Land vehicles – Wheeled – Attachment
Reexamination Certificate
1997-03-31
2001-05-22
Culbreth, Eric (Department: 3611)
Land vehicles
Wheeled
Attachment
C280S741000, C280S742000
Reexamination Certificate
active
06234521
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to airbag inflators and systems utilizing same for the enhancement of driver and passenger protection, including side impact protection, in motor vehicles and the like.
BACKGROUND OF THE INVENTION
Conventional airbag inflators are relatively complex structures with 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 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.
Non-azide gas generating materials have been developed which 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 we assume that the linear burning velocity is about 20 mm/sec and that the gas generating material is manufactured in the form of pellets 2 mm in diameter or disks 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 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 is shown a conventional airbag inflator such as disclosed in U.S. Pat. No. 4,547,342 of Adams et al., Oct. 15, 1985.
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 with 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 an ignition means comprising an igniter 56 and a transfer charge 47. In the combustion chamber 54 there are installed 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. In the coolant/filter chamber 55 is installed a second coolant/filter 59 to further cool the combustion gas and arrest combustion particulates.
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, increasing the number of manufacturing processes and therefore 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 and 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 and works to cool a combustion gas generated in the combustion chamber of the airbag inflator as it passes therethrough and to entrap 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 are disposed an ignition means or an igniter 235 and a transfer charge 236, in the combustion chamber 233 is disposed a canister 238 filled with a gas generating material 237 which is ignited by the ignition means and generates a gas, and in the coolant/filter chamber 234 are disposed a coolant 239 for cooling the combustion gas generated in the combustion chamber 233 and a filter 240 for cleaning the combustion gas. 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 containing a filter 240 and the lower chamber containing 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 is cooled as it passes through the coolant 239. Here, relatively large combustion particulates are entrapped and the remaining combustion particulates are entrapped as the gas further passes thr
Katsuda Nobuyuki
Oda Shingo
Ueda Masayuki
Culbreth Eric
Daicel Chemical Industries Ltd.
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