m. Tech. Automotive Electronics

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Transcript of 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

    6.Crank rotates by 180o

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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

    6.Crank rotates by 180o

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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

    4.Crank rotates by 180o

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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 co