Automatic sequencing scheme for reversing directions of electric traction motors

Claim 1

An improved electric drive system for a self-propelled vehicle comprising a reversible, variable speed traction motor, a speed controller, means for energizing said motor under the control of said speed controller so that the motor runs at variable speeds depending on the setting of said controller, said motor being adapted to be connected to operate in a dynamic retardation mode when said speed controller calls for deceleration thereof, and selector means having alternative forward and reverse states and being manually changeable from either one of said states to the other regardless of the motor speed, wherein the improvement comprises means adapted to reverse the motor energization under the control of said selector means so that the motor can run in a forward direction when the selector means is in its forward state or in a reverse direction when the selector means is in its reverse state, said reversing means comprising: a. normally inactive first means operable in response to a change in the state of said selector means while the motor is running faster than a predetermined relatively slow speed in either direction for overriding said speed controller and for initiating said dynamic retardation mode of operation so as automatically to decrease the motor speed; b. second means for reversing motor energization and for inactivating said first means in response to the motor decelerating to said predetermined relatively slow speed as a consequence of operation of said first means; and c. third means effective after said second means reverses motor energization for preventing another reversal of motor energization by said second means as the motor subsequently accelerates in the opposite direction to a speed higher than said predetermined relatively slow speed in the absence of any further change in the state of said selector means.