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Chapter 26 Ignition Systems.

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Presentation on theme: "Chapter 26 Ignition Systems."— Presentation transcript:

1 Chapter 26 Ignition Systems

2 Ignition Systems Part of the computerized engine control system
Three basic types Distributor-based Distributorless Direct ignition

3 Purposes of the Ignition System
It must generate spark with enough heat to ignite the air/fuel mixture It must maintain the spark long enough to allow for complete combustion It must deliver the spark so combustion can begin at the precise time

4 Basic Circuitry - Primary
Battery Ignition switch Ballast resistor (older systems) Ignition coil primary winding Triggering device Switching device or control module

5 Basic Circuitry - Secondary
Ignition coil secondary winding Distributor cap and rotor (DI systems) High-voltage cables Spark plugs

6 Primary Circuit Operation
Ignition switch on Current flows into primary coil winding A primary switching device stops current flow through the coil This causes the magnetic field to collapse


8 Secondary Circuit Components
Ignition coil secondary winding Distributor cap and rotor (DI systems) Spark plug cables (some systems) Spark plugs

9 DI Secondary Circuit

10 Secondary Circuit Operation
Collapse of the magnetic field in the primary induces high voltage into the coil secondary This voltage is used to establish a complete circuit so current can flow The excess energy is used to maintain the current flow across the spark plug gap

11 Knowledge Check Which of the following is NOT part of the primary circuit? A. Ignition switch B. Primary coil winding C. Spark plug D. Switching device C – Spark plug

12 EI Systems May have a single coil for each cylinder or two cylinders may share a coil The ignition module controls firing order and spark timing Additional energy is released as current flow This allows higher firing current and longer firing times, 1.5 ms compared to DI’s 1 ms

13 Coil at Plug Secondary Circuit

14 DIS Secondary Circuit

15 Ignition Coils Coils are pulse transformers
Output dependant upon the number of windings and current flow CEMF increases time to become fully saturated Dwell is the period of current flow


17 Ignition Coils (Cont.) Typical coil requires 2-6 ms to be saturated
Dwell period and primary current are controlled

18 Secondary Voltage Typical voltage requirement to jump the plug gap is 10,000 volts Most coils have at least 25,000 volts available – called secondary reserve voltage Reserve necessary to compensate for high cylinder pressures

19 Spark Jumping the Gap

20 Spark Plugs Provides the air gap Resistor reduces RFI
Standard plug electrodes are copper Platinum and iridium electrodes extend plug life

21 Platinum tipped spark plug

22 Spark Plug Reach Reach is critical for proper gap placement

23 Heat Range Heat must be dissipated quickly
Heat travels from the electrode through the insulator to the cylinder head

24 Spark Plug Gaps Correct gap is necessary for proper operation
Too wide can cause misfiring Too narrow can cause fouling and misfires

25 Electrodes May be made of copper, platinum, iridium, or yttrium
Various styles of positive and ground electrodes in use

26 Ignition Cables Carry high voltage to spark plugs
Carbon fiber core acts as a resistor Reduces RFI and increases firing voltage Reduces plug wear by reducing current


28 Knowledge Check Which is not a common spark plug electrode material?
A. Copper B. Yttrium C. Nickel D. Platinum C – Nickel

29 Triggering and Switching Devices
A triggering device monitors crankshaft position

30 Triggering and Switching Devices (Cont.)
A switching device controls current flow through the coil primary winding Electronic switching components are part of an ignition control module or the PCM

31 Engine Position Sensors
Magnetic Pulse Generator Consists of a reluctor and pickup coil Metal Detection Sensor The electromagnet is in the pickup coil Hall-effect Sensor Produces a square wave signal Is most commonly used Magnetoresistive Sensor Looks like a magnetic sensor but outputs a signal like a Hall-effect Photoelectric Sensor Uses an LED and moving slotted disc





36 DI System Operation The camshaft drives the distributor at one-half crankshaft speed The position sensor triggers the switching device The coil is triggered by the switching device

37 Distributor May contain pick up assembly, ignition module, and coil
Rotor sits on top of distributor shaft and spins inside of distributor cap

38 Electronic Ignition Systems
No moving parts Cylinders individually controlled Flexible mounting locations Less radio frequency interference No timing adjustments More time for coil saturation

39 Double-Ended Coil or Waste Spark Systems
One coil fires two plugs These are the companion cylinders One plug fires positive to negative The other fires negative to positive

40 Coil-Per-Cylinder Ignition
Coil-on-plug and coil-near-plug Allows for more time between firings and increased saturation time A single coil failure affects only one cylinder COP require adaptors or plug wires to connect an ignition scope


42 Twin Spark Plug Systems
One plug on intake side of combustion chamber and one on exhaust side Results in cleaner combustion

43 EI System Operation Biggest differences are in number of coils and the use of CKT and CMP sensors Layout and operation of the sensors are designed to provide fast engine starts and synchronization of the fuel and ignition systems

44 Hall-Effect Sensors

45 Magnetic Pulse Generators

46 Knowledge Check Technician A says a waste-spark system uses one coil per plug. Technician B says a waste-spark system fires one plug positive to negative and the other plug negative to positive. Who is correct? Technician B

47 Misfire Detection The CKP identifies which cylinder
Detected by variation in crank speed PCM uses wheel speed data to determine if crank speed variation is from rough road conditions or misfire


49 Basic Timing The PCM controls timing and is not adjustable
Timing is fixed during cranking Once a certain engine speed is reached, the PCM adjusts timing Timing inputs include RPM, load, throttle position, and coolant temperature

50 Timing Retard and Advance
Timing controlled by ignition module Older systems used mechanical and vacuum systems

51 Timing Corrections Temperature Engine Knock Stabilizing Idle
Advanced with low coolant temperature Engine Knock Timing retarded when knock is detected Stabilizing Idle Used if desired idle speed is not correct

52 Timing Corrections (Cont.)
EGR Advanced when EGR is opened Transition Correction During rapid acceleration/decelerations Torque Control To smooth automatic transmission shifting Traction Control Reduces engine torque by retarding timing

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