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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.
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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
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8/39COIL IGNTION SYSTEM:
Layout of Coil Ignition System
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9/39Ignition Circuits
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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.
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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.
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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.
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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.
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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
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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.
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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.