Note: Descriptions are shown in the official language in which they were submitted.
CA 022228~6 1997-12-19
Steering wheel with built-in airbag
Description
The invention relates to a steering wheel for
motor vehicles with an integrated airbag, a covering
for the central airbag region being formed in one piece
with a sheathing which adjoins on the outside for the
steering-wheel spokes and the steering-wheel rim, and
the steering wheel inclusive of all accessory parts
forming a finished structural unit which can be
connected to the steering column during final assembly.
Since the introduction of the airbag, such
steering wheels have been realized in the widest
variety of embodiments. Understandably, the widespread
technique for producing steering wheels was initially
taken as a basis, this technique comprising providing
the metal skeleton of the steering wheel, at least on
the steering-wheel rim, with a sheathing of foamed
plastic which either, as a so-called integral foam,
inherently has an impermeable outer layer with good
feel, or else is sheathed in leather or a leather-like
plastic layer. The central region of the steering
wheel, receiving the airbag module, was then also
designed in a similar way, many proposals having been
disclosed concerning the cover cap for the airbag and
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attempting to meet the to some extent conflicting
requirements in a way which is functionally
satisfactory and favorable in terms of production
technology.
International competition means that automobile
manufacturers are increasingly demanding from suppliers
complete components, which on the one hand require
little assembly work but on the other hand are becoming
ever more complicated, because they have to perform an
ever greater number of functions. Steering wheels are
equipped with all possible switches and buttons to
enable the driver to actuate all the operating
functions of the radio, the various vehicle lighting
systems, the automatic window openers, etc., without
having to take a hand off the steering wheel. All
these switches and buttons must be taken into
consideration during the design of the steering wheel
and its sheathing and must be configured in such a way
that on the one hand they have the required freedom of
movement but on the other hand they are integrated in a
way which is satisfactory with respect to appearance
and feel.
In the case of a first known example (EP 0648
661 A1), it is provided that a central steering-wheel
part with hub, spoke stubs, airbag and other functional
parts is first of all connected to the steering column,
that then the rear covering is fastened to this
steering-wheel part and that, finally, the peripheral
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steering-wheel part with the steering-wheel rim, outer
spoke stubs and covering for the airbag module is
fastened to the central steering-wheel part,
overlapping ends of the spoke stubs, which are
connected to one another by means of screws inserted at
the rear, being provided. Alternatively, the central
steering-wheel part and the rear covering may also
first of all be connected and then fitted onto the
steering column. During this operation and during
possible disassembly of the steering wheel, the
fastening means can be reached with a tool through an
opening in the rear covering.
It is regarded as disadvantageous in the case
of both embodiments that a relatively great assembly
effort is required and that the two steering-wheel
parts, which in their final form are expediently
screwed to each other for transportation and storage,
first have to be taken apart again for assembly.
In the case of another embodiment (ES-U-
9303374), it is provided that a central hub part with
an airbag module fastened to it, but without a special
rear plastic covering, is connected to the steering
column and that the steering wheel, assembled in one
piece with inner ring, spokes, steering-wheel rim and
sheathing, and integrated covering for the airbag
module, is then connected to the hub part by means of
screws which are to be inserted at the rear.
Objections here are the excessive amount of final
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assembly and the effort involved during possible
disassembly.
The same also applies to the third and fourth
embodiments (WO 95/23712A1 and EP 0691245A1), in which
again a hub part with airbag module and a one-piece
steering wheel with inner ring, spokes, steering-wheel
rim, sheathing and integrated covering for the airbag
module is provided and the only differences are in the
fastening means for connecting the steering wheel and
steering column. In all cases, although the part of
the steering wheel to be grasped by the driver is
designed relatively favorably in terms of production
technology, this is not true of the fastening part,
which is decisive for final assembly, with the result
that - as far as we know - none of the known versions
has so far gone into series production. This may be
due not least to the fact that the fastening part has
been left behind in development technology in favor of
simple production of the steering-wheel parts relevant
to feel.
The invention is based on the object of further
developing the generic steering wheel in such a way
that the production standard achieved can be
maintained, that the assembly of the various parts for
various additional functions on the steering wheel can
be made simple and variable and that, in particular,
the entire steering wheel can be transported, stored
and assembled on the steering column in the simplest
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possible way, and if need be also disassembled again,
as a single component.
To achieve this object, it is provided
according to the invention that the steering wheel
comprises a steerlng-wheel skeleton and a two-shell
sheathing,
- the steering-wheel skeleton having a hub region to be
fastened to the steering column,
- an airbag module being fastened to the steering-wheel
skeleton,
- the sheathing comprising an upper shell with airbag
covering and a lower shell with a central opening in
the hub region and
- the upper shell and lower shell being connected to
each other along a parting surface.
The invention is based on the idea that
considerable degrees of freedom are gained with regard
to the arrangement and assembly of the airbag module
and of the other functional parts to be fitted to the
steering wheel if a substantially three-part steering-
wheel form is provided, the metal skeleton serving as a
carrier for all the components to be assembled and the
upper and lower shells, to be produced from plastic,
enclosing the steering wheel and all the components
fastened to it in a sandwich-like manner. In this way,
a finished steering wheel which just has to be fitted
onto the steering column and fastened with the union
nut in final assembly can be created, without having to
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dispense with the customary serration with taper
between steering-wheel hub and steering column. A
simple plug connection also suffices here for the
electrical part.
The design according to the invention has the
further advantage that the metal steering-wheel
skeleton, with the components fastened to it, some of
which are sensitive to heat, no longer has to be placed
into an injection mold and that the upper and lower
shells can each be produced on their own as independent
components. This gains degrees of freedom for the
plastics to be used, with the result that different
plastics and shells made up of different plastic
components can also be realized more easily. Instead
of foaming, a mechanical fastening between the shells
and the steering-wheel skeleton is provided, which
brings with it further degrees of freedom in the design
of the shapes of the shells. Finally, in the
connection of the shells to each other and to the
steering-wheel skeleton, it is possible to have
recourse to all common types of connection and to
select the most favorable for the respective case.
Advantageous refinements and modifications of
the idea of the invention are described in subclaims 2
to 22. Further details and advantages are explained in
more detail with reference to the exemplary embodiments
represented in Figures 1 to 7, in which:
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Figure 1 shows an exploded drawing of an
embodiment of the invention
Figure 2 shows an assembled embodiment in
elevation and two sections
Figure 3 shows in an enlarged representation a
section through an embodiment of the steering-wheel rim
Figure 4 shows in an enlarged representation a
section through another embodiment of the steering-
wheel rim
Figure S shows a third embodiment as a section
through a spoke and steering-wheel rim
Figure 6 shows a fourth embodiment as a section
through the steering-wheel rim
Figure 7 shows a further embodiment as a
section through a spoke and steering-wheel rim.
In the case of the exemplary embodiment
according to Figure 1, the steering wheel comprises a
steering-wheel skeleton 1 with a hub region 5, spokes
10 and steering-wheel rim 9, an airbag module, an upper
shell 2 with airbag covering 2a and a lower shell 3
with a central opening 8. The steering-wheel skeleton
1 takes the form of a die casting and is configured for
fastening the airbag module 6. Also provided are
screws 11, to allow the lower shell 3 and upper shell 2
to be connected to each other. In this arrangement,
the steering-wheel skeleton can be held and clamped in
just by a corresponding form-fitting type of design
between the two shells or else be additionally fixed in
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relation to the shells by means of through-bores for
the screws 11.
In the present case, four spokes 10, extending
in a funnel-shaped manner from the steering-wheel rim 9
to the hub region 5, are provided, and in both shells
2, 3 there are accordingly provided four spoke-like
regions, which in the assembled state enclose the
spokes 10 of the steering-wheel skeleton 1 and
consequently form at the same time four grip-through
openings, through which the driver can grasp the
steering-wheel rim 9. The parting plane between lower
and upper shells 2,3 lies exclusively in the plane of
the steering-wheel rim 9, i.e. the wall regions of the
lower shell are drawn up on both sides of the spokes 10
to the height of the steering-wheel rim 9. Since the
lower shell 3 is consequently of a funnel-shaped
overall design and undertakes the sheathing of the
steering-wheel skeleton 1 in the regions extending out
of the plane of the steering-wheel rim 9 in the
direction of the steering column 4, the upper shell 2
may be of a relatively flat configuration and the
parting surface may be arranged at the height of the
steering-wheel rim.
Figure 2 shows an assembled steering wheel with
the basic configuration according to Figure 1, Figure
2a showing a plan view and Figures 2b and 2c showing
two sections running perpendicular to each other and to
the plane of the drawing of Figure 2a.
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Fastened on the steering-wheel skeleton 1 with
hub region 5, spokes 10 and steering-wheel rim 9 is an
airbag module 6. The steering-wheel skeleton 1 is
sheathed by lower and upper shells 3, 2, the lower
shell having a central opening 8 and the upper shell 2
comprising the airbag covering 2a. The hub region 5 is
provided in a known way with a serration and a taper
and is fitted on the corresponding part of the steering
column. The axial bracing takes place by means of a
union nut 7, which is supported on a peripheral stop on
the steering-wheel column 4 and is screwed up on a
thread formed on the outside of the hub region 5.
This type of fastening, combined with the two-
shell sheathing 2, 3 according to the invention of the
steering-wheel skeleton 1, allows the steering wheel as
a whole to be configured as a one-part component which
is easy to handle during transportation and storage and
requires no special protective measures. The one-part
steering wheel can go straight into final assembly and
is very easy to fasten. Consequently, a steering wheel
which can be equipped with all the currently customary
and planned additional functions and at the same time
is extremely easy to handle and (dis)assemble is
obtained.
Figure 3 shows as a section through the
steering-wheel rim 9 a first possible way in which the
lower shell 3 and upper shell 2 can be connected to
each other. In the region of the steering-wheel rim 9,
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the steering-wheel skeleton 1 is of a U-shaped design
in cross section, with a base region 16c and two
slightly outwardly diverging legs 16a, 16b, and has a
series of through-holes 9a. The two shells 2 and 3 are
made up of a number of plastic components, according to
the different hatching, and can thus be adapted
optimally to the different requirements regarding
strength and to the demands with respect to appearance
and feel. They are matched in a form-fitting manner to
each other in the parting surface, like a tongue-and-
groove joint, and are connected to each other by means
of screws 11. In this arrangement, the upper shell 2
bears against the steering-wheel rim 9 in certain
regions and has corresponding bores for the screws 11.
The lower shell 3 engages by a cross-sectionally
trapezoidal part 17 in the cross-sectionally U-shaped
steering-wheel rim 9. It has clearances 18, in which
the screw heads lla may be countersunk and which may,
if appropriate, be covered by a subsequently applied
~n layer of plastic. They may, however, also remain open,
since, being on the underside of the steering wheel,
they are not obtrusive visually or in terms of feel.
In the case of the embodiment according to
Figure 9, the steering-wheel skeleton 1 is again of a
U-shaped design, with slightly diverging legs, in the
region of the steering-wheel rim 9. In this case, the
lower shell 3 and upper shell 2 are, however, connected
to each other in a form-fitting manner by means of a
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snap connection 20, an elastically deformable body 20a
ensuring that the snap connection 20 is permanently
under tensile stress.
Figure 5 shows a section through a spoke 10 and
through the steering-wheel rim 9. The lower shell 3
and upper shell 2 bear against the steering-wheel
skeleton only in certain regions, via webs, and are
held together by means of a flexible ring 12 of
approximately semicircular cross section, it being
ensured by recesses 13 and 14 that, on the outside, the
ring 12 terminates flush with the inwardly adjoining
regions of the two shells 2, 3.
Figure 6 shows an embodiment in which the upper
shell 2 and lower shell 3 are surrounded, at least in
the region of the steering-wheel rim 9, by a covering
layer 15 of leather or the like in each case. The
borders 15a, 15b of the covering layers 15 are turned
inward in the region of the parting surfaces and
clamped in between the two shells 2, 3. Provided
between the shells 2, 3 is a form-fitting tongue-and-
groove joint, which is held together by screws (not
shown).
Figure 7 shows an embodiment in which the
steering-wheel skeleton is completely embedded in the
lower shell 3 in the region of the spokes 10 and of the
steering-wheel rim 9. The upper shell 2 is connected
by means of tongue-and-groove joint 19 and screws 11 to
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the lower shell 3, the screw heads lla again being
countersunk in clearances 18.
Further modifications and types of fastening
are within the scope of the basic idea of the
invention, providing a one-part steering wheel suitable
for final assembly in which the steering-wheel skeleton
is embedded with all the functional parts between
plastic parts in the form of half shells.
