U.S. patent number RE34,204 [Application Number 07/658,760] was granted by the patent office on 1993-03-30 for pressure regulation device for vehicle safety air bag.
Invention is credited to Juichiro Takada.
United States Patent |
RE34,204 |
Takada |
March 30, 1993 |
Pressure regulation device for vehicle safety air bag
Abstract
Stitched thread seams between fabric elements of the envelope of
a vehicle safety air bag induce localized distension and opening up
of the envelope fabrics along the seams, thereby causing the film
coatings of the envelope fabric to rupture along the seam and allow
gas to escape and maintain a substantially constant overall maximum
pressure, regardless of variations in ambient temperature.
Inventors: |
Takada; Juichiro (Shin-machi,
Setagaya-ku Tokyo, JP) |
Family
ID: |
14995397 |
Appl.
No.: |
07/658,760 |
Filed: |
February 20, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
089581 |
Aug 26, 1987 |
04805930 |
Feb 21, 1989 |
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Foreign Application Priority Data
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Aug 26, 1986 [JP] |
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61-128870[U] |
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Current U.S.
Class: |
280/739;
280/728.1 |
Current CPC
Class: |
B60R
21/239 (20130101) |
Current International
Class: |
B60R
21/16 (20060101); B61R 021/16 (); B61R
021/28 () |
Field of
Search: |
;280/728,729,731,732,735,737,738,739,740,743 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rice; Kenneth R.
Attorney, Agent or Firm: Brumbaugh, Graves, Donohue &
Raymond
Claims
I claim:
1. In a vehicle safety air bag having an inflatable envelope of
fabric coated with a polymeric film to make it gas tight and
pressure-relief means associated with the envelope for enabling gas
to escape from the envelope when the gas pressure exceeds a
predetermined level, the improvement wherein the pressure relief
means comprises first and second fabric elements of the envelope
disposed in overlapping relation along their respective margins and
a stitched thread seam along said overlapping margins adapted to
induce opening up of the fabric elements and rupture of the films
thereof along the seam to degrees that vary in accordance with the
level of gas pressure in the envelope above said predetermined
level and to allow gas to escape along the opened up seam.
2. The improvement claimed in claim 1 wherein said one element of
the envelope is a main body having a hole and the second element is
a patch covering the hole.
3. The improvement claimed in claim 1 wherein the first element is
a major part of the envelope that includes its perimeter and the
second element is a minor part within the perimeter, whereby the
seam is subject to shear stresses due to gas pressure.
4. The improvement claimed in claim 1 wherein the first and second
elements are also adhesively joined along said margins. .Iadd.5. In
a vehicle safety air bag having an envelope of fabric coated with a
polymeric film to make it gas tight and inflatable by pressurized
gas from an inflator, the improvement wherein the envelope includes
at least one fabric element consisting of a woven fabric and a
lining film coating of silicone rubber
on the inner surface of the woven fabric. .Iaddend. .Iadd.6. The
improvement according to claim 5 wherein all fabric elements of the
envelope consist of a woven fabric and a lining film coating of
silicone rubber on the inner surface of the woven fabric. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a pressure regulation device for a
vehicle safety air bag which is provided to protect a passenger of
a car or other vehicle from a secondary collision. In an air bag of
this type a bulbous-shaped envelope is folded and stored at the
center of the steering wheel and is rapidly inflated by a gas
generated virtually instantaneously by an inflator at the moment of
a collision in order to prevent the driver, who is thrown forward
by inertial force, from hitting the steering wheel directly, to
absorb and damp the energy imposed on the driver by the inertial
force, and to spread the load of the impact over the driver's
torso.
The maximum internal pressure of the air bag main envelope is
typically 1.0 kg/cm.sup.2 when it is inflated, and its normal
pressure is 0.7 kg/cm.sup.2. Therefore, the air bag envelope must
be fabricated so as to withstand these pressures, but if the
pressure is too high, a high repelling or rebound force will
develop and will propel the driver back away from the air bag,
thereby possibly causing whiplash injury to the driver. It is
known, therefore, to provide a pressure-relief device in order to
keep the internal pressure from exceeding a predetermined level.
One such device is simply a vent orifice that allows gas to escape
when the driver strikes the inflated envelope and the internal
pressure rises.
In particular, the conventional pressure-relief vent hole
structures are of the type wherein a normally-open vent hole is
disposed in the envelope and of the type wherein a film of a
synthetic resin or the like is disposed in the vent hole so that
the film is broken by a gas pressure above a predetermined
pressure. In the case of the open vent hole, if the size of the
hole is determined based on a low external or ambient temperature,
the gas pressure will become excessive when the temperature is
high, and if the size of the hole is determined based on a high
ambient pressure, the gas pressure will be insufficient when the
temperature is low. In the case of vent holes with a rupturable
film, when the film is broken at pressures above a predetermined
level, the fragments of the film scatter. Therefore, the open area
of the vent hole remains substantially the same irrespective of the
gas pressure, and the gas pressure, which varies with the ambient
temperature, cannot be regulated. Thus, there is in both types of
vent devices variation in the damping property when the driver hits
the bag, as a function of ambient temperature.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved
pressure relief device for vehicle safety air bags and, in
particular, to provide a pressure relief device in which the sizes
of openings in the envelope for release of gas increase, the
greater the internal gas pressure.
In accordance with the present invention, the air bag envelope,
which is made of a conventional coated fabric, comprises first and
second portions disposed in overlapping relation along their
respective margins and a stitched thread seam along the overlapping
margins that is adapted to open up to a degree that varies in
accordance with the level of gas pressure in the envelope and to
allow gas to escape along the opened-up seam.
For a better understanding of the invention reference may be made
to the following description of exemplary embodiments, taken in
conjunction with the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic elevational view of a typical air bag
installation in which the present invention is useful;
FIG. 2 is a plan view of a first embodiment of the invention, the
view being of the aspect that faces away from the driver;
FIG. 3A is a plan view of a portion of the main envelope of the
first embodiment;
FIG. 3B is a plan view of a patch that forms a second portion of
the envelope;
FIG. 3C is a plan view of the assembly of the first embodiment;
FIG. 4A is a diagrammatic view of the first embodiment in which the
pressure-relief seam is intact;
FIG. 4B is a diagrammatic view in which the seam has opened up;
FIG. 5A is a side cross-sectional view of a second embodiment;
FIG. 5B is a plan view of the aspect of the envelope of the second
embodiment that faces away from the driver;
FIG. 6A is a fragmentary cross-section of a seam that is intact;
and
FIG. 6B is a detail cross-section of a seam that has opened up for
pressure relief.
DESCRIPTION OF THE EMBODIMENTS
In FIG. 1 reference numeral 1 designates a bulbous air bag main
envelope and reference numeral 2 an inflator which is fitted to an
opening of the envelope and consists of an instantaneous gas
generator. The air bag envelope 1 is folded and stored in a storage
receptacle built into the center of a steering wheel 3. When the
car undergoes a collision, the inflator 2 is operated by a sensor
(not shown), releases a pressurized gas into the air bag envelope 1
and inflates it.
Stitched thread seams 4 for regulating the gas pressure are
disposed on the air bag envelope 1 on the steering wheel side (the
aspect facing the steering wheel), as shown in FIG. 1 and these
seams 4 are arranged equidistantly around the opening 2a of the air
bag main body 1 as shown in FIG. 2. Reference numeral 2b represents
holes for fasteners that secure the air bag to the steering
wheel.
Each pressure-regulation seam 4 is constituted in the following
way. As shown in FIG. 3A, the air bag envelope consists of a cloth
1c produced by disposing a lining film 1b of a polymeric material,
such as silicone rubber, on the inner surface of a woven fabric 1a.
For each pressure relief seam 4 an oblong vent hole 4a is formed on
this bag cloth 1c with the longer dimension placed along the bias
of the threads of the fabric 1c. A patch is applied over the vent
hole 4a, as shown in FIG. 3B. The margin of the patch 4b overlaps
the margin of the envelope around the hole 4a.
The patch 4b is produced by disposing a resin coat film 4b-2 of
silicone resin, rubber, or the like on a plain woven fabric 4b-1.
The patch 4b is applied to the envelope 1c in such a manner as to
cover the vent hole 4a and is stitched by sewing threads along the
margin of the hole. The remaining outer portion of the patch 4b
outwardly of the seam 4c is bonded to the envelope cloth by an
adhesive.
When the gas pressure in the inflated envelope is below a certain
pressure, the patch 4b remains substantially intact, the state
shown in FIG. 4A, even if it expands. When the gas pressure exceeds
the predetermined pressure, shearing stress develops between the
sewing threads 4c and the patch 4b, which is distended by the gas
pressure as shown in FIG. 4B, so that deviation of threads, that
is, opening of the cloth, occurs in the patch cloth 4b. The resin
coat film 4b-2 is broken and the gas leaks out through the ruptures
in the film. The opening up of the cloth becomes greater with a
higher gas pressure, and the greater area of the openings allows
greater rates of gas leakage.
The overall operation of the embodiment is as follows. When the car
impinges accidentally against anything, the sensor senses the
collision, and the inflator 2 generates and supplies the gas into
the folded air bag envelope 1 through its opening 2a, thereby
inflating the air bag envelope 1. Assuming that the ambient
temperature is low, such as in winter, for example, the pressure of
the generated gas is relatively low, for example, below 0.7
kg/cm.sup.2. Then, the patch 4b of the pressure regulation seam
portion 4 remains intact (FIG. 4A) and, hence, the gas does not
leak. When the external temperature is high, such as in summer,
however, the pressure of the gas becomes relatively greater, and if
it is above 0.7 kg/cm.sup.2, for example, the patch 4b is deformed
and opened up by the gas pressure, and the resin coat film 4b-2 is
ruptured. The degree of deformation and opening up of the cloth
increases with an increasing gas pressure so that the quantity of
the leaking gas becomes greater and the inner pressure can be kept
constant. In this manner, the inner pressure can be regulated to a
predetermined level, even when the generated gas pressure is high,
and if the driver hits the bag under this state, the energy can be
absorbed and the driver is not repelled back.
Though the embodiment described above illustrates the case where
vent holes are made in small regions of the envelope fabric, it is
also possible to employ the structure shown in FIGS. 5 and 6. A
cloth piece 5 having a resin coat film 4b on a plain woven fabric
5a and a cloth piece 6 having a resin coat film 6b on a plain woven
fabric 6a are sewn together to form a portion of a bulbous
envelope. The piece 6 has an opening 6c, and a cloth 7 piece having
a resin coat film 6b on a plain woven fabric 7a is sewn by a thread
to form a seam 4' along the respective overlapping margins of the
pieces 6 and 7. An opening 7c is formed at the center of the piece
7, and bolts are inserted into bolt holes 7d around the periphery
of the opening 7c so that the inflator 2 can be fitted, as shown in
FIG. 4(a).
In this construction when the inflator 2 generates the gas and the
envelope inflates, the seam 4' under the intact state where the gas
pressure is low and the gas does not leak, as shown in FIG. 6A,
changes when the gas pressure is high to the state where shearing
stress develops between the piece 6 and the piece 7 due to the high
gas pressure, as shown in FIG. 6B, so that the threads oriented at
right angles to the stretching direction of the respective fabrics
6a and 7a on one side, with the stitching threads 8 being the
boundary, are pushed while the .[.treads.]. .Iadd.threads
.Iaddend.on the other side are stretched and the resin coat films
6b and 7b are broken. This breakage occurs on the mutually opposite
sides of the pieces 6 and 7, and the gas leaks through the open
fabrics on the stretched sides, thereby keeping the gas pressure
constant.
In summary, as described above, in accordance with the present
invention, the stitched thread seams between portions of the
envelope cause the fabrics to open up and the coatings to break to
degrees that are variable in accordance with the gas pressure above
a predetermined gas pressure. The intrusion of the threads of the
stitched seams between threads of the fabrics in the overlapping
margins of portions of the envelope inhibits normal stretching of
the fabrics and creates localized high stresses, which is what
causes the fabrics to distend and open up along the seams and
produces ruptures in the film coatings. The greater the internal
gas pressure, the greater the stresses and the consequent ruptures
of the film. Accordingly, gas is released in increasing amounts,
the greater the pressure, and the overall gas pressure can be kept
constant. Therefore, even though ambient temperature changes, such
as in summer and winter, cause the generated gas pressure of the
inflator to change, the gas leakage is reduced when the generated
gas pressure is low, thereby to prevent the drop of the internal
pressure, and is increased when the generated gas pressure is high,
thereby to prevent the inner pressure from being excessive. In this
manner, the performance of the air bag in protecting the driver can
be kept at a sufficient level, irrespective of differences in the
ambient temperatures.
In the conventional pressure regulators of air bags, wherein a
resin film is disposed on the vent hole, the film is broken
substantially uniformly if the pressure is above a predetermined
pressure, and the gas is often released from the envelope
unnecessarily. In comparison with the conventional devices of this
type, the present device can utilize the gas pressure more
efficiently, so that the inflator can be made more compact, and a
great advantage can be obtained in connection with the amount of
space required for the inflator.
* * * * *