Tripod-type constant velocity universal joint

Abstract

To realize a tripod-type constant velocity universal joint having excellent NVH characteristics.SOLUTION: A pair of guide surfaces 7 are provided on both sides in a width direction of a roller guide surface 16. The guide surfaces 7 are formed as tapered surfaces inclined with respect to a transverse cross section orthogonal to an axial line of a leg shaft 32, and a guided surface 17 of an outer ring 11 guided by the guide surfaces 7 is formed as a convex arc surface capable of point contact with the guide surfaces 7. An inner ring 12 has a cylindrical surface-shaped inner circumferential surface 18, and an outer circumferential surface of the leg shaft 32 has, in each of a longitudinal cross section and a transverse cross section, a convex curve bulged to both sides in a torque transmission direction X. The convex curve in the transverse cross section of the outer circumferential surface of the leg shaft 32 is arranged to separate from the inner circumferential surface 18 of the inner ring 12 toward both sides in a joint axial direction as a distance from an end portion in the torque transmission direction X increases. Of the convex curve in the longitudinal cross section of the outer circumferential surface of the leg shaft 32, a curvature radius r at both ends in the torque transmission direction X is made larger than a curvature radius at both ends in the torque transmission direction X of the convex curve in the transverse cross section of the outer circumferential surface of the leg shaft 32.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] A constant velocity universal joint connects two shafts, a driving side and a driven side, and has a structure that allows torque to be transmitted at a constant velocity regardless of the operating angle of these two shafts (even if there is a relative angular displacement), and is broadly divided into a fixed type that allows only relative angular displacement of the two shafts, and a sliding type that allows relative angular displacement and axial displacement of the two shafts. For example, in a drive shaft used to transmit power output from a driving source such as an engine or motor mounted on the chassis of an automobile to the driving wheels, a sliding type constant velocity universal joint is provided on the inboard side (driving source side) and a fixed type constant velocity universal joint is provided on the outboard side (driving wheel side).

[0003] A known sliding-type constant velocity universal joint is a tripod-type constant velocity universal joint, which is available in single-roller and double-roller types. The single-roller type has rollers as rolling elements inserted into track grooves of an outer joint member, which are rotatably attached to the trunnions of the tripod members via a plurality of needle rollers. As shown in Figures 8 and 9, the double-roller type has rollers (also referred to as "outer rings") 111 disposed in track grooves 105 of an outer joint member 102, and inner rings 112 fitted onto trunnions 132 of a tripod member 103 to rotatably support the rollers 111 (see, for example, Patent Documents 1 and 2 listed below).

[0004] In a double-roller tripod constant velocity universal joint, the cross section of the trunnion 132 (a cross section perpendicular to the axis of the trunnion) is formed into an ellipse as shown in Fig. 10, and the inner circumferential surface of the inner ring 112 is formed into a convex arc cross section as shown in Fig. 8. This makes it possible to oscillate the rollers 111 relative to the trunnion 132 as shown in Fig. 11, which has the advantage of reducing induced thrust (axial force induced by friction between parts inside the joint) and thrust resistance compared to a single-roller type. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-320563 [Patent Document 2] Patent No. 2957121 Summary of the Invention [Problem to be solved by the invention]

[0006] In the above-described tripod-type constant velocity universal joint, as shown in Fig. 9, outer peripheral surfaces 115 of rollers 111 are formed as convex curved surfaces having arc-shaped generatrix lines, and roller guideways 106 that come into contact with outer peripheral surfaces 115 of rollers 111 are formed as concave cross-sectional shapes (Gothic arch shapes) that follow the shape of roller outer peripheral surfaces 115, and these are in angular contact. Due to this structure, when the constant velocity universal joint rotates with an operating angle, a phenomenon occurs in which roller units 104 including rollers 111 and inner ring 112 tilt in the direction of arrow B in a cross section perpendicular to the joint axial direction (transverse cross section of the joint) as shown in Fig. 12 (hereinafter referred to as "left-right tilt"), and a phenomenon in which roller units 104 tilt in the direction of arrow C in a cross section parallel to the joint axial direction (longitudinal cross section of the joint) as shown in Fig. 13 (hereinafter referred to as "front-rear tilt") occurs.

[0007] When the roller unit 104 tilts left and right or front and rear, the rolling and sliding resistance at the contact points between the rollers 111 and the roller guideways 106 and the rotational resistance of the roller unit 104 relative to the trunnion 32 increase. Furthermore, the needle rollers 117 in the roller unit 104 are unable to roll in the axial direction of the outer joint member 102 relative to the roller guideways 106, increasing sliding resistance. If these factors become significant, the induced thrust and sliding resistance increase, which can cause problems such as a deterioration in the NVH characteristics of the joint.

[0008] Furthermore, in the above-described tripod-type constant velocity universal joint, the trunnion 132 has an elliptical cross section and the inner peripheral surface of the inner ring 112 has a convex arc cross section, so that the inner ring 112 and the trunnion 132 make approximately point contact, suppressing the friction moment that acts to tilt the roller unit 104 as the trunnion 132 moves. Furthermore, even when the joint has an operating angle, the trunnion 132 comes into contact with the center of the inner ring 112 in the width direction (the axial direction of the trunnion 132), so the structure is able to suppress left and right tilt. However, when the joint has a large operating angle, the elliptical cross section of the trunnion 132 generates a force that causes the roller unit 104 to tilt forward and backward (see Figure 13). Furthermore, since the contact area between the trunnion 132 and the inner ring 112 is small, the surface pressure on the contact surface between the two increases under high torque loads due to extremely harsh vehicle usage conditions, which may have a negative impact on the durability of the trunnion 132.

[0009] In contrast to this, in the tripod type constant velocity universal joint described in the above Patent Document 2, as shown in Figures 14 and 15, the outer peripheral surface of the trunnion 226 of the tripod member 230 is spherical, and this spherical outer peripheral surface is fitted with the cylindrical inner peripheral surface of the holder 234. In addition, the outer peripheral surface of the roller 222 is cylindrical, and the roller guide surface 224 that comes into contact with this cylindrical outer peripheral surface is flat.

[0010] In a tripod type constant velocity universal joint employing such a configuration, the inclination of the rollers is restricted by the following action. The first function is that the end surface 236 on the joint outer diameter side of the holder 234 abuts against the flat portion 220 of the track groove, thereby restricting the inclination of the roller 222. The roller 22 slides along the roller guide surface 224 in the axial direction of the leg shaft 226 (direction E in FIG. 13), thereby restricting the inclination of the roller 222. The third function is to restrict the inclination of the roller 222 by the roller 222 rolling while contacting the bulge 228 formed at the end of the roller guide surface 224 on the inner diameter side of the joint.

[0011] In the tripod-type constant velocity universal joint of Patent Document 2, the inner peripheral surface of the holder 234 is cylindrical and the outer peripheral surface of the trunnion 226 is spherical. Therefore, when a torque load is applied, a contact portion P' (the scattered dotted area in FIG. 15 ) between the inner peripheral surface of the holder 234 and the outer peripheral surface of the trunnion 226 assumes an elongated elliptical shape that is long in the circumferential direction of the trunnion 226. Therefore, when the joint forms an operating angle, a friction moment that acts to tilt the roller 222 in accordance with the movement of the trunnion 226 is likely to be generated at the contact portion P'. Therefore, even if the joint has a structure that exhibits the first to third effects described above, the roller 222 is likely to tilt forward and backward, and the sliding resistance generated by contact between the roller 222 and the track groove flat portion 220 and the bulge portion 228 increases.

[0012] Therefore, the present invention aims to reduce the contact resistance between parts and improve NVH characteristics by suppressing or preventing tilting of the roller unit while maintaining durability by suppressing the contact surface pressure between the trunnion and inner ring in a double roller type tripod constant velocity universal joint. [Means for solving the problem]

[0013] The present invention, which has been devised to achieve the above object, a tripod-type constant velocity universal joint comprising: an outer joint member having three track grooves formed on its inner circumferential surface extending in the joint axial direction, each track groove being provided with a pair of roller guide surfaces opposing each other in the joint circumferential direction; a tripod member arranged on the inner periphery of the outer joint member and having three trunnions protruding in the joint radial direction toward the track grooves; and three roller units individually accommodated in each track groove, each roller unit having a roller arranged on the outer periphery of the trunnion and an inner ring arranged between the roller and the trunnion, and supported rotatably and swingably by the corresponding trunnion, The roller has a cylindrical outer circumferential surface, A pair of roller guide surfaces of each track groove are formed into flat surfaces parallel to each other, A pair of guide surfaces is provided on both sides of the roller guide surface in the width direction, The inner ring has a cylindrical inner peripheral surface, The outer peripheral surface of the trunnion has a convex curve that bulges out on both sides in the torque transmission direction in a longitudinal section including the trunnion axis and a transverse section perpendicular to the trunnion axis, The convex curve in the cross section of the outer circumferential surface of the trunnion deviates from the cylindrical inner circumferential surface of the inner ring as it goes from the torque transmission end to both sides in the joint axial direction, The radius of curvature (r) of the convex curve in the longitudinal cross section of the outer circumferential surface of the trunnion is greater than the radius of curvature (R) of the convex curve in the transverse cross section of the outer circumferential surface of the trunnion at both ends in the torque transmission direction, The present invention is characterized in that either the guide surface or the guided surface of the roller guided by this guide surface is formed as a tapered surface inclined with respect to a cross section perpendicular to the axis of the leg shaft, and the other is formed as a convex arc surface that can make point contact with the tapered surface.

[0014] In the tripod-type constant velocity universal joint according to the present invention, as described above, the rollers have cylindrical outer peripheral surfaces, and a pair of roller guideways that guide the outer peripheral surfaces of the rollers are formed as flat surfaces. In this case, when a torque load is applied, the roller guideway and the outer peripheral surface of the roller press against each other via a linear contact portion, thereby suppressing left and right tilt of the roller (see FIG. 12). In addition, a pair of guide surfaces that can abut against the roller from both axial sides of the roller are provided on both widthwise sides of the roller guideway, thereby enhancing the effect of suppressing left and right tilt of the roller.

[0015] Either the guide surface or the guided surface of the roller guided by the guide surface can be formed as a tapered surface inclined with respect to a cross section perpendicular to the trunnion axis. In this case, assuming that the guide surface is formed as the tapered surface, it is preferable to form the guided surface of the roller guided by the guide surface as a surface that can make surface contact with the guide surface (a surface parallel to the guide surface) in order to reliably prevent the roller from tilting left or right. However, due to dimensional variations that inevitably occur during manufacturing, it is difficult to achieve surface contact between the opposing guide surface and the guided surface. In particular, in a tripod-type constant velocity universal joint, three track grooves (and rollers) are provided at intervals around the joint. However, it is difficult to standardize the surface contact pattern between the opposing guide surface and the guided surface at all contact points. This results in differences in sliding resistance at each contact point. If this difference in sliding resistance (variation in sliding resistance) becomes large, there is a concern that the operability of the joint and, ultimately, the NVH characteristics will deteriorate.

[0016] Therefore, in the present invention, the other of the guide surface and the guided surface is formed as a convex arc surface that can make point contact with the one of the guide surface and the guided surface formed on the tapered surface. In this case, even if the inclination angle of the tapered surface or the curvature of the convex arc (surface) varies slightly due to dimensional variations that inevitably occur during manufacturing, the one (tapered surface) and the other (convex arc surface) can make point contact, so the contact state between the two surfaces does not change significantly. Therefore, it is possible to avoid a situation where the sliding resistance generated at the contact portion between the tapered surface and the corresponding convex arc surface differs significantly between multiple contact portions. This can improve the NVH characteristics of the joint.

[0017] In addition, in the present invention, the inner ring has a cylindrical inner peripheral surface, and the outer peripheral surface of the trunnion has a convex curve that bulges toward the inner peripheral surface of the inner ring in both longitudinal and transverse cross sections. The convex curve in the transverse cross section of the outer peripheral surface of the trunnion is shaped to move away from the cylindrical inner peripheral surface of the inner ring as it moves from the torque transmission end to both sides in the joint axial direction. This shortens the circumferential length of the trunnion at the contact point between the outer peripheral surface of the trunnion and the inner peripheral surface of the inner ring in the transverse cross section (i.e., the major axis of the osculating ellipse), thereby reducing the force (moment) tending to tilt the roller. However, in this case, the contact area between the trunnion and the inner ring is reduced, raising concerns about increased surface pressure at these contact points. Therefore, in the present invention, as described above, the radius of curvature (r) of the convex curve in the longitudinal cross section of the outer peripheral surface of the trunnion is made larger than the radius of curvature (R) of the convex curve in the transverse cross section of the outer peripheral surface of the trunnion. This increases the length in the axial direction of the trunnion of the contact area between the outer circumferential surface of the trunnion and the inner circumferential surface of the inner ring (i.e., the minor axis of the contact ellipse), thereby suppressing an increase in surface pressure at these contact areas.

[0018] It is preferable that the radius of curvature (r) of the convex curve in the longitudinal cross section of the outer peripheral surface of the trunnion at both ends in the torque transmission direction is greater than half the maximum dimension of the trunnion in the torque transmission direction, and that the radius of curvature (R) of the convex curve in the transverse cross section of the outer peripheral surface of the trunnion at both ends in the torque transmission direction is smaller than half (=A / 2) of the maximum dimension of the trunnion in the torque transmission direction.

[0019] It is preferable that the outer peripheral surface of the trunnion and the cylindrical inner peripheral surface of the inner ring are in contact with each other in the torque transmission direction, and that a gap is formed between them in the joint axial direction.

[0020] In a tripod-type constant velocity universal joint having the above configuration, when torque is applied, the roller is pressed against one of the roller guideways of each track groove. At this time, a gap is formed between the roller and the other of the roller guideways of each track groove. In the present invention, the flat roller guideway faces the cylindrical outer peripheral surface of the roller, and guide surfaces are provided on both sides of the roller guideway in the width direction. Therefore, if the roller tilts slightly, the outer peripheral surface of the roller or a portion adjacent to the outer peripheral surface may come into contact with the roller guideway or guide surface on the non-torque-loading side, potentially increasing contact resistance. Therefore, in the tripod-type constant velocity universal joint according to the present invention, when torque is applied, the roller contacts the roller guideway on one side of each track groove (the torque-loading side) and does not contact the roller guideway on the other side of each track groove (the non-torque-loading side) and the guide surfaces on both sides of the roller guideway in the width direction. This configuration can be achieved, for example, by setting the initial gap between the roller and the roller guideway (the difference between the distance between the pair of roller guideways and the outer diameter of the roller) to an appropriate value.

[0021] In the tripod-type constant velocity universal joint according to the present invention, rolling elements can be provided between the rollers and the inner ring. These rolling elements can be, for example, a plurality of needle rollers arranged in a full complement state between the rollers and the inner ring. [Effects of the Invention]

[0022] As described above, according to the present invention, it is possible to realize a double-roller type tripod constant velocity universal joint with excellent NVH characteristics, in which the contact resistance between parts is reduced by suppressing the occurrence of left and right tilt of the rollers, while maintaining durability by suppressing the contact surface pressure between the trunnion and inner ring. [Brief explanation of the drawings]

[0023] [Figure 1]1 is a cross-sectional view (longitudinal cross-sectional view) of a tripod constant velocity universal joint according to an embodiment of the present invention, taken in the joint axial direction in a state where the operating angle is 0°. [Figure 2] FIG. 2 is a cross-sectional view taken along line KK in FIG. [Figure 3] 2, and FIG. 2(b) is an enlarged view of part M in FIG. 2(a). [Figure 4] FIG. 1 is an enlarged view of part M when a torque load is applied. [Figure 5] FIG. 2 is a cross-sectional view taken along line LL in FIG. [Figure 6] FIG. 2 is an enlarged view of the tripod member of FIG. 1. [Figure 7] 2 is a diagram showing a state in which the tripod constant velocity universal joint of FIG. 1 has an operating angle. [Figure 8] FIG. 1 is a longitudinal cross-sectional view of a conventional tripod-type universal joint at an operating angle of 0°. [Figure 9] FIG. 9 is a cross-sectional view taken along line KK in FIG. 8. [Figure 10] FIG. 9 is a cross-sectional view taken along line LL in FIG. 8. [Figure 11] 9 is a diagram showing a state in which the tripod constant velocity universal joint of FIG. 8 has an operating angle. [Figure 12] 9 is a cross-sectional view (horizontal cross-sectional view) of the tripod constant velocity universal joint of FIG. 8 in a direction perpendicular to the joint axial direction, showing a state in which a roller unit is tilted left and right. [Figure 13] 9 is a cross-sectional view of the tripod constant velocity universal joint of FIG. 8 in the joint axial direction, showing a state in which a roller unit is tilted forward and backward. FIG. [Figure 14] FIG. 10 is a cross-sectional view of another conventional tripod type constant velocity universal joint in a direction perpendicular to the joint axial direction. [Figure 15] 15 is a cross-sectional view of a tripod member constituting the tripod type constant velocity universal joint of FIG. 14 in the joint axial direction. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0025] The tripod constant velocity universal joint 1 (specifically, a double-roller tripod constant velocity universal joint) according to the embodiment of the present invention shown in FIGS. 1 to 5 is a type of sliding constant velocity universal joint that allows angular and axial displacement of two axes, a drive side and a driven side, and is connected to a fixed constant velocity universal joint via a shaft 8 (see the dashed line in FIG. 1) to form a drive shaft. The drive shaft is mounted, for example, on an automobile and transmits rotational torque output from a drive source, such as an engine or electric motor, mounted on the chassis to the drive wheels. In this drive shaft, the tripod constant velocity universal joint 1 is located on the drive source side (inboard side), and the fixed constant velocity universal joint is located on the drive wheel side (outboard side). The left side of FIG. 1 is the drive wheel side, and the right side of FIG. 1 is the drive source side.

[0026] 1 and 2, a tripod-type constant velocity universal joint 1 (hereinafter also simply referred to as "constant velocity universal joint 1") includes an outer joint member 2, a tripod member 3 as an inner joint member, and a roller unit 4 as a torque transmission member. In the following description, the axial direction of the constant velocity universal joint 1 in a state where the operating angle is 0° shown in FIG. 1 is referred to as the "joint axial direction," and the circumferential direction and radial direction centered on the axis at this time are referred to as the "joint circumferential direction" and the "joint radial direction," respectively.

[0027] As shown in Fig. 1, the outer joint member 2 has a cylindrical cup portion with a bottom that is open at one end in the joint axial direction and closed at the other end, and on the inner peripheral surface of the cup portion, three linear track grooves 5 extending in the joint axial direction are formed at equal intervals in the joint circumferential direction, as shown in Fig. 2. Each track groove 5 is formed with a pair of roller guide surfaces 6 that are arranged opposite each other in the joint circumferential direction and extend in the joint axial direction. A tripod member 3 and a roller unit 4 are housed inside the outer joint member 2 (cup portion).

[0028] The tripod member 3 integrally comprises a body portion (trunnion body portion) 31 having a central hole 30, and three trunnion journals 32 protruding radially outward from positions equally dividing the outer circumferential surface of the body portion 31 into three equal parts in the joint circumferential direction. A female spline is formed in the central hole 30 of the body portion 31, and a male spline formed on the shaft 8 is fitted into this female spline, thereby connecting the tripod member 3 and the shaft 8 so that torque can be transmitted. In addition, although not shown in the figure, a retaining ring is attached to the outer circumferential surface of the shaft, and by engaging this retaining ring with the tripod member 3 in the direction in which the shaft 8 is pulled out, the shaft 8 is prevented from coming off the tripod member 3.

[0029] The roller units 4 are provided on the outer periphery of each trunnion 32 and are housed in the track grooves 5 of the corresponding outer joint member 2. The roller unit 4 includes an outer ring 11 as a "roller" having an annular shape centered on the axis of the trunnion 32, an annular inner ring 12 disposed on the inner periphery of the outer ring 11 and fitted onto the trunnion 32, and rolling elements interposed between the outer ring 11 and the inner ring 12. In this embodiment, a large number of full-complement needle rollers 13 without a cage are used as the rolling elements. The needle rollers 13 are disposed so as to roll freely between the cylindrical inner peripheral surface of the outer ring 11 as the outer raceway surface and the cylindrical outer peripheral surface of the inner ring 12 as the inner raceway surface. The roller unit 4, consisting of the outer ring 11, inner ring 12, and the large number of needle rollers 13, is configured to not disassemble naturally by a pair of snap rings 14 disposed on both radial sides of the needle rollers 13 in the joint.

[0030] The shapes of the roller guideway 6 and the outer peripheral surface 15 of the outer ring 11, which are one of the characteristic features of the present invention, will be described in detail below with reference to Figures 3(a) and 3(b) and 5. In Figures 3 and 4, the joint axial direction is shown as the Z direction, the axial direction of the trunnion 32 is shown as the Y direction, and the torque transmission direction perpendicular to both the joint axial direction Z and the trunnion axial direction Y is shown as the X direction.

[0031] A pair of roller guideways 6 constituting each track groove 5 provided in the outer joint member 2 are flat surfaces parallel to each other. A pair of guide surfaces 7 is provided on both sides of each roller guideway 6 in the width direction (Y direction). The pair of guide surfaces 7 are tapered surfaces inclined with respect to a cross section perpendicular to the axis Y of the trunnion 32, and are formed as tapered surfaces in which the distance from each other gradually increases as one approaches the axis Y of the trunnion 32.

[0032] The outer peripheral surface 15 of the outer ring 11 is a cylindrical surface centered on the axis of the leg shaft 32. End faces 16 of the outer ring 11 on both sides in the axial direction thereof are flat surfaces perpendicular to the axis thereof [see FIG. 3(a)]. The outer peripheral surface 15 and both end faces 16 of the outer ring 11 are continuous via guided surfaces 17 that are guided by the guide surfaces 7 of the outer joint member 2, and the guided surfaces 17 are formed as convex arc surfaces that can make point contact with the guide surfaces 7, specifically, as convex arc surfaces of a single arc that bulge toward the guide surface 7.

[0033] 3(a) and 3(b), when no torque is input to the outer joint member 2 and the tripod member 3, the roller guideway 6 and the outer peripheral surface 15 of the outer ring 11 are parallel to each other, and the distance W between the pair of roller guideways 6 is slightly larger than the diameter of the outer peripheral surface 15 of the outer ring 11. As a result, a small gap in the X direction is formed between the roller guideway 6 and the outer peripheral surface 15 of the outer ring 11 (the gap is not shown). Furthermore, the distance in the Y direction between the pair of guide surfaces 7 provided on both sides of the roller guideway 6 in the width direction is slightly larger than the distance in the Y direction between the pair of guided surfaces 17 provided on both sides of the outer peripheral surface 15 of the outer ring 11 in the width direction. As a result, a small gap in the Y direction is formed between the guide surface 7 and the guided surfaces 17.

[0034] When torque is input to the outer joint member 2 in the direction of arrow T shown in FIG. 3(a), the outer peripheral surface 15 of the outer ring 11 is pressed against the roller guideway 6 on the left side in the figure. In this embodiment, as described above, the roller guideway 6 is a flat surface and the outer peripheral surface 15 of the outer ring 11 is a cylindrical surface, so they press against each other via a linear contact portion. As a result, the orientation of the outer ring 11 is corrected so that the outer peripheral surface 15 of the outer ring 11 is parallel to the roller guideway 6 in the cross section shown in FIG. 3(a), thereby suppressing left-right tilt of the outer ring 11 (see FIG. 12). Furthermore, as shown in FIG. 4, with the input of the torque, the convex arc-shaped guided surface 17 of the outer ring 11 that faces the tapered guide surface 7 on the left side in FIG. 3(a) comes into contact (contact at point N). This enhances the effect of suppressing forward-backward tilt of the outer ring 11.

[0035] In addition, when the guide surface 7 provided on the outer joint member 2 is formed as a tapered surface, it is preferable to form the guided surface 17 of the outer ring 11, which is guided by the guide surface 7, as a surface parallel to the guide surface 7 and capable of line contact with the guide surface 7 in order to reliably prevent the outer ring 11 from tilting forward or backward. However, due to dimensional variations that inevitably occur during manufacturing, it is difficult to achieve line contact between the opposing guide surface 7 and the guided surface 17. In particular, in the tripod-type constant velocity universal joint 1, three track grooves 5 (and roller units 4 including the outer ring 11) are provided at intervals around the joint. However, it is impossible to uniformly form line contact between the opposing guide surfaces 7 and the guided surfaces 17 at all contact points. Therefore, differences in sliding resistance occur at each contact point. If this difference in sliding resistance (variation in sliding resistance) becomes large, there is a concern that the operability of the joint and, ultimately, the NVH characteristics will deteriorate.

[0036] Therefore, in this embodiment, as described above, the guided surface 17 guided by the guide surface 7 is formed as a convex arc surface that can come into point contact with the guide surface 7 that is formed as a tapered surface. In this case, even if the inclination angle of the guide surface 7 that is a tapered surface or the curvature of the guided surface 17 that is a convex arc surface varies slightly due to dimensional variations that inevitably occur during manufacturing, the guide surface 7 and the guided surface 17 can come into point contact, so the contact state between both surfaces 7, 17 does not change significantly. Therefore, it is possible to avoid a situation where the sliding resistance generated at the contact points (point contact points) between the opposing tapered surface 7 and the guided surface 17 varies greatly between multiple contact points. This makes it possible to improve the NVH characteristics of the constant velocity universal joint 1.

[0037] Next, the shapes of the inner peripheral surface 18 of the inner ring 12 and the outer peripheral surface 33 of the trunnion 32, which are other characteristic features of the present invention, will be described in detail with reference to FIG. 3(a) and FIG.

[0038] The inner peripheral surface 18 of the inner ring 12 is formed into a cylindrical surface parallel to the axial direction Y of the trunnion 32 , and this cylindrical inner peripheral surface 18 is fitted onto the outer peripheral surface 33 of the trunnion 32 .

[0039] As shown in Figure 3(a), when the trunnion 32 is viewed from the joint axial direction (when viewed in a longitudinal cross section including its own axis), the outer peripheral surface 33 of the trunnion 32 has a convex curve that bulges out on both sides in the torque transmission direction X. In the illustrated example, the convex curve is formed by an arc 33a with a curvature radius r. As a result, the apex (X-direction end) of the arc 33a of the outer peripheral surface 33 of the trunnion 32 comes into contact (point contact) with the cylindrical inner circumferential circle 18 of the inner ring 12, and the gap between the outer peripheral surface 33 of the trunnion 32 and the inner circumferential surface 18 of the inner ring 12 gradually increases from the apex of the arc 33a toward both sides in the Y direction.

[0040] In a cross section perpendicular to the axis of the trunnion 32 shown in FIG. 5, the outer circumferential surface of the trunnion 32 has a convex curve that bulges out on both sides in the torque transmission direction X. In the illustrated example, this convex curve is formed by an arc 33b with a curvature radius R. When the maximum dimension of the trunnion 32 in the torque transmission direction X is A, the curvature radius R of the arc 33b is smaller than half A / 2 (≈the radius of the inner circumferential surface 18 of the inner ring 12). Therefore, the arc 33b on the outer circumferential surface of the trunnion 32 contacts the cylindrical inner circumferential surface 18 of the inner ring 12 at its apex (end in the X direction) and moves away from the inner circumferential surface 18 of the inner ring 12 as it moves from the apex to both sides in the Z direction. As a result, the outer circumferential surface 33 of the trunnion 32 and the inner circumferential surface 18 of the inner ring 12 contact each other 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 a region including both ends in the Z direction of the outer circumferential surface 33 of the trunnion 32. This increases the gap G in the Z direction between the flat surface 33c of the outer circumferential surface 33 of the trunnion 32 and the inner circumferential surface 18 of the inner ring 12.

[0041] As a result, the outer peripheral surface 33 of the trunnion 32 has an aspherical shape in which the curvature radius r of the convex curve (arc 33a) in the vertical cross section is different from the curvature radius R of the convex curve (arc 33b) in the horizontal cross section.

[0042] The inner peripheral surface 18 of the inner ring 12 is cylindrical, and the longitudinal and transverse cross sections of the outer peripheral surface of the trunnion 32 have convex curves, which enables the inner ring 12 to oscillate relative to the trunnion 32. The roller unit 4 is an assembly in which the inner ring 12 and the outer ring 11 are rotatable relative to each other via a large number of needle rollers 13, so the outer ring 11 can oscillate integrally with the inner ring 12 relative to the trunnion 32. In other words, the axes of the outer ring 11 and inner ring 12 can tilt relative to the axis of the trunnion 32 within a plane including the axis of the trunnion 32.

[0043] As shown in Figure 7, when the tripod type constant velocity universal joint 1 rotates through an operating angle, the axis of the tripod member 3 is inclined relative to the axis of the outer joint member 2, but because the roller unit 4 is swingable, it is possible to prevent the outer ring 11 and the roller guideway 6 from intersecting at an angle. As a result, the outer ring 11 rolls horizontally relative to the roller guideway 6, which makes it possible to reduce induced thrust and sliding resistance and achieve low vibration of the constant velocity universal joint 1.

[0044] When torque is applied to the tripod member 30, the outer peripheral surface 33 of the trunnion 32 is pressed against the inner peripheral surface 18 of the inner ring 12, forming a contact portion P as shown in Fig. 6. In this embodiment, as described above, the radius of curvature R (see Fig. 5) of the arc 33b in the cross section of the outer peripheral surface 33 of the trunnion 32 is smaller than half (= A / 2) of the maximum dimension A of the trunnion 32 in the torque transmission direction X. Therefore, the length in the Z direction of the contact portion P (the major axis a of the contact ellipse) can be made shorter than when these dimensions are equal. This reduces the force (moment) that tends to tilt the roller unit 4 including the inner ring 12 with respect to the joint axis.

[0045] As described above, when the major axis a of the contact portion P is shortened, the area of ​​the contact portion P is reduced, which raises concerns about an increase in surface pressure at the contact portion P. In this embodiment, the radius of curvature r [see FIG. 3(a)] of the arc 33a in the vertical cross section of the outer circumferential surface 33 of the trunnion 32 is larger than the radius of curvature R (see FIG. 5) of the arc 33b in the horizontal cross section of the outer circumferential surface 33 of the trunnion 32, and is also larger than half the maximum dimension A of the trunnion 32 in the torque transmission direction X. As a result, the length in the Y direction of the contact portion P between the outer circumferential surface 33 of the trunnion 32 and the inner circumferential surface 18 of the inner ring 12 shown in FIG. 6 (i.e., the minor axis b of the contact ellipse) is longer, which makes it possible to suppress an increase in surface pressure.

[0046] As described above, by adjusting the radius of curvature R of the arc 33b in the cross section of the outer peripheral surface 33 of the trunnion 32 and the radius of curvature r of the arc 33a in the vertical section of the outer peripheral surface 33 of the trunnion 32, it is possible to adjust the ratio of the major axis a to the minor axis b of the contact portion P between the outer peripheral surface 33 of the trunnion 32 and the inner peripheral surface 18 of the inner ring 12. In other words, the radii of curvature r and R are set so that the surface pressure of the contact portion P between the inner ring 12 and the trunnion 32 is kept within an allowable range to ensure durability, while the tilt of the outer ring 11 is kept within an allowable range to sufficiently reduce induced thrust and sliding resistance. For example, the radii of curvature r and R are set so that the ratio of the major axis a to the minor axis b of the contact portion P (= a / b) is within a range of 2 to 10, preferably within a range of 3 to 6.

[0047] Although the tripod type constant velocity universal joint 1 according to one embodiment of the present invention has been described above, the present invention is not limited to this. Other embodiments of the present invention will be described below, but redundant description of configurations that are substantially the same as those of the above embodiment will be omitted.

[0048] In the above embodiment, the guide surface 7 provided on the outer joint member 2 is formed as a tapered surface, and the guided surface 17 of the outer ring 11 (roller unit 4) guided by this guide surface 7 is formed as a convex arc surface that can come into point contact with the tapered guide surface 7, but conversely, the guided surface 17 of the outer ring 11 may be formed as a tapered surface, and the guide surface 7 of the outer joint member 2 may be formed as a convex arc surface that can come into point contact with the tapered guided surface 17. Even in this case, the same effect (effect of improving the NVH characteristics of the constant velocity universal joint 1) can be obtained.

[0049] In the above embodiment, the convex curves in the longitudinal and transverse cross sections of the outer circumferential surface of the trunnion 32 are both formed as arcs, but this is not limited thereto. For example, the convex curve in the longitudinal cross section of the outer circumferential surface of the trunnion 32 may be formed as a non-circular curve such as an ellipse. In this case, the radius of curvature of the convex curve (ellipse) in the longitudinal cross section of the outer circumferential surface of the trunnion 32 at least at both ends in the torque transmission direction (i.e., the contact portions with the inner ring 12) (because the convex curve is a non-circular arc, the radius of curvature of a pseudo-arc at both ends in the torque transmission direction; the same applies below) is set to be larger than the radius of curvature R of the arc 33b in the transverse cross section of the outer circumferential surface of the trunnion 32, and preferably larger than half (=A / 2) of the maximum dimension A of the trunnion 32 in the torque transmission direction X.

[0050] The convex curve in the cross section of the outer circumferential surface of the trunnion 32 may be a non-circular curve such as an ellipse. In this case, the radius of curvature of the convex curve (ellipse) in the cross section of the outer circumferential surface of the trunnion 32 at least at both ends in the torque transmission direction (contact portions with the inner ring 12) is set to be smaller than half the maximum dimension A of the trunnion 32 in the torque transmission direction X.

[0051] Furthermore, both the convex curves in the longitudinal and transverse cross sections of the outer circumferential surface of the trunnion 32 may be non-circular curves such as ellipses. In this case, the radius of curvature of the convex curve (ellipse) in the longitudinal cross section of the outer circumferential surface of the trunnion 32 at least at both ends in the torque transmission direction (contact portions with the inner ring 12) is set to be larger than the radius of curvature of the convex curve (ellipse) in the transverse cross section of the outer circumferential surface of the trunnion 32 at least at both ends in the torque transmission direction (contact portions with the inner ring 12). Preferably, the radius of curvature of the convex curve (ellipse) in the longitudinal cross section of the outer circumferential surface of the trunnion 32 at least at both ends in the torque transmission direction is set to be larger than half the maximum dimension A of the trunnion 32 in the torque transmission direction X, and the radius of curvature of the convex curve (ellipse) in the transverse cross section of the outer circumferential surface of the trunnion 32 at least at both ends in the torque transmission direction is set to be smaller than half the maximum dimension A of the trunnion 32 in the torque transmission direction X.

[0052] In the above embodiment, as shown in FIG. 4, flat surfaces 33c are provided on both ends of the leg axle 32 in the joint axis direction. However, even if these flat surfaces 33c are not provided, the flat surfaces 33c can be omitted if a gap sufficient to allow the roller unit 4 to swing relative to the leg axle 32 is formed between the leg axle 32 and the inner ring 12 in the joint axis direction.

[0053] Furthermore, the tripod type constant velocity universal joint 1 of the present embodiment described above can be used not only in drive shafts for automobiles, but also in power transmission paths of automobiles, industrial machines, and the like. [Explanation of symbols]

[0054] 1 Tripod-type constant velocity universal joint 2 Outer joint member 3 Tripod member 4 Roller unit 5 Track groove 6 Roller guideway 7 Guide surface 11 Outer Ring (Roller) 12 Inner Ring 13 Rolling elements 17 Guided surface 32 Leg axis X Torque transmission direction Y leg axis direction Z Joint axial direction

Claims

1. a tripod-type constant velocity universal joint comprising: an outer joint member having three track grooves formed on an inner peripheral surface thereof, the track grooves extending in a joint axial direction, and a pair of roller guide surfaces opposed in a joint circumferential direction, each track groove being provided with a pair of roller guide surfaces; a tripod member arranged on an inner peripheral surface of the outer joint member and having three trunnions protruding in a joint radial direction toward the track grooves; and three roller units individually accommodated in each track groove, each roller unit having a roller arranged on an outer periphery of the trunnion and an inner ring arranged between the roller and the trunnion, and supported rotatably and swingably by the corresponding trunnion, The roller has a cylindrical outer circumferential surface, The pair of roller guide surfaces of each track groove are formed into flat surfaces parallel to each other, A pair of guide surfaces is provided on both sides of the roller guide surface in the width direction, the inner ring has a cylindrical inner peripheral surface, the outer peripheral surface of the trunnion has a convex curve bulging out on both sides in the torque transmission direction in a longitudinal section including the axis of the trunnion and in a transverse section perpendicular to the axis of the trunnion, the convex curve of the outer peripheral surface of the trunnion in the cross section is spaced apart from the cylindrical inner peripheral surface of the inner ring as it goes from the torque transmission direction end to both sides in the joint axial direction, a curvature radius (r) of the convex curve of the outer peripheral surface of the trunnion in the longitudinal cross section at both ends in the torque transmission direction is larger than a curvature radius (R) of the convex curve of the outer peripheral surface of the trunnion in the transverse cross section at both ends in the torque transmission direction; A tripod-type constant velocity universal joint characterized in that either the guide surface or the guided surface of the roller guided by this guide surface is formed as a tapered surface inclined with respect to a cross section perpendicular to the axis of the trunnion, and the other is formed as a convex arc surface that can make point contact with the tapered surface.

2. the radius of curvature (r) of the convex curve of the outer peripheral surface of the trunnion at both ends in the torque transmission direction is greater than half (=A / 2) of the maximum dimension of the trunnion in the torque transmission direction; 2. The tripod-type constant velocity universal joint according to claim 1, wherein the radius of curvature (R) of the convex curve in the cross section of the outer peripheral surface of the trunnion at both ends in the torque transmission direction is smaller than half (= A / 2) of the maximum dimension of the trunnion in the torque transmission direction.

3. 3. A tripod-type constant velocity universal joint according to claim 1, wherein the outer peripheral surface of the trunnion and the cylindrical inner peripheral surface of the inner ring are in contact with each other in the torque transmission direction, and there is a gap between them in the joint axial direction.

4. 3. A tripod-type constant velocity universal joint according to claim 1 or 2, wherein, under torque load, the rollers come into contact with one roller guide surface of each track groove, but do not come into contact with the other roller guide surface of each track groove or the guide surfaces on both sides of the other roller guide surface in the width direction.

5. 3. A tripod-type constant velocity universal joint according to claim 1, further comprising rolling elements disposed between said rollers and said inner ring.

6. 6. A tripod-type constant velocity universal joint according to claim 5, wherein said rolling elements are a plurality of needle rollers arranged in a full complement state between said roller and said inner ring.

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