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 for Safety Restrain Systems (SRS).

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, US 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.

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 uses one or more of the features defined in the dependant claims.

Brief description of the drawings

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.

On the drawings, Figures 1, 2 and 3 are schematic exploded views of an electrical circuit according to respectively a first, a second and a third embodiments of the invention.

On the different figures, the same references signs designate like or similar elements.

Detailed description

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 electrically linked to a 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 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 30A, 32A, 34A of each terminal is designed to be inserted in the apertures 24, 26, 28. According to this embodiment, the second extremity 32B of the second terminal 32 and the second extremity 34B 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 US 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 ground 14 of the squib 6 and the second terminal 32 transmits the triggering signal in the differential mode. Due to the link between the first conductor 40 and the ground 14 of the squib 6, 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 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 US 7,162,388.

Alternatively, as shown on Fig. 2, the electrical connector 8 comprises an insulating block comprising three apertures in which pins bonded to the wires 36, 38 and 39 are fitted.

The second extremity 30B of the first terminal 30 is electrically connected to the first conductor 40 as well as to the ground 10 of the control module 4, through a wire 39.

Advantageously in this embodiment, the filtering element 20 is connected to a ground through both extremities 3 OA, 30B of the first terminal 30, in the differential mode.

According to a third embodiment of the electrical circuit referenced 37 on Fig. 3, the first conductor 40 of the filtering element 20 is connected only to the ground 10 of the control module 4.

To this end, the second extremity 30B of the first terminal is connected to the ground

10 of the control module through the wire 39. The second extremity 30B of the first terminal is only in electrical contact to the conductor 40 of the filtering element.

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 ground 10 of the control module 4. 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; wherein it comprises the step of 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;

wherein it comprises the step of connecting the first conductor to the ground of the control module.