GB2625064A - A stator core for an electric machine - Google Patents

Abstract

A stator core 12 for a stator 10 of an electric machine (100, fig 6) preferably in a vehicle (200, fig 13). The stator core 1 has a central stator axis (16, fig 6); and a plurality of winding slots 20. A first plurality of cooling ducts 30 extend from a first end to a second end of the stator core. The cooling ducts 30 are radially separated from the winding slots 20 by regions of the stator core 12. The cooling ducts may be positioned corresponding to a winding slot 20, or tooth 25. Second cooling ducts (32, fig 5) may be provided radially outward of the first ducts 30. Cooling fluid may be circulated through the cooling ducts via manifolds (60, 80, fig 6) at the ends of the electric machine. The cooling ducts may be circular, or polygons (figs 14 & 15).

Description

A STATOR CORE FOR AN ELECTRIC MACHINE

TECHNICAL FIELD

The present disclosure relates to a stator core for an electric machine. Particularly, but not exclusively, the present disclosure relates to a stator core for use in an electric machine that can be used as a motor or generator. The stator core forms a part of a stator for the electric machine.

BACKGROUND

It is known to use one or more electric machine in a vehicle. Such electric machines may operate as motors or as generators. Electric machines may operate as traction motors for propelling a vehicle such as an automobile, van, truck, motorcycle, boat, or aeroplane. Electric machines may be used in place of, or in addition to, an internal combustion engine.

Such electric machines comprise a stator and a rotor, separated by an air gap, for example as part of a permanent magnet synchronous motor. The stator is a stationary element of the electric machine which may comprise a plurality of slots within which electrical stator windings are located. The rotor is a rotating element of the electric machine allowing a transfer of electrical energy input into the motor to a mechanical output, such as the rotation of a driveshaft of the vehicle.

The vehicle may, for example, comprise a battery electric vehicle (BEV), a plug-in hybrid electric vehicle (PHEV) or a hybrid electric vehicle (HEV) where the electric machine is a traction motor for the vehicle. It is desirable to have the lightest possible traction motor with optimised energy conversion from an electrical energy input to a mechanical energy output whilst maintaining the integrity of the traction motor.

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 stator, an electric machine, and a vehicle as claimed in the appended claims According to an aspect of the present invention there is provided a stator core for a stator of an electric machine, the stator core comprising: a central stator axis; a plurality of winding slots in the stator core; and a first plurality of cooling ducts extending through the stator core from a first end of the stator core to a second end of the stator core; wherein the cooling ducts are radially separated from the winding slots by regions of the stator core. The stator core may comprise a cylindrical inner channel. The cylindrical channel may have a central axis coincident with the central stator axis. The plurality of winding slots may extend through the stator core. The plurality of winding slots may extend along a respective radial slot axis, each of the respective radial slot axes extending from, and orthogonal to, the central stator axis. The winding slots may each have a winding slot opening, for example disposed at or near the inner surface of the stator core. The winding slots may extend radially outwardly relative to the central stator axis from the winding slot opening. Each of the first plurality of cooling ducts may extend substantially parallel to the central stator axis.

An advantage of this aspect of the invention is that cooling fluid or coolant media can be passed through the stator from a first end of the stator to a second end of the stator in order to transport heat generated by the electrical stator windings in the plurality of winding slots of the stator away from the electric machine.

Each of the plurality of winding slots may comprise a central slot axis. The central slot axis may extend radially from the central stator axis. One of the first plurality of cooling ducts may be positioned on the central slot axis of a corresponding winding slot.

Each of the first plurality of cooling ducts may comprise a geometric centre. The geometric centre of each of the first plurality of cooling ducts may be positioned on the central slot axis of the corresponding winding slot. Alternatively, the geometric centre of each of the second plurality of cooling ducts may be positioned on the on the central slot axis of the corresponding stator tooth.

Each of the plurality of winding slots may terminate at a respective winding slot base within the stator, each of the first plurality of cooling ducts being positioned on the radial axis of a corresponding winding slot adjacent a corresponding winding slot base.

This provides the advantage of proving a cooling solution for the stator whilst minimising the effect on the magnetic flux lines through the stator generated by current in windings disposed in the winding slots.

Each of the plurality of winding slots may have an associated cooling duct of the first plurality of cooling ducts positioned on the radial axis of the corresponding winding slot, adjacent the corresponding winding slot base.

This provides the advantage of ensuring a minimal thermal path between stator windings and cooling duct without detrimentally affecting flux lines through the stator.

The stator may comprise a second plurality of cooling ducts. Each of the second plurality of cooling ducts may be radially and/or circumferentially separated from the first plurality of cooling ducts. The second plurality of cooling ducts may be disposed at a greater radial distance or a smaller radial distance from the central stator axis than the first plurality of cooling ducts. Alternatively, or in addition, the second plurality of cooling ducts may be circumferentially offset from the first plurality of cooling ducts.

This provides the advantage of increasing the heat transport within the stator, and hence in the electric machine, away from the electrical stator windings in the plurality of winding slots of the stator whilst maintaining a low impact on the flux lines within the stator and hence will not significantly detrimentally impact torque creation.

The stator core may comprise a plurality of stator teeth. The stator teeth may extend radially inwardly. The winding slots may be formed between the stator teeth. Each of the plurality of stator teeth may comprise a central tooth axis. The central tooth axis may extend radially from the central stator axis. One of the second plurality of cooling ducts may be positioned on the central tooth axis of a corresponding stator tooth.

Each of the second plurality of cooling ducts may comprise a geometric centre. The geometric centre of the second plurality of cooling ducts may be positioned on the central slot axis of the corresponding stator tooth. Alternatively, the geometric centre of each of the second plurality of cooling ducts may be positioned on the central slot axis of the corresponding winding slot.

The first plurality of cooling ducts may have an equiangular distribution around the stator core.

The second plurality of cooling ducts may have an equiangular distribution around the stator core. Adjacent cooling ducts of the first plurality of cooling ducts may have a first angular separation around the central stator axis. The second plurality of cooling ducts may be displaced circumferentially from the first plurality of cooling ducts by half of the first angular separation between adjacent cooling ducts of the first plurality of cooling ducts.

This may provide the advantage of increasing the heat transport within the stator, and hence in the electric machine, away from the electrical stator windings in the plurality of winding slots of the stator whilst maintaining a low impact on the flux lines within the stator thereby not significantly detrimentally impacting torque creation. It may also provide the advantage of creating a spring effect in the stator. Such an arrangement may be beneficial in the torque transfer from the stator to the housing.

In some embodiments the housing of the electric machine may be shrink fitted or interference fitted with the stator. In other embodiments, the stator may be provided with a clearance fit within the housing and be subsequently affixed in place via fixings, such as bolts.

The second plurality of cooling ducts may have the same cross section as the first plurality of cooling ducts.

This provides the advantage of maintaining flow balance, that is, avoiding flow imbalance, as each of the ducts provides the same resistance to fluid flow therein such that the fluid flow in each cooling duct is substantially the same.

Each of the first plurality of the cooling ducts may be circular in transverse section. Alternatively, or in addition, each of the second plurality of the cooling ducts may be circular in transverse section. Other shapes are contemplated for the first and second cooling ducts.

The first cooling ducts and/or the second cooling ducts may, for example, comprise an ellipse in transverse section. Alternatively, the first cooling duct and/or the second cooling duct may comprise a polygon, such as a triangle, a rhombus or a rectangle, in transverse section. At least in certain embodiments, the polygon may have a line of (reflection) symmetry. The polygon may comprise a plurality of edges and a plurality of corners. One or more of the edges may be substantially linear (resulting in a sidewall which is at least substantially planar in transverse section). Alternatively, or in addition, one or more of the edges may be curved, for example to form a sidewall which is concave or convex in transverse section. The corners of the polygon may be rounded, for example comprising a substantially continuous curve. The cooling ducts may comprise a rounded polygon in transverse section.

The cooling ducts in the first plurality of cooling ducts may have a line of (reflection) symmetry. The cooling duct may be oriented such that the line of symmetry is at least substantially aligned with a radial axis extending from the central stator axis.

The cooling ducts in the second plurality of cooling ducts may have a line of (reflection) symmetry. The cooling duct may be oriented such that the line of symmetry is at least substantially aligned with a radial axis extending from the central stator axis.

According to an aspect of the present invention there is provided a stator core for a stator of an electric machine, the stator core comprising: a central stator axis; a plurality of winding slots in the stator core; and at least one cooling duct in the stator core, the at least one cooling duct extending substantially parallel to the central stator axis and being radially separated from the winding slots by regions of the stator core; wherein the or each cooling duct has a profile in transverse section comprising or consisting of a polygon composed of a plurality of edges and corners.

The polygon may comprise one or more line of (reflection) symmetry. The or each cooling duct may be oriented such that a first line of symmetry is aligned with a radial axis extending from the central stator axis. Alternatively, the or each cooling duct may be oriented such that a first line of symmetry is substantially perpendicular to a radial axis extending from the central stator axis.

The polygon may comprise one or more of the following: a triangle, for example an equilateral or isosceles triangle; a rhombus; a kite; a trapezoid, for example an isosceles trapezoid; a rectangle; a square, a pentagon; and a hexagon.

The polygon may be an equilateral polygon and/or an equiangular polygon. The polygon may be a regular polygon.

The stator core may comprise a first cooling duct and a second cooling duct. The first and second cooling ducts may be disposed adjacent to each other in the stator core. The first and second cooling ducts may be offset from each other in a circumferential direction and/or a radial direction. The first and second cooling ducts may at least partially overlap each other in a radial direction. The first and second cooling ducts may have a partially interlocking (or tessellated) arrangement.

The first cooling duct may have a first profile comprising or consisting of a first polygon; and the second cooling duct may have a second profile comprising or consisting of a second polygon. The first and second cooling ducts may have like profiles. The first and second profiles may be at least substantially the same as each other. The first and second polygons may have the same orientation as each other. Alternatively, the first and second polygons may have different orientations. For example, the first and second polygons may be oriented in opposite directions. The first polygon may be a reversed or mirror image of the second polygon about an axis extending perpendicular to a radial axis of the stator core. At least in certain embodiments, this may form an interlocking arrangement of the first and second cooling ducts.

The adjacent edges of the first and second cooling ducts may be at least substantially parallel to each other.

The opposing edges of the first and second cooling ducts are oriented at an acute (non-zero) angle to a radial axis of the stator core.

The winding slots may be formed between stator teeth. Each of the plurality of stator teeth may comprise a central tooth axis. Each central tooth axis may extend in a radial direction. 20 The first cooling duct may comprise a first edge (side) disposed in a radially innermost position. The first edge may extend substantially perpendicular to a radial axis of the stator core. The first cooling duct may comprise a first line of (reflection) symmetry. The first cooling duct may be aligned with one of the winding slots in the stator core. The first line of symmetry of the first cooling duct may be at least substantially aligned with a central slot axis of the winding slot.

Alternatively, the first cooling duct may be aligned with one of the stator teeth. The first line of symmetry of the first cooling duct may be at least substantially aligned with a central tooth axis of the stator tooth.

The second cooling duct may comprise a first edge disposed in a radially outermost position.

The first edge may extend substantially perpendicular to a radial axis of the stator core. The second cooling duct may comprise a second line of (reflection) symmetry. The second cooling duct may be aligned with one of the stator teeth in the stator core. The second line of symmetry of the second cooling duct may be at least substantially aligned with a central tooth axis of the stator tooth. Alternatively, the second cooling duct may be aligned with one of the winding slots. The second line of symmetry of the second cooling duct may be at least substantially aligned with a central slot axis of the winding slot.

The first and second cooling ducts may comprise respective first and second triangles. The first and second triangles may, for example, be equilateral triangles or isosceles triangles. The first and second triangles may be oriented in opposite directions. The first and second triangles may be oriented in opposite direction to form an interlocking arrangement of the first and second cooling ducts. The first triangle may be a reversed or mirror image of the second triangle about an axis extending perpendicular to a radial axis of the stator core. The first and second cooling ducts may have a partially interlocking (or tessellated) arrangement.

The profile of the first cooling duct may comprise or consist of a first triangle. In one arrangement, the first triangle may comprise a first edge disposed in a radially outermost position. Alternatively, the first triangle may comprise a first edge disposed in a radially innermost position. The first edge may extend substantially perpendicular to a radial axis of the stator core. The first cooling duct may be aligned with one of the stator slots formed in the stator core. The first edge of the first cooling duct may be disposed closest to the stator slots.

The profile of the second cooling duct may comprise or consist of a second triangle. In one arrangement, the second triangle may comprise a first edge disposed in a radially innermost position. Alternatively, the second triangle may comprise a first edge disposed in a radially outermost position. The first edge may extend substantially perpendicular to a radial axis of the stator core. The second cooling duct may be aligned with one of the stator teeth in the stator core.

The first and second cooling ducts may comprise respective first and second rhombuses. The first and second rhombuses may be a regular rhombus. The first and second rhombuses may be offset from each other in a radial direction and/or a circumferential direction. The first and second rhombuses may be arranged to form an interlocking arrangement of the first and second cooling ducts.

The first and second cooling ducts may comprise respective first and second trapezoids. The trapezoids may be isosceles trapezoids. The orientation of the first and second trapezoids may be reversed to form an interlocking arrangement of the first and second cooling ducts.

According to an aspect of the present invention there is provided an electric machine comprising: a stator as described above.

The electric machine may comprise: a substantially cylindrical housing surrounding the stator core; a first manifold provided at the first end of the stator core and configured to fluidly couple respective first ends of a first plurality of cooling ducts formed in the stator core; and a second manifold provided at the second end of the stator core and configured to fluidly couple respective second ends of the first plurality of cooling ducts. The first manifold and the second manifold may be arranged to retain a cooling fluid to be conveyed through the first plurality of cooling ducts in use.

An advantage of this aspect of the invention is that cooling fluid, or coolant media, can be passed through the stator from a first end of the stator to a second end of the stator in order to transport heat generated by the electrical stator windings in the plurality of winding slots of the stator away from the electric machine, whilst maintaining dry electrical stator windings in the electric machine. This may also assist in removing windage losses generated by splashing of a motor coolant at the electrical stator windings.

At least one of the first manifold and the second manifold may be secured to the stator core. The at least one of the first manifold and the second manifold may be secured, at least in part, by the housing.

This provides the advantage of assisting the manifolds to retain cooling fluid or coolant media, such as oil or a dielectric fluid, which is to be directed into the cooling ducts, and prevent such cooling fluid or coolant media from coming into contact with the electrical stator windings of the electric machine.

The first manifold may cooperate with the stator core to form a first cooling fluid chamber, the first plurality of cooling ducts being open into the first cooling fluid chamber. The second manifold may cooperate with the stator core to form a second cooling fluid chamber, the first plurality of cooling ducts being open into the second cooling fluid chamber.

At least one of the first manifold and the second manifold may be part annular. At least one of the first manifold and the second manifold may be annular or substantially annular.

A first surface of the first manifold may be located adjacent the first end of the stator. The first surface of the first manifold may therefore be considered to be a first stator abutment surface or a first stator sealing surface. A second surface of the first manifold may be located adjacent an inner surface of the housing at the first end of the stator. The second surface of the first manifold may therefore be considered to be a first housing abutment surface or a first housing sealing surface. The first surface of the first manifold and the second surface of the first manifold form a first cooling fluid chamber, with the first plurality of cooling ducts being open into the first cooling fluid chamber.

A first surface of the second manifold may be located adjacent the second end of the stator.

The first surface of the second manifold may therefore be considered to be a second stator abutment surface or a second stator sealing surface. A second surface of the second manifold may be located adjacent an inner surface of the housing at the second end of the stator. The second surface of the second manifold may therefore be considered to be a second housing abutment surface or a second housing sealing surface. The first surface of the second manifold and the second surface of the second manifold form a second cooling fluid chamber, with the first plurality of cooling ducts being open into the second cooling fluid chamber.

The electric machine may comprise a cooling fluid inlet in fluid communication with the first cooling fluid chamber, and a cooling fluid outlet in fluid communication with the second cooling fluid chamber. In use, cooling fluid may be supplied to the first plurality of cooling ducts via the cooling fluid inlet and may be discharged through the cooling fluid outlet.

The housing may comprise a cooling fluid inlet between the first surface of the first manifold and the second surface the first manifold. The housing may comprise a cooling fluid outlet between the first surface of the second manifold and the second surface of the second manifold.

This provides the advantage of allowing a cooling fluid or coolant media, such as oil or a dielectric fluid, to be controllably directed into a first end of the stator, and allows flow of cooling fluid or coolant media through stator core in one direction to reduce the temperature of the electric machine whilst avoiding high back pressures that may reduce cooling fluid or coolant media flow to unacceptable levels. When the cooling fluid or coolant media is an oil, such as a transmission oil, this may also provide the advantage of increasing the temperature of the oil which may be beneficial to components using the oil as a lubricant, such as a vehicle transmission.

The cooling fluid inlet may be at a lower portion of the first manifold when the electric machine is in use. The cooling fluid outlet may be at an upper portion of the second manifold when the electric machine is in use.

This provides the advantage of improved purging of a significant proportion of air bubbles from the cooling fluid or coolant media by the flow of the cooling fluid or coolant media from a low point in the electric machine to a high point of the electric machine. In particular, this feature helps to get air out of the system when initially filling the stator and manifold arrangement with cooling fluid or coolant media, and the introduction of cooling fluid or coolant media at a low point forces the air to rise and be expelled from a high point of the electric machine. This arrangement may also provide the benefit of inducing thermal siphoning even when a cooling pump, which is arranged or configured to circulate cooling fluid or coolant media through the stator, is switched off.

Each of the second plurality of cooling ducts may be open into the first cooling fluid chamber and open into the second cooling fluid chamber.

According to an aspect of the present invention there is provided a vehicle comprising a stator according to any preceding aspect or an electric machine according to any preceding aspect.

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

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 illustrates a cross sectional image of a stator according to an embodiment of the invention with cooling ducts aligned with teeth of the stator; Figure 2 illustrates a cross sectional image of a stator according to an embodiment of the invention with cooling ducts aligned with slots of the stator; Figure 3 illustrates a cooling duct arrangement according to an embodiment of the invention; Figure 4 illustrates a cooling duct arrangement according to an embodiment of the invention; Figure 5 illustrates a cooling duct arrangement according to an embodiment of the invention; Figure 6 illustrates a cross sectional image of an electric machine according to an embodiment of the invention with the cooling duct arrangement of Figure 3; Figure 7 illustrates a cross sectional image of an electric machine according to an embodiment of the invention with the cooling duct arrangement of Figure 5; Figure 8 illustrates a cross sectional image of a portion of the first side of the electric machine; Figure 9 illustrates a cross sectional image of a portion of the second side of the electric machine; Figure 10 illustrates a perspective view showing a first side of an electric machine according to an embodiment of the invention; Figure 11 illustrates a perspective view showing a second side of an electric machine according to an embodiment of the invention; Figure 12 illustrates a cross sectional image of an alternative electric machine with the cooling duct arrangement of Figure 5; Figure 13 illustrates a vehicle in accordance with an embodiment of the invention; Figure 14 illustrates a stator core having first and second cooling ducts according to another embodiment of the present invention; and Figure 15 illustrates a stator core having first and second cooling ducts according to a further embodiment of the present invention.

DETAILED DESCRIPTION

Examples of the present disclosure relate to a stator. In particular, examples of the present invention relate to stator in an electric machine. Such an electric machine may be of a synchronous type or asynchronous type, for example a permanent magnet synchronous motor. Non-limiting examples will now be described with reference to accompanying Figures 1 to 13, where the figures illustrate a stator 10, an electric machine 100, and a vehicle 200.

The stator 10 is intended for use in an electric machine 100, as illustrated in cross sectional view in Figure 6, in magnified detail in Figure Band Figure 9, and in perspective view in Figure 10 and Figure 11, where the electric machine 100 comprises the stator 10 and a rotor 112.

As illustrated in the cross-sectional views of Figure 1 and Figure 2 the stator 10 comprises an annular stator core 12 with a plurality of winding slots 20 extending radially to support electrical stator windings 150. The electrical stator windings 150 are only illustrated in one winding slot 20 for simplicity. For example, the electric machine 100 may comprise forty eight slots and eight rotor poles. Other combinations of winding slot numbers and rotor pole numbers are useful. The electric machine 100 may provide the function of a motor and/or generator for operation in a vehicle 200, as illustrated in Figure 13. For example, the electric machine 100 may be a traction motor for an electric vehicle 200.

With reference to Figure 1, there is shown a stator 10 with a system of cooling ducts 30. The stator 10 has a stator core 12 and a central stator axis 16 which is also a rotational axis 16 about which a rotor 112, as illustrated in Figure 6, is arranged or configured to rotate. The cooling ducts 30 are intended to remove heat from the stator core 12 and from electrical stator windings 150 in the electric machine 100 where the heat is generated in the electric machine 100.

Figure 13 illustrates a vehicle 200 having a first electric machine 100-1 for driving one or more front wheels of the vehicle 200 and a second electric machine 100-2 for driving one or more rear wheels of the vehicle 200. In other embodiments the vehicle 200 may comprise only a single electric machine 100, arranged or configured to drive one of one or more front wheels of the vehicle 200 or one or more rear wheels of the vehicle 200. At a vehicle axle the electric machine 100 may be arranged to drive both wheels, either directly or through other transmission components. In other arrangements there may be more than one electric machine 100 arranged to provide torque to a vehicle axle, for example, to provide torque vectoring functionality for the vehicle 200. Other arrangements may have one electric machine arranged or configured to drive each wheel of the vehicle 200. The electric machine 100 comprised in the vehicle 200 may have a stator as described herein.

The stator 10 is a stator assembly comprising a stator core 12 and the electrical stator windings 150. With reference to Figure 1, the stator core 12 having a cylindrical inner channel 14 with a central stator axis 16. As shown in the cross-sectional view of Figure 6, which is a view orthogonal to the view of Figure 1, the cylindrical inner channel 14 extends from a first end 64 of the stator 10 to a second end 84 of the stator 10.

The central stator axis 16 is parallel to a curved surface 18 of the cylindrical inner channel 14, that is, the inner surface of the stator 10. The central stator axis 16 is therefore the central axis of the cylindrical inner channel 14. A rotor 112 is configured to fit within the cylindrical inner channel 14 of the stator 10 with a small air gap 34 therebetween. The outside surface of the rotor 112 provides a surface concentric with the curved surface 18 of the stator 10, such that as the rotor 112 rotates within the cylindrical inner channel 14 of the stator, a consistent air gap 34 is maintained between the rotor 112 and the stator 10.

The stator 10 comprises a plurality of winding slots 20 through the stator core 12, from the first end 64 of the stator 10 to the second end 84 of the stator 10, configured to receive electrical stator windings 150 of the electric machine 100. Each of the plurality of winding slots 20 has a length 24 extending along a respective central slot axis 22. The central slot axes 22 each extend in a radial direction from, and are orthogonal to, the central stator axis 16. Each of the plurality of winding slots 20 has a winding slot opening 26 at or near the curved surface 18 of the cylindrical inner channel 14 and extends radially outward relative to the central stator axis 16 from the winding slot opening 26. The stator core 12 comprise a plurality of stator teeth 25 extending radially inwardly. The stator teeth 25 are disposed between the winding slots 20.

Each of the plurality of stator teeth 25 extending along a respective central tooth axis 27. The central tooth axes 27 each extend in a radial direction from, and are orthogonal to, the central stator axis 16.

The winding slot opening 26 may be open to the air gap 34, that is, open to the cylindrical inner channel 14 such that there is a non-continuous curved surface 18 in the cylindrical inner channel 14. In other embodiments the winding slot opening 26 is closed to the air gap 34 to provide a continuous curved surface 18 such that electrical stator windings are required to be inserted, during manufacture, into the winding slot 20 at the first end 64 of the stator 10 and passed through the winding slot 20 to the second end 84 of the stator 10.

The stator 10 comprises a first plurality of cooling ducts 30 through the stator core 12, where each of the first plurality of cooling ducts 30 extends parallel or substantially parallel to the central stator axis 16, from the first end 64 of the stator 10 to the second end 84 of the stator 10. The first plurality of cooling ducts 30 extends continuously from the first end 64 of the stator 10 to the second end 84 of the stator 10, such that cooling fluid which is arranged to enter the cooling ducts 30 passes from the first end 64 of the stator 10 to the second end 84 of the stator 10. In the embodiment of Figure 1 the cooling ducts 30 are radially separated from the winding slots 20 by regions 36 of the stator core 12, such that there is sufficient space for the electromagnetic flux in the stator 10 to pass through the stator core 12 without significant electromagnetic interference of the flux paths or lines. Therefore, the arrangement of cooling ducts 30 illustrated in Figure 1 provides cooling for the stator 10 whilst providing a minimum of interference in the creation of torque by the electric machine 100.

Cooling fluid, such as oil, can be passed through the cooling ducts 30 of the stator 10 from the first end 64 of the stator 10 to the second end 84 of the stator 10 in order to transport heat generated by the electrical stator windings 150 in the plurality of winding slots 20 of the stator 10, and the stator core 12, away from the electric machine 100, the electrical stator windings and the stator core 12 being a source of heat in the electric machine 100. The cooling fluid passing through the cooling ducts 30 therefore transports or conveys heat from the source of heat in the electric machine 100.

A major loss component on an electrical powertrain, in which the electric machine 100 may form part, is the loss produced in the gear set due to oil viscosity. When at low temperatures, these losses can be significant and can ultimately affect the range of the vehicle 200. By utilising oil as the cooling fluid in the electric machine 100, where this oil can be used as the transmission oil in the electrical powertrain, the losses in the electrical powertrain can be minimised or mitigated. The temperature of the oil can be elevated by absorbing the heat generated by the electrical stator windings 150 in the plurality of winding slots 20 of the stator 10 and the stator core, thereby reducing the viscosity of the oil and reducing the losses in the gear set.

Each winding slot 20 terminates at a slot base 28 within the stator 10. The base 28 is distal from the slot opening 26. In the embodiment of Figure 1, each of the first plurality of cooling ducts 30 are positioned off the central slot axis 22 of the winding slots 20. In order to avoid detrimentally affecting the flux paths in the stator 10, the cooling ducts 30 are positioned outside of the stator teeth 25 formed between adjacent winding slots 20.

Figure 2 illustrates a different embodiment of the invention, which is similar in form to the stator 10 of Figure 1, but where each of the first plurality of cooling ducts 30 are positioned on the central slot axis 22 of a corresponding winding slot 20 adjacent a corresponding winding slot base 28.

Although, with significant separation of the first plurality of cooling ducts 30 from the winding slots 20, the electromagnetic interference with the flux paths or lines is not particularly detrimental in the generation of torque by the electric machine 100, as illustrated in Figure 3, this significant separation reduces the effectiveness of the cooling provided by the cooling ducts 30. Therefore, whilst the arrangements of Figure 1, Figure 2, and Figure 3 provide stator cooling without detrimentally affecting the flux paths in the stator 10, the cooling may be further increased, or optimised, by reducing the separation between the cooling ducts 30 and the winding slots 20.

By having the first plurality of cooling ducts 30 on the central slot axis 22 of a corresponding winding slot 20, the separation between the cooling ducts 30 and the winding slots 20 can be reduced by a greater amount than if the first plurality of cooling ducts 30 are off of the central slot axis 22 of a corresponding winding slot 20, without detrimentally affecting the flux paths in the stator 10. That is, the regions 36 of the stator core 12 between the winding slots 20 and the cooling ducts 30 can be reduced. Such an arrangement is illustrated in Figure 4, where it can be seen that the cooling ducts 30 are significantly closer to the winding slots 20 than in Figure 3. The embodiment of Figure 4 therefore provides increased cooling of the stator 10 whilst minimising the effect on the flux paths through the stator 10.

In Figures 1 and 2, it can be seen that there are half as many cooling ducts 30 as there are winding slots 20. In order to increase the cooling capacity of the arrangement, that is to minimise the thermal path in the stator 10 from the source of heat at the electrical stator windings 150, each of the plurality of winding slots 20 can have an associated cooling duct 30 of the first plurality of cooling ducts 30 positioned on the central slot axis 22 of the corresponding winding slot 20, adjacent the corresponding winding slot base 28, as illustrated in Figure 3 and Figure 4. By providing each of the cooling ducts 30 on the central slot axis 22 of the corresponding winding slot 20 a minimal thermal path is provided without detrimentally affecting flux paths through the stator 10. Each of the first plurality of cooling ducts 30 comprise a geometric centre Cl. As shown in Figure 4, the geometric centre Cl of each of the first plurality of cooling ducts 30 may be positioned on the central slot axis 22 of the corresponding winding slot 20.

Each of the first plurality of cooling ducts 30 may be circular in cross section perpendicular to the central stator axis 16. The cooling ducts 30 are arranged to extend along the length of the stator 10, terminating in openings at each end 64, 84 of the stator 10 forming continuous passages therethrough. The cooling ducts 30 are preferably rounded or comprise rounded corners to help minimise stress concentrations in the stator 10, and optimise the hydraulic behaviour of the cooling arrangement of the stator 10.

In the present embodiment, each of the cooling ducts 30 is circular in transverse section. Other shapes are contemplated for the cooling ducts 30. The cooling ducts 30 may, for example, comprise an ellipse. Alternatively, the cooling ducts 30 may comprise a polygon, such as a triangle, a rhombus or a rectangle, in transverse section. The polygonal shape may comprise a plurality of edges and a plurality of corners. One or more of the edges may be substantially linear (resulting in a sidewall which is at least substantially planar in transverse section). Alternatively, or in addition, one or more of the edges may be curved, for example to form a sidewall which is concave or convex in transverse section. The corners of the polygon may be rounded, for example comprising a substantially continuous curve. The cooling ducts 30 may comprise a rounded polygon in transverse section.

In order to minimise the effect on the flux paths in the stator 10, each of the first plurality of cooling ducts 30 may have a width, orthogonal to the central stator axis 16 and orthogonal to the respective central slot axis 22, less than or equal to the width, orthogonal to the central stator axis 16 and orthogonal to the respective central slot axis 22, of the corresponding winding slot 20.

In order to further optimise cooling of the stator 10, the stator 10 may comprise a second plurality of cooling ducts 32 as illustrated in Figure 5. The second plurality of cooling ducts 32 are radially separated from the first plurality of cooling ducts 30 and at a greater radial distance from the central stator axis 16 than the first plurality of cooling ducts 30. In such an arrangement the heat transport within the stator 10 is significantly increased, whilst maintaining a low impact on the flux paths within the stator 10, and therefore such an arrangement may not significantly detrimentally impact torque creation by the electric machine 100. Each of the second plurality of cooling ducts 32 comprise a geometric centre 02. As shown in Figure 5, the geometric centre C2 of each of the second plurality of cooling ducts 32 is positioned on the central tooth axis 27 of the corresponding stator tooth 25.

In the present embodiment, each of the first and second cooling ducts 30, 32 is circular in transverse section. The first and second cooling ducts 30, 32 may have different shapes. For example, the first and second cooling ducts 30, 32 may each comprise a rounded polygon in transverse section. The first and second cooling ducts 30, 32 may have the same shape as each other or may have different shapes. For example, the first cooling ducts 30 may each comprise a rounded triangle in transverse section; and the second cooling ducts 32 may each comprise a rounded rhombus in transverse section. Other shapes and combinations of shapes are contemplated.

Adjacent cooling ducts 30 of the first plurality of cooling ducts 30 are angularly separated around the central stator axis 16. For example, a first cooling duct 30-1 may lie on a first central slot axis 22-1 and a second cooling duct 30-2 may lie on a second central slot axis 22-2. The second plurality of cooling ducts 32 may be displaced circumferentially by half of the angular separation between adjacent cooling ducts 30-1, 30-2 of the first plurality of cooling ducts 30.

In the embodiment of Figure 5, a cooling duct 32 of the second plurality of cooling ducts 32 lies midway between the first cooling duct 30-1 of the first plurality of cooling ducts 30 and the second cooling duct 30-2 of the first plurality of cooling ducts 30, on a central tooth axis 27 centrally disposed between the first central slot axis 22-1 and the second central slot axis 22-2.

Such an arrangement provides for increased heat transport within the stator 10, and hence in the electric machine 100, away from the electrical stator windings 150 in the plurality of winding slots 20 of the stator 10, and the stator core 12, whilst maintaining a low impact on the flux paths within the stator 10 thereby not significantly detrimentally impacting torque creation.

In an alternative embodiment, the second plurality of cooling ducts 32 may be in line with the first plurality of cooling ducts 30, that is both sets of cooling ducts 30, 32 may be on the central slot axis 22 of an associated winding slot 20. However, having the first plurality of cooling ducts 30 in line with the second plurality of cooling ducts 30 may interfere with the flux paths.

In some embodiments the second plurality of cooling ducts 32 comprises the same number of cooling ducts as the first plurality of cooling ducts 30. Such an arrangement helps to avoid flow imbalance and helps to maintain an even cooling of the stator 10, as described further below.

The second plurality of cooling ducts 32 may have the same cross section as the first plurality of cooling ducts 30. Having the same cross section for each of the first plurality of cooling ducts 30 and second plurality of cooling ducts 32 helps to maintain flow balance for the cooling fluid, that is, flow imbalance is reduced or avoided, as each of the cooling ducts 30, 32 provides the same resistance to fluid flow, such that the fluid flow in each cooling duct 30, 32 is substantially the same.

In some embodiments, the number and cross-section of the second plurality of cooling ducts 32 may be selected so as to provide a total cross-sectional area substantially matching the total cross-sectional area of the first plurality of cooling ducts 30, so as to minimise cooling fluid flow imbalance between the first plurality of cooling ducts 30 and the second plurality of cooling ducts 32.

Figure 6 shows a cross sectional side view of an electric machine 100 according to the present invention. The electric machine 100 comprises a stator 10 as described above. The electric machine 100 also comprises a housing 50 surrounding the stator 10. In some embodiments the housing 50 is a cylindrical housing, though it will be understood that the stator 10 may have a non-circular cross section, in particular where the outer form of the stator 10 is oblate or has projections thereon, such that the housing 50 may be non-circular.

The electric machine 100 comprises a first manifold 60 provided at the first side or first end 64 of the stator 10 and configured to fluidly couple respective first ends 92 of a first plurality of cooling ducts 30 formed in the stator 10.

The electric machine 100 comprises a second manifold 80 provided at the second side or second end 84 of the stator 10 and configured to fluidly couple respective second ends 94 of the first plurality of cooling ducts 30 formed in the stator 10.

The first manifold 60 and second manifold 80 are arranged to hold or retain a cooling fluid to be conveyed through the first plurality of cooling ducts 30, in use. That is, the first manifold 60 and second manifold 80 retain cooling fluid such that the cooling fluid can be passed through the stator 10 from the first end 64 of the stator 10 to the second end 84 of the stator in order to transport heat generated by the electrical stator windings 150 in the plurality of winding slots 20 of the stator 10, and the stator core 12, away from the electric machine 100, whilst maintaining dry electrical stator windings 150 in the electric machine 100. A cooling system for the electric machine 100 may comprise a closed system with the first manifold 60 and second manifold 80 comprising sealed sections of that closed system.

The first manifold 60 and second manifold 80 facilitate the supply and draining of the cooling fluid, such as oil, to and from the plurality of cooling ducts 30, where the first manifold 60 and the second manifold 80 can receive and retain a volume of cooling fluid that is to either be passed through the cooling ducts 30 or which has already passed through the cooling ducts 30. The cooling system may further comprise a cooling fluid pump and a heat exchanger (not shown). The cooling system may be arranged to service both the electric machine 100 and a transmission or gear set, the transmission may be arranged to convey torque from the electric machine 100 to one or more road wheels of a vehicle 200.

In embodiments with a second plurality of cooling ducts 32 the first manifold 60 provided at the first end 64 of the stator 10 is further configured to fluidly couple respective first ends 96 of the second plurality of cooling ducts 32 formed in the stator 10. The second manifold 80 provided at the second end 84 of the stator 10 is further configured to fluidly couple respective second ends 98 of the second plurality of cooling ducts 32 formed in the stator 10. The first manifold 60 and second manifold 80 are then arranged to hold or retain the cooling fluid to be conveyed through both the first plurality of cooling ducts 30 and the second plurality of cooling ducts 32, in use. That is, the first manifold 60 and second manifold 80 retain cooling fluid such that the cooling fluid can be passed through the stator 10 from the first end 64 of the stator 10 to the second end 84 of the stator in order to transport heat generated by the electrical stator windings 150 in the plurality of winding slots 20 of the stator 10, and the stator core 12, away from the electric machine 100, whilst maintaining dry electrical stator windings in the electric machine 100. The cooling ducts 30, 32 contain the cooling fluid so that it does not come into direct contact with the stator windings 150 in their respective winding slots 20 or the rotor 112 of the electric machine 100.

The first manifold 60 and the second manifold 80 may be secured to the stator, at least in part, by the housing 50. That is, the first manifold 60 and the second manifold 80 are connected to the housing 50 to be sealed thereto in order to retain cooling fluid, such as oil, which is to be directed into the cooling ducts 30, 32, and prevent such cooling fluid from coming into contact with the electrical stator windings 150 of the electric machine 100.

Figure 7 illustrates an embodiment of an electric machine 100 where there is only a first plurality of cooling ducts 30, the first plurality of cooling ducts 30 being arranged to lie on the radial axes 22 of respective stator winding slots 20, as illustrated in Figures 2, 3, and 4. The first manifold 60 of Figure 7 is illustrated in detail in Figure 8 and the second manifold 80 of Figure 7 is illustrated in detail in Figure 9.

In Figure 8, illustrating a magnified section of the electric machine 100 of Figure 7 at the first end 64 of the stator 10, the first manifold 60 has a first seal 102 or stator seal 102 to be disposed, in use, between a body 104 of the first manifold 60 and the stator 10, in particular the first end 64 of the stator 10. The first seal 102, may be for example an 0-ring seal or a lip seal. The first manifold 60 has a second seal 106 or housing seal 106 disposed, in use, between the body 104 of the first manifold 60 and the housing 50, in particular the inner surface 68 of the housing 50 at the first end 64 of the stator 10. The second seal 102, may be for example an 0-ring seal or a lip seal.

In Figure 9, illustrating a magnified section of the electric machine 100 at the second end 84 of the stator 10, the second manifold 80 has a first seal 108 or stator seal 108 to be disposed, in use, between the body 110 of the second manifold 80 and the stator 10, in particular the second end 84 of the stator 10. The first seal 108, may be for example an 0-ring seal or a lip seal. The second manifold 80 has a second seal 114 or housing seal 114 disposed, in use, between the body 110 of the second manifold 80 and the housing 50, in particular the inner surface 88 of the housing 50 at the second end 84 of the stator 10. The second seal 114, may be for example an 0-ring seal or a lip seal.

In an alternative embodiment at least one of the manifolds 60, 80 may be integrally formed with the housing 50 or connected to or integrally formed with an end-cap of the housing 50.

The first manifold 60 and the second manifold 80 may be annular. A first surface 62 of the first manifold 60 in the form of a stator sealing surface or section 62 of the first manifold 60 may be located adjacent the first end 64 of the stator 10 and a housing sealing surface or section 66 of the first manifold 60 may be located at an inner surface 68 of the housing 50 at the first end 64 of the stator 10 to form a first cooling fluid chamber 70, with the first plurality of cooling ducts 30 being open into the first cooling fluid chamber 70. In embodiments where there is also a second plurality of cooling ducts 32, these are also open into the first cooling fluid chamber 70.

A first surface 82 of the second manifold 80 in the form of a stator sealing surface or section 82 of the second manifold 80 may be located adjacent the second end 84 of the stator 10 and a housing sealing surface or section 86 of the second manifold 80 may be located at an inner surface 88 of the housing 50 at the second end 84 of the stator 10 to form a second cooling fluid chamber 90, with the first plurality of cooling ducts 30 being open into the second cooling fluid chamber 90. In embodiments where there is also a second plurality of cooling ducts 32 (shown in dotted lines in Figure 8, but here internally of the first plurality of cooling ducts 30), these are also open into the second cooling fluid chamber 90.

In some embodiments at least one of the first manifold 60 and the second manifold 80 is frustoconical or substantially frustoconical. Figure 6 illustrates frustoconical manifolds, with the stator sealing surface or section 62 of the first manifold 60 being the smaller diameter portion 130, of the first frustoconical manifold 60, the smaller diameter portion 130 being located adjacent the first end 64 of the stator 10. The housing sealing surface 66 of the first manifold 60 is the larger diameter portion 132, of the first frustoconical manifold 60, the larger diameter portion 132 being located at an inner surface 68 of the housing 50 at the first end 64 of the stator 10 to form the first cooling fluid chamber 70 with the first (and second) plurality of cooling ducts 30 (32) being open into the first cooling fluid chamber 70.

The stator sealing surface 82 of the second manifold 80 is the smaller diameter portion 134, of the second frustoconical manifold 80, where the smaller diameter portion 134 is located adjacent the second side end 84 of the stator 10. The housing sealing surface 86 of the second manifold 80 is the larger diameter portion 136, of the second frustoconical manifold 80, the larger diameter portion 136 being located at an inner surface 88 of the housing 50 at the second end 84 of the stator 10 to form a second cooling fluid chamber 90 with the first (and second) plurality of cooling ducts 30 (32) being open into the second cooling fluid chamber 90.

The housing 50 may comprise a cooling fluid inlet 52 between the stator sealing surface 62 of the first manifold 60 and the housing sealing surface 66 of the first manifold 60. The housing 50 may comprise a cooling fluid outlet 54 between the stator sealing surface 82 of the second manifold 80 and the housing sealing surface 86 of the second manifold 80. Cooling fluid, such as oil, is controllably directed into a first end 64 of the stator 10 via the cooling fluid inlet 52. The cooling fluid passes through stator core 12 in one direction to reduce the temperature of the electric machine 100 whilst avoiding high back pressures that may reduce cooling fluid flow to unacceptable levels. When the cooling fluid is an oil, such as a transmission oil, the increase in the temperature of the oil may lead to improved operation of the components lubricated by the oil, such as a vehicle transmission.

The cooling fluid inlet 52 is at a lower portion of the first manifold 60 when the electric machine 100 is in use. The cooling fluid outlet 54 is at an upper portion of the second manifold 80 when the electric machine 100 is in use. In alternative embodiments, the cooling fluid inlet 52 may be at a lower portion of the second manifold 80 and the cooling fluid outlet 54 may be at an upper portion of the first manifold 60, when the electric machine is in use.

The positioning of the cooling fluid inlet 52 at a lower portion of a manifold 60. 80 means that, upon charging of the electric machine 100 with cooling fluid, a significant proportion of gas bubbles can be purged from the cooling fluid by the flow of the cooling fluid from a low point in the electric machine 100 to a high point of the electric machine 100.

In order to provide the best degassing performance, the cooling fluid inlet 52 is at a lower region or the lowest region of the electric machine 100 and the cooling fluid outlet 54 outlet is on top, that is a higher region or the highest region, of the electric machine 100, so the bubbles of gas, such as air, otherwise entrained in the cooling fluid or trapped inside the electric machine 100 will naturally rise towards the cooling fluid outlet 54 and be carried out by the direction of cooling fluid flow. This may be particularly useful when the cooling fluid is oil and that oil is shared with other vehicle systems or components, such as a vehicle transmission. Oil may tend to drain from the stator 10 when the electric machine 100 and an associated pump is not active and therefore this arrangement of the cooling fluid inlet 52 and cooling fluid outlet 54 helps to reduce gas introduced into the system on each initialisation.

In particular, this feature helps to get air out of the system when initially filling the stator 10 and manifold 60, 80 arrangement with cooling fluid, and the introduction of cooling fluid at a low point in the electric machine 100 forces any entrained air or other gases to rise and be expelled from a high point of the electric machine 100.

Figure 10 illustrates an electric machine 100 without a housing 50, in order to more clearly see components of the electric machine 100. In Figure 10, the first manifold 60 is located on the stator 10 with a first tab or flange 120 extending from the first manifold 60 over the radially outer surface of the stator 10 at the first end 64 of the stator 10. The first tab or flange 120 may be located within a slot or cut-out in the radially outer surface of the stator 10 such that the first tab or flange 120 is flush with the outer surface of the stator 10. The first tab or flange 120 may be securely connected to the stator 10 with fixings through the first tab or flange 120 into the stator 10. The fixings may be, for example, bolts or locking pins. There may be a plurality of first tabs or flanges 120 disposed around the circumference of the stator 10. For example, there may be three first tabs or flanges 120.

Figure 11 illustrates an electric machine 100 without a housing 50, in order to more clearly see components of the electric machine 100. In Figure 11, the second manifold 80 is located on the stator 10 with a first portion 124 of a second tab or flange 122 extending from the first manifold 80 to the radially outer surface of the stator 10 at the second end 84 of the stator 10. The second tab or flange 122 may have a second portion 126 extending at substantially ninety degrees from the first portion 124 to overlap the radially outer surface of the stator 10. In some embodiments the second portion 126 of the second tab or flange 122 may be located within a slot or cut-out in the radially outer surface of the stator 10 such that the second portion 126 of the second tab of flange 122 is flush with the outer surface of the stator 10. The second tab or flange 122 may be securely connected to the stator 10 either with fixings through the second portion 126 of the second tab or flange 122 or with fixings through the first portion 124 of the second tab or flange 122 into the second end 84 of the stator 10. The fixings may be, for example, bolts or locking pins. There may be a plurality of second tabs or flanges 122 disposed around the circumference of the stator 10. For example, there may be three second tabs or flanges 122. The first portion 124 may be separated by a gap from the second end 84 of the stator 10 in order to not occlude any of the cooling ducts 30, 32.

Whilst an electric machine 100 has been described, in relation to Figures 6 toll having a first manifold 60 and a second manifold 80 for directing cooling fluid from a first end 64 of a stator to a second end 84 of the stator 10, with cooling fluid flow being unidirectional along the stator 10, an alternative arrangement can be provided whereby the cooling fluid passes from a first cooling fluid chamber 70 at a first end 64 of the stator 10, to a second cooling fluid chamber 90 at a second end 84 of the stator 10, via a first plurality of cooling ducts 30, and then the cooling fluid passes from the second cooling fluid chamber 90 on the second end 84 of the stator 10, to a third cooling fluid chamber 170 on the first end 64 of the stator 10, via a second plurality of cooling ducts 32. In this alternative arrangement, the cooling fluid passes around the stator 10 with a U-flow, entering and exiting the stator 10 from the same end of the electric machine 100.

One example of this alternative manifold arrangement is illustrated in Figure 12. Figure 12 illustrates frustoconical manifolds, though it will be understood that other forms and shapes of manifolds can be provided to function in the same or a similar manner as described in relation to Figure 12.

In Figure 12, a first frustoconical manifold 160 comprises a first frustoconical section 162 and a second frustoconical section 164, where the second frustoconical section 164 is smaller than the first frustoconical section 162 and is located between the first frustoconical section 162 and the first end 64 of the stator 10, the smaller diameter portion 166 of the first frustoconical section 162 being located adjacent the first side 64 of the stator 10 and the larger diameter portion 168 of the first frustoconical section 162 being located at an inner surface 68 of the housing 50 adjacent the first end 64 of the stator 10. The volume formed in the first manifold 160 between the first frustoconical section 162 and the second frustoconical section 164 forms a first cooling fluid chamber 70 with a first plurality of cooling ducts 30 being open into the first cooling fluid chamber 70.

The smaller diameter portion 172 of the second frustoconical section 164 is located adjacent the first end 64 of the stator 10 and the larger diameter portion 174 of the second frustoconical section 164 is located at an inner surface 68 of the housing 50 at the first end 64 of the stator 10 to form a third cooling fluid chamber 170 with a second plurality of cooling ducts 32 being open into the third cooling fluid chamber 170. The first plurality of cooling ducts 30 and the second plurality of cooling ducts 32 are open into the second cooling fluid chamber 90, which chamber defines a return chamber for the cooling fluid at the second end 84 of the stator 10.

In the arrangement of Figure 12 cooling fluid, such as oil can flow in both directions parallel to the stator central axis 16 through the stator core 12 to provide more even cooling along the stator core 12.

A cooling fluid inlet 152 is located between a base 168 of the first frustoconical section 162 of the first frustoconical manifold 160 and the base 174 of the second frustoconical section 164 of the first frustoconical manifold 160, and wherein the electric machine 100 comprises a cooling fluid outlet 154 between the first end of the stator 64 and the base 174 of the second frustoconical section 164 of the first frustoconical manifold 160. The cooling fluid inlet 152 is positioned at a lower part of the first frustoconical manifold 160 and the cooling fluid outlet 154 is positioned at a higher part of the first frustoconical manifold 160.

The arrangement of a first manifold 160 with two cooling fluid chambers 70, 170 and a second manifold 180 with one cooling fluid chamber 90 therefore provides a U-flow cooling fluid path, the two cooling fluid chambers 70, 170 of the first manifold 160 providing two concentric annular volumes, an innermost volume 70 in fluid communication with the first plurality of cooling ducts 30 and the outermost volume 170 arranged to be in fluid communication with the second plurality of cooling ducts 32. In use, the cooling fluid is introduced into the first plurality of cooling ducts 30 via an inlet 152 at a first end 64 of the stator 10, the inlet 152 being in fluid communication with the innermost volume 70. The cooling fluid then flows along the first plurality of cooling ducts 30 to a second manifold 180 located at the second end 84 of the stator 10. This second manifold 180 comprises a second cooling chamber 90 which is in fluid communication with both the first and second pluralities of cooling ducts 30, 32, and directs the cooling fluid entering the second cooling chamber 90 from the first plurality of cooling ducts 30 into the second plurality of cooling ducts 32, where it flows back to the first manifold 160 to an outlet 154 in fluid communication with the outermost volume 170. As shown in Figure 12, the inlet 152 is located adjacent a lowermost region of the electric machine 100 and the outlet 154 is adjacent an uppermost region of the electric machine 100.

The first plurality of cooling ducts 30 and the second plurality of cooling ducts 32 have been described herein as having a profile comprising or consisting of a circle. It will be understood that the first and second cooling ducts 30, 32 may have different profiles. For example, at least one of the first and second cooling ducts 30, 32 may have a profile comprising or consisting of a polygon in transverse section. The polygon may be composed of a plurality of edges and a plurality of corners. The polygon may be equilateral and/or equiangular. The polygon may a line of (reflection) symmetry. At least in certain embodiments, the polygon may be a regular polygon. Further variants having different profiles are illustrated by way of example in Figures 14 and 15.

The first and second cooling ducts 30, 32 in the arrangement illustrated in Figure 14 have like profiles. However, the first and second cooling ducts 30, 32 have opposite orientations. The first cooling ducts 30 are a mirror image (or a reversed image) of the second cooling ducts 32. The configuration of the first and second cooling ducts 30, 32 will now be described in more detail.

In the arrangement illustrated in Figure 14, the first cooling duct 30 each have a profile comprising or consisting of a first triangle in transverse section. The first triangle is composed of a plurality of first edges 31-n and a plurality of first corners 33-n. The first edges 31-n in the present embodiment are linear such that the sidewalls of the first cooling ducts 30 are at least substantially planar. In a variant, the first edges 31-n may be curved, for example concave or convex. The first corners 33-n of the first triangle are rounded. Each of the first cooling ducts 30 comprises a first major axis which is a line of (reflection) symmetry. The first cooling ducts 30 are oriented such that the first major axis is at least substantially coincident with the central slot axis 22. In the present embodiment, the first triangle is an equilateral triangle, but other types of triangle are contemplated. For example, the first triangle may be an isosceles triangle.

A first one of the first edges 31-1 is disposed in a radially innermost position. The first one of the first edges 31-1 extends substantially perpendicular to the central slot axis 22. The first one of the first edges 31-1 is disposed closest to the winding slot 20. In particular, the first one of the first edges 31-1 is disposed closest to the slot base 28. The first one of the first edges 31-1 is presented to the winding slot 20. At least in certain embodiments, the positioning of an edge 31-n (rather than a corner 33-n) of the first cooling duct 30 closest to the winding slot 20 may provide improved heat transfer properties when in use. A first one of the first corners 33- 1 is disposed opposite the first said first edge 31-1. The first one of the first corners 33-1 is disposed in a radially outermost position. The first one of the first corners 33-1 is oriented radially outwardly away from the winding slot 20.

In the arrangement illustrated in Figure 14, the second cooling ducts 32 each have a profile comprising or consisting of a second triangle in transverse section. The second triangle is composed of a plurality of second edges 35-n and a plurality of second corners 37-n. The second edges in the present embodiment are linear such that the sidewalls of the second cooling ducts 32 are at least substantially planar. In a variant, the second edges 35-n may be curved, for example concave or convex. The second corners 37-n of the second triangle are rounded. Each of the second cooling ducts 30 comprises a first major axis which is a second line of (reflection) symmetry. The second cooling ducts 32 are oriented such that the second major axis is at least substantially coincident with the central tooth axis 27. In the present embodiment, the second triangle is an equilateral triangle, but other types of triangle are contemplated. For example, the second triangle may be an isosceles triangle. A first one of the second edges 35-1 is disposed in a radially outermost position. The first one of the second edges 35-1 extends substantially perpendicular to the central tooth axis 27. The first one of the second edges 35-1 is disposed in a radially outermost position. A first one of the second corners 37-1 is disposed closest to the stator tooth 25. The first one of the second corners 371 is oriented radially inwardly towards the stator tooth 25. At least in certain embodiments, orienting the first one of the second corners 37-1 inwardly may, in use, provide improved flux distribution within the stator core 12.

The first and second cooling ducts 30, 32 are arranged in the stator core 12 so as at least partially to overlap with each other in a radial direction. The first one of the first corners 33-1 of the first cooling ducts 30 is disposed radially outwardly of the first one of the second corners 37-1 of the second cooling ducts 32. The first and second cooling ducts may have a partially interlocking (or tessellated) arrangement. In a variant, the first and second ducts 30, 32 may be spaced apart from each other in a radial direction so that there is no overlap in a radial direction. The first and second cooling ducts 30, 32 in the present embodiment are spaced apart from each other in a circumferential direction. In other words, there is no overlap between the first and second cooling ducts 30, 32 in the circumferential direction. In a variant, the first and second cooling ducts 30, 32 may be arranged in the stator core 12 so as at least partially to overlap with each other in a circumferential direction.

The first and second cooling ducts 30, 32 in the arrangement illustrated in Figure 15 have like profiles. Furthermore, the first and second cooling ducts 30, 32 have like orientations. The configuration of the first and second cooling ducts 30, 32 will now be described in more detail.

In the arrangement illustrated in Figure 15, the first cooling ducts 30 each have a profile comprising or consisting of a first rhombus in transverse section. The first rhombus is composed of a plurality of edges and a plurality of corners. The edges in the present embodiment are linear such that the sidewalls of the first cooling ducts 30 are at least substantially planar. The corners of the first rhombus are rounded. Each of the first cooling ducts 30 comprises a first major axis which is a line of (reflection) symmetry. The first cooling ducts 30 are oriented such that the first major axis is at least substantially coincident with the central slot axis 22. Each of the first cooling ducts 30 comprises a first minor axis which is a line of (reflection) symmetry. The first cooling ducts 30 are oriented such that the first minor axis is at least substantially perpendicular to the central slot axis 22.

In the arrangement illustrated in Figure 15, the second cooling ducts 32 each have a profile comprising or consisting of a second rhombus in transverse section. The second rhombus is composed of a plurality of edges and a plurality of corners. The edges in the present embodiment are linear such that the sidewalls of the second cooling ducts 32 are at least substantially planar. The corners of the second rhombus are rounded. Each of the second cooling ducts 30 comprises a first major axis which is a second line of (reflection) symmetry. The second cooling ducts 32 are oriented such that the second major axis is at least substantially coincident with the central tooth axis 27. Each of the second cooling ducts 32 comprises a second minor axis which is a line of (reflection) symmetry. The second cooling ducts 32 are oriented such that the second minor axis is at least substantially perpendicular to the central tooth axis 27.

The first and second cooling ducts 30, 32 are arranged in the stator core 12 so as at least partially to overlap with each other in a radial direction. The outermost corner of each of the first cooling ducts 30 is disposed radially outwardly of the innermost corner of each of the second cooling ducts 32. This radial overlap may optionally be applied to the other configurations described herein. The first and second cooling ducts 30, 32 may have a partially interlocking (or tessellated) arrangement. Alternatively, the first and second ducts 30, 32 may be spaced apart from each other in a radial direction so that there is no overlap in a radial direction.

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.

Claims (15)

1. CLAIMS1. A stator core for a stator of an electric machine, the stator core comprising: a central stator axis; a plurality of winding slots in the stator core; and a first plurality of cooling ducts extending through the stator core from a first end of the stator core to a second end of the stator core; wherein the cooling ducts are radially separated from the winding slots by regions of the stator core.
2. 2. A stator core according to claim 1 wherein each of the plurality of winding slots has a central slot axis, wherein one of the first plurality of cooling ducts is positioned on the central slot axis of a corresponding winding slot.
3. 3. A stator core according to claim 2, wherein each of the first plurality of cooling ducts has a geometric centre, the geometric centre of each of the first plurality of cooling ducts being positioned on the central slot axis of the corresponding winding slot.
4. 4. A stator core according to any preceding claim, the stator core comprising a second plurality of cooling ducts radially and/or circumferentially separated from the first plurality of cooling ducts.
5. 5. A stator core according to claim 4 comprising a plurality of stator teeth, each of the plurality of stator teeth having a central tooth axis, wherein one of the second plurality of cooling ducts is positioned on the central tooth axis of a corresponding stator tooth.
6. 6. A stator core according to claim 5, wherein each of the second plurality of cooling ducts has a geometric centre, the geometric centre of each of the second plurality of cooling ducts being positioned on the central tooth axis of the corresponding stator tooth.
7. 7. A stator core according to any one of claims 4, 5 or 6, wherein the second plurality of cooling ducts have the same cross section as the first plurality of cooling ducts.
8. 8. An electric machine comprising: a stator core according to any preceding claim.
9. 9. An electric machine according to claim 8 comprising: a substantially cylindrical housing surrounding the stator core; a first manifold provided at the first end of the stator core and configured to fluidly couple respective first ends of a first plurality of cooling ducts formed in the stator core; and a second manifold provided at the second end of the stator core and configured to fluidly couple respective second ends of the first plurality of cooling ducts.
10. 10. An electric machine according to claim 9, wherein the first manifold and the second manifold are secured to the stator core, at least in part, by the housing. 10
11. 11. An electric machine according to claim 9 or claim 10, wherein the first manifold cooperates with the stator core to form a first cooling fluid chamber, the first plurality of cooling ducts being open into the first cooling fluid chamber, and wherein the second manifold cooperate with the stator core to form a second cooling fluid chamber, the first plurality of cooling ducts being open into the second cooling fluid chamber.
12. 12. An electric machine according to claim 11 comprising a cooling fluid inlet in fluid communication with the first cooling fluid chamber, and a cooling fluid outlet in fluid communication with the second cooling fluid chamber; wherein, in use, cooling fluid is supplied to the first plurality of cooling ducts via the cooling fluid inlet and is discharged through the cooling fluid outlet.
13. 13. An electric machine according to claim 12, wherein the cooling fluid inlet is at a lower portion of the first manifold and the cooling fluid outlet is at an upper portion of the second manifold when the electric machine is in use.
14. 14. An electric machine according to any of claims 9 to 13, when dependent directly or indirectly on claim 4, wherein each of the second plurality of cooling ducts is open into the first cooling fluid chamber and open into the second cooling fluid chamber.
15. 15. A vehicle comprising a stator core according to any of claims 1 to 7 or an electric machine according to any one of claims 8 to 14.