Electric drive unit having rotor heat sink formed by heat sink elements

Abstract

An electric drive unit includes an electric motor having a motor output shaft and a heat sink received therein. The heat sink consists of a plurality of discrete heat sink elements stacked together and inserted into the motor output shaft. The heat sink element has a central hub that cooperates to form a coolant supply channel extending centrally through the heat sink. Each heat sink element defines a plurality of discrete coolant return channels that are relatively shorter in length than the central hub such that an empty annular space is formed between the coolant return channels of adjacent heat sink elements.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Patent Application No. 17 / 690,440, filed on March 9, 2022, the disclosure of which is incorporated by reference as if fully set forth herein. Background Art

[0003] This section provides background information related to the present disclosure which is not necessarily prior art.

[0004] Some vehicle manufacturers are increasingly interested in incorporating electric motors into vehicles for the purpose of providing propulsion power. In order to minimize the cost and size of the electric motor, it is often necessary to cool components of the electric motor, such as the rotor of the electric motor, using a liquid coolant flow. One known method for cooling the rotor of an electric motor is to use a heat exchanger inside the hollow shaft of the rotor. The liquid coolant flow is input to the heat exchanger at a first end of the rotor to a first channel formed along the axis of rotation of the rotor. At least a portion of the liquid coolant flow that leaves the first channel at an opposite second end of the rotor is returned to the first end of the rotor through a plurality of second channels that are concentrically arranged around the first channel.

[0005] While this configuration is suitable for its intended purpose, the inventors note that known configurations may be relatively expensive and / or difficult to manufacture. In this regard, the outer surface of the heat exchanger must contact the inner surface of the hollow shaft over the entire length of the heat exchanger to maximize the potential heat transfer between the hollow shaft and the heat exchanger. Therefore, known designs have the practical effect of requiring close tolerances between the outer surface of the heat exchanger and the inner surface of the hollow shaft. Configurations in this manner may be relatively expensive and / or relatively difficult to manufacture. Summary of the invention

[0006] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0007] In one form, the present disclosure provides an electric drive unit including a stator, a rotor, an electrode output shaft and a radiator. The rotor is received in the stator and is rotatable about an axis. The motor output shaft is received through the rotor and is coupled to the rotor to rotate with the rotor. The motor output shaft includes a hollow tubular portion. The radiator is received in the hollow tubular portion of the motor output shaft and is formed by a plurality of radiator elements. Each of the radiator elements is integrally and integrally formed to include a central hub, an outer rim, and a plurality of first rib members that fixedly couple the central hub to the outer rim. The central hub is hollow and concentrically disposed about the axis. The outer rim is concentrically disposed about the central hub and engages an inner circumferential surface of the hollow tubular portion of the motor output shaft. Each of the first rib members extends generally radially between the central hub and the outer rim, so that a plurality of discrete coolant return channels are formed through the radiator element. The radiator elements are adjacent to each other so that the central hub of the radiator element forms a coolant supply channel extending through the radiator. At least one axial end of the central hub extends further along the axis than the outer edge and the first rib member to provide an empty annular space between the discrete coolant return passages of adjacent pairs of the radiator elements.

[0008] Further areas of applicability will become apparent from the description provided herein.The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0010] Figure 1 is a longitudinal cross-sectional view of an exemplary electric drive module constructed in accordance with the teachings of the present disclosure;

[0011] Figure 2 yes Figure 1 an enlarged portion of , illustrating a portion of a rotor assembly in greater detail;

[0012] Figure 3 and Figure 4 are front and rear perspective views of an exemplary heat sink element for forming a portion of a rotor assembly;

[0013] Figure 5 yes Figure 3 A longitudinal cross-sectional view of a radiator element;

[0014] Figure 6 is taken perpendicular to the longitudinal axis of the radiator element Figure 3 a cross-sectional view of a heat sink element; and

[0015] Figures 7 to 10 is similar to Figure 6 , but depicting alternately configured heat sink elements.

[0016] Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION

[0017] Refer to the attached figure Figure 1 An exemplary electric drive unit constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral 10. The electric drive unit may include a housing assembly 12, an electric motor 14, a transmission 16, and at least one output shaft 18. In the particular example provided, the electric drive unit 10 includes a differential assembly 20 and employs a pair of output shafts 18.

[0018] The housing assembly 12 can be configured to accommodate the motor 14, the transmission 16 and the differential assembly 20. The motor 14 includes a stator 32 and a rotor assembly 34 having a rotor 36, a motor output shaft 38 and a radiator 44. The rotor 36 is received in the stator 32 and can rotate around the motor axis 46. The motor output shaft 38 is received through the rotor 36 and is coupled to the rotor 36 to rotate with it around the motor axis 46. The radiator 44 is received in the motor output shaft 38. The transmission 16 includes a transmission input gear 50, a transmission output gear 52, and a plurality of intermediate gears 56 that transmit rotational power between the transmission input gear 50 and the transmission output gear 52, and the transmission input gear 50 is coupled to the motor output shaft 38 to rotate with it. The differential assembly 20 includes a differential input member 60 and a differential gear set 62 including a pair of differential output members 64. In the example provided, the differential input member 60 is a differential case, and the differential gear set 62 is a helical gear set, wherein the differential output member 64 is a side gear. However, it will be appreciated that the differential gear set 62 may be configured slightly differently, such as having a helical differential pinion and side gears, or may be a planetary gear set having a planet carrier and a helical sun gear, ring gear, and planet gears. Each output shaft 18 is coupled to rotate with an associated one of the differential output members 64.

[0019] Refer to the attached figure Figure 2, showing a portion of the rotor assembly 34 in more detail. The motor output shaft 38 can have a shaft member 70 and an end member 72. The shaft member 70 includes a hollow tubular portion 76 and a first bearing journal 78. The hollow tubular portion 76 can be assembled to the core 80 of the rotor 36 using an engineering fit such as an interference fit or a press fit. A first motor output shaft bearing 84 can be received on the first bearing journal 78 and engaged to the housing assembly 12 to support the motor output shaft 38 for rotation about the motor axis 46. The end member 72 can include a plug portion 88, an end stop 90, and a second bearing journal 92 ( Figure 1 ). The plug portion 88 is configured to be received in the open end of the hollow tubular portion 76 and sealingly engage the inner peripheral surface 98 of the motor output shaft 38. The plug portion 88 can be assembled to the inner peripheral surface 98 of the motor output shaft 38 using an engineering fit such as a press fit. In addition or alternatively, a sealant can be used between the inner peripheral surface 98 of the motor output shaft 38 and the plug portion 88 to form a seal therebetween. The end stop 90 can be axially disposed between the plug portion 88 and the second bearing journal 92 ( Figure 1 ) and can abut the axial end of the shaft member 70 to limit the distance that the end member 72 is received into the hollow tubular portion 76. The second motor output shaft bearing 100 ( Figure 1 ) can be received in the second bearing journal 92 ( Figure 1 ) and is engaged to the housing assembly 12 to support the motor output shaft 38 for rotation about the motor axis 46. The heat sink 44 can be received in the hollow tubular portion 76 of the shaft member 70 and can include a plurality of heat sink elements 104 aligned with each other (i.e., adjacent to each other in series) along the motor axis 46.

[0020] refer to Figures 3 to 6 , each heat sink element 104 can be integrally and unitarily formed of a suitable material such as aluminum, and can define a central hub 120, an outer edge 122, and a plurality of first rib members 124. In the example provided, the heat sink element 104 is formed as an extrusion and then machined as desired. It will be understood that other manufacturing processes such as die casting can be used, and the heat sink element 104 can be used and the various features of the heat sink element 104 are formed in a net shape or near net shape manner to eliminate or reduce machining of the heat sink element 104.

[0021] The central hub 120 is hollow and is concentrically disposed about the longitudinal axis of the heat sink element 104. The central hub 120 defines a central bore 150 extending through the heat sink element 104. An inner peripheral surface 152 of the central bore 150 may be net-shaped, such as when the heat sink element 104 is formed in an extrusion or die casting operation, or may be machined in whole or in part. In the example provided, a first portion 154 of the central bore 150 is machined (i.e., bored) to a predetermined diameter that is configured to receive a bushing 156 ( Figure 2 ), while the remaining portion 158 of the center hole 150 is not finished (not machined after extrusion). Figure 2 ) is configured to receive therein a fixed coolant supply tube 160 ( Figure 2 ).

[0022] refer to Figure 2 , Figure 3 and Figure 5 , the outer rim 122 is concentrically disposed about the central hub 120 and is configured to engage the inner circumferential surface 98 of the hollow tubular portion 76 of the motor output shaft 38 in a desired manner, such as by utilizing an interference fit (e.g., a press fit or a shrink fit), thereby not only rotationally coupling the heat sink element 104 to the motor output shaft 38, but also allowing a desired heat transfer between the heat sink element 104 and the motor output shaft 38. In the example provided, a shrink fit that provides an interference of 12 microns to 52 microns at room temperature is used between the outer circumferential surface 170 of the outer rim 122 and the inner circumferential surface 98 of the hollow tubular portion 76 of the motor output shaft 38. In the example provided, the outer rim 122 extends around the entire circumference of the heat sink element 104. Optionally, a plurality of longitudinally extending, circumferentially spaced grooves 176 may be formed on the outer circumferential surface 170 of the outer rim 122.

[0023] Although the outer edge 122 has been shown as extending around the entire perimeter of the heat sink element 104, it should be understood that the outer edge may be formed slightly differently. Figure 7 The heat sink element 104 a employs an outer rim 122 a formed by a plurality of circumferentially spaced rim segments 180 that are each fixedly coupled to an associated one of the first rib members 124 .

[0024] Back to Figure 3 and Figure 6 Each first rib member 124 may extend generally radially between the central hub 120 and the outer edge 122, such that a plurality of discrete coolant return channels 190 are formed through the radiator element 104. The discrete coolant return channels 190 may have any desired cross-sectional shape. Furthermore, the first rib members 124 need not extend in a purely radial direction. Figure 8 In the example of FIG. 1 , a portion of each first rib member 124 b extends in the circumferential direction, while increasing in the radial direction from the center hub 120. If desired, one or more longitudinally extending fin members 194 may be formed on each first rib member 124, such as Figure 6 , Figure 7 and Fig. 9 as shown in the example.

[0025] Alternatively, if Figure 8 and Fig.10 As shown, a plurality of second rib members 200 may be formed onto the outer edge 122. The second rib members 200 may extend radially inward from the outer edge 122 to associated coolant return channels in the discrete coolant return channels 190. Fig.10 In the example of FIG. 1 , the second rib member 200 is formed with a uniform radial height. However, it will be understood that Figure 8 As shown, the second rib member 200 may adopt two or more different radial heights.

[0026] Back to Figure 2 , Figure 3 and Figure 5 , the radiator elements 104 may abut against each other to form the radiator 44. In this case, the central hubs 120 of the radiator elements 104 abut against each other and cooperate to form a coolant supply channel 210 extending through the radiator 44. At least one axial end 212 of the central hub 120 of each radiator element 104 may be located along the longitudinal axis of the radiator element 104 relative to the outer edge 122, the first rib member 124, and the second rib member 200 ( Figure 8 ) (if the second rib member 200 is included) and the longitudinally extending fin members 194 extend axially far to provide empty annular spaces 220 between the discrete coolant return passages 190 of adjacent pairs of radiator elements 104.

[0027] Alternatively, a rotational offset may be employed between adjacent radiator elements 104 such that the discrete coolant return passages 190 in each radiator element 104 are rotationally offset relative to an adjacent one of the radiator elements 104 about the longitudinal axis of the radiator 44 . Figures 2 to 5, the heat sink elements 104 in each pair of adjacent heat sink elements 104 may optionally employ a clocking element 230 and a mating clocking element 232, respectively, which engage one another to rotationally stagger the discrete coolant return passages 190 in the adjacent pair of heat sink elements 104 about the longitudinal axis of the heat sink 44 by a predetermined rotational offset. In the example provided, the clocking element 230 is a protrusion extending axially from the central hub 120 of the first of the abutting heat sink elements 104, and the mating clocking element 232 is a recess formed in the central hub 120 of the second of the abutting heat sink elements 104. The protrusion may be received in the recess in a sliding fit.

[0028] The heat sink elements 104 can be assembled to each other (i.e., to form the heat sink 44) such that the central hubs 120 abut against each other and, if a clock element 230 and a mating clock element 232 are employed, the clock element 230 and the mating clock element 232 engage each other. If desired, the heat sink 44 can be cooled, for example, using liquid nitrogen, and / or the motor output shaft 38 can be heated to allow the heat sink 44 to be inserted through the open end of the hollow tubular portion 76 of the motor output shaft 38 and positioned in the desired position. In the example provided, the heat sink 44 is cooled in liquid nitrogen to allow the heat sink 44 to shrink so that the heat sink 44 slides into the hollow tubular portion 76 of the motor output shaft 38 with little or no force.

[0029] In operation, a flow of liquid coolant may be supplied into the coolant supply passages 210 in the radiator 44 through the fixed coolant supply tubes 160. The liquid coolant may exit the axially opposite sides of the radiator 44 and impact or contact the axial ends 250 of the hollow tubular portion 76 of the plug portion 88 that face the motor output shaft 38. The axial ends 250 may be shaped in any desired manner and direct the flow of liquid coolant radially outward and rearward toward the radiator 44 where the liquid coolant enters the discrete coolant return passages 190 in the radiator element 104 closest to the end member 72. Coolant exiting the discrete coolant return passages 190 of the radiator element 104 closest to the end member 72 enters the empty annular space 220 disposed between adjacent radiator elements 104 before entering the discrete coolant return passages 190 in the adjacent radiator element 104. The empty annular space 220 and the rotational displacement (if rotational displacement is included) between the discrete coolant return passages 190 of an adjacent pair of heat sink elements 104 disrupt the flow of the liquid coolant, thereby creating turbulence in the flow and reducing the thickness of the boundary layer of the liquid coolant formed on the inner surface of the discrete coolant return passages 190. Thus, improved heat transfer from the heat sink 44 to the liquid coolant is obtained relative to a monolithic heat sink.

[0030] Although the heat sink 44 has been described as being formed from the same heat sink element 104, it will be appreciated that the heat sink 44 may be formed from two or more different types of heat sink elements 104. In one example, the two or more different types of heat sink elements 104 may employ differently configured outer edges 122 and / or first rib members 124 and / or second rib members 200. In another example, the inner heat sink element (i.e., the heat sink element 104 located between the first heat sink element 104 and the last heat sink element 104 in the heat sink 44) may be formed as described above, except that the outer peripheral surface 170 of the outer edge 122 of the inner heat sink element 104 is slightly smaller in diameter, for example, to provide a transition fit between the inner heat sink element and the hollow tubular portion 76 of the motor output shaft 38. It will be appreciated that the heat sink elements 104 at the opposite axial ends of the heat sink 44 are fixedly engaged to the motor output shaft 38, thereby inhibiting relative axial movement of the heat sink 44 along the motor axis 46. If desired, a clocking element and a mating clocking element 232 may be employed to additionally inhibit relative rotational movement of the inner heat sink element 104 relative to the heat sink element 104 at the opposite axial end of the heat sink 44 .

[0031] For the purpose of illustration and description, the foregoing description of the embodiments has been provided. It is not intended to be exhaustive or to limit the present disclosure. The individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but are interchangeable and can be used in selected embodiments where applicable, even if not specifically shown or described. It can also be varied in many ways as well. These variations should not be considered as departing from the present disclosure, and all such modifications are intended to be included within the scope of the present disclosure.

Claims

1. An electric drive unit, comprising: stator; a rotor received in the stator and rotatable about an axis; a motor output shaft received through the rotor, the motor output shaft coupled to the rotor for rotation therewith, the motor output shaft having a hollow tubular portion; a heat sink received in the hollow tubular portion of the motor output shaft, the heat sink being formed by a plurality of heat sink elements, each of the heat sink elements being integrally and unitarily formed to include a central hub, an outer rim, and a plurality of first rib members fixedly coupling the central hub to the outer rim, the central hub being hollow and concentrically disposed about the axis, the outer rim being concentrically disposed about the central hub and engaging an inner peripheral surface of the hollow tubular portion of the motor output shaft, each of the first rib members extending generally radially between the central hub and the outer rim such that a plurality of discrete coolant return passages are formed through the heat exchanger element, the heat sink elements being abutted against one another such that the central hubs of the heat sink elements form coolant supply passages extending through the heat sink, wherein at least one axial end of the central hub extends further along the axis than the outer rim and the first rib members, thereby providing an empty annular space between the discrete coolant return passages of adjacent pairs of the heat sink elements. 2 . The electric drive unit of claim 1 , wherein the discrete coolant return channels in each pair of adjacent radiator elements are rotationally offset relative to each other about the axis.

3. An electric drive unit according to claim 2, wherein the radiator elements in each pair of abutting radiator elements respectively have a clock element and a mating clock element, wherein the clock element and the mating clock element engage each other to rotationally stagger the discrete coolant return channels by a predetermined rotational offset.

4. An electric drive unit according to claim 3, wherein the clock element is a protrusion fixedly connected to the central hub of a first radiator element in a pair of adjacent radiator elements and extending from the central hub of the first radiator element, and wherein the mating clock element is a recess formed in the central hub of the other radiator element in the pair of adjacent radiator elements, wherein the protrusion is received in the recess. The electric drive unit of claim 4 , wherein the male portion engages the female portion in a sliding fit.

6. The electric drive unit of claim 1, wherein the outer edge of at least a first portion of the heat sink element is dimensioned to engage the inner peripheral surface of the hollow tubular portion of the motor output shaft with an interference fit.

7. The electric drive unit of claim 6, wherein the outer edge of the second portion of the heat sink element is dimensioned to engage the inner peripheral surface of the hollow tubular portion of the motor output shaft with a transition fit.

8. The electric drive unit of claim 1, wherein the outer edge of each heat sink element extends completely around the periphery of the heat sink element.

9. An electric drive unit according to claim 8, wherein a plurality of longitudinally extending, circumferentially spaced grooves are formed in the outer edge of each of the heat sink elements.

10. The electric drive unit of claim 1, wherein each of the heat sink elements includes a plurality of second rib members, each of the second rib members being fixedly coupled to the outer rim and extending radially inwardly from the outer rim.

11. The electric drive unit of claim 1, further comprising a transmission and at least one output shaft, the transmission transmitting rotational power between the motor output shaft and the at least one output shaft.

12. The electric drive unit of claim 11 further comprising a differential assembly having a differential input and a pair of differential outputs, the differential input being directly driven by the transmission.

13. The electric drive unit of claim 1, wherein the heat sink element is formed from aluminum.

14. The electric drive unit of claim 1, further comprising a housing to which the stator is fixedly coupled and a coolant supply tube coupled to the housing and extending into the central hub of a first one of the radiator elements.

15. The electric drive unit of claim 14, wherein a bushing is disposed radially between the central hub of the first of the radiator elements and the coolant supply tube.

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