Pyrotechnic actuator and method of actuating a pyrotechnic actuator

Abstract

A pyrotechnic actuator and a method of actuating the same are described. The actuator comprises a pressure chamber and a piston having such an outer diameter that it is snugly fitted into the pressure chamber. A gas generating ignition and output charge generates gas that pressurizes the pressure chamber and the piston when ignited. The piston is designed such that at least part of its outer diameter expands under the pressure in the pressure chamber such that at least a part of the external piston surface is forced into a press fit against the internal wall of the pressure chamber and therefore seals the pressure chamber. This prevents exhaust gas and flames from escaping from the device in an uncontrolled manner.

1 . A pyrotechnic actuator comprising:
 a pressure chamber that is defined by an internal pressure chamber wall and an outer piston wall;   a piston having such an outer diameter that it is snugly fitted into the pressure chamber such that at least a part of an external piston surface extends in close proximity to or abuts against at least a part of the internal pressure chamber wall;   a gas generating ignition and output charge generating gas that pressurizes the pressure chamber and the piston when ignited; and   an igniter for igniting the gas generating ignition and output charge; wherein   the piston is designed such that at least part of its outer diameter expands under the pressure in the pressure chamber such that at least a part of the external piston surface is forced into a press fit against the internal wall of the pressure chamber.   
     
     
         2 . The pyrotechnic actuator of  claim 1 , wherein the piston is at least in part hollow comprising an internal piston wall that forms a part of a piston surface defining the pressure chamber together with the internal pressure chamber wall. 
     
     
         3 . The pyrotechnic actuator of  claim 1 , wherein the internal piston wall is formed as a depression in a rear end face of the piston. 
     
     
         4 . The pyrotechnic actuator of  claim 3 , wherein the depression has such a shape and size that it determines which part of the piston expands in its outer diameter and to what extent it expands. 
     
     
         5 . The pyrotechnic actuator of  claim 4 , wherein the depression starts from the rear end face as a cylindrical depression that is followed towards a front end face of the piston by a conical section narrowing towards the front end face. 
     
     
         6 . The pyrotechnic actuator of  claim 4 , wherein the depression starts from the rear end face as a cylindrical depression that is followed towards a front end face of the piston by a semi-spherical section narrowing towards the front end face. 
     
     
         7 . The pyrotechnic actuator of  claim 4 , wherein the depression starts from the rear end face as a cylindrical depression that comprises a dome-shaped bottom that deepens from an intersection with a piston center line towards an outer circumference of the bottom. 
     
     
         8 . The pyrotechnic actuator of  claim 3 , wherein the depression in the rear end face of the piston comprises an inner diameter that is at least half of the outer diameter of the piston and extends over at least one third of a length of the piston. 
     
     
         9 . The pyrotechnic actuator of  claim 3 , wherein the gas generating ignition and output charge is provided in an output can that is ignited by electrical contacts and the output can is accommodated in the depression before the ignition and output charge is ignited. 
     
     
         10 . The pyrotechnic actuator of  claim 1 , wherein the external piston surface comprises a plurality of semicircular ridges which are press-fitted into the internal pressure chamber wall. 
     
     
         11 . The pyrotechnic actuator of  claim 1 , further comprising a stop limiting the maximum movement of the piston along the pressure chamber such that the press-fit between the external piston surface and the internal wall of the pressure chamber is maintained. 
     
     
         12 . The pyrotechnic actuator of  claim 1 , wherein the press-fit between the external piston surface and the internal wall of the pressure chamber substantially seals the pressure chamber retaining the generated gas within the pressure chamber. 
     
     
         13 . The pyrotechnic actuator of  claim 1 , wherein the pyrotechnic actuator is a part of one of the group consisting of: pyrotechnic power disconnect devices, pyrotechnic battery disconnect devices, pyrotechnic fuses, pyrotechnic switches, pyrotechnic cable cutters, pyrotechnic release devices, pyrotechnic locking devices, pyrotechnic interrupters, and pyrotechnic dislodging devices. 
     
     
         14 . The pyrotechnic actuator of  claim 1 , wherein a front end face of the piston is connected to at least one of a latch and a knife. 
     
     
         15 . A method of actuating a pyrotechnic actuator that comprises a pressure chamber that is defined by an internal wall and a piston having such an outer diameter that the piston is fitted snugly into the internal wall of the pressure chamber such that at least a part of an external piston surface extends in close proximity to or abuts against at least a part of the internal wall surface; the method comprising:
 igniting a gas generating charge of an explosive;   pressurizing the pressure chamber and at least one surface of the piston with the gas generated by the ignited charge of an explosive;   expanding the piston in its outer diameter by pressure within the pressurized pressure chamber such that at least a part of the external piston surface is forced into a press-fit against the internal wall of the pressure chamber; and   propelling the piston by the pressure in the pressure chamber along the same while maintaining the press fit created by the pressure induced piston expansion.   
     
     
         16 . The method of  claim 15 , further comprising stopping the piston at a maximum traveling range by running the piston against a stop. 
     
     
         17 . The method of  claim 15 , further comprising at least one of cutting, latching and releasing by the moving piston. 
     
     
         18 . The method of  claim 15 , further comprising substantially sealing the pressure chamber by expanding the piston into the press-fit. 
     
     
         19 . The method of  claim 15 , further comprising imperfectly sealing the pressure chamber by expanding the piston into the press-fit such that a gradual releasing of the pressure within the pressure chamber takes at least 1 minute.