Ignition System Upload

8/3/2019 Ignition System Upload

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Ignition systemGenerations - Overview


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Contents

Introduction

Ignition System Requirements

Generation - 1 Ignition System: Distributor Type Ignition Components Ignition Advancement Types

Genration 2 -Electronic Ignition System: TAC Ignition system CDI

Generation 3 & 4 - Electronic System: Distributorless ignition system Electronic Ignition

Limitations of point contact system

Advantages of Electronic ignition


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Introduction

Purpose:

To supply a spark inside the cylinder near the end ofcompression stroke, to ignite the compressed charge of air-fuel mixture.

Requirements:

Provide sufficient voltage

Provide sufficient energy under all operating conditions.

Able vary the ignition timing as e/g speed, load and otherconditions change.


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Introduction

Typical Voltage:

Min 10kV ~ Max. 20kV

Spark energy:

To be sufficient to produce voltage at High Temperature

It should have sufficient Heat for burning At Warmed up condition, Min.0.1 mJ/spark

upto max.50 mJ/Spark (Lean burn,Cold start,etc)

Discharge time

Min: 0.1ms ~ 0.5ms


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Ignition Timing

How early or late:Depends on Cylinder Pressure & A/F Mixture Quality/Quantity

Ignition timing must change with the changes in enginespeed, load, and temperature.

When to Give Spark:

Timing Advance : When the plug fires sooner on compression

(High engine speed)

Timing Retard :When plug fires later on compression stroke

(Lower engine speed)


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Ignition Timing

Timing the Ignition:

If start of combustion is too early work is done against piston and

if too late then peak pressure is reduced.

The optimum spark timing that gives the maximum brake torque,called MBT timing occurs when these two opposite factors cancel.


7/39Types of Ignition system

An Ignition System Consists of

Coil Ignition System

Distributor Point contact

Electronic advance Coil

Ignition System

DistributorlessWaste spark (DDLi)

Individual coil for each cyl.

Stick coil (SDLi)-Coil on

plug.

Coil Ignition System also known as Battery Ignition System

Which replaces the Magneto IgnitiedEngine in Early 1920s

This is base for the Modern Ignition System development


8/39COIL IGNTION SYSTEM:

Layout of Coil Ignition System


9/39Ignition Circuits


10/39Primary circuit

Battery- supplies electrical energy to the primary windingscreating a magnetic field around them.

Ignition switch - to open or close the primary circuit when thekey is turned off or on.

Conductors - to electrically connect the primary circuitcomponents.

Contace Points Cam Operated Switch make and break the primary circuit.

- When points are closed a magnetic field is built up is in thecoil primary windings.

-When the points open the magnetic field in the primarywindings collapses.

- This induces a high voltage in the secondary windings.


11/39Ignition Coil Construction

Called as Pulse Generator:

Acts as a step up transformer.

It takes low voltage highcurrent and converts it tohigh voltage low current.

At center is a Laminated IronCore

Primary windings approx. 200windings of 20 gauge wire

Secondary windings approx.20,000 windings of 40 gaugewire.

Separated by Layer of

varnished paper for ImproveInsulation


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Secondary circuit

Secondary coil: it produces high voltage by mutual inductancein the coil

High tension Leads: Responsible for getting the electricity fromthe coil to the cap & plugs.

Distributor cap and Rotor: Distribute the high voltage to thespark plug as per firing order.

Spark plug: Produces spark with sufficient energy to ignite thecombustible mixture in the cylinder.


13/39Contact Breaker

Cam actuated Switch

No. Of Lobes on cam = Noof Cylinder

Points made of Tungstonsteel alloy. (ResistsElectrical burning)

Spark plug: Produces sparkwith sufficient energy toignite the combustiblemixture in the cylinder.


14/39Distributor Operation:


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Condenser/capacitor :

- Has the ability to store electrical energy.

-It can absorb or retain surges of electricity.

-It is required when the points first open to absorb the voltagesurge caused by self induction.

Approx. 200-300 volts

-The condenser helps the primary magnetic field collapse veryrapidly, thus giving a strong secondary voltage.

-A defective condenser can cause premature point failure orpoor engine performance.

- It provides a temporary holding spot for electrical surges.

Condensor/capacitor


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Dwell control:

Dwell: Angle moved by camduring contacts closedperiod

Dwell is stated in % dwell.

Dwell = Dwell angle/ Phaseangle *100

Phase angle = t point close+ tpoint open

Phase angle = 360 / No ofCylinder

Points made of Tungstonsteel alloy. (ResistsElectrical burning)


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Ignition Timing Advance control

Types Ignition Advance:

Centrifugal

Vacuum


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Methods of controlling Advance

Distributor Centrifugal Advance

Controlled by engine speed.

Consists of two weights and two springs.At high speeds the weights fly out(held by the springs),rotating the cam, hence advancing the timing.


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Methods of controlling Timing

Vacuum Advance

Controlled by engine intake manifold vacuum and engine load.

The vacuum diaphragm rotates the Contact points againstthe direction of distributor shaft rotation.


20/39Gneration-2

TAC system (Transistor assisted Contacts)

Uses a normal mechanical breaker to drive transistor.

Used a low Inductive coil

Transistor performed the duty of Breaker to Make / break theprimary circuit

Advantage:

Gives Long spark to burn lean mixtures

Gives Quicker break of the circuit

Maintins good coil output.

Application: Racing, High speed Engines


21/39CDI SOLUTION

Further Highspeed engine required

To provide a high energy

Give very short and Fast Ignitionmultiple spark discharge to burn lean mixtureEfficient circuitry for minimum heat generation


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CDI

Inductive discharge (Transistor Controlled Ignitions) systemsare very simple in design requiring only one energy storageelement.

Capacitive Discharge Ignition systems work by storing energyin an external capacitor, which is then discharged into theignition coil primary winding when required.

This rate of discharge is much higher than that found in

inductive systems, and causes a corresponding increase in therate of voltage rise in the secondary coil winding.

This faster voltage rise in the secondary winding creates aspark that can allow combustion in an engine that has excessoil or an over rich fuel air mixture in the combustion chamber.

Controlled CDI are used in high speed engines.


23/39CDI vs TCI

The later semiconductor technologies, have provided theinductive discharge ignition systems with comparable CDI sparkrise times, energy .

The issues of reliability and cost become more significant forcoil-over-plug (DIS - direct igntion systems) when considering a

CDI versus a TCI ignition system, thus favoring TCI.

The spark duration is smaller than TCI.


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Distributor with electronic advance

Position of the individual cylinder is determined with the help ofrotor and sensor.

Point contact circuit breaker is removed

Based on this signal ECU sends timely signal to transistor switchwhich controls current through primary coil i.e. dwell time andignition timing.


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Generation 3 & 4 Ignition System

Cont.


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Distributorless Ignition system


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No Distributor.

Uses multiple ignition coils.

Camshaft position sensor is installed in place of ignition distributor.ECM fires two plugs at the same time.Spark plug wear is morePolarity at both spark plug is oppositeAlmost similar discharge voltage as distributor type

Less moving parts.

+ -

- +

Strong

Weak


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Inputs

Crank position sensor or Cam position sensor for determination of position of piston in each ofthe cylinders

Dwell time based on engine rpm and batteryvoltage

Ignition timing- Calculated from variousoperating conditions idle, running, accelaration,fuelcut recovery


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Dwell time

Dwell time:With inductive ignition systems the time taken tocharge the ignition coil is called the Dwell'.

This dwell can be increased or decreased for differing engine

applications. If longer spark duration is required to improve combustion of lean

mixtures or engines with large cylinders the dwell time isincreased, inputting more energy into the primary coil.

Dwell time is decreased when there is more than enough sparkenergy to combust the mixture, this decrease will reduce spark

plug wear, therefore increase spark plug life.

Longer dwell time can also increase coil heating which can reducecoil life.


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Ignition Timing

Electronic Advance Sensors input influences theignition timing.

Crank shaft Position Sensorand rotorTells position and speed(rpm)

Cam Position Sensor androtorTells position and speed(rpm)

Manifold Absolute Pressure(MAP)Engine load


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Ignition timing

Electronic Advance Sensors input influences theignition timing.

Intake Air Temperature Sensor

Knock Sensor (Retards timing

when pinging or knocking issensed)

Throttle Position Sensor(TPS)

Engine coolant Temperature
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Direct ignition system


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Direct ignition sytem

The driver circuit and ignition coil isintegrated into one assembly.

Better packaging Each cylinder has its own coil.

Reduced electrical interference

High Energy Low spark plug wear.

Stronger spark voltage


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Spark plug construction


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Spark Plug Specification

Heat Range

Gap

Electrode material Voltage


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Advantage of distributorlessignition

No moving parts

Cylinders individually controlled

Longer parts life

Flexible mounting locations

Less radio frequency interference

No timing adjustments

More time for coil saturation


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Summary

The ignition system supplies high voltage toignite the air/fuel mixture.

The arrival of the spark is timed to coincide nearthe compression stroke of the piston.

The ignition system has two interconnectedelectrical circuits: a primary circuit and asecondary circuit.


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Summary

The distributor may house the primary switching

device plus centrifugal or vacuum timing advancemechanisms.

The secondary circuit carries high voltage surges tothe spark plugs.

Ignition timing is directly related to the position ofthe crankshaft.


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Summary

Computer-controlled ignition eliminates the need forcentrifugal and vacuum timing mechanisms.

Nearly all of todays engines are equipped with anElectronic Ignition system, which does not use adistributor.

There are primarily two different designs of Distributorlesssystems, coil-on-plug and waste spark.

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Ignition System Upload