Power transmission device

Abstract

The case needed to be strong enough to withstand the thrust force acting on the ring gear, which could have led to an increase in the case's size. [Solution] The power transmission device comprises a sun gear fixed to a rotatable shaft, a ring gear coaxially arranged with the sun gear and fixed to a case housing a planetary gear mechanism, planetary gears meshing with the sun gear and the ring gear, and a carrier that rotatably supports the planetary gears, is coaxially arranged with the sun gear, and is rotatably supported relative to the case. The sun gear and the ring gear are each helical gears, and the twist angles of the teeth of the sun gear and the ring gear are set such that the thrust force acting on the sun gear and the thrust force acting on the ring gear are in opposite directions. The device further comprises a load transmission path between the sun gear and the ring gear through which the thrust force acting on the sun gear and the thrust force acting on the ring gear are transmitted, and the load transmission path is configured to include at least a part of the carrier.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a power transmission device including a planetary gear mechanism and a case for housing the planetary gear mechanism.

Background Art

[0002] As one of the power transmission devices, Patent Document 1 discloses a transaxle that transmits the power of an electric motor to an axle via a planetary gear reducer and a differential device. According to Patent Document 1, the planetary gear reducer is a planetary type planetary gear mechanism that uses a sun gear formed on the output shaft of the electric motor as an input element, a ring gear fixed to a case that houses the planetary gear reducer as a reaction element, and a carrier as an output element. The carrier rotatably supports a stepped pinion having a large-diameter pinion meshing with the sun gear and a small-diameter pinion meshing with the ring gear.

[0003] Further, according to Patent Document 1, it is disclosed that each gear constituting the planetary gear reducer is a helical gear.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above planetary gear mechanism, as the ring gear is a helical gear, a thrust force acts on the ring gear. The thrust force acting on the ring gear is received by the case that fixes the ring gear. Therefore, in the case, it is necessary to ensure the strength to receive the thrust force acting on the ring gear, and there is a problem that the size of the case is increased, such as thickening the case. [[ID=四十]]

Means for Solving the Problems

[0006] This specification discloses a power transmission device comprising a planetary gear mechanism and a case housing the planetary gear mechanism. The planetary gear mechanism comprises a sun gear fixed to a rotatable shaft, a ring gear coaxially arranged with the sun gear and fixed to the case, planetary gears meshing with the sun gear and the ring gear, and a carrier rotatably supporting the planetary gears, coaxially arranged with the sun gear and rotatably supported relative to the case. The sun gear and the ring gear are helical gears, respectively. The helix angles of the teeth of the sun gear and the ring gear are set such that the thrust force acting on the sun gear and the thrust force acting on the ring gear are in opposite directions. The power transmission device further includes a load transmission path between the sun gear and the ring gear through which the thrust force acting on the sun gear and the thrust force acting on the ring gear are transmitted, and the load transmission path is configured to include at least a portion of the carrier.

[0007] According to the above configuration, the thrust force acting on the ring gear and the thrust force acting on the sun gear, which is a force opposite to the thrust force acting on the ring gear, are transmitted to the load transmission path. Therefore, at least a portion of the thrust force acting on the ring gear is offset by the thrust force acting on the sun gear. This reduces the strength required of the case to withstand the thrust force acting on the ring gear, thereby suppressing an increase in the size of the case. Furthermore, since the load transmission path is configured to include at least a portion of the carrier, an increase in the number of parts can be suppressed when providing the load transmission path. [Brief explanation of the drawing]

[0008] [Figure 1] A simplified diagram showing the configuration of the power transmission system. [Figure 2] A simplified perspective view showing the exterior of the case and its contents. [Figure 3] A partial cross-sectional view mainly showing the planetary gear mechanism inside the case. [Figure 4] A simplified diagram showing a vehicle equipped with a power transmission system from the side. [Modes for carrying out the invention]

[0009] The main features of the embodiments described below are listed below. The load transmission path may include a first bearing interposed in the path between the sun gear and the carrier, and a second bearing interposed in the path between the ring gear and the carrier. According to the above configuration, by using the first bearing and the second bearing to construct the load transmission path, it is possible to construct the load transmission path while ensuring the smooth rotation of the sun gear and carrier, and while suppressing an increase in the number of parts.

[0010] The carrier may be connected to a differential case housing a differential, and the first bearing may be sandwiched between the sun gear and the differential case. According to the above configuration, in a power transmission system in which the carrier is connected to a differential case housing the differential, the load transmission path can be easily configured using the differential case.

[0011] The load transmission path may include a structure extending from the ring gear, and the second bearing may be sandwiched between the structure and the carrier. According to the above configuration, the load transmission path can be easily constructed by using a structural element.

[0012] The aforementioned structure may be integrally molded with the ring gear. According to the above configuration, by pre-forming the ring gear into a shape that includes the structure, the structure as an independent component can be eliminated, thereby simplifying the assembly of the power transmission device.

[0013] The planetary gear is a stepped pinion having a large-diameter pinion that meshes with the sun gear on one side in the axial direction parallel to the shaft, and a small-diameter pinion that meshes with the ring gear on the other side in the axial direction, and the load transmission path may be provided on the other side of the large-diameter pinion in the axial direction. According to the above configuration, the shape of the planetary gear, which is a stepped pinion, can be effectively utilized to simplify and compact the load transmission path, thereby suppressing the need for a larger case to house the load transmission path.

[0014] The twist angles of the teeth of the sun gear and the ring gear may be set such that the magnitude of the thrust force acting on the sun gear is equal to the magnitude of the thrust force acting on the ring gear. According to the above configuration, the thrust force acting on the sun gear and the thrust force acting on the ring gear can ideally be completely canceled out through the load transmission path, making it possible to reduce the thrust force input from the ring gear to the case to zero.

[0015] An embodiment of this technology will be described with reference to the drawings. Each drawing is for illustrative purposes only, and this embodiment is not limited to what is shown. Furthermore, because each drawing is illustrative, some parts may be omitted.

[0016] Figure 1 shows a simplified skeletal diagram of the power transmission device 10. The case 11 generally houses the motor 20, the planetary gear mechanism 30, and the differential gear 50. The power transmission device 10 includes the planetary gear mechanism 30 and the case 11. The concept of the power transmission device 10 may include, for example, both or either the motor 20 and the differential gear 50.

[0017] The motor 20 includes a cylindrical stator 21 fixed within the case 11, a rotor 22, and a rotor shaft 23 disposed on the radially inner circumferential side of the stator 21. The rotor 22 and the rotor shaft 23 are rotatably supported about the axis Ax. As is known, a coil (not shown) is wound around the stator 21, and when power is supplied to the coil, the rotor 22 and the rotor shaft 23 rotate about the axis Ax due to the action of a magnetic field. The direction parallel to the axis Ax is referred to as the axial direction.

[0018] A sun gear 31 is fixed to one end portion of the rotor shaft 23 in the axial direction. That is, the sun gear 31 is fixed to the rotor shaft 23 and rotates together with the rotor shaft 23. The rotor shaft 23 is an example of a shaft that is rotatable with respect to the case 11.

[0019] The planetary gear mechanism 30 includes a sun gear 31, a ring gear 32, planetary gears 33, and a carrier 34. The ring gear 32 is disposed coaxially with the rotor shaft 23 and is fixed to the case 11. The planetary gears 33 mesh with the sun gear 31 and the ring gear 32 and are capable of自转 and公转. The revolution of the planetary gears 33 is rotation about the axis Ax. In the example of FIG. 1, for the sake of convenience, the planetary gears 33 are shown at respective upper and lower positions sandwiching the axis Ax. The number of planetary gears 33 included in the planetary gear mechanism 30 is not particularly limited and may be, for example, three.

[0020] The carrier 34 rotatably supports the planetary gears 33. Further, the carrier 34 is disposed coaxially with the sun gear 31 and the ring gear 32 and is rotatably supported with respect to the case 11. Thereby, the carrier 34 is configured to be rotatable about the axis Ax together with the revolution of the planetary gears 33. That is, the carrier 34 is a rotating element that extracts the revolution motion of the planetary gears 33 while rotatably supporting each planetary gear 33.

[0021] According to Figure 1, the planetary gear 33 is a stepped pinion having a large-diameter pinion 33a that meshes with the sun gear 31 on one side in the axial direction (left side in Figure 1) and a small-diameter pinion 33b that meshes with the ring gear 32 on the other side in the axial direction (right side in Figure 1). The terms "large diameter" and "small diameter" are relative, and the small-diameter pinion 33b is smaller in diameter than the large-diameter pinion 33a.

[0022] According to Figure 1, the carrier 34 is connected to a differential case 35 that houses the differential 50. The differential case 35 is located axially opposite the motor 20 to the sun gear 31. The differential 50 is also called a differential gear, or simply a differential. Inside the differential case 35, the differential 50 houses left and right side gears 51 and 52 connected to the left and right drive shafts 1 and 2, and pinions 53 and 54 that mesh with the side gears 51 and 52. Both drive shafts 1 and 2 are located on axle Ax, and each is connected to the left and right wheels (not shown) outside the case 11. In the example in Figure 1, the rotor shaft 23 is a hollow cylindrical shape, and the left drive shaft 1 of the drive shafts 1 and 2 passes through the inside of the rotor shaft 23 and exits the case 11.

[0023] Side gear 51 connected to drive shaft 1 and side gear 52 connected to drive shaft 2 are positioned opposite each other on the same axis, and a pinion shaft 55 passes between them in a radial direction perpendicular to the axial direction. The pinion shaft 55 is fixed inside the differential case 35. A pair of radially opposing pinions 53 and 54 are pivotally supported on the pinion shaft 55.

[0024] The power transmission flow in this power transmission device 10 will be briefly explained. The rotational force of the rotor shaft 23 is transmitted to the planetary gear 33 as input from the rotation of the sun gear 31. The planetary gear 33, having received this input, rotates on its own axis and revolves along the inner circumference of the fixed ring gear 32, receiving the reaction force from the ring gear 32. The orbital motion of the planetary gear 33 is output as the rotation of the carrier 34. Inside the differential case 35, which rotates together with the carrier 34, power is transmitted from the pinions 53 and 54 to the side gears 51 and 52, and the drive shafts 1 and 2 rotate as the side gears 51 and 52 are driven.

[0025] Figure 2 shows a simplified perspective view of the exterior of case 11 and its contents. The case 11 houses a motor 20 and a gear group 60 arranged axially. In Figure 2, the configuration including the planetary gear mechanism 30 and the differential gear 50 is collectively shown as the gear group 60. Furthermore, as shown in Figure 2, an inverter 3 may also be housed in case 11. The inverter 3 drives the motor 20 by converting the DC power supplied from an external power source to AC power and then supplying it to the motor 20. The inside of case 11 may be divided into multiple compartments as appropriate to accommodate the various components such as the inverter 3, motor 20, and gear group 60.

[0026] Figure 3 shows a partially cross-sectional view of the planetary gear mechanism 30, which is mainly housed in the first chamber 12 within the case 11. The arrangement and shape of each component shown in Figure 3 do not necessarily match the arrangement and shape of each component shown in Figure 1, but these discrepancies do not pose a problem for understanding this embodiment. For example, one side in the axial direction is the left side in Figure 1, but the right side in Figure 3. The other side in the axial direction is the right side in Figure 1, but the left side in Figure 3. Figure 3 mainly shows the area of ​​the first chamber 12 above axis Ax. According to Figure 3, the space within the case 11 is divided in the axial direction into the first chamber 12 and the second chamber 14 by a partition wall 13, which is part of the case 11. Although omitted in Figure 3, the motor 20 is housed in the second chamber 14.

[0027] The rotor shaft 23 is rotatably supported by bearings 45 fixed to the bulkhead 13. A sun gear 31 is fixed to the end of the rotor shaft 23 that extends beyond the bulkhead 13 into the first chamber 12. The relationship between the planetary gear 33, which is a stepped pinion having a large-diameter pinion 33a and a small-diameter pinion 33b, the sun gear 31, and the ring gear 32 has already been described. The outer surface of the ring gear 32 is fixed to the inner surface 12a that defines the first chamber 12.

[0028] The specific configuration for the carrier 34 to support the planetary gear 33 is not particularly limited. The carrier 34 may, for example, have a plurality of support shafts 34a parallel to the axial direction. The number of support shafts 34a is the same as the number of planetary gears 33. One support shaft 34a passes through the center of one planetary gear 33. The planetary gear 33 is capable of rotating around the support shaft 34a. In addition, according to the example in Figure 3, the carrier 34 may have boss portions 34b and 34c at both ends of the support shaft 34a that support the support shaft 34a while restricting the axial movement of the planetary gear 33.

[0029] The carrier 34, including the support shaft 34a and boss portions 34b and 34c, rotates about axis Ax. On one axial side (right side in Figure 3), the carrier 34 is rotatably supported by a bearing 46 positioned between the boss portion 34c and the partition wall 13. On the other axial side (left side in Figure 3), the carrier 34 is rotatably supported by a bearing 47 positioned between the end of the carrier 34 and the case 11.

[0030] The sun gear 31 and the ring gear 32 are helical gears. A helical gear is a gear in which the teeth (tooth traces) are twisted (angled) relative to the gear axis. The planetary gears 33 that mesh with the sun gear 31 and the ring gear 32 can also be understood as helical gears. In this embodiment, the twist angles of the teeth of the sun gear 31 and the ring gear 32 are set so that the thrust force acting on the sun gear 31 and the thrust force acting on the ring gear 32 are in opposite directions.

[0031] Thrust force is a load applied in a direction parallel to the axial direction. In other words, in the planetary gear mechanism 30, the helical gears are designed so that the direction of the thrust force acting on the sun gear 31 when the sun gear 31 and planetary gear 33 mesh is opposite to the direction of the thrust force acting on the ring gear 32 when the ring gear 32 and planetary gear 33 mesh. In Figure 3, the direction of the thrust force acting on the sun gear 31 is indicated by arrow A, and the direction of the thrust force acting on the ring gear 32 is indicated by arrow B.

[0032] According to this embodiment, the power transmission device 10 further includes a load transmission path 40 between the sun gear 31 and the ring gear 32, through which the thrust force acting on the sun gear 31 and the thrust force acting on the ring gear 32 are transmitted. The load transmission path 40 is configured to include at least a portion of the carrier 34.

[0033] The details of the load transmission path 40 will now be described. As mentioned above, the load transmission path 40 is a path that transmits load between the sun gear 31 and the ring gear 32. In other words, the load transmission path 40 is a path between the sun gear 31 and the ring gear 32. The load transmission path 40 comprises a path between the sun gear 31 and the carrier 34, and a path between the ring gear 32 and the carrier 34. A first bearing 48 is interposed in the path between the sun gear 31 and the carrier 34. That is, the load transmission path 40 includes a first bearing 48 interposed in the path between the sun gear 31 and the carrier 34. In addition, a structure 43 extending from the ring gear 32 and a second bearing 49 are interposed in the path between the ring gear 32 and the carrier 34. That is, the load transmission path 40 includes a structure 43 extending from the ring gear 32 and a second bearing 49 interposed in the path between the ring gear 32 and the carrier 34.

[0034] The first bearing 48 is positioned between the sun gear 31 and the first part 41 of the differential case 35. In other words, the first bearing 48 is sandwiched between the sun gear 31 and the differential case 35. The first bearing 48 is a bearing that receives thrust force. The second bearing 49 is positioned between the structure 43 and the second part 42 of the carrier 34. In other words, the second bearing 49 is sandwiched between the structure 43 and the carrier 34. The second bearing 49 is also a bearing that receives thrust force.

[0035] The first part 41 and the second part 42 are separated from each other in the axial direction, but as mentioned above, they are connected as objects because the carrier 34 and the differential case 35 are connected. Figure 3 shows a simplified example of the state in which the first part 41 and the second part 42 are connected by dashed lines. The first part 41 is the part of the differential case 35 that is close to the sun gear 31 in the axial direction. The second part 42 is the part of the carrier 34 that includes, for example, a part of the support shaft 34a and / or the boss portion 34b located on the other side (left side in Figure 3) of the small diameter pinion 33b in the axial direction, or a part of the support shaft 34a near the said part and / or boss portion 34b. Also, according to Figure 3, the second part 42 can be said to be located on one side in the axial direction (right side in Figure 3) of the end of the carrier 34 on the other side in the axial direction.

[0036] The structure 43 extends from the other axial end (left side in Figure 3) of the ring gear 32, and extends to cover a part of the carrier 34, such as the end of the support shaft 34a or the boss portion 34b, from that other side.

[0037] The structure 43 is fixed to the ring gear 32. There are various methods for fixing the structure 43 to the ring gear 32. For example, the structure 43 and the ring gear 32 are fixed by welding. Alternatively, the structure 43 may be fixed to the ring gear 32 by press-fitting it between the inner surface 12a of the first chamber 12 to which the ring gear 32 is fixed and a recess formed in the ring gear 32. The structure 43 and the ring gear 32 may also be fixed via other fixing members (not shown).

[0038] Alternatively, the structure 43 may be integrally molded with the ring gear 32. In other words, the structure 43 and the ring gear 32 may be a single component. By pre-molding the ring gear 32 in a shape that includes the structure 43, the structure 43 as a separate component can be eliminated, simplifying the assembly of the power transmission device 10. Note that the end 43b of the structure 43 opposite to the end 43a that connects to the ring gear 32 is separated from the case 11.

[0039] According to this load transmission path 40, the thrust force acting on the sun gear 31 in the direction indicated by arrow A is received by the first bearing 48. The thrust force received by the first bearing 48 is transmitted from the first part 41 to the carrier 34. This thrust force is further transmitted to the ring gear 32 via the second part 42 of the carrier 34, the second bearing 49, and the structure 43.

[0040] On the other hand, a thrust force acts on the ring gear 32 in the direction indicated by arrow B. Conventionally, this thrust force is supported by the case 11, but in this embodiment, the thrust force acting on the sun gear 31 is also transmitted to the ring gear 32. Therefore, in the ring gear 32 or the load transmission path 40, the thrust force acting on the sun gear 31 and the thrust force acting on the ring gear 32 cancel each other out, and only the excess thrust force that is not canceled out is input to the case 11.

[0041] As described above, in the power transmission device 10 according to this embodiment, the sun gear 31 and the ring gear 32 are helical gears, and the helical angles of the teeth of the sun gear 31 and the ring gear 32 are set so that the thrust force acting on the sun gear 31 and the thrust force acting on the ring gear 32 are in opposite directions. Furthermore, by providing a load transmission path 40 between the sun gear 31 and the ring gear 32, the thrust force input to the case 11 is reduced compared to conventional designs. Consequently, the strength required of the case 11 to withstand the thrust force acting on the ring gear 32 is reduced, which suppresses the enlargement of the case 11 and improves the freedom of the case shape. In addition, since the load transmission path 40 includes at least a part of the carrier 34 which is inherently required by the planetary gear mechanism 30, it is possible to suppress an increase in the number of parts when providing the load transmission path 40.

[0042] Furthermore, according to this embodiment, the load transmission path 40 includes a first bearing 48 interposed in the path between the sun gear 31 and the carrier 34, and a second bearing 49 interposed in the path between the ring gear 32 and the carrier 34. With this configuration, by using the first bearing 48 and the second bearing 49 when constructing the load transmission path 40, it is possible to construct the load transmission path 40 while ensuring the smooth rotation of the sun gear 31 and the carrier 34, while suppressing an increase in the number of parts.

[0043] Furthermore, according to this embodiment, the carrier 34 is connected to the differential case 35 that houses the differential 50, and the first bearing 48 is sandwiched between the sun gear 31 and the differential case 35. With this configuration, in a power transmission device 10 of the type in which the carrier 34 is connected to the differential case 35 that houses the differential 50, the load transmission path 40 can be easily configured using the differential case 35.

[0044] Furthermore, according to this embodiment, the load transmission path 40 includes a structure 43 extending from the ring gear 32, and the second bearing 49 is sandwiched between the structure 43 and the carrier 34. With this configuration, the load transmission path 40 can be easily constructed by using the structure 43.

[0045] Furthermore, referring to Figure 3, it can be said that the load transmission path 40 is located on the other side (left side in Figure 3) of the large-diameter pinion 33a in the axial direction, that is, on the side of the small-diameter pinion 33b. In other words, when the planetary gear 33 is a stepped pinion having a large-diameter pinion 33a and a small-diameter pinion 33b, the shape of the stepped pinion is effectively utilized to provide the load transmission path 40 on the side of the small-diameter pinion 33b in the axial direction, rather than on the large-diameter pinion 33a. This allows for a simpler configuration of the load transmission path 40 and suppresses the need to enlarge the case 11 that houses the load transmission path 40.

[0046] In this embodiment, the twist angles of the teeth of the sun gear 31 and the ring gear 32 are set so that the direction of the thrust force acting on the sun gear 31 and the direction of the thrust force acting on the ring gear 32 are opposite. In this configuration, the twist angles of the teeth of the sun gear 31 and the ring gear 32 may be set so that the magnitude of the thrust force acting on the sun gear 31 is equal to the magnitude of the thrust force acting on the ring gear 32. For example, the thrust force acting on the sun gear 31 and the thrust force acting on the ring gear 32 can be measured or calculated by experimenting with or simulating the operation of the power transmission device 10 under standard operating conditions, and various parameters, including the twist angles of the teeth of the sun gear 31 and the ring gear 32, can be set so that their magnitudes are equal. With this configuration, the thrust force acting on the sun gear 31 and the thrust force acting on the ring gear 32 are ideally completely canceled out through the load transmission path 40, making it possible to reduce the thrust force input from the ring gear 32 to the case 11 to zero.

[0047] The specific configuration of the load transmission path 40 is not limited to that shown in the illustration. The load transmission path 40 only needs to be a path that connects the sun gear 31 and the ring gear 32, includes at least a part of the carrier 34, and transmits the thrust force acting on the sun gear 31 and the thrust force acting on the ring gear 32. Furthermore, the configuration of the power transmission device 10 can include various modifications. For example, the functions of the carrier 34 and the differential case 35 may be separated. Also, the relative positional relationship of the rotor shaft 23, carrier 34, differential case 35, etc., is not limited to that shown in the illustration. In addition, instead of the sun gear 31 being the input and the carrier 34 being the output, the carrier 34 may be the input and the sun gear 31 may be the output. The planetary gear does not have to be of the stepped pinion type.

[0048] Figure 4 shows a simplified side view of a vehicle 70 equipped with a power transmission device 10. The vehicle 70 has a rechargeable battery 72 mounted under the floor of the passenger compartment 71. The vehicle 70 can run by driving the motor 20 with power supplied from the battery 72, and examples of such vehicles include BEVs (Battery Electric Vehicles) and PHEVs (Plug-in Hybrid Electric Vehicles). According to Figure 4, the power transmission device 10 is mounted coaxially with the front wheel 73 of the vehicle 70, and the power transmission device 10 is mounted coaxially with the rear wheel 74 of the vehicle 70. If the vehicle 70 is a two-wheel drive vehicle, only one of the front or rear power transmission devices 10 shown in Figure 4 is required, while if the vehicle 70 is a four-wheel drive vehicle, both the front and rear power transmission devices 10 shown in Figure 4 are required.

[0049] By arranging the power transmission unit 10 as a unit, as shown in Figure 2, coaxially with the wheels, the height of the unit can be relatively lowered. As a result, at the front of the vehicle 70, for example, the degree of freedom in arranging various components such as the radiator 75, the air conditioning control system 76 that controls heating, ventilation, and air conditioning, and the EPS (Electric Power Steering) 77 is improved, making it possible to secure more space in the passenger compartment 71. At the rear of the vehicle 70, for example, it leads to securing luggage space and improving the degree of freedom in rear seat design.

[0050] The specific examples of the technologies disclosed herein have been described in detail above, but 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 described above. Furthermore, the technical elements described herein or in the 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. In addition, the technologies illustrated herein or in the drawings achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical usefulness in itself. [Explanation of Symbols]

[0051] 10: Power transmission device, 11: Case, 20: Motor, 21: Stator, 22: Rotor, 23: Rotor shaft, 30: Planetary gear mechanism, 31: Sun gear, 32: Ring gear, 33: Planetary gear, 33a: Large diameter pinion, 33b: Small diameter pinion, 34: Carrier, 35: Differential case, 40: Load transmission path, 41: First part, 42: Second part, 43: Structure, 48: First bearing, 49: Second bearing, 50: Differential, Ax: Shaft

Claims

1. A power transmission device comprising a planetary gear mechanism and a case housing the planetary gear mechanism, The aforementioned planetary gear mechanism is, A sun gear fixed to a rotatable shaft, A ring gear is arranged coaxially with the sun gear and fixed to the case, A planetary gear that meshes with the sun gear and the ring gear, The planetary gear is rotatably supported, and the carrier is arranged coaxially with the sun gear and rotatably supported relative to the case, The sun gear and the ring gear are each helical gears. The twist angles of the teeth of the sun gear and the ring gear are set such that the thrust force acting on the sun gear and the thrust force acting on the ring gear are in opposite directions. The sun gear and the ring gear are further provided with a load transmission path through which the thrust force acting on the sun gear and the thrust force acting on the ring gear are transmitted. The load transmission path comprises a power transmission device comprising at least a portion of the carrier.

2. The aforementioned load transmission path is A first bearing interposed in the path between the sun gear and the carrier, The power transmission device according to claim 1, further comprising a second bearing interposed in the path between the ring gear and the carrier.

3. The carrier is connected to the differential case that houses the differential, The power transmission device according to claim 2, wherein the first bearing is sandwiched between the sun gear and the differential case.

4. The load transmission path includes a structure extending from the ring gear, The power transmission device according to claim 2, wherein the second bearing is sandwiched between the structure and the carrier.

5. The power transmission device according to claim 4, wherein the structure is integrally molded with the ring gear.

6. The planetary gear is a stepped pinion having a large-diameter pinion that meshes with the sun gear on one side in the axial direction parallel to the shaft, and a small-diameter pinion that meshes with the ring gear on the other side in the axial direction. The power transmission device according to claim 1, wherein the load transmission path is provided in the axial direction on the other side of the large-diameter pinion.

7. The power transmission device according to claim 1, wherein the twist angles of the teeth of the sun gear and the twist angles of the teeth of the ring gear are set such that the magnitude of the thrust force acting on the sun gear is equal to the magnitude of the thrust force acting on the ring gear.

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