Patent ID: 7793629

Claim:
A valve timing control system provided in a drive force transmission system, which transmits a drive force from a driving shaft of an internal combustion engine to a driven shaft that is driven to open and close at least one of an intake valve and an exhaust valve of the engine, the valve timing control system controlling opening and closing timing of at least one of the intake valve and the exhaust valve and comprising: a valve timing mechanism that controls a rotational phase of the driven shaft relative to the driving shaft according to a fluid pressure of working fluid exerted in at least one retarding chamber of the valve timing mechanism and a fluid pressure of working fluid exerted in at least one advancing chamber of the valve timing mechanism; at least one fluid control valve that is connected to a fluid supply passage and a fluid drain passage at a first side of the at least one fluid control valve and is connected to a retarding passage communicated with the at least one retarding chamber and an advancing passage communicated with the at least one advancing chamber at a second side of the at least one fluid control valve, wherein the at least one fluid control valve controls a communication state of the retarding passage and the advancing passage relative to the fluid supply passage and the fluid drain passage; a communication control valve that enables and disables communication of a bypass passage, which extends from the fluid supply passage and bypasses the at least one fluid control valve, to at least one of the retarding passage and the advancing passage; and a bypass control means for controlling the communication control valve, wherein the bypass control means controls the communication control valve to enable the communication of the bypass passage to the at least one of the retarding passage and the advancing passage when a temperature is equal to or less than a predetermined temperature, and the bypass control means controls the communication control valve to disable the communication of the bypass passage to the at least one of the retarding passage and the advancing passage when the temperature is higher than the predetermined temperature.