Airbag system

An embodiment of an airbag system includes a cavity configured to store an airbag, wherein the cavity has an aperture that provides an outlet for the airbag during deployment. The embodiment also includes a cover releasably attached over the aperture via an attachment mechanism having an initial attachment strength. The initial attachment strength is configured to reduce to a release attachment strength in response to receipt of a release signal at the attachment mechanism.

TECHNICAL FIELD

The present invention relates generally to airbag systems, and more particularly to an attachment mechanism configured to selectively prepare an airbag cover for release from an airbag housing, such as prior to airbag deployment.

BACKGROUND OF THE INVENTION

Current vehicle airbag systems include an inflatable airbag that is positioned in an airbag housing. When inside the housing, a cover is situated over the airbag. The cover may be, for example, an airbag deployment door, seat trim, substrate, or closeout. These covers, which are intended to be permanent and irreversible following airbag deployment, are either integral with the housing or are attached via an attachment mechanism. Exemplary attachment mechanisms may include irreversible stitching, rivets, or threaded fasteners. The portion of the surface acting as the cover is typically demarked by a weakened region around all or a portion of its perimeter, which is not typically visible to the end consumer. The weakened region is designed to fail under airbag loading during deployment, creating an opening through which the airbag may deploy.

The fracture forces necessary to open an airbag cover may experience some level of variation from part to part due to manufacturing and part tolerance differences. The inherent variability of the separation and release of the airbag cover causes variation in both the timing and the manner in which the airbag deploys through the cover. Such variability requires the airbag system to have an inflator with a higher power than may otherwise be necessary to provide accurate and predictable deployment.

As such, it is desirable to control the deployment of an airbag past the airbag cover, reduce the cover fracture forces, and, thus, minimize the required power of the airbag inflator.

SUMMARY OF THE INVENTION

An embodiment of an airbag system includes a cavity configured to store an airbag, wherein the cavity has an aperture that provides an outlet for the airbag during deployment. The embodiment also includes a cover releasably attached over the aperture via an attachment mechanism having an initial attachment strength. The attachment mechanism may include a hook-and-loop type fastener, a knob-and-receiving cavity type fastener, one or more aligning tables, and/or a seam. The seam may consist of stitching that attaches one or more pieces of material, such as fabric or flexible plastic, together. The initial attachment strength is configured to reduce in force level to a release attachment strength in response to receipt of a release signal at the attachment mechanism. The release signal may be transmitted as a voltage, a current, a magnetic field, or a thermal trigger and may be transmitted in response to a preliminary impact condition, an impact condition, or a manual input.

The attachment mechanism may be at least partially formed from a shape memory alloy, a shape memory polymer, an electro active polymer, a piezo electric, a magnetorheological elastomer, and/or an electrorheological elastomer. As such, reducing the initial attachment strength to the release attachment strength may include activating at least one of the shape memory alloy, the shape memory polymer, the electro active polymer, the piezo electric, the magnetorheological elastomer, and/or the electrorheological elastomer. The attachment mechanism may increase substantially from the release attachment strength to the initial attachment strength in response to recognition of a cessation of the receipt of the release signal at the attachment mechanism, a receipt of an attachment signal at the attachment mechanism, or the passing of a predetermined length of time.

If the attachment mechanism is a seam, then reducing the attachment strength to the release attachment strength may include at least substantially weakening the seam. The seam may be at least substantially weakened in at least one location via: a direct fracture by the attachment mechanism, the attachment mechanism pulling on a ribbon system directly sewn into the seam and configured to create at least one high stress point on the system, and/or a lever system on the attachment mechanism configured to multiply a pulling motion on the ribbon system. Further, the system may include a sheath that substantially prevents a cutting mechanism from at least weakening the seam during a state of non-actuation.

An embodiment of a method of activating an airbag system having an airbag housing with a cavity configured to store an airbag deployable by an airbag inflator, the cavity having an aperture providing an outlet for the airbag during deployment, and a cover releasably attached over the aperture via an attachment mechanism having an initial attachment strength includes receiving a release signal at the attachment mechanism. The embodiment also includes reducing the initial attachment strength to a release attachment strength in response to the receipt of the release signal at the attachment mechanism, receiving a deployment signal at the airbag inflator, and deploying the airbag via the aperture.

The method may further include: transmitting, at a first time prior to receiving the release signal at the attachment mechanism, the release signal from a sensing system to the attachment mechanism in response to one of a preliminary impact condition, an impact condition, or a manual input; and transmitting, at a second time prior to receiving the deployment signal at the airbag inflator, the deployment signal from the sensing system to the airbag inflator in response to one of the preliminary impact condition, the impact condition, or the manual input. It is understood that the first time may occur before or substantially at the same time as the second time.

Optionally, the method may include increasing the release attachment strength substantially to the initial attachment strength, after reducing the initial attachment strength to the release attachment strength, in response to a triggering event. As non-limiting examples, the triggering event may include: detection, at the attachment mechanism, of a cessation of receipt of the release signal; a receipt, at the attachment mechanism, of an attachment signal; or a detection, at the attachment mechanism, of a passing of a predetermined length of time.

The above features and advantages, and other features and advantages of the present invention will be readily apparent from the following detailed description of the preferred embodiments and best modes for carrying out the present invention when taken in connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment(s) of the system and method disclosed herein advantageously provide an improved attachment system for an airbag system cover. Embodiment(s) of the system and method advantageously improve airbag maintenance and/or deployment. It is believed that such a method and/or system may provide for reduced air bag cover breakout forces.

Referring toFIGS. 1 and 2, an embodiment of an airbag system10having an airbag housing14is depicted. The airbag system10is configured for use in a vehicle, such as a car, truck, plane, or boat. As non-limiting examples, the airbag system10may be located in the vehicle headliner, quarter panel, instrument panel, steering wheel, door, ceiling, seat, and/or any other suitable packaged vehicle location. The airbag housing14may be produced from any suitable materials such as, for example, cloth, plastic, or metal, and may be formed as a solid one-piece housing or from two or more pieces. To maintain positioning, the housing14may be attached to another vehicle structure, such as the seat structure32, or may be formed integral therewith. The airbag housing14includes a cavity22with an aperture26. The cavity22is configured to house an airbag30, which selectively deploys via the aperture26.

A cover34is releasably attached over the aperture26via an attachment mechanism38. The cover34is attached (either directly or indirectly) to the housing14or vehicle structure such as the seat structure32and is releasable to create an opening through which the airbag30may deploy. As a non-limiting example, the cover34may be substantially rectangularly-shaped and attached (either directly or indirectly) to the housing14or vehicle structure such as the seat structure32along a portion of the perimeter of the cover34. As such, the cover34may be slightly larger than the aperture26that it covers. The cover34may completely disengage from the airbag housing14/vehicle structure (e.g., seat structure32) or may remain partially attached when the cover34is released from the housing14. As an example, where the cover34remains attached to the airbag housing14even when released therefrom, the cover34, when released, may function as a flap or a door, allowing a passage for the airbag30to deploy while remaining partially attached to the airbag housing14. The cover may have any suitable configuration and may include one or more layers of material. For example, the embodiment of the cover34depicted inFIGS. 1 and 2has a first cover layer34and a second cover layer34A, which together form the cover34.

The airbag30may optionally be located within airbag packaging25, which is located in the housing14. The airbag packaging25is formed with a lid27attached to the packaging25at hinge28and releasably attached to the packaging25at tear seam29. Lid27acts as an internal cover that will fracture at the tear seam29upon airbag30deployment, allowing the airbag30to escape toward the cover34and the fastener42. A partially deployed airbag31is shown inFIG. 1. In this embodiment, aperture26is covered by lid27before airbag30deployment. Upon deployment, the lid27opens by tearing at the tear seam29and rotating about the hinge28. This allows aperture26to be realized and the airbag30to deploy therethrough and approach cover34. It is to be understood that the packaging25and lid27and/or the housing14may be formed from fabric (i.e., a fabric wrap) that breaks in a controlled fashion upon airbag30deployment.

The attachment mechanism38includes the fastener42, which is located at the interface between the housing14and the cover34, and an actuatable material46. The fastener42is the portion of the attachment mechanism38that physically retains the cover34over the aperture26. The fastener42may be any suitable structure or device that provides for releasable attachment of the cover34to the housing14. As non-limiting examples, the fastener42may include a hook-and-loop type fastener, a knob-and-receiving cavity type fastener, one or more aligning tabs, one or more retaining strips, and/or a seam. The seam may consist of the stitching that attaches one or more pieces of material such as fabric or flexible plastic together.

The attachment mechanism38has an initial attachment strength, which is a measurement of the amount of force that must be applied to the cover34during airbag30deployment to release the cover34from the airbag housing14and provide an outlet for the airbag30when the actuatable material46is not actuated. This initial attachment strength is, thus, related to the strength of the fastener42.

The actuatable material46may have any suitable composition that is capable of being actuated in a manner to reduce the initial attachment strength to a release attachment strength. As such, the release attachment strength is the amount of force required by the airbag30during deployment to release the cover34from the housing14when the actuatable material46is actuated. Upon actuation, the actuatable material46may, for example, soften or decrease in length to pre-load or fracture a portion of the fastener42. Exemplary embodiments illustrating how the actuatable material46may lower the initial attachment strength are described hereinbelow. Reducing the initial attachment strength to the release attachment strength advantageously reduces the amount of force that must be exerted by the airbag30upon deployment by reducing the amount of force required to release the cover34from the housing14. As such, an airbag system10that reduces the initial attachment strength to the release attachment strength may enable an airbag30inflator with a lower power than would be necessary for a system10that maintains the initial attachment strength during deployment.

The actuatable material46may be included in the fastener42or may be separate therefrom. As non-limiting examples, the actuatable material46may be at least partially formed from: a shape memory alloy (SMA), which may involve cutting or pulling the material46; a shape memory polymer (SMP), which may include softening the material46; an electro active polymer (EAP), which may involve pulling the material46; a piezo electric; a magnetorheological (MR) elastomer; or an electrorheological (ER) elastomer. It is to be understood that actuation of the actuatable material46may be triggered by any suitable release signal. The release signal may be transmitted as, for example, a voltage, a current, a magnetic field, or a thermal trigger (e.g., thermal activation or heating of the material46).

When the release signal is transmitted as a thermal trigger, the actuatable material46may be thermally activated, whereby heat is applied to the material46in a quantity sufficient to raise the temperature of the thermally active actuatable material46(e.g., a shape memory alloy or a shape memory polymer). Heating of the actuatable material46may be achieved by any suitable means, including resistive heating, inductive heating, and/or convective and conductive heat transfer from a hot gas or hot fluid, respectively. As a non-limiting example, heat may transfer to the actuatable material46from the relatively hot gas that results from a pyrotechnic charge.

The airbag cover34may be released in any suitable manner, such as: decreasing the attachment strength of a solid non-stitched seam system, irreversibly fracturing a solid non-stitched seam, decreasing the attachment strength of a stitched seam (i.e., pre-loading the fastener42to require less additional load to fracture the seam), irreversibly fracturing a stitching material, and irreversibly fracturing the material in a stitched seam.

Exemplary methods of decreasing the attachment strength of a solid non-stitched seam system include: reversibly reducing the actuatable material46modulus (e.g., heating of an SMP or SMA in super elastic mode); reversibly or irreversibly (depending upon the seam material) thinning the actuatable material46or decreasing the amount of additional energy needed to fracture the seam material (e.g., using field activated movement of a SMA, piezo electric, or EAP to stretch the material46); and displacing rigid supporting elements adjacent the seam either reversibly (so only a few supports or support sections are engaged) or irreversibly.

Irreversibly fracturing a solid non-stitched seam may be achieved through tensile fracture of the cover34by activation of a SMA, piezo electric, or EAP. As an example, a SMA may be embedded within or attached to the inward-facing surface of the cover34.

Exemplary methods of decreasing the attachment strength of a stitched seam include: reversibly reducing the modulus of the seam (e.g., heating of an SMP or SMA in super elastic mode); activating the shape memory effect and increase in modulus of a SMA seam whereby the cover34is pinched or cut proximate to the stitches; and activating SMA, EAP, and/or piezo electric materials to cause crimps136, shown inFIG. 12, (formed from or engaged with the actuatable materials46) to reversibly or irreversibly release the actuatable material46.

Non-limiting examples of irreversibly fracturing the stitching material include: cutting the seam at one or more points by an embedded cutting mechanism130,230,330,430, shown inFIGS. 12A and 14through15B, activated by a piezo electric, an EAP, or a SMA; stretching the seam past its ultimate stress/strain failure through the activation of a SMA, an EAP, or a piezo electric to which it is physically linked (e.g., in series); and by increasing the tension in the seam sufficiently to cause it to pull out of at least one crimp136,236,336,436.

A non-limiting example of irreversibly fracturing the material in a stitched seam includes actuating the shape memory effect and increase in modulus of a SMA seam, which results in fracturing the cover34and opening and/or initiating a seam proximate to the stitches. More specifically, the SMA seam is a SMA in wire form that is used as stitching material (i.e. a fastener) in a prestretched form. Actuating the SMA both decreases the length of the wire and increases its modulus, which both help the SMA to cut through the more flexible, lower modulus material, through which it is stitched, upon actuation.

Referring to the specific embodiment ofFIGS. 1,2, and2A, the fastener42is part of a tear seam interface between the cover34and the housing14. More specifically, the fastener42is a seam holding together the cover34, the housing14, and two ribbons50. The ribbons50are indirectly connected to the actuatable material46via the o-ring54. It is to be understood that any number of ribbons50may be utilized and the ribbon(s)50may alternately be directly attached to the actuatable material46. The actuatable material46is anchored to a substantially stable fixture or structure58. Exemplary fixtures/structures58include a vehicle body frame, sub frames such as a seat frame or instrument panel, or show surface related components such as the seat trim or the instrument panel show surface/substrate. The actuatable material46is also connected to an actuating system62. InFIGS. 1,2, and2A, the actuating system62is a power source64(depicted in later embodiments) connected to the actuatable material46via an electrical connector66. The actuating system62actuates the actuatable material46by transmitting electricity to the actuatable material46via the electrical connector66in response to a release signal. When actuated, the actuatable material46decreases in length, causing the ribbons50to pull on the fastener42, which creates at least one high stress point on the seam and causes the seam to weaken or break. Upon air bag30deployment, the deploying air bag cushion30will contact the cover34, further breaking the seam if necessary, causing the cover34to move away from the seam, and enabling the air bag cushion30to deploy through the resulting opening. It is understood that weakening or breaking the seam results in a reduction of the initial attachment strength to a release attachment strength.

The release signal may be transmitted from a sensing system, such as an impact and/or occupant environment sensing system. Inputs to the sensing system may include a roll-over sensor; a gyroscope; one or more accelerometers; a seat belt connection monitor; an occupant sensing monitor such as, but not limited to, an air bag suppression system; and/or a seat position monitor. An impact sensing system may monitor the vehicle for preliminary impact conditions (which warn of a likely impending collision) and/or impact conditions (which indicates a vehicle collision) and may transmit the release signal in response thereto. An occupant environment sensing system may monitor, for example, vehicle seat and mirror positioning as well as passenger seat occupancy, restraint usage, occupant size, and/or occupant position. Alternately, the release signal may be transmitted in response to a manual input, such as by a technician requiring access to the airbag system10. Allowing manual access to the airbag30facilitates removal of the cover34, for example, for airbag system10repair/replacement and/or repair/replacement of components adjacent the air bag system10. The manual input may be, for example, a button push, a switch toggle, and/or a key turn. It could also be an electronic input provided by an electronic service/diagnostic tool that is plugged into the vehicle. It is recognized that the release signal may prepare the airbag cover34for airbag30deployment or service access but may not trigger the deployment.

Similar to the embodiment illustrated inFIGS. 1,2, and2A, the embodiment of the attachment mechanism138illustrated inFIG. 3includes a fastener42, which is a seam that connects the cover34, the housing14, and a ribbon50. The ribbon50is engaged with a lever arm70of the actuating system162, wherein the lever arm70is fixed at a pivot point74and attached to the actuatable material46. The pivot point74is located, for example, on the substantially stable fixture or structure58. The actuatable material46is connected to an electrical connector66, which transmits a release signal to the actuatable material46. When the actuatable material46is actuated, it reduces in length, which pulls on the lever arm70and, thus, the ribbon50, thereby weakening or tearing the seam42and reducing the initial attachment strength to a release attachment strength. It is to be understood that the lever arm70functions as a motion multiplier, whereby the distance that the ribbon50is pulled by the actuatable material46is multiplied by the lever arm70, resulting in a greater distance pulled on the ribbon50by the lever arm70.

In an alternate embodiment, a motion multiplier may utilize a spool having at least two diameters whereby at least a portion of the actuatable material46routes around a portion of the spool having a relatively small diameter and where the ribbon50routes around a portion of the spool having a relatively large diameter. In this configuration, when the actuatable material46changes length (decreases during actuation or increases in response to deactivation), the spool rotates, causing the actuation of the actuatable material46to be effectively multiplied as realized by the ribbon50.

Referring toFIGS. 4 and 5, an embodiment of an airbag system110is depicted having an attachment mechanism238utilizing a plurality of aligning tabs78. In alternate embodiments any number of aligning tabs78may be utilized. The system110includes an airbag30in a housing14, which is fixed to a substantially stable fixture or structure58, such as an instrument panel beam. The airbag30is in communication with an inflator82, which selectively receives a deployment signal from a sensing system, such as an impact and/or occupant environment sensing system. The deployment signal may be transmitted in response to a preliminary impact condition, an impact condition, and/or a manual input. As an example, the deployment signal may trigger a pyrotechnic charge, which deploys the airbag30. In response to the deployment signal, the inflator82will inflate and, thus, deploy the airbag30via the aperture26.

For the airbag30to deploy through the aperture26, the fastener142adjusts to decrease the initial attachment strength to the release attachment strength. The cover134of the attachment mechanism238includes a ledge86. The ledge86is equipped with a plurality of fingers90that are selectively engageable and disengageable with the aligning tabs78. More specifically, when the actuatable material46is in its non-actuated state, the aligning tabs78align with the fingers90, resulting in a relatively high initial attachment strength and substantially prevents the cover134from opening away from the housing14. When the actuatable material46is actuated, such as by a signal transmitted via the electrical connector66, the actuatable material46reduces in length, which slides the aligning tabs78with respect to the fingers90. While the actuatable material46is actuated, the aligning tabs78misalign with the fingers90such that the aligning tabs78are aligned with the spaces94between the fingers90. When the aligning tabs78are misaligned with the fingers90, the resulting release attachment strength is lower than the initial attachment strength, and the cover134may release from the housing14, allowing deployment of the airbag30through the aperture26once the airbag30is commanded to deploy and the air bag cushion starts to expand and pushes on the cover134.

Referring now toFIG. 6, the attachment mechanism338of the present invention may have a plurality of seam release tethers98engaged with the seam. The seam release tethers98may be of any shape or composition able to suitably engage the seam. While three seam release tethers98are shown inFIG. 6, it is to be understood that any number of tethers98may be utilized. In the embodiment ofFIG. 6, the fastener242is a seam running through a ring102of each of the seam release tethers98and releasably holding the airbag cover34to the housing14. In one embodiment, the seam release tethers98are composed of the actuatable material46, whereby the tethers decrease in length (i.e., actuate) in response to a release signal. Decreasing the length of the seam release tethers98creates at least one high stress point on the seam (i.e., at the points where the seam passes through each ring102). It is to be understood that the high stress points result in a release attachment strength, which is lower than the initial attachment strength realized by the fastener242before actuation. The release attachment strength may occur due to a non-fractured seam having a high tension (i.e., pre-loading) or may be due to a fractured seam.

Alternately, the seam release tethers98may be formed of a substantially static (i.e., non-elastic) material that is engaged with the actuatable material46. As such, actuation results in a decrease in length of the actuatable material46, which pulls on the seam release tethers98and creates one or more stress points in the fastener242.

Referring now toFIG. 7, a fastener342, which is a seam at least partially formed from the actuatable material146, is depicted releasably connecting the airbag cover34to the airbag housing14. It is to be understood that the actuatable seam is depicted in an exaggerated sense of looseness for illustration purposes only. The seam has an initial attachment strength when the actuatable material146in the seam is not actuated. In response to a release signal, the actuatable material146reduces in length, thereby putting the seam in high tension and reducing the initial attachment strength to a release attachment strength.

The cover34and/or the housing14may optionally be at least partially composed of an actuatable material46, such as a shape memory polymer, where the seam passes therethrough. It is to be understood that actuating the actuatable material46may soften the shape memory polymer and allow the seam to more easily tear the cover34and/or housing14, thereby reducing the initial attachment strength to the release attachment strength.

In a similar embodiment, the actuatable material146in the seam may soften upon actuation. As such, softening the seam results in a decrease in the initial attachment strength to a release attachment strength while allowing for complete reversibility. More specifically, the fastener342may reach a release attachment strength in preparation for airbag30deployment, but may return to the initial attachment strength if deployment does not occur. In such an event, a release signal is transmitted to the actuatable material, causing the seam to soften. If a deployment signal is not received at the airbag inflator82within a predetermined time after receipt of the release signal, the actuatable material146may return substantially to its original state, returning the attachment mechanism438substantially to the initial attachment strength. As a non-limiting example, the predetermined time may be approximately 10 milliseconds to approximately one minute. Alternately, the actuatable material146may remain actuated while continuing to recognize receipt of the release signal and may return, or be commanded to return, substantially to the initial attachment strength in response to a triggering event, such as recognition of a cessation to receive the release signal. In another embodiment, the actuatable material146is actuated in response to the release signal and maintains actuation until receiving a subsequent attachment signal from the sensing system at the attachment mechanism438.

In preparation for and during airbag30deployment, two signals may be transmitted: the release signal (which triggers the initial attachment strength to reduce to the release attachment strength) and the deployment signal (which triggers airbag30deployment). The release signal and deployment signal may be transmitted substantially simultaneously or the release signal may be transmitted before the deployment signal. It is recognized that separation of the release signal and the deployment signal allows the attachment mechanism438to prepare for airbag30deployment before the inflator82receives the deploy signal inflating the air bag cushion30to the point that it pushes on the cover34and, if necessary, allows the attachment mechanism438to return to the initial attachment strength in the event of non-deployment.

Referring toFIGS. 8 and 9, an attachment mechanism538having an actuatable hook-and-loop fastener442is depicted. It is recognized that hook-and-loop fasteners442are relatively strong in resisting shear and pull-off forces and relatively weak only in resisting peel forces.FIG. 8illustrates the fastener442in the attached position whileFIG. 9shows the fastener442in the released position. The cover234is equipped with a plurality of loops106. The loops106engage with a plurality of hooks112formed from the actuatable material246and located on (or in communication with) the housing14. The actuatable hooks112are in communication with a power source64via electrical connector66. Alternately, power source64may be a heat source and electrical connector66may be a conduit to transfer heat to a thermally actuatable material246. Upon receipt of a release signal, the power source64triggers the actuatable hooks112via the electrical conduit66. In response to the trigger, the actuatable hooks112soften or straighten and, thus, release their hook shape, resulting in a release attachment strength. Following recognition of a cessation of the release signal, or in response to an attachment signal, the hooks112are no longer actuated and may regain their original hook shape. As such, the release attachment strength may increase substantially to the initial attachment strength.

Alternately, the fastener442may include a combination of hooks112having two or more actuation levels. For example, the fastener442may include hooks112that activate at a first temperature and also hooks112that activate at a second temperature, which is higher or lower than the first temperature. There may be a larger number of the hooks112that actuate at a lower temperature, more of the hooks112that actuate at the higher temperature, or substantially equal number of each type of hook112. Including hooks112with varying actuation levels allows the fastener442to be actuated to a degree that only some of the hooks112are actuated, while the remaining (non-actuated) hooks112aid in maintaining the relative position of the cover234during actuation.

Referring toFIGS. 10 and 11, an embodiment of a fastener542having a retaining strip114including the actuatable material346is depicted, wherein the retaining strip114is operatively connected to the airbag housing14. The retaining strip114may be formed integral with the housing14or may be connected thereto.FIG. 10illustrates the actuatable retaining strip114in the attached position andFIG. 11shows the actuatable retaining strip114in the released position. The retaining strip114, when in a non-actuated state, engages a lip118of the airbag cover334and results in an initial attachment strength. Upon activation, the retaining strip114softens and, thus, reaches a release attachment strength. If the retaining strip114re-attains a non-actuated state, the retaining strip114may re-engage the lip118and substantially reach the initial attachment strength. Optionally, a portion of the retaining strip114may be non-actuatable, whereby the portion remains engaged with the lip118when the actuatable lip118is disengaged to maintain relative position of the cover334to facilitate re-engagement. Alternately, it is to be understood that the actuatable retaining strip114may be mounted to the air bag cover334and the lip118mounted to the housing14.

Referring toFIGS. 12,12A, and12B, the attachment mechanism638is embodied as a seam cutter configured to at least substantially weaken the fastener642. As such, the seam cutter may result in a direct fracture of the fastener642. The seam cutter includes a guide122, having any suitable composition (e.g., relatively flexible or relatively inflexible) through which the actuatable material446passes. The guide122and/or the actuatable material446are operatively connected to the housing14. A loop126of the actuatable material446extends from the guide122, through which the fastener642passes. It is to be understood that the fastener642is formed from an actuatable or non-actuatable material. Extending substantially between the open ends of the guide122is a cutting mechanism130. The actuatable material446is connected to an actuating mechanism, such as the electrical connector66, wherein actuation causes a decrease in the length of the actuatable material446. When the actuatable material446is actuated, the decrease in length causes the loop126to retract and pull the fastener642against the cutting mechanism130, which causes the fastener642to be substantially weakened or fractured, as is depicted inFIG. 12B. The crimps136attached to the actuatable material446substantially prevent the electrical connector66from being pulled into the guide122during actuation of the actuatable material446. Crimps136may be embodied in any suitable form to attach the actuatable material446to the electrical connector66and/or to prevent the electrical connector66from being retracted into the guide122. Non-limiting examples of the crimp136include a wire crimp, soldering, and/or brazing.

It is to be understood that the actuatable material446may be at least weakened by the attachment mechanism638in any suitable manner. For example, the cutting mechanism130may have a relatively sharp cutting edge that the fastener642is pulled against when the actuatable material446decreases in length. Alternately, the cutting mechanism130may have a relatively blunt cutting edge whereby the fastener642is at least weakened by the actuatable material446, which, upon actuation, may act as a fine wire cutting tool and/or may be abrasive against the fastener642. More specifically, the actuatable material446may be substantially fine (i.e., have a very narrow diameter) and may actuate very quickly, which results in a very high contact force against the fastener642. Additionally, the actuatable material446may experience an increase in temperature in response to excess electrical current, which may at least weaken the fastener642by softening (e.g., melting) or burning.

It is to be understood that the diameter of a wire-shaped actuatable material446may have any suitable diameter, which may vary depending upon, for example, the composition of the material being used. Non-limiting examples of wire diameters range from about 250 microns to about 380 microns, but may range both significantly higher and lower, as desired. In exemplary embodiments, actuation of a wire formed from the actuatable material446having a diameter of 250 microns or 380 microns repeatedly produce about 9 N of tension or 19 N of tension (respectively) and produce up to about 36 N or about 76 N of tension (respectively) in a one-time actuation.

To further promote weakening of the fastener642by abrasion, one crimp136may be configured to yield during actuation. More specifically, during actuation, the actuatable material446contracts within the guide122toward the crimps136. If both crimps136are fixed, then there is symmetrical contraction of the actuatable material446toward the cutting mechanism130. If one crimp136is configured to yield during actuation, then the actuatable material446will contract to the cutting mechanism130and will then slide against the fastener642as the crimp136yields, which will increase the abrasion against the fastener642, substantially creating a “sawing” effect.

Similarly,FIG. 13depicts another embodiment of a seam cutter. The actuatable material446passes through the substantially continuous guide222, which is formed at least partially from a relatively soft and flexible material. For example, guide222may be a soft material loop. Guide222provides protection for the fastener642from the actuatable material446during normal, non-actuated use. When actuated, the actuatable material446contracts toward the cutting mechanism130, at least weakening the fastener642as described hereinabove with respect toFIG. 12. Such actuation causes the fastener642to be substantially weakened or fractured, thereby decreasing the initial attachment strength to the release attachment strength. It is understood that the relatively small diameter of the actuatable material446, the relatively soft material of the guide222, and/or the relatively high speed at which the actuatable material446contracts allows the actuatable material446to cut through the guide222near the fastener642during actuation. The cutting mechanism130,230may also include a protective sheath or geometric offset such as a bump adjacent the cutting mechanism130,230that substantially prevents the cutting mechanism130,230from inadvertently weakening/fracturing the seam in a non-actuated situation. For example, the sheath/geometric offset may prevent the cutting mechanism130,230from weakening/fracturing the seam in an airbag system10located in a vehicle seat during passenger entry and/or egress, which may result in the seam being compressed, pushed, and/or shifted. It is to be understood that the sheath/geometric offset may have any suitable embodiment that substantially prevents the cutting mechanism130,230from at least weakening the fastener642during non-actuation.

Referring now toFIGS. 14,14A, and14B, another seam cutter selectively operated by the actuatable material546is depicted. The guide322is formed in a case140, which slidably engages the cutting mechanism330, wherein the cutting mechanism330may slide in the direction indicated by the arrow132. Upon activation via the electrical connector66, the actuatable material546decreases in length, while the crimps336substantially prevent the electrical connector66from being pulled into the guide322. As depicted inFIG. 14B, activation of the actuatable material546causes the cutting mechanism330to slide toward the fastener642and results in the fastener642being pinched between the cutting mechanism330and the loop144of the case140, resulting in substantial weakening or fracture of the fastener642. The loop144may have an opening148to increase the ease in passing the fastener642through the loop144prior to use.

Alternatively, the actuatable material546may attach to the hook shaped loop144and, upon actuation, pull it toward the case140. Such motion either pinching or cutting the fastener642as previously described.

Referring toFIGS. 15,15A, and15B, the fastener42may include a seam utilizing a first thread150and a second thread150A. The seam cutter includes a case240having substantially continuous guide422through which the actuatable material646passes. The crimps436substantially fix the portion of the actuatable material646extending from the case240to the cutting mechanism430. The cutting mechanism430is slidably engaged with the case240such that one or more cutting mechanism apertures154substantially align with one or more case apertures158when the actuatable material646is not actuated. When the actuatable material646is actuated, its length decreases, thereby sliding the cutting mechanism430within the case240and misaligning the cutting mechanism apertures154and the case apertures158. The misalignment of the apertures154,158causes the fastener42passing through the apertures154,158to be pinched between the case240and the cutting mechanism430, thereby substantially weakening or fracturing the fastener42.

It is recognized that the cutting mechanism430may be of any suitable configuration. As a non-limiting example, rather than having one or more cutting mechanism apertures154that misalign with the one or more case apertures158, the cutting mechanism may have a ladder-type configuration. In such an embodiment, the fastener42passes between the ladder “rungs” when the actuatable material646is not actuated. When the actuatable material646is actuated, the cutting mechanism430slides with respect to the case240and the ladder rungs align with the case apertures158, thereby substantially weakening or fracturing the fastener42.

FIG. 17depicts a flow diagram of an embodiment of a method of activating an airbag system10,110having an airbag housing14with a cavity22configured to store an airbag30deployable by an airbag inflator82. The cavity22has an aperture26, which provides an outlet for the airbag30during deployment, and a cover34,134,234,334releasably attached over the aperture26via an attachment mechanism38,138,238,338,438,538,638having an initial attachment strength. The method generally includes receiving a release signal at the attachment mechanism38,138,238,338,438,538,638, as depicted at reference numeral164and reducing the initial attachment strength to a release attachment strength in response to the receipt of the release signal at the attachment mechanism38,138,238,338,438,538,638, as depicted at reference numeral166. The method also includes receiving a deployment signal at the airbag inflator82, as depicted at reference numeral170and deploying the airbag30via the aperture26, as depicted at reference numeral174.

As used herein, the term “fracture” is to be interpreted broadly to include any form of break. Non-limiting examples of means of fracturing include cutting, tearing, separating, softening and stretching to create one or more gaps, and/or melting. Furthermore, “at least weakening” the fastener42,142,242,342,442,542,642is to be interpreted as decreasing the strength of, as well as fracturing, the fastener42,142,242,342,442,542,642.