Patent ID: 7765968

Claim:
A variable valve timing system that changes opening/closing timing of at least one of an intake valve and an exhaust valve provided in an engine and opened/closed by a camshaft, comprising: a changing mechanism that changes the opening/closing timing of the intake valve or the exhaust valve in accordance with an operation amount of an actuator that uses an electric motor; a command value preparation unit that obtains a current value of the opening/closing timing at least based on a signal from a sensor that detects a rotational speed of the camshaft and a signal from a sensor that detects a rotational speed of the electric motor, and that prepares an operation command value for the electric motor based on a deviation of the current value of the opening/closing timing from a target value of the opening/closing timing, which is set based on an operating state of the engine, such that the opening/closing timing changes in accordance with the target value; an electric motor drive unit that controls an amount of electric power supplied to the electric motor such that the electric motor operates in accordance with the operation command value provided from the command value preparation unit; a reference value setting unit that variably sets a reference value used to control the amount of electric power supplied from the electric motor drive unit to the electric motor in accordance with one of the rotational speed of the electric motor and a rotational speed of the engine, wherein the reference value is used for an overheating determination; an overheating determination unit that determines whether at least one of the electric motor and the electric motor drive unit needs to be restricted from heating up based on a result of comparison between information indicating the amount of electric power supplied from the electric motor drive unit to the electric motor and the reference value; and a command value restriction unit that restricts the operation command value for the electric motor to a value within a predetermined range when the overheating determination unit determines based on the result of the comparison between information indicating the amount of electric power supplied from the electric motor drive unit to the electric motor and the reference value, that at least one of the electric motor and the electric motor drive unit needs to be restricted from heating up.