Tripod type constant velocity universal joint

Abstract

In a tripod-type constant velocity universal joint in which the outer surface of the roller and the roller guide surface are in contact with each other on substantially flat surfaces under torque load, the induced thrust and sliding resistance are reduced to improve NVH characteristics. [Solution] A pair of guide surfaces 7 are provided on both sides in the width direction of the roller guide surface 6, which can contact the roller 11 from both sides in the direction of the leg axis. The inner ring 12 has a cylindrical inner circumferential surface 23. The outer circumferential surface 33 of the leg axis 32 has arcs 33a and 33b that bulge on both sides in the torque transmission direction in the longitudinal and transverse sections. The radius of curvature r of the arc 33a in the longitudinal section of the outer circumferential surface 33 of the leg axis 32 is greater than the radius of curvature R of the arc 33b in the transverse section. Of the outer circumferential surface 15 of the roller 11, a crowning portion 15b is provided at the end in the direction of the leg axis (Y direction) of the contact surface that can contact the roller guide surface 6 when a torque load is applied.

Description

[Technical Field]

[0001] The present invention relates to a tripod-type constant velocity universal joint. [Background Art]

[0002] In drive shafts used in power transmission systems of automobiles, a sliding type constant velocity universal joint is often provided on the inboard side (the central side in the vehicle width direction), and a fixed type constant velocity universal joint is often provided on the outboard side (the outer side in the vehicle width direction). The sliding type constant velocity universal joint mentioned herein allows both angular displacement between two shafts and relative axial movement, while the fixed type constant velocity universal joint allows angular displacement between the two shafts but does not allow relative axial movement between the two shafts.

[0003] A tripod-type constant velocity universal joint is known as a sliding type constant velocity universal joint. There are a single roller type and a double roller type for tripod-type constant velocity universal joints. In the single roller type, a roller inserted into a track groove of an outer joint member is rotatably attached to a leg shaft of a tripod member via a plurality of needle rollers. The double roller type includes a roller inserted into a track groove of an outer joint member, and an inner ring that is externally fitted onto a leg shaft of a tripod member and rotatably supports the roller. Since the double roller type allows the roller to swing relative to the leg shaft, it has the advantage that compared with the single roller type, induced thrust (axial force induced by friction between components inside the joint) and slide resistance can each be reduced.

[0004] As double roller type tripod-type constant velocity universal joints, there are known ones in which the cross section (a cross section perpendicular to the axis of the leg shaft) of the outer peripheral surface of the leg shaft is formed into an elliptical shape, and the longitudinal cross section of the inner peripheral surface of the inner ring is formed into a convex arc shape (see Patent Document 1 below), and ones in which the outer peripheral surface of the leg shaft is formed into a spherical shape, and the inner peripheral surface of the inner ring (holder) is formed into a cylindrical surface shape (see Patent Document 2 below).

[0005] Furthermore, Patent Document 3, described below, shows a double-roller type tripod-type constant velocity universal joint having a different structure from the above. The basic structure of this constant velocity universal joint 101 is the same as that of a general tripod-type constant velocity universal joint, and as shown in Figure 11, it has an outer joint member 102, a tripod member 103 housed in the inner circumference of the outer joint member 102 and having three leg shafts 132 protruding outwards, and a roller unit 104 mounted on each leg shaft 132 of the tripod member 103 and housed in the track groove 105 of the outer joint member 102. The roller unit 104 has a roller 111 and an inner ring 112 and is housed in the track groove 105 of the outer joint member 102.

[0006] In this constant velocity universal joint 101, as shown in Figures 12 and 13, the roller 111 has a cylindrical outer surface 115, and the roller guide surface 106 of the track groove 105 is a flat surface. On both sides in the width direction of the roller guide surface 106, a pair of tapered guide surfaces 107 are provided that can contact the roller 111 from both sides in the axial direction of itself. The outer surface 133 of the leg shaft 132 of the tripod member 103 has arcs 133a and 133b in the longitudinal section (see Figure 12) and the cross section (see Figure 13). The radius of curvature r of the arc 133a in the longitudinal section of the outer surface 133 of the leg shaft 132 is greater than the radius of curvature R of the arc 133b in the cross section. The inner surface 118 of the inner ring 112 is a cylindrical surface and contacts the torque transmission direction (X direction) end of the outer surface 133 of the leg shaft 132. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2000-320563 [Patent Document 2] Patent No. 2957121 [Patent Document 3] Japanese Patent Publication No. 2024-086274 [Overview of the project] [Problems that the invention aims to solve]

[0008] In the constant velocity universal joint 101 described above, when a torque load is applied, the cylindrical outer surface 115 of the roller 111 is pressed against the roller guide surface 106, which is the flat surface of the outer joint member 102, thereby suppressing the tilt of the roller 111 in the direction of arrow B in Figure 12 (hereinafter referred to as "left-right tilt"). At this time, the cylindrical outer surface 115 of the roller 111 and the roller guide surface 106 are in linear contact, but stress concentration occurs at the end of this linear contact portion in the Y direction (axis direction of the leg shaft 132), and the contact pressure in this portion may become excessive (see dotted line in Figure 8). This phenomenon in which stress concentration occurs at the end of the contact portion is also called edge load. When a moment that causes left-right tilt is applied to the roller unit 104, the edge load generated at the end of the contact portion between the roller 111 and the roller guide surface 106 increases further.

[0009] When the contact pressure between the roller 111 and the roller guide surface 106 increases locally due to edge loading, these sliding resistances increase, leading to increased induced thrust and slide resistance. Furthermore, the difference in sliding resistance between the roller 111 and the roller guide surface 106 at each phase (track groove 105) becomes large, causing the operation of the constant velocity universal joint 101 to become unstable. As described above, the increase in induced thrust and slide resistance, and the instability of the operation of the constant velocity universal joint, may worsen the NVH characteristics.

[0010] For the reasons described above, the present invention aims to improve NVH characteristics by reducing induced thrust and sliding resistance in a tripod-type constant velocity universal joint in which the outer surface of the roller and the roller guide surface are in contact with each other on substantially flat surfaces when a torque load is applied. [Means for solving the problem]

[0011] The present invention, made to solve the aforementioned problems, comprises an outer joint member having three track grooves formed on its inner circumferential surface extending in the direction of the joint axis, and each track groove provided with a pair of roller guide surfaces facing each other in the direction of the joint circumference; a tripod member disposed on the inner circumference of the outer joint member and having three leg shafts projecting in the direction of the joint radius toward the track grooves; and three roller units having rollers disposed on the outer circumference of the leg shafts and inner rings disposed between the rollers and the leg shafts, supported on the leg shafts in a rotatable and swingable manner and housed in the track grooves. A pair of guide surfaces are provided on both sides in the width direction of the roller guide surface, which can contact the roller from both sides in the direction of the leg axis. The inner ring has a cylindrical inner surface, The outer circumferential surface of the leg shaft has a convex curve that bulges out on both sides in the torque transmission direction in a longitudinal section including the axis of the leg shaft and a cross section perpendicular to the axis of the leg shaft. The convex curve in the cross-section of the outer surface of the leg shaft moves away from the cylindrical inner surface of the inner ring as it moves from the torque transmission end toward both sides in the coupling axis direction, In a tripod-type constant velocity universal joint, the radius of curvature (r) at both ends in the torque transmission direction of the convex curve in the longitudinal section of the outer surface of the leg shaft is greater than the radius of curvature (R) at both ends in the torque transmission direction of the convex curve in the cross section of the outer surface of the leg shaft, The invention is characterized in that a crowning portion is provided at the end of at least one of the contact surfaces of the roller's outer circumferential surface and the roller guide surface, which can come into contact with each other when a torque load is applied, in the direction of the leg axis.

[0012] Furthermore, "contact surfaces that may come into contact with each other under torque load" includes not only regions that can geometrically come into contact with each other, but also regions that can come into contact with each other due to elastic deformation under torque load. Hereafter, such contact surfaces will also be simply referred to as "contact surfaces."

[0013] As described above, by providing a crowning portion at the end of at least one of the contact surfaces between the outer circumferential surface of the roller and the roller guide surface in the direction of the leg axis (the axial direction of the leg axis), edge load generated at the end of the contact portion between the outer circumferential surface of the roller and the roller guide surface in the direction of the leg axis during torque loading is suppressed, and the surface pressure at this end is reduced. As a result, the sliding resistance between the roller and the roller guide surface is reduced, and the induced thrust and sliding resistance of the tripod-type constant velocity universal joint are reduced. In addition, the variation in sliding resistance between the roller and the roller guide surface in the three phases (track grooves) is reduced, so the operation of the tripod-type constant velocity universal joint becomes more stable.

[0014] In the tripod-type constant velocity universal joint described above, for example, the roller guide surface can be made flat, and a crowning portion can be provided on the contact surface of the outer circumferential surface of the roller.

[0015] In this case, it is preferable that the contact surface of the outer circumferential surface of the roller has a cylindrical surface formed in the center in the direction of the leg axis and crowning portions connected to both sides of the cylindrical surface in the direction of the leg axis. When a torque load is applied, the roller guide surface, which consists of a cylindrical surface and a flat surface, comes into contact with the outer circumferential surface of the roller, thereby suppressing the lateral tilt of the roller.

[0016] Furthermore, when L1 is the width of the contact surface on the outer circumference of the roller in the direction of the leg axis, and L1a is the width of the cylindrical surface in the direction of the leg axis, it is preferable that L1a / L1 ≥ 1 / 3. In this way, by having a cylindrical surface with a width greater than a predetermined value, the lateral tilt of the roller can be reliably suppressed.

[0017] The maximum drop amount of the crowning portion formed on the contact surface of the outer circumferential surface of the roller is preferably 30 μm or more. This ensures that the generation of edge load at the contact point between the outer circumferential surface of the roller and the roller guide surface is reliably suppressed.

[0018] In the tripod-type constant velocity universal joint described above, the outer surface of the roller may be a cylindrical surface, and a crowning portion may be provided on the contact surface of the roller guide surface.

[0019] In this case, it is preferable that the contact surface of the roller guide surface includes a flat surface formed at a central portion in the leg shaft axial direction, and crowning portions connected to both sides of the flat surface in the leg shaft axial direction. When a torque load is applied, the cylindrical outer peripheral surface of the roller comes into contact with the flat surface of the roller guide surface, thereby suppressing lateral tilting of the roller.

[0020] Furthermore, when the width of the contact surface of the roller guide surface in the leg shaft axial direction is defined as L2, and the width of the flat surface in the leg shaft axial direction is defined as L2a, it is preferable that the relationship L2a / L2≧1 / 3 is satisfied. Since the flat surface has a width equal to or greater than a predetermined value in this configuration, lateral tilting of the roller can be reliably suppressed.

[0021] Furthermore, it is preferable that the maximum drop amount of the crowning portion formed on the contact surface of the roller guide surface is 30 µm or more. With this configuration, occurrence of edge load at the contact portion between the outer peripheral surface of the roller and the roller guide surface can be reliably suppressed. [Effects of the Invention]

[0022] As described above, according to the present invention, in a tripod-type constant velocity universal joint that brings the outer peripheral surface of the roller and the roller guide surface into contact with each other via substantially flat surfaces when a torque load is applied, induced thrust and sliding resistance can be reduced, thereby improving NVH characteristics. [Brief Description of the Drawings]

[0023] [Figure 1] It is a cross-sectional view in the joint axial direction of a tripod-type constant velocity universal joint according to an embodiment of the present invention. [Figure 2] It is a cross-sectional view taken along line K-K in FIG. 1. [Figure 3] It is an enlarged view of FIG. 2. [Figure 4] It is an enlarged view of the contact portion between the outer peripheral surface of the roller and the roller guide surface in FIG. 3. [Figure 5] It is an enlarged view of the outer peripheral surface of the roller. [Figure 6] It is a cross-sectional view taken along line M-M in FIG. 1. [Figure 7]Figure 1 is a cross-sectional view showing a tripod-type constant velocity universal joint in the state where the operating angle θ is taken. [Figure 8] This diagram schematically shows the contact pressure between the outer surface of the roller and the roller guide surface. [Figure 9] This is an enlarged view of the contact area between the outer circumferential surface of the roller and the roller guide surface according to another embodiment. [Figure 10] Figure 9 is an enlarged view of the roller guide surface. [Figure 11] This is a cross-sectional view of a conventional tripod-type universal joint in the axial direction. [Figure 12] Figure 11 is a cross-sectional view along the KK line. [Figure 13] Figure 11 is a cross-sectional view along the MM line. [Modes for carrying out the invention]

[0024] Embodiments of the present invention will be described based on the drawings.

[0025] A tripod-type constant velocity universal joint 1 according to one embodiment of the present invention is of the double-roller type and comprises an outer joint member 2, a tripod member 3, and a roller unit 4, as shown in Figures 1 and 2. In this specification, the direction of the axis O (left-right direction in Figure 1) of the tripod-type constant velocity universal joint 1 when the operating angle is 0° is referred to as the "joint axis direction," and the circumferential and radial directions of the circle centered on the axis O at this time are referred to as the "joint circumferential direction" and the "joint radial direction," respectively.

[0026] The outer joint member 2 has a cup shape with one end open in the joint axial direction and the other end closed (see Figure 1). Three linear track grooves 5 extending in the joint axial direction are formed on the inner circumferential surface of the outer joint member 2 at equal intervals in the joint circumferential direction (see Figure 2). Each track groove 5 has a pair of roller guide surfaces 6 arranged opposite each other in the joint circumferential direction. Each roller guide surface 6 extends in the joint axial direction. The tripod member 3 and the roller unit 4 are housed inside the outer joint member 2.

[0027] The tripod member 3 integrally comprises a body portion 31 having a central hole 30 and three leg shafts 32 projecting radially from three equally spaced positions in the circumferential direction of the joint on the outer surface of the body portion 31. By fitting the male splines formed on the shaft 10 into the female splines formed in the central hole 30 of the body portion 31 and fixing them in the axial direction of the joint with a retaining ring 21, the tripod member 3 and the shaft 10 are coupled in a manner that enables torque transmission.

[0028] The roller units 4 are provided on the outer circumference of each leg shaft 32 of the tripod member 3. Each roller unit 4 is housed in a track groove 5 of the outer joint member 2. The roller unit 4 comprises an annular roller 11 centered on the axis of the leg shaft 32, an annular inner ring 12 arranged on the inner circumference of the roller 11 and fitted onto the leg shaft 32, and a plurality of rolling elements 13 interposed between the roller 11 and the inner ring 12. In this embodiment, a large number of needle rollers in a full-roller configuration without cages are used as the plurality of rolling elements 13. The needle rollers 13 are arranged to roll freely between the outer and inner raceway surfaces, with the cylindrical inner surface of the roller 11 serving as the outer raceway surface and the cylindrical outer surface of the inner ring 12 serving as the inner raceway surface. The roller 11, inner ring 12, and needle rollers 13 are constructed to not disassemble naturally by a pair of snap rings 14, and these constitute the roller unit 4.

[0029] A boot 22 is fitted to the opening of the outer joint member 2. The larger diameter end of the boot 22 is fixed near the opening end of the outer circumferential surface of the outer joint member 2, and the smaller diameter end of the boot 22 is fixed to the outer circumferential surface of the shaft 10. Grease is sealed inside the outer joint member 2, which is closed by the boot 22.

[0030] The structure of the fitting portion between the roller 11 and the track groove 5 will be described in detail below using Figures 3, 4, and 6. In the following, the coupling axis direction will be the Z direction, the axis direction of the leg shaft 32 will be the Y direction, and the torque transmission direction perpendicular to both the coupling axis direction Z and the leg shaft axis direction Y will be the X direction.

[0031] The roller 11 has a substantially cylindrical outer surface 15 (the detailed shape of the outer surface 15 will be described later). The end faces 16 on both sides of the roller 11 in the width direction (Y direction) are flat surfaces perpendicular to their own axis (see Figure 3). The outer surface 15 and the end faces 16 of the roller 11 are continuous via tapered surfaces 17. The tapered surfaces 17 are connected to the outer surface 15 and the end faces 16 via chamfers 18 and 19, which are convex curved surfaces with a curved cross-section (for example, an arc shape) (see Figure 4).

[0032] The pair of roller guide surfaces 6 of each track groove 5 of the outer joint member 2 are made of flat surfaces parallel to each other (see Figure 3). The distance in the X direction between the opposing pair of roller guide surfaces 6 is slightly larger than the diameter of the widest part of the outer circumferential surface 15 of the roller 11. As a result, a small gap in the X direction is formed between the roller guide surfaces 6 and the outer circumferential surface 15 of the roller 11.

[0033] A pair of guide surfaces 7 are provided on both sides of each roller guide surface 6 in the width direction (Y direction). The guide surfaces 7 are flat surfaces parallel to the joint axis direction. In the cross-sections shown in Figures 3 and 4, the guide surfaces 7 and the tapered surface 17 of the roller 11 are in a straight line parallel to each other. The guide surfaces 7 are smoothly connected to the roller guide surface 6 via a concave curved surface 20 with a curved cross-section (e.g., an arc shape) (see Figure 4). A flat surface 8 is provided at the center of the outer diameter side of each track groove 5 in the X direction. The flat surface 8 and the guide surface 7 are smoothly connected via a concave curved surface with a curved cross-section (e.g., an arc shape) (see Figure 3). The distance in the Y direction between the pair of guide surfaces 7 provided on both sides of the width direction of the roller guide surface 6 is slightly greater than the distance in the Y direction between the pair of tapered surfaces 17 provided on both sides of the width direction of the outer peripheral surface 15 of the roller 11. As a result, a small gap in the Y direction is formed between the guide surfaces 7 and the tapered surface 17 of the roller 11 (see Figure 4).

[0034] When torque is applied to the outer joint member 2, the substantially cylindrical outer surface 15 of the roller 11 is pressed against the flat roller guide surface 6. As a result, the orientation of the roller 11 is corrected so that the substantially cylindrical outer surface 15 of the roller 11 is parallel to the roller guide surface 6 in the cross-section shown in Figure 3, thereby suppressing the lateral tilt of the roller 11 (tilt in the direction of arrow B in Figure 3). In addition, the tapered surface 17 of the roller 11 comes into contact with the guide surface 7, further suppressing the lateral tilt of the roller 11, as well as the forward and backward tilt of the roller 11 (tilt in the direction of arrow C in Figure 1).

[0035] Furthermore, when torque is applied to the outer joint member 2 in the direction of arrow T in Figure 3, the outer circumferential surface 15 of the roller 11 is pressed against the roller guide surface 6 on the left side of the figure (hereinafter referred to as the "torque-loaded roller guide surface"), while the roller 11 is not pressed against the roller guide surface 6 opposite to it (hereinafter referred to as the "torque-unloaded roller guide surface") and the guide surfaces 7 on both sides in the width direction. At this time, if the roller unit 4 tilts and the outer circumferential surface 15 or tapered surface 17 of the roller 11 come into contact with the torque-unloaded roller guide surface 6 or guide surface 7, the rotational resistance of the roller 11 increases.

[0036] Therefore, in this embodiment, when torque is applied to the outer joint member 2, the initial gap between the roller 11 and the roller guide surface 6 (the difference between the distance between the pair of opposing roller guide surfaces 6 and the outer diameter of the roller 11), and the shape of the guide surface 7 are designed so that the roller 11 contacts the roller guide surface 6 on the torque-loaded side, while not contacting the roller guide surface 6 on the non-torque-loaded side or the guide surfaces 7 on both sides of its width.

[0037] Next, the structure of the fitting portion between the inner ring 12 and the leg shaft 32 will be explained in detail using Figures 3 and 6.

[0038] The inner ring 12 has a cylindrical inner surface 23 that fits with the outer surface 33 of the leg shaft 32.

[0039] The outer circumferential surface 33 of the leg shaft 32 has a convex curve that bulges out on both sides in the torque transmission direction X in the longitudinal section (cross-section in the plane containing the axis of the leg shaft 32) shown in Figure 3. In the illustrated example, the convex curve in the longitudinal section of the outer circumferential surface of the leg shaft 32 is composed of a circular arc 33a with a radius of curvature r. The center of curvature of the circular arc 33a is offset from the axis of the leg shaft 32 to the opposite side of the circular arc 33a. The circular arc 33a of the outer circumferential surface of the leg shaft 32 fits with the cylindrical inner surface 23 of the inner ring 12 at its apex (X-direction end), and moves away from the cylindrical inner surface 23 of the inner ring 12 as it moves from the apex to both sides in the Y direction.

[0040] The outer circumferential surface 33 of the leg shaft 32 has a convex curve that bulges out on both sides in the torque transmission direction X in the cross-section shown in Figure 6 (a cross-section in a plane perpendicular to the axis of the leg shaft 32). In the illustrated example, the convex curve in the cross-section of the outer circumferential surface of the leg shaft 32 is composed of a circular arc 33b with a radius of curvature R. The center of curvature of the circular arc 33b is offset toward the circular arc 33b side with respect to the axis of the leg shaft 32. The radius of curvature R of the circular arc 33b is smaller than half A / 2 of the maximum diameter A of the outer circumferential surface 33 of the leg shaft 32 (maximum dimension of the outer circumferential surface 33 in the torque transmission direction X ≈ diameter of the cylindrical inner surface 23 of the inner ring 12). The circular arc 33b of the outer circumferential surface of the leg shaft 32 fits with the cylindrical inner surface 23 of the inner ring 12 at its apex (X-direction end), and moves away from the cylindrical inner surface 23 of the inner ring 12 as it moves toward both sides in the Z-direction from the apex. As a result, the outer circumferential surface 33 of the leg shaft 32 and the cylindrical inner surface 23 of the inner ring 12 are in contact in the X direction, and a gap G is provided between them in the Z direction. In the illustrated example, a flat surface 33c perpendicular to the Z direction is provided in the region of the cross-section of the outer circumferential surface 33 of the leg shaft 32 that includes both ends in the Z direction. As a result, the gap G in the Z direction between the flat surface 33c of the outer circumferential surface 33 of the leg shaft 32 and the cylindrical inner surface 23 of the inner ring 12 is increased.

[0041] As described above, in this embodiment, the radius of curvature r of the convex curve (arc 33a) in the longitudinal section of the outer surface 33 of the leg shaft 32 shown in Figure 3 is greater than the radius of curvature R of the convex curve (arc 33b) in the cross section of the outer surface 33 of the leg shaft 32 shown in Figure 6, resulting in an aspherical shape.

[0042] The inner ring 12 is provided with a cylindrical inner surface 23, and the longitudinal and transverse sections of the outer surface of the leg shaft 32 have convex curves, allowing the inner ring 12 to pivot relative to the leg shaft 32. As described above, the inner ring 12 and the roller 11 are assembled to be rotatable relative to each other via the needle roller 13, so the roller 11 can pivot together with the inner ring 12 relative to the leg shaft 32. In other words, within the plane containing the axis of the leg shaft 32, the axes of the roller 11 and the inner ring 12 can be inclined with respect to the axis of the leg shaft 32 (see Figure 7).

[0043] As shown in Figure 7, consider the case where the tripod-type constant velocity universal joint 1 rotates with an operating angle θ (the angle between the axis of the outer joint member 2 and the axis of the tripod member 3). In this case, the axis of the tripod member 3 is inclined with respect to the axis of the outer joint member 2, but because the roller unit 4 is oscillating, it is possible to avoid a state where the roller 11 and the roller guide surface 6 are at an oblique angle. As a result, the roller 11 rolls horizontally with respect to the roller guide surface 6, which reduces induced thrust and sliding resistance, and enables low vibration of the tripod-type constant velocity universal joint 1.

[0044] The basic structure of the tripod-type constant velocity universal joint 1 of this embodiment is as described above. Below, the shape of the outer circumferential surface 15 of the roller 11, which is a characteristic feature of this embodiment, will be described in detail.

[0045] As shown in Figures 3 and 4, the outer circumferential surface 15 of the roller 11 has a cylindrical surface 15a provided in the center in the Y direction (axis direction of the leg shaft 32) and crowning portions 15b provided at both ends in the Y direction. The center of the cylindrical surface 15a coincides with the axis of the leg shaft 32. The crowning portions 15b are smoothly continuous with the ends of the cylindrical surface 15a, and their diameter gradually decreases as they move toward the ends in the Y direction (away from the cylindrical surface 15a). In this embodiment, the crowning portions 15b provided at both ends of the outer circumferential surface 15 of the roller 11 have a similar shape. That is, the outer circumferential surface 15 of the roller 11 has a symmetrical shape with respect to the center in the Y direction. In the cross-section shown in Figure 4, the crowning portions 15b of this embodiment have a curved shape in which the radius of curvature continuously decreases toward the ends in the Y direction. The shape of the crowning portion 15b is not limited to this; for example, the cross-sectional shape of the crowning portion 15b shown in Figure 4 may be a curve consisting of a single circular arc, a composite curve combining multiple circular arcs, or a logarithmic curve.

[0046] As described above, by providing a crowning portion 15b at the Y-direction end of the outer circumferential surface 15 of the roller 11, edge load generated at the Y-direction end of the contact area between the outer circumferential surface 15 of the roller 11 and the roller guide surface 6 during torque loading is suppressed, and the surface pressure in this area is reduced (see solid line in Figure 8). As a result, the sliding resistance between the outer circumferential surface of the roller 11 and the roller guide surface 6 is reduced, thereby reducing induced thrust and sliding resistance during torque transmission of the tripod-type constant velocity universal joint 1. In addition, the variation in sliding resistance between the roller 11 and the roller guide surface 6 in the three phases (track groove 5) is reduced, so the operation of the tripod-type constant velocity universal joint 1 becomes more stable. As a result, the NVH characteristics of the tripod-type constant velocity universal joint 1 are improved.

[0047] In this embodiment, the maximum drop amount δ1 (see Figure 5) of the crowning portion 15b is set to 30 μm or more, preferably 40 μm or more. This ensures that edge load generated at the Y-direction end of the contact portion between the outer circumferential surface 15 of the roller 11 and the roller guide surface 6 is reliably suppressed when torque is applied. The maximum drop amount of the crowning portion is the distance between both ends of the crowning portion in a direction perpendicular to the surface on which the crowning portion is provided. In this embodiment, the distance between both ends of the crowning portion 15b in a direction perpendicular to the outer circumferential surface 15 of the roller 11 (radial direction of the roller 11) is the maximum drop amount δ1 of the crowning portion 15b. Specifically, the difference between the radius R1 at the boundary between the crowning portion 15b and the cylindrical portion 15a (i.e., the radius of the cylindrical portion 15a) and the radius R2 at the boundary between the chamfer 18 of the crowning portion 15b is the maximum drop amount δ1 of the crowning portion 15b.

[0048] In this case, if the width L1b in the Y direction of the crowning portion 15b (see Figure 4) is too small, it may not be possible to provide a sufficiently large drop amount δ1, and there is a risk that edge loading cannot be adequately suppressed. Therefore, it is preferable that the ratio L1b / L1 of the width L1b in the Y direction of each crowning portion 15b and the width L1 in the Y direction of the outer circumferential surface 15 of the roller 11 be 1 / 8 or more.

[0049] In this embodiment, a cylindrical surface 15a is formed in the center of the outer circumferential surface 15 of the roller 11 in the Y direction. Therefore, when torque is applied, this cylindrical surface 15a is pressed against the roller guide surface 6, which is a flat surface, thereby suppressing the left-right tilt of the roller 11 (tilt in the direction of arrow B in Figure 3). In this embodiment, the width L1a of the cylindrical surface 15a in the Y direction (see Figure 4) is 1 / 3 or more (L1a / L1≧1 / 3), preferably 1 / 2 or more (L1a / L1≧1 / 2), of the width L1 of the outer circumferential surface 15 of the roller 11 in the Y direction. By providing a cylindrical surface 15a with a predetermined or greater width on the outer circumferential surface 15 of the roller 11 in this way, the effect of suppressing the left-right tilt of the roller 11 when torque is applied is enhanced.

[0050] When a large torque is applied to the outer joint member 2, the outer circumferential surface 15 of the roller 11 and the roller guide surface 6 undergo elastic deformation, causing not only the cylindrical surface 15a of the outer circumferential surface 15 of the roller 11 but also the crowning portion 15b to come into contact with the roller guide surface 6. In this embodiment, the maximum drop amount δ1 of the crowning portion 15b is set so that when the maximum expected torque is applied, the entire Y-direction of the outer circumferential surface 15 of the roller 11 comes into contact with the roller guide surface 6. In other words, in this embodiment, the entire outer circumferential surface 15 of the roller 11 becomes a contact surface that can come into contact with the roller guide surface 6 when torque is applied. Specifically, the maximum drop amount δ1 of the crowning portion 15b is set to, for example, 150 μm or less, preferably 120 μm or less. This ensures a contact area between the outer circumferential surface 15 of the roller 11 and the roller guide surface 6 when torque is applied, thereby suppressing the increase in surface pressure at these contact points.

[0051] The roller 11 is manufactured by forging, turning, and heat treatment (e.g., quenching and tempering), followed by sequential finishing processes on the outer circumferential surface 15 and, if necessary, the end face 16, tapered surface 17, and chamfer 19. By performing these finishing processes on the outer circumferential surface of the roller 11, the cylindrical surface 15a and crowning portion 15b can be formed with high precision, and in particular, the shape of the crowning portion 15b and the drop amount δ1 can be set with high precision.

[0052] In this embodiment, when finishing the outer circumferential surface 15 of the roller 11, the cylindrical surface 15a and the crowning portion 15b are processed simultaneously or continuously. For example, when finishing the outer circumferential surface 15 of the roller 11 by polishing, the cylindrical surface 15a and the crowning portion 15b are polished with a full-type grinding wheel that has these polishing surfaces as one unit. Alternatively, when finishing the outer circumferential surface 15 of the roller 11 by a cutting process (so-called hardened steel cutting), the cylindrical surface 15a and the crowning portion 15b are continuously cut (turned) with the same chip while the roller 11 is rotated around its axis. By performing the above finishing processes, the boundary between the cylindrical surface 15a and the crowning portion 15b can be made smooth and continuous.

[0053] As described above, after heat treatment of the roller 11, finishing is performed on the outer surface 15 to remove the oxide film (black scale) on the outer surface 15 that was formed by the heat treatment. On the other hand, if finishing is not performed on areas of the roller 11 other than the outer surface 15 (end face 16, tapered surface 17, chamfers 18, 19), the oxide film (black scale) formed by the heat treatment will remain in these areas. Furthermore, by performing finishing (polishing or grinding) only on the outer surface 15 of the roller 11, a slight edge is formed at the boundary between the crowning portion 15b and the chamfer 18 of the outer surface 15. Note that finishing may also be performed on some or all of the end face 16, tapered surface 17, and chamfers 18, 19 of the roller 11.

[0054] The outer joint member 2 is manufactured by forging and then heat-treating it. The outer joint member 2 is made of a relatively soft material, such as machine structural steel, specifically S45C or S55C, taking into consideration its formability by forging. In contrast, the roller 11 has a relatively simple shape and is easy to forge, so it is made of a harder material than the outer joint member 2, such as bearing steel, specifically SUJ2.

[0055] As described above, since the roller guide surface 6 is made of a material with lower hardness than the roller 11, if the constant velocity universal joint 1 is used continuously while edge loading occurs, the relatively lower hardness roller guide surface 6 is prone to wear and dents. When dents occur on the roller guide surface 6 in this way, the sliding resistance deteriorates significantly, which can lead to a substantial increase in induced thrust and sliding resistance, and a significant deterioration of NVH characteristics.

[0056] In this embodiment, by providing crowning portions 15b at both ends in the Y direction of the outer peripheral surface 15 of the roller 11 as described above, edge loading at the contact portion between the roller 11 and the roller guide surface 6 is suppressed. As a result, wear of the roller guide surface 6, which is made of a relatively soft material, is suppressed, and deterioration of NVH characteristics can be avoided.

[0057] When a relatively small torque is applied to the outer joint member 2, a portion of the crowning portion 15b (the Y-direction end) of the outer circumferential surface 15 of the roller 11 does not come into contact with the roller guide surface 6, and a small gap is formed between them. Grease can enter this small gap, suppressing the breakdown of the oil film at the contact point between the outer circumferential surface of the roller 11 and the roller guide surface 6, thereby improving the durability of the constant velocity universal joint 1.

[0058] The present invention is not limited to the embodiments described above. Other embodiments of the present invention will be described below, but redundant explanations of points similar to those described above will be omitted.

[0059] In the above embodiment, a crowning portion 15b is shown on the outer circumferential surface 15 of the roller 11. However, conversely, a crowning portion may be provided on the roller guide surface 6. For example, in the embodiment shown in Figure 9, the outer circumferential surface 15 of the roller 11 is a cylindrical surface, and a crowning portion 6b is provided on the roller guide surface 6.

[0060] Specifically, the roller guide surface 6 has a flat surface 6a formed in the center in the Y direction and crowning portions 6b provided at both ends in the Y direction. The flat surfaces 6a provided on a pair of opposing roller guide surfaces 6 are parallel. The crowning portions 6b are smoothly continuous with the ends of the flat surface 6a and are displaced outward in the X direction (away from the outer circumferential surface 15 of the roller 11) as they move toward the Y direction end side (away from the flat surface 6a) (see Figure 10). In this embodiment, the crowning portions 6b provided at both ends of the roller guide surface 6 have a similar shape. That is, the roller guide surface 6 has a symmetrical shape with respect to the center in the Y direction. In the cross-section shown in Figure 9, the crowning portions 6b of this embodiment have a curved shape in which the radius of curvature continuously decreases toward the Y direction end side. The shape of the crowning portion 6b is not limited to this; for example, the cross-sectional shape of the crowning portion 6b shown in Figure 9 may be a curve consisting of a single circular arc, a composite curve combining multiple circular arcs, or a logarithmic curve.

[0061] In this embodiment, the maximum drop amount δ2 of the crowning portion 6b (see Figure 10) is 30 μm or more, preferably 40 μm or more. In this embodiment, the distance between both ends of the crowning portion 6b in the direction perpendicular to the flat surface 6a of the roller guide surface 6 (X direction) is the maximum drop amount δ2 of the crowning portion 6b. Specifically, the distance in the X direction between the plane extending from the flat surface 6a (see the dotted line in Figure 10) and the boundary between the crowning portion 6b and the concave curved surface 20 is the maximum drop amount δ2 of the crowning portion 6b.

[0062] The ratio L2b / L2 of the width L2b in the Y direction of each crowning portion 6b to the width L2 of the roller guide surface 6 in the Y direction is preferably 1 / 8 or more. The width L2a in the Y direction of the flat surface 6a is 1 / 3 or more (L2a / L2≧1 / 3), preferably 1 / 2 or more (L2a / L2≧1 / 2), of the width L2 of the roller guide surface 6 in the Y direction.

[0063] In this embodiment, the maximum drop amount δ2 of the crowning portion 6b of the roller guide surface 6 is set so that when the maximum expected torque is applied, the entire area of ​​the outer circumferential surface 15 of the roller 11 in the Y direction contacts the roller guide surface 6. That is, in this embodiment, the entire area of ​​the roller guide surface 6 that faces the outer circumferential surface 15 of the roller 11 in the X direction becomes a contact surface that can contact the outer circumferential surface 15 of the roller 11 when torque is applied. In this embodiment, the maximum drop amount δ2 of the crowning portion 6b is 150 μm or less, preferably 120 μm or less.

[0064] The track groove 5 of the outer joint member 2 is formed by forging, then heat-treated (e.g., quenching and tempering), and no further finishing is performed. In this case, the flat surface 6a and crowning portion 6b of the roller guide surface 6 are formed simultaneously by forging, so their boundaries are smoothly continuous. An oxide film (black scale) formed by the heat treatment remains on the entire surface of the outer joint member 2, including the roller guide surface 6, more specifically, on the surface of the cup-shaped mouth portion.

[0065] When the outer joint member 2 is formed by forging, the dimensional accuracy of the roller guide surface 6 cannot be made very high. Therefore, even if an attempt is made to make the roller guide surface 106 a flat surface as shown in Figure 12, variations occur in the X-direction position of the roller guide surface 106, and for example, the area near the Y-direction end of the roller guide surface 106 may tilt toward the outer circumferential surface 15 of the roller 11. In this case, the area near the Y-direction end of the roller guide surface 106 comes into strong contact with the Y-direction end of the outer circumferential surface 15 of the roller 11, resulting in a large edge load.

[0066] Therefore, as in this embodiment, by providing a crowning portion 6b at the Y-direction end of the roller guide surface 6 and receding this portion toward the side away from the outer circumferential surface 15 of the roller 11, even if there is variation in the X-direction position of the crowning portion 6b, it is possible to reliably avoid strong contact between the Y-direction end of the outer circumferential surface 15 of the roller 11 and the roller guide surface 6.

[0067] When a relatively small torque is applied to the outer joint member 2, a portion of the crowning portion 6b of the roller guide surface 6 (the Y-direction end) does not come into contact with the outer circumferential surface 15 of the roller 11, and a small gap is formed between them. Grease can enter this small gap, suppressing the breakdown of the oil film at the contact point between the outer circumferential surface 15 of the roller 11 and the roller guide surface 6, thereby improving the durability of the constant velocity universal joint 1.

[0068] In the embodiments described above, a crowning portion is provided on the outer circumferential surface 15 of the roller 11 or on the roller guide surface 6. However, the invention is not limited to this, and crowning portions may be provided on both the outer circumferential surface 15 of the roller 11 and the roller guide surface 6. For example, the outer circumferential surface 15 of the roller 11 may have a shape having a cylindrical portion 15a and a crowning portion 15b as shown in Figure 5, and the roller guide surface 6 may have a shape having a flat surface 6a and a crowning portion 6b as shown in Figure 10. In this case, it is desirable that the sum of the maximum drop δ1 of the crowning portion 15b of the outer circumferential surface 15 of the roller 11 and the maximum drop amount δ2 of the crowning portion 6b of the roller guide surface 6 be 30 μm or more, preferably 40 μm or more.

[0069] Furthermore, when a crowning portion is provided on the outer circumferential surface 15 of the roller 11, the cylindrical surface 15a may be omitted, and the entire outer circumferential surface 15 may be made into a crowning portion. That is, the outer circumferential surface 15 of the roller 11 may be a convex curved surface with the center in the Y direction bulging outwards toward the outer diameter. Also, when a crowning portion is provided on the roller guide surface 6, the cylindrical surface 6a may be omitted, and the entire region of the roller guide surface 6 facing the outer circumferential surface 15 of the roller 11 may be made into a crowning portion. That is, the above region of the roller guide surface 6 may be a convex curved surface with the center in the Y direction bulging toward the center in the X direction of the track groove 5 (the side closer to the outer circumferential surface 15 of the roller 11).

[0070] In the embodiments described above, the case in which both the convex curve in the longitudinal section and the transverse section of the outer surface of the leg shaft 32 are composed of circular arcs is shown, but the invention is not limited to this. For example, one or both of the convex curve in the longitudinal section and the convex curve in the transverse section of the outer surface of the leg shaft 32 may be composed of a non-circular curve such as an ellipse.

[0071] Furthermore, in the embodiments described above, as shown in Figure 6, flat surfaces 33c are provided at both ends of the leg shaft 32 in the coupling axial direction. However, even without the flat surfaces 33c, if a sufficient gap is formed between the leg shaft 32 and the inner ring 12 in the coupling axial direction to allow the roller unit 4 to swing relative to the leg shaft 32, the flat surfaces 33c may be omitted.

[0072] The tripod-type constant velocity universal joint 1 described above is not limited to automobile drive shafts, but can be widely used in power transmission paths for automobiles, industrial equipment, and the like. [Explanation of symbols]

[0073] 1. Tripod type constant velocity universal joint 2. Outer joint member 3. Tripod Member 4 Roller Units 5 Track grooves 6. Roller guide surface 6a flat surface 6b Crowning Club 7 Guide surface 10 shafts 11 Laura 12 Inner Ring 13 Rolling element 14 snap rings 15 Outer surface 15a Cylindrical surface 15b Crowning Club 17 Tapered surface 31 Torso 32 Leg axis 33a Circular arc (convex curve) 33b Circular arc (convex curve) O axis X Torque transmission direction Y leg axis direction Z joint axial direction δ1, δ2 Maximum drop amount of the crowning section

Claims

1. The outer joint member has three track grooves formed on its inner surface that extend in the direction of the joint axis, and each track groove is provided with a pair of roller guide surfaces that face each other in the direction of the joint circumference; the tripod member is disposed on the inner circumference of the outer joint member and has three leg shafts that protrude in the direction of the joint radius toward the track grooves; and the tripod unit has rollers disposed on the outer circumference of the leg shafts and inner rings disposed between the rollers and the leg shafts, and is supported on the leg shafts in a manner that allows it to rotate and swing, and is housed in the track grooves. A pair of guide surfaces are provided on both sides in the width direction of the roller guide surface, which can contact the roller from both sides in the direction of the leg axis. The inner ring has a cylindrical inner surface, The outer circumferential surface of the leg shaft has a convex curve that bulges out on both sides in the torque transmission direction in a longitudinal section including the axis of the leg shaft and a cross section perpendicular to the axis of the leg shaft. The convex curve in the cross-section of the outer surface of the leg shaft moves away from the cylindrical inner surface of the inner ring as it moves from the torque transmission end toward both sides in the coupling axis direction, In a tripod-type constant velocity universal joint, the radius of curvature (r) at both ends in the torque transmission direction of the convex curve in the longitudinal section of the outer surface of the leg shaft is greater than the radius of curvature (R) at both ends in the torque transmission direction of the convex curve in the cross section of the outer surface of the leg shaft, A tripod-type constant velocity universal joint characterized in that a crowning portion is provided at the end of at least one of the contact surfaces of the outer circumferential surface of the roller and the roller guide surface, which can come into contact with each other when a torque load is applied, in the direction of the leg axis axis.

2. The roller guide surface is made flat, The tripod-type constant velocity universal joint according to claim 1, wherein the crowning portion is provided on the contact surface of the outer circumferential surface of the roller.

3. The tripod-type constant velocity universal joint according to claim 2, wherein the contact surface of the outer circumferential surface of the roller has a cylindrical surface formed in the central part in the direction of the leg axis and crowning portions connected to both sides of the cylindrical surface in the direction of the leg axis.

4. A tripod-type constant velocity universal joint according to claim 3, wherein L1a / L1 ≥ 1 / 3 is satisfied when L1 is the width of the contact surface on the outer circumference of the roller in the direction of the leg axis and L1a is the width of the cylindrical surface in the direction of the leg axis.

5. The tripod-type constant velocity universal joint according to claim 2, wherein the maximum drop amount of the crowning portion formed on the contact surface of the outer circumferential surface of the roller is 30 μm or more.

6. The outer surface of the roller is made cylindrical, The tripod-type constant velocity universal joint according to claim 1, wherein the crowning portion is provided on the contact surface of the roller guide surface.

7. The tripod-type constant velocity universal joint according to claim 6, wherein the contact surface of the roller guide surface has a flat surface formed in the central part in the direction of the leg axis and crowning portions connected to both sides of the flat surface in the direction of the leg axis.

8. A tripod-type constant velocity universal joint according to claim 7, where L2 is the width of the contact surface of the roller guide surface in the direction of the leg axis, and L2a is the width of the flat surface in the direction of the leg axis, and L2a / L2 ≥ 1 / 3.

9. The tripod-type constant velocity universal joint according to claim 6, wherein the maximum drop amount of the crowning portion formed on the contact surface of the roller guide surface is 30 μm or more.

Images