Abstract: Provided is a brushless DC motor speed controller in which the speed feedback signal needed for speed control is obtained from the commutation signals generated by the magnetic-pole sensor in the brushless DC motor. The-brushless DC motor speed controller includes an edge detector, which generates a pulse each time a rising or falling edge is detected in the signal from the magnetic-pole sensor of the brushless DC motor. A frequency multiplier is used to multiply the frequency of the pulse train from said edge detector. A frequency-to-voltage converter is used to convert the output pulse train from said frequency multiplier into a positive analog voltage, with the level of the positive analog voltage being in proportion to the speed of the brushless DC motor. A motor rotating direction detecting circuit receives the output signal from said magnetic-pole sensor and thereby detects in which direction the brushless DC motor currently rotates.

Abstract: The speed of a brushless DC motor driving an electric vehicle is controlled with a speed feedback signal proportional to rotation speed of the motor by processing the back electromotive force (EMF) waves of the brushless DC motor. In this method, the back EMF waves of plural phases are taken to pass the differential amplifiers for each phase, and the back EMF signals in the rising and falling regions of the back EMF waves of each phase are obtained to synthesize, by the commutation signals of a magnetic pole sensor passing the phase detecting circuit, after full-wave rectification and low-pass filtering, a [speed feedback signal. This method differs from normal speed control of a motor, in which a speed feed-back element such as a DC tachometer or an encoder is necessary for controlling the speed. This invention permits the brushless DC motor to control the speed without a feedback element such as a DC tachometer or an encoder, thereby decreasing the cost of the brushless DC motor speed control system.

Abstract: A current limiting device to limit the maximum allowable electric current to be supplied to a motor in driving an electric vehicle. The current limiting device includes (a) a first thermal switch to prevent the power switching element of the motor from being abnormally overheated, (b) a second thermal switch to prevent the motor from being abnormally overheated, and (c) a brake switch. The three switches altogether and in association with a certain hysteresis band work to switch the limits of the electric current passing through the motor between two or more predetermined electric current values. Under normal operating conditions, the limit of the current is set at a high level which is associated with a hysteresis action, and when one of the thermal switches or the brake switch is actuated, the limit of the electric current is switched to a lower value which is still associated with a hysteresis action.