Patent ID: 8413624

Claim:
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 control at the full retard position; and (b) a second position of the relative rotation 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, the other one of the first and second positions is a comparison position, the valve timing control apparatus further comprising: comparison position learning means for learning the comparison position; and phase difference computing means for computing a phase difference between (a) the comparison position learned by the comparison position learning means and (b) the reference position learned by the reference position learning means, wherein: the abnormality determining means determines that the lock mechanism is under the abnormal state when the phase difference falls beyond a predetermined phase difference range.