Valve timing control system for internal combustion engine

Abstract

There is provided a valve timing control system for an internal combustion engine, which is capable of properly setting the reference position of the cam phase by learning, and at the same time promptly establishing a learned value of the reference position when the learned value is lost, thereby accurately changing the cam phase for proper control of the valve timing of the engine. A cam phase change mechanism changes the cam phase. A reference value indicative of a reference position of the cam phase is learned at a predetermined learning speed based on the cam phase detected when the cam phase change mechanism is in a predetermined operative state, and the learned reference value (learned value) is stored in a RAM. When the loss of the learned value from the RAM is detected, a learning speed at the reference value is learned is corrected such that the learning speed is increased from the predetermined learning speed for a predetermined time period.