GB2467362A

GB2467362A - Inserts to reduce windage in a reluctance rotor

Info

Publication number: GB2467362A
Application number: GB0901608A
Authority: GB
Inventors: Adam Pride; Shinichiro Iwasaki
Original assignee: IMRA Europe SAS; IMRA Europe SAS UK Research Center
Current assignee: IMRA Europe SAS; IMRA Europe SAS UK Research Center
Priority date: 2009-01-30
Filing date: 2009-01-30
Publication date: 2010-08-04
Anticipated expiration: 2029-01-30
Also published as: GB0901608D0; GB2467362B8; GB2467362B

Abstract

There is provided a rotor insert assembly 150, 152, 200 for a reluctance motor arrangement, the reluctance motor arrangement including a stator and a rotor 104 rotatable about an axis X-X with respect to the stator and having a plurality of rotor teeth 110. The rotor insert assembly 150, 152, 200 comprises at least one insert 200 locatable between adjacent rotor teeth 110 and first and second end portions 150, 152 locatable on first and second axial ends of the rotor 104 respectively. The or each insert 200 has a bridging portion 202 and insert securing means 212, the bridging portion 202 being arranged to define a substantially continuous outer perimeter surface between said adjacent rotor teeth 110. Each of the first and second end portions 150, 152 has complementary end securing means 162, 164 for engaging with respective insert securing means 212 on the or each insert 200 to secure the or each insert 200 between adjacent rotor teeth 110. The securing means may contain recesses to reduce weight.

Description

A Rotor Assembly The present invention relates to rotor insert assemblies. Particularly, but not exclusively, the present invention relates to rotor insert assemblies for reluctance motors having a rotor and a stator.

Reluctance motors are a class of motor capable of operating at high speeds, typically in excess of 30,000 rpm. A cross-sectional view of a typical reluctance motor arrangement is shown in Figure 1. The reluctance motor 10 comprises a stator 12 and a rotor 14. The stator 12 has a plurality of stator poles 16. The rotor 14 is attached to a rotor shaft 18 such that the rotor 14 is rotatable relative to the stator 12 about an axis X-X. The rotor 14 comprises a plurality of rotor teeth 20 which are spaced circumferentially about the axis X-X.

For efficient operation of reluctance motors, it is useful that the spacing between the external edge of the rotor teeth and the stator or stator poles is relatively small.

Typically, a spacing is in the region of 1 mm is desirable. However, the combination of the high rotational speeds achievable in these motors and the small air gap between the rotor and the stator can result in unwanted aerodynamic effects occurring within the motor. As the rotor turns, the air in the space between the motor and the stator creates an aerodynamic drag force which acts to resist the rotation of the rotor. This phenomenon is known in the art as "windage". Windage increases the amount of power required to operate the motor at a given speed, reduces the maximum speed at which the rotor can turn and increases the noise generated by the motor in operation.

It is, therefore, desirable to reduce the effects of windage in a reluctance motor in order to increase the power efficiency of the motor and to improve the rotational speeds achievable in such a motor.

A known approach to reduce windage effects in a reluctance motor is to fill the spaces between the teeth of the rotor with inserts. Examples of such arrangements are disclosed in US 5,023,502 and US 5,053,666. The spaces between the rotor teeth are filled with inserts to provide a rotor which is more aerodynamic. However, the above-mentioned arrangements require the rotor to be appropriately shaped such that the inserts can be secured thereto; for example, by providing grooves or channels that the inserts may be inserted into. Consequently, when the rotor is rotating, the generated centrifugal forces acting upon the inserts can induce mechanical stresses on the rotor.

This may lead to damage (for example, cracks or splintering) to parts of the rotor, reducing the lifetime of the motor. Further, because the rotor is shaped to couple mechanically to the inserts, the rotor may not be the most optimal shape for electromagnetic efficiency.

An alternative arrangement is disclosed in EP 0 736 952. The arrangement described therein comprises a first end plate having a plurality of shaped support bars integrally formed therewith. The support bars are arranged to accommodate a toothed rotor therebetween such that the support bars form inserts between the teeth of the rotor. A second end plate is then attached to the distal ends of the support bars such that a cage is formed around the rotor. This arrangement does not require a direct mechanical coupling between the rotor and the support bars. However, it is relatively complicated to manufacture. Further, the support bars are solid and completely fill the space between the rotor teeth. This adds extra weight to the rotor assembly and increases the inertia of the rotor as a whole.

It is an object of the present invention to provide an improved rotor insert assembly.

According to one aspect of the invention there is provided a rotor insert assembly for a reluctance motor arrangement, the reluctance motor arrangement including a stator and a rotor rotatable about an axis with respect to the stator and having a plurality of rotor teeth, the rotor insert assembly comprising at least one insert locatable between adjacent rotor teeth and first and second end portions locatable on first and second axial ends of the rotor respectively, the or each insert having a bridging portion and insert securing means, the bridging portion being arranged to define a substantially continuous outer perimeter surface between said adjacent rotor teeth, wherein each of the first and second end portions has complementary end securing means for engaging with respective insert securing means on the or each insert to secure the or each insert between adjacent rotor teeth.

By providing such an arrangement, windage effects can be reduced, resulting in increased aerodynamic efficiency of a rotor so equipped. Further, this arrangement is inexpensive to manufacture and assemble.

Usefully, said bridging portion has an arcuate outer surface. Advantageously, said arcuate outer surface has a curvature such that, when the or each insert is located between adjacent rotor teeth, a substantially continuous circumferential surface is formed therebetween. This arrangement is useful for achieving a low drag coefficient.

It is desired that the outer surface of said bridging portion is substantially smooth.

This further improves the aerodynamic efficiency of the arrangement.

It is an advantage if said insert securing means includes first and second insert securing means located on either side of the bridging portion. It is also useful if said insert has opposing first and second end walls attached to said bridging portion, the first and second insert securing means being located on the first and second end walls respectively. This allows the insert to be secured to parts other than the rotor itself.

It is desired that the first and second insert securing means are located adjacent the first and second axial ends of the rotor respectively when the or each insert is located between adjacent rotor teeth. This enables the inserts to be coupled to other parts of the insert assembly.

It is also desirable that the first and second insert securing means comprise projecting lugs which are, desirably, arcuate. This is a convenient and cost-effective arrangement to provide securing means for the inserts. Usefully, the end securing means comprises at least one recess formed in each of the first and second end portions. It is an advantage if at least one recess is provided for each projecting lug. This makes location of the inserts and end portions more straightforward, increasing the speed and convenience of assembly of the rotor insert assembly.

It is an advantage if the or each insert is formed from a non-magnetic, non-conductive material, desirably a thermoplastic, in particular a carbon-reinforced thermoplastic.

By providing such an arrangement, the inserts are electromagnetically decoupled from the rotor and stator, and thus do not influence the electromagnetic properties thereof.

It is advantageous if each of the first and second end portions is cylindrical and has a similar diameter to said rotor. This produces a more aerodynamic arrangement which has greater power efficiency.

Usefully, each of the first and second end portions is arranged to be secured against the respective axial end of the rotor by clamping means. This is a convenient and quick method of assembly.

It is an advantage if the first and second end portions are formed from insulating laminate made of glass fabric bonded with epoxy resin. This material has suitable strength for high-speed applications and is cheap to manufacture.

According to another aspect of the invention, there is provided a rotor assembly for a reluctance motor arrangement, the rotor assembly being rotatable about an axis with respect to a stator and comprising a rotor and at least one insert, the rotor having a plurality of rotor teeth circumferentially spaced about the axis, and the or each insert being entirely located between adjacent rotor teeth and having a bridging portion arranged to extend between said adjacent consecutive rotor teeth such that a substantially Continuous outer perimeter surface is defined thereby, wherein the or each insert is arranged to bound a closed cavity space between said consecutive rotor teeth. Such an arrangement allows the aerodynamic properties of a rotor to be improved without increasing the weight of the arrangement significantly.

Preferably, said bridging portion has an arcuate outer surface. More preferably, said arcuate outer surface has a curvature such that, when the or each insert is located between adjacent rotor teeth, a substantially continuous circumferential surface is iS formed therebetween.

Advantageously, the rotor assembly further comprises first and second end portions located on first and second axial ends of the rotor respectively, wherein the first and second end portions close the sides of the cavity space. This makes the arrangement more aerodynamic and reduces drag forces.

Usefully, the or each insert has first and second insert securing means located on either side of the bridging portion.

It is desirable that said insert has opposing first and second end walls attached to said bridging portion, the first and second insert securing means being located on the first and second end walls respectively.

Usefully, the first and second end portions have respective end securing means for engaging with respective insert securing means on the or each insert to secure the or each insert between adjacent rotor teeth.

According to another aspect of the invention there is provided a method of assembling a rotor assembly for a reluctance motor, the rotor assembly having a rotor shaft, a rotor, a plurality of inserts and first and second end portions, the rotor being attached to the rotor shaft having a plurality of rotor teeth circumferentially spaced about an axis of the rotor shaft and each insert having first and second insert securing means and a bridging portion, the method comprising the steps of: attaching the first end portion having first end securing means to the rotor shaft such that the first end portion is located adjacent a first axial end of the rotor; inserting the plurality of inserts between adjacent teeth of said rotor such that the bridging portions thereof defme a substantially continuous outer perimeter surface between said adjacent rotor teeth and that each respective first insert securing means engages with said first end securing means; and attaching the second end portion having second end securing means to the rotor shaft such that the second end portion is located adjacent a second axial end of the rotor and that said second end securing means engages with the second insert securing means to secure said inserts between said teeth.

An embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a cross-section taken through an illustrative example of a reluctance motor; Figure 2 is a perspective view of a rotor assembly according to the present invention; Figure 3 is a cross-sectional perspective view of the rotor insert assembly of Figure 1 taken along a line normal to the longitudinal centre axis of the drive shaft; Figure 4 is a top perspective view of an insert in accordance with the invention; Figure 5 is an underside perspective view of the insert of Figure 4; and Figure 6 is a cross-sectional perspective view of the rotor insert assembly of Figure 1 taken along the longitudinal centre axis of the drive shaft.

Figure 2 shows a rotor assembly 100 according to the invention. The rotor assembly 100 is suitable for use with a suitable stator (not shown) as part of a reluctance motor arrangement (not shown). The rotor assembly 100 comprises a rotor shaft 102 and a rotor 104. The rotor 104 is attached to the rotor shaft 102 and is rotatable therewith about an axis X-X. The rotor shaft 102 is supported on bearings 106 to enable the rotor shaft 102 to rotate within a motor arrangement (not shown).

Referring now to Figure 3, the rotor 104 comprises a cylindrical portion 108 and a plurality of rotor teeth 110. The rotor teeth 110 are disposed around the circumference of the cylindrical portion 108 and extend radially outwardly therefrom. Each rotor tooth 110 has an end face 112 and a pair of side faces 114. The rotor teeth 110 are circumferentially spaced about the axis X-X such that open-ended cavities 116 are formed between adjacent consecutive rotor teeth 110. The cavities 116 are delimited by the opposing side faces 114 of adjacent consecutive rotor teeth 110.

First and second end caps 150, 152 are located on either side of the rotor 104. Each of the first and second end caps 150, 152 has a through-hole 154, 156 to enable the end cap 150, 152 to be located on the rotor shaft 102. Each end cap 150, 152 is secured against the rotor 104 by means of respective first and second clamps 158, 160 provided on the rotor 104. Consequently, when in operation, the first and second end caps 150, 152 rotate with the rotor shaft 102 and rotor 104.

Both of the first and second end caps 150, 152 have substantially equal diameters to the rotor 104 such that the end caps 150, 152 lie flush with the end faces 112 of the rotor teeth 110. This improves the aerodynamic properties of the rotor assembly 100.

The end caps 150, 152 may be formed from any light weight, durable, non-conductive material; for example, insulating laminate made of glass fabric bonded with epoxy resin or a suitably durable plastic such as ABS.

A plurality of rotor inserts 200 are provided in the cavities 116. Each rotor insert 200 is inserted between adjacent consecutive rotor teeth 110 as shown in Figures 2 to 4.

The rotor inserts 200 may be made from any relatively lightweight, non-conductive material that can endure the centrifugal forces created during high speed rotation of the rotor without experiencing significant levels of flexure. Suitable materials may include PEEK with carbon fibre reinforcement, carbon fibre or an appropriate plastic such as ABS. A rotor insert 200 is shown in more detail in Figures 4 and 5.

The rotor insert 200 has a bridging portion 202, end faces 204 and support members 206. The bridging portion 202 has a curved and arcuate outer surface 208 and an inner surface 210. The outer surface 208 is dimensioned and arranged to fit between consecutive end faces 112 of adjacent rotor teeth 110. This is shown in Figures 2 and 3. The outer surface 208 of the bridging portion 202 is preferably smooth to improve the aerodynamic properties of the rotor assembly 100, although this is not essential.

The end faces 204 are attached on either side of the bridging portion 208 and extend perpendicularly thereto. The two support members 206 extend perpendicularly between the end faces 204 and are attached to the inner surface 210 of the bridging portion 202. The support members 206 provide structural rigidity to secure the end faces 204 to the bridging portion 202 and also to ensure that the bridging portion 202 does not distort when the rotor insert 202 is attached to the rotor 104 and the rotor 104 is rotating at high speed.

Securing lugs 212 project outwardly from each end face 204. The securing lugs 212 are arranged to engage with the first and second end caps 150, 152 to secure the rotor insert 200 to the remainder of the rotor assembly 100. The securing lugs 212 have apertures therein. These apertures reduce the weight thereof and improve manufacturing of the insert 200. Figure 5 shows the function of the securing lugs 212 when the inserts 200 are inserted into the remainder of the rotor assembly 100.

Figure 5 shows a perspective cross-section of the rotor assembly 100 taken along the axis X-X. As also shown in Figures 2 and 3, a rotor insert 200 is inserted into each cavity 116 between adjacent pairs of rotor teeth 110. Each of the first and second end caps 150, 152 has a plurality of circumferential securing grooves 162, 164 formed therein. The securing grooves 162, 164 are located adjacent the rotor 104 and face inwardly thereto. As shown in Figure 5, each securing groove 162, 164 is dimensioned and arranged to receive a securing lug 212 therein. Consequently, the securing lugs 212 and securing grooves 162, 164 function as complementary securing means to secure the rotor inserts 200 in the cavities 116 between the rotor teeth 110.

This arrangement enables the rotor inserts 200 to be held secure with respect to the rotor 104 without being physically attached thereto. Consequently, the design of the rotor 104 can be chosen to give optimal electromagnetic properties without the need for securing mechanisms to secure the rotor inserts 200 thereto. Further, in use, the rotor 104 does not support the weight of the rotor inserts 200 which may lead to stress on, and potential damage to, the rotor 104.

As shown in Figures 2, 3 and 5, the outer surface 208 of the bridging portion 202 of each rotor insert 200 extends between the end faces 112 of consecutive adjacent rotor teeth 110, forming a substantially continuous outer surface therebetween. In other words, a substantially circumferential outer perimeter is formed. This improves the aerodynamic efficiency of the rotor 104 when rotated with respect to the stator.

Further, each rotor insert 200 is located in a respective cavity 116 such that the outer surface 208 of the bridging portion 202 lies flush with the end faces 112 of adjacent rotor teeth 110.

With particular reference to Figures 3 and 5, it can also been seen that each bridging portion 202 closes the upper end of a respective cavity 116. Further, each end cap 150, 152 closes the open sides of each cavity 116. Consequently, a closed, hollow cavity is formed between adjacent rotor teeth 110. In other words, each cavity 116 forms a closed, empty space when the end caps 150, 152 and rotor inserts 200 are assembled with the rotor 104. This arrangement enables the rotor assembly 100 not only to be optimised for aerodynamic efficiency in order to reduce windage losses, but also to be light in weight. Since there is only air present in each closed cavity 116, the inertia of the rotor assembly 100 is lower and the rotor assembly 100 is able to rotate at a higher speed. Further, the inserts 200 are only provided between the rotor teeth 110 and not across the top of them. This reduces the weight of the insert assembly because the inserts 200 are only located on the preferential part of the rotor, i.e. where they are most needed.

In use, the rotor assembly 100 is assembled as follows. One end of the rotor shaft 102 is inserted through the through-hole 154 of the first end cap 150 and the first end cap 150 is secured to the side of the rotor 104 by the first clamp 154 secured to the rotor shaft 102. The rotor inserts 200 are then placed between the rotor teeth 110 such that the securing lugs 212 engage with the complementary securing grooves 162 of the first end cap 150. The second end cap 152 is then is then attached to the opposite end of the rotor shaft 102 through the through-hole 156 formed therein. The second end cap 152 is located such that the securing Jugs 212 of the rotor inserts 200 engage with the complementary securing groove 164 of the second end cap 152. This enables each of the rotor inserts 200 to be firmly secured between respective adjacent rotor teeth 110. The second end cap 152 is then secured in place by the second clamp 160 attached to the rotor shaft 102. The rotor assembly 100 is now assembled.

Once assembled, the rotor assembly 100 can be connected to a fixed stator (not shown) forming part of a reluctance motor assembly (not shown). When connected, the rotor assembly 100 is rotatably mounted on the bearings 106 relative to the stator.

The stator has an inner surface having a plurality of poles (not shown). When located in a reluctance motor assembly, the outer circumference of the rotor 104 is spaced from the inner surface of the stator by approximately 1 mm.

The rotor assembly 100 is operable as part of the reluctance motor assembly. The stator poles are energised with current pulses in a specific sequence to rotate the rotor assembly 100. When a stator pole is energised, a torque acts on the rotor 104 in a direction that will reduce reluctance. Thus the nearest rotor tooth 110 is pulled from an unaligned position into alignment with the magnetic field (a position of less reluctance) of a stator pole. This rotates the rotor 104 with respect to the stator. This process continues and the stator poles are energised in a specific sequence to maintain the rotation of the rotor 104.

When the rotor 104 is rotating at high speed, a significant drag force (or windage) from the air between the rotor 104 and the stator is generated. The windage is due to a turbulent airflow between the rotor 104 and the stator, and is increased by the combination of the high rotational velocity of the rotor 104 and the small spacing between the outer circumference and the stator poles or inner surface of the stator.

However, the arrangement of the present invention enables the rotor 104 to have a smooth, circumferential outer perimeter, improving the aerodynamics thereof. This reduces windage effects by lowering the drag coefficient of the rotor 104. Further, the present invention does not significantly increase the weight of the rotor 104, reducing the energy demands thereof. This is in part assisted by providing the inserts only on the preferential, required parts of the rotor, and does not increase weight by providing any form of cover where it is not required; for example, on the ends of the rotor teeth 110.

Although the invention has been described with reference to the above specific examples, the invention is not limited to the detailed description given above.

Variations will be apparent to the person skilled in the art. For example, the invention may be applicable to different types of reluctance motors; for example, synchronous reluctance motors, variable reluctance motors and switched reluctance motors.

Additionally, the bridging portion need not have an arcuate outer surface nor need the inserts and rotor teeth form a circumferential perimeter; the surface of the or each bridging portion may be flat such that a slab-sided rotor is formed, or it may take another, preferably geometric, shape.

Further, the insert securing means and end securing means need not have the form explicitly described in the above embodiment. Variations of securing means will be apparent to the skilled person; non-exhaustive examples of such may include pins, snap-fit parts, or grooves formed in the or each insert which couple with lugs formed on the end portions.

Whilst it is preferred that the or each insert is formed from a non-magnetic, non-conductive material, this need not be so. Other materials may be used; for example, aluminium or steel. If a non-magnetic, non-conductive material is used, materials other than thermoplastics reinforced with carbon fibre may be used. Any suitable plastic materials, such as ABS, PVC, or polyurethane may be used.

While the invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the scope of the appended claims.

Claims

CLAIMS1. A rotor insert assembly for a reluctance motor arrangement, the reluctance motor arrangement including a stator and a rotor rotatable about an axis with respect to the stator and having a plurality of rotor teeth, the rotor insert assembly comprising at least one insert locatable between adjacent rotor teeth and first and second end portions locatable on first and second axial ends of the rotor respectively, the or each insert having a bridging portion and insert securing means, the bridging portion being arranged to define a substantially Continuous outer perimeter surface between said adjacent rotor teeth, wherein each of the first and second end portions has complementary end securing means for engaging with respective insert securing means on the or each insert to secure the or each insert between adjacent rotor teeth.
2. A rotor insert assembly as claimed in claim 1, wherein said bridging portion has an arcuate outer surface.
3. A rotor insert assembly as claimed in claim 2, wherein said arcuate outer surface has a curvature such that, when the or each insert is located between adjacent rotor teeth, a substantially continuous circumferential surface is formed therebetween.
4. A rotor insert assembly as claimed in any one of claims 1 to 3, wherein the outer surface of said bridging portion is substantially smooth.
5. A rotor insert assembly as claimed in any one of the preceding claims, wherein said insert securing means includes first and second insert securing means located on either side of the bridging portion.
6. A rotor insert assembly as claimed in claim 5, wherein said insert has opposing first and second end walls attached to said bridging portion, the first and second insert securing means being located on the first and second end walls respectively.
7. A rotor insert assembly as claimed in claim 5 or 6, wherein the first and second insert securing means are located adjacent the first and second axial ends of the rotor respectively when the or each insert is located between adjacent rotor teeth.
8. A rotor insert assembly as claimed in claim 7, wherein the first and second insert securing means comprise projecting lugs.
9. A rotor insert assembly as claimed in claim 8, wherein the projecting lugs are arcuate.
10. A rotor insert assembly as claimed in claim 8 or 9, wherein the end securing means comprises at least one recess formed in each of the first and second end portions.
11. A rotor insert assembly as claimed in claim 10, wherein at least one recess is provided for each projecting lug.
12. A rotor insert assembly as claimed in any one of the preceding claims, wherein the or each insert is formed from a non-magnetic, non-conductive material.
13. A rotor insert assembly as claimed in claim 12, wherein the or each insert is formed from a thermoplastic, in particular a thermoplastic reinforced with carbon fibre.
14. A rotor insert assembly as claimed in any one of the preceding claims, wherein each of the first and second end portions is cylindrical and has a similar diameter to said rotor.
15. A rotor insert assembly as claimed in any one of the preceding claims, wherein each of the first and second end portions is arranged to be secured against the respective axial end of the rotor by clamping means.
16. A rotor insert assembly as claimed in any one of the preceding claims, wherein the first and second end portions are formed from insulating laminate made of glass fabric bonded with epoxy resin.
17. A rotor assembly for a reluctance motor including a rotor insert assembly as claimed in any one of the preceding claims.
18. A reluctance motor including a rotor assembly as claimed in claim 17.
19. A rotor assembly for a reluctance motor arrangement, the rotor assembly being rotatable about an axis with respect to a stator and comprising a rotor and at least one insert, the rotor having a plurality of rotor teeth circumferentially spaced about the axis, and the or each insert being entirely located between adjacent rotor teeth and having a bridging portion arranged to extend between said adjacent consecutive rotor teeth such that a substantially continuous outer perimeter surface is defined thereby, wherein the or each insert is arranged to bound a closed cavity space between said consecutive rotor teeth.
20. A rotor assembly as claimed in claim 19, wherein said bridging portion has an arcuate outer surface.
21. A rotor assembly as claimed in claim 20, wherein said arcuate outer surface has a curvature such that, when the or each insert is located between adjacent rotor teeth, a substantially continuous circumferential surface is formed therebetween.
22. A rotor assembly as claimed in any one of claims 19 to 21, wherein the outer surface of said bridging portion is substantially smooth.
23. A rotor assembly as claimed in any one of claims 19 to 22, further comprising first and second end portions located on first and second axial ends of the rotor respectively, wherein the first and second end portions close the sides of the cavity space.
24. A rotor assembly as claimed in claim 23, wherein the or each insert has first and second insert securing means located on either side of the bridging portion.
25. A rotor assembly as claimed in claim 24, wherein said insert has opposing first and second end walls attached to said bridging portion, the first and second insert securing means being located on the first and second end walls respectively.
26. A rotor assembly as claimed in claim 24 or 25, wherein the first and second end portions have respective end securing means for engaging with respective insert securing means on the or each insert to secure the or each insert between adjacent rotor teeth.
27. A rotor assembly as claimed in any one of claims 19 to 26, wherein the or each insert is formed from a non-magnetic, non-conductive material.
28. A rotor assembly as claimed in claim 27, wherein the or each insert is formed from a thermoplastic, in particular a thermoplastic reinforced with carbon fibre.
29. A rotor insert assembly as claimed in any one of claims 23 to 28, wherein the first and second end portions are formed from insulating laminate made of glass fabric bonded with epoxy resin.
30. A reluctance motor including a rotor assembly as claimed in any one of claims 19 to 29.
31. A method of assembling a rotor assembly for a reluctance motor, the rotor assembly having a rotor shaft, a rotor, a plurality of inserts and first and second end portions, the rotor being attached to the rotor shaft having a plurality of rotor teeth circumferentially spaced about an axis of the rotor shaft and each insert having first and second insert securing means and a bridging portion, the method comprising the steps of: attaching the first end portion having first end securing means to the rotor shaft such that the first end portion is located adjacent a first axial end of the rotor; inserting the plurality of inserts between adjacent teeth of said rotor such that the bridging portions thereof define a substantially continuous outer perimeter surface between said adjacent rotor teeth and that each respective first insert securing means engages with said first end securing means; and attaching the second end portion having second end securing means to the rotor shaft such that the second end portion is located adjacent a second axial end of the rotor and that said second end securing means engages with the second insert securing means to secure said inserts between said teeth.
32. A rotor insert assembly substantially as hereinbefore described with reference to the accompanying drawings.
33. A rotor assembly substantially as hereinbefore described with reference to the accompanying drawings.