Telescopic column

The invention relates to a telescopic column with one outer and at least one inner rod element capable of telescoping relative to each other, where at least the outer rod element surrounds at least one ball arrangement with at least one ball, which acts as a rolling bearing between the outer and inner rod elements during telescoping movement. In order to create a telescopic column which, while having a low weight and low manufacturing costs, displays high lateral stability, the at least one inner rod element is provided with a longitudinal groove, which surrounds part of the circumference of at least one ball of the ball arrangement and serves as a ball guide. The longitudinal groove can provide two or more laterally separated running surfaces for the at least one ball. An area with a larger radial distance can be provided on at least one rod element between adjacent running tracks for an assigned ball, this being able to act as an abutment for the ball in the manner of an overload protector.

DETAILED DESCRIPTION OF THE INVENTION In the practical example illustrated in FIGS. 1 to 6 , telescopic column 1 consists of three rod elements 2 , 3 , 4 , which can be telescoped relative to each other and each have an essentially rectangular cross-section. Radially outer rod elements 2 and 3 display roughly or exactly the same wall thickness, while the wall thickness of inner rod element 4 is approx. 50% greater. The corner areas of inner rod elements 3 and 4 display guide grooves 5 , 6 (see FIG. 2 ) which are open towards the outside, run in the longitudinal direction of the rod elements, serve to accommodate running balls 7 , 8 and surround these over a circumferential angle of approx. 90 degrees (radially outer running ball 7 ) or approx. 70 degrees (radially inner running ball 8 ) on the respective inner side. The axes connecting opposite ball running surfaces enclose an angle of 70 degrees. Running balls 7 , 8 are capable of moving relative to both adjacent rod elements ( 2 and 3 or 3 and 4 ) in the longitudinal direction of the rod elements. Radially outer running ball 7 is guided on outer rod element 2 on two running surfaces 9 , which are a distance apart on the circumference of the ball and enclose an angle of approx. 90 degrees. On the opposite side of the ball, a running surface is provided for each of these running surfaces on the corresponding guide groove. In this context, the running surface is located at roughly the level of the adjacent side wall 10 of rod element 3 , which forms the narrower side wall of rod element 3 , so that laterally acting forces can be absorbed. A similar situation applies to the two other radially outer and inner ball running surfaces 9 and 11 , which are opposite each other in relation to the center point of the ball, where ball running surface 11 lies essentially at the level of lateral surface 12 , in this case at a radial distance of roughly one wall thickness of the same. Ball running surfaces 9 and 11 are each located roughly or exactly at the level of the turning points or end-points of the essentially linear sections of the adjacent side walls of the rod elements or of areas 14 parallel to them. With a ball diameter of approx. 10 mm, the width of the ball running surfaces is approx. 1 to 2 mm. Ball running surfaces 9 , 11 and 20 , 21 are essentially worked into the rod elements by the balls themselves during the first telescoping movement of the rod elements relative to each other, where, during a preceding process step, only running grooves 38 ( FIG. 1 ) were incorporated into the rod elements, their width being small compared to the width of the definitive ball running surfaces, for instance &frac13; to &frac15; of the same or less. Thus, the definitive running surfaces are formed during the first telescoping movement, or the first few telescoping movements, the direction of ball travel being defined by running grooves 38 provided. Ball running surfaces 20 , 21 of the radially inner ball—the same could also apply, at least facultatively, to balls lying radially farther inwards—are located on a side wall 12 and on a concave groove rear side 22 in relation to the outer rod element. The same applies to the radially inner running surfaces of the same ball on the inner rod element, where, instead of the side wall, a section 14 running parallel to it is provided with a ball running surface. In this context, the lines connecting radially separated balls 7 , 8 , which are each assigned to different rod elements, are located on a connecting line that does not pass through the geometrical center point or the center of gravity of the rod elements. The connecting line in the practical example includes a smaller angle in relation to the side wall against which the balls lie. The same design principle can also be applied to triangular, pentagonal or polygonal cross-sectional profiles or to curved, e.g. round, oval or elliptical cross-sectional profiles. Thus, if a further, inner rod element were to be provided, the further balls would preferably be located in angular area 23 , although location in angular area 24 would, however, also be possible, in which case the balls of the radially separated rod elements would then not lie on a straight or essentially straight line. According to the practical example with groups of two radially separated balls 7 , 8 each, three ball running surfaces lie on an at least essentially straight line V 1 . According to the practical example, this line runs between the diagonal and the side walls of the rod elements. It is also possible for more than three ball running surfaces to lie on one line, particularly if more than two radially inner rod elements 3 , 4 are provided. The ball running surfaces lying on a line can be the immediately consecutive ones in the radial direction, as in the practical example, although, if appropriate, ball running surfaces can be provided between these, whose position deviates substantially from the straight line. This deviation can also apply to the radially innermost and/or outermost ball running surfaces in each case, preferably only to these. According to the practical example, the deviation of the ball running surfaces from the straight line is approx. ¼ to &frac15; of the ball diameter or less, without being limited to this. Provided between adjacent running surfaces assigned to a ball are rod areas 15 , 16 , 17 , which are at a slightly larger radial distance from the balls, so that a gap arises between the ball and the rod area. The gap depth according to the practical example is approx. 0.1 to 0.2 mm. If the rod elements are deformed in the area of the ball guides, these areas 15 to 17 can support the ball and form additional running surfaces. The overload abutments are preferably located radially inwards relative to the ball, or alternatively or additionally radially outwards relative to the ball, if appropriate, and lie roughly on connecting line V 2 between the respective corner of the idealized profile of the rod element and its center point. The deviation from the straight line is preferably ¼ to &frac15; or less of the ball diameter, without being limited to this. The deviation mentioned can apply to some or all of the overload areas. The rod elements are manufactured from sheet metal material by means of a rolling process with subsequent formation of a weld seam, which runs in the longitudinal direction of the rod element and can be provided in the side area. The rolling process makes it particularly easy to incorporate the grooves, where inner shaping angles 18 can be made to be particularly sharp, while outer shaping angles 19 are rounded. At the same time, this also makes it possible to manufacture ball guide grooves 5 , 6 with sufficient accuracy. FIG. 3 shows a telescopic column with guide elements 25 , which are fitted onto or inserted into the face ends of the rod elements and can be fixed in position by means of snap-in connections provided in the corner areas. The snap-in connections can be released from the outside via slits in the rod elements. In this context, the snap-in tabs of the snap-in connections are located at the level of the ball guide grooves, so that the snap-in tabs have sufficient play. This permits simple fastening of the guide elements if, over virtually the entire circumference, essentially only with the exception of the areas of the ball guide grooves, the inner and outer walls of adjacent rod elements are only separated by a small distance that is essentially in the region of the wall thickness of the rod elements, for instance in the region of once to twice the wall thickness, or even less. Supplementary to FIG. 1 , FIG. 4 shows ball retainers 27 , which each jointly retain ball arrangements of adjacent corner areas of the rod elements and span the respective side walls for this purpose. The ball retainers display conventional ball cages 28 and intermediate connecting pieces 29 , these being interconnected via articulated connections 30 in the style of integral hinges. Thus, when in disassembled condition, ball cages 28 can be swung essentially into the plane of connecting piece 29 or into a parallel plane, this greatly facilitating the manufacture of the ball retainers, which can be made of a plastic material. Ball retainers 27 and 31 are assigned in pairs to opposite lateral surfaces of rod elements 3 and 4 and are arranged in staggered fashion in the circumferential direction of the rod elements or arranged with gaps between them. It goes without saying that, particularly also in the case of other cross-sectional geometries of the rod elements, ball retainers 27 and 31 can be assigned to several or just one guide groove or guide groove arrangement with several immediately adjacent guide grooves. FIGS. 5 and 6 show rod elements 3 , 4 with the respective ball retainers 27 , 31 . Ball retainers 27 and 31 each display axially separated retaining areas 33 and 34 , which are each assigned to adjacent corners of the polygonal profiles. Ball arrangements 35 each display two axially separated balls 37 , one behind the other in the longitudinal direction of the rod element. In this context, main piece 29 extends over a relatively great axial length of the respective rod element, roughly over once to twice the transverse extension of the longer cross-sectional axis of the inner or outer rod element. In this context, retaining areas 33 themselves extend only slightly more over the respective ball circumference, meaning that the axially and laterally separated retaining areas can be pivoted independently of each other relative to connecting area 33 . FIG. 7 shows a section of a further telescopic column according to the present invention having inner and outer rod elements 40 , 41 . The inner rod element 40 is provided with a guiding longitudinal groove 46 and a ball 42 being in engaging contact with a side wall 44 of the outer rod element. The diameter of the ball is chosen so that it makes two running surfaces in the inner rod element and one running surface in the outer rod element at least during the first telescopic movement. It is obvious for someone skilled in the art that rod element may be designed so that the ball is positioned between two walls of a groove of the outer rod element and one side wall of the inner rod element, so that during the at least first telescopic movement two running surfaces are made in the outer rod element and one running surface is made in the inner side element. In both embodiments two running surfaces 44 are made in opposite walls of one groove.