Patent Application
20060137786
1. Field of the Invention
The present invention relates to a gas generator, and more particularly to a gas generator for use in an air bag system installed in an automobile.
2. Description of Related Art
A gas generator which is capable of generating a desired amount of gas arbitrarily is used conventionally in various applications such as an air bag apparatus which serves as a safety device in a vehicle, or a side thruster for a flying object including a spacecraft.
An example of a gas generator used in a side thruster or the like for a flying object including a spacecraft is disclosed in JP-A No. 2002-204947. The gas generator disclosed in JP-A No. 2002-204947 is an end-face-burning type gas generator in which an end face of a gas generating agent burns. More specifically, the end surface of the gas generating agent is ignited by an igniter such that end-face-burning progresses in the direction shown by the arrow in FIG. 1 of JP-A No. 2002-204947. The generated gas is discharged from a flow hole to a gas flow pipe via a flow control valve, and is ejected to the outside through the gas flow pipe. In this gas generator, the sectional area of combustion during the combustion process is set at a substantially fixed value so that a fixed amount of combustion gas is discharged.
Meanwhile, in the case of gas generators that are used in various applications, it is sometimes desirable to be able to adjust the amount of gas that is generated during the operating period (i.e. during gas discharge) at will, depending on the application of the gas generator.
For example, in an air bag apparatus for restraining a passenger during a vehicle collision, it is desirable that the air bag be inflated in a two-stage or multi-stage process whereby the inflation speed of the air bag during an initial inflation stage is reduced to prevent an excessive impact on the passenger when the air bag deploys, and the air bag is deployed sufficiently in the latter stage. Accordingly, a gas generator (i.e. a gas generator for generating an air bag-inflating gas) which generates gas in two or more stages, such that gas is discharged slowly during the initial stage and in a sufficient amount during the latter stage, has been proposed for use in such an air bag apparatus.
JP-A No. 2001-97175 discloses a dual type gas generator in which a plurality of igniters and gas generating agents that are burned independently thereby are disposed in separate combustion chambers, and the amount of generated gas is adjusted by adjusting the ignition timing of each igniter.
The invention provides a gas generator containing a gas generating agent that generates a gas when burned and an ignition device for igniting and burning the gas generating agent in the interior of a housing having a gas discharge port, the gas generating agent being formed in lump form, and a combustion restricting member for restricting combustion of the gas generating agent, the member being provided on all surfaces of the gas generating agent other than a combustion starting end surface to be ignited and burned by the ignition device, the gas generating agent taking a form or structure according to which a combustion surface area thereof varies as the gas generating agent is burned.
The invention also provides a gas generator containing a gas generating agent that generates a gas when burned and an ignition device for igniting and burning the gas generating agent in the interior of a housing having a gas discharge port, the gas generating agent being formed in lump form, disposed inside a gas generating agent chamber provided within a housing and being in a condition enabling end-face-burning, the gas generating agent taking a form or structure according to which a combustion surface area thereof varies as the gas generating agent is burned.
The invention also provides a gas generator containing a gas generating agent that generates a gas when burned and an ignition device for igniting and burning the gas generating agent in the interior of a housing having a gas discharge port, the gas generating agent being formed in lump form such that all or a part thereof is capable of end-face-burning, the gas generating agent taking an overall form or structure (i.e. the entirety of the gas generating agent within the space storing the gas generating agent)according to which a combustion surface area thereof varies as the gas generating agent is burned.
The invention also provides a manufacturing method for a gas generator containing a gas generating agent that generates a gas when burned and an ignition device for igniting and burning the gas generating agent in the interior of a housing having a gas discharge port, the manufacturing method comprising the steps of: charging a gas generating agent chamber with a fluid-state gas generating agent; and curing the fluid-state gas generating agent to form a lump-form gas generating agent having a combustion starting end surface and a form or structure according to which a combustion surface area thereof varies as the gas generating agent is burned.
The invention also provides a manufacturing method for a gas generator containing a gas generating agent that generates a gas when burned and an ignition device for igniting and burning the gas generating agent in the interior of a housing having a gas discharge port, the manufacturing method comprising the steps of: charging a container formed by a member that comprises a gas generating agent chamber, or the interior of a container stored in the gas generating agent chamber, with a fluid-state gas generating agent; curing the fluid-state gas generating agent to form a lump-form gas generating agent having a combustion starting end surface and a form or structure according to which a combustion surface area thereof varies as the gas generating agent is burned; and incorporating the container charged with the cured gas generating agent in the interior of the housing.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein:
The present invention relates to a gas generator with which the amount of gas generated in an end-face-burning type gas generator can be varied during an operation (i.e. during gas discharge).
The present invention also relates to a gas generator in which the manufacture and internal structure of the gas generator are not increased in complexity, and the weight of the gas generator itself is not increased.
The present invention also relates to a gas generator comprising an ignition device and a lump-form gas generating agent and having a simplified internal structure, with which the amount of generated gas can be varied.
A gas generator according to the present invention realizes the aspects described above by providing a gas generator which has a simple structure and is capable of varying an amount of generated gas. In this gas generator, a gas generating agent is formed or disposed so as to perform the end-face-burning, and the combustion surface area of the gas generating agent varies during combustion process of the gas generating agent.
Furthermore, the present invention provides a gas generator containing, in the interior of a housing having a gas discharge port, a solid, lump-form gas generating agent which generates a gas when burned and an ignition device for igniting and burning the gas generating agent, wherein at least one end portion of the gas generating agent serves as a combustion starting end surface that is ignited and burned by the ignition device, the surfaces other than the combustion starting end surface are combustion-restricted such that end-face-burning progresses substantially from the one end portion toward a final end portion, and the sectional area of the gas generating agent varies in a combustion progression direction.
The gas generator according to the present invention uses a lump-form gas generating agent, and therefore has a simple internal structure. Moreover, the lump-form gas generating agent performs end-face-burning, and the combustion surface area thereof is varied over time as combustion progresses. Hence, the gas generator is capable of varying the amount of generated gas. The gas generator of the present invention which exhibits this effect may be used as a general gas generator for use in various applications, and is particularly suited to use as a gas generator for an air bag, which is a device for restraining a passenger in the event of a vehicle collision.
In this gas generator, the entirety of the gas generating agent within the space (i.e. the combustion chamber) storing the gas generating agent takes a form or structure according to which the combustion surface area thereof varies as combustion progresses, and therefore the amount of generated gas can be varied during an operation of the gas generator.
The gas generating agent used in the present invention is formed in a “lump form”. In this specification, the term “lump form” indicates a form in which the end-face-burning to be described below can be performed, and a form in which end-face-burning is performed in at least one point at time during combustion of the gas generating agent. The lump-form gas generating agent is preferably provided such that approximately one to three, and a maximum of approximately ten, lumps of the gas generating agent are disposed in the gas generator, for example. However, there are no particular limitations on the number of lumps of gas generating agent used. Moreover, a large number of small-form gas generating agents such as pellets, single-perforated forms, and porous forms may be used as a part of the gas generating agent of the present invention, similarly to a gas generating agent used in a typical gas generator. However, in this case the gas generating agent should contain at least a constitutional unit which is formed in lump form so as to be capable of performing end-face-burning, and in containing this constitutional unit, the gas generating agent of the present invention differs from a conventional gas generating agent using only a large number of small-form agents such as pellets, single-perforated forms, and porous forms. When small-form gas generating agents are used in the present invention, the small-form gas generating agents are preferably disposed such that no gaps occur therebetween.
Conventional, small-form gas generating agents such as pellets, single-perforated forms, and porous forms basically perform allover burning, whereas the gas generating agent used in the present invention differs greatly from that of a conventional gas generator in that, when the gas generating agent is constructed in a plurality units, the end surface thereof bums from one end portion to the final end portion during at least one or all of the combustion stages thereof, and when the end surface is burning, the other surfaces do not bum (in other words, end-face-burning is performed).
Hence, the gas generating agent of the present invention is preferably formed partially or entirely in a lump form which fills a space for storing the gas generating agent. The lump-form gas generating agent may be formed as a single lump from the beginning, or may be formed by binding a powder or the like, or integrating a plurality of bodies. The gas generating agent of the present invention may also be formed as a plurality of gas generating agents juxtaposed with no gaps therebetween. Particularly when a plurality of gas generating agents is laminated in the combustion progression direction of the end-face-burning, a constitution is possible whereby one of adjacent gas generating agents has to burn out before the end surface of the other gas generator is exposed. Furthermore, when a plurality of gas generating agents is laminated in a direction which intersects the combustion progression direction of the end-face-burning, adjacent gas generating agents are preferably stacked tightly enough to prevent a flame or the like generated by the end-face-burning of adjacent gas generating agents from entering the gap between the gas generating agents.
For example, the gas generating agent of the present invention may be formed as a substantially cylindrical lump having a through hole or a substantially columnar lump having no through hole, and having a sufficient magnitude to fill a gas generating agent storage chamber which serves as the space for storing the gas generating agent.
Further, the gas generating agent of the present invention may employ approximately two to six disk-form gas generating agents stacked within the gas generating agent storage chamber. Note, however, that when the gas generating agents are formed in disk-form and stacked, the gas generating agents should be formed and disposed such that no grooves, gaps, or the like through which a flame can pass occur between the stacked gas generating agents, and such that end-face-burning can be achieved.
By providing a small number of lump-form gas generating agents, the thickness of each gas generating agent increases, leading to a reduction in variation of the combustion surface area caused by cracks or grinding caused by the shock of an operation of the ignition device or the like, and hence a stable performance can be maintained.
Moreover, by providing a small number of lump-form gas generating agents, gaps between adjacent gas generating agents are eliminated, and both the gas generating agent chamber and the entire gas generator itself can be reduced in size.
When the gas generating agent is provided in a single lump, the single lump of gas generating agent is disposed in the gas generating agent chamber in the interior of the housing, and hence handling of the gas generating agent during assembly is easy, weighing errors are eliminated, and the performance of the gas generating agent during an operation can be stabilized.
In the present invention, the gas generating agent formed in lump form as described above should be ignited by the ignition device upon activation of the gas generator such that end-face-burning, whereby combustion advances from the ignition point (ignition surface) toward a final end side, is performed within the space in which the gas generating agent exists (i.e. the gas generating agent chamber space or the combustion chamber). Accordingly, the gas generating agent formed in lump form as described above should be ignited such that combustion begins from one end portion (the combustion starting end surface) thereof, and such that combustion does not progress from any surface other than the one end portion (surfaces other than the combustion starting end surface). Here, the combustion starting end surface denotes the surface (or part) of the gas generating agent that is ignited first, and generally corresponds to one of the end surfaces of a gas generating agent formed in lump form. Which end face corresponds to the combustion starting end surface is determined on the basis of the manner in which the gas generating agent is disposed, its positional relationship with the ignition device, and so on.
In the present invention, to ensure that combustion begins from the one end portion (the combustion starting end surface), the ignition device for igniting the gas generating agent should be disposed facing the one end portion (combustion starting end surface) from which combustion of the gas generating agent begins, and if not directly facing this one end portion, then the ignition device should be disposed such that the high-temperature gas and flame that are combustion products of the ignition device reach the one end portion (combustion starting end surface) of the gas generating agent.
An electric igniter that is activated by an ignition current may be used alone as the ignition device, or to enhance the explosive power of the electric igniter, a typically-employed transfer charge (boron niter or the like) may be used alongside the igniter. There are no particular limitations on the type and specifications of the transfer charge as long as it increases the explosive power of the igniter and causes combustion of the gas generating agent.
Further, in the present invention, to ensure that combustion does not progress from surfaces of the gas generating agent other than the one end portion (surfaces other than the combustion starting end surface), combustion of the surfaces other than the combustion starting end surface should be restricted, and these surfaces should not be ignited by the ignition device.
To restrict combustion of the surfaces other than the combustion starting end surface, a combustion restricting member(s) which restricts combustion of the gas generating agent by enveloping the surfaces other than the combustion starting end surface may be employed. As the combustion restricting member, there may be employed a component for defining the gas generating agent chamber within the housing, a component which defines the gas generating agent chamber within the housing and also constitutes the housing (these components will be referred to together as “gas generating agent chamber constitutional components” hereafter), or a separate container which envelops the surfaces of the gas generating agent other than the combustion starting end surface.
The combustion restricting member is formed from a material and with a thickness that prevents direct contact between the combustion products generated by the ignition device and all surfaces of the gas generating agent other than the one end portion (combustion starting end surface), and preferably a material and thickness that prevent ignition of all surfaces of the gas generating agent other than the one end portion (combustion starting end surface) by heat transfer and radiation during combustion of the gas generating agent from the one end portion (combustion starting end surface) to the final end portion. For example, the combustion restricting member may be formed using a material such as stainless steel, iron, or aluminum, at a thickness (1 mm, for example) which satisfies the above conditions. The combustion restricting member formed in this manner is disposed to envelop all surfaces of the gas generating agent other than the combustion starting end surface, and preferably in contact with and tightly attached to these surfaces.
For example, when the gas generating agent takes a single-perforated cylindrical form having a through hole in its center, an inner tube which covers the inner peripheral surface of the through hole and an outer tube which covers the outer peripheral surface of the gas generating agent are used as the member forming the gas generating agent chamber (the combustion restricting member), and the gas generating agent is disposed in the interior of the housing in contact with these tubes. On the other hand, when the gas generating agent takes a columnar form having no through hole in its center, a tube covering the outer peripheral surface of the gas generating agent is used as the member forming the gas generating agent chamber (the combustion restricting member), and both the gas generating agent and the tube are disposed in the interior of the housing such that the gas generating agent contacts the tube. In so doing, combustion of the gas generating agent does not progress from the surfaces which contact the inner tube and outer tube, or the surface which contacts the tube, and hence end-face-burning is maintained.
The term “inner tube” in this specification denotes a cylindrical member defining the inside of the gas generating agent storage chamber, and the terms “outer tube” and “tube” denote a cylindrical portion defining the outside of the gas generating agent storage chamber. All of these tubes cover the surfaces of the gas generating agent other than the combustion starting end surface, and are therefore capable of functioning as the combustion restricting member.
Note that in order to simplify the internal structure of the gas generator of the present invention, a single ignition device is preferably provided. However, this does not exclude the use of two or more ignition devices, and when two or more ignition devices are used, the plural ignition devices are disposed to ignite and burn a common end surface of the same gas generating agent. Hence, even when plural ignition devices are used, the gas generator of the present invention differs from a conventional dual-type gas generator in which the ignition device each ignites individual gas generating agents, in that the ignition devices ignites and bums a common end surface of the same gas generating agent.
In the present invention, as described above, the gas generating agent performs end-face-burning whereby combustion progresses from one end portion (the combustion starting end surface) to the final end portion. The gas generating agent is preferably formed such that the combustion surface progresses in a substantially identical manner regardless of the location on the gas generating agent, and such that combustion progresses in the same direction.
This end-face-burning gas generating agent takes a form or structure according to which the combustion surface area thereof (in other words, the surface area of the burning part of the gas generating agent) varies as the combustion goes on. Therefore, the amount of gas generated per unit time can be varied, and as a result the air bag inflation timing and degree of inflation can be optimized.
In other words, in the gas generator of the present invention, the gas generating agent performs end-face-burning, and the combustion surface area thereof varies during combustion. Therefore, the amount of gas generated per unit time can be adjusted at will. In cases such as when the air bag inflation speed is to be suppressed at the initial stage of the air bag operation to prevent excessive impact on the passenger, and the air bag is then to be inflated far enough to obtain sufficient restraint, for example, the gas generator should generate gas gently at the initial stage, and then generate a sufficient amount of gas at the latter stage. When gas is to be generated in this manner, the sectional area of the burning part of the gas generating agent may be reduced in the initial stage to reduce the amount of generated gas, and when combustion has progressed by a fixed distance, the sectional area may be increased so that a larger amount of gas is generated.
For example, when the gas generating agent is formed in a lump form having no cavities or the like in its interior, the surface perpendicular to the combustion progression direction serves as the end-face-burning combustion face, and the sectional area thereof (the combustion sectional area) corresponds to the combustion sectional area of the end-face-burning. Hence, the amount of generated gas is commensurate with the sectional area of the surface perpendicular to the combustion progression direction. Accordingly, by varying the sectional area of the surface perpendicular to the combustion progression direction of the gas generating agent, the combustion surface area varies as combustion progresses, and as a result, the amount of generated gas can be adjusted in accordance with the variation in the sectional area.
On the other hand, when the gas generating agent includes interior cavities or the like, these cavities are exposed as combustion progresses, and the combustion surface area varies in accordance with the exposed cavity. Hence, the amount of generated gas varies in accordance therewith. Therefore, in this case, the amount of generated gas can be adjusted at will by adjusting the form, formation extent (the proportion of cavities), and so on of the cavities existing in the interior of the lump-form gas generating agent.
The gas generating agent of the present invention takes a lump-form, and may also be formed in a single-perforated form having a through hole opened in the center thereof, or a columnar form having no through hole, for example. When the gas generating agent is formed in this substantially cylindrical or substantially columnar form and the end surface thereof is ignited so as to prevent the inner and outer peripheral side faces from burning (to maintain end-face-burning), the variation in the sectional area which intersects the axial direction of the substantially cylindrical or substantially columnar gas generating agent matches the mass flow as an inflator. Hence in this case, by adjusting the sectional form of the gas generating agent, the operating performance of the gas generator (the manner in which the air bag is inflated) can also be adjusted arbitrarily. When the gas generating agent takes a single-perforated cylindrical form having a through hole in its center, the inner peripheral surface of the through hole is covered by the inner tube, and the outer peripheral surface of the gas generating agent is covered by the outer tube, or when the gas generating agent takes a columnar form having no through hole and the outer peripheral surface thereof is covered by the tube, the operating performance of the gas generator (the manner in which the air bag is inflated) can be adjusted theoretically in any way by adjusting the sectional form of the gas generating agent formed by the inner tube and outer tube or the tube. Note that the form of the sectional area of the gas generating agent is not limited to the circle described above, and may take a polygonal form (also, a through hole may be formed regardless of the sectional form).
In the present invention, the combustion surface area of the gas generating agent can be varied in the combustion progression direction by varying at least one of the outer diameter of the inner tube and the inner diameter of the outer tube in the axial direction to adjust the sectional area of the gas generating agent, or by varying the inner diameter of the tube in the axial direction to adjust the sectional area of the gas generating agent. Accordingly, the gas generator exhibits simple combustion control.
Moreover, in the gas generator of the present invention, the housing preferably includes a ceiling plate, a base plate on which the ignition device is disposed, and a peripheral wall portion connecting the ceiling plate and base plate, the ignition device is preferably disposed in the interior of a member forming an inner peripheral side wall of a gas generating agent chamber, the gas generating agent is preferably disposed so that the axis thereof overlaps the axis of the housing, and the combustion starting end surface is preferably formed on the ceiling plate side.
The inner tube serves as the member forming the inner peripheral side wall of the gas generating agent chamber, and by employing the interior of the inner tube as the ignition device storage chamber storing the ignition device, the ignition device can be prevented from protruding from the inflator, and the overall height of the inflator can be suppressed.
Furthermore, in the gas generator of the present invention, the lump-form gas generating agent having a form or structure according to which the combustion surface area thereof varies during combustion is preferably formed by charging the gas generating agent storage chamber (the space between the inner tube and outer tube, or the interior of the tube, for example) with a fluid-state gas generating agent and then curing the gas generating agent, or by charging a container serving as the member that forms the gas generating agent chamber, or the interior of a container accommodated the gas generating agent chamber, with a fluid-state gas generating agent and then curing the gas generating agent. Particularly in a case where a fluid-state gas generating agent is cured in a container serving as the member that forms the gas generating agent chamber or the interior of a container accommodated the gas generating agent chamber, the container accommodating the cured gas generating agent should be incorporated into the interior of the housing.
A “fluid state” indicates a liquid, powder, colloid, or the like, for example, and by charging the interior of the gas generating agent storage chamber (in other words, the combustion chamber) with a gas generating agent in this state, and then subjecting the gas generating agent to a method such as drying, reactive curing, compression, or gelation, the gas generating agent can be formed into a solid or colloidal block having a substantially cylindrical shape, a substantially columnar shape, or an arbitrary polygonal shape or angled cylindrical shape.
Further, the gas generating agent in the gas generator of the present invention preferably uses one or a mixture of fuels selected from RDX, HMX, 5-nitrotetrazole, 1H-tetrazole, 5-aminotetrazole, 1H-tetrazole-1,5-diamine, guanidine nitrate, mono-amine guanidine nitrate, carbodihydrazide, triamine guanidine nitrate, 1,2,4-triazole-3-on, 5,5′-bi-1H-tetrazole, dicyandiamide, azodicarbonamide, glycine, semicarbazone, 1H-1,2,4-triazole-3,5-diamine, 4-amino guanazole, and guanylurea nitrate, and preferably uses one or a mixture of oxidants selected from potassium perchlorate, ammonium perchlorate, sodium perchlorate, strontium perchlorate, potassium nitrate, ammonium nitrate, sodium nitrate, and strontium nitrate.
The gas generating agent used in the present invention differs from a conventional gas generating agent, in which all of the used gas generating agents (a plurality of gas generating agents such as pellets or single-perforated forms) burn in a substantially overall burning state, in that the gas generating agent is formed in lump form and performs end-face-burning. Therefore, a gas generating agent that has the best possible ignitability and combustion performance is preferably used. Accordingly, the burning rate of the gas generating agent under 10 MPa of pressure is preferably not less than 30 mm/sec.
Furthermore, a combustion accelerator is preferably mixed into and dispersed throughout the gas generating agent. One of the following combustion accelerators (i) and (ii) may be used as the combustion accelerator:
(i) a combustion accelerator which contributes directly to combustion of the gas generating agent by burning itself in order to further raise the combustion temperature; and
(ii) a combustion accelerator which does not contribute directly to combustion of the gas generating agent, but provides conditions for accelerating combustion.
An example of the combustion accelerator described in (i) is a conventional boron niter or a gas generating agent using nitroguanidine or the like as a fuel and strontium nitrate or the like as an oxidant, which creates an environment with a higher combustion temperature than the gas generating agent (the original gas generating agent) into which the combustion accelerator is mixed and dispersed.
An example of the combustion accelerator described in (ii) is a microcapsule, which is a hollow micro-particle, the combustion surface area of which increases at one of the combustion stages of the gas generating agent(the original gas generating agent) into which the combustion accelerator is mixed and dispersed, thereby accelerating combustion. The microcapsule is preferably formed to bum out or split open as the gas generating agent bums.
The combustion accelerator may also be formed to contain metallic particles.
A combustion accelerator such as that described above, which is used to accelerate combustion of the gas generating agent, preferably has an average particle diameter between 1 to 1000 μn, and more preferably between 3 and 500 μm. More particularly, the particle diameter per particle of the combustion accelerator is preferably between 1 to 1000 μn, and more preferably between 3 and 500 μm.
In accordance with the above, as the gas generating agent of the present invention, such a gas generating agent may be used that contains 40% by weight of RDX as a fuel, 58% by weight of potassium perchlorate as an oxidant, 1% by weight of sodium carboxymethyl cellulose as a molding binder, and 1% by weight of plastic microcapsule as the combustion accelerator.
Further, the gas generating agent used as the gas generating agent of the present invention is preferably provided with a reinforcing member for preventing irregularities such as cracks and chips occurring in the combustion starting end surface of the gas generating agent due to shock generated by the impact of an operation of the inflator (an operation of the ignition device) or when the inflator is dropped. The reinforcing member is formed by adhering a film or a porous thin plate to the combustion starting end surface, or coating the combustion starting end surface with a hardening resin or the like. By preventing cracks and chips in the gas generating agent, a stable performance can be maintained without variation in the surface area of the end surface. A device such as a film member provided on the combustion starting end surface of the gas generating agent, or a resin material applied to the combustion starting end surface of the gas generating agent through coating or impregnation and then cured, may be used as the reinforcing member.
Further, an ignition aid including a material having greater ignitability than the gas generating agent is preferably provided on the combustion starting end surface of the gas generating agent. A film-form member coated on one surface or both surfaces thereof with a transfer charge, a porous thin plate member impregnated with a black powder such as boron niter, or a slurry-form substance mixed with an explosive and cured on the combustion starting end surface of the gas generating agent may be used as the ignition aid. The ignition aid may also be formed to function as a reinforcing member for preventing the occurrence of cracks or chips on the combustion starting end surface of the gas generating agent caused by shock when the inflator is dropped and so on. By providing this ignition aid, ignition of the gas generating agent by the ignition device can be assisted.
In the gas generator according to the present invention, the explosive used in the ignition device is preferably mixed into and dispersed through the lump-form gas generating agent as a combustion accelerator which contributes directly to combustion of the gas generating agent by burning itself in order to further raise the combustion temperature. This transfer charge includes mainly a black powder such as boron niter, for example, and has greater ignitability than the gas generating agent so that the ignitability of the gas generating agent can be improved by mixing and dispersing the transfer charge into the gas generating agent.
Further, a gas generating agent having a high combustion temperature may be used as the ignition aid, and this ignition aid may be provided on the combustion starting end surface of the gas generating agent.
According to the gas generator of the present invention, a solid, lump-form gas generating agent is used, and combustion progresses from one end portion thereof to a final end portion while the combustion surface area varies during combustion. As a result, the amount of gas generated per unit time can be varied easily. Particularly when the surfaces of the gas generating agent other than the end surface are covered by a constitutional member of the gas generating agent chamber in order to maintain end-face-burning, the amount of generated gas can be controlled by adjusting the sectional area formed by this constitutional member. Hence, the gas generator has a simple internal structure, is easy to assemble, and has an operating performance that can be controlled easily. Furthermore, in order to achieve end-face-burning, the gas generating agent contains a small number of lumps, and no gaps occurs between the gas generating agents. Therefore, the overall size of the gas generator can be reduced.
As above shown, the present invention relates to a gas generator, and more particularly to a gas generator which is suitable for use in an air bag system installed in an automobile.
Embodiments of the present invention will be described below on the basis of the drawings.
A gas generator 100 of this embodiment contains a housing 3 having a diffuser shell 1 and a closure shell 2, an ignition device, or more specifically an igniter 4 and a transfer charge 5, disposed in a storage space inside the housing 3, a gas generating agent 6 which is ignited and burned by the ignition device to generate combustion gas, and an outer tube 8 and an inner tube 9 which define a combustion chamber 7 in which the gas generating agent 6 is stored.
The diffuser shell 1 is formed by pressing a stainless steel plate, and includes a circular portion 12, a peripheral wall portion 10 formed in the outer peripheral portion of the circular portion 12, and a flange portion 19 which extends radially outward from the tip end portion of the peripheral wall portion 10. Sixteen gas discharge ports 11 having a diameter of 3 mm in this embodiment are arranged with equal intervals circumferentially in the peripheral wall portion 10. An ignition device storage chamber 31 is formed on the inside of the inner tube 9, and the igniter 4 and transfer charge 5 are disposed inside the ignition device storage chamber 31.
The closure shell 2 is formed by pressing a stainless steel plate, and includes a circular portion 30, a central hole 15 formed in the center of the circular portion 30, a peripheral wall portion 47 formed in the outer peripheral portion of the. circular portion 30, and a flange portion 20 which extends radially outward from the tip end portion of the peripheral wall portion 47. The inner tube 9 is disposed to be fitted into the central hole 15. The inner tube 9 includes a stepped portion 50 which engages with the igniter 4, but is formed as a pipe with a fixed thickness and a fixed diameter in the other portion.
The housing 3 is formed as follows: the respective flange portions 19 and 20 of the diffuser shell 1 and closure shell 2 are superimposed on each other and welding 21 is performed, and further the inner tube 9 is welded to the central hole 15 of the closure shell. The tip end (on the diffuser side) of the inner tube 9 is disposed away from the diffuser.
The outer tube 8 defining the outer peripheral surface of the combustion chamber 7 is joined, by welding, to the circular portion 30 of the closure 2 at one end, while the opposite end portion (on the diffuser side) is slightly removed from the circular portion 12 of the diffuser 1 and left in a non-welded state. Further, the outer tube 8 takes a pipe form having a constant thickness, but varies in diameter at the part denoted by “a” in
A single gas generating agent 6 formed in lump-form is disposed in the combustion chamber 7. The gas generating agent is a hollow columnar body disposed such that the inner peripheral surface and outer peripheral surface thereof contact the inner tube 9 and outer tube 8, respectively. The gas generating agent is also disposed such that a closure side end portion 32 thereof contacts the circular portion 30 of the closure shell, while a diffuser side end portion 40 thereof is removed from the circular portion 12 of the diffuser shell. In other words, the space to which the diffuser side end portion 40 of the gas generating agent 6 is exposed communicates with the ignition device storage chamber 31.
The gas generating agent of this embodiment has favorable ignitability, and is formed from 40% by weight of RDX as a fuel, 58% by weight of potassium perchlorate as an oxidant, 1% by weight of sodium carboxymethyl cellulose as a molding binder, and 1% by weight of plastic microcapsule as a combustion accelerator. The gas generating agent used in this embodiment has 32 mm/sec of the linear burning rate under the pressure of 10 MPa.
The gas generating agent is formed by stirring and melting 1% by weight of carboxymethyl cellulose (“CMC DAICEL #2260” produced by Daicel Chemical Industries Ltd.) into 50% by weight of ion-exchanged water at a controlled temperature of 40° C. so that the two substances are mixed evenly. Once the two substances are mixed evenly, 40% by weight of RDX (a powder produced by Nippon Koki Co., Ltd.), 58% by weight of potassium perchlorate (“KPD2” produced by Japan Carlit Co., Ltd.), and a plastic microcapsule (“MYS F-80E” produced by Matsumoto Yushi-Seiyaku Co., Ltd.) are introduced, and the mixture is stirred for another hour until mixed evenly. The mixture is then left to cool to ambient temperature, whereby a colloidal, hydrous gas generating composition is obtained. A predetermined amount of the composition is charged into an inflator container and dried for twenty-four hours at 110° C. to form a molded product.
A coolant/filter 42 is arranged to surround the outer tube 8, defining an annular chamber 41 on the periphery of the tube. The coolant/filter 42 is formed by radially laminating a stainless steel plain stitch wire mesh and compressing the laminated wire meshes in the radial direction and axial direction. With the coolant/filter 42, the combustion gas generated by combustion of the gas generating agent 6 is cooled, and the combustion residue contained therein is trapped.
A gap 43 is formed between the peripheral wall portions 10, 47 of the housing and the coolant/filter 42. The gap 43 forms a gas passage having an annular radial cross-section on the periphery of the coolant/filter 42. Thus the combustion gas passes through the entire portion of the coolant/filter, enabling effective use of the coolant/filter and effective cooling and purification of the combustion gas. The cooled and purified combustion gas passes through the gas passage to the gas discharge ports 11 in the diffuser shell.
The gas discharge ports 11 in the diffuser shell are sealed by an aluminum tape 44 to prevent the infiltration of external moisture into the interior of the housing 3.
Next, operation of the gas generator shown in
Upon reception of the high-temperature gas, flame, shock wave, and so on, the transfer charge 5 ignites and burns, generating a flame, high-temperature gas, high-temperature thermo-particles, and so on (“combustion products” hereafter). In the gas generator shown in the drawing, the diffuser side end portion 40 of the gas generating agent 6 communicates with the ignition device storage chamber 31, and therefore the combustion products generated inside the ignition device storage chamber 31 ignite the end portion 40 of the gas generating agent 6. Note that the outer peripheral portion and inner peripheral portion of the gas generating agent 6 contact the outer tube 8 and inner tube 9 respectively, and the opposite end portion 32 contacts the circular portion 30 of the closure shell 2, and therefore combustion does not occur from the surfaces of the gas generating agent 6 that contact these members. Hence the gas generating agent 6 performs end-face-burning which progresses from the end portion 40 toward the opposite end portion 32.
Furthermore, the inner diameter of the outer tube 8 varies in the axial direction, and therefore the gas generating agent 6 used in the gas generator shown in
When the gas generating agent burns upon activation of the gas generator, combustion gas is generated from the gas generating agent 6, and the internal pressure of the combustion chamber 7 rises. However, since the lower end of the outer tube 8 and the circular portion 12 of the diffuser 1 are not welded together, the housing receives this pressure and deforms as shown in
Combustion of the gas generating agent advances from the diffuser side end surface 40 (in other words, the combustion starting end surface), which is ignited by the combustion products produced by the ignition device, and since the sectional area of the gas generating agent (in other words, the combustion surface area) increases at the curved portion “a”, the amount of gas generated per unit time increases from this location. Accordingly, the gradient of the tank curve increases from the point of the curved portion “a” as the amount of gas generated per unit time increases. Hence, a gas generator which generates gas in a small amount at the initial operative stage and generates a sufficient amount of gas at the latter stage is obtained. Note that in the gas generator of
The same effects can be achieved by modifying the form (outer diameter) of the inner tube 9 instead of the outer tube 8, and also by modifying both outer tube 8 and inner tube 9.
Further, in the embodiment shown in
The gas generator shown in
The combustion products (a flame, high-temperature gas, thermo-particles, and so on) produced inside the ignition device storage chamber 31 enter the combustion chamber 7 which communicates with the chamber 31, thereby igniting and burning the diffuser side end portion. As combustion progresses, the gas generating agent generates combustion gas which increases the internal pressure of the combustion chamber and deforms the housing 3, thereby enlarging the gap between the outer tube 38 and the circular portion 12 of the diffuser shell 1. The combustion gas flows through this gap toward the filter 42, and as the gas passes through the filter 42, it is purified and cooled. The gas is then discharged through the gas discharge ports 11.
As the end-face-burning of the gas generating agent progresses such that the combustion face reaches a curved portion “b”, the inner diameter of the outer tube 38 increases. Accordingly, the sectional area of the gas generating agent in contact therewith and the combustion surface area also increase, leading to an increase in the amount of gas generated per unit time. When combustion progresses further to reach the point of a curved portion “c”, the diameter of the gas generating agent 36 decreases, and hence the combustion surface area and the amount of gas generated per unit time decrease. At the point of a subsequent curved portion “d”, the combustion surface area and the amount of gas generated per unit time increase again.
Similarly to
When the gas generator is activated, combustion of the gas generating agent advances from the diffuser side end portion 46, and at the location of the curved portion “b”, the sectional area of the gas generating agent 36 increases, leading to an increase in the amount of gas generated per unit time from this point. This is reflected in the graph in
Similarly to the gas generator in
Likewise in
A cylindrical filter 84 is disposed in the interior space of the housing 81 formed as described above with a constant gap from the inner peripheral wall of the housing 81. An outer tube 86 is disposed on the inside of the cylindrical filter 84 with a constant gap from the inner peripheral surface of the filter 84, and an inner tube 88 is disposed on the inside of the outer tube 86 so as to secure a space into which a gas generating agent 89 is charged. In this embodiment, the filter 84, outer tube 86, and inner tube 88 are all disposed concentrically with the housing 81. An igniter storage space 90 is formed in the interior of the inner tube 88, and an igniter 91 is disposed in the storage space 90 together with a transfer charge 96 that is ignited by the igniter 91. A communication hole 92 is formed in the outer tube 86 on the closed end surface 83 side of the housing 81, and this communication hole 92 is sealed by a sealing member (sealing tape or the like) 93. A communication hole 94 is also formed in the inner tube 88 on the side of the closed end surface 83 of the housing 81. A combustion starting end surface 95 of the gas generating agent 89 is provided on the side of the closed end surface 83, and hence end-face-burning is performed from this surface toward the final end surface (on the closure 82 side).
In the gas generator 300, the transfer charge 96 is burned upon activation of the igniter 91, and the high-temperature gas generated as a result passes through the communication hole 94 together with heat residue and the like to reach the combustion starting end surface 95, where combustion of the gas generating agent 89 begins. The gas generated as a result raises the internal pressure, thereby rupturing the sealing member 93, and passes through the communication hole 92 to reach the filter 84. The gas is filtered and cooled as it passes through the filter 84, and then discharged through the gas discharge ports 80.
Note that the communication hole 92 may be formed in a position that is offset from the communication hole 94 to make the communication hole 92 less likely to be directly affected by the combustion products that has passed through the communication hole 94.
In the gas generator 300, the inner diameter of the inner tube 88 is larger on the side of the closed end surface 83 of the housing 81 than at the part denoted by the reference symbol “a” in
Note that these embodiments were described on the basis of a case in which the present invention is applied in particular to a pyrotechnic gas generator using a solid gas generating agent disposed within a housing. However, the present invention may be used in a hybrid gas generator which also uses a pressurized gas.
The invention thus described, it will be obvious that the same may be varied in many ways. Such variation s are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-358646 | Dec 2004 | JP | national |
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2004-358646 filed in Japan on 10 Dec. 2004 and 35 U.S.C. § 119(e) on U.S. Provisional Application No. 60/639,322 filed on 28 Dec. 2004, which are incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60639322 | Dec 2004 | US |
