GB2616841A

GB2616841A - Electrical machine cooling

Info

Publication number: GB2616841A
Application number: GB2203811.1A
Authority: GB
Inventors: Shi Juntao; Pranay Deodhar Rajesh; Umemura Chiaki
Original assignee: IMRA Europe SAS
Current assignee: IMRA Europe SAS
Priority date: 2022-03-18
Filing date: 2022-03-18
Publication date: 2023-09-27
Anticipated expiration: 2042-03-18
Also published as: GB202203811D0; GB2616841B

Abstract

An electrical machine 300 comprising a stator, the stator comprising: one or more stator windings comprising: a central winding region, and an end winding region 225, and one or more chambers 250 in which the end winding region of the stator windings are located, where the chamber comprises a ferrofluid. The machine comprises a rotor 230, a rotor shaft, and one or more magnets 210 mounted to the shaft; where at least a portion of the magnets is arranged to overlap, in an axial direction of the machine, at least a portion of the one or more chambers in which the ferrofluid is located. The magnets may be arranged in distinct groups based on their length and magnetic coercive forces. The use of a reduction gear may rotate the second magnets at an angular velocity that is lower than an angular velocity of first magnets. End plates 270 may form axial ends of the chambers to form a thermally conductive pathway to transfer heat away from the ferrofluid. The machine may be arranged so that the stator is arranged further from the axis of rotation or that the rotor is arranged further from the axis of rotation. Similar features may be applied to a linear electrical machine arrangement.

Description

ELECTRICAL MACHINE COOLING

Field of the Invention

The invention relates generally to electrical machines, and more specifically to the use of a ferrofluid to cool an electrical machine.

Background

As the world transitions away from fossil fuels and to cleaner, renewable sources of power, electrical machines are becoming increasingly important. Electrical machines include electric generators to generate electricity in, for example, a wind turbine or for regenerative braking applications in vehicles. Alternatively, electric motors, such as induction motors, can use electrical energy to generate torque to power vehicles, aeroplanes and many other machines.

With the use of electrical machines becoming increasingly prevalent in the modern word, improving the performance and efficiency of these electrical machines is an area of intense research. However, there are a number of separate ways in which performance or efficiency might be improved.

Certain types of electrical machine, such as resonant induction motors, can produce significant quantities of heat due to comparatively large currents in the windings of the motor. This heat decreases the efficiency of the motor and can potentially lead to component damage. As such, managing the temperature of electrical machines is crucial.

Furthermore, while traditional electrical machines are often provided with a ferromagnetic core, some more modern electrical machines are provided without such a ferromagnetic core, but rather with a non-magnetic core, or a so-called 'air-core'. In such air-core electrical machines, leakage of magnetic flux from the electrical machine can be greater than in traditional electrical machines with ferromagnetic cores. Such magnetic flux leakage can lead to decreases in performance as well as electromagnetic interference. Accordingly, managing magnetic flux leakage is essential in electrical machines, in particular air-core electrical machines.

The present inventors have identified an improved approach for cooling an electrical machine, as well as increasing the output and reliability of an electrical machine.

Summary

Aspects of the invention are set out in the accompanying claims In a first aspect of the invention there is provided an electrical machine comprising a stator and a rotor. The stator comprises one or more stator windings comprising: a central winding region, and an end winding region, and one or more chambers in which the end winding region of the one or more stator windings are located, wherein the chamber comprises a ferrofluid. The rotor comprises: a rotor shaft, and one or more magnets mounted to the rotor shaft; wherein at least a portion of the one or more magnets is arranged to overlap, in an axial direction of the electrical machine, at least a portion of the one or more chambers in which the ferrofluid is located.

As a result, active heat transfer can be made to occur within the one or more chambers during standard operation of the electrical machine, thereby improving cooling of the end winding region of the stator windings. Consequently, the reliability of the electrical machine can be improved by reducing the likelihood of hotspot formation within the end winding region, and this increased reliability allows the electrical machine to be operated at higher currents and/or torques. As such, the overall performance (i.e. output) of the electrical machine can be increased.

In some examples, the one or more magnets may include one or more first magnets having an axial length that is greater than an axial length of the central winding region of the one or more stator windings. In this manner, a single magnet (or set of magnets) can be used to not only magnetically interact with the stator windings, but also to cause active heat transfer within the one or more chambers. Accordingly, the arrangement can minimise the number of components required in the electrical machine.

In some examples, the one or more magnets may include one or more first magnets and one or more second magnets distinct from the one or more first magnets, wherein the one or more second magnets are arranged to overlap at least a portion of the one or more chambers in the axial direction of the electrical machine. As such, greater flexibility in the choice of magnets can be afforded, as the one or more second magnets may be different to the one or more first magnets, allowing for more precise control over rotating magnetic field produced by the magnets in the vicinity of the ferrofluid, and as such the degree of active heat transfer within the one or more chambers.

Advantageously in this example, a magnetic coercive force of the one or more first magnets may be greater than a magnetic coercive force of the one or more second magnets. Accordingly, the one or more second magnets may therefore be less expensive than the one or more first magnets, while still inducing active heat transfer, thereby providing cost-saving benefits.

In some examples, the one or more second magnets are each mounted to the rotor shaft via a reduction gear. Accordingly, the rotational velocity of the one or more second magnets, and therefore the rotating magnetic field produced by the rotating one or more second magnets, can be controlled. As such, the magnetic force exerted on the ferrofluid by the rotating magnetic field can be controlled to maximise the flow of the ferrofluid within the one or more chambers.

In some examples, the one or more second magnets are arranged to rotate at an angular velocity that is lower than an angular velocity of the one or more first magnets. In this manner, in comparatively high rotor speed implementations, or when a comparatively high viscosity ferrofluid is used, the rate of change of the rotating magnetic field of the one or more second magnets may be adjusted to maximise active heat transfer within the ferrofluid.

Advantageously, the one or more first magnets and the one or more second magnets may have respectively different numbers of magnetic poles. This allows for the rate of change in direction of the rotating magnetic field produced by the one or more second magnets to be different to that of the one or more first magnets. Accordingly, the magnetic force exerted by the one or more second magnets can be adjusted based on a variety of factors (such as ferrofluid viscosity and/or rotational speed of the rotor) to maximise the rate of flow of the ferrofluid within the one or more chambers.

In some examples, the stator may comprise one or more end plates forming axial ends of the one or more chambers, wherein the end plate forms at least a part of a thermally conductive pathway to transfer heat away from the ferrofluid. As such, heat can be effectively transferred away from the end winding regions via the ferrofluid.

Advantageously, the stator may further comprise one or more cooling channels comprising a cooling fluid, and wherein the one or more end plates provide a thermally conductive pathway between the ferrofluid and the cooling fluid within the one or more cooling channels.

Accordingly, the heat transferred away from the end windings can be effectively dissipated away from the vicinity of the end windings, thereby improving the overall cooling capabilities of the electrical machine.

In some examples, the central winding region of the one or more stators is enclosed by one or more laminations. Accordingly, the stator windings may be held in place, while increasing the magnetic flux linkage between the stator and rotor, thereby increasing the output of the electrical machine.

In some examples, the one or more magnets may include one or more permanent magnets. Furthermore, in some examples, the one or more magnets may include one or more electrical windings configured to carry an electrical current. As such, the above-described techniques are applicable for a variety of electrical machine configurations.

In some examples, the stator may be arranged further from the axis of rotation of the electrical machine than the rotor. Alternatively, the rotor may be arranged further from the axis of rotation of the electrical machine than the stator.

In a second aspect of the invention, there is provided a linear electrical machine comprising a stator and a mover. The stator comprises: one or more stator windings comprising: a central winding region, and an end winding region, and one or more chambers in which the end winding region of the one or more stator windings are located, wherein the chamber comprises a ferrofluid. The mover is arranged in use to move along a length direction of the electrical machine, and comprises: a plurality of magnets arranged in the length direction of the electrical machine, wherein the plurality of magnets are arranged to have alternating polarities in the length direction, and wherein the plurality of magnets includes a plurality of central magnets arranged to at least partially overlap a central winding region of the one or more stator windings. At least a portion of the plurality of magnets is arranged to overlap, in a width direction of the electrical machine, at least a portion of the one or more chambers in which the ferrofluid is located.

As a result, active heat transfer can be made to occur within the one or more chambers during standard operation of the linear electrical machine, thereby improving cooling of the end winding region of the stator windings. Consequently, the reliability of the electrical machine can be improved by reducing the likelihood of hotspot formation within the end winding region, and this increased reliability allows the electrical machine to be operated at higher currents and/or torques. As such, the overall performance (i.e. output) of the electrical machine can be increased.

In some examples, the plurality of central magnets have a width that is greater than a width of the central winding region of the one or more stator windings. In this manner, a single set of magnets can be used to not only magnetically interact with the stator windings, but also to cause active heat transfer within the one or more chambers. Accordingly, the arrangement can minimise the number of components required in the electrical machine.

In some examples, the plurality of magnets includes a plurality of edge magnets distinct from the plurality of central magnets, and wherein the plurality of edge magnets are arranged to overlap at least a portion of the one or more chambers in the width direction of the electrical machine. As such, greater flexibility in the choice of magnets can be afforded, as the edge magnets may be different to the central magnets, allowing for more precise control over moving magnetic field produced by the magnets in the vicinity of the ferrofluid, and as such the degree of active heat transfer within the one or more chambers.

Advantageously, a magnetic coercive force of the central magnets may be greater than a magnetic coercive force of the edge magnets. Accordingly, the edge magnets may therefore be less expensive than the central magnets, while still inducing active heat transfer, thereby providing cost-saving benefits.

In some examples, a number of poles of the plurality of edge magnets is different to a number of poles of the plurality of central magnets. This allows for the rate of change in direction of the moving magnetic field produced by the one or more edge magnets to be different to that of the central magnets. Accordingly, the magnetic force exerted by the edge magnets can be adjusted based on a variety of factors (such as ferrofluid viscosity and/or rotational speed of the rotor) to maximise the rate of flow of the ferrofluid within the one or more chambers.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the following figures.

In accordance with one (or more) embodiments of the present invention the Figures show the following: Figure 1 shows an example of a conventional electrical machine.

Figure 2 shows an example of an example electrical machine Figure 3 shows a cross-section of an electrical machine according to an example teaching of the present disclosure.

Figure 4 shows a cross-section of an electrical machine according to an example teaching of the present disclosure.

Figure 5 shows a cross-section of an electrical machine according to an example teaching of

the present disclosure.

Figure 6 shows a cross-section of an electrical machine according to an example teaching of the present disclosure.

Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field. As used in this specification, the words "comprises", "comprising", and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean "including, but not limited to". The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. It will also be recognised that the invention covers not only individual embodiments but also combination of the embodiments described herein.

The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and/or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the spirit and scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc., other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future.

Detailed Description

Figure 1 is a cross-section of an example of a conventional electrical machine 100. The electrical machine 100 includes a stator including a stator housing 140 and one or more stator windings 120, which may be mounted to the stator housing 140. The electrical machine 100 also includes a rotor comprising a rotor hub 130 and one or more permanent magnets 110 mounted to the rotor hub 130. In operation, the rotor rotates relative to the stator, where the stator housing 140 may be mounted to the rotor hub 130 via one or more bearings (not shown). The electrical machine 100 may have many use cases. For example, an input electrical current in the stator windings 120 may be used to induce a torque in the rotor, or an input torque in the rotor may be used to generate an electrical current in the stator windings 120.

As shown in Figure 1, the stator windings 120 include end windings 125 (i.e. end winding regions). The end windings 125 are the end-most region of the stator windings 120 and may include the turns in the windings. In some electrical machines, the stator windings 120 may be substantially enclosed or confined within one or more laminations 160, as shown in Figure 1. Accordingly, in such examples, the end windings 125 may be the region of the stator windings 120 that is not enclosed or contained by the laminations 160. The region of the stator windings 120 not classed as the end windings 125 may be referred to as a central winding region.

The end windings 125 of the electrical machine 100 may be the source of significant heat. For example, these regions can harbour the location of hot spots within the windings. Accordingly, the heat produced or located within the end windings 125 can cause failures or can limit the performance capabilities of the electrical machine 100, for example through a need to operate the electrical machine 100 at lower currents to avoid failures.

Figure 2 is a cross-section of an example approach for cooling the end windings of electrical machines 200. The electrical machine 200 is substantially similar to the electrical machine 100 of Figure 1, however the electrical machine 200 of Figure 2 includes one or more chambers 150 in which the end windings 125 are located. The one or more chambers 150 are each closed chambers and contain (e.g. are filled with) a ferrofluid. A ferrofluid is a colloidal fluid of ferromagnetic or ferrimagnetic particles. The ferrofluid is heated by the end windings 125, however this heating will not be perfectly uniform and as such, a temperature gradient will be created within the ferrofluid, causing varying magnetic susceptibility within the ferrofluid. The presence of the temperature gradient and leakage magnetic flux gradient results in a Kelvin body force in the ferrofluid, leading to thermomagnetic convection. Thus, the ferrofluid flows within the chamber 150 and is able to divert heat way from the end windings 125.

While this approach does improve cooling of the end windings 125 and therefore improve the performance of the electrical machine 200, heat located within the end windings 125 is still often a limiting factor for electrical machine performance. Accordingly, the present inventors have identified a desire to further improve the cooling of the end windings 125 of electrical machines.

Figure 3 illustrates an example teaching of the disclosure for further improving the cooling of the end windings of an electrical machine. The electrical machine 300 includes a stator including a stator housing 240 and one or more stator windings 220, which may be mounted to the stator housing 240. The electrical machine 300 also includes a rotor comprising a rotor hub 230 and one or more magnets 210 mounted to the rotor hub 230. The one or more magnets 210 may take a variety of forms depending on the type of electrical machine. For example, the one or more magnets 210 may be permanent magnets, or may be one or more rotor windings. In addition, the rotor may include both rotor windings and permanent magnets in some implementations. In operation, the rotor rotates relative to the stator, where the stator housing 240 may be mounted to the rotor hub 230 via one or more bearings (not shown). The electrical machine 300 may have many use cases. For example, an input electrical current in the stator windings 220 may be used to induce a torque in the rotor, or an input torque in the rotor may be used to generate an electrical current in the stator windings 220.

The stator windings 220 include end windings 225 (i.e. end winding regions), which in some examples may be the region of the stator windings 220 enclosed or confined within one or more laminations 260, as shown in Figure 3. In such an example, the region of the stator windings 220 not classed as the end windings 225 may be referred to as a central winding region. The end windings 225 are located within one or more chambers 250. For example, the electrical machine 300 of Figure 3 includes two chambers 250, where each chamber extends fully in a circumferential direction of the electrical machine to have a substantially toroidal shape, and each chamber 250 encloses respective end windings 225. It should be noted, however, that other arrangements with varying numbers of end windings and chambers are possible.

The central winding region of the stator windings 220 has an axial length (a length along the axis of rotation of the electrical machine), where the end windings 225 extend in an axial direction from the central winding region. As shown in Figure 3, the axial length of the one or more magnets 210 is set such that the one or more magnets 210 overlap the one or more chambers 250 (or the end windings 225) in an axial direction of the electrical machine 300. As a result, a rotating magnetic field is produced in the vicinity of the ferrofluid within the chambers 250, thereby further inducing the flow of the ferrofluid within the chambers 250.

In particular, in the electrical machine 200 of Figure 2, the ferrofluid flows between the end windings 125 and the stator housing 140 in a primarily axial direction (and to a lesser extent radial direction) of the electrical machine as a result of thermomagnetic convention.

Hereinafter, this process is referred to as passive heat transfer. In the example of Figure 3, the presence of the rotating magnetic field produces a rotational force on the ferrofluid, thereby causing the ferrofluid to additionally flow in a circumferential (rotational) direction of the electrical machine 300. Hereinafter, this process is referred to as active heat transfer. By combining both passive and active heat transfer mechanisms in the same electrical machine 300, the flow of the ferrofluid within the chambers 250 can be increased, thereby improving heat transfer away from the end windings. Moreover, this improved heat transfer is achieved through normal operation of the electrical machine 300.

As an example, the stator of the electrical machine 300 may include an end plate 270 which may be formed of a thermally conductive material. In this way, the end plate 270 may provide at least a portion of a thermally conductive pathway to transfer heat away from the ferrofluid (and hence away from the end windings 225). For example, the electrical machine 300 may additionally include one or more cooling channels 280 (such as a water jacket), containing a cooling fluid such as water. The end plate 270 may provide a thermally conductive pathway between the ferrofluid and the cooling fluid, thereby diverting heat away from the ferrofluid and the end windings. By inducing active heat transfer within the electrical machine 300, the flow of the ferrofluid within the chamber 250 is increased, and the rate of heat transfer from the ferrofluid to the end plate 270 is increased.

While an electrical machine such as the electrical machine 200 shown in Figure 2 may, in some implementations, produce a weak magnetic field in the vicinity of the ferrofluid, the axial overlap of the one or more magnets 210 and the chambers 250 significantly increases the strength and uniformity of the magnetic field to reliably induce active heat transfer in a manner that is not achieved by the electrical machine 200 of Figure 2.

As a result of the techniques described herein, cooling of the end windings 225 of the electrical machine 300 can be improved. As such, the presence and formation of hotspots in the stator coils 220 can be reduced, thereby providing a more reliable electrical machine. Moreover, with this increased reliability it is possible to operate the electrical machine 300 at higher currents/torques without increased risk of heat-related failures, and as such the overall performance (i.e. output current/torque) of the electrical machine 300 can be improved.

This axial overlapping of the magnets and the ferrofluid-filled chambers can take many forms, with Figure 3 being only one example implementation. In particular, in Figure 3 the axial length of the magnets 210 is chosen such that the magnets 210 extend across and beyond the central winding region and overlap axially with the chambers 250. However, the rotating magnetic field in the vicinity of the chambers 250 described can be achieved in a number of ways.

Figure 4 shows an example electrical machine 400 where the rotor includes one or more first magnets 210 and one or more second magnets 310 distinct from the first magnets 210. The second magnets 310 are located so as to axially overlap with the chambers 250, while the first magnets 210 may or may not partially overlap with the chambers 250. By having distinct first and second magnets, various advantageous implementation options are available. As just one example, the first and second magnets may be chosen to be different magnets, where the first magnet 210 may have a different magnetic coercive force than the second magnet 310. As an example, the first magnet 210 may be a high coercive force magnet, such as NbFeB, while the second magnet 310 may be formed of a ferrite material with low coercive force. Lower coercive force magnets are generally lower in cost, and as such this approach can provide cost-saving benefits.

Furthermore, as shown in Figure 5, in an example electrical machine 500, the one or more second magnets 310 may be mounted to the rotor shaft via one or more reduction gears 320. In this way, the second magnets 310 may be arranged to rotate at a lower rotational velocity than the first magnets 210. This may be advantageous, for example, when a comparatively high viscosity ferrofluid is used within the chambers 250, as the ferrofluid may be comparatively slow to respond to the rotating magnetic field caused by the second magnets 310. If the second magnets 310 were to rotate at the same rate as the first magnet 210, the flow of the ferrofluid within the chambers 250 may be reduced as compared to when the second magnets 310 rotate slower than the first magnet 210.

In some examples, the second magnets 310 may have a different (for example fewer) number of magnetic poles to the first magnet 320. For example, the first magnet 210 may be provided with a total of 8 poles (4 North poles and 4 South poles), however the second magnets may be provided with fewer poles, such as 4 poles (2 North poles and 2 South poles). Providing second magnets 310 with fewer poles provides a similar effect to the use of a reduction gear, namely a rotating magnet field that changes less rapidly. Accordingly, higher viscosity ferrofluids may be more responsive in this arrangement.

The aforementioned examples are all illustrated with internal rotor electrical machines, however it should be understood that the above-described approaches are generally applicable to substantially any type and style of electrical machine. Figure 6 shows an electrical machine 600 including an external rotor (i.e. a rotor located further from the axis of rotation than the stator). The electrical machine 600 includes a stator hub 640 to which stator windings 620 are mounted. The stator windings 620 include end windings 625, where the end windings 625 are located within one or more chambers 650 containing a ferrofluid. The electric machine 600 includes a rotor body 630 to which one or more magnets are mounted.

The one or more magnets may include a first magnet 610 and a second magnets 615 On a similar manner to the electrical machine 400 of Figure 4), where the second magnets 615 are optionally mounted to the rotor body 630 via reduction gears 670 (in a similar manner to the electrical machine 500 of Figure 5), or where the second magnets 615 are provided with a different number of magnetic poles to the first magnet 610. The electrical machine 600 may additionally or alternatively include a magnet having an axial length that is longer than the central winding region of the stator windings 620 so as to axially overlap the one or more chambers 650 and/or the end windings 625, in a similar manner to the electrical machine 300 of Figure 3. As such, the techniques of the present disclosure are applicable to substantially any electrical machine arrangement.

For example, the techniques of this disclosure are described above in reference to magnets mounted on a rotor, with a stator including windings located within a ferrofluid-filled chamber.

However, any arrangement of electrical machine components (i.e. stator and rotor) is envisioned. For example, magnets (i.e. permanent magnets or windings/coils) may be mounted to a stator, with the rotor including rotor windings located within a ferrofluid-filled chamber, in a similar manner as described above. As such, the techniques of this disclosure can be applied at least to: stator permanent magnet (PM) synchronous electrical machines (including e.g. switched flux PM machines, flux reversal PM machines, double salient PM machines, and biased flux PM machines, corresponding to the electrical machines with permanent magnets located in the stator yoke/tooth/slot opening), stator wound-field synchronous electrical machines (where stator permanent magnets are replaced by DC coils) and stator hybrid excited electrical machines (including both DC-excited and stator PM-excited electrical machine), as well as other flux modulation machines with PMs in both/either the stator and rotor.

This general applicability of the invention to any type of electrical machine also extends beyond rotary electrical machines. For example, the techniques of this disclosure can be equally applied to linear electrical machines. Figure 7 shows an example linear electrical machine 700 according to a teaching of the disclosure. The electrical machine 700 includes a stator 710 and a mover 730. In use, the mover 730 moved along a length direction of the electrical machine 700, which in Figure 7 is into/out of the page.

The stator 710 includes a stator housing 712 in which some or all of stator windings 718 are located. Stator windings 718 may be mounted on the stator 710 via a stator yoke 724, which may include stator teeth 722, around which the stator windings 718 are coiled. The stator teeth 722 may extend in a height direction of the electrical machine 700, which in Figure 7 is the up-down direction. The stator windings 718 may include a central winding region 714 and an end winding region 716. The central winding region 714 may be the portion of the stator windings 718 that overlaps the stator teeth 722 in a width direction (left-right direction in Figure 7), while the end winding 716 may be the portion of the stator windings 718 that does not overlap the stator tooth 722 in the width direction of the electrical machine 700. However, other definitions of the central winding region 714 and end windings 716 are possible. For example, the central winding region 714 may be encased within one or more laminations (not shown), in a similar manner to the central winding regions of Figures 3-6, where the end winding 716 is the region of the stator windings 718 that is not encased by the laminations.

The stator 710 further includes one or more chambers 720 which may be defined by the housing 712. At least the end winding region 716 of the stator windings 718 is located within the chambers 720, however some or all of the central winding region 716 may also be located within the chambers 720 in some implementations. The chambers 720 contain (e.g. are filled with) a ferrofluid. The ferrofluid is heated by the end windings 716 in use, however this heating will not be perfectly uniform and as such, a temperature gradient will be created within the ferrofluid, causing varying magnetic susceptibility within the ferrofluid. The presence of the temperature gradient and leakage magnetic flux gradient results in a Kelvin body force in the ferrofluid, leading to thermomagnetic convection. Thus, the ferrofluid flows within the chamber 720 and is able to divert heat way from the end windings 716.

The mover 730 includes a mover housing 732, permanent magnets 736, and a mover yoke 734 which mounts the permanent magnets 736 to the mover housing 732. The permanent magnets 736 are arranged along a length direction of the electrical machine 700 (i.e. into/out of the page). The permanent magnets 736 are arranged to have alternating poles in the length direction of the electrical machine 700. While the present example uses permanent magnets, it is appreciated that in other implementations other types of magnet may be used, such as mover windings which produce a magnetic field in the presence of an electrical current. Furthermore, the mover may include a combination of mover windings and permanent magnets in some implementations.

In use, the stator windings 718 may be provided with an electrical current which in turn creates a moving magnetic field, causing an electromotive force on the permanent magnets 736. As a result, the mover 730 is made to move in a linear direction of the electrical machine 700, as would be understood by the person skilled in the art. Various stator winding 718 arrangements are possible which may produce a moving magnetic field in order to induce the electromotive force, as would be appreciated by the person skilled in the art, such as three-phase winding arrangements, concentrated three-phase winding arrangements, and double stator arrangements. The techniques of this example are applicable to substantially any form of linear electrical machine, such as planar linear electrical machines such as that shown in Figure 7, or rotationally symmetric linear electrical machines.

In the electrical machine 700 of Figure 7, the permanent magnets 736 have a width that is greater than the width of the central winding region 714 of the stator windings 718. As such, the permanent magnets 736 overlap the one or more chambers 720 (or the end windings 716) in a width direction of the electrical machine 700. As a result, a moving magnetic field is produced in the vicinity of the ferrofluid within the chambers 720, thereby further inducing the flow of the ferrofluid within the chambers 720.

In particular, in the electrical machine 700 of Figure 7, passive heat transfer occurs as the ferrofluid flows between the end windings 716 and the stator housing 712 primarily along the width direction (and to a lesser extent height direction) of the electrical machine 700 as a result of thermomagnetic convention. In addition, in the electrical machine 700 active heat transfer occurs as the additional moving magnetic field produced by the permanent magnets 736 produces force on the ferrofluid which induces additional flow of the ferrofluid in a length direction of the electrical machine 700. By combining both passive and active heat transfer mechanisms in the same electrical machine 700, the flow of the ferrofluid within the chambers 720 can be increased, thereby improving heat transfer away from the end windings 716. Moreover, this improved heat transfer is achieved through normal operation of the electrical machine 700.

As with rotary electrical machines, these techniques for inducing both passive and active heat transfer can take multiple forms. For example, Figure 8 shows an electrical machine 800 with an alternative permanent magnet arrangement. Specifically, the mover 830 of the electrical machine 800 includes central permanent magnets 836 and edge permanent magnets 838. The edge magnets 838 are located so as to overlap with the chambers 720 in a width direction, while the central magnets 836 may or may not partially overlap with the chambers 720. By having distinct central and edge magnets, various advantageous implementation options are available, as described above in relation to Figures 4 and 5.

As just one example, the central and edge magnets may be chosen to be different magnets, where the central magnets 836 may have a different magnetic coercive force than the edge magnets 838. Moreover, the number of poles of the central and edger magnets may be different. Figures 9A-C shows a top-down view of a number of arrangements for the central magnets 836 and edge magnets 838 of the rotor 830 of Figure 8. In Figures 9A-C, the length direction of the electrical machine 800 is the left-right direction, the width direction is the up-down direction, and the height direction is into/out-from the page.

In Figure 9A, the number of poles of the edge magnets 838 is equal to the number of poles of the central magnets 836. In contrast, in Figure B, the number of poles of the edge magnets 838 is less than the number of poles of the central magnets 836. This arrangement increases the extent of active heat transfer when the electrical machine 800 operates at comparatively high-speeds. Figure 9C shows an arrangement where the number of poles of the edge magnets 838 is greater than the number of poles of the central magnets 836. This arrangement increases the extent of active heat transfer when the electrical machine 800 operates at comparatively low-speeds.

Accordingly, the techniques described in this disclosure provide for improved cooling and performance benefits in substantially any form of electrical machine, whether rotary or linear.

Therefore, from one perspective there has been described an electrical machine including a stator and a rotor, comprising stator windings and rotor magnets respectively. The end windings of the stator windings are located within a chamber filled with a ferrofluid. The rotor magnets are arranged to overlap the end windings in an axial direction, causing the ferrofluid to flow within the chamber and providing active heat transfer away from the end windings.

Claims

CLAIMS1. An electrical machine comprising: a stator, the stator comprising: one or more stator windings comprising: a central winding region, and an end winding region, and one or more chambers in which the end winding region of the one or more stator windings are located, wherein the chamber comprises a ferrofluid; and a rotor, the rotor comprising: a rotor shaft, and one or more magnets mounted to the rotor shaft; wherein at least a portion of the one or more magnets is arranged to overlap, in an axial direction of the electrical machine, at least a portion of the one or more chambers in which the ferrofluid is located.
2. The electrical machine according to claim 1, wherein the one or more magnets includes one or more first magnets having an axial length that is greater than an axial length of the central winding region of the one or more stator windings.
3. The electrical machine according to claim 1 or claim 2, wherein the one or more magnets include one or more first magnets and one or more second magnets distinct from the one or more first magnets, wherein the one or more second magnets are arranged to overlap at least a portion of the one or more chambers in the axial direction of the electrical machine.
4. The electrical machine according to claim 3, wherein a magnetic coercive force of the one or more first magnets is greater than a magnetic coercive force of the one or more second magnets.
5. The electrical machine according to claim 3 or claim 4, wherein the one or more second magnets are each mounted to the rotor shaft via a reduction gear.
6. The electrical machine according to any of claims 3-5, wherein the one or more second magnets are arranged to rotate at an angular velocity that is lower than an angular velocity of the one or more first magnets.
7. The electrical machine according to any of claims 3-6, wherein the one or more first magnets and the one or more second magnets have respectively different numbers of magnetic poles.
8. The electrical machine according to any preceding claim, wherein the stator comprises one or more end plates forming axial ends of the one or more chambers, wherein the end plate forms at least a part of a thermally conductive pathway to transfer heat away from the ferrofluid.
9. The electrical machine according to claim 8, wherein the stator further comprises one or more cooling channels comprising a cooling fluid, and wherein the one or more end plates provide a thermally conductive pathway between the ferrofluid and the cooling fluid within the one or more cooling channels.
10. The electrical machine according to any preceding claim, wherein the central winding region of the one or more stators is enclosed by one or more laminations.
11. The electrical machine according to any preceding claim, wherein the one or more magnets include one or more permanent magnets.
12. The electrical machine according to any preceding claim, wherein the one or more magnets include one or more electrical windings configured to carry an electrical current.
13. The electrical machine according to any preceding claim, wherein the stator is arranged further from the axis of rotation of the electrical machine than the rotor.
14. The electrical machine according to any of claims 1-12, wherein the rotor is arranged further from the axis of rotation of the electrical machine than the stator.
15. An electrical machine comprising: a first component, the first component comprising: one or more windings comprising: a central winding region, and an end winding region, and one or more chambers in which the end winding region of the one or more windings are located, wherein the chamber comprises a ferrofluid; and a second component, the second component comprising: one or more magnets; wherein at least a portion of the one or more magnets is arranged to overlap, in an axial direction of the electrical machine, at least a portion of the one or more chambers in which the ferrofluid is located, and wherein the first component and the second component are different ones of a stator and a rotor configured to rotate relative to one another.
16. A linear electrical machine comprising: a stator, the stator comprising: one or more stator windings comprising: a central winding region, and an end winding region, and one or more chambers in which the end winding region of the one or more stator windings are located, wherein the chamber comprises a ferrofluid; and a mover arranged in use to move along a length direction of the electrical machine, the mover comprising: a plurality of magnets arranged in the length direction of the electrical machine, wherein the plurality of magnets are arranged to have alternating polarities in the length direction, and wherein the plurality of magnets includes a plurality of central magnets arranged to at least partially overlap a central winding region of the one or more stator windings; wherein at least a portion of the plurality of magnets is arranged to overlap, in a width direction of the electrical machine, at least a portion of the one or more chambers in which the ferrofluid is located.
17. The linear electrical machine according to claim 16, wherein the plurality of central magnets have a width that is greater than a width of the central winding region of the one or more stator windings.
18. The linear electrical machine of claim 16 or claim 17, wherein the plurality of magnets includes a plurality of edge magnets distinct from the plurality of central magnets, and wherein the plurality of edge magnets are arranged to overlap at least a portion of the one or more chambers in the width direction of the electrical machine.
19. The linear electrical machine according to claim 18, wherein a magnetic coercive force of the one or more central magnets is greater than a magnetic coercive force of the one or more edge magnets.
20. The linear electrical machine according to claim 18 or claim 19, wherein a number of poles of the plurality of edge magnets is different to a number of poles of the plurality of central magnets.