Ball joint assembly and method of construction

Abstract: A ball joint assembly (5) includes a ball stud (7) and bearing sub-assembly (9) that is economical to manufacture, strong, durable and long-lasting. The bearing is molded directly on the ball surface (15) of the ball (6), thereby eliminating the need for precise tolerances in machining the ball. Microcavities formed on the ball surface facilitate the introduction of lubricant between the ball and the bearing. A two-piece stud and collar nut adds ease of manufacture.

Description: FIELD OF THE INVENTION This invention relates in general to ball joint assemblies. It relates particularly to a ball joint of the type which is normally used for connecting movable parts in a vehicle suspension system. BACKGROUND OF THE INVENTION Automobiles and other vehicles normally incorporate suspension systems designed to absorb road shock and other vibrations. Many vehicles are provided with independent suspensions located at each wheel. These suspensions are designed to independently minimize the effect of shock loading on each of the wheels. Suspension systems commonly employ stabilizer bars which interconnect independent suspensions on opposite wheels and are effective to increase the roll rigidity and improve the steering stability of the vehicle. The stabilizer bars are connected to each wheel suspension by suspension links through ball joint assemblies. Conventional ball joint comprise a ball stud seated in a socket. In a suspension link, each end of the link incorporates a socket and a ball is seated in each socket. The stud which extends from the ball in one ball joint assembly is connected to a wheel suspension component. The stud extending from the ball in the other ball joint assembly is connected to one end of a stabilizer bar. The socket in a ball joint typically incorporates a bearing made from a plastic resin. The outer surface of the ball seats on the inner surface of the bearing and the stud extends out of the socket. The ball stud is free to move universally through a conical angle of approximately 30 degrees relative to the socket. A ball joint according to the first part of the claim 1 is disclosed in Jordan GB Patent No. 806,897. A frusto-conical surface of a collar formed at a stud engages a correspondingly tapered aperture of a suspension component of a vehicle and the suspension component is firmly secured to the stud by a clamp nut threaded onto a conical threaded portion of the stud. A further nut is threaded onto the stud between the frusto-conical surface and the ball of the ball stud, whereby under normal condition there exists a small distance between the further nut and suspension component. The further nut is only used for releasing the suspension component from the stud, after the clamp nut has been removed by turning the further nut to exert pressure against the suspension component, whereby the suspension component is bodily displaced and disengagement between the frusto-conical surface and the tapered aperture is effected. In further prior art ball joint assemblies it was conventional to machine the ball surface to reduce friction between the ball and the bearing. It is also known in the prior art, as shown in Jackson U.S. Patent No. 4,290,181, to construct a ball joint wherein a plastic bearing member is molded in the ball joint socket with the ball in place. Jackson states that the ball must be rotated while the bearing material congeals in order to form a suitable bearing surface. The stud portion of the ball is conventionally connected to a wheel suspension component, for example, by fastening the component between a plate fitted onto an inner portion of the stud and a nut threaded onto the threaded outer end of the stud, as seen in Kidokoro U.S. Patent No. 5,011,321. It is also known to form the plate integrally with the stud, in the form of a flange or collar, as seen in Shirai et al. U.S. Patent No. 5,009,538. In any event, substantial forces are brought to bear on a ball joint and these load forces produce stresses throughout the joint. The stresses must be absorbed by the various components of the joint, including the plate or collar and nut. SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved ball joint. It is another object to provide a ball joint which is simple and inexpensive to manufacture. It is yet another object to provide a ball joint with an improved stud and collar construction, which is easily manufactured and in which the ability of the stud to absorb stress is enhanced. The foregoing and other objects are realized in accord with the present invention as defined in the claim 1. Further, the stud is made with a collar roll-formed between its threads and the ball. The collar is formed in such a manner that an upper groove encircles the stud above the collar and a lower groove below the collar. The upper and lower collar surfaces are inclined away from the respective grooves. The upper groove creates space so that the stud can be moved angularly. The lower groove forms a relief which permits a threaded collar nut to be seated snugly against it with a sealant in the groove. The stud threads that engage the collar nut below the collar have a minor diameter that can be 1) larger than the remaining stud threads, or 2) greater than or equal to the normal pitch diameter of the remaining stud threads. BRIEF DESCRIPTION OF THE DRAWINGS The invention, including its construction and method of operation, together with additional object and advantages thereof, is illustrated more or less diagrammatically in the drawings, in which: Figure 1 is a sectional view through a ball joint assembly embodying features of the present invention, with parts removed; Figure 2 is an elevational view of a ball stud and bearing sub-assembly embodying features of the present invention; Figure 3 is a sectional view of the ball stud shown in Figure 2, seated in a mold; Figure 4 is a sectional view of the ball stud and bearing sub-assembly of Figure 2 placed in a clamp, including shadow lines illustrating the movement of the ball stud in the clamp; Figure 5 is a sectional view of the ball stud of Figure 2 attached to a wheel suspension component; Figure 6 illustrates a collar nut; and Figure 7 illustrates a ball stud embodying features of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and particularly to Figure 1, a ball joint assembly embodying features of the present invention is seen generally at 5. The assembly 5 includes a unitary ball 6 and stud 7, with the ball seated in a bearing 8 to form a ball stud and bearing sub-assembly 9. The bearing 8 of the sub-assembly 9 is clamped into one end of an automobile suspension link 10. The ball 6 and stud 7 are a one-piece construction made from steel. Generally speaking, the ball stud illustrated in the drawings may be achieved by cold forming and roll-forming steel in a manner well within the ability of one skilled in the art. The ball 6 is then treated to create a myriad of microcavities on its surface 15. The microcavities are formed by impelling cast steel shot at the ball surface under pressure. This may be accomplished by "wheelabrating" using a conventional machine known as a "Wheelabrator". The Wheelabrator machine tumbles parts on an endless belt during the impelling of shot. The microcavities must be small enough to prevent viscous bearing material from flowing into them. Small shot size is used in the machine to assure this result. Referring now to Figure 3, the bearing 8 is formed directly on the surface 15 of the ball 6 by placing the ball in a mold 20 and injecting viscous bearing material therein. Prior to placing the ball 6 inside the mold 20, the ball is cleaned to remove any grease, mold release or other foreign matter from the ball surface 15 so that such matter is not pushed by the advancing viscous bearing material to a point farthest from the inlet, thereby causing the hardened bearing to have a knit line which can crack easily. The mold 20 comprises an upper mold section 21 and a lower mold section 22. When mated together in the manner illustrated over the surface 15 of the ball, they form a generally ring-shaped mold cavity 25 over a portion of that surface. The cavity 25 conforms generally to the shape of the ball surface 15 except that an annular cavity extension 26 is defined around its periphery. An injection inlet 27 provides access to the cavity 25, 26. Viscous bearing material in the form of a thermoplastic resin is injected into the mold through inlet 27. In the preferred embodiment, acetal is injected at a temperature between 365° and 435° F. After the viscous bearing material hardens, the ball stud 6, 7 and bearing 8 are removed from the mold by separating the mold halves 21 and 22. The bearing 8 is generally ring-shaped and has a plastic flange 29 formed around its circumference, as best seen in Figures 2 and 4. The projected area of the bearing is equally divided above and below the annular flange so that resultant force passes through the center of the ball, creating the shortest moment-arm for force applied to the stud. After removal from the mold, full shrinkage of the plastic bearing 8 takes place in approximately 24 hours. At this point the ball 6 is locked inside the bearing 8, i.e., it will not move freely. In order to facilitate the desired movement of the ball 6 on the bearing 8, lubricant is introduced between the ball 6 and the bearing 8. This is accomplished in the manner shown in Figure 4. As seen in Figure 4, the ball stud and bearing sub-assembly 9 is placed between two fixtures 31 and 32. These fixtures 31, 32 seat tightly against the outside surface of the bearing 8 with the flange 29 between them. The fixtures 31, 32 are pressed against the bearing 8 by clamps (not shown) so as to rigidly fix the ball 6 and bearing 8 in place. An inlet port 40 is located at one end of the fixture 31 and provides a path for the introduction of lubricant into the space 41 overlying the bearing surface 15 at the free end of the ball 6. A lubricant having a coefficient of viscosity low enough to flow into the microcavities is introduced to the space 41 through the port 40. The ball stud 7 is moved back, forth and around as the lubricant is introduced. Part of the desired movement is illustrated by the phantom lines shown in Figure 4. As the ball 6 moves, lubricant in the microcavities on the surface 15 exposed in space 41 works its way between the opposed surfaces of the ball 6 and the bearing 8. Figure 4 also illustrates the full range of motion for the ball stud 6, 7 in relation to the bearing 8. This full range of motion is accommodated in the entire ball stud sub-assembly 9 when seated in a link 10, as shown in Figure 1. It will be seen that the aforedescribed method of manufacturing the ball stud sub-assembly 9 provides substantial advantages. For example, the need for precise tolerances in machining the ball 6 is eliminated, and a well lubricated joint is achieved in a simple and efficient manner. In this regard, it should be recognized that a suitable ball 6 surface may be achieved by methods other than wheelabrating. As seen in Figure 1, the ball stud and bearing sub-assembly 9 is seated in the end of a suspension link 10 to form a ball joint assembly 5. The bearing 8 is held in place inside the link 10 end by securing the flange 29 between the sandwiched halves 45 and 46 of the link end. Because the bearing 8 is fixed in place inside the link end 10 by the flange 29, there is no need for the bearing 8 to conform completely to the inner surface of the link end halves 45 and 46. Thus, there is no need for maintaining close tolerances in forming the bearing 8. Turning now to Figure 5, a ball and stud 6, 7 are shown secured to a component 50 of a wheel suspension. The stud 7 has external threads 51. A reinforcing collar nut 52 having internal threads 54 and shown in detail in Figure 6 is threaded onto the stud 7. The stud 7 is then passed through an aperture 55 in the component 50 and the exposed outer end of the stud 7 is secured by a clamp nut 56. The ball stud 6, 7 and collar nut 52, being rigidly connected to the suspension component 50, is subjected to load forces that are placed on it through the vehicle suspension system. An example of one of these load forces is graphically illustrated by the double-head arrow in Figure 5. The construction of the ball stud 6, 7 and collar nut 52 is particularly effective in transmitting these forces without damage. Specifically, the stud 7 is roll-formed during manufacture to form a collar 60 around its mid-section. In forming the collar 60, which has converging frusto-conical faces 61, a groove 62 is left surrounding the stud below the collar and another groove 63 is left above it. The collar nut 52 is threaded on and seated against the collar 60 with only a low torque. This low torque application of the collar nut avoids simple cantilever loading of the shank of the ball-stud by redistributing the "work-load" to the outer diameter of the collar nut and, therewith, clamping the stabilizing bar 50 between the collar nut and the flanged locknut. It also avoids algebraic addition of the loads on the ball-stud shank. The separate collar nut, beside the favorable force distribution, provides a ball stud that does not require machining to achieve proper operating clearance. This construction enhances the ability of the stud to withstand stress by effectively redirecting the load forces applied to the ball stud in order to distribute these forces throughout the ball stud. This enhanced ability can be demonstrated best by comparing the section moduli of a ball stud and nut without a collar construction versus the ball stud and collar nut as described herein. For ease of analysis, the "non-collar" construction may be modeled by a simple cantilever for which load forces are applied in a direction perpendicular to the cantilever beam; and the "collar" construction may be modeled by a simple cantilever for which the load forces are applied in a direction parallel to the cantilever beam (i.e., the forces are "offset"). SIMPLE CANTILEVER Moment of inertia = π 4 R 4 = I SC Section modulus = π 4 R 3 = Z SC OFFSET SIMPLE CANTILEVER (by the parallel axis theorem) RATIO OF SECTION MODULI = 5 4 π R 3 1 4 π R 3 =5:1 I SC = moment of inertia (simple cantilever) Z SS = section modulus (simple cantilever) I OSC = moment of inertia (offset simple cantilever) Z OSC = section modulus (offset simple cantilever) R = radius of ball stud at 62 The strength benefits gained by using the offset cantilever approach are derived from the "fulcrum" action applied at 60. This action places most of the fibers in the stud in near pure tension. In comparison, forces acting on the simple cantilever place less than 1/2 of the fibers in tension. As illustrated above, the section moduli with the collar 60 is approximately 5 times higher than it is without the collar 60, i.e., the former increases the maximum load strength by approximately 5 times under ideal conditions. Figures 6 and 7 illustrate further details of the preferred thread connection between the stud 7 and the collar nut 52. As seen in Figure 7, the minor diameter of the threads 51 immediately below the collar 60 is larger than the minor diameter of the remaining threads 53 of stud 7. For ease of forming, the minor diameter of the threads immediately below the collar 60 may be made approximately equal to the normal pitch diameter of the remaining threads 53 on the stud 7. The mating threads 54 of the collar nut 52, as seen in Figure 6, include a minor diameter corresponding to the size of the minor diameter of the threads 51 immediately below the collar 60. The collar nut 52 is also formed with an annular groove 70 around its periphery. This groove is adapted to receive the outer end of a dust cover (not shown) in sealing relationship. The inner end of that same dust cover is then seated over the outwardly extending lip 71 on the link end half 46. The separate collar nut, beside the favorable force distribution, provides a ball stud that does not require machining to achieve proper operating clearance.

Claims: A ball joint for connecting two movable components of a vehicle suspension system together comprising: a ball stud having a ball (6) for seating in a socket formed in one suspension component (10) and connecting the ball stud to the one component (10); a stud (7) extending from said ball (6) for connecting said ball stud to another suspension component (50) and having a cylindrical portion which is threaded with external screw threads (51,53); said stud (7) having a collar (60) formed around it between said threaded portion and said ball (6); a frusto-conical surface (61) formed on said collar (60) immediately adjacent said threaded portion; said threaded portion extending to adjacent an exposed end of the stud (7); a clamp nut (56) threaded onto said threaded portion from said exposed end; a collar nut (52) threaded onto said stud (7); characterized by: said collar nut (52) having a face and being threaded onto said threaded portion of said stud (7) to where said surface (61) and said face engage each other and secure said collar nut (52) against said collar (60); said threaded portion being adapted to pass loosely through an aperture (55) in the other suspension component (50); and said clamp nut (56) being adapted for clamping the other suspension component (50) tightly against said collar nut (52) to form a rigid connection between the ball stud (7) and the other suspension component (50). The ball joint defined in claim 1 further characterized in that at least one (51) of said screw threads (51, 53) on said stud (7) has a minor diameter that is approximately equal to the pitch diameter of other screw threads (53) on said stud (7). The ball joint defined in claim 1 or 2 further characterized in that at least one (51) of said screw threads (51, 53) on said stud (7) has a minor diameter that is greater than a minor diameter of other screw threads (53) on said stud (7). The ball joint defined in claim 2 or 3 characterized in that a minor diameter of said inner screw threads (54) of said collar nut (52) corresponds to the minor diameter of said at least one screw thread (51) that is greater than the minor diameter of other screw threads (53) on said stud (7). The ball joint defined in one of the claims 1 to 4 further characterized in that: the face of said collar nut (52) is formed thereon in a conical shape complementary to said frusto-conical surface (61) formed on said collar (60). The ball joint defined in one of the claims 1 to 5 further characterized in that: said collar nut (52) is seated against said collar (60) with a force exerted by a low torque applied to the nut (52). The ball joint of claim 1 further characterized in that: said collar nut face is frusto-conical in shape.

Inventors: HELLON KEITH, PAZDIREK JIRI, HELLON, KEITH, PAZDIREK, JIRI
Applicants: MAC LEAN FOGG CO, MAC LEAN-FOGG COMPANY
Application year: 1992
Main classification: F16C11
IPC codes: F16C11, B29C45