Abstract:
A bolster spring assembly is adapted for securement to a vehicle having a primary suspension system for securing an axle to the vehicle. The bolster spring assembly is located and secured between the leaf spring over the axle and the undercarriage of the vehicle as a supplement to the primary suspension system.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This Application claims the benefit of Provisional U.S. Patent Application No. 60/482,956 filed 27 Jun. 2003 by Howard E. Sellers. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention relates to a suspension system assembly for use with a leaf spring suspension system.  
           [0004]    2. Discussion of the Prior Art  
           [0005]    In vehicle suspension systems, the use of leaf springs and bolster springs is well known. For example one such use of a bolster spring is described in U.S. Pat. No. 5,676,356 to Ekonen. Ekonen discloses a suspension system in which a leaf spring is carried by the undercarriage of the vehicle. A bolster spring is connected between each end of the leaf spring and the underlying end of the axles.  
           [0006]    Another example of a vehicle suspension system that utilizes both a leaf spring and a bolster spring is described in U.S. Pat. No. 6,079,723 to Choi. Choi discloses a suspension assembly for a vehicle having a leaf spring with a mounting block affixed to the end of the leaf spring. The mounting block is attached to a bolster spring, and the bolster spring is mounted to the vehicle frame with a bracket.  
           [0007]    Both the Ekonen and Choi disclosures combine a leaf spring with a bolster spring to produce a suspension system that provides a smoother ride. However, in both of these disclosures the bolster spring is an integral part of the overall suspension system and can not be easily added to the system as an aftermarket item. It would be desirable, however, to have a method of retrofitting or mounting a bolster spring to an existing leaf spring suspension system without having to completely redesign the entire suspension system.  
           [0008]    In early developments leading up to the invention, a layered rubber bolster spring was substituted for the hanger arm at the rear of a leaf spring such that the bolster spring was compressed to accommodate the upwardly flexing of the leaf spring that occurs when the wheel goes over a bump. This, however, provided unsatisfactory results in that it did not control the jounce, or roll of the vehicle chassis in relation to the axle, as well as desired. In addition, it required substantial modification of the entire suspension system.  
         SUMMARY OF THE INVENTION  
         [0009]    A bolster spring suspension assembly is disclosed in which a bolster spring is adapted for mounting to a vehicle between the axle and the undercarriage as a supplement to a second suspension element securing the axle to the vehicle.  
           [0010]    One object of the invention is to provide an improved suspension system for providing a smoother ride. Another object of the invention is to provide a way to modify an existing leaf spring suspension to provide a smoother ride. A further object of the invention is to provide a suspension system that reduces jounce. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    These and other aspects of the invention will be apparent from the following description, with reference to the accompanying drawings, in which:  
         [0012]    [0012]FIG. 1 is a perspective view of the bolster spring suspension assembly;  
         [0013]    [0013]FIG. 2 is a side view of the bolster spring suspension assembly under a normal load or downwardly flexed condition;  
         [0014]    [0014]FIG. 3 is a sectional view of the bolster spring suspension assembly as seen from line  3 - 3  of FIG. 2;  
         [0015]    [0015]FIG. 4 is a side view of the bolster spring in isolation from the other parts of the suspension assembly;  
         [0016]    [0016]FIG. 5 is a cross sectional view of the bolster spring as seen from the line  5 - 5  of FIG. 6; and  
         [0017]    [0017]FIG. 6 is a cross sectional view of the bolster spring as seen from the line  6 - 6  of FIG. 5. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    Referring now to the drawings, a vehicle as partially shown in FIGS. 1-4 includes a wheel  10  shown in broken line form for illustrative purposes mounted to an axle  12 . The suspension system for the wheel includes a leaf spring  14  secured to a vehicle frame member  16  with a fixed mounting bracket  18  connected to one end of the leaf spring and a shackle  20  connected to the opposite end of the leaf spring and carried by a second mounting bracket  22  attached to the frame member. Axle  12  is secured to leaf spring  14  with a leaf spring support block  24  disposed between the leaf spring and the axle and a pair of U-bolts  26  on either side of the leaf spring fastened around the axle. The U-bolts  26  extend through the anchor plate  27  of a bolster spring suspension assembly  28  to secure the axle to the leaf spring  14 . The opposite end  29  of suspension assembly  28  is secured to frame member  16  with bolts  44 . End  29  of suspension assembly  28  is shown both laterally and vertically spaced from the opposite end with anchor plate  27 .  
         [0019]    Suspension assembly  28  as shown in FIG. 5 includes a bolster spring  30  and mounting brackets  32 ,  34  secured to opposite ends of the bolster spring. Bolster spring  30  includes a plurality of resilient core members  36 , separator plates  38  between adjacent core members, and end plates  40 ,  42  on either end of the bolster spring. Core members  36  and separator plates  38  are alternatingly stacked with each core laterally offset a similar distance from its adjacent core thereby forming an angularly disposed or diagonally oriented bolster spring  30 . Resilient core members  36  are a rubber like substance that encase the metal plate separator plates  38 . Separator plates  38  are preferably cupped or have indentions  46  in the core area to provide resistance to shear forces exerted parallel to the plane of the separator plates, as best seen in FIGS. 5 and 6. Bolster spring  30  is known in the art and is preferably of the type distributed under the trade name HMX BOLSTER SPRING KIT by Hendrickson International Truck Suspension Systems located in Woodridge, Ill., but other similarly constructed bolster springs could also be used. Mounting bracket  32  includes anchor plate  27  which is adapted to be clamped over leaf spring  14  with U-bolts  26 . End  29  of mounting bracket  34  is adapted to be attached to frame member  16  with bolts  44 .  
         [0020]    As best shown in FIG. 2, mounting brackets  32 ,  34  are adapted such that bolster assembly  28  may be mounted over axle  12  between frame member  16  and leaf spring  14  with separator plates  38  positioned essentially vertically and bolster spring  30  extending toward mounting bracket  18  and upwardly from axle  12 , or generally diagonally, between mounting bracket  32  and mounting bracket  34 . The angle of separator plates  38  with respect to vertical affects the resulting ride and jounce control of the vehicle. As the plates approach the vertical, the ride becomes smoother, but jounce is controlled less and the carrying capacity decreases. As the plates deviate from the vertical, jounce is controlled more and carrying capacity increases, but the ride becomes less smooth. In the preferred embodiment for a class  7  chassis, plates  38  are positioned between approximately 5° and 25° from the vertical to produce both a smooth ride and provide substantial jounce control. In this position and location, bolster spring  30  may deform in both shear and compression when axle  12  is urged generally upwardly with respect to frame member  16  as illustrated by arrow  33  shown in FIG. 3. The majority of the deformation of bolster spring  30  is in shear caused by the vertical movement of axle  12 . A significantly smaller amount of compressive deformation in bolster spring  30  may be caused due to other various forces. In addition, a small compressive deformation in bolster spring  30  may be caused by the rotation of bracket  32  about mounting bracket  18  as leaf spring  14  is flexed upwardly. In this configuration, bolster spring  30  will be engaged immediately upon any vertical shifting of axle  12  with respect to the frame  16 .  
         [0021]    Bolster spring suspension assembly  28  may be either installed as original equipment or easily retrofitted or attached to an existing leaf spring suspension system. When retrofitting suspension assembly  28  to an existing leaf spring suspension, the original mounting brackets for U-bolts  26  are removed and appropriate holes for bolts  44  are formed in frame member  16 . A backing plate  48 , best seen in FIG. 3, is preferably fastened to the side of frame member  16  opposite mounting bracket  34  with bolts  44  in order to compensate for additional stresses imparted on the frame by the bolster spring suspension assembly. Backing plate  48  is adapted to have holes (not shown) for accepting each bolt  44 , and is preferably the same shape as end  29  of bracket  34  for simple manufacture. Assembly  28  is then mounted as shown and previously described by securing U-bolts  26  to anchor plate  27  and securing bracket  34  to frame  16 .  
         [0022]    The description given herein is not considered to be a limitation on other minor and obvious variations, but is only meant to exemplify and encompass the full scope of the invention as set forth in the claims.