Abstract:
An inflator for an airbag has a cylindrical housing forming a pressure vessel for storing inert gas within a first end portion; a second end portion forming a separate combustion chamber, and an intermediate diffusion portion interposed between the first and second end portions for exhausting gases from the inflator into an airbag. The inflator has a first gas generator subassembly disposed within the first end portion and in communication with the stored inert gas. A second gas generator subassembly has a combustion chamber which is disposed within the second end portion and isolated from the inert gas by one or more rupturable sealing disks. The actuation of the inflator can be accomplished such that one or both of the gas generators can be ignited. The ignition can be simultaneously or sequential permitting either very rapid full filling of the airbag or slower prolonged filling.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to a device for inflating an airbag and more specifically to a dual stage inflator capable of providing various levels of inflation.  
       BACKGROUND OF THE INVENTION  
       [0002]     Inflatable restraints or airbags have been shown to reduce the seriousness of vehicle occupant injury during a vehicle crash. An airbag, filled with inflation gas, provides a cushion between a vehicle occupant and the instrument panel or steering wheel. The likelihood of injury is minimized by the airbag absorbing some or all of the kinetic energy associated with the vehicle occupant during a crash.  
         [0003]     An inflator provides the inflation gas utilized to inflate an airbag. Inflators generally provide inflation gas by burning a pyrotechnic material, releasing stored gas, or by some combination thereof. During a crash, the inflator is actuated to rapidly inflate an airbag. Aggressive airbag deployment has the advantage of getting the inflated airbag in front of the vehicle occupant as soon as possible. The problem associated with aggressive airbag deployment is the possibility of a child, a small adult, or an out of position adult interacting with the airbag while it is being inflated. Out of position is a phrase utilized in the safety restraint industry that refers to a vehicle occupant that is not sitting properly in his/her seat or sitting too close to the airbag module.  
         [0004]     Dual stage inflators have been developed to reduce the injury to small adults or children by reducing the aggressiveness of airbag deployment. These inflators provide varying output levels of inflation gas in accordance with the size and position of the vehicle occupant. Dual stage inflators are able to provide a full output of inflation gas to protect a full size vehicle occupant who is not out of position. The dual stage inflator is also able to provide a staged output of inflation gas for vehicle occupants who are smaller in size or out of position. The staged output deployment operates by providing a portion of inflation gas to partially inflate the airbag and after a period of time, the inflator provides more inflation gas to fill the airbag.  
         [0005]     Inflators with varying output levels of inflation gas or dual stage inflators have been shown in the past. The dual stage inflators shown in U.S. Pat. No. 6,189,922 B1 and U.S. Pat. No. 6,168,200 B1 have a first and second gas generant. Another variation of the dual stage inflator has two separate burst disks which are illustrated in U.S. Pat. No. 5,022,674, U.S. Pat. No. 5,351,988 and U.S. Pat. No. 5,016,914.  
         [0006]     U.S. Pat. No. 6,557,890 teaches a hybrid type inflator that has two charges for gas production arranged outside on opposite sides of a gas chamber charged with compressed gas. The compressed gas is therefore completely separated from the ignitable gas charges. A similar construction is taught in Japanese publication number 2004-026025 entitled “Gas Generator for Air Bag”. U.S. Pat. No. 6,557,890 relies on a piston (plug) to separate the ignition gas from the compressed gas which according to the Japanese references is very difficult to move causing unusual pressure rises internal to the inflator which may destroy the housing. To avoid this the Japanese inflator employs a ball-like destructive means that acts presumably like a check valve that can normally seal the inert gas, but upon ignition of a charge is unseated and moved into the gas chamber colliding with a rupture disk.  
         [0007]     Both of these systems while very clever require extra components and increase the length of the inflator accommodating the ignitable charges thereby reducing the amount of length available for the compressed gas. To accommodate this loss of volume the compressed gas chamber in each case typically has an enlarged diameter of 60 mm or greater.  
         [0008]     Ideally a hybrid inflator should be small in size, but extremely reliable. Reliability often requires a desire to simplify and eliminate unnecessary features or elements.  
         [0009]     The present team of inventors includes some of those who had earlier developed a “Low Onset Dual Stage Hybrid Inflator” which is described in U.S. Pat. No. 6,769,714 B2. As shown in FIG. 4 of U.S. Pat. No. 6,769,714 B2 the prior art inflator 100 has a housing 110 wherein a gas generator subassembly 122 was deployed internal of a pressure vessel 112 and two separate igniters 121, 122 were used. One igniter 122 would ignite an enhancer charge 130 and gas generant charge 140 in the subassembly 120 while the second igniter 121 could be used to rupture a seal 150 to allow the compressed gas 111 to release. The igniters 121, 122 could be used sequentially or separately or simultaneously if so desired to achieve variations in the airbag fill rate.  
         [0010]     The present invention provides some of the very reliable aspects of this earlier invention in combination with new elements to achieve the extremely reliable dual stage inflator described herein. The present invention provides a more efficient use of the space available for the inflator while providing a variety of inflation fill rates and volumes.  
       SUMMARY OF THE INVENTION  
       [0011]     An inflator for an airbag in accordance with the present invention has a cylindrical housing forming a pressure vessel for storing inert gas within a first end portion. A second end portion forms a separate combustion chamber. An intermediate diffusion portion is interposed between the first and second end portions for exhausting gases from the inflator into the airbag. The inflator has a first gas generator subassembly disposed within the first end portion and in communication with the stored inert gas. A second gas generator subassembly is disposed within the second end portion and isolated from the inert gas by one or more rupturable sealing disks. The actuation of the inflator can be accomplished such that one or both of the gas generators can be ignited. The ignition can be simultaneously or sequential permitting either very rapid full filling of the airbag or slower prolonged filling, if so desired.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a cross sectional view of the dual stage inflator in the present invention.  
         [0013]      FIGS. 2A, 2B ,  2 C, and  2 D show various burst disk configurations.  
         [0014]      FIG. 3  is a perspective view of the first gas generator subassembly.  
         [0015]      FIG. 4  shows a prior art inflator according to U.S. Pat. No. 6,769,714 B2. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     The present invention provides a dual stage inflator  10  able to gently inflate an automotive airbag so as not to injure an out of position child or small adult while still being capable of providing crash protection to a full size adult. The dual stage inflator  10  provides various output levels of inflation gas for inflating an airbag usable with a vehicle occupant restraint system. The dual stage inflator  10  comprises a cylindrical elongated outer housing  11  forming a pressure vessel  12  in a first portion  10 A that is filled with stored gas  13 , which is released from the inflator during a crash to inflate a vehicle airbag. The dual stage inflator  10  has a generally cylindrical shape and may be formed of stainless steel, low carbon steel, or any other suitable material, which has sufficient strength and extremely low gas permeability.  
         [0017]     The ideal characteristics for the stored gas  13  are that the gas is inert, is not highly temperature sensitive, and is capable of inflating an airbag at a high inflation rate. The stored gas  13  can include one or more gases, which include but are not limited to argon, carbon dioxide, oxygen, helium, and nitrogen.  
         [0018]     The pressure vessel  12  is filled with stored gas  13  through the gas fill port  14 , which is preferably located on a first end closure  20  of the dual stage inflator  10 . The gas fill port  14  is sealed by a plug  15  made from low carbon steel to prevent gas from escaping after the dual stage inflator  10  has been filled to the desired pressure. It is preferred that the plug  15  is secured to the gas fill port  14  by a resistance weld, but one skilled in the art realizes that other types of welding could be utilized to fuse the plug  15  to the outer housing  11 .  
         [0019]     As shown in  FIG. 1 , the dual stage inflator  10  has a first end closure  20  and a central support column  21  holding a first gas generator subassembly  23 . The first gas generator subassembly  23  lies centrally disposed within the pressure vessel and extends longitudinally along the axis of the inflator housing  11  a distance extending nearly the entire length L of the internal chamber of the pressure vessel  12 , as shown about 85% of L.  
         [0020]     With further reference to  FIG. 1 , the gas generator subassembly  23  is situated on the support column  21  of the inflator first end closure  20 . The gas generator subassembly  23  has an igniter  40  for receiving an electrical signal from a controller (not shown) via two or more electrodes  41  that in turn communicate with a sensor means (not shown). The igniter  40  is an electrical device which initiates the deployment of the inflator when a suitable electric current is passed through a resistor element embedded in one or more layers of pyrotechnic compositions. The igniter may be of the standard direct fire design, receiving the firing current directly from the controller, or the igniter  40  may be of an advanced design which communicates with the controller by digital signals and which contains on board the igniter an ASIC (application specific integrated circuit), firing capacitor, and related components.  
         [0021]     The pyrotechnic compositions and load weight contained within the igniter  40  are designed to break through the gas tight sealing disk  46  and fully ignite the enhancer  47 . An example of a suitable pyrotechnic composition or ignition material for the present invention is zirconium potassium perchlorate, however, one skilled in the art realizes that other ignition materials can be utilized in the present invention. The igniter  40  is encased in an igniter housing opening  42  in the support column  21  of the end closure  20 , which is attached to the outer housing  11 .  
         [0022]     The enhancer  47  may be any of a number of known compositions that are readily ignited by the igniter  40  and burn at a high rate and temperature. Examples of enhancers include boron potassium nitrate and non-azide formulations containing a metal. The gases and hot burning particles from the ignited enhancer  47  exit through the pellet retainer  43  and ignite the gas generant  48 . The gas generator subassembly  23  has a spring like cushion  44  located on the end furthest away from the enhancer  47 . The cushion  44  is a resilient member that is utilized to bias the gas generant  48  against the pellet retainer  43  to ensure the gas generant  48  pellets occupy a predetermined volume without being able to rattle. The pellet retainer  43  is a porous wall that divides the enhancer  47  from the gas generant  48 . An optional sealing foil may be used to cover the openings of the pellet retainer  43 . The hot gases from the ignition of the enhancer  47  flow through the pellet retainer  43  but neither the enhancer  47  material nor the gas generant  48  pellets can pass through the pellet retainer  43 .  
         [0023]     Representative gas generant  48  compositions useful in the dual stage inflator  10  include fuels such as aminotetrazoles, tetrazoles, bitetrazoles, triazoles, the metal salts thereof, nitroguanidines, guanidine nitrate, amino guanidine nitrate, and mixtures thereof; in combination with an oxidizer such as the alkali and alkaline earth metal nitrates, chlorates, perchlorates, ammonium nitrate, and mixtures thereof. The gas generant  48  can be formed into various shapes using various techniques known to those skilled in the art.  
         [0024]     The gas generant subassembly  23  inside the pressure vessel  12  has a housing  49  retains the gas generant  48  and is made from stainless steel, low carbon steel, or other suitable material. The gas generant subassembly housing  49  has a plurality of apertures  45 , which can be seen in  FIG. 3 . The plurality of apertures  45  are situated along the length of the gas generant subassembly housing  49 , and an important facet about the size and number of apertures  45  is that the gas generator subassembly  23  remains thrust neutral during the burning of the gas generant  48 . Importantly, the apertures  45  directly expose the gas generant  48  in the gas generator subassembly  23  to the stored gas  13  present in the pressure vessel  12 . The location of the apertures  45  allows the hot gases to be discharged on the walls of the outer housing  11  thus cooling and retaining solid particulates preventing a portion of the particulates from entering the diffuser  26 . When the pressure vessel  12  is filled with stored gas  13 , some of the stored gas  13  is able to flow into the gas generator subassembly  23  equalizing the pressure in the pressure vessel  12  with the gas generant subassembly  23 . A sealing disk  46  is utilized in the present invention to prevent the stored gas  13  from escaping from the dual stage inflator  10  through the gas generator subassembly  23 . The sealing disk  46  is attached by laser welding over the igniter housing opening  42  to an enhancer retaining washer  54  or optionally to the end of the support column  21 , but could be attached by other welding techniques. Preferably the support column  21  includes an annular depression  51  for retaining the gas generant subassembly housing  49  which includes an inwardly directed annular protrusion  52  that snaps into the depression  51  upon assembly. Additionally a crimped protrusion  53  extends inwardly to provide a mechanical stop for the pellet retainer  43  that separates the enhancer charge  47  from the gas generant pellets  48 .  
         [0025]     At a second end  70  of the pressure vessel  12  is a gas diffuser  26  located in an intermediate diffuser portion  10 B of the cylindrical housing  11 . This intermediate portion  10 B has a first bulkhead  62  adjacent the first end portion  10 A forming an internal second end  70  of the pressure vessel  12 . The first bulkhead  62  has one or more openings  28 A sealed by a rupture disk  24 A. A second bulkhead  63  is located adjacent the second end portion  10 C an internal end  72  of the separate combustion chamber  90 . The second bulkhead  63  has one or more openings  28 B sealed by a rupture disk  24 B. Interposed between said first and second bulkheads  62 ,  63  are a plurality of circumferentially aligned exhaust openings  29 . The circumferentially aligned exhaust openings  29  provide passages for the gas to escape into the airbag for inflation when one or both igniters  30 ,  40  are activated. Inside the diffuser portion  10 B is a porous filtration means  74  situated between said first and second bulkheads  62 ,  63  covering the exhaust openings  29  as shown in  FIG. 1 . The exhaust openings  29  are preferably sized and oriented in a radially opposed manner to create a thrust neutral condition as the gases leave the inflator  10 . As shown the diffuser portion  10 B is cylindrically shaped and is welded at end  70  that aligns with the second end of the first end portion  10 A of the pressure vessel  12 .  
         [0026]     At the opposite or second end of the diffuser  10 B, the second end portion  10 C is shown similarly welded along the circumferential ends  73  to the diffuser portion  10 B thus forming a second gas generator subassembly  80  with a separate combustion chamber  90 . The second bulkhead  63  as shown has a plurality of openings  28 B sealed by a rupture disk  24 B on the diffuser facing side of the bulkhead  63 . The gas generant  88  is contained in a region spaced slightly from the second bulkhead  63  by a porous filter or screen  81  which both cushions the gas generant pellets  88  and prevents most of the ignited burning particles from spewing into the airbag upon ignition.  
         [0027]     An end cap  33  is welded to the second end portion  10 B. Internally contained is a separator bulkhead  75  with a plurality of small holes  28 C preferably sealed by a rupture disk  24 C. The separator bulkhead  75  isolates the second generant charge of pellets  88  from an enhancer charge  86  which as shown is held in a small cavity  34  in the end cap  33 . To activate the charges  86 ,  88  in the separate combustion chamber  90  an opening device is employed.  
         [0028]     The opening device comprises an electrically actuated igniter  30  and the end cap  33 . The opening device is positioned so that the longitudinal axis of the opening device is essentially parallel with a longitudinal axis A of the dual stage inflator  10 . The igniter  30  communicates with a controller (not shown) via two or more electrodes  31 , which in turn communicate with a sensor means (not shown). The igniter  30  is an electrical device that initiates the deployment of the inflator when a suitable electric current is passed through a resistor element embedded in one or more layers of pyrotechnic compositions. The igniter  30  may be of the standard direct fire design, receiving the firing current directly from the controller, or the igniter  30  may be of an advanced design which communicates with the controller by digital signals and which contains on board the igniter an ASIC (application specific integrated circuit), firing capacitor, and related components. The pyrotechnic compositions and load weight contained within the igniter are designed to generate an output energy that will reliably ignite the enhancer charge  86  which will rupture the burst disk or foil  24 C. An example of a suitable pyrotechnic composition or ignition material for the present invention is zirconium potassium perchlorate or ZPP, however, one skilled in the art realizes that other ignition materials could be used in the present invention.  
         [0029]     The end cap  33  is a metal member that houses the igniter  30 . The end cap  33  may also be made of a plastic material made with an injection molding process. The end cap  33  as seen in  FIG. 1  has threads, which are utilized for attachment to an airbag module (not shown).  
         [0030]     The opening device may also include reinforced walls  35  for directing an output energy from the ignition of the ignition material towards the burst disk  24 C. The reinforced walls extend inward in the direction of the burst disk  24 C. Without the walls  35 , the igniter  30  would still rupture the burst disk  24 C but would need to be loaded with extra ignition material to provide consistent opening at −40° C. It is also possible to utilize an igniter  30  with a nozzle, which would eliminate the need for reinforced walls  35 . These reinforcement walls  35  act in a similar fashion to a nozzle by focusing the output energy in the direction of the burst disk  24 C.  
         [0031]     The burst disk  24 A is attached to the first bulkhead  62  of the diffuser  10 B and seals the first bulkhead  62  so that stored gas  13  can not exit the dual stage inflator  10 . The burst disk  24 A shown in  FIG. 2A  is made from stainless steel, inconel material, monel material, or any other suitable material that allows the burst disk  24 A to open reliably at −40° C. The hardness of the burst disk  24 A should be between “half hard” and “full hard” to minimize burst disk  24 A thickness. Hardness is the degree to which a metal will resist cutting, abrasion, penetration, bending and stretching. The indicated hardness of metals will differ somewhat with the specific apparatus and technique of measuring. The radially outer portion of the burst disk  24 A is attached to the bulkhead  62  by a laser weld  60  but could be attached by other welding techniques. The radially inner portion of the burst disk  24 A is not attached to any portion of the diffuser  26  and bulges upon filling of the pressure vessel  12 . The burst disk  24 A adopts a dome shape configuration due to the force of the stored gas  13  being applied to the burst disk  24 A. Alternatively, the burst disk  24 A can be bulged in the direction of the opening device by a hydro-forming process after the burst disk  24 A is attached to the bulkhead  62 .  
         [0032]     Upon actuation of the igniter  30 , the enhancer  86  ignites and ruptures the burst disk  24 C, which ignites the gas generant charge  88 , which ruptures the disk  24 B resulting in discharge openings  28 B, which allows the ignited gases to flow into the diffuser  26  and out of the dual stage inflator  10 . The burst disks  24 A, B or C can have one or more secondary discharge openings  61  to control the internal pressure and flow within the inflator  10 .  FIGS. 2B-2D  illustrate various burst disk configurations having one discharge opening  28  and at least one secondary discharge opening  61 . The actuation of the igniters  30 ,  40  ruptures the burst disks  24  A, B or C so there is one or more discharge flow paths through the openings  28 A,  28 B,  28 C and  61  allowing the ignited gases to flow out of the inflator  10  through the exhaust openings  29 . The actuation of the second gas generator subassembly can be accomplished without rupturing the burst disk  24 A by sizing the openings  28 A,  28 B,  28 C and  61  such that the airbag can be more slowly and gently filled to accommodate a small child or out of position occupant. However, more typically the first gas generant subassembly  23  is actuated before or at the same time the second combustion chamber  90  is activated. Typically in normal operation the igniter  40  is fired bursting the disk  46  and igniting the enhancer  47  which then ignites the generant pellets  48  which rapidly heats the inert gas  13  causing the internal pressure of the pressure vessel  12  to increase and rupture the burst disk  24 A in such a way that one or more discharge opening(s)  28 ,  61  are created allowing the gases to enter the diffuser portion and exit out the exhaust openings.  
         [0033]     The cylindrical elongated shape of the inflator  10  provides a compact device that can be made in a size more compact diametrically while still providing various deployment scenarios. As shown the housing  11  has an outside diameter of 50 mm, and can be made even smaller. A 45 mm diameter is feasible without necessarily increasing the length of the device. This ability to reduce the size of the inflator  10  without sacrificing performance is valuable to many vehicle manufacturers whose need to accommodate the airbag module takes space away from other features such as the glove box on the instrument panel.  
         [0034]     The inflator as shown can be deployed in many different deployment scenarios.  
         [0035]     The normal deployment involves activating the first gas generant subassembly  23 , heating the inert gas  13  and rupturing the first disk  24 A to fill the airbag. This scenario arrives at maximum airbag inflation pressure the quickest.  
         [0036]     The second deployment scenario would be to fire both gas generant charges  48 ,  88  simultaneously; this fills the airbag the quickest to the largest volume and also achieves maximum airbag inflation pressure the quickest.  
         [0037]     A third deployment scenario is to employ the first deployment scenario followed by a sequentially delayed activation of the second gas generator subassembly  80  to prolong inflation of the airbag.  
         [0038]     A fourth deployment scenario is to activate only the second gas generator subassembly  80  in the second combustion chamber  90 . This results in a lower output of gases to provide a gentler airbag opening to accommodate a child or out of position occupant.  
         [0039]     The primary advantage of the present invention is that the time delays possible are greatly increased by the fact that the inflator has separate gas generating sources. One gas generating source combined with pressurized charge of inert gas the other gas generating source separate from and isolated from the pressure vessel. A key advantage of the present invention is the ignition of one gas generator subassembly will not cause the other gas generator subassembly to ignite. The sizing of the discharge openings  28 A,  28 B,  28 C and  61  and the large exhaust openings  29  are designed to insure the internal pressures are quickly vented to fill the airbag avoiding a secondary undesired ignition. Only by igniting both igniters will both the charges ignite and thus ignition can be simultaneously timed or sequentially triggered as desired.  
         [0040]     Many changes and modification in the above-described embodiments of the invention can, of course, be carried out without departing from the scope thereof. Accordingly, that scope is intended to be limited only by the scope of the appended claims.