FIELD OF INVENTION

The present invention relates to a suspension bushing for the heavy duty vehicle and more particularly relates to a polyurethane bushing for the self steer lift axle suspension system.

BACKGROUND OF INVENTION

Auxiliary axle is commonly used in heavy duty trucks and trailers to increase load carrying capacity of the vehicle and distribute the load onto the road surface. The auxiliary axle suspension can be lifted-off from the road surface when the vehicle is operated unladen and partially loaded conditions. The lift axle extends the tire life and increases fuel efficiency by reducing rolling resistance of the vehicle. The lift axle suspension is typically retained in a lifted position until it is needed. The lift axle suspension is lowered into contact with the road surface to provide another axle (i.e., suspension) over which the load of the vehicle is distributed.

FIG.1 shows a conventional assembly view of the self-steer lift axle suspension system (1). The steerable lift axle suspension (1) should perform the functions of the lifting the axle assembly (2), allow the tires to self-steer, carry a required load and provide a required ride quality. Usually, the lift axle suspension (1) is made self-steering by using a appropriate caster angle of the axle assembly (2); so that the friction of the tires causes the wheels assembly to steer automatically to respond to the steering of the front axle of the vehicle, which is generally performed by using hydraulic power and steering linkages, and to respond to steering created by other vehicle motion such as vehicle cornering.

In the commercial available self-steered parallelogram type lift axle (2), anti-twist rubber bushing is used. That is, the rubber bush freely rotates on the steel sleeve provided along with the pivot bolt. Therefore, no twisting torque (which leads to shear stress in the bush) is developed in the rubber bush; thereby force required to lift the axle is minimized. The rubber bushing, having appropriate hardness and stiffness, is commonly used in the pivot joints of the pull arms (i.e., parallelogram arms or linkages) for absorb the shock load. The rubber bush is experienced a sever fatigue loads when the vehicle is operated in undulated road and pot holes; therefore, the life of the rubber is limited. A pre-determine failure is observed in the rubber bushing assembly.

FIG.2 shows the conventional rubber bushing assembly (7) which is having two halve sleeve rubber bushes (8) and flange (9) at one end (prior art). Such type of the rubber bushing assembly (7) is commonly used in the pivot joint of the shock absorbers and independent suspension. Practically, such type of rubber bushing assembly (7) performs well in the shock absorber and independent suspension. One of a main advantage of this conventional rubber bushing assembly (7) is less time required to assemble the bushes (8) compared to the single sleeve type rubber bushing. In addition, now a days, polyurethane is also used in a few suspension systems such as independent suspension and parabolic suspension spring's eye end for a better alternative to the rubber. The polyurethane bush is behaved better than the rubber bush (8), which is in term of life and performance of the suspension assembly system. However, if the same assembly (i.e., construction) is used in the lift axle's pivot joint, it fails frequently in the flange portion ( 9) of the bush. It is mainly due to sever cornering load which is experienced in the pull arms (4) pivot joints.

In view of the above, the present invention is essentially required to address the above mentioned drawbacks which are found in the commercially available self steer lift axle. It is required to provide a better bushing assembly for the self steer lift-able suspension system (1). Moreover, the bushing which is used to solve these problems could also be applied to other types of the suspension systems.

OBJECTIVE OF THE PRESENT INVENTION

A principal object of the present invention is to provide an anti-twist type elastomeric bushing for the self-steer lift axle suspension.

Another objective of the present invention is to provide a polyurethane bushing for the self steer- lift axle which should be manufactured easily.

Another objective of the present invention is to provide a polyurethane bushing for the self steer-lift axle which should be assembled easily.

Another objective of the present invention is to provide a bushing for the self steer-lift axle which should be non-lubricated.

Another objective of the present invention is to provide a bushing for the self steer-lift axle which should have high durability.

Yet another objective of the present invention is to provide a bushing for the self steer-lift axle which should perform better than rubber bushing.

Yet another objective of the present invention is to provide a bushing for the self steer-lift axle which reduces the shock load experience in the pull arms of the lift axle.

Yet another objective of the present invention is to provide a bushing for the self steer-lift axle which reduces the vibration of the structure member of the lift axle.

SUMMARY OF THE PRESENT INVENTION

The present invention provides a simple elastomeric bushing for the self steer lift axle suspension system. It dampens the shock load experienced in the pull arms of the lift axle. In addition it reduces the vibration of the structure member of the lift axle. Therefore, the pre-mature failure of the structural component is prevented.

The lift axle bushing in accordance with the present invention, comprising of a polyurethane push, a pair of wear pads, a steel sleeve and a bolt and nut. The polyurethane bush preferably made of single piece or made into two halves (i.e., two sleeves) with a small flange at one end. The polyurethane bush has few straight grooves at the inner surface of the bush. It is mainly used to fill grease before assembly.

The wear pads are placed at the both end of the bush (i.e., at the both end of the pull arm). The wear pads are preferably made of wear resistance with low frictional coefficient materials such as cast nylon or vesconite. The wear pads are mainly withstands the cornering load experienced in the pull arms (when vehicle is operated.

A steel sleeve, having an appropriate length, is inserted in the polyurethane bush. The bushing assembly is pivotally secured with the hanger bracket and bottom air bellows mounting bracket by means of the bolt and nut. In the lift axle bushing assembly for self steer lift axle suspension system, the bolt is used as pivot pin. Therefore, the pull arm assembly freely rotates with respective the bolt axis when the vehicle operated.

The polyurethane bush is made with an appropriate hardness to achieve required stiffness. So that, the polyurethane bush withstands the heavy shock load experienced in the pull arm assembly when the vehicle is operated. The wear pad withstands the thrust load experienced in the pull arm assembly when the vehicle turns.

BRIEF DESCRIBTION OF THE DRAWINGS

FIG.1 shows the self-steered lift axle suspension system in accordance with the prior art.

FIG.2 shows the conventional rubber bushing assembly in accordance with the prior art.

FIG.3 shows the exploded views of the pivot bushing assembly for the self steer lift axle suspension system in accordance with the present invention.

FIG.4 is a view of polyurethane bush, in accordance with the preferred embodiment of the present invention.

FIG.5 is a view of single sleeve polyurethane bush shapes, in accordance with the preferred embodiment of the present invention.

FIG.6 shows the cross sectional views of the two halve sleeve polyurethane bushing assembly, in accordance with one of the embodiment of the present invention.

FIG.7 is the cross sectional views of the pivot bushing with single sleeve, in accordance with embodiment of the present invention.

DETAILED DESCRIPTION

FIG.3 shows the exploded view of the lift axle bushing (10) for the self-steered lift axle suspension system (1) according to present invention. The lift axle bushing (10), described, herein, comprises a pair of polyurethane bushes (11); a pair of wear pads (12) (i.e., trust washers), a steel sleeve (13) and a bolt (14) and nut (15). The polyurethane bushes (11) are inserted in both the eyes (3) of the pull arms (4) of fig 1. The steel sleeve (13) is a steel tube and is inserted in the hole (16) of the polyurethane bushes (11). The lift axle bushing assembly (10) is pivotally clamped with the hanger bracket (5) and the bottom air bellow mounting bracket (6) of the self steer lift axle suspension system (1) of fig 1.

FIG.4 shows the polyurethane bush (11) having a flange (23) in one end. The polyurethane lift axle bushing assembly (10) is initially lubricated by grease. Therefore, polyurethane bush (11) is designed such that few straight grooves (17) are provided in the inner surface (18) of the polyurethane bush (11); so that grease can be filled before assembling the bushes (11) with the pull arms (4) of fig 1. The straight grooves (17) are capable of functioning as a lubrication pockets.

FIG.5 shows the various shapes of the single sleeve polyurethane bush (19) according to present invention. A special attention is provided to the design of the bush (19). The bush (19) is designed with side chamfers (20) (which are beveled edges) or without the side chamfers (20). In addition, a groove (21) (i.e., center cut out) is also provided at the center of the outer surface (22) of the bush (19). The chamfers (20) and groove (21) are used to allow the polyurethane bush (19) to compress radically and expand side ward when the bush (19) experiences load.

FIG. 6 shows the cross section of the polyurethane bushing assembly (10) according to the present invention. The polyurethane bush is either made of two halves sleeves bush (11) or single sleeve bush (19). In the two halve sleeves type bush (11), a small flange (23) is only provided. The small flange (23) portion limits the full insert (i.e., contact) of the bush (11) in the eye end (3) of the pull arm (4); thereby, required gap (24) in between the two halve sleeves (25) is maintained. The gap (24) allows the polyurethane bush (11) to expand side ward when the bush (11) experiences radial load and conical load. If the two halves sleeves type bushing (is used a grease nipple is provided (not shown in Figures) in the pull arm (4); so that further lubrication can also applied. The inner steel sleeve (13) is made of steel tube to maintain a required side clearance (i.e., a small gap in between the wear pad (12) and the hanger bracket structure (5) or the bottom air bellow mounting brackets structured); so that, the polyurethane bush (11) revolves (i.e., rotates) on the steel sleeve (13) when the vehicle is operated. The wear pads (12) are located at the both side of the polyurethane bushes (11) which reduces the frictional coefficient at the contact surface of the wear pad (12) and the hanger bracket's (5) structure or the bottom air bellow mount bracket's structure (6). The wear pad (12) is made of low friction wear resistance and high load bearing materials. Especially, it is made of cast nylon or vesconite. The wear pad is (12) mainly used to withstand the cornering load experienced in the pull arm (4) when the vehicle is operated in turning. Thereby, the polyurethane bush (11) is protected from the failure occurred in the flange (23).

FIG. 7 shows the cross sectional of the various possible polyurethane bushing assemblies (10) with single bush sleeve (19). In the configurations, chambers at both the corners (26) and/or a groove (27) is provided at the center of the outer periphery (22) of the bush (19) which allows the polyurethane bush to expand side ward when the bush experiences radial load. The size of the side chamber (26) and groove (27) is designed based on the load experienced in the pivot joint, stiffness of the bush and expansion allowed in the bush. As the polyurethane bush (19) reduces the vibration of the structure member of the lift axle suspension (1), the pre-mature failure of the structural component is prevented.

The polyurethane bush (11,19) has sufficient stiffness such as radial stiffness, axial stiffness and conical stiffness to withstand the loads experienced in the pushing assembly (10) of the lift axle suspensions (1) such as the acceleration force, braking force and cornering force. The lift axle suspension (1) also experiences road undulates and debris which leads an impact load in the pull arms (4). The impact load is suppressed by the polyurethane bush (11,19).

Many modifications and other embodiments of the invention may come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. In addition, some changes such as removing the grooves and changing the profile of groove may be made to these specific embodiments, and such modifications are contemplated by the principle of the present invention. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.

WE CLAIM :

1. A lift axle suspension bushing (10) comprises :

a polyurethane bush (11) slight forcibly inserted in the eyes (3) of pull arms (4) of a self steer lift axle suspension system (1);

a pair of wear pads (12) are located at the both side of the polyurethane bush (11); and

a steel tube sleeve (13) is inserted in the hole (16) which is provided at of the polyurethane bush (11).

2. The lift axle suspension bushing (10) according to the claim1, wherein said bushing comprises a bolt and nut which are capable of a functioning as a pivot pin in the lift axle suspension system.

3. The lift axle suspension bushing (10) according to the claim1, wherein said polyurethane bush is provided with a flange at other end.

4. The lift axle suspension bushing (10) according to the claim1, the polyurethane bush (11) is made of two halve sleeves (25)or a single sleeve(19).

5. The lift axle suspension bushing (10) according to the claim1 and 5, wherein said single sleeve polyurethane bush (19) is preferably provided with side chamfers (20).

6. The lift axle suspension bushing (10) according to the claim1 and 5, wherein said single sleeve polyurethane bush (19) is preferably provided with a groove (21) at the center of the outer periphery surface (22) of the polyurethane bush.

7. The lift axle suspension bushing (10) according to the claim 1,6 and 7, wherein said side chamfers (20) and/or grooves (21) are provided to allow the bush for expanding side ward when it is experienced load.

8. The lift axle suspension bushing (10) according to the claim 1, he polyurethane bush (11) has a few straight lubrication grooves (17) at the inner surface (18) in which lubrication is filled before assembling with pull arms (4).

9. The lift axle suspension bushing (10) according to the claim1, the wear pad (12) is preferably made of wear resistant and high load bearing materials such as Cast Nylon or Vesconite.

10. The lift axle suspension bushing (10) according to the claim1 and 2, wherein the bolt(14) is inserted in the hole (16) of the steel sleeve (13) and pivotally tightened with the hanger bracket structure (5) and the bottom air bellow mounting bracket structure (6)preferably by using the bolted nuts (15).

11. The lift axle suspension bushing (10) according to the claim 1,4 and 5, wherein said flange portion of two halve sleeves polyurethane bush limits the full insert of the bush (11) in the eye end (3) of the pull arm (4);thereby maintaining the required gap between the two halve sleeves.

12. The lift axle suspension bushing (10) according to the claim 1 and 13, wherein said gap allows the bush (3) to expand side ward when the bush (11) experiences the load.

13.The lift axle suspension bushing (10) according to the claim1, the polyurethane bush (11) is capable of rotating freely on the steel sleeve (13).