Tripod constant velocity universal joint

Abstract

A roller 11 has a cylindrical surface-shaped outer peripheral surface, and a pair of roller guide surfaces 6 of each track groove 5 are flat surfaces parallel to each other. A pair of guide surfaces 7 capable of abutting on the roller 11 from both sides in the axial direction are provided on both sides of the roller guide surface 6 in the width direction. An inner ring 12 has a cylindrical surface-shaped inner peripheral surface 18. An outer peripheral surface 33 of a leg shaft 32 has, in a longitudinal cross-section and a transverse cross-section thereof, arcs 33a, 33b that bulge out toward both sides in a torque transmission direction. A curvature radius r of the arc 33a in the longitudinal cross-section of the outer peripheral surface 33 of the leg shaft 32 is larger than a curvature radius R of the arc 33b in the transverse cross-section. An inner flat surface 8a is provided at the center, in a joint circumferential direction, of a large inner diameter part 8 of an inner peripheral surface of an outer joint member 2. A ratio L / W between an interval W between the pair of roller guide surfaces 6 and a width L of the inner flat surface 8a is 0.50 or more.

Description

Tripod constant velocity joint

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

[0002] In a drive shaft used in an automobile power transmission system, a sliding constant velocity joint is often provided on the inboard side (center side in the vehicle width direction), and a fixed constant velocity joint is provided on the outboard side (outer side in the vehicle width direction). The sliding constant velocity joint here allows both angular displacement and axial relative movement between two shafts, and the fixed constant velocity joint allows angular displacement between two shafts but does not allow axial relative movement between two shafts.

[0003] A tripod constant velocity joint is known as a sliding constant velocity joint. As the tripod constant velocity joint, there are a single roller type and a double roller type. The single roller type is one in which rollers inserted into the track groove of the outer joint member are rotatably attached to the leg shafts of the tripod member via a plurality of needle rollers. The double roller type includes a roller inserted into the track groove of the outer joint member and an inner ring that fits over the leg shaft of the tripod member and rotatably supports the roller. The double roller type has the advantage that it can reduce the induced thrust (axial force induced by friction between components inside the joint) and the slide resistance respectively compared to the single roller type because the roller can be swung with respect to the leg shaft.

[0004] As a double roller type tripod constant velocity joint, there is one in which the cross-sectional shape (a cross-section perpendicular to the axis of the leg shaft) of the outer peripheral surface of the leg shaft is elliptical and the longitudinal cross-sectional shape of the inner peripheral surface of the inner ring is a convex arc shape (see Patent Document 1 below), and one in which the outer peripheral surface of the leg shaft is spherical and the inner peripheral surface of the inner ring (holder) is cylindrical (see Patent Document 2 below).

[0005] Furthermore, Patent Document 3, described below, shows a double-roller type tripod-type constant velocity universal joint having a different structure from the above. The basic structure of this constant velocity universal joint 101 is the same as that of a general tripod-type constant velocity universal joint, and as shown in Figure 10, it has an outer joint member 102, a tripod member 103 housed in the inner circumference of the outer joint member 102 and having three leg shafts 132 protruding outwards, and a roller unit 104 mounted on each leg shaft 132 of the tripod member 103 and housed in the track groove 105 of the outer joint member 102. The roller unit 104 has a roller 111 and an inner ring 112 and is housed in the track groove 105 of the outer joint member 102.

[0006] In this constant velocity universal joint 101, as shown in Figures 11 and 12, the roller 111 has a cylindrical outer surface 115, and the roller guide surface 106 of the track groove 105 is a flat surface. On both sides in the width direction of the roller guide surface 106, a pair of tapered guide surfaces 107 are provided that can contact the roller 111 from both sides in the axial direction of itself. The outer surface 133 of the leg shaft 132 of the tripod member 103 has arcs 133a and 133b in the longitudinal section (see Figure 11) and the transverse section (see Figure 12). The radius of curvature r of the arc 133a in the longitudinal section of the outer surface 133 of the leg shaft 132 is greater than the radius of curvature R of the arc 133b in the transverse section. The inner surface 118 of the inner ring 112 is a cylindrical surface and contacts the torque transmission direction (X direction) end of the outer surface 133 of the leg shaft 132. With the above configuration, the tilt of the roller 111 during the operation of the constant velocity universal joint can be suppressed, thereby reducing induced thrust and sliding resistance and improving NVH characteristics.

[0007] Japanese Patent Publication No. 2000-320563, Japanese Patent Publication No. 2957121, Japanese Patent Publication No. 2024-086274

[0008] In tripod-type constant velocity universal joints, a phenomenon occurs in which the roller unit 104 tilts in the direction of arrow B in a cross section perpendicular to the joint axis direction (see Figure 11) (hereinafter referred to as "left-right tilt"), and a phenomenon occurs in which the roller unit 104 tilts in the direction of arrow C in a cross section parallel to the joint axis direction (see Figure 10) (hereinafter referred to as "front-back tilt"). In the tripod-type constant velocity universal joint 101 with the structure shown in Figures 10 to 12, left-right tilt is suppressed by bringing the cylindrical outer surface 115 of the roller 111 into contact with the flat roller guide surface 106 of the track groove 105 of the outer joint member 102, and front-back tilt of the roller 111 is suppressed by bringing the chamfered portions 117 at both axial ends of the outer surface of the roller 111 into contact with tapered guide surfaces 107 provided on both sides of the roller guide surface 106. Therefore, the shape accuracy of the roller guide surface 106 and guide surface 107 of the track groove 105 greatly affects the posture of the roller 111 and, consequently, the NVH characteristics of the constant velocity universal joint 101.

[0009] When torque is applied to a constant velocity universal joint, deformation occurs in each component of the constant velocity universal joint. When torque is applied to the constant velocity universal joint 101, and the guide surface 107 of the track groove 105 of the outer joint member 102 deforms significantly, the posture of the roller 111 may be disrupted, increasing the tilt angle of the roller 111, or the contact between the tapered guide surface 107 and the chamfered portion 117 of the roller 111 may become uneven, increasing sliding resistance, which can worsen the NVH characteristics. The greater the torque applied to the constant velocity universal joint, the greater the deformation of the outer joint member 102, so in the constant velocity universal joint of the above structure, the NVH characteristics deteriorate significantly when a large torque is applied.

[0010] For example, increasing the outer diameter or wall thickness of the outer joint member can reduce the amount of deformation under torque load, but this leads to an increase in the size and weight of the constant velocity universal joint.

[0011] For the reasons described above, the present invention aims to prevent deterioration of NVH characteristics by reducing the amount of deformation of the outer joint member under torque load without increasing size or weight, in a tripod-type constant velocity universal joint that maintains the posture of a roller by bringing the cylindrical outer surface and chamfered portion of the roller into contact with a flat roller guide surface and a pair of guide surfaces provided on both sides thereof.

[0012] As shown in Figure 13, the outer joint member of a tripod-type constant velocity universal joint often has a cylindrical surface on the large inner diameter portion 108 (the outer diameter side of the track groove 105). When torque is applied to such an outer joint member 202, a load Q is applied to the roller guide surface 106 that contacts the roller. At this time, as shown by the dotted line in Figure 14, the load Q causes the roller guide surface 106 to tilt outward (to the left in the figure) (see part S1 in Figure 14), the circumferential end of the large inner diameter portion 108 is pulled outward (to the left in the figure) (see part S2 in Figure 14), and as a result, the circumferential center of the large inner diameter portion 108 is displaced inward (to the lower side in the figure) (see part S3 in Figure 14).

[0013] The inventors focused on the deformation modes of the outer joint member under torque load as described above, and considered that the deformation near the roller guide surface could be suppressed by the shape of the large inner diameter surface of the outer joint member, leading to the invention described below.

[0014] The present invention relates to a tripod-type constant velocity universal joint comprising: an outer joint member having three track grooves formed on its inner circumferential surface extending in the direction of the joint axis, with a pair of roller guide surfaces facing each other in the circumferential direction of the joint provided in each track groove; a tripod member disposed on the inner circumference of the outer joint member and having three leg shafts projecting in the radial direction of the joint toward the track grooves; and three roller units having rollers disposed on the outer circumference of the leg shafts and inner rings disposed between the rollers and the leg shafts, supported on the leg shafts in a rotatable and swingable manner and housed in the track grooves, wherein the rollers have a cylindrical outer circumferential surface, the pair of roller guide surfaces of each track groove are parallel flat surfaces, a pair of guide surfaces are provided on both sides in the width direction of the roller guide surfaces so as to be able to contact the rollers from both sides in the axial direction, and the inner rings have a cylindrical inner circumferential surface. The outer circumferential surface of the leg shaft has a convex curve that bulges out on both sides in the torque transmission direction in a longitudinal section including the axis of the leg shaft and a cross section perpendicular to the axis of the leg shaft, the convex curve in the cross section of the outer circumferential surface of the leg shaft moves away from the cylindrical inner circumferential surface of the inner ring as it goes from the torque transmission direction end to both sides in the coupling axis direction, the radius of curvature (r) at both ends in the torque transmission direction of the convex curve in the longitudinal section of the outer circumferential surface of the leg shaft is greater than the radius of curvature (R) at both ends in the torque transmission direction of the convex curve in the cross section of the outer circumferential surface of the leg shaft, an inner flat surface is provided at the center of the coupling circumferential direction of the outer diameter side surface of the track groove of the outer coupling member, and the ratio L / W of the distance W between the pair of roller guide surfaces to the width L of the inner flat surface is 0.50 or more.

[0015] As described above, in the tripod-type constant velocity universal joint of the present invention, an inner flat surface of a predetermined width or greater is provided at the center of the joint circumferential direction of the outer diameter side surface of the track groove of the outer joint member (hereinafter referred to as the "large inner diameter portion"). This makes it possible to suppress the displacement of the large inner diameter portion toward the inner diameter when torque is applied, compared to the case where the large inner diameter portion is a cylindrical surface as shown in Figure 13. When torque is applied to this constant velocity universal joint and a load is applied to the roller guide surface, the inner flat surface at the center of the joint circumferential direction of the large inner diameter portion hardly displaces toward the inner diameter, so that the end of the joint circumferential direction of the large inner diameter portion is less likely to be pulled outward, thereby suppressing the roller guide surface from tilting outward. In this way, by suppressing the deformation of the roller guide surface and the pair of guide surfaces provided on both sides thereof, the contact state between them and the roller is stabilized, so that the collapse of the roller's posture and sliding resistance are suppressed and the NVH characteristics are improved.

[0016] An outer flat surface may be provided in the circumferential region of the inner flat surface of the outer joint member.

[0017] The roller maintains its position by contacting the roller guide surface and guide surface of the track groove. However, in order to allow the roller to roll within the track groove, a small gap is provided between the roller and the roller guide surface and guide surface of the outer joint member. As a result, the roller may tilt relative to the outer joint member by the amount of this gap. If the roller tilts and comes into contact with the large inner diameter portion of the outer joint member, the sliding resistance increases and the NVH characteristics deteriorate. Therefore, it is preferable to set the radial position of the large inner diameter portion such that the roller does not come into contact with the inner flat surface when the roller experiences the maximum front-to-back tilt angle α (see Figure 7) relative to the outer joint member.

[0018] In this case, by reducing the maximum front-to-back tilt angle of the roller relative to the outer joint member (for example, to 7° or less), the inner flat surface of the large inner diameter portion of the outer joint member can be moved towards the inner diameter side while avoiding contact with the roller. As a result, the width of the inner flat surface can be increased, making it less likely for the inner flat surface to displace further towards the inner diameter side when torque is applied, and further increasing the rigidity of the roller guide surface and guide surface of the outer joint member.

[0019] As described above, according to the present invention, in a tripod-type constant velocity universal joint that maintains the roller's posture by bringing the cylindrical outer surface and chamfered portion of the roller into contact with a flat roller guide surface and a pair of guide surfaces provided on both sides thereof, it is possible to reduce the amount of deformation of the outer joint member under torque load and prevent deterioration of NVH characteristics without increasing size or weight.

[0020] This is a cross-sectional view in the joint axis direction of a tripod-type constant velocity universal joint according to one embodiment of the present invention. This is a cross-sectional view along the line K-K in Figure 1. This is an enlarged view of Figure 2. This is a cross-sectional view showing only the outer joint member of Figure 3. This is a cross-sectional view along the line M-M in Figure 1. This is a cross-sectional view showing the tripod-type constant velocity universal joint of Figure 1 in the state where it has taken an operating angle θ. This is a cross-sectional view in the joint axis direction showing the state in which the roller has reached its maximum front-to-back tilt angle α. This is a cross-sectional view along the line K-K in Figure 7. This is a cross-sectional view of the outer joint member according to another embodiment. This is a cross-sectional view in the joint axis direction of a conventional tripod-type constant velocity universal joint. This is a cross-sectional view along the line K-K in Figure 10. This is a cross-sectional view along the line M-M in Figure 10. This is a cross-sectional view of an outer joint member in which the large inner diameter portion is a cylindrical surface. This is a cross-sectional view showing the state when torque is applied to the outer joint member of Figure 13.

[0021] Embodiments of the present invention will be described based on the drawings.

[0022] A tripod-type constant velocity universal joint 1 according to one embodiment of the present invention is of the double-roller type and comprises an outer joint member 2, a tripod member 3, and a roller unit 4, as shown in Figures 1 and 2. In this specification, the direction of the axis O of the tripod-type constant velocity universal joint 1 when the operating angle is 0° (left-right direction in Figure 1) is referred to as the "joint axis direction," and the circumferential and radial directions of the circle centered on the axis O at this time are referred to as the "joint circumferential direction" and the "joint radial direction," respectively.

[0023] The outer joint member 2 has a cup shape with one end open in the joint axial direction and the other end closed (see Figure 1). Three linear track grooves 5 extending in the joint axial direction are formed on the inner circumferential surface of the outer joint member 2 at equal intervals in the joint circumferential direction (see Figure 2). Each track groove 5 has a pair of roller guide surfaces 6 arranged opposite each other in the joint circumferential direction. Each roller guide surface 6 extends in the joint axial direction. The tripod member 3 and the roller unit 4 are housed inside the outer joint member 2.

[0024] The tripod member 3 integrally comprises a body portion 31 having a central hole 30 and three leg shafts 32 projecting radially from three equally spaced positions in the circumferential direction of the joint on the outer surface of the body portion 31. By fitting the male splines formed on the shaft 10 into the female splines formed in the central hole 30 of the body portion 31 and fixing them in the axial direction of the joint with a retaining ring 21, the tripod member 3 and the shaft 10 are coupled in a manner that enables torque transmission.

[0025] The roller units 4 are provided on the outer circumference of each leg shaft 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 comprises an annular roller 11 centered on the axis of the leg shaft 32, an annular inner ring 12 arranged on the inner circumference of the roller 11 and fitted onto the leg shaft 32, and a plurality of rolling elements 13 interposed between the roller 11 and the inner ring 12. In this embodiment, a large number of needle rollers in a full-roller configuration without cages are used as the plurality of rolling elements 13. The needle rollers 13 are arranged to roll freely between the outer and inner raceway surfaces, with the cylindrical inner surface of the roller 11 serving as the outer raceway surface and the cylindrical outer surface of the inner ring 12 serving as the inner raceway surface. The roller 11, inner ring 12, and needle rollers 13 are constructed to not disassemble naturally by a pair of snap rings 14, and these constitute the roller unit 4.

[0026] A boot 22 is fitted to the opening of the outer joint member 2. The larger diameter end of the boot 22 is fixed near the opening end of the outer circumferential surface of the outer joint member 2, and the smaller diameter end of the boot 22 is fixed to the outer circumferential surface of the shaft 10. Grease is sealed inside the outer joint member 2, which is closed by the boot 22.

[0027] The structure of the fitting portion between the roller 11 and the track groove 5 will be explained in detail below using Figures 3 to 5. In Figures 3 to 5, the coupling axis direction is shown as the Z direction, the axis direction of the leg shaft 32 is shown as the Y direction, and the torque transmission direction perpendicular to both the coupling axis direction Z and the leg shaft axis direction Y is shown as the X direction.

[0028] The roller 11 has a cylindrical outer surface 15. The end faces 16 on both sides of the roller 11 in the width direction (Y direction) are flat surfaces perpendicular to their own axis (see Figure 3). The cylindrical outer surface 15 and the end faces 16 of the roller 11 are continuous via tapered chamfers 17. The chamfers 17 are smoothly connected to the cylindrical outer surface 15 and the end faces 16 via a convex curved surface with a curved cross-section (for example, an arc shape).

[0029] The pair of roller guide surfaces 6 of each track groove 5 of the outer joint member 2 are flat surfaces parallel to each other (see Figure 4). A pair of guide surfaces 7 are provided on both sides of each roller guide surface 6 in the width direction (Y direction). The guide surfaces 7 are flat surfaces parallel to the joint axis direction and inclined with respect to the roller guide surface 6. The shapes of the roller guide surface 6 and the guide surfaces 7 follow the shapes of the cylindrical outer surface 15 and chamfer 17 of the roller 11.

[0030] In the cross-sections shown in Figures 3 and 4, the roller guide surface 6 is parallel to the cylindrical outer surface 15 of the roller 11, and the distance W (see Figure 4) between a pair of opposing roller guide surfaces 6 is slightly larger than the diameter of the cylindrical outer surface 15 of the roller 11. As a result, a small gap in the X direction is formed between the roller guide surface 6 and the cylindrical outer surface 15 of the roller 11.

[0031] In the cross-sections shown in Figures 3 and 4, the guide surface 7 is substantially parallel to the tapered chamfer 17 of the roller 11. The guide surface 7 smoothly connects to the roller guide surface 6 via a concave curved surface with a curved cross-section (for example, an arc shape). The distance in the Y direction between the pair of guide surfaces 7 provided on both sides in the width direction of the roller guide surface 6 is slightly greater than the distance in the Y direction between the pair of chamfers 17 provided on both sides in the width direction of the cylindrical outer peripheral surface 15 of the roller 11. As a result, a small gap in the Y direction is formed between the guide surface 7 and the chamfer 17 of the roller 11.

[0032] When torque is applied to the outer joint member 2, the cylindrical outer surface 15 of the roller 11 is pressed against the flat roller guide surface 6. As a result, the orientation of the roller 11 is corrected so that the cylindrical outer surface 15 of the roller 11 is parallel to the roller guide surface 6 in the cross-section shown in Figure 3, thereby suppressing the lateral tilt of the roller 11 (tilt in the direction of arrow B). In addition, the chamfer 17 of the roller 11 comes into contact with the guide surface 7, which further suppresses the lateral tilt of the roller 11, as well as the forward and backward tilt of the roller 11 (tilt in the direction of arrow C in Figure 7).

[0033] Furthermore, when torque is applied to the outer joint member 2 in the direction of arrow T in Figure 3, the cylindrical outer surface 15 of the roller 11 is pressed against the roller guide surface 6 on the left side of the figure (hereinafter referred to as the "torque-loaded roller guide surface"), while the roller 11 is not pressed against the roller guide surface 6 opposite to it (hereinafter referred to as the "torque-unloaded roller guide surface") and the guide surfaces 7 on both sides in the width direction. At this time, if the roller unit 4 tilts and the cylindrical outer surface 15 or chamfer 17 of the roller 11 come into contact with the torque-unloaded roller guide surface 6 or guide surface 7, the rotational resistance of the roller 11 increases.

[0034] Therefore, in this embodiment, when torque is applied to the outer joint member 2, the initial gap between the roller 11 and the roller guide surface 6 (the difference between the distance W between the opposing pair of roller guide surfaces 6 and the outer diameter of the roller 11), and the shape of the guide surface 7 are designed so that the roller 11 contacts the roller guide surface 6 on the torque-loaded side, while not contacting the roller guide surface 6 on the non-torque-loaded side or the guide surfaces 7 on both sides of it in the width direction.

[0035] Next, the structure of the fitting portion between the inner ring 12 and the leg shaft 32 will be explained in detail using Figures 3 and 5.

[0036] The inner ring 12 has a cylindrical inner surface 18 that fits with the outer surface 33 of the leg shaft 32.

[0037] The outer circumferential surface 33 of the leg shaft 32 has a convex curve that bulges out on both sides in the torque transmission direction X in the longitudinal section (cross-section in the plane containing the axis of the leg shaft 32) shown in Figure 3. In the illustrated example, the convex curve in the longitudinal section of the outer circumferential surface of the leg shaft 32 is composed of a circular arc 33a with a radius of curvature r. The center of curvature of the circular arc 33a is offset from the axis of the leg shaft 32 to the opposite side of the circular arc 33a. The circular arc 33a of the outer circumferential surface of the leg shaft 32 fits with the cylindrical inner surface 18 of the inner ring 12 at its apex (X-direction end), and moves away from the cylindrical inner surface 18 of the inner ring 12 as it moves from the apex to both sides in the Y-direction.

[0038] The outer circumferential surface 33 of the leg shaft 32 has a convex curve that bulges out on both sides in the torque transmission direction X in the cross-section shown in Figure 5 (a cross-section in a plane perpendicular to the axis of the leg shaft 32). In the illustrated example, the convex curve in the cross-section of the outer circumferential surface of the leg shaft 32 is composed of a circular arc 33b with a radius of curvature R. The center of curvature of the circular arc 33b is offset toward the circular arc 33b side with respect to the axis of the leg shaft 32. The radius of curvature R of the circular arc 33b is smaller than half A / 2 of the maximum diameter A of the outer circumferential surface 33 of the leg shaft 32 (maximum dimension of the outer circumferential surface 33 in the torque transmission direction X ≈ diameter of the cylindrical inner surface 18 of the inner ring 12). The circular arc 33b of the outer circumferential surface of the leg shaft 32 fits with the cylindrical inner surface 18 of the inner ring 12 at its apex (X-direction end), and moves away from the cylindrical inner surface 18 of the inner ring 12 as it moves toward both sides in the Z-direction from the apex. As a result, the outer circumferential surface 33 of the leg shaft 32 and the cylindrical inner 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 the region of the cross-section of the outer circumferential surface 33 of the leg shaft 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 circumferential surface 33 of the leg shaft 32 and the cylindrical inner surface 18 of the inner ring 12 is increased.

[0039] As described above, in this embodiment, the radius of curvature r of the convex curve (arc 33a) in the longitudinal section of the outer circumferential surface 33 of the leg shaft 32 shown in Figure 3 is greater than the radius of curvature R of the convex curve (arc 33b) in the cross section of the outer circumferential surface 33 of the leg shaft 32 shown in Figure 4, resulting in an aspherical shape.

[0040] The inner ring 12 is provided with a cylindrical inner surface 18, and the longitudinal and transverse sections of the outer surface of the leg shaft 32 have convex curves, allowing the inner ring 12 to pivot relative to the leg shaft 32. As described above, the inner ring 12 and the roller 11 are assembled to be rotatable relative to each other via the needle roller 13, so the roller 11 can pivot together with the inner ring 12 relative to the leg shaft 32. In other words, within a plane containing the axis of the leg shaft 32, the axes of the roller 11 and the inner ring 12 can be inclined with respect to the axis of the leg shaft 32 (see Figure 6).

[0041] As shown in Figure 6, consider the case where the tripod-type constant velocity universal joint 1 rotates with an operating angle θ (the angle between the axis of the outer joint member 2 and the axis of the tripod member 3). In this case, 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 oscillating, it is possible to avoid a state where the roller 11 and the roller guide surface 6 are at an oblique angle. As a result, the roller 11 rolls horizontally with respect to the roller guide surface 6, which reduces induced thrust and sliding resistance, and enables low vibration of the tripod-type constant velocity universal joint 1.

[0042] The basic structure of the tripod-type constant velocity universal joint 1 of this embodiment is as described above. Below, the shape of the large inner diameter portion 8 (the outer diameter side surface of the track groove 5), which is a characteristic feature of the present invention, will be described in detail.

[0043] As shown in Figures 3 and 4, a flat surface (inner flat surface 8a) is provided at the center of the large inner diameter portion 8 on the inner circumferential surface of the outer joint member 2 in the joint circumferential direction (hereinafter also simply referred to as the "circumferential direction"). In the illustrated example, the large inner diameter portion 8 is formed with an inner flat surface 8a provided at the center in the circumferential direction and guide surfaces 7 provided at both ends in the circumferential direction. The inner flat surface 8a and the guide surfaces 7 are smoothly connected via a concave curved surface 8b with a curved cross-section (for example, an arc shape). The inner flat surface 8a, the concave curved surface 8b, and the guide surfaces 7 are formed over the entire axial area of ​​the track groove 5 and have the cross-sectional shape shown in Figure 4 over the entire axial area.

[0044] The width L (dimension in the X direction) of the inner flat surface 8a is set such that the ratio L / W with the distance W between the pair of roller guide surfaces facing each other is 0.5 or more. In the illustrated example, both ends in the width direction of the inner flat surface 8a are arranged on the outer diameter side with respect to the center of the thickness in the radial direction of the inner ring 12. In the present embodiment, since the distance between the pair of guide surfaces 7 provided on both sides in the circumferential direction (X direction) of the inner flat surface 8a widens toward the inner diameter side, the width L of the inner flat surface 8a can be increased as the inner flat surface 8a is moved closer to the inner diameter side. Thus, by adjusting the position of the joint in the radial direction of the inner flat surface 8a, the width L of the inner flat surface 8a can be adjusted.

[0045] Also, the width L of the inner flat surface 8a can be adjusted by adjusting the radius of curvature of the concave curved surface 8b that connects the inner flat surface 8a and the guide surface 7. That is, by reducing the radius of curvature of the concave curved surface 8b, the width L of the inner flat surface 8a can be increased.

[0046] As shown in FIG. 2, in the outer peripheral surface of the outer joint member 2, a recess 9a is formed in the circumferential intermediate region of the track groove 5, and an outer flat surface 9b is provided in the circumferential region of the track groove 5. The outer flat surface 9b is provided in the circumferential region that overlaps the inner flat surface 8a.

[0047] When a torque in the direction of arrow T in FIG. 3 is applied to the outer joint member 2, the roller guide surface 6 on the torque load side on the left side in the figure receives a load Q from the roller 11 (see FIG. 4), and this load Q causes the roller guide surface 6 on the torque load side to deform so as to fall outward (left side in the figure). At this time, since an inner flat surface 8a having a width L of a predetermined value or more is provided at the center in the circumferential direction of the large inner diameter portion 8 of the outer joint member 2, compared with the case where the large inner diameter portion is a cylindrical surface (see FIG. 14), the center in the circumferential direction of the large inner diameter portion 8 is less likely to be displaced toward the inner diameter side. Therefore, the vicinity of the circumferential end portion of the large inner diameter portion 8 (the region where the guide surface 7 is formed) is less likely to be pulled outward, and the fall of the roller guide surface 6 on the torque load side to the outside can be suppressed.

[0048] As described above, the roller 11 is held in position by contacting the roller guide surface 6 and the guide surface 7. However, in order to allow the roller 11 to roll in the track groove 5, minute gaps are provided respectively between the roller 11 and the track groove 5, specifically, between the cylindrical outer peripheral surface 15 and the chamfer 17 of the roller 11 and the roller guide surface 6 and the guide surface 7 of the track groove 5. Therefore, the roller 11 can tilt within the track groove 5 by the amount of this gap.

[0049] In the present embodiment, as shown in FIGS. 7 and 8, when the maximum forward and backward tilt angle α occurs in the roller 11, the distance J (see FIGS. 4 and 7) between the inner flat surface 8a and the axis O is set so that the roller 11 does not contact the inner flat surface 8a of the large inner diameter portion 8 of the outer joint member 2. In this case, if the maximum forward and backward tilt angle α of the roller 11 is large, the inner flat surface 8a needs to be displaced outward in diameter to a position where it does not contact the roller 11, so the distance J between the inner flat surface 8a and the axis O increases. In the present embodiment, the maximum forward and backward tilt angle α of the roller 11 is reduced by making the gap between the roller 11 and the roller guide surface 6 and the guide surface 7 as small as possible. Specifically, the maximum forward and backward tilt angle α of the roller 11 is set to 7° or less. Thereby, while avoiding interference with the roller 11, the inner flat surface 8a can be brought closer to the inner diameter side to reduce the distance J from the axis O, so that the width L of the inner flat surface 8a can be increased.

[0050] The present invention is not limited to the above-described embodiment. Other embodiments of the present invention will be described below, and redundant descriptions of the same points as those in the above-described embodiment will be omitted.

[0051] In the embodiment shown in FIG. 9, a cylindrical surface 9c centered on the axis O is provided in the circumferential region of the outer peripheral surface of the outer joint member 2 that overlaps with the inner flat surface 8a of the large inner diameter portion 8. Thus, by making the outer peripheral surface of the outer joint member 2 a cylindrical surface, the shape of the large-diameter side end portion of the boot 22 can be simplified, and the adhesion with the boot 22 is improved, enhancing the sealing performance. Incidentally, the recess 9a on the outer peripheral surface of the outer joint member 2 may also be omitted, and the entire outer peripheral surface of the outer joint member 2 may be a cylindrical surface.

[0052] In the above embodiment, the case in which both the longitudinal section and the transverse section of the outer surface of the leg shaft 32 are composed of circular arcs is shown, but it is not limited to this. For example, one or both of the convex curves in the longitudinal section and the convex curves in the transverse section of the outer surface of the leg shaft 32 may be composed of non-circular curves such as ellipses.

[0053] Furthermore, in the above embodiment, as shown in Figure 5, a case is shown in which flat surfaces 33c are provided at both ends of the leg shaft 32 in the coupling axial direction. However, even without the flat surfaces 33c, if a sufficient gap is formed between the leg shaft 32 and the inner ring 12 in the coupling axial direction to allow the roller unit 4 to swing relative to the leg shaft 32, the flat surfaces 33c may be omitted.

[0054] The tripod-type constant velocity universal joint 1 described above is not limited to automobile drive shafts, but can be widely used in power transmission paths for automobiles, industrial equipment, and the like.

[0055] 1. Tripod type constant velocity universal joint 2. Outer joint member 3. Tripod member 4. Roller unit 5. Track groove 6. Roller guide surface 7. Guide surface 8. Large inner diameter section 8a. Inner flat surface 8b. Concave curved surface 9b. Outer flat surface 10. Shaft 11. Roller 12. Inner ring 31. Body section 32. Leg axis 33a. Arc (convex curve) 33b. Arc (convex curve)

Claims

1. A tripod-type constant velocity universal joint comprising: an outer joint member having three track grooves formed on its inner circumferential surface extending in the direction of the joint axis, with a pair of roller guide surfaces facing each other in the direction of the joint circumference provided in each track groove; a tripod member disposed on the inner circumference of the outer joint member and having three leg shafts projecting in the direction of the joint radius toward the track grooves; and three roller units having rollers disposed on the outer circumference of the leg shafts and inner rings disposed between the rollers and the leg shafts, supported on the leg shafts in a rotatable and swingable manner and housed in the track grooves, wherein the rollers have a cylindrical outer circumferential surface, the pair of roller guide surfaces of each track groove are flat surfaces parallel to each other, a pair of guide surfaces are provided on both sides in the width direction of the roller guide surfaces, capable of contacting the rollers from both sides in the axial direction, and the inner rings have a cylindrical inner circumferential surface. A tripod-type constant velocity universal joint wherein the outer circumferential surface of the leg shaft has a convex curve that bulges out on both sides in the torque transmission direction in a longitudinal section including the axis of the leg shaft and a cross section perpendicular to the axis of the leg shaft, the convex curve in the cross section of the outer circumferential surface of the leg shaft moves away from the cylindrical inner circumferential surface of the inner ring as it goes from the torque transmission direction end to both sides in the joint axis direction, the radius of curvature (r) at both ends in the torque transmission direction of the convex curve in the longitudinal section of the outer circumferential surface of the leg shaft is greater than the radius of curvature (R) at both ends in the torque transmission direction of the convex curve in the cross section of the outer circumferential surface of the leg shaft, an inner flat surface is provided at the center in the joint circumferential direction of the side surface on the outer diameter side of the track groove of the outer joint member, and the ratio L / W of the distance W between the pair of roller guide surfaces to the width L of the inner flat surface is 0.50 or more.

2. The tripod-type constant velocity universal joint according to claim 1, wherein the outer flat surface of the outer joint member is provided in the joint circumferential region of the inner flat surface.

3. The tripod-type constant velocity universal joint according to claim 1, wherein the roller does not come into contact with the inner flat surface when the roller experiences the maximum front-to-back tilt angle with respect to the outer joint member.

4. The tripod-type constant velocity universal joint according to claim 3, wherein the maximum front-to-back inclination angle of the roller with respect to the outer joint member is 7° or less.

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