Abstract:
The invention relates to a suspension for the wheels of an axle of a motor vehicle, especially for the steered front wheels. Said wheel suspension comprises wheel carriers that rotatably bear the wheels and are arranged so as to create straight-line steering via several individual links which are pivotally connected to the motor vehicle body and one respective track rod. Resilient means which directly or indirectly impress a certain prestress that acts around the spread axle of the wheels and in the opposite direction are provided in the wheel suspension in order to improve steering return and steering precision.

Description:
This application is a §371 application of PCT/EP2003/013447, which claims priority from DE 10304567.8, filed Feb. 5, 2003. 
   BACKGROUND 
   This invention relates to a wheel suspension for the wheels of an axle of a motor vehicle, especially for the steered front wheels. 
   The steering return motion for front wheel suspensions of motor vehicles (front axle) and the joint loads for rear wheel suspensions (rear axle) among other factors are determined by the kinematic design of the wheel suspensions. Thus for example for the front axles the tilt of the steering axis or expansion axis determines the roll radius, the caster, and for the driven wheels the so-called quantity a, the disturbing force lever arm for the driving forces in the wheel center. If these parameters are to be kept small to prevent disturbing forces when the vehicle is driving in a straight line, under lateral forces, and when accelerating, the indicated parameters must be defined accordingly. This applies especially in wheel suspensions with so-called released links or multilink axles, in which the expansion axis can be virtually defined by the corresponding three-dimensional orientation of the individual links. But the reduction of the aforementioned disturbing forces is also accompanied by a reduction of the steering return motion or reduced kinematic prestress of the wheel suspension parts. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to devise a wheel suspension of the generic type in which further improved stabilization and optionally steering return motion can be produced by relatively simple means while maintaining low disturbing forces while driving. 
   It is proposed that elastically resilient means be provided in the wheel suspension which directly or indirectly apply to the wheel carriers prestress which acts around the expansion axis of the wheels in opposite directions. Thus, regardless of the kinematic design of the wheel suspension, prestress which is generated similarly to a large spread angle of the expansion axis is produced in the wheel suspension and track rods and improves the response behavior and/or steering the vehicle in a straight line and can eliminate minor joint play which may be present. This applies both to the steered wheels of the motor vehicle and also for multilink wheel suspensions to unsteered wheels in which one of the individual links is designed similarly to a track rod to achieve a defined resonant intrinsic steering behavior of the wheel suspension. 
   It is further proposed that the spring means prestress the wheels of the motor vehicle in the direction of the toe-in. This is especially advantageous for the driven wheels of the motor vehicle, although depending on the kinematic design of the wheel suspension the opposite prestress may also be appropriate. 
   The means can act additionally to damp vibrations, by which advantageously a double function can be achieved, in which vibration excitation in the wheel suspensions can be increasingly suppressed. 
   The elastically resilient means can be metallic springs such as helical springs, leg springs, leaf springs, etc., or rubber-elastic springs. But preferably it is suggested that the means are hydropneumatic gas springs which are each configured asymmetrically to the expansion axis between the body of the motor vehicle and a wheel suspension part. Such telescoping gas springs can be structurally configured in a favorable manner and work reliably. With respect to the coupling to the body of the motor vehicle this can be an auxiliary frame which is connected to the body or can be the body directly, and optionally an already present coupling point can be used at the same time for example for one of the links of the wheel suspension. 
   The gas springs can be coupled in a structurally favorable manner directly to the wheel carriers. Here likewise already existing attachment points such as for example the calipers of the hydraulic service brakes of a motor vehicle can optionally be used. Moreover, the indicated prestress forces can be applied especially effectively to the wheel suspension, especially when gas springs act on the wheel carrier behind the expansion axis for track rods which likewise are attached behind the indicated expansion axis of the wheels in the direction of travel. 
   One structurally advantageous configuration of the gas springs arises when the latter, viewed in the direction of travel, extend in the shape of an arrow obliquely to the longitudinal center axis of the motor vehicle, the body-side coupling point being located in front of the indicated expansion axis of the wheels. In this way it is relatively easy to configure the gas springs past the existing individual links according to the required geometry. 
   For a front axle with steered wheels driven by way of drive shafts, the gas springs can be positioned above the lower links and underneath the drive shafts. 
   In addition or as an alternative, the spring means can be formed by at least one rubber-elastic link bearing each which is elastically prestressed in the installation position. As a result of the detached link configuration the required prestress in the wheel suspension and torsional stress around the expansion axis can be produced with the cited advantages. 
   On the basis of commercial rubber-metal sleeve bearings which are generally used in link bearings, said rubber-metal sleeve bearings can be prestressed by suitable interleaving in the installation position. In order not to adversely affect the characteristics of the sleeve bearings, it can however prove to be necessary to design them asymmetrically such that for the bearing areas of the rubber sleeves subject to compression there are thickened areas, in cross section similar to cam contours. 
   Preferably there are elastically prestressed link bearings for track rods located in the upper link plane of the wheel suspension on the upper links. As a result of direct application of the prestress forces to the track rods of the steering of the motor vehicle this also effects even higher steering precision. 
   Finally, the elastically prestressed link bearings can be located in an especially structurally with highly favorable results on the body-side coupling points of the links. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Two embodiments of the invention will be described in greater detail below, in which in diagrammatic form 
       FIG. 1  presents a wheel suspension for the steered wheels of a front axle for motor vehicles, with a gas spring which is configured between the body and the wheel carrier; and 
       FIG. 2  presents a body-side link bearing in a longitudinal section, used in a modified form to achieve inner prestress in the wheel suspension as shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In  FIG. 1  the right front wheel suspension for the steered wheels  12  of a motor vehicle which is not shown is designated as  10 . The left front wheel suspension can be imagined as the identical mirror image. Let it be noted that the wheel suspension  10  is described only to the extent that this is necessary for an understanding of this invention. For example, the stabilizer, the bearing springs and the telescoping shock absorbers or a similar spring element are not shown. The direction of travel of the motor vehicle is identified by the arrow F. 
   The wheel suspension  10  in the lower link plane has two (individual) links  14 ,  16  which are analogously configured with regard to their three-dimensional area and two other (individual) links  18 ,  20  in the upper link plane. 
   The indicated links  14  to  20  are pivot-connected to the body (not shown) of the motor vehicle by way of rubber-metal sleeve joints  22 ,  24 ,  26 ,  28 . The body can be a frame structure or an auxiliary frame connected to the body. 
   Furthermore, the links  14  to  20  are pin-jointed by way of ball joints (uniformly designated as  30 ) to the guiding wheel carrier  32  which pivotally supports the wheel  12 . 
   A drive shaft  34  which is shown only in a segment drives the wheel  12  of the front-wheel or all-wheel drive motor vehicle. The caliper of the disk brake of the service brakes of the motor vehicle is mounted on the wheel carriers  32  at  36  in the conventional manner which is not shown. 
   A steering link  38  projects up tilted at an angle from the wheel carrier  32  opposite the direction of travel F and is drive-connected by way of ball joints  40  to the rack-and-pinion steering  44  which is only suggested on a track rod  42  which extends more or less in the transverse direction in the upper link plane. 
   With reference to the left wheel suspension which is not shown, to the front on the wheel suspensions  10  in the shape of an arrow there is a gas spring  46  each which acts to damp vibrations in an elastically resilient manner. The gas spring  46  can be of hydropneumatic design, as are conventional for example in supporting shock absorbers of motor vehicles or for hatch actuations. 
   The gas springs  46  are coupled on the one hand to the body (or auxiliary frame) of the motor vehicle and on the other hand at  36  in the area of the caliper by way of ball joints  48 . 
   The respective gas springs  46  extend from the lower front link bearing  22  of the link  14  obliquely to the longitudinal axis of the motor vehicle and against the direction of travel F above the link plane formed by the lower links  14 ,  16 , but underneath the drive shaft  34  to the wheel carrier  32 . The corresponding ball joint  48  can be fixed uniformly on the mount for the caliper at  36 . 
   Viewed from overhead, the body-side coupling point  48  of the gas springs  46  lies in front of the steering axis or expansion axis  50  of the wheel suspension  10 , which axle is shown by the broken line, while, as is clearly apparent, the wheel carrier-side coupling point  48  (at  36 ) lies clearly behind expansion axis  50  which extends essentially in the vertical direction. For the sake of form it should be mentioned that the indicated expansion axis  50 , as is recognized, intersects the intersection points of the imaginary extensions of the straight connecting lines of the links  14 ,  16  and  18 ,  20  and thus forms the virtual steering axis of the motor vehicle in order to turn the steered wheels  12  during steering movements. 
   The prestress forces applied by the gas springs  46  (which of course must be of the same strength when driving in a straight line) impart to the wheel carriers  12  a torque around the expansion axis  50  in the direction of toe-in of the wheels  12 . Based on the described configuration these prestress forces as an internal force cancel out one another and are supported by way of the track rods  42  and rack-and-pinion steering  44 . 
   Regardless of the aforementioned, this prestress causes compensation of play in the described ball joints  32  and  40 , and conjunction with that, improved response sensitivity and steering precision. 
   Furthermore, improved steering return motion to straight-line driving is achieved because the gas springs  46  which telescopically retract at the maximum steering angle (for example in a right-hand curve the illustrated right-hand gas spring  46 ) exerts a higher prestress force than the opposite, telescopically extended gas spring  46 . 
   Finally, the gas springs  46  which have a conventional hydraulic damping means effect additional vibration damping in the wheel suspensions  10  so that such a wheel suspension runs more smoothly and experiences fewer disruptive effects from the roadway and/or rotating masses. 
   As an alternative or in addition, the spring means can also be link bearings  22  to  28  which are accordingly prestressed in the installation position and which are configured and/or installed such that they exert at least indirectly a prestress around the expansion axis  50 , as described above. 
   This prestress is show in  FIG. 1  using the upper, front link  18  with the arrow  60 . 
   The corresponding link bearing  26  is shown by  FIG. 2 . The link bearing is a rubber-metal sleeve bearing of conventional design. 
   It has an outer link eye  62  which is welded fast to the link  18 , an inner metal sleeve  64  and an annular rubber bushing  66  which lies in between. 
   The link bearing  26  is inserted into a body-side bracket  68  which is shown only partially and its inner metal sleeve  64  is attached to the bracket  68  by means of a through screw (not shown). 
   Deviating from the prior art, the link eye  62  is welded on a slant to the link  18  offset by an angle α such that in the installation position of the link  18  (defined by the three-dimensional configuration of the links  18  to  24  and the track rod  42 ) it causes tilting or interleaving with the slant shown in  FIG. 2  or asymmetrical deformation of the rubber bushing  66 . So that when driving no unwanted friction can occur between the bracket  68  and the link bearing  26 , the faces of the rubber bushing  66  and especially of the link eye  62  are made crowned, as is apparent. 
   The described interleaving of the link bearings  26  produces a torque according to arrow  60  in  FIG. 1  on the links  18  (looking at the two wheel suspensions  10 ) or indirectly on the wheel carrier  32  which is supported in turn by way of the track rods  42  and the rack-and-pinion steering  44  as an internal force. This bracing in turn produces the prestress which acts around the expansion axis  50  on the described ball joints  30  and  40 . 
   The invention is not limited to the described embodiments. Thus, the spring means for exerting the described prestress can also be metal springs such as helical springs, leg springs, leaf springs, etc. Furthermore the illustrated gas springs  46 , to the extent this can be structurally represented, can also be located transversely to the direction of travel F of the motor vehicle or in another orientation. 
   Instead of one link bearing  26 , several link bearings  22  to  28  accordingly can also be used prestressed. It can be regarded as essential to the invention that the spring means do not apply any pure reset forces to the steering of the motor vehicle (for example, within the steering gear), but keep the described joints  30 ,  40  prestressed as an internal force. 
   Instead of the described offset (angle α) of the link eye  62  to the link  18  (symmetrical construction of the link bearing  26 ) the metal sleeve  64  can also be offset relative to the link eye  62  (asymmetrical construction). 
   The wheel suspension  10  can also be provided only in one link plane, that is to say, at the top or bottom, with released (individual) links. Furthermore, instead of a wheel suspension  10  with steered wheels, a rear wheel suspension with wheels of the wheel suspension which have only defined resonant intrinsic steering can also be provided with the described features. The track rods are likewise coupled to the body or auxiliary frame of the motor vehicle in this wheel suspension without a steering gear connected in between.