The present invention relates generally to inflators for use in inflatable occupant restraint systems in motor vehicles and, more particularly, to inflators that do not incorporate a filter for removal of particulates from combustion gases and cooling of the gases.
Installation of inflatable occupant restraint systems, generally known as “airbags,” as standard equipment in all new vehicles has intensified the search for smaller, lighter and less expensive restraint systems. Accordingly, since the inflator used in such systems tends to be the heaviest and most expensive component, there is a need for a lighter and less expensive inflator.
A typical inflator includes a cylindrical steel or aluminum housing having a diameter and length related to the vehicle application and characteristics of a gas generant propellant contained therein. Inhalation by a vehicle occupant of particulates generated by propellant combustion during airbag activation can be hazardous. Thus, the inflator is generally provided with an internal, more rarely external, filter comprising one or more layers of steel screen of varying mesh and wire diameter. Gas produced upon combustion of the propellant passes through the filter before exiting the inflator. Particulate material, or slag, produced during combustion of the propellant in a conventional system is substantially removed as the gas passes through the filter. In addition, heat from combustion gases is transferred to the material of the filter as the gases flow through the filter. Thus, as well as filtering particulates from the gases, the filter acts to cool the combustion gases prior to dispersal into the airbag. However, inclusion of the filter in the inflator increases the complexity, weight, and expense of the inflator.
Various gas generant formulations have been developed in which the particulates resulting from combustion of the gas generant are substantially eliminated or significantly reduced. To solve the problems of reducing airbag inflator size, weight, cost and efficiency, the present invention obviates the need for a conventional filter by appropriate selection of a smokeless gas generant and by incorporation of combustion gas retainer which cools the combustion gases prior to dispersal of the gases into an airbag. Obviating the need for a filter in an inflator allows the inflator to be simpler, lighter, less expensive and easier to manufacture.
The present invention provides a filterless airbag module comprising an inflator including a housing and a smokeless gas generating propellant contained within the housing. At least one aperture is formed in the housing to enable fluid communication between an interior of the housing and an exterior of the housing. An airbag is arranged to fluidly communicate with the aperture (or apertures). A combustion gas retainer is positioned exterior of the housing and in alignment with the apertures. In one embodiment, the retainer has a base portion extending from the housing, a wall extending from the base portion, and a flange extending from the wall in a direction toward the housing. The retainer and a surface of the housing combine to define a cooling chamber for cooling combustion gases received from the housing via the apertures. A heat-absorbing material may be positioned in the cooling chamber to aid in cooling combustion gases received therein.
In a particular embodiment, the inflator housing is generally cylindrical in shape and has a central axis. The retainer base portion extends radially outwardly from the housing, and the retainer flange extends generally radially inwardly from the wall to form an annular cooling chamber centered on the central axis.
In another aspect of the present invention, a method is provided for cooling combustion gases prior to dispersal of the gases into an inflatable occupant safety device in a vehicle occupant protection system. A housing is provided which defines a combustion chamber and which has at least one aperture formed in the housing to enable fluid communication between the combustion chamber and an exterior of the housing. A combustion gas retainer is positioned exterior of the housing and in alignment with the aperture (or apertures). The retainer and a surface of the housing combine to define a cooling chamber for cooling combustion gases received from the combustion chamber via the apertures. The cooling chamber is dimensioned to affect an average residence time of combustion gases received in the chamber so that the gases reside in the cooling chamber for a length of time sufficient to cool the gases to a temperature within a predetermined temperature range prior to the gases exiting the cooling chamber. Combustion gases are conveyed from the combustion chamber via the apertures to the cooling chamber where the gases are retained for the length of time sufficient to cool the gases to a temperature within the predetermined temperature range.
The retainer has a base portion extending from the housing, a wall extending from the base portion, and a flange extending from the wall in a direction generally toward the housing. The component dimensions of the retainer may be specified so as to affect the average residence time of combustion gases in the cooling chamber.
In one embodiment of the gas cooling method, the retainer base portion, the wall, and the flange are dimensioned to provide the cooling chamber with a predetermined volume in which the gases are retained for cooling to a temperature within the predetermined temperature range. The desired predetermined volume is determined taking into account such factors as the flow rate of the gases into the cooling chamber, the flow rate of the gases out of the cooling chamber, and the temperature of the gases entering the cooling chamber from the combustion chamber.
In another embodiment of the gas cooling method, a combination of the base portion, the wall, and the flange define a flow path for combustion gases through the cooling chamber. The base portion, the wall, and the flange are dimensioned so that the average time required for the gases to travel along the flow path is sufficient to cool the gas to a temperature within the predetermined temperature range prior to exiting the cooling chamber. A heat-absorbing material may be positioned along the flow path so that combustion gases flowing along the flow path impinge upon the heat-absorbing material, further cooling the gases.
In yet another embodiment of the gas cooling method, an end portion of the flange and an exterior surface of the housing are spaced apart to define an exit port for combustion gases from the cooling chamber. The flange is dimensioned to control the size of the exit port to affect a flow rate of the gases from the combustion chamber so that the average residence time of the combustion gas within the cooling chamber is sufficient to cool the gases to a temperature within the predetermined temperature range prior to the gases exiting the cooling chamber.
Referring to
Inflator 12 has a perforated and centrally disposed igniter support tube 30 welded therein for the support of an igniter 32. The perforated tube allows a frame front generated by the igniter 32 to pass to the propellant 20, thereby igniting propellant 20 and producing an inflating gas. The propellant 20 may be any known smokeless gas generant composition useful for airbag application and is exemplified by, but not limited to, compositions and processes described in U.S. Pat. Nos. 5,872,329, 6,074,502, 6,287,400, 6,306,232 and 6,475,312 incorporated herein by reference. As used herein, the term “smokeless” should be generally understood to mean such propellants as are capable of combustion yielding at least about 90% gaseous products based on a total product mass; and, as a corollary, less than about 10% solid products based on a total product mass. It has been generally found that filters as used in other inflator designs can be eliminated by using compositions having the described combustion characteristics. Other suitable compositions are set forth in the U.S. patent application Ser. Nos. 10/407,300 and 60/369,775, incorporated herein by reference.
Referring to
Referring again to
The mathematical formula for the volume of a solid circular cylinder is calculated using the relation:
JIr2h (1)
where r is the radius of the cylinder and h is the length of the cylinder. Similarly, the volume of an annular space residing between two concentric cylinders may be calculated by computing the volume of each cylinder using equation (1), then subtracting the volume of the inner cylinder from the volume of the outer cylinder. For example, in calculating the annular volume formed by rotating the area X about axis 70, the volume of the outer cylinder is given by the relation JIDr12, and the volume of the inner cylinder is given by the relation JID(r1−L cos θ)2. Thus, the annular volume formed by rotating the area X about axis 70 is given by the relation:
JIDr12−JID(r1−L cos θ)2 (2)
Similarly, the annular volume formed by rotating area Y about axis 70 is given by the relation:
½(JI(D+L sin θ)r12−JI(D+L sin θ)(r1−L cos θ)2 (3)
Also, the annular volume formed by rotating area Z about axis 70 is given by the relation:
JI(D+L sin θ)(r1−L cos θ)2−JI(D+L sin θ)r22 (4)
In view of the above, the total annular volume is approximated by the sum of the computed component volumes obtained by rotating cross-sectional areas X, Y, and Z about axis 70. Thus, the cooling chamber volume is approximated by adding the component volumes obtained using equations (2), (3) and (4). As an example, for L=2 inches, r1=10 inches, r2=7 inches, D=2 inches, and θ=30°, the addition of component volumes obtained using equations (2), (3), and (4) yields a total cooling chamber volume of approximately 530 in.3.
Combustion gases exiting inflator housing 18 are volumetrically expanded and cooled in cooling chamber 50, prior to entering airbag 16. As illustrated by arrow A in
Also in accordance with the present invention, a method is contemplated for cooling combustion gases received from the inflator housing prior to dispersal of the gases into an inflatable device of a vehicle occupant protection system. It is believed that the dimensions of cooling chamber 50 may be controlled to affect the average residence time of combustion gases in the cooling chamber. This is done to ensure that the gases reside in the cooling chamber for a length of time sufficient to cool the gases to a temperature within a predetermined temperature range prior to the gases exiting cooling chamber 50. The appropriate dimensions of the cooling chamber are selected taking into account such factors as the flow rate of the combustion gases from the combustion chamber into the cooling chamber, the desired flow rate of gases out of the cooling chamber (determined by such factors as the desired airbag inflation profile), and the temperature of the gases entering the cooling chamber from the combustion chamber.
Referring to
Referring again to
In yet another embodiment of the gas cooling method, an end portion 49 of flange 48 is dimensioned so as to be spaced apart from exterior surface 72 of housing 18 to define an exit port 74 for combustion gases from cooling chamber 50. Length L of flange 48 is dimensioned to control the size of exit port 74 to affect a flow rate of the gases from cooling chamber 50, thereby affecting the average residence time of the combustion gas within cooling chamber 50. By suitably constricting exit port 74, the combustion gases may be retained in cooling chamber 50 for a time sufficient to cool the gases to a temperature within the desired temperature range prior to the gases exiting cooling chamber 50.
In any of the methods described above for affecting the average residence time of the combustion gases in cooling chamber 50, cooling of the gases may be enhanced by positioning a heat-absorbing material (not shown) in the cooling chamber. One example of such material is a carbon compound formed into, for example, a grating that acts as a heat sink.
Referring to
Safety belt assembly 150 may be in communication with a crash event sensor 158 (for example, an inertia sensor or an accelerometer) including a known crash sensor algorithm that signals actuation of belt pretensioner 156 via, for example, activation of a pyrotechnic igniter (not shown) incorporated into the pretensioner. U.S. Pat. Nos. 6,505,790 and 6,419,177, previously incorporated herein by reference, provide illustrative examples of pretensioners actuated in such a manner. Airbag module 10 may also be in communication with a crash event sensor 210 including a known crash sensor algorithm that signals actuation of airbag module 10 via, for example, activation of airbag inflator 12 in the event of a collision.
It will be understood that the foregoing descriptions of various embodiments of the present invention is for illustrative purposes only. As such, the various structural and operational features herein disclosed are susceptible to a number of modifications, none of which departs from the scope of the present invention as defined in the appended claims.
This application claims the benefit of provisional application Ser. No. 60/512049 filed on Oct. 17, 2003.
Number | Date | Country | |
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60512049 | Oct 2003 | US |