Abstract:
A leaf spring arrangement for a motor vehicle axle includes a leaf spring which is made of a fiber composite and has ends, each end having a flat underside to provide a joining surface. Bonded flatly by an adhesive against the underside of each end of the leaf spring in an area of the joining surface is a mount for attachment onto a further axle component. The mount has an opening for receiving a metallic bearing or screw bolt.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of German Patent Application, Serial No. 10 2014 101 429.4, filed Feb. 5, 2014, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference in its entirety as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a leaf spring arrangement for a motor vehicle axle. 
     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. 
     It is known in the art to equip motor vehicles with axle systems so that the wheels of the motor vehicle are resiliently supported. At standstill, static wheel loads act on the motor vehicle and are superimposed during operation of the motor vehicle with dynamic wheel loads. 
     Different axle concepts are known, for example a suspended rigid axle or independent wheel suspensions, in order to realize the desired suspension of the motor vehicle. In principle, the wheel is acted upon by a suspension and an attenuation to absorb the static and dynamic wheel loads. Mechanical springs are especially used hereby and may be designed, for example, as round wire springs or also as leaf springs. In order for the leaf springs to be coupled with the motor vehicle axle components, e.g. with the motor vehicle control arms, in particular transverse control arms, it is known to provide a leaf spring at each end thereof with a mount which can be threadably engaged, for example, to a respective transverse control arm and which is typically screwed to the end of the leaf spring by a bolt received in a throughbore in the leaf spring. 
       FIG. 1  shows a conventional leaf spring  1  configured as transverse leaf spring  2 . The transverse leaf spring  2  has a midsection  3  and two ends  4 . A mount  5  is connected to the each end  4  of the transverse leaf spring by drilling a bore through the end  4  of the transverse leaf spring  2  for passage of a screw bolt  6  so as to couple the end  4  to the mount  5 . The midsection  3  is further provided with attachments  7  to connect the transverse leaf spring  2  to a not-shown motor vehicle body or subframe. A mechanical drilling of the transverse leaf spring  2  in this way to realize the connection between the mount  5  and the end  4  of the leaf spring  2  adversely affects the durability and life of the leaf spring. 
     It would be desirable and advantageous to provide an improved leaf spring arrangement which obviates prior art shortcomings and which has a long-lasting life while yet being producible in a simple and cost-effective way and reliable in operation. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a leaf spring arrangement for a motor vehicle axle includes a leaf spring made of a fiber composite and having ends, each end having a flat underside to provide a joining surface, and mounts for attachment onto an axle component, the mounts being bonded by an adhesive flatly against the underside of the ends of the leaf spring in an area of the joining surface, each mount having an opening for receiving a metallic bearing or screw bolt. 
     The present invention resolves prior art problems by applying an adhesive to bond the mount to the end of the leaf spring. Examples of an adhesive include a single-component adhesive or two-component adhesive. Currently preferred is the use of an adhesive that can be thermally activated or an anaerobically curable adhesive. The mount has a flat joining surface which complements the flat joining surface at the end of the leaf spring and is bonded thereto via the adhesive to connect the joining surfaces of leaf spring and mount to one another. The bond at the ends of the leaf spring is effective and allows movements by the suspension and thus any changes in shape of the leaf spring in the inner zone or midsection, while the ends of the leaf spring are able to move in kinematic movement direction but not to move within themselves. Thus, the presence of microcracks, in particular in the bonding zone, is effectively prevented in accordance with the present invention. 
     According to another advantageous feature of the present invention, the mount may be made of a metallic material. Examples include a steel alloy or light metal alloy. 
     According to another advantageous feature of the present invention, the leaf spring may be configured as a transverse leaf spring. Currently preferred is the provision of a transverse leaf spring which is made of several layers of a fiber composite. An example of a fiber composite includes a fiberglass composite. 
     According to another advantageous feature of the present invention, the opening of the mount may extend in substantial orthogonal relation to the joining surface and can be used for receiving a bearing or a bolt to enable connection of the mount with a further axle component, e.g. directly with a transverse control arm or connection to a respective control arm of the wheel suspension via a tie rod or pressure bar. 
     According to another advantageous feature of the present invention, the flat underside of the ends of the leaf spring may be provided in installation direction. The mount with its joining surface rests flatly against the underside and is bonded thereto by a suitable adhesive. 
     According to another advantageous feature of the present invention, the mount may be configured to embrace, at least in part, an end face of the leaf spring. Advantageously, an adhesive is applied between the end face of the leaf spring and the mount. 
     According to another advantageous feature of the present invention, a tie rod or pressure bar may be provided and coupled to the mount to exert a force from the mount in a direction of the end of the leaf spring. The bonding zone in particular is thus acted upon by a compressive force or pressing force such that the presence of a shearing is prevented and any movement to undo the bond between the end of the leaf spring and the mount is avoided. 
     According to another advantageous feature of the present invention, the mount may include a joining surface and a support shoulder configured to extend beyond the joining surface of the mount with respect to a vertical motor vehicle direction, with the support shoulder resting against the end face of the leaf spring. 
     According to another advantageous feature of the present invention, the support shoulder may have a contact surface which is bonded with the end face of the leaf spring. 
     The provision of a bonded joint allows a cost-effective and simple production of the leaf spring. Furthermore, in particular the predominantly transmitting force in pressure direction results in a long durability of the leaf spring arrangement according to the present invention with bonded mount. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       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: 
         FIG. 1  shows a conventional transverse leaf spring arrangement; 
         FIG. 2 a    shows an exploded perspective view of a leaf spring arrangement according to the present invention; 
         FIG. 2 b    shows a perspective view of the leaf spring arrangement of  FIG. 2 a    in assembled state; 
         FIG. 3 a    shows a schematic illustration of a leaf spring arrangement according to the present invention with attachment of a tie rod; and 
         FIG. 3 b    shows a schematic illustration of a leaf spring arrangement according to the present invention with attachment of a pressure bar. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Throughout all the figures, same or corresponding elements may generally be 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 figures 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. 
     Turning now to the drawing, and in particular to  FIG. 2 a   , there is shown an exploded perspective view of a leaf spring arrangement  100  according to the present invention. The leaf spring arrangement  100  includes a leaf spring  20  having opposite ends  4 . Each end  4  has an underside  8  with a flat joining surface  9  which complements a joining surface  10  of a mount  50 . Using an adhesive, the joining surface  10  of the mount  50  is bonded to the joining surface  9 , as shown in  FIG. 2 b   . The mount  50  is provided with an opening  11  which is arranged below the joining surface  9 , as viewed in motor vehicle Z direction, indicated by an arrow. The opening  11  is defined by a longitudinal axis  18  which extends in orthogonal relation to a longitudinal direction  17  of the transverse leaf spring  2  and to the motor vehicle Z direction. With respect to the motor vehicle Z direction, the underside  8  points downwards. The opening  11  of each of the mounts  50  on the opposite ends  4  of the leaf spring  4  can be used for receiving a bearing, in particular a metallic bearing, or a screw bolt, for example. 
     As shown in  FIG. 2 b   , the mount  50  is provided with a support shoulder  16  which embraces, at least in part, an end face  12  of the transverse leaf spring  20  so that the support shoulder  16  form fittingly rests against the end face  12 . Advantageously, the support shoulder  16  is bonded by an adhesive to the end face  12  of the transverse leaf spring  20 . The support shoulder  16  provides a self-centering function with respect to the longitudinal direction  17  of the transverse leaf spring  20 , when the mount  50  is connected to the transverse leaf spring  20 . During later operation, the transverse leaf spring  20  undergoes a deflection in motor vehicle Z direction which coincides with a change in length in the longitudinal direction  17  of the transverse leaf spring  20 . The applied forces during changes in length in compressive direction are then additionally compensated by the support shoulder  16 , and the applied forces during changes in length in tensile direction are compensated by the bond between the end face  12  of the transverse leaf spring  20  and the support shoulder  16 . 
     Advantageously, the support shoulder  16  rests form fittingly against only part of the end face  12 . In particular, the support shoulder  16  covers 10% to 80%, preferably 20% to 60% of the overall area of the end face  12 . Currently preferred is a coverage of 25% to 50%. Advantageously, the end  4  of the transverse leaf spring  20  is not fully encased by the mount  50 , and the mount  50  does not embrace the end  4  of the transverse leaf spring  20  in its entirety so that the mount  50  rests only against the underside  8  and in part against the end face  12 . The adjacent surfaces are advantageously bonded to one another. Also, the mount  50  is sized such that no sides of the transverse leaf spring  20  are embraced. 
     Adhesive is advantageously applied also between the mount  50  and the end face  12 . This results in a self-centering of the mount  50  upon the transverse leaf spring  20  and additional stability in motor vehicle Y direction. 
       FIGS. 3 a  and 3 b    show installation scenarios of the leaf spring arrangement  100  according to the invention. In  FIG. 3 a   , the end  4  of the transverse leaf spring  20  is coupled with the mount  50  and in kinematic connection with an upper control arm  14 , e.g. a transverse control arm, via a tie rod  13 . A force F, exerted by the control arm  14 , is primarily transmitted upwards through the tie rod, as viewed in the drawing, and causes a compression in the bonded joining surface  10  between the end  4  of the transverse leaf spring  20  and the mount  50 . Stress for both static and dynamic wheel loads mainly occurs in direction of action of the force F so that the tie rod  13  predominantly transmits a depicted tensile load, causing a compression in the joining surface  10 . 
       FIG. 3 b    shows an arrangement with a lower control arm  14 , e.g. transverse control arm, which is coupled by a pressure bar  15 . Thus, a force F is applied via the control arm  14  predominantly in pressing direction of the pressure bar  15 , causing again a compression in the joining surface  10 . Also in this case, the primary force introduction by both static and dynamic wheel loads is established in pressing direction of the pressure bar so that the bond provides sufficient strength and durability between the transverse leaf spring  20  and the mount  50  and is easy to implement. 
     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 and scope of the present invention. The embodiments were chosen and described in order to 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.