AU5800401A - Reinforcing spring for a vehicle leaf spring - Google Patents

Description

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AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant: JSW PARTS PTY LTD Invention Title: REINFORCING SPRING FOR A VEHICLE LEAF SPRING The following statement is a full description of this invention, including the best method of performing it known to me/us: 2 REINFORCING SPRING FOR A VEHICLE LEAF SPRING The present invention relates to a reinforcing spring for attachment to a leaf spring assembly in a vehicle for improving the spring characteristics of the leaf spring.

BACKGROUND OF THE INVENTION Multileaf springs are used in rear axle suspension systems in many road vehicles, in particular four wheel drive vehicles and small commercial vehicles such as vans, small trucks and utilities. Many of these vehicles fail to carry their rated payload and suffer from rear spring sag as a result of inadequate leaf spring design. This problem is not confined to older vehicles, but is often a problem with new vehicles.

In correcting this problem it is known to have the springs reset with an extra leaf. This requires removing the springs from the vehicle and is an expensive and labour intensive process. Alternatively, products such as overslung or underslung full-length stabiliser springs are available for attaching onto the leaf spring to increase S the leaf spring strength and improve overall vehicle suspension. However, such stabiliser springs can sometimes be complicated to install requiring the assistance of a .skilled person. Furthermore, failure of these springs is not uncommon under severe flexing.

30 The present invention addresses the above problems by providing a reinforcing spring that will increase the load carrying capacity of a vehicle suspension system whilst maintaining smooth vehicle performance.

H:\Shonal\Keep\Speci\P43102 (CAP) REINFORCING SPRING 14/08/01 3 SUMMARY OF THE PRESENT INVENTION According to the present invention there is provided a reinforcing spring adapted to be mounted above a leaf spring in a vehicle, the leaf spring being secured to the vehicle at a midpoint and at its ends, the reinforcing spring being adapted to be attached to the leaf spring on one side of the midpoint and comprising a first end secured onto the leaf spring adjacent the midpoint by a first securing means, and a second end spaced above the leaf spring, the second end being secured at a constant height above the leaf spring by a second securing means, whereby the reinforcing spring is shaped to, in use, be tensioned against the leaf spring to alter the stiffness characteristics of the leaf spring under varying vehicle loads.

According to the present invention there is further provided a reinforcing spring adapted to be mounted above a 20 leaf spring in a vehicle, the leaf spring being secured across an axle assembly on the vehicle with its front and rear ends secured to the vehicle chassis, the reinforcing spring having a first end and a second end and is shaped .to, in use, have an effective length that is shorter than the length between the first and second ends, whereby a *-.first securing means is adapted to secure the first end S- onto the leaf spring and adjacent the axle assembly with the second end spaced above the leaf spring, and a second securing means is adapted to secure the second end at a constant height above the leaf spring; whereby the reinforcing spring is adapted, in use, to be tensioned against the leaf spring, the effective length of the reinforcing spring altering under varying vehicle loads thereby altering the stiffness characteristics of the leaf spring.

H:\Shonal\Keep\Speci\P43102 (CAP) REINFORCING SPRING 14/08/01 4 Preferably, the reinforcing spring is a curved beam member which, when the leaf spring is loaded, flexes at a flexing point. The effective length in this case is the length of the reinforcing spring between the flexing point and the second end, wherein the flexing point shifts under increasing load to increase the effective length. For optimum results the curved spring has a point of inflection at substantially its midpoint when at rest.

The height of the second end above the leaf spring is preferably adjustable so as to adjust the tension of the reinforcing spring against the leaf spring and hence the spring rate of the leaf spring.

The securing means is preferably clamps comprising U-bolts, cross plates, washers and nuts. More preferably, the second securing means has tightening nuts to adjust the :::height of the second end, and lock nuts to fix the height.

20 The first end of the reinforcing spring preferably includes a lip against which the first securing means is adapted to abut. The second end of the reinforcing spring is preferably provided with a cross plate through which a U- S. bolt extends.

In accordance with the present invention there is still further provided a reinforcing leaf adapted to be mounted above a leaf spring in a vehicle, the leaf spring being secured to the vehicle at a midpoint and at its ends, the 30 reinforcing leaf being adapted to be attached onto the leaf spring on either side of the midpoint, the reinforcing leaf comprising a first end spaced above the leaf spring on a first side of the midpoint and a second end spaced above the leaf spring on a second side of the midpoint, and first and second securing means respectively securing the first and second ends at a constant height above the leaf spring; wherein the reinforcing leaf is shaped such that, in use, H:\Shonal\Keep\Speci\P43102 (CAP) REINFORCING SPRING 14/08/01 5 it is tensioned against the leaf spring to alter the stiffness characteristics of the leaf spring under varying vehicle loads.

BRIEF DESCRIPTION OF DRAWINGS The present invention is described further by way of example with reference to the accompanying drawings of which: Figure 1 illustrates a reinforcing spring according to the present invention mounted on a leaf spring suspension; Figure 2 illustrates the mounted reinforcing spring in a loaded condition; Figure 3 illustrates the front clamp of the reinforcing spring; *.20 Figure 4 illustrates the rear clamp of the reinforcing spring; and Figure 5 is a graph comparatively illustrating vertical load against deflection of suspension springs with and without the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF INVENTION Figures 1 and 2 illustrate a reinforcing spring 10 mounted 30 on a rear axle leaf spring 11 of a vehicle. The leaf spring 11 is secured at its midpoint to the rear axle assembly 12 whilst its front end (not shown) and rear end 14 are secured to the vehicle chassis (not shown). The example of vehicle leaf spring described herein is of a longitudinal leaf spring located across a vehicle axle, although the present reinforcing spring could, of course, be used on other types of leaf springs, such as the H:\Shonal\Keep\Speci\p43102 (CAP) REINFORCING SPRING 14/08/01 6 transverse kinds.

Reinforcing spring 10 is mounted on the leaf spring to reinforce the leaf spring between its midpoint and rear end 14 since the rear half of the leaf spring is more likely to suffer from greater load deflection than the front half.

It is, however, understood that the reinforcing spring can extend across the axle over both the front half and the rear half of the leaf spring in the manner of a reinforcing leaf. In effect, the reinforcing spring increases the leaf spring's existing vertical stiffness.

Reinforcing spring 10 comprises a curved steel beam spring having a mounting end 16, an opposite free end 17 and a point of inflection 35 therebetween. High tensile clamps 21 secure the spring at each end to the leaf spring.

Front clamp 20 is illustrated in figure 3 and comprises a short U-bolt 22, washers 23, tightening nuts 24 and a first cross plate 25. Rear clamp 21 illustrated in figure 4 comprises a longer U-bolt 26, washers 23, tightening nuts 24 and lock nuts 27.

Spring 10 is mounted on the rear half of leaf spring 11 in S. a cantilever fashion with mounting end 16 secured on top of the leaf spring by front clamp 20 and abutting the rear axle assembly. With cross plate 25 placed across mounting "end 16, U-bolt 22 hooks underneath leaf spring 11 and extends through apertures 30 of cross plate 25. Cross plate 25 and U-bolt 22 are secured together with washers 23 30 and tightening nuts 24 to clamp the reinforcing spring in tension. A lip 31 at the mounting end 16 wedges between axle assembly 12 and front clamp 20 to securely fix the mounting end on the leaf spring.

With mounting end 16 fixed, the reinforcing spring extends rearwardly of the leaf spring and curves upwardly such that free end 17 is located spaced above the leaf spring. In H:\Shonal\Keep\Speci\P43102 (CAP) REINFORCING SPRING 14/08/01 7 one embodiment free end 17 is provided with a second cross plate 32 having apertures 33. Long U-bolt 26 of rear clamp 21 hooks underneath the leaf spring and through apertures 33 and is secured to second cross plate 32 with washers 23, tightening nuts 24 and lock nuts 27. Reinforcing spring is shaped to bias free end 17 upwardly away from leaf spring 11. Consequently, the rear clamp is always in tension and able to maintain the free end at a constant height above the leaf spring. The distance between free end 17 and the leaf spring can be adjusted by threading tightening nuts 24 along U-bolt 26 and setting the distance with lock nuts 27.

Reinforcing spring 10 is curved to enable it to be securely mounted while still cantilevered above leaf spring 11.

Specifically, the mounting and free ends of reinforcing spring 10 are slightly convex in opposite directions whereas a point of inflection exists in a middle section of the reinforcing spring in a state of rest. Free end 17 is clamped on leaf spring 11 so as to bias the reinforcing spring away from the leaf spring. Forces acting on the reinforcing spring at both ends through the clamps cause the reinforcing spring to flex thereby creating a flexing point 35 in the middle portion 34, which is the point of inflection under load. The spring therefore has an "-"effective length shorter than its actual length, that is, between flexing point 35 and free end 17, and acts as if clamped just behind the flexing point 30 Reinforcing spring 10 is a steel spring with sufficient stiffness to raise the leaf spring's rear end 14 and hence the vehicle chassis. In other words, reinforcing spring increases the spring rate of leaf spring 11 by increasing its curvature and improving the existing leaf spring's overall characteristics enabling the leaf spring suspension in the vehicle to endure greater payloads and reduce incidence of spring damage. In the preferred embodiment H:\Shonal\Keep\peci\P43102 (CAP) REINFORCING SPRING 14/08/01 8 the spring is a high carbon, silicon-manganese alloy.

Spring rate improvement in the leaf spring can be precisely adjusted to desired levels by simply adjusting the distance between free end 17 and the leaf spring. Adjusting this spacing directly affects chassis height above the axle.

For example, decreasing the spacing increases the curvature of leaf spring 11 thereby raising rear end 14, and thus the chassis. This in turn increases the distance between the chassis and rear axle assembly 12 as well as the vehicle's load carrying capacity.

Figure 5 is a graph illustrating the comparative vertical load versus deflection curves for a suspension fitted with: standard spring; present reinforcing spring, no pre-load; and present reinforcing spring, with pre-load.

As is evident from the graph a suspension fitted with the oooo S.0. 20 present reinforcing spring demonstrates a significant increase in vertical stiffness particularly with payloads greater than 800 kg per spring. In comparison, a vehicle suspension fitted with the present reinforcing spring is capable of supporting a 1000 kg payload at the same ride height as the standard vehicle spring with a 550 kg payload. The significant differences can be attributed to the increase in control of spring deflection and increased spring stiffness when required that are brought about by the present reinforcing spring. The graph also illustrates the reinforcing spring's influence of non-linear behaviour of the leaf spring which enables the leaf spring to experience a lower than normal stiffness under low vertical loading as well as a higher than normal stiffness under a large vertical loading.

Aside from significantly improving load carrying capacity, the reinforcing spring is able to compensate for loaded and H:\Shonal\Keep\Speci\P43102 (CAP) REINFORCING SPRING 14/08/01 9 unloaded axles by progressively bearing the load on the leaf spring to allow for stable travel regardless of whether the vehicle is loaded. Specifically, the nature of the vehicle ride is altered from a soft ride when unloaded to a hard ride when loaded, as graphically illustrated by the non-linear curve in figure 5. This is achieved by a progressive change in the effective length of the reinforcing spring, and hence its spring rate, as the payload on the vehicle changes. Figure 1 illustrates the reinforcing spring mounted on an unloaded leaf spring.

With the flexing point 35 approximately midway along the reinforcing spring, the effective length is between the flexing point and free end 17. A loaded leaf spring is illustrated in figure 2. Flexing point 35 has clearly shifted towards the axle assembly thereby elongating the effective length of reinforcing spring. A progressive increase in effective length progressively changes the spring rate of the leaf spring in accordance with the load forces on the chassis so that the leaf spring suspension assembly is capable of appropriately accommodating varying p: ayloads.

The stabilising effects of the reinforcing spring are p artially attributed to the capacity of the spring to dampen exaggerated rebound forces in the existing leaf S. spring suspension. Specifically, the non-effective length of the reinforcing spring, that is the spring length between the mounting end and flexing point, is largely in S.biased contact against the leaf spring and provides a i 30 reactive surface against which leaf spring vibrations are dampened. Vibration dampening is particularly relevant to soften vehicle ride in unloaded conditions. A stiffened suspension system copes adequately with a heavy loaded vehicle but overcompensates when the vehicle is unladen.

The changing effective length of the present reinforcing spring alters the leaf spring's original stiffness and provides dampening properties so as to alter the original H:\Shona1\Keep\Speci\P43102 (CAP) REINFORCING SPRING 14/08/01 10 leaf spring suspension according to the load.

The benefits of a strengthened and progressively adjusted suspension with combined dampening are noticeable under any load condition. The reinforcement spring provides a more stable ride with a heavy payload as well as when unladen than previously achieved with conventional stabilisers.

The reinforcement spring enables superior vehicle performance over the vehicle's original suspension eliminating sway and jolting and ensuring a safer, more comfortable ride. Tests into the performance of a vehicle's suspension reinforced with the present spring have shown up to a 40% improvement in vehicle handling characteristics. The manoeuvring range before unsafe oversteering is found to have effectively doubled for heavily laden light commercial vehicles. Static roll stability of vehicles fitted with the reinforcing spring has been found to improve by 5% compared with un-reinforced vehicles, whilst vehicles with suspension reinforced with 2 .hanethe present spring are 35% less likely to roll in a lane change manoeuvre.

More importantly the present spring increases a vehicle's load carrying capacity by stiffening and strengthening the original suspension, in many cases enabling the vehicle to reach its rated payload without rear spring sag.

Additional advantages include ease of installation on an existing suspension system. Removal of running wheels is not necessary for installation nor is a high level of 30 skill. Increases in fuel efficiency can be expected as can wear reduction on tyres, brakes and suspension. On the whole, the reinforcement spring provides a safer, stable and more comfortable ride.

It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention.

H:\Shonal\Keep\Speci\P43102 (CAP) REINFORCING SPRING 14/08/01

Claims (17)

1. A reinforcing spring adapted to be mounted above a leaf spring in a vehicle, the leaf spring being secured to the vehicle at a midpoint and at its ends, the reinforcing spring being adapted to be attached to the leaf spring on one side of the midpoint and comprising a first end secured onto the leaf spring adjacent the midpoint by a first securing means, and a second end spaced above the leaf spring, the second end being secured at a constant height above the leaf spring by a second securing means, whereby the reinforcing spring is shaped to, in use, be tensioned against the leaf spring to alter the stiffness characteristics of the leaf spring under varying vehicle loads. 2 The reinforcing spring claimed in claim 1 wherein ooo the spring is shaped to, in use, have an effective length that is shorter than the length between the first and second ends and which effective length alters with varying vehicle loads thereby altering the stiffness characteristics of the leaf spring. S3 The reinforcing spring claimed in claim 2 wherein an increase in vehicle load increases the effective length o°.of the reinforcing spring thereby increasing the spring characteristics of the leaf spring.

4. The reinforcing spring claimed in any one of the 30 preceding claims wherein the spring is a curved beam member having a point of inflection. The reinforcing spring claimed in any one of claims 2 to 4 wherein when loaded the reinforcing spring flexes at a flexing point, the effective length being the length of the reinforcing spring between the flexing point H:\Shona\Keep\Speci\P43102 (CAP) REINFORCING SPRING 14/08/01 12 and the second end, whereby the flexing point shifts towards the first end under increasing load.

6. The reinforcing spring claimed in any one of the preceding claims wherein the height of the second end above the leaf spring is adjustable so as to adjust the tension of the reinforcing spring against the leaf spring and hence the spring rate.

7. The reinforcing spring claimed in any one of the preceding claims wherein the first and second securing means are clamps comprising U-bolts, adapted to extend underneath the leaf spring, cross-plates and nuts.

8. The reinforcing spring claimed in claim 7 wherein a cross-plate through which the U-bolt extends is attached to the second end of the reinforcing spring. oeoo

9. The reinforcing spring claimed in any one of the 20 preceding claims wherein the first end of the reinforcing spring is provided with a lip against which the first securing means is adapted to abut. .eeeoi

10. The reinforcing spring claimed in any one of the preceding claims wherein the reinforcing spring material is S steel.

11. The reinforcing spring claimed in claim 8 wherein the spring material is a high carbon, silicon-manganese 30 alloy.

12. A reinforcing spring adapted to be mounted above a leaf spring in a vehicle, the leaf spring being secured across an axle assembly on the vehicle with its front and rear ends secured to the vehicle chassis, the reinforcing spring having a first end and a second end and is shaped to, in use, have an effective length that is shorter than H:\ShonaI\Keep\Speci\P43102 (CAP) REINFORCING SPRING 14/08/01 13 the length between the first and second ends, whereby a first securing means is adapted to secure the first end onto the leaf spring and adjacent the axle assembly with the second end spaced above the leaf spring, and a second securing means is adapted to secure the second end at a constant height above the leaf spring; whereby the reinforcing spring is adapted, in use, to be tensioned against the leaf spring, the effective length of the reinforcing spring altering under varying vehicle loads thereby altering the stiffness characteristics of the leaf spring.

13. The reinforcing leaf claimed in claim 12 having the features recited in any one of claims 3 to 11.

14. A reinforcing leaf adapted to be mounted above a leaf spring in a vehicle, the leaf spring being secured to the vehicle at a midpoint and at its ends, the reinforcing leaf being adapted to be attached onto the leaf spring on either side of the midpoint, the reinforcing leaf comprising a first end spaced above the leaf spring on a first side of the midpoint and a second end spaced above the leaf spring on a second side of the midpoint, and first and second securing means respectively securing the first and second ends at a constant height above the leaf spring; wherein the reinforcing leaf is shaped such that, in use, it is tensioned against the leaf spring to alter the stiffness characteristics of the leaf spring under varying vehicle loads. oo 0 The reinforcing leaf claimed in claim 14 wherein, in use, the reinforcing leaf has an effective length at each of the first side and at the second side of the midpoint, the effective lengths each extending between a flexing point on either side of the midpoint and the closest reinforcing leaf end, the flexing point shifting towards the midpoint under increasing loads thereby H:\Shonal\Keep\Speci\P43102 (CAP) REINFORCING SPRING 14/08/01 14 increasing the effective lengths to alter the stiffness characteristics of the leaf spring.

16. The reinforcing leaf claimed in claim 14 wherein, the reinforcing leaf is a curved beamed member having two points of inflection, one to each side of the midpoint.

17. The reinforcing leaf claimed in any one of claims 14 to 16 wherein, the height of the first and second ends above the leaf spring are adjustable so as to adjust the tension of the reinforcing leaf against the leaf spring and hence the spring rate of the leaf spring.

18. The reinforcing leaf claimed in any one of claims 14 to 17 wherein, the first and second securing means are clamps comprising U-bolts, adapted to extend underneath the leaf spring, cross-plates and nuts.

19. The reinforcing leaf claimed in any one of claims 14 to 18 wherein, the reinforcing leaf material is steel and specifically a high carbon, silicon-manganese alloy.

20. A reinforcing spring substantially as herein described with reference to and as illustrated by the accompanying drawings.

21. A reinforcing leaf substantially as herein described with reference to and as illustrated by the accompanying drawings. Dated this 14th day of August 2001 JSW PARTS PTY LTD By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia H:\Shonal\Keep\Speci\P43102 (CAP) REINFORCING SPRING 14/08/01