SUSPENSION SPRING ASSEMBLY FOR VEHICLES AND VEHICLE SUSPENSION SYSTEM

Field of invention:

The present invention relates to a suspension spring assembly for use in a vehicle suspension system comprising a pair of upstanding spaced-apart leaf springs, a stabilizer spring and a pair of radius arms. The present invention also relates to a vehicle suspension system which includes a pair of suspension spring assemblies each mounted on either side of a vehicle axle by means of an axle mounting bracket.

Background of invention:

The primary function of vehicular suspension system is to take a vehicle's vertical, cornering, braking and driving loads and to provide good ride comfort. Leaf springs of conventional mechanical suspension systems help in taking the vertical, cornering, braking and driving loads.

Such leaf spring suspension system has been disclosed in prior WO2006/121438, which includes a pair of leaf springs arranged to extend longitudinally on a frame of an associated vehicle on respective opposed sides thereof, each leaf spring having one of its ends connectable pivotally to the vehicle frame at a fixed location with respect thereto and arranged to have mounted thereto intermediate its ends an axle extending transversely of the vehicle frame; a first bracket attached rigidly to each leaf spring at or adjacent the fixed location at which the one end of each leaf spring is connectable pivotally to the vehicle frame; a radius arm arranged to extend longitudinally on each side of the vehicle frame and having one end thereof connected pivotally to the first bracket in spaced relationship to said fixed location; and a second bracket which is attachable rigidly to the axle and to which is connected the other end of the corresponding radius arm in spaced relationship to the axle.

US patent document US 5137300 also discloses a selectively engagable auxiliary leaf springs for vertically supporting a vehicle chassis on an axle assembly in parallel with main suspension springs, wherein forward and rear ends of the auxiliary leaf springs are pivotally attached to the vehicle chassis and the axle assembly, and pivotal movement of the forward ends is inhibited or prevented by engagement of actuator assemblies to engage the auxiliary leaf springs. A control system automatically engages the actuator assemblies in response to load added to the vehicle and/or vehicle steering movement and/or rapid vehicle acceleration.

But the draw back associated with conventional leaf springs it that they offer higher vertical stiffness, which affects the ride comfort. To overcome this shortcoming, it is commonly combined with air spring which though does not take any lateral load but offers low natural frequency to the sprung mass for better ride comfort. Thus, air suspension systems used in conjunction with the leaf springs are known as air-leaf suspension systems. These systems have the advantage of providing good ride and handling properties and are relatively lighter in weight as compared to full air suspension system.

Prior US patent document US 3,850,445 discloses such an air-spring suspension system in which a pair of leaf spring, each comprising of many leaves, is horizontally positioned adjacent to the axle and adapted to be secured to the vehicle frame with the help of U-shaped bolts and an air spring mounted on the beam running parallel to the axle and adapted to transmit vertical load between the said beam and the vehicle frame and an anchor placed longitudinally center of the said axle. The anchor further comprises of hanger attached to each of the leaf spring through which the load is transmitted between the leaf spring and the beam.

US5,024,462 describes a suspension system comprising of an air-leaf spring suspension to which at one end of the leaf spring is attached a load and shock transmitting lever, one end of which has a air-inflated balloon.

US2004/056398 discloses a U-shaped stabilizer along with air leaf spring where the stabilizer is connected to the axle comprised in the air leaf suspension and produces an anti-rolling force instantly when there is lateral displacement of the chassis of the vehicle thus increasing the riding comfort ability.

WO 2006/121438, in which a vehicle suspension system is disclosed, includes a pair of leaf springs arranged to extend longitudinally of a frame of an associated vehicle on respective opposed sides thereof which in turn has radial projecting arms connected to the axle of the frame.

As is seen, in all prior leaf spring suspension systems or air-leaf suspension systems, very long longitudinally mounted leaf springs mounted with bulky brackets on the chassis have been utilized. This causes the suspension system weight to increase to a larger extent. Also these systems offers higher unsprung (which includes 50% of the weight of the springs) mass which affects the vehicle ride comfort. The unsprung mass acts as a store house of vibration energy. When the vehicle crosses the irregularity, the unsprung mass first absorbs the vibration energy and then transfers the same to the sprung mass, which affects the sprung mass ride comfort. As per force equation:

Where:

Msm and Mum denote sprung mass and unsprung mass respectively (kg) Asm and Aum denote sprung mass acceleration and unsprung mass acceleration respectively (m/s2).
Therefore, more the unsprung mass more is the acceleration induced in the sprung mass, which hampers ride comfort. Yet another disadvantage is that when leaf springs are longitudinally placed with one end pivoted to the axle, causes the axle to move in an arc while articulation. This leads to the rubbing of tires on ground in rebound stroke, resulting in abnormal tire wear.

In all the prior arts the leaf springs are mounted on the axle using U-shaped bolts, which require timely maintenance (re-torque) because the U-shaped bolts tend to loosen out after certain distance coverage.

Further, the existing suspension systems offer very less modularity, which often leads to redesigning of the components of the suspension system for catering the loading requirement of any new vehicle.

Therefore, a need was felt by the inventors to develop a suspension system which overcomes not only the technical problems cited in the prior arts but also provides better riding comfort.

Summary of the invention:

Accordingly, the present invention provides a suspension spring assembly for use in a vehicle suspension system and mounted on the vehicle axle by means of an axle mounting bracket, said suspension spring assembly comprises:

a stabilizer spring in abutment with the vehicle chassis frame; a pair of upstanding spaced-apart leaf springs, each said leaf spring pivotally connected at its one end to said stabilizer spring and its other end to said axle mounting bracket; and at least two radius arms, an upper radius arm and a lower radius arm, said upper radius arm is connected at its one end to said vehicle axle through a first mounting bracket and at its other end to the chassis of the vehicle by means of a hanger bracket, and said lower radius arm is connected at its one end to said vehicle axle through a second mounting bracket and at its other end to the vehicle chassis frame by means of a tie rod.

In the subject invention, since the radius arms secure the suspension spring assembly to the vehicle chassis frame, the forces that are generated during driving and braking the vehicle, are transferred smoothly without any lag. Thereby, longitudinal movement between the chassis and the axle is prevented. Moreover the upper radius arm and the lower are mounted in such mechanism that it facilitates straight line motion of axle while articulating.

When brakes are applied, the wheels of the vehicle tend to come to rest immediately while the vehicle body maintaining its state of motion, owing to inertia, tends to move forward. Thus the instantaneous load gets transferred from the rear to front while braking. Due to this effect, the axle which is connected to wheels via brakes on one side and chassis via springs on the other side, tends to rotate about its centre. This rotation of axles, both front and rear, about their own centres should be prevented because rotation of the rear (live) axle induces additional loads on propeller shaft and rotation of front axle induces loads on drag link assembly. This may lead to premature failure of the said propeller shaft and drag assembly. Thus, it is required to have controlled articulation of the axle without rotation.

According to a preferred embodiment of the present invention, said stabilizer spring is secured to said vehicle chassis frame by means of a support bracket. The support bracket may either be bolted or welded to the chassis frame. The stabilizer spring serves the purpose of supporting the leaf springs in bearing the vertical, cornering, driving and braking loads. The stiffness of the leaf springs and stabilizer spring is utilized in two different stages to bear the vehicular load; first the leaf springs start deflecting and then, with the increase in vehicular load, both leaf springs and stabilizer start deflecting to bear the load. This sharing of load between the leaf springs and the stabilizer spring provides better ride comfort both under laden and unladen condition of the vehicle. The required ride stiffness can be obtained by proper selection of the spring stiffness properties. Further by compelling the axle to move in a straight path during articulation and arresting its natural curvilinear sway, it imparts directional stability to the axle movement in bump and rebound stroke.

In the invented suspension spring assembly, the leaf springs are pivotally connected to the stabilizer spring and to the axle mounting bracket by means of metal or metalastic bushes. Thus, for mounting the leaf springs U-shaped bolts are not required. Each leaf spring comprises of at least one leaf, arranged in upstanding position. The leaves of the leaf springs may have parabolic profile or conventional straight profile.

An advantage provided by this upstanding disposition of the leaf springs is that a smaller length of leaf can be utilized for giving necessary stiffness to the suspension system. This reduces the overall system weight and avoids the timely maintenance required because of absence of U-shaped bolts. Also it provides adequate space between the vehicle chassis frame and the axle for incorporating therein a secondary suspension system. The secondary-suspension system may be an air spring, rubber spring or coil spring. Advantageously, the stiffness of the stabilizer spring and leaf springs can be altered by altering the spring cross section or increasing the number of leaves, to get the required ride and handling characteristics.

A tailor-made profile can be created depending on the nature of application such as to enhance vertical, cornering driving load carrying capability.

The present invention also provides a vehicle suspension system which includes of a pair of invented suspension spring assemblies, a right suspension spring assembly and a left suspension spring assembly, each mounted on either side of the vehicle axle.

Preferably, the invented suspension system is provided with an anti roll bar for improving cornering stability of the vehicle while turning by imparting torsional stiffness to the vehicle. The anti roll bar is secured to lateral cross member of the vehicle by means of a pair of tie rods and is connected at its ends to the axle by means of second mounting brackets. According to this embodiment of the present invention, the lower radius arm of each suspension spring assembly is integrated with said anti roll bar in such a way that it constitutes an arm of the anti roll bar. During straight ahead motion, braking and driving, this anti roll bar performs the function of lower radius arm only, but during cornering or single wheel bump, it acts as a pure anti roll bar. In other words, the anti roll bar performs the function of the lower radius arm also. This in-turn leads to reduction of components in suspension system which facilitates weight reduction. The anti roll bar also imparts stability to the vehicle when vehicle encounters single wheel bump by avoiding excessive body roll.

According to a preferred embodiment of the invention, each suspension spring assembly is provided with at least a secondary suspension unit disposed between the vehicle chassis frame and said vehicle axle for providing better riding comfort. The secondary suspension unit may be in the form of air spring, coil spring or rubber spring,. Thus, according to this embodiment, the suspension system has at least two secondary suspension systems, one for the right suspension spring assembly and one for the left suspension spring assembly.

According to a most preferred embodiment of the invented suspension system, the secondary suspension unit is an air spring attached with the vehicle chassis frame by means of top mounting plate and is mounted on the axle of the vehicle by means of a bottom axle plate.

According to another embodiment of the invented suspension system, the secondary suspension unit comprises more than one air spring disposed on both sides of the vehicle axle or on top of the axle dome.

According to a further embodiment, where a vehicle requires higher weight carrying capacity, the air spring is convolute type without any piston.

The present invention provides a suspension system in which the arrangement of various components allows the axle to move relatively in a straight path while articulating, thereby avoiding tire rubbing with ground in the rebound stroke.

Advantageously, the leaf springs, as proposed in the subject invention, are of shorter length as compared to the known conventional leaf springs. This has reduced the assembly weight appreciably and thereby have lowered unsprung mass as compared to the prior art. Thus the vehicle can be loaded with higher payload for the same gross vehicle load rating offering better ride quality. Thus the present invention provides modular designs of suspension systems where the spring stiffness can be altered by using different combinations of upstanding leaf springs and stabilizer spring thereby catering to various requirements of vehicles of different load capacities. The fusion of lower radius arm with anti roll bar facilitates reduction of weight and number of components of the suspension assembly without compromising on the necessary features of the suspension system. The invented suspension system can be adopted for and mounted on both live (driven) axle and dead axle.

Brief Description of the drawings:

For better understanding, an illustrative embodiment of the invention will now be described with reference to the accompanying drawings. It will however be appreciated that the embodiment exemplified in the drawings is merely illustrative and not limitative to the scope of the invention.

Figure 1 illustrates a side view of a vehicle suspension system attached to a vehicle chassis according to a particular embodiment of the invention.

Figure 2 illustrates isometric view of a vehicle suspension system attached to a vehicle chassis according to a particular embodiment of the invention.

Figure 3 illustrates a side view of a side view of a suspension system attached to a vehicle chassis according to another preferred embodiment of the invention.

Figure 4 illustrates isometric view a side view of a suspension system attached to a vehicle chassis according to another preferred embodiment of the invention.

Figure 5 illustrates a schematic representation of air suspension system according to a particular embodiment of the invention.

Detailed Description of the invention:

In the accompanying drawings, like reference numerals refer to like structures and the invented suspension spring assembly has been commonly referred, for the sake of convenience, by the reference numeral 1.

Referring to the embodiments of the suspension systems as show in figures 1 to 4 of the accompanying drawings, each suspension spring assembly (1) comprises of a pair of upstanding spaced-apart leaf springs (2), a stabilizer spring (3) and two radius arms, an upper radius arm (4) and a lower radius arm (5), said lower radius arm is integrated with and into an anti roll bar (6). Each suspension spring assembly (1) is mounted on either side of vehicle axle (7) by means of an axle mounting bracket (8). Each leaf spring (2) is pivotally connected at its one end with said stabilizer spring (3) and at its other end to said axle mounting bracket (8) by means of metal or metalastic bushes (9). The stabilizer spring (3) is secured to the vehicle chassis frame (10) by means of a support bracket (11) and a centre bolt (12). Displacement of the stabilizer spring (3) is prevented by the support bracket (11).

The stabilizer spring (3) serves the purpose of supporting the leaf springs (2) in bearing the vertical, cornering, driving and braking loads. Further it provides directional stability to the axle movement in bump and rebound stroke, by compelling the axle (7) to move in a straight path during articulation and thereby arresting its natural curvilinear sway.

The upper radius arm (4) is secured to the vehicle chassis frame (10) though a hanger bracket (13) and is connected to the axle (7) by means of a mounting bracket, the first mounting bracket (14); while the anti roll bar (6) is secured to the lateral cross member (15) of the vehicle though a pair of tie rods (16). The tie rods (16) are rigidly connected to the lateral cross member (15). The anti roll bar (6j is connected at its either end to the axle (7) by means of a second mounting bracket (17). The anti roll bar (6) has dual functionality; firstly performing the function of an anti roll bar and secondly performing the function of a radius arm. When the vehicle experiences braking and driving loads, the portion of the anti roll bar in proximity with the vehicle axle (7) act as the lower radius arm (5) and when vehicle experiences cornering, it acts as a typical anti roll bar by providing required torsional stiffness to the vehicle. The diameter of the "arm" portion of the anti roll bar (6) can be varied to provide required cornering stiffness to the vehicle. Thus, with this arrangement the inventors have been able to reduce the number of parts in the suspension system.

The upstanding configuration of the leaf springs (2), as proposed in the subject invention, provides adequate space between the vehicle chassis frame (10) and the axle (7) to accommodate a secondary suspension unit therein.

Although the leaf springs (2) with parabolic profile have been depicted in figures 1 to 4, conventional leaf springs having straight profile may also be used in the invented suspension spring assembly (1).

According to a most preferred embodiment, as shown in figures 3 and 4 of the accompanying drawings, each invented suspension spring assembly (1) is provided with an air spring (18) as secondary suspension unit. Accordingly, the invented suspension system has two air springs, one associated with the right suspension spring assembly and the other associated the left suspension spring assembly. The secondary suspension unit offers low natural frequency to the suspension system and thereby provides better ride comfort. The air spring (18) is mounted with the help of a pair of mounting plates, a top mounting plate (19) and bottom mounting plates (20), to prevent its displacement. Since the air spring (17) is mounted under the vehicle chassis frame (10), there is no need to weld any overhanging hanger or a similar component thereof on the axle for mounting the air spring (18).

The air springs (18) are integral part of an air suspension device (21) as shown in figure 5 of the accompanying drawings. The air suspension system (21) comprises of various components, such as air springs (18), pressure gauge (22), leveling valve (23), air supply lines (24), compressed air reservoir (25) and air compressor (26).

According to the most preferred embodiment, as shown in figures 3 to 5, the suspension spring assembly (1) is an air-spring assembly, wherein resilience of two leaf springs (2), a stabilizer spring (3) and an air spring (18) have been utilized to provide suspension to the vehicle. Such air-spring suspension system helps in stabilizing the chassis of the vehicle under various load conditions. In vertical load, when the load starts acting, the leaf springs (2) of the system starts deflecting first followed by deflection of the stabilizer spring (3). The sharing of the load between the leaf springs (2) and the stabilizer spring (3) depends on the stiffness variation i.e. spring constants, of the individual springs.

After certain limit of load, the air spring (18), preset using leveling valve (23) setting, starts taking any further increase in load, thereby using required air pressure inside the bellows with the help of leveling valve (23), maintains the chassis height. Thus the process follows multiple steps, starting from mechanical type and later acting as air suspension. The stiffness of the suspension system keeps varying, from initially when only leaf springs (2) are acting to the stage when both leaf springs (2) and stabilizer spring (3) act owing to this unique series and parallel combinations of the springs. Finally, the entire additional load is borne by the air spring (18), owing to the provision of variation in air pressure inside the air spring bellow through leveling valve (23) which in turn opens or closes the pneumatic air lines by sensing the change in chassis height due to variation in load.

During cornering, the vehicle tends to move outwards due to centrifugal force. This causes the load transfer to happen from the inner to the outer side of the vehicle. The anti roll bar (6) provided in the suspension assembly bears such loads generated by centrifugal force. The anti roll bar (6) is mounted on the rear side of the axle (7) at certain distance from the axle centreline. The anti roll bar (6) is fitted with two tie rods (16) to arrest its vertical motion. When the vehicle starts cornering, the anti roll bar (6), being mounted on the axle (7), provides torsional resistance to the rolling of the axle (7) and the vehicle chassis (10) and thus stabilizes the vehicle. For vehicles having higher centre of gravity or carrying high overloads the anti roll bars can be designed using vehicle roll stability calculations for different cornering velocities and radius of turn.

The leaf springs (2) in collaboration with stabilizer spring (3) also contributes to overall roll stability of the vehicle. The amount of roll stiffness provided by the springs depends on their track i.e. the lateral distance between springs on the vehicle, and stiffness value. Since the track is fixed for the suspension in the vehicle, the suitable selection of the stiffness of the leaf spring (2) and that of the stabilizer spring (3) will take the requiring cornering load.

During braking, the instantaneous vehicle load gets shifted towards the front due to the inertia of motion, while during acceleration (driving), it acts towards the rear. When brake is applied, the tires come to rest while the body, following the laws of inertia, remains in motion. This causes the axle (7) to rotate about its axis. This rotation of axle (7) is prevented by the upper radius arm (4) and lower radius arm (5), which helps in maintaining the straight ahead position of axle and takes the braking and driving loads. The lower radius arm (5) is actually part of anti roll bar (6). This horizontal force is further retarded by longitudinal disposition of the stabilizer spring (3), which is stiff in this loading condition. The similar response is achieved in case of driving loads.

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

CLAIM :

1. A suspension spring assembly for use in a vehicle suspension system
and mounted on the vehicle axle by means of an axle mounting bracket, said suspension spring assembly comprises :

- a stabilizer spring in abutment with the vehicle chassis frame;

- a pair of upstanding spaced-apart leaf springs, each said leaf spring being pivotally connected at its one end to said stabilizer spring and its other end to said axle mounting bracket; and

- at least two radius arms, an upper radius arm and a lower radius arm, said upper radius arm is connected at its one end to said vehicle axle through a first mounting bracket and at its other end to the chassis of the vehicle by means of a hanger bracket, and said lower radius arm is connected at its one end to said vehicle axle through a second mounting bracket and at its other end to the vehicle chassis frame by means of a tie rod.

2. The suspension spring assembly as claimed in claim 1, wherein said
stabilizer spring is secured to said vehicle chassis frame by means of a support bracket.

3. The suspension spring assembly as claimed in claims 1 and 2, wherein said leaf springs are pivotally connected to said stabilizer spring and to said axle mounting bracket by means of bushes.

4. The suspension spring assembly as claimed in claims 1 to 3, wherein each said leaf spring is comprised of atleast one leaf having parabolic profile.

5. The suspension spring assembly as claimed in claims 1 to 3, wherein each said leaf spring is comprised of atleast one leaf having straight profile.

6. A vehicle suspension system which includes a pair of suspension spring assemblies, a right suspension spring assembly and a left suspension spring assembly, each mounted on either side of the vehicle axle, wherein each suspension spring assembly comprises:

- a stabilizer spring in abutment with the vehicle chassis frame;

- a pair of upstanding spaced-apart leaf springs, each said leaf spring being pivotally connected at its one end to said stabilizer spring and its other end to said axle mounting bracket; and

- at least two radius arms, an upper radius arm and a lower radius arm, said upper radius arm is connected at its one end to said vehicle axle through a first mounting bracket and at its other end to the chassis of the vehicle by means of a hanger bracket, and said lower radius arm is connected at its one end to said vehicle axle through a second mounting bracket and at its other end to the vehicle chassis frame by means of a tie rod.

7. The vehicle suspension system as claimed in claim 6, wherein said stabilizer spring is secured to said vehicle chassis frame by means of a support bracket.

8. The vehicle suspension system as claimed in claims 6 and 7, wherein said leaf springs are pivotally connected to said stabilizer spring and to said axle mounting bracket by means of bushes.

9. The vehicle suspension system as claimed in claims 6 to 8, wherein each said leaf spring is comprised of atleast one leaf having parabolic profile.

10. The vehicle suspension system as claimed in claims 6 to 8, wherein each said leaf spring is comprised of atleast one leaf having straight profile.

11. The vehicle suspension system as claimed in claims 6 to 10, wherein said suspension system is provided with an anti roll bar connected at its ends to said axle by means of said second mounting brackets and secured to lateral cross member of the vehicle by means of a pair of tie rods, and wherein the lower radius arm of each suspension spring assembly is integrated with said anti roll bar.

12. The vehicle suspension system as claimed in claims 6 to 11, wherein each suspension spring assembly is provided with at least a secondary suspension unit disposed between the vehicle chassis frame and said vehicle axle.

13. The vehicle suspension system as claimed in claim 12, wherein said secondary suspension unit is an air spring.

14. The vehicle suspension system as claimed in claim 13, wherein said air spring is convolute type.

15. The vehicle suspension system as claimed in claims 13 and 14, wherein said air spring is attached with the vehicle chassis frame by means of top mounting plate and is mounted on the axle of the vehicle by means of a bottom axle plate.