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An inflator including a piston which can reliably break a sealing plate. The inflator includes a piston which is two-forked at an end thereof and is provided with two cutting edges. The cutting edges come into contact with portions of a sealing plate which swells toward the piston side by being push

An inflator including a piston which can reliably break a sealing plate. The inflator includes a piston which is two-forked at an end thereof and is provided with two cutting edges. The cutting edges come into contact with portions of a sealing plate which swells toward the piston side by being pushed by a high-pressure gas stored in a bottle. The portions being offset from the vertex of the swelling sealing plate. Each cutting edge is tapered at the outer side thereof, and the tip of the cutting edge is thereby positioned at the inner side of the periphery of the piston. The angle formed between the axis of each cutting edge and the surface of the sealing plate is increased. Deformation of the cutting edges toward the outside and slip thereof along the spherical surface can be suppressed.

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1. An inflator comprising:a bottle provided with an opening, to be charged with a high-pressure gas;a sealing plate for sealing the bottle at the opening thereof;an initiator for generating a gas blast as a motive force to break the sealing plate; anda piston including a cutting edge for breaking th

1. An inflator comprising:a bottle provided with an opening, to be charged with a high-pressure gas;a sealing plate for sealing the bottle at the opening thereof;an initiator for generating a gas blast as a motive force to break the sealing plate; anda piston including a cutting edge for breaking the sealing plate, the piston accelerating with the gas blast of the initiator,wherein the sealing plate swells toward the piston due to the pressure of the high-pressure gas;wherein the cutting edge of the piston comes into contact with a portion of the sealing plate offset from the vertex of the swell of the sealing plate; andwherein the cutting edge is provided with a tapered face formed at the side away from the vertex of the sealing plate side of the cutting edge;wherein the piston is arranged so that an angle between the tapered face and a line disposed on a longitudinal axis of the piston is less an acute angle between a line normal to the sealing plate at a contact point between the cutting edge and the sealing plate and the line disposed on the longitudinal axis of the piston. 2. An inflator according to claim 1, wherein the tapered face is formed so that an angle between the tapered face and the line normal to the sealing point at the point where the cutting edge contacts the sealing plate is smaller than an angle α of friction determined in accordance with the materials of the piston and the sealing plate. 3. An inflator according to one of claim 1, wherein the length in the axial direction of the piston of the tapered face is greater than or equal to 0.5 mm. 4. The inflator of claim 1, wherein the tapered face is arranged so that an angle between the tapered face and the line formal to the sealing plate at a contact point between the cutting edge and the sealing plate is greater than zero and less than an angle of friction determined based on sealing plate and the piston. 5. An inflator comprising:a bottle containing pressurized gas;a sealing plate for sealing an opening in the bottle; anda piston for breaking the sealing plate;wherein the piston includes a cutting edge having a tapered face formed on an outer side of the cutting edge away from the center of the sealing plate;wherein the piston is arranged so that an angle between the tapered face and a line disposed on a longitudinal axis of the piston is less an acute angle between a line normal to the sealing plate at a contact point between the cutting edge and the sealing plate and the line disposed on the longitudinal axis of the piston. 6. The inflator of claim 5, wherein the tapered face is formed so that an angle between the tapered face and the line normal to the sealing point at the point where the cutting edge contacts the sealing plate is smaller than an angle α of friction determined based on the materials of the piston and the sealing plate. 7. The inflator of claim 6, wherein the length of the tapered face in the axial direction of the piston is greater than or equal to 0.5 mm. 8. The inflator of claim 5, wherein the angle between the tapered face and the line normal to the sealing point at the point where the cutting edge contacts the sealing plate is smaller than or equal to an angle between an elongation of the tapered face and a line disposed along a peripheral surface of the piston parallel to the longitudinal axis of the piston. 9. A stored gas inflator having a sealing plate and a punch for puncturing the sealing plate and releasing the gas, wherein the punch is forked shaped and includes two prongs, each of the prongs having a surface tapering inward from the outside of the punch; wherein each of the prongs is arranged so that an angle between the tapered surface and a line disposed on a longitudinal axis of the punch is less an acute angle between a line normal to the sealing plate at a contact point between a cutting edge of the tapered surface and the sealing plate and the line disposed on the longitudinal axis of the punch. 10. The inflator of claim 9, wherein the tapered surface is arranged so that an angle between the tapered surface and a line formal to the sealing plate at a contact point between a cutting edge of the tapered surface and the sealing plate is greater than zero and less than an angle of friction determined based on sealing plate and the punch.