Connecting rod comprising a ball pivot

Abstract

The invention relates to a joint comprising a ball pivot, a bearing and a support rod (40), the ball pivot comprising a spherical end and a stud extending from the spherical end,- the bearing being configured to house the spherical end of the pivot, and the support rod (40) comprising a body and an annular head formed by bending one end of the rod (40), in which joint the head (42) comprises a cylindrical central recess configured to receive the bearing.

Description

CONNECTING ROD INCLUDING A BALL JOINT Technical field of the invention [1] The invention relates to the field of ball joints for assembling a pair of elements in such a way as to allow relative pivoting movement of the pair of elements and, more specifically, to a ball joint of simple construction, mechanically strong and capable of being manufactured at reduced manufacturing costs. State of the art [2] Such a ball joint, and more specifically a two-ball joint, commonly called a tie rod, is conventionally used to pivotally connect, for example, the shock absorber leg and the anti-roll bar of an automobile. [3] Document Dl = US5855447 describes such a ball joint which comprises a ball stud, for connection to a first element, the ball stud comprising a spherical end and a stud extending from the spherical end for connection to the first element, - a bearing configured to house the spherical end of the ball stud, and a support rod, one end of which is shaped into an annular head for receiving the bearing. The support rod is a metal rod with a round section, one end of which is curved to form an annular head. The bearing made of elastomeric material has on an outer surface a circular collar which, after assembly, forms a stop for the bearing against a toroidal surface of the annular head. Compared to prior joints, the document presents a solution where the production of the rod is facilitated by the use of a curved wire. [4] However, such an articulation has disadvantages. In practice, it has been observed that the mechanical holding of the bearing in the annular head is not perfect and, during movements of the ball joint, results in friction at the contact zone between the flange of the bearing and the toroidal surface of the annular head. This phenomenon can create parasitic movements in the connecting rod and can generate noise phenomena, which are harmful when using the product incorporating the connecting rod. This also results in premature wear of the bearing. Also, for the mechanical assembly to hold properly, the edge of the flange of the bearing must be able to come to bear on the toroidal surface of the annular head which receives the bearing. The shape and dimensions of the bearing must therefore be adapted to the diameter of the bent wire and to the internal diameter of the annular head formed at the end of the rod.Therefore, the head of the rod must be adapted to the bearing and vice versa. This complicates the technical development of the joints and increases their manufacturing cost. Statement of the invention [5] The invention provides a novel ball joint which does not have all or part of the disadvantages of the rod and ball joint described above. [6] For this purpose, the invention provides a ball joint comprising a ball pivot (30), a bearing and a support rod (40), - the ball joint (30) comprising a spherical end (31) and a stud (32) extending from the spherical end, - the bearing (20) being configured to house the spherical end (31) of the pivot, and - the support rod (40) comprising a body (41) and an annular head (42) formed by the bending of one end of the rod (40). articulation characterized in that the head (42) comprises a central cylindrical recess (43) configured to receive the bearing. [7] The contact area between the head of the rod and the body of the bearing is thus generally cylindrical. Tests have shown that a cylindrical recess makes it possible to obtain an optimal distribution of contact pressures between the spherical end of the pivot, the bearing and the annular head, as will be seen more clearly below; this limits premature wear of the bearing. In addition, a cylindrical recess prevents any unwanted rotation of the bearing in the head of the rod along an axis parallel to a median plane of the head. Friction between the bearing and the head is thus greatly reduced; the mechanical strength of the bearing in the annular head is thus improved. [8] The annular head (42) may also comprise a flat external bearing surface (44) extending in a plane intersecting an axis (Ac) of the recess (43). The bearing surface will be able to serve as a stop for a collar of the bearing to facilitate the installation of the bearing and it improves the resistance to tearing of the pivot as will be seen more clearly below. [9] In addition, the bearing surface may have a textured surface condition. Thus, after the pad has been placed in the recess, rotation of the pad along the axis of the recess is prevented, even under extreme conditions of use of the joint.

[0010] More preferably, the head is made so that, after assembly of the ball joint, an extension of a longitudinal axis Ax of the body (41) of the rod (40) passes through a center (Cs) of the spherical end (31) of the ball pivot (30). This improves the mechanical strength of the assembly, in particular buckling and fatigue strength of the assembly.

[0011] Also, to improve the mechanical strength of the head, a free end (40a) of the rod (40) can be secured, for example by welding or brazing, to the body (41) of the rod so that the head (42) forms a closed ring.

[0012] In the ball joint (10), preferably, the bushing comprises an interior space (21) having a spherical shape and dimensions adjusted to receive the spherical end (31) of the pivot (30), the bushing comprises an opening (22) shaped to allow insertion of the spherical end (31) of the pivot and the bushing comprises a cylindrical outer surface (23); and the cylindrical central recess (43) of the head (42) of the rod has dimensions adjusted to receive the bushing.

[0013] Finally, the invention relates to a method for producing a ball joint as described above, comprising a ball pivot (30), a bearing (20) and a support rod (40), a method comprising the following steps: - a step of bending one end of a wire of circular section to form the rod 40 comprising an annular head 42 at one end of a body 41, - a step of stamping the head (42) to form a flat external bearing surface (44) configured to serve as a stop for a collar (24) of the bearing, and - a step of grinding the annular head 42 to form a cylindrical central recess 43 configured to receive the bearing of the ball joint, and Presentation of figures

[0014] The invention will be better understood, and other characteristics and advantages of the invention will appear in light of the following description of an example of implementation of the invention. This example is given without limitation. The description should be read in conjunction with the appended drawings in which: • Figure 1 is a perspective view of a ball joint according to the invention • figure 2 is a top view of a support rod according to the invention, at an intermediate stage of production • figure 3 is a front view of a support rod according to the invention, at another intermediate stage of production, • figure 4 is a top view of a support rod according to the invention, in its final version • Figures 5 to 7 are schematic views of assembly steps of the ball joint of Fig. 1, and • Figures 8 to 9 show test results of different support rod shapes. Detailed description

[0015] As previously stated, the invention relates to a ball joint.

[0016] The example shown more particularly shows a two-ball joint such as a connecting rod adapted to connect the shock absorber bracket and the anti-roll bar of an automobile. More generally, the ball joint is arranged to connect a first and a second element so as to allow a relative pivoting movement of the two elements with respect to each other. Other applications of the invention are of course possible, for a single-ball joint or a two-ball joint.

[0017] Subsequently, although Figs. 1-4 show a rod 40 and a double-headed ball joint 42, only one end of the rod 40 and the joint 10 are described, the second end possibly being identical to the first.

[0018] The ball joint typically includes: - a ball joint 30 comprising a spherical end 31 and a stud 32 extending to from the spherical end; - a bearing 20 (also called a cage) configured to house the spherical end 31 of the pivot, and - a support rod 40 comprising a body 41 and an annular head 42 (also called a housing or box).

[0019] In a manner known per se, the stud 32 allows connection to the first element by means of a connection means, for example a threaded free end (fig. 1, 6). The ball joint 30 is conventionally made of metal, for example steel.

[0020] The bearing 20 comprises (fig. 5-6) an interior space 21 whose spherical shape and dimensions (in particular an internal diameter) are adjusted to receive the spherical end 31 of the pivot 30 in a fitted fit; the bearing comprises an opening 22 shaped to allow the insertion of the spherical end 31 of the pivot; in the context of the invention, the bearing comprises a cylindrical outer surface 23, a collar 24 extending from one end of the outer surface 23 and a rib 26 extending from another end of the surface 23. The collar 24 comprises a flat edge 25 extending from the outer surface 23; the edge 25 forms a stop as will be seen more clearly below. The rib 26 is used for crimping the bearing as will be seen more clearly below. The pad is made of thermoplastic polymer material, for example polyoxymethylene or polyamide.Such a material is slightly elastic, which makes it easier to insert the spherical end of the pivot into the bearing. And the physical properties of such a material allow the bearing to be crimped into the head of the rod.

[0021] The body 41 allows connection to the second element via a connection means, here a second head 42, coupled to a second bearing 20 and a second pivot 20 (fig. 1).

[0022] According to the invention, the rod 40 is formed by bending one of its ends 40a, to form the annular head 42 at the end of the body 41 of the rod 40. In the example shown, the head 42 (and even the two heads 42) extends in a plane parallel to an axis of the body 41 of the rod. Alternatively, the head 42 may extend in a plane intersecting the axis of the body 41. As a further alternative, the two heads of the same rod may extend in parallel planes or intersecting planes.

[0023] And the head 42 comprises a cylindrical central recess 43 configured to receive the bearing. The recess is produced by grinding the head 42, and preferably by grinding a central portion of the annular head, along an axis Ac of symmetry of the head. The grinding can be carried out by machining, boring, drilling, punching or any other technique allowing a cylindrical cavity to be precisely formed. The diameter of the recess is adjusted to the diameter of the external surface 23 of the bearing. The cylindrical central recess allows a close fitting of the bearing in the head of the rod, with a large contact surface between a cylindrical wall of the recess 43 and the external surface 23 of the bearing, a fitting which ensures perfect retention of the bearing.

[0024] Tests have shown that the cylindrical shape for the central recess of the rod is the most effective for maximizing the mechanical performance of the bearing.

[0025] Figure 8 shows results of tests carried out on three embodiments A, B and C of a ball joint, when a thrust force is applied to the pivot 30 in a direction (grey arrow) parallel to a main plane of the head 40 of the rod. For these three embodiments, A (invention), B and C, the distribution of the pressure exerted on the wall of the central recess of the head is shown in a direction parallel to the axis of the cylindrical central recess.

[0026] In the case of a toric central recess and a bearing with a cylindrical external surface (Case C), the contact area between the bearing and the toric recess is very small and is limited to the equator (or mid-height) of the bearing. All the mechanical forces transmitted by the pivot via the bearing are concentrated on this contact area of ​​very limited dimensions and are therefore very significant. In the case of a toric central recess and a bearing with an external surface that is also toric (Case B), the contact area between the bearing and the central recess is maximum. However, a distribution of mechanical forces is noted with a peak at the equator of the bearing. At the edges, the thickness of the bearing wall is greatest; thus, under pressure, the edges of the bearing deform less and transmit less force to the toric surface of the head.On the contrary, at the equator of the bearing where the thickness of the bearing wall is the smallest, the bearing wall deforms more and transmits more pressure forces onto the wall of the central recess of the head.

[0027] In the case of a cylindrical central recess and a bearing with an external surface that is also cylindrical (Case A), the contact area between the bearing and the central recess is maximum and the thickness of the bearing wall is constant; the distribution of forces on the internal surface of the central recess of the head is more regular and does not have a central peak. It is thus possible to minimize the thickness of the bearing wall while maximizing the mechanical performance of the bearing.

[0028] Preferably, a free end 40a of the rod 40 is secured to the body 41 of the rod so that the head 42 forms a closed ring, more resistant to mechanical stresses. This can be achieved by welding or brazing.

[0029] Also, the annular head 42 may here comprise a flat external bearing surface 44 extending in a plane intersecting (in the example shown, a plane perpendicular) to the axis Ac of the recess 43. The bearing surface 44 is configured to serve as a stop for the edge 25 of the collar 24 of the bearing during assembly of the ball joint (fig. 6), as will be seen more clearly below.

[0030] In the example shown, the head 42 also comprises a second bearing surface 45, which can serve as a support for immobilizing the pad on the annular head 42. For this purpose, the pad can comprise, on the side opposite the opening 22, a rib 26 configured to, after placing the pad in the recess 43 (fig. 6), be deformed (fig. 7) for example by a crimping technique, to crimp the pad on the annular head 42 of the rod. The deformation is facilitated by the fact that the pad is made of thermoplastic material.

[0031] In the example also shown, the two surfaces 44, 45 are flat, parallel, and parallel to the axis of the body 41; alternatively, they may also have a textured surface condition; for example, in FIG. 4, different surface conditions are shown on the surface 44 of the two heads 42 of the rod. In one example, the two surfaces 44, 45 are produced by crushing the annular head using a stamping technique as will be seen more clearly below. Also, one and / or the other of the surfaces 44, 45 may have a textured surface condition.

[0032] Figure 9 shows results of pull-out resistance tests carried out on the three previous embodiments A (invention), B and C when a traction (upward arrows Fta, Ftb, Ftc) or a thrust (downward arrows).

[0033] In the case of a toric central recess and a bearing having a cylindrical external surface, a flat collar 24 and a flat rib 26 perpendicular to the axis of the cylindrical external surface (Case C), the contact area between the bearing and the toric recess is very small: it is limited to the equator (mid-height) of the bearing, to one end of the edge 25 of the collar 24 of the bearing and to one end of the rib 26. When the pivot is pushed, the retention of the bearing in the recess of the head is reduced to the contact area at the edge 25, and is therefore very limited. During traction, the free space under the collar 24, between the toric wall of the recess of the head and the wall of the bearing allows deformation of the bearing so that the pivot is not retained in the bearing, and the retention of the bearing in the recess of the head is very limited.In the case of a toric central recess and a bearing having an external surface that is also toric (Case B), the thickness of the bearing wall that participates in the tear-off function in the vicinity of the collar 24 is greater. This reduces the resistance to tearing (traction) of the bearing. And when the pivot is pushed, only the edge 25 of the collar 24 exerts a retaining force so that the resistance to the push is quite limited.

[0034] In the case of a cylindrical central recess and a bearing having an external surface that is also cylindrical (Case A), in the event of traction of the pivot, the contact between the bearing and the central recess under the collar 24 prevents the extraction of the pivot from the bearing, and the contact of the rib 26 on the flat surface 45 of the head of the rod prevents the extraction of the bearing from the head of the rod. In the event of pushing, the contact of the collar 24 on the flat surface 44 prevents the ejection of the bearing from the head of the rod.

[0035] The mechanical properties of the polymer in which the bearing is made being less important than those of the head of the rod, the tests show that the resistance to tearing of the pivot in cases B and C is reduced by more than 30% compared to case A, the case of the invention.

[0036] The thickness Ep of the head 42, that is to say here the distance between the two flat surfaces 44, 45 is chosen by tests to find the best compromise to obtain a desired mechanical resistance, using the least possible material, and for a minimized cost. Note that the thickness Ep of the head 42 and the diameter Dp of the recess 43 are here decorrelated. of the diameter of the wire used to form the rod 40. Thus, it is possible to produce rods 40 from wires of different diameters (depending on the mechanical strength desired for the body 41 in particular), having heads 42 of the same thickness Ep and the same recess diameter Dp, which then makes it possible to use the same bearings. This facilitates the overall production of the joints and reduces their manufacturing cost.

[0037] Preferably, according to another aspect of the invention, a rod according to the invention is such that, after assembly of the ball joint, an extension of a longitudinal axis Ax of the body 41 of the rod passes through a center Cs of the spherical end 31 of the ball pivot 30. This can be obtained for example by a stamping step during which the median plane of the head is offset. In the particular case shown, the longitudinal axis Ax of the body 41 of the rod 40 is parallel to the median plane Pt of the annular head 42 (the head 42 is thus parallel to the axis Ax of the body) and a distance Dd between the longitudinal axis of the body and the median plane of the head is chosen so that, after assembly of the ball joint, an extension of the longitudinal axis of the body of the rod passes through a center Cs of the spherical end 31 of the ball pivot 30. This reinforces the mechanical resistance of the connecting rod.The median plane of the head 42 is parallel to the surfaces 44, 45, and equidistant from these surfaces. In the example shown, it is also perpendicular to the axis Ac.

[0038] Finally, as previously stated, although only one head 42 of the rod has been described above, the rod shown comprises two annular heads, each formed by bending each of the ends of the rod. The rod shown is thus symmetrical, and suitable for connection to two separate elements.

[0039] The rod according to the invention and as described above can be made from a metal wire in the following manner. The formation of a single head 42 is described, but two heads, one at each end of the rod, can of course be formed in a similar manner, either simultaneously or successively depending on the tools used.

[0040] First, a bending step is carried out (fig. 2): one end of a wire of circular section is bent to form the rod 40 comprising an annular head 42 at one end of a body 41.

[0041] A stamping (or pressing or crushing) step is then carried out to press the head 42 and form one or two external bearing surfaces 44, 45 of the head 42. Another stamping step is carried out to offset the median plane Pt of the head 42 relative to a longitudinal axis Ax of the body 41 of the rod 40 (offset in a plane parallel or a plane intersecting the axis Ax). Another stamping step can be carried out to texture the surface condition of the bearing surface(s) 44, 45. Depending on the tools available, the stamping steps can be carried out successively or simultaneously (a single stamping step to simultaneously flatten and texturize the flattened surface). The result of the stamping steps is shown in Figure 3.

[0042] A welding or brazing step can then be carried out to secure the curved end of the rod 40 to the end of the body 41 of the rod, and thus close the annular head 42.

[0043] Finally, a step of grinding the annular head 42 is carried out: the central cylindrical recess 43 is ground to form the cylindrical housing intended to receive the bearing (fig. 4).

[0044] It should be noted that, among the steps described above, only the bending and grinding steps are essential for implementing the invention. The other steps of stamping and welding / brazing improve the retention of the bearing and the overall mechanical strength of the final ball joint; they are not essential; they can be considered alone or separately. Also, the stamping, welding and grinding steps can be considered in a different order from the order described above. The grinding step will however preferably be carried out at the end to obtain a cylindrical central recess of optimal quality.

[0045] The ball joint 10 according to the invention and as described above can finally be assembled in the following manner, described in connection with Figures 5, 6. Here again, the assembly of one ball joint is described, but two ball joints, one at each end of the rod, can of course be assembled in a similar manner, either simultaneously or successively depending on the tools used.

[0046] The spherical end 31 of the pivot 30 is first inserted into the bearing 20 (arrow A, fig. 5). Then the bearing is introduced into the annular head 42 of the rod, until the flat edge 25 of the collar 24 of the bearing comes into abutment against the flat external surface 44 of the head 42 (arrow B, fig. 6). Finally, the rib 26 of the bearing 23 is crimped (or riveted) against the bearing surface 25 to crimp the bearing in the recess 43 of the head of the rod 40.

[0047] Texturing the surface condition improves the robustness of the contact between the collar or rib of the bearing on the one hand, and the head of the rod on the other.

[0048] The support and contact between the bearing and the annular head of the rod is achieved in 3 distinct zones: the upper face, the cylindrical recess and the lower part of the head of the rod. In a joint according to the invention, the ball joint (or spherical mechanical connection) is ensured by the spherical end of the pivot and the internal surface of the bearing. An additional rotation of the bearing in the head of the rod is not desired because it causes premature wear of the bearing which reduces the internal stresses of the ball joint; this reduction in stresses accelerates the premature damage of the bearing and therefore its end of life.

[0049] The crimping (or crimping - see above) of the bearing on the head of the rod aims to inhibit this additional rotation of the bearing in the head of the rod. This is effective at room temperature. However, tests carried out at -40°C show the persistence of this phenomenon of additional rotation at low temperature, due to structural modifications at low temperature of the polymer material from which the bearing is made. The addition of a texturing on at least one of the flat surfaces 44, 45 of the head of the rod increases the friction torque, because the bearing preforms in the texturing during crimping.

[0050] List of reference signs • 10: ball joint • 20: pad ° 21: interior space ° 22: opening ° 23: exterior surface ° 24: collar ° 25: edge of the collar ° 26: rib • 30: pivot ° 31: spherical end ° 32: stud • 40: support rod ° 40a: end ° 41: body ° 42: annular head ° 43: recess ° 44: first support surface ° 45: second support surface • Ax: longitudinal axis of the body 41 • Pt: median plane of the head 42 • Dd: distance between the longitudinal axis and the median plane • Cs: center of the spherical end • Ep: head thickness 42 • Dp: diameter of the recess 43

Claims

Claims

1. Joint (10) comprising a ball pivot (30), a bearing (20) and a support rod (40) - the ball joint (30) comprising a spherical end (31) and a stud (32) extending from the spherical end, - the bearing (20) being configured to house the spherical end (31) of the pivot, and - the support rod (40) comprising a body (41) and an annular head (42) formed by the bending of one end of the rod (40), articulation characterized in that the head (42) comprises a central cylindrical recess (43) configured to receive the bearing.

2. Articulation according to claim 1 in which the annular head (42) comprises a flat external bearing surface (44) extending in a plane secant to an axis (Ac) of the recess (43).

3. Joint according to claim 2 in which the bearing surface has a textured surface condition.

4. Joint according to one of claims 1 to 3 in which, after assembly of the ball joint, an extension of a longitudinal axis Ax of the body (41) of the rod (40) passes through a center (Cs) of the spherical end (31) of the ball pivot (30).

5. Joint according to one of claims 1 to 4 in which a free end (40a) of the rod (40) is secured by welding or brazing to the body (41) of the rod so that the head (42) forms a closed ring.

6. Joint according to one of claims 1 to 5, comprising two annular heads, each formed by the bending of each of the ends of the rod.

7. Joint according to one of claims 1 to 6 in which the bearing comprises an interior space (21) whose spherical shape and dimensions are adjusted to receive the spherical end (31) of the pivot (30), in which the bearing comprises an opening (22) shaped to allow the insertion of the spherical end (31) of the pivot, in which the bearing comprises a cylindrical exterior surface (23), and in which the cylindrical central recess (43) of the head (42) of the rod has dimensions are adjusted to receive the bearing.

8. Joint according to claim 7 in which the annular head of the rod comprises a flat external surface (44) in a plane intersecting an axis (Ac) of the recess (43), and in which the bearing (20) comprises a circular collar 24 extending from the cylindrical external surface (23) of the bearing and comprising a flat edge (25) configured to, during assembly of the joint, come into abutment against a flat external surface 44 of the annular head (42) of the rod.

9. A method of producing a ball joint comprising a ball pivot (30), a bearing (20) and a support rod (40), the method comprising the following steps: - a step of bending one end of a wire of circular section to form the rod 40 comprising an annular head 42 at one end of a body 41, - a step of stamping the head (42) to form a flat external bearing surface (44) configured to serve as a stop for a collar (24) of the bearing, and - a step of grinding the annular head 42 to form a cylindrical central recess 43 configured to receive the bearing of the ball joint.

10. Method according to claim 9, also comprising a welding or brazing step to secure the curved end of the rod 40 to the end of the body 41 of the rod.

11. Method according to one of claims 9 to 10, also comprising a step of texturizing a surface condition of the bearing surface (44).

12. Method according to one of claims 9 to 11 also comprising a stamping step for offsetting a median plane (Pt) of the head (42) relative to a longitudinal axis (Ax) of the body (41) of the rod.

Images