Patent Publication Number: US-2003227117-A1

Title: Anti-walkout spool bushing

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to a bushing which secures a spring to a vehicle for use in suspension systems for trucks, buses, trailers and the like. More particularly, the present invention is related to an improved spring bushing which is disposed between a leaf spring and the attachment point for the leaf spring. The improved spring bushing includes an anti-walkout feature which improves the securing of the spring to the vehicle.  
       BACKGROUND OF THE INVENTION  
       [0002] Truck, trailer and bus suspensions are commonly designed using at least a pair of leaf springs between either or both of the front and rear axles of the vehicle (the unsprung portion) and the body of the vehicle (the sprung portion). The leaf springs are normally one or more arcuately shaped steel or composite leafs that are stacked together to form the leaf spring. The axle of the vehicle is normally secured to the approximate center of the arcuate leafs with the ends of the leafs extending upwards. The upward end of one of the leafs is normally formed into a tubular section or eye which is adapted to receive a spring or spool bushing. The spring or spool bushing usually comprises an outer metal housing which is pressed into the eye of the spring, a cylindrical shaped elastomeric bushing positioned within the outer metal housing and an inner metal housing which extends through the center of the cylindrical shaped elastomeric bushing. In some applications, the cylindrical shaped elastomeric bushing is assembled directly into the eye of the spring thus eliminating the need for the outer metal.  
       [0003] The inner metal housing of the spring or spool bushing can be adapted to be secured directly to the vehicle using bolts or other fasteners or the inner metal housing can be designed to have a bolt extend through the inner metal to secure the end of the leaf spring to the frame or the sprung portion of the vehicle by mating with an appropriate bracket or other mounting structure.  
       [0004] As the vehicle travels, relative motion between the sprung and the unsprung portions of the vehicle is accommodated by the flexing of the leaf springs. The flexing of the leaf springs causes the ends of the leaf springs to pivot at each of the tubular sections or eyes which were used to secure the leaf spring to the sprung portion of the vehicle. The spring or spool bushings are used to facilitate this pivotal motion and to isolate the vehicle from shock. The cylindrical shaped elastomeric bushing located between the eye of the spring and the inner metal housing isolates the sprung portion of the vehicle from the unsprung portion of the vehicle. In certain high load applications which utilize the outer metal, the ends of the outer metal are curved over towards the inner metal in order to further encapsulate the cylindrical shaped elastomeric bushing. The curving of the ends and thus the further encapsulating of the cylindrical shaped elastomeric bushing improves the radial spring rate, it improves the axial spring rate, it improves the axial retention and it improves the durability of the bushing.  
       [0005] While the spring or spool bushings which include the outer metal housing are able to improve the axial retention of the assembly, the spring or spool bushings which do not include the outer metal housing, those where the cylindrical shaped elastomeric bushing is assembled directly to the eye of the spring, this improvement in axial retention is not possible. Leaf springs have a tendency to walk off of the bushing during the flexing of the suspension and the bushing. Due to the design of the suspension systems, the leaf springs always walk off the bushings in the same direction. In order to improve the durability of the spring or spool bushing and the assembly of it with the eye of the leaf spring, it would be advantageous to provide an anti-walkout device which would stop the tendency of the eye of the spring to walk out of the bushing. Because the leaf spring always walks out in a single direction, this anti-walkout device is only needed on one side of the bushing.  
       SUMMARY OF THE INVENTION  
       [0006] The present invention provides the art with a pivot bushing which provides the necessary axial retention and thus provides the anti-walkout feature. The present invention includes an integrally molded flange on one end of the cylindrical shaped elastomeric bushing. The flange extends radially outwardly to a diameter that exceeds the inside diameter of the eye of the leaf spring. Inside the flange is a rigid member or retaining ring that is mold bonded within the flange. The inside rigid member or retaining ring is also designed to be larger in diameter than the inside diameter of the eye of the leaf spring to act as an axial retention device. The flange is provided at only one end of the cylindrical shaped elastomeric bushing due to the fact that the walkout of the eye of the leaf spring occurs in only one direction. This allows for the assembly of the bushing within the eye by the insertion of the bushing beginning with the non-flanged end. The bushing is inserted into the eye in such a manner that the flanged end will resist the tendency of the eye of the leaf spring to walk out.  
       [0007] Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008] The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
     [0009]FIG. 1 is a typical rear suspension for a vehicle which incorporates unique pivot bushing in accordance with the present invention;  
     [0010]FIG. 2 is an enlarged view showing the end of the leaf spring and the pivot bushing shown in FIG. 1;  
     [0011]FIG. 3 is a cross-sectional view of the pivot bushing shown in FIG. 1;  
     [0012]FIG. 4 is a cross-sectional view of the elastomeric bushing and inner metal housing prior to being assembled into the eye of the leaf spring.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0013] The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
     [0014] Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in FIG. 1 a truck or bus rear suspension incorporating the unique bushing in accordance with the present invention and which is designated generally by the reference numeral  10 . Rear suspension  10  comprises a frame  12 , a drive axle  14  and a pair of leaf springs  16 . Frame  12  supports a body (not shown) and other components of the vehicle which are generally identified as the sprung portion or the sprung mass. Drive axle  14  includes a differential  20  which receives torque from an engine (not shown) through a rotating propeller shaft (not shown). Drive axle  14  also includes a pair of hollow tubes  22  that each extend out to a respective wheel assembly (not shown). Disposed within each of tubes  22  is a drive shaft  26  that extends from differential  20  to a wheel hub (not shown) to which is attached a wheel and tire (not shown). The engine transmits rotation and torque to differential  20  through the propeller shaft. Differential  20  transfers the rotation and torque from the propeller shaft to drive shafts  26  to rotate and thus drive the wheels and tires of the vehicle. Leaf springs  16  are disposed between frame  12  and drive axle  14  as will be discussed later herein. Additionally, a shock absorber  28  is disposed between each rail of frame  12  and drive axle  14  to dampen the motion between these components. A torque rod (not shown) can be disposed between frame  12  and drive axle  14  to assist in the control of the motion of the drive axle  14  with respect to frame  12 , if desired.  
     [0015] Referring now to FIGS. 1 and 2, leaf springs  16  are each attached to a respective tube  22  using a spring plate  40  and a pair of spring clips  42 . The front loop of each leaf spring  16  is attached to a bracket  44  attached to frame  12 . A pivot bushing  46  is disposed between leaf spring  16  and bracket  44  to accommodate motion between these two components and to isolate the vehicle from shocks. The rear loop of each leaf spring  16  is attached to a shackle  50  which is disposed between frame  12  and the rear loop of each leaf spring  16 . A pivot bushing  46  can be disposed between leaf spring  16  and shackle  50  and a pivot bushing  46  can be disposed between shackle  50  and frame  12  to accommodate motion between these components and isolate the vehicle from shocks, if desired.  
     [0016] While the present invention is being illustrated as having only one pivot bushing  46  disposed between each leaf spring  16  and frame  12 , it is within the scope of the present invention to have two, three or possibly more pivot bushings  46  disposed between leaf spring  16  and frame  12 , if desired. In addition, while the present invention is being described as possibly having three identical pivot bushings  46  disposed between spring  16  and frame  12 , it is within the scope of the present invention to use a different design for each pivot bushing, if desired. Finally, while the present invention is being illustrated as having shackle  50  disposed between the rear loop of leaf spring  16  and frame  12 , it is within the scope of the present invention to have shackle  50  disposed between the front loop or leaf spring  16  and frame  12  or between the front and rear loops of leaf spring  16  and frame  12 , if desired.  
     [0017] Referring now to FIGS.  2 - 4 , pivot bushing  46  comprises an inner metal  60 , an elastomeric bushing  62  and a retaining ring  64 . Inner metal  60  includes a generally cylindrical center section  66  and a pair of generally rectangular sections  68 , one rectangular section  68  being disposed at each end of center section  66 . Each rectangular section  68  has an aperture  70  extending through it which is used to secure pivot bushing  46  to the appropriate bracket on the vehicle. While center section  66  is illustrated as a solid generally cylindrical section, it is within the scope of the present invention to utilize a tubular inner metal, if desired. If a tubular metal is used, generally rectangular sections  68  or formed from the ends of the tubular center section. Also, when a tubular section is utilized, generally rectangular sections  68  can be eliminated and a through bolt can be used to secure the pivot bushing to the frame of the vehicle.  
     [0018] Elastomeric bushing  62  is an annular member which is located between inner metal  60  and the associated loop in the end of leaf spring  16 . The diameter of elastomeric bushing  62  in its free state is larger than the space between inner metal  60  and the inside diameter of the loop on the end of leaf spring  16  such that a specified percent compression is applied to elastomeric bushing  62  when it is assembled into leaf spring  16 . The assembly of pivot bushing  46  is preferably a accomplished by first bonding elastomeric bushing to inner metal  60  and then inserting this combination into the inside diameter of the eye of leaf spring  16 . As shown in FIG. 4, elastomeric bushing  62  includes one or more cutout sections  76  which are used to tune elastomeric bushing  62 .  
     [0019] Retaining ring  64  is an annular shaped ring which is mold bonded within elastomeric bushing  62  inside a flange  78  molded as an integral part of elastomeric bushing  62 . The outside diameter of retaining ring  64  and thus the outside diameter of flange  78  is designed to be larger than the inside diameter of the eye of leaf spring  16 . By having the diameter of retaining ring  64  larger than the inside diameter of the eye of leaf spring  16 , any tendency of leaf spring  16  to walk off of pivot bushing  46  will be resisted by the contact of retaining ring  64  with the side of the eye of leaf spring  16 . By encasing retaining ring  64  within flange  78  of elastomeric bushing  62 , a direct metal to metal contact and thus a direct metal noise path between retaining ring  64  and the eye of leaf spring  16  is prevented.  
     [0020] Retaining ring  64  can be a metal or plastic washer, a metal or plastic ring or a stamping. Retaining ring  64  and flange  78  need only be incorporated on one side of elastomeric bushing  62  because leaf springs  16  always walk off of pivot bushing  46  in the same direction. Therefore, by molding retaining ring  64  into elastomeric bushing  62  and having it larger in diameter than the inside diameter of the spring eye of leaf spring  16 , leaf spring  16  cannot walk off pivot bushing  46  unless elastomeric bushing  62  tears. The tear strength of the material for elastomeric bushing  62  is designed to be much higher than the axial loads in this application. Also, because retaining ring  64  and flange  78  are located on only one side of pivot bushing  46 , the assembly of pivot bushing  46  into the eye of leaf spring  16  is not compromised.  
     [0021] The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.