Abstract:
The invention relates to a vehicle steering wheel for a vehicle having a horn, said steering wheel having a longitudinal axis and comprising a gas bag module, a steering wheel skeleton, a gas bag module, at least one detent connection for connecting the gas bag module with the steering wheel skeleton. The gas bag module is displaceably mounted to the skeleton to allow a displacement of the gas bag module in the direction of the longitudinal axis to actuate the horn. The detent connection has first and second electrical contact surfaces, which come into contact with each other by displacement of the gas bag module to actuate the horn.

Description:
BACKGROUND OF THE INVENTION 
     In steering wheels, usually, a separate horn contact switch is provided between the gas bag module and the steering wheel skeleton, which switch is actuated on displacement of the gas bag module in the direction of the longitudinal axis. This horn contact switch is an additional component which has to be mounted as an extra component and hence entails additional costs in the production of the vehicle steering wheel. Furthermore, the separate horn contact switch takes up a portion of the already confined space in the vehicle steering wheel. A further disadvantage consists in that these switches generally cause noises on contacting. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is therefore based on the problem of providing a vehicle steering wheel with few components and a reduced installation expenditure. This is achieved in a vehicle steering wheel for a vehicle with a horn, said steering wheel having a longitudinal axis and comprising a gas bag module, a steering wheel skeleton, a gas bag module, at least one detent connection for connecting the gas bag module with the steering wheel skeleton. The gas bag module is displaceably mounted to the skeleton to allow a displacement of the gas bag module in the direction of the longitudinal axis to actuate the horn. The detent connection has first and second electrical contact surfaces, which come into contact with each other by displacement of the gas bag module to actuate the horn. In this way, the vehicle steering wheel is provided with a horn contact switch, without additional components being necessary. 
     According to an advantageous embodiment of the invention, provision is made that the detent connection has a detent element and a locking element, a first contact surface being constructed on the detent element and a second contact surface being constructed on the locking element. When the horn is actuated, the locking element lies with its second contact surface against the first contact surface, which is provided on the detent element. When the horn is not actuated, the locking element lies against a holding surface on the detent element, an electrical insulation being provided on the holding surface or on the locking element, which insulation when the horn is not actuated prevents an electrical contact between the locking element and the holding face and between the detent and locking elements, respectively. In this particularly simple development, the detent connection consists of merely two parts, which at the same time form the contact elements of the horn contact. The insulated holding surface on the detent element offers the possibility of using the detent element and the locking element as contacts and nevertheless, when the horn is not actuated, of bringing about via the two elements a mechanical connection between gas bag module and steering wheel skeleton. 
     Further developments of the invention and their advantages will be apparent from the sub-claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic cross-section through a first embodiment of a vehicle steering wheel according to the invention; 
     FIG. 2 a  shows an enlarged cross-section of the detail II of the vehicle steering wheel of FIG. 1 with the horn not actuated; 
     FIG. 2 b  shows a cross-section through the detail II of the vehicle steering wheel of FIG. 1 with the horn actuated; 
     FIG. 3 shows a perspective view of the detail II of the vehicle steering wheel of FIG. 1; 
     FIG. 4 shows a detent connection of a vehicle steering wheel according to a second embodiment of the invention from a first perspective; 
     FIG. 5 shows the detent connection of FIG. 4 from a second perspective; 
     FIG. 6 shows a cross-section through a detent connection of a vehicle steering wheel according to a third embodiment of the invention with non-actuated horn; and 
     FIG. 7 shows a cross-section through the detent connection of FIG. 6 with actuated horn. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The vehicle steering wheel illustrated diagrammatically in FIG. 1 has a steering wheel skeleton  10  and a gas bag module  12 . The longitudinal axis A of the steering wheel is illustrated by a dot-and-dash line. The steering wheel skeleton  10  has a steering wheel rim  14  encased in foam and connected via spokes  16  with a cup-shaped steering wheel hub  18 . In the longitudinal axis A of the vehicle steering wheel, a sleeve  20  is provided on the hub  18  for fastening the steering wheel to a steering column in a conventional manner. 
     The gas bag module  12  is illustrated by way of example and has a cup-shaped module housing  22  with a base  23 , which forms at the same time the support for a gas generator  24 . The module housing  22  is closed towards the vehicle occupant side with a covering  26 , which covers a folded gas bag  28  inside the module housing  22 . The gas bag module  12  is connected by means of detent connections  30  with the hub  18 , only two of which are to be seen in FIG. 1, which, however, are illustrated in greater detail in FIGS. 2 a ,  2   b  and  3 . 
     Each of the detent connections  30  comprises a detent element in the form of a pin  32  with a cylindrical shaft  38  which is pressed by its foot end  33  into the base  23  of the module housing  22 . At its head end, the pin  32  has a conical end section  34  to which a narrower intermediate section  36  adjoins. The transition from the intermediate section  36  to the cylindrical shaft  38  of the pin is formed by a section in the shape of a truncated cone, the envelope surface of which forms a first contact surface  40 . On the rear face of the end section  34  a flat holding surface  42  is formed perpendicular to the longitudinal axis of the pin  32 , which runs parallel to the longitudinal axis A. This holding surface  42  is electrically insulated from the pin  32 , for example by a coating or a disc of insulating material which is placed on it. 
     As can best be seen from FIG. 3, an opening  50  is provided in the hub  18 , through which the pin  32  can extend. On the underside of the hub, facing away from the gas bag module  12 , there is a locking element in the form of a spring wire  52  as part of the detent element. The spring wire  52  is fastened to the hub  18 , for example by its first end being pressed into an opening of a projection  53  on the underside of the hub. The second end of the spring wire  52  is able to be bent elastically parallel to the plane of the hub between the underside of the hub and a tongue  54  constructed thereon, the tongue  54  largely preventing a bending of the spring wire  52  parallel to the longitudinal axis A. The spring wire  52  extends eccentrically over the opening  50 . Its surface forms a second contact surface  55  in the region of the opening  50 . 
     Both contact surfaces  40 ,  55  are connected electrically in a conventional manner with the signal arrangements of the control apparatus for triggering the horn H, so that together they form a horn switch. When the pin  32  and the base  23  of the module housing  22  consist of metal, in an advantageous manner the contact surface  40  can lie on the mass potential of the vehicle, because the module housing  22  is generally connected in any case with the vehicle mass. 
     On installation of the gas bag module  12 , the pin  32  is inserted through the opening  50 , the frustum-shaped end section  34  bending the spring wire  52  elastically to the side, until the intermediate section  36  passes through the opening and the spring wire  52  can snap back again into its initial position. In this state, the spring wire  52  engages behind the end section  34 , so that the pin  32  can no longer be drawn out from the opening  50 , because the spring wire  52  lies against the holding surface  42 . 
     Between the gas bag module  12  and the steering wheel skeleton  10 , spring elements  56  are provided, which are illustrated in FIG. 1 as compression springs. The compression springs  56  exert a force on the gas bag module  12  so that the spring wire  52  lies free of play against the holding surface  42  when the horn is not actuated. With this, a basic position is established and the gas bag module  12  is prevented from rattling and causing disturbing noises whilst travelling. 
     To actuate the horn H, pressure is exerted by the vehicle occupant onto the gas bag module  12  contrary to the force of the springs  56  via the covering  26 , so that the gas bag module  12  is displaced in the direction of the longitudinal axis A (see arrows in FIG.  1 ). Here, the pin  32  is also displaced with respect to the hub  18 , until the first contact surface  40  comes into contact with the second contact surface  55  on the spring wire  52 , whereby the horn contact is closed. In this way, the tolerance path of the detent connection, which is present in any case, is used as actuating path for the signal emission and hence space is saved with respect to solutions, in which the gas bag module is mounted so as to be displaceable separately. Through the fact that the first contact surface  40  on the pin  32  is inclined in relation to the displacement direction of the gas bag module  12 , the spring wire  52  slides with contact on the contact surface  40 . In this way, the electrical contact not only takes place at a single point, whereby the contact safety is increased; in addition, through the relative movement of the two contact surfaces  40 ,  55 , a self-cleaning effect is produced and hence an increased lifespan of the horn contact. Advantageously, the two contact surfaces are provided with a conductive coating, are for instance galvanically silver-plated, in order to reduce the transition resistance and to reduce the risk of corrosion. 
     Of course, various modifications are conceivable for the construction of the contact surfaces. The pin  32 , for example, can be metallic as shown and can have an insulation on the holding surface  42 . Alternatively, it would also be conceivable to construct the pin  32  in plastic and to provide the contact surface  40  with a metallization. This would be particularly advantageous if the module housing  22  likewise consists of plastic, so that the pin  32  can also be molded on in one operating step. 
     Furthermore, the pin  32  can alternatively also be arranged on the hub  18  and the opening  50  and the spring wire  52  can be provided on the gas bag module  12 , so that the detent connection is arranged in reverse. 
     A particularly simple embodiment is produced when the pin  32  and the openings  50  lie on a circular line around the longitudinal axis A, because in this case a ring-shaped spring wire, which is guided by means of tongues  54 , can be used as single locking element for all detent connections. 
     In FIGS. 4 and 5 a further embodiment of a detent connection  130  is illustrated for a vehicle steering wheel according to the invention, reference numbers being used, increased by 100, for components which are already known. In this embodiment, a detent hook  132  is provided as detent element, which consists of a contact body  143  and an insulation  144 . The contact body  143  is formed by a flat metal strip which can be produced for example by punching out and subsequent bending off from the base of the module housing and has an electrically insulating material injected around it, which forms the insulation  144 . In FIG. 4 on the left-hand side the insulation  144  is cut open, to show clearly the metallic contact body. As can be seen, the contact body has a shaft  138  and an end section  134 , which is connected via a narrower intermediate section  136  with the shaft  138 . 
     Owing to the narrower intermediate section  136 , the contact body has on a narrow side, which is designated hereinbelow as the contact side  146 , a recess  148 , the side of which adjoining the end section  134  runs at right angles to the longitudinal axis of the detent hook  132 , so that on the rear face of the end section  134  a holding surface  142  is formed perpendicular to the direction of displacement (arrow in FIG.  4 ). The edge  149  between the free end of the end section  134  and the contact side  146  is chamfered. The side of the recess  148  adjoining the shaft  138  is inclined in relation to the direction of displacement and represents a first contact surface  140 . The insulation  144  almost completely surrounds the contact body; only a region around the contact side  146  of the shaft  138  and in particular the first contact surface  140  are kept free. As locking element in turn a spring wire  153  is provided which, as already described, can be fastened to the hub  118 . At the edge of the opening  150  two tongues  154  are formed, which guide the spring wire  152  parallel to the plane of the hub  118 . The detent hook  132  engages into an opening  150  in the hub  118 . 
     On insertion of the detent hook  132 , the spring wire  152  is bent to one side by the chamfered edge  149  on the end section  134  of the detent hook, until the detent hook  132  is plunged so far into the opening  150  that the spring wire  152  can snap into the recess  148 . Thereby, the detent hook  132  is secured against being pulled out by the spring wire  152  resting against the holding surface  142 . As already described in the first embodiment, the holding surface  142  is held by compression springs between gas bag module and steering wheel skeleton in abutment against the spring wire  152 . 
     Through the extensive insulation of the detent hook  132 , an additional guidance of the detent hook in the opening  150  to avoid short-circuits between detent hook  132  and hub  118  is not necessary. 
     This embodiment also offers the possibility of various construction variants. Thus it would be conceivable to construct the detent hook with a contact body of metal, as illustrated in FIGS. 4 and 5, however without an insulating injection-molded casing, and instead to arrange alongside it and in parallel an insulating body of identical or similar design from an electrically insulating material, which is partially staggered in the displacement direction, so that with a displacement of the detent hook a contact of the spring wire with the first contact surface is permitted, however is prevented with the holding surface of the contact body. 
     Advantageously, as an alternative, instead of the detent hook  146 ′, the spring wire  152 ′ can be provided with an insulation  153 , which is recessed in the region of the contact surface  155 ′ which lies opposite the first contact surface  140 ′, as is illustrated in a variant in FIGS. 6 and 7. This embodiment offers advantages in terms of manufacturing technique, because the detent hook is generally connected electrically with the generator housing and therefore carries earth potential, whereas the spring wire in any case has to be insulated against earth. In addition, the insulation of the spring wire is easier to produce. The holding surface is designated by  142 ′, against which the insulation  154  lies in FIG.  6 . 
     A further variant consists in using a substantially solid wire for the locking element, instead of a spring wire, and instead in constructing the detent hook so elastically that it can be pushed aside on insertion into the opening by sliding along the chamfered edge of the end section on the locking element, until the recess snaps in behind the locking element. This can take place for instance in that the detent hook in itself is elastic perpendicular to the displacement direction. Another possibility would be to construct the detent hook so as to be pivoting perpendicular to the displacement direction and to act upon it elastically by means of a spring.