Abstract:
A top element of a convertible roof which is formed from a plastic component  2  and a sheet metal part  3  as a composite part and in which major areas of the plastic component  2  and the sheet metal part  3  are spaced apart from one another and form a stiff cavity structure.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a top element for a convertible top and to a convertible top. 
     2. Description of Related Art 
     In current tops of convertibles, especially in folding tops, individual parts of the top linkage, such as the roof rod, control rod, cross bow, front bow, roof tip, main column, main rod or clamp clips are made of metal by punching, deep drawing, diecasting, stretching-bending or forging processes. However, these metal parts have high weight and can form a injury hazard due to splinters in case of a fracture of the part, splintering occurring especially in aluminum and magnesium diecast parts. The metal parts, furthermore, require corrosion protection and cannot be decorated so that separate optical covers are needed. This results in high production costs for a convertible top prepared using these components. In addition, top linkage parts formed especially as single-shell castings have only low bending and torsional stiffness. 
     SUMMARY OF THE INVENTION 
     An object of the invention is, therefore, to devise a top element for a convertible top which has high strength with low weight and can be produced at comparatively low cost. Another object of the invention is to devise a convertible top which has at least one such top element. 
     The initially mentioned object is achieved with a top element that is formed from a plastic component and from a sheet metal part as a composite component. One such composite structure enables combination of the advantages of sheet metal with those of plastic and leads to saving of weight with at least the same or even increased bending and torsional stiffness. Moreover, plastic offers the advantage that corrosion protection is not necessary and that the desired colors and surface structures can be considered directly in production. 
     Increased component strength of the top element is achieved especially in that major areas of the plastic component and the sheet metal part are spaced apart from one another and form a stiff cavity structure. The major areas are established depending on the shape of the component with consideration of the strength requirements and depending on the type of top element can be located at different points of the top element. Preferably, these major spaced areas form most of the plastic component or the entire top element. 
     When the plastic component and the sheet metal part form a thin-walled composite part with at least one large-volume cavity, an especially light composite part can be formed which still meets high strength requirements. Here, the size of the entire component and especially its extension on the greatest cross section of the cavity are limited solely by the available space for the closed and open convertible top. 
     Feasibly, the sheet metal part is joined to the plastic component by cementing, clinching or casting, and also any other joining techniques can be used. 
     The sheet metal part can have been put into the required form, for example, by deep drawing. The sheet metal can be especially thin and, thus, also light since it performs its support function only in an arrangement on the composite part. The plastic component can be produced as an injection molding, deep drawn part or laminated part, thus ensuring great freedom in shaping and also the bearing surfaces necessary for attaching the sheet metal can be optimally shaped. 
     For the structure of the composite part different arrangements of the sheet metal part and the plastic component can be chosen. Thus, the sheet metal part can form the bottom or inside and the plastic component can form the top or outside of the composite part of the convertible top in its arrangement with the convertible top closed. On the other hand, the plastic component can also form the bottom or inside and the sheet metal part can form the top or outside of the composite part. The arrangement is chosen essentially with consideration of the attachment of decoration and the fracture behavior of the materials being used at the time, such as especially plastic. A high-strength, but splintering plastic is placed on the outside of the top and is covered by sheet metal to the inside towards the passengers. 
     Preferably, the top element is the front bow of the convertible top, the plastic component being the bottom of the front bow and the sheet metal part being the top of the front bow. 
     To increase the strength it is feasible if the plastic component of the front bow has an essentially U-shaped cross channel. Additional components such as locks or drives can be accommodated and integrated into this cross channel. 
     Furthermore, it is feasible if the plastic component has reinforcements and especially stiffening ribs. When the stiffening ribs extend to the roof contour they can be used as bearing and support for the sheet metal part. 
     Other components can be integrated into the composite part, for example screens, pivots for rods, receivers for locks, catch hooks and the like. Receivers for rocker bearings of rods or guides can be made in the plastic component. 
     Furthermore, additional sheet metal parts, which can be joined directly to the sheet metal part, can be inserted or integrated in the plastic component. 
     For the plastic component different plastics such as polyamide (PA6.6) can be used, the plastic component being formed especially from a plastic with an essentially splinter-free fracture behavior if it is pointed towards the vehicle interior. 
     Feasibly, a top linkage part, such as especially a roof rod, a control rod, a main column, a cross bow, a front bow or a roof tip or a part combined from at least two of these linkage parts can be feasibly used as the top element, here the advantages of the composite construction with a plastic component having an especially positive benefit as a result of the freedom of configuration. 
     The second object is achieved in that the convertible top has at least one top element which is made as a composite part which is produced from a combination of a sheet metal part with a plastic component. Feasibly, the top element is made according to the aforementioned details and is especially a roof rod, a control rod, a main column, a cross bow, a front bow or a roof tip. 
     These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective top view of the right half of a front bow of a convertible cover with a bottom plastic component and a top sheet metal cover; 
     FIG. 2 is a lengthwise cross section view of the front bow; 
     FIG. 3 is a perspective of the right edge area of the front bow from below; 
     FIG. 4 is an exploded top perspective view of the main column of a convertible top; 
     FIG. 5 is an exploded perspective top view of a center bow with a side roof rod of the convertible top molded to it; 
     FIG. 6 is a cross sectional view of the main column of FIG. 4; and 
     FIG. 7 is a cross sectional view of the roof rod taken along line A—A of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The front bow  1  of a convertible top contains a plastic component  2  as the bottom and a shell-like sheet metal part  3  of steel or aluminum sheet attached thereto as the top (see FIGS.  1  and  2 ). The plastic component  2  has a front edge surface  4 , a side edge surface  5  and a rear edge surface  6  which establish the shape of the roof contour and on which the sheet metal part  3 , which is formed into an arched or crowned shape according to the roof contour rests, is attached, especially cemented. Thus, the front bow  1  is a composite part made of the plastic part  2  and the sheet metal part  3 . 
     The plastic component  2  contains a crossbeam section  7  which is recessed in a roughly U-shape in the lengthwise cross section and which extends essentially over the entire width of the front bow  1  and imparts high bending and torsional stiffness to the composite part as a result of the voluminous rectangular hollow section. Here, in the middle area of the front bow  1  the crossbeam section  7  can have a thicker depression in order to offer sufficient stiffness to this area of high stress. 
     The front section of the plastic component  2  is a flat recess  8  which is offset from the front edge surface  4  and which also contributes to the component strength as a result of its distance to the sheet metal part  3 . One or more lengthwise crosspieces  9  and  10  are made on the inside  11  of the plastic component  2  and extend from the front edge surface  4  to the rear edge surface  6 . They stiffen the plastic component  2  and, additionally, offer, in the front section  11  and  12 , a rest and support for the sheet metal part  3  which then either only rests on it or is also cemented. There can be additional stiffening ribs in the highly stressed component areas. 
     The coupling points  13  provided for moving the front bow  1  when the convertible top is opened and closed (see FIG. 3) or the rod bearings for the auxiliary rods on the two opposite sides of the front bow  1  are incorporated as metal or sheet metal parts in the production of the plastic components  2  and are integrated as inserts which are molded into the plastic component  2  or inserted subsequently into the corresponding recesses. 
     As another top element a main column  14  (see FIG. 4) of the convertible top is produced from a plastic part  15  and a machined sheet metal part  16  cemented to it, as a composite part. Bearing holes  17  and  18  in the machined sheet metal part  16  coincide with assigned openings  19  and  20  which are stiffened by moldings on the plastic part  15  and hold connecting hinges for side roof rods. The connection of the plastic part  15  to the machined sheet metal part  16  is done on the edge sections  21  and  22  of the plastic part  15  (see FIG.  6 ). High bending and torsional stiffness is also achieved by the voluminous cavity cross section of the main column  14  in this composite part. 
     Another example of a top element formed as a composite part is shown in FIG. 5 in a half view and shows a roof assembly  23  which contains a side roof rod  24  and a bow  25  which joins the roof rods  24 . For example, a middle or main bow of the convertible top which is a plastic part  26  formed in one piece with the side roof rods  24  and a sheet metal part  27  which is cemented from underneath to the plastic part  26 . The plastic part  26  is produced from high-strength plastic. In order to protect the passengers in case of a crash from sharp plastic fragments, in this composite part the sheet metal part  27  is attached to the bottom of the plastic part  15  facing the passenger compartment. In the roof rod  24  bearing receivers  28  for hinged connections to the rods  29  (see also FIG. 7) are made. The box-shaped profile of the roof rod  24  offers the necessary bending and torsional strength. 
     While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto, and is susceptible to numerous changes and modifications as known to those skilled in the art. Therefore, this invention is not limited to the details shown and described herein, and includes all such changes and modifications as are encompassed by the scope of the appended claims.