Patent Document

[0001]     This application claims benefit of United States provisional application 60/737,761 filed Nov. 18, 2005. 
     
    
       [0002]     This invention relates to leaf springs and more particularly to a leaf spring having at least one slipper end with improved wear resistance.  
       BACKGROUND OF THE INVENTION  
       [0003]     Leaf springs are typically used to resiliently support one component on another. For example, leaf spring assemblies are often used to connect one or more axles to a frame in vehicle suspension systems. Different types of leaf springs are known to have different mounting elements by which they are supported. This application is concerned with the type of leaf spring having at least one slipper end for mounting on one of the two components it resiliently connects.  
         [0004]     Referring to the example of vehicle suspension, a plurality of leaf springs in a stacked arrangement may be connected to a vehicle frame by hangers provided at opposite ends of the springs. A slipper end of the springs is an end that extends in a straight or curved manner into a respective hangar between a pair of horizontal elements. Typically, this pair of hanger elements consists of a transverse pin and a wear pad disposed below and above the springs respectively. Between the frame supported hangars at opposite ends, the springs are connected to an axle of the vehicle, thereby resiliently connecting the frame and axle. Leaf spring slipper suspensions can be used on large commercial trailers for on and/or off highway use, such as logging trailers, where loads can be in the range of 50,000 lbs. Under loading of such magnitude, tremendous wear can occur at the interface between the springs and the hanger.  
         [0005]     As a result, there is a desire to increase the durability and reliability of leaf springs having slipper ends in order to increase the level of safety involved in the use of such springs.  
       SUMMARY OF THE INVENTION  
       [0006]     According to a first aspect of the invention there is provided a slipper end leaf spring assembly comprising:  
         [0007]     a main leaf spring comprising a central portion disposed between first and second end portions, said central portion having a predetermined thickness profile for achieving desired spring characteristics; and  
         [0008]     first and second mounting members disposed at the first and second end portions of the main leaf spring respectively;  
         [0009]     the first mounting member comprising an upper transverse element extending across the main leaf spring above the first end portion thereof such that said first mounting member can be at least partially supported by contact between said first end portion and said upper element;  
         [0010]     the first end portion being greater in thickness than an end of the central portion nearest said first end portion to improve resistance to wear of said first end portion due to contact thereof with the upper element of the first mounting member.  
         [0011]     Providing end portions of greater thickness allows the desired spring characteristics to be maintained by leaving the thickness profile of the central portion unchanged and only providing extra material at the end portions that experience wear under loading of the mounting members.  
         [0012]     Preferably the first end portion of the main leaf spring is generally uniform in thickness.  
         [0013]     Preferably the main leaf spring gradually increases in thickness toward the first end portion from the end of the central portion nearest said first end portion.  
         [0014]     Preferably the main leaf spring has been roll forged to gradually increase in thickness toward the first end portion from the end of the central portion nearest said first end portion.  
         [0015]     Preferably an upper surface of the main leaf spring slopes upward with respect to a bottom surface thereof toward the first end portion from the end of the central portion nearest said first end portion. Providing the increased thickness of the end potions through shaping of the upper surface allows the bottom surface to retain the shape of a conventional leaf spring so that it can fit properly atop other leaf springs for use in a stacked arrangement.  
         [0016]     Preferably the upper transverse element of the first mounting member comprises a wear plate.  
         [0017]     The first end portion of the main leaf spring may extend generally linearly. Alternatively, the first end portion of the main leaf spring may curve about an axis transverse thereto.  
         [0018]     The first mounting member may further comprise a lower transverse element extending across the main leaf spring below the first end portion thereof and the first end portion may comprise an extension portion extending downward on a side of said lower element opposite the second mounting member such that contact between said extension portion and said lower element prevents sliding of said main leaf spring toward the second mounting member, thereby preventing separation of said first end portion and said first mounting member.  
         [0019]     According to a second aspect of the invention there is provided a slipper end leaf spring assembly comprising:  
         [0020]     a main leaf spring comprising a central portion disposed between first and second end portions, said central portion having a predetermined thickness profile for achieving desired spring characteristics; and  
         [0021]     first and second mounting members disposed at the first and second end portions of the main leaf spring respectively, each mounting member comprising an upper transverse element extending across the main leaf spring above the respective end portion thereof such that the mounting members can be at least partially supported by contact between the end portions of the main leaf spring and the upper elements of the mounting members;  
         [0022]     the end portions being greater in thickness than ends of the central portion to improve resistance to wear of said end portions due to contact thereof with the upper elements of the mounting members.  
         [0023]     According to a third aspect of the invention there is provided a slipper end leaf spring comprising:  
         [0024]     first and second end portions; and  
         [0025]     a central portion disposed between the first and second end portions and having a predetermined thickness profile for achieving desired spring characteristics;  
         [0026]     at least one of the end portions being greater in thickness than a respective end of the central portion nearest said end portion to improve resistance to wear of said end portion. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     In the accompanying drawings, which illustrate an exemplary embodiment of the present invention:  
         [0028]      FIG. 1  is a side view of a leaf spring assembly mounted on a vehicle frame for use in a four spring suspension system.  
         [0029]      FIG. 2  is a close up side view of a mounting point of the assembly of  FIG. 1 .  
         [0030]      FIG. 3  is a partial side view of a main leaf spring from the leaf spring assemblies of  FIG. 1 .  
         [0031]      FIG. 4  is a partial side view of a conventional leaf spring.  
         [0032]      FIG. 5  is a side view of a leaf spring stack from the assembly of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION  
       [0033]      FIG. 1  shows leaf spring assembly  10  mounted on a frame  12  of a vehicle as part of a four spring suspension system used to distribute the vehicle&#39;s weight between two separate axles  14 . The resilience of the suspension system is provided between the frame  12  and axles  14  by stacks  16  of leaf springs. The leaf spring stacks  16  are each disposed between an end hanger  20  and a center hanger  22 , each of which are attached to the frame  12  to extend downward therefrom. An equalizer  24  pivotally supported on the center hanger  22  serves to transfer loading between the leaf spring stacks  16  in order to maintain a desired weight distribution between the axles  14 .  
         [0034]     Each end of the equalizer  24  and each end hangar  20  is provided with a wear pad  26  extending thereacross. A main spring  28  of each stack  16  bears against its respective wear pads  26  at end portions  30  in order to support the vehicle frame  12  by means of the hangers. Engagement of an upper surface  32  of the main spring  28  with a lower surface  34  of the wear pad  26  defines a slipper type end of the stack  16 , as opposed to other end types such as an eye end at which a leaf spring stack is supported by a pin passed through a cylindrical opening defined in the main spring. While each leaf spring stack  16  in the detailed embodiment is shown as having two slipper ends, it should be appreciated that the present invention may be applied to any application in which a stack or individual spring has at least one slipper type end.  
         [0035]     Loading of the vehicle frame  12  causes large amounts of force to be exerted between the main spring  28  and wear pad  26 . Coupled with relative movement of the spring stack  16  with respect to the frame  12 , these forces cause a high degree of wear at the end portions  30  of the main spring  28  as a result of contact between the engaging surfaces  32  and  34 . In order to increase resistance to this wearing, the main spring  28  of the present invention features a thickness at its end portions  30  greater than that of the main spring of a conventional leaf spring assembly.  FIGS. 3 and 4  respectively show thickness profiles in the vicinity of end portions  30  of a main spring  28  according to the present invention and conventional teachings. In each case, a central portion  36  of the spring  28  is profiled to achieve desired spring characteristics. In the prior art of  FIG. 4 , the central portion  36  thins moving distally outward toward an end portion  30  of constant thickness. The main spring of the present invention also has an end portion  30  of constant thickness, except that it is thicker than that of the prior art. The central portion  36  still grows thinner moving distally outward, but the spring  28  increases in thickness between the central portion  36  and end portion  30 . The central portion  36  retains the profile necessary for the desired spring characteristics, but the increase thickness of the end portion  30  provides better resistance to wear of the upper surface  32 .  
         [0036]     Comparing the springs of  FIGS. 3 and 4 , it should be appreciated that the shape of the bottom surface  40  of the main spring in the present invention is generally unchanged from the prior art. The increased thickness at the end portion  30  is the result of changing the shape of the upper surface  32 . Adding material to the top of the spring  28  prolongs the life of the spring by providing extra wear resistance without affecting the way the main spring  28  sits atop the other springs in the stack  16 . Changing the spring&#39;s profile by adding material to the bottom would alter the shape of the bottom surface  40  and affect the flush engagement of the stacked springs at the end portions  30 . The increased thickness at the end portions  30  may be achieved by precision roll forging.  
         [0037]      FIG. 5  shows one of the stacks  16  of the leaf spring assembly wherein only the main spring  28  at the top of the stack has its end portions  30  thickened to resist wear, as it is the spring on which the wear pads  26  sit to support the frame  12 . The central portion  36  of each spring extends between line A-A and A′-A′ and the uniform thickness end portions  30  of each spring extend outward from lines B-B and B′-B′ to the ends of the stack  16 . From this illustration, it should be appreciated that in the main spring  28  of the present invention the end portion  30  has a thickness greater than the nearest end of the central portion  36 . This differs from the conventional springs beneath the main spring  28  which are thinner at the end portion than at the nearest end of the central portion. From A-A to B-B and A′-A′ to B′-B′, the upper surface  32  of the main spring  28  slopes upwardly away from the bottom surface  40  to increase the thickness of the spring gradually between the central portion  36  and end portions  30 .  
         [0038]     The leaf spring assembly  10  features conventional coupling mounts  41  each of which features an axle seat  42  disposed below the spring stack  16  for receiving a respective one of the axles  14 , The axle  14  is held in the seat  42  by U-bolts  44  that are engaged thereabout and fastened to a top plate  46  disposed on the top surface  32  of the stack  16 . The U-bolts clamp the axle  14  and seat  42  to the stack  16  of springs which are held together by a fastener  48  passing centrally therethrough. The fastener  48  also holds spacer blocks  50  in the stack  16  in order to provide a desired spacing between the axle  14  and the springs. In this arrangement, the axle seat  42  and spring stack  16  are said to be overlsung as they are positioned above the axle  14  and the U-bolts are arranged in a standard configuration about the axle  14 . Underslung and inverted U-bolt arrangements are known to those of skill in the art and can be applied to the present invention. A torque arm  52  extends between each axle seat  42  and a respective hangar in order to retain axle alignment and control axle torque.  
         [0039]     At the ends at which the hangers and axle seats  42  are not connected by torque arms  52 , an extension portion  54  extends downward from the bottom spring  56  of the stack. Each end hanger  20  and each end of the equalizer  24  includes a pin  58  extending thereacross beneath the spring stack  16  such that the respective end portion  30  is received between the wear pad  26 , the pin  58  and spaced apart side walls of the hangar or equalizer. The extension portion  54  forms a hook end that will engage the pin  58  to prevent inadvertent withdrawal of the spring stack  16  from the hangar or equalizer. It should be appreciated that extension elements may also be provided at the ends having torque arms  52 .  
         [0040]     Although the detailed embodiment has been described in the context of a leaf spring assembly  10  for a four spring suspension system, it should be appreciated that a spring  28  having a profile that increases the height of the spring&#39;s cross section to provide a thicker slipper portion  30  can be used in a number of applications. Depending on the application, slipper springs may feature flat or curved slipper ends which may or may not have an extension portion to form a hook end. Leaf springs arranged to be supported by an eye at one end and having a sliding slipper arrangement at the other end are often used in suspension systems. Since the thickened slipper end portions  30  of the present invention provides increased wear resistance without modifying the central portion  36  of a conventional leaf spring, they may be applied to springs having tapered or constant cross section central portions. It should be appreciated that a single leaf spring may be used in some applications, in which case if a hook end is desired, then the extension portion  54  would be integral to the single spring. In cases where a stack of springs is used, the extension portion  54  used to create a hook end may not necessarily be part of the bottom spring. For example, in a stack of untapered springs, the overall thickness of the stack is varied along its length by providing a relatively long main spring stacked on and centrally aligned with a series of progressively shorter springs. In this case, the shorter springs may not extend past the pin  58  in order to provide a useful hook end. In the detailed embodiment, the bottom spring  56  features the extension portion  54  because the springs are generally equal in length as they are individually tapered from the center to their opposite ends in order to provide the varying thickness of the stack  16  along its length.  
         [0041]     In the figures, each end portion  30  is shown to have uniform thickness and the increase in thickness between the central portion  28  and the end portions  30  is defined by the upper surface  32  of the main spring  28  sloping upwardly away from the bottom surface  40 . While this particular shaping provides even wear resistance over the length of the end portion  30  and allows flush stacking of additional springs beneath the mains spring, it should be appreciated that the different profiles may be employed to provide an improved wear zone and that the end portion  30  may vary in thickness over its length.  
         [0042]     Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without department from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.

Technology Category: b