injection system. These

controls will allow the team the ability to tune the engine for particular aspects of

the competition and for weather conditions.

Powerplant Selection

With the limitations on the engine displacement, there are no automobile

engines that would meet this constraint. However mid-size motorcycles have

engines with a displacement of 600cc and are 4-stroke. The engines in this class

are generally used for high performance and racing applications, which make this

type of engine a suitable option for a Formula SAE car. With the car weight just

above that of the motorcycle the engine is coming from, the power and torque

outputs are also suitable for this type of application.

Before the engine selection process began, some constraints had to be

set. We wanted to select an engine that has had proven reliability and

performance, while maintaining cost within our budget. Another recommendation

that was made early on was that we should have two engines for this project, one

for dynamometer (dyno) testing and one for the FSAE competition. The reason

for two engines is due to the stress and extensive wear associated with dyno

testing and tuning. This would also help to reduce the chance of failure during

the competition.

There are a number of motorcycle manufactures that produce the mid-size

600cc high performance motorcycles. These companies are Honda, Yamaha,

Suzuki, and Kawasaki. Through researching these manufactures we found that

all of them have been manufacturing these types of bikes for sometime and have

had good success with them in motorsport competitions. But through contact

with Momentum Racing in Fairfield, CT, we learned more about these


42

manufactures. The engines from Yamaha and Kawasaki have shown evidence

of failure under hard loading in a short period of time. These engines also have a

high cost for repairs and parts. The Suzuki manufacture has had great success

in recent months with their new 600GSXR engine in races. However due to its

recent development the cost associated with this was still high, and would not

allow for two engines under the budget. The engines produced by Honda have

had very good success and are well respected by racers.

These 600cc engines have been in development for almost 15 years now,

with four different generations of these engines. The last generation of engines

is known as the F4, which are only two years old. This engine produces the most

horsepower out of all of the Honda motors and is known for is reliability.

However it too is still costly due to is recent development and availability. For us

to afford two engines for the project we looked at the Honda F3. This motor is

also known for its power and reliability. The F3 and F4 engines are similar but

have different dimensions, the power is also decreased with the F3, but the

torque is higher than that in the F4. The F4 engine is rated at 92-95 Hp and the

F3 is rated at 88-90 Hp, these power ratings are from the manufacturer. The

increase of torque over the F4 is due to the shorter piston stroke and this

increase was an important consideration due to the fact that it would help the

cars performance. Another note was that some of the components for the F3

and F2 engine were the same. This was a consideration due to the abundance

of F2 engine components from previous teams.

The decision to use the Honda CBR 600 F3 engine was the most practical

option to meet the driving conditions and budget constraints for the team. The

F3 engine is rated at 90 Hp, which is a significant increase over previous year

models and only a 5-7 Hp decrease in power from the F4 model. The high torque

rating from the F3 also would work better for the car performance due to the

layout of the competition. The power output is also comparable to other

manufactures engines. The extra parts from previous teams also were a deciding

factor in the choice of engines.


43

Additional Engine Decisions

Under the rules from SAE, we have options as far as induction and fuel.

For the induction, we can use natural aspiration or forced aspiration systems. A

naturally aspirated induction system for the engine would be a tube or scoop to

pull air to the carburetor or fuel injection system. A forced aspiration set-up

would utilize a supercharger or turbo-charger to intake air to the carburetor or

fuel injection system. The benefit, if properly tuned to that particular engine, is

between a 30% and 40% power increase due to the extra air fed to the engine.

In looking at the previous teams both at UConn and elsewhere, there has

been difficulty in finding a turbo-charger small enough to match the engine’s

displacement. When forced induction is used the compression ratio needs to be

lowered to handle the extra air mass being delivered. This would require internal

engine modifications to lower the compression, such as different pistons.

Another difficulty has been the tuning of the turbo to produce maximum power. It

has been noted by other teams that their vehicles have also not been able to

achieve decent fuel economy when forced induction is used. In looking at the

power output numbers from the dynamometer in last year’s competition, more

horsepower was created with natural aspiration induction. Therefore, we have

decided that we would use a naturally aspirated system and avoid the problems

of forced induction.

The other decision was as to what fuel type and octane to use. The SAE

offers three choices on fuel; they are Sunoco 94 and 100-octane gasoline and

M85 (methanol). Looking at the pros and cons of gasoline and methanol we

were able to select our fuel type. Methanol is rated at about 118-octane, and has

a higher energy associated with it than gasoline. However methanol is corrosive,

and can do serious damage to internal engine components, which leads to power

losses if the components are not replaced. With this side effect considered it

was clear that methanol would be risky to use. This was also based on an

already tight budget. Now the choice was which octane level to use. The engine

we will be using has a compression ratio of 11:1. This number is relatively high


44

for a gasoline engine. Therefore to prevent pre-detonation or “knocking”, the

100-octane gasoline will be used. Generally, as the compression ratio increases

a higher-octane level is needed to prevent knocking. The 94-octane fuel would

more appropriately be used for forced induction systems, where the compression

ratio is lower.

EFI Requirements

The EFI system uses particular constraints to properly control the engine.

Therefore, before the computer code can be written the engine’s fuel needs, the

air/fuel ratio, and injecting timing must be known. Other system configurations

need to be addressed also to properly design the computer to the engine and

competition requirements.

The fuel required by the engine can be determined based on the engine's

displacement. An engine is essentially a pump and the displaced mass the

pump creates is what the engine needs to intake. Therefore, the first variable

that needs to be determined is the mass of the air that the engine displaces.

This can be done using the Ideal Gas Law.

This law will be used to model one cylinder to determine its requirements; this is

due to each cylinder having its own injector.

Before the mass of air can be calculated, there are some variables that

need to be determined. These variables are the pressure in the cylinder on the

intake stroke, the volume of the cylinder, and the temperature of air within the

cylinder. When an engine is at idle, the pressure in the manifold is at about 1/3

atm. When the engine is at WOT, the pressure increases to 1 atm. So when the

engine is running at these conditions, the pressure in the cylinder is at the

respective pressure based on the throttle positions. For the cylinder pressure in

this calculation, we are assuming that the throttle is wide open, and the resulting

pressure is 1 atm. The reason for assuming WOT is that maximum power will be

produced around this position of the throttle. The cylinder volume is determined

by summing the piston displacement volume and the cylinder clearance volume.


45

The volume the cylinder displaces can be determined by dividing the total engine

displacement by the number of cylinders. In this case the engine has a total

displacement of 599cm3 with 4 cylinders, which make the displaced volume of

one cylinder 149.75cm3. The clearance volume is the volume in the cylinder

above the piston when it is at top dead center (TDC) and the volume of the

cylinder head. To determine this the following equation is used:

This can be applied, using the compression ratio (CR) and the known

displacement of the piston. For our engine, a 11:1 compression ratio was listed

by the manufacturer, which made the clearance volume equal to 13.623 cm3.

Using the determined volume the total cylinder volume can be calculated and is

equal to 163.373 cm3.

The temperature determination is a variable that is tough to control in this

type of situation; the weather conditions usually dictate the air temperature.

When the engine is operating at WOT, the temperature of the air in the cylinder

can be assumed to be equal to that of the ambient air. This assumption is due to

the fact the air velocity is so great that it does not sit in the manifold to be heated.

Also additional heat shields and cooling ducts can be added to insure this

assumption. The EFI computer will have an air temperature sensor to input the

temperature for the current conditions. For the mass of air determination here,

the temperature will be equal to 70oF, room temperature. This assumption is

based on the temperature when the injectors will be experimentally tested for

verification.

The final variable needed for the Ideal Gas Law is the volumetric

efficiency, v. The volumetric efficiency is the measure of the efficient volume of

air that is actually being inducted to the cylinders. This measurement is

essentially a percentage of air volume inducted. As engine speed and throttle

position increase, this value for v will increase as well. For the injector testing

this variable will be equal to one, normalizing the equation. This assumption is

also based on the throttle position set at WOT. The change in engine speed


46

versus volumetric efficiency can be viewed in the following plot. This graphical

representation will also be used for the microcontroller programming.

Figure 30 – Engine Speed vs. Volumetric Efficiency

Now that the assumptions for the Ideal Gas Law have been made the

mass of air can be calculated. The units for this will be in metric for ease of use;

therefore the constant R will be equal to 8.314. The mass of air was determined

to be equal to 0.006769 kg.

To determine the mass of the fuel, the stoichiometric ratio must be used.

The stoichiometric ratio is also known at the chemically correct ratio, and this is

the ratio of air to fuel. For gasoline the operation limits are roughly 11:1 (rich)

mixture to a 20:1 (lean) mixture. The stoichiometric ratio for optimum operation

and lowest emissions is 14.5:1. At this ratio it is represented by letting = 1.

This is what the initial calculations will be based on. However for fuel economy

purposes a ratio of 20% lean can be used for fuel mass calculations, this would

be about a 17:1 mix. For maximum performance the fuel mixture would be

richened about 10% to achieve max power, this would be a ratio of 13:1.

Using the stoichiometric ratio it was determined that the mass of fuel

needed at = 1, to be equal to 4.6686 E -4 kg. This mass can now be converted


47

to a volume using the specific weight for gasoline, which is equal to 45.9 lb/ft3.

This value will need to be converted to metric units. The volume of fuel needed

for one cylinder at stoichiometric conditions is 0.63497cm3. The change in the

volume of fuel compared to stoichiometric ratio can be seen in the graphical

representation below.

Figure 31 – Fuel volumes compared to stoichiometric ratios

This is the volume that each injector will discharge every cycle at the appropriate

time. The equation posted on the graph is for the represented curve. This will be

used also in the future programming to fine tune the air/fuel ratio for different

engine requirements and driving conditions. The injection timing will be

discussed later.

Pulse Width Determination

Now that the volumes of fuel have been determined at different

stoichiometric ratios, the pulse widths for the injectors need to be determined so

that the correct fuel volume can be delivered. Fuel injectors are voltage


48

dependent and this voltage input is used to open the pintle and allow fuel to flow

by. The duration of the voltage signal is a variable, which controls the volume of

fuel discharged. The fuel pressure is another variable consideration. To

determine the pulse width for the injectors, a test rig was designed to represent

the fuel delivery system. This can be seen in the layout below.

Figure 32 – Fuel Injector Test Rig

Using this test rig, a particular pulse width can be produced from the

signal generator. This signal from the generator will be a square wave. This

signal will be transmitted through the fuel injector drivers. The drivers will then

send the conditioned signal to the injector. As for the fuel delivery to the injector,

this will be done just as it would in an actual car set-up. The fuel will be delivered

from the tank via a high-pressure fuel pump (95-psi max.) to the injector. The

pressure at the injector will be regulated, to control the pressure input. The fuel

pressure regulator is critical to maintain a constant pressure at the injector. This

will also allow us to vary the pressure during the test. Most fuel injection systems

operate at a fuel pressure of 40 psi. However it is recommended that the fuel

pressure should not exceed 60 psi, this recommendation was made by the fuel

injector manufactures due to internal component design limits.


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The actual fuel volume will be determined by firing the injector for a given

number of injections, the total volume of fuel will be collected and divided by this

number to determine the volume of fuel per injection. The fuel will be collected in

the beaker shown in the diagram. The ice pack that surrounds the beaker is

used to minimize the amount of fuel vaporized during the injections. This will

result in a more accurate fuel volume per injection measurement.

The fuel injector calibration test was preformed as discussed before.

From this test, an equation was developed for programming the microcontroller

to regulate the fuel delivered by inputting a certain pulse width. To achieve this,

a number of different pulse widths were used and the volume of fuel was

determined. The results of the test proved to be a linear as shown in the graph

below.

Figure 33 – Fuel Volume vs. Pulse Width

The equation that was determined from this calibration test is only suitable for the

injector used during the test. If injectors with a different flow rate are used this

test should be preformed again with those injectors to insure proper fuel delivery

per injection.

As mentioned earlier the duration of the pulse width and the fuel pressure

inputted to the injector have an effect on the volume of fuel discharged. In an


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automotive application, the fuel pressure will vary with respect to the manifold

pressure and therefore also with respect to engine load. This is because a fuel

injector works on the principle of differential pressure across the injector. And

this differential pressure is the systems operating pressure. In an earlier section

it was noted that as throttle position increases the manifold pressure begins to

increase, therefore to maintain a constant differential pressure the absolute fuel

pressure must increase. The fuel regulator will control the absolute fuel pressure

from a vacuum tube from the intake manifold. The diagram below shows the

layout of the fuel rail, fuel regulator and manifold.

Figure 34 – Injector differential pressure layout

The differential pressure is governed by Bernoulli’s equation. This can be

applied to determine an absolute fuel pressure based on the desired fuel volume.

Since Bernoulli’s equation always equals a constant, setting two different

conditions equal to each other can solve variables. The determination of the

proper differential fuel pressure is critical, if this is not maintained and the pulse


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width is constant, it could mean that the engine would be starved for fuel. This

starvation will cause the engine to operate at lean conditions causing power

losses and possible engine damage if the ratio is very lean.

Valve Train Timing

The timing of the valves is an important variable that is needed for fuel

injection systems. This timing of the valves is the point at which the intake and

exhaust valves for each cylinder open and close. This measurement is based on

the position of the crankshaft, and is measured in degrees. Using the

manufacture’s specifications from the owner’s manual, a linear valve-timing

diagram can be produced. This is a graphical representation using linear bars to

indicate when each of the individual valves is opening and closing with respect to

one another. A valve timing plot was developed for the Honda F1 engine and

can be viewed in appendix D. This tool will allow the EFI program a

measurement of when to fire the injectors in either the bank firing or sequential

firing method.

Engine Intake Manifold Design

Since a new fuel injection system will be utilized a different intake manifold

will be required to deliver the fuel and air to each of the cylinders. The manifold

will consist of a throttle plate, restrictor, plenum, runners, and fuel rail. The main

focus of the design will be the restrictor, plenum, and runners, since this is where

the majority of tuning will be done. Calculations can be made to optimize these

components for maximize engine performance. A typical 4-cylinder intake

manifold would look like something like the figure below.


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Figure 35 – Intake manifold for a 4-cylinder engine

The restrictor is a requirement through the SAE rulebook. This is used to

restrict the engines from making their ultimate power. Restrictors are used in

other racing sports to reduce power and in turn lower speeds. This is more of a

safety item, to limit the vehicle from extreme high speeds. The rules state that a

20mm restriction will be placed on the intake after the throttle plate. The

restrictor does not have to be the normal restrictor plate design, which is a thin

plate (about ¼” thick) with the required bore. This is a restriction anywhere in the

intake after the throttle plate and before the intake valves. Therefore, a venturi

can be utilized to restrict the intake system, also with the use of a venturi a

considerable amount of the air mass that is lost when using a conventional

restrictor can be regained. It should be noted that, due to the restrictor, the

engine could only produce power to a maximum of about 9000 rpm. The venturi

will be designed to minimize the air mass loss. This was done with the following

equations:

where = exit area


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= venturi throat area

= inlet area

where m = mass flow rate

= cross sectional area

The next portions of the intake that need to be studied are the plenum and

intake runners. These two work together to deliver the air to the engine. Inside

the intake manifold the air flowing through can experience pulsations or waves.

This occurs due to the air flowing in and hitting a closed valve then traveling back

up the intake runner. This resonates can be used to help increase performance

if the runners and plenum are designed correctly. The runners need to be a

certain length so that as the pulse waves travel away from they engine, they

bounce back at the proper moment in which the intake valve opens again. This

is called a tuned induction or “ramming” and can result in considerable power

improvement of 10–20%. The length of the induction pipe will influence the

engine speed at which maximum benefit is obtained from the pulsating flow. This

can be seen in the following plot of the pipe length versus engine speed (Stone

pg. 310).


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Figure 36 – Pipe length benefits at particular engine speeds

This plot is only applicable to engines, which have individual carburetors

or fuel injectors per cylinder. This is primarily due to the difficulty in designing an

intake manifold with a single carburetor or fuel injector, because of the difficulty in

optimizing the volumetric efficiency and the mixture distribution. From the plot it

is shown that a shorter pipe is used when engine speeds increase. In our case

the intake will be designed to take advantage of this phenomenon at the optimum

power band, which is 0.35 m or about 14 inches in length.

The intake can also be acoustically modeled to study the propagation of

these pulsating waves. A tuned induction system can be considered an organ

pipe or Helmholtz resonator. This is modeled by the Helmholtz equation below.

where C = speed of sound

A = pipe area

L = pipe length

V = resonator volume


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The pipe variables are representatives of the intake runners, and the resonator is

the plenum. The other model for the resonant frequency is that of the organ

pipe, and is represented by the following equation

L = l + 0.3d

where L = effective length

l = pipe length

d = pipe diameter

Either of these can be used for the determination of the resonate frequencies.

This tuning technique benefits both volumetric efficiency and power. However

the resonates frequency will only be good for particular engine speeds. The

intake can experience more than one resonating frequency. Therefore, a focus

needs to be made to ensure that these resonating frequencies are present at

particular engine speeds, mainly at speeds the engine will be run at during the

competition.

To confirm that the runner lengths were correct, the effective length was

determined and used in the pipe organ equation. This proved that the effective

length was in fact 0.35 m, and that the airflow would resonate at about 230 Hz.

Using this frequency and the effective length in the Helmholtz equation, the

plenum volume could be determined. The plenum volume was calculated to be

4.7646E-4 m3 or about 29 in3. This was verified by a rule of thumb measure that

stated that the plenum volume should be about the volume displaced by the

engine.

Other design considerations are the intake runners from the plenum.

From the plenum air needs to be funneled into each of the intake runners. There

is a tendency in intake design to just connect the two. But at this junction a

boundary layer is present. Therefore to help minimize the boundary layer

experienced at the mouth of the runners, the runners are tapered or flared. This

shape is sometimes called a velocity stack. This runner shape at the mouth

minimizes the boundary layer by helping the air to flow more smoothly. With the


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reduction of the boundary layer the runner is less prone to choking the flow.

These runner shapes at the mouth can be seen in the following figure.

Figure 37 – Runner Shapes at the Mouth

As far as the rest of the intake systems components they do not need as

much attention to maximize the performance. The throttle plate needs to have a

matching bore to the front end of the venturi to minimize airflow losses. The

throttle plate also needs to have a linear opening motion. If this motion is not

achieved then, when the engine is run the driver will not be able to adequately

control the engine speed and output. A throttle with non-linear motion will result

in maximum engine speeds with out have fully opening the throttle plate. This is

undesirable for driving conditions.

The fuel rail is the last point of concern for the intake system. The fuel rail

will provide fuel to each of the injectors through a common pipe. The only

concern for the fuel rail is adequate fuel delivery for the injectors. Therefore the

volume of the rail needs to be examined to insure it will hold enough fuel to

provide the injectors adequately under hard accelerations. However this should

not be too big of a concern with a fuel regulator that has a quick time response to

meet the need for a higher fuel pressure in the rail. To ensure that the fuel

pressure did not drop significantly when the throttle was opened quickly, a

pressure gauge was installed on the inlet of the fuel rail. It was determined that

the fuel injectors would be delivered fuel at 50 psi based on the fuel regulator

setting. To adjust the fuel pressure an adjustable fuel regulator was used, but it


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was decided that this would provide to many problems in tuning without any

performance enhancing characteristics. It was also suggested that mild steel or

stainless steel be used for the construction of the fuel rail, instead of aluminum.

This is because after a hot shutdown steel gathers far less heat, which could lead

to fuel boiling in the rail and causing vapor lock (sdsefi.com/tech).

The intake layout was based on the space constraints of the car its self.

The air intake for the system was placed above the driver’s head and just under

the main roll bar. This can be seen in the following photograph, Figure 39. The

rest of the intake manifold would also need to fit within the main roll bar brace.

This is to protect the manifold from being hit in the event of an accident.

Therefore the manifold would have to incorporate some bends to meet these

constraints. The use of bends in the manifold layout is not very critical, minor

bends do not have a significant effect on the airflow through the manifold. It was

decided that the intake runners would be bent 35 degrees to originate the plenum

in a vertical plane with respect to the runners. Also by bending the intake runners

35 degrees the injectors could be mounted to the runners so that they fired

directly at the base of the intake valves. This design consideration would help to

ensure that all the fuel is injected to the cylinder.

Figure 38 – Intake Manifold and Fuel Rail (Side View)


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145o

Intake Runner

Fuel Injector

Fuel Rail

With the plenum in the vertical plane, this would also then allow the air

intake runners to be originated parallel to the main roll bar brace. This would

result in the fewest number of bends and maximize the space above the engine

head. With this location placement the manifold would receive the most external

cooling effect from the open air. The last consideration was to place a vacuum

port on the end of the manifold as close as possible to the fuel regulator vacuum

port. Placing the vacuum ports as close as possible would help to minimize any

delay effects noticed when the manifold pressure changed especially under hard

accelerations.

Testing

When it was time to test the system on the engine, we used an engine

dynamometer to decrease testing time. Before engine testing could begin with

the intake manifold, a series of leak checks were necessary. With the fuel

system plumbed to the fuel rail, fuel was delivered to check for any leaks. A fuel

leak can pose a potentially dangerous situation especially when the engine is

running. The fuel rail was leaking around the injectors. The fittings were

tightened and this proved to be unsuccessful. After looking at the injector o-

rings, which seated the injectors to the fuel rail, they looked to be ineffective.

The o-rings were replaced with smaller inside diameter and thicker o-rings, which

provided a tighter seal at the fuel rail. This proved to be the solution to the fuel

leaks, and engine testing could begin safely. With the engine running the

manifold needed to be checked for adequate vacuum pressure. This was to

ensure that the manifold had no leaks in any of the welds, which could decrease

the engine's performance. The vacuum gauge showed that the manifold held 10

in Hg, which is within manufacture's specifications. Below is a picture of the

intake on the dyno during testing.


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Figure 39 – Intake Manifold and Fuel Rail (Front View)


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Throttle

Fuel Rail

Plenum

Intake Runners

20mm Restrictor

Engine Control Design

Fuel Injection

We decided to design our own electronic fuel injection (EFI) system similar

to commercially available systems, instead of purchasing a complete system.

This approach allows us to design the EFI system to the exact constraints of the

Honda engine with the specific features that we desire. One of these desired

features is the ability to set the system to either performance or economy mode.

Using the performance mode, we can produce maximum power only when

needed. The economy mode would be used to reduce fuel consumption during

certain portions of the competition.

A number of different designs were considered before the final control

system scheme was chosen. Initially, the fuel injection was going to be

controlled using multi-port fuel injection, which involves firing all the injectors at

once, and the spark would be delivered to pairs of companion cylinders using a

waste spark system. Our design was developed originally for a Honda F4

engine, but our final design uses a Honda F1 engine and the ignition coils from a

Honda F4 engine.

Since the engine we originally expected to receive was a Honda F4

motorcycle engine, which has a coil-on-plug ignition system (an individual coil for

each cylinder) the waste spark system is redundant and inefficient since it is not

necessary to fire two ignition coils at once. The F4 system has no camshaft

position sensor so the engine position with respect to which cylinder is on a

power stroke is not readily available. This system does not lead to a

straightforward design for sequential fuel injection

The EE/CMPE team devised a scheme to obtain the engine’s power

stroke position from the voltage difference found at two companion ignition coils

primary windings during the inductive discharge. The way that this is

accomplished is to start the engine in a waste spark mode while using multi-port

fuel injection. At start-up the only information available is the overall engine


61

position from the crankshaft position sensor. This is only half of the information

needed for sequential fuel injection.

A four-stroke engine’s cylinders go up and down twice for each complete

cycle. This means that the engine is either on the first or fourth cylinder

compression stroke when the crankshaft is at 0. Therefore, it is necessary to

start the engine in a waste spark mode. The first and fourth spark plugs are fired

simultaneously just before 0, and the second and third spark plugs are fired

simultaneously just before 90. Once the engine is running, the primary voltage

drop across two ignition coils will be measured simultaneously. This will be

performed at the 1-4 or the 2-3 cylinder pairs. This has been successfully

simulated using MicroSim PSpice software (see Appendix J).

Engine Control System

The inputs to the fuel injection control system are engine speed, engine

load, throttle position and ambient air temperature. The fuel injector is an

electromechanical device that is activated by a voltage pulse, which induces a

current in the injector’s solenoid opening the injector and allowing fuel into the

intake manifold. The amount of fuel injected is controlled by the pulse duration

(or pulse width) of the voltage signal. The pulse duration is required to change

with respect to the load on the engine (i.e. with a higher load, the amount of fuel

supplied increases and therefore the pulse width is increased). As engine speed

changes, the frequency of the pulses also changes in direct proportion to engine

speed.

Throttle position refers to the position of the throttle plate. The throttle

plate is located at the opening of the intake manifold. It opens in order to let

more air in as the accelerator is depressed. When the engine load increases,

more air is allowed in as the throttle is depressed. If the throttle is opened, the

fuel injection system will increase the pulse width to supply more fuel. Ambient

air temperature affects the air to fuel ratio. When the temperature is lower the

density of the air changes and more fuel is required to achieve the stoichiometric

ratio.


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The crankshaft sensor determines engine speed and position. On the end

of the crankshaft there is a sensor wheel with seven teeth followed by a gap

known as the missing tooth region. The sensor mounted on the engine case will

send a signal as each tooth passes. The frequency of these signals will tell the

speed of the engine. When the gap is encountered, the exact position of the

crankshaft is known. Knowing the position of each piston is not enough to find

the exact position of the engine. Since the pistons are moving in pairs, the

crankshaft sensor will not tell us which of the cylinders is on a power stroke and

which is on an exhaust stroke.

To find this a different approach was taken. When the car is first started

the position of the engine needed for proper sequential fuel injection is not

known. Starting in a waste spark mode is a solution to this problem.

In a pair of companion cylinders, one of the cylinders is in the power stroke and

the other is in the exhaust stroke. When the pair of spark plugs fire, the spark to

the cylinder in the power stroke is the only spark that will induce combustion.

Since the other cylinder is in its exhaust stroke no combustion will occur in that

cylinder. At this time the injection is performed in a bank-firing mode.

When the spark plugs are fired there is a transient voltage present at both

ignition coils. The size of the voltage is directly proportional to the pressure in

each cylinder. When the pressure is greater, the voltage is greater.

When a cylinder is in its compression stroke, the piston comes to the top

of the cylinder compressing the fuel mixture. This creates a pressure on the

order of 8-40 atmospheres (ATMs) from idle to high engine speeds. When a

cylinder is in its exhaust stroke, the pressure in the cylinder is only 1-3 atm.

There is a vast pressure difference between the two cylinders, so there is a

difference in the transient voltage present at the ignition coils. This voltage

difference can be used by a comparator whose output will indicate which cylinder

has the greater voltage, and thus, which cylinder is in the power stroke. Once

the correct engine position is known, the injection and ignition system can be

synchronized and fired sequentially.


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The inputs to the ignition control system are engine speed, crankshaft

position, and engine load. Engine speed is used because as speed increases

the frequency of the sparks will increase. The frequency of the sparks is directly

proportional to engine speed. Crankshaft position is required as an input to the

ignition system because the position of the pistons determines when the spark

plugs should fire. Engine load is used because as the engine load is increased

there is a need to adjust the timing. All of these inputs are sent to a

microcontroller. Based on these inputs, the microcontroller is coded

appropriately to send the required pulse to the driver circuits.

The driver circuit is placed to act as a switch, which provides 12 volts to

the primary ignition coil based on the position of the pistons. Then the 12-volt

supply voltage is applied at the primary coil, and then transformed (step-up)

voltage resides at the secondary coil. The interruption of the voltage supply at

the primary coil causes an inductive discharge at the secondary coil. This

amount of voltage at the secondary coil fires the spark plug. The high voltage at

the secondary coil induces a large transient voltage at the primary coil during the

secondary discharge. In order to protect the microcontroller, and to source

enough current to the ignition coil, an insulated gate bipolar transistor (IGBT) is

placed as the driver circuit for the ignition coil.

The Manifold Absolute Pressure (MAP) sensor measures the amount of

pressure or vacuum in the manifold. This sensor tells the engine load. With

more pressure, the engine load increases. With greater load on the engine,

more fuel is required. This is an input to the microcontroller and will be a factor

when setting the voltage pulse width for the fuel injectors.

The Throttle Position Sensor (TPS) returns the position of the throttle

plate. When the TPS measures a wider opening, this indicates a greater engine

load. When the TPS changes rapidly a hard acceleration is indicated causing a

need for more fuel. The TPS senses the position by using a potentiometer that

turns when the position of the throttle plate changes. Since this is a

potentiometer, there will be a change in voltage at different positions. This

voltage is then returned to the microcontroller.


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The ambient air temperature is measured using a thermistor. A thermistor

is a variable resistor that varies with temperature. If a voltage is applied to this

thermistor in series with another resistor the voltage between the two will change

as temperature changes according to the voltage divider rule.

Engine Control Overview

This section discusses the parameters of the control system, which

consists of the Fuel Injection system and the Ignition system. A large part of our

design requires the use of a microcontroller to control the operation of these

systems. All of the necessary inputs to the microcontroller are further described

in this section. The table below shows each control variable and the sensors that

produce the signals.

CONTROL VARIABLE SENSORFuel supply frequency Crank SensorSpark frequency Crank SensorFuel supply amount (volume) MAP Sensor/Crank sensor/Air

temperature sensorSpark timing (advance/retard) Crank Sensor/MAP SensorFuel quantity correction (rich/lean) Driver controls

Figure 40 – Control Variables

Crankshaft Sensor (Variable Reluctance Sensor)

The crankshaft position sensor detects the speed and position of the

engine. The Variable Reluctance Sensor (VRS) reacts to variations in flux

density created by a rotating multi-toothed wheel with a missing tooth region.

The sensor contains a coil of wire, a magnet, and a pole piece. The changing

flux field induces an alternating current (AC) voltage in the VRS. One AC cycle is

generated for each tooth on the wheel, and no signal is produced for the 1/8 of a

revolution when the missing tooth region passes the sensor. It can then be

determined that one revolution has occurred when the missing tooth region is

encountered. The VRS sensor in the Honda F1 engine generates a 0.6V signal

at cranking speeds, and a 40V signal at 6000 RPM.


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Variable Reluctance Sensor (VRS) Interface Circuit

Figure 41 – Variable Reluctance Sensor (VRS) Interface Circuit

The VRS interface circuit is designed to translate the analog sinusoidal

signal from the engine’s crankshaft sensor into a square wave that can be

recognized by the microcontroller. The circuit converts a sinusoidal signal that

varies from about 0.6V at 6.7 Hz for cranking speed, to greater than 40V at 166.7

Hz for 10,000 RPM into a square wave that is either 0V or 5V over the same

frequency range.

The VRS interface uses a non-inverting operational amplifier (Op Amp)

circuit to condition the crankshaft signal. We chose to use an LM324 Op Amp for

this circuit since it operates with a single power supply, eliminating the need for a

negative power supply, since the microcontroller requires only positive voltage

inputs. The two 10V Zener diodes (D1 and D2) are configured as a Zener limiter

to isolate the Op Amp from the higher voltage signal as engine speed increases.

The Schottky diode (D3) prevents the input of the Op Amp from going more than

0.3V negative. The Op Amp has a +6V supply so it will have a +5V output at


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saturation (due to a 1V internal drop in the Op Amp). The Op Amp has a gain of

(R3+R4)/R3 which is 21. This amplifies a small signal of 0.6V to 12.6V, and since

the Op Amp saturates at 5V, its output is 5V. The resulting wave is a close

approximation to a square wave at low engine speeds, and virtually a square

wave at higher engine speeds. This results in a TTL signal that is a series of 7

pulses corresponding to the teeth of the VRS followed by a gap that corresponds

to the missing tooth region of the VRS. This signal allows the microcontroller to

recognize both engine speed and position.

MAP Sensor

The MAP sensor detects the pressure in the intake manifold. Knowledge

of this pressure is vital for proper engine performance since the amount of fuel

necessary for any given engine load is determined by the pressure in the intake

manifold. The MAP sensor’s output is a voltage whose level depends on the

manifold pressure in the engine. As engine load increases, the MAP voltage will

decrease. The MAP sensor’s output voltage range is 1V - 6V for an 8V supply.

Based on the voltage present at the MAP sensor, the corresponding

pressure can be deduced by means of a pressure-voltage graph exclusive to the

particular MAP sensor being used

The MAP sensor signal is proportional to the fuel that is necessary at any

given engine speed. The MAP sensor operates as follows:

Light load (cruise): Low manifold pressure, high voltage at MAP sensor

reference (5V)

Heavy load (wide open throttle): High manifold pressure, low voltage at

MAP sensor reference (1V)

High voltage: Smaller fuel pulse width and advance spark timing

Low voltage: Larger fuel pulse width and retard spark timing

The previous relationships depict how intake manifold pressure and load

affect the MAP sensor output. The spark timing is varied based on the engine


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speed and the pressure in the intake manifold. The intake manifold pressure and

MAP sensor voltage have a linear relationship. Using the pressure-voltage

relationship of our sensor, the pressure in the intake manifold can be determined

by the MAP sensor voltage. This pressure along with the RPM of the engine is

used to determine a parameter known as the spark-angle (θspk). Spark-angle is

determined from the θspk vs. RPM graph or from look-up tables developed by the

ME team during dynamometer testing. Spark-angle is simply the number of

degrees of rotation left in the crankshaft before the piston gets to the top of the

cylinder.

Manifold Absolute Pressure (MAP) Sensor Circuit

Figure 42 – Manifold Absolute Pressure (MAP) Sensor Circuit

The MAP sensor returns a voltage between 1V and 6.2V DC depending

on manifold pressure. Therefore, a voltage divider is needed to provide the

microcontroller with a voltage less than or equal to 5V DC.


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Rich/Lean Adjustment Circuit

Figure 43 – Rich/Lean Adjustment Circuit

The rotary switch allows the user to select how rich or lean the engine is to

run. When the switch is turned clockwise the pulsewidth is increased making the

engine run richer. When it is turned counterclockwise the pulsewidth is

decreased to make the engine run leaner. Using a 6V supply and six resistors of

1.8k in series creates a voltage divider circuit in -1V/step increments to ground

with a current of 6V/(6 x 1.8 k) = 0.55mA. As the contact within the switch


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alternates between each step, the output voltage changes in 1 volt incrememnts.

This voltage is then sent to the microcontroller to determine how much to

increase or decrease the fuel. It is understood from the circuit diagram that

between R1/2 is 5V, R2/3 is 4V, R3/4 is 3V, R4/5 is 2V, and R5/6 is 1V. These

five steps will be mapped to rich, semi-rich, stoichometric,semi lean, lean,

respectively.

Ambient Air and Throttle Position sensors

The final two sensors used are the Ambient Air Temperature sensor (AAS)

and the Throttle Position sensor (TPS). The AAS is a thermistor, a device that

changes resistance with air temperature, which is used by the microcontroller to

make corrections or adjustments to fuel volume. The TPS is a potentiometer, a

device that changes resistance when its center terminal changes position. The

TPS is mounted on the intake plate to determine the position of the plate. During

a hard acceleration, there can be a delay if the MAP sensor is not quick enough

to pick up the pressure change in the intake. The TPS voltage is used by the

microcontroller improve the throttle response.

Driver Circuits

The outputs from the microcontroller for ignition and fuel injection control

are interfaced to the engine using driver circuits. These circuits are designed to

source enough current to the ignition coils and injector solenoids. The

microcontroller will also use the outputs of a comparator circuit to detect which

cylinder is in a compression stroke. That information is used to inject fuel

sequentially, and to fire only the appropriate ignition coil depending on which

cylinder is on a compression stroke.


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Fuel Injector Driver Circuit

Figure 44 – Fuel Injector Driver Circuit

The Fuel Injection Driver (FID) circuit is needed between the

microcontroller and the injector solenoids to source enough current to turn the

fuel injectors on. Pull down resistors were added to this circuit to prevent floating

inputs from allowing the injectors to turn on if there is no control signal to the

driver circuit.

Ignition System

Using the information from the crankshaft position sensor, the

microcontroller will supply the signal to the ignition driver circuit and adjust the

timing as needed. The spark angle indicates how many degrees before top

center for spark activation. The following equation is used by the microcontroller

to determine the time it takes to reach top dead center.


71

Ignition Coil Driver Circuit

Driving the ignition coils presents a distinct design problem due to the high

current and voltage levels present at the ignition coils. The ignition coils are

actually transformers that step 12V up to as much as 50kV. Pairs of inductors

that are in close proximity form a transformer. The transformer steps up, or steps

down the primary voltage based on the turns ratio of the inductors, given by

,

where Ns and Np are the number of turns in the primary and secondary windings.

The voltages and currents in a transformer are proportional to the ratio of turns.

When the current changes in one inductor, it induces a voltage in the other

inductor. This effect is known as self-inductance. The induced voltage is given

by

where L is the inductance in Henrys.

Self-inductance is used to fire the spark plugs in an internal combustion

engine. When the voltage supply is interrupted at the primary side, it causes the

magnetic field developed in the primary side to collapse as the high

secondary voltage arcs across the spark gap. The resultant secondary current in

turn induces a voltage in the primary windings.

The current drawn by the Honda F4 ignition coils we will use is 7.1A as the

primary side charges, and the induced voltage at the primary side of the ignition

coil caused by the secondary discharge is in the 150V to 200V range (depending


72

on the compression level of the cylinder). These are both orders of magnitude

too high for the microcontroller to handle. This requires a driver circuit between

the microcontroller and the ignition coils.

The device that best handles these conditions is an insulated gate bipolar

transistor (IGBT). This is a combination of a bipolar transistor and a field effect

transistor (FET). This device can source large amounts of current, and it can

handle the high voltage transients found at the primary side of the ignition coil

during secondary discharge. This specialized transistor has been used

extensively as an automotive ignition coil driver. IRGS14C40L’s were selected

for our ignition coil drivers since they are specifically designed for coil-on-plug

ignition systems.

One important control variable is the charge time for the primary ignition

coil. The time to fully charge the ignition coil must be known in order to deliver

the spark at the right time. Since the interruption of the primary voltage triggers

the secondary discharge, the coil should be fully charged when the spark is

needed. This is accomplished by working backwards from the necessary time for

ignition spark. The microcontroller will turn on the ignition driver circuit at a time

just before the spark is actually needed. The time must be at least sufficient to

fully charge the ignition coil for the control system to maximize engine

performance.

The primary ignition time to saturation (full charge) was found by first

measuring the inductance and resistance of the ignition coils. Then the charging

of the ignition coil primary was simulated as an inductor in series with a resistor

using MicroSim Pspice software. The time to saturation for our ignition coils is

approximately 6ms.


73

Figure 45 – Ignition Driver Circuit (Including Microcontroller)

Cylinder Compression Detector

In order to perform sequential fuel injection with out a camshaft sensor, it

is necessary to compare the transient voltage spikes at the companion ignition

coils for cylinder compression detection. The Cylinder Compression Detector is

essentially a comparator circuit. It is designed to convert the transient pulses

found at the primary ignition coils during spark plug firing into a TTL signal that

will correspond to the compression stoke of number four and number one

cylinders. This signal will allow the microcontroller to supply fuel sequentially

without the use of a camshaft sensor.


74

The ignition coil primaries of number one and four cylinders are connected

to two voltage dividers to reduce the voltage to acceptable levels for the Op Amp.

Using the voltage divider rule for two series resistors,

,

the transient voltages at the primary ignition coils are lowered from 150V to 15V

and 200V to 20V using R2 = 10R1 and R4 = 10R3. Using 1nF capacitors in parallel

with R2 and R4, we added two low-pass filters (LPF) to the circuit to spread the

voltage spikes out in time for easier comparison. The cut off frequency of the

LPF must be set above 166 Hz, which is the frequency of the spark events at

10,000 RPM when both coils are being fired simultaneously. The equation is

The cutoff frequency is determined to be 175 kHz, which is well above our limit.

This results in a TTL signal corresponding to the compression cycles of number

one and four cylinders. An example of the logic of the Op Amp output is:

If V cylinder 4 > V cylinder 1, then the comparator output is 5V.

If V cylinder 4 < V cylinder 1, then the comparator output is 0V.

(See Appendix J for the circuit simulation.)

This signal is then sampled at the same time as the firing of the ignition

coils one and four in order to determine where the engine is in regards to power

and exhaust stroke on either cylinder. The schematic is shown on the next page

as Fig. 46.


75

Figure 46 – Cylinder Compression Detector

Microcontroller

The microcontroller is used to determine the correct time to fire each

injector and how long to leave them open. It must be able to establish the engine

position, speed, and manifold pressure. It receives three inputs from the

Crankshaft Position sensor, Manifold Pressure sensor, and the Rich/Lean

Adjustment. It outputs four signals with each corresponding to an injector driver

for each cylinder.


76

The microcontroller first starts out by calling the subroutine FIND_14. This

subroutine is a capture of the crankshaft signal. The capture command gives the

period of the signal. At cranking speed, the duration of the open tooth region is

approximately 25ms. When the captured time reaches this value, the position of

the cylinders are known.

For the first 50 revolutions of the engine, the pulse width of the fuel supply

is a constant 3ms. This is because the engine needs extra fuel on startup and

the MAP sensor is not used yet. After the position of the engine is determined, a

subroutine, FUEL_SPARK, is called. FUEL_SPARK first sends five volts to

appropriate output pins connected to the driver circuits of cylinders 1 and 4 for

the 3ms fuel supply. The subroutine then counts three teeth on the crankshaft

wheel, which corresponds to the position of cylinders 2 and 3. When the third

tooth is found 5 volts is sent to the corresponding pins of the driver circuits for

cylinder 2 and 3 for a 3ms fuel supply. To determine the position of cylinders 1

and 4 again, the subroutine is set up to count three more teeth and generate an

interrupt after the third count. FUEL_SPARK is now called whenever this

interrupt is generated.

After the 50th revolution, the duration of fuel supply is determined based on

the manifold pressure. The subroutine FUELMASS is called after the 50th

revolution. FUELMASS calculates the mass of fuel and determines the fuel

supply pulse width depending on the manifold pressure. The subroutine then

performs an A/D conversion of the MAP sensor voltage. The linear relationship

between manifold pressure and MAP sensor voltage is y = -111x + 135200,

where x is the MAP voltage and y is the manifold pressure. The mass of fuel

(mg) is then calculated using the Ideal Gas Law equation:

The pulse width is determined from the linear equation y = 486x + 400, where x

is the calculated fuel mass (mg) and y is the pulse width (in microseconds). This

equation was obtained from the injector calibration tests mentioned earlier.


77

The volumetric efficiency from the ideal gas law equation is determined

by implementing a look up table. The volumetric efficiency is a correction factor

to change the amount of fuel at different times. A perfect engine would have an

efficiency of one. To obtain this value, manifold pressure and engine speed are

needed. To determine engine rpm, the subroutine RPM is called. RPM performs

a capture of the crank sensor signal to determine the frequency of the engine,

which gives engine speed. The manifold pressure is obtained from the stored

value in the FUELMASS subroutine.

The lookup table gives different volumetric efficiency values for different

manifold pressures and different engine speeds. These tables are for engine

speeds from 1000rpm to 10000rpm and for manifold pressure from 0.1 atm to 1

atm. Each speed and pressure has corresponding volumetric efficiency values.

To determine the appropriate volumetric efficiency the subroutine RPMCHECK is

called. RPMCHECK obtains the rpm value determined in the RPM subroutine

and finds what table is to be called. The table with the rpm value closest to the

actual rpm is chosen. Once the correct table for rpm is called then the pressure

is used to determine the volumetric efficiency. This is done the same way in

which the rpm table was determined. The microcontroller finds which pressure in

the table is the closest to the actual pressure. When it finds the correct pressure

the volumetric efficiency is found.

A subroutine called RICHLEAN adjusts the fuel mass based on the

driver’s settings. The RICHLEAN subroutine performs an A/D conversion on the

voltage from the five-position switch. For the rich end the fuel mass is adjusted

by a factor of 1.4 and by a factor of 0.6 for the lean end. The linear relationship

between driver control voltage and adjusting factor is y = .0009x + 0.401, where x

is the driver control voltage and y is the adjusting factor. The subroutine

calculates the adjusting factor using this equation. The mass of fuel calculated in

the FUELMASS subroutine is multiplied by this factor to determine the adjusted

fuel mass.


78

Figure 47 – Complete Engine Control System


79

Implementation

The actual engine control system we implemented differs from the original

design in a number of ways. The engine we used was a Honda F1 instead of a

Honda F4. The ignition system we designed was not implemented for the

competition, and therefore the cylinder compression detector was not

implemented either. Two sensors were eliminated from the final system as well.

The throttle position sensor and the ambient air temperature sensor were both

omitted. The justification for these changes follows.

The implementation was done incrementally to effectively test each

system. Each interface circuit was built and tested on a proto-board before the

total system was assembled. The microcontroller was then tested on a proto-

board with a signal generator to emulate the crankshaft sensor, and LED’s

representing the outputs of the microcontroller. Following the bench testing, the

complete fuel injection system was tested on the engine using the Honda ignition

system instead of our own ignition system. The reason for this was that the

Honda F1 engine was already equipped with a working ignition system, so this

would eliminate one variable from our initial testing. We would only need to

diagnose one system in the event of a problem.

The testing and tuning of the fuel injection system was much more time

consuming than expected. This lead to a lack of time for testing the ignition

system on the vehicle, instead our ignition driver circuit was only tested on the

bench. There were concerns about implementing an ignition system at the last

minute, when a reliable system was already present. The durability of our

system was a concern since there was not ample time to test it. This combined

with not having accurate dynamometer data to tune the ignition system, lead us

to believe that we would not increase the performance or reliability of the engine

by the addition of our ignition system. We opted to use the Honda ignition

system for the competition.

The throttle position sensor was not used because we decided that the

added benefit would not be worth the required time to implement it. This input

would only affect hard accelerations when the throttle is opened quickly. This


80

would require an algorithm for the microcontroller to recognize large changes in

the throttle position reference voltage, and disregard small changes. The

microcontroller team was not able to implement a throttle position algorithm since

they were busy fixing other problems. Instead, the microcontroller team

compensated for this by sampling the MAP sensor once every revolution. The

MAP sensor response time is 1 ms, and for an engine speed of 10,000 RPM, one

revolution is 6 ms, so the change in MAP sensor voltage should be sufficient to

characterize the changes in load.


81

Patent Opportunities

After completing a patent search it was apparent that there were not any

current patents on a system for performing sequential fuel injection without the

use of a camshaft sensor. There were two earlier patents from 1996 and 1997

(US # 5,668,311 and US# 5,493,496) for determining which of two companion

cylinders is under compression for systems using waste spark. Delphi

Automotive Systems has a system that they produce called Compression Sense

Ignition that provides this particular feature. This system, like the previously

patented systems, is for a waste spark system that uses one ignition coil for two

cylinders. The description of their system mentions that it could possibly be

adapted to coil on plug systems, but it does not indicate that they have already

accomplished this.

It seemed apparent that this type of system would be fairly straightforward

to implement on a coil-on-plug application like the F4 Honda engine we were

originally scheduled to receive. The idea being that the primary ignition

waveform will be different for a cylinder firing under compression than it will be

for a cylinder firing when there is no compression present. So, if the pair of

companion cylinders A and B is fired simultaneously, then the two primary

waveforms can be compared through the use of a comparator circuit. The

comparator can be set up such that it’s output will be 5V for cylinder A on

compression, and 0V for cylinder B on compression. This information can then

be used by the microcontroller to send fuel sequentially, and fire the ignition coils

only when they are needed (every second revolution for each cylinder). See

appendix J for simulations and circuit diagram.


82

Budget

Suspension

Listed below in Figure 48 is the suspension budget. Essentially it is a

compilation of existing parts and those that have been manufactured by the

team. Fortunately, there were several sponsors that helped reduce the price of

components by selling specifically to Formula SAE groups at reduced costs.

Parts that were reused have been inspected by the group members and

determined to be safe and compatible with the new vehicle. This considerably

lowered the total cost of the suspension budget, and reduced the time spent

manufacturing many components by April.

Part Re-used Cost Quantity Total Total Needed

Steering Rack TRUE 215.00 1 215.00 $0.00Tie Rods FALSE 21.00 2 42.00 $42.00Steering Shaft TRUE 50.00 1 50.00 $0.00Steering Wheel TRUE 32.00 1 32.00 $0.00Steering Wheel Quick Release Fasteners TRUE 28.00 1 28.00 $0.00Front Dampers FALSE 90.00 2 180.00 $180.00Rear Dampers FALSE 90.00 2 180.00 $180.00Front Springs FALSE 40.00 2 80.00 $80.00Rear Springs FALSE 40.00 2 80.00 $80.00Front Upper Control Arms FALSE 7.20 2 14.40 $14.40Rear Upper Control Arms FALSE 7.20 2 14.40 $14.40Front Lower Control Arms FALSE 19.20 2 38.40 $38.40Rear Lower Control Arms FALSE 7.20 2 14.40 $14.40Push Rods FALSE 20.00 2 40.00 $40.00Rod Ends FALSE 16.00 32 512.00 $512.00Front Rockers FALSE 12.00 2 24.00 $24.00Rear Rockers FALSE 12.00 2 24.00 $24.00Fasteners FALSE 0.18 55 9.90 $9.90Front Uprights TRUE 16.00 2 32.00 $0.00Rear Uprights TRUE 18.00 2 36.00 $0.00Front Axle 20.50 2 41.00 $41.00


83

Front Hub 38.35 2 76.70 $76.70Rear Hub 32.00 2 64.00 $64.00Total Cost $1,828.20 Total Cost Needed $1,253.50

Figure 48 – Suspension & Steering Budget

Engine Intake

Again, through the reuse of parts and those that have been paid for by

sponsors, the cost of the intake system for fuel injection was minimized. Below is

the portion of the budget that is for mechanical aspects of the engine.

Part Re-used Cost Quantity Total Total Needed

Engine TRUE 250.00 2 500.00 $0.00Exhaust Manifold TRUE 40.00 1 40.00 $0.00Exhaust Tubing FALSE 20.00 1 20.00 $20.00Fire Wall FALSE 30.00 1 30.00 $30.00Mufflers TRUE 40.00 2 80.00 $0.00Intake Manifold FALSE 100.00 1 100.00 $100.00Restrictor FALSE 50.00 1 50.00 $50.00Air Filter TRUE 30.00 1 30.00 $0.00Throttle Body TRUE 100.00 1 100.00 $0.00Injectors TRUE 50.00 4 200.00 $0.00Wiring Harness TRUE 95.00 1 95.00 $0.00Oil Filter FALSE 5.00 2 10.00 $10.00Spark Plugs FALSE 1.50 8 12.00 $12.00Engine Oil FALSE 2.50 16 40.00 $40.00Fuel Tank TRUE 50.00 1 50.00 $0.00Fuel Pump TRUE 100.00 1 100.00 $0.00Fuel Pressure Regulator

FALSE 15.00 1 15.00 $15.00

Fuel Rail FALSE 40.00 1 40.00 $40.00Fuel Filter FALSE 5.00 2 10.00 $10.00Fuel Lines FALSE 20.00 1 20.00 $20.00Radiator TRUE 50.00 1 50.00 $0.00Thermostat Housing TRUE 15.00 1 15.00 $0.00Thermostat FALSE 5.00 2 10.00 $10.00Water Hose TRUE 15.00 2 30.00 $0.00Hose Clamps FALSE 2.00 6 12.00 $12.00Oil Cooler TRUE 35.00 1 35.00 $0.00Misc. FALSE 50.00 1 50.00 $50.00Total Cost $1,744.00Total Cost Needed $419.00

Figure 49 – Engine Budget


84

Engine Control

Listed below in Figure X is the final engine control budget. As seen below,

the final engine control budget of $1220.61 is very close to the projected of

$1132.00, so we did an excellent job of estimating. Although the ignition system

we designed was not implemented, all the components necessary were ordered.

Catalog Number Description Quantity Unit Price Shipping AmountPIC16F877-20P IC MCU 8K 20MHz Flash 40-DIP

MICROCONTROLLER4 9.50 38.00

A152-ND 0 INSERTION FORCE SOCKET 40 PI

2 12.63 25.26

526-NTE5205A DO-4 39V 10W ZenerNTE DIODE/RECTIFIER

4 7.32 29.28

520-ZTT400MG SIP-3 CER RES 4MHzECS CERAMIC RESONATOR

4 0.46 1.84

511-LM324N DIP-14 QUAD OP AMPSTM OPERATIONAL AMPLIFIER

4 0.22 0.88

511-L7805CV TO-220 +VRG 1.5A 5VSTM VOLTAGE REGULATOR

4 0.34 4.00 5.36

N/A Ign. coil & wire assembly for 99'GSXR600

4 15.00 60.00

N/A CDI (Ign. controller) for 99' GSXR600

1 75.00 75.00

KC006E-ND THERMISTOR 10K OHM TEMP MEASUR

1 2.88 2.88

23J10K-ND RESISTOR WIREWOUND 10K OHM

2 1.99 3.98

P300W-2BK-ND RES 300 OHM 2W 5% METAL OXIDE

4 0.29 1.16

2EZ10D5MSCT-ND

ZENER DIODE 10V 5% 2W DO-41 2 0.75 8.81 10.31

PX241-15NG5V PRESSURE TRANSDUCER(MAP SENSOR)

1 159.00 7.35 166.35

0280150715 BOSCH INJECTOR 4 80.00 27.68 347.6878560 Wire 12 Ga. Black 15' 1 2.00 2.0078550 Wire 14 Ga. Black 25' 1 2.00 2.00785305 Wire 18 Ga. Green 45' 1 2.00 2.00785309 Wire 12 Ga. White 45' 1 2.00 5.50 7.50905501 In Circuit Debugger Module (ICD) 1 86.00 5.50 91.5011DQ04-ND SCHOTTKY RECT 40V 1.1A DO-

4110 0.32 3.22

IRLZ44NS-ND HEXFET (N) 55V 47A SMD-220 10 1.60 16.00LM78L62ACZ-ND IC 6.2V POS REGULATOR TO-92 2 1.02 2.04LM7808CT-ND IC 8V 1.0 A V REG TO-220 2 0.88 1.76F1015-ND ATO FUSE 10A 32 VOLTS 5 0.51 2.55F1086-ND IN-LINE ATO FUSE HLDR 20A

RATED4 2.53 3.75 10.12

563-AU1028MG ENCLOSURE 1 15.57 15.57563-CU622A ENCLOSURE 1 18.94 18.94520-ZTT400MG CERAMIC RESONATORS 4 0.49 12.26 14.22IRLZ44-NS-ND HEXFET (N) 55V 47A 12 1.60 19.20GH5601-ND Rotary Switch 1 pole 12 pos 200 1 9.90 3.75 13.65


85

170036 Accel Crimpers 1 60.00 60.008170 MSD weather-pack connector 3 12.50 37.508171 MSD weather-pack connector 2 10.50 21.008173 MSD weather-pack connector 1 8.50 8.508174 MSD weather-pack connector 1 8.50 8.13 16.63

106 86.73 1220.61Figure 50 – Engine Control Budget


86

Timeline

A timeline for the spring semester was created at the end of the fall

semester and updated throughout the spring semester. It was originally broken

down into two teams (microcontroller and circuitry, respectively) and the main

tasks that were needed to complete the project. The main bulk of the

components were ordered early in and during the spring semester of 2001. The

original proposed completion date of April 26, 2001 could not be attained due to

monthly delays in getting the F1 engine, which delayed experimental results

needed to finalize electronic fuel injection design and coding. Considerable time

was spent on this project to ensure that we would finish on time. This timeline

has been included in appendix B.


87

Conclusion

This project was a combination of two smaller design projects involving

interdisciplanary teamwork. The finished projects were incorporated into the

racecar built by the Formula SAE Chapter at the University of Connecticut. The

overall goal of the project was to create and intergrate two components into a

highly competitive vehicle. The suspension portion of the project was designed

specifically as a mechanical engineering senior design project, and the engine

was completed through the interdisciplinary teamwork of Mechanical, Electrical,

and Computer Engineers.

The goal of the suspension team was to incorporate a system that is both

reliable and adjustable. In the design, both driving conditions and different

drivers were accounted for in creating a versitle car. The suspension had to

maintain the maximum accelerations in the lateral, positive, and negative during

the Formula SAE challenge. The major restriction was the reuse of many parts

due to budget constraints.

The goal of the engine team was to produce a high performance engine

control system for the racecar. The system runs on an electronically controlled

fuel injection system. Feedback from the engine was combined with pre-

programmed information to deliver the correct amount of fuel to the cylinders at

the correct time for peak engine performance. The system was designed to be

competitive with both the cost and performance of the current fuel injection

systems available on the market. Sequential fuel injection was incorporated in

the optimum design to increase performance, but in the practical design could

not be implemented due to time constraints. However, we were able to

implement a multiport electronic fuel injection.

The overall goals of our project were met by producing a working vehicle.

As a result of the design process, we have learned a great deal about different

engineering disciplines. All of the mechanical and electrical systems are

interrelated, the engine is controlled by the electronic fuel injection system, and

the engine’s power is transmitted via the drivetrain and the suspension system.


88

We think the University of Connecticut will be well represented at this year’s SAE

student design competition.


89

References

Bosch, Robert. Automotive Handbook. Bosch; Stuttgart, Germany. 4th ED, 1996.

Metzger, Daniel L. Electronics Pocket Handbook. 3rd ED Prentice Hall PTR; UpperSaddle River, NJ, 1998.

Milliken, William and Douglas. Race Car Vehicle Dynamics. Society of AutomotiveEngineers; Warrendale, PA, 1995.

Moran, M and Shaprio, M. Fundamentals at Engineering Thermodynamics. Wiley & Sons; New York, NY. 3rd ED, 1996.

Motorbooks International Publisher. Racecar Chassis Design. Osceola, WI, 1997.

Peatman, John B. Design with PIC Microcontrollers. Prentice Hall; UpperSaddle River, NJ, 1998.

PIC16F87X Data Sheet. Microchip Technology, 1999.

Rashid, Muhammad H. Microelectronic Circuits: Analysis and Design. PWS Publishing Company; Boston, MA, 1999.

Staniforth, Allan. Altair SuspensionGen User’s Manual. Altair Computing Inc.; Troy, MI. Version 1.13, 1998.

Stone, Richard. Introduction to Internal Combustion Engines. Society of Automotive Engineers, Warrendale, PA. 3rd ED, 1999.

Thomas, Roland E. and Rosa, Albert J. The Analysis and Design of Linear Circuits. Prentice Hall PTR; Upper Saddle River, NJ, 1998.


90

Acknowledgements

Society of Automotive Engineers, University of Connecticut Chapter

Dr. John Ayers for continuous help, technical and non-technical support

Dr. Jim Cowart for guidance and technical support and answers to

questions concerning automotive theory

UConn Engineering Machine Shop personnel Tom, Rich, and Serge for

their help and support with the project

Mr. Peter Boardman for his advice and facilities support

Mr. Marty Wood for his help getting us started with Formula SAE and

support throughout the project.


91

Appendix

Appendix A – Figure List

Figure 1 – Vehicle Coordinates.........................................................................................................................8Figure 2 – Various Commercially Available Fuel Injection/Ignition Systems..................................................13Figure 3 – Suspension Setup Types...............................................................................................................15Figure 4 – Roll Center Location......................................................................................................................16Figure 5 – Graph of Roll Center Height vs. Wheel Displacement...................................................................18Figure 6 – Demonstration of Negative and Positive Camber..........................................................................19Figure 7 – Graph of Camber vs. Wheel Displacement...................................................................................20Figure 8 – Scrub Radius.................................................................................................................................21Figure 9 – Toe-In/Out vs. Wheel Displacement..............................................................................................21Figure 10 – Graph of Caster Angle vs. Wheel Displacement.........................................................................22Figure 11 – Graph of Kingpin Angle vs. Wheel Displacement........................................................................23Figure 12 – Diagram of Ackerman’s Principle.................................................................................................23Figure 13 – Acceleration Data used for Calculations......................................................................................25Figure 14 – Graph of Relevant Forces............................................................................................................25Figure 15 – Vertical Tire Force Calculation.....................................................................................................26Figure 16 – Lateral Acceleration Loads..........................................................................................................26Figure 18 – Longitudinal Weight Transfer.......................................................................................................26Figure 19 – Maximum Achievable Loads........................................................................................................27Figure 20 – Schematic of tire with axes..........................................................................................................27Figure 21 – Horizontal Tire Force...................................................................................................................28Figures 22a & 22b – Force Schematic & Truss Design..................................................................................30Figure 23 – Material Properities for a 14 inch pin-pin beam...........................................................................31Figure 24 – Front Uprights..............................................................................................................................32Figure 25 – Rear Uprights...............................................................................................................................33Figure 26 – Rockers........................................................................................................................................34Figure 27 – Push Rods...................................................................................................................................35Figure 28 – Steering Arms..............................................................................................................................36Figure 30 – Engine Speed vs. Volumetric Efficiency......................................................................................47Figure 31 – Fuel volumes compared to stoichiometric ratios..........................................................................48Figure 32 – Fuel Injector Test Rig...................................................................................................................49Figure 33 – Fuel Volume vs. Pulse Width.......................................................................................................50Figure 34 – Injector differential pressure layout..............................................................................................51Figure 35 – Intake manifold for a 4-cylinder engine........................................................................................53Figure 36 – Pipe length benefits at particular engine speeds.........................................................................55Figure 37 – Runner Shapes at the Mouth.......................................................................................................57Figure 38 – Intake Manifold and Fuel Rail (Side View)...................................................................................58Figure 39 – Intake Manifold and Fuel Rail (Front View)..................................................................................60Figure 40 – Control Variables.........................................................................................................................65Figure 41 – Variable Reluctance Sensor (VRS) Interface Circuit...................................................................66Figure 42 – Manifold Absolute Pressure (MAP) Sensor Circuit......................................................................68Figure 43 – Rich/Lean Adjustment Circuit......................................................................................................69Figure 44 – Fuel Injector Driver Circuit...........................................................................................................71Figure 45 – Ignition Driver Circuit (Including Microcontroller).........................................................................74Figure 47 – Complete Engine Control System................................................................................................79Figure 48 – Suspension & Steering Budget....................................................................................................84Figure 49 – Engine Budget.............................................................................................................................84Figure 50 – Engine Control Budget.................................................................................................................86


92

Appendix B – Timeline


93

Appendix C – Tire Data


94

Appendix D – Valve Timing


95

Appendix E – String Model


96

Appendix F – Microcontroller

Port Schema

Port I/O Name PinMCLR/VPP/THV I 5V Regulator Circuit 1VDD I 5V Regulator Circuit 11VDD I 5V Regulator Circuit 32VSS I GND 12VSS I GND 31OSC1/CLKIN I Resonator (RES) Circuit 13OSC2/CLKOUT I Resonator (RES) Circuit 14RA0/AN0 I Manifold Air Pressure (MAP) Circuit 2RC0/T1OSO/T1CKI I Variable Reluctance Sensor (VRS) Circuit 15RC2/CCP1 I Variable Reluctance Sensor (VRS) Circuit 17RE0/RD/AN5 I Cylinder Compression Detector (CCD) Circuit 8RA1/AN1 I Rich/Lean Sensor (R/LS) Circuit 3RA2/AN2/VREF- I Ambient Air Sensor (AAS) Circuit 4RA3/AN3/VREF+ I Throttle Position Sensor (TPS) Circuit 5RD0/PSP0 O Fuel Injector Driver (FID) Circuit 1 19RD5/PSP5 O Fuel Injector Driver (FID) Circuit 2 28RD6/PSP6 O Fuel Injector Driver (FID) Circuit 3 29RD7/PSP7 O Fuel Injector Driver (FID) Circuit 4 30RD1/PSP1 O Ignition Driver (IGD) Circuit 1 20RD2/PSP2 O Ignition Driver (IGD) Circuit 2 21RD3/PSP3 O Ignition Driver (IGD) Circuit 3 22RD4/PSP4 O Ignition Driver (IGD) Circuit 4 27


97

Microcontroller Code

;;;;;;;;;;;;;;;;;;;;;;;;; UCONN - FORMULA SAE RACE CAR ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; Engine control system - Ignition System and Fuel Injection System ;;This program controls the fuel supply and spark to the engine of the Formula SAE race car ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

list P=PIC16F877, F=INHX8M, C=160, N=77, ST=OFF, MM=OFF, R=DEC, X=OFF#include P16F877.inc__config(_CP_OFF & _PWRTE_ON & _XT_OSC & _WDT_OFF & _BODEN_OFF)

;;;;;;; Equates ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

Bank0RAM equ H'20' ;Start of Bank 0 RAM areaMaxCount equ 50 ;Number of loops in half a second

;;;;;;;;;;;;;;;;;; VARIABLES ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

cblock Bank0RAMSCALER ; register associated with looptimeRTIMEH ; captured rise time of crank signal (high byte)RTIMEL ; captured rise time of crank signal (low byte)FTIMEH ; captured fall time of crank signal (high byte)FTIMEL ; captured fall time of crank signal (low byte)TIMEH ; calculated pulse width (high byte)TIMEL ; calculated pulse width (low byte)RPMREGH ; rpm register (high byte)RPMREGL ; rpm register (low byte)SECHSECLW_TEMPSTATUS_TEMPCONTROLFALLTIMEHFALLTIMELRISETIMEHRISETIMELMAXHMAXLY1INT1Y1INT2Y1INT3Y2INT0Y2INT1MAPREGHMAPREGLCHARGETIMEREVCOUNTRLREGHRLREGLY3INT1Y3INT0HIGHHHIGHLTIMERHTIMERLTRANSCHECKADDH


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ADDLFMASSendcinclude math.inc

;;;;;;;;;;;;;;;;;; VECTORS ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

org H'000' ; Reset vectornop ; For debuggoto Mainline; Branch past tablesorg H'004' ; Interrupt vectorgoto IntService ; Branch to interrupt service routine

;;;;;;;;;;;;;;;;;; MACRO DEFINITIONS ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

MOVLF macro literal,destmovlw literalmovwf destendm

MOVFF macro source,destmovf source,Wmovwf destendm

;;;;;;;;;;;;;;;;;; Mainline Program ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

Mainlinecall Initial ; call to initial all registerscall FIND_14 ; find engine position

MainLoopnopnopgoto MainLoop ; go back up (loop)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; INITIAL SUBROUTINE ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

InitialMOVLF 4,SCALERMOVLF 0,CONTROLMOVLF 50,REVCOUNTbcf STATUS,RP0 ; set register access to bank 0MOVLF B'00001101',T2CON ; set up timer2 to use 4MHz clockbsf INTCON,PEIE ; Timer2 set up (pg. 60)clrf PORTD ; clear portdbsf STATUS,RP0 ; set register access to bank 1bsf PIE1,TMR2IE ; Timer2 set up (pg. 60)MOVLF B'10000000',ADCON1 ; select PORTA/E pins, right justifiedMOVLF B'00001011',TRISA ; set I/O for PORTAMOVLF B'00000100',TRISE ; set I/O for PORTEMOVLF B'11111001',PR2 ; set up timer2 to use 4MHz clock MOVLF B'00000101',TRISC ; Make RC2/CCP1 an input (pin 17) and RC1/CCP2 (pin 16)

an output

MOVLF B'11110001',TRISB ; declare bit 0 of RB0/INT (pin 33) as an inputclrf TRISD ; make PORTD pins output pinsbcf STATUS,RP0 ; back to bank 0MOVLF B'11000000',INTCON ; enable global, peripheral interrupts.return

;;;;;;;;;;;;; Capture subroutine for cranksensor signal pulse width ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Using timer1 here, crank signal goes to RC2/CCP1 pin 17 ;;;;;;;;;;;;;;;;;;;;;;;;


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CRANKPULSEbcf PIR1,CCP1IF ; clear to set up for falling edgebsf PIE1,CCP1IE ; set to set up for falling edgeMOVFF CCPR1H,RTIMEH ; move captured time to defined register (high byte)MOVFF CCPR1L,RTIMEL ; move captured time to defined register (low byte)bcf CCP1CON,0 ; clear bit 0 to capture falling edgeMOVFF CCPR1H,FTIMEH ; move captured time to defined register (high byte)MOVFF CCPR1L,FTIMEL ; move captured time to defined register (low byte)clrf CCPR1H ; Clear all times after pulse width is foundclrf CCPR1L ; Clear all times after pulse width is foundmovf RTIMEH,W ; move rise time (high) to W registersubwf FTIMEH,F ; subtract high bytes and store in F registermovf RTIMEL,W ; move rise time to W registersubwf FTIMEL,F ; subtract low bytes and store in F registerbtfss STATUS,C ; if a borrow occured then decrementdecf FTIMEH,F ; decrement if borrow occured call RPMreturn

;;;;;;;;;;;;;; This subroutine calculates the rpm of the engine ;;;;;;;;;;;;;;;;;;;;;;;;;;;;

RPMMOVFF FTIMEH,AARGB0MOVFF FTIMEL,AARGB1MOVLF 0,BARGB0MOVLF 16,BARGB1call FXM1616UMOVLF B'00000011',BARGB0 ; high byte, putting 1000 inMOVLF B'11101000',BARGB1 ; low byte, putting 1000 incall FXD3216U ; converting from usecs to secsMOVLF B'00000011',BARGB0 ; high byte, putting 1000 inMOVLF B'11101000',BARGB1 ; low byte, putting 1000 incall FXD3216U ; converting from usecs to secs, max # obtainable is 4295

(16bit)MOVFF AARGB2,SECHMOVFF AARGB3,SECLMOVLF 0,AARGB0MOVLF 60,AARGB1MOVFF SECH,BARGB0MOVFF SECL,BARGB1call FXD1616UMOVFF AARGB0,RPMREGHMOVFF AARGB1,RPMREGLreturn

FXM1616U CLRF ACCB2 CLRF ACCB3 MOVF AARGB0,W MOVWF TEMPB0 MOVF AARGB1,W MOVWF TEMPB1 UMUL1616L RETLW 0x00

FXD3216U CLRF REMB0 CLRF REMB1 UDIV3216L RETLW 0x00

FXD1616U CLRF REMB0 CLRF REMB1 UDIV1616L RETLW 0x00


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;;;;;;;;;;;;; Send spark when missing teeth show up (falling edge) ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Rectified and clipped crank signal goes into RB0/INT (pin 33) ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Using Timer1 here also ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Call CRANKPULSE here, want to find rpm only after missing teeth have passed ;;;;;;;;;;;;;;;;;;;;;;; Clipped signal goes to RC0/T1OSO/T1CKI ;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;;;; Timer1 is set up as timer initially ;;;;;;;;;;;;;;;;;;;;;

FUEL_SPARKclrf INTCON ; disable all interruptsMOVLF B'10000001',PORTD ; Send fuel to cylinder 1 and 4 (pins 0

and 7 of PORTD)clrf T1CON ; stop timer 1clrf TMR1H ; clear Timer1 (High Byte)clrf TMR1L ; clear Timer1 (Low Byte)btfss REVCOUNT,7call load3msbtfsc REVCOUNT,7call PWVALUEclrf PIR1bsf T1CON,TMR1ON ; start clocking timer

check btfsc PIR1,TMR1IF ; keep sending fuel as long as time is not up (no interrupt)

nopbtfss PIR1,TMR1IF ; proceed to send spark if interrupt has

occuredgoto check ; repeatnopclrf T1CONclrf PORTD ; stop sending fuel only after interrupt

has occuredbcf PIR1,TMR1IFMOVLF B'00010010',PORTD ; Send spark to cylinder 1 and 4 (pins 1

and 4 of PORTD)clrf TMR1Hclrf TMR1LMOVLF B'10011100',TMR1L ; To generate 100us delay between on

and off time for coils

MOVLF B'11111111',TMR1H ; To generate 100us delay between on and

off time for coilsclrf PIR1 ; clear peripheral interrupt flagbsf T1CON,TMR1ON ; Start clocking TMR1 again

check1 btfsc PIR1,TMR1IF ; Keep charging coil until 100us are upnopbtfss PIR1,TMR1IF ; skip next instruction if interrupt has

occuredgoto check1 ; repeatnopclrf T1CON ; Stop timer 1clrf PORTD ; remove signal from PORTD, sparks

explodebcf PIR1,TMR1IFclrf TMR1L ; new clear timer 1clrf TMR1H ; new clear timer 1MOVLF B'11111110',TMR1L ; Set up timer to generate overflow after

3rd count (rising edge)MOVLF B'11111111',TMR1H ; Set up timer to generate overflow after

3rd count (rising edge)clrf PIR1 ; clear peripheral interrupt flagmovlw 0x0E ; external clock set upmovwf T1CON ; external clock set upbsf T1CON,TMR1ON

check2 btfsc PIR1,TMR1IF ; skip next command if 3rd tooth has not been counted


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nopbtfss PIR1,TMR1IFgoto check2 ; repeatnopclrf T1CON ; stop timercall LOAD_23bcf PIR1,TMR1IFclrf TMR1L ; clear timerclrf TMR1H ; clear timerbtfss REVCOUNT,7call load3ms ;load 3ms into timer1btfsc REVCOUNT,7call PWVALUEclrf PIR1 ; clear peripheral interrupt flagbsf T1CON,TMR1ON ; start timer

check3 btfsc PIR1,TMR1IF ; keep sending fuel until .03s are upnopbtfss PIR1,TMR1IF ; skip if interrupt has occuredgoto check3 ; repeatnopclrf T1CON ; stop timer1clrf PORTD ; remove fuel supplyMOVLF B'00001100',PORTD ; send spark to cylinder 2 and 3 (pins 2

and 3 of PORTD)bcf PIR1,TMR1IFclrf TMR1L ; clear timer1clrf TMR1H ; clear timer1MOVLF B'10011100',TMR1L ; To generate 100us delay between on

and off time for coils

MOVLF B'11111111',TMR1H ; To generate 100us delay between on and

off time for coilsclrf PIR1 ; disable peripheral interrupt flagbsf T1CON,TMR1ON ; start timer1

check4 btfsc PIR1,TMR1IF ; Keep charging coil until 100us are upnopbtfss PIR1,TMR1IF ; Do not repeat if interrupt has occuredgoto check4 ; repeatnopclrf T1CON ; stop timer1clrf PORTD ; remove signal from PORTD, sparks

explodebcf PIR1,TMR1IF ; clear timer1 interruptMOVLF B'00000001',CONTROLcall CHECK_7btfss REVCOUNT,7decf REVCOUNT,F ; decrement REVCOUNTnopMOVLF B'11000000',INTCON ; re-enable global and peripheral

interrupts, RB0 interrupt is disabled permanently

return

;;;;;;;;;;;;;;;;;;;;;;load_23;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;LOAD_23

MOVLF B'01100000',PORTDreturn

;;;;;;;;;;;;;;;;;;;;;load3ms;;;;;;;;;;;;;;;;;;;;;;;;;;;;;load3ms

clrf TMR1Lclrf TMR1HMOVLF B'01001000',TMR1L ; generate 3ms


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MOVLF B'11110100',TMR1H ; generate 3msreturn

;;;;;;;;;;;;;; Subroutine to count 7th tooth, timer1 is running after FUEL_SPARK is exited ;;;;;;

CHECK_7bcf STATUS,RP0 ; bank 0clrf T1CON ; Stop timer 1clrf TMR1H ; new clear timer 1clrf TMR1L ; new clear timer 1MOVLF B'11111111',TMR1H ; Set up timer to generate overflow after

4th count (rising edge)MOVLF B'11111110',TMR1L ; Set up timer to generate overflow after

4th count (rising edge)bsf STATUS,RP0 ; enter bank 1clrf PIE1 ; disable peripheral interruptbcf STATUS,RP0 ; bank 0clrf PIR1 ; clear peripheral interrupt flagmovlw 0x0E ; external clock set upmovwf T1CON ; external clock set upbsf STATUS,RP0 ; enter bank 1bsf PIE1,TMR1IE ; enable timer1 interruptbcf STATUS,RP0 ; bank 0bsf T1CON,TMR1ON ; start clocking TMR1 (counter)return

;;;;;;;;;;;;;;;;;;; This subroutine is called to find engine position ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Signal in CCP1 pin ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

FIND_14btfsc CONTROL,0goto last

start clrf T1CON ; stop timer1clrf CCP1CON ; CCP module is offclrf TMR1Hclrf TMR1Lclrf INTCONclrf PIR1 ; clear peripheral interrupt flagsbsf STATUS,RP0 ; enter bank 1clrf PIE1 ; disable peripheral interruptsbcf STATUS,RP0 ; bank 0MOVLF H'04',CCP1CON ; capture falling edgebsf T1CON,TMR1ON ; start timer

cap btfss PIR1,CCP1IFgoto capMOVFF CCPR1H,FALLTIMEH ; move captured time (high byte)MOVFF CCPR1L,FALLTIMEL ; move captured time (low byte)bcf PIR1,CCP1IF ; clear flagMOVLF H'05',CCP1CON ; capture rising edgebcf PIR1,CCP1IF ; safety clear, avoid false interrupt

cap1 btfss PIR1,CCP1IFgoto cap1MOVFF CCPR1H,RISETIMEHMOVFF CCPR1L,RISETIMELbcf PIR1,CCP1IFclrf CCP1CON ; CCP module is offclrf T1CON ; stop timer1movf FALLTIMEH,W ; move rise time (high) to W registersubwf RISETIMEH,F ; subtract high bytes and store in F

registermovf FALLTIMEL,W ; move rise time to W registersubwf RISETIMEL,F ; subtract low bytes and store in F

registerbtfss STATUS,C ; if a borrow occured then decrementdecf RISETIMEH,F ; decrement if borrow occured


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nop ; cushionnop ; cushionbtfsc RISETIMEH,6call FUEL_SPARKbtfss RISETIMEH,6goto start

last nopreturn

;;;;;;;;;;;;; This subroutine calculates pulse width ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

FUELMASSclrf INTCON ;disable interuptsMOVLF B'01000001',ADCON0 ; select analog input on PORTA, bit 0MOVLF 15,CHARGETIME ;

keep decfsz CHARGETIME,Fgoto keepbsf ADCON0,GO_DONE ; stored in ADRESL and ADRESH

DELAYbtfsc ADCON0,GO_DONE ; tests if conversion is complete

i.e GO_DONE (O or 1?)

goto DELAY ; repeat above test if GO_DONE = 1bsf STATUS,RP0 ; bank 1movf ADRESL,Wbcf STATUS,RP0movwf MAPREGL ;load adresl into mapreglmovf ADRESH,Wmovwf MAPREGH ;load adresh into mapreghMOVFF MAPREGL,AARGB1 ; moveMOVFF MAPREGH,AARGB0 ; moveMOVLF B'01101111',BARGB1 ; store 111 for slopeMOVLF 0,BARGB0 ; store 111 for slopecall FXM1616U ; 32 bit output, AARGB0 is emptyMOVLF B'00100000',Y1INT3 ; move 135200MOVLF B'00010000',Y1INT2 ; move 135200MOVLF B'00000010',Y1INT1 ; move 135200movf AARGB1,W ; subract (straight line equation)subwf Y1INT1,F ; result stored in Y1INT1movf AARGB2,Wsubwf Y1INT2,Fbtfss STATUS,Cdecf Y1INT1,Fbsf STATUS,C ; fixmovf AARGB3,Wsubwf Y1INT3,Fbtfss STATUS,Cdecf Y1INT2,FMOVLF 0,AARGB0MOVFF Y1INT1,AARGB1MOVFF Y1INT2,AARGB2MOVFF Y1INT3,AARGB3MOVLF B'00000001',BARGB0 ; move 300MOVLF B'00101100',BARGB1 ; move 300call FXD3216U ; call math, 16 bit outputMOVFF AARGB3,AARGB1MOVFF AARGB2,AARGB0MOVLF 150,BARGB1MOVLF 0,BARGB0call FXM1616U ; 32 bit outputMOVLF B'00011111',BARGB1 ; store 287MOVLF B'00000001',BARGB0 ; store 287call FXD3216U ; 8 bit out putMOVFF AARGB3,AARGB1MOVFF AARGB2,AARGB0


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MOVLF 0,BARGB0MOVLF 14,BARGB1call FXD1616UMOVFF AARGB1,FMASSMOVFF REMB1,AARGB1MOVLF 0,AARGB0MOVLF 10,BARGB1MOVLF 0,BARGB0call FXM1616U ; 32 bit outputMOVFF AARGB3,AARGB1 ; maximum is 13*10 = 130MOVFF AARGB2,AARGB0 ; 0 here alwaysMOVLF 14,BARGB1MOVLF 0,BARGB0call FXD1616U ; 16 bit output, whole number value for

remainderMOVLF 50,BARGB1MOVLF 0,BARGB0call FXM1616U ; 32 bit output, max value is 450 in

AARGB2, AARGB3

MOVFF AARGB3,ADDL ; to be added to timerMOVFF AARGB2,ADDH ; to be added to timerMOVFF FMASS,AARGB1MOVLF 0,AARGB0MOVFF Y3INT1,BARGB1 ; rich/lean value

MOVFF Y3INT0,BARGB0 ; rich/lean valuecall FXM1616U ; 32 bit output, AARGB2, AARGB3MOVFF AARGB3,AARGB1MOVFF AARGB2,AARGB0MOVLF B'00000011',BARGB0 ; store 1000MOVLF B'11101000',BARGB1 ; store 1000call FXD1616U ; 16 bit output, rich/lean adjusted fuel

massMOVLF 0,AARGB0MOVLF B'11100110',BARGB1 ; store 486 for slopeMOVLF B'00000001',BARGB0 ; store 486 for slopecall FXM1616U ; 32 bit outputMOVLF B'10010000',Y2INT1 ; store 400 (y-intercept) gives 2.6ms

idleMOVLF B'00000001',Y2INT0 ; store 400 (y-intercept) gives 2.6ms

idlemovf AARGB3,Waddwf Y2INT1,Fmovf AARGB2,Wbtfsc STATUS,Cincfsz AARGB2,Waddwf Y2INT0,Fmovf ADDL,Waddwf Y2INT1,Fmovf ADDH,Wbtfsc STATUS,Cincfsz ADDH,Waddwf Y2INT0,Fnopreturn

;;;;;;;;;;;;;;;;;;; Find value for timer 1 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

PWVALUEMOVLF 255,TIMERH ;calculating of valuesMOVLF 255,TIMERLmovf Y2INT0,Wsubwf TIMERH,Fmovf Y2INT1,W


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subwf TIMERL,Fbtfss STATUS,Cdecf TIMERH,Fclrf TMR1Hclrf TMR1LMOVFF TIMERH,TMR1H ;loading of valuesMOVFF TIMERL,TMR1Lreturn

;;;;;;;;;;;;;;;;;;;; This subroutine determines fuel amount correction from driver controls ;;;;;;;;;;

RICHLEANclrf INTCON ; disable global interruptsMOVLF B'01001001',ADCON0 ; select bit 1 of PORTAMOVLF 15,CHARGETIME ; capacitor chargetime

keep1 decfsz CHARGETIME,Fgoto keep1bsf ADCON0,GO_DONE ; stored in ADRESL and ADRESH

DELAY1btfsc ADCON0,GO_DONE ; tests if conversion is complete

i.e GO_DONE (O or 1?)

goto DELAY1 ; repeat above test if GO_DONE = 1bsf STATUS,RP0 ; bank 1movf ADRESL,Wbcf STATUS,RP0movwf RLREGLmovf ADRESH,Wmovwf RLREGHMOVFF RLREGH,AARGB0MOVFF RLREGL,AARGB1MOVLF 0,BARGB0MOVLF 5,BARGB1call FXM1616UMOVFF AARGB3,AARGB1MOVFF AARGB2,AARGB0MOVLF 10,BARGB1MOVLF 0,BARGB0call FXD1616U ; 16 bit output AARGB0 and AARGB1MOVLF B'10111101',Y3INT1 ; move 701 (y-intercept)MOVLF B'00000010',Y3INT0 ; move 701 (y-intercept)movf AARGB1,Waddwf Y3INT1,Fmovf AARGB0,Wbtfsc STATUS,Cincfsz AARGB0,Waddwf Y3INT0,Freturn

;;;;;;;;;;;;; Interrupt Service - Change from 00000000 to 11111111 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ; ;

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

IntServicemovwf W_TEMP ; Copy W to RAM, set aside W and STATUSswapf STATUS,W ; Move STATUS to W without affecting Z bitmovwf STATUS_TEMP ; Copy to RAM (with nibbles swapped)

Pollbtfsc PIR1,TMR2IF ; Don't call Timer2 if interrupt hasn't occured,

callbcf PIR1,TMR2IF ; Timer2 if interrupt has occured (i.e clear

interrupt flag)


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btfsc PIR1,TMR1IF ; always clear until 7th toothcall RICHLEANbtfsc PIR1,TMR1IF ; always clear until 7th toothcall FUELMASS ; call FUEL_SPARKbtfsc PIR1,TMR1IFcall FUEL_SPARKswapf STATUS_TEMP,W ; Restore STATUS bits (unswapping nibbles)movwf STATUS ; without affecting Z bitswapf W_TEMP,F ; Swap W_TEMPswapf W_TEMP,W ; and swap again into W without affecting Z bitretfie ; Return from mainline code, reenable interruptsend


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Appendix G – PCBoards Circuit Layout


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Appendix H – RC Compression Damping


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Appendix I – RC Rebound Damping


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Appendix J – Simulations of Cylinder Compression Detector


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Appendix K – Thank you to all of our Sponsors

Project Sponsors


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Yard Apes Landscaping

Parker Medical

CFR Welding

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