Vehicle drive systems

Abstract

This technology provides a way to suppress the decrease in strength of a transmission shaft that has a channel through which lubricating fluid flows. [Solution] The vehicle drive system comprises a rotating electric machine having a hollow output shaft, a reduction gear connected to the output shaft, a differential gear that distributes the driving force of the rotating electric machine transmitted via the reduction gear to a pair of drive wheels, and a transmission shaft that extends through a through hole in the output shaft along the axial direction of the rotating electric machine and is spline-fitted to a side gear of the differential gear by a spline provided on the outer circumferential surface of one end of the transmission shaft. The transmission shaft has a first flow path that extends along the axial direction, and a second flow path that opens at one end to the first flow path and at the other end to the outer circumferential surface of the transmission shaft. The other end of the second flow path is located at the tooth root portion of the spline.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a drive device for a vehicle.

Background Art

[0002] Patent Document 1 discloses a drive device for a vehicle in which a rotary electric machine, a speed reducer, and a differential gear are arranged coaxially. In this type of drive device, the output shaft of the rotary electric machine is hollow, and a transmission shaft extends along the axial direction of the rotary electric machine within the through hole of the output shaft. One end of the transmission shaft is connected to the differential gear, and the other end of the transmission shaft is connected to the drive shaft.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A flow path through which a lubricating fluid for lubricating a lubrication target part such as a speed reducer flows is provided in the transmission shaft. The flow path provided in the transmission shaft has a flow path extending along the axial direction and a flow path extending radially from the flow path and opening to the outer peripheral surface. The lubricating fluid flowing out from the flow path extending radially is supplied to the lubrication target part.

[0005] At the part where the flow path extending radially in the transmission shaft opens to the outer peripheral surface, a decrease in the strength of the transmission shaft is a concern. This specification provides a technology for suppressing a decrease in the strength of a transmission shaft provided with a flow path through which a lubricating fluid flows.

Means for Solving the Problems

[0006] The vehicle drive system disclosed herein may include a rotating electric machine having a hollow output shaft, a reduction gear connected to the output shaft, a differential gear that distributes the driving force of the rotating electric machine transmitted via the reduction gear to a pair of drive wheels, and a transmission shaft that extends through a through-hole of the output shaft along the axial direction of the rotating electric machine and is spline-fitted to a side gear of the differential gear by a spline provided on the outer circumferential surface of one end. The transmission shaft may have a first flow path extending along the axial direction and a second flow path that opens at one end to the first flow path and at the other end to the outer circumferential surface of the transmission shaft. The other end of the second flow path may be located at the tooth root of the spline.

[0007] When the transmission shaft rotates, the load applied to the splined portion of the transmission shaft is concentrated on the gear portion (i.e., the convex portion) of the spline, while not concentrated on the tooth root portion. In the above-mentioned vehicle drive system, a second flow path is opened at the tooth root portion of the spline, where no large load is applied. Therefore, a second flow path can be provided in the transmission shaft while suppressing a decrease in the strength of the transmission shaft. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram provides a schematic overview of the vehicle's configuration. [Figure 2] This is a diagram showing the skeleton of the drive system installed in the vehicle. [Figure 3] This figure schematically shows a cross-sectional view of the main part near the spline fitting portion of the transmission shaft and differential gear in one embodiment. [Figure 4] This diagram schematically shows a perspective view of the end of the transmission shaft that is connected to the differential gear. [Modes for carrying out the invention]

[0009] The following describes the drive system mounted on the vehicle, referring to the drawings. Here, the directions in some of the drawings correspond to the vehicle's direction. Direction FR indicates the front in the vehicle's longitudinal direction, and direction RR indicates the rear in the vehicle's longitudinal direction. Direction LH indicates the left in the vehicle's lateral direction, and direction RH indicates the right in the vehicle's lateral direction. Direction UP indicates the upward in the vehicle's vertical direction, and direction DW indicates the downward in the vehicle's vertical direction.

[0010] Figure 1 shows the configuration of Vehicle 1. Vehicle 1 is a vehicle that has at least a rotating electric machine as one of its drive sources, and may be, for example, an electric vehicle, a hybrid vehicle, or a fuel cell vehicle.

[0011] Vehicle 1 comprises a battery pack 2 mounted beneath the floor and a pair of drive units 3. The battery pack 2 supplies power to each of the pair of drive units 3. One of the pair of drive units 3 uses the supplied power to drive the front wheels FW, and the other of the pair of drive units 3 uses the supplied power to drive the rear wheels RW. Although vehicle 1 is exemplified as a four-wheel drive vehicle, it may also be a two-wheel drive vehicle equipped with only one of the pair of drive units 3. The pair of drive units 3 have a common structure. Hereafter, the pair of drive units 3 will be described without distinction.

[0012] The drive unit 3 comprises a rotating electric machine 4, a transmission device 5, a power control unit 6, and a case 7. The rotating electric machine 4, the transmission device 5, and the power control unit 6 are housed within the case 7. The power control unit 6 is positioned adjacent to the rotating electric machine 4 and the transmission device 5 in the longitudinal direction of the vehicle (rear in this example). The power control unit 6 converts the power supplied from the battery pack 2 from direct current to alternating current and supplies it to the rotating electric machine 4. The rotating electric machine 4 generates driving force based on the alternating current power supplied from the power control unit 6. The transmission device 5 amplifies the driving force generated by the rotating electric machine 4 into torque and then distributes it to the left and right wheels.

[0013] The rotating electric machine 4 and the transmission device 5 are arranged coaxially. As a result, the vertical size of the case 7 housing the rotating electric machine 4 and the transmission device 5 is reduced. Consequently, the case 7 is positioned so that, when viewed from the left or right direction of the vehicle, it fits within the range of the corresponding wheels FW and RW. As a result, for example, at the front of the vehicle 1, the degree of freedom in arranging various mechanical components, such as the radiator and the air conditioning control system, is improved, and a larger user space can be secured. Furthermore, at the rear of the vehicle 1, for example, a larger trunk space can be secured, or the range of the rear seat reclining angle can be widened.

[0014] Figure 2 shows a skeleton diagram of the drive unit 3, including the rotating electric machine 4 and the transmission device 5 housed in the case 7. In this example, the rotating electric machine 4 is located on the right side of the case 7, and the transmission device 5 is located on the left side of the case 7. Alternatively, the transmission device 5 may be located on the right side of the case 7, and the rotating electric machine 4 on the left side of the case 7. In the following explanation, for convenience, the names of the components may include left-right directions, but such designations do not limit the position of the components.

[0015] The rotating electric machine 4 comprises a stator core 12, a rotor 14, and an output shaft 16. The stator core 12 is fixed to the case 7. The rotor 14 is supported by the case 7 so as to be rotatable around the rotation axis of the rotating electric machine 4. The output shaft 16 is connected to the rotor 14 and rotates together with the rotor 14. The output shaft 16 is hollow and has a through hole 18 that extends along the rotation axis of the rotating electric machine 10.

[0016] The transmission device 5 comprises a reduction gear 20 and a differential gear 30. The reduction gear 20 reduces the rotation of the output shaft 16 of the rotating electric machine 4. The differential gear 30 distributes the driving force of the rotating electric machine 4 transmitted via the reduction gear 20 to the left and right wheels 8 and 9. The rotating electric machine 4, the reduction gear 20, and the differential gear 30 are arranged coaxially. Note that the configuration of the transmission device 5 described below is just one example, and other types of configurations can be adopted as appropriate.

[0017] The reduction gear 20 comprises a sun gear 22, a plurality of stepped pinion gears 24, a ring gear 26, and a carrier 28. The sun gear 22 is connected to the output shaft 16 of the rotating electric machine 4 and rotates together with the output shaft 16. Each of the plurality of stepped pinion gears 24 has a large-diameter pinion gear P1 and a small-diameter pinion gear P2 which is smaller in diameter than the large-diameter pinion gear P1. The large-diameter pinion gear P1 meshes with the sun gear 22. The small-diameter pinion gear P2 meshes with the ring gear 26. The ring gear 26 is fixed to the case 7. The carrier 28 rotatably supports each of the plurality of stepped pinion gears 24. Thus, in the reduction gear 20, the sun gear 22 is the input element, the ring gear 26 is the reaction element, and the carrier 28 is the output element.

[0018] The differential gear 30 comprises a differential case 31 and a differential gear mechanism 32. The differential case 31 is supported by the case 7 so as to be rotatable around the rotation axis of the rotating electric machine 4. The differential case 31 is connected to the carrier 28 of the reduction gear 20 and rotates together with the carrier 28. The differential gear mechanism 32 is housed inside the differential case 31.

[0019] The differential gear mechanism 32 comprises a pinion shaft 33, a pair of differential pinion gears 34 and 35, a right-side gear 36, and a left-side gear 37.

[0020] The pinion shaft 33 is connected to the differential case 31 and rotates integrally with the differential case 31. The pinion shaft 33 extends in the differential case 31 along a direction orthogonal to the rotational axis direction of the rotating electric machine 4. Each of the pair of differential pinion gears 34, 35 is supported by the pinion shaft 33 so as to be rotatable about the axis of the pinion shaft 33. The right side gear 36 is a member that outputs driving force to the right wheel 8 and meshes with each of the pair of differential pinion gears 34, 35. The left side gear 37 is a member that outputs driving force to the left wheel 9 and meshes with each of the pair of differential pinion gears 34, 35.

[0021] The drive device 3 further includes a transmission shaft 40, a right drive shaft 50 connected to the right wheel 8, and a left drive shaft 60 connected to the left wheel 9.

[0022] The transmission shaft 40 extends in the through hole 18 of the output shaft 16 along the rotational axis direction of the rotating electric machine 4. The left end portion of the transmission shaft 40 is connected to the right side gear 36 of the differential gear 30, and the right end portion of the transmission shaft 40 is connected to the right drive shaft 50.

[0023] The right drive shaft 50 has a drive shaft inboard 52, an intermediate drive shaft 54, and a drive shaft outboard 56. The drive shaft inboard 52 is the left end portion on the side inserted into the case 7 among both end portions in the axial direction of the right drive shaft 50 and refers to the portion from the constant velocity joint to the left end face. The drive shaft outboard 56 is the right end portion on the side connected to the right wheel 8 among both end portions in the axial direction of the right drive shaft 50 and refers to the portion from the constant velocity joint to the right end face. The drive shaft inboard 52 of the right drive shaft 50 is connected to the right side gear 36 of the differential gear 30 via the transmission shaft 40. The driving force output by the right side gear 36 is transmitted to the right drive shaft 50 via the transmission shaft 40.

[0024] The left drive shaft 60 has a drive shaft inboard 62, an intermediate drive shaft 64, and a drive shaft outboard 66. The drive shaft inboard 62 is the right end of the left drive shaft 60 in the axial direction that is inserted into the case 7, and refers to the portion from the constant velocity joint to the right end face. The drive shaft outboard 66 is the left end of the left drive shaft 60 in the axial direction that is connected to the left wheel 9, and refers to the portion from the constant velocity joint to the left end face. The drive shaft inboard 62 of the left drive shaft 60 is connected to the left side gear 37 of the differential gear 30. The driving force output by the left side gear 37 is transmitted directly to the left drive shaft 60.

[0025] Figure 3 shows a cross-sectional view of the vicinity of the spline fitting portion 70 where the transmission shaft 40 and the right side gear 36 of the differential gear 30 are spline fitted. The left end of the transmission shaft 40 is spline fitted with the right side gear 36. The left end of the transmission shaft 40 passes through the right side gear 36, and the left end face 41 of the transmission shaft 40 faces the pinion shaft 33. The drive shaft inboard 62 of the left drive shaft 60 is spline fitted with the left side gear 37. The drive shaft inboard 62 passes through the left side gear 37, and the right end face 61 of the drive shaft inboard 62 faces the pinion shaft 33.

[0026] The spline fitting portion 70 of the left end of the transmission shaft 40 and the right side gear 36 will be described in detail. Outer spline teeth 43 are formed on the outer circumferential surface 42 of the left end of the transmission shaft 40. Inner spline teeth 39 are formed on the inner circumferential surface 38 of the right side gear 36. The transmission shaft 40 and the right side gear 36 are spline fitted by the outer spline teeth 43 of the transmission shaft 40 and the inner spline teeth 39 of the right side gear 36. The spline fitting portion 70 is the part formed by the outer spline teeth 43 of the transmission shaft 40 and the inner spline teeth 39 of the right side gear 36, and refers to the part in which at least one of the outer spline teeth 43 and the inner spline teeth 39 is present.

[0027] In the drive unit 3, a passage for lubricating fluid to lubricate and cool the parts to be lubricated, such as the rotating electric machine 4 and the transmission device 5, is provided in the transmission shaft 40. The passage in the transmission shaft 40 is configured to supply lubricating fluid to the parts to be lubricated. The lubricating fluid is drawn in by a pump or the like from a reservoir located at the bottom of the case 7, cooled by a heat exchanger or the like, and then supplied to the passage in the transmission shaft 40.

[0028] The following describes in detail the passage that supplies lubricating fluid to the reduction gear 20, which is one of the passages provided in the transmission shaft 40. As mentioned above, a portion of the reduction gear 20 is located between the rotating electric machine 4 and the differential gear 30 in the axial direction of the rotating electric machine 4. The passage described below is a passage that supplies lubricating fluid to the space between the rotating electric machine 4 and the differential gear 30.

[0029] The transmission shaft 40 is provided with a first flow path 82 that extends along the axial direction of the transmission shaft 40. The arrows indicated within the first flow path 82 indicate the direction of flow of the lubricating fluid within the first flow path 82. The first flow path 82 opens to the left end face 41 of the transmission shaft 40. As a result, a portion of the lubricating fluid flowing through the first flow path 82 is supplied to the internal space of the differential gear 30, lubricating each of the gears 34, 35, 36, and 37.

[0030] The transmission shaft 40 is further provided with a second flow path 84 that extends radially from the first flow path 82 along the transmission shaft 40. One end of the second flow path 84 opens into the first flow path 82, and the other end opens into the outer circumferential surface 42 of the transmission shaft 40. The second flow path 84 opens at the spline fitting portion 70 on the outer circumferential surface 42 of the transmission shaft 40.

[0031] As shown in Figure 4, some of the external spline teeth 43 provided on the outer circumferential surface 42 of the transmission shaft 40 are missing teeth. As a result, an enlarged tooth root portion 44 is formed on the outer circumferential surface 42 of the transmission shaft 40, where the adjacent tooth root portions are connected due to the missing teeth of the external spline teeth 43.

[0032] The enlarged tooth root portion 44 is provided on a portion of the spline fitting portion 70's axial length. That is, the enlarged tooth root portion 44 does not extend from one end edge to the other end edge of the spline fitting portion 70 in the axial direction, i.e., to the left end face 41 of the transmission shaft 40. The second flow channel 84 opens at the end of the enlarged tooth root portion 44 that is closer to the left end face 41. In other words, the enlarged tooth root portion 44 extends from the position where the second flow channel 84 opens toward the end edge of the spline fitting portion 70 toward the opposite side of the left end face 41. In this example, the enlarged tooth root portion 44 extends to the outside of the differential case 31 of the differential gear 30 (see Figure 3). In this example, the enlarged tooth root portion 44 is formed by missing teeth on one of the outer spline teeth 43. Alternatively, the enlarged root portion 44 may be formed by connecting three or more root portions, with some of each of the multiple external spline teeth 43 arranged circumferentially on the transmission shaft 40 being missing teeth.

[0033] The spline fitting portion 70 has a passage through which lubricating fluid flows along the axial direction of the transmission shaft 40. This passage in the spline fitting portion 70 is referred to as the third passage. This passage is formed by the gap between the outer spline teeth 43 and the inner spline teeth 39 that constitute the spline fitting portion 70. In particular, the spline fitting portion 70 has an enlarged tooth root portion 44, which forms a passage with an enlarged cross-sectional area.

[0034] Furthermore, as shown in Figures 3 and 4, the spline fitting portion 70 is provided with a sealing portion 72. The sealing portion 72 has a groove 45 extending along the circumferential direction of the transmission shaft 40 and an annular sealing member 46 attached to the groove 45. The sealing portion 72 is positioned between the location where the second flow path 84 is formed in the spline fitting portion 70 and the left end face 41. The sealing member 46 seals the gap between the outer spline teeth 43 and the inner spline teeth 39, preventing lubricating fluid from flowing axially beyond the sealing member 46. The sealing member 46 is not particularly limited, but may be an O-ring made of a material such as resin.

[0035] The lubricating fluid that flows out from the second flow path 84 into the spline fitting portion 70 flows through the flow path formed in the spline fitting portion 70. Since a sealing portion 72 is provided in the spline fitting portion 70, the lubricating fluid that flows out into the spline fitting portion 70 flows toward the opposite side from the left end face 41 of the transmission shaft 40. In particular, since there is a flow path whose cross-sectional area is enlarged by the enlarged tooth root portion 44, the lubricating fluid that flows out into the spline fitting portion 70 can smoothly flow out of the differential case 31 of the differential gear 30 beyond the edge of the spline fitting portion 70. As a result, lubricating fluid is supplied to the space between the rotating electric machine 4 and the differential gear 30.

[0036] For example, in order to supply lubricating fluid to the space between the rotating electric machine 4 and the differential gear 30, it is conceivable to provide a radial flow channel in a part of the transmission shaft 40 located directly below that space, that is, in a part different from the part where the spline fitting portion 70 is provided. However, when the transmission shaft 40 rotates, the maximum shear stress applied to the transmission shaft 40 occurs on the outer surface of the part with the largest diameter. If a radial flow channel is provided in such a part, there is a concern that the strength of the transmission shaft 40 will decrease. On the other hand, in the above example, the second flow channel 84 is provided in the spline fitting portion 70. When the transmission shaft 40 rotates, a large load is applied to the gear portion (i.e., the convex portion) of the outer spline teeth 43, while a large load is not applied to the tooth root portion of the outer spline teeth 43. In the above example, the second flow channel 84 opens to the tooth root portion of the outer spline teeth 43, where a large load is not applied. Therefore, even if a second flow path 84 is provided in the transmission shaft 40, the reduction in the strength of the transmission shaft 40 can be suppressed. Furthermore, because the reduction in the strength of the transmission shaft 40 is suppressed, the diameter of the transmission shaft 40 can be reduced.

[0037] The embodiments disclosed herein are summarized below. Note that the technical elements described below are independent technical elements that exhibit technical usefulness individually or in various combinations.

[0038] (Aspect 1) A vehicle drive system comprising: a rotating electric machine having a hollow output shaft; a reduction gear connected to the output shaft; a differential gear that distributes the driving force of the rotating electric machine transmitted via the reduction gear to a pair of drive wheels; and a transmission shaft that extends through a through hole in the output shaft along the axial direction of the rotating electric machine and is spline-fitted to a side gear of the differential gear by a spline provided on the outer circumferential surface of one end thereof, wherein the transmission shaft has a first flow path extending along the axial direction and a second flow path that opens at one end to the first flow path and at the other end to the outer circumferential surface of the transmission shaft, the other end of the second flow path being located at the tooth root portion of the spline.

[0039] (Aspect 2) Vehicle drive device according to Embodiment 1, wherein at least a portion of the reduction gear is positioned between the rotating electric machine and the differential gear in the axial direction, and the spline fitting portion in which the transmission shaft and the side gear are spline fitted has a third passage, and the third passage is at least a portion of a passage that allows the lubricating fluid that has flowed out from the other end of the second passage to flow in the axial direction toward the side where at least a portion of the reduction gear is located and to lead it out of the case of the differential gear.

[0040] (Aspect 3) The vehicle drive device according to embodiment 2, wherein the spline fitting portion has a sealing portion that seals the third flow path, and the sealing portion is located in the axial direction opposite to the side where at least a part of the reduction gear is located, with respect to the position of the other end of the second flow path.

[0041] (Aspect 4) A vehicle drive device according to any one of embodiments 1 to 3, wherein a portion of the spline provided on the outer circumferential surface of the transmission shaft is missing teeth, and the other end of the second flow path is located in an enlarged tooth root portion where adjacent tooth root portions are connected by the missing teeth.

[0042] (Appendix 5) The vehicle drive device according to embodiment 4, wherein the enlarged tooth root portion is positioned on the side of the axial direction where at least a part of the reduction gear is located relative to the position of the other end of the second flow path.

[0043] Although embodiments have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical usefulness in itself. [Explanation of Symbols]

[0044] 3: Drive unit, 4: Rotating electric machine, 5: Transmission unit, 10: Rotating electric machine, 16: Output shaft, 18: Through hole, 20: Reducer, 30: Differential gear, 31: Differential case, 32: Differential gear mechanism, 33: Pinion shaft, 34, 35: Differential pinion gear, 36: Right side gear, 37: Left side gear, 40: Transmission shaft, 82: First flow path, 84: Second flow path

Claims

1. A rotating electric machine having a hollow output shaft, A reduction gear connected to the output shaft, A differential gear that distributes the driving force of the rotating electric machine transmitted via the reduction gear to a pair of drive wheels, A transmission shaft extends through the through-hole of the output shaft along the axial direction of the rotating electric machine, and is spline-fitted to the side gear of the differential gear by a spline provided on the outer circumferential surface of one end thereof, It is equipped with, The aforementioned transmission shaft is A first flow path extending along the axial direction, It has a second flow channel, one end of which opens into the first flow channel and the other end of which opens into the outer circumferential surface of the transmission shaft, The other end of the second flow path is located at the tooth root portion of the spline, in a vehicle drive device.

2. At least a portion of the reduction gear is positioned between the rotating electric machine and the differential gear in the axial direction. The spline fitting portion in which the transmission shaft and the side gear are spline fitted has a third flow path, The vehicle drive device according to claim 1, wherein the third flow path is at least part of a flow path that causes the lubricating fluid flowing out from the other end of the second flow path to flow in the axial direction toward the side where at least part of the reduction gear is located and to lead it out of the case of the differential gear.

3. The spline fitting portion has a sealing portion that seals the third flow path, The vehicle drive device according to claim 2, wherein the sealing portion is located on the opposite side in the axial direction from the side where at least a part of the reduction gear is located, with respect to the position of the other end of the second flow path.

4. A portion of the spline provided on the outer surface of the transmission shaft is missing teeth. The other end of the second flow path is located in an enlarged tooth root portion where adjacent tooth root portions are connected by the missing teeth, as described in claim 1.

5. The vehicle drive device according to claim 4, wherein the enlarged tooth root portion is positioned on the side of the other end of the second flow path that contains at least a portion of the reduction gear in the axial direction.

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