Abstract:
A ball link assembly in which a link member has a semi-spherical cavity formed in each end for rotatably receiving a respective complementary spherical bearing ball formed, preferably, of a ceramic material. Each ball is freely retained by a ball retainer formed of spring steel, the ball retainer extending just over the equator of the ball and mounting to the link by a sideways snap-on action. In one form, the link is designed to accommodate an existing link retainer which is fixed internally of the injector assembly, while in a second form the link assembly is retained by a link retainer which is externally tethered.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to pivot links, such as that by which the rocker lever of a fuel injector drive train acts on the upper plunger of a fuel injector. In particular, the invention relates to such pivot links in which the pivot surface is formed on an element made of a ceramic material. 
     2. Description of Related Art 
     Links of the type to which the present invention is directed are comprised of shaft and ball surface portions and act to transfer compressive loads between contact surfaces at a sliding interface without bending moments. Such links are commonplace in engine subsystem drive trains, e.g., valve and fuel injector drive trains, and to reduce wear at the sliding interface, recent developments have been directed toward making the ball surface portion(s) of a ceramic material. For example, U.S. Pat. Nos. 4,806,040; 4,848,286; 4,966,108; and 5,083,884, as well as Japanese Patent Application 57-13203 disclose pivot rods in which the pivot surface is provided by a ceramic element that is fixed to the end of a shaft by such techniques as interference fitting, diffusion bonding and deforming of a sleeve. 
     However, the performance and durability of links and link joints are largely dependent on the geometric precision (i.e., size, form and finish) of the mating surfaces. Operating stresses, wear and travel (lash) caused by wear are all directly related to dimensional uncertainties (manufacturing tolerances) of critical feature characteristics, such as radius, radius offset, profile, and surface finish. Furthermore, links and link joints are generally designed at the limits of manufacturing and inspection capabilities making the incremental cost of improving geometric precision great, especially when ceramic materials are used, due to the difficulties encountered in machining and non-destructively evaluating component integrity. Bearing type balls made of ceramic materials, e.g., silicon nitride, are commercially available; but, to date, no arrangement has been developed which offers a low cost means of incorporating a free-rolling ceramic ball into a precision component, such a pivot link of the type to which this invention is directed. 
     U.S. Pat. No. 4,141,329 shows a fuel injection system in which a cam acts on a ball which is rotatable in a socket in the end of a piston stem cap, but such an arrangement cannot be used to provide a ball at both ends of a link shaft and since the ball is not positively retained in its socket by anything other than the force of a spring used to urge the stem cap toward the cam, should lash develop with wear, the potential exists for the ball to become dislodged from the stem cap with possibly disastrous results. U.S. Pat. No. 2,636,757 discloses a ball and socket joint for an engine valve drive train in which a free ball is disposed between a pair of sockets that are coupled by a housing that encloses the ball. However, this arrangement is impractical since the housing coupling the pair of sockets and enclosing the free ball inhibits the pivotal movement that the free ball is intended to facilitate. 
     Thus, there is still a need for an improved pivot link arrangement by which a free ball can be retained on one or both ends of a pivot link, especially so as to enable a pivot link to be provided with a ceramic ball surface in a way that will reduce manufacturing costs operating stresses, wear and travel (lash). 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide an improved pivot link arrangement by which a free ball can be retained on one or both ends of a pivot link. 
     It is a further object of the present invention to provide a pivot link with a ceramic ball surface in a way that will reduce manufacturing costs operating stresses, wear and travel (lash). 
     Still another object of the present invention is to achieve the foregoing objects in a way which will allow the pivot link to be used in existing fuel injector drive trains being attachable by the existing link retainer. 
     An additional object of the present invention, is to provide an alternative embodiment which is retainable by an improved link retainer arrangement. 
     These and other objects of the invention are obtainable in accordance with preferred embodiments of the present invention in which a link assembly has a body member with a semi-spherical cavity formed in each end for rotatably receiving a respective complementary spherical bearing ball formed, preferably, of a ceramic material. Each ball is freely retained by a ball retainer formed of spring steel, the ball retainer extending just over the equator of the ball and mounting to the link body by a sideways snap-on action. In one form, the link assembly is designed to accommodate an existing link retainer which is fixed internally of the injector assembly, while in a second form, the link assembly is retained by novel link retainer which is externally tethered. 
     These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic depiction of a fuel injector drive train of the type in which the ball link assembly of the present invention is intended to be used; 
     FIG. 2 is sectional side view of an existing injector with a known pivot link assembly; 
     FIG. 2A is an enlarged sectional view of the pivot link assembly of the injector of FIG. 2; 
     FIG. 3 is a view corresponding to FIG. 2A but with a ball pivot link in accordance with the present invention substituted for the existing unitary pivot link shown in FIGS. 2 &amp; 2A; 
     FIG. 4 is a partial cross-sectional view of the ball pivot link shown in FIG. 3; 
     FIGS. 5 &amp; 6 are a plan view and a cross-sectional view of the ball retainer of FIGS. 3 &amp; 4, FIG. 6 being a section taken along line 6--6 in FIG. 5; 
     FIG. 7 is a view corresponding to that of FIG. 3 but with a modified ball pivot link and external link retainer, the retainer being sectioned along line 7--7 in FIG. 11; 
     FIG. 8 is a partial cross-sectional view of the ball pivot link shown in FIG. 7; 
     FIGS. 9 &amp; 10 correspond to FIGS. 5 &amp; 6 but show the ball retainer of FIGS. 7 &amp; 8, FIG. 10 being a section taken along line 10--10 of FIG. 9; 
     FIG. 11 is a plan view of the external ball pivot link retainer shown in FIG. 7; 
     FIG. 12 is cross-sectional view showing the injector of FIG. 2 which has been modified to receive the external ball link retainer of FIG. 11; 
     FIGS. 13 &amp; 14 are partial side cross-section views of a second external ball link retainer installed on an existing link assembly and on a ball link assembly in accordance with the present invention, respectively; 
     FIG. 15 is a plan view of the second external ball pivot link retainer shown in FIGS. 13 &amp; 14; 
     FIG. 16 is a plan view of a third external ball pivot link retainer; and 
     FIGS. 17 &amp; 18 are partial side cross-section views of the retainer of FIG. 16 installed on an existing link assembly and on a ball link assembly in accordance with the present invention, respectively. 
     In all of the figures of the Drawings, corresponding elements bear the same reference numerals with prime designations (&#39;,&#34;, etc.) being used to identify those components which have been modified from one embodiment to another. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     From the schematic depiction of FIG. 1, it can be seen that a fuel injector drive train 1 of the type in which the ball link assembly of the present invention is intended to be used comprises a cam 2 which, via a cam follower 3 and pivot rod 4, acts on a rocker lever 5. In turn, movement of the rocker arm 5 produces reciprocation of a plunger assembly 6 of a fuel injector 7 via a pivot link 8. 
     FIG. 2 shows a known fuel injector 10, corresponding to fuel injector 7 of FIG. 1, which has a conventional, one-piece pivot link 12 retained therein which corresponds to pivot link 8 of FIG. 1. In this case, the plunger assembly 6 is comprised of a lower injection plunger 13, an intermediate timing plunger 15 and an upper plunger 17. Retention of pivot link 12 in contact with a complementarily shaped socket at the top end of upper plunger 17 is achieved by radially sliding an internal pivot link retainer 18 onto the pivot link 12 in the area of a retention groove 12a which is formed on the pivot link for this purpose. Link retainer 18 has an internal diameter which is small enough to prevent it from moving axially beyond the confines of retention groove 12a while being large enough so as not to interfere with the ability of the pivot link 12 to rock on the top end of the upper plunger 17 (as represented in phantom outline in FIG. 2A). Additionally, the link retainer has an outer diameter that is sized to produce a friction fit securement of the link retainer 18 within an upper plunger coupling member 19 that is secured on the upper end of the upper plunger 17. This plunger coupling member 19 serves to enable a return spring 21 to raise the upper plunger and pivot link 12, so that they follow the upward return movement of the end of the rocker lever 5 which acts thereon. 
     With the above in mind, a first embodiment of a ball link assembly 22 will now be described with reference to FIGS. 3-6, which is intended to be substitutable for the prior art pivot link 12 in an injector 10. Ball link assembly 22 is comprised of a body 23 having spherically shaped sockets 23a, 23b at opposite ends thereof for receiving pivot balls 24. The pivot balls 24 can be commercially available bearing balls made of AFBMA Grade 48 52100 steel or a ceramic material, such as pressureless sintered silicon nitride, use of ceramic balls 24 being preferred for wear-reduction purposes. To retain the balls 24 in the sockets 23a, 23b, a pair of ball retainers 26 are provided that are made of spring steel. 
     The ball retainer 26, as can be seen from FIG. 5, has a C-shape when viewed axially in order that they can be radially snapped onto the body 23 where it is retained by the spring force of the spring steel, which is in a stressed condition when mounted. Additionally, when mounted on the body 23, recessed mounting portions 26a of the ball retainer 26 are positively seated within annular recesses 23c of the body 23 to which portions 26a are cross-sectionally match. These recesses 23c correspond to annular recess 12a of link 12 and provide an axial symmetry to the ball link assembly 22 which, thereby, allows identical ball retainers to be used at both ends and enables either end of the link assembly to be coupled to the injector. However, since the location of the recesses 23c is axially shifted relative to that of recess 12a, due to the provision of sockets 22a, 22b, instead of an integral pivot surface, the link retainer 18&#39; and plunger coupling member 19&#39; have been modified relative to link retainer 18 and plunger coupling member 19. In particular, the interior of plunger coupling member 19 has been modified to provide a larger diameter retaining surface member 19&#39;a at an appropriate vertical location and the outer diameter of the link retainer has been correspondingly increased. 
     As is apparent from FIG. 3, the ball holding portion 26b of the ball retainer 26 extends just over the equator E of the pivot ball 24 to an extent that is sufficient to grip the pivot ball at the opposite side of the equator E to prevent the ball from falling out of the socket 23a, 23b of the link body 23 while not extending so far that ball retainer would interfere with seating of the pivot ball 24 in the lever arm pivot socket (which is represented in phantom in FIG. 3 by a rocker lever pivot insert 5a). Not only does the ball retainer 26 effectively retain the pivot ball 24, but it also permits the pivot ball 24 to freely rotate therein. As a result of the pivot ball 24 being able to freely rotate, the effective area over which wear is distributed is greatly increased relative to that of a link having a fixed pivot surface, such as link 12. 
     As mentioned in connection with the above described embodiment, a modified plunger coupling member 19&#39; is required so that, in instances where the invention is to be retrofit installed, it would be necessary to replace the existing plunger coupling member 19 as a first step, and this cannot be done without disassembling the injector itself due to the manner in which coupling member 19 is normally joined to the upper plunger 17. However, with the external retainers and ball links assembly embodiment described below, a ball pivot link in accordance with the present invention can be retrofit installed in the existing plunger coupling member 19 of an injector 10. 
     A comparison of the modified ball link assembly 22&#39; of FIGS. 7 &amp; 8 with that of FIGS. 3 &amp; 4 and of the ball retainer 26 of FIGS. 5 &amp; 6 with the ball retainer 26&#39; of FIGS. 9 &amp; 10 reveals that the sole difference between these two ball link assemblies 22, 22&#39; lies in the reduction of annular recesses 23c to annular grooves or slots 23&#39;c and to eliminate the recess of the mounting portion 26a, reducing the mounting portion 26&#39;a to a simple flange which engages in the annular grooves 23&#39;c. Elimination of the recess of the mounting portion 26a allows the length of the ball holding portion 26&#39;b that overlies the body 23&#39; to be increased sufficiently to provide an area upon which an external link retainer 30 can be mounted. 
     As can be seen in FIGS. 7 &amp; 11, the external link retainer 30 is comprised of a pair of annular rings 30a, 30b which are interconnected by a resiliently flexible strap portion 30c which spirals between them. This external link retainer 30 can be formed of a heat resistant plastic with the annular rings 30a, 30b formed of a single molded piece with the interconnecting strap portion 30c. The inner, link-retaining ring 30a has an inner diameter sized to friction fit onto the circumference of the upper ball retainer 26&#39; as shown in FIG. 7. The outer diameter of the outer, mounting ring 30b is sufficient to extend onto the spring stop flange 19a of the coupling member 19. The mounting ring 30b is loosely retained on flange 19a by the cap 32 (FIG. 12) of return spring enclosure 34 which can be easily modified to provide sufficient room for the ring 30b. Unlike replacement of coupling member 19, the original return spring enclosure cap 32 can be easily replaced without disassembling the injector. As is also apparent from FIG. 12, the external link retainer 30 is usable with an existing link 12 in order to simplify the installation process by eliminating the need to force fit an internal retainer 18 into the coupling member 19. 
     FIG. 15 shows another embodiment of an external link retainer 30&#39; which can be used with either an existing pivot link 12 (FIG. 13) or a pivot link 22&#39; in accordance with the present invention (FIG. 14). In this case, the link-retaining ring 30&#39; is a resiliently flexible split ring 30&#39;a which is tethered via its strap portion 30&#39;c which is formed snap-in mounting portion 30&#39;b which has a tapered head with an annular groove. As is represented in FIGS. 13 &amp; 14, mounting portion 30&#39;b is secured in an aperture that is provided in a plate 35 which is mounted to the engine, the plate 35 being either specially attached, e.g., to the cylinder head for this purpose or being a portion of a component or bracket already mounted thereon. This external link retainer 30&#39; eliminates the need to make any modifications to the fuel injector 10. 
     Yet another embodiment of an external link retainer 30&#34; which can be used with either an existing pivot link 12 (FIG. 17) or a pivot link 22&#39; in accordance with the present invention (FIG. 18) is shown in FIG. 16. In this version, the mounting portion 30&#34;b is in the form of a mounting ring that can be friction-fit over the body of the return spring enclosure 34 as represented diagrammatically in FIGS. 17 &amp; 18. Like the external link retainers 30 and 30&#39;, the external link retainer 30&#34; is preferably made of a one-piece molded plastic construction. Furthermore, not only does it eliminate the need to make any modifications to the fuel injector 10, but it also eliminates the need for an apertured mounting plate 35. 
     The above-described invention will afford numerous advantages over existing pivot link assemblies. Firstly, the ball pivot link achieves greater geometric precision with reduced operating stresses, improved ball-socket fit and extended cost savings due, e.g., to reduced wear. For example, the precision previously required for the socket in the upper end of injector plunger 17 and in the rocker lever 5 (socket insert 5a) can be reduced without increasing operating stresses so that sufficient control of the mating socket geometry can be achieved by cold forming instead of more expensive machining and grinding approaches. In this regard, it is also noted that spherical sockets can be used in place of off-set socket designs without an operating stress penalty. Moreover, instead of having to machine a ball surface on the link end or on an element to be attached thereto, commercially available bearing type balls can be used on the pivot link with improved wear characteristics. In fact, estimates indicate that a pivot link 22, 22&#39; in accordance with the present invention can be produced at a cost that is forty-five percent (45%) less than that for a conventional one-piece link 12. 
     While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto, and is susceptible to numerous changes and modifications as known to those skilled in the art. Therefore, this invention is not limited to the details shown and described herein, and includes all such changes and modifications as are encompassed by the scope of the appended claims. 
     Industrial Applicability 
     The present invention will find applicability to a wide range of uses where loadbearing pivot links are required, especially in pivot links for motor vehicle engine drive trains, such as for a pivot link used in a fuel injection system for transmitting motion from a rocker lever to a reciprocating plunger of a fuel injector.