Land vehicles – Wheeled – Attachment
Reexamination Certificate
1998-12-31
2002-06-25
Culbreth, Eric (Department: 3611)
Land vehicles
Wheeled
Attachment
C280S736000
Reexamination Certificate
active
06409214
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to airbag inflators and systems utilizing same for enhancement of driver and passenger protection, including side impact protection, in motor vehicles and the like.
BACKGROUND OF THE INVENTION
Conventional airbag inflators have relatively complex structures with elements such as forged housings defining internal ignition, combustion, and filter chambers by integrally formed and/or welded internal partitions. Furthermore, coolant structures, such as filters formed from heat conductive materials and the like, in many cases require the foregoing structural complexities in order to withstand the temperatures and pressures generated within these inflator structures.
Many of such conventional inflators use azide based gas generating materials such as sodium azide based materials which have relatively high burn rates and undesirable toxicity levels and products of combustion such as mists and ash associated therewith.
Accordingly, there is a need in the prior art for more simplistic inflator structures, such as those formed from sheet metal having internal chambers formed in part by improved coolant/filter structures and utilizing non-azide propellants having controllable burn rates, gas volume production, internal pressures, and internal temperatures to increase the effectiveness of airbag inflators while reducing the size and the cost thereof and producing lesser amounts of undesirable products of combustion such as mists and ash.
The azide-based gas generating material (NaN
3
/CuO, for example) has a relatively high linear burning velocity of about 45-50 mm/sec under the pressure of 70 kg/cm
2
. Because of the relatively high linear burning velocity, the azide-based gas generating material, even in the form of relatively large pellets or disk-shaped pieces with an excellent shape retention capability, can satisfy the required complete combustion time of 40-60 msec when used, for example, in the airbag inflator for the airbag at the driver's seat side.
Non-azide gas generating materials, which have been developed, are excellent in terms of impacts on environment and safety of passengers. Such materials, however, have the linear burning velocity of less than 30 mm/sec in general. If it is assumed that the linear burning velocity is about 20 mm/sec and that the gas generating material is manufactured in the form of pellets of 2 mm in diameter or disks of 2 mm thick, which are advantageous in retaining their shapes, the combustion speed will be about 100 mm/sec, which fails to meet the desired combustion time of 40-60 msec. When the linear burning velocity is approximately 20 mm/sec, to obtain the desired combustion time requires that the material's pellet diameter or disk thickness to be about 1 mm. When the linear burning velocity is less than 10 mm/sec, the gas generating material's disk is required to have a thickness of 0.5 mm or less. Thus, it is practically impossible to manufacture the gas generating material in the form of pellets or disks that are industrially stable and can withstand many hours of vibrations of an automobile. It has been difficult to develop the airbag inflator that meets the desired performances.
By way of specific example, reference is made to
FIG. 9
wherein a conventional airbag inflator such as disclosed in U.S. Pat. No. 4,547,342 of Adams et al., Oct. 15, 1985 is shown.
A housing
40
has a diffuser shell
41
and a closure shell
42
. The diffuser shell
41
is formed by forging and has three concentric cylinders
43
,
44
,
45
formed integral with a circular portion
46
. Like the diffuser shell
41
, the closure shell
42
is also formed by forging and has three concentric welded portions
50
,
51
,
52
. The diffuser shell
41
and the closure shell
42
are joined together at these welded portions
50
,
51
,
52
by friction welding. It is common in the prior art to form the shells of the airbag inflator by forging.
In this airbag inflator, the cylinder
43
defines an ignition means accommodating chamber
53
, the cylinder
44
defines a combustion chamber
54
, and the cylinder
45
defines a coolant/filter chamber
55
. The ignition means accommodating chamber
53
accommodates ignition means comprising an igniter
56
and a transfer charge
47
. In the combustion chamber
54
, pellets of a gas generating material
57
, ignited by the ignition means to produce a gas, and a first coolant/filter
58
surrounding the gas generating material
57
to cool the combustion gas and arrest combustion particulates are installed. In the coolant/filter chamber
55
, a second coolant/filter
59
to further cool the combustion gas and arrest combustion particulates is installed.
A Problem to Be Solved by the Invention
Forged products, though they are homogeneous in the metal structure and highly tenacious, have a drawback of high cost. When the shell members having many concentric cylinders as disclosed in the above U.S. patent are manufactured by forging, the circular portion
46
is not flat and requires a cutting work, which increases the number of manufacturing processes and therefore increasing cost. In the shell member having the cylinder
43
formed integral with the circular portion
46
as in the above U.S. patent, when the volume of the cylinder
43
is to be changed, the overall shape of the diffuser shell
41
needs to be changed. Changing the volume of the cylinder
43
, therefore, is not easy. In the above conventional airbag inflator, because the coolant/filter chamber is formed outside the combustion chamber, the diameter of the airbag inflator becomes large, increasing its size and weight. Further, because the combustion chamber is defined by the cylinder
44
of the diffuser shell, the diffuser shell is complex in shape, making the manufacture of the airbag inflator difficult, thus increasing the cost.
As a further example, a coolant for an airbag inflator is obtained by rolling a strip-like metal mesh into a multi-layer cylinder. The coolant cools a combustion gas generated in the combustion chamber of the airbag inflator as it passes therethrough and entraps relatively large combustion particulates.
FIG. 12
illustrates an airbag inflator equipped with a conventional coolant similar to that shown in U.S. Pat. No. 4,902,036 to Zander et al., issued Feb. 20, 1990. The airbag inflator comprises a housing
231
having gas discharge ports
230
, an ignition means accommodating chamber
232
defined at a central portion in the housing
231
, a combustion chamber
233
defined on the outer side of the ignition means accommodating chamber
232
, and a coolant/filter chamber
234
defined on the outer side of the combustion chamber
233
. In the ignition means accommodating chamber
232
, ignition means or an igniter
235
and a transfer charge
236
are disposed, and in the combustion chamber
233
, a canister
238
filled with a gas generating material
237
which is ignited by the ignition means and generates a gas is disposed, and in the coolant/filter chamber
234
, a coolant
239
for cooling the combustion gas generated in the combustion chamber
233
and a filter
240
for cleaning the combustion gas are disposed. The combustion chamber
233
is defined by a cup-like combustor cup
243
, having ports
244
for releasing the combustion gas, and a center hole
245
formed in the bottom thereof. The coolant/filter chamber
234
is divided by a retainer
242
into an upper chamber and a lower chamber. The upper chamber contains a filter
240
and the lower chamber contains a coolant
239
.
When a sensor (not shown) detects an impact, a signal is sent to the igniter
235
, which is then actuated to ignite the transfer charge
236
to produce flame of a high temperature and high pressure. The flame passes through an opening
241
, breaks through the wall of the canister
238
and ignites the gas generating material
237
contained therein. Thus, the gas generating material
237
burns to generate a gas which gushes through the ports
244
formed in the combustor cup
243
and th
Katsuda Nobuyuki
Oda Shingo
Ueda Masayuki
Culbreth Eric
Daicel Chemical Industries Ltd.
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