Tripod constant velocity universal joint

Abstract

To prevent a roller unit from being detached from a leg shaft of a tripod member without deteriorating assemblability or increasing manufacturing costs in a tripod constant velocity universal joint of a double roller type.SOLUTION: An outer periphery of a leg shaft 32 has convex curves (arcs 33a, 33b) swollen on both sides in a torque transmission direction on a vertical cross section and a horizontal cross section. An inner periphery 18 of an inner ring 12 comprises: a cylindrical part 18a fitted with an outer periphery 33 of the leg shaft 32; and an annular protrusion 18b provided inside the cylindrical part 18a in a joint radial direction, projecting on an inner diameter side than the cylindrical part 18a, and having an inside diameter smaller than a maximum diameter A of the outer periphery of the leg shaft 32. A curvature radius (R) at both ends in the torque transmission direction on the convex curve (arc 33b) on the horizontal cross section of the outer periphery 33 of the leg shaft 32 is smaller than a radius (D / 2) of the cylindrical part 18a of the inner periphery 18 of the inner ring 12.SELECTED DRAWING: Figure 10

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-type constant velocity universal joint is well known as a sliding-type constant velocity universal joint. Tripod-type constant velocity universal joints are available in single-roller and double-roller types. The single-roller type has rollers inserted into track grooves of an outer joint member, rotatably attached to the trunnions of the tripod members via multiple needle rollers. The double-roller type has rollers inserted into track grooves of an outer joint member and inner rings fitted onto the trunnions of the tripod members to rotatably support the rollers. Because the double-roller type allows the rollers to oscillate relative to the trunnions, it has the advantage of being able to reduce induced thrust (axial force induced by friction between parts inside the joint) and sliding resistance compared to the single-roller type.

[0004] For example, Patent Document 1 listed below discloses a double-roller type tripod constant velocity universal joint as shown in Fig. 11. In this constant velocity universal joint, the outer peripheral surface of the trunnion 104 of the tripod member 102 is spherical, and the cylindrical inner peripheral surface of the inner ring 110 is fitted onto this spherical outer peripheral surface.

[0005] As shown in Figure 12, a plurality of needle rollers 112 are disposed between an inner ring 110 and rollers 111, and these are integrated with snap rings 117 to form a roller unit 109. Annular protrusions 115 are provided on both ends of the cylindrical inner peripheral surface of the inner ring 110 in the width direction (the vertical direction in Figure 12). These annular protrusions 115 restrict movement of the inner ring 110 in the width direction relative to the trunnions 104 of the tripod member 102. This prevents the roller unit 109, which includes the inner ring 110, rollers 111, and needle rollers 112, from falling off from the trunnions 104 of the tripod member 102 when assembling the tripod constant velocity universal joint.

[0006] Furthermore, in Patent Document 2 below, chamfered portions and bulged portions are provided on both widthwise ends of the inner peripheral surface of the inner ring to prevent the roller unit from falling off the tripod member. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-297814 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-177994 Summary of the Invention [Problem to be solved by the invention]

[0008] 11, it is necessary to press-fit the trunnions 104 of the tripod member 102 into the inner periphery of the inner ring 110 so that they climb over the annular protrusions 115. In this type of tripod-type constant velocity universal joint, the cross-sectional shape (circle) of the spherical outer periphery of the trunnions 104 of the tripod member 102 approximately matches the cross-sectional shape (circle) of the inner periphery of the inner ring 110. In this case, when the trunnions 104 are press-fitted into the inner periphery of the inner ring 110, the spherical outer periphery of the trunnions 104 and the annular protrusions 115 of the inner ring 110 interfere with each other over the entire circumference, requiring a large press-fitting load and reducing ease of assembly.

[0009] On the other hand, if a chamfered portion and a bulged portion are provided on the inner peripheral surface of the inner ring as in Patent Document 2, press-fitting is not required, and the deterioration of assembly due to press-fitting can be avoided. However, the shape of the inner ring becomes complex, which increases the number of processing steps and increases manufacturing costs. In addition, the roller unit needs to be tilted when assembled to the tripod member, which complicates the assembly method.

[0010] Therefore, an object of the present invention is to prevent the roller units from falling off the trunnions of the tripod members in a double roller type tripod constant velocity universal joint without reducing assembly efficiency or increasing manufacturing costs. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention provides a tripod-type constant velocity universal joint including an outer joint member having three track grooves formed on an inner peripheral surface thereof and extending in a joint axial direction, a tripod member arranged on an inner peripheral surface of the outer joint member and having three trunnions protruding in a joint radial direction toward the track grooves, and three roller units each having a roller arranged on an outer periphery of the trunnion and an inner ring arranged between the roller and the trunnion, the three roller units being rotatably and swingably supported by the trunnion and housed in the track grooves, the outer peripheral surface of the trunnion has a convex curve that bulges out on both sides in the torque transmission direction in a longitudinal section and a transverse section, an inner peripheral surface of the inner ring including a cylindrical portion that fits onto an outer peripheral surface of the trunnion; and an annular protrusion that is provided radially inward of the cylindrical portion, protrudes radially inward beyond the cylindrical portion, and has an inner diameter smaller than the maximum diameter of the outer peripheral surface of the trunnion; A tripod-type constant velocity universal joint is provided in which the radius of curvature (R) of the convex curve in the cross section of the outer peripheral surface of the trunnion at both ends in the torque transmission direction is smaller than the radius (D / 2) of the cylindrical portion of the inner peripheral surface of the inner ring.

[0012] As described above, in the present invention, an annular protrusion is provided on the cylindrical inner surface of the inner ring, radially inward of the joint. This annular protrusion interferes with the maximum diameter portion of the trunnion, restricting the inner ring from moving toward the trunnion end, thereby preventing the roller unit, including the inner ring, from falling off the trunnion. Furthermore, in the present invention, the radius of curvature (R) of the convex curve in the cross section of the outer circumferential surface of the trunnion is smaller than the radius (D / 2) of the cylindrical portion of the inner circumferential surface of the inner ring. As a result, when the inner ring is assembled to the trunnion of the tripod member, the interference area between the annular protrusion of the inner ring and the outer circumferential surface of the trunnion is limited to the apex of the convex curve in the cross section of the outer circumferential surface of the trunnion. This reduces the press-fit load compared to when the inner ring and the trunnion are press-fitted around the entire circumference, improving assembly. The longitudinal cross section of the outer circumferential surface of the trunnion is a cross section in a plane including the axial center of the trunnion, and the cross section of the outer circumferential surface of the trunnion is a cross section in a plane perpendicular to the axial center of the trunnion.

[0013] As described above, by providing a cylindrical portion on the inner peripheral surface of the inner ring and making the radius of curvature (R) of the convex curve in the cross section of the outer peripheral surface of the trunnion smaller than the radius (D / 2) of the cylindrical portion on the inner peripheral surface of the inner ring, the length in the circumferential direction of the trunnion of the contact area between the outer peripheral surface of the trunnion and the inner peripheral surface of the inner ring in the cross section (i.e., the major axis of the osculating ellipse) is shortened, thereby reducing the force (moment) that tends to tilt the roller. However, in this case, the contact area between the trunnion and the inner ring is reduced, which raises concerns about an increase in surface pressure at these contact areas.

[0014] Therefore, in the above-mentioned tripod constant velocity universal joint, it is preferable that 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 transverse cross section of the outer circumferential surface of the trunnion. This increases the length in the axial direction of the trunnion of the contact area between the outer circumferential surface of the trunnion and the inner circumferential surface of the inner ring (i.e., the minor axis of the contact ellipse), making it possible to suppress an increase in surface pressure at these contact areas.

[0015] In addition, in the above-mentioned tripod-type constant velocity universal joint, it is preferable that the rollers have cylindrical outer peripheral surfaces, and that each track groove is provided with a pair of roller guideways consisting of flat surfaces that face each other circumferentially around the joint and are parallel to each other. In this case, 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 (see arrow B in Figure 3). Furthermore, by providing a pair of guide surfaces on both sides of the roller guideway in the width direction that can abut against the roller from both sides in the axial direction, left and right tilt of the roller can be more reliably prevented.

[0016] In the above-described tripod-type constant velocity universal joint, another annular protrusion may be provided on the inner peripheral surface of the inner ring in a region radially outward of the cylindrical portion of the joint, protruding radially inward from the cylindrical portion and having an inner diameter smaller than the maximum diameter of the outer peripheral surface of the trunnion. The another annular protrusion does not function to prevent the roller unit from falling off the tripod member, but by providing annular protrusions on both ends of the inner peripheral surface of the inner ring in the width direction (direction of its own axis), the inner ring can be made symmetrical with respect to the center in the width direction. In this case, the inner ring can be assembled to the trunnions of the tripod member without regard to its orientation, which prevents incorrect assembly of the inner ring and improves assembly ease.

[0017] The tripod-type constant velocity universal joint can have a plurality of rolling elements disposed between the roller and the inner ring, which can be, for example, a plurality of needle rollers disposed in a full complement state between the roller and the inner ring. [Effects of the Invention]

[0018] As described above, according to the present invention, in a double roller type tripod constant velocity universal joint, it is possible to prevent the roller units from falling off from the trunnions of the tripod members without reducing assembly ease or increasing manufacturing costs. [Brief explanation of the drawings]

[0019] [Figure 1]FIG. 1 is a cross-sectional view of a double-roller type tripod constant velocity universal joint taken along the joint axis. [Figure 2] FIG. 2 is a cross-sectional view taken along line KK in FIG. [Figure 3] FIG. 3 is an enlarged view of FIG. [Figure 4] FIG. 2 is a cross-sectional view taken along line LL in FIG. [Figure 5] FIG. 2 is an enlarged side view showing the tripod member of FIG. 1. [Figure 6] 2 is a cross-sectional view showing a state in which the tripod constant velocity universal joint of FIG. 1 has an operating angle θ. [Figure 7] FIG. [Figure 8] FIG. 8 is an enlarged view of a portion Q in FIG. 7. [Figure 9] FIG. 2 is a cross-sectional view of the cylindrical portion of the inner ring and the maximum diameter portion of the trunnion. [Figure 10] 10 is a diagram in which a cross section of the annular protrusion of the inner ring and a cross section of the maximum diameter portion of the trunnion are superimposed. [Figure 11] FIG. 1 is a cross-sectional view of a conventional tripod-type constant velocity universal joint. [Figure 12] 12 is an enlarged view of a roller unit of the tripod type constant velocity universal joint of FIG. 11. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a tripod type constant velocity universal joint according to the present invention will be described with reference to the drawings.

[0021] A tripod type constant velocity universal joint according to one embodiment of the present invention is of a double roller type, and 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, as shown in Figures 1 and 2. In this specification, the axial direction of the tripod type constant velocity universal joint when the operating angle is 0° (the left-right direction in Figure 1) is referred to as the "joint axial direction," and the circumferential direction and radial direction of a circle centered on the axis at this time are referred to as the "joint circumferential direction" and the "joint radial direction," respectively.

[0022] 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.

[0023] The tripod member 3 integrally comprises a body 31 having a central hole 30 and three trunnions 32 protruding radially from three equal 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 (see dotted lines in Figure 1) is fitted into a female spline formed in the central 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.

[0024] The roller units 4 are provided on the outer periphery of each trunnion 32 of the tripod member 3. Each roller unit 4 is housed in a track groove 5 of the outer joint member 2. The roller unit 4 includes an outer ring 11, which is an annular roller centered on the axis of the trunnion 32; an inner ring 12, which is an annular roller disposed on the inner periphery of the outer ring 11 and fitted onto the trunnion 32; and a plurality of 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 the plurality of 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 outer ring 11, inner ring 12, and needle rollers 13 are secured together by a pair of snap rings 14 to prevent them from disassembling naturally, and together they form the roller unit 4.

[0025] The shapes of the roller guideway 6 and the outer peripheral surface 15 of the outer ring 11 will be described in detail below with reference to Figures 3 and 4. In Figures 3 and 4, the joint axial direction is indicated as Z direction, the axial direction of the trunnion 32 is indicated as Y direction, and the torque transmission direction perpendicular to both the joint axial direction Z and the trunnion axial direction Y is indicated as X direction.

[0026] The outer peripheral surface 15 of the outer ring 11 is a cylindrical surface. End faces 16 on both sides in the width direction (Y direction) of the outer ring 11 are flat surfaces perpendicular to its axis (see FIG. 3). The outer peripheral surface 15 and both end faces 16 of the outer ring 11 are connected via chamfers 17 (see FIG. 4). 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 arc shape) that smoothly connects the tapered surface with the outer peripheral surface 15 and both end faces 16.

[0027] 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 side closer to the axis Y of the trunnion 32. The shapes of the roller guideway 6 and the guide surfaces 7 follow the shapes of the outer peripheral surface 15 and chamfer 17 of the outer ring 11. Specifically, in the cross section shown in FIG. 3 , the roller guideway 6 and the outer peripheral surface 15 of the outer ring 11 are parallel, and the distance W between the pair of opposing roller guideways 6 is slightly larger than the diameter of the outer peripheral surface 15 of the outer ring 11. As a result, a small gap in the X direction is formed between the roller guideway 6 and the outer peripheral surface 15 of the outer ring 11. 3, the guide surfaces 7 are substantially parallel to the chamfers 17 of the outer ring 11 and are composed of, for example, an inclined surface with a linear cross section and a concave surface with a curved cross section (for example, an arc-like shape) that smoothly connects the inclined surface and the roller guideway surface 6. The distance in the Y direction between the pair of guide surfaces 7 provided on both sides in the width direction of the roller guideway surface 6 is slightly larger than the distance in the Y direction between the pair of chamfers 17 provided on both sides in the width direction of the outer peripheral surface 15 of the outer ring 11. This forms a small gap in the Y direction between the guide surfaces 7 and the chamfers 17 of the outer ring 11.

[0028] When torque is applied to the outer joint member 2 in the direction of arrow T in FIG. 3, the outer peripheral surface 15 of the outer ring 11 is pressed against the roller guideway 6 on the left side of the figure. In this embodiment, as described above, the roller guideway 6 is a flat surface and the outer peripheral surface 15 of the outer ring 11 is a cylindrical surface, and therefore they press against each other via a linear contact portion. As a result, the orientation of the outer ring 11 is corrected so that the outer peripheral surface 15 of the outer ring 11 is parallel to the roller guideway 6 in the cross section shown in FIG. 3, and left / right tilt of the outer ring 11 (tilt in the direction of arrow B in FIG. 3) can be suppressed. Furthermore, the guide surface 7 abuts against the chamfer 17 of the outer ring 11 from the Y direction, which restricts the front / rear tilt of the outer ring 11 (tilt in the direction of arrow C in FIG. 1) and further suppresses the left / right tilt of the outer ring 11.

[0029] When torque is applied to the outer joint member 2 in the direction of arrow T in Fig. 3 as described above, the outer peripheral surface 15 of the outer ring 11 is pressed against the roller guideway 6 on the left side in the figure (hereinafter referred to as the "torque-loaded roller guideway 6"), while gaps are formed between the roller guideway 6 on the right side in the figure (hereinafter referred to as the "non-torque-loaded roller guideway 6") and the guide surfaces 7 on both sides of it in the width direction, and the outer peripheral surface 15 and chamfers 17 of the outer ring 11. At this time, if the roller unit 4 tilts and the outer peripheral surface 15 and chamfers 17 of the outer ring 11 come into contact with the roller guideway 6 and guide surfaces 7 on the non-torque-loaded side, the rotational resistance of the outer ring 11 increases.

[0030] Therefore, in this embodiment, the initial gap between the outer ring 11 and the roller guideway 6 (the difference between the spacing W between a pair of opposing roller guideways 6 and the outer diameter of the outer ring 11) and the shape of the guide surface 7 are designed so that, when torque is applied to the outer joint member 2, the outer ring 11 comes into contact with the roller guideway 6 on the torque-loading side, but does not come into contact with the roller guideway 6 on the non-torque-loading side or the guide surfaces 7 on both sides of the roller guideway 6 in the width direction.

[0031] 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.

[0032] A cylindrical portion 18a is provided in an area including the center in the width direction (Y direction) (an area excluding an annular protrusion 18b described later) of the inner peripheral surface 18 of the inner ring 12. The cylindrical portion 18a is fitted onto an outer peripheral surface 33 of the trunnion 32.

[0033] As shown in Figure 3, the outer peripheral surface 33 of the trunnion 32 has a convex curve in a vertical cross section (a cross section on a plane including the axis of the trunnion 32) 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. The center of curvature of the arc 33a is offset from the axis of the trunnion 32 to the opposite side of the arc 33a. The arc 33a of the outer peripheral surface of the trunnion 32 fits into the cylindrical portion 18a of the inner peripheral surface 18 of the inner ring 12 at its apex (end in the X direction), and the gap between the arc 33a and the cylindrical portion 18a of the inner peripheral surface 18 of the inner ring 12 gradually increases from the apex to both sides in the Y direction.

[0034] As shown in Figure 4, the outer circumferential surface 33 of the trunnion 32 has a convex curve in a cross section (a cross section in a plane perpendicular to the axis of the trunnion 32) 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. The center of curvature of the arc 33b is offset toward the arc 33b with respect to the axis of the trunnion 32. The curvature radius R of the arc 33b is smaller than half A / 2 of the maximum diameter (maximum dimension in the torque transmission direction X) of the outer circumferential surface 33 of the trunnion 32 (≈ the radius of the cylindrical portion 18a of the inner circumferential surface 18 of the inner ring 12). The arc 33b of the outer peripheral surface of the trunnion 32 fits into the cylindrical portion 18a of the inner peripheral surface 18 of the inner ring 12 at its top (end in the X direction), and the gap between the arc 33b and the cylindrical portion 18a of the inner peripheral surface 18 of the inner ring 12 gradually increases from the top to both ends in the Z direction. As a result, the outer peripheral surface 33 of the trunnion 32 and the cylindrical portion 18a of the inner peripheral surface 18 of the inner ring 12 are in contact in the X direction, and a gap G is provided between them in the Z direction. In the illustrated example, a flat surface 33c perpendicular to the Z direction is provided in a region of the cross section of the outer peripheral surface 33 of the trunnion 32 that includes both ends in the Z direction. As a result, the gap G in the Z direction between the flat surface 33c of the outer peripheral surface 33 of the trunnion 32 and the cylindrical portion 18a of the inner peripheral surface 18 of the inner ring 12 increases.

[0035] As described above, in this embodiment, the radius of curvature r of the convex curve (arc 33a) in the longitudinal section of the outer peripheral surface 33 of the trunnion 32 shown in Figure 3 and the radius of curvature R of the convex curve (arc 33b) in the transverse section of the outer peripheral surface 33 of the trunnion 32 shown in Figure 4 form different aspherical shapes.

[0036] The inner ring 12 is provided with a cylindrical portion 18a on the inner peripheral surface 18, and the longitudinal and transverse cross sections of the outer peripheral surface of the trunnion 32 have convex curves, which enables the inner ring 12 to oscillate relative to the trunnion 32. As described above, the inner ring 12 and the outer ring 11 are assembled to be relatively rotatable via the needle rollers 13, so the outer ring 11 can oscillate integrally with the inner ring 12 relative to the trunnion 32. In other words, within a plane including the axis of the trunnion 32, the axes of the outer ring 11 and inner ring 12 can tilt relative to the axis of the trunnion 32 (see Figure 6).

[0037] As shown in Figure 6, consider the case where the tripod type constant velocity universal joint 1 rotates at an operating angle θ (the angle formed between the axis of the outer joint member 2 and the axis of the tripod member 3, i.e., the axis of the shaft 8). At this time, the axis of the tripod member 3 is inclined with respect to the axis of the outer joint member 2, but because the roller unit 4 is swingable, it is possible to prevent the outer ring 11 and the roller guideway 6 from intersecting at an angle. As a result, the outer ring 11 rolls horizontally with respect to the roller guideway 6, which makes it possible to reduce induced thrust and sliding resistance and to achieve low vibration in the tripod type constant velocity universal joint 1.

[0038] When torque is applied to the outer joint member 2, the outer peripheral surface 33 of the trunnion 32 is pressed against the inner peripheral surface 18 of the inner ring 12, forming a contact portion P as shown in Fig. 5. In this embodiment, as described above, the radius of curvature R (see Fig. 4) of the arc 33b in the cross section of the outer peripheral surface 33 of the trunnion 32 is smaller than half the maximum diameter A / 2 of the outer peripheral surface 33 of the trunnion 32 (≈ the radius of the cylindrical portion 12a of the inner peripheral surface of the inner ring 12). Therefore, the length in the Z direction of the contact portion P shown in Fig. 5 (i.e., the major axis a of the contact ellipse) can be made shorter than when these radiuses are equal. This reduces the force (moment) that tends to tilt the roller unit 4 including the inner ring 12 with respect to the joint axis.

[0039] As described above, when the major axis a of the contact portion P between the outer peripheral surface 33 of the trunnion 32 and the inner peripheral surface 18 of the inner ring 12 is shortened, the area of ​​the contact portion P is reduced, which raises concerns about an increase in surface pressure at the contact portion P. In this embodiment, the radius of curvature r (see FIG. 3) of the arc 33a in the vertical cross section of the outer peripheral surface 33 of the trunnion 32 is larger than the radius of curvature R (see FIG. 4) of the arc 33a in the horizontal cross section of the outer peripheral surface 33 of the trunnion 32, and is also larger than half the maximum diameter A / 2 of the outer peripheral surface 33 of the trunnion 32. As a result, the length in the Y direction of the contact portion P between the outer peripheral surface 33 of the trunnion 32 and the inner peripheral surface 18 of the inner ring 12 shown in FIG. 5 (i.e., the minor axis b of the contact ellipse) is longer, which makes it possible to suppress an increase in surface pressure.

[0040] As described above, by adjusting the radius of curvature R of the arc 33b in the transverse cross section of the outer peripheral surface 33 of the trunnion 32 and the radius of curvature r of the arc 33a in the longitudinal cross section of the outer peripheral surface 33 of the trunnion 32, it is possible to adjust the ratio of the major axis a to the minor axis b of the contact portion P between the outer peripheral surface 33 of the trunnion 32 and the inner peripheral surface 18 of the inner ring 12. In other words, the radii of curvature r and R are set so that the surface pressure of the contact portion P between the inner ring 12 and the trunnion 32 is kept within an allowable range to ensure durability, while the tilt of the outer ring 11 is kept within an allowable range to sufficiently reduce induced thrust and sliding resistance. Specifically, the radii of curvature r and R are set so that the ratio a / b of the major axis a to the minor axis b of the contact portion P is within a range of 2 to 10, preferably 3 to 6.

[0041] Next, the annular protrusion 18b provided on the inner peripheral surface 18 of the inner ring 12 will be described in detail.

[0042] As shown in FIG. 7, an annular protrusion 18b is provided on the inner peripheral surface 18 of the inner ring 12, on the radially inner side of the cylindrical portion 18a of the joint (the lower side in the Y direction in FIG. 7). In the illustrated example, the annular protrusions 18b are provided on both sides of the cylindrical portion 18a in the radial direction of the joint. As shown enlarged in FIG. 8, the inner diameter d of the annular protrusion 18b is smaller than the inner diameter D of the cylindrical portion 18a (d <D)。

[0043] The annular protrusion 18b is formed, for example, by machining after heat treatment. Specifically, the entire inner peripheral surface 18 of the inner ring 12 is turned to form a cylindrical surface, and then heat treated (hardened). The cylindrical inner peripheral surface 18 is then ground with a grinding wheel having a shape corresponding to the shape of the cylindrical portion 18a and the annular protrusions 18b on both sides thereof, thereby forming the cylindrical portion 18a and the annular protrusions 18b. In this case, both the cylindrical portion 18a and the annular protrusions 18b are ground surfaces and have the same surface roughness.

[0044] Alternatively, the annular protrusion 18b may be formed by machining before the heat treatment. Specifically, the inner peripheral surface 18 of the inner ring 12 is turned to form the cylindrical portion 18a and the annular protrusions 18b on both sides thereof, and after heat treatment (quenching), only the cylindrical portion 18a is ground. In this case, the cylindrical portion 18a is a ground surface, the annular protrusion 18b is a cut surface, and the surface roughness of the cylindrical portion 18a is smaller than that of the annular protrusion 18b.

[0045] FIG. 9 is a cross-sectional view (cross-sectional view taken along line X in FIG. 3) of the inner ring 12 and the leg shaft 32 of the tripod member 3 at the maximum diameter portion of the leg shaft 32. The radius of curvature R of the arc 33b in the cross-section of the outer peripheral surface 33 of the leg shaft 32 is smaller than the radius D / 2 of the cylindrical portion 18a of the inner peripheral surface 18 of the inner ring 12 (R < D / 2). The inner diameter D of the cylindrical portion 18a of the inner peripheral surface 18 of the inner ring 12 is slightly larger than the maximum diameter A of the leg shaft 32 (D > A). Thereby, a gap (this gap is referred to as a "journal gap") is formed between the cylindrical portion 18a of the inner ring 12 and the maximum diameter portion of the leg shaft 32.

[0046] By the way, when the center of curvature of the convex curve (arc 33a) in the longitudinal section of the outer peripheral surface of the leg shaft 32 is offset to the side opposite to the arc 33a with respect to the axis of the leg shaft 32, and this arc 33a fits with the cylindrical portion 18a of the inner peripheral surface 18 of the inner ring 12, the journal gap becomes clogged as the left-right tilt angle (see arrow B in FIG. 3) between the tripod member 3 and the inner ring 12 increases. When the journal gap is too small, the left-right tilt angle becomes large when the constant velocity joint takes a high operating angle, and the gap between the leg shaft 32 and the inner peripheral surface 18 of the inner ring 12 becomes negative and interferes, which may cause deterioration of NVH performance due to generation of abnormal noise and vibration, and early damage. On the contrary, when the journal gap is too large, the circumferential play increases and the NVH performance deteriorates.

[0047] Therefore, in the present embodiment, by setting the journal gap S, that is, the difference between the inner diameter D of the cylindrical portion 18a of the inner ring 12 and the maximum diameter A of the leg shaft 32, to satisfy the following Equation 1 and Equation 2, interference between the leg shaft 32 and the inner peripheral surface 18 of the inner ring 12 can be avoided. In Equation 1 and Equation 2 below, F is the offset amount (see FIG. 3) of the convex curved surface (arc 33a) in the longitudinal cross-section of the leg shaft 32 with respect to the axis of the leg shaft 32, and α is the left-right inclination angle of the axis of the leg shaft 32 with respect to the axis of the inner ring 12 when the constant velocity joint 1 takes the maximum operating angle θ. The maximum operating angle θ of the constant velocity joint 1 is the maximum operating angle during actual use. Specifically, it is the maximum operating angle that occurs during actual driving in a state where the drive shaft including the constant velocity joint 1 is mounted on an automobile. The maximum operating angle θ is set, for example, within the range of 23 to 28 degrees.

[0048] [Equation] [Equation]

[0049] FIG. 10 shows a superposition of the cross-section of the annular protrusion 18b on the inner peripheral surface 18 of the inner ring 12 and the cross-section of the maximum diameter portion of the leg shaft 32. The inner diameter d of the annular protrusion 18b on the inner peripheral surface 18 of the inner ring 12 is slightly smaller than the maximum diameter A of the leg shaft 32 (d < A). Thereby, when the roller unit 4 moves to the shaft end side of the leg shaft 32, the annular protrusion 18b on the inner side in the joint radial direction (the axis side of the tripod member 3) of the inner peripheral surface 18 of the inner ring 12 interferes with the maximum diameter portion of the leg shaft 32, so that further movement of the roller unit 4 including the inner ring 12 to the shaft end side of the leg shaft 32 is restricted, and the dropout of the leg shaft 32 during the assembly of the constant velocity joint 1 can be prevented.

[0050] When assembling the inner ring 12 to the leg shaft 32, the inner ring 12 is externally fitted from the shaft end side of the leg shaft 32, and the maximum diameter portion of the leg shaft 32 is press-fitted into the inner circumference of the annular protrusion 18b on the inner side in the joint radial direction. Thereby, while elastically deforming the annular protrusion 18b of the inner ring 12 and the maximum diameter portion of the leg shaft 32, the maximum diameter portion of the leg shaft 32 gets over the annular protrusion 18b and fits with the cylindrical portion 18a. In the present embodiment, the radius of curvature R of the convex curved surface (arc 33b) in the cross section of the outer peripheral surface 33 of the leg shaft 32 is smaller than the radius D / 2 of the cylindrical portion 18a of the inner peripheral surface 18 of the inner ring 12 (R<D / 2). In the illustrated example, it is smaller than the radius d / 2 of the inner peripheral surface of the annular protrusion 18b of the inner peripheral surface 18 of the inner ring 12 (R<d / 2). Thereby, the interference region between the outer peripheral surface 33 of the leg shaft 32 and the inner peripheral surface 18 of the inner ring 12 is only the region E near the maximum diameter portion (the top of the arc 33a in the longitudinal section and the top of the arc 33b in the cross section) of the leg shaft 32. In this case, compared with the case of press-fitting the entire circumference of the leg shaft 32 into the inner ring 12, the press-fitting load is reduced, so that the assembly of the inner ring 12 to the leg shaft 32 is facilitated.

[0051] Of the annular protrusions 18b provided at both ends in the width direction of the inner peripheral surface 18 of the inner ring 12, the annular protrusion 18b on the outer side in the joint radial direction does not interfere with the maximum diameter portion of the leg shaft 32 and does not contribute to preventing the inner ring 12 from falling off the leg shaft 32. However, by providing the annular protrusions 18b at both ends in the width direction of the inner peripheral surface 18 of the inner ring 12, the inner ring 12 can be made into a shape symmetric with respect to the center in the width direction (line X in FIG. 7). Thereby, when assembling the inner ring 12 to the leg shaft 32, it can be assembled to the leg shaft 32 from either side in the axial direction (the vertical direction in FIG. 7), so that the assembly property is improved.

[0052] If the protruding amount of the annular protrusion 18b with respect to the cylindrical portion 18a is too small, the interference amount with the maximum diameter portion of the leg shaft 32 may be insufficient, and there is a risk that the roller unit 4 cannot be prevented from falling off. Therefore, the protruding amount (D-d) / 2 of the annular protrusion 18b with respect to the cylindrical portion 18a is preferably 0.020 mm or more.

[0053] On the other hand, if the amount of protrusion of the annular protrusion 18b relative to the cylindrical portion 18a is too large, the amount of interference with the maximum diameter portion of the trunnion 32 will be excessive, which may make it difficult to assemble the inner ring 12 to the trunnion 32. Therefore, it is preferable that the amount of protrusion (Dd) / 2 of the annular protrusion 18b relative to the cylindrical portion 18a be 0.100 mm or less.

[0054] The present invention is not limited to the above-described embodiment. Other embodiments of the present invention will be described below. Duplicate explanations of the same points as in the above embodiment will be omitted.

[0055] The shape of the inner ring 12 is not limited to the above. For example, in the above embodiment, the annular protrusions 18b are provided on both widthwise ends of the inner circumferential surface 18 of the inner ring 12, and the inner ring 12 is shaped symmetrically with respect to the center in the widthwise direction, but this is not limiting, and the annular protrusions 18b may be provided only on the inner circumferential surface 18 of the inner ring 12, on the radially inner side of the cylindrical portion 18a, as long as there is no problem with assembly.

[0056] The shapes of the outer ring 11 and the roller guideway 6 are not limited to those described above. For example, the outer peripheral surface of the outer ring 11 may be spherical, and the roller guideway 6 may be cylindrical so as to fit with the spherical outer peripheral surface of the outer ring 11. In this case, the guide surfaces 7 on both sides of the roller guideway 6 in the width direction may be omitted.

[0057] In the above embodiment, the convex curves in the longitudinal and transverse cross sections of the outer circumferential surface of the trunnion 32 are both formed as circular arcs, but this is not limiting. For example, the convex curve in the longitudinal cross section of the outer circumferential surface of the trunnion 32 may be formed as a non-circular curve such as an ellipse. In this case, the radius of curvature of the convex curve (ellipse) in the longitudinal cross section of the outer circumferential surface of the trunnion 32 at least at both ends in the torque transmission direction (i.e., the contact portions with the inner ring 12) is larger than the radius of curvature R of the convex curve (arc 33b) in the transverse cross section of the outer circumferential surface of the trunnion 32, and is preferably larger than half (A / 2) of the maximum dimension A of the trunnion 32 in the torque transmission direction X.

[0058] The convex curve in the cross section of the outer circumferential surface of the trunnion 32 may be a non-circular curve such as an ellipse. In this case, the radius of curvature of the convex curve (ellipse) in the cross section of the outer circumferential surface of the trunnion 32 at least at both ends in the torque transmission direction (i.e., the contact portions with the inner ring 12) is smaller than half (A / 2) of the maximum dimension A of the trunnion 32 in the torque transmission direction X.

[0059] Furthermore, both the convex curves in the longitudinal and transverse cross sections of the outer circumferential surface of the trunnion 32 may be non-circular curves such as ellipses. In this case, the radius of curvature of the convex curve (ellipse) in the longitudinal cross section of the outer circumferential surface of the trunnion 32 at least at both ends in the torque transmission direction (i.e., the contact portions with the inner ring 12) is larger than the radius of curvature of the convex curve (ellipse) in the transverse cross section of the outer circumferential surface of the trunnion 32 at least at both ends in the torque transmission direction (i.e., the contact portions with the inner ring 12). Preferably, the radius of curvature of the convex curve (ellipse) in the longitudinal cross section of the outer circumferential surface of the trunnion 32 at least at both ends in the torque transmission direction is larger than half (A / 2) of the maximum dimension A of the trunnion 32 in the torque transmission direction X, and the radius of curvature of the convex curve (ellipse) in the transverse cross section of the outer circumferential surface of the trunnion 32 at least at both ends in the torque transmission direction is smaller than half (A / 2) of the maximum dimension A of the trunnion 32 in the torque transmission direction X.

[0060] In addition, in the above embodiment, as shown in Figure 4, flat surfaces 33c are provided on both ends of the leg axle 32 in the joint axis direction, but even if there is no flat surface 33c, the flat surface 33c may be omitted if a sufficient gap is formed between the leg axle 32 and the inner ring 12 in the joint axis direction to allow the roller unit 4 to oscillate relative to the leg axle 32.

[0061] 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]

[0062] 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 18 Inner surface 18a Cylindrical part 18b Annular protrusion 31 Torso 32 Leg axis 33 Outer surface 33a Arc (convex curve) 33b Arc (convex curve) 33c flat surface

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 and extending in a joint axial direction; a tripod member arranged on an inner peripheral surface of the outer joint member and having three trunnions projecting in a joint radial direction toward the track grooves; and three roller units each having a roller arranged on an outer periphery of the trunnion and an inner ring arranged between the roller and the trunnion, the three roller units being rotatably and swingably supported by the trunnion and housed in the track grooves, the outer peripheral surface of the trunnion has a convex curve that bulges out on both sides in the torque transmission direction in a longitudinal section and a transverse section, an inner peripheral surface of the inner ring including a cylindrical portion that fits onto an outer peripheral surface of the trunnion; and an annular protrusion that is provided radially inward of the cylindrical portion, protrudes radially inward beyond the cylindrical portion, and has an inner diameter smaller than the maximum diameter of the outer peripheral surface of the trunnion; A tripod-type constant velocity universal joint, wherein the radius of curvature (R) of the convex curve in the cross section of the outer peripheral surface of the trunnion at both ends in the torque transmission direction is smaller than the radius (D / 2) of the cylindrical portion of the inner peripheral surface of the inner ring.

2. 2. The tripod-type constant velocity universal joint according to claim 1, wherein the radius of curvature (r) of the convex curve in the longitudinal cross section of the outer peripheral surface of the trunnion at both ends in the torque transmission direction is larger than the radius of curvature (R) of the convex curve in the transverse cross section of the outer peripheral surface of the trunnion at both ends in the torque transmission direction.

3. The roller has a cylindrical outer circumferential surface, A pair of roller guide surfaces, each consisting of flat surfaces parallel to each other and facing each other in the joint circumferential direction, is provided in each track groove; 3. A tripod-type constant velocity universal joint according to claim 1, wherein a pair of guide surfaces capable of contacting the roller from both sides in the axial direction thereof are provided on both sides in the width direction of the roller guide surface.

4. 3. The tripod-type constant velocity universal joint according to claim 1, wherein another annular protrusion is provided on the inner peripheral surface of the inner ring, radially outward of the cylindrical portion, protruding radially inward from the cylindrical portion and having an inner diameter smaller than the maximum diameter of the outer peripheral surface of the trunnion.

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

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

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