GB2490972A

GB2490972A - Dual rotor axial flux electrical machines with internal bearing assembly

Info

Publication number: GB2490972A
Application number: GB1109064.4A
Authority: GB
Inventors: Lloyd Ash; Richard Strong
Original assignee: Ashwoods Automotive Ltd
Current assignee: Dana TM4 UK Ltd
Priority date: 2011-05-18
Filing date: 2011-05-31
Publication date: 2012-11-21
Anticipated expiration: 2031-05-31
Also published as: GB201109064D0; GB201108298D0; WO2012156719A2; GB2490972B; WO2012156719A3

Abstract

An axial flux electrical machine comprises a stator assembly 20, a rotor shaft 13 extending through the stator assembly carrying first and second permanent magnet rotors 22,23, the rotors being arranged to respective sides of the stator assembly. The stator assembly comprises a stator housing 201 which has first and second end covers 203,213 defining a substantially cylindrical aperture that extends between the end covers, a stator winding assembly 210,211 being located in the aperture. The poles 210 may be assembled as a two part structure surrounding the winding 211. The first and second covers defining respective apertures through which, the shaft extends and a bearing assembly 205 located in the aperture supports the shaft, the only the bearing (226,236 Fig 9) being located in the assembly. Each cover is located between a respective rotor and the stator. Coolant is circulated within the stator and external fins may be present. Resin, gel or phase-change material may fill and spare space within the stator. Sensors and a processor are located in the machine. The rotor magnets may mount to a back iron or yoke members of a powdered iron, grain oriented laminations or a combination thereof may be provided.

Description

AXIAL FLUX ELECTR1CAL MACH1NES The present invention relates to axial flux electrical machines.

BACKGROUND OF THE INVENTiON

Electrical machines, including motors and generators, are important in a wide range of S applications, including vehicle propulsion systems, power generation systems induding wind, and water power generation systems, and in industrial applications. One particular application is in hybrid vehicle power systems in which an electric motor is used in combination with an internal combustion engine. Axial flux electrical machines are particularly suited to vehicle applications, due to their relatively high torque density.

However, existing designs of axial flux electrical machines can be difficuft and expensive to assemble with a desired high level of quality.

It is therefore desirable to provide a design of axial flux electrical machine which overcomes the drawbacks of the previously-considered designs.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided an axial flux electrical machine comprising a stator assembly, a shaft that extends through the stator assembly for rotation with respect to the stator assembly, and first and second rotors attached to the shaft so as to be rotatable with respect to the stator assembly, the first and second rotors being arranged to respective sides of the stator assembly, wherein the stator assembly comprises a stator housing that defines a substantially cylindrical aperture therethrough, the shaft extending through the aperture, coaxially therewith, a stator winding assembly located in the aperture, and a bearing located in the aperture for supporting the shaft, the shaft being supported only by the bearing.

According to another aspect of the present invention, there is provided an axial flux electrical machine comprising a stator assembly, a shaft that extends through the stator assembly for rotation with respect to the stator assembly, and first and second rotors attached to the shaft so as to be rotatable with respect to the stator assembly, the first and second rotors being arranged to respective sides of the stator assembly, wherein the stator assembly comprises a stator housing which has first and second ends and which defines a substantially cylindrical aperture that extends from the first end to the second end, a stator winding assembly located in the aperture. and first and second covers which engage with the first and second ends of the stator housing respectively, so as to close the aperture, the first and second covers defining respective apertures through which the shaft extends, such that the first cover is located between the first rotor and the stator winding assembly, and such that s the second cover is located between the second rotor and the stator winding assembly.

The first and second covers may be of a heat insulating material. The covers may of a composite material, and provide a therm& barrier between the stator assembly and the rotors. The covers are of a magnetically inert material.

In one example, the stator winding assembly comprises a plurality of stator pole portions arranged around the shaft, and a plurality of electrical windings arranged around respective stator pole portions. Each such stator pole portion may comprise a pair of interengaged stator pole components.

Each rotor may comprise a rotor disk having first and second substantially planar sides, a plurality of magnets engaged with the first side of the disk, and a plurality of flux conduit portions engaged with the second side of the disk, the magnets and conduit portions being arrange to overlap one another in circumferential direction such that one conduit portion overlaps a pair of adjacent magnets. The conduit portions may be of a grain oriented laminated steel construction.

In an alternative example, each rotor may comprise a steel rotor disk on a first surface of which is mounted a plurality of magnets.

Such a machine may further comprise a fluid conduit that defines a fluid flow path through the stator housing. The fluid conduit may be arranged for the transport of a cooling fluid through the stator housing.

In such a machine, any spare space in the aperture may be filled with a resin, gel or phase-change material.

Such a machine may further comprise a cooling structure located external to the stator housing. The cooling structure may be provided by fins defined by the stator housing.

According to another aspect of the present invention, there is provided a method of manufacturing an axial flux electrical machine comprising the steps of: a. providing a first cover having a first surface; b. locating a plurality of first stator pole portion components on the first surface of the first cover; c. locating a plurality of windings around respective stator pole portion components; S d. engaging a plurality of second stator pole portion components on respective ones of the first stator pole portion components; e. locating a bearing housing substantially centrally on the first surface of the first cover; f. locating the first cover on a first end of a stator housing such that the stator pole portions components, the windings, and the bearing housing are located within a substantially cylindrical aperture defined by the stator housing; g. locating a second cover on a second end of the stator housing, so as to close the aperture, the second cover engaging with the second stator pole portion components and the bearing housing; h. engaging a first rotor with a shaft; i. locating the shaft through the stator housing such that it is supported by at least one bearing located in the bearing housing, and such that the first rotor is adjacent the first cover; j. engaging a second rotor with the shaft such that the second rotor is adjacent the second cover; and k. providing at least one external cover to enclose the first and second rotors.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an end view of an axial flux electrical machine embodying the present invention; Figure 2 is a side view of the machine of Figure 1; Figure 3 is a side cross-sectional side view of the machine of Figure 1; Figure 4 is a side cross-sectional side view of a stator assembly of the machine of Figure 1; Figure 5 is an end view of the stator assembly of Figure 4; Figure 6 is a side view of part of a stator component; Figure 7 is a perspective view of the part of Figure 6; Figure 8 is a side view of a rotor assembly of the machine of Figure 1; and S Figure 9 is a cross-sectional side view of the rotor assembly of Figure 8.

DETA1LED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An electrical machine embodying the present invention will be described in more detail below. The embodiment to be described is an electric motor, but such a design may also be used as a generator. The principles of construction to be described apply equally to both types of electrical machine.

Figures 1 and 2 show an electric motor I embodying the present invention, which motor 1 comprises a casing 10 provided with external covers 11 a and 11 b. An output shaft 13 extends through the first external cover ha. An electrical terminal housing 12 is provided by the casing 10 and an aperture 14 for electrical connections is provided. The casing 10 is is provided with coolant connections 15, and a number of cooling fins 16. ltwill be readily appreciated that the coolant connection 15 and cooling fins 16 are not essential to the construction of the motor 1.

Figure 3 illustrates a cross-sectional side view of the motor I of Figures 1 and 2, and shows a stator assembly 20 through which the shaft 13 extends, and first and second rotors 22 and 23 which are mounted on the shaft 13. As will be described in more detail below, the shaft 13 and rotors 22 and 23 are mounted to be rotatable with respect to the stator assembly 20, and casing 10.

The motor of the Figure 1, 2 and 3 incorporates a single stator assembly and twin rotors, with the rotors being located to opposite sides of the single central stator assembly. ln one embodiment of the present invention, the stator assembly incorporates bearings for supporting the shaft 13. These internal bearings provide the only support for the shaft 13 and rotors 22 and 23 inside the motor 1.

S

The motor I shown in Figures I, 2 and 3 also includes a shaft encoder and processor 24 within the overall casing of the motor 1. The processor 24 receives shaft position information from the encoder for determining shaft speed and position. In addition, the motor 1 includes a number of sensors (not shown for clarity) which operate to produce measurement signals in dependence upon operating characteristics of the motor 1. For example, the sensors may include temperature sensors for determining the temperatures of the stator windings, stator pole positions, rotor components, rotor bearings, and other components of the motor 1.

The processor 24 operates to receive such operating measurement signals and processes those signals to produce operating data which is stored in a memory device within the motor 1. The stored data can be used and processed by the processor to determine possible future wear or failure modes, such as local high temperatures indicative of a decaying electrical connection, and can be output, either fully, or as an alarm condition. Such data processing within the motor can serve to optimise the life of the motor by providing advance notification for servicing and maintenance requirements. The processor is preferably connected to an industry-standard shielded connector, such as a CAN (controller area network) bus connector, for enabling output of processed data and alarm condition data.

The processor may be connected with a second output connector which can be accessed directly by a service technician to provide diagnostic information and servicing inputs. The processor may a'so be connected to a wireless transmitter/receiver which is operable to transmit and receive data for the processor. In such a manner, the motor I can be remotely accessed and can indicate status and alarm conditions remotely.

As will be described in more detail below, a motor embodying the present invention is manufactured as a series of modules, which enable the manufacturing process to be kept straightforward, and hence tess expensive than previous designs. A motor embodying the present invention also has the advantage that the manufacturing process works with the high forces provided by the magnets and stator, rather than working against them. Such a design enables the manufacturing process to be kept straightforward.

The stator assembly 20 is shown in more detail in the cross-sectional view of Figure 4. The stator assembly 20 comprises a stator housing 201 (which also provides the motor casing 10, and the &ectrical connector housing 12 for the motor I of Figures 1, 2 and 3). The stator housing 201 defines a cylindrical aperture 202 in which stator components are located. The cylindrical aperture 202 is defined between the casing 201 and first and second stator covers 203 and 213. The first and second stator covers 203, 213 are secured to the stator casing 201 via stator cover fixings 204 and 214 respectively. The fixings 204, 214 may be provided by any suitable means, such a bolts, screws or a bonding material. Located centrally in the cylindrical aperture 202, and attached to the first and second stator covers 203, 213, is a rotor bearing assembly 205. The rotor bearing assembly 205 is attached to the first and second stator covers 203 and 213 via fixing means 206 and 216 respectively. The rotor bearing assembly 205 defines a cylindrical passage therethrough 208 to which the shaft 13 extends when the motor is assembled. Each of the stator covers 203 and 213 defines a circular aperture through which the shaft 13 can pass. The rotor assembly housing 205 defines bearing region 207 and 217 into which support bearings for the rotor are located.

The stator assembly 20 also comprises a plurality of stator pole portions 210 around which stator windings 211 are located.

In me with conventional axial motor construction, the stator is provided with a p'urality of windings, which when in use carry electric current to provide a rotating magnetic flux. This magnetic flux is reacted by the magnets on the rotors which causes the rotors and hence the drive shaft, to turn. In order to maxim ise the effect of the magnetic flux produced in the stator, the windings are located around central cores (or "stator pole portions"). These stator po'e portions can be of an iron-based material. ln an embodiment of the present invention are provided by grain oriented laminated steel sheets, or powder iron, or a combination of the two. Such constructions serves to reduce magnetic losses and, therefore, improve efficiency of the machine.

Figure 6 illustrates a first pole component 2101 of a stator pole portion 210. The first pole component 2101 has a body portion 2102 and an en'arged end portion 2103 which extends from the body portion 2102. The body portion 2102 and enlarged end portion 2103 define a winding receiving region 2104 in which the statorwindings 211 are located.

The stator pole portion 210 is made up of two such pole components 2101, having their respective body portions 2102 engaged with one another.

Since the stator pole portion is made up from a pair of identical stator pole components 2101, the manufacture of the stator assembly can be simplified, as will be described below.

In addition, since a single design of stator pole component is used, the cost of the component can be reduced.

In order to manufacture the stator pole portion 210, a first component 2101 is located in a siütable jig with its end face 2106 placed against a receiving surface. A pre-wound winding 211 is placed over the part 2101 such that the stator winding is located in the region 2104 and is in contact with the end portion 2103. A second pole component 2101 is then placed s with its body portion 2102 extending into the winding 211 so as to come into contact with the first pole component 2101. The parts are fixed together, for example using adhesive, or other bonding agent. In one embodiment, the windings 211 are formed of relatively thick, flat copper bar which is bent into a suitable shape. Alternatively, the windings can be provided by the more conventional multi-wound copper wire type. In any event, in order to allow speedy and efficient manufacturing of the stator part, the windings are pre-wound before being located onto the first part of the stator portions, before attachment of the second half of the stator portion. The required number of stator portions are produced, and can be produced in advance and stored ready for manufacture into a stator assembly, and then into a motor.

In one example manufacturing process, the first stator cover 203 is placed in a jig with its inner surface accessible to a worker and/or assembly machine. The rotor bearing assembly 205 is located on the first cover 203 and secured to it using the appropriate fixings or bonding. The required number of pre-constructed stator pole portions 210 are placed in position on the first cover 203 around the bearing assembly 205, and the appropriate electrical connections are made to the windings 211. The first cover 203 is then secured to the stator hou&ng, so that one end of the cylindrical aperture is closed, and so that the stator components and bearing housing are located within the stator housing. The second cover is then located on the casing and secured to the casing 210 using fixings 214 (or suitable bonding material). After the second cover 213 is placed on the assembly, the assembly may be filled with a suitable potting material, such as gel, resin or phase-change material.

In another example manufacturing process, the first stator cover is placed in a jig with its inner surface accessible to a worker and/or assembly machine. The rotor bearing assembly 205 is located on the first cover 203 and secured to it using the appropriate fixings or bonding. The required number of first stator pole portion components are secured in position on the first cover 203. A pre-formed winding assembly is then placed over the first stator pole portion components. The winding assembly is pre-assembled, so that all of the electrical and mechanical connections between the sets of windings are made. In this way the manufacturing process can be simplified. Following location of the winding assembly, the second stator pole portion components are located in contact with the first components so as to extend into respective apertures provided in the winding assembly. The first cover 203 is then secured to the stator housing, so that one end of the cylindrical aperture is closed, and so that the stator components and bearing housing are located within the stator housing. The second cover is then located on the casing and secured to the casing 210 using fixings 214 (or suitable bonding material). After the second cover 213 is placed on the assembly, the assembly may be filled with a suitable potting material, such as gel, resin or phase-change material.

As an alternative, the first cover may be secured to the housing before location of the stator pole portions or first stator pole portion components.

The first and second covers 203, 213 are of a heat insulating material in order to provide a thermal barrier to reduce heat transfer to and from the stator assembly. Reducing heat transfer serves to help maintain the components within an appropriate temperature range.

An optional feature of a motor embodying the present invention is the provision of a fluid conduit located in the stator housing. The conduit may be provided by a suitable flexible is tube, for example of glass fibre. The conduit defines a fluid flow path around the internal space of the stator housing 201 through which cooling fluid, such as water, can be pumped.

The fluid conduit is in fluid communication with the coolant connections 15, for transfer of cooling fluid in and out of the motor housing 10.

The stator assembly is then ready for the introduction of the rotor assembly, which includes the first and second rotors 22 and 23 and the shaft 13.

The rotor assembly is illustrated in Figures 8 and 9, and comprises the shaft 13 onto which the first rotor 22 and the second rotor 23 are mounted. The first and second rotors 22 and 23 are fixed to the shaft 13 and rotatable with the shaft 13. ln Figure 8, the rotor assembly is shown mounted on the rotor bearing assembly housing 205, which is shown in the stator assembly described previously. Figure 9 shows a cross-sectional view of the rotor assembly of Figure 8.

The shaft 13 extends through the rotor shaft bearing housing 205 and is supported by bearings 226 and 236. The shaft is solely supported by the internal bearings in the motor.

The first rotor 22 comprises a rotor disk 221 and a plurality of magnets 222 mounted on a surface of the rotor disk 221. Mounted on a reverse surface of the rotor disk 221 is a plurality of magnetic flux conduit portions. Each such conduit portion overlaps a pair of magnets, and provides a flux path between the magnets, thereby increasing the efficiency of the rotor. In one example, the rotor disk is of a composite material, such as carbon fibre composite. The second rotor 23 is attached to the shaft 13 using fixing means 235 and 235, spaced apart from the first rotor, to the opposite side of the bearing housing 205. The S second rotor assembly 23 also comprises a rotor disk 231, a plurality of magnets 232, and a pluraflty of flux conduit portions 233 attached to the disk.

In order to assemble the motor, bearings 226 and 236 are inserted into the bearing locating regions 207 of the rotor bearing housing 205 in the stator assembly 20. The first rotor assembly 22 is attached to the shaft 13, and then the shaft 13 is inserted into the stator assembly through the cylindrical aperture 208. The drive shaft 13 is supported in the stator assembly by the bearings 226 and 236, and enables the fitting of the second rotor assembly 23 to the shaft 13. The fixings in Figures 8 and 9 are illustrated as being provided by a bolt 234 and locking nut 235. Any suitable means for attaching the second rotor assembly to the shaft can be provided.

Such a motor design enables the shaft 13 to be located in the bearing in an accurate manner. In addition, provision of the internal bearing enables the shaft insertion to be completed without the need for complex manipulation tools, since the magnetic forces exerted between the rotor magnets and the stator assembly serve to pull the rotor and shaft into position. Any off centre forces are resisted by the shaft in the bearing.

In order to complete the motor, the first and second external covers 11 a and 11 b are attached to the casing 10.

In this way, the axial flux motor of the present invention is able to be manufactured in a simple, straightforward and modular manner, which reduces complexity and cost.

Claims

CLAIMS: 1. An axial flux electrical machine comprising a stator assembly, a shaft that extends through the stator assembly for rotation wh respect to the stator assembly, and first and second rotors attached to the shaft so as to be rotatable with respect to the stator assembly, s the first and second rotors being arranged to respective sides of the stator assembly, wherein the stator assembly comprises a stator housing that defines a substantially cylindrical aperture therethrough, the shaft extending through the aperture, coaxially therewith, a stator winding assembly located in the aperture, and a bearing located in the aperture for supporting the shaft, the shaft being supported only by the bearing.
2. An axial flux electrical machine comprising a stator assembly, a shaft that extends through the stator assembly for rotation with respect to the stator assembly, and first and second rotors attached to the shaft so as to be rotatable with respect to the stator assembly, the first and second rotors being arranged to respective sides of the stator assembly, wherein the stator assembly comprises a stator housing which has first and second ends and which defines a substantially cylindrical aperture that extends from the first end to the second end, a stator winding assembly located in the aperture, and first and second covers which engage with the first and second ends of the stator housing respectively, so as to close the aperture, the first and second covers defining respective apertures through which the shaft extends, such that the first cover is located between the first rotor and the stator winding assembly, and such that the second cover is located between the second rotor and the stator winding assembly.
3. A machine as claimed in claim 2, wherein the first and second covers are of a heat insulating material, such as a composite material, thereby to provide a thermal barrier between the rotors and the stator assembly.
4. A machine as claimed in any one of the preceding claims, wherein the stator winding assembly comprises a plurality of stator pole portions arranged around the shaft, and a plurality of electrical windings arranged around respective stator pole portions.
5. A machine as claimed in claim 4, wherein each stator pole portion comprises a pair of interengaged pole components.
6. A machine as claimed in any one of the preceding claims, wherein each rotor comprises a rotor disk having first and second substantially planar sides, a plurality of magnets engaged with the first side of the disk, and a plurality of flux conduit portions engaged with the second side of the disk, the magnets and conduit portions being arrange to overlap one another in circumferential direction such that one conduit portion overlaps a pair of adjacent magnets.
7. A machine as claimed in claim 6, wherein the conduit portions are of grain oriented laminated steel, or of powder iron, or of a combination of grain oriented laminated steel and powder iron.
8. A machine as claimed in any one of the preceding claims, further comprising a fluid conduit that defines a fluid flow path through the stator housing.
9. A machine as claimed in claim 8, wherein the fluid conduit is arranged for the transport of a cooling fluid through the stator housing.
10. A machine as claimed in any one of the preceding claims, wherein any spare space in the aperture is filled with a resin, gel or phase-change material.
11. A machine as claimed in any one of the preceding claims, further comprising a cooling structure located external to the stator housing.
12. A machine as claimed in claim 11, wherein the cooling structure is provided by fins defined by the stator housing.
13. A machine as claimed in any one of the preceding claims, further comprising a shaft encoder connected with the shaft, at least one sensor operable to produce an output signal indicative of an operating parameter of the machine, or of a component of the machine, and a processor located within the machine, and operable to receive signals from the encoder, and from the sensor, to process such received signals to produce operating data for the machine, and to store such operating data.
14. A machine as claimed in claim 13, wherein the processor is operable to output such stored data when requested by a user input.
15. A machine as claimed in claim 13 or 14, comprising a plurality of temperature sensors operable to generate respective signal indicative of temperatures of associated components of the machine.
16. A machine as claimed in claim 15, wherein the processor is operable to generate such operating data from the plurality of temperature signals, and to compare such data with store model data, thereby to provide output data indicative of wear or failure of the machine.
17. A method of manufacturing an axial flux electrical machine comprising the steps of: a. providing a first cover having a first surface; b. locating a plurality of first stator pole portion components on the first surface of the first cover; S c. locating a plurality of windings around respective pole portion components; d. engaging a plurality of second stator pole portion components on respective ones of the first stator pole portion components; e. locating a bearing housing substantially centrally on the first surface of the first cover; f. locating the first cover on a first end of a stator housing such that the stator pole portions components, the windings, and the bearing housing are located within a substantially cylindrical aperture defined by the stator housing; g. locating a second cover on a second end of the stator housing, so as to close the aperture, the second cover engaging with the second stator pole portion components and the bearing housing; h. engaging a first rotor with a shaft; i. locating the shaft through the stator housing such that it is supported by at least one bearing located in the bearing housing, and such that the first rotor is adjacent the first cover; j. engaging a second rotor with the shaft such that the second rotor is adjacent the second cover; and 1<. providing at least one external cover to enclose the first and second rotors.
18. A method as claimed in claim 17, further comprising injecting a resin, gel or phase-change material into the aperture.
19. An axial flux electrical machine substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.Amendments to the claims have been made as follows: CLAIMS: 1. An axial flux electrical machine comprising a stator assembly, a shaft that extends through the stator assembly for rotation with respect to the stator assembly, and first and second rotors attached to the shaft so as to be rotatable with respect to the stator assembly, the first and second rotors being arranged to respective sides of the stator assembly, wherein the stator assembly comprises a stator housing which has first and second ends and which defines a substantially cylindrical aperture that extends from the first end to the second end, a stator winding assembly located in the aperture, and first and second covers which engage with the first and second ends of the stator housing respectively, so as to close the aperture, the first and second covers defining respective apertures through which the shaft extends, such that the first cover is located between the first rotor and the stator winding assembly, and such that the second cover is located between the second rotor and the stator winding assembly, wherein the first cover C\i 15 carries a bearing housing located within the cylindrical aperture of the stator housing through which the shaft extends, the bearing housing including at least one bearing on Ft.. which the shaft is supported.2. A machine as claimed in claim 1, wherein the first and second covers are of a heat o insulating material, such as a composite material, thereby to provide a thermal barrier between the rotors and the stator assembly.3. A machine as claimed in claim 1 or 2, wherein the stator winding assembly comprises a plurality of stator pole portions arranged around the shaft, and a plurality of electrical windings arranged around respective stator pole portions.4. A machine as claimed in claim 3, wherein each stator pole portion comprises a pair of interengaged pole components.5. A machine as claimed in any one of the preceding claims, wherein each rotor comprises a rotor disk having first and second substantially planar sides, a plurality of magnets engaged with the first side of the disk, and a plurality of flux conduit portions engaged with the second side of the disk, the magnets and conduit portions being arrange to overlap one another in circumferential direction such that one conduit portion overlaps a pair of adjacent magnets.6. A machine as claimed in claim 5, wherein the conduit portions are of grain oriented laminated steel, or of powder iron, or of a combination of grain oriented laminated steel and powder iron.7. A machine as claimed in any one of the preceding claims, further comprising a fluid conduit that defines a fluid flow path through the stator housing.8. A machine as claimed in claim 7, wherein the fluid conduit is arranged for the transport of a cooling fluid through the stator housing.9. A machine as claimed in any one of the preceding claims, wherein any spare space in the aperture is filled with a resin, gel or phase-change material.10. A machine as claimed in any one of the preceding claims, further comprising a cooling structure located external to the stator housing.11. A machine as claimed in claim 10, wherein the cooling structure is provided by fins defined by the stator housing.12. A machine as claimed in any one of the preceding claims, further comprising a shaft encoder connected with the shaft, at least one sensor operable to produce an output 0 signal indicative of an operating parameter of the machine, or of a component of the CY) machine, and a processor located within the machine, and operable to receive signals 0 from the encoder, and from the sensor, to process such received signals to produce operating data for the machine, and to store such operating data.13. A machine as claimed in claim 12, wherein the processor is operable to output such stored data when requested by a user input.14. A machine as claimed in claim 12 or 13, comprising a plurality of temperature sensors operable to generate respective signal indicative of temperatures of associated components of the machine.15. A machine as claimed in claim 14, wherein the processor is operable to generate such operating data from the plurality of temperature signals, and to compare such data with store model data, thereby to provide output data indicative of wear or failure of the machine.16. A method of manufacturing an axial flux electrical machine comprising the steps of: a. providing a first cover having a first surface; b. locating a plurality of first stator pole portion components on the first surface of the first cover; c. locating a plurality of wind ings around respective pole portion components; S d. engaging a plurality of second stator pole portion components on respective ones of the first stator pole portion components; e. locating a bearing housing substantially centrally on the first surface of the first cover; f. locating the first cover on a first end of a stator housing such that the stator pole portions components, the windings, and the bearing housing are located within a substantially cylindrical aperture defined by the stator housing; g. locating a second cover on a second end of the stator housing, so as to close the aperture, the second cover engaging with the second stator pole portion components and the bearing housing; h. engaging a first rotor with a shaft; CY) i. locating the shaft through the stator housing such that it is supported by at 0 least one bearing located in the bearing housing, and such that the first rotor is adjacent the first cover; j. engaging a second rotor with the shaft such that the second rotor is adjacent the second cover; and k. providing at least one external cover to enclose the first and second rotors.17. A method as claimed in claim 16, further comprising injecting a resin, gel or phase-change material into the aperture.18. An axial flux electrical machine substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.