Variable valve timing system

A variable valve timing system comprising:

• a housing member provided in the driving force transmitting system for transmitting the driving force from a crankshaft of a combustion engine to a camshaft for controlling the opening and closing of either one of an intake valve or a exhaust valve of the combustion engine;
• a rotor member relatively rotatably mounted into the housing member and forming an advanced angle chamber and a retarded angle chamber at a vane portion in the housing member, said rotor member rotating as one unit with either the camshaft or the crankshaft;
• a torsion spring disposed between the housing member and the rotor member rotatably biasing the rotor member relative to the housing member;
• a lock mechanism for restricting relative rotation between the housing member and the rotor member at the initial volume of the relative rotation;
• a hydraulic pressure circuit for controlling supply and discharge of operation fluid to the advanced angle chamber and the retarded angle chamber and for controlling supply and discharge the operation fluid to the lock mechanism;
• and
• an energization controlling device for controlling the hydraulic pressure control condition of the hydraulic pressure circuit when a volume of either the advanced angle chamber or the retarded angle chamber shifts from an initial volume to a target volume,
• wherein the hydraulic pressure control condition of the hydraulic pressure circuit is shifted from an initial hydraulic pressure control condition in which the volume is maintained at the initial volume and locked by the lock mechanism to a transitional hydraulic pressure control condition in which the volume is maintained at the initial volume and the lock mechanism is released in a predetermined time, and to reach a volume shiftable hydraulic pressure control condition in which the volume is being varied to the target volume.