Triggered-stroke actuator for a safety device incorporated into a motor vehicle to protect a pedestrian in the event of a frontal impact

Abstract

A triggered-stroke actuator with a damped return stroke. According to the invention, the actuator houses a piston ( 15 ), and a gas generator ( 19 ) including a fast combustion pyrotechnic charge, and further houses a pyrotechnic charge ( 38 ) of combustion that is slower than the combustion of said gas generator ( 19 ).

1 . A triggered-stroke actuator comprising a body housing a piston linked to a rod that projects from one end of said body, and a controlled gas generator mounted in said body facing said piston and at a predetermined distance from an initial position thereof prior to triggering so as to define an expansion chamber between said gas generator and said piston, said gas generator including a fast combustion pyrotechnic charge, wherein the actuator includes a pyrotechnic charge of combustion that is slower than the combustion of said gas generator and that is housed in a location that communicates with said expansion chamber. 
     
     
         2 . A triggered-stroke actuator according to  claim 1 , said slow combustion pyrotechnic charge is placed in a cavity in the piston, the cavity opening out into said expansion chamber. 
     
     
         3 . A triggered-stroke actuator according to  claim 2 , wherein said cavity opens out into said expansion chamber axially facing said gas generator. 
     
     
         4 . A triggered-stroke actuator according to  claim 1 , wherein a calibrated leakage passage communicating with said expansion chamber is formed in the piston and optionally in said rod. 
     
     
         5 . A triggered-stroke actuator according to  claim 4 , wherein said piston and said rod are rigidly secured to each other, and said leakage passage opens out through the surface of said rod into an annular space defined between the rod and the inside wall of said body. 
     
     
         6 . A triggered-stroke actuator according to  claim 5 , wherein a sealing gasket is carried by said rod in the vicinity of its free outer end, and in that, in the non-activated position of the actuator, said gasket extends between said rod and the inside wall of said body in the vicinity of its corresponding end. 
     
     
         7 . A triggered-stroke actuator according to  claim 4 , wherein said leakage passage communicates with said cavity in the piston that houses said slow combustion pyrotechnic charge. 
     
     
         8 . A triggered-stroke actuator according to  claim 7 , wherein a filter is arranged in the piston between said cavity and said calibrated leakage passage. 
     
     
         9 . A triggered-stroke actuator according to  claim 5 , wherein the annular space is isolated from the expansion chamber by means of an O-ring arranged between said piston and said body. 
     
     
         10 . An actuator according to  claim 1 , wherein is included a breakable or disconnectable connection element holding the piston at a predetermined distance from the pyrotechnic generator to act, prior to actuation, to stabilize the position of the rod and the initial volume of the expansion chamber. 
     
     
         11 . A triggered-stroke actuator according to  claim 1 , wherein said slow combustion pyrotechnic charge is placed in the gas generator including said fast combustion pyrotechnic charge, opening out into said expansion chamber.