the cam shaft, wherein the torque change may be generated when driving to open and close the intake and/or exhaust valves. When the torque change is applied to the vane rotor in a retarding direction during an advancing operation, the working fluid in the fluid chambers may be compressed so that the working fluid tends to flow out from the fluid chambers. On the other hand, when the torque change is applied to the vane rotor in an advancing direction during a retarding operation, the working fluid in the fluid chambers may be likewise compressed so that the working fluid tends to flow out from the fluid chambers. The push-out of the working fluid from the fluid chambers may adversely affect the advancing and/or retarding operation, according to which the vane rotor is moved to its target position relative to the cam shaft. As a result, it may take a longer time until the vane rotor reaches its target position. Namely, the response is decreased.
According to Japanese Patent Publication No. 2003-106115, a check valve is provided in a fluid passage for supplying working fluid to fluid chambers, so that the push-out of the working fluid from the fluid chambers is prohibited when the torque change is applied to the cam shaft, in order to quickly achieve a target phase.
It is, however, a problem in the above valve timing adjusting apparatus, in that the vane rotor in the housing is not stably positioned due to the torque change applied to the vane rotor, when the fluid pressure in the fluid chambers is still low, shortly after the engine has been started. And a slapping sound may be generated.
According to another prior art, Japanese Patent Publication No. 2003-343218, a lock member is provided in a vane rotor, and the lock member is engaged with a housing, so that the vane rotor is locked with respect to the housing. According to the prior art, the locked condition of the vane rotor to the housing is released shortly after the start-up of the engine, wherein the fluid pressure in a certain fluid chamber is used to mov