Land vehicles – Wheeled – Attachment
Reexamination Certificate
2000-09-15
2002-06-18
Johnson, Brian L. (Department: 3618)
Land vehicles
Wheeled
Attachment
C280S741000
Reexamination Certificate
active
06406060
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a gas generator for an air bag for protecting a passenger from an impact, and an air bag system. In particular, this invention is concerned with a gas generator for an air bag wherein the ratio (A/At) of the total surface area A of solid bodies of gas generating agent contained in a housing to the total opening area At of gas discharge ports formed through the housing is controlled to a specified range.
DESCRIPTION OF THE PRIOR ART
In a conventional gas generator for an air bag, igniting means that is actuated when an impact sensor detects an impact, a gas generating agent that is ignited by the igniting means and burned to generate combustion gas, and filter means for cooling the combustion gas and/or scavenging combustion residues are accommodated in a housing having gas discharge ports. In this type of gas generator, when the igniting means is actuated upon detection of an impact, the gas generating agent is ignited and burned to generate combustion gas. The combustion gas is cooled and purified by the filter means in the housing, and discharged from the housing through gas discharge ports. Gas generating agents used for generating the combustion gas may be roughly classified into azide-containing gas generating agents, and other gas generating agent containing no azide.
The azide-containing gas generating agent (such as NaN
3
/CuO) has a relatively high linear burning velocity, for example, about 45-50 mm/sec under a pressure of 70 kg/cm
2
. Accordingly, even when the gas generating agent is formed into a relatively large pellet-like shape or disc-like shape that can be maintained with high stability, the gas generating pellets or discs may be completely burned in a desired period of time, i.e., 40 to 60 msec, when used in the gas generator for an air bag installed on the side of a driver seat, for example.
On the other hand, the non-azide gas generating agent generally has a linear burning speed of 30 mm/sec or lower. If this gas generating agent is formed into a pellet-like shape with a diameter of 2 mm, or a disc-like shape with a thickness of 2 mm, for example, the shape of the gas generating pellet or disc can be maintained with high stability, but it takes as much as about 100 msec to burn the gas generating agent where its linear burning velocity is about 20 mm/sec, which is longer than a desired burning time of 40 to 60 msec. Where the linear burning velocity is around 20 mm/sec, the diameter of the gas generating pellet or the thickness of the gas generating disc must be controlled to be around 1 mm to achieve a desired burning time. Where the linear burning velocity is 10 mm/sec or lower, the thickness of the gas generating pellet or disc must be reduced to 0.5 mm or smaller. It is, however, practically impossible to produce pellets or discs of the gas generating agent having such diameter or thickness, which can withstand vibrations of an automobile for a long period of time, while being held in an industrially stable condition. The gas generator containing such gas generating pellets or discs does not perform its functions satisfactorily. Thus, it has been difficult to develop a gas generator that contains a non-azide gas generating agent and can be advantageously used in practical applications.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a gas generator for an air bag which permits its gas generating agent to be completely burned within a desired period of time, and also shows satisfactory operating characteristics.
Since the maximum pressure in the housing upon actuation of the gas generator varies with the temperature of the outside air or atmosphere, it is difficult to provide a gas generator for an air bag which exhibits stable operating characteristics, and does not substantially depend upon the temperature of the atmosphere.
It is, therefore, another object of the present invention to provide a gas generator for an air bag which can be manufactured at a reduced cost, and which is able to operate with high stability, without depending upon the temperature of the atmosphere.
The gas generator for an air bag according to the present invention is characterized in that the ratio (A/At) of the total surface area A of solid bodies of gas generating agent stored in a housing to the total opening area At of gas discharge ports formed through the housing is controlled to a specified range.
More specifically, in the gas generator for an air bag of the present invention, wherein igniting means that is actuated when an impact sensor detects an impact, a gas generating agent that is ignited by the igniting means and burned to generate combustion gas, and filter means for cooling the combustion gas and scavenging combustion residues are accommodated in a housing having gas discharge ports, the ratio (A/At) of the total surface area A of solid bodies of the gas generating agent to the total opening area At of the gas discharge ports is controlled to be larger than 300.
With the ratio (A/At) of the total surface area A of the gas generating agent to the total opening area At of the gas discharge ports being controlled to be larger than 300, a difference between maximum output pressures at 85° C. and 20° C. and a difference between maximum output pressures at 20° C. and −40° C. in tank pressure tests are respectively not higher than 40 kPa. In the gas generator for an air bag to be used for a driver seat side and a passenger seat side, the ratio (A/At) of the total surface area A of the gas generating agent to the total opening area At of the gas discharge ports may be controlled to be larger than 300, but not larger than 1300, and preferably controlled to be in a range of 450 to 1300, more preferably, in a range of 450 to 1000.
The above-explained housing may be formed by casting or forging, or may be formed by pressing a diffuser shell having gas discharge ports through which the gas generated by burning the gas generating agent is discharged, and a closure shell having a central aperture in which the igniting means is disposed, and joining these shells together by various welding methods, such as plasma welding, friction welding, projection welding, electron beam welding, laser welding and TIG welding. The housing thus formed by press working can be easily manufactured at a reduced cost. Each of the diffuser shell and closure shell may be formed from a stainless steel sheet having a thickness of 1.2 to 3.0 mm, for example. The volume content of the housing is desirably in the range of 60 to 130 cc. The gas discharge ports formed through this housing are desirably circular holes, each having an inside diameter of 2 to 5 mm, and the total opening area of these discharge ports is desirably in a range of 50 to 200 mm
2
where the gas generator is used for an air bag for a driver seat side, and in a range of 60 to 500 mm
2
where the gas generator is used for an air bag for a passenger seat side.
The gas discharge ports of the housing are preferably closed by an aluminum tape having a width that is 2 to 3.5 times the diameter of each discharge port, for inhibiting entry of moisture from the exterior space into the housing. The aluminum tape may be an adhesive aluminum tape, or may be attached to the housing by means of various kinds of adhesives, such as those that are fused by heat to provide secure bonding. For example, a hot melt adhesive may be used to attach the aluminum tape to the housing.
The gas generating agent is more effectively used in the present gas generator particularly when its linear burning velocity is in the range of 7 to 30 mm/sec, preferably 7 to 15 mm/sec, under a pressure of 70 kg/cm
2
. The gas generating agent having such a property may be a non-azide gas generating agent containing a nitrogen containing organic compound, an oxidizing agent, and a slag-forming agent, for example. The content of the nitrogen containing compound in the gas generating agent may be in the range of 25 to 60% by weight, and the content of the oxidizing agent may b
Katsuda Nobuyuki
Tomiyama Shogo
Daicel Chemical Industries Ltd.
Fleming Faye M.
Johnson Brian L.
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