Cooling device for an axial flux electric machine

Abstract

Cooling device for an axial flux electrical machine. Cooling device (10) for an axial flux electrical machine (1), the cooling device (10) being intended to be arranged around at least one winding (2) disposed inside said electrical machine (1), the cooling device (10) comprising a hollow structure (12) within which a heat transfer fluid is intended to circulate, at least one fluid inlet (14) configured to permit the passage of the heat transfer fluid into said hollow structure (12) and at least one fluid outlet (16) configured to permit the passage of the heat transfer fluid out of said hollow structure (12), the hollow structure (12) further comprising reliefs (18) on an inner face. Figure for the abbreviation: Fig. 3

Description

Title of the invention: Cooling device for an axial flux electrical machine

[0001] The invention relates to a cooling device for cooling an axial flux electric machine, and more particularly for cooling the coils of a stator magnetic circuit of such an axial flux electric machine. The invention further relates to an axial flux electric machine equipped with such a cooling device.

[0002] Generally, two types of cooling methods are used to cool axial flux electrical machines: water cooling in the casings of the electrical machine in question and oil cooling, in which the oil is in direct contact with the active stator parts.

[0003] Each of the two types of cooling has advantages and disadvantages. The typical advantages of water cooling over oil cooling include the ease of implementation and the fact that pressure losses at low temperatures are more favorable with water than with oil. However, the classic disadvantages of water cooling are the significant thermal resistance between the cooling circuit and the heat source(s), as well as a lower capacity for dissipating heat than oil, which means that water cooling systems are insufficient above a certain power level for axial flux electrical machines.

[0004] Typical advantages of oil cooling include a good capacity to dissipate heat and the possibility of direct heat exchange between the cooling circuit and the heat source(s), as the oil circulates in direct contact with the active stator parts. The classic disadvantages of oil cooling are the technical complexity of its implementation, particularly in ensuring the oil circuit is sealed against the rotor. Certain components of such an oil cooling system, especially membranes and sealing plates, often require a complex design and the integration of a pump, necessary to ensure oil pressure build-up in the circuit, since oil is more viscous than water within a given temperature range.

[0005] The object of the invention is to remedy the drawbacks described above by providing a cooling device with a design that facilitates the circulation of oil around the coils so as to limit turbulence and prevent oil stagnation inside the cooling device, while retaining the multiple advantages afforded by state-of-the-art oil cooling systems.

[0006] To this end, the invention relates to a cooling device for an axial flux electrical machine, the cooling device being intended to be arranged around at least one winding disposed inside said electrical machine to cool said at least one winding, the cooling device comprising a hollow structure inside which a heat transfer fluid is intended to circulate, the cooling device comprising at least one fluid inlet configured to allow the passage of the heat transfer fluid into the interior of said hollow structure and at least one fluid outlet configured to allow the passage of the heat transfer fluid to the exterior of said hollow structure, the hollow structure further comprising reliefs on an inner face, said reliefs being intended to at least partially envelop the at least one winding disposed inside the electrical machine.

[0007] The reliefs on the inner face of the hollow structure can be in the form of concave and / or convex reliefs.

[0008] The hollow structure may include an annular shell having an external portion and an internal portion, and the reliefs on the inner face of the hollow structure may be arranged on the external portion of the annular shell and / or on the internal portion of the annular shell.

[0009] The internal portion of the annular shell may exhibit an alternation between concave and convex reliefs.

[0010] The hollow structure may further include a tray configured to cover the annular shell in the manner of a lid.

[0011] At least one fluidic inlet can be arranged in the tray and / or at least one fluidic outlet can be arranged in the tray.

[0012] An outer face of the hollow structure may have at least one stiffening rib.

[0013] At least a portion of the inner face of the hollow structure intended to be in contact with the heat transfer fluid may have a surface treatment configured to optimize the flow of said heat transfer fluid around the windings arranged inside the axial flux electric machine.

[0014] The invention also relates to an axial flux electric machine comprising at least one cooling device as defined above.

[0015] The number of reliefs on the inner face of the hollow structure can be greater than or equal to the number of windings of the electrical machine.

[0016] The invention also relates to a vehicle equipped with such a cooling device.

[0017] These objects, features and advantages of the present invention will be described in detail in the following description of a particular embodiment, given by way of non-limiting example, with reference to the accompanying figures, among which:

[0018] Fig. 1 illustrates an exploded cavalier perspective view of an axial flux electrical machine.

[0019] Fig. 2 is a front view of an embodiment of the annular shell of the hollow structure of the axial flux electric machine.

[0020] Fig. 3 illustrates a detailed view of the annular shell of Fig. 2.

[0021] Figure 4 is a front view of one embodiment of the platform of the structure hollow of the axial flux electric machine.

[0022] Generally, an axial flux electric machine 1 comprises a stator, which is generally cylindrical in shape, and a rotor, also generally cylindrical in shape, disposed inside the stator. The rotor is intended to be driven in rotation about an axis of rotation, the axis of rotation being substantially coaxial with the axis of revolution of the stator. Such an electric machine 1 also comprises at least one winding disposed inside the electric machine 1. More particularly, a plurality of salient poles are arranged between the moving rotor and the fixed stator. This plurality of poles is arranged with angular repetition about an axis of revolution that is then substantially parallel to the axis of rotation of the rotor. The salient poles are arranged radially so as to define an alternation of arms and slots. The arms of the salient poles are intended to be surrounded by conducting wire so as to form a plurality of windings 2.

[0023] Figure 1 illustrates an exploded cavalier perspective view of an example of an axial flux electric machine 1. Generally, the axial flux electric machine 1 comprises a stator and a rotor, as well as at least one winding 2 arranged inside said electric machine 1. Typically, a plurality of windings 2 are arranged inside the electric machine 1. The number of windings 2 arranged inside the electric machine 1 is generally a multiple of three.

[0024] According to the invention, the axial flux electric machine 1 also includes

[0025] a cooling device 10 for cooling at least one winding 2 located inside said electric machine 1. Common to all embodiments of the cooling device 10, it comprises a hollow structure 12 within which a heat transfer fluid is intended to circulate. The at least one winding 2 is then arranged inside said hollow structure 12 so as to be surrounded by the heat transfer fluid and thus cooled by it.

[0026] Preferably, the heat transfer fluid is a liquid, and in particular oil. However, other types of fluids in liquid form may be considered. It is also possible to imagine a fluid in the form of a gas circulating inside the hollow structure 12 of the cooling device 10.

[0027] In order to allow circulation of the heat transfer fluid inside the hollow structure 12 of the cooling device 10, the cooling device 10 includes at least one fluid inlet 14 configured to allow the passage of the heat transfer fluid into the interior of said hollow structure 12 and at least one fluid outlet 16 configured to allow the passage of the heat transfer fluid to the exterior of said hollow structure 12.

[0028] At least one fluid inlet 14 allows the hollow structure 12 to be supplied with heat transfer fluid to allow cooling of the components of the axial flow electric machine 1, while at least one fluid outlet 16 allows this same heat transfer fluid, heated by the heat transfer it undergoes, to be evacuated in order to replace it with cooler heat transfer fluid and / or to cool the heat transfer fluid thus evacuated before reinjecting it into the hollow structure 12 of the cooling device 10 of the axial flow electric machine 1.

[0029] According to a preferred embodiment, the cooling device 10 may include several fluid inlets 14 and / or several fluid outlets 16. The cooling device 10 may, in particular, include as many fluid inlets 14 as there are windings 2. Similarly, the hollow structure 12 of the cooling device 10 may include as many fluid outlets 16 as there are windings 2. Furthermore, the fluid inlet(s) 14 and the fluid outlet(s) 16 may be arranged directly within the hollow structure 12 of the cooling device 10.

[0030] The arrangement and / or number and / or size and / or shape of the fluidic inlet(s) 14 and of the fluidic outlet(s) 16 of the cooling device 10 may be chosen so as to optimize the flow of the heat transfer fluid inside said hollow structure 12 in order to obtain efficient cooling of the components of the electrical machine 1 with axial flow and cooling of the windings 2 in particular.

[0031] In order to facilitate the circulation of the oil around the windings 2 so as to limit turbulence, and in order to avoid the stagnation of the oil inside the cooling device 10, the hollow structure 12 further includes reliefs 18 which are located on an inner face of said hollow structure 12, that is to say reliefs 18 intended to be arranged opposite the windings 2 located inside the electrical machine 1. Said reliefs 18 are intended to at least partially envelop at least one winding 2 located inside the electrical machine, that is to say that the reliefs 18 on the inner face of the hollow structure 12 of the cooling device 10 have shapes which follow the contour of the windings 2.

[0032] The arrangement and / or number and / or size and / or shape of the reliefs 18 on the inner face of the hollow structure 12 of the cooling device 10 can be chosen so as to optimize the flow of the heat transfer fluid inside said hollow structure 12 in order to obtain efficient cooling of the components of the axial flow electrical machine 1 and cooling of the windings 2 in particular.

[0033] Indeed, the reliefs 18 on the inner face of the hollow structure 12 of the cooling device 10 make it possible to delimit passage sections through which the heat transfer fluid flows around the windings 2, so that these passage sections have similar sizes at every point of the cooling device 10. In other words, the reliefs 18 on the inner face of the hollow structure 12 of the cooling device 10 make it possible to ensure a homogeneous size of the passage sections through which the heat transfer fluid is intended to circulate, which limits the turbulence of the heat transfer fluid inside the cooling device 10.

[0034] Ideally, the reliefs 18 on the inner face of the hollow structure 12 of the cooling device 10 have shapes that allow for an identical size for all the passage sections inside the hollow structure 12 of the cooling device 10 of the axial flux electric machine 1. The reliefs 18 are, for example, three-dimensional and preferably have a rounded shape.

[0035] Thus, according to a preferred embodiment illustrated in Figures 1 to 4, the reliefs 18 on the inner face of the hollow structure 12 of the cooling device 10 are in particular in the form of concave reliefs 181 and / or convex reliefs 182.

[0036] An example of a preferential distribution of these reliefs 18 on the inner face of the hollow structure 12 of the cooling device 10 will be presented in the continuation of this description.

[0037] Thus, according to a preferred embodiment of the cooling device 10, the hollow structure 12 comprises, for example, an annular shell 12a, which is more particularly illustrated in Figures 2 and 3. The annular shape of the shell allows it to be inserted between the rotor and the stator of the axial flux electric machine 1. The annular shell 12a of the hollow structure 12 of the cooling device 10 has, in particular, a geometry of revolution; it may also have rotational symmetry. In the assembled state, this axis of symmetry of the annular shell 12a of the hollow structure 12 of the cooling device 10 then coincides with the axis of rotation of the rotor of the axial flux electric machine 1.

[0038] The annular shell 12a of the hollow structure 12 of the cooling device 10 can be in the form of a single-piece plastic part with a relatively thin wall. In particular, the wall thickness of the annular shell 12a can be between 0.75 mm and 2 mm. The thickness of this wall can more specifically be equal to 1 mm. An annular shell 12a with a thin wall has the advantage of being lighter and more compact, while an annular shell 12a with a thicker wall can be stronger and better withstand the pressure exerted within the axial flux electrical machine 1.

[0039] According to an embodiment not shown in the figures, an outer face of the hollow structure 12 may have at least one stiffening rib. This is particularly useful when the hollow structure 12 has a thin wall, for example, with an annular shell 12a having a wall thickness of less than 1 mm. Such a rib on the outer face of the hollow structure 12 can meet a given stiffness criterion, enabling the hollow structure 12 of the cooling device 10 to withstand the pressure exerted within the electrical machine 1. There may be one or more stiffening ribs on the outer face of the hollow structure 12 of the cooling device 10.

[0040] Although it is a single piece, the annular shell 12a of the hollow structure 12 of the cooling device 10 may have an external portion and an internal portion. The external portion corresponds to a part of the annular shell 12a intended to surround the head of at least one winding 2. The external portion of the annular shell 12a is then delimited by a peripheral edge 13a of generally circular shape with an external diameter.

[0041] Similarly, the inner portion corresponds to a part of the annular shell 12a intended to be located as close as possible to the other end of at least one winding 2, near the axis of rotation of the rotor of the axial flux electric machine 1. The inner portion of the annular shell 12a is then delimited by a peripheral edge of generally circular shape with an inner diameter that is smaller than the outer diameter. The inner portion is substantially concentric with the outer portion of the annular shell 12a.

[0042] In the embodiment illustrated in the various figures, the reliefs 18 on the inner face of the hollow structure 12 are arranged on the outer portion of the annular shell 12a and / or on the inner portion of the annular shell 12a.

[0043] As illustrated in this [Fig.2], the annular shell 12a comprises both concave 181 and convex 182 reliefs. Thus, the internal portion of the annular shell 12a notably presents an alternation between concave 181 and convex 182 reliefs. As for the external portion of the annular shell 12a, it presents more concave 181 reliefs than convex 182 reliefs.

[0044] As illustrated in [Fig.2], the set of convex reliefs 182 on the external portion of the annular shell 12a are arranged opposite convex reliefs 182 on the internal portion of the annular shell 12a.

[0045] Furthermore, the radius or radii of curvature of the concave reliefs 181 on the external portion of the annular shell 12a may be greater than that or those of the concave reliefs 181 on the internal portion of the annular shell 12a.

[0046] This particular arrangement of the reliefs 18 allows for a better fit to the contour of the windings 2 arranged inside the electrical machine, and therefore to homogenize the size of the passage sections through which the heat transfer fluid is intended to circulate in order to limit turbulence within the heat transfer fluid.

[0047] Generally, the hollow structure 12 of the cooling device 10 can comprise at least as many reliefs 18 as there are windings 2 arranged inside said electrical machine. In other words, the number of reliefs on the inner face of the hollow structure 12 is greater than or equal to the number of windings 2 intended to be arranged inside the axial flux electrical machine 1 equipped with such a cooling device 10.

[0048] For example, the annular shell 12a illustrated in [Fig.2] is notably dimensioned for an electrical machine 1 configured to receive eighteen windings 2. Thus, the internal portion of the annular shell 12a illustrated in [Fig.2] has, for example, eighteen convex reliefs 182. In this same embodiment, the total number of reliefs in the form of concave reliefs 181 is greater than the number of windings 2 intended to be arranged inside the axial flux electrical machine 1.

[0049] As illustrated in [Fig.2], the annular shell 12a has a geometry of revolution in which the various reliefs 18 are present with angular regularity over the entire inner face of the cooling device 10.

[0050] In the embodiment of the cooling device 10 illustrated in [Fig. 1], the hollow structure 12 further comprises a tray 12b configured to cover the annular shell 12a like a lid. An example of such a tray 12b is illustrated in particular in [Fig. 4]. The tray 12b can be likened to a round disk with a peripheral edge 13b whose outer diameter is substantially equal to the outer diameter of the external portion of the annular shell 12a of the hollow structure 12.

[0051] Thus, when the hollow structure 12 is mounted, the peripheral edge 13b of the plate 12b is placed on the peripheral edge 13a of the external portion of the annular shell 12a of the hollow structure 12. The peripheral edge 13b of the plate 12b on the one hand and the peripheral edge 13a of the external portion of the annular shell 12a of the hollow structure 12 may have one or more through holes 19 intended to accommodate fastening means such as mechanical fastening means, for example screws, to secure the plate 12b and the annular shell 12a in order to form together the hollow structure 12 of the cooling device 10.

[0052] As illustrated in [Fig.4], the peripheral edge 13b of the tray 12b more particularly includes eighteen through holes 19 intended to accommodate mechanical fastening means to secure the tray 12b and the annular shell 12a in order to form together the hollow structure 12 of the cooling device 10.

[0053] According to the embodiment illustrated in [Fig. 4], at least one fluid inlet 14 of the cooling device 10 can be arranged in the tray 12b of the hollow structure 12. Similarly, at least one fluid outlet 16 can be arranged in the tray 12b of the hollow structure 12. Thus, the tray 12b illustrated in [Fig. 4] comprises several fluid inlets 14 configured to allow the passage of the heat transfer fluid into the interior of said hollow structure 12 through the tray 12b and several fluid outlets 16 configured to allow the passage of the heat transfer fluid out of said hollow structure 12 through this same tray 12b. The fluid inlets 14 and the fluid outlets 16 may, in particular, be in the form of circular orifices.However, other shapes can be considered for these fluidic inlets 14 and these fluidic outlets 16, such as an elliptical, oblong, or polygonal shape.

[0054] The circular orifices forming the fluid inlets 14 are preferably evenly distributed on a first circle centered on the axis of rotation of the rotor. Similarly, the circular orifices forming the fluid outlets 16 are preferably evenly distributed on a second circle centered on the axis of rotation of the rotor. The fluid outlets 16 can be arranged in an annular gallery 20. The diameter of the second circle is strictly greater than the diameter of the first circle. The heat transfer fluid therefore flows overall in a centrifugal direction between the fluid inlets 14 and the fluid outlets 16.

[0055] Advantageously, the cooling device 10 includes at least one fluidic inlet 14 and / or at least one fluidic outlet 16 for each winding 2. According to the embodiment presented, the cooling device 10 includes two fluidic inlets 14 and only one fluidic outlet 16 for each winding 2, i.e. thirty-six fluidic inlets 14 and eighteen fluidic outlets 16.

[0056] As illustrated in [Fig. 3], each winding 2 may comprise a roughly trapezoidal cross-section. An inner edge 21 of each winding 2 comprises the smaller base of the trapezoidal shape, and an outer edge 22 of each winding comprises the larger base of the trapezoidal shape. Advantageously, at least one fluidic inlet 14 is positioned along the inner edge 21 of each winding, and at least one fluidic outlet 16 is positioned along the outer edge 22 of each winding.

[0057] In addition or alternatively, some or all of the fluidic inlets 14 and / or some or all of the fluidic outlets 16 may be arranged in the wall of the annular shell 12a of the hollow structure 12 of the cooling device 10 of the axial flux electric machine 1.

[0058] Furthermore, and according to an embodiment not illustrated in the figures, at least a portion of the inner face of the hollow structure 12 intended to be in contact with the heat transfer fluid may have a surface treatment configured to optimize the flow of said heat transfer fluid around the windings 2 arranged inside the axial flux electric machine 1. Such a surface treatment may, in particular, take the form of a layer or coating applied to the inner face of the hollow structure 12. Alternatively, such a surface treatment may take the form of a particular roughness of the inner face of the hollow structure 12 of the cooling device.

[0059] It is thus possible to imagine various embodiments of a cooling device 10 for an axial flux electrical machine 1 which facilitates the circulation of a heat transfer fluid around the windings 2 arranged inside the axial flux electrical machine 1 so as to limit turbulence and avoid stagnation of said heat transfer fluid inside the cooling device 10, while retaining the multiple advantages allowed by the cooling devices known in the state of the art.

Claims

Demands

1. Cooling device (10) for an axial flux electrical machine (1), the cooling device (10) being intended to be arranged around at least one winding (2) disposed inside said electrical machine (1) to cool said at least one winding (2), the cooling device (10) being characterized in that it comprises a hollow structure (12) within which a heat transfer fluid is intended to circulate, the cooling device (10) comprising at least one fluid inlet (14) configured to permit the passage of the heat transfer fluid into said hollow structure (12) and at least one fluid outlet (16) configured to permit the passage of the heat transfer fluid out of said hollow structure (12), the hollow structure (12) further comprising reliefs (18) on an inner face,said reliefs (18) being intended to at least partially enclose the at least one winding (2) disposed inside the electrical machine (1).

2. Cooling device (10) according to the preceding claim, characterized in that the reliefs (18) on the inner face of the hollow structure (12) are in the form of concave reliefs (181) and / or convex reliefs (182).

3. Cooling device (10) according to any one of the preceding claims, characterized in that the hollow structure (12) comprises an annular shell (12a) having an external portion and an internal portion, and in that the reliefs (18) on the inner face of the hollow structure (12) are arranged on the external portion of the annular shell (12a) and / or on the internal portion of the annular shell (12a).

4. Cooling device (10) according to claims 2 and 3, characterized in that the internal portion of the annular shell (12a) has an alternation between concave reliefs (181) and convex reliefs (182).

5. Cooling device (10) according to any one of claims 3 to 5, characterized in that the hollow structure (12) further comprises a tray (12b) configured to cover the annular shell (12a) in the manner of a lid.

6. Cooling device (10) according to the preceding claim, characterized in that at least one fluidic inlet (14) is arranged in the tray (12b) and / or characterized in that at least one fluidic outlet (16) is arranged in the tray (12b).

7. Cooling device (10) according to any one of the preceding claims, characterized in that an outer face of the hollow structure (12) has at least one stiffening rib.

8. A cooling device (10) according to any one of the preceding claims, characterized in that at least a portion of the inner face of the hollow structure (12) intended to be in contact with the heat transfer fluid has a surface treatment configured to optimize the flow of said heat transfer fluid around the windings (2) arranged inside the axial flux electric machine (1).

9. An axial flux electric machine (1) characterized in that it comprises at least one cooling device (10) according to any one of claims 1 to 8.

10. An axial flux electric machine (1) characterized in that it comprises at least one cooling device (10) according to the preceding claim, characterized in that the number of reliefs on the inner face of the hollow structure (12) is greater than or equal to a number of windings (2) of the electric machine (1).

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