Abstract:
A steering column slider shaft assembly includes a shaft and yoke assembly having yoke at a first end and an attached non-cylindrical shaft extending therefrom to a second end. The second end is engaged with a non-cylindrical tube which forms a second end of a tube and yoke assembly, the tube being congruent with and adapted to slidably receive the shaft and provide a slip fit therefor. The shaft and yoke assembly and the tube and yoke assembly each have interengaging provisions which are over-molded or otherwise attached, for sealing the slider shaft assembly. The interengaging provisions also serve to limit extension of the slider assembly to resist inadvertent separation of the slider shaft assembly during assembly of the steering column.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to steering column slider assemblies and more particularly to steering column slider assemblies with combined sealing and anti pull-apart features. 
     Steering columns in motor vehicles include slider assemblies, made up of a shaft and yoke, or shaft and foot, assembly slidably inserted within a tube and yoke, or tube and foot assembly, to accommodate variations in the distance between the vehicle dash panel and the steering gear box due to manufacturing tolerances. Use of the slider shafts facilitates assembly of the vehicle by accommodating slight variances in the positions of the steering gear box and the steering column. Slider shafts are also required for providing reach, or length, adjustability in steering columns. 
     Normal driving conditions also entail road shocks which cause relative motion between the body and frame. These move the steering gear box and the steering shaft connected to it. The slider shaft permits telescopic compliance of the steering shaft and absorbs the road shocks with minimal effect on the upper portion of the steering column and, thus, comfort of the operator. The normal telescopic motion of the slider is in the range of ½″ or less. 
     Vehicle designs have become smaller and often require the steering column to have one or more bends to reach the steering gear box. Each such bend requires at least one universal joint which requires a significant axial space. As a result, slider shafts have become quite short in some designs in which the distance between the dash panel and the steering gear box is small and the angular deviation is relatively large. 
     Because of their location in the vehicle, the slider shafts are exposed to water, salt, and road debris which cause corrosion and wear and which ultimately lead to deterioration of the slide function and an objectionable degree of rotational lash in the steering mechanism. Rubber sealing boots are installed on the shafts and tubes of many slider assemblies to retain lubricant and exclude contamination, but they do not seal the ends of the shaft and the tube. Also, they eventually crack, due to mechanical, thermal, or chemical attack, or otherwise develop leaks which permit loss of lubricant and entry of the contamination at the slider joint. 
     Currently, in order to prevent inadvertent separation of the tubes and shafts of slider assemblies during subsequent assembly into the steering column of the vehicle, the end of the shaft is deformed, by staking or otherwise, after insertion into the tube. This is a very effective retention measure, and, except when the slider becomes too short, suffices. However, at or near some lower limit of slider length, there is insufficient space to permit such deformation of the end of the shaft after assembly, and another method must be found to provide the anti-pull-apart feature. 
     The foregoing illustrates limitations known to exist in present sealing and anti pull-apart features of steering shaft slider assemblies. Thus, it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, this is accomplished by providing a steering column slider shaft assembly which comprises a shaft assembly with a yoke at a first end thereof and an attached non-cylindrical shaft extending therefrom to a second end; a tube assembly comprising a non-cylindrical tube with an attached yoke at a first end, the tube being congruent with and adapted to slidably receive the shaft and to provide a slip fit therefor within a second end thereof; and means for sealing the slider shaft assembly. 
     The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic longitudinal sectional view of a slider assembly of the prior art; 
     FIGS. 2 a  and  2   b  are schematic longitudinal sectional views of the tube and yoke and the shaft and yoke, or foot, respectively, of a slider assembly according to the invention; 
     FIG. 3 is a schematic longitudinal sectional view of the slider assembly embodying the invention; 
     FIGS. 4 a  and  4   b  are cross-sectional views of the slider assembly taken along line  4 — 4  of FIG. 3 showing two possible embodiments of the non-cylindrical shape of the tube and shaft; 
     FIG. 5 is a schematic overall view of the slider shaft of the invention as shown cut away in FIG. 3; and 
     FIGS. 6 a,    6   b,  and  6   c  are schematic sectional illustrations of a long slider embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     A slider shaft assembly  100  of the prior art, as seen in FIG. 1, has a yoke or foot  110  with an attached non-cylindrical tube  115  which is slidably engaged with a yoke  120  with an attached non-cylindrical shaft  125  to provide rotational drive transmission between the yokes. (Note that “non-cylindrical” denotes shafts and tubes of any shape which have one or more axially extending radial projections or recesses to provide rotational interlock between the shafts and tubes.) The shaft  125 , which may be hollow, as shown, or solid, nests inside the tube  115  to provide smooth extension and collapse of the slider shaft assembly  100  to accommodate relative axial movement of the tube and shaft during assembly or due to road shocks and vibrations in service. In motor vehicle steering shafts, such accommodation isolates the operator from the movements and reduces fatigue. To protect the slide function from deterioration due to contamination and corrosion, some slider assemblies incorporate a flexible boot  130  to provide a seal over the slider joint while still permitting smooth axial extension and collapse. This is effective as a seal over the engaging ends of the shaft  125  and tube  115  until the seal between the boot  130  and shaft  125  or tube  115  begins to leak or until the boot becomes embrittled and cracks. However, it does not seal the ends of the shaft and tube where they penetrate the yokes  110 ,  120 . During operation of the vehicle, road debris, water, salt, and mud may splash on the slider shaft assembly and enter the slider mechanism through the yoke ends of the shaft and tube to cause wear and corrosion of the slider assembly. Also, this type of boot  130  clamps directly to the engaging surface of the inner shaft  125  and to the outer shaft or tube  115 , thereby reducing the available telescopic capability of the slider assembly. 
     FIGS. 2 a,    2   b,  and  3  show the slider shaft assembly  10  of the invention. It comprises a yoke or foot  20 , with an attached non-cylindrical tube  25 , which is preferably over-molded with a low-modulus flexible polymeric cover  45 , and another yoke or foot  30 , with an attached non-cylindrical shaft  35 , over-molded with a convoluted boot  40 , also of a low-modulus flexible polymeric material. It is important, especially in cases involving short sliders, that the over molded boot  40 , as seen in FIG. 3, does not interfere with full-length telescopic action of the shaft  35  and tube  25 . In some cases, depending on the material chosen, it may be preferred to press or stake or otherwise attach the low-modulus coating on the tube and the shaft. The cover  45  and boot  40  completely seal the ends of the shaft  35  and tube  25  where they penetrate the feet or yokes  30 ,  20 , respectively. The cover  45  has an external circumferential ridge  47  about its interengaging end, and the boot  40  has an internal circumferential ridge  37  about its interengaging end. When assembling the slider shaft assembly  10 , the shaft  35  is inserted into the tube  25  until the interengaging ends of the cover  45  and the boot  40  are in contact with each other. The circumferential ridge  37  of the boot is stretched and pushed past the external circumferential ridge  47  of the flexible cover  45  to lock the boot to the cover and to seal the interengaging joint. Because of the low modulus of the polymer of the cover and boot, the seal is sufficiently tight to exclude contamination from the slider. By proper selection of the thickness and the modulus of the polymer of the boot  40  and cover  45 , it is possible to tailor the axial compliance of the slider shaft assembly to provide a desired degree of axial damping for a slider of any particular vehicle for its intended service. This invention also provides a continuous seal over the yoke ends of the shaft and tube and over a substantial portion of the yoke ears as well. Thus, once the cover  45  and boot  40  are interengaged, the slider assembly is completely sealed to exclude contaminants and to retain any lubricant desired for the slider. A clamp ring  55  may be installed on the boot  40  over the internal ridge  37  to increase the clamping force at the seal. This ring  55  also serves as an added anti pull-apart feature for the slider shaft assembly  10 . In cases in which the slider is very short due to vehicle design restrictions, there is a heightened possibility of the slider assembly separating during assembly of the automobile. The anti pull-apart feature is especially important in such designs to avoid loss of or contamination of lubricant and mis-orientation between the tube and shaft which can occur on separation, especially with geometries such as splines or others susceptible to re-assembly in slightly incorrect orientations. 
     Reinforcement fibers  70  or mats may be molded in the cover  45  and boot  40 , and, in combination with the clamp ring  55 , can provide added anti-pull-apart protection. FIG. 5 shows a non-cut-away view, as in FIG. 3, of the seal and anti-pull-apart device, including the clamp ring  55 , illustrating the sealing extent of the cover and boot on the yokes of the assembly. 
     The non-cylindrical tube  25  and shaft  35  are illustrated in FIGS. 4 a  and  4   b  which are transverse sections taken on line  4 — 4  of FIG.  3 . The shaft  35  is shown solid, but it is often made as a hollow tubular part. The tube  25  and shaft  35  are surrounded by the boot  40 . The shaft  35  is slidably inserted in the tube and has a non-cylindrical outer surface which meshes with a congruent non-cylindrical inner surface of the tube  25  to permit relative axial movement between the two parts but no relative rotation between them. These two figures show only two of a virtually infinite selection of non-cylindrical forms for such rotary drive shafts. It is sufficient that the shaft and tube each have at least one congruent radially projecting feature on their outer and inner surfaces, respectively, to provide the rotational interlock needed while still permitting relative axial movement. 
     Comparing FIGS. 3 and 5 to FIG. 1, the sealing improvement provided by the invention over that of the prior art is clear. The prior art slider assembly  100  is open at the ends where the yokes  110 ,  120  are penetrated by the tube  115  and the shaft  125 . The boot  130 , in addition to reducing the telescoping capability of the assembly, only seals the outside of the interengaged portion of the assembly, while the inside is open at both ends. The slider assembly  10  of the invention is completely encapsulated, except for only the ends of the ears of the yokes or feet  20 ,  30 . Once the tube and yoke (FIG. 2 a ) and the shaft and yoke (FIG. 2 b ) are interengaged (FIGS.  3  and  5 ), the slider shaft assembly  10  is sealed on all sides to exclude contaminants and to retain lubricant. The external ridge  47  on the cover  45  and the internal ridge  37  on the boot  40  provide a very strong anti-pull-apart function compared to the boot  130  of the prior art in FIG.  1 . With incorporation of the clamp ring  55 , as preferred, and with addition of molded-in reinforcement fibers or mats, the strength of the anti pull-apart function is increased by a large multiple. 
     The components of a long slider embodiment of the invention are shown in FIGS. 6 a,    6   b,  and  6   c,  in which the shaft and foot  80 , the outer tube and yoke (or foot)  90 , and the long slider boot  85  are illustrated. The long hollow shaft  35 ′ has a cover  145  which extends from the yoke end of the shaft partially over the ears of the foot  30 ′. An external ridge  147  is provided at the end of the cover  145  for engagement with an internal ridge  37 ′ on the boot  40 ′ after assembly of the slider. The long outer tube or shaft  25 ′ in FIG. 6 b,  except for the length of the tube  25 ′, is the same in all respects as the shaft  25 , in FIG. 2 a.  The cover  45 , with its external ridge  47 , extends from the foot end of the tube  25 ′ partially over the ears of the yoke  20 ′. The boot  40 ′, seen in FIG. 6 c,  has, substantially, end-to-end functional symmetry with an internal ridge  37 ′ at each end for engaging with the external ridges  47 ,  147  of the tube and yoke  90  and the shaft and yoke  80 . A clamp ring  55  may be used at each end of the boot  40 ′ after assembly with the covers  145 ,  45  to increase sealing and anti-pull-apart features for the long slider. 
     It is possible, if a solid shaft  35 ,  35 ′ is used, to dispense with the cover  45 ,  145  and to provide an embossed or otherwise formed external ridge on the yoke end of the shaft for interengagement with the internal ridge  37 ,  37 ′ of the boot  40 ,  40 ′. The sealing and anti-pull-apart behavior of the slider assembly would still be acceptable. The low-modulus of the boot provides excellent sealing engagement with hard or soft surfaces. This invention provides the sealing needed to exclude abrasive and corrosive road dirt and spatter from the slider, while also retaining grease or other lubricant within the slider joint. In addition, it provides anti pull-apart features to resist inadvertent separation of the shaft and tube during assembly of the vehicle without reducing the axial compliance needed to reduce transmission of road shocks.