Crimped bushing

[0002] The present invention is related to a device which secures a spring to a vehicle for use in suspension systems for trucks, buses and the like. More particularly, the present invention is related to an improved bushing design which interfaces between a leaf spring and the attachment point on the frame for the leaf spring.

[0003] Truck and bus suspensions are commonly designed using a pair of leaf springs between both 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 a plurality of 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 end of the leafs extending upwards. The upward end 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 spring, a layer of elastomer positioned within the outer metal housing and an inner metal housing which extends through the center of the layer of elastomer. A bolt extends through the inner metal and secures the end of the leaf spring to the frame or sprung portion of the vehicle by mating with an appropriate bracket. As the vehicle travels, relative movement between the sprung and unsprung portions of the vehicle is accommodated by flexing of the leaf springs. The flexing of the leaf springs causes the ends of the leaf springs to pivot on both of the tubular sections or eyes which secure the leaf spring to the sprung portion of the vehicle.

[0004] The spring pivot bushings are used to facilitate this pivotal motion and to isolate the vehicle from shock. The layer of elastomer located between the inner and outer metal housings effectively isolates the sprung portion of the vehicle from the unsprung portion of the vehicle. In certain high load applications, the ends of the outer metal are curved over towards the inner metal in order to further encapsulate the layer of elastomer. The curving of the ends and thus the further encapsulating of the layer of elastomer 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 these elastomer isolated pivot bushings have performed satisfactorily in the field, they are not without their problems. The various problems associated with these prior art pivot bushings include variations in the diameters of the spring ends and distortion of the cross section in the area where the pivot bushing is pressed into the spring ends. These manufacturing variations in the configuration of the spring end, often allow the bushing to slip out of the spring when the spring undergoes an axial load.

[0006] In the higher load applications, it is not uncommon for the outer metal to split due to high loads. This splitting or the outer metal can be avoided by heat treating of the outer metal. However, the outer metal in the higher load applications must remain soft in order for it to be crimped over. Thus, with curled end bushings, the heat treatment of the entire bushing is not a possibility. Another option for improving the strength of the outer metal is to manufacture the outer metal from drawn over mandrel (DOM) tubing which is superior in strength. While this DOM tubing will increase the strength of the tubing, it also significantly increases the manufacturing costs associated with the pivot bushing.

[0007] Thus, the continued development of pivot bushings has been directed to the improvement of performance, strength and durability while minimizing the manufacturing costs associated with the pivot bushing.

[0008] The present invention provides the art with a pivot bushing which provides the improved performance of the double-ended crimped bushings while still allowing for the use of the lower cost drawn shell outer metal. The present invention includes an outer metal having one end crimped toward the inner metal with the other end forming a radially outwardly extending flange. A separate stamping is attached to the flanged end in order to provide the compression and restriction for the elastomer. The outer metal of the present invention can be manufactured from the lower cost drawn shell material and because of its open configuration at one end, the outer metal can be heat treated prior to assembly with the inner metal and elastomer. Also, since axial motion for the pivot bushings is normally in one direction, the pivot bushing of the present invention can be assembled to restrict motion.

[0009] Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.

[0010] In the drawings which illustrate the best mode presently contemplated for carrying out the present invention:

[0011] FIG. 1 is a typical rear suspension for a vehicle which incorporates the unique pivot bushing in accordance with the present invention;

[0012] FIG. 2 is an enlarged end view showing the end of the leaf spring and the pivot bushing shown in FIG. 1;

[0013] FIG. 3 is a cross-sectional view of the pivot bushing shown in FIG. 1;

[0014] FIG. 4 is a cross-sectional view of a prior art high load pivot bushing;

[0015] FIG. 5 is a cross-sectional view of a pivot bushing in accordance with another embodiment of the present invention; and

[0016] FIG. 6 is an end view of the pivot bushing shown in FIG. 5.

[0017] 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 springs 16. Frame 12 supports a body (not shown) and other components of the vehicle which are generally identified as 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 to a hub (not shown) to which is attached a wheel (not shown). The engine transmits rotation and torque to differential 20 though 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 of the vehicle. 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 two 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 drive axle 14 with respect to frame 12.

[0018] Referring now to FIGS. 1 and 2, 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 spring 16 is attached to a bracket 44 attached to frame 12. A pivot bushing 46 is disposed between spring 16 and bracket 44 to accommodate motion between these two components and to isolate the vehicle from shock. The rear loop of each spring 16 is attached to a shackle 50 which is disposed between frame 12 and the rear loop of each spring 16. A pivot bushing 46 can be disposed between 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 to isolate the vehicle from shock.

[0019] While the present invention is being illustrated as having only one pivot bushing 46 disposed between spring 16 and frame 12, it is within the scope of the present invention to have two or possibly three or more pivot bushings disposed between 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 bushing position if desired. Finally, while the present invention is being illustrated as having shackle 50 disposed between the rear loop of spring 16 and frame 12, it is within the scope of the present invention to have shackle 50 disposed between the front loop of spring 16 and frame 12 or between both the front and rear loops of spring 16 and frame 12 if desired.

[0020] Referring now to FIGS. 2 and 3, pivot bushing 46 comprises an inner metal 60, an elastomeric bushing 62 and an outer metal assembly 64. Inner metal 60 includes a generally cylindrical center section 66 and a pair of generally rectangular sections 68, one 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. 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 inner metal is used, generally rectangular sections 68 are eliminated and a through bolt is used to secure the pivot bushing to the frame.

[0021] Elastomeric bushing 62 is an annular member which is located between inner metal 60 and outer metal assembly 64. The free diameter of elastomeric bushing 62 is larger than the space between inner metal 60 and outer metal assembly 64 such that a specified percent compression is applied to elastomeric bushing 62 when assembled into pivot bushing 46. The assembly of pivot bushing 46 can be accomplished by first bonding elastomeric bushing 62 to inner metal 60 and then inserting this combination into outer metal assembly 64. Another method of assembling pivot bushing 46 would be to first bond elastomeric bushing within outer metal assembly 64 and then inserting inner metal 60 within elastomeric bushing 62 if desired. The present invention provides advantage to both methods of assembly.

[0022] Outer metal assembly 64 comprises a cup shaped body 76 and a cover 78. Cup shaped body 76 includes an annular wall 80 which has an inwardly curved portion 82 at one end and an outwardly extending flange 84 at the opposite end. Annular wall 80 can also include an optional stepped portion 86 in order to compensate for spring distortion. Cup shaped body 76 is assembled over elastomeric bushing 62. Because flange 84 extends outwardly, elastomeric bushing 62 can always be assembled from this flanged end. Thus, inwardly curved portion 82 and outwardly extending flange 84 can be formed prior to the assembly of cup shaped body 76 and elastomeric bushing 62. This, therefore, provides the opportunity to heat treat and thus strengthen cupshaped body 76 prior to being assembled with elastomeric bushing 62.

[0023] In order to increase the strength of pivot bushing 46 for use in high load applications, elastomeric bushing 62 must be further encapsulated or restrained. Elastomeric bushing 62 is a generally non-compressible fluid. Thus, by encapsulating elastomeric bushing 62 further, the spring rate and thus the load supporting characteristics of pivot bushing 46 are increased. The prior art method for encapsulating the elastomeric bushing is shown in FIG. 4 which illustrates a prior art bushing 100. Bushing 100 includes an inner metal 102, an annular elastomeric bushing 104 and an outer metal 106. As can be seen in FIG. 4, elastomeric bushing 104 is further encapsulated by having an inwardly curved portion 108 located at both ends of outer metal 106. While this formation of two curved portions 108 effectively encapsulates elastomeric bushing 104, the formation of these curved portions 108 can only be accomplished by forming them after assembly with elastomeric bushing 104. If curved portions 108 are formed prior to assembly with elastomeric bushing 104, the assembly of the two components is extremely difficult if not impossible. Thus, it is not possible to effectively heat treat outer metal 106 prior to assembly with elastomeric bushing 104 since it must remain soft or ductile for the formation of curved portions 108. Also it is not possible to effectively heat treat outer metal 106 after assembly due to the deterioration of elastomeric bushing 104.

[0024] Referring back to FIGS. 2 and 3, the present invention overcomes this handicap with the prior art by using cup shaped body 76 and cover 78. As stated above, the flanged end of cup shaped body 76 always allows the assembly of body 76 and elastomeric bushing 62. Once these two components are assembled, cover 78 is secured to cup shaped body 76 to complete the encapsulation of elastomeric bushing 62.

[0025] Cover 78 is an annular member having a ring portion 90, a contoured portion 92 and a plurality of radially outwardly extending crimp portions 94. Ring portion 90 is disposed adjacent flange 84 and crimp portions 94 are bent around flange 84 as shown in FIG. 3 to secure cover 78 to body 76. Contoured portion 92 provides the mating surface to elastomeric bushing 76 and thus will control the spring rate for pivot bushing 46 by controlling the encapsulation and the flow of elastomeric bushing 62. Another advantage associated with pivot bushing 46 is that pivot bushing 46 will limit axial motion of pivot bushing 46 with respect to spring 16 in one direction due to flange 84 and cover 78. Because the axial loading for a pivot bushing is significantly higher in one direction, pivot bushing 46 can be assembled to spring 16 in the appropriate direction such that flange 84 and cover 78 resist the significantly higher axial loading.

[0026] In certain applications it is desirable to utilize a flangeless design for the pivot bushing. FIGS. 5 and 6 illustrate a pivot bushing 146 in accordance with another embodiment of the present invention. Pivot bushing 146 comprises inner metal 60, elastomeric bushing 62 and an outer metal assembly 164. Thus, pivot bushing 146 is the same as pivot bushing 46 except that outer metal assembly 64 is replaced with outer metal assembly 164.

[0027] Outer metal assembly 164 comprises a cup shaped body 176 and a cover or retaining ring 178. Cup shaped body 176 includes an annular wall 180 which has an inwardly curved portion 182 at one end. Cup shaped body 176 is assembled over elastomeric bushing 62. Because the end of cup shaped body 176 opposite to inwardly curved portion 182 is generally straight and open, elastomeric bushing 62 can always be assembled from this open end. Thus, inwardly curved portion 182 can be formed prior to the assembly of cup shaped body 176 and elastomeric bushing 62. This, therefore, provides the opportunity to heat treat and thus strengthen cup shaped body 176 prior to being assembled with elastomeric bushing 62.

[0028] Once cup shaped body 176 and elastomeric bushing 62 are assembled, retaining ring 178 is inserted into the open end of cup shaped body 176 adjacent elastomeric bushing 62 and the open end of cup shaped body 176 is crimped or deformed in a plurality of places 184 to secure retaining ring 178 within body 176. Retaining ring 178 provides the mating surface to elastomeric bushing 62 and thus will control the spring rate for pivot bushing 46 by controlling the encapsulation and the flow of elastomeric bushing 62.

[0029] This design only requires cup shaped body 176 to be crimped or deformed at a plurality of places 184. The open end of cup shaped body 176 is not required to form a contour similar to that of inwardly curved portion 182. Retaining ring 178 forms the contour similar to portion 92. Thus the demand for a soft and ductile end which would require the open end of body 176 to not be heat treated is not present in this design. The open end of cup shaped body 176 only needs to be soft or ductile enough to be crimped or deformed to retain retaining ring 178.

[0030] While the above detailed description describes the preferred embodiment of the present invention, it should be understood that the present invention is susceptible to modification, variation and alteration without deviating from the scope and fair meaning of the subjoined claims.