FR2624398A1 - FILTRATION SYSTEM FOR INFLATORS OF AIR SAFETY CUSHIONS - Google Patents

Abstract

A method of making a filtration system for an airbag inflator 10 90, which comprises introducing a preformed unitary knitted metal yarn module 42 into the inflator 10.

Description

Filtration system for cushion inflators

  The present invention relates to filtration systems for inflators. More particularly, the present invention relates to a method of producing a

  filtration system in a tire cushion inflator

matic

  Currently, the main effort in the area of re-

  airbag research is

  reduce system costs. The high cost of previous systems is considered to be the main obstacle to their use and a major obstacle to their

public acceptance.

  Airbags are designed to absorb the impact of an occupant of a vehicle in a collision, when their head or chest hits a part of the interior passenger compartment. During the collision, a sensor mounted in the vehicle activates a gas generator. Typically, a gas generator containing about 100 g of sodium nitride is used for the conductor side. The generator can

  be actuated, either mechanically or electrically.

  In either case, the sodium nitride is ignited, which releases nitrogen gas. Nitrogen inflates the airbag and the airbag, thus inflated, prevents the occupants of the vehicle from striking the windshield, the steering wheel

management or the dashboard.

  Filters are necessary in the inflators to cool this hot gas and to extract materials from the gas.

into particles.

  Airbags have clear air holes

  bre to allow gas to escape. These vent holes allow the pressure inside the air bag to escape to dissipate the kinetic energy of the passenger. Because as little as 100 mg of sodium nitride can cause acute toxic symptoms and possibly long-term health effects, one must completely

  filter the nitrogen gas before it enters the necks

  pneumatic sins. Furthermore, hot particles

  from combustion inside the inflator may

  wind cause by combustion the appearance of a hole in the air bag, and even cause the combustion of

  this last. Consequently, these particles must also

  be filtered to prevent them from entering the

pneumatic cushion.

  Currently, we have developed cushion systems

  tires fitted with filtration systems, which do not

  risk minimal leakage of nitride residue and other particles. The method for producing these filters consists in cutting and rolling a woven fabric of metallic threads and in positioning the filter in the appropriate positions in the inflation device. This process

  filters are labor intensive

  so much and, therefore, is expensive. In the past, we had

  regarded these high labor costs as necessary

  to avoid the disastrous consequences that could result from filters that are either incorrectly

  trained, or incorrectly positioned.

  In order for the filter material to fit tightly in the inflator, it must have a certain elasticity. This

  goal is achieved in the conventional inflator filters

  using a woven fabric of metallic thread, which is cut at an angle, as appropriate to 45. This

  allows the filter to expand and contract slightly

  when placed in the inflator housing. As a result, however, a large number of wire ends protrude from the top and bottom of the filter. The ends of these wires are sometimes fixed by crimping a metal ring on each end of the filter. In addition, the retention in place of the fixed filter material depends on the friction between the wires. This combination of numerous free ends and friction holding means that a wire can relatively easily move slightly

  compared to the others, thus opening a larger hole.

  When these larger holes form a path for the

  gas evacuation, this is known as "for-

  channeling ". Extreme care should therefore be taken to ensure that the woven material filter is tightly packed to reduce

minimum this channel formation.

  The filters made from knitted materials do not have these numerous ends of threads, because they are made in the form of a long tube,

  then compressed axially to form the desired filter.

  Because each strand is individually knitted with

  other threads in intertwined loops, it is very diffi-

  that one wire moves relative to the others, and from that

  done, we effectively eliminate channel formation.

  As a result, the designer of the inflation device is much more free to obtain the porosity and thermal transfer characteristics of the inflator. It is

  thus much easier to produce a product inflator

  sant a gas having a known temperature and a power

given filtration.

  Due to the number of free ends and metal wires-

  interlaced characteristics of knitted materials, as opposed to woven materials, filters made from knitted materials are considerably more resistant than those made from woven materials, especially when the filters made from woven materials are made from material that has been cut out at an angle, exposing many more free ends. Knitted metal filters can resist pressure differences

  as high as 138 MPa for example.

  Because woven metal filters are formed by winding a flat sheet of material, there is always one position where the filter material begins and another where it ends. It is therefore difficult to seal the periphery of the filter and this can constitute a path by which the gas can escape without crossing

  the filter. It is not the same for metal filters-

  knitted spikes, because they are compressed from

of a tube of knitted material.

  Filters made of knitted material have elasticity.

  natural city which allows them to expand slightly

  during assembly without risking an alternative route

  native to the gas flow around the filter. To get

  this elasticity, standard filters must be manufactured

  made from woven materials that have been cut

from a certain angle.

  Other embodiments have been proposed for the filters of

  airbag inflators, such as threads

  very in sintered metals. Sintered metal filters have

  the unwanted characteristic that they can break.

  Filters made from knitted materials do not

  can neither fall apart nor crack in this way

  niere. The main object of the present invention is to provide

  an improved process for making filter systems

  air bag inflators

  security ticks, which allow a relative realization

  Easy to install with little risk of improper assembly.

  This production method uses a unitary filter structure, in which the filter is previously formed

  to facilitate its introduction into the inflator.

  Another object of the present invention is to provide a

  inexpensive filtration system, which does not allow

  no exhaust of nitride dust from

sodium, or other particles.

  An additional object of the present invention is to provide

  a filtration system, which allows easy adjustment-

  the degree of particle filtration and cooling

gas smoothing.

  Another object of the present invention is to provide a filtration system which makes it possible to easily adjust the degree of filtration of the particles of the gas with less

  cooling with the present gon devices, -

  flage. Another object of this invention is to provide a source of high temperature gas very well filtered to be

  used in suction inflators.

  According to a first aspect, the invention therefore provides a pro-

  assigned to the realization of a filtration system for a dispo-

  air bag inflation pressure, which consists of preforming filtration means to conform to a geometric pattern known inside

  of the inflation device, these filtration means comprise

  as a unitary knitted metal module for filtering the particulate material in the inflation gas, these filtration means reducing the temperature of the

  inflation, and to provide an inflator housing to receive

see these filtration means.

  The inflation device may include a lower casing

  laughing and an upper casing together forming a chamber,

  this casing having at least one casing opening connected

  in the outer wall of the housing, the sensor for igniting a gas generator for inflating the airbag, means for receiving the gas generator and means for directing the gas thus produced through

filtration means.

  According to a characteristic of the invention, these filtration means consist of a fabric of metal wires

  knitted with a density between about 45 and 70.

  In another proposal of the invention, it provides

  re a method for producing a filtration system for an inflation device for an airbag which consists in preforming filtration means from a knitted mesh of metal son to conform to a geometric pattern known in the art. inside the inflator, these

  filtration means comprising a single metal module

  shut up to filter the particulate material contained in the gas

  inflation, these filtration means reducing the temperature

  rator of this inflation gas, to provide a

  cylindrical inflator to receive these filtering means

  tion, this inflator housing comprising a lower housing, an upper housing fixed on the lower housing in order to

  form a chamber, at least one crankcase opening

  cording the outer and inner walls of this inflator housing, a cylindrical sensor for initiating inflation, sensor which is fixed on the inside of the lower housing and which is axially aligned with the housing, a cylindrical combustion wall axially aligned with this housing and disposed between the sensor and the housing

  lower to define an exterior chamber and a

  interior bre, this combustion wall containing at least one combustion wall opening connecting the exterior chamber and the interior chamber, a screen

  inside the combustion wall

  tion cylindrical, and to introduce these preformed filtration means inside the outer chamber so that the inflation gas must pass through these

  filtration means before exiting through the housing opening.

  The filtration means include a pre-filter which adjusts

  tightly between the combustion wall and the inner surface of the casing, this pre-filter extending only over part of the length of the outer chamber and covering the openings of the combustion wall so that the inflation gas must pass through this prefilter to exit the interior channel, and

  a final filter which is preformed to fit closely

  against the inside surface of the housing, this filter

  nal covering the crankcase openings so that the inflation gas must pass through this final filter

  to exit the inflator through the housing openings.

  In another aspect, the invention provides an improved filtration system for an airbag inflator, comprising: a housing comprising a lower housing and an upper housing having at least one housing opening connecting the exterior wall of the housing in the room; a final filter which is preformed to fit tightly against the inner surface of the housing, this final filter covering the housing opening

  so that the inflation gas must pass through

  to the final filter to exit the inflator through the

  middle of the crankcase opening, this final filter being

  made of fabric of knitted metallic threads having a den-

  sity of between about 45 and 70%, means for receiving a sensor for switching on a gas generator for

  initiate inflation; means for receiving a general

  gas rator; and means for directing the ignited gas

through the final filter. -

  This prefilter is made of fabric of tri- metallic wires.

  sides with a density between 10 and 30%.

  In another aspect, the invention also provides a system

  improved filtration system for an inflation device of a

  pneumatic safety cushion, comprising a filter

  formed by intertwined metal wires, a housing and

  means for retaining the filter inside the casing.

  The invention will be better understood on reading the description.

  detailed information, given below by way of example only-

  ment, of a preferred embodiment of the invention, in conjunction with the accompanying drawing, in which: - Figure 1 is a view of a preferred embodiment of the present invention, showing the exterior of the inflator;

  - Figure 2 is a cross-sectional view of the pre-

  invention is attached to an air bag, showing the flow of gas as it passes through the inflator; - Figure 3 is a large-scale view showing the knitted structure of the filter, before this structure is compacted to form the filter; and - Figure 4 is an enlarged view of a conventional filter material before being rolled up to form

the filter.

  In all the figures of the drawing, the identical numbers and letters of reference designate corresponding parts. Referring now to Figure 2, which shows a cross-sectional view of the inflator 10 fixed on a cushion: pneumatic 90. The inflator casing is constituted by a lower casing 30 in the form of a cup having an orifice disposed axially along its lower surface and a cap-shaped upper casing 32, these two

  crankcases screwing together to form a one-piece unit.

  The upper casing has a series of casing openings 34, arranged symmetrically with respect to the axis to allow the gas to exit the inflator and inflate a pneumatic cushion. The upper casing 32 also has

  a collar 54 for fixing the inflator.

  The casing has a combustion wall 26 which divides the interior of the inflator 10 between a combustion chamber

  interior 24 and an exterior filtration chamber 25.

  The combustion wall 26 contains a series of openings 36 arranged symmetrically around the axis to allow a uniform stream of gas to settle from the combustion chamber 24 to the filtration chamber

  25. A combustion screen 22, disposed along the surface

  inner face of the combustion wall 26, surrounds the

  gas generating material. The lower portion of the e-

  combustion wall notch has several layers.

  The filtration chamber 25 contains a prefilter 38 and a final filter 42. The prefilter covers the combustion chamber openings 36 so that all of the gas leaving the combustion chamber must pass through the prefilter. The prefilter is a knitted fabric of metallic threads, compressed to the desired shape for

  obtain a density of approximately 10 to 30%. The filter 42 covers

  vre the upper casing openings and is arranged so that the gas produced inside the inflator must pass through this filter to exit the casing 10. A set of final filter supports, comprising a lower support 44 and a support upper 46, keeps the filter in position during use. The filter 42 is a preformed unitary module, which can be quickly positioned during manufacture. This filter is a fabric of knitted multi-layer metallic threads, having a density of about 45 to 70%, which has been compressed

  from a knitted tubular structure.

  Because filters have two different functions

  in an airbag inflator, namely removing

  worm the particles and cool the gases, achieving a filter is typically dominated by one of these goals. When using knitted materials to make the filter, there is much more freedom in the design of the filter. If, for example, we want to increase the cooling for a comparable degree of filtration, we can then use larger wires and

  can make a thicker and less dense filter. If all

  However, we wish to evacuate the gases at higher temperatures, we can then use finer wires and

  make a thinner filter. When using materials

  woven rials, this freedom is considerably less due to the intrinsic weakness of the structure of the

  woven material. In addition, the need to prevent the for-

  channeling requires woven filters to be compressed to reduce the risk of a thread slipping out of

  its position and opens a larger hole.

  Since air bags are more commonly used in vehicles, one should

  try to optimize a filter for a partial inflator

  culier. This is much easier when using a filter made from a knitted fabric of metal threads compared to a filter made from a woven fabric of metal threads. The preferred material is stainless steel. However, other materials can be used, for example ceramics,

  glass fibers, graphite, er-bond with stainless steel-

  dable to form a composite material, or separately for certain applications. These additional materials are becoming increasingly important as progress is made in optimizing the inflators, in particular in conjunction with

  improved air cushion materials that

  put the use of higher temperature gases in the air bag. The desire to use

  gas at higher temperature also comes from uti-

  luction of suction systems, in which the gases from the inflator are mixed with ambient air to inflate

pneumatic cushions.

  A sensor 20 is housed inside the control chamber.

  bustion 24. The sensor has an upper case 28 and a lower casing 27. The lower casing of the sensor has an orifice 50 for connecting the sensor to the outside of the inflator in order to arm the sensor when it is mounted

on the vehicle.

  In operation, the sensor-trigger 20 detects the deceleration during a collision, if it is of sufficient severity. The sensor 20 then ignites the material

  gas generator located inside the combustion chamber

  bustion 24. A cartridge, introduced into the combustion chamber, contains the preferred gas-generating material, namely sodium nitride. Sodium nitride is stable over a wide range of temperatures but, when

2624398.

  is lit, it breaks down quickly, releasing from

large volumes of nitrogen gas.

  The nitrogen gas produced in the combustion chamber 24 passes through the openings 36 and then enters the prefilter. The pre-filter stops larger particles of dust and is also used to reduce the temperature of nitrogen gas. The nitrogen gas then circulates through the external filtration chamber 25 to arrive in the filter 42. This filter is much denser than the prefilter and stops practically all the dust of nitride and other particles contained in the nitrogen. gaseous; in addition, it cools the latter before it

  comes out through the openings 34 to inflate the tire cushion

matic.

  Figures 3 and 4 easily show the differences

  these in the filter structures. Figure 3 shows this intertwined nature of knitting, in which each thread loops and bends, alternately intertwining

  with other sons on either side of him. He re-

  realize that it is very difficult for sons to

  move and separate once they are in place.

  On the contrary, in the case of a woven fabric, the threads are essentially rectilinear and can move and separate relatively easily from each other. In the case of a knitted fabric, the density of the filter can vary from values as low as 10% to values as

  as high as 70 or 80% with no risk of the wires moving

  hundred and open channels. This is not the case for woven metal filters, which must be compressed to a density within a limited range so that the different layers of the filter, as well as

  the proximity of the adjacent wires, combine to maintain

  tie the wires in place. This possibility is special-

  important to design filters for

  air cushion flowers. As opposed to most

  share of other filter applications, the filters of a

  airbag inflator serve both to re-

  cooling and filtration. By using a knitting of metallic threads with intertwined threads, the two filtration and cooling functions can be adjusted.

  independently of each other. This is very diffi-

  ie in the case of filters produced from a woven structure. Thus, the production and mounting of an airbag inflator are notably improved thanks to the invention. For the purposes that we propose here, a woven material is a material in which the different strands of material are formed in loops, are knotted or

  are twisted together in such a way that the wires already

  cents cannot slide relative to each other.

  The driver side inflator has been chosen for illus-

  to teach the invention. Naturally, this filtration system can be used in passenger side inflators, similar, but larger than the driver side inflator shown here, or in the more conventional elongated cylindrical tubular inflator, in

  which the cylinder axis is arranged obliquely with respect to

* port alongside the vehicle.

  Although the invention has been particularly shown

  and described with reference to certain preferred embodiments

  rees of it, it is understood that variations of forms can be made by those skilled in the art,

  without departing from the spirit and scope of the invention.

Claims (9)

Claims   1. - Method for producing a filtration system   for an inflation device (10) for a pneumatic cushion   security tick (90), characterized in that it consists - preforming filtration means to conform to a known geometric pattern inside the inflator (10), these filtration means comprising a knitted unitary metal module for filtering the particulate material contained in the inflation gas, these filtration means reducing the temperature of the inflation gas; and - provide an inflator housing to receive these means filtration.   2. - Method according to claim 1, characterized in that the inflator (10) comprises: - a lower casing (30) and an upper casing (32) which   constitute a chamber, this casing having at least one or   housing green (34) connecting the outer wall of the housing to the chamber, - a sensor (20) for igniting a gas generator for inflating the airbag, - means for receiving the gas generator, and - means for directing the gas produced through the 30. means of filtration.   3. - Method according to claim 1, characterized in that the filtration means further comprise a fabric of knitted metal son having a density included between 45 and 70%.   4. - Method for producing a filtration system for an inflation device for an air safety cushion, characterized in that it consists in: - preforming filtration means from a knitted mesh of metallic threads to conform to a known geometric pattern inside the inflator (10), these   filtration means comprising a single metal module   shut up to filter the material - into particles contained in the inflation gas, these filtration means further reducing the temperature of the inflation gas, - provide a cylindrical inflator casing to receive these filtration means, this inflator casing comprising a lower casing (30), an upper casing (32) fixed on the lower casing to form a chamber, at least one casing opening (34) connecting the outer wall and the inner wall of the inflator casing, a cylindrical sensor (20) to trigger inflation, sensor which   is fixed on the inside of the lower casing (30) and axially   In line with it, a cylindrical combustion wall   plate (26) axially aligned with the housing and disposed between the sensor (20) and the lower housing (30) to   define an exterior chamber (25) and an interior chamber   lower (24), the combustion wall containing at least one   combustion opening (36) connecting the external chamber   the inner room and a combustion screen   (22) lining the inside of the cylinder combustion wall drique; and   - introduce these preformed filtration means inside   laughter of the outer chamber so that the inflation gas must pass through these filtration means   before exiting through the housing opening (34).   5. - Method according to claim 4, characterized in that the filtration means comprise: - a prefilter (38) which fits tightly between the combustion wall (26) and the inner surface of the casing, this prefilter not extending that over part of the length of the outer chamber (25) and covering the combustion wall openings (34) so that the inflation gas must pass through this prefilter to exit the inner chamber (24); and   - A final filter (42) which is preformed to be housed narrowly   firmly against the inner surface of the housing, this final filter covering the housing openings (34) in such a way   so the inflation gas has to pass through this wire-   be final to exit the inflator through the openings of casing (34).   6. - Method according to claim 4, characterized in that the filtration means further comprise a knitted fabric   metal wires having a density of between approx. ron 45 and about 70%.   7. - Improved filtration system for an airbag inflation device, characterized in that it comprises: i) a casing comprising a lower casing (30) and a   upper casing (32) having at least one car opening   ter (34) connecting the outer wall of the housing to the chamber, ii) a final filter (42), which is preformed to fit tightly against the interior surface of the housing, this final filter covering the housing opening (34) such that the inflation gas must pass through   this final filter to exit the inflator through this opening   crankcase structure (34), this final filter being produced from a fabric of knitted metallic threads having a density of between approximately 45 and approximately 70%, iii) means for receiving a sensor (20) for igniting a generator of gas to initiate inflation, iv) means for receiving a gas generator, and   v) means for directing the ignited gas through the wire be final.   8. - filtration system according to claim 7, ca-   characterized in that it contains a prefilter which is produced from a fabric of knitted metallic threads having a   density between about 10 and about 30%.   9. - Improved filtration system for a device   for inflating an airbag, characteristic   in that it includes a filter made from interlaced metal wires, a housing and means for   retain the filter inside the housing.