Engine management system - MEMS (Ignition coil): Description and operation

IGNITION COMPONENTS - VVC

Ignition coil

The coils for the programmed ignition system are mounted on the rear face of the engine block. Each coil has a low primary winding resistance (0.71 to 0.81 ohms at 20°C). This allows the full h.t. output to be reached faster and so makes the coil operation more consistent throughout the engine speed range.

VVC MECHANISM CONTROL

Hydraulic control solenoid

The ECM controls two solenoids in order to control the VVC mechanism. Only one solenoid will be energised at a time to either drive the VVC mechanism towards minimum cam period, or towards maximum cam period. The desired cam period is calculated by the ECM using engine speed and manifold pressure (engine load). The current cam period is measured by the ECM using the camshaft position sensor. The ECM then energises the correct solenoid in order to move the mechanism towards the desired position.

Oil Temperature sensor

An oil temperature sensor is mounted in the hydraulic control unit (HCU). The oil temperature measured by the ECM is used to derive the viscosity of the oil passing through the HCU which indicates how quickly the VVC mechanism will respond.