FR2819752A1 - Vehicle wheel support and suspension system has suspension rods giving wheel a degree of camber freedom - Google Patents

Abstract

The support, connecting a vehicle wheel (2) of radius R to a suspension system, incorporates suspension rods (6, 7) which give the wheel a degree of camber freedom and a first instantaneous centre of rotation (CIR r/s) situated within an interval between 0.5 R above the ground and R below it. For an average position of the wheel the centre of rotation is located beneath the ground plane (S) and transversely beneath the wheel's area of contact (AC).

Description

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The present invention relates to the ground connection of vehicles, in particular the suspension devices, and more particularly the guidance of the wheels. Suspension devices have two main functions which must be carried out simultaneously at all times during operation. One of these functions is that of suspending the vehicle, that is to say allowing substantially vertical oscillations of each wheel as a function of the load applied to this wheel. The other of these functions of these devices is that of guiding the wheel, that is to say controlling the angular position of the wheel plane.

couramment de"carrossage"ou de"carrossage positif". A l'inverse, lorsque cet angle est négatif, on parle de "contre-carrossage" ou de "carrossage négatif". L'angle de braquage d'une roue est l'angle séparant, dans un plan horizontal parallèle au sol, le plan de roue du plan médian du véhicule. The plane, linked to the wheel, which is perpendicular to the axis of the wheel and which passes through the center of the area of contact with the ground, is called "wheel plane". The angular position of the wheel plane relative to the vehicle body 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 median plane of the vehicle. This angle is positive when the upper part of the wheel deviates from the median plane towards the outside of the vehicle, we then speak

commonly known as "camber" or "positive camber". Conversely, when this angle is negative, we speak of "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 median plane of the vehicle.

On most vehicles, the camber angle (we will use camber for camber angle later) is fixed for a particular position of the suspension and steering, i.e. it cannot theoretically vary independently of the suspension or steering travel. However, it undergoes variations induced by the deformations of the constituent elements of the suspension device caused by the forces exerted by the ground on the wheel.

These variations can be significant. For example, a current passenger vehicle sees its camber vary by several degrees under the transverse forces developed on the tire in a curve, independently of the contribution of the roll of the vehicle body (which generally tilts in the same direction under the effect of centrifugal force). This elastic variation in the camber causes the camber to tend towards positive values for the wheel outside the bend and towards negative values for the wheel inside the bend. These foreseeable variations have long been incorporated into the design or adjustment compromises of the suspension devices of these current vehicles in order to limit the harmful effects they have on the functioning of the ground connection.

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The camber has a great influence on the behavior of the vehicle and the performance of the ground connection. In particular, the performance of a tire varies widely depending on the configuration of its contact area on the ground and this configuration depends to a large extent on the camber. It is these variations that mainly motivate the choice of the static camber angle. Thus, for example, a large negative static camber is generally introduced on a competition vehicle in order to compensate for variations due to deformations of the tire, suspension elements which are however much more rigid than on passenger vehicles and the roll of the body. This configuration is both useful and acceptable in competition because the cornering grip criteria are predominant. On the contrary, on a passenger vehicle, the wear of the tires and the stability in a straight line having more weight in the desired compromise, one chooses an initial static camber very slightly negative and one accommodates reduced thrusts of drifts, mainly in curves, when the deformations of the tire and of the elements of the connection to the ground under the lateral forces see their effects on the positioning of the wheel plane add to the effects of the roll of the vehicle.

In order to optimize the camber, in particular during transverse accelerations, suspension devices have been designed, the camber of which varies as a function of the vertical travel of the wheel. In this way, the roll taken by the vehicle body can induce a useful variation of the camber which partially or totally compensates for the inclination of the vehicle body and the deformations described above. This is the case of systems called multi-arm. These devices require a specific vehicle design and architecture, which cannot, for reasons of space and cost, be implemented on most current vehicles. These systems react only to the consequence (clearance, roll) of a transverse acceleration and not to the forces which cause it which on the one hand delays the effect of the correction and on the other hand forces to tolerate a roll generally higher than the user might want. In addition, to allow a sufficient variation of the camber, the kinematics of these systems impose displacements of the position of the contact area relative to the vehicle, called lane variations and these variations can also constitute discomfort. The amplitude of the camber corrections made possible by such systems is therefore relatively limited.

From a kinematic point of view, in terms of degrees of freedom, the suspension devices generally have only one degree of freedom (of the wheel or of the wheel carrier relative to the vehicle). This degree of

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 freedom allows vertical suspension movements which, as we have just seen, can be combined with limited camber variations.

However, systems are known where the camber control is active, that is to say that the geometry modifications are controlled by movements of jacks, as described, for example, in documents US 4515390, US 4700972, and DE 19717418. In these systems, at least one additional degree of freedom has been allowed controlled by actuators. These systems are very specific since they cannot relate to the most common vehicles in particular because of their size and the large power required for the actuators.

In addition, the camber variations are accompanied by significant variations in body or track height.

An objective of the invention is a suspension device of simple construction, which allows a camber control without energy input or with a low input, substantially independently of 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 lane variations.

This objective is achieved by a suspension device connecting a wheel carrier to a body of a vehicle, said wheel carrier being intended to carry a wheel of radius 'r', said wheel being intended to rest on the ground by means of a contact area, said device comprising means giving the wheel carrier, with respect to the body, a degree of freedom of camber and a degree of freedom of suspension suspension travel independent of each other, characterized in that said device is configured so that the camber movement of the wheel carrier relative to the body admits, around a medium position, an instantaneous center of rotation located in an interval ranging from 0.5 r above the ground at r below the ground. The suspension device of the invention in fact comprises two degrees of freedom allowing independent suspension and camber movements. The camber movement takes place around an instantaneous center of rotation located at a limited distance from the contact area in order to limit track variations when taking camber or counter-camber and to limit the intake energy required in the case of an active camber control.

In a preferred embodiment, said instantaneous center of rotation is situated in an interval ranging from 0.2 r above the ground to 0.4 r below the ground and preferably still, from 0.1 r above the ground to 0.3 r below the ground .

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In order to ensure stable operation, the device is preferably configured so that it is close to equilibrium in said average position in the absence of transverse force exerted by the ground on the wheel in the contact area and preferably still, configured so that, in the absence of camber variations, the transverse force exerted by the ground on the wheel in the contact area generated during the suspension travel does not exceed not a limit corresponding to 0.3 P, P being the weight of the vehicle.

A preferred embodiment of the invention comprises an intermediate support linked on the one hand to the body and on the other hand to the wheel carrier, the connection of said intermediate support to the wheel carrier allowing said degree of camber freedom and the connection of said intermediate support to the body allowing said degree of freedom of suspension travel.

Preferably, to ensure better stability of the suspension device, the movement of the wheel carrier relative to the intermediate support admits, around said average position, an instantaneous center of rotation situated substantially in the plane of the wheel.

To allow passive operation, said instantaneous center of rotation may preferably be located under the ground plane so that transverse forces exerted by the ground on the wheel in the contact area induce an inclination of the wheel carrier relative to the body in the direction of a reduction in camber when said transverse forces are directed towards the interior of the vehicle and in the direction of an increase in camber when said transverse forces are directed towards the outside of the vehicle. In this case of passive operation linked to transverse forces, the device may include means for measuring the movement of the rocker in order to deduce said transverse forces.

One embodiment provides that the intermediate support is linked to the wheel carrier by connecting rods configured so as to allow the camber movement of the wheel carrier by an instantaneous movement of rotation of the wheel carrier relative to the intermediate support.

Under certain conditions, it may be necessary or advantageous to further provide control means capable of influencing the camber of the wheel. These means may include an elastically deformable element opposing the camber movement, the deformable element being constituted for example by elastomeric joints.

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Finally, the invention also relates to a vehicle equipped with such a suspension device. Several embodiments of the invention will be described in order to illustrate the characteristics and to set out the principles thereof. Of course, many other embodiments of the invention are possible as suggested by the many variations.

-Fig 1: Diagrams of principle and operation of a device according to the invention.

-Fig 2,3: Diagrams of a device according to a first embodiment of the invention in longitudinal view, -Fig 4,5, 6: Diagrams of principle and operation of different embodiments.

Figure 1 shows in plan longitudinal view the principle of a suspension device according to the invention. This planar representation (that is to say in 2 dimensions) is very convenient because it clearly shows how the device according to the invention differs from the devices of the prior art.

The suspension device 1 comprises a wheel carrier 3 intended to maintain the plane PR of a wheel 2, relative to the body 5 of a vehicle. The wheel of radius r is supported on the ground S by means of its contact area AC. The camber movement of the wheel is allowed by a connection of the wheel carrier 3 with the intermediate support 4 by links 6 and 7. The movement of suspension travel is allowed by a connection of the intermediate support 4 with the body 5 by upper arm 8 and lower 9. Thus, the suspension device 1 is configured so as to give the wheel carrier, relative to the body 5, a degree of camber freedom since the wheel carrier can tilt relative to the body and a degree of freedom of suspension since the wheel carrier can perform substantially vertical movements in a manner known per se, for example in the manner of multi-arm systems.

mouvement de suspension du support intermédiaire 4 par rapport à la caisse (CIR s/c) et celui du mouvement du porte-roue par rapport au support intermédiaire (CIR r/s). Ce raisonnement cinématique est d'usage courant dans le domaine de la liaison au sol. On comprend alors que c'est By admitting the classic hypothesis of a point connection of the wheel 2 on the ground S, the theory of the collinearity of the instantaneous centers of rotation in a planar movement makes it possible to locate the instantaneous center of rotation of the camber movement (CIR r / c) at the intersection of the wheel plane PR and the line (DC) carrying the two other instantaneous centers of rotation, that of

movement of suspension of the intermediate support 4 relative to the body (CIR s / c) and that of the movement of the wheel carrier relative to the intermediate support (CIR r / s). This kinematic reasoning is in common use in the field of ground connection. We understand then that it is

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 the choice of configuration, that is to say of the dimensions and of the orientation of the various constituent elements of the suspension device which (by defining the positions of the characteristic axes of the suspension elements) makes it possible to obtain a desired position of the instantaneous center of rotation (CIR r / c) of the camber movement. FIG. 1 represents the suspension device in a medium position, which could be defined as the position corresponding to driving in a straight line on flat ground, the vehicle carrying its rated load. The static camber is represented here by the angle a formed by the wheel plane PR with the vertical plane PV.

FIG. 2 represents an embodiment of the suspension device of the invention. In this example, the suspension movement movement is ensured by a Macpherson system comprising a strut 18 and a lower arm or triangle 19. The pivot axis AP is the axis around which the strut pivots to allow steer the vehicle in a manner known per se. On this strut is articulated a wheel carrier 3 by links 6 and 7. The strut plays in this embodiment constitutes the intermediate support 4 of Figure 1. The instantaneous center of rotation (CIR r / s) of the movement of the wheel carrier relative to this intermediate support is at the intersection of the axes of the links 6 and 7, under the contact area AC, in the wheel plane PR. In this preferred configuration, in application of the principle of collinearity, the instantaneous center of camber rotation (CIR r / c) is coincident with the instantaneous center of rotation (CIR r / s) of the movement of the wheel carrier relative to the intermediate support / strut 18.

This configuration presents a perfectly stable equilibrium, that is to say that even in the absence of stiffness at the level of the joints (as is the case for mechanical ball joints), the device in equilibrium in its average position in the absence transverse force (Fy) exerted by the ground on the wheel in the contact area. In practice, taking into account the various deformable elements such as the tire, a configuration close to equilibrium is satisfactory in terms of operation. Experiments have shown that when the position of the instantaneous center of rotation (CIR r / s) relative to the center of the wheel forms an angle less than 150 with the plane of the wheel, this condition is satisfied.

Figure 4 shows a different configuration from Figure 2 but uses similar elements. The difference lies in the fact that the wheel carrier 31 being located under the points of connection to the strut, the links 6 and 7 work in compression. Thus, the equilibrium of the wheel carrier is an unstable equilibrium while it is stable in the case of FIG. 2. In order to allow direct comparison with the other figures, the instantaneous centers of rotation (CIR r / b, CIR b / c, CIR r / c) have the same positions (in the middle position of the wheel). However,

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en terme de carrossage. Ainsi, ce point constitue également le centre instantané de rotation (CIR r/c) du mouvement de carrossage. On a représenté également en pointillé, un moyen de contrôle, de préférence actif, sous la forme d'un vérin apte à commander les variations de carrossage. Dans le cas d'un contrôle actif, la position du centre instantané de rotation (CIR r/c) du degré de liberté de carrossage se situera avantageusement au niveau du sol S ou au dessus de ce niveau mais à une distance réduite pour permettre un contrôle à faible énergie. this, as for the first mode, is only an example, an infinity of configurations being possible as described in figure 1. Figure 5 shows an architecture close to that of figure 1. Indeed, the degree of freedom suspension here is provided by a multi-arm or double triangle system known per se. In this example, the arms 81 and 91 being mutually parallel and horizontal, the straight line DC carrying the instantaneous centers of rotation is also horizontal. This device differs from that of FIG. 1 in that, according to a preferred embodiment similar to that of FIGS. 2 and 3, the instantaneous center of rotation (CIR r / s) of the movement of the wheel carrier 32 relative to the intermediate support 41 is positioned in the wheel plane PR, for an average position of the wheel 2

in terms of bodywork. Thus, this point also constitutes the instantaneous center of rotation (CIR r / c) of the camber movement. There is also shown in dotted lines, a control means, preferably active, in the form of a jack capable of controlling the camber variations. In the case of an active control, the position of the instantaneous center of rotation (CIR r / c) of the degree of camber freedom will advantageously be located at ground level S or above this level but at a reduced distance to allow a low energy control.

On the contrary, the control means can have a passive role of regulating the camber movements caused for example by transverse forces as shown in FIG. 3.

Whether passive or active, the control means, if it can be controlled, can be controlled as a function of various vehicle running parameters (for example, longitudinal or transverse acceleration, position of the steering wheel, roll, yaw sensor, efforts on the wheels, type of driving, behavior desired by the driver).

According to a similar construction, the control means can comprise a means of measuring camber movements. In the case of camber movements caused by transverse forces, this measurement makes it possible, by methods known per se, to know these forces. This information is useful for example for piloting safety systems or regulating the behavior of the vehicle.

FIG. 6 represents a device comparable to that of FIG. 5 in terms of kinematics but different in terms of balance as has been described for FIG. 4. The rods 6 and 7 work in compression between the wheel carrier 31 and the intermediate support 42. The spring 60 is shown

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 bearing on the intermediate support 42 but it can naturally bear on one of the upper 81 or lower 91 arms as in known suspension systems.

As we have seen, we can choose, depending on the desired operation, a position of the instantaneous center of rotation of the camber degree of freedom (CIR r / c) in an interval ranging from 0.5 r above the ground to r under the ground (r being the radius of the wheel). Positioning this point close to the ground limits the lane variation. For example, in the case of an instantaneous center of rotation located at r of the ground and for a wheel with a radius of 300 mm, a camber of 50 causes an offset of the contact area relative to the body (variation of half track) of about 25 mm. It was found that this value should be considered as a limit not to be exceeded. However, when the instantaneous center of rotation of the camber degree of freedom (CIR r / c) is situated above the ground, that is to say that the device of the invention must include an actuator in order to actively orient the plane wheel (see Figure 5), experiments have shown that beyond a certain height, the power required for this active operation makes the system too complex and above all too energy consuming. This limit height has been found to correspond substantially to a half wheel radius.

The different examples of the figures illustrate the fact that the suspension device of the invention can be produced from very different suspension principles, provided that the desired kinematic definition is obtained. In particular, the elements which have been represented in arbitrary forms can take any suitable form making it possible to adequately position the articulation axes and naturally to withstand the stresses of the suspension.

A particularity of the suspension device of the invention is that it is adaptable to all known suspension schemes since elements which allow a degree of camber freedom in addition to the existing suspension freedom are added to these existing systems. . An advantage of this device is its compactness which allows not to question the design of current vehicles.

The figures represent in projection on a plane orthogonal to the ground and transverse to the vehicle passing through the point of application of the resultant of the forces in the contact area, the principles and several embodiments of the invention. This two-dimensional representation is advantageous in order to clearly illustrate the essential characteristics of the device of the invention, the objective of which is a controlled variation of the camber. In this representation, the movement

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 Camber is a rotation in the plane around a pivot point (instantaneous center of rotation). However, it should not be forgotten that a rotation takes place in reality (in three dimensions) around a pivot axis, real or virtual (instantaneous axis of rotation). This axis is represented by a point in the planar representation. This axis can be constructed substantially parallel to the ground plane and to the longitudinal axis of the vehicle to allow the intended camber variations. However, by varying the orientation of this axis, it is possible to create additional turning, gripping, opening or winding effects as a function of the transverse (curve) and longitudinal (braking, acceleration) forces undergone by the wheel. in the contact area. A person skilled in the art knows, by carrying out tests and / or by theoretical methods, determining the orientation which should be adopted as a function of the behavior which he expects from this device. Experiments have for example shown that an inclination of the pivot axis of 6 relative to the horizontal makes it possible to induce a deflection linked to the camber, at an angle 10 times less than that of the camber. So when the transverse forces induce a camber of 5, the turning is around 0. 5. The inclination of the pivot axis can be obtained for example by equipping the vehicle with a device inclined by 60 relative to the vertical.

The articulations of the various elements of the suspension device of the invention can be produced in various ways. The elastomeric joints commonly used in the field of ground connection can make it possible to simplify the obtaining of the balance of the system because they introduce stiffnesses. On the other hand, it is known that they promote the comfort of the vehicle.

The device of the invention can be implemented in order to compensate for the deformations of the elements of the ground connection of current vehicles and allow better performance. That is to say that the device of the invention can be used to guarantee that the wheel plane remains, in all circumstances, substantially orthogonal to the ground plane or slightly inclined to also take account of any possible deformation of the tire. This object is achieved by a device of the invention whose useful camber amplitude is only a few degrees. However, the device of the invention can also be implemented with the aim of allowing a much greater variation in the camber, that is to say allowing an operation of the ground connection closer to that of a motorcycle than of that of vehicles with three wheels and more, currently on the market.

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 In general, the figures represent a wheel (2) comprising a pneumatic tire, but the invention is naturally intended for any type of wheel with or without an elastic tire, pneumatic or non-pneumatic, an essential characteristic being the position of the center. instantaneous rotation relative to the contact area, whatever it is.

Claims (11)

 Claims 1. Suspension device (1) connecting a wheel carrier (3) to a body (5) of a vehicle, said wheel carrier being intended to carry a wheel (2) of radius 'r', said wheel being intended to rest on the ground (S) via a contact area (AC), said device comprising means (4,6, 7,8, 9) giving the wheel carrier, relative to the body, a degree of freedom of camber and a degree of freedom of suspension travel independent of each other, characterized in that said device is configured so that the camber movement of the wheel carrier relative to the body admits, around an average position, an instantaneous center of rotation (CIR r / c) located in an interval going from 0.5 r above the ground to r below the ground. 2. Device according to claim 1, said instantaneous center of rotation (CIR r / c) being in an interval ranging from 0.2 r above the ground to 0.4 r below the ground. 3. Device according to one of the preceding claims, configured so that said device is close to equilibrium in said average position in the absence of transverse force (Fy) exerted by the ground on the wheel in the contact area. 4. Device according to one of the preceding claims, comprising an intermediate support (4) linked on the one hand to the body (5) and on the other hand to the wheel carrier (3), the connection of said intermediate support to the carrier wheel allowing said degree of freedom of camber and the connection of said intermediate support to the body allowing said degree of freedom of suspension travel. 5. Device according to claim 4, the movement of the wheel carrier (3) relative to the intermediate support (4,18, 41,42) admitting, around said average position, an instantaneous center of rotation (CIR r / b) located substantially in the plane of the wheel (PR). 6. Device according to one of the preceding claims, said instantaneous center of rotation (CIR r / c) being located under the ground plane (S) so that transverse forces (Fy) exerted by the ground on the wheel (2) in the contact area (AC) induce an inclination of the wheel carrier (3) relative to the body in the direction of a reduction in camber when said forces <Desc / Clms Page number 12>  transverse are directed towards the interior of the vehicle and in the direction of an increase in camber when said transverse forces are directed towards the exterior of the vehicle.

7. Device (1) according to one of claims 4 to 6, the intermediate support being connected to the wheel carrier by links (6,7) configured so as to allow the camber movement of the wheel carrier by an instantaneous movement of rotation of the wheel carrier relative to the intermediate support (4). 8. Device (1) according to one of the preceding claims, the intermediate support being linked to the body via a Macpherson system (18,19). 9. Device according to one of the preceding claims, further comprising control means (50) capable of influencing the camber of the wheel. 10. Device according to claim 9, the control means comprising an elastically deformable element opposing the camber movement, the deformable element being constituted by elastomeric joints. 11. Vehicle equipped with the device according to one of the preceding claims.