FR2809363A1 - Actuator for safety device such as motor vehicle air bag has primary pyrotechnic compound designed to control decomposition of secondary compound - Google Patents

Abstract

The actuator (1) has a gas generator (3) connected e.g. to an air bag (2) and comprising an explosive charge (4) made up of a primary pyrotechnic compound (5) designed to control the decomposition of a secondary compound (6). This allows a an interaction of the products of combustion of both compounds within a volume (7) that is not confined or only slightly confines, the interaction being at least partly an oxidation-reduction reaction.

Description

The present invention relates to the field of shock absorbing devices with an airbag for the protection of the occupants of motor vehicles, in the event of an accident.

The present invention relates more particularly to a shock absorbing device for protes on at least one occupant of a motor vehicle, of the type consisting of at least one safety airbag connected to a gas generation system comprising a load. explosive formed less by a pyrotechnic compound and an oxidant source.

prior art essentially knows three types of shock absorption devices for occupant protection of motor vehicles gas generators by pure combustion of a pyrotechnic compound; gas generators by combustion of a pyrotechnic compound for heating a neutral gas, also called hybrid generators; and the gas generators by combustion of a pyrotechnic compound in the presence of an oxidant, also called reactive hybrid generators, such as that described in the European patent application EP 673 809 A1.

major drawbacks of the devices of the prior art reside in the fact that for the first two, combustion generates a dust production detrimental to the comfort and health of the vehicle occupants and for the third that the combustion creates an overpressure in the structure of the gas generator, which must, therefore, be reinforced. In addition, for the latter type of gas generator, the characteristics of the gases generated (composition, temperature) are not constant during implementation and are not optimized.

The present invention intends to remedy disadvantages of the prior art by proposing a reactive hybrid generator with reduced mass and dimensions that do not require over-dimensioning of the structure because they do not undergo overpressure when it is used.

To do this, the present invention is of the type described above and is remarkable, in its broadest sense, in that said gas generation system comprises at least two gas sources for reacting in an unconfined volume. or weakly confined.

An explosive charge is defined as a set of elements that can produce a chemical reaction in which gases are produced under pressure within a very short period of time.

The present invention essentially presents three variants.

In a first variant, said pyrotechnic compound is positioned in an expeller, said oxidizing source is in the form of a gaseous mixture under pressure positioned in a gas reservoir stored said unconfined volume is constituted by a post-combustion chamber positioned, of preferably, between said expeller and said stored gas reservoir.

In a second variant, said oxidant source is not in the form of a gaseous mixture under pressure, but in the form of a solid compound.

In a third variant, said pyrotechnic compound and said oxidant source are each in the form of a bi-component positioned in at least one reaction tube and said unconfined volume is constituted by said reaction tube.

Advantageously, all the variants of the gas generator make it possible to perfectly control the chemical composition and the temperature of the gases as well as their expulsion kinetics out of the generation system for the inflation of the airbag.

In addition, in all variants, the combustion of the explosive charge being carried out under low confinement, the generators are not or propulsive and the effects of an overpressure in the structure of the gas generator according to the invention are therefore much less the effects of such overpressure in gas generators of the prior art.

Advantageously also, during the implementation of the variants of the gas generator according to the invention, amounts of solid particles are zero or very greatly reduced compared to the amounts of solid particles emitted during the implementation of the gas generators. of the prior art, and the quantities of pyrotechnic materials are limited to the strict functional requirement, in order to inflate the airbag with the strict amount of gas required and at the preset temperature.

Advantageously, all the variants make it possible to use, in the expeller or the reaction tube, energetic materials of the ballistic powder type consisting of nitrocellulose or energetic binders loaded with secondary explosives (Lova). The characteristic of these materials is to provide gases that can be re-combusted. These materials are inexpensive, widely available industrially and present only reduced risks for the environment even after the end of life of the gas generator. Advantageously also, the second variant and the third variant make it possible to use, as a main oxidant source, ammonium nitrate in solid form which has the advantage of being easy to implement in a structure that is not or only slightly confined. .

An important advantage of the third variant of the invention to allow placing the gas generator inside the airbag. This advantage finds applications in the realization of thorax and curtain airbags.

From its flexibility, it can also be imagined that the third variant of the invention is positioned on particular elements, such as, for example, on a seat belt.

The invention further proposes to use in gas generator of the third variant, a two-component formed by propellant and ammonium nitrate.

The invention will be better understood using the description, given below for purely explanatory purposes, of one embodiment of the invention, with reference to the appended figures - FIG. 1 illustrates a longitudinal sectional view first variant. of the device according to the invention; FIG. 2 illustrates a view in longitudinal section of the second variant of the device according to the invention; FIG. 3 illustrates a view in longitudinal section of the third variant of the device according to the invention; FIG. 4 illustrates a cross-sectional view of the third variant of the device according to the invention; and FIGS. 5 to 7 illustrate cross-sectional views of heterogeneous monolithic bi-components for implementing the third variant.

The device (1) according to the invention is a shock absorbing device for protecting at least one occupant of a motor vehicle, of the type consisting of at least one airbag 2) connected to a system for generating gas (3) comprising an explosive charge (4) formed at least by a pyrotechnic compound (5) and an oxidant source (6).

The device according to the invention is characterized in that said gas generation system (3) comprises at least two gas sources intended to react in a confined volume (7) or in a slightly confined volume.

Indeed, when the pyrotechnic compound (5) undergoes combustion, it forms gases that are capable of reacting with the oxidant source (6) either directly or after decomposition of the latter.

The gases emitted by said pyrotechnic compound (5) then drive the decomposition of the oxidant source (6).

Thus, the temperature of the gases formed and their expulsion kinetics out of the gas generating system (3 for inflating the airbag (2) is perfectly controlled during the entire inflation period.

The present invention thus makes it possible to quickly pressurize the airbag (2) and keep it pressurized for 0.1 seconds for protection at the thorax level for several seconds for curtain-type embodiments. In a first variant of the invention, illustrated in FIG. 1, said pyrotechnic compound (5) is positioned in an expeller (10), said oxidant source (6) is in the form of a gaseous mixture under pressure which is positioned in a stored gas reservoir (13) and said unconfined volume (7) is constituted by an afterburner (16) positioned between said expeller (10) and said stored gas reservoir (13).

In this variant, the expeller (10) comprises an initiator (24), possibly equipped with a reinforcing filler (25), at least one storage chamber (11) inside which said pyrotechnic compound can be positioned ( 5) and at least one nozzle type outlet (12). This outlet orifice is of course kept closed for example by means of a lid, until implementation of the device (1) during an impact.

In this variant also, said storage tank (13) comprises at least one orifice (14) hermetically closed by means of a closure means (15), said stored gas reservoir (13) being intended, during the rupture said closing means (15), to allow the release of the stored gases. These gases will then carry out the post-combustion of the pyrotechnic compound (5) and participate in the swelling of said airbag. The rupture of said closure means (15) is obtained either under the effect of the heat of the gas of the expeller, or under the mechanical effect of a firing pin projected by these hot gases.

Said stored gas reservoir (13) has, inside, a movable membrane (26) having an orifice whose diameter is smaller than that of the orifice (14), in order to maintain a sufficient internal pressure to the inside the tank after the start of the gas release and thus promote the rapid evacuation of gas stored by its displacement.

Said post-combustion chamber (16) is in communication on the one hand with at least said nozzle (12) of said expeller (10) and on the other hand with said orifice (14) of the stored gas reservoir (13) and comprises means of discharging (17) stored gases in communication with said airbag (2). Said evacuation means (17) are preferably constituted by an evacuation grid comprising a plurality of recesses.

In a second variant, illustrated in FIG. 2, said source of oxidant (6) is not in the form of a gaseous mixture under pressure, but in solid compound form.

 The expeller (10) is of the same type as the first variant.

In the bright reactive hybrid generator FIG. 2, the afterburner chamber (16) is positioned between the expeller (10) and the chamber containing oxidant source (6), but it is also possible to produce the gas generator of such such that the gases from the expeller (10) pass through the oxidant source chamber (6) and the post combustion chamber is positioned after the chamber containing the oxidant source (6).

In the first two variants, said expeller (10) may comprise two casing chambers (11) each comprising a pyrotechnic compound (5) whose implementation is controlled separately.

In addition, said unconfined volume (7) can be made in two parts, separated by a separation grid (18) having a plurality of recesses (19), to achieve a high turbulence zone T near the orifice (14) of the expeller (10) and a stabilization zone S near the evacuation means (17) of the afterburner chamber (16).

Thus, the time during which the airbag (2) remains inflated can be perfectly controlled.

In a third variant, illustrated in FIG. 3, said pyrotechnic compound (5) and said oxidant source (forming said explosive charge (4) are positioned in at least one cylindrical reaction tube (20) said uncontained volume (7) or weakly confined is constituted by said reaction tube (20).

reaction tube (20) is of the high pressure type whose flexibility and mechanical strength ensure an opening after the combustion of the pyrotechnic compound (5).

The opening of the reaction tube (20) is preferably programmed by break primers (21). reaction tube (20) is preferably positioned in said airbag (2).

The initiator (24) may optionally be provided with a reinforcing charge (25).

reaction tube (20) can be positioned in a porous secondary reaction tube (22), at least partially resistant to the reaction, as shown in FIG. 4.

During the implementation, the pressure increase opens the reaction tube from its break primers the secondary reaction tube nevertheless allows to maintain a moderate pressure.

The reaction tube (20) may further comprise a cylindrical stabilization chamber (23) made, for example with another tube or a fabric bag.

This third variant allows, as a first variant and the second variant, to perfectly control the time during which the airbag (2) remains inflated.

This third variant also makes it possible to provide a protection device having an essentially elongated shape and which can be placed, for example, above a door.

In the second and the third variant, said solid oxidant source (6) is preferably composed mainly of ammonium nitrate.

Said pyrotechnic compound (5) and said solid oxidizing source (6) can form an explosive charge (4) homogeneous or heterogeneous monolith.

When said pyrotechnic compound (5) and said solid oxidant source (6) form a heterogeneous heterogeneous explosive charge (4), said pyrotechnic compound (5) is then in bulk or in the form of at least one sheet (8), flat or wound, or at least one strand (9) and said source of oxidant (6) solid then present in bulk or in the form of at least one sheet, flat or wound, or at least one strand .

FIG. 4 illustrates a plurality of strands (9) of pyrotechnic compound (5) positioned inside a source of oxidant (6), in bulk.

Said pyrotechnic compound (5) can be positioned at least partially at the periphery of said solid oxidant source (6), as illustrated in FIG. 5, in order to create a first pressurization effect of the airbag and a second effect of maintaining the airbag. the pressure in the airbag. When said pyrotechnic compound (5) is produced in the form of at least one sheet (8) and said source of oxidant (6) is loose, the two-component constitutes the pyrotechnic compound (5) and the source of oxidant (6) can then be in the flat sandwich form, as shown in FIG. 6 or a rolled sandwich, as illustrated in FIG.

Said pyrotechnic compound (5) can also be produced in the form of a plurality of strands having different diameters.

For clarity, the secondary reaction tube (22) and the stabilization chamber (23) are not shown in FIGS. 3 and 5 to 7.

In a preferred version of the invention, said pyrotechnic compound (5) consists of at least one propellant and said oxidant source (6) consists essentially of ammonium nitrate.

Thus, by its very rapid combustion, the propellant provides the energy necessary for the decomposition of ammonium nitrate and this decomposition will provide the amount of oxidant necessary for the oxidation of carbon monoxide from the combustion of propellant.

In addition, to promote the decomposition of ammonium nitrate, certain additives may be added such as inorganic oxidants, such as for example alkaline or alkaline earth nitrates, organic compounds such as nitrocellulose. These additives can also contribute to the mechanical strength of ammonium nitrate during its lifetime.

For a better understanding of the invention, several exemplary embodiments of an explosive charge (4) are given below using, as pyrotechnic compound (5), a propellant of the nitrocellulose type. One gram of propellant delivers substantially one liter of gas, of which 50 % of carbon monoxide C0, toxic that should be oxidized.

In the first variant or in the second variant of the invention, if the source of oxidant (6) is stored gas, 1 liter of stored gas may contain 0.2 liter of oxygen Oz which can oxidize 0.4 liter of CO in C02.

In this case, the ratio to be considered must be greater than 1.2 liters of gas stored per gram propellant.

In the second variant or in the third variant of the invention, if the oxidant source (6) is ammonium nitrate, 80 grams of ammonium nitrate produce 1 mole of H2O water and half a mole of oxygen. O2.

In this case, the ratio to be considered must be greater than 2 grams of ammonium nitrate per gram of propellant.

To illustrate the gain in space and weight that can be obtained with a device according to the invention, the three points below show two examples of dimensioning for the first variant and example of dimensioning for the second variant <U> 1 / - </ U> 1st <U> variant: </ U> the source of oxidant is in the form of a gaseous mixture under pressure, for the realization of a protective device of a passenger.

The gaseous volume of the gas mixture is of the order of 25 liters under normal conditions of pressure and temperature; The volume of the stored gas reservoir is of the order of 83 cm 3 and the internal pressure is of the order of 300 bars.

11 grams of propellant are introduced into the expeller.

The afterburner chamber has a diameter of the order of millimeters and a length of the order of 30 millimeters.

For a performance of 100 liters of gas generated, the generating diameter is less than 40 mm, its length is less than 200 mm and its total mass is less than 900 g.

<U> 2 / - </ U> 1st <U> variant: </ U> the source of oxidant is in the form of a gaseous mixture under pressure, for the realization of a protective device in the form of a curtain.

The gaseous volume of the gas mixture is of the order of 15 liters under normal conditions of pressure and temperature; The volume of the stored gas tank is of the order of 50 cm3 and the internal pressure is of the order of 300 bars.

3 grams propellant are introduced into the expeller.

The afterburner chamber has a diameter of the order of 25 millimeters and a length of the order of 22 millimeters.

For a performance of 22 liters of gas generated, the diameter of the gas generator is less than 25 mm, its length is less than 200 mm and its total mass is less than 800 g.

<U> 3 / - 2nd variant: </ U> the oxidant source is in the form of a solid compound, for the realization of a protection device of a passenger. The expeller has 10 grams of propellant and 36 grams of ammonium nitrate are provided.

The t-combustion chamber has a diameter of the order of 40 millimeters and a length of the order of 30 millimeters.

For a performance of 100 liters of gas generated, the diameter of the generator is less than 40 mm, its length is less than 150 mm and its total mass is less than 600 g.

Claims (14)

Impact absorbing device (1) for the protection of at least one occupant of a motor vehicle, of the type consisting of at least one airbag (2) connected to a gas generating system (3) having an explosive charge (4) formed by at least one pyrotechnic compound (5) and an oxidizing source (6), characterized in that said gas generating system (3) comprises at least two gas sources for reacting in an unconfined volume (7) weakly confined. 2. Device (1) according to claim 1, characterized in that said source of oxidant (6) is in the form of a gaseous mixture under pressure or a solid compound. 3. Device (1) according to claim 2, characterized in that the gases emitted by said pyrotechnic compound (5) drive the decomposition solid oxidant source (6). 4. Device (1) according to claim 2 or claim 3, characterized in that said pyrotechnic compound (5) and said source of oxidant (6) solid form a homogeneous explosive charge (4) monolith. 5. Device (1) according to claim 2 or claim 3, characterized in that said pyrotechnic compound (5) and said source of solid oxidant (6) form an explosive charge (4) heterogeneous monolith and in that said compound pyrotechnic material (5) is in bulk or in the form of at least one sheet, flat or rolled, or at least one strand (9) and said source of solid oxidant (6) is in bulk or in the form of form of at least one sheet, flat or rolled, or at least one strand. 6. Device (1) according to claim 5, characterized in that said pyrotechnic compound (5) is positioned at least partially on the periphery of said solid oxidizing source (6). 7. Device (1) according to claim 5 or claim 6, characterized in that said pyrotechnic compound (5) is formed as a plurality strands having different diameters. 8. Device (1) according to any one of claims 2 to 7, characterized in that said source of oxidant (6) solid is mainly composed of ammonium nitrate. 9. Device (1) according to any one of claims 1 to 8, characterized in that said unconfined volume (7) is made in two parts, separated a separation gri (18) having a plurality of recesses (19) , in order to achieve a zone with high turbulence T and a stabilization zone S. 10. Device (1) according to any one of claims 1 to 9, characterized in that said pyrotechnic compound (5) and said source of oxidant (6) solid are positioned in at least one reaction tube (20 cylindrical and in that said unconfined (7) or weakly confined volume is constituted by said reaction tube (20). 11. Device (1) according to claim characterized in that said reaction tube (20) can be positioned in a secondary reaction tube (22 porous, at least partially resistant to the reaction. 12. Device (1) according to claim 10 or claim 11, characterized in that said reaction tube (20) comprises a stabilization chamber (23). 13. Device (1) according to any one of claims 1 to 9, said pyrotechnic compound (5) being positioned in an expeller (10), characterized in that ledi expeller (10) comprises two storage chambers (11) each comprising a pyrotechnic compound (5) whose implementation is ordered separately. 14. Device (1) according to any one of claims 1 to 3, said storage tank (13) comprising comprises at least one orifice (14) sealed with a closure means (15), characterized in that said storage tank (13) has, on the inside, a movable membrane (26) having an orifice whose diameter is smaller than that of the orifice (14).