Land vehicles – Wheeled – Running gear
Patent
1996-06-07
1998-11-24
English, Peter C.
Land vehicles
Wheeled
Running gear
280124135, 280124179, 280 5515, 267248, 267255, B60G 320, B60G 1114
Patent
active
058397426
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a suspension system for wheeled vehicles, and in particular to a modular suspension system in which the energy storage medium may releasably store energy to any predetermined degree at any relative position between the wheel and hub assembly and the vehicle body.
2. Discussion of the Prior Art
Although not as old as the wheel itself, suspension can be traced back to well before the internal combustion engine and what we refer to as the car. The wheel has always been considered the key invention as it provided a means to transport objects that had previously been immovable. Once its usage became widespread, however, inherent problems became obvious. A vehicle (whether a farm cart or modern Formula 1 car) consists of a relatively large mass rolling on a surface by means of wheels. Most vehicles will operate acceptably, without suspension, if the surface in question is as smooth as a billiard table. If a bump is introduced which one or all of the wheels have to negotiate, however, three significant drawbacks become immediately evident. The entire vehicle is forced to travel up and over the bump resulting in:
(a) the passenger being directly subjected to the effect of the entire bump, so that what the industry refers to as "ride" suffers greatly;
(b) significant energy being expended as the mass of the entire vehicle is forced to rise up over the bump, which can significantly reduce the forward speed of the vehicle; and
(c) the vehicle becoming increasingly difficult to steer as forward speeds increase (to anything above that of a brisk walk) as it is pitched around by the bump, or by multiple bumps.
All of these drawbacks are significant and it should be understood that suspension is not installed just to improve "ride" quality. Modern racing cars do not use suspension for "ride" at all; it is included to deal with items (b) and (c) above almost exclusively, namely speed reduction and "pitch".
Suspension has evolved from leather straps on vehicles such as the Hansom cab to the almost universally accepted spring and damper arrangement. Some energy storage medium such as a spring is always included.
To understand how a modern suspension functions, one has to consider the vehicle as being comprised of five distinct mass systems (the main body and four wheel systems) as shown in FIG. 1 (assuming four wheel independent suspension). Obviously the primary system is the main vehicle weight which is referred to as the "sprung mass". Each wheel, tire and hub (usually with braking hardware attached) obviously has a significant weight and, being `upstream` of the suspension, is referred to as "unsprung mass". The root concept of modern suspension is to isolate the "unsprung mass" from the "sprung mass" by means of an energy storage medium, which is typically a spring. This allows the "unsprung mass" (wheel and hub assembly) to travel up and over bumps independently of the main vehicle mass. The lighter "unsprung mass" can move against the heavier "sprung mass" without upsetting the latter because of the large differential in inertias between them. The relatively lighter the "unsprung mass" (or conversely, the relatively heavier the "sprung mass") is, the better is the system performance. A spring (whether coil, leaf, torsion bar, air
itrogen, rubber etc.) is used to allow the wheel and hub assembly to move independently of the main vehicle mass.
This standard suspension configuration works well and such a suspension system can be tuned to a particular vehicle by changing the spring rate. However, a spring in isolation possesses an inherent deficiency in that once upset, it will continue to oscillate for a lengthy period unless external forces are brought to bear on it. A damper is thus included to offset the oscillatory nature of the spring and bring it to rest expeditiously.
The root of suspension theory is Newton's second law of motion (F=Ma). Force is equal to the mass times its acceleration. A spring generates force in reaction to a giv
REFERENCES:
patent: 1875314 (1932-08-01), Armstrong
patent: 1991911 (1935-02-01), Riley
patent: 2198544 (1940-04-01), Leighton
patent: 3157394 (1964-11-01), Kelley
patent: 3161420 (1964-12-01), Rix
patent: 3460852 (1969-08-01), Benson
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