Friction transmission device

Abstract

A friction transmission device 100 according to an embodiment of the present invention includes: a planetary rolling element 20 disposed about a rotation axis La; a first support raceway ring 26 and a second support raceway ring 28 in contact with the planetary rolling element 20; and a pressing force application mechanism 7 for pressing the second support raceway ring 28 to generate a pressing force on a contact surface between the second support raceway ring 28 and the planetary rolling element 20. The friction transmission device 100 has a cover 67 for covering this friction transmission device 100 from the axial direction. The pressing force application mechanism 7 has a pressing part 72 for pressing the second support raceway ring 28. The pressing force application mechanism 7 has an abutment part 56b in abutment against the cover 67 at a position overlapping the pressing part 72 in the axial direction or is formed integrally with the cover 67.

Description

Friction transmission

[0001] The present disclosure relates to friction transmissions.

[0002] A continuously variable transmission capable of an infinitely large gear ratio, known as an IVT (Infinitely Variable Transmission), is known. The present applicant disclosed in Patent Document 1 a friction transmission device including an input raceway, planetary rolling elements, and an output raceway. In this device, the planetary rolling elements are arranged around the rotation axis of the input raceway and contact the input raceway, while the output raceway is in contact with the planetary rolling elements and connected to an output shaft. This device also has a plurality of support raceways in contact with the planetary rolling elements, and changes the speed of rotation input to the input raceway and outputs it from the output shaft.

[0003] International Publication No. 2021 / 182001

[0004] Friction transmissions are expected to be used in many applications, such as robots and self-propelled vehicles. To be installed in a variety of applications, friction transmissions are required to be able to transmit larger torque. However, conventional friction transmissions require a complex mechanism for applying preload between the planetary rolling elements and the bearing rings, making it difficult to increase the transmission torque of the friction transmission.

[0005] The object of the present disclosure has been made in view of the above-mentioned problems, and is to provide a friction transmission device capable of transmitting a larger torque.

[0006] In order to solve the above problems, one aspect of the friction transmission device disclosed herein is a friction transmission device including planetary rolling elements arranged around a rotation axis, first and second support rings that contact the planetary rolling elements, and a pressing force applying mechanism that presses the second support ring to generate a pressing force on the contact surface between the second support ring and the planetary rolling elements, and the friction transmission device has a cover that covers the friction transmission device from the axial direction. The pressing force applying mechanism has a pressing part that presses the second support ring. The pressing force applying mechanism has an abutting part that abuts against the cover at a position that axially overlaps with the pressing part, or is configured integrally with the cover.

[0007] Any combination of the above components, or mutual substitution of the components or expressions of the present disclosure between methods, systems, etc., are also valid aspects of the present disclosure.

[0008] According to the present disclosure, a friction transmission capable of transmitting a larger torque can be provided.

[0009] 16 is a perspective view showing an example of a friction transmission device according to an embodiment. FIG. 16 is a cross-sectional view showing a cross section along line A-A of the friction transmission device of FIG. 1. FIG. 16 is a perspective view showing an input raceway of the friction transmission device of FIG. 1. FIG. 16 is a perspective view showing a first support raceway of the friction transmission device of FIG. 1. FIG. 16 is a perspective view showing a planetary rolling element of the friction transmission device of FIG. 1. FIG. 16 is a perspective view showing a cage of the friction transmission device of FIG. 1. FIG. 16 is a perspective view showing a planetary rolling element unit of the friction transmission device of FIG. 1. FIG. 16 is a perspective view showing a second support raceway of the friction transmission device of FIG. 1. FIG. 16 is a perspective view showing an output raceway of the friction transmission device of FIG. 1. FIG. 16 is a perspective view showing a roller cage of the friction transmission device of FIG. 1. FIG. 16 is a perspective view showing a pressing cam of the friction transmission device of FIG. 1. FIG. 16 is a perspective view showing a cover of the friction transmission device of FIG. 1. FIG. 16 is a schematic view illustrating the operation of a pressing force imparting mechanism of the friction transmission device of FIG. 1. FIG. 16 is a perspective view showing a speed ratio control mechanism of the friction transmission device of FIG. 1. FIG. 16 is a cross-sectional view showing a spigot portion of the pressing force imparting mechanism of FIG. 1. FIG. 16 is a cross-sectional view showing a second configuration example of the friction transmission device of an embodiment. FIG. 16 is a perspective view showing a cover of the second configuration example of FIG. 10 is a cross-sectional view showing a support structure for a pressing cam of a friction transmission device according to a reference example.

[0010] The present disclosure will be described below based on preferred embodiments with reference to the drawings. In the embodiments, reference examples, and modified examples, identical or equivalent components and members are designated by the same reference numerals, and redundant explanations will be omitted where appropriate. Furthermore, the dimensions of the members in each drawing are enlarged or reduced as appropriate for ease of understanding. Furthermore, some members that are not important for explaining the embodiments are omitted from the drawings.

[0011] Furthermore, terms including ordinal numbers such as first and second are used to describe various components, but these terms are used only to distinguish one component from another and do not limit the components.

[0012] [Embodiment] First, the overall configuration of a friction transmission 100 according to an embodiment of the present disclosure will be described. Fig. 1 is a perspective view showing an example of a friction transmission 100 according to an embodiment. The friction transmission 100 has a casing 37 that surrounds the internal mechanism, an input shaft 64, an output member 32, and an attachment member 38. The attachment member 38 is a flange-shaped member provided on the outer periphery of the casing 37 to attach the friction transmission 100 to an external device (not shown).

[0013] The friction transmission device 100 is configured such that the rotation input to the input shaft 64 rotates the input raceway, thereby causing the planetary rolling elements to rotate and revolve about their own axes, and the rotational components thus generated are output to a driven device (not shown) from the output member 32 connected to the output raceway.

[0014] FIG. 2 is a cross-sectional view showing a longitudinal section of the friction transmission device 100 taken along line A-A. FIG. 2 shows the state in which the mounting member 38 has been removed. The friction transmission device 100 mainly includes an input mechanism 2, a transmission mechanism 3, an output mechanism 5, a pressing force imparting mechanism 7, and a speed ratio control mechanism 6. The input mechanism 2 is a mechanism that transmits rotation input from a prime mover to an input raceway 14. The transmission mechanism 3 is a mechanism that changes the speed of the rotation transmitted to the input raceway 14 and transmits it to an output raceway 30. The output mechanism 5 is a mechanism that outputs the rotation transmitted to the output raceway 30 from an output member 32 to a driven device. The pressing force imparting mechanism 7 imparts an axial pressing force to the transmission mechanism 3. The speed ratio control mechanism 6 is a mechanism that controls the gear ratio by changing the relative positions of the raceways of the transmission mechanism 3.

[0015] The input mechanism 2 will be described with reference to Fig. 2. The input mechanism 2 according to the embodiment includes an input shaft 64, a ball spline nut 65, an input bearing 66, a cover 67, a first oil seal S1, a shaft 68, a shaft cap 69, an input bearing ring 14, a sleeve 15, a first support bearing ring 26, and a first bearing ring bearing 27.

[0016] Hereinafter, the direction along the rotation axis La of the input race 14 will be referred to as the "axial direction," and the circumferential direction and radial direction of a circle centered on the rotation axis La will be referred to as the "circumferential direction" and the "radial direction," respectively. For convenience, one side in the axial direction (the right side in the drawing) will be referred to as the "input side," and the other side (the left side in the drawing) will be referred to as the "anti-input side."

[0017] Unless otherwise specified, the circular portions surrounding the rotation axis La of each member of the friction transmission 100 are formed around the rotation axis La. The centers of these circular portions may be offset from the rotation axis La within a margin of error.

[0018] The input shaft 64 is an input portion to which rotation from a prime mover is input. In this embodiment, the prime mover is the motor 50, and the input shaft 64 is connected to a motor shaft 51 to which rotation of the motor 50 is output. The ball spline nut 65 transmits the rotation of the input shaft 64 to the shaft 68 and supports the shaft 68 so that it can move in the axial direction. The input shaft 64 has an outer cylinder that houses the ball spline nut 65. The ball spline nut 65 is key-coupled to the input shaft 64 by a key 65k and rotates integrally with the input shaft 64. The shaft 68 is axially movable relative to the ball spline nut 65 and rotates integrally with the ball spline nut 65.

[0019] The cover 67 is a hollow, disk-shaped member that covers part or all of the input side of the friction transmission 100 and has a hollow portion 67c that surrounds the rotation axis La. The cover 67 is fixed to the input side of the casing 37 with a plurality of bolts B1. The input bearing 66 is disposed between the hollow portion 67c and the ball spline nut 65 and supports the ball spline nut 65 and the input shaft 64 so that they can rotate relative to each other. The outer ring of the input bearing 66 is supported in the hollow portion 67c, and the inner ring supports the input shaft 64. The input bearing 66 in this example is a ball bearing. The first oil seal S1 is disposed on the input side of the input bearing 66 in the hollow portion 67c and seals the input bearing 66.

[0020] The shaft 68 is a rod-shaped shaft extending in the axial direction and has axial grooves (not shown) through which balls pass. The input side of the shaft 68 is housed in the ball spline nut 65, and the tip of the shaft 68 extends further toward the anti-input side than the planetary rolling elements 20. The shaft cap 69 is a member that regulates the positional relationship between the shaft 68 and the first support race 26. The shaft cap 69 has a cup shape consisting of a disk portion 69b and a cylindrical portion 69c that extends from the outer periphery of the disk portion 69b toward the input side. The tip of the shaft 68 is inserted into the cylindrical portion 69c and fixed to the disk portion 69b by a bolt B3 that passes through the disk portion 69b.

[0021] The input raceway 14 will be described with reference to Figure 3 as well. In Figures 3 to 12, 14, and 16, (A) is a view from diagonally above the non-input side, and (B) is a view from diagonally above the input side. Figure 3 is a perspective view of the input raceway 14. In the example of Figure 3, the input raceway 14 is formed integrally with the sleeve 15.

[0022] The sleeve 15 is a hollow cylindrical member fixed to the outer periphery of the shaft 68 by interference fit or the like, and has, from the input side to the non-input side, a first cylindrical portion 15b and a second cylindrical portion 15c. The first cylindrical portion 15b is surrounded by the control portion bearing 63 and rotatably supported by the control portion bearing 63. The second cylindrical portion 15c is continuous with the first cylindrical portion 15b at a portion having a larger diameter than the first cylindrical portion 15b. A step portion 15d is formed at the boundary between the first cylindrical portion 15b and the second cylindrical portion 15c. A circumferential groove 15g is formed around the first cylindrical portion 15b, into which a snap ring W1 is attached to regulate the positional relationship with the control portion bearing 63.

[0023] The input race 14 is a hollow cylindrical member fixed to the outer periphery of the shaft 68, has a larger diameter than the second cylindrical portion 15c, and is continuous with the second cylindrical portion 15c. The input race 14 is a hole into which the shaft 68 is fitted, and has a hollow portion 14e that penetrates from the non-input side of the input race 14 to the input side of the sleeve 15. A rolling surface 14h that comes into contact with the planetary rolling elements 20 is provided on the outer periphery of the input race 14. The input race 14 has a bearing accommodating portion 14j for accommodating a portion of the input side of the first race bearing 27. In this example, the bearing accommodating portion 14j is a circular recess that is recessed from the end face of the non-input side of the input race 14 toward the input side.

[0024] The input raceway 14 is a member that supports the planetary rolling elements 20 in a predetermined position and transmits rotation to the planetary rolling elements 20. The rolling surface 14h is the surface on which the planetary rolling elements 20 roll, and is in point contact or surface contact with the planetary rolling elements 20. The rolling surface 14h may be inclined in the axial and radial directions. The rolling surface 14h may include a tapered surface that narrows in diameter toward the input side. The rolling surface 14h may be a flat surface or a curved surface such as a concave surface, but in this example it is a convex surface.

[0025] The first support race 26 will be described with reference to FIG. 4 as well. FIG. 4 is a perspective view showing the first support race 26. The first support race 26 is a cylindrical member that fits onto the outer periphery of the shaft 68 and is rotatably supported by the shaft 68. It is a hollow cylindrical member with approximately the same diameter as the input race 14. The first support race 26 has a through hole 26d that circumscribes the shaft 68. A rolling surface 26h that contacts the planetary rolling elements 20 is provided on the outer periphery of the first support race 26. The first support race 26 has a bearing accommodating portion 26j that accommodates a portion of the non-input side of the first race bearing 27. In this example, the bearing accommodating portion 26j is a circular recess that is recessed from the non-input side end face of the first support race 26 toward the non-input side.

[0026] The first support race 26 is a member for supporting the planetary rolling elements 20 in a predetermined position. The rolling surface 26h is the surface on which the planetary rolling elements 20 roll, and is in point contact or surface contact with the planetary rolling elements 20. The rolling surface 26h may be inclined in the axial and radial directions. The rolling surface 26h may include a tapered surface that reduces in diameter toward the non-input side. The rolling surface 26h may be a flat surface or a curved surface such as a concave surface, but in this example it is a convex surface. The first support race 26 is freely rotatable with respect to the shaft 68 and the planetary rolling elements 20, and is sometimes referred to as an idler race.

[0027] The first bearing ring bearing 27 is a thrust bearing that rotatably supports the first support bearing ring 26 relative to the input bearing ring 14. For example, the first bearing ring bearing 27 can be configured with two rings facing each other in the axial direction and a plurality of spheres interposed between the two rings.

[0028] 5 to 9. The transmission mechanism 3 of the embodiment includes a plurality of planetary rolling elements 20, a cage 21, an input race 14, a first support race 26, a second support race 28, and an output race 30. The input race 14, the first support race 26, the second support race 28, and the output race 30 are collectively referred to as "races."

[0029] 5 is a perspective view showing the planetary rolling elements 20. A plurality of planetary rolling elements 20 (for example, five) are arranged at predetermined intervals in the circumferential direction. The number of planetary rolling elements 20 is not particularly limited and may be more or less than five, but is preferably 5 to 12. Each planetary rolling element 20 has a contact surface 20a that contacts the rolling surface 14h of the input raceway 14, a contact surface 20b that contacts the rolling surface 26h of the first support raceway 26, a contact surface 20c that contacts the rolling surface 28h of the second support raceway 28, and a contact surface 20d that contacts the rolling surface 30h of the output raceway 30.

[0030] The rolling surfaces 14h, 26h, 28h, and 30h of these raceways are collectively referred to as the rolling surfaces of the raceways. The contact surfaces 20a, 20b, 20c, and 20d are collectively referred to as the contact surfaces of the planetary rolling elements. The contact surfaces 20a and 20b may be flat or convex, but in this example they are concave. The contact surfaces 20c and 20d may be flat or concave, but in this example they are convex.

[0031] The axial position, radial position, and orientation of the planetary rolling elements 20 are restricted by contact with the rolling surfaces of the raceways. The shape of the planetary rolling elements 20 may be any shape as long as their orientation is determined by contact with the rolling surfaces of the raceways and they can roll while in contact with the rolling surfaces of the raceways. The planetary rolling elements 20 of this embodiment are rotating elements obtained by rotating a trapezoid whose upper base and legs are curved around a predetermined axis. The predetermined axis is an axis parallel to and spaced from the lower base of the trapezoid on the opposite side of the upper base. In this specification, the "equator" refers to a circle formed by the intersection of a plane (hereinafter referred to as the "equatorial plane") that passes through the center of the upper base of the trapezoid and is perpendicular to the rotation axis Lb of the planetary rolling elements 20 and the outer circumferential surface of the planetary rolling elements 20. In this example, the equator 20e is a circle formed by the intersection of the equatorial plane and the outer circumferential surface of the planetary rolling elements 20.

[0032] The inclination of the rotation axis Lb of the planetary rolling element 20 with respect to the rotation axis La varies depending on the relative position of the rolling surface of the bearing ring. In other words, the rotation axis Lb may be parallel to the rotation axis La or may be inclined with respect to the rotation axis La.

[0033] FIG. 6 is a perspective view showing the cage 21. The friction transmission 100 of this embodiment is equipped with the cage 21 for holding the plurality of planetary rolling elements 20 in desired positions. The cage 21 restricts circumferential movement of the plurality of planetary rolling elements 20. The cage 21 holds the plurality of planetary rolling elements 20 at predetermined intervals in the circumferential direction so as to prevent contact between the planetary rolling elements 20. The cage 21 has two ring portions 22 and a plurality (e.g., five) of column portions 23. The ring portions 22 and column portions 23 of the cage 21 can be integrally formed from resin or metal.

[0034] The two ring portions 22 are arranged axially apart, with the planetary rolling elements 20 sandwiched between them. The ring portion 22 is a hollow, annular portion having a central hole 22c. The multiple pillar portions 23 are strip-shaped members extending axially, and are arranged circumferentially at predetermined intervals between the multiple planetary rolling elements 20. One end of each pillar portion 23 is fixed to the outer periphery of one ring portion 22, and the other end is fixed to the outer periphery of the other ring portion 22. In other words, the pillar portion 23 spans between the two ring portions 22. A pocket 24 for holding the planetary rolling elements 20 is formed between two adjacent pillar portions 23.

[0035] 7 is a perspective view showing the planetary rolling element unit 4. A plurality of planetary rolling elements 20 are incorporated into each pocket 24 of the cage 21 to form the planetary rolling element unit 4. The planetary rolling elements 20 are rotatably held in the pockets 24.

[0036] FIG. 8 is a perspective view showing the second support raceway 28. The second support raceway 28 has a ring shape that surrounds the sleeve 15 and the planetary rolling elements 20. The second support raceway 28 has a rolling surface 28h on the non-input side and a cam surface 28p on the input side. The rolling surface 28h is the surface on which the planetary rolling elements 20 roll, and is in point contact or surface contact with the planetary rolling elements 20. The rolling surface 28h is inclined with respect to the axial and radial directions. The rolling surface 28h includes a tapered surface that narrows in diameter toward the input side. In this example, the rolling surface 28h is a conical surface composed of a flat surface. Because the conical surface is concave, the contact surface 20c, which is a convex surface, and the rolling surface 28h are in uneven contact.

[0037] The cam surface 28p has a plurality of (e.g., six) concave cam grooves 28j each consisting of a first inclined surface 28f and a second inclined surface 28g. The cam grooves 28j have a V-shape when viewed radially from the outer diameter side. The plurality of cam grooves 28j are arranged at predetermined intervals in the circumferential direction and are connected to each other by connecting surfaces 28e. The connecting surfaces 28e can be formed parallel to a plane perpendicular to the rotation axis La. The first inclined surfaces 28f are inclined relative to the plane perpendicular to the rotation axis La. The second inclined surfaces 28g are inclined in the opposite direction to the first inclined surfaces 28f relative to the plane perpendicular to the rotation axis La.

[0038] The second support race 28 is fitted onto the inner peripheral surface of the casing 37 so as to be slidable in the axial direction. An axial pressing force is applied to the second support race 28 from the cam surface 28p toward the non-input side by the pressing force applying mechanism 7. The pressing force presses the planetary rolling elements 20 against the output race 30.

[0039] FIG. 9 is a perspective view showing the output race 30. The output race 30 has a hollow circular shape that surrounds the shaft 68 and the shaft cap 69. The output race 30 has a rolling surface 30h on the input side. The rolling surface 30h is the surface on which the planetary rolling elements 20 roll, and is in point contact or surface contact with the planetary rolling elements 20. The rolling surface 30h is inclined in the axial and radial directions. The rolling surface 30h includes a tapered surface that narrows in diameter toward the non-input side. In this example, the rolling surface 30h is a conical surface composed of a flat surface. Because the conical surface is concave, the contact surface 20d, which is a convex surface, and the rolling surface 30h are in uneven contact.

[0040] The output bearing ring 30 contacts the planetary rolling elements 20 and rotates about the rotation axis La as the planetary rolling elements 20 rotate. The output bearing ring 30 is connected to an output member 32 of the output mechanism 5, so that the output member 32 rotates as the output bearing ring 30 rotates. The output bearing ring 30 has a connecting hole 30e that surrounds the rotation axis La and penetrates in the axial direction. The connecting hole 30e is provided with a recess 30k that engages with the parallel key 35. The output bearing ring 30 is provided with a circular protrusion 30b that protrudes toward the non-input side.

[0041] The operation of the transmission mechanism 3 will now be described. When the input race 14 rotates, the planetary rolling elements 20 rotate about the rotation axis Lb while revolving around the revolution axis. In this example, the revolution axis of the planetary rolling elements 20 coincides with the rotation axis La, and therefore, the following description will be given assuming that the rotation axis La is the revolution axis.

[0042] When the first support bearing ring 26 rotates freely and the second support bearing ring 28 is stationary and non-rotating, an output rotation obtained by multiplying the input rotation by the speed ratio R is output to the output bearing ring 30. The speed ratio R is determined according to the shape of the planetary rolling elements 20 and the inclination of the rotation axis Lb with respect to the rotation axis La. Therefore, the speed ratio R can be changed by changing the inclination of the rotation axis Lb. In this embodiment, a speed ratio control mechanism 6 is provided to change the speed ratio R by changing the inclination of the rotation axis Lb. The speed ratio control mechanism 6 will be described later.

[0043] The output mechanism 5 will be described with reference to Fig. 2. The output mechanism 5 includes an output bearing ring 30, a thrust bearing 33, an output member 32, an output bearing 34, a second oil seal S2, and a casing 37.

[0044] The casing 37 functions as an outer shell that encloses the internal mechanism of the friction transmission 100. The casing 37 is a cylindrical member having a cylindrical portion 37b and an inward protruding portion 37h. A cover 67 is fixed to the input side end of the cylindrical portion 37b of the casing 37. The inward protruding portion 37h is a ring-shaped portion that protrudes radially inward from the inner periphery of the cylindrical portion 37b. The output bearing 34 is housed on the opposite input side of the inward protruding portion 37h of the cylindrical portion 37b.

[0045] The output bearing 34 is disposed between the output member 32 and the cylindrical portion 37b, and the input side of the output bearing 34 is supported by the inner protruding portion 37h. The output bearing 34 rotatably supports the output member 32. In this example, the output bearing 34 is a cross roller bearing. The outer ring of the output bearing 34 is supported by the casing 37. The inner ring of the output bearing 34 supports the output member 32.

[0046] The second oil seal S2 is disposed on the inner peripheral surface of the cylindrical portion 37b on the non-input side of the output bearing 34, and seals between the inside and outside of the friction transmission device 100.

[0047] The thrust bearing 33 rotatably supports the output race 30. The thrust bearing 33 is disposed axially between the inward protrusion 37h and the output race 30. The thrust bearing 33 has a ring shape that is housed in the annular space between the casing 37 and the circular protrusion 30b of the output race 30. In other words, the thrust bearing 33 fits onto the outer periphery of the circular protrusion 30b. The thrust bearing 33 in this example includes a hollow, disk-shaped rolling ring 33e and a plurality of rolling elements 33b that roll on the rolling ring 33e. As an example, the rolling elements 33b are rollers.

[0048] The output member 32 is a substantially circular member having an output annular portion 32b and a connecting portion 32d. The output annular portion 32b is a circular portion to which a driven device is connected on the side opposite to the input side. A retaining ring W2 is attached to the outer periphery of the output annular portion 32b to regulate the positional relationship with the output bearing 34. The output annular portion 32b is supported by the output bearing 34.

[0049] The connecting portion 32d is a hollow circular portion that extends from the output annular portion 32b toward the input side. The outer periphery of the connecting portion 32d fits into the inner periphery of the output race 30, and a parallel key 35 is inserted between them. This configuration connects the output member 32 to the output race 30. In this state, the output member 32 and the output race 30 are movable relative to each other in the axial direction and rotate integrally in the circumferential direction. The tip of the shaft 68 and a shaft cap 69 are housed in the inner periphery of the connecting portion 32d.

[0050] The pressing force applying mechanism 7 will be described with reference to Figures 2 and 10 to 13. The pressing force applying mechanism 7 converts the rotational motion of the preload bearing ring into linear motion of this preload bearing ring to apply a preload to the transmission mechanism 3. In the example of Figure 2, the second support bearing ring 28 functions as the preload bearing ring. The pressing force applying mechanism 7 includes a pressing cam 56, a roller cage 52, a roller 53, a cover 67, and the second support bearing ring 28.

[0051] FIG. 10 is a perspective view showing the rollers 53 and the roller cage 52. The roller cage 52 is a hollow, disk-shaped member having a through hole 52c and is disposed between the cam surface 28p of the second support raceway 28 and the pressing cam surface 56p of the pressing cam 56. The roller cage 52 has multiple (e.g., six) pockets 52b arranged at predetermined intervals in the circumferential direction. The pockets 52b are rectangular holes when viewed from the axial direction. Multiple (e.g., six) rollers 53 are provided corresponding to the cam grooves 56j. The rollers 53 are cylindrical and rotatably housed in the pockets 52b. The roller cage 52 has a notch 52k cut out in part of its circumferential direction at a position corresponding to the radial protrusion 62c of the control ring 62 to allow the control shaft 61 of the speed ratio control mechanism 6 to pass through to the outside of the cover 67.

[0052] 11 is a perspective view showing the pressing cam 56. The pressing cam 56 is a hollow disk-shaped member having a through hole 56c, and is arranged axially between the roller cage 52 and the cover 67. The pressing cam 56 has a notch 56k formed by cutting out a portion of its circumferential surface at a position corresponding to the radial protrusion 62c of the control ring 62, in order to allow the control shaft 61 of the speed ratio control mechanism 6 to pass through to the outside of the cover 67.

[0053] The pressing cam 56 of the pressing force applying mechanism 7 has a first spigot portion 56n that is spigot-fitted with the cover 67. The first spigot portion 56n is provided on the outer peripheral surface of the pressing cam 56.

[0054] The pressing cam 56 has a pressing cam surface 56p on the non-input side. The pressing cam surface 56p is composed of a placement surface 56a on which the multiple rollers 53 are placed and a non-placement surface 56e on which the multiple rollers 53 are not placed. The placement surface 56a has a concave cam groove 56j consisting of a first inclined surface 56f and a second inclined surface 56g. The pressing cam surface 56p has multiple placement surfaces 56a (e.g., six). The cam grooves 56j have a V-shape when viewed radially from the outer diameter side. The multiple cam grooves 56j are arranged at predetermined intervals in the circumferential direction and are connected to each other by the non-placement surfaces 56e.

[0055] The non-placement surface 56e can be formed parallel to a plane perpendicular to the rotation axis La. The first inclined surface 56f is inclined relative to the plane perpendicular to the rotation axis La. The second inclined surface 56g is inclined in the opposite direction to the first inclined surface 56f relative to the plane perpendicular to the rotation axis La.

[0056] The pressing cam 56 has a plurality of connected portions 56h arranged at predetermined intervals in the circumferential direction at positions offset from the rotation axis La. In this example, the connected portions 56h are bolt holes that penetrate in the axial direction and are arranged at equal intervals in the circumferential direction. The connected portions 56h do not need to be arranged at strictly equal intervals and may deviate from equal intervals within a margin of error. In the example of FIG. 11 , three connected portions 56h are provided at 120° intervals. The connected portions 56h penetrate in the axial direction from the non-positioning surface 56e. The pressing cam 56 is fixed to the cover 67 by a bolt B5 that passes through the connected portions 56h and is screwed into a screw hole 67f provided in the cover 67.

[0057] The cover 67 will be described with reference to Figures 1, 2, and 12. Figure 12 is a perspective view showing the cover 67. The cover 67 is a hollow, disk-shaped member having a hollow portion 67c surrounding the rotation axis La. The cover 67 has a plurality of (e.g., 15) bolt holes 67d arranged at predetermined intervals in the circumferential direction at positions offset from the rotation axis La. The cover 67 is fixed to the input side of the casing 37 by screwing a plurality of bolts B1 into the input side of the casing 37 through the bolt holes 67d.

[0058] The cover 67 has a through hole 67e for allowing the control shaft 61 to pass therethrough. The through hole 67e is located at a position offset from the rotation axis La and on the inner peripheral side of the pitch circle of the bolt holes 67d. A plurality of screw holes 67f are provided on the non-input side of the cover 67 at positions offset from the rotation axis La and arranged at predetermined intervals in the circumferential direction. In the example of FIG. 12 , three screw holes 67f are provided at 120° intervals.

[0059] The hollow portion 67c is provided with a circumferential step 67h that contacts the input side of the input bearing 66 and a circumferential groove 67g in which a snap ring W3 is fitted. The snap ring W3 that contacts the non-input side of the input bearing 66 is fitted in the circumferential groove 67g. The axial position of the input bearing 66 is regulated by the snap ring W3 and the circumferential step 67h.

[0060] The pressing cam 56 is fixed to the opposite input side of the cover 67, and the roller retainer 52 is attached to overlap the opposite input side of the pressing cam 56. The control ring 62 is housed in the hollow portion of the pressing cam 56 and the roller retainer 52, and the control shaft 61 passes through a cylindrical seal 58 attached to a through-hole 67e and protrudes from the cover 67 to the input side. The cylindrical seal 58 functions as an oil seal that prevents the outflow of lubricant.

[0061] The operation of the pressing force applying mechanism 7 will be described with reference to Figures 2 and 13. Figure 13 is a diagram for schematically explaining the operation of the pressing force applying mechanism 7, showing the cam surface 28p, the roller 53, and the pressing cam surface 56p. The pressing cam 56 is fixed to the cover 67 and is stationary, and the second support race 28 receives a rotational force (torque) as the planetary rolling elements 20 rotate, and rotates within a certain range. Figure 13(A) shows a state in which no rotational force is being applied, and Figure 13(B) shows a state in which a rotational force is being applied.

[0062] 13(B), when the second support race 28 rotates, the relative positions of the cam grooves 28j and 56j shift as indicated by the arrow W, causing the rollers 53 to ride up onto the first inclined surfaces 56f and the second inclined surfaces 28g. As a result, a reaction force F0 from the rollers 53 is applied to the inclined surfaces, and a component of the reaction force F0 becomes a pressing force F, pressing the second support race 28 to the non-input side. The pressing force F presses the second support race 28, planetary rolling elements 20, output race 30, and thrust bearing 33 against the inward protrusion 37h, and functions as a preload for the transmission mechanism 3.

[0063] The preload adjustment function of the pressing force applying mechanism 7 will now be described. When the load from the driven device increases and the preload between the output race 30 and the planetary rolling elements 20 becomes insufficient, an increasing proportion of the rotational force input from the input race 14 to the planetary rolling elements 20 is transmitted to the second support race 28. When the rotational force of the second support race 28 increases, the pressing force F, which is a component of the rotational force of the second support race 28, increases, and the preload increases. When the load from the driven device decreases, the rotational force transmitted to the second support race 28 decreases due to the opposite mechanism, and the pressing force F and preload also decrease. In this way, the pressing force applying mechanism 7 can apply a pressing force F to the transmission mechanism 3 according to the load from the driven device, thereby automatically adjusting the preload.

[0064] The speed ratio control mechanism 6 will be described with reference to FIGS. 2, 3, and 14. FIG. 14 is a perspective view showing the speed ratio control mechanism 6. As described above, the speed ratio control mechanism 6 controls the speed ratio R by changing the relative position of the input bearing ring 14 of the transmission mechanism 3. The speed ratio control mechanism 6 includes a control shaft 61, a control ring 62, and a control unit bearing 63. The control shaft 61 is a rod-shaped member extending axially at a position radially offset from the rotation axis La, and its non-input end is attached to a radial protrusion 62c of the control ring 62. The radial position of the control shaft 61 may be offset radially outward from the input shaft 64 or from the input bearing ring 14. The control ring 62 is a hollow annular member having a hollow portion 62e. The hollow portion 62e is provided with a circumferential extending portion 62f extending radially inward from the non-input side of the hollow portion 62e, and a circumferential groove 62g in which a retaining ring W4 is fitted, in order to support the control portion bearing 63. The axial movement of the control portion bearing 63 is restricted by the circumferential extending portion 62f and the retaining ring W4.

[0065] The control section bearing 63 is disposed between the hollow portion 62e of the control ring 62 and the first cylindrical portion 15b of the sleeve 15. The control section bearing 63 rotatably supports the sleeve 15 relative to the speed ratio control mechanism 6. The outer ring of the control section bearing 63 is supported in the hollow portion 62e of the control ring 62, and the inner ring supports the first cylindrical portion 15b. In this example, the control section bearing 63 is a cross roller bearing. The control shaft 61 extends from the radial protrusion 62c to the input side, penetrates the cover 67, and protrudes from the input side of the cover 67. The control shaft 61 is connected to an actuator (not shown) that outputs driving force in the axial direction. The non-input side of the control ring 62 is housed in the through hole 52c of the roller cage 52.

[0066] The operation of the speed ratio control mechanism 6 will now be described. When an axial driving force is input from the actuator to the control shaft 61, the control ring 62 moves axially. In conjunction with the movement of the control ring 62, the control unit bearing 63, sleeve 15, input race 14, first race bearing 27, first support race 26, shaft 68, and shaft cap 69 move integrally. At this time, the second support race 28 and output race 30 are stationary in the axial direction, so the rotation axis Lb of the planetary rolling element 20 tilts with respect to the rotation axis La.

[0067] When the input race 14 and the first support race 26 move toward the opposite input side, the opposite input side of the rotation axis Lb moves away from the rotation axis La, and the input side of the rotation axis Lb tilts toward the rotation axis La. As a result, the rotation radius and revolution radius of each contact point between each race and the planetary rolling elements 20 change, and the speed ratio R also changes. The speed ratio R (output rotation / input rotation) of the friction transmission 100 increases as the inclination with respect to the rotation axis La increases. Similarly, when the input race 14 and the first support race 26 move toward the input side, the rotation axis Lb tilts toward the opposite side, and the speed ratio R of the friction transmission 100 decreases as the inclination with respect to the rotation axis La increases. By maintaining a constant position of the control shaft 61, the attitude of the planetary rolling elements 20 remains constant, and the speed ratio R is maintained constant.

[0068] The operation of the friction transmission device 100 configured as described above will now be described. When rotation is transmitted from the motor shaft 51 to the input shaft 64, the input race 14 rotates about the rotation axis La. The rotation of the input race 14 causes the planetary rolling elements 20 to rotate and revolve. The rotation of the planetary rolling elements 20 is transmitted to the output race 30, which rotates at a speed corresponding to the speed ratio R. The rotation of the output race 30 is output to the output member 32 via the output mechanism 5. When the positions of the input race 14 and the first support race 26 are changed by the speed ratio control mechanism 6, the speed ratio R also changes.

[0069] The following describes the characteristic configuration of the friction transmission device 100 of this embodiment. One of the characteristics of the friction transmission device 100 of this embodiment is the support structure of the pressing portion 72 that presses the second support bearing ring 28. As an example, the second support bearing ring 28 has a pressing cam 56 as the pressing portion 72.

[0070] (Reference Example) A specific support structure for the pressing portion 72 of the pressing force imparting mechanism 7 will be described. To facilitate understanding of the characteristic configuration, the support structure for the pressing portion 72 in Reference Example 200 of a friction transmission device will be described. Reference Example 200 was created by the inventor during the process of developing this embodiment. The pressing portion 72 in Reference Example 200 is a pressing cam 56. Figure 18 is a cross-sectional view showing the support structure for the pressing cam 56 in Reference Example 200.

[0071] Reference Example 200 differs from the friction transmission 100 of the embodiment in that the casing 37 and the cover 67 sandwich the pressing cam 56 and fasten them with a bolt B1, but the other configurations are similar to those of the embodiment. In Reference Example 200, the pressing cam 56 has a flange 56m that protrudes radially from its outer periphery. The flange 56m is housed in the axial space between a recess 37d provided on the input side of the casing 37 and a recess 67b provided on the non-input side of the cover 67. The flange 56m is provided with 15 through holes 56d at positions corresponding to the bolt holes 67d of the cover 67. The cover 67 and the flange 56m are fastened to the input side of the casing 37 by threading a bolt B1 into the casing 37 through the bolt holes 67d and the through holes 56d.

[0072] In Reference Example 200, the axial load (reaction force of the pressing force) generated by the pressing force applying mechanism 7 applies bending stress to the flange 56m of the pressing cam 56. This is because there is a large radial offset between the position of the pressing cam 56 that receives the reaction force of the pressing force (pressing cam surface 56p) and the support position of the flange. Therefore, if the transmission torque is increased in Reference Example 200, the reaction force of the pressing force also increases, and the bending stress generated in the flange 56m also increases, resulting in insufficient strength in this portion. This is disadvantageous in increasing the transmission torque. Below, several configuration examples for improving the strength of the pressing portion 72 will be described.

[0073] (First Configuration Example) A first configuration example of the friction transmission 100 of the embodiment will be described with reference to Figures 2, 11, 12, and 15. In the first configuration example, the pressing portion 72 is a pressing cam 56, and the pressing cam 56 has an abutment portion 56b that abuts against the cover 67 at a position that axially overlaps with the pressing cam 56. In other words, the abutment portion 56b on the input side of the pressing cam 56 abuts against the cover 67 at a position on the pressing cam surface 56p that receives the reaction force of the pressing force. With this configuration, almost no bending stress is generated in the pressing cam 56. With the pressing cam 56 abutting against the cover 67, the bolt B5 is passed through the connected portion 56h and screwed into the screw hole 67f of the cover 67, thereby fixing the pressing cam 56 to the cover 67.

[0074] The spigot portion of the pressing force imparting mechanism 7 of the first configuration example will be described. FIG. 15 is a cross-sectional view showing the spigot portion of the pressing force imparting mechanism 7. The first configuration example has a spigot portion to ensure radial positional accuracy of the pressing force imparting mechanism 7. Specifically, the pressing cam 56 of the pressing force imparting mechanism 7 has a first spigot portion 56n that fits in a spigot-fit relationship with the cover 67 and a second spigot portion 56q that fits in a spigot-fit relationship with the casing 37. The first spigot portion 56n and the second spigot portion 56q are integrally and continuously formed on the outer circumferential surface of the pressing cam 56. A surrounding portion 67k that surrounds the pressing cam 56 is provided on the non-input side of the cover 67, and the first spigot portion 56n fits in a spigot-fit relationship with the inner circumferential surface 67n of the surrounding portion 67k. The casing 37 includes a surrounding portion 37k that surrounds the pressing cam 56 at the input-side end of the cylindrical portion 37b. The second spigot portion 56q is spigot-fitted to the inner circumferential surface 37q of the surrounding portion 37k of the cylindrical portion 37b of the casing 37.

[0075] While the cover 67 needs to be machined into various shapes depending on requirements, the cam surface 28p needs to be hard. Therefore, in the first configuration example, the pressing cam 56 is separate from the cover 67, and the pressing cam 56 has a higher hardness than the cover 67. By making these separate, the cam surface 28p can be formed from a high-hardness material and the cover 67 can be formed from an easy-to-machine material, so that both hardness and ease of machining can be achieved at low cost.

[0076] According to the first configuration example, the flange to which bending stress is applied is eliminated, thereby ensuring strength and enabling transmission torque to be increased.

[0077] (Second Configuration Example) A second configuration example of the friction transmission 100 of the embodiment will be described with reference to Figures 16 and 17. Figure 16 is a cross-sectional view showing the second configuration example of the friction transmission 100. Figure 17(A) is a perspective view of the cover 167 of the second configuration example, viewed obliquely from above on the non-input side. Figure 17(B) is a perspective view of the cover 167 of the configuration example, viewed obliquely from above on the input side. The second configuration example differs from the first configuration example in that the pressing portion 72 is formed integrally with the cover 167, but the other configurations are similar. Therefore, redundant explanations will be omitted and the explanation will focus on the differences from the first configuration example.

[0078] As shown in FIG. 17(B), the input side of cover 167 is the same as the input side of cover 67 of the first configuration example (see also FIG. 12), and there are no differences. As shown in FIG. 17(A), cover 167 differs from cover 67 of the first configuration example in that a pressing portion 72 having a pressing cam surface 56p is provided on the non-input side. The pressing portion 72 can be considered a pressing cam integrated with cover 167. The pressing cam surface 56p of cover 167 differs from the pressing cam surface 56p of the pressing cam 56 of the first configuration example (see also FIG. 11) in that it does not have a connected portion 56h, but the other configurations are the same.

[0079] According to the second configuration example, since the pressing portion 72 is integrated with the cover 167, it is easier to ensure strength against the reaction force of the pressing force than in the reference example, and it is possible to increase the transmitted torque. Furthermore, in the second configuration example, under the same transmitted torque conditions, the cover 167 including the pressing portion 72 can be configured to be thinner in the axial direction than in the reference example.

[0080] The operation and effect of the friction transmission device 100 of the embodiment will be described. The friction transmission device 100 of the embodiment is a friction transmission device including planetary rolling elements 20 arranged around a rotation axis La, a first support raceway 26 and a second support raceway 28 that contact the planetary rolling elements 20, and a pressing force applying mechanism 7 that presses the second support raceway 28 to generate a pressing force on the contact surface between the second support raceway 28 and the planetary rolling elements 20. The friction transmission device 100 has a cover 67 that covers the friction transmission device 100 from the axial direction, and the pressing force applying mechanism 7 has a pressing portion 72 that presses the second support raceway 28, and the pressing force applying mechanism 7 has an abutting portion 56b that abuts against the cover 67 at a position that axially overlaps with the pressing portion 72, or is configured integrally with the cover 67.

[0081] According to this configuration, the pressing portion 72 (pressing cam 56) is fixed to the cover 67, so that almost no bending stress due to the reaction force of the pressing force is generated in the pressing portion 72. This makes it possible to eliminate the lack of strength of the pressing portion 72, and in turn makes it possible to provide a friction transmission that can transmit a larger torque.

[0082] As an example, the pressing force applying mechanism 7 includes a cam surface 28p provided on the second support raceway 28, a pressing cam 56 axially opposed to the cam surface 28p, and a plurality of rollers 53 arranged between the cam surface 28p and the pressing cam 56 and functioning as a pressing portion 72. The pressing cam 56 has a pressing cam surface 56p configured with a placement surface 56a on which the plurality of rollers 53 are arranged and a non-placement surface 56e on which the plurality of rollers 53 are not arranged. A connected portion 56h for connecting to the cover 67 is provided on the non-placement surface 56e. The pressing force applying mechanism 7 is configured integrally with the cover 67 by connecting the connected portion 56h to the cover 67. In this case, compared to when the connected portion 56h is provided on the placement surface 56a, because the connected portion 56h is provided on the non-placement surface 56e, interference between the rollers 53 and the connected portion 56h can be avoided.

[0083] For example, the coupled portions 56h are arranged at equal intervals in the circumferential direction, which can improve the variation in strength depending on the position in the circumferential direction.

[0084] As an example, the pressing force imparting mechanism 7 has a first spigot portion 56n that abuts against and fits radially with the cover 67. In this case, the first spigot portion 56n functions as a guide, so that when the pressing force imparting mechanism 7 is attached to the cover 67, they can be easily fitted together.

[0085] As an example, the friction transmission 100 has a casing 37 that surrounds the planetary rolling elements 20 and to which the cover 67 is connected, and the pressing force applying mechanism has a second spigot portion 56q that abuts and fits radially against the casing 37. In this case, because the second spigot portion 56q functions as a guide, the pressing force applying mechanism 7 can be easily fitted to the casing 37 when attached to the casing 37.

[0086] As an example, the pressing force applying mechanism 7 includes a cam surface 28p provided on the second support raceway 28, a pressing cam 56 axially opposed to the cam surface 28p, and a plurality of rollers 53 disposed between the cam surface 28p and the pressing cam 56. The pressing cam 56 is separate from the cover 67, and the hardness of the pressing cam 56 is greater than the hardness of the cover 67. In this case, the cam surface 28p can be formed from a high-hardness material, and the cover 67 can be formed from an easy-to-machine material, so that both hardness and ease of machining can be achieved at low cost.

[0087] As an example, the pressing portion 72 is formed integrally with the cover 167. In this case, it is easy to ensure strength against the reaction force of the pressing force, and it becomes possible to increase the transmission torque.

[0088] The above is a description of the embodiment.

[0089] The above description is based on the embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications and variations are possible and that such modifications and variations are also within the scope of the present disclosure. Therefore, the description and drawings in this specification should be treated as illustrative rather than restrictive.

[0090] (Modifications) Modifications will be described below. In the drawings and descriptions of the modifications, the same components and members as those in the embodiment will be denoted by the same reference numerals. Explanations that overlap with the embodiment will be omitted as appropriate, and the description will focus on the configurations that differ from the embodiment.

[0091] In the explanation of the second configuration example, an example was shown in which the pressing portion 72 is formed integrally with the cover 167, but they may also be formed separately and then connected to be integrated. If they are formed integrally, the entire structure needs to be made of high hardness, but if they are connected to be integrated, the pressing portion 72 can be formed from a high-hardness material and the cover 167 can be formed from a material that is easy to process.

[0092] In the description of the embodiment, an example has been shown in which the cover 67 covers the entire friction transmission 100 in the axial direction, but the cover may be configured to cover only a portion of the friction transmission in the axial direction.

[0093] Although an example has been shown in which the output member 32 and the output bearing ring 30 are key-coupled by the parallel key 35, there are no limitations on the coupling structure. The coupling structure may be any structure that allows them to move relatively in the axial direction and rotate integrally in the circumferential direction, and may be, for example, a spline coupling, an involute spline coupling, or a coupling using an elastic body such as a spring that has low rigidity in the axial direction and high rigidity in the circumferential direction.

[0094] In the description of the embodiment, an example has been shown in which the rolling surfaces 30h and 28h are conical surfaces formed of flat surfaces, but these may also be curved surfaces such as convex or concave surfaces.

[0095] The configuration of the input bearing 66 is not limited, and may be, for example, a bearing having rollers as rolling elements. The configuration of the first bearing ring 27 is not limited, and may be, for example, a bearing having rollers as rolling elements. The configuration of the thrust bearing 33 is not limited, and may be, for example, a bearing having spheres as rolling elements. The configuration of the output bearing 34 is not limited, and may be, for example, a bearing having spheres as rolling elements.

[0096] The configuration of the control section bearing 63 is not limited, and may be, for example, a bearing having spheres as rolling elements, a thrust bearing, a sliding bearing, or the like.

[0097] For example, the pressing force applying mechanism 7 may have a sphere instead of the roller 53, and the pocket 52b of the roller retainer 52, the cam groove 56j of the pressing cam 56, and the cam groove 28j of the second support raceway 28 may each have a shape corresponding to the sphere.

[0098] For example, the pressing force applying mechanism 7 may be configured so that the roller 53 and the roller retainer 52 are eliminated, and the cam groove 28j of the second support raceway 28 is a convex cam lobe with a V-shaped slope, which is in direct contact with the cam groove 56j of the pressing cam 56. Conversely, the area of ​​the pressing cam corresponding to the cam groove 56j may be a cam lobe.

[0099] The positional relationship of each component of the friction transmission, including the first support race 26 and the second support race 28, is not limited to the example shown in the embodiment. These positional relationships may be different from those in the embodiment as long as they do not contradict the content of this disclosure. For example, the positional relationship between the first support race 26 and the second support race 28 may be different from that in the embodiment.

[0100] In the description of the embodiment, the input race 14 is disposed radially inward and the output race 30 is disposed radially outward with respect to the rotation axis of the planetary rolling elements 20. However, this is not limited to this, and the input race 14 may be disposed on the outside and the output race 30 on the inside, or both may be disposed on the inside, or both may be disposed on the outside.

[0101] In the description of the embodiment, an example has been shown in which the cover 67 covers a portion of the input side of the friction transmission 100 in the axial direction, but this is not limited to this. For example, a portion of the casing may protrude inward, and the protruding portion may serve as a cover that axially covers the input side of the friction transmission.

[0102] The pressing cam 56 may have a contact portion 56 b separate from the cover 67 , or may be integral with the cover 67 .

[0103] Each of these modifications provides the same functions and effects as the embodiment.

[0104] Any combination of the above-described embodiments and modifications is also useful as an embodiment of the present disclosure. A new embodiment resulting from the combination has the combined effects of the combined embodiments and modifications.

[0105] The present disclosure relates to friction transmissions.

[0106] 7 Pressing force imparting mechanism, 20 Planetary rolling element, 26 First support raceway ring, 28 Second support raceway ring, 28p Cam surface, 32d Connecting portion, 33b Rolling element, 37 Casing, 53 Roller, 56 Pressing cam, 56a Arrangement surface, 56e Non-arrangement surface, 56h Connected portion, 56n First spigot portion, 56q Second spigot portion, 67, 167 Cover, 72 Pressing portion, 100 Friction transmission device.

Claims

1. A friction transmission device comprising planetary rolling elements arranged around a rotation axis, a first support raceway and a second support raceway in contact with the planetary rolling elements, and a pressing force imparting mechanism that presses the second support raceway to generate a pressing force on the contact surface between the second support raceway and the planetary rolling elements, the friction transmission device having a cover that covers the friction transmission device from the axial direction, the pressing force imparting mechanism having a pressing portion that presses the second support raceway, and the pressing force imparting mechanism having an abutment portion that abuts against the cover at a position that axially overlaps with the pressing portion, or the friction transmission device is configured integrally with the cover.

2. The friction transmission device of claim 1, wherein the pressing force imparting mechanism includes a cam surface provided on a second support raceway, a pressing cam axially opposed to the cam surface, and a plurality of rollers arranged between the cam surface and the pressing cam and functioning as the pressing portion, the pressing cam has a pressing cam surface constituted by an arrangement surface on which the plurality of rollers are arranged and a non-arrangement surface on which the plurality of rollers are not arranged, the non-arrangement surface is provided with a connected portion for connection to the cover, and the pressing force imparting mechanism is constructed integrally with the cover by connecting the connected portion to the cover.

3. A friction transmission device as set forth in claim 2, wherein the connected portions are arranged at equal intervals in the circumferential direction.

4. A friction transmission device according to any one of claims 1 to 3, wherein the pressing force imparting mechanism has a first spigot portion that abuts radially against the cover and fits in a spigot-fit manner.

5. A friction transmission as set forth in claim 4, further comprising a casing surrounding said planetary rolling elements and to which said cover is connected, said pressing force imparting mechanism having a second spigot portion which abuts radially against said casing and engages with said spigot portion.

6. A friction transmission device as claimed in any one of claims 1 to 5, wherein the pressing force imparting mechanism includes a cam surface provided on the second support raceway, a pressing cam axially opposed to the cam surface, and a plurality of rollers arranged between the cam surface and the pressing cam, the pressing cam being separate from the cover, and the hardness of the pressing cam being greater than the hardness of the cover.

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