The present invention relates to an affixation device affixing a motor-vehicle sheetmetal or plate. Such fastening devices are used to affix heat-shielding sheetmetal to motor vehicles, illustratively being exhaust-system heat shields configured at the lower side of the vehicle body. Several threaded bolts are mounted for that purpose on the body and constitute sheetmetal affixation sites. The sheetmetal is fitted with apertures corresponding to the bolts. It is known to affix the sheetmetal using three elements for each aperture. In this procedure a plastic spacer fitted with radially resilient detent tangs is forced from one side into the sheetmetal aperture and thereby is locked into said sheetmetal. Next a plastic retention disk is fastened from the opposite sheetmetal side to the aperture. Then a metallic, resilient disk is inserted into said retention disk, also called "cage". After each sheetmetal aperture has been fitted with these three elements, the sheetmetal can be deposited in such a way on the bolts that latter can be forced from the spacer side through said aperture and said resilient disk. The resilient disk is centrally fitted with a star-shaped passage allowing the individual star elements to lock into the bolt threads when the bolts are being pushed through. As a result the bolts keep the sheetmetal on the vehicle body.

Because of the many parts required for each aperture, also their manufacture and assembly, the above procedure is costly.

Based on the cited state of the art, the objective of the present invention therefore is to create an affixation device of the initially cited kind allowing simplifying manufacture and assembly. The present invention solves this problem by the object of claim 1. Advantageous embodiment modes are defined in the dependent claims, the specification and the Figures.

Said problem is solved by the present invention by means of a device designed to affix a sheetmetal to a motor vehicle and comprising a nut fitted at its underside with a flange. The nut is fitted with several locking elements that, when loaded, are preferably radially resilient, said locking elements each forming a segment of an external face conically tapering from the flange in the nut's axial direction. The locking element undersides each are spaced from the mutually opposite flange surface in a manner to form an undercut receiving the sheetmetal.

Accordingly the nut of the affixation device of the present invention is fitted with resilient locking elements. The locking elements and the nut and the entire device as well therefore can be manufactured integrally in especially simple manner. The affixation device of the present invention in particular may be a grommets or the like.

The sheetmetal to be affixed may be a heat shield fastened to the motor vehicle's underside for instance to screen its exhaust system. The sheetmetal comprises several circular apertures by means of which it shall be affixed to matching bolts mounted on the vehicle body. In the present invention, the locking elements by means of their outer faces form surface elements of a (conceptual) circular cone respectively circular conical frustrum. The maximum conical frustrum diameter is formed by the lower edges of said locking elements' outer faces and is larger than the aperture diameter in the sheetmetal. The smallest conical frustrum diameter formed by the upper edges of the locking elements outer faces on the other hand is smaller than said aperture diameter. To affix the sheetmetal, first an affixation device of the present invention inclusive its nut shall be forced into each sheetmetal aperture, the aforementioned conical outer surface acting as a centering means. In this process, the locking elements are compressed preferably radially inward, in this manner reducing said aperture's effective diameter, and allowing the sheetmetal to be moved over the locking elements. An undercut free space is formed between the locking elements' undersides and the opposite flange surfaces. The sheetmetal shall be received in said free space after the nut has been forced through. In that configuration, the sheetmetal is secured against detachment on account of the locking elements preferably returning to their outward position. To further secure the sheetmetal when in its affixed condition, its apertures may be flanged.

Once an affixation device has been affixed in each of the sheetmetal's apertures, the vehicle body's threaded bolts matching these apertures each may be forced into an optional inside thread turn of the nuts. This is how the sheetmetal is affixed by means of the affixation devices onto the vehicle body. Accordingly the present invention also applies to such a sheetmetal fitted with only one aperture and with at least one affixation device of the present invention forced through said aperture, in particular also when affixed to a vehicle.

Therefore, in the present invention, only one part instead of three is required for affixation at each sheetmetal aperture. Both the manufacture and the assembly are simplified relative to the state of the art. Being flanged, the affixation devices furthermore assure spacing the vehicle body from the thermally shielding sheetmetal. Accordingly, said devices of the present invention, besides their affixation function, also serve as spacers. The affixation devices even when in their insertion state through the sheetmetal remain rotatable; the fastening of the sheetmetal to the body may be dissolved by unscrewing the affixation devices from said bolts, for instance for purposes of repairs. The externally accessible nut illustratively may be hexagonal.

In an especially pertinent design, the locking elements each may be joined in the circumferential direction of the nut by their one end to said nut's external surface, the other locking element ends each being free, and said free locking element ends being resilient when being loaded radially. Accordingly, in this design, the nut is fitted with hook-shaped locking elements having resilient tangs. The locking elements run in both the peripheral and in the axial directions of said nut. In particular both the junction of the locking elements to the nut and the free locking element ends run over a given segment of the periphery. However the free ends run peripherally over a substantially larger zone than do the locking element portions joined to the nut. Moreover the free ends and/or the junction zones may also run over the full height of the locking elements. In that design, when the device of the present invention inserted through a sheetmetal aperture, the free ends are pressed radially inward, thereby reducing the effective diameter, as a result of which the sheetmetal may be displaced through said zones. On the other hand the portions joined to the nut are substantially non-compliant in the radial direction. Because, following insertion through the aperture, the free locking element ends move radially back in the externally radial direction, they then secure jointly with the firmly joined portions the sheetmetal over a large peripheral zone against slipping from the device of the invention. Illustratively the hook-shaped locking elements may be open in the clockwise direction, as a result of which their free ends run counter- clockwise when the affixation devices are screwed off. This feature facilitates unscrewing.

Starting from its end joined to the nut, the locking element thickness may taper toward its free end. This feature improves the radial resiliency of the free ends and simplifies forcing the affixation device into the sheetmetal.

In one embodiment mode of the present invention, the undersides of the locking elements may form an angle with the opposite flange surface at least in their zone joined to the nut, in a manner that the spacing between the said locking elements and the opposite flange surface tapers from the outside toward the inside. This design further simplifies forcing the affixation device into the sheetmetal, said device, after having passed through the largest diameter, being guided by the oblique locking element faces into the undercut. Also, in the zone of their free ends, the locking elements each may be spaced more from the opposite flange surface than in their zone joined to the nut. This feature allows said free ends to return unhampered, i.e. without danger of jamming, into their unloaded positions after said device was inserted to the sheetmetal. Nevertheless the full peripheral sheetmetal zone of the free ends shall be secured against loosening.

In a further embodiment, the spacing between (i) the outer edge bounding the locking elements at their end joined to the nut on one hand, and on the other hand (ii) a conceptual/imaginary line between the lower end of said edge and the tip of the cone formed at least partly by the locking elements (cone generatrix), may increase in the upward direction. This feature implements device guidance in a manner that, when this device is forced into the sheetmetal, it shall be slightly rotated in the process. Said feature facilitates device insertion into the sheetmetal hole(s). In a further embodiment also facilitating device insertion into the sheetmetal hole(s), the spacing between the outer edge bounding the locking elements at their ends joined to the nut on one hand and on the other hand to the outer edge bounding the locking elements at their free edges may decrease in the upward direction. Said two edges laterally bound outer locking element faces partly forming the said cone.

At its inner periphery, the nut may comprise at least three detent tangs which are resilient in the nut's axial direction and which, when a threaded bolt is inserted into the nut, interlock with the outer thread of said bolt. Such detent tangs are known per se and may be configured for instance equidistantly from each other by 120°. They are designed in a way allowing a threaded bolt for instance affixed to a vehicle underbody to be forced into the nut, the detent tangs yielding in the axial direction and each engaging the bolt's thread. The detent tangs secure the bolt against being pulled out of the nut. Nevertheless the nut may be screwed off the bolt, for instance for repairs.

Contrary to the case of the state of art within which a metal leaf spring is required for adequate affixation, the affixation device may be made entirely of plastic. Plastic is economical and lighter than metal. Furthermore, using plastic to manufacture an integral affixation device, even of complex geometry, for instance by injection molding or similar methods known per se, is especially simple.

An illustrative embodiment of the present invention is elucidated below in relation to the appended schematic Figures.

Fig. 1 is a topview of an affixation device of the invention,

Fig. 2 is a perspective from above of the affixation device of Fig. 1 , Fig. 3 is a sideview of the affixation device of Fig. 1 ,

Fig. 4 is a view from below of the affixation device of Fig. 1 ,

Fig. 5 is a perspective view from below of the affixation device of Fig. 1 , Fig. 6 is a cutaway sideview of the affixation device of Fig. 1 in its operating state, and

Fig. 7 is a perspective view from above of the affixation device of Fig. 1 in its operating state.

Unless stated otherwise, the same references shown in the Figures denote the same objects. The affixation device 10 shown in the Figures comprises a nut 12, in the present case a hexagonal nut. The nut 12 is fitted at its underside with a flange 14 of thickness d. Several locking elements 16, six in the present instance, are peripherally configured at the nut 12. In particular, one locking element 16 is configured at each of the segments formed by the nut's hexagon. Seen in the peripheral direction around the nut 12, the locking elements 16 each are joined to the outer surface of the nut 12. At their peripheral end 20, the locking elements 16 are not joined to the nut 12. Accordingly this end 20 is free and when loaded it shall be radially resilient. The said locking elements are hook- shaped, their free ends 20 constituting elastic tangs. In the shown embodiment mode, the locking elements 16 are open in the clockwise direction.

As indicated in Figs. 1 and 2, the locking elements 16 each constitute one segment of a conceptual circular conic frustrum tapering from the flange 14 axially toward the nut 12. As shown in sideview in Fig.

3, the undersides of the locking elements 16 are spaced in such a way from the opposite flange upper side 22 that an undercut 24 that shall receive a sheetmetal to be affixed is formed between the locking elements 16 and the flange top side 22. Fig. 3 also shows that the spacing between the undersides of the locking elements 16 and the opposite flange surface 22 constricts from the outside to the inside in the zone 18 joined to the nut 12. For that purpose the undersides 26 of the locking elements 16 form in their zone 18 joining the nut 12 an angle α with the opposite flange surface 22. The spacing between the locking elements' free ends 20 and their opposite flange surface 22 is larger in the zone of said free ends 20 than in their junction zone to the nut. The thickness of the locking elements 16 decreases from their ends 18 joined to the nut 12 toward their free ends 20. Radial resiliency is improved by this feature.

The outer face of the locking elements 16 is bounded by an outer edge 28 at its end 18 joined to the nut 12. When looking at a conceptual circular cone formed segment-wise by the outer faces of the locking elements 16, it is possible to conceive of a generatrix of said circular cone running from the lower end of the edge 26 and through the tip of said cone. The spacing between the edge 28 and said generatrix increases in the upward direction. This feature simplifies inserting the device 10 through a sheetmetal aperture. On the other hand the spacing between the edge 28 of the locking elements 16 and the outer edge 30 bounding the locking elements 16 at their free ends 20 decreases downward.

As shown in Figs. 4 and 5, the flange 14 is fitted at its underside with several recesses 32 in the region of which the thickness d of the flange 14 is reduced to save weight. In this embodiment mode the nut 12 is fitted at its inside surface with three axially resilient detent tangs 34. They are configured equidistantly from each other at an angle of 120°. The nut 12 moreover comprises at its inside surface three guides elements 36 also configured at 120° from each other and offset from the detent tangs 34.

The affixation device 10 of the shown embodiment is integral and made of plastic. Illustratively it shall be manufactured by injection molding.

To affix a heat-shielding sheetmetal 38 shown illustratively in Fig. 6 and serving to thermally screen a motor vehicle's exhaust system, said sheetmetal 38 comprises several omitted circular apertures. The aperture diameter is less than that of the circle formed segment-wise by the lower edges of the particular outer faces of the locking elements 16 (Fig. 1). On the other hand the diameter of the circle formed segment-wise by the upper edges of the outer faces of the locking elements 16 is smaller than the aperture diameter. To carry out the assembly, first and while still separate from the motor vehicle, an affixation device 10 of the present invention together with its nut 12 is forced through each aperture in the sheetmetal 38. Centering is implemented by the cone formed by the outer faces of the locking elements 16. In the process the free ends 20 of the locking elements are forced radially inward. Consequently the diameter of the cone formed at least segment-wise by the locking elements 16 is reduced, allowing forcing the sheetmetal over the nut's locking elements. As soon as the sheetmetal 38 has moved past the lower end of the outer edge 28, it shall be guided by the oblique facet 26 into the undercut between the locking elements 16 and the flange surface 22. Thereupon the free ends 20 of the locking elements 16 move radially outward again into their unstressed position. Once this state has been attained, the sheetmetal 38 is secured against upward detachment by the locking elements 16 over most of the periphery of the nut 12. It is secured against downward displacement by the flange 14,

As shown in Fig. 6 in a cutaway view of an affixation site, threaded bolts 42 are fitted onto the motor vehicle body underside 40. The sheetmetal 38 can be fitted with one or more bolts 42 matching the apertures onto said underbody to allow affixation. For this affixation, the sheetmetal 38 fitted with the affixation devices 10 is applied in such manner against the body underside 40 that the bolts are forcibly moved upwards through the nuts 12 of these affixation devices 10. In the process, the detent tangs 34 shall yield in the axial direction of the nut 12 and then lock into the individual thread turns of the bolt 42. This process is shown schematically in Fig. 7 from which both the sheetmetal 38 and the flange 14 have been omitted. The reference 44 schematically indicates the edge of the circular aperture in said sheetmetal. Fig. 6 illustrates the final assembled state for one affixation site. The detent tangs 34 reliably preclude pulling the nut 12 and hence the sheetmetal 38 off the bolt 42. At the same time, however, the affixation devices 10, and therefore jointly with them the sheetmetal, may still be disassembled from the bolts 42 by screwing the hexagonal nuts 12 off said bolts, for instance for purposes of repairs. In addition, due to the thickness d of the flange 14, the affixation devices 10 of the invention act as spacers between the sheetmetal 38 and the body underside 40.

The affixation device 10 of the present invention can be manufactured in simple manner and allows rapid assembly/disassembly while reliably securing the heat-shielding sheetmetals 38 of a motor vehicle.