Patent Publication Number: US-6987231-B2

Title: Multifunctional pushbutton switch

Description:
FIELD OF THE INVENTION 
   The invention relates to a multifunctional pushbutton switch with several pushbutton switching units whose pushbutton surfaces are close to each other in a shared operating surface, especially for a vehicle steering wheel, with a shared switch housing in which the actuation tappets of the pushbutton switching units are configured so that they can move. 
   BACKGROUND OF THE INVENTION 
   With multifunctional pushbutton switches, especially in multifunction steering wheels for vehicles, the individual pushbutton switches are grouped next to each other and they project individually from openings of a cover. As a result, they can be felt and operated without visual contact. The assembly of such a multifunctional pushbutton switch, however, is highly complex. 
   BRIEF SUMMARY OF THE INVENTION 
   The invention provides a multifunctional pushbutton switch that can be visually and functionally well integrated into an existing environment, especially into the steering wheel of a vehicle. The multifunctional pushbutton switch according to the invention has a cap that is made by means of a two-component injection-molding technique and that is mounted onto the actuation tappets and onto the switch housing. The cap consists of a relatively rigid plastic frame with cutout windows whose shape and size each correspond to the circumference of one of the pushbutton surfaces and consists of a silicone membrane stretched over the windows. In this manner, the multifunctional pushbutton switch has a completely contiguous operating surface that is formed by the outer surface of the silicone membrane. The actuation tappets of the pushbutton switching units can be felt through the silicone membrane and can be actuated by pressure exerted on the outer surface of the silicone membrane. The silicone membrane preferably extends continuously over the entire outer surface of the cap, which is integrated into the surface of the steering wheel body. 
   In the case of multifunctional pushbutton switches whose individual pushbutton surfaces lie closely adjacent to each other, the possibility exists that several pushbuttons might be actuated at the same time. This can be prevented if, according to an embodiment of the invention, the individual pushbutton surfaces of the pushbutton switching units are delineated by a star-shaped or cross-shaped support structure that is formed in one piece with the plastic frame. The actuation tappets are preferably pressed resiliently against the inner surface of the silicone membrane, but are retained by stop members in their unactuated resting positions. These stop members are formed by lateral projections that are molded onto the actuation tappets and that interact with the surface of the support structure that faces away from the silicone membrane and that is covered with a layer of silicone material. The multifunctional pushbutton switch preferably has an altogether convex operating surface. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     Additional features and advantages of the invention ensue from the following description of a preferred embodiment and from the drawing to which reference is made. The drawing shows the following: 
       FIG. 1  a perspective view of a cap; 
       FIG. 2  a top view of the inside of a cap; 
       FIG. 3  a sectional view of a multifunctional pushbutton switch; 
       FIG. 3   a  a detailed view from  FIG. 3 ; and 
       FIG. 4  a sectional view of the cap of the multifunctional pushbutton switch. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The cap of a multifunctional pushbutton switch generally designated with the reference numeral  10  in  FIGS. 1 and 2  has a frame  12  made of relatively rigid plastic from which windows  14  are cut out, over which a silicone membrane  16  is stretched. The silicone membrane  16  forms a completely contiguous operating surface on the outer surface of the cap. The windows  14  are delineated from each other by a cross-shaped support structure  17  that is formed in one piece with the plastic frame  12 . Moreover, fastening domes  19  are shaped onto the plastic frame  12 . 
     FIG. 3  shows a switch housing  20  onto which the cap  10  has been placed. A baseplate  21  that has a switching mat  22  on a printed circuit board  23  is inserted into the switch housing  20 . The switching mat  22  has shaped-in domes with contact tabs as movable contacts  24 ,  26  that are each actuated by an actuation tappet  28  or  30 . Of the total of four actuation tappets of the multifunctional pushbutton switch, only the actuation tappets  28  and  30  can be seen in FIG.  2 . The actuation tappets  28 ,  30  are pressed from the inside against the silicone membrane  16 , giving it a convex curvature. On its actuation surface lying against the inner surface of the silicone membrane  16 , two of the total of four actuation tappets  28 ,  30  have a concave form that can be felt through the membrane. The other two actuation surfaces can be convex. 
   The actuation tappets  28 ,  30  are provided with lateral projections  32  that project underneath the support structure  17  and that come to rest against the underside of the support structure  17  that is covered with a layer of silicone material, as long as the appertaining actuation tappet is not actuated. The stop noise is muffled by the silicone material. 
   The cap  10  consisting of the frame  12  and of the silicone membrane  16  is configured as a two-component injection-molded part. The outer surface of the frame  12  is completely covered by a continuous layer of silicone material. Between the material of the frame  12  and the layer of silicone material, there is a bonded connection that can be mechanically stressed and that is splash-proof. Since the layer of silicone material surrounds the frame  12  on its outer circumference, there is also a positive connection that further increases the mechanical stressability. Moreover, this creates not only a completely contiguous operating surface over the actuation tappets, but also a visually attractive appearance. If the operating surface is to be labeled, for example, with symbols indicating the function of the individual pushbutton switches, then a high positional accuracy is ensured since the rigid frame  12  cannot shift with respect to the silicone layer that covers it. In this case, the operating surface is preferably provided in symbol color and then coated in a dark color; the symbols are cut out from the dark coating layer by means of a laser beam.