Planetary gearset

Abstract

Provided is a planetary gearset that can yield wide-ratio transmission, from low reduction ratios to high reduction ratios, and at the same time has ideal power transmission efficiency and is of low-profile structure along the axial orientation. This planetary gearset (1) comprises: a sun gear (2); first planetary gears (3); a first inner spline (4) fixed to a case (15); second planetary gears (6) linked to the first planetary gears (3) via a linking shaft (5); a carrier (7) that rotatably supports the linking shaft (5); and a second inner spline (8) that meshes with the second planetary gears (6). The carrier (7) is an annular carrier disposed between the first planetary gears (3) and the second planetary gears (6). The sun gear (2) is provided with a support shaft (9) that rotatably supports the carrier (7).

Description

Planetary gear mechanism

[0001] This application claims the benefit of priority from Japanese Patent Application No. 2024-054801, filed March 28, 2024, the contents of which are incorporated herein by reference.

[0002] A known conventional planetary gear mechanism has a carrier as an input element, and a first planetary gear and a second planetary gear supported by the carrier are meshed with a first sun gear and a second sun gear fixed to a case, respectively, thereby making the second sun gear an output element (see, for example, Patent Document 1).

[0003] The planetary gear mechanism described in Patent Document 1 is also called a 2K-HII type planetary gear mechanism, and is capable of achieving a wide range of reduction ratios from low to high, and has a thin structure in the axial direction.

[0004] However, the planetary gear mechanism described in Patent Document 1 has room for improvement in terms of power transmission efficiency.

[0005] On the other hand, another known conventional planetary gear mechanism uses a sun gear as an input element, and a first planetary gear and a second planetary gear supported by a carrier are meshed with a first internal gear and a second internal gear fixed to a case, respectively, so that the second internal gear serves as an output element (see, for example, Patent Document 2).

[0006] The planetary gear mechanism described in Patent Document 2 is also called a 3K type planetary gear mechanism, and is capable of achieving a wide range of reduction ratios from low to high, and also has improved power transmission efficiency compared to a 2K-HII type planetary gear mechanism.

[0007] JP 2010-144839 A JP 2023-150298 A

[0008] However, the planetary gear mechanism described in Patent Document 2 has room for improvement in terms of making it thinner in the axial direction.

[0009] An object of the present invention is to provide a planetary gear mechanism that can achieve a wide range of reduction ratios from low reduction ratios to high reduction ratios, has good power transmission efficiency, and has a thin structure in the axial direction.

[0010] (1) The planetary gear mechanism of the present invention comprises a sun gear that is one of the input rotating element and the output rotating element, a first planetary gear that meshes with the sun gear, a first internal gear that meshes with the first planetary gear and is fixed to a case, a second planetary gear that is connected to the first planetary gear via a connecting shaft, a carrier that rotatably supports the connecting shaft, and a second internal gear that meshes with the second planetary gear and is the other of the input rotating element and the output rotating element, wherein the carrier is an annular carrier arranged between the first planetary gear and the second planetary gear, and the sun gear has a support shaft that rotatably supports the carrier.

[0011] (2) In the planetary gear mechanism of (1) above, it is preferable that one end of the connecting shaft is integrally formed with either the first planetary gear or the second planetary gear, and the other end of the connecting shaft is fitted into a fitting hole provided in the other of the first planetary gear or the second planetary gear.

[0012] (3) In the planetary gear mechanism described in (2) above, it is preferable that the outer surface shape of the other end of the connecting shaft and the inner surface shape of the mating hole each include a corresponding flat surface extending in the axial direction and a corresponding curved surface extending in the axial direction and protruding radially outward.

[0013] (4) In the planetary gear mechanism of (3) above, it is preferable that the outer surface shape of the other end of the connecting shaft and the inner surface shape of the fitting hole each have two flat surfaces and two curved surfaces, the two flat surfaces are positioned opposite each other across the central axis of the fitting hole, and the two curved surfaces are each positioned so as to be connected between the two flat surfaces.

[0014] According to the present invention, it is possible to provide a planetary gear mechanism that can obtain a wide range of reduction ratios from low reduction ratios to high reduction ratios, has good power transmission efficiency, and has a thin structure in the axial direction.

[0015] Fig. 1 is a cross-sectional view that schematically shows a planetary gear mechanism that is one embodiment of the present invention. Fig. 2 is a graph that shows the results of calculating the transmission efficiency relative to the tooth surface efficiency of a 3K type planetary gear mechanism for each reduction ratio. Fig. 3 is a graph that shows the results of calculating the transmission efficiency relative to the tooth surface efficiency of a 2K-HII type planetary gear mechanism for each reduction ratio. Fig. 4 is a schematic diagram that schematically shows, from the axial direction, an assembled state of a first planetary gear and a second planetary gear in the planetary gear mechanism of Fig. 1. Fig. 5 is a schematic diagram that schematically shows, from the axial direction, another assembled state of the first planetary gear and the second planetary gear in the planetary gear mechanism of Fig. 1.

[0016] Hereinafter, a planetary gear mechanism according to one embodiment of the present invention will be described in detail with reference to the drawings.

[0017] In the following description, unless otherwise specified, the meanings of terms are defined as follows.

[0018] For example, "axial direction" refers to the direction in which the axis extends. "Input side" refers to one side in the axial direction. "Output side" refers to the other side in the axial direction. "Circumferential direction" refers to the circumferential direction around the axis. "Radial direction" refers to the direction perpendicular to the axis. In particular, "radially inner" refers to the side closer to the axis. "Radially outer" refers to the side farther from the axis.

[0019] FIG. 1 shows a schematic diagram of a planetary gear mechanism 1 according to an embodiment of the present invention.

[0020] The planetary gear mechanism 1 includes a sun gear 2 which serves as either an input rotation element or an output rotation element, a first planetary gear 3 which meshes with the sun gear 2, a first internal gear 4 which meshes with the first planetary gear 3 and is fixed to a case 15, a second planetary gear 6 which is connected to the first planetary gear 3 via a connecting shaft 5, a carrier 7 which rotatably supports the connecting shaft 5, and a second internal gear 8 which meshes with the second planetary gear 6 and serves as the other of the input rotation element and the output rotation element. The carrier 7 is an annular carrier arranged between the first planetary gear 3 and the second planetary gear 6. The sun gear 2 includes a support shaft 9 which rotatably supports the carrier 7.

[0021] Reference symbol O1 denotes a central axis of the planetary gear mechanism 1. In this embodiment, the planetary gear mechanism 1 connects an input shaft 11 and an output shaft 12. In this embodiment, the input shaft 11 and the output shaft 12 are arranged coaxially with the central axis O1 (hereinafter also simply referred to as "axis O1") of the planetary gear mechanism 1 as the same central axis. The input shaft 11 and the output shaft 12 are each a rotating shaft that rotates circumferentially around the axis O1.

[0022] In this embodiment, the sun gear 2 is an external gear serving as an input rotation element. In this embodiment, the sun gear 2 is connected to an input shaft 11.

[0023] In this embodiment, the sun gear 2 and the support shaft 9 are included in a sun gear member 20. In this embodiment, the sun gear member 20 includes the sun gear 2, the support shaft 9, and a connection portion 21.

[0024] In this embodiment, the connection portion 21 is provided integrally with the input side of the sun gear 2. In this embodiment, the input shaft 11 is fixed to the connection portion 21. In this embodiment, the input shaft 11 is fixed by fitting the input shaft 11 externally to the connection portion 21. However, the input shaft 11 can also be fitted internally to the connection portion 21, for example. In other words, various means can be used to fix the connection portion 21, such as bolt fastening.

[0025] In this embodiment, the support shaft 9 is provided on the output side of the sun gear 2. In this embodiment, the carrier 7 is supported by the support shaft 9 via a ring bearing 13a. In this embodiment, the support shaft 9 has an outer peripheral surface F2 whose central axis is the axis O1.

[0026] The carrier 7 has a through hole A7 that penetrates in the axial direction. In this embodiment, the carrier 7 has an annular flange 7a and a sleeve 7b. In this embodiment, the sleeve 7b is provided on the output side of the flange 7a. In this embodiment, the inner circumferential surface of the through hole A7 is defined by a flange-side inner circumferential surface F71 on the flange 7a side and a sleeve-side inner circumferential surface F72 on the sleeve 7b side. In this embodiment, the ring bearing 13a supports the outer circumferential surface F2 of the support shaft 9 and the flange-side inner circumferential surface F71 of the carrier 7. That is, in this embodiment, the ring bearing 13a rotatably supports the sun gear member 20 and the carrier 7.

[0027] In this embodiment, the flange-side inner peripheral surface F71 and the sleeve-side inner peripheral surface F72 have the same diameter in the axial direction. As a result, in this embodiment, the inner peripheral surface of the carrier 7 forms a straight inner peripheral surface extending in the axial direction. However, the flange-side inner peripheral surface F71 and the sleeve-side inner peripheral surface F72 may have different diameters. In this case, the inner peripheral surface of the carrier 7 forms an inner peripheral surface with a step.

[0028] The carrier 7 has a mounting hole h7 for mounting the connecting shaft 5. In this embodiment, the mounting hole h7 is a through-hole formed in the flange 7a. In this embodiment, the connecting shaft 5 is rotatably supported by the flange 7a via a ring bearing 13b arranged in the mounting hole h7. This allows the connecting shaft 5 to rotate relative to the carrier 7 in the circumferential direction around the planetary gear central axis O5. In this embodiment, the connecting shaft 5 is supported by the carrier 7 via two ring bearings 13b arranged at an interval in the axial direction. However, the number of ring bearings 13b may be at least one. In this embodiment, the carrier 7 has a plurality of mounting holes h7. The plurality of mounting holes h7 are arranged at intervals in the circumferential direction around the axis O1.

[0029] One end of the connecting shaft 5 can be provided integrally with either the first planetary gear 3 or the second planetary gear 6. In this case, the other end of the connecting shaft 5 can be fitted into a fitting hole A1 provided in the other of the first planetary gear 3 and the second planetary gear 6.

[0030] In this embodiment, the input side end (one end) of the connecting shaft 5 is integral with the first planetary gear 3. The output side end (the other end) of the connecting shaft 5 is press-fitted into a fitting hole A1 provided in the second planetary gear 6. In this embodiment, the first planetary gear 3 and the second planetary gear 6 are arranged on the same planetary gear central axis O5 (hereinafter also simply referred to as "axis O5").

[0031] In this embodiment, the first planetary gear 3 meshes with the sun gear 2 on the radially inner side, and meshes with the first internal gear 4 on the radially outer side.

[0032] In this embodiment, the first internal gear 4 is an internal gear fixed to a case 15. The case 15 is a fixed part that does not rotate around an axis, such as the case of a planetary gear device. This allows the first planetary gear 3 to rotate around the axis O5 along the inside of the first internal gear 4 due to the input rotation from the sun gear member 20, while revolving around the axis O1 around the inside of the first internal gear 4 along the internal teeth of the first internal gear 4.

[0033] The second planetary gears 6 are connected to the first planetary gears 3 by the connecting shaft 5. This allows the second planetary gears 6 to also rotate about the axis O5 while revolving around the axis O1. In this embodiment, the second planetary gears 6 mesh with the second internal gear 8 on the radially outer side. This allows the second internal gear 8 to also rotate in the circumferential direction around the axis O1.

[0034] In this embodiment, the second internal gear 8 is an internal gear serving as an output rotation element. In this embodiment, the second internal gear 8 is connected to an output shaft 12.

[0035] In this embodiment, the second internal gear 8 is included in the internal gear member 80. In this embodiment, the internal gear member 80 includes the second internal gear 8, a connection portion 81, and a connecting wall 82.

[0036] In this embodiment, the connecting wall 82 is a wall that connects the second internal gear 8 and the connection portion 81. In this embodiment, the connecting wall 82 connects the output side of the second internal gear 8 and the output side of the connection portion 81. In this embodiment, the internal gear member 80 is rotatably supported by the case 15 via a ring bearing 13d.

[0037] In this embodiment, the output shaft 12 is fixed to the connection portion 81. In this embodiment, the output shaft 12 is fixed by fitting the output shaft 12 internally into the connection portion 81. However, the connection portion 81 can also be provided on the output side of the connecting wall 82, for example, so that the output shaft 12 is fitted internally or externally into the connection portion 81. In other words, various means, such as bolt fastening, can be used as a fixing means for the connection portion 81. As a result, in this embodiment, the output shaft 12 can be rotated circumferentially around the axis O1 by the input rotation from the second internal gear 8.

[0038] In this embodiment, the connection portion 81 is a sleeve for fixing the output shaft 12. In this embodiment, the carrier 7 is supported by the connection portion 81 via a ring bearing 13c. In this embodiment, the connection portion 81 has an outer peripheral surface F8 whose central axis is the axis O1. In this embodiment, the ring bearing 13c supports the sleeve-side inner peripheral surface F72 of the carrier 7 and the outer peripheral surface F8 of the connection portion 81 of the internal gear member 80. That is, in this embodiment, the ring bearing 13c rotatably supports the carrier 7 and the second internal gear 8.

[0039] According to the planetary gear mechanism 1, the sun gear 2 serves as an input element, and the first planetary gear 3 and the second planetary gear 6 supported by the carrier 7 are meshed with the first internal gear 4 fixed to the case 15 and the second internal gear 8 supported on the case 15 via a ring bearing 13d, respectively, thereby making it possible to use the second internal gear 8 as an output element. In other words, the planetary gear mechanism 1 functions as a 3K type planetary gear mechanism.

[0040] 2 is a graph showing the results of calculations of the transmission efficiency relative to the tooth surface efficiency of the 3K type planetary gear mechanism for each reduction ratio. The graph in FIG. 2 shows the results of calculations using the planetary gear mechanism 1 according to this embodiment as a model of the 3K type planetary gear mechanism.

[0041] In Fig. 2, the horizontal axis represents the tooth surface efficiencies η1 and η2 of the entire planetary gear mechanism 1. The vertical axis represents the transmission efficiency (power transmission efficiency) of the planetary gear mechanism 1. The graph in Fig. 2 shows the transmission efficiency relative to the tooth surface efficiency when the reduction ratio is fixed.

[0042] 2 shows four cases: a reduction ratio of 50, a reduction ratio of 100, a reduction ratio of 150, and a reduction ratio of 200. Note that this calculation result is calculated with the sun gear 2 as the input rotating element and the second internal gear 8 as the output rotating element.

[0043] 2, the planetary gear mechanism 1 can achieve a wide range of reduction ratios from low to high and has good transmission efficiency. In particular, even at a high reduction ratio (for example, the highest reduction ratio of 200), the lowest transmission efficiency exceeds 0.40.

[0044] Next, Fig. 3 is a graph showing the results of calculating the transmission efficiency relative to the tooth surface efficiency of a 2K-HII type planetary gear mechanism for each reduction ratio. In Fig. 3, the horizontal axis shows the tooth surface efficiency η2 of the 2K-HII type planetary gear mechanism as a whole. The vertical axis shows the transmission efficiency (power transmission efficiency) of the 2K-HII type planetary gear mechanism. Here, the graph in Fig. 3 is the result of calculations using the planetary gear mechanism described in Cited Document 1 as a model of the 2K-HII type planetary gear mechanism.

[0045] The graph in Fig. 3 also shows four cases: a reduction ratio of 50, a reduction ratio of 100, a reduction ratio of 150, and a reduction ratio of 200. Note that this calculation result is calculated by setting the revolution arm (carrier) as the input rotating element and the second sun gear (second sun gear) as the output rotating element.

[0046] As shown in Figure 3, a wide range of reduction ratios from low to high can be achieved, but there is room for improvement in power transmission efficiency. In particular, even at low reduction ratios (for example, the lowest reduction ratio of 50), the transmission efficiency of the planetary gear mechanism 1 is below 0.40. At high reduction ratios (for example, the highest reduction ratio of 200), the lowest transmission efficiency is below 0.10.

[0047] As is clear from the comparison between the graphs of FIG. 2 and FIG. 3, the planetary gear mechanism 1 of the 3K type planetary gear mechanism can obtain a wide range of reduction ratios from low reduction ratios to high reduction ratios and has good transmission efficiency compared to the 2K-HII type planetary gear mechanism.

[0048] On the other hand, the conventional 3K type planetary gear mechanism described in Patent Document 2 holds the planetary gears so that they are sandwiched between carriers with spaces in the axial direction. For this reason, the conventional 3K type planetary gear mechanism has room for improvement in terms of making its structure thinner in the axial direction.

[0049] In contrast, in the planetary gear mechanism 1 according to this embodiment, the connecting shaft 5 connecting the first planetary gear 3 and the second planetary gear 6 is rotatably supported by a carrier 7 disposed between the first planetary gear 3 and the second planetary gear 6. In other words, the planetary gear mechanism 1 rotatably supports two types of planetary gears, the first planetary gear 3 and the second planetary gear 6, by a single carrier 7. That is, the planetary gear mechanism 1 can eliminate one of the two carriers disposed axially at a distance in a conventional 3K planetary gear mechanism. Therefore, the planetary gear mechanism 1 has a thinner structure in the axial direction than the conventional 3K planetary gear mechanism. In addition, because the planetary gear mechanism 1 requires only a single carrier 7, it can maintain a similar thinness to the conventional 2K-HII type planetary gear mechanism described in Cited Document 1.

[0050] Therefore, the planetary gear mechanism 1 can provide a planetary gear mechanism that has a wide range of reduction ratios from low reduction ratios to high reduction ratios, has good power transmission efficiency, and is thin in the axial direction.

[0051] In this embodiment, the first planetary gears 3 and the second planetary gears 6 are assembled by providing the input end of the connecting shaft 5 integrally with the first planetary gears 3 and fitting the output end of the connecting shaft 5 into the fitting hole A1 provided in the second planetary gears 6. The first planetary gears 3 and the second planetary gears 6 can also be assembled by providing the output end of the connecting shaft 5 integrally with the second planetary gears 6 and fitting the input end of the connecting shaft 5 into the fitting hole A1 provided in the first planetary gears 3. In these cases, the first planetary gears 3 and the second planetary gears 6 can be easily assembled. However, the first planetary gears 3 and the second planetary gears 6 can also be assembled by fitting the input end of the connecting shaft 5 into the fitting hole A1 provided in the first planetary gears 3 and fitting the output end of the connecting shaft 5 into the fitting hole A1 provided in the second planetary gears 6.

[0052] Fig. 4 shows a schematic axial view of an assembled state of the first planetary gear 3 and the second planetary gear 6. In addition, Fig. 5 shows another schematic axial view of an assembled state of the first planetary gear and the second planetary gear of the planetary gear mechanism 1.

[0053] For example, the shape of the mating hole A1 illustrated in FIG. 5 is square when viewed in the axial direction. In this case, the inner surface F1 of the mating hole A1 is formed by four flat surfaces F11 equally spaced around the axis OA. Therefore, if the output end of the connecting shaft 5 has the same square cross-sectional shape, there are four equal options for fitting the output end of the connecting shaft 5 into the mating hole A1. In this case, the output end of the connecting shaft 5 can be equally fitted into the shape of the mating hole A1 every time it is rotated 90 degrees around the axis OA. Therefore, if the shape of the output end of the connecting shaft 5 and the shape of the mating hole A1 are square, there is a 1 / 4 probability that a predetermined tooth position of the first planetary gear 3 and a predetermined tooth position of the second planetary gear 6 will be assembled so as to have the desired relative positional relationship in the circumferential direction.

[0054] On the other hand, the planetary gear mechanism 1 according to this embodiment is a planetary gear reduction mechanism. Therefore, in the planetary gear mechanism 1, the number of teeth of the first planetary gear 3 and the number of teeth of the second planetary gear 6 are different. Therefore, when assembling the first planetary gear 3 and the second planetary gear 6, it is necessary to align the phase difference between the tooth phase of the first planetary gear 3 and the tooth phase of the second planetary gear 6. For example, as shown in FIG. 5 , in this embodiment, the number of teeth of the first planetary gear 3 is greater than the number of teeth of the second planetary gear 6. Therefore, when assembling the first planetary gear 3 and the second planetary gear 6, it is necessary to align the phase difference between the teeth of the first planetary gear 3 and the second planetary gear 6 in a desired relative positional relationship in the circumferential direction. Therefore, in this embodiment, when assembling the first planetary gear 3 and the second planetary gear 6, particular attention must be paid to the positions of the teeth of the first planetary gear 3 and the second planetary gear 6 in order to align the phase differences between the teeth.

[0055] In addition, in the planetary gear mechanism 1, if the shape of the mating hole A1 is square, for example, when the output end of the connecting shaft 5 provided in the first planetary gear 3 has a square cross section and the output end of the connecting shaft 5 is press-fitted into the square mating hole A1 provided in the second planetary gear 6, it is difficult to keep the coaxiality (the degree of deviation between the central axes of the first planetary gear 3 and the second planetary gear 6) between the first planetary gear 3 and the second planetary gear 6 small. In other words, if the shape of the mating hole A1 is square like the mating hole A1 shown in the figures, it is difficult to assemble the first planetary gear 3 and the second planetary gear 6 on the same central axis when the output end of the connecting shaft 5 provided in the first planetary gear 3 is press-fitted into the mating hole A1 provided in the second planetary gear 6.

[0056] In contrast, the outer surface shape of the output-side end of the connecting shaft 5 and the inner surface shape of the fitting hole A1 can each include a flat surface F11 extending in the axial direction and a curved surface F12 extending in the axial direction and protruding radially outward. In this case, the outer surface shape of the output-side end of the connecting shaft 5 and the inner surface shape of the fitting hole A1 are formed into a similar surface F1. In this embodiment, the surface F1 includes the flat surface F11 and the curved surface F12. That is, in this embodiment, the outer surface shape of the output-side end of the connecting shaft 5 and the inner surface shape of the fitting hole A1 each include the corresponding flat surface F11 and curved surface F12. Therefore, when the outer surface shape of the output side end of the connecting shaft 5 is a shape including the same plane F11 and curved surface F12 as the inner surface shape of the fitting hole A1 including the plane F11 and curved surface F12, in order to fit the output side end of the connecting shaft 5 identically to the shape of the fitting hole A1, it is sufficient to align the plane F11 (curved surface F12) of the fitting hole A1 with the corresponding plane F11 (curved surface F12) provided on the output side end of the connecting shaft 5. Therefore, when the inner surface shape of the fitting hole A1 is made to include the plane F11 and the curved surface F12, if the shape of the output side end of the connecting shaft 5 also includes the plane F11 and the curved surface F12, the options for fitting the output side end of the connecting shaft 5 into the fitting hole A1 are reduced compared to when the fitting hole A1 is square. Therefore, when the shape of the output side end of the connecting shaft 5 and the shape of the fitting hole A1 are each made to include a flat surface F11 and a curved surface F12, the probability that the positions of predetermined teeth of the first planetary gear 3 and the positions of predetermined teeth of the second planetary gear 6 can be assembled so as to have the desired relative positional relationship in the circumferential direction is higher than in the case of a square.

[0057] In this embodiment, the outer surface shape of the output-side end of the connecting shaft 5 and the inner surface shape of the fitting hole A1 each include two flat surfaces F11 and two curved surfaces F12, and the two flat surfaces F11 are positioned opposite each other across the central axis OA of the fitting hole A1 (hereinafter simply referred to as the "axis OA"). In this embodiment, the axis OA is the same central axis as the axis O5. Furthermore, the two curved surfaces F12 are positioned so as to be connected between the two flat surfaces F11. In this embodiment, the two curved surfaces F12 are each curved surfaces that are convex radially outward, for example, arc-shaped.

[0058] In other words, in this embodiment, as viewed in the axial direction, the contour shapes of the two planes F11 are formed by linear contour shapes L1 that are parallel to each other and sandwich the axis OA, as shown in Fig. 5. Also, in this embodiment, as viewed in the axial direction, the contour shapes of the two curved surfaces F12 are formed by curved contour shapes L2 that are convex radially outward, as shown in Fig. 4.

[0059] According to this embodiment, the outer surface shape of the output end of the connecting shaft 5 and the inner surface shape of the fitting hole A1 each have two flat surfaces F11 that face each other across the axis OA, thereby imparting a certain directionality to the shape of the fitting hole A1 in the circumferential direction. For example, as shown in FIG. 4 , if the shape of the fitting hole A1 is designed to include two flat surfaces F11 and two curved surfaces F12, and the shape of the output end of the connecting shaft 5 also includes two flat surfaces F11 and two curved surfaces F12, the number of options for fitting the output end of the connecting shaft 5 into the fitting hole A1 is reduced to two options compared to a square shape. Therefore, when the outer surface shape of the output end of the connecting shaft 5 and the inner surface shape of the fitting hole A1 each include two flat surfaces F11 and two curved surfaces F12, the probability of assembling them so that a predetermined tooth position of the first planetary gear 3 and a predetermined tooth position of the second planetary gear 6 are in the desired relative positional relationship in the circumferential direction is 1 / 2. Therefore, as shown in FIG. 5, if the outer surface shape of the output end of the connecting shaft 5 and the inner surface shape of the fitting hole A1 each include two flat surfaces F11 and two curved surfaces F12, the probability that the positions of predetermined teeth of the first planetary gear 3 and the positions of predetermined teeth of the second planetary gear 6 will be assembled so as to have the desired relative positional relationship in the circumferential direction can be increased compared to the case of a square.

[0060] That is, if the outer surface shape of the output end of the connecting shaft 5 and the inner surface shape of the mating hole A1 each include two flat surfaces F11 and two curved surfaces F12, the two flat surfaces F11 can serve as a reference for aligning the phase difference between the first planetary gear 3 and the second planetary gear 6 when the connecting shaft 5 is press-fitted and fixed into the mating hole A1. Therefore, by imparting directionality to the mating hole A1, it is possible to prevent misassembly of the first planetary gear 3 and the second planetary gear 6 without aligning the phases of the first planetary gear 3 and the second planetary gear 6, thereby reducing the rate of defects. Furthermore, the two flat surfaces F11 function as a rotation stopper around the axis OA after the connecting shaft 5 is press-fitted and fixed into the mating hole A1.

[0061] In addition, according to this embodiment, the outer surface shape of the output-side end of the connecting shaft 5 and the inner surface shape of the mating hole A1 each have two flat surfaces F11 and two curved surfaces F12 that face each other across the axis OA. This allows deformation of the connecting shaft 5, which may occur when the two flat surfaces F11 on the output-side end of the connecting shaft 5 come into contact with the two flat surfaces F11 on the mating hole A1 when the connecting shaft 5 is press-fitted, to be relieved by each of the two curved surfaces F12 on the mating hole A1. This makes it easy to minimize the coaxiality of the first planetary gear 3 and the second planetary gear 6. In other words, when the connecting shaft 5 is press-fitted and fixed into the mating hole A1, it is easy to assemble the first planetary gear 3 and the second planetary gear 6 on the same central axis. This prevents a decrease in transmission efficiency due to axial misalignment between the first planetary gear 3 and the second planetary gear 6. Furthermore, the two curved surfaces F12 provided in the fitting hole A1 have the function of releasing deformation of the connecting shaft 5 when the connecting shaft 5 is press-fitted, thereby reducing the press-fitting load required when press-fitting the connecting shaft 5. This reduces the effects of deformation of the first planetary gear 3 or the second planetary gear 6 that may occur when the connecting shaft 5 is press-fitted, and as a result, prevents a decrease in transmission efficiency.

[0062] In this embodiment, by defining the outer surface shape of the output end of the connecting shaft 5 and the inner surface shape of the fitting hole A1 using two mutually facing flat surfaces F11 and a curved surface F12 connecting them, it is possible to achieve both phase alignment (matching the phase difference) between the first planetary gear 3 and the second planetary gear 6 and fixing them together using a simple assembly method. Furthermore, the two curved surfaces F12 provided in the fitting hole A1 reduce deformation during press-fitting of the connecting shaft 5, thereby reducing the press-fit load. As shown in FIG. 4 , an example of the outer surface shape of the output end of the connecting shaft 5 and the inner surface shape of the fitting hole A1 is a double-chamfered shape, with both ends of a circular hole notched, when viewed in the axial direction.

[0063] However, the outer surface shape of the output-side end of the connecting shaft 5 and the inner surface shape of the fitting hole A1 may be any shape as long as they include a corresponding flat surface F11 extending in the axial direction and a corresponding curved surface F12 extending in the axial direction and convex radially outward. Examples of such shapes include an end of the connecting shaft 5 and a fitting hole that are D-shaped when viewed in the axial direction, i.e., a D-cut end of the connecting shaft 5 and a fitting hole. This also allows for a simple assembly method to achieve both phase alignment (matching the phase difference) between the first planetary gear 3 and the second planetary gear 6 and their fixation. Furthermore, this also allows for the single curved surface F12 to relieve deformation of the connecting shaft 5 during press-fitting, thereby reducing the press-fit load.

[0064] The above is merely an illustrative embodiment of the present invention, and various modifications are possible within the scope of the appended claims.

[0065] 1: Planetary gear mechanism, 2: Sun gear, 3: First planetary gear, 4: First internal gear, 5: Connecting shaft, 6: Second planetary gear, 7: Carrier, 7a: Flange, 7b: Sleeve, 8: Second internal gear, 9: Support shaft, 11: Input shaft, 12: Output shaft, 13a, 13b, 13c: Ring bearing, 15: Case, 20: Sun gear member, 21: Connection portion, 80: Internal gear member, 81: Connection portion, 82: Connecting wall, A1: Fitting hole, A7: Through hole, F1: Inner surface of fitting hole, F11: Flat surface, F12: Curved surface, F2: Outer surface of support shaft, F71: Inner surface of carrier on flange side, F72: Inner surface of carrier on sleeve side, F8: Outer surface of connection portion of internal gear member h7: mounting hole, L1: linear contour shape, L2: curved contour shape, O1: central axis of planetary gear mechanism, O5: central axis of planetary gear, OA: central axis of fitting hole

Claims

1. A planetary gear mechanism comprising: a sun gear which is one of the input rotating element and the output rotating element; a first planetary gear which meshes with the sun gear; a first internal gear which meshes with the first planetary gear and is fixed to a case; a second planetary gear which is connected to the first planetary gear via a connecting shaft; a carrier which rotatably supports the connecting shaft; and a second internal gear which meshes with the second planetary gear and is the other of the input rotating element and the output rotating element; the carrier is an annular carrier arranged between the first planetary gear and the second planetary gear; and the sun gear has a support shaft which rotatably supports the carrier.

2. A planetary gear mechanism as described in claim 1, wherein one end of the connecting shaft is integrally formed with either the first planetary gear or the second planetary gear, and the other end of the connecting shaft is fitted into a fitting hole formed in the other of the first planetary gear and the second planetary gear.

3. A planetary gear mechanism as described in claim 2, wherein the outer surface shape of the other end of the connecting shaft and the inner surface shape of the mating hole each include a corresponding flat surface extending in the axial direction and a curved surface extending in the axial direction and protruding radially outward.

4. A planetary gear mechanism as described in claim 3, wherein the outer surface shape of the other end of the connecting shaft and the inner surface shape of the fitting hole each have two of the flat surfaces and two of the curved surfaces, the two flat surfaces are positioned opposite each other across the central axis of the fitting hole, and the two curved surfaces are positioned so as to be connected between the two flat surfaces.

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