Controller for electric vehicle

Abstract

The invention provides an electric vehicle controller in which the generated motor torque is limited when the voltage of the vehicle battery decreases during running, in order to suppress over-discharge of the battery. A high torque can be obtained for a short period, however, even in the torque limiting period, and over-discharge is prevented by stopping electric power converting means in a final stage of discharge voltage of the battery. According to the invention, during operation of the vehicle, the battery terminal voltage is monitored and compared with a first comparison value V.sub.1. If the battery voltage falls below V.sub.1, a first counter commences measurement of the time period during which this condition continues. If the time period measured by the first counter reaches a preset value t.sub.1, torque limitation is initiated. In the torque limitation state, a torque command signal, generated by the control to operate the vehicle motor, is compared with the signal generated by the vehicle accelerator, and the signal having the lower value is thereafter used to control operation of the vehicle motor. In order to provide the capability to generate higher levels of torque for brief periods during torque limitation, the torque limitation process is terminated if the accelerator pedal is released completely.