Patent GB-269930-A (GB)
Title: Improvements in and relating to brush mechanism for dynamo electric machines
IPC: H02K23/18
Filed: 1927-04-23
Abstract: 269,930. British Thomson-Houston Co., Ltd., (Assignees of Compagnie Francaise pour l'Exploitation des ProcÚdÚs Thomson-Houston). April 26, 1926, [Convention date]. Alternating - current commutator machines; motors, controlling.-In air alternating-current commutator machine having two sets of brushes relatively movable for speed control, the angular displacement of each brush-carrying ring is effected during one part of its travel directly by, or by means of, gearing and during the other part of its travel by means of a connecting rod pivoted at one end to the ring and operated by the gearing past the dead centre so that the direction of movement, of the ring is reversed, the movement of one ring by the rod in general taking place while the displacement of the other ring is being effected by the gearing. The object is to secure automatically such relative positions of the brushes during displacement as to obtain a compensating component of electromotive force always in the same direction and capable of being either substantially constant or varying from a maximum at the lowest speeds to a minimum at the highest speeds. The application of the invention to frequency modifiers used for the speed control of induction motors is referred to. Fig. 3 shows a brush ring C1 and in connection therewith a pair of toothed wheels A1, A1<SP>1> connected together by an endless chain B1. Rigidly attached to one of the links is a pin P, which is connected to an abutment M1 on the ring by means of a rod D1. Fig. 4 shows a similar system for the second brush ring C2. On the machine, the two brush rings are in line with one another and the toothed wheels A1, A1<SP>1> on the ring C1 are rigidly connected respectively with the wheels A2<SP>1> and A2 on the ring C2.In the position of the parts shown, the ring C1 is driven through the rod D, but the ring C2 is driven directly by the engagement of the pin P2 with a notch E,. If the wheel A, is rotated in the direction of the arrow, the ring C2 rotates uniformly in one direction whereas the ring C1 performs an oscillating movement at varying speed. Rotation of the wheel A, in the reverse direction causes the brush C, firstly to perform an oscillating movement and then a uniform clockwise rotation: at the same time, the brush ring C2 first rotates clockwise uniformly and afterwards performs an oscillating movement. The notches E1, E2 in the brush rings may be dispensed with. The wheels A1, A2 have the same diameter only if a compensating E.M.F. of constant magnitude is required. Modified results may be obtained by varying the form of the wheels. A single chain carrying the two pins P1, P2 may be employed if the wheels are mounted on common shafts. Where the radius of curvature of the brush rings is too small, the toothed wheels may be separately disposed in which case the abutments M1, M2 may be placed respectively on two racks engaging with the brush rings. The chains B1, B, may be replaced by any funicular system. In another modification, Fig. 6, a toothed wheel A, associated with one ring is mounted on the same shaft as another wheel associated with the second brush ring. The ring is adapted to gear with a rack on the lower part of a member F1. Motion is communicated from the wheel A, to the member F, either through through the teeth or indirectly through a pivoted rod D, and a pin and slot connection H1, E1. When the member F1 has moved sufficiently forward in the direction of the arrow for the teeth on the upper part to engage the wheel A1, a fixed abutment L, raises the rod D, into an inoperative position.