CERAMIC BALL AND SOCKET JOINT

Abstract: A ball and socket joint which allows the precise positioning of the line of contact between the ball and the socket utilizing a spherically curved socket and an offset radius ball. The significant manufacturing difficulties associated with the shaping of an offset radius socket is avoided by the use of the spherical socket and offset radius ball. Furthermore, the ball and socket configuration enables use of ceramic materials to produce the socket and/or ball components which, in turn, results in a dramatic increase of the life of the ball and socket joint.

Description: The present invention relates to ball and socket joints, particularly those of the type found included in fuel injector valve trains and cylinder valve trains of engines. In particular this invention relates to a ball and socket joint comprising the features of the generic part of claim 1. In the manufacture of ball-socket joints for such applications as the push rods of fuel injector drive train components and cylinder valve drive train components it has, for a long time, been standard practice to ensure that contact between the two socket parts is along a line at a desired location and not at some undesired point. To achieve a precise positioning of the line of contact between the ball and the socket of a ball-socket joint, precise tolerances in the mating surfaces are required and the precise positioning of the line for contact has been achieved by making the socket of a non-spherical shape (i. e., a so-called "gothic arch" of offset radius socket that is machined with a spherical radius that is offset from the radial centerline), while making the ball end part of the joint spherical. An example of such a conventional offset socket ball-socket joint is illustrated in Figure 1. However, production of such a gothic arch, offset radius, socket requires a machining operation that is twice as difficult as for formation of a spherical socket. Prior art is a ball-socket joint that forms the starting point of the invention (DD-A-147 384). Here not the socket is produced with an offset radius but the ball part. Here the radius of curvature of the offset ball surface is offset from the center line axis of symmetry of the socket. Although it is easier to have the ball part machined in a spherical form with an offset radius of curvature, this is still a difficult construction, because the offset ball surface is continued away from the socket through a radial plane extending normal to the center line axis of symmetry of the socket and containing the center of the radius of curvature of the offset ball surface. With this construction undesirable tensile stresses are induced in the area of the reentrant curvature on the ball part. Furthermore, the high compressive loads imposed between the ball and the socket components of such engine sub-system drive trains can result (within as little as 20 to 30 thousand miles) in the metallic surfaces of the ball and/or the socket becoming worn to such an extent that undesirably large amounts of play occur which adversely impact upon the operation of the associated fuel injectors, valves, etc. Thus, when such wear occurs, it is necessary to perform major servicing of the engine and the vehicle equipped with the associated engine must be taken out of use for a day or more. Moreover, as such, the use of ceramic in ball and socket joints with the advantage of wear reduction is well known from prior art (DE-A-3 239 325, "machine design", vol. 53 no. 14, page 5, published June 18, 1981). In view of the foregoing, it is the object of the present invention to provide a ball and socket joint that can be produced in a simpler, and thus less costly, manner than the conventional offset radius socket type ball and socket joint, and simultaneously to avoid the wear problems associated with ball and socket joints formed of metal ball and socket components. Above mentioned object is achieved with a ball and socket joint comprising the features of the generic part of claim 1 and in addition the features of the characterizing part of claim 1. The offset ball part-curvature according to the present invention is particularly suitable when the socket is of a ceramic material. Choosing the spherical socket of a ceramic material means avoiding to have to manufacture in a ceramic material an offset socket which is particularly difficult. Instead it is easier to manufacture even from ceramic material a ball part with an offset radius of curvature. Moreover, possible tensile stresses in the area of the reentrant curvature of the ball part are specifically avoided by merging the offset ball surface with a cylindrically shaped portion of the ball part. Although a pure ceramic ball and socket joint would be capable of handling significantly higher compressive loads than a joint with a metal ball part, even that joint achieves the manufacturing advantages to a still significant extent. Further preferable features may be obtained from claims 2 through 5. Further benefite of the present invention will become more apparent from the following detailed description and accompanying drawings. Fig. 1 schematically illustrates in cross-section a conventional offset radius ball and socket joint configuration in exploded view, Fig. 2 is a view similar to that of Fig. 1, but illustrating a ball and socket joint configuration in accordance with the present invention, Fig. 3 is a diagrammatic illustration of a cylinder head valve drive train incorporating a plurality of ball and socket joints of the type to which the present invention is directed, Fig. 4 is a diagrammatic illustration of the fuel injector drive train incorporating a plurality of ball and socket joints of the type to which the present invention is directed, Fig. 5 is a perspective view of a drive train component incorporating a ceramic ball and a ceramic socket in accordance with the present invention, Fig. 6 is a cross-sectional view of the ball end part of the Fig. 5 drive train component, Fig. 7 is a cross-sectional view of a socket end part of the Fig. 5 drive train component, Fig. 8 and 9 represent geometric ball and socket configurations to be avoided in accordance with the present invention and serve as a guide to the selection of offset radii usable in accordance with the present invention. As noted initially, it has been conventional to form a ball and socket joint whereby a line of contact between the ball and socket is controlled to occur at a desired location through the use of an offset radius socket and spherical ball type ball and socket joint of the type illustrated in Figure 1. In such an arrangement, the socket takes on a so-called "gothic arch" shape in cross-section. The arch-shaped socket is formed in the end of a rod 1 by rotation of the rod 1 relative to a machining tool about an axis of symmetry X so that a curvature is produced having a radius R₁ that is offset from axis X to the extent represented, by way of example, in Figure 1. On the other hand, the ball element is constituted by a rod 3 having a spherical ball end 5 whose curvature has a radius R₂ that is symmetrical with respect to the center line axis of symmetry X. When the spherical ball end 5 of the rod 3 is brought into engagement with the offset radius socket 2 of the rod 1, a circular line of contact results at an intermediate location between the apex of the arch and the outer edge thereof. As also noted, production of such an offset radius socket is twice as difficult to produce in a metal component as is a spherical one, but due to the hardness of ceramic materials, such as silicon nitride, silicion carbide, zirconia, etc., the manufacturing difficulties associated with the production of such a socket become so significant as to make it economically impractical to produce. On the other hand, as schematically depicted in Figure 2, the socket rod 1 is provided with a spherical socket 7 having a curvature with a radius R₁ that is symmetrical with respect to the center line axis of symmetry X, while the ball end of the rod 3 is an offset radius ball 9 with a rounded edge curvature that is produced by rotation of the rod 1 relative to the machining tool in a manner producing a rounded corner curvature having a radius R₂ that is offset with respect to the center line axis of symmetry X by an amount as represented, for example, in Figure 2. This new configuration for a ball and socket joint in accordance with the present invention is half as difficult to produce as an offset socket type ball and socket joint and, for the first time, makes it economically feasible to use ball and/or socket components formed of ceramic materials such as silicon nitride, silicon carbide, zirconia, etc., although, basically, in prior art it was already considered to utilize ceramic ball and socket joints (DE-A-3 239 325 etc.). However, it has been found that in a drive train of the type schematically indicated in either Fig. 3 or Fig. 4, by way of example, ceramic ball and socket joints can increase the compressive loads to which such joints may be subjected and, even when only the ball part is formed of a ceramic material, the life of the joint achievable before an unacceptably large amount of wear occurs can be increased by over an order of magnitude to, for example, 500.000 miles. In this regard, it is noted that Figure 3 depicts an engine cylinder head valve drive train wherein ball and socket joints 11 are provided at each of opposite ends of a push rod 13 used to transmit movement produced by a cam 15 to a valve rocker lever 17, the lever 17 being used to seat and unseat valves 19 with respect to the valve seat inserts 21 via the cross head 23. Figure 4, on the other hand, depicts a fuel injector drive drain having four ball and socket joints 25. A first pair of joints 25 are disposed at opposite ends of a push rod 27 similar to the arrangement of Figure 3, while motion is transmitted from the injector rocker lever 29 to the injector piston 31 through the intermediary of a modified push rod 33 which also forms a pair of ball and socket joints 24 at each of opposite ends thereof. It is noted that while the present invention finds particular utility in drive trains of the type shown in Figures 3 and 4 (wherein high loads are experienced, servicing of the ball and socket joints is costly and time consuming, and the required frequency of servicing can be an important factor in the purchase of an engine for a vehicle or piece of equipment of which it is a part), the inventive ball and socket joint will also find utility in numerous other environments which require ball and socket joints of the type wherein a precisely located line of contact can be maintained between the ball and the socket of the joint. With reference to Figures 5-7, a preferred embodiment push rod 35 (which may be either the push rod 13 of the Figure 3 drive train or the pus rod 27 of the Figure 4 drive train, for example) is shown. Push rod 35 utilizes a ceramic ball end part 37 and a ceramic socket end part 39 in accordance with the present invention. It should also be appreciated that the ball parts B and socket parts S (Figs. 3, 4) that cooperate with the ball parts 37 and socket parts 39 may also be ceramic or may be formed of metal. Likewise, the modified push rod 33 can be formed in the same manner as push rod 35 simply by substituting a second ball end part 37 for the socket end part 39. The push rod 35 is formed of a rod part 41 that may either be a hollow tube or a solid rod the ends of which have been provided with cylindrical recesses. Thus, the ball end and socket end parts 37, 39 are formed with plug ends 37a, 39a, as shown in Figures 6 and 7, by way of which these parts may be secured to the ends of rod 41 in a manner that forms no part of the present invention. In addition to the plug end portion 37a, the ball end part 37 has an abutment rib portion 37b and a ball portion 37c, break edges 37d of the abutment portion 37b merging into the plug portion 37a and the ball portion 37c by way of radius curved surfaces 37e and 37f. In accordance with the present invention, the ball portion 37c is a radial offset ball having a spherical radius offset surface 41 that is defined by the locus of points swept by the offset radius R 0 (which is radially offset by a distance 0 form the axis of symmetry X) as it is rotated about the axis of symmetry X and swung in an angular direction between an axial line Y that is parallel to and offset from the center line axis of symmetry X and the lines Z defining a radius plane extending normal to said axis of symmetry X and containing the points at which said radii R 0 originate. Below line Z, the peripheral portion 43 is of cylindrical shape having a radius corresponding to that of the curved surface 41 at the base line Z. It is equal to the radius R 0 plus the radial offset 0. Within the circular area 45 at the top of the ball portion 37c the surface can be left flat and parallel to the base line Z. The manner in which the radius R 0 and the radial offset 0 are selected is described in greater detail below. The socket end part 39 has a socket portion 39b within which a hemispherically curved socket surface 27 is formed having a radius R s . However, surface 47 may be a spherical surface of less than hemispherical extent in some cases. When a part having a socket 7, 47 is brought into engagement with a part having an offset radius ball 9, 37c, with their parts axially aligned (disposed on a common axis of symmetry), a circular locus of points of contact will occur. If this locus of contact points occurs at the edge of the ball surface (Figure 8), the contact will produce undesirably high levels of stress at the point of contact. Likewise, if points of contact occur at the perimeter of area 45 or at the edge of a socket drilling 50 (of the type commonly provided for supplying lubrication to the joint), undesirably high stress levels will occur at the line of contact as well. The same holds true if contact between the ball and socket occurs at the apex of the ball if, instead of utilizing a flat-topped offset radius ball, a gothic arched ball is utilized. Thus, in addition to the usual considerartions in the design of a ball and socket joint for a drive linkage, the radii and offset should be selected so as to form a line of contact that will be as far as practical from contact points which would produce high stress levels. For example, usually it would be desirable to produce a line of contact at a location approximately at the mid point of the 90 degree angle defined between the axial line Y and the base line Z, but in joints wherein the socket has an undercut, this line of contact might have to be shifted to avoid any such undercut. With this in mind, it has been found that an offset 0 from the center line axis of symmetry X will usually be most advantageously selected in the range of 4 to 7 percent of the length of the radius R 0 . Furthermore, apart from the fact that the radius R₁ will be larger than the radius R₂ to ensure that the ball end will fit within the spherical socket, no specific relationship between these two radii need be maintained apart from the noted constraint of selecting of these radii so as to achieve a line of contact between the ball and socket surfaces which will not result in the described high stress concentrations occurring. Apart from the inventive characteristics of the described ball and socket joint, it should be recognized that the radii and extent of the socket surface will be dictated by the usual considerations attendant to avoiding any obstruction to achieving the degree of pivoting motion required to be produced during operation of the drive train, as might occur if, for example, the radii and extent of the socket surface were such that the push rod 13, 27 33 abuts the break edge 55 (Fig. 2) of the socket under operating conditions that can be anticipated. Also, by way of example, for a push rod 35 of a fuel injector drive train, a socket end part 39 having a spherical radius of 6.34 + 0.05 inches has been found suitable for use with a radial offset ball having a radial offset of 0.510 + 0.025 inches and an offset radius of 7.10 + 0.05 inches.

Claims: 1. A ball and socket joint comprising a socket part (1, 39) having a socket (7) therein, and a ball part (9, 37), wherein said socket (7) is defined by a spherically curved surface (47) having a radius of curvature (R₁, R S ) originating at a center line axis of symmetry (X) of the socket (7), and the ball part (9, 37) has an offset ball surface (41) with a radius of curvature (R₂, R₀) originating at an axial line (Y) that is parallel to and offset from the center line axis of symmetry (X) of the socket (7) as well as the ball part (9, 37), wherein said offset ball surface (41) is defined by a locus of points swept by the offset radius of curvature (R₂, R₀) as said axial line (Y) is rotated about said center line axis of symmetry (X) of the ball part (37) and said offset radius of curvature (R₂, R₀) is swung in an angular direction between said axial line (Y) and the radial lines (Z) defining a radial plane extending normal to said center line axis of symmetry (X) and containing the points at which the said radius of curvatures (R₂, R₀) originates, characterized in that said socket part (1, 39) is formed of a ceramic material and said ball part (9, 37) is preferably also formed of a ceramic material, wherein said ceramic material preferably is silicon nitride, silicon carbide, or zirconia, and in that said offset ball surface (41) terminates in said radial plane at which it merges with a cylindrically shaped portion (43) of the ball part (9, 37) that has a radius corresponding to the radius of curvature (R₂, R₀) of the offset ball surface (41) plus its offset (0) from the center line axis of symmetry (X) of the ball part (37). 2. A ball and socket joint according to claim 1, characterized in that said offset (0) is approximately in the range from 4 to 7% of the length of the radius of curvature (R₀) of the ball surface (41). 3. A ball and socket joint according to claim 1 or 2, characterized in that said ball part (37) is provided with a plug-in end portion (37a) for attachment thereof within a recess in an end of a rod (35). 4. A ball and socket joint according to any of the claims 1 to 3, characterized in that said ball part (37) has an abutment portion (37b) that merges into said plug-in end portion (37a) or into a rod portion, and into said cylindrically shaped portion (43) via a respective radius curved surface (37e, 37f). 5. A drive train of the type having at least one push rod (35) drivingly connected to another drive train component by a ball and socket joint according to any of the claims 1 to 4.

Inventors: GILL, DANIEL E., SAKATA, YASUO, SUZUKI, SHIGEO
Applicants: CUMMINS ENGINE COMPANY, INC., KABUSHIKI KAISHA TOSHIBA
Application year: 1988
Main classification: F01L1
IPC codes: F16C11, F01L1, F02M59, F02M57