WO2013057466A2

WO2013057466A2 - Housing for electrical machines

Info

Publication number: WO2013057466A2
Application number: PCT/GB2012/000796
Authority: WO
Inventors: Martin Christopher STEWART; Richard Gray; Christopher MICALLEF; Michael Green; Andy Hutchinson; Christopher Robert GREENHAM; Gurpreet Saini
Original assignee: Cummins Generator Technologies Limited
Priority date: 2011-10-18
Filing date: 2012-10-18
Publication date: 2013-04-25
Also published as: WO2013057466A8; GB2495726A; GB201117933D0; GB2511664A; GB201408254D0; WO2013057466A3

Abstract

A housing for a rotating electrical machine is disclosed. The housing (14, 16) comprises a cooling passage (26) for cooling the machine. A removable manifold (50) is provided, the removable manifold comprising an inlet and outlet for the cooling passage. The housing is arranged such that the removable manifold can be located at a plurality of different positions around the machine. An arrangement with a hollow rotor hub is also disclosed. The invention can allow the design of the machine to be adjusted to fit different applications.

Description

HOUSING FOR ELECTRICAL MACHINE The present invention relates to a housing for a rotating electrical machine, and in particular a housing with a cooling passage for cooling the machine. The present invention has particular (but not exclusive) application with electrical machines for traction applications, such as electric or hybrid vehicles, as well as in marine applications and power generation.

Electrical machines generally comprise a rotor arranged to rotate inside a stator. The stator is usually retained inside a stator housing. Permanent magnets or windings on the rotor produce a magnetic flux between the rotor and the stator. The stator is provided with stator windings which intersect the magnetic flux. In the case of motor operation, a commutated electrical current is applied to the stator windings, which causes the rotor to rotate. In the case of generator operation, rotation of the rotor produces an electrical output in the stator windings.

When the machine is in operation, the electrical current through the stator windings may cause the windings to become hot. To ensure efficient operation of the machine and to prevent damage or failure/the temperature within the windings needs to be controlled.

EP 1041699 and US 2010/0181873 disclose housing arrangements for electrical machines where a cooling passage is formed through a stator housing. A cooling fluid (coolant) is passed through the cooling passage to cool the machine. Known stator housings include an inlet and outlet in order to take coolant into and out of a cooling passage. The housing is usually designed with a specific application in mind, and the locations of the inlet and outlet are chosen for ease of interface with other components. However, this arrangement may make it difficult to use the machine in other applications with different space constraints. For example, if the electrical machine is to be used in a hybrid vehicle or an electrical vehicle, it may be difficult to retro-fit the machine in an existing vehicle.

According to a first aspect of the present invention there is provided a housing for a rotating electrical machine, the housing comprising a cooling passage and a removable manifold, the removable manifold comprising an inlet and outlet for the cooling passage, wherein the housing is arranged such that the removable^"" manifold can be located at a plurality of different positions around the housing. The present invention may provide the advantage that the inlet and outlet can be located at different positions around the machine. This can allow the design of the machine to be readily adjusted to fit different applications with different space constraints. The present invention can therefore increase the flexibility of the machine to be used in different applications.

The electrical machine may be arranged for use in the drive train of a vehicle, or in other applications such as marine applications or power generation.

Preferably the removable manifold is located in a hole in the housing. The hole in the housing may be formed once the desired locations of the inlet and outlet for the cooling passage are known. For example the housing may be cast in advance, and the hole may be machined in the housing at a later stage. This can allow flexibility in the positioning of the manifold. Preferably the outside of the housing comprises a pad for supporting the manifold. The pad preferably comprises a rib of thicker material in the surface of the housing, which preferably raises the profile in a radial direaion. This arrangement may serve to strengthen the housing around the manifold, and provide a seat for the manifold. Preferably the pad is continuous around the periphery of the manifold. This may help to ensure that the manifold is adequately supported and sealed. A hole for the manifold may be located inside the pad.

The pad may be in the form of a rib pattern. The rib pattern may be repeated at a plurality of locations around the outside of the housing. For example, the rib pattern may be repeated at regular intervals around the outside of the housing. This can allow a plurality of potential locations for the manifold to be provided at the time of manufacturing the housing. The actual location for the manifold may then be chosen at a later stage, for example by machining a hole in the housing. Preferably the repeating rib pattern provides structural strength for the housing. Using a rib pattern for structural strength can allow rigidity to be achieved while minimising the weight. Thus the repeated rib pattern may perform the dual function of strengthening the housing, and providing flexibility in the location of the manifold.

The housing may comprise a drain hole for draining coolant from the cooling channel. This can allow coolant to be drained from the cooling channel if required, for example, during servicing. During normal operation, a drain plug may be provided for sealing the drain hole.

The drain hole is preferably located diametrically opposite the manifold. For example, the manifold may be located at the top of the machine and the drain hole may be located at the bottom in the assembled machine. This may facilitate the circulation of coolant through the cooling passage, and draining of the cooling passage when required.

The drain hole is preferably located in a boss in the housing. The boss may provide the strength necessary to retain a drain plug. Preferably a plurality of bosses is provided around the outside of the housing. This can allow flexibility in the positioning of the drain hole. For example, the drain hole may be drilled through the appropriate boss once the desired position of the drain hole is known. Each boss is preferably located diametrically opposite a pad which provides a potential location for the manifold.

Preferably each boss is part of a repeating rib pattern. The repeating rib pattern may also be used to provide potential locations for fitting the manifold and/or structural strength for the housing. In this case each boss may be located at the centre of a rib pattern which provides a potential location for the manifold.

The housing may also be arranged to support a terminal for bringing an electrical signal into or out of the housing. For example, the housing may support an electrical terminal for the motor/generator and/or a low voltage terminal for devices such as thermocouples or other sensors inside the machine. The terminal is preferably located on a pad which is designed for this purpose on the outside of the housing, in order to give sufficient strength.

In order to increase flexibility, the housing may comprise a plurality of pads where a terminal, such as a low voltage terminal, may be fitted. This can allow the terminal to be fitted at one of number of different locations around the outside of the housing. For example, a repeating rib pattern may provide a plurality of locations where a terminal may be fitted. A hole may be machined in the housing at a location where the terminal is to be fitted, in order to allow electrical connections to be made through the housing. This can allow a hole for the terminal to be created once the desired location for the component is known. Thus the housing may comprise a hole allowing electrical connections to be made through the housing to the terminal.

Preferably the manifold is made from the same or a (functionally) similar material as the housing. This can allow the manifold to have the same or similar expansion characteristics and other properties as the housing, which may increase stability. The housing and/or the manifold may be made from a metal such as aluminium or any other suitable material.

The manifold may comprise a flange which sits on the outside surface of the housing. This can allow the manifold to be held in place on the housing. The underside of the flange is preferably a flat surface which interfaces with a pad on the outside surface of the housing.

The housing may further comprise a seal for sealing the manifold and the housing. This can prevent coolant from leaking out between the housing and the manifold. The seal is preferably located between a flange on the manifold and the housing. The seal may be fitted in a groove in the housing and/or the manifold.

The manifold may comprise an inlet passage which runs at an angle to the radius of the machine. This can allow coolant to enter the cooling passage at an angle, thereby reducing the pressure drop and increasing the efficiency of the cooling. The manifold may also comprise an outlet passage which runs at an angle to the radius of the machine, in order reduce the pressure drop as the coolant exits the cooling passage. The cooling passage may run around the periphery of the machine, and the inlet passage and outlet passage may be angled in opposite directions. The manifold may comprise a baffle on its inside surface {i.e. the surface that is radially inwards). The baffle may act to direct circulated coolant out of the cooling passage and into the outlet, and/or to facilitate entry of fresh coolant from the inlet into the cooling passage. In order to achieve this, the baffle is preferably located (circumferentially) between the exit of an inlet passage and the entry of an outlet passage in the manifold. By providing the baffle as part of the manifold (rather than as part of the housing), the baffle can be located in the desired position together with the manifold. This arrangement may therefore increase the flexibility in the set-up of the machine.

The manifold preferably comprises inlet and outlet ports for connecting (external) inlet and outlet pipes. This can facilitate connection of the machine to external components.

The housing may further comprise means for securing the manifold to the housing. The securing means is preferably arranged to compress a seal between the manifold and the housing to prevent leakage of coolant. The securing means may comprise, for example, screws or bolts.

As disclosed in co-pending UK patent application number 1 1 17931.4 in the name of the present applicant, the contents of which are incorporated herein by reference, a housing arrangement for an electrical machine may comprise an inner housing and an outer housing. This can allow the machine to be provided as a self-contained unit suitable for use in different applications. Thus, in accordance with a preferred embodiment of the present invention, the housing comprises an inner housing and an outer housing. In this arrangement the manifold is preferably located in the outer housing. Preferably the outer housing is arranged to fit around the inner housing. For example, the inner housing and the outer housing may both be substantially cup-shaped, and the unit may be formed by sliding the outer housing over the inner housing.

Preferably the cooling passage is formed between the inner housing and the outer housing. This can allow the cooling passage to be formed easily by bringing together the inner and the outer housing, thereby facilitating manufacturing of the machine. The cooling passage may be formed from a circumferential channel in either the outer surface of the inner housing, or the inner surface of the outer housing, or both.

According to another aspect of the invention there is provided a motor/generator unit comprising a housing in any of the forms described above, and an electrical machine accommodated in the housing.

The motor/generator unit may be arranged for use in the drive train of a vehicle. For example, the motor/generator unit may be arranged to fit between the engine and gearbox of a hybrid vehicle, or may be for use in an electric vehicle. Alternatively, the unit may be arranged for use in other applications such as marine applications or power generation.

The motor/generator unit above may be provided as a universal unit suitable for use in a variety of different applications with different space constraints. In order to facilitate use of the unit in different applications, the unit may comprise a standard interface for an engine and/or gearbox. For example, an interface prescribed by the Society of Automotive Engineers (SAE) may be used in order to connect to the engine and/or gear box. Examples of such interfaces are SAE 1 and SAE 2.

Preferably the motor/generator unit is provided as a self contained unit, suitable for connection in a variety of different applications.

It will be appreciated that the arrangements described above provide flexibility in terms of adapting the motor/generator unit for use in different applications.

In order to further increase the flexibility of the motor/generator unit, the electrical machine may comprise a hollow rotor hub. This can allow the unit to be used, for example, with a variety of different drive shaft designs.

This important feature may also be provided independently. Thus, according to another aspect of the present invention there is provided a motor/generator unit comprising an electrical machine accommodated in a housing, wherein the electrical machine comprises a hollow rotor hub. By providing a motor/generator unit with a hollow rotor hub, a universal machine may be provided which may be connected to a shaft which is chosen for the specific application. This may allow the unit to be used in a variety of different applications and/or retro-fined in an existing application such as in an existing vehicle. In this case the unit may be arranged for use in the drive train of a vehicle.

The unit is preferably provided as a self contained unit suitable for connection to a replaceable shaft. For example, the unit may be arranged to fit between the engine and gearbox of a hybrid vehicle, and may comprise a standard interface for an engine and/or gearbox.

Preferably the rotor hub is arranged to connect to a replaceable shaft. This can facilitate the use of a standard unit in a variety of different applications. Furthermore, by arranging the rotor hub to connect to a replaceable shaft, the shaft can be removed for servicing or in case of damage, or to allow the machine to be used in a different application.

Preferably means are provided for securing the shaft to the rotor hub. For example, the rotor hub and removable shaft may be arranged to be connected by means of bolts. In this case the rotor hub may comprise holes for receiving bolts. The removable shaft may comprise corresponding holes for receiving bolts, and/or one or more of the hub and the shaft may themselves include bolts. Alternatively any other suitable securing means could be provided. Preferably the replaceable shaft is arranged to transfer torque from one side of the machine to the other. For example, the replaceable shaft may transfer torque between an engine and a gearbox. This can reduce the need for the rotor to be made from a higher strength material, since the rotor only needs to transfer the torque produced by the electrical machine, and not that produced by the engine.

According to another aspect of the invention there is provided a method of

manufacturing a housing for an electrical machine, the housing comprising a cooling passage, the method comprising:

machining a hole through the housing to the cooling passage; and inserting a removable manifold into the hole, the removable manifold comprising an inlet and outlet for the cooling passage,

wherein the housing is arranged such that the removable manifold can be located at a plurality of different positions around the housing.

Preferably the housing is manufactured in advance, for example by casting, and the hole for the manifold is machined at a later stage once the desired location for the inlet and outlet is known. According to another aspect of the invention there is provided a method of installing a motor/generator unit comprising an electrical machine accommodated in a housing, the method comprising connecting a removable shaft to a hollow rotor hub in the electrical machine. Features of one aspect of the invention may be applied to any other aspect. Any of. the apparatus features may be provided as method features and vice versa.

In the present specification, terms such as "axial", "radial", "circumferentially" etc. are generally used with reference to the axis of rotation of the electrical machine.

Preferred embodiments of the invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a cross section through a motor/generator unit;

Figure 2 is a cross section through another part of the motor/generator unit;

Figure 3 is an axial cross section through part of the motor/generator unit;

Figure 4 is an isometric view of the motor/generator unit;

Figure 5 is another view of the motor/generator unit; and

Figure 6 is another cross section through the motor generator unit.

Figure 1 is a cross section through a motor/generator unit. The unit includes an electrical machine comprising rotor 10 and stator 12. The rotor 10 is mounted on a shaft 18, and rotates inside the stator 12. A two-part housing arrangement consisting of inner housing 14 and outer housing 16 is arranged to fit around the electrical machine. The unit is designed to be placed between the engine and gearbox of a hybrid vehicle, such as a commercial road vehicle.

The rotor 10 includes a number of permanent magnets 20. Magnetic flux produced by the permanent magnets 20 crosses an air gap 22 between the rotor ) 0 and the stator 12, and combines with stator windings 24. In the case of generator operation, an engine (not shown) causes the rotor 10 to rotate, thereby generating an electrical output in the stator windings 24. In the case of motor operation, a commutated electrical current is supplied to the stator windings, which causes the rotor to rotate. A terminal box 32 provides the electrical connections to the stator windings.

A cooling passage 26 is provided through the inside of the assembled housing. The cooling passage 26 is created by forming a channel on the outer surface of the inner housing 14. When the inner housing 14 and outer housing 16 are brought together, the channel creates a gap between the housings, thereby creating cooling passage 26. O- rings 30 are provided to seal the cooling passage 26 when the inner housing 14 and the outer housing 16 are brought together. The cooling passage 26 runs circumferentially around the outside of the machine, and is used to carry coolant in order to control the temperature of the stator windings.

Figure 2 is a cross section through another part of the motor/generator unit. Referring to Figure 2, a removable manifold 50 is located in a hole 52 in the outer housing. The manifold includes a flange 60 which is used to seat the manifold on the outer housing. The manifold 50 provides an inlet and outlet for the coolant. Inlet and outlet passages 54, 56 run through the manifold, in order to carry coolant into and out of the cooling passage.

Figure 3 is an axial cross section through part of the motor/generator unit showing the manifold 50 and the surrounding area. Referring to Figure 3, the cooling passage 26 runs circumferentially around the machine in a gap ^'created between the inner housing 14 and the outer housing 16. Figure 3 shows the inlet passage 54 which is used to carry coolant into the cooling passage 26. A corresponding outlet passage (not visible in Figure 3) is used to carry coolant out of the cooling passage. As can be seen from Figure 3, the inlet passage 54 is angled to minimise the pressure drop as the coolant enters the cooling passage. This helps to ensure a smooth flow of coolant into the cooling passage. The outlet passage is angled in the opposite direction to take coolant out of the cooling passage.

The manifold 50 includes a baffle 58. The baffle 58 is a rib on the underside of the manifold which extends axially across the width of the cooling channel. It is located circumferentially between the entry of the outlet passage 56 and the exit of the inlet passage 54. The baffle acts to divert coolant which has circulated through the cooling channel 26 into the outlet passage 56, and thus prevents the coolant from circulating continuously. This ensures fresh coolant can continue to enter the cooling passage through the inlet, thereby ensuring efficient cooling. The height of the baffle is set to ensure that it does not clash with the adjacent surface of the cooling passage. As can be seen from Figures 2 and 3, the flange 60 has a flat lower surface which is used to seat the manifold on the outer housing 16. A pad 62 on the outer housing is used to provide a seat for the flange 60. The pad 62 is machined in order to present a flat surface to the underside of the flange 60. A seal 64 is fitted into a groove in the flat surface of the pad 62. The seal 64 acts to prevent coolant from seeping out between the manifold and the outer housing.

In operation, heat from the stator windings 24 is drawn out through the stator core 12 and the inner housing 14. The cooling passage 26 runs in a concentric channel around the stator core, and allows the flow of a coolant, such as a 50-50 water-glycol mix, through the machine, The temperature regulated fluid is pumped in through the manifold 50 absorbing heat as it travels round the cooling passage 26, and is then pumped out again, This process takes place continuously thereby drawing out excess heat and controlling the temperature of the stator windings; Referring back to Figure 3, the manifold 50 includes a threaded o-ring port 65 in the inlet passage 54. A corresponding port is also provided in the outlet passage 56. This allows a range of external inlet and outlet connector pipes to be fitted to the manifold. Hoses from the relevant cooling system of the vehicle can then be connected to these pipes. Figure 4 is an isometric view of the motor/generator unit. The unit is a ready-assembled, self-contained unit designed to be placed between the engine and gearbox of a hybrid vehicle. Referring to Figure 4, outer housing 16 fits around inner housing 14, in order to enclose the electrical machine. Manifold 50 is located on a pad 62 on the outer housing 16. The manifold has four counter-bored holes which line up with four tapped holes in the pad. The four holes accept bolts 66, which are used to secure the manifold to the outer housing. When the bolts are tightened the manifold seal 64 is compressed, which prevents coolant from escaping.

As can be seen from Figure 4, a plurality of pads 62 is provided around the outside of the outer housing 16. Each pad 62 consists of a rectangular rib of thicker material in the surface of the housing. The pads thus form a rib pattern which is repeated around the outside of the housing. The repeating rib pattern performs the dual function of strengthening the outer housing, and providing a plurality of potential locations for the manifold.

In this embodiment, the unit is a universal unit which is designed for use in different applications. For example, the unit may be designed for retro-fitting to an existing vehicle. In such situations, different applications may have different space constraints. For example, external parts on the housing may potentially clash with other components in the vehicle to which the unit is to be fitted. Furthermore, in different applications it may be desirable for the terminal box to have different orientations. For example, if the unit is to be fitted to a vehicle which is to be used in areas which are prone to flooding, it may be desirable for the terminal box to be located away from the bottom of the unit to avoid water ingress.

In the arrangement described above, the manifold 50 is designed as a separate component which can be attached to the outer housing at one of a number of different _. locations. This allows flexibility in the orientation of the motor/generator unit. The manifold 50 is usually positioned at the top of the motor/generator unit. If it is desired to assemble the motor/generator unit with a different orientation (for example, with the driveline and/or terminal box at a different angle radially) the manifold can be repositioned back to the top by using another one of the various pad locations provided around the outer surface of the outer housing. Once the desired position of the manifold is known, a hole for the manifold is machined at the appropriate location. The outer housing also includes a drain hole in order to drain the coolant should this be required. The drain hole is located diametrically opposite the manifold. During normal operation the drain hole is closed with a drain plug.

The drain hole is drilled into one of a number of bosses 68 which are provided for this purpose in the outer surface of the outer housing. Each boss 68 is located at the centre of a pad 62. This arrangement can allow the drain hole to be repositioned directly opposite the manifold by drilling a hole through the appropriate boss.

Also shown in Figure 4 is low voltage terminal 70 which is located on a pad 72. The low voltage terminal is used to provide the connections for components inside the machine, such as a thermocouple or other sensor. The pad 72 is also repeated around the outside of the outer housing 16. This can provide flexibility in positioning the low voltage terminal. The terminal box 32 is provided on the outside of the outer housing 16 to provide electrical connections for the stator windings.

Figure 5 is another view of the motor generator unit, showing how the manifold 50 and low voltage terminal 70 are assembled on the outer housing 16.

The manifold 50 is manufactured from cast aluminium. The grade of the aluminium is chosen to ensure that the material will not be degraded by the 50-50 water-glycol fluid which is used as a coolant. The grade of aluminium is also chosen to ensure the manifold will be dimensionally and functionally stable at the intended operating temperature range (-40 degrees C up to +⁾ 20 degrees C). This is achieved by using the same material as the casting material used for the inner and outer housings, thereby ensuring that the contraction and expansion rates of all components are similar. In the embodiment described above the removable manifold 50 is used with a cooling channel which is formed between an inner and outer housing. However the manifold could also be used with a cooling channel formed through a solid housing. The motor/generator unit described above is designed to be placed between the engine and gearbox of a hybrid vehicle, such as a commercial road vehicle. The motor/generator unit is provided as a standard self-contained unit which can be adapted to the space requirements of a variety of different vehicles. A standard bolt pattern fitment, such as SAE 1 or SAE 2, is provided for interfacing with the engine and gear box.

Referring again to Figure 4, it can be seen that the motor/generator unit is provided without a drive shaft. This is achieved by virtue of hollow rotor hub 74.

Figure 6 is a cross section through the motor generator unit showing the hollow rotor hub in more detail. The hub 74 comprises a number of holes 76 which are used to connect a shaft. This can allow the unit to be used with a variety of different drive shafts, thereby further enhancing the flexibility of the unit to be used in a variety of different applications.

Referring back to Figure 1 , the unit is shown with a drive shaft in place. The drive shaft 18 passes through the centre of the hollow rotor hub 74. A number of bolts 19 are used to connect the shaft 18 to the hub 74 using the holes 76 in the hub. The bolts 19 are removable, allowing the shaft to be removed for servicing or to be replaced. The drive shaft 18 connects to an engine on the left hand side of Figure 1 and a gear box on the right hand side.

The universal design of the rotor enables the machine to be coupled up to any appropriate drive shaft design. The hollow rotor arrangement also provides the advantage that the rotor only needs to cope with the loading from the electrical machine. This is because the replaceable shaft through the centre of the rotor transmits the engine torque directly to the gearbox. This arrangement therefore reduces the need for a high grade material to be used for the rotor, thereby reducing the cost of manufacture.

While preferred embodiments of the invention have been described with reference to particular examples, it will be appreciated that variations of detail are possible within the scope of the invention. Although embodiments have been described with reference to a hybrid vehicle, the invention is equally applicable to other applications such as marine applications and power generation, as well as to a purely electric vehicle. The electrical machine may be powered by batteries, fuel cells, or any other source of electrical energy and/or by a prime mover such as an engine.

Claims

1. A housing for a rotating electrical machine, the housing comprising a cooling passage and a removable manifold, the removable manifold comprising an inlet and outlet for the cooling passage, wherein the housing is arranged such that the removable manifold can be located at a plurality of different positions around the housing.

2. A housing according to claim 1 , wherein the removable manifold is located in a hole in the housing.

3. A housing according to claim 2, wherein the hole is machined in the housing.

4. A housing according to any of the preceding claims, wherein the outside of the housing comprises a pad for supporting the manifold.

5. A housing according to claim 4, wherein the pad comprises a rib of thicker material in the surface of the housing.

6. A housing according to claim 4 or 5, wherein the pad is continuous around the periphery of the manifold.

7. A housing according to any of claims 4 to 6 wherein the pad is in the form of a rib pattern.

8. A housing according to claim 7, wherein the rib pattern is repeated at a plurality of locations around the outside of the housing.

9. A housing according to claim 7 or 8, wherein the rib pattern provides structural strength for the housing.

10. A housing according to any of the preceding claims, wherein the housing comprises a drain hole for draining coolant from the cooling channel.

1 1. A housing according to claim 10, wherein the drain hole is diametrically opposite the manifold.

12. A housing according to claim 10 or 1 1 , wherein the drain hole is located in a boss in the housing.

13. A housing according to claim 12, wherein a plurality of bosses is provided around the outside of the housing.

14. A housing according to claim 13, wherein each boss is part of a repeating rib pattern.

15. A housing according to any of the preceding claims, wherein the housing is arranged to support a terminal for bringing an electrical signal into or out of the housing.

16. A housing according to claim 15, wherein the housing comprises a plurality of pads where a terminal may be fitted.

17. A housing according to claim 15 or 16, wherein a repeating rib pattern provides a plurality of locations where a terminal may be fitted.

18. A housing according to any of claims 15 to 17, wherein the housing comprises a hole allowing electrical connections to be made through the housing to the terminal.

19. A housing according to any of the preceding claims, wherein the manifold is made from the same or a similar material as the housing.

20. A housing according to any of the preceding claims, wherein the manifold comprises a flange which sits on the outside surface of the housing.

21. A housing according to any of the preceding claims, further comprising a seal for sealing the manifold and the housing.

22. A housing according to any of the preceding claims, wherein the manifold comprises an inlet passage which runs at an angle to the radius of the machine.

23. A housing according to any of the preceding claims, wherein the manifold comprises an outlet passage which runs at an angle to the radius of the machine.

24. A housing according to claim 23 when dependent on claim 22, wherein the inlet passage and outlet passage are angled in opposite directions.

25. A housing according to any of the preceding claims, wherein the manifold comprises a baffle on its inside surface.

26. A housing according to claim 25, wherein the baffle acts to direct circulated coolant out of the cooling passage, and/or to facilitate entry of fresh coolant into the cooling passage.

27. A housing according to claim 26, wherein the baffle is located between the exit of an inlet passage and the entry of an outlet passage.

28. A housing according to any of the preceding claims, wherein the manifold comprises inlet and outlet ports for connecting inlet and outlet pipes.

29. A housing according to any of the preceding claims, further comprising means for securing the manifold to the housing.

30. A housing according to claim 29, wherein the securing means is arranged to compress a seal between the manifold and the housing.

31. A housing according to any of the preceding claims, wherein the cooling passage runs circumferentially around the machine.

32. A housing according to any of the preceding claims, wherein the housing comprises an inner housing and an outer housing.

33. A housing according to claim 32, wherein the manifold is located in the outer housing.

34. A housing according to claim 32 or 33, wherein the cooling passage is formed between the inner housing and the outer housing.

35. A housing according to claim 34, wherein the cooling passage is formed from a circumferential channel in the outer surface of the inner housing and/or the inner surface of the outer housing.

36. A motor/generator unit comprising a housing according to any of the preceding claims and an electrical machine accommodated in the housing.

37. A motor/generator unit according to claim 36, wherein the unit is arranged for use in the drive train of a vehicle.

38. A motor/generator unit according to claim 36 or 37, wherein the unit is arranged to fit between the engine and gearbox of a hybrid vehicle.

39. A motor/generator unit according to any of claims 36 to 38, wherein the unit comprises a standard interface for an engine and/or gearbox.

40. A motor/generator unit according to any of claims 36 to 39, wherein the unit is provided as a self contained unit.

41. A motor/generator unit according to any of claims 36 to 40, wherein the electrical machine comprises a hollow rotor hub.

42. A motor/generator unit comprising an electrical machine accommodated in a housing, wherein the electrical machine comprises a hollow rotor hub.

43. A motor/generator unit according to claim 42, wherein the unit is arranged for use in the drive train of a vehicle.

44. A motor/generator according to any of claims 41 to 43, wherein the hollow rotor hub is arranged to connect to a removable shaft.

45. A motor/generator unit according to claim 44, further comprising means for securing the shaft to the rotor hub.

46. A motor/generator unit according to claim 44 or 45, wherein the rotor hub and removable shaft are arranged to be connected by means of bolts.

47. A motor/generator unit according to claim 46, wherein the rotor hub comprises holes for receiving bolts.

48. A motor/generator unit according to any of claims 44 to 47, wherein the removable shaft is arranged to transfer torque from one side of the machine to the other.

49. A method of manufacturing a housing for an electrical machine, the housing comprising a cooling passage, the method comprising:

machining a hole through the housing to the cooling passage; and

inserting a removable manifold into the hole, the removable manifold comprising an inlet and outlet for the cooling passage,

50. A method of installing a motor/generator unit comprising an electrical machine accommodated in a housing, the method comprising connecting a removable shaft to a hollow rotor hub in the electrical machine.