STATOR HOUSING FOR ELECTRIC MACHINE, ELECTRIC MACHINE FOR VEHICLE, AND VEHICLE

Abstract

A stator housing (2) for an electric machine (1) comprises an inlet (9) for a cooling fluid, an outlet (10) for the cooling fluid, and a cooling duct (11) formed between the inlet (9) and the outlet (10), through which the cooling fluid can flow in a flow direction from the inlet (9) to the outlet (10). The cooling duct (11) comprises a first heat transfer structure (12) and a second heat transfer structure (13), each of which extends along the flow direction and is designed to transfer heat from the cooling fluid to the stator housing (2). The first heat transfer structure (12) is arranged in the first section (16) of the cooling duct (11), and the second heat transfer structure (13) is arranged in the second section (17) which is on the inlet side of the first section (16) of the cooling duct (11), and the first heat transfer structure (12) in the first section (16) forms a larger heat transfer area for the cooling fluid per unit length based on the flow direction than the second heat transfer structure (13) in the second section (17).

Description

[Technical field]

[0001] The present invention relates to a stator housing for an electric machine, comprising a cooling fluid inlet, a cooling fluid outlet, and a cooling duct formed between the inlet and the outlet, through which the cooling fluid can flow in a flow direction from the inlet to the outlet.

[0002] Furthermore, the present invention relates to an electric machine for a vehicle. [Background technology]

[0003] During operation, electric machines generate heat due to electrical losses in the stator windings. Unacceptably high temperatures can lead to thermal failure of the windings. To increase the utilization of electric machines, particularly when used as a traction machine for vehicles, it is known to provide the stator housing of the electric machine with cooling ducts, which dissipate heat from the stator to a cooling fluid.

[0004] Such a stator housing is known from EP 3358721 A1. EP 3358721 A1 discloses a housing for an electric machine having a fluid connection with an inlet and an outlet and a housing wall with a fluid duct for receiving a fluid for cooling the electric machine. The housing wall has an axial extent between two end faces along a first spatial direction and a radial extent with an extension radius along two further spatial directions. The fluid duct is part of a cooling jacket that extends over the entire housing wall.

[0005] When the cooling fluid flows through the cooling ducts, the temperature distribution increases from the inlet to the outlet, which causes the heat dissipation from the stator to be uneven. Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THEINVENTION A basic object of the invention is to make the temperature distribution along the cooling ducts of the stator housing more uniform. [Means for solving the problem]

[0007] To this end, the proposal according to the invention is that in the case of a stator housing of the type mentioned at the beginning, the cooling duct has a first heat transfer structure and a second heat transfer structure, each extending along the flow direction and designed to transfer heat from the cooling fluid to the stator housing, the first heat transfer structure being arranged in a first section of the cooling duct and the second heat transfer structure being arranged in a second section of the cooling duct, which is on the inlet side with respect to the first section, the first heat transfer structure in the first section forming a larger heat transfer area for the cooling fluid per unit length in the flow direction than the second heat transfer structure in the second section.

[0008] The concept of the invention is to provide a larger heat transfer area in relation to length on the outlet side than on the inlet side, so that when the already heated cooling fluid flows into the first section located on the outlet side, the heat dissipation by the first heat transfer structure to the cooling fluid is increased, thereby making it possible to compensate for the inherently poor heat transfer due to the relatively low temperature difference between the stator components, from which the heat has to be dissipated, and the cooling fluid, which advantageously allows a more uniform temperature distribution along the stator housing.

[0009] Typically, the first section and / or the second section each occupy at least 10%, preferably at least 20%, particularly preferably at least 30% of the length of the cooling duct. The sections of the cooling duct can be directly adjacent to each other, or it is also possible to provide a transition section between the sections that is not related to any of the sections. The sections advantageously do not overlap. The cooling duct typically has an inner boundary surface extending circumferentially and axially at a predetermined radial position. In particular, the cooling duct has an outer boundary surface extending circumferentially and axially at a predetermined radial position, advantageously located outside the inner boundary surface. The cooling duct typically has a side wall extending radially and at least one further spatial direction. The side wall is preferably of a fluid-tight design.

[0010] In the case of the stator housing according to the invention, the heat transfer structures each preferably divide the cooling duct into a number of partial cooling ducts extending along the flow direction. Typically, the partial cooling ducts are designed to be fluid-tight with respect to one another. The flow cross sections of the partial cooling ducts formed by the respective heat transfer structures are preferably of equal size.

[0011] As an advantageous development, the second heat transfer structure may divide the cooling duct into at least two second partial cooling ducts and the first heat transfer structure may divide the cooling duct into a number of first partial cooling ducts which is at least one more than the number of second partial cooling ducts.

[0012] In the stator housing according to the invention, it is advantageously envisaged that in the further section on the inlet side with respect to the second section, the cooling duct has a smaller heat transfer area for the cooling fluid per unit length based on the flow direction than in the second section. In particular, the further section is bounded only by an inner boundary surface, an outer boundary surface and a side wall. Typically, the further section is directly adjacent to the inlet and / or the second section.

[0013] In a preferred embodiment of the stator housing according to the present invention it is further envisaged that the first heat transfer structure is formed by at least two heat transfer elements and the second heat transfer structure is formed by a number of heat transfer elements which is preferably one less than the number of heat transfer elements of the first heat transfer structure.

[0014] In this case, in order to achieve a hydrodynamically favourable transition between each section, the heat transfer element of the first heat transfer structure may be defined to be located in the transition section between the first and second sections and adjacent to an extension element extending towards the outer edge of the cooling duct.

[0015] Alternatively, a mechanically robust transition can be achieved if the heat transfer elements of the second heat transfer structure are connected to the heat transfer elements of the first heat transfer structure by a branch element, which in the transition section between the first and second sections extends less radially into the cooling duct than the heat transfer elements. Simulations have made it possible to verify that the branch element significantly reduces the mechanical stresses and thus the risk of cracking the stator housing. The branch element is advantageously of Y-shaped design, over which the coolant flows.

[0016] By means of the branch element it is advantageously possible to achieve lower mechanical stresses in the stator housing for a given manufacturing tolerance or to achieve higher manufacturing tolerances and higher transferable moments in the press-fit connecting the stator housing to the stator for a given maximum permissible mechanical stress. Furthermore, it is possible to allow higher manufacturing tolerances for a given maximum permissible mechanical stress, which reduces the manufacturing effort and costs.

[0017] The branching elements preferably have a radial extent of at least 0.1 times, preferably at least 0.25 times, particularly preferably 0.4 times, and / or at most 0.9 times, preferably at most 0.75 times, particularly preferably 0.6 times, the radial extent of the heat transfer element.

[0018] A preferred design alternative envisions that the heat transfer elements extend continuously along each section.

[0019] As an alternative to this, each heat transfer structure is formed by a plurality of heat transfer units comprising at least one heat transfer element, which extend partially along the respective section and form an interruption between two adjacent heat transfer units.

[0020] The principles of the present invention may be used in a variety of cooling duct configurations.

[0021] A preferred configuration of the stator housing according to the invention therefore envisages that the cooling ducts run helically in the circumferential direction of the stator housing. Such a design of the stator housing is also called a helical design and typically achieves the same orientation of the flow direction over the entire length of the cooling duct. In this case, the longitudinal zones of the cooling duct preferably run only in the circumferential direction, while axially adjacent longitudinal zones are connected by offset zones, in which the flow direction runs both circumferentially and axially. The first section and / or the second section and / or the further section can extend both in the longitudinal zones and in the offset zones.

[0022] An alternative configuration of the stator housing according to the invention provides that the cooling duct is formed in a serpentine manner by a number of main zones extending in the circumferential or axial direction and by deflection zones connecting adjacent main zones, whereby there is a change in the direction of the flow direction at the transition from one main zone to the adjacent main zone. Typically, each deflection zone ensures a change in the direction of the cooling fluid of at least 170° and / or up to 190°.

[0023] In this case, it is particularly preferred that at least one heat transfer unit is arranged in each main zone, in particular the interruption can be provided so as to extend completely along the deflection zone.

[0024] It is further preferred in the case of a stator housing according to the invention if the cooling ducts are formed by cavities in the stator housing.

[0025] According to a preferred configuration of the stator housing, it is envisaged here that it consists of an inner housing element and an outer housing element, the inner housing element being arranged coaxially within the outer housing element, and a cavity being formed in the inner housing element and / or in the outer housing element.

[0026] The object on which the invention is based is further achieved by an electric machine for a vehicle, comprising a stator housing according to the invention and a stator arranged in the stator housing. [Brief description of the drawings]

[0027] Further advantages and details of the invention emerge from the exemplary embodiments described below and on the basis of the drawings, which are schematic diagrams. [Figure 1] FIG. 1 is a cross-sectional view of an exemplary embodiment of an electric machine according to the present invention. [Diagram 2] FIG. 2 is an exploded perspective view illustrating a first exemplary embodiment of a stator housing according to the present invention. [Diagram 3] FIG. 3 is a plan projection view of the cooling ducts of the first exemplary embodiment of the stator housing. [Figure 4] FIG. 4 is a diagram illustrating the temperature distribution in the press-fit portion of the stator housing according to the first exemplary embodiment during operation. [Diagram 5] FIG. 5 shows the temperature distribution during operation when a conventional stator housing is press-fitted. [Figure 6] FIG. 6 is a perspective view of a cooling duct in the region of the transition section according to a second exemplary embodiment of a stator housing according to the invention. [Figure 7] FIG. 7 is a perspective view of a housing element according to a third exemplary embodiment of a stator housing according to the present invention. [Figure 8] FIG. 8 is a plan projection view of a cooling duct according to the third embodiment. [Figure 9] FIG. 9 is a perspective view of a housing element according to a fourth exemplary embodiment of a stator housing according to the present invention. [Figure 10] FIG. 10 is a plan projection view of a cooling duct of the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] FIG. 1 illustrates a cross-sectional view of an exemplary embodiment of an electric machine 1 .

[0029] The electric machine 1 comprises a stator housing 2, a stator 3 connected to the stator housing 2, for example by press fitting, a rotor 4 rotatably arranged in the stator 3, and a shaft 5 to which the rotor 4 is fixed. By way of example, the rotor 4 comprises a number of permanent magnets 6. The stator housing 2 corresponds to one of the exemplary embodiments described below.

[0030] FIG. 2 is an exploded perspective view of a first exemplary embodiment of a stator housing 2. As shown in FIG.

[0031] The stator housing 2 accommodates a cylindrical receiving space 7 having a cylindrical axis 8 for the stator 3 (see FIG. 1). The stator housing 2 includes an inlet 9 for a cooling fluid, an outlet 10 for the cooling fluid, and a cooling duct 11 formed between the inlet 9 and the outlet 10 and through which the cooling fluid can flow in a flow direction from the inlet 9 to the outlet 10. The inlet 9 and the outlet 10 are formed on side surfaces of the stator housing 2 on opposite sides in the axial direction.

[0032] The cooling ducts 11 each extend along the flow direction and include a first heat transfer structure 12 and a second heat transfer structure 13 for transferring heat from the cooling fluid to the stator housing 2 .

[0033] 3 is a plan view of the cooling duct 11 of the stator housing 2. In this case, the inlet end 14 of the cooling duct 11 is shown on the right and the outlet end 15 of the cooling duct 11 is shown on the left.

[0034] The cooling duct 11 includes a first section 16 in which the first heat transfer structure 12 is disposed, and a second section 17 disposed on the inlet side of the first section 16 in which the second heat transfer structure 13 is disposed. In this case, the first heat transfer structure 12 of the first section 16 forms a larger heat transfer area of ​​the cooling fluid per unit length based on the flow direction than the second heat transfer structure 13 of the second section 17. Furthermore, the cooling duct 11 includes a third section 18 located on the inlet side of the second section 17. In the third section 18 of the cooling duct 11, the heat transfer area of ​​the cooling fluid per unit length based on the flow direction is smaller than that of the second section 17.

[0035] During operation of the electric machine 1, the cooling fluid is heated while flowing through the cooling ducts 11, so that already heated cooling fluid flows on the outlet side. Thanks to the fact that the heat transfer area in the first section 16 is larger than in the second section 17 and larger in the second section 17 than in the third section 18, the axial temperature distribution over the stator housing 2 is substantially more uniform compared to a stator housing without heat transfer structures, i.e. compared to a stator housing with a heat transfer area that is substantially constant over the entire length of the cooling ducts.

[0036] In this case, the cooling duct 11 is divided by the second heat transfer structure 16 into two partial cooling ducts 19 and by the first heat transfer structure into three partial cooling ducts 20. The cross-sectional areas of the partial cooling ducts 19 are substantially equal to one another. Similarly, the cross-sectional areas of the partial cooling ducts 20 are substantially equal to one another. Between the respective partial cooling ducts 19, 20, the stator housing 2 is designed to be fluid-tight in a direction perpendicular to the flow direction, i.e. here in the axial direction.

[0037] The first heat transfer structure 12 is formed by two heat transfer elements 21, 22 each extending continuously along the flow direction in the first section 16. The second heat transfer structure 13 is formed by one heat transfer element 23 extending continuously along the flow direction in the second section 17. No heat transfer element is provided in the third section 18.

[0038] In the transition section 24 between the first section 16 and the second section 17, extension elements 25 are provided - essentially optional - each of which adjoins a heat transfer element 21, 22 and extends towards the outer edge of the cooling duct 11. This improves the hydrodynamic transition between the second section 17 and the first section 16.

[0039] In the present exemplary embodiment, the cooling duct 11 runs helically in the circumferential direction of the stator housing 2. The cooling duct 11 thus has four longitudinal zones 26 whose flow direction runs in the circumferential direction and three offset zones 27 whose flow directions run in the circumferential and axial directions and connect adjacent longitudinal zones 26.

[0040] 2 further shows that the stator housing 2 comprises an inner housing element 28 and an outer housing element 29. The housing elements 28, 29 are arranged coaxially with each other so as to completely delimit the cooling duct 11 when the inner housing element 28 is pressed into the outer housing element 29. In this case, the side walls and the radially inner boundary of the cooling duct 11 are formed by a cavity in the inner housing element 28, while the outer housing element 29 has a smooth inner surface which forms the radially outer boundary of the cooling duct 11. As can be seen, the inlets 9 and the outlets 10 are provided on the lateral surfaces of the outer housing element 29.

[0041] Each housing element 28, 29 further comprises a bearing plate 30, 31 having a through opening 32 for the shaft 5 (see FIG. 1).

[0042] Fig. 4 shows the temperature distribution in the press-fit of the stator housing 2 during operation of the electric machine 1. Fig. 5 shows the temperature distribution in the press-fit of a conventional stator housing without heat transfer. In this case, the temperature contour lines L are spaced apart by 2 K each. As can be seen from a comparison of Fig. 4 and Fig. 5, the contour lines L in Fig. 4 are less closely spaced and therefore there is a substantially more uniform temperature distribution in the axial direction than in the case of a conventional stator housing.

[0043] The temperature distribution shown is a simulation with characteristic values. The following table shows the simulation results of the pressure loss between the inlet and the outlet, the average surface temperature during pressing and the average volume temperature in the inner housing element for a conventional stator housing (column A), a stator housing 2 according to the first exemplary embodiment (column B) and a stator housing with an increased number of longitudinal zones from 4 to 6 compared to the conventional stator housing (column C). [Table 1]

[0044] It can be seen that a significant reduction in the average temperature is achieved with the heat transfer structures 12, 13, with only a slight increase in pressure loss. It should be noted that both the temperature reduction and the increase in pressure loss are more favorable in the first exemplary embodiment than in the case of the stator housing with an increased number of main zones. These results can be qualitatively transferred to the exemplary embodiments described below.

[0045] FIG. 6 is a perspective view of the cooling duct 11 in the region of the transition section 24 according to a second exemplary embodiment of the stator housing 2, which corresponds to the first exemplary embodiment except for the differences described below.

[0046] In this exemplary embodiment, the heat transfer element 23 of the second heat transfer structure 13 is connected to the heat transfer elements 21, 22 of the first heat transfer structure 12 by a branch element 33. The branch element 33 has a Y-shape and extends less radially outward than the heat transfer elements 21, 22, 23, allowing the cooling fluid to flow over it, as indicated by the two arrows. Due to the branch element 33, the mechanical stresses in the transition section 24 are significantly reduced compared to the first exemplary embodiment or to an exemplary embodiment corresponding to the first exemplary embodiment with a free transition section. Purely by way of example, the branch element 33 here has half the radial extent of the heat transfer elements 21, 22, 23.

[0047] In the simulation, a 3 kW heat source was assumed during injection, the inlet temperature of the water used as the coolant was 70°C, and the volumetric flow rate was 10 l min -1 It was then possible to determine that a pressure loss of 128 mbar occurred at an average surface temperature of 78.1° C. during pressing. In the case of a stator housing without branching elements, i.e. a free transition section 24, a pressure loss of 5 mbar higher occurred at an average surface temperature of 78.0° C. during pressing.

[0048] From a mechanical point of view, a von Mises stress of 184.7 MPa for the stator housing without branch elements in the transition section and 94.6 MPa for the second exemplary embodiment was determined in an exemplary simulation. The tensile stress can be reduced from 210 MPa for the stator housing without branch elements to 101 MPa. In this case, there is no significant deviation in the average contact pressure during press-fit between the two stator housings compared here.

[0049] FIG. 7 is a perspective view of the inner housing element 28 of a third exemplary embodiment of the stator housing 2, which corresponds to the first exemplary embodiment, except for the differences described below.

[0050] In the third exemplary embodiment, the cooling duct 11 is formed in a serpentine manner by a number of axially extending main zones 34 and a deflection zone 35 connecting adjacent main zones 34. In this case, the deflection zones bring about a change in the flow direction of 180°. Here, by way of example, the inlet 9 and the outlet 10 are located on one axial side of the stator housing 2, contrary to Figures 1 and 2.

[0051] FIG. 8 is a plan projection view of a cooling duct 11 of the third exemplary embodiment.

[0052] The first section 16 extends over eight main zones 34 from the outlet end 15 to the second section 17, which extends over seven main zones 34 to the third section 18, which extends over three main zones 34 to the inlet end 14.

[0053] The first heat transfer structure 12 comprises a number of heat transfer units 36 corresponding to the number of main zones 34 through which the first section 16 extends. The heat transfer units 36 comprise heat transfer elements 21, 22 extending axially discontinuously along the first section 16.

[0054] The second heat transfer structure 13 also comprises a number of heat transfer units 37 corresponding to the number of main zones 34 through which the second section 17 extends. The heat transfer units 37 comprise heat transfer elements 23 extending axially intermittently along the second section 17.

[0055] The interrupts are each located in the area of ​​the deflection section 35 .

[0056] FIG. 9 is a perspective view of an inner housing element 28 of a fourth exemplary embodiment of a stator housing 2, which corresponds to the third exemplary embodiment except for the differences described below.

[0057] In the fourth exemplary embodiment, the cooling duct 11 is formed in a serpentine shape with a number of circumferentially extending main zones 34 connected by deflection zones 35. In this case, the inlet and the outlet are at the same radial position on axially opposite sides of the stator housing 2 (see FIG. 2). The first section 16 extends over the two main zones 34 from the outlet end 15 to the second section 17, which in turn extends over the two main zones 34 to the third section 18. The third section 18 extends over the two main zones 34 to the inlet end 14.

[0058] The first heat transfer structure 12 comprises two heat transfer units 36 corresponding to the number of main zones 34 through which the first section 16 extends. The heat transfer units 36 comprise heat transfer elements 21, 22 extending circumferentially with interruptions along the first section 16.

[0059] The second heat transfer structure 13 comprises two heat transfer units 37 corresponding to the number of main zones 34 through which the second section 17 extends. The heat transfer units 37 comprise heat transfer elements 23 extending circumferentially with interruptions along the second section 17.

Claims

1. A stator housing (2) for an electric machine (1), comprising: an inlet (9) for a cooling fluid, an outlet (10) for said cooling fluid, and a cooling duct (11) formed between said inlet (9) and said outlet (10), The cooling fluid may flow through the cooling duct (11) in a flow direction from the inlet (9) towards the outlet (10), the cooling duct (11) comprises a first heat transfer structure (12) and a second heat transfer structure (13), each of which extends along the flow direction and is designed to transfer heat from a cooling fluid to the stator housing (2); the first heat transfer structure (12) is arranged in a first section (16) of the cooling duct (11); the second heat transfer structure (13) is disposed in a second section (17) of the cooling duct (11) on the inlet side of the first section (16), the first heat transfer structure (12) in the first section (16) is formed to have a larger heat transfer area for the cooling fluid per unit length based on the flow direction than the second heat transfer structure (13) in the second section (17), the first heat transfer structure (12) is formed by at least two heat transfer elements (21, 22), and the second heat transfer structure (13) is formed by a number of heat transfer elements (23) that is smaller than the number of the heat transfer elements (21, 22) of the first heat transfer structure (12); The heat transfer elements (21, 22, 23) extend continuously and spirally along each section (16, 17) in the circumferential direction of the stator housing (2).

2. 2. A stator housing according to claim 1, wherein each of the heat transfer structures (12, 13) divides the cooling duct (11) into a plurality of partial cooling ducts (19, 20) extending along the flow direction.

3. The second heat transfer structure (13) divides the cooling duct (11) into at least two second partial cooling ducts (20), The stator housing according to claim 2, wherein the first heat transfer structure (12) divides the cooling duct (11) into a number of first partial cooling ducts (19) which is at least one more than the number of the second partial cooling ducts (20).

4. A stator housing as described in any one of claims 1 to 3, wherein in a further section (18) on the inlet side of the second section (17), the cooling duct (11) has a smaller heat transfer area for the cooling fluid per unit length based on the flow direction than the second section (17).

5. the heat transfer elements (21, 22) of the first heat transfer structure (12) are adjacent to an extension element (25); The stator housing according to any one of claims 1 to 4, wherein the extension element (25) is located in a transition section (24) between the first section (16) and the second section (17) and extends towards an outer edge of the cooling duct (11).

6. the heat transfer element (23) of the second heat transfer structure (13) is connected to the heat transfer elements (21, 22) of the first heat transfer structure (12) by a branch element (33); The stator housing according to any one of claims 1 to 4, wherein the branch element (33) has a smaller radial extent in the cooling duct (11) than the heat transfer elements (21, 22, 23) in a transition section (24) between the first section (16) and the second section (17).

7. A stator housing according to any one of the preceding claims, wherein the cooling ducts (11) are formed by cavities in the stator housing (2).

8. The stator housing comprises an inner housing element (28) and an outer housing element (29); The inner housing element (28) is coaxially disposed within the outer housing element (29); The stator housing of claim 7, wherein the cavity is formed in the inner housing element (28) and / or in the outer housing element (29).

9. An electric machine (1) for a vehicle, comprising: A stator housing (2) according to any one of claims 1 to 8; and a stator (3) disposed inside the stator housing (2).

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