Abstract:
A method of filling containers ( 50 ) with gases ( 12 ) provides each container, when filled, with a first predetermined amount of a first gas and a second predetermined amount of a second gas. The method comprises the step of forming a mixture comprising first and second amounts of the first and second gases, respectively. The first and second amounts are greater than and are in proportion to the first and second predetermined amounts, respectively. The method further comprises the steps of: determining a sum of the first and second predetermined amounts; and adding a third amount of the mixture to each of the containers. The third amount is equal to the sum of the first and second predetermined amounts.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a method of filling containers with gases. More particularly, the present invention relates to a method of filling containers with predetermined amounts of first and second gases. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is known to provide an inflator for inflating an inflatable vehicle occupant protection device. One particular type of inflator is a heated gas inflator. In a heated gas inflator, a combustible mixture of gases is stored under pressure in a gas storage chamber. The heated gas inflator may include an outlet that is closed by a burst disk. An igniter assembly is associated with the gas storage chamber and is actuatable to ignite the combustible mixture of gases. When the combustible mixture of gases is ignited, the pressure of the gases within the gas storage chamber increases. The increased pressure ruptures the burst disk enabling the gases to exit the inflator through the outlet. 
         [0003]    The combustible mixture of gases in a heated gas inflator generally includes hydrogen, an inert gas, and air. Actuation of the igniter assembly ignites the hydrogen to heat the inert gas and the air. Typically, the combustible mixture of gases has a precise amount of hydrogen. For example, the amount of hydrogen in the combustible mixture of gases may have a tolerance of approximately 0.001 grams. Additionally, since the molecular weight of hydrogen is low, the total mass of the hydrogen in the combustible mixture of gases may be less than one gram. When the total mass of the empty inflator is, for example, 1000 grams, adding less than one gram of hydrogen, with a tolerance of approximately 0.001 grams, tends to be difficult. 
         [0004]    Currently, the process for adding the combustible mixture of gases to the inflator is time consuming and labor intensive. The process includes placing an empty inflator on a high precision scale and determining the mass of the empty inflator. The scale must be protected from air drafts, vibrations, and other variables that may alter the measured weight and thus, the determined mass, of the inflator. After the mass of the empty inflator is determined, hydrogen is introduced into the gas storage chamber of the inflator. After the hydrogen is added to the inflator and the scale has stabilized, the mass of the inflator and the stored hydrogen is determined. If the additional mass of the hydrogen is outside of the required tolerance, the amount of hydrogen in the gas storage chamber is adjusted and a subsequent determination of the mass of the inflator and the stored hydrogen is made. 
         [0005]    When the amount of hydrogen added to the inflator is within its required tolerance, the inert gas is added to the gas storage chamber of the inflator. Generally, the combustible mixture of gases also has a precise amount of the inert gas. The inert gas is added to the gas storage chamber of the inflator using the same process as was used to add the hydrogen. After the precise amount of the inert gas has been added to the inflator, air is added to the gas storage chamber of the inflator to bring the pressure within the gas storage chamber to a predetermined level. When the pressure within the gas storage chamber reaches the predetermined level, the fill port for the gas storage chamber is sealed. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention relates to a method of filling containers with gases. Each container, when filled, includes a first predetermined amount of a first gas and a second predetermined amount of a second gas. The method comprises the steps of: forming a mixture comprising first and second amounts of the first and second gases, respectively. The first and second amounts are greater than and are in proportion to the first and second predetermined amounts, respectively. The method also comprises the steps of: determining a sum of the first and second predetermined amounts; and adding a third amount of the mixture to each of the containers. The third amount is equal to the sum of the first and second predetermined amounts. 
         [0007]    In accordance with another aspect, the present invention relates to a method of filling inflators with gases. Each inflator, when filled, includes a first predetermined amount of a first gas and a second predetermined amount of a second gas and is actuatable for inflating an inflatable safety device of a vehicle safety system. The method comprises the steps of: forming, in a mixing vessel, a mixture comprising first and second amounts of the first and second gases, respectively, wherein a ratio of the first amount to the second amount equals a ratio of the first predetermined amount of the first gas to the second predetermined amount of the second gas; determining a sum of the first and second predetermined amounts; and adding a third amount of the mixture to each of the inflators. The third amount is equal to the sum of the first and second predetermined amounts. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The foregoing and other features of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which: 
           [0009]      FIG. 1  illustrates an inflator that has been filled with a combustible mixture of gases, in accordance with the method of the present invention; 
           [0010]      FIG. 2  illustrates a vehicle safety system having the inflator of  FIG. 1 ; 
           [0011]      FIG. 3  schematically illustrates an apparatus for filling the inflator of  FIG. 1 ; and 
           [0012]      FIGS. 4A and 4B  are schematic block diagrams illustrating a process of filling inflators, in accordance with the method of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]      FIG. 1  illustrates an inflator  10  that has been filled with a combustible mixture of gases  12 , in accordance with the method of the present invention. The inflator  10  illustrated is a heated gas inflator. The combustible mixture of gases  12  is stored under pressure in a gas storage chamber  14  of the inflator  10 . Alternatively, the inflator  10  may be any type of inflator that includes a mixture of gases stored under pressure in a gas storage chamber  14 . 
         [0014]      FIG. 2  illustrates a vehicle safety system  18  having the inflator  10  of  FIG. 1 . The vehicle safety system  18  of  FIG. 2  includes an inflatable safety device. The inflatable safety device of  FIG. 2  is an inflatable curtain  20 . The inflator  10 , when actuated, provides inflation fluid for inflating the inflatable curtain  20 . As an alternative to an inflatable curtain  20 , the inflatable safety device may include an inflatable air bag, an inflatable seat belt, an inflatable knee bolster, an inflatable headliner, or a knee bolster operated by an inflatable air bag. 
         [0015]    The inflatable curtain  20  of  FIG. 2  is in a deflated condition and is stored within a housing  22  at a location adjacent both the side structure of a vehicle  26  and a roof of the vehicle. The side structure of the vehicle  26  includes an A-pillar  28 , a B-pillar  30 , a C-pillar  32 , and side windows  34  and  36 , respectively.  FIG. 2  shows four brackets  40  securing the housing  22  and the inflatable curtain  20  to the side structure of the vehicle  26 . 
         [0016]    A conduit  44  connects the inflator  10  to the inflatable curtain  20 . Upon actuation of the inflator  10 , inflation fluid flows through the conduit  44  and into the inflatable curtain  20 . In response to receiving the inflation fluid, the inflatable curtain  20  deploys from the deflated condition to an inflated condition to cover portions of the side structure of the vehicle  26 , such as side windows  34  and  36 . 
         [0017]    As shown in  FIG. 1 , the inflator  10  includes a cylindrical, metal container  50 . The container  50  includes a tubular body portion  52  having cylindrical inner and outer surfaces  54  and  56 , respectively, and opposite first and second ends  58  and  60 , respectively. An igniter end cap  66  closes the first end  58  of the tubular body portion  52 . The igniter end cap  66  includes an annular flange portion  68  that is fixed to the tubular body portion  52  and an igniter support portion  70  that supports an actuatable igniter  74 . The igniter support portion  70  of the igniter end cap  66  includes a passage  76  through which combustion products produced by actuation of the igniter  74  may pass. Prior to actuation of the igniter  74 , a rupturable burst disk  78  closes the passage  76 . 
         [0018]    A diffuser end cap  84  closes the second end  60  of the tubular body portion  52 . The diffuser end cap  84  includes a tubular end portion  86  having inner and outer surfaces  88  and  90 , respectively. A circular gas fill port  92  extends through the tubular end portion  86  of the diffuser end cap  84 . The diffuser end cap  84  also includes an end portion  96  that includes an annular end wall portion  100  and a tubular discharge portion  102 . The tubular discharge portion  102  of the end portion  96  extends axially away from the annular end wall portion  100  in a direction parallel to an axis A. The tubular discharge portion  102  includes a passage  106  that provides an exit path for inflation fluid to flow out of the container  50 . 
         [0019]    Prior to actuation of the igniter  74 , a rupturable burst disk  110  closes the passage  106  of the tubular discharge portion  102  of the diffuser end cap  84 . The burst disk  110  is designed to rupture when subjected to a predetermined pressure differential. 
         [0020]    The tubular body portion  52 , the igniter end cap  66 , and the diffuser end cap  84  collectively define the gas storage chamber  14 . The gas storage chamber  14  extends along axis A between the igniter end cap  66  and the diffuser end cap  84 . The inner surface  54  of the tubular body portion  52  and the inner surface  88  of the tubular end portion  86  of the diffuser end cap  84  define a radial outer boundary of the gas storage chamber  14 . 
         [0021]    When the igniter  74  of the inflator  10  receives an actuation signal from electronic circuitry  114  ( FIG. 2 ) of the vehicle safety system  18 , the igniter  74  is actuated. Combustion products from actuation of the igniter  74  travel through the passage  76  in the igniter end cap  66 , rupture the burst disk  78 , and enter the gas storage chamber  14 . The combustion products heat and ignite the combustible mixture of gases  12  that is stored under pressure within the gas storage chamber  14 . The heating and ignition of the combustible mixture of gases  12  increases the pressure within the gas storage chamber  14 . When the predetermined pressure differential across the burst disk  110  is reached, the burst disk  110  is ruptured. Inflation fluid resulting from heating and igniting the combustible mixture of gases  12  exits the inflator  10  through the passage  106  of the tubular discharge portion  102  of the diffuser end cap  84 . 
         [0022]      FIG. 3  schematically illustrates an apparatus  120  for filling the inflator  10  with a combustible mixture of gases. As an example, the apparatus  120  of  FIG. 3  will be described as filling the inflator  10  with a combustible mixture of gases that includes hydrogen, argon, and air. The apparatus  120  of  FIG. 3  illustrates three vessels  122 ,  124 , and  126 . Vessel  122  contains a stored quantity of hydrogen gas, under pressure. Vessel  124  contains a stored quantity of argon, under pressure. Vessel  126  contains a stored quantity of air, under pressure. 
         [0023]    The apparatus  120  also includes a mixing vessel  130 . The mixing vessel  130  has a volume that is significantly greater than the volume of the gas storage chamber  14  of the inflator  10 . In a preferred embodiment of the invention, the volume of the mixing vessel  130  is over one thousand times greater than the volume of the gas storage chamber  14  of the inflator  10 . 
         [0024]    A conduit  134  connects vessel  122  to the mixing vessel  130 . A valve  136  attaches the conduit  134  to the mixing vessel  130 . When the valve  136  is open, hydrogen flows into the mixing vessel  130 . A conduit  140  connects vessel  124  to the mixing vessel  130 . A valve  142  attaches the conduit  140  to mixing vessel  130 . When the valve  142  is open, argon flows into the mixing vessel  130 . 
         [0025]      FIG. 3  illustrates a scale  146  that is associated with the mixing vessel  130 . The scale  146  is used for monitoring the amounts of hydrogen and argon in the mixing vessel  130 . The amounts of hydrogen and argon that are mixed together in the mixing vessel  130  are proportional to predetermined amounts of hydrogen and argon in the combustible mixture of gases  12  contained in the inflator  10 . For example, assume that a ratio of the predetermined amount, by mass, of hydrogen in the combustible mixture of gases  12  to the predetermined amount, by mass, of argon in the combustible mixture of gases  12  is 1/33. The ratio of the amount, by mass, of hydrogen and the amount, by mass, of argon that are mixed together in the mixing vessel  130  is also 1/33. The amounts of hydrogen and argon mixed together in the mixing vessel  130 , however, are significantly greater than the predetermined amounts used to fill one inflator  10 . In a preferred embodiment, the mixing vessel  130  holds enough hydrogen and argon to fill over one thousand inflators. 
         [0026]    To ensure a proper mixture of the hydrogen and argon in the mixing vessel  130 , the scale  146  is used to determine the mass of the empty mixing vessel  130 . The valve  136  is then opened and a quantity of hydrogen flows into the mixing vessel  130 . The valve  136  is closed and the scale  146  is used to determine mass of the hydrogen that was added to the mixing vessel  130 . Since the amount of hydrogen added to the mixing vessel  130  is preferably enough to fill over one thousand inflators, the added hydrogen will have a sufficient mass so as to be easily monitored using the scale. 
         [0027]    After the amount of hydrogen that was added to the mixing vessel  130  is determined, the amount of argon to be added to the mixing vessel  130  is calculated. The amount of argon to be added to the mixing vessel  130  is determined from the ratio of the predetermined amount of hydrogen to the predetermined amount of argon in the combustible mixture of gases  12  and from the determined amount of hydrogen so that mass ratio of hydrogen to argon in the mixing vessel  130  is equal to the mass ratio of hydrogen to argon to be added to the inflator, e.g., a mass ratio of 1/33. 
         [0028]    With reference again to  FIG. 3 , the apparatus  120  also includes a member  150  for temporarily attaching to the inflator  10 . The member  150  includes first and second input lines  152  and  154 , respectively, and a single output line  156 . A first valve  160  is associated with the first input line  152 . A second valve  162  is associated with the second input line  154 . 
         [0029]    A conduit  166  connects the mixing vessel  130  to the first valve  160 . When the first valve  160  is open, a mixture of hydrogen and argon flows into the first input line  152  of the member  150  and is directed into the gas storage chamber  14  of the inflator  10 . As a result, when the first valve  160  is open, hydrogen and argon are added simultaneously to the gas storage chamber  14  of the inflator  10 . 
         [0030]    A conduit  168  connects the vessel  126  to the second valve  162 . When the second valve  162  is open, air flows into the second input line  154  of the member  150  and is directed into the gas storage chamber  14  of the inflator  10 . 
         [0031]    To fill the inflator  10  with the combustible mixture of gases  12 , the member  150  is secured to the inflator  10  so that the output line  156  of the member directs a flow of gas through the fill port  92  ( FIG. 1 ) and into the gas storage chamber  14  of the inflator  10 . 
         [0032]    Next, the sum of the predetermined amounts of hydrogen and argon is determined. For purposes of example, assume that the inflator  10  is a 180 cm 3  inflator that holds approximately 75 grams of the combustible mixture of gases  12 . Also, for purposes of example, assume that the combustible mixture of gases  12  includes 12% by volume hydrogen, 20% by volume argon, and 68% by volume air. When filled with the combustible mixture of gases  12 , the inflator  10  will hold approximately 0.65 grams of hydrogen, 21.47 grams of argon, and 52.88 grams of air at a pressure of 6000 p.s.i. to 7000 p.s.i. 
         [0033]    As set forth in the Background of the Invention, adding such a small mass of hydrogen to the inflator, with a tolerance of approximately 0.001 grams, tends to be difficult. Instead of adding the approximately 0.65 grams of hydrogen to the inflator  10  and then later adding the approximately 21.47 grams of argon, the hydrogen and argon are simultaneously added to the inflator  10  according the method of the present invention. 
         [0034]    In our example, the determined sum of the predetermined amounts of hydrogen and argon equals approximately 22.12 grams (the sum of 0.65 grams and 21.47 grams). After the sum of the predetermined amounts is determined, an amount of the mixture of hydrogen and argon equal to the sum of the predetermined amounts, e.g., 22.12 grams, is added to the gas storage chamber  14  of the inflator  10 . A scale  174  is used for determining the amount (mass) of the mixture of hydrogen and argon that has been added to the inflator  10 . 
         [0035]    Since both the hydrogen and the argon have associated tolerances, assuming the proportion of the hydrogen and argon in the mixture is proper (e.g., a ratio of 1/33) and assuming that the mixture of hydrogen and argon flowing into the inflator  10  is homogenous, the tolerance for the mixture of hydrogen and argon will be larger than the individual tolerances for the hydrogen and the argon. For example, if the tolerance for the hydrogen is 0.001 grams and the tolerance for the argon is 0.005 grams, the tolerance for the mixture of hydrogen and argon may be greater than 0.005 grams while still maintaining the proper amounts of hydrogen and argon in the inflator  10 . This results from the fact that the hydrogen only accounts for approximately 1/34 (0.65 grams H 2 /22.12 grams mixture) of the total added mass of the mixture and the argon only accounts for 33/34 (21.47 grams Ar/22.12 grams mixture) of the total added mass. Thus, when the amount of the mixture of hydrogen and argon added to the inflator  10  is within a 0.005 gram tolerance, the amount of hydrogen added is within its 0.001 gram tolerance (0.005 grams times 1/34 equals 0.000147 grams) and the amount of argon added is also within its 0.005 gram tolerance (0.005 grams times 33/34 equals 0.000485 grams). 
         [0036]    After the mixture of hydrogen and argon is added to the gas storage chamber  14  of the inflator  10 , the second valve  162  is opened and air is added to the gas storage chamber  14  of the inflator  10 . the scale  174  is used to determine the weight of the air added to the storage chamber  14  of the inflator  10 . After the air is added to the inflator, the fill port  92  of the inflator  10  is closed and the inflator is removed from the apparatus  10 .  FIG. 1  illustrates a closure member  180  closing the fill port  92  of the inflator  10 . 
         [0037]      FIGS. 4A and 4B  are schematic block diagrams illustrating a process  400  of filling inflators. For purposes of example, the discussion of  FIGS. 4A and 4B  will refer to the example given above, i.e., an inflator holding 75 grams of a combustible mixture of gases of which approximately 0.65 grams is hydrogen, approximately 21.47 grams is argon, and approximately 52.88 grams is air. 
         [0038]    As shown in  FIG. 4A , the process  400  begins at step  402 . At step  404 , a first gas, e.g., hydrogen, is added to the mixing vessel  130 . At step  406 , the amount of the first gas added to the mixing vessel  130  is determined. To determine the amount of the first gas added to the mixing vessel  130 , the mass of the mixing vessel  130 , when empty, is determined prior to the first gas being added. The mass of the mixing vessel  130  is then determined after the addition of the first gas. The difference between the two determined masses represents the mass of the first gas added to the mixing vessel. Step  406  does not require any precise amount of the first gas to be added to the mixing vessel  130  as long as the amount of first gas added is greater than a predetermined amount for filling one inflator. As set forth above, the amount of the first gas added to the mixing vessel  130  is preferably enough to fill a large number of inflators, such as one thousand inflators. For purposes of example, assume that 700 grams of hydrogen was added to the mixing vessel  130  at step  406 . 
         [0039]    At step  408 , the amount of the second gas, e.g., argon, to be added to the mixing vessel  130  is calculated. The mass ratio of the first and second gases in the mixing vessel  130  should be equal to the mass ratio of the predetermined amounts of the first and second gases in the inflator. In our example, the mass ratio of hydrogen to argon is 1/33. Thus, the amount of argon to be added to the mixing vessel  130  at step  408  equals thirty-three times the amount of hydrogen added at step  406 . In our example, 700 grams of hydrogen was added to the mixing vessel  130  at step  406 . Therefore, at step  408 , the calculated amount of the argon is 23.1 kilograms. 
         [0040]    At step  410 , the calculated amount of the second gas is added to the mixing vessel  130 . At step  412 , the amount of the second gas added to the mixing vessel  130  is determined. To determine the amount of the second gas added to the mixing vessel  130 , the mass of the mixing vessel  130  after the addition of the second gas is determined. The previously determined mass of the mixing vessel  130  after the addition of the first gas and prior to the addition of the second gas is subtracted from the determined mass of the mixing vessel  130  after the addition of the second gas. The difference between the two determined masses represents the mass of the second gas added to the mixing vessel  130 . 
         [0041]    At step  414 , a determination is made as to whether the correct amount of the second gas has been added to the mixing vessel  130 . The determination at step  414  is made by comparing the determined amount of the second gas added to the mixing vessel  130  from step  412  to the calculated amount of the second gas from step  408 . When the determined amount of the second gas added is within a predetermined tolerance of the calculated amount of the second gas, the determination at step  414  is affirmative. 
         [0042]    In response to a negative determination at step  414 , the process  400  proceeds to step  416  and the amount of the second gas in the mixing vessel  130  is increased if the amount of the second gas is too low. The amount of the second gas can not become too high, because the systems (in a manner not shown), is constantly being monitored by continually weighing the second gas in the mixing vessel and closing off the flow of the second gas when the correct weight is in the mixing vessel  130 . From step  416 , the process  400  returns to step  414 . In response to an affirmative determination at step  414 , the process proceeds to step  418 . 
         [0043]    At step  418 , the sum of the predetermined amounts of the first and second gas to be added to an inflator is determined. In our example, the predetermined amount of the first gas, hydrogen, is 0.65 grams and the predetermined amount of the second gas, argon, is 21.47 grams. Therefore, the sum of the predetermined amounts that is determined at step  418  is 22.12 grams grams. 
         [0044]    As shown with reference to  FIG. 4B , the process  400  proceeds from step  418  to step  420 . At step  420 , an empty inflator is inserted into the apparatus  120 . When the empty inflator is inserted into the apparatus  120 , the member  150  of the apparatus  120  for directing gases into the inflator is connected to the inflator so as to direct gases through the fill port of the inflator and into the gas storage chamber. At step  422 , a mass of the empty inflator is determined. 
         [0045]    At step  424 , the mixture of the first and second gases is added to the inflator. The amount of the mixture added to the inflator is the amount determined at step  418 . At step  426 , the amount of the mixture of the first and second gases added to the inflator is determined. To determine the amount of the mixture added to the inflator, the mass of the inflator after the addition of the mixture of gases is determined. The previously determined mass of the empty inflator is subtracted from the determined mass of the inflator after the addition of the mixture of gases. The difference between the two determined masses represents the mass of the mixture of gases added to the inflator. 
         [0046]    At step  428 , a determination is made as to whether the correct amount of the mixture of gases has been added to the inflator. The determination at step  428  is made by comparing the determined amount of the mixture of gases added to the inflator from step  426  to the determined sum from step  418 . When the determined amount of the mixture of gases added is within a predetermined tolerance of the determined sum, the determination at step  428  is affirmative. 
         [0047]    In response to a negative determination at step  428 , the process  400  proceeds to step  430 , and the amount of the mixture of gases in the inflator is adjusted by either adding or removing an amount of the mixture. From step  430 , the process  400  returns to step  428 . In response to an affirmative determination at step  428 , the process  400  proceeds to step  432 . At step  432 , a predetermined amount of air is added to the inflator. As noted above the air added to the inflator is weighted. The air increases the pressure of the gases in the gas storage chamber of the inflator to a predetermined pressure. At step  434 , the fill port of the inflator is closed and sealed and, at step  436 , the inflator is removed from the apparatus. 
         [0048]    From step  436 , the process  400  proceeds to step  438 . At step  438 , the amount of the mixture of the first and second gases remaining in the mixing vessel  130  is determined. The amount of the mixture remaining may be determined by monitoring the total mass of the mixing vessel  130  and the mixture of gases. At step  440 , a determination is made as to whether the remaining amount of the mixture of gases is greater than the sum of the predetermined amounts from step  418 . When the determination at step  440  is affirmative, and the amount of the mixture of gases remaining in the mixing vessel  130  is greater than the sum of the predetermined amounts from step  418 , the process  400  proceeds to step  442  and another empty inflator is inserted into the apparatus  120  to be filled. From step  442 , the process  400  returns to step  422 . When the determination at step  440  is negative, the process  400  proceeds to step  444  and ends. 
         [0049]    From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, nitrogen may be used in the process as a substitute for argon. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.