Improved control method for electro-hydraulic control valves over temperature range

摘要

In a variable cam timing (VCT) system (10a) which has a feedback control loop wherein an error signal (36) relating to at least one sensed position signal of either a crank shaft position (24a) or at least one cam shaft position (22a) is fed back for correcting a predetermined command signal (12). The system further includes a valve (14) for controlling a relative angular relationship of a phaser (42); and includes a variable force solenoid (20) for controlling a translational movement of the valve (14). An improved control method comprising the steps of: providing a dither signal (38) sufficiently smaller than the error signal (36); as temperature varies, changing at least one parameter relating to the dither signal (38); and applying the dither signal (38) upon the variable force solenoid (20), thereby using the dither signal (38) for overcoming a system hysteresis without causing excessive movement of valve (14).