Tripod-type constant velocity universal joint

Abstract

To provide a tripod-type constant velocity universal joint in which durability of a leg shaft is improved through reduction of contact surface pressure between the leg shaft and an inner ring.SOLUTION: An inner ring 12 has a cylindrical surface-shaped inner circumferential surface 18. An outer circumferential surface 33 of a leg shaft 32 has, in each of a longitudinal cross section including an axial line of the leg shaft 32 and a transverse cross section orthogonal to the axial line of the leg shaft, a convex curve bulged to both sides in a torque transmission direction. The convex curve in the transverse cross section of the outer circumferential surface 33 of the leg shaft 32 is arranged to increasingly separate from the cylindrical surface-shaped inner circumferential surface 18 of the inner ring 12 toward both sides in a joint axial direction from a torque transmission part. Of the convex curve in the longitudinal cross section of the leg shaft 32, a curvature radius R at the torque transmission part is made larger than a curvature radius r at the torque transmission part of the convex curve in the transverse cross section of the leg shaft. When a journal diameter of the leg shaft 32 is defined as DJ, the curvature radius R at the torque transmission part of the convex curve in the longitudinal cross section of the leg shaft 32 is defined as R≥DJ×0.62, and the curvature radius r at the torque transmission part of the convex curve in the transverse cross section of the leg shaft 32 is defined as r≥DJ×0.42.SELECTED DRAWING: Figure 3

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, Patent Document 1 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 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 is to restrict the inclination of the roller 222 by sliding and displacing the roller 222 along the roller guide surface 224 in the axial direction of the trunnion 226 (direction H in FIG. 19). 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. [Prior art documents] [Patent documents]

[0007] [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]

[0008] 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.

[0009] 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.

[0010] Furthermore, in the tripod-type constant velocity universal joint disclosed in Patent Document 2, 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 Q' (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 Q'. Therefore, even if the joint has a structure that achieves 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.

[0011] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a tripod-type constant velocity universal joint in which the durability of the trunnion is improved by reducing the contact surface pressure between the trunnion and the inner ring. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides a tripod-type constant velocity universal joint comprising: an outer joint member having three track grooves formed on its inner peripheral 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 peripheral surface of the outer joint member and having three trunnions protruding in the joint radial direction toward the track grooves; and three roller units each having rollers arranged on the outer peripheral surfaces 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 housed in the track grooves, and in which torque is transmitted between the trunnions and the inner ring, the inner ring having a cylindrical inner peripheral surface, and the outer peripheral surface of the trunnion being formed in a cylindrical shape such that the outer peripheral surface of the trunnion is in contact with the axis of the trunnion. In each of a longitudinal section including a line and a transverse section perpendicular to the axis of the trunnion, the trunnion has a convex curve bulging on both sides in the torque transmission direction, the convex curve in the transverse section of the outer surface of the trunnion becomes more distant from the cylindrical inner surface of the inner ring as it goes from the torque transmission portion to both sides in the joint axial direction, the radius of curvature R of the torque transmission portion of the convex curve in the longitudinal section of the trunnion is larger than the radius of curvature r of the torque transmission portion of the convex curve in the transverse section of the trunnion, where DJ is the journal diameter of the trunnion, the radius of curvature R of the torque transmission portion of the convex curve in the longitudinal section of the trunnion satisfies R≧DJ×0.62, and the radius of curvature r of the torque transmission portion of the convex curve in the transverse section of the trunnion satisfies r≧DJ×0.42.

[0013] In this way, by setting the radius of curvature R of the torque transmission portion of the convex curve in the longitudinal section of the trunnion to R≧DJ×0.62, and by setting the radius of curvature r of the torque transmission portion of the convex curve in the transverse section of the trunnion to r≧DJ×0.42, the contact surface pressure between the trunnion and the inner ring can be reduced, thereby improving the durability of the trunnion.

[0014] In this tripod type constant velocity universal joint, it is preferable to set r≦DJ×0.48.

[0015] This prevents the major axis of the contact ellipse at the contact point between the trunnion and inner ring from becoming excessively large when the operating angle is reached, thereby reducing the force (moment) that tends to tilt the roller and inner ring, improving NVH characteristics.

[0016] In this tripod type constant velocity universal joint, it is preferable to set R≦DJ×0.84.

[0017] This prevents the journal gap between the trunnion and inner ring from becoming excessively large, thereby suppressing play in the circumferential direction of the joint between the trunnion and inner ring and improving NVH characteristics.

[0018] In this tripod-type constant velocity universal joint, it is desirable that the rollers have cylindrical outer peripheral surfaces, and that the pair of roller guide surfaces of each track groove be flat surfaces parallel to each other.

[0019] As a result, when torque is applied, the flat roller guide surface and the cylindrical outer peripheral surface of the roller press against each other via the linear contact portion, thereby suppressing left and right tilt of the roller (see FIG. 17).

[0020] Furthermore, it is preferable to provide a pair of guide surfaces on both sides of the roller guide surface in the width direction, which are capable of contacting the roller from both sides in the axial direction.

[0021] This makes it possible to more reliably prevent the roller from tilting to the left or right. [Effects of the Invention]

[0022] As described above, the tripod type constant velocity universal joint according to the present invention can reduce the contact surface pressure between the trunnion and the inner ring, thereby improving the durability of the trunnion. [Brief explanation of the drawings]

[0023] [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. 2 is a vertical cross-sectional view of a roller cassette. [Figure 4] FIG. 2 is a cross-sectional view taken along line LL in FIG. [Figure 5] 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 6] FIG. 1 shows the shape of an osculating ellipse. [Figure 7] FIG. 2 is a side view (partial cross-sectional view) of a tripod member. [Figure 8] FIG. 4 is a cross-sectional view of a main part showing the left and right tilt angles between the trunnion and the inner ring. [Figure 9] FIG. 9 is an enlarged cross-sectional view of a main part of FIG. 8. [Figure 10] FIG. 4 is a cross-sectional view of a main part showing the relationship between the journal diameter and the left-right inclination angle. [Figure 11] FIG. 1(a) is a diagram illustrating the relationship between the axial radius of curvature R, the lateral tilt angle α, the whirling radius e, and PCR, and FIG. 1(b) is a diagram illustrating the relationship between the lateral tilt angle α, the whirling radius e, and PCR. [Figure 12] 1 is a graph showing the relationship between r / DJ and the major axis of the osculating ellipse. [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

[0024] Hereinafter, one embodiment of a tripod type constant velocity universal joint of the present invention will be described with reference to FIGS.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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 1 to 4. In Figures 3 and 4, the joint axial direction is shown as Z direction, the axial direction of the trunnion 32 is shown as Y direction, and the torque transmission direction perpendicular to both the joint axial direction Z and the trunnion axial direction Y is shown as X direction.

[0031] 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 made up of, for example, a tapered surface with a linear cross section and a convex curved surface with a curved cross section (for example, an arcuate shape) that smoothly connects the tapered surface with the outer peripheral surface 15 and both end faces 16.

[0032] 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. 2 , the roller guideway 6 and the outer peripheral surface 15 of the outer ring 11 are parallel, and the distance 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. 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 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.

[0033] When torque is applied to the outer joint member 2 in the direction of arrow T in FIG. 2, 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, so they press against each other via a linear contact portion. This corrects the posture of the outer ring 11 so that the outer peripheral surface 15 of the outer ring 11 is parallel to the roller guideway 6, thereby suppressing left and right tilt of the outer ring 11 (see FIG. 17). Furthermore, the guide surface 7 abuts against the chamfer 17 of the outer ring 11 from the Y direction, thereby restricting the front and rear tilt of the outer ring 11 (see FIG. 18) and further suppressing left and right tilt of the outer ring 11.

[0034] When torque is applied to the outer joint member 2 in the direction of arrow T in Fig. 2 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 side 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 side 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.

[0035] Therefore, in this embodiment, the initial gap between the outer ring 11 and the roller guideway 6 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 guideway 6 on the torque-loaded side, but does not come into contact with the roller guideway 6 on the non-torque-loaded side and the guide surfaces 7 on both sides of it in the width direction.

[0036] 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.

[0037] 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 with the outer peripheral surface 33 of the trunnion 32 with a clearance fit.

[0038] As shown in FIG. 3, in any longitudinal cross-section including the axis of the trunnion 32, the outer peripheral surface 33 of the trunnion 32 has a convex curve that bulges outward in the torque transmission direction X. In the illustrated example, the convex curve in each longitudinal cross-section of the outer peripheral surface 33 of the trunnion 32 is formed by an arc 33a with a curvature radius R. The curvature radius R of the arc 33a is greater than half the maximum diameter (referred to as the journal diameter DJ) of the outer peripheral surface 33 of the trunnion 32 (R > DJ / 2). As a result, on the torque load side, the apex (X-direction end) 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, forming a torque transmission section. 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. In the following description, the curvature radius R of the arc 33a appearing in the longitudinal cross-section is referred to as the axial curvature radius R.

[0039] In the longitudinal cross section shown in Figure 3, the center of curvature of arc 33a is located on a straight line in the X direction passing through the intersection P of the axis of leg axis 32 and the PCR (hereinafter referred to as the leg axis center), offset by a distance F from the leg axis center P.

[0040] In the cross-section in the direction orthogonal to the axis of the leg shaft 32 shown in FIG. 4, the outer peripheral surface 33 of the leg shaft 32 has convex curves bulging on both sides in the torque transmission direction X. In the illustrated example, the convex curve in the cross-section passing through the maximum diameter portion of the outer peripheral surface of the leg shaft 32 is composed of an arc 33b with a radius of curvature r. The radius of curvature r of the arc 33b is smaller than half of the journal diameter DJ of the leg shaft 32 (r < DJ / 2). Therefore, on the torque load side, the arc 33b of the outer peripheral surface of the leg shaft 32 contacts the cylindrical inner peripheral surface 18 of the inner lining 12 at its top (the end in the X direction), constituting the torque transmission portion. As going from the top of the arc 33b to both sides in the Z direction, it separates from the inner peripheral surface 18 of the inner lining 12. Thereby, the outer peripheral surface 33 of the leg shaft 32 and the inner peripheral surface 18 of the inner lining 12 contact in the X direction, and a gap is provided between them in the Z direction. In the following description, the radius of curvature r of the arc 33b is referred to as the circumferential radius of curvature r. The circumferential radius of curvature r is smaller than the axial radius of curvature R (r < R).

[0041] As shown in FIG. 4, the center of curvature of the arc 33b in the cross-section passing through the maximum diameter portion of the leg shaft 32 is at a position offset by a distance E from the leg shaft center P on the straight line in the X direction passing through the leg shaft center P. Among the cross-sections of the leg shaft 32, the arc of the convex curve also has a constant radius of curvature in the cross-section located away from the cross-section passing through the maximum diameter portion of the leg shaft 32 in the Y direction. However, the radius of curvature of the arc is smaller than the radius of curvature r of the arc 33b in the cross-section passing through the maximum diameter portion of the leg shaft 32, and the radius of curvature of the arc becomes smaller as it is farther from the cross-section passing through the maximum diameter portion.

[0042] On both ends in the joint axis direction Z of the outer peripheral surface 33 of the leg shaft 32, a set of relief portions 33c with the contour retracted in the axial direction of the leg shaft 32 are provided. In the present embodiment, the case where a flat surface 33c orthogonal to the Z direction is provided as the relief portion 33c is illustrated.

[0043] By providing the recess 33c on the outer peripheral surface 33 of the trunnion 32 in this way, the volume of the gap G (see FIG. 4) 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. 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.

[0044] 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.

[0045] As described above, the outer peripheral surface 33 of the trunnion 32 has an aspherical shape with different axial and circumferential curvature radii R and r. 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, allowing 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, and therefore the outer ring 11 can oscillate integrally with the inner ring 12 relative to the trunnion 32. In other words, as shown in FIG. 5, the axes of the outer ring 11 and the inner ring 12 can tilt relative to the axis of the trunnion 32 within a plane including the axis of the trunnion 32.

[0046] 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 from intersecting the roller guideway 6 at an angle. As a result, the outer ring 11 rolls horizontally relative to the roller guideway 6, which reduces induced thrust and sliding resistance and enables the tripod type constant velocity universal joint 1 to achieve low vibration.

[0047] In a tripod type constant velocity universal joint having the above configuration, a contact ellipse Q having a major axis 2a and a minor axis 2b as shown in Figure 6 is formed at the contact portion between the inner peripheral surface of the inner ring 12 in the torque load direction and the outer peripheral surface 33 of the trunnion 32. As shown in Figure 7, when the differential angle is 0°, the contact ellipse Q is close to a circle with a small major axis / minor axis ratio a / b. In contrast, when the tripod type constant velocity universal joint has an operating angle, the major axis of the contact ellipse Q tilts in accordance with the operating angle, and the major axis becomes longer, increasing the major axis / minor axis ratio a / b (the contact ellipses when a working angle is formed are designated Q1 and Q2).

[0048] The inventors of the present application have considered that the shape of the contact ellipse changes depending on the values ​​of the axial radius of curvature R and the circumferential radius of curvature r, which in turn affects the durability of the leg axle 32 and also makes it necessary to improve the NVH characteristics, and have therefore conducted the following verification of the optimal ranges for the values ​​of the axial radius of curvature R and the circumferential radius of curvature r.

[0049] [Verification of axial curvature radius R] The larger the axial radius of curvature R, the larger the minor axis 2b of the contact ellipse, and the lower the surface pressure of the contact ellipse. A reduction in surface pressure is advantageous for improving the durability of the trunnion 32. To ensure the durability of the trunnion 32, it is desirable that the maximum surface pressure of the contact ellipse Q be less than 4.0 GPa. The maximum surface pressure occurs when the operating angle θ is 0°. From this perspective, it is preferable that the axial radius of curvature R be R≧DJ×0.62.

[0050] The above calculations were performed assuming the operating angle θ to be 0° and the load torque to be Tsd torque. Tsd torque is the substantial maximum torque that is applied to a tripod constant velocity universal joint mounted on a vehicle. Specifically, Tsd torque is 0.3 times the minimum static torsional torque that causes torsional fracture of the shaft 8 connected to the tripod member 3.

[0051] On the other hand, if the axial radius of curvature R is too large, the journal clearance S required for the joint to achieve a large operating angle increases. The journal clearance S is the value obtained by subtracting the journal diameter DJ from the inner diameter dimension D of the inner ring 12 shown in Figure 3 (S = D - DJ). As the journal clearance S increases, the backlash in the circumferential direction of the joint between the inner ring 12 and the trunnion 32 increases, deteriorating the NVH characteristics. This phenomenon will be explained in detail below.

[0052] When the joint has an operating angle θ, a left-right tilt angle α occurs in the trunnion 32, as shown in Figure 8. From Figures 10 and 11, the left-right tilt angle α is expressed by the following formula (1). O is the center of the tripod member 3, P is the trunnion center, and O' is the point of contact when a tangent is drawn from P to a circle with a whirl radius e.

number

[0053] In formula (1), PO represents the length of the line segment connecting the trunnion center P and the center of the tripod member 3, and OO' represents the length of the line segment connecting the center O of the tripod member 3 and the contact point O'. The line segment PO is PCR, and the line segment OO' is the whirling radius e. Therefore, formula (1) can be replaced with the following formula (2).

number

[0054] The whirling radius e can be expressed by the following equation (3) using PCR and operating angle θ. By substituting equation (3) into equation (2), equation (5) can be obtained via equation (4) below.

number

number

number

[0055] Next, we will explain how to calculate the maximum outer diameter DJ' (see Figure 9) of the trunnion 32 when the trunnion 32 is tilted at a lateral tilt angle α as shown in Figure 10. In Figure 10, if the centers of curvature of the convex curve in the vertical cross section of the trunnion 32 are A and A', and the intersections of a horizontal line drawn from each center of curvature A and A' with the arc of the convex curve are C and C', the dimension between C and C' is the maximum outer diameter DJ' (DJ' = CC'). If the intersection point between the perpendicular line dropped from the trunnion center P to the line segment AC is P', the following equation holds true. DJ' / 2 = AC-AP' = R-Fcosα

[0056] Therefore, DJ'=2(R-Fcosα) holds.

[0057] The journal diameter DJ is expressed as 2(RF) and the journal gap S is expressed as S=DJ'-DJ, so the journal gap S is S=DJ'-DJ = 2(R-Fcosα)-2(RF) =2F(1-cosα) You can ask for more.

[0058] Therefore, if the offset amount of the center of curvature of the arc portion 33a having the axial radius of curvature R is F (see Figure 3) and the left / right inclination angle of the trunnion 32 is α, the journal clearance S required for the tripod constant velocity universal joint to have an operating angle θ can be calculated from the following equations (6) and (7).

number

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[0059] If the journal clearance S is too small, when the constant velocity universal joint assumes a high working angle and the left-right tilt angle α of the trunnion 32 increases, the journal clearance S will become negative, causing a buffer between the inner ring 12 and the trunnion 32, which could result in noise and vibration, degrading NVH characteristics, or even early damage. To avoid this, it is desirable to set the journal clearance to a value equal to or greater than the value calculated from equations (6) and (7).

[0060] On the other hand, as already mentioned, in order to improve the durability of the trunnion 32 by reducing the contact surface pressure, it is preferable to increase the axial curvature radius R. However, the larger the axial curvature radius R, the larger the offset F of the center of curvature (A, A' in Figure 10) becomes. Therefore, according to equation (6), the required value of journal clearance S increases. If the journal clearance S becomes too large, the backlash in the joint circumferential direction between the inner ring 12 and the trunnion 32 increases, resulting in a deterioration of the NVH characteristics. Therefore, there is an upper limit to the value of the axial curvature radius R. This upper limit of the axial curvature radius R can be obtained by the following procedure.

[0061] Since F=R-(DJ / 2), the following equation (8) is derived from equation (6). S≧(2R-DJ)(1-cosα) (8)

[0062] Furthermore, the maximum operating angle of a tripod constant velocity universal joint (maximum operating angle of the joint alone before being mounted on a vehicle) is generally about θ = 23° to 28°. When θ = 28°, 1-cosα=2.20×10 -3 This becomes:

[0063] From the viewpoint of suppressing backlash in the circumferential direction of the joint, it is preferable that the minimum value of the journal gap S is 0.15% or less of DJ. Therefore, from the formula (8), (2R-DJ)(1-cosα)≦DJ×0.15% 2R-DJ≦(0.0015×DJ) / (2.20×10 -3 ) 2R-DJ≦0.68×DJ R≦DJ×0.84 This becomes:

[0064] For the above reasons, in order to suppress backlash in the circumferential direction of the joint, it is preferable to set the axial radius of curvature R to 0.84 times or less of DJ. Furthermore, to achieve both a reduction in contact pressure and suppression of backlash in the circumferential direction of the joint, it is preferable to set the axial radius of curvature R in the range of DJ × 0.62 ≦ R ≦ DJ × 0.84.

[0065] [Verification of circumferential curvature radius r] The larger the circumferential radius of curvature r, the larger the major axis 2a of the contact ellipse, and the lower the surface pressure of the contact ellipse. A reduction in surface pressure is advantageous for improving the durability of the trunnion 32. To ensure the durability of the trunnion 32, it is desirable that the maximum surface pressure of the contact ellipse Q be less than 4.0 GPa, just like the axial radius of curvature R. From this perspective, it is preferable that the circumferential radius of curvature r be r≧DJ×0.42. The calculation conditions are the same as for the axial radius of curvature R.

[0066] On the other hand, if the circumferential radius of curvature r is too large, the major axis 2a of the contact ellipse becomes large, which increases the force (moment) that tends to tilt the roller cassette 4 when a working angle is taken, deteriorating the NVH characteristics. In particular, when a tripod constant velocity universal joint takes a high working angle, the major axis 2a of the contact ellipse becomes rapidly large.

[0067] Figure 12 shows the relationship between r / DJ and the major axis 2a of the contact ellipse when a tripod-type constant velocity universal joint is provided with the maximum practical operating angle (θ = 18°) when mounted on a vehicle. As is clear from the figure, when r / DJ exceeds 0.48, the major axis 2a increases rapidly and approaches line contact, resulting in a rapid increase in the force tending to tilt the roller cassette 4. Therefore, it is preferable to set r ≦ DJ × 0.48. Note that Figure 12 shows the case where R = DJ × 0.7. In Figure 12, the plotted values ​​will vary slightly if the value of R is different, but the same tendency as in Figure 12 is obtained.

[0068] Therefore, if the goal is not just to improve the durability of the leg shaft 32 but also to improve both the durability of the leg shaft 32 and the NVH characteristics, it is preferable to set the circumferential radius of curvature r in the range DJ×0.42≦r≦DJ×0.48.

[0069] In the above embodiment, the convex curves in the longitudinal and transverse cross sections of the outer peripheral surface of the trunnion 32 are both formed as arcs, but the convex curves are not limited to arcs. For example, the convex curve in the longitudinal cross section of the outer peripheral surface of the trunnion 32 may be formed as a non-arc curve such as an ellipse. In this case, in the torque transmission portion of the convex curve (ellipse) in the longitudinal cross section of the outer peripheral surface of the trunnion 32, the convex curve becomes a non-arc, so the radius of curvature of the pseudo-arc of the convex curve is treated as the axial radius of curvature R.

[0070] Furthermore, the convex curve in the cross section of the outer circumferential surface of the trunnion 32 may be configured as a non-circular curve such as an ellipse. In this case, the convex curve (ellipse) in the torque transmission section of the convex curve in the cross section passing through the maximum diameter portion of the outer circumferential surface of the trunnion 32 becomes a non-circular curve, so the radius of curvature of the pseudo-arc of the convex curve is treated as the circumferential radius of curvature r. Of course, the convex curves in both the vertical and horizontal cross sections of the outer circumferential surface of the trunnion can also be configured as non-circular curves such as an ellipse.

[0071] 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]

[0072] 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) DJ journal diameter 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 the joint axial direction, and a pair of roller guide surfaces opposed in the joint circumferential direction; a tripod member arranged on the inner peripheral surface of the outer joint member and having three trunnions protruding in the joint radial direction toward the track grooves; and three roller units each having rollers arranged on the 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 housed in the track grooves, wherein torque is transmitted between the trunnions and the inner ring, 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 both a vertical cross section including the axis of the trunnion and a horizontal cross section perpendicular to the axis of the trunnion, the convex curve of the outer circumferential surface of the trunnion in the cross section is spaced apart from the cylindrical inner circumferential surface of the inner ring as it goes from the torque transmission portion to both sides in the joint axial direction, a radius of curvature R of a torque transmission portion of the convex curve in the longitudinal cross section of the trunnion is larger than a radius of curvature r of a torque transmission portion of the convex curve in the transverse cross section of the trunnion; When a journal diameter of the trunnion is DJ, a curvature radius R of the torque transmission portion of the convex curve in the longitudinal cross section of the trunnion satisfies R≧DJ×0.62; and A tripod-type constant velocity universal joint, characterized in that the radius of curvature r of the torque transmission portion of the convex curve in the cross section of the trunnion satisfies r≧DJ×0.

42.

2. 2. A tripod type constant velocity universal joint according to claim 1, wherein r≦DJ×0.

48.

3. 2. A tripod type constant velocity universal joint according to claim 1, wherein R≦DJ×0.

84.

4. 2. A tripod-type constant velocity universal joint according to claim 1, wherein said rollers have cylindrical outer peripheral surfaces, and said pair of roller guide surfaces of each track groove are flat surfaces parallel to each other.

5. 5. A tripod-type constant velocity universal joint according to claim 4, wherein a pair of guide surfaces capable of contacting the rollers from both sides in the axial direction thereof are provided on both sides in the width direction of the roller guide surface.

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