GB2508022A

GB2508022A - Segmented stator arrangement for an electric machine

Info

Publication number: GB2508022A
Application number: GB1220816.1A
Authority: GB
Inventors: Alexandros Michaelides
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2012-11-20
Filing date: 2012-11-20
Publication date: 2014-05-21
Anticipated expiration: 2032-11-20
Also published as: GB2508022B; GB201220816D0

Abstract

An electric machine comprises a substantially circular rotor 242 and a stator, wherein the stator comprises at least one substantially arcuate segment 200. Stator segments may be spaced apart (e.g. two segments arranged diametrically) and configured so that when in use the magnetic flux paths generated in one stator segment are contained within that segment as shown in fig 4. The end portions of the segments 320RST which form tabs may be slotted to engage mounting hooks 320F or the hooks may be arranged to engage the inner radial surface of the segment (fig 6b not shown). Alternatively the tabs maybe provided with a bore to receive a fixing element. A number of segments may define a complete circle. The pole ratio between stator and rotor may be expressed as R= (2P*360/(segment arc)) Â± 2. The machine may be used in a motor vehicle component

Description

ELECTRIC MACHINE AND METHOD OF OPERATION THEREOF

TECHNICAL FIELD

The present invention relates to electric machines. In particular but not exclusively the invention relates to electric machines for use as propulsion motors and/or generators for motor vehicles. Aspects of the invention relate to an electric machine, to a method and to a vehicle.

BACKGROUND

It is known to provide an electric machine having a substantially circular stator and a coaxial rotor rotatably mounted within the stator. A wide variety of designs are known including the switched reluctance motor (SRM), permanent magnet synchronous motor (PMSM), doubly salient permanent magnet (DSPM) motor, induction motor and wound field motor. The DSPM motor is a SRM motor incorporating permanent magnets (AMs) into the switched reluctance structure.

SEM-type motors are of particular interest for use in electric vehicles (EVs) and hybrid electric vehicles (HEVs) due to good power density, robustness, fault tolerance and relatively low cost compared with permanent magnet (FM) machines.

It is desirable to provide improved electric machines for use in motor vehicles as propulsion motors, generators or combined motor/generators.

SUMMARY OF THE INVENTION

Aspects of the present invention provide an electric machine, a vehicle and a method as claimed in the appended claims.

In one aspect of the invention for which protection is sought there is provided an electric machine comprising a substantially circular rotor and a stator, wherein the stator comprises at least one substantially arcuate segment.

In one embodiment, the at least one substantially arcuate segment defines, at least in part, a discontinuous ring or annulus.

The stator may still be substantially circular but comprise a plurality of segments. The number of segments required to define a complete circle will depend on the angle subtended by each segment comprising the stator. Embodiments of the invention have the advantage that an electric machine may be provided that is formed from modular components. Thus, a designer has a flexibility to design a plurality of motors having differently shaped stators and different power ratings made from similar segment components, eliminating the requirement to provide stator components having different shapes (such as circular and non-circular) in some arrangements.

By substantially arcuate segment is meant that a surface of the segment facing the stator is substantially arcuate. The stator may have radially inner and radially outer surfaces that are substantially arcuate in some embodiments such as that illustrated in FIG. 3 and described in detail below.

Advantageously the stator may be substantially non-circular. By non-circular is meant that the stator does not describe a substantially complete circle. Whilst the stator describes one or more portions of a circle, it does not describe a full circle. It is to be understood that the stator may be comprised of a plurality of segments.

Embodiments of the present invention have the advantage that a stator may be fitted into a package space that does not permit a circular stator to be accommodated. Some embodiments of the invention allow an electric machine of increased torque capacity to be fabricated compared with a machine of reduced diameter but employing a substantially circular stator. This is made possible by enlarging the diameters of the stator and rotor, and segmenting the stator to fit within the available package space. Advantageously, the larger diameter rotor may house other components such as a clutch arrangement.

Some embodiments of the invention enable an electric machine to be produced that generates less noise than an electric machine having a circular stator of reduced diameter.

Alternatively, the stator may be substantially circular and comprise a plurality of arcuate segments.

The stator may comprise a pair of diametrically opposed stator segments.

This feature has the advantage that forces acting on the rotor may be balanced thereby to reduce vibration and noise associated with motor operation. Furthermore, a reduction in wear of rotor bearings may be enjoyed.

The stator may comprise only two stator segments.

The rotor may be provided with R teeth and the at least one stator segment may be provided with S teeth where P and S are both integer values greater than 1.

It is to be understood that the number of teeth provided on the rotor and the number of teeth provided on the stator must be selected to enable a working machine to be produced Advantageously a machine may be provided where S=2P where P is the number of phases of current supplied to operate the machine.

The electric machine may for example be a 3-phase switched reluctance machine (P=3) where S=6, R=12.

Alternatively the electric machine may be a 4-phase switched reluctance machine (P=4) where S=8, 11=18.

In a further alternative the electric machine may be a 5-phase switched reluctance machine (P=5) wherein S=10, 11=24.

Advantageously a machine may be provided wherein P=(2P x 360/(segment arc)) + 2 or wherein R=(2P x 360/(segment arc)) -2.

For the avoidance of doubt it is to be understood that by segment arc is meant the angle subtended at the origin of the radius of curvature of the segment (which will normally correspond to the axis of rotation of the rotor) expressed in degrees. It is to be understood that other numbers of stator segment teeth and rotor teeth are also useful.

Advantageously an electric machine may be provided comprising a plurality of segments and configured wherein in use magnetic flux paths generated in one stator segment are substantially self-contained within that segment and not shared between segments.

Advantageously an electric machine may be provided configured wherein in use magnetic flux paths passing from a segment to the rotor pass substantially through segment teeth and not through circumferentially opposed free ends of the segment.

This feature has the advantage that the free end may be arranged to have one or more coupling features such as one or more through-bores or other feature thereby to facilitate coupling of the segment to a support member without adversely affecting substantially flow of magnetic flux through the segment in use.

The at least one segment may comprise at least one tab portion at at least one ciicumferential free end thereof, the tab portion protruding circumferentially away from a ring portion of the segment from which stator teeth protrude radially inwardly. The tab portions may in some embodiments be considered to be circumferential extensions of the ring portion of the segment. Thus in some embodiments the ring portion may continue beyond one or both end teeth being teeth provided at opposed ends of the segment.

The ring portion may be referred to as a ring segment in some embodiments since it defines a segment of a ring. Teeth of the segment may be integrally formed with the ring portion or attached thereto.

Tab portions may be provided at each end of a segment.

The tab poi-tions may be arianged to allow segments to be placed adjacent to one another to define a substantially continuous multi-segment stator or portion thereof. Segments may for example be placed substantially adjacent to one another to form a substantially continuous circular stator.

The one or more coupling features may for example be provided in, through or on the tab portion, such as one or more through-bores.

The at least one tab portion may be provided with at least one bore therein to accommodate a fixing element e.g. a screw or bolt.

The machine may comprise a hooked fixing element arranged to grip a radially inner surface of a segment and to prevent the segment from moving radially inwardly.

The machine may comprise a hooked fixing element arranged to key into a corresponding formation provided in a circumferential free end of a segment thereby to prevent the segment from moving radially inwardly.

In a further aspect of the invention for which protection is sought there is provided a motor vehicle component comprising an electric machine as claimed in any preceding claim.

The component may comprise a portion of a driveline, optionally a transmission.

In a further aspect of the invention for which protection is sought there is provided a motor vehicle comprising an electric machine or a component according to a preceding aspect.

In one aspect of the invention for which protection is sought there is provided a method of fabricating an electric machine comprising providing a substantially circular rotor and a stator comprising at least one substantially arcuate segment.

The method may comprise causing rotation of the rotor by application of a magnetic field to one or more teeth of the stator.

A portion of the segment facing the rotor may have a radius of curvature corresponding to that of the rotor.

The one or more segments may be formed by a variety of different methods including one or a combination of two or more of the following: pressing of a material provided in powder or granular form; lamination of multiple layers of sheet material; casting; machining and/or any other suitable technique.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives, and in particular the individual features thereof, set out in the preceding paragraphs, in the claims and/or in the following description and drawings may be taken independently or in any combination. Features described with reference to one embodiment are applicable to all embodiments, unless there is incompatibility of features.

For the avoidance of doubt, it is to be understood that features described with respect to one aspect of the invention may be included within any other aspect of the invention, alone or in appropriate combination with one or more other features.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying figures in which: FIGURE 1 is a schematic illustration of a switched reluctance motor (SRM) installed inside a motor vehicle component; FIGURE 2 is a schematic illustration showing conceptually how the SRM of FIG. 1 may be converted to a segment motor according to an embodiment of the present invention; FIGURE 3 is a schematic illustration of a SRM according to an embodiment of the present invention having a segmented stator installed in the motor vehicle component shown in FIG. 1; FIGURE 4 is a schematic illustration of the stator and rotor of the SRM of FIG. 3 showing flux lines present in the structure at a particular angular position of the rotor with respect to the stator; FIGURE 5 is a schematic illustration of a segment of the stator of FIG. 4; FIGURE 6(a) and (b) are schematic illustrations of doubly salient permanent magnet (DSPM) electric machines according to embodiments of the present invention having respective different fastener element arrangements; and FIGURE 7 is a schematic illustration of a switched reluctance electric machine according to an embodiment of the invention having a substantially circular stator formed from a plurality of stator segments.

DETAILED DESCRIPTION

FIG. 1 is a schematic illustration showing a switched reluctance motor (SRM) 100 installed in a package 150. In the SRM 100 shown, the package 150 is provided by a portion of a motor vehicle component 150. The component 150 has an available package space A that is not occupied by the SRM 100. The area shaded U corresponds to an internal volume of the component 150 that is unavailable to house the stator or rotor of the SRM 100.

The SRM 100 shown has a substantially circular stator 120 that is rigidly fixed to the component 150. The stator 120 is formed from a ferromagnetic material and has 24 teeth 122 that project radially inwardly from a ring portion 120R of the stator 120. Each tooth 122 has a coil 124 wrapped therearound which may be energised selectively in order to generate magnetic flux in the tooth 122. Coils of different teeth may be connected to form phases.

The SRM 100 has a substantially circular rotor 140 located coaxially of the stator 120. The rotor 140 is free to rotate within the stator 120. The rotor 140 has 18 teeth 142 that project radially outwardly from a ring portion 1 40R of the rotor 140.

The present inventors have recognised that improved use may be made of the available package space within the component 150 by employing a stator of larger diameter but which is discontinuous. That is, the stator does not define a circle and is therefore non-circular (or may be considered to define only a portion of a circle).

FIG. 2(a) shows schematically the SRM 100 of FIG. 1 with the stator of FIG. 1 divided into three substantially arcuate segments Si, S2, S3 of substantially equal size. The segments Si, S2, S3 each have 8 teeth.

FIG. 2(b) shows the SRM 100 of FIG. 1 after removal of one of the three segments S3 to form a motor having only two segments Si, S2. FIG. 2(c) shows the SRM of FIG. 2 with the segments Si, S2 positioned diametrically opposite one another about the rotor 140.

FIG. 3 shows an SRM 200 according to an embodiments of the invention installed in the motor vehicle component 150 shown in FIG. 1. Like features of the embodiment of FIG. 3 to that of FIG. 1 are provided with like reference signs incremented by 100. The resulting SRM 200 has a greater maximum torque capability than the SRM 100 of FIG. 1. It also enjoys more quiet operation. Additionally, the larger rotor diameter may house a clutch or other component.

The SlIM 200 employs a rotor 240 having a diameter that is substantially the same as to that of the stator 120 of the SRM 100 of FIG. 1. As described above, the SRM 200 has a non-circular stator 220 in the form of a pair of segments Si, S2 provided at diametrically opposed locations about the rotor 240. The pair of segments Si, S2 each have 8 teeth 222.

The angular spacing of the teeth 222 is equivalent to that of a circular stator of equivalent diameter having 24 teeth. The rotor 240 has 18 teeth 242 as per the SRM 100 of FIG. 1.

Around each tooth 222 of the stator 220 is provided a coil 224 operable to induce magnetic flux in the corresponding tooth 222 when current is passed therethrough.

As noted above, each stator segment Si, S2 has 8 teeth projecting radially inwardly therefrom. In general, the stator segment tooth number, rotor tooth number and stator segment arc are selected such that the resulting flux paths within a given segment are substantially self-contained. The stator segment tooth number, rotor tooth number and stator segment arc may also be selected to enable relatively high, substantially continuous torque to be produced. That is, flux paths may be established through each segment Si, S2 iO and the rotor 240 so as to form complete flux circuits without a requirement for flux to close via the other stator segment S2, Si.

Each segment Si, S2 may be considered to have two halves each having 4 teeth. In the case of segment Si, a first half of segment Si has teeth ST1 -814 whilst a second half has iS teeth STS-ST8. The coils 224 are operable to generate magnetic flux in their respective tooth when energised such that flux flows through teeth STi, ST3, STG and ST8 in a radially inward direction and through teeth ST2, ST4, ST5 and 817 in a radially outward direction. In an alternative embodiment the coils 224 are arranged to generate magnetic flux in their respective tooth when energised such that flux flows through teeth ST1, ST2, 813 and ST4 in a radially inward direction and through teeth STS, ST6, ST7 and ST8 in a radially outward direction. In a further alternative embodiment the coils 224 are arranged to generate flux in their respective tooth when energised such that flux flows through teeth ST1, ST3, ST5 and S17 in a radially outward direction and 5T2, ST4, S16 and S18 in a radially inward direction.

Other arrangements are also useful. The coil arrangement sequence may differ in different combinations of phases, stator teeth and rotor teeth.

A sequence in which coils 224 of each tooth 222 of the embodiment of FIG. 3 are energised will now be described.

In the particular position illustrated in FIG. 3, the rotor 240 is shown in a position where tooth ST1 of the stator 220 is aligned with a tooth RTi of the rotor 240. If the coil 224 associated with tooth ST1 is energised, the rotor 240 will resist rotation since in the rotational position shown the resistance to flow of magnetic flux through RT1 is at a minimum. In contrast, tooth ST2 adjacent tooth ST1 is in only partial alignment with tooth RT2 of the rotor 240 such that if the rotor 240 rotates in a clockwise direction tooth RT2 of the rotor 240 will come into alignment with tooth 812 of the stator 220, reducing the resistance to flow of magnetic flux through tooth 512. If the coil 224 associated with tooth 512 is energised, a torque will act on the rotor 240 in a direction to rotate the rotor 240 in a clockwise direction to bring rotor tooth 1112 into alignment with stator tooth 5T2.

FIG. 4 is a schematic illustration of the stator 220 and rotor 240 of the embodiment of FIG. 3, showing flux lines established in the magnetic circuit defined by the stator 220 and rotor 240 at a particular angular position of the rotor 240. Indicated on the figure is the polarity of the magnetic field established in each stator tooth ST1 -S18 in a particular configuration of operation. Letter N indicates that the coil 224 of a given tooth is arranged to generate a magnetic field with a north pole at a radially outward end of the coil (towards ring segment or ring portion 220RS which may also be referred to as a backiron' of the stator 220) with a south pole at a radially inward end of the coil 224. Letter S indicates that a south pole is present at the radially outward end of the coil, with a north pole at a radially inward end. The polar configurations in the particular arrangement illustrated in FIG. 4 are: ST-i: North pole generated at the radially outward end of the coil 224 ST-2: South pole generated at the radially outward end of the coil 224 ST-3: North pole generated at the radially outward end of the coil 224 ST-4: South pole generated at the radially outward end of the coil 224 ST-5: South pole generated at the radially outward end of the coil 224 ST-6: North pole generated at the radially outward end of the coil 224 ST-7: South pole generated at the radially outward end of the coil 224 ST-B: North pole generated at the radially outward end of the coil 224 In this mode of operation, the coils 224 of the stator 220 are energised in the following sequence in order to induce rotation of the rotor 240 in a clockwise direction: 1. Coils of teeth ST1, 512 2. Coils of teeth ST2, 513 3. Coils of teeth ST3, S14 4. Coils of teeth ST4, STi The cycle of energising coils 224 then repeats at step 1. It is to be understood that in the embodiment shown the coils 224 of teeth ST5 to ST8 are energised in a corresponding manner to those of teeth ST1 to 514. Other arrangements are also useful.

S

The coils 224 of the second stator segment 32 are energised in a corresponding manner to the coils 224 of segment Si. Other modes of operation are also useful.

The machine may be provided where each stator segment has S=2P teeth and the rotor has Fi=(2P x 360/(Segment Arcfl-4-2 teeth or R=(2P x 360/(segment arc))-2 teeth.

It is to be understood that, as discussed above, some embodiments of the present invention are designed such that magnetic flux paths are not established between stator segments Si, S2. Thus it is not required for magnetic flux lines to flow through a circumferential end 220E of a given stator segment Si, 52. This feature has the advantage that fixings may be passed through portions of the segments Si, 32 at circumferential end portions thereof without disturbing substantially a flow of magnetic flux through the segments Si, 52.

FIG. 5 is an enlarged view of stator segment Si. The stator segment Si may be considered to comprise a ring segment 220RS from which teeth 222 of the stator 220 project radially inwardly towards the rotor 240. At circumferentially opposed ends of the ring segment 220RS, ring segment tabs 22ORST are provided. The tabs 22ORST are portions of the ring segment 220RS that project circumferentially beyond stator teeth STi, ST8 at circumferentially opposed ends of the segment Si. Since magnetic flux flowing through the stator segment Si is arranged not to flow from one segment Si to the other S2, flux is not required to flow through the tabs 22ORST. Accordingly, the tabs 220R5T are each provided with a through-bore 220R5B in order to accommodate fixing elements for fixing the segments 51, S2 to a support structure such as component iSO. More than one through-bore 220R5B may be provided in some embodiments. In some embodiments, instead of a through-bore one or more other features may be formed to facilitate fixing of the segments Si, S2 to a support structure such as one or more recesses, grooves or the like as discussed in further detail below. In some embodiments one or more features may be provided to secure the segments to one another either in abutment or in spaced apart relationship. The segments may in some embodiments have complimentary inter-engaging formations by means of which the segments may be coupled to one another. In some embodiments the segments may interlock with one another and/or with a portion of a structure in which the segments are provided. A range of different types of formation may be provided, such as a dove-tail type arrangements, tongue and groove or any other suitable types of formation.

It is to be understood that this feature represents a substantial advantage over the prior art SRM 100 of FIG. 1. Stators in electric machines are subject to not inconsiderable forces seeking to reduce an air gap between the stator and rotor. It is therefore important to secure the stator to a housing or other support to prevent relative movement between the rotor and stator without causing substantial disturbance to or disruption of the flow of magnetic flux through the stator. Disturbance or disruption of the flow can readily occur when apertures, recesses or the like are formed in a rotor. Accordingly, some embodiments of the present invention allow improved attachment of the stator resulting in enhanced component service life. In some embodiments improved attachment allows reduced noise and vibrations during motor operation, for example by suppressing acoustic vibrations.

It is to be understood that embodiments of the present invention have the advantage that an amount of torque that may be developed by the subject electric machine is in some embodiments greater than that which would be produced by a known machine having a circular stator of a diameter substantially equal to that of the rotor of the subject machine.

Embodiments of the invention enable more powerful electric machines to be developed that fit within available non-circular package space.

It is to be understood that embodiments of the present invention having a segmented stator may have any suitable number of segments, provided that the resulting flux paths are substantially self-contained within each segment. Embodiments of the invention allow a more flexible modular design since a designer may design a motor with any required number of segments, the segments being provided at any appropriate circumferential location. An electric machine according to an embodiment of the invention is advantageously operated with one or more pairs of stators at diametrically opposed locations about the rotor so that forces acting to close an air gap between rotor and stator act in opposite directions thereby substantially to cancel one another. However not all embodiments have this arrangement. In some embodiments an electric machine may be provided having substantially only one stator segment.

FIG. 6(a) shows an electric machine 300 according to an embodiment of the present invention based on a doubly-salient permanent magnet (DSPM) electric machine design.

Like features of the embodiment of FIG. 6(a) to those of the embodiment of FIG. 3 are provided with like reference signs incremented by 100. The machine 300 has a segmented stator 320 having first and second segments 51, S2. Each of the segments Si, S2 has a ring segment 320RS (or backiron) from which stator teeth 322 protrude radially inwardly.

Each tooth 322 has a winding therearound as in the embodiment of FIG. 3 and FIG. 5. In contrast to the segments Si, S2 of the embodiment of FIG. 3 and FIG. 5 the segments Si, 52 of the embodiment of FIG. 6(a) have permanent magnet elements PM1, PM2 inserted in the ring segment 320RS of the segments Si, S2 between the first and second stator teeth ST-i, ST-2 and the fourth and fifth stator teeth ST-4, ST-S respectively. The magnets PM are oriented in the circumferential (azimuthal) direction but opposing each other. In the embodiment shown magnet PMi is oriented to generate a magnetic field in an anticlockwise circumferential direction (arrow Mi of FIG. 6(a) pointing in a direction from south pole to north pole) whilst magnet PM2 is oriented to generate a magnetic field in a clockwise iO direction. (arrow M2 of FIG. 6(a) pointing in a direction from south pole to north pole) . As a result, flux generated by the magnets AM1, PM2 is encouraged to flow through one or more of enclosed stator teeth ST-2, ST-S and/or 51-4, being teeth enclosed circumferentially by the magnets PMi, PM2.

is For the DSPM machine 300 of FIG. 6(a) the rotor 340 has i2 teeth 342 and each stator segment Si, S2 has 6 teeth 322. The angular spacing between the stator teeth 322 is equivalent to that of a circular stator having i8 teeth. The DSPM machine 300 is arranged for 3 phase operation. Other arrangements of stator/rotor teeth combinations are also useful.

It is to be understood that the permanent magnet elements PMi, PM2 may be inserted at any suitable location. In general, the magnet elements PMi, PM2 are typically arranged to be spaced apart by a number of teeth that is equal to half the total number of teeth of that segment. Furthermore, the number of teeth enclosed by the magnets PMi, PM2 is typically equal to the number of phases. The number of teeth in a given segment is therefore typically equal to twice the number of phases, as noted above. Other arrangements are also useful.

In the embodiment of FIG. 6(a), the component iSO in which the stator segments Si, S2 are provided has fastener elements 320F that grip a free end of a ring segment tab 32ORST of each segment Si, S2. It can be seen that the component has an internal wall i5OW having a portion having a radius of curvature corresponding to an outer radius of curvature of each segment Si, S2. Thus the segments Si, S2 may be arranged to rest snugly against this portion of the internal wall i5OW. The fastening elements 320F protrude substantially radially inwardly from this portion of the internal wall i5OW and have a hooked end 320FH projecting in a substantially circumferential direction that keys into a corresponding recess 32ORSR in the circumferential free end of the ring segment tab 320RST. By circumferential free end of the ring segment tab 320RS1 is meant a free end of the ring segment 320RS with respect to a circumferential direction.

At an opposite end of the ring segment 320115 to the element 320F the respective segments Si, 52 abut a portion of the internal wall 150W of the component 150 that projects radially inwardly with respect to the portion of the wall 150W against which a radially outer surface of each segment Si, S2 is in abutment. A corresponding fastener element 320F' may be provided at this free end of the segment Si, S2 that keys into a corresponding recess 32011511' in the ring segment tab 32011ST. It is to be understood that the provision of fastener elements 320F, 320F' at one or both ends of the segments Si, S2 promotes rigid positioning of the segment Si, S2 with respect to the housing iSO and rotor 340, reducing noise and/or vibrations associated with operation of the electric machine 300.

FIG. 6(b) shows an electric machine 400 similar to that of the embodiment of FIG. 6(a). Like features of the embodiment of FIG. 6(b) to those of the embodiment of FIG. 6(a) are shown with like reference signs incremented by 100.

In the embodiment of FIG. 6(b) the fastener element 420F at one end of each segment Si, 52 is arranged to protrude radially inwardly from the inner wall 150W in a similar manner to the element 320F of the embodiment of FIG. 6(a). However, instead of keying into recesses 32011511, 32011511' in the free ends of the segments Si, S2 the fastener elements 420F protrude circumferentially to grip a radially inner surface of the respective ring segments 320R5. At an opposite end of each of the segments Si, S2, fastener elements 420F' protrude circumferentially from the inwardly protruding portion of wall 150W. The elements 420F' abut the radially inner surface of the respective ring segment 320RS to prevent the segments Si, S2 from moving radially inwardly and out from abutment with the inner wall 150W.

Some non-limiting examples of stator/rotor teeth combinations will now be described where the number of stator teeth and rotor teeth given is that for an equivalent circular stator. For SRM machines a 24116 tooth combination and multiples thereof may be employed for 3 phase operation (90 degree segments). An 18112 tooth combination may also be employed for 3 phase operation (120 degree segments). A 24118 tooth combination and multiples thereof may be employed for 4 phase operation (120 degree segments). A 30/24 tooth combination and multiples thereof may be employed for 5 phase operation (120 degree segments). Other ratios are also useful.

It is to be understood that in some embodiments flux patterns established during operation of the electric machine in use are arranged to have similar torque ripple to an electric machine of similar rotor/stator diameter having a substantially circular stator. The flux patterns may be designed to include short and long path flux loops or a combination thereof.

For a Permanent Magnet Synchronous Machine (PMSM), for 3 phase operation an 18/12, 36/24 or 18/24 tooth combination and multiples thereof may be employed. Other ratios are also useful.

For the DSPM machine, for 3 phase operation a 24/16 or 18/12 tooth combination and multiples thereof may be employed. Other ratios are also useful.

It is to be understood that embodiments are applicable to the modification of a number of different types of electric machine and a number of different topologies including radial, axial and transverse flux topologies and technologies including SRM, DSPM, PMSM, induction

and wound field electric machines.

It is to be understood that for a given electric machine, the number of teeth on a given segment is preferable selected so that during operation magnetic flux lines developed in the segment and rotor as it rotates are substantially self-contained, i.e. the flux lines developed in one segment flow through that one segment only and not through an adjacent segment.

Furthermore, the flux lines may be arranged not to flow out of a segment in a circumferential direction through a circumferential end thereof, but flow between the segment and rotor through teeth of the rotor and segment.

Embodiments of the present invention have the advantage that more constrained stator laminations may be constructed. The laminations may be constructed to have different natural frequencies of vibration, thereby reducing radiated noise as well as reducing transmitted vibrations.

As discussed above, embodiments of the invention allow an electric machine to be fabricated having a larger rotor diameter and therefore the potential to provide more space within the rotor for the provision of a clutch or other mechanical device such as a power split device. Other components can be integrated into the electric machine in addition or instead such as one or more electronic components.

Some embodiments of the present invention allow electric machines of increased rotor and therefore stator diameter to be provided in situations where a volume in which the machine is to be packaged does not permit a circular stator describing an angle of substantially 360 degrees to be provided.

Some embodiments of the invention overcome the problem by providing a non-circular stator in the form of one or more segments of an otherwise circular stator. The rotor may remain substantially circular. The stator may curve to subtend any suitable angle such as 600, 900, 1200, 1800, 240° or any other suitable angle.

The number of stator/rotor teeth may be arranged to enable operation of the motor such that each segment is magnetically independent of the other, i.e. the flux associated with one segment is substantially unaffected by the flux associated with another one or more segments in the case the electric machine has a plurality of stator segments. It is to be understood that where a plurality of stator segments are provided, the application of magnetic fields to respective teeth of respective segments may be coordinated to prevent respective segments from applying opposing torques to the rotor.

The number of segments and/or the angles subtended by the one or more segnients of a given electric machine may be selected depending on available package space. In some embodiments an electric machine may be designed to employ as much of the available package space as reasonably possible.

Where a plurality of segments are employed, the segments may advantageously be positioned at selected circumferential locations so as to balance forces associated with motor operation such as magnetic forces between stator and rotor. For example, in the case of an electric machine comprising a pair of segments, the segments may be located at substantially diametrically opposite locations.

One or more fastener elements may be provided to wedge one or more of the segments in a substantially fixed position with respect to a housing and/or axis of rotation of the rotor. This feature has the advantage that it may reduce one or more of noise and vibration associated with machine operation.

FIG. 7 shows a switched reluctance electric machine (SRM) 500 according to a further embodiment of the present invention. Like features of the machine of FIG. 7 to those of the machine of FIG. 6(b) are shown with like reference numerals incremented by 100.

In the SRM 500 of FIG. 7 the stator 520 is substantially circular. The stator 520 in the embodiment shown has three segments Si, S2, S3 although circular stators 520 with other numbers of segments are also useful such as 2, 4, 5 or more. The segments Si, S2, S3 each subtend an angle of 120° at the axis of rotation R of the rotor 540.

The machine 500 is arranged to operate in a corresponding manner to the machine 100 of FIG. 1 having a non-segmented stator 120.

In the embodiment of FIG. 7, each stator segment Si, S2 S3 has a ring segment tab 52ORST similar to that of the segments Si, S2 of the embodiment of FIG. 6(a). A single fastener element 520F is provided between adjacent tabs 52ORST of adjacent segments Si, S2, S3. Each fastener element 520F therefore grips respective adjacent pairs of segments Si, S2, S3. Each segment Si, S2, S3 is thereby gripped at both circumferential free ends in a similar manner to that in which the elements 320F of FIG. 6(a) grip a single free end of each segment Si, S2. In order to grip two tabs S2ORST by means of one fastener element 520F instead of only one, however, the fastener elements 520F have two hook portions S2OFH that protrude in circumferentially opposite directions into respective recesses 52ORSR, 52ORSR' in the circumferential free ends of the segments Si, S2, 53. In combination with the radially-protruding portion of each element 520F, each fastener element 520F defines a substantially T-shaped fastener element 520F.

The embodiment of FIG. 7 has the advantage that an electric machine 500 having a substantially circular stator may be provided that is composed of respective modular segments. The concept of modular stator segments has the advantage that respective electric machines having different numbers of stator segments may be produced from similar components. A designer of electric machines therefore has at their disposal a further degree of freedom when designing an electric machine to fit in a given component space and to hence provide solutions of varying output power by using an appropriate number of segments. i6

Electric machines according to embodiments of the present invention may have any suitable number of stator segments such as 1, 2, 3, 4, 5 or more.

It is to be understood that the amount of available component space for an electric machine may vary according to vehicle model, and in some embodiments according to the options specified by a purchaser. In the event that the model and/or options specified require a reduction in available space for a stator of an electric machine the designer may configure the electric machine to make more full use of the available space by employing stator segments of larger radius of curvature than would be possible with a circular stator. The segments may be similar to those employed in vehicle models or vehicles with options that do not reduce the available stator space, but fewer in number.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example comprising" and comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

CLAIMS: 1. An electric machine comprising a substantially circular rotor and a stator, wherein the stator comprises at least one substantially arcuate segment.
2. An electric machine as claimed in claim 1 wherein the stator is substantially non-circular.
3. An electric machine as claimed in claim 1 wherein the stator is substantially circular and comprises a plurality of arcuate segments.
4. An electric machine as claimed in any preceding claim wherein the stator comprises a pair of diametrically opposed stator segments.
5. An electric machine as claimed in any preceding claim wherein the stator comprises only two stator segments.
6. An electric machine as claimed in any preceding claim wherein the rotor is provided with R teeth and the at least one stator segment is provided with S teeth where P and S are both integer values greater than 1.
7. An electric machine as claimed in claim 6 wherein S=2P where P is the number of phases of current supplied to operate the machine.
8. An electric machine as claimed in claim 6 or claim 7 wherein R=(2P x 360/(segment arc)) + 2 or wherein R=(2P x 360/(segment arc)) -2.
9. An electric machine as claimed in any preceding claim comprising a plurality of segments and configured wherein in use magnetic flux paths generated in one stator segment are substantially self-contained within that segment and not shared between segments.
10. An electric machine as claimed in any preceding claim configured wherein in use magnetic flux paths passing from a segment to the rotor pass substantially through segment teeth and not through circumferentially opposed free ends of the segment.
11. An electric machine as claimed in any preceding claim wherein the at least one segment comprises at least one tab portion at at least one circumferential free end thereof, the tab portion protruding circumferentially away from a ring portion of the segment from which stator teeth protrude radially inwardly.
12. An electric machine as claimed in any preceding claim wherein the at least one tab portion is provided with at least one bore therein to accommodate a fixing element e.g. a sciew 01 boll.
13. An electric machine as claimed in any preceding claim comprising a hooked fixing element arranged to grip a radially inner surface of a segment and to prevent the segment from moving radially inwardly.
14. An electric machine as claimed in any preceding claim comprising a hooked fixing element arranged to key into a corresponding formation provided in a circumferential free end of a segment thereby to prevent the segment from moving radially inwardly.
15. A motor vehicle component comprising an electric machine as claimed in any preceding claim.
16. A component as claimed in claim 15 wherein the component comprises a portion of a drivelinc, optionally a transmission.
17. A motor vehicle comprising an electric machine as claimed in any one of claims 1 to 13 or a component as claimed in claim 15 or 16.
18. A method of fabricating an electric machine comprising providing a substantially circular rotor and a stator comprising at least one substantially arcuate segment.
19. A method as claimed in claim 18 comprising causing rotation of the rotor by application of a magnetic field to one or more teeth of the stator.
20. A method as claimed in claim 18 or 19 whereby a portion of the segment facing the rotor has a radius of curvature corresponding to that of the rotor.
21. An electric machine, a motor vehicle component, a vehicle or a method substantially as hereinbefore described with reference to one or more of the accompanying drawings.