Thin-wall expanded metal filter

Abstract

A filter (21) comprising a wound expanded metal strip (13) is provided. The expanded metal strip (13) has inlet regions (e.g., layer 1 and layer 2), nozzle regions (e.g., layer 3), and optionally outlet regions (e.g., layer 4 and layer 5). The filter may also include an optional woven wire mesh layer (e.g., layer 6). The filter has a thin wall (39) such that, in an embodiment, the ratio of the thickness (t) of the wall to the outer diameter (OD) of the filter is less than or equal to 0.07, whereby the filter may be lighter and / or have a smaller envelope size than existing expanded metal filters. In an embodiment, a filter (21) may be used to filter and cool a flow of gas generated by rapid combustion of a solid propellant (26) of an airbag inflator (157).

Description

TECHNICAL FIELD

[0004] The present disclosure relates to filters made at least in part of expanded metal. In certain embodiments, the filters are used in airbag inflators. BACKGROUND ART

[0006] A. Expanded Metal

[0007] Expanded metal has been found to have a variety of uses, from mats for fire extinguishing to filters for airbag inflators. Expanded metal can be made in a variety of ways. For example, expanded metal can be made by taking a sheet of metal, piercing the sheet to create a plurality of slits, and pulling the sheet in a direction perpendicular to the slits to elongate the slits and provide openings (holes) in the sheet. Another common method for making expanded metal is by punching and cold forming openings that are typically referred to as "diamonds" due to their final shape. The final length of the sheet with holes is longer than the original length, and thus the sheet is expanded, and the formed holes are also expanded.

[0008] Thus, while the details may vary depending on the specific process, expanded metal sheets are typically made by creating perforations in the sheet using a row of teeth in a punch or a drill bit. The side of the sheet facing the punch will have dimples around the perforations, while the opposite side of the sheet will have corresponding raised portions (burrs) around the perforations. In certain embodiments, the expanded metal sheet is passed through rollers to flatten the burrs.

[0009] B. Filters for Airbag Inflators

[0010] Filters for airbag inflators need to meet many stringent criteria. Such filters are used to capture a large amount of debris (slag) generated during the rapid combustion of the airbag solid propellant. The slag can damage the airbag and, if released from the airbag, can harm the occupants of the vehicle in which the airbag deploys. Additionally, slag is generally harmful to the human body. To address these issues, manufacturers of airbag inflators have established strict standards for the amount of slag that may be emitted when the airbag inflator is activated. In the United States, the conventional standard for all types of airbag assemblies is that the maximum amount of total particulate matter (total slag) reaching the airbag cushion due to the deployment of the airbag assembly is 1,000 milligrams.

[0011] To enable an airbag inflator to meet this conventional standard, its filter needs to have an efficient filtering function. However, the filter must also allow the gases generated by the combustion of the solid propellant to quickly reach the airbag and inflate it. That is, the filter must not generate an excessive level of backpressure. In addition, the filter needs to meet these conflicting criteria, namely, to effectively filter with a low backpressure while under the high forces generated by the rapid combustion of the solid propellant. In addition to these criteria, the filter also acts as a pre-diffuser for the inflator to help the expanding gases entering the airbag flow more evenly, and acts as a heat sink serving as a thermodynamic diffuser to help reduce the temperature of the gases so that these gases will not harm the airbag cushion or the person protected by the airbag cushion.

[0012] The expanded metal filter sold by the assignee of the present application under the VEM trademark and produced according to the technology of co-assigned U.S. Patent No. 10,717,032 has achieved the above performance standards and has achieved wide commercial success through its extensive adoption by manufacturers of airbag inflator assemblies. Despite this success, there has long been a need for a filter that meets the performance standards but has a smaller weight or a smaller envelope size or both a smaller weight and a smaller envelope size compared to existing VEM filters.

[0013] The challenge is to reduce its weight and / or size without sacrificing the performance of the filter. As discussed in detail below, it has been found that the weight and / or size of the filter can be reduced by using the expanded metal hole patterns discussed below and set forth in the claims. Unexpectedly, these patterns allow a significant reduction in the thickness of the walls of the filter, which in turn allows a reduction in the weight and / or its envelope size, all without sacrificing the performance of the filter when the airbag inflator deploys. In addition, these improvements can be achieved while controlling the cost of the filter, which is always an issue for mass-produced items, especially those used in the automotive field.

[0014] Although low weight and / or small size and / or thin wall thickness in relation to filters for airbag inflators are particularly valuable, these attributes of the expanded metal filters disclosed herein are generally valuable for filters made entirely or in part of expanded metal. SUMMARY OF THE INVENTION

[0016] According to a first aspect of the present disclosure, there is provided a filter comprising an expanded metal strip wound around an axis to form a plurality of layers, the expanded metal strip having a longitudinal axis and a transverse axis and comprising a plurality of holes arranged in rows oriented perpendicular to the longitudinal axis, the strip being wound along the longitudinal axis to form the filter, wherein: (I) The rolled-up filter has an inner surface with diameter ID, an outer surface with diameter OD, and a wall thickness t = 1 / 2(OD - ID); (II) Each layer in the filter: (a) includes multiple rows of holes; and (b) is characterized by: (i) The spacing between rows of holes, referred to as S 纵向 and expressed as holes / cm, (ii) The spacing between holes within a row, referred to as S 横向 and expressed as holes / cm, (iii) The opening area of each hole in the holes of the layer is referred to as OA 孔洞 and expressed as cm² / hole, (iv) The total opening area of the layer, referred to as TOA 层 and is given as a percentage by the formula: TOA 层 = 100 * S 纵向 * S 横向 * OA 孔洞 , and (v) The hole density of the layer, referred to as D 层 and expressed as holes / cm²; (III) The expanded metal strip includes an inlet zone that forms at least two layers in the rolled-up filter and a nozzle zone that forms a single layer in the rolled-up filter, with the inlet zone closer to the inner surface of the rolled-up filter than the nozzle zone; (IV) The TOA of the single layer of the nozzle zone 层 is less than the TOA of all layers of the inlet zone 层 ; (V) For each layer of the inlet zone and the nozzle zone, S 横向 is greater than or equal to 4 holes / cm (or in the range of greater than or equal to 4 holes / cm to less than or equal to 10 holes / cm, or in the range of greater than or equal to 4 holes / cm to less than or equal to 6 holes / cm); (VI) At least one layer of the inlet zone has a D greater than or equal to 64 holes / cm² (or greater than or equal to 67 holes / cm², or greater than or equal to 69 holes / cm²) 层 ; and (VII) t / OD ≤ 0.07 (or t / OD ≤ 0.072, or t / OD ≤ 0.074) [[ID=�6]]

[0017] In some embodiments, the filter of the first aspect of the present disclosure has one, more than one, or all of the following characteristics:

[0018] (1) The thickness of the expanded metal strip is less than or equal to 0.54 mm (or less than or equal to 0.57 mm, or less than or equal to 0.060 mm);

[0019] (2) Each layer in the inlet zone has a D greater than or equal to 64 holes per square centimeter (or greater than or equal to 67 holes per square centimeter, or greater than or equal to 69 holes per square centimeter) 层 ;

[0020] (3) The TOA of a single layer in the nozzle zone 层 is in the range of greater than or equal to 4% to less than or equal to 20% (or greater than or equal to 4% to less than or equal to 15%, or greater than or equal to 4% to less than or equal to 10%)

[0021] (4) The expanded metal strip further includes an outlet zone that forms at least two layers in the rolled-up filter, and the outlet zone is farther from the inner surface of the rolled-up filter than the nozzle zone, wherein: (a) For each layer in the outlet zone, S 横向 is greater than or equal to 4 holes per centimeter (or in the range of greater than or equal to 4 holes per centimeter to less than or equal to 10 holes per centimeter, or in the range of greater than or equal to 4 holes per centimeter to less than or equal to 6 holes per centimeter); (b) The TOA of a single layer in the nozzle zone 层 is less than the TOA of all layers in the outlet zone 层 ;

[0022] (5) The expanded metal strip consists of an inlet zone, a nozzle zone, and an outlet zone;

[0023] (6) The rows of holes are staggered such that the hole opening areas of adjacent layers are at different circumferential angles, where the circumferential angle is the angle of the hole center as viewed from the axis around which the filter has been rolled up;

[0024] (7) The inlet zone has an innermost layer that forms the inner surface of the filter;

[0025] (8) The filter further includes a woven metal mesh layer that forms the outer surface of the filter;

[0026] (9) The filter does not include ceramic paper; and / or

[0027] (10) The filter is exclusively used for an airbag inflator filter.

[0028] According to a second aspect of the present disclosure, there is provided an apparatus for assisting in protecting an occupant of a vehicle, the apparatus comprising: (I) a vehicle occupant inflatable protection device; and (II) An inflator that can be actuated to provide inflation fluid for inflating an inflatable vehicle occupant protection device; Wherein, the inflator includes: (A) A solid propellant; and (B) A filter according to the first aspect of the present disclosure.

[0029] In certain embodiments, the device of the second aspect of the present disclosure has one, more than one, or all of the following features:

[0030] (1) For a temperature drop of the inflation fluid from about 1700°K (in the filter cavity) to about 850°K (at the outlet of the filter housing), the cooling efficiency of the filter of the device is at least 6 degrees Celsius / gram of filter;

[0031] (2) The mass of the filter of the device is less than or equal to 160 grams (or less than 165 grams, or less than 170 grams);

[0032] (3) The solid propellant is located within the inner surface of the filter, the inflator includes a housing for the filter, and the filter and the housing can be manually separated into separate components after the rapid combustion of the solid propellant.

[0033] According to a third aspect of the present disclosure, a method of filtering and cooling a fluid is provided, the method comprising passing the fluid through a filter according to the first aspect of the present disclosure, wherein: (I) The fluid includes a gaseous component and liquid, solid, and liquid / solid particles, and the size distribution of these particles includes particles that can increase the back pressure of the filter due to blockage of the holes in the nozzle region; (II) The inlet region of the filter cools the fluid and filters out particles, including a large number of particles that can increase the back pressure of the filter; and (III) The nozzle region of the filter filters out particles and increases the velocity of the fluid.

[0034] In certain embodiments of the third aspect of the present disclosure, the fluid is an inflation fluid for inflating an inflatable vehicle occupant protection device.

[0035] According to a fourth aspect of the present disclosure, a method of filtering and cooling a fluid is provided, the method comprising passing the fluid through a filter according to the first aspect of the present disclosure, wherein: (I) In addition to the inlet region and the nozzle region of the filter, the expanded metal strip of the filter further includes an outlet region that forms at least two layers in the rolled-up filter, and the outlet region is further away from the inner surface of the rolled-up filter than the nozzle region; (II) The fluid includes gaseous components as well as liquid, solid, and liquid / solid particles, and the size distribution of these particles includes particles capable of increasing the back pressure of the filter due to blockage of the holes in the nozzle region; (III) The inlet region of the filter cools the fluid and filters out particles, including a large number of particles capable of increasing the back pressure of the filter; (IV) The nozzle region of the filter filters out particles and increases the velocity of the fluid; and (IV) The outlet region of the filter filters out particles and cools the fluid by expansion.

[0036] In certain embodiments of the fourth aspect of the present disclosure, the fluid is an inflation fluid for inflating an inflatable restraint device for a vehicle occupant.

[0037] Additional features and advantages of the techniques disclosed herein are set forth in the following detailed description, and those of ordinary skill in the art will readily appreciate or will recognize, in part, these additional features and advantages from the description or by practicing the techniques described herein. The drawings are included to provide a further understanding of the techniques and are incorporated in and constitute a part of this specification. It should be understood that the various aspects and features of the techniques disclosed in this specification and the drawings can be used alone and in any and all combinations. It should also be understood that the foregoing general description and the following detailed description are merely exemplary of the invention and are intended to provide an overview or framework for understanding the nature and characteristics of the invention as defined by the claims. Brief Description of the Drawings

[0039] Figure 1 is a schematic depiction of an airbag filter according to an embodiment of the present disclosure, where the filter is in the form of a tube having an inner surface, an outer surface, and a generally flat end section extending between the inner and outer surfaces that define a central hole or cavity. Pellets of the pyrotechnic composition are located within the holes of the filter. In this embodiment, the filter includes an outer layer of woven wire mesh or expanded metal.

[0040] Figure 2 is a schematic depiction of an airbag filter according to an embodiment of the present disclosure, where as Figure 1 in, the filter is in the form of a tube having an inner surface, an outer surface, and a generally flat end section extending between the inner and outer surfaces that define a central hole or cavity. Again, pellets of the pyrotechnic composition are located within the holes of the filter. In this case, the filter does not include an outer layer of woven wire mesh, but rather the outer layer is expanded metal.

[0041] Figure 3 is a schematic depiction of a strip for forming Figure 1 or Figure 2 the filter when to be formedFigure 1 When forming the filter of, the strip includes an expanded metal layer, while when forming the filter of Figure 2 , the strip includes an additional woven wire mesh layer.

[0042] Figure 4 is Figure 3 A schematic depiction of the longitudinal and transverse axes of the strip of.

[0043] Figure 5 is Figure 3 A schematic depiction of the strip of after being rolled up to form a filter.

[0044] Figure 6 is Figure 3 A schematic depiction of the strip of after being rolled up, showing the inner diameter (ID), outer diameter (OD), and wall thickness (t) of the filter.

[0045] Figure 7 A schematic depiction of an embodiment of equipment for manufacturing expanded metal.

[0046] Figure 8 A schematic depiction of an airbag assembly.

[0047] Figure 9 A photograph of an airbag inflator housing that can be used with the filter disclosed herein.

[0048] Figure 10 is Figure 1 A schematic depiction of the filter of after the solid propellant in the inflator burns rapidly.

[0049] Figure 11 Shows an exemplary camera configuration for strip / aperture opening area image acquisition;

[0050] Figure 12 is Figure 11 An exemplary strip image acquired with the camera configuration shown in.

[0051] Figures 13 to 17 Shows Figures 20A to 20G The aperture and percentage results of the opening area of the exemplary strip in presented in tabular and graphical formats;

[0052] Figures 18A to 18G Shows an exemplary prior art strip and representative opening area data points, showing an inlet zone and a nozzle zone without sharply decreasing values;

[0053] Figures 19A to 18G Shows another exemplary prior art strip and representative opening area data points, showing an inlet zone and a nozzle zone without sharply decreasing values;

[0054] Figures 20A to 18G Shows an exemplary strip and representative opening area data points in accordance with the teachings of the present invention, showing an inlet zone and a nozzle zone that do not have sharply decreasing values;

[0055] Figures 21A to 18G Shows another exemplary strip and representative opening area data points in accordance with the teachings of the present invention, showing an inlet zone and a nozzle zone that do not have sharply decreasing values; and

[0056] Figures 22A to 18G Shows an exemplary strip and representative opening area data points in accordance with the teachings of the present invention, showing an inlet zone and a nozzle zone that do not have sharply decreasing values.

[0057] The reference numerals used in the figures correspond to the following: 11 Metal strip before winding 13 Expanded metal strip 14 Woven metal mesh 15 Filter housing 17 Holes in the filter housing 19 Upper part of the filter housing 20 Thin gap between the used filter and the filter housing 21 Generally cylindrical filter 22 Generally cylindrical inner surface of filter 21 23 Cavity of filter 21 defined by inner surface 22 24 Generally cylindrical outer surface of filter 21 25 Generally flat end section of filter 21 26 Solid propellant 27 Residue captured by filter 21 after combustion of the solid propellant 31 Holes in the expanded metal strip 33 Longitudinal axis of strip 11 35 Transverse axis of strip 11 37 Axis of the wound-up filter 39 Filter wall 101 Metal sheet roll 103 Press 105 Punch 107 Tooth or drill bit 109 Tensile machine 111 Camera 113 Computer controller 115 Monitor 121 Roller 123 Cutter 125 Expansion metal part 155 Airbag assembly 157 Airbag inflator 159 Inflatable vehicle occupant protection device Detailed implementation mode

[0059] Figure 1 and Figure 2 is a schematic depiction of an embodiment of an expanded metal filter 21 suitable for an airbag inflator assembly. In each embodiment, the filter has an inner surface 22 defining a central hole or cavity 23, an outer surface 24, and a generally flat end section 25 extending between the inner surface 22 and the outer surface 24. The outer surfaces of the two embodiments differ in that the woven metal mesh 14 of the expanded metal strip welded to the filter forms the outer surface in the Figure 1 embodiment, while the expanded metal strip 13 itself forms the outer surface in the Figure 2 embodiment. The use of the woven metal mesh increases the circumferential strength of the filter and is advantageous in embodiments where, for example, it is desired to reduce the expansion of the filter during airbag inflator deployment.

[0060] In the assembled inflator, the holes of the filter typically accommodate a portion of the solid propellant 26 of the inflator and, in many cases, all of the solid propellant of the inflator. The solid propellant typically takes the form of compressed pellets of a pyrotechnic composition. During airbag inflator deployment, the gas that fills the airbag is generated by the solid propellant, which is most commonly based on guanidine nitrate. The propellant is typically rich in copper and other metals and can, in some cases, account for 60% or more of the overall composition. During airbag inflator deployment, the metals in the propellant liquefy and are entrained in the gas generated by the combustion of the propellant. In this very dynamic system, this phase change from solid to liquid occurs within a few tens of milliseconds.

[0061] The function of the inflator filter is to thermally diffuse and cool the hot combustion gases so that the liquid copper and other metals are transformed back into the solid phase and can thus be trapped in the filter, and only the cooled gas escapes. Automobile companies are very concerned about the amount of slag coming out of the inflator. If the total amount of residues discharged from the inflator and / or particulate matter in the air (collectively referred to as slag) is more than 1 gram, the inflator will be rejected by automobile companies because it does not meet the USCAR standards established by NHTSA and other safety automobile organizations (for protecting occupants with asthma and other people prone to health problems from exposure to particulate matter in the air). The filters produced using the technology disclosed herein, despite their thin walls, are capable of meeting the USCAR standards.

[0062] Figure 3 and Figure 4is a schematic depiction of the metal strip 11 before it is rolled up to form Figure 1 and Figure 2 the filter. In Figure 3 , the strip 11 includes an expanded metal strip 13 to which a piece of woven wire mesh 14 (the use of which is optional) has been welded. As Figure 4 schematically shown, the strip 11 has a longitudinal axis 33 and a transverse axis 35.

[0063] Figure 5 is a schematic cross-section of the filter formed by rolling up Figure 3 the strip about the longitudinal axis 33 of the strip. The axis about which the strip is rolled is identified by reference numeral 37 in Figure 5 . For purposes of illustration, the spacing between the layers has been exaggerated in Figure 5 ; the layers of the filter are in contact in an actual filter, for example, by contact of burrs on the outer surface of one layer with the inner surface of the next outer layer. Figure 6 is a schematic cross-section of the filter showing its outer diameter OD, its inner diameter ID, and its wall thickness t (t = 1 / 2(OD - ID)).

[0064] As Figure 3 shown, the strip 11 has a plurality of regions which, as Figure 5 shown, become layers 1 to 6 in the rolled-up filter. In this embodiment, layers 1 to 5 are expanded metal layers and optional layer 6 is a woven wire mesh layer.

[0065] Although the expanded metal strip 13 is shown in Figure 3 as having five regions, it should be understood that this number is for illustrative purposes only and the expanded metal strip may have more or fewer regions, with a minimum number of three regions (see below). Also, although Figure 3 shows only a single woven wire mesh region, additional woven wire mesh regions forming additional layers in the rolled-up filter may be used, where these regions have the same or different properties. A single woven wire mesh region forming a single layer in the rolled-up filter is preferred. For purposes of illustration, in Figure 3 , the expanded metal strip 13 is shown as having the same set of regions regardless of whether the optional woven wire mesh is used; it should be understood that in practice, the expanded metal strips employed in the two embodiments may differ in the number of regions used and / or the hole pattern of the regions.

[0066] Based on a large number of experimental studies, it has been found that the following parameters of the layers of the rolled-up filter are effective and in fact crucial for achieving one or more and preferably all of a thin wall thickness, low weight, and small size of the filter: (1) the opening area OA 孔洞 , expressed as square centimeters per hole; (2) the spacing S 纵向 between rows of holes, expressed as holes per centimeter; (3) the spacing S 横向 between holes within a row, expressed as holes per centimeter; (4) the hole density D 层 , expressed as holes per square centimeter; and (5) the total opening area TOA 层 , given as a percentage by the following formula: TOA 层 = 100 * S 纵向 * S 横向 * OA 孔洞 .

[0067] Since each layer of the rolled-up filter corresponds to the area of the expanded metal strip 13, these parameters also apply to the strip. The parameters S 纵向 and S 横向 are accordingly in the Figure 4 directions of the longitudinal axis 33 and the transverse axis 35. In practice, the values of the above parameters are the average values of the layers obtained by measuring the corresponding areas of the strips used to manufacture the filter. The measurement is carried out optically by passing light through the holes of the strip and analyzing the transmitted light using a camera similar to those manufactured by Teledyne or AndonStar with appropriate analysis; and the camera is positioned at 60 degrees upward from the flat plane and at a distance of 6" from the light source (see Figures 11 to 12 ). Thus, the camera counts the number of pixels of light passing through each hole, where every 0.01 pixel is equal to 0.00265458 mm. Therefore, the number of light pixels is converted to OA 孔洞 using a simple algorithm.

[0068] A more detailed explanation of the method is as follows:

[0069] Microscope

[0070] Andonstar Digital Microscope AD207

[0071] Magnification from 8X to 20X. This project typically uses 12X.

[0072] Modified to enable transmission mode.

[0073] Captured image properties

[0074] Size: 5.93 MB

[0075] Width = 1920 pixels

[0076] Height = 1080 pixels

[0077] Resolution = 300 ppi

[0078] Width = 6.4”

[0079] Height = 3.6”

[0080] Image analysis software: Image J

[0081] Set the scale using a stage micrometer

[0082] Import the image

[0083] Remove low-intensity pixels (brightness / contrast)

[0084] Threshold is set to the Image J default value

[0085] Use the Wand Tool to select 15 - 20 consecutive orifices. A 5x4 matrix is an option.

[0086] Create a mask to eliminate other orifices and noise.

[0087] Use the Analyze Particles function to automatically collect orifice data. [Area, size, perimeter]

[0088] Calculate the average value.

[0089] Excel spreadsheet

[0090] The current model combines line count (orifices per inch) data with Image J area data

[0091] The results are presented in tabular and graphical formats, as Figures 13 to 17 visible in

[0092] Turn back Figure 3 , the area forming the extended metal strip 13 forms an inlet zone identified as zone 1, a nozzle zone identified as zone 2, and an optional outlet zone identified as zone 3. The inlet zone includes at least two regions in the rolled-up filter and thus includes at least two layers, the nozzle zone consists of a single region in the rolled-up filter and thus consists of a single layer, and the outlet zone includes at least two regions in the rolled-up filter and thus includes at least two layers in use.

[0093] In order to achieve some and preferably all of the thin wall thickness, low weight, and small size of the filter, it has been found that: (1) the TOA of the single region (layer) of the nozzle zone 层 needs to be less than the TOA of all regions (layers) of the inlet zone层 ; (2) For each region (layer) of the inlet zone and the nozzle zone, S 横向 needs to be greater than or equal to 4 holes / cm; and for at least one region (layer) of the inlet zone, D 层 needs to be greater than or equal to 67 holes / cm².

[0094] Filters having these characteristics can meet the demanding performance criteria required for filters used in airbag inflators, while having at least one and preferably all of the following properties not previously achieved in the art: (1) a ratio of wall thickness t to OD less than or equal to 0.07; (2) a ratio of wall volume to envelope volume less than or equal to 0.30 (or less than or equal to 0.32, or less than or equal to 0.36); and / or (3) a ratio of envelope volume to internal volume less than or equal to 1.29 (or less than or equal to 1.30, or less than or equal to 1.32, or less than or equal to 1.35), where the envelope volume (EV) of a cylindrical filter is equal to 1 / 4πh OD 2 , whose internal volume (IV) is equal to 1 / 4πh ID 2 , and whose wall volume (WV) is equal to 1 / 4πh(OD 2 - ID 2 ), where h is the height of the filter. The t / OD ratio is a measure of the thinness of the filter wall; the WV / EV ratio is a measure of the weight of the filter, where for a given material forming the filter wall at a given bulk density, a smaller ratio corresponds to a lower weight; and the EV / IV ratio is a measure of the size of the filter, where for a given amount of solid propellant contained in the filter at a given bulk density, a smaller ratio corresponds to a smaller size.

[0095] Examples 1 - 7 herein list non - limiting examples of strip formulations according to the present disclosure and their properties (including their t / OD, WV / EV, and EV / IV values). Filters having formulations of the type exemplified in Examples 1 - 7 can meet the performance criteria required for filters to be used in airbag inflators.

[0096] For expanded metal made of steel and having a substrate thickness of 0.267 mm, and for woven wire mesh that, when in use, has a 7x7 mm square weave per CM mesh and is made of wire having a thickness of approximately 0.81 mm. Filters of the type having an OD of 55 mm disclosed in Examples 1 - 7 will have a weight in the range of 1.3 g / mm HT to 1.4 g / mm HT to 1.6 g / mm HT to 1.8 g / mm HT. As will be apparent to those skilled in the art, expanded metal strips having different compositions and thicknesses, as well as woven wire meshes having different meshes and made of wires having different compositions and thicknesses, can be used in the practice of the present disclosure.

[0097] Example

[0098] Without in any way limiting the scope of the present disclosure, the present disclosure is further illustrated by the following examples.

[0099] Example 1

[0100] This example shows a filter that, in order from its ID to its OD, includes: an expanded metal inlet zone (zone 1) forming 4 layers of the rolled-up filter, an expanded metal nozzle zone (zone 2) forming 1 layer in the rolled-up filter, an expanded metal outlet zone (zone 3) forming 2 layers in the rolled-up filter, and a wire mesh layer forming the OD of the rolled-up filter. These three expanded metal zones are made of steel stock having a thickness of 0.27 mm and have the following formulations: Inlet zone (zone 1) Nozzle zone (zone 2) Outlet zone (zone 3)

[0101] The rolled-up filter has the following properties: Filter OD (cm) 55.3 Filter ID (cm) 50.0 Filter wall thickness (t; cm) 2.65 Filter height (h; cm) 40.0 <![CDATA[Internal volume of the filter (IV; cm 3 )]]> 78500 <![CDATA[Filter envelope volume (EV; cm 3 )]]> 96024 <![CDATA[Filter wall volume (WV; cm 3 )]]> 17524 t / OD ratio 0.05 WV / EV ratio 0.18 EV / IV ratio 1.22

[0102] When tested, it was found that the filter meets the performance criteria required for use of a filter in an airbag inflator. The filter is suitable for all types of airbag inflator assemblies.

[0103] Example 2

[0104] This example shows a filter that, in order from its ID to its OD, includes: an expanded metal inlet zone (zone 1) that forms 5 layers of the rolled-up filter, an expanded metal nozzle zone (zone 2) that forms 1 layer in the rolled-up filter, an expanded metal outlet zone (zone 3) that forms 1 layer in the rolled-up filter, and a wire mesh layer that forms the OD of the rolled-up filter. These three expanded metal zones are made of steel stock with a thickness of 0.27 mm and have the following formulation: Inlet zone (zone 1) Nozzle zone (zone 2) Outlet zone (zone 3)

[0105] The rolled-up filter has the following properties: Filter OD (cm) 65.0 Filter ID (cm) 56.4 Filter wall thickness (t; cm) 4.30 Filter height (h; cm) 37.0 <![CDATA[Internal volume of the filter (IV; cm 3 )]]> 92391 <![CDATA[Filter envelope volume (EV; cm 3 )]]> 122715 <![CDATA[Filter wall volume (WV; cm 3 )]]> 30324 t / OD ratio 0.07 WV / EV ratio 0.25 EV / IV ratio 1.33

[0106] When tested, it was found that the filter meets the performance criteria required for use of a filter in an airbag inflator. The filter is suitable for all types of airbag inflator assemblies.

[0107] Example 3

[0108] This example shows a filter that, in order from its ID to its OD, includes: an expanded metal inlet zone (zone 1) that forms 4 layers of the rolled-up filter, an expanded metal nozzle zone (zone 2) that forms 1 layer in the rolled-up filter, an expanded metal outlet zone (zone 3) that forms 2 layers in the rolled-up filter, and a wire mesh layer that forms the OD of the rolled-up filter. These three expanded metal zones are made of steel stock with a thickness of 0.27 mm and have the following formulation: Inlet zone (zone 1) Nozzle zone (zone 2) Outlet zone (zone 3)

[0109] The rolled-up filter has the following properties: Filter OD (cm) 57.0 [[ID= 50.7 ​ 3.15 ​ 38.0 <![CDATA[Internal volume of the filter (IV; cm 3 )]]> 76678 <![CDATA[Filter envelope volume (EV; cm 3 )]]> 96918 <![CDATA[Filter wall volume (WV; cm 3 )]]> 20240 ​ 0.06 ​ 0.21 ​ 1.26

[0110] When tested, it was found that the filter meets the performance criteria required for use of a filter in an airbag inflator. The filter is suitable for all types of airbag inflator assemblies.

[0111] Example 4

[0112] This example shows a filter that, in order from its ID to its OD, includes: an expanded metal inlet zone (zone 1) that forms 4 layers of the rolled-up filter, an expanded metal nozzle zone (zone 2) that forms 1 layer in the rolled-up filter, an expanded metal outlet zone (zone 3) that forms 2 layers in the rolled-up filter, and a wire mesh layer that forms the OD of the rolled-up filter. These three expanded metal zones are made of steel stock with a thickness of 0.27 mm and have the following formulation: Inlet zone (zone 1) Nozzle zone (zone 2) Outlet zone (zone 3)

[0113] The rolled-up filter has the following properties: ​ 49.0 ​ 42.6 ​ 3.20 ​ 25.0 <![CDATA[Internal volume of the filter (IV; cm 3 )]]> 35615 <![CDATA[Filter envelope volume (EV; cm 3 )]]> 47120 <![CDATA[Filter wall volume (WV; cm 3 )]]> 11505 ​ 0.07 ​ 0.24 ​ 1.32

[0114] When tested, it was found that the filter meets the performance criteria required for use of a filter in an airbag inflator. The filter is suitable for all types of airbag inflator assemblies.

[0115] Example 5

[0116] This example shows a filter that, in order from its ID to its OD, includes: an expanded metal inlet zone (zone 1) that forms 4 layers of the rolled-up filter, an expanded metal nozzle zone (zone 2) that forms 1 layer in the rolled-up filter, an expanded metal outlet zone (zone 3) that forms 1 layer in the rolled-up filter, and a wire mesh layer that forms the OD of the rolled-up filter. These three expanded metal zones are made of steel stock with a thickness of 0.27 mm and have the following formulation: Inlet zone (zone 1) Nozzle zone (zone 2) Outlet zone (zone 3)

[0117] The rolled-up filter has the following properties: ​ 57.0 ​ 52.0 ​ 2.50 ​ 30.0 <![CDATA[Internal volume of the filter (IV; cm 3 )]]> 63679 <![CDATA[Filter envelope volume (EV; cm 3 )]]> 76514 <![CDATA[Filter wall volume (WV; cm 3 )]]> 12835 ​ 0.04 ​ 0.17 ​ 1.20

[0118] During testing, it was found that the filter met the performance criteria required for use in an airbag inflator. The filter is suitable for all types of airbag inflator assemblies.

[0119] Example 6

[0120] This example shows a filter that, in order from its ID to its OD, includes: an expanded metal inlet zone (zone 1) forming 4 layers of the rolled-up filter, an expanded metal nozzle zone (zone 2) forming 1 layer in the rolled-up filter, an expanded metal outlet zone (zone 3) forming 1 layer in the rolled-up filter, and a wire mesh layer forming the OD of the rolled-up filter. These three expanded metal zones are made of steel stock with a thickness of 0.27 mm and have the following formulations: Inlet zone (zone 1) Nozzle zone (zone 2) Outlet zone (zone 3)

[0121] The rolled-up filter has the following properties: ​ 46.0 ​ 41.0 ​ 2.50 ​ 32.0 <![CDATA[Internal volume of the filter (IV; cm 3 )]]> 42227 <![CDATA[Filter envelope volume (EV; cm 3 )]]> 53154 <![CDATA[Filter wall volume (WV; cm 3 )]]> 10927 ​ 0.05 ​ 0.21 ​ 1.26

[0122] During testing, it was found that the filter met the performance criteria required for use in an airbag inflator. The filter is suitable for all types of airbag inflator assemblies.

[0123] Example 7

[0124] This example shows a filter that, in order from its ID to its OD, includes: an expanded metal inlet zone (zone 1) forming 2 layers of the rolled-up filter, an expanded metal nozzle zone (zone 2) forming 1 layer in the rolled-up filter, and a wire mesh layer forming the OD of the rolled-up filter. These two expanded metal zones are made of steel stock with a thickness of 0.27 mm and have the following formulations: Inlet zone (zone 1) Nozzle zone (zone 2)

[0125] The rolled-up filter has the following properties: ​ 52.5 ​ 48.5 ​ 2.00 ​ 28.0 <![CDATA[Internal volume of the filter (IV; cm 3 )]]> 51702 <![CDATA[Filter envelope volume (EV; cm 3 )]]> 60582 <![CDATA[Filter wall volume (WV; cm 3 )]]> 8880 ​ 0.04 ​ 0.15 ​ 1.17

[0126] During testing, it was found that the filter met the performance criteria required for use in an airbag inflator. The filter is suitable for all types of airbag inflator assemblies.

[0127] Now referring to ​ , the manufacture of the expanded metal strip according to certain aspects of the present disclosure begins with the winding of a metal sheet 101. For filters for airbag inflators, stainless steel such as SS304, 309, 310, 409, 410, or 430 can be used. Carbon steels C1006 to C1008 are generally preferred for various applications. Depending on the environment in which the expanded metal is used, metal compositions available in sheet form can be used. In an embodiment, the thickness of the sheet metal for producing the expanded metal is less than or equal to 0.25 mm (or less than or equal to 0.27 mm, or less than or equal to 0.28 mm).

[0128] For embodiments in which the filter has an outer layer composed of a woven metal mesh, the wires forming the mesh can have a composition similar to those listed above for the expanded metal sheet. In some embodiments, the expanded metal and the wire mesh will have the same composition, and in other embodiments, the two components will have different compositions. The woven wire mesh can have the following characteristics: a mesh density of 7x7 (or 9x9, or a hybrid 7x9) and a wire thickness of 0.43 mm (or 0.48 mm, or 0.53 mm). The woven metal mesh layer can provide an air flow inflation chamber outside the expanded metal layer. Since the wire meshes are woven over and under each other, they provide a mechanical benefit: they will not collapse even under extreme load conditions. Thus, even if the filter loses all its hoop strength and presses against the metal housing of the inflator or the adhesive seal foil, the mesh will allow gas to flow to the outside of the filter.

[0129] Returning to ​ , first the sheet is fed into a press 103, in which a punch 105 having a plurality of teeth or drills 107 moves into the sheet such that the teeth perforate the sheet, and then the punch is removed, as in a stamping operation. The geometry of the drills (preferably identical to each other) preferably causes slits to be formed in the sheet. Depending on the geometry of the drills, the penetration depth of the drills will determine the length of the slits formed; the deeper the penetration, the longer the slits, and thus the larger the openings in the final structure after stretching. Although a single punch is shown, multiple punches can be used to provide different perforation spacings, geometries, and / or depths. For an airbag inflator filter, the size of the openings is based on the specifications of the airbag manufacturer for the opening area of the sheet, the porosity of the sheet, or other parameters required for the filter.

[0130] Preferably, the sheet is advanced by a servo motor (not shown) or other mechanism, whereby the longitudinal advancement of the sheet can be precisely controlled. The advancement of the sheet preferably occurs in discontinuous steps such that the sheet is stationary during punching. Although not preferred, toothed rollers can be used in a continuously moving sheet.

[0131] Then the perforated sheet produced in the press is fed to a stretcher 109, in which differential rollers stretch the perforated sheet in the axial direction (i.e., along the traveling direction) such that the slits open into diamond-shaped holes. (Of course, a hexagonal drill bit can be used to make hexagonal openings, or other drill bit geometries can be used, but the slits forming diamonds are the common shape.)

[0132] Although slitting and stretching can be carried out as separate operations, when a fine pattern is to be formed, it is generally preferred to produce expanded metal sheets by slitting and stretching in the same action with the same teeth. During this operation, the material is suspended above a flat bottom blade, and the angled upper teeth or drill bits slit the sheet and then continue into the sheet. The sheet bends downward, and the angle formed due to this bending in relation to the teeth causes a stretching movement of the sheet. Thus, the degree of stretching of the sheet depends more or less on the depth of penetration of the teeth. The amount of stretching achieved in this way typically ranges from 20% to 25% and can be as high as 37%. Compared with the slitting and stretching method, the one-step method produces perforations that are more triangular in shape than diamond-shaped. Like the separate slitting and stretching methods, the one-step method forms holes by: (i) forming slits in the metal sheet, and (ii) stretching the slits in the direction of the longitudinal axis of the metal, but in one step rather than two steps.

[0133] Once the expanded metal sheet is formed, it can be flattened by, for example, one or a pair of rollers 121. If desired, the expanded metal sheet can be passed through multiple pairs of rollers to achieve the desired degree of flatness. A cutter (such as the cutter 123 shown in ​ can be used to cut the expanded metal sheet into pieces 125 of a desired shape for further processing. Further processing can include winding into a generally cylindrical shape, where spot welding is used at the leading and trailing edges of the strip to hold the strip in its wound configuration. Further processing can also include welding the expanded metal strip to a section of a woven metal mesh (when used) before winding and spot welding at the leading and trailing edges.

[0134] A video control system can be used to control the manufacture of expanded metal strips. The video control system includes: at least one camera 111, which is connected to a computer controller 113 running software; and an optional monitor 115, which is used to check the area of holes or openings and thereby determine whether the perforations in the sheet are within specifications (after the parameters are input into the controller). The software of the controller checks the size and / or shape (geometry) of the openings to determine whether each opening or the area of the openings (actual or estimated or calculated) is within specifications. Additional cameras (not shown) can be placed between the punch and the stretcher to determine whether the initial punching is within specifications, and additional cameras can be placed after the leveling rolls to determine whether the desired level of leveling has been achieved. The video control system optically inspects the expanded metal sheet product and determines whether the product is within specifications. To change the forward and return processes or change the specifications, the longitudinal pitch of the perforations can be changed by adjusting the servo motor (via the computer controller) to change the forward movement of the sheet. The stretcher can also be adjusted to increase or decrease the amount of stretching of the perforated sheet.

[0135] In an embodiment, the expanded metal strip is a variable expanded metal (VEM) strip according to commonly assigned U.S. Patent No. 10,717,032, the content of which is incorporated herein by reference in its entirety. Preferably, the filter only includes the expanded metal strip and, when in use, includes an attached woven wire mesh layer and does not include one or more other material layers or sections, such as metal screens, ceramic fabrics, etc. The filters of Table 1 are of this type: in those embodiments where a woven wire mesh is used, the only components of the filter are the expanded metal and the woven wire mesh. However, additional materials can be included in the filter if desired.

[0136] Once completed, the filter can be installed in a housing having a plurality of holes that allow the gas generated by the combustion of the solid propellant of the inflator to leave the housing and inflate an airbag fixed around the outside of the housing. ​ is a schematic view showing the general construction of an airbag assembly 155 including an inflator 157, the inflator including a filter that houses a solid propellant that inflates the airbag or, more generally, an inflatable vehicle occupant protection device 159 when burned.

[0137] ​A photograph of an embodiment of the housing 15 that can be used with the filters disclosed herein. The housing includes an upper portion 19 that includes apertures 17 that allow inflation gas to enter the airbag after passing through the filter. It has surprisingly been found that, unlike expanded metal filters of the prior art, the filters disclosed herein, and in particular filters having an outer layer formed of a woven metal mesh, are so robust that they can be easily removed (manually separated) from their housing even after experiencing the high forces associated with the rapid combustion of the solid propellant of the inflator. In many cases, the filter will simply fall out of its housing when the housing is inverted.

[0138] ​ This feature is illustrated. As shown in this figure, even after the rapid combustion of the solid propellant, a thin gap 20 remains between the woven metal mesh 14 and the upper portion 19 of the filter housing, which allows the used filter to be easily removed from the housing. This ease of removability is particularly surprising given the fact that the walls of the filters disclosed herein are thin, which would suggest that the forces generated by the rapid combustion of the solid propellant should result in more deformation and thus more adhesion to the filter housing, rather than less adhesion or, in many cases, substantially no adhesion to the housing.

[0139] Given the fact that expanded metal can be made from thin feedstock materials having low tensile strength, the robustness of the filters disclosed herein is particularly unexpected. It was previously thought that such feedstock materials would not be suitable for use in filters and, in particular, not in filters for airbag inflators. Although not wishing to be bound by any particular theory of operation, it is believed that the thermodynamic and gas flow properties of the filter, obtained through the structure of the inlet zone, nozzle zone, and outlet zone of the filter, enable the use of such materials, with the structure of the inlet zone and nozzle zone being the most important.

[0140] Regarding thermodynamics, by making the TOA of a single layer of the nozzle zone 层 less than the TOA of all layers of the inlet zone 层 , the overall opening area shape of the inlet of the filter is inwardly funnel-shaped. This inward funnel shape promotes the thermodynamic cooling of the gas passing through the filter, thereby reducing the need for a high level of heat transfer of the gas to the filter mass. This in turn allows the filter to have a smaller mass (smaller weight) while still achieving the high level of cooling required for a filter for an airbag inflator. The ability to achieve a high level of cooling with a reduced filter mass allows the expanded metal to be made from thinner feedstock. When using the outlet zone, by making the TOA of all its layers 层 greater than the TOA of a single layer of the nozzle zone 层and has an outwardly funnel-shaped configuration that further promotes thermodynamic cooling. This combination of inlet zone / nozzle zone / outlet zone produces an overall TOA that starts large (inlet zone), constricts to small (nozzle zone), and then expands to large (outlet zone), which is particularly effective in achieving thermodynamic cooling and thereby reduces the need for heavy (high mass) filters. 层 The configuration of the inlet zone, nozzle zone, and outlet zone (when used) of the filter also allows the filter to have a low level of back pressure. In each of these zones, the holes are arranged such that S

[0141] is greater than or equal to 4 holes / cm. Moreover, at least one layer of the inlet zone has a D 横向 greater than or equal to 67 holes / cm². This high D 层 value results in improved capture of slag produced by the rapid combustion of the solid propellant of the inflator, as well as more efficient cooling. Further, the larger TOA of the inlet zone 层 means that the inlet zone preferentially captures large particles in the gas stream, which, if passed through to the nozzle zone, could clog the zone and thereby increase the back pressure of the filter. Through the combination of these structural features, the gas flow through the filter is promoted, thereby reducing the back pressure of the filter. This reduced back pressure in turn reduces the force that the filter must withstand during the rapid combustion of the solid propellant, thereby allowing the filter to be constructed of a weaker material. 层 Another measure defining the improved configuration of the thin-walled filter of the present invention is by comparing the TOA of consecutive layers of these zones, where there is an inlet zone (zone 1), a nozzle zone (zone 2), and an outlet zone (zone 3). A key aspect of designing the consecutive layers of these zones is that the multiple layers in the inlet zone leading to the nozzle zone have a monotonically decreasing opening area (OAa). The relationship between the layers and the zones is best described below, where:

[0142] An exemplary filter includes

[0143] an expanded metal strip wound around an axis to form multiple layers, the expanded metal strip having a longitudinal axis and a transverse axis and including a plurality of holes arranged in rows oriented perpendicular to the longitudinal axis, the strip being wound along the longitudinal axis to form the filter, where:

[0144] (I) the wound filter has an inner surface and an outer surface;

[0145] (II) each layer of the filter includes a plurality of holes having an average opening area OA;

[0146] (III) the average opening area OA of the holes in the layers of the filter satisfies the following relationship:

[0147] (III) The expanded metal strip includes an inlet region that forms multiple layers in the rolled-up filter and a nozzle region that forms a single layer in the rolled-up filter. The inlet region is adjacent to the nozzle region, where the inlet region is closer to the inner surface of the rolled-up filter than the nozzle region;

[0148] (IV) The overall area (OA) of the single layer of the nozzle region is less than the OA of all layers of the inlet region; and

[0149] (V) The multiple layers of the inlet region include a set of at least three adjacent layers, characterized in that:

[0150] (a) The OA of the set decreases monotonically from the layer closest to the inner surface to the layer closest to the outer surface; and

[0151] (b) The linear fit of the OA of the set has an R-squared value of at least 0.80.

[0152] The filter is further characterized in that the magnitude of the slope of the linear fit is at least 0.04 square millimeters per layer.

[0153] The filter is further characterized in that the inner surface of the rolled-up filter has an average diameter ID, the outer surface has an average diameter OD, and the filter has an average wall thickness t given by the following formula:

[0154] t = 1 / 2(OD - ID),

[0155] where:

[0156] t / OD ≤ 0.07.

[0157] Another exemplary filter includes

[0158] an expanded metal strip wound around an axis to form multiple layers. The expanded metal strip has a longitudinal axis and a transverse axis and includes a plurality of holes arranged in rows oriented perpendicular to the longitudinal axis. The strip is wound along the longitudinal axis to form the filter, where:

[0159] (I) The rolled-up filter has an inner surface and an outer surface;

[0160] (II) Each layer of the filter includes a plurality of holes having an average longitudinal dimension LD;

[0161] (III) The expanded metal strip includes an inlet region that forms multiple layers in the rolled-up filter and a nozzle region that forms a single layer in the rolled-up filter. The inlet region is adjacent to the nozzle region, where the inlet region is closer to the inner surface of the rolled-up filter than the nozzle region;

[0162] (IV) The LD of the single layer of the nozzle region is less than the LD of all the layers of the inlet region; and

[0163] (V) The plurality of layers of the inlet region includes a set of at least three adjacent layers, characterized in that:

[0164] (a) The LD of the set decreases monotonically from the layer closest to the inner surface to the layer closest to the outer surface; and

[0165] (b) The linear fit of the LD of the set has an R-squared value of at least 0.8.

[0166] The filter is further characterized in that the magnitude of the slope of the linear fit is at least 0.04 millimeters per layer.

[0167] The filter is further characterized in that the inner surface of the rolled-up filter has an average diameter ID, the outer surface has an average diameter OD, and the filter has an average wall thickness t given by:

[0168] t = 1 / 2(OD - ID),

[0169] where:

[0170] t / OD ≤ 0.07.

[0171] Yet another exemplary filter includes

[0172] an expanded metal strip wound around an axis to form a plurality of layers, the expanded metal strip having a longitudinal axis and a transverse axis and including a plurality of holes arranged in rows oriented perpendicular to the longitudinal axis, the strip being wound along the longitudinal axis to form the filter, wherein:

[0173] (I) The rolled-up filter has an inner surface and an outer surface;

[0174] (II) Each layer of the filter includes a plurality of holes having an average transverse-to-longitudinal aspect ratio AR;

[0175] (III) The expanded metal strip includes an inlet region that forms a plurality of layers in the rolled-up filter and a nozzle region that forms a single layer in the rolled-up filter, the inlet region being adjacent to the nozzle region, wherein the inlet region is closer to the inner surface of the rolled-up filter than the nozzle region;

[0176] (IV) The AR of the single layer of the nozzle region is greater than the AR of all the layers of the inlet region; and

[0177] (V) The plurality of layers of the inlet zone includes a set of at least three adjacent layers, characterized in that:

[0178] (a) The AR of the set increases monotonically from the layer closest to the inner surface to the layer closest to the outer surface; and

[0179] (b) The linear fit of the AR of the set has an R-squared value of at least 0.8.

[0180] The filter is further characterized in that the magnitude of the slope of the linear fit is at least 0.04 per layer.

[0181] The filter is characterized in that the inner surface of the rolled-up filter has an average diameter ID, the outer surface has an average diameter OD, and the filter has an average wall thickness t given by:

[0182] t = 1 / 2(OD - ID),

[0183] where:

[0184] t / OD ≤ 0.07.

[0185] Yet another filter comprises

[0186] an expanded metal strip wound around an axis to form a plurality of layers, the expanded metal strip having a longitudinal axis and a transverse axis and comprising a plurality of holes arranged in rows oriented perpendicular to the longitudinal axis, the strip being wound along the longitudinal axis to form the filter, wherein:

[0187] (I) The rolled-up filter has an inner surface and an outer surface;

[0188] (II) Each layer of the filter has an average percentage open area POA;

[0189] (III) The expanded metal strip includes an inlet zone forming at least three layers in the rolled-up filter and a nozzle zone forming a single layer in the rolled-up filter, the inlet zone being adjacent to the nozzle zone, wherein the inlet zone is closer to the inner surface of the rolled-up filter than the nozzle zone;

[0190] (IV) The POA of the single layer of the nozzle zone is less than the POA of all layers of the inlet zone; and

[0191] (V) The plurality of layers of the inlet zone includes a set of at least three adjacent layers, characterized in that:

[0192] (a) The linear fit of the POA of the set has an R-squared value of at least 0.85.

[0193] The filter is further characterized in that the magnitude of the slope of the linear fit is at least five percent per layer.

[0194] The filter is further characterized in that the inner surface of the rolled-up filter has an average diameter ID, the outer surface has an average diameter OD, and the filter has an average wall thickness t given by:

[0195] t = 1 / 2(OD - ID),

[0196] where:

[0197] t / OD ≤ 0.07.

[0198] In certain embodiments, the filters disclosed herein can be up to 48% lighter than traditional airbag filters while cooling and cleaning more efficiently and enabling more canister performance output. For example, compared to traditional expanded metal filters, the cooling efficiency can increase by up to 40% per gram of filter weight, meaning more moles of gas can be produced at the same or lower outlet gas temperature. With the filters disclosed herein, manufacturers of airbag inflators can build smaller envelope inflators at lower cost, not only because of the filter weight savings, but also because the entire inflator (including the steel housing of the inflator) can be made smaller. In some cases, the amount of solid propellant required to produce the airbag inflation gas can be reduced. Compared to traditional filters, the wall thickness of the filter can be 50% or more less than that of traditional airbag filters while achieving the same or better cooling efficiency.

[0199] Based on the foregoing disclosure, various modifications that do not depart from the scope and spirit of the present invention will be apparent to those of ordinary skill in the art. For example, although the filters have been described in the context of airbag inflators, they can also be used in a variety of other applications. The appended claims are intended to cover the specific embodiments set forth herein as well as modifications, variations, and equivalents of these embodiments.

Claims

1. A filter, the filter comprising an expanded metal strip wound around an axis to form a plurality of layers, the expanded metal strip having a longitudinal axis and a transverse axis and comprising a plurality of holes arranged in rows oriented perpendicular to the longitudinal axis, the strip being wound along the longitudinal axis to form the filter, wherein: (I) The wound filter has an inner surface and an outer surface; (II) Each layer of the filter comprises a plurality of holes having an average opening area, i.e., OA; (III) The expanded metal strip comprises an inlet region that forms a plurality of layers in the wound filter and a nozzle region that forms a single layer in the wound filter, the inlet region being adjacent to the nozzle region, wherein the inlet region is closer to the inner surface of the wound filter than the nozzle region; (IV) The OA of the single layer of the nozzle region is less than the OA of all layers of the inlet region; and (V) The plurality of layers of the inlet region comprises a set of at least three adjacent layers, characterized in that: (a) The OA of the set decreases monotonically from the layer closest to the inner surface to the layer closest to the outer surface; and (b) The linear fit to the OA of the set has an R-squared value of at least 0.

80.

2. The filter according to claim 1, wherein, The magnitude of the slope of the linear fit is at least 0.04 square millimeters per layer.

3. The filter according to claim 1, wherein, The inner surface of the wound filter has an average diameter, i.e., ID, the outer surface has an average diameter, i.e., OD, and the filter has an average wall thickness t given by the following formula: t = 1 / 2(OD-ID), Where: t / OD ≤ 0.

07.

4. A filter, the filter comprising an expanded metal strip wound around an axis to form a plurality of layers, the expanded metal strip having a longitudinal axis and a transverse axis and comprising a plurality of holes arranged in rows oriented perpendicular to the longitudinal axis, the strip being wound along the longitudinal axis to form the filter, wherein: (I) The wound filter has an inner surface and an outer surface; (II) Each layer of the filter comprises a plurality of holes having an average longitudinal dimension, i.e., LD; (III) The expanded metal strip comprises an inlet region that forms a plurality of layers in the wound filter and a nozzle region that forms a single layer in the wound filter, the inlet region being adjacent to the nozzle region, wherein the inlet region is closer to the inner surface of the wound filter than the nozzle region; (IV) The LD of the single layer of the nozzle region is less than the LD of all layers of the inlet region; and (V) The plurality of layers of the inlet region comprises a set of at least three adjacent layers, characterized in that: (a) The LD of the set decreases monotonically from the layer closest to the inner surface to the layer closest to the outer surface; and (b) The linear fit to the LD of the set has an R-squared value of at least 0.

8.

5. The filter according to claim 4, wherein, The magnitude of the slope of the linear fit is at least 0.04 millimeters per layer.

6. The filter according to claim 4, wherein The inner surface of the wound filter has an average diameter ID, the outer surface has an average diameter OD, and the filter has an average wall thickness t given by the following formula: t = 1 / 2(OD-ID), Where: t / OD ≤ 0.

07.

7. A filter, the filter comprising an expanded metal strip wound around an axis to form a plurality of layers, the expanded metal strip having a longitudinal axis and a transverse axis and comprising a plurality of holes arranged in rows oriented perpendicular to the longitudinal axis, the strip being wound along the longitudinal axis to form the filter, wherein: (I) The wound filter has an inner surface and an outer surface; (II) Each layer of the filter comprises a plurality of holes having an average transverse to longitudinal aspect ratio, i.e., AR; (III) The expanded metal strip comprises an inlet zone that forms a plurality of layers in the wound filter and a nozzle zone that forms a single layer in the wound filter, the inlet zone being adjacent to the nozzle zone, wherein the inlet zone is closer to the inner surface of the wound filter than the nozzle zone; (IV) The AR of the single layer of the nozzle zone is greater than the AR of all layers of the inlet zone; and (V) The plurality of layers of the inlet zone comprises a set of at least three adjacent layers, characterized in that: (a) The AR of the set increases monotonically from the layer closest to the inner surface to the layer closest to the outer surface; and (b) The linear fit of the AR of the set has an R-squared value of at least 0.

8.

8. The filter according to claim 7, wherein, The magnitude of the slope of the linear fit is at least 0.04 per layer.

9. The filter according to claim 7, wherein, The inner surface of the wound filter has an average diameter ID, the outer surface has an average diameter OD, and the filter has an average wall thickness t given by the following formula: t = 1 / 2(OD-ID), Where: t / OD ≤ 0.

07.

10. A filter, the filter comprising an expanded metal strip wound around an axis to form a plurality of layers, the expanded metal strip having a longitudinal axis and a transverse axis and comprising a plurality of holes arranged in rows oriented perpendicular to the longitudinal axis, the strip being wound along the longitudinal axis to form the filter, wherein: (I) The wound filter has an inner surface and an outer surface; (II) Each layer of the filter has an average percentage open area, i.e., POA; (III) The expanded metal strip comprises an inlet zone that forms at least three layers in the wound filter and a nozzle zone that forms a single layer in the wound filter, the inlet zone being adjacent to the nozzle zone, wherein the inlet zone is closer to the inner surface of the wound filter than the nozzle zone; (IV) The POA of the single layer of the nozzle zone is less than the POA of all layers of the inlet zone; and (V) The plurality of layers of the inlet zone comprises a set of at least three adjacent layers, characterized in that: (a) The linear fit of the POA of the set has an R-squared value of at least 0.

85.

11. The filter according to claim 10, wherein, The magnitude of the slope of the linear fit is at least five percent per layer.

12. The filter according to claim 10, wherein, The inner surface of the wound filter has an average diameter ID, the outer surface has an average diameter OD, and the filter has an average wall thickness t given by the following formula: t = 1 / 2(OD-ID), Where: t / OD ≤ 0.07.

Images