Variable Valve Timing: Description and Operation

Diagnosis of Variable Camshaft Timing Control

Camshaft position sensor and variable valve actuator
The variable valve control mostly consists of an camshaft actuator and a position sensor for each camshaft. Intake and exhaust camshafts can be adjusted continuously. The variable valve actuator is controlled by a PWM signal to adjust the required oil pressure for proper camshaft positioning.

While the engine is running, for each camshaft sensor, a counter is incremented with every signal edge detected.

Signal activity and rationality check

Signal activity check
The monitor checks at every crankshaft revolution, if the camshaft signal edge count has changed at least once. If the signal edge count has not changed for a number of crankshaft revolutions the fault management will be triggered.

Rationality check
The monitor compares the period between camshaft signal edges to a minimum time, and to a modeled value derived from the mechanical design of the camshaft target wheel, and time periods measured between previous signal edges.
An error counter is incremented, if the period between camshaft signal edges is smaller than the calibrated minimum threshold, or does not fit within a window range around the modeled value. Exceeds the error counter a calibrated threshold, the fault code management will be triggered.






Variable valve actuator functional check
At engine operation the actual camshaft position has to follow the given set point in a certain amount of time, below a defined adjustment angle difference threshold (thd1).
Does the continuously monitored adjustment angle difference exceed thd1 and falls below thd2, an adaptation procedure will be executed, once per given set point, to reduce the difference below thd1. Is the adaptation process unsuccessful to reduce the adjustment angle difference below thd1 the fault management will be triggered.
Exceeds the adjustment angle difference thd2, the fault management will be triggered.