GB2341732A

GB2341732A - Layout of rotor poles in an electric motor

Info

Publication number: GB2341732A
Application number: GB9825173A
Authority: GB
Inventors: Michael John Flowerday
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-09-18
Filing date: 1998-11-18
Publication date: 2000-03-22
Also published as: GB9820251D0; GB9825173D0

Abstract

A unidirectional electric motor, axial, radial or linear incorporating a stator provided with salient poles and a permanent magnet rotor comprised of a number of poles, a number having substantially the same pole face angular span as each stator pole, the remainder having a longer pole face angular span than each stator pole, such poles being arranged so that adjacent poles are of the opposite magnetic polarity. The motor being disconnected from the supply the poles with the same pole face angular span as each rotor/armature pole being set to align with the stator poles, the rotor/armature poles with the longer span being arranged so that their trailing edges, in the selected direction of movement, coincide with the leading edges of a stator poles, whilst their leading edges project towards, but do not cover, the adjacent stator poles in the direction of movement. The rotor may include non-permanent magnet poles.

Description

1. 2341732 PATENT APPLICATION In the name of Michael John Flowerday of 24

Kennedy Avenue, Gorleston, Great Yarmouth, Norfolk, England, a British Subject.

ASYMMETRIC POLE ELECTRIC MOTORS Several types of electric motors suitable for connection to a single phase supply exist. Many single phase induction motors employ control or supply techniques to derive from the single phase supply a second phase, to be connected to a second phase winding at start up or continuously, to provide a guaranteed direction of rotation and optimum starting and running conditions. Both phases, either only at start up or continuously, being energised simultaneously. Such motors and controllers are well known. These may operate either from an alternating current supply or a direct current supply in cooperation with a suitable inverter.

Another well known type, the 'Universal' motor, employs an armature with a commutator and brushes to provide the necessary switching of the armature windings, thereby energising the armature poles, to generate, in co-operation with the energised field poles, torque and to provide a guaranteed direction of rotation. This type of motor may be employed to operate directly from an alternating current or a direct current supply. Its maximum speed without external control is limited by the torque demand of the load. These motors are well known.

Various forms of fail safe brakes may be added or included using well known technology.

Disclosure of Invention.

According to the first aspect of the present invention a brushless electric motor may be provided which will operate from a single phase alternating current supply without the need to generate a second phase, or from a direct current supply in co-operation with a simple single phase inverter. It will provide synchronous rotation when connected to a suitable single phase supply. It may also provide a series motor or traction motor characteristic when used in co-operation with a single phase inverter using feedback. Such an inverter, integral or external, being supplied from a direct current source, which may be derived from a battery or an alternating current source using known technology.

The motor has one preferred direction of rotation which is set during manufacture.

When disconnected from the supply the motor exhibits a major braking effect and will maintain this high resistance to rotation or movement.

The motor configured as a radial motor comprises; a simple salient pole stator, preferably made of laminated electrical steel or another suitable magnetic material, provided with energising coils so arranged to provide, if connected in series to a supply, adjacent poles of the opposite magnetic polarity. The number of stator poles being an even number. Such poles being substantially uniformly spaced.

a permanent magnet rotor with the same number of poles as the stator. Adjacent permanent magnet poles being of opposite magnetic polarity. The rotor magnet pole faces having alternately, either substantially the same size and angular span as each stator pole face, or a longer angular span than each stator pole face but less than one stator pole face and one adjacent winding space or slot. The motor may also be configured as a radial motor to comprise: a simple salient pole stator as described above.

a permanent magnet rotor with the same number of poles as the stator. Adjacent permanent magnet poles being of the opposite magnetic polarity. The number of rotor pole faces having substantially the same size and angular span as each stator pole face being unequal to the remainder having a longer angular span.

The motor may also be configured as an axial or linear motor employing the same techniques. In the case of a linear motor the number of stator poles may exceed the number of rotor poles. The objects of this aspect of the present invention are to provide:

an electric motor, radial, axial or linear, incorporating a simple salient pole stator and a permanent magnet rotor or armature, providing a single predetermined direction of shaft rotation, ( or linear movement). Such motor Men connected to a suitable single phase alternating current supply providing a synchronous output rotation or movement. When disconnected from the supply such motor exhibiting a substantial fail safe braking force, maintaining this resistance to movement.

an electric motor, radial, ayial or linear, incorporating a simple salient pole stator and a permanent magnet rotor or armature, providing a single predetermined direction of shaft rotation, (or linear movement). Such motor when connected to a simple single phase bipolar inverter providing, without feedback a synchronous characteristic, with feedback a series motor or traction characteristic.

3.

According to a second aspect of the present inventioh an electric motor may be provided where the motor, configured for example as a radial motor comprises:

a simple salient pole stator, preferably made of laminated electrical steel or another suitable magnetic material, provided with energising coils so arranged to provide, if connected in series to a supply, adjacent poles of the opposite magnetic polarity, the number of stator poles being an even number, such poles being substantially uniformly spaced.

a hybrid permanent magnet rotor with the same number of poles as the stator, alternate poles being either of permanent magnet material or magnetic material, for example electrical steel lamination. The poles formed from the magnetic material each having the same pole face shape and angular span as each stator pole. The permanent magnet poles each having a longer angular span than each stator pole face but less than that required to span one stator pole face and one adjacent winding space or slot.

The motor may also be configured to comprise:

the same stator and rotor. The stator coils being connected alternately in two phases to operate in co-operation with a single phase supply and two diodes, providing stator pole energisation such that with each half cycle of supply alternate stator poles will be energised to exhibit the same magnetic polarity.

Or the motor may be configured to comprise:

the same stator and rotor. The stator coils being connected alternately in two phases to operate in co-operation with a simple two phase unipolar switched reluctance type of supply providing stator pole energisation such that with each half cycle of supply alternate stator poles will be energised to exhibit the same magnetic polarity.

Motors made in accordance with this second aspect of the present invention may employ 50% less magnets and are therefore cheaper to manufacture. They may be connected directly to a suitable single phase supply or an alternative simple control without the need to generate a second simultaneous phase at any time. Due to the low reluctance magnetic paths provided by the permanent magnet rotor poles in cooperation with the magnetic material rotor poles and the stator poles, substantial fail safe braking may be maintained.

4.

Brief Description of Drawings.

Examples of the present invention will now be described in detail with reference to the accompanying drawings in which:

Fig. 1 Shows the 12 pole stator and the 12 pole rotor of a radial motor with salient stator poles, the rotor incorporating adjacent magnets of opposite polarity and different angular span, employing six magnets with substantially the same pole face shape and angular span as each stator pole face and six magnets with a greater angular span.

Fig. 2a-2d Show simplified diagrams illustrating the relative rotor stator relationship of the motor illustrated in Fig.1, from pre-start up through the first three half cycles of supply input.

Fig. 3 Shows in simple outline the 12 pole stator and the 12 pole rotor of a radial motor with salient stator poles, the rotor incorporating adjacent magnets of opposite polarity, employing nine magnets with substantially the same pole face shape and angular span as each stator pole face and three magnets each with a greater angular span.

Fig. 4 Shows in simple outline the 12 pole stator and the 12 pole rotor of a radial motor with salient stator poles, the rotor incorporating adjacent magnets of opposite polarity, employing three magnets with substantially the same pole face shape and angular span as each stator pole face and nine magnets each with a greater angular span.

Fig. 5 This shows a simplified plan view of the stator of a 12 pole axial motor.

Fig. 6 This shows a simplified plan view of the 12 pole rotor for use with the stator shown in Fig 5.

Fig. 7 This shows a simplified plan view of the rotor illustrated in Fig. 6 superimposed on the stator shown in Fig. 5.

Fig. 8 This shows a sectioned view of the assembled axial motor employing the stator shown in Fig. 5 and the rotor in Fig. 6 Fig.9 This shows a simplified linear representation of the stator/rotor pole relationship of a motor employing a rotor with asymmetric permanent magnet rotor poles as shown in Figs. I & 2 with the supply disconnected.

5.

Fig. 10 This shows a Simplified linear representation of the stator/rotor pole relationship of a motor employing a rotor with asymmetric rotor poles wherein the rotor poles that have the same angular span as each stator pole are made of the magnetic backing material. Poles 34 being energised as south poles and poles 35 as north poles.

Fig. 11 This shows a simplified linear representation of the stator/rotor pole relationship of a motor employing a rotor with asymmetric rotor poles wherein the rotor poles that have the same angular span as each stator pole are made of the magnetic backing material. Poles 34 being energised as north poles and poles 35 as south poles.

Fig. 12 This shows the stator and rotor pole arrangement as in Fig. 10 with the motor shown connected to a simple two phase supply derived from a single phase alternating current supply using two diodes wherein each phase is alternately energised for one half of the supply cycle.

Fig. 13 This shows the stator and rotor pole arrangement as in Fig. 10 with the motor shown connected to a simple unipolar two phase switched reluctance type of supply wherein each phase is alternately energised for one half of each supply cycle.

Detailed Description.

An example of a radial motor configured in accordance with the first aspect of the present invention isillustrated in Fig. 1. It incorporates:

a stator 2 with twelve salient stator poles 3, each with the same pole face shape, provided with windings 9 which when energised produce adjacent stator poles of the opposite magnetic polarity.

a permanent magnet rotor 1 comprised of twelve magnets 4 and 5, arranged so that adjacent magnets are of the opposite magnetic polarity. Six magnets 4 having substantially the same pole face 6 shape and angular span as each stator pole face 8, each with an span of 22", and six magnets 5 having longer angular pole faces 7 each with a span of 280.

Disconnected from the supply the rotor 1 comprised of magnets 4 and 5 will take up a position which minimises the reluctance of the magnetic circuits formed by the stator and rotor poles so that each of the magnets 4, with the same pole face span 6 as the salient stator pole faces 8, will align itself with a stator pole face 8. Given an intended clockwise rotation 10, the trailing edges 11 of the magnets 5, each with a longer span, will be aligned with the leading edges 13 of a salient stator poles 3, the leading magnet edges 12 projecting towards the next adjacent salient stator pole in the clockwise direction.

6.

The direction of intended rotation is reversed by reversing the direction of the rotor pole projection.

The operation of the motor illustrated in Fig. I is shown in the sequence of Figs. 2a to 2d.

Fig. 2a shows the motor as in Fig. 1, disconnected from the supply. The salient stator poles 3 have been numbered I through to 12 to simplify the explanation. The rotor has been aligned so that pole 4 having substantially the same pole face shape and angular span as stator pole 3 is in alignment with stator pole number 1. The rotor pole 4 being directly under stator pole number 1 is assumed to have a south facing pole face.

Disconnected from the supply the alignment of the rotor poles provides for a substantial fail safe braking torque if attempts are made to turn the rotor due to the normal resistance to movement associated with strong magnetic circuits attempting to maintain minimum reluctance In Fig.2b we assume that the first positive half cycle of the applied alternating current supply causes current to flow in the coil windings 9 to magnetise the stator poles as shown, with pole number 1 as a north pole, stator pole number 2 as a south pole.

With this polarisation of the stator poles there will be no rotation of the rotor 1. The magnetic attraction of the opposing stator and rotor poles increases the resistance to rotation.

Progressing to Fig. 2c we assume that the supply waveform has progressed 180" and that the coils 9 are being energised by the negative going half cycle of current, thereby reversing the magnetic polarity of the stator poles. The stator poles have forced the rotor poles to take up the positions shown. Due to the net magnetic circuit associated with the poles with longer angular spans 5 not allowing their extended magnetic pole faces to pass anti-clockwise over the changed stator poles, and being greatly attracted clockwise by the close proximity of the adjacent stator poles, the rotor has rotated in the clockwise direction.

The projection of the rotor poles 5 with their longer span projecting towards the next clockwise stator poles, which became highly magnetically attractive to them, removed the uncertainty as to the direction of rotation that would otherwise exist if all rotor poles were of the same span as the stator poles 3. The overall effect was for the rotor to rotate clockwise to re-align itself with the new magnetic field pattern. All rotor and stator poles contribute to the rotational force providing a high torque.

The sequence is followed through in Fig. 2d where the positive half cycle of mains is now assumed to be present the waveform having progressed 360 ". The rotation of 30" Fig.2c during the negative half cycle is followed by another 30" to sum to 60", Fig.2d.

7.

Further explanation of the cycle will not be given here, the rotation of a permanent magnet rotor in synchronism with a circulating magnetic field is well known to those skilled in the art.

The rotor illustrated in Figs. 1 through to 2d is shown to employ an equal number of rotor magnets 4 and 5 with spans of the same angular length as the stator poles 4 or longer than the stator poles 5. Other examples using rotors making use of the same technique as discussed above are shown in Fig.3 and Fig 4.

In Fig. 3 the twelve pole rotor incorporates nine magnets with pole faces having the same angular span 4 as the stator poles 3 and three that have a longer angular span.

The 12 pole rotor illustrated in Fig.4 incorporates three magnets with spans of the same angular length as the stator poles 4 and nine that have a longer angular span 5.

An example of an axial permanent magnet motor employing the same techniques as in Figs. 1 & 2 is illustrated in Figs. 5 through to Fig.8. In this example the stator shown in Fig.5, incorporates 12 identical salient stator poles 21. The rotor 27, Fig.6, incorporates 12 permanent magnet poles, six poles 23 having the same pole face shape and span as the stator poles 21, and six having a larger pole face area with a longer span 22. The actual shape of the magnets with the larger area and span in this example being dictated by the shapes required to optimise the cutting of them from rectangular slabs.

Fig.7 shows the rotor shown in Fig.6 superimposed above the stator shown in Fig.5. Here it can be seen that the rotor poles 23 exactly cover the stator poles 21 where as the rotor poles 22 have been set to overlap the stator poles 21, the overlap projecting clockwise for a clockwise rotation.

Fig. 8 shows a cross section of the same motor assembled to incorporate the stator assembly 29 and the rotor 27 with magnets inserted 28. This motor represents a single sided single stator axial motor, it will be obvious to those skilled in the arts that a double sided, double stator, motor can easily be provided.

The number, size and shape of the stator and rotor poles can be many and various, provided the number of a full compliment of rotor poles is an even number and the number of a full compliment of rotor poles equals the number of stator poles. Selection of the number of poles is otherwise made to achieve the required speed and torque. A number of stator poles may be omitted to enable a control function such as an inverter and or a position sensor(s) to be incorporated.

Fig. 9 shows the same stator/rotor relationship of the motors illustrated in Figs. 1,2,5,6,7 & 8 simply displayed as a unidirectional linear motor. In this example 8.

the coils 38 around each of the stator poles 34 are shown wound for connection to a single phase supply. The armature or rotor poles, 32 and 33, are each made of a permanent magnet material, poles 33 having substantially the same span and surface profile as the stator poles 34, armature or rotor poles 32 having a span length that is longer than the stator poles so that they project towards the adjacent stator poles in the intended direction of movement.

An example of the second aspect of the present invention is shown in Fig. 10. Here again, for simplicity in illustration, the stator/rotor relationship of a radial, axial or linear motor made in accordance withe the present invention is displayed as a unidirectional linear motor.

Fig. 10 & 11 show a simplified linear representation of the stator/rotor pole relationship of a motor employing a hybrid permanent magnet rotor with asymmetric rotor poles wherein the rotor poles 36 that have the same angular span as each stator pole are made of the magnetic backing material 31. Fig.10 shows a motor with the supply disconnected, if a single phase supply were to be connected to the coils 38 such that during a positive going half cycle the magnetic polarity of pole 34 was S (south) and pole 35 was N (north) there would be no movement.

Fig. 11 shows that with the progression to a negative going half cycle the magnetic polarity of the poles 34 and 35 has been reversed. This has forced the permanent magnet north poles 32 away from stator poles 34 and towards stator poles 35. Each of the permanent magnet rotor poles 32 being of the same magnetic polarity the adjacent rotor poles 36 of magnetic material are by induction effectively south poles. The adjacent rotor poles 36 made of the backing steel, having the same span and shape as the stator poles, have aligned themselves with the stator poles 34, reducing the magnetic circuit reluctance, completing the magnetic circuit. The direction of movement was as shown, for as in the case where an all permanent magnet rotor is employed Fig.9 the magnetic field of the permanent magnet poles 32 which extend towards the adjacent stator poles will not allow their extended pole faces to pass in the reverse direction over the changed stator poles.

The continued application of the supply would generate movement in the same direction as has been shown in Figs. 2a to 2d.

This aspect of the present invention shown in Figs. 10 & 11 provides for economy in permanent magnet material.

Arrangements as previously illustrated may also be exploited when connected to alternative power supplies as shown in Figs. 12 & 13.

The example shown in Fig. 12 illustrates a motor with coils 38 and 39 connected to an alternating current supply 40 via diodes 41 to provide stator pole energisation such that during a positive half cycle of supply stator poles 34 are energised to produce North poles at their pole faces and during a negative half cycle stator poles 35 are energised 9.

to produce North poles at their pole faces, producing the direction of movement shown. Without the use of the asymmetric permanent magnet armature or rotor, poles 32 in conjunction with the adjacent armature or rotor poles 36 having the same span as the rotor poles 34 & 35, the armature or rotor would not be able to determine its direction of movement.

The example shown in Fig. 13 shows a motor wherein adjacent stator poles 34 & 35 are energised by coils connected alternately to the two phases of a simple unipolar switched reluctance type controller. Movement of the armature or rotor 42 is in this example again produced in the direction indicated by alternately energising the stator poles 34 and 35 to produce North poles at their pole faces.

As described above, where a two phase unipolar supply is used to consecutively energise adjacent stator poles to exhibit the same magnetic polarity, for example Figs.12 & 13, the direction of coil winding, supply polarity and interconnection must be such as to ensure that such energised stator pole polarity opposes that of each rotor or armature pole having a greater angular span than each stator pole.

Other types of controllers and supplies may be employed by those skilled in the art. Various arrangements of pole geometry, numbers of poles, magnetic materials, permanent magnets and winding arrangements may be used to achieve such motors.

10.

Claims

Claims. I. An electric motor, radial or axial, incorporating- a salient

pole stator with a number of poles of substantially equal shape and pole face area, these poles being wound with coils variously arranged to provide, when connected to a single phase alternating current or bi- polar supply, simultaneously, adjacent stator poles of the opposite magnetic polarity or when connected to a suitable two phase unipolar supply, consecutively energised adjacent poles of the same magnetic polarity.

a permanent magnet rotor comprised of the same number of poles, a number having substantially the same pole face angular span as each stator pole, the remainder having a longer pole face angular span than each stator pole, such poles being arranged so that adjacent poles are of the opposite magnetic polarity, the motor being disconnected from the supply the poles with the same pole face angular span as each rotor pole being set to align with the stator poles, the rotor poles with the longer span being arranged so that their trailing edges, in the selected direction of rotation, coincide with the leading edges of a stator poles, whilst their leading edges project towards, but do not cover, the adjacent stator poles in the direction of rotation.
2. An electric motor as in claim I wherein the number of rotor poles having the same pole face angular span as each stator pole face equals the number of rotor poles each with a longer pole face angular span than a stator pole face.
3. An electric motor as in claim 1 wherein a number of stator poles are omitted to enable the incorporation of control and or sensing devices.
4. An electric motor, radial or axial, incorporating:

a salient pole stator with a number of poles of substantially equal shape and pole face area, these poles being wound with coils variously arranged to provide, when connected to a single phase alternating current or bipolar supply, simultaneously, adjacent stator poles of the opposite magnetic polarity or when connected to a suitable two phase unipolar supply, consecutively energised adjacent poles of the same magnetic polarity.

a rotor comprised of the same number of poles, alternate poles being made of magnetic material having substantially the same pole face angular span as each stator pole, the remainder being made of permanent magnet material having a longer pole face angular span than each stator pole, such permanent magnet poles being arranged so that all are of the same magnetic polarity, the poles with the same pole face angular span as each stator pole being set to align with the stator poles, the motor being disconnected from the supply, the rotor poles with the longer span being arranged so that their trailing edges, in the selected direction of rotation, coincide with the leading edges of the stator poles, whilst their leading edges project towards, but do not cover, the adjacent stator poles in the direction of rotation.

11.
5. An electric motor as in claim 4 wherein a number of stator poles are omitted to enable the incorporation of control and or sensing devices.
6. A linear electric motor incorporating:

a salient pole stator with a number of poles of substantially equal shape and pole face area, these poles being wound with coils variously arranged to provide, when connected to a single phase alternating current or bipolar supply, simultaneously adjacent stator poles of the opposite magnetic polarity or when connected to a suitable two phase unipolar supply, consecutively energised adjacent poles of the same magnetic polarity.

a permanent magnet armature comprised of a number of poles, some having substantially the same pole face angular span as each stator pole, the remainder having a longer pole face angular span than each stator pole, such poles being arranged so that adjacent poles are of the opposite magnetic polarity, the motor being disconnected from the supply the poles with the same pole face angular span as each armature pole being set to align with the stator poles, the armature poles with the longer span being arranged so that their trailing edges, in the selected direction of movement, coincide with the leading edges of a stator poles, whilst their leading edges project towards, but do not cover, the adjacent stator poles in the direction of movement.
7. A linear electric motor incorporating:

a salient pole stator with a number of poles of substantially equal shape and pole face area, these poles being wound with coils variously arranged to provide, when connected to a single phase alternating current or bipolar supply, simultaneously adjacent stator poles of the opposite magnetic polarity or when connected to a suitable two phase unipolar supply, consecutively energised adjacent poles of the same magnetic polarity.

a hybrid permanent magnet armature comprised of a number of poles, alternate poles being made of magnetic material having substantially the same pole face angular span as each stator pole, the remainder being made of permanent magnet material having a longer pole face angular span than each stator pole, such permanent magnet poles being arranged so that all are of the same magnetic polarity, the motor being disconnected from the supply the poles with the same pole face angular span as each stator pole being set to align with the stator poles, the armature poles with the longer span being arranged so that their trailing edges, in the selected direction of movement, coincide with the leading edges of the stator poles, whilst their leading edges project towards, but do not cover, the adjacent stator poles in the direction of movement.