Patent GB-491749-A (GB)
Title: Improvements in or relating to electric motor control systems
IPC: B60L15/12
Filed: 1937-07-20
Abstract: 491,749. Master control of D.C. motors; actuating controllers. WESTINGHOUSE ELECTRIC & MANUFACTURING CO. July 20, 1937, No. 20072. Convention date, Aug. 29,1936. [Class 38 (iii)] Non - regenerative braking.-A resistance controller for a vehicle motor is actuated by means controlled by a relay responsive to the motor current, and a gravity actuated device responsive to the weight carried by the vehicle is effective to vary the proportionate amount of motor current passing through the relay. Upon actuation of a master controller MC to a position a switches LS and M1 are closed to connect the motors 10 and 11 in parallel to the supply in series with resistance 53, and acceleration is effected by operating the controller MC to position b to energize a pilot motor 44 which operates an arm carrying a roller 43 to press contact fingers 21, 22, 23 ... into engagement with a conductor 20 in turn and cut out steps of the resistance 53. The acceleration is controlled by a current limit relay L which is connected across a resistance 57 in the main motor circuit and is effective to close a shunt around the armature of the motor 44 when the main motor current exceeds a certain value. The current value at which the relay L operates is adjusted in accordance with the load on the vehicle by an arm 58 which adjusts the amount of the resistance 57 in shunt with the coil of the relay L, and the arm 58 is operated by a link 61 connected to a pivoted bar 62 carried by the frame 59 of the vehicle and operated on by the inclined surface of a member 64 resting on a portion of the vehicle which is not affected by load changes. Thus as the load on the vehicle varies the bar 62 is rotated to operate the arm 58. The acceleration continues until the roller 43 operates the contact finger 33 whereupon a cam switch D, operated by the motor 44, energizes a switch M2 which connects the motors directly to the supply. The pilot motor 44 continues to operate until the last contact finger is operated and a cam limit switch opens its circuit. The controller MC may be returned to the " off position to open switches LS, M1, and M2, and allow the vehicle to coast, a switch T being closed to energize separately excited fields 14, 17 of the motors. A relay S R has its operating coil connected across the armature of the motor 11 in series with a resistance 56, and controls the pilot motor 44 to return the resistance controller, the movement of the controller also varying the resistance 56 so that the pilot motor positions the controller to match the speed of the vehicle. In this way the appropriate amount of resistance 53 is included in the motor circuit for transfer from coasting to driving or braking operation. To brake the vehicle a controller BC is operated to energize switches B1, B2, which complete rheostatic braking connections with the series field of one motor connected across the armature of the other, and each motor in series with the effective part of the resistance 53. The fields 14, 17 are also effective. The braking operation is controlled by the motor 44 returning the resistance controller to its " off " position, the control of the motor 44 being effected by the relay L and the arm 58 as for motoring.