Abstract:
A deformation element, a motor vehicle fender bracket with the deformation element, and a method for producing a deformation element are provided. The deformation element serves to receive external impulses introduced into the deformation element and includes, but is not limited to at least two sleeves that are displaceable relative to one another, and a spring-elastic pressure element that is supported in each case on the at least two sleeves that are displaceable relative to one another. In this case, it is provided that at least one of the sleeves has at least one embossing that forms a sliding surface for the other sleeve. The at least one embossing is preferably introduced by electromagnetic pulse forming.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Patent Application No. 102009056923.5, filed Dec. 3, 2009, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The technical field relates to a deformation element, a motor vehicle fender bracket with a deformation element, and a method for producing a deformation element. The deformation element serves to receive and possibly transfer external impulses introduced into the deformation element. The deformation element comprising at least two sleeves that are displaceable relative to one another, and a spring-elastic pressure element, which is supported in each case on the at least two sleeves that are displaceable relative to one another. 
     BACKGROUND 
     Deformation elements are known in the prior art. Modern motor vehicles have to fulfill a number of different demands. In particular, the fender devices of the motor vehicle should satisfy a number of requirements which are in some cases difficult to combine. The regulations for the protection of pedestrians that are becoming more stringent in some countries require, for example, that in the event of a front impact with a motor vehicle, pedestrians can no longer be pushed under the vehicle but that they must rather be lifted away over the motor vehicle. This serves as protection from running over and furthermore has the advantage that an appreciable fraction of the impact energy can be absorbed by a correspondingly softly configured front hood of the motor vehicle, whereby the impulse loading on the pedestrian can be reduced. 
     Furthermore, modern fenders should withstand an impact at low speed without damage to the fender system and without visible external traces. To this end, the fender must be able to store impact energy and then release it again. Finally, fender systems must be able to absorb high forces in the event of an impact of the motor vehicle and introduce them specifically into the load paths of the motor vehicle. 
     DE 103 26 783 A1 discloses a motor vehicle bumper for connection to a supporting structure of a motor vehicle body, in which a decoupling device is provided comprising a first and a second force element which can be displaced relative to one another in the direction of force and a locking device which locks the first and the second force transfer element relative to one another. Further provided is a pull-back device that is connected between the first and the second force transfer element in such a manner that after removing the locking between the first and the second force transfer element. The device actively brings about a relative movement between the two. The pull-back device is configured as a prestressed spring. A disadvantage is that the system uses a number of components that increases the assembly effort and the manufacturing costs of the bumper device described there. 
     It is at least one object to provide a deformation element, a motor vehicle fender bracket with a deformation element, and a method for producing a deformation element, which is able to combine the different requirements and which allows cost-effective manufacture of a fender bracket system. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
     SUMMARY 
     A deformation element has at least two sleeves that are displaceable relative to one another, between which a spring-elastic pressure element is disposed. The spring-elastic pressure element is supported in each case on the at least two sleeves that are displaceable relative to one another. With the aid of the spring-elastic pressure element and the sleeves that are displaceable relative to one another, the deformation element can absorb external impulses acting on the deformation element. Under the action of such external impulses, the at least two sleeves that are displaceable relative to one another are displaced toward one another against the force of the spring-elastic pressure element, and the energy transmitted with the impulses is absorbed in the spring-elastic pressure element up to the maximum possible energy capable of being absorbed by the spring-elastic pressure element and is intermediately stored there. If the energy acting on the deformation element is less than the energy capable of being absorbed by the spring-elastic element, the spring-elastic pressure element can release the absorbed energy again by relaxation and the deformation element remains undamaged. 
     At least one of the sleeves has at least one embossing that forms a sliding surface for the other sleeve. In this way, the deformation element can be produced with an extremely small number of parts so that fewer production and assembly steps are used as compared to the case with known deformation elements and furthermore, the assembly can be carried out very simply. Complex assembly steps involving a complex fastening of a plurality of components to one another can be avoided with the deformation element according to the invention. In addition, the implementation effects a low-friction sliding of the at least two sleeves onto one another so that low break-loose forces exist and at low collision speeds, no damage should be expected to a fender fitted with a deformation element according to the invention. 
     According to another embodiment of the deformation element, it can be provided that the at least two sleeves which are displaceable relative to one another, are arranged to be at least partially overlapping. By this means it can be achieved that the transversal stiffness of the deformation element is high and any undefined deformation of the deformation element outside the axis of translation or compression can thereby be prevented. 
     According to a further embodiment, it can be provided that the at least one embossing is provided on the inner sleeve. In this way, easy assembly of the deformation element and a particularly low-friction sliding of the two sleeves onto one another can be accomplished. 
     According to a further embodiment, it can be provided that in the region of the at least one embossing, the inner sleeve has an extension which is smaller than or equal to the internal extension of the outer sleeve. This is used for low-play or free-from-play guidance of the outer sleeve on the inner sleeve. 
     According to a further embodiment, it can be provided that at least two embossings are provided that are spaced apart axially with respect to one another. In this way, canting of the two sleeves under a non-purely axial force can be avoided, and the ease of movement of the two sleeves is additionally increased. 
     According to a further embodiment, the at least one embossing has a height of approximately 0.5 mm to approximately 3 mm, preferably approximately 1 mm to approximately 2 mm. Thus, an optimal compromise is achieved between structural strength of the sleeves with the embossings, ease of assembly, and ease of movement of the deformation element. 
     According to a further embodiment, it can be provided that the external sleeve has an embossing that forms a translation stop with the at least one embossing of the inner sleeve. The two embossings form a defined stop which allows the overall length of the deformation element to be fixed very precisely. In the event of a gentler impact in which the deformation element can absorb all the impact energy, it can furthermore be ensured with the aid of the translation stop that the deformation element returns to the same position as prior to the impact. 
     According to a further embodiment, it can be provided that the at least one embossing is produced by electromagnetic pulse forming. Electromagnetic pulse forming allows precise forming of the sleeves without weakening the material in the formed region. The structural stiffness of the deformation element can thus be maintained. 
     According to a further embodiment, it can be provided that the sleeves comprise tubular elements, which have a circular, oval, rectangular, or square cross-section. Such tubes can easily be formed and easily mounted. 
     In a further embodiment, it can be provided that the deformation element has fastening elements provided for fastening to longitudinal members, preferably lower longitudinal members, of an engine bearer module and fastening elements for fastening a transverse strut, which fastening elements are preferably connected nonpositively, seamlessly, or positively to the sleeves by electromagnetic pulse forming. This allows easy manufacture of the deformation element according to the invention. In particular, the assembly or production steps can be combined with pulse forming and executed in one operation. 
     A motor vehicle fender bracket system is also provided that comprises at least one fastening element for fastening the motor vehicle fender bracket to an engine bearer module and a deformation element according to the previous described invention. 
     A method is also provided for producing a deformation element, in particular a deformation element explained initially comprising: having ready a first sleeve, a second sleeve, and a spring-elastic element; introducing at least one first embossing into the first sleeve; inserting the spring-elastic element into the first sleeve, in particular with prestressing; pushing the second sleeve onto the first sleeve, as well as introducing an embossing into the second sleeve to produce a tight fit with the at least one embossing of the first sleeve. Such a deformation element can be produced particularly simply and cost-effectively since it has a small number of components and the manufacturing steps can be executed in an uncomplicated manner. 
     According to a further embodiment of the method, it can be provided that the at least one embossing is produced by electromagnetic pulse forming and/or by roll forming. In a further embodiment of the method, it can be provided that fastening elements are attached nonpositively, seamlessly, or positively to the first sleeve and/or the second sleeve by electromagnetic pulse forming. This makes it possible to use an electromagnetic pulse forming station for carrying out all the pulse forming steps. Further forming steps or forming stations can be saved in this way. 
     Further aims, features, and advantageous possible applications are obtained from the following description of an exemplary embodiment with reference to the drawings. All the features described and/or depicted pictorially form the subject matter, independently of the claims and their back-references. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: 
         FIG. 1  shows a perspective view of a motor vehicle fender bracket on an engine bearer module according to an embodiment; 
         FIG. 2  shows an exploded view of a deformation element according to the embodiment; 
         FIG. 3  shows a perspective view of the rear section of the deformation element according to the embodiment from  FIG. 2 ; 
         FIG. 4   a  shows a sectional view along the line of intersection A-A through the rear section of the deformation element according to  FIG. 3 ; 
         FIG. 4   b  shows an enlarged view of a section from  FIG. 4   a;    
         FIG. 5  shows a schematic perspective view of the front section of the deformation element according to  FIG. 2 ; 
         FIG. 6  shows a sectional view through a mounted deformation element; 
         FIG. 7   a  shows a sectional view through a deformation element mounted in a motor vehicle in relation to a further fender bracket; 
         FIG. 7   b  shows the view from  FIG. 7   a  with compressed deformation element; 
         FIG. 8   a  shows a section through a deformation element according to a second embodiment; and 
         FIG. 8   b  shows a deformation element according to the second embodiment in the compressed state. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. 
       FIG. 1  shows a schematic perspective view of a motor vehicle fender bracket  2  mounted on an engine bearer module  4  of a motor vehicle. The engine bearer module  4  is preferably a unit which comprises an engine bearer  6  with lower longitudinal members  8 , disposed thereon or integrated. The engine bearer module  4  serves to accommodate engine and transmission components of the motor vehicle and for the simplified installation of these components into the motor vehicle. The engine bearer module  4  is an additional structural component which serves to relieve the stress of the central structural load path on the body side. 
     The motor vehicle fender bracket  2  has two deformation elements  14 ,  16  that at one end are connected to the lower longitudinal members  8 ,  10  of the engine bearer module  4  and which at the other end are connected to the lower transverse member  18 , to which the front fender of the motor vehicle can be fastened directly or indirectly. Fastening elements  20 ,  22  are provided for fastening the deformation elements  14 ,  16  on the lower longitudinal member  8 ,  10 . 
     The embodiments are is explained in connection with a front motor vehicle fender bracket system, but can naturally can also be used for all other fender brackets attached to the motor vehicle. When used as a rear motor vehicle fender bracket, the terms “front” and “rear” should be exchanged. 
       FIG. 2  shows a schematic perspective exploded view of the deformation element  14 . The deformation element  14  has three main components. A rear deformation element sleeve  24  is provided in the rear region, and a front deformation element sleeve  26  is provided in the front region. Provided between the rear deformation element sleeve  24  and the front deformation element sleeve  26  is a compression spring  28 , which in the exemplary embodiment shown is designed as a helical spring, but can easily be present in other known forms of compression spring. 
     The rear deformation element sleeve  24  has two peripheral embossings  30 ,  32 , whose function will be explained more precisely hereinafter. Furthermore, the rear deformation element sleeve  24  has the fastening element  20 , which serves to connect the deformation element  14  to the lower longitudinal member  8  of the motor vehicle.  FIG. 3  shows the rear deformation element sleeve  24  in an enlarged, perspective view. The rear deformation element sleeve  24  is composed of a rear tubular element  38 , in which the embossings  30 ,  32  are introduced by means of electromagnetic pulse forming, and the fastening element  20 . The rear tubular element  38  is connected nonpositively to the rear fastening element  20 , which has fastening holes  34  for fastening to the lower longitudinal member  8 . The two embossings  30 ,  32  are disposed on the rear tubular element  38  spaced apart from one another axially. The embossings  30 ,  32  form sliding surfaces  33 , on which the front deformation element sleeve  26  not shown in  FIG. 3  can slide. 
       FIG. 4   a  shows a cross-section along the line of intersection A-A according to  FIG. 3 . The rear fastening element  20  has a flange  36  that projects into the rear tubular element  38  and is connected positively or nonpositively to the rear tubular element  38  in the overlap region formed by electromagnetic pulse forming. Alternatively, a seamless connection could be made by means of ultrasound welding or laser welding. As can be seen in the enlarged view of the section according to  FIG. 4   b , the two peripheral embossings  30 ,  32  have a height h of about 1 mm. 
       FIG. 5  shows the front deformation element sleeve  26  in a schematic perspective view. The front deformation element sleeve  26  has a front tubular element  40  and a fastening element connected nonpositively to the front tubular element  40  for connection of the deformation element according to the invention to the transverse member  18 . A peripheral embossing  44  is provided at the rear end of the front tubular element  40 . 
       FIG. 6  shows a cross-section through a mounted deformation element  14 . The front deformation element sleeve  26  is in this case pushed onto the rear deformation element sleeve  24 . The compression spring  28  is disposed between the deformation element sleeves  24 ,  26 . The rear flange  36  forms a rear stop surface  46  for the compression spring  28 , the front fastening element  42  forms a front stop surface  48 . The length of the compression spring  28  in the relaxed state is at least somewhat longer than the maximum distance of the stop surfaces  46 ,  48  so that the compression spring  28  is easily prestressed in the deformation element  14 . 
     The length of the deformation element  14  is determined by a translation stop that is formed from the rear embossing  30  of the rear tubular element  38  and the end embossing  44  of the front tubular element  40 . These form a tight fit in the mounted state, which prevent the deformation element  14  according to the invention from expanding further in the axial direction. 
       FIG. 7   a  shows the deformation element  14  in the expanded state in positional relationship to a fender bracket  50 . The fender bracket  50  is preferably the upper fender bracket attached in front of the longitudinal frame of the motor vehicle body. In practice, the apparent installation position of deformation element  14  and fender bracket  50  with respect to one another can appear differently, the position shown in  FIG. 7   a  relates to an imaginary, exactly perpendicularly running mounting plane for the front fender (not shown). The diagram according to  FIG. 7   a  therefore shows the functional mode of action of the deformation element  14 . 
     In the relaxed state of the deformation element  14 , the deformation element  14  lies vertically in front of the mounting plane of the fender bracket  50 . Both are spaced apart from one another at a vertical distance d 1 . This has the effect that a fender, which in modern motor vehicles is preferably made of plastic and is disposed in front of the fender bracket  50  and the lower transverse member  18  (e.g., bracket), and on which a force acts in the direction opposite to the direction of travel of the motor vehicle, can pivot about the upper fender bracket  50 , whereby the deformation element  14  is shortened. 
     Depending on the impulse introduced, the compression spring  28  is compressed so far until it completely becomes a block as shown in  FIG. 7   b . At this time, the distance between the mounting position of the fender bracket  50  and the lower transverse member is reduced to a very small but still positive vertical distance d 2 . Up until this time, it is possible for the deformation element  14  to relax again due to the force of the compression spring  28 . No damage to the fender or the frame structure located there behind is to be expected. Only in the case of impulses which introduce a greater energy into the deformation element  14 , are these energies introduced into the motor vehicle frame structure and must be reduced by this accompanied by permanent material deformation. 
     Furthermore, the arrangement of lower transverse member  18  and deformation element  14  relative to the fender bracket  50  has the result that in the event of a collision with a pedestrian, the lower part of the fender is initially compressed, which produces a counteracting force through the compression spring  28 , which imparts an angular momentum to the pedestrian in such a manner that he is raised onto the front hood of the motor vehicle. The probability of the pedestrian being run over is considerably reduced in this way. 
       FIG. 8   a  shows a further embodiment of a deformation element  54 . The deformation element  54  according to the second embodiment differs from the deformation elements  14 ,  16  according to the first embodiment primarily in that the deformation element  54  according to the second embodiment has an additional deformation path that is not elastic, but is configured as a desired deformation space. In the case of medium-sized introduced impulses, this is permanently deformed while absorbing energy before the longitudinal or transverse members of the engine bearer module  4  are acted upon. In the case of an impact at such low speeds, it is thus sufficient to replace the deformed deformation element  54 . 
     In order to achieve such specific deformation, the tubular elements  60 ,  62  are provided with profilings  72 ,  74 . By analogy with the first exemplary embodiment, a compression spring  64  is clamped between the rear deformation sleeve  56  and the front deformation sleeve  58 . Unlike the first exemplary embodiment shown, the rear tubular element  60  forms a guide section  70  for the compression spring  64 . 
     While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.