WO2007141335A1

WO2007141335A1 - A pyrotechnic gas generator for use in automobile safety

Info

Publication number: WO2007141335A1
Application number: PCT/EP2007/055663
Authority: WO
Inventors: Xavier Abaziou; Bernard Dechoux
Original assignee: Autoliv Development Ab
Priority date: 2006-06-09
Filing date: 2007-06-08
Publication date: 2007-12-13
Also published as: FR2902060B1; FR2902060A1

Abstract

The invention relates to a pyrotechnic gas generator for inflating an airbag used in automobile safety, the generator comprising a tank (5) for storing a cooling liquid, a combustion chamber (2) within which gas is generated when the generator is triggered, and a filter and plenum chamber (4), the two chambers being interconnected by at least one nozzle (120) that allows said hot gas to pass from said combustion chamber (2) to said plenum chamber (4), from which the gas can be exhausted via at least one discharge opening (106) so as to inflate said airbag. The generator is remarkable in that it includes an activator device (6, 8) enabling said cooling liquid (50) to be exhausted from its storage tank (5) in such a manner as to be sprayed into said airbag, said activator device (6, 8) being actuated by a control device in manner that is selective and independent from the operation of the combustion chamber (2).

Description

A PYROTECHNIC GAS GENERATOR FOR USE IN AUTOMOBILE SAFETY

The present invention relates to a pyrotechnic gas generator for inflating an airbag used in automobile safety. The invention relates more particularly to a pyrotechnic gas generator comprising, inside an enclosure :

^• two chambers, namely a first chamber constituting a combustion chamber within which hot gas is generated when the generator is triggered, and a second chamber constituting a filtering and plenum chamber, these two chambers being connected to each other via at least one nozzle that allows said hot gas to pass from said combustion chamber to said filter and plenum chamber from which the hot gas can be exhausted via at least one discharge opening in such a manner as to inflate said airbag .

The present invention seeks to propose an improvement to this type of generator, to enable the absorption capacity of the airbag to be adapted to the nature and/or to the severity of the impact that results from an accident suffered by the motor vehicle, and/or to parameters associated with the occupants of the vehicle. The place occupied by the occupant inside the vehicle, depending on whether the occupant is the driver or a passenger, the occupant's morphology, and the occupant's position on the seat, depending on whether or not the occupant is or is not properly seated, all influence the way in which the occupant comes into contact with the airbag.

However, a given pyrotechnic generator of the type specified above corresponds to a single value of pressure and volume for the gas generated within an airbag.

When the energy absorption characteristics desired for the airbag cannot be achieved solely by selecting a suitable generator, one potential solution consists in causing the pressure that exists inside the airbag to drop and in matching the pressure drop to the various parameters mentioned above.

One solution for achieving such a pressure drop consists in controlling venting from the airbag. Thus, in the prior art, there exists a pyrotechnic generator of the type specified above associated with an airbag that includes a vent with opening of the vent being activated by a pyrotechnic signal. One such device is known under the trademark ATE (Autoliv Trigger Electric) .

When the system is not activated, the vent acts as a conventional "passive" vent of the kind that is to be found in all airbags and that serves solely to contribute to deflating the airbag in order to hold the passenger's head.

When the system is activated, the vent becomes active and opens to a greater extent, thereby causing the airbag to be vented to a greater extent.

Such a system nevertheless presents the drawback of being expensive, bulky, and not very robust. In addition, it is not very effective in contributing to attenuating injuries to passengers if they are not normally positioned on their seat.

In order to generate the pressure drop inside an airbag, the state of the art also discloses pyrotechnic generators that include a tank for storing a cooling liquid. This liquid is sprayed into the plenum chamber or into an intermediate mixer chamber, where it is mixed with the hot gas leaving the combustion chamber. Patent documents US-6 076 468, US-6 196 583, and US- 3 813 007 describe such generators. The liquid is expelled from the tank by a displacement movement of a piston or by deformation of one of the walls of the tank, with the movement always being generated by the thrust that is exerted by the hot gas being released. That expulsion of cooling liquid thus takes place simultaneously with the release of hot gas and cannot be eliminated or deferred in time.

Such devices do not enable the pressure drop within the airbag to be adjusted as a function of parameters associated with the accident.

Patent document US—6 412 814 seeks to improve generators of the above-specified kind by controlling the ejection of the cooling fluid into the mixer chamber. Such a generator includes an electrical control valve placed on a duct connecting the combustion chamber to the rear face of the piston. The valve can be operated to limit the passage of hot gas towards the piston, thus regulating not only the quantity of cooling liquid that is expelled into the mixer chamber, but also the instant at which such expulsion takes place.

Nevertheless, such a device presents the drawback of fluid ejection being possible only while the gas generator is in operation. Furthermore, some of the gas is used to perform the ejection, thereby changing the performance of the gas generator.

Finally, in all of the above-described generators, the encounter between the cooling liquid and the hot gas takes place at the moment when the gas is leaving the combustion chamber, i.e. when it is still at a very high temperature. This leads to a risk of the cooling liquid bursting into flame.

An object of the invention is to remedy the above- mentioned drawbacks of the state of the art. A particular object of the invention is to propose a pyrotechnic gas generator of the type mentioned in the introduction, that further comprises at least one cooling liquid storage tank, and that enables the pressure drop inside the airbag to be adapted to different types of occupant and to the conditions of the accident.

The generator must also be reliable and must not produce toxic gas. In accordance with the invention, these objects are achieved by the fact that said generator also comprises an activation device enabling said cooling liquid to be exhausted from said storage tank so as to be sprayed into the airbag, said activation device being actuated by a control device in a manner that is selective and independent of the operation of said combustion chamber.

According to other characteristics of the invention that are advantageous but not limiting, and that can be taken singly or in combination:

• said tank for storing the cooling liquid communicates with at least one exhaust orifice provided through the wall of said enclosure in such a manner as to allow the cooling liquid to be sprayed directly into the inside of said airbag;

^• said activation device comprises an ignitor and a piston suitable for moving under the action of the gas generated by the ignitor so as to reduce the volume of said storage tank and expel the cooling liquid therefrom; ^• said piston constitutes a portion of the wall of the cooling liquid tank;

^• the control device acts on the activator device as a function of parameters associated with the type of impact on the motor vehicle, its violence, and the morphology or the positioning of the occupants;

^• said cooling liquid presents a freezing point below about minus 39°C and a boiling point above about 109⁰C;

^• the cooling liquid is a mixture comprising about 50% water and about 50% glycol;

^• the enclosure is tubular in shape and comprises a cylindrical wall closed at each of its ends by a closure ring, the enclosure is subdivided internally by a first partition and by a second partition extending perpendicularly to its longitudinal axis, said first partition, having the nozzle passing therethrough, separating the first combustion chamber from the plenum chamber, said second partition separating the plenum chamber from the cooling liquid tank, and said piston is suitable for sliding axially inside said enclosure towards said second wall, the discharge opening and the exhaust orifice being formed through said cylindrical wall of the enclosure; and

^• the second ignitor is secured in the central portion of the second closure ring.

The invention also provides a method of inflating an airbag used in automobile safety, the method comprising a step consisting in ejecting hot gas into the inside of said airbag in order to deploy it.

In accordance with the invention, the method further comprises a step consisting in spraying a cooling liquid directly into the inside of said airbag, simultaneously with the release of said hot gas, or subsequently thereto .

Other characteristics and advantages of the invention appear from the description below given with reference to the accompanying drawings which show one possible embodiment by way of non-limiting indication. In the drawings:

^• Figure 1 is an axial section view of a conventional pyrotechnic gas generator forming part of the state of the art; and

^• Figure 2 is an axial section view on a scale that is slightly smaller than that of Figure 1, showing a pyrotechnic gas generator in accordance with the invention . There follows a description of a prior art pyrotechnic gas generator as shown in Figure 1.

As can be seen, the generator comprises an enclosure 1 defined by a cylindrical wall 10 that is crimped at each of its ends onto closure rings 11, 13 that are generally in the form of disks. References 101 and 103 designate annular beads that project inwards and serve to hold the wall 10 in place on the closure rings 11 and 13.

The generator extends along a longitudinal axis X- X' .

The wall 10 is also crimped in its central portion onto a disk-shaped transverse partition referenced 12. The corresponding annular crimping bead is given reference 102. The partition 12 and the closure rings 11 and 13 occupy planes that are perpendicular or substantially perpendicular to axis X-X'.

In its central portion, the partition 12 is pierced by at least one nozzle-forming orifice 120 which, by way of example, is in the form of a cylinder extended by a slightly flared portion.

The wall 10, the rings 11 and 13, and the intermediate partition 12 are traditionally made of metal having high strength and suitable for withstanding high temperatures. Nevertheless, the wall 10 is made of a metal that is sufficiently ductile to make crimping possible .

The intermediate partition 12 subdivides the inside of the enclosure 1 into two chambers, a "combustion" chamber 2 and a "filtering and plenum" chamber 4. For simplification purposes, this chamber is referred to in the description below as the "plenum" chamber. These two chambers are contiguous.

The generator also includes an ignitor 3 associated with a pyrotechnic charge 20, the ignitor 3 and the charge 20 both being situated in the combustion chamber 2.

The charge 20 is generally in the form of a cylindrical annular sleeve that is engaged inside the wall 10 of the enclosure.

As can be seen, the ignitor 3 is mounted in the central portion of the ring 11 and it is retained and centered against the inside face of said ring by means of an appropriate mounting member 30.

An 0-ring 31 provides sealing in this location.

The ignitor 3 is also provided with a pair of pins 32 for enabling it to be connected to an electric current source .

The major portion of the ignitor 3 penetrates into the inside space of the annular charge 20. The charge 20 is held in place inside the chamber 2 by appropriate sintering means (not shown in the figure) , and it is also prevented from moving in translation by a grid 21 in the form of a cup that is interposed between the charge 20 and the intermediate partition 12.

The ignitor 3 is of conventional type and is advantageously an electro-pyrotechnic initiator. It includes an electrical initiator system and a fragmentable cap containing a pyrotechnic composition.

On being activated, the pyrotechnic composition releases flame and hot gas that in turn cause the pyrotechnic charge 20 to enter into combustion.

By way of example, this charge is made up of a solid propellant suitable for generating a large quantity of hot gas very quickly.

A gas-permeable sleeve 40 of filter material is mounted inside the plenum chamber 4.

Its function is to retain certain particles that are present in the gas generated by combustion of the charge 20 so as to prevent these particles from escaping from the generator and penetrating into the airbag (not shown in the figures) .

Facing the chamber 4 and the filter sleeve 40, the wall 10 of the enclosure is pierced by at least one radial hole 106, and preferably by a plurality of radial holes that are regularly distributed angularly if it is desired to have a generator that delivers neutral thrust.

In the event of the vehicle suffering an accident, a deceleration sensor produces an electrical signal which is transformed by the ignitor 3 into a pyrotechnic signal leading to combustion of the propellant charge 20. The propellant generates hot gas in the combustion chamber 2 and the escape of the gas into the plenum chamber 4 is controlled by the nozzle orifice 120.

This escape of gas takes place via the plenum chamber 4, through the filter wall 40, towards the discharge holes 106 into the inside of the airbag.

The generator of the invention is described below with reference to Figure 2.

It comprises a portion shown on the right in Figure 2 that is identical to the corresponding portion of the generator described above with reference to Figure 1. This identical portion and its various component elements are given the same numerical references and they are not described again.

The generator in accordance with the invention is longer than the prior art generator, i.e. its cylindrical wall 10 extends beyond the plenum chamber 4 (to the left in Figure 2 ) .

The closure ring 13 is omitted and replaced by a second intermediate partition 14 of disk shape, preferably made of metal.

The wall 10 is crimped onto said partition 14 and the annular crimping bead is given reference 104.

This partition 14 defines the end of the plenum chamber 4.

The generator is also closed at its other end by a closure ring 15 identical to the ring 11. The crimping bead is given reference 105.

An ignitor 8 is mounted in the central portion of the ring 15 and is held and centered against the inside face of said ring by means of a mounting member 80.

An O-ring 81 provides sealing in this location. The ignitor 8 is also provided with a pair of electrically conductive pins 82. Advantageously, the ignitor is an electro- pyrotechnic initiator of the same type as that referenced 3.

The ignitor 8 is connected to a control device (not shown in the figures) , and constituted for example by the computer on board the vehicle or by an electronics unit.

The generator also includes a disk-shaped piston 6 interposed between the ignitor 8 and the second intermediate partition 14. The piston 6 is preferably made of metal.

Like the closure ring 15 and the partition 14, it extends in a plane that is perpendicular or substantially perpendicular to the longitudinal axis X-X' of the generator . The piston 6 co-operates with a portion of the wall 10 and the second partition 14 to define a tank 5 for storing a cooling liquid 50. It also co-operates with the ring 15 to define a second combustion chamber 7.

An O-ring 61 penetrates into a receiving peripheral groove 60 provided for this purpose around the periphery of the piston 6. Its function is to prevent the cooling liquid 50 from flowing into the inside of the second combustion chamber 7.

By way of example, the O-ring 61 can be made of rubber.

The cooling liquid 50 must withstand the extreme operating temperatures to which the generator is exposed. For this purpose, it preferably presents a freezing point below -39°C (minus 39° Celsius) and a boiling point above about 109⁰C.

Furthermore, it must not react with the gas obtained by combustion of the charge 20, and it must not be toxic for passengers of the vehicle. Finally, once mixed with the combustion gas, it must not present any risk of burning, in the event of a passenger accidentally receiving such a mixture on the skin. By way of example, it is advantageous to select a mixture comprising 50% water and 50% glycol.

This mixture also has the advantage of not burning within the airbag and thus of not generating any additional combustion gas.

The piston 6 is movable in translation along the axis X-X' of the generator towards the partition 14.

In register with the liquid storage tank 5, the wall 10 of the enclosure is pierced by at least one radial exhaust orifice 51, and preferably by a plurality of radial orifices that are regularly distributed angularly.

Initially, each orifice 51 is closed by a closure membrane 52.

The orifice (s) 51 open(s) out directly into the inside of the airbag.

The generator operates as follows.

In the event of an accident, a deceleration sensor activates the ignitor 3 as explained above, thereby causing the airbag to be inflated. A fraction of the gas contained in the airbag can escape through a passive vent formed in the airbag so as to damp reception of the body of the vehicle passenger.

Furthermore, the control device can selectively activate triggering of the ignitor 8, i.e. it can ignite it or it can decide not to ignite it, and it can ignite it simultaneously with triggering of the ignitor 3, or subsequently.

Activation is performed as a function of various parameters, e.g. selected from: ^• the type of impact on the vehicle: for example a frontal impact or a lateral impact or a plurality of successive impacts;

^• the violence of the impact, generally associated with the speed of the vehicle and/or the speed, if any, of the obstacle encountered; ^• the morphology of the occupants who can be children or adults and who can be tall or corpulent to a greater or lesser extent; and

^• the positions of the occupants in the vehicle, where the occupants can include the driver or the passengers and where they can be properly seated, or on the contrary leaning over or lying down at the moment of the impact .

The control device senses these various items of information using sensors that are present in the vehicle .

If the control device determines that it is necessary to activate the ignitor 8, it does this by delivering an electrical signal thereto. This causes the pyrotechnic composition contained in the fragmentable cap of the ignitor 8 to enter into combustion.

The pyrotechnic combustion releases a flame and a certain amount of hot gas that applies pressure against the piston 6, thereby causing it to move axially towards the partition 14. This reduces the volume of the tank 5 so the cooling liquid 50 is expelled therefrom, through the exhaust orifice 51 by piercing the membrane 52.

The cooling liquid 50 is sprayed directly into the inside of the airbag. The exhaust orifice 51 is calibrated so that the liquid 50 is sprayed uniformly in very fine droplets into the inside of the airbag.

By conduction and convection with the gas mixture present in the airbag, the droplets of liquid are heated and vaporized. This endothermic reaction causes a certain quantity of heat to be absorbed, thereby reducing the temperature of the mixture and thus the pressure that exists inside the airbag.

The instant at which cooling liquid begins to be sprayed is also selected to optimize not only the beginning of the pressure drop, but also the extent of the pressure drop. The pressure drop depends on the initial temperature of the gas in the airbag, which itself decreases as a function of time by heat exchange with the airbag and by leakage through the passive vent.

The advantage of the invention also lies in the fact that the cooling liquid is sprayed directly into the airbag and not into a mixer chamber as in prior art devices .

In accordance with the invention, the cooling liquid is sprayed into the gas present in the airbag when said gas is at a temperature that is generally lower than

200⁰C, i.e. well below the temperature of around 600⁰C to 800⁰C at which the gas penetrates into the plenum chamber 4. The gas obtained by vaporizing the liquid therefore does not run the risk of bursting into flame or of producing toxic derivatives.

The generator in accordance with the invention also makes it possible for the airbag to do without an active vent with controlled opening.

Finally, it should be observed that the generator could be of some other shape and that the second combustion chamber 7 and the liquid tank 5 could be positioned in some other way relative to the plenum chamber 4 and the combustion chamber 2.

Furthermore, the piston 6 could be omitted. An ignitor on its own generates sufficient pressure to eject the cooling liquid.

Claims

1. A pyrotechnic gas generator for inflating an airbag used in automobile safety, the generator comprising inside an enclosure (1) : ^• at least one tank (5) for storing a cooling liquid (50); and

^• two chambers, namely a first chamber (2) constituting a combustion chamber within which hot gas is generated when the generator is triggered, and a second chamber (4) constituting a filtering and plenum chamber, these two chambers (2, 4) being connected to each other via at least one nozzle (120) that allows said hot gas to pass from said combustion chamber (2) to said filter and plenum chamber (4) from which the hot gas can be exhausted via at least one discharge opening (106) in such a manner as to inflate said airbag; the generator being characterized in that it also comprises an activation device (6, 8) enabling said cooling liquid (50) to be exhausted from said storage tank (5) so as to be sprayed into the airbag, said activation device (6, 8) being actuated by a control device in a manner that is selective and independent of the operation of said combustion chamber (2) .

2. A generator according to claim 1, characterized in that said tank (5) for storing the cooling liquid (50) communicates with at least one exhaust orifice (51) provided through the wall (10) of said enclosure (1) in such a manner as to allow the cooling liquid to be sprayed directly into the inside of said airbag.

3. A generator according to claim 1 or claim 2, characterized in that said activation device comprises an ignitor (8) and a piston (6) suitable for moving under the action of the gas generated by the ignitor (8) so as to reduce the volume of said storage tank (5) and expel the cooling liquid (50) therefrom.

4. A generator according to claim 3, characterized in that said piston (6) constitutes a portion of the wall of the cooling liquid tank (5) .

5. A generator according to any preceding claim, characterized in that the control device acts on the activator device (6, 8) as a function of parameters associated with the type of impact on the motor vehicle, its violence, and the morphology or the positioning of the occupants.

6. A generator according to any preceding claim, characterized in that said cooling liquid (50) presents a freezing point below about minus 39°C and a boiling point above about 109⁰C.

7. A generator according to claim 6, characterized in that the cooling liquid (50) is a mixture comprising about 50% water and about 50% glycol.

8. A generator according to any one of claims 3 to 7, characterized in that the enclosure (1) is tubular in shape and comprises a cylindrical wall (10) closed at each of its ends by a closure ring (11, 15), in that the enclosure (1) is subdivided internally by a first partition (12) and by a second partition (14) extending perpendicularly to its longitudinal axis X-X', said first partition (12) having the nozzle (120) passing therethrough, separating the first combustion chamber (2) from the plenum chamber (4), said second partition (14) separating the plenum chamber (4) from the cooling liquid tank (5), and in that said piston (6) is suitable for sliding axially inside said enclosure (1) towards said second wall (14), the discharge opening (106) and the exhaust orifice (51) being formed through said cylindrical wall (10) of the enclosure (1).

9. A generator according to claim 8, characterized in that the second ignitor (8) is secured in the central portion of the second closure ring (15) .

10. A method of inflating an airbag used in automobile safety, the method comprising a step consisting in ejecting hot gas into the inside of said airbag to enable it to be deployed, and the method being characterized in that it further comprises a step consisting in spraying a cooling liquid (50) directly into the inside of said airbag, simultaneously with the release of said hot gas, or subsequently thereto.