US Patent 7762222 Variable valve timing controller for internal combustion engine

A motor current (driving current of motor) is estimated based on a target motor speed, an actual motor speed, and an engine speed. When the estimated motor current exceeds the upper limit value equivalent to a heat generation limiting current, the motor current is restricted by restricting a variation (motor speed F/B amount) in target motor speed outputted to an EDU from an ECU. Thereby, the heat value of motor may not exceed the heat generation limit, and it can be prevented that the coil temperature of motor exceeds an allowable temperature range. A durability deterioration and failure of motor can be prevented.