Patent ID: 8159173

Claim:
A control device for a travel motor mounted to a vehicle which is equipped with a travel motor and a resolver, where the travel motor drives the vehicle, and the resolver works as a rotation angle sensor to detect a rotation angle of the travel motor, generate and output rotation detection signals, which correspond to a rotation angle of the travel motor, such as a first rotation detection signal and a second rotation detection signal, the first rotation detection signal has a waveform obtained by amplitude modulation of an exciting signal by sin θ which is an angle obtained by multiplying the rotation angle of the travel motor by an integer of “n” times of not less than 1, and the second rotation detection signal has a waveform obtained by amplitude modulation of an exciting signal by cos θ, the control device capable of controlling a supply of an electric power to the travel motor based on a rotation angle output value φ, comprising: a resolver digital converter (RDC) of a tracking type for receiving a first rotation detection signal and a second rotation detection signal supplied from a resolver, and calculating a value of sin(θ−φ) as an error deviation ε based on the first rotation detection signal, the second rotation detection signal, and a current rotation angle output value φ every constant time period, and integrating a value which is obtained by multiplying the error deviation ε by a gain as a predetermined value in order to calculate and output a next rotation angle output value φ; judgment means that judges whether or not the travel motor rotates at a constant rotation speed based on the error deviation ε transferred from the RDC; and gain adjustment means that decreases the gain when the judgment result of the judgment means indicates that the travel motor rotates at a constant rotation speed.