Variable valve timing system

A variable valve timing system for an internal combustion engine comprising:

• a housing member rotating as a unit with either a crankshaft or a camshaft of the internal combustion engine;
• a rotor member relatively rotatably assembled on a shoe portion provided at the housing member and forming an advanced angle chamber and a retarded angle chamber at a vane portion in the housing member, the rotor member rotating as a unit with either the camshaft or the crankshaft of the internal combustion engine;
• a relative rotation controlling mechanism actuated in response to supply and discharge of an operation fluid, and allowing relative rotation of the housing member and the rotor member under an unlock condition while restricting relative rotation of the housing member and the rotor member at a lock phase between a most advanced angle phase and a most retarded angle phase, excluding the most retarded angle phase or the most advanced angle phase, under a lock condition;
• a fluid pressure circuit controlling the operation fluid to be supplied to and discharged from the advanced angle chamber, the retarded angle chamber, and the relative rotation controlling mechanism;
• and
• an auxiliary controlling mechanism actuated in response to the operation fluid supplied to and discharged from the fluid pressure circuit, and allowing the relative rotation of the housing member and the rotor member under the unlock condition, and restricting the rotation of the rotor member to the retarded angle side or to the advanced angle side relative to the housing member at a set phase between the most retarded angle phase or the most advanced angle phase and the lock phase under the lock condition.