Abstract:
A motor vehicle fitted with a system for controlling the camber (θ) of the wheels of the vehicle on a bend, including, for each wheel of at least one front axle and/or rear axle of the vehicle, a suspension having a pair of suspension upper and lower arms, articulated at their outboard ends to a hub carrier and attached at their inboard ends to the body of the vehicle. The lower and upper arms of each pair are articulated at their respective inboard ends to a pivot transfer lever which is, in turn, mounted on the body by an articulation, the axis of rotation of which is contained in a longitudinal and vertical plane of the vehicle, the pivot transfer lever being capable of pivoting in such a way as to incline the wheels on the appropriate side.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a motor vehicle equipped with a system for controlling the camber of the wheels of the vehicle on a bend. 
     Motor vehicles are generally fitted with a spring suspension system minimizing the transmission of jolts and allowing for comfortable driving conditions. Parasitic wheel movements are caused, as the suspension travels, depending on the quality of the suspension. The position of the wheels with respect to the body and with respect to the ground can vary, according to the vehicle and according to the vehicle running conditions. In order to determine the position of the wheels of a vehicle, there have been defined the lock, which is the angle formed by the steered wheels with respect to the longitudinal axis of the vehicle when the steering wheel is turned, the toe-in (or toe-out), which is the angle of lock of the wheels in opposition directions from one another when the steering wheel is pointing in a straight line, and the camber, which is the inclination of the wheels with respect to the ground. The wheels of the vehicle are generally also allowed a certain degree of longitudinal travel in order not to detract from the comfort if the wheels slam into a pot hole, for example. 
     When a vehicle enters a bend, the body tends to lean toward the outside of the bend under the effect of centrifugal force, because of the presence of the suspension, and this causes body roll. At the same time, most of the weight of the vehicle is transferred onto the wheels of the vehicle on the outside of the bend. If the plane of the wheel is not correctly maintained, this additional load on the wheels on the outside of the bend will have a highly unfavorable loading effect on the tire, because the tire will then be in contact with the ground only by an outboard and reduced peripheral portion of the tread strip of the pneumatic tire and this will furthermore lead to premature tire wear. 
     Specifically, the wheels often incline toward the outside of the bend in a motor vehicle, unlike the situation with motorcycles in which the wheels are always inclined toward the inside of the bend. U.S. Pat. No. 4,159,128 has already proposed a vehicle suspension system equipped with a system for controlling the camber of the wheels of the vehicle on a bend and comprising, for each wheel of the vehicle front suspension, a pair of superposed suspension upper and lower arms articulated at their outboard end to a wheel support, the suspension lower arm being articulated at its inboard end to the vehicle body, while the upper arm is articulated to the upper end of a control lever, this control lever being articulated at its center to the body, and connected at its lower end to a means for controlling a steering rod for the front wheel of the vehicle. In this system, when the vehicle driver turns the steering wheel to cause the wheels to turn toward the inside of the bend, the means for controlling the steering rod causes the control lever to pivot so as to incline the wheel toward the inside of the bend. 
     However, in a system such as this, the inclination of the wheels can be applied only to steered wheels, and depends only on the wheel lock. It is therefore not able to take account of the centrifugal force or of the speed or of the acceleration of the vehicle. 
     French Patent Application Publication No. 2 745 757 proposes an assembly forming a suspended axle, comprising a pair of superposed suspension arms articulated, on the one hand, to the wheel support and, on the other hand, to the vehicle body, a damper articulated, on the one hand, to the suspension lower arm and, on the other hand, to a control lever articulated in turn on the body, the pivoting of the control lever being controlled by an actuator in order selectively to incline the vehicle wheels and body with respect to the ground. 
     In a more conventional and simpler way, to avoid the outboard wheels inclining toward the outside of the bend, certain vehicles have been fitted with negative camber, that is to say with wheels which are preinclined toward the inside of the vehicle, when driving in a straight line, so that on bends, the wheels on the outside of the bend at worst adopt a vertical position with respect to the ground. However, an arrangement such as this leads to excessive fatigue in the tires which, in a straight line, run on the inside of the tread strip. 
     SUMMARY OF THE INVENTION 
     The aim of the invention is to eliminate the aforementioned drawbacks and to propose a motor vehicle fitted with a system for controlling the camber of the wheels of the vehicle on a bend, which makes it possible to cause at least a slight inclination of the wheels of the vehicle toward the inside of the bend, in order to keep a good area of contact between the tires and the ground, without in any way influencing the body roll and without necessarily being slaved to the lock of the wheels of the vehicle. 
     To this end, the subject of the invention is a motor vehicle fitted with a system for controlling the camber of the wheels of the vehicle on a bend, comprising, for each wheel of at least one front axle and/or rear axle of the vehicle, a suspension means consisting of a pair of suspension upper and lower arms, articulated at their outboard end to a hub carrier and attached at their inboard end to the body of the vehicle, characterized in that the suspension lower and upper arms of each pair are articulated by their respective inboard end to one and the same pivot transfer lever which is, in turn, mounted on the body by an articulation, the axis of rotation of which is contained in a longitudinal and vertical plane of the vehicle, said pivot lever being capable of pivoting in such a way as to incline the wheels on the appropriate side. 
     Advantageously, for each pair of suspension arms, the inboard end of the suspension upper arm is articulated approximately at the upper free end of the pivot transfer lever, the inboard end of the suspension lower arm is articulated at an intermediate point on the pivot transfer lever, between its lower and upper ends, the said pivot lever being articulated to the body of the vehicle approximately at its lower end. 
     In a first embodiment, the two pairs of suspension arms associated respectively with the two transversely opposed wheels of one and the same, front or rear, suspension of the vehicle, are articulated to one and the same central pivot transfer lever. Of course, in this case, the suspension arms have to be long enough to reach a central, longitudinal, vertical plane of the vehicle. 
     In another preferred embodiment, the two pairs of suspension arms associated respectively with the two transversely opposed wheels of one and the same, front or rear, suspension of the vehicle, are articulated to two separate pivot transfer levers, said pivot levers being articulated on the body at points spaced apart in the transverse direction of the vehicle, so that the suspension is symmetric with respect to a central, vertical, longitudinal plane of the vehicle. In this case, the said pivot levers may be connected together by a connecting rod to form, with the said pivot levers and the body, an articulated parallelogram. 
     Advantageously, the ratio between the distance separating the lower end and the intermediate point of the pivot lever and the distance separating the upper and lower ends of the pivot lever, is chosen to be greater than a predetermined value so that the centrifugal force applied to the body of the vehicle will automatically, by reaction, cause the pivot lever to incline on the inside of the bend. 
     It is possible to envisage that, in the case of a front suspension, the suspension arms are connected at their outboard end to the hub carrier by a ball joint connection, a steering rod being connected to the hub carrier, and a damper connecting the body to the said suspension upper arm. 
     It is also possible to envisage that, in the case of a rear suspension, the suspension lower arm is connected to the hub carrier by a connection with just one axis of articulation parallel to the longitudinal direction of the vehicle, and a damper connects the suspension upper arm to the body. 
     Advantageously, the pivot lever is articulated with respect to the body of the vehicle in such a way that rotation of the pivot lever with respect to the body is about an instantaneous axis of pivoting separate from mechanical articulation points. 
     The instantaneous axis of pivoting of the pivot lever may be designed to be horizontal or alternatively inclined in order to induce a steering effect. 
     The instantaneous axis of pivoting of the pivot, lever may be designed to be above or below ground level, and preferably below the level of the mechanical articulation points. 
     In a first alternative form, the aforementioned control system comprises an elastic link with limited torsional deformation, connecting the pivot lever to the body at its aforementioned articulation, so that the said elastic link returns the pivot lever to an approximately vertical and longitudinal plane of the vehicle when the vehicle is running in a straight line, and limits the inclination of the said pivot lever with respect to the said plane, on a bend, the inclination of the pivot lever on a bend being brought about by reaction to the centrifugal force applied to the vehicle body. 
     In another alternative form, the aforementioned control system comprises an actuator carried by the body of the vehicle and connected to the pivot lever, the said actuator being capable of influencing the angular position of the pivot lever in a bend, it being possible for the said actuator to be slaved to the lock of the wheels, to the centrifugal force applied to the body, to the speed of the vehicle and/or to its acceleration. 
     The invention is also aimed at a motor vehicle equipped with a system for controlling the camber of the wheels of the vehicle on a bend, comprising, for each wheel of a front and/or rear suspension of the vehicle, a suspension means articulated, at its outboard end, to a hub carrier and borne on its inboard end by the body of the vehicle, characterized in that each suspension means is articulated to the body with a degree of freedom in rotation about an axis parallel to the longitudinal direction of the vehicle in order to vary the camber of the associated wheel, and the aforementioned control system comprises an elastic return means for urging the wheel in an approximately vertical and longitudinal plane of the vehicle when the vehicle is running in a straight line, and for limiting the inclination of the said wheel with respect to the ground in a bend, the said suspension means being designed in such a way as to cause the wheel to become inclined with respect to the ground on the inside of the bend, under the effect of the centrifugal force applied to the body. Advantageously, the aforementioned suspension means and the aforementioned control system are as defined in the vehicle described above. 
     In order to allow for a better understanding of the subject matter of the invention, three embodiments thereof, depicted in the appended drawings will now be described by way of purely illustrative and non limiting examples. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a diagrammatic partial perspective view of a front suspension of a motor vehicle according to the invention; 
     FIG. 2 is a diagrammatic partial perspective view of a rear suspension of a vehicle according to the invention; 
     FIG. 3 is a view in front elevation of the rear suspension of FIG. 2, in a position of running in a straight line; 
     FIG. 3A is a larger scale detail of FIG. 3; 
     FIG. 4 is a view similar to FIG. 3, but in a bend; 
     FIG. 5 is a view similar to FIG. 1, but for a rear suspension according to a third embodiment of the vehicle of the invention; 
     FIG. 6 is a diagrammatic view of one example of a suspension according to a fourth embodiment of the vehicle according to the invention; 
     FIG. 7 is a diagrammatic view of an alternative form of FIG.  6 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 depicts a front suspension for a motor vehicle. Each front wheel  1  consists of a pneumatic tire  2  and of a hub carrier  3  intended to carry the steering knuckle of the front axle of the vehicle. The hub carrier  3  comprises, on its inboard face, an upper lug  3   a  and a lower lug  3   b  which are diametrically opposed and capable of accommodating a ball joint for connecting them to the outboard end  4   a ,  5   a  of a suspension upper arm  4  and a suspension lower arm  5 , respectively. Articulated, approximately mid-way along the suspension upper arm  4  is the lower end  6   a  of a damper  6 , the upper end  6   b  of which is intended to be mounted, via a pivot connection, on the chassis C of the vehicle (depicted in FIGS.  3  and  4 ). The damper  6  consists, in a way known per se, of a cylinder and of a damper rod associated with a helical compression spring. 
     A steering rod  7  is mounted, at its outboard end  7   a , via a ball joint, on the hub carrier  3 , to control the lock of the wheels  1 . The rod  7  is connected, by a mechanism known per se, to the steering column which is operated by the vehicle steering wheel. 
     The inboard end  4   b  of the suspension upper arm is articulated to the free upper end of a pivot transfer lever  8  which is articulated, at its lower end, to an articulation spindle  9  extending in the longitudinal direction of the vehicle on its body. 
     The suspension lower arm  5  is in the form of a wishbone, the vertex of the triangular shape of which constitutes the outboard end  5   a  mounted on the hub carrier  3 , and the two ends of the base of the triangle of which are fork shaped and constitute the inboard ends  5   b  of the suspension lower arm, which are articulated at an intermediate point along the pivot transfer lever  8 . This pivot transfer lever  8  is, in fact, formed of a first longer link rod  8   a , to which the inboard end  4   b  of the suspension upper arm  4 , an inboard branch  5   b  of the suspension lower wishbone  5  and the aforementioned articulation spindle  9  are articulated, and of a second, shorter, link rod  8   b  to which only the other branch  5   b  of the suspension lower wishbone  5  and the articulation spindle  9  are articulated. The pivot lever  8 , the arms  4  and  5  and the hub carrier  3  together form an articulated quadrilateral. 
     A connecting rod  10  extends in the transverse direction of the vehicle and connects the two pivot transfer levers associated with the front left and front right wheels. The connecting rod  10  is connected to each pivot transfer lever  8  by one of its ends  10   a  at an intermediate point between the articulation spindle  9  and the point of articulation with the suspension lower arm  5 . Thus, the two pivot transfer levers  8  and the connecting rod  10  form, with the chassis, an articulated parallelogram. 
     FIGS. 2 to  4  depict the rear suspension, in which elements which are identical to or similar to those of the front suspension carry the same reference numerals increased by  10 . 
     The main differences between the rear suspension and the front suspension relate to the steering rod  17  which, in this instance, is attached at its outboard end to the hub carrier  13  and, at its inboard end to the rear of the body of the vehicle, to prevent the rear wheels  11  from steering. The suspension lower arm  15  and the suspension upper arm  14  are connected to the hub carrier  13  by pivot connections with just one axis of articulation oriented in the longitudinal direction of the vehicle as best visible in FIG.  2 . 
     FIG. 5 depicts an alternative form of the rear suspension, in which elements which are identical or similar to those of the front suspension carry the same reference numerals increased by  20 . 
     In this alternative form, the connecting rod  10  has been omitted and there is just one pivot lever  28  located at the center of the chassis and to which the suspension arms  24 ,  25  of each transversely opposed wheel are connected, the arms  24 ,  25  being envisaged longer for this purpose. 
     The way in which the invention works will now be described with reference to FIGS. 3 and 4. 
     In the alternative form illustrated in FIG. 3, it is possible to envisage for the articulation spindle  19  of the pivot lever  18  to be equipped with an elastic sleeve S (see FIG. 3A) for connecting it to the body C, the said elastic sleeve being able to deform in terms of torsion so as to limit the pivoting of the pivot lever  18  with respect to the articulation spindle  19  and to return it to its approximately vertical position, when not in bends. 
     In this case, when the vehicle enters a bend, the weight of the body C is transferred to the outside of the bend because of the centrifugal force and the asymmetric compression of the dampers  16 . In FIG. 4, the arrow V has been used to indicate the direction of the bend in which the vehicle has to turn. Given that the chassis C is carried toward the outside of the bend, the articulation spindle  19  of the pivot lever  18  is moved to the left in FIG. 4, that is to say toward the outside of the bend with respect to the wheels  11  of the vehicle. This causes the pivot lever  18  to pivot in a clockwise direction in FIG. 4 about the articulation spindle  19  by an angle θ approximately equal to 10-15°. The pivoting of the pivot lever  18  causes the suspension lower arm  15  and the upper arm  14  to move at the same time, thus causing a corresponding inclination of the wheels  11  on the inside of the bend. Of course, to cause the pivot lever  18  to pivot automatically on the inside of the bend in reaction to the centrifugal force applied to the chassis C, the values L and l have to be chosen in such a way that the ratio l/L exceeds a predetermined value, l being the distance between the articulation spindle  19  and the inboard end  15   b  of the suspension lower arm  15  and L being the distance between the articulation spindle  19  and the inboard end  14   b  of the suspension upper arm  14 . 
     FIG. 4 depicts the wheels in an inclined position, on a bend, without depicting the body C in its true position inclined toward the outside of the bend under the effect of centrifugal force. In reality, the slight inclination of the wheels  11  of the vehicle will at least compensate for the inclination in the opposite direction of the wheels on the outside of the bend, under the effect of centrifugal force, so that the area for contact between the pneumatic tires  12  of the wheels  11  and the ground will remain sufficient. As indicated by the arrows F in FIG. 4, the force with which the wheels  11  press on the ground is oriented toward the inside of the bend, which contributes to good road holding, as is the case in motorcycles, in which the wheels exert thrust with the camber oriented toward the inside of the bend. 
     In another alternative, it would be possible to envisage one pivot lever  18  being controlled in terms of rotation by an actuator  21  depicted in broken line in FIG. 4, for influencing the inclination of the pivot lever  18  in a bend, on the basis of parameters detected, such as the wheel lock, the centrifugal force, the speed and/or the acceleration of the vehicle. 
     One of the principles of the invention consists in attaching the suspension lower and upper arms to an intermediate pivot transfer lever rather than attaching them directly to the body. 
     In the case of an elastic sleeve with torsional deformation, it is possible to speak of the vehicle having reactive camber control whereas, in the case of the actuator  21 , the control is said to be active camber control. 
     In the embodiment of FIG. 5, the articulation spindle  29  of the pivot lever  28  is an instantaneous axis of pivoting of the pivot lever  28 . The location of this axis with respect to the ground is limited by the ground clearance of the vehicle. Thus, the instantaneous axis of pivoting of the pivot lever  28  is always above ground level. 
     To optimize the position of the instantaneous axis of pivoting in terms of performance, it has been sensible to provide a pivot lever capable of pivoting about a virtual axis transferred to any desired position, particularly one below ground level. 
     Two embodiments of a pivot lever such as this are depicted diagrammatically in FIGS. 6 and 7. 
     In FIG. 6, each wheel  11  has a hub carrier  33  on which a suspension upper arm  34  and a suspension lower arm  35  are articulated. A U-shaped pivot lever  36  is provided, this lever having a central part  37  extending transversely with respect to the vehicle and two arms  38  and  39  extending downward, parallel to the respective hub carrier  33 , and converging downward. 
     Each suspension upper arm  34  is articulated, on the one hand, to the upper part of the respective hub carrier  33  and, on the other hand, to the upper part of the arm  38  (or  39 ) of the pivot lever  36 . Each suspension lower arm  35  is articulated, on the one hand, to the lower part of the respective hub carrier  33  and, on the other hand, to an intermediate point on the arm  38  (or  39 ) of the pivot lever. Thus, the hub carrier and the arms  34 , 35  and  38  (or  39 ) constitute articulated parallelograms. 
     Articulated to the lower ends  42 ,  43  of the arms  38 ,  39  of the pivot lever  36  are the rods  40 ,  41  respectively. The other ends  44 ,  45  of the rods  40 ,  41  are articulated to the vehicle body. The rods  40 ,  41  are arranged approximately parallel to the arms  38 ,  39  of the pivot lever  36 , that is to say converging downward, at a point  46  which corresponds to the instantaneous axis of pivoting of the pivot lever  36 . This instantaneous axis of pivoting can be placed above or below ground level, and preferably below the level of the mechanical articulation points. 
     In FIG. 7, the pivot lever  36  has the same structure as in FIG. 6, but the connection with the vehicle body is obtained via a curved sliding connection  47  made of an elastic component. 
     The point  46  in FIGS. 6 and 7 constitutes a kind of virtual pivot, corresponding to an instantaneous axis of pivoting separate from mechanical articulation points. 
     The pivot lever  36  has been described in conjunction with FIGS. 6 and 7 in a particular embodiment. It should be noted that the pivot lever can have any arbitrary shape and that only the points at which the various elements are articulated to the pivot lever are functional. The shape of the pivot lever is determined according to the constraints on space under the vehicle and to the method of assembling the suspension means to the body of the vehicle. Thus, the pivot lever may be of a closed shape or may be open, for example towards the top or towards the bottom (as is the case in FIG.  6 ). 
     The virtual axis of pivoting, symbolized by the point  46 , may be horizontal or may be inclined in order, for example, to induce a steering effect when going round a bend. 
     Although the invention has been described in conjunction with a number of particular embodiment variations, it is quite obvious that it is not in any way restricted thereto and that it comprises all technical equivalents of the means described and combinations thereof where these fall within the scope of the invention.