Axle suspension for rigid axles in vehicles

An axle suspension for rigid axles in vehicles, especially utility vehicles, with longitudinal control arms extending in the longitudinal direction of the vehicle and connecting the vehicle axle to the vehicle body in a vertically movable manner. The longitudinal control arms are arranged for axle guiding on each side of the vehicle approximately at the same level. A four-point torsional connecting element is articulated to the vehicle axle, on the one hand, and to the vehicle body, on the other hand. The four-point torsional connecting element is arranged above the vehicle axle and is connected as a flexible cross to the vehicle axle and to the vehicle body via two body and axle joints located at spaced locations from one another in the transverse direction of the vehicle. The arms of the four-point connecting rod are designed in whole as a one-piece forged part and are girders subject to bending with an approximately rectangular cross section. One of the arms has a predetermined breaking point.

FIELD OF THE INVENTION 
The present invention pertains to an axle suspension for rigid axles in 
vehicles, especially in commercial vehicles. One longitudinal connecting 
rod connecting the vehicle axle and the vehicle body in a vertically 
movable manner and extending in a longitudinal direction of the vehicle is 
arranged on either side of the vehicle approximately at the same height. A 
multiple connecting rod, which is offset in terms of height, is connected 
by means of joints, with the vehicle axis and with the vehicle body and 
includes a stabilizing device which actively opposes lateral rolling and 
tilting motions by means of torsional stresses for guiding the axle. 
BACKGROUND OF THE INVENTION 
Axle suspensions have become known which comprise an axle guided by means 
of longitudinal connecting rods, which are arranged on both sides of the 
vehicle and are coupled, on the one hand, to the vehicle axle, and on the 
other hand, to the vehicle body, in conjunction with a triangular 
connecting rod, which is, on the one hand, usually anchored to the vehicle 
axle in the center of the vehicle with a central joint, and on the other 
hand, is coupled to the vehicle body with the ends of its two struts. Such 
a design is apparent, e.g., from German Patent Document G 92 18 307.7. As 
is well known, this triangular connecting rod axle suspension is combined 
with a stabilizing bar, which is usually U-shaped in the top view, whose 
angular side ends are attached to the vehicle body at a lateral distance 
from one another in a limited universal joint manner and whose web section 
is mounted in a movable manner in at least two stabilizing bearings on the 
vehicle axle about a transverse axis to the longitudinal direction of the 
vehicle. This stabilizing bar is used for the transverse stabilization of 
the axle suspension. 
In addition, an axle suspension has become known from Japanese Patent 
Document JP 64-3-9915, in which two longitudinal connecting rods are 
coupled under the rear vehicle axle via molecular joints, on the one hand, 
and on the other hand, these connecting rods are attached to the vehicle 
body. Two longitudinal connecting rods, which are connected via a 
transverse strut, are additionally arranged in this prior-art embodiment 
approximately in the center of the axle. However, it is disadvantageous in 
such an axle suspension that the tendency of the vehicle to roll cannot be 
sufficiently compensated for. Due to the centrally arranged transverse 
strut between the longitudinal connecting rods, such a design is not rigid 
in terms of torsion and is not able to guarantee any sufficient transverse 
stability. 
SUMMARY AND OBJECT OF THE INVENTION 
The basic technical object of the present invention is to optimize a 
prior-art axle suspension in terms of weight and stability and at the same 
time to increase the reliability of righting of the axle suspension. 
In the axle suspension of the present invention, longitudinal connecting 
rods connect the axle of the vehicle with a vehicle body in a vertically 
movable manner. The longitudinal connecting rods extend in a longitudinal 
direction of the vehicle and are arranged on either side of the vehicle. A 
torsional connecting element includes first and second body joints 
pivotally connecting the torsional connecting element to the vehicle. The 
first and second body joints are spaced apart from one another in a 
transverse direction of the vehicle. The torsional connecting element also 
includes first and second axle joints pivotally connecting the torsional 
connecting element to the axle. The first and second axle joints are 
spaced apart from one another in a transverse direction of the vehicle. 
The first body and axle joints are positioned on a first side of the 
vehicle, and the second body and axle joints are positioned on a second 
side of the vehicle. The first and second sides of the vehicle are 
diametrically opposite. The torsional connecting element includes a first 
arm with one end connected to the first body joint and another end 
connected to the second axle joint. The torsional connecting element also 
includes a second arm with one end connected to the second body joint and 
another end connected to the first axle joint. The arms of the four-point 
torsional connecting element or rod are designed in whole, as a one-piece 
forged part and are girders subject to bending with an approximately 
rectangular cross section. One of the arms has a predetermined breaking 
point. 
Reference is first explicitly made to the features described in the patent 
application Ser. No. 08/696,972 as they appear especially from FIGS. 1 
through 10 contained therein and the corresponding description. These 
features are part of this application. For example, there is an idea that 
an axle suspension according to application Ser. No. 08/696,972 can be 
combined with the present invention. The four-point connecting rod 
connected above the vehicle axle to the vehicle axle, on the one hand, and 
to the vehicle body, on the other hand, is designed according to the 
present invention as a flexible cross and is connected to the vehicle 
axle, on the one hand, and to the vehicle body, on the other hand, via two 
joints located at spaced locations from one another in the transverse 
direction of the vehicle. The arms of the four-point connecting rod, which 
is made as a whole as a one-piece forged or cast part, are designed as 
girders subject to bending with an, e.g., round, approximately rectangular 
or similar cross section. 
According to the present invention, one of these arms has a predetermined 
breaking point, which is advantageously provided on one of the axle-side 
arms, so that no additional manufacturing expense is needed for this. In 
the area of the predetermined breaking point, the arm has a cross section 
that is larger, taking the specified safety factor into account, than the 
cross section necessary for the expectable loads of the four-point 
connecting rod. One essential advantage of the present invention is that 
even in the case of axle loads far exceeding the expectable maximum 
requirements and the destruction of the four-point connecting rod that 
could possibly be associated with this, the destruction would first take 
place in the area of the predetermined breaking point and consequently in 
a controllable manner. However, axle guiding is still guaranteed according 
to the present invention even in such an extreme case, because one of the 
two arms of the four-point connecting rod is still fastened to the vehicle 
axle, so that the vehicle can be driven to the nearest repair shop, e.g., 
without external support. 
A special advantage of the design according to the present invention is the 
possibility of using already existing joint connections and to substitute 
a single four-point connecting rod according to the present invention for 
a plurality of axle guiding elements (longitudinal control arms) according 
to the state of the art. In an axle suspension according to the present 
invention, it is possible to determine the tendency of the vehicle to roll 
in a very simple manner and accurately, so that the four-point connecting 
rod can be designed optimally while optimizing its weight at the same 
time. Markedly stronger forces and torques can be absorbed with a 
four-point connecting rod according to the present invention compared with 
prior-art designs. Along with this, the axle suspension according to the 
present invention is compact compared with prior-art designs, because it 
has a smaller number of individual parts and requires less assembly work. 
Additional embodiments of the present invention are the subject of the 
subclaims. 
Thus, it is suggested that the joints be designed, e.g., as ball joints 
with an elastomer arranged between the joint housing and the ball piece. 
These molecular joints can be correspondingly adapted to the loads to be 
expected by selecting an elastomer with a corresponding Shore hardness. In 
addition, recesses, which influence the characteristics of the joint in a 
specific manner, may be provided within the elastomer and/or the housing 
and on the inner part of the joint. For example, the molecular joints may 
have a lower damping in one direction and a higher damping in at least one 
direction that is offset thereto. Besides the above-described ball joints, 
other types of joints, e.g., pivot joints or other types are, of course, 
also conceivable for this application. 
The idea according to the present invention is especially to design the 
joints and the four-point connecting rods receiving same as a modular 
system with individual parts that can be interchanged corresponding to the 
loads. It is thus possible to coordinate joints and four-point connecting 
rods with one another, depending on the customers' requirements. The 
joints are provided for this purpose with a standard external diameter and 
the joint mounts of the arms of the four-point connecting rod with 
standardized internal diameters. Thus, the molecular joints and the 
metallic basic body of the four-point connecting rod offer cumulative 
opposing forces to the forces introduced via the xle. 
Other preferred embodiments of an axle suspension according to the present 
invention for rigid axles in vehicles provide for a stabilizing torque 
between 10 and 60 kNm but preferably between 40 and 50 kNm for the 
four-point connecting rod, a distance of 300 to 700 mm but preferably 
about 500 mm for the vehicle body-side joints of the four-point connecting 
rod, a distance of 300 to 700 mm but preferably about 350 mm for the 
vehicle axle-side joints of the four-point connecting rod, and a distance 
of 300 to 1,000 mm but preferably about 550 mm between the vehicle 
body-side and vehicle axle-side joints of the four-point connecting rod. 
On the whole, an axle suspension according to the present invention 
provides a compact system, which meets the requirements on heavy and very 
heavy utility vehicles, whose special advantages are a four-point 
connecting rod which can be combined in a flexible manner and meets the 
highest safety requirements. Furthermore, for the first time ever, it has 
become possible with an axle suspension according to the present invention 
to achieve a passive roll steer effect in a specific manner due to the 
geometrically determinable arrangement of the center of rotation of the 
four-point connecting rod, corresponding to the position of the crossing 
point of the arms. This leads to advantages, e.g., improved steering 
target behavior, improved load change behavior, reduced tire wear, and a 
reduction in the load on the components of the chassis due to 
overdetermined statics being avoided. Due to the four-point connecting rod 
being arranged above the vehicle axle, there is an increased ground 
clearance, which is of considerable significance, e.g., in the case of 
vehicles used on construction sites. 
The above-mentioned features of the present invention and the features yet 
to be explained may, of course, be used not only in the combination 
described, but also in ombinations or alone without leaving the scope of 
the present invention. 
The four-point connecting rod preferably has a torsional cross design with 
a defined characteristic curve for torsional stress produced by the 
torsion. Two cross arms of the four-point connecting rod are preferably 
connected to the vehicle body by means of ball-and-socket joints and two 
cross arms of the four-point connecting rod are preferably connected to 
the vehicle axle by means of ball-and-socket joints. 
The four-point connecting rod may be provided as a plane load-bearing 
structure with a defined characteristic curve for torsional stress 
produced by torsion. The four-point connecting rod may also be designed as 
a torsional framework construction with a defined characteristic curve for 
torsional stresses produced by the torsion. 
An integration in one component of the elements for guiding the axle and of 
the elements for the transverse stabilization of the vehicle body against 
the vehicle axle is achieved by means of these embodiment features. The 
torsional connecting element is arranged directly between the longitudinal 
connecting rods to guide the axle and is coordinated with these 
longitudinal connecting rods to rotate in unison, transversely to the 
longitudinal direction of the vehicle, but in a cardanically movable 
manner by means of friction-free bearing elements, which are known per se. 
A special advantage of the design according to the present invention is 
that axle guide elements, which have already been installed, are able to 
be replaced with an axle suspension designed according to the present 
invention by means of using the bearing elements available on the vehicle 
body and on the vehicle axle. 
In addition, it is possible to determine the roll stability very precisely 
in an embodiment of an axle suspension according to the present invention, 
and greater forces and torques can be absorbed compared with prior-art 
embodiments. 
Separate space for storing a torsional connecting element is no longer 
necessary. The bearing elements for the torsional connecting element are 
omitted on the vehicle axle as well as on the vehicle body. In addition to 
this, the axle suspension according to the present invention is 
cost-effective compared to prior-art embodiments since it has fewer 
individual components and requires less mounting work. 
However, there are also functional advantages. The torsional connecting 
element may be used as a straight bar, such that the cost of its 
manufacture is also reduced. 
In a preferred embodiment, each of the ends of the torsional connecting 
element, which is designed as a torsion bar, and ends of the longitudinal 
connecting rods are connected at two places against the longitudinal 
direction of the vehicle, but in a movable manner, so that the torsional 
connecting element can rotate in unison with the longitudinal connecting 
rod, on the one hand, but which can be designed as sufficiently movable in 
the transverse direction of the vehicle, on the other hand. The 
arrangement of the torsional connecting element between the longitudinal 
connecting rods for guiding the axle may be carried out at any place 
between the couplings of the longitudinal connecting rods to the vehicle 
axle and the couplings of the longitudinal connecting rods to the vehicle 
body. However, it is also possible to combine the connection of the 
torsional connecting element with the longitudinal connecting rods for 
guiding the axle with their bearings on the vehicle axle. 
The above-mentioned features of the present invention and the features yet 
to be explained may, of course, be used not only in the combination 
described, but also in combinations or alone without leaving the scope of 
the present invention. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its uses, reference 
is made to the accompanying drawings and descriptive matter in which 
preferred embodiments of the invention are illustrated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings, in the exemplary embodiment, the vehicle axle 1 
is connected to the vehicle body by longitudinal control arms 2 and 3 at a 
considerable distance from the longitudinal center of the vehicle and on 
both sides of the vehicle. A four-point torsional connecting rod or 
element 4 is arranged above the vehicle axle in the middle of the vehicle. 
In the embodiment shown, the connection of the vehicle axle to the vehicle 
is such that the vehicle axle can perform rolling movements, i.e., 
movements around an axis located in the longitudinal axis of the vehicle, 
of +60 depending on the driving circumstances. 
Some areas of the vehicle body are shown schematically in FIG. 1. The 
connection of the four-point connecting element to the vehicle chassis 11 
is shown in FIG. 1. The joint connections of the longitudinal control arms 
2 and 3 are located under the vehicle axle 1, while the four-point 
connecting element 4 is arranged above the vehicle axle 1 at a level that 
is different from that of the longitudinal control arms 2 and 3. All joint 
connections are designed as cardanically movable connections and consist 
of molecular joints with an elastomer 13 arranged between a joint housing 
14 and a ball piece 15. 
The four-point connecting element 4 comprises two stable arms 9 and 10 in a 
mutually crossing arrangement and is designed as a one-piece forged or 
cast part with approximately rectangular cross section. Its torsion obeys 
a defined characteristic. The 20 cross section of the arms can be 
dimensioned in a simple manner according to the following formula at a 
preset section modulus "W:" W=b h.sup.2 /6. Here, "b" is the width and "h" 
is the height of the cross section of the arm. 
The arms 9 and 10 can be fastened to the vehicle body via the body joints 5 
and 6, and they are fastened with the axle joints 7 and 8 arranged at the 
other ends of the arms 9 and 10 to the vehicle axle 1 or to a support body 
1.1, which is connected to the vehicle axle 1. This design of the 
four-point connecting element 4 counteracts rolling movements of the 
vehicle axle 1. The torsion of the four-point connecting element that 
occurs during rolling movements causes restoring forces for restoring the 
zero roll position due to torsional stresses. FIG. 2 shows a 
three-dimensional view of the X-shaped four-point connecting element 
according to the present invention. The joints 5 and 6 for fastening to 
the body and the joints 7 and 8 for fastening to the vehicle axle 1 are 
arranged at the ends of the arms of the X-shaped cross. A predetermined 
breaking point 12 is recognizable on the arm 10 in the embodiment 
according to FIG. 2. 
The cross-sectional profile of the arms is approximately rectangular in 
this example, as is also indicated in the drawing figure. Various 
materials may be used. 
The four-point connecting rod 4 has the two stable articulated arms 9 and 
10 firmly connected to one another by a stabilizing means subject to a 
defined characteristic curve. A framework construction is formed from the 
articulated arms 9 and 10 with the stabilizing means. The dynamometric 
course within the plane load-bearing structure can be determined exactly 
in this case, so that a structural design that is adapted exactly to the 
load conditions is possible. 
The cross-sectional profile of the arms is adapted to the structural 
conditions and may have, e.g., a double-T or I shape, or it may comprise a 
hollow profile. Various materials can be used for this. 
The above-mentioned features of the present invention and the features yet 
to be explained may, of course, be used not only in the combination 
described, but also in combinations or alone without leaving the scope of 
the present invention. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the principles of the 
invention, it will be understood that the invention may be embodied 
otherwise without departing from such principles. 
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LIST OF REFERENCE NUMBERS 
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1 Vehicle axle 
1.1 Support body 
2 Longitudinal control rod 
3 Longitudinal control rod 
4 Four-point connecting rod 
5 Joint 
6 Joint 
7 Joint 
8 Joint 
9 Arm 
10 Arm 
11 Vehicle body 
12 Predetermined breaking point 
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