WO1995010134A1

WO1995010134A1 - Electronically commutated permanent magnet motor

Info

Publication number: WO1995010134A1
Application number: PCT/AU1994/000603
Authority: WO
Inventors: Bruce Eric Grinter; George Charles Mcrae
Original assignee: Ncbf Pty. Ltd.
Priority date: 1993-10-05
Filing date: 1994-10-05
Publication date: 1995-04-13

Abstract

An electric motor (10) including a stator and a rotor, the rotor includes a plurality of equispaced permanent magnets mounted on a non-magnetic disk, the stator includes a plurality of equispaced windings energised by a circuit means (12, 14) to cyclically attract opposite polarity magnets and then cease energisation when the facing poles are substantially aligned to reverse the polarity of the windings causing said opposite polarity magnets to be repelled in the same turning direction.

Description

ELECTRONICALLY COM UTATED PERMANENT MAGNET MOTOR

The present invention relates to an electric motor and relates particularly, although not exclusively, to an electric motor producing high revolutions from a low power DC source. It is an object of the present invention to provide a high speed electric motor which can be powered by a DC source.

A further object of the invention is to provide an efficient electric motor.

With these objects in view the invention provides an electric motor including a stator and a rotor, one of said stator or rotor having at least one magnetic means secured thereto, the other of stator or rotor including at least one winding and circuit means to control energisation of said at least one winding.

Preferably said at least one magnetic means are permanent magnets and said rotor includes said at least one magnetic means.

In a preferred embodiment a plurality of windings and permanent magnets are provided. Preferably the winding(s) are energised by said circuit means to cyclically attract said at least one magnetic means and then cease energisation when the facing poles are substantially aligned to reverse the polarity of said winding(s) to cause said at least one magnetic means to be repelled in the same turning direction. In one practical embodiment a plurality of magnets are circumferentially mounted on the rim of a non-magnetic disk secured to said rotor.

In further practical embodiments a plurality of magnets protrude through the parallel faces of a non-magnetic disk and windings are located on either side of said disk. In another variation a plurality of magnets are provided on a flanged non- magnetic wheel and said windings are located between the axle of said wheel and the flange. These and other objects and aspects of the present invention will be more fully described with reference to the preferred non-limitative embodiments shown in the accompanying drawings, in which:- Fig. 1 is a schematic view of an electric motor made according to the invention;

Fig. 2 is a cross-sectional view along and in the direction of arrows 2-2 of the electric motor shown in Fig. 1 ;

Fig. 3 is a cross-sectional view along and in the direction of arrows 3-3 of the electric motor shown in Fig. 2;

Fig. 4 is a similar view to that of Fig. 3 showing a second embodiment of an electric motor;

Fig. 5 is a cross-sectional view along and in the direction of arrows 5-5 of Fig. 4; Fig. 6 is a similar view to that of Fig. 3 of a third embodiment of an electric motor;

Fig. 7 is a cross-sectional view along and in the direction of arrows 7-7 of Fig. 6;

Fig. 8 is a similar view to that of Fig. 3 of a fourth embodiment of an electric motor;

Fig. 9 is a cross-sectional view along and in the direction of arrows 9-9 of Fig. 8;

Fig. 1 0 is a similar view to that of Fig. 4 with the magnets alternating in polarity; Fig. 1 1 is a cross-sectional view along and in the direction of arrows 1 1 -1 1 of Fig. 1 0;

Fig. 1 2 is an exploded perspective view of the rotor of the electric motor shown in Fig. 1 0; and

Fig. 1 3 is a similar view to that of Fig. 2 showing a variation with the polarity of the magnets alternating.

In Figs. 1 to 3 there is shown a first embodiment of an electric motor 1 0 which is powered by an electronic controller 1 2

SUBSTITUTE SHEET {RULE 26) using a battery 14. Battery 14 is typically a 12V car or motorcycle battery or above but could be readily substituted by dry cells, solar cells, an AC-DC converter or other suitable power source. Controller 1 2 provides a pulsed square wave to the windings 16 inside motor 10. The timing for the pulses can be a simple switching device (not shown) attached to shaft 1 8 of motor 10 e.g. apertured timing plate with light sensor, Hall-effect device, distributor points or any other device which allows an on-off transition detection. The application of voltage to the windings 1 6 can be controlled by fast electronic switching devices e.g.

MOSFET or IGBT (isolated gate bipolar-transistor) transistors which are easy to turn off.

Electric motor 10 includes a casing 20 having bosses 22 for supporting shaft bearings 24. Windings 16 are equispaced and secured to the inner periphery 26 of casing 20. Windings 16 have an iron core 28 which can be secured to inner periphery 26 by any suitable manner e.g. welding, gluing or locking. Iron cores 28 will be radially aligned with respect to shaft 18.

Shaft 18 is coupled to a non-magnetic disk 30 by key 32. Disk 30 includes a plurality of equispaced pockets 34 in the outer periphery thereof for reception of permanent magnets 36. It is preferred that the magnets are rare earth magnets. Magnets 36 all have their polarities aligned in the same direction. A band 38 can be secured to the outer periphery of disk 30 to retain magnets 36 in pockets 34. Magnets 36 could also be adhesively retained in pockets 34.

In use, windings 1 6 are energised by controller 12. As each winding 16 will produce a magnetic field, magnets 36 will be attracted to windings 16 and rotate shaft 1 8. When the magnets are substantially in line with windings 16 controller 12 switches off current to the windings. The de-energisation of windings 16 will cause a reversal of the polarity of windings 16 which will repel magnets 36. As disk 30 is already rotating the repulsion will be in the same direction of rotation. Windings 1 6 can then be energised to repeat the sequence of operations. The successive attraction- repulsion sequencing will allow high speed rotation with fairly small energy requirements. The duty cycle of the square wave pulses is typically in the order of 70%. The speed of the motor can be readily controlled by increasing or decreasing the voltage supplied to windings 1 6.

Although the preferred embodiment illustrates equal numbers of magnets 36 and windings 1 6 this is not essential. In one practical embodiment only one coil was used with three equispaced magnets. An increase in magnets and windings will cause an increase in the torque from shaft 1 8.

Figs. 4 and 5 illustrate a second embodiment of an electric motor. In order to avoid repetition of description similar integers in this embodiment, and the embodiments shown in Figs 6 to 9, 1 0 to 1 2 and 1 3, to those in Figs. 1 to 3 will be referenced with the same numerals. In this embodiment disk 30 has magnets 36 mounted transversely to their position in Figs 1 to 3. The magnets are again equispaced and protrude through the parallel faces 40 of disk 30 rather than through the circumferential periphery. The polarities of magnets 36 are aligned in the same direction. As both ends of each magnet 36 protrude through disk 30, two sets of windings 1 6 can be provided. This embodiment has two sets of equispaced windings 1 6 on opposite sides of disk

30. This embodiment provides a compact unit with high torque.

The embodiment shown in Figs. 6 and 7 is almost identical to the embodiment shown in Figs. 4 and 5. The differences are that the number of magnets 36 has doubled and the two sets of windings have been offset from one another rather than inline as in Figs. 4 and 5. The embodiment shown in Figs. 8 and 9 is similar to that shown in Fig. 6 and where the sets of windings are offset from one another. Windings 1 6 are secured to cylindrical sleeves 42 which are co-axial with shaft 1 8. Windings 1 6 are radially mounted as best seen in Fig. 9. Disk 30 has been replaced by a wheel 44 having a flange 46. In cross-section wheel 44 has an I- shape. Magnets 36 are located in opposing ends of flange 46 in bores 48. Windings 1 6 are located under flange 46.

If required, an alternator 50 can be driven by motor 1 0 to charge battery 14. In the embodiment shown alternator 50 has a magnetic wheel 52 secured to shaft 54. Rotation of wheel 46 will cause rotation of magnetic wheel 52. Magnetic wheel 52 could include magnets (not shown) on the rim to react with magnets 36. Alternator 50 could also be driven from shaft 1 8 through a belt or gear system.

In the embodiment shown in Figs. 1 0 to 1 2 the number of magnets 36 is double the number of magnets windings 16. Magnets 36 are equispaced adjacent the periphery of disk 30. In this embodiment disk 30 is formed of three parts. An annulus or ring member 56 to which magnets 36 are affixed on both sides of ring member 56. The magnets may be adhesively affixed or held by any other suitable method. Ring member 56 may be formed of steel, plastics material or other suitable material. Magnets 36 protrude through apertures 58 of circular disk members 60, 62. A peripheral flange 64 on each circular disk member 60, 62 ensures ring^'member 56 is encapsulated. Circular disk members 60, 62 could be formed from aluminium, plastics material or other suitable material. Circular disk members may be clamped, glued or secured by fasteners to ring member 56. Magnets 36 will alternate in polarity i.e. a south pole magnet will have a north pole magnet on either side thereof. The operation of the embodiment shown in Figs. 1 0 to 1 2 is the same as that described with reference to the embodiments of Figs. 1 to 9. The difference is the enhanced effect of the intermediate magnet. Each winding 1 6 will attract an opposite pole of the approaching magnet 36 but repel the magnet in front of it. This will result in an increase in torque of the motor. Energisation of windings will occur when each intermediate magnet has moved past the respective winding in order that the repelling effect occurs in the same direction as the attraction effect of the following magnet.

Fig. 1 3 illustrates a variation which combines the embodiment shown in Figs. 2 and 3 with the embodiment shown in Figs. 1 0 to 1 2. In Fig. 1 3 magnets 36 are affixed to a band 66 made of steel, plastics material or other suitable material. Again there are twice as many magnets 36 as there are windings 1 6. A further peripheral band 68 links the magnets 36. Band 68 could be replaced by a cover or suitable protector. The polarity of the magnets again alternates. The operation of this embodiment will be the same as the embodiment shown in Figs. 1 0 to 1 2. It is evident that the positions of magnets 36 and windings 1 6 could be interchanged. In addition magnets 36 could be replaced by windings as well.

It is believed that the invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement of the parts and that changes may be made in the form, construction and arrangement of the electric motor described without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the forms hereinbefore described being merely preferred embodiments thereof.

Claims

1 . An electric motor including a stator and a rotor, one of said stator or rotor having at least one magnetic means secured thereto, the other of stator or rotor including at least one winding and circuit means to control energisation of said at least one winding.

2. The electric motor of claim 1 , wherein said at least one magnetic means are permanent magnets and said rotor includes said at least one magnetic means.

3. The electric motor of claim 2, wherein a plurality of windings and permanent magnets are provided.

4. The electric motor of any one of the preceding claims, wherein said winding(s) are energised by said circuit means to cyclically attract said at least one magnetic means and then cease energisation when the facing poles are substantially aligned to reverse the polarity of said winding(s) to cause said at least one magnetic means to be repelled in the same turning direction.

5. The electric motor of claim 2, wherein a plurality of magnets are circumferentially mounted on the rim of a non- magnetic disk secured to said rotor.

6. The electric motor of claim 2, wherein a plurality of magnets protrude through the parallel faces of a non-magnetic disk and windings are located on either side of said disk.

7. The electric motor of claim 2, wherein a plurality of magnets are provided on a flanged non-magnetic wheel and said windings are located between the axle of said wheel and the flange.

8. The electric motor of claim 1 , wherein said rotor includes a plurality of equispaced magnets and a plurality of equispaced windings on the stator, there being double the magnets than windings, said magnets being in sequential alternating polarities, said windings being energised by said circuit means to cyclically attract opposite polarity magnets and then cease energisation when the facing poles are substantially aligned to reverse the polarity of the windings, causing said opposite polarity magnets to be repelled in the same turning direction whilst attracting the other magnets, and said circuit means energising said windings when the other magnets have passed said adjacent windings.