Power transmission device

Abstract

To provide a power transmission device which can achieve reduction of torque loss.SOLUTION: A power transmission device includes: a fixing member having a cylindrical surface; an output shaft having a facing surface facing the cylindrical surface; an input shaft having a pressing portion disposed between the cylindrical surface and the facing surface; and a pair of rolling elements disposed at both sides of the pressing portion in a circumferential direction. The facing surface is provided with a concave surface in which the pressing portion and the pair of rolling elements are housed. The concave surface has a bottom surface and a pair of pressed surfaces. A surface in the circumferential direction of the pressing portion is formed as a pressing surface which presses the pressed surface through the rolling element. The bottom surface has: a central surface located at a center part in the circumferential direction; and a pair of cam surfaces located at both ends in the circumferential direction. A distance between the cam surface and the cylindrical surface increases from the central surface toward the pressed surface. The distance between the cam surface and the cylindrical surface is smaller than a diameter of the rolling element in a portion located close to the central surface of the cam surface, and is greater than the diameter of the rolling element in a portion located close to the pressed surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a power transmission device.

Background Art

[0002] A power transmission device is a device that transmits torque generated by a motor or the like. Such a power transmission device is used, for example, to drive an arm of an industrial robot. The power transmission device includes an input shaft to which torque is input and an output shaft that outputs torque. An object to be driven is connected to the output shaft, and an external force such as the weight of the object (hereinafter referred to as an external force) is input. If the output shaft rotates, the position of the object cannot be maintained. Therefore, in order to keep the angle of the output shaft held, it is necessary to continuously issue commands to the motor to hold the position of the object. On the other hand, in the power transmission device of Patent Document 1, while it is possible to transmit torque from the input shaft to the output shaft, when an external force is input to the output shaft, the rotation of the output shaft is restricted.

[0003] Describing the power transmission device of Patent Document 1 in detail, the power transmission device includes a carrier (input shaft), a flange plate, a lock release plate, and an output shaft arranged coaxially. Further, the power transmission device includes an outer ring into which the output shaft is inserted, and a plurality of cylindrical rollers and elastic bodies arranged between the outer ring and the output shaft. The cylindrical rollers are biased by the elastic bodies. Also, when the cylindrical rollers move in the biased direction, they are sandwiched between the inner peripheral surface of the outer ring and the outer peripheral surface of the output shaft. Thereby, the rotation of the output shaft is restricted. The flange plate is connected to the output shaft. When the lock release plate rotates, the lock release plate pushes out the cylindrical rollers against the biasing force of the elastic bodies. As a result, the state in which the cylindrical rollers are sandwiched between the outer ring and the output shaft is released, and the lock of the output shaft is released. Also, when the carrier rotates, the carrier first transmits torque to the lock release plate via the convex portion and then transmits torque to the flange plate with a delay. That is, after the lock release plate rotates and the lock of the output shaft is released, the flange plate rotates and torque is transmitted to the output shaft.

Prior Art Documents

Patent Document

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in the power transmission device of Patent Document 1, the loss of torque transmitted from the input shaft to the output shaft (hereinafter referred to as torque loss) is large.

[0006] The present disclosure has been made in view of the above, and an object thereof is to provide a power transmission device that reduces torque loss.

Means for Solving the Problems

[0007] To achieve the above object, a power transmission device according to one aspect of the present disclosure includes a fixed member having a cylindrical surface facing radially inward or radially outward, an output shaft having a facing surface facing the cylindrical surface, an input shaft having at least one pressing portion disposed between the cylindrical surface and the facing surface, and a pair of rolling elements disposed between the cylindrical surface and the facing surface and on both circumferential sides of the pressing portion. A concave surface that is recessed in the radial direction and houses the pressing portion and the pair of rolling elements therein is formed on the facing surface. The concave surface has a bottom surface and a pair of pressed surfaces that extend radially from an end portion in the circumferential direction of the bottom surface and face the circumferential direction. The circumferential surface of the pressing portion is a pressing surface that presses the pressed surface via the rolling element. The bottom surface is located at a central portion in the circumferential direction of the concave surface, and includes a central surface where the pressing portion is disposed between the bottom surface and the cylindrical surface, and a pair of cam surfaces that are located at both end portions in the circumferential direction of the concave surface and where the rolling element is disposed between the bottom surface and the cylindrical surface. The distance between the cam surface and the cylindrical surface gradually increases as the cam surface approaches the pressed surface from the central surface. A portion of the cam surface closer to the central surface has a distance between the cam surface and the cylindrical surface that is smaller than the diameter of the rolling element. A portion of the cam surface closer to the pressed surface has a distance between the cam surface and the cylindrical surface that is larger than the diameter of the rolling element.

Effect of the Invention

[0008] According to the power transmission device of the present disclosure, torque is transmitted from the input shaft to the output shaft via the rigid rolling element, so that torque loss is reduced.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Embodiments for Carrying Out the Invention

[0010] The embodiments for carrying out the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited by the content described in the following description. Also, the constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be combined as appropriate.

[0011] (Embodiment 1) FIG. 1 is a cross-sectional view of the power transmission device of Embodiment 1 taken in a direction orthogonal to the axial direction, and more specifically, is a cross-sectional view taken along the arrow I-I line in FIG. 2. FIG. 2 is a cross-sectional view of the power transmission device of Embodiment 1 taken in the axial direction, and more specifically, is a cross-sectional view taken along the arrow II-II line in FIG. 1. FIG. 3 is an enlarged view of the concave surface in FIG. 1.

[0012] As shown in FIG. 1, the power transmission device 100 of Embodiment 1 includes a fixed member 1, an output shaft 2, an input shaft 3, and a plurality of cylindrical rollers (rolling elements) 4.

[0013] The fixing member 1 is a component for fixing the power transmission device 100 to other components. As shown in FIG. 2, the fixing member 1 has an outer ring portion 10, an outer flange portion 11 protruding from the outer ring portion 10 to the outer peripheral side, and an inner flange portion 12 protruding from the outer ring portion 10 to the inner peripheral side. As shown in FIG. 1, the outer ring portion 10 is formed in an annular shape. The inner peripheral surface 13 and the outer peripheral surface 14 of the outer ring portion 10 are formed in a circular shape centered on the center line O1. That is, the outer ring portion 10 is formed in a cylindrical shape. Hereinafter, the inner peripheral surface 13 may be referred to as a cylindrical surface. Also, the direction parallel to the center line O1 of the inner peripheral surface 13 is referred to as the axial direction. Also, the direction orthogonal to the center line O1 is referred to as the radial direction. Also, the direction of rotation around the center line O1 is referred to as the circumferential direction.

[0014] The outer flange portion 11 and the inner flange portion 12 each extend in the circumferential direction along the outer ring portion 10 and are annular. A through hole 11a penetrating in the axial direction is formed in the outer flange portion 11. The shaft portion of a bolt (not shown) is inserted into the through hole 11a. Then, the outer flange portion 11 is tightened by the head of a bolt (not shown). Thereby, the fixing member 1 is fixed to another device.

[0015] As shown in FIG. 2, the outer flange portion 11 is provided at one axial end portion of the outer ring portion 10. The inner flange portion 12 is provided at the other axial end portion of the outer ring portion 10. Hereinafter, among the axial directions, the direction in which the outer flange portion 11 is arranged as viewed from the inner flange portion 12 is referred to as the first direction X1, and the opposite direction is referred to as the second direction X2. Also, as shown in FIG. 1, with respect to the circumferential direction, the explanation is based on the case when viewed from the second direction X2. Then, the counterclockwise (anticlockwise) direction as viewed from the second direction X2 is referred to as the first rotation direction L1. The clockwise direction as viewed from the second direction X2 is referred to as the second rotation direction L2.

[0016] As shown in FIG. 2, the output shaft 2 includes an annular inner ring portion 20 disposed on the inner peripheral side of the outer ring portion 10, and an annular first connecting portion 21 provided on the inner peripheral side of the inner ring portion 20.

[0017] As shown in Fig. 1, the outer peripheral surface 22 of the inner ring portion 20 is a facing surface that faces the inner peripheral surface 13 of the outer ring portion 10. In some cases, the outer peripheral surface 22 may be referred to as the facing surface. The outer diameter of the outer peripheral surface 22 is substantially the same as the diameter of the inner peripheral surface 13 of the outer ring portion 10. And the outer peripheral surface of the inner ring portion 20 is slidably abutted against the inner peripheral surface 13 of the outer ring portion 10 in the circumferential direction. Thereby, the output shaft 2 is arranged coaxially with the center line O1 of the fixing member 1 and is rotatably supported by the fixing member 1.

[0018] On the outer peripheral surface 22 of the inner ring portion 20, a concave surface 23 that is recessed radially inward is formed. In this embodiment, six concave surfaces 23 are formed. The six concave surfaces 23 are arranged at equal intervals in the circumferential direction. Inside one concave surface 23, a pressing portion 32 (to be described later) of the input shaft 3 and two cylindrical rollers 4 are arranged. The details of the concave surface 23 will be described later.

[0019] As shown in Fig. 2, an inner flange portion 12 is arranged in the second direction X2 of the inner ring portion 20. Therefore, the output shaft 2 does not drop off from the fixing member 1 in the second direction X2. Also, the inside of the concave surface 23 is covered by the inner flange portion 12 from the second direction X2. Therefore, the cylindrical roller 4 does not drop off from the inside of the concave surface 23 in the second direction X2.

[0020] The outer diameter of the first connecting portion 21 is smaller than the inner diameter of the inner flange portion 12. That is, the first connecting portion 21 is arranged on the inner circumferential side of the inner flange portion 12. The inner circumferential surface of the first connecting portion 21 serves as a fitting surface into which another component 101 that transmits torque from the power transmission device 100 (output shaft 2) is fitted.

[0021] The input shaft 3 has a second connecting portion 30 arranged in the first direction X1 of the first connecting portion 21, a main body portion 31 extending radially outward from the second connecting portion 30, and a plurality of pressing portions 32 protruding from the main body portion 31 in the second direction X2.

[0022] As shown in Fig. 1, the second connecting portion 30 is formed in an annular shape. The inner diameter and outer diameter of the second connecting portion 30 are the same as those of the first connecting portion 21. The inner peripheral surface of the second connecting portion 30 is a fitting surface on which another component 102 that transmits torque to the power transmission device (input shaft) is fitted.

[0023] The main body portion 31 extends in the circumferential direction along the outer peripheral surface of the second connecting portion 30 and is annular. As shown in Fig. 2, the outer diameter of the main body portion 31 is substantially the same as the diameter of the inner peripheral surface 13 of the outer ring portion 10. The outer peripheral surface of the main body portion 31 is slidably in contact with the inner peripheral surface 13 of the outer ring portion 10 in the circumferential direction. Thereby, the input shaft 3 is arranged coaxially with the center line O1 of the outer ring portion 10 and is rotatably supported by the fixing member 1.

[0024] The inner ring portion 20 of the output shaft 2 is arranged in the second direction X2 of the main body portion 31. The main body portion 31 covers the inside of the concave surface 23 from the first direction X1. For this reason, the cylindrical roller 4 does not fall off from the inside of the concave surface 23 in the first direction X1. A retaining ring 5 is provided at the end of the inner peripheral surface 13 of the outer ring portion 10 in the first direction X1. The retaining ring 5 is in contact with the main body portion 31 from the first direction X1. Therefore, the input shaft 3 and the output shaft 2 do not fall off from the fixing member 1 in the first direction X1.

[0025] As shown in Fig. 1, the pressing portion 32 is formed in an arc shape when viewed axially. The pressing portion 32 is arranged inside the concave surface 23. The circumferential surface of the pressing portion 32 is a pressing surface 33. The pressing surface 33 extends along a virtual line K1 (see Fig. 3) that extends radially from the center line O1. Further, with respect to the pressing surface 33, the pressing portion 32 has two surfaces: a first pressing surface 133 facing the first rotation direction L1 and a second pressing surface 233 facing the second rotation direction L2.

[0026] The cylindrical roller 4 is formed in a cylindrical shape and has a diameter of H1 (see Fig. 1). The cylindrical roller 4 is made of steel and is a rigid body that is difficult to deform. Two cylindrical rollers 4 are arranged inside one concave surface 23. Also, the two cylindrical rollers 4 are arranged separately on both sides in the circumferential direction of the pressing portion 32. Hereinafter, the cylindrical roller 4 arranged in the first rotation direction L1 as viewed from the pressing portion 32 is referred to as the first cylindrical roller 41, and the cylindrical roller 4 arranged in the second rotation direction L2 is referred to as the second cylindrical roller 42.

[0027] Next, the details of the concave surface 23 will be described with reference to Fig. 3. As shown in Fig. 3, the concave surface 23 is formed symmetrically about a virtual line K2 that passes through the central portion in the circumferential direction of the bottom surface 24 from the center line O1. The concave surface 23 has a bottom surface 24 and two pressed surfaces 25.

[0028] The bottom surface 24 has a central surface 26 located at the central portion in the circumferential direction of the bottom surface 24 and a pair of cam surfaces 27 located at the end portions in the circumferential direction of the bottom surface 24. Here, the direction in which the pressed surface 25 is arranged as viewed from the central surface 26 is referred to as the outer circumferential direction. Also, the direction in which the central surface 26 is arranged as viewed from the pressed surface 25 is referred to as the inner circumferential direction.

[0029] The central surface 26 is formed in an arc shape. Between the central surface 26 and the outer ring portion 10, the pressing portion 32 of the input shaft 3 is arranged.

[0030] The pair of cam surfaces 27 are the first cam surface 127 arranged in the first rotation direction L1 with respect to the central surface 26 and the second cam surface 227 arranged in the second rotation direction L2. Note that the first cam surface 127 and the second cam surface 227 are symmetric about the virtual line K2. Therefore, in the description of the cam surface 27, the first cam surface 127 will be described as a representative example, and the description of the second cam surface 227 will be omitted.

[0031] A first cylindrical roller 41 is disposed between the first cam surface 127 and the inner peripheral surface 13 of the outer ring portion 10. The diameter from the center line O1 to the cam surface 27 is formed to gradually decrease as it approaches the pressed surface 25 from the center plane 26. That is, the distance H2 between the inner peripheral surface 13 of the outer ring portion 10 and the cam surface 27 gradually increases as it approaches the pressed surface 25.

[0032] Also, the distance H2 between the inner peripheral surface 13 and the cam surface 27 is the same as the diameter H1 (see FIG. 1) of the first cylindrical roller 41 at the central portion in the circumferential direction of the cam surface 27. Therefore, when the first cylindrical roller 41 moves closer to the center plane 26, the first cylindrical roller 41 is sandwiched between the cam surface 27 and the inner peripheral surface 13. On the other hand, when the first cylindrical roller 41 moves closer to the pressed surface 25, the first cylindrical roller 41 is in a state of being loosely fitted without being sandwiched between the cam surface 27 and the inner peripheral surface 13.

[0033] The pressed surface 25 extends radially outward from the circumferential end of the bottom surface 24. The two pressed surfaces 25 are the first pressed surface 125 disposed in the first rotation direction L1 with respect to the center plane 26 and the second pressed surface 225 disposed in the second rotation direction L2. The first pressed surface 125 is tilted outward in the circumferential direction with respect to the virtual line K3 drawn from the center line O1 to the base end portion 25a of the pressed surface 25 (the portion where it merges with the circumferential end of the bottom surface 24). Since the second pressed surface 225 is symmetrical to the first pressed surface 125 with respect to the virtual line K2, the description of the second pressed surface 225 is omitted.

[0034] FIG. 4 is an enlarged view of the concave surface when an external force in the first rotation direction is input to the output shaft of Embodiment 1. FIG. 5 is an enlarged view of the concave surface when an external force in the second rotation direction is input to the output shaft of Embodiment 1. FIG. 6 is an enlarged view of the concave surface when a torque in the first rotation direction is input to the input shaft of Embodiment 1. FIG. 7 is an enlarged view of the concave surface when a torque in the second rotation direction is input to the input shaft of Embodiment 1.

[0035] Next, the operation of the power transmission device according to Embodiment 1 will be described with reference to FIGS. 3 to 7. In the following description, the torque input to the output shaft 2 from another component 101 (see FIG. 2) is referred to as an external force, and is distinguished from the torque input to the input shaft 3 from another component 102 (see FIG. 2).

[0036] First, the state of the power transmission device 100 shown in FIG. 3 will be described. As shown in FIG. 3, the two cylindrical rollers 4 are arranged closer to the pressed surface 25 among the cam surfaces 27. Therefore, the two cylindrical rollers 4 are not sandwiched between the cam surface 27 and the inner peripheral surface 13, and are in a loose-fitting state. Therefore, the output shaft 2 can rotate, and hereinafter, this state will be referred to as a neutral state.

[0037] When an external force in the first rotation direction L1 is input to the output shaft 2 from the neutral state, as shown in FIG. 4, the output shaft 2 rotates in the first rotation direction L1 (see arrow A1 in FIG. 4). As a result, the first cylindrical roller 41 is sandwiched between the inner peripheral surface 13 and the first cam surface 127. Thereby, the rotation of the output shaft 2 in the first rotation direction L1 is restricted.

[0038] On the other hand, when an external force in the second rotation direction L2 is input to the output shaft 2 from the neutral state, as shown in FIG. 5, the output shaft 2 rotates in the second rotation direction L2 (see arrow A2 in FIG. 5). As a result, the second cylindrical roller 42 is sandwiched between the inner peripheral surface 13 and the second cam surface 227. Thereby, the rotation of the output shaft 2 in the second rotation direction L2 is restricted.

[0039] Also, as shown in FIG. 4, when torque in the first rotation direction L1 is input to the input shaft 3 in a state where the rotation of the output shaft 2 in the first rotation direction L1 is restricted, as shown in FIG. 6, the pressing portion 32 moves in the first rotation direction L1 (see arrow A3 in FIG. 6). The first pressing surface 133 of the pressing portion 32 presses the first cylindrical roller 41 in the first rotation direction L1. When the first cylindrical roller 41 moves in the first rotation direction L1, the state where the first cylindrical roller 41 is sandwiched between the inner peripheral surface 13 and the first cam surface 127, that is, the state where the rotation of the output shaft 2 in the first rotation direction L1 is restricted is released.

[0040] When the pressing part 32 further moves in the first rotation direction L1, the first cylindrical roller 41 abuts against the first pressed surface 125. Then, the pressing part 32 presses the first pressed surface 125 via the first cylindrical roller 41 (see arrow A4 in FIG. 6). As a result, torque in the first rotation direction L1 is transmitted to the output shaft 2, and the output shaft 2 rotates in the first rotation direction L1.

[0041] On the other hand, as shown in FIG. 4, when torque in the second rotation direction L2 is input to the input shaft 3 from a state where the rotation of the output shaft 2 in the first rotation direction L1 is restricted, as shown in FIG. 7, the pressing part 32 moves in the second rotation direction L2 (see arrow A5 in FIG. 7). Then, when the second pressing surface 233 of the pressing part 32 abuts against the second cylindrical roller 42, the pressing part 32 presses the second pressed surface 225 via the second cylindrical roller 42 (see arrow A6 in FIG. 7). As a result, torque in the second rotation direction L2 is transmitted to the output shaft 2, and the output shaft 2 rotates in the second rotation direction L2.

[0042] Further, when the output shaft 2 starts to rotate in the second rotation direction L2, since the first cam surface 127 moves in the second rotation direction L2 with respect to the first cylindrical roller 41, the state where the first cylindrical roller 41 is sandwiched between the inner peripheral surface 13 and the first cam surface 127 is released.

[0043] In addition, when rotating the output shaft 2 in the second rotation direction L2 from a state where the rotation of the output shaft 2 in the first rotation direction L1 is restricted, in the above description, an example of inputting torque in the second rotation direction L2 to the input shaft 3 as shown in FIG. 7 is given for explanation, but the present disclosure is not limited to this operation example. In the above operation method, when the pressing part 32 starts to press the second pressed surface 225 via the second cylindrical roller 42, the first cylindrical roller 41 is in a state of being sandwiched between the inner peripheral surface 13 and the first cam surface 127. That is, there is a possibility that the output shaft 2 may not rotate smoothly. Therefore, after the input shaft 3 once rotates in the first rotation direction L1 and the state where the first cylindrical roller 41 is sandwiched between the inner peripheral surface 13 and the first cam surface 127 is released, the input shaft 3 may rotate in the second rotation direction L2 to transmit torque to the output shaft 2.

[0044] As described above, the power transmission device 100 of Embodiment 1 includes a fixed member 1 having a cylindrical surface (inner peripheral surface 13) facing radially inward, an output shaft 2 having a facing surface (outer peripheral surface 22) facing the cylindrical surface, an input shaft 3 having at least one or more pressing portions 32 disposed between the cylindrical surface and the facing surface, and a pair of rolling elements (cylindrical rollers 4) disposed between the cylindrical surface and the facing surface and on both circumferential sides of the pressing portion. A concave surface 23 that is recessed in the radial direction and houses the pressing portion 32 and the pair of rolling elements therein is formed on the facing surface. The concave surface 23 has a bottom surface 24 and a pair of pressed surfaces 25 that extend radially from the circumferential end of the bottom surface 24 and face the circumferential direction. The circumferential surface of the pressing portion 32 is a pressing surface 33 that presses the pressed surface 25 via the rolling element. The bottom surface 24 is located at the circumferential center of the concave surface 23 and has a central surface 26 where the pressing portion is disposed between the cylindrical surface, and a pair of cam surfaces 27 that are located on both circumferential sides of the concave surface 23 and where the rolling elements are disposed between the cylindrical surface. As the cam surface 27 approaches the pressed surface 25 from the central surface 26, the distance H2 between the cam surface 27 and the cylindrical surface gradually increases. The portion of the cam surface 27 closer to the central surface 26 has a distance H2 smaller than the diameter H1 of the rolling element. The portion of the cam surface 27 closer to the pressed surface 25 has a distance H2 larger than the diameter H1 of the rolling element.

[0045] According to the above-described Embodiment 1, the torque of the input shaft 3 is transmitted to the output shaft 2 via the cylindrical roller 4, which is a rigid body. The cylindrical roller 4 is a rigid body and has a small amount of deformation when torque acts thereon. Thereby, torque loss can be reduced. Further, since the rotation of the output shaft 2 is restricted, the position of other components 101 (for example, an arm of an industrial robot) connected to the output shaft 2 can be held. Further, since control of a motor or the like is not required for restricting the rotation of the output shaft, power consumption of the equipment equipped with the power transmission device 100 can be reduced. Furthermore, according to the technique of Patent Document 1 described above, a flange plate and a lock release plate are required in addition to the output shaft and the input shaft, but in the power transmission device 100, the flange plate and the lock release plate are not required. Therefore, the number of parts of the power transmission device 100 can be reduced.

[0046] The above describes Embodiment 1. In Embodiment 1, an example using cylindrical rollers as rolling elements is given. However, the present disclosure may use balls and is not particularly limited. Next, a modified example obtained by modifying Embodiment 1 will be described. Also, in the following description, the description will be focused on the differences from the power transmission device described above.

[0047] (Modified Example 1) FIG. 8 is a cross-sectional view of the power transmission device of Modified Example 1 taken in a direction perpendicular to the axial direction, and more specifically, is a cross-sectional view taken along the arrow VIII-VIII in FIG. 9. FIG. 9 is a cross-sectional view of the power transmission device of Modified Example 1 taken in the axial direction, and more specifically, is a cross-sectional view taken along the arrow IX-IX in FIG. 8.

[0048] As shown in FIG. 8, the power transmission device 100A of Modified Example 1 differs from Embodiment 1 in that the number of concave surfaces 23 is two. Even with such a power transmission device 100A, the same operational effects as in Embodiment 1 can be achieved, and torque loss can be reduced. Thus, the number of concave surfaces 23 of the present disclosure is not limited to six shown in Embodiment 1. That is, in the power transmission device of the present disclosure, there may be at least one or more concave surfaces 23, and there is no particular limitation on the number of concave surfaces 23.

[0049] As shown in FIG. 9, the fixed member 1A differs from Embodiment 1 in that it is composed of parts divided in the axial direction. Specifically, the fixed member 1A includes a first fixed member 201 and a second fixed member 202 arranged in the second direction X2 of the first fixed member 201. The first fixed member 201 and the second fixed member 202 are axially tightened and integrated by bolts (not shown). Thus, the fixed member of the present disclosure may be composed of two or more parts and is not limited to the shape shown in Embodiment 1.

[0050] The output shaft 2A of Modification 1 is different from that of Embodiment 1 in that it has a shaft-shaped first connecting shaft 21A instead of the first connecting portion 21 (see FIG. 2). Similarly, the input shaft 3A of Modification 1 is different from that of Embodiment 1 in that it has a shaft-shaped second connecting shaft 30A instead of the second connecting portion 30 (see FIG. 2). Further, through holes 203 and 204 extending in the axial direction are formed in the first connecting shaft 21A and the second connecting shaft 30A, respectively. Electrical wiring or the like is arranged in the through holes 203 and 204. Thus, the output shaft and the input shaft of the present disclosure are not limited to the shapes shown in Embodiment 1.

[0051] (Modification 2) FIG. 10 is a cross-sectional view of the power transmission device of Modification 2 taken in a direction orthogonal to the axial direction, and more specifically, is a cross-sectional view taken along the arrow of line X-X in FIG. 11. FIG. 11 is a cross-sectional view of the power transmission device of Modification 2 taken in the axial direction, and more specifically, is a cross-sectional view taken along the arrow of line XI-XI in FIG. 10. FIG. 12 is a view of the power transmission device of Modification 2 when torque in the first rotational direction is input to the input shaft.

[0052] As shown in FIG. 10, the power transmission device 100B of Modification 2 is different from Modification 1 in that it has a plurality of coil springs (elastic bodies) 50. The coil springs 50 are arranged between the pressed surface 25 and the cylindrical roller 4. Further, the coil springs 50 are arranged in a state of being compressed from their natural lengths. That is, the coil springs 50 are compression springs, and the cylindrical roller 4 is constantly biased inward in the circumferential direction by the coil springs 50. According to this, even when no external force is input to the output shaft 2B, the cylindrical roller 4 is sandwiched between the inner peripheral surface 13 of the outer ring portion 10 and the cam surface 27, and the rotation of the output shaft 2B is restricted. In Embodiment 1, the rotation of the output shaft 2 is restricted after the output shaft 2 rotates slightly by an external force. That is, in Embodiment 1, there is play in the circumferential direction of the output shaft 2B. On the other hand, according to Modification 2, the play in the circumferential direction of the output shaft 2B is suppressed. For this reason, the position and posture of other components connected to the output shaft 2B are maintained.

[0053] Further, as shown in FIG. 10, the output shaft 2B of the second modification is different from the output shaft 2A of the first modification in that the hole 51 is formed in the pressed surface 25. A part of the coil spring 50 is accommodated in this hole 51. As shown in FIG. 11, the hole 51 is formed in a circular shape corresponding to the coil spring 50. As shown in FIG. 12, when torque is input to the input shaft 3A and the pressing portion 32 moves in the circumferential direction, the coil spring 50 receives a compressive load between the pressed surface 25 and the cylindrical roller 4 and contracts. Then, the entire coil spring 50 is accommodated in the hole 51 in the contracted state. As a result, the cylindrical roller 4 abuts against the pressed surface 25. Then, with the cylindrical roller 4 abutting against the pressed surface 25, the inner ring portion 20 is pressed and the output shaft 2B rotates. From the above, the coil spring 50 is not interposed between the cylindrical roller 4 and the pressed surface 25 during torque transmission.

[0054] As described above, the second modification has been explained. However, in the present disclosure, the cylindrical roller 4 may be urged using an elastic body other than the coil spring 50. Further, in the second modification, an example in which an elastic body (compression spring) is disposed between the pressed surface 25 and the cylindrical roller 4 has been given. However, in the present disclosure, the elastic body may be disposed between the pressing surface 33 and the cylindrical roller 4. When the elastic body is disposed between the pressing surface 33 and the cylindrical roller 4, the elastic body needs to be a tension spring that urges the cylindrical roller 4 toward the pressing surface 33 instead of a compression spring.

[0055] (Second Modification) FIG. 13 is a cross-sectional view of the power transmission device of the third modification taken in a direction orthogonal to the axial direction. As shown in FIG. 13, the output shaft 2C of the power transmission device 100C of the third modification is different from the second modification in that a through hole 51C is formed instead of the hole 51. The through hole 51C penetrates the pressed surface 25 of another concave surface 23 on the back side of the pressed surface 25. That is, the through hole 51C communicates the interiors of the concave surfaces 23 adjacent to each other in the circumferential direction.

[0056] The power transmission device 100C of Modification 3 is different from Modification 2 in that a long coil spring 50C is used instead of the coil spring 50. The central portion in the length direction of the coil spring 50C is disposed in the through hole 51C. And both ends of the coil spring 50C bias the two cylindrical rollers 4 disposed on different concave surfaces 23. Even in this Modification 3, similar to Modification 2, the play in the circumferential direction of the output shaft 2C is suppressed.

[0057] (Modification 4) FIG. 14 is a cross-sectional view of the power transmission device of Modification 4 taken axially. FIG. 15 is a side view viewed from the direction of arrow XV in FIG. 14. As shown in FIG. 14, the power transmission device 100D of Modification 4 is different from Modification 2 in that it includes a friction portion 160. The friction portion 160 abuts against the output shaft 2B and exerts a frictional force. The friction portion 160 of Modification 4 includes a friction plate 60 and a disc spring 61.

[0058] The friction plate 60 includes a plate 62 serving as a base material and a friction material 63 having a high coefficient of friction attached to the surface of the plate 62 in the first direction X1. The friction plate 60 is formed in an annular shape as shown in FIG. 15. And the friction material 63 abuts against the side surface 220 of the inner ring portion 20 of the output shaft 2B in the second direction X2.

[0059] The disc spring 61 is disposed between the inner flange 206 of the second fixing member 202 and the friction plate 60. The disc spring 61 is assembled in a state of exerting a biasing force in the axial direction. Therefore, the friction material 63 is pressed by the disc spring 61 in the first direction X1 and exerts a high frictional force against the side surface 220 of the inner ring portion 20.

[0060] Next, the operation of the power transmission device 100D of Modification 4 will be described. For example, when a torque in the first rotation direction L1 is input to the input shaft 3A, the pressing portion 32 moves in the first rotation direction L1. And the first pressing surface 133 presses the first cylindrical roller 41. As a result, the coil spring 50 between the first cylindrical roller 41 and the first pressed surface 125 is compressed, and the biasing force of the coil spring 50 increases.

[0061] If the friction plate 60 is not pressed against the inner ring portion 20, the inner ring portion 20 may rotate in the first rotation direction L1 due to the increased biasing force of the coil spring 50. That is, the first cylindrical roller 41 may not contact the first pressed surface 125. On the other hand, according to the fourth modification, since the friction plate 60 is pressed against the inner ring portion 20, it is difficult for the inner ring portion 20 to rotate. That is, even if the biasing force of the coil spring 50 increases, it is difficult for the inner ring portion 20 to rotate in the first rotation direction L1. Therefore, the first cylindrical roller 41 moving in the first rotation direction L1 surely contacts the first pressed surface 125, and torque is transmitted to the inner ring portion 20 of the output shaft 2A.

[0062] As described above, the fourth modification has been explained. In the fourth modification, an example in which the friction portion 160 is composed of the friction plate 60 and the disc spring 61 has been given. However, in the present disclosure, the friction portion 160 may be composed of only the friction plate 60, or may be composed of only the disc spring 61, or may have a configuration other than the friction plate 60 and the disc spring 61. Further, although the disc spring 61 is used as the member for pressing the friction plate 60, the present disclosure may be other elastic bodies.

[0063] (Modification 5) FIG. 16 is a cross-sectional view of the power transmission device of the fifth modification taken axially. FIG. 17 is an enlarged view of a part of the power transmission device of the fifth modification. The power transmission device 100E of the fifth modification is different from the second modification in that the shape of the pressing surface 33E is changed. Specifically, the pressing surface 33E has an outer surface 331 disposed outside the virtual line K4 and an inner surface 332 disposed inside the virtual line K4. The virtual line K4 is a circle centered on the center line O1. The virtual line K4 passes through the center O2 of the cylindrical roller 4 sandwiched between the inner peripheral surface 13 and the cam surface 27.

[0064] The inner surface 332 extends along the virtual line K1 (see FIG. 3). The outer surface 331 protrudes inward in the circumferential direction from the virtual line K1 (see FIG. 3). Therefore, the portion of the pressing surface 33E that contacts the cylindrical roller 4 is the outer surface 331, not the inner surface 332. Further, the outer surface 331 is inclined radially inward with respect to the virtual line K1. Therefore, as shown in FIG. 17, when torque is input to the input shaft 3A and the pressing surface 33E presses the inner ring portion 20 with the cylindrical roller 4 interposed therebetween, the outer surface 331 and the surface to be pressed 25 are substantially parallel.

[0065] Here, as shown in FIG. 12, the pressing surface 33 in Embodiment 1, Modification 1, etc. is along the virtual line K1 (see FIG. 3). And the pressing force F1 of the pressing surface 33 includes a component F3 directed radially outward in addition to the normal vector F2 of the surface to be pressed 25. Therefore, the amount of torque loss transmitted from the pressing portion 32 to the inner ring portion 20 is large. On the other hand, according to Modification 5, the vector F in the direction in which the pressing surface 33E presses is the normal vector of the surface to be pressed 25. Therefore, the amount of torque loss transmitted from the pressing portion 32 to the inner ring is extremely small, and torque is efficiently transmitted.

[0066] The above has been described up to Modification 5. The power transmission device described above is an example applying a so-called inner cam structure in which the outer ring portion 10 is constituted by the fixing member 1 and the inner ring portion 20 is constituted by the output shaft 2. However, the present disclosure may be a so-called outer cam structure in which the inner ring portion is constituted by the fixing member 1 and the outer ring portion is constituted by the output shaft 2. Hereinafter, a power transmission device applied to the outer cam structure will be briefly described.

[0067] (Modification 6) FIG. 18 is a cross-sectional view of the power transmission device of Modification 6 taken in a direction orthogonal to the axial direction, and more specifically, is a cross-sectional view taken along the line XVIII-XVIII in FIG. 19. FIG. 19 is a cross-sectional view of the power transmission device of Modification 6 taken in the axial direction, and more specifically, is a cross-sectional view taken along the line XIX-XIX in FIG. 18. As shown in FIG. 18, the power transmission device 100F of Modification 6 includes a fixing member 1F, an output shaft 2F, an input shaft 3F, and a plurality of cylindrical rollers 4. Note that the cylindrical rollers 4 are the same as those in Embodiment 1, and the same reference numerals are given.

[0068] As shown in FIG. 19, the fixing member 1F has an inner ring portion 10F, an outer flange portion 11F, and an inner flange portion 12F. As shown in FIG. 18, the outer peripheral surface (cylindrical surface) 14F of the inner ring portion 10F is formed in a circular shape centered on the center line O1. The outer flange portion 11F and the inner flange portion 12F are respectively arranged at the ends of the inner ring portion 10F in the second direction X2. A through hole 11a is formed in the inner flange portion 12F. Therefore, by tightening the inner flange portion 12F with bolts (not shown), the power transmission device 100F can be fixed to other components.

[0069] The output shaft 2F has an outer ring portion 20F and a flange 121. The outer peripheral surface 124 of the outer ring portion 20F is a fitting surface to which another component 101 that transmits torque from the power transmission device 100 (output shaft 2F) is fitted. The flange 121 is in contact with the end surface of the component 101 in the first direction X1. Retaining rings 7 and 8 are provided on the inner peripheral side of the outer ring portion 20F at the ends in the first direction X1 and the second direction X2. By these retaining rings 7 and 8, the fixing member 1F and the output shaft 2F are axially sandwiched. Thereby, the fixing member 1F, the output shaft 2F, and the input shaft 3F are assembled so as not to separate.

[0070] As shown in FIG. 18, the inner peripheral surface (opposing surface) 122 of the outer ring portion 20F is an opposing surface that opposes the outer peripheral surface 14F of the inner ring portion 10F. The inner peripheral surface 122 of the outer ring portion 20F is slidably in contact with the outer peripheral surface 14F of the inner ring portion 10F in the circumferential direction.

[0071] Six concave surfaces 23F that are recessed radially outward are formed on the inner peripheral surface 122 of the outer ring portion 20F. The concave surface 23F has a bottom surface 24F and a surface to be pressed 25F. The bottom surface 24F has a central surface 26F and a cam surface 27F.

[0072] A cylindrical roller 4 is disposed between a cam surface 27F and an outer peripheral surface 14F of an inner ring portion 10F. The diameter from a center line O1 to the cam surface 27F is formed so as to gradually increase as it approaches a pressed surface 25F from a center surface 26F. That is, the distance between the outer peripheral surface 14F of the inner ring portion 10F and the cam surface 27F gradually increases as it approaches the pressed surface 25. Therefore, when the cylindrical roller 4 moves closer to the center surface 26F, the cylindrical roller 4 is sandwiched between the cam surface 27F and the outer peripheral surface 13F. On the other hand, when the cylindrical roller 4 moves closer to the pressed surface 25F, the cylindrical roller 4 is in a loose-fitting state without being sandwiched between the cam surface 27F and the outer peripheral surface 13F.

[0073] As shown in FIG. 19, an input shaft 3F includes a second connecting portion 30F, a main body portion 31F extending radially outward from the second connecting portion 30F, and a plurality of pressing portions 32F protruding from the main body portion 31F in a second direction X2. An inner peripheral surface of the second connecting portion 30F is a fitting surface with which another component 102 that transmits torque to a power transmission device (input shaft) 100F is fitted.

[0074] As shown in FIG. 19, an outer peripheral surface of the main body portion 31F is slidably abutted against an inner peripheral surface 122 of an outer ring portion 20F in a circumferential direction. Further, the main body portion 31F covers the inside of a concave surface 23F from a first direction X1. For this reason, the cylindrical roller 4 does not drop off from the inside of the concave surface 23F in the first direction X1.

[0075] As shown in FIG. 18, the pressing portion 32F is inside the concave surface 23F and is disposed on the inner peripheral side of the center surface 26F. Therefore, when torque is transmitted to the input shaft 3F and it rotates, a pressing surface 33F of the pressing portion 32F presses the pressed surface 25F via the cylindrical roller 4. Thereby, torque is transmitted to the outer ring portion 20F, and the output shaft 2F rotates. As described above, even in the power transmission device 100F of Modification 6, the same operational effects as those of Embodiment 1 are produced.

[0076] Note that the present disclosure may also be a combination of the following configurations. (1) A fixed member having a cylindrical surface facing radially inward or radially outward, An output shaft having a facing surface facing the cylindrical surface, An input shaft having at least one or more pressing portions disposed between the cylindrical surface and the facing surface, A pair of rolling elements disposed between the cylindrical surface and the facing surface and on both circumferential sides of the pressing portion, Comprising, On the facing surface, a concave surface is formed that is recessed in the radial direction and houses the pressing portion and the pair of rolling elements therein, The concave surface, A bottom surface, A pair of surfaces to be pressed that extend radially from the circumferential end of the bottom surface and face the circumferential direction, Having, The circumferential surface of the pressing portion is a pressing surface that presses the surface to be pressed via the rolling element, The bottom surface, Is located at the central portion in the circumferential direction of the concave surface, and is a central surface where the pressing portion is disposed between it and the cylindrical surface, A pair of cam surfaces located at both ends in the circumferential direction of the concave surface, where the rolling elements are disposed between them and the cylindrical surface, Having, The cam surface gradually increases the distance between it and the cylindrical surface as it approaches the surface to be pressed from the central surface, The portion of the cam surface closer to the central surface has a distance between it and the cylindrical surface smaller than the diameter of the rolling element, The portion of the cam surface closer to the surface to be pressed has a distance between it and the cylindrical surface larger than the diameter of the rolling element Power transmission device. (2) Comprising an elastic body for biasing the rolling element, The elastic body is a compression spring disposed between the surface to be pressed and the rolling element, biasing the rolling element toward the pressing surface, or a tension spring disposed between the pressing surface and the rolling element, pulling the rolling element toward the pressing surface The power transmission device according to (1). (3) The output shaft has a side surface facing in the axial direction parallel to the center line of the cylindrical surface, It is provided with a friction part that abuts against the side surface and exerts a frictional force. is provided with The power transmission device according to (2). (4) Taking the center line of the cylindrical surface as the center, and taking the virtual circle passing through the center of the rolling element sandwiched between the cylindrical surface and the cam surface as the first virtual circle, The pressing surface has an inner surface disposed radially inward of the first virtual circle, and an outer surface disposed radially outward of the first virtual circle, and has The outer surface protrudes more than the inner surface. The power transmission device according to any one of (1) to (3). (5) The fixed member has an annular outer ring portion whose inner peripheral surface is the cylindrical surface, The output shaft is disposed inside the outer ring portion and has an inner ring portion whose outer peripheral surface is the opposing surface. The power transmission device according to any one of (1) to (4). (6) The fixed member has an inner ring portion whose outer peripheral surface is the cylindrical surface, The output shaft has an annular outer ring portion with the inner ring portion disposed therein and whose inner peripheral surface is the opposing surface. The power transmission device according to any one of (1) to (4).

Explanation of Reference Numerals

[0077] 1, 1F Fixed member 2, 2F Output shaft 3 Input shaft 4 Cylindrical roller 10 Outer ring portion 10F Inner ring portion 13 Inner peripheral surface (cylindrical surface) 20 Inner ring portion 20F Outer ring portion 22 Outer peripheral surface (opposing surface) 23, 23F Concave surface 24, 24F Bottom surface 25, 25F Pressed Surface 26, 26F Central Surface 27, 27F Cam Surface 31 Body Part 32 Pressing Part 33 Pressing Surface 41 First Cylindrical Roller 42 Second Cylindrical Roller 100, 100A, 100B, 100C, 100D, 100E, 100F Power Transmission Device 122 Inner Peripheral Surface (Opposing Surface) 125 First Pressed Surface 127 First Cam Surface 133 First Pressing Surface 160 Friction Part 227 Second Cam Surface 225 Second Pressed Surface 233 Second Pressing Surface

Claims

1. A fixed member having a cylindrical surface facing radially inward or radially outward, An output shaft having a facing surface facing the cylindrical surface, An input shaft having at least one or more pressing portions disposed between the cylindrical surface and the facing surface, A pair of rolling elements disposed between the cylindrical surface and the facing surface and on both circumferential sides of the pressing portion, Comprising, On the facing surface, a concave surface is formed that is recessed in the radial direction and houses the pressing portion and the pair of rolling elements therein, The concave surface is, A bottom surface, A pair of surfaces to be pressed that extend radially from the circumferential end of the bottom surface and face the circumferential direction, Having, The circumferential surface of the pressing portion is a pressing surface that presses the surface to be pressed via the rolling element, The bottom surface is, A central surface located at the central portion in the circumferential direction of the concave surface and having the pressing portion disposed between it and the cylindrical surface, A pair of cam surfaces located at both ends in the circumferential direction of the concave surface and having the rolling element disposed between them and the cylindrical surface, Having, The cam surface gradually increases the distance from the central surface to the surface to be pressed between it and the cylindrical surface, The portion of the cam surface closer to the central surface has a distance between it and the cylindrical surface smaller than the diameter of the rolling element, The portion of the cam surface closer to the surface to be pressed has a distance between it and the cylindrical surface larger than the diameter of the rolling element Power transmission device.

2. Comprising an elastic body for biasing the rolling element, The elastic body is a compression spring disposed between the surface to be pressed and the rolling element for biasing the rolling element toward the pressing surface, or a tension spring disposed between the pressing surface and the rolling element for biasing the rolling element toward the pressing surface The power transmission device according to claim 1.

3. The output shaft has a side surface facing in the axial direction parallel to the center line of the cylindrical surface, Comprising a friction portion that abuts against the side surface to exert frictional force The power transmission device according to claim 2.

4. Taking a virtual circle passing through the center of the rolling element in a state of being sandwiched between the cylindrical surface and the cam surface with the center line of the cylindrical surface as the center as the first virtual circle, The pressing surface is, An inner surface disposed radially inside the first virtual circle, An outer surface disposed radially outside the first virtual circle, Having, The outer surface protrudes more than the inner surface The power transmission device according to claim 1.

5. The fixed member has an annular outer ring portion whose inner peripheral surface is the cylindrical surface, The output shaft is disposed inside the outer ring portion and has an inner ring portion whose outer peripheral surface serves as the opposing surface. The power transmission device according to any one of claims 1 to 4. **Claim 6** The fixing member has an inner ring portion whose outer peripheral surface serves as the cylindrical surface. The output shaft has an annular outer ring portion in which the inner ring portion is disposed and whose inner peripheral surface serves as the opposing surface. The power transmission device according to any one of claims 1 to 4.

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