Collector-less D-C motor

• US 3,873,897 A
• Filed: 05/23/1973
• Issued: 03/25/1975
• Est. Priority Date: 05/25/1972
• Status: Expired due to Term

• Current Assignee: Papst Licensing GmbH & Company Kg
• Original Assignee: Rolf Muller
• Inventors: Muller, Rolf
• Primary Examiner(s): Rubinson, G. Z.
• Application Number:
  US05/363,290
• Time in Patent Office: 671 Days
• Field of Search: 318/138,254 310/172,192,193
• US Class Current: 318/400.41
• CPC Class Codes: H02K 29/08 using magnetic effect devices, e.g. Hall-plates, magneto-resistors H02K29/12 takes precedence
• CPC Class Codes: H02P 2209/07 Trapezoidal waveform
• CPC Class Codes: H02P 6/08 Arrangements for controlling the speed or torque of a single motor H02P6/10, H02P6/28 take precedence
• CPC Class Codes: H02P 6/26 Arrangements for controlling single phase motors

Abstract

A permanent magnet rotor operates within the air gap of a stator magnetic circuit which has a stator winding. Current through the winding is controlled by a selectively energized semiconductor switch, which is energized over a portion of rotor rotation and in synchronism therewith. The air gap included in the magnetic circuit is non-uniform along its length, increasing to a maximum intermediate the extent of a pole, for example between 10 to 50 electrical degrees, and then decreasing to a minimum over the remainder to 180 electrical degrees over a pole. The winding is energized to cause rotation of the rotor while the permanent magnet is within a predetermined angular range, resulting in storage of magnetic energy which is released as torque upon further rotation of the rotor in another angular range. The timing of energization of the winding by a control circuit can be used to control motor speed.

Claims

1. Brushless d-c motor having a permanent magnet rotor (11);

a stator (13, 14,

     15);

a winding (18,

     19) on the stator to generate an electromagnetic field when energized; and

an air gap (26, 27, 111, 112, 116-119) separating the rotor and the stator;

controlled semiconductor switching means (38,

     39) controlling pulsed current flow through the winding;

wherein the width of said air gap is non-uniform, in zones, so that the reluctance of the magnetic circuit which includes said stator, said air gap and said rotor varies with angular position over the circumference of the stator, said zones, in the direction of rotation of the motor being defined by;

a zone of increasing width of the air gap and hence increasing reluctance of the magnetic circuit extending over a first angular range ( Alpha ) to a maximum (d2), and then a zone of decreasing width of the air gap and hence decreasing reluctance of the magnetic circuit extending over a second angular range ( Beta ) to a minimum (d1), and means (25) synchronizing pulsed energization of the semiconductor switching means and hence of the winding with the angular position of the rotor to generate, electrodynamically, an interrupted, pulsed electromagnetic torque during such pulsed energization of the winding by interaction of the magnet of the rotor with the electromagnetic field, due to energization of the winding and to store during such pulsed energization of the winding a portion of said generating torque in form of magnetic reluctance torque by interaction of the magnet of the rotor with the magnetic structure of the stator when the magnet of the rotor is in an angular range which includes at least part of said zone of increasing width of the air gap, the reluctance torque stored in magnetic form being released to the rotor, during pulse gaps, or interruptions in the generated electromagnetic field, by interaction of the magnet of the rotor with the magnetic structure of the stator when the magnet of the rotor is in an angular range which includes at least part of said zone of decreasing width of the air gap, the alternating component of the electrodynamically generated torque and the magnetic reluctance torque being in phase opposition and, together, providing a net driving torque to the rotor upon its rotation with respect to the stator.

2. Motor according to claim 1, wherein the first angular range ( Alpha ) is approximately 10* to 100*-electrical.

3. Motor according to claim 1, wherein the air gap decreases from a maximum (d2) at the beginning of the second angular range ( Beta ) approximately monotonically to a minimum (d1), said minimum being located by a third angle ( gamma ) in advance of the centeR of the electromagnetic field when the winding is energized.

4. Motor according to claim 3, wherein said second angular range ( Beta ) is about 80*-160*-electrical.

5. Motor according to claim 3, wherein said third angular range ( gamma ) is from 0* to 30*-electrical.

6. Motor according to claim 3, wherein the air gap increases approximately monotonically in a fourth angular range ( delta ) to the maximum (d2), said fourth range including said first angular range ( Alpha ).

7. Motor according to claim 6, wherein said fourth angular range ( delta ) is about 20*-100*-electrical.

8. Motor according to claim 1, wherein the motor is a two-pole external rotor motor and the stator (13) has approximately elliptical cross section.

9. Motor according to claim 8, wherein the main axis (32) of the ellipse includes an angle ( epsilon ) having a value between about 40*-80*-electrical, with an axis (33) passing through the center of the stator poles.

10. Motor according to claim 1 (FIG. 5), wherein the motor is a two-pole internal rotor motor and the stator is formed with an internal essentially cylindrical space in which the rotor may turn, which space is approximately elliptical in cross section.

11. Motor according to claim 1 (FIG. 6), wherein the stator of the motor has a circumference facing the air gap which has portions flattened with respect to a complete circle coaxial with the motor.

12. Motor according to claim 11, wherein the motor is a four-pole motor and the stator structure has four flattened portions uniformly distributed above the circumference of the stator;

the windings are located in winding slots (120-123), said slots being located at portions of the rotor between said flattened portions.

13. Motor according to claim 1, wherein the synchronization means (25) comprises a magnetic semiconductor sensing means located at an angular position corresponding to that between adjacent stator poles.

14. Motor according to claim 1, wherein the permanent magnet rotor (11) has approximately sinusoidal distribution of magnetism.

15. Motor according to claim 1, wherein the permanent magnet rotor (11) has approximately trapezoidal distribution of magnetism.

16. Motor according to claim 1, wherein the permanent magnetic rotor has approximately rectangular-shaped distribution of magnetization.

17. Motor according to claim 1, wherein the synchronizing means comprises a magnetic sensing element (25) and a speed controller circuit (FIG. 3) including the sensing element, said circuit controlling the semiconductor switching means (38, 39) to interrupt energization of the winding before the theoretical commutation instant sensed by the sensing element and to re-energize the winding after the theoretical commutation instant sensed by the sensing element.

18. Motor according to claim 17, wherein the winding is a two-part winding and the duration of energization of any part of the winding at the desired speed is less than 120*-electrical to generate a driving torque (Mel).

19. Motor according to claim 17, wherein the driving torque (Mel) generated during energization of the winding and the torque (Mrel) released or delivered by stored magnetic energy are substantially complementary, whereby the added instantaneous values provide a substantially uniform output torque.

20. Motor according to claim 1, wherein the synchronizing means comprises magnetic sensing means (25) and a control circuit comprising means (68, 69) sensing induced a-c voltages in the stator winding during operation of the motor;

means (85) phase-shifting the sensed a-c voltages; and

means (100,

     84) deriving a control signal to energize the semiconductor switching means in dependence on a characteristic of the phase-shifted voltage.

21. Motor according to claim 20, wherein the phase-shift means (85) comprises means shifting the phase of the induced a-c voltageS by about 180*-electrical.

22. Motor according to claim 20, wherein the phase-shift means (85) comprises a multi-stage filter.

23. Motor according to claim 22, wherein the multi-stage filter comprises a plurality of series-connected R-C circuits.

24. Motor according to claim 20, further comprising voltage reference means (95) and wherein said characteristics comprise a comparison of amplitude of the phase-shifted voltage with respect to the reference means.

25. Motor according to claim 24, wherein the comparison level is adjustable.

26. Motor according to claim 20, wherein the phase-shift means comprises a multi-stage filter (85) and a control amplifier connected thereto.

27. Motor according to claim 20, further comprising a temperature sensitive element (87) included in the control circuit, said temperature sensitive element being dimensioned to compensate for temperature dependency of remanent induction of the permanent magnetic rotor.

28. Motor according to claim 20, wherein the means sensing the induced voltage comprises a multi-phase half-wave rectifier (68, 69).

29. Brushless d-c permanent magnet rotor and control circuit combination comprising a stator having at least one winding thereon to selectively energize at least two poles, in respective directions of magnetization;

semiconductor control means selectively energizing the winding, alternately, in respective directions of magnetization in pulses, leaving pulse gaps between energizing pulses;

a permanent magnet rotor opposed to the poles of the stator;

an air gap separating the rotor and the stator poles, said air gap being characterized in that progressing in the direction of rotation of the motor, the air gap has a first zone of increasing width, so that the reluctance of the magnetic path between rotor and stator increases in said first zone, said first zone extending over a first angular range ( Alpha ) to a maximum (d2), and the air gap has a second zone of decreasing width, so that the reluctance of said magnetic path then decreases in said second zone, said second zone extending over a second angular range ( Beta ) to a minimum (d1), to store magnetic energy by interaction of the magnetism of the rotor with the magnetic structure of the stator when a pole of the rotor is in said first zone and to release the stored energy in the form of delivered torque by interaction of the permanent magnetism of the rotor with the magnetic structure of the stator when a pole of the rotor is in said second zone;

magnetic sensing means sensing the angular position of a pole of the rotor with respect to the winding on the stator;

a control circuit responsive to and connected to said magnetic sensing means and controlling said semiconductor control means to energize the winding in respective direction of current flow and generate a magnetic field, in alternate direction, in synchronism with the position of a pole of the rotor in said first zone, and to de-energize the winding when the pole of the rotor is in the second zone, to generate electrodynamically, an interrupted pulsed torque having an alternating component in phase opposition to the torque applied to the rotor as the magnets of the rotor interact with the respective zones of the magnetic structure.

30. Motor and control circuit combination as in claim 29, further comprising speed control means comprising means deriving a signal representative of motor speed;

command means connected to said signal deriving means and delivering a speed command signal; and

means controlling the duration of energization of said winding by said semiconductor control means in dependence on said speed command signal.

31. Motor and control circuit combination as in claim 29, wherein the air gap decreases from a maximum (d2) at the beginning of the second angular range ( Beta ) approximately monotonically to a minimum (d1), said minimum being located By a third angle ( gamma ) in advance of the center of the electromagnetic field when the winding is energized.

32. Motor and control circuit combination as in claim 31, wherein said control circuit controls said semiconductor control means to energize the winding in respective direction of current flow when a pole of the rotor has rotated beyond said third angle ( gamma ) and while said pole is still in said first zone.

33. Motor and control circuit combination as in claim 29, wherein the permanent magnet rotor (11) has approximately sinusoidal distribution of magnetism.

34. Motor and control circuit combination as in claim 29, wherein the permanent magnet rotor has approximately trapezoidal distribution of magnetism.

35. Motor as in claim 1, wherein the synchronization means (25) comprises a magnetic field sensing means located at an angular position corresponding to that between adjacent stator poles.