Background Art Dump trucks and off highway trucks are designed to carry heavy loads and often are required to work in areas of uneven grade. Suspension systems for these machines need to be robust and capable of supporting these loads while withstanding forces due to shifting loads during normal operation. In the case of tandem axle machines the suspension components need to allow for pitch and roll of each axle while overcoming obstacles and still maintain balance of the load. To prevent such shear stresses it is important that proper placement of all components are optimized.

The present invention is directed to overcome one or more of the problems as set forth above.

Disclosure of the Invention In one aspect of the present invention, a suspension system for a load carrying machine having a frame is provided. A first and a second longitudinally spaced apart axle assemblies each having opposite end portions are positioned transversely relative to the frame. A first suspension member having a first end portion and a second end portion is pivotally connected at the first

end portion to the frame at a predetermined location.

The second end portion of the first suspension member is secured to the first axle assembly at a predetermined location. A second suspension member having a first end portion and a second end portion is pivotally connected at the first end portion to the frame at a predetermined location. The second end portion of the second suspension member is secured to the second axle assembly at a predetermined location.

A first and a second balance beams each has a first and a second end portion, and a middle portion. The first and the second balance beams are pivotally connected to the frame at predetermined locations between the first and the second end portions of the balance beams. The pivotal location of the first end portion of the second suspension member and the predetermined pivotal locations of the balance beams are each generally along a common axis. The axis extends transversely relative to the frame. A pair of first flexible members are positioned between and connected to the first axle assembly and the first end portion of the balance beam. A pair of second flexible members are positioned between and connected to the second axle assembly and the second end portion of the balance beam.

Brief Description of the Drawings Fig. 1 is a diagrammatic longitudinal side view of an embodiment of the present invention showing, a suspension system of a load carrying machine with the load carrying body in phantom and wheels not shown for clarity; Fig. 2 is diagrammatic plan view of the embodiment shown in Fig. 1;

Fig. 3 is an enlarged diagrammatic longitudinal side view of a portion of the embodiment of Fig. 1 showing the rear axle as the tire traverses an obstacle, the tire is shown in phantom for clarity; Fig. 4 is a diagrammatic rear view of the embodiment shown in Fig. 1; and Fig. 5 is the rear view of Fig. 4 showing the axle as one tire traverses an obstacle.

Best Mode for Carrying Out the Invention With reference to the drawings and in particular to Figs. 1 and 2, a suspension system 10 is shown for a load carrying body 12 of a load carrying machine 14 (not shown). The suspension system 10 comprised of a longitudinal frame 20, first and second axle assemblies 22,24, first and second suspension members 26,28, first and second balance beams 30,32, a first pair of flexible members 34, and a second pair of flexible members 36.

The longitudinal frame 20 consists of two box beam sides 38 and includes a first end portion 40 and a second end portion 42.

The first and second axle assemblies 22,24 are longitudinally spaced apart and disposed beneath the box beam sides 38 of the frame 20 at the second end portion 42. Each of the first and second axle assemblies 22,24 define an axis 23,25 and has opposite end portions 46 that are positioned transversely relative to the frame 20. Wheels 48 are mounted to the opposite end portions 46 of the first and second axle assemblies 22,24.

The first suspension member 26 has a first end portion 50 and a second end portion 52 being bifurcated. The first end portion 50 is pivotally

connected to the first end portion 40 of the frame 20 at a predetermined location 54 beneath the box beam sides 38. The pivotal connection is ideally a universal type connection 56, but could be a spherical or ball joint type connection or any or configuration that allows for two axis movement. The second end portion 52 is secured to the opposite end potions 46 of the first axle assembly 22.

The second suspension member 28 has a first end portion 60 and a second end portion 62 being bifurcated. The first end portion 60 is pivotally connected to the frame 20 at a predetermined location 64. The pivotal connection is ideally a universal type connection 66, but could be a spherical or ball joint type connection or any or configuration that allows for two axis movement. The second end portion 62 is secured to the opposite end potions 46 of the second axle assembly 24.

The first and the second balance beams 30,32 each have a first end portions 70,80 a second end portions 72,82 and a middle portions 74,84. The first and the second balance beams 30,32 are pivotally connected to opposite sides of the frame 20 beneath the box beams 38 at a predetermined locations 76,86 between the first end portions 70,80 and the second end portions 72,82. The predetermined locations 76,86 create a common axis 90 extending transversely relative to the frame 20. The predetermined location 64 that the second suspension member 28 is pivotally connected to the frame 20 is generally on common axis 90. As best seen in Fig. 3 the arcuate path 91 that the second end portions 72,82 of the balance beams 30,32 and the axis 25 of the second axle assembly 24 swing is also generally the same. In this application

the predetermined location 64 of the pivotal connection of the first end portion 60 of the second suspension member 28 is within a circle of tolerance 92 of axis 90. The circle of tolerance 92 has a radius"R"in the range of between about 15mm to about 55 mm. Ideally the radius"R"is less than about 40mm.

The pair of first flexible members 34 are a rubber steel composite, but could be an air strut or other means for cushioning load. The pair of first flexible members 34 are positioned between and connected to the first axle assembly 22 and the first end portions 70,80 of the balance beams 30,32.

Mounting of the pair of first flexible members 34 is accomplished by fasteners at a vertical distance"D1" above axis 23 in the range of about 100mm to about 140mm. Ideally the vertical distance"D1"is about 120mm.

The pair of second flexible members 36 are a rubber steel composite, but could be an air strut or other means for cushioning load. The pair of second flexible members 36 are positioned between and connected to the second axle assembly 24 and the second end portions 72,82 of the balance beams 30,32.

Mounting of the pair of second flexible members 36 is accomplished by fasteners at a vertical distance"D2" above axis 25 in the range of about 100mm to about 140mm. Ideally the vertical distance"D2"is about 120mm.

As seen in Fig. 4 a pair of stabilizer bars 100 have a first ends 102 and a second ends 104 are also included. The first ends 104 are pivotally to the frame 20 and are pivotally connected at the second

end portions 104 to the second end portions 52,62 of the first and the second axle assemblies 22,24.

Industrial Applicability With reference to the drawings and in operation, the placement of the first pair and the second pair of flexible members 30,32 with respect to the axis 23,25 of the first and second axle assemblies 22,24, and the predetermined locations 76,86 of the pivotal connections of the balance beams 30,32 and the predetermined location of the pivotal connection of the second suspension member reduce or optimize the amount of shear realized by the first pair and the second pair of flexible members 30,32.

For example, as shown in Fig. 3 when a wheel 48 on the second axle assembly 24 traverses an obstacle. The shear encountered by the second pair of flexible members 36 is limited. This is accomplished by the second end portions 72,82 of the balance beams 30,32 and the axis 25 of the second axle assembly 24 generally swinging the same arcuate path 91.

As best seen in Fig. 5 when one tire 48 of the first axle assembly 22 or the second axle assembly 24 encounters an obstacle, the first or the second axle assembly 22,24 rolls with respect to the first or the second balance beam 30,32. The pair of first and the pair of second flexible members 34,36 are mounted to the first and the second axle assemblies 22,24 at a predetermined distance D1, D2 above a centerlines 23,25 of the axle assemblies 22,24 and are moveable in a lateral direction with respect to the balance beams 30,32 between a non-deflected and a deflected condition upon roll of the axle assemblies 22,24 about the pivotal connections of the first and the second

suspension members 26,28, said predetermined location being adapted to limit the amount of deflection of the flexible members to an amount of less than about 52mm.

Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.