Land vehicles – Wheeled – Attachment
Reexamination Certificate
2000-07-21
2001-05-01
Dickson, Paul N. (Department: 3618)
Land vehicles
Wheeled
Attachment
C280S741000
Reexamination Certificate
active
06224096
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 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 is available at a reduced manufacturing 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 the maximum output pressures at 85° C. and 20° C. and a difference between the maximum output pressures at 20° C. and −40° C. in tank pressure tests using a tank whose capacity is 60 &lgr; may be each respectively 25% or less of the maximum output pressure in the tank test at 20° C. Particularly, the difference between the maximum output pressures is preferably 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.
In the invention, A/At essentially depends on gas-discharging ports and a gas generating agent. No other factor can be taken in account. It is proposed that the inflator of the invention should be necessarily designed and worked with no other means, installed in the inflator, having any substantial influence on A/At. For example, it may be proposed not to place a member of a large resistance-having member upstream before parts which will choke the flow of the gas and control the internal burning (combusting) pressure.
For example, as explained also in the below described embodiments, a coolant/filter is, in general placed before controling means of the burning pressure, i.e. the gas discharge ports, in order to cool the generated gas and scavenge (trap) solid residues of the gas.
The coolant/filter is made by forming a porous mesh member from a metallic wire so that the gas may pass through the inside of the member and the coolant/filter may exhibit the above shown functions. The physical contact between the generated gas and the coolant/filter causes heat-exchanging and collecting of residues as well as produces resistance to the gas flow at the same time. A similar flow resistance appears also at the gas discharge ports controling the internal burning pressure. When the flow resistance of the coolant/filter is lower than that of the gas discharge ports, the ratio A/At can be designed and determined accurately as described above at the time of installing the coolant/filter.
The flow resistance of the gas discharge ports has an interrelation to their open area. Then the flow resistance of the coolant/filter has an interrelation to the area where the gas passes. An example of these interrelations will be described later.
The air bag gas generator for the driver seat side described above has a suitable structure to be installed on the driver side, for example, in a steering wheel, etc. That is, the air bag gas generator for the driver seat side is a gas generator used for air bag system to protect the driver by activation of the air bag sys
Katsuda Nobuyuki
Nakashima Yoshihiro
Tomiyama Shogo
Daicel Chemical Industries Ltd.
Dickson Paul N.
Fleming Faye M.
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