Lift axle suspension system

Field of Invention;

The present invention relates to a lift axle suspension system for desirably lifting and lowering an auxiliary axle of a vehicle. The invented lift axle suspension system is self-steerable type and is pneumatically operated.

Background of invention

Auxiliary axle is generally used in heavy duty trucks and trailers to increase load carrying capacity of the vehicle and distribute the load onto the road surface. Usually, vehicles having auxiliary axle do not operate in full load condition all the time. It has been found that nearly half of the time a vehicle runs empty i.e. unladen condition. In the empty run condition or partially loaded condition, the service of an auxiliary axle is not required because the load borne on each axle is much less than the maximum permissible load of the axles. Thus, one of the axles may be lifted in unladen condition to reduce tyre wear and to improve fuel efficiency of the vehicle. Such auxiliary axle suspension which can be lifted off the road surface when the vehicle is operated unladen and partially loaded conditions is known as lift axle suspension.

The lift axle suspension system is becoming increasingly important in the multi axle vehicle and trailers because it extends the tyre 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 service is required.

Commercially, two types of lift axle system are available; namely, self-steerable lift axle and non-steered lift axle. The self-steereable lift axle is usually used as a pusher axle and is generally disposed between the front axle and rear drive axle of the vehicle i.e., at the rear side of the front axle, whereas the non-steered lift axle is used as tag axle which is positioned rear side of the drive axle.

US 7131652, discloses a self-steerable lift axle suspension system for heavy duty vehicles. Disadvantageously, such lift axle suspension system cannot be used as a pusher axle in heavy vehicles such as trucks because such systems are unable to maintain constant caster angle; the self-centering ability of the axle is varied when it operates in undulated road surfaces.

The steerable lift axle suspension should perform the following functions:

- lift the auxiliary axle assembly as and when required
- allow the tyres to self-steer,
- carrying required load, and
- providing required ride quality.

The lift axle suspensions are made self-steering by using a appropriate caster angle of the wheel so that the friction of the tyres causes the wheels 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. .

Although various types of lift axle suspensions have been developed over the past two decades, parallelogram type steerable suspension system has proved to be the most commercially acceptable for heavy dusty vehicle since it maintains a constant caster angle. Caster is defined as an angle between a vertical direction and the inclination of the axis about which wheels turn for steering. Therefore, for pusher axle application the parallelogram type self-steerable suspension system is the most used and recommended system.

In the parallelogram type suspension two identical parallelogram linkages are positioned at the side of the vehicle frame. Each parallelogram linkages has an eye at its ends and is pivotally connected to the hanger bracket connected to the frame of the vehicle.

These systems are designed in such a way that the axle can be desirably lowered down into road surface for sharing the load and can be raised off the road when the vehicle is operating in unladen condition to a required distance. Under lifted condition, the axle should be stably retained in position so that advertent road surface contact is prevented even when the tyres experience bumps or pot holes. This axle lifting mechanism aims at extending tyre life and reducing fuel consumption because these auxiliary axles can be lifted when reversing or when not need the axle.
In lift axle suspension systems air bellows are used for actuating the parallelogram linkages. Generally the parallel linkages comprises of an upper pull arm and a lower pull arm. Numerous types of auxiliary lift axle suspension systems have been devised by altering the position of the lift air bellows.

The lift force exerted on the parallel linkage depends on the position and the size of the air bellows. Accordingly, by varying the position of the lift air bellows the force required to lift the axle can be varied. It is known in the art to attach the lift air bellows with the parallel linkage in the following manners:

(i) one end of the lift air bellows attached to the upper pull arm while the other end mounted to the lift air bellow support bracket and the lift force is applied only to the upper pull arm,

(ii) the lift air bellow is linked with both the upper pull arm and the lower pull arm and the lift force is applied to both the upper pull arm and the lower pull arm,

(iii) the lift air bellow is attached only with the lower pull arm and the lift force is applied only to the lower pull arm.

Disadvantageously, the numbers of joints used in conventional lift axle suspension systems are large; this not only reduces the stability of the system but also increases the maintenance cost.

The conventional lift axle suspension systems have been designed in such a way that it poses an inherent constraint on the size of the lift air bellows being used in the system. The size of the lift air bellows to be used is determined by the space available between the parallelogram linkages, i.e. the space between the upper pull arm and the lower support pull arm. This is yet another limitation of conventional self steerable lift axle suspension systems.

Accordingly, the inventors felt the need to develop a simple self steerable lift axle suspension system with enhanced stability and at the same time cost effective.

Summary of invention;

Accordingly, the present invention provides a lift axle suspension system comprising:

- a pair of transversely-spaced lift arm assemblies, a right lift arm assembly disposed proximal to right side frame of the vehicle and a left pull arm assembly disposed proximal to left side frame of the vehicle, for desirably lifting and lowering a vehicle axle assembly each said lift arm-assembly comprises a pair of pull arms, an upper pull arm and a support pull arm, pivotally linked with said vehicle axle assembly at their respective fore ends , wherein in each said lift arm assembly the support pull arm is disposed below and outwardly offset with regard to the upper pull arm,

- a pair of hanger brackets, a right hanger bracket secured to the right side frame of the vehicle and a left hanger bracket secured to the left side frame of the vehicle, for connecting the lift arms with the side frames of the vehicles and for providing pivotal support to the pull arms of said lift arm assemblies at their respective rear ends,

- a cross member connecting said hanger brackets, a pair of lift air bellows, a right air bellow operatively linked at its one end with the upper pull arm of said right lift arm assembly, and a left air bellow operatively linked at its one end with the upper pull arm of said left pull arm assembly, for actuating said lift arm assemblies, wherein each said lift air bellow is pivotally attached with said cross member at their other ends,

- a pair of shock absorbing ride air bellows, right ride air bellow and left air bellow, wherein said right air bellow is connected with right side frame of the vehicle at its upper end and said left ride air bellow connected with left side frame of the vehicle at its upper end, and wherein each said air bellow is connected with the axle assembly at its bottom end,

- a pair of steering stabilizer assemblies for maintaining cornering stiffness of said vehicle axle assembly, each said steering stabilizer assembly is disposed proximate to an extremity of said vehicle axle assembly.

According to a preferred embodiment of the invented lift axle suspension said lift pull arm comprises:

- a front pivotal portion having hollowing cylindrical profile for providing pivotal linkage with said axle assembly,

- a rear pivotal portion having hollow cylindrical profile for providing pivotal linkage with one of said hanger brackets,

- an intermediate load bearing portion having hollow rectangular profile, and

- a lever arm connected with said intermediate load bearing portion for providing linkage with respective lift air bellow.

According to another embodiment of the lift axle suspension system said support pull arm comprises:

- a front pivotal portion having a hollow cylindrical profile for providing pivotal linkage with said axle assembly,

- a rear pivotal portion having a hollow cylindrical profile for providing pivotal linkage with one of said hanger brackets, and

- an intermediate load bearing portion having hollow rectangular profile.

The upper pull arm and support pull arm may be of the same length. Simple components such as L shaped plates and cylindrical pipes are used in fabricating the pull arm. The brackets and the pipes are welded together by using welding rods of high tensile strength. Not only do these pull arms have higher strength; their manufacturing cost is also much lesser than the molded pull arms used in conventional lift axle suspension systems.

Preferably, said upper pull arm is connected with the inner side of said side frame of the vehicle and said support pull arm is connected with the outer side of said side frame of the vehicle. This ensure that pull arms of each pull arm assembly do not lie along the same vertical plane. Such arrangement of the pull arms imparts more stability to the lifted axle as compared to prior art.

According to a preferred embodiment of the invention, said hanger bracket is provided with a top pivot hole for pivotal connection with said upper pull arm and a bottom pivot hole for pivotal connection with said support pull arm, said top pivot hole sustains a predetermined angle with respect to bottom pivot hole fro maintaining a constant caster angle

According to a further embodiment of the invention , the lift air bellows are pivotally connected with said cross member by means of lift air bellow mounting brackets, each said lift bellow mounting bracket has,

- a flat circular portion to which said lift air bellow is secured, and,

- a pivot portion for pivotally engaging said lift air bellow with said cross member.

According to yet another embodiment of the invention, each said ride air bellow is connected with side frame of the vehicle by means of a top air bellow mounting bracket and is secured to the axle assembly by means of a bottom air bellow mounting bracket.

The top air bellow mounting bracket has,

- a flat circular portion to which said ride air bellow is secured, and,

- an upright portion which secures said ride air bellow with said side frame of vehicle .

Preferably, each said pull arms is pivotally connected with the vehicle axle assembly at its fore end through said lower air bellow mounting bracket. The steering stabilizer assembly is pivotally connected at its one end with track rod lever of said axle assembly and with the said bottom air bellow mounting bracket at its other end. The lift air bellow may be linked with said upper pull arm by means of a lever arm.

According to a preferred embodiment of the invention, said steering stabilizer assembly comprises

- a shock absorber to dampen oscillation,

- an opened coil spring for providing self-centering force to the wheel assembly of the axle.

According to a preferred embodiment of the invention, each said pull arm is pivotally attached with the respective hanger bracket at its rear end by means of a bushing assembly comprising:

- a bolt for fastening said pull arm with said hanger bracket,

- a pair of black-graphite polyurethane bushes for lubricating and absorber mild shock said pivot assembly, each of said black-graphite polyurethane bushes is provided with a helical inner groove for providing proper lubrication in the joints,

- a pair of black-graphite polyurethane washers to withstand side thrust.

- a sleeve type metal bush, made of steel or aluminum bronze, having four holes at center circumferentially for providing lubrication between the said bolts and the bush.

Preferably, each said lift air bellow mounting bracket is pivotally connected with said cross member by means of a pivot assembly comprising,

- a pivot bolt for securing said lift air bellow mounting bracket with said cross member,

- a pair of black graphite polyurethane pivot washers to withstand side thrust,

- an aluminum bronze bush , and

- a sleeve type metal pivot bush for maintaining the required clearance.
In conventional self steerable lift axle suspension systems rubber bushings are used in lift axle and trail arm suspension. The life of the rubber is limited due to high fatigue load. Moreover, while lifting the axle assembly; a large force is required to twist the rubber bushing about its longitudinal axis even though the rubber bushing provides a sufficient flexibility. Due to the flexibility provided in the pivot joints, the shimmy in the axle is increased. In order to overcome this disadvantage associated with the rubber bushing, black-graphite impregnated polyurethane bushes have been used in the bushing assembly of the invented lift axle suspension system.

According to a further embodiment of the invention , said cross member consist of a hat shaped plate to which said hanger brackets are attached, and a pair of U shaped plates to which said ride bellow mounting brackets are pivotally connected, said U shaped plates are welded on said had shaped plate.

Advantageously, the axle suspension system is retrofit in nature and can fitted to the front axle of a vehicle

Brief Description of the Drawings;

For better understanding, an illustrative embodiment of the invention will be described with reference to the accompanying drawings. It will however be appreciated that the embodiments exemplified in the drawings is merely illustrative and not limitative to the scope of the invention, because it is quite possible, indeed often desirable, to introduce a number of variations in the particular embodiment that has been shown in the drawings.

Figure 1 is an isometric view the self-steered lift axle suspension system attached to a vehicle axle.

Figure 2 is a schematic perspective view of the support bottom pull arm.

Figure 3 is a schematic perspective view of the upper pull arm.

Figure 4 is a schematic perspective view of the hanger bracket.

Figure 5 is a schematic perspective view of the bottom air bellow mounting bracket.

Figure 6 is a schematic perspective view of the top ride air bellow mounting bracket.

Figure 7 is a schematic view of the lift air bellow mounting bracket. Figure 8 is a schematic perspective view of a cross member.

Figure 9 is the exploded view of the pivot assembly of lift air bellows mounting bracket with cross member.

Figure 10 is a cross sectional view of the pivot joint of lift air bellows mounting bracket with cross member.

Figure 11 is the exploded view of the bushing assembly of the pull arms and support pull arms.

Figure 12 is the cross sectional view of the pivot joint of a pull arm with the hanger bracket.

Figure 13 is a schematic perspective view of the shock absorber mounting bracket.

Figure 14 is a force diagram of a conventional self steerable lift axle suspension system

Figure 15 is a force diagram of the invented lift axle suspension system.

Detailed description of the drawing;

Referring to figure 1 of the accompanying drawing, the invented lift axle suspension system (1) comprises:

- a pair of transversely-spaced lift arm assemblies, a right lift arm assembly (2R) disposed proximal to right side frame of the vehicle (not shown) and a left pull arm assembly (2L) disposed proximal to left side frame of the vehicle (not shown), for desirably lifting and lowering the vehicle axle assembly (3),

- a pair of hanger brackets, a right hanger bracket (4R) secured to the right side frame of the vehicle (not shown) and a left hanger bracket (4L) secured to the left side frame of the vehicle (not shown),

- a cross member (5) connecting said hanger brackets (4R, 4L),

- a pair of lift air bellows, a right air bellow (6R) and a left air bellow (6L),

- a pair of shock absorbing ride air bellows, a right shock absorbing ride air bellow (7R) and a left shock absorbing ride air bellow (7L), and

- a pair of steering stabilizer assemblies (8) for maintaining cornering stiffness of said vehicle assembly, each said steering stabilizer assembly (8) is pivotally disposed proximate to an extremity of said vehicle axle assembly (1).

Each said lift arm assembly (2) comprises a pair of pull arms, an upper pull arm (9) and a support pull arm (10). The upper pull arms (9) and the support pull arms (10) are pivotally linked with said vehicle axle assembly (3) at their respective fore ends and pivotally linked with respective hanger bracket (4R or 4L) at their rear ends. The right hanger brackets (4R) connects the right lift arm assembly (2R) with the right side frame of the vehicle and the left hanger brackets (4L) connects the left lift arm assembly (2L) with the left side frame of the vehicle. In order to enhance the stability of the invented lift axle suspension system the support pull arm (10) is disposed below and outwardly offset with regard to the upper pull arm (9). The right air bellow (6R) is operatively linked at its one end with the upper pull arm (9) of said right lift arm assembly (2R), and the left air bellow (6L) is operatively linked at its one end with the upper pull arm (9) of said left pull arm assembly (2L); the other end of each lift air bellow (6R and 6L) are pivotally attached with the cross member (5). The lift arm assemblies (2R and 2L) are actuated by inflation and deflation of the lift air bellows (6R and 6L). The right ride air bellow (6R) is connected with right side frame of the vehicle and said left ride air bellow (6L) is connected with left side frame of the vehicle at their respective upper ends. The ride air bellows {6R and 6L) are connected with the axle assembly (3) at their bottom ends.

In the description, which follows hereinafter, the lift arm assemblies (2R,2L), the hanger brackets (4R, 4L), the lift air bellows (6R,6L) and the ride air bellows (7R,7L) have sometimes been commonly referred, for the sake of convenience, by the reference numerals 2, 4, 6 and 7 respectively.

A support pull arm (10) has been schematically shown in figure 2 of the accompanying drawings. The support pull arm (10) comprises a front pivotal portion (11) having hollowing cylindrical profile for providing pivotal linkage with said axle assembly (2), a rear pivotal portion (12) having hollow cylindrical profile for providing pivotal linkage with one of said hanger brackets (4), and an intermediate load bearing portion (13) having hollow rectangular profile. The front pivotal portion (11) and the rear pivotal portion (12) are also known as "eyes" of the support pull arm. The load bearing portion (13) is formed by welding two L shaped plates. The front pivotal portion (11) and the rear pivotal portion (12) are formed of two hollow pipes welded together with the load bearing portion (13). Each of the eyes (11 and 12) is provided with a pair of greased nipples (not shown) for lubrication. For lubricating these greased nipples a grease hole (14) in provided on the surface of eyes (11 and 12).

The upper pull arm (9) has been schematically shown in figure 3 of the accompanying drawings. The upper pull arm (9) is structurally similar with the support pull arm (10) except being provided with a lever arm (14). Similar to the support pull arm (10), the upper pull arm (9) comprises two eyes (11, and 12) , each disposed at an end of the upper pull arm (9) ,and an intermediate load bearing portion (13). The lever arm (15) is attached with the intermediate portion (13) of the upper pull arm (9). The lever arm (15) links the upper pull arm (9) with its respective lift air bellows (6R or 6L) as seen in figure 1. Each of the eyes (11 and 12) of the upper pull arm (9) is provided with a pair of greased nipples (not shown) for lubrication. A grease hole (14) in provided on the surface of eyes (11 and 12) for lubricating these greased nipples. The load bearing portion (13) is formed by welding two L shaped plates. Like the support pull arm (10), the front pivotal portion (11) and the rear pivotal portion (12) of the upper pull arm (9) are also formed of two hollow pipes, welded together with the load bearing portion (13). The intermediate load bearing portion (13) is formed by welding two L shaped plate.

Mechanical means such as fasteners are used to secure the hanger brackets (4) with the side frame (not shown) of the vehicle. The hanger brackets (4) provide pivotal support to the upper pull arm (9) and support pull arm (10). The hanger bracket also links the upper pull arm (9) with the inner side of the side frame (not shown) of the vehicle and the support pull arm (9) is linked with the outer side of said side frame (not shown) of the vehicle.

Figure 4 of the accompanying drawings shows a schematic of the hanger bracket (4) .The hanger bracket (4) is provided with a top pivot hole (16) and a bottom pivot hole (17) for providing pivotal connection to the upper pull arm (8) and to the support pull arm (9) respectively. In order to maintain a predetermined caster angle, which assists to self-turning of the wheels, top pivot hole (16) is made in a desired angle with respect to the bottom pivot hole (17).

Each of the shock absorbing ride air bellows (7) is secured with the vehicle axle assembly (3) at its lower end through a bottom air bellow mounting bracket (18). A bottom air bellow mounting bracket (18) has been schematically shown in figure 5 of the accompanying drawings. The bottom air-bellow mounting bracket (18) is provided with two pivot holes (19) for providing pivotal connection to the upper pull arm (9) and the support pull arm (10) at their respective front ends. The hanger brackets (4) are fabricated in such a way that they are robust and free from conventional welding. Thus poor manufacturing tolerance at the place of the pivot positions, a disadvantage associated with conventional list axle suspension assemblies.

The upper pull arms (9) and the support pull arms (10) are pivotally connected between the hanger brackets (4) and the bottom air bellow mounting brackets (18) about the pivotal point (20) in such a way that the upper pull arm (9) and support pull arm (10) are always parallel to each other when they rotate vertically upward or counter clockwise about the pivotal point (20) as seen figure 1, thereby both these arms (9 and 10) act as a couple in lifting the axle assembly (2) in the upward or in the downwardly, desirably. In other works the lift arm suspension system (1) is a parallelogram type steerable suspension system and the upper pull arm (9) and support pull arm (10) constitute the parallelogram linkage.

Each ride air bellow (7R, 7L) is secured to its respective side frame of the vehicle by means of a top air bellow mounting bracket (21) as shown in figure 1. The purpose of the top air bellows mounting bracket (21) is to hold the ride air bellows (6) rigidly. One end of the ride air bellow (7) is attached to the bottom air bellow mounting bracket (18) using fasteners, such as bolts and nuts, while the other end of the ride air bellow (7) is attached to the top air bellow mounting bracket (21) using bolts and nuts.

The top air bellows mounting bracket (21) is secured to the frame of the vehicle at an appropriate distance from the hanger bracket (4) as shown in figure 1.

A schematic of the top air bellows mounting bracket (21) has been shown in figure 6.

The top air bellows mounting bracket (21) comprises of a flat circular portion (22) to which the ride air bellow (7) is secured, and, an upright portion (23) which secures said ride air bellow (7) with the side frame of the vehicle.

Each lift air bellow (6) is pivotally connected at its rear ends with the cross member (5) by means of a lift air bellow mounting bracket (24). Figure 7 shows schematics of the lift air bellows mounting bracket (24). It consists of a round plate shaped portion (25) to which a lift air bellow (6) is attached at its rear end and a pivoting portion (26) for providing pivotal connection with the cross-member (4). The pivoting portion is formed of a "U" shaped plate (27) and a cylindrical pipe (28) secured between the side walls of the "U" shaped plate (27).

The cross member (5) has been schematically shown in figures 8 and 9 of the accompanying drawings. The cross member (5) comprises of a hat shaped member (29) and a pair of spaced-apart "U" shaped members (30). The hanger brackets (4) are secured to the hat shaped member (29) by means of bolts as seen in figure 1 of the accompanying drawings. The "U" shaped plates of the lift air bellow mounting brackets (24) are secured with the "U" shaped members (30) of the cross member (5).

Each lift air bellow mounting bracket (24) is pivotally connected the cross member (5) by means of a pivot assembly (31) as seen in figure 9 of the accompanying drawing. Each pivot assembly (31) comprises a pivot bolt (32) for securing the lift air bellow mounting bracket (24) with the cross member (5), a pair of black graphite polyurethane pivot washers (33) to withstand side thrust, an aluminum bronze bush (34), and a sleeve type metal pivot bush (35) for maintaining the required clearance.
Figure 10 of the accompanying drawings shows the cross sectional view of the pivot joint (36) between lift air bellow mounting bracket (24) and the cross member (5).

The aluminum bronze bush (34) has a helical grooved and is forcibly inserted in the cylindrical pipe (28) (not shown in figure 10) of lift air bellows mounting bracket (24). A grease hole (37) with nipple nut (38) is provided in the cylindrical pipe (28) for lubricating the pivot joint (36). The pivot bolt (32) is provided with a nut (39) for securing the lift air bellow mounting bracket (24) and the cross member (5) pivotally.

Each pull arm (9 and 10) of the lift arm assembly (2) is pivotally attached with the respective hanger bracket (3) at its rear end by means of a bushing assembly (40) as shown in figure 11. Figure 12 of the accompanying drawings shows the cross sectional view of the pivotal connection between the upper pull arm (9) and the lower pull arm (10) with the hanger bracket (4). The bushing assembly (40) comprises of a bolt (41) for pivotally fastening a pull arm (8 or 9) with a hanger bracket (4), a pair of black-graphite polyurethane bushes (42) for lubricating said bushing assembly (31), a pair of black-graphite polyurethane washers (43) to withstand side thrust and a sleeve type metal bush (44), for maintaining the required clearance in the bushing assembly (40) as seen in figures 11 and 12 of the accompanying drawings. The metal bush (44) has four holes (not shown) at center circumferentially for providing lubrication. The black-graphite polyurethane bushes (42) are provided with a helical inner groove (not shown) for lubrication of the bushing assembly (40). The polyurethane bushes (42) are forcibly inserted within the eyes (12 and 13) of the support pull arm (10). The bushing assembly (40) is provided with a grease hole (45) for greasing the bushing assembly (31). The bolts (41) are provided with nuts (46) at their ends.

Referring to figure 1, the lift axle system (1) is provided with a pair of steering stabilizer assemblies (8) for maintaining cornering stiffness of the vehicle assembly. Each steering stabilizer assembly (7) is pivotally connected with track rod lever (47) of the lift axle assembly (2) at its one end, and with the said bottom air bellow mounting bracket (18) at its other end. The steering stabilizer assembly (7) comprises a shock absorber (48) to dampen oscillation, and an opened coil spring (49) for providing self-centering force to the wheel assembly of the axle with appropriate spring stiffness. In order to protect the shock absorber (48) from damage, caused by road debris such as dust and mud, a plastic cover (50) is provided. This damper system is especially used for maintaining a desired cornering performance criteria (i.e., cornering stiffness) of the self steered lift axle. The steering stabilizer assemblies (8) dampen down the oscillations experienced in the wheel assembly during vehicle operation resulting from wheel shimmy and road shock due to road irregularities; thereby, tracking is stabilized.

A pair of shock absorbers (51) is provided between the axle assembly (3) and the frame of the vehicle via shock absorber mounting bracket (52) and lift axle suspension system (1) is attached to the front stub axle (53) of a vehicle as seen in figure 1 of the accompanying drawing. The shock absorbing bracket (52) has been schematically shown in figure 13.

When the vehicle is operated, the axle assembly (3) experiences a number of bumps or pot holes. When the axle assembly (3) experiences a bump it moves upward towards the vehicle frame. In order to negotiate this jerk caused by the bumps the ride air bellows (7) and the shock absorbers (51) compress while the lift air bellows (6) expand. On the other hand when a wheel of the vehicle falls on a pot hole in the road, the axle assembly (3) moves downward relatively to the frame. The ride air bellows (7) and the shock absorber (51) expand simultaneously whereas the lift air bellows (6) compress.

The lift axle suspension system (1) is provided with a control system (not shown) consisting of direction control valves, pressure gauge, control box and electrical switch. The control system provides requisite air to the ride air bellows (7) during normal operation of the vehicle. When the auxiliary axle is not required, such as the situation that when the vehicle is operated with partially loaded condition or vehicle is operated in empty condition, the vehicle control system deflates the ride air bellows (7) of the suspension and inflates the lift air bellows (6). As the lift air bellows (6) are disposed between the lift arm assemblies (2) and the cross member (5), the lifting force is transmitted to lever arm (15) welded to the upper pull arm (9) of each lift arm assembly (2). Therefore, the upper pull arms (9) and support pull arms (10) are rotated counter clockwise about the pivotal points (20). Thereby, the axle assembly (3) is moved vertically upward and the axle assembly (3) is held in position by lift air bellows (6) i.e., the vehicle axle assembly (3) is lifted off from the road surface and maintained at required distance from the road surface.

A reverse operation of the above mechanism brings the axle assembly (3) down to its initial position and in contact with the road surface.

Referring to the force diagrams depicted in figures 14 and 15 it can be seen that in conventional self-steerable lift axle suspension system (l'), wherein the lift air bellow (6') is linked with both the upper pull arm (9') and the lower pull arm (10'), the lift force is applied to both the pull arms (9' and 10'). Comparatively, in the invented lift axle suspension system the air bellow (6) is linked with the upper pull arm (9) at its fore end and is pivotally attached with the cross member (5) at its back end; therefore the lift force is required to be applied only to the upper pull arm (5).

As already mentioned, the foregoing description is illustrative of the invention and not limitative to its scope, because it will be apparent to persons skilled in the art to devise other alternative embodiments without departing from the broad ambit of the disclosures made herein.

WE CLAIM :

1. A lift axle suspension system comprising:

- a pair of transversely-spaced lift arm assemblies, a right lift arm assembly disposed proximal to right side frame of the vehicle and a left pull arm assembly disposed proximal to left side frame of the vehicle, for desirably lifting and lowering a vehicle axle assembly, each said lift arm-assembly comprises a pair of pull arms, an upper pull arm and a support pull arm, pivotally linked with said vehicle axle assembly at their respective fore ends , wherein in each said lift arm assembly the support pull arm is disposed below and outwardly offset with regard to the upper pull arm,

- a pair of hanger brackets, a right hanger bracket secured to the right side frame of the vehicle and a left hanger bracket secured to the left side frame of the vehicle, for connecting the lift arms with the side frames of the vehicles and for providing pivotal support to the pull arms of said lift arm assemblies at their respective rear ends,

- a cross member connecting said hanger brackets, a pair of lift air bellows, a right air bellow operatively linked at its one end with the upper pull arm of said right lift arm assembly, and a left air bellow operatively linked at its one end with the upper pull arm of said left pull arm assembly, for actuating said lift arm assemblies, wherein each said lift air bellow is pivotally attached with said cross member at their other ends,

- a pair of shock absorbing ride air bellows, right ride air bellow and left air bellow, wherein said right air bellow is connected with right side frame of the vehicle at its upper end and said left ride air bellow connected with left side frame of the vehicle at its upper end, and wherein each said air bellow is connected with the axle assembly at its bottom end,

- a pair of steering stabilizer assemblies for maintaining cornering stiffness of said vehicle axle assembly, each said steering stabilizer assembly is disposed proximate to an extremity of said vehicle axle assembly.

2. The lift axle suspension system as claimed in any of claim 1, wherein said lift pull arm comprises :

- a front pivotal portion having hollowing cylindrical profile for providing pivotal linkage with said axle assembly,

- a rear pivotal portion having hollow cylindrical profile for providing pivotal linkage with one of said hanger brackets,

- an intermediate load bearing portion having hollow rectangular profile, and

- a lever arm connected with said intermediate load bearing portion for providing linkage with respective lift air bellow.

3. The lift axle suspension system as claimed in claims 1 and 2, wherein said support pull arm comprises:

- a front pivotal portion having a hollow cylindrical profile for providing pivotal linkage with said axle assembly,

- a rear pivotal portion having a hollow cylindrical profile for providing pivotal linkage with one of said hanger brackets, and

- an intermediate load bearing portion having hollow rectangular profile.

4. The lift axle suspension system as claimed in any of claims 1 to 3, wherein said upper pull arm and support pull arm are of same length.

5. The lift axle suspension system as claimed in claim any of claims 1 to 4, wherein said upper pull arm is connected with the inner side of said side frame of the vehicle and said support pull arm is connected with the outer side of said side frame of the vehicle.

6. The lift axle suspension system as claimed in claim any of claims 1 to 5, wherein said hanger bracket is provided with a top pivot hole for pivotal connection with said upper pull arm and a bottom pivot hole for pivotal connection with said support pull arm, said top pivot hole sustains a predetermined angle with respect to bottom pivot hole fro maintaining a constant caster angle.

7. The lift axle suspension system as claimed in any of claims 1 to 6, wherein lift air bellows are pivotally connected with said cross member by means of lift air bellow mounting brackets, each said lift bellow mounting bracket has,

- a flat circular portion to which said lift air bellow is secured, and,

- a pivot portion for pivotally engaging said lift air bellow with said cross member.

8. The lift axle suspension system as claimed in any of claims 1 to 7, wherein each said ride air bellow is connected with side frame of the vehicle by means of a top air bellow mounting bracket and is secured to the axle assembly by means of a bottom air bellow mounting bracket.

9. The lift axle suspension system as claimed in any of claim 1 to 8, wherein said top air bellow mounting bracket has,

- a flat circular portion to which said ride air bellow is secured, and,

- an upright portion which secures said ride air bellow with said side frame of vehicle .

10. The lift axle suspension system as claimed in claims 1 to 9, wherein each said pull arms is pivotally connected with the vehicle axle assembly at its fore end through said lower air bellow mounting bracket.

11. The lift axle suspension system as claimed in any of claims 1 to 10, wherein each said steering stabilizer assembly is pivotally connected at its one end with track rod lever of said axle assembly and with the said bottom air bellow mounting bracket at its other end.

12. The lift axle suspension system as claimed in any of claims 1 to 11, wherein said steering stabilizer assembly comprises

- a shock absorber to dampen oscillation,

- an opened coil spring for providing self-centering force to the wheel assembly of the axle.

13. The lift axle suspension system as claimed in any of claims 1 to 12, wherein said lift air bellow is linked with said upper pull arm by means of a lever arm.

14. The axle suspension system as claimed in any claims 1 to 13 , wherein each said pull arm is pivotally attached with the respective hanger bracket at its rear end by means of a bushing assembly comprising:

- a bolt for fastening said pull arm with said hanger bracket,

- a pair of black-graphite polyurethane bushes for lubricating said pivot assembly, each of said black-graphite polyurethane bushes is provided with a helical inner groove,

- a pair of black-graphite polyurethane washers to withstand side thrust,

- a sleeve type metal bush for maintaining the required clearance in said pivot assembly, the metal bushes is provided with four holes at center circumferentially for providing proper lubrication.

15. The axle suspension system as claimed in any claims 1 to 14 , wherein each said lift air bellow mounting bracket is pivotally connected with said cross member by means of a pivot assembly comprising,

- a pivot bolt for securing said lift air bellow mounting bracket with said cross member,

- a pair of black graphite polyurethane pivot washers to withstand side thrust,

- an aluminum bronze bush , and

- a sleeve type metal pivot bush for maintaining the required clearance

16. The axle suspension system as claimed in any claims any of claims 1 to 15, wherein said cross member consist of a hat shaped plate to which said hanger brackets are attached and a pair of U shaped plates to which said ride bellow mounting brackets are pivotally connected, said U shaped plates are welded on said had shaped plate.

17. The axle suspension system as claimed in any claims of claims 1 to 15, wherein said axle suspension system is fitted to the front axle of a vehicle.