Land vehicles – Wheeled – Running gear
Reexamination Certificate
2002-09-27
2004-02-10
English, Peter C. (Department: 3616)
Land vehicles
Wheeled
Running gear
C280S124150, C280S005521
Reexamination Certificate
active
06688620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to chassis systems for vehicles, in particular suspension devices, and more particularly the guidance of the wheels. Suspension devices have two main functions which must be fulfilled simultaneously at any moment during operation. One of these functions is that of suspending the vehicle, that is to say, permitting substantially vertical oscillations of each wheel in accordance with the load applied to the wheel. The other function of these devices is that of guiding the wheel, that is to say, controlling the angular position of the wheel plane.
2. The Related Art
The term “wheel plane” refers to the plane, associated with the wheel, which is perpendicular to the axis of the wheel and which passes through the center of the contact area with the ground. The angular position of the wheel plane with respect to the body of the vehicle is defined by two angles, the camber angle and the steering angle. The camber angle of a wheel is the angle separating, in a transverse plane perpendicular to the ground, the wheel plane from the mid-plane of the vehicle. This angle is positive when the upper part of the wheel deviates from the mid-plane towards the outside of the vehicle, this being commonly termed “camber” or “positive camber”. Conversely, when this angle is negative, the term used is “counter-camber” or “negative camber”. The steering angle of a wheel is the angle separating, in a horizontal plane parallel to the ground, the wheel plane from the mid-plane of the vehicle.
On most vehicles, the camber angle (“camber” or “camber angle” will be used without distinction hereinbelow) is fixed for a particular position of the suspension and the steering; that is to say, that theoretically it cannot vary independently of the suspension deflection or the steering. However, it undergoes variations induced by the deformations of the elements constituting the suspension device caused by the forces exerted on the wheel by the ground. These variations may be considerable. For example, an ordinary passenger car experiences camber variations of several degrees under the transverse forces developed on the tire on a curve, irrespective of the contribution of the rolling of the vehicle body (which generally tilts in the same direction under the effect of centrifugal force). This “elastic” variation of the camber causes the camber to increase (the camber tends towards positive values) for the outer wheel on the curve. Conversely, the camber decreases (it tends towards negative values) for the inner wheel on the curve. For a long time, these predictable variations have been incorporated in the design and adjustment compromises of the suspension devices of ordinary vehicles in order to limit the harmful effects which they have on the functioning of the chassis system.
The camber has a great influence on the behavior of the vehicle and the performance of the chassis system. In particular, the performance of a tire is very variable depending on the configuration of its contact area with the ground, which configuration depends largely on the camber. The choice of the static camber angle is based mainly on these variations. Thus, for example, a large negative static camber is generally introduced on a racing vehicle in order to compensate for the variations due to the deformations of the tire under transverse force, as well as the suspension elements, even though they are much more rigid than on passenger cars, and due to the rolling of the body. This configuration is both useful and acceptable in racing, since the criteria of grip on cornering are a major concern here. In contrast, on a passenger car, since the wear of the tires and the straight-line stability have more weight in the compromise being sought, a very slightly negative initial static camber is chosen. It is necessary to accept reduced slip thrusts when the deformations of the tire and the elements of the ground contact system under the lateral forces have their effects on the positioning of the wheel plane added to the effects of the rolling of the vehicle.
In order to optimize the camber, in particular during transverse accelerations, suspension devices whose camber varies in accordance with the vertical deflection of the wheel have been designed. In this way, the rolling experienced by the body of the vehicle can induce a useful variation of the camber which partly or totally compensates for the inclination of the body of the vehicle and the deformations described above. This is the case of the so-called “multi-link” systems. These devices require a specific design and vehicle architecture, which cannot be implemented on most current vehicles for reasons of space requirement and cost. These systems react only to the consequence (deflection, rolling) of a transverse acceleration and not to the forces which cause it, thereby, on the one hand, delaying the effect of the correction. Moreover, to permit a sufficient variation of the camber, the kinematics of these systems require displacements of the position of the contact area with respect to the vehicle, called “track changes”, and these variations can also create difficulty. The range of camber corrections made possible by such systems is therefore relatively limited when the compromise necessary for the correct functioning of the other load cases, such as travelling on a bumpy road, unilateral or in contrast simultaneous bouncing, is to be observed.
From the point of view of kinematics, in terms of degrees of freedom, suspension devices generally have only one degree of freedom (of the wheel or wheel carrier with respect to the vehicle). This degree of freedom permits vertical suspension movements which, as explained above, can be combined with limited camber variations.
Systems are known, however, in which the control of the camber is active; that is to say, the geometry modifications are controlled by movements of actuating cylinders, as described, for example, in the United States patent documents U.S. Pat. Nos. 4,515,390, 4,700,972 and German patent document DE 19717418. In these systems, at least a certain degree of additional freedom controlled by actuators has been permitted. These systems are very specific, since they cannot be used in the most ordinary vehicles, in particular because of their space requirement and the considerable power necessary for the actuators.
SUMMARY OF THE INVENTION
An object of the invention is a device of simple construction, which allows control of the camber without added energy, or with limited added energy, substantially independently from the vertical oscillations of the suspension and, more generally, of the movements of the body of the vehicle, and which makes it possible to minimize the track variations.
This object is achieved by a support device which is designed to connect a wheel to suspension elements of a vehicle, wherein the wheel, of a radius “R”, is designed to be supported on the ground, and the support device comprises camber means which provide the wheel with a degree of freedom of camber relative to the suspension elements. The support device is configured such that, about a mean position, the wheel allows a first instantaneous center of rotation, which is situated in an interval ranging from 0.5 R above the ground to R beneath the ground. In fact, this support device replaces the rigid wheel carrier according to the state of the art. The term “suspension elements” means the elements which assure that the load is carried and impart the generally vertical suspension movement to the wheel, such as the arms, springs, shock absorbers or anti-roll connections.
Preferably, the first instantaneous center of rotation is situated beneath the plane of the ground.
Also preferably, the first instantaneous center of rotation is situated transversely beneath the contact area.
According to one embodiment, the support device is configured such that it is close to equilibrium in the mean position, in the absence of transverse force exerted by the ground on the wheel in
Serra Loic
Tetaz Christian
Baker & Botts L.L.P.
English Peter C.
Michelin & Recherche et Technique S.A.
LandOfFree
Vehicle suspension with camber control does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Vehicle suspension with camber control, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Vehicle suspension with camber control will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3352751