Abstract:
A leaf spring assembly features a stack of leaf springs having mounting couplings attached at opposite ends. The mounting couplings each have first and second mounting elements clamped together about at least a main spring and a safety spring. The safety spring has retaining elements at opposite ends each having an extension portion and a blocking portion. The extension portion extends past the end of the main spring. Here the blocking portion extends generally perpendicularly from the extension portion to block motion of the mounting coupling should failure cause it to be detached from the stack of springs. This ensures that failure does not cause complete separation of the spring stack and mounting couplings.

Description:
This application claims benefit of U.S. provisional application 60/716,521 filed Sep. 14, 2005. 

   This invention relates to leaf spring suspension assemblies, and more particularly to a way to maintain connection between a stack of leaf springs and mounts coupled to a main spring at either end of the stack should the main leaf fail. 
   BACKGROUND OF THE INVENTION 
   Leaf spring assemblies are conventionally used for suspending one component relative to another. Vehicle suspension is one example of an application using such assemblies. However a leaf spring assembly can be used in many different situations and the present invention is applicable to any of these and is not intended to be limited to vehicle suspensions. 
   Single point suspension systems are often utilized in heavy duty truck and trailer suspension systems. These systems typically use leaf spring assemblies featuring a plurality of individual leaf springs stacked one atop the other and connected together at approximately a center point along their length. The stack of leaf springs is connected to the frame at this center point, for example by a trunnion. At each end of the stack of springs the main leaf is connected to an axle by means of a cast or fabricated mount. These axle seats are often located on the spring stack by dowels extending into corresponding holes through the main leaf. These axle seats are typically open at the end of the spring stack in order to allow for interleaf movement. 
   In the event of failure of the main leaf or the dowels, the attachment would become unstable and could result in the axle coming free from the vehicle on which the leaf spring assembly is mounted as a result of the open ends. There is a demand for a safety device that compliments the locating of the mounts, for example by the dowels, by further securing the mounts to the stack of leaf springs. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of the invention there is provided a leaf spring assembly comprising: 
   a plurality of leaf springs held in a stacked relationship, said plurality of leaf springs comprising a main spring and a safety spring, each spring having opposite first and second surfaces and opposite ends, said springs being vertically stacked first surface to second surface and the first surface of said main spring being opposite said safety spring; 
   mounting couplings coupled to the main spring at opposite ends thereof, each mounting coupling comprising: 
   a first mounting element coupled to the main spring and disposed against the first surface thereof; and 
   a second mounting element disposed to a side of the safety spring opposite said main spring in opposition to said first mounting element; 
   said first and second mounting elements being clamped together with at least the main and safety springs therebetween; and 
   retaining elements each disposed at a respective one of the opposite ends of said safety spring, each of said retaining elements comprising: 
   an extension portion extending to a respective one of the opposite ends of the main spring; and 
   a blocking portion extending from the extension portion at least one of a first vertical distance to a first side of said extension portion and a second vertical distance to a second side of said extension portion, said first and second vertical distances being respectively greater than a first vertical space between said extension portion and said first mounting element and a second vertical space between said extension portion and said second mounting element; 
   the blocking portions of the retaining elements thereby being arranged to block movement of the mounting couplings longitudinally off the plurality of leaf springs should at least one of the opposite ends of the main spring break off or at least one of said mounting couplings become uncoupled from said main spring. 
   The retaining elements at each end of the safety spring in the stack of leaf springs block the main leaf and the mounting couplings so that they cannot slide off the end of the stack in the event of failure. The safety leaf thereby reduces the safety risk associated with leaf spring failure without having to add extra components to the assembly outside of the stack. The safety spring is located somewhere in the stack between the first and second mounting elements of the mounting couplings. The blocking portion of each retaining element can extend upward and/or downward from the extension portion to block the first and/or second mounting element of the respective mounting coupling. 
   Preferably the first and second mounting elements of each mounting coupling are clamped together by bolts. 
   Preferably each first mounting element comprises a dowel plate having a dowel and the main spring has holes therein, each hole receiving a respective one of the dowels for coupling said first mounting element and said main spring. 
   Preferably each second mounting element is disposed against the second surface of the safety spring. 
   The plurality of stacked leaf springs may further comprise a third spring disposed at the side of the safety spring opposite the main spring. In this case the second mounting element of each mounting coupling is disposed against the second surface of the third spring. Alternatively, the plurality of leaf springs may further comprise a third spring between the main spring and the safety spring. 
   Preferably there are provided axles. 
   Preferably the first mounting element of each mounting coupling comprises a cradle for engaging a side face of a respective one of the axles and the bolts comprise U-bolts which engage around the axle to clamp the cradle between the axle and the second mounting element. 
   Preferably the second mounting element of each mounting coupling comprises a channel member extending parallel to a longitudinal axis of the plurality of leaf springs. 
   Preferably each channel member comprises side walls, the respective ends of at least the safety and main springs being received between said side walls, said side walls extending to the first mounting element for clamping connection thereto on opposite sides of the plurality of stacked leaf springs. 
   Preferably the second mounting element of each mounting coupling further comprises rubber pads disposed between the channel member and the safety spring. 
   Preferably the retaining elements are integral to the safety spring. 
   Preferably the blocking portion of each retaining element extends from the extension portion of said retaining element toward the first mounting element of the mounting coupling at the respective end of the main spring. Alternatively, the blocking portion of each retaining element may extend from the extension portion of said retaining element toward the second mounting element of the mounting coupling at the respective end of the main spring. As a further alternative, the blocking portion of each retaining element extends between the first and second mounting elements of the mounting coupling at the respective end of the main spring. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, which illustrate an exemplary embodiment of the present invention: 
       FIG. 1  is an isometric view of a leaf spring stack having a safety spring with retaining elements at either end. 
       FIG. 2  is an isometric view of the leaf spring stack of  FIG. 1  having mounting couplings at either end of a top spring for connection to respective axles. 
       FIG. 3  is a side view of an end portion of the leaf spring stack of  FIGS. 1 and 2 . 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a stack  10  of leaf springs  12  according to the present invention. The stack  10  is made up of progressively shorter leaf springs  12  which are held in the stacked relationship by a fastener  14  located centrally between the ends  20  of each spring  12 . Located two springs down from a top or main spring  16  is a safety spring  22  which breaks from the pattern progressively shorter springs  12  moving downward from the top spring  16 . At either end  20  of the safety spring  22  is a retaining element  24  having an extension portion  26  and a blocking portion  28 . The extension portion  26  simply extends the length of the safety spring  22  out past the end  20  of the top spring  16 . The blocking portion extends upward from the extension portion past the top spring  16  so as to block its ends  20 . These retaining elements  24  are integral parts of the safety spring  22 . 
     FIG. 2  illustrates a leaf spring assembly  5  featuring the leaf spring stack  10  of  FIG. 1 . As typically found in single point suspension systems, a mounting coupling  40  is found at each end  20  of the top spring  16 . Each coupling consists of a top mounting element  39  and a bottom mounting element  41  disposed above the top spring  16  and below the safety spring  22  respectively. The top mounting element  39  includes a dowel plate  42  having a dowel extending downward into a respective hole  43  through the top spring  16  near the opposite ends  20 . A cradle  44  having an arcuate recess therein is mounted atop the dowel plate  42  for receiving an axle  45  of the vehicle on which the leaf spring assembly  5  is installed. The bottom mounting element  41  includes a channel member  46  and rubber pads  48 . The rubber pads  48  are placed across the channel member  46  on its bottom center portion  50 . The channel member  46  is longitudinally parallel to the stack  10  and positioned to receive an end portion of the safety spring  22  such that a bottom surface  52  of the safety spring sits atop the rubber pads  48  such that the uppermost three springs (the top spring  16 , the safety spring  22 , and the spring between them) are positioned between vertical side walls  54  of the channel member  46 . These side walls  54  extend to the dowel plate  42  on the upper surface  47  of the top spring  16  on either side thereof at which point they contact the cradle  44 . Here the cradle  44  and channel member  46  are connected by bolts  56 . U-bolts  58  are used to further connect together the cradle  44  and the channel member  46 . The curved section of the U-bolts engage around the axle  45  and pass through the cradle  44  and the channel member  46  to clamp the cradle  44  and dowel plate  42  between the axle  45  and spring stack  10 . 
   In typical leaf spring assemblies of this type where the retaining elements  24  are not provided at either end  20  of the top spring  16 , failure of the top spring  16  or the dowel (on the dowel plate  42 ) used to locate the mounting coupling  40  on the top spring  16  could cause a loss of connection between the spring stack  10  and the axle  45 . With the safety spring  22  in place in the present invention, the likelihood of separation of the axle  45  and spring stack  10  is reduced. As seen in  FIG. 3 , the blocking portion  28  of the retaining element  24  at either end of the safety spring  22  extends upward past the top surface  47  of the top spring  16 . Looking at  FIG. 2 , it should be appreciated that should the top spring  16  break into two pieces between the fastener  14  and the dowel receiving hole  43 , the piece with the mounting coupling  40  will be prevented from sliding off the end of the spring stack  10  by the blocking portion  28  of the retaining element  24 . The side walls  54  of the channel member  46  will prevent the piece from falling of either side of the stack  10  due to the enclosure of the top three springs by the mounting coupling  40 . Should the dowel plate  42  fail such that the mounting coupling  40  is no longer located by the receiving hole  43 , the blocking portion  28  and the retaining element  24  and the clamped arrangement of the mounting coupling  40  will act in the same way to prevent separation of the axle  45  and the spring stack  10 . 
   The type of fastener  14  used to hold the leaf springs  12  in the stacked relationship is known to those of skill in the art. The fastener features a shaft that is passed through aligned holes in the plurality of leaf springs  12  with end portions at either end having a greater diameter than the shaft. This difference in diameter defines shoulders at the top surface  47  of the top spring  16  and the bottom surface  60  of the bottom spring between which the springs  12  are clamped. The spring located directly beneath the safety spring  22  in the stack  10  is sufficiently short to leave enough room between the end of that spring and the end of the safety spring  22  for the bottom element  41  of the mounting coupling  40 . 
   While the present invention has been described in terms of a stack of leaf springs in a single point suspension system, it should be appreciated that the safety spring  22  can be incorporated into multiple leaf suspensions of other types where it would be desirable prevent a clamped coupling from sliding of the end of a leaf spring stack in the event of a failure. The described leaf spring assembly features mounting couplings  40  having a standard U-bolt arrangement in which the U-bolts engage around the axle  45  to clamp the top  39  and bottom  41  mounting elements to the axle  45 . Alternate mounting coupling arrangements having top and bottom elements clamped together are known to those of skill in the art and can be used with the safety spring  22  according to the present invention. For example, inverted U-bolt arrangements in which the U-bolts clamp the axle between two cradles are often used in leaf spring assemblies. In addition, the mounting couplings  40  can be located on the stack  10  of springs by means other than the dowel plates  42  and corresponding holes  43 . 
   The number of springs in the stack  10  can be altered to suit the requirements of a particular application. The safety spring  22  does not have to be positioned as the third spring from the top of the stack  10  as shown in the figures, but should be positioned on the side of the top spring  16  opposite the top mounting elements  39 . Positioning the safety spring  22  near the top spring  16  helps retain a stack shape similar to a conventional stack  10  of leaf springs that narrows from the top down. It should be appreciated that positioning the safety spring  22  too low in the stack  10  would significantly interfere with this arrangement, as the safety spring  22  (including the retaining elements  24  at its ends) is the longest in the stack  10 . An example of an alternate position of the safety spring  22  would be to switch the positions of the safety spring and the spring between the main and safety springs such that the safety spring  22  is adjacent the main spring  16 . In such an arrangement, the bottom mounting element  41  could be positioned against the bottom surface of either the safety spring  22  or the spring below it. 
   In the detailed embodiment shown in the figures, the blocking portion extends  28  upward in order to block the ends of the two top springs and the top mounting element. The blocking portions  28  of the retaining elements  24  could also extend downward to block movement of the mounting couplings  40  off the ends of the stack  10 . In this case, the blocking portion  28  would extend down from the extension portion  26  past the center portion  50  of the bottom mounting element  41 . Clamped to the top mounting element  39 , the bottom element  41  would hit the blocking portion  28  of the retaining element  24  in the event of detachment from the top spring  16 , thereby preventing the mounting coupling  40  from sliding off the end  20 . In other words, the retaining element  24  should be shaped and oriented to obstruct motion of the mounting coupling  40  in a direction parallel to a longitudinal axis of the stack  10  of leaf springs  12  past the ends  20  of the top spring  16 . So the blocking portion  28  can extend upward, downward or both upward and downward from the extension portion  26  to serve its function. 
   In  FIG. 2 , the leaf spring assembly  5  according to the detailed embodiment of the present invention was shown in an under-slung arrangement where the stack  10  of springs  12  is supported below the axles  45 . It should be appreciated that the safety retaining  22  would also function to retain the mounting coupling  40  in an over-slung arrangement in which the springs  12  are supported above the axles  45 . In such an arrangement, the top  39  and bottom  41  mounting elements would switch positions above and below the top spring  16  and the safety spring would have downward extending blocking portions and would be positioned on top of the top spring  16 . With the mounting couplings  40  be rotated 180 degrees from their about a longitudinal axis of the stack  10  of leaf springs  12 , the holes  43  would be in the spring below the top spring  16 , as the dowel plate  42  would be mounted on its lower surface. In this arrangement, the top three springs of the stack would include, from the top down, the safety spring  22 , the top spring  16  and a third spring. Here the third spring from the top would be considered the main spring, as opposed to the illustrated embodiment in which the top spring  16  is the main spring. The main spring is the spring to which the mounting couplings  40  are coupled. It should be realized that the terms top and bottom refer to the orientations shown in the figures and that the spring assembly  5  can be oriented in any number of ways to suit specific applications. 
   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.