Electric motor

Abstract

An electric motor, perhaps for an electric vehicle, comprising: a stator with coolant flow channels A (and 60, Fig. 9) extending from end to end; a housing having coolant inlets 22 and outlets 24; a f

Description

TECHNICAL FIELD The present disclosure relates to an electric motor. Aspects of the invention relate to an electric motor, a method of cooling an electric motor and to a vehicle. BACKGROUND The common construction of an electric motor is to have a stator core surrounding a rotor. The stator core is made up of thin metal sheets, called laminations, which are together often referred to as the lamination stack. The stator comprises a plurality of windings which are applied around the lamination stack. When current is applied to the windings, a magnetic field is created which generates a force to act on the rotor to drive it. It is a problem in electric motors that the heat generated in the windings as the current is applied needs to be dissipated. The heat passes through the coating on the windings, through varnish or resin applied to the stator core and into the lamination stack, increasing the temperature of the stator which is not desirable. It is known in existing electric motors to use coolant channels in the lamination stack to dissipate the heat. The coolant channels are defined near the outer circumference of the stator core and take some heat that is generated in the windings, and transferred to the lamination stack, away from the stator. However, the coolant channels are not in proximity to the windings and so the heat dissipation is not optimum, and there remains a need for improved cooling of the electric motor. The invention has been devised against this background to address heat generation in electric motors with electrical windings or hairpins. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide an electric motor comprising a rotor configured to rotate about an axis of rotation; and a stator comprising one or more coolant flow channels which extends from a first end of the stator towards a second end of the stator. The electric motor comprises a housing comprising one or more coolant inlets; and one or more coolant outlets, wherein the rotor and the stator are located within the housing. A first sleeve extends between the first end of the stator and a first portion of the housing, wherein the first sleeve, the first end of the stator and the first portion of the housing together define a first cooling chamber; and a second sleeve which extends between the second end of the stator and a second portion of the housing, wherein the second sleeve, the second end of the stator and the second portion of the housing together define a second cooling chamber. The first cooling chamber, the second cooling chamber and the one or more coolant flow channels are in fluidic communication with one another and together comprise a cooling system, wherein the one or more coolant inlets are configured to deliver coolant fluid to the cooling system in use, and wherein the one or more coolant outlets are configured to evacuate cooling fluid from the cooling system in use. In one embodiment, the first and / or second sleeve may have a constant diameter along at least a portion of its length. Alternatively, the first and / or second sleeve may have a variable diameter along at least a portion of its length. In this case flow into the cooling chambers is less likely to stagnate against the first and / or second sleeve because the shaping of the sleeve (e.g. a curved profile) encourages flow into the coolant flow channels. For example, at least a portion of the first and / or second sleeve may be curved in longitudinal profile. For example, the first and / or second sleeve may have a diameter which increases with distance from the rotor along at least a portion of its length. In embodiments of the invention, the cooling system may comprise one or more circumferential channel which extends around the circumference of the stator, wherein each circumferential channel is in fluidic communication with one or more of the one or more coolant flow channels. The one or more circumferential channel may comprise a groove located on the outermost surface of the stator. One or more of the coolant inlets may be configured to deliver coolant fluid to one of the first or second cooling chambers, and one or more of the coolant outlets are configured to evacuate coolant fluid from the other of the first or second cooling chambers. In embodiments, one or more of the coolant inlets may be configured to deliver coolant fluid to the one or more circumferential channel, and one or more of the coolant outlets are configured to evacuate coolant fluid from the first and second cooling chambers. Alternatively, or in addition, one or more of the coolant inlets may be configured to deliver coolant fluid to the first and second cooling chambers. In one example, one or more of the coolant inlets may be configured to deliver coolant fluid to the first and second cooling chambers, and one or more of the coolant outlets may be configured to evacuate or allow the passage of coolant fluid from the one or more circumferential channel. In one embodiment, the one or more of the coolant inlets may be located longitudinally in line with one or more of the coolant outlets when viewed from one end of the electric motor along the axis of rotation. Additionally, or alternatively, one or more of the coolant inlets may be located on the opposite side of the electric motor to one or more of the coolant outlets when viewed from one end of the electric motor along the axis of rotation. Additionally, or alternatively, one or more of the coolant inlets may be located on the opposite side of the electric motor to another one of the coolant inlets when viewed from one end of the electric motor along the axis of rotation. Additionally, or alternatively, one or more of the coolant inlets may be oriented at right angles to one or more of the coolant outlets when viewed from one end of the electric motor along the axis of rotation. Another aspect of the invention relates to a vehicle comprising an electric motor for providing a drive force for the vehicle, the electric motor being in accordance with the previous aspect of the invention. A still further aspect of the invention relates to a method of cooling the stator of an electric motor comprising introducing a liquid coolant into one or more flow channels located in the stator; a cooling chamber located at a first end of the stator; and a cooling chamber located at a second end of the stator, wherein introducing the liquid coolant comprises passing the coolant from one or both of the cooling chambers into one or more of the coolant flow channels, or passing the coolant from one or more of the coolant flow channels into one or both of the coolant chambers. It will be appreciated that preferred and / or optional features of one aspect of the invention may be incorporated alone or in appropriate combination in other aspects of the invention also. 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(a) is a schematic side view of an upper portion of an electric motor of a first embodiment of the invention, including a cooling system for the electric motor, and Figures 1(b) and (c) are a schematic end views of the electric motor in Figure 1(a), from opposite ends (the drive end and the non-drive end) of the electric motor; Figure 2 is a cross section view of the electric motor in Figure 1, to show the full extent of a stator core surrounding the rotor; Figure 3 is an enlarged view of one end of the stator core of the electric motor in Figure 2; Figure 4 is an enlarged perspective view of one end of the stator core of the electric motor in Figure 2; Figure 5 is a perspective view of one end of the stator core of the electric motor in Figure 2 to illustrate the lamination stack of the core and hairpins on the core; Figure 6 is an end view of the stator of the electric motor in Figure 2 to illustrate coolant channels of the cooling system; Figure 7 is an enlarged view of a portion of Figure 6, to better illustrate the coolant channels; Figure 8(a) is a schematic side view of a part of an electric motor of a second embodiment of the invention, and Figure 8(b) is a schematic end view of the electric motor in Figure 8(a); Figure 9 is a perspective view of the stator of Figure 8; Figure 10(a) is a schematic side view of a part of an electric motor of a third embodiment of the invention, and Figure 10(b) is a schematic end view of the electric motor in Figure 10(a); Figure 11 (a) is a schematic side view of a part of an electric motor of a fourth embodiment of the invention, and Figure 11 (b) is a schematic end view of the electric motor in Figure 11 (a); Figure 12(a) is a schematic side view of a part of an electric motor of a fifth embodiment of the invention, and Figure 12(b) is a schematic end view of the electric motor in Figure 12(a); Figure 13 is a schematic side view of a part of an electric motor of a sixth embodiment of the invention, to illustrate an alternative arrangement for sleeve components of the electric motor; and Figure 14 is an enlarged cross section view, similar to Figure 3, of one end of the stator core of the electric motor in Figure 13. DETAILED DESCRIPTION Embodiments of the invention provide an electric motor, having a rotor and a stator, in which a cooling system is provided to cool the stator, in use. The cooling system comprises one or more coolant flow channels which extend from a first end of the stator towards a second end of the stator. A housing for the rotor and the stator is provided with one or more coolant inlets and one or more coolant outlets. A sleeve is provided at each end of the stator. A first sleeve extends between the first end of the stator and a first portion of the housing and a second sleeve extends between the second end of the stator and a second portion of the housing remote from the first portion. The first portion of the housing and the first end of the stator together define a first cooling chamber and the second portion of the housing and the second end of the stator together define a second cooling chamber. The first cooling chamber, the second cooling chamber and the one or more coolant flow channels are in fluid communication with one another and together define the cooling system as cooling fluid introduced to the first cooling chamber, via a coolant inlet at one end of the stator, is able to flow through the coolant channels, towards the other end of the stator before evacuation through a coolant outlet. As the coolant flow passes along the stator, a cooling effect is achieved to counter the heating effect due to current flow through the windings of the stator. Referring more specifically to Figures 1(a), (b) and (c), an electric motor assembly of a first embodiment of the invention, referred to generally as 10, includes a stator core 12 which comprises a plurality of laminations arranged in a lamination stack and a rotor 14. It will be appreciated that Figure 1 only shows the upper part of the electric motor 10, showing only one part of the stator core 12 and the rotor 14, whereas in fact the stator core 12 extends fully around the rotor 14. The rotor 14 extends along an axis of rotation R-R through a central core of the stator core 12 between a first end 12a of the stator core 12 and a second, opposed end 12b of the stator core 12. The rotor 14 is shown schematically in Figure 1(a) to be contained entirely within the outer boundary of the stator core 12, but in practice projects beyond the ends of the stator core 12. The rotor 14 4 extends along an axis of rotation, R-R, which defines the central axis of the motor 10 and resides within a chamber comprising a first rotor chamber 18 at one end of the rotor 14 and a second rotor chamber 20 at the other end of the rotor 14. It will be appreciated that in Figure 1 only the upperpart of the first and second rotor chambers 18,20 is visible, whereas in fact the rotor chambers 18, 20 are annular and extend symmetrically about the axis A-A to the lower part of the electric motor also. The rotor 14 has a driving end and a non-driving end, although for the purpose of the illustration in Figure 1 either end could be the driven end and either end could be the non-driving end. The rotor 14 and the stator core 12 are located within an electric motor housing, referred to generally as 16. The housing 16 includes an upper portion 16a, a first end portion 16b, a second end portion 16b opposed to the first end portion 16b, and a further lower portion (not shown in Figure 1). The first and second housing-end portions 16a, 16b define first and second side walls, respectively, of the housing 16. The electric motor 10 has a cooling system including a plurality of coolant flow channels provided through a circumferential region of the stator core. In Figure 1(a) the coolant flow through the coolant flow channels is represented by the arrow, A. A coolant inlet 22 is provided in the upper portion of the housing 16a at one end of the stator (the second end 12b) and a coolant outlet 24 is provided in the housing 16 at the other end of the stator core (the first end 12a). The coolant inlet 22 is located longitudinally in line with the coolant outlets 24 when viewed from one end of the electric motor along the axis of rotation (as seen in Figures 1 (b) and 1 (c)). Considering initially the left hand end of the assembly in Figure 1(a) (i.e. the first end 12a of the stator core 12), a first cylindrical sleeve 30 extends between the first end of the stator core 12a and the first housing portion 16b. The full extent of the first sleeve 30 is not illustrated in the partial view of the electric motor in Figure 1(a), but it will be appreciated that the first sleeve 30 has an axis which is co-axial with the axis of rotation, R-R, of the rotor 14 and that it surrounds the rotor 14 entirely, so that the rotor extends through the first sleeve 30. A second sleeve 32 is provided at the second end of the stator core 12b and is essentially the same as the first sleeve 30 so will not be described in further detail. The first sleeve 30, the first housing-end portion 16b and the first end 12a of the stator core 12 together define a first cooling chamber 32 at the first end 12a of the stator core. A similar arrangement is provided at the other, second end 12b of the stator core 12. Here, the second cylindrical sleeve 32 extends between the second end 12b of the stator core 12 and the second housing-end portion 16c. As for the first sleeve 30, the second sleeve 32 extends entirely around the rotor 14 so that the axis of the second sleeve 32 is co-axial with the axis of rotation, R-R, of the rotor 14. The second sleeve 32, the second housing-end portion 16c and the second end 12b of the stator core 12 together define a second cooling chamber 42. The second cooling chamber 42 communicates with the coolant inlet 22 in the upper portion 16a of the housing 16. The first cooling chamber 40 communicates with the coolant outlet 24 in the upper portion 16a of the housing 16. The first and second cooling chambers 40, 42 communicate with each other via the plurality of coolant channels, represented by arrow A, in the stator core 12. As seen in Figures 1(b) and 1 (c), the coolant inlet 22 is located longitudinally in line with the coolant outlet 24 when viewed from one end of the electric motor along the axis of rotation, R-R. The first and second cooling chambers 40, 42 are annular chambers which extend to the lower part of the electric motor (not shown in Figure 1 (a), arranged symmetrically about the axis A-A. The construction of the stator core 12 and the rotor 14 within the housing 16 is described in more detail with reference to Figures 2 and 3. Here it can be seen that the rotor 14 projects beyond the ends of the stator core 12. The stator comprises a stator core 12 comprised of a stack of laminates arranged in a lamination stack 44, and a plurality of hairpin windings (or hairpins) 46 which are wound on and supported by the lamination stack 44. The hairpins 46 are rectangular conductive components to which a current is applied, in use, to generate the magnetic field which generates the force to drive the rotor 14 via the stator. Only a few of the hairpins 46 are visible in the illustration of Figure 3, but in practice many such hairpins 46 are used to provide optimum use of the space available around the lamination stack 44. In Figure 3, the lamination stack 44 is just visible through the hairpins 46 wound on, but can be seen more clearly in Figure 4. The hairpins 46 are mounted on the lamination stack 44 such that some extend beyond the end of the stack 44 into the first and second cooling chambers 40, 42. Relative to the motor axis R-R, the lamination stack 44 includes a radially outer circumferential region 44a and a radially inner circumferential region 44b. The radially inner circumferential region 44a defines an inner diameter of the stack 44 and the radially outer circumferential region defines an outerdiameterofthe stack 44. The radially outer circumferential region is provided with the coolant channels, as will be described in further detail below. The radially inner circumferential region is adjacent to the rotor 14 on the inner diameter. The stack 44 has an end lamination 48 which cooperates with one end of the first sleeve 30. The end lamination 48 defines the end surface of the stator core 12 which defines the first cooling chamber 32. The first sleeve 30 includes a first sleeve portion 30a towards one end of the sleeve and a second sleeve portion 30b towards the other end of the sleeve. The second sleeve portion 30b extends into the lamination stack 44. An adhesive (not shown) is applied at the interface of the lamination stack 44 with the second sleeve portion 30b to hold the first sleeve 30 in position at this end. At the other end of the first sleeve 30, a C-clip 52 is attached to the first sleeve portion 30a to mount the first sleeve 30 to an annular seal 50 which engages with the first end portion 16b of the housing 16. The annular seal 50 has a central axis which aligns with the motor axis R-R and has a rectangular cross section in side view (as in Figures 2 and 3). The annular seal 50 is compressed axially after the stator is assembled to the housing (16). The provision of the annular seal 50 on the first sleeve 30 ensures that no coolant can leak between the first cooling chamber 40 and the rotor chamber 18, hence sealing the first cooling chamber 40 from the rotor chamber 18. The radially outer diameter of the first sleeve 30 is substantially uniform along the axial length of the sleeve, as best seen in Figure 3, except for a small region of stepped diameter at the first sleeve end 30a which mounts to the annular seal 50. In other words, between the annular seal 50 and the lamination stack 44, the first sleeve 30 has a uniform outer diameter. The relative positions of the first sleeve 30, the annular seal 50 and the lamination stack 44 of the stator core 12 can be seen in more detail in Figure 4. Referring also to Figures 5 to 7, the outer circumferential region 44a of the lamination stack 44 is provided a plurality of axially-extending coolant channels 60 which extend along the length of the stack and provide a communication path between the first cooling chamber 40 at one end of the stator core 12 and the second cooling chamber 42 at the other end of the stator core 12. The channels 60 are arranged circumferentially around the radially outer region 44a of the stack 44 so that their axes extend parallel to one another, along the length of the lamination stack 44, and in parallel with the motor axis R-R. Each axially extending coolant channel 60 has a triangular cross section taken in a plane perpendicular to the motor axis, R, as best seen in Figures 6 and 7. Referring specifically to Figure 7, the triangular cross section of each coolant channel 60 is defined by a base 62 of the channel and two channel side walls 64. Each channel 60 is shaped so that the base 62 and the side walls 64 are of equal length, forming a triangular cross section of equilateral form. The coolant channels 60 are configured circumferentially around the stack 44 such that the bases of a first set 60a of alternate ones of the channels 60 face in one direction, radially inwards to the motor axis R-R, and the bases of a second set 60b of other alternate ones of the channels 60 face in the opposite direction, radially outwards from the motor axis R-R. Adjacent ones of the channels 80 are therefore facing in opposite directions. This alternating orientation of the triangular cross-section coolant channels 60 ensures that more channels can be provided (for example, compared to a single orientation of the channels) to give a higher surface area for the cooling effect. The cooling effect of the coolant as it flows through the channels 60 is therefore an optimum. Additionally, the alternating orientation of the channels gives enough tolerance for the manufacturing of the higher number of channels by maintaining a uniform gap between any two adjacent channels. The arrangement at the other end of the stator core 12 is the same for the second sleeve 32 which is provided to fluidly isolate the second cooling chamber 42 and the rotor chamber 18,20. The second sleeve 32 is supported on the lamination stack 44 in the same way as for the first sleeve 30, via adhesive at one end and via a second annular seal (not shown) to the housing end portion 16c. In use, coolant is introduced through the coolant inlet 22 into the second cooling chamber 42 and is able to flow through the coolant channels 60 in the lamination stack 44 towards the first cooling chamber 40. In so doing, heat that is generated upon a current being applied to the hairpin windings 46 is dissipated into the coolant, reducing the temperature of the stator core 12 which otherwise heats up via the current in the hairpin windings 46. Once coolant has entered the first cooling chamber 40 it is evacuated from the cooling system through the coolant outlet 24 in the housing to remove heat from the system. In an alternative arrangement the position of the coolant inlet 22 and the coolant outlet 24 may be reversed, so that the inlet 22 and the outlet 24 each may be at either the driving or the non-driving end of the rotor 14. In an alternative embodiment, as shown in Figures 8(a), (b) and Figure 9, the coolant inlet and coolant outlet in the housing 16 are configured differently. In this case a first coolant inlet 122 is provided in the upper housing portion 16a at a position corresponding to an approximate centre point of the axial length of the stator core 12. The lamination stack 44 is provided with a circumferential groove 126 (as shown in Figure 9) at the mid-point along its axial length to correspond to the position of the coolant inlet 122 so that the first coolant inlet 122 communicates with the circumferential groove 126 at a first communication point. Although not visible in Figure 8(a), an equivalent coolant inlet may be provided in a lower portion of the housing 16 to communicate with the circumferential groove at a diametrically opposite communication point to the first communication point. As coolant is introduced into the first coolant inlet 122 (and the equivalent coolant inlet in the lower part of the housing) it therefore flows into the circumferential groove 126 and along the axially-extending coolant channels 60, starting from the mid-point of the coolant channels 60, and flowing towards both the first cooling chamber 40 and the second cooling chamber 42 in two opposed directions. The coolant therefore flows away from the coolant inlet 122 through one half of each coolant channel in one direction and in the other half of each coolant channel in the other direction. First and second coolant outlets 124a, 124b are provided to communicate with the first and second cooling chambers, 40, 42, in the upper portion of the electric motor, so that coolant which flows into the firstand second cooling chambers 40, 42 is able to exit or evacuate from the housing 16 to dissipate heat within the stator core 12. Coolant therefore exits the motor from each of the first and second cooling chambers 40, 42 via the respective coolant outlet 124a, 124b. Third and fourth coolant outlets (not visible in the side view of Figure 8(a)) may be provided in the housing to communicate with the otherside of the cooling chambers 40,42, respectively, in the lower portion ofthe electric motor (i.e. the lower portion which is not visible in the side view of Figure 8(a)). The third coolant outlet 124c is visible in the end view of Figure 8(b). The third coolant outlet 124c is positioned in the housing 16 diametrically opposite to the first coolant outlet 124a. This is best illustrated when viewing the rotor 14 from one end along the axis of rotation, R-R, as in Figure 8(b). Figures 10(a) and 10(b) show a further alternative configuration in which first, second and third coolant inlets 222a, 222b, 222c are provided in the housing 16. The first coolant inlet 22a is positioned in the upper part pf the housing 16 at a central or mid-position along the axis R-R, as for the coolant inlet 122 in Figure 8. The second and third coolant inlets 222b, 222c are positioned at two diametrically opposed positions on either side ofthe housing 16 (the second and third coolant inlets 222b, 222c are not visible in Figure 10(a)). The additional second and third coolant inlets 222b, 222c may be provided in a manifold cover forming a part ofthe housing 16. In this case some ofthe coolant channels 60 carry coolant flow in one direction along the stator core 12 and some of the coolant channels 60 carry coolant flow in the other direction along the stator core 60. The additional coolant inlets 222b, 222c may be provided towards the ends 12a, 12b of the stator core 12, for example to communicate with the end hairpin windings, where additional cooling may be required, with the advantage that the coolest coolant is introduced directly to the most heat affected area of the stator core 12. As in Figure 8, coolant outlets 224a, 224b are provided in the upper part of the housing 16 to communicate with each of the first and second cooling chambers 40, 42 to allow coolant to exit the housing 16 once it has passed through the coolant channels 16. Equivalent third and fourth coolant outlets are provided in the lower part of the housing 16 to communicate with the first and second cooling chambers, 40, 42 respectively, on the other side of the axis R-R. The third coolant outlet 224c is only visible in Figure 10(b) and is located diametrically opposite the first coolant outlet 224a (i.e. the outlets 224a, 224c are located on diametrically opposite sides of the first cooling chamber 40). Coolant delivered through the additional cooling inlets 222b, 222c is at a lower temperature, and mixes with the coolant coming in from the coolant inlet 222a which is at a higher temperature (due to the proximity to the heat extraction from the stator core 12). This results in mixing of coolant of different temperatures and a lowering of the temperature of the combined coolant flow as it passes the end windings. As seen in Figure 10(b), the coolant inlets 222b, 222c are located on the opposite sides of the electric motor to each other, and coolant outlets are located on the opposite sides of the electric motor to each other, when viewed from one end of the electric motor along the axis R-R. The four coolant inlets and outlets of the first cooling chamber 40 (i.e. 222b, 222c, 224a, 224c) are approximately equi-angularly spaced from one another around the housing 16 when viewed from one end of the electric motor along the axis of rotation, R-R. The same is true of the equivalent ‘set’ of coolant inlets and outlets for the second cooling chamber 42. In this example one or more of the coolant inlets is located on the opposite side of the electric motor to another one of the coolant inlets when viewed from one end of the electric motor along the axis of rotation (see Figure 10(b)). One further benefit of the embodiments of Figures 8 to 10 is that coolant flow, having been heated by the hairpin windings 46 as it passes along the axial length of the stator core 12, exits via both the driving and nondriving ends of the rotor 14, via the first and second cooling chambers 40,42, so that the cooling effect is more uniform along the length of the stator core 12. Figures 11 (a) and 11(b) show a further alternative embodiment in which only one coolant inlet 322 is provided in the upper part of the housing 16, at a central or mid-position along the axis of the stator core 12, to communicate with the circumferential groove 126 in the stator core 12 (as shown in Figures 8 and Figure 9). However, there is no equivalent coolant inlet in the lower part of the housing 16. First, second, third and fourth coolant outlets 324a, 324b, 324c, 324d are provided. The provision of the third and fourth coolant outlets, 324c, 324d, as well as the first and second coolant outlets 324a, 324b, has the effect of decreasing the pressure drop across the system, which becomes most effective when dealing with relatively high flow rates. The third and fourth coolant outlets 324c, 324d are not visible in the side view of Figure 11 (a), but can be seen in the end view of Figure 11(b) when view along the axis of rotation R-R. The first and third coolant outlets 324a, 324c communicate with the first cooling chamber 40 at one end of the stator core 12 and the second and fourth coolant outlets 324b, 324d communicate with the second cooling chamber 42 at the other end of the stator core 12. In this example one or more of the coolant outlets is located on the opposite side of the electric motor to another one of the coolant outlets when viewed from one end of the electric motor along the axis of rotation (see Figure 11 (b)). Figure 12 is a further alternative embodiment in which a first coolant inlet 422a is positioned centrally along the axis of the stator core 12 to communicate with the circumferential groove 126 in the stator core 12 (as shown in Figures 8 and 9). A second coolant inlet 422(d) (as shown in Figure 12(d)) is positioned diametrically opposite the first coolant inlet 422a. Additional second and third coolant inlets 422b, 422c are provided at opposed ends of the stator core 12 to communicate with the first and second cooling chambers 40, 42, respectively, rather than just having centrally positioned inlets as in previous embodiments. In other words, in this embodiment there are three coolant inlets 422a, 422b, 422c in the upper part of the housing 16 (as shown in Figure 12(a)) which communicate, respectively, with (i) the circumferential groove 126 in the lamination stack 44, (ii) the first cooling chamber 40 and (iii) the second cooling chamber 42. In this case, as the coolant is introduced to the driving and non-driving end of the rotor 14, there is direct cooling of the end windings which may be in most need of cooling. The first and second coolant outlets 424a, 424b are positioned on opposite sides of the housing, as illustrated in Figure 12(b). The first and second coolant outlets 424a, 424b communicate with the first cooling chamber 40 at one end of the stator core 12 and an equivalent pair of coolant outlets (not shown) communicate with the second cooling chamber 42 at the other end of the stator core. It will be appreciated that the first and second coolant outlets 424a, 424b (and the equivalent coolant outlets at the other end of the stator core 12) shown in Figure 12(b) are not visible in the side view of Figure 12(a). In this example one or more of the coolant inlets is located on the opposite side of the electric motor to another one of the coolant inlets when viewed from one end of the electric motor along the axis of rotation, and one or more of the coolant outlets is located on the opposite side of the electric motor to another one of the coolant outlets when viewed from one end of the electric motor along the axis of rotation (see Figure 12(b)). In each of Figures 10 to 12, one or more of the coolant inlets is oriented at right angles to one or more of the coolant outlets when viewed from one end of the electric motor along the axis of rotation. Figures 13 and 14 show a further alternative embodiment of the invention which may be used with any configuration of coolant inlet(s) and outlet(s), but which in Figure 13 is shown with the arrangement of coolant inlets 422a, 422b, 422c of Figure 12. In this case the first sleeve 130 has a different configuration in which the radially outer diameter of the sleeve is variable along its axial length. The first sleeve 130 has a first portion 130a which is received within the hairpin windings 46 and is adhered to the end of the lamination stack 44. The first sleeve 130 also has a second portion 130b having a radially outer diameter which varies along its axial length. The first sleeve 130 also has a third sleeve portion 130c which is mounted to the annual seal 50. It will be appreciated that the first and third sleeve portions have equivalent portions in the embodiment of Figure 3. However, the sleeve profile is different in Figures 3 and 14 because, between the first end portion 130a and the third end portion 130c (i.e. between the lamination stack 4 and the annular seal 50), the radially outer diameter of the first sleeve portion 130b varies to define a curved or tapered profile. The radially outer diameter reduces or tapers from the third sleeve portion at the annular seal 50 to a minimum value, spaced a short distance from the first sleeve portion 130a, before increasing again towards the lamination stack 44. In other words, the diameter of the first sleeve 130 increases with distance from the rotor 14 along at least a portion of its length. It is an advantage of the reducing diameter of the sleeve between the lamination stack 44 and the annular seal 50 that the coolant flow which is introduced to the first cooling chamber 40, via the associated coolant inlet, is encouraged by the sleeve 130 to flow into the coolant channels 60 in the lamination stack, and avoids any tendency for the coolant to stagnate in the region against the sleeve 130. The same effect is achieved in the second cooling chamber 42 due to a similar shaping of the second sleeve 132 (as shown in Figure 13) at the other end of the stator 12 which serves to encourage the coolant flow in the second cooling chamber 42 into the coolant channels from the other end of the stator core 12 due to the tapered outer profile of the sleeve. In other words, the diameter of the second sleeve 132 increases with distance from the rotor 14 along at least a portion of its length. The invention has been described in the context of an electric motor apparatus in which first and second sleeves are provided to ensure respective cooling chambers are fluidically isolated from the rotor of the apparatus, but deliver or receive a coolant flow through the lamination stack of the stator core. The invention extends to the way in which the cooling effect is achieved, and thus also extends to a method of cooling an electric motor in which a coolant flow is passed through the stator, via one or more of the first and second cooling chambers. The steps of the method of cooling relate to the apparatus of the electric motor shown in the accompanying Figures. It will be appreciated that other embodiments are envisaged beyond those described here, without departing from the scope of the invention set out in the appended claims.

Claims

1. An electric motor comprising:a rotor configured to rotate about an axis of rotation;a stator comprising one or more coolant flow channels which extends from a first end of the stator towards a second end of the stator;a housing comprising:one or more coolant inlets andone or more coolant outlets, wherein the rotor and the stator are located within the housing;a first sleeve which extends between the first end of the stator and a first portion of the housing, wherein the first sleeve, the first end of the stator and the first portion of the housing together define a first cooling chamber; anda second sleeve which extends between the second end of the stator and a second portion of the housing, wherein the second sleeve, the second end of the stator and the second portion of the housing together define a second cooling chamber,wherein the first cooling chamber, the second cooling chamber and the one or more coolant flow channels are in fluidic communication with one another and together comprise a cooling system, wherein the one or more coolant inlets are configured to deliver coolant fluid to the cooling system in use, and wherein the one or more coolant outlets are configured to evacuate cooling fluid from the cooling system in use.

2. The electric motor according to claim 1, wherein the first sleeve and / or the second sleeve has a constant diameter along at least a portion of its length.

3. The electric motor according to claim 1, wherein the first sleeve and / or the second sleeve has a variable diameter along at least a portion of its length.

4. The electric motor according to claim 3, wherein the diameter of the first sleeve and / or the second sleeve increases with distance from the rotor along at least a portion of its length.

5. The electric motor according to claim 4, wherein at least a portion of the first sleeve and / or the second sleeve is curved in longitudinal profile.

6. The electric motor according to any preceding claim, wherein the cooling system comprises one or more circumferential channel which extends around the circumference of the stator, wherein each circumferential channel is in fluidic communication with one or more of the one or more coolant flow channels.

7. The electric motor according to any preceding claim, wherein one or more of the coolant inlets are configured to deliver coolant fluid to one of the first or second cooling chambers, and one or more of the coolant outlets are configured to evacuate coolant fluid from the other of the first or second cooling chambers.

8. The electric motor according to claim 6, wherein one or more of the coolant inlets are configured to deliver coolant fluid to the one or more circumferential channel, and one or more of the coolant outlets are configured to evacuate coolant fluid from the first and second cooling chambers and wherein optionally one or more of the coolant inlets are configured to deliver coolant fluid to the first and second cooling chambers.

9. The electric motor according to any preceding claim, wherein one or more of the coolant inlets is located longitudinally in line with one or more of the coolant outlets when viewed from one end of the electric motor along the axis of rotation.

10. The electric motor according to any preceding claim, wherein one or more of the coolant inlets is located on the opposite side of the electric motor to one or more of the coolant outlets when viewed from one end of the electric motor along the axis of rotation.

11. The electric motor according to any preceding claim, wherein one or more of the coolant inlets is located on the opposite side of the electric motor to another one of the coolant inlets when viewed from one end of the electric motor along the axis of rotation.

12. The electric motor according to any preceding claim, wherein one or more of the coolant inlets is oriented at right angles to one or more of the coolant outlets when viewed from one end of the electric motor along the axis of rotation.

13. A vehicle comprising an electric motor for providing a drive force for the vehicle, the electric motor being in accordance with any of claims 1 to 12.

14. A method of cooling the stator of an electric motor comprising introducing a liquid coolant into: one or more flow channels located in the stator;a first cooling chamber located at a first end of the stator; and a second cooling chamber located at a second end of the stator, wherein introducing the liquid coolant comprises passing the coolant from one or both of the cooling chambers into one or more of the coolant flow channels, or passing the coolant from one or more of the coolant flow channels into one or both of the coolant chambers.Application No: GB2411528.9Examiner:James GulliverClaims searched: 1-14Date of search: 22 January 2025Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X 1-3, 6-8, 10, and 12-14 CN 117791968 A (HUAWEI DIGITAL POWER TECH CO LTD) - See especially Figs. 16 and 18, and discussion of same X 1-3,6, 8, 10, and 13-14 CN 116155017 A (SHAANXI FAST SONGZHENG ELECTRIC DRIVE SYSTEM CO LTD) - See especially Fig. 1 and discussion of same X 1-2, 7, 9, 11, and 14 US 8558422 B2 (BAUMANN et al.) - See especially Fig. 7 and Column 5 Lines 19-46 X 1-2, 7, 10, and 13-14 CN 104253509 A (YIN TIANMING) - See especially Fig. 3 and discussion of same X 1, 3-6, 8, 10, and 14 US 2011 / 0234029 Al (PAL) - See especially Figs 3B and 4, and discussion at [0016] and [0019]Categories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of before the filing date of this invention. same category. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:International Classification:Subclass Subgroup Valid From H02K 0009 / 197 01 / 01 / 2006 TjnOIZ rlUZix 0005 / 128 01 / 01 / 2006

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