Variable valve timing control system

Abstract

A variable valve timing adjuster with an intermediate lock mechanism learns a lock position and a lock release control. During a lock control, a learning of the lock position from a real camshaft phase is repeated to update the learned value, and the learning is ended when it is judged that the learned values have converged. At this time, when the learned values of the lock position do not converge even if the number of learning of the lock position exceeds a predetermined value, an insufficient lock state is judged, and the learned value of the lock position is set to an initial value or the learned value at the previous lock control thereby to make a lock release control. During the lock release control, on the other hand, the control (or the lock release control) of a hydraulic control valve is learned. When the lock cannot be released during the lock release control, the lock release control (or the learned value) is corrected in a direction to facilitate the lock release. When the correction of the lock release control is repeated a predetermined or more number of times or when the lock release control goes outside a predetermined range, the lock release failure is judged.