IMPROVEMENTS IN AND RELATING TO DIRECT CURRENT ELECTRICAL MACHINES

1,240,455. Dynamo electric machines. INTERNATIONAL RESEARCH & DEVELOPMENT CO. Ltd. 14 Oct., 1968 [18 Oct., 1967], No. 47509/67. Heading H2A. A D.C. machine has a stator with a ring of uniformly spaced poles of alternate polarity, a rotor having conductors connected in series to form two or more separate windings having the ends only of the windings connected to a commutator comprising a number of insulated conducting segments-engaging brushes and interconnections between the segments to ensure continuous D.C. at the brushes. Conductors R1, R3, R5, R7 are connected in series to form one winding and conductors R2, R4, R6, R8 form a second winding. The ends of the windings are connected to commutator segments S1 S7 and S2, S8 respectively and interconnections are made between the segments as shown. Brushes B1, B2 are spaced apart by an odd number of pole pitches, i.e. one as shown, and four brushes may be used. In operation, the current flow in a winding is zero between the poles P1, P2, P3, P4 and reverses direction at this position so that the current always flows in a brush B1 and out at brush B2. The stator structure preferably comprises a cylindrical magnetizing coil 2 enclosed within a pole structure 1 having polepieces 1a, 1b both axially and circumferentially spaced from each other. In a modification, each polepiece may be provided with an axially extending shoe which is separated from the opposite polarity pole by insulating material. The machine may be discoidal with radially extending conductors and the commutator around the outer periphery, Fig. 10 (not shown). The machine may be used as a generator and a second set of windings connected to a commutator at the other end of the machine may be used to increase output.