A rotor

Abstract

A rotor for a rotor assembly of an electric machine comprising a body 30 defining a magnet aperture 32, a permanent magnet 34 and a compressible component 40, where the compressible component surround

Description

TECHNICAL FIELD The present disclosure relates to a rotor. Aspects of the invention relate to a rotor, to a rotor assembly, to an electric machine, to a vehicle, to a method of assembling a rotor, and to a method of disassembling a rotor. BACKGROUND It is known to provide electric machine rotor assemblies comprising a body in vehicles. The body having a magnet aperture to receive a permanent magnet which is fixed into the magnet aperture by a bonding agent. The boding agent is provided along the whole length of the permanent magnet to secure it into the magnet aperture. Such arrangements securely hold the permanent magnet in place during the normal working life of the electric machine. However, on disassembly of the rotor assembly, for example for recycling, it can be difficult to remove the permanent magnet from the magnet aperture without causing damage to the permanent magnet (or a coating of the permanent magnet). This can make recycling of the permanent magnet more difficult during subsequent processing should the permanent magnet have become damaged during removal. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a rotor, to a rotor assembly, to an electric machine, to a vehicle, to a method of assembling a rotor, and to a method of disassembling a rotor as claimed in the appended claims. According to an aspect of the present invention there is provided a rotor for a rotor assembly of an electric machine comprising: a body defining a magnet aperture, a permanent magnet and a compressible component; wherein the compressible component surrounds at least a portion of the permanent magnet, the permanent magnet and compressible component being received within the magnet aperture with at least a portion of the compressible component being located between the permanent magnet and a first wall of the magnet aperture, and the said at least a portion of the compressible component being compressed between the permanent magnet and the first wall to retain the permanent magnet in the magnet aperture. By utilising a compressible component the permanent magnet may be more securely retained within the magnet aperture without the need for an adhesive or bonding agent (such as glue) along the whole or a substantial portion of the length of the permanent magnet. The compressible component aids further by reducing the likelihood of the permanent magnet coming into contact with the side of the body which may be made up of solid material or a number of laminated sheets. As a permanent magnet used in a rotor of an electric machine may be, for example, of the NdFeBtype which typically have an epoxy or other coating, direct contact between the coating and the metallic rotor laminations can cause scratches in the coating. These scratches could lead to the exposure of the underlying NdFeB (if the magnet is an NdFeB type magnet) to the atmosphere which may cause premature degradation of the magnet by oxidation or ingress of water (for example). By utilising a compressible component less strict machining tolerances may be employed during manufacture of the body and permanent magnet. As the compressible component sits in use between the wall of the magnet aperture and the magnet it can compressibly deform to make up for any dimensional mismatch which may otherwise be solved by increasingly fine tolerances between the permanent magnet and magnet aperture. As a result a rotor assembly and electric machine incorporating such a rotor may be made more cheaply and efficiently and with reduced wastage. By utilising a compressible component the permanent magnet may be more easily removed from the rotor at the end of the useable life of the electric machine or vehicle into which it is incorporated compared to systems employing a bonding agent, such as glue, to retain the permanent magnet in place. As a result, the permanent magnet can be removed by means of a suitable force pushing on one end of the permanent magnet. The permanent magnet may then be recycled by means known in the art. Such an arrangement (compared to a glued in arrangement) enables easier recyclability of the body. Not least because: i) the permanent magnet can be slid out of the magnet aperture, ii) there is no need to dissolve large quantities of bonding agent, iii) the permanent magnet does not need to be machined out of the body, and iv) there is a reduced chance of damaging any coating of the permanent magnet during removal. According to an additional aspect of the present invention there is provided a rotor for a rotor assembly of an electric machine comprising: a body defining a magnet aperture, a permanent magnet and a compressible component; wherein the compressible component abuts at least a portion of the permanent magnet, the permanent magnet and compressible component being received within the magnet aperture with at least a portion of the compressible component being located between the permanent magnet and a first wall of the magnet aperture, and the said at least a portion of the compressible component being compressed between the permanent magnet and the first wall to retain the permanent magnet in the magnet aperture. The aspect has the advantages as described previously for the prior aspect. Additionally, or optionally, the rotor of the previously described aspects may further comprise additional features which will be described below. Optionally, the permanent magnet comprises a coating and a permanent magnetic material, the coating encapsulating the permanent magnetic material. The coating may be an epoxy coating. The coating may of a type known in the art commonly used with permanent magnetic materials. The permanent magnet may be any one of: a rare earth magnet, an NdFeB magnet, a SmCo magnet, a Ferrite magnet, an AINiCo magnet, a ceramic magnet, or any other suitable permanent magnetic material. The permanent magnet may be in a magnetised state or a demagnetised state. Optionally, the body comprises a group of laminations, the group of laminations together define the body. Optionally, the compressible component is either: removably connected to the permanent magnet, or fixedly attached to the permanent magnet. By removably connecting to the permanent magnet the compressible material can be separated more easily from the permanent magnet during recycling at the end of life. This may mean that components can be more readily sorted during recycling. By fixedly attaching the compressible component to the permanent magnet it may facilitate easier insertion of the permanent magnet and compressible component assembly into the magnet aperture. Fixedly attached may mean that the compressible component and permanent magnet are connected in such a manner that the two components cannot be removed without some form of destructive machining operation or substantial force or by some other means of disconnection (e.g. removal of a retaining clip or other such retaining fixture) to separate the two components. In other words, at the very least during insertion of the compressible component plus permanent magnet assembly, the two components may be inserted into a magnet aperture at the same time as a single unit. Fixedly attached may mean that the compressible component is: co-moulded / bonded / in-moulded / glued / fixed / attached / or otherwise fastened to the permanent magnet. Optionally, the compressible component is resiliently compressible. By utilising a resiliently compressible component the compressible component may be configured to return to its undeformed shape after insertion therefore providing a greater ability to retain the permanent magnet in the magnet aperture. Optionally, the compressible component extends across a first side of the permanent magnet. By extending across the first side of the permanent magnet the compressible component may reduce the likelihood of damage to any coating or surface of the permanent magnet in use. Optionally, wherein the compressible component further extends around at least a portion of a second side of the permanent magnet. By extending across the second side of the permanent magnet the compressible component may reduce the likelihood of damage to any coating or surface of the permanent magnet in use. Optionally, the compressible component has an L-shaped or U-shaped cross-section and the permanent magnet is located within the L-shaped or U-shaped cross-section. Provision of an L-shaped or U-shaped cross section in use may reduce the likelihood of damage to the permanent magnet and / or permanent magnet coating as at least a portion of the permanent magnet is cradled by the compressible component. Optionally, the compressible component is a sleeve, the sleeve having a cup configured to receive one end of the permanent magnet. Utilising a sleeve with a cup may make insertion of the permanent magnet into the magnet aperture easier on the assembly line. For example, the permanent magnet may be pre-inserted into the sleeve prior to placing at an assembly station for insertion into the magnet aperture. This reduces time at the assembly station. The sleeve may reduce the likelihood of the permanent magnet and compressible component becoming misaligned in use as the two components may be inserted together into the magnet aperture. Optionally, the compressible component at least partially encapsulates the permanent magnet. The compressible component encapsulating the permanent magnet may reduce the likelihood of the permanent magnet and compressible component becoming misaligned in use as the two components may be inserted together into the magnet aperture. The compressible component encapsulating the permanent magnet may reduce the likelihood of the permanent magnet surface becoming damaged during insertion, in use, and / or during removal. Optionally, the compressible component encapsulates the entire permanent magnet or a portion of the surface of the permanent magnet, the portion of the surface being 50 to 100% of the surface, 60 to 100% of the surface, 75 to 100% of the surface, 80 to 100% of the surface, 90 to 100% of the surface, or 100% of the surface. An increased surface covering may reduce the likelihood of damage of the permanent magnet in use. Optionally, the compressible component extends around 50% to 100% of the surface of the permanent magnet. This may reduce the likelihood of damage of the permanent magnet in use. Around the surface of the permanent magnet may mean that the compressible component extends around a peripheral surface of the permanent magnet. Optionally, the compressible component extends around: 60 to 100% or 75 to 100% or 80 to 100% or 90 to 100% or 100% of the surface of the permanent magnet. An increased surface covering may reduce the likelihood of damage of the permanent magnet in use. Optionally, wherein one or both ends of the permanent magnet and / or compressible component are connected by adhesive to the magnet aperture. By utilising a compressible component this may mean that adhesive (such as a bonding agent or glue) may only be required on the ends of the permanent magnet rather than along the entire length of the permanent magnet. Optionally, the adhesive may be a bead of adhesive. Optionally, the rotor may further comprise a second compressible component, the second compressible component surrounds at least a portion of the permanent magnet, such that, when the permanent magnet and second compressible component are received within the magnet aperture with at least a portion of the second compressible component being located between the permanent magnet and the first wall or a second wall of the magnet aperture, the said at least a portion the second compressible component is compressed between the permanent magnet and the first or second wall to retain the permanent magnet in the magnet aperture. The provision of a second compressible component may provide additional protection from damage to the surface of the permanent magnet during insertion, in use, and / or during removal. Optionally, the second compressible component may be any one of the previously described compressible components. The second compressible component may be the same, similar or different in configuration to the first compressible component. The second compressible component may component at least a portion of the first compressible component or the entirety of the first compressible component. Optionally, the rotor comprises a plurality of said bodies each with a magnet aperture, a permanent magnet and a compressible component, each of the bodies being axially located along a rotational axis of the rotor. The provision of a plurality of bodies can make assembly of the rotor easier as each of the bodies can be assembled separately and assembled to form a part of the rotor assembly. The plurality of bodies may be rotationally offset relative to each other. The plurality of bodies may be rotationally offset relative to each other such that the magnet apertures or a feature of the bodies are rotationally offset relative to each other. Optionally, each body comprises a group of laminations, the group of laminations together define the body and the magnet aperture being defined by the group of laminations. Optionally, the plurality of bodies may be rotationally aligned relative to each other. According to a further aspect of the invention, there is provided a rotor for a rotor assembly of an electric machine comprising: a plurality of bodies axially spaced along a rotational axis of the rotor, wherein each of the bodies define a magnet aperture, and each of the bodies has a permanent magnet and a compressible component; wherein the compressible component surrounds at least a portion of the permanent magnet, the permanent magnet and compressible component being received within the magnet aperture with at least a portion of the compressible component being located between the permanent magnet and a first wall of the magnet aperture, and the said at least a portion of the compressible component being compressed between the permanent magnet and the first wall to retain the permanent magnet in the magnet aperture. The present aspect has the advantages of the prior aspect. The present aspect may further comprise any embodiment of the previous aspect. According to a yet further aspect of the invention, there is provided a rotor assembly comprising the rotor of any embodiment of the preceding aspects and a rotor shaft defining a rotational axis of the rotor. A rotor assembly comprising the rotor provides the benefits as described above. Optionally, the body being disposed on the rotor shaft. According to an even further aspect of the invention, there is provided an electric machine comprising the rotor of any embodiment of any aspect describing a rotor or a rotor assembly of any embodiment of the previous aspect. An electric machine comprising the rotor or rotor assembly provides the benefits as described above. According to a yet even further aspect of the invention, there is provided a vehicle comprising the electric machine of the previous aspect. A vehicle comprising the electric machine provides the benefits as described above. According to a yet additional aspect of the invention, there is described method of assembling a rotor for a rotor assembly of an electric machine, the method comprising the steps of: providing a body defining a magnet aperture, a permanent magnet and a compressible component; wherein the compressible component surrounds at least a portion of the permanent magnet; and inserting the permanent magnet and compressible component into the magnet aperture with at least a part of the compressible component being located between the permanent magnet and a first wall of the magnet aperture so as to compress the compressible component such that the permanent magnet is retained within in the magnet aperture by the compressed compressible component. The method provides a methodology for fixing a permanent magnet within a magnet aperture of a rotor body without the need for adhesive to be employed as in prior systems, or where adhesive is used using the method only a small volume of adhesive may be utilised (for example a bead of adhesive at one or both ends of the permanent magnet). According to a yet even additional aspect of the invention, there is described a method of disassembling a rotor of a rotor assembly of an electric machine, the method comprising the steps of: providing a body defining a magnet aperture, a permanent magnet and a compressible component; wherein the compressible component surrounds at least a portion of the permanent magnet, the permanent magnet being retained within the magnet aperture by compression of the compressible component between the permanent magnet and a wall of the magnet aperture, and applying a force to the permanent magnet to move the permanent magnet and compressible component out of the magnet aperture. The methodology advantageously provides a technique for removal of permanent magnets which reduces the likelihood of damage to the permanent magnet as compared with prior methods which utilise machining steps to machine away the body or a cover or an adhesive which may cause damage to the surface of the permanent magnet. 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 anyway 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. 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 drawings, in which: Figure 1 shows a vehicle in accordance with an embodiment of the invention; Figure 2 shows a sub-system of the vehicle of Figure 1 in accordance with an embodiment of the invention; Figure 3 shows a rotor assembly in accordance with an embodiment of the invention; Figure 4 shows an end on view body of the rotor assembly in accordance with an embodiment of the invention; Figure 5A-5H show a section of the body of Figure 4 in accordance with embodiments of the invention; Figure 6A-6D shows a section of the body of Figure 3 in accordance with embodiments of the invention; Figure 7 shows a permanent magnet and compressible component being inserted into a magnet aperture in accordance with an embodiment of the invention; the permanent magnet and compressible component in a partially inserted position; and Figure 8 shows a method of assembling a rotor assembly in accordance with an embodiment of the invention. DETAILED DESCRIPTION A vehicle 1, an electric machine 12, rotor assembly 20, body 30 (also referred to as a rotor puck 30) will be described with the aid of Figures 1 to 8. As shown in Figure 1, the vehicle 1 is a wheeled passenger vehicle having a subsystem 10 and an optional charging port 6. The passenger vehicle 1 depicted is of the 4x4 or SUV type, however the vehicle 1 may be a car, a van, a light goods vehicle, or other such vehicle. A sub-system 10 of the vehicle 1 including a portion of a powertrain 2 comprising the electric machine 12 is shown in schematically in Figure 3 as well as an electrical storage means. The powertrain 2 comprises a propulsion system comprising at least one electrical machine 12 (also known as a prime mover). The electrical machine(s) 10 are selectively operable for the purpose of providing drive torque for accelerating the vehicle 1. In alternative configurations with two electric machines 12, the first electric machine 10 may provide drive to a front axle and the electric machine 12 may provide drive to a rear axle, or vice versa. Alternatively, each wheel may be driven by its own electric machine 12. In any of these embodiments the electric machine(s) 10 may be supplied electrical energy from electrical storage means 8. The electric machine 12 comprises the rotor assembly 20. The rotor assembly 20 will be discussed in more detail below. The vehicle 1 may be a fully electric vehicle having only an electric machine 12 as a power source for propulsion and no internal combustion engine or may be a hybrid vehicle having both an electric machine 12 and an internal combustion engine arranged to propel the vehicle 1. The electric machine 12 is powered by a battery which may be a traction battery or battery module. The vehicle 1 may be a plug-in hybrid electric vehicle (PHEV) or a mild hybrid electric vehicle (MHEV). It shall be appreciated that in alternative embodiments, the vehicle 1 may be a hydrogen electric vehicle (HEV) and hence the electric machine 12 may be powered by a hydrogen fuel cell arrangement comprising one or more hydrogen fuel cells. It shall be appreciated that the following description directed to a battery powered electric vehicle may also apply to a hydrogen electric vehicle. The at least one electric machine 12 comprises an electric traction motor. This is an electric motor arranged to convert electrical energy into kinetic energy in the form of mechanical torque and may also be arranged to convert kinetic energy into electrical energy. The electric traction motor may be an alternating current induction motor or a permanent magnet motor, or another type of suitable electric machine. The electric traction motor is a traction motor configured to enable at least an electric mode comprising electric-only driving. That is, the electric traction motor can drive the vehicle 1 by itself (without additional torque provided by a second torque source such as an engine). The electric traction motor may form part of an electric drive unit (EDU). The terms “electric traction motor” and “electric drive unit” may be used interchangeably throughout the present application. The EDU may be a 400 V EDU 10. A 400 V EDU is an EDU configured to provide drive at a supply voltage of 400 V alternating current. Alternatively, the EDU may be an 800 V EDU. An 800 V EDU 10 is an EDU configured to provide drive at a supply voltage of 800 V alternating current. An 800 V EDU is a relatively high voltage EDU as compared to more standard 400 V EDUs, 800 V EDUs can as a result provide greater power and at the same time be connected to batteries which charge more quickly. In order to store electrical energy for the electric machine 12, the vehicle 1 comprises an electrical energy storage means 8. The electrical energy storage 8 means may be a traction battery 8. The traction battery 8 provides a nominal voltage required by electrical power users such as the electric machine 12. The traction battery 8 may be a high voltage battery. The traction battery 8 may have a voltage and capacity to support electric only driving for sustained distances. The traction battery 8 may have a capacity of several kilowatt-hours, to maximise range. The capacity may be in the tens of kilowatt-hours, or even over a hundred kilowatt-hours. The traction battery 8 may be charged using a charging port 6 located on the vehicle as shown schematically in Figure 1. The traction battery 8 may also be charged by the conversion of kinetic energy into electrical energy by the electric machine 12. In alternative configurations there may be additional electrical storage means 8 located in different points of the vehicle 1 each of the electrical storage means 8 providing electrical energy to electric machine 12. An inverter 14 may be provided to convert between the direct current (DC) output of the traction battery 8 and the alternating current (AC) input required for the electric machine 10. For example, the DC output may be converted to a three-phase electrical power AC input, or a two-phase electrical power AC input. The EDU may therefore be a three-phase traction motor or a two-phase traction motor as appropriate. The rotor assembly 20 will now be described in more detail with respect to the appended Figures 1 to 6D. The rotor assembly 20 forms part of the electric machine 12, for reasons of clarity the rotor housing, windings and other components associated with the electric machine 12 have been omitted from the Figures. An embodiment of the rotor assembly 20 is depicted schematically in Figure 3. The rotor assembly 20 comprises at least one body 30. The body 30 defines a magnet aperture 32. The rotor assembly 20 also comprises a permanent magnet 34 and a compressible component 40A-G. As shown in Figure 3 the body 30 is disposed on a rotor shaft 22 which defines a rotational axis of the rotor R about which the rotor assembly 20 is configured to turn in use. In the depicted embodiment of Figure 3, the rotor assembly 20 comprises a plurality of bodies. In this example five bodies. However, there may be any number of bodies 30. For example, there may be one body 30, two bodies 30, three bodies 30, four bodies 30, five bodies 30, six bodies 30, seven bodies 30, eight bodies 30, nine bodies 30, or ten bodies 30, or any range or subset thereof. There may be one to ten bodies 30, two or more bodies 30, two to ten bodies 30 or two to five bodies 30. The bodies 30 may cast or machined from a billet as known in the art. For example, the bodies may be made of an aluminium alloy, or steel alloy, or other suitable alloy. Alternatively, the bodies 30 may be made up of a plurality of layers stacked together to form the body 30. As shown in Figure 4 each body 30 may have a shaft aperture 36 and a slot 38. The slot 38 is configured to receive a key or extension on the rotor shaft 22 (not depicted) to aid in securing the body 30 to the rotor shaft 22. Optionally, there may be a second slot 38 offset from the other slot 38 by 180 degrees. In such an embodiment there may be a second corresponding key on the shaft 22. Alternatively, the slot(s) may be located on the shaft 22 and the key(s) may be located on the body 30. The magnet aperture 32 is a through hole which extends through the body 30 from a first side to a second side of the body 30. Whilst the depicted magnet apertures 32 are shown as oblongs or circles in Figures 3 to 5F they may be of any shape or configuration suitable for receipt of a permanent magnet 34 and a compressible component 40. The oblong shape is not intended to be limiting but merely to aid in teaching the invention. There may be at least one magnet aperture 32, or a plurality of magnet apertures 32. There is a corresponding permanent magnet 34 and compressible component 40 for each of the magnet apertures 32. The permanent magnet 34 may be any one of: a rare earth magnet, an NdFeB magnet, a SmCo magnet, a Ferrite magnet, an AINiCo magnet, a ceramic magnet, or any other suitable permanent magnetic material. The permanent magnet 34 may be in a magnetised state or a demagnetised state in the body 30. Where it is in a demagnetised state the whole body 30 (or rotor assembly 20) and the permanent magnets 34 contained therein may be subsequently magnetised together. This may reduce the likelihood of assembly error where an assembler inserts a magnetised permanent magnet 34 in an incorrect orientation into the body 30. Whilst not depicted, there may be additional apertures defined by the body 30 for the purpose of cooling or weight saving, and / or balancing, for example, as known in the art. The compressible component 40A-G may be made of a polymer or polymer blend. For example, the polymer may be nylon or polyurethane or polyamide. Figure 4 shows a schematic end on view of one of the bodies 30 of the rotor assembly 20. As can be seen from Figure 4, there are four magnet apertures 32 in the depicted embodiment, as previously described this number is not intended to be limiting but to teach the invention. In practice there may be a greater number of magnet apertures 32, for example two to one hundred magnet apertures 32, or ten to fifty magnet apertures 32, or twelve to forty-eight magnet apertures 32, or any range or subset thereof. Each of the permanent magnets 34 and compressible component 40, as shown in Figure 4, are received within the magnet aperture 32 with at least a part of the compressible component 40 being located between the permanent magnet and a first wall 42 of the magnet aperture 34. This is shown in more detail in Figure 5A which is a zoomed in view of a section S of the body 30 shown in Figure 4. Figure 5A shows one embodiment of the invention, Figures 5B to 5F show alternative embodiments of the invention. As will be apparent to the skilled reader the rotor assembly 20 may comprise one or a more of the different configurations depicted in Figures 5A to 5F where more than one magnet aperture 32 is provided in the rotary assembly 20. Alternatively, all of the permanent magnets 24 may be retained in the same fashion using any one of the configurations of Figures 5A to 5F. Figure 6A shows the embodiment of Figure 5A in cross-section of section T shown in Figure 3. As can be seen the compressible component 40A and the permanent magnet 34 extend between the first side 33 and second side 35 of the body 30 such that the compressible component 50A and permanent magnet 34 are flush with the first and second sides 33, 35 of the body 30. Alternatively, one or both of the compressible component 50A and permanent magnet 34 may not be flush with the body 30 side 33 or side 35. In such a configuration one or both ends of the permanent magnet 34 and / or compressible component 40A may be offset from the first or second side 33, 35 by an offset distance. As shown in Figure 6A compressible component 40A is located between the first wall 42 and the permanent magnet 34. Figure 5B shows a different configuration for retaining a permanent magnet 34 in the magnet aperture 32. In the depicted embodiment there are two compressible components 40A and 40B. The first compressible component 40A is retained between the permanent magnet 34 and the first wall 42. The second compressible component 40B is retained between the permanent magnet 34 and a second wall 44 of the magnet aperture 32. Figure 6B shows the embodiment of Figure 5B with two compressible components 40A, 40B in cross-section of section T shown in Figure 3. As can be seen the compressible components 40A, 40B and the permanent magnet 34 extend between the first side 33 and second side 35 of the body 30 such that the compressible components 40A, 40B and permanent magnet 34 are flush with the first and second sides 33, 35 of the body 30. Alternatively, one or both of the compressible components 40A, 40B and permanent magnet 34 may not be flush with the body 30 side 33 or side 35. In such a configuration one or both ends of the permanent magnet 34 and / or compressible components 40A, 40B may be offset from the first or second side 33, 35 by an offset distance. As shown in Figure 6A compressible component 40A is located between the first wall 42 and the permanent magnet 34. The second compressible component 40B is located between the second wall 44 and the permanent magnet 34. Figure 5C shows a different configuration for retaining a permanent magnet 34 in the magnet aperture 32. In the depicted embodiment an alternative compressible component 40C is used. In this embodiment the compressible component 40C surrounds the entire periphery of the permanent magnet 34. In this embodiment the compressible component 40C may be a sleeve. The compressible component 40C is located between the side wall 42 and the permanent magnet 34. In this configuration one or both ends of the permanent magnet may not be covered by the compressible component 40C such that the permanent magnet 34 is visible from. Figure 6C shows the embodiment of Figure 5C with the compressible components 40C in cross-section of section T shown in Figure 3 viewed from the second side 34. Alternatively Figure 5C shows the compressible component 40H side on where compressible component 40H is does not cover the permanent magnet 34 and is open at the second side 32. As can be seen the compressible components 40C, 40H and the permanent magnet 34 extend between the first side 33 and second side 35 of the body 30 such that the compressible components 40C, 40H and permanent magnet 34 are flush with the first and second sides 33, 35 of the body 30. Alternatively, one or both of the compressible components 40C, 40H and permanent magnet 34 may not be flush with the body 30 side 33 or side 35. In such a configuration one or both ends of the permanent magnet 34 and / or compressible components 40C, 40H may be offset from the first or second side 33, 35 by an offset distance. As shown in Figure 6C a first portion of the compressible component 40C, 40H is located between the first wall 42 and the permanent magnet 34. A second portion of the compressible component 40C, 40H is located between the second wall 44 and the permanent magnet 34. Figure 5D shows a different configuration for retaining a permanent magnet 34 in the magnet aperture 32. In the depicted embodiment an alternative compressible component 40D is used. In this embodiment the compressible component is configured to be located along a side. Figure 5E shows a different configuration for retaining a permanent magnet 34 in the magnet aperture 32. In the depicted embodiment an alternative compressible component 40E is used. The compressible component 40E is substantially C-shaped or U-shaped in cross section as shown in Figure 5E. The C-shaped or U-shaped compressible component 40E receives a side wall of the permanent magnet 34. The arms of the C-shaped or U-shaped compressible component 40E extend along a portion of the upper and / or lower surfaces (relative to the view in Figure 5E) of the permanent magnet 34. Figure 5F shows a different configuration for retaining a permanent magnet 34 in the magnet aperture 32. In the depicted embodiment an alternative compressible component 40F is used. The compressible component 40F is substantially L-shaped as shown in Figure 5F. The compressible component 40F is located between the sidewall of the magnet aperture 32 and the permanent magnet 34. Figure 5G shows a different configuration for retaining a permanent magnet 34 in the magnet aperture 32 that is similar in configuration to the embodiment of Figure 5E. The compressible component 40F is similar to the compressible component 40E however, the arms extend across the whole upper and lower surfaces of the permanent magnet 34. Figure 6B shows a cross-sectional view through the configuration of the embodiments of Figures 5B, 5C, 5E or 5G. As will be apparent to the skilled reader, where there is a C-shaped or U-shaped compressible component 40E, 40G it will appear in cross-section in the same manner. Figure 5H shows a different configuration for retaining a permanent magnet 34 in the magnet aperture 32 that has a permanent magnet 34 partially or completely encapsulated by the compressible component 40H. One end of the permanent magnet 34 may be uncovered or partially uncovered as in Figure 5C. In this Figure the permanent magnet 34 is represented by the dashed lines as it is contained, at least partially, within the compressible component 40H. Figure 6D shows the embodiment of Figure 5H in cross-section of section T shown in Figure 3. As can be seen the compressible component 40H extends between the first side 33 and second side 35 of the body 30 such that the compressible component 50A is flush with the first and second sides 33, 35 of the body 30. Alternatively, one or both sides of the compressible component 50A may not be flush with the body 30 side 33 or side 35. In such a configuration one or both ends of the compressible component 40H may be offset from the first or second side 33, 35 by an offset distance. As shown in Figure 6D at least a first portion of the compressible component 40H is located between the first wall 42 and the permanent magnet 34. A second portion of the compressible component 40H is located between the second wall 44 and the permanent magnet 34. For any of the previously described compressible components 40A-H the compressible component 40A-H may optionally have at least one chamfered edge. The chamfered edge may be on a leading edge of the compressible component 40A-H. The leading edge 40A-H may be the edge of the compressible component 40A-H that is inserted into the magnet aperture 32 first. The chamfered edge may aid in alignment and reduce friction during the initial insertion of the compressible component 40A-H into the magnet aperture 32. A method of assembling a rotor for a rotor assembly 20 will now be described with the aid of Figures 7 and 8. Figure 7 shows a section T of the body 30 with the permanent magnet 34 and compressible component 40A in a partially inserted position. The permanent magnet 34 and compressible component 40A are being inserted into the magnet aperture 32 by a force F. The force F may be provided by a press to press fit the permanent magnet 34 and compressible component 40A into the magnet aperture. Alternatively, the force F may be provided by manual tools or the like. The force F may be in the range of 0.1 to 5 kN. As can be seen in Figure 7 the compressible component 34 is being compressed from a first thickness D1 to a second thickness D2 as the compressible component is being compressed into the magnet aperture 32 with the permanent magnet 34. Whilst Figure 7 shows an arrangement with a compressible component 40A it is envisioned that each of the depicted embodiments of compressible components 40A to 40H may be inserted into a body 30 in the same fashion. In any of the previously described embodiments the permanent magnet 34 and / or compressible component 40A to 40G may be connected by adhesive to the magnet aperture 32. The adhesive may be a bonding agent or glue known in the art. The adhesive may only be required on the ends of the permanent magnet 34 rather than along the entire length of the permanent magnet 34 and as such may be a bead of adhesive. The use of a compressible component 40A to 40G reduces the volume of adhesive required (or removes the need for adhesive) as compared to prior systems. Figure 8 shows a flowchart 100 with method steps describing a method of assembling a rotor for a rotor assembly 20 of an electric machine 12. The method comprises the steps 110 to 130. At step 110a body 30 defining a magnet aperture 32, a permanent magnet 34 and a compressible component 40A are provided. The compressible component 40A surrounds at least a portion of the permanent magnet 34. At step 120 the permanent magnet 34 and compressible component 40A are placed or located adjacent to the magnet aperture 32. Subsequently at step 130 the permanent magnet 34 and compressible component 40A are inserted into the magnet aperture 32 with at least a part of the compressible component 40A being located between the permanent magnet 34 and a first wall 42 of the magnet aperture 32 so as to compress the compressible component 40A such that the permanent magnet 34 is retained within in the magnet aperture 32 by the compressed compressible component 40A. The permanent magnet 34 and compressible component 40A are inserted by action of the force F. During the compression the compressible component 40A compresses from a first depth D1 to a second depth D2. The force F may be applied until the compressible component 40A and permanent magnet 34 are completely inserted into the magnet aperture 34 as previously described. As will be apparent alternative compressible components 40B, 40C, 40D, 40E, 40F, 40G or40H may be utilised instead of compressible component 40A. Optionally, or alternatively, the permanent magnet 34 and compressible component 40A may be inserted into the magnet aperture 32 separately as will be described below. The permanent magnet 34 may be first inserted into the magnet aperture 32. Subsequently, the compressible component 40A may then be inserted into the gap between the permanent magnet 34 and one or more walls of the magnet aperture 34. Optionally, the compressible component 40A may be inserted into the magnet aperture 32 whilst, at the same time, the permanent magnet 32 is prevented from moving out of the magnet aperture 32. This may be achieved by the means of placing a surface or blocking part against the opposite opening of the magnet aperture 34 in respect of the opening which the compressible component 40A is being pushed into. Alternatively, additionally, or optionally, the permanent magnet 34 may be retained in place by means of a bead of adhesive to prevent movement of the permanent magnet 34 during insertion of the compressible component 40A. To aid insertion of the compressible component 40Athe compressible component may be made from a material, such as polyamide, which has a relatively high stiffness as compared to other similar polymers. Alternatively, additionally, or optionally, the compressible component 40A maybe supported during insertion into the magnet aperture 32 to reduce the likelihood of buckling or bending of the compressible component 40A during assembly. The support may be provided by a supporting component or supporting device which may aid in aligning of the compressible component 40A and the gap between the magnet aperture 32 and the permanent magnet 34. As will be apparent alternative compressible components 40B, 40C, 40D, 40E, 40F, 40G or40H may be utilised instead of compressible component 40A. As will be apparent to the skilled reader, where the rotor comprises a plurality of magnet apertures 32 the permanent magnet 32 and compressible components 40A may be inserted into the magnet aperture 32 in any previously described fashion. A method of disassembling a rotor of a rotor assembly 20 of an electric machine 12 is also described. The method enables easier removal of permanent magnet 34 and compressible component 40A for the purpose of recycling. The method comprises the steps of: providing a body 30 defining a magnet aperture 32, a permanent magnet 34 and a compressible component 40A. The compressible component 40A surrounds at least a portion of the permanent magnet 34 with the permanent magnet 34 being retained within the magnet aperture 32 by compression of the compressible component 40A between the permanent magnet 34 and a wall 42 of the magnet aperture 32. The method further comprises the step of applying a force F to the permanent magnet to move the permanent magnet 34 and compressible component 40A out of the magnet aperture 32. The force F may be the same force used to insert the compressible component 40A and permanent magnet 34 into the magnet aperture 32. The force F may be applied until the compressible component 40A and the permanent magnet 34 are partially or completely out of the magnet aperture 32. The compressible component 40A and the permanent magnet 34 may then be separated from each other and enter a recycling processing stream to recycle or reuse said components. As will be apparent alternative compressible components 40B, 40C, 40D, 40E, 40F, 40G or40H may be utilised instead of compressible component 40A. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application. NO. FEATURE D1 First Depth D2 Second Depth F Force 5 R Rotational Axis of the Rotor S Section of Body, Section of Rotor Puck T Section of Body, Section of Rotor Puck 1 Vehicle 2 Powertrain 10 6 Charging Port 8 Electrical Storage Means 10 Sub-system 12 Electric machine 14 Inverter 15 20 Rotor Assembly 22 Rotor Shaft 30 Body, Rotor Puck 32 Magnet Aperture 33 First Side 20 34 Permanent Magnet 35 Second Side 36 Shaft Aperture 38 Slot 40A-F Compressible Component 25 42 First Wall 44 Second Wall 46 Side Wall 100 Flow Chart 110 Step 30 120 Step 130 Step

Claims

1. A rotor for a rotor assembly of an electric machine comprising:a body defining a magnet aperture, a permanent magnet and a compressible component; wherein the compressible component surrounds at least a portion of the permanent magnet,the permanent magnet and compressible component being received within the magnet aperture with at least a portion of the compressible component being located between the permanent magnet and a first wall of the magnet aperture, andthe said at least a portion of the compressible component being compressed between the permanent magnet and the first wall to retain the permanent magnet in the magnet aperture.

2. The rotor of claim 1, wherein the compressible component is either:removably connected to the permanent magnet, orfixedly attached to the permanent magnet.

3. The rotor of any preceding claim, wherein the compressible component is resiliently compressible.

4. The rotor of any preceding claim, wherein the compressible component extends across a first sideof the permanent magnet.

5. The rotor of any of claims 1 to 4, wherein the compressible component has an L-shaped or U-shaped cross-section and the permanent magnet is located within the L-shaped or U-shaped cross-section.

6. The rotor of any of claims 1 to 5, wherein the compressible component is a sleeve, the sleeve having a cup configured to receive one end of the permanent magnet.

7. The rotor of any of claims 1 to 6, wherein the compressible component at least partially encapsulates the permanent magnet.

8. The rotor of any of claims 1 to 7, wherein the compressible component extends around 50% to 100% of the surface of the permanent magnet.

9. The rotor of any preceding claim, wherein one or both ends of the permanent magnet and / or compressible component are connected by adhesive to the magnet aperture.

10. The rotor of any preceding claim, further comprising a second compressible component, the second compressible component surrounds at least a portion of the permanent magnet,such that, when the permanent magnet and second compressible component are received within the magnet aperture with at least a portion of the second compressible component being located between the permanent magnet and the first wall or a second wall of the magnet aperture,the said at least a portion the second compressible component is compressed between the permanent magnet and the first or second wall to retain the permanent magnet in the magnet aperture,11. The rotor of any preceding claim, wherein the rotor comprises a plurality of said bodies eachwith a magnet aperture, a permanent magnet and a compressible component, each of the bodies being axially located along a rotational axis of the rotor.12, A rotor assembly comprising the rotor of any preceding claim and a rotor shaft defining arotational axis of the rotor.

13. An electric machine comprising the rotor of any of claims 1 to 11 or the rotor assembly of claim12.

14. A vehicle comprising the electric machine of claim 13.

15. A method of assembling a rotor for a rotor assembly of an electric machine, the methodcomprising the steps of:providing a body defining a magnet aperture, a permanent magnet and a compressible component; wherein the compressible component surrounds at least a portion of the permanent magnet; andinserting the permanent magnet and compressible component into the magnet aperture with at least a part of the compressible component being located between the permanent magnet and a first wall of the magnet aperture so as to compress the compressible component such that the permanent magnet is retained within in the magnet aperture by the compressed compressible component.19

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