GB2278504A - Assembling disc rotors: Cooling jacket construction: Radiation cooling in rotary electrical machines - Google Patents

Abstract

A retention ring 1 is applied to a disc rotor assembly 3 which comprises an assembly 5 of a plurality of substantially equiangularly spaced magnets. The ring is expanded by application of hydraulic fluid under pressure so that it fits over the rim of the assembly. Stators 53 - 59 are joined together at their circumference to form housings 61 - 69 around rotors to provide a forced air cooling jacket. Alternatively, the rotors 81 - 89 can be arranged in an evacuated chamber through which the stators 95 - 101 protrude to act as cooling fins. <IMAGE>

Description

ROTARY ELECTRICAL MACHINES The present invention relates to rotary electrical machines such as electrical generators and electric motors and to particularly advantageous components for use in such machines.

British Patent Specification GB 2 222 031 A describes an axial field electrical generator capable of operation at very high speeds. This document describes an axial field electrical generator having a disc rotor with a ring of permanent magnet segments equiangularly spaced around a hub. Engagement with the hub is maintained by means of a pre-stressed hoop. The hoop is formed initially as a push fit and stressed during assembly by expanding the hub by forcing into it, an oversize boss.

As a practical matter, this means of retention has severe disadvantages which have been overcome by the present invention.

Thus, a first aspect of the present invention provides a method of applying a retention ring to a disc rotor assembly comprising a plurality of substantially equiangulalry spaced magnets, the method comprising expanding the retention ring by application of hydraulic fluid under pressure so that it fits over a rim of the rotor assembly, and then reducing the pressure of the hydraulic fluid so that the ring shrinks onto the rim..

The applicants' co-pending UK patent application No.

9123576. 2 (GB 2 261 327 A) describes a form of rotary electrical machine which provides a number of improvements over the arrangment disclosed in GB 2 222 031 A.

The generator described in the latter patent specification employs air cooling for the stators. The air is directed by means of radial channels entering at the rim. The channels conduct air towards the centre of the stators and back again to the rim. The multiplicity of channels detracts from the strength of the stators.

In the generator according to GB 2 261 327 A, each stator comprises at least one radial channel for ducting of cooling air. The channel has an entrance at or substantially near the rim of the stator and an exit at or substantially near the centre of the stator.

Although this cooling arrangment overcomes the aforementioned problem, we have now devised two new arrangements which afford still further improvements.

Thus according to a second aspect of the present invention, there is provided a rotor-stator assembly for an electrical machine, the assembly comprising at least one generally disc shaped rotor, either side of which are arranged respective stators, said stators being joined to form a housing enveloping the rotor and defining a cooling path across either side of said rotor.

Preferably, the housing so formed is generally cylindrical and has an opening in its rim, which joins the stators. In a preferred embodiment of an electrical machine, a plurality of stators are arranged alternately with the rotors and are joined to form housings arranged in contiguous fashion enveloping the rotors so that each has a cooling path either side thereof. In that case, respective openings can be provided in each housing so that they can function as air inlets and outlets, alternately from one housing to the next.

The advantage of this cooling arrangement over that described in GB 2 261 327 A which incorporates cooling air channels in the stator, is that it allows to incorporate much more conductor material in each stator while maintaining the same distance between the rotors.

This has beneficial effects for the construction of the electrical machine. At the same time a larger mass flow of cooling air is achievable for a given rotor spacing and stator thickness.

The second new arrangement constitutes a third aspect of the present invention which provides a rotor-stator assembly comprising at least one stator and at least one rotor coaxial therewith, a sealed chamber surrounding the at least one rotor and the at least one stator protruding through the chamber in sealed fashion, whereby the pressure within the chamber can be reduced and the at least one stator can function as a radiator of heat.

This is especially suited to very high speed operations where windage losses need to be minimised by operating in a vacuum. However, the stator or stators still need to be cooled being predominantly heated through i2R losses.

Very preferably, the at least one stator is made of a material which is a good conductor of heat, for example copper or aluminum.

In a preferred embodiment, a plurality of stators and a plurality of rotors are arranged alternately in co-axial alignment. Then, it is preferred for all the rotors to be within the chamber and all the stators to protrude through the chamber in sealed fashion.

The present invention will now be explained in more detail by the following non-limiting descriptions of preferred embodiments and with reference to the accompanying drawings, in which Figure 1 shows a jig assembly for fitting of a retention ring in accordance with the first embodiment of the present invention; Figure 2 shows a first arrangement for air cooling of an electrical machine in accordance with the second embodiment of the present invention; and Figure 3 shows a second arrangement for air cooling of an electrical machine in accordance with the third embodiment of the present invention.

Figure 1 shows a carbon fibre retention ring to be compressed onto a rotor assembly 3 comprising equiangularly spaced permanent magnets (not shown).

The retention ring 1 and rotor assembly 3 are located in a jig 7 comprising a block 9 and cover plate 11 sealed together by means of clamping bolts 13, 15. The retention ring is located in a first chamber 17 bridging the plane of abutment of the block and cover plate. The retention ring is held in place by O-ring seals 19,21 respectively above and below.

The rotor assembly 3 is located co-axially with the retention ring 1 in a second chamber 23 in the block, contiguous with the first chamber 17. A piston 25 abuts a face 27 at the rotor assembly remote from the retention ring. The piston is slidable within the second chamber by means of an actuator 29 which emerges from the block through a bore 31 and is sealed with respect thereto by virtue of another O-ring seal 33.

An oil inlet opening 35 is arranged in the cover plate 11 and communicates with the first chamber 17. Oil is introduced under pressure through this opening as indicated by arrow 37 to expand the retention ring 3 to accomodate the magnet assembly 5. The piston 25 is then driven by actuator 29 in the direction denoted by arrow 39. The causes the rotor assembly to enter the retention ring, whereupon the hydraulic pressure is released so that the retention ring shrinks securely onto the rotor assembly.

Next, a cooling arrangement in accordance with the second aspect of the invention will be described with reference to Figure 2. As illustrated, a plurality of disc-shaped rotors t 43, 45, 47, 49 are spaced at equal distances along a shaft. These rotors are constructed according to the embodiment of Figure 1.

The rotors are interspersed by respective annular stators 53, 55, 57, 59 which touch neither the rotors nor the shaft.

The stators are joined by a cylindrical bridging member 61 at their circumferences so that adjacent pairs of stators define respective housings 63, 65, 67, 69 around each rotor. Each housing is provided with a respective opening 71, 73, 75. The openings are arranged alternately relative to the length of the shaft 51 to function as air inlets or outlets.

As shown in Figure 2, openings 71 and 75 are inlets and opening 73 is an outlet. Air flows in the direction of the arrows shown in this diagram. Thus, each stator is cooled by air flowing inwards along one of its faces and radially outwards along the other face. Each rotor is cooled by air flowing either radially inwards or radially outwards along both of its faces.

Turning now to Figure 3, in an embodiment of the third aspect of the present invention is shown. Respective rotors 81, 83, 85, 87, 89 are spaced along a shaft 91, all of which are encased in a cylindrical sealed chamber 93. The rotors are constructed according to the embodiment shown in Figure 1.

The rotors are interspersed with respective stators 95, 97, 99, 101 co-axial with the rotors but spaced apart therefrom and from the shaft 91. The stators are made predominently of copper and are of a diameter such that they protrude from the chamber 93 to act as cooling fins. However, the stators are sealed to the chamber where they emerge so that in use, the chamber can be pumped down to sub-atmospheric pressure.

Electrical power is predominately generated in the inner part of each stator whilst the outer part of each is either placed in a flow of cooling air or is enclosed in a cooling liquid jacket.

In the light of this disclosure, modifications of the preferred embodiments as well as other embodiments, all within the scope of the present invention as defined by the appended claims will now become apparent to persons skilled in the art.

Claims (16)

1. A method of applying a retention ring to a disc rotor assembly comprising a plurality of substantially equiangularly spaced magnets, the method comprising expanding the retention ring by applciation by hydraulic fluid under pressure so that it fits over a rim of the rotor assembly, and then reducing the pressure of the hydraulic fluid so that the ring shrinks onto the rim.

2. A method according to claim 1, wherein the retention ring is made from carbon fibres.

3. A method according to claim 1 or claim 2, wherein the retention ring and rotor assembly are placed in a sealed container into which the hydraulic fluid is pumped.

4. A method according to claim 3, wherein a piston arrangement is provided in the container for inserting the rotor assembly into the ring after expansion.

5. A rotor-stator assembly for an electrical machine, the assembly comprising at least one generally disc shaped rotor, either side of which are arranged respective stators, said stators being joined to form a housing enveloping the rotor and defining a cooling path across either side of said rotor.

6. An assembly according to claim 5, wherein the housing is generally cylindrical and has a rim which joins the stators, an opening being provided in said rim.

7. An assembly according to claim 5 or claim 6, wherein a plurality of stators are arranged alternately with the rotors and are joined to form a continuous housing comprising separate compartments respectively enveloping the rotors so that each rotor has a cooling path either side thereof.

8. An assembly according to claim 7, wherein each compartment is provided with a respective opening and the openings are arranged to function as air inlets and outlets, alternately from one housing to the next.

9. An electrical machine comprising an assembly according to any of claims 5-8.

10. A rotor-stator assembly comprising at least one stator and at least one rotor substantially co-axial therewith, a sealed chamber surrounding the at least one rotor, the at least one stator protruding through the sealed chamber in sealed fashion, whereby the pressure within the chamber can be reduced and the at least one stator can function as a radiator of heat.

11. An assembly according to claim 10, wherein the at least one stator is made of a material which is a good conductor of heat.

12. An assembly according to claim 10 or claim 11, wherein a plurality of stators and a plurality of rotors are arranged alternately in co-axial alignment.

13. An electrical machine comprising an assembly according to any of claims 10-12.

14. A method of applying a retention ring to a disc rotor, the method being substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

15. A rotor-stator assembly substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

16. A rotor-stator assembly substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.