Abstract:
A wheel segment for the pivotal mounting of a base plate to a support jack, wherein the wheel segment has a partially cylindrical jacket element having a winding surface that is curved on the underside of said jacket element, and two side walls positioned radially on the jacket element, wherein a stop point is configured in the upper section thereof. An arrangement of a wheel segment is further protected at a support jack. The aim of the invention, among others, is to produce a wheel segment in a cost-effective manner while maintaining equal stability. Said aim is attained according to the invention by a wheel segment that is produced as a one-piece casting.

Description:
FIELD OF THE INVENTION 
     The invention concerns a wheel segment for the pivoting mounting of a base plate on a support jack, wherein the wheel segment has a partly cylindrical shell element with a curved rolling surface on its bottom side and two side walls positioned radially on the shell element, with a stopping point configured in the upper section of each of them. An arrangement of the wheel segment on a support jack is likewise specified. 
     BACKGROUND OF THE INVENTION 
     Such support jacks are usually found in paired arrangement on the bottom of semitrailers. Usually they comprise an outer tube which can be mounted stationary on the trailer and a second inner tube, telescoping in the former tube, and having a base plate located at its end. To uncouple the trailer, the support jacks are extended, so that they support the trailer in its front region and allow the tractor to drive off from underneath the trailer. In presently used pneumatic cushioned trailers, a sinking of the back region of the trailer can occur during lengthy standstill, caused by a loss of pressure in the pneumatic bellows of the trailer. Due to the sinking of the trailer, shear forces also act in the longitudinal axis of the support jacks, resting on the ground with their support surfaces frictionally engaged, and therefore exposed to a substantial bending and buckling stress. 
     To counteract this effect, efforts had already been undertaken in the past to arrange a wheel segment at the lower region of the support jack, which equalizes the shear forces occurring by a rolling against the base plate located underneath. 
     A known wheel segment is described in DE 40 03 414 A1, consisting of several individual components that are welded together. Such a fabrication is extremely costly, since the side walls have to first be oriented exactly relative to each other before being welded to the rolling surface. Then additional reinforcing plates are welded individually by hand to the side walls and the cross arms running between them. 
     SUMMARY OF THE INVENTION 
     Consequently, the problem on which the invention is based was to make a wheel segment more cheaply, with at least the same strength. 
     The problem is solved according to the invention with a wheel segment that is fabricated as a single-piece cast iron part. By single piece is meant all undetachable structural elements of the wheel segment are in the ready to install condition. This includes, in particular, reinforcing plates and cross arms joining the side walls. 
     It has been found to be favorable to have an opening in the shell element on either side of the bottom vertex point. By vertex point is meant, in the case of a vertically upright support jack, the segment of the rolling surface of the wheel segment located directly underneath, lying at the center between the two ends of the rolling surface in the circumferential direction. Spring elements in the form of helical springs, for example, can be led through these openings, which ensures a return movement of the base plate in the unloaded condition. 
     The respective openings are advantageously configured not as a slot with a rectangular contour, but instead have at least one widening in the circumferential direction of the shell element, at a distance outwardly from the vertex point. The widening can be shaped as a parabola or half-round, as compared to the original slot contour. 
     Thanks to the contour of the opening being at least partly widened toward the outside, a shell element with relatively much material in the region of the vertex point remains with a large surface to absorb vertically acting peak loads. On either side of the vertex point of the wheel segment, on the other hand, a large rolling surface is not needed, since the loads expected there are smaller. Hence, a rolling surface reduced by the widening with increasing distance from the vertex point in the circumferential direction is sufficient. The widening again diminishes toward the outer edge of the rolling surface and the rolling surface becomes larger in equal measure. On the whole, this preferred embodiment offsets the disadvantage of the intrinsically heavier fabrication of the wheel segment as a cast iron part by material savings in the less heavily loaded surfaces. 
     The side walls should be joined together by cross arms at either end in the circumferential direction. In the first place, these cross arms serve as an end stop when the base plate is fully deflected. In addition, spring elements can be suspended from the cross arms, exerting a restoring force on the base plate in the direction of a central position underneath the vertex point of the wheel segment. 
     Preferably, the shell element has a flattening at its bottom vertex point. 
     Thanks to the flattening or level surface in the region of the vertex point, when the support jack is in the deployed condition and peak loads are acting in the vertical direction on the wheel segment or the base plate situated underneath, there is a larger surface available to absorb the impacts and deflect the forces than would be the case with a partly cylindrical rolling surface. The latter only enables a line-type contact between the wheel segment and the base plate with correspondingly high surface pressures. And these are especially disadvantageous in the case of cast iron material with its tendency to brittle fracture. 
     According to an especially advisable embodiment, each cross arm has an inwardly slanted end stop surface. The end stop surfaces are oriented so that they lie in two dimensions against the tube of the support jack when making contact with it. The line-type contact between a cross arm of round cross section (for example) and the tube of the support jack which usually occurs with the known wheel segments is avoided in this way. This, in turn, substantially reduces the notch effect on the structural parts in question. A slanted end stop surface is particularly easy to accomplish on a cast iron part. 
     The wheel segment can be cast without a core, which is favorable to the fabrication technology. 
     The above specified wheel segment is usually integrated in a support jack in the installed condition and forms, together with the base plate, a support base, wherein the support jack has a lower tube segment on which the wheel segment is pivoted, and the wheel segment is able to roll against the base plate. 
     Preferably, the flattening in a starting position makes two dimensional contact with the base plate. By starting position is meant a central position of the support base and thus the base plate in the unloaded condition of the support jack. 
     Likewise, when the wheel segment is at maximum deflection, the respective end stop surface of the cross arm lies in two dimensions against the lower tube segment of the support jack, so that the surface pressure acting on the structural parts is substantially diminished. 
     Advantageously, a spring element is arranged between each cross arm and the support base. The spring element is preferably suspended by its first end from the cross arm and by its opposite second end from the base plate. This lower stopping point of the spring element on the base plate should be provided at either end of the vertex point of the wheel segment. If the cross arms are displaced outwardly relative to the lower stopping points, the spring elements will have a V-shaped orientation to each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For better understanding, the invention will be explained more closely below by means of a total of nine figures. There are shown: 
         FIG. 1 : a perspective view of a wheel segment according to the invention; 
         FIG. 2 : a top view of the wheel segment of  FIG. 1 ; 
         FIG. 3 : a section through the wheel segment along plane A-A in  FIG. 2 ; 
         FIG. 4 : a section through plane B-B along the wheel segment in  FIG. 2 ; 
         FIG. 5 : a section through the wheel segment along plane C-C in  FIG. 4 ; 
         FIG. 6 : a section through the wheel segment along plane D-D in  FIG. 2 ; 
         FIG. 7 : a head-on view of a support base with wheel segment and base plate, mounted on a lower tube segment; 
         FIG. 8 : a cross section through a support base with wheel segment and base plate in a starting position, and 
         FIG. 9 : a cross section through the support base of  FIG. 8  in a maximum deflected position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a perspective view of a wheel segment  1 , which is mounted on a lower tube segment  15  of a support jack  30  (see  FIG. 7 ). 
     The wheel segment  1  has two parallel side walls  6   a ,  6   b , which are joined together at their bottom end  4  by a partly cylindrical shell element  3 , which has two convex curved rolling surfaces  5 , and by cross arms  12   a ,  12   b  and a middle web  19  (see  FIG. 2 ). At the upper end, the side walls  6   a ,  6   b  are each provided with a stopping point  7   a ,  7   b , the two stopping points  7   a ,  7   b  being aligned in a swivel axis. The swiveling mounting of the wheel segment  1  on the lower tube segment  15  (see  FIG. 7 ) can be done, for example, by means of a continuous bolt or two individual bolts, not further depicted, which stand out to the side relative to the tube segment  15  or a bearing element installed therein and are actively engaged with the stopping points  7   a ,  7   b.    
     The shell element  3  extends in the circumferential direction in approximately semicircular shape as far as a horizontal plane beneath the stopping points  7   a ,  7   b . At the end of the shell element  3  on both sides are the cross arms  12   a ,  12   b , running across the entire width. Each cross arm  12   a ,  12   b  has a material thickening with a flat end stop surface  13   a ,  13   b . The end stop surface  13   a ,  13   b  upon making contact with the lower tube segment  15  (see  FIG. 7 ) abuts against it in two dimensions and thereby lessens the risk of damage both on the part of the wheel segment  1  and on the part of the lower tube segment  15 . When the wheel segment  1  is standing perfectly upright, the end stop surfaces  13   a ,  13   b  are sloping inward at an angle of around 45 degrees. The vertex point  8  of the shell element  3  is located in the middle between the cross arms  12   a ,  12   b , precisely underneath the stopping points  7   a ,  7   b  in the circumferential direction. 
     The side walls  6   a ,  6   b  have a wall segment  18   a ,  18   b  that is set back underneath the stopping points  7   a ,  7   b , merging directly into the shell element  3  in the region of the bottom end  4 . The set-back wall segment  18   a ,  18   b  serves, first, for the fabrication with no core. Furthermore, the stability is enhanced thanks to the increased cross section of the wall segments  18   a ,  18   b  in the direction of the stopping points  7   a ,  7   b.    
       FIG. 2  shows the wheel segment  1  in a top view, in which the basic rectangular shape can be recognized in the region of the equidistant side walls  6   a ,  6   b  and the two cross arms  12   a ,  12   b.    
     Between the two side walls  6   a ,  6   b , one notices openings  10  formed in the shell element  3  on either side of the sectioning line B-B. The openings  10 , first, make possible a chordlike passing of a spring element  16   a ,  16   b  through the shell element  3  according to  FIGS. 8 and 9 . Especially when the wheel segment  1  is tilted, one of the spring elements  16   b  runs for a considerable portion inside the shell element  3 . Each opening  10  is bounded in the circumferential direction by a middle web  19 , joining the side walls  6   a ,  6   b  in the axial direction, beneath the stopping points  7   a ,  7   b , in the region of the vertex point  8 , and by the cross arms  12   a ,  12   b . The openings  10  have an essentially rectangular contour, whose width corresponds at least to the diameter of the spring elements  16   a ,  16   b  (see  FIGS. 8 and 9 ). 
     The opening  10  is formed with a semicircular widening at opposite ends in the circumferential direction between the middle web  19  and the particular cross arm  12   a ,  12   b . The representation of  FIG. 2  in top view does not reveal the segments of the opening  10  lying outside of the widening  11  in the circumferential direction; however, these can be seen in the cross section of  FIG. 5 . The widenings  11  lie in less heavily loaded regions of the rolling surface  5  and serve to reduce the weight of the cast iron design, which would otherwise be heavier than welded wheel segments  1 . 
       FIG. 3  shows a magnified cutout of the wheel segment  1  in the region of the cross arm  12   a . The end stop surface  13   a  project upward from the cross arm  12   a  as a material thickening, due to the cast design. Beneath the cross arm  12   a  is a pocket  17   b  between the side wall  6   a  and the opening  10  in the rolling surface  5 , and behind this another pocket  17   a , being designed to avoid a buildup of material with the risk of forming shrinkage cavities. Moreover, the mass of the wheel segment  1  will be decreased by the pockets  17   a - d.    
       FIG. 4  shows a longitudinal section through the wheel segment  1  corresponding to line B-B in  FIG. 2 . In the region of the vertex point  8 , the rolling surface  5  has a flattening  9 . When the support jack  30  is placed on the ground, this region is in contact with the support base  14  located underneath (see  FIG. 8 ) and usually absorbs the greatest anticipated forces. For this reason, the formation of the flattening  9  also provides a correspondingly large surface for diverting the forces into the wheel segment  1 . The flattening  9  has at least the length of the middle web  19 . It is especially easy to make the flattening, due to the wheel segment  1  being produced as a cast iron part. 
       FIG. 5  shows especially well the course of the opening  10  inside the rolling surface  5 , running from the middle web  19  to the cross arm  12   b . Above the widenings  11 , the opening  10  continues in uniform width, corresponding to its course beneath the widenings  11 . In this way, the loss in standing surface due to the pockets  17   a - d  is compensated. 
     The cross arm  12   b , like the identically shaped cross arm  12   a , each have a notch  20  within the lengthwise axis in the region of the end stop surface  13   a ,  13   b . The notch  20  simplifies the suspending of a spring element  16   a ,  16   b  directly from the cross arm  12   a ,  12   b  of the wheel segment  1  (see  FIG. 8 ,  9 ). 
       FIG. 6  shows a section along line D-D in  FIG. 2 . The cross arms  12   a ,  12   b  have no end stop surfaces  13   a ,  13   b  in this side region, since they lie outside the action zone of the lower tube segment  15 . Beneath the cross arms  12   a ,  12   b , one notices the pockets  17   b ,  17   d . The pockets  17   a ,  17   b ,  17   c ,  17   d  are formed by a partial vertical wall of the rolling surface  5 , which passes into the respective cross arms  12   a ,  12   b  at its upper segment. 
     The middle web  19  rises above the top of the rolling surface  5  as a thickening and thereby increases the strength of the wheel segment  1  in the region of the flattening  9 . 
       FIG. 7  shows in front view the lower end of an otherwise not further depicted support jack  30 , or its lower tube segment  15  with a support base  14  mounted thereon. The support base  15  comprises the wheel segment  1  and the base plate  2  engaging with it. The wheel segment  1  is pivoted to the lower tube segment  15  in familiar manner by its stopping points  7   a ,  7   b . The base plate  2 , in turn, is arranged removably or nonremovably on the wheel segment  1  by means of the rod  21 , while the rod  21  passes through the wheel segment  1  above the middle web  19  (see  FIG. 6 ). Inside the opening  10  is the spring element  16   b , which is secured by its top end to the cross arm  12   b  and by its opposite bottom end to the base plate  2 . A second spring element  16   a  is arranged in identical manner on the back side, not visible in the view shown. 
     The two spring elements  16   a ,  16   b  hold the unloaded support base  14  in a neutral position per  FIG. 8 , in which the wheel segment  1  is oriented centered above the base plate  2 . In this position, the two spring elements  16   a ,  16   b  are under a certain pretension. 
       FIG. 9  shows the support base  14  after a lateral shift, the wheel segment  1  having rolled to one side on the base plate  2  by its rolling surfaces  5 . The rolling process is limited by the end stop surface  13   b  of the cross arm  12   b  abutting against the schematically indicated wall  15   a  of the lower tube segment  15 . The spring element  16   a  is in a compressed state and the spring element  16   b  in a maximum stretched state. 
     LIST OF REFERENCE ELEMENTS 
     
         
           1  wheel segment 
           2  base plate 
           3  partly cylindrical shell element 
           4  bottom end 
           5  rolling surface 
           6   a, b  side wall 
           7   a, b  stopping point 
           8  vertex point of rolling surface 
           9  flattening 
           10  opening 
           11  widening 
           12   a, b  cross arm 
           13   a, b  end stop surface 
           14  support base 
           15  lower tube segment of support jack 
           15   a  wall of lower tube segment 
           16   a, b  spring element 
           17   a - d  pocket 
           18   a, b  set-back wall segment 
           19  middle web 
           20  notch 
           21  rod 
           30  support jack