GB632723A - Improvements in or relating to electrically driven power transmission systems - Google Patents

Abstract

632,723. Control of motors. WATSON, C. D., and READ, F. W. June 27, 1947, No. 17030. [Class 38 (iii)] [Also in Group XXXIV] An electricallydriven power transmission system comprises an electric motor, centrifugallyoperated braking means sensitive to and adapted to limit the speed of the motor, and electromagnetic means adapted to oppose the centrifugal action of such braking means with a force proportional to the current being taken by the motor. A reversible electric motor 1 drives a non-magnetic shaft 2 upon which is mounted a member 11 carrying centrifugal brake plungers 3. An armature 9, which is slidable along the shaft but non- rotatable therewith, is coupled to the members 3 by means of bell-crank levers 14 which are pivotally mounted on the member 11. Compression springs 18 exert a force through an armature 10, a sleeve 20, the armature 9, and levers 14 to the brake plungers 3 so as normally to apply the brake. The simultaneous application of voltage to the motor and to a coil 13 causes the armature 10 to move and overcome the effect of the compression springs. During rotation the centrifugal force upon the members 3 is opposed by a force which is substantially proportional to the motor current. This force is provided by means of a coil 12 which is connected in series with the motor and which acts upon the armature 9. When the motor-voltage is removed the springs 18 are effective to provide full braking-torque. The shaft 2 is coupled to a load-shaft 22 which carries a member 23 receiving the end of the shaft 2 and having bifurcations 25 which embrace the member 11. Drive between the members 11 and 23 is effected through surfaces 26 on the former which alternatively cooperate with inclined surfaces 27 and 28 on the latter according to the direction of rotation. The inclined surfaces of the member 23 provide a desired degree of lost-motion between the shafts 2 and 22. The member 23 carries centrifugal brake shoes 37 which are slidable between pins 32 and 33, and are urged to a braking-position by leaf-springs 38 opposed by tension springs 29. Additional braking- effect is afforded by the brake shoes 37 pivoting about the leading guide-pin in the direction of motor-rotation. When the shafts 2 and 22 rotate together the braking-force exerted by the shoes 37 aids that of the members 3 but the springs 29 prevent full application of the braking-force of the shoes 37. If the alignment of the shafts is altered due to a following load, for example, the springs 29 offer minimum resistance against application of braking by the shoes 37 and excessive speed of the shaft 22 is prevented. The reduction of motor-load reduces the motor-current and increases the braking-effect of the members 3.