Rack-and-pinion steering system mounting

An axial mounting of a rack-and-pinion steering system takes transverse forces and, at the same time, permits a defined resilience of the rack mounting in the transverse direction of the vehicle for affecting steering behavior of the vehicle and, in particular, permitting desired understeer during cornering. Mountings of this kind are particularly applicable to passenger vehicles in which the track rods are arranged behind the steered axle in the direction of travel. The rack-and-pinion steering system is mounted by two bearings arranged upright and at a relatively great distance from one another at the ends of the steering gear casing. The bearing bodies are either V-shaped or Y-shaped as viewed in longitudinal section. One upper and one lower bearing body together with damping elements are in each case arranged symmetrically and in alignment with one another in the top and bottom parts respectively of the bearing guide, with the smaller end faces of the V-shaped or Y-shaped bearing bodies facing one another. The upright arrangement of the bearing bodies with damping elements subjects the damping elements axially to compressive stress and also to shear stress. A desired stiffness and spring hardness in the vertical and longitudinal directions of the vehicle are thereby achieved.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to a mounting of a rack-and-pinion steering 
system for motor vehicles and, more particularly to a mounting for 
passenger motor vehicles in which the track rods are arranged behind the 
axle in the direction of travel and in which a defined resilience of the 
rack mounting in the transverse direction of the vehicle is of particular 
importance to the behavior of the steering system. 
The simplest form of a rack-and-pinion steering system of a motor vehicle 
is fastened by rigid bolting to frame or body parts, such as the front 
cross-member or the front bulkhead. In order to take vibrations and shocks 
transmitted via the wheels and wheel suspensions, elastic mountings for 
the rack-and-pinion steering system are used. 
According to REIMPELL, Fahrwerktechnik-Lenkung, [translated: Running-gear 
technology--steering], Vogel-Verlag, 1984, mounting arrangements are known 
in which the rack-and-pinion steering system is elastically connected to 
the vehicle frame by a tubular damping rubber. A spacer tube integrated 
into the damping rubber prevents compression of the rubber body and also 
limits axial compressive stresses. 
In, another known form, the casing of the rack-and-pinion steering system 
is almost completely surrounded by an elastomer body which is screwed into 
nonpositive engagement with the vehicle frame by fastening clips which 
engage therearound. The thick-walled elastomer body permits movements of 
the rack-and-pinion steering system in all three main spatial directions. 
This resilience of the steering system is however, undesirable, 
particularly in the longitudinal or travel direction of the vehicle and in 
a vertical direction because it leads to instability of the vehicle. 
In addition, this known configuration involves considerable space 
requirements and, particularly in passenger motor vehicles, leads to 
design problems in the arrangement of the steering gear in the available 
region between the engine/gearbox unit and the stabilizer, taking into 
account the necessary ground clearance of the vehicle. Furthermore, an 
undesirable slewing or torsion movement of the rack-and-pinion steering 
system about its longitudinal axis is not completely prevented by the 
positive clip connection. 
DE 37 04 412 shows a steering gear fastening having a plurality of shaped 
elastomer bodies which consist of a single part or two parts. The bodies 
are arranged in the longitudinal direction of the rack-and-pinion steering 
system. The identically shaped, homogeneous elastomer bodies enable only 
transverse forces to be absorbed. Similarly, a wheel suspension for 
steerable front wheels of a motor vehicle shown in DE 31 18 177 has a 
plurality of spaced shaped rubber parts which are arranged on the cross 
strut of the steering gear. 
In DE 24 21 498, a U-shaped elastomer body is described and, with the aid 
of a peripheral tension band, permits slight axial movability of the 
rack-and-pinion steering system. This arrangement does not, however, 
permit automated installation of the completed rack-and-pinion steering 
system on the vehicle. 
EP 0 351 146 shows a rack mounting which consists of a plurality of 
"silentblocs" in the form of hollow cylinders. This embodiment permits 
only slight resilience in the transverse direction of the vehicle, and 
thus does not allow the deflection of the mounted rack-and-pinion steering 
system which is necessary for under-steer of the vehicle. 
EP 0 107 781 describes a plurality of asymmetrically () shaped multipart 
elastomer mounting bodies for the elastic mounting of a rack-and-pinion 
steering system. The spring elements subjected to compressive or shear 
stresses have a substantially annular shape. The elastomer parts, which 
together form a movable bearing and a fixed bearing, are connected to the 
vehicle body by holding straps gripping around, them. This mounting 
arrangement requires considerable space and does not permit automated 
installation on the complete assembly on the vehicle. 
DE 34 25 730 shows a wheel suspension for a rear axle carrying steerable 
wheels and has a total of four asymmetrically arranged profiled rubber 
bodies spaced apart from one another. Two mountings arranged horizontally 
in the direction of travel serve to take longitudinal forces, while the 
two silentblocs arranged transversely to them take the resultant 
transverse forces acting on the co-steering rear axle. This known 
construction, which is expensive with respect to design and installation 
techniques, likewise does not permit automated final installation of the 
completed vehicle steering system. 
An object of the present invention is to provide a mounting for a 
rack-and-pinion steering system which, through a tautly seated steering 
system, ensures stable guiding of the vehicle in the travel direction to 
prevent the dreaded "wandering" of the vehicle. 
Transversely to the direction of travel, that is in the longitudinal 
direction of the rack-and-pinion steering system, limited elasticity of 
the mounting construction is required, in order to ensure the desired 
understeer of the vehicle during cornering. In addition, when the track 
rods are inclined in relation to the axis of the rack during deflection 
and rebound movements, the suspension of the rack-and-pinion steering 
system should intercept obliquely directed forces such that tilting of the 
rack about the vehicle longitudinal axis and also twisting about its own 
axis are largely avoided. Moreover, the rack-and-pinion steering system of 
the present invention is now installable automatically on the vehicle from 
below. 
The object of the present invention has been achieved by providing that the 
two bearing guides arranged upright in longitudinal and transverse 
directions of the motor vehicle and spaced apart in the longitudinal 
direction of the steering gear and connected to a casing of the steering 
gear. In the bearing guide, two bearing bodies tapering towards the center 
of the respective bearing guide are aligned with one another in a mirror 
image arrangement. The bearing bodies have through-holes in a longitudinal 
direction of the bearing guide, and a damping element is arranged on the 
outer periphery of the bearing body. A wall thickness of the damping 
element in the longitudinal direction of the motor vehicle is greater than 
a wall thickness in the transverse direction of the motor vehicle. An 
inner wall of the bearing guide is shaped in accordance with an external 
contour of the bearing bodies with damping elements, and opposing bearing 
bodies, with the associated damping elements, are clamped axially together 
with a defined initial stress when installed in the bearing guide. 
The rack-and-pinion steering system is mounted by two bearings which are 
arranged upright and at a relatively great distance from one another at 
the ends of the steering gear casing. The two bearings consist essentially 
of the bearing holder which is joined to the steering gear and of two 
bearing bodies having damping elements. The bearing bodies are V-shaped or 
Y-shaped in longitudinal section and have axial through holes for the 
passage of the clamp bolts. One upper and one lower bearing body together 
with damping elements are arranged symmetrically and in alignment with one 
another in the top and bottom pares respectively of the bearing guide. The 
smaller end faces of the V-shaped or Y-shaped bearing bodies face one 
another. 
Through the upright arrangement of the bearing bodies with their damping 
elements, the latter are subjected axially to compressive stress and at 
the same time also to shear stress. Thus, the desired great stiffness and 
spring hardness in the vertical direction and also in the longitudinal 
direction of the vehicle are achieved. 
The softness of the bearings in the transverse direction of the vehicle is 
achieved through the fact that the damping elements of the bearings are 
provided on their periphery, in the longitudinal direction of the steering 
gear, with depressions or flats on one side or diametrically opposite on 
both sides. A damping element flattened on both sides in the transverse 
direction of the vehicle is shown in FIG. 2 where the bearing gap on both 
sides in the transverse direction of the vehicle in the static state can 
be clearly seen. During cornering, this configuration permits soft 
deflection of the rack-and-pinion steering system. With correspondingly 
great forces the damping element makes contact over its entire surface 
with the inner wall of the bearing guide and is automatically centered by 
the bearing guide. Because of the greater spring hardness, further 
swinging-out of the rack-and-pinion steering system in the transverse 
direction of the vehicle is prevented. 
Flattening of the damping element on one side is likewise shown solely by 
way of example in FIGS. 7 and 8. Using, on both sides, this kind of 
damping element, which has outwardly directed flats, in both the bearings 
brings about an initially steeper rise of the characteristic line of the 
spring force in the transverse direction of the vehicle. After a short 
spring travel, the lifting-off of the unloaded side produces a flat 
pattern of spring force over the spring travel, with a nearly linear rise. 
This spring characteristic at first causes around the middle position a 
better stability of the vehicle and gives the driver the impression of 
driving with steering stability. Only when transverse forces become 
greater does the soft spring characteristic of the damping elements then 
occur, thus permitting the desired understeer of the vehicle. The V-shaped 
or Y-shaped configuration of the bearings offers the further advantage 
that obliquely directed supporting forces, which act on the steering gear 
via the track rods, are more effectively introduced. 
Effective supporting of the rack-and-pinion steering system against tilting 
about the longitudinal axis of the vehicle is achieved through a large 
support base, in that in an advantageous embodiment the two bearings are 
arranged at a correspondingly great distance from one another on one 
longitudinal side of the rack casing. 
In order to automate the installation of the rack-and-pinion steering 
system on the vehicle, the steering system is mounted on a mounting 
member, which in a preferred embodiment is in the form of a substantially 
C-shaped, beaded metal sheet. The mounting member receives the entire unit 
and is brought from below against the vehicle body. The bearings are taken 
to mounting holes in a cross-member and then bolted to the latter. This 
mounting bolting achieves at the same time the desired axial initial 
stress of the one-piece elastomer bodies which are preferably used damping 
elements for the two bearings in order to adjust the desired bearing 
hardnesses of the latter. 
According to another aspect of the present invention, the bearing body is 
in the form of a truncated cone which is provided with a through hole and 
has a V-shape in longitudinal section. Through the mirror-image 
arrangement of two V-shaped bearing bodies aligned with one another, whose 
smaller end faces lie opposite one another, extremely small overall 
heights of the bearings can be achieved. In addition, because of their 
simple shape the bearing bodies are easy to produce in terms of the 
manufacturing technology involved. 
In another aspect of the present invention, the bearing body is in the form 
of a truncated cone which is provided with a through hole and has a 
Y-shape in longitudinal section and which is provided with a hollow 
cylindrical extension on its smaller end face. The mirror-image 
arrangement of two Y-shaped bearing bodies lying with their smaller end 
faces aligned opposite one another offers the advantage that obliquely 
directed reaction forces on the steering gear, which forces occur in 
particular in the event of a large angle of lock (cornering, 
manoeuvering), can be dependably absorbed. 
In an advantageous embodiment of the present invention, the damping element 
is in the form of a one-piece elastomer body which can be produced in a 
simple manner and is joined to the bearing body by elastic initial stress. 
Alternatively, the damping element is vulcanized to the bearing body. 
In a currently preferred embodiment, the damping element is shaped to form 
on its periphery or end face a sealing lip which, in the installed state, 
is applied with a positive fit to the bearing guide and forms a dustproof 
covering for the bearing interior. 
In order to ensure great bearing stability of the rack-and-pinion steering 
system in relation to tilting movements transversely to the longitudinal 
direction of the vehicle, the two bearings are arranged at the outer-most 
end points of the steering gear casing. When the steering gear casing is 
constructed in the form of a pressure diecasting, the bearing guides can 
in a simple manner be integrated into the wall of the casing. 
To ensure automated installation of the steering system use is made of a 
mounting member which receives the preassembled rack-and-pinion steering 
system and, in an advantageous development is at the same time configured 
to protect the steering system against thrown-up stones and as 
underclearance protection. 
It is particularly advantageous that the solution provided by the present 
invention makes possible achievement of a defined spring characteristic of 
the steering arrangement in the x-, y- and z-directions. This is 
accomplished through the different configuration of the bearing bodies and 
damping elements in conjunction with the adjustable initial stress of the 
spring system in the installation of the unit. 
In addition, the arrangement of the present invention offers the advantage 
that, particularly on the rebound of the vehicle or with a large lock 
angle, the geometrically defined position of the steering gear relative to 
the other elements of the steering arrangement is retained. This results 
from the greater spring hardness in the x- and y-directions which prevents 
deflection of the rack-and-pinion steering system, whereas in the 
y-direction a defined deflection can occur. Because of the arrangement 
selected, however, torsion of the rack-and-pinion steering system about 
the y-axis is impossible.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 1 shows in an exploded view the most essential elements of the 
steering gear of a passenger motor vehicle. The tubular steering gear 
casing 1 surrounds the rack (not shown in detail), which on axial 
deflection is protected by the steering system sleeves 2. Two bearings 6 
and 7 are lid situated at the outer ends of the steering gear casing 1. 
The steering movements are transmitted in a known manner via the steering 
wheel (not shown) and the steering column to the pinion in the pinion 
casing 5 and the rack. A steering damper 3 serves for additional 
stabilization of steering behavior. 
The steering gear casing 1 is received on a C-shaped mounting member 4 in 
preassembling the unit. The mounting member 4 is a sheet metal pressing 
and has two through holes 18 which are in alignment with the centers of 
the bearings 6, 7. The steering gear is fastened to a cross-member 8 
arranged above by two clamp bolts 9, so that the mounting member 4, 
together with the steering gear casing 1, is bolted to the cross-member 8 
and, at the same time, the desired initial stress of the two bearings is 
adjusted thereby. The upper and lower bearing bodies 15 arranged in the 
bearing guide 14, together with the damping elements 16, are axially 
clamped, whereby the bearing bodies 15 (FIG. 2) are supported in the inner 
wall of the bearing guide 14. 
The bearing shown in a sectional view in FIG. 2 in the transverse direction 
of the vehicle shows the bearing gap between the inner wall of the bearing 
guide 14 and the bearing body 15 with the damping element 16. Automatic 
installation of the completed unit from a position below the vehicle is 
achieved by the aligned positioning of the mounting member 4 with the 
steering gear casing 1 arranged thereon. Securing in position and, at the 
same time, adjusting of the axial initial stress of the bearings are 
effected by way of the clamp bolt 9 in conjunction with a nut 13 arranged 
on the cross-member 8. 
Through the upright arrangement of the bearing bodies 15 with their damping 
elements 16, the latter are subjected axially to compressive stress and at 
the same time also to shear stress. Thus, the desired great stiffness and 
spring hardness in the vertical direction and also in the longitudinal 
direction of the vehicle are achieved. 
The softness of the bearings in the transverse direction of the vehicle is 
achieved through the fact that the damping elements 16 of the bearings 6, 
7 are provided on their periphery, in the longitudinal direction of the 
steering gear, with depressions or flats on one side or diametrically 
opposite on both sides. A damping element 16 flattened on both sides in 
the transverse direction of the vehicle is shown in FIG. 2 where the 
bearing gap BG on both sides in the transverse direction of the vehicle in 
the static state can be clearly seen. During cornering, this configuration 
permits soft deflection of the rack-and-pinion steering system. With 
correspondingly great forces the damping element 16 makes contact over its 
entire surface with the inner wall of the bearing guide 14 and is 
automatically centered by the bearing guide. Because of the greater spring 
hardness further swinging-out of the rack-and-pinion steering system in 
the transverse direction of the vehicle is prevented. 
This spring characteristic at first causes around the middle position a 
better stability of the vehicle and gives the driver the impression of 
driving with steering stability. Only when transverse forces become 
greater does the soft spring characteristic of the damping elements then 
occur, thus permitting the desired understeer of the vehicle. The V-shaped 
or Y-shaped configuration of the bearings offers the further advantage 
that obliquely directed supporting forces, which act on the steering gear 
via the track rods, are more effectively introduced. 
FIGS. 3 to 6 show preferred embodiments of the bearing body 15 and damping 
element 16. FIGS. 3 and 4 show a substantially V-shaped bearing body 15 
which has a short cylindrical extension on which the clamp bolt 9 is 
supported with the aid of a washer 12. The central through hole 17 is 
cylindrically shaped and the clamp bolt 9 extends therethrough. Two 
identical bearing bodies 15 with damping elements 16 are disposed in a 
mirror image arrangement, with the smaller end faces towards one another, 
in the bearing guide 14 and clamped against each other by the clamp bolt 
9, washer 12 and nut 13. The wall thickness of the damping element 16 is 
at its maximum in the longitudinal direction of the vehicle. On the 
clamping of the bearing bodies 15 relative to the bearing guide 14 a firm 
press fit is thereby achieved in the longitudinal direction of the vehicle 
and in the vertical direction. In contrast thereto, in the transverse 
direction of the vehicle the damping element 16 according to FIG. 4 has a 
distinct reduction of wall thickness. Through this bearing play an elastic 
deflection of the steering gear in the transverse direction of the vehicle 
is obtainable. A peripheral sealing lip 19 protects the interior of the 
bearing against penetration of particles of dirt. An advantage of the 
V-shape of the bearing body 15 is the extremely short overall height of 
the entire bearing. Through this structural shape and the bearings 6, 7 
arranged directly next to the steering gear casing 1 the available ground 
clearance of the vehicle is not restricted. 
In FIGS. 5 and 6, another preferred configuration is shown which consists 
of a Y-shaped bearing body 15 with a damping element 16 vulcanized 
thereto. Just as in FIGS. 3 and 4, the reduction of the wall thickness of 
the damping element 16 in the transverse direction of the vehicle serves 
to achieve an elastic deflection of the steering gear and therefore the 
desired understeer of the vehicle during cornering. In contrast thereto, 
the wall thickness of the damping element 16 is constant in the 
longitudinal direction of the vehicle. For dependable absorption of 
obliquely acting reaction forces which are transmitted via the track rods 
to the steering gear, the upper part of the Y-shaped bearing body 15 has 
an angle of inclination of 45.degree. relative to the adjoining 
cylindrical part. The bearing bodies 15 are advantageously made of an 
aluminum-magnesium alloy. The one-piece damping element 16 consists of an 
elastomer. 
In FIG. 7, the bearings 6, 7 mounted on the cross-member 8 are shown 
assembled together. FIG. 8 shows in a sectional view the different 
configuration of the wall thickness of the damping element 16 in the 
longitudinal and transverse directions of the vehicle in accordance with 
FIG. 7. FIG. 9 shows in comparison with FIG. 2, where the wall of the 
damping element is thinner in the transverse direction, a part of the 
steering gear mounting with a section through the bearing in the 
longitudinal direction of the vehicle with the wall of the damping element 
16 being thicker in that direction. 
Flattening of the damping element on one side is likewise shown solely by 
way of example in FIGS. 7 and 8. Using, on both sides, this kind of 
damping element (16), which has outwardly directed flats, in both the 
bearings (6) and (7) brings about an initially steeper rise of the 
characteristic line of the spring force in the transverse direction of the 
vehicle. After a short spring travel the lifting-off of the unloaded side 
produces a flat pattern of spring force over the spring travel, with a 
nearly linear rise. 
Although the invention has been described and illustrated in detail, it is 
to be clearly understood that the same is by way of illustration and 
example, and is not to be taken by way of limitation. The spirit and scope 
of the present invention are to be limited only by the terms of the 
appended claims.