Note: Descriptions are shown in the official language in which they were submitted.
.% CA 02707533 2010-06-01
WO 2009/040001 PCT/EP2008/007590
Description
Wheel bearing for a motor vehicle
The invention relates to a wheel bearing for a motor
vehicle, in particular for a commercial vehicle, with a
wheel bearing unit which supports a wheel hub on a
steering knuckle by means of a rolling bearing acting
axially and radially.
Tapered rolling bearings which are generally fitted in
an 0 arrangement are customary for supporting in
particular commercial and trailer axles. In this case,
two tapered roller bearings are positioned in as play-
free a manner as possible or with a slight prestress in
order to support the wheel hub on the steering knuckle.
The two tapered roller bearings therefore serve as a
combined radial and axial bearing.
It has also been known to use multi-row angular-contact
ball bearings to support a wheel hub, with up to four
rows of bearings being arranged next to one another. It
is therefore endeavored to reduce the friction moment
or the loss of power of the bearing in relation to the
abovementioned solution with two tapered roller
bearings and thus to arrive at a reduction in the fuel
consumption.
Even the abovementioned bearing arrangements with a
plurality of angular-contact ball bearings still have a
not inconsiderable bearing friction resulting in
corresponding fuel consumption. There is consequently
the requirement to develop the wheel bearing unit,
which has to support the wheel hub radially and axially
on the steering knuckle, in such a manner that an even
smaller loss of power during operation can be achieved.
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Therefore, the invention is based on the object of
developing a wheel bearing for a motor vehicle of the
type mentioned at the beginning in such a manner that a
further reduced bearing friction can be obtained during
operation, as a result of which the fuel consumption
and therefore also the exhaust emission output can be
reduced. At the same time, the rigidity of the bearing
is to be improved.
The achievement of said object by means of the
invention is characterized in that the wheel hub is
provided directly or indirectly with two cylindrical
raceways for cylinder rollers and with two raceways for
balls, said raceways being placed on the end side of at
least one radially extending annular section, and that
the steering knuckle is provided directly or indirectly
with two cylindrical raceways for the cylinder rollers
and with two raceways for the balls, said raceways
being placed on the end side of radially extending
annular sections, the cylinder rollers being arranged
between the cylindrical raceways and the balls being
arranged between the raceways.
The two cylinder roller bearings are preferably
arranged lying axially on the outside and enclose the
two ball bearings.
The rolling bearing is advantageously formed
symmetrically with respect to a center plane which is
perpendicular to the axis of rotation of the steering
knuckle.
The two cylinder roller bearings may be designed to be
identical in size. The two ball bearings may also be
designed to be identical in size.
The cylindrical raceways of the two cylinder roller
bearings are preferably incorporated directly into the
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material of the wheel hub. The raceways for balls of
the two ball bearings may likewise be incorporated into
at least one radially extending annular section
directly into the material of the wheel hub. Other
solutions, for example with outer rings pressed into a
cast hub, are likewise possible.
The bearing rings which are placed onto the steering
knuckle may be of L-shaped design in radial section and
have both a cylindrical raceway of the two cylinder
roller bearings and a raceway for balls of the two ball
bearings. In this case, it has proven worthwhile if the
cylindrical raceway of the two cylinder roller bearings
of the bearing rings is bounded on both sides by a
respective restraining flange. In this case, the two
bearing rings may be held at a defined axial distance
by means of a spacer sleeve.
Another development makes provision for the two axial
ends of the spacer sleeve to be pushed into grooves in
the two inner bearing rings, there being a radial press
fit between the spacer sleeve and the bearing ring. The
effect thereby advantageously achieved is that a
transport and installation aid is produced without
further components or elements, since the entire
bearing unit is then captive owing to the frictional
holding action of the press fit.
The wheel hub, as a part which is of single-piece
design, may have the two cylindrical raceways of the
two cylinder roller bearings and the two raceways for
balls of the two ball bearings.
The wheel bearing unit is preferably designed as a
prestressed unit which is lubricated to last its
working life. It may be prestressed by means of an axle
nut screwed onto the steering knuckle.
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The wheel bearing unit may be sealed off from the surroundings
by means of at least one sealing element.
To simplify the transport and/or installation operation, a
sleeve may also be provided, the outside diameter of which
corresponds to the inner bore in the wheel bearing unit and
which is temporarily located in the preassembled wheel bearing
unit. In this case, the sleeve is preferably composed of
plastic. It may be arranged in the wheel bearing unit with a
press fit.
In some embodiments of the invention, there is provided a wheel
bearing for a motor vehicle with a wheel bearing unit which
supports a wheel hub on a steering knuckle by means of a
rolling bearing, including two cylinder roller bearings and two
ball bearings, acting axially and radially, wherein the wheel
hub is provided directly with a first pair of cylindrical
raceways for cylinder rollers and with a first pair of raceways
for balls, the first pairs of raceways being placed on the end
side of at least one radially extending annular section,
wherein the first pair of cylindrical raceways of the two
cylinder roller bearings is incorporated directly into the
material of the wheel hub and wherein the first pair of
raceways for balls of the two ball bearings is incorporated
into the at least one radially extending annular section
directly into the material of the wheel hub, wherein the
steering knuckle is provided directly or indirectly with a
second pair of cylindrical raceways for the cylinder rollers
and with a second pair of raceways for the balls, the second
pairs of raceways being placed on the end side of radially
extending annular sections, the cylinder rollers being arranged
between the first and second pairs of cylindrical raceways and
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the balls being arranged between the first and second pairs of
raceways for balls, wherein the two cylinder roller bearings
are arranged lying axially on the outside and enclose the two
ball bearings, wherein bearing rings which are placed onto the
steering knuckle are of L-shape design in radial section and
have both one of the second pair of cylindrical raceways of the
two cylinder roller bearings and one of the second pair of
raceways for balls of the two ball bearings, wherein the wheel
hub, as a part of single-piece design, has the first pair of
cylindrical raceways of the two cylinder roller bearings and
the first pair of raceways for balls of the two ball bearings,
and wherein the first pair of raceways for balls are arranged
at face sides of the at least one radially extending annular
section, which are facing away from one another.
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=
According to the present invention, the radial and .
=
axial forces acting on the wheel and the resulting
tilting moments are therefore absorbed by two cylinder '
roller bearings and two axial ball bearings which form
a self-retaining bearing unit. The proposed refinement
permits a very low-friction transmission of force
between the wheel hub and the steering knuckle and
therefore a noticeable reduction in the frictional =
losses during operation of the vehicle. At the same
= time, an increase in bearing rigidity is made possible
by the separate absorption of the radial and axial
forces.
In the case of the 'customary support by means of
tapered rolling bearings, because of the structural =
characteristics of the tapered rolling bearing, an
= axial force which is induced in both bearings is in
action even when the vehicle is travelling straight
ahead, i.e. during a pure radial force, said axial
force again being partially supported on the=
restraining guide flange of the two inner rings via the
. roller end sides and being effective as sliding .
friction. The comparatively high sliding friction
= between the roller end sides and the restraining guide
flange of the inner ring is particularly apparent in
the low speed range.
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In contrast thereto, the proposed solution operates in
all driving states with a pure rolling friction at a
consistently low level. Consequently, a lower
frictional moment and accordingly a lower steady-state
temperature are produced for comparable operating
forces, and this ultimately also has a positive
influence on the duration of use of the grease. As a
result of the lower operating temperatures, there is a
higher kinematic viscosity of the lubricant and
therefore also, as a prerequisite for a long duration
of use of the bearings, reliable lubrication.
A sufficiently high moment rigidity of the bearing
unit, which is of importance particularly in
combination with disk brakes, is ensured by the two
sets of cylinder roller bearings with the design-
induced pressure angle (a = 00) and a sufficiently
large distance therebetween.
Previously known bearing arrangements for wheel
bearings generally revolve with a frictional moment of
up to 5 Nm, that is to say, in the case of a
semitrailer having three axles, i.e. six wheels hubs, a
total frictional moment of approx. 30 Nm is calculated.
With the proposed solution, said value can be
significantly reduced.
Finally, the installation of the unit is significantly
simplified, since a wheel bearing basically does not
need to be positioned. The installation is restricted
to pushing the bearing unit onto the steering knuckle
and bracing the inner rings and the spacer sleeve with
a defined tightening moment by means of the axle nut.
After installation on the steering knuckle and
tightening of the axle nut, the bearing unit is
minimally prestressed via the two axial ball bearings.
A slight axial prestress merely ensures that the balls
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are acted upon with a minimal load in all load states
in order to avoid slippage.
The proposed arrangement is furthermore distinguished
by a lower degree of wear.
A lower generation of heat advantageously also results
in less ageing of the lubricant and a longer duration
of use of the bearing.
The proposed wheel bearing can be used in all
commercial vehicle axles (truck and trailer axles).
An exemplary embodiment of the invention is illustrated
in the drawing. The single figure shows the radial
section through a wheel bearing of a truck or trailer.
A wheel bearing 1 for a truck can be seen in the
figure. The wheel (not illustrated) is supported by a
wheel bearing unit 2 which consists of four rolling
bearings 4, 5, 6 and 7. A wheel hub 3 is mounted
relative to a steering knuckle 8 of the wheel axle by
the wheel bearing unit 2. In this case - as in the
exemplary embodiment - the steering knuckle 8 may have
a minimally stepped stem, which is advantageous for the
installation of the wheel bearing unit.
The four rolling bearings 4, 5, 6 and 7 are two
cylinder roller bearings 4 and 7 and two axial ball
bearings 5 and 6.
The cylinder roller bearings 4, 7 have cylindrical
raceways 9 and 10 of an outer ring which, in the
present case, is formed by the wheel hub 3 itself. The
cylindrical raceways 19 and 20 are formed by bearing
rings (inner rings) 27 and 28 which are placed onto the
steering knuckle 8. Cylinder rollers 11 and 12 are
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arranged between the cylindrical raceways 9, 10, 19,
20.
The two axial ball bearings 5 and 6 are positioned
axially between the two cylinder roller bearings 4 and
7. The balls 17, 18 are arranged between in each case
two annular or disk-shaped components which have the
corresponding raceways for the balls. For this purpose,
the wheel hub 3 has one or two radially extending
annular sections 13, 14 into which raceways 15, 16 are
incorporated, in each case on the end side. The bearing
rings 27 and 28 have an L-shaped contour in radial
section, thus producing radially extending annular
sections 21 and 22 into which respective raceways 23
and 24 are incorporated.
As can be seen, the entire wheel bearing unit 2 with
its four bearings 4, 5, 6, 7 is designed symmetrically
with respect to a center plane 26 which is
perpendicular to the axis of rotation 25 of the
steering knuckle 8.
The cylinder rollers 11, 12 transmit pure radial
forces. For the axial guidance of the cylinder rollers,
the inner rings 27, 28 have restraining flanges 29 and
on either side of the bearing ring 27 and
restraining flanges 31 and 32 on either side of the
bearing ring 28. On the corresponding outer ring, the
cylindrical raceway 9, 10 is not bounded by restraining
30 flanges.
A spacer sleeve 33 keeps the two bearing rings 27, 28
at a defined distance when an axle nut 34 is screwed
onto the steering knuckle 8 during the installation of
the wheel bearing unit. The width of the spacer sleeve
should preferably be selected such that, after the axle
nut is tightened, the two axial ball bearings 5, 6 are
slightly prestresed.
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In addition, the spacer sleeve 33 may also serve as a
frictional connecting element between the two inner
rings 27 and 28. In this case, the sleeve sits with an
overlap over the outside diameter thereof, i.e. with a
press fit, in grooves 37 which are provided in the
inner rings 27 and 28. This produces a captive unit,
which has a noticeably positive effect on transport and
installation.
A sealing element 35 in the form of a radial shaft seal
ensures sealing off from the surroundings. The wheel
bearing unit may optionally be sealed off on both
sides. The radial shaft sealing ring for sealing off
from the inside of the wheel should therefore be
understood here as being by way of example.
The cylinder roller bearing on the inside of the wheel
may be of stronger design, because of the generally
higher radial force acting there, than the cylinder
roller bearing arranged on the outside of the wheel;
however, this is in no way compulsory.
For economical reasons, the use of identical sets of
rollers is preferred for the respectively identical
bearings 4 and 7 and 5 and 6.
In the case of steering knuckles without a step and
with the inner rings having identical bore diameters,
the provision of a sleeve 36 (shown in addition to the
steering knuckle 8 in the figure) which is preferably
composed of plastic and which permits very simple
installation is particularly advantageous. The sleeve
36 which is pressed with its outside diameter D into
the bore in the wheel bearing unit 2 keeps the bearing
unit together during transportation. While the bearing
unit 2 is being slid onto the steering knuckle 8, the
sleeve 36 is pushed out of the bearing bore at the same
time.
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As an alternative, to assist in the handling during
transportation and/or installation, use may be made of
the abovementioned solution, according to which the
spacer sleeve 33 sits with a moderate press fit in the
grooves 37 in the inner rings 27, 28 such that the two
inner rings are held together in the axial direction.
The bearing unit is lubricated with a use-optimized
smooth movement grease.
During straight-ahead travel, a share of the wheel
force acting at the tire contact point and
corresponding to the axial position of the wheel
pressure line is absorbed by the two cylinder roller
bearings. The axial force resulting from the wheel
camber is absorbed by one of the two axial ball
bearings. Otherwise, the axial prestressing force
applied during installation acts in both rows of balls.
During cornering, a share of the radial wheel contact
force corresponding to the axial position of the wheel
pressure line is absorbed by the two cylinder roller
bearings and the tilting moment which is induced by the
axial force and the dynamic tire radius is likewise
supported via the two cylinder roller bearings. The
axial force which is produced at the wheel hub by the
centrifugal force acting on the vehicle is transmitted
by the central housing disk to the respectively loaded
axial ball bearing as a function of the direction of
the force (wheel on the inside or outside of the
corner) and conducted via the "shaft disk" of the
respective inner ring into the steering knuckle.
For the installation of the wheel bearing unit, the
procedure is as follows:
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First of all, the wheel bearing unit is pushed over the
end side of the outer inner ring of the cylinder roller
bearing. The inner rings sit on the steering knuckle
with a loose fit (recommended tolerance range: "f7").
The transport sleeve (sleeve 36) prevents separation of
the bearing components. When the bearing unit is pushed
on, the transport sleeve is pushed off.
The central axle nut 34 is then tightened with a
previously specified tightening moment. In the process,
the two inner rings 27, 28 and the intermediate sleeve
(spacer sleeve) 33 are braced against each other. The
bracing force at the same time secures the axle nut
against release.
The radial play in the cylinder roller bearings is
preset and is very close to zero; a change during
installation is prevented by the loose fit of the inner
rings.
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List of designations
1 Wheel bearing
2 Wheel bearing unit
3 Wheel hub
4 Rolling bearing (cylinder roller bearing)
5 Rolling bearing (axial ball bearing)
6 Rolling bearing (axial ball bearing)
7 Rolling bearing (cylinder roller bearing)
8 Steering knuckle
9 Cylindrical raceway
10 Cylindrical raceway
11 Cylinder roller
12 Cylinder roller
13 Annular section
14 Annular section
15 Raceway
16 Raceway
17 Ball
18 Ball
19 Cylindrical raceway
20 Cylindrical raceway
21 Annular section
22 Annular section
23 Raceway
24 Raceway
25 Axis of rotation
26 Center plane
27 Bearing ring
28 Bearing ring
29 Restraining flange
30 Restraining flange
31 Restraining flange
32 Restraining flange
33 Spacer sleeve
34 Axle nut
35 Sealing element
36 Sleeve
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37 Groove
D Diameter
