A valve timing adjuster for an engine having a camshaft and an output shaft, the camshaft opening and closing one of an intake valve and an exhaust valve of the engine, the valve timing adjuster comprising:
- 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, the second rotor defining a retard chamber and an advance chamber between the first rotor and the second rotor;
- a control valve configured to control supply of hydraulic oil to the retard chamber and the advance chamber;
- controlling means for controlling the control valve to increase oil pressure of hydraulic oil in the retard chamber in order to shift a relative rotational phase between the first rotor and the second rotor in a retard direction, the controlling means controlling the control valve to increase oil pressure of hydraulic oil in the advance chamber in order to shift the relative rotational phase in an advance direction;
- and
- a lock mechanism configured to lock the first rotor and the second rotor at a lock position located between a full retard position and a full advance position such that the first rotor is limited from being rotated relative to the second rotor, wherein:
- the lock mechanism includes a retard limitation pin and an advance limitation pin, each of which is provided to the second rotor;
- each of the retard limitation pin and the advance limitation pin is displaced from a corresponding retraction position, at which each of the limitation pins is retracted within the second rotor, to a corresponding projection position, at which each of the limitation pins projects from the second rotor, when a projection condition is satisfied;
- each of the limitation pins is displaced to the corresponding retraction position when a retraction condition is satisfied;
- the lock mechanism includes a retard limitation groove and an advance limitation groove, each of which is formed to the first rotor;
- the retard limitation groove limits the retard limitation pin, which is located at the corresponding projection position, from being displaced in the retard direction;
- the advance limitation groove limits the advance limitation pin, which is located at the corresponding projection position, from being displaced in the advance direction;
- the retard limitation groove and the advance limitation groove are designed to limit the displacement of the retard limitation pin in the retard direction and simultaneously limit the displacement of the advance limitation pin in the advance direction in order to lock the first rotor and the second rotor such that the first rotor is limited from being rotated relative to the second rotor;
- the controlling means includes lock release controlling means for alternately increasing the oil pressure in the retard chamber and the oil pressure in the advance chamber when the lock of the first and second rotors is released by displacing each of the retard limitation pin and the advance limitation pin from the corresponding projection position to the corresponding retraction position.