8367 Project Documentationn

7/21/2019 8367 Project Documentationn

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LITERATURE REVIEW

1. INTRODUCTION

The act of guiding the vehicle is called steering. Wheeled vehicles are steered by aiming or

pointing the wheels in the direction we want the vehicle to go. The driver of a car or truck

guides it by turning the steering wheel. The function of a steering system is to convert the

rotary movement of the steering wheel in driver's hand into the angular turn of the front

wheels on road. Additionally, the steering system should provide mechanical advantage over

front wheel steering knuckles, offering driver an easy turning of front wheels with minimum

effort in any desired direction. The steering system of cars and trucks consists of levers, links,

rods, and a gearbox and sometimes a hydraulic system that assists the driver's steering effort.

The steering system is of critical importance in the safe operation of the vehicle. There must

be no looseness between the steering wheel and the front wheels if the driver is to keep

control over the direction the wheels point. The tires must meet the road at the correct angle

to get good traction and to prevent unnecessary tire wear. Also, the driver should be able to

hold the wheels in the straight ahead position and change them to the right or left with very

little effort.

The steering system is the key interface between the driver and the vehicle. The main

reuirement is that the steering should be precise, with no play. !n addition, the steering

system should be smooth, compact and light. !t must also provide the driver with a perfect

feel for the road surface and help the wheels return to the straight"ahead position. The

standard steering arrangement is to turn the front wheels using a hand"operated steering

wheel via the steering column. The steering column may contain several #oints to allow it to

deviate somewhat from a straight line. These #oints may also be part of the collapsiblesteering column design to protect the driver in frontal crash situations.

The steering system components are a common source of driver complaints. Tire wear is

almost completely dependent on the condition and ad#ustment of the steering components.

This chapter covers the construction and operation of both conventional and rack"and"pinion

steering systems. The direction of motion of a motor vehicle is controlled by a steering

system.

1



A basic steering system has three main parts$ A steering box connected to the steering wheel.

The linkage connecting the steering box to the wheel assemblies at the front wheels. And

front suspension parts to let the wheel assemblies pivot. When the driver turns the steering

wheel, a shaft from the steering column turns a steering gear. The steering gear moves tie

rods that connect to the front wheels. The tie rods move the front wheels to turn the vehicle

right or left. There are two basic types of steering boxes " those with rack"and"pinion gearing,

and those with worm gearing. !n both cases, the gearing in the steering box makes it easier

for the driver to turn the steering wheel, and hence, the wheels.

A rack"and"pinion steering system has a steering wheel, a main"shaft, universal #oints, and an

intermediate shaft. When the steering is turned, movement is transferred by the shafts to the

pinion. The pinion is meshed with the teeth of the rack, so pinion rotation moves the rack

from side to side. This type of steering is used on passenger vehicles because it is light, and

direct. This steering system has worm gearing. !t provides a gear reduction, and a %& degree

change in direction. !t has more parts and #oints than the rack type, but it is more robust, and

may be used on heavier vehicles.

To allow heavy transport vehicles to carry extra weight, two steering axles may be used.

Theyre connected by a link to a common steering box. These vehicles are called tandem, or

twin"steered vehicles. (ome passenger vehicles also steer the rear wheels slightly. This gives

improved maneuverability. The system is known as )"wheel steering. !t can be controlled

mechanically, through a direct connection, between the front and rear steering boxes. *r it

can be computer"controlled. With heavier vehicles, increased use of front"wheel"drive, and

wider, low"profile tyres, more steering effort is needed, so power steering is used. An engine"

driven hydraulic pump provides pressure that helps the driver steer the vehicle. The power

steering system is designed so that the vehicle can still be controlled, even if the engine or the

power steering system, fails.

+



+. FUNCTIONS OF A STEERING SYSTEM

The steering system is a group of parts that transmit the movement of the steering wheel to

the front, and sometimes the rear, wheels. The primary purpose of the steering system is to

allow the driver to guide the vehicle. When a vehicle is being driven straight ahead, the

steering system must keep it from wandering without reuiring the driver to make constant

corrections. The steering system must also allow the driver to have some road feel feedback

through the steering wheel about road surface conditions-. The steering system must help

maintain proper tire"to"road contact. or maximum tire life, the steering system should

maintain the proper angle

/ontrol of front wheel sometimes rear wheel- direction.

Transmit road feel slight steering wheel pull caused by the road surface- to the

drivers hand.

0aintain correct amount of effort needed to turn the wheels

Absorb most of the shock going to the steering wheel as the tire hits holes and bumps

in the road.

Allow for suspension action.



. LAYOUT OF A STEERING SYSTEM

1. Steering Wheel

The only part of the steering system the average driver is familiar with is the steering wheel.

*lder wheels are made of hard plastic, are larger in diameter, and are relatively thin when

compared to modern steering wheels. The modern steering wheel is generally padded. 0ost

steering wheels have two or three spokes or a large center section that connects the wheel

portion to the hub. To prevent slippage, the steering wheel hub has internal splines, which

match external splines on the steering shaft. (ome shafts and steering wheels have a master

spline, which is larger than the others. The master spline prevents the installation of the wheel

in the wrong position. A large nut holds the hub to the steering shaft.

2. Steering Col!n

The steering shaft is installed in the steering column. 2earings are generally used to hold the

shaft in position. The shaft and column assembly is usually removed and replaced as a unit.

)



3owever, individual parts are often replaced without removing the shaft or column. !n this

section, we will discuss the individual parts that make up the steering column and shaft

assembly.

". Steering Sh#$t

0odern steering shafts are made of two sections of steel rod. *ne section is hollow and the

other is solid. The solid section slides into the hollow section. This design allows the steering

shaft to collapse when the vehicle is in a collision. or this reason it is called collapsible

shaft. /ollapsible shafts are often referred to as telescoping shafts, since the shaft length is

reduced as one section of the shaft slides into the other in the same way a portable telescope

is collapsed. 4uring normal driving, the two halves of the steering shaft are held in position

by shear pins. (hear pins are purposely made of a relatively weak material, usually plastic.

Their purpose is to break when sufficient pressure is placed on them, preventing in#ury to the

driver. !f a collision occurs that is severe enough to cause the driver to strike the steering

wheel, the shear pins break, allowing the shaft to collapse.

%. Steering ge#r &o'

The heart of the steering system is the steering gear. This unit is also called steering

mechanism. This unit is ordinarily fixed to the bottom of the steering column. This unit is

located between the steering shaft and the steerable stub axles which carry the road wheels.

The input shaft of the steering gear is operated by the steering shaft. The steering gear

performs two functions$ 1. !t converts the rotary motion of the steering wheel into linear

motion of the steering linkage which moves the front wheels. +. !t introduces a leverage

between the steering wheel and the stub axles. This leverage reduces the effort that has to be

applied by the driver to the steering wheel in order to overcome the frictional forces opposing

the turning of the stub axles and the road wheels. !n order to have the above leverage, the

steering wheel has to be turned through larger angles than the stub axles. !n the case of

automotive vehicles, normally the road wheels are deflectable to about 5&& on each side of

the straight ahead position. The extreme wheel positions are called full lock positions of the

wheels. To effect this extent of turning of the road wheels, the steering wheel may have to be

turned through from ) to % or 1& times that angle. This relationship is called steering ratio.

The term steering ratio is the ratio of the 6 number of degrees of movement at the hand wheel

steering wheel- which will produce one degree of movement of the front wheels. The

5



amount of leverage provided by the steering gear depends upon several factors. The most

important among them are the weight of the vehicle and the type of tyre used. The typical

gear ratios are 1)$1 or higher. !n heavy duty vehicles this ratio is sometime as high as &$1 to

5$ 1. The greater the ratio, steering gear ratio, the easier the steering wheel turns. Trucks are

provided with higher leverage than cars. The steering gear incorporates another important

feature called back locking. The steering gear is so constructed that it is easy to turn the

vehicle by the steering wheel but it is difficult to turn the steering wheel by turning the front

wheels. This irreversible character of the steering gear prevents the bumps and shocks

experienced by the wheel at the road surface from being transmitted to the steering wheel, but

still give the driver the feel of the road. The steering gear is mounted to the vehicle frame by

bolts in the mounting pad of the steering gear.

(. )it!#n #r!

!t is also called the drop arm. !t converts the output torue from the steering gear into a force

to the drag link. !t is attached to the sector shaft of the steering gear by a split #oint. !n this

construction either full serrations or partial spline is used to transmit the torue from the

sector shaft to the pitman arm. The split arm is tightened around the sector shaft by the

clamping bolt to mate the male and female serrations or splines. The end of the pitman arm

which connects with the drag link has a taper hole in it. The ball stud on the drag link is fitted

into this hole.

*. Dr#g lin+

!t connects the pitman arm and the steering arm. !n some cases, it is a one piece forging with

a ball #oint socket formed in the end.

,. Steering #r!

!t is usually a forged component and is attached to the steering knuckle. !t converts the drag

link force into a turning moment about the left king pin. The steering arm is attached to the

spindle by a keyway, a locking taper and a nut. The arm extends either to the front or rear of

the spindle, depending upon the package constraints and then bends to locate the steering arm

ball #oint at the correct geometric location. The end of the steering arm which connects with

the drag link has a tapered hole in it to accept the ball stud on the drag link.

-. Tie ro

6



The tie rod is a tubular member which connects the left and right tie rod arms. As such it

transmits the force between these two components. The tie rod ends have female threads. The

ball #oint shafts have mating male threads. The threaded connections can be held together

firmly by the locking clamps after the proper length has been set. The length of the tie rod has

to be ad#usted so that the front axle toe in will be to the specified amount. 7ight tie rod arm,

spindle and kingpin " The right tie rod arm is a mirror image of the left. This converts the

force from the tie rod into a moment to turn through the knuckle arm, the right spindle wheel

and the tyre about the king pin. The right spindle and the king pin assembly is similar to the

assembly on the left side except that it has no steering arm attached to it.

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). STEERING SYSTEMS

%.1 T/0e o$ teering /te!

The purpose of steering gear is to enable the driver to alter the vehicles steered direction with

a minimum of effort. Three of the most common types in use are

1. Worm and peg steering system

+. 7ecirculating ball steering system

. 7ack and pinion steering system

1. Wor! #n 0eg teering /te!

A worm drive is a gear arrangement in which a worm which is a gear in the form of a screw-

meshes with a worm gear which is similar in appearance to a spur gear, and is also called a

worm wheel-. The terminology is often confused by imprecise use of the term worm gear to

refer to the worm, the worm gear, or the worm drive as a unit.

With with this type of steering mechanism the lower part of the steering column shaft is

machined with a worm"type screw thread, which meshes with a peg protuding from the arm

of the cross"shaft. When the steering wheel is rotated, worm moves the peg along and the arm

transfered to a steering drop arm and linkage to move the roadwheels.

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Wor! #n 0eg teering /te!

2. Reirl#ting &#ll teering /te!

The recirculating ball steering mechanism contains a worm gear inside a block with a

threaded hole in it: this block has gear teeth cut into the outside to engage the sector shaft

also called a sector gear- which moves the ;itman arm. The steering wheel connects to a

shaft, which rotates the worm gear inside of the block. !nstead of twisting further into the

block, the worm gear is fixed so that when it spins, it moves the block, which transmits the

motion through the gear to the pitman arm, causing the road wheels to turn.

%



The recirculating"ball steering gear contains a worm gear. <ou can image the gear in two

parts. The first part is a block of metal with a threaded hole in it. This block has gear teeth cut

into the outside of it, which engage a gear that moves the pitman arm see diagram above-.

The steering wheel connects to a threaded rod, similar to a bolt, that sticks into the hole in the

block. When the steering wheel turns, it turns the bolt. !nstead of twisting further into the

block the way a regular bolt would, this bolt is held fixed so that when it spins, it moves the

block, which moves the gear that turns the wheels.

". R#+ #n 0inion teering /te!

!t is very simple and common type mechanism, the system is shown in simplified sketch.

This type is very well suitable in an independent suspension system. The system consists of a

rack housed in a tubular casing. The casing is supported on the frame near its ends. The ends

of the rack are connected to the track rods with the help of ball and socket #oints. The pinion

shaft is carried in the plain bearings housed in casing. The pinion is meshed with the rack and

the clearance is ad#usted with the ad#usting screw. When the pinion is given rotary motion

1&



with the steering wheel, then the rack slides in either sides. This sliding motion of the rack is

used through the track rods to turn the wheels in desired side.

R#+ #n 0inion teering /te!

%.2 )o3er teering

;ower steering, assists the driver of an automobile in steering by directing a portion of the

vehicle's power to traverse the axis of one or more of the road wheels. As vehicles have

become heavier and switched to front wheel drive, particularly using negative offset

geometry, along with increases in tire width and diameter, the effort needed to turn the

steering wheel manually has increased = often to the point where ma#or physical exertion is

reuired.

A hydraulic power steering 3;(- uses hydraulic pressure supplied by an engine"driven

pump to assist the motion of turning the steering wheel. >lectric power steering >;(- is

more efficient than the hydraulic power steering, since the electric power steering motor only

needs to provide assistance when the steering wheel is turned, whereas the hydraulic pump

must run constantly. !n >;(, the assist level is easily tunable to the vehicle type, road speed,

and even driver preference.

There are a couple of key components in power steering in addition to the rack"and"pinion or

recirculating"ball mechanism

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• )!0

The hydraulic power for the steering is provided by a rotary"vane pump see diagram

below-. This pump is driven by the car's engine via a belt and pulley. !t contains a set

of retractable vanes that spin inside an oval chamber

• Rot#r/ V#l4e

A power"steering system should assist the driver only when he is exerting force on the

steering wheel such as when starting a turn-. When the driver is not exerting force

such as when driving in a straight line-, the system shouldn't provide any assist. The

device that senses the force on the steering wheel is called the rotary valve.

The key to the rotary valve is a torsion bar. The torsion bar is a thin rod of metal that

twists when torue is applied to it. The top of the bar is connected to the steering

wheel, and the bottom of the bar is connected to the pinion or worm gear which turns

the wheels-, so the amount of torue in the torsion bar is eual to the amount of torue

the driver is using to turn the wheels. The more torue the driver uses to turn the

wheels, the more the bar twists.

1+



Steering lin+#ge

The steering linkage is a combination of rods, and arms, that transmit the movement of the

steering gear to the front wheels. !t must transmit this movement to the front wheels, while

still allowing for any up"and down movement they may make, while the vehicle is in motion.

The type of steering mechanism, and the number of linkages, depends on the type of steering

box, its location, and the type of suspension on the vehicle.

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(. STEERING MEC5ANISMS

(.1 Introtion to # Steering Ge#r Meh#ni!

The steering gear mechanism is used for changing the direction of two or more of the wheel

axles with reference to the chassis, so as to move the automobile in any desired path. ?sually

the two back wheels have a common axis, which is fixed in direction with reference to the

chassis and the steering is done by means of the front wheels. A good steering mechanism is

must for a vehicles stability at the time of turning. (teering of four wheeler is designed in a

manner so that it will not permit lateral slip of front wheels during steering. There must be

true rolling of wheels at the time of steering. The front wheels are mounted on front axles to

allow their left and right swing for steering the vehicle. (teering is done by providing asuitable gearing and linkage between front wheels and steering wheel

(.2 Conition $or orret teering

!n automobiles, the front wheels are placed over the front axles, which are pivoted at the

points A and B, as shown in ig. These points are fixed to the chassis. The back wheels are

placed over the back axle, at the two ends of the differential tube. When the vehicle takes a

turn, the front wheels along with the respective axles turn about the respective pivoted points.The back wheels remain straight and do not turn. Therefore, the steering is done by means of

front wheels only.

Steering ge#r !eh#ni!

1)



!n order to avoid skidding i.e. slipping of the wheels sideways-, the two front wheels must

turn about the same instantaneous centre ! which lies on the axis of the back wheels. !f the

instantaneous centre of the two front wheels do not coincide with the instantaneous centre of

the back wheels, the skidding on the front or back wheels will definitely take place, which

will cause more wear and tear of the tyres.

Thus, the condition for correct steering is that all the four wheels must turn about the

same instantaneous centre. The axis of the inner wheel makes a larger turning angle than

the angle subtended by the axis of outer wheel.

@et a Wheel track,

b Wheel base, and

c 4istance between the pivots A and 2 of the front axle.

Bow from triangle !2;,

2; /ot """"""""

!;

and from triangle !A;,

A; A2 D 2; A2 2; c /ot E """"""""" """"""""""""" """""""" D """""" """""" D cot

!; !; !; !; b

c

/ot " /ot E """""""" b

This is the fundamental euation for correct steering. !f this condition is satisfied, there will

be no skidding of the wheels, when the vehicle takes a turn.

(." Steering ge#r !eh#ni!

The following are commonly used layouts

1. 4avis steering gear principle

+. Ackermann steering principle

15



1. D#4i teering ge#r 0rini0le

The 4avis steering gear is shown in ig. !t is an exact steering gear mechanism. The slotted

links AM and BH are attached to the front wheel axle, which turn on pivots A and B

respectively.

The rod CD is constrained to move in the direction of its length, by the sliding members at P

and Q. These constraints are connected to the slotted link AM and BH by a sliding and a

turning pair at each end. The steering is affected by moving CD to the right or left of its

normal position. C D shows the position ofCD for turning to the left

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+. A+er!#nn teering 0rini0le

To ensure that the front steered wheels rotate around a common centre the inner and outer

roadwheels must be moved by differnt amounts. This achieved by setting the steering arms at

an angle so that their pro#ected centrelines meet on or near the centre of the rear axle.

The intention of Ackermann geometry is to avoid the need for tyres to slip sideways when

following the path around a curve.F+G The geometrical solution to this is for all wheels to have

their axles arranged as radii of a circle with a common centre point. As the rear wheels are

fixed, this centre point must be on a line extended from the rear axle. !ntersecting the axes of

the front wheels on this line as well reuires that the inside front wheel is turned, when

steering, through a greater angle than the outside wheel.

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*. STEERING GEOMETRY

When a four wheeler takes a turn, all its four wheels should roll without slipping laterally.

This is possible only when the axes of four wheels intersect at one point. This point is the

centre about which the vehicle turns at that instant. At this instant, rear rotate along two

circles, where the centre of two circles is at H*. The front wheels have their different axes.

These wheels also rotate along two other circles with same centre H*. igure shows the

steering geometry of all the four wheels of the vehicle. or correct steering, the centre of the

wheels of the rear axles and centre of front wheels must coincide.

1. C#!&er #ngle

/amber angle is the angle between the vertical line and centre line of the tyre when viewed

from the front of the vehicle. /amber angle is positive when this is outward. This happens

when wheels are further apart at top than at bottom. *n the contrary, camber angle is negative

when angle is inward. This happens when wheels are further apart at bottom than at top. The

camber, should not be more than + degrees, because this causes uneven or more tyre wear on

one side than on other side. The front wheels are usually fitted with positive camber angle.

This is done to prevent tilting of top of wheels inward due to excessive load or play in the

king pin and wheel bearing. The load brings the wheels to vertical position. >xcessive camber

19



is not good because it prevents proper wheel contact with the road. ront Axle and (teering

?neual camber causes the vehicle in that direction in which camber is more. This disturbs

the directional stability.

C#!&er #ngle

+. 6ing 0in inlin#tion

!t is the angle between king pin centre line and vertical line when seen from the front of the

vehicle. !t is also called steering axle inclination. Iing pin inclination and caster are used toimprove directional stability in cars. 2ecause of these provisions wheels tend to return to the

straight ahead position after the vehicle completes any turn due to steering left or right-. This

is also used to reduce steering effort when steering a stationary vehicle. !n addition to this, it

reduces tyre wear. This inclination varies from ) to 9 degrees in modern cars. The king pin

inclination is shown in igure. !t should be eual on both sides, i.e. on both front wheels.

6ing 0in inlin#tion

1%



. C#ter #ngle

/aster angle is the tilt of king pin centre line towards front of back from the vertical line. !t is

the angle between the vertical line and king pin centre line in the p wheel plane when looked

from side. !t is shown in igure. /aster Angle ;ositive- /aster angle is positive when top of

the king pin is backward and negative when it is forward. The value of this angle in vehicles

ranges from + to 9 degrees. The caster angle provides directional stability to vehicle by

making wheels to follow in the direction of movement of vehicle. The vehicle tends to roll

out on turns when caster angle of both front wheels is positive. 2ut it tends to back or lean in

on turns when caster angles are negative. ;ositive caster angle increases the steering effort

and tends to keep the wheels straight. Begative caster is provided in heavy duty vehicles to

reduce steering effort.

C#ter #ngle

). Toe in #n Toe ot

The front wheels are slightly turned in at front side such that the distance between wheels at

front is little less than the distance at back when seen from top. This difference in distance is

called to"in. !t is shown in igure. The distance 2 is greater than A by to 5 mm.

+&



;urpose of Toe"in

a- To ensure that wheels are rolling parallel.

b- To stabiliJe steering and prevent slipping towards sides.

c- To prevent excessive tyre wear.

d- To offset the effect of small deflections in the wheel support system.

The wheels are set with to"in but they move parallel when car moves forward.

The difference in the angles between the two front wheels and frame of the car during turns is

called toe"out. While taking the turn, the inside wheel makes larger angle than outer wheel to

satisfy the condition of correct steering. The toe"out is shown in igure.

+1



At turns, inner wheels makes an angle which is more than angle of outer wheel. Toe"out is set

by maintaining proper relation between the steering knuckle arm, tie rods and pitman arm.

++



REFERENCES

F1G http$KKresearch.omicsgroup.orgKindex.phpK(teering

F+G http$KKwww.i#rame.comKvol+issueKL+i&5.pdf

FG http$KKwww.i#ett#ournal.orgK+&15Kvolume"++Knumber"9K!M>TT"L++;+8).pdf

F)G http$KKwww.i#ser.orgKresearchpaperN5/Oero"Turn"our"Wheel"(teering"(ystem.pdf

F5Ghttp$KKwww.i#ser.orgKonline7esearch;aperLiewer.aspxP/omparision"*f"(teering

Qeometry";arameters"*f"ront"(uspension"*f"Automobile.pdf

+

8367 Project Documentationn

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