Abstract:
A high axial spring rate spring pivot bushing has an inner metal to which is press fit a ferrule at one end. An outer metal is disposed around the inner metal and an elastomeric bushing is located between the inner metal, the ferrule and the outer metal. The spring pivot bushing is manufactured by pressing the ferrule on the inner metal, placing the inner metal, ferrule and outer metal in a mold and then injecting an elastomeric material to create the elastomeric bushing.

Description:
FIELD 
       [0001]    The present disclosure relates to a bushing for a suspension system for a bus, a truck, an automobile or the like. More particularly, the present disclosure relates to a bushing for a suspension system which is designed with a high axial spring rate and a method of manufacturing the bushing. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0003]    Truck, bus and automotive suspensions are commonly designed using either a pair of leaf springs or at least a pair of control arms located between both the front and rear axles of the vehicle (the unsprung portion) and the body of the vehicle (the sprung portion). 
         [0004]    The leaf springs are normally a plurality of arcuately shaped steel or composite leafs that are stacked together to form the leaf spring. The axle assembly of the vehicle is normally secured to the approximate center of the arcuate leafs with the ends of the leafs extending upwards. The upward ends of one of the leafs are normally formed into a tubular section or eye which is adapted for receiving a spring pivot bushing. The spring pivot bushing usually consists of an outer metal housing which is pressed into the eye of the leaf spring, a layer of elastomeric material positioned within the outer metal and an inner metal housing which extends through the center of the elastomeric material. A bolt or other fastener extends through the inner metal and secures the end of the leaf spring to the frame or to another component of the sprung portion of the vehicle by mating with an appropriate bracket. As the vehicle travels, relative movement between the sprung portion and the unsprung portion of the vehicle is accommodated by flexing of the leaf springs. The flexing of the leaf springs causes the ends of the leaf spring to pivot on both of the tubular sections or eyes which secure the leaf spring to the sprung portion of the vehicle. 
         [0005]    The spring pivot bushing are utilized to facilitate this pivotal motion and also to isolate the sprung portion of the vehicle from the unsprung portion of the vehicle. In certain high load applications, it becomes advantageous to encapsulate the elastomeric material between the inner and outer metals. The encapsulating of the elastomeric member improves the axial retention, it improves the radial spring rate and it improves the durability of the spring pivot bushing. 
         [0006]    Leaf springs have a tendency to walk off of the spring pivot bushing during the flexing of the suspension and the spring pivot bushing. Due to the design of the suspension systems, the leaf springs always attempt to walk off of the spring pivot bushings in the same direction. 
       SUMMARY 
       [0007]    The present disclosure details a spring pivot bushing and a method of manufacturing the spring pivot bushing. The spring pivot bushing comprises an inner metal, an outer metal and an elastomeric member disposed between the inner and the outer metals. The inner metal includes a ferrule which encapsulates the elastomeric member. The inner and outer metals are inserted into a mold cavity and the elastomeric member is injected into the space between the inner and the outer metals through injection apertures formed through the ferrule. 
         [0008]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0009]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0010]      FIG. 1  is a typical rear suspension for a vehicle which incorporates the spring pivot bushing in accordance with the present disclosure; 
           [0011]      FIG. 2  is an enlarged end view of the spring pivot bushing illustrated in  FIG. 1 ; 
           [0012]      FIG. 3  is a cross-sectional view of the spring pivot bushing illustrated in  FIG. 2 ; 
           [0013]      FIG. 4  is a cross-sectional schematic view of the molding method for the spring pivot bushing illustrated in  FIG. 2 ; and 
           [0014]      FIG. 5  is an enlarged end view similar to  FIG. 3  but illustrating a spring pivot bushing in accordance with another embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0016]    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, bus, trailer or automotive suspension incorporating a spring pivot bushing in accordance with the present disclosure and which is designated generally by the reference numeral  10 . Suspension  10  comprises a frame  12 , a drive axle assembly  14  and a pair of leaf springs  16 . Frame  12  is part of and supports a body (not shown) and other components of the vehicle which are generally identified as the sprung portion or sprung mass of vehicle  10 . Drive axle assembly  14  comprises a differential  20  which receives a driving force from an engine (not shown) through a rotating propeller or drive shaft (not shown). Drive axle assembly  14  further comprises 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 axle  26  that extends from differential  20  to a respective wheel assembly. The engine transmits a drive force to differential  20  through the propeller or drive shaft. Differential  20  transfers the drive force from the propeller or drive shaft to drive axles  26  to rotate and thus drive the wheel assemblies of vehicle  10 . Leaf springs  16  are disposed between frame  12  and drive axle assembly  14  as will be discussed later herein. Additionally, a shock absorber  28  is disposed between each rail of frame  12  and drive axle assembly  14  to dampen the relative motion between these components. A torque rod (not shown) can be disposed between frame  12  and drive axle assembly  14  to assist in the control of the motion of drive axle assembly  14  with respect to frame  12 . 
         [0017]    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 or eye of each leaf spring  16  is attached to a bracket  44  which is secured to frame  12 . A spring pivot bushing  46  is disposed between the eye of leaf spring  16  and bracket  44  to accommodate motion between these two components and to isolate frame  12  from drive axle assembly  14 . The rear loop or eye of each leaf spring  16  is attached to a shackle  50  which is disposed between frame  12  and the rear loop or eye of leaf spring  16 . A spring pivot bushing  46  is disposed between leaf spring  16  and shackle  50  and a pivot bushing can be disposed between shackle  50  and frame  12  to accommodate motion between these components and to isolate frame  12  from drive axle assembly  14 . 
         [0018]    While the present disclosure is illustrated as having spring pivot bushing  46  located at three connecting points between frame  12 , leaf spring  16  and drive axle assembly  14 , it is within the scope of the present disclosure to have fewer than three spring pivot bushings  46  for each attachment and to replace one or more spring pivot bushings  46  with a different bushing. Finally, while the present disclosure is being illustrated as having shackle  50  disposed between the rear loop or eye of leaf spring  16  and frame  12 , it is within the scope of the present disclosure to have shackle  50  between the front loop or eye of leaf spring  16  and frame  12 , or to have bracket  44  disposed between the rear loop or eye of leaf spring  16  and frame  12 . 
         [0019]    Referring now to  FIGS. 2 and 3 , spring pivot bushing  46  comprises an inner metal assembly  60 , an elastomeric bushing  62  and an outer metal  64 . Inner metal assembly  60  comprises an inner metal  66  and a ferrule  68  press fit or otherwise secured to inner metal  66 . 
         [0020]    Inner metal  66  is a tubular member which is non-circular in order to provide a different radial rate in different radial directions.  FIG. 5  illustrates a spring pivot bushing  46 ′ which includes an inner metal  66 ′ which has a circular shape and thus will have the same radial rate in all radial directions. Ferrule  68  is an annular member which defines a central bore  70  which is contoured to mate with inner metal  66  and a plurality of injection apertures  72  through which elastomeric bushing  62  is injected as described below. Ferrule  68  is press-fit or otherwise secured to inner metal  66  and ferrule  68  defines an annular flange  74  which increases the area of contact between ferrule  68  and inner metal  66 . 
         [0021]    Outer metal  64  is a cylindrical member that includes an annular flange  76  which is positioned as illustrated in  FIG. 3  to oppose ferrule  68 . Elastomeric bushing  62  is disposed between inner metal assembly  60  and outer metal  64 . Elastomeric bushing  62  defines one or more voids  78  which are sized, shaped and located to tune the rate of spring pivot bushing  46  to a specified rate. 
         [0022]      FIG. 4  illustrates the manufacturing process for spring pivot bushing  46 . First, ferrule  68  is press-fit or otherwise secured to inner metal  66  to create inner metal assembly  60 . Inner metal assembly  60  and outer metal  64  are coated with a bonding agent  80  which is designed to react with and bond elastomeric bushing  62  to inner metal assembly  60  and outer metal  64 . Inner metal assembly  60  is inserted in a first mold  82  of a mold assembly  84  and outer metal  64  is inserted into a second mold  86  of mold assembly  84 . Mold assembly  84  is then closed to form a mold cavity  88 . Second mold  86  defines one or more mold extensions or inserts  90  which create the one or more voids  78 . 
         [0023]    Once mold assembly  84  is closed, as is illustrated in  FIG. 4 , an elastomeric material is injected into mold cavity  88  through a series of gates  92  formed in an injection head  94 . Gates  92  are in communication with a plurality of gates  96  in first mold  82  and each of the plurality of gates  96  are in communication with a respective injection aperture  72  formed in ferrule  68 . The injected elastomeric material creates elastomeric bushing  62  including voids  78 . Elastomeric bushing  62  is bonded to inner metal assembly  60  and outer member  64  over its entire contact area with these components due to bonding agent  80  that was applied to inner metal assembly  60  and outer metal  64 . 
         [0024]    Referring now to  FIG. 5 , spring pivot bushing  46 ′ is illustrated. As detailed above, spring pivot bushing  46 ′ is the same as spring pivot bushing  46  except that inner metal  66  has been replaced by inner metal  66 ′. Inner metal  66 ′ is circular in shape to provide the same radial rate in all radial directions.