Land vehicles – Wheeled – Attachment
Reexamination Certificate
2002-05-10
2003-12-02
Jordan, Charles T. (Department: 3616)
Land vehicles
Wheeled
Attachment
Reexamination Certificate
active
06655712
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to inflators such as for use in inflating inflatable restraint airbag cushions to provide impact protection to occupants of motor vehicles. More particularly, the invention relates to inflators which rely primarily on reaction of a combustible material for the production of an inflation gas and such as may provide a gas flow orifice for adaptive inflation gas output.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an “airbag,” that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the cushion begins being inflated in a matter of no more than a few milliseconds with gas produced or supplied by a device commonly referred to as an “inflator.”
Various types of inflator devices have been disclosed in the art for the inflation of an airbag such as used in inflatable restraint systems. One type of known inflator device derives inflation gas from a combustible pyrotechnic gas generating material which, upon ignition, generates a quantity of gas sufficient to inflate the airbag.
In general, the burn rate for a gas generant composition can be represented by the equation (1), below:
r
b
=k
(
P
)
n
(1)
where,
r
b
=burn rate (linear)
k=constant
P=pressure
n=pressure exponent, where the pressure exponent is the slope of a linear regression line drawn through a log-log plot of burn rate versus pressure.
As will be appreciated, the pressure exponent generally corresponds to the performance sensitivity of a respective gas generant material, with lower burn rate pressure exponents corresponding to gas generant materials which desirably exhibit corresponding lesser or reduced pressure sensitivity.
Typical pyrotechnic-based inflator devices commonly include or incorporate certain component parts including, for example: a pressure vessel wherein the pyrotechnic gas generating material is burned; various filter or inflation medium treatment devices to properly condition the inflation medium prior to passage into the associated airbag cushion; and a diffuser to assist in the proper directing of the inflation medium into the associated airbag cushion.
To date, sodium azide has been a commonly accepted and used gas generating material. While the use of sodium azide and certain other azide-based gas generant materials meets current industry specifications, guidelines and standards, such use may involve or raise potential concerns such as involving handling, supply and disposal of such materials. Further, economic and design considerations have also resulted in a need and desire for alternatives to azide-based pyrotechnics and related gas generant materials. For example, interest in minimizing or at least reducing overall space requirements for inflatable restraint systems and particularly such requirements related to the inflator component of such systems has stimulated a quest for gas generant materials which provide relatively higher gas yields per unit volume as compared to typical or usual azide-based gas generants. Still further, automotive and airbag industry competition has generally lead to a desire for gas generant compositions which satisfy one or more conditions such as being composed of or utilizing less costly ingredients or materials and being amenable to processing via more efficient or less costly gas generant processing techniques.
As a result, the development and use of other suitable gas generant materials has been pursued. Through such efforts, various azide-free pyrotechnics have been developed for use in such inflator device applications including at least some which have or exhibit a relatively high burn rate pressure dependency, e.g., have a burn rate pressure exponent of 0.4 or more, at 1000 psi.
Typical pyrotechnic-based inflators involve the reaction of a gas generant to form an inflation gas which is released from the inflator device to effect the desired inflation of an associated airbag cushion. The rate at which inflation gas is produced or formed in an inflator is typically a significant factor in the rate at which an associated airbag cushion is inflated. While a rapid or high inflation rate is generally required in order to achieve inflation and deployment of an associated airbag cushion in order to provide desired vehicle occupant protection, efforts have been directed to reduce the mass flow rate of inflation gases into the airbag cushion during the initial stages of deployment such as to minimize or avoid the risk of injury to a vehicle occupant who are out of the desired traveling position (with such vehicle occupants often referred to as “out of position occupants”).
Airbag installations providing a slower initial deployment rate, also referred to as low onset inflation, followed by an increased deployment rate can have the benefit of providing a more gradual initial deployment of the associated airbag cushion into the occupant-containing vehicle compartment yet still achieve desired full or complete inflation within the desired time frame. Current low onset inflation is generally best achieved via two-stage inflator devices. However, two-stage inflators commonly require two electrical initiators and are generally more expensive than single stage inflator devices.
Methods of obtaining low onset inflation via single stage inflators have generally not provided the desired deployment rate curve. Such single-stage inflator methods include: inhibiting the surface of the gas generant such as by coating or otherwise covering a surface portion or side of a gas generant tablet; initially cooling the inflation gasses in a heat sink that saturates quickly, wherein the saturated heat sink will no longer cool the gasses resulting in an increased pressure; methods for altering generant grain shape; and other methods that alter the ignition conditions to provide a non-synchronous ignition of all gas generant material.
In view of the above, there is a need and a demand for improved arrangements and methods for providing low onset inflation of airbag cushions, particularly with single stage inflator devices such as employ only a single electrical initiator. Further, there is a need and a demand for combustible material-based inflator devices which provide or result in a slower initial rate of deployment followed by an increase in deployment rate. Further, there is a need and a demand for such an inflator device which more freely permits the use of azide-free pyrotechnics, such as those which have or exhibit a relatively high burn rate pressure dependency. Still further, there is a need and a demand for such a low onset inflator device that is less costly to manufacture or produce. Yet still further, there is a need and a demand for single stage inflator devices that provide or result in low onset inflation without requiring the inclusion of complex or costly control devices or arrangements.
SUMMARY OF THE INVENTION
A general object of the invention is to provide an improved inflator and associated or corresponding methods of supplying inflation gas.
A more specific objective of the invention is to overcome one or more of the problems described above.
The general object of the invention can be attained, at least in part, through an improved inflator device having at least one orifice wherethrough inflation gas can pass. In accordance with one preferred embodiment of the invention, the at least one orifice is at least in part defined by a shape memory alloy material having an austenite finishing temperature (T
f
), wherein the at least one orifice defines a first fluid flow through area (A
1
) when at a temperature less than T
f
and a second fluid flow through area (A
2
) when at a temperature greater than T
f
, where A
2
<A
1
.
As described in greater detail below, shape memory alloys in accordance with the invention can b
Larsen Alan R.
Rouesche Clark
Autoliv ASP Inc.
Brown Sally J.
Erickson James D.
Jordan Charles T.
Smith Kimberly S.
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