Sun gear unit of planetary gear mechanism, and transmission

Abstract

To support a sun gear shaft in a manner that ensures stable rotation.SOLUTION: A sun gear unit 11 of a planetary gear mechanism 10 comprises: a sun gear shaft 110 having a first end 110a to which rotational force is input and a second end 110b positioned opposite the first end 110a, with a shaft raceway surface 110e being formed on an outer circumferential surface between the first end 110a and the second end 110b; a sun gear 111 provided at the second end 110b; an outer ring 112 having an outer ring raceway surface 112a formed on an inner circumferential surface thereof; and a plurality of balls 113 positioned between the shaft raceway surface 110e and the outer ring raceway surface 112a.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a sun gear unit of a planetary gear mechanism and a transmission. [Background technology]

[0002] For example, as described in Patent Document 1, there is a transmission (reduction gear) that reduces the rotation speed of the drive shaft of a drive unit and outputs it. This transmission has multiple rotating shafts with gears, and reduces the rotation speed by sequentially transmitting the rotation of the drive shaft to the multiple rotating shafts. There is also a transmission that changes the rotation speed using a planetary gear mechanism. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-3048 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a transmission equipped with a planetary gear mechanism, a sun gear shaft of a sun gear unit of the planetary gear mechanism is rotatably supported by a support part via a bearing. If wobble occurs in this sun gear shaft, it is possible that rotation performance, durability, etc. may be reduced.

[0005] SUMMARY OF THE PRESENT EMBODIMENTS In view of the above, an object of the present invention is to provide a sun gear unit of a planetary gear mechanism that can stably and rotatably support a sun gear shaft, and a transmission. [Means for solving the problem]

[0006] The sun gear unit of the present invention is [1] "a sun gear unit for a planetary gear mechanism, comprising: a sun gear shaft having a first end for inputting and outputting rotational force and a second end opposite to the first end, the sun gear shaft having an axial raceway surface formed on its outer peripheral surface between the first end and the second end; a sun gear provided at the second end and meshing with a planet gear of the planetary gear mechanism; an outer ring attached to a support portion that supports the sun gear shaft and arranged to surround the raceway surface, the outer ring having an outer ring raceway surface formed on its inner peripheral surface; and a plurality of rolling elements arranged between the axial raceway surface and the outer ring raceway surface."

[0007] In this sun gear unit, the sun gear shaft is supported by the support portion via the rolling elements and the outer ring. In other words, the sun gear shaft also functions as the inner ring of the bearing. In this way, this sun gear unit can reduce the number of parts in the mechanism that supports the sun gear shaft, and can suppress a decrease in the support accuracy of the sun gear shaft due to variations in part accuracy, etc. Therefore, this sun gear unit can support the sun gear shaft stably and rotatably.

[0008] The sun gear unit according to the present invention may be [2] "the sun gear unit according to the above [1], in which a spline is formed on an outer circumferential surface or an inner circumferential surface of the first end portion." This allows the sun gear unit to more reliably transmit rotational force between itself and other rotating members via the spline.

[0009] The sun gear unit according to the present invention may be the sun gear unit according to the above [1] or [2], [3] "wherein the sun gear shaft has a groove shoulder surface forming portion having a groove shoulder surface adjacent to the shaft raceway surface on its outer circumferential surface at a position closer to the first end than the shaft raceway surface, and a fitting portion adjacent to the groove shoulder surface forming portion at a position closer to the first end than the groove shoulder surface forming portion, and the size of the groove shoulder surface forming portion in the radial direction of the sun gear shaft is larger than the size of the fitting portion in the radial direction of the sun gear shaft." In this case, a step is formed between the groove shoulder surface forming portion and the fitting portion on the outer circumferential surface of the sun gear shaft. As a result, the sun gear unit can position the member to be fitted into the fitting portion by abutting the member fitted into the fitting portion on this step portion.

[0010] The sun gear unit according to the present invention may be [4] "the sun gear unit according to any one of the above [1] to [3], wherein the sun gear shaft has a first groove shoulder surface and a second groove shoulder surface adjacent to the shaft raceway surface so as to sandwich the shaft raceway surface in the axial direction of the sun gear shaft, the first groove shoulder surface and the second groove shoulder surface each have an annular shape extending along the circumferential direction of the sun gear shaft, and the outer diameter of the first groove shoulder surface and the outer diameter of the second groove shoulder surface are different from each other." The rolling elements arranged on the shaft raceway surface are less likely to ride up on the larger diameter side of the first groove shoulder surface and the second groove shoulder surface than on the smaller diameter side of the groove shoulder surface. In this way, the sun gear unit can receive an axial load while suppressing the rolling elements from riding up on the groove shoulder surface by making the outer diameters of the first groove shoulder surface and the second groove shoulder surface different from each other.

[0011] The sun gear unit according to the present invention may be [5] "the sun gear unit according to any one of the above [1] to [4], wherein an engaging portion is provided on an outer peripheral surface of the outer ring to engage with the support portion in the axial direction of the sun gear shaft." In this case, the engaging portion provided on the outer ring can suppress misalignment between the outer ring and the support portion in the axial direction of the sun gear shaft.

[0012] The sun gear unit according to the present invention may be [6] "the sun gear unit according to any one of the above [1] to [5], wherein gaps are provided between the sun gear and the outer ring and between the sun gear and the rolling elements in the axial direction of the sun gear shaft." In this case, the sun gear unit can have a higher degree of freedom in design and can improve the ease of assembly around the rolling elements and the outer ring.

[0013] The sun gear unit according to the present invention may be [7] "the sun gear unit according to any one of the above [1] to [6], wherein the sun gear shaft is provided with a shaft through hole that extends along the axis of the sun gear shaft and through which a rotating shaft passes." In this way, since another rotating shaft can be disposed inside the sun gear shaft, it is possible to miniaturize a device using the sun gear unit.

[0014] The sun gear unit according to the present invention may be the sun gear unit according to [8] above, in which a hardened layer is provided on a surface portion of the sun gear shaft, the portion provided with the hardened layer has a higher hardness than the portion of the sun gear shaft other than the hardened layer, and the thickness of the hardened layer is greater than half the thickness of the shaft raceway surface of the sun gear shaft. Here, the inner circumferential surface of the shaft through hole of the sun gear shaft also becomes the surface of the sun gear shaft. Therefore, in addition to the surface portion of the sun gear shaft facing radially outward, a hardened layer is also provided on the inner circumferential surface portion of the shaft through hole of the sun gear shaft. By making the thickness of the hardened layer greater than half the thickness of the shaft raceway surface, the shaft raceway surface portion of the sun gear shaft is provided with a hardened layer over the entire radial thickness. This allows the sun gear unit to further improve the internal hardness of the shaft raceway surface.

[0015] The transmission according to the present invention is [9] "a transmission comprising: a planetary gear mechanism having a sun gear unit described in [7] or [8] above; and a differential gear unit having a differential case to which rotational force is transmitted from the planetary gear mechanism and in which a differential mechanism is provided within the differential case, wherein a drive shaft connected to the differential mechanism is passed through the shaft through hole as the rotating shaft."

[0016] In this transmission, the sun gear shaft is supported by the support portion via the rolling elements and the outer ring. In other words, the sun gear shaft also functions as the inner ring of the bearing. In this way, this sun gear unit can reduce the number of parts in the mechanism that supports the sun gear shaft, and can suppress a decrease in support accuracy of the sun gear shaft due to variations in part accuracy, etc. Therefore, in a transmission equipped with this sun gear unit, the sun gear shaft can be stably supported for rotation. Also, in this transmission, a drive shaft connected to a differential gear can be disposed inside the sun gear shaft. This allows the transmission to be made more compact. Effect of the Invention

[0017] According to the present invention, the sun gear shaft can be stably supported for rotation. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a cross-sectional view showing a main part of a transmission according to an embodiment. [Diagram 2] FIG. 2 is a perspective view of the sun gear unit in FIG. 1 as viewed from the spline side. [Diagram 3] FIG. 3 is a perspective view of the sun gear unit in FIG. 1 as viewed from the sun gear side. [Figure 4] FIG. 4 is an enlarged cross-sectional view of the sun gear unit of FIG. [Diagram 5] FIG. 5 is a diagram showing an example of a process for manufacturing the sun gear shaft according to the embodiment. [Figure 6]FIG. 6 is a cross-sectional view of a sun gear shaft according to a modified example. [Figure 7] FIG. 7 is an enlarged cross-sectional view of the vicinity of the shaft raceway surface for explaining how the shaft raceway surface and the sun gear are formed. [Figure 8] FIG. 8 is an enlarged cross-sectional view of the vicinity of a shaft raceway surface of a sun gear unit according to a first modified example. [Figure 9] FIG. 9 is an enlarged cross-sectional view of a sun gear unit according to a second modified example. [Figure 10] FIG. 10 is a cross-sectional view showing a hardened layer provided on the surface of a sun gear unit according to a second modified example. [Figure 11] 11(a) to 11(c) are enlarged cross-sectional views of a sun gear unit according to a third modified example. [Figure 12] FIG. 12 is a cross-sectional view showing a main part of a transmission equipped with a sun gear shaft according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same or corresponding elements are denoted by the same reference numerals, and duplicated explanations will be omitted. In addition, in the following, a reduction gear that reduces the rotational speed of a drive unit will be used as the transmission according to the present invention.

[0020] As shown in Fig. 1, in this embodiment, as an example, the transmission 1 is configured as a reducer for an EV (Electric Vehicle) equipped with a drive unit 30 having an electric motor. The transmission 1 includes a planetary gear mechanism 10 and a differential gear unit 20. Although omitted in Fig. 1, the transmission 1 also includes a housing that houses each mechanism such as the planetary gear mechanism 10.

[0021] The drive unit 30 constitutes an electric motor unit that serves as a drive source for the vehicle. More specifically, the drive unit 30 includes a motor rotor 31 and a rotor shaft 32. The motor rotor 31 constitutes a rotor of an electric motor. Although not shown in the figure, the drive unit 30 includes components such as magnets that constitute an electric motor as a drive mechanism. The drive unit 30 may also include electronic components such as an inverter.

[0022] The rotor shaft 32 is provided at the center of the motor rotor 31. The rotor shaft 32 is rotationally driven by the motor rotor 31. The rotor shaft 32 serves as an output shaft for the driving force (rotational force) of the drive unit 30. The rotor shaft 32 is connected to the planetary gear mechanism 10. The rotor shaft 32 has a cylindrical shape. A first drive shaft 41 passes through the inside of the rotor shaft 32. A rotor spline 32a is formed on the inner circumferential surface of the end of the rotor shaft 32 that is connected to the planetary gear mechanism 10.

[0023] The planetary gear mechanism 10 of the transmission 1 reduces the speed of the rotational force transmitted from the rotor shaft 32 of the drive unit 30 and transmits the reduced speed to the differential gear unit 20. The planetary gear mechanism 10 includes a sun gear unit 11, a plurality of planetary gear units 12, a carrier 13, and an outer gear 14. The sun gear unit 11 is connected to the rotor shaft 32 of the drive unit 30. The rotational force is transmitted to the sun gear unit 11 from the rotor shaft 32. The rotation axis of the sun gear unit 11 is on the same line as the rotation axis of the rotor shaft 32. The sun gear unit 11 has a sun gear 111. Details of the sun gear unit 11 will be described later.

[0024] The plurality of planetary gear units 12 are arranged around the sun gear 111 of the sun gear unit 11 with a predetermined interval in the circumferential direction. Rotational force is transmitted to each of the plurality of planetary gear units 12 from the sun gear 111. The planetary gear unit 12 includes a first planetary gear (planetary gear) 121, a second planetary gear 122, and a planetary gear shaft 123. The first planetary gear 121 and the second planetary gear 122 are arranged on the same rotation axis and are connected to each other. That is, the first planetary gear 121 and the second planetary gear 122 rotate integrally. The first planetary gear 121 has a larger diameter than the second planetary gear 122. The first planetary gear 121 meshes with the sun gear 111 of the sun gear unit 11. The planetary gear shaft 123 serves as the rotation axis of the first planetary gear 121 and the second planetary gear 122. The planetary gear shaft 123 rotatably supports the first planetary gear 121 and the second planetary gear 122.

[0025] The carrier 13 supports the ends on the drive unit 30 side of the planetary gear shafts 123 of the plurality of planetary gear units 12. The rotation axis of the carrier 13 is on the same line as the rotation axis of the sun gear unit 11. At the ends of the planetary gear shafts 123 of the plurality of planetary gear units 12 on the side opposite to the side supported by the carrier 13, they are respectively supported by the differential case 21 of the differential gear unit 20.

[0026] The outer gear 14 is annular and has a gear on its inner peripheral surface. The outer gear 14 is arranged so as to surround the plurality of second planetary gears 122 and meshes with each of the plurality of second planetary gears 122. In the present embodiment, the outer gear 14 is fixed to, for example, the housing of the transmission 1.

[0027] Thereby, when the sun gear unit 11 rotates, the plurality of planetary gear units 12 orbit around the sun gear unit 11. As the planetary gear units 12 orbit around the sun gear unit 11, the differential gear unit 20 rotates.

[0028] The differential gear unit 20 receives rotational force from the planetary gear mechanism 10. The rotation axis of the differential gear unit 20 is on the same line as the rotation axes of the planetary gear mechanism 10 and the rotor shaft 32. The differential gear unit 20 includes a differential case 21 and a differential mechanism 22.

[0029] A rotational force is transmitted to the differential case 21 from the planetary gear unit 12 of the planetary gear mechanism 10. The differential case 21 has a space therein.

[0030] The differential mechanism 22 is provided in the differential case 21. The differential mechanism 22 is, for example, a differential mechanism of a vehicle differential gear unit including a pinion gear, a side gear, and the like. Various well-known mechanisms can be used as the differential mechanism 22. The differential case 21 is provided with a first insertion port h1 and a second insertion port h2 on the rotation axis of the sun gear unit 11. A first drive shaft (rotating shaft) 41 is inserted through the first insertion port h1, and a second drive shaft 42 is inserted through the second insertion port h2 into the differential mechanism 22. The first drive shaft 41 and the second drive shaft 42 are each provided on the rotation axis of the sun gear unit 11.

[0031] Next, the sun gear unit 11 will be described in detail. As shown in FIG. 2 to FIG. 4, the sun gear unit 11 includes a sun gear shaft 110, a sun gear 111, an outer ring 112, a plurality of balls (rolling elements) 113, and a cage 114. The sun gear shaft 110 is disposed on the rotation axis of the rotor shaft 32. The sun gear shaft 110 has a first end 110a connected to the rotor shaft 32, and a second end 110b opposite to the first end 110a. A rotational force is input from the rotor shaft 32 to the first end 110a. In this embodiment, a sun gear spline (spline) 110c is formed on the outer circumferential surface of the first end 110a. The sun gear spline 110c meshes with the rotor spline 32a of the rotor shaft 32. As a result, the rotational force is transmitted from the rotor shaft 32 to the sun gear unit 11.

[0032] A sun gear 111 is provided on the outer circumferential surface of the second end 110b of the sun gear shaft 110. The sun gear 111 rotates integrally with the sun gear shaft 110. In this embodiment, the sun gear 111 is provided integrally with the sun gear shaft 110. The sun gear 111 transmits the rotational force transmitted to the sun gear unit 11 to a first planetary gear 121 of the planetary gear unit 12.

[0033] An axial raceway surface 110e is formed on the outer circumferential surface of the sun gear shaft 110 between the first end 110a and the second end 110b. That is, the axial raceway surface 110e is formed on the outer circumferential surface of the sun gear shaft 110 between the sun gear spline 110c and the sun gear 111. The axial raceway surface 110e is provided over the entire circumferential area of ​​the outer circumferential surface of the sun gear shaft 110. The axial raceway surface 110e is a groove extending in the circumferential direction of the sun gear shaft 110. In this embodiment, the cross-sectional shape of the axial raceway surface 110e is substantially arc-shaped.

[0034] The shaft raceway surface 110e on the outer circumferential surface of the sun gear shaft 110 is formed on a raceway surface forming portion 110f (see FIG. 4) between the sun gear spline 110c and the sun gear 111. The raceway surface forming portion 110f is a portion of the sun gear shaft 110 that faces the inner circumferential surface of the outer ring 112. In the present embodiment, as an example, the outer diameter of the raceway surface forming portion 110f is larger than the outer diameter of the first end portion 110a where the sun gear spline 110c is formed. In the present embodiment, as an example, the outer diameter of the raceway surface forming portion 110f is smaller than the outer diameter of the sun gear 111. However, the size relationship between the raceway surface forming portion 110f and other portions is not limited to this relationship, and may be the opposite of the size relationship described here.

[0035] The outer ring 112 is attached to a shaft support portion (support portion) 50 that supports the sun gear shaft 110. In this embodiment, the shaft support portion 50 is formed by the carrier (support portion) 13 of the planetary gear mechanism 10. However, the shaft support portion 50 may be formed by, for example, a part of a housing that houses the planetary gear mechanism 10 and the like.

[0036] The outer ring 112 is provided so as to surround an axial raceway surface 110e formed on the sun gear shaft 110. An outer ring raceway surface 112a is formed on the inner peripheral surface of the outer ring 112. The outer ring raceway surface 112a is provided over the entire circumferential area of ​​the inner peripheral surface of the outer ring 112. The outer ring raceway surface 112a is a groove extending in the circumferential direction of the outer ring 112. In this embodiment, the cross-sectional shape of the outer ring raceway surface 112a is substantially arc-shaped. The outer ring raceway surface 112a of the outer ring raceway surface 112a faces the axial raceway surface 110e of the sun gear shaft 110.

[0037] The plurality of balls 113 are disposed between the outer ring raceway surface 112a of the outer ring raceway surface 112a and the shaft raceway surface 110e of the sun gear shaft 110. The balls 113 are spherical. The cage 114 holds each of the plurality of balls 113 between the outer ring raceway surface 112a and the shaft raceway surface 110e so that they can roll freely.

[0038] The sun gear shaft 110 is provided with a shaft through hole 110d that extends along the axis of the sun gear shaft 110. The first drive shaft 41 connected to the differential mechanism 22 of the differential gear unit 20 passes through the shaft through hole 110d. In other words, the rotation axis of the sun gear shaft 110 and the rotation axis of the first drive shaft 41 are on the same line.

[0039] As described above, in the sun gear unit 11 of the planetary gear mechanism 10, the sun gear shaft 110 is supported by the shaft support portion 50 via the balls 113 and the outer ring 112. In other words, the sun gear shaft 110 also functions as the inner ring of the bearing. In this way, the sun gear unit 11 can reduce the number of parts in the mechanism that supports the sun gear shaft 110, and can suppress a decrease in the support accuracy of the sun gear shaft 110 due to variations in part accuracy, etc. Therefore, in the sun gear unit 11, the sun gear shaft 110 can be stably and rotatably supported.

[0040] An axial load may also be applied to this sun gear unit 11. For example, if the sun gear shaft is supported by a bearing having an inner ring, it may be necessary to attach a retaining ring to the sun gear shaft to prevent the inner ring from shifting, or a spacer to abut the inner ring against the sun gear, etc. However, in this sun gear unit 11, the sun gear shaft 110 also functions as the inner ring of the bearing and the bearing portion is positioned, so there is no need to provide a retaining ring, spacer, etc. to prevent the inner ring from shifting.

[0041] In sun gear unit 11 according to this embodiment, sun gear shaft 110 also functions as the inner ring of the bearing, so there is no need to provide a separate inner ring of the bearing. As a result, sun gear unit 11 can be made smaller in diameter and lighter in weight.

[0042] A sun gear spline 110c that meshes with the rotor spline 32a of the rotor shaft 32 is provided at a first end 110a of the sun gear shaft 110. This allows the sun gear unit 11 to more reliably transmit rotational force to the rotor shaft 32, which is another rotating member, via the sun gear spline 110c.

[0043] A shaft through hole 110d is provided on the inside of the sun gear shaft 110. In this sun gear unit 11, another rotating shaft can be arranged on the inside of the sun gear shaft 110. In the present embodiment, a first drive shaft 41 connected to the differential gear unit 20 is arranged in the shaft through hole 110d of the sun gear shaft 110. As a result, in the sun gear unit 11, it is possible to reduce the size of a device having the sun gear unit 11 (the transmission 1 in this embodiment).

[0044] As described above, the sun gear unit 11 does not have an inner ring as a separate member, and does not require a retaining ring or spacer to prevent the inner ring from slipping. The axial length of the sun gear shaft 110 can be shortened by the amount of space required to provide a retaining ring or the like. Generally, the inner ring of the bearing is held by a magnet chuck at its axial end face, and a raceway groove (raceway surface) is formed on the outer circumferential surface of the inner ring by a grinding shoe. For example, when the length of the sun gear shaft 110 is short, the axial raceway surface 110e can be formed on the outer circumferential surface of the sun gear shaft 110 by a device similar to the device that forms the raceway groove on the inner ring of the bearing. Specifically, as shown in FIG. 5, for example, the second end 110b of the sun gear shaft 110 is held by a magnet chuck G1. With the sun gear shaft 110 held by the magnet chuck G1, the grinding shoe G2 forms the axial raceway surface 110e on the raceway surface forming portion 110f on the outer circumferential surface of the sun gear shaft 110. In this manner, the shaft raceway surface 110e can be formed on the raceway surface forming portion 110f of the sun gear shaft 110 by a device similar to a device for forming the inner ring of a general bearing.

[0045] Here, when a bearing having an inner ring is attached to the sun gear shaft, the inner ring of the bearing may be abutted against the end of the sun gear to position the inner ring. In this case, the sun gear and the inner ring are related to each other, and restrictions are imposed on the installation positions of the two and the size of the sun gear. On the other hand, in the sun gear unit 11 according to this embodiment, the sun gear shaft 110 also functions as the inner ring of the bearing. Therefore, in the sun gear unit 11, it is not necessary to position the inner ring by the sun gear 111. In other words, there is no relationship between the sun gear 111 and the shaft raceway surface 110e that functions as the inner ring of the bearing, and there are no restrictions on the installation positions of the two and the size of the sun gear 111.

[0046] For this reason, as shown in FIG. 4, a gap is provided between the sun gear 111 and the outer ring 112 and the balls 113 in the axial direction of the sun gear shaft 110. Also, as shown in FIG. 6, a large gap of a desired size may be provided between the sun gear 111 and the outer ring 112 and the balls 113 in the axial direction of the sun gear shaft 110. As shown in FIG. 6, a ball insertion jig G3 used when arranging the balls 113 between the outer ring 112 and the shaft raceway surface 110e may be placed in the gap between the sun gear 111 and the outer ring 112 and the balls 113. In this case, the ball insertion jig G3 is placed in the gap between the sun gear 111 and the outer ring 112. Then, the balls 113 are placed between the outer ring 112 and the shaft raceway surface 110e from the first end 110a side of the sun gear shaft 110. The ball insertion jig G3 functions as a jig that prevents the balls 113 from falling out from between the outer ring 112 and the shaft raceway surface 110e when the balls 113 are placed. In this way, the sun gear unit 11 can increase the degree of freedom in design because there is no correlation between the sun gear 111 and the shaft raceway surface 110e. Also, because the ball insertion jig G3 can be placed in the gap between the sun gear 111 and the outer ring 112, the assembly of the sun gear unit 11 can be improved.

[0047] For example, in the case of a configuration in which an inner ring is attached to a sun gear shaft, the width of the sun gear (the axial length of the sun gear shaft) may be extended in order to position the inner ring against the sun gear. As described above, in the sun gear unit 11 according to this embodiment, there is no correlation between the position of the sun gear 111 and the position of the axial raceway surface 110e. Therefore, in the sun gear unit 11, it is not necessary to extend the width of the sun gear 111 just to abut the inner ring. In the sun gear unit 11, the width of the sun gear 111 can be set to only the width necessary for transmitting the rotational force. As a result, in the sun gear unit 11, the width of the sun gear 111 is not unnecessarily extended, so that the weight can be reduced. In addition, in the sun gear unit 11, the width of the sun gear 111 is not unnecessarily extended, so that the processing time for forming the sun gear 111 can be shortened, and the life of the tool for forming the sun gear 111 can be extended.

[0048] For example, as shown in FIG. 7, the axial raceway surface 110e may be ground by a grinding wheel G4. As described above, there is no correlation between the position of the sun gear 111 and the position of the axial raceway surface 110e. Therefore, the installation positions of the sun gear 111 and the axial raceway surface 110e can be adjusted so that the tool for forming the axial raceway surface 110e, such as the grinding wheel G4, does not interfere with the sun gear 111. Similarly, the tooth surface of the sun gear 111 may be ground by a tooth grinding wheel. In this case, too, the installation positions of the sun gear 111 and the axial raceway surface 110e can be adjusted so that the tool for forming the sun gear 111, such as the tooth grinding wheel, does not interfere with the groove shoulder of the axial raceway surface 110e. In this way, the sun gear unit 11 can increase the degree of freedom in designing the sun gear 111 and the axial raceway surface 110e, and the sun gear shaft 110 including the sun gear 111 and the axial raceway surface 110e can be easily formed.

[0049] In this embodiment, the sun gear 111 is provided integrally with the sun gear shaft 110. The axial raceway surface 110e is formed on the outer peripheral surface (raceway surface forming portion 110f) of the sun gear shaft 110. That is, the sun gear shaft 110, the sun gear 111, and the axial raceway surface 110e are provided integrally. Therefore, when forming the sun gear 111 and the axial raceway surface 110e, the sun gear 111 and the axial raceway surface 110e can be formed using the same machining reference. As a result, the sun gear unit 11 can ensure the concentricity between the sun gear 111 and the axial raceway surface 110e with higher accuracy.

[0050] The transmission 1 includes a planetary gear mechanism 10 having the above-mentioned sun gear unit 11, and a differential gear unit 20 to which rotational force is transmitted from the planetary gear mechanism 10. In this manner, the transmission 1 including the sun gear unit 11 can stably support the sun gear shaft 110 for rotation.

[0051] (First Modification) A first modified example of the sun gear unit will be described. As shown in FIG. 8, the sun gear unit 11A according to this modified example includes a sun gear shaft 110A instead of the sun gear shaft 110 in the embodiment. The sun gear shaft 110A has a first groove shoulder surface (groove shoulder surface) S1 and a second groove shoulder surface S2 adjacent to the shaft raceway surface 110e so as to sandwich the shaft raceway surface 110e in the axial direction of the sun gear shaft 110A. The first groove shoulder surface S1 is adjacent to the shaft raceway surface 110e on the first end 110a side of the shaft raceway surface 110e. The second groove shoulder surface S2 is adjacent to the shaft raceway surface 110e on the sun gear 111 side (the second end 110b side opposite to the first end 110a) of the shaft raceway surface 110e.

[0052] The first groove shoulder surface S1 and the second groove shoulder surface S2 are surfaces facing radially outward of the sun gear shaft 110A and extend in an annular shape along the circumferential direction of the sun gear shaft 110A. In this modified example, the first groove shoulder surface S1 and the second groove shoulder surface S2 are cylindrical surfaces with the rotation axis of the sun gear shaft 110A as their axis. The outer diameter (diameter of the cylindrical surface) of the first groove shoulder surface S1 and the outer diameter (diameter of the cylindrical surface) of the second groove shoulder surface S2 are different from each other. In this modified example, the outer diameter of the first groove shoulder surface S1 is larger than the outer diameter of the second groove shoulder surface S2.

[0053] The sun gear shaft 110A has a first groove shoulder surface forming portion (groove shoulder surface forming portion) 110g and a fitting portion 110h. The first groove shoulder surface forming portion 110g is a portion of the sun gear shaft 110A closer to the first end 110a than the shaft raceway surface 110e. The first groove shoulder surface forming portion 110g has a first groove shoulder surface S1 adjacent to the shaft raceway surface 110e at a position closer to the first end 110a than the shaft raceway surface 110e on its outer circumferential surface. The fitting portion 110h is adjacent to the first groove shoulder surface forming portion 110g at a position closer to the first end 110a than the first groove shoulder surface forming portion 110g. A sun gear spline 110c is formed at a portion of the outer circumferential surface of the first groove shoulder surface forming portion 110g on the first end 110a side. Another member B is fitted into the outer circumferential surface of the fitting portion 110h. The member B to be fitted into the fitting portion 110h is not particularly limited.

[0054] In the radial direction of the sun gear shaft 110A, the size of the first groove shoulder surface forming portion 110g is larger than the size of the fitting portion 110h. That is, a step D is formed at the connection portion between the first groove shoulder surface forming portion 110g and the fitting portion 110h.

[0055] As described above, in this modified example, the first groove shoulder surface S1 has a larger diameter than the second groove shoulder surface S2. Therefore, the balls 113 arranged between the outer ring 112 and the shaft raceway surface 110e are less likely to ride up on the first groove shoulder surface S1 on the larger diameter side than the second groove shoulder surface S2 on the smaller diameter side. In this way, the sun gear unit 11A can receive the axial load while suppressing the balls 113 from riding up on the groove shoulder surface on the larger diameter side by making the outer diameters of the first groove shoulder surface S1 and the second groove shoulder surface S2 different from each other. Note that in this modified example, the first groove shoulder surface S1 has a larger diameter than the second groove shoulder surface S2, but the second groove shoulder surface S2 may have a larger diameter than the first groove shoulder surface S1. The outer diameters of the first groove shoulder surface S1 and the second groove shoulder surface S2 may be set according to the direction of the axial load to be received.

[0056] Furthermore, a step D is formed on the outer circumferential surface of the sun gear shaft 110A between the first groove shoulder surface forming portion 110g and the fitting portion 110h (at the connection portion). This allows the sun gear unit 11A to position the member B fitted into the fitting portion 110h by abutting the member B fitted into the fitting portion 110h against this step D.

[0057] (Second Modification) A second modified example of the sun gear unit will be described. As shown in FIG. 9, a sun gear unit 11B according to this modified example includes a sun gear shaft 110B instead of the sun gear shaft 110 in the embodiment. As shown in FIG. 10, a hardened layer F is provided on a surface portion of the sun gear shaft 110B. The portion provided with the hardened layer F has a higher hardness than the portion of the sun gear shaft 110B other than the hardened layer F. For example, the hardened layer F may be provided on the surface of the sun gear shaft 110B by a carburizing process. However, the method of providing the hardened layer F is not limited to the carburizing process.

[0058] The hardened layer F is provided from the surface of the sun gear shaft 110B to a predetermined depth position. The inner circumferential surface of the shaft through hole 110d of the sun gear shaft 110B also forms the surface of the sun gear shaft 110B. Therefore, in addition to the surface portion facing radially outward of the sun gear shaft 110B, the hardened layer F is also provided on the inner circumferential surface portion of the shaft through hole 110d of the sun gear shaft 110B.

[0059] The thickness L of the hardened layer F is greater than half the thickness of the shaft raceway surface 110e of the sun gear shaft 110B. In this modification, the shaft raceway surface 110e is groove-shaped. In this modification, the thickness L of the hardened layer F is greater than half the thickness of the groove bottom of the groove-shaped shaft raceway surface 110e. The thickness of the groove bottom of the shaft raceway surface 110e is the thickness T of the smallest diameter portion of the shaft raceway surface 110e, as shown in FIG. 9. This thickness T is the length from the smallest diameter portion of the shaft raceway surface 110e to the shaft through hole 110d. The thickness L of the hardened layer F may be a target value (design value) of the thickness of the hardened layer F when performing a process of providing the hardened layer F on the sun gear shaft 110B.

[0060] In this case, the hardened layer F is provided over the entire radial thickness T at the groove bottom of the axial raceway surface 110e of the sun gear shaft 110B. This allows the sun gear shaft 110B to further improve the internal hardness of the axial raceway surface 110e. This hardened layer F may also be provided on the sun gear 111. This allows the internal hardness of the axial raceway surface 110e to be improved while ensuring the toughness of the sun gear 111.

[0061] (Third Modification) A third modified example of the sun gear unit will be described. As shown in FIG. 11(a), the sun gear unit 11C according to this modified example includes an outer ring 112C instead of the outer ring 112 in the embodiment. A recess (engagement portion) 112b is provided on the outer peripheral surface of the outer ring 112C. The recess 112b may be provided over the entire circumferential area of ​​the outer ring 112C, or may be provided only in a portion of the circumferential area. In this example, the recess 112b is provided on the outer peripheral surface of the outer ring 112C at the end on the sun gear 111 side in the axial direction of the outer ring 112C.

[0062] The shaft support portion 50, which supports the outer ring 112C, is provided with a protrusion 50a that protrudes toward the outer ring 112C. The protrusion 50a of the shaft support portion 50 is fitted into a recess 112b of the outer ring 112C. The recess 112b of the outer ring 112C engages with the shaft support portion 50 in the axial direction of the sun gear shaft 110. In this case, the recess 112b provided in the outer ring 112C can suppress misalignment between the outer ring 112C and the shaft support portion 50 in the axial direction of the sun gear shaft 110.

[0063] As shown in FIG. 11(b), the recess 112b of the outer ring 112C may be engaged with the shaft support 50 via an engaging member W such as a retaining ring. Specifically, a recess 50b is provided on the inner circumferential surface of the shaft support 50 (the mounting surface of the outer ring 112C). The engaging member W is engaged by fitting into the recess 112b of the outer ring 112C and the recess 50b of the shaft support 50. As shown in FIG. 11(b), the recess 112b of the outer ring 112C into which the engaging member W is fitted may be provided on the outer circumferential surface of the outer ring 112C at a portion other than both ends in the axial direction. As shown in FIG. 11(c), the recess 112b of the outer ring 112C into which the engaging member W is fitted may be provided on the outer circumferential surface of the outer ring 112C at an end in the axial direction.

[0064] A recess 112b is provided on the outer peripheral surface of the outer ring 112C as an engagement portion that engages with the shaft support portion 50. This is not limited, and a protrusion may be provided on the outer peripheral surface of the outer ring 112C as an engagement portion that engages with the shaft support portion 50. As long as it can engage with the shaft support portion 50, the shape of the engagement portion (e.g., recess 112b, protrusion) provided on the outer ring 112C is not limited. In addition, the engagement portion provided on the outer ring 112C may directly engage with the shaft support portion 50 as shown in FIG. 11(a), or may engage with the shaft support portion 50 via an engagement member W or the like as shown in FIG. 11(b).

[0065] Although the embodiment and modified examples of the present invention have been described above, the present invention is not limited to the above-mentioned embodiment and modified examples. For example, the sun gear spline 110c formed on the first end 110a of the sun gear shaft 110 etc. is not limited to being formed on the outer circumferential surface of the sun gear shaft 110 etc. The sun gear spline formed on the first end 110a may be formed on the inner circumferential surface of the sun gear shaft 110 etc. In this case, it is only necessary that the rotor spline is formed on the outer circumferential surface of the rotor shaft 32.

[0066] Furthermore, the sun gear shaft 110 and the like are not limited to a configuration in which the first end 110a is provided with the sun gear spline 110c. The rotational force of the drive unit 30 may be directly transmitted to the first end of the sun gear shaft. Specifically, as shown in FIG. 12, the sun gear unit 11D includes a sun gear shaft 110D instead of the sun gear shaft 110 in the embodiment. The configuration of the sun gear unit 11D is the same as that of the sun gear unit 11 described above, except for the sun gear shaft 110D.

[0067] One end of the sun gear shaft 110D is provided with a first end 110a to which a rotational force is input from the drive unit 30. The first end 110a extends to the inside of the motor rotor 31. The motor rotor 31 of the drive unit 30 is attached to the first end 110a. The sun gear shaft 110D rotates integrally with the motor rotor 31. In other words, the sun gear shaft 110D functions as both the sun gear shaft 110 and the rotor shaft 32 in the above-mentioned embodiment. As a result, the rotational force of the drive unit 30 is directly input to the first end 110a of the sun gear shaft 110D.

[0068] The sun gear shaft 110D has an axial raceway surface 110e between the first end 110a and the second end 110b, similar to the sun gear shaft 110 in the embodiment. The sun gear shaft 110D is rotatably supported by the shaft support portion 50 via balls 113 and a cage 114. The second end 110b is provided with a sun gear 111. Even in this case, the sun gear unit 11D including the sun gear shaft 110D can achieve the same effects as the sun gear unit 11 in the embodiment.

[0069] Furthermore, the sun gear shaft 110, etc. are not limited to being rotatably supported by the balls 113. The sun gear shaft 110, etc. may be rotatably supported by "rollers" as rolling elements other than the balls 113. In this case, it is sufficient that the shaft raceway surface 110e formed on the outer circumferential surface of the sun gear shaft 110, etc. and the outer ring raceway surface 112a formed on the inner circumferential surface of the outer ring 112 are formed in a shape corresponding to the rollers as rolling elements.

[0070] The configuration of the planetary gear mechanism 10 is not limited to the above-mentioned configuration. The planetary gear mechanism 10 may at least include the above-mentioned sun gear unit 11, etc., and a planetary gear unit that rotates around the sun gear unit 11, etc. In the above embodiment and modified example, the planetary gear mechanism 10 has been described as transmitting a rotational force from the drive unit 30 to the sun gear unit 11, etc. That is, the rotational force is transmitted to the first end 110a of the sun gear shaft 110, etc., of the sun gear unit 11, etc. This is not limited to this, and the rotational force may be transmitted from the first end 110a of the sun gear shaft 110, etc., to another mechanism. That is, the rotational force may be output from the first end 110a of the sun gear shaft 110, etc., of the sun gear unit 11, etc. The planetary gear mechanism 10 is not limited to reducing the rotational speed. The planetary gear mechanism 10 may increase the rotational speed. In this case, the transmission 1 functions as a speed increaser.

[0071] At least some of the embodiments and various modified examples described above may be combined in any desired manner. [Explanation of symbols]

[0072] 1... transmission, 10... planetary gear mechanism, 11, 11A to 11D... sun gear unit, 13... carrier (support portion), 20... differential gear unit, 21... differential case, 22... differential mechanism, 41... first drive shaft (rotating shaft), 50... shaft support portion (support portion), 110, 110A to 110D... sun gear shaft, 110a... first end portion, 110b... second end portion, 110c...sun gear spline, 110d...shaft through hole, 110e...shaft raceway surface, 110g...first groove shoulder surface forming portion (groove shoulder surface forming portion), 110h...fitting portion, 111...sun gear, 112, 112C...outer ring, 112a...outer ring raceway surface, 112b...recess (engagement portion), 113...ball (rolling element), 121...first planetary gear (planetary gear), F...hardened layer, S1...first groove shoulder surface (groove shoulder surface), S2...second groove shoulder surface.

Claims

1. A sun gear unit of a planetary gear mechanism, a sun gear shaft having a first end portion for inputting and outputting a rotational force and a second end portion opposite to the first end portion, the sun gear shaft having an axial raceway surface formed on an outer circumferential surface between the first end portion and the second end portion; a sun gear provided at the second end and meshing with a planetary gear of the planetary gear mechanism; an outer ring attached to a support portion that supports the sun gear shaft and provided so as to surround the shaft raceway surface, and having an outer ring raceway surface formed on an inner peripheral surface thereof; a plurality of rolling elements disposed between the shaft raceway surface and the outer ring raceway surface; A sun gear unit comprising:

2. The sun gear unit according to claim 1 , wherein a spline is formed on an outer circumferential surface or an inner circumferential surface of the first end portion.

3. The sun gear shaft is a groove shoulder surface forming portion having a groove shoulder surface adjacent to the shaft raceway surface on an outer circumferential surface at a position closer to the first end portion than the shaft raceway surface; a fitting portion adjacent to the groove shoulder surface forming portion at a position closer to the first end portion than the groove shoulder surface forming portion; having 2. The sun gear unit according to claim 1, wherein a size of the groove shoulder surface forming portion in a radial direction of the sun gear shaft is larger than a size of the fitting portion in the radial direction of the sun gear shaft.

4. the sun gear shaft has a first groove shoulder surface and a second groove shoulder surface adjacent to the shaft raceway surface so as to sandwich the shaft raceway surface in an axial direction of the sun gear shaft, The first groove shoulder surface and the second groove shoulder surface each have an annular shape extending along a circumferential direction of the sun gear shaft, 2. The sun gear unit according to claim 1, wherein an outer diameter of the first groove shoulder surface and an outer diameter of the second groove shoulder surface are different from each other.

5. The sun gear unit according to claim 1 , wherein an engaging portion is provided on an outer peripheral surface of the outer ring, the engaging portion being engaged with the support portion in the axial direction of the sun gear shaft.

6. The sun gear unit according to claim 1 , wherein a gap is provided between the sun gear and the outer ring and between the sun gear and the rolling elements in the axial direction of the sun gear shaft.

7. The sun gear unit according to any one of claims 1 to 6, wherein the sun gear shaft is provided with a shaft through hole extending along an axis of the sun gear shaft and through which a rotating shaft passes.

8. A hardened layer is provided on a surface portion of the sun gear shaft, The portion on which the hardened layer is provided has a higher hardness than a portion of the sun gear shaft other than the hardened layer, The sun gear unit according to claim 7 , wherein a thickness of the hardened layer is greater than half a thickness of the sun gear shaft at the axial raceway surface.

9. A planetary gear mechanism having the sun gear unit according to claim 7; a differential gear unit having a differential case to which a rotational force is transmitted from the planetary gear mechanism and in which a differential mechanism is provided within the differential case; Equipped with A transmission, wherein a drive shaft connected to the differential mechanism is passed through the shaft through hole as the rotating shaft.

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