Patent GB-843150-A (GB)
Title: Improvements in and relating to regulable electro-magnetic driving means
IPC: H02K11/23
Filed: 1957-11-29
Abstract: 843,150. Clutch control. SCHMID, W. K. Nov. 29, 1957 [Nov. 30, 1956], No. 37312/57. Class 80 (2). [Also in Group XXXVII] The speed of a polyphase induction motor or of a coupling having a rotating D.C. field is controlled by a centrifugal device which increases the rotor resistance in steps as the speed rises and finally, at a predetermined speed, disconnects it completely. In one embodiment, shown as applied to an induction motor, the delta-connected rotor winding 22 is opened at one corner 23, 24 and connected across three split or otherwise subdivided slip rings 3, 4; 5, 6 and 7, 8 as shown in Fig. 4a. These rings are engaged by two interspaced sets of three brushes 9a, 9b, 9c and 10a, 10b, 10c, one set being slightly axially displaced from the other, as shown in Fig. 3b. These brushes are axially displaced by centrifugal force acting on a flywheel which is mounted on pivots so that it is forced into the oblique position shown by a spring 16 and a slanting member 17, the spring pressure being adjusted by a screw 19 to adjust the speed of the rotor. At a preset speed, centrifugal force on the flywheel forces the member 17 towards the left and so displaces the brushes from their short-circuited position on ring 7, 8 over the other rings to include resistors 25, 26, and finally off the rings altogether. At intermediate positions in which two rings are contacted, resistors interconnecting the brushes 10a, 10b and 10c become effective. Instead of using resistors, different rotor coil tappings may be connected to the slip-ring. In a modification, Fig. 5, a disc 29 rotating with the output shaft carries a centrifugal weight 34 restrained by adjustable springs 32, 33 and arranged to open contacts I, II, III and IV in succession as the speed rises. This causes relays R1, R2, R3, R4 to drop out in turn so that the rotor slip-rings 44, 45, 46 are first shorted and then bridged by increasing resistance as resistors 54, 55; 52, 53 are open circuited, and finally the rotor is completely open-circuited as resistors 50, 51 are disconnected by relay R4. A modification is described in which relays are controlled by contacts made by a plate moving axially under the control of a centrifugal governor. In a further modification the plate makes successive contact with a series of brushes projecting axially by different amounts and connected through various resistances to the rotor sliprings. In a further modification, Fig. 8a, the rotor 2 has squirrel-cage bars shorted at one end by a plate 85 and selectively connected by a series of axially projecting brushes 88 on a plate 87 which is axially slidable by a centrifugal governor 73, 74. The regulated speed is set by axial adjustment of a disc 91 by a screw 89. The rotor may be stopped by axial withdrawal of the disc 87 by a rod 93 connected to the armature 95 of an electromagnet 92 energized by a button 96. The machine is cooled by a fan 88b driven by a separate rotor 87c. In yet a further modification (Figs. 9a, b, c, not shown) the deltaconnected rotor winding is opened at one corner as before and selectively connected to a series of commutator segments interconnected by resistances by a brush which is angularly displaceable over the commutator surface against spring- pressure by frictional engagement with a disc which is axially displaced by a centrifugal governor. An alternative arrangement is described in which the commutator segments are connected to tappings on the delta-connected rotor winding and progressively short-circuited by the angularly displaceable brush. Alternatively, a series of brushes may be lifted from a commutator surface by a centrifugal flywheel obliquely mounted as previously described. Specifications 730,677, 740,603, 744,350, 748,255, 773,474, 796,998 and 842,622 are referred to.