GB2349748A - Rotor/stator relationship in a brushless machine - Google Patents

Abstract

A multi-phase brushless machine has a stator comprising air cored windings, each coil providing a fictive stator pole, the rotor comprising alternating permanent magnet poles 2 of equal number to the coils per phase, the angular span of each magnetic pole being equal or less than the angular span of each coil. The machine may be a motor or generator and may be an axial or radial air gap machine (rotary or linear). A yoke is provided against the air cores. The windings may be in the form of individual coils 1 or in the form of a continuous strip 25 or skeins 19,20. In the linear motor embodiment the coil/magnet number relationship does not hold.

Description

PATENT APPLICATION IMPROVEMENTS TO PERMANENT MAGNET BRUSHLESS MOTORS Many forms of multiphase permanent magnet brushless electric motors exist. Most employ electronic commutation, many with feedback to the electronic control from an encoder, hall effect devices or other sensors. Most employ stators formed from laminations which are shaped to provide winding slots and poles.

According to the present invention an efficient, high torque, multi phase, axial, radial or linear electric machine, without stator poles and winding slots, with the maximum winding and magnet density, low hysteresis loss, a very low resistance to rotation or linear movement when disconnected, a low weight and a low cost of manufacture is provided, incorporating air cored overlapping windings providing fictive stator poles, permanent magnet or permanently magnetised rotor/translator poles and a magnetic yoke.

The objects of the present invention are to provide: an axial motor, easily manufactured, low cost, efficient, and of low weight incorporating two stators and a double sided rotor. an axial motor of very short axial length, easily manufactured, low cost, efficient, and of low weight incorporating a single stator. a radial motor, easily manufactured, low cost and weight, efficient, with an external rotor. a radial motor, easily manufactured, low cost and weight, efficient, with an internal rotor. a linear motor, easily manufactured, efficient and with low cost and weight.

The present invention provides an efficient, high torque, axial or radial electric machine incorporating brushless electronic switching which operates simultaneously as a motor and a generator comprising: at least one stator with a number of air cored coils mounted equidistantly around said stator and positioned so that said air cored coils are energised in equilaterally balanced groups or phases, each group being connected and energised by a different phase, said number of air cored coils per group or phase being equal to the number of magnets in the rotor. a rotor, radial or axial, suitably supported to revolve radially within or without a radially arranged stator, or axially around the centre line of, parallel to and in front of an axially arranged stator (s), said rotor incorporating an even number of magnets distributed equidistantly around said rotor to provide a number of adjacent alternatively north and south magnetic poles, the angular span of each magnetic rotor pole being less than that of each individual coil. in some examples, at least one yoke made of a suitable magnetic material which is provided as a tube mounted within or without radially arranged stator windings, or as a disc mounted axially around the centre line of, parallel to and behind an axially arranged stator winding. a suitable means of transferring the rotor torque from the rotor to the load, via a shaft, gears, coupling or via a wheel, separately or in combination. a suitable means for energising each air cored coil in each stator phase.

It also provides an efficient, high linear. force, linear electric motor incorporating brushless electronic switching, which simultaneously operates as a linear generator, comprising: one stator with a number of air cored coils mounted equidistantly along said stator and positioned so that said air cored coils are energised in equilaterally balanced groups or phases, each group being connected and energised by a different phase. a linear armature or translator, suitably supported to move linearly along and above the stator, said translator incorporating a number of magnets distributed equidistantly along said translator to provide a number of adjacent alternatively north and south magnetic poles, the linear span of each magnetic translator pole being less than that of each individual coil. in some examples, a yoke made of a suitable magnetic material which is provided as a plate or strip of magnetic material mounted behind the linearly arranged stator windings. a suitable means of transferring the linear force from the translator to the load. a suitable means for energising each air cored coil in each stator phase.

The back ground to and examples of the present invention will now be described with reference to the accompanying drawings in which: Fig. 1 Shows a simplifie diagram of a motor described in United States Patent Number 5,514,923 Fig. 2 Shows an alternative arrangement of the motor illustrated in Fig. 1 Fig. 3 This illustrates a simplifie plan view of an axial stator for use with one aspect of the present invention Fig. 4 This illustrates an example of an axial motor complete with two stators and a double sided rotor.

Fig. 5 This illustrates a simplifie plan view of a rotor for use with the stator shown in Figs. 3 & 4.

Fig. 6 A simplifie view of the rotor shown in Fig. 4 shown in position above the axial stator shown in Fig. 3 Fig. 7 An enlarged view of a section of Fig. 6 is shown.

Fig. 8a An altemative method of producing an axial stator winding employing a continuous skein of wire is illustrated.

Fig. 8b A method of producing an axial stator winding using a continuous flat strip or lamination.

Fig. 9 This illustrates an alternative axial stator winding arrangement showing a single phase arrangement.

Fig. 10 The arrangement shown in Fig 9 is shown complete with a second phase overlaying the first phase.

Fig. 10a This illustrates the arrangement shown in Fig. 10 employing continuous strips or laminated windings.

Fig. 11 An axial stator is shown with a single phase comprised of overlapping coils.

Fig. 12 The axial stator shown in Fig. 11 is illustrated complete with an identical second phase overlaying the first phase.

Fig. 13 This shows a single stator axial motor with a rotor incorporating embedded poles.

Fig. 14 A partial section of the rotor shown in Fig. 13 taken at A-A.

Fig. 15 This illustrates a radial motor with an external embedded magnet rotor completely manufactured within a wheel with stator windings incorporating wire.

Fig. 16 An enlargement of a section of the motor and wheel shown in Fig. 15 Fig. 16a An alternative rotor pole arrangement for the motor shown in Fig 16.

Fig. 17 This illustrates a similar radial motor to that shown in Fig. 15 but with two continuous strips or laminations replacing the wire.

Fig. 18 This shows the relative positions of a two phase lamination or strip type winding as may be used in the motor shown in Fig. 17, before rolling and wrapping around the central yoke.

Fig. 19 A section view of a linear motor is illustrated with windings of continuous strips or laminations incorporating a translator employing surface mounted magnets.

Fig. 20 A sectional view of a linear motor is illustrated with windings of continuous strips or laminations incorporating a translator employing embedded magnets.

Description of Background Art With reference to Fig. 1, United States Patent Number 5,514,923 describes an efficient electric DC brushless motor which incorporates the principle, as described therein, that a magnet 2 will attempt to align itself at the centre of an appropriately energised air cored coil 1. An array of magnets 2 is shown distributed circularly and equidistantly around a stator 3 centrally about the centre line of the shaft 7. The magnets 2 and hence the rotor structure to which they are fixed, (not shown), may be caused to rotate by the appropriate sequential and repetitive energisation of the coils 1. Fifteen coils 1 are shown. These would be connected in three phases of five coils. The stator in accordance with this patent would be manufactured in,"strong lightweight plastic structural materiaSst.

It can easily be seen by those skilled in the art that the example illustrated in Fig. 1 could be re-arranged as shown in Fig. 2, to employ trapezoidal air wound coils 1 arranged circularly around the stator 3, centrally around the centre line of the shaft 7 to work in co-operation with trapezoidal shaped rotor magnets 2.

Description of examples of the present invention.

Fig. 3 shows in plan view a circular array of air cored coils 1 arranged within a circular recess in the stator 3, centrally around the centre line. The stator may be made of a suitable thermally conductive light weight material, for example aluminium. Two such stators 3a and 3b can be seen in the section view Fig. 4. Behind each stator coils 1 is incorporated a circular plate or toroid of strip of a suitable magnetic material to provide a yoke 5. These yokes 5, Fig. 4, are of such internal and external diameters as to substantially cover the straight radial sides 19 of the coils 1, Fig. 3.

The rotor 6 shown in Fig. 4 and again in Fig. 5 shows a circular array of trapezoidal magnets 2 alternately north and south. These magnets 2 are substantially the same shape as the stator coils 1, their radial length being substantially the same as the straight radial length 19 of the coils 1, the angular span of each magnet 31 being less than the angular span of each coil 30. The yoke 5, Fig. 4, ensures that the magnetic flux emanating from each magnet 2 pole face has a preferred straight line path through the coils 1, thus enabling maximum interaction with the coils 1 when energised.

In the example shown in Fig. 3 a single phase winding is shown which when energised is intended to interact with the magnets 2 of the rotor 6, Figs. 4 & 5. Such energisation being sequential bi-polar, the coils being connected so that when energised at any point in time they will present alternately adjacent north and south seeking fictive poles.

Now this will not guarantee a direction of rotation. This is guaranteed by the inclusion as shown in Fig. 4 of a second stator and coil arrangement 3b. This second stator is arranged so that its radial magnetic axis is one half of a pole pitch different from the first stator 3a. This second stator 3b incorporating the second phase enables the direction of rotation to be guaranteed, the sequential bi-polar supply to the second phase being 90 degrees out of phase with the first phase.

We have therefore as shown in Figs. 3,4 & 5 a very simple inexpensive axial two phase motor which, because of the improved magnetic circuit by the inclusion of the yoke 5 and the simultaneous continuous energisation of all coils, is capable of producing substantial power. The operation and control of which may be improved by the inclusion of hall effect devices embedded within the stators to give precise commutation control. Such control is well known to those skilled in the arts and therefore will not be explained further.

The use of the yokes 5, Fig. 4, enabling much better interaction between the flux of the permanent magnets 2 and the energised coils 1 provides torque very closely in accordance to the formula F = BLI which is known to all those skilled in the art, where F = Force, B = Flux density, L = total radial conductor length and I = coil current. The yokes also enable the direct cooling of the windings enabling greater currents to be employed.

In other versions of the motor the yoke 5, Fig. 4, may be omitted.

The motor described and illustrated in Figs. 3,4 & 5 is further illustrated in Figs. 6 & 7. Here shown in plan view is the rotor 6 in position over one of the stators 3 with coils 1 assemble.

An altemative method of providing the windings for such a two phase motor is shown in Fig. 8a. Here a continuous wound skein 4 of wire 8 has been formed to provide the radial sides of the fictive air cored poles.

For low voltage operation such windings may be replace, as in Fig 8b, by a continuous strip 17 or a punched or cut lamination of a suitable conductive material for example aluminium or copper, the terminations being made to the extended strip or lamination ends 18. More than one lamination, provided with suitable insulation, may be laid on top of the first lamination and connected to provide multiple tums, (not shown).

Where such strip or laminations 18 are used they may be insulated from the underlying yokes using for example, conventional varnishes, epoxy materials or when aluminium is selected by hard anodisation of the strip or lamination to provide an insulative coating. The lamination or strip may be held in place by a suitable adhesive or the insulating material itself.

A second example of the present invention is now described with reference to Figs. 9 to 14. All coil interconnections have been omitted for clarity.

Fig 9 illustrates an alternative axial stator winding provided by nine wound coils which may be interconnected to provide a single phase winding. Fig. 10 illustrates how a second set of such coils 10 may be made to overlap the first set of coils 9, thereby enabling two phase windings to be incorporated in one stator 3.

It can be seen from Fig. 1 Oa that windings made of continuous strip or laminations 19 & 20 may be employed to provide two such phase windings. These are specially suited to low voltage machines. As before, the insulation between the strips or laminations 19 & 20 and the strips or laminations and the yoke 5 and stator 3 may be vamish, lacquer, epoxy or some other suitable thermally conductive electrical insulation material, or if aluminium strips or laminations are used the insulation may be provided by hard anodising the strips or laminations 19 & 20.

The use of continuous strips or laminations 19 & 20, Fig. 1 Oa, provides an inexpensive robust winding which may as in Fig. 13 enable the thickness of the windings 1 to be reduced thereby allowing the permanently magnetic pole segments 15 of rotor 6 to be closer to the yoke 5. This will provide for a much greater flux density in the airgap between the yoke 5 and the pole segments 15, the airgap reluctance being reduced. Figs. 11 and 12 show, using coils, how the overall thickness of each coil may be reduced by the overlapping of their adjacent radial sides to provide composite radial coil sides 9 & 10. Similarly it will be clear that the adjacent radial coil sides may be positioned side by side with the same effect, (not shown).

An example of a complete machine can be seen in Fig. 13. This single stator axial permanent magnet motor may use any of the afore mentioned techniques to provide a motor of very short axial length. It may be enhanced by the use of the embedded magnet technique, Fig. 14, making the yoke 5 essential in this version by also providing the magnetic return path for the rotor magnets 12. Fig. 14 shows the magnets 12 embedded within the rotor 6 together with segments 15 of a suitable magnetic material. The magnets 12 are arranged as shown to provide adjacent segment pole faces of alternative north and south magnetic polarity. This section view, Fig. 14, of the rotor 6, Fig. 13, taken at A-A, shows the magnets 12 arranged either side of segments 15 in a continuous circular array within a recess formed in the rotor. The base of the rotor 16 and all material adjacent to the magnets but outside the circular array provided by the magnets 12 and the segments 15 is preferably non magnetic. In this way by selection of the segment width and the magnet vertical height very high composite flux densities may be achieved and used to advantage.

Robust lamination or strip windings 1, Fig 13, in co-operation with the high flux densities in the air gap between the yoke 5 and the permanently magnetised poles provided by the magnets 12 and the segments 15, Figs. 13 & 14, and the large cooling surface provided by the yoke 5 and the stator 3 enable light, easily assembled, powerful, efficient single sided axial motors to be made.

It will be clear to those skilled in the art that each of the techniques described and illustrated above may be applied to the manufacture of radial motors with either internal or extemal rotors.

One such example is shown in Figs. 15 & 16. Here an external rotor motor is illustrated in section. It has been arranged within a wheel. The complete rotor, made up of the permanent magnets 23 and the magnetic material segments 22 within the rim and tyre 21, is arranged to revolve around the central shaft 27, supported by suitable members and bearings, (not shown). The stator is provided by a yoke 26 of a suitable magnetic material, for example electrical steel lamination, around which two phase windings 24 and 25 are circularly arranged and attached, the windings projecting axially through the motor. The yoke 26, Fig. 15, may be supported on a thermally conductive hub 29 made of, for example, aluminium. The yoke 26 and hub 29 are used to conduct the heat from the stator windings 24 & 25. Fig. 16 shows an enlarged section of Fig. 15.

Fig. 16a shows a similar motor to that shown in Fig. 16 but with an alternative rotor pole construction. Here, Fig. 16a, the curved magnets 23 are fixed to the internal diameter of a tube of suitable magnetic material 28, being held in place by epoxy resin 27 or by some other fixative. Here in this example, Fig. 16a, the yoke of magnetic material 26, Figs. 15 & 16, has been omitted, the coils being affixed to a thermally conductive stator hub 29, made for example of aluminum.

Another such motor may be provided Figs 17 & 18. Fig 17 shows a similar construction to the previous radial motor shown in Fig. 15 but here the windings 24 and 25 are manufactured from overlapping laminations or strips. The simplifie drawing Fig. 18 shows such windings 24 and 25 before they are rolled or shaped to provide a continuous annuli around and attached to the yoke 26.

Again such thin strip or lamination windings 24 & 25 together with the rotor formed of the magnets 23 and segments 22 as shown provide for a light, powerful, easily assemble, efficient motor with very low resistance to rotation when de-energised, the air cored windings providing low inductance.

Internal rotor motors, (not shown), may be made using the same techniques with the same advantages.

Examples of two linear motors are shown Figs. 19 & 20 which incorporate the same techniques and advantages.

Fig. 19 illustrates a section view of a linear motor incorporating an armature or translator 50 which is arranged to move linearly along above the stator 51, it being suitably supported on bearings or slides, (not shown).

The magnets 41 are here shown surface mounted to the translator mounting plate 40 made of a suitable magnetic material and secured in position with a suitable epoxy adhesive 49 or by some other means. Said magnets are arranged so that adjacent magnets exhibit alternatively north and south seeking pole faces projecting towards the stator 51.

The stator 51 shown here incorporates a two phase winding 44 & 45 made as laminations or continuous strips of a suitable material such as copper or aluminium as previously shown in Fig. 18. These windings may be attached to the stator mounting plate 43 by a suitable adhesive 49. Such windings 44 and 45 are shown fixed to project substantially at 90 to the direction of motion. The stator mounting plate 43 may be made of a suitable magnetic material or aluminium depending upon the application.

The motor comprised of a translator 50 and a stator 51 shown in Fig. 20 differs from the motor shown in Fig. 19 in that the permanent magnets 41 and magnetic segments 42 are mounted within a non magnetic translator mounting plate 48, arranged as previously illustrated in Fig. 14.

The stator 51 Fig. 20 shows again a two phase winding 44 & 45 made as a laminations or continuous strips attached to a mounting plate or yoke 46 of a suitable magnetic material. This yoke or mounting plate 46 may then be attached to a support member 49 made of, for example, aluminium to transfer any heat generated in the windings or the magnetic material during operation, thereby cooling the assembly.

All of the motors described above and others that may be made using the same techniques may benefit from the inclusion of hall effect devices or the provision of an encoder to work in co-operation with a particular controller. Such motors may benefit from the finning or water cooling of the stators or the use of a fan to provide extra cooling. They may be made as complete items or the techniques may be incorporated within a product to provide integral motors. To those skilled in the art it will be clear that other materials may be employed in the manufacture of such motors.

The two phases of the motors shown may be energised simultaneously in a bi-polar fashion with an appropriate phase angle difference, from a controller which is well understood to those skilled in the art, or they may be energised altemately.

In this latter case a similar bi-polar supply may be used where, for example, the first phase being energised positively is de-energised before the second phase is energised positively, similarly with the negative energisation.

Although two phase motors have been described, dependant on the application of such devices multiphase motors may be made using overlapping air cored coils, skeins, strips or laminations. Dependant also on the application the yokes may in some cases be omitted for the purpose of making a very light assembly. The'windings'may also in some case be skewed. Such modifications to the above will be clear to those skilled in the art and will not be explained further here.

Claims (3)

1. CLAIMS 1. An efficient, multiphase axial or radial or linear electric machine employing brushless electronic switching which may operate as a motor or a generator incorporating; when arranged as an axial or radial machine: at least one stator with a number of air cored coils mounted equidistantly around said stator and positioned so that said air cored coils are energised in equilaterally balanced groups or phases, each coil providing a fictive pole, such coils overlapping as necessary, each group being connected to and energised by a different phase, said number of air cored coils per group or phase being equal to the number of magnets in the rotor. a rotor, radial or axial, suitably supported to revolve radially within or without a radially arranged stator, or axially around the centre line of, parallel to and in front of an axially arranged stator (s), said rotor incorporating an even number of magnets distributed equidistantly around said rotor to provide a number of adjacent alternatively north and south magnetic poles, the angular span of each magnetic pole being equal to or less than the angular span of each individual coil. at least one yoke made of a suitable magnetic material which is provided as a tube mounted within or without a radially arranged stator, or as a disc mounted axially around the centre line of, parallel to and behind an axially arranged stator (s). a suitable means of transferring the rotor torque from the rotor to the load, via a shaft, gears, coupling or via a wheel, separately or in combination. a suitable means for energising each air cored coil in each phase. when arranged as a linear machine: at least one stator with a number of air cored coils mounted equidistantly along said stator and positioned so that said air cored coils are arranged in equilaterally balanced groups or phases, such coils overlapping as necessary, each group being connected to and energised by a different phase. a linear armature or translator, suitably supported to move linearly above and along the stator, said translator incorporating a number of magnets distributed equidistantly along said translator to provide a number of adjacent alternatively north and south magnetic poles, the linear span of each magnetic pole being equal to or less than the span of each individualcoil. at least one yoke made of a suitable magnetic material provided as a plate or strip mounted behind the linearly arranged stator windings. a suitable means of connecting the translator to the load. a suitable means of energising each air cored coil in each phase.
2. 2. An efficient, high torque, multiphase axial radial or linear machine as in claims 1 and 2 wherein the stator windings are configured to provide a two phase machine.
3. 3. An efficient high torque, multiphase axial, radial or linear machine as in claims 1 and 2 wherein the air cored fictive poles may be made from at least one continuous skein of wire, a conductive strip or from a shaped lamination of a suitable conductive material.

   3. An efficient, high torque, multiphase axial, radial or linear machine as in claims 1 and 2 wherein the air cored fictive poles may be made from at least one continuous skein of wire, a conductive strip or from a shaped lamination of a suitable conductive material.

   4. An efficient, high torque, multiphase axial, radial or linear machine as in claims 1, 2 & 3 in which the rotor/translator magnets are assembled each adjacent to a segment of a magnetic material wherein the polarity of each magnet is such that the opposite sides of each segment substantially perpendicular to the stator surface is adjacent to a magnet pole of the same polarity, the rear surfaces of both magnets and segments being not adjacent to magnetic material.

   5. An efficient, high torque, multiphase axial, radial or linear machine as in claims 1,2 & 3 wherein the yoke is omitted.

   Amendments to the claims have been filed as follows An An efficient, multiphase axial or radial or linear electric machine employing brushless electronic switching which may operate as a motor or a generator incorporating; when arranged as an axial or radial machine: at least one stator providing a number of fictive poles by means of either, a number of air cored coils mounted equidistantly around said stator and positioned so that said air cored coils are energised in equilaterally balanced groups or phases, each coil providing a fictive pote, such coils overlapping as necessary, each group being connected to and energised by a different phase, said number of air cored coils per group or phase being equal to the number of magnetic poles in the rotor, or, one or more continuous meander like windings of wire or strip arranged and energised to provide such fictive poles. a rotor, radial or axial, suitably supported to revolve radia ! ! y within or without a radially arranged stator, or axially around the centre line of, parallel to and in front of an axially arranged stator (s), said rotor incorporating an even number of magnetic pole pieces magnetised by embedded permanent magnets, distributed equidistantly around said rotor to provide a number of adjacent altematively north and south magnetic poles, the angular span of each magnetic pole being equal to or less than the angular span of each individual coil, such pole pieces providing by themselves magnetic retum paths towards the stator yoke. a yoke made of a suitable magnetic material which is provided as a tube mounted within or without a radially arranged stator, or as a disc mounted axially around the centre line of, parallel to and behind an axially arranged stator (s). a suitable means of transferring the rotor torque from the rotor to the load, via a shaft, gears, coupling or via a wheel, separately or in combination. a suitable means for energising each air cored coil in each phase. when arranged as a linear machine: at least one stator providing a number of fictive poles by means of either, a number of air cored coils mounted equidistantly along said stator and positioned so that said air cored coils are arranged in equilaterally balanced groups or phases, such coils overlapping as necessary, each group being connected to and energised by a different phase, or, one or more continuous meander like windings of wire or strip arranged and energised to provide such fictive poles. a linear armature or translator, suitably supported to move linearly above and along the stator, said translator incorporating a number of magnetic pole pieces magnetised by embedded permanent magnets distributed equidistantly along said translator to provide a number of adjacent alternatively north and south magnetic poles, the linear span of each magnetic pole being equal to or less than the span of each individual coil, such pole pieces providing by themselves magnetic return paths towards the stator yoke. a yoke made of a suitable magnetic material provided as a plate or strip mounted behind the linearly arranged stator winding (s). a suitable means of connecting the translator to the load. a suitable means of energising each air cored coil in each phase.

   2. An efficient, high torque, multiphase axial radial or linear machine as in claim 1 wherein the stator windings are configure to provide a two phase machine.