Variable Valve Timing Monitors

Variable Valve Timing
Variable Valve Timing (VVT) is a mechanically operated, electronically controlled system and is fitted to all current Jaguar engines except the 4.2L V8 Supercharger. The system comprises of a actuator (phaser) built into the camshaft chain sprocket and an oil control valve (OCV) which controls the flow of oil to the cam phaser. Control of the system is done via the OCV and cam position sensors. The OCV varies the oil flow into the cam phaser and creates a variable offset between the camshaft and the camshaft sprocket, feedback for this system is provided by the cam position sensors

The monitors for this topic are best described in two sections. The first section is concerned with VVT position failure and normal operation counters. If calibratable conditions are met for a failure condition then fault counters are incremented. The same applies for normal operation of the VVT system. The counters are then compared to a calibratable constant (threshold) and a judgement made. For a failure judgement the failure counter has to be of an equal or higher value than the threshold constant and likewise, for a normal judgement the normal counter has to be equal or greater than the normal counter. Once these comparisons have been carried out the relevant failure/judgement flags are set.

The second section of this monitor is concerned with monitoring the OCV on both A and B banks. The OCV duty output is compared to an upper and lower threshold and the state of the latch port (1 = output 0 = no output). If OCV duty output is outside of the upper/lower band and the latch has no output then a failure counter is incremented. If conditions are not met then the monitor moves onto the next comparison. The OCV duty output is compared to an upper and lower threshold and the state of the latch port (output/no output). If OCV duty output is outside of the upper/lower band and the latch has an output then the failure counter is set to zero, normal judgement flag set to 1 and failure judgement flag set to zero. If conditions are not met then the monitor moves onto the next comparison. The failure time counter is compared to the failure judgement time threshold and if equal or greater than the threshold a failure flag is set and a present failure flag is set. If none of the comparison conditions are met then the OCV latch port is set to zero. This is also performed after the comparisons have been carried out. The monitor now moves onto the flag control section and restarts.