BALL JOINT

Abstract: A ball joint includes a pair of generally hemispheric head members (13, 15) including facing surfaces (14, 17). A bearing member (18) is disposed between the facing surfaces (14, 17). One of the haed members (13) is connected to a ball stud (11), the other includes a shank hole (16) through which the ball stud (11) passes. Both head members (13, 15) are enclosed in a ball seat (28) which is deformed into conformity with a generally spherical outer surface of the combined first and second head members (13, 15) by a socket (23) that is formed about them. An elastic member (34) between the socket (23) and the ball seat (28) applies an axial force to said first and second head members (13, 15) , whereby a substantial preload on the ball joint permits take-up of wear during use.

Description: The present invention relates to a ball joint and is particularly directed to a ball joint wherein load is principally applied in the direction parallel to the shank of the ball stud with the ball stud and the socket rotating relative to each other. According to conventional ball joints used for a rack and pinion type steering system for automotive vehicles, the main load is applied in the direction parallel to the shank portion of the ball stud, with either the ball stud or the socket rotating. A known example of such type of ball joint is described in Japanese Utility Model Publication No. 27085/1985. The above conventional ball joint comprises a ball stud provided with a ball bearing around the end of the shank portion thereof to rotatably support a head member which has a spherical outer surface and is contained inside a socket with a ball seat in between. Such conventional ball joint is further characterized by either the shank portion of the ball stud or the socket being connected to the rack bar side of the steering mechanism of an automobile to be moved and rotated in the direction parallel to the rack bar and that the other is connected to the tie rod at the wheel side and interlocked with the said movements in the direction parallel to the rack. At the time of assembling such a conventional ball joint, preload is applied to the head member with a ball seat made of elastic synthetic resin in order to compensate for abrasion of the contact surface between the ball seat and the head member, but, in this way, the ball bearing does not receive sufficient preload. In other words, preload such as above is applied to a certain extent to the raceway in which the balls roll, but when the raceway has been worn with abrasion, it will produce play around the ball stud in the direction of its shank center. And wear of the ball stud in the direction of the shank portion center is fatal to the functioning of this type of ball joint. Therefore means to compensate for abrasion is necessary. US-A-3,007,728 discloses a ball joint having the features of the preamble of Claim 1. GB-A-2,081,369 discloses a ball joint in which the socket has a connecting shank portion which extends generally coaxially with the ball stud. The object of the present invention is to compensate for abrasion at the bearing section to rotate the ball stud and the socket relative to each other and thereby to provide a ball joint with a long life-span. The invention provides a ball joint according to Claim 1. According to the present invention, while in operation, when, for example, a connected shank portion of the socket rotates and simultaneously advances and retreats in the direction parallel to the shank to move a shank portion of the ball stud in the same direction, the socket rotates, together with the ball seat, around the first head member, and the second head member supported inside the socket rotates through the bearing member between the second head member and the first head member. Therefore, the turning effect is not conveyed to the ball stud. In this manner, preload from the elastic member acts on the bearing member through the ball seat and the first and second head members. Therefore, even though wear occurs to the ball seat and/or the bearing member due to abrasion, such wear is compensated because of preload, which is applied at all times, so no play will occur to the ball stud in the direction of its shank portion. Figure 1 is a schematic section view according to one embodiment of the present invention; Figure 2 is a schematic section view of a ball seat before assembly of same; Figure 3 is a schematic plan view of the ball seat of Figure 2; and Figure 4 through 6 are schematic side views respectively showing other embodiments of the present invention. The illustrated preferred embodiment of the present invention will be described hereunder referring to the attached drawings; In Fig. 1, numeral 11 denotes a metal ball stud comprising a cylindrical shank portion 12 and a hemispherical first head member 13 integrally provided at the end of shank portion 12. A flat surface 14 perpendicular to the shank portion 12 is formed around the shank portion 12, at the large-diameter-end of the first head member 13. Numeral 15 denotes a second head member made of metal. This second head member 15 is shaped like a ring having a nearly hemispherical outer surface. A shank hole 16 formed at the center of second head member 15 to fit around the shank portion 12. A flat surface 17 is disposed perpendicular to the shank hole 16 and formed at the larger-diameter-end. The second head member 15 is rotatably fitted, at the shank hole 16 thereof, around the shank portion 12. The flat surface 17 of second head member 15 faces the flat surface 14 of the first head member 13. A bearing member 18 is provided between the flat surfaces 14 and 17 of the first head member 13 and the second head member 15 respectively. The bearing member 18 consists of numerous cylindrical rollers 20 radially arranged and rotatably supported by a ring-shaped cage 19. Each roller 20 is in contact at both sides of the cage 19 with the flat surfaces 14 and 17. In this manner, the said first head member 13 and the second member 15, which together have a globe-like shape, form a spherical head portion 21. Numeral 23 denotes a metal socket, at one end of which an inner chamber 25 having an opening 24 is formed. A shank portion 26, at the other end of the metal socket 23, is integrally provided to protrude therefrom. The first head member 13 and the second head member 15, which together form the spherical head portion 21 of the ball stud 11, are contained in the inner chamber 25 of the socket 23. The shank portion 12 protrudes from the opening 24. The shank portion 12 of the ball stud 11 and the connected shank portion 26 of the socket 23 are remain aligned with each other. A ball seat 28 is attached inside the inner chamber 25 of the socket 23 and envelopes the first head member 13 and the second head member 15. A conventional lubricant in the ball seat 28 permits the first head member 13 and the second head member 15 to slide therein. A hard synthetic resin with a good load resistance and good bearing characteristics, such as, for example, a polyacetal resin, is a suitable material for the ball seat 28. As shown in Figs. 2 and 3, the ball seat 28, before installation in the socket 23 has a cylindrical portion 29 that is open at one end and include a step portion 30 and a tapered portion 31 of inwardly reducing diameter at the other end. The step portion 30 is located between the cylindrical portion 29 and the tapered portion 30. A plurality of ridges 32 are formed at specified intervals on the outer surface of the tapered portion 31 and in the direction of the shank portion 26. One slit 33 is formed between each two ridges 32, in the direction of the shank portion 26. An elastic member 34 with a dish-like shape is provided in the socket 23, at the side opposite to the opening 24, i.e. between the bottom of the inner chamber 25 of the socket 23 and the ball seat 28. The elastic member 34 is in contact with the step portion 30 of the ball seat 28 and the outer surface of each ridge 32 of the tapered portion 31. A highly elastic synthetic resin or synthetic rubber, such as, for example, polyurethane or polyester, is a suitable material for the elastic member 34. The entire side where the opening 24 is provided of the said socket 23 is swaged on, inwardly deformed, at the time of assembly to contain the first head member 13 and the second head member 15 together with the ball seat 28, thereby to envelope the first head member 13 and the second head member 15 and to produce a preload to compensate for abrasion of the ball seat 28. By the deformation of the ball seat 28, the elastic member 34 is simultaneously shrunk so that it receives preload, which produces pressure via the ball seat 28 upon the opposite surfaces of the first and second head members 13 and 15 respectively of the ball stud 11 in the direction to support the bearing member 18 between them. Then, the connected shank portion 26 of an socket 23 is connected, for example, to a bar side of the operation mechanism of a steering system of an automobile (not shown) and moved and rotated in the direction parallel to the shank portion 26. The shank portion 12 of the ball stud 11 is connected to the tie rod of the wheel side (not shown) and interlocked with the forward and backward movement in a direction parallel to the shank portion 12. In the above condition, when the connected shank portion 26 of the socket 23 moves in a direction parallel to the shank portion 26, the shank portion 12 of the ball stud 11 moves in the same direction. Simultaneously as the shank potion 26 rotates, the socket 23 and the ball seat 28 also rotate, around the first head member 13. The second head member 15, supported at the socket 23, rotates on the bearing member 18 between the first and the second head members 13 and 15, so that the rotation of the shank portion 26 is not conveyed to the ball stud 11. During the above operation, preload from the elastic member 34 works through the ball seat 28, the first head member 13 and through the second head member 15 upon each roller 20 of the bearing member 18. Therefore, if abrasion of the ball seat 28, the rollers 20 and/or the flat surface 14 and 17 occurs, such abrasion is compensated for by the continually applied preload, and no play occurs around the ball stud 11 in the direction of its shank portion. Further, by providing the ball seat 28 with a plurality of slits 33, the elastic member 34 works more evenly and smoothly, in applying the preload, thereby achieving a better effect. In addition, a plurality of slits (not shown) can be provided in the direction of the shank portion on the other surface of the ball seat 28, i. e. the surface facing the second head member 15. Although a bearing member 18 is provided with rollers 20 according to this embodiment, it is also possible to use another type of bearing member, such as various kinds of ball-and-roller bearings and plain bearings in other embodiments of the present invention. For example, the embodiment shown in Fig. 4 calls for forming ring-shaped raceways 36 and 37 along the respective edges of the flat surfaces 14 and 17 of the first and the second head members 13 and 15 of the ball stud 11 and providing numerous balls 38, adjacent to each other, between the raceways 36 and 37. Furthermore, the embodiment shown in Fig. 5 calls for using a ring 39 of a disk-like shape as the bearing member 18. A synthetic resin with a low coefficient of friction, such as a fluororesin, polyacetar, etc., or a metal alloy or composite material with a low coefficient of friction is suitable for use in rings 39. Moreover, according to the embodiment shown in fig. 6, the first head member 13 and the second head member 15 are arranged at positions opposite to those according to the embodiment shown in Fig. 1. According to the embodiment shown in Fig. 6, the first head member 13 is integrally formed around the shank portion 12 of the ball stud 11, leaving a fitting portion 12a at the end of shank portion 12. The the second head member 15 is rotatably fitted around the fitting portion 12a. In other words, the head can be divided at the surface perpendicular to the shank portion 12 into the first head member 13 and the second head member 15, each member arranged to the each other. Although this embodiment also shows a bearing member 18 consisting of a cage 19 and rollers 20, it is possible to use balls 38 shown in Fig. 4 or rings 39 shown in Fig. 5. According to the present invention, the ball stud 11 and the socket 23 rotate smoothly in relation with each other due to the bearing member 18 provided between the first and the second head members 13 and 15. Since a preload is applied at all times upon the bearing member 18, abrasion due to load on the ball stud 11 in the direction parallel to the shank portion 26 is compensated for. It is hereby possible to provide a ball joint which is small and at the same time has a large load rating as well as high rigidity and a long life-span.

Claims: A ball joint comprising: a first head member (13) including a first generally hemispherical surface; a second head member (15) including a second generally hemispherical surface; said first and second members (13,15) being disposed so that said first and second generally hemispherical surfaces together form a generally spherical outer surface; bearing means (18) provided between opposed end surfaces (14,17) of the first and second members (13,15) to enable relative rotation between said first and second opposed end surfaces (14,17) to take place; a ball seat (28) enclosing said first and second head members (13,15); a socket (23) enclosing said ball seat (28); a ball stud (11) affixed to one of said first and second head members (13,15) and projecting through an opening (24) in said ball seat (28) and said socket (23); the other of said first and second head members (13,15) including a shank hole (16) for accommodating passage of said ball stud (11) therethrough, thereby permitting relative rotation between the head members; characterized in that said ball seat (28) is made of a load resistant, bearing material and a disc-like member (34) of a more highly elastic material, is provided in the socket (23) at the base thereof, opposite to said opening (24) therein, to apply, by a resilient deformation thereof, a preloading force on the ball joint components; and, a shank portion (26) is connected to said socket (23) and extends generally coaxially with said ball stud (11). A ball joint according to Claim 1, wherein said bearing means (18) includes cylindrical rollers (20). A ball joint according to Claim 2, wherein a cage (19) is disposed about said cylindrical rollers (20). A ball joint according to Claim 1, wherein said bearing means (18) includes a plurality of balls (38). A ball joint according to Claim 4, wherein said bearing means further includes at least one raceway (36,37) into which said plurality of balls (38) are rollably disposed. A ball joint according to Claim 1, wherein said bearing means (18) includes a ring (39) disposed between said first and second opposed end surfaces (14,17). A ball joint according to Claim 1, wherein: said ball seat (28) includes a plurality of ridges (32) on an external surface thereof; and at least some of said plurality of ridges (32) contacting said elastic member (34). A ball joint according to Claim 7, wherein said external surface includes at least one slit (33) between an adjacent two of said plurality of ridges (32). A ball joint according to Claim 1, wherein said ball seat (28) includes at least one slit (33) therethrough. A ball joint according to Claim 9, wherein said at least one slit (33) faces said elastic member (34). A method for making a ball joint as claimed in any one of Claims 1 - 10, comprising:- inserting said elastic member (34) into the base of said socket (23); inserting said ball seat (28) enclosing said first and second head members (13,15), into said socket to engage said elastic member (34); and deforming a portion of said ball seat (28) about said first and second head members (13,15) to deform resiliently said elastic member (34) thereby preloading the ball joint components.

Inventors: HATTORI, TAKAJI C/O ISHIKAWA TEKKO K.K., HYODO, YOUICHI C/O TOYOTA JIDOSHA K.K., MURAMATSU, TADAO C/O TOYOTA JIDOSHA K.K.
Applicants: KABUSHIKI KAISHA SOMIC ISHIKAWA, TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1989
Main classification: F16C11
IPC codes: F16C11, B62D7