Axial flux electric machine with cooling channel passing through the rotor shaft

Abstract

The present invention relates to an axial flux electric machine comprising a rotating part and a fixed part, the rotating part comprising a rotor shaft (7) of longitudinal axis and at least one rotor fixed on the rotor shaft (7) and the fixed part comprising a casing and at least one stator. The at least one rotor and the at least one stator are positioned longitudinally successively inside the casing and separated by at least one air gap (11). Each stator comprises coils (3). Furthermore, the rotor shaft (7) comprises at least one radial cooling channel (6) leading to an orifice facing the inner surface of the coils (3) of the at least one stator, preferably of each stator, in order to spray them.

Description

[0001] AXIAL FLUX ELECTRIC MACHINE WITH COOLING CHANNEL THROUGH THE ROTOR SHAFT

[0002] Technical field

[0003] The invention relates to the field of axial flux electrical machines.

[0004] This type of axial flux electric machine can find applications in particular in electric or hybrid vehicles, such as cars, buses, trucks, construction machinery. This type of machine can also be used for stationary applications, such as industrial charging machines or electric generators.

[0005] Prior art

[0006] In recent decades, the development of electrical machines has focused mainly on radial flux electrical machines.

[0007] Radial flux electrical machines typically comprise a coaxial rotor and stator, one surrounding the other. Thus, the magnetic flux can pass radially from the rotor to the stator and vice versa, via a radial air gap which is defined as the radial clearance between the rotor and the stator.

[0008] In contrast, axial flux machines are characterized by at least one rotor and at least one stator that are arranged successively one behind the other in the axial direction (of the rotor's axis of rotation), so that the magnetic flux path between the rotor and the stator is axial. In other words, the rotor and the stator face each other and are separated by an axially thick air gap (or axial clearance between the rotor and the stator).

[0009] The rotor of permanent magnet axial flux electric machines typically comprises permanent magnets bonded to the rotor yoke or inserted into a rotor body, and in this case, the permanent magnets are separated by radial arms from the rotor body. The stator typically comprises a ferromagnetic stator body with or without teeth. An electrical winding in the stator slots can be distributed or concentric, i.e., each winding then surrounds a tooth.

[0010] In the context of the development of high power and torque density machines for electric or hybrid traction, particularly for electric or hybrid vehicle applications, the topology of axial flux machines is positioned among those with the highest potential, in particular due to the high axial size constraint. Axial flux electric machines are also of interest for stationary applications as well as for wind turbine applications.

[0011] Generally, axial flux electric machines allow higher power and torque densities than radial flux electric machines.

[0012] This gain is generally achievable by increasing the number of pole pairs in the rotor, which increases the rotation frequency as well as the rotor losses (i.e. losses in the magnets). In addition, the use of a tooth winding allows for a reduction in the coil heads, but increases the harmonic content in the air gap, causing increased losses in the stator iron and in the magnets.

[0013] As a result, axial flux machines tend to heat up more, and controlling heating and cooling is therefore an important issue for this type of machine.

[0014] Patent application US2020 / 274410 relates to the cooling of a rotor with magnets bonded to a rotor disc. Cooling channels are positioned in the rotor disc, behind the magnets. They are therefore far from the stator located between two rotors. The cooling channels therefore do not allow for effective cooling of the stator.

[0015] The technical problem that we propose to solve consists of improving the cooling of the stator of the axial flux electric machine, while facilitating the implementation of this cooling.

[0016] Summary of the invention

[0017] The invention relates to an axial flux electrical machine comprising a rotating part and a fixed part, the rotating part comprising a rotor shaft with a longitudinal axis and at least one rotor fixed on the rotor shaft, the fixed part comprising a casing and at least one stator, the at least one rotor and the at least one stator being positioned longitudinally successively inside the casing while being separated by at least one air gap, each stator comprising coils. In addition, the rotor shaft comprises at least one radial cooling channel leading to an orifice facing the internal surface of the coils of the at least one stator, the cooling channel serving for the circulation of a cooling fluid.Advantageously, the electrical machine comprises a sealing means between the rotor shaft and each stator to prevent the cooling fluid from entering the at least one air gap, the sealing means preferably comprising a baffle, located between the rotor shaft and the stator concerned and preferably fixed or integrated into the rotor shaft or the stator concerned.

[0018] According to one configuration of the invention, the rotor shaft comprises several cooling channels facing each stator, preferably regularly distributed around the circumference of the rotor shaft.

[0019] Preferably, the electrical machine comprises a means for collecting said cooling fluid positioned in the lower part of the casing, or in the upper part of the casing, when the electrical machine is operating. According to a variant of the invention, the electrical machine comprises scoops fixed to the fixed part, the scoops extending substantially in the longitudinal direction over substantially the entire longitudinal length of the coils of the at least one stator and extending radially between the rotor shaft and the coils of the at least one stator.

[0020] Advantageously, the electrical machine comprises a cooling fluid supply system, each cooling channel being fluidically connected to the cooling fluid supply system.

[0021] According to one aspect of the invention, the power system comprises a conduit passing through the housing and a sealed chamber formed between the housing and the rotor shaft, the sealed chamber being fluidically connected to the conduit, the inlet of each cooling channel being fluidically connected to said sealed chamber to convey the cooling fluid from said sealed chamber to each cooling channel.

[0022] Preferably, the electric machine has its longitudinal axis horizontal or substantially horizontal, in the operating position.

[0023] According to one embodiment of the invention, the rotor comprises a cooling duct passing radially through the rotor and preferably, the casing comprises machining forming a deflector for orienting and directing the cooling fluid leaving the cooling duct in the direction of the coils of the at least one stator, preferably on the external surface of the coils of the at least one stator.

[0024] The invention also relates to the use of the electric machine according to one of the variants or combinations of variants described above, in an electric or hybrid vehicle, or in a stationary application, such as an industrial charging machine, an electric generator or a wind turbine.

[0025] List of figures

[0026] Other characteristics and advantages of the electrical machine according to the invention will appear on reading the following description of non-limiting examples of embodiments, with reference to the figures appended and described below.

[0027] Figure 1 represents a first embodiment of the axial flux electric machine according to the invention.

[0028] Figure 2 represents the path of the cooling fluid arriving from the rotor shaft of an axial flux electric machine according to the invention. Figure 3 represents a second embodiment of the axial flux electric machine according to the invention.

[0029] Figure 4 shows an example of an axial flux electric machine according to the invention where the electric machine is filled with cooling fluid.

[0030] Figure 5 represents a third embodiment of the axial flux electric machine according to the invention.

[0031] Figure 6 represents a first variant of a power supply system for an axial flux electric machine according to the invention.

[0032] Figure 7 represents a second variant of a power supply system for an axial flux electric machine according to the invention.

[0033] Description of the embodiments

[0034] The terms “vertical”, “horizontal”, “upper”, “lower” and equivalent relative terms are understood to apply to the electrical machine of the invention in operating conditions.

[0035] The "longitudinal" direction is the direction of the rotor shaft axis and the electric machine.

[0036] The invention relates to an axial flux electric machine comprising a casing enclosing at least one rotor and at least one stator.

[0037] The casing may comprise two flanges directly connected to each other, or two flanges and an outer cylinder (also called a "liner"), or any similar design, with one flange positioned at each axial end of the outer cylinder. Thus, the casing forms an outer envelope of the electrical machine. This outer envelope serves as protection for the stator(s) and rotor(s) located inside this outer envelope. The outer envelope also serves to position and fix the active parts of the electrical machine. In addition, this outer envelope may serve to cool the electrical machine, by convection with the ambient outside air or by the circulation of a heat transfer fluid in and / or around the outer envelope (in and / or around the cylinder and / or the flanges). The casing is then considered as a cold source.

[0038] Each stator comprises a stator body, teeth regularly distributed circumferentially on the stator body, the teeth being fixed to the stator body. The teeth extend axially (i.e., longitudinally). The stator also comprises coils wound around the teeth.

[0039] The heat transfer fluid can advantageously be a liquid, and more particularly cooling oil.

[0040] The axial flux electric machine according to the invention comprises a rotating part and a fixed part:

[0041] - the rotating part comprises a rotor shaft with a longitudinal axis and at least one rotor fixed on the rotor shaft. Thus, the rotor shaft can drive the different rotors in rotation or the rotor shaft can transmit the rotation generated by the rotors to other members.

[0042] - the fixed part includes the casing and at least one stator.

[0043] Since the machine is an axial flux electric machine, the at least one rotor and the at least one stator are positioned longitudinally successively inside the housing, being separated by at least one air gap. An air gap is a space (of axial length for an axial flux electric machine) separating a stator and a rotor. Thus, the at least one rotor and the at least one stator are arranged successively one behind the other in the axial direction (along the longitudinal axis of rotation formed by the rotor shaft), so that the path of the magnetic flux between each successive rotor and stator (i.e., which directly follow one another), passing through each air gap, is axial. In other words, each successive rotor and stator face each other and are separated by an air gap of axial thickness.

[0044] The axial flux electric machine may comprise an alternating succession of rotors and stators. In other words, each rotor is separated from the next rotor by a stator and each stator is separated from the next stator by a rotor.

[0045] The electrical machine according to the invention can operate with the longitudinal axis substantially horizontal, substantially vertical or even at a non-zero inclined angle relative to the horizontal and relative to the vertical.

[0046] Additionally, each stator includes coils to generate a magnetic field or generate a current induced by the permanent magnets of the rotor.

[0047] Furthermore, the rotor shaft comprises at least one radial cooling channel leading to an orifice facing the internal surface of the coils of the at least one stator (preferably of each stator), for spraying its coils (of the at least one stator and preferably of each stator) with a cooling fluid circulating in each cooling channel.

[0048] The cooling channel is used for the circulation of a cooling fluid, for example water. Thanks to the orifice opposite the inner surface of the coils, the cooling fluid can exit through this orifice and thus spray the coils. Indeed, when it leaves the orifice, it is projected opposite the coils. As a result, the cooling fluid is in contact, at least partially and preferably completely, with the inner surface of the coils.

[0049] The cooling fluid may advantageously be a liquid, a gas or a multiphase fluid. The cooling fluid may advantageously be a liquid and more particularly cooling oil. For example, the cooling fluid may be water, glycol water or oil. In the case of direct contact of the cooling fluid with the winding, it is preferable for the cooling fluid to be a dielectric fluid.

[0050] The inner surface of the coils is the surface of the coils closest to the rotor shaft, i.e. approximately on the inner diameter of the coils. This allows the coils to be cooled efficiently and simply by rotating the rotor shaft. In addition, the rotation of the radial cooling channels of the rotor shaft generates a suction of the coolant from the inside to the outside. This makes it possible to do without a pump.

[0051] For example, the at least one cooling channel may include an axial inlet in the rotor shaft and one or more radial channels.

[0052] The cooling fluid that reaches the internal surface of the coils can then pass between the coils to reach the external part of the stator.

[0053] Each rotor may, for example, comprise a rotor disc made of metallic material and permanent magnets. Thus, when an electric current passes through the coils of a stator of the electrical machine, an electromagnetic torque is produced and drives a rotor of the machine into rotation, thanks to the interaction between the stator field produced by the winding and the rotor field produced by the permanent magnets. Conversely, when a rotor is driven into rotation by any rotation means (the rotor shaft, for example), the permanent magnets generate a magnetic field that creates an induced voltage in the coils of a stator. This makes it possible to transform the mechanical energy of rotation of the rotor into electrical energy in the stator.Therefore, the electric machine can be used as an electric motor that transforms electricity into mechanical energy by rotating the rotor, or as an electric generator that transforms rotating mechanical energy into electrical energy.

[0054] The rotor disk can then serve as a support for carrying permanent magnets and to do this, it can for example comprise housings, preferably of substantially trapezoidal section (but other shapes can of course be envisaged), distributed circumferentially within the rotor disk, the permanent magnets being positioned in the housings. The rotor disk can also comprise radial arms separating said housings. Preferably, when the section of the housings is trapezoidal, the largest base of the trapezoid is on the external side of the rotor.

[0055] Radial arms mean spokes located between the housings which extend radially from an inner end to an outer end.

[0056] For example, the rotor disk may be composed of an inner ring (or central hub) intended to be mounted on a shaft, an outer ring (or outer hoop) and the radial arms which form the connection between the inner ring and the outer ring and which leave the necessary space for the introduction of the permanent magnets. The spaces located between the radial arms (and limited by the inner and outer rings) thus form the housings. Advantageously, the housings can axially pass through the rotor disk to open at the two axial ends of the rotor disk. Thus, the permanent magnets can pass through the rotor disk axially on each side. This configuration is particularly advantageous when the electrical machine comprises a rotor and two stators, each stator being on either side of the rotor disk.This type of machine comprising a rotor and two stators, one stator on either side of the rotor with the permanent magnets passing completely through the rotor disc is called a "through permanent magnet electric machine".

[0057] The rotor disc may, for example, have an annular shape between a cylindrical surface of inner diameter and a cylindrical surface of outer diameter. In addition, it may have an axial external thickness (i.e., the axial length of the disc, taken at its outer surface) at its cylindrical outer surface.

[0058] Advantageously, the electrical machine may comprise a sealing means between the rotor shaft and each stator to prevent the cooling fluid (arriving from the cooling channels) from entering the at least one air gap separating each stator from the rotor(s) preceding and / or following the stator concerned, preceding and following being understood along the longitudinal axis of the electrical machine. By preventing the cooling fluid from entering an air gap and preferably all the air gaps, the energy losses due to friction of the electrical machine are limited.

[0059] Preferably, the sealing means may comprise a baffle. Indeed, this type of sealing means is effective on dynamic seals, as is the case between the rotating rotor shaft and the fixed stator. The baffle is installed between the rotor shaft and the stator concerned and it may be fixed or integrated into the rotor shaft or the stator concerned. Preferably, the rotor shaft may comprise several cooling channels opposite each stator to further cool the internal surface of the coils of the stator concerned.

[0060] Preferably, the different cooling channels facing each stator can be regularly distributed around the circumference of the rotor shaft to better homogenize the temperatures of the stator, in particular when the longitudinal axis is horizontal. Indeed, when the longitudinal axis is horizontal, the cooling fluid tends to descend by gravity into the lower part of the casing, which tends to increase the temperature difference between the upper part and the lower part of the stator.

[0061] The terms "lower" and "upper", as well as "top" and "bottom" refer to the electrical machine in operating condition with the longitudinal axis horizontal and relative to the vertical axis.

[0062] According to one configuration of the invention, the electrical machine may comprise a means for collecting the coolant positioned in the lower part of the casing, or in the upper part of the casing. When the collecting means is in the lower part of the casing, the coolant arrives by gravity in the collecting means. The collection of the coolant is therefore simplified. When the collecting means is in the upper part of the casing, the collection of the coolant is then only possible with the casing immersed in coolant. This configuration is advantageous because the coolant then surrounds the coils, which makes it possible, on the one hand, to improve the cooling of the machine, and on the other hand, to improve the homogeneity of the cooling between the upper part and the lower part of the stator, that is to say between the coils located on the upper part and those located on the lower part.Furthermore, in this submerged configuration, the coolant passes between the coils and also wets the outer surface of the coils, even though the suction generated by the rotation would be insufficient to allow the coolant to radially cross the space between the coils.

[0063] The collection means may have a calibrated outlet: for example, the outlet may be an opening of predefined diameter to improve the circulation of the cooling fluid. In addition, this calibrated outlet may be adjustable or modulated depending on the state of the electrical machine (depending on its power and / or its temperature for example).

[0064] Advantageously, the electrical machine may comprise scoops fixed to the fixed part, the scoops extending substantially in the longitudinal direction over substantially the entire longitudinal length of the coils of the at least one stator (preferably of each stator) and extending radially between the rotor shaft and the coils of the at least one stator (preferably of each stator). The scoops are therefore guide parts intended to guide the flow exiting the orifice of the rotor shaft towards the internal surface of the coils. Thanks to the scoops, a substantially identical flow can be guaranteed in all the coils. The scoops serve to form receptacles around the rotor shaft to distribute the cooling fluid equally in the different coils of the stator.

[0065] The scoops can be attached to the stator or to the casing, for example to a casing flange.

[0066] Preferably, the electrical machine may also optionally comprise a fixed membrane secured to at least one stator (preferably a fixed solar membrane for each stator) to electrically insulate the stator coils. The membrane (or skin) serves to prevent contact between the cooling fluid and the coils. It thus serves as a sealing system. The membrane is a thin wall (preferably less than 1 mm) and preferably flexible to easily come into contact with the coils. The membrane may in particular be adapted to the cooling fluid and the temperature of the cooling fluid in the electrical machine. It may in particular be made of polymer(s).

[0067] Advantageously, the electric machine may comprise a cooling fluid supply system, each cooling channel being fluidically connected to the cooling fluid supply system. As a result, the supply system can supply all the cooling channels directly and almost simultaneously, which simplifies the electric machine.

[0068] Furthermore, the collection means and the supply system can be fluidically connected by a pipe so as to form a closed-loop circuit for the coolant. In addition, the centrifugal effects linked to the rotation of the rotor shaft allow a "pump" effect, i.e. a suction effect making it possible to generate a circulation of the coolant in the closed-loop circuit without using a pump per se. Of course, it is also possible to add a pump to the closed-loop circuit to better control the flow rate of the coolant and thus improve the cooling of the coolant.

[0069] The closed loop circuit may also include a radiator or heat exchanger to cool the coolant.

[0070] According to a variant of the invention, the power supply system may comprise a conduit, for example passing through the casing, and a sealed chamber formed between the casing and the rotor shaft. The sealed chamber may then be fluidically connected to the conduit and the inlet of each cooling channel may be fluidically connected to the sealed chamber to convey the cooling fluid from the sealed chamber to each cooling channel. The conduit allows the introduction of the cooling fluid into the electrical machine. The sealed chamber may comprise dynamic sealing means (by succession of grooves and without the use of seals, also called "labyrinth seals") or sealing means comprising seals (made of elastomer for example) to ensure its sealing.

[0071] As the rotor rotates, a centrifugal force is generated. This force creates a vacuum in the sealed chamber, and as a result, the coolant is drawn into the cooling channels.

[0072] Advantageously, the supply system may comprise a means for extending the conduit (such as a tube fixed to the end of the conduit on the casing) towards the rotor shaft so that the cooling fluid arrives in the rotor shaft, by gravity. The rotor shaft may then comprise an annular enclosure into which the cooling fluid leaving the extension means falls under the effect of gravity, in particular when the rotor shaft is horizontal or substantially horizontal. The annular enclosure is connected to the different inlets of the different cooling channels and can therefore supply the different cooling channels with cooling fluid. This solution does not require sealing means and operates in a simple manner.

[0073] According to another variant of the invention, the rotor shaft may have a longitudinal bore, preferably axial, the cooling fluid being able to arrive through this longitudinal bore to supply the different cooling channels. As a result, the longitudinal bore is then in fluid connection with the different cooling channels.

[0074] According to one configuration of the invention, the electrical machine may have its longitudinal axis horizontal or substantially horizontal in the operating position.

[0075] According to one version of the invention, the rotor (in particular the rotor disk) may comprise at least one cooling duct passing radially through the rotor (advantageously through a radial arm) to circulate the cooling fluid in the rotor disk. As a result, the rotor, in particular the permanent magnets, and the stator can be effectively cooled simultaneously. Preferably, the rotor may comprise at least one cooling duct in each of the radial arms to cool the rotor homogeneously.

[0076] Each cooling duct may be fluidically connected to the power system and / or to the cooling channels to facilitate the overall cooling system of the electrical machine with a single cooling fluid allowing both the cooling of the stator(s) and the rotor(s).

[0077] Preferably, the casing may comprise a machining (or several machinings) forming a deflector to orient and direct the cooling fluid leaving the cooling duct towards the coils of the at least one stator (preferably each stator), preferably on the external surface of the coils of the at least one stator (each stator). These machinings in the casing make it possible to guide the flow of cooling fluid leaving the cooling ducts towards a stator, in particular towards the coils of the stator. By using machinings, it is possible to dispense with additional parts to guide the flow leaving the rotor towards the coils of the stator. Therefore, this solution is simple and low cost. In addition, the rotation of the rotor and the machinings make it possible to ensure that very little cooling fluid reaches the air gap separating the rotor and the stator.Advantageously, each machining can be located at a predetermined position so as to improve the guidance of the cooling fluid to the coils.

[0078] Preferably, when the electric machine has a horizontal longitudinal axis, these machining operations can be located on the upper part of the casing, with the electric machine in the operating position: in this configuration, the machining operations of the casing are then only on at most one half of the casing.

[0079] According to one embodiment of the invention, each machining can thus comprise at least one concave bowl facilitating the guidance of the flow towards the coils. If the outlet of the cooling duct is used to cool two stators, one on each side of the rotor, each machining can then comprise two concave bowls juxtaposed to each other so as to separate the flow rate of the flow leaving the rotor into two, preferably into two substantially equal flows, to cool the stators on either side of the rotor.

[0080] These machining operations also allow the cooling fluid to flow into the upper part of the stator, to spray the external surface of the coils. Thus, the cooling fluid can then pass, in the stator, from the inside to the outside, arriving through the cooling channels of the rotor shaft and from the outside to the inside, arriving through the machining operations of the casing in the upper part of the casing.

[0081] The invention also relates to the use of the electric machine according to one of the variants or combinations of variants described above in an electric or hybrid vehicle, a wind turbine, or in a stationary application, such as an industrial charging machine, an electric generator. An “electric” vehicle is a vehicle which comprises an electric machine and which does not comprise an internal combustion engine. A “hybrid” vehicle comprises an electric machine and an internal combustion engine (petrol or diesel for example). A stationary application is an application in which the electric machine is not in a means of transport. It is stationary relative to a terrestrial reference point. An industrial charging machine is a machine used in industry and an electric generator is a machine capable of supplying electricity to a machine, a system or a factory.A wind turbine may be stationary when it is on land or placed on the seabed. A floating offshore wind turbine may not be completely stationary in the sense that it may undergo movements around an average position.

[0082] Figure 1 illustrates, in a schematic and non-limiting manner, a first embodiment of an axial flux electric machine according to the invention.

[0083] The axial flux electric machine consists of a rotating part and a static part.

[0084] The rotating part comprises a rotor shaft 7 and a rotor comprising a rotor disc 4. The static (or fixed) part comprises a casing (not shown) and a stator comprising a stator body 2 and coils 3.

[0085] The rotor and the stator are arranged successively along the longitudinal axis of the rotor shaft 7, thus forming an axial flux electric machine with an air gap 11 whose thickness (distance between the rotor and the coils 3) is in the direction of the longitudinal axis (i.e. the axis of the rotor shaft 7).

[0086] The rotor shaft 7 comprises a central supply channel 1 for supplying cooling fluid to the electric machine.

[0087] The central supply channel 1 is fluidically connected to the radial cooling channel 6 located in the rotor shaft 7. The radial outlet of the radial cooling channel 6 faces the internal surface of the coils 3 to spray them and thus facilitate their cooling.

[0088] In order to prevent the cooling fluid leaving the radial cooling channel 6 from entering the air gap 11, a sealing means, here corresponding to a baffle 5, is placed between the rotor shaft 7 and the stator. This baffle 5 prevents access of the cooling fluid to the air gap 11.

[0089] The electric machine may also optionally include a fixed membrane attached to the stator to insulate the stator coils.

[0090] Figure 2 illustrates, in a schematic and non-limiting manner, a portion of an axial flux electric machine according to the invention.

[0091] The axial flux electric machine comprises a rotating part and a static part. The rotating part comprises a rotor shaft 7 and a rotor (not shown). The static (or fixed) part comprises a housing (not shown) and a stator comprising a stator body 2 and coils 3.

[0092] The rotor and the stator are arranged successively along the longitudinal axis of the rotor shaft 7, thus forming an axial flux electric machine with an air gap whose thickness is in the direction of the longitudinal axis.

[0093] The rotor shaft 7 here comprises several radial cooling channels 6 arriving opposite the coils 3 to spray them and thus cool them.

[0094] As the rotor shaft 7 rotates around its longitudinal axis, the various radial cooling channels 6 allow the spraying of all the coils 3.

[0095] The arrows illustrate the path of the cooling fluid arriving through the radial cooling channels 6 to arrive in an area located between the external surface of the rotor shaft 7 and the internal surface of the coils 3. Then the cooling fluid passes between the coils 3 radially to reach an area located between the external surface of the coils 3 and the external casing (not shown).

[0096] Figure 3 illustrates, in a schematic and non-limiting manner, a second embodiment of an axial flux electric machine according to the invention.

[0097] Diagram a) represents a sectional view in a longitudinal plane of the axial flux electric machine while diagram b) represents a sectional view in a plane orthogonal to the longitudinal axis of the electric machine.

[0098] The axial flux electric machine consists of a rotating part and a static part.

[0099] The rotating part comprises a rotor shaft 7 and a rotor comprising a rotor disc 4. The static (or fixed) part comprises a casing 18 and a stator comprising a stator body 2 and coils 3.

[0100] The rotor and the stator are arranged successively along the longitudinal axis of the rotor shaft 7, thus forming an axial flux electric machine with an air gap 11 whose thickness (distance between the rotor and the stator) is in the direction of the longitudinal axis.

[0101] The rotor shaft 7 comprises a central supply channel 1 for supplying cooling fluid to the electric machine.

[0102] The central supply channel 1 is fluidically connected to the radial cooling channel 6 located in the rotor shaft 7 and to the cooling ducts 10 in the rotor disc 4. The radial outlet of the radial cooling channel 6 faces the internal surface of the coils 3 to spray them and thus facilitate their cooling.

[0103] The passage of the cooling fluid in the cooling ducts 10 of the rotor disc 4 makes it possible to cool the permanent magnets (not shown) of the rotor.

[0104] The radial outlets of the cooling ducts 10 arrive opposite machinings in the casing 18, these machinings forming deflectors to guide the cooling fluid, in particular to guide it towards the coils 3 of the stator. These machinings here take the form of two concave bowls 28 but a single concave bowl in the direction of the coils 3 of the stator could also be used or a shape other than a concave bowl.

[0105] In order to prevent the cooling fluid leaving the radial cooling channel 6 from entering the air gap 11, a sealing means, here corresponding to a baffle 5, is placed between the rotor shaft 7 and the stator. This baffle 5 prevents access of the cooling fluid to the air gap 11.

[0106] The arrows in diagram b) illustrate the path of the cooling fluid when the electric machine has its longitudinal axis horizontal. In the upper part, the cooling fluid emerging from the machining, such as the concave bowls 28, flows over the external part of the coils (see the arrows in the upper part between the coils 3 and the casing 18). In addition, the cooling fluid arriving through the cooling channels 6 arrives in the annular space between the external surface of the rotor shaft 7 and the internal surface of the coils 3, passes radially between the coils 3 to reach the area between the external surface of the coils 3 and the casing 18. The cooling fluid then flows over the external part of the coils located between the coils 3 and the casing 18. The cooling fluid exits in the lower part through the collecting means 8.The path of the cooling fluid in the electric machine from the concave bowls 28 is substantially by gravity.

[0107] The electric machine may also optionally include a fixed membrane attached to the stator to insulate the stator coils.

[0108] Figure 4 illustrates, in a schematic and non-limiting manner, another example of an axial flux electric machine.

[0109] The axial flux electric machine comprises a rotating part and a static part. The rotating part comprises a rotor shaft 7 and a rotor comprising a rotor disc. The static (or fixed) part comprises a housing 18 and a stator comprising a stator body 2 and coils 3.

[0110] The rotor and the stator are arranged successively along the longitudinal axis of the rotor shaft 7, thus forming an axial flux electric machine with an air gap whose thickness is in the direction of the longitudinal axis.

[0111] The rotor shaft 7 includes a central supply channel for supplying cooling fluid to the electric machine.

[0112] The central supply channel is fluidically connected to the radial cooling channels 6 located in the rotor shaft 7. The radial outlet of each radial cooling channel 6 faces the internal surface of the coils 3 to spray them and thus facilitate their cooling. Unlike the embodiment of diagram b) of Figure 3, the electrical machine here comprises a means 8 for collecting the cooling fluid in the upper part of the casing, when the electrical machine has its longitudinal axis horizontal. As a result, the stator of the electrical machine is completely immersed in the cooling fluid during operation.

[0113] Figure 5 illustrates, in a schematic and non-limiting manner, a third embodiment of an axial flux electric machine according to the invention.

[0114] Diagram a) represents a sectional view in a longitudinal plane of the axial flux electric machine while diagram b) represents a sectional view in a plane orthogonal to the longitudinal axis of the electric machine.

[0115] The axial flux electric machine consists of a rotating part and a static part.

[0116] The rotating part comprises a rotor shaft 7 and a rotor comprising a rotor disc 4. The static (or fixed) part comprises a casing 18 and a stator comprising a stator body 2 and coils 3.

[0117] The rotor and the stator are arranged successively along the longitudinal axis of the rotor shaft 7, thus forming an axial flux electric machine with an air gap 11 whose thickness (distance between the rotor and the stator) is in the direction of the longitudinal axis.

[0118] The rotor shaft 7 comprises a central supply channel 1 for supplying cooling fluid to the electric machine.

[0119] The central supply channel 1 is fluidically connected to the radial cooling channels 6 located in the rotor shaft 7 (and could be fluidically connected to cooling ducts not shown in the rotor disc 4, such as the cooling ducts 10 of Figure 3). The radial outlet of each radial cooling channel 6 faces the inner surface of the coils 3 to spray them and thus facilitate their cooling.

[0120] In order to prevent the cooling fluid leaving each radial cooling channel 6 from entering the air gap 11, a sealing means, here corresponding to a baffle 5, is placed between the rotor shaft 7 and the stator. This baffle 5 prevents access of the cooling fluid to the air gap 11.

[0121] The electrical machine here comprises scoops 9 fixed to the fixed part (to the stator or to the casing 18 in particular). The scoops 9 extend substantially over the entire longitudinal length of the coils 3 in the longitudinal direction, for example from the baffle 5 to the opposite longitudinal end of the coils 3 and they extend radially between the rotor shaft 7 and the coils 3. The arrow on the rotor shaft in diagram b) indicates the direction of rotation of the rotor shaft 7 (clockwise in this case but obviously the rotor shaft 7 could rotate in the opposite direction without departing from the scope of the invention). As shown, the scoops 9 are oriented, that is to say curved, so as to follow the orientation given to the cooling fluid leaving the radial cooling channels 6, by the rotation of the rotor shaft 7 in the direction indicated.This curvature makes it easier to guide the cooling fluid to the area between two consecutive coils, limiting disturbances in the flow of the cooling fluid.

[0122] Alternatively or additionally, the scoops (or at least part of them) could be completely radial (in this case, they would not have curved shapes). Thus, they would essentially serve as obstacles to force the cooling fluid to go to each coil. This solution would allow the same efficiency to be obtained, regardless of the direction of rotation of the rotor shaft.

[0123] Preferably and as shown, the electrical machine may comprise the same number of scoops facing a stator as this stator comprises coils (but it could comprise fewer scoops than the stator comprises coils). For example, if the stator comprises eighteen coils, the electrical machine may comprise eighteen scoops facing this stator. The scoops 9 may be equally distributed around the rotor shaft 7 so as to better distribute the cooling fluid towards the stator and each scoop 9 may in particular be positioned at a separate coil 3.

[0124] The electric machine may also optionally include a fixed membrane attached to the stator to insulate the stator coils.

[0125] Figure 6 illustrates, in a schematic and non-limiting manner, a first variant of a cooling fluid supply system for an axial flux electric machine according to the invention.

[0126] The electric machine comprises a casing 18 (the casing 18 is only partially shown) and a rotor shaft 7.

[0127] The casing 18 comprises a conduit 24 passing through the casing 18 so as to allow the supply of cooling fluid to the electric machine.

[0128] The housing 18 is connected to the rotor shaft 7 by a bearing 19 so as to allow rotation of the rotor shaft 7 in the housing 18 which is fixed.

[0129] The casing 18 extends to the rotor shaft 7 and sealing means 22 and 23 (dynamic seals for example) are positioned between the casing 18 and the rotor shaft 7 so as to form a sealed chamber 21.

[0130] The conduit 24 opens into the sealed chamber 21 to supply this sealed chamber 21 with cooling fluid. In addition, the inlet of the radial cooling channels 6 arrives in the sealed chamber 21. In other words, the conduit 24, the sealed chamber 21 and the radial cooling channels 6 are fluidically connected to each other.

[0131] The rotation of the rotor shaft 7 drives the cooling fluid contained in the sealed chamber 21 into the radial cooling channels 6 of the rotor shaft 7.

[0132] The bold black arrows represent the cooling fluid supply. The cooling fluid arrives via the conduit 24, it passes through the casing 18 to arrive in the sealed chamber 21 then it joins the radial cooling channels 6 and thus sprays the internal surface of the coils 3 which are opposite the radial cooling channels 6. This solution could also supply the rotor cooling conduits.

[0133] Figure 7 illustrates, in a schematic and non-limiting manner, a second variant of a cooling fluid supply system for an axial flux electric machine according to the invention.

[0134] The electric machine comprises a housing 18 (the housing 18 is only partially shown), a rotor shaft 7 (also partially shown) and a rotor disc 20.

[0135] As shown, the rotor shaft 7 and the rotor disc 20 are in one piece but they could be made in two separate pieces and assembled by any means allowing them to be fixed to each other, by welding or screwing for example.

[0136] The figure shown illustrates two variants which can be used independently of each other or in combination. In one case, the cooling fluid arrives through the central shaft via the conduit 24b. In another case, the cooling fluid arrives through the housing flange via the conduit 24a. Of course, the electric machine can combine these two variants.

[0137] The casing 18 comprises a conduit 24a passing through the casing 18 and / or a conduit 24b passing through the rotor shaft 7 so as to allow the supply of cooling fluid to the electric machine. In other words, the supply of cooling fluid to the electric machine can arrive either via the conduit 24a, or via the conduit 24b, or via both the conduit 24a and the conduit 24b.

[0138] The housing 18 is connected to the rotor shaft 7 by a bearing 19 so as to allow rotation of the rotor shaft 7 in the housing 18 which is fixed.

[0139] In this embodiment, the supply system does not require sealing means between the casing 18 and the rotor disc 20. In the case where the cooling fluid is supplied via the conduit 24b, the cooling fluid arrives in the rotor disc 20 by gravity in the collection zone 28 of the rotor disc 20.

[0140] In the case where the coolant is supplied by the conduit 24a, the conduit is extended by the extension means 25 (which may be a tube partly shrunk to the casing or welded to the casing). The extension means terminates in the collection zone 28 of the rotor disc 20 so as to supply the coolant into the collection zone 28, by gravity.

[0141] Once in the collection zone 28, the cooling fluid can feed the cooling ducts 10. The rotation of the rotor disc 20 makes it possible to feed the different cooling channels 10 one after the other.

[0142] The collection zone 28 thus forms an annular enclosure of the rotor disk 20 connected to the different inlets of the different cooling ducts 10.

[0143] In this embodiment, the inlets of the cooling ducts 10, connected to the supply system, are substantially radial, arriving in the collection zone 28. The bold black arrows represent the supply of cooling fluid. The cooling fluid arrives via the duct 24a and / or via the duct 24b.

[0144] If it arrives via the conduit 24a, it passes through the casing 18. On leaving the conduit 24a, it is routed by the extension means 25 to arrive in the collection zone 28.

[0145] If it leaves the conduit 24b, it arrives directly in the collection zone 28. From this collection zone 28 which forms an annular enclosure, it then joins the cooling conduits 10 of the rotor disk 20.

[0146] Examples

[0147] A solution of the invention was compared, by simulation, with a prior art solution in which the stator is cooled solely by air convection in the housing, inside the housing. The housing, for its part, is cooled via water cooling. In other words, for this prior art solution, no cooling duct is placed in the rotor and no cooling channel opening opposite the coils is used.

[0148] For the solution of the invention, several hypotheses were considered:

[0149] - (a): it is assumed that the internal surface of the coils is in contact with the cooling fluid leaving the orifices of the rotor shaft;

[0150] - (b): it is assumed that the internal and external surfaces of the coils are in contact with the cooling fluid leaving the holes in the rotor shaft;

[0151] - (c): it is assumed that all surfaces of the coils are in contact with the cooling fluid exiting the rotor shaft orifices, i.e. the internal and external surfaces as well as the surfaces connecting the internal and external surfaces which separate two consecutive coils circumferentially.

[0152] According to these assumptions, for the operating point of the electric machine, the temperature of the coils is reduced by 44°C for case (a), by 65°C for case (b) and by 72°C for case (c) and the temperature of the stator body is reduced by 40°C for case (a), by 54°C for case (b) and by 59°C for case c), all other things being equal, which demonstrates the cooling efficiency of the solution of the invention.

Claims

Claims 1. Axial flux electrical machine comprising a rotating part and a fixed part, the rotating part comprising a rotor shaft (7) with a longitudinal axis and at least one rotor fixed on the rotor shaft (7), the fixed part comprising a casing (18) and at least one stator, the at least one rotor and the at least one stator being positioned longitudinally successively inside the casing (18) while being separated by at least one air gap (11), each stator comprising coils (3), characterized in that the rotor shaft (7) comprises at least one radial cooling channel (6) leading to an orifice facing the internal surface of the coils (3) of the at least one stator, the cooling channel serving for the circulation of a cooling fluid.

2. Electrical machine according to claim 1, wherein the electrical machine comprises sealing means between the rotor shaft (7) and each stator to prevent the cooling fluid from entering the at least one air gap (11), the sealing means preferably comprising a baffle (5), located between the rotor shaft (7) and the stator concerned and preferably fixed or integrated into the rotor shaft (7) or the stator concerned.

3. Electrical machine according to one of the preceding claims, in which the rotor shaft (7) comprises several cooling channels (6) facing each stator, preferably regularly distributed around the circumference of the rotor shaft (7).

4. Electrical machine according to one of the preceding claims, in which the electrical machine comprises a means (8) for collecting said cooling fluid positioned in the lower part of the casing (18), or in the upper part of the casing (18), in the operating situation of the electrical machine.

5. Electrical machine according to one of the preceding claims, wherein the electrical machine comprises scoops (9) fixed on the fixed part, the scoops (9) extending substantially in the longitudinal direction over substantially the entire longitudinal length of the coils (3) of the at least one stator and extending radially between the rotor shaft (7) and the coils (3) of the at least one stator.

6. An electrical machine according to one of the preceding claims, wherein the electrical machine comprises a cooling fluid supply system, each cooling channel (6) being fluidically connected to the cooling fluid supply system.

7. An electrical machine according to claim 6, wherein the power supply system comprises a conduit (24) passing through the casing (18) and a sealed chamber (21) formed between the casing (18) and the rotor shaft (7), the sealed chamber (21) being fluidly connected to the conduit (24), the inlet of each cooling channel (6) being fluidly connected to said sealed chamber (21) to convey the cooling fluid from said sealed chamber (21) to each cooling channel (6).

8. Electrical machine according to one of the preceding claims, in which the electrical machine has its longitudinal axis horizontal or substantially horizontal, in the operating position.

9. Electrical machine according to one of the preceding claims, in which the rotor comprises a cooling duct (10) passing radially through the rotor and preferably, the casing (18) comprises machining forming a deflector for orienting and directing the cooling fluid leaving the cooling duct (10) in the direction of the coils (3) of the at least one stator, preferably on the external surface of the coils (3) of the at least one stator.

10. Use of the electric machine according to one of the preceding claims in an electric or hybrid vehicle, or in a stationary application, such as an industrial charging machine, an electric generator or a wind turbine.

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