Inflator

1. An inflator, comprising:

an ignition device chamber accommodating therein an igniter and having a gas discharge port;

a pressurized gas chamber filled with a pressurized gas inside a bottle;

a rupturable plate closing between the ignition device chamber and the pressurized gas chamber;

a partition wall provided with a rod serving as a fracturing device for the rupturable plate and the partition wall axially separating an interior of an ignition device unit housing, corresponding to the ignition device chamber, into two chambers;

a combustion chamber provided on the side of a first end of the ignition device unit housing and provided with an electric igniter mounted at an opening of the first end; and

a diffuser chamber having the gas discharge port and provided on the side of a second end, which is an opposite end to the first end of the ignition device unit housing,

the rupturable plate being circular and having,

a circumferential edge fixing portion that is fixed to either one of the bottle and the ignition device unit housing,

a circular non-fixing portion on an inner portion other than the circumferential edge fixing portion,

a fragile portion formed by not less than three grooves provided on a first surface facing the bottle, the grooves extending from a circumference of the circular non-fixing portion or from positions in the vicinity thereof, as a start point, toward a center of the circular non-fixing portion such that each of end points of the grooves does not reach the center of the circular non-fixing portion,

no fragile portion formed on a second surface on the side of the ignition device unit housing, and

the rod provided at the partition wall and serving as the fracturing device, the rod being fixed to the partition wall and extending toward the rupturable plate, and the rod coming into contact with all of the end points in the fragile portion and rupturing the rupturable plate when the partition wall upon receipt of a gas pressure generated by activation of the ignition device moves in an axial direction and the rod collides with the rupturable plate.

2. The inflator according to claim 1 , wherein

the cross-sectional shape of the rod is circular, and an a 2 /a 1 ratio of the maximum cross-sectional area (a 2 ) of the rod in the radial direction to the area (a 1 ) of the circle formed by connecting the end points of the grooves forming the fragile portion is in a range of 1 to 1.2.

3. The inflator according to claim 1 , wherein the rod has a sharp portion at a tip thereof.

4. An inflator, comprising:

an ignition device chamber accommodating therein an igniter and having a gas discharge port;

a pressurized gas chamber filled with a pressurized gas inside a bottle;

a rupturable plate closing between the ignition device chamber and the pressurized gas chamber;

a partition wall provided with a rod serving as a fracturing device for the rupturable plate and the partition wall axially separating an interior of an ignition device unit housing, corresponding to the ignition device chamber, into two chambers;

a combustion chamber provided on the side of a first end of the ignition device unit housing and provided with an electric igniter mounted at an opening of the first end; and

a diffuser chamber having the gas discharge port and provided on the side of a second end, which is an opposite end to the first end of the ignition device unit housing,

the rupturable plate being circular and having,

a circumferential edge fixing portion that is fixed to either one of the bottle and the ignition device unit housing,

a circular non-fixing portion on an inner portion other than the circumferential edge fixing portion,

a fragile portion formed in a polygon in the circular non-fixing portion on a first surface facing the bottle, the fragile portion including,

first fragile portions formed by grooves forming a perimeter of the polygon, and

second fragile portions formed by grooves that extend from all vertices of the polygon as a start point toward a center of the polygon such that each of end points of the grooves does not reach the center of the polygon,

a plurality of substantially triangular shapes formed by the first fragile portions as a base and the second fragile portions as remaining two sides,

a depth (h 1 ) of the first fragile portion and a depth (h 2 ) of the second fragile portion satisfying the relationship h 1 <h 2 ,

the second fragile portions having the same length as one other, and the rod coming into contact with all of the end points of the second fragile portions and rupturing the rupturable plate when the partition wall upon receipt of a gas pressure generated by activation of the ignition device moves in an axial direction and the rod collides with the rupturable plate.

5. The inflator according to claim 4 , wherein

a ratio (h 1 /T) of the depth (h 1 ) of the first fragile portion formed by the groove to a thickness (T) of a portion in the rupturable plate devoid of the first fragile portions is in a range of 0.05 to 0.50,

a ratio (h 2 /T) of the depth (h 2 ) of the second fragile portion formed by the groove to a thickness (T) of a portion in the rupturable plate devoid of the second fragile portions is in a range of 0.20 to 0.60, and

the relationship h 1 <h 2 is satisfied.

6. The inflator according to claim 4 , wherein

the cross-sectional shape of the rod is circular, and an a 2 /a 1 ratio of the maximum cross-sectional area (a 2 ) of the rod in the radial direction to the area (a 1 ) of the circle formed by connecting the end points of the grooves of the second fragile portions is in a range of 1 to 1.2.

7. The inflator according to claim 4 , wherein the rod has a sharp portion at a tip thereof.