Patent GB-648949-A (GB)
Title: Improvements relating to electric motor control systems
Inventor: CALDBECK CHARLES JAMES
IPC: H02P7/00
Filed: 1948-12-01
Abstract: 648,949. Controllers. ENGLISH ELECTRIC CO.. Ltd. Dec. 1, 1948, No. 31134. [Class 38(iii)] A control system for an electric motor comprises means for retarding or arresting forward movement of the controller if the motor current should exceed a predetermined value, a control member being adapted to advance the controller in step therewith so long as the controller is not retarded in any way, the control member being free to move in advance of the controller if the controller is retarded or arrested, a piston and cylinder, one of which is mechanically coupled to the controller, valve means controlled by a device responsive to motor current so as to restrict the flow of fluid from the cylinder and thus retard forward movement of the controller whenever the motor current exceeds a predetermined value, contact means on the controller arranged to maintain the valve means in the fluid-restricting position independently of motor current for a predetermined initial movement of the controller, and means for advancing the controller to a position corresponding to the position of the control member when the retarding action on the controller is removed. When pedal 1 is depressed to accelerate an electrically-driven vehicle from rest a controller 6 is moved freely by a quadrant 2 to the second notch of the controller, further movement resulting in lostmotion in a link 7 being taken up. This link couples quadrant 2. through rigidly-connected levers 8, 9 to a piston 10 in hydraulic cylinder 11, the two ends of which are connected by pipe 12. A non-return valve 10a allows substantially unrestricted movement of the controller in the decelerating direction. Movement of the pedal beyond the second notch-position in the accelerating direction may be governed by a needle valve 19. If the motor-current falls below a predetermined value, however, a relay 15 closes contacts 15a to energize an operating coil 13a through controller-contact 6b which closes on the third notch. Valve 13 then opens to allow unrestricted movement of the controller. When a predetermined high value of motor-current is exceeded a relay 17 closes contacts 17a to energize coil 14a. Valve 14 closes and prevents the controller from following the movement of the pedal until the current falls and the controller is moved forward by the spring 4 to a position corresponding to that of the pedal. If the pedal is returned to the " off " position when the vehicle is at speed and is then depressed before the speed falls appreciably, the movement of the control- 1er is unrestricted from the " off " position to the second notch, delay is provided by valve 19 between the second and third notches, and thereafter undelayed forward movement to the original speed position is afforded. In the modification of Fig. 2 the valve 13 is of the normally-open type and contacts 6b are closed in the " off " position and on the first three notches of the controller. The relay 15 maintains its contacts open at low current values. The valve 14 is replaced by a device comprising ratchet wheel 30 and pawl 31 operated by electromagnet 32. If the motor-current exceeds a predetermined high value, relay 17 is operated and the pawl is actuated to prevent further movement of the controller. The teeth on the ratchet wheel are arranged so that free movement of the controller is permissible up to the second notch position whatever the position of the pawl.