Patent GB-980666-A (GB)
Title: An improved variable reluctance motor
IPC: H02P25/08
Filed: 1963-01-21
Abstract: 980,666. Control of A.C. motors; A.C. motors. P. A. GUINARD. Jan. 21, 1963 [Jan. 23, 1962], No. 2542/63. Headings H2A and H2J. [Also in Division H3] A motor has two rotor members 7, 8 mounted in thermosetting resin 9 with aligned pole teeth 10, 11 co-operating with similar stator teeth which are formed on two annular stator members 1, 2, respectively. The stator members, again embedded in a housing of thermosetting resin, carry annular exciting windings 13, 14 and are displaced by half-a-tooth pitch relative to each other. The stator coils are connected to the power supply through transistor switches whose operation is controlled in sequence by a transistor R.C. coupled oscillator or multivibrator. In order to ensure that the motor starts in one direction only the leading edges of the rotor poles which, although having the same pitch are substantially wider than the stator teeth, are tapered so that as the motor rotates the air gap between stator and rotor decreases until the position shown in Fig. 2 is reached. In a modification having a planar air gap the stators are mounted on either side of the rotor which comprises two discs having shaped poles separated by a mounting disc of insulating material, Fig. 11 (not shown). A further modification has the rotor as a single toothed disc and each stator comprises shaped sheet metal rings cut away to form depending teeth and co-operating with the rotor, with the teeth of one stator spaced by the teeth of the other stator. The exciting coils in this case are also flat annular discs and the windings may be conveniently formed by use of printed circuit techniques, Fig. 15 (not shown). All modifications employ rotor poles that are wider than those of the stator and have the extra width portion tapered to give one direction of rotation. The motor is suitable for use as a fluid pump drive motor having the rotor immersed in the pumped fluid, Fig. 18 (not shown). The astable multivibrator circuit comprises transistors 23, 24 capacitors 27, 28 and variable resistors 29, 30 and supplies alternate pulses to the base electrodes of transistors 19, 20 to alternately energized windings 15, 16 respectively. Thermistors 31, 32 included in the supply leads to the variable resistors 29, 30 provide a low frequency output on starting, while the frequency increases as the thermistor resistance decreases until the running frequency, determined by the settings of the variable resistors, is reached. In order to prevent the reverse transients produced when the windings are suddenly de-energized from harming. the multivibrator, low impedance discharge paths comprising resistor 36 and diodes 34, 35 are provided; these may be replaced by thyrites 37, 38. A series choke 21 in series with the parallel windings ensures a rapid build up of current in the motor windings when the respective transistor switch conducts and also serves to limit the stall current. Curves of field winding current, Fig. 8 (not shown), voltage appearing across the choke, Fig. 9 (not shown) and the discharge curves for the capacitors, Fig. 10 (not shown) are given.