Land vehicles – Wheeled – Attachment
Reexamination Certificate
2002-05-28
2004-06-29
Jordan, Charles T. (Department: 3644)
Land vehicles
Wheeled
Attachment
Reexamination Certificate
active
06755439
ABSTRACT:
BACKGROUND
The present invention relates to an inflator for generating gas for inflating and deploying an airbag.
As a gas generator for deploying an airbag, a type (combustion type) of inflator which burns a gas-generating agent (propellants) and generates gases by chemical reaction, and another type (stored-gas type) of inflator which ejects a high-pressure gas stored in a container are known.
A stored-gas-type inflator is shown in FIG.
5
.
FIG. 5
is a schematic longitudinal-sectional view of a known stored-gas-type inflator which is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 10-250525 (incorporated by reference herein).
The inflator
100
includes a bottle
101
to be charged with a high-pressure gas. A sleeve
109
is connected at an opening
103
of the bottle
101
via a ring
106
. The ring
106
is provided with an aperture
106
a
formed at a central part of the ring
106
.
A burst disk or sealing plate
107
is mounted by welding or similar methods to the sleeve
109
side of the ring
106
(i.e., the left side of the ring
106
as shown in FIG.
5
). The burst disk
107
is made of steel and has a thickness of approximately 0.3 mm. As shown in
FIG. 5
, the burst disk
107
bows toward the sleeve
109
side due to the pressure of the gas stored in the bottle
101
.
A plurality of gas outlets
104
are formed in the sidewall of the sleeve
109
. During operation of the inflator the high-pressure gas in the bottle
101
is ejected through the outlets
104
. A housing
110
mates with the sleeve
109
at an end (the left side open end in FIG.
5
). The housing
110
includes an initiator fixing or retaining part
110
a
and a cylinder
110
b
protruding from the fixing part
110
a
. The fixing part
110
a
is affixed and held by the sleeve
109
at the end thereof. An initiator
112
is embedded in the fixing part
110
a
. An end (right side end)
112
a
of the initiator
112
extends into the cylinder
110
b.
A piston
115
is disposed in the cylinder
110
b
of the housing
110
. An end
115
a
of the piston
115
is tapered in a cone-shape. The piston
115
is provided with a hole
115
b
formed in the rear end of the piston
115
. The end
112
a
of the initiator
112
is inserted into the hole
115
b
. The burst disk
107
is disposed at a predetermined distance from an end
110
c
of the cylinder
110
b
of the housing
110
.
The gas outlets
104
of the inflator
100
communicate with an airbag body (not shown). In a normal state, a gas fills the bottle
101
and is sealed in the bottle
101
with the burst disk
107
. When the automobile receives an impact, a sensor (not shown) operates and the initiator
112
generates a gas blast. The gas blast moves the piston
115
away from the housing toward the burst disk (i.e., to the right of FIG.
5
).
The end
115
a
of the piston
115
breaks the burst disk
107
at a central part. The high-pressure gas filling the bottle
101
is ejected and is supplied into the airbag body from the inside of the sleeve
109
through the gas outlets
104
formed in the peripheral surface of the sleeve
109
.
The end
115
a
of the piston
115
must be keen-edged so that the piston
115
reliably breaks the burst disk
107
. In the above example, the end
115
a
is formed tapered in a cone-shape.
A gas generator used in an inflator or the like is disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 5-201304, 10-138862, and 12-250525 (all three incorporated by reference herein), in which the piston of the gas generator takes the shape of a cylinder, a cone, and a pyramid (polygonal), respectively.
FIG. 6
shows an end of the piston having another shape. As show in FIGS.
6
(A),
6
(B) and
6
(C), respectively, the end of the piston may be formed as a needle, a cylinder shown, or as a punch.
As shown in FIG.
6
(A), the needle
121
includes a fine pointed tip. As shown in FIG.
6
(B), the cylinder
123
is provided with a circular recess formed at one end. The circular recess includes a cutting edge
125
around the periphery. As shown in
FIG. 6
(C), the punch includes a cylinder
127
having a two-forked end. The forked end includes two cutting edges
129
.
From among the shapes of the end of the piston discussed above, the punch-shaped two-forked end is currently thought to be the most effective shape for reliably breaking the sealing plate with the smallest force. The punch-shaped piston cuts into the burst disk at two positions located away from the vertex of the swelling burst disk. However, the two-forked punch-shaped piston has a problem described below.
FIG. 7
is a schematic view of the two-forked punch-shaped piston being deformed at an instant when the piston comes into contact with the burst disk. Although the piston is arranged so that its longitudinal axis
131
is aligned with the vertex of the burst disk swelling in a spherical shape, the tip of each cutting edge
129
is offset to the outside from the axis
131
of the piston. As a result, when the piston comes into contact with the spherically swelling burst disk, the tips of the two cutting edges
129
come into contact with the burst disk at positions remote from the vertex of the disk. The cutting edges do not contact the disk at a right angle and, instead, contact the disk at a smaller angle. As a result, the cutting edges
129
sometimes slide on the surface of the burst disk
129
′ and are bent toward the outside, as shown by dotted lines in FIG.
7
. Therefore, the cutting edges do not sharply cut and there is a risk that the burst disk is not broken smoothly.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an inflator that includes a piston which is capable of reliably breaking a burst disk or sealing plate with a small force.
According to one embodiment of the present invention an inflator is provided. The inflator comprises a bottle to be charged with high-pressure gas and having an opening. The inflator also includes a sealing plate for sealing the bottle at the opening and an initiator for generating a gas blast. The gas blast provides the motive force to break the sealing plate. A punch or piston that includes a cutting edge is provided for breaking the sealing plate. The punch being accelerated toward the sealing plate by the gas blast of the initiator. The sealing plate swells toward the punch by being pressed by the high-pressure gas. The cutting edge of the punch comes into contact with a portion of the sealing plate offset from the vertex of the swell of the sealing plate. The cutting edge of the punch is formed by a tapered face formed at the outer side of the cutting edge (i.e., at the side away from the vertex of the sealing plate).
Due to the tapered cutting edge of the punch, the tip of the cutting edge is positioned inside the periphery of the punch. An angle between the central line of the cutting edge and the surface of the sealing plate is increased. Therefore, the cut made by the cutting edge into the swelling sealing plate is improved, and the deformation of the cutting edge away from the vertex of the sealing plate and the slippage of the cutting edge along the spherical surface of the sealing plate are reduced. As a result, the reliability of the punch breaking the sealing plate is increased.
According to an embodiment of the present invention, the tapered face is preferably formed so as to have an angle smaller than an angle oh of friction with respect to the normal line on a contact point between the cutting edge and the sealing plate, the angle &agr; of friction being determined in accordance with the materials of the punch and the sealing plate. The length (in the axial direction of the punch) of the tapered face is preferably set to 0.5 mm or greater. With the arrangement of the shape and the size as described above, the cutting edge can effectively and reliably break the sealing plate.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and exp
Foley & Lardner LLP
Jordan Charles T.
Nguyen T.
Takata Corporation
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