Patent GB-574035-A (GB)
Title: Improvements in or relating to electromechanical brake mechanisms
IPC: F16D65/14
Filed: 1943-12-10
Abstract: 574,035. Electromagnetically - operated brakes. WESTINGHOUSE ELEOTRIC INTERNATIONAL CO. Dec. 10, 1943, No. 20731. Convention date, Dec. 10, 1942. [Class 103 (i)] In brakes of the kind that are spring-applied and released by an electromagnet a switch operated by the magnet plunger puts a resistance in series with the magnet coil during the release movement, thus reducing the current and, during the application movement after the supply current has been cut off connects a low resistance in shunt to the coil to delay the decay of the flux in the coil and thus to soften the application of the brake. A third resistance of high value may be permanently connected across the magnet coil to permit a rapid initial flux decay when the supply current is cut off and thus a quick initial application movement of the plunger. The brake shown comprises a. pair of levers 4, 5 pivoted at 7, 8 to a fixed frame 3 and carrying brake shoes 9, 10. When a magnet 22, 23 mounted on the frame is deenergized the shoes are applied to a drum 1 by springs 12, 13 which abut on the levers and on adjusting nuts 18, 19 on rods 14, 15 pivoted to the frame 3. The levers are moved to the release position when the magnet is energized, by the downward movement of the plunger 23 acting through bell-crank levers 25, 26 pivoted to the frame at 27, 28 and engaging adjusting screws 30, 31 on the levers. A switch BK operated by the plunger 23 comprises contacts carried respectively by a fixed arm 38 and a spring arm 39 mounted on the plunger, the point in the travel of the plunger at which the switch opens and closes being adjustable by a screw 42 on a rigid arm 43 carried by the plunger. A control circuit for an elevator is shown and comprises a control switch CS, coils U, D of up and down direction switches and relays P, Q which operate contacts PI and Q1, Q2, Q3, respectively. In the stop position of the switch CS shown the brake magnet coil 22 is de-energised so that the brake is applied and the plunger switch BK is closed. When the switch CS is moved to a starting position, for example, to the left the circuit L +, 46, 45, U, P, Q is completed so that contacts Q3 are opened to cut out the low shunt resistance R2 and contacts P1, Q1, Q2 are closed and the coil 22 is thus energized to release the brake by the brake circuit L+, P1, BK, 22, Q1, L-. When the plunger 23 is near the end of its stroke it opens the switch BK thus putting the resistance R effectively in series with the coil 22 so that a reduced current passes through the coil while the brake is off. When the switch CS is returned to the stop position, the relays P, Q are deenergized. The consequent opening of the contacts P1, Q1 cuts off the coil 22 from the supply lines L + , L - and the switch and contacts BK, Q2 being open, a discharge circuit for the coil is provided through the high' resistance R3 so that the flux starts to decay rapidly. After initial application movement of the plunger 23 however, the switch BK is closed and the contacts Q3 also being closed a further discharge for the coil circuit is completed through the low resistance R2 thus delaying the flux decay and so retarding the further movement of the plunger to give a soft braking action.