Land vehicles – Wheeled – Attachment
Reexamination Certificate
2000-05-09
2001-05-15
Rice, Kenneth R. (Department: 2167)
Land vehicles
Wheeled
Attachment
C280S741000
Reexamination Certificate
active
06231079
ABSTRACT:
The present invention relates to the field of protecting the occupants of a motor vehicle using an inflatable airbag. More specifically, the invention relates to a hybrid gas generator of tubular shape for inflating such an airbag.
In order to inflate an airbag to protect the occupants of a motor vehicle, use has been made, in the past, of pressurized gas reservoirs opened by a pyrotechnic valve. Thus, U.S. Pat. No. 3,690,695 describes a device for inflating a protective airbag. This device consists of a reservoir of gas under pressure which is isolated from the duct leading to the airbag by a gastight diaphragm against which a finned solid piston rests.
In the event of a collision, a pyrotechnic primer placed behind the piston causes the piston to move forward, tear the diaphragm and allow the pressurized cold gases to enter the said duct. As the hot gases resulting from the combustion of the pyrotechnic charge cannot mix with the cold gases, these are heated up by passing over a bed of magnesium which reacts with them. A device such as this is dangerous in terms of its principle of operation, and has to be produced in a complex way.
Attempts have therefore been made at developing hybrid gas generators containing, on the one hand, a reservoir of cold gases under pressure and, on the other hand, a pyrotechnic charge capable of fulfilling two functions: opening the gas reservoir and heating the cold gases.
PCT application WO 98/09850 thus describes a hybrid generator of tubular shape containing a pressurized gas and a piston coupled to a pyrotechnic initiator. In the event of a collision, the triggering of the initiator causes the piston to move and open the generator at its opposite end to the pyrotechnic initiator and also to heat up the cold gases by mixing, inside the generator, of these gases with the hot gases supplied by the pyrotechnic initiator. As this takes place, an abrupt rise in pressure inside the generator is observed and, for obvious safety reasons, the amount of gas that can be stored in the generator is limited to well below its theoretical maximum value. Finally, a generator in which the stroke of the piston has to be guided along the entire length of the generator is relatively expensive to produce.
To simplify the actual production of the generator, there has therefore been proposed, for example in PCT application WO 98/12078, a type of tubular hybrid generator with lateral gas outlet orifices, the reservoir for pressurized cold gases being located on one side of these orifices, and the pyrotechnic chamber being located on the other side. The gas reservoir is opened by a hollow piston which has a central duct which, after opening, allows the hot gases to enter the reservoir to mix with the cold gases. The heated mixture then leaves the reservoir via the gap around the piston resulting from the breakage of the diaphragm which used to close the reservoir.
Although this solution does indeed yield tubular hybrid generators which are relatively simple to produce, it does not do away with the drawbacks that result from the fact that the hot gases from the combustion of the pyrotechnic charge enter the inside of the reservoir for pressurized cold gases.
This type of drawback is seen also in the solutions which, for opening the reservoir, use a projectile instead of a piston, as described, for example, in U.S. Pat. No. 5,464,247.
Tubular hybrid generators are particularly wanted for inflating front or side airbags for protecting the passengers of motor vehicles, but those skilled in the art do not currently have such tubular hybrid generators available to them which, simultaneously, are simple to produce and perform all of the mixing of the hot gases originating from the combustion of the pyrotechnic charge with the cold gases stored in the reservoir, outside the latter.
The object of the present invention is precisely to provide such a generator.
The invention therefore relates to a hybrid gas generator consisting of a tubular body with an upstream end closed by a pyrotechnic primer device and a downstream end which is closed in a gastight manner, the said tubular body also having gas outlet orifices and containing an internal partition with a central orifice of cross section S closed by a diaphragm, the said partition dividing the said tubular body into two parts:
an upstream part forming a combustion and mixing chamber and containing the primer device, the gas outlet orifices and a pyrotechnic charge that generates hot gases,
a downstream part forming a reservoir chamber containing at least one pressurized gas,
characterized in that the said tubular body in its upstream part, between the pyrotechnic charge and the said internal partition, contains a support piece which is fixed to the said tubular body without coming into contact with the said internal partition or with the said gas outlet orifices and which contains a solid mobile piston consisting of at least one column of cross section s, smaller than the cross section S, which rests against the diaphragm, closing the central orifice of the internal partition, the said column, at its opposite end to the said partition, having a solid base of cross section So larger than S and which bears peripheral ribs preventing the said base from coming into contact with the said central orifice. In general, the support piece will be hollow and the peripheral ribs will be located away from the said central orifice.
It is the use of a solid mobile piston which, in its downstream part, has a column which can enter the central orifice of the internal partition without blocking it off and, in its rear part, has a widened solid base extended by ribs peripheral to the column so as to prevent the said central orifice from being blocked off by the said base which makes it possible to achieve the objective of the invention. Specifically, once the reservoir chamber has been opened by the column of the mobile piston, the cold gases can leave the reservoir chamber via that part of the central orifice of the internal partition which is left uncovered by the column of the piston to enter the combustion and mixing chamber. At the same time, the widened base of the piston acts as a deflector for the hot gases which originate from the combustion of the pyrotechnic charge. These hot gases cannot enter the reservoir chamber but are made to mix with the cold gases to constitute the gaseous mixture which leaves the generator through its outlet orifices.
According to a first preferred embodiment of the invention, prior to pyrotechnic operation, the said hollow support piece and the said solid mobile piston isolate the said pyrotechnic charge from the said gas outlet orifices.
This embodiment makes it possible to ensure good protection and good preservation of the pyrotechnic charge over time.
According to a second preferred embodiment of the invention, the said support piece consists of a hollow ring crimped against the body of the generator, the said ring having a central cylindrical recess which has an internal shoulder so that it has a diameter d
1
facing the pyrotechnic charge and a diameter d
2
facing the internal partition, d
2
being greater than d
1
, the said ring being extended, facing the internal partition, by a hollow cylindrical neck, the inside diameter of which is equal to d
2
, and the outside diameter of which is smaller than the inside diameter of the tubular body.
In this case, the said solid mobile piston advantageously consists, on the one hand, of a cylindrical body which has a cylindrical shank of outside diameter d
1
, a cylindrical base of outside diameter d
3
between d
1
and d
2
and a cylindrical column of cross section s and of length l and, on the other hand, of fins of height h smaller than l which surround the column and which rest on the base of the said body, the said fins constituting the peripheral ribs.
In this embodiment, the base of the mobile piston rests on the internal shoulder exhibited by the support ring and the shank of the piston, the height of which has to be less than the stroke of the pist
Haegeman Christophe
Lebaudy Franck
Perotto Christian
Livbag SNC
Oliff & Berridg,e PLC
Rice Kenneth R.
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