Patent ID: 7685994

Claim:
A variable valve timing apparatus for changing a timing of opening/closing at least one of an intake valve and an exhaust valve provided in an engine, comprising: an actuator; a changing mechanism for changing the opening/closing timing, by changing difference in rotation phase of a camshaft driving the valve, of which opening/closing timing is to be changed, from rotation phase of a crankshaft by an amount of change in accordance with an operation amount of said actuator; first detecting means for detecting a rotation angle of said crankshaft; second detecting means for detecting a rotation angle of said camshaft; third detecting means for detecting the operation amount of said actuator; and phase detecting means for detecting actual opening/closing timing of said valve of which opening/closing timing is to be changed, based on outputs of said first to third detecting means, said phase detecting means including first calculating means for calculating said actual opening/closing timing based on a relative relation between the rotation angle of said crankshaft and the rotation angle of said camshaft, second calculating means for calculating said actual opening/closing timing based on an accumulation of amount of change of said difference in rotation phase of said camshaft in accordance with the operation amount of said actuator, first selecting means for selecting one of said first and second calculating means dependent on engine speed, for detecting said actual opening/closing timing, second selecting means for selecting both said first calculating means and said second calculating means for detecting said actual opening/closing timing, in a prescribed range of engine speed, third calculating means for calculating said actual opening/closing timing by modifying a value calculated by said first calculating means by a value calculated by said second calculating means, in said prescribed range of engine speed, and fourth calculating means for calculating said actual opening/closing timing, based on the value calculated by said first calculating means, without using the value calculated by said second calculating means, when abnormality occurs in said third detecting means in said prescribed range of engine speed.