CONTROL SYSTEM FOR VARIABLE SPEED DRIVE

摘要

A control system for a variable speed drive unit having an actuating piston for modulating the clamping pressure between a first series of discs mounted for rotation with an input shaft and a second series of plates carried by an output shaft and interleaved with the first series, the system comprising: a sensor associated with the output shaft for providing pulses representative of preselected increments of rotation thereof; a digital delay circuit for delaying the pulses by the period of repetition of a pulse at a desired speed for the drive, a comparator for receiving the delayed pulse and the next subsequent pulse from the sensor for providing output pulses with each pulse having a width representative of the time delay between the receipt of a respective pair of pulses and a polarity representative of whether the delayed pulse led or lagged the subsequent pulse from the sensor, and an integrator for integrating the pulses from the comparator to provide a control signal for a servo relief valve. The servo relief valve provides a variable restriction between a flow line and a fluid reservoir surrounding the plates and discs. The flow line is connected between a source of pressurized fluid and the actuating piston, and the pressure therein is varied by the valve in response to the control signal to control the speed of the output shaft. The discharge from the servo valve is directed to the first and second series of discs and plates, respectively, whereby to maintain viscous shear and also to transfer the heat generated by friction.