Patent GB-318977-A (GB)
Title: Improvements in and relating to brush shifting devices for alternating current motors with commutating windings
IPC: H02K23/18
Filed: 1929-09-13
Abstract: 318,977. British Thomson-Houston Co., Ltd., (Assignees of Hull, J. I.). Sept. 13, 1928, [Convention date]. Motors, controlling; alternating-current motors. -A brush-shifting arrangement for an alternating- current motor having a commutating winding on the rotor comprises two adjustable brush yokes, two adjusting means for the yokes, pivotallyconnected, a stationary cam and means for moving the pivotal connection around the cam. The invention is applicable to a motor having polyphase secondary windings on the stator connected to adjustable brushes in the manner described in Specification 221,806, and comprises also means for giving an abnormally high or low starting torque and for adjusting the speed independently. In addition, power-factor improvement may be effected by moving the brushes in such a way that the voltage injected into the secondary circuit always contains a quadrature component in a manner illustrated in the Specification with the aid of vector diagrams. Figs. 6 and 7 show gear for moving the yokes 22, 23 of the brush pairs 13, 14 according to a predetermined law on the commutator 21 of a motor of the above-named type. The yokes are pivotally connected to links 31, 32 which are pivoted on a bolt 24 carried by an operating arm 26 and guided in a slotted supporting plate 34 on the motor framing. The arm 26 is slotted to engage a frame bolt 28 and is coupled by a rod 30 to another operating arm or to the machine driven by the motor which, in this case, is arranged to move the rod 30 so as to give the required sequence of brush positions. Radial and angular movements of the arm 26 respectively cause the brushes to move in the opposite and same directions. As the bolt 24 moves from a to b in the slot the two yokes move in the same direction, i.e. the inter-brush distance of a phase is unchanged but the brush axis rocks, the angular velocity of the yoke 22 meanwhile decreasing and that of the yoke 23 increasing; while the bolt moves from b to c the rockers move in opposite directions at varying angular velocities; at position c the yoke 23 becomes stationary; thereafter, from c to d, yoke 23 reverses its direction of rotation and moves in the same direction as yoke 22 until the position d is reached. A similar sequence occurs if the arm 6 is swung in the opposite direction. Fig. 8 shows an arrangement for hand control with separate starting and speedcontrolling handles 36, 35 which allows the motor, after a stoppage, to have the brushes so set that the starting current will be low and, further, allows the starting torque to be increased or decreased with respect to its value with the brushes in their running position. The handle 36, loosely pivoted at 28, and the brushes are moved to give the desired starting torque by means of this handle while the speed-adjusting handle 35 is locked at 38. The two handles are joined by a spring 37 so that when the handle 36 is moved to give the desired starting condition and the machine is up to speed, the handle 36, when released, is drawn back on to a stop 39, thus moving the brushes back to their original running position. This double-lever arrangement may also be connected to the driven machine, as in Fig. 7. The cam plate 34, Fig. 7, may be dispensed with,'in which case the pivoted connection 24 simply rotates in a circular arc 40, Fig. 9. Specification 25358/11 is referred to.