GAS GENERATING APPARATUS FOR INFLATING AN AIR BAG

Abstract: This invention concerns a gas generating apparatus for inflating an air bag whereby any shortfall in the quantity of gas required for inflating the air bag can be overcome by replenishing the air bag with air. If the gas generating apparatus is reduced in size and weight with a corresponding reduction in the quantity of gas generating agent used therein, the air bag is not inflated to a sufficient extent and its function as a safety apparatus in time of collision is thereby compromised. This problem is solved by an open joint portion connected to said air bag; a combustion chamber 9 formed at the center inside said housing body 1, wherein a high-pressure gas is generated upon combustion of a gas generating agent; a partition 12 which forms a mixing chamber 15 in a ring-like configuration by being concentrically disposed such as to be spaced apart from the opening of said housing body 1 by a desired interval, whereby said high-pressure gas from said combustion chamber 9 is introduced into said mixing chamber 15; a nozzle 16 in a ring-like configuration which is provided at said high-pressure gas introducing portion, whereby said high-pressure gas is ejected toward said opening of said mixing chamber 15 formed by said partition 12; and an air intake port 5 formed along said nozzle 16 on sail housing body 1.

Description: This invention relates to a gas generating apparatus for inflating an air bag, comprising a housing, an open joint portion connected to said air bag, a nozzle in a ring-like configuration ejecting high pressure gas from a mixing chamber and an ambient air intake part is formed along said nozzle on said housing body. Such air bags are used for safety apparatusses for protection against collision, also for life bags, rubber boats, escape chutes, etc.. Moreover particularly, this invention concerns a gas generating apparatus for inflating an air bag whereby any shortfall in the quantity of gas required for inflating the air bag can be overcome by replenishing the air bag with air. According to a known impact energy absorbing apparatus for vehicles of the above-mentioned kind (US-A-3 843 152) the pressure source is fixed on the vehicle body and the fluid discharge of the steering column tube and they are connected with a communication means for inflating the bag a pneumatic mechanism is used which is working rather slowly. Moreover, the housing body is not an integrated part, but consists of a base end portion for rotating with the steering wheel and a separated cylindrical gas discharger. The discharger chamber for the high pressure gas is formed by a coaxial cylinder provided with one open end and the other end covered by a bottom of natural or synthetic rubber. Moreover, the arrangement with respect to the gas flow is such that the gas leaving the discharging chamber flows in the same direction as the gas ejected from the nozzle. Conventionally, in a passenger car, a safety apparatus adapted to protect passengers against physical shock at the time of a collision comprise an air bag with a volume of 60 liters and a gas generating apparatus which inflates this air bag, the gas generating apparatus being filled either with an explosiver or a gas generating agent comprising similar constituents which is ignited and burnt at the time of a collision so as to immediately inflate the air bag with a gas generated thereby, thus protecting the driver from the effects of the collision, and preventing him from being seriously injured. In such an apparatus, the quantity of gas generating agent requires for inflating the air bag is between 70 and 100g, and the total weight of the body of the gas generator is between 600 and 1100g. With the above apparatus, the air bag is inflated merely by the generation of gas upon combustion of the gas generating agent, therefore, even an air bag with a 60-liter volume uses from 70 to 100g of the generated gas, which is a relatively large amount for the gas inflation and, consequently, the volume of the combustion chamber in the body of the gas generator has to be increased to raise the gas temperature and the temperature inside the gas generating unit by combustion of a relatively large amount of gas generating agent since the volume of the combustion chamber in the gas generating unit also has to be increased, it is relatively large and heavy, and this involves such hazards as the possibility of passengers being burnt. If the gas generating apparatus is reduced in size and weight with a corresponding reduction in the quantity of gas generating agent used therein, the air bag is not inflated to a sufficient extent and its function as a safety apparatus in time of collision is thereby compromised. Therefore, the shortfall in the quantity of gas generated needs to be overcome by supplementing the gas or the like. For this purpose it is conceivable to incorporate in the gas generating apparatus an air ejector for replenishing air by ejecting a high-pressure gas or a vapor ejector. However, since the primary high pressure gas in these kind of ejector has a pressure as low as 10 kg/cm² or less, such an ejector also needs to be relatively increased large in size to be effective when used with such an air bag in a safety apparatus of the type described in order that a sufficient amount of air can be sucked in some tens of milliseconds. Accordingly, such a gas generating apparatus is inevitably increased in size and weight and this means that it remains impossible for this type of bag to be used as an air bag for an automobile. The present invention aims to solve such problems as those described above,and the object of the present invention is to provide a small , lightweight and safe gas generating apparatus for inflating an air bag wherein the quantity of gas generating agent used for inflating the air bag is reduced without resulting in any attendant disadvantages. This object is solved in accordance with the teaching of claim 1. Further advantageous embodiments of the invention are stated in the subclaims. In the present invention, the high-pressure gas is generated when the gas generating agent in a combustion chamber is combusted, and this high-pressure gas is ejected in the direction of an opening from an annular nozzle into a mixing chamber, so that air is sucked from air intakes into the mixing chamber by virtue of the ejector effect. This sucked air is mixed with and cools the gas and flows into the air bag to inflate the same. Thus since the nozzle and air intakes are formed on the outer periphery of the housing body, a large quantity of outside air can be sucked positively owing to the ejector effect obtained by the ejecting gas. Consequently, it is possible to decrease the quantity of gas generating agent used and to reduce the size and weight of the gas generating apparatus in proportion to the decrease in volume of the combustion chamber. In the following a description will be made of an embodiment of the present invention. Fig. 1 is a vertical sectional view of an embodiment of the gas generating apparatus for inflating an air bag according to the present invention; Fig. 2 is a plan view thereof. As illustrated in Figs. 1 and 2, reference numeral 1 denotes a housing body one end of which is choked and the other end opened, which includes a cylinder portion 2 with a small diameter and a cylinder portion 4 with a large diameter connected to an opening end of this cylinder portion 2 by means of a flange portion 3. A multiplicity of air intakes 5 comprising slotted holes arrayed in a ring-like configuration are provided in the flange 3, and an inner circumferential wall surface 4a of the cylinder portion 4 with a large diameter is formed into a tapered face whose greater diameter is at opening end. Reference numeral 6 indicates a flange which is formed integrally with the outer periphery of the large-diameter cylinder portion 4, and an opening of the air bag (not shown) can be mounted on this flange. A threaded portion 7 which is concentrically formed at the center of the choked portion inside the housing body 1 is screwed into the cylinder 8 such as to face the opening thereof. This cylinder 8 forms a combustion chamber 9 wherein its entire outer circumferential wall on the closed side is provided with a multiplicity of combustion gas orifices 10. A gas generating agent (not shown) in the form of either granules or pellets, which is composed of sodium azide and an oxidizing agent such as sodium nitrate or potassium perchlorate, is stored in the combustion chamber 9 Reference numemeral 11 denotes a device igniting a gas generating agent mounted at the center of the threaded portion 7. In Fig. 1, reference numeral 12 denotes a cylindrical partition which is concentrically disposed around the periphery of the cylinder portion 8 inside the large-diameter cylinder portion 4 of the housing body 1 in such a manner as to surround the gas orifices 10. A flange 13 of the cylindrical partition 12 is integrally connected with the outer periphery of the cylinder 8 on the choked side thereof by welding, and a filter 14 is provided inside the partition 12 in order to filtrate combustion residues in a gas. Further, the outer circumferential wall surface 12a of the partition 12 is so formed as to have a tapered face which is in parallel with the inner circumferential wall surface 4a of the cylinder portion 4, wherein the inner circumferential wall 4a and outer circumferential wall surface 12a form a mixing chamber 15 for a combustion gas and air which is sucked from the intake 5. A nozzle 16 is formed into a ring-like configuration between the inner circumferential angle portion of the flange portion 3 in close proximity to the air intakes 5 of the housing body 1 and the opening end portion of the cylindrical partition 12 which faces this inner circumferential angle portion, whereby a high-pressure combustion gas is throttled and ejected into the mixing chamber 15 at high speed. The ratio of the entire sectional area of the air intakes 5 to the sectional area of the throat of the nozzle 16 is preferably set at at least 10:1 or more and, more preferably, 50:1 or more. The ratio L/D of the length L of the combustion chamber 15 which is formed by the inner circumferential wall surface 4a and the outer circumferential wall surface 12a to the space D between these wall surfaces is set between 1:1 and 8:1, and the ratio of air taken thereinto becomes maximum when it is set between 5:1 and 7:1. In a gas generating apparatus configured as described above, a high-pressure gas with a pressure of 50 to 200 kg/cm² is produced when the gas generating agent is ignited by the igniting device 11 and combusted in the combustion chamber 9. This high-pressure gas flows from the orifices 10 into the cylinder 12 whereas solid residues in the gas is removed when passing through the filter 14, and the gas is ejected from the nozzle 16 into the mixing chamber 15 at high speed. Since the pressure in the opening portion A of the air intake 5 which is open to the mixing chamber 15 is reduced remarkably to less than the atmospheric pressure at this moment, a large quantity of air from the inside of an automobile is sucked in through the air intakes 5. This sucked air is mixed with the mixing chamber 15 with the high-temperature, high-pressure gas ejected from the nozzle 16, whereby the gas is cooled and an air bag (not shown) is instantly inflated (within some tens of milliseconds) with the air which is discharged thereinto from an opening 15a of the mixing chamber 15. It should be noted that the lower the pressure in the combustion chamber 9 is, the larger the ratio of the quantity of sucked air to the quantity of combustion gas becomes. However, since the speed of the entire mixture of gas flowing into the air bag is reduced, resulting in the delay of inflation of the air bag, the pressure in the combustion chamber is preferably set at between 50 and 200 kg/cm² in order that the air bag can be completely inflated in the steering compartment in such a short time as some tens of milliseconds. The ratio of the total sectional area of the air intakes 5 to the total sectional area of the throat of the nozzle 16 is set at at least 50:1 or more. Further, the ratio L/D is preferably set between 5:1 and 7:1. Thus, the mixing rate of air becomes high, with the result that cooling of the combustion gas and consequently cooling of the gas generating apparatus itself can be performed effectively. This allows the gas generating apparatus to be reduced in size and weight, since the temperatures of the gas and gas generating apparatus are lower and the quantity of gas generating agent used is reduced. In addition, safety of the apparatus is improved due to the absence of any danger of burns or other hazards. The pressure inside the automobile can be prevented from rising by virtue of the air bag being inflated in a conventional manner, because the air in the automobile is sucked into the air bag during its expansion. Also, costs can be reduced in proportion to the decrease in the quantity of gas generating agent used. It is considered that 20 to 30g of the gas generating agent will fully inflate the air bag, since the gas generating apparatus of the embodiment according to the present invention positively sucks air, whereas a conventional gas generating apparatus requires 70 to 100g of gas generating agent to inflate an air bag with volume of 60 liters provided for a driver's seat. It should be noted that a gas generating apparatus according to the present invention is not limited to the one having the arrangement described in the above embodiment. In addition, a gas generating apparatus according to the present invention can be applied not only to an air bag for the driver's seat of an automobile but can also be employed as a gas generating apparatus for inflating an air bag for an assistant's seat, life boat, rubber boat, escape chute, etc. where a larger quantity of air is required for inflation. Thus, in accordance with the present invention, a gas generating apparatus is arranged such that a combustion chamber for a gas generating agent is disposed at the center of a housing body, and air intakes, a nozzle for gas ejection, and a mixing chamber for mixing sucked air and ejected gas are provided on the outer peripheral side of the housing. Therefore, a large quantity of outside air can be positively sucked into the air bag during an operation of the gas generating apparatus and, consequently, the quantity of the gas required for inflating the air bag can be sufficiently maintained even if there is an inherently insufficient quantity of the gas generating agent employed for this purpose, thereby allowing the volume of the combustion chamber to be reduced in parallel with the lower quantity of gas generating agent used. A further effect is that the lower gas temperatures offer an improved level of safety, since the gas and air may flow into the air bag after being mixed with each other.

Claims: A gas generating apparatus for inflating an air bag, comprising a housing body (1), an open joint portion connected to said air bag, a nozzle (16) in a ring-like configuration ejecting high-pressure gas from a mixing chamber (15), and an ambient air intake part formed along said nozzle (16) on said housing body (1) characterized by a combustion chamber (9) formed at the center inside said housing body (1), wherein said high-pressure gas is generated upon combustion of a gas generating agent, the mixing chamber (15) being concentrically disposed such as to be spaced apart from the opening of said housing body (1) by a desired interval so that said high-pressure gas from said combustion chamber (9) is introduced into said mixing chamber (15) and the nozzle (16) is positioned such that said high pressure gas is ejected towards said opening of said mixing chamber (15). A gas generating apparatus for inflating an air bag according to claim 1, wherein said housing body (1) whose section is of a substantially U-like form with one end choked and the other end open, characterized by a cylinder portion (2) with a small diameter and a cylinder portion (4) with a large diameter connected by means of a flange portion (3) to the opening of said cylinder portion (2) with a small diameter; said flange portion (3) is provided with a plurality of air intake ports (5) formed by slotted holes which are arrayed in a ring-like configuration; and the inner circumferential wall (4a) of said cylinder portion (4) with a large diameter is formed on a tapered face whose diameter is widened toward a direction from said flange portion (3) to said opening. A gas generating apparatus for inflating an air bag according to claim 2, characterized in that a flange (6) is formed integrally with the outer circumference of said cylinder portion (4) with a large diameter so as to allow the opening of said air bag being to be mounted on said flange. A gas generating apparatus for inflating an air bag according to claim 1, characterized in that said combustion chamber (9) comprises said opening portion of said cylinder (8), one end thereof being choked, is screwed onto a threaded portion (7) which is concentrically formed at the center of said choked portion inside said housing (1). A gas generating apparatus for inflating an air bag according to claim 4, characterized in that a multiplicity of combustion gas orifices (10) are provided on the entire circumference of said circumferential wall at said choked end of said cylinder (8). A gas generating apparatus for inflating an air bag according to claim 1, characterized in that said partition (12) which forms a cylindrical configuration is located inside said cylinder portion (4) with a large diameter of said housing body (1) and, is concentrically disposed at the outer periphery of said cylinder (8) in such a manner s to surround said combustion gas orifices (10). A gas generating apparatus for inflating an air bag according to claim 6, characterized in that said partition (12) comprises said flange (13) and is welded by means of said flange on said choke portion of said cylinder (8) to be integrally formed with said cylinder (8). A gas generating apparatus for inflating an air bag according to claim 1, characterized in that a filter (14) for the filtration of combustion residues in a combustion gas is provided inside said partition (12). A gas generating apparatus for inflating an air bag according to claim 1, characterized in that the outer circumferential wall of said partition (12) is formed on said tapered face which is in parallel with the inner circumferential wall (4a) of said cylinder portion (4) with a large diameter in said housing body (1). A gas generating apparatus for inflating an air bag according to claim 1, characterized in that said combustion chamber (9) is formed so as to mix a combustion gas with air sucked from said air intake which is formed on said housing body (1) by said inner circumferential wall (4a) of said cylinder portion (4) and said outer circumferential wall (12a) of said partition (12) in said housing body (1). A gas generating apparatus for inflating an air bag according to claim 1, characterized in that said nozzle (16) in the ring-like configuration is formed between the inner circumferential angle portion of said flange portion (3) in close proximity of said air intake port of said housing body (1) and said opening end portion of said partition (12) which faces said inner angle portion, whereby a combustion gas with high pressure is throttled to eject toward said miying chamber (15) at high speed. A gas generating apparatus for inflating an air bag according to claim 1, characterized in that the ratio of the sectional area of said air intake port to the sectional area of the throat of said nozzle (16) is set at at least 10:1 or more. A gas generating apparatus for inflating an air bag according to claim 12, characterized in that the ratio of the total sectional area of said air intake port to the sectional area of said throat of said nozzle (16) is set at at least 50:1 or more. A gas generating apparatus for inflating an air bag according to claim 1, characterized in that the ratio L/D of the length L formed by said inner circumferential wall and outer circumferential wall at said combustion chamber (9) in said housing body (1) to the interval D between both of said inner circumferential walls (4a, 12a) is set between 1:1 and 8:1. A gas generating apparatus for inflating an air bag according to claim 14, characterized in that the ratio L/D of the length L formed by said inner circumferential wall at said combustion chamber (9) in said housing body (1) to the interval D between both of said inner circumferential walls (4a, 12a) is set between 5:1 and 7:1.

Inventors: HAYASHI, MINORU, KISHIMOTO, JUNICHI NIPPON KOKI CO., LTD, KOBARI, KOICHI, SATO, KIMIHARU
Applicants: NIPPON KOKI CO., LTD.
Application year: 1988
Main classification: B60R21
IPC codes: C06D5, B60R21