Tripod type constant velocity universal joint

Abstract

To improve durability and an NVH character by reducing contact face pressure between a leg shaft and an inner ring, and restraining inclination of a roller unit, in a tripod constant velocity universal joint of a double roller type.SOLUTION: An outer periphery 33 of a leg shaft 32 has convex curves swollen on both sides in a torque transmission direction on a vertical cross section and a horizontal cross section. A curvatures radius of the convex curve on the vertical cross section of the outer periphery of the leg shaft 32 is larger than a curvature radius R of a convex curve (arc 33b) on the horizontal cross section passing through a maximum diameter part of the outer periphery of the leg shaft 32. A set of clearance parts 33c are provided on both sides in a joint axial direction of the outer periphery 33 of the leg shaft 32. When a distance in the joint axial direction between the set of clearance parts 33 is designated as F, and a maximum value of the distance in the joint axial direction between two peaks of a contact ellipse formed between the outer periphery 33 of the leg shaft 32 and an inner periphery of an inner ring during torque transmission is designated as Lmax, Lmax<F is satisfied.SELECTED DRAWING: Figure 8

Description

[Technical Field]

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

[0002] In driveshafts used in automotive power transmission systems, a sliding-type constant velocity universal joint is often provided on the inboard side (the center side in the vehicle width direction) and a fixed-type constant velocity universal joint is provided on the outboard side (the outside side in the vehicle width direction).The sliding-type constant velocity universal joint here allows both angular displacement and relative axial movement between the two shafts, 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 constant velocity universal joint is known as a sliding type constant velocity universal joint. This tripod constant velocity universal joint is available in single roller and double roller types. A single roller type tripod constant velocity universal joint has rollers inserted into track grooves of an outer joint member rotatably attached to the trunnions of the tripod members via a plurality of needle rollers. A double roller type tripod constant velocity universal joint, as shown in FIGS. 13 and 14 , has rollers 111 disposed in track grooves 105 of an outer joint member 102, and an inner ring 112 fitted onto the trunnions 132 of a tripod member 103 to rotatably support the rollers 111 (see, for example, the following patent document).

[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 elliptical as shown in Fig. 15, and the inner circumferential surface of the inner ring 112 has a convex arc cross section as shown in Fig. 13. This allows the rollers 111 to oscillate relative to the trunnion 132 as shown in Fig. 16, which has the advantage of reducing induced thrust (axial force induced by friction between parts inside the joint) and sliding resistance compared to a single-roller type.

[0005] Another known example of a double-roller type tripod constant velocity universal joint is that described in Patent Document 2. In this tripod constant velocity universal joint, as shown in Figures 19 and 20, the outer peripheral surface of a trunnion 226 of a tripod member 230 is spherical, and the cylindrical inner peripheral surface of a holder 236 is fitted onto this spherical outer peripheral surface. Also, the roller guide surface 224 is a flat surface, and the outer peripheral surface of the roller 222 that slides against it is cylindrical.

[0006] In this tripod-type constant velocity universal joint, the inclination of the rollers is restricted by the following action. The first action 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. A second function of restricting the inclination of the roller 222 by the roller 222 sliding and displacing along the roller guide surface 224 in the axial direction of the trunnion 226 (direction E in FIG. 13). 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.

[0007] An improved version of the tripod type constant velocity universal joint described in Patent Document 2 is also known, as described in Patent Document 3. This tripod type constant velocity universal joint has a pair of flat portions 233 (portions shown by two-dot chain lines in Figure 20) on the outer circumferential surface of the trunnion 226, which are perpendicular to the joint axial direction, in order to reduce the size and weight of a tripod member 230 shown in Figures 19 and 20. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-320563 [Patent Document 2] Patent No. 2957121 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-127626 Summary of the Invention [Problem to be solved by the invention]

[0009] In the tripod type constant velocity universal joint described in Patent Document 1, as shown in Fig. 14, outer peripheral surfaces 115 of rollers 111 are convex curved surfaces having arc-shaped generatrix lines, and roller guideways 106 that come into contact with these have a cross-sectional concave shape (Gothic arch shape) that follows the shape of outer peripheral surfaces 115 of rollers 111, and these form angular contact. Therefore, due to the structure, when the constant velocity universal joint rotates with an operating angle, a phenomenon occurs in which roller unit 104 including rollers 111 and inner ring 112 tilts in the direction of arrow B in a cross section perpendicular to the joint axial direction as shown in Fig. 17 (hereinafter referred to as "lateral tilt"), and a phenomenon in which roller unit 104 tilts in the direction of arrow C in a cross section parallel to the joint axial direction as shown in Fig. 18 (hereinafter referred to as "front-rear tilt"). 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 relative to the roller guideways 106 in the axial direction of the outer joint member 102, increasing the sliding resistance. If these factors become significant, the induced thrust and sliding resistance increase, causing a problem of deterioration in the NVH (Noise, Vibration, Harshness) characteristics of the constant velocity universal joint.

[0010] 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. This results in a substantially point contact between the inner ring 112 and the trunnion 132, thereby suppressing the friction moment that acts to tilt the roller unit 104 as the trunnion 132 moves. Even when the joint has an operating angle, the trunnion 132 contacts the center of the inner ring 112 in the width direction (the axial direction of the trunnion 132), thereby suppressing left-right tilt. However, when the joint has a large angle, the elliptical cross section of the trunnion 132 generates a force that causes the roller unit 104 to tilt forward and backward (see FIG. 18 ). Furthermore, because the contact area between the trunnion 132 and the inner ring 112 is small, the surface pressure at their contact surfaces increases under high torque loads, such as those caused by extremely harsh vehicle operating conditions, raising concerns about the impact on the durability of the trunnion 132.

[0011] In the tripod-type constant velocity universal joints shown in Patent Documents 2 and 3, as shown in FIG. 19, 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, the contact portion P' (osculating ellipse: dotted area in FIG. 20) between the inner peripheral surface of the holder 234 and the trunnion 226 assumes the shape of an elongated ellipse that is long in the major axis direction. 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 provides the above-mentioned first to third effects, the roller 222 is likely to tilt forward and backward, and the sliding resistance generated by contact between the roller 222 and the bulge portion 228 or the track groove flat portion 220 increases.

[0012] In particular, as in Patent Document 3, when a set of flat portions 233 perpendicular to the joint axial direction is provided on the outer peripheral surface of the trunnion 226, the contact portion P' may have an elongated elliptical shape that is long in the major axis direction, and the contact portion P' becomes a non-elliptical shape in which both vertices of the ellipse are missing. This leads to an increase in contact surface pressure due to the generation of edge load, and the durability and NVH characteristics of the tripod constant velocity universal joint are reduced.

[0013] Therefore, an object of the present invention is to improve durability and NVH characteristics in a double-roller type tripod constant velocity joint by reducing the contact pressure between the leg shaft and the inner lining and suppressing the inclination of the roller unit.

Means for Solving the Problems

[0014] To solve the above problems, the present invention provides an outer joint member having three track grooves extending in the joint axis direction formed on its inner peripheral surface, and a pair of roller guide surfaces facing each other in the joint circumferential direction provided in each track groove, a tripod member disposed on the inner periphery of the outer joint member and having three leg shafts protruding in the joint radial direction toward the track grooves, rollers disposed on the outer periphery of the leg shafts, and an inner lining disposed between the rollers and the leg shafts. In a tripod constant velocity joint including three roller units that are supported on the leg shafts in a rotatable and swingable state and accommodated in the track grooves, the rollers have a cylindrical outer peripheral surface, the pair of roller guide surfaces of each track groove are flat surfaces parallel to each other, and a pair of guide surfaces capable of contacting the rollers from both sides in the axial direction are provided on both sides in the width direction of the roller guide surfaces. The inner lining has a cylindrical inner peripheral surface, and the outer peripheral surface of the leg shaft has a convex curve bulging on both sides in the torque transmission direction in a longitudinal section including the axis of the leg shaft and a cross section orthogonal to the axis of the leg shaft. The convex curve in the cross section of the outer peripheral surface of the leg shaft moves away from the cylindrical inner peripheral surface of the inner lining as it goes from the end in the torque transmission direction to both sides in the joint axis direction. Among the convex curves in the longitudinal section of the outer peripheral surface of the leg shaft, the radius of curvature (r) at both ends in the torque transmission direction is larger than the radius of curvature (R) at both ends in the torque transmission direction among the convex curves in the cross section passing through the maximum diameter portion of the outer peripheral surface of the leg shaft. A set of relief portions are provided on both sides in the joint axis direction of the outer peripheral surface of the leg shaft to form a clearance in the joint axis direction between the relief portions and the cylindrical inner peripheral surface of the inner lining. The distance in the joint axis direction between the set of relief portions is defined as F, and the maximum value of the distance in the joint axis direction between the two vertices of the contact ellipse formed between the outer peripheral surface of the leg shaft and the inner peripheral surface of the inner lining during torque transmission is defined as Lmax, and the feature is that Lmax < F.

[0015] In the present invention, as described above, the roller has a cylindrical outer peripheral surface, and the roller guide surface is a flat surface. In this case, when a torque load is applied, the flat roller guide surface and the cylindrical outer peripheral surface of the roller press against each other via a linear contact portion, so that the left and right inclination of the roller (see FIG. 17) can be suppressed. Further, by providing a pair of guide surfaces on both sides in the width direction of the roller guide surface that can abut against the roller from both sides in the axial direction thereof, the left and right inclination of the roller can be more reliably prevented.

[0016] Also, in the present invention, the inner lining has a cylindrical inner peripheral surface, and a convex curve that bulges toward the inner peripheral surface of the inner lining is provided on the outer peripheral surface of the leg shaft in the longitudinal section and the cross section. And, the convex curve in the cross section of the outer peripheral surface of the leg shaft has a shape that separates from the cylindrical inner peripheral surface of the inner lining as it goes from the end portion in the torque transmission direction toward both sides in the joint shaft direction. Thereby, since the length in the circumferential direction of the leg shaft (that is, the major axis of the contact ellipse) of the contact portion between the outer peripheral surface of the leg shaft and the inner peripheral surface of the inner lining in the cross section becomes short, the force (moment) for tilting the roller is reduced. However, in this case, since the contact area between the leg shaft and the inner lining becomes small, an increase in the surface pressure at these contact portions is a concern. Therefore, in the present invention, as described above, the radius of curvature (r) of the convex curve in the longitudinal section of the outer peripheral surface of the leg shaft is made larger than the radius of curvature (R) of the convex curve in the cross section passing through the maximum diameter portion of the outer peripheral surface of the leg shaft. Thereby, since the length in the axial direction of the leg shaft (that is, the minor axis of the contact ellipse) of the contact portion between the outer peripheral surface of the leg shaft and the inner peripheral surface of the inner lining becomes long, an increase in the surface pressure at these contact portions can be suppressed.

[0017] Furthermore, the maximum value Lmax of the distance in the joint shaft direction between the two vertices of the contact ellipse is obtained, and this Lmax is made smaller than the distance F in the joint shaft direction between the relief portions (Lmax < F), so that it is possible to surely prevent the omission of the contact ellipse.

[0018] The relief portion in the cross section of the outer peripheral surface of the leg shaft can be in any shape of a straight line, a single arc, or a composite arc.

[0019] It is preferable to set Lmax=2R×0.30 to 0.75. If Lmax is too small, the surface pressure becomes too large, and if Lmax is too large, sufficient effects such as weight reduction cannot be obtained.

[0020] The recessed portion has a fillet or a chamfer at both ends in the torque transmission direction. With this configuration, it is possible to suppress the occurrence of edge load and reduce contact surface pressure. [Effects of the Invention]

[0021] As described above, the double roller type tripod constant velocity universal joint of the present invention can improve durability and NVH characteristics by reducing the contact surface pressure between the trunnion and the inner ring and suppressing tilt of the roller unit. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a cross-sectional view of a double-roller type tripod constant velocity universal joint taken along the joint axis. [Figure 2] FIG. 2 is a cross-sectional view taken along line KK in FIG. [Figure 3] FIG. 3 is an enlarged view of FIG. [Figure 4] FIG. 2 is a cross-sectional view taken along line LL in FIG. [Figure 5] FIG. 2 is an enlarged side view showing the tripod member of FIG. 1. [Figure 6] 2 is a cross-sectional view showing a state in which the tripod type constant velocity universal joint (FIG. 1) of FIG. 1 has an operating angle. [Figure 7] FIG. 10 is a cross-sectional view showing a tripod-type constant velocity universal joint in which a relief portion is omitted. [Figure 8] This is a diagram showing both a cross-sectional view passing through the maximum diameter part of the leg shaft and a side view (partial cross-sectional view) of the tripod member. [Figure 9] FIG. 10 is a diagram showing a calculation formula for the major axis diameter and the minor axis diameter of an osculating ellipse. [Figure 10] FIG. 2 is a cross-sectional view passing through the maximum diameter portion of the trunnion. [Figure 11] FIG. 2 is a cross-sectional view passing through the maximum diameter portion of the trunnion. [Figure 12] FIG. 2 is a cross-sectional view passing through the maximum diameter portion of the trunnion. [Figure 13] FIG. 1 is a cross-sectional view of a conventional tripod-type constant velocity universal joint taken in the joint axial direction. [Figure 14] FIG. 14 is a cross-sectional view taken along line KK in FIG. [Figure 15] FIG. 14 is a cross-sectional view taken along line LL in FIG. [Figure 16] 14 is a cross-sectional view showing a state in which the tripod type constant velocity universal joint of FIG. 13 has an operating angle. [Figure 17] 14 is a cross-sectional view of the tripod constant velocity universal joint of FIG. 13, perpendicular to the joint axial direction, showing a state in which a roller unit is tilted left and right. FIG. [Figure 18] 14 is a cross-sectional view of the tripod constant velocity universal joint of FIG. 13 in the joint axial direction, showing a state in which a roller unit is tilted forward and backward. FIG. [Figure 19] 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 20] 20 is a side view (partial cross-sectional view) of a tripod member of the tripod type constant velocity universal joint of FIG. 19. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, one embodiment of a tripod type constant velocity universal joint of the present invention will be described with reference to FIGS.

[0024] 1 to 4 is a double-roller type tripod constant velocity universal joint 1. In the following description, the axial direction of the tripod constant velocity universal joint when the operating angle is 0° is referred to as the "joint axial direction," and the circumferential and radial directions centered on the axis at this time are referred to as the "joint circumferential direction" and the "joint radial direction," respectively.

[0025] As shown in FIGS. 1 and 2, this tripod type 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.

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

[0027] The tripod member 3 integrally comprises a body 31 (trunnion body) having a center hole 30, and three trunnion journals 32 protruding in the radial direction of the joint from trisecting positions in the circumferential direction of the joint on the outer peripheral surface of the body 31. A male spline formed on the shaft 8 is fitted into a female spline formed in the center hole 30 of the body 31, and these are fixed in the axial direction of the joint with a retaining ring or the like, thereby connecting the tripod member 3 and the shaft 8 so as to be able to transmit torque.

[0028] The roller units 4 are provided on the outer periphery of each trunnion 32 of the tripod member 3 and are respectively housed in the track grooves 5 of the outer joint member 2. The roller unit 4 includes an outer ring 11, which is an annular roller centered on the axis of the trunnion 32; an annular inner ring 12, which is disposed on the inner periphery of the outer ring 11 and fitted onto the trunnion 32; and rolling elements 13 interposed between the outer ring 11 and the inner ring 12. In this embodiment, a large number of full-complement needle rollers without a cage are used as an example of the rolling elements 13. The needle rollers 13 are disposed so as to roll freely between the cylindrical inner peripheral surface of the outer ring 11 as an outer raceway surface and the cylindrical outer peripheral surface of the inner ring 12 as an inner raceway surface. The roller unit 4, consisting of the outer ring 11, inner ring 12, and needle rollers 13, is held together by a pair of snap rings 14 to prevent spontaneous disassembly.

[0029] The shapes of the roller guideway 6 and the outer peripheral surface 15 of the outer ring 11 will be described in detail below with reference to Figures 3 and 4. In Figures 3 and 4, the joint axial direction is indicated as Z direction, the axial direction of the trunnion 32 is indicated as Y direction, and the torque transmission direction perpendicular to both the joint axial direction Z and the trunnion axial direction Y is indicated as X direction.

[0030] 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). The outer peripheral surface 15 and both end faces 16 of the outer ring 11 are connected via chamfers 17. The chamfers 17 are, for example, made up of a tapered surface with a linear cross section and a convex curved surface with a curved cross section (for example, an arc shape) that smoothly connects the tapered surface with the outer peripheral surface 15 and both end faces 16.

[0031] A pair of roller guideways 6 of each track groove 5 of 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 guide surfaces 7 rise from both ends of the roller guideway 6 in the width direction in a direction approaching the axis Y of the trunnion 32. The shapes of the roller guideway 6 and the guide surfaces 7 follow the shapes of the outer peripheral surface 15 and chamfer 17 of the outer ring 11. Specifically, in the cross section shown in FIG. 3 , the roller guideway 6 and the outer peripheral surface 15 of the outer ring 11 are parallel, and the distance W between the pair of opposing 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. 3, the guide surfaces 7 are substantially parallel to the chamfers 17 of the outer ring 11 and are composed of, for example, an inclined surface with a linear cross section and a concave surface with a curved cross section (for example, an arc-like shape) that smoothly connects the inclined surface and the roller guideway surface 6. The distance in the Y direction between the pair of guide surfaces 7 provided on both sides in the width direction of the roller guideway surface 6 is slightly larger than the distance in the Y direction between the pair of chamfers 17 provided on both sides in the width direction of the outer peripheral surface 15 of the outer ring 11. This forms a small gap in the Y direction between the guide surfaces 7 and the chamfers 17 of the outer ring 11.

[0032] When torque is applied to the outer joint member 2 in the direction of arrow T in FIG. 3, the outer peripheral surface 15 of the outer ring 11 is pressed against the roller guideway 6 on the left side of 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, and therefore they press against each other via a linear contact portion. As a result, in the cross section shown in FIG. 3, the posture 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, and left-right tilt of the outer ring 11 (see FIG. 17) can be suppressed. Furthermore, as the guide surface 7 abuts against the chamfer 17 of the outer ring 11 from the Y direction, forward-backward tilt of the outer ring 11 (see FIG. 18) is restricted and left-right tilt of the outer ring 11 is further suppressed.

[0033] When torque is applied to the outer joint member 2 in the direction of arrow T in Fig. 3 as described above, the outer peripheral surface 15 of the outer ring 11 is pressed against the roller guideway 6 on the left side in the figure (hereinafter referred to as the "torque-loaded roller guideway 6"), while gaps are formed between the roller guideway 6 on the right side in the figure (hereinafter referred to as the "non-torque-loaded roller guideway 6") and the guide surfaces 7 on both sides of it in the width direction, and the outer peripheral surface 15 and chamfers 17 of the outer ring 11. At this time, if the roller unit 4 tilts and the outer peripheral surface 15 and chamfers 17 of the outer ring 11 come into contact with the roller guideway 6 and guide surfaces 7 on the non-torque-loaded side, the rotational resistance of the outer ring 11 increases.

[0034] Therefore, in this embodiment, the initial gap between the outer ring 11 and the roller guide surface 6 (the difference between the spacing W between a pair of opposing roller guide surfaces 6 and the outer diameter of the outer ring 11) and the shape of the guide surface 7 are designed so that when torque is applied to the tripod member 3, the outer ring 11 comes into contact with the roller guide surface 6 on the torque-loaded side, but does not come into contact with the roller guide surface 6 on the non-torque-loaded side and the guide surfaces 7 on both sides of it in the width direction.

[0035] Next, the shapes of the inner peripheral surface 18 of the inner ring 12 and the outer peripheral surface 33 of the trunnion 32 will be described in detail with reference to FIGS.

[0036] The inner peripheral surface 18 of the inner ring 12 is a cylindrical surface parallel to the axial direction Y of the trunnion, and this cylindrical inner peripheral surface 18 is fitted onto the outer peripheral surface 33 of the trunnion 32 .

[0037] As shown in FIG. 3, in a plan view of the trunnion 32 from the joint axial direction (a direction perpendicular to the plane of FIG. 3), i.e., in a longitudinal cross-section including the axis of the trunnion 32 itself, 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 in the longitudinal cross-section of the outer peripheral surface of the trunnion 32 is formed by an arc 33a with a curvature radius r. As a result, the apex (end in the X direction) of the arc 33a on the outer peripheral surface of the trunnion 32 comes into contact with the cylindrical inner peripheral surface 18 of the inner ring 12, and the gap between the outer peripheral surface 33 of the trunnion 32 and the inner peripheral surface 18 of the inner ring 12 gradually increases from the apex of the arc 33a toward both sides in the Y direction. The apex of the arc 33a (the maximum diameter portion of the outer peripheral surface 33 of the trunnion 32) is located in the middle of the outer peripheral surface 33 of the trunnion 32 in the trunnion axis direction Y.

[0038] In a cross section (cross section perpendicular to the axis of the trunnion 32) passing through the maximum diameter portion of the outer circumferential surface of the trunnion 32 shown in FIG. 4, 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, the convex curve in the cross section of the outer circumferential surface of the trunnion 32 is formed by an arc 33b with a curvature radius R. When the maximum diameter of the trunnion 32 in the torque transmission direction X is defined as A, the curvature radius R of the arc 33b is smaller than half A / 2 (≈ the radius of the cylindrical inner circumferential surface 18 of the inner ring 12). Therefore, the arc 33b of 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 becomes increasingly separated from the inner circumferential surface 18 of the inner ring 12 as it goes from the apex to both sides in the Z direction. As a result, the outer peripheral surface 33 of the trunnion 32 and the inner peripheral surface 18 of the inner ring 12 are in contact with each other in the X direction, and a gap is provided between them in the Z direction.

[0039] A pair of recesses 33c, the contours of which are recessed in the axial direction of the trunnion 32, are provided at both ends of the outer peripheral surface 33 of the trunnion 32 in the joint axis direction Z. In this embodiment, a case is exemplified in which the recesses 33c are flat surfaces 33c that are perpendicular to the Z direction. In this case, if the distance between the pair of recesses 33c in the joint axis direction is F, then F<2R.

[0040] By providing the recess 33c on the outer peripheral surface 33 of the trunnion 32 in this way, the volume of the gap G in the joint axial direction Z between the recess 33c and the inner peripheral surface 18 of the inner ring 12 becomes larger than when the recess 33c is not provided (see FIG. 7). By providing the recess 33c on the outer peripheral surface 33 of the trunnion 32 in this way, it is possible to achieve a reduction in the weight of the tripod member 3. Furthermore, since it is possible to hold a large amount of grease in the gap G, it is possible to improve the lubrication between the outer peripheral surface 33 of the trunnion 32 and the inner peripheral surface 18 of the inner ring 12.

[0041] The tripod member 3 described above is manufactured by sequentially undergoing the processes of forging, turning the end face of the body 31, heat treatment, and grinding the outer circumferential surface 33 of the leg shaft 32. In the grinding process of the outer circumferential surface 33, the relief portion 33c is not ground. Therefore, the relief portion 33c remains in the product as the forged surface.

[0042] As described above, 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.

[0043] The inner peripheral surface 18 of the inner ring 12 is a cylindrical surface, 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. As described above, the inner ring 12 and the outer ring 11 are assembled to be relatively rotatable via the needle rollers 13, so the outer ring 11 can oscillate integrally with the inner ring 12 relative to the trunnion 32. In other words, within a plane including the axis of the trunnion 32, the axes of the outer ring 11 and inner ring 12 can tilt relative to the axis of the trunnion 32 (see Figure 6).

[0044] As shown in Figure 6, 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, thereby enabling the tripod type constant velocity universal joint 1 to achieve low vibration.

[0045] In this embodiment, in order to avoid chipping near the apex of the osculating ellipse formed between the outer peripheral surface 33 of the trunnion 32 and the inner peripheral surface 18 of the inner ring 12, which is a problem in the invention described in Patent Document 3, the following measures are taken.

[0046] 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. 5. The contact portion P has an elliptical shape (called a contact ellipse). In this embodiment, as described above, the radius of curvature R (see FIG. 4) of the arc 33b in a cross section passing through the maximum diameter portion of the outer peripheral surface 33 of the trunnion 32 is smaller than half (A / 2) of the maximum diameter dimension A of the trunnion 32 in the torque transmission direction X. Therefore, the length in the Z direction of the contact portion P shown in FIG. 5 (i.e., 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.

[0047] Thus, when the major diameter a of the contact portion P between the outer peripheral surface 33 of the leg shaft 32 and the inner peripheral surface 18 of the inner ring 12 becomes short, the area of the contact portion P becomes small, so there is concern about an increase in the surface pressure at the contact portion P. In the present embodiment, the radius of curvature r of the arc 33a in the longitudinal section of the outer peripheral surface 33 of the leg shaft 32 (see FIG. 3) is larger than the radius of curvature R of the arc 33a in the cross section passing through the maximum diameter portion of the outer peripheral surface 33 of the leg shaft 32 (see FIG. 4). As a result, the length in the Y direction of the contact portion P between the outer peripheral surface 33 of the leg shaft 32 and the inner peripheral surface 18 of the inner ring 12 shown in FIG. 5 (that is, the minor diameter b of the contact ellipse) becomes long, so an increase in surface pressure can be suppressed.

[0048] In this case, the larger the radius of curvature r of the arc 33a in the longitudinal section of the outer peripheral surface 33 of the leg shaft 32 and the smaller the radius of curvature R of the arc 33a in the cross section of the outer peripheral surface 33 of the leg shaft 32, the smaller the major diameter to minor diameter ratio a / b of the contact ellipse P, and the contact ellipse P can be made closer to a circle.

[0049] When the tripod constant velocity joint takes an operating angle, as shown in FIG. 8, the major axis of the contact ellipse P tilts at the same angle as the operating angle, and the major axis becomes longer (the contact ellipses when taking the operating angle are represented by P1 and P2). Considering this point, the maximum value Lmax of the distance in the joint axis direction between the two vertices of the contact ellipses P1 and P2 that occurs in the state where the tripod constant velocity joint is incorporated into the final product (for example, the state of being incorporated into the drive shaft of an automobile) is obtained, and by determining the distance F such that this Lmax is smaller than the distance (minimum distance) F in the joint axis direction Z between a pair of relief portions 33c (Lmax < F), it is possible to surely prevent the dropout of the contact ellipses P1 and P2.

[0050] The maximum value Lmax of the distance in the joint axis direction between the two vertices of the contact ellipses P1 and P2 can be obtained from the sizes of the contact ellipses P1 and P2 that occur when the tripod constant velocity joint 1 is given the maximum operating angle that it can take and the maximum torque that can be applied to itself in the state where the tripod constant velocity joint 1 is incorporated into the final product.

[0051] To simplify this calculation, the maximum working angle of the tripod type constant velocity universal joint 1 may be set to a constant value, for example, 18°, regardless of its size (for tripod type constant velocity universal joints 1 incorporated into automobile drive shafts, it is practically acceptable to consider the maximum working angle to be 18°). In this case, the shapes of the contact ellipses P1 and P2 are calculated when the working angle is set to 18° and the maximum torque that can be applied to the tripod type constant velocity universal joint 1 is applied, and the value of Lmax is determined from the calculation results. Furthermore, not only the maximum working angle but also the maximum torque may be set to a constant value, for example, 1190 Nm, regardless of the size of the tripod type constant velocity universal joint 1 (for tripod type constant velocity universal joints 1 incorporated into automobile drive shafts, the maximum torque rarely exceeds 1190 Nm). In this case, the contact ellipses P1 and P2 are calculated when the working angle is 18° and the torque is 1190 Nm, and the value of Lmax is determined from the calculation results.

[0052] The maximum torque may be set to 0.3 times the minimum static torsional torque at which the shaft 8 connected to the tripod member 3 will suffer torsional fracture (in the tripod constant velocity universal joint 1 incorporated into the drive shaft of an automobile, the maximum torque rarely exceeds 0.3 times the minimum static torsional torque at which the shaft 8 will suffer torsional fracture). For example, when the minimum static torsional torque at which the shaft 8 connected to the tripod member 3 will suffer torsional fracture is 4000 Nm, the osculating ellipses P1 and P2 are calculated with the operating angle set to 18° and the torque set to 1200 Nm, and the value of Lmax is found from the calculation results.

[0053] The contours of the contact ellipses P, P1, and P2 can be calculated uniquely from the shapes (radii of curvature) of the two contacting objects, the load, and the physical properties of the two objects using Hertz's contact theory. Specifically, the major axis a and minor axis b of the contact ellipse can be determined from the equations shown in Figure 9. In each equation in Figure 9, Q is the load, E1 and E2 are the modulus of elasticity (MPa) of the contacting objects, 1 / m1 and 1 / m2 are the Poisson's ratios of the contacting objects, ρ is the principal curvature of the contacting objects, and μ and ν are constants determined from the contact state (radii of curvature) of the two objects.

[0054] As described above, by adjusting the radius of curvature R of the arc 33b in the cross section passing through the maximum diameter portion of the outer peripheral surface 33 of the leg shaft 32 and the radius of curvature r of the arc 33a in the longitudinal section of the outer peripheral surface 33 of the leg shaft 32, and further adjusting the distance F in the joint axis direction between the flat surfaces 33c such that Lmax < F, it is possible to sufficiently secure the volume of the gap G and arrange the entire contact ellipses P1 and P2 in the region formed by the arc 33b having the radius of curvature R of the outer peripheral surface 33 of the leg shaft 32 even in the state of taking the maximum operating angle. That is, it is possible to prevent the contact ellipses P1 and P2 from being damaged. As a result, it is possible to avoid an increase in surface pressure due to the occurrence of edge load or the like and improve the durability of the tripod constant velocity joint.

[0055] Particularly, as in the present embodiment, by making the radius of curvature r of the arc 33a in the longitudinal section of the outer peripheral surface 33 of the leg shaft 32 larger than the radius of curvature R of the arc 33a in the cross section of the maximum diameter portion of the outer peripheral surface 33 of the leg shaft 32 (r > R), the major-minor diameter ratio of the contact ellipses P, P1, and P2 becomes smaller, so that Lmax can be made smaller. Therefore, it becomes easy to realize Lmax < F while sufficiently securing the volume of the gap G. If Lmax is too small, the surface pressure becomes too large, and if Lmax is too large, sufficient effects such as weight reduction cannot be obtained. Therefore, the radii of curvature r and R are set such that Lmax = 2R × 0.30 to 0.75, and more preferably, Lmax = 2R × 0.40 to 0.55.

[0056] In addition, the radii of curvature r and R should be set so as to suppress the inclination of the outer ring 11 within an allowable range while suppressing the surface pressure of the contact portion P between the inner lining 12 and the leg shaft 32 within an allowable range. From this viewpoint, it is preferable to set the above radii of curvature r and R such that the ratio a / b of the major diameter a and the minor diameter b of the contact ellipse P (the contact ellipse at a contact angle of 0°) is within the range of 2 to 10, and preferably within the range of 3 to 6.

[0057] The present invention is not limited to the above-described embodiments. Hereinafter, other embodiments of the present invention will be described, but redundant descriptions of the contents common to the above-described embodiments will be omitted.

[0058] In the embodiment described above, the case where a flat surface is formed as the relief portion 33c provided on the outer peripheral surface of the leg shaft 32 is exemplified, but the form of the relief portion 33c is not limited to the flat surface. For example, as shown in FIG. 10, in the cross section of the leg shaft 32, the relief portion 33c can also be formed by an arc (single arc) having a single radius of curvature R'. In this case, the maximum diameter dimension F' of the relief portion 33c satisfies F'<2R. In addition, although not shown, in the cross section of the leg shaft 32, the relief portion 33c can also be formed by a composite arc connecting a plurality of arcs with different radii of curvature. In any case, the radius of curvature (R') of the arc constituting the relief portion 33c is made larger than the radius of curvature R of the arc 33b of the outer peripheral surface 33 (R'>R). Incidentally, when the relief portion is formed by the flat surface 33c, in the cross section of the leg shaft 32, the relief portion 33c becomes a straight line with an infinite radius of curvature. Therefore, the radius of curvature of the relief portion 33c in the cross section is larger than the radius of curvature R of the arc 33b regardless of the shape of the relief portion 33c.

[0059] Also, as shown in FIG. 11, fillets 35 may be provided at both ends of the relief portion 33c in the torque transmission direction, or as shown in FIG. 12, tapered chamfers 36 with an angle α may be provided at both ends of the relief portion 33c in the torque transmission direction. Both the fillets 35 and the chamfers 36 are included in the relief portion 33c that forms a gap G in the joint axis direction Z between the inner peripheral surface 18 of the inner lining 12. Therefore, in the embodiments shown in FIGS. 11 and 12, the distance (minimum distance) F in the joint axis direction of a set of relief portions 33c is the distance in the joint axis direction Z between the boundary portions of the fillets 35 and the arc 33b having the radius of curvature R, and is the distance in the joint axis direction Z between the boundary portions of each chamfer 36 and the arc 33b having the radius of curvature R. Also in this case, the radius of curvature r, R, and the distance F are set so that Lmax<F.

[0060] 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 arcs, but this is not limiting. For example, the convex curve in the longitudinal cross section of the outer circumferential surface of the trunnion 32 may be a non-arc 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 portion with the inner ring 12) (because it is a non-arc, the radius of curvature of a pseudo-arc at both ends in the torque transmission direction; the same applies below) is larger than the radius of curvature R of the convex curve (arc 33b) in the transverse cross section passing through the maximum diameter portion 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.

[0061] 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 maximum diameter portion 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) is smaller than half (A / 2) of the maximum dimension A of the trunnion 32 in the torque transmission direction X.

[0062] Furthermore, both the convex curves in the longitudinal cross section and the transverse cross section 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 (i.e., the contact portion with the inner ring 12) is larger than the radius of curvature of the convex curve (ellipse) in the transverse cross section passing through the maximum diameter portion of the outer circumferential surface of the trunnion 32 at least at both ends in the torque transmission direction (i.e., the contact portion 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 larger than half (A / 2) of 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 passing through the maximum diameter portion of the outer circumferential surface of the trunnion 32 at least at both ends in the torque transmission direction is smaller than half (A / 2) of the maximum dimension A of the trunnion 32 in the torque transmission direction X.

[0063] The application of the tripod constant velocity universal joint 1 described above is not limited to the drive shaft of an automobile, but can be widely used in power transmission paths of automobiles, industrial equipment, and the like. [Explanation of symbols]

[0064] 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 8 shafts 11 Outer Ring (Roller) 12 Inner Ring 13 Rolling elements 14 Snap ring 31 Torso 32 Leg axis 33 Outer surface of leg shaft 33a Arc (convex curve) 33b Arc (convex curve) 33c Relief 35 Fillet 36 Chamfering F: Distance in the joint axial direction between a pair of reliefs Lmax: The maximum distance in the joint axial direction between the two vertices of the contact ellipse P, P1, P2 Contact ellipse (contact area) 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, in each track groove; 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 each having rollers arranged on outer peripheries of the trunnions and an inner ring arranged between the rollers and the trunnions, the three roller units being rotatably and swingably supported by the trunnions and accommodated in the track grooves, The roller has a cylindrical outer circumferential surface, The pair of roller guide surfaces of each track groove are flat surfaces parallel to each other, a pair of guide surfaces are provided on both sides of the roller guide surface in the width direction, the guide surfaces being capable of contacting the roller from both sides in the axial 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) at both ends in the torque transmission direction of the convex curve in the longitudinal cross section of the outer circumferential surface of the trunnion is larger than a curvature radius (R) at both ends in the torque transmission direction of the convex curve in the transverse cross section passing through the maximum diameter portion of the outer circumferential surface of the trunnion; a pair of relief portions are provided on both sides of the outer peripheral surface of the trunnion in the joint axial direction, the relief portions forming a gap in the joint axial direction between the outer peripheral surface of the trunnion and the cylindrical inner peripheral surface of the inner ring; a tripod-type constant velocity universal joint, characterized in that the distance in the joint axial direction between the pair of relief portions is F, the maximum value of the distance in the joint axial direction between two vertices of an osculating ellipse formed between the outer peripheral surface of the trunnion and the inner peripheral surface of the inner ring during torque transmission is Lmax, and Lmax < F.

2. 2. A tripod-type constant velocity universal joint according to claim 1, wherein the recess in the cross section of the outer circumferential surface of the trunnion is formed in the shape of a straight line, a single arc, or a compound arc.

3. 2. The tripod type constant velocity universal joint according to claim 1, wherein Lmax=2R×0.30 to 0.

75.

4. 2. A tripod type constant velocity universal joint according to claim 1, wherein the recessed portion has a fillet or a chamfer on both ends in the torque transmission direction.

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