Abstract:
An inflator ( 10 ) includes a container ( 12 ) having a chamber ( 120 ). An exit opening ( 48 ) is provided in the container ( 12 ) and is connected to the chamber ( 120 ). A substance ( 122, 180 ) is stored in the chamber ( 120 ) and is responsive to heat for providing inflation fluid. An igniter ( 130 ) is associated with the container ( 12 ) and is actuatable to provide combustion products for heating the substance ( 122, 180 ). A nozzle ( 80 ) is interposed between the igniter ( 130 ) and the chamber ( 120 ). A passage ( 90 ) extends from the igniter ( 130 ) and through the nozzle ( 80 ). The passage ( 90 ) includes a divergent portion ( 110 ) for focusing a flow of combustion products from the igniter ( 130 ) into the chamber ( 120 ).

Description:
TECHNICAL FIELD 
   The present invention relates to an inflator, and particularly, to an inflator for use in inflating an inflatable vehicle occupant protection device. 
   BACKGROUND OF THE INVENTION 
     FIGS. 5 and 6  illustrate a known inflator  500  for inflating an inflatable vehicle occupant protection device. The inflator  500  include includes a container  502  that is formed from a cylindrical member  504 , a diffuser endcap  506 , and an igniter endcap  508 . A chamber  510  is defined in the container  502 . A gaseous propellant  512  is stored in the chamber  510 . The gaseous propellant  512  is ignitable for providing inflation fluid. 
   A flow opening  518  extends through the diffuser endcap  506 . A rupturable burst disk  520  closes the flow opening  518  for maintaining the gaseous propellant  512  in the chamber  510 . 
   A through-hole  524  extends through the igniter endcap  508 . The through-hole  524  narrows slightly at an end adjacent the chamber  510 . A rupturable burst disk  526  closes an opening of the through-hole  524  adjacent the chamber  510 . 
   An igniter  530  is secured to the igniter endcap  508 . The igniter  530  is actuatable for providing combustion products for igniting the gaseous propellant  512  in the chamber  510 . 
     FIG. 6  illustrates the inflator  500  in an actuated condition. When the igniter  530  is actuated, combustion products generated from ignition of the igniter  530  fill the through-hole  524  of the igniter endcap  508  and rupture the burst disk  526 . When the burst disk  526  ruptures, the combustion products flow from the through-hole  524  into the chamber  510 . When the combustion products enter the chamber  524 , the combustion products are at a pressure that is higher than the pressure of the gaseous propellant  512  within the chamber  510 . As a result, upon entering the chamber  510 , the combustion products fan outwardly in a radial direction relative to a central axis of the through-hole  524 . The outward fanning of the combustion products results in a generally conical flow pattern for the combustion products, as is illustrated at  534  in  FIG. 6 . 
   When the flow opening  518  for inflation fluid is located on an opposite end of the container  502  from the igniter  530 , as is illustrated in  FIGS. 5 and 6 , the outward fanning of the combustion products results in a burn zone that is located adjacent the igniter endcap  508  and away from the flow opening  518 . As a result, when the burst disk  520  covering the flow opening  518  is ruptured, some of the gaseous propellant  512  may exit the chamber  510  through the flow opening without being combusted. 
   To help minimize the amount of uncombusted gaseous propellant  512  exiting the chamber  510  through the flow opening  518 , a high burn efficiency is desired. A higher burn efficiency may be achieved by locating the burn zone closer to the flow opening. 
   SUMMARY OF THE INVENTION 
   The present invention relates to an inflator that comprises a container having a chamber. An exit opening is provided in the container. The exit opening connects to the chamber. A substance is stored in the chamber. The substance is responsive to heat for providing inflation fluid. An igniter is associated with the container and is actuatable to provide combustion products for heating the substance. The inflator also comprises a nozzle that is interposed between the igniter and the chamber. A passage extends from the igniter and through the nozzle. The passage includes a divergent portion for focusing a flow of combustion products from the igniter into the chamber. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
       FIG. 1  is a sectional view of an inflator constructed in accordance with a first embodiment of the present invention and prior to actuation of an igniter; 
       FIG. 2  illustrates the inflator of  FIG. 1  after actuation of the igniter and after rupturing of a burst disk of the inflator; 
       FIG. 3  is a sectional view of an inflator constructed in accordance with a second embodiment of the present invention and prior to actuation of an igniter; 
       FIG. 4  illustrates the inflator of  FIG. 3  after actuation of the igniter and after rupturing of a burst disk of the inflator; 
       FIG. 5  is a sectional view of a prior art inflator prior to actuation of an igniter; and 
       FIG. 6  illustrates the inflator of  FIG. 5  after actuation of the igniter and after rupturing of a burst disk of the inflator. 
   

   DESCRIPTION OF PREFERRED EMBODIMENT 
     FIG. 1  is a sectional view of an inflator  10  constructed in accordance with a first embodiment of the present invention. The inflator  10  of  FIG. 1  includes a container  12  having axially opposite first and second ends  14  and  16 , respectively. 
   The container  12  includes a tubular body portion  22 , a diffuser endcap  26 , and an igniter endcap  28 . The body portion  22  includes cylindrical inner and outer surfaces  30  and  32 , respectively. Both of the inner and outer surfaces  30  and  32  are centered on axis A. The body portion  22  also includes first and second open ends  34  and  36 , respectively. The first open end  34  is located near the first end  14  of the container  12  and the second open end  36  is located near the second end  16  of the container. 
   The diffuser endcap  26  includes a cylindrical outer surface  40  and first and second radially extending side surfaces  42  and  44 , respectively. The cylindrical outer surface  40  is centered on axis A and has a diameter that is approximately equal to the diameter of the outer surface  32  of the body portion  22 . The first side surface  42  of the diffuser endcap  26  is fixed to the second open end  36  of the body portion  22 .  FIGS. 1 and 2  illustrate the diffuser endcap  26  welded to the body portion  22 . 
   A flow passage  48  extends axially through the diffuser endcap  26  from the first side surface  42  to the second side surface  44 . The flow passage  48  is centered on axis A. A cylindrical surface  50  of the diffuser endcap  26  defines the flow passage  48 . The flow passage  48  forms a first circular opening (not shown) on the first side surface  42  of the diffuser endcap  26  and a second circular opening  56  on the second side surface  44  of the diffuser endcap  26 . 
   A burst disk  60  closes the flow passage  48  of the diffuser endcap  26 . The burst disk has a domed central portion  62  and a radially outwardly extending flange portion  64 . The flange portion  64  of the burst disk is affixed to the first side surface  42  of the diffuser endcap  26 .  FIGS. 1 and 2  illustrate the flange portion  64  of the burst disk  60  welded to the first side surface  42 . When the flange portion  64  of the burst disk  60  is affixed to the first side surface  42  of the diffuser endcap  26 , the domed central portion  62  of the burst disk  60  closes the flow passage  48 . The domed central portion  62  of the burst disk  60  is designed to rupture when subjected to a pressure differential of a predetermined amount. 
   The igniter endcap  28  includes a cylindrical outer surface  70  and first and second radially extending side surfaces  72  and  74 , respectively. The cylindrical outer surface  70  is centered on axis A and has a diameter that is approximately equal to the diameter of the outer surface  32  of the body portion  22 . The second side surface  74  of the igniter endcap  28  is fixed to the first open end  34  of the body portion  22 .  FIGS. 1 and 2  illustrate the second side surface  74  of the igniter endcap  28  welded to the first open end  34  of the body portion  22 . 
   The inflator  10  also includes a nozzle  80 .  FIGS. 1 and 2  illustrate the nozzle  80  as being formed as one piece with the igniter endcap  28  and not from separate pieces secured together. Alternatively, the nozzle  80  may be formed as a separate piece from the igniter endcap  28  and subsequently fixed to the igniter endcap. 
   The nozzle  80  extends outwardly from the second side surface  74  of the igniter endcap  28 . The nozzle  80  includes a cylindrical outer surface  82  that has a diameter that is less than the diameter of the inner surface  30  of the body portion  22 . As shown in  FIG. 1 , the nozzle  80  extends into the body portion  22  from the first open end  34 . The nozzle  80  terminates at an end surface  84 . The end surface  84  extends in a direction perpendicular to axis A. 
   A passage  90  extends axially through the igniter endcap  28  and the nozzle  80 . An uninterrupted surface  92  defines the passage  90  along its entire axial length between the first side surface  72  of the igniter endcap  28  and the end surface  84  of the nozzle  80 . The uninterrupted surface  92  includes a beveled portion  96 , a cylindrical portion  98 , a tapered portion  100 , and a curved portion  102 . The beveled portion  96  and the cylindrical portion  98  of the surface  92  collectively define a generally cylindrical portion  106  of the passage  90 . The cylindrical portion  106  of the passage  90  is associated with the igniter endcap  28 . The tapered portion  100  of the surface  92  defines a convergent portion  108  of the passage  90 . The curved portion  102  of the surface  92  defines a divergent portion  110  of the passage  90 . The divergent portion of the passage terminates at the end surface  84  of the nozzle  80  with a circular opening  112 . The convergent and divergent portions  108  and  110  of the passage  90  are associated with the nozzle  80 . A throat  114  of the passage  90  is formed at the location where the convergent portion  108  of the passage  90  and the divergent portion  110  meet. 
   A burst disk  116  closes the passage  90 . The burst disk  116  is located in the cylindrical portion  106  of the passage  90  near the convergent portion  108 . The burst disk  116  is secured to the cylindrical portion  98  of the uninterrupted surface  92 . The burst disk  116  is designed to rupture when subjected to a pressure differential of a predetermined amount. 
   A chamber  120  is located within the container  12 . A fluid  122  is stored in the chamber  120 . The fluid  122  in the chamber  120  of the inflator  10  of  FIGS. 1 and 2  is a combustible mixture of gases. The combustible gas mixture  122  is stored under pressure in the chamber  120 . The pressure of the combustible gas mixture  122  is approximately 6,000 psi (pounds per square inch). The combustible gas mixture  122  preferably includes an inert gas, hydrogen, and oxygen. Trace amounts of helium may be added to the combustible gas mixture to aid in leak detection. When heated beyond a predetermined temperature, the combustible gas mixture  122  combusts. Combustion of the combustible gas mixture  122  heats the inert gas. The heated inert gas is an inflation fluid. 
   As an alternative to the combustible gas mixture  122 , the fluid stored in the chamber  120  may be a combustible liquid that is combusted when heated beyond the predetermined temperature or a liquid that experiences gasification upon being heated beyond a predetermined temperature. A refrigerant, for example, Freon, is an example of a liquid that experiences gasification when heated beyond a predetermined temperature. As a further alternative, the fluid may undergo decomposition when heated beyond the predetermined temperature. Nitrous oxide is an example of a gas that undergoes decomposition when heated beyond a predetermined temperature. 
   The inflator  10  also includes an actuatable igniter  130 . The igniter  130  includes an actuatable portion  132  ( FIG. 1 ) and a support portion  134 . The actuatable portion  132  typically contains a pyrotechnic material (not shown) and a resistive wire (not shown) for igniting the pyrotechnic material. The support portion  134  of the igniter  130  is wider in diameter, relative to axis A, than the actuatable portion  132  and includes opposite tapered end surfaces  140  and  142 , respectively, and leads  144  for connecting the igniter to electronic circuitry (not shown) of a vehicle safety system (not shown). 
   The inflator  10  also includes a support member  150  for supporting the igniter  130  relative to the igniter endcap  28 . The support member  150  is generally tubular and includes a frustoconical surface  152 . The support member  150  is affixed to the first side surface  72  of the igniter endcap  28  for securing the igniter  130  relative to the igniter endcap. When the igniter  130  is secured relative to the igniter endcap  28 , as is shown in  FIG. 1 , the tapered end surface  140  of the support portion  134  of the igniter  130  abuts the beveled portion  96  of the surface  92  and the tapered end  142  of the support portion abuts the frustoconical surface  152  of the support member  150 . Also, when the igniter  130  is secured relative to the igniter endcap  28 , the actuatable portion  132  of the igniter  130  is located in the cylindrical portion  106  of the passage  90 , as is illustrated in  FIG. 1 . 
   The inflator  10  of the present invention is actuatable for providing inflation fluid having a low concentration of the combustible gas mixture  122 . To actuate the inflator  10 , an electrical signal is sent to the igniter  130 . When the igniter  130  receives the electrical signal, the igniter  130  is actuated, i.e., the pyrotechnic material of the actuatable portion  132  of the igniter is ignited. 
   Actuation of the igniter  130  produces combustion products. The combustion products result from ignition of the pyrotechnic material of the actuatable portion  132  of the igniter  130 . The combustion products fill the cylindrical portion  106  of the passage  90  between the igniter  130  and the burst disk  116 , and pressure from the combustion products acts on the burst disk. The combustion products from actuation of the igniter  130  may reach a pressure of approximately 14,000 psi. Since the burst disk  116  is subjected to pressure from the chamber  120  of approximately 6,000 psi, the pressure from the combustion products is sufficient to rupture the burst disk  116 . 
   When the burst disk  116  ruptures, the combustion products begin to flow through the passage  90  toward the chamber  120 . The combustion products flow from the higher pressure cylindrical portion  106  of the passage  90  toward the lower pressure chamber  120 . The pressure of combustion products in the higher pressure cylindrical portion  106  is typically greater than twice the pressure of the lower pressure chamber  120 . During the flow toward the chamber  120 , the combustion products enter the convergent and divergent portions  108  and  110  of the passage  90 . As the combustion products flow through the convergent portion  108  of the passage  90  toward the chamber  120 , the flow area of the passage decreases. As a result, the pressure of the combustion products increases and the flow of the combustion products is accelerated. When the flow of the combustion products at the throat  114  of the passage  90  is not choked, the flow of the combustion products through the passage  90  remains subsonic. The flow of the combustion product is choked at the throat  114  when the mass flow of the combustion products through the throat  114  reaches a maximum level for the flow area of the throat. Thus, when the mass flow of the combustion products through the throat  114  of the passage  90  may still be increased, for example, by increasing the pressure differential between the cylindrical portion  106  of the passage and the chamber  120 , the flow of the combustion products through the throat  114  is not choked. As a result, the flow of the combustion products through the passage  90  remains subsonic. 
   After the combustion products pass through the throat  114  of the passage  90 , the combustion products enter the divergent portion  110  of the passage  90 . As the combustion products flow through the divergent portion  110  of the passage  90  toward the chamber  120 , the flow area of the passage increases. During the flow of the combustion products through the divergent portion  110  of the passage  90 , the pressure of the combustion products decreases and the flow of the combustion products is accelerated. The pressure of the combustion products decreases in the divergent portion  110  of the passage  90 . As a result, the combustion products have a pressure that is approximately equal to the pressure of the combustible gas mixture  122  in the chamber  120  when the combustion products reach the opening  112  at the end of the divergent portion of the passage. 
   Since the combustion products exiting the passage  90  at the opening  112  have a pressure equal to the pressure within the chamber  120 , little to no radial expansion, relative to axis A, of the combustion products occurs upon the combustion products entering the chamber  120 . Specifically, upon entering the chamber  120 , the flow of combustion products is in a direction parallel to axis A and radial flow is minimized, relative to axis A. As a result, the flow of combustion products from the divergent portion  110  of the passage  90  is said to be focused.  FIG. 2  illustrates this focused flow of combustion products at  160 . The focused flow of the combustion products into the chamber  120  results in the combustion products traveling at a greater velocity and through a greater axial distance of the chamber  120  as compared to inflators in which radial expansion of the combustion products occurs, as was described with reference to the inflator  500  of  FIGS. 5 and 6 . 
   Since the focused flow of the combustion products travels a greater axial distance, the burn zone that results from the combustion products igniting the combustible gas mixture  122  is located nearer the flow passage  48  of the diffuser endcap  26 . Generally, the nearer the burn zone is located to the flow passage  48  of the diffuser endcap  26 , the greater the quantity of the combustible gas mixture  122  that passes through the burn zone and is combusted prior to exiting the chamber  120 . As a result, the inflation fluid provided by the inflator  10  has a lower concentration of the combustible gas mixture  122 . 
     FIG. 2  illustrates the inflator  10  shortly after actuation of the igniter  130  and after rupturing of the burst disks  116  and  60 . Arrow  162  in  FIG. 2  illustrates inflation fluid having a low concentration of the combustible gas mixture  122  exiting the chamber  120  of the inflator  10  through the flow passage  48 . 
     FIG. 3  is a sectional view of an inflator  10 ′ constructed in accordance with a second embodiment of the present invention. Features of the inflator  10 ′ of  FIG. 3  that are the same as or similar to those in  FIGS. 1 and 2  are labeled with the same reference number with the addition of a prime. Additionally, only the differences between the inflator  10 ′ of  FIG. 3  and the inflator  10  of  FIGS. 1 and 2  are discussed in detail below. 
   The inflator  10 ′ of  FIG. 1  includes a solid propellant material  180  that is ignitable upon the application of heat. The solid propellant material  180  illustrated in  FIG. 1  is in the form of small pellets. The chamber  120 ′ of the container  12 ′ of the inflator  10 ′ is filled with the solid propellant material  180 . Since the chamber  120 ′ of the container  12 ′ is not pressurized, there is no need for a burst disk, similar to burst disk  116  of  FIG. 1 , in the passage  90 ′. Instead, a foil material  182  may extend over the opening to the passage  90 ′ and may be adhered to the end surface  84 ′ of the nozzle  80 ′. The foil material  182  prevents the solid propellant material  180  from entering the passage  90 ′. 
   Additionally, in the inflator  10 ′ of  FIG. 3 , the igniter  130 ′ and the passage  90 ′ are designed for providing supersonic flow of the combustion products in the divergent portion  110 ′ of the passage. Supersonic flow of the combustion products in the divergent portion  110 ′ of the passage  90 ′ occurs when the flow of combustion products at the throat  114 ′ is choked. The flow of combustion products at the throat  114 ′ is choked when the mass flow of the combustion products through the throat  114 ′ reaches a maximum level. The mass flow of the combustion products through the throat  114 ′ reaches a maximum level when, for the given flow area of the throat  114 ′, the mass flow of the combustion products through the throat  114 ′ will not increase, even in response an increase in the pressure differential between the cylindrical portion  106 ′ of the passage  90 ′ and the chamber  120 ′. Given data regarding the combustion products produced by actuation of the igniter  130 ′ and the pressure within the chamber  120 ′, one of ordinary skill in the art of nozzles will be able to determine the appropriate flow area for the throat  114 ′ of the passage  90 ′ for causing choking. 
   When the flow of the combustion products at the throat  114 ′ is choked, the flow speed of the combustion products at the throat  114 ′ equals the speed of sound, i.e., Mach 1. A region of supersonic flow forms just downstream of the throat  114 ′ in the divergent portion  110 ′ of the passage  90 ′. The region of supersonic flow is terminated by the occurrence of either a normal shock wave or shock patterns. The region of supersonic flow may terminate within the divergent portion  110 ′ of the passage  90 ′ or may terminate in the chamber  120 ′ downstream of the divergent portion  110 ′ of the passage  90 ′. The location at which the region of supersonic flow terminates is a function of pressure difference between the combustion products in the cylindrical portion  106 ′ of the passage  90 ′ and the pressure in the chamber  120 ′. Controlling the location at which a region of supersonic flow terminates is well known to those of ordinary skill in the art of nozzles. 
   When the region of supersonic flow terminates in the divergent portion  110 ′ of the passage  90 ′, a normal shock wave occurs. A normal shock wave involves a near instantaneous deceleration of the flow of combustion products to a subsonic speed. After the normal shock wave, the subsonic flow of combustion fluid decelerates through the remainder of the divergent portion  110 ′ and exits the passage  90 ′ as a focused flow of combustion products, as was discussed with reference to  FIG. 2 . 
   When the region of supersonic flow terminates in the chamber  120 ′ downstream of the divergent portion  110 ′ of the passage  90 ′, a complex pattern of shocks and reflections is formed in the focused flow of combustion products that exits the passage  90 ′. The complex pattern of shocks and reflections typically involves a mixture of subsonic and supersonic flows.  FIG. 4  schematically illustrates the complex pattern of shocks and reflections as shock diamonds that are located in the focused flow of combustion products exiting the passage  90 ′. 
   Providing supersonic flow of the combustion products through the divergent portion  110 ′ of the passage  90 ′ in the nozzle  80 ′ increases the distance into the chamber  120 ′ that the combustion products travel. As a result, the burn zone formed from ignition of the solid propellant material  180  is located nearer the flow passage  48 ′ of the diffuser endcap  26 ′. Additionally, the higher speed of the combustion products yields a higher heat transfer rate to the surfaces of the solid propellant material  180  to improve ignition of the solid propellant material. The normal shock wave or the shock patterns resulting from the termination of the supersonic flow may be used to pulverize some of the solid propellant material  180  so as to increase the burn surface area of the solid propellant material. 
     FIG. 4  illustrates the inflator  10 ′ shortly after actuation of the igniter  130 ′ and after rupturing of the foil material  182  and the burst disk  60 ′. Inflation fluid formed from combustion of the solid propellant material  180  exits the chamber  120 ′ of the inflator  10 ′ through the flow passage  48 ′. 
   From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, the convergent and divergent passages  108  and  110  and the throat  114  of the nozzle  80  of the inflator  10  of  FIGS. 1 and 2  may also be designed for enabling supersonic flow of the combustion products. Also, the chamber  120 ′ of the container  12 ′ of  FIGS. 3 and 4  may be pressurized with a stored gas. When the chamber  120 ′ is pressurized with a stored gas, a burst disk similar to the burst disk  116  of  FIG. 1  may be used in the passage  90 ′ to prevent the loss of pressure from the chamber  120 ′. Such improvements, changes, and modifications within the skill of the art are intended to be covered by the appended claims.