Valve timing control apparatus for internal combustion engine

A valve timing control apparatus for changing a timing of a valve driven by rotation of a camshaft by varying a rotational phase of said camshaft relative to a crankshaft in an internal combustion engine, said valve timing control apparatus comprising:

• a first sensor detecting an operating condition of said engine;
• a camshaft position sensor detecting a rotational position of said camshaft;
• a crankshaft position sensor detecting a rotational position of said crankshaft;
• an electronic control unit receiving an output of said first sensor, said camshaft position sensor and said crankshaft position sensor, wherein said electronic control unit:
• calculates an optimum timing of said valve based on said operating condition of said engine detected by said first sensor,
• detects a present timing of said valve corresponding to a rotational phase difference between said rotational position of said camshaft and said rotational position of said crankshaft,
• determines which direction to change said rotational phase relationship between said camshaft and said crankshaft in order to change said present timing to said optimum timing, and
• calculates a control value used to control said timing of said valve, wherein a magnitude of said control value is larger when said electronic control unit determines that an increase in said timing of said valve is required to achieve said optimum timing than when said electronic control unit determines that a decrease in said timing of said valve is required to achieve said optimum timing;
• and
• a control value assembly for varying said timing of said valve based on a signal provided by said electronic control unit.