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Chapter 27 Ignition Systems Primary Circuit Components • • • • • • Battery Ignition switch Ballast resistor (older systems) Ignition coil primary winding Triggering device Switching device or control module 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 Secondary Circuit Components • • • • Ignition coil secondary winding Distributor cap and rotor (DI systems) Spark plug cables (some systems) Spark plugs 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 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 ms 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 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 Spark Plugs • Provides the air gap • Resistor reduces RFI • Standard plug electrodes are copper • Platinum and iridium electrodes extend plug life 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 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 Hall-Effect Sensors Magnetic Pulse Generators 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 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 Timing Corrections • Temperature – Advanced with low coolant temperature • Engine Knock – Timing retarded when knock is detected • Stabilizing Idle – Used if desired idle speed is not correct Coil Cross-Section • Platinum tipped spark plug Vacuum advance ... • • • • Battery Ignition switch Ballast resistor (older systems) Ignition coil primary winding Triggering device Switching device or control module Primary Circuit Operation • Ignition switch... Retard and Advance • Timing controlled by ignition module • Older systems used mechanical and vacuum systems Distributor • May contain pick up assembly, ignition module, and coil • Shaft driven... to collapse Secondary Circuit Components • • • • Ignition coil secondary winding Distributor cap and rotor (DI systems) Spark plug cables (some systems) Spark plugs Secondary Circuit Operation