Patent Publication Number: US-2013241281-A1

Title: Electrical circuit and method of manufacturing said electrical circuit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage application under 35 U.S.C. §371 of PCT Application Number PCT/IB2011/002067 having an international filing date of Jul. 28, 2011, which designated the United States, which PCT application claimed the benefit of PCT Application Number PCT/IB2010/002569, filed Jul. 29, 2010, the entire disclosure of each of which are hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to an electrical circuit and a method of manufacturing such an electrical circuit. More particularly, the invention applies to a circuit and a method of manufacturing such an electrical circuit for Safety Restraint Systems (SRS) devices. 
     BACKGROUND OF THE INVENTION 
     SRS devices are widespread in the automotive environment. They are often triggered by ignition. This ignition is controlled by an electrical signal. 
     Automotive vehicles are submitted to electromagnetic interferences. These interferences may induce current in conductors leading to SRS devices. Consequently, interferences may cause accidental ignitions of SRS devices. 
     Therefore, these conductors leading to the SRS devices have to be protected against electromagnetic interferences, in order to avoid their unwanted triggering. To this aim, a filtering element is usually used. For instance, U.S. Pat. No. 6,799,999 teaches the implementation of a filtering assembly including a printed circuit board and a filter circuit, preferably comprising a plurality of capacitors. The prior art filtering assembly is connected to the wire connection section of an airbag connector terminal. 
     BRIEF SUMMARY OF THE INVENTION 
     An aim of the present invention is to propose an improved electrical circuit for EMI filtering, in particular for SRS devices which is adapted to work in common or differential mode, depending on the surrounding electrical environment,. Such an electrical circuit should further be compact enough to be housed in an automotive SRS connector. 
     Then, an electrical circuit is provided wherein a first conductor of the filtering element is connected to the ground of at least one of the control module and the squib. 
     With this feature, the filtering element (be it active or passive) connected to a ground, it is possible to dissipate the induced current(s) caused by the electromagnetic interference directly via a ground (dedicated) element of the car in which the electrical circuit is implemented. 
     The electrical circuit of the invention facilitates the electrical connection to the SRS device and therefore reduces the cost of assembly. It also provides added flexibility and increased functionality; depending on the electrical environment topography, it is possible to have a filter element capable to operate either in a common or a differential mode. 
     In some embodiments, one might also use one or more of the features defined in the dependent claims. 
     Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       Other characteristics and advantages of the invention will readily appear from the following description of three of its embodiments, provided as non-limitative examples, and of the accompanied drawings, in which: 
         FIG. 1  is a schematic exploded view of an electrical circuit in accordance with a first embodiment; 
         FIG. 2  is a schematic exploded view of an electrical circuit in accordance with a second embodiment; and 
         FIG. 3  is a schematic exploded view of an electrical circuit in accordance with a third embodiment. 
     
    
    
     On the different figures, the same references signs designate like or similar elements. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , the electrical circuit  2  according to the first embodiment of the invention comprises a control module  4  for generating a triggering signal, a squib  6  intended to trigger the actuation of a SRS device, such as an airbag, upon reception of the triggering signal, and an electrical connector  8  for connecting the control module  4  to the squib  6 . 
     The control module  4  is, for example upon detection that a car crash is occurring, adapted to emit a differential triggering AC signal to the squib  6 , through the electrical connector  8 , for triggering the airbag. It comprises a conductor  39  electrically linked to a control module ground  10 . 
     The squib  6  comprises a socket  12  having two conductive pins for receiving the triggering signal and one conductive pin connected to a squib ground  14 . This later part comprises for example a metallic shell surrounding the squib  6 . 
     The electrical connector  8  comprises a housing  16 , contact pins  18  for transmitting the triggering signal, and a filtering element  20  electrically connected to the contact pins  18  for filtering a current possibly induced by electromagnetic interferences present in the vehicle. 
     The housing  16 , typically made of an electrically insulating material, is adapted to carry the contact pins  18 . It comprises, on a back face, a cylindrical plug  22  adapted to be mated into the socket  12  and, on the front face, three apertures  24 ,  26 ,  28  adapted to receive terminals of the contact pins  18 . 
     The contact pins  18  comprise a first terminal  30 , a second terminal  32  and a third terminal  34 , for example made of deflectable L shaped fingers. 
     A first extremity  30 A,  32 A,  34 A of each terminal is designed to be inserted in the apertures  24 ,  26 ,  28 . According to this embodiment, the second extremity  32 B of the second terminal  32  and the second extremity  34 B of the third terminal  34  are electrically connected, for example by soldering or crimping, to a respective wire  36 ,  38  which extends to the control module  4 . 
     In order to make sure that no any electromagnetic interference will trigger an unwanted deployment of the airbag, the filtering element  20  filters out from the signal transmitted on the second terminal  32  and on the third terminal  34 , the signals due to these typical types of interferences. 
     To this end, the filtering element  20  comprises capacitor elements having a first conductor  40  designed to be connected to a ground, a second conductor  42  designed to receive the triggering signal, and a third conductor  44  designed to receive the filter signal. 
     Advantageously, according to the invention, the filtering element  20  is used to operate in a differential mode. But it can also be used in a common mode. 
     In the differential mode, the filtering element  20  is connected to a positive potential, a negative potential and to the ground. In the common mode, the filtering element  20  is only connected to a potential. 
     Such a filtering element is described in U.S. Pat. No. 7,162,388 herewith incorporated by reference. It can be for example a X2Y module. 
     In this embodiment, the first terminal  30  is connected to the squib ground  14  and the second terminal  32  transmits the triggering signal in the differential mode. 
     Due to the link between the first conductor  40  and the squib ground  14 , the conductor  40  of the filtering element  20  is connected to a ground, in particular to the same ground as the squib  6 . Advantageously, this link is made through the first terminal  30  of the electrical connector  8  i.e. over a short electrical path. 
     Alternatively, the filtering element  20  comprises capacitor elements and ferrite members. 
     Alternatively, the filter element  20  is soldered on a printed circuit board as shown on  FIG. 12  of U.S. Pat. No. 7,162,388. 
     Alternatively, as shown on  FIG. 2 , the electrical connector  8  comprises an insulating block comprising three apertures  24 ,  26 ,  28  in which pins bonded to the wires  36 ,  38  and  39  are fitted. 
     The second extremity  30 B of the first terminal  30  is electrically connected to the first conductor  40  as well as to the control module ground  10 , through a wire  39 . 
     Advantageously in this embodiment, the filtering element  20  is connected to a ground through both extremities  30 A,  30 B of the first terminal  30 , in the differential mode. 
     According to a third embodiment of the electrical circuit  37  on  FIG. 3 , the first conductor  40  of the filtering element  20  is connected only to the control module ground  10 . 
     To this end, the second extremity  30 B of the first terminal is connected to the control module ground  10  through the wire  39 . The second extremity  30 B of the first terminal is only in electrical contact to the conductor  40  of the filtering element  20 . 
     In this embodiment, in the differential mode, the second terminal  32  and the third terminal  34  transmit the triggering signal and the first conductor  40  is electrically connected to the control module ground  10 . In the common mode, the wire  39  is not connected to the ground. 
     The invention is also related to a method of manufacturing an electrical circuit for an automotive electrical system, comprising providing a filtering element for filtering trigger signal for a SRS device, the filtering element having a first conductor for connecting to a ground, providing a SRS squib intended to trigger the SRS device upon reception of said trigger signal, the squib having a ground, and connecting the first conductor to the ground of the squib. 
     Finally, the invention relates further to a method of manufacturing an electrical circuit for an automotive SRS system comprising providing a filtering element for filtering for filtering trigger signal for a SRS device, the filtering element having a first conductor for connecting to a ground, providing a control module generating said trigger signal, the control module having a ground, and connecting the first conductor to the ground of the control module.