Field of invention:

The present invention relates to a load carrying member, particularly the present invention relates to a load carrying member of an air suspension system and process for manufacturing the same.

Background of the invention:

In heavy vehicles generally leaf springs are used to absorb or dampen the shocks received through the axels. Due to the high wear and tear in case of leaf springs, better ride comfort and better performance, now the present trend is to replace the leaf springs with air suspension systems.

The air suspension systems are generally used with axle of the vehicles. Figure 1 illustrates an air suspension system which is mounted on the chassis or frame of a vehicle and the axle of the vehicle. As shown in figure 1 , the air suspension system comprises four air bellows/ air springs and main load carrying assembly which comprises a pair of load carrying member. The air suspension system also comprises hanger assembly and outrigger assembly having horizontal members extending laterally outwardly from the chassis on both sides. As can be observed from figure 1 , the lateral members are provided so as to mount the air bellows below the chassis and symmetrically on both sides of the rear axles. As shown in figure 1, with the above constructions, there are two air bellows are disposed on both sides of the chssis. The air bellows disposed on each side of the chassis are supported by one load carrying member. Similarly, the air bellows disposed on other side of the chassis are supported by other load carrying member of the main load carrying assembly.

The air bellows take load from the chasis and simultaneously, transfers the load to the load carrying members. The load carrying members thus take all loads from the chassis and transfer the same to the wheels through rear axles. The load carrying member of the air suspension system is shown in figure 2. The load carrying member of the air suspension system also called as Cow Horn Beam since its shape look like a cow horn. The cow horn beam is a structural beam which caries the load of the chassis. The failure of this beam in vehicle running will leads to serious issues to the vehicle and passenger safety.

Traditionally, the load carrying member is made by stamping process where the two symmetrical half of the stamping are made to a shape and is welded as shown in figure 2 to form a box like component. The raw material for making this stamping is sheet and then the part is cut from this and bent to the required shape using press and dies. Figure 3 shows stamping sheet for manufacturing the conventional load carrying member.

Traditional process for manufacturing the load carrying member or cow horn beam comprises the following steps:

1. Profile cutting - CNC laser/plasma cutting machine

2. Heating - Walking beam furnace( with 7 burners - 40 sees cycle time)

3. Hot forming - 1000 ton hyd press

4. Trimming - SPM plasma/oxy fuel cutting or Robot cutting

5. Edge chamfering - SPM plasma/oxy fuel cutting or Robot cutting (Manual for protos)

6. Shot blasting - Inner surface cleaning

7. Manual painting - inner surface protection before painting

8. Tack welding - manual in fixture

9. Welding of cow horn - Robot welding in fixture

10. Drilling - Using jig and radial drilling machine or multi spindle drilling heads 1 1. Welding of Sub assembly - using fixtures and robot/manual

12. Inspection

13. Machining

14. Shot blasting - outer surface cleaning

15. Painting - outer surface protection

16. Marking/Stamping - for traceability

The number of steps involved in the above process = 16

Investment cost on machines/equipment/tooling:

The cost of investment on the machines for the above process estimated =Rs. 9.5 crores Product cost:

The estimated product cost of the part =Rs.33000

The process of manufacturing the cow-horn beam is very critical and should be consistent. Conventional process of making the load carrying member or cow horn beam uses welding of two stamped parts at the neutral axis. The process of welding needs lot of supervision and stringent process controls. If process controls are not maintained properly leads to defect part. The traditional process not only includes large number of process steps but also generates large amount of scrap which can be understood from the following example,

1. No of stamped parts required per suspension = 4 nos

2. Weight of each stamped part = 39 kgs

Weight of sheet = 1 130 kgs

No of parts from sheet = 15 nos

Raw material weight per part = 1 130/15 = 75 kgs

Total weight of Raw material required for suspension =75x4=300 kgs

3. % of scrap generation = (75-39)/75 = 48 % Figure 4 shows the main load carrying member assembly. As described earlier, the conventional main load carrying member is made by welding of the two symmetrical halves. The welding seam line (as shown in figures 2 and 4) is a weaker part and area of high stress concentration at high load conditions makes the load carrying member prone to get damaged.

The failure of the load carrying member or cow horn beam had lead to damage to passenger as well to the vehicle. Even though welding is a proven technology, the process of welding reliability depends on the process parameters/manual skill/ process consistency/selection of machine/thorough inspection. There are cases that even with so much tough controls, welding failures have been observed in existing beam and it took lot of money and efforts to fix the issue in the field. Therefore, there is a need exists to develop a load carrying member which overcomes the above problem.

Objects of the present invention:

The main object of the present invention is to provide a load carrying member or a load carrying beam.

Another object of the present invention is to provide a load carrying member or a load carrying beam of an air suspension system.

Still another object of the present invention is provide a load carrying member which avoids field failures of the air suspension by avoiding the conventional welding process.

Yet another object of the present invention is to provide a load carrying member or a load carrying beam or air suspension system which overcomes the at least one of the problem of the conventional load carrying member or cow-horn beam.

A further object of the present invention is to improve the safety and reliability of the suspension and thereby protect the parts, vehicle , passenger & cargo

One more object of the present invention is to provide a process for manufacturing the load carrying member which involves less number of steps and reduce scrap generation.

Summary of invention:

The present invention provides a novel load carrying member or load carrying beam for an air suspension system. The load carrying member of the present invention not only obviates the problem of frequent failure, it also involves less number of process steps of manufacturing.

Brief description of figures:

Figure 1 shows an air suspension system.

Figure 2 shows the conventional load carrying member or cow horn beam.

Figure 3 shows stamping sheet for manufacturing the main load carrying member of the prior art.

Figure 4 illustrates the conventional load carrying member assembly. Figure 5 shows the load carrying member according to an embodiment of the present invention.

Figure 6 shows a tube bending arrangement according to an embodiment of the present invention.

Figures 7(a), 7(b), 7(c) and 7(d) illustrates process steps for manufacturing the load carrying member according to an embodiment of the present invention.

Figure 8 shows load carrying member assembly according to an embodiment of the present invention.

Figure 9 shows an air suspension system with the load carrying member according to an embodiment of the present invention.

Detailed description of the invention:

Accordingly, the present invention provides a load carrying member for an air suspension system, said load carrying member is a seamless tube comprising a straight mid portion, a left end portion and a right end portion; each of the said left and right end portions being bent or curved with a predetermined radius of curvature so that the said straight mid portion and both the curved left and right end portions form a shape of a cross-section of bath tub; and wall of the tube at the bent portion having a thickness substantially same as the thickness of wall of the straight mid portion.

In an embodiment of the present invention the said seamless tube has a cross section selected from rectangular, circular, triangular or polygonal cross section.

In another embodiment of the present invention, the said seamless tube has a uniform cross section throughout the length of the load carrying member.

In one more embodiment of the present invention, the first end portion and the second end portion comprises a first open end and a second open end. In still another embodiment of the present invention the right and left end portions are bent at an angle in the range of 45 deg to 150 deg. In yet another embodiment of the present invention wherein each of the first end portion and the second end portion comprises a straight part of length T starting from the first open end and the second open end; where ratio of length (1) of straight part to the radius of curvature (R) of the bent portions i.e. 1 : R is in range of 0.2 to 1.

In a further embodiment of the present invention the wall thickness of the tube is in the range of 6 mm to 13 mm.

The present invention also provides an air suspension system for vehicle having a chassis or frame, said air suspension system comprising plurality of air bellows disposed across axle of the vehicle and mounted symmetrically below the chassis so as to take load from the chassis; said air bellows are supported by a pair of load carrying members disposed on each side of chassis; wherein each of the load carrying member is a seamless tube comprising a straight mid portion, a left end portion and a right end portion; each of the said left and right end portions being bent or curved with a predetermined radius of curvature so that the said straight mid portion and both the curved left and right end portions form a shape of a cross-section of bath tub; and wall of the tube at the bent portion having a thickness substantially same as the thickness of wall of the straight mid portion.

In an embodiment of the present invention the chassis is provided with lateral members outwardly extending on both sides of the chassis so as to mount the air bellows.

In another embodiment of the present invention the four air bellows are mounted on the chassis so that there are two air-bellows each side of the chassis.

The present invention also provides a process for manufacturing the load carrying member, said process comprising the steps of:

a. obtaining a seamless tube of a required length having a first end portion with a first open end, a mid portion and a second end portion with a second open end; b. rigidly holding one of the end portion using a split clamp coupled with a rigid swivel arm;

c. providing a split type bending die for supporting the first end portion from out side;

d. inserting a roller-chain mandrel inside the tube using a cylinder-piston type push mechanism; and

e. pushing the roller-chain mandrel and the tube together towards the bending die and swivel arm thereby bending the end portion.

In an embodiment of the present invention the roller chain mandrel comprises an elongated rigid member coupled with a roller chain; the rigid member is adapted to be coupled with the piston of the cylinder-piston type push mechanism.

Still another embodiment of the present invention comprising the steps of:

(a) rigidly holding the first end portion of the tube using the split clamp which is coupled with the rigid swivel arm;

(b) providing the split type bending dye for supporting the first end portion from outside;

(c) inserting the roller-chain mandrel inside the tube from the second open end using the piston-cylinder type push mechanism;

(d) pushing the roller-chain mandrel and the tube together towards the bending die and swivel arm which forces the first end portion towards the swivel arm thereby bending the first end portion.

Yet another embodiment of the present invention comprising the steps of:

(a) rigidly holding the second end portion at or near junction of second end portion and mid portion using the split clamp coupled with a swivel arm;

(b) providing the split type bending dye for supporting the second end portion from outside;

(c) providing a dummy tube disposed so that one end of the dummy tube abuts with the second end of the tube; (d) inserting the roller-chain mandrel through the dummy tube through the second open end using the piston-cylinder type push mechanism;

(e) pushing the roller-chain mandrel and the dummy tube together towards the bending die and swivel arm which forces the second end portion towards the swivel arm thereby bending the second end portion.

In a further embodiment of the present invention the swivel arm is a rigid arm mounted on a swivel base and adapted to swing about the said swivel base. The present invention is described with reference to the figures and specific embodiments; this description is not meant to be construed in a limiting sense. Various alternate embodiments of the invention will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such alternative embodiments form part of the present invention.

Accordingly, the present invention provides a load carrying member for an air suspension system. Figure 5 shows the load carrying member for the air suspension according to an embodiment of the present invention. As shown in figure 5, the load carrying member is a seamless tube or a hollow beam. The seam less tube can be of any suitable cross section. In an embodiment of the present invention, the cross section of the seamless tube can be rectangular, circular, triangle or polygonal. According to an embodiment of the present invention the seamless tube has a rectangular cross section (as shown in figure 5). Referring to figures 5 (a) and (b), the load carrying member (10) comprises a mid portion (20), a first end portion (30) and a second end portion (40). The mid portion (20) of the load carrying member is a straight portion. The first (30) and second end portions (40) are curved or bent portions having a predetermined radius of curvature. Length of the first end portion (30) can be different from length of the second end portion (40). In an embodiment of the present invention, the first end portion (30) and second end portion (40) are equal in length. As can be observed from figure 5, the curved first end portion (30) and curved second end portion (40) together with the straight mid portion (20) form a shape of a cross-section of bath tub. The radius of curvature (R) of the bent portions can be chosen on basis of type of vehicle. In an embodiment of the present invention the first end portion and second end portion have a first open end and a second open end. As shown in figure 5, both the first end portion and the second end portion comprise a straight part of length (1) starting from the respective open ends. In an embodiment of the present invention, the ratio of length of the straight part (1) to the radius of curvature (R) of the bent portion/part is in the range of 0.2 to 1. The bend created at both end portion of the tube is predetermined and selected based on the structure and load carrying capacity of the vehicle. The bend provided at both end portions for a particular vehicle will be same as that of such bends made on the conventional cow horn beam. According to another embodiment of the present invention the angle (a) at which the end portions of the tube are bent is in the range of 45 deg to 150 deg.

According to an embodiment of the present invention, the thickness of wall (t) of the bent portion is substantially same as the thickness of wall of the straight mid portion. The wall thickness (t) of the straight mid portion and the bent portions is in the range of 6 mm to 13 mm.

The seamless tube for manufacturing the load carrying member of the present invention can be made with the help of any suitable steel rolling methods. The seamless tube can be formed by passing steel billets through number of rolls to undergo size reduction and thereafter forming hollow sections by continuous rolling using mandrel and die.

The seamless tube can be made up of any suitable steel alloys or any other metallic material/alloys. According to a embodiment of the present invention the metallic material for making the seam less tube is S420NH steel per DIN std EN 10210 -1 : 2006. This is a typical fine grain steel grade with increased strength and possesses good bendability properties. The ultimate tensile strength of this material is 600 Mpa and yield strength is 420Mpa. The composition for the S420NH steel includes C- 0.22%, Mn - 1.35%, P-0.035%, S-0,03%, Si-0.6%, Cr-0.3%, Ni-0.8%, MO-0.1%.

Referring to figures 6 and 7(a)-{d), the present invention also provides a process for making the load carrying member for an air suspension system which broadly include the following steps,

(a) obtaining the seamless tube (4) having a first end portion (4f) with a first open end (4'), a second end portion (4s) with a second open end (4") and a mid portion (4m);

(b) cutting the seamless tube (4) to the required length; and

(c) bending the tubes using tube bending arrangement/ facility of the present invention.

Figure 6 illustrate a tube bending arrangement or facility for making the load carrying member according to an embodiment of the present invention. As shown in figure 6, the tube bending arrangement comprises a split clamp (1), a swivel base and arm (2), split type bending die (3), roller chain mandrel (5), push-mechanism (6).

Referring to figure 6, the split-clamp (1 ) locates, clamp and hold one end (4f) of the straight seamless tube. The split-clamp is connected with the swivel arm which is mounted on the swivel base. The swivel arm is a rigid arm which swivels about the swivel-base thereby for forcing the tube (4) to rotate along the radius R + (w/2) so as to form a bend portion of the seamless tube; In other words, the length of the arm is R + (w/2); where R is the radius curvature of bend and w is width of the cross section of the tube and w is the width of the cross section (as shown in figure 5(b). The push- mechanism (6) is a hydraulic piston-cylinder mechanism which pushes the seamless tube (4) and the roller chain mandrel (5) towards the bending die and swivel. The split type bending die (3) supports the tube from outside to avoid distortions and wrinkles. The roller chain mandrel (5) supports the tube (4) from inside to avoid distortion and wrinkles. Figures 7 (a)-(d) illustrate a steps for bending the seamless tube (4) for making the load carrying member according to an embodiment of the present invention. Figure 7(a) illustrates the step of forming a curved end portion (i.e. curved first end portion) of the seamless tube according to an embodiment of the present invention. Figure 7(a) shows the position just before the bending starts. As shown in figure 7(a), the first end portion (4f) of the seamless tube which is to be bent is clamped and located using the split clamp (1). At this position, the split type bending die (3) moves and supports the tube (4) from outside. As shown in figure 6 and 7(a), the roller chain mandrel (5) has an elongated rigid member (5a) connected with flexible roller chain element (5b). In an embodiment, the push type mechanism comprises a piston (6a) and a cylinder. The rigid member (5a) of the roller chain mandrel (5) is coupled with the piston (6a). Therefore, the movement of the piston (6a) pushes the roller chain mandrel (5).

As shown in figure 6 and 7(a), that due to the movement of the piston (6a) of the push- mechanism (6), the roller chain mandrel (5) is inserted inside the tube (4) through the second open end (4"). The size or diameter of the piston (6a) is larger than the diameter of the tube (4) so that when the mandrel (5) is completely inserted inside the tube (4), the piston (6a) abuts with the said second open end (4") and pushes tube (4) along with the mandrel (5) towards the bending die (3) and swivel arm (1) thereby forming a bend portion. Figure 7(b) shows the curved or bent first end portion (4f) just after the completion of the bending.

According to an embodiment of the present invention, for bending the second end portion (4s) of the tube (4), a dummy tube (7) is used. Figure 7(c) shows a position just before the bending of the second end portion (4s) starts. As shown in figure 7(c), the second end portion (4s) of the tube (4) which is to be bent, is kept inside the split type bending die (3) while the split-clamp (1) hold the tube (4) at a location at or near junction of the straight mid portion (4m) and second end portion (4s). The dummy tube (7) is kept having its one end (7') in contact or abutted with the second open end (4") of the tube (4) which lies inside the bending die (3). In this position, the roller chain mandrel (5) is inserted inside the dummy tube (7) and to the tube (4) through the second open end (4") so that second end portion (4s) is supported by the roller chain (5b) of the mandrel (5) from inside. The rigid member (5a) of the roller chain mandrel (5) is coupled with the piston (6a) and the other end (7") of the dummy tube is kept abutted with the piston (6a). In this position, the movement of piston towards the bending die (3) forces the dummy tube (7) and the mandrel (5) together towards the bending die (3) which forces the second end portion (4s) of the tube towards the split clamp (1) and the swivel arm (2). In turn the swivel arm (1) force the second end portion (4s) to rotate thereby forming a curved or bent second end portion (4s). Figure 7(d) illustrate the position just after the completion of bending of second end portion (4s).

The reason for keeping this dummy tube is that the piston and cylinder head will need to travel as close as to the bending which can make the bending die weak and leads to failure of the die. Secondly, the machine stroke or stroke of the piston is not sufficient enough to reach the final position without the dummy tube.

The above process for making the load carrying member of the present invention is a novel process wherein the seamless tube is pushed towards the bending portion so that the dents/wrinkles and thinning is adjusted by allowing material movements while pushing in a hydraulic bending machine. Also, in the process of the present invention, a moving roller chain mandrel is used on the bent location to support the inner sides to avoid deformations while bending. The following are the observations of bending tube according to the process of the present invention,

(a) Thinning at outer wall of tube at radius portion is less than 5%.

(b) Dent mark at inner radius of tube reduced towards zero.

(c) Dimension variation found ±3mm which is very much well within the limits of acceptance.

After obtaining the load carrying member with the help of the above process, the following operations are performed to make a load carrying member assembly,

1. Drilling - Using jig and radial drilling machine or multi spindle drilling heads 2. Welding of subassembly- using fixtures and robot/manual

3. Inspection

4. Shot blasting - outer surface cleaning 5. Painting - outer surface protection

6. Marking/Stamping - for traceability

Therefore, number of process involved including cutting and bending seamless tube is (6 + 2) = 8.

Figure 8 shows the load carrying member assembly according to an embodiment of the present invention. The raw material for making this part as shown in figure 8 is a rectangular tube of section 160 100 with a wall thickness of 12mm.

Requirement of raw material for manufacturing load carrying member o f the present invention is as follows:

Number of parts required per suspension = 2 (i.e. two seamless tubes)

Weight of each part = 83 kgs

Total weight of Raw material required for suspension = 166 kgs

% of scrap generation = 0 % Investment cost on machines/equipment/tooling for manufacturing the load carrying member of the present invention is as follows:

The cost of investment on the machines for the above process estimated =Rs.2.5 crores

The estimated product cost or cost of the load carrying member of the present invention is as follows:

The estimated product cost of the part =Rs.17000

As can be observed that present invention provides a cost saving which is achieved due to the following reasons,

1. Raw material usage has come down from 300 kg to 166 kg per vehicle.

2. Number of process steps has come down from 16 to 8

3. % of scrap generation reduced from 48% to 0 %

4. Investment cost has come down from Rs 9.5 crores to 2.5 crores

The present invention also provides an air suspension system for vehicle having chassis. Figure 9 shows an air suspension system with load carrying member according to an embodiment of the present invention. As shown in figure 9, the air suspension system comprises four air bellows mounted below the chassis. The air bellows are mounted so that two air bellows are mounted on both sides of the axles and on both lateral sides of the chassis. For this purpose, there are lateral members are mounted on the chassis extending outwardly from the chassis and parallel to the axle of the vehicle. The air bellows disposed on each side of the chassis are supported by one load carrying member assembly of according to an embodiment of the present invention.

The load carrying member assembly takes all the load of the chassis through the air bellows and transfers the same to the wheels through the axle.

As can be clearly understood from the above description that the main load carrying member of the present invention has a tubular construction without any seam which has exceptional or surprising results such as the failure along the seam line can be avoided.

The conventional load carrying member is made from metallic sheet by stamping which is cut from a sheet. Therefore, the scrap generation in the traditional process of producing load carrying member is high. Whereas, in present invention reduces the scrap generation to zero.

Further, the stamping process calls for lot of welding and therefore, it is not a preferred process where the part is undergoing severe stresses due to the 3 axis loads acting on it. Whereas, in the present invention single part tubular construction eliminates a critical welding process on the load carrying member. Secondly, the cost involved on the welding electrode is hence nullified which approximately costing Rs.2000 per suspension and weight on the vehicle pay load can be reduced to 10 kg. Apart from above, the following are the some other advantages of the present invention,

(a) In the present invention raw material usage comes down from 300 kg to 166 kg per vehicle.

(b) In the present invention the number of process steps comes down from 16 to 8. (c) In the present invention the percentage (%) of scrap generation reduces from 48% to 0 %.

(d) In the present invention investment cost of setting up the air suspension project comes down significantly.

(e) In the present invention the product cost comes down from Rs.33000 to Rs.17000 per air suspension system.