GB1571692A - Tandem suspension assembly - Google Patents

Description

(54) TANDEM SUSPENSION ASSEMBLY (71) We, GOULD INC., a corporation organized and existing under the laws of the State of Delaware, of 10 Gould Center Rolling Meadows, Illinois 60008, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a tandem suspension assembly for heavy duty trucks. Tandem suspension units have been employed for many years on heavy duty on- or off- the-road trucks. The suspension employs equalizing beams which act as levers to distribute the load between the axles and to reduce the effect of bumps and road irregularities. Torque rods assist in the absorption of torque, which is the tendency of the axles to turn backwards or forwards on their neutral axes, due to drive or braking forces. Resilient supports, such as rubber bushings, are employed at the ends of most equalizing beams to connect those beams to the axle brackets and a center bushing is located at the midportion of each equalizing beam to connect a spring saddle or frame bracket to each beam. The bushings eliminate the necessity for lubrication fittings at those locations.

Center bushings which mount the equalizing beams for movement relative to a spring saddle or frame bracket comprise an inner sleeve and an outer sleeve. An elastomeric insert is provided between those sleeves and is intended to cushion the loading between the equalizing beam and frame bracket as the tandem wheels are subjected to road irregularities. Thus, at rimes, the elastomeric insert is subjected to torsional loads as one of the wheels encounters a bump or hole in the road to attain a different elevation as compared to the other wheels. The insert is at times subjected to shear forces when the sleeves move axially and in opposite directions, for example, when the vehicle turns a comer.

Furthermore, under some driving conditions, such as the vehicle turning a corner, the center beam bushing is subjected to conical deflection wherein the axes of the inner and outer sleeves become misaligned and tend to trace a conical path. In these motions, it is important that slippage between the metal sleeves and the insert is minimized to ensure dissipation of energy in the insert rather than at the inter-face between the insert and its sleeves. If there exists continued or excessive relative movement between the insert and the sleeves, abrasion, wear, and, eventually, failure of the part will occur.

An attempt to improve the fatigue life of the beam center bushing is set forth in U.S.

Patent No. 3,666,335, granted to Arthur Mundy. In that patent, there is disclosed a beam center bushing comprising a pair of concentric, spaced-apart, rigid sleeves, one inside the other, and an elastomeric insert radially compressed and occupying between about 70 to 90 percent of the space therebetween. Abrasion-resitant sleeves are provided at the ends of the insert between the two rigid sleeves in contact with one of those sleeves and normally spaced a distance from the other sleeve. This arrangement has some drawbacks, in that the elastomeric insert does not occupy substantially all of the available space between the rigid sleeves, thus decreasing the amount of metal-to-insert contact, which increases the radial stresses on the insert. Furthermore, since the abrasion-resistant sleeve is relatively hard as compared to the insert, radial or conical cushioning is counteracted, and this defeats one purpose of the bushing and produces an impact effect due to the sudden contact between the rigid sleeve and the semirigid abrasion-resistant bushing.

Truck tandem suspension systems are subjected to conditions which very frequently apply a conical load on the center bushing.

When this conical load is repeatedly severe it deflects the bushing so that the elastomeric insert is released from a state of compression at its axial ends, and the insert starts to abrade which causes a progressive reduction in the compression. Repeated abrasion and reduction of compression results in the disintegration of the elastomeric member.

It is an object of the present invention to overcone or nwiimiise the foregoing prior art problems.

According to the present invention there is provided a tandem suspension assembly for heavy duty trucks and the like, comprising a pair of parallel equalizing beams, a pair of parallel axles extending transversely of and connected to the ends of said beams, bracket means rotatably mounted on said beams respectively and centrally thereof by means of respective center bushings each of which comprises a first and a second longer cylindrical sleeve one received within the other, and an elongate tubular elastomeric insert arranged between said sleeves and being adhesively bonded thereto, said insert having a first portion occupying substantially all of the available space between said sleeves, and said insert having a second portion which in an unloaded condition of the assembly engages the longer of said sleeves beyond said available space, the end surfaces of said tubular insert being unconstrained such as to permit deformation thereof both axially and radially of said innermost sleeve under loading of said assembly, and said first portion of said insert being in a state of radial compression.

For a better understanding of the present invention, reference is had to the following description of a preferred embodiment thereof taken in connection with the accompanying drawings wherein: Figure 1 is a fragmentary, perspective view of a tandem suspension assembly according to the present invention; Figure 2 is across sectional view of a beam center bushing of the suspension assembly of Fig. 1, showing the bushing in a normal, unloaded state; Figure 3 is a cross sectional view similar to Figure 2, but showing the bushing in one mode of conical stress; Figure 4 is a cross sectional view similar Figure 4 is a cross sectional view similar to Figure 2, but showing the bushing in another mode of conical stress; Figure 5 is a schematic view of the tandem suspension assembly showing the front axle and its wheel riding over a bump.

Referring now to the drawings, and par ticularly to Figure 1, there is illustrated one type or style of tandem suspension assembly 10 which is particularly suitable for heavy duty trucks and the like. The assembly 10 comprises a pair of parallel equalizing beams 11 and 12 which carry bushings 13 and 14 at their ends. End brackets 15 and 16 res pectively connect the bushings 13 and 14 to a pair of spaced, parallel cross axles 17 and 18. There is provided a center bushing 19 at the midportion of each equalizing beam 11 and 12 and each bushing 19 provides a rotatable mounting for a bracket means in the form of a spring saddle 20, in a manner which will hereinafter become apparent. Each spring saddle carries a leaf spring 21 or other springing device, such as an air bag, rubber shear, or rubber pad, and each leaf spring 21 is provided with spring hangers 22 which support the truck body. Although leaf springs are illustrated, as was noted above, the invention includes the use of other spring means between the truck body and the unsprung amass. To prevent axle rotation due to driving and braking forces, torque rods 23 are provided, connected to the truck's chassis.

Referring now in greater detail to the beam center bushings 19, each bushing 19 includes an inner cylindrical sleeve 24 which may have an end plate 25 closing one end thereof. A cross tube 34 (Figure 1) is received within the inner sleeves of the bushings 19 to thereby connect the equalizing beams. The ends of the inner sleeve 24 are mounted in aligned apertures 26 and 27, which are respectively provided in depending legs 29 and 28 of each spring saddle 20. Each bushing 19 also includes an outer cylindrical sleeve 30 and a tubular, cylindrical, elastomeric insert 31 positioned between the sleeves and adhesively bonded thereto. The insert 31 completely fills the available space between the inner and outer sleeves 24, 30.

The insert 31 is subjected to stresses caused by the relative movement of the inner and outer sleeves and their associated parts.

One coiirion stress situation is illustrated in Figures 3 and 4 and includes the application of conical stresses to the rubber insert 31 as the imaginary perpendicular planes 32 and 33 of the inner and outer sleeves 24 and 30 become misaligned. Such misalignment may occur if the vehicle encounters a bump in the road, which causes the equalizing beam 11 and the beam center bushing 19 to be raised relative to the other beam center bushing. This is illustrated in Figure 5. Sub stantially more conical stress occurs when the vehicle turns a corner.

Prior art beam center bushings have failed after relatively short stress cycles. The life of the bushings in a suspension assembly according to this invention is greatly increased by adhesively bonding the insert 31 to the inner and outer sleeves 24 and 30. The insert is also radially compressed preferably by swaging the outer sleeve radially inwardly and/or by expanding the inner sleeve radially outwardly.

The bushing may be fabricated by coating the outside surface of the sleeve 24 with an adhesive and coating the insert surface of the sleeve 30 with an adhesive. The sleeves are placed in a mould and rubber is injected between the sleeves. The rubber is then cured to establish adhesion. However, during the cure, the rubber expands upon being heated and bonds itself to the adjacent sleeve surfaces. Upon cooling, shrinkage obtains, but the rubber is held by the bond against contracting, thereby establishing tensile stresses within the rubber. To eliminate tensile stresses, and to establish compressive stresses within the rubber, either the outer sleeve 30 is radially compressed by swaging or the inner sleeve 24 is radially expanded. Therefore, depending upon the final desired dimension, the sleeve 30 would be made oversized or the sleeve 24 would be made undersized. Furthermore, in those instances where conical stress is high, the axial length of the insert as compared to its thickness is desirably a ratio in excess of 12:1. The insert 31 includes annular end surfaces which project axially beyond the available space between the inner and outer sleeves. As shown in Figures 2, 3 and 4, these end faces are each unconstrained both axially by the legs 29 and 28 and radially by the outer sleeve 30, much as to permit deformation of the ends both radially and axially of the innermost sleeve 24.

A conventional post bonding technique may be employed to place the insert 31 in a state of compression and to adhesively bond the insert between the linner and outer sleeves, for instance see U.S. Patent 3,387,839. The elastomeric insert is premoulded and has a wall thickness which exceeds the radial space between the inner and outer sleeves by an amount which corresponds to a desired degree of compression of the insert. The outer surface of the inner sleeve and the inner surface of the outer sleeve are coated with a heat activated adhesive. The insert is then forced between the sleeves and the adhesive is heat activated to bond the insert to the sleeve.

Prior art beam center bushings include elastomeric insents which are under compression but which are not adhesively bonded to their sleeves. Those bushings have been tested ;by subjecting them to accelerated forces and articulation similar to that received in field use. The mode of failure is very similar to the pattern observed from field failures. The test results indicate that beam center bushings produced for a suspension assembly in accordance with this invention should last three to four ties the life in field use over current production of non-adhesively bonded bushings.

WHAT WE CLAIM IS:- 1. A tandem suspension assembly for heavy duty trucks and the like, comprising a pair of parallel equalizing beams, a pair of parallel axles extending transversely of and connected to the ends of said beams, bracket means rotatably mounted on said beams respectively and centrally thereof by means of respective center bushings each of which comprises a first and a second longer cylindrical sleeve one received within the other, and an elongate tubular elastomeric insert arranged between said sleeves and being adhesively bonded thereto, said insert having a first portion occupying substantially all of the available space between said sleeves, and said insert having a second portion which in an unloaded condition of the assembly engages the longer of said sleeves beyond said available space, the end surfaces of said tubular insert being uncunstrained such as to permit deformation thereof both axially and radially of said innermost sleeve under loading of said assembly, and said first portion of said insert being in a state of radial compression.

2. A tandem suspension assembly according to claim 1, wherein one of said sleeves is radially deformed substantially along its entire axial length thereby placing said insert under radial compression.

3. A tandem suspension assembly according to claim 1 or 2 wherein the axial length of the insert as compared to its thickness is a ratio in excess of 12:1.

4. A tandem suspension assembly according to any preceding claim wherein the inner most of said sleeves has been radially expanded so as to put the insert in a state of compression.

5. A tandem suspension assembly for heavy duty trucks and the like, comprising a pair of parallel equalizing beams, support means at the ends of each beam, end brackets connected to each support means; a pair of spaced, parallel cross axles mounted on said end brackets, a center bushing at the midportion of each said equalizing beam, and bracket means connected to each equalizing beam by its center bushing; each said center bushing comprising an inner cylindrical sleeve, a shorter outer cylindrical sleeve surrounding the inner sleeve, and a tubular elastomeric insert positioned between said sleeves and being adhesively bonded thereto, said insert having a first portion occupying substantially all of the available space between said inner and outer sleeves, said insert having a second portion engaging the inner sleeve beyond said available space in an unloaded condition of the assembly, the ends of said tubular insert being unconstrained such as to permit deformation thereof both radially and axially of the innermost sleeve under loading of the assembly, and said first portion of said insert being in a state of radial compression.

6. A tandem suspension assembly for heavy duty trucks and the like, substantially as herein before described with reference to the accompanying drawings.

7. A heavy duty truck including a tandem suspension assembly as claimed in any pre

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. the rubber is held by the bond against contracting, thereby establishing tensile stresses within the rubber. To eliminate tensile stresses, and to establish compressive stresses within the rubber, either the outer sleeve 30 is radially compressed by swaging or the inner sleeve 24 is radially expanded. Therefore, depending upon the final desired dimension, the sleeve 30 would be made oversized or the sleeve 24 would be made undersized. Furthermore, in those instances where conical stress is high, the axial length of the insert as compared to its thickness is desirably a ratio in excess of 12:1. The insert 31 includes annular end surfaces which project axially beyond the available space between the inner and outer sleeves. As shown in Figures 2, 3 and 4, these end faces are each unconstrained both axially by the legs 29 and 28 and radially by the outer sleeve 30, much as to permit deformation of the ends both radially and axially of the innermost sleeve 24. A conventional post bonding technique may be employed to place the insert 31 in a state of compression and to adhesively bond the insert between the linner and outer sleeves, for instance see U.S. Patent 3,387,839. The elastomeric insert is premoulded and has a wall thickness which exceeds the radial space between the inner and outer sleeves by an amount which corresponds to a desired degree of compression of the insert. The outer surface of the inner sleeve and the inner surface of the outer sleeve are coated with a heat activated adhesive. The insert is then forced between the sleeves and the adhesive is heat activated to bond the insert to the sleeve. Prior art beam center bushings include elastomeric insents which are under compression but which are not adhesively bonded to their sleeves. Those bushings have been tested ;by subjecting them to accelerated forces and articulation similar to that received in field use. The mode of failure is very similar to the pattern observed from field failures. The test results indicate that beam center bushings produced for a suspension assembly in accordance with this invention should last three to four ties the life in field use over current production of non-adhesively bonded bushings. WHAT WE CLAIM IS:-

1. A tandem suspension assembly for heavy duty trucks and the like, comprising a pair of parallel equalizing beams, a pair of parallel axles extending transversely of and connected to the ends of said beams, bracket means rotatably mounted on said beams respectively and centrally thereof by means of respective center bushings each of which comprises a first and a second longer cylindrical sleeve one received within the other, and an elongate tubular elastomeric insert arranged between said sleeves and being adhesively bonded thereto, said insert having a first portion occupying substantially all of the available space between said sleeves, and said insert having a second portion which in an unloaded condition of the assembly engages the longer of said sleeves beyond said available space, the end surfaces of said tubular insert being uncunstrained such as to permit deformation thereof both axially and radially of said innermost sleeve under loading of said assembly, and said first portion of said insert being in a state of radial compression.

2. A tandem suspension assembly according to claim 1, wherein one of said sleeves is radially deformed substantially along its entire axial length thereby placing said insert under radial compression.

3. A tandem suspension assembly according to claim 1 or 2 wherein the axial length of the insert as compared to its thickness is a ratio in excess of 12:1.

4. A tandem suspension assembly according to any preceding claim wherein the inner most of said sleeves has been radially expanded so as to put the insert in a state of compression.

5. A tandem suspension assembly for heavy duty trucks and the like, comprising a pair of parallel equalizing beams, support means at the ends of each beam, end brackets connected to each support means; a pair of spaced, parallel cross axles mounted on said end brackets, a center bushing at the midportion of each said equalizing beam, and bracket means connected to each equalizing beam by its center bushing; each said center bushing comprising an inner cylindrical sleeve, a shorter outer cylindrical sleeve surrounding the inner sleeve, and a tubular elastomeric insert positioned between said sleeves and being adhesively bonded thereto, said insert having a first portion occupying substantially all of the available space between said inner and outer sleeves, said insert having a second portion engaging the inner sleeve beyond said available space in an unloaded condition of the assembly, the ends of said tubular insert being unconstrained such as to permit deformation thereof both radially and axially of the innermost sleeve under loading of the assembly, and said first portion of said insert being in a state of radial compression.

6. A tandem suspension assembly for heavy duty trucks and the like, substantially as herein before described with reference to the accompanying drawings.

7. A heavy duty truck including a tandem suspension assembly as claimed in any pre

ceding claim and including spring means mounted on the chassis of the truck and on said bracket means, and torsion rods connected between the chassis and the axles.