Tripod constant-velocity universal joint and closed-die forging method

Abstract

Provided are a tripod constant-velocity universal joint and a closed-die forging method. A tripod member having radially projecting leg shafts is molded by closed-die forging. The outer peripheral surface of each of the leg shafts is formed in a protruding spherical shape. The leg shafts each have a projecting part bulging radially outwardly from the projecting end surface of the leg shaft. The projecting parts are unmachined parts molded during the closed-die forging molding.

Description

Tripod-type constant velocity universal joint and closed-end forging method

[0001] The present invention relates to a tripod-type constant velocity universal joint and a closed-end forging method.

[0002] Constant velocity universal joints used in power transmission sections of automobiles and various industrial machines include fixed constant velocity universal joints and sliding constant velocity universal joints, with tripod-type constant velocity universal joints being a type of sliding constant velocity universal joint. As shown in Figure 7, a tripod-type constant velocity universal joint comprises, for example, an outer joint member 3 having three linear track grooves 2 extending axially on its inner circumferential surface 1, a tripod member 6 disposed inside the outer joint member 3 and having a boss portion 4 and three leg shafts 5 projecting radially from the outer diameter surface of the boss portion 4, and a torque transmission element 7 supported by the leg shafts 5 and guided in the track grooves 2. In this case, the torque transmission element 7 consists of an outer roller 8, an inner roller 9, and a plurality of rollers 10 interposed between the outer roller 8 and the inner roller 9.

[0003] Furthermore, the tripod member 6 is manufactured by a forging method described in Patent Document 1, etc. That is, it is formed in a closed forging die equipped with an openable and closable die and a punch that presses the material inside the die. The closed forging die 13, for example as shown in Figure 8, is equipped with openable and closable dies 11 and 12 and punches 14 and 15 that are drivable on the central axis of the dies 11 and 12. That is, by closing the dies 11 and 12 and pressing with the punches 14 and 15, a cavity 16 corresponding to the shape of the leg shaft 5 and boss portion 4 of the product is formed. Therefore, when the billet (material) is placed in the die and the die is clamped and pressed by the punches 14 and 15, the billet undergoes plastic deformation, and a product (i.e., tripod member 6) is formed with a boss portion 4 and a shaft portion 5, as shown in Figure 8.

[0004] Incidentally, there are tripod members 6 whose leg shafts 5 have outer peripheral surfaces of cylindrical shape (Patent Document 2) and convex spherical shape (Patent Document 3). For the cylindrical outer peripheral surface, since the cross-sectional shape is constant along the axial direction, in order to avoid complete sealing of the leg shaft forming cavity of the closed forging die, the leg shaft is set to be longer than necessary to cause sagging on the end face (axial end face) of the leg shaft, and the tip end of the leg shaft is machined. That is, it is not necessary to restrain the tip end of the extruded material. Here, sagging in forging refers to a phenomenon in shearing processing where the material pressed by the upper punch is pulled, resulting in a smooth periphery around the inlet, and the material sags from the intended regular shape.

[0005] In addition, in the structure described in Patent Document 1, during closed forging, a caulking boss is integrally formed at the tip end of the leg shaft. Specifically, a roller is fitted onto the leg shaft via a bearing, and a retainer for preventing the bearing from coming off is externally fitted onto the caulking boss, and the retainer is attached to the leg shaft by caulking the caulking boss.

[0006] Japanese Patent No. 4100602 Japanese Unexamined Patent Application Publication No. 2018-200109 Japanese Unexamined Patent Application Publication No. 2002-286046

[0007] Incidentally, as shown in Figure 10, the tripod member 6A is also composed of a boss portion 4A and a leg shaft 5A, but in this case, the outer surface of the leg shaft 5A is convex spherical. In the case where the outer surface of the leg shaft 5A is convex spherical (as described in Patent Document 3), as shown in Figure 11, when the length dimension (axial length) of the leg shaft forming cavity 19A1 of the cavity 19A of the closed forging die 13A is set to the length dimension of the leg shaft 5A, an air pocket 20 is formed on the neck side where the leg shaft 5A is formed, resulting in insufficient material. That is, when forming a convex spherical leg shaft 5A, it is necessary to change the cross section perpendicular to the direction of extrusion along the convex spherical shape, and it is necessary to restrain, set, and expand the material extruded during closed forging. At that time, it is necessary to fill the mold in order to form the convex spherical shape, but if the mold is to be completely filled, it will be a completely sealed state with no escape route for the material, and there is a risk that the surface pressure of the mold will become excessive and cause the mold to break. Therefore, the molding process must be completed while there is still a small gap remaining before complete sealing. However, applying high surface pressure is necessary to mold the functionally required area, which leads to a short mold life. In addition, variations in the weight of the material being used and variations in the amount molded due to thermal expansion of the mold can increase the degree of filling, which can increase the surface pressure acting on the mold and lead to mold breakage, or it can decrease the degree of filling and result in poor quality.

[0008] Therefore, in view of the above problems, the present invention provides a tripod member for a constant velocity universal joint and a closed forging method that can improve the lifespan of the closed forging die and effectively prevent damage to the closed forging die, and moreover, does not require a lot of machining after closed forging, thus not increasing manufacturing costs.

[0009] The tripod-type constant velocity universal joint of the present invention is a tripod-type constant velocity universal joint comprising a tripod member having radially projecting leg shafts, wherein the outer circumferential surface of the leg shafts is formed in a convex spherical shape, and the leg shafts have projections that bulge radially outward from the projecting end faces of the leg shafts, and the surface of the projections is a forged surface formed by closed forging. Here, the forged surface refers to the surface of a product that has undergone a closed forging process, and includes the surface that was in contact with (satisfied with) the mold and the surface of the parts that were not in contact with (satisfied with) the mold.

[0010] According to the tripod-type constant velocity universal joint of the present invention, by providing a projection at the tip of the leg shaft, the convex spherical surface on the outer surface of the leg shaft is formed while the material flows out to the projection during closed forging. Therefore, it is possible to increase the saturation of the convex spherical surface while suppressing the increase in surface pressure acting on the closed forging die. Furthermore, if excess material is input, the excess material flows out to the projection, preventing the die from becoming completely sealed. Also, if the input weight decreases, only the amount of material flowing out to the projection decreases, and this does not affect the saturation of the convex spherical surface.

[0011] It is preferable that the outer surface of the protrusion is parallel to the axis of the leg shaft. When configured in this way, there is no need to form a convex spherical portion or the like on the molding surface of the cavity in the closed forging die for forming the protrusion, and die manufacturing can be simplified.

[0012] It is preferable that the cross-sectional area of ​​the outer surface of the protrusion, when measured parallel to a plane perpendicular to the axis of the leg shaft, be 20% to 70% of the smallest cross-sectional area of ​​the neck of the leg shaft that is parallel to a plane perpendicular to the axis of the leg shaft, and more preferably 20% to 50%. That is, if it is less than 20%, the effect of reducing the surface pressure of the closed forging die is low, and an improvement in die life cannot be expected. If it exceeds 70%, the convex spherical portion of the outer surface of the leg shaft is difficult to satisfy, and if it exceeds 50%, the axial length of the protrusion may become long enough to interfere with the outer joint member before the convex spherical portion is satisfied. For this reason, it is preferable that the cross-sectional area of ​​the outer surface of the protrusion, when measured parallel to a plane perpendicular to the axis of the leg shaft, be 20% to 50% of the smallest cross-sectional area of ​​the neck of the leg shaft that is parallel to a plane perpendicular to the axis of the leg shaft. However, if we consider only the closed forging die and disregard the external joint members, a ratio of 20% to 70% is preferable.

[0013] The present invention relates to a closed-forging method for forming a tripod member in a tripod-type constant velocity universal joint, the tripod member having a radially projecting leg shaft and a projection that bulges radially outward from the projecting end face of the leg shaft, wherein during the closed-forging process in which the leg shaft, whose outer surface is a convex spherical shape, is formed, material is allowed to flow into a recess in the die that forms the projection, thereby forming the discharge portion of the unmachined part that remains as formed during the closed-forging process.

[0014] According to the closed-forging method of the present invention, by providing a projection at the tip of the leg shaft, the convex spherical surface of the outer surface of the leg shaft is formed while the material flows out into the projection during closed-forging. Therefore, it is possible to increase the saturation of the convex spherical surface while suppressing the increase in surface pressure acting on the closed-forging die. Furthermore, if an excess of material is input, the excess material flows out into the projection, preventing the die from becoming completely sealed. Also, if the input weight decreases, only the amount of material flowing out into the projection decreases, and this does not affect the saturation of the convex spherical surface.

[0015] This method allows for increased saturation of the convex spherical surface while preventing an increase in the surface pressure acting on the closed forging die for forming tripod components. Therefore, it is possible to improve the lifespan of the closed forging die and prevent sudden die failure. Furthermore, since there is no need to remove the protruding portion by machining, it significantly contributes to reducing manufacturing costs.

[0016] This is a perspective view of the tripod member of the tripod-type constant velocity universal joint according to the present invention. This is a cross-sectional view of the tripod-type constant velocity universal joint according to the present invention. This is a cross-sectional view of a closed forging die. This is a cross-sectional plan view of a closed forging die. This shows a general tripod-type constant velocity universal joint, a cross-sectional view of the main part having a leg axis with a circular cross-sectional shape. This shows a general tripod-type constant velocity universal joint, a cross-sectional view of the main part having a leg axis with an elliptical cross-sectional shape. This shows a general tripod-type constant velocity universal joint, a cross-sectional view of the main part having a leg axis with an oblong cross-sectional shape. This shows a simplified cross-sectional view of a protruding part, with a circular cross-sectional shape. This shows a simplified cross-sectional view of a protruding part, with an elliptical cross-sectional shape. This shows a simplified cross-sectional view of a protruding part, with a rectangular cross-sectional shape. This shows a simplified cross-sectional view of a protruding part, with an elliptical cross-sectional shape when the longitudinal direction is perpendicular to Figure 6B. This shows a simplified cross-sectional view of a protruding part, with a rectangular cross-sectional shape when the longitudinal direction is perpendicular to Figure 6C. This is a cross-sectional view of a conventional tripod-type constant velocity universal joint. This is a cross-sectional view of a conventional closed forging die. This is a cross-sectional plan view of a conventional closed-type forging die. This is a perspective view of a triboard member having a leg axis with a convex spherical outer surface. This is a simplified cross-sectional view illustrating the problems of conventional closed-type forging dies.

[0017] Embodiments of the present invention will be described below with reference to Figures 1 to 6E. Figure 2 shows a tripod-type constant velocity universal joint according to the present invention, and Figure 1 shows the tripod member of the tripod-type constant velocity universal joint according to the present invention. As shown in Figure 2, the tripod-type constant velocity universal joint comprises an outer joint member 33 having three linear track grooves 32 extending axially on its inner circumferential surface 31, a tripod member 36 disposed inside the outer joint member 33 and having a boss portion 34 and three leg shafts 35 projecting radially from the outer diameter surface of the boss portion 34, and a torque transmission element 37 supported by the leg shafts 35 and guided by the track grooves 32. In this case, the torque transmission element 37 consists of an outer roller 38, an inner roller 39, and a plurality of rollers 40 interposed between the outer roller 38 and the inner roller 39. Furthermore, the roller unit 41 is not separated from the inner roller 39 and 40 and the outer roller 38 by washers 42 and 43.

[0018] In this case, as shown in Figure 1, the leg shaft 35 of the tripod member 36 has a convex curved surface portion 35b on its outer circumferential surface, and the cross-sectional shape of this convex curved surface portion 35b is circular as shown in Figure 5A. Furthermore, the tip surface of the leg shaft 35 has a projection 45 that bulges radially outward from the protruding end surface 35a of the leg shaft 35, and the projection 45 is an unmachined portion that remains as it was formed during the closed forging process. In other words, the surface of the projection 45 becomes the forged surface as it was formed during the closed forging process. Here, the forged surface refers to the surface of the product after the closed forging process, and includes the surface that was in contact with (satisfied with) the mold and the surface of the parts that were not in contact with (satisfied with) the mold.

[0019] The outer circumferential surface of the protruding portion 45 extends parallel to the axial direction of the leg shaft 35, and its cross-sectional shape can be circular as shown in Figure 6A, elliptical as shown in Figures 6B and 6D, rectangular as shown in Figures 6C and 6E, etc. In Figure 6C, the longitudinal sides are tapered surfaces that gradually approach from the midpoint, and in Figure 6E, the longitudinal sides extend in a straight line. Also, in Figures 6C and 6E, each corner is chamfered with an R-chamfer. Furthermore, Figures 6B and 6D are mutually orthogonal.

[0020] The tripod member 36 is formed by closed forging, using a closed forging apparatus as shown in Figure 3. The closed forging apparatus comprises a mold 50 having openable and closable dies 51 and 52, and punches 54 and 55 arranged to be drivable on the central axis of the dies 51 and 52. That is, by pressing with the punches 54 and 55 with the dies 51 and 52 in the closed state, a cavity 59 corresponding to the shape of the leg shaft 35, boss portion 34, and protrusion portion 45 of the tripod member 36 is formed. Specifically, as shown in Figure 4, the cavity 59 consists of a boss portion forming section 59a for forming the boss portion 34, a leg shaft forming section 59b for forming the leg shaft 35, and a protrusion portion forming section 59c for forming the protrusion portion 45. Therefore, when the billet (material) is placed in the die and then clamped and pressed by the punches 54 and 55, the billet undergoes plastic deformation, and a product (tripod member 36) can be formed with a boss portion 34, a leg shaft 35, and a projection portion 45, as shown in Figure 2. At this time, the material flows out into the projection portion forming portion 59c (see Figure 4), which is a recess formed in the dies 51 and 52 for forming the projection portion 45.

[0021] The protruding portion 45 is an unmachined portion that remains as it was formed during the closed forging process (the surface of the protruding portion 45 is the forged surface as it was formed during the closed forging process). Therefore, the tip surface 45a of the protruding portion 45 may be flat, convex, or concave.

[0022] In this case, it is preferable that the outer surface of the projection 45 is parallel to the axis of the leg shaft 35. In the illustrated example, the cross-sectional shape is circular as shown in Figure 6A. Furthermore, it is preferable that the cross-sectional area of ​​the outer surface of the projection 45 parallel to a plane perpendicular to the axis of the leg shaft be 20% to 70% of the smallest cross-sectional area of ​​the neck portion 35c of the leg shaft 35 parallel to a plane perpendicular to the axis of the leg shaft, and more preferably 20% to 50%.

[0023] By providing a projection 45 on the tip projection surface (tip surface 35a) of the leg shaft 35, the convex spherical portion 35b on the outer surface of the leg shaft 35 is formed while the material flows out into the projection 45 during closed forging. This makes it possible to increase the saturation of the convex spherical portion 35b while suppressing the increase in surface pressure acting on the closed forging die 50. In addition, if excess material is input, the excess material flows out into the projection 45, preventing the die from becoming completely sealed. Furthermore, if the input weight decreases, only the amount of material flowing out into the projection 45 decreases, and this does not affect the saturation of the convex spherical portion 35b.

[0024] It is preferable that the outer surface of the protrusion 45 is parallel to the axis of the leg shaft 35. When configured in this way, it is not necessary to form a convex spherical surface or the like on the protrusion forming portion 59c of the cavity 59 in the closed forging die for forming the protrusion 45, and die manufacturing can be simplified.

[0025] It is preferable that the cross-sectional area of ​​the outer surface of the protrusion 45, in a section parallel to a plane perpendicular to the axis of the leg shaft, be 20% to 70% of the smallest cross-sectional area of ​​the neck portion 35c of the leg shaft 35 in a section parallel to a plane perpendicular to the axis of the leg shaft, and more preferably 20% to 50%. That is, if it is less than 20%, the effect of reducing the surface pressure of the closed forging die 50 is low, and an improvement in die life cannot be expected. If it exceeds 70%, it becomes difficult to satisfy the convex spherical portion 35b on the outer surface of the leg shaft 35, and if it exceeds 50%, the axial length of the protrusion 45 may become long enough to interfere with the outer end joint member before the convex spherical portion 35b is satisfied. Therefore, it is more preferable that the cross-sectional area of ​​the outer surface of the protrusion 45, in a section parallel to a plane perpendicular to the axis of the leg shaft, be 20% to 50% of the smallest cross-sectional area of ​​the section of the leg shaft 35c parallel to a plane perpendicular to the axis of the leg shaft. However, if only the closed forging die 50 is considered without considering the outer joint member, then 20% to 70% is preferable.

[0026] Incidentally, as shown in Figure 5A, the cross-sectional shape of the leg shaft 35 of the tripod member 36 may be circular, as shown in Figure 5B, or elliptical, as shown in Figure 55C, or oblong. However, in the present invention, any of the cases shown in Figures 5A to 5C may be used. However, the outer circumferential surface of the leg shaft 35 is formed in the shape of a convex spherical surface. Here, an oblong shape means that the sides in the longitudinal direction have flat surfaces.

[0027] Furthermore, as described above, the protruding portion 45 can be configured with a cross-sectional shape (transverse surface) such as a circular shape as shown in Figure 6A, an elliptical shape as shown in Figures 6B and 6D, or a rectangular shape as shown in Figures 6C and 6E. In this case, if the cross-sectional shape of the leg shaft 35 is circular, the cross-sectional shape of the protruding portion 45 is not limited to a circular shape, but may also be an elliptical or oblong shape. If the cross-sectional shape of the leg shaft 35 is elliptical, the cross-sectional shape of the protruding portion 45 is not limited to an elliptical shape, but may also be a circular or oblong shape.

[0028] Furthermore, if the cross-sectional shape of the leg shaft 35 is elliptical or oblong, and the cross-sectional shape of the protruding portion 45 is also elliptical or oblong, the longitudinal direction of the cross-sectional shape of the leg shaft 35 and the cross-sectional shape of the protruding portion 45 may be aligned or perpendicular. Note that aligning them orthogonally offers the advantage of better moldability.

[0029] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and is capable of various modifications. For example, the tripod-type constant velocity universal joint is not limited to the double-roller type, but may also be a single-roller type. Furthermore, when the outer diameter surface of the leg shaft of the tripod member 36 is formed in a convex spherical shape, it is optimal to provide a protrusion 45 that bulges radially outward from the protruding end face of the leg shaft 35 for the tripod member 36 that is formed by closed forging. However, the closed forging method of the present invention may also be applied to the tripod member 36 in which the outer diameter surface of the leg shaft 35 is not formed in a convex spherical shape. In addition, since the protrusion 45 does not require a high-precision shape, it is preferable to leave it as an unmachined portion without machining, but the protrusion 45 may be machined.

[0030] The relationship between the area ratio (A1 / AO) and the projection length of the projection portion 45 was investigated for a tripod member 36 formed using the closed-forging apparatus shown in Figures 3 and 4. In this case, a cylindrical billet with a billet diameter of 35.5 mm and a billet length of 34.7 mm was used, and the punch diameter was set to 35.7 mm. The projection length of the projection portion 45 was investigated at area ratios (A1 / AO) of 20%, 30%, 40%, 50%, and 60%. Here, AO is the smallest cross-sectional area of ​​the neck portion 35c of the leg shaft 35 within a cross-section parallel to a plane perpendicular to the axis of the leg shaft, and A1 is the cross-sectional area of ​​the outer surface of the projection portion 45 within a cross-section parallel to a plane perpendicular to the axis of the leg shaft.

[0031] The results are shown in Table 1. When the area ratio (A1 / AO) was 20%, the protruding length of the protruding portion 45 was 2.6 mm; when the area ratio (A1 / AO) was 30%, the protruding length of the protruding portion 45 was 3.2 mm; when the area ratio (A1 / AO) was 40%, the protruding length of the protruding portion 45 was 3.7 mm; when the area ratio (A1 / AO) was 50%, the protruding length of the protruding portion 45 was 4.4 mm; and when the area ratio (A1 / AO) was 60%, the protruding length of the protruding portion 45 was 6.3 mm. In this case, when the area ratio (A1 / AO) was 70% or higher, it became difficult to satisfy the convex spherical portion 35b on the outer circumference of the leg shaft 35. Furthermore, when the area ratio (A1 / AO) exceeded 50%, the protruding length of the protruding portion 35 exceeded 5 mm. Thus, if the projection exceeds 5 mm, there is a risk that the protrusion 45 may come into contact with the outer joint member 33 when the tripod member is assembled to the outer joint member 33.

[0032] Therefore, when considering a tripod-type constant velocity universal joint, it is necessary to set the area ratio (A1 / AO) so that the protruding length of the projection 45 is less than or equal to the allowable length of 5 mm, and it is preferable that the area ratio (A1 / AO) be around 20% to 50%. However, since the tripod member itself does not have a problem even if it exceeds the allowable length of 5 mm, the area ratio (A1 / AO) may be around 20% to 70%, in which case it is sufficient to make it a shape that does not interfere with the projection 45 on the outer joint member side.

[0033] The relationship between the area ratio (A1 / AO) and the surface pressure of the closed forging die 50 was investigated for tripod members 36 formed using the closed forging apparatus shown in Figures 3 and 4. In this case, a cylindrical body with a billet diameter of 35.5 mm and a billet length of 34.7 mm was used, and the punch diameter was set to 35.7 mm. The relationship with the surface pressure of the closed forging die 50 was investigated for area ratios (A1 / AO) of 20%, 30%, 40%, 50%, and 60%.

[0034] As shown in Table 2, when the area ratio (A1 / AO) is 20%, the surface pressure is 3720 MPa; when the area ratio (A1 / AO) is 30%, the surface pressure is 3550 MPa; when the area ratio (A1 / AO) is 40%, the surface pressure is 3360 MPa; when the area ratio (A1 / AO) is 50%, the surface pressure is 3180 MPa; and when the area ratio (A1 / AO) is 60%, the surface pressure is 2780 MPa. In this case, if the surface pressure of the closed forging mold exceeds 3800 MPa, the mold may be damaged. Therefore, the allowable surface pressure was set to 3800 MPa. For this reason, considering the surface pressure of the closed forging mold, when the area ratio (A1 / AO) is less than 20%, the effect of reducing the surface pressure of the closed forging mold is low, and improvement in mold life cannot be expected. Furthermore, if the area ratio (A1 / AO) exceeds 50%, the surface pressure is too low, and the leg axis will not be adequately supported.

[0035] Therefore, considering the surface pressure of the mold, it is preferable that the area ratio (A1 / AO) be between 20% and 50%.

[0036] The tripod-type constant velocity universal joint may be a double-roller type or a single-roller type. For tripod members that are closed-forge formed, it is optimal to provide a projection that bulges radially outward from the protruding end face of the tripod member's leg shaft.

[0037] 34 Boss section 35 Leg shaft 35c Neck section 36 Tripod member 45 Projection section 45b Base section

Claims

1. A tripod-type constant velocity universal joint comprising a tripod member having radially projecting leg shafts, wherein the outer circumferential surface of the leg shafts is formed in a convex spherical shape, the leg shafts have a projection that bulges radially outward from the projecting end face of the leg shafts, and the surface of the projection is a forged surface formed by closed forging.

2. The tripod-type constant velocity universal joint according to claim 1, characterized in that the outer surface of the protruding portion is parallel to the axis of the leg shaft.

3. The tripod-type constant velocity universal joint according to claim 1, characterized in that, in the cross-section of the protruding portion, the largest cross-sectional area among the cross-sections perpendicular to the axis of the leg shaft is 20% to 70% of the smallest cross-sectional area among the cross-sections perpendicular to the axis of the leg shaft in the cross-section of the neck portion of the leg shaft.

4. The tripod-type constant velocity universal joint according to claim 1, characterized in that, in the cross-section of the protruding portion, the largest cross-sectional area among the cross-sections perpendicular to the axis of the leg shaft is 20% or more and 50% or less of the smallest cross-sectional area among the cross-sections perpendicular to the axis of the leg shaft in the cross-section of the neck portion of the leg shaft.

5. A closed-forging method for forming a tripod member in a tripod-type constant velocity universal joint, the tripod member having a radially projecting leg shaft and a projection that bulges radially outward from the projecting end face of the leg shaft, characterized in that, during closed forging in which a leg shaft having a convex spherical outer surface is formed, material is allowed to flow into a recess in a die for forming the projection, thereby forming the unmachined portion of the projection.

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