Variable Valve Timing: Description and Operation

Variable Camshaft Timing Control

Detection of mechanical IVVT error
The VVTI is a combined hydraulic and mechanical camshaft control unit, managed by the ECU. The VVTI allows the engine to control valve-timing continuously for intake camshafts. The electronically control of the VVTI positions is dependant on engine speed, load and temperature.

The diagnosis is monitoring the correct mechanical function of the variable camshaft timing. The diagnosis carries out a continuous rationality check of the VVTI function.

If a malfunction is detected, an error bit will be set and sent to the Error management module. This module produces the final information for setting the corresponding DTC.

Control deviation of the camshaft position controller
In this diagnosis module the difference between the actual and target position of the VVTI unit ("control deviation") is checked.

Description "target":
The target position has to be in a limited stable range for a certain time. If the actual position is near the target (calibratable range) the diagnosis is ok, otherwise not. This will be checked by calculating two integrals (Reset integral and Failure integral). Both integral values have the same threshold to reach. If the failure integral reaches this threshold at first, an anti-bounce counter is started, otherwise the counter will be decremented. If the counter exceeds an adjustable limit, a Rationality Fault (DTC) is stored.

Description "slow response":
The set point and camshaft position are saved at the beginning of a set point change. If this change over a time is big enough (gradient), the camshaft phasing change is evaluated. If the change after the diagnostic time is smaller than a threshold, a slow response is detected, and if the value is greater, then there is no malfunction. By detecting a malfunction, an anti-bounce counter is incremented otherwise the counter will be decremented. If the counter exceeds an adjustable limit, a Rationality Fault (DTC) is stored.

Description "cold start monitoring"
The target position has to be in a limited stable range for a certain time during catalyst heating. If the actual position is near the target (calibratable range) the diagnosis is ok, otherwise not. This will be checked by calculating two integrals (Reset integral and Failure integral). Both integral values have the same threshold to reach. If the failure integral reaches this threshold at first, an anti-bounce counter is started, otherwise the counter will be decremented. If the counter exceeds an adjustable limit, a Rationality Fault (DTC) is stored.