Abstract:
An airbag control device comprises a housing with a cover that enclose a printed circuit board with an acceleration sensor and electronic components. The housing and the cover have a substantially central passage, from which the housing interior is closed off. The substantially central passage has, at least in one region thereof, an asymmetrical shape that enables the control device to be installed with a single bolt having a shape complementary to that of the substantially central passage.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation of copending International Application PCT/DE97/01561, filed Jul. 23, 1997, which designated the United States. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an airbag control device, and specifically to an airbag control device having a housing and a printed circuit board with electronic components disposed within an interior of the housing. 
     Electronic control devices providing personal protection in motor vehicles, such as airbags, seat-belt pre-tensioning systems etc., include a printed circuit board with various electronic components. The printed circuit board is enclosed by a housing provided with a cover, such as is described, for example, in German Patent DE 44 06 499 C2. For fastening the housing on the motor vehicle, the cover of the housing has fastening lugs or flanges which also fixes the orientation of the control device with respect to the motor vehicle. This fixed orientation of the control device is compulsory, since the acceleration sensor usually used has a predetermined direction of sensitivity. The printed circuit board is fastened to the housing by screws. To reduce radiation caused by long line routes, a screw is usually provided centrally on the housing as a discharging element. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide an airbag control device that allows simple, low-cost installation of the airbag control device in a motor vehicle, while minimizing vibration problems occurring in the region of the printed circuit board. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, an airbag control device, comprising: 
     a housing having a cover and an interior formed therein; 
     a printed circuit board including electronic components, the printed circuit board disposed in the interior of the housing; and 
     a substantially central passage for fastening the airbag control device to a motor vehicle and being closed off from the interior of the housing, the substantially central passage extending through the housing, the cover, and the printed circuit board. 
     In accordance with an added feature of the invention, a fastening part is provided; the substantially central passage is formed with an asymmetrical shape in at least one region thereof; and the fastening part has a region with a shape complementary to the asymmetrical shape of the substantially central passage for fixing a position of the airbag control device with respect to a position of the fastening part. 
     In accordance with an additional feature of the invention, a location adjacent the substantially central passage fastening the printed circuit board to the housing is provided. 
     In accordance with another feature of the invention, at least one further location fastening the printed circuit board to the housing is provided. 
     In accordance with a further feature of the invention, a screw fastening the printed circuit board to the housing and the cover at a further location is provided. 
     In accordance with again an added feature of the invention, the printed circuit board includes an acceleration sensor disposed between the substantially central passage and the further location. 
     In accordance with again an additional feature of the invention, the housing includes a support adjacent the central passage for restraining the printed circuit board. 
     In accordance with again another feature of the invention, the housing includes a support adjacent the substantially central passage for restraining the printed circuit board; and the cover has a shape that presses the printed circuit board against the support of the housing. 
     In accordance with again a further feature of the invention, the cover includes an outer supporting boarder; and an inner supporting boarder adjacent the substantially central passage that is lower than the outer supporting boarder. 
     In accordance with a further added feature of the invention, a mass bond attaches the cover, the housing, and the printed circuit board at the support of the housing. 
     In accordance with a further additional feature of the invention, the printed circuit board includes an acceleration sensor. 
     In accordance with yet another feature of the invention, a location adjacent the substantially central passage fastening the printed circuit board to the cover is provided. 
     In accordance with a concomitant feature of the invention, at least one further location fastening the printed circuit board to the cover is provided. 
     Using parts that can be produced at a low cost, for instance a diecast housing and a stamped sheet metal cover, the airbag control device according to the invention can be fastened on a vehicle body quickly with few fastening parts. Installation costs are also minimized. This is made possible, according to the invention, by providing only one central fastening location for the complete airbag control device, consequently only one fastening operation is required to attach the airbag control device to a motor vehicle. Prior art airbag control devices required, for example, four screws to attach the airbag control device to a motor vehicle. The invention saves at least two bolts and nuts, and consequently not only material, but also installation time. 
     By dispensing with previously customary fastening lugs, there is more space available for the control device itself, and the interior volume of the control device can be enlarged. The surface area of the printed circuit board can therefore be enlarged, so that a two-sided board population or a multilayer configuration is not necessary. 
     In addition, the central fastening location provides a central restraint for the printed circuit board. As a result, vibrations of the printed circuit board, which have disadvantageous effects on the vibration-sensitive electronic acceleration sensor, can be significantly reduced or even avoided. If appropriate, it is possible to dispense with encapsulation of the acceleration sensor, as is described in the above-mentioned German Patent DE 44 06 499 C2. 
     If a positive connection of the control device and the relevant fastening part with an asymmetrical form is provided, a torsionally secure and positionally exact installation of the control device in the motor vehicle is automatically obtained. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in an airbag control device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective plan view of a base of a housing of an airbag control device; 
     FIG. 2 is a perspective view of the housing showing a cover attached to the housing; 
     FIG. 3 is a sectional view taken along the line III—III shown in FIG. 1; 
     FIG. 4 is a sectional view taken along the line IV—IV shown in FIG. 1; and 
     FIG. 5 is a perspective view of a threaded welding stud used for installation of the housing. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1-5, in general, the invention is seen to be an airbag control device  10  which comprises a housing  20 , for example, an aluminum diecast housing having a base  22  and side walls  24 . A cover  26  (shown in FIGS.  2  and  3 ), for example, can be obtained from stamped sheet metal. Within the housing  20  is a printed circuit board  40  having an evaluation circuit with various components  42  and an acceleration sensor  44  connected to the evaluation circuit. 
     A plug-in connector  46  serves as the interface and connection with respect to the airbag and other control devices in the motor vehicle. The housing  20  has a central passage  30 , with the base  22  of the housing  20  being drawn inward into the housing  20  and extending with formed-on parts through the housing  20  to the other outer side. 
     The base  22  of the housing  20  is bent inward in the center of the housing  20 , so that it forms a blind hole having a blind-hole base  32  with a central opening  34 . The blind-hole base  32  is approximately at the height of the printed circuit board  40  and has, on the inner side of the housing  20 , a stepped portion extending to the end of the base  22  of the housing  20 . The stepped portion forms a supporting shoulder  70  (shown in FIG.  3 ), the function of which will be explained later. The blind-hole base  32  is drawn up on the cover  26  to form a cylindrical ring  36 , which protrudes beyond the cover  26  and the height of the side wall  24 , as can be seen in FIG.  3 . The cylindrical ring  36  is designed with an asymmetrical interior space, with the effect of forming a solid segment portion  38 , which will likewise be explained later (See FIG.  2 ). The outside diameter of the cylindrical ring  36  is less than the diameter of the outer circumference of the blind-hole wall forming the passage  30 . As the above description shows, the central passage  30  of the housing  20  is hermetically shielded from the housing interior. 
     The cover  26  has a central opening  261  and is drawn downward, i.e. toward the housing interior, in the region of the opening  261  and part of the outer edges, with the effect of forming supporting borders  262 ,  263 . In the region of the corners, the supporting borders are widened to form fastening lugs  264  as shown in FIG.  2 . The cover  26  is shaped in such a way that the inner supporting border  263  is lower than the outer supporting border  262  and the fastening lugs  264 . 
     The side wall  24  of the housing  20  is drawn inward in the corner regions, at the height of the printed circuit board  40 , with the effect of forming supporting shoulders  72 , which are represented in FIG.  4 . The cover  26  comes to lie on these supporting shoulders  72  in the region of the fastening lugs  264 , as shown in FIG.  2 . 
     The perspective view of FIG. 2 illustrates the assembly of the cover  26 , printed circuit board  40  and housing  20  which are attached by four screws  80 ,  82 ,  84 ,  86 . Alternatively, only three screws may be used, in which case, screws  80  and  86 , are replaced with screw  88 , which is additionally illustrated. The printed circuit board  40  is restrained in the center by the form of the cover  26  described and the centrally provided supporting shoulder  70 . This dispenses with screws or other fastening means in the center for the printed circuit board  40  and prevents vibrations of the printed circuit board  40 . By installing the acceleration sensor  44  closer to a restraining location of the printed circuit board  40 , thus in the vicinity of the border, additional vibration protection of the acceleration sensor can be provided. The fastening and/or restraining of the printed circuit board  40  to the housing  20  or to the cover  26  in the region of the central passage  30  creates an additional supporting point at the center of the printed circuit board  40 . Previously, this support at the center of the printed circuit board  40  necessitated providing an additional screw or a similar device. The central restraining location fixes the printed circuit board  40  in a central region, which would otherwise show a strong tendency to vibrate. The distances between fastening points allowing for oscillation are kept small on all sides by the central restraining location. The central restraining location also permits a mass bonding of the printed circuit board to the housing  20  and to the cover  26 . 
     FIG. 5 illustrates a threaded welding stud  90 , which is welded to the schematically indicated body panel  100  and has an asymmetrical head  92  with a segment relief  94  and a shank  96 . 
     In the installation of the control device  10 , i.e. the housing  20  with the attached cover  26 , on the vehicle body, the cover  26  of the housing  20  is placed onto the shank  96  of the welding stud  90 . Because of the positive engagement between the head  92  and the cylindrical ring  36 , correct orientation of the control device  10  is guaranteed. On the opposite side, i.e. in the blind hole of the passage  30 , it is then merely necessary to tighten a fastening nut onto the shank  96 . The welding stud  90  provides fastening of the control device  10  onto the motor vehicle, and also serves as a discharging element for spurious radiation.