Abstract:
The invention relates to a rear wheel suspension system for motor vehicles having a composite link axle that has two wheel-carrying longitudinal links that are each articulated pivotably on a vehicle body by one body-side pivoting bearing and a flexurally rigid, torsionally soft transverse strut that connects the longitudinal links to one another. The pivoting bearings are set at a predefined yaw angle in relation to an initial position with the pivoting bearing axes aligned with a connecting line between the centers of the pivoting bearings. The pivoting bearings are also set at a predefined roll angle relative to a horizontal plane.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to German patent application DE 10 2010 017 812.8, filed Jul. 8, 2010, the disclosure of which is hereby incorporated by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The invention relates to a rear wheel suspension system for motor vehicles having a composite link axle having two wheel-carrying longitudinal links that each are articulated pivotably on a vehicle body by a body-side pivoting bearing, and a flexurally rigid, torsionally soft transverse strut that connects the longitudinal links to one another. The pivoting bearings are set at a predefined yaw angle in relation to an initial position, in which the pivoting bearing axes are aligned with a connecting line between the centers of the pivoting bearings. 
       BACKGROUND 
       [0003]    A rear wheel suspension system having a composite link axle, the links of which are connected to one another by a torsion rod, is known, for example, from DE 37 07 162 A1. A rear wheel suspension system of this type generally has a left-hand and a right-hand longitudinal link which are articulated with their front ends on the vehicle body by means of rubber elements, with the result that they can perform a vertical pivoting movement with regard to a roadway plane, and a torsion rod which connects the center regions of the longitudinal links to one another. The rear wheels are supported at the rear ends of the longitudinal links, with the result that vertical movements of the rear wheels relative to one another on account of roadway unevennesses are delimited by the torsional counterforce of the torsion rod. 
         [0004]    As is known, composite link axles of this type tend to oversteer under lateral force. In order to counteract this oversteer tendency and to improve the driving behavior of the motor vehicle when driving around bends, DE 37 07 162 A1 proposes rotating the pivoting axes of the pivoting bearings by a predefined yaw angle in a horizontal plane which is parallel to the roadway plane, with the result that the pivoting axes intersect in front of the connecting line between the body-side ends of the longitudinal links. The pivoting bearings are set in this way to control the toe of the rear wheels as a function of a lateral force which acts on the rear wheels when driving around bends (toe control). 
         [0005]    Furthermore, DE 35 24 763 A1 discloses a motor vehicle rear axle, in which the body-side pivoting bearings of wheel control elements carry the wheels are arranged and configured elastically or elastokinematically to counteract a tendency of the wheel control elements to yield in the direction of oversteer when driving around bends under the action of lateral forces that act on the wheels. In particular, the pivoting axes of the pivoting bearings are guided in each case in elastomeric elements and in a slotted guide that extends at an angle obliquely with respect to the vehicle longitudinal axis. 
         [0006]    DE 36 36 878 A1 describes an axle suspension system for motor vehicles which consists of two longitudinal links, that are articulated pivotably on the vehicle body and carry the vehicle wheels. The ends of a flexurally rigid but torsionally soft transverse strut are connected to the two longitudinal links in an angularly rigid manner. In particular, the bearing axes of the link bearings are set obliquely to the front in such a way that their extensions intersect in the vehicle center plane and in front of the link bearings. 
         [0007]    Finally, DE 10 2008 035 625 A1 describes a motor vehicle rear axle as composite link axle with two wheel-carrying, rigid longitudinal links, that are articulated elastically on the vehicle body, and a flexurally stiff but torsionally soft transverse strut. The pivoting axes of the pivoting bearings of the rear axle are set obliquely to the front in relation to a connecting line between the pivoting bearings. 
         [0008]    The kinematic behavior of composite link axles is fixed by a few design parameters. The behavior is fixed, in particular, by the position of the elastomeric bearing bushes which are preferably arranged in the body-side pivoting bearings and by the shear center height of the torsion profile. The orientation of the pivoting bearing bushes plays an important role on account of the elastic properties of the bearing bushes. As a rule, the elastomeric bearing bushes are configured to be substantially softer in the axial direction than in the radial direction. 
         [0009]    Controlling the roll steer of the composite link axle during rolling, wheel camber change during rolling and the roll center height are the most important parameters for rear wheel suspension systems. These parameters cannot be set independently of one another. With the given design parameters, a partially undesired elevation of the roll center results from an increase in the roll control and an increase in the wheel camber change during rolling. 
       SUMMARY 
       [0010]    According to one aspect of this disclosure, a rear wheel suspension system is provided that has a composite link axle. The composite link axle affords satisfactory toe behavior by way of its elastokinematic behavior and additionally presents the option of increasing the roll control, while at the same time the roll center is lowered and, moreover, the wheel camber change during rolling is positively influenced. 
         [0011]    According to one aspect of the disclosure, the rear wheel suspension system comprises a composite link axle which has body-side pivoting bearings that are set at a predefined yaw angle in relation to an initial position. The pivoting bearing axes are aligned with a connecting line between the centers of the body-side pivoting bearings and are set at a predefined roll angle. 
         [0012]    A yaw angle is set by rotating the pivoting bearings about a yaw axis (vertical axis) that extends through the center of the respective pivoting bearings and parallel to a vehicle yaw axis (vehicle vertical axis). After rotation, the pivoting bearing axes are inclined with respect to the connecting line between the centers of the pivoting bearings. A roll angle is set by rotating the pivoting bearings about a roll axis (longitudinal axis) that extends through the center of the respective pivoting bearings and parallel to a vehicle roll axis (vehicle longitudinal axis). After rotation, the pivoting bearing axes are inclined with respect to a horizontal plane that extends through the centers of the pivoting bearings and parallel to the roadway plane. The center of a pivoting bearing is understood to be a point that, with regard to the width, lies in the center of the pivoting bearing and on the pivoting bearing axis of the associated pivoting bearing. 
         [0013]    Surprisingly, it has been shown in a comparison between composite link axles according to the invention and link axles that have the pivoting bearings set merely at a yaw angle, that the additional setting of the pivoting bearings at a roll angle substantially influences the elastokinematic behavior of the composite link axle and presents the option of increasing the roll control. The composite link axle lowers the roll center and, moreover, the wheel camber change is positively influenced during rolling. 
         [0014]    The pivoting bearings have a three-dimensional (spherical) setting with respect to the abovementioned initial position after the rotation about the yaw axis and the rotation about the roll axis. Rotation about the yaw axis brings about a planar setting of the pivoting bearings with respect to the initial position. The penetration point of the pivoting bearing axes through the vehicle longitudinal center plane preferably lies in front of the connecting line between the centers of the pivoting bearings and horizontal plane which extends parallel to the roadway plane. As a result, the roll control of the composite link axle is increased with satisfactory toe control, and at the same time the roll center is lowered. Moreover, the wheel camber change is positively influenced during rolling. 
         [0015]    The setting of the pivoting bearings is not restricted to a defined roll or yaw angle. Preferably, the roll angle is selected from a range from approximately 5° to approximately 25°, preferably from 5° to 15°, more preferably 6°, and the yaw angle is selected from a range from approximately 5° to approximately 45°. The selection of the roll angle depends on the service life of the bush and the mounting conditions. 
         [0016]    The pivoting bearings are preferably configured as elastomeric bearings, for example by rubber elements or elastomeric bearing bushes that are inserted in each pivoting bearing. The construction of the rubber elements is known in principle. The elastomeric bearings are advantageously configured to be softer and more compliant in the axial direction than in the radial direction. This makes possible a defined axial displacement of the bearings as a function of longitudinal, transverse and/or rolling forces which occur in the respective driving state. The rigidity ratio between the axial and radial rigidity is advantageously approximately 1:10. That is to say, the elastomeric bearing bushes have a rigidity which is 10 times higher in the radial direction than in the axial direction. Axial displacement is defined to configure the elastokinematic behavior of the rear wheel suspension system in a targeted manner. The rolling behavior and the toe behavior can be varied within a wide range by the selection of the setting of the longitudinal links in the roll angle and yaw angle and by the elastic properties of the elastomeric bearings. The respective setting magnitude (roll angle left/right) may be identical, but it is also possible for different setting magnitudes to be selected. 
         [0017]    The above advantages are achieved by a rear wheel suspension system having the features of patent claim  1 . Further, particularly advantageous refinements of the invention are disclosed by the subclaims. It is to be noted that the features that are described individually in the patent claims can be combined with one another in any desired, technically appropriate way and indicate further refinements of the invention. The description additionally characterizes and specifies the invention with reference to the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Further advantageous details and effects of the invention are explained in greater detail in the following text using an exemplary embodiment which is not to be considered restrictive and is illustrated in the drawing, in which, diagrammatically: 
           [0019]      FIG. 1  shows a front view of an embodiment of the rear wheel suspension system according to the invention, 
           [0020]      FIG. 2  shows a plan view of the rear wheel suspension system according to the invention of  FIG. 1 , 
           [0021]      FIG. 3  shows a front view of a rear wheel suspension system according to the prior art, and 
           [0022]      FIG. 4  shows a plan view of the rear wheel suspension system according to the prior art of  FIG. 3 . 
       
    
    
       [0023]    Further advantageous details and effects of the invention are explained in greater detail in the following text using an exemplary embodiment which is not to be considered restrictive and is illustrated in the drawing, in which, diagrammatically: 
         [0024]    In the different figures, identical parts are always provided with the same designations, with the result that they are also as a rule described only once. 
       DETAILED DESCRIPTION 
       [0025]    A coordinate system is illustrated in each case in  FIGS. 1 to 4 . In  FIGS. 1 to 3 , the Z axis is oriented to the upper figure edge, and in reality is oriented to the top. In this context, reality means the natural perception of the driver. The Y-axis is oriented to the left-hand figure edge, but in reality is oriented to the right, that is to say to the right-hand vehicle side. In  FIGS. 2 and 4 , the X axis is oriented to the upper figure edge, and is oriented to the rear in reality. The Y axis is oriented to the left-hand figure edge, but is oriented to the right in reality, that is to say to the right-hand vehicle side. In the following text, the realistic side designation is chosen for the side designations in a deviation from the respective drawing plane. 
         [0026]      FIG. 1  and  FIG. 2  show a preferred embodiment of the rear wheel suspension system according to the invention having a composite link axle  1 ,  FIG. 1  representing a front view and  FIG. 2  representing a plan view of the latter. The composite link axle  1  comprises a left-hand longitudinal link  2  (not on the left in the drawing plane) and a right-hand longitudinal link  3  (not on the right in the drawing plane), as can be seen in the plan view in  FIG. 2 . Furthermore, each longitudinal link  2 ,  3  has, at its body-side ends that are directed to the front in the vehicle longitudinal direction, a left-hand body-side pivoting bearing  4  (not on the left in the drawing plane) and a right-hand body-side pivoting bearing  5  (not on the right in the drawing plane). 
         [0027]    The composite link axle  1  is articulated pivotably via the pivoting bearings  4 ,  5  on an auxiliary frame or vehicle body (not shown). The longitudinal links  2 ,  3  carry a left-hand wheel  6  (not on the left in the drawing plane) and a right-hand wheel  7  (not on the right in the drawing plane) at their ends that face away from the body-side pivoting bearings  4 ,  5 . The wheels  6 ,  7  are mounted rotatably on the longitudinal links  2 ,  3  by bearing elements (not shown). The longitudinal links  2 ,  3  are connected to a flexurally rigid, preferably torsionally soft transverse strut  14  in a front region of the longitudinal links  2 ,  3  but spaced apart somewhat to the rear from the body-side pivoting bearings  4 ,  5  in the drawing plane. 
         [0028]    In each case a left-hand reinforcing element  8  and a right-hand reinforcing element  9  extend between the ends of the transverse strut  14  that are connected to the longitudinal links  2 ,  3  and the wheel-side ends of the longitudinal links  2 ,  3 . The reinforcing elements  8 ,  9  are each connected to a narrow side of the respective longitudinal link  2 ,  3  and in a region along the end sections of the transverse strut  14  to the latter, preferably in a material to material manner, such as by welding. The reinforcing elements  8 ,  9  are configured to each to receive and support a damping element  10 ,  11 , for example a shock absorber, and a spring element  12 ,  13 , for example a coil spring. The reinforcing elements  8 ,  9  are arranged between the longitudinal links  2 ,  3  and the transverse strut  14  to reinforce the longitudinal links  2 ,  3  with respect to lateral forces that act on the wheels  6 ,  7 . The reinforcing elements also hold the longitudinal links  2 ,  3  in an angularly rigid manner with respect to the transverse strut  14 . 
         [0029]    As can be seen in  FIG. 1 , the pivoting bearings  4 ,  5  are each set at a roll angle  18  with respect to the horizontal plane  26  that extends through the centers of the pivoting bearings  4 ,  5  and parallel to the roadway plane. The left-hand pivoting bearing  4  is rotated by the roll angle  18  about a left-hand roll axis  20  (longitudinal axis) that is assigned to the left-hand pivoting bearing  4 , as shown in  FIG. 2 , and extends through the center of the left-hand pivoting bearing  4  and parallel to the vehicle longitudinal axis. Referring to  FIG. 1 , the rotation of the left-hand pivoting bearing  4  by the roll angle  18  is in the clockwise direction. The right-hand pivoting bearing  5  is rotated by the roll angle  18  about a right-hand roll axis  21  (longitudinal axis) that is assigned to the right-hand pivoting bearing  5 , as shown in  FIG. 2  and extends through the center of the right-hand pivoting bearing  5  and parallel to the vehicle longitudinal axis. Referring to  FIG. 1 , the rotation of the right-hand pivoting bearing  5  by the roll angle  18  takes place in the counterclockwise direction. 
         [0030]    After the rotation of the pivoting bearings  4 ,  5  by the roll angle  18 , the corresponding pivoting bearing axes  16 ,  17  are inclined by the roll angle  18  with respect to the horizontal plane  26  that extends through the centers of the pivoting bearings  4 ,  5  and parallel to the roadway plane. As shown in  FIG. 2 , the end sides of the pivoting bearings  4 ,  5  are oriented to the vehicle longitudinal center plane  27 . The pivoting bearing axes  16 ,  17  of the pivoting bearings  4 ,  5  are set at the roll angle  18  to intersect, as shown in  FIG. 1 , at an intersection point  28  that lies in the vehicle longitudinal center plane  27 . The intersection point  28  of the pivoting bearing axes  16 ,  17  is equal to the penetration point  28  of the pivoting bearing axes  16 ,  17  through the vehicle longitudinal center plane  27 . The intersection point  28  lies above the horizontal plane  26  or above the connecting line  25 . The connecting point  25  and the horizontal plane  26  coincide as illustrated in  FIG. 1 . 
         [0031]    Referring to  FIG. 2 , the pivoting bearings  4 ,  5  are each at a yaw angle  19  with respect to the connecting line  25  that extends through the centers of the pivoting bearings  4 ,  5  and perpendicular relative to the vehicle longitudinal center plane  27 . The left-hand pivoting bearing  4  is rotated by the yaw angle  19  about a left-hand yaw axis  22  (vertical axis) that is assigned to the left-hand pivoting bearing  4 , as shown in  FIG. 1  and extends through the center of the left-hand pivoting bearing  4  and parallel to the vehicle vertical axis. As shown in  FIG. 2 , rotation of the left-hand pivoting bearing  4  by the yaw angle  19  takes place in the counterclockwise direction. The right-hand pivoting bearing  5  is rotated by the yaw angle  19  about a right-hand yaw axis  23  (vertical axis) that is assigned to the right-hand pivoting bearing  5 , as shown in  FIG. 1 , and extends through the center of the right-hand pivoting bearing  5  and parallel to the vehicle vertical axis. Referring to  FIG. 2 , rotation of the right-hand pivoting bearing  5  by the yaw angle  19  is in the clockwise direction. 
         [0032]    After the rotation of the pivoting bearings  4 ,  5  by the yaw angle  19 , the corresponding pivoting bearing axes  16 ,  17  are inclined by the yaw angle  19  with respect to the connecting line  25  that extends through the centers of the pivoting bearings  4 ,  5  and perpendicular relative to the vehicle longitudinal center plane  27 . The pivoting bearing axes  16 ,  17  of the pivoting bearings  4 ,  5  are set at the yaw angle  19  to intersect, as shown in  FIG. 2 , at an intersection point  28  that lies in the vehicle longitudinal center axis  27 . The intersection point  28  of the pivoting bearing axes  16 ,  17  is identical to the penetration point  28  of the pivoting bearing axes  16 ,  17  through the vehicle longitudinal center plane  27 . The intersection point  28  lies in front of the connecting line  25 . 
         [0033]    In the preferred exemplary embodiment shown in  FIGS. 1 and 2 , the pivoting bearings  4 ,  5  are set at a roll angle of approximately 6° (the figures are of course not to scale) relative to the horizontal plane  26  and a yaw angle of approximately 27° relative to the connecting line  25  between the centers of the pivoting bearings  4 ,  5 . Surprisingly, with this embodiment of the rear wheel suspension system the roll center height can be lowered by 6 mm and the roll control could be increased by 0.5°/m compared to a rear wheel suspension system having a composite link axle having pivoting bearings set merely at a yaw angle, that is to say in a planar manner. At the same time, the wheel camber change may be positively influenced. 
         [0034]    In order to clarify the difference of the three-dimensional or spherical setting of the pivoting bearings  4 ,  5  according to the invention from a rear wheel suspension system having a composite link axle, in which the pivoting bearings are set merely at the yaw angle, in a planar manner,  FIGS. 3 and 4  represent a rear wheel suspension system having a composite link axle  30  made according to the prior art. In particular,  FIG. 3  shows a front view of said rear wheel suspension system, while  FIG. 4  shows a plan view of the same rear wheel suspension system. 
         [0035]    In  FIGS. 3 and 4 , parts which are identical or functionally identical to the parts which are shown in  FIGS. 1 and 2  of the rear wheel suspension system according to the invention are provided with the same designations. A renewed description of said parts will be dispensed with in the following text. Reference is made merely to the differences between the rear wheel suspension system according to the invention and the rear wheel suspension system according to the prior art. 
         [0036]    As illustrated in  FIG. 3 , the left-hand pivoting bearing  31  and the right-hand pivoting bearing  32  have no inclination with respect to the horizontal plane  26  or connecting line  25  that coincide in this view, in contrast to the embodiment of the invention in  FIG. 1 . The pivoting bearing axes  33 ,  34  shown in  FIG. 4  of the pivoting bearings  31 ,  32  are aligned in each case with the connecting line  25  or extend in the horizontal plane  26 , as shown in  FIG. 3 . Accordingly, the pivoting bearing axes  33 ,  34  intersect at an intersection point  36  that lies both in the vehicle longitudinal center plane  27  and in the horizontal plane  26 . In the exemplary embodiment shown in  FIG. 1 , the intersection point  28  lies above the horizontal plane  26 . 
         [0037]    As shown in  FIG. 4 , the pivoting bearings  31 ,  32  are set at a yaw angle  35  with respect to the connecting line  25  that extends through the centers of the pivoting bearings  31 ,  32  and perpendicularly with respect to the vehicle longitudinal center plane  27 . The left-hand pivoting bearing  31  is rotated by the yaw angle  35  merely about a left-hand yaw axis  22  (vertical axis) that is assigned to said left-hand pivoting bearing  31 , as shown in  FIG. 3  and extends through the center of the left-hand pivoting bearing  31  and parallel to the vehicle vertical axis. The right-hand pivoting bearing  32  is rotated by the yaw angle  35  about a right-hand yaw axis  23  (vertical axis) that is assigned to the right-hand pivoting bearing  32 , as shown in  FIG. 3 , and extends through the center of the right-hand pivoting bearing  32  and parallel to the vehicle vertical axis. 
         [0038]    The pivoting bearing axes  33 ,  34  of the pivoting bearings  31 ,  32  which are set at the yaw angle  35  in this way intersect, as shown in  FIG. 4 , at an intersection point  36  that lies in the vehicle longitudinal center plane  27 . As illustrated in  FIG. 4 , the intersection point  36  lies in front of the connecting line  25 . 
         [0039]    According to the prior art, substantially only the toe behavior of the composite link axle  30  is influenced or controlled by only setting of the pivoting bearings  31 ,  32  by the yaw angle  35 . An increase in the roll control and/or lowering of the roll center height as proposed cannot be achieved with the composite link axle  30  according to the prior art. 
         [0040]    While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.