WO2018082973A1

WO2018082973A1 - Cooling of an electrical machine

Info

Publication number: WO2018082973A1
Application number: PCT/EP2017/077177
Authority: WO
Inventors: Michael FINNEGAN; Jack Johnson
Original assignee: Jaguar Land Rover Limited
Priority date: 2016-11-02
Filing date: 2017-10-24
Publication date: 2018-05-11
Also published as: GB2558368A; DE112017005515T5; GB2558368B; GB201618464D0; GB201717461D0

Abstract

An electrical machine (300) comprises a stator (120), a rotor (110) and a shaft (130). A heat transfer device (340) is located within at least a part of the rotor (110). The heat transfer device (340) comprises a reservoir (341) which contains a quantity of a phase-change material. The heat transfer device (340) is configured to transfer heat radially towards the shaft (130). The heat transfer device (340) may comprise an axial reservoir portion.

Description

COOLING OF AN ELECTRICAL MACHINE

TECHNICAL FIELD

The present invention relates to cooling of an electrical machine. Aspects of the invention relate to an electrical machine, an electrical system and to a vehicle.

BACKGROUND

It is known to use an electrical machine to generate a traction force to propel a vehicle, such as an automobile. The electrical machine may be used alone in an electric vehicle, or the electrical machine may be used in combination with an internal combustion engine (ICE) in a hybrid electric vehicle (HEV).

The electrical machine may be used as a motor to provide a traction force to propel the vehicle. The electrical machine may also be used as a generator to generate electrical energy during some periods of vehicle operation, such as during regenerative braking.

Electrical machines can generate a considerable amount of heat during operation. Types of electrical machine which are used in a vehicle are permanent magnet machines (e.g. permanent magnet synchronous motor (PMSM)) and switched reluctance machines. A PMSM and a switched reluctance machine have an annular stator. A rotor and shaft are mounted within the stator. An air gap separates the rotor and stator. The rotor rotates about a longitudinal axis of the shaft. One known solution to cooling an electrical machine is provide a heat sink around an exterior of the stator. Water is passed around the heat sink to cool the heat sink. This is known as a water jacket. This cooling solution can cool the stator, but has limited effectiveness at cooling the rotor. Heat is thermally transferred from the rotor to laminations and windings of the stator, across the air gap, and then thermally transferred to the exterior heat sink. One disadvantage with the above cooling solution is that the amount of heat transferred from the rotor via the stator is fairly low. SUMMARY OF THE INVENTION

Embodiments of the invention may be understood with reference to the appended claims.

Aspects of the present invention provide an electrical machine and a vehicle. In one aspect of the invention for which protection is sought there is provided an electrical machine comprising: a stator;

a rotor;

a shaft having a longitudinal axis of rotation; and

a heat transfer device located within at least a part of the rotor, the heat transfer device comprising a reservoir which contains a quantity of a phase-change material, the heat transfer device configured to transfer heat radially towards the shaft, wherein the phase-change material is a material which changes between solid and liquid states at the operational temperatures of the electrical machine. The heat transfer device may comprise a radial reservoir portion and an axial reservoir portion located within the rotor, wherein the radial reservoir portion is in fluid communication with the axial reservoir portion of the rotor.

The heat transfer device may comprise a radial reservoir portion located within the rotor and an axial reservoir portion located within the shaft, wherein the radial reservoir portion is in fluid communication with the axial reservoir portion of the shaft.

The rotor may comprise an annular portion and a radial connecting structure, wherein the axial reservoir portion is provided within the annular portion of the rotor and the radial reservoir portion is provided within the radial connecting structure.

The rotor may comprise an annular portion and a radial connecting structure, wherein the heat transfer device is only located within the radial connecting structure, the heat transfer device having a first radial end nearest to the annular portion and a second radial end nearest to the shaft.

The rotor may comprise an annular portion and a radial connecting structure, wherein the heat transfer device is only located within the annular portion of the rotor. The rotor may comprise an annular portion and a radial connecting structure, the radial connecting structure comprising a first radial element nearest to the rotor and a second radial element nearest to the shaft, the first radial element and the second radial element connected together, and the heat transfer device comprises a first reservoir which is located within the first radial element and a second reservoir which is located within the second radial element, wherein the first reservoir is not in fluid communication with the second reservoir. The heat transfer device may comprise a plurality of radial reservoirs which are spaced apart in an axial direction along the rotor. The heat transfer device may comprise a plurality of radial reservoirs which are angularly spaced apart around the rotor.

The reservoir of the heat transfer device may be annular. The rotor may be mounted coaxially with the shaft and the stator may be mounted coaxially with the shaft and the rotor.

The rotor may be located within the stator. Alternatively, the rotor may be located outside the stator.

The phase-change material may be one of: sodium, wax, mercury.

The rotor may comprise permanent magnets.

The electrical machine may be used as an electrical motor and/or as an electrical generator.

In a further aspect there is provided an electrical system for a vehicle comprising an electrical machine according to the previous aspect.

In a further aspect there is provided a motor vehicle comprising an electrical machine according to one of the previous aspects.

An advantage of at least one embodiment is improved cooling of the rotor. This can extend an operating time of the electrical machine, such as a time period for which the electrical machine can be operated in a high current/high torque mode when a large amount of heat is generated in the rotor. Additionally, or alternatively, this can allow the electrical machine to be operated at a higher performance level (e.g. higher current, higher torque) as the electrical machine can dissipate the higher heat more efficiently. An advantage of at least one embodiment is an extended operating lifetime of the electrical machine.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

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

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying figures in which:

FIGURE 1 schematically shows a vehicle with an electrical system;

FIGURE 2 shows a cross-section through an electrical machine;

FIGURE 3 shows a cross-section through an embodiment of an electrical machine with a rotor cooling scheme;

FIGURE 4 shows a reservoir containing phase-change material;

FIGURE 5 shows a cross-section through an embodiment of an electrical machine with a rotor cooling scheme having multiple reservoirs offset along in an axial direction;

FIGURE 6 shows a cross-section through an embodiment of an electrical machine with a rotor cooling scheme having an axial reservoir portion within the rotor; FIGURE 7 shows a cross-section through an embodiment of an electrical machine with a rotor cooling scheme having an axial reservoir portion within the shaft;

FIGURE 8 shows a cross-section through an embodiment of an electrical machine with a rotor cooling scheme with access to the reservoir;

FIGURE 9 shows a cross-section through an embodiment of an electrical machine with a radial connecting structure having two parts and a rotor cooling scheme; FIGURE 10 shows an embodiment of an electrical machine with a stator inside a rotor and a rotor cooling scheme;

FIGURES 1 1 A to 1 1 C show two embodiments of an electrical machine with axially-directed flux paths and a rotor cooling scheme.

DETAILED DESCRIPTION

Figure 1 shows an example of a vehicle 10 in which an electrical machine according to an embodiment of the present invention may be used. Figure 1 shows a hybrid electric vehicle (HEV) but the vehicle may be an electric vehicle. The vehicle 10 has an internal combustion engine (ICE) 21 releasably coupled to a crankshaft integrated motor/generator (CIMG) 23 by means of a clutch 22. The CIMG 23 is coupled to a transmission 24, which is in turn coupled to the driveline 30 of the vehicle 10. The vehicle 10 is operable to provide drive torque to the transmission 24 by means of the engine 21 alone in an ICE mode, the CIMG 23 alone in an EV mode or the engine 21 and CIMG 23 in parallel in an HEV mode.

The transmission 24 may be a manual transmission, a paddle-shift operated semi-automatic transmission, an automatic transmission, a sequential manual transmission, a constant velocity transmission, an electric variable or power sharing transmission or any other suitable transmission. The transmission 24 may be arranged to: drive only a pair of front wheels 1 1 , 12 (i.e. front wheel drive); drive only a pair of rear wheels 13, 14, (i.e. rear wheel drive); or drive all four wheels (i.e. four wheel drive). Embodiments of the invention are also suitable for vehicles having less than four wheels or more than four wheels.

The vehicle 10 has an electrical energy source 50, such as a battery or a plurality of batteries. An inverter 51 is connected to an output of the battery 50. The inverter 51 generates a three-phase electrical supply that is supplied to the CIMG 23 when the CIMG 23 is operated in a first mode, as a motor. The battery 50 is arranged to receive electrical energy from the CIMG 23 when the CIMG 23 is operated in a second mode, as an electrical generator. The battery 50 stores the electrical energy generated by the electrical generator. The vehicle 10 has a controller 40 configured to control the vehicle 10 to operate in one of a plurality of modes, including the aforementioned modes.

In addition to the aforementioned ICE, EV and HEV modes, the vehicle 10 may be arranged to operate in one of a parallel charge mode, a coast charge mode, a parallel coast mode and a brake mode. In the parallel charge mode the engine 21 applies a positive or drive torque whilst the CIMG 23 applies a negative or charge torque whereby charge is generated by the CIMG 23 to charge the battery 50, whether the vehicle 10 is stationary or moving. In the coast charge mode the clutch 22 is open, the engine 21 is switched off and the CIMG 23 applies a selectable negative or charge torque whereby charge is generated by the CIMG 23 to charge the battery 50 and the vehicle 10 decelerates. In the parallel coast mode the clutch 22 is open, the engine 21 is switched off and the CIMG 23 applies substantially no torque. In the brake mode, which is typically initiated by the application of a brake pedal, the clutch 22 is open, the engine 21 is switched off and a friction braking mechanism (not shown) is applied, which may be done in conjunction with the CIMG 23 applying a negative or charge torque to charge the battery 50 according to a relationship determined and/or controlled by the controller 40.

Figure 2 shows part of a longitudinal cross-section through an electrical machine 100. This electrical machine 100 is an example of the type of machine in which a rotor cooling scheme can be implemented. The electrical machine 100 may be used in the CIMG 23 shown in Figure 1 . The electrical machine 100 comprises a stator 120, a rotor 1 10 and a shaft 130. The stator 120 is an annular (ring-shaped) element. A rotor 1 10 is located within the stator 120. An air gap 109 is provided between the rotor 1 10 and the stator 120. The rotor 1 10 and the stator 120 are coaxial with a longitudinal axis 131 of the shaft 130. The rotor 1 10 may comprise permanent magnets, depending on the type of electrical machine. In the following disclosure, the term "axial" refers to a dimension along, or parallel to, the longitudinal axis 131 of the shaft 130 and the term "radial" refers to a dimension which is perpendicular to the longitudinal axis 131 of the shaft 130. In this example the rotor 1 10 comprises an annular-shaped portion 1 1 1 and a connecting structure 1 12, 1 15 which radially connects the annular portion 1 1 1 to the shaft 1 15. The annular-shaped portion 1 1 1 is the main region of the machine in which magnetic flux paths occur. The connecting structure 1 12, 1 15 provides mechanical support for the annular portion 1 1 1 , and connects the annular portion 1 1 1 to the shaft 130. The connecting structure may comprise an axial hub 1 12 located radially inside the annular portion 1 1 1 of the rotor. The hub 1 12 may be a separate component from the annular portion 1 1 1 , or may be integral with the annular portion 1 1 1 of the rotor. In this example the connecting structure 1 12, 1 15 is shown as a single element. The connecting structure 1 12, 1 15 may extend continuously around the shaft 130 or the connecting structure 1 12, 1 15 may be discontinuous around the shaft. Examples of discontinuous connecting structures are: a connecting structure with apertures defined in the structure to reduce mass of the structure; a connecting structure comprising a set of spokes. A portion 1 15 of the connecting structure may be disc-shaped, with the shaft 130 at the centre of the disc. In other examples the connecting structure may comprise two or more interconnected elements, such as a first flange extending radially inwardly from the annular portion 1 1 1 , or from the hub 1 12, and a second flange extending radially outwardly from the shaft 130. The rotor 1 10 comprises a plurality of laminations of a ferromagnetic material to form a rotor iron. The laminations are stacked in the axial direction to form a rotor of a particular length. Bearings 132 are provided between the shaft 130 and a support (not shown). In use, the rotor 1 10 and the shaft 130 rotate in unison about longitudinal axis 131 .

In this example the rotor 1 10 comprises a single connecting structure 1 15 which has a shorter thickness (i.e. the dimension in the direction of the longitudinal axis of the shaft) compared to the annular portion 1 1 1 of the rotor. In other examples, the electrical machine may comprise more than one connecting structure 1 15, such as a connecting structure at, or near, each axial end of the machine. In other examples, such as rotors for switched reluctance machines, flux paths are created across the entire rotor 1 10. The rotor may have a substantially uniform thickness (i.e. the dimension in the direction of the longitudinal axis of the shaft) without the provision of a separate annular portion 1 1 1 and connecting structure 1 12, 1 15.

The stator 120 may comprise a plurality of radial teeth separated by radial cavities. A tooth and an adjacent cavity can be called a stator slot. The stator cavities support coil windings. By energising the coil windings, a torque is generated to rotate the rotor 1 10 about the longitudinal axis 131 .

In use, heat is generated within the rotor 1 10. For example, eddy current flows within the rotor 1 10 generate heat due to resistive losses.

Figure 3 shows an electrical machine 300 which is similar to the electrical machine 100 shown in Figure 2. Electrical machine 300 has an embodiment of a rotor cooling scheme. For clarity, Figure 3 shows only one half of the cross-section of Figure 2. Features which are the same, or similar, as shown in Figure 2 have the same reference numerals. A heat transfer device 340 is incorporated within the rotor 1 10. In this embodiment, the heat transfer device 340 is incorporated within the radial connecting structure 1 15 of the electrical machine. The heat transfer device 340 extends radially between the rotor hub 1 12 and the shaft 130. The heat transfer device 340 comprises a reservoir, or a cavity, 341 formed within the radial connecting structure 1 15. The reservoir 341 may be annular in a plane perpendicular to the longitudinal axis 131 , i.e. it may extend continuously around the radial connecting structure 1 15. Alternatively, the heat transfer device 340 may comprise a set of discrete radial pipes spaced around the connecting structure 1 15. The reservoir 341 contains a quantity of phase-change material (PCM). A phase-change material is a material which is capable of storing and releasing thermal energy when the material changes phase (state). In use, thermal energy (i.e. heat) is transferred from the rotor hub 1 12 and the rotor 1 10 to the phase-change material at a first end 341 A of the heat transfer device 340. The heat causes the phase-change material to change state, e.g. from solid to liquid. Heat is passed along the heat transfer device 340 towards the second end 341 B. At the second end 341 B heat is transferred to the shaft 130. Reservoir 341 is thermally coupled to the surrounding structure of the electrical machine. For example, where the reservoir is formed within an iron radial connecting structure 1 15, there is thermal transfer through the iron between the annular portion 1 1 1 of the rotor (and the rotor hub 1 12, if present) to the reservoir 341 and the phase-change material within the reservoir 341 . In this embodiment the heat transfer device 340 extends radially between the rotor hub 1 12 and the shaft 130. In other embodiments the heat transfer device 340 may extend for a shorter radial distance, and may stop short of the shaft 130.

A typical maximum operating temperature of the rotor is around 140 ^. A typical maximum operating temperature of the shaft is around 90 °C. Heat is transferred towards the shaft 130 and a temperature gradient forms across the rotor 1 10, with a hottest end nearest the annular portion 1 1 1 /hub 1 12 and the coolest end nearest the shaft 130.

Figure 4 shows a cross-section through the heat transfer device 340. An example will be described with a phase change material (e.g. Sodium) which changes between solid and liquid states at the operational temperatures of the electrical machine. At the hot end 341 A of the heat transfer device, there is a phase change solid→ liquid. At the cooler end 341 B of the heat transfer device there is a phase change liquid→ solid. There is a continuous operational cycle, with a flow of PCM as shown by the arrows. The flow of material can be achieved due to a change in density of the PCM as it changes state, combined with centrifugal/centripetal forces on the PCM due to rotation of the heat transfer device. PCM at the hot end 341 A changes to a liquid state and moves (due to lighter density) in direction 345 towards the cooler end 341 B. As the liquid PCM reaches end 341 B it surrenders heat and returns to a solid state. The denser solid material is returned towards the hot end 341 A by the assistance of the higher centrifugal force on the solid material.

In other examples, the PCM changes between liquid and gas states at the operational temperatures of the electrical machine. The heat transfer device operates as a heat pipe. The heat pipe may include a wick to assist return of condensate to the hot end of the heat pipe.

An example of a suitable phase-change material which changes between solid and liquid states at the operational temperatures of the electrical machine is Sodium (Na). Sodium has a melting point around 97.8^. Other examples of suitable phase-change materials which change between solid and liquid states at the operational temperatures of the electrical machine are: wax; mercury. Examples of suitable phase-change materials which change between liquid and gas states at the operational temperatures of the electrical machine are: Ammonia; Methanol; water. Figure 5 shows an electrical machine 500 which includes another embodiment of a rotor cooling scheme. Features of the electrical machine 500 which are the same, or similar, as shown in previous Figures have the same reference numerals. A heat transfer device 540 is incorporated within the rotor 1 10. In this embodiment, the heat transfer device 540 is incorporated within the radial connecting structure 1 15 of the electrical machine. Similar to Figure 3, the heat transfer device 540 comprises a reservoir 541 of phase-change material which extends radially between the rotor hub 1 12 and the shaft 130. In this embodiment the heat transfer device 540 comprises two separate reservoirs 541 of phase-change material. The reservoirs 541 are offset from one another in an axial direction of the electrical machine. A larger number of reservoirs 541 may be provided. Each of the reservoirs may have the same length, or different lengths. The reservoirs may extend for a shorter or longer distance than shown in Figure 5. Each of the reservoirs may contain the same type of PCM, or different PCMs, such as PCMs with different properties (e.g. different melting points).

Figure 6 shows an electrical machine 600 which includes another embodiment of a rotor cooling scheme. Features of the electrical machine 600 which are the same, or similar, as shown in previous Figures have the same reference numerals. A heat transfer device 640 is incorporated (embedded) within the rotor 1 10. In this embodiment, the heat transfer device

640 is incorporated within the radial connecting structure 1 15 of the electrical machine. Similar to Figure 3, the heat transfer device 640 comprises a reservoir 641 . The reservoir

641 comprises a radial reservoir portion 651 which extends radially between the rotor hub 1 12 and the shaft 130. In this embodiment the heat transfer device 640 also comprises an axial reservoir portion 652 which extends axially within the rotor hub 1 12. The radial reservoir portion 651 is in fluid communication with the axial reservoir portion 652. The reservoir 641 contains a quantity of a phase-change material. Figure 7 shows an electrical machine 700 which includes another embodiment of a rotor cooling scheme. Features of the electrical machine 700 which are the same, or similar, as shown in previous Figures have the same reference numerals. A heat transfer device 740 is incorporated (embedded) within the rotor 1 10. In this embodiment, the heat transfer device 740 is incorporated within the radial connecting structure 1 15 of the electrical machine. The heat transfer device 740 comprises a reservoir 741 . The heat transfer device 740 comprises: a radial reservoir portion 751 which extends radially between the rotor hub 1 12 and the shaft 130; an axial reservoir portion 752 which extends axially within the rotor hub 1 12; and an axial reservoir portion 753 which extends axially within the shaft 130. The radial reservoir portion 751 is in fluid communication with the axial reservoir portions 752, 753. The reservoir 741 contains a quantity of a phase-change material. Portion 753 can help to transfer heat out of the shaft 130 to a surrounding element of the machine, or to a heat sink at one or both ends of the shaft 130.

Figure 8 shows an electrical machine 800 which includes another embodiment of a rotor cooling scheme. Features of the electrical machine 800 which are the same, or similar, as shown in previous Figures have the same reference numerals. The heat transfer device 840 comprises a reservoir 841 . The reservoir 841 is the same as shown in Figure 7. The reservoir 841 comprises: a radial reservoir portion 851 which extends radially between the rotor hub 1 12 and the shaft 130; an axial reservoir portion 852 which extends axially within the rotor hub 1 12; and an axial reservoir portion 853 which extends axially within the shaft 130. A cover plate 846 is provided. One or more conduits 847 communicate between the reservoir portion 851 and an exterior surface of the radial connecting structure 1 15. When the cover plate 846 is removed, phase-change material can be added or removed from the reservoir via conduit(s) 847. The annular cover may extend all of the way around the connecting structure 15, or it may be located only in regions where the conduits 847 communicate with the exterior surface.

In the embodiments described above the radial connecting structure comprises a single disc-shaped element. Figure 9 shows another embodiment of a rotor cooling scheme. The electrical machine 900 is similar to the one previously shown. The main difference is that the radial connecting structure 1 15 comprises a pair of interconnected elements 1 16, 1 17. The connecting structure comprises a first radial element 1 16 nearest to the rotor 1 10 and a second radial element 1 17 nearest to the shaft 130. The first radial element 1 16 and the second radial element 1 17 are connected together. As shown in Figure 9, the first radial element 1 16 and the second radial element 1 17 can comprise a pair of flanges. The rotor hub 1 12 has a radially-extending flange 1 16 which extends radially inwardly from the rotor hub 1 12. The shaft 130 has a radially-extending flange 1 17 which extends radially outwardly from the shaft 30. The flanges 1 16, 1 17 are fastened together by a suitable fastening 1 18 which passes through the flanges 1 16, 1 17. A heat transfer device is incorporated (embedded) within the radial connecting structure 1 16, 1 17 of the electrical machine. As the radial connecting structure comprises a pair of interconnected elements 1 16, 1 17, the heat transfer device comprises two separate reservoirs 941 , 942. The first reservoir 941 extends radially inwardly from the rotor hub towards the region where the flange 1 16 connects to the flange 1 17. The first reservoir 941 may also extend axially along the rotor hub 1 12, as shown. The second reservoir 942 extends radially outwardly from the shaft 130 towards the region where the flange 1 17 connects to the flange 1 16. The second reservoir 942 may also comprise a portion 953 which extends axially along the shaft 130, as shown. In use, heat transfer occurs from the rotor 1 10 and the rotor hub 1 12 to the first reservoir 941 . Heat transfer occurs between the radially innermost end of the first reservoir 941 and the region where the flange 1 16 connects to the flange 1 17. Heat transfer occurs from the flange 1 16 to the flange 1 17. Heat transfer occurs between the flange 1 17 and the radial outermost end of the second reservoir 942. Heat is transferred to the radially innermost end of the second reservoir 942 and to the shaft 130.

The heat transfer device 940 may have a simpler form to the one shown in Figure 9. For example: it may only have the first reservoir 941 ; it may only have the second reservoir 942; the first reservoir 941 may lack the axially-extending portion or the radially extending portion; the second reservoir 942 may lack the axially-extending portion 953.

The aforementioned simpler form of the heat transfer device 940 described with reference to figure 9 may be utilised in conjunction with the previously described embodiments where the radial connecting structure of the rotor comprises a single disc shaped element. In such an embodiment (not shown) the heat transfer device may only have the first reservoir 941 lacking the radially extending portion and be located in the rotor. As such, the heat transfer device may have a configuration similar to that shown in figure 6, but with the radial reservoir portion 651 omitted.

The embodiments described so far show a machine with a rotor located within a stator, i.e. the stator surrounds the rotor. Figure 10 shows an embodiment of an electrical machine 1000 with a stator located within a rotor, i.e. stator 1020 is inside rotor 1010. Rotor 1010 and stator 1020 are coaxially mounted with respect to a shaft 1030. The stator 1020 comprises windings 1025. A housing 1052 is provided within the stator 1020. A radial connecting structure 1015 connects the rotor 1010 to the shaft 1030. A heat transfer device 1040 is incorporated within the rotor 1010. In the example shown in Figure 10, the heat transfer device 1040 is incorporated within the radial connecting structure 1015. The heat transfer device 1040 extends radially within the radial connecting structure 1015 towards the shaft 130. The heat transfer device 1040 comprises a reservoir, or a cavity, formed within the radial connecting structure 1015. The reservoir contains a quantity of PCM. Any of the features of the heat transfer device(s) described previously can be applied to the heat transfer device shown in Figure 10. For example, the heat transfer device may be annular, or may comprise a set of radial pipes.

All of the electrical machines described above have radially-directed flux paths, i.e. flux is radially directed between the stator and the rotor. Figures 1 1 A to 1 1 C show two embodiments of an electrical machine with axially-directed flux paths. Figure 1 1 A shows an electrical machine with a rotor 1 1 10, a stator 1 120 and a shaft 1 130. The stator comprises two portions which are displaced axially along the shaft 1030, each side of the rotor 1 1 10. Stated another way, the rotor 1 1 10 is located between the two stator portions 1 120. A housing 1 152 surrounds the stator 1 120. The rotor 1 1 10 and stators 1 120 are coaxially mounted about the shaft 1 130. A radial connecting structure 1 1 15 connects the rotor 1 1 10 to the shaft 1 130. Figure 1 1 B shows an electrical machine with a rotor 1 1 10, a stator 1 120 and a shaft 1 130. The rotor 1 1 10 comprises two portions which are displaced axially along the shaft 1030, each side of the stator 1 120. Stated another way, the stator 1 120 is located between the two rotor portions 1 1 10. The rotor 1 1 10 and stators 1 120 are coaxially mounted about the shaft 1 130. A radial connecting structure 1 1 15 connects the rotor 1 1 10 to the shaft 1 130. Figure 1 1 C shows the rotor 1 1 10 of these machines. In this example the heat transfer device 1 140 comprises a plurality of radial reservoir portions 1 141 which are radially offset around the rotor. The heat transfer device 1 140 also comprises an annular reservoir portion 1 142 near a radially outermost part of the rotor and an annular reservoir portion 1 143 near a radially innermost part of the rotor.

In the electrical machine shown in Figures 1 1 A to 1 1 C a heat transfer device 1 140 is incorporated within the rotor 1 1 10. The rotor may comprise a radial connecting structure 1 1 15. The heat transfer device 1 140 comprises a reservoir, or a cavity, formed within the rotor, or within the radial connecting structure 1 1 15. The reservoir contains a quantity of PCM. Any of the features of the heat transfer device(s) described previously can be applied to the heat transfer device shown in Figures 1 1 A to 1 1 C. For example, the reservoir portions may extend for a shorter or a longer distance than shown in Figures 1 1 A to 1 1 C. The heat transfer device 1 140 may comprise an axially-extending reservoir portion within the rotor 1 1 10. The heat transfer device 1 140 may comprise an axially-extending reservoir portion within the shaft 1 130.

The electrical machine may use circumferential flux paths, transverse flux paths, or a combination of any one or more of radial flux paths, axial flux paths, circumferential flux paths, transverse flux paths. Similar to the embodiments described above, the electrical machine comprises a heat transfer device within at least part of a radial connecting structure of the electrical machine.

In any of the embodiments the electrical machine may comprise a heat sink (150, Figure 9) thermally mounted to the stator 120. A housing 152 surrounds the heat sink. Spaces 151 between the heat sink 150 and the housing 152 form a cooling jacket. In use, a fluid is circulated around through the cooling jacket. The fluid may be a coolant liquid, or air. 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 electrical machine comprising:

a stator;

a rotor;

a shaft having a longitudinal axis of rotation; and

a heat transfer device located within at least a part of the rotor, the heat transfer device comprising a reservoir which contains a quantity of a phase-change material, the heat transfer device configured to transfer heat radially towards the shaft, wherein the phase-change material is a material which changes between solid and liquid states at the operational temperatures of the electrical machine.

2. An electrical machine according to claim 1 wherein the heat transfer device comprises a radial reservoir portion and an axial reservoir portion located within the rotor, wherein the radial reservoir portion is in fluid communication with the axial reservoir portion of the rotor.

3. An electrical machine according to claim 1 or 2 wherein the heat transfer device comprises a radial reservoir portion located within the rotor and an axial reservoir portion located within the shaft, wherein the radial reservoir portion is in fluid communication with the axial reservoir portion of the shaft.

4. An electrical machine according to claim 2 wherein the rotor comprises an annular portion and a radial connecting structure, wherein the axial reservoir portion is provided within the annular portion of the rotor and the radial reservoir portion is provided within the radial connecting structure.

5. An electrical machine according to claim 1 wherein the rotor comprises an annular portion and a radial connecting structure, wherein the heat transfer device is only located within the radial connecting structure, the heat transfer device having a first radial end nearest to the annular portion and a second radial end nearest to the shaft.

6. An machine according to claim 1 wherein the rotor comprises an annular portion and a radial connecting structure, wherein the heat transfer device is only located within the annular portion of the rotor.

7. An electrical machine according to any one of claims 1 to 3 wherein the rotor comprises an annular portion and a radial connecting structure, the radial connecting structure comprises a first radial element nearest to the rotor and a second radial element nearest to the shaft, the first radial element and the second radial element connected together, and the heat transfer device comprises a first reservoir which is located within the first radial element and a second reservoir which is located within the second radial element, wherein the first reservoir is not in fluid communication with the second reservoir.

8. An electrical machine according to any one of the preceding claims wherein the heat transfer device comprises a plurality of radial reservoirs which are spaced apart in an axial direction along the rotor.

9. An electrical machine according to any one of the preceding claims wherein the heat transfer device comprises a plurality of radial reservoirs which are angularly spaced apart around the rotor.

10. An electrical machine according to any one of claims 1 to 8 wherein the reservoir of the heat transfer device is annular.

1 1 . An electrical machine according to any one of the preceding claims wherein the rotor is mounted coaxially with the shaft and the stator is mounted coaxially with the shaft and the rotor.

12. An electrical machine according to any one of the preceding claims wherein the rotor is located within the stator.

13. An electrical machine according to any one of the preceding claims wherein the phase-change material is one of: sodium, wax, mercury.

14. An electrical machine according to any one of the preceding claims wherein the rotor comprises permanent magnets.

15. An electrical system for a vehicle comprising an electrical machine according to any one of the preceding claims.

16. A motor vehicle comprising an electrical machine according to any one of the preceding claims.

17. An electrical machine or a motor vehicle substantially as hereinbefore described with reference to the accompanying drawings.