Ignition System: Description and Operation

22R ENGINE

The system used on these engines includes a conventional ignition coil, an igniter which controls current flow within the system, and a distributor which contains a magnetic pulse type triggering unit. A conventional type distributor cap, rotor and spark plug wires are used to deliver secondary voltages to the spark plugs, and centrifugal and vacuum advance assemblies are used to tailor ignition timing to vehicle operating conditions. On some models, a ballast resistor or resistance wire is used between the ignition switch and coil, while on most models, the igniter acts as the system current limiter.
The magnetic pulse generator consists of pick-up coil which replaces the conventional breaker points and a reluctor which replaces the distributor shaft mounted cam. The pickup coil consists of a coil of wire wound around a pole piece and a permanent magnet. The reluctor, which has the same number of teeth as the engine has cylinders rotates within the magnetic field of the pickup coil, and when aligned, the pole piece and reluctor teeth are separated by a narrow air gap. The action of each reluctor tooth passing through this air gap causes a voltage signal to be induced in the pick-up coil windings, and this signal is transmitted to the igniter as a control signal.
Battery voltage is applied directly to the igniter and either directly or through a resistor to the ignition coil primary windings. The coil primary circuit is completed to ground through a switching transistor within the igniter. As each reluctor tooth passes the pick-up coil pole piece, the resulting signal voltage causes the igniter switching transistor to momentarily open the primary circuit ground path. When this occurs, the magnetic field within the ignition coil collapses and high voltage is induced in the coil secondary windings.


22R-E & 22R-TE ENGINES

The ignition system on these models includes an open or closed type coil and igniter assembly, a single, twin or triple pick-up distributor, and spark control circuitry within the TCCS system computer. A specially constructed distributor cap, rotor and spark plugs are used to insulate higher secondary voltages produced by the open type ignition coil, and there are no centrifugal or vacuum advance mechanisms, as spark timing is controlled entirely by the TCCS computer.
Timing signals are generated through magnetic induction by the pick-up coils, as in conventional electronic ignition systems, but these signals are transmitted to the TCCS computer rather than to the igniter assembly. The TCCS computer is programmed with optimum ignition timing values for all operating conditions. It uses signals from the pick-up coils to compute crankshaft position and signals from other sensors to compute engine and vehicle operating conditions, then adjusts ignition timing by controlling the switching function of the igniter assembly. The igniter assembly controls current switching through the ignition coil primary circuit, and therefore induction of secondary spark voltage.