Abstract:
A guide tube ( 4 ) for the rotatable mounting of a steering spindle ( 2 ) of a motor vehicle is described, wherein the guide tube ( 4 ) is rolled cylindrically from a single sheet-metal section and is connected at an axial contact point ( 12 ), and wherein the guide tube ( 4 ) has elements ( 13 - 15 ) for the definably axially displaceable fastening in a bearing unit ( 1 ). The guide tube ( 4 ) is characterized in that the elements ( 13 - 15 ) are designed in the form of at least two heads ( 13 ) which are distributed over the circumference, run axially, are formed circumferentially on both sides by ribs ( 14, 15 ) expanding the cylinder circumference and are formed in the sheet-metal section. A production method for such a guide tube ( 4 ) is also described.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a guide tube for a steering shaft for a motor vehicle, and to a particularly simple, quick, robust and favorable method for producing same. 
       PRIOR ART 
       [0002]    The steering in a motor vehicle is generally constructed such that a steering spindle to which the steering wheel is fastened is rotatably mounted in a bearing unit. In order that the steering wheel is adjustable in terms of its height, the bearing unit can be fastened to the chassis in such a way that the steering spindle can he fixed. in different positions. In this case, there is generally a guide tube which receives the outer bearing bushings of the bearing for the steering spindle. 
         [0003]    Such a guide tube is generally designed as a cylindrical tube, as is known generically in particular, for instance, from EP 0 502 761. 
         [0004]    Such a guide tube can be mounted in the bearing unit in an also axially movable manner, so that the steering spindle can to some extent be altered in terms of its length detectable to the user, wherein the different axial positions can be fixed by a force closure and/or form closure, usually with a lever or an electric motor. 
         [0005]    To this end, to such a guide tube according to the prior art (compare, for instance, the generic type according to EP 1 464 560) are welded, on the outer side, separate rail-shaped mounting elements, which enable the guide tube to be fixed in an axially displaceable manner in the bearing unit in different positions. 
         [0006]    The production methods of such guide tubes comprise several steps and, apart from processes for stamping and forming a plurality of parts, they have the drawback that in joining processes the various components have to be joined together, for instance in a welding process. 
       REPRESENTATION OF THE INVENTION 
       [0007]    Accordingly, the object of the invention is, inter alia, to provide an easily and precisely producible light guide tube for a steering shaft in a motor vehicle, which guide tube, moreover, can be cost-effectively produced. 
         [0008]    The object of this invention is achieved by a guide tube and a method for producing same, as defined in the claims. 
         [0009]    A fundamental core of the invention here consists in wholly dispensing with the separate mounting elements on the outer side of a cylindrical tube, as were provided according to the prior art, and in ensuring the interfaces for the axially displaceable mounting of the guide tube directly by an appropriate design of the wall of the tube per se with at least 2 grooves, distributed over the circumference. Thus, from a single stamped sheet metal part in a pure forming process, such a guide tube, inclusive of interface for the axially displaceable mounting, can be provided, in that this guide tube is not only rolled and connected and/or welded at the contact point, but that, at the same time, axial beads are configured from the sheet metal material. 
         [0010]    Specifically, the present invention relates to a guide tube for the rotatable mounting of a steering spindle of a motor vehicle, wherein the guide tube is rolled cylindrically from a single metal sheet portion and is connected at an axial contact point, and wherein the guide tube has elements for the definably axially displaceable fastening in a bearing unit. According to the invention, such a guide tube is characterized, in particular, in that the elements are configured in the form of at least two beads, which are distributed over the circumference, are axially running, and are configured circumferentially on both sides by ribs that broaden the cylinder circumference, which beads are shaped in the metal sheet portion. At least 4 balls, normally a whole ball cage, which ball cage is provided in a corresponding groove in the bearing unit, can then engage in these beads, so that a neat axial mounting is obtained. 
         [0011]    According to a first preferred embodiment, such a guide tube is characterized in that precisely two beads are configured, and these are directed symmetrically at two opposite sides. This means that, as is represented, for instance, in  FIG. 7 , they are intended to be supported by two ball bearings disposed on opposite and parallel running walls in the interior of the bearing unit. 
         [0012]    According to a further preferred embodiment, the two heads are disposed in the same half-space, in relation to a center axis of the guide tube. This means that, as is represented, for instance, in  FIG. 7 , they are disposed with their lowest point, in relation to the axis, at an angle of less than 180°. 
         [0013]    The axial contact point is preferably disposed on a circumferential portion between the two beads, preferably on the longer circumferential portion. According to a further preferred embodiment, the beads extend not only over a portion, but over the entire axial length of the guide tube. 
         [0014]    The beads can form an outer contour different from a circular form, so that therein running balls come to bear at two opposite defined points against flanks of the ribs. For instance, it is preferred if these points, in relation to the balls, are arranged at an angle of in the region of 60-100°. Such a guide tube is preferably produced from a metal, preferably from a steel, in particular preferably from a black steel. This preferably having a thickness in the region of 1.5-2.5 mm. 
         [0015]    According to a further preferred embodiment, such a guide tube can additionally have clinches as stops for the outer bearing bushing of the steering spindle, wherein preferably at one end, in particular at both ends of the guide tube, at least two, preferably at least 3 clinches of this type are arranged distributed over the circumference. 
         [0016]    A further preferred embodiment of such a guide tube is characterized in that the metal sheet portion is connected at the contact point by a welded joint and/or spot-welded joint and/or a dovetail joint. 
         [0017]    In addition, the present invention relates to a method for producing a guide tube of this type. Such a method is in particular preferably characterized in that, starting from a stamped metal sheet portion, in a forming process the guide tube is rolled and, at the same time, the ribs and the beads are configured. According to a first preferred embodiment of this method, the method is implemented in multiple stages and the individual circumferential portions are preferably formed sequentially, starting from a central axial center line, on both sides, wherein, in a last step, at the contact point, the guide tube is closed, preferably using exclusively forming operations and without any welding operations. 
         [0018]    The method can have at least four, preferably at least eight stages, in particular between 8 and 12 stages. According to a further preferred embodiment of the proposed method, the stamped metal sheet portion has at at least one, preferably at both axial ends, handling portions, which in the region of the axial center line are connected to the sheet of the actual guide tube during the production method and are afterwards separated from the guide tube. 
         [0019]    A further preferred embodiment of the proposed method aims to improve the roundness of the bearing seat in a beaded guide tube still further. To this end, a cylindrical mandrel, the external diameter of which substantially corresponds to the desired internal diameter of the guide tube, can be introduced in the region of the bearing seat into the interior of the guide tube, and the material can subsequently be specifically made to flow plastically in the circumferential direction of the mandrel with the aid of a tool which acts from outside. This is effected by an application of force to the guide beads with the aid of a specific tool comprising two dies. In first tests, by the use of this method, an improvement in the roundness tolerance from about 0.13 mm to about 0.06 mm was able to be achieved. It should be emphasized that this particular calibration method is a method which can be used not only in connection with a guide tube as has been described above, but generally with a rolled metal tube, preferably with a metal tube rolled from a single piece of metal. In the case of a guide tube as has been described. above, the tool, which acts from outside, engages in the concave transition region from both sides in order to bring about the displacement. In a more general application of this type, for instance, a metal tube which has on only one side just a single axially running rib, in which case the tool engages in the concave transition region to this rib at the top or bottom, can be calibrated, or a metal tube in which a single rib of this type can be disposed on two to some extent opposite sides can be calibrated. Tubes which have more than one bead on each side, or tubes in which fundamentally other axial structures which enable application of force by the tool are provided, can also be worked. In general terms, with respect to this specific implementation of the method, in the following whenever a guide tube is mentioned, a rolled metal tube having an axially extending connection point should thus also generally be understood. 
         [0020]    Correspondingly, the present invention, according to a further preferred embodiment, relates to a method as has been described above, which method is characterized in that, after the closure of the guide tube (or generally of a rolled metal tube), this, at least in one of the end regions intended to receive the bearing, is reworked in order to increase the roundness, by a cylindrical mandrel being introduced into the interior of the end region and being made with two dies to flow plastically in the circumferential direction of the mandrel. This is preferably realized such that the dies, preferably in one work step on both sides of the guide tube, by means of corresponding contact regions, displace the transition region from the lower area of curvature to the lower axial rib in the circumferential direction of the transition region from the upper area of curvature to the upper axial rib, through the application of force. Prior to this method step for increasing the roundness, the guide tube can possibly firstly be reworked, for example by the point-by-point or region-by-region rewelding of a created dovetail joint at the contact point and/or by the welding of further elements, such as, in particular, reinforcement profiles and/or crash elements, onto the guide tube. In order to limit this calibration to the axial portion, which must actually be brought to higher precision, it can be advantageous if the guide tube possesses a circumferential portion in the region of the beads or ribs, preferably on both sides, a slot, a so-called free stamping. This slot separates to some extent, in this circumferential region, the region to be worked (to be calibrated) from the region not to be worked. This has the result that the worked region is decoupled from the other, unworked region, and thus the stabilizing effect of the ribs in the unworked region has no influence on the worked region. The calibration can hence be performed in the worked region with yet greater precision. 
         [0021]    According to a further preferred embodiment of this method, at least one of the contact regions, preferably both, has a circumferential contact region which follows the outer circumference of the guide tube over a limited circumferential portion and faces away from the respective rib. 
         [0022]    Further embodiments are defined in the dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    Preferred embodiments of the invention are described below on the basis of the drawings, which have merely an illustrative function and should not be interpreted as restrictive. In the drawings: 
           [0024]      FIG. 1  shows an entire bearing unit in a side view; 
           [0025]      FIG. 2  shows the bearing unit according to  FIG. 1  in a perspective view; 
           [0026]      FIG. 3  shows a section according A-A, as indicated in  FIG. 1 , through such a bearing unit; 
           [0027]      FIG. 4  shows a section according to B-B, as indicated in  FIG. 1 , through such a bearing unit; 
           [0028]      FIG. 5  shows a guide tube in a perspective view from below; 
           [0029]      FIG. 6  shows a guide tube in a perspective view from above; 
           [0030]      FIG. 7  shows a section through such a guide tube; 
           [0031]      FIG. 8  shows in a)-l) the individual stages of the production method in the forming process after the stamping of the blank, wherein respectively at the top is represented a top view, in the middle a perspective view, and at the bottom a sectional representation in a plane perpendicular to the axis of the resulting guide tube; 
           [0032]      FIG. 9  shows various views of a device for reworking a guide tube (or generally a metal tube) in order to increase the roundness in a portion, in particular in the region of the bearing seat, wherein in a) the open tool is represented in a perspective view, in b) the closed tool is represented in a perspective view, respectively with guide tube, in c) a view of the tool in the axial direction in the open position without guide tube, in d) a view of the tool in the axial direction in the closed position with guide tube, and in e) the detailed view according to B in  FIG. 9 d   ; and 
           [0033]      FIG. 10  shows a guide tube in a perspective view from below, from one (a) and the other (b) side. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0034]    In  FIGS. 1 to 4 , an entire bearing unit  1  is represented with a guide tube  4  installed. In  FIG. 1 , a lateral view, it is in particular apparent how, on the upper front side, the steering spindle  2  protrudes from the bearing unit  1 . As is revealed in particular from  FIG. 4 , the steering spindle  2  is mounted in a bearing, to be precise with an outer bearing bushing which is fastened in the guide tube  4 . In concrete terms, the bearing, with the bearing hushing  7  and the balls  11 , is pressed into the guide tube. There is a corresponding bearing also at the other end of the guide tube, though this is not apparent in  FIGS. 1 to 3 , but very clearly apparent in  FIG. 4 , where it is represented in section directly through the balls. On the actual bearing unit.  1  there are fastening elements  5  for functional components, as well as, in particular, a fastening element  6 , arranged over a pivot bearing, for the direct or indirect fastening to the cross member of the chassis. The box-shaped outer casing  3  is here generally a die casting (cf. in particular  FIG. 2 ), which provides an axially running cavity for the reception of the guide tube  4 . As can be seen from  FIG. 3 , in this box-shaped outer casing, in the interior, there are two opposite channel-shaped depressions  10 , which are axially running and respectively receive opposite ball bearing cages containing the balls  9 . These balls  9  are thus trapped in the depressions  10  on one side and on the other side by axially running beads  13 , which are shaped in the sheet of the guide tube  4 , likewise running over the entire length. Thus the guide tube  4  is mounted in an axially displaceable manner in the box  3  by means of the ball bearing  9 . This in a manner which is definable given a specific desired setting, i.e. there is additionally a mechanism which allows the guide tube, following displacement to the correct axial position, to be fixed in this, for example via a force closure or a form closure, or a combination thereof. For this purpose, there is here a connecting element  8 , which, when actuated by means of a lever or a motor, fixes the axial position by force closure. 
         [0035]    Alternatively it is possible to here replace a force closure by a rod gear or a similar solution, which is actuated by means of, for example, an electric motor or a crank. 
         [0036]    As can be seen from  FIG. 4 , the guide tube possesses two lateral beads  13  of this type, which are facing toward the parallelly arranged and opposite walls of the interior of the box  3 . The actual beads  13  are formed by two axially running ribs, by respectively a lower rib  14  and an upper rib  15 . The two beads  13  are both disposed above an equatorial plane (in the upper half-space according to the sectional representation in  FIG. 7 ), so that then, owing to the mutual alignment laterally outward, the upper rib  15  projects substantially further from the circumference of the guide tube. 
         [0037]    In  FIGS. 5 to 7 , the guide tube is represented in a perspective view from below ( FIG. 5 ) and from above ( FIG. 6 ), and in an axial section ( 7 ). Here it is apparent that the guide tube is produced from a single metal sheet portion, which is connected on the bottom side by a dovetail joint closure, possibly supported by a welding or spot welding. The dovetail joint  12  is thus disposed in the lower area of curvature  26 . i.e. in the long area of curvature. The short area of curvature  22  forms the top side. The upper area of curvature  22  and the lower area of curvature  26  are disposed on the same circular-cylindrical surface and form the actual cylindrical hollow body, which encloses the interior  16  of the guide tube and defines the longitudinal axis  20 . 
         [0038]    Starting from the kinks  24  and  25 , from this cylindrical basic structure are shaped the two lateral beads  13 , which are formed by the ribs  14  and  15 . Moreover the guide tube possesses clinches  19 , which serve as stops for the outer bearing bushing  7  both on the front side  17  and on the rear side  18  (not represented in  FIGS. 5 to 7 , but represented in  FIG. 8 ). 
         [0039]    In  FIG. 8  is represented a production method for such a guide tube. Starting from a stamped metal sheet portion as represented in  FIG. 8 a   , where already on the lateral edges the contour for the dovetail joint is preformed and, in addition, at the two ends handling strips  21  are provided, which handling strips are not further worked in the forming process, but serve to secure the component during the forming processes, i.e. are connected only in the region of the center line  27  to the sheet forming the final guide tube. 
         [0040]    In a first forming step, a first part of the upper area of curvature  22  is now formed. After this first stage in figure b), in a next step the kink  24  is configured for the transition to the upper rib  15 , as is then represented in figure c). In a following step, the crest of the rib  15  is formed and the lateral metal sheet portions are shifted back upward, as is represented in the end result in figure d). In the next steps e)-g), the individual ribs are configured, wherein this can possibly also be effected in one or just in two stages. Here, three stages are represented: in a first stage the inner rib is completed, which then forms the upper rib  15 ; in a second step, the outermost rib  14 , which will then form the lower rib; and in the last step, the result of which is represented in figure g), the configuration of these two ribs is then once again calibrated and adjusted relative to each other. 
         [0041]    In the following step, the result of which is represented in figure h), a first region of the lower area of curvature is now configured; in the following steps, the results of which are represented in i) and j), this region is substantially closed, so as then to be fully closed in the concluding steps k) and l) in such a way, that then the dovetail joint  12  too is closed and the lower area of curvature  26  is of completely cylindrical configuration. Here the final operation, comprising the removal, of the handling strips  21 , is no longer represented. 
         [0042]    Such a method allows a guide tube in which elements are provided for the axially displaceable, yet fixable mounting in a box made of the material of the tube and in one piece therewith. The method is simple, quick, cost-effective and very robust and accordingly allows a very efficient production of such a bearing box with high rigidity and low weight. 
         [0043]    As a result of the multistage rolling operation, a guide tube which is produced according to the above-described method has superb precision over the entire length. In order to ensure in the region of the bearing seat, that is to say at at least one end of the tube, a still more precise roundness, it can be advantageous, in a further downstream step, to calibrate the region of the bearing seat. This method, with which, in particular, the roundness in this end region can be improved, shall be explained on the basis of the representations in  FIG. 9 . 
         [0044]    For the calibration a tool is provided, which tool has a cylindrical central mandrel  30 , which is intended to be inserted into the end portion of the interior  16  of the guide tube  4  during the working of one or both sides, depending on whether one or both ends are due to be reworked. The cylindrical outer surface  30 ′ of this mandrel  30  here substantially corresponds to the desired internal diameter of the two areas of curvature  22  and  26  of the guide tube. 
         [0045]    In addition, the tool comprises a lower die  28  and an upper die  29 , which have guide elements  38  in the form of guide openings, so that they can be guided directly coupled to one another. Alternatively it is also possible, however, to mount the two tools in a column mount, so that they are not guided directly coupled to one another. The dies  28  and  29  respectively possess a cutout, which embraces the guide tube and which respectively on opposite sides has a contact region  31 ,  32 . In the intervening regions  34  and  35 , the cutouts do not come into contact with the guide tube  4  in the course of the working. In other words, the contact regions  31  and  32  are to some extent only regionally and quite specifically at the critical places in contact with the guide tube  4 , each tool possessing two symmetrically arranged contact regions. 
         [0046]    The contact regions  31  and  32  are here configured as protrusions extending axially along the outer contour of the guide tube, which protrusions respectively engage in the concave kink between the lower area of curvature  26  and the lower axial rib  14  and in the transition region between the upper area of curvature  22  and the upper axial rib  15 . As can be discerned, in particular, on the basis of the detailed drawing according to  FIG. 9 e   , the moving closer together of the two dies  28 / 29  according to the arrows represented in  FIG. 9 e    results in the contact regions  31  and  32  engaging to some extent in the respective concave transition region  37  and  36 , respectively, and there displacing the material in the circumferential direction and thus making it flow, and in this way moving the regions  37 / 36  closer together in the circumferential direction. The material of the guide tube is thus formed out of the original position shown in dashed representation in  FIG. 9 e    and displaced relative to the solid line, and since in this operation a more extensive forming around the whole of the circumference is effected as a consequence of the plastic flowing, the roundness is in this way substantially improved around the whole of the circumference. 
         [0047]    In order to be able to effectively control the process, it can be advantageous if the contact regions have respectively in the region facing away from the ribs a circumferential contact region  31 ′ and  32 ′, which there substantially follow the circumference on the outer side of the guide tube. 
         [0048]    Typically, if the effective displacement in a guide tube having a diameter of 45 mm moves in the region of no more than 1.5 mm, typically in the region of 0.5-1.0 mm, the relative displacement of the two dies one toward the other along the arrows represented in the figure is viewed in the phase involving contact between the tool and the worked. workpiece. 
         [0049]    Ultimately, as a result of this downstream calibration method, the roundness tolerance can be reduced from typically about 0.13 mm to about 0.06 mm. 
         [0050]    The roundness tolerance can further be increased by the provision of a free stamping  33  represented in the figures, i.e. to some extent a slot which separates the worked region from the unworked region of the tube, in particular in the region of the ribs and only in this region. As a result, the calibration region is decoupled from the rest of the tube and the calibration becomes more accurate because the beads in the region of the unworked tube cannot have a stabilizing effect. That method for improving the roundness in the end regions of the guide tube which is set out above in connection with  FIG. 9  can be realized either, as represented in  FIG. 9 , on the fundamentally not yet further processed guide tube  4 . It is also possible, however, to apply the method for improving the roundness to a not yet further processed unit, i.e. to the sub-assembly. Thus it is possible, for instance, that the guide tube  4 , after it has to some extent, after having passed through the steps represented in  FIG. 8 , been brought into the state according to  FIGS. 5-7 , is further worked before the method for calibrating the end regions is implemented. This in particular by, as is represented in  FIG. 10 , prior to the implementation of the method for improving the roundness, the dovetail joint being reinforced by additional welds, denoted in  FIG. 10  by the reference symbol  41 . The corresponding welded joints  41  are preferably located on the respectively axially running portions of the joint, are represented in  FIG. 10  as axially extending joints, but can also be spot-welded joints. Furthermore, additional elements can be fastened to the guide tube. Represented concretely in  FIG. 10  is a reinforcement profile  39 , which with welds  42  spread out in the axial direction is fastened to the guide tube such that it bridges the dovetail joint. In addition, a further element, such as, for instance, the crash element  40  represented in  FIG. 10 , can be fastened, once again by means of appropriate welds  43 . It is evident that from a reworking of this type to a sub-assembly according to  FIG. 10 , in particular if welding operations are passed through, certain dimensional distortions can possibly result. If, in other words, the improvement of the roundness is realized prior to these working steps, the additional benefit, achieved by this method, of better precision of the position support points can possibly be destroyed again. Correspondingly, the approach can preferably be adopted that firstly these further working steps (welding of the dovetail joint and welding-on of further elements) are performed, and only then does that method for improving the roundness in the end regions which is represented in  FIG. 9  and is described above come to be implemented. In general terms, it can be said that the method for improving the roundness in the end regions is preferably applied as shortly as possible before (i.e. for example as the last processing step before) the effective introduction of the bearings into the improved end regions of the bearing box. 
       REFERENCE SYMBOL LIST 
       [0000]    
       
           1  bearing unit 
           2  steering spindle 
           3  box-shaped outer casing of  1   
           4  guide tube 
           5  fastening element for functional components 
           6  fastening element for pivotable direct or indirect fastening to the chassis 
           7  outer bearing hushing of steering spindle 
           8  connecting element for non-positive axial fixing of the position of  4  in  3   
           9  ball bearings 
           10  depressions in  3  for  9   
           11  balls of steering spindle mounting 
           12  zip fastening of guide tube 
           13  beads in the guide tube 
           14  lower axial rib 
           15  upper axial rib 
           16  interior of guide tube 
           17  front end of guide tube 
           18  rear end of guide tube 
           19  clinch as bearing stop 
           20  longitudinal axis of guide tube 
           21  handling strips 
           22  upper area of curvature of the guide tube 
           24 ,  25  kink in transition to  14 / 15   
           26  lower area of curvature of the guide tube 
           27  center line 
           28  lower die 
           29  upper die 
           30  cylindrical mandrel 
           30 ′ cylindrical outer surface of  30   
           31  contact region of  28   
           31 ′ circumferential contact region of  28   
           32  contact region of  29   
           32 ′ circumferential contact region of  29   
           33  free stamping, incision in circumferential direction in the bead region 
           34  contactless region at  26   
           35  contactless region at  22   
           36  transition region from  22  to  15   
           37  transition region from  26  to  14   
           38  guide openings 
           39  reinforcement profile 
           40  crash element 
           41  weld on dovetail joint 
           42  weld on reinforcement profile 
           43  weld on the crash element