Motor and method of cooling a motor

Abstract

A motor is described comprising a rotor shaft comprising a cooling channel having at least one inlet for receiving a cooling fluid, and at least one outlet section fluidically connected with the cooling channel at an outer side of the rotor shaft and arranged to allow the cooling fluid to flow out of the cooling channel, wherein an outlet opening of the at least one outlet section is provided at a larger radial distance from an inner cross-sectional area of the rotor shaft interior cooling channel.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to the cooling of a motor. BACKGROUND

[0002] A motor (engine) is considered to be a machine with a rotor shaft that rotates when the motor is in operation, such as an electric motor or a gas turbine. An electric motor generally comprises a stator in which a rotor is rotatably mounted. The rotor is provided with a rotor shaft. A gas turbine comprises a rotor shaft that is cooled during operation.

[0003] Generally, for cooling purposes, the rotor shaft is at least partly hollow and comprises a cooling channel arranged to receive a cooling fluid. The cooling fluid absorbs heat from the hollow rotor shaft by conduction and / or convection heat transfer, thereby cooling the hollow rotor shaft. The cooling channel can have an outlet via which the cooling fluid exits the cooling channel. The cooling fluid is re-collected in a fluid reservoir, such as a sump. Generally, an electric pump is provided to pump the cooling fluid from the reservoir into the cooling channel. Also, when the electric motor is in a standstill, the cooling fluid flows out of the cooling channel, the cooling channel is emptied and filled with air. When the electric motor is started again and the rotor starts rotating, the pump first needs to fill the channel with cooling fluid and to chase the air out of the cooling channel. This can generate some noise, as the air and the coolant are mixed. During this start-up phase, the cooling is also rather inefficient due to the presence of air and / or air bubbles that need to be removed first.

[0004] There is a need for a motor cooling system that is less costly and / or can require less space, while providing an effective cooling of the motor. SUMMARY

[0005] According to an aspect of the present invention, a motor is provided, comprising a rotor shaft comprising a cooling channel having at least one inlet for receiving cooling fluid, and at least one outlet located at an outer side of the rotor shaft, arranged to allow cooling fluid to flow out of the cooling channel, wherein the outlet of the cooling channel is provided at the same end of the rotor shaft as the inlet of the cooling channel, the motor further comprising at least one outlet section fluidly connected to the outlet of the cooling channel and arranged to allow cooling fluid to flow out of the cooling channel, wherein the radial position of the outlet section, measured from the rotational axis of the rotor shaft, is larger than the radial position of the cooling channel inside the rotor shaft, and wherein the at least one outlet section comprises an outlet passage arranged to fluidly connect the outlet of the cooling channel with the outside of the rotor shaft, wherein the outlet passage is arranged mostly in the radial direction of the rotor shaft. By providing an outlet section fluidly connected to the cooling channel in the rotor shaft, but with its outlet opening provided at the outer radius of the rotor shaft, centrifugal forces act on the fluid in the outlet section, which can result in the outlet section having a pumping function. The outlet section can then pump cooling fluid from the cooling channel, without the need for a separate electric pump. During operation, the rotation of the rotor shaft generates centrifugal forces on the cooling fluid. By providing an outlet opening with a larger radial distance to the rotational axis of the rotor shaft than the cooling channel through which the cooling fluid passes, a pressure difference is generated. This pressure difference provides a pumping for the cooling fluid. During operation, the cooling fluid is pumped towards the outlet opening, so that a separate pump for pumping the cooling fluid can be saved. Since a pump is no longer needed to pump the cooling fluid, the cooling system of the motor can be made simpler and more cost-effective. By providing the outlet passage mostly in the radial direction of the rotor shaft, the cooling fluid flowing through the outlet passage is accelerated, locking the cooling fluid in the radial direction out of the outlet passage with a speed sufficient to splash the cooling fluid onto the coil winding of the stator of the motor. The outlet of the cooling channel is at the same end of the rotor shaft as the inlet of the cooling channel. In order to allow the cooling fluid to pass approximately through the axial length of the rotor shaft, the cooling channel can be provided with an inner channel and an outer channel arranged concentrically around the inner channel. At the end of the rotor shaft opposite to the inlet end, the inner channel and the outer channel are fluidly connected to each other, for example by means of a radial hole in the rotor shaft, to allow the cooling fluid to flow from the inner channel to the outer channel. The outer channel can thus be considered as a return channel for the cooling fluid. Typically, the inner channel comprises the inlet fluidly connected to a fluid reservoir, while the outlet passage comprises the outlet section with its outlet opening provided at the same end as the inlet. This can also save space and provide a compact construction for the cooling system with the cooling fluid reservoir, the inlet and the outlet opening.

[0006] Advantageously, the cooling channel has an inlet which is in fluid connection with a fluid reservoir, typically a sump collecting cooling fluid. Due to the larger radius of the outlet opening compared to the radius of the cooling channel, a suction function can be provided which allows the outlet section to suck cooling fluid from the cooling fluid reservoir via the cooling channel. In this way, a separate electric pump can be omitted, which is advantageous in terms of costs and / or use of space for the powertrain, and reduces the risk of cavitation associated with a separate electric pump. In addition, cooling can become more effective, since the suction effect can increase with increasing rotational speed, since the pressure difference between the inlet and the outlet due to centrifugal forces increases with increasing rotational speed. Typically, the losses of the motor and / or the heat generation of the motor also increase with increasing rotational speed, which creates a cooling mechanism which delivers effective cooling only when it is needed, i.e. more cooling fluid is provided at higher rotational speeds.

[0007] Advantageously, the fluid reservoir is elevated with respect to the cooling channel. By providing the cooling fluid reservoir at a higher level than the cooling channel, in particular at a higher level than the inlet of the cooling channel, cooling fluid can flow into the cooling channel when the rotor shaft is at rest, and thus the cooling channel can be pre-filled at rest. For example, when starting from a state of rest, air present in the cooling channel can gradually be sucked out of the cooling channel, while coolant is sucked in. By providing an elevated reservoir filled with cooling fluid, the filling process of the cooling channel can be accelerated when the motor is started. Thus, mixing and / or interference between air and / or coolant can be less, thus reducing noise and increasing efficiency.

[0008] Advantageously, the cooling fluid reservoir is passively filled by fluid splashing from a rotating component present in the same housing as the rotor shaft, preferably the rotating component can be a gearwheel. For example, the reservoir can be passively filled with cooling fluid which is splashed around or upwards by one or more gearwheels present in the same housing as the rotor shaft. The gearwheels can be directly or indirectly coupled to the rotor shaft. Thus, no additional energy, for example by an actively operable pump, is required to transfer fluid from the motor assembly to the reservoir. This additionally provides a cost-effective and space-efficient cooling system.

[0009] When the motor is an electric machine having a rotor mounted on a rotor shaft and a stator arranged around the rotor, the cooling system of the electric machine can thus be provided without an additional pump. Thus, in the cooling system according to the application, an electric pump which is typically present in known cooling systems can be omitted. Thus, the cooling system can be based on gravitational energy, with the cooling fluid reservoir elevated with respect to the inlet of the cooling channel, on centrifugal energy, with the outlet opening having a larger radial distance than the inlet, and on splashing of cooling fluid to fill the reservoir.

[0010] Alternatively, the outer channel can be provided outside the rotor shaft, and there is a rotor shaft wall between the inner channel inside the rotor shaft and the return outer channel outside the rotor shaft. This can be advantageous in a configuration where the rotor shaft can have a limited diameter. Alternatively, such a configuration can also be advantageous in an electric machine. The outer channel can then be provided as a plurality of axial slots in the rotor set, thereby providing a more efficient heat transfer from the rotor set to the cooling fluid.

[0011] Advantageously, the cooling channel comprises a cooling rib. By providing a cooling rib, the area where the cooling fluid makes contact is larger, and thus the convective heat transfer can be increased, thereby providing a more efficient and / or effective cooling. When the cooling channel comprises an inlet channel and an outlet channel, the cooling rib can be provided in the inlet channel or the outlet channel.

[0012] Advantageously, the cooling rib can comprise an inner channel and an outer channel separate from the inner channel, wherein the inner channel is in fluid connection with the inlet of the cooling channel, and wherein the outer channel is in fluid connection with the outlet of the cooling channel, wherein the cooling rib can further comprise at least one cooling rib opening arranged in fluid connection with the inner channel and the outer channel, wherein the at least one cooling rib opening is arranged close to the opposite end of the rotor shaft from the inlet and the outlet of the cooling channel. In this way, an inner channel is provided in fluid connection with an outer channel, and wherein the inner channel is used as a first part of the cooling channel, which brings the coolant from the inlet opening towards the opposite end of the rotor shaft, and wherein the outer channel is used as a second part of the cooling channel, and brings the coolant back from the axially opposite end of the rotor shaft towards the outlet of the cooling channel, thus enabling a configuration where the outlet opening is provided at the same end of the rotor shaft as the inlet. The inner channel allows the cooling fluid to flow in one direction, while in the outer channel the cooling fluid flows in the other direction towards the outlet.

[0013] In an embodiment, the cooling rib can comprise an inner tube in which the fluid can flow, and which forms the inlet channel. The inner tube has outwardly extending protrusions, such as external fins or pads, which keep it centered inside the rotor shaft chamber. The fluid can exit the inner tube and enter a space between the inner tube and the rotor shaft chamber to return. The space between the cooling fins of the inner tube and the rotor shaft chamber thus forms the outlet channel.

[0014] The outward protrusions can be spring biased towards the inner wall of the rotor shaft, thereby increasing the contact surface with the inner wall of the rotor shaft, and keeping it centered in the rotor shaft. The outward protrusions of the cooling rib that keep it centered can be designed to be flexible, slightly oversized, acting like a spring to establish a clamping force during assembly. This clamping force keeps the cooling rib in place during operation of the electric machine.

[0015] The cooling ribs can be manufactured in a material having a higher thermal conductivity than the rotor shaft material, preferably an aluminium or copper alloy. Also, for cost saving reasons, they can be produced as extruded profiles, preferably extruded aluminium.

[0016] The shape of the cooling rib protrusions, like fins or ribs, is designed to allow proper centering and clamping, but also to have a large contact surface with the rotor shaft, allowing heat to flow from the rotor shaft into the cooling ribs. Furthermore, a large contact surface with the coolant flow outside the inner tube should be provided. There should be enough fins connected to the inner tube, preferably three or more, to provide heat conduction to the inner tube, where the coolant can also absorb heat. Finally, for extruded profiles, a minimum clearance of 3 mm and a wall thickness of 1.5 mm needs to be respected.

[0017] Advantageously, the outlet section comprises a flow restriction. By providing a flow restriction in the outlet section, the back pressure in the cooling channel is increased, reducing the flow of cooling fluid towards the outlet opening. The flow restriction allows the cooling fluid to exit the outlet section, but restricts the outlet flow. Such a flow restriction creates a back pressure, reducing the volume flow, so that a suitable flow at maximum rotational speed can be made according to the cooling requirements. Such a flow restriction also reduces the underpressure created in the cooling channel and can be used to prevent cavitation phenomena in the coolant channel, which would otherwise reduce the cooling performance. For example, the flow restriction can be provided as a smaller cross-sectional area in the outlet section than the cooling channel or another part of the outlet section. To provide a smaller cross-sectional area in the outlet section, the outlet section can be locally narrowed, or a plate or rib can be provided to provide a narrowing of the cross-sectional area in the outlet section. The smaller cross-sectional area in the outlet section can locally result in an increase of both the dynamic pressure and the friction of the viscous forces. The increase in friction over the smaller cross-sectional area, like a part of the outlet section, can reduce the flow speed of the cooling fluid in the cooling channel.

[0018] Another effect of the smaller cross-sectional area at the outlet is an increase in back pressure, which can prevent cavitation. Due to the acceleration of the flow towards the outlet, a higher pressure is built up throughout the cooling channel. As a result, the centrifugal force cannot accelerate a part of the liquid towards the outlet, leaving a partial vacuum or vapor bubble in between. This cavitation phenomenon reduces the overall benefit of the centrifugal pumping action, because the pressure cannot be reduced further and the part of the liquid on the other side of the vapor bubble can only be accelerated by the pressure difference between the inlet and the vacuum. Therefore, if a straight outlet hole without a flow restriction is used and cavitation starts to occur from a given rotational speed, the inlet flow will not benefit from the additional centrifugal force acting on the outlet. However, the shaft torque loss and the power loss of the pumping mechanism will still increase with increasing rotational speed, because the centrifugal acceleration is still effective. This is why an outlet restriction or nozzle-shaped outlet increases the overall efficiency of the pumping mechanism.

[0019] It will be appreciated that, regardless of the rotational speed of the shaft, an increase in both dynamic pressure and viscous friction can exist at the smaller cross-section. However, it will be appreciated that both effects increase with increasing flow, which counteracts the effect of increasing rotational speed on flow.

[0020] Advantageously, the at least one outlet passage of the at least one outlet section is provided as a radially extending bore. Thus, the outlet section can be radially fluidly connected with the outlet in a radial direction through a wall of the rotor shaft. More advantageously, the inner diameter of the radially extending bore is decreasing in an outward direction. Thus, the radially extending bore can have a conical shape in a direction away from the rotor shaft. The inner diameter of the outer end of the radial bore is smaller than the inner diameter of the inner end of the radial bore, thereby providing a flow restriction for the cooling fluid output via the outlet section.

[0021] Advantageously, a ring is provided which can be engaged with the outer surface of the rotor shaft, wherein the ring comprises the at least one outlet section. By providing a ring comprising the outlet section, the assembly of the outlet section with the rotor shaft becomes relatively easy. Preferably, the ring has a circumferential recess on its inner side. Providing such an inner circumferential recess allows the ring to be positioned without the need for alignment with the outlet of the rotor shaft. Via the recess, cooling fluid can be distributed over the recess and can further enter the outlet section.

[0022] Alternatively and / or additionally, the outlet section can comprise a nozzle. Such a nozzle can achieve the same or similar effects as a smaller cross-sectional area and can be used for additional cooling applications, such as spraying a coolant to end windings extending axially from a laminated iron of a motor stator or to other components, such as a gear, typically arranged in the same housing as the rotor shaft, preferably at or near the outlet opening.

[0023] Advantageously, the nozzle can be positioned adjacent to the outlet opening. Preferably, the nozzle can be positioned at the outlet opening such that the nozzle can form the outlet opening. Positioning the nozzle at the outlet opening can provide an easy way to construct the outlet section of the cooling channel. The nozzle can also provide a smaller cross-sectional area, obviating the need to implement a separate smaller cross-sectional area in the outlet section, resulting in that the outlet section can be easier to manufacture.

[0024] Advantageously, the nozzle adjacent to the outlet opening can be arranged backwards with respect to its normal direction of rotational movement, thereby reducing the momentum of the fluid particles leaving the nozzle. This can reduce the reaction torque of the rotor shaft caused by the cooling mechanism compared to similar systems using friction-dominated small cross-section flow restrictions. The nozzle can be provided in the outlet opening for spraying or the outlet section itself can be shaped as a nozzle having only the effect of a flow restrictor, such as a conically tapered radial bore with a decreasing cross-section outwardly.

[0025] The stator of the electric machine can comprise an end winding extending outwardly at least at one end of the stator. The outlet opening can then be configured to spray cooling fluid towards the extending winding to cool said end winding. Thus, additional cooling of the stator can be provided.

[0026] In another embodiment, a cooling surface can be provided at or near the outlet opening, against which cooling fluid exiting the outlet opening can be splashed to cool the cooling fluid for further use. The cooled cooling fluid can then flow back to the reservoir, where it can be reused in the cooling system.

[0027] Advantageously, a part of the outlet section is at a larger distance from the rotational axis of the rotor shaft than the outlet opening, forming a siphon. By providing such a part of the outlet section, evacuation of the cooling channel can be somewhat slower when the rotor shaft is stopped rotating. This can cause some amount of cooling fluid to remain in the cooling channel, in particular in the outlet section of the cooling channel. Another advantage of such a part of the outlet section is that it can prevent ambient fluid from entering the cooling channel when the rotor shaft is rotating. The centrifugal pressure in the part of the outlet section can be larger than the centrifugal pressure at the outlet opening, because the radial distance of the outlet opening from the rotational axis of the shaft is smaller. This can result in that, at least above a certain rotational speed of the shaft, the total pressure is at its highest at said part of the outlet section, while the total pressure drops between said part of the outlet section and the outlet opening. The drop in total pressure near the outlet opening can also prevent ambient fluid from entering the cooling section. Thus, the outlet section comprises a siphon, which is able to retain a portion of the liquid fluid and seal the outlet against ambient gas when the rotational speed is high enough. Said part of the cooling section can remain filled with cooling fluid when the rotor shaft is rotating, thereby also preventing air from entering the cooling section and further into the cooling channel. This can reduce noise and can improve the efficiency of the cooling.

[0028] Advantageously or alternatively, a part of the outlet section can be U-shaped, the bridge of the U of said part being at a larger radial distance from the rotational axis of the rotor shaft than the outlet opening. The U-shaped section forms a siphon and provides a siphon effect, in which some amount of cooling fluid can remain in the outlet section.

[0029] Additionally or alternatively, a check valve can also be installed in the outlet section, which only opens when there is sufficient fluid pressure from the inside. Such a check valve can effectively prevent ambient air from entering the pumping mechanism. It can also serve to keep the oil inside the rotor shaft during low rotational speeds and at standstill. If installed in a radial manner, the centrifugal force acting on the valve body adds to the fluid pressure, and thus the opening characteristic depends on the rotational speed of the rotor shaft. Thus, the check valve provides another way to control the fluid flow through the shaft depending on the rotational speed of the rotor. Another advantage is that the check valve can be used as a standard component, which can result in a more cost-effective assembly compared to a self-designed design with a siphon.

[0030] Alternatively, the portion of the cooling channel that returns fluid from the opposite axial end to the inlet and outlet of the fluid connection channel of the outlet section can be formed between an axially extending recess on the inner surface of the laminated stack and the outer surface of the rotor shaft. By providing the portion of the cooling channel between the axially extending recess on the inner surface of the laminated stack and the outer surface of the rotor shaft, direct cooling of the laminated stack by the cooling fluid is achieved, increasing the overall cooling efficiency of the motor.

[0031] Alternatively, the outlet section is integrally formed in the rotor shaft, comprising a drilled channel connecting the cooling channel and at least one outlet opening.

[0032] The rotor shaft can provide two shaft portions that are engageable with each other. To engage the two shaft portions, an axially movable splined connection can be used, which allows axial movement but not rotational movement between the two shaft portions. Between the splines of the connection, a channel can be provided to allow cooling fluid to pass through. In practice, this can be achieved by omitting at least one spline of the splined connection between the two shafts, the omitted spline thus forming the outlet channel. As an alternative, the two shaft portions can be connected using a threaded connection. Between the threads of the threaded connection, a channel can be provided to allow cooling fluid to pass through. In practice, this can be achieved by omitting at least one thread of the threaded connection, the omitted thread forming the outlet channel. Advantageously, as an outlet opening providing a pumping effect of the cooling fluid, the last thread or spline end of such a threaded or splined connection has a large radial distance from the rotating shaft. Thus, in an advantageous manner, the threaded or splined connection can be integrated into the cooling system, fluidly connected to the cooling channel provided in the shaft component, providing a compact construction of the cooling system. Now, not only the pump, but also any additional elements or any additional interference with the rotor shaft to provide the outlet section can be saved.

[0033] According to another aspect of the present invention, an electric or hybrid vehicle transmission is provided, comprising a motor as described above, wherein the cooling channel of the rotor shaft is arranged to be connected with a cooling system of the electric or hybrid vehicle transmission to allow cooling fluid to flow into the channel.

[0034] The motor, such as an electric machine, can be comprised in a vehicle powertrain. Advantageously, the outlet section can then be integrated in a park lock wheel connectable with the rotor shaft. To this end, the park lock wheel can comprise a plurality of holes in fluid connection with the cooling channel of the rotor shaft, which holes are in fluid connection with at least one outlet opening to allow the cooling fluid to exit the cooling channel. Thus, the outlet section in the park lock wheel can comprise the plurality of holes provided in the park lock wheel. The radial diameter of the outlet opening can thus be larger than the inlet of the cooling channel, and the outlet section can additionally comprise the flow restriction described above.

[0035] According to another aspect of the present invention, a method for cooling a machine is provided, comprising providing a motor having a rotor with a rotor shaft and a stator mounted on the rotor; the rotor shaft having a cooling channel with at least one inlet for receiving a cooling fluid, and at least one outlet at an outer side of the rotor shaft arranged to allow the cooling fluid to flow out of the cooling channel, wherein the outlet of the cooling channel is provided at the same end of the rotor shaft as the inlet of the cooling channel, the motor further comprising at least one outlet section in fluid connection with the outlet of the cooling channel and arranged to allow the cooling fluid to flow out of the cooling channel, wherein the radial position of the at least one outlet section, measured from the rotational axis of the rotor shaft, is larger than the radial position of the cooling channel inside the rotor shaft, and wherein the at least one outlet section comprises an outlet passage arranged to fluidly connect the outlet of the cooling channel with the outside of the rotor shaft, wherein the outlet passage is arranged mostly in the radial direction of the rotor shaft. BRIEF DESCRIPTION OF DRAWINGS

[0036] The present disclosure is further illustrated by means of a schematic drawing. In this drawing, the following drawing is shown.

[0037] Figure 1 A cross-sectional view of an embodiment of the present invention is shown.

[0038] Figure 2 A cross-sectional view of an exemplary embodiment of the hollow shaft of the present invention is shown.

[0039] Fig. 3a, 3b, 3c, 3d and 3e show exemplary schematic embodiments of an outlet section according to the present invention. Fig. 3f is a schematic perspective view of a rotor shaft with a ring comprising the outlet section of Fig. 3d. Fig. 3g is a schematic perspective view of a ring comprising the outlet section of Fig. 3e.

[0040] Figure 4 An example of an outlet section at a threaded or splined connection between two shaft parts is shown.

[0041] Figure 5 An alternative embodiment of the example of Figure 1 is shown.

[0042] Figure 6 An example of a rotor shaft with an outlet section is shown.

[0043] Figure 7 An example of a cooling body close to an outlet opening is shown.

[0044] Figure 8 A graph showing the cooling fluid flow rate and static pressure as a function of the number of revolutions per minute of the shaft at the inlet of the present invention is shown.

[0045] Figure 9 An example of an exemplary schematic embodiment of an outlet section with a check valve according to the present invention is shown.

[0046] Figures 10a, 10b, 10c, 10d, 10e and 10f show embodiments of cooling fins according to the present invention.

[0047] Figure 11 A cooling channel is shown, where a return channel is formed in the outside of the rotor shaft, in a channel between the rotor shaft and the laminated iron of the rotor stack of the electric machine.

[0048] Figure 12 shows an outlet opening integrated in a parking lock wheel of a transmission. DETAILED DESCRIPTION

[0049] Embodiments of the present disclosure are illustrated by means of schematic drawings. Similar features are denoted by the same or similar reference numerals throughout the drawings. The drawings are not to scale and are only schematic.

[0050] Figure 1 A cross-sectional schematic view of an embodiment of the present invention is shown. Figure 1 An electric machine 1 is shown, comprising a rotor shaft 2 comprising a cooling channel 4. The electric machine 1 further comprises a rotor 6 fixedly connected with the shaft 2, for example by means of an interference fit or by means of a shaft key. The rotor 6 and the shaft 2 are rotatably mounted in a stator 8 using bearings 10. There can be more bearings, for example at the end of the shaft 2 extending outside the rotor 6, but these are not shown in order not to complicate the drawing too much. The electric machine 1 further comprises two outlet sections 12. The outlet sections 12 are here provided as ring-like elements mounted on the rotor shaft 2 and can engage with the outer wall of the rotor shaft 2. The cooling channel 4 is fluidly connected with a cooling fluid reservoir 14 through a cooling fluid inlet 16. The inlet 16 can remain stationary while the shaft 2 is rotating, for example by means of a seal (not shown) mounted between the water inlet 16 and the shaft 2 preventing leakage of cooling fluid, such as a lip seal or a labyrinth seal.

[0051] The electric machine 1 generates heat during operation. The reservoir 14 provides cooling fluid, which flows from the reservoir 14 through the inlet 16 into the channel 4. AsFigure 1 As shown, the passage 4 is divided into an inner and outer portion, fluidly connected at an opposite side of the shaft 2 from the inlet 16. Cooling fluid flowing through the passage 4 absorbs heat from the shaft 2 by conduction and convective heat transfer, thereby cooling the shaft 2 and the rotor 6.

[0052] The outlet opening 32 is positioned at a greater radius than the cooling fluid inlet 16. As the rotor shaft 2 rotates, centrifugal forces create a pressure differential between the outlet opening 32 and the inlet 16. This pressure differential allows for a pumping function that enables the outlet section 12 to draw cooling fluid from the reservoir 14. As such, a separate electrically powered pump can be eliminated. An increase in rotational speed increases the centrifugal forces acting on the cooling fluid. The increase in centrifugal forces results in an increase in the pressure differential between the inlet 16 and the outlet opening 32, thereby increasing the effect of the pumping function.

[0053] The outlet section 12 includes an outlet opening 32 that allows cooling fluid to exit the cooling passage 4. As shown, Figure 1 As shown, the portion of the outlet section 12 that is further from the axis of rotation A than the outlet opening. As the shaft 2 rotates, the pressure in the portion of the outlet section 12 that is further from the axis of rotation A is higher than the pressure in the outlet opening 32 due to centrifugal forces acting on the cooling fluid. The hydrostatic pressure caused by the centrifugal forces can prevent ambient air from entering the cooling passage 4 through the outlet opening 32. It is beneficial to prevent ambient air or other fluids from entering the cooling passage 4 through the outlet opening because the ambient air or other fluids can interfere with the pumping function of the outlet section 12 and generally have lower heat exchange characteristics than the cooling fluid.

[0054] Figure 1 The hollow shaft 2 with the cooling passage 4 and the outlet section 12 as a single entity are shown. However, it is understood that the hollow shaft 2 can include multiple connectable components. For example, the outlet section 12 can be arranged as a separate ring-like structure that is arranged to be mounted on the hollow shaft 2.

[0055] Figure 2 A cross-sectional view of an exemplary embodiment of the hollow shaft 2 of the present application is shown. As shown, Figure 2As shown, the hollow shaft 2 is divided into a first shaft section 2a and a second shaft section 2b. The first shaft section 2a can be arranged in fixed connection with the rotor 6. The second shaft section 2b can be arranged in fixed connection with the first shaft section 2a, for example by means of a threaded connection 20 or a spline shaft connection 20. The spline shaft connection 20 can allow axial movement of the second shaft section 2b relative to the first shaft section 2a and provide rotational locking of the first shaft section 2a and the second shaft section 2b. The second shaft section 2b can comprise a transmission gear 22 arranged for transmitting torque from the shaft 2 to, for example, a transmission. The second shaft section 2b further comprises the outlet section 12 and the inlet 16. The cooling channel 4 extends along the first shaft section 2a and the second shaft section 2b and is divided into an inner part and an outer part by a separating element 24, such as a tube 24. The first shaft section 2a further comprises a fixation member 26 and a heat exchanger 28. The heat exchanger 28 is arranged in the outer part of the cooling channel 4 extending along the first shaft section 2a, for example can be a set of fins. The heat exchanger 28 increases the contact surface between the first shaft section 2a and the cooling fluid, resulting in improved heat transfer between the first shaft section 2a and the cooling fluid. The heat exchanger 28 is further arranged to prevent radial movement of the tube 24, to prevent the tube 24 from bending away from the rotational axis of the shaft 2 when rotating and thus creating imbalance. The fixation member 26 is arranged to prevent axial movement of the tube 24. The fixation member 26 is further arranged to guide the cooling fluid from the inner part of the cooling channel 4 to the outer part of the cooling channel 4. The fixation member 26 and / or the heat exchanger 28 can be optimized to minimize pressure loss, thus optimizing the pressure difference between the inlet 16 and the outlet section 12. Significant pressure loss over the fixation member 26 or the heat exchanger 28 can affect the suction function of the outlet section 12.

[0056] As Figure 2 The embodiment of the hollow shaft 2 as shown can provide a method of how to assemble a hollow shaft according to the present invention. For example, the heat exchanger 28 and the fixation member 26 can be mounted on the tube 24 as a first step. Then, the combination of the tube 24, the fixation member 26 and the heat exchanger 28 can be positioned inside the first shaft section 2a, while the tube 4 extends partly outside the first shaft section 2a. The second shaft section 2b can now be mounted on the tube 4 and connected to the first shaft section 2a using the connection 20. Next, the outlet section 12 can be mounted on the second shaft section 2b. The outlet section 12 can also be mounted on the second shaft section 2b before the connection of the second shaft section 2b to the first shaft section 2a. The assembly described above can also be performed when the first shaft section 2a is already rotatably connected to the stator and / or fixedly connected to the rotor.

[0057] Figures 3a, 3b, 3c, 3d and 3e show four different embodiments of an example of an outlet section 12. Each of Figures 3b, 3c, 3d and 3e shows an outlet section 12 having at least a portion of at least one outlet section 12 at a greater distance from the rotational axis of the rotor shaft 2 relative to the inlet of the cooling channel 4.

[0058] Figure 3a shows an outlet section 12, wherein the inner cross-sectional area of the outlet section 12 is smaller than the inner cross-sectional area of the cooling channel 4 inside the rotor shaft 2. Figure 3a shows an outlet section 12 comprising an outlet section body 30 and an outlet opening 32. The outlet section 12 is shown as a separate annular part arranged to be mounted onto the hollow shaft 2. In another embodiment of the invention, the outlet section 12 can be part of the hollow shaft 2. The outlet opening 32 is shown here as a straight hole integrated in the rotor shaft 2, which can for example be manufactured by drilling. The inner cross-sectional area of the outlet 32 can be constant over the length of the outlet section 30. This design does not comprise an inner cross-section of the outlet section that is larger than the radius of the outlet opening, and therefore, it is possible for ambient fluid, for example air, to enter the outlet section.

[0059] Figure 3b shows a schematic cross-section of an outlet section 12 comprising an outlet section body 30, an outlet 32 and an outlet section cover 34. The outlet section body 30 is shown as a separate annular part arranged to be mounted onto the hollow shaft 2. In another embodiment of the invention, the outlet section 12 can be part of the hollow shaft 2. The outlet section body 30 can for example be formed by techniques such as turning and drilling. The outlet section cover 34 is arranged to be mounted on the outlet section body 30. The outlet 32 can be formed between the outlet section body 30 and the outlet section cover 34. The outlet section 12 comprises a circumferential recess 39. The circumferential recess 39 is present around the entire inner circumference of the outlet section 12. The circumferential recess 39 collects fluid leaving the cooling channel 4 and directs the fluid to the outlet channel 38 of the outlet section 12. Together with the outlet section body 30, the outlet section cover forms an inner cross-section at a greater radius than the outlet opening 32. This can prevent ambient fluid, for example air, from entering the outlet section 12. Figure 3F A perspective view of the outlet section 12 shown in Figure 3b is shown.

[0060] Figure 3c shows a schematic cross-section of an outlet section 12 comprising an outlet section body 30 and an outlet 32. The outlet section body 30 is shown as one separate part arranged to be mounted onto the hollow shaft 2. In another embodiment of the invention, the outlet section 12 can be part of the hollow shaft 2. The outlet 32 is shown here as having two straight holes connected to each other at an angle. The two straight holes can for example be formed by drilling holes in the outlet section body 30. The angle can be such that the distance of at least a part of the outlet section 12 from the axis of rotation of the rotor shaft 2 is larger than the distance of the outlet opening. The outlet section 12 comprises a circumferential recess 39. The circumferential recess 39 is present around the entire inner circumference of the outlet section 12. The circumferential recess 39 collects fluid leaving the cooling channel 4 and directs the fluid to the outlet channel 38 of the outlet section 12.

[0061] Figure 3d shows a schematic cross-section of an outlet section 12 comprising an outlet section body 30 and an outlet 32. The outlet section 12 is shown here as one separate part arranged to be mounted at one end of the hollow shaft 2, in contrast to the embodiments shown in figures 3a, 3b, 3c and 3e which can be mounted onto the hollow shaft 2. The outlet 32 has less corners compared to the embodiments shown in figures 3b and 3c, which can result in more laminar flow of the cooling fluid. More laminar flow of the cooling fluid can result in a stronger suction function compared to more turbulent flow of the cooling fluid. Manufacturing of this geometry can be done by plastic 3D printing.

[0062] Figure 3e shows a schematic cross-section of an outlet section 12 comprising an outlet section body 30 and an outlet 32. At least one outlet channel 38 towards the outlet 32 is nozzle-shaped in order to arrange a minimum flow cross-section at the outlet 32. This results in a back pressure and prevents cavitation inside the outlet channel from occurring due to centrifugal forces. The outlet section 12 comprises a circumferential recess 39. The circumferential recess 39 is present around the entire inner circumference of the outlet section 12. The circumferential recess 39 collects fluid leaving the cooling channel 4 and directs the fluid to the outlet channel 38 of the outlet section 12. Figure 3G A perspective view of the outlet section 12 shown in figure 3e is shown. In the ring, multiple outlets 32 can be provided which are distributed circumferentially over the ring. Similar to the example of figure 3f, the outlets 40 through the rotor shaft wall are provided as radial holes. The outlet channels of the outlet section 12 are then also provided as radial holes, preferably as tapered holes with a decreasing cross-section towards the outside. In this way, the outlet channels of the cooling channel are essentially radially extending and formed by the outlets 40 through the wall of the rotor shaft, the circumferential recess 39 of the ring of the outlet section 12 and the outlets 38 in the ring.

[0063] Each of the example embodiments of the outlet section 12 shown in Figures 3b, 3c, 3d and 3e show the outlet opening 32 located at the same side of the outlet section 12. However, it should be understood that the outlet opening can be located at any side of the outlet section 12, for example, to align the cooling fluid in a generally axial direction towards the rotor, as in Figure 3b, in a generally radial direction away from the hollow shaft 2, as in Figure 3a, in a generally axial direction away from the rotor, in a generally tangential direction or in any direction between the above mentioned directions.

[0064] The example embodiments of the outlet section 12 shown in Figures 3a, 3b, 3c and 3e are arranged to be mounted to the hollow shaft 2. Figures 3a, 3b and 3c show an increased inner diameter of the axial bore through which the hollow shaft 2 can extend. The increased inner diameter allows for greater tolerances when mounting the outlet section 12 to the hollow shaft 2, thereby reducing drawbacks due to misalignment between the cooling channel 4 of the hollow shaft 2 and the outlet 32 of the outlet section 12.

[0065] The example embodiments of the outlet section 12 shown in Figures 3a, 3b and 3c all show the outlet section 12 having a portion 36 of the outlet section 12 with a radial diameter larger than the outlet opening 32, thereby providing for siphoning during rotation.

[0066] The outlet section 12 comprises an outlet channel 38 fluidly connected with the cooling channel 4 of the rotor shaft 2, the other end of the outlet channel 38 ending at the outlet opening 32. In Figure 3a, the outlet channel 38 is straight, but it can be curved or U-shaped, such as shown in Figures 3b or 3d. The outlet channel 38 can be integrally formed in the rotor shaft, or can be a part of the outlet section 12 provided to the rotor shaft as an additional element. There can be many variations. In the outlet channel 38, a flow restriction can be provided to regulate the outlet flow, especially at higher rotational speeds. The flow restriction can be a portion of the outlet channel 38 having a smaller cross-sectional area than the other portions of the outlet channel. Alternatively, the flow restriction can be the outlet opening 32 having a smaller cross-sectional area than the outlet channel 38.

[0067] Figure 4An alternative example of the outlet section 12 is shown. In this example, the rotor shaft 2 comprises two shaft portions 2a, 2b which are joined to each other via a threaded or splined connection 70. The threaded or splined connection 70 comprises several threads or teeth 71a, 71b which are joined to each other to form the connection. In this connection, passages 72, 73 are provided which fluidly connect the cooling channel 4 with the outlet opening 32. The passages 72, 73 can be established, for example, by intermittently providing threads or teeth, or by providing recesses in the threads or teeth. Due to the last thread or tooth, here 71a, the passage 72 and the radial position of the outlet opening 32 of this passage are larger than the rotational axis at the connection of the inlet of the cooling channel, during rotation an aspiration effect is obtained due to the pressure difference caused by the centrifugal force. Thus, cooling fluid is sucked out of a cooling fluid reservoir, not shown here. The outlet 32 can be positioned radially inwards with respect to the radial position of the passages 72, 73. When rotating, such an arrangement provides a higher fluid pressure inside the passages 72, 73 than inside the outlet 32, thereby keeping part of the fluid inside the passages and preventing ambient fluid from entering the outlet section, thus forming a siphon. The cooling channel 4 here is provided with an inner passage 4a which is fluidly connected with the inlet, and an outer passage 4b which is fluidly connected with the outlet. The inner passage 4a and the outer passage 4b are also fluidly connected to form the cooling channel. In the inner passage 4a, the cooling fluid flows in one direction, while in the outer passage 4b the cooling fluid flows in the other, opposite direction towards the outlet, since the inlet and the outlet of the cooling channel are provided on the same side of the cooling channel.

[0068] In Figure 5 , the outlet section 12 is provided as a separate element which is mounted to the outside of the shaft 2. In the outlet section, an outlet passage 38 is provided, here in the form of a U, with a portion 36 which has a larger radial position than the outlet opening 32, which provides a siphon effect during rotation. Also, here, the cooling fluid reservoir 14 is provided at a higher position with respect to the inlet 16, so that during standstill of the rotor shaft 2, the cooling channel 4 is pre-filled due to the effect of the force of gravity. In Figure 5 , it is also shown that the cooling channel 4 has an inlet 16 at one end, while the outlet opening 32 is provided at the same end of the inlet 16. For this, the cooling channel 4 comprises an inner passage 4a and an outer passage 4b which are divided by a passage wall 17. The inner passage 4a and the outer passage 4b are fluidly connected to each other at the end of the rotor shaft 2 opposite the inlet 16, the outer passage 4b comprising a return flow of the cooling fluid towards the outlet opening 32. The cooling fluid flows from the inner passage 4a to the outer passage 4b around an edge 4c of the passage wall 17. Alternatively, the outer passage 4b can be provided outside the rotor shaft 2, for example, as a hole in the rotor laminate stack 6.

[0069] In Figure 6In the middle, the outlet section 12 is integrated in the rotor shaft 2 as a simple outlet channel 38. Of course, other examples of outlet sections 12 can be provided or formed integrally in the rotor shaft. Thus, the rim 4c is provided with a displacement member 44 that directs the cooling fluid radially outward at the rim 4c and reduces the risk of cavitation or other fluid flow phenomena that deteriorate the fluid flow. The fluid displacement member is preferably configured to generate an angular acceleration of the cooling fluid and is preferably configured to divert the fluid from the inner channel to the outer channel. In fact, it contributes to a sharp turn of the cooling fluid towards the outer channel. This angular acceleration can be facilitated by providing displacement member ribs 44a that extend radially outward from the displacement member so that the fluid near the ribs is forced to follow the angular velocity of the rotor. This can result in a more efficient and effective fluid flow of the fluid from the inner channel towards the outer channel. At least one displacement member rib can direct the fluid radially outward. This can improve the flow of the liquid from the inner channel towards the outer channel.

[0070] Figure 7 A cooling body 90 is shown positioned near the outlet opening 32 of the outlet section 12. The heated cooling fluid exiting from the outlet opening 32 is then splashed against the cooling body 90, thereby cooling the cooling fluid so that the cooling fluid, once cooled, can be returned into the cooling fluid reservoir 14 for further use in the cooling system. The cooling body 90 can be provided with a channel 91 via which cooling fluid can be provided to cool the cooling body 90.

[0071] Figure 8 A graph of the cooling fluid flow rate and static pressure at the inlet of the present invention as a function of the number of revolutions per minute (RPM) of the shaft is shown. The graph shows that as the rotational speed of the electric machine 1 increases, the flow rate of the cooling fluid increases and the inlet static pressure decreases. At point B, the inlet static pressure is 0 Pa, indicating that the pressure difference caused by the suction function of the outlet section 12 is offset by the pressure loss over the cooling channel 4. Beyond point B, an increase in rotational speed will result in a negative static pressure at the inlet, indicating that beyond this point, no external energizing is required, such as a separate pump to maintain the flow of cooling fluid. The graph also shows that the suction function starts to influence the flow rate at low rotational speeds.

[0072] Figure 9 An alternative outlet section 12 for use on a hollow shaft 2 is shown. In the figure, the check valve 60 is partially integrated in the shaft, while the valve seat is manufactured as an integral part of the shaft, the valve body 62 is fixed with a thread connection 63, and the spring 64 and ball 65 are clamped between the valve body and the valve seat. The outlet channel 38 and its fluid connection to the cooling channel 4 are also integrated in the shaft. The suction pump body 62 can be turned and has a radially drilled outlet hole opening 32. The stiffness of the spring 64 needs to be taken into account for the centrifugal force of the ball 65.

[0073] Figure 10 shows a geometry for a cooling rib 80 for a rotor shaft. The shown geometry of the cooling rib 80 comprises a tube 86 forming an inner channel 4a, and a protrusion 81 forming an outer channel 4b, which protrusion 81 contacts on its outer diameter towards the inner wall of the rotor shaft. A large contact area to the hollow shaft is desirable to transfer heat to the cooling fins. A large surface towards the fluid is also desirable to transfer heat to the coolant. The protrusion or extension 81 contains a flexible element 82, which has a slightly oversized diameter with respect to the inner shaft surface, which creates a clamping force upon insertion and fixes the cooling rib in place. The flexible element 82 has a radial part 83, which conducts heat to the inner tube forming the inner channel 4a. The flexible element 82 further has a spring part 84, which biases a part 85 of the flexible element 82 outwardly, so that this part 85 clamps on the inner surface of the rotor shaft. The inner tube 86 acts as an inner channel 4a, which brings the fluid towards the opposite end of the shaft. If the borehole is inserted with a conical end, the fluid will be allowed to flow from the inner tube towards the outer part of the cooling rib, using the conical chamber that cannot be occupied by the geometry of the cooling rib 80. Thus, the protrusion 81 forms an outer channel 4b together with the inner bore of the rotor shaft 2, where the fluid returns to the side where the inlet and outlet are located.

[0074] Figure 10a shows a perspective view of the cooling rib shown in figure 10d. It shows that the cooling rib is a straight profile with constant cross section, which can be manufactured as an extruded profile and cut to the appropriate length needed.

[0075] Figure 10b shows a cross section design of the cooling rib, which maximizes the metal contact surface towards the rotor shaft. The diameter of the top and bottom part of the protrusion 81 is slightly undersized, presenting a loose fit inside the shaft, while the outer diameter towards the left and right is slightly oversized. Thus, the top and bottom part of the protrusion acts as a spring part 84, while the left and right part of the protrusion acts as a part 85 clamping on the inner shaft surface. This makes each outer quarter circle a spring, clamping the tube to the left and right.

[0076] Figure 10c shows a cross section design of the cooling rib 80, which maximizes the wetted perimeter of the cooling rib 80. The increase in wetted perimeter is at the expense of metal contact to the shaft, since the spring element has fluid contact on both sides.

[0077] Figure 10d shows a design that balances the two designs discussed earlier in terms of wetted perimeter and metal contact towards the shaft. Additionally, there are three radial parts 83 that can conduct heat to the inner tube 86, instead of two.

[0078] Figure 10e shows an improvement to the design of figure 10d by increasing the number of sections 85 clamped to the inner shaft surface and increasing the fourth radial section 83 for metal conduction towards the inner tube, further increasing the metal contact towards the shaft. However, due to the smaller spring sections 84, tighter tolerances can be required to achieve the desired clamping force.

[0079] Figure 10f shows a design that maximizes heat conduction towards the inner tube 4a using nine radial sections 83.

[0080] All designs of figure 10 feature similar flow cross sections and the resulting pressure drops are comparable. The choice of cooling rib design depends on different factors. If the cooling fluid used, for example water, has a very high heat exchange with the wall surface, for example due to easy transition to turbulent flow and high thermal conductivity, then the contact surface with the shaft wall is the most important, as it can be the bottleneck for bringing heat out of the shaft. This can lead to the design in figure 10b. If the cooling fluid, again for example water, has a high heat capacity, then the number of heat conducting feet towards the inner tube is important, as the fluid will be able to extract heat on the way in the inner tube without changing its temperature too much to be useless when returning in the outer passage. This can lead to the design in figure 10f. If the coolant has a very low heat exchange with the passage wall, for example transmission oil, then maximizing the wetted surface is the most important, which leads to the design of figure 10c. Designs 10d and 10e are compromises between different design requirements.

[0081] Figure 11 A motor rotor 1a with cooling passages 4 is shown, where the inner cooling passage 4a runs through the rotor shaft, but the outer cooling passage 4b runs outside the rotor shaft. This can be achieved by recesses 43 in the lamination stack of iron, which together with the outer surface of the rotor shaft 2 form the passages. Drilled holes 45 at the other end of the shaft allow fluid to run from the inner passage 4a inside the shaft towards the outer passage 4b outside the shaft. The recesses in the rotor stack 43 can be sealed towards the axial direction by appropriate rotor end plates 41 and 42. This way of cooling is very effective in keeping the shaft at low temperature, as the recesses inhibit heat conduction from the rotor stack towards the shaft, while the shaft is cooled from both the inside and the outside. A suction pump ring 12 can be mounted on the extension of the end plate 42, with holes 40 drilled in it to allow fluid to run to the outlet of the suction pump.

[0082] Figures 12a, 12b and 12c show different designs of the outlet section of the suction pump mechanism integrated in the parking lock wheel of the transmission. Figure 12a shows a solution with at least one straight outlet hole 38. The hole can be drilled angled to form the outlet 32 at the side surface of the parking lock wheel, so as not to interfere with the geometry 50 of the parking lock. On the inner radius, at the location 51, several teeth of the spline connection need to be omitted in order to make space for the matching pair of holes for the fluid to travel from the shaft towards the parking lock wheel. At least one outlet hole can be drilled at a location with low mechanical stress when the parking lock is engaged. Such integration can minimize the number of parts needed in the assembly.

[0083] Figure 12b shows an outlet section integrated into the parking lock wheel with a dedicated fluid connection face 52, which does not interfere with the spline teeth, and with a built-in siphon section, since a part of the outlet hole 38 is located at a greater radius than the outlet 32.

[0084] Figure 12c shows a different solution for an outlet section integrated into the parking lock wheel, where the outlet hole is achieved by milling a recess 53 from the axial direction. The channel 38 is then only completed by an adjacent component 54 in the assembly, which has a specific radius, such as a gear or bearing, which seals the recess 53 in the axial direction to form the channel 38. The recess 53 extends beyond the radius of the adjacent component, where the outlet 32 naturally forms due to the lack of axial sealing of the recess. The recess can be formed so that the channel forms a siphon, with a part of the fluid remaining in a U-bend to prevent air from entering the channel.

[0085] Although the present application is explained by way of example with a motor, the present application can be provided in any type of motor having a rotor shaft, a cooling channel passing through the rotor shaft, and an outlet opening through which cooling fluid flows out.

[0086] Herein, the present application is described with reference to the specific examples of embodiments thereof. However, it will be readily apparent to those skilled in the art that various modifications, alterations, substitutions and changes can be made without deviating from the essence of the application. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, alternative embodiments having a combination of all or some of the features described in the separate embodiments are also contemplated and understood to fall within the framework of the application outlined by the claims. Therefore, the description, drawings and examples are to be regarded as illustrative in nature and not restrictive. The application is intended to cover all alternatives, modifications and variations which fall within the scope of the claims. Further, many of the elements described are functional entities that can be implemented as separate or distributed components or combined with other components in any suitable combination and location.

[0087] Many modifications are possible and are included in the scope of the following claims.

Claims

1. A motor comprising: a rotor shaft comprising a cooling channel having at least one inlet for receiving a cooling fluid and at least one outlet on an outer side of the rotor shaft arranged to allow the cooling fluid to flow out of the cooling channel, wherein the outlet of the cooling channel is provided at the same end of the rotor shaft as the inlet of the cooling channel, the motor further comprising: at least one outlet section fluidly connected to the at least one outlet of the cooling channel and arranged to allow the cooling fluid to flow out of the cooling channel, wherein a radial position of the at least one outlet section, measured from an axis of rotation of the rotor shaft, is larger than a radial position of the cooling channel inside the rotor shaft, and wherein the at least one outlet section comprises an outlet channel arranged to fluidly connect the outlet of the cooling channel with an outside of the rotor shaft, the outlet channel comprising an outlet opening for ejecting cooling fluid, wherein the outlet channel is arranged mostly in a radial direction of the rotor shaft, at least a part of the at least one outlet section is at a larger distance from the axis of rotation of the rotor shaft than the outlet opening to form a siphon section.

2. The motor of claim 1, wherein the cooling channel comprises an inner channel and an outer channel separate from the inner channel, wherein the inner channel is fluidly connected to the inlet of the cooling channel and wherein the outer channel is fluidly connected to the outlet of the cooling channel, wherein the inner channel and the outer channel are fluidly connected to form the cooling channel at an end of the rotor shaft opposite to an end having the inlet and the outlet.

3. The motor of claim 1, wherein the inlet of the cooling channel is fluidly connected to a cooling fluid reservoir.

4. The motor of claim 3, wherein the cooling fluid reservoir is at an elevated position relative to the cooling channel.

5. The motor of claim 3 or 4, wherein, the reservoir is passively filled by fluid ejection from a rotating component present in the same housing as the rotor shaft.

6. The motor of claim 5, wherein, the rotating component is a gear.

7. The motor of claim 1, wherein the at least one outlet channel of the at least one outlet section is provided as a radially extending bore.

8. The motor of claim 7, wherein, an inner diameter of the radially extending bore decreases in an outward direction.

9. The motor of claim 1, wherein the outlet section comprises a flow restriction.

10. The motor of claim 1, wherein the outlet section comprises a nozzle.

11. The motor of claim 1, wherein a ring is provided that is engageable with an outer surface of the rotor shaft, wherein the ring comprises the at least one outlet section.

12. The motor of claim 1, wherein the cooling channel comprises a cooling rib.

13. The motor of claim 12, wherein, the cooling rib comprises a tube forming an inner channel and protrusions forming an outer channel of the cooling channel.

14. The motor of claim 13, wherein, the cooling rib comprises a plurality of protrusions extending outwardly from the tube to increase a contact surface with the cooling fluid.

15. The motor of claim 14, wherein, the protrusions of the cooling rib comprise a spring portion biased towards an inner wall of the rotor shaft such that at least a part of the protrusions engage the inner wall of the rotor shaft.

16. The motor of claim 1, wherein the at least one outlet section is U-shaped such that a bridge between legs of the U-shaped section is at a larger distance from a center line of the shaft than the outlet opening.

17. The motor of claim 1, wherein the motor is an electric machine having a rotor mounted to the rotor shaft and a stator arranged around the rotor.

18. The motor of claim 17, wherein, The stator comprises an end winding extending outwardly at at least one end of the stator, wherein the outlet opening is configured to jet cooling fluid towards the extending winding to cool the end winding.

19. The motor of claim 1, wherein A cooling surface is provided at or near the outlet opening, the cooling fluid exiting the outlet opening being sprayed onto the cooling surface to cool the cooling fluid for further use.

20. The motor of claim 1, wherein, The motor is included in a vehicle powertrain, and wherein the outlet section of the cooling channel is integrated in a park lock wheel connectable with the rotor shaft.

21. The motor of claim 1, wherein, The outlet section comprises a check valve adapted to close the outlet opening when the cooling fluid pressure inside the outlet section is below a threshold value.

22. The motor of claim 1, wherein, The rotor shaft comprises two shaft portions joined to each other with a splined connection, the outlet opening being provided at a final spline end of the splined connection, and the outlet opening being realized by omitting at least one tooth of the splined connection.

23. The motor of claim 1, wherein, A portion of the cooling channel fluidly connecting the inlet and the outlet is formed between an axially extending recess in an inner surface of the laminated stack of the rotor and an outer surface of the rotor shaft.

24. An electric or hybrid vehicle powertrain comprising: The motor according to any one of the preceding claims, wherein the motor is an electric machine; wherein the cooling channel of the rotor shaft is arranged in fluid connection with a cooling system of the electric or hybrid vehicle transmission to allow cooling fluid to flow into the channel for cooling the electric machine.

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