Tripod constant-velocity universal joint

Abstract

This tripod constant-velocity universal joint is of a double-roller type. In the present invention, protrusion curves bulging toward both sides in the torque transmission direction are provided on the outer peripheral surface of a leg shaft at a longitudinal section and a transverse section. The center of curvature of the protrusion curve at the longitudinal section is offset toward the opposite side from said protrusion curve. The center of curvature of the protrusion curve surface at the transverse section is offset toward said protrusion curve. When the radius of curvature of the protrusion curve at the longitudinal section is r and the radius of curvature of the protrusion curve surface at the transverse section is R, r>R is satisfied such that the shape of the transverse section of the leg shaft is oval. A tripod member is formed from a body part and the leg shaft which projects in the joint radial direction via a leg shaft neck section smaller than the leg shaft. The shape of the transverse section of the leg shaft neck section is oval. A diameter difference is provided between the outer peripheral portion of the leg shaft neck section and the outer peripheral portion of the leg shaft.

Description

Tripod type constant velocity universal joint

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

[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 classified into a single roller type and a double roller type. 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. As shown in FIGS. 16 and 17 , a double roller type tripod constant velocity universal joint includes 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).

[0004] In a double-roller tripod constant velocity universal joint, as shown in Fig. 18, the cross section of the trunnion 132 (cross section perpendicular to the axis of the trunnion) is elliptical, and the inner circumferential surface of the inner ring 112 has a convex arc cross section, as shown in Fig. 16. This allows the rollers 111 to oscillate relative to the trunnion 132, as shown in Fig. 19, 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. Also, as shown in Fig. 18, the trunnion 132 has an elliptical cross section, but in this case, its major axis a is arranged parallel to the torque load direction and its minor axis b is arranged perpendicular to the torque load direction.

[0005] Japanese Patent Application Laid-Open No. 2000-320563

[0006] In the above-described tripod type constant velocity universal joint, as shown in Fig. 17, the outer peripheral surfaces 115 of the rollers 111 are convex curved surfaces having arc-shaped generatrix lines, and the roller guideways 106 that come into contact with these have a concave cross-sectional shape (Gothic arch shape) that follows the shape of the outer peripheral surfaces 115 of the 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 the roller unit 104 including the 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. 20 (hereinafter referred to as "left-right tilt"), and a phenomenon in which the roller unit 104 tilts in the direction of arrow C in a cross section parallel to the joint axial direction as shown in Fig. 21 (hereinafter referred to as "front-rear tilt"). If 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 trunnions 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.

[0007] 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 frictional moment that acts to tilt the roller unit 104 as the trunnion 132 moves. Even when the joint is angled, 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 is angled, the elliptical cross section of the trunnion 132 generates a force that causes the roller unit 104 to tilt forward and backward (see FIG. 21 ). 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.

[0008] Therefore, the present invention can provide a tripod type constant velocity universal joint that can ensure high strength in the neck, achieve a large operating angle as a tripod type constant velocity universal joint, and achieve improved grinding workability of the trunnion.

[0009] The tripod constant velocity universal joint of the present invention comprises 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 consisting of an inner ring arranged on the outer peripheral surface of the trunnions and supported rotatably and swingably by the trunnions, rollers arranged in the track grooves and arranged on the outer radial side of the inner ring, and a plurality of rolling elements arranged between the inner ring and the rollers and between the inner ring and the outer ring, wherein the outer peripheral surface of the trunnions has a shape such that, in longitudinal section and transverse section, the tripod member has a body and a trunnion that protrudes radially from the body via a trunnion neck that is smaller than the trunnion, the trunnion neck having an oval cross section, and a radius difference between the arc-shaped portion of the outer periphery of the trunnion neck and the arc-shaped portion of the outer periphery of the trunnion.

[0010] According to the tripod constant velocity universal joint of the present invention, the necks of the tripod members have an oval cross section with a greater thickness on the torque load side, allowing the necks to be thicker in the torque load direction of the tripod members. Conversely, the dimension (width) in the direction perpendicular to the torque load direction can be reduced, making it possible to avoid interference between the necks and the inner diameter of the roller cassette (i.e., the inner diameter of the inner ring) at high operating angles.

[0011] In this type of tripod-type constant velocity universal joint, the tripod member generally consists of a body portion and a trunnion that protrudes radially through a trunnion neck that is smaller than the trunnion. The trunnion neck has a circular cross-sectional shape and a cylindrical outer circumferential surface. In such a case, if the neck diameter is large, the neck will interfere with the inner diameter of the roller cassette when the joint has a working angle. This prevents a high working angle from being achieved. In other words, to achieve a high working angle, the neck diameter must be reduced. However, reducing the neck diameter may result in a decrease in strength.

[0012] Furthermore, if the transverse cross section of the trunnion is oval and the transverse cross section of the neck is circular, the difference in diameter between the two outer peripheries will be small on the short shaft side of the trunnion. This small difference in diameter can make it difficult to perform finish processing. Generally, the neck is forged and the trunnion is ground, which means that grinding wheels and tools interfere with the neck during grinding, which is undesirable from a manufacturing perspective.

[0013] In contrast, the tripod constant velocity universal joint according to the present invention has a difference in diameter between the outer periphery of the trunnion neck and the outer periphery of the trunnion, which eliminates any areas where the difference in diameter is small, effectively preventing interference with grinding stones, tools, etc., from occurring with the neck when the trunnion is being ground.

[0014] The convex curve in the cross section of the outer circumferential surface of the trunnion gradually moves away from the cylindrical inner circumferential surface of the inner ring as it moves from the torque transmission end to both sides in the joint axial direction. This shortens the circumferential length of the contact area between the outer circumferential surface of the trunnion and the inner circumferential surface of the inner ring in the cross section (i.e., the major axis of the osculating ellipse), thereby reducing the force (moment) tending to tilt the roller. However, in this case, the contact area between the trunnion and the inner ring is reduced, raising concerns about increased surface pressure at these contact areas. Therefore, in the present invention, as described above, the radius of curvature (r) of the convex curve in the longitudinal cross section of the outer circumferential surface of the trunnion is made larger than the radius of curvature (R) of the convex curve in the cross section of the outer circumferential surface of the trunnion. This increases the axial length of the contact area between the outer circumferential surface of the trunnion and the inner circumferential surface of the inner ring (i.e., the minor axis of the osculating ellipse), thereby suppressing an increase in surface pressure at these contact areas.

[0015] It is preferable that the inner periphery of the inner ring be a flat cylindrical surface. The outer periphery of the trunnion has a convex curve that bulges toward the inner periphery of the inner ring in both longitudinal and transverse sections. The convex curve in the transverse section of the outer periphery of the trunnion has a shape that moves away from the cylindrical inner periphery of the inner ring as it moves from the torque transmission end to both sides in the joint axial direction. This shortens the circumferential length of the trunnion at the contact area between the outer periphery of the trunnion and the inner periphery of the inner ring in the transverse section (i.e., the major axis of the osculating ellipse), thereby reducing the force (moment) that tends to tilt the roller.

[0016] It is preferable that the outer peripheral surface of the roller has a cylindrical shape and the roller guideway has a flat surface. By setting it in this way, when torque is applied, the flat roller guideway and the cylindrical outer peripheral surface of the roller press against each other via a linear contact portion, thereby suppressing left and right tilt of the roller.

[0017] When the center of curvature of the convex curved portion in the cross section of the trunnion neck is aligned with the center of curvature of the end arc portion in the cross section of the trunnion, and the radius of curvature of the end arc portion in the cross section of the trunnion neck is R', and the radius of curvature of the convex curved portion in the cross section of the trunnion is R, it is preferable that R' < R. It is particularly preferable that R' / R is 0.80 to 0.95. Setting it in this way stabilizes grinding workability and trunnion strength.

[0018] When the neck width dimension, which is the minor axis direction in the cross section of the trunnion neck, is W' and the trunnion diameter (journal diameter), which is the dimension between the arc portions in the cross section of the trunnion, is D, it is preferable that W' / D is 0.70 to 0.90. By setting it in this way, it is possible to set it so that the neck does not interfere with the inner ring even when the maximum operating angle is taken.

[0019] If the width dimension of the trunnion in the minor axis direction in the cross section of the trunnion is W, and the neck width dimension of the trunnion neck in the minor axis direction in the cross section of the trunnion neck is W', then W' = W may be satisfied. In this way, grinding a portion of the trunnion that is the same size as the neck does not adversely affect the neck. Furthermore, in a portion with a diameter difference, no portion where the diameter difference is smaller is formed, effectively preventing interference with grinding stones, tools, etc. during grinding of the trunnion.

[0020] The minor axis side of the trunnion neck in cross section may be linear or have a slight arc shape. Even if it is linear or has a slight arc shape, a difference in diameter is provided between the outer periphery of the trunnion neck and the outer periphery of the trunnion, which effectively prevents interference of grinding stones, tools, etc. with the neck when grinding the trunnion.

[0021] The present invention allows the thickness of the neck to be increased in the torque load direction of the tripod member, thereby ensuring high neck strength. It also makes it possible to avoid interference between the neck and the inner diameter of the inner ring at high operating angles, allowing the tripod constant velocity universal joint to achieve a high operating angle. It also effectively prevents interference with grinding wheels, tools, etc., from occurring with the neck during grinding of the trunnion, improving the grinding workability of the trunnion.

[0022] 1. A cross-sectional view in the joint axial direction of a tripod-type constant velocity universal joint according to the present invention. A cross-sectional view taken along line K-K in FIG. 1. A longitudinal cross-sectional view of a roller cassette. A cross-sectional view of a roller cassette. A side view showing a partial cross-section of a tripod member. A front view showing a partial cross-section of a tripod member. A cross-sectional view of a neck of the tripod member shown in FIG. 6. A relationship diagram showing the diameter difference between the trunnion and the trunnion neck. A side view showing a partial cross-section of another tripod member. A front view of another tripod member. A relationship diagram showing the diameter difference between the trunnion and the trunnion neck of the tripod member shown in FIG. 10. A cross-sectional view of an elliptical neck consisting of a pair of parallel straight portions and a pair of arc portions provided at the ends of the parallel straight portions. A cross-sectional view of a neck consisting of a pair of flattened arc portions and a pair of arc portions at the ends of the flattened arc portions. A cross-sectional view of a neck having a circular cross-sectional shape. A cross-sectional view showing a problem when using a tripod member having the neck shown in FIG. 13. 16. A simplified diagram of a case where the diameter difference between the trunnion and the trunnion neck changes. A cross-sectional view in the joint axial direction of a conventional tripod type constant velocity universal joint. A partial cross-sectional view taken along line K-K in FIG. 16. A cross-sectional view taken along line L-L in FIG. 16. A cross-sectional view showing a state where the tripod type constant velocity universal joint of FIG. 16 has an operating angle. A cross-sectional view perpendicular to the joint axial direction of the tripod type constant velocity universal joint of FIG. 16, showing a state where the roller unit is tilted left and right. A cross-sectional view in the joint axial direction of the tripod type constant velocity universal joint of FIG. 16, showing a state where the roller unit is tilted forward and backward.

[0023] An embodiment of the present invention will now be described with reference to Figures 1 to 8. Figures 1 to 4 show a tripod type constant velocity universal joint 1 according to the present invention, which is a double roller type. In the following description, the axial direction of the tripod type constant velocity universal joint when the operating angle is 0° will be referred to as the "joint axial direction," and the circumferential and radial directions centered on the axis at this time will be referred to as the "joint circumferential direction" and the "joint radial direction," respectively.

[0024] 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.

[0025] 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.

[0026] The tripod member 3 integrally comprises a body 31 (trunnion body) having a central hole 30, and three trunnion journals 32 projecting radially from positions equally dividing the outer peripheral surface of the body 31 in the joint circumferential direction. In this case, the trunnion journals 32 project radially from the body 31 via small trunnion necks 29. A male spline formed on the shaft 8 is fitted into a female spline formed in the central hole 30 of the body 31, and these are fixed in the joint axial direction 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.

[0027] The roller units 4 are provided on the outer periphery of each trunnion 32 of the tripod member 3 and are housed in the track grooves 5 of the outer joint member 2, as shown in FIGS. 3 and 4 . 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, the inner ring 12, and the needle rollers 13, is secured together by a pair of snap rings 14 to prevent spontaneous disassembly.

[0028] Next, the relationship between the roller guideway 6 and the outer ring 11 will be described. In this case, the joint axial direction is indicated as the Z direction, the axial direction of the trunnion 32 is indicated as the Y direction, and the torque transmission direction perpendicular to both the joint axial direction Z and the trunnion axial direction Y is indicated as the X direction.

[0029] The outer peripheral surface 15 of the outer ring 11 is a cylindrical surface centered on the axis of the trunnion 32. End faces 16 of the outer ring 11 on both sides in the axial direction thereof are flat surfaces perpendicular to the axis (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 (e.g., an arcuate shape) that smoothly connects the tapered surface with the outer peripheral surface 15 and both end faces 16.

[0030] 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 toward 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, 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. This forms a slight gap in the X direction 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, for example, of 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.

[0031] When torque in the direction of arrow T is applied to the outer joint member 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-right tilt of the outer ring 11 (see FIG. 13 ). Furthermore, the guide surface 7 abuts against the chamfer 17 of the outer ring 11 from the Y direction, thereby restricting forward-backward tilt of the outer ring 11 (the conventional tilt in the direction of arrow C in FIG. 21 ) and further suppressing left-right tilt of the outer ring 11.

[0032] 3 is applied to the outer joint member 2, 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 chamfer 17 of the outer ring 11. At this time, if the roller unit 4 tilts and the outer peripheral surface 15 and chamfer 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.

[0033] Therefore, in this embodiment, 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 or the guide surfaces 7 on both sides of the roller guide surface 6 in the width direction. The initial gap between the outer ring 11 and the roller guide surface 6 and the shape of the guide surface 7 are designed so that the outer ring 11 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 the roller guide surface 6 in the width direction.

[0034] 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 Figures 3 and 4. The inner peripheral surface 18 of the inner ring 12 is a cylindrical surface parallel to the trunnion axis direction Y.

[0035] In a vertical 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 vertical 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 (X-direction end) of the arc 33a on the outer peripheral surface of the trunnion 32 closely faces 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. In this case, the centers of curvature Oa, Oa of the arc 33a of the convex curve in the vertical cross section are offset by a dimension E to the opposite side of the convex curve.

[0036] In a cross section of the trunnion 32 taken in a direction perpendicular to its own axis as shown in Figure 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. In this case, the centers of curvature Ob, Ob of the arc 33b of the convex curve in the cross section are offset by a dimension F toward the convex curve side.

[0037] The arc 33b on the outer peripheral surface of the leg shaft 32 closely faces the cylindrical inner peripheral surface 18 of the inner ring 12 at its top (end in the X direction), and as it goes from the top to both sides in the Z direction, it moves away from the inner peripheral surface 18 of the inner ring 12, so that a gap G is provided between them in the Z direction.

[0038] As described above, the outer peripheral surface 33 of the trunnion 32 has an aspherical shape in which the radius of curvature r of the convex curve (arc 33a) in the longitudinal cross section is different from the radius of curvature R of the convex curve (33b) in the transverse cross section. The radius of curvature r is set to be larger than the radius of curvature R, i.e., r > R. In this case, the radius of curvature r is set to be larger than half the maximum dimension of the trunnion 32 in the torque transmission direction (the maximum diameter of the trunnion 32 when the operating angle, which will be described later, is 0°), and the radius of curvature R is set to be smaller than half the maximum diameter of the trunnion 32.

[0039] If the trunnion neck 29 has a circular cross-sectional shape as shown in Fig. 13, it is necessary to increase the diameter of the neck 29 for strength reasons. However, if the diameter of the neck 29 is large, when an operating angle is taken, interference occurs between the neck 29 and the inner diameter end of the inner ring 12 of the roller cassette (roller unit) 4, as shown in Fig. 14. For this reason, the operating angle θ cannot be made very large, and to obtain a large operating angle (for example, 20° to 28°) required for a sliding type constant velocity universal joint, it is necessary to make the diameter of the cross-sectional shape of the neck 29 small, but a small diameter results in poor strength.

[0040] Furthermore, the trunnion 32 according to the present invention has an oval cross-sectional shape consisting of a pair of parallel straight portions 33c, 33d and arcs 33b at both ends of the straight portions. Therefore, if the trunnion neck 29 had a circular cross-sectional shape as shown in Fig. 13, when compared with the external shapes of the cross-sectional shapes of the trunnion neck 29 and trunnion 32, as shown in Fig. 15, the radial difference between the outer surface of the trunnion 32 and the outer surface of the trunnion neck 29 would not be uniform over the entire circumference. That is, the radial difference decreases as one approaches the straight portion of the trunnion 32 from the portion of the trunnion 32 corresponding to arc 33b. For example, if the radial difference at the portion of the trunnion 32 corresponding to arc 33b is A1 and the radial difference near the trunnion 32 is B1, then A1 > B1.

[0041] In this type of tripod member, the neck 29 is generally forged and the trunnion 32 is ground. Therefore, as shown in Figure 15, the difference in diameter between the outer circumferential surface of the trunnion 32 and the outer circumferential surface of the trunnion neck 29 is not uniform. If this difference in diameter becomes small (shrinks), interference with the grinding wheel or grinding tool occurs with the neck 29 during grinding, resulting in reduced machining accuracy. In the tripod constant velocity joint according to the present invention, as shown in Figure 7, the arc 33b of the leg 32 is the grinding area, and the sides 33c and 33d on the short shaft end side are non-grinding areas. Therefore, the difference in diameter in the grinding area is not uniform.

[0042] For this reason, in the present invention, as shown in Figures 4 and 7, the cross-sectional shape of the neck 29 is an oval whose outer shape is smaller than and similar to the oval cross-sectional shape of the trunnion. That is, the cross-sectional shape of the neck 29 is also an oval consisting of a pair of parallel straight portions 29c, 29d and arcs 29b, 29b provided at both ends of these straight portions, and as shown in Figure 8, the difference in diameter between the two arc-shaped portions is uniform. Furthermore, the major axis of the oval cross-section of the neck 29 is parallel to the load direction. Figure 8 shows the cross-sectional shape of the P-P cross section shown in Figure 6, i.e., the cross-sectional shape of the neck 29 at the smallest diameter point, and this portion is called the "end arc portion."

[0043] In this case, the center of curvature Ob of the arc 33b of the trunnion 32 in the cross section coincides with the center of curvature Ob1 of the arc 29b of the neck 29 in the cross section, and when the radius of curvature of the arc 33b of the trunnion 32 in the cross section is R and the radius of curvature of the arc 29b of the neck 29 in the cross section is R', R > R' is satisfied, and when the length in the minor axis direction of the trunnion 32 in the cross section (trunnion width dimension) is W and the length in the minor axis direction of the neck 29 in the cross section (neck width dimension) is W', W > W' is satisfied. This makes the radius difference R-R' between both arc-shaped portions uniform.

[0044] Specifically, when R' / R is set to 0.80 to 0.95, W' is the neck width dimension which is the minor axis direction in the cross-sectional shape of the trunnion neck 32, and D is the trunnion diameter which is the dimension between the arc portions in the cross-sectional shape of the trunnion, W' / D is set to 0.70 to 0.90.

[0045] According to the tripod constant velocity universal joint of the present invention, the neck portion 32 of the tripod member 3 has an oval cross section with a greater thickness on the torque load side, and the thickness of the neck portion 29 can be increased in the torque load direction of the tripod member 3. This ensures high strength of the neck portion 29. Conversely, the dimension (width) in the direction perpendicular to the torque load direction can be reduced, making it possible to avoid interference between the neck portion 29 and the inner diameter of the roller cassette 4 (i.e., the inner diameter of the inner ring 12) at high operating angles. This allows the tripod constant velocity universal joint to achieve a high operating angle.

[0046] That is, a diameter difference is provided between the outer periphery of the trunnion neck 29 and the outer periphery of the trunnion 32, and this diameter difference is set to be constant. As a result, there are no areas where the diameter difference is small, and interference between the neck 29 and a grinding stone, tool, etc. is effectively prevented when grinding the trunnion 32. This "constant" width is within the range that can be processed using general processing methods such as turning and grinding. As a guideline, this diameter difference should be within ±10%. More preferably, it should be within ±5% of this diameter difference.

[0047] It is preferable that the inner peripheral surface 18 of the inner ring 12 has a flat cylindrical shape. The outer peripheral surface of the trunnion 32 has a convex curve that bulges out toward the inner peripheral surface 18 of the inner ring 12 in both longitudinal and transverse sections. The convex curve in the transverse section of the outer peripheral surface of the trunnion 32 has a shape that moves away from the cylindrical inner peripheral surface of the inner ring 12 as it moves from the torque transmission end to both sides in the joint axial direction. This shortens the circumferential length of the trunnion 32 at the contact portion between the outer peripheral surface of the trunnion 32 and the inner peripheral surface 18 of the inner ring 12 in the transverse section (i.e., the major axis of the osculating ellipse), thereby reducing the force (moment) that tends to tilt the roller.

[0048] It is preferable that the outer peripheral surface 15 of the roller 11 is formed into a flat cylindrical surface, and the roller guideway 6 is formed into a flat surface. By setting it in this way, when a torque load is applied, the flat roller guideway 6 and the cylindrical outer peripheral surface 15 of the roller 11 press against each other via a linear contact portion, thereby suppressing left and right tilt of the roller.

[0049] When the center of curvature of the convex curved portion in the cross section of trunnion neck 29 is aligned with the center of curvature of the end arc portion in the cross section of trunnion 32, and the radius of curvature of the end arc portion in the cross section of trunnion neck 29 is R', and the radius of curvature of the convex curved portion in the cross section of trunnion 32 is R, it is preferable that R' < R. It is particularly preferable that R' / R be 0.80 to 0.95. Setting it in this way stabilizes grinding workability and trunnion strength.

[0050] When the neck width dimension, which is the minor axis direction in the cross section of the trunnion neck 29, is W' and the trunnion diameter, which is the dimension between the arc portions in the cross section of the trunnion 32, is D, it is preferable that W' / D be 0.70 to 0.90. By setting it in this manner, it is possible to set the neck 29 not to interfere with the inner ring 12 even when the maximum operating angle is taken.

[0051] If the trunnion width dimension, which is the minor axis direction in the cross section of the trunnion 32, is defined as W, and the neck width dimension, which is the minor axis direction in the cross section of the trunnion neck 29, is defined as W', then W' = W. In this way, grinding a portion of the trunnion 32 that has the same dimensions as the neck 29 does not adversely affect the neck 29. Furthermore, in portions with a diameter difference, no portion where the diameter difference becomes smaller is formed, which effectively prevents interference with grinding stones, tools, etc. when grinding the trunnion.

[0052] The joint can also be used in constant velocity universal joints with a maximum operating angle of 23 to 28 degrees. That is, in a constant velocity universal joint with such a maximum operating angle, even when the operating angle is set, the gap (journal gap) between the trunnion 32 and the inner peripheral surface of the unit within the roller (inner peripheral surface 18 of the inner ring 12) does not become negative, preventing the generation of abnormal noise and vibration, suppressing circumferential backlash, and preventing a deterioration in NVH performance.

[0053] 9 and 10 show another tripod member. In this case, the minor axis length of the trunnion 32 in the cross section is set to be the same as the minor axis length of the neck 29 in the cross section. That is, if the minor axis length of the trunnion 32 in the cross section (trunnion width dimension) is W and the minor axis length of the neck 29 in the cross section (neck width dimension) is W', then W = W'. In this case, too, if the radius of curvature of the arc 33b of the trunnion 32 in the cross section is R and the radius of curvature of the arc 29b of the neck 29 in the cross section is R', then R > R', and R - R' is a constant.

[0054] In this way, even when using tripod members 3 with W = W', the cross section has an oval shape with the wall thickness on the torque load side being greater, and the wall thickness of the neck portion can be made thicker in the torque load direction of the tripod member. Conversely, the dimension (width dimension) in the direction perpendicular to the torque load direction can be made smaller, and moreover, a portion with a diameter difference does not have a portion with a smaller diameter difference. Therefore, it is possible to achieve the same effects as the tripod-type constant velocity universal joint using the tripod member 3 shown in the above embodiment.

[0055] In the above embodiment, neck portion 29 has an oval shape consisting of a pair of parallel straight portions and arcs at the ends, as shown in Fig. 12A. In contrast, as shown in Fig. 12B, neck portion 29 has a pair of arc-shaped portions 29e and 29f with a large radius of curvature, i.e., a small curvature, instead of a pair of parallel straight portions 29c and 29d.

[0056] In the tripod member 3 having the neck portion 29 shaped as shown in FIG. 12B, the straight portions 33c and 33d in the cross-sectional shape of the leg shaft 32 need to be changed to arc-shaped portions 33e and 33f with small curvature.

[0057] In this way, even if the shape is straight or an arc with a small curvature, a diameter difference is provided between the outer periphery of the leg axis neck 29 and the outer periphery of the leg axis 32, and the diameter difference can be made constant, which effectively prevents interference between grinding wheels, tools, etc. and the neck 29 when grinding the leg axis 32.

[0058] While the above describes an embodiment of the present invention, the present invention is not limited to the above embodiment and various modifications are possible. The difference in diameter between the outer periphery of the trunnion neck and the outer periphery of the trunnion can be set as desired, but is preferably, for example, approximately 0.05 to 0.20 times the diameter of the outer periphery of the trunnion. If the difference in diameter is less than 0.05, the difference is too small and workability deteriorates. Conversely, if it exceeds 0.20, the strength of the neck may decrease. Furthermore, as a tripod-type constant velocity universal joint, it can be used in drive shafts equipped in the torque transmission system of an automobile. However, the use of constant velocity universal joints is not limited to automobiles, and they can naturally be used widely in the power transmission systems of automobiles and general industrial equipment.

[0059] Used in double-roller tripod constant velocity universal joints with inner and outer rings, it can achieve a high operating angle and improve the grindability of the leg shaft.

[0060] 2 outer joint member 3 tripod member 4 roller unit 5 linear track groove 6 roller guideway 11 roller (outer ring) 12 inner ring 29 trunnion neck 31 body 32 trunnion

Claims

1. 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 guideways opposing 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 consisting of an inner ring arranged on the outer peripheral surface of the trunnions and supported rotatably and swingably by the trunnions, rollers arranged in the track grooves and positioned on the outer radial side of the inner ring, and a plurality of rolling elements arranged between the inner ring and the rollers and positioned between the inner ring and the outer ring, a tripod-type constant velocity universal joint, characterized in that the outer peripheral surface of the trunnion is a convex curve in the longitudinal section and the transverse section, bulging out on both sides in the torque transmission direction, the center of curvature of the convex curve in the longitudinal section is offset from the central axis of the trunnion to the side opposite the convex curve, the center of curvature of the convex curved surface in the transverse section is offset from the central axis of the trunnion to the convex curve side and in the rotational direction of the tripod member, and when the radius of curvature of the convex curve in the longitudinal section is r and the radius of curvature of the convex curved surface in the transverse section is R, r > R so that the transverse cross section of the trunnion is an ellipse, and the tripod member has a body and trunnions protruding in the radial direction of the joint via trunnion necks that are smaller than the trunnions, and the trunnion necks have an ellipse cross section, and a radius difference is provided between the arc-shaped portion of the outer peripheral part of the trunnion neck and the arc-shaped portion of the outer peripheral part of the trunnion.

2. A tripod-type constant velocity universal joint according to claim 1, characterized in that the inner periphery of the inner ring is cylindrical.

3. A tripod type constant velocity universal joint according to claim 1, wherein the outer peripheral surfaces of the rollers have a cylindrical shape, and the roller guide surfaces have flat surfaces.

4. A tripod-type constant velocity universal joint as described in claim 1, characterized in that the center of curvature of the convex curved portion in the cross-sectional shape of the trunnion neck is aligned with the center of curvature of the end arc portion in the cross-sectional shape of the trunnion, and when the radius of curvature of the end arc portion in the cross-sectional shape of the trunnion neck is R' and the radius of curvature of the convex curved portion in the cross-sectional shape of the trunnion is R, R' < R.

5. A tripod type constant velocity universal joint according to claim 4, characterized in that R' / R is set to 0.80 to 0.

95.

6. A tripod-type constant velocity universal joint as described in claim 1, characterized in that W' is the neck width dimension in the minor axis direction in the cross-sectional shape of the trunnion neck, and D is the trunnion diameter which is the dimension between the arc portions in the cross-sectional shape of the trunnion, and W' / D is 0.70 to 0.

90.

7. A tripod-type constant velocity universal joint as described in claim 1, characterized in that when W is the neck width dimension in the minor axis direction in the cross-sectional shape of the trunnion and W' is the neck width dimension which is the distance between the straight portions in the cross-sectional shape of the trunnion neck, W' = W.

8. A tripod-type constant velocity universal joint according to claim 1, characterized in that the minor axis side in the cross section of the trunnion neck is a straight line or a circular arc with a slight curvature.

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