Land vehicles – Wheeled – Attachment
Reexamination Certificate
1998-05-14
2001-05-01
Rice, Kenneth R. (Department: 3611)
Land vehicles
Wheeled
Attachment
C280S731000
Reexamination Certificate
active
06224098
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, the invention is concerned with a gas generator for an air bag, which enables a stable combustion of a nonazide gas generating agent.
BACKGROUND OF THE INVENTION
In a conventional gas generator of the above type, a gas generating agent containing sodium azide as a base has been used. Since harmful slags and mist are generated due to the use of sodium azide, it has been proposed to use a nonazide gas generating agent in which a nitrogen containing compound other than inorganic azide is combined with an oxidizer. However, the nonazide gas generating agent generally has a linear burning velocity of 30 mm/sec or less under a pressure of 70 kg/cm
2
, and it is difficult to burn this type of gas generating agent with high stability to achieve stable or constant output performance. An example of a gas generator for an air bag using a nonazide gas generating agent for achieving stable combustion has been proposed in International Publication No. WO 96/10494, wherein a rupture plate is provided at an opening that allows passage of a gas generated by the gas generating agent, and the maximum pressure inside the gas generator is controlled by adjusting the strength and thickness of the rupture plate and the size of the opening. When the rupture plate is used in an attempt to control the internal pressure of the gas generator in this manner, however, it was found that the start of actuation or operation of the gas generator tends to be delayed since the rupture plate does not rupture unless a pressure greater than a certain level is applied to the plate, burning of the nonazide gas generating agent is not stabilized, which often results in variations in the output performance of the gas generator, and the amount of CO gas generated as a result of the combustion is increased.
SUMMARY OF THE INVENTION
The present invention has been developed to overcome the above-described problems encountered in the prior art. It is an object of the invention to provide a gas generator for an air bag which is suite for stably burning a nonazide gas generating agent having a linear burning velocity of 30 mm/sec or less under a pressure of 70 kg/cm
2
, and an air bag system using such a gas generator.
As a result of diligent studies for solving the problems, as described above, the inventor have found that in a small-sized container (having an internal volume of 120 cc or less), a desired output curve or characteristic suitable for inflation of an air bag can be obtained if the internal pressure of the gas generator, when the generator is being activated, is controlled by adjusting the total area of openings. The present invention was developed based on this finding.
The present invention relates to a gas generator for an air bag wherein a gas generating agent is stored in a housing, and a plurality of openings are provided for controlling combustion of the gas generating agent so that the gas generated by the gas generating agent passes through the openings, to be directed toward the air bag. The gas generator is characterized in that the internal pressure of the gas generator, when the generator is being activated, is controlled by adjusting the total area of the openings relative to an amount of the gas generated by the gas generating agent.
In practicing the present invention, it is preferable that each of the openings has a diameter of 2 to 5 mm assuming that the opening has a circular shape. Since the opening does not necessarily have a circular shape, but may have a shape that can be approximated to a circle, the size of the opening is define not as an actual dimension measured in a certain direction, but as a diameter of the circle to which the opening is approximated. The size thus defined is a diameter of a complete round having the same area as the opening. If the diameter of the opening, when it is regarded as a circle, is less than 2 mm, an air bag component provided at outlets of the openings may be damaged even if the ratio of the total area of the openings to the amount of the generated gas is equal to or smaller than 2.50 cm
2
/mol. The air bag component located at the outlets of the openings may be an air bag in the case where the openings are gas discharge ports formed through a diffuser shell of a housing, or a filter or a coolant in the case where the openings are formed through a partition wall of a combustion chamber inside the housing. If the number of the openings is increased to prevent such damages, the number of holes that provide the openings will be excessively large, resulting in an increased process cost for producing the gas generator.
In a preferred form of the present invention, in which the housing consists of a small-size container having an internal volume of 120 cc or less the ratio of the total area of the openings to the amount of the generated gas is adjusted to 0.50 to 2.50 cm
2
/mol, preferably, 0.50 to 2.0 cm
2
/mol, and a suitable nonazide composition for the gas generating agent is selected, and the diameter and number of the openings are suitably determined, such that the maximum internal pressure is controlled to be equal to or greater than 60 kg/cm
2
and less than 100 kg/cm
2
. In this manner, a desired output curve or characteristic suitable for inflation of the air bag can be achieved. The total area of the openings is determined by multiplying the area of a single hole by the number of holes. Thus, the diameter or size of a single opening or hole is determined by taking damages to the air bag into account, as described above, and the number of openings is then determined based on the diameter of the single opening.
In the gas generator of the present invention, the gas generating agent is stored inside the generator, and a plurality of openings for controlling combustion of the gas generating agent are formed through the housing of the generator, and/or a partition wall located inside the housing, such that the openings extend in a direction in which the gas generated by the gas generating agent flows toward the air bag. The opening area of each of the openings corresponds to that of a circle having an inside diameter of 2 to 5 mm, and a total of 12 to 24 openings, preferably, 16 to 20 openings, are formed through the housing, or the partition wall inside the housing, or both of the housing in a circumferential direction and the partition wall inside the housing. In the present invention, the maximum internal pressure of the gas generator, when it is actuated, is regulated by the openings formed through the housing or the partition wall inside the housing, or the openings formed through both the housing and the partition wall. For instance, where the openings are formed through both of the housing and the partition wall inside the housing, and the interior pressure of the housing is controlled or regulated by the openings of either one of the housing and the partition wall, the openings of the other of the housing and the partition wall may be suitably formed so that these openings do not contribute to control of the internal pressure.
The openings through which the gas generated by the gas generating agent passes may be arranged in an array or in a stagger form, in a circumferential Direction of the housing and/or the partition wall.
The above-indicated housing may be formed by casting or forging, or by press working a diffuser shell having openings (hereinafter, called gas discharge ports) through which the gas is discharged or ejected, and a closure shell having a central aperture, and joining the diffuser shell and the closure shell by a known welding method, such as plasma welding, friction welding, projection welding, electron beam welding, laser welding, or TIG welding. The housing is provided with gas discharge ports. The housing thus formed by press working can be easily manufactured at a reduced manufacturing cost. Each of the diffuser shell and closure shell may be formed from,
Katsuda Nobuyuki
Ueda Masayuki
Daicel Chemical Industries Ltd.
Rice Kenneth R.
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