Patent Document

RELATED APPLICATIONS 
     This application corresponds to PCT/DE2011/000147, filed Feb. 18, 2011, which claims the benefit of German Application No. 10 2010 008 535.9, filed Feb. 18, 2010, the subject matter, of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a steering wheel for accommodating an airbag module by means of a detachable snap-fit connection, wherein the steering wheel includes a steering wheel skeleton and a foamed steering wheel cover and wherein a detent pin is provided as part of the snap-fit connection. Furthermore, the invention relates to an airbag module provided for being accommodated in the steering wheel as well as an assembly of a steering wheel for an automotive vehicle, an airbag module and a detachable snap-fit connection for fastening the airbag module to the steering wheel. 
     Such arrangement is known, for instance, from the German Utility Model DE 201 17 140 U1. In the case of assemblies and steering wheel-airbag module arrangements of this type the steering wheel and the airbag module are two prefabricated and separate components connected to each other by a detachable snap-fit connection. High demands as regards tolerance and gap widths are made to the connection between the steering wheel and the airbag module, as they are provided in the driver&#39;s direct field of vision and grasp. Moreover, the connection between the airbag module and the steering wheel must ensure extreme holding forces upon release of the airbag module. At the same time, the connection between the airbag module and the steering wheel is to be detachable in a quick and simple manner for mounting the steering wheel in the vehicle and dismounting it during workshop operation. For this purpose, snap-fit connections between the airbag module and the steering wheel have established themselves in the meantime. 
     When, in addition, for actuating the horn the airbag module is to be movable also in axial direction toward the steering wheel, the constructional costs for the detachable connection between the steering wheel and the airbag module are considerably increased, as the visible gap widths between the module and the foamed steering wheel are to be kept as little as possible while the mobility of the module must be guaranteed. 
     Usually the module is engaged vis-à-vis the steering wheel skeleton in the form of a metal pressure die casting, mostly of magnesium, in order to ensure that the module is safely anchored at the steering wheel upon release of the airbag. However, it might happen that inaccuracies of tolerance which affect the gap between the module and the foamed steering wheel cover occur during foam-covering of the steering wheel skeleton. 
     SUMMARY OF THE INVENTION 
     Therefore the object underlying the invention is to provide a steering wheel that takes the high demands regarding positioning and guiding and the great holding forces required upon release of the airbag module into account. 
     For a steering wheel of the type mentioned in the beginning this object is achieved in accordance with the invention by the fact that the detent pin is positively embedded in the foamed steering wheel cover. 
     As the detent pin is positively embedded in the foamed steering wheel cover, upon engaging the module with the detent pin the module is primarily aligned vis-à-vis the foamed steering wheel cover, whereby possible inaccuracies between the foamed steering wheel cover and the steering wheel skeleton do not affect the gap between the module and the steering wheel cover visible on the driver&#39;s side. Also the required free space for the horn movement of the module is ensured. 
     Preferably two engaging concepts are combined, i.e. a first snap-fit connection having great holding forces and larger tolerances and a second snap-fit connection having lower holding forces and clearly reduced tolerances. The connection exhibiting great holding forces is usually formed between the airbag module and the steering wheel skeleton, the connection exhibiting a reduced tolerance and higher dimensional stability is formed, on the other hand, between the airbag module and the foamed steering wheel cover. In the latter connection detent hooks are provided at the airbag module for engaging in undercuts at the detent pin foamed in the steering wheel cover. 
     The invention further provides an assembly of a steering wheel, an airbag module and a detachable snap-fit connection in which a tolerance optimized manufacture is possible and in which the mounting forces are reduced. The positive embedding of the detent pin in the foamed steering wheel cover permits very accurate positioning of the detent pin during insertion in the foaming tool. Embedding the detent pin in the foamed steering wheel cover moreover has the advantage that, due to the properties of the foam, small tolerances can be compensated for and in total very small gap widths can be obtained during mounting the airbag module. 
     A very high strength of the snap-fit connection is obtained by forming an engaging contour at the detent pin to interact with a corresponding engaging contour at the steering wheel skeleton. 
     According to a further preferred embodiment, the detent pin can also have, instead of a snap-fit connection to the steering wheel skeleton, a different type of connection with undercut, e.g. a screw connection. In this case the detent pin is preferably screwed to the steering wheel skeleton by means of a central or eccentric bolt, wherein a head end of a stud bolt substantially T-shaped in cross-section fixes the detent pin toward the steering wheel skeleton or at least prevents a movement of the detent pin in the direction away from the steering wheel skeleton or restricts the same to a predetermined extent. 
     In accordance with a preferred embodiment, the detent pin can thus be fixed to be immobile at the steering wheel skeleton. 
     According to another embodiment, the detent pin can be arranged to be movable relative to the steering wheel skeleton. The mobility can be restricted to a radial direction, i.e. to a direction perpendicular to the support surface of the detent pin on the steering wheel skeleton (or perpendicular to the central axis of the detent pin or of the stud bolt holding the same). This permits an adjustability of the detent pin vis-à-vis the steering wheel skeleton during foam-covering. 
     This snap-fit or screwed connection acting in addition to the positive embedding is adapted to absorb by far greater forces that occur, for instance, upon release of the airbag module. When designing the snap-fit connection in an appropriate manner, thus additional catch or safety hooks or straps for holding or catching the module upon the pyrotechnical release thereof can be dispensed with. 
     Particularly good guiding during assembly is obtained when the detent pin has a substantially cylindrical shape and includes a guiding portion interacting with a guiding sleeve at the airbag module. 
     Especially when the airbag module is to be movably supported—e.g. as horn member—in the steering wheel, a guiding of a compression spring interacting with the airbag module is possible in a simple and advantageous manner by an axial recess in the detent pin. 
     Preferably the invention relates to a steering wheel in which at the detent pin a first engaging contour interacting with a corresponding second engaging contour at the airbag module is formed, wherein the first engaging contour is preferably formed as a substantially tangential recess in the detent pin and/or wherein the second engaging contour is preferably formed as a spring member, especially as a spring wire. 
     It is especially preferred that at the detent pin a third engaging contour is formed so as to interact with a corresponding fourth engaging contour at the steering wheel skeleton, the third engaging contour being preferably in the form of a substantially radial, especially T-shaped projection at a lower end of the detent pin and/or the fourth engaging contour being preferably formed as an especially hook-shaped step at the steering wheel skeleton. 
     It is further preferred that the detent pin is formed substantially cylindrically and/or at least in an upper area has a substantially cylindrical outer contour formed as a guide for a guiding sleeve provided at the airbag module and/or wherein the detent pin has a substantially H-shaped configuration in its cross-section. 
     Also it is preferred that the detent pin includes an axial guiding portion, especially a recess and/or an elevation for receiving and guiding a compression spring acting on the airbag module, the axial guiding portion preferably being formed as a separate insert accommodated in an especially cup-shaped receiving compartment of the detent pin. 
     In one embodiment the detent pin is additionally fixed at the steering wheel skeleton at least in axial direction, the fixing being preferably formed as engagement and/or as screw joint. 
     It is further preferred that the detent pin has at its upper end a first especially cup-shaped receiving compartment and/or that the detent pin has at its lower end a second, especially inversely cup-shaped receiving compartment in which a preferably trapezoidal, especially conical extension of the steering wheel skeleton is accommodated and/or that the detent pin has an axial through passage, the through passage especially connecting the first and second receiving compartments and/or a central axis of the axial through passage being parallel to but spaced apart from a central axis of the detent pin or an outer contour formed at the same. 
     Preferably the steering wheel is designed so that between the detent pin and the steering wheel skeleton and/or between a bolt, especially a bolt accommodated between an axial through passage and a first and/or second receiving compartment of the detent pin and tightly connected, especially screwed with the steering wheel skeleton, a distance or contact-free area is formed which is preferably at least partially filled with a foam material of the foamed steering wheel cover. 
     Preferably two or three or four detent pins are provided at the steering wheel. 
     Furthermore, the subject matter of the invention is an airbag module provided and formed for fastening to a steering wheel by means of a detachable snap-fit connection, wherein the steering wheel has at least one of the afore-mentioned features. The airbag module includes an airbag and an inflator as well as at least one guiding sleeve as part of the snap-fit connection. 
     Preferably two or three or four guiding sleeves are provided for receiving a respective detent pin. 
     Moreover, the subject matter of the invention is an assembly of a steering wheel for an automotive vehicle, an airbag module and a detachable snap-fit connection for fastening the airbag module to the steering wheel, the steering wheel, the airbag module and/or the detachable snap-fit connection including at least one of the afore-listed features. 
     Further features are the subject matter of the subclaims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Hereinafter the invention will be illustrated in detail by way of preferred embodiments including further features and advantages with reference to the enclosed drawing disclosing in 
         FIG. 1  a top view on a steering wheel according to the invention as part of the assembly according to the invention, 
         FIG. 2  a perspective, partially cut part view of the steering wheel and of the airbag module according to a first embodiment of the invention, 
         FIG. 3  a part sectional view according to a first embodiment of the invention, 
         FIG. 4  a perspective part view of the steering wheel skeleton before foam-covering including three detent pins screwed thereon according to a second or third embodiment of the invention, 
         FIG. 5  a part sectional view of the steering wheel skeleton before foam-covering including detent pins tightly screwed thereon according to a second embodiment of the invention, 
         FIG. 6  a perspective, partly cut part view of the steering wheel and of the airbag module prior to engagement according to a third embodiment of the invention in which the detent pin is also spaced apart from the head of the stud bolt and is positioned on the steering wheel skeleton through the foamed steering wheel cover, 
         FIG. 7  a perspective partly cut part view of the steering wheel and of the airbag module after engagement according to the third embodiment of the invention. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     In  FIG. 1  a steering wheel  10  is shown which includes a metallic steering wheel skeleton  12  having a support plate  14 , steering wheel spokes  16  and a steering wheel rim  18 . The steering wheel rim  18 , the steering wheel spokes  16  and parts of the support plate  14  are foam-covered with foam forming the steering wheel cover  20 . In the area of the support plate  14  four detent pins  22  are disposed at the steering wheel. These four detent pins serve for guiding and fastening an airbag module known per se of which only a part of the casing or of the inflator support  24  is shown in  FIG. 3 . 
     The detent pin  22  illustrated in more detail in the  FIGS. 2 and 3  includes a multiple-stepped cylindrical body  26  at which a peripheral collar  28  is formed. The detent pin is supported flush with said peripheral collar  28  on the part of the steering wheel cover  20  disposed in the area of the support plate  14 . Starting from said collar  28  the detent pin has a cylindrical anchoring portion  30  embedded in the foam of the steering wheel cover  20 . The front end of the anchoring portion is provided with a peripheral thickening  32  forming a respective peripheral edge  34  and  36  both outside and inside. The anchoring portion  30  further includes an indentation  38  starting from the open end face and extending to the area of the collar  28 . Said indentation is arranged so that it points toward the support plate  14 . On the side of the collar  28  opposite to the anchoring portion  30  the detent pin includes a guiding portion  40  having a spherical outer contour. Starting from the end face an axial recess  42  is formed in said guiding portion. At the side located radially outside in the mounting position of the detent pin the guiding portion  40  has an indentation  44  interacting with a detent spring  46  fixed at the airbag module or the inflator support  24  formed at the same or connected to the same. In this embodiment having a movable airbag module  24  the height of the indentation  44  is greater than the diameter of the detent spring  46  so that an axial mobility of the airbag module is possible for actuating the horn. 
     At the inflator support  24  four guiding sleeves  48  corresponding to the detent pins  22  are formed which enclose the spherical guiding portion of the detent pin. Radially outside each of said guiding sleeves has an indentation  50  through which the detent spring  46  can move in the direction of the detent pin. 
     In each of the recesses  42  of the guiding portions  40  a compression spring  52  contacting the bottom of the inflator support  24  and loading the same toward its home position is guided. 
     During manufacture of the steering wheel the steering wheel skeleton  12  and the detent pins are inserted in a foaming mold. When closing the mold the detent pins are positioned so that detent hooks  54  at the support plate  14  protrude into the indentations  38  of the anchoring portions  30  and engage behind the edges  36  pointing inwards. The closed foaming mold is then filled with steering wheel foams known per se so that the steering wheel cover is formed. By virtue of the open design of the anchoring portions and the indentations in the same, foam can flow into the interior of the anchoring portions during the foaming operation and can safely fix the detent pins in the foam and in the steering wheel cover. By interaction of the detent hooks  54  at the support plate  14  and the inner edge  36  of the anchoring portions acting as engaging contour an additional fixing of the detent pins to the support plate and the steering wheel skeleton is obtained. This connection is adapted to withstand even the forces occurring upon release of the airbag module and to safely fix the module. 
     The detent pins can also be secured to the steering wheel skeleton, according to a further preferred embodiment as described hereinafter by way of the  FIGS. 4 to 7 , by a connecting bolt, especially by a stud bolt  154 . This can be effectuated both from the open end face of the anchoring portion and from the open end face of the guiding portion. In contrast to the narrowly tolerated positioning from the steering wheel cover, this connection can be made with larger tolerances especially in the radial direction. 
       FIG. 4  shows a perspective partial view of a steering wheel skeleton  112  before foam-covering including three detent pins  122  screwed thereon by respective stud bolts  154  in accordance with a second and a third embodiment of the invention. 
       FIG. 5  illustrates one of the screwed detent pins of the steering wheel skeleton  112  according to  FIG. 4  before foam-covering in accordance with a second embodiment of the invention in which a support area  157  of the stud bolt  154  presses onto a pressing area  123  of the detent pin  122 , thereby the detent pin  122  being fixed or adapted to be fixed onto the steering wheel skeleton. The pressing area  123  of the detent pin  122  is formed in parallel to a support area  113  of the steering wheel skeleton on which the detent pin is movable to a predetermined extent so as to compensate for inaccuracies of tolerance when inserting in the foaming mold. The detent pin is finally fixed or screwed on the steering wheel skeleton preferably after foam-covering. 
     In order to allow for the optimum positioning of the detent pin on the steering wheel skeleton, the detent pin  122  has at its upper end a first especially cup-shaped receiving compartment  143  for the screw head  156 . Furthermore, the detent pin  122  has at its lower end a second inversely cup-shaped receiving compartment  160  in which a preferably trapezoidal, especially conical, extension  162  of the steering wheel skeleton  112  is received. However, also a configuration without such second receiving compartment and/or without such extension  162  of the steering wheel skeleton is possible. 
     Preferably the detent pin  22 ,  122  includes, as illustrated in  FIGS. 6 and 7 , an axial guiding portion, especially a recess  42  ( FIG. 2 ) and/or an elevation  142  for receiving and guiding a compression spring  52  acting on the airbag module. The axial guiding portion is preferably in the form of a separate insert  144  received in an especially cup-shaped receiving compartment  143  of the detent pin  122 . 
     The detent pin  122  shown in  FIGS. 4 to 7  further includes an axial through passage  163  connecting the first and second receiving compartments  143 ,  160  or the first receiving compartment  143  to a lower outer contour of the detent pin  122 . In this case, a central axis K of the axial through passage  163  is arranged in the detent pin such that it is parallel to but spaced from a central axis Z of the detent pin  122  or an outer contour  40  formed at the latter. Thus one side of the detent pin at which a detent hook  29  or undercut  129  is formed for engaging with a spring element  46  of the airbag module  24  can be formed to have a larger wall thickness than in the case of a concentric design of the outer contour and the through passage, just as in the first afore-described embodiment. 
     Depending on the positioning of the detent pin on the steering wheel skeleton, after screwing in the stud bolt  154  a central axis B of the stud bolt  154  received in the through passage  163  is identical with or parallel to but spaced apart from the central axis Z of the detent pin  122  and/or identical with or parallel to but spaced apart from the central axis B of the through passage  163 . 
     In the second embodiment of the steering wheel according to the invention described here a contact-free area  170  is formed between the detent pin  122  and the stud  154 , especially between the stud  154  received in the axial through passage  163  and the first and/or second receiving compartment  143 ,  160  of the detent pin  122  and tightly screwed with the steering wheel skeleton  112 . 
     Said area can be filled at least partially with a foam material of the foamed steering wheel cover  20 , but it can also be empty (filled with air). 
     The contact-free area  170  extends along a peripheral area  171  of a shaft  155  and of a head  156  of the stud  154  so as to permit free positioning (in the predetermined range, preferably within the range of up to 2 mm) of the detent pin vis-à-vis the steering wheel skeleton. 
     According to the third embodiment shown in  FIGS. 6 and 7 , the contact-free area  170  in addition extends at least partially to a support area  157  of the head  156  located between the peripheral area  171  of the shaft  155  and the head  156  of the stud  154 . Hereby a slight adaptation in height is additionally possible. 
     In particular, the detent pin  122  is fixed and positioned to the steering wheel skeleton  112  exclusively by the foamed steering wheel cover  20 . 
     This is shown in  FIGS. 6 and 7  which illustrate a perspective partly cut part view of the steering wheel and the airbag module before and after engagement according to the third embodiment of the invention. The detent pin is also spaced apart from the head of the stud bolt and is positioned and held on its support  113  on the steering wheel skeleton exclusively by the foamed steering wheel cover. 
     The detent pin is additionally held at the steering wheel skeleton by the head  156  of the stud bolt  154  merely in the case of release of the airbag. 
     In all embodiments of the invention the foamed steering wheel cover  20  encloses at least partially the detent pin or pins  22 ,  122  and the steering wheel skeleton. 
     The detent pin of all embodiments can have, as shown merely in the  FIGS. 4 to 7 , one (or two or more) projection(s)  139  for a horn contact  149  which upon interaction with the airbag module  24  closes or opens the horn contact upon pressing down the airbag module. Furthermore a second projection or second projections can be provided at the detent pin and/or at the airbag module for restricting the distance of pressing down to an admissible extent. Those projections are preferably integrally formed with the detent pin. Those projections and the detent pin preferably extend from a joint base plate which is supported on a support surface  113  on the steering wheel skeleton. Especially the detent pin (preferably with base plate and/or projections) is in the form of an injection-molded part made of plastic material.

Technology Category: b