SELF STEER LIFT AXLE SUSPENSION SYSTEM
Field of Invention:
[001] The present invention relates to an innovation in the lift axle of a motor
vehicle. More particularly, the invention relates to an automotive vehicle's self steer lift axle suspension system which has optimized austenite ductile iron or cast iron control arms.
Background of invention
[002] Auxiliary axle is generally used in heavy duty trucks and tractors to
increase load carrying capacity of the vehicle and distribute load onto the road surface. It has been found that nearly 25-35% of the time a vehicle runs empty, i.e., unladen condition. In the empty run condition or partially loaded condition, the auxiliary axle is not required, because the load acts on each axle is much less than the maximum permissible load of the axles. Therefore, the auxiliary axle is lifted from the road surface in unladen condition to reduce tyre wear and to improve fuel efficiency of the vehicle. Such auxiliary is known as lift axle suspension. The lift axle suspension system is becoming increasingly important in the multi-axle vehicle, because it extends the tyre life and increases fuel efficiency by reducing rolling resistance of the vehicle.
[003] 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 coil spring, hydraulic power and steering linkages, and to respond to steering created by other vehicle motion such as vehicle cornering.
[004] Although various types of lift axle suspensions have been developed over
the past two decades, parallelogram type self- steerable lift axle (1) suspension system (FIG.l) has proved to be the most commercially acceptable for heavy duty 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, the parallelogram type self-steerable lift axle suspension system (1) is the most used and recommended system for pusher axle application.
[005] In the parallelogram type self steerable lift axle suspension system (1), two
identical parallelogram linkages, namely control arms (2), are positioned at the side of the vehicle frame. Each parallelogram linkages (i.e., control arms (2)) have an eye (i.e.,

cylindrical hollow shape) at its ends and are pivotally connected to the hanger bracket (3) connected to the chassis frame of the vehicle. The control arms (2) are generally made of fabrication process. It consists of a rectangular tube or cylindrical tube and a pair of eyes at both ends which are made from a cylindrical hollow tube. The eyes are made of high strength steel and are welded at the both ends of the rectangular tube or cylindrical tube. As the OEMs are generally procuring the welded components from several manufactures. Therefore, it is difficult to maintain a required quality. It leads an assembly problem and field failure issues. In order to solve such problem, generally, a high quality checking is essentially employed. Therefore, it increases the production cost of the lift axle suspension system.
[006] In addition, it is essential that the control arms (2) have sufficient stiffness
and strength to resist the substantial loadings that are imparted upon them. It is, therefore, important that suspension control arms (2) should be strong and stiff to function well when loaded, as well as light in weight (to reduce the mass). Reducing weight normally results in a reduction of both strength and stiffness. Great ingenuity is required to design parts with reduced weight but equivalent structural performance characteristics. The operational loads imparted on suspension control arms are discrete and well understood; so that non-uniform structures can be developed to provide selective stiffness and strength in the directions and locations required by the application. Now a day, topology optimization technique is used to reduce weight of structural components. It gives most effective shapes for resisting these induced loads; thereby optimized structure is achieved.
[007] In addition, many failures are observed in the ride air springs (4) (having
internal bump stoppers) in the parallelogram type self- steerable lift axle suspension system (1) operated rugged operation. The bump stopper (which is usually made of rubber) provided with in the ride air springs (4) is failed before the warranty period. If the internal bump stopper fails, both the ride air spring (4) and lift air spring (5) are expanded above the desired height or even expanded the maximum permissible limit of the air spring. It leads a failure in the air springs (4, 5) which is either in rubber bellows or bead plate. It is a severe problem in the conventional lift axle suspension. Once the internal bump stopper is failed, the air spring should be replaced. Therefore, maintenance cost of the system is increased.

[008] Accordingly, the inventors felt the need to develop a simple self steerable
lift axle suspension system which should have a compact assembly package (within the available packaging area/ volume). In addition, it should have a higher durability and at the same cost effective.
*""""' Object of the invention
[009] The main object of the present invention is to provide a self steer lift axle
suspension system, which is highly reliable, and retrofit-ably mountable in the vehicle.
[010] Another object of the present invention is to provide a self steer lift axle
suspension system, which should not have weld in the control arms.
[011] Another object of the present invention is to provide a self steer lift axle
suspension system, which should have fewer welds compared to conventional lift axle.
[012] Another object of the present invention is to provide a self steer lift axle
suspension system, which should have less mass.
[013] Another object of the present invention is to provide a self steer lift axle
suspension system, which should have better kinematics; so that it minimizes the air springs failure.
[014] Another object of the present invention is to provide a self steer lift axle
suspension system, which should have external jounce and reboimd stoppers to minimize the air springs failure.
[015] Another object of the present invention is to provide a self steer lift axle
suspension system, which should withstand dynamic loads and shocks.
[016] Another object of the present invention is to provide a self steer lift axle
suspension system, which should extend tire life of the vehicle.
[017] Another object of the present invention is to provide a self steer lift axle
suspension system, which should improve fuel efficiency.
[018] Another object of the present invention is to provide a self steer lift axle
suspension system, which should be manufactured easily and inexpensive.
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Summary of invention:
[019] It is an object of the present invention to provide an automotive self steer
axle suspension system, in which the control arms are made of austenite ductile iron or cast iron. It improves durability of the system.
[020] In order to accomplish the above mentioned objectives, a self steer lift axle
suspension system is provided. According to the present invention, the self steer lift axle suspension system comprises first and second hanger bracket assemblies, securely attached with each sides of the chassis frame, first and second lower beam brackets attached with the axle assembly, transversely spaced first and second upper control arms, and transversely-spaced first and second lower control arms, which are pivotally attached in between the first and second hanger bracket assemblies and the first and second lower beam brackets to form a parallelogram mechanism and to lift and lower the axle assembly, a hanger to hanger cross member connecting said first and second hanger brackets assemblies, a first and second ride air springs, disposed in between a first and second air spring brackets, attached with the chassis frame, and the first and second lower beam brackets, a first and second lift air springs, disposed in between the first and second upper control arms and hanger to hanger cross member via a first and second swinging brackets, a first and second steering stabilizers pivotally connected in between the first and second lower beam brackets and the first and second track rod of the axle assembly, a first and second jounce stoppers attached with the chassis frame, a first and second rebound stoppers belt assemblies pivotally attached with the first and second lower beam brackets and chassis frame. Rubber bushings (not shown) are inserted in the pivotal hole provided in both the first and second upper control arms and first and second lower control arms. The first and second steering stabilizers are used for mamtaining cornering stiffness of the axle assembly.
[021] The aim of the present invention is to utilize casting process in to
manufacturing of the lift axle's first and second upper control arms and first and second lower control arms for reducing weight. In addition, weight and structure of the first and second upper control arms and first and second lower control arms are optimized by topology optimization method. The shape of the first and second upper control arms and first and second lower control arms are more efficient to resistance to bending, buckling and torsion. The geometrical shape of the first and second upper control arms and first and second lower control arms enables reduction in the amount of weights.

[022] The self steer lift axle suspension system is designed in such a way that the
axle assembly 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. During normal operation of the vehicle, the first and second ride air springs are inflated and maintained a constant ride height using the pneumatic control system (not the part of the present invention). During unladen condition, the first and second ride air springs are deflated and the first and second lift air springs are inflated. The first and second lift air springs expand and the first and second upper control arms and first and second lower control arms rotate anti-clockwise direction. Thereby, the axle assembly is lifted and held at a desired height from the road surface. Under lifted condition, the axle assembly is stably retained in position so that advertent road surface contact is prevented even when the tires experience bumps or pot holes. When the first and second lift air springs are deflated, and the first and second ride air springs are inflated, the axle assembly is lowered into engagement with road surface due to the downward force of the first and second ride air springs and mass of axle assembly. As the axle assembly is lifted to a sufficient height; such that it does not interfere with undulant from the road surface. Thereby, rolling resistance of the vehicle is reduced in unladen condition and partially loaded condition. Therefore, fuel economy, vehicle maneuverability are improved. In addition, life of the tires and self steer lift axle suspensions system components are extended.
[023] In order to inflate and deflate both the first and second ride air springs and
first and second lift air springs, a pneumatic control system is used. It consists of a level sensing device, timing device, dash board manual switch operating switch and quick release valves. The pneumatic control system is not the part of present invention.
Brief Description of the Drawings:
[024] The present invention will be understood more fully from the detailed
description given here below and from the accompanying drawings of the preferred embodiments of the present invention, which, however, should not be taken as limitative to the invention but for explanation and illumination only.
In the drawings:
[025] Figure. 1 shows schematic of the multi-axle vehicle having self-steered lift
axle suspension system, in accordance to prior art.

[026] Figure.2 shows an assembled model of a self steer lift axle air suspension
system, fitted in a chassis frame, of a multi axle vehicle, in accordance to the present invention.
[027] Figure.3 shows the details of the self steer lift axle air suspension system,
in accordance with an exemplary embodiment of the present invention.
[028] Figure.4 illustrates the hanger bracket assembly, in accordance with an
exemplary embodiment of the present invention.
[029] Figure.5 illustrates the upper control arm, in accordance with the
embodiment of the present invention.
[030] Figure.6 illustrates the lower control arm, in accordance with the
embodiment of the present invention
[031] Figure.7 illustrates the lower beam bracket, in accordance with an
exemplary embodiment of the present invention.
[032] Figure.8 illustrates the hanger to hanger cross member, in accordance with
an exemplary embodiment of the present invention.
[033] Figure.9 illustrates the air spring bracket, in accordance with an exemplary
embodiment of the present invention.
[044] Figure.lO illustrates the swinging bracket, in accordance with an
exemplary embodiment of the present invention.
[045] Figure.lO illustrates the assembled model of the swinging bracket with the
hanger to hanger cross member, in accordance with an exemplary embodiment of the present invention.
[046] Figure. 11 illustrates the rebound stopper belt assembly, in accordance with
an exemplary embodiment of the present invention.
[047] Figure. G illustrates the external jounce stopper, in accordance with an
exemplary embodiment of the present invention.

Since the first and second parts of the trailing arm air suspension system are similar to each other in constructional view and design, only the first part figures are represented in the drawings.
Detailed description of the drawing:
[048] The present invention relates to a self steer lift axle air suspension system
(6). The axle assembly (15) is lifted off the road surface and held in a desired height from the road surface in unladen and partially loaded condition of the vehicle. In the present invention, austenite ductile iron arms or cast iron arms are used for the first and second upper control arms (10, 10A) and for the first and second lower control arms (11, 11 A). First and second lift air springs (16, 16A) are employed to lift the axle assembly (15) from the road surface.
[049] FIG. 2 shows an assembled model of the self steer lift axle air suspension
system (6) attached in a chassis frame (8) of a heavy duty multi axle vehicle, in accordance with an exemplary embodiment of the present invention. The self steer lift axle suspension system (6) is designed especially for a multi-axle vehicle having less packaging space in the chassis frame (8).
[050] The self steer lift axle suspension system (6) comprises first and second
hanger bracket assemblies (7,7A), first and second upper control arms (10,10A),first and second lower control arms (11,11 A),first and second lower beam brackets (9, 9A), first and second steering stabilizers (21, 21 A), first and second ride air springs (13, 13A),first and second lift air springs (16, 16A), first and second air spring brackets (14, 14A),first and second swinging brackets (17, 17A), first and second jounce stoppers (19,19A), first and second rebound stopper belts assemblies (20, 20A), a hanger to hanger cross member (12), eight rubber bushings (23) and a pneumatic control system.
[051] The first hanger brackets assembly (7) is rigidly attached to the chassis
frame (8) of the vehicle by conventional means bolts and nuts. A first pair of pivot holes (24) is provided in the first hanger brackets assembly (7) which is used for connecting the first upper control arm (10) and the first lower control arm (11) pivotally by the first pivot bolts (24) and nuts. It is made of fabrication process. A special attention is given to design the hanger bracket (7) that it has high bending stiffness to withstand loads

experienced in the self steer lift axle suspension system (6). The first hanger bracket assembly (7) consists of a first U shaped hanger plate (25), first L shaped support plate (26), two first stiffener plates (27AA, 27BA) and a first connecting plate (28). The first stiffener plates (27AA, 27BA) are welded with the first U shaped hanger plate (25). They are provided to bear a cornering load experienced in the first hanger bracket assembly (7). The first U shaped hanger plate (25) and first L shaped support plate (26) are weld together with the first connecting plate (28).
[052] The second hanger brackets assembly (7A) is rigidly attached to the
chassis frame (8) of the vehicle by conventional means bolts and nuts and extended downwardly there-from. A second pair of pivot holes (24A) is provided in the second hanger brackets assembly (7A) which is used for connecting the second upper control arm (10A) and second lower control arm (11 A) pivotally by the pivot bolts (24A) and nuts. It is made of fabrication process. A special attention is given to design the first and second hanger bracket assemblies (7, 7A) that it has high bending stiffness to withstand loads experienced in the self steer lift axle suspension system (6). The second hanger bracket assembly (7A) consists of a second U shaped hanger plate (25A), second L shaped support plate (26A), two second stiffener plates (27AB, 27BB) and a second connecting plate (28A). The second stiffener plate (27B) is welded with the second U shaped hanger plate (25A). It is provided to bear a cornering load experienced in the second hanger bracket assembly (7A). The second U shaped hanger plate (25A) and the second L shaped support plate (26A) are weld together with the second connecting plate (28A).
[053] The shape of the first upper control arms (10) is optimized using topology
optimization. It is a single piece control arm. The first upper control arm (10) is a solid rectangular cross section with appropriate chamber provided at the corners. It has a first hole (29) at the first leg (30) which is used to connect with the first lift air spring (16) by conventional bolts and nuts.
[054] The shape of the second upper control arm (10A) is optimized using
topology optimization. It is a single piece control arm. The second upper control arm (10A) is a solid rectangular cross section with appropriate chamber provided at the corners. It has a second hole (29A) at the second leg (30A) which is used to-connect with the second lift air spring (16A) by conventional bolts and nuts.

[055] The shape of the first and second lower control arms (11, 11 A) are also
optimized by topology optimization. . In order to reduce weight and to have in single piece of the first and second lower control arms (11), many first and second holes (31, 31 A) are provided in the respective lower control arms. The first and second lower control arms (11, 11 A) are made of casting process to ensure a high reliability and maintain a uniform quality.
[056] Both the first upper control arm (10) and first lower control arm (11) have
first eyes (32) (a hollow cylindrical profile for providing pivotal linkage with hanger brackets assembly and lower beam brackets) at both ends, in which rubber bushings (23) are forcibly inserted. The shape of first upper and lower control arms (10, 11) is more efficient to resistance to bending, buckling and torsion. The first upper control arm (10) and the first lower control arm (11) are pivotally connected between the first hanger bracket assembly (7) and the first lower beam bracket (9) about the first pivotal points (24) in such a way that the first upper control arm (10) and the first lower control arm (11) are always parallel to each other when they rotate clockwise or counter clockwise direction about the first pivotal points (24) as seen Figure 3; thereby both the first upper and lower control arms (10,11) and second upper and lower control arms (10A, 11 A) act as a couple in lifting the axle assembly (15) in the upward or in the downwardly, desirably.
[057] Both the second upper control arm (10A) and second lower control arm
(11 A) have second eyes (32A) (a hollow cylindrical profile for providing pivotal linkage with hanger brackets assembly and lower beam brackets) at both ends, in which rubber bushings (23) are forcibly inserted. The shape of second upper and lower control arms (10A, 11 A) is more efficient to resistance to bending, buckling and torsion. The second upper control arm (10A) and the second lower control arm (11 A) are pivotally connected between the second hanger bracket assembly (7A) and the second lower beam bracket (9A) about the second pivotal points (24) in such a way that the second upper control arm (10A) and the second lower control arm (11 A) are always parallel to each other when they rotate clockwise or counter clockwise direction about the second pivotal points (24A) as seen Figure 3; thereby both the first upper and lower control arms (10, 11) and second upper and lower control arms (10A, 11 A) act as a couple in lifting the axle assembly (15) in the upward or in the downwardly, desirably.
[058] The first lower beam bracket (9) is made of fabrication process. Tne first
lower beam bracket (9) is provided with two first pivot holes (33) for providing pivotal

connection to the first upper control arm (10) and the first lower control arm (11) at their respective front ends. It has four first holes (34) at bottom side, which are used to connect the axle assembly (15). At the top side, it has another four first holes (35) which are used to attach the first ride air spring (13). Main function of the first and second lower beam brackets (9, 9A) are to hold the axle (36, Figure 3) and it should have a caster angle which is provided to have a required self steer-ability in the lift axle suspension system (6). In order to maintain a predetermined caster angle(~5-6degree), which assists to self-turning of the wheels, first bottom plate (37) of the first lower beam bracket (9) is made in a desired angle with respect to the first top plate (38) of the first lower beam bracket (9).
[059] The second lower beam bracket (9A) is made of fabrication process. The
second lower beam bracket (9A) is provided with two second pivot holes (33A) for providing pivotal connection to the second upper control arm (10A) and the second lower control arm (11 A) at their respective front ends. It has four second holes (34A) at bottom side which are used to connect the axle assembly (15). At the top side, it has another four second holes (3 5A) which are used to attach the second ride air spring (13A). Main function of the first and second lower beam brackets (9, 9A) are to hold the axle (36, Figure 3) and it should have a caster angle which is provided to have a required self steer-ability in the lift axle suspension system (6). In order to maintain a predetermined caster angle(~5-6degree), which assists to self-turning of the wheels, second bottom plate (3 7 A) of the second lower beam bracket (9A) is made in a desired angle with respect to the second top plate (3 8 A) of the second lower beam bracket (9A).
[060] The hanger to hanger cross member (12) has a U shaped plate (39). The
hanger1 to hanger cross member (12) is connected in between the first and second hanger bracket assemblies (7, 7A) attached with both sides of chassis frame (8) through four slotted holes (40) provided at the both ends (41) of the U shaped plate (39). In order to connect the first and second swinging bracket (17, 17A), a first and second L shaped plates (42, 42A) with first and second stiffener plates (43, 43A) are welded with the U shaped plate (39). The hanger to hanger cross member (12) provided in the self steer lift axle suspension system (6) withstands the cornering load experienced in the first and second hanger bracket assemblies (7, 7A).
[061] The first air spring bracket (14) consists of a first bottom flat plate (44),
first L shaped plate (45), first stiffener plate (46) and first U shaped plate (47). The first L shaped plate (45) is welded vertically with the first bottom flat plate (44). In the present

embodiment, the first ride air spring (13) is attached with the chassis frame (8) with an offset. Therefore, a first stiffener plate (46) is welded with the first L shaped plate (45) and first bottom flat plate (44). In addition, a first U shaped plate (47) is welded on the first bottom flat plate (44) which is used to maintain an appropriate ride height in the first ride air spring (13).
[062] The second air spring bracket (14A) consists of a second bottom flat plate
(44A), second L shaped plate (45A), second stiffener plate (46A) and second U shaped plate (47A). The second L shaped plate (45A) is welded vertically with the second bottom flat plate (44A). In the present embodiment, the second ride air spring (13A) is attached with the chassis frame (8) with an offset. Therefore, a second stiffener plate (46A) is welded with the second L shaped plate (45A) and second bottom flat plate (44A). In addition, a second U shaped plate (47A) is welded on the second bottom flat plate (44A) which is used to maintain an appropriate ride height in the second ride air spring (13 A).
[063] The first swinging bracket (17) consists of a first circular plate (48) and
first U bent plate (49) and first tube (50). The first tube (50) is welded with the first U bent plate (49) to make a pivot hole. It is welded with the first circular plate (48). The first circular plate (48) has two first holes (51) which are provided to attach the first lift air springs (16) within. First and second swinging brackets (17, 17A) are pivotally attached with the hanger to hanger cross member (12) using first and second pivot bolts (53, 53A) and first and second L brackets (52, 52A).
[064] The second swinging bracket (17A) consists of a second circular plate
(48A) and second U bent plate (49A) and second tube (50A). The second tube (50A) is welded with the second U bent plate (49A) to make a pivot hole. It is welded with the second circular plate (48A). The second circular plate (48A) has two second holes (51 A) which are provided to attach the second lift air springs (16A) within.
[065] The first rebound stopper belt assembly (20) consists of a first belt (54), a
first top mounting bracket (55), a first pair of pivot bolts (56), a first pair of pivot bolt sleeves (57), and a first bottom mounting bracket (58). The first bottom mounting bracket (58) is made of two Z bent plates and welded together. It has a first pivot hole (59) which is used to pivot the first belt (54) at bottom side. The first top mount bracket (55) is securely attached with the chassis frame (8). One pivot bolt is welded with the first top

mount bracket (55) in which the first belt (54) is pivotally attached using the first pivot bolt sleeve (57) at top side. Other end of the first belt (54) is pivotally attached with the first bottom mounting bracket (58) by using the first pivot bolt sleeve (57) and the first pivot bolts (56) and nuts. The first bottom mounting bracket (58) securely attached with the first pivot bolts (33) of the first lower beam bracket (9).
[066] The second rebound stopper belt assembly (20A) consists of a second belt
(54A), a second top mounting bracket (55A), a second pair of pivot bolts (56A), a second pair of pivot bolt sleeves (57A), and a second bottom mounting bracket (58A). The second bottom mounting bracket (58A) is made of two Z bent plates and welded together. It has a second pivot hole (59A) which is used to pivot the second belt (54A) at bottom side. The second top mount bracket (55A) is securely attached with the chassis frame (8). One pivot bolt is welded with the second top mount bracket (55A) in which the second belt (54A) is pivotally attached using the second pivot bolt sleeve (57A) at top side. Other end of the second belt (54A) is pivotally attached with the second bottom mounting bracket (58A) by using the second pivot bolt sleeve (57A) and the second pivot bolts (56A) and nuts. The second bottom mounting bracket (58A) securely attached with the second pivot bolts (3 3 A) of the second lower beam bracket (9A).
[067] The first external jounce bump stopper (19) is securely attached with the
chassis frame (8). It consists of a first mounting bracket (60) and a first polyurethane or nylon stopper pad (61). The first mounting bracket (60) is a first L bent plate, made of fabrication process. To withstand the impact load, exerted in the axle (36), a first stiffener plate (62) is welded at the center of the first L bent plate. At the bottom, two first holes (63) are provided. It is used to attach the first polyurethane or nylon stopper pad (61). The first polyurethane or nylon stopper pad (61) has concave shape. In order to attach the first polyurethane or nylon stopper pad (61) with the first mounting bracket (60), two first screws (64) are molded within. When the axle (36) is lifted, the first upper control arm's eye (32) end hits the first polyurethane or nylon pad (61); thereby the jounce height is limited.
[068] The second external jounce bump stopper (19A) is securely attached with
the chassis frame (8). It consists of a second mounting bracket (60A) and a second polyurethane or nylon stopper pad (61 A). The second mounting bracket (60A) is a second L bent plate, made of fabrication process. To withstand the impact load, exerted in the axle (36), a second stiffener plate (62A) is welded at the center of the second L bent plate. At the bottom, two second holes (63 A) are provided. It is used to attach the second polyurethane or nylon stopper pad (61A). The second polyurethane or nylon stopper pad

(61 A) has concave shape. In order to attach the second polyurethane or nylon stopper pad (61 A) with the second mounting bracket (60A), two second screws (64A) are molded within. When the axle (36) is lifted, the second upper control arm's eye (32A) end hits the second polyurethane or nylon pad (61 A); thereby the jounce height is limited.
[069] The self steer lift axle suspension system (6) is provided with first and
second steering stabilizers (21, 21 A) for maintaining cornering stiffness (lateral stiffness) of the axle assembly (15). First steering stabilizer (21) is pivotally connected with first track rod lever (18) of the axle assembly (15) at its one end, and with the first lower beam bracket (9) at its other end. A second steering stabilizer (21 A) is pivotally connected with the second track rod lever (18A) of the axle assembly (15) at its one end, and the second lower beam bracket (9A) at its other end. This first and second steering stabilizers (21) are especially used for maintaining a desired cornering performance criteria (i.e., cornering stiffness) of the self steered lift axle suspension system (6). The first and second steering stabilizer (21, 21 A) dampens 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.
[070] The self steer lift axle suspension system (6) is provided with a control
system (not shown) consists of direction control valve, a control box and an electrical switch. The control system provides a required air to the first and second ride air springs (13,13A) 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 first and second ride air springs (13,13A) of the self steer lift axle suspension and inflates the first and second lift air springs (16, 16A). The first and second lift air springs (16, 16A) are expanded. Therefore, the first and second upper control arm (10, 10A) and first and second lower control arm (11, 11 A) are rotated counter clockwise about the first and second pivotal points (34, 34A). Thereby, the vehicle axle assembly (15) is lifted from the road surface and maintained at required distance from the road surface.
[071] A unique of the present invention is the position of control arms (10,10A,
11, 11A) in the self steer lift axle suspension system (6). The control arms (10,10A, 11, 11A) and first and second ride air springs (13, 13A) are properly positioned in such a way that the first and second ride air springs (13, 13A) are operated in a least lateral offset, which prevents the premature failure of first and second ride air springs (13,13A).

[072] Another unique of the present invention is the design of first and second
upper control arms (10, 10A). It is made of casting process. The first upper control arm (10) is pivotally attached with the first hanger bracket assembly (7) and the first lower beam bracket (9). The second upper control arm (10A) is pivotally attached with the second hanger bracket assembly (7A) and the second lower beam bracket (9A).
[073] Similarly, another unique of the present invention is the design of first and
second lower control arms (11,11A). It is also made of casting process. It is one of the advantages of the present design of self steer lift axle. In addition, the shape of both the first and second upper control arms (10, 10A) and first and second lower control arms (11, 11A) are more efficient to resistance to bending, buckling and torsion. The geometrical shape of the control arms (10,10A, 11,11 A) enables reduction in the amount of complexity in manufacturing with consequent advantage in terms of weights and costs.
[074] Yet another advantage of the present invention is the use of less packaging
area to mount the lift axle air suspension system (6) in the chassis frame (8). As the hanger to hanger cross member (12) is packaged within the first and second hanger bracket assemblies (7, 7A), the self steer lift axle suspension system (6) can be fit in the rigid vehicle and tractor which have limited package area at the rear end of the vehicle. The present invention can be used in the vehicle having single rear drive axle as well as tandem rear axles (i.e., two or more rear axles) in which the tag axle can be lifted if the present lift system is fitted in the tag axle.
[075] Another unique of the present invention is that employing external stoppers
(19,20). That is, first and second jounce stoppers (19, 19A) and first and second rebound stoppers (20, 20A). They limits the dynamics operation height (i.e., addition of jounce height and rebound height) of the air springs (13,13A 16, 16A). The external stoppers (19,20) are used to mimmize the premature failure of the first and second ride air springs (13, 13A) and first and second lift air springs (16, 16A). The first and second jounce stoppers (19, 19A) are securely attached with the chassis frame (8) just above first and second lower beam brackets (9, 9A) respectively. When the axle (36) is lifted the first and second upper control arm eye (32, 32A) touches the first and second polyurethane or nylon pad (61, 61A) respectively; such that the lift height of the axle (36) is limited. If the first and second lift air springs (16, 16A) experience a failure, such failure will in turn

affect the first and second upper control arm (10, 10A) as these parts are interlinked to each other. The inclusion of the external stoppers (19, 20) not only limits the dynamic travel height of the suspension but also protects the first and second upper control arms (10,10A).
[076] Similarly, to limit the rebound height of the self steer lift axle suspension
(6) the first and second rebound resilient belts (54, 54A) are used. One end of each first and second resilient belts (54, 54A) are pivotally connected with the chassis frame (8). Other end of each first and second resilient belts (54, 54A) are pivotally connected to the first and second lower beam bracket (9, 9A) respectively. The resilient belt used in the embodiment of the present invention is made up of nylon.
[077] The foregoing description is a specific embodiment of the present
invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

WE CLAIM:
1. A self steer lift axle suspension system (6) comprises:
a first ride air spring (13) connected in between a first spring bracket (14) and a first lower beam bracket (9);
a second ride air spring (13 A) connected in between a second spring bracket (14A) and a second lower beam bracket (9A);
a first lift air spring (16) connected in between a first upper control arm (10) and a hanger to hanger cross member (12);
a second lift air spring (16A) connected in between a second upper control arm (10A) and the hanger to hanger cross member (12);
characterized in that
the first upper control arm (10), a first lower control arm (11), the second upper control arm (10A) and a second lower control arm (11 A) acts jointly in lifting a axle assembly (15).
2. A self steer lift axle suspension system (6) according to claim 1, wherein
a first rebound stopper belt assembly (20), which limits the rebound height of the self steer lift axle suspension system (6), is attached in between a chassis (8) and the first lower beam bracket (9);
a second rebound stopper belt assembly (20A), which limits the rebound height of the self steer lift axle suspension system (6), is attached in between the chassis (8) and the second lower beam bracket (9A);
a first external jounce stopper (19), which limits the jounce height of the self steer lift axle suspension system (6), is securely attached to the side of the chassis frame (8);
a second external jounce stopper (19A), which limits the jounce height of the self steer lift axle suspension system (6), is securely attached to the other side of the chassis frame (8).

3. A self steer lift axle suspension system (6) according to claim 1, wherein
the first upper control arm (10) and the first lower control arm (11) rotates counter clockwise about a first pivotal point (34) and the second upper control arm (10A) and the second lower control arm (11A) rotates counter clockwise about a second pivotal point (34A) when the first lift air spring (16) and the second lift air spring (16A) are expanded.
4. A self steer lift axle suspension system (6) according to claim 2, wherein
a first rebound resilient belt (54) is connected in between the chassis frame (8) and the first lower beam bracket (9);
a second rebound resilient belt (54A) is connected in between the chassis frame (8) and the second lower beam bracket (9A).
5. A self steer lift axle suspension system (6) according to claim 2, wherein
a first polyurethane pad (61) attached to the bottom of the first mounting bracket (60) of the first external jounce stopper (19) collides with a first upper control arm's eye (32) when a axle (36) gets over lifted;
a second polyurethane pad (61 A) attached to the bottom of the second mounting bracket (60A) of the second external jounce stopper (19A) collide with a first upper control arm's eye (32A) when the axle (36) gets over lifted.
6. A self steer lift axle suspension system (6) according to claim 1, wherein
a first steering stabilizer (21) is pivotally connected in between a first track rod lever (18) of the axle assembly (15) and the first lower beam bracket (9);
a second steering stabilizer (21 A) is pivotally connected in between a second track rod lever (18A) of the axle assembly (15) and the second lower beam bracket (9A).
7. A self steer lift axle suspension system (6) according to claim 1, wherein

a first swinging plate (17) holds the first lift air spring (16) in between the first upper control arm (10) and hanger to hanger cross member (12);
a second swinging plate (17A) holds the second lift air spring (16A) in between the second upper control arm (10A) and hanger to hanger cross member (12).
8. A self steer lift axle suspension system (6) according to claim 1, wherein
the first upper control arm (10), the first lower control arm (11), the second upper lower control arm (10A) and the second lower control arm (11 A) are manufactured utilizing casting process.
9. A self steer lift axle suspension system (6) according to claim 1, wherein
the first upper control arm (10) and the first lower control arm (11) is pivotally attached in between a first hanger bracket assembly (7) and the first lower beam bracket (9).
10. A self steer lift axle suspension system (6) according to claim 1, wherein
the second upper control arm (10A) and the second lower control arm (11A) is pivotally attached in between a second hanger bracket assembly (7A) and the second lower beam bracket (9A).