Low pressure switch/initiator/gas generator

A combination low pressure switch/initiator/gas generator device 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,
• pyrotechnic means contained in said hermetically sealed chamber, said pyrotechnic means igniting when heated to a predetermined level,
• a bridgewire resistor having a first end and a second end, said bridgewire resistor being located in said hermetically sealed chamber and having said first end electrically connected to said first diaphragm and said second end electrically connected to said second diaphragm,
• 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,
• electrical circuit means in which said bridgewire resistor and said pressure monitoring resistor are connected in parallel relation when both said first and second ends of said pressure monitoring resistor are in electrical contact with said diaphragms, said electrical circuit means normally having a flow of electrical monitoring current therein which is too low to cause sufficient heating of said bridgewire resistor to ignite said pyrotechnic means in said hermetically sealed chamber, but having a capability of having produced therein a flow of electrical current at a level high enough to cause such heating of said bridgewire resistor,
• 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 with said second diaphragm 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 the ends of said pressure monitoring resistor to make electrical contact with said diaphragms and cause a change in the resistance of 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 between one end of said pressure monitoring resistor and said respective diaphragm and cause a change in the resistance of said circuit means, and
• whereby with a flow of a large electrical current through said bridgewire resistor, that is, an electrical current at a level high enough to cause heating thereof, said bridgewire resistor heats up to a point that causes ignition of said pyrotechnic means in said hermetically sealed chamber.