m. Tech. Automotive Electronics

8/11/2019 m. Tech. Automotive Electronics

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UNIT-1Automotive Fundamentals Overview

Four Stroke Cycle,EngineControl,

Ignition System: Spark plug, Spark pulse generation, Ignition

Timing,

Drive Train, Transmission, Brakes,

Steering System

Battery

Starting System.

Air/Fuel Systems Fuel Handling, Air Intake System, Air/

FuelManagement


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EVOLUTION OF AUTOMOTIVE ELECTRONICS

The first electronics introduced Between 1950s and early1960s. Features were not well received by customers. So

they were discontinued from automobiles.

Two major events occurred during the 1970 starting the

trend of use of modern electronics in the automobile:

(1)Introduction of government regulations for exhaust

emissions and fuel economy

(2) Development of relatively low cost digital electronics thatcould be used for engine control and other applications.


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Some of the applications of electronics

1. Electronic engine control: For minimizing exhaust

emissions and maximizing fuel economy

2. Instrumentation for measuring vehicle performance

parameters

3. Diagnosis of on-board system malfunctions

4. Driveline control5. Vehicle motion control

6. Safety and convenience

7. Entertainment & communication navigation


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THE AUTOMOBILE PHYSICAL CONFIGURATION

These systems include

1.Engine2. Drive train (transmission, differential, axle)

3. Suspension

4. Steering5. Brakes

6. Instrumentation

7. Electrical/ electronic

8. Motion control

9. Safety

10. Comfort/ convenience

1 1. Entertainment/ communication/ navigation


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The 4-Stroke CycleEngine Construction


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The 4-Stroke Cycle- Working Principle One complete cycle in the 4-stroke/ cycle SI (SPARK

IGNITION ) engine requires two complete rotations of the

crankshaft. As the crankshaft rotates, the piston moves up and down in

the cylinder.

In the two complete revolutions of the crankshaft , there

are four separate strokes of the piston from the top of the

cylinder to the bottom or from the bottom to the top.

The 4 stroke in a cycle are

1. Intake

2. Compression

3. Power

4. Exhaust


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IntakeSpark Plug

ExhaustValve

1.Piston: TDC to BDC

2.Valves: Intake- open, exhaust-

closed3.Vacuum created

4.Air fuel mixture sucked into

cylinder through intake valve

5. Intake valve closes when piston

reaches BDC

6.Crank rotates by 180o


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Compression

1.Piston: BDC to TDC

2.Valves: Intake- closed, exhaust-

closed3.Air fuel mixture compressed

4.when piston nears TDC, spark

plug gives spark

5.Air fuel mixture burns giving out

high pressure and high

temperature gases



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Power

1.Piston: TDC to BDC

2.Valves: Intake- closed, exhaust-

closed3.Gases [push piston down to BDC

4.Force from piston transmitted to

crank shaft

5.Power is produced



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Exhaust

1.Piston: BDC to TDC

2.Valves: Intake-closed, exhaust-

open3.Piston pushes burnt gases

(exhaust) out through exhaust

valve



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ENGINE CONTROL Control of the engine means regulating the power

produced by the engine.

The driver controls engine power via the accelerator pedal

to which throttle plate is connected through a mechanicallinkage system.

The throttle plate is located in the air intake passage of the

carburettor . It is a rotary valve that controls the quantity of

air flowing through it .


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When the accelerator pedal is operated, the throttle plate

rotates, which regulates the supply of air.

Fuel is delivered to each cylinder at a rate that isproportional to air .

In modern engines, fuel injector supplies fuel into the airpassage. The injector is controlled electronically so that

exhaust gas pollutant is minimized .


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Ignition system

It consists of several components: The spark plug

Pulse transformers (typically called coils)

Timing control circuitry

Distribution apparatus - which supplies high-

voltage pulse to the correct cylinder.


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IGNITION SYSTEM Spark from the spark plug ignites the air fuel

mixture and causes combustion. The electric arc or spark provides sufficient energy

to cause combustion. This phenomenon is called

ignition. The spark must persist for a period of about a

millisecond (one thousandth of a second).

Highly efficient pulse transformer circuit is requiredto produce spark in this short period.


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a. Spark Plug

A spark plug configuration is shown in Figure.

The spark plug consists of a pair of electrodes,

called the centre and ground electrodes, with a

small gap between them

The spark is produced by applying a high-voltage

pulse of 20 kV to 40 kV between the center

electrode and ground.

Once the arc is started, the voltage required tosustain it is much lower because the gas mixture

near the gap becomes highly ionized (An ionized gas

allows current to flow more freely.)

Th i i d l h i i h i


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The arc is sustained long enough to ignite the air-

fuel mixture.

The gap size is important and is specified for each

engine - it may be 0.6 mm to 1 mm

The centre electrode is insulated from the ground

electrode and the metallic shell assembly.

The ground electrode is at electrical ground

potential because one terminal of the battery that

supplies the current to generate the high-voltage

pulse for the ignition system is connected to theengine block and frame.


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b. High-Voltage Circuit and Distribution

The ignition system provides the high-voltagepulse that initiates the arc.

The high-voltage pulse is generated by inductive

discharge of a special high-voltage transformercommonly called an ignition coil

The high-voltage pulse is delivered to the

appropriate spark plug at the correct time forignition by a distribution circuit.

ln a modern engine, the breaker points have been

replaced with an electronic control module

I ti l i th di t ib ti f hi h


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In conventional engine, the distribution of high

voltage pulses was accomplished with a rotary

switch called the distributor

The rotor is mechanically driven by the camshaft

and rotates at camshaft speed (i.e., one-half of

crankshaft speed).

The distributor distributes of the spark to the

appropriate spark plug depending on the number of

engines.


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c. Spark Pulse Generation The actual generation of the high-voltage pulse is

accomplished by switching the current through the primarycircuit

The distributor of a traditional ignition system consists of

opening and closing the breaker points (of a switch) by a

rotary cam.

During the intervals between ignition pulses (i.e., when the

rotor is between contacts), the breaker points are closed

(known as dwell). Current flows through the primary of the coil, and a

magnetic field is created that links the primary and

secondary of the coil.

At the instant the spark pulse is required the breaker


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At the instant the spark pulse is required, the breaker

points are opened.

This interrupts the flow of current in the primary of the coil

and the magnetic field collapses rapidly. The rapid collapse of the magnetic field induces the high-

voltage pulse in the secondary of the coil.

capacitorabsorbs the primary current, which continues to

flow during the short interval in which the points are

opening, and limits arcing at the breaker points.

The waveform of the primary current is illustrated in

Figure The primary current increases with time after the break

point close (point aon waveform).

At the instant the points open this current begins to fall


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At the instant the points open, this current begins to fall

rapidly.

It is during this rapid drop in primary current that the

secondary high-voltage pulse occurs (point b). The primary current oscillates (the wavyportion; point c)

because of the resonant circuit formed between the coil

and capacitor.


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The mechanism for opening and closing the breaker


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The mechanism for opening and closing the breaker

points of a conventional distributor uses a cam

mounted on the distributor shaft. It has a number

of lobes equal to the number of cylinders is.

As this cam rotates, it alternately opens and closes

the breaker points.

The movable arm of the breaker points has an

insulated rubbing block that is pressed against the

cam by a spring.

Then the rubbing block is aligned with a flat surfaceon the cam, the points are closed(i.e., dwell period)

As the cam rotates the rubbing block is moved by


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As the cam rotates, the rubbing block is moved by

the lobe (high point) on the cam shown in Figure

1.12b.

At this time, the breaker points open

(corresponding to point b of Figure 1.11) and spark

occurs.

The distributor shaft is coupled to the camshaft and

rotates at the same speed

The relative position of distribution and camshaft is

known as ignitiontiming.


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d IGNITION TIMING


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d. IGNITION TIMING

Ignition occurs before top dead center (BTDC)

during the compression stroke of the piston. This time is measured in degrees of crankshaft

rotation

For a modern SI engine, this timing is typically 8 to10 degrees at low speed (low rpm).

As the engine speed increases, the speed of the

crankshaft increases. For this reason, the spark must occur at a larger

angle before TDC for higher engine speeds.

This change in ignition timing is called spark


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This change in ignition timing is called spark

advance.

In a conventional ignition system, the mechanism

for this is called a centrifugal spark advance.

As engine speed increases, the distributor shaft

rotates faster, and the weights are thrown outward

by centrifugal force.

The movement of weights causes a change in the

relative angular positionbetween the rubbing block

and the cam, and advances the time when the lobeopens the points.


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DRIVETRAIN


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DRIVETRAINThe engine drivetrain system of the automobile

consists of The engine

Transmission

Drive shaft Differential

Driven wheels.

Transmission


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Transmission

The transmission is a gear system that adjusts the

ratio of engine speed to wheel speed. It provides a gear ratio between the engine speed

and vehicle speed such that the engine provides

sufficient power to drive the vehicle at any speed. The driver selects the correct gear ratio from a set

of possible gear ratios (usually three to five for

passenger cars).

An automatic transmission selects this gear ratio by

means of an automatic control system.

An automatic transmission consists of


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An automatic transmission consists of

Torque converter

System of planetary gear sets.

Torque converter


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Torque converter

The torque converter is formed from a pair of


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The torque converter is formed from a pair of

semitoroidal structures (i.e., a donut-shaped object

split along the plane of symmetry).

One of the toroids is driven by the engine and is

called pump.

The other is very close to pump and is called the

turbine.

Both the pump and the turbine have vanes.(blades)

In addition, a series of vanes are fixed to the frame

and are called the reactor.

The entire structure is mounted in a fluid tight(leak


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The entire structure is mounted in a fluid tight(leak

proof) chamber and is filled with a hydraulic fluid

(i.e., transmission fluid).

As the pump is rotated by the engine, the fluid

circulates as shown by the arrows .

The fluid impinges on the turbine blades, imparting

a torque to it.

The torque converter transmits engine torque and

power to the turbine from the engine.


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Th l


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The planetary gear system


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It consists of a set of three types of gears connected


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together as depicted in Figure .

The inner gear is known as the sun gear.

There are three gears meshed with the sun gear at

equal angles, known as planetary gears.

These three gears are tied together with a cage that

supports their axles.

The third gear, known as a ring gear, with gear teeth

on the inside meshes with the three planetary

gears.

Operation


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p

one or more of these gear systems are held fixed to

the transmission housing.

If the ring gear is held fixed and input power

(torque) is applied to the sun gear, then the three

planetary gears rotate in the same direction as the

sun gear but at a reduced rate and at an increasedtorque.

If the planetary gear cage is fixed, then the sun gear

drives the ring gear in the opposite direction

If all three sets of gears are held fixed to each other

, then direct drive (gear ratio = 1) is achieved.

A typical automatic transmission has a cascade


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yp

(parallel) connection of a number of planetary gear

systems

Most automatic transmissions have three forward

gear ratios.


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BRAKES


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BRAKES


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Brakes are responsible for slowing and stopping


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p g pp g

the vehicle.

Most of the kinetic energy of the car is dissipated

by the brakes during deceleration and stopping

There are two major types of automotive brakes:

drum and disk brakes.

Drum brakes were used on early cars .

These days automobile manufacturers are using

disk brakes.

A flat disk is attached to each wheel and rotates


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with it as the car moves.

A wheel cylinder assembly (called a caliper) is

connected to the axle assembly

A pair of pistons having brake pad material are

mounted in the caliper assembly and are close to

the disk.

Under normal driving conditions, the pads are not

in contact with the disk, and the disk is free to

rotate.

When the brake pedal is depressed, hydraulic

pressure is applied through the brake fluid to force

the brake pads against the disk.

Due to friction between the disk and the pads,


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braking force is applied that decelerates the car

Electronic control of braking benefits safety by

improving stopping performance in poor or

marginal braking conditions.

STEERING SYSTEM


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STEERING SYSTEM


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The inclination of this axis gives rise to a restoring


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torque

This restoring torque provides a steering stability for

the car.

Due to restoring torque, considerable driver effort is

required for large cars, particularly at low speeds

and when parking.

In order to overcome this effort in relatively large

cars, a power steering system is added.

This system consists of an engine-driven hydraulic

pump, a hydraulic actuator, and control valve.

Traditionally, mechanical means is used for rotating

the wheels by rotating the steering wheel.

Whenever the steering wheel is turned, a valve


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opens and allows hydraulic pressure to activate the

actuator.

The high-pressure hydraulic fluid pushes on oneside of the piston.

The piston, in turn, is connected to the steering

linkage and provides mechanical torque to assistthe driver in turning.

This hydraulic force is often called steering boost.

In modern engines, electronic control system is

used to adjust the available boost as a function of

speed to desirable levels.


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