Joints and connections – Having a joining piece extending through aligned openings in...
Reexamination Certificate
2000-03-21
2001-11-20
Kim, Harry C. (Department: 3629)
Joints and connections
Having a joining piece extending through aligned openings in...
C403S011000, C403S209000, C411S903000
Reexamination Certificate
active
06318927
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to a fastening system for fastening a first structural component to a second structural component for use especially in the motor vehicle industry, and more particularly to a fastening system which has at least one fastening screw, a corresponding first preassembly thread on the first structural component, in which the fastening screw is fastened after the preassembly and a fastening thread on the first structural component or the said second structural component for fixing the first structural component to the second structural component by means of the fastening screw, whereby the said fastening screw, after fixing, is fastened in the associated fastening thread and has at least one front threaded area arranged on the free end of the screw shank and a second area adjacent to the screw head.
BACKGROUND OF THE INVENTION
A fixing device for a cap screw as a fastening screw has become known from DE-GM 18 20 586. A flange can be fastened to a structural component by means of this fastening screw. At least one hole with a preassembly thread is provided in the flange. The fastening screw has a shank area between the head and the threaded area, whereby the length of the threaded area for fastening the fastening screw is dimensioned such that this screw leaves the preassembly thread to be traversed within the framework of the preassembly before the screwing-in process in the fastening thread begins. In this case, the thread inner diameter of the fastening screw corresponds to the outer diameter of the shank area, as a result of which the loss protection of the fastening screw is realized. This means that the fastening screw is only held in the hole by the small threaded area in case of the solution according to DE-GM 18 20 586.
Also, a necked-down screw, which is used to seal a threaded hole, is disclosed in DE 15 30 27 417 A1. The shank area of this fastening screw is provided with a coating made of elastomer material, whose outer diameter corresponds to the outer diameter of the thread. An exclusively elastic, that is, reversible deformation of the elastomer material should take place during the screwing in.
The fastening systems of the type mentioned in the introduction are also used, for example, to fasten preassembled structural components, such as steering column modular units, or the like, to the body of a motor vehicle within the framework of the final assembly. In this case, in the preassembly of a steering column modular unit, one or more fastening screws are each screwed into a preassembly thread which is preferably fastened to the housing of the steering column modular unit. This has the advantage that, in the final assembly of the steering column modular unit to the body, no individual fastening structural elements have to be additionally provided. If the steering column modular unit is brought into its final position during the final assembly to the body, then the fastening screws are screwed into a second fastening thread. This fastening screw may be located both directly on the body structure of a motor vehicle and/or likewise as an extension of the preassembly thread on the steering column housing. In the latter case, the steering column modular unit is clamped by means of a bracket on the body side, which is arranged between the preassembly thread and the fastening thread. Both forms of fastening make it necessary that the fastening screw with its thread must have left either the preassembly thread before the screw enters the fastening thread with its first turns, or the preassembly thread is broken over, i.e., destroyed, during the entry of the fastening screw into the fastening thread.
Both assembly variants described have a serious drawback in terms of a possible disassembly of the steering column modular unit again.
The variant mentioned first, in which the fastening screw came completely out of the preassembly thread, results in the difficulty that a loosening of the fastening screw means inevitably a return of the screw into the first preassembly thread. In the usually only possible introduction of a pressing power in the longitudinal axis of the screw, this return is very difficult and is almost entirely ruled out under normal disassembly conditions. This means that the disassembly of the steering column is possible only with special difficulties.
In the second of the variants described above the preassembly thread is already often almost entirely destroyed after the initial assembly of the steering column. This means that, after a disassembly of the steering column, this thread must be rethreaded, since it is no longer usable, and as a result, the steering column is limited in its ability to be assembled.
SUMMARY AND OBJECTS OF THE INVENTION
Therefore, the object of the present invention is to eliminate the above-described drawbacks of the state of the art as well as to provide a fastening system that guarantees a problem-free assembly and disassembly of a component or a structural component to a second component and at the same time can be handled in a problem-free manner and can be produced at a favorable cost.
According to the invention, the fastening screw has at least one front threaded area arranged on the free end of the screw shank and a second area adjacent to the screw head, whereby this screw is provided with a plastic coating, into which a thread corresponding to the preassembly thread is incorporated only when screwing the fastening screw into the preassembly thread.
This special design causes, during the screwing and unscrewing process of the fastening screw, this fastening screw to be able to be screwed with its front threaded part in the corresponding fastening thread, in which case at the same time first the fastening screw is guided by the plastic-coated area during the screwing-in process and at the same time during the tightening process an overwinding of the thread impressed in this plastic-coated area is possible. This overwinding prevents a damage to the preassembly thread at the first structural component and makes possible a problem-free removal of the fastening screw from the fastening thread and preassembly thread. Moreover the adhesion between the plastic coating and the preassembly thread after completion of the process of tightening the fastening screw forms an additional prevention against unintentional loosening of the fastening screw. Another advantage of the fastening system according to the present invention lies in the fact that, after a disassembly cycle, only one new fastening screw must be used for a reassembly, which means a considerable cost savings compared with the state of the art.
It proved to be especially advantageous to make the plastic coating from a ductile, plastic material, and preferably polyethylene or polyurethane. These materials offer the guarantee that the so-called overwinding moment within the preassembly thread during the process of tightening the fastening screw lies within a range of 2 to 6 Nm and thus affects the actual tightening moment only extremely slightly. Moreover the special ductility of the materials offers the guarantee that the plastic material can yield during the overwinding of the fastening screws in the turns of the preassembly thread and thus only minimal material shearing occurs.
Furthermore, it proved to be advantageous that the length of the first threaded area of the fastening screw used for fastening is dimensioned such that this screw leaves the preassembly thread to be traversed within the framework of the preassembly before the screwing-in process in the fastening thread begins. This special design form facilitates the “threading” of the front threaded area into the fastening thread during the process of screwing in the fastening screw.
In addition, it is advantageous to arrange, in the area of the plastic coating, a circumferential screw knurl radially between the screw shank and plastic coating of the fastening screw. This screw knurl increases the adhesive force of the plastic coating at the shank area of the faste
Klumpe Stephan
Michalski Herniu
Rauterberg Thomas
Schafer Burkhard
Kim Harry C.
McGlew and Tutle, P.C.
Nacam Deutschland GmbH
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