United States Patent [19J
`Breed et al.
`
`[54] EFFICIENT AIRBAG MODULE
`
`[75]
`
`Inventors: David S. Breed, Boonton Township; W.
`Thomas Sanders, Rockaway Township,
`both of N.J.
`
`[73] Assignee: Automotive Technologies
`International Inc., Denville, N.J.
`
`[21] Appl. No.: 571,247
`
`[22] Filed:
`
`Dec. 12, 1995
`
`Int. Cl.6
`..................................................... B60R 21/20
`[51]
`[52] U.S. Cl. ..................................... 280/728.2; 280/730.1;
`280/738
`[58] Field of Search .............................. 280/728.2, 730.1,
`280/738, 732, 730.2
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`9/1936 Coanda ................................... 406/181
`2,052,869
`3,158,314 11/1964 Young eta!. ........................... 417/191
`3,204,862
`9/1965 Hadeler ..................................... 230/95
`3,370,784
`2/1968 Day ........................................... 230/95
`3,414,292 12/1968 Oldberg eta!. .
`1!1972 Hass ........................................ 280/150
`3,632,133
`3,791,669
`2/1974 Hamilton ................................ 280/150
`3,801,127
`4/1974 Katter et a!. ............................ 280/150
`9/1975 Stewart ................................... 280/150
`3,909,037
`3,910,595 10/1975 Katter et a!. ............................ 280/150
`3,938,826
`2/1976 Giorgini et a!.
`........................ 280/150
`3,947,056
`3/1976 Schwanz .............................. 280/730.1
`4,043,572
`8/1977 Hattori et a!.
`.......................... 280/738
`4,130,298 12/1978 Shaunnessey ........................ 280/730.1
`4,833,996
`5/1989 Hayashi et a!. ......................... 102/530
`4,877,264 10/1989 Cuevas .................................... 280/731
`4,909,549
`3/1990 Pool et a!.
`.............................. 280/738
`4,928,991
`5/1990 Thorn ...................................... 280/738
`
`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US005772238A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,772,238
`Jun.30, 1998
`
`5,004,586
`5,060,973
`5,085,465
`5,100,172
`5,129,674
`5,193,847
`5,207,450
`5,286,054
`5,332,259
`5,406,889
`5,423,571
`5,435,594
`5,437,473
`5,458,367
`5,489,117
`5,509,686
`5,599,042
`
`4/1991 Hayashi et a!. ......................... 422/164
`10/1991 Giovanetti . ... ... ... ... ... .... ... ... ... .. 280/736
`2/1992 Hieahim .................................. 280/738
`3/1992 Van Voorhies et a!. ................ 280/738
`7/1992 Levosinki .. ... ... ... ... ... .... ... ... ... .. 280/738
`3/1993 Nakayama .............................. 280/738
`5/1993 Pack, Jr. et a!. ... .... ... ... ... ... ..... 280/738
`2/1994 Cuevas .................................... 280/738
`7/1994 Conlee eta!. .......................... 280/738
`4/1995 Letendre et a!. ........................ 102/201
`6/1995 Hawthorn ................................ 280/738
`7/1995 Gille ..................................... 280/728.2
`8/1995 Henseler .
`......................... 280/730.1
`10/1995 Marts et a!.
`2/1996 Huber ...................................... 280/738
`4/1996 Shepherd et a!. . ... .... ... ... ... ... ... 280/738
`2/1997 Shyr et a!.
`........................... 280/730.1
`
`FOREIGN PATENT DOCUMENTS
`
`7/1995 European Pat. Off ..
`0663325 A1
`2191450 12/1987 United Kingdom .
`
`Primary Examiner-Christopher P. Ellis
`ABSTRACT
`[57]
`
`An airbag module to protect an occupant in the passenger
`compartment in the event of a crash of the vehicle. In a most
`basic embodiment, the module includes an elongate housing
`having a length in the longitudinal direction which is sub(cid:173)
`stantially larger than its width or thickness in a direction
`transverse to the longitudinal direction, an airbag situated
`within the housing, an inflator arranged in the housing to
`produce pressurized gas to inflate the airbag, mounting
`members for mounting the module in the passenger com(cid:173)
`partment and an initiator for initiating the inflator to produce
`the pressurized gas in response to the crash of the vehicle.
`The housing includes a cover for releasably retaining the
`airbag so that it can deploy upon inflation of the airbag.
`
`29 Claims, 17 Drawing Sheets
`
`Page 1 of 35
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`U.S. Patent
`U.S. Patent
`
`Jun.30, 1998
`Jun. 30, 1998
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`Sheet 1 of 17
`Sheet 1 of 17
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`5,772,238
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`Jun.30, 1998
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`Jun.30, 1998
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`Jun.30, 1998
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`Jun. 30, 1998
`Jun.30, 1998
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`Sheet 5 of 17
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`Page 6 of 35
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`U.S. Patent
`U.S. Patent
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`Jun.30, 1998
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`Jun. 30, 1998
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`Jun. 30, 1998
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`Jun.30, 1998
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`Jun. 30, 1998
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`Jun. 30, 1998
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`Jun.30, 1998
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`
`Jun. 30, 1998
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`U.S. Patent
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`Jun. 30, 1998
`Jun.30, 1998
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`Jun. 30, 1998
`Jun.30, 1998
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`5,772,238
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`1
`EFFICIENT AIRBAG MODULE
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`This application is related to U.S. patent application Ser.
`No. 08/550,217 entitled "Airbag System" filed Oct. 30,
`1995, U.S. patent application Ser. No. 08/247,763 entitled
`"Plastic FilmAirbag" filed May 23, 1994 (now U.S. Pat. No.
`5,505,485) and U.S. patent application Ser. No. 08/539,676
`entitled "Airbag System With Self Shaping Airbag", filed
`Oct. 5, 1995, (now U.S. Pat. No. 5,653,464) all of which are
`incorporated by reference herein.
`
`FIELD OF THE INVENTION
`
`This invention is in the field of inflator devices for
`inflating airbag occupant restraints mainly for the protection
`of occupants of automobiles and trucks although it also is
`applicable to the protection of occupants of other vehicles
`and for inflating other inflatable objects. In particular, by
`means of the present invention, a more efficient utilization of
`the energy in a propellant is attained resulting in the need for
`a lower amount of propellant than in currently existing
`inflators, and thus a smaller inflator, to inflate a given size
`inflatable object. This is accomplished in part through a
`more efficient aspirating nozzle design and an improved
`geometry of a gas generator which houses the propellant.
`
`BACKGROUND OF THE INVENTION
`
`Most airbag modules in use today are large, heavy,
`expensive, and inefficient. As a result, airbags are now
`primarily only used for protecting the passenger and driver
`in a frontal impact, although at least three automobile
`manufacturers currently offer a small airbag providing lim(cid:173)
`ited protection in side impacts. The main advantage of
`airbags over other energy absorbing structures is that they
`utilize the space between the occupant and vehicle interior
`surfaces to absorb the kinetic energy of the occupant during
`a crash, cushioning the impending impact of the occupant
`with the vehicle interior surfaces. Airbags have been so
`successful in frontal impacts that it is only a matter of time
`before they are effectively used for side impact protection,
`protection for rear seat occupants and in place of current
`knee bolsters. Substantial improvements, however, must be
`made in airbags before they assume many of these additional
`tasks
`A good place to start describing the problems with current
`airbags is with a calculation of the amount of energy used in
`a typical airbag inflator and how much energy is required to
`inflate an airbag. By one analysis, the chemical propellant in
`a typical driver's side inflator contains approximately
`50,000 foot pounds (68,000 joules) of energy. A calculation
`made to determine the energy required to inflate a driver's
`side airbag yields an estimate of about 500 foot pounds (680
`joules). A comparison of these numbers shows that approxi(cid:173)
`mately 99% of the energy in a chemical propellant is lost,
`that is, generated but not needed for inflation of the airbag.
`One reason for this is that there is a mismatch between the
`output of a burning propellant and the inflation requirements
`of an airbag. In engineering this is known as an impedance
`mismatch. Stated simply, propellants naturally produce
`gases having high temperatures and high pressures and low
`gas flow rates. Airbags, on the other hand, need gases with
`low temperatures and low pressures and high gas flow rates.
`In view of this impedance mismatch, inflators are, in
`theory at least, many times larger then they would have to be
`
`5
`
`10
`
`2
`if the energy of the propellant contained within the inflator
`were efficiently utilized. Some attempts to partially solve
`this problem have resulted in a so called "hybrid" inflator
`where a stored pressurized gas is heated by a propellant to
`inflate the airbag. Such systems are considerably more
`energy efficient, however, they also require a container of
`high pressure gas and means for monitoring the pressure in
`that container. Other systems have attempted to use asp ira(cid:173)
`tion techniques, but because of the geometry constraints of
`current car inflator designs and mounting locations, and for
`other reasons, currently used aspiration systems are only
`able to draw up to about 30% of the gas needed to inflate an
`airbag from the passenger compartment. Theoretical studies
`have shown that as much as 90% or more of the gas could
`15 be obtained in this manner.
`Furthermore, since inflators are large and inefficient,
`severe restrictions have been placed on the type of propel(cid:173)
`lants that can be used since the combustion products of the
`propellant must be breathable by automobile occupants. It is
`20 of little value to save an occupant from death in an auto(cid:173)
`mobile accident only to suffocate him from an excessive
`amount of carbon dioxide in the air within the passenger
`compartment after the accident. If inflators operated more
`efficiently, then alternate, more efficient but slightly toxic
`25 propellants could be used. Also, current inflators are made
`from propellants, namely sodium azide, which are not totally
`consumed. Only about 40% of the mass of sodium azide
`propellants currently being used, for example, enters the
`airbag as gas. This residual mass is very hot and requires the
`30 inflator to be mounted away from combustible materials
`further adding to the mass and size of the airbag system.
`It is a persistent problem in the art that many people are
`being seriously injured or even killed today by the airbag
`itself. This generally happens when an occupant is out-of-
`35 position and against an airbag module when the airbag
`deploys. In order to open the module cover, sometimes
`called the deployment door, substantial pressure must first
`build up in the airbag before enough force is generated to
`burst open the cover. This pressure is even greater if the
`40 occupant is in a position which prevents the door from
`opening. As a result, work is underway to substantially
`reduce the amount of energy required to open the deploy(cid:173)
`ment doors and devices have been developed which pop off
`the deployment door or else cut the deployment door mate-
`45 rial using pyrotechnics, for example.
`One reason that this is such a significant problem is that
`the airbag module itself is quite large and, in particular, the
`airbags are made out of thick, heavy material and packaged
`in a poor, folded geometry. The airbag, for example, which
`50 protects the passenger is housed in a module which is
`typically about one third as long as the deployed airbag. All
`of this heavy airbag material must be rolled and folded
`inside this comparatively small module, thus requiring sub(cid:173)
`stantial energy to unfold during deployment. This situation
`55 could be substantially improved if the airbag module were to
`have an alternate geometry and if the airbag material were
`substantially lighter and thinner and, therefore, less massive
`and folded mainly parallel to the inflator. Even the time to
`deploy the airbag is substantially affected by the mass of the
`60 airbag material and the need to unfold an airbag with a
`complicated folding pattern. Parallel folding, as used herein,
`means that the airbag material is folded with the fold lines
`substantially parallel the axis of the inflator without being
`folded over lengthwise as is now done with conventional
`65 airbag folding patterns.
`Devices are under development which will monitor the
`position of the occupant and prevent the airbag from deploy-
`
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`5,772,238
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`5
`
`3
`ing if the occupant is dangerously close to the module where
`he or she can be seriously injured by the deployment. Some
`systems will also prevent deployment if the seat in connec(cid:173)
`tion with which the airbag operates is unoccupied. An
`alternate approach is to move the deployment doors to a
`location away from normal occupant positions. One such
`location is the ceiling of the vehicle. One problem with
`ceiling mounted airbags is that the distance required for the
`airbag to travel, in some cases, is longer and therefore a
`larger airbag is needed with greater deployment time. With
`the use of light airbag materials, such as thin plastic film, as
`disclosed in the above referenced patent applications Ser.
`Nos. 08/247,763 and 08/539,676, and the use of more
`efficient inflators, both of these problems can be solved
`especially for the front and rear seat passengers. The driver
`poses a different problem since it would be difficult to
`position a ceiling mounted airbag module where the airbag
`would always be projected properly between the occupant
`and the steering wheel.
`This problem for the driver's airbag system is not the
`concept of mounting the airbag on the ceiling, but the design
`of the steering wheel and steering column. These designs
`come from the time when the only way of steering an
`automobile was through mechanical linkages. The majority
`of vehicles manufactured today have power assisted steering
`systems and, in fact, most drivers would have difficulty 25
`steering a car today if the power steering failed. If servo
`power steering were used, the need for a mechanical linkage
`between a steering wheel, or other such device, and the
`power steering system would no longer be necessary. Servo
`power steering for the purposes here will mean those cases 30
`where the linkage between the manually operated steering
`device, which regardless of what that device is, will herein
`be called a steering wheel, is done with a servo system either
`electrically or hydraulically and the system does not have an
`operative mechanical connection between the steering wheel 35
`and the steering mechanism which moves the wheels.
`The problem of educating the general population, which
`has become secure in the feeling of a steering wheel and
`steering column, might be insurmountable if it were not for
`the substantial safety advantage resulting from substituting 40
`servo power steering for conventional steering systems and
`using a non-steering wheel mounted airbag module for the
`driver.
`The steering wheel and steering column are among the
`most dangerous parts of the vehicle to the occupant. Small 45
`people, for example, who are wearing seatbelts can still be
`seriously injured or killed in accidents as their faces slam
`into the steering wheel hubs. The problem of properly
`positioning an airbag, when the comfort and convenience
`features of telescoping and tilting steering columns are 50
`considered, results in substantial safety compromises.
`Deployment induced injuries which result when a small
`person is close to the steering wheel when the airbag deploys
`have already caused several deaths and numerous serious
`injuries. Future vehicles, therefore, for safety reasons should 55
`be constructed without the massive steering wheel and
`steering column and substitute therefor a servo steering
`assembly. With this modification, a ceiling mounted airbag
`module, such as discussed herein, becomes feasible for the
`driver as well as the other seating positions in the vehicle. 60
`The front seat of the vehicle today has an airbag for the
`passenger and another for the driver. In some accidents, an
`occupant, and particularly a center seated occupant, can pass
`between the two airbags and not receive the full protection
`from either one. If a ceiling mounted airbag system were 65
`used, a single airbag could be deployed to cover the entire
`front seat greatly simplifying the airbag system design.
`
`4
`One method of partially solving many of these problems
`is to use an efficient aspirated airbag system. There have
`been numerous patents granted on designs for airbag sys(cid:173)
`tems using aspirated inflators. In these patents as well as in
`the discussion herein the term "pumping ratio" is used. The
`pumping ratio as used in the art is defined as the ratio of the
`mass of gas aspirated from the environment, either from
`inside or outside of the vehicle, to the mass of gas generated
`by burning the propellant. A brief description of several
`10 pertinent patents, all of which are included herein by
`reference, follows:
`U.S. Pat. No. 2,052,869 to Coanda illustrates the manner
`in which a fluid jet is caused to change direction, although
`no mention is made of its use in airbags. This principle, the
`15 "Coanda effect", is used in some implementations of the
`instant invention as well as in U.S. Pat. No. 3,909,037 to
`Stewart discussed below. It's primary contribution is that
`when used in inflator designs, it permits a reduction in the
`length of the nozzle required to efficiently aspirate air into
`20 the airbag. No disclosure is made of a pumping ratio in this
`system and in fact it is not an object of Coanda to aspirate
`fluid.
`U.S. Pat. No. 3,204,862 to Hadeler also predates the
`invention of vehicular airbags but is nonetheless a good
`example of the use of aspiration to inflate an inflatable
`structure. In this device, an inflating gas is injected into an
`annular converging-diverging nozzle and some space effi(cid:173)
`ciency is obtained by locating the nozzle so that the flow is
`parallel to the wall of the inflatable structure. No mention is
`made of a pumping ratio of this device and furthermore, this
`device is circular.
`U.S. Pat. No. 3,632,133 to Hass provides a good example
`of a nozzle in a circular module with a high pumping ratio
`in an early construction of an airbag. Although analysis
`indicates that pumping ratios of 4:1 or 5:1 would be difficult
`to achieve with this design as illustrated, nevertheless, this
`reference illustrates the size and rough shape of an aspirating
`system which is required to obtain high pumping ratios
`using the prior art designs.
`U.S. Pat. No. 3,909,037 to Stewart provides a good
`example of the application of the Coanda effect to airbag
`aspirating inflators. Stewart, nevertheless, still discards most
`of the energy in the propellant which is absorbed as heat in
`the inflator mechanism. Most propellants considered for
`airbag applications burn at pressures in excess of about 1000
`psig. Stewart discloses that the maximum efficiency corre(cid:173)
`sponding to a 5:1 pumping ratio occurs at inflator gas
`pressures of about 5 to about 45 psig. In order to reduce the
`pressure, Stewart utilizes a complicated filtering system
`similar to that used in conventional inflators. Stewart
`requires the use of valves to close off the aspiration ports
`when the system is not aspirating. Through the use of the
`Coanda effect, Stewart alludes to a substantial reduction in
`the size of the aspiration system, compared to Hass for
`example. Also, Stewart shows only a simple converging
`nozzle through which the burning propellant is passed.
`U.S. Pat. No. 4,833,996 to Hayashi et al. describes a gas
`generating apparatus for inflating an airbag which is circular
`and allegedly provides an instantaneous pumping ratio of up
`to 7:1 although analysis shows that this is unlikely in the
`illustrated geometry. The average pumping ratio is specified
`to be up to 4:1. This invention is designed for the driver side
`of the vehicle where unrestricted access to the aspirating
`port might be difficult to achieve when mounted on a
`steering wheel. The propellant of choice in Hayashi et al. is
`sodium azide which requires extensive filtering to remove
`
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`5,772,238
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`5
`particulates. No attempt has been made in this design to
`optimize the nozzle geometry to make use of a converging(cid:173)
`diverging nozzle design, for example. Also, the inflator has
`a roughly conventional driver side shape. It is also interest(cid:173)
`ing to note that no mention is made of valves to close off or
`restrict flow through the aspiration port during deflation.
`Since most aspiration designs having even substantially
`smaller pumping ratios provide for such valves, the elimi(cid:173)
`nation of these valves would be a significant advance in the
`art. Analysis shows, however, that the opening needed for
`the claimed aspiration ratios would in general be far too
`large for it also to be used for exhausting the airbag during
`a crash. Since this is not discussed, it should be assumed that
`valves are required but not illustrated in the figures.
`U.S. Pat. No. 4,877,264 to Cuevas describes an aspirating/ 15
`venting airbag module assembly which includes a circular
`gas generator and contemplates the use of conventional
`sodium azide propellants or equivalent. The aspiration or
`pumping ratio of this inflator is approximately 0.2:1, sub(cid:173)
`stantially below that of Hayashi et al., but more in line with 20
`aspiration systems in common use today. This design also
`does not require use of aspiration valves which is more
`reasonable for this case, but still unlikely, since the asp ira(cid:173)
`tion port area is much smaller. Again, no attempt has been
`made to optimize the nozzle design as is evident by the short 25
`nozzle length and the low pumping ratio.
`U.S. Pat. No. 4,909,549 to Poole et al. describes a process
`for inflating an airbag with an aspiration system but does not
`discuss the aspiration design or mechanism and merely
`asserts that a ratio as high as 4:1 is possible but assumes that
`2.5:1 is available. This patent is significant in that it dis(cid:173)
`closes the idea that if such high pumping ratios are obtain(cid:173)
`able (i.e., 2.5:1 compared with 0.2:1 for inflators in use),
`then certain propellants, which would otherwise be unac(cid:173)
`ceptable due to their production of toxic chemicals, can be
`used. For example, the patent discloses the use of tetrazol
`compounds. It is interesting to note that there as yet is no
`commercialization of the Poole et al. invention which raises
`the question as to whether such high aspiration ratios are in
`fact achievable with any of the prior art designs. Analysis
`has shown that this is the case, that is, that such large
`aspiration ratios are not achievable with the prior art designs.
`U.S. Pat. No. 4,928,991 to Thorn describes an aspirating
`inflator assembly including aspiration valves which are
`generally needed in all high pumping ratio aspiration sys(cid:173)
`tems. Sodium azide is the propellant used. Pumping ratios of
`1:1 to 1.5:1 are mentioned in this patent which by analysis
`is possible. It is noteworthy that the preamble of this patent
`discloses that the state of the art of aspirating inflators yields 50
`pumping ratios of 0.1:1 to 0.5: 1, far below those specified in
`several of the above referenced earlier patents. Once again,
`little attempt has been made to optimize the nozzle design.
`U.S. Pat. No. 5,004,586 to Hayashi et al. describes a
`sodium azide driver side inflator in which the aspirating air 55
`flows through a series of annular slots on the circumference
`of the circular inflator in contrast to the earlier Hayashi et al.
`patent where the flow was on the axis. Similar pumping
`ratios of about 4:1 are claimed however, which by analysis
`is unlikely. Once again, aspiration valves are not shown and 60
`the reason that they can be neglected is not discussed. An
`inefficient nozzle design is again illustrated. The lack of
`commercial success of these two Hayashi patents is prob(cid:173)
`ably due to the fact that such high pumping ratios as claimed
`are not in fact achievable in the geometries illustrated.
`U.S. Pat. No. 5,060,973 to Giovanetti describes the first
`liquid propellant airbag gas generator wherein the propellant
`
`6
`burns clean and does not require filters to trap solid particles.
`Thus, it is one preferred propellant for use in the instant
`invention. This system however produces a gas which is too
`hot for use directly to inflate an airbag. The gas also contains
`5 substantial quantities of steam as well as carbon dioxide.
`The steam can cause burns to occupants and carbon dioxide
`in significant quantities is toxic. The gas generator is also
`circular. Aspirating systems are therefore required when
`using the liquid propellant disclosed in this patent, or
`10 alternately, the gas generated must be exhausted outside of
`the vehicle.
`U.S. Pat. No. 5,129,674 to Levosinski describes a
`converging-diverging nozzle design which provides for
`more efficient aspiration than some of the above discussed
`patents. Nevertheless, the airbag system disclosed is quite
`large and limited in length such that the flow passageways
`are quite large which requires a long nozzle design for
`efficient operation. Since there is insufficient space for a long
`nozzle, it can be estimated that this system has a pumping
`ratio less than 1:1 and probably about 0.2:1. Once again a
`sodium azide based propellant is used.
`U.S. Pat. No. 5,207,450 to Pack, Jr. et al. describes an
`aspirated air cushion restraint system in which no attempt
`was made to optimize the nozzle design for this sodium
`azide driver side airbag. Also, aspiration valves are used
`although it is suggested that the exhaust from the airbag can
`be made through the aspirating holes thereby eliminating the
`need for the flapper valves. No analysis, however, is pro(cid:173)
`vided to prove that the area of the aspiration holes is
`30 comparable to the area of the exhaust holes normally pro(cid:173)
`vided in the airbag. Although no mention is made of the
`pumping ratio of this design, the device as illustrated
`appears to be approximately the same size as a conventional
`driver side inflator. This, coupled with an analysis of the
`35 geometry, indicates a pumping ratio of less than 1:1 and
`probably less than 0.2: 1. The statement that the aspiration
`valves are not needed also indicates that the aspiration ratio
`must be small. Large inlet ports which are needed for large
`aspiration ratios are generally much larger than the typical
`40 airbag exhaust ports.
`U.S. Pat. No. 5,286,054 to Cuevas describes an aspirating/
`venting motor vehicle passenger airbag module in which the
`principal of operation is similar to the '264 patent discussed
`above. Once again the aspiration pumping ratio of this
`device is 0.15:1 to 0.2:1 which is in line with conventional
`aspirated inflators. It is interesting to note that this pioneer
`in the field does not avail himself of designs purporting to
`yield higher pumping ratios. Again the nozzle design has not
`been optimized.
`Other U.S. patents which are relevant to the instant
`invention but which will not be discussed in detail are: U.S.
`Pat. No. 3,158,314 to Young et al., U.S. Pat. No. 3,370,784
`to Day, U.S. Pat. No. 5,085,465 to Hieahim, U.S. Pat. No.
`5,100,172 to Van Voorhies et al., U.S. Pat. No. 5,193,847 to
`Nakayama, U.S. Pat. No. 5,332,259 to Conlee et al. and U.S.
`Pat. No. 5,423,571 to Hawthorn.
`None of the prior art inflators contain the advantages of
`the combination of (i) a linear inflator having a small cross
`section thereby permitting an efficient nozzle design wherein
`the length of the nozzle is much greater than the aspiration
`port opening, (ii) a non sodium azide propellant which may
`produce toxic gas if not diluted with substantial quantities of
`ambient air, and (iii) an inflator where minimal or no
`65 filtering or heat absorption is required.
`It is interesting to note that in spite of the large aspiration
`pumping ratios mentioned and even claimed in the prior art
`
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`7
`references mentioned above, and to the very significant
`advantages which would result if such ratios could be
`achieved, none has been successfully adapted to an auto(cid:173)
`mobile airbag system. One reason is that pumping ratios
`which are achievable in a steady state laboratory environ-
`ment are more difficult to achieve in the transient conditions
`of an actual airbag deployment.
`None of these prior art designs have resulted in a thin
`linear module which permits the space necessary for an
`efficient nozzle design as disclosed herein. In spite of the
`many advantages claimed in the prior art patents, none have
`resulted in a module which can be mounted within the
`vehicle headliner trim, for example, or can be made to
`conform to a curved surface