Electric powertrain

Abstract

This electric powertrain comprises an electric motor, and a gear mechanism including: a first rotary shaft that serves both as a rotor shaft of the electric motor and as a rotary shaft of a gear; and a plurality of rotary shafts that are parallel to the first rotary shaft. The gear of the n-th rotary shaft and the gear of the (n+1)-th rotary shaft are meshed with each other. The electric powertrain further comprises a motor housing that is provided with a recessed first accommodation portion, and a gear case that is provided with a recessed second accommodation portion. The motor housing and the gear case are fastened together in an orientation in which an opening of the first accommodation portion and an opening of the second accommodation portion face each other. The electric motor and the gear mechanism are accommodated inside a space defined by fastening the motor housing and the gear case together.

Description

Electric powertrain

[0001] The present invention relates to electric powertrains.

[0002] Electric powertrains used in electric vehicles and the like are known to be integrated with a motor housing that houses an electric motor and a gear case that houses a reduction gear mechanism. To ensure ease of assembly, such devices often have a configuration that includes three cases: the motor housing, the gear case, and an intermediate case disposed between them. However, such a configuration requires a large number of parts and tends to increase the overall dimensions of the electric powertrain.

[0003] JP2023-102121A discloses an electric drive device with a simplified configuration, in which a cylindrical motor housing that houses a rotor, a stator, and a control board is integrated with a reduction gear having a motor-side rotating body and a second gear.

[0004] However, although the electric drive device in the above document is integrated, it is simply a combination of a motor housing and a reduction gear unit, and the wall of the motor housing and the wall of the reduction gear unit overlap at the joint, so there is room for improvement in terms of dimensions and weight.

[0005] SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an electric powertrain with a simple configuration.

[0006] According to one aspect of the present invention, there is provided an electric powertrain including an electric motor, a gear mechanism having a rotor shaft of the electric motor and a first rotation shaft that also serves as a rotation shaft of a gear, and a plurality of rotation shafts parallel to the first rotation shaft, wherein the gear of the nth rotation shaft meshes with the gear of the (n+1)th rotation shaft. This electric powertrain includes a motor housing having a first concave accommodating portion, and a gear case having a second concave accommodating portion, the motor housing and the gear case are fastened together with the opening of the first accommodating portion facing the opening of the second accommodating portion, and the electric motor and the gear mechanism are housed in a space defined by the fastening of the motor housing and the gear case.

[0007] Fig. 1 is a cross-sectional view showing a schematic configuration of an electric powertrain. Fig. 2 is a schematic view showing an example of the positional relationship between a second rotating shaft, a bearing support member, a stator of an electric motor, and a third rotating shaft when viewed from direction II in Fig. 1. Fig. 3 is a schematic view showing another example of the positional relationship between the second rotating shaft, a bearing support member, a stator of an electric motor, and a third rotating shaft when viewed from direction II in Fig. 1. Fig. 4 is a cross-sectional view showing a schematic configuration of an electric powertrain of a first comparative example. Fig. 5 is a cross-sectional view showing a schematic configuration of an electric powertrain of a second comparative example.

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0009] 1 is a cross-sectional view showing a schematic configuration of an electric powertrain 1 according to this embodiment. In this embodiment, the electric powertrain 1 is described as being used as a drive device for a battery electric vehicle (BEV), but the present invention is not limited to this. For example, the electric powertrain 1 can also be used as a rear-wheel drive device for a four-wheel drive hybrid electric vehicle (HEV), in which the front wheels are driven by an internal combustion engine and an electric motor, and the rear wheels are driven by an electric motor.

[0010] The electric powertrain 1 includes an electric motor 2 and a gear mechanism 3. The electric motor 2 is accommodated in a first recessed housing portion 4A provided in a motor housing 4, and the gear mechanism 3 is accommodated in a second recessed housing portion 5A provided in a gear case 5. The motor housing 4 and the gear case 5 are fastened together with bolts or the like (not shown) so that the openings of the first housing portion 4A and the second housing portion 5A face each other and close each other's openings. In other words, by fastening the motor housing 4 and the gear case 5 together, a space is defined therein that combines the first housing portion 4A and the second housing portion 5A, and the electric motor 2 and the gear mechanism 3 are accommodated within this space.

[0011] The electric motor 2 includes a rotor 10 and a stator 11. The rotor 10 is fixedly supported by a first rotating shaft 6. The stator 11 is fixedly supported in a first housing portion 4A. A first gear 20A is also fixedly supported by the first rotating shaft 6. In other words, the first rotating shaft 6 serves as both the rotor shaft and the rotating shaft of the first gear 20A.

[0012] The first rotating shaft 6 has an end on the electric motor 2 side rotatably supported by the motor housing 4 via a first bearing 30, and an end on the gear mechanism 3 side rotatably supported by the gear case 5 via a second bearing 31. The portion near the end on the electric motor 2 side is hollow, and rotor shaft fixing bolts 12 are disposed therein. Note that the method of fixing the first rotating shaft 6 with the rotor shaft fixing bolts 12 is merely an example, and other methods may be used.

[0013] A through hole is provided in the motor housing 4 at a location facing the end of the first rotating shaft 6 on the electric motor 2 side, and the rotor shaft fixing bolt 12 is inserted through this through hole. After the rotor shaft fixing bolt 12 is inserted, this through hole is closed with a lid 15. Another through hole is provided in the motor housing 4 at a location facing the end of the first rotating shaft 6 on the gear mechanism 3 side, and this through hole is closed with a lid 16. Note that this through hole and the lid 16 are not essential components.

[0014] The gear mechanism 3 includes a first rotating shaft 6, a first gear 20A fixedly supported on the first rotating shaft 6, a second rotating shaft 7, a second gear 20B fixedly supported on the second rotating shaft 7, a third gear 21A fixedly supported on the second rotating shaft 7, a differential device 22, and a fourth gear 21B fixedly supported on the differential device 22. The first gear 20A and the second gear 20B, and the third gear 21A and the fourth gear 21B, mesh with each other. Note that in this embodiment, the first to fourth gears are helical gears, but this is not limiting.

[0015] The differential device 22 includes a third rotating shaft 8, which is an output shaft connected to a drive shaft (not shown). The fourth gear 21B is a so-called final gear, which is fixed to the outer periphery of the case of the differential device 22. The second rotating shaft 7 and the third rotating shaft 8 are disposed parallel to the first rotating shaft 6.

[0016] The second rotating shaft 7 has an end on the gear case 5 side fixedly supported by the gear case 5 via a third bearing 32, and an end on the motor housing 4 side fixedly supported by the motor housing 4 via a fourth bearing 33 and a bearing support member 9. The bearing support member 9 will be described later.

[0017] One end of the third rotating shaft 8 is fixedly supported by the gear case 5 via a fifth bearing 34 , and the other end is fixedly supported by the gear case 5 via a sixth bearing 35 .

[0018] In this embodiment, as described above, there are three parallel shafts, the first rotation shaft 6 to the third rotation shaft 8, but this is not limitative and there may be three or more parallel shafts. For example, a configuration may be adopted in which a gear and its rotation shaft are added between the third gear 21A and the fourth gear 21B.

[0019] Next, the bearing support member 9 will be described with reference to Figures 1 to 3. Figures 2 and 3 are schematic diagrams showing the positional relationship between the second rotating shaft 7, bearing support member 9, stator 11 of the electric motor 2, and third rotating shaft 8 when viewed from direction II in Figure 1 (hereinafter also referred to as axial view). The circle drawn with a dashed line in the figures indicates the outer periphery of the stator 11.

[0020] The bearing support member 9 includes a hollow cylindrical retaining portion 9A that retains the fourth bearing 33, and a flange portion 9B that protrudes from the retaining portion 9A radially outward from the fourth bearing 33 at a portion of the circumference of the fourth bearing 33. The bearing support member 9 is positioned by fixing and supporting the flange portion 9B to the motor housing 4 using a plurality of bolts 14 as fastening members. The plurality of bolts 14 are inserted from the outside of the motor housing 4 through through holes formed in the motor housing 4 and engage with bolt holes 9C formed in the flange portion 9B.

[0021] As shown in Fig. 3, the central axis of the second rotating shaft 7 may be located inside the outer periphery of the stator 11 when viewed in the axial direction, but it is preferable that the central axis of the second rotating shaft 7 be located outside the outer periphery of the stator 11 as shown in Fig. 2. The reason for this is as follows.

[0022] When the center axis of the second rotating shaft 7 is located inside the outer periphery of the stator 11, the range in which the flange portion 9B can be provided is less than half of the outer periphery of the retaining portion 9A. However, when the flange portion 9B is located outside the periphery, the range can be more than half of the outer periphery of the retaining portion 9A. If the flange portion 9B is less than half of the outer periphery of the retaining portion 9A, the center axis of the second rotating shaft 7 is located on the opposite side of the bolt hole 9C from the line connecting both ends of the flange portion 9B in the axial direction. In other words, the fastening portion between the flange portion 9B and the motor housing 4 is offset from the center axis of the second rotating shaft 7. In contrast, if the flange portion 9B is more than half of the outer periphery of the retaining portion 9A, the center axis of the second rotating shaft 7 is located on the same side as the bolt hole 9C from the line connecting both ends of the flange portion 9B in the axial direction. In other words, the center axis of the second rotating shaft 7 is surrounded by the fastening portion between the flange portion 9B and the motor housing 4.

[0023] Furthermore, the longer the circumferential length of the flange portion 9B, the larger the contact area between the motor housing 4 and the flange portion 9B, and the more bolts 14 can be used.

[0024] From the above, a configuration in which the central axis of the second rotating shaft 7 is positioned outside the outer periphery of the stator 11 has higher support rigidity for supporting the fourth bearing 33 than a configuration in which the central axis is positioned inside.

[0025] Next, an example of an assembly process for the electric powertrain 1 configured as described above will be described.

[0026] In the first step, the stator 11 and the first bearing 30 are fixed to the motor housing 4. In this embodiment, the bearing that supports the end of the second rotating shaft 7 facing the motor housing is fixed and supported using a bearing support member 9 that is separate from the motor housing 4. In other words, in this step, the motor housing 4 does not have a structure for holding the bearing that supports the end of the second rotating shaft facing the motor housing. Therefore, the stator 11 can be inserted into the first accommodating portion 4A of the motor housing 4 regardless of the axial distance between the first rotating shaft 6 and the second rotating shaft 7. In other words, by reducing the axial distance between the first rotating shaft 6 and the second rotating shaft 7, the device can be made more compact.

[0027] In the second step, the first rotating shaft 6, to which the rotor 10 and first gear 20A are fixed, is inserted into the inside of the stator 11 from the side opposite the first bearing 30, and the end is inserted into the first bearing 30 and fixed with the rotor shaft fixing bolts 12. This completes the motor-side assembly.

[0028] In the third step, the end of the third rotating shaft 8 is fixed to the fifth bearing 34 , thereby assembling the differential device 22 to the gear case 5 .

[0029] In the fourth step, the third gear 21A is meshed with the fourth gear 21B while one end of the second rotating shaft 7 is fixed to the third bearing 32, thereby assembling the second rotating shaft 7 to which the second gear 20B and the third gear 21A are fixed to the gear case 5.

[0030] In the fifth step, the fourth bearing 33 and the bearing support member 9 are attached to the other end of the second rotating shaft 7. This completes the gear-side assembly.

[0031] In a sixth step, the motor-side assembly and the gear-side assembly are fastened together while the first gear 20A and the second gear 20B are meshed with each other and the end of the first rotating shaft 6 is fixed to the second bearing 31. Furthermore, the bearing support member 9 is fixed to the motor housing 4 from the outside of the motor housing 4 using a plurality of bolts 14.

[0032] With the above steps, the electric powertrain 1 is completed.

[0033] Next, a description will be given of the effects of configuring the electric powertrain 1 as described above. Figures 4 and 5 are cross-sectional views showing the schematic configurations of a first comparative example and a second comparative example, respectively, of the electric powertrain 1. Both the first comparative example and the second comparative example are known electric powertrains.

[0034] In the configuration of the first comparative example, the housing of the motor housing MH opens in the opposite direction to the gear case GC, and one end of the rotor shaft RS is fixedly supported by the motor housing MH, while the other end is fixedly supported by a rotor cover RC that closes the opening of the housing. An extension shaft ES, to which a gear is fixed, is coaxially connected to one end of the rotor shaft RS. One end of the extension shaft ES is fixedly supported by the gear case GC, and the other end is fixedly supported by the motor housing MH. The gear mechanism 3 is housed in the space defined by fastening the motor housing MH and the gear case GC together. In other words, the housing of the electric powertrain of the first comparative example is composed of three members: the motor housing MH, the rotor cover RC, and the gear case GC.

[0035] In contrast, the housing of the electric powertrain 1 according to this embodiment is composed of two components, the motor housing 4 and the gear case 5, and therefore, compared to the configuration of the first comparative example, the number of components can be reduced, making it smaller, lighter, and less expensive.

[0036] Furthermore, in the configuration of the first comparative example, the shaft corresponding to the first rotating shaft 6 in the configuration of this embodiment is composed of two members, the rotor shaft RS and the extension shaft ES, and it is necessary to provide a bearing holder for the rotor shaft RS and a bearing holder for the extension shaft ES adjacent to each other on the same axis in the motor housing MH. In contrast, in the configuration of this embodiment, it is sufficient to provide bearing holders on both ends of the first rotating shaft 6, which simplifies the shape of the motor housing 4 and simplifies the assembly process compared to the configuration of the first comparative example.

[0037] In the configuration of the second comparative example, the accommodation portion of the motor housing MH opens toward the gear case GC, and the accommodation portion of the gear case GC opens toward the motor housing MH. However, a center plate CP is interposed between the motor housing MH and the gear case GC, and one end of the second rotating shaft 7 and the third rotating shaft 8 are fixedly supported by the gear case GC and the other end is fixedly supported by the center plate CP. In other words, the housing of the electric powertrain of the second comparative example is composed of three members: the motor housing MH, the center plate CP, and the gear case GC. In contrast, the housing of the electric powertrain 1 according to this embodiment is composed of two members: the motor housing 4 and the gear case 5. Therefore, compared to the configuration of the second comparative example, the number of parts is reduced, resulting in a smaller size, lighter weight, and lower costs.

[0038] Furthermore, in the configuration of the second comparative example, positioning is required when assembling the motor housing MH and the center plate CP and when assembling the center plate CP and the gear case GC, whereas in the configuration of this embodiment, positioning is required only when assembling the motor housing 4 and the gear case 5. In other words, with the configuration of this embodiment, the assembly process can be simplified compared to the configuration of the second comparative example.

[0039] As described above, this embodiment provides an electric powertrain 1 including an electric motor 2, a first rotating shaft 6 that also serves as a rotor shaft of the electric motor 2 and a rotational shaft of a gear, and a gear mechanism 3 that has multiple rotating shafts 7 and 8 parallel to the first rotating shaft 6, in which a gear of the nth rotating shaft meshes with a gear of the (n+1)th rotating shaft. The electric powertrain 1 also includes a motor housing 4 that has a recessed first accommodating portion 4A and a gear case 5 that has a recessed second accommodating portion 5A. The motor housing 4 and the gear case 5 are fastened together such that the opening of the first accommodating portion 4A faces the opening of the second accommodating portion 5A, and the electric motor 2 and the gear mechanism 3 are accommodated in a space defined by the fastening of the motor housing 4 and the gear case 5. This simplifies the configuration of the electric powertrain 1, reduces the number of parts, and makes the electric powertrain 1 more compact.

[0040] In this embodiment, one end of the first rotating shaft 6 is rotatably supported by the motor housing 4 via a first bearing 30, and the other end is rotatably supported by the gear case 5 via a second bearing 31. One end of the second rotating shaft 7 is rotatably supported by the motor housing 4 via a bearing support member 9, and the other end is rotatably supported by the gear case 5 via a third bearing 32. One end of the third rotating shaft 8 is rotatably supported by the motor housing 4 via a sixth bearing 35, and the other end is rotatably supported by the gear case 5 via a fifth bearing 34. When there are three or more rotating shafts, the support configuration for the rotating shafts after the third rotating shaft 8 is the same as that for the third rotating shaft 8. In this way, by using the bearing support member 9 to support the second rotating shaft 7 on the motor housing 4 side, the support portion of the second rotating shaft 7 does not get in the way when inserting the stator 11 into the accommodation portion (first accommodation portion) 4A of the motor housing 4.

[0041] In this embodiment, the bearing support member 9 includes a retaining portion 9A that retains the fourth bearing 33, and a flange portion 9B that protrudes from the retaining portion 9A radially outward from the fourth bearing 33 at a portion of the circumference of the fourth bearing 33. The fourth bearing 33 is positioned by being fixed and supported by the flange portion 9B on the motor housing 4. By providing the flange portion 9B in this manner, the retaining portion 9A can be fixed at a location away from the outer periphery of the retaining portion 9A, and therefore the axial distance between the first rotating shaft 6 and the second rotating shaft 7 can be reduced.

[0042] In this embodiment, the flange portion 9B is fixed to and supported by the motor housing 4 with bolts 14 attached from the outside of the motor housing 4. This makes it easy to fix the bearing support member 9 to the motor housing 4 during the assembly process.

[0043] In this embodiment, when viewed in the axial direction of the first rotating shaft 6, the central axis of the second rotating shaft 7 is disposed outside the outer periphery of the stator 11. This increases the fastening rigidity of the bearing support member 9 to the motor housing 4, thereby improving the support rigidity of the second rotating shaft 7.

[0044] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

Claims

1. An electric powertrain comprising: an electric motor; a first rotation shaft that also serves as the rotation shaft of the rotor shaft of the electric motor and the gear; and a gear mechanism having a plurality of rotation shafts parallel to the first rotation shaft, wherein the gear of the nth rotation shaft meshes with the gear of the (n+1)th rotation shaft; a motor housing having a first concave accommodating portion; and a gear case having a second concave accommodating portion, wherein the motor housing and the gear case are fastened together such that the opening of the first accommodating portion faces the opening of the second accommodating portion, and the electric motor and the gear mechanism are accommodated within a space defined by the fastening of the motor housing and the gear case.

2. An electric powertrain as claimed in claim 1, wherein one end of the first rotating shaft is rotatably supported by the motor housing via a first bearing, and the other end is rotatably supported by the gear case via a second bearing; one end of the second rotating shaft is rotatably supported by the motor housing via a bearing support member, and the other end is rotatably supported by the gear case via a third bearing; and each of the third and subsequent rotating shafts has one end rotatably supported by the motor housing via a bearing, and the other end is rotatably supported by the gear case via a bearing.

3. An electric powertrain as claimed in claim 2, wherein the bearing support member comprises a retaining portion that retains the bearing, and a flange portion that protrudes from the retaining portion radially outward of the bearing at a portion of the circumference of the bearing, and the flange portion is fixedly supported by the motor housing to position the bearing.

4. An electric powertrain according to claim 3, wherein the flange portion is fixedly supported on the motor housing by a fastening member attached from the outside of the motor housing.

5. An electric powertrain according to claim 4, wherein, when viewed in the axial direction of the rotor shaft, the central axis of the second rotating shaft is disposed outside the outer periphery of the stator.

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