JP2010181015A - Universal coupling - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure preventing deterioration of sealability caused by a small difference in level 28 existing at the end of a coating film 25. <P>SOLUTION: The end of a radial seal lip 18a is formed into a forked shape, and includes a pair of axially separated seal edges 26a, 26b. An axial interval L<SB>26</SB>between both the seal edges 26a, 26b is set equal to or wider than the axial displacement of a shaft portion 12 and a bearing cup 11 when in use from a neutral position in a direction where the insertion rate of the shaft portion 12 into the bearing cup 11 is increased. With this structure, the seal edge 26a at a base end is prevented from being moved beyond a step 28. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an improvement in a universal joint used in a state where it is incorporated in a steering device of an automobile, for example, to transmit the movement of a steering shaft to a steering gear. Specifically, with respect to the structure in which the surface is coated for corrosion prevention or the like, the sealing performance is prevented from being deteriorated due to a minute step existing at the end of the coating film.

  The steering apparatus for an automobile is configured as shown in FIG. 8 as described in, for example, Patent Documents 1 and 2. The movement of the steering wheel 1 operated by the driver is transmitted to the input shaft 6 of the steering gear unit 5 through the steering shaft 2, the universal joint 3, the intermediate shaft 4, and another universal joint 3. A pair of left and right tie rods 7 and 7 are pushed and pulled by a rack and pinion mechanism built in the steering gear unit 5, and the operation amount of the steering wheel 1 is applied to a pair of left and right steering wheels (generally, front wheels). Depending on the situation, an appropriate rudder angle is provided.

  In general, a cross joint called a cardan joint is widely used as a universal joint incorporated in such a steering apparatus. 9 to 10 show an example of a universal joint that has been widely known so far, as described in Patent Documents 1 and 2 above. The structure shown in FIGS. 9 to 10 is a so-called vibration-proof joint that prevents transmission of vibration, but the universal joint that is the subject of the present invention does not necessarily have to have a vibration-proof structure. Therefore, in the following description, the structure of the main body portion of the universal joint 3 will be described with the vibration-proof structure omitted.

  The universal joint 3 includes a pair of yokes 8a and 8b each formed in a bifurcated shape by a metal material having sufficient rigidity, and a cross shaft 9 made of a hard metal such as an alloy steel such as bearing steel. Consists of Concentric holes 10 and 10 are formed at both ends of each of the yokes 8a and 8b. And in these circular holes 10 and 10, bearing cups 11 and 11 made of a hard metal plate material such as bearing steel and case-hardened steel are formed in a state where the openings face each other. It is fitted and fixed. The cross shaft 9 has a shape such that the middle portions of the pair of column portions are orthogonal to each other, and has four shaft portions 12 and 12 each having a cylindrical shape. In other words, the base end portions of the shaft portions 12 and 12 are fixedly coupled to four positions at equal intervals in the circumferential direction of the coupling base portion 13 provided in the center portion. The central axes of these shaft portions 12 and 12 exist on the same plane.

  The axial direction intermediate part thru | or the front-end | tip part of each such shaft part 12 and 12 are inserted in each said bearing cup 11 and 11. FIG. Further, radial bearings 14, 14 such as needle bearings are provided between the inner peripheral surfaces of the bearing cups 11, 11 and the front half outer peripheral surfaces of the shaft portions 12, 12. The yokes 8a and 8b are oscillated and displaced with a light force. Due to such a configuration, even when the central axes of the yokes 8a and 8b do not coincide with each other, the rotational force can be transmitted between the yokes 8a and 8b with little transmission loss.

  Of the universal joints 3 and 3 as described above, in the case of the universal joint 3 installed on the outside of the passenger compartment (lower side in FIG. 8), the base ends of the shaft portions 12 and 12 constituting the cross shaft 9. Seal rings 15 and 15 are provided between the portion (the end portion on the coupling base 13 side) and the opening of each of the bearing cups 11 and 11, respectively. The seal rings 15 and 15 prevent muddy water and the like from entering the installed portions of the radial bearings 14 and 14, thereby ensuring the durability of the universal joint 3. Each of the seal rings 15, 15 is formed by reinforcing an elastic material 17 with a cored bar 16. Of these, the metal core 16 is formed in an annular shape with an L-shaped cross section by a metal plate such as a mild steel plate. The elastic member 17 is made of an elastomer such as rubber, covers the core 16 over the entire circumference, and has a pair of seal lips 18 and 19 including a radial seal lip 18 and a thrust seal lip 19. .

  Each of the seal rings 15 and 15 having such a structure is formed by tightening a base portion embedded with the core metal 16 on a base end portion of each of the shaft portions 12 and 12 (part of the elastic material 17). By being externally fitted (in a state of being elastically deformed), the base end portions of the shaft portions 12 and 12 are supported in a state in which the sealing performance of the fitting portions is ensured. In this manner, the seal rings 15 and 15 are supported on the base end portions of the shaft portions 12 and 12, and the seal lips 18 are combined with the cross shaft 9 and the bearing cups 11 and 11. 19, the seal edge of the radial seal lip 18 is elastically abutted over the entire periphery of the outer peripheral surface of each of the bearing cups 11 and 11 toward the end near the opening. Further, the seal edge of the thrust seal lip 19 is elastic over the entire circumference on the outer surface of the inward flange portion 20 formed in the opening of each of the bearing cups 11 and 11 (the surface facing the coupling base portion 13). Abut.

  Furthermore, the axial direction of each said shaft part 12 and 12 in the state which opened the bottomed insertion hole 21 and 21 in the center part of each said shaft part 12 and 12 at the front end surface of these each shaft part 12 and 12, respectively. Is formed. Then, synthetic resin pins 22 and 22 are inserted inside these insertion holes 21 and 21, respectively. The pins 22 and 22 are stretched between the bearing cups 11 and 11 and the shafts 12 and 12, so that the distance between the opening end of the bearing cups 11 and 11 and the base 13 is increased. Preventing it from shrinking too much. Then, the thrust seal lip 19 of each of the seals 15 and 15 is prevented from being excessively compressed, and conversely, the amount of compression is not excessively reduced. That is, when the universal joint 3 is used, the thrust load acting side (anchor side) seal ring 15 is excessively compressed on the basis of the thrust load applied between the cross shaft 9 and the bearing cups 11, 11. Is prevented, and the amount of compression of the seal ring 15 on the opposite side (anti-anchor side) is excessively reduced, thereby preventing the sealing performance of the seal ring 15 from being impaired. Each of the pins 22 and 22 supports the thrust load as described above while elastically deforming in the axial direction. The above-described seal rings 15 and 15 can be obtained without particularly increasing the dimensional accuracy and assembly accuracy of the constituent members 8a, 8b, 9, 11, and 15 of the universal joint 3 due to the change in the axial dimension due to the elastic deformation. The amount of compression can be kept within the proper range.

  However, a cross shaft type universal joint that does not have the pins 22 and 22 as described above has been widely known, for example, as described in Patent Documents 3 to 4. FIG. 11 shows the structure of a universal joint described in Patent Document 4 among them. In the case of this second example of the conventional structure, the ridges 24, 24 are formed on the portion near the center of the inner surface of the bottom 23 of the bearing cup 11a, and the tip edges of these ridges 24, 24 are the shaft portions constituting the cross shaft. It is made to contact | abut to the 12 front end surface. Even with such a structure, the compression amount of the seal ring provided between the bearing cup 11a and the shaft portion 12 can be maintained within an appropriate range as long as the dimensional accuracy and assembly accuracy of the components of the universal joint are ensured.

  In any structure, the universal joint 3 constituting the steering device is coated for rust prevention. In particular, in the steering device shown in FIG. 8 described above, the front lower universal joint 3 that connects the intermediate shaft 4 and the input shaft 6 is provided outside the vehicle compartment (inside the engine room), and rainwater and muddy water are received. Because it is easy to adhere, the need to paint is high. This painting is performed in a completed state of the universal joint 3 (a state in which the constituent members 8a, 8b, 9, 11, and 15 are assembled). This is because, in order to simplify the painting work, in order to prevent the paint from adhering to the unnecessary parts such as the inner surface of the bearing cup 11, and further, if painting is performed before the assembling work, This is because the coating film is scraped off. The coating is performed by a method in which fine particles of paint are adhered to the surface as in electrodeposition coating. Therefore, as shown in FIG. 12, the coating film 25 is formed only on a portion exposed to the surface in the assembled state. For this reason, for example, the portion covered with the radial seal lip 18 at the opening end of the bearing cup 11 is not covered with the coating film, and the metal remains exposed. Then, a step 28 corresponding to the thickness of the coating film 25 is generated at the portion where the seal edge of the radial seal lip 18 is in contact with the universal joint 3 as assembled.

  On the other hand, during the operation of the universal joint, the seal edge of the radial seal lip 18 is displaced not only in the circumferential direction but also in the axial direction with respect to the outer peripheral surface of the bearing cup 11. That is, when torque is transmitted between the yokes 8a and 8b in a state where there is a joint angle between the pair of yokes 8a and 8b, the shaft portions 12 are moved inside the bearing cups 11. Swing displacement in the torsional direction. With this swinging displacement, the seal edge of the radial seal lip 18 is displaced in the circumferential direction with respect to the outer peripheral surface of the bearing cup 11. At the same time, a thrust load is applied between the cross shaft 9 and the bearing cups 11. Then, the elastic deformation of each constituent member based on this thrust load causes the seal edge of the radial seal lip 18 to be displaced in the axial direction with respect to the outer peripheral surface of the bearing cup 11. This axial displacement becomes significant in the case of the structure provided with the pins 22 and 22 as shown in FIG. 10, but also in the case of the structure as shown in FIG. 11, the elasticity of the bottom 23 and the like of the bearing cup 11a. Occurs with deformation. In any case, along with the axial displacement, the seal edge of the radial seal lip 18 moves over the level difference present at the edge of the coating film 25. As a result, the contact state of the contact portion between the seal edge and the outer peripheral surface of the bearing cup 11 becomes unstable, and the sealing performance of the contact portion may deteriorate.

  Patent Document 5 describes a structure in which a cover is provided around the radial seal lip to prevent the paint from adhering to the radial seal lip. Such a structure described in Patent Document 5 is intended to prevent the elasticity of the radial seal lip from being lowered due to adhesion of the paint, and the step 28 of the coating film 25 that leads to a decrease in the sealing performance as described above. It cannot prevent the occurrence. Patent Document 6 describes a structure that improves the contact state between the seal edge of the thrust seal lip and the inward flange of the bearing cup by forming an annular groove at the tip of the thrust seal lip. However, it is not possible to prevent a decrease in sealing performance based on the step 28 of the coating film 25.

Japanese Patent Application Laid-Open No. 8-135684 Japanese Patent Laid-Open No. 9-60650 JP-A-6-280890 JP 7-208492 A JP-A-7-217668 JP 2006-29551 A

  In view of the above-described circumstances, the present invention was invented to realize a structure capable of preventing a deterioration in sealing performance based on a minute step present at an end of a coating film.

The universal joint of the present invention is a pair of yokes, four circular holes, four bearing cups, a cross shaft, and four sets of radial bearings, similar to the previously known universal joints. And four seal rings.
Each of the pair of yokes is formed in a bifurcated shape.
The circular holes are concentrically formed at both ends of the yokes.
Each of the bearing cups has a bottomed cylindrical shape, and is fitted and fixed inside the circular holes with the openings facing each other.
Further, the cross shaft is formed by radially fixing four shaft portions on the outer peripheral surface of the coupling base portion, and these shaft portions are inserted into the bearing cups and combined with the yokes. Yes.
Each radial bearing is provided between the inner peripheral surface of each bearing cup and the outer peripheral surface of each shaft portion.
The seal rings are provided between the base end portions of the shaft portions and the opening portions of the bearing cups, with the base portions fitted and supported on the base end portions of the shaft portions. It has been.
Each of the seal rings is provided with a seal lip that is in contact with the entire periphery of the outer peripheral surface of each of the bearing cups at the end closer to the opening. The surface is painted in a state where it is brought into contact with the outer peripheral surface.

In particular, in the universal joint of the present invention, each of the seal lips has a pair of seal edges that are bifurcated at the tip and separated in the axial direction.
In the case of carrying out the present invention as described above, preferably, as in the invention described in claim 2, the axial interval between the pair of seal edges provided at the front end portions of the respective seal lips is determined in use. The amount of axial displacement from the neutral position in the direction in which the amount of insertion of each shaft portion into the bearing cup increases between the shaft portion and the bearing cup.
Alternatively, as in the invention described in claim 3, the axial distance between a pair of seal edges provided at the tip of each seal lip is set to be neutral with the tip surface of each of the shafts. It is more than the minimum thickness of the clearance gap which exists between the bottom part inner surface of each said bearing cup.
According to the present invention, as in the invention described in claim 4, a bottomed insertion hole is formed in the axial direction inside each of the shaft portions so as to open to the end face of each of the shaft portions. The other end of the synthetic resin pin inserted into each insertion hole and having one end abutted against the inner end of the insertion hole is abutted against the bottom inner surface of each bearing cup. However, the effect of the invention can be remarkably obtained. Such a structure is because the amount of axial displacement of each shaft portion increases.

According to the universal joint of the present invention configured as described above, it is possible to prevent deterioration of the sealing performance based on a minute step existing at the end of the coating film.
That is, in the case of the universal joint of the present invention, the tip end of the seal lip that makes the seal edge contact the outer peripheral surface of each bearing cup is bifurcated, and a pair of seal edges is provided at the tip of the seal lip. Therefore, even when the bearing cups and the seal rings are displaced relative to each other in the axial direction, at least one seal edge is present at a portion deviated from the stepped portion. For this reason, at least one seal edge abuts on the mating surface with no gap over the entire circumference, and sealing performance can be ensured.

  In particular, according to the invention described in claim 2 and claim 3, the seal edge near the opening end of each bearing cup out of the pair of seal edges overcomes the step existing at the end of the coating film. It will not move. For this reason, the sealing performance by the seal edge can be sufficiently ensured regardless of the existence of the step.

[First example of embodiment]
1 and 2 show a first example of an embodiment of the present invention corresponding to claims 1, 2, and 4. FIG. The feature of the present invention including this example is related to the axial displacement between the shaft portion 12 of the cross shaft 9 and the bearing cup 11 fitted in the circular hole 10 of the yoke, which occurs during the operation of the universal joint. The structure for maintaining a good sealing property between the shaft portion 12 and the bearing cup 11 is provided. The structure and operation of other parts are the same as those of the first example of the conventional structure shown in FIGS. 9 to 10 or the second example of the conventional structure shown in FIG. In addition, the description will be omitted or simplified, and the following description will focus on the features of the present invention.

Between the base end portion (the lower end portion in FIGS. 1 and 2) of the shaft portion 12 and the opening side end portion (the lower end portion in FIGS. 1 and 2) of the bearing cup 11, from the core metal 16 and the elastic material 17a. A seal ring 15a is provided. The elastic member 17 a has a pair of seal lips 18 a and 19 including a radial seal lip 18 a and a thrust seal lip 19. Of these, the radial seal lip 18a is formed with a bifurcated tip, and has a pair of seal edges 26a and 26b spaced apart in the axial direction. That is, the thickness of the tip of the radial seal lip 18a is made larger than the thickness of the tip of the radial seal lip 18 having the conventional structure shown in FIG. A concave groove 27 that opens to the inner peripheral surface side is formed over the entire circumference. The both sides of the concave groove 27 are the seal edges 26a and 26b, respectively. These seal edges 26a and 26b are separated by L ₂₆ (see FIG. 2) in the axial direction. On the other hand, the thrust seal lip 19 is the same as the conventional structure described above, and its seal edge is in contact with the outer surface of the inward flange portion 20 formed on the bearing cup 11 over the entire circumference.

  The portion including the outer peripheral surface of the bearing cup 11 excluding the portion covered with the elastic material 17a of the seal ring 15a is for rust prevention as in the conventional structure shown in FIG. A coating film 25 based on this coating is formed. Accordingly, in the portion of the outer peripheral surface of the bearing cup 11 that is close to the opening end, the portion of the coating film 25 that is in contact with the seal edge 26a on the distal end side (the upper side in FIGS. 1 and 2) of the radial seal lip 18a is in contact. There is a step 28 (see FIG. 2, omitted in FIG. 1) corresponding to the thickness. In the case of this example, the radial seal lip 18a is generated regardless of the axial displacement between the shaft portion 12 of the cross shaft 9 and the bearing cup 11 fitted in the circular hole 10 of the yoke, which occurs during the operation of the universal joint. The seal edge 26b on the base end side (the lower side in FIGS. 1 and 2) is prevented from moving across the step 28. In other words, the seal edge 26b on the base end side is in contact (sliding contact) only with the portion near the opening end of the outer peripheral surface of the bearing cup 11 and not covered with the coating film 25. . The coating operation for forming the coating film 25 is carried out in a neutral state in which no external force is applied (torque transmission is not performed) after assembling the constituent members of the universal joint. In this neutral state, each of the four bearing cups 11, seal rings 15a, and pins 22 constituting the universal joint is elastically deformed by substantially the same amount.

  In contrast, when the universal joint is used, the bearing cup 11 and the shaft portion 12 are relatively displaced in the axial direction based on a thrust load applied between the bearing cup 11 and the shaft portion 12. This relative displacement is caused by the rigidity in the thrust direction of the synthetic resin pin 22 provided between the shaft portion 12 and the bearing cup 11, the rigidity in the thrust direction of the bearing cup 11, and the thrust direction of the seal ring 15a. This is done against rigidity. Then, the amount of elastic deformation of each member 11, 15a, 22 existing on the front side in the displacement direction of the cross shaft 9 is increased, and the amount of elastic deformation of each member 11, 15a, 22 also present on the rear side is decreased. The rigidity of each of the members 11, 15a, and 22 and the thrust load can be obtained by calculation or experiment. Therefore, the relative displacement amount (maximum value) in the axial direction between the bearing cup 11 and the shaft portion 12 that occurs when the universal joint is used can also be obtained by calculation or experiment.

In the case of this example, the axial distance L ₂₆ between the seal edges 26a and 26b is obtained as described above, and the axial displacement amount from the neutral position between the bearing cup 11 and the shaft portion 12 is obtained. Is larger than the maximum value L _MAX (L ₂₆ ≧ L _MAX ), preferably slightly larger (for example, about 0.5 mm) than this maximum value L _MAX of the axial displacement (L ₂₆ > L _MAX ). Accordingly, among the pair of seal edges 26a and 26b provided at the tip of the radial seal lip 18a, the seal edge 26b near the opening end of each bearing cup 11 exists at the end of the coating film 25. It will not move over the step 28. That is, of the two seal edges 26a and 26b, the seal edge 26a on the distal end side slides with respect to the outer peripheral surface of the bearing cup 11 while overcoming the step 28 when the universal joint is used. Therefore, the sealing performance by the seal edge 26a on the tip side is likely to deteriorate. On the other hand, the seal edge 26b on the base end side comes into contact (sliding contact) only with a portion of the outer peripheral surface of the bearing cup 11 that is not covered with the coating film 25. For this reason, the sealing performance by the sealing edge 26b on the base end side can be sufficiently ensured regardless of the presence of the step 28. Note that the maximum value of the axial distance L ₂₆ is determined in terms of design within a range in which the tip edge of the radial seal lip 18a does not interfere with the arm portion of the yoke.

[Second Example of Embodiment]
FIG. 3 shows a second example of an embodiment of the present invention corresponding to claims 1 to 4. In the case of this example, the axial distance L ₂₆ between the pair of seal edges 26a, 26b provided at the distal end portion of the radial seal lip 18a is set to the neutral state with the distal end surface of the shaft portion 12 and the bottom portion 23a of the bearing cup 11 in the neutral state. It is regulated in relation to the minimum thickness T ₂₉ of the gap 29 existing between the inner surface and the inner surface. That is, the axial distance L ₂₆ is not less than the minimum thickness T ₂₉ (L ₂₆ ≧ T ₂₉ ), preferably slightly larger (for example, about 0.5 mm) than the minimum thickness T ₂₉ (L ₂₆ > and T ₂₉₎ and.

When the universal joint is used, the shaft portion 12 and the bearing cup 11 are relatively displaced in the axial direction. The displacement in the direction in which the shaft portion 12 enters the bearing cup 11 is theoretically the shaft portion 12. This is possible until the front end surface of the bearing abuts against the inner surface of the bottom 23a of the bearing cup 11. The actual case, before the front end surface of the above by the minimum thickness T ₂₉ of the gap 29 (if the minimum thickness T ₂₉ is large) the shaft portion 12 abuts the inner surface of the bottom portion 23a, the pin 22 In some cases, the thrust force of the shaft portion 12 becomes larger than the thrust load generated with the use of the universal joint, and the tip surface of the shaft portion 12 does not contact the inner surface of the bottom portion 23a.

On the other hand, when the minimum thickness T ₂₉ is small, the tip surface of the shaft portion 12 and the inner surface of the bottom portion 23a may come into contact while the tension force of the pin 22 is smaller than the thrust load. Conceivable. In such a case, there is room for the shaft portion 12 to be displaced in the direction of entering the bearing cup 11 based on the elastic deformation of the bottom portion 23a. However, the contact portion between the tip end surface of the shaft portion 12 and the inner surface of the bottom portion 23a is a portion of the bottom portion 23a near the outer diameter having high rigidity. For this reason, the amount of displacement based on the elastic deformation as described above is negligible and almost negligible.

Considering the above, as in the structure of this example, the axial distance L ₂₆ between the seal edges 26a and 26b is set between the tip surface of the shaft portion 12 and the inner surface of the bottom portion 23a of the bearing cup 11. If the gap T ₂₉ is set to be equal to or greater than the minimum thickness T ₂₉ , the seal edge 26 b on the proximal end side of the seal edges 26 a and 26 b is the end of the coating film 25 that covers the outer peripheral surface of the bearing cup 11. There is almost no possibility of moving over the step 28 (see FIG. 2 and omitted in FIG. 3) existing in the section. Further, as in the case of the first example of the above-described embodiment, the sealing performance by the base end side seal edge 26b can be sufficiently ensured regardless of the presence of the step 28. Further, if the pin 22 is bent, even if the axial displacement amount of the shaft portion 12 increases, the sealing performance by the seal edge 26b on the base end side can be ensured (the tensile force of the pin 22 is initially reduced). If greater than the thrust load).

[Third example of embodiment]
FIG. 4 shows a third example of an embodiment of the present invention corresponding to claims 1, 2, and 4. In the case of this example, the shape of the synthetic resin pin 22a assembled between the bearing cup 11 and the shaft portion 12 is the same as that of the first example of the embodiment described above and the second example of the embodiment described above. It is different from the case. The pin 22a incorporated in the structure of this example is provided with a flange portion 30 having an outward flange shape at the distal end, and the flange portion 30 is abutted against the opening peripheral portion of the insertion hole 21 at the distal end surface of the shaft portion 12. ing. A protrusion 31 is formed at the center of the tip surface of the pin 22a. Further, the base end portion (the lower end portion in FIG. 4) of the pin 22a has a small diameter and abuts against the center portion of the bottom surface of the insertion hole 21. In a neutral state in which a universal joint is assembled and no external force is applied, only the projection 31 abuts against the center of the inner surface of the bottom 23a of the bearing cup 11, and the flange 30 and the inner surface of the bottom 23a have a minute gap. To be separated from each other. On the other hand, when a thrust load is applied in the direction in which the shaft portion 12 is pushed into the bearing cup 11 with the use of the universal joint, the elastic deformation amount (compression amount) of the protrusion 31 increases. The flange portion 30 and the inner surface of the bottom portion 23a abut. In this state, the rigidity of the pin 22a in the thrust direction is improved.

In short, in the structure of this example, the rigidity related to the force in the direction in which the shaft portion 12 is pushed into the bearing cup 11 changes in two stages. For this reason, in the structure of this example, the amount of the shaft portion 12 pushed into the bearing cup 11 based on the thrust load can be reduced while securing the buffering action by the pin 22a. Therefore, even if the axial distance L ₂₆ between the pair of seal edges 26 a and 26 b provided at the distal end portion of the radial seal lip 18 a is shortened, the proximal-side seal edge 26 b covers the outer peripheral surface of the bearing cup 11. It is possible to prevent movement over the step 28 (see FIG. 2, omitted in FIG. 4) present at the end of the coating film 25. Accordingly, it is possible to reduce the size of the universal joint by reducing the size of the tip of the radial seal lip 18a.

[Fourth Example of Embodiment]
FIGS. 5-6 has shown the 4th example of embodiment of this invention corresponding to Claim 1,2. This example relates to a structure that does not have a pin made of synthetic resin, and shows a case where the present invention is applied. The bearing cup 11b incorporated in the structure of this example forms a partially spherical convex portion 32 at the center of the inner surface of the bottom 23b by causing the center of the bottom 23b to bulge inward. The central portion of the convex portion 32 is brought into contact with the central portion of the tip end surface of the shaft portion 12.

In the case of such a structure of this example, when a thrust load is applied between the bearing cup 11b and the shaft portion 12 with the use of a universal joint, the bearing cup 11b and the bearing cup 11b The shaft portion 12 is relatively displaced in the axial direction. Since the relative displacement amount based on the elastic deformation is small, the axial distance between the pair of seal edges 26a and 26b provided at the tip of the radial seal lip 18a is considered only by the relative displacement amount based on the elastic deformation. L ₂₆ can be made extremely short. However, in the case of the structure of this example, the convex portion 32 is gradually worn with use over a long period of time, and the amount of insertion of the shaft portion 12 into the bearing cup 11b increases accordingly. there is a possibility. Therefore, in the case of this example, the axial distance L ₂₆ between the seal edges 26a, 26b is set to a relative displacement amount based on elastic deformation of the bottom portion 23b and a relative displacement amount based on the wear (maximum, the convex portion). 32 heights) is the total length. As a result, even after use for a long period of time, the seal edge 26b on the base end side has a step 28 (see FIG. 2 and FIG. 4) present at the end of the coating film 25 covering the outer peripheral surface of the bearing cup 11b. Can be avoided.

[Fifth Example of Embodiment]
FIG. 7 shows a fifth example of an embodiment of the present invention corresponding to claims 1 and 2. This example relates to a case where the present invention is applied to a structure that does not have a pin made of a synthetic resin and has a simple space between the tip surface of the shaft portion 12 and the inner surface of the bottom portion 23a of the bearing cup 11. Show. In such a structure, in a neutral state where no external force is applied to the universal joint, the positional relationship between the shaft portion 12 and the bearing cup 11 is neutral only by the elastic force of the thrust seal lip 19 constituting the seal ring 15a. Become.

In the case of the present example in order to apply the present invention to such a structure, as in the second example of the embodiment shown in FIG. The axial distance L ₂₆ between the seal edges 26a and 26b is set to be equal to or greater than the minimum thickness T ₂₉ of the gap 29 existing between the tip end surface of the shaft portion 12 and the inner surface of the bottom portion 23 of the bearing cup 11 in the neutral state (L ₂₆ ≧ T ₂₉ ), and preferably slightly larger (for example, about 0.5 mm) than this minimum thickness T ₂₉ (L ₂₆ > T ₂₉ ). For this reason, of the two seal edges 26a, 26b, the seal edge 26b on the proximal end side is a step 28 (see FIG. 2 and FIG. 7) present at the end of the coating film 25 covering the outer peripheral surface of the bearing cup 11. The possibility of moving over the other is almost eliminated, and the sealing performance by the sealing edge 26b on the base end side can be sufficiently ensured regardless of the presence of the step 28.

  The present invention is not limited to a universal joint for a steering device, but can be applied to a cross-shaft type universal joint that is incorporated in a non-linear connection portion of various conductive force transmission devices.

The figure equivalent to the AA cross section of FIG. 10 which shows the 1st example of embodiment of this invention. The B section enlarged view of FIG. The figure equivalent to the right part of FIG. 1 which shows the 2nd example of embodiment of this invention. The figure similar to FIG. 1 which shows the 3rd example. The figure similar to FIG. 1 which shows the 4th example. The right part enlarged view of FIG. The figure similar to FIG. 1 which shows the 5th example of embodiment of this invention. The perspective view which shows an example of the steering device incorporating a universal joint. The partial cut side view which shows the 1st example of the universal joint known conventionally. FIG. 10 is an enlarged CC cross-sectional view of FIG. The figure equivalent to the lower end part of FIG. 10 which shows the 2nd example of the universal joint known conventionally. The same figure as FIG. 2 for demonstrating the problem of a conventional structure.

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Universal joint 4 Intermediate shaft 5 Steering gear unit 6 Input shaft 7 Tie rod 8a, 8b Yoke 9 Cross shaft 10 Circular hole 11, 11a, 11b Bearing cup 12 Shaft part 13 Connection base part 14 Radial bearing 15, 15a Seal ring 16 Core 17, 17 a Elastic material 18, 18 a Radial seal lip 19 Thrust seal lip 20 Inward flange 21 Insert hole 22, 22 a Pin 23, 23 a, 23 b Bottom 24 Projection 25 Coating film 26 a, 26 b Seal edge 27 Concave Groove 28 Step 29 Clearance 30 Gutter 31 Projection 32 Projection

Claims (4)

  A pair of yokes each formed in a bifurcated shape, four circular holes formed concentrically with each other at both ends of both yokes, and inside each of these circular holes with the openings facing each other Four bearing cups each having a bottomed cylindrical shape that are internally fitted and fixed, and four shaft portions are radially fixed on the outer peripheral surface of the coupling base portion. A cross shaft combined with both yokes in a state of being inserted into each bearing cup, and four sets of radial bearings provided between the inner peripheral surface of each bearing cup and the outer peripheral surface of each shaft portion; Four seal rings provided between the base end portions of the shaft portions and the opening portions of the bearing cups in a state in which the base portions are externally supported by the base end portions of the shaft portions. Each of these seal rings has an entire circumference at the end near the opening of the outer peripheral surface of each of the bearing cups. In a universal joint whose surface is coated with the seal lip of each seal lip in contact with the outer peripheral surface of each bearing cup, the seal lip is provided. However, the universal joint is characterized in that it has a pair of seal edges that are formed with a bifurcated tip and separated in the axial direction.   The axial distance between a pair of seal edges provided at the tip of each seal lip is determined by the insertion of each shaft into the bearing cup between the shaft and each bearing cup during use. The universal joint according to claim 1, wherein the universal joint is greater than or equal to an axial displacement amount from a neutral position in a direction in which the amount increases.   The minimum thickness of the gap that exists between the tip end surface of each shaft portion and the bottom inner surface of each bearing cup when the axial interval between a pair of seal edges provided at the tip portion of each seal lip is in a neutral state The universal joint according to any one of claims 1 and 2, wherein the universal joint is equal to or greater than the above.   A bottomed insertion hole is formed inside each shaft portion in the axial direction of each shaft portion so as to open to the end face of each shaft portion, and one end of each of the shaft portions is inserted into each insertion hole. The universal joint according to any one of claims 1 to 3, wherein the other end of the synthetic resin pin butted against the back end of the insertion hole is butted against the bottom inner surface of each bearing cup.

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