Abstract: A method for minimizing torque ripple in a permanent magnet brushless DC motor includes the steps of energizing a first winding of the motor to generate a first current, energizing a second winding of the motor to generate a second current, and overlapping the first and second currents in time by a preselected time to reduce torque ripple. The structure for performing the method includes conventional brushless DC motor drive circuitry responsive to a motor rotor position signal, and a speed control signal, to sequentially generate a gate drive signal for driving a respective semiconductor switch to energize each winding of the motor. The structure further includes a phase overlapping circuit interposed between the conventional brushless DC motor control circuitry output and the semiconductor switches used to energize each winding of the motor. The phase current overlap circuit includes a monostable multi-vibrator for generating a "one-shot.

Abstract: A wiper apparatus using a three brush, permanent magnet motor in which a zener diode has a cathode connected to the low speed brush and an anode connected to the high speed brush. The zener breakdown voltage of the zener diode is chosen so that it reverse conducts during at least some portion of each wipe cycle during operation with the high speed brush on a wet window to limit peak wiper speeds and reduce strain on the wiper mechanism. Variations including a transistor, relay or additional zener diode controlled by the zener diode and connected in parallel therewith provide for reduced current and therefore power dissipation in the zener diode at the expense of somewhat limited speed limiting.