Abstract:
In a method for producing a tubular stabilizer, an original outer diameter of a tube is reduced in a swaging process thereby producing one-piece tubular stabilizer halves of uniform material.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of German Patent Application, Ser. No. 10 2012 106 423.7, filed Jul. 17, 2012, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a method for producing a tubular stabilizer for a motor vehicle. 
         [0003]    The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention. 
         [0004]    It is known from the state of the art to use stabilizers on motor vehicle axes in order to optimize the driving properties, in particular the rolling behavior of the motor vehicle. By way of the stabilizer, the wheel loads of the left and right vehicle side are distributed as a result of force distribution and the rolling behavior of a superstructure, which is also coupled with the stabilizer, is reduced. The stabilizer itself is known in particular as torsion stabilizer, which builds up a torsional moment as a result of rotating a tube section and transfers a corresponding occurring wheel load from one wheel to the other wheel. 
         [0005]    Regarding the stabilizer itself, there is a conflict of goals between driving dynamic and driving comfort. In particular in off-road vehicles or small transporters, high rolling behavior is to be expected, which would require a torsion stiff stabilizer, which however diminishes the driving comfort during straight ahead drive. 
         [0006]    From the state of the art, semi-active or active stabilizers are known which by incorporating an actuator, for example an electric actuating motor, can be adjusted in their stiffness characteristics so as to have a high resistance moment against torsion for example when negotiating curves, and thus only allow a small rolling behavior of the motor vehicle, however when driving straight ahead only have a small resistance moment against torsion and thus ensure a corresponding driving comfort. 
         [0007]    Such a motor vehicle stabilizer is for example known from EP 1 814 748 B1. 
         [0008]    The stabilizer halves that are connected to the corresponding actuator are for example known as stabilizer rods or tubular stabilizers, i.e. as hollow components. 
         [0009]    The stabilizer halves are often bent multiple times three dimensionally due to the packaging inside the motor vehicle, in particular due to the surrounding axle components and the kinematic coupling for spring extension and compression of the wheel, so that lines, shock absorbers or other components do not come into contact with the stabilizer half during spring extension and compression of the wheel. 
         [0010]    At the same time, stabilizer halves have to be produced cost effectively and with a low own weight in order to keep the proportion of the un-sprung wheel masses low and thus establish a high level of driving dynamics of the motor vehicle. 
         [0011]    However, as a result of the torsion, the stabilizer halves are exposed to long-term high varying loads throughout the service life of a motor vehicle, often over more than ten years, and therefore have to be produced particular durable. Thus, the goal is to produce the components with a durability, which is as high as possible. 
         [0012]    It would therefore be desirable and advantageous to provide an improved method for producing a tubular stabilizer with which a tubular stabilizer for a motor vehicle in particular a tubular stabilizer half for a semi-active or active stabilizer for motor a motor vehicle can be produced particularly cost effectively and durably. 
       SUMMARY OF THE INVENTION 
       [0013]    According to one aspect of the present invention, a method for producing a tubular stabilizer for a motor vehicle, in particular for producing a tubular stabilizer half for an active or semi-active motor vehicle stabilizer, includes swaging at least a section of a tube having a constant cross sectional geometry from outside the tube in a swaging device, thereby reducing an outer diameter of the tube and providing the tube with cross sectional geometries that vary along a longitudinal direction of the tube, wherein a connection flange or an actuator sleeve is formed on the tubular stabilizer by the swaging. 
         [0014]    For this, a tube in particular a metallic tube having a constant cross sectional geometry, and in particular having a round outer cross sectional geometry, is processed by a swaging device, in particular a rotary swaging device, so that the outer diameter is reduced. This is in particular a rotary swaging method, which represents a chipless forming process for reducing the cross section of rods, tubes or wires. 
         [0015]    The rotary swaging device itself contains multiple swaging tools arranged at an angle distance form one another, which carry out simultaneous radial oscillating movements in quick succession. At each inwardly oriented movement of the swaging tools, a portion of the tube to be formed is formed so as to reduce the outer diameter. The tube is moved through the swaging device with a forward movement, which occurs pulsed so as to be adjusted to the oscillating movements of the swaging tools. 
         [0016]    This allows to producing a one-piece tubular stabilizer from uniform material, in particular a one-piece tubular stabilizer half from one material, which has a connection sleeve or a connection flange as well as cross sectional geometries which differ from one another over the length of the tubular stabilizer half, and is thus optimized with regard to the load characteristics and its specific own weight. In contrast to a widening process known from the state of the art, the rotary swaging process is advantageous in that micro cracks that occur during widening inside the material structure or on the outer sheath surface or inner sheath surface of the tube to be worked on, are avoided. As a result of the swaging process, the material is condensed which avoids the occurrence of micro cracks during widening. 
         [0017]    Within the scope of the invention, it is thus possible to also produce inner profiles or outer profiles that enable a form fitting engagement with further components, for example a toothing with an actuator. As an alternative, it is also conceivable to configure at least sub sections of the longitudinal section angled, which can be advantageous in particular with regard to a three dimensional deformation of the stabilizer half following the swaging process depending on the geometry to be produced. 
         [0018]    According to the invention, a connection flange or an actuator sleeve is formed one-piece and from uniform material on the tubular stabilizer half by the swaging process. By this, in particular a one-piece tubular stabilizer made of uniform material, in particular a tubular stabilizer half is produced, which has a high service life with regard to an ongoing, alternating bending loads. 
         [0019]    In the case of a connection flange, in particular the end of the tube to be worked on is initially either not or only to a minor degree, worked on or increased in its wall thickness. The longitudinal section of the tube adjoining the end is further preferably reduced in its cross sectional geometry in particular in its outer diameter so that it is configured smaller relative to the original tube. The connection flange can be formed with a profiling for connection to an actuator during or after the swaging process or the connection flange can be welded to the actuator. 
         [0020]    In the case of an actuator sleeve, such a longitudinal section of the end of the tube is in particular not or only to a minor degree deformed by the swaging process so that an actuator sleeve or a sleeve shaped body is formed, wherein then the longitudinal section of the tubular stabilizer adjoining the sleeve-shaped body is reduced in its cross sectional geometry by the swaging process. Within the framework of the invention, the swaging process in particular allows introducing toothings inside the sleeve or in a transitional section of sleeve to tubular stabilizer half, so that for example an actuator which is introduced or inserted into the sleeve for example in the form of an electromotor can be form fittingly coupled with the tubular stabilizer half. 
         [0021]    According to another advantageous feature of the present invention, the wall thickness can be increased during the swaging process. As a result of the reduction of the outer diameter an inward shift occurs while the material remains constant over the length, whereby the wall thickness per longitudinal section increases while the outer diameter decreases. Corresponding counter holders or forming mandrels allow reducing the wall thickness with the method according to the invention, wherein the outer diameter remains essentially constant or is only slightly reduced. The at least partial reduction of the wall thickness allows selecting as initial material a tube with great diameter ratios and which has a high resistance moment against torsion at simultaneous small wall diameter and due to a small wall thickness has a low own weight to work on at least parts such that for a subsequent bending process a slight bending is enabled and a high resistance moment against torsion remains over the longitudinal sections which extend essentially straight. 
         [0022]    According to another advantageous feature of the present invention, the tube is pushed through the swaging device in axial direction with a forward movement, wherein the speed of the forward feed is adjustable. The forward feed is in particular carried out pulsed however it can also be set within the framework of the invention as constant forward feed speed or as a continuous forward feed with adjustable speed can be set so that a respective outer diameter to be produced and a corresponding wall thickness results in the tube to be worked on. 
         [0023]    According to another advantageous feature of the present invention, at least the section that is to be swaged before can be heated prior to the swaging process, wherein the heating is carried out in particular by an induction coil arranged upstream of the swaging device. The upstream located heating in particular enables providing a particularly homogenous structure within the component so that the workpiece is not weakening as a result of the heat treatment or the forming in the hot condition at local high deformation degrees. 
         [0024]    According to another advantageous feature of the present invention, the swaging tool itself can be heated, wherein then a conductive heat conduction occurs at contact with the work piece. It is further possible within the scope of the invention to position a quenching sprinkler immediately downstream of the swaging device, which quenching sprinkler effects a hardening or alternatively to arrange a heating device downstream of the swaging tool so that an at least partial tempering occurs after the forming. 
         [0025]    According to another advantageous feature of the present invention, the end section of the tube can be placed into the swaging device and passed through the swaging device and retained in its original state or starting condition, wherein the actual swaging process, i.e. the forming of the tube only occurs in a middle longitudinal section of the tube, i.e. after passing of the end section through the swaging device. In contrast to a widening known from the state of the art, this allows working on longitudinal sections, which are not accessible during classical widening by mechanical forming. From the state of the art it is known at best to use high pressure forming processes, which however is only possible with significant production costs and limited degrees of freedom. 
         [0026]    According to another advantageous feature of the present invention, the swaged tubular stabilizer can be further formed relative to its center longitudinal axis after finishing of at least a first swaging forming. Within the context of the invention, this means a three dimensional forming, for example a bending or bending around of at least the end regions, but also a multiple three dimensional bending of the tubular stabilizer which is pre processed by the swaging. 
         [0027]    According to another advantageous feature of the present invention, a mandrel can be introduced into the tube during the forming process, wherein the mandrel in particular has an outer profile, which is embossed into the tube inner sheath surface during the swaging process. It is in particular possible to form an inner toothing with this inside the tubular stabilizer to be produced, preferably of the tubular stabilizer half to be produced. 
         [0028]    According to another advantageous feature of the present invention, the swaging step can include forming at least a section of the tube from a round starting geometry to an elliptic, polygonal and rectangular cross sectional geometry. This is to be selected in dependence on the loads to be expected and on the subsequently available mounting space for mounting the tubular stabilizer. 
         [0029]    According to another advantageous feature of the present invention, the tube can be worked work on by introducing a mandrel into the tube and a counter holding mandrel so that the wall thickness is reduced by the swaging process at least in sections in longitudinal direction of the tube. 
         [0030]    The previously mentioned steps and embodiments of the method according to the invention can be combined with each other at in any combination within the scope of the invention with the respectively associated advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0031]    Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
           [0032]      FIGS. 1   a - d  show ends of tubular stabilizer halves produced according to the method according to the invention; 
           [0033]      FIG. 2  shows a first possible processing method of an end of a tubular stabilizer; 
           [0034]      FIG. 3  shows a second possible processing method of an end of a tubular stabilizer; 
           [0035]      FIG. 4  shows a further alternative embodiment for processing an end of a p[tubular stabilizer; 
           [0036]      FIG. 5  shows a possible method step for processing a middle longitudinal section of a tubular stabilizer; 
           [0037]      FIG. 6  shows a further possibility for processing a middle longitudinal section of a tubular stabilizer and 
           [0038]      FIG. 7  shows a possibility for processing a tube section with upstream located heating device. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0039]    Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
         [0040]    Turning now to the drawing, and in particular to  FIGS. 1   a - d , there are shown different ends  1  of tubular stabilizer halves  2 , which are produced with the method according to the invention. 
         [0041]    In  FIG. 1   a , a sleeve  3  is formed on the end  1 , wherein the sleeve  3  serves for receiving a not further shown actuating system, which can be inserted into an inner space  4  of the sleeve  3 . From the sleeve  3 , a transitional section  5  whose outer diameter decreases extends in longitudinal direction  6  of the tubular stabilizer halve  2 . Adjoining the transitional section  5  itself is a longitudinal section  7  of the tubular stabilizer half  2  with constant outer diameter. Adjoining this longitudinal section  7  in longitudinal direction  6  of the tubular stabilizer half  2  is a second transitional section  8  again followed by a second longitudinal section  9  with constant outer diameter. All longitudinal sections  7  and the sleeve  3  in the embodiment of the tubular stabilizer half  2  shown in FIG. la have in common that they have the same wall thickness  10 . The transitional section  5  and the longitudinal section  7  are produced according to the invention with the rotary swaging method. The sleeve  3  has the original geometric dimensions of the starting tube or has been worked on in no significant degree with the rotary swaging method. 
         [0042]      FIG. 1   b  shows a second embodiment of a tubular stabilizer half  2 , wherein this has a connection flange  11  at its end  1 , wherein the connection flange  11  is configured tapered in longitudinal direction of the tubular stabilizer half  2  and is adjoined by a longitudinal section  7  with a constant outer diameter, again followed by a second transition section  8  which is adjoined again by a second longitudinal section  9  with constant outer diameter. The embodiment according to  FIG. 1   b  has an essentially constant wall thickness  10  wherein at its end  1  in the region of the connection flange  11 , the embodiment has an increased wall thickness  12 , wherein the increased wall thickness  12  in particular serves for connection of a further component for example a coupling member of a not further shown actuator and a thermal joining is possible via the increased wall thickness  12 . 
         [0043]      FIG. 1   c  shows a further embodiment of tubular stabilizer half  2  produced according to the invention, wherein the latter essentially over its entire length has an essentially constant wall thickness  10  and is constructed analogous to the embodiment according to  FIG. 1   a , with the difference that at its end  1  no sleeve but a connection sleeve  13  is formed. The connection sleeve  13  has the same wall thickness  10  of the tubular stabilizer half produced according to the invention. 
         [0044]      FIG. 1   d  shows a fourth embodiment of a tubular stabilizer half  2  which was produced with the method according to the invention, wherein this embodiment analogous to  FIG. 1   c  also has a connection sleeve  13 , wherein the connection sleeve  13  has an increased wall thickness  12  relative to the longitudinal section  7  which adjoins the connection sleeve  13  in longitudinal direction  6 . 
         [0045]      FIG. 2  shows a first embodiment of the production method according to the invention for a tubular stabilizer half  2 , wherein in a swaging device  14  which has in this case exemplary shown two swaging tools  15 , which carry out a pulsed linear movement  16 , wherein the linear movement  16  is directed toward a center and the original outer diameter  17  of the tube is reduced to an outer diameter  19  after the swaging process. At the same time, as shown here, the original wall thickness  10  of the tube  18  is thickened to an increased wall thickness  12 . 
         [0046]      FIG. 3  shows a second embodiment of a swaging tool  15  for carrying out a swaging process according to the invention, wherein the swaging device  14  has again two swaging tools  15  which perform a linear movement  16  toward each other in pulsing steps. Into the swaging device  14 , and end  1  of a tube  18  is inserted, wherein an inner mandrel  20  is inserted into the tube  18 , which inner mandrel  20 , in turn is form fittingly coupled with a counter holding mandrel  21 , so that the end  1  of the tube  18  comes to rest against the counter holder mandrel  21 . This enables, to reduce the wall thickness  12 , relative to an original wall thickness  10  of the tube  18 . The original outer diameter  17  of the tube  18  is also reduced by the swaging process to an outer diameter  19 . 
         [0047]      FIG. 4  shows a further embodiment of the production method according to the invention, wherein again in a swaging device  14  two swaging tools  15  are arranged so that they carry out a pulsing linear movement  16  toward each other. For this, a tube  18  is reduced in the swaging device  14  in its outer diameter  17  and also in its wall thickness  10 , wherein an inner mandrel with profiled outer surface is introduced into the tube  18  and the outer profile of the inner mandrel  23  is swaged or embossed into an inner sheath surface  24  of the tube  18  by the swaging process. It is possible for this inner mandrel to form a corresponding profile onto the inner sheath surface of the actuator sleeve or the connection flange, so that an inner toothing with an actuator can be produced by means of form fitting connection. Also, a corresponding profiling can be worked onto the front surface of the connection flange or the actuator sleeve, so that the profiling can also be form fittingly coupled with an actuator. 
         [0048]      FIG. 5  shows a further embodiment of the present invention, wherein here in a center section  25  of the tube  18  the wall thickness  26  is configured greater than the wall thickness  10  a the end of the tube  18  or the wall thickness  10  in the longitudinal section  7  that which follows the center section  25  in longitudinal direction of the tube  18 . For this, an inner mandrel  20  is inserted into the tube  18  and at the end  1 , a counter holding mandrel  21  comes to rest formfitting against the tube  18 . The inner mandrel has a headpiece  20   a  wherein headpiece  20   a  and inner mandrel  20  are separated via a separation point  29 . 
         [0049]      FIG. 6  shows a further embodiment, wherein here an induction coil  27  is arranged upstream of the swaging device  14  and the tube  18  carries out a pushing in movement  28  so that it passes the induction coil  27  and is heated. Again shown is an inner mandrel  20 , which is arranged in the tube  18  and a counter holding mandrel  21 , which comes to rest form fittingly with an end  1  of the tube  18 . The swaging tools used according to  FIG. 6  allow thickening of a wall thickness of a middle section  25  of the tube  18 . As a result, this middle section  25  attains a greater wall thickness  26  than the remaining section of the tube  18  in longitudinal direction  6 . Within the scope of the invention, the induction coil  27  can however be used in any other widening or compression method. For removal, the turned tube is removed with the tool halves  15 . 
         [0050]      FIG. 7  shows a further embodiment of the production method according to the invention, wherein here a middle section  25  is configured reduced in its outer diameter  19  relative to the outer diameter  17  of the remaining tube  18 . In this case as well, the turned tube is removed with the tool halves  15 . 
         [0051]    While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 
         [0052]    What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: