GB974830A - Improvements in electric motors - Google Patents

Abstract

974,830. Electric motors. G. & R. WRENN Ltd. May 13, 1963, No. 18824/63. Heading H2A. A small D.C. motor has a permanent magnet rotor 53 and a wound stator having a plurality of windings 45-50 with one end of each winding connected to a brush which co-operates with a two-segment commutator 14, the other ends of the windings being connected together, so that a rotating magnetic field is produced. As shown, T-shaped polepieces 44 are located by moulded nylon end plates 54, 55 which also act as the shaft bearings, the poles are machine wound with three coils 45-46, 47-48, 49-50, and enclosed by hexagonal yoke 57. A third nylon moulding is located in the yoke and used as the brush holder and outboard bearing support for the commutator assembly. Commutator 14 is built up by forming steps on two pieces of shaft and after inserting insulation 82 (epoxy resin) between them, reassembling the segments 80, 81 and when the insulating resin has set grinding the shaft to the required diameter. Holes 60-62 bored in the moulding act as holders for the carbon brushes 63-65 and pins 66-68 support springs 71 which are anchored in the moulding at 74 and apply pressure to the brushes. In order to replace the commutator, contact plate 84 can be removed by releasing spring 91 and the commutator withdrawn from tongue and slot coupling 78. Connection between the two segments and the resulting short circuit to the supply due to the brush being wider than the insulation between segments is prevented by designing the commutator to run eccentrically so that the bush face remains relatively flat, Fig. 2 (not shown). In operation tags 89, 92 are connected to the supply and current passes via the motor shaft to the commutator and hence in sequence to the stator windings to produce a rotating magnetic field, Figs. 3-8 (not shown).