8/26/2016
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`Development of a New Downsized Airbag System for Use in Passenger Vehicles
`
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`Development of a New Downsized Airbag System for Use in Passenger
`Vehicles
`
`Technical Paper
`
`Paper #: 940804
`
`DOI:
`
`10.4271/940804
`
`Published: 1994-03-01
`
`Citation:
`
`Karlow, J., Jakovski, J., and Seymour, B., "Development of a New
`Downsized Airbag System for Use in Passenger Vehicles," SAE Technical
`Paper 940804, 1994, doi:10.4271/940804.
`
`Author(s):
`
`James P. Karlow
`
`J. John Jakovski
`
`Brian Seymour
`
`Affiliated:
`
`Takata, Inc.
`
`Pages:
`
`13
`
`Abstract: An issue placing significant pressure on airbag systems development at
`
`the current time is the need to downsize the entire airbag module in
`
`order to reduce weight and cost, offer better styling options for
`
`automotive original-equipment manufacturer (OEM) design engineers,
`
`and improve occupant safety. However, because components of the
`
`module are interrelated - both functionally and physically - size and
`
`weight reductions necessitate a total systems approach to engineering.
`
`This paper will discuss an integrated approach to airbag systems design
`
`and will describe new airbag systems that offer significant weight and
`
`size reductions over current configurations.
`
`Also in:
`
`Safety Technology - SP-1041
`
`SAE 1994 Transactions: Journal of Passenger Cars - V103-6
`
`Event:
`
`International Congress & Exposition
`
`Sector:
`
`Automotive
`
`Topic:
`
`Design processes
`
`Safety
`
`http://papers.sae.org/940804/
`
`1/1
`
`TG Ex. 1018
`
`

`
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`
`940804
`
`Development of a New Downsized Airbag
`System for Use in Passenger Vehicles
`
`James P. Karlow, J. John Jakovski, and Brian Seymour
`Takata, Inc.
`
`ABSTRACT
`
`An issue placing significant pressure on airbag systems
`development at the current time is the need to downsize the
`entire airbag module in order to reduce weight and cost, offer
`better styling options for automotive original—equipment
`manufacturer (OEM) design engineers, and improve occupant
`safety. However, because components of the module are
`interrelated -- both functionally and physically — size and
`weight reductions necessitate a total systems approach to
`engineering.
`This paper will discuss an integrated approach to airbag
`systems design and will describe new airbag systems that offer
`significant weight and size reductions over current
`configurations.
`
`INTRODUCTION
`
`Under strong pressure from consumers and regulatory
`agencies, OEMS are rushing to incorporate airbag systems into
`all passenger cars, light trucks, vans, and multi-purpose vehicles
`by the end of the decade. To date, however, OEMS have been
`primarily focused on meeting legislative deadlines for airbag
`installation. Their designers are just now beginning to look
`beyond immediate supply concerns to consider desirable longer
`range performance and safety improvements in airbag
`components and systems design. There are many reasons for
`this change in focus.
`TRENDS DRIVING IMPROVED AIRBAG DESIGN -
`
`First, airbag technology has matured steadily over the past 20
`years. There have been successive generations of airbag fabric,
`cover, and inflator designs, with each new iteration bringing
`performance improvements to the system.
`Second, the industry’s experience base — at both the OEM
`and supplier levels — has broadened as airbags have been
`incorporated into a wider variety of platforms. Similarly, the
`experience base has also deepened as time has passed and a
`more robust database for this technology has been developed.
`Hence, it is now easier to see where design and performance
`improvements are called for to increase the overall effectiveness
`of airbag systems.
`Third, because vehicle development cycles stretch 3 to 7
`
`29
`
`years for new platforms, advance teams are now beginning to
`consider technological innovations to incorporate in these
`programs. Rather than work with initial airbag installations
`where the OEM had to incorporate what was previously
`developed and already available, engineers working on new
`platfonns now have the latitude to consider technological
`improvements on a component and systems level to further
`improve occupant safety and comfort. Finally, a number of
`other issues are impacting airbag materials and design, as well.
`Smaller package size - The first airbags were installed on
`full-size, high-end platforms because it was felt the prospective
`customers for these vehicles would appreciate and be willing
`to pay for this added safety feature, and because the additional
`cost of the airbag system would not represent as significant an
`increase in the price of the car. These early airbag systems
`were conservatively designed [l]. Airbag modules were large
`because the most reliable materials at the time were bulky. Even
`given this conservative design, with low seatbelt utilization in
`the U.S. (around 14%), as well as no legally mandated child
`restraint, incidents occurred where the occupant was not
`positioned favorably to receive full protection from the airbag
`system. While airbags performed satisfactorily in many
`instances, some claims arose regarding inflation-induced injury
`to out-of-position occupants.
`By the late 1980s, the climate had grown more conducive
`to airbag application. People were becoming more aware of
`safety-related issues. Favorable press reports about occupants
`surviving severe collisions with only minor injuries in cars
`with the old air cushion restraint system (ACRS) systems began
`to surface. Seatbelt usage was increasing and states were
`beginning to legislate seatbelt use. Courts were also willing to
`consider the contribution of the occupant to his/her own injury,
`including the use of seatbelts and alcohol impairment as
`grounds to mitigate the liability of OEMS. Use of seatbelts
`also reduced the potential for the occupant to be out ofposition
`at the time of deployment. Use of child safety seats helped to
`better protect infants and young children in crashes severe
`enough for airbag deployment.
`Airbag technology had also improved. Studies based on
`original system applications, along with advances in
`biomechanics, led to a better understanding of crash injury
`mechanisms as well as improved test devices. The result was
`
`

`
`
`
`the rest of the car; in other words, that the vehicle should be
`inoperable before the safety systems cease to function. Since
`vehicle service life and warranty coverage are increasing, more
`pressure is being placed on OEMS and suppliers to provide
`safety systems that will stand the test of time.
`Improved occupant safety - The availability of airbag
`technology has become an important marketing issue for OEMs.
`However, it is also understood by the automotive industry that
`a small percentage of airbag deployments will result in
`incidental injuries to the occupant. Given this situation, OEMs
`are scrutinizing all safety systems to find new technologies
`and designs that will improve system performance and reduce
`incidental occupant injuries, in turn providing a better product
`and lowering the OEM’s exposure to litigation.
`Increased occupant safety as well as reduced airbag-related
`injuries are possible through design improvements to module
`components and positioning of the airbag. Development of
`the new, downsized airbag module can positively address these
`concerns. Smaller, more compact modules can provide greater
`design flexibility, lower raw material expenditures, simplified
`assembly, improved visibility of instrument panel and control
`levers for safety, enhanced recyclability, and reduced potential
`for incidental injuries.
`The key to successful downsizing of an airbag module lies
`in a systems approach to integration of all airbag component
`technologies. By approaching airbag design in a systematic
`way, a much smaller and simpler module can be produced than
`would be possible by incorporating each revised component
`independently.
`_
`This paper will describe a systems approach to the design
`of a new, downsized driver-side airbag module that provides
`significant commercial, weight, and design advantages to
`OEMs. This smaller module can, in turn, be used in a systems
`approach to improve occupant safety and reduce incidental
`injuries that can result from non-normal deployment of the
`airbag.
`
`THEORY OF OPERATION
`
`A typical driver-side airbag module consists of a trim cover,
`folded airbag cushion, inflator (gas generator), and mounting
`hardware to secure the module’s components and attach it to
`the surrounding steering wheel.
`‘
`During a normal deployment, driver-side airbag modules
`are designed to function as follows:
`
`- An electrical signal is received from the crash-sensor sys-
`tem and passed to the initiator of the inflator;
`- The initiator, acting like an electric match, ignites a boosting
`compound in the inflator module;
`- The ignited booster, in turn, ignites the main propellant,
`which has traditionally been composed of sodium azide plus
`an oxidizer;
`'
`- The propellant burns, generating, in the case of the sodium
`azide propellant, a stream of nitrogen gas from the
`combustion process;
`- The rapidly expanding gas is forced through a series of filters
`and out into the folded bag;
`- The increasing gas pressure from the gas generator fills the
`bag and begins to put pressure on the module’s trim cover;
`
`improved airbag components. For model year (MY) 1990,
`requirements for Federal Motor Vehicle Safety Standard
`(FMVSS) 208 became more stringent, requiring “passive
`protection" -—- protection without intervention of the occupant.
`Because of the less-intrusive nature of airbag systems when
`compared to motorized seatbelts on interior vehicle space, and
`very favorable customer acceptance, inflatable restraints quickly
`became the preferred method of achieving required passive
`protection.
`As demand for airbag applications initially proliferated,
`engineers had to re—design steering columns and instrument
`panels UPS) to accommodate the large modules of the time.
`However, downsizing ofmany vehicle platforms and the current
`emphasis on highly styled, ergonomic contours in vehicle
`interiors have increased pressure to reduce module size in order
`to give OEMs greater design flexibility.
`Cost reduction - As one of the key pressures on the
`automotive industry, cost reduction confers a competitive
`advantage on any supplier in the global automotive marketplace.
`The downsizing of airbag modules can play an important role
`in this effort because a significant percentage of an airbag’s
`cost is based on the cost of accommodations in the vehicle
`
`design, such as structural reinforcement of steering column
`mountings and placement of gauges, indicators, and signal
`levers, as well as through reduction of the cost of the airbag
`components themselves.
`Environmental considerations - A movement that
`
`originated in Europe to require recycling ofvehicle components
`is also expected to be adopted in the U.S. and is driving the
`need to produce recyclable airbag modules. Within a few years,
`OBMS and suppliers may be required to find ways to recycle
`certain airbag components, including the cushion. Simplified
`airbag assemblies require fewer diverse types of materials,
`thereby facilitating separation and recycling efforts.
`Longer service life - As the most recent Delphi Studies
`from the University of Michigan demonstrate, car owners keep
`their vehicles for longer periods before trade-in, primarily due
`to the increased costs of new models. Because of this, OEMs
`are now extending warranty periods as an important marketing
`tool to maintain share (see Figure 1).
`
`LP.5
`U)
`Eat
`
`U 3
`
`?:
`lo-
`CW
`
`
`
`E 3'
`
`59-4
`
`1980
`
`Fig. 1: Cars in the U.S. 9+ years old [2]
`
`Along with increased expectations regarding vehicle life,
`there is a corresponding increase in expectations concerning
`the longevity of the vehicle’s safety systems.
`In fact, the
`consumer ‘s expectation is that the safety systems should outlive
`
`30
`
`

`
`
`
`- Rising pressure on the trim cover causes that material to
`elongate and a designed-in weak region (tear seam) begins
`to yield;
`° As the tear seams give way, the cover doors open, providing
`the filling bag with a preferred escape route;
`° Under continued pressure of gas flow from the inflator, the
`deploying air cushion moves out into the vehicle interior;
`- The bag continues to fill until the fabric becomes taut, a point
`in time and space that has been established from the system
`timing budget (see Figure 2) so as to allow for sufficient
`cushion pressurization to provide required occupant energy
`dissipation during ridedown;
`- At this point in the deployment sequence, the occupant will
`contact and begin loading the inflated cushion;
`- Occupant energy is absorbed and dissipated through viscous
`damping effects as gas in the cushion is displaced out through
`vent holes rather than through chest compression.
`
`'
`tT'
`Infl tabl R tra' tD l
`8 .:,e..2n:.i::...'“**“g
`A
`ximately loomm
`,..._......._._
`otp8?:upant Movement
`0 T Sensors
`
`T lntlators
`
`Fig. 2:
`
`Inflatable restraint deployment timing
`
`A time budget for a normal deployment has been established
`to allow a vehicle to meet the requirements of FVMSS 208.
`Timing for an.airbag system is based on occupant movement
`during the crash. Therefore, the total time interval to achieve
`a full airbag, as well as the allocation of time for events within
`the interval, are based on the degree ofcrash pulse transmission
`of the body structure of a given vehicle and the resultant timing
`and magnitude of occupant acceleration.
`The time budget allows the airbag system to provide
`supplemental occupant protection by being fully deployed at a
`point where the occupant has translated far enough forward
`from the specified normal seating position to begin loading
`the now-full bag. This in turn means that maximum pressure
`is available to dissipate energy of the decelerating occupant.
`For some typical passenger vehicles designed in North America,
`this will occur somewhere around 60-75 ms after the initial
`
`point of impact. For some cars designed in Europe or Japan,
`as well as for light trucks, the timing may be shorter, depending
`on the specific characteristics ofthe vehicle body in transmitting
`the crash pulse.
`
`INTEGRATED SYSTEMS DESIGN OF A SMALL
`AIRBAG MODULE
`
`OVERALL CONSTRUCTION OF AN AIRBAG SYSTEM
`
`~ Figure 3 shows an exploded view of a standard-size, driver-
`side airbag module assembly.
`In comparison, a new downsized driver-side airbag module
`assembly is shown as an exploded view in Figure 4. The smaller
`size, lighter weight, and greater simplicity of this new module
`
`31
`
`have been achieved through the systematic integration of
`component technologies.
`In addition to reducing total airbag
`size and mass, the module design yields performance
`improvements, simplifies production, and provides greater
`design freedom. The development of this integrated module
`and its benefits to both the OEM and the vehicle occupant will
`be discussed in detail.
`
`Fig. 3: Exploded view of standard-size, driver-side airbag
`module assembly
`
`
`
`Fig. 4: Exploded view of new downsized driver—side airbag
`module assembly
`
`COVER - The cover of an airbag module performs several
`important ftmctions. From the time the module is assembled
`into the vehicle until it is deployed, the cover is expected to
`present an attractive appearance whose color, grain, and gloss
`are in harmony with the interior decor. The surface must closely
`match the surrounding steering wheel, while potentially made
`of another material. Along with these stringent aesthetic
`requirements, the cover is becoming a preferred location for
`mounting horn pads and redundant accessory switches, such
`
`

`
`
`
`
`
`incorporation of accessory controls are important GEM criteria.
`Single—shot cover — The simplest of the four cover
`technologies is the single-shot cover, which is produced with
`one injection of a 38 Shore D thermoplastic elastomer. With
`the potential ofbeing the least expensive, thinnest, and smallest
`cover type, single-shot covers are predicted to grow in demand
`in the future.
`In addition, Single—shot covers can also
`accommodate membrane switches and backlighting and are
`recyclable.
`However, one disadvantage of the single-shot cover
`technology is a slight increase in hardness (from 47 Shore A to
`38 Shore D). This technology is expected to find growth among
`OEMs for whom softness of touch is not a critical design
`criterion.
`
`Recent advances in the use of waterborne, sofi—touch paint
`and material technologies are allowing this type of cover to
`approach the two-shot cover in tactile response. As one—shot
`cover technology is refined, it will be more frequently
`considered as a substitute for other cover types in selected airbag
`modules.
`
`Table I summarizes the advantages and disadvantages of
`the four cover technologies.
`
`Table 1: Cover technology comparison
`
`Cover
`Technology
`
`Advantages
`
`_
`Disadvantages
`
`RIM-SCRIM — Color&Gloss
`
`Matching
`
`size
`
`
`
`- Feel
`- Quality Problems
`- Cost
`- Not Recyclable
`
`
`
`
`
`
`
`
`- Silt?
`- Assembly
`Cost
`
`
`
`
`
`Capital Intensive
`
`
`- Soft Feel
`- Visual Appearance
`- Recyclable
`
`- Feel
`
`- Visual Appearance '
`- Size
`- Redundant Switches
`- Cost
`
`
`
`
`
`
`TWO-PIECE
`
`TWO—SHOT
`
`ONE-SHOT
`
`
`
`- Recyclable
`
`- Visual Appearance
`- Cost
`- Size
`
`
`
`— Feel (Without
`Soft-Touch Paint)
`
`
`
`
`
`
`- Redundant Switches
`- Easily Manufactured
`Recyclable
`
`CUSHION FABRICS AND COATINGS ~ The airbag
`cushion is comprised of two main elements: woven fabric and
`protective coating. The fabric forms the cushion. The coating
`is applied to the fabric prior to fabrication in order to facilitate
`cutting and handling of the cushion parts prior to fabrication,
`increase fabric lubricity (for easier packing and deployment),
`protect the material from hot gases, and precisely regulate the
`permeability of the cushion during deployment.
`Recent developments in airbag cushion design and
`materials offer opportunities for significant size, bulk, and
`
`32
`
`as radio and cruise control.
`
`During the anticipated 10- to 15-year service life of the
`vehicle, the cover must withstand a variety ofharsh conditions,
`including direct exposure to sunlight and temperature extremes
`of ~30 to 80C (-22 to I76F), resist sagging, and maintain its
`shape, not fade, or lose grain definition or gloss.
`Most important, during deployment the cover must
`predictably and reliably release the airbag cushion fabric into
`the vehicle interior without ejection of fragments that could
`injure occupants or tear the airbag.
`RIM—scrim cover - Currently, four types of cover
`technologies are in use. The first type to be introduced was the
`polyurethane RIM~scrim cover, produced using the reaction
`injection molding (RIM) process. These covers are usually
`made of the same material as the steering wheel for color, grain,
`and gloss compatibility. To allow a RIM-scrim cover to perform
`properly at temperature extremes,‘ a piece of scrim (woven
`nylon) is embedded in the polyurethane polymer during
`molding. The scrim supplies additional support to the urethane
`to prevent fragmentation as well as imparting strength to the
`doors during deployment by providing a preferred path of tear.
`While RIM—scrim covers are thinner than some other
`
`technologies, they offer potentially low process yield due to
`bubble formation and the potential for improper scrim
`placement during molding -- quality, not safety-related issues.
`Quality problems such as paint adhesion can also be a concern.
`In addition, they do not provide the soft tactile properties desired
`by consumers. Finally, RIM—scrim covers cannot be cost-
`effectively recycled.
`Two-piece cover - The second technology is the two-piece
`cover, which consists of a soft polyvinyl chloride (PVC) outer
`section over a stiff thermoplastic elastorner (TPE) retainer.
`Mechanical fasteners are used to attach the two components.
`This type of cover meets performance and aesthetic
`requirements, but its two-part construction adds undesirable
`size and thickness, reduces flexibility, and increases labor and
`equipment costs. However, the soft qualities of the cover can
`help reduce occupant injuries in non-deployment situations.
`Further, the two-piece cover is recyclable.
`Two-shot cover ~ The third technology is the two—shot,
`injection molded cover. This cover appears to be a single piece
`but is actually comprised of two types of material. In the first
`step, a hard polyolefin retainer is injection molded to provide
`rigidity. Through a proprietary process,’a top covering of TPE
`is next injected into the tool to provide the aesthetically pleasing
`show surface.
`
`The resulting part has a retainer with a Shore D hardness
`of SO and a soft outer surface with a Shore A hardness of 47,
`offering visual aesthetics and tactile feel in a thin cover for
`maximum styling flexibility. Two-shot covers can be painted
`or a pre-colored material can be used for the exposed surface.
`If a specific color is required, a waterborne paint can be used
`. for environmental compatibility.
`Further, the unique configuration of the two-shot cover
`lends itself to incorporation of membrane switches and
`backlighting for redundant accessory controls.
`In addition,
`the cover is comprised of two recyclable polymers, addressing
`growing environmental concerns about vehicle recycling.
`Therefore, the two-shot cover is a viable candidate for use in
`the downsized airbag module where softness of touch and
`
`

`
`
`
`actually reduce the service life of the airbag fabric (see Figure
`5 [3]). An organic rubber, neoprene is prone to heat—aging
`effects from temperature cycling, ozone, and other oxidative
`agents that can compromise its long-term performance.
`In
`contrast, silicone coatings currently used in some applications
`have extended the fabric’s service life to l5 years, as opposed
`to the 10—year life of neoprene.
`
`UIO
`
`bO
`
`U)C
`
`.5
`s.
`.8.
`'3
`
`§Q: S*5’
`
`Nylon
`
`1 Neoprene/Nylon
`Silicone/Nylon
`
`
`
`k\\\\\\\\\\\\\\\\\\;I
`
`i\\\\\\\\\\\\\\\\\\\\V
`
`i\\\\\\\\\\\\\\\\\\\
`
`b\\\\\\\\\\\\\\\\\V‘
`
`
`
`°°i\\\\\\\\\\\\\\\\\\‘
`
`K\\\\\\\\\\\\\\V\'
`
`
`
`"’k\\\\\\\\\\\\\\V
`
`Fig. 5: Fabric service life [3]
`
`Silicones are characterized by a high level ofenvironmental
`stability and chemical inertness, attributes that extend the useful
`life of airbag fabrics. Further, silicone coatings are more
`compatible with proposed airbag fabric recycling efforts because
`silicone polymers can tolerate the high heat required to melt-
`reprocess the airbag fabric. Also, during reprocessing silicone
`does not release chemicals that could compromise equipment
`or the performance of the reprocessed fiber, whereas neoprene
`releases some highly corrosive and toxic materials during
`heating.
`Further, silicone coatings offer good wear and abrasion
`resistance, especially in comparison with softer neoprene
`coatings (Table III [3]), making them better suited for rough-
`duty vehicles that will subject airbags to increased vibration,
`wear, and abrasion.
`
`Table III: Abrasion/wear properties of neoprene-coated nylon
`and silicone»coated nylon [3]
`
`w.........
`
` Condition
`
`
`10,000 Cycles
`
`300 Cycles
`
`
`
`46 x 46
`,
`
`
`
`Silicone Advanced
`Based
`Silicone
`
`
`
`
`
`0.38
`
`0.34
`
`0.32
`
`0.30
`
`260
`
`45
`
`I 2
`
`
`
`Second-generation fabrics - About 60% of current airbag
`systems utilize 420 (1 nylon fabric, which, although also coated
`with neoprene, is noticeably lighter, sofier, and thinner than
`the 840 d fabric.
`The fabrics shown in Table II were used to make similar
`
`airbag cushions. When these cushions were compared, it was
`detennined that the ones constructed of 420 denier neoprene-
`coated fabric had about 12% less mass than those made of 840
`
`d neoprene-coated nylon. A reduction in bulk of l0% was also
`gained with the 420 d fabric.
`Further reductions of 5% each in mass and bulk have been
`
`achieved through the use of a new and improved higher-tenacity
`nylon yarn that permits a looser weave with equivalent strength.
`Silicone coatings - Silicone rubber coatings have been
`substituted for the neoprene coatings in some airbags, primarily
`to extend the service life of the airbag system as demanded by
`OEMs. Neoprene is not fully compatible with nylon and can
`
`
`
` 80% Minimum
`
`Requirement
`
`Strength Retention
`
`50 mg Maximum
`Weight Loss
`
`
`
`
` 86%
` Neoprene Result
` 91%
`6mg Silicone Result
`
`
`27 mg
`
`‘Denier is the weight, in grams, of 9,000 meters of a given
`constant-density yarn. The higher the denier number, the
`thicker the yarn and the coarser the woven fabric.
`
`33
`
`The major drawback of silicone coatings is their higher
`cost in comparison with neoprene. However, due to a low
`coefficient of friction and excellent short~term temperature
`resistance, silicone coatings can be utilized successfully in very
`
`weight reductions as well as performance and environmental
`improvements for the next generation of airbag modules [2].
`New lightweight fabrics and advanced coating technologies
`are making a crucial contribution to the successful design of a
`downsized module.
`
`Traditional airbag fabrics ~ Table 11 provides a comparison
`of properties for fabric types that have historically been used
`in airbag cushion construction. Initial airbag systems designed
`in the 1970s utilized fabric woven from 840 denier"' (d) nylon
`6,6 with a black neoprene (chloroprene rubber) coating. With
`its high denier number, this fabric was thick, coarse, and bulky.
`Furthennore, the neoprene coating added extra thickness.
`
`Table II: History of fabric construction for airbags
`
`840
`Denier
`
`420
`Denier
`
`420
`Denier
`
`Nylon 66 Nylon 66 Nylon 66
`
`420
`420
`Denier
`Denier
`Nylon 55 Nylon 66
`
`25 x 25
`
`49 x 49
`
`46 x 46
`
`46 x 46
`
`C°3ii1'|8
`Type
`
`Neoprene Neoprene Neoprene
`Based
`Based
`Based
`
`Constmction
`(Weave)
`
`
`
`Thickness
`mm
`+/- 0.01
`
`Weight
`
`

`
`
`
`not require talc or cornstarch to prevent blocking. Also, use of
`talc or cornstarch in the manufacturing environment could
`cause nuisance dust.
`
`Advances in silicone technology address this potential
`source of irritation. Due to silicone’s high coefficient of friction,
`transfer of the coating between layers does not occur. Silicone-
`coated fabrics thus can remain safely packed for the service
`life of the vehicle without the use of talc or cornstarch.
`
`Non—coated fabrics ~ Another trend in driver-side airbag
`development is the use of non—coated fabrics. The major
`technical challenge in this development is the control of fabric
`permeability. Two directions are currently being investigated.
`One is the development of specialized fabrics that undergo high
`shrinkage afler weaving to reduce porosity. In this alternative
`a tight fabric weave coupled with the use of high-shrink yarns
`are used to control fabric permeability. The other is the use of
`a calendering process on the finished fabric. The calendering
`process compresses and smooths the yarn, filling in the holes
`in the weave and potentially eliminating the need for a coating
`(see Figure 7).
`
`EFFECT OF CALENDERING"'
`
`
`
`Normal Non—Coated Fabric
`
`thin layers, mitigating the cost difference.
`Advanced fabric technology - A new generation of airbag
`fabric has been developed to take advantage of the new high»
`tenacity nylon yarn and silicone’s ability to maintain
`performance even when applied in very thin layers. This 420
`d fabric, which features a light coating of a blue addition—cure
`liquid silicone rubber, combines the benefits of longer service
`life, reduced mass and bulk, and competitive cost.
`The new silicone coating system, which was developed
`specifically for airbag fabric applications, has low viscosity.
`The coating’s low viscosity enables it to encapsulate the fabric’s
`weave more easily and in a much thinner layer than neoprene
`or heat-cured rubber (HCR) silicone.
`Compared to earlier materials, advanced airbag fabrics can
`reduce overall package size and weight. Tests have shown
`that cushions produced with the new silicone-coated fabric had
`20% less mass than those made from 420 d neoprene-coated
`material, and 10% less mass than cushions made from 420
`HCR silicone-coated fabric. A reduction of 10% in cushion
`bulk was also achieved.
`
`From a design standpoint, a thinner coating layer and a
`lighter, sofier material yield an airbag cushion that can be more
`easily folded into a compact shape. The new fabric’s pliability
`and reduced bulk allow the folded cushion to occupy a smaller
`space, greatly facilitating downsizing of the module. Figure 6
`provides a comparison ofpacking volume among different types
`of airbag fabrics.
`
`PACKING VOLUME STUDY
`Different Fabric: and Coatings
`0.9 in x 0.9 m Squaru
`
`A mechanical finishing process for fabrics to produce
`special effects, such as high luster, glazing, moire’, and
`embossed effects. In this operation, the fabric is passed
`between heated rolls under pressure.
`
`
`
`Fig. 7: Effect of calendering
`
`Recent non—coated alternatives offer improvements in bulk
`over the ear1ier—generation 840 and 420 d neoprene-coated
`alternatives and approach the advanced nylon fabric in
`thickness. While development continues, a comparison offabric
`mass still confers an advantage on the advanced nylon fabrics,
`based on present data. Either the specialized fabric or fabric
`finished with a calendering process has the potential for use in
`driver—sidc air cushion programs; however it has yet to be
`determined if fabric permeability can be maintained within tight
`enough limits between fabric lots.
`CUSHION DESIGN - Cushion design of the small airbag
`module integrates special features that improve its performance,
`enhance occupant safety, and streamline assembly operations.
`Bag tethers - The small airbag module design incorporates
`two or four tethers (depending on OEM requirements) that aid
`in effective deployment of the driver-side cushion. The 70-
`mm (3-in.) fabric tethcrs sewn inside the bag help define the
`inflation of the cushion, limiting forward extension to
`approximately 230 to 270 mm (9.1 to 10.6 in.).
`In addition,
`the tethers force the bag to fill laterally. This configuration
`provides enhanced protection for an out-of—position passenger
`in two ways. First, the forward motion of the bag is significantly
`
`420 d
`HCR Silicone
`Nylon
`
`420 d
`Neoprene
`Nylon
`
`420 d
`840 d
`Neoprene Advanced Silicone
`Nylon
`Nylon
`
`Fig. 6: Packing volume study
`
`Respirable particulate reduction - An additional benefit of
`_the advanced airbag fabric is elimination of the use of talc and
`cornstarch during the coating operation. Neoprene and HCR
`silicone coatings require application of talc or cornstarch to
`prevent the folded layers from sticking to each other (blocking).
`Adhesion can occur when friction causes transfer of the coating
`between layers of fabric. Recent concerns regarding potential
`adverse reactions from asthmatics who might breathe respirable
`particulates have also driven development of fabrics that do
`
`34
`
`
`
`-cummnmo:
`
`Calendered Fabric
`
`
`
`
`
`
`
`
`

`
`
`
`Assumes non«belted occupant
`Fig. 8: Air cushion without tethers
`
`Air cushion in
`final deployed
`
`Assumes non-beltai occupant
`
`Fig. 9: Air cushion with tethers
`
`Cushion ring - A patented ring sewn inside the orifice of
`the airbag cushion has been integrated into the design of the
`downsized module to help eliminate the use of traditional rivets
`for assembly. The flat, thin, 0.8 mm (0.03 in.) ring, made of
`injection-molded nylon, features 8 moldcd—in posts for
`conventional airbags and 4 for the downsized airbag. These
`posts take the place of metal rivets. This unique system is
`significantly less costly than standard assembly hardware.
`In
`addition, one cushion ring replaces from 4 to 8 or more rivets,
`thus simplifying production and assembly.
`
`35
`
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`
`I%,%.«:;a..>:.€t:.:;7<.s.2:a,
`
`
`
`reduced, lessening the risk of bag slap. Second, the lateral
`expansion of the cushion provides a wider area of cushioning
`for occupants who are positioned off—center to the steering
`colmnn. A new tether construction offers further improvements
`in manufacturing and performance (Figures 8 and 9).
`
`Air cushion in
`final deployed
`position
`
`Air cushion in
`initial deployment
`
`Venting - Conventional venting for dn'ver—side air cushions
`is achieved through inclusion of two or more discrete holes in
`the module side (back) of the cushion to allow the gas to be
`pushed out of the bag at a rate consistent with the occupant
`protection needs of the vehicle. Conventional airbag vents
`usually require reinforcement to achieve required strength. A
`cloth reinforcement is usually sewn on the vent hole and then
`die cut with the vent. While discrete vent holes are the
`
`predominant type of bag venting, other alternatives are also
`bein