GB324632A - Improvements in electric motors - Google Patents

Abstract

324,632. Fairweather, W. C., (Underwood Elliott Fisher Co.). Sept. 29, 1928. Alternating - current commutator motors; cores; motors, controlling.- A universal electric motor for operation on continuous - current or on alternating current circuits of different frequencies comprises a pair of main brushes and a pair of auxiliary brushes on the commutator and main and auxiliary field coils, the coils and brushes being adapted for interconnection in different ways, all the brushes being mounted for simultaneous angular movement for speed control. An end plate 29, Fig. 1, carries the main and auxiliary brushes and is formed with slots through which pass screws 39 which can be loosened to permit angular movement of the end plate. The screws engage with threaded blocks 40 supported from the other end plate by screws 41. In a modification, screws similar to 39 and 41 are connected together by a sleeve and a tension spring, whereby the end plate 39 can be drawn axially and turned, the extent of the axial movement being limited by stops on the shaft. The field magnet comprises U-shaped laminae 31, Fig. 3, which are formed with interlocking extensions 32, 33, alternate layers being reversed as shown in Fig. 4. The main coils 49 - - 52 and the auxiliary coils 66, 67, 70, 71 are disposed as shown in Fig. 3, and the coils and the main and auxiliary brushes 19, 20, 22, 23 are connected to a contact plate 83 with which co-operates a plate 96 having contacts for connecting together the brushes and coils as desired. Figs. 10 - - 13 show respectively the connections for operation on continuous-current and an alternating current of 25, 60 and 100 cycles. In Fig. 10, the motor is connected as a short-shunt compound motor with the main field coils 49, 52 and 50, 51 connected across main and auxiliary brushes 19, 22 and 20, 23 respectively. In Fig. 11 for 25-cycle operation, part of the auxiliary coil 70 acts as the secondary of a transformer to apply a voltage across the auxiliary brushes 22, 23, and in Fig. 12, a part of the auxiliary coil acts as the secondary of a transformer to increase the voltage applied to the main brushes 19, 20. For operation on 100 cycles, the connections, Fig. 13 are such that the operation is similar to that of a repulsion motor but without the tendency to overspeed at light loads. In all cases, speed control is effected by moving the end plate 29 by means of a handle 42, Fig. 3.