FIELD OF INVENTION

[001] The present invention relates to a suspension system for a vehicle, and more particularly to a trailing arm air suspension system having air springs and trailing arms integrated with the rear drive axle of the vehicle.

BACKGROUND OF INVENTION

[002] Suspension systems have been designed and developed for supporting the weight of the road vehicles. Many vehicles are equipped with a steel suspension system, composed of coil springs or leaf springs. The suspension system in general has leaf spring elements and damping elements. The simple leaf spring suspension is still commonly used in trucks and buses in developing countries; because of its robustness and simplicity in manufacturing. It is very compliant in vertical direction, laterally rigid and capable of carrying heavy loads. However, the leaf springs generally have greater weight than other type of springs such as air spring and coil spring with equivalent weight carrying capabilities. In addition, a great deal of work and mechanical knowledge would be required to detail design of the traditional leaf spring suspension and coil spring suspension.

[003] Air spring suspension replaces the steel components with heavy-duty rubber airbags that can be inflated and deflated. Air spring suspension system has several advantages over the traditional steel spring suspension. The most important benefit of the air spring suspension is that it allows to easily adjusting the ride height. In addition, the degree of (i.e., value of/amount of) stiffness of the suspension can be adjusted to the load that is being hauled, the vehicle is made more adaptable and safety is improved. A major limiting factor is that the conventional vehicle air suspensions must account for lateral stability of the axle and offer a degree of lateral stability. One typical (i.e., conventional) means for providing lateral stability is to use of a torque rod (i.e., track rod) coupled in between the frame and a component of the axle or suspension.

[004] Vehicles that are equipped with air spring suspension systems can be driven over a variety of terrains as it maintains a smoother ride and better handling. This is achieved, because an air spring works on a closed volume of compressed air at a desired pressure. Therefore, it gives to the driver and/or passengers a greater feel when the vehicle is operated on the road. Moreover, the air suspension maintains a good tire contact (with road surface). Therefore, tire wear is also reduced. Thus, the air suspension system will save money in the long run as less expenditure (i.e., spend) for tires, as well as other components such as axles and tie-rods, that may be affected by inadequate leaf spring suspensions and coil spring suspension. The smoother ride offered by air spring also will result in a steady, constant aim of the headlights, further improving safety. Those in favor of street modifications will find that an air spring suspension system also is effective in creating the low-rider look. Furthermore, buses and trucks with air springs are also easier to raise or lower.

[005] In terms of function, leaf spring suspensions are much simpler, since the axle is suspended by the steel spring, and does not require the complicated suspension geometry. Leaf springs are much stronger, and are capable of handling much higher loads with less deflection than air springs.

[006] Air suspension systems have been developed to the passenger vehicles such as mini bus, midi bus and trucks. Various rear air suspension systems such as parallelogram air suspension system, trailing air suspension system are designed and developed for improving the ride comfort of the vehicle. The rear air suspension systems are used with single drive axle and tandem axles of buses, trucks and tractors.

[007] The trailing arm air suspension is used in bus and trucks for many decades. The trailing arm suspension system is literally that-a suspension arm is joined at the front to the chassis, allowing the rear to swing up and down. More clearly, the trailing arm air suspension comprises a trailing arm having one end is pivotally connected to the chassis frame through a hanger bracket and another end is connected to the vehicle frame by an air spring. A pair of trailing arms supports a drive axle or auxiliary axle (i.e., pusher and tag axle) which includes wheel. Road induced reaction forces acting on the wheels are controlled by the pivoting of the trailing arm in response to these forces being resisted by the air spring. The trailing arm air suspension can be easily attached with the existing chassis frame with minimal changes in the frame structure. In addition, the construction of the trailing arm air suspension is usual and simple which is compared to parallelogram air suspension. In addition, the trailing arm air suspension system has low price compared to other air suspension systems. Therefore, the trailing arm air suspension is more preferable for developing low cost buses and trucks.

[008] FIG.l shows the conventional trailing arm air spring suspension (1) (i.e., trailing arm Z leaf under-slung air suspension) for the vehicle having single rear drive axle. The conventional trailing arm air spring suspension (1) consists of hanger brackets (2), trailing arm leafs (3), air springs (4), air spring mounting brackets (5), leaf seats (6), torque rod (7) (i.e., track rod), shock absorbers (not shown), U brackets (8), U bolts (9) and axle bracket (10). The hanger brackets (2) are attached with the chassis side frames. The trailing arm leafs (3) are pivotally connected with the hanger brackets (2). The air springs (4) are mounted at the trailing arm leafs (3) ends and attached with the vehicle chassis frame through air spring mounting brackets (5). The drive axle of the vehicle is clamped with the trailing arm leaf (3) (near to the center) by using the U bracket (8), U bolts (9), and axle bracket (10). The torque rod (7) is connected in between the chassis frame and rear drive axle. The shock absorbers (not shown) are connected in between the chassis frame and axle bracket (10). An air supply system and level sensing valve (not shown) are used to maintain a constant ride height of the rear drive axle in the vehicle. When the vehicle is operated in a smooth road/good road (i.e., road has less undulated), in general, the track rod (7), which is provided for lateral stability, is not required. At the same time, when the vehicle is operated in an undulated road, the track rod (7) or a system should be incorporated for maintain a required lateral stability of the vehicle. Therefore to increase the lateral stability of the vehicle in the present invention, partial load exerted on the rear drive axle is shared, the cornering load experienced in the suspension system is endured, and a constant height of the suspension system is maintained.

[009] Generally, the conventional trailing arm rear air suspension system (1) is used in both the buses and trucks. In these vehicles, many failures are observed in the conventional trailing arm rear air suspension system (1). Especially, many failures are observed in the shock absorber where in the rubber bushing and eye end welding. Many cracks are observed in the chassis where the torque rod (7) is attached with the chassis frame of bus in which low thickness frame is used compared to trucks. It is mainly due to entire cornering load that acts on the rear axles is transferred to the chassis frame through the torque rod (7). That is, the entire load leads a high stress concentration in a small portion (track rod pivotally attached area) of the chassis frame. It is, usually, solved by adding a small stiffener plate at the region of chassis frame where higher stress is experienced.

[010] In addition, the position of track rod (torque rod (7)) in the conventional trailing arm rear air suspension (1) limits the desired design of the bus floor in a flat. More clearly, the torque rod (7) is mounted on the rear axle. It limits to maintain a required height of the bus floor. To solve such problem, a ramp is usually provided in the bottom side of the bus body where the rear axle is located; otherwise, the track rod (7) is connected in between the chassis frame and end of the trailing arm leaf (3) by suitable brackets and bar pin rubber joints (not shown). However, it needs more space and the chassis frame is subjected a high torsional stress.

[011] Numerous mechanisms and methods are employed in the vehicle for solving above said problems in the conventional trailing arm rear air suspension system (1). Despite the many designs, only a few mechanisms are commercially viable due to important factors such as easy manufacturability, simple function, low maintenance, high reliability, easy assembly and serviceability. Therefore, it is desirable to provide a reliable and more stable rear air suspension system with wide load distribution to the chassis frame for the bus and trucks.

OBJECT OF THE INVENTION

[012] An object of the present invention is to provide a simple rear air suspension system.

[013]Yet another object of the present invention is to provide trailing arm air suspension system, which should improve ride and handling of the vehicle.

[014] Another object of the present invention is to provide a trailing arm air suspension system, which should have more reliable.

[015] Another object of the present invention is to provide a trailing arm air suspension system, which should not have lubricated joints.

[016] Another object of the present invention is to provide a trailing arm air suspension system, which should have more lateral stability like leaf suspension system.

[017] Another object of the present invention is to provide a trailing arm air suspension system, which should have high roll stability.

[018] Another object of the present invention is to provide a trailing arm air suspension system, which has minimal change in the existing rear drive axle.

[019] Another object of the present invention is to provide a trailing arm air suspension system, which should withstand dynamic loads and shocks.

[020] Yet another object of the present invention is to provide a trailing arm air suspension system, which should be retrofit-ably mountable in the vehicle.

SUMMARY OF THE INVENTION

[021] The trailing arm air suspension system consists of first and second trailing arm leafs , first and second hanger brackets, first and second air springs, first and second catch plates, first and second leaf springs, first and second spring shackle assemblies, first and second spring brackets, six rubber bushings, first and second belts assemblies, first and second axle holding assemblies, first and second air spring mounting brackets a transverse beam assembly and a pneumatic control system. The first and second hanger brackets are securely attached with chassis's side frame by conventional bolts and nuts. The first and second trailing arm leafs are pivotally attached to the first and second hanger bracket respectively. Center portion of the first and second trailing arm leafs and the first and second leaf springs are clamped with the rear drive axle using the first and second axle holding assemblies. First and second eye end of the first and second leaf springs are pivotally connected with first and second spring shackle assemblies which are pivotally connected with the first and second spring brackets respectively. The first and second spring brackets are securely attached with the chassis side frame by conventional manner. The first and second leaf springs and the first and second spring shackle assemblies are mainly used to increase the lateral stability of the suspension. A first and second jounce stopper assemblies are securely attached with the chassis frame just above the rear drive axle. First and second belt assemblies are pivotally attached in between the chassis frame and rear drive axle. The first and second jounce stopper assemblies and the first and second belt assemblies are used to limit the dynamic travel height of the air suspension when it is operated in undulated roads; so that angle between propeller shaft ( not shown) of the vehicle and the rear drive axle is maintained with in a required angle. It is to minimize the pinion gear failure of differential gear box which is used in the rear drive axle and to prevent the failure of air spring by over extension. The incorporation of the first and second jounce stopper assemblies and first and second belt assemblies further ensures the lateral stability by preventing the air springs from failure. The first and second air springs are connected in between the first and second trailing arm leafs and the first and second air bellows mounting brackets which is securely attached with the chassis frame. The first and second air springs are inflated and maintained at a required pressure and a constant ride height using by the pneumatic control system.

BRIEF DESCRIPTION OF THE DRAWINGS

[022] The invention will be discussed in greater detail with reference to the accompanying Figures.

[023] FIG.l shows a conventional rear air suspension system.

[024] FIG.2 shows an assembled model of a trailing arm air suspension system fitted in a chassis frame of bus, in accordance with an exemplary embodiment of the present invention.

[025] FIG.3 illustrates the details of the trailing arm air suspension system, in accordance with an exemplary embodiment of the present invention.

[026] FIG.4 illustrates the hanger bracket, in accordance with the embodiment of the present invention.

[027] FIG.5 illustrates the trailing arm leaf, in accordance with an exemplary embodiment of the present invention.

[028] FIG.6 illustrates the leaf spring, in accordance with an exemplary embodiment of the present invention.

[029] FIG.7 illustrates the axle holding assembly, in accordance with the embodiment of the present invention.

[030] FIG. 8 illustrates the spring bracket, in accordance with the embodiment of the present invention.

[031] FIG.9 illustrates the spring shackle assembly of the trailing arm air suspension system, in accordance with an exemplary embodiment of the present invention.

[032] FIG. 10 illustrates the jounce stopper assembly, in accordance with the embodiment of the present invention.

[033] FIG. 11 illustrates the air springs bracket, in accordance with the embodiment of the present invention;

[034] FIG. 12 illustrates the transverse beam assembly, in accordance with the embodiment of the present invention;

[035] FIG. 13 illustrates the belts assembly, in accordance with the 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 INVENTION

[036] Referring to FIG. 2, an assembled model of a trailing arm air suspension system (11) attached in a chassis frame (26) is illustrated, in accordance with an exemplary embodiment of the present invention. The trailing arm air suspension system (11) is especially used for both the bus and truck having single rear drive axle (27). The trailing arm air suspension system (11) consists of a first and second trailing arm leafs (12, 12A) and first and second air springs (14, 14A) which are attached to the vehicle's chassis frame (26) and vehicle's rear drive axle (27).

[037] The first and second hanger brackets (13, 13A) are made of conventional fabricating process. A special attention is given to design the first and second hanger brackets (13,13 A) as it withstands the loads acting on the rear drive axle (27) of the vehicle. The first and second hanger brackets (13,13 A) have wide footprint on the chassis frame (26) with multiples of holes (18) which reduce magnitude of stress in the region of chassis frame (26) where the first and second hanger brackets (13, 13A) are attached. A first and second pivot holes (35, 35A) are provided in the first and second hanger brackets (13, 13A) which are used for pivotally holding the first and second trailing arm leafs (12,12A).

[038] The first trailing arm leaf (12) is made of spring steel and bent to Z shape. It has first eyes (30) in both the ends and the center of the first trailing arm leaf (12) is bent into a required length to hold the first air spring (14) properly. The first air spring (14) is mounted with the bottom side of the chassis frame (26) without offset through first air spring mounting bracket (23); thereby a twist in the chassis frame (i.e., stress) caused by the first air spring (14) is minimized. The rubber bushing (20) is inserted in the first eye (36) of the first trailing arm leaf (12). Once the rubber bushing (20) is inserted, the first trailing arm leaf (12) is pivotally attached with the first hanger bracket (13). At the first tail of the trailing arm leaf (37) a first pair of holes (38) is provided which are used to attach the first air spring (14). At the center portion of the first trailing arm leaf (12), a first guide pin (i.e., cotter pin, 41) is provided. It is used to place the first trailing arm leaf (12) in a desired location of the rear drive axle (27). The first spring catch plate (15), is attached with the rear drive axle (27) along with first the trailing arm leafs (12). It is used to grab (capture) the first trailing arm leaf (12) if it is broken. In the present trailing arm air suspension system (11), one leaf is used as a trailing arm in each side of the rear drive axle (27). If it is broken, it may leads to tear the tire of the vehicle. To prevent such failure, the first and second catch plates (15,15A) are used along with the first and second trailing arm leafs (12,12A).

[039] The second trailing arm leaf (12A) is made of spring steel and bent to Z shape. It has second eyes (30A) in both the ends and the center of the second trailing arm leaf (12A) is bent into a required length to hold the second air spring (14A) properly. The second air spring (14A) is mounted with the bottom side of the chassis frame (26) without offset through second air spring mounting bracket (23A); thereby a twist in the chassis frame (i.e., stress) caused by the second air spring (14A) is minimized. The rubber bushing (20) is inserted in the second eye (36) of the second trailing arm leaf (12A). Once the rubber bushing (20) is inserted, the second trailing arm leaf (12A) is pivotally attached with the second hanger bracket (13 A). At the second tail of the trailing arm leaf (37 A) a second pair of holes (38A) is provided which are used to attach the second air spring (14A). At the center portion of the second trailing arm leaf (12A), a second guide pin (i.e., cotter pin, 41A) is provided. It is used to place the second trailing arm leaf (12A) in a desired location of the rear drive axle (27). The second spring catch plate (15 A) is attached with the rear drive axle (27) along with the second trailing arm leaf (12A). It is used to grab (capture) the second trailing arm leaf (12A) if it is broken. In the present trailing arm air suspension system (11), one leaf is used as a trailing arm in each side of the rear drive axle (27). If it is broken, it may leads to tear the tire of the vehicle. To prevent such failure, the first and second catch plates (15,15A) are used along with the first and second trailing arm leafs (12,12A).

[040] The first leaf spring (16) has a first Z shape bend (39) and first eyes (40) in both the ends. In the first eye ends (40), the rubber bushings (20) are forcibly inserted. After inserting the rubber bushing (20), one of the first eye end (40) of the first leaf spring (16) is privately connected to the first spring shackle assembly (17) and other end is pivotally clamped with the first belt assembly (21). Centre of the first leaf spring (16) is attached with the rear drive axle (27) along with the first trailing arm leafs (12) using the first axle holding assembly (22).

[041] The second leaf spring (16A) has a second Z shape bend (39A) and second eyes (40A) in both the ends. In the second eyes end (40A), the rubber bushings (20) are forcibly inserted. After inserting the rubber bushing (20), one eye end (40A) of the second leaf spring (16A) is privately connected to the second spring shackle assembly (17A) and other end is pivotally clamped with the second belt assembly (21 A). Centre of the second leaf spring (16A) is attached with the rear drive axle (27) along with the second trailing arm leafs (12A) using the second axle holding assembly (22A).

[042] The first axle holding assembly (22) consists of first U bracket (28), first axle seat bracket (29), first trailing arm seating bracket (33) and first U bolts and nuts (24). The first U bracket (28), first axle seat bracket (29), first trailing arm seating bracket (33) are made of conventional casting process. The first trailing arm seating bracket (33) is welded with the axle. It has a first locate hole (34) in which the first guide pin (41) of the first trailing arm leaf (12) is properly located; thereby the rear drive axle (27) is properly positioned with the first trailing arm leaf (12). The first U bracket (28) has a first projection (42). The first projection is used as jounce stopper for the trailing arm air suspension system (11). That is, it limits the upward movement of the rear axle (27) beyond a desired height (i.e., "jounce height" of air suspension) with the jounce stopper assembly (31) attached with the chassis frame (26) when the vehicle is operated in an undulated road. Similarly, the first belt assembly (21) is used to limits the downward movement of the rear drive axle (27) beyond a desired height (i.e., "rebound height" of air suspension). The first jounce stopper assembly (31) and the first rebound belt assembly (21) are provided in the suspension system to maintain the required dynamic travel height of the suspension; and; thereby ensure reliability of the trailing arm air suspension system (11) by preventing failure of first and second air springs (14,14A).

[043] The second axle holding assembly (22A) consists of second U bracket (28A), second axle seat bracket (29A), second trailing arm seating bracket (3 3 A) and second U bolts and nuts (24A). The second U bracket (28A), second axle seat bracket (29A), second trailing arm seating bracket (33 A) are made of conventional casting process. The second trailing arm seating bracket (3 3 A) is welded with the axle. It has a second locate hole (34A) in which the second guide pin (41 A) of the second trailing arm leaf (12A) is properly located; thereby the rear drive axle (27) is properly positioned with the second trailing arm leaf (12A). The second U bracket (28A) has a second projection (42A). The projection is used as jounce stopper for the trailing arm air suspension system (11). That is, it limits the upward movement of the rear axle (27) beyond a desired height (i.e., "jounce height" of air suspension) with the second jounce stopper assembly (31 A) attached with the chassis frame (26) when the vehicle is operated in an undulated road. Similarly, the second belt assembly (21 A) is used to limit the downward movement of the rear drive axle (27) beyond a desired height (i.e., "rebound height" of air suspension). The second jounce stopper assembly (31 A) and second rebound belt assembly (21 A) are provided in the suspension system to maintain the required dynamic travel height of the suspension; and; thereby ensure reliability of the trailing arm air suspension system (11) by preventing failure of first and second air spring (14.14A).

[044] The first spring bracket (19) is made of casting process. It has a first circular hole (43), two first ribs (44) and three first mounting holes (45). The first circular hole (43) is used for holding a rubber bushing (20). The two first ribs (44) are provided to strengthen the first spring bracket (19). The three first mounting holes (45) are used to attach the first spring bracket (19) with the chassis frame (26). A rubber bushing (20) is forcibly inserted in the first circular hole (43) .The rubber bushing (20) is a conventional single bonded rubber bushing. Rubber is molded directly on a steel sleeve (i.e., tube). The preferred durometer of bushing is about 60. The rubber bushing (20) damps the entire sock load experienced in the trailing arm air suspension system (11).

[045] The second spring bracket (19A) is made of casting process. It has a second circular hole (43A), two second ribs (44A) and three second mounting holes (45A). The second circular hole (43A) is used for holding a rubber bushing (20). The two second ribs (44A) are provided to strengthen the second spring bracket (19A). The three second mounting holes (45A) are used to attach the second spring bracket (19A) with the chassis frame (26). A rubber bushing (20) is forcibly inserted in the second circular hole (43A) .The rubber bushing (20) is a conventional single bonded rubber bushing. Rubber is molded directly on a steel sleeve (i.e., tube). The preferred durometer of bushing is about 60. The rubber bushing (20) damps the entire sock load experienced in the trailing arm air suspension system (11).

[046] The first spring shackle assembly (17) consists of a first pair of flat shackle plates (46) and first a pair of pivot bolts and nuts (47). The first spring shackle assembly (17) is pivotally connected in between the first leaf spring (16) and first spring bracket (19).

[047] The second spring shackle assembly (17A) consists of a second pair of flat shackle plates (46A) and a second pair of pivot bolts and nuts (47A). The second spring shackle assembly (17A) is pivotally connected in between the second leaf spring (16A) and the second spring bracket (19A).

[048] The first jounce stopper assembly (31) consists of a first jounce stopper bracket (48) and a first polyurethane sheet (49) in which multiples of first screws (50) are molded together. The first jounce stopper brackets (48) consists of a first L shaped plate (51) and first U shaped plate (52). They are welded together. The first L shaped plate (51) has four first holes (53) at side which are used to attach the first jounce stopper bracket (48) with the chassis frame (26) and four holes (not shown) at bottom side which is used to attach the first polyurethanes sheet (49). Polyurethane sheet (49) is molded with the first screws (50) in a conventional manner. Therefore, it can be securely attached with the first jounce stopper brackets (48) which are securely attached with the chassis frame (26). It is provided to limit the upward movement of the rear drive axle (27) (i.e., it acts as bump stopper and limits to over compression of the air spring); thereby, it protect the first and second air springs (14, 14A) from failure.

[049] The second jounce stopper assembly (31 A) consists of a second jounce stopper bracket (48A) and a second polyurethane sheet (49A) in which multiples of second screws (50A) are molded together. The second jounce stopper bracket (48A) consists of an second L shaped plate (51 A) and second U shaped plate (52A). They are welded together. The second L shaped plate (51 A) has four second holes (53 A) at side which are used to attach the second jounce stopper bracket (48A) with the chassis frame (26) and four holes (not shown) at bottom side which is used to attach the second polyurethanes sheet (49A). The second Polyurethane sheet (49A) is molded with the second screws (50A) in a conventional manner. Therefore, it can be securely attached with the second jounce stopper bracket (48A) which is securely attached with the chassis frame (26). It is provided to limit the upward movement of the rear drive axle (27) (i.e., it acts as bump stopper and limits to over compression of the air spring); thereby, it protect the first and second air springs (14,14A) from failure.

[050] The first air spring bracket (23) consists of a first lower flat plate (54), a first vertical plate (55), two first stiffener plates (56).The first lower flat plate (54) is welded with the first vertical plate (55) and the two first stiffener plates (56). Four holes (57) are provided in the vertical plate (55). The four first holes (57) are used to connect the first air springs bracket (23) with the chassis frame (26). Similarly, first lower flat plate (54) has two holes (not shown) which are used to connect with the first air springs (14) by mechanical means.

[051] The second air spring bracket (23A) consists of a second lower flat plate (54A), a second vertical plate (55A), two second stiffener plates (56A).The second lower flat plate (54A) is welded with the second vertical plate (5 5A) and the second stiffener plates (56A). Four second holes (57) are provided in the second vertical plate (55A). The four second holes (57A) are used to connect the second air springs bracket (23A) with the chassis frame (26). Similarly, second lower flat plate (54A) has two holes (not shown) which are used to connect with the second air springs (14A) by mechanical means.

[052] The transverse beam assembly (25) consists of a hat section bent plate (58) and Z bent plate (59). The transverse beam assembly (25) connects both the first training arm leaf (12) and the second trailing arm leaf (12A) at the respective tailing ends by four bolts and nuts (60). Two stiffener plates are welded with the Z bent plate (59) which is provided for strengthening (i.e., increasing bending stiffness) the transverse beam assembly (25). Two holes (61) are provided at each ends of the hat section bent plate (58) which is used to attach both the first and second air springs (14,14A) rigidly.

[053] The first belt assembly (21) consists of a first mounting bracket (32), a first pair of spacers (62); a first pair of pivot bolts (63 A, 63 AA); a first pair of split pins (64) and a first belt (65). The first mounting bracket (32) is a hat section bent plate having four first holes (66) at the four corners. The first belt assembly (21) is securely attached with the chassis frame (26) by conventional bolts and nuts. The first pair of spacers (62) are pivotally attached with the pivot bolt (63A) and bottom pivot bolts (63AA). The bottom pivot bolts (63AA) are connected with the first eye end (40) of the first leaf spring (16). The first belts (65) are freely placed over both the spacers (62) and locked using fastening means (63). In the present embodiment of the invention the fastening means (63) are first lock nuts (67), first pair of split pins (64) and the first pair of pivot bolts (63A,63AA).So that when the trailing arm air suspension system (11) is operated, the first trailing arm leaf (12) and rear drive axle (27) assembly swings with respective the first hanger bracket's (13) pivot bolts (35). That is, the assembly moves up and down according to the undulated condition and of road surface. During the operation, the first belt (65) rotates over the first pair of spacers (62) and limits the rebound travel height of the rear drive axle assembly (27).

[054] The second belt assembly (21 A) consists of a second mounting bracket (32A), a second pair of spacers (62A); a second pair of pivot bolts (63B, 63BB); a second pair of split pins (64A) and a second belt (65A). The second mounting bracket (32A) is a hat section bent plate having four first holes (66A) at the four corners. The second belt assembly (21 A) is securely attached with the chassis frame (26) by conventional bolts and nuts. The second pair of spacers (62A) are pivotally attached with the top pivot bolt (63B) and bottom pivot bolts (63BB). The bottom pivot bolts (63BB) are connected with the second eye end (40A) of the second leaf spring (16A). The first belt (65A) is freely placed over both the second spacers (62A) and locked using fastening means (63A). In the present embodiment of the invention the fastening means (63A) are the second pair of lock nuts (67A), the second pair of split pins (64A) and the second pair of pivot bolts (63B, 63BB). So that when the trailing arm air suspension system (11) is operated, the second trailing arm leaf (12A) and rear drive axle (27) assembly swings with respective the second hanger bracket (13A) pivot bolts (3 5A). That is, the assembly moves up and down according to the undulated condition and of road surface. During the operation, the second belt (65A) rotates over the second pair of spacers (62 A) and limits the rebound travel height of the rear drive axle assembly (27).

[055] After assembled the trailing arm air suspension system (11) with the vehicle chassis frame (26), compressed air is supplied to both the first and second air springs (14, 14A) using the pneumatic control system and a level sensing valve. It maintains a required a constant height with required pressure in both the first and second air springs (14,14A). The pneumatic control system and level sensing valve are not the part of present invention.

[056] A unique of the present invention is the incorporation of the first and second leaf springs (16, 16A) with the first and second spring shackle assemblies (17, 17A). As the first and second leaf springs (16,16A) share a partial load of the rear drive axle (27), the load is widely distributed to the chassis frame (26) and load experienced in the first and second hanger brackets (13, 13A) are also reduced substantially; thereby the life of the rubber bushing (20) in both the first and second trailing arm leafs (12, 12A), is considerably extended.

[057] The first and second leaf springs (16, 16A) and the first and second spring shackle assemblies (17, 17A) are mainly used to withstand the cornering load experienced in the suspension; thereby, the lateral stability of the suspension is increased. It is an alternative design solution of track rod (7) used in the conventional rear air suspension (1) system.

[058] Another unique of the present invention is the incorporation of first and second jounce stopper assemblies (31, 31 A) and the first and second belt assemblies (21, 21 A). The incorporation of said assemblies further ensures the lateral stability by the prevention of air springs (14,14A) from failure.

[059] Another unique of the present invention is the non-lubricated joints used in the suspension system. Conventional rubber bushes (20) are employed in all the pivot joints. They absorb the shocks experienced in the suspension system when the vehicle is operated in undulated road surface. Thereby, ride of the vehicle is substantially increased.

[060] Another unique of the present invention is the position of the first and second air springs (14, 14A). The first and second air springs (14, 14A) are positioned such that to avoid accordion effect (i.e., angular expansion of the first and second air springs (14, 14A). More clearly, the angle should not exceed 30 degree due to restriction in the first and second air springs (14,14A) construction.

[061] Yet another unique of the present invention is the design of first and second hanger brackets (13, 13A) and first and second spring brackets (19, 19A). The suspension system can be attached with the existing chassis frame retro-fitly.

[062] 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. It is evident to those skilled in the art that although the invention herein is described in terms of specific embodiments thereof, there exist numerous alternatives, modifications and variations of the invention. It is intended that all such modifications and alterations be included insofar as they come within the spirit and scope of the invention as claimed or the equivalents thereof. Hence all variations, modifications and alternatives that fall within the broad scope of the appended claims come under the gamut of the invention.

WE CLAIM:

1. A trailing arm air suspension system (11) comprises

a first leaf spring (16), which shares a partial load of a rear drive axle (27), clamped with the rear axle drive (27) along with a first trailing arm leaf (12);

a second leaf spring (16A), which shares the partial load of the rear drive axle (27), clamped with the rear axle drive (27) along with a second trailing arm leafs (12A);

a first spring shackle assembly (17), capable of withstanding a cornering load experienced in the suspension system, pivotally attached to the first leaf spring (16) and to a first spring bracket (19A);

a second spring shackle assembly (17A), capable of withstanding the cornering load experienced in the suspension system, pivotally attached to the second leaf spring (16A) and to a second spring bracket (19A);

a first air spring (14) and a second air spring (14A), which maintains a constant and shares the partial load, secured in between the rear drive axle (27) and the chassis frame (26);

2. A trailing arm air suspension system (11) according to claim 1, wherein

a first rebound belt assembly (21) is attached in between the chassis frame (26) and the first leaf spring (16) to limit the rebound travel height of the drive axle assembly

a second rebound belt assembly (21 A) is attached in between the chassis frame (26) and the second leaf spring (16A) to limit the rebound travel height of the drive axle assembly;

a first jounce stopper assembly (31) and a second jounce stopper assembly (31 A) which limits the jounce height of the rear axle (27) are attached to the chassis frame (26);

3. A trailing arm air suspension system (11) according to claim 2, wherein

the first rebound belt assembly (21) comprises a first pair of spacers (62), a first belt (65) a first mounting bracket (32) and a first fastening means (63), said first belt (65) rotates over the first pair spacers (62);

4. A trailing arm air suspension system (11) according to claim 2, wherein

the second rebound belt assembly (21 A) comprises a second pair of spacers (62A), a second belt (65A) a second mounting bracket (32A) and a second fastening means (63A), said second belt (65A) rotates over the second pair spacers (62A);

5. A trailing arm air suspension system (11) according to claim 2, wherein

the first jounce stopper assembly (31) comprises a first jounce stopper bracket (48) to which a first polyurethane sheet (49) is secured at the bottom of said first jounce stopper bracket (48).

6. A trailing arm air suspension system (11) according to claim 2, wherein

the second jounce stopper assembly (31 A) comprises a second jounce stopper bracket (48A) to which a second polyurethane sheet (49A) is secured at the bottom of the second jounce stopper bracket (48A).

7. A trailing arm air suspension system (11) according to claim 2, wherein
a first axle holding assembly (22) comprises a first U bracket (28), said first U bracket (28) has a first projection (42) on its top which, during vertical movement of the rear axle (27) hits the first polyurethane sheet (49) to limit the jounce height of the rear axle (27).

8. A trailing arm air suspension system (11) according to claim 2, wherein

a second axle holding assembly (22A) comprises a second U bracket (28A), said second U bracket (28A) has a second projection (42A) on its top which, during vertical movement of the rear axle (27) hits the second polyurethane sheet (49A) to limit the jounce height of the rear axle (27).

9. A trailing arm air suspension system (11) according to claim 1, wherein

a transverse beam assembly (25) is attached in between the first trailing arm leaf (12) and the second trailing arm leaf (12A) to securely hold the first air spring (14) and the second air spring (14A)