Patent GB-474028-A (GB)
Title: Improvements in or relating to the braking of electric railless trolley vehicles
IPC: B60L7/24
Filed: 1936-04-20
Abstract: 474,028. Control of D.C. motors. GENERAL ELECTRIC CO., Ltd., and CROFT, E. H. April 20, 1936, No. 11278. [Class 38 (iii)] Non-regenerative braking.-An electric railless trolly vehicle is provided with means for effecting electric braking and with mechanical brakes arranged to act on the driving wheels of the vehicle, together with means adapted, when electric braking is in progress and a control is exerted to apply the mechanical brakes with a strength beyond a predetermined value, to effect termination of the electric braking. In the arrangement shown, the armature 1 of a compound-wound motor is connected across the power lines by trolleys 2, 3, circuit-breakers 4, 5, line switches 27, 28, a series resistance 6, the series field 7, a cut-out relay coil 29C, and a reversing switch 8. The shunt field 9 is connected across the line through a resistance 10 and contactor 15. The resistance 6 is adapted to be short-circuited in steps by contactors 21 ... 24, and the resistance 10 by contactors 16, 17. A contactor 26 is adapted to connect a resistance 14 in shunt with the series field 7. For rheostatic braking, the armature and series field are adapted to be short-circuited through a part of the resistance 6 by a contactor 25. The contactor coils 15C ... 17C and 21C .... 28C are connected across the line through power and braking master controllers 11, 12 and the braking cut-out switch 13. In running the motor up to speed, the series resistance 6 is first short-circuited, then the sections of the resistance 10 are inserted to weaken the shunt field, and finally the contactor 26 closes to weaken the series field. On returning the power controller towards its " off " position, the shunt field contactors 16, 17 reclose. If regenerative current flows through the relay coil 29C, the contactor 29 opens and de-energizes the coils 27C, 28C of the line contactors 27, 28, thereby disconnecting the motor from the line. In the first position of the braking controller 12, the power controller is de-energized, and the contactors 25 and 15 are closed to establish the braking circuit. Further movement of the controller 12 cause contactors 16, 17 to close, thus strengthening the shunt field. The braking-controller is actuated by depression of a pedal 31, Fig. 2, which also actuates the mechanical brakes by a linkage operated through a shaft 32. Between the pedal and the shaft 32 is arranged a spring 33 which is contained in a cylinder 34 connected to the pedal by a rod 35 and bears against a plunger 41 mounted at the end of the shaft 32 and adapted to slide in the cylinder. The arrangement is such that if the pressure on the pedal exceeds a predetermined value, the spring is compressed to such a degree that contacts 37, 39, carried respectively by the cylinder and shaft, are separated. These contacts form the cut-out switch 13, which on opening interrupts the circuits of the operating coils 15C and 25C of the contactors 15, 25 to terminate the electric braking. In an alternative arrangement in which the brakes are pneumatically operated, contacts adapted to terminate the electric braking are operated in response to the pressure or vacuum acting on the brakes reaching a predetermined value.