Abstract:
The invention relates to a method for inspecting the mechanical fastening of a component including an electrical conductor to a base body including an electric conductor. According to the method, the electric conductors for mechanically connecting the component to the base body such that an electric connection between the component and the base body is formed when a rigid mechanical connection is established, such that the resistance between the conductors is measured and a resistance value which lies below a predetermined value attests the existence of a rigid mechanical connection.

Description:
CLAIM FOR PRIORITY 
   This application claims priority to International Application No. PCT/DE00/02004 which was published in the German language on Dec. 20, 2001. 
   TECHNICAL FIELD OF THE INVENTION 
   The invention relates to a method and a device for checking the mechanical attachment of a component including an electrical conductor to a base body including an electrical conductor. 
   BACKGROUND OF THE INVENTION 
   In practice, the operational capability of devices is frequently conditional on their satisfactory attachment to a base body. For example, an airbag controller must be satisfactorily attached to the bodywork of a vehicle, or the vehicle body, if the airbag controller contains an acceleration sensor, where the sensor senses accelerations which act on the bodywork of a vehicle when a collision occurs. If the attachment is not satisfactory, an accident may not be satisfactorily detected so that the airbag is not properly triggered. There is also the risk of the airbag being inadvertently triggered if the controller is not carefully handled. 
   SUMMARY OF THE INVENTION 
   In one embodiment of the invention, an electrical connection is produced between the component to be attached and the base body when satisfactory attachment has occurred. It is easy to check for the existence of the electrical connection, and to detect the satisfactory attachment and to set specific functions in operation or activate warning indications as a function of the result of the check. 
   The invention can be used advantageously wherever the operational capability of a system is conditional on satisfactory attachment of a component associated with the system to a base body. This may apply to housings with electrical circuits which have an acceleration sensor for sensing accelerations of the base body, or devices which have a temperature sensor for sensing the temperature of the base body, or devices which must bear in a satisfactory fashion against a base body in order to cool components which are included in them, and so on. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained below with reference to drawings using an example in which the component to be attached is the housing of an airbag controller, and the base body is the sheet metal panel of the bodywork of a vehicle. 
     In the drawings: 
       FIG. 1  shows a controller attached to a sheet metal panel. 
       FIG. 2  is a plan view of an attachment eyelet. 
       FIG. 3  is a cross section through an attachment eyelet. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   According to  FIG. 1 , a housing  2  of an airbag controller is attached to a sheet metal panel  4  of the bodywork of a vehicle. The housing  2  includes a printed circuit board  6  which includes, in a manner known to the skilled artisan, an acceleration sensor (not illustrated) and an evaluation circuit. The printed circuit board  6  is connected via a line  8 , preferably a multi-conductor line, via which power is supplied and signals are evaluated, to a controller  10 , the controller  10  controlling, for example, the electronics of the bodywork of the vehicle and having a microprocessor with associated storage devices. The design and function of the vehicle-occupant protection systems which include an airbag and/or further safety devices such as seatbelt pretensioners etc. and their control, if appropriate via a bus system, are known to the skilled artisan and are therefore not explained. 
   The satisfactory function of the vehicle-occupant protection system and the satisfactory integration of the airbag are conditional on the housing  2  having a rigid mechanical connection to the sheet metal panel  4 . Otherwise, accelerations cannot be transmitted from the sheet metal panel  4  to the printed circuit board  6  which is fitted with one or more acceleration sensors. Furthermore, when the housing  2  is not satisfactorily attached to the sheet metal panel  4 , there is the possibility that, due to external manipulation, the housing  2  experiences vibrations which lead to the airbag being triggered. 
   The housing which is made of plastic or some other electrically non-conductive material has attachment eyelets  12  for its attachment.  FIG. 2  shows a plan view of such an attachment eyelet  12 , and  FIG. 3  shows the detail marked by broken lines in  FIG. 1 , on an enlarged scale. 
   As illustrated, a contact element  14  which is composed of metal is cast into the attachment eyelet  12  which is constructed in one piece with the housing  2  or a housing part, this contact element being surrounded, with the exception of the direction of the inside of the housing  2 , by the non-conductive housing material. Toward the inside, the contact element  14  ends in a contact lug  16  which, when the printed circuit board  6  is fastened to the housing  2 , comes into secure mechanical abutment against a conductor track  18  of the printed circuit board  6  so that electrical connection is made between the contact lug  16  and the conductor track  18 . The housing  2  may, for example, be constructed in two pieces, the printed circuit board  6  being clamped in between an upper part of the housing and a lower part and being firmly accommodated in the housing, and at the same time coming to bear against the contact lug  16 , when the upper part is connected to the lower part. The contact lug  16  can additionally be soldered to the conductor track  18 . 
   The contact element  16  is formed such that it surrounds a hole  20  of the attachment eyelet  12  and forms an annular disk  22  which is held in the attachment eyelet  12 . In each case between the upper side of the annular disk and the lower side of the annular disk there is still a predetermined material thickness of the material of the attachment eyelet  12  which is perfectly formed from plastic. 
   Contact-cutting parts  24  which protrude into the electrically non-conductive material of the attachment eyelet  12  are constructed on the upper side and the underside of the annular disk  22 . In order to attach the housing  2  to the sheet metal panel  4 , screws  26  which are made of metal are used, the screws  26  being screwed through the hole  20  into a threaded hole  28  in the sheet metal panel  4 . 
   The controller  10  is connected in an electrically conductive fashion to the sheet metal panel  4  via a line  30 , the line  30  being, for example, soldered to the sheet metal panel  4  at  32 . 
   The arrangement described operates as follows: 
   If the housing  2  is attached to the sheet metal panel  4  by screwing in the screws  26 , the contact-cutting parts  24  which are constructed in one part with the annular disk  22  of the contact element  14  pierce the electrically non-conductive material of the attachment eyelet  12  when the screws  26  are tightened, the contact-cutting parts  24  bearing in an electrically conductive fashion against the head of the screw  26  and the sheet metal panel  4 . In this way, a secure electrical connection is produced between the conductor track  18  and the sheet metal panel  4  when the screw or screws  26  is/are tightened. 
   The controller  10 , which is electrically conductively connected to the sheet metal panel  4  via the line  30 , includes a testing circuit (not illustrated) which can be used to detect whether there is an electrical connection whose electrical resistance is below a predetermined threshold value between the conductor  18  and the sheet metal panel  4 . This testing circuit takes the form, for example, of a predetermined electrical voltage being applied between the line  18  and the line  30 , and the resulting flow of current being measured. Of course, the sheet metal panel  4  can form the ground of the system. 
   The testing circuit is integrated into the composite circuit for controlling a vehicle-occupant protection system in such a way that when there is no mechanical attachment of the housing  2  to the sheet metal panel  4 , and thus no electrical connection between the conductor track  18  and the sheet metal panel  4  or the conductor  30 , a warning signal is generated which indicates the absence of an attachment and deactivates the vehicle-occupant protection system. The warning signal does not cease, and the operation of the vehicle-occupant protection system is not enabled, until the testing circuit indicates a satisfactory electrical connection. 
   Of course, the arrangement described can be modified in various ways. For example, the contact-cutting parts  24  can be provided merely on the underside of the head of the screw  26 . Furthermore, the screw  26  and the contact element  14  may be constructed such that when the screw screws through the contact element it comes into electrical contact with the contact element. To this end, the contact element  14  may, for example, be embodied as a thin piece of sheet metal in the region of the attachment eyelet  12 , and the screw may be provided with a self-tapping thread so that the screw screws into the sheet metal panel  4  through the attachment eyelet  12  and the contact element  14  provided in it, even when there is no hole  20 . The sheet metal panel  4  does not necessarily need to produce the connection between the contact element  14  and the line  30  of the controller  10 . Instead, a separate conductor may be provided which comes into contact with the contact element  14  at the location of the sheet metal panel  4  when the housing  2  is attached to the sheet metal panel  4 . This may be brought about, for example, by virtue of the fact that a contact lug which is electrically insulated with respect to the sheet metal panel  4  by the intermediate arrangement of an insulating element is positioned between the attachment eyelet  12  and the sheet metal panel  4 , the contact lug coming into electrical contact with the lower contact-cutting parts  24  ( FIG. 3 ) when the screw  26  is tightened, and said contact lug being directly connected to the controller  10  via a line. Similarly, the contact element does not necessarily need to be integrated into the attachment eyelet or into some other attachment region of the housing but rather can be led out of the housing separately and arranged, for example, between the insulating elements. The housing could then even be composed of electrically conductive material. Instead of an attachment screw, other attachment devices, for example, clamping elements etc., may be provided. The testing circuit included, for example, in the controller  10  for checking the electrical connection between the conductor  18  and the sheet metal panel  4  which directly forms a conductor, or a further conductor, may have very different designs, the resistance being measured directly or indirectly. The printed circuit board  2  can also be equipped with evaluation modules and/or control modules in very different ways.