Tri-lobe type constant velocity universal joint

Abstract

In a triple-pin type constant-velocity universal joint (1) of a double-row roller type, a pitch circle diameter of a roller guide surface (6) of an outer joint member (2) is set to PCD, a radius of curvature at an intermediate portion between a main body portion (31) and a foot shaft (32) of a triple-pin member (3) is set to R, and a minimum distance from a large diameter portion (34a) of a spline (34) to an intermediate portion (33) of the triple-pin member (3) is set to t, R / PCD ≥ 0.0850 and t / PCD ≥ 0.145.

Description

Technical Field

[0001] This invention relates to a three-ball pin type constant velocity universal joint used in power transmission of motor vehicles and various industrial machinery. Background Technology

[0002] In the drive shafts used in the power transmission systems of motor vehicles, it is common for the inner side (the central side in the vehicle width direction) of the intermediate shaft to be combined with a sliding constant velocity universal joint, and the outer side (the end side in the vehicle width direction) to be combined with a fixed constant velocity universal joint. The sliding constant velocity universal joint allows both angular displacement and axial relative movement between the two shafts, while the fixed constant velocity universal joint allows angular displacement but not axial relative movement between the two shafts.

[0003] Three-ball pin type constant velocity universal joints are well-known as sliding constant velocity universal joints. These three-ball pin type constant velocity universal joints include single-row roller type and double-row roller type. In the single-row roller type, rollers inserted into the raceway grooves of the outer coupling member are rotatably mounted to the foot axle of the three-ball pin member via multiple needle rollers. The double-row roller type includes: rollers inserted into the raceway grooves of the outer coupling member, and an inner ring externally fitted into the foot axle of the three-ball pin member, supporting the rollers in a freely rotatable manner. The double-row roller type allows the rollers to oscillate relative to the foot axle, thus offering advantages over the single-row roller type such as reduced induced thrust (axial force induced by friction between components inside the coupling) and reduced sliding resistance.

[0004] In the double-row roller type three-ball pin constant velocity universal joint of Patent Document 1, on the torque load side, the outer circumferential surface of the foot shaft of the three-ball pin member contacts the inner circumferential surface of the inner ring in a near-point manner. Therefore, in this type of three-ball pin constant velocity universal joint, especially under high load torque, the surface pressure at the contact portion between the outer circumferential surface of each shaft and the inner circumferential surface of the inner ring increases. Consequently, there is a problem of reduced durability at the contact portion of the foot shaft's outer circumferential surface.

[0005] To eliminate this problem, Patent Document 1 below discloses a double-row roller type three-ball pin type constant velocity universal coupling, wherein a hardened layer is formed on the foot shaft by carburizing, quenching and tempering, and the three-ball pin component is formed of steel with a carbon content of 0.23 to 0.44%, having an effective hardened layer with a critical hardness of 600 Hv.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2020-106087 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] The double-row roller type three-ball pin type constant velocity universal joint described in Patent Document 1 is obtained, for example, by carburizing and quenching chromium-molybdenum steel with a carbon content of 0.34% followed by high-temperature tempering. In this structure, the carbon content in the steel can be increased compared to the past, so even when the contact surface pressure at the contact portion between the outer peripheral surface of the axle and the inner ring increases due to excessive torque load, the durability of the axle at that contact portion can be improved.

[0011] On the other hand, after further research on the three-ball pin type constant velocity universal joint described in Patent Document 1, the inventors of this application found that, as described above, the durability of the contact portion of the outer peripheral surface of the axle under torque load can be ensured. However, in exchange, the strength of the axle root is weak. At the axle root, tensile loads are repeatedly applied along with torque transmission, but due to the reduced fatigue strength at the root, the torsional strength at the axle root is insufficient.

[0012] Therefore, the purpose of this invention is to improve the strength at the root of the foot shaft of the three-ball pin component.

[0013] Solution for solving the problem

[0014] Based on the above insights, the present invention is a three-ball-pin type constant velocity universal coupling, comprising: an outer coupling member having axially extending raceway grooves at three locations in the circumferential direction, each raceway groove having a pair of roller guide surfaces arranged opposite each other in the circumferential direction; a three-ball-pin member having a main body portion having a central hole, three foot shafts protruding radially along the main body portion, and an intermediate portion located between the main body portion and the foot shafts with an arc-shaped longitudinal section, wherein a spline is formed in the central hole of the main body portion; rollers fitted onto each of the foot shafts; and an inner ring externally fitted onto the foot shafts, supporting the rollers for free rotation, the rollers being able to rotate along the roller guide surfaces on the outer coupling member. The shaft component moves axially upwards, forming a roller unit with the rollers and the inner ring. The roller unit can swing relative to the foot shaft. The carbon content at the core of the three-ball pin component is 0.23% to 0.44%, and a hardened layer is formed by over-carburizing, quenching, and tempering. The three-ball pin type constant velocity universal coupling is characterized in that the pitch circle diameter of the roller guide surface of the outer coupling component is set as PCD, the radius of curvature at the middle part of the three-ball pin component is set as R, and the minimum distance from the major diameter of the spline of the three-ball pin component to the middle part is set as t. Then R / PCD≥0.0850 and t / PCD≥0.145.

[0015] By setting R / PCD ≥ 0.0850, the wall thickness of the middle section, i.e., the minimum distance t between the large diameter section of the spline and the middle section, can be increased. Specifically, it can be set to t / PCD ≥ 0.145. By increasing the wall thickness of the middle section in this way, even if the depth of the hardened phase layer increases and the toughness of the three-ball pin component decreases, the strength of the root (middle section) of the axle can be improved, especially the fatigue strength. Therefore, the torsional strength of the axle can be improved, thereby increasing the design freedom of the three-ball pin component.

[0016] The surface hardness of the foot axle of the three-ball pin component is preferably 653 HV or higher. This improves the durability of the outer circumferential surface of the foot axle under high torque loads, especially the durability of the contact portion with the inner circumferential surface of the inner ring.

[0017] The internal hardness of the three-ball pin component is preferably 513HV or higher. By setting the internal hardness to 513HV or higher, the required effective hardened layer depth of the three-ball pin component can be obtained.

[0018] Invention Effects

[0019] According to the present invention, the durability at the root of the foot shaft of the three-ball pin component can be improved. Attached Figure Description

[0020] Figure 1 This is a longitudinal sectional view showing a double-row roller type three-ball pin type constant velocity universal coupling.

[0021] Figure 2 Is Figure 1 The longitudinal sectional view is obtained by looking at the KK line.

[0022] Figure 3 Is Figure 1 The transverse sectional view is obtained by looking at the LL line.

[0023] Figure 4 It means Figure 1 A longitudinal sectional view of the working angle state of the three-ball pin type constant velocity universal coupling was obtained.

[0024] Figure 5 This is a longitudinal cross-sectional view showing the hardened layer formed on the three-ball pin member.

[0025] Figure 6 This is a graph showing the hardness distribution at the hinge of an existing product.

[0026] Figure 7 This is a diagram showing the hardness distribution at the hinge of the improved product.

[0027] Figure 8 It is Figure 2An enlarged cross-sectional view showing the middle part of the three-ball pin component. Detailed Implementation

[0028] based on Figures 1 to 8 The embodiments of the three-ball pin type constant velocity universal coupling of the present invention will be described.

[0029] Figures 1-4 The three-ball pin type constant velocity universal coupling 1 shown in this embodiment is a double-row roller type. It should be noted that... Figure 1 This is a longitudinal sectional view showing a double-row roller type three-ball pin type constant velocity universal coupling. Figure 2 Is Figure 1 A partial transverse cross-sectional view obtained by looking at the KK line. Figure 3 Is Figure 1 The transverse sectional view obtained by looking towards the LL line. Figure 4 This is a longitudinal sectional view showing a three-ball pin type constant velocity universal coupling when the working angle is achieved.

[0030] like Figure 1 as well as Figure 2 As shown, the main components of the three-ball-pin type constant velocity universal joint 1 include an outer coupling member 2, a three-ball-pin member 3 serving as an inner coupling member, and a roller unit 4 serving as a torque transmission member. The outer coupling member 2 is cup-shaped with one end open, and has three straight raceway grooves 5 extending axially at equal intervals in the circumferential direction on its inner circumferential surface. Roller guide surfaces 6 are formed in each raceway groove 5, and these roller guide surfaces 6 are arranged opposite each other in the circumferential direction of the outer coupling member 2, extending axially along the outer coupling member 2. The three-ball-pin member 3 and the roller unit 4 are housed inside the outer coupling member 2.

[0031] The three-ball pin component 3 integrally comprises: a main body 31 (trunnion main body) having a center hole 30; three foot pins 32 (trunnion journals) protruding radially from three equally spaced positions in the circumferential direction of the main body 31; and an intermediate portion 33 connecting the main body 31 and the foot pins 32. The three-ball pin component 3 is formed by external splines 81 (see reference 8) formed on the shaft 8, which serves as the shaft. Figure 1 The three-ball pin member 3 is engaged with the inner spline 34 formed in the center hole 8 of the trunnion body 31, and is connected to the shaft 8 in a manner that can transmit torque. The three-ball pin member 3 is fixed axially relative to the shaft 8 by engaging one end face of the three-ball pin member 3 with the shoulder 82 provided on the shaft 8, and by engaging the retaining ring 10 assembled at the front end of the shaft 8 with the other end face of the three-ball pin member 3.

[0032] The main components of the roller unit 4 include: an outer ring 11 serving as rollers, an annular inner ring 12 disposed inside the outer ring 11 and externally fitted into the foot axle 32, and a plurality of needle rollers 13 sandwiched between the outer ring 11 and the inner ring 12. The roller unit 4 is housed in the raceway groove 5 of the outer coupling member 2. The roller unit 4, composed of the inner ring 12, the needle rollers 13, and the outer ring 11, is formed in a structure that does not separate due to the washers 14 and 15.

[0033] In this embodiment, the outer peripheral surface of the outer ring 11 is a convex curved surface with a circular arc having a center of curvature on the axis of the foot shaft 32 as its generatrix. The outer peripheral surface of the outer ring 11 makes angular contact with the roller guide surface 6.

[0034] The needle roller 13 uses the cylindrical inner circumferential surface of the outer ring 11 as the outer track surface and the cylindrical outer circumferential surface of the inner ring 12 as the inner track surface, and is freely arranged between these outer track surfaces and inner track surfaces.

[0035] The outer peripheral surfaces of each foot axle 32 of the three-ball pin component 3 are straight in any longitudinal section containing the axis of the foot axle 32. Additionally, as... Figure 3 As shown, the outer peripheral surface of the foot axle 32 is approximately elliptical in a cross-section orthogonal to the axis of the foot axle 32. The outer peripheral surface of the foot axle 32 contacts the inner peripheral surface 12a of the inner ring 12 in the direction orthogonal to the axis of the coupling, i.e., the direction of the major axis a. A gap m is formed between the outer peripheral surface of the foot axle 32 and the inner peripheral surface 12a of the inner ring 12 in the axial direction of the coupling, i.e., the direction of the minor axis b.

[0036] like Figure 1 As shown in Figure 2, the middle portion 33 between the main body 31 of the three-ball pin component 3 and the foot axle 32 is concave in an arc shape in any longitudinal section containing the axis of the foot axle 32.

[0037] The inner circumferential surface 12a of the inner ring 12 is convex arc-shaped in any longitudinal section containing the axis of the inner ring 12. Furthermore, since the cross-sectional shape of the foot axle 32 is approximately elliptical as described above, and a predetermined gap m is provided between the foot axle 32 and the inner ring 12, the inner ring 12 can swing relative to the foot axle 32. As described above, the inner ring 12 and the outer ring 11 are rotatably combined relative to each other via the needle roller 13, thus the outer ring 11 and the inner ring 12 become one unit and can swing relative to the foot axle 32. That is, in the plane containing the axis of the foot axle 32, the axes of the outer ring 11 and the inner ring 12 can be inclined relative to the axis of the foot axle 32 (see reference). Figure 4 ).

[0038] like Figure 4As shown, when the three-ball pin type constant velocity universal coupling 1 achieves its working angle and rotates, the axis of the three-ball pin component 3 is inclined relative to the axis of the outer coupling component 2, but the roller unit 4 can oscillate, thus avoiding the state where the outer ring 11 is obliquely perpendicular to the roller guide surface 6. As a result, the outer ring 11 rolls horizontally relative to the roller guide surface 6, thereby reducing the induced thrust and sliding resistance, and thus achieving low vibration of the coupling.

[0039] Furthermore, as described above, the cross-section of the foot axle 32 is approximately elliptical, and the longitudinal section of the inner circumferential surface 12a of the inner ring 12 is a convex arc-shaped section. Therefore, the outer circumferential surface of the foot axle 32 on the torque load side contacts the inner circumferential surface 12a of the inner ring 12 with a small, almost point-contact area. As a result, the force required to tilt the roller unit 4 is reduced, and the stability of the outer ring 11's posture is improved.

[0040] The three-ball pin component 3 described above is manufactured from steel through the following main processes: forging (cold forging) → machining (turning) → broaching of spline 34 → heat treatment → grinding of the outer peripheral surface of the foot pin 32. Alternatively, the outer peripheral surface of the foot pin 32 can be precision machined by cutting quenched steel, replacing the grinding process. Furthermore, a spheroidizing annealing process and a phosphating process can be added before cold forging. If the forgeability during cold forging is not an issue due to the use of materials with low carbon content, the spheroidizing annealing process can be omitted. Carburizing, quenching, and tempering are performed as heat treatment.

[0041] Figure 5 This is a cross-sectional view showing the hardened layer 16 formed by heat treatment of the three-ball pin member 3. (See diagram below.) Figure 5 As shown, a hardened layer 16 is formed on the entire surface of the three-ball pin component 3, including the outer peripheral surface of the foot pin 32, the outer peripheral surface of the main body 31, the surface of the middle part 33, and the surface of the inner spline 23. For the finished three-ball pin component 3, the outer peripheral surface of the foot pin 32 is finished by grinding (or cutting hardened steel), therefore the depth of the hardened layer 16 on the outer peripheral surface of the foot pin 32 is shallower than other areas due to grinding or other machining allowances. It should be noted that this machining allowance is typically around 0.1 mm and is relatively small, therefore... Figure 5 The thickness of the hardened layer 16 is depicted as uniform across the entire surface.

[0042] As mentioned above, such as Figure 3 As shown, in a double-row roller type three-ball pin type constant velocity universal joint, on the torque load side, the outer circumferential surface of the foot shaft 32 and the inner circumferential surface 12a of the inner ring 12 make point contact or near-point contact in region X. Therefore, there is a problem that the surface pressure at this contact point increases under high torque loads. When the surface pressure is too high, it will lead to a decrease in the durability of the contact point X of the foot shaft 32.

[0043] To address this issue, the inventors conducted the following verification.

[0044] Typically, in the three-ball pin component 3, chromium-molybdenum steel, a type of surface-hardening steel, is forged and then subjected to carburizing, quenching, and tempering as a heat treatment, thereby forming a hardened layer 16 on the surface. Figure 6 The diagram shows the hardness distribution from the surface to the core of the foot pin 32 when using a material (e.g., JIS G4052 chromium-molybdenum steel, a comparable material with a carbon content of less than approximately 0.23%) for the existing three-ball pin component 3 and subjected to carburizing, quenching, and tempering (quenching temperature 860°C, tempering temperature 180°C). In this case, according to Figure 6 It is clearly known that the surface hardness exceeds 513 HV, but the hardness in areas very shallowly from the surface is lower than 513 HV. Therefore, when excessive torque is applied, the durability of the contact portion of the foot axle 32 is affected. Therefore, to solve the above problem, it is necessary to form the hardened layer 16 as deep as possible.

[0045] It should be noted that the effective hardened layer depth refers to the distance from the surface of the steel to the position of the critical hardness. According to JIS G0557, the critical hardness of the effective hardened layer is 550 HV, but it also stipulates that "if the hardness at a position at a distance of 3 times the hardened layer from the surface exceeds the Vickers hardness of 450 HV, a critical hardness exceeding 550 HV may be adopted by agreement between the parties." As will be described later, in this embodiment, the internal hardness (hardness of the unquenched area) of the three-ball pin member 3 is 513 HV or higher, thus falling under the above exception. In this embodiment, the critical hardness of the effective hardened layer depth is specified as 600 HV. It should be noted that the higher the hardness of the hardened layer 16, the better the durability of the foot pin 7. Therefore, it is preferable to specify the critical hardness of the effective hardened layer depth as 653 HV or higher.

[0046] To deepen the hardened layer 16, increasing the depth of the carburized layer is the simplest method. However, forming a deeper carburized layer requires a significant amount of carburizing time, leading to increased manufacturing costs. Using steels with higher carbon content, such as S50C to S55C carbon steels used in mechanical structures, was also considered, and the heat treatment method was changed to high-frequency quenching, which allows for deeper quenching than carburizing and quenching. However, in this case, the increased carbon content results in a correspondingly harder material, leading to increased processing loads during forging of the three-ball pin component 3, and consequently, larger forging equipment.

[0047] Based on the above investigation, the inventors have verified the effectiveness of using the same carburizing and quenching / tempering conditions as before, but employing surface-hardening steel with a higher carbon content compared to previous methods. Figure 7The image shows the hardness distribution when using chromium-molybdenum steel with a carbon content of approximately 0.34% as the material, after carburizing, quenching, and tempering. The quenching temperature was 850℃, and the tempering temperature was 180℃. It should be noted that... Figure 7 The horizontal axis (depth from the surface) is compared with... Figure 6 The same scale is shown.

[0048] according to Figure 7 The results clearly show that increasing the carbon content of the surface-hardened steel can increase the depth of the hardened layer 16 as expected. As a result of this increased depth of the hardened layer 16, the internal hardness can also be understood to be above 513 HV. On the other hand, the hardness (internal hardness) of the core after carburizing, quenching, and tempering reaches approximately 550 HV, thus potentially leading to a decrease in the toughness of the foot pin 32 and a reduction in the repeated fatigue strength of the three-ball pin component 3. Countermeasures to this problem will be described later.

[0049] It should be noted that the above description illustrates the use of a material with a carbon content of approximately 0.34% as the material for the three-ball pin component 3, but the types of materials that can be used are not limited. For example, as long as it is chromium-molybdenum steel, in addition to SCM435, SCM440 and other similar materials can also be used. Furthermore, so-called H-steels (such as SCM435H, SCM440H, etc., as specified in JIS G4052) with guaranteed hardenability can also be used. As long as it is surface-hardened steel, other types of steel can also be used, such as chromium steels (such as SCr435, SCr440, etc.) as specified in JIS G4053. Chromium steels, for example, H-steels such as SCr435H and SCr440H can also be used. It is not limited to surface-hardened steels such as chromium-molybdenum steel and chromium steel; carbon steels for mechanical structures such as S10C to S35C (as specified in JIS G4051) can also be used as materials.

[0050] Considering the formability of the three-ball pin component 3 during cold forging, steel with a carbon content of 0.44% or less is preferred. It should be noted that steel with a carbon content exceeding 0.44% can also be used if formability during forging is not a problem, such as in the case of hot forging. If surface-hardened steel with a carbon content of 1% or less is used, no particularly adverse conditions will occur during hot forging.

[0051] In the improved product described above, as mentioned, it is known that the root (middle portion 33) of the foot axle 32 has a weakness in strength. This is presumably because the entire three-ball pin member 3 is hardened from the surface to the deeper regions, thus reducing its toughness. Consequently, the fatigue strength of the three-ball pin member 3 decreases in the middle portion 33, which is repeatedly subjected to tensile loads during torque transmission, affecting the overall strength of the middle portion 33. If this problem is to be solved through a re-examination of materials or heat treatment methods, the durability of the contact portion X of the foot axle 32 must be reduced. Therefore, it is desirable to solve this problem from a different perspective.

[0052] Based on the above verification, in order to improve the strength at the root of the foot axle 32, the shape of the three-ball pin component 3 was re-examined in this invention.

[0053] Specifically, in this invention, the pitch circle diameter of the roller guide surface 6 of the outer coupling component 2 is set as PCD (refer to...). Figure 2 Let R be the radius of curvature of the arc-shaped intermediate portion 33 located between the foot shaft 32 and the main body 31 of the three-ball pin component 3, and let t be the minimum distance from the major diameter portion 34a of the spline 34 formed on the inner circumferential surface of the main body 31 of the three-ball pin component 3 to the intermediate portion 33 (refer to...). Figure 5 Let R / PCD ≥ 0.0850 and t / PCD ≥ 0.145. It should be noted that PCD, R, and t are all in the same unit (mm).

[0054] Figure 8 It is Figure 2 An enlarged cross-sectional view is shown near the middle portion 33 of the three-ball pin member 3. (See image below.) Figure 8 As shown by solid lines, the inner diameter side of the intermediate portion 33 is smoothly connected to the outer peripheral surface of the main body portion 31 by a tangent. On the other hand, the outer diameter side of the intermediate portion 33 is connected to the outer peripheral surface of the foot axle 32 by a small step Z. This step Z is generated when the outer peripheral surface of the foot axle 32 is ground after the cold forging of the three-ball pin member 3, and the outer peripheral surface of the foot axle 32 is correspondingly retracted with respect to the grinding allowance. As shown by double-dotted lines, when the radius of curvature R of the intermediate portion 33' is increased, the arc-shaped intermediate portion 33' reaches the predetermined grinding area G before grinding on the outer diameter side of the intermediate portion 33', and the grinding allowance Y increases. The increase in the grinding allowance Y will have an adverse effect on the grinding accuracy. From the viewpoint of preventing the reduction of grinding accuracy, R / PCD < 0.0850 has always been set.

[0055] In this invention, R / PCD is set to ≥ 0.0850, thus enabling an increase in the wall thickness of the intermediate portion 33, i.e., the large diameter portion 34a of the spline 34 (see reference). Figure 5 The minimum distance t between the middle part 33 and the middle part 33 Figure 8 (Refer to wall thickness). Specifically, it can be set to t / PCD ≥ 0.145. By increasing the wall thickness of the intermediate portion 33 in this way, even if the depth of the hardened layer increases and the toughness of the three-ball pin member 3 decreases, the strength, especially the fatigue strength, of the root (intermediate portion 33) of the foot axle 32 can be improved. Therefore, the torsional strength of the foot axle 32 can be improved, thereby increasing the design freedom of the three-ball pin member.

[0056] By increasing the radius of curvature R of the intermediate portion 33 in this way, the grinding allowance Y increases on the outer diameter side of the intermediate portion 33. However, through verification by the inventors, it has been confirmed that as long as R / PCD ≤ 0.20, it will not adversely affect the grinding accuracy when grinding the outer peripheral surface of the foot pin 32. Therefore, the upper limit of R / PCD is preferably 0.20. That is, it is preferably set to 0.0850 ≤ R / PCD ≤ 0.20. In addition, if the value of t / PCD is too large, the three-ball pin component 3 will become unnecessarily large, resulting in an increase in weight. Therefore, the value of t / PCD is preferably upper limit of 0.20 (t / PCD ≤ 0.20).

[0057] The embodiments of the invention described above can also be applied to double-row roller type three-ball pin type constant velocity universal couplings with other structures.

[0058] For example, the outer peripheral surface of the axle 32 can be formed as a convex curved surface (e.g., a convex arc cross-section), and the inner peripheral surface 12a of the inner ring 12 can be formed as a cylindrical surface. Alternatively, the outer peripheral surface of the axle 32 can be formed as a convex curved surface (e.g., a convex arc cross-section), and the inner peripheral surface 12a of the inner ring 12 can be formed as a concave spherical surface that fits into the outer peripheral surface of the axle. In this case, washers 14 and 15 can be omitted by providing flanges at both ends of the inner diameter of the outer ring.

[0059] The three-ball pin type constant velocity universal joint 1 described above is not limited to the application of drive shafts in motor vehicles, but can also be widely used in power transmission routes of motor vehicles, industrial machines, etc.

[0060] Explanation of reference numerals in the attached figures

[0061] 1. Three-ball pin type constant velocity universal coupling; 2. Outer coupling component; 3. Three-ball pin component; 4. Roller unit; 5. Raceway groove; 6. Roller guide surface; 8. Shaft; 11. Roller (outer ring); 12. Inner ring; 13. Needle roller; 16. Hardened layer; 30. Center hole; 31. Main body; 32. Foot shaft; 33. Intermediate part; 34. Internal spline.

Claims

1. A three-ball pin type constant velocity universal coupling, comprising: The outer coupling component has three axially extending raceway grooves in the circumferential direction, each raceway groove having a pair of roller guide surfaces arranged opposite each other in the circumferential direction. The three-ball pin component has a main body with a central hole, three foot pins protruding in the radial direction of the main body, and an intermediate part located between the main body and the foot pins with an arc-shaped longitudinal section. A spline is formed in the central hole of the main body. Rollers, which are assembled on each of the aforementioned foot axles; as well as The inner ring, which is fitted onto the foot axle, supports the roller for free rotation. The roller is axially movable along the roller guide surface of the outer coupling member. The roller and the inner ring form a roller unit, which is capable of oscillating relative to the foot axle. The carbon content in the core of the three-ball pin component is 0.23%~0.44%, and a hardened layer is formed on the surface of the foot pin through carburizing, quenching and tempering. The three-ball pin type constant velocity universal coupling is characterized in that... A step is provided between the middle part and the foot axle, which narrows in diameter from the arc-shaped surface of the middle part in the radial direction of the foot axle and connects to the outer peripheral surface of the foot axle. Let the pitch circle diameter of the roller guide surface of the outer coupling component be PCD, the radius of curvature at the middle part of the three ball pin component be R, and the minimum distance from the major diameter of the spline of the three ball pin component to the middle part be t. Then R / PCD≥0.0850 and t / PCD≥0.

145.

2. The three-ball pin type constant velocity universal coupling according to claim 1, wherein, The surface hardness of the foot axle of the three ball pin component is above 653HV.

3. The three-ball pin type constant velocity universal joint according to claim 1 or 2, wherein, The internal hardness of the three-ball pin component is above 513HV.

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