A valve timing control system of an internal combustion engine, comprising:
- a drive force conveyer driven by a crank shaft of the internal combustion engine;
- a cam shaft having an outer periphery formed with a drive cam for driving a valve of the internal combustion engine, the drive force conveyer being mounted to the cam shaft in such a manner as to make a rotation relative to the cam shaft when so requested, the cam shaft receiving a drive force from the drive force conveyer to rotate as a follower;
- a housing rotating integrally with one of the drive force conveyer and the cam shaft;
- a vane rotor housed in the housing, the vane rotor rotating integrally with the other of the drive force conveyer and the cam shaft;
- an advanced angle chamber and a retarded angle chamber housed in the housing, and turning the vane rotor with an oil pressure;
- an oil pressure supply-drain measure for supplying the oil pressure to the advanced angle chamber and the retarded angle chamber and for draining the oil pressure from the advanced angle chamber and the retarded angle chamber, the oil pressure supply-drain measure carrying out the supplying and the draining of the oil pressure selectively for the advanced angle chamber and the retarded angle chamber;
- a lock gear formed with a lock hole, the lock gear including a lock pin having a small diameter section and a large diameter section,
- the lock pin received in a pin hole in such a manner as to emerge and submerge, the pin hole being formed in one of the vane rotor and the housing, the lock pin having a head end adapted to engage with the lock hole which is formed in the other of the vane rotor and the housing, the head end and the lock hole, when thus engaged, locking a relative rotation of the vane rotor and the housing at one of a most retarded angle and a most advanced angle;
- and
- an unlock gear for disengaging the lock pin from the lock hole with the oil pressure conveyed from one of the advanced angle chamber and the retarded angle chamber to a pressure face of the lock pin;
- wherein the pin hole includes:
- a head side on which the lock pin is engaged with and disengaged from, the head side forming a small diameter hole, and
- a bottom side opposite to the head side, and forming a large diameter hole which is larger than the small diameter hole;
- wherein the lock pin includes:
- a small diameter section on a head side of the lock pin, the small diameter section being disposed toward the lock hole, and
- a large diameter section on a bottom side of the lock pin opposite to the head side of the lock pin, the large diameter section being increased in diameter in such a manner as to form a stepped face relative to the small diameter section;
- wherein the pressure face of the lock pin includes:
- a face defined on a head side of the small diameter section, and subjected to the oil pressure from the one of the advanced angle chamber and the retarded angle chamber, and
- the stepped face of the large diameter section, the stepped face facing the small diameter section and being subjected to the oil pressure from the other of the advanced angle chamber and the retarded angle chamber;
- and
- wherein the large diameter section of the lock pin and an inner periphery of the pin hole define a first clearance while the small diameter section of the lock pin and the inner periphery of the pin hole define a second clearance, such that the first clearance is larger than the second clearance.