GB2219646A - Eccentric ring nest suspension - Google Patents

Abstract

A vehicle suspension unit is made up from a number of cylindrical spring steel rings 5 of decreasing radius, commonly secured at their base to a wheel axle 8 so as to form an eccentric ring nest, with the outer ring 1 secured at its uppermost point 9 to the vehicle body. This provides a simple method of obtaining a variable spring rate which is low for small deflections and high for larger deflections of the suspension. <IMAGE>

Description

Eccentric Ring Nest Suspension This invention relates to a flexible suspension system for vehicles, based upon an eccentric ring nest.

Rll vehicles utilise a flexible suspension system between the wheel axles or arms and the vehicle body, in order to minimise the level of vibration and shock loading transmitted from road undulations during horizontal motion.

Passenger comfort is thereby enhanced and cyclical stress on the vehicle body structure is reduced. The most widely used suspension system has been the steel spring support, configured either as a helical coil or as a composite laminar leaf spring.

In terms of their elastic response, both coil and leaf springs are linear over their effective working range, that is to say that a doubling of applied force produces a doubling of spring displacement. This ratio of force over displacement is known as the Spring Rate of the suspension system. The geometry of a spring can be arranged to provide a high spring rate for 'hard* suspension or a low rate for MsoftI suspension.

The vehicle designer's problem is that a soft suspension gives maximum passenger comfort for steady cruising, but allows body roll during cornering manoeuvers, nose dip on sharp braking, and lurching from shock loads. Conversely, a hard suspension gives good dynamic performance during cornering and braking, but poor comfort for cruising.

The ideal solution is a suspension which is soft for small displacements, but which becomes progressively harder for larger displacements. This has been achieved by combining steel springs with hydraulic shock absorbers and torsion bars, to give a variable spring rate to the ruspension. This combination is complex and relatively expensive. So too are the sophisticated suspension systems which derive a variable spring rate from hydro-pneumatic pistons and chambers.

According to the present invention, a variable spring rate is more simply provided by an Eccentric Ring Nest, made up from a number of cylindrical rings of decreasing radius, commonly secured at their base to the wheel axle, and with the outer ring secured at its uppermost point to the vehicle body. Thus as the outer ring is compressed by road forces, it makes contact with an increasing number of rings, thereby progressively increasing the effective spring rate of the suspension. The quantity of rings in the nest and their individual geometry is determined by the mass of the vehicle, the static load to be carried at each wheel location, and the desired shape of the non-linear elastic response curve of the suspension.

With reference to the accompanying drawings, Figure 1 shows the effect on an eccentric ring nest of a vehicle static weight FO, a moderate road force F1, and a shock load F2, together with the resultant displacements D1 and 02.

In Figure 2, those effects are shown as an elastic response curve where displacement D is plotted against force F, to demonstrate the variable spring rate.

R specific embodiment of the invention will now be described by way of example, with reference to the accompanying drawings, in which Figure 3 shows an eccentric ring nest applied to rear axle suspension of a vehicle.

In this example, a 4 ring nest is fitted to the vehicle chassis using high tensile strength U-bolts 2, which penetrate pre-drilled holes in the chassis, and are tightened by nuts 3 and locking washers 4. The ring nest is fitted to the rear axle 8 using similar U-bolts 6, clamp plates 7, nuts 3, and locking washers 4.

The outer ring 1 is comprised of spring grade solid or laminated steel strip rolled into a tulip shaped profile to accomodate the upper U-bolts 2 in the lip portion 9, and sized to compress into circular profile in the bowl portion 10 under static force loading. The inner rings 5 are comprised of spring grade solid or laminated steel strip rolled and welded into circular profile.

Increasing road forces compress the outer ring in the vertical plane until it makes contact with the first inner ring 5.

Further increases in road forces compress the outer and first inner rings into elliptical shape until the first and second inner rings make contact, and so on. The spring rate increases with each ring contact.

Upon release of the road force the ring nest restores to its static condition. Any overshoot caused by vehicle body momentum is arrested by the compression of the ring nest in the horizontal plane.

Forced oscillations of increasing amplitude are prevented by the fact that each component ring of the nest exhibits a different natural frequency of vibration.

The suspension system's reliance upon contacting faces of the eccentric rings will give rise to some noise. This can be attenuated by fitting replaceable rubber sleeves 17 to the rings, where such noise is not desirable.

Claims (6)

Claims

1.Pn Eccentric Ring Nest suspension made up from a number of cylindrical rings of decreasing radius, commonly secured at their base to the wheel axle of a vehicle, and with outer ring secured at its uppermost point to the vehicle.

2.Pn Eccentric Ring Nest suspension as claimed in Claim 1 wherin the spring rate of the suspension increases as more rings are brought into contact during compression.

3.Pn Eccentric Ring Nest suspension as claimed in Claim 1 wherein the outer ring is ovally profiled so as to assume a circular shape when subjected to the static weight of the vehicle..

4.fln Eccentric Ring Nest suspension as claimed in Claim 1 wherein there is no single natural frequency of oscillation over the deflection range.

5.An Eccentric Ring Nest suspension as claimed in Claim 1 which can carry replaceable rubber sleeves on each ring for nose attenuation.

6.Pn Eccentric Ring Nest suspension substantially as described herein with reference to figures 1-3 of the accompanying drawings.