Patent Publication Number: US-2009218740-A1

Title: Highly elastic leaf spring

Description:
The invention relates to a multilayered spring, in particular for rail vehicles, having an inner connecting part and an outer connecting part and having at least two spring layers which are located between the connecting parts. The spring layers include alternately an elastomer layer and a sheet-metal layer and the elastomer layers are each vulcanized together with the connecting parts and the sheet-metal layers. The elastomer layers of the spring layers have different thicknesses from one another with each elastomer layer being manufactured from the same material. 
     Such multilayered springs are also referred to as primary springs because they frequently form the primary spring stage, that is, the spring stage between the wheel and the swivel truck in rail vehicles. The multilayered springs can have different shapes. For example, the individual spring layers can be arranged concentrically with respect to one another in a cylindrical or conical fashion. However, multilayered springs made of differently arranged horizontal or vertical spring layers are also possible. The shape, position and number of the spring layers are adapted to the particular application. 
     Individual multilayered springs are usually manufactured for each application and a specific spring characteristic line has to be achieved. Given low loading, which is particularly critical for protection against derailing during the travel operation, the spring must be made very soft. In contrast, when the loading is high, the spring should be hard so that the vehicle remains within the free space profile. 
     DE 85 20 180 U1 discloses a multilayered spring which has an additional rubber layer with a Shore hardness which is lower than that of the other layers in order to achieve a specific spring characteristic. However, this multilayered spring requires a limiting stop in order to limit the spring compression of this additional layer. The spring characteristic line is therefore composed of two line segments, a soft, flat segment up to the time when the spring abuts against the limiting stop and a hard, steep segment. The characteristic line therefore has an unevenness which has an unfavorable effect on the suspension behavior. 
     In order to obtain an optimal characteristic line of the multilayered spring, it is known to manufacture the elastomer layers of the spring layers from different materials. Such a multilayered spring is shown in DE 28 19 306 A1 or DE 103 01 756 B4. 
     However, the use of different materials requires considerable complexity with respect to manufacture, especially when there are different materials within one layer. 
     The invention is based on the object of providing a multilayered spring of the type described above which has an improved, constant spring characteristic line while avoiding the above-mentioned disadvantages. 
     This object is achieved by virtue of the fact that the multilayered spring has a support plate which is contoured substantially in the shape of a cone, is arranged above the thickest spring layer in the loading direction and corresponds to the spring layers of different thicknesses in such a way that initially the inner part of the softest layer is supported on the support plate and, as the loading increases, the outer parts of the softest layer and the further spring layers are supported in a constantly increasing fashion on the support plate. 
     The support plate produces a continuous spring characteristic line since, as a result of this configuration, only the inner, soft spring layer of the multilayered spring experiences spring compression under relatively low loads and the further spring layers increasingly participate in the spring compression under higher loads. Because of the support plate, the thickest, softest spring layer is not overloaded. The characteristic line can be adapted to the application, for example, as a continuously progressive characteristic line depending on the contour of the support plate. 
     According to one embodiment of the invention, the elastomer layer of the inner spring layer is thicker than the elastomer layers of the other spring layers by a factor of three. 
     As a result, the inner spring layer is considerably softer than the other spring layers. The hardness of such a spring layer is determined both by the hardness of the material and by the geometry of the layer, with the influence of the geometry being determined by the form factor F. The form factor F describes the ratio of free elastomer area to bound elastomer area of an elastomer layer. If the free surface of an elastomer layer becomes larger while the fixedly vulcanized, that is, bound area remains the same, the form factor increases. High values of F describe a soft spring property, while low values of F describe a hard spring property. 
     Such a multilayered spring can be adapted in the inventive fashion to various applications with a constant characteristic line and does not require complex production methods since, for example, the omission of one or more sheet-metal layers allows the freely deformable elastomer area of the resulting, relatively thick elastomer layer to be easily enlarged. There is no need to use different materials. 
    
    
     
       An exemplary embodiment of the invention will be explained in more detail below with reference to the drawing. 
       The single FIGURE shows a multilayered spring  1  in a longitudinal section in the installed position without loading with an inner connecting part  2  directed upwardly with a connecting lug  3  and bearing a load (not shown here). 
     
    
    
     Furthermore, the multilayered spring  1  has an outer connecting part  4  and a plurality of conical, concentrically-arranged sheet-metal intermediate layers ( 5 ,  6 ,  7 ,  8 ) with average diameters which become larger toward the outside. Conical elastomer layers ( 9 ,  10 ,  11 ,  12 ) are arranged between each two sheet-metal intermediate layers  5  to  8 . The conical elastomer layers ( 9 ,  10 ,  11 ,  12 ) are fixedly vulcanized with their respective surfaces to corresponding surfaces of the inner connecting part  2 , the sheet-metal intermediate layers  5  to  8  and the outer connecting part  4 . These surfaces of the elastomer layers face toward the main axis  13  of the multilayered spring  1  or face away from the main axis  13 . 
     The sheet-metal intermediate layers  5  to  8  and the elastomer layers  9  to  12  are arranged with respect to one another in such a way that the multilayered spring  1  has an upwardly tapering truncated cone-like shape. 
     A support plate  14 , which has a conical shape on its underside  15  facing toward the inner-lying elastomer layer  9 , is fixedly mounted on the connecting lug  3  concentrically with respect to the inner connecting part  2 . 
     The inner-lying elastomer layer  9  has a significantly larger radial thickness than the other elastomer layers  10  to  12 . The increased thickness gives rise to a form factor F which is increased compared to the other elastomer layers  10  to  12 . The inner elastomer layer  9  is therefore significantly softer than the other elastomer layers  10  to  12 . 
     Under load, the inner connecting part  2  moves downwardly toward the outer connecting part  4  and the multilayered spring  1  is compressed. In the process, at first only the inner-lying elastomer layer  9  experiences spring compression owing to the softer spring characteristic line. The elastomer layer  9  is supported against the support plate  14 . The configuration of the underside  15  of the support plate  14  thereby contributes to the determination of the spring characteristic line of the inner-lying elastomer layer  9 . The thickness of the inner-lying elastomer layer  9  and the shape of the underside  15  of the support plate  14  are matched to one another in such a manner that, when the inner-lying elastomer layer  9  experiences complete spring compression, the support plate  14  comes to rest on the inner sheet-metal intermediate layer  5  and the other elastomer layers  10  to  12  are increasingly involved in the further spring compression. This results in a continuously progressive spring characteristic line for the entire multilayered spring  1 . 
     List Of Reference Numerals 
     (part of the description)
 
 1  Multilayered spring
 
 2  Inner connecting part
 
       3  Connecting lug 
       4  Outer connecting part
   5  Sheet-metal intermediate layer
   6  Sheet-metal intermediate layer
   7  Sheet-metal intermediate layer
   8  Sheet-metal intermediate layer
   9  Inner-lying elastomer layer
   10  Elastomer layer
   11  Elastomer layer
   12  Elastomer layer
   13  Main axis of the multilayered spring  1     14  Support plate
   15  Underside of the support plate