Ignition System Knock Control

IGNITION SYSTEM, KNOCK CONTROL

The Saab Trionic ignition system is of capacitive type and consists of tour ignition coils and electronic circuitry built into the ignition discharge module. The ignition coils are controlled by the electronic circuitry incorporated in the ignition discharge module which in its turn is controlled by low-level output signals from the control module.

When the engine is started, the ignition system produces a spark in two spark plugs simultaneously, in cylinders 1 and 4 or 2 and 3, for a number of consecutive complete combustion processes. Following this, on the basis of the ionization current flowing through the spark plugs and signals from the crankshaft position sensor, the system acquires sufficiently reliable information to synchronize spark generation and fuel injection in the different cylinders.

To improve starting performance when engine temperature is below 0°C, the ignition system generates a large number of sparks in quick succession (multi-spark function) while the starter motor is turning the engine over (1O°BTDC - 2O°ATDC).

The crankshaft position sensor consists of an inductive sensor mounted in the wall of the crankcase and a rotor, a perforated disc with 58 ribs, mounted on the crankshaft's rear counterweight.



Ignition timing--is calculated by the control module, mainly on the basis of the following information:

- engine load
- engine rpm
- knocking, if any
- throttle position (idling only)





By analyzing the ionization current passing through the spark plugs, the control module determines whether knocking occurs in any of the cylinders. If knocking is detected, the ignition will be retarded. If the ignition is heavily retarded or if charging pressure is high, fuel enrichment will also take place. As a last resort, charging pressure will be reduced.