Spline fittings and speed reducers

Abstract

To provide highly practical spline fittings and speed reducers. [Solution] A spline fitting body is formed by spline fitting a first member 30 having a shaft 36 portion with an external spline formed on its outer circumference, and a second member 32 having a hole 38 with an internal spline formed on its inner circumference, wherein each of the external spline teeth 50 constituting the external spline has a mountain-shaped cross-section extending in the axial direction, with a first inclined surface portion 52, which is the portion on one side from the apex in the circumferential direction, having a curved shape that bulges radially outward, and a second inclined surface portion 54, which is the portion on the other side from the apex in the circumferential direction, having a shape in which the length in the circumferential direction is shorter than that of the first inclined surface portion 52, and the internal spline has a configuration in which a plurality of grooves 60 are formed, each having a shape that follows the shape of a plurality of external spline teeth 50. The reduction gear is mainly composed of a planetary gear mechanism that employs this spline fitting body as a pinion gear.

Description

Technical Field

[0001] The present invention relates to a spline fitting, and also to a speed reducer using the spline fitting.

Background Art

[0002] Patent Document 1 below discloses a speed reducer that reduces and outputs the rotational speed of a motor. This speed reducer is configured to include a planetary gear mechanism. This planetary gear mechanism is a composite type and includes two sets of planetary gears (planetary gears). Each of these planetary gears has a configuration in which a large gear and a small gear are coaxially connected. For the connection between the large gear and the small gear, for example, spline fitting is used. Further, Patent Document 2 below discloses a propeller shaft for transmitting the power output from the engine of a vehicle to a final reduction gear. The propeller shaft includes a cross shaft joint and a steel pipe, and spline fitting is used for the portion connecting them. That is, Patent Documents 1 and 2 below disclose a spline fitting in which a first member having a shaft portion with an external spline formed on its outer peripheral surface and a second member having a hole portion with an internal spline formed on its inner peripheral surface are spline-fitted to each other.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In conventional spline fittings, as described in Patent Document 2 above, spline teeth are often involute splines with a shape based on an involute curve, or square splines. When using these conventional spline teeth, a certain amount of clearance is generally provided between the outer spline and the inner spline. For example, in a spline fitting (planetary gear) connecting a large gear and a small gear, as described in Patent Document 1 above, multiple gears mesh with these large and small gears, so if the above clearance is large, assembly can be done easily. However, the presence of this large clearance can lead to problems such as the generation of abnormal noise and a decrease in power transmission efficiency. On the other hand, if a configuration is used in which the clearance is small and the gears are press-fitted, the phase accuracy in the circumferential direction between the first member and the second member must be greatly increased, otherwise it becomes impossible to assemble multiple gears to the spline fitting (planetary gear) connecting the large and small gears. In other words, by addressing these various problems without increasing or decreasing the clearance between the outer spline and the inner spline, a highly practical spline fitting structure can be realized. Consequently, by using a highly practical spline structure, it is possible to realize a highly practical spline fitting body and a highly practical speed reducer.

[0005] This invention has been made in view of such circumstances, and aims to provide a highly practical spline fitting and a gearbox. [Means for solving the problem]

[0006] To solve the above problems, the spline fitting disclosed in this application has the following structure. (1) A spline fitting body comprising a first member having a shaft portion on which an external spline is formed on its outer circumference, and a second member having a hole portion on which an internal spline is formed on its inner circumference, wherein the two members are spline fitted together, Each of the external spline teeth constituting the external spline is, It has a mountain-shaped cross-section that extends in the axial direction. The first inclined surface portion, which is the part on one side of the vertex in the circumferential direction, has a curved shape that bulges radially outward, and the second inclined surface portion, which is the part on the other side of the vertex in the circumferential direction, has a shape in which the length in the circumferential direction is shorter than that of the first inclined surface portion. The internal spline is a spline fitting body having multiple grooves formed therein, each groove having a shape similar to that of the multiple external spline teeth.

[0007] In the spline fitting disclosed in this application, each of the external spline teeth has an asymmetrical shape on one side and the other side in the circumferential direction, with the second inclined surface being more upright compared to the first inclined surface; in other words, the first inclined surface having a gentler slope compared to the second inclined surface. To put it simply, in the spline fitting disclosed in this application, the external spline has a cross-sectional shape, when viewed from the axial direction, that resembles the teeth of a saw blade. That is, the first inclined surface has a larger surface area compared to the second inclined surface. Furthermore, the first inclined surface is bulging radially outward, which increases its surface area compared to a planar inclined shape. The spline fitting disclosed in this application is configured such that, during power transmission, the first inclined surface portion with a large surface area and the curved portion of the groove of the inner spline that faces the first inclined surface portion (hereinafter sometimes referred to as the "first opposing surface portion") come into contact with each other, thereby reducing the surface pressure acting between them during power transmission and improving strength. Furthermore, for example, in an involute spline, the side surface of the outer spline tooth forms an involute curve, so it comes into contact with the inner spline in a line, making it difficult for the position of contact to be constant, and there is a risk of a shift in the relative rotational position (phase) in the circumferential direction between the first member and the second member. However, the spline fitting disclosed in this application is configured such that, during power transmission, the first inclined surface portion and the first opposing surface portion come into contact, thereby ensuring that the phase between the first member and the second member is reliably fixed.

[0008] The second inclined surface may be curved or flat. However, a flat shape is considered to offer better assembly because the circumferential clearance between the second inclined surface and the portion of the groove of the internal spline facing the second inclined surface (hereinafter sometimes referred to as the second opposing surface) remains nearly constant in the radial direction.

[0009] Furthermore, the spline fitting with the above configuration can be made into various forms as shown below.

[0010] (2) The spline fitting according to item (1), wherein the length of the first inclined surface in the circumferential direction is greater than the radial dimension of the outer spline teeth.

[0011] (3) The spline fitting according to item (1) or (2), wherein the length of the first inclined surface in the circumferential direction is 3 times or more and 5 times or less the length of the second inclined surface.

[0012] The spline fittings with the two configurations described above have a gentler incline in the first inclined surface, making them suitable for achieving the aforementioned effects.

[0013] (4) The first member is a first gear having a gear portion provided coaxially with the shaft portion and having a plurality of teeth formed on its outer surface, The spline fitting according to any one of items (1) to (3), wherein the second member is a second gear having a different number of teeth on its outer circumferential surface than the number of teeth on the gear portion of the first member.

[0014] In this spline fitting configuration, the first and second members are gears. The first gear and the second gear have different numbers of teeth, and the phase between the first gear and the second gear is important. Therefore, the spline fitting disclosed herein, which can fix the phase between the first gear and the second gear during power transmission, is suitable for this gear configuration.

[0015] To solve the above problems, the speed reducer disclosed in this application has the following structure.

[0016] (5) A reduction gear that reduces the rotational speed of a drive motor and outputs the result, Each of these consists of multiple planetary gears, which are spline fittings as described in section (4), A carrier that holds multiple planetary gears so that they can rotate around an axis, A sun gear that meshes with multiple planetary gears on the inside of the second gear, A first outer gear, which is an internal gear that meshes with a plurality of planetary gears on the outside of the second gear, A reduction gear mainly composed of a planetary gear mechanism, which includes a second outer gear that is an internal gear that meshes with a plurality of the aforementioned planetary gears on the outside of the first gear.

[0017] The speed reducer disclosed in this application is mainly composed of a planetary gear mechanism that includes gears which are spline-fitted bodies disclosed in this application. In particular, in this planetary gear mechanism, the planetary gear is a two-stage type in which the first gear and the second gear are spline-fitted, and since many gears mesh together, there is a risk that assembly will not be possible if there is a phase misalignment between the first gear and the second gear. In contrast, the speed reducer disclosed in this application has high assembly ease because the planetary gear is the aforementioned spline-fitted body. For example, consider the case in which the first outer gear and the second outer gear mesh with multiple planetary gears, and then the sun gear meshes with them. In the case of a general spline, as mentioned above, it is necessary to increase the phase accuracy by widening the clearance between the outer spline and the inner spline of the planetary gear, or by making the clearance extremely small and press-fitting it. In contrast, the speed reducer disclosed in this application does not require press-fitting of the first gear and the second gear, and an appropriate clearance is secured between the outer spline and the inner spline, thus relaxing the machining accuracy requirements. Furthermore, even if the circumferential clearance of the spline fitting disclosed in this application is the same as that of a general spline, when the curved first inclined surface portion and the curved first opposing surface portion are brought into contact, the occurrence of abnormal noise, insufficient strength, and deterioration of power transmission efficiency can be suppressed compared to a general spline. For these reasons, the speed reducer disclosed in this application improves ease of assembly while suppressing the occurrence of abnormal noise, insufficient strength, and deterioration of power transmission efficiency.

[0018] (6) The sun gear is rotated by the drive motor, The reduction gear according to item (5), wherein the planetary gear has a first inclined surface portion of the first gear that acts as a surface receiving force from the second gear in response to an input from the sun gear.

[0019] In the speed reducer with this configuration, the driving force of the drive motor is transmitted to the second gear of the planetary gear via the sun gear. That is, in the planetary gear, the rotational force input to the second gear is applied to the first gear. More specifically, force is applied from the first opposing surface portion of the second gear to the first inclined surface portion of the first gear. The first inclined surface portion and the first opposing surface portion have a relatively large surface area, which can reduce the surface pressure acting between them during power transmission and improve the strength.

[0020] (7) The planetary gear mechanism is provided with an even number of the planetary gears, Half of the plurality of the planetary gears are the first planetary gears in which each of the outer spline teeth has the first inclined surface portion on one side in the circumferential direction and the second inclined surface portion on the other side, The remaining half of the plurality of the planetary gears are the second planetary gears in which each of the outer spline teeth has the first inclined surface portion on the other side in the circumferential direction and the second inclined surface portion on the one side, The carrier holds the first planetary gear and the second planetary gear alternately in the circumferential direction. The speed reducer according to item (5) or (6).

[0021] In the speed reducer with this configuration, the spline directions in the first planetary gear and the second planetary gear are formed in opposite directions. Thereby, when the drive motor rotates forward, the first inclined surface portion functions as the acting surface in one of the first planetary gear and the second planetary gear, and when the drive motor rotates reversely, the first inclined surface portion functions as the acting surface in one of the first planetary gear and the second planetary gear. Therefore, the speed reducer with this configuration can reduce backlash.

Effects of the Invention

[0022] According to the present invention, a highly practical spline fitting and a speed reducer can be provided.

Brief Description of the Drawings

[0023] [Figure 1] Cross-sectional view of a speed reducer according to an embodiment of the present invention. [Figure 2] Perspective view of multiple planetary gears and the carrier that holds them. [Figure 3] A diagram showing multiple planetary gears and the carriers that hold them, viewed from the axial direction. [Figure 4] Planetary gear exploded view [Figure 5] A perspective view showing a magnified view of the external spline of the first gear. [Figure 6] Enlarged cross-sectional view showing the spline structure of the first planetary gear. [Figure 7] Enlarged cross-sectional view showing the spline structure of the second planetary gear. [Modes for carrying out the invention]

[0024] An embodiment of the present invention, the gearbox 10, will be described with reference to Figures 1 to 7. Parts of each drawing show the X, Y, and Z axes, and each axis is depicted in the direction shown in the drawing.

[0025] The reduction gear 10 of this embodiment is mounted on an electric vehicle and converts the rotational force of the drive motor into driving force. Specifically, the reduction gear 10 is positioned between the motor (only the motor shaft 12 is shown in Figure 1) that provides driving force to the vehicle and the axle 14, and reduces the rotational speed of the motor and transmits it to the axle 14. As shown in Figure 1, the reduction gear 10, together with the motor and differential gear (only the differential ring gear 16 is shown in Figure 1), is housed in a housing 18 and is a unitized motor with a reduction gear. The motor shaft 12 is cylindrical, and the axle 14 is held in a state where it passes through the inside of the motor shaft 12.

[0026] The reduction gear 10 is mainly composed of a planetary gear mechanism 20. As shown in Figure 1, the planetary gear mechanism 20 is a 3K type composite planetary gear mechanism and consists of two-stage planetary gears (pinion gears) 22A, 22B, 22C, and 22D, a carrier 24 that holds these four planetary gears (see Figure 3), a sun gear 26 which is an external sun gear that meshes with the four planetary gears 22A, 22B, 22C, and 22D, and two internal sun gears, a fixed ring gear 28 and a differential ring gear 16, which mesh with the four planetary gears 22A, 22B, 22C, and 22D. Note that all of these gears 22A, 22B, 22C, 22D, 24, 26, 28, and 16 are helical gears.

[0027] The four planetary gears 22A, 22B, 22C, and 22D are spline-fitted bodies formed by spline-fitting a first gear 30 and a second gear 32, each having a different outer diameter and number of teeth, as shown in Figures 1 to 3. In other words, these four planetary gears 22A, 22B, 22C, and 22D represent embodiments of the spline-fitted body of the present invention. As shown in Figure 4, the first gear 30 is the one with the relatively smaller outer diameter and consists of a gear portion 34 with helical teeth formed on its outer circumference and a spline shaft portion 36 that protrudes from the gear portion 34 and has an outer spline formed on its outer circumference. On the other hand, the second gear portion 32 is annular in shape with a hole portion 38, with helical teeth formed on its outer circumference and an inner spline formed on the inner circumference of the hole portion 38. The spline shaft portion 36 of the first gear 30, which corresponds to the first component, is spline-fitted into the hole portion 38 of the second gear portion 32, which corresponds to the second component, thereby forming the planetary gears 22A, 22B, 22C, and 22D, which are spline-fitted bodies.

[0028] As shown in Figure 4, the four planetary gears 22A, 22B, 22C, and 22D are each rotatably held around the rotation axis 40 at equiangled positions by the annular carrier 24. Although the four planetary gears 22A, 22B, 22C, and 22D are identical in appearance, the spline structures of one pair of planetary gears 22A, 22C and the other pair of planetary gears 22B, 22D, which are positioned opposite each other across the center of the carrier 24, differ from each other. This embodiment is characterized by this spline structure, and therefore, a detailed explanation of the spline structure of these planetary gears 22A, 22B, 22C, and 22D will be reserved here and will be provided later.

[0029] The sun gear 26 meshes with the four planetary gears 22A, 22B, 22C, and 22D, which are held on the carrier 24, on the inside of the second gear 32. The sun gear 26 is also connected to the motor shaft 12 and is rotated by the motor. In other words, rotation is transmitted from the sun gear 26 to each of the planetary gears 22A, 22B, 22C, and 22D.

[0030] Furthermore, the second gear 32 of the planetary gears 22A, 22B, 22C, and 22D meshes with a fixed ring gear 28, which is fixed to the housing 18, on the outside. In other words, the fixed ring gear 28 corresponds to the first outer gear. On the other hand, the carrier 24 is held by bearings 43, etc., to the housing 18 coaxially with the motor shaft 12 and the axle 14, and rotatable around their axes. Therefore, when rotation is transmitted from the sun gear 26 to the second gear 32 of the planetary gears 22A, 22B, 22C, and 22D, the planetary gears 22A, 22B, 22C, and 22D rotate (rotate on their own axis) around the rotation axis 40 while moving along the fixed ring gear 28, that is, they revolve around the sun gear 26.

[0031] Furthermore, the first gear 30 of the planetary gears 22A, 22B, 22C, and 22D has a differential ring gear 16 meshing with it on the outside. In other words, the differential ring gear 16 corresponds to the second outer gear. This differential ring gear 16 is connected to the axle 14. In short, when the four planetary gears 22A, 22B, 22C, and 22D revolve, the differential ring gear 16 rotates, and this rotation is transmitted to the axle 14 as driving force.

[0032] Here, we will explain the spline structure of the planetary gears 22A, 22B, 22C, and 22D, which were previously withheld from explanation. Figures 5 and 6 show the spline structure of the first planetary gears, planetary gears 22A and 22C. The external splines of the first gear 30 are generally of a sawtooth shape. That is, each of the external spline teeth 50 constituting the external spline extends along the axial direction of the spline shaft portion 36, and its cross-section is mountain-shaped. More specifically, the external spline tooth 50 has a shape that includes a first inclined surface portion 52, which is the portion on one side (clockwise side in Figure 6) from the apex in the circumferential direction, and a second inclined surface portion 54, which is the portion on the other side (counterclockwise side in Figure 6). Furthermore, the external spline tooth 50 has an asymmetrical shape with respect to the apex in the circumferential direction. Specifically, the second inclined surface portion 54 has a circumferential length L2 that is shorter than the circumferential length L1 of the first inclined surface portion 52, so that the external spline teeth 50 are asymmetrical in the circumferential direction around the apex, and have a shape like the teeth of a saw blade. More specifically, the length L1 of the first inclined surface portion 52 is set to be between 3 and 5 times the length L2 of the second inclined surface portion 54. It is preferable that the length L1 of the first inclined surface portion 52 be between 4 and 5 times the length L2 of the second inclined surface portion 54, and in this embodiment, the length L1 is set to be approximately 4 times the length L2.

[0033] Furthermore, the length L1 of the first inclined surface portion 52 is longer than the height H of the external spline teeth 50, while the length L2 of the second inclined surface portion 54 is shorter than the height (radial dimension) H of the external spline teeth 50. Moreover, while the second inclined surface portion 54 of the external spline teeth 50 has a planar shape, the first inclined surface portion 52 has a curved shape that bulges radially outward.

[0034] The internal splines of the second gear 32 are configured with multiple grooves 60 that are shaped like the external spline teeth 50. In other words, each groove 60 has a first opposing surface portion 62 that faces the first inclined surface portion 52 and a second opposing surface portion 64 that faces the second inclined surface portion 54. A suitable clearance is provided between the external spline teeth 50 and the grooves 60, allowing the first gear 30 and the second gear 32 to be easily fitted together.

[0035] When the motor is rotating forward, that is, when the vehicle is moving forward, the second gear 32 of the first planetary gears 22A and 22C is rotated by the sun gear 26 in the direction indicated by the black arrows in Figures 3 and 6. As a result, the first opposing surface 62 of the second gear 32 comes into contact with the first inclined surface 52 of the first gear 30. The first inclined surface 52 of the first gear 30 then functions as a surface that receives force from the first opposing surface 62 of the second gear 32. The first inclined surface 52 and the first opposing surface 62 are curved, and their surface area is larger than that of a flat surface, which reduces the surface pressure acting between them during power transmission and improves strength.

[0036] Furthermore, in an involute spline, for example, the side surface of the outer spline teeth traces an involute curve, and is in contact with the inner spline by a line (a straight line extending in the axial direction). Because the position of contact changes, the relative rotational position (phase) of the first member and the second member in the circumferential direction is not constant. In contrast, according to this embodiment, by configuring the first opposing surface portion 62 to contact the first inclined surface portion 52 during forward rotation, the phase of the first gear 30 with respect to the second gear 32 is reliably fixed.

[0037] On the other hand, when the motor is rotating in the reverse direction, that is, when the vehicle is moving backward, if the first planetary gears 22A and 22C are used, the second gear 32 will be rotated by the sun gear 26 in the direction indicated by the white arrow in Figure 3. In other words, when the motor is changed from forward rotation to reverse rotation, as shown in Figure 6, the second opposing surface 64 of the second gear 32 comes into contact with the second inclined surface 54 of the first gear 30, and a force is applied from the second opposing surface 64 of the second gear 32 to the second inclined surface 54 of the first gear 30. However, because a clearance is maintained between the outer spline teeth 50 and the groove 60, backlash occurs. In contrast, the reduction gear 10 of this embodiment is designed to reduce backlash when the motor is changed from forward rotation to reverse rotation.

[0038] Specifically, the reduction gear 10 of this embodiment achieves its objective by having a spline structure of the second planetary gears 22B and 22D that is different from the spline structure of the first planetary gears 22A and 22C. As shown in Figure 7, the spline structure of the second planetary gears 22B and 22D is the same as that of the first planetary gears 22A and 22C, but in the circumferential direction. In other words, the outer spline teeth 80 of the first gear 30 have a second inclined surface portion 84 on one side (clockwise in Figure 7) from the apex in the circumferential direction, and a first inclined surface portion 82 on the other side (counterclockwise in Figure 7). Similarly, in the groove 90 that constitutes the internal spline of the second gear, one portion from the apex in the circumferential direction is designated as the second opposing surface portion 94, and the other portion is designated as the first opposing surface portion 92.

[0039] As a result, when the motor is in reverse rotation, the first opposing surface 92 of the second gear 32 contacts the first inclined surface 82 of the first gear 30 before the second opposing surface 64 of the second gear 32 contacts the second inclined surface 54 of the first gear 30 in the first planetary gears 22A and 22C, which are the first planetary gears. Thus, the reduction gear 10 of this embodiment is configured to transmit the rotational force of the motor mainly using the first planetary gears 22A and 22C when the motor is in forward rotation, and to transmit the rotational force of the motor mainly using the second planetary gears 22B and 22D when the motor is in reverse rotation. This reduces backlash when the motor's forward and reverse rotation is changed, and improves power transmission efficiency. Furthermore, by reducing backlash, it is possible to reduce abnormal noise caused by changes in the contact points of the spline mating during reversal.

[0040] Furthermore, the reduction gear 10 of this embodiment has a configuration in which a sun gear 26, a fixed ring gear 28, and a differential ring gear 16 are meshed with each planetary gear 22A, 22B, 22C, and 22D, which presents an assembly problem. More specifically, the phase between the first gear 30 and the second gear 32 in the planetary gears 22A, 22B, 22C, and 22D is important. For example, in this embodiment, first, the differential ring gear 16 is meshed with the first gear 30 for the four planetary gears 22A, 22B, 22C, and 22D held by the carrier 24. Next, the fixed ring gear 28, which is fixed to the first member 18A of the housing 18, is meshed with the second gear 32. Finally, the sun gear 26 is meshed with the second gear 32. During assembly, a suitable clearance is provided in the spline fitting structure of the first gear 30 and the second gear 32. This allows the axial and rotational positions of the second gear 32 to be adjusted relative to the first gear 30, resulting in the sun gear 26, fixed ring gear 28, and differential ring gear 16 meshing with the four planetary gears 22A, 22B, 22C, and 22D. This makes assembly relatively easy.

[0041] <Other Embodiments> The present invention is not limited to the embodiments described above, and can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. For example, the following embodiments are also included within the technical scope of the present invention.

[0042] In this embodiment, the second inclined surface portion 54 of the external spline teeth 50 was planar in shape, but it may also be curved in shape together with the first inclined surface portion 52.

[0043] In this embodiment, the planetary gear mechanism 20 was assumed to have four planetary gears 22A, 22B, 22C, and 22D, but the number is not limited. However, by having an even number and staggering the orientation of the external spline teeth, the aforementioned backlash can be reduced.

[0044] In this embodiment, the planetary gear mechanism 20 was a 3K type composite planetary gear mechanism, but it is not limited to this. The reduction gear of the present invention can be used in a device having a two-stage planetary gear.

[0045] Furthermore, the spline fitting of the present invention is not limited to pinion gears of planetary gear mechanisms, but can be used in configurations that spline-fit two gears. Moreover, the spline fitting of the present invention is not limited to fitting two gears, but can be widely used in configurations that fit two power-transmitting members. [Explanation of Symbols]

[0046] 10…Reduction gear, 16…Differential ring gear [second outer gear], 20…Planetary gear mechanism, 22A, 22C…First planetary gear [spline fitting], 22B, 22D…Second planetary gear [spline fitting], 26…Sun gear, 28…Fixed ring gear [first outer gear], 30…First gear [first component], 32…Second gear [second component], 34…Gear section, 36…Spline shaft section [shaft section], 38…Hole section, 50…External spline teeth, 52…First inclined surface section, 54…Second inclined surface section, 60…Groove, 80…External spline teeth, 82…First inclined surface section, 84…Second inclined surface section, 90…Groove

Claims

1. A spline fitting body comprising a first member having a shaft portion with an external spline formed on its outer circumference, and a second member having a hole portion with an internal spline formed on its inner circumference, wherein the two members are spline-fitted together, Each of the external spline teeth constituting the external spline is, It has a mountain-shaped cross-section that extends in the axial direction. The first inclined surface portion, which is the part on one side from the vertex in the circumferential direction, has a curved shape that bulges radially outward, and the second inclined surface portion, which is the part on the other side from the vertex in the circumferential direction, has a shape in which the length in the circumferential direction is shorter than that of the first inclined surface portion. The internal spline is a spline fitting body having multiple grooves formed therein, each groove having a shape similar to that of the multiple external spline teeth.

2. The spline fitting according to claim 1, wherein the length of the first inclined surface portion in the circumferential direction is greater than the radial dimension of the outer spline teeth.

3. The spline fitting according to claim 1 or claim 2, wherein the length of the first inclined surface in the circumferential direction is three times or more and five times or less the length of the second inclined surface.

4. The first member is a first gear having a gear portion provided coaxially with the shaft portion and having a plurality of teeth formed on its outer circumferential surface. The spline fitting according to claim 1 or claim 2, wherein the second member is a second gear having a different number of teeth on its outer circumferential surface than the number of teeth on the gear portion of the first member.

5. A reduction gear that reduces the rotational speed of a drive motor and outputs the reduced speed, Each of the planetary gears is a spline fitting as described in claim 4, A carrier that holds multiple planetary gears so that they can rotate around an axis, A sun gear that meshes with a plurality of the aforementioned planetary gears on the inside of the second gear, A first outer gear, which is an internal gear that meshes with a plurality of planetary gears on the outside of the second gear, A reduction gear mainly composed of a planetary gear mechanism, which includes a second outer gear that is an internal gear that meshes with a plurality of the aforementioned planetary gears on the outside of the first gear.

6. The sun gear is rotated by the drive motor, The reduction gear according to claim 5, wherein the planetary gear has a first inclined surface portion of the first gear that receives force from the second gear in response to an input from the sun gear.

7. The planetary gear mechanism is provided with an even number of planetary gears. Half of the multiple planetary gears are first planetary gears in which each of the external spline teeth has a first inclined surface on one side in the circumferential direction and a second inclined surface on the other side. The remaining half of the multiple planetary gears are second planetary gears in which each of the external spline teeth has a first inclined surface on the other side in the circumferential direction and a second inclined surface on the one side. The reduction gear according to claim 5, wherein the carrier alternately holds the first planetary gear and the second planetary gear in the circumferential direction.

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