Abstract:
A vehicular leaf spring tip insert is provided. The insert includes a pad portion providing a liner between adjacent leaf spring tips, at least one shank portion extending from the pad portion to a free end, the shank portion having a generally axial bore, the shank portion also having a protuberance extending outward therefrom with a leaf spring engagement surface facing toward the pad portion at an axial distance therefrom, the protuberance being dimensionally adapted and configured so that the protuberance is compressed radially inward sufficiently to be received through the tip opening upon insertion of the shank portion therethrough, and a pin for insertion into the shank bore, the pin being formed from a semi-liquid material poured into said shank axial bore or material from the protuberance that has been thermally deformed.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the installation and retention of a low friction pad at the ends of the supporting leaves of a vehicular leaf spring to improve ride characteristics and reduce noise and wear between adjacent leaves of a multi-leaf spring assembly during operation of a vehicle. 
     BACKGROUND OF THE INVENTION 
     For many years, non-metallic, generally polymeric, tip inserts or separator pads have been used between adjacent vehicular leaf spring plates (or leaves), as a means of reducing friction, noise and wear and improving ride as the plates slide relative to each other when the spring flexes during operation of vehicle. Examples involving the use of leaf spring separator pads at the ends of the leaves which support the main leaf attached to the vehicle chassis may be found In U.S. Pat. Nos. 5,219,151 and 5,706,559. The most common and expedient approach to attachment is to integrally mold a projecting solid or tubular shank or post on the underside of the tip insert pad which is then inserted in a through hole centrally located near the ends or tips of some or all of the supporting leaves and second stage leaves in a multi-leaf spring assembly. 
     Prior leaf spring tip inserts have been commonly designed following either or both of two approaches. The first has been specification of an intentional interference fit between the diameter of the tip insert post or shank and the diameter of the receiving hole in the spring leaf relying on compression of that polymer shank and resulting radial forces and friction with the surface of the receiving hole in the spring leaf to accomplish tip insert retention. The second and most common means has been to provide some form of an integrally molded radial projection or protuberance near the free end of the tip insert shank which substantially exceeds the diameter of the receiving hole in the spring leaf. Such a tip insert design commonly employs a tubular shank with two or more axial slots through the shank wall to allow inward deflection of the post to accommodate passing of the said shank end projection through the receiving hole in the spring leaf. When the shank is fully inserted in the leaf spring plate the projection extends beyond the lower surface of the spring and overlaps the outer edges of the receiving hole to achieve retention of the tip insert in vehicle service. 
     It is recognized that it is desirable to provide a tip insert that may be easily installed with minimum force using simple tools, but requires high force to be removed or disengaged once it has been installed in the spring leaf. Generally tip inserts which are the easiest to install provided the least retention to the leaf spring as a result of the lack of sufficient interference fit of the tip insert shank diameter with the receiving hole and/or the amount of overlap of the shank end protuberance with the receiving hole. Increasing the interference fit and/or the overlap of the tip insert shank end protuberance with its receiving hole in the spring leaf has been employed to increase the reliability of tip insert retention, as measured by the force to push the tip insert shank in reverse, back out of the hole in the spring leaf. However, the degree of difficulty and force required to insert the shank through the hole in the spring plate increases greatly in this situation and result s in a high level of permanent deformation of the polymer shank and/or the radial protuberance which decreases its ultimate interference and retention capability. As a result, the retention capability and reliability of past tip insert designs has been limited and less than needed to achieve acceptable durability in many vehicle leaf spring applications. 
     SUMMARY OF THE INVENTION 
     To fulfill the above-noted and other unmet desires, the revelation of the present invention is brought forth. The present invention provides a leaf spring tip insert which requires high force to be removed from the spring leaf, but can be manually installed relatively easily with simple hand tools. In a preferred embodiment, the present invention provides a leaf spring tip insert that includes a pad portion providing a low friction, wear-resistant separator between adjacent leaf spring tips. Extending from the pad portion is at least one shank portion that has a central bore and a plurality of axial slots starting from a free end of the shank. The shank also has protuberances extending radially outward therefrom with leaf spring engagement surfaces facing toward the pad portion at an axial distance therefrom. The protuberances are dimensionally adapted and configured so that the shank and protuberances are deflected and compressed radially inward sufficiently to be easily passed through a receiving hole in the tip of the spring leaf. The tip insert has a pin which is essentially molded in place in the shank bore after the shank has been inserted in the receiving hole of the spring leaf by inserting or extruding an appropriate hot or cold semi-liquid material into the shank bore until sufficiently partially or totally filled and the material is solidified and/or cured to a state having the rigidity and compressibility to resist inward deflection and compression of the shank protuberances. 
     In an alternative preferred embodiment of the present invention, the function of the pin is generated by subjecting a free end of the shank to thermal contact by a hot mandrel or pad which melts or flows the individual protuberances together. 
     It is a desire of the present invention to provide a leaf spring tip insert that has a low force requirement for installation and a high force requirement for removal or disengagement of the insert from the leaf spring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a vehicular leaf spring tip insert illustrating the pad portion, shank portion and an insertable preformed pin. 
     FIG. 2 is a bottom plan view of the spring tip insert shown in FIG.  1 . 
     FIG. 3 is a sectional view illustrating the tip insert shown in FIGS. 1 and 2 being installed in a leaf spring assembly. 
     FIG. 3 a  is a partial sectional view of a spring tip insert similar to that shown in FIG. 3, wherein the groove and ledge interconnect between the pin and an interior axial bore of the shank has the groove in the bore of the shank instead of in the pin as shown in FIG.  3 . 
     FIG. 4 is a view similar to that of FIG. 3, illustrating the utilization of the tip insert being installed in a spring leaf, wherein the supporting spring leaf has a greater thickness dimension than the supporting spring leaf shown in FIG.  3 . 
     FIGS. 5 a ,  5   b ,  5   c ,  5   d ,  5   e ,  5   f ,  5   g ,  5   h ,  5   i ,  5   j ,  5   k  and  5   l  illustrate insertable preformed pins. 
     FIG. 6 illustrates an insertable pin wherein the pin is inserted into the tip insert shank on a side of the shank opposite the pad. 
     FIG. 7 illustrates an alternate preferred embodiment pin, wherein the pin is formed in-place in the shank bore by a glue or other semi-liquid material which subsequently cures in place. 
     FIG. 8 illustrates an alternate preferred embodiment wherein the function of the pin is generated by fusing the individual shank segments together. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1, insert  70  has a pad portion  3  adapted to provide a low friction, wear-resistant separator between leaf spring plate tip ends, as shown in FIGS. 3 and 4. A shank portion  4  extends preferably substantially perpendicular from pad portion  3  to free end  7 . 
     In the embodiment shown in FIG. 2, orthogonal slots  12  and  12 ′ extend from free end  7  for a prescribed axial distance toward pad portion  3  and divide shaft  4  into four resilient elongated segments having corresponding diametrically-opposed protuberances  14 ,  14 ′ and  16 ,  16 ′ that respectively radially extend outward to provide a diametrical width “Z” that, along with the width of slots  12  and  12 ′, is predetermined to enable the segments to radially deflect and compress inward sufficiently to enable them to be received through the leaf spring tip opening into which shaft  4  is inserted. Diametrically-opposed protuberances  14  and  14 ′ have corresponding leaf spring engagement surfaces  18  and  18 ′ that face toward pad portion  3  and are in substantial registration with each other at a prescribed axial distance “X” therefrom. Likewise, diametrically-opposed protuberances  16  and  16 ′ have corresponding arcuate leaf spring engagement surfaces  20  and  20 ′ that face toward pad portion  3  and are in substantial registration with each other at an axial distance “Y” from pad portion  3  that is greater than distance “X.” 
     The difference in axial lengths “X” and “Y” enables insert  70  to be securely attached to spring leaves or plates having a range of thicknesses, as shown in FIGS. 3 and 4 
     As shank portion  4  is inserted into the leaf spring tip opening, protuberances  14 ,  14 ′ and  16 ,  16 ′ are configured to radially compress inward such as by having their respective outer surfaces tapered angularly inward directionally toward free end  7  at an angle “A,” for which 20° has been found to be particularly effective in reducing force of inserting/installation. 
     To enhance compressibility by minimizing interference of converging inner bore and slot surfaces of the shank segments under inward deflection and compression of the shank  4 , and protuberances  14 , slots  12  and  12 ′ may be flared outward at angle “B” for a prescribed length from free end  7 , for which 5-6° from the center line to provide a preferred included angle of about 10-12°, has been found to be particularly effective for a particular design. 
     In FIG. 3, insert  50  is being utilized to provide a space (pad portion  3 ) between adjacent leaf spring plates  22  and  24 . The thickness of plate  24  (not referenced) is the same or less than length “X” in FIG. 1 such that when shaft portion  4  is inserted through opening  26  of leaf spring plate  24  until the underside of pad portion  3  abuts against plate  24 , protuberances  14 ,  14 ′ and  16 ,  16 ′ spring or expand outward to enable surfaces  18  and  18 ′ to engage with the underside of spring plate  24  to lockingly secure insert  50  to spring plate  24 , while plate engagement surfaces  20  and  20 ′ of protuberances  16  and  16 ′ respectively remain at a prescribed distance “T” away from the underside of spring plate  24 . 
     In FIG. 4, leaf spring plate  34  has a thickness (not referenced) that is greater than length “X” and the same or less than length “Y” in FIG. 1 such that arcuate surfaces  20  and  20 ′ of protuberances  16  and  16 ′ respectively are engaged with the underside of leaf spring plate  34 , while protuberances  14  and  14 ′ remain compressed within opening  26 . 
     To extend the protuberances  14 ,  14 ′,  16 ,  16 ′ outward and to lockingly retain them in the outward position, there is provided a pin  50 . As best shown in FIG. 2, pin  50  has a non-constant radius oval cross-sectional shape. The pin  50  is integrally molded with the pad  3  and shank  4 . Common materials utilized for such a molding are high density polyethylene with graphite additive for friction and wear reduction or nylon  6 - 6  with polytetrafluoroethylene (known under name trademark TEFLON) additive for the same purpose, while other suitable material alternatives may be used for this application. As shown in FIGS. 1-3, pin  50  has an annular groove  53 . At the intersection  56  of the two portions of tip insert  70 , pin  50  is held to pad  3  by a thin webbing material. Underneath pin  50 , the shank  4  has an interior axial bore  59 . The shank bore  59  typically will have a cross-sectional geometry approximately matching that of the pin  50 . To install the tip insert  70  into the spring assembly provided by the leaf springs  22 ,  24  or  32 ,  34 , the tip insert shank  4  is inserted through the leaf spring receiving hole  27 . After insertion of the shank, the protuberances  14 ,  14 ′ or  16 ,  16 ′ will radially expand approximately to their as-molded position so that their leaf spring engagement surfaces  18 ,  18 ′ or  20 ,  20 ′ may engage with the adjacent leaf springs. A hammer, mallet or other simple impact tool is then utilized to impart a force onto the upper surface  62  of the pin. In the embodiment having an integrally molded rather than separate pin, the force upon the upper surface  62  of the pin will cause the material at intersection  56  to be sheared and for the pin  50  to be thrust downward into the bore  59  of the shank. When fully assembled, the top surface  62  of the pin will be flush with a top surface  65  of the pad portion. The oval shape of the pin  50  prevents it from rotating within the bore  59  and thereby holds it more securely in position. Additionally, the bore of the shank has an inward projecting radial ledge  68 . The ledge  68  interlocks into the radial groove  53  of the pin to retain pin  50  in position. As will be obvious to those skilled in the art, the pin  50  prevents the protuberances  14 ,  14 ′,  16 , or  16 ′ from deflecting inward thereby locking them to the adjacent leaf spring  24  or  34 . 
     In the embodiment of the present invention shown in FIG. 3 a , a shank  104  has a bore  159  with a groove  107 . The groove  107  is mated with a ledge  110  of a pin  50 . 
     FIG. 5 a  provides an alternate preferred embodiment pin  201  according to the present invention with a head  203  which is designed to be flush or slightly above the upper/outer surface of the pad when the pin is fully inserted in the shank bore. 
     Referring to FIG. 5 b , a tapered pin  206  is shown having a large diameter end  209  and a small diameter end  212 . Typically, the end  212  will be inserted into the bore  59  from the side of the tip insert more adjacent to the pad. The taper of pin  206  aids in insertion of the pin while achieving high interference fit to increase the force required for its removal. 
     FIG. 5 c  illustrates a pin  215  which has a tapered lead  218 . Tapered lead  218  aids in insertion of the pin  215 . Pin  215  may be circular or have a non-constant radius cross-section such as an oval. 
     FIG. 5 d  illustrates a hairpin-type pin  221  having a main body  223  with extending legs  224 . The legs  24  are sized to be radially compressed upon insertion into the shank bore. 
     FIG. 5 e  illustrates an alternate preferred embodiment simple cylindrical separate pin  227  which provides the advantage of its ease of manufacture. 
     FIG. 5 f  illustrates an alternate preferred embodiment pin  229  having multiple facets  231  which engage into the sides of the shank bore to produce multiple line interference fit to retain the pin  229  within the shank bore. 
     FIG. 5 g  illustrates an alternate preferred embodiment pin  331  which has a central bore  330  to allow the pin  331  to slightly collapse upon insertion to allow insertion with a high interference fit within the bore of the shank. 
     FIG. 5 h  is an alternate embodiment pin  333  having an oval cross-sectional shape without the circumferential grooves as shown in FIGS. 1-3. 
     FIG. 5 i  shows yet another alternate preferred embodiment of the present invention providing a pin  337  with a plurality of generally axial ribs  339  along its lower end. As will be apparent to those skilled in the art, the number, axial location, and length of the ribs  339  may be modified in light of the application utilized to produce the desired interference for retention of the pin. 
     FIG. 5 j  shows another alternate preferred embodiment pin  341  which has a plurality of axially-spaced circumferential or radial ribs  343  to produce multiple line interference fit. 
     FIG. 5 k  illustrates an alternate preferred embodiment pin  347  having a geometrically patterned surface  349  to produce multiple line interference fit. 
     FIG. 5 l  illustrates an alternative preferred embodiment pin  351  having an axial angular slot  353  which is compressed upon insertion into a shank bore to insure the interference fit of the pin  351  within the shank bore is retained through the radial residual force of a high interference fit. 
     FIG. 6 illustrates an alternative preferred embodiment  670  tip insert according to the present invention wherein the pin  650  is installed into the bore  59  of the tip insert  670  opposite the pad  3 . The pin  650  has a tapered head  648  to assist in its installation. The pin  650  may be a separate piece or a piece that is connected to the remainder of the tip insert  670  by a thin webbing which can be severed. 
     FIG. 7 illustrates an alternative embodiment tip insert  670  in which the pin  650  is essentially molded in place in the shank bore  59  after the shank portion  4  has been inserted in the receiving hole (opening)  26  of the spring leaf by inserting or extruding an appropriate hot or cold semi-liquid material  650  into the shank bore  59  until shank bore  59  is sufficiently partially or totally filled. The material is solidified and/or cured to a state having the rigidity and compressibility to resist inward deflection and compression of the shank protuberances. 
     FIG. 8 illustrates an alternative preferred embodiment tip insert  850  wherein the function of the pin is generated by subjecting the free end of the shank portion  4 , after the shank has been inserted in the receiving hole of the spring leaf, to thermal contact by a hot mandrel or pad which melts or flows their surfaces thereby either fusing the individual protuberances  14 ,  16  together and/or filling the axial slots  12 ,  12 A and thereby reducing their width to resist subsequent inward deflection and compression of the protuberances  14 ,  16  to prevent disengagement of the tip insert. 
     It is apparent to those skilled in the art that as the pin has been shown in various embodiments, in a similar manner the interior bore of the shank may also be modified in order to bring about an interference interface between the pin and the shank interior bore which aids in retention of the pin within the bore. Additionally, the pin may be inserted into the shank from the free end of the shank  4  opposite the pad. 
     In another embodiment of the present invention (not shown), an adhesive is pre-applied to the pin or within the shank bore to aid in retention of the pin. 
     The present inventive leaf spring tip insert has been shown in various preferred embodiments. However, it will be apparent to those skilled in the art that various modifications can be made to the present invention from that described in the specification and drawings without departing from the spirit or scope of the present invention as it is encompassed in the specification and drawings and by the following claims.