Principle of Operation
Principle of Operation
Ignition Management provides ignition to the combustion chambers with the required voltage at the correct lime. Based on the combination of inputs, the ECM calculates and controls the ignition timing and secondary output voltage by regulating the activation and dwell of the primary ignition circuit The ECM controls and monitors the primary ignition circuit as well as the secondary ignition output (Misfire Detection).
The ECM has a very "broad" range of ignition timing. This is possible by using a Direct Ignition System, or sometimes referred to as "Static Ignition System". Reliability is also increased by having separate individual ignition circuits
The Ignition Control is determined by the ECM (load dependent). The ECM will calculate the engine "load" based on a combination of the following:
The dwell time will be regulated based on battery voltage. When cranking, the voltage is low and the ECM will increase the dwell to compensate for saturation "lag time". When the engine is running and the battery voltage is higher, the ECM will decrease the dwell due to a faster saturation time.
The Crankshaft Position/RPM signals the ECM to start ignition in firing order (1-5-4-8-6-3-7-2) as well as providing information about the engine operation. This input is used in combination with other inputs to determine engine load which advances/retards the ignition timing. Without this input, the ECM will not activate the ignition.
Cold start is determined by the ECM based on the engine coolant temperature and rpm during start up. A cold engine will crank over slower than a warm engine, the ignition timing will range between top dead center to slightly retarded providing optimum starting.
When starting a warm engine, the rpm is higher which results in slightly advanced timing. If the engine coolant and intake air temperature is hot, the ignition timing will not be advanced reducing starter motor "load".
During cranking, the ECM recognizes the Camshaft Position (compression stroke) and activates the ignition per cylinder (firing order).
Multiple Ignition Pulses ensure good spark quality during engine start up. The ECM will activate the ignition coils multiple times (1) per 720° of crankshaft revolution.
The ignition timing will be progressively advanced assisting the engine in coming up to speed. As the engine speed approaches idle rpm, the timing remains slightly advanced to boost torque. When the engine is at idle speed, minimum timing advance is required. This will allow faster engine and catalyst warm up. The multiple pulsing switches to single pulse when engine speed > 1350 RPM (varied with engine temperature).
The timing will be advanced when the ECM observes low engine rpm and increasing accelerator/air volume inputs (acceleration torque). As the Valvetronic valve lift is increased, the ECM advances the timing based on the engine acceleration request (and at what rate). The ECM will fully advance timing for the "full throttle" position indicating maximum acceleration (torque).
The Air Flow Volume signal provides the measured amount of intake air volume. This input is used by the ECM to determine the amount of timing advance to properly combust the air/fuel mixture.
The Air Temperature Signal assists the ECM in reducing the risk of detonation (ping). If the intake air is hot the ECM retards the ignition timing. If the intake air is cooler, the ignition timing will be advanced.
As the Valvetronic valve lift is decreased, the ECM decreases the ignition timing if the rpm is above idle speed (coasting). This feature lowers the engine torque for deceleration. When the engine rpm approaches idle speed, the timing is slightly advanced to prevent the engine from stalling. The amount of advance is dependent upon the engine temperature and the rate of deceleration.