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Chapter 26

Chapter 26. Ignition Systems. Ignition Systems. Part of the computerized engine control system Three basic types Distributor-based Distributorless Direct ignition. Purposes of the Ignition System. It must generate spark with enough heat to ignite the air/fuel mixture

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Chapter 26

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  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

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

  8. DI Secondary Circuit

  9. 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

  10. 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

  11. 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

  12. Coil at Plug Secondary Circuit

  13. DIS Secondary Circuit

  14. 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

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

  16. 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

  17. Spark Jumping the Gap

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

  19. Platinum tipped spark plug

  20. Spark Plug Reach Reach is critical for proper gap placement

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

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

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

  24. 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

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

  26. Triggering and Switching Devices • A triggering device monitors crankshaft position

  27. 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

  28. 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

  29. 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

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

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

  32. Double-Ended Coil orWaste Spark Systems One coil fires two plugs These are the companion cylinders One plug fires positive to negative The other fires negative to positive

  33. 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

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

  35. 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

  36. Hall-Effect Sensors

  37. Magnetic Pulse Generators

  38. 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?

  39. 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

  40. 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

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

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