Valve timing control apparatus

A valve timing control apparatus for a valve timing adjusting unit that adjusts valve timing of opening and closing one of an intake valve and an exhaust valve of an engine having a camshaft and an output shaft, wherein the camshaft opens and closes the one of the intake valve and the exhaust valve, wherein the valve timing adjusting unit includes:

• a first rotor that is rotatable synchronously with one of the camshaft and the output shaft;
• a second rotor that is rotatable synchronously with the other one of the camshaft and the output shaft;
• a hydraulic actuator that changes a relative rotational phase between the first rotor and the second rotor;
• and
• a lock mechanism that is configured to lock the relative rotational phase at an intermediate position located between a full retard position and a full advance position such that the relative rotational phase is unchanged, wherein the valve timing adjusting unit adjusts the valve timing by controlling the hydraulic actuator to perform a phase control for controlling the relative rotational phase, the valve timing control apparatus comprising:
• reference position learning means for learning, as a reference position, one of:
• (a) a first position of the relative rotational phase that is controlled through the phase control at the full retard position;
• and
• (b) a second position of the relative rotational phase that is locked by the lock mechanism at the intermediate position;
• actual phase computing means for computing an actual phase based on the learned reference position;
• target phase computing means for computing a target phase based on an operational state of the engine;
• feed-back controlling means for controlling the hydraulic actuator to perform the phase control based on a difference between the target phase and the actual phase;
• and
• abnormality determining means for determining whether the lock mechanism is under an abnormal state, wherein:
• when the abnormality determining means determines that the lock mechanism is under the abnormal state, the feed-back controlling means is prohibited from performing the phase control that uses the reference position.