GB989170A - Reversible driving system - Google Patents

Abstract

989,170. Winch drives. PYE Ltd. Nov. 17, 1961 [Nov. 17, 1960], No. 39505/60. Heading B8B. [Also in Division H2] A reversible driving system for a crane or winch comprises a differential gear 3 having two input shafts driven from an A.C. motor 1, through an electromagnetic induction coupling 2, and reversing gears 4, 5 which provide an output speed half that of the motor 1. The speed and direction of rotation of the output shaft 6 is controlled by varying the speed of the shaft driven by the coupling 2 between zero and full motor value, this being effected by a speed control circuit 7, which varies the current through the excitation coil of the coupling 2, Fig. 2 (not shown) and which is controlled by a tachometer generator 8 driven from the coupling shaft. When the shaft 6 is used to drive the winding drum of a crane, hoisting or lowering corresponds to operation of the coupling 2 over the top or bottom half of its speed range. An electromagnetic brake 9 is fitted to the shaft of coupling 2 but is inoperative during hoisting and lowering of a loaded hook. When the shaft 6 is accelerated by the lowering of a light hook or upon rapid acceleration when lowering other loads, the acceleration of the coupling shaft causes the current through its coil to fall and so energize the coil of the brake 9, Fig. 2 (not shown). The brake 9 is thus applied until the coupling speed is restored to its set value, the braking torque being determined by the variation in coupling current. The coupling 2 may be similar to that of Specification 871,437, and the brake control circuit similar to that of Specification 948,467.