Electric machine with optimized cooling

Abstract

The present invention relates to an electric machine comprising two complementary casings (100, 200) each having a tubular wall - the first casing (100) surrounding a rotor (30) surrounded by a stator (20) having N wound teeth (25) extending radially with respect to a cylindrical yoke (21) in thermal contact with the wall of the first casing (100): - the first and / or the second casing (100, 200) having two angularly offset fluidic couplings, - the tubular walls of the casings (100, 200) defining between them a tubular flow chamber (300) for fluid when the complementary casings (100, 200) are assembled. This tubular flow chamber (300) has a succession of L angular frames (310) of which the cross section of flow varies between a maximum angular zone at the two ends and a minimum angular zone (340) at the corresponding wound tooth (25).

Description

Electric machine with optimized cooling FIELD OF INVENTION

[0001] The present invention relates to the field of cooling for enclosed electrical machines and closed-circuit cooling using a liquid coolant. More particularly, it relates to a cooling chamber for a rotating electrical machine, as well as a rotating electrical machine comprising such a cooling chamber.

[0002] This type of rotating electrical machine can be cooled by convection using fans mounted on the rotor, which circulate airflow, notably through the stator. This type of cooling is particularly effective when the machine operates at high speeds. Indeed, the faster the rotor spins, the more air the fan can circulate. However, this type of cooling may not be sufficient when the machine operates at low rotational speeds. Furthermore, air cooling is limited by the size of the fan, which must fit within a confined space.

[0003] Cooling solutions involving the circulation of a heat transfer fluid, typically water or oil, in a tubular pocket surrounding the stator have also been proposed in the prior art. State of the art

[0004] Prior art includes patent application EP3726063, which describes an electric compressor with an integrated motor whose stator is housed in a casing incorporating an annular cooling fluid circulation chamber. This chamber, delimited by internal and external walls, includes angularly offset fluid inlet and outlet. To improve thermal efficiency, this patent provides for flow deflectors projecting from the walls, designed to locally deflect the fluid flow from the shortest path and generate turbulence. These circumferentially distributed deflectors promote a more homogeneous fluid distribution and improved heat extraction from the stator.

[0005] This solution offers cooling for a very specific motor topology: a toroidal motor that does not have teeth, but rather coils arranged around a core, and for which the inter-coil space is accessible for cooling. In the case of typical toothed topologies, the stator head prevents access to the inter-coil space from the periphery to improve cooling. It does not optimize cooling in specific geographical areas, but only improves overall cooling.

[0006] Patent EP3048699 describes a stator housing designed to improve cooling while simplifying assembly. The housing comprises two sealed, radially coupled annular sections (inner and outer) that together define at least one cooling channel around the axis. The channel is structured in alternating sections: first sections arranged to circulate the fluid around the axis, and second sections formed in internal protrusions inserted between the radial heads of the windings. The fluid path becomes serpentine and three-dimensional, with changes in direction, radial depth, and cross-section, generating variable velocities and turbulence to optimize heat extraction from the windings and the stator core.

[0007] This solution aims to prevent laminar fluid flow from inlet to outlet by creating deflectors on the internal and external walls of the cooling cavity. This generates turbulence, improving overall heat dissipation capacity. However, this does not allow for highly localized improvement of heat dissipation at hot spots without creating excessive pressure drops.

[0008] US patent application 2023 / 013463 describes a stator housing for an electrical machine, particularly in automobiles, incorporating a cooling duct between a fluid inlet and outlet. The duct is subdivided, along the flow direction, into successive sections with varying heat exchange capacities. A first downstream section, near the outlet, features an enhanced heat transfer device (larger exchange surface area per unit length) to compensate for the higher fluid temperature, while a second upstream section has a smaller exchange surface area, or even none at the inlet. This gradation helps to uniformize the stator's thermal distribution. The duct can be helical or meandering and is formed between two coaxial housing elements.

[0009] US patent 7049716 describes a fluid-cooled electric machine that compactly integrates the stator, rotor, and power electronics. The machine includes a peripheral cooling device with channels through which a fluid (water or oil) flows, thermally coupled to both the stator and power electronic modules. These modules, distributed around the periphery of the machine, are directly connected to the windings by short radial links and are cooled by protruding elements entering the channels, generating turbulent flow. The mechanical and thermal integration of the electronics and the machine reduces size, wiring complexity, electromagnetic shielding requirements, and facilitates maintenance. Disadvantages of prior art

[0010] Prior art solutions are not entirely satisfactory because the reliefs formed on the tubular surface of the tubular walls between which the cooling fluid circulates cause significant pressure losses, increasing the electrical consumption of the circulation pump, and can also disrupt the flow of the fluid and create hot spots in certain areas.

[0011] The invention aims to improve the efficiency and homogeneity of cooling of a toothed stator, particularly at the level of the wound teeth, without complicating the cooling chamber with added internal elements or excessively increasing pressure losses. Solution provided by the invention

[0012] In order to address these drawbacks, the invention, in its most general sense, relates to an engine having the technical characteristics stated in the main claim.

[0013] The engine according to the invention has, in particular, the following characteristics:

[0014] It comprises two complementary housings, each with a tubular wall

[0015] - the first housing surrounding a rotor surrounded by a stator having N wound teeth extending radially with respect to a cylindrical cylinder head in thermal contact with said wall of said first housing,

[0016] - the first and / or second casing having two angularly offset fluid connections,

[0017] - the tubular walls of said housings defining between them a tubular fluid circulation chamber when said complementary housings are assembled.

[0018] The tubular circulation chamber has a succession of L angular frames whose passage section varies between a maximum angular zone at both ends and a minimum angular zone at the level of the corresponding wound tooth.

[0019] According to variants of the machine according to the invention:

[0020] The configuration of said tubular cooling fluid circulation chamber mainly presents, for each angular frame angularly encompassing a tooth and an inter-tooth sector: A first angular zone where the inner surface of the annular wall of the outer casing has a protrusion of increasing thickness to form an angular sector whose upstream section is greater than the average section of the circulation duct, and whose downstream section is less than the average section of the circulation duct; A second angular zone, downstream of said first angular zone, where the inner surface of the annular wall of the outer casing has an oblique face whose downstream tangent forms an angle with the radial plane between 30° and 75°; A third angular zone, downstream of said second angular zone, with a cross-section less than the average section of the circulation duct.A fourth angular zone of increasing cross-section to reach the cross-section of the upstream section of said first angular zone.

[0021] The thickness of the annular wall of the inner casing is essentially constant with variations of less than 20%.

[0022] The minimum cross-section area extends over an angle between Mx360 / N, where M is between 5 and 15%.

[0023] The beginning of this minimum section zone starts after the upstream edge of the corresponding tooth.

[0024] The circulation chamber is extended by an additional cooling zone towards a hollow volume located opposite the electronic board.

[0025] The number N of wound teeth is equal to the number L of angular frames.

[0026] The stator has N wound teeth, and in addition unwound teeth, the number L of angular frames being equal to the total number of wound or unwound teeth.

[0027] The angular frames located at the level of the inlet and outlet of the fluid, have in cross-section a different geometry from the other frames (310).

[0028] Detailed description of a non-limiting example of implementation

[0029] The present invention will be better understood upon reading the following description, concerning a non-limiting example of an embodiment illustrated by the accompanying drawings where:

[0030] Figure 1 represents a top view of an example embodiment of an engine according to the invention.

[0031] Figure 1 represents a longitudinal cross-sectional view of an example embodiment of an engine according to the invention.

[0032] This represents a perspective view of the inner casing of an example embodiment of an engine according to the invention.

[0033] This represents a perspective view of the outer casing of an example embodiment of an engine according to the invention.

[0034] This represents a section of the engine allowing visualization of the fluid circulation chamber of an example embodiment of an engine according to the invention.

[0035] This represents an exploded perspective view of an example embodiment of an engine according to the invention.

[0036] lare represents a schematic “unfolded” view of the fluid circulation chamber. General principle of the invention

[0037] The general principle of the invention relates to improving convective cooling by circulating a liquid in a tubular circulation chamber (300) formed between two coaxial annular walls (160, 260) of the housings (100, 200). The inner housing (100) contains the rotor (30) surrounded by the stator (20). The wound teeth (25) of the stator extend radially with respect to a cylindrical yoke and are in thermal contact with the wall of this inner housing. Preferably, the tubular circulation chamber (300) extends axially over the entire height of the stator teeth (20).

[0038] The tubular circulation chamber (300) has a discontinuity along its planar cross-section that prevents fluid circulation. Two inlets (210, 220) are located on either side of this discontinuity and are extended by fluid connections to allow the fluid to enter and exit the tubular circulation chamber (300). The discontinuity (305) ensures a specific direction of fluid flow, allowing it to travel around the entire circumference of the engine before leaving the tubular circulation chamber (300).

[0039] The two fluidic fittings (380, 390) are preferably arranged on the base (105) of the lower housing (100) and oriented axially to simplify the connection of the fittings with the fluidic system, but could also be arranged on either of the housings and oriented radially, tangentially, or at a particular angle to the radial orientation.

[0040] The improved heat transfer between the circulating fluid and the housings (100, 200) is achieved through a series of angular frames (310) of varying cross-sections, the number of which corresponds to the number of teeth. These angular frames create variations in the flow cross-section and deflections of the flow direction. The flow cross-section varies between a maximum value at the two ends of these angular frames and a minimum value at the corresponding wound tooth. An average cross-section of this flow channel is determined to categorize areas of reduced cross-section and areas of increased cross-section.

[0041] The desired effects are: to break the establishment of a laminar regime to improve the convective interaction between the cooling fluid and the wall of the inner casing (100), which is in thermal contact with the stator head (20), and to improve the heat dissipation of the wall of said inner casing (100) by removing heat through the fluid, to direct the flow of the cooling fluid by imposing a radial component towards the tooth (25) in the angular area of ​​narrowing where the fluid is accelerated.

[0042] The challenge is to create singularities where the dissipation coefficient is maximized and to position these singularities at the level of the teeth (25). This must be done while maintaining acceptable pressure losses.

[0043] The configuration of the cooling fluid circulation duct mainly presents, for each angular section comprising a tooth and an inter-tooth: An upstream angular zone (320), according to the nominal flow direction (500) of the cooling fluid, whose inlet section is maximal, relative to the average section of the circulation duct, and where the inner surface of the outer casing (200) has a protrusion of increasing radial thickness to restrict the section of the circulation duct, in order to locally accelerate the circulation of the fluid and improve convective heat transfer,This upstream angular zone extends into a zone where the protrusion formed on the inner surface of the outer casing approaches a radial orientation to create a turbulent zone preferentially upstream of the center of the wound tooth and to direct the flow of the coolant towards the outer wall of the inner casing (100), thus increasing the convective transfer of heat produced by the corresponding wound tooth. This turbulent zone is extended by an angular zone of minimal cross-section relative to the average cross-section of the circulation duct, where the coolant flows more rapidly to maximize heat recovery and transfer. This constriction zone extends into an angular zone of increased cross-section of the duct, relative to the average cross-section of the circulation duct, in order to present, downstream of the frame,a maximum cross-section corresponding to the input cross-section of the next frame and to reduce load losses.

[0044] These differences produce a combined and measurable technical effect, without the addition of internal parts, without obstacles, and with controlled pressure loss: local acceleration of the fluid at the wound teeth, areas of maximum heat loss, targeted increase of the heat transfer coefficient exactly where heat generation is highest, circumferential thermal homogenization of the stator,

[0045] The effect is structurally induced by the geometry of the room, and not by added elements.

[0046] Description of an example of an engine according to the invention

[0047] Figures 1 to 6 illustrate an example of an embodiment of an engine according to the invention. The engine (10) comprises a metal inner casing (100) flared at one end by a base (105) on which an outer casing (200) is sealed, forming a metal bell with two openings (210, 220) for connecting fluid fittings (310, 320) for supplying coolant. These two fittings (310, 320) are shown in the above figures with a radial orientation and opening into the outer casing (200). However, one or both of the fittings (310, 320) may also be oriented with a tangential component, or open axially into the transverse flange of the inner casing (100).

[0048] The sealing of the tubular circulation chamber (300), defined by the annular walls (160, 260) of the housings (100, 200), is ensured by means of seals (410, 420) one inserted in a groove in the inner surface of said annular wall (160) and in contact with the annular wall (260) and the other in a groove located in the base (105) of the inner housing (100) and bearing on the axial end of the outer housing (200).

[0049] The base (105) also includes two electrical connectors (610, 620), namely a power connector (620) and a low power connector (610) for digital control signals.

[0050] The motor comprises, in a known manner, a rotor (30) coupled to a shaft (35), and a stator comprising a ring of N teeth (25) surrounded by coils (26).

[0051] The base (105) of the inner casing (100) is extended by an annular wall (160) defining with an annular wall (260) of the outer casing (200) a tubular circulation chamber (300) inside which the coolant circulates.

[0052] The rotor (30) has peripheral magnets (31) supported by a transverse hub with an axial height shorter than that of the magnets, so as to free up the space required for housing the bearings (102, 202). This solution makes it possible to reduce the overall height of the electric machine and to reduce its axial dimensions, thanks to the insertion of the bearings within the axial thickness of the rotor (30).

[0053] The plate (100) also has a reception area (101) for the positioning of a bearing (102) ensuring the guidance of the shaft (35).

[0054] The outer casing (200) also has a mounting area (201) for positioning a bearing (202) which guides the shaft (35). A seal (430) provides sealing of the shaft output.

[0055] Example of an inner casing configuration (100)

[0056] The inner casing (100), as illustrated in Figures 3 and 5, has a generally tubular configuration with protrusions (161) on the inner surface of the annular wall (160). These protrusions ensure the angular alignment of the stator head while also providing a complementary shape to facilitate heat transfer between the wound stator and the inner surface of the annular wall (160) of the inner casing (100), through which the coolant flows. In the example described, the number of protrusions (161) corresponds to the number of stator teeth, and these protrusions (161) are radially aligned with the wound stator teeth.

[0057] The outer surface of the annular wall (160) of the inner casing (100) has protrusions (165) aligned radially with the stator teeth, and optionally with the protrusions (161), to form local constrictions of the tubular circulation chamber (300) inside which the coolant circulates.

[0058] These protuberances (165) have an angular extent less than the angular pitch of the stator teeth. They have an upstream face (162) of increasing emergence (relative to a tubular reference section), a middle face (163) of substantially constant emergence and a downstream face (164) of decreasing emergence.

[0059] The thickness of the annular wall (160) of the inner casing (100) is substantially constant over the entire periphery, and for this purpose the inner surface of the annular wall (160) has complementary angular recesses of the sides (162, 163, 164).

[0060] In the example described, the protuberances (165) have, from the front, an ogival shape, that is to say that the thickness of the annular wall (160) decreases, between its part connected to the base (105) and its upper axial end, so as to be able to generate the inner casing (100) by molding process.

[0061] The base (105) of the inner housing (100) also has in the described example a semi-circular channel (351) communicating with the tubular circulation chamber (300) to ensure the cooling of the electronic circuit fixed in a housing (106) provided on the outer face of said base (105). Example of outer casing configuration

[0062] Laillustrates an example of an embodiment of the outer casing (200) in which the fluid flows clockwise. It has an annular wall (261) provided on its inner surface with protrusions (265), the number of which preferably corresponds to the number of stator teeth.

[0063] The shape of these protuberances (265) has an attack face (262) with increasing thickness, with a broken slope with two surfaces of different slopes, a median face (263) of substantially constant thickness and an exhaust face (264) of decreasing section.

[0064] More visible in the exploded view of the, the mouths (210, 220) of the annular wall (261) cooperate with the conduits (110, 120) to which the fluidic connectors (380, 390) are connected to ensure the arrival of the fluid and its evacuation from the tubular circulation chamber (300).

[0065] Details of the circulation duct configuration

[0066] Figure 1 illustrates an example of a tubular circulation chamber configuration (300), and more specifically an angular frame (310) that is repeated L times, L preferentially corresponding to the number N of wound teeth of the machine. To simplify the illustration, the tubular circulation chamber (300) is represented in an "unwound" state, that is, as if the radius of the tubing were infinite.

[0067] The angular pattern (310) corresponds to a complete pattern, which is repeated L times. It extends between the upstream dotted line (301) and the downstream dotted line (302), "upstream" and "downstream" referring throughout the document to the direction of flow of the cooling fluid.

[0068] The angular frame (310) extends over 360 / L°, L preferentially designating the number of wound stator teeth (25), but the machine may also have unwound teeth for which it is optional to match an angular frame.

[0069] This angular frame (310) has a first angular zone (320) of mainly decreasing section delimited: by the median pan (163) of constant emergence of the inner casing (100) then by the pan (164) of the inner casing (100), on the one hand, and by the first part of the attack pan (262), of slowly increasing thickness, of the protuberance (265) of the outer casing (200) on the other hand.

[0070] This angular zone (320) has the function of progressively accelerating the cooling fluid upstream of the tooth (25) to be cooled, while limiting pressure losses by a moderate decrease.

[0071] This first angular zone (320) is extended, in the direction of the cooling fluid flow, by a second angular zone (330), where the cross-section decreases more rapidly, so as to create turbulence in the cooling fluid upstream of the tooth (25) to be cooled, to redirect the flow with a radial component towards the tooth (25), and more generally to create a singularity opposing laminar flow of the circulating fluid. This function is performed by the second part of the leading edge (262) of the protrusion (265), the thickness of which increases more rapidly so that at the downstream end of the leading edge (262), the inner surface of the annular wall (260) forms, with the radial direction of the engine, an angle (321) between 30 degrees and 75 degrees.

[0072] This second angular zone (330) is extended, in the direction of the flow of the cooling fluid, by a third angular zone (340) of minimum section, where the cooling fluid circulates locally at its highest speed so as to maximize the heat transfer of the calories produced by the tooth (25) located in this angular sector.

[0073] This third angular zone (340) is extended, in the direction of the flow of the cooling fluid, by a fourth angular zone (350) of expansion where the section increases again to slow down the fluid and open into the inlet of the next angular frame without excessive pressure losses.

[0074] The invention relates essentially to the configuration of this circulation conduit, presenting a succession of N angular frames (310) presenting the four angular zones (320, 330, 340 and 350) mentioned above, the variations in section of which can result from protrusions formed indifferently on the outer casing (200) or on the inner casing (100), or distributed between the two casings (100, 200).

[0075] However, in preferred embodiments, the most pronounced protrusions are formed on the outer casing (200), while the inner casing (100) may optionally be entirely tubular, without radial projections. The fact that the protrusions are formed primarily on the outer casing (200) facilitates the deflection of the coolant flow towards the teeth (25) to be cooled.

[0076] As can be seen in the figure, the angular frames (310) located at the fluid inlet and outlet openings (210, 220) are designed to have a different geometry. These areas are singularities where the flow is naturally turbulent, which helps maintain the fluid's ability to dissipate heat.

[0077] Secondary cooling of the electronic circuit

[0078] According to one embodiment, the cooling circuit has a branch in the form of a semi-annular cavity opening into an additional cooling zone (360) delimited by the base (105) of the inner casing (100) to which the electronic circuit (600), and in particular the power components, for example the MOSFET transistors, are attached. The electronic circuit (600) is more specifically fixed in a recess (106) of the base (105), and the power components of said circuit are judiciously arranged opposite the wall (107) defining the bottom of the additional cooling zone (360) so as to maximize the heat exchange between the coolant and these components.

[0079] This additional cooling zone (360) of the electronic circuit (600) communicates fluidly with the main cooling circuit previously described and has fins increasing the convection surface with the fluidic liquid.

[0080] The angular bypass zone (370) has in the corresponding angular frame a reduced section of the cavity defined by the annular walls (161, 261), to partially compensate for the increase in the section of the tubular circulation chamber (300) resulting from the addition of the additional cooling zone (360) on this angular bypass zone (370).

[0081] The inlet and outlet of this additional cooling zone (360) has a bevel (361, 362) to promote the introduction and outlet of the cooling fluid without the formation of a lost pocket.

[0082] Advantageously, this bypass can be located in the vicinity of the inlet and outlet fittings (380, 390) to take advantage of the turbulent flow which is conducive to improving heat dissipation.

[0083] By way of non-limitation, thermal paste may be disposed between the power components and the wall (107) defining the bottom of the additional cooling zone (360).

Claims

An electrical machine comprising two complementary housings (100, 200), each having a tubular wall; the first housing (100) surrounding a rotor (30) surrounded by a stator (20) having N wound teeth (25) extending radially with respect to a cylindrical yoke (21) in thermal contact with said wall of said first housing (100); the first and / or the second housing (100, 200) having two angularly offset fluid connections; the tubular walls of said housings (100, 200) defining between them a tubular fluid circulation chamber (300) when said complementary housings (100, 200) are assembled, characterized in that said tubular circulation chamber (300) has a succession of L angular frames (310) whose cross-sectional area varies between a maximum angular zone at both ends and a minimum angular zone (340) at the level of the corresponding wound tooth (25). An electric machine according to claim 1 characterized in that the configuration of said tubular circulation chamber (300) of the cooling fluid mainly has, for each angular frame (310) angularly encompassing a tooth (150) and an inter-tooth sector: A first angular zone (320) where the inner surface of the annular wall (261) of the outer casing (200) has a protrusion (265) of increasing thickness to form an angular sector whose upstream section is greater than the average section of the circulation conduit, and whose downstream section is less than the average section of the circulation conduit; A second angular zone (330), downstream of said first angular zone (320), where the inner surface of the annular wall (261) of the outer casing (200) has an oblique face whose downstream tangent forms an angle with the radial plane between 30° and 75°; A third angular zone (340),downstream of said second angular zone (330), with a cross-section smaller than the average cross-section of the circulation conduit, a fourth angular zone (350) with a cross-section increasing to reach the cross-section of the upstream section of said first angular zone (320). Electric machine according to claim 1 characterized in that the thickness of the annular wall (160) of the inner casing (100) is substantially constant with variations of less than 20%. electric machine according to claim 1 characterized in that said minimum section zone (330) extends over an angle between Mx360 / N, M being between 5 and 15%. Electric machine according to claim 1 characterized in that the beginning of said minimum section zone (340) begins after the upstream edge of the corresponding tooth. Electric machine according to claim 1 characterized in that said circulation chamber (150) is extended by an additional cooling zone (360) towards a hollow volume located opposite the electronic board (600). Electric machine according to claim 1 characterized in that the number N of teeth (25) wound is equal to the number L of angular frames (310). Electric machine according to claim 1 characterized in that the stator (20), having N wound teeth (25), also has unwound teeth, the number L of angular frames (310) being equal to the total number of wound or unwound teeth. Electric machine according to claim 1 characterized in that the angular frames (310) located at the level of the inlet and outlet of the fluid, have in cross section, a geometry different from the other frames (310).

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