GB2157393A

GB2157393A - Improvements in and relating to leaf spring assemblies

Info

Publication number: GB2157393A
Application number: GB08409396A
Authority: GB
Inventors: Duncan Forbes Roberts
Original assignee: British Steel Corp
Current assignee: British Steel Corp
Priority date: 1984-04-11
Filing date: 1984-04-11
Publication date: 1985-10-23
Also published as: GB8409396D0

Abstract

A replacement leaf spring assembly comprises in combination tapered leaf springs 4 and shock absorbers each adapted to be compatible dimensionally and physically with the requirements of the vehicle into which they are to be assembled. The pack thickness of the tapered leaf springs when assembled as with packers 6 is no greater than the pack thickness of the leaf spring assembly to be replaced. The replacement leaf spring assembly may be provided in kit form. <IMAGE>

Description

SPECIFICATION Improvements in and relating to leaf spring assemblies This invention relates to leaf spring assemblies and more especially to tapered leaf spring replacement assemblies for vehicle suspensions.

Conventional vehicle suspensions comprise a multi-leaf laminated system of springs in which the individual leaf springs are generally of constant thickness throughout their length or a spring assembly in which the several leaf springs are tapered from their mid-portions towards their opposite ends. The latter spring system has been found to have increased spring life and give improved ride characteristics particularly on heavy goods vehicles and on buses, due to its reduced and more consistent frictional hysteresis. In addition, tapered leaf springs offer significant savings in weight and cost.

Consequently, when replacing the suspension system of vehicles originally fitted with a multi-leaf spring system, it would often be preferable to install a tapered spring assembly. To do so, however, presents severe design problems which hitherto, were believed either to be insurmountable or to be such as to render conversions to tapered leaf spring assemblies commercially unacceptable.

One particular problem which appeared to present a bar to conversions from standard to tapered leaf spring assemblies was the constraints imposed by the inability to vary the fixing points in the existing vehicle with the consequent need to retain the essential dimensional parameters of the original spring assembly. Thus, the essential dimensions of the replacement assembly are predetermined whereas the performance characteristics of the replaced and replacement assemblies are different. There is the additional and essential requirement that the vehicle, when converted, achieves the statutory requirements as defined by Instrument No. 257 Public Service Vehicles (Conditions of Fitness, Equipment, Use and Certification) Regulations 1981.

It is an object of the present invention to provide a leaf spring assembly which can readily replace the spring assembly of a suspension system of a vehicle such as a bus, coach or other heavy goods vehicle.

According to the present invention in one aspect there is provided a replacement leaf spring assembly comprising in combination tapered leaf springs and shock absorbers each adapted to be compatible dimensionally and physically with the requirements of the vehicle into which they are to be assembled, the pack thickness of the tapered leaf springs when assembled being no greater than the pack thickness of the leaf spring assembly to be replaced. Preferably the pack thickness of the tapered leaf springs is approximately the same as that of the assembly to be replaced.

According to the present invention in another aspect there is provided a replacement leaf spring assembly kit for a vehicle suspension comprising a plurality of tapered leaf springs and shock absorbers which assemble into a pack of thickness and camber at unladen suitable to replace the suspension system of the vehicle. Preferably each leaf of the assembly is tapered parabolically in thickness. Alternatively each leaf may be linearly tapered.

The invention will now be described by way of example only with reference to the accompanying diagrammatic drawings in which: Figure 1 is a side elevational view of a conventional multi-leaf spring assembly of a vehicle suspension system not in accordance with the invention; Figure 2 is a side elevational view of a tapered spring assembly in accordance with the invention which has been adapted to replace the spring assembly illustrated in Fig.

1; and Figures 3 and 4 are side elevational views in more detail of a spring assembly in accordance with the invention.

Tapered leaf springs offer significant advantages when employed in suspension units of heavy goods vehicles such as buses, coaches and lorries. Compared with conventional laminated springs, leaf springs which are tapered parabolically in thickness (as supplied under our registered trade mark "TAPERLITE") offer significant savings in weight and cost, increased durability and enhanced ride characteristics. Close uniformity of bending stress along the length of a tapered leaf is achieved and where several leaves are used, each leaf is of the same effective length and carries an equal proportion of the applied load. In addition, because the individual leaves of a tapered leaf spring assembly are separated over their working lengths, frictional forces are minimised giving improved conditions on which to base shock absorber design.

In view of the foregoing, the advantages of replacing conventional laminated spring assemblies in existing vehicles with tapered leaf spring assemblies will be appreciated. However, as mentioned above, the problems associated with such conversions appeared, on the face of it insurmountable or commercially nonviable.

Following extensive development and trials, the present invention was conceived which enables the conversions to take place.

A conventional multi-leaf spring assembly is illustrated in Fig. 1 and comprises a pack 1 of leaf springs, each spring being of constant thickness throughout its length. A tapered leaf spring assembly adapted to replace this spring assembly is illustrated in Fig. 2. In this assembly, each individual leaf spring 2 is ta pered parabolically in thickness to achieve a close uniformity of bending stress along its length.

To achieve substantially the same pack thickness, individually designed packers 3 are secured to the upper and lower surfaces of the spring assembly. In the assemblies illustrated in Figs. 1 and 2, the respective pack thicknesses are 120.7" and 120.5", the loaded cambers are 73.7" and 71.2" and the main leaf geometries are generally identical.

The spring assembly illustrated in Fig. 3 is suitable for installation in the rear suspension of a bus and includes three tapered leaf springs 4 spaced by shims 5 and including upper and lower packers 6. The leaf springs are clamped together towards their ends by clasps 7. The uppermost leaf spring extends in eyelets 8.

The spring assembly illustrated in Fig. 4 is suitable for installation in the front suspension of a double decker bus and includes two tapered leaf springs 4 spaced by shims 5. In this assembly, the two leaves are clamped by a single clasp 7. As for the assembly illustrated in Fig. 3, the uppermost leaf spring extends in eyelets 8. However, in the Fig. 4 assembly, one eyelet 8 is surrounded by a wrap 9 extending from the corresponding end of the lower leaf spring.

In each of the illustrated assemblies in accordance with the invention, the pack thickness of the replacement assembly is no greater than the thickness of the pack thickness of the assembly to be replaced. In some cases, the replacement pack thickness is significantly less than the pack thickness of the existing multi-leaf springs. In such cases, it may be necessary to reduce the length of the respective axle clamp 'U' bolts to accommodate the reduction in pack thickness.

In this case, the full steering geometry, brake geometry (in particular the mechanical linkages) and the drive lines between the gearbox and engine may need modification.

Furthermore, to reduce large negative laden cambers on some existing multi-leaf springs and so improve ride characteristics, increases in laden camber on replacement tapered springs may be necessary.

Tapered leaf spring assemblies in accordance with the invention may be supplied to the consumer as a kit of brackets, separate leaf springs, dampers, packers and other relevant parts which can readily be assembled by the consumer for conversion of existing multileaf suspension systems of vehicles. The brackets are designed specifically to withstand the shock absorber forces which are significantly higher, being capable of being fitted without substantially dismantling chassis components and do not transmit these excess forces to established weak areas of the chassis frame.

Claims

1. A replacement leaf spring assembly comprising in combination tapered leaf springs and shock absorbers adapted to be compatible dimensionally and physically with the requirements of the vehicle into which they are to be assembled, the pack thickness of the tapered leaf springs when assembled being no greater than the pack thickness of the leaf spring assembly to be replaced.

2. The assembly as claimed in claim 1 wherein the pack thickness of the tapered leaf springs is approximately the same as that of the assembly to be replaced.

3. A replacement leaf spring assembly kit for a vehicle suspension comprising a plurality of tapered leaf springs and shock absorbers which assemble into a pack of thickness and camber at unladen suitable to replace the suspension system of the vehicle.

4. An assembly as claimed in claim 3 wherein each leaf of the assembly is tapered parabolically in thickness.

5. An assembly as claimed in claim 3 wherein each leaf is linearly tapered.

6. A replacement leaf spring assembly substantially as herein described with reference to the accompanying drawings.