HYDRAULICALLY BRAKEABLE ELECTRICAL MACHINE

An electrical machine is presented. The electrical machine comprises a rotor, a stator, a housing and a first and a second fluid chamber in fluid communication via at least one fluid passage of the rotor. The rotor upon rotation is adapted to provide a difference in pressure between the first fluid chamber and the second fluid chamber by transfer of fluid there between, whereby a braking torque is exerted on the rotor.

TECHNICAL FIELD

The disclosure relates generally to electrical machines. In particular aspects, the disclosure relates to hydraulically breakable electrical machines. The disclosure can be applied to general electrical machines and in particular to electrical propulsion machines for heavy-duty vehicles, such as trucks, buses, and construction equipment, among other vehicle types. Although the disclosure may be described with respect to a particular vehicle, the disclosure is not restricted to any particular vehicle.

BACKGROUND

Modern vehicles may be provided with electrical machines. One particular use of electric machines in vehicles is for traction purpose, i.e. the electrical machines are arranged as part of the drive train to perform the desired propulsion of the vehicle. These electrical machines are connected to one or more battery arrangements which provide the electrical machines with the required electrical power.

Electrical machines can also be used to provide retardation of the vehicle, changing the operational mode of the electrical machine from propulsion mode to regeneration mode. In such case the regeneration of electrical power will cause a retarding effect on the vehicle.

However, braking of the electric vehicle using the electrical machine can only be performed as long as the associated battery arrangement is capable of receiving the regenerated electrical power. If the battery arrangement is fully (or close to fully) charged, braking can no longer be achieved by means of the electrical machine.

Some vehicles utilize a brake resistor to dissipate excess power from regenerative braking also when the battery arrangement is fully charged. This option is comparably expensive.

Based on this, there is a need for improved solutions enabling the electrical machine of a vehicle to brake the vehicle even if the associated battery arrangement is not capable of receiving the generated electrical power.

SUMMARY

In a first aspect, an electrical machine is presented. The electrical machine comprises a rotor, a stator, a housing and a first and a second fluid chamber in fluid communication via at least one fluid passage of the rotor. The rotor, upon rotation, is adapted to provide a difference in pressure between the first fluid chamber and the second fluid chamber by transfer of fluid there between, whereby a braking torque is exerted on the rotor. The first and second fluid chambers are provided at, along a rotational axis of the electrical machine, respective opposite sides of the rotor. A technical benefit may comprise providing a braking effect internal to the electrical machine with very few design modifications to the electrical machine, and that a distance between the rotor and the stator may be reduced to reduce losses.

In some examples, including in at least one preferred example, optionally, the first and second fluid chambers are provided between an interior of the housing and the rotor. This is beneficial as it provides a clearly delimited and straight forward delimitation of the fluid chamber.

In some examples, including in at least one preferred example, optionally, the at least one fluid return passage is provided between the first fluid chamber and the second fluid chamber. This is beneficial as it allows the electrical machine to be self-resettable after a braking effect has been exerted.

In some examples, including in at least one preferred example, optionally, at least one internal fluid return passage is provided between the stator and the rotor. This is beneficial as such a fluid return passage may be provided with minimum redesign of the electrical machine.

In some examples, including in at least one preferred example, optionally, the first fluid chamber is provided with a first chamber fluid port for fluidly filling and/or draining the first fluid chamber and the second fluid chamber is provide with a second chamber fluid port for fluidly filling and/or draining the second fluid chamber. This is beneficial as the fluid ports enables further means of controlling a flow of fluid and to perform service and maintenance on the electrical machine.

In some examples, including in at least one preferred example, optionally, the first chamber fluid port is in fluid communication with the second chamber fluid port by a fluid port return passage. This is beneficial as it allows the electrical machine to be self-resettable after a braking effect has been exerted.

In some examples, including in at least one preferred example, optionally, the fluid port return passage between the first and second chamber fluid ports is provided with at least one controllable valve device configurable to control a flow of fluid in the fluid port return passage. This is beneficial as it allows the braking effect to be controlled by control of the controllable valve device.

In some examples, including in at least one preferred example, optionally, the first fluid chamber comprises a first chamber fluid inlet for receiving fluid and a first chamber fluid outlet for draining fluid, and the second fluid chamber comprises a second chamber fluid inlet for receiving fluid and a second chamber fluid outlet for draining fluid. This is beneficial as the fluid ports, outlets, inlets enables further means of controlling a flow of fluid and to perform service and maintenance on the electrical machine.

In some examples, including in at least one preferred example, optionally, the rotor is provided with at least one impeller arranged at the first or the second fluid chamber of the electrical machine. This is beneficial as it increases a flow of fluid through the fluid passages.

In a second aspect, a vehicle comprising the electrical machine according to the first aspect is presented.

In some examples, including in at least one preferred example, optionally, the electrical machine is a propulsion motor of the vehicle. This is beneficial as a fluid brake will be incorporated in the propulsion motor of the vehicle.

In some examples, including in at least one preferred example, optionally, the vehicle further comprises a fluid circuit connected between the first chamber fluid port and the second chamber fluid port. This is beneficial as the fluid circuit enables further means of controlling a flow of fluid and to perform service and maintenance on the electrical machine.

In some examples, including in at least one preferred example, optionally, the fluid circuit comprises at least one pump device configurable to pump fluid into a the first fluid chamber or the second fluid chamber and at least one drain valve device configurable to prevent fluid from draining from the other of the first fluid chamber or the second fluid chamber. This is beneficial as the fluid circuit enables further means of controlling a flow of fluid and to perform service and maintenance on the electrical machine.

In some examples, including in at least one preferred example, optionally, an inlet valve device is provided between the pump device and the fluid receiving one of the first chamber fluid port and the second chamber fluid port. This is beneficial as the fluid circuit enables further means of controlling a flow of fluid and to perform service and maintenance on the electrical machine.

In some examples, including in at least one preferred example, optionally, the fluid circuit further comprises a fluid reservoir. A technical benefit may include increased braking capacity, since the reservoir may hold a larger volume of oil. A further technical benefit may include increased, when applicable, cooling capacity, as heat can be dissipated more efficiently.

In some examples, including in at least one preferred example, optionally, the fluid circuit is operatively connected to a temperature system of the vehicle. This is beneficial as it allows heat from the fluid to be exchanged with other parts of the vehicle, decreasing a cooling time of the fluid.

In some examples, including in at least one preferred example, optionally, the vehicle is a heavy-duty vehicle, such as a truck, a bus, or a construction equipment.

In a third aspect, a method for braking an electrical machine of the first aspect is presented. The method comprises providing fluid to a fluid chamber at a first axial side of the electrical machine, pumping, responsive to rotation of a rotor of the electrical machine, the fluid from the fluid chamber at the first axial side of the electrical machine to a fluid chamber at a second opposite axial side of the electrical machine through at least one fluid passage extending along the rotor of the electrical machine, and controlling a reverse flow of fluid from the second axial side to the first axial side such that the flow through the at least one fluid passage exceeds the reverse flow, whereby a braking torque is exerted on the rotor by the fluid at the second axial side of the electrical machine.

In a fourth aspect, an electrical machine is presented. The electrical machine comprises a rotor, a stator, a housing and a first and a second fluid chamber in fluid communication via at least one fluid passage of the rotor. The rotor, upon rotation, is adapted to provide a difference in pressure between the first fluid chamber and the second fluid chamber by transfer of fluid there between, whereby a braking torque is exerted on the rotor. The first and second fluid chambers are provided at, along a rotational axis of the electrical machine, respective opposite sides of the rotor. The first and second fluid chambers are provided between an interior of the housing and the rotor. The electrical machine further comprises at least one fluid return passage provided between the first fluid chamber and the second fluid chamber. At least one internal fluid return passage is provided between the stator and the rotor. The first fluid chamber is provided with a first chamber fluid port for fluidly filling and/or draining the first fluid chamber and the second fluid chamber is provide with a second chamber fluid port for fluidly filling and/or draining the second fluid chamber. The first chamber fluid port is in fluid communication with the second chamber fluid port by a fluid port return passage. The fluid port return passage between the first and second chamber fluid ports is provided with at least one controllable valve device configurable to control a flow of fluid in the fluid port return passage. The first fluid chamber comprises a first chamber fluid inlet for receiving fluid and a first chamber fluid outlet for draining fluid. The second fluid chamber comprises a second chamber fluid inlet for receiving fluid and a second chamber fluid outlet for draining fluid. The at least one fluid passage of the rotor is provided by an impeller of the rotor. The electrical machine is a propulsion motor for a vehicle.

DETAILED DESCRIPTION

Details of an electrical machine will be described in the following. The electrical machine according to the present disclosure aims to add a braking functionality to the electrical machine by utilizing oil or any other suitable fluid. Such oil may be oil already provided to e.g., cool down the electrical machine during operation. By implementing the electrical machine in a vehicle, a braking force may be applied to the vehicle by means of the electrical machine even if regeneration of electrical power is not available due to e.g. the associated battery arrangement being fully, or almost fully, charged.

With reference toFIG.1, a vehicle10, here embodied as a heavy duty truck10, is disclosed for which an electrical machine100and a method200(seeFIG.8) for braking an electrical machine100are advantageous. However, the electrical machine100and/or the method200may as well be implemented in other types of applications, in particular in other types of vehicles such as a busses, light-weight trucks, passenger cars, marine applications, etc.

The vehicle10is preferably an electric vehicle, such as a full electric vehicle or a hybrid vehicle, comprising at least one electrical machine100for propulsion. Typically the vehicle10also comprises an energy storage system20comprising energy storage or energy transformation devices, typically batteries or fuel cells. The energy storage system20is arranged and configured to power the electrical machine100.

The vehicle10typically further comprises other parts of a powertrain such as a transmission, drive shafts, and wheels (not shown in details inFIG.1).

An example of an electrical machine100is shown inFIG.2A. The electrical machine100has a rotor120, a stator110, and a housing130. The rotor120is rotatably supported by the housing130e.g. by means of one or more bearings122, allowing the rotor120to rotate around a rotational axis A. The stator110is also enclosed by the housing130and arranged radially to the rotational axis A outside of the rotor110.

The electrical machine100is further provided with a first fluid chamber140and the second fluid chamber150between the rotor120and the housing130. The fluid chambers140,150are arranged along the rotational axis A, one at either side of the rotor120. The fluid chambers140,150are configured such that a braking torque is exerted on the rotor120responsive to a fluid pressure in the fluid chambers140,150. This braking torque will provide a braking effect on the rotor120.

In order to provide for the desired braking effect, the rotor120comprises one or more fluid passages125, sometimes referred to as channels125. In the shown example, the rotor120is provided with a plurality of fluid passages125substantially evenly distributed around the rotor120. The fluid passages125extend along the rotor120from a first axial side at the first fluid chamber140to an opposite second axial side at the second fluid chamber150. Each fluid passage125is configured to guide fluid, advantageously oil, from the first fluid chamber140to the, along the second fluid chamber150along the rotational axis A. The fluid passages125and/or the axial side(s) of the rotor120and/or the fluid chamber(s)140,150is/are advantageously formed such that, upon rotation of the rotor120, fluid will flow though the fluid passages125and is transferred between the fluid chambers140,150. Responsive to fluid flowing through the fluid passages125, a pumping action will be obtained, causing a braking action to the electrical machine100.

In the example ofFIG.2A, the electrical machine100is provided with fluid return passages101radially between the rotor120and the stator110. The fluid return passages101may, as shown inFIG.2Abe, arranged axially around the rotor120. However, this is but one example and electrical machines100with one or more fluid return passages101each extending only partially around a circumference of the rotor120are well within the scope of the present disclosure. The one or fluid return passages101are, as the name suggest, provided to allow fluid to flow between the fluid chambers140,150regardless of rotation of the rotor120.

InFIG.2B, the corresponding electrical machine100as inFIG.2Ais shown, but with fluid102inside the housing130. In the first fluid chamber140, the fluid102is at a first fluid level L1. In the second fluid chamber150, the fluid102is a second fluid level L2being different from the first fluid level L1. If the rotor120would be stationary, the fluid102would, due to the fluid passages125and the fluid return passage101level such that the first fluid level L1is substantially equal to the second fluid level (assuming the electrical machine100is arranged with the rotational axis A horizontal). Due to the rotation of the rotor102, fluid102will flow through the fluid passages125of the rotor120from the second fluid chamber150(right side inFIG.2B) to the first fluid chamber140(left side inFIG.2A). The pumping action provided by the rotor120will cause a pressure of the fluid102in the first fluid chamber140to increase. As the pressure increases, it will require more power to continue the pumping action of the rotor120, and eventually a hydraulically locking effect will be provided by the difference in pressure between the fluid chambers140,150.

If a rotational direction of the rotor120was opposite to the one shown inFIG.2B, the fluid levels would be reversed and the second fluid chamber150would be a high pressure side.

The electrical machine100inFIGS.2A and2Bforms a closed fluid system in that fluid102never leaves the housing of the electrical machine100. This exemplary embodiment will provide a braking effect as soon as a rotational speed of the rotor120causes a flow of fluid102through the fluid passages125that exceeds a flow permitted by the fluid return passages101. By dimensioning e.g. the fluid return passages101, the fluid passages125the electrical machine100may be configured to brake at a predetermined rotational speed of the rotor120. This may be usable as e.g., an emergency brake in elevators or as a general over-speed governor of electrical machines100. It should be noted that the electrical machine100is self-resettable as at standstill, the pressure of the fluid102in the fluid chambers will normalize and further operation of the machine is permitted.

InFIG.3, a further exemplary electrical machine100is shown. In this example, the first fluid chamber140is provided with a first chamber fluid port145and the second fluid chamber150is provided with a second chamber fluid port155. The fluid ports145,155are provided to fluidly fill and/or drain the respective fluid chambers140,150. InFIG.3, the electrical machine is formed without the fluid return passage101and a fluid return path will be provided by fluidly connecting the first chamber fluid port145to the second chamber fluid port155by a fluid port return passage103, fluid return passage103for short. It should be noted that the fluid ports145,155may very well be combined with the fluid return passage between the rotor120and the stator110.

In the example ofFIG.3, the fluid return passage103is provided with a controllable valve device104. In some examples, more than one controllable valve devices104may be provided along the fluid return passage103. The controllable valve device104is configurable to control a flow of fluid102in the fluid port return passage103. In some examples, the controllable valve device104is controller between an open state and a closed state. When at the open state, fluid102may flow between the fluid chambers140,150by the fluid passages125of the rotor120and by the fluid return passage103. Assuming that the fluid return passage103is dimensioned to permit a flow of fluid102equal to, or exceeding a flow of fluid102permitted by the fluid passages125of the rotor120, the pressure in the respective fluid chambers140,150will be substantially the same. However, if the controllable valve device104is at its closed state, fluid102will not be permitted to flow between the fluid chamber by the fluid return passage103and a difference in pressure between the fluid chambers140,150will provided. This difference in pressure will, as explained above, provide a braking torque on the rotor120. The controllable valve device104enables control of braking of the electrical machine100.

It should be mentioned that the controllable valve device104may be linearly, or proportionally controlled such that it may controlled to partly open or close depending on e.g. control signals provided to the proportional valve device104.

The fluid port return passage103is inFIG.3shown as external to the housing130. This is one example, and the fluid port return passage103may very well be arranged inside the housing130, forming part of the housing130or a combination thereof. In some examples, the fluid return passage103is, at least partly, internal to the stator110.

InFIG.4, a further example of the electrical machine100is shown. In this example, the first fluid chamber140and the second fluid chamber150each comprises three fluid ports141,143,145,151,153,155. Each of the fluid ports141,143,145,151,153,155may be bidirectional fluid ports, but in this example, the vertically lower ports143,153may be outlets for draining fluid102from the chambers140,150and the vertically higher ports141,151may be inlets for receiving fluid102. Providing fluid outlets143,145vertically below fluid inlets141,151, will allow for drainage of the associated fluid chamber140,150by means of gravity.

Although not shown inFIG.4, the fluid outlet143of the first fluid chamber140is advantageously connected to the fluid inlet151of the second fluid chamber150. Correspondingly, the fluid outlet153of the second fluid chamber150is advantageously connected to the fluid inlet141of the first fluid chamber140.

The example inFIG.4is shown comprising both the fluid return passage103and associated ports145,155introduced inFIG.3and the fluid inlets141,151and outlets143,153. This is to show that these features may be combined, but it should be mentioned that they may very well be separated and implemented individually. Further, in some examples, wherein e.g. the electrical machine100only rotates in one direction, only one fluid chamber140,150may be provided with a fluid inlet141,151and the other fluid chamber may be provided with a fluid outlet143,153.

The fluid passages125may be configured according to various principles, as exemplified inFIGS.5A-C. Starting inFIG.5A, the rotor120is shown in cross-section. The rotor120is provided with a plurality of fluid passages125, or oil channels, arranged at an outer radius (i.e. close to the outer circumference of the rotor120). The fluid passages125as shown inFIG.5Aextend straight through the rotor120, at a constant radius.

InFIG.5Banother example is shown also in cross-section. Here, the fluid passages125extend straight through the rotor120but at a varying, in particular an increasing, radius. At a first axial side (i.e. the low pressure side) the fluid passages125are arranged at an inner radius, while their radial position increase along the rotor120. At an opposite axial side, the fluid passages125are arranged at an outer radius.

InFIG.5Ca further example is shown. Here, the fluid passages125are no longer straight, but the circumferential position is varying along the length of the rotor120. In particular, each fluid passages125is twisted whereby the length of each fluid passages125is increased in comparison to straight fluid passages125. The twist angle may be small (as shown inFIG.5C) or significantly larger, resulting in a helical distribution of a fluid passages125.

It should be mentioned that the different examples of the fluid passages125shown inFIGS.5A-Care non-limiting examples and many different arrangements and formations of the fluid passages125are possible. Further, the different examples ofFIGS.5A-Cmay very well be combined with each other in any suitable way.

InFIG.6A, the corresponding electrical machine100ofFIG.2Ais shown but with an optional axial flow pump127is provided in order to enhance the pumping effect provided by the fluid passages125. The axial flow pump127is in this example shown as an impeller127, arranged on the rotor120at the second fluid chamber150. When the rotor120is spinning, the impeller127will throw oil from the first axial side S1towards the opposite axial side, i.e. the first fluid chamber140, thereby causing a forced fluid flow through the fluid passages125. Preferably, the axial flow pump127is designed to direct the flow of fluid102towards a center of the rotor120rather than spraying the fluid radially outwards.

InFIG.6B, a partial cross sectional view of the electrical machine100is shown looking along the a rotational axis A. In this example, the axial flow pump127is an impeller with a plurality of impeller elements127distributer around the rotor120and extending radially from the rotor120.

It should however be appreciated that the pumping effect may be achieved also without the provision of an axial flow pump127, as the increase of oil at one axial side will cause the oil to flow through the fluid passage(s)125to the opposite axial side of the rotor120. Further to this, there may be an axial flow pump127provided at each axial side of the rotor120, i.e. at each fluid chamber140,150. In such examples, each axial fluid pump127is advantageously formed such that it a direction of the fluid102flowed by the axial pump may be reversed by reversing a rotational direction of the rotor120. This further implies that an axial fluid pump127provided at a high pressure side of the rotor will provide an axial sucking action on the fluid passages125and an axially opposite fluid pump will provide an axial blowing action on the fluid passages125.

Returning toFIG.1, wherein a vehicle10comprising the electrical machine100was shown. The electrical machine100is advantageously a propulsion motor100of the vehicle10, but may in some examples be an alternator of the vehicle10. Regardless, the electrical machine100may be the electrical machine100according to any suitable example presented herein.

InFIG.7, the electrical machine100is shown when forming part of the vehicle10. In this example, the electrical machine100comprises the first chamber fluid port145and the second chamber fluid port155. The first chamber fluid port145and the second chamber fluid port155are connected by a fluid circuit30. The fluid circuit30may form a return passage for the fluid102in addition to, or in place of, the fluid return passage101and/or the fluid port return passage103.

The fluid circuit30may comprise one or more pump devices35. The pump device35may be configurable to pump fluid into/out from the first fluid chamber140or the second fluid chamber150of the electrical machine100. The pump device35will increase the pumping and/or draining effect of the fluid passages125depending on arrangement and rotation of the rotor120. If the pump device35is configured to pump fluid102into the first fluid chamber140, and the rotation of the rotor120is such that fluid is moved from the first fluid chamber140to the second fluid chamber150, the fluid pumped into the first fluid chamber will flow to the second fluid chamber150and exert a braking torque on the rotor120. This will increase the flow of oil into the first fluid chamber and decrease a time it takes before the electrical machine100is braked. If the pump device35, e.g. at a later stage of operation, is configured to drain fluid102from the second fluid chamber150, a time it takes to decrease and remove a braking force exerted by the fluid102on the rotor120will decrease and the electrical machine100may operate without any braking torque applied via the fluid102.

Advantageously, each side of the fluid circuit30, i.e. at both sides of the pump device35, valve devices31,33are provided. If the electrical machine100is configured to operate in only one direction, one valve device31,33may suffice, advantageously a drain valve device31,33at the fluid port145,155at the high pressure fluid chamber140,150. Such a drain valve device31,33is provided to prevent fluid102from draining the high pressure fluid chamber140,150. Optionally, an inlet valve device31,33may be provided between the pump device35and the other of the fluid ports145,155.

The fluid circuit30may further comprise a fluid reservoir37. The fluid reservoir37may be a sump or any other suitable reservoir37. The pump device35may be configured to pump fluid102between the reservoir37and the fluid circuit30.

As the fluid102brakes the rotor120of the electrical machine100. The friction caused between the fluid and the rotor120may cause the fluid102to heat. In order to dissipate this heat, the fluid circuit may be operatively connected to, or form part of a temperature system of the vehicle10. The temperature system may be configured to transfer heat to e.g. an interior of the vehicle10and/or to the energy system20of the vehicle10.

As previously indicated, the fluid102is advantageously an oil.

With reference toFIG.8, a method200for braking an electrical machine100is schematically shown. The method200may be performed e.g. by the electrical machine100according to any suitable example of the present disclosure.

The method200comprises providing202fluid102to a first axial side of the electrical machine100, i.e. to a first fluid chamber140,150of the electrical machine100.

The method200further comprises pumping204, responsive to rotation of a rotor120of the electrical machine100, the fluid102from the first axial side, i.e. from the first fluid chamber140, of the electrical machine100to a second, opposite axial side, i.e. the second fluid chamber150, of the electrical machine100through at least one fluid passage125extending along the rotor120of the electrical machine100.

The method200further comprises controlling206a reverse flow of fluid102from the second fluid chamber150to the first fluid chamber140such that the flow through the at least one fluid passage125exceeds the reverse flow, whereby a braking torque is exerted on the rotor120by the fluid102of the second fluid chamber. The reverse flow may be controlled by dimensioning the fluid return passages101,103and/or the fluid circuit30in relation to the fluid passages125such that the braking effect is provided at a specific speed. Alternatively, or additionally, the reverse flow may be controlled by controlling valves31,33,104in a flow of the reverse flow.

Example 1. An electrical machine100comprising a rotor120, a stator110, a housing130and a first and a second fluid chamber140,150in fluid communication via at least one fluid passage125of the rotor120, wherein the rotor120upon rotation is adapted to provide a difference in pressure between the first fluid chamber140and the second fluid chamber150by transfer of fluid102there between, whereby a braking torque is exerted on the rotor120.

Example 2. The electrical machine100of Example 1, wherein the first and second fluid chambers140,150are provided at, along a rotational axis A of the electrical machine100, respective opposite sides of the rotor120.

Example 3. The electrical machine100of Example 2, wherein the first and second fluid chambers140,150are provided between an interior of the housing130and the rotor120.

Example 4. The electrical machine100of any one of the preceding Examples, further comprising at least one fluid return passage101,103provided between the first fluid chamber140and the second fluid chamber150.

Example 5. The electrical machine100of Example 4, wherein at least one internal fluid return passage101is provided between the stator110and the rotor120.

Example 6. The electrical machine100of any one of the preceding Examples, wherein the first fluid chamber140is provided with a first chamber fluid port145for fluidly filling and/or draining the first fluid chamber140and the second fluid chamber150is provided with a second chamber fluid port155for fluidly filling and/or draining the second fluid chamber150.

Example 7. The electrical machine100of Example 6, wherein the first chamber fluid port145is in fluid communication with the second chamber fluid port155by a fluid port return passage103.

Example 8. The electrical machine100of Example 7, wherein the fluid port return passage103between the first and second chamber fluid ports145,155is provided with at least one controllable valve device104configurable to control a flow of fluid102in the fluid port return passage103.

Example 9. The electrical machine100of any one of the preceding, wherein the first fluid chamber140comprises a first chamber fluid inlet141,145for receiving fluid102and a first chamber fluid outlet143,145for draining fluid102, and the second fluid chamber150comprises a second chamber fluid inlet151,155for receiving fluid102and a second chamber fluid outlet153,155for draining fluid102.

Example 10. The electrical machine100of any one of the preceding Examples, wherein the rotor120is provided with at least one impeller127arranged at the first or the second fluid chamber140,150of the electrical machine100.

Example 11. The electrical machine100of any one of the preceding Examples, wherein the electrical machine100is a propulsion motor for a vehicle10.

Example 12. A vehicle10comprising the electrical machine100according to any of the preceding Examples.

Example 13. The vehicle10of Example 12, wherein the electrical machine100is a propulsion motor of the vehicle10.

Example 14. The vehicle10of Example 12 or 13, wherein the electrical machine100is the electrical machine100of any one of Examples 6 to 11, and the vehicle10further comprises a fluid circuit30connected between the first chamber fluid port145and the second chamber fluid port155.

Example 15. The vehicle10of Example 14, wherein the fluid circuit30comprises at least one pump device35configurable to pump fluid102into the first fluid chamber140or the second fluid chamber150and at least one drain valve device31,33configurable to prevent fluid102from draining from the other of the first fluid chamber140or the second fluid chamber150.

Example 16. The vehicle10of Example 15, wherein an inlet valve device31,33is provided between the pump device35and the fluid receiving one of the first chamber fluid port145and the second chamber fluid port155.

Example 17. The vehicle10of any one of Examples 14 to 16, wherein the fluid circuit30further comprises a fluid reservoir37.

Example 18. The vehicle10of any one of Examples 14 to 17, wherein the fluid circuit is operatively connected to a temperature system of the vehicle.

Example 19. The vehicle10of any one of Examples 12 to 18, wherein the fluid102transferred between the first and a second fluid chambers140,150is an oil based fluid.

Example 20. The vehicle10of any one of Examples 12 to 19, wherein the vehicle is a heavy-duty vehicles, such as a truck, a bus, or a construction equipment.

Example 21. A method200for braking an electrical machine100of any one of Examples 1 to 11, the method200comprises: providing202fluid102to a fluid chamber140,150at a first axial side of the electrical machine100; pumping204, responsive to rotation of a rotor120of the electrical machine100, the fluid102from the fluid chamber140,150at the first axial side of the electrical machine100to a fluid chamber140,150at a second opposite axial side of the electrical machine100through at least one fluid passage125extending along the rotor120of the electrical machine100; and controlling206a reverse flow of fluid102from the second axial side to the first axial side such that the flow through the at least one fluid passage125exceeds the reverse flow, whereby a braking torque is exerted on the rotor120by the fluid102at the second axial side of the electrical machine100.

Example 22. The electrical machine100of Example 1, wherein the first and second fluid chambers140,150are provided at, along a rotational axis A of the electrical machine100, respective opposite sides of the rotor120; the first and second fluid chambers140,150are provided between an interior of the housing130and the rotor120; the electrical machine100further comprising at least one fluid return passage101,103provided between the first fluid chamber140and the second fluid chamber150, at least one internal fluid return passage101is provided between the stator110and the rotor120; the first fluid chamber140is provided with a first chamber fluid port145for fluidly filling and/or draining the first fluid chamber140and the second fluid chamber150is provide with a second chamber fluid port155for fluidly filling and/or draining the second fluid chamber150, the first chamber fluid port145is in fluid communication with the second chamber fluid port155by a fluid port return passage103, wherein the fluid port return passage103between the first and second chamber fluid ports145,155is provided with at least one controllable valve device104configurable to control a flow of fluid102in the fluid port return passage103; the first fluid chamber140comprises a first chamber fluid inlet141,145for receiving fluid102and a first chamber fluid outlet143,145for draining fluid102, and the second fluid chamber150comprises a second chamber fluid inlet151,155for receiving fluid102and a second chamber fluid outlet153,155for draining fluid102; the at least one fluid passage125of the rotor120is provided by an impeller127of the rotor120, wherein the electrical machine100is a propulsion motor for a vehicle10.