Steering wheel with integrated gas bag

A steering wheel has a skeleton with a foamed sheathing, a hub, spokes and a steering wheel rim. A gas bag module is inserted in a central recess of the steering wheel. The gas bag module has a cover cap at the side facing the driver. For actuating a horn switch the module is movable in the direction of the steering wheel axis relative to the steering wheel. A movement gap is formed between the cover cap and the foamed sheathing. Mounting studs on the skeleton extend parallel to the steering wheel axis. The positioning of the mounting studs is defined by the foamed sheathing. The mounting studs have free ends which are slidingly accommodated in guide recesses provided in the cover cap.

The present invention relates to a steering wheel having a skeleton
 provided with a foamed sheathing, a hub, spokes and a steering wheel rim,
 and including a gas bag module which is inserted in a central recess of
 the steering wheel, with a cover cap at the side facing the driver.
 BACKGROUND OF THE INVENTION
 Numerous proposals have already been made for securing a gas bag module in
 a steering wheel. When steering wheels in the final assembly are secured
 by means of a nut screwed to the end of the steering column, the gas bag
 module cannot be inserted until the steering wheel has been fitted since
 the module is located centrally above the steering wheel hub which must
 remain freely accessible for screwing on the nut. Alternatively, when the
 steering wheel is furnished with the completely assembled gas bag and is
 mounted to the steering column, then some other means of securing the
 steering wheel is needed. For this, proposals have already been made as
 well, but all of which are more expensive in design and thus more costly
 than the usual solution of securing the steering wheel by a central nut.
 If the gas bag cover is to be used for actuating the horn switch, the gas
 bag module needs to be shiftably arranged in the steering wheel, allowing
 for a contact stroke parallel to the steering wheel axis.
 With many mounting systems for gas bag module in a steering wheel, it is a
 nuisance that the cover cap on the side facing the driver may be
 positioned relative to the surface of the steering wheel only with
 considerable complication such that movement gaps existing between the
 cover cap and the steering wheel, as needed for actuating the horn switch,
 are equally wide, because between any fastening points at which bolts are
 inserted and these portions in which movement gaps are provided, a
 plurality of components is arranged whose inevitable production tolerance
 in the worst case add up, resulting in significantly differing wide
 movement gaps. This is unacceptable in terms of a neat appearance.
 An object of the invention is to provide a steering wheel with a fastening
 means permitting to maintain any movement gaps within close tolerances,
 using conventional bolt connections to reduce production cost, and without
 necessitating additional space.
 To achieve this object it is proposed in accordance with the invention that
 mounting studs are provided which extend parallel to the steering wheel
 axis. The positioning of these studs is defined and determined by a foamed
 sheathing which covers the steering wheel rim and at least part of the
 spokes. The cover cap has recesses wherein free ends of the mounting studs
 are slidingly received.
 BRIEF SUMMARY OF THE INVENTION
 In this arrangement it is assumed that the constructional alignment
 coordinates, for correctly positioning the cover cap relative to the
 steering wheel surface, need to be provided as near as possible to the
 movement gaps and where possible in the same component which in
 conjunction with the cover cap itself is responsible for the width of the
 movement gap to be judged by appearance only. This is the foamed sheathing
 applied to the steering wheel. When in accordance with the invention the
 portions juxtaposing the cover cap are produced in the same mold and in
 the same step of production as the coordinates determining the
 positioning, then the production tolerances may be reduced to such an
 extent that they are no longer able to influence the movement gaps.
 The mounting studs to be used in accordance with the invention are
 accordingly positioned in the foamed sheathing and so precisely determine
 the positioning of the cover cap which in turn is attachable to the
 mounting studs by the guide recesses in the cover cap. It will readily be
 appreciated that the movement gaps may be very closely toleranced in this
 way, particularly when the mounting studs are arranged directly
 juxtaposing the movement gaps where possible.
 The gas bag module may be preassembled with the cover cap via the mounting
 studs and then inserted together with the cover cap in the steering wheel
 already arranged in the vehicle. Subsequently, all that is needed is to
 tighten the studs on the rear side of the steering wheel, this
 corresponding to the present scope of work in fitting bolt connections.

DETAILED DESCRIPTION OF THE INVENTION
 Referring now to FIG. 1 there is illustrated a partial section of a
 steering wheel in which a skeleton consisting of a hub 1, spokes 2 and a
 steering wheel rim 3 is provided with a foamed sheathing 4. The gas bag
 module 5 comprising a cover cap 6 at the side facing the driver is
 inserted in a pot-shaped cavity in the steering wheel, a movement gap 7
 being provided between the foamed sheathing 4 and the cover cap 6. For
 movingly securing the gas bag module 5, mounting studs 10 are provided
 which extend parallel to the steering wheel axis. The positioning of the
 mounting studs 10 is defined by the foamed sheathing 4, largish
 foam-coated through-holes 9 being provided for this purpose in the spokes
 2. Provided concentrically to the foam-coated through-holes 9 and on the
 upper and lower sides of the foamed sheathing 4 are supporting portions 8
 and 8' extending in a plane perpendicular to the steering wheel axis.
 These supporting portions 8, 8' serve as a buttress for the bolt
 connection, a flange 11 of the mounting stud 10, on the one hand, and the
 head of a bolt 12, on the other, resting on the supporting portions 8, 8'
 in the fitted condition. Arranged above the flange 11 is a washer 13 of an
 insulating material in which a support for the hot electrical contacts 14
 is embedded. At the end of the mounting stud 10, at the side facing the
 driver, a nut 21 is screwed in place, the final fitted positioning of
 which is defined by a stop on the mounting stud 10. The cover cap is
 attached to the nut 21 by means of a guide recess 25. In turn, the
 recesses 25 provided on cover cap 6 accommodate the mounting studs 10.
 Consequently, the positioning of the recesses 25 is indirectly defined by
 the sheathing 4. The nut 21 is secured onto the male-threaded end of the
 mounting stud 10 facing the driver.
 Clamped in place between the nut 21 and the washer 13 of insulating
 material is a helical spring 15 and the dished recess 19 of a mounting tab
 17 of the gas bag module 5. Secured to the mounting tab 17 is an
 electrical mass contact 18. Additionally arranged between the nut 21 and
 the dished recess 19 of the mounting tab 17 is a washer 35 of
 noise-dampening material.
 In the embodiment shown the gas bag module 5 comprises an inflator 16 with
 a mounting flange 16' to which the gas bag 36 is secured via a mounting
 ring (not shown). By means of the same fasteners an inwardly angled tab
 23' of a surrounding web 23 of the cover cap 6 and the mounting tab 17 are
 secured. Gas bag module 5 and cover cap 6 thus form an assembly unit which
 is positioned relative to the foamed sheathing 4 via the guide recess
 configured in the cover cap 6. The dished recess 19 of the mounting tab 17
 comprises for this purpose a through-hole 20, the diameter of which is
 larger by the required clearance than the outer diameter of the mounting
 stud 10. Reference numeral 24 identifies the outer portion of the cover
 cap 6, i.e. the portion forming together with the foamed sheathing 4 the
 movement gap 7 in the fitted condition.
 The assembly consisting of gas bag module 5 and cover cap 6 is positioned
 in a plane perpendicular to the steering wheel axis by the mounting stud
 10 relative to the steering wheel whilst being arranged such that for
 actuating the horn switch contacts 14 and 18, it may be depressed parallel
 to the steering wheel axis and against the resistance of the return spring
 15. For fitting the assembly unit consisting of gas bag module 5 and cover
 cap 6, the mounting studs 10 are inserted into the foam-coated
 through-holes and secured to the steering wheel via the bolts 12, the
 foamed sheathing 4 being configured such that the bolts are unable to drop
 out downwards even when totally screwed out of the threaded bore of the
 mounting stud.
 Referring now to FIG. 2 there is illustrated an embodiment employing
 similar mounting studs 10 including a thickened portion 26 at one end
 which in the fitted condition engages blind holes 9' in the foamed
 sheathing 4. In this arrangement two mounting studs 10 each are connected
 to a plate 28 through washers 13 of an insulating material such that any
 clearance needed for positioning the mounting studs 10 in the foamed
 sheathing 4 is maintained.
 The plate 28 carries the hot electrical contacts 33 whilst the mass
 contacts are carried by a mounting plate 30 secured to the gas bag module.
 The mounting plate 30 is, the same as in the embodiment as shown in FIG.
 1, provided with mounting tabs 17 which for actuating the horn switch
 contacts may be depressed parallel to the steering wheel axis or may be
 tilted. The cover cap 6 is, here again, attached by means of guide
 recesses 25 to the nuts 21 screwed onto the mounting studs 10, at the side
 facing the driver.
 Unlike the embodiment as shown in FIG. 1, however, here in FIG. 2 a snap-in
 or latch-type connection is provided, comprising for two fastening points
 each a snap-action stud 29 extending in the direction of the steering
 wheel axis and a latching pawl secured to the mounting plate 30. The
 snap-action stud 29 is secured by its rear end in a skeleton part 1 of the
 steering wheel and provided by known ways and means with a conical front
 end, it being by this end that the snap-action stud 29 is able to pass
 through a through-opening 31 in the mounting plate 30 to engage behind a
 latching pawl 32 in the finished fitted condition. By means of such a
 snap-in or latch-type connection the time needed for final assembly of the
 gas bag module may, of course, be further reduced as compared to a bolt
 connection.
 It is understood that components in the scope of the description relating
 to FIG. 2 and not identified by reference numerals are the same in
 configuration and function as those already described regarding the
 embodiment as shown in FIG. 1.
 Referring now to FIG. 3 there is illustrated a variant which differs from
 the embodiments as shown in FIGS. 1 and 2 merely by the cover cap 6 with a
 guide recess 25' being directly attached to the end, at the side facing
 the driver, of the mounting stud 10, 26 and not to the nut 21'. In this
 way it is prevented that the unavoidable thread clearance between the nut
 21' and the mounting stud 10, 26 influences the movement gap 7 between
 cover cap 6 and foamed sheathing 4.
 It is evident from the magnified illustration as shown in FIG. 3 that
 between the outer limitation of the mounting stud 10, 26 and the
 surrounding component a radial clearance is provided so that this
 component cannot obstruct orienting the cover cap 6 relative to the foamed
 sheathing 4 in a plane perpendicular to the steering wheel axis. Thus,
 there is provided a way of securing a gas bag module in a steering wheel,
 in which the cover cap may be precisely oriented in a plane perpendicular
 to the steering wheel axis, the cover cap, however, being arranged movable
 and parallel to the axis for actuating the horn contacts.
 In the embodiment as shown in FIG. 1 the mounting studs are designed such
 that they are able to take up the reaction forces occurring on actuation
 of the gas bag, they being made of steel or some other high-tensile
 material. In the embodiment as shown in FIG. 2 the reaction forces are
 taken up by the snap-in or latch-type connections, so that the mounting
 studs as regards their strength need to be designed merely for positioning
 the cover cap relative to the steering wheel. For these purposes they may
 be made of suitable synthetic materials, thus making for an additional
 weight-saving as compared to the embodiment as shown in FIG. 1.