Patent GB-555128-A (GB)
Title: Improvements in and relating to electric control systems
IPC: B60T13/74
Filed: 1942-01-19
Abstract: 555,128. Switching systems for electromagnets. BRITISH THOMSON-HOUSTON CO., Ltd. Jan. 19, 1942, No. 755. Convention date, Jan. 21, 1941. [Classes 35 and 38 (iv)] [Also in Groups XXXIV and XXXVII] An electromagnet device for releasing a spring- applied brake or for other purposes comprises an armature having a high-voltage pick-up coil and a low-voltage holding coil that are successively energized, the pick-up coil being automatically de-energized when the holding coil is energized but with a time lag to ensure prior fall energization of the holding coil. The time delay may be effected by short circuiting or shunting a relay coil that operates the switch of the pick-up coil prior to breaking the circuit of the relay coil. Brake shoes 22 applied by springs 23 to brake drums of the driving motors 10, 11 of a vehicle are released by the armatures of magnets 20, 27 having pick-up coils 26, 28 and holding coils 29, 30 controlled by a brake controller 41. With the controller in the off position shown the switch 43 may be closed to connect the battery 42 to the bus bar BX thus energizing the coil 50 of a contactor S1 through controller contact 52 contacts 53 of contactor S2 and resistor 54. The coil 51 of contactor S3 is similarly energized through controller contact 55 contacts 56 of contactor S4 and resistor 54. Contacts 57, 58 are thus closed to energize the pick-up coils 26, 28 from the trolley 14 and contacts 59, 60 are closed to complete circuits from the bus-bar BX through the coils 61, 62 of contactors S2, S4. Operation of the contactor S2 closes contacts 63 to energize the holding coil 29 from the bus-bar BX, closes contacts 65 to shunt coil 50 subsequently opens contacts 53 to break the circuit of this coil and closes 59a to complete a holding circuit for the coil 61. Operation of contactor 54 similarly controls the circuits of coils 27, 51, 62 through contacts 64, 56, 70, 60a. The short circuiting of the coils 50, 51 acts momentarily to maintain the flux and thus to delay the dropping of the contactors S1, S3 and the de-energizing of the pick-up coils. Movement of the controller 41 from the off position successively breaks the contacts 52, 55 and thus the circuits of coils 61, 62 to apply the brakes. The motors may be connected in series between the trolley 14 and ground by closing switches 15, 16 and may be cross-counted through a resistor 17 for dynamic braking by opening switches 15, 16 and closing switch 18 as described in Specification 514,263, [Group XXXVII]. To ensure that the brakes 22 are held released during dynamic braking, a coil 71 connected across part of the resistor 17, is arranged to close contacts 72, 73 shunt the contacts 52, 55. The magnet comprises a casing 31 of magnetic material containing the pick-up and holding coils 26, 29. A pin 33 of magnetic material is slidable in a recess in the fixed core 26 against the resistance of a rubber buffer 36. When the magnet is energized and the armature 21, moves upwards the pin 33 enters a recess 38 in the armature and the buffer prevents the shock of engagement of the armature and the core. The entry of the pin into the recess 38 reduces the rate of increase of the pull as the armature moves un. Specification 308,329, [Class 103 (i)], is referred to.