Hybrid inflator

Details Hybrid inflator Hybrid inflator

2001-06-13

2004-10-26

Fleming, Faye M. (Department: 3616)

Land vehicles

Wheeled

Attachment

Reexamination Certificate

active

06808204

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an inflating-type safety system of motor vehicles, and more particularly to a hybrid inflator capable of inflating an air bag rapidly and being made more compact and lighter, and an air bag apparatus using the same inflator.
PRIOR ART
With the development of an inflator for an inflating-type safety system of motor vehicles, a hybrid inflator using both a pressurized gas and a solid gas generating agent is attracting attention. A main design requirement for the hybrid inflator is that the inflator inflates an air bag by a predetermined volume in a predetermined time so that the air bag is effectively activated. Various proposals concerning a structure to meet the requirement have heretofore been made. As the prior arts, there have been known JP-A No. 8-282427, EP No. 0844148, U.S. Pat. Nos. 5,351,988, 5,882,036, 5,851,027, 3,868,124 and 3,758,131, etc.
Further, since the hybrid inflator is manufactured to be installed in the motor vehicle, the weight of the inflator, which has influence upon the weight of the motor vehicle, particularly constitutes an important design requirement. Therefore, it is required to consider such points.
However, in the conventional hybrid inflator using a pressurized gas together with a solid gas generating agent, the design requirement mentioned above can not be sufficiently satisfied in some cases. For example, in the case of the structure in which an internal pressure is increased by utilizing a heat generated due to a combustion of the solid gas generating agent and an air bag is deployed by emitting the pressurized gas, it is necessary to increase a thickness of the housing in order to increase a pressure resistance. Further, in the case that the oxygen is contained in the pressurized gas, there is a problem such that the weight is increased by the oxygen. Further, there is a hybrid inflator structured such that the oxygen is not contained in the pressurized gas by utilizing the gas generating agent in perchlorate system. In this case, however, there is a problem such that fine particles which are harmful to a passenger are generated due to the combustion of the gas generating agent. Further, the conventionally employed solid gas generating agent is mainly made of a gun type such as RDX.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a hybrid inflator being made more compact and lighter without deteriorating a function as an inflator and guaranteeing a high safety, and an air bag apparatus using the same.
The present invention provides a hybrid inflator for an inflating-type safety system of vehicles provided with an air bag, which comprises an inflator housing, a gas generator installed in the inflator housing, an ignition unit chamber connected to the gas generator, wherein the interior of the inflator housing is filled with a pressurized medium containing an inert gas and no oxygen, the gas generator has one or two or more gas generating chambers including a gas generating agent, and a molar ratio (A/B) between an amount (A moles) of the pressurized medium and an amount (B moles) of gas generated due to combustion of the gas generating agent is between 8/2 and 1/9.
It is possible to reduce a charged amount of the pressurized medium by adjusting the molar ratio between the amount of the pressurized medium charged inside the hybrid inflator and the amount of the gas generated due to the combustion of the gas generating agent. Accordingly, even in the case of reducing a capacity of the housing (that is, reducing a length and/or a width (a diameter) of the housing), the charged pressure of the pressurized medium (the internal pressure of the housing) does not have to be increased, and it can be maintained under the same pressure as that before reducing the capacity.
The ratio A/B is preferably set to 8/2 to 3/7. In this case, in the hybrid inflator according to the present invention, the weight ratio (a/b) between the weight (a) of the pressurized medium and the weight (b) of the gas generating means is set to 0.1 to 0.7, and preferably set to 0.5 to 5.
In the above hybrid inflator, desirably, the pressurized medium does not contain oxygen for achieving, more effectively, the operation and effect mentioned above. And further, it is desirable to use the gas generating agent containing a fuel and an oxidizing agent. Still, it is preferable to use the gas generating agent containing a fuel, an oxidizing agent, and a slug-forming agent, in addition to the operation and effect mentioned above, generation of the fine particles, which are harmful to the passenger, can be suppressed.
Further, the above hybrid inflator can be structured such that a pressure index at combustion of the gas generating agent defined by the following formula rb=&agr;P
n
(in the formula, rb: burning rate, &agr;: coefficient, P: pressure, n: pressure index) is less than 0.8. The pressure index (n) is preferably set to 0.1 to 0.8, and more preferably to 0.1 to 0.7.
In this case, the pressure index n is obtained in accordance with two formulas, rb
1
=&agr;P
1
n
and rb
2
=&agr;P
2
n
, after measuring the burning rate rb1 in a tank having a pressure P
1
(70 kg/cm
2
) and measuring the burning rate rb2 within a tank having a pressure P
2
(100 kg/cm
2
).
By setting the pressure index (n) to be less than 0.8 in this manner, the burning rate at the initial stage of the combustion of the gas generating agent can be prevented from rapidly increasing, and therefore, an increase of the housing internal pressure is small. Accordingly, even in the case of reducing the thickness of the housing, a sufficient pressure resistance can be maintained. Further, since the combustion of the gas generating agent is stably performed due to the small increase of the housing internal pressure (that is, the change of the internal pressure is small), a combustion residue of the gas generating agent is never generated.
Further, the present invention provides a hybrid inflator for an inflating-type safety system of vehicles provided with an air bag, which comprises an inflator housing, a gas generator installed in the inflator housing, an ignition unit chamber connected to the gas generator, wherein the interior of the inflator housing is filled with a pressurized medium containing an inert gas, the gas generator has one or two or more gas generating chambers including a gas generating agent, the pressurized medium contains no oxygen, and the gas generating agent contains a fuel and an oxidizing agent.
Further, the present invention provides, as still another way of solving the problem, a hybrid inflator for an inflating-type safety system of vehicles provided with an air bag, which comprises an inflator housing., a gas generator installed in the inflator housing, an ignition unit chamber connected to the gas generator, wherein the interior of the inflator housing is filled with a pressurized medium containing an inert gas, the gas generator has one or two or more gas generating chambers including a gas generating agent, the pressurized medium contains no oxygen, and a pressure index at the combustion of the gas generating agent defined by the following formula rb=&agr;P
n
(in the formula, rb: burning rate, &agr;: coefficient, P: pressure, n: pressure index) is burnt is less than 0.8.
The pressurized medium used in the hybrid inflator according to the present invention comprises an inert gas and substantially contains no oxygen. As the inert gas, for example, argon and helium can be used, and, additionally, nitrogen can be used together. Accordingly, the inert gas in the present invention contains nitrogen. Argon works to promote a thermal expansion of the pressurized medium, and a leakage of the pressurized medium can be easily detected if the helium is contained, so that, preferably, defective inflators can be prevented from being distributed. The charged pressure of the pressurized medium is set to 10,000 to 70,000 kPa and preferably 20,000 to 60,000 kPa.
Further, the present invention provides a hyb

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