Liquid-fueled device to combine the functions of a low pressure switch (LPS), squib, and gas generator

• US 5,496,062 A
• Filed: 02/21/1995
• Issued: 03/05/1996
• Est. Priority Date: 02/16/1994
• Status: Expired due to Fees

• Current Assignee: Autoliv ASP Incorporated (Autoliv Incorporated)
• Original Assignee: Morton International Incorporated (Autoliv Incorporated)
• Inventors: Clark, Marcus T., Rink, Karl K.
• Primary Examiner(s): Focarino, Margaret A.
• Assistant Examiner(s): English, Peter C.
• Application Number:
  US08/392,633
• Time in Patent Office: 378 Days
• Field of Search: 280/737, 280/741, 280/736, 280/740, 280/735, 102/202.5, 102/202.7, 102/202.14, 102/530, 102/531, 200/83 R, 200/83 A, 200/83 N, 200/83 P, 200/83 Y, 200/61.08, 73/716, 73/717, 73/719, 73/723, 73/725
• US Class Current: 280/737
• CPC Class Codes: B60R 2021/26052 using fluid materials
• CPC Class Codes: B60R 2021/2725 using a fluid fuel gas generator
• CPC Class Codes: B60R 21/264 using instantaneous generation of gas, e.g. pyrotechnic B60R21/268 takes precedence
• CPC Class Codes: B60R 21/272 with means for increasing the pressure of the gas just before or during liberation, e.g. hybrid inflators

Abstract

Featured for use with a hybrid air bag inflator containing inert stored gas under high pressure is a liquid fueled construction which combines the functions of an initiator, gas generator, and differential low pressure switch into a single device. Instead of being filled with a mixture of combustible gases, the device is filled with a combination of gases and liquids. Alternatively, it makes use of a hybrid squib in conjunction with different combinations of gases and liquids. A pyrotechnic material is used to ignite the mixture regardless of the combination of fuel and oxidant used in the device. A ceramic body is used to house the device. Upon combustion of the mixture, the ceramic body ruptures violently, permitting efficient transfer of the explosive energy to the inert stored gas in the hybrid inflator.

Claims

1. A liquid-fueled device to combine the functions of a low pressure switch, squib and gas generator for a compressed gas air bag inflator comprising,

first and second diaphragms each of which are electrically conducting,

electrically non-conductive spacer means having a first side and a second side,

attaching means attaching said first diaphragm and said second diaphragm in opposed and sealing relation to said first and second sides, respectively, of said spacer means thereby forming a hermetically sealed chamber, with said first diaphragm and said second diaphragm being movable toward and away from each other from a predetermined spaced relationship as the pressure of the environment externally of said hermetically sealed chamber increases and decreases relatively to the pressure in said hermetically sealed chamber,

a liquid fuel normally stored under a high pressure oxidizing environment in said hermetically sealed chamber,

a pyrotechnic initiator contained in said hermetically sealed chamber, said pyrotechnic initiator igniting in response to an electrical current of predetermined level thereto,

a pressure monitoring resistor having first and second ends positioned so as to make and break electrical-contact with said first and second diaphragms as said first and second diaphragms are moved toward and away from each other from a predetermined spaced relation, and

electrical circuit means to which said pressure monitoring resistor and said pyrotechnic initiator are connected, said electrical circuit means normally having a flow of electrical monitoring current therein which is too low to ignite said pyrotechnic initiator in said hermetically sealed chamber, but having a capability of having produced therein a flow of electrical current at a predetermined level high enough to cause initiation of said pyrotechnic initiator,

whereby, with said hermetically sealed chamber pressurized to a predetermined reference level, in atmospheric environment conditions the pressure in said chamber is higher than atmospheric pressure and said first and second diaphragms are caused to move away from each other and thereby break the electrical contact of said pressure monitoring resistor and cause a change of resistance in said electrical circuit means,

whereby with the pressure of the environment external to said hermetically sealed chamber higher by a predetermined amount than said predetermined reference level in said chamber, said first and second diaphragms are caused to move toward each other and cause said pressure monitoring resistor to make electrical contact with said diaphragms and cause a change of resistance in said electrical circuit means,

whereby, if the seal of said hermetically sealed chamber fails, the resulting equalization of the chamber pressure and the pressure of the environment external to said chamber causes said first diaphragm and said second diaphragm to move away from each other and break the electrical contact of said pressure monitoring resistor and cause a change in the resistance of said electrical circuit means, and

whereby with a flow of a large electrical current through said pyrotechnic initiator, that is, an electrical current at a level high enough to cause initiation thereof, said pyrotechnic initiator is initiated and ignites said liquid fuel in said hermetically sealed chamber.

2. A device as defined by claim 1 wherein said liquid fuel comprises a hydrocarbon or hydrocarbon-derivative fuel.

3. A device as defined by claim 2 wherein said liquid fuel is ethyl alcohol.

4. A device as defined by claim 1 wherein the thermal expansion characteristics of the oxidizing environment in said hermetically sealed chamber are similar to those of the gas external to said hermetically sealed chamber.

5. A device as defined by claim 4 wherein the gas external to said hermetically sealed chamber comprises a stored compressed inert gas in an air bag inflator.

6. A device as defined by claim 5 wherein said spacer means forms an external wall of said device and comprises a spacer ring made of a brittle material such as a ceramic that offers adequate tensile strength to withstand the internal pressure of the stored flammable mixture of said liquid fuel and said oxidizing environment and enough compressive strength that it can withstand the differential pressure created by the difference in storage pressure between the external, inert gas and that of the internal flammable mixture,

whereby, upon combustion of said flammable mixture, the high internal pressure generated within said device immediately causes brittle fracture of said spacer ring with subsequent escape of the combustion products into the stored compressed inert gas in the air bag inflator.

7. A device as defined by claim 6 wherein said device includes a fill port so that the liquid fuel can be added to the device before it is filled with oxidant to produce the oxidizing environment in said hermetically sealed chamber.

8. A device as defined by claim 1 wherein said pyrotechnic initiator comprises a hybrid squib to aid in long-term storage of the flammable mixture, wherein the quantity of fuel, whether liquid or gaseous, stored in contact with the oxidant would be insufficient to allow combustion of the mixture during any ambient condition, but when initiated the hybrid squib would ignite, discharging hot fuel and radiant particles into said hermetically sealed chamber.

9. A device as defined by claim 8 which incorporates in said hybrid squib all of the fuel in said hermetically sealed chamber,

whereby only an oxidant inert gas mixture is stored within said hermetically sealed chamber,

thereby facilitating tailoring of the thermal expansion characteristics of the stored oxidant in said hermetically sealed chamber to those of the compressed inert gas in the air bag inflator.

10. A device as defined by claim 1,

wherein said spacer means comprises a spacer ring, and

wherein said attaching means includes first and second protective rings each of which has an aperture therein in a central portion thereof and has a first side and a second side, said first diaphragm being attached in sealing relationship to said second side of said second protective ring symmetrically with respect to the aperture therein, with the first side of said first protective ring being disposed in sealing relationship with the first side of said spacer ring and the second side of said second protective ring being disposed in sealing relationship with the second side of said spacer ring.

11. A device as defined by claim 10,

wherein said first and said second diaphragms are attached to said first and second protective rings by mechanical bonding.

12. A device as defined by claim 10,

wherein said first and said second protective rings are each electrically conductive.

13. A device as defined by claim 12 further including a separate electrical lead attached to each of said first and second protective rings.

14. A device as defined by claim 10,

further including a pressure disc provided in at least one of said protective rings to rupture and allow the heated gases to flow out of said hermetically sealed chamber upon ignition of said pyrotechnic initiation.

15. A combination low pressure switch/initiator/gas generator device for an inflator of a hybrid inflatable air bag safety restraint system that includes a storage chamber containing stored inert inflation gas under high pressure comprising,

an ignition train and pressure differential switch positioned in said storage chamber,

said ignition train and differential switch comprising first and second diaphragms each of which is electrically conducting,

electrically non-conductive spacer means having a first side and a second side, attaching means attaching said first diaphragm and said second diaphragm in opposed and sealing relation to said first and second sides, respectively, of said spacer means thereby forming a hermetically sealed chamber with said first diaphragm and said second diaphragm being movable toward and away from each other from a spaced relationship as the pressure in said inflator storage chamber increases and decreases relatively to the pressure in said hermetically sealed chamber,

pyrotechnic means contained in said hermetically sealed chamber, said pyrotechnic means comprising a liquid fuel, a high pressure oxidizing environment, and squib means having a housing to effect ignition in said oxidizing environment of said fuel,

a pressure monitoring resistor having first and second ends with said ends positioned so as to make and break electrical contact with said first and second diaphragms as said first and second diaphragms are moved toward and away from each other from a predetermined spaced relationship, and

electrical circuit means to which said pressure monitoring resistor is connected when said ends of said pressure monitoring resistor are in electrical contact with said first and second diaphragms, said electrical circuit means being connected to said squib means for effecting initiation thereof but normally having a flow of electrical current therein which is too low to cause initiation thereof, but having a capability of having produced therein a flow of electrical current at a level high enough to cause immediate initiation of said squib means.

16. A device as defined by claim 15 wherein the external wall of said device includes a portion that is made of a brittle material such as a ceramic that offers adequate tensile strength to withstand the internal pressure of the stored flammable mixture of liquid fuel and said oxidizing environment and enough compressive strength that it can withstand the differential pressure created by the difference in storage pressure between the external inert gas and that of the internal flammable mixture,

whereby, upon combustion of the flammable mixture, the high internal pressure generated within the device immediately causes brittle fracture of said external wall with subsequent escape of the combustion products into the stored inert gas under high pressure in the air bag inflator.

17. A combination as defined by claim 15 wherein said squib means comprises a hybrid squib having a core pyrotechnic charge contained in a pyrotechnic charge holder sealed to said squib housing, and an output can containing said liquid fuel and sealed to said squib housing.

18. A combination as defined by claim 17 wherein a sealing separation is provided on said hybrid squib to separate the core pyrotechnic charge and said liquid fuel.

19. A liquid-fueled device to combine the functions of a low pressure switch, squib and gas generator for a compressed gas air bag inflator comprising,

a hermetically sealed chamber containing a liquid fuel normally stored under a high pressure oxidizing environment,

a brittle ceramic body in which said hermetically sealed chamber is housed,

a first diaphragm partly bounding said hermetically sealed chamber,

a pressure monitoring resistor situated adjacent said first diaphragm,

a squib contained in said hermetically sealed chamber, and

first and second externally located monitoring terminals electrically connected such that a predetermined excess of external pressure results in displacement of said first diaphragm causing electrical interconnection of the monitoring terminals via said pressure monitoring resistor, and

electrical circuit means to which said pressure monitoring resistor and said squib are connected, said electrical circuit means normally having a flow of electrical current therein which is too low to ignite said squib in said hermetically sealed chamber, but having a capability of having produced therein a flow of electrical current at a predetermined level high enough to cause initiation of said squib,

whereby upon combustion of the flammable mixture in said hermetically sealed chamber the high pressures generated immediately causes brittle fracture of said ceramic body with subsequent venting of the combustion products to the compressed gas air bag inflator.

20. A device as defined by claim 19 wherein said liquid fuel in said hermetically sealed chamber comprises a hydrocarbon or hydro-carbon derivative fuel.

21. A device as defined by claim 19 wherein said liquid fuel is ethyl alcohol.

22. A device as defined by claim 19 wherein said squib is a hybrid squib which incorporates therein a portion, at least, of the liquid fuel contained in said hermetically sealed chamber.

23. A device as defined by claim 19 wherein said squib is a hybrid squib which incorporates therein all of the fuel in said hermetically sealed chamber with only an oxidant otherwise being contained in said hermetically sealed chamber.