Abstract:
An energy absorbing airbag system includes one or more vent valve assemblies for controlling the release of airbag inflation gases to maintain inflation gas pressure within an airbag at a substantially constant pressure during a ride-down of an energy absorbing event. Each vent valve assembly includes a cantilever spring that is flat in an unstressed condition and that has a free end portion. The cantilever spring is secured to an exterior surface of the airbag housing and flexed to cause the second free end portion of the cantilever spring to be pressed, with a preset force, against a vent port or a closure covering the vent port to seal the vent port until inflation gas pressure within the airbag reaches a preselected value determined by the preset force whereupon the free end portion of the cantilever spring is lifted from the vent port by the inflation gases within the airbag to vent the inflation gases from within the airbag. The resilience of the cantilever spring maintains a substantially constant pressure within the airbag during a ride-down portion of an energy absorbing event by causing the cantilever spring to vent gases through the vent port whenever the pressure of the inflation gases reaches the preselected value and by causing the cantilever spring to close the vent port whenever the pressure of the inflation gases falls below the preselected value.

Description:
The U.S. Government has certain rights with respect to this invention, as provided for by the terms of NASA Contract 99011, dated Dec. 14, 1998. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to devices or systems for improving the performance of airbags, and specifically to pressure-control devices that retain and release the inflation gases in a controlled manner and are further capable of quickly venting the gases when necessary. 
     BACKGROUND OF THE INVENTION 
     The first airbag systems for automobiles were developed in the 1970&#39;s. Since then, airbag systems have saved lives and prevented or reduced serious injury in numerous automobile crashes. Statistically, the effectiveness of airbag systems is without question. The success of airbag systems has also prompted their use in areas other than automobiles. In recent years, airbag systems have been developed for helicopters and general aviation aircraft. Airbags are also being used in various recovery systems, as energy absorbing devices, to reduce the landing impact of aircraft escape capsules, rockets or other space vehicles, and to reduce the landing impact of military cargo drops. Despite several years of development, improvement, and widespread use of airbag systems, problems still remain. 
     Where airbags are used for vehicle recovery or for cargo drops, problems are primarily related to poor efficiency, and therefore to excessive bag height which can result in payload rollover. In such uses, airbag performance requirements are generally described by the maximum impact force permitted (deceleration) and the mass and velocity of the payload at touchdown. Maximum efficiency is achieved when the system operates at a constant deceleration force slightly less than the maximum permissible deceleration force. This results in the minimum possible distance over which the kinetic energy of the payload can be absorbed. 
     When airbags are used for vehicle occupant protection, system efficiency is also very important. Of greater concern however, are system performance, reliability and safety considerations. Although a statistically small number, there have been some incidents where the airbag caused severe injury or even death. Many of these incidents have occurred in what is commonly called an out of position situation (OOPS). Simply stated, the occupant is too close to the airbag when the airbag deploys. 
     Some of the airbag induced injuries are due to crash sensor systems which do not adequately discriminate between crashes and minor impacts. 
     Some injuries are due to the very aggressive airbag developed in the United States because of requirements for protecting occupants not wearing lap and shoulder belts. The less aggressive airbags developed in Europe, where unbelted occupants are not a design concern, inflict fewer injuries. However, even with perfect sensors and less aggressive airbags, some out of position occupants would still be injured. 
     Some other airbag induced injuries relate to the wide variation in occupant size and weight. Conventional airbag systems are designed to produce a fixed set of performance parameters, e.g. inflation time, initial pressure, and venting. This set of parameters is intended to protect the widest possible range of occupant sizes. Unfortunately, the system may not provide adequate protection for a very large occupant and conversely, may be injurious to a very small individual. 
     These cases of airbag injury have attracted considerable media attention, especially when children are involved. This negative publicity has somewhat overshadowed the benefits of airbags, and has caused a fear of airbags among some vehicle owners. Some are even opting to have a lockout switch installed so the airbag system can be completely turned off. Doing so will indeed prevent airbag induced injuries but, unfortunately, the vehicle occupants are also forfeiting any possible benefits of the airbag system. 
     A unique problem also exists in the present U.S. Army cockpit airbag system (CABS) for Blackhawk, Seahawk, and Kiowa helicopters. These airbag systems are not vented like auto airbag systems are vented. The reason is that the typical crash scenario is much more protracted (e.g. tree strikes prior to ground impact or effects of very rough terrain) so a longer period of bag inflation is required. Therefore, the design and production of the inflator must be very precise to achieve the proper initial pressure. This is particularly difficult to achieve under the temperature extremes in which these helicopters operate. In very cold temperatures, the inflator must provide a certain minimum bag pressure for crew member protection. Unfortunately, in some instances, similar inflators may cause bag ruptures during high temperature use. 
     Another problem with conventional airbag systems is their size and bulk. This is particularly true of passenger airbag modules. Typical airbags must be larger than their ideal size because of their relatively inefficient fixed vent design. The “oversize” bags then require bulky modules for stowage and increase chances for airbag induce injury. 
     An ideal airbag system would inflate to a pre-determined pressure, provide an acceptable level of deceleration for the occupant, and maintain that deceleration at a nearly constant value during a crash event. The system would be adjustable to provide the proper deceleration for various size occupants. It would also have the ability to prevent serious injury to any occupant, by venting a large amount of propellant gases very early in the inflation cycle if the occupant is too close to the airbag. In contrast, a typical automotive airbag module only has nonadjustable vents in the airbag fabric. This conventional approach of “one size fits all”, presents obvious compromises relative to occupant size and crash situation. Also, having vents in the airbag fabric requires that the airbag must unfold before any gas flow can reach the vents. In a very close OOPS, all of the inflation gases are confined in the airbag module creating a very high pressure, and therefore, a potentially hazardous force on the occupant. 
     The high media publicity focused on these problems (especially those in the public domain) has prompted numerous proposed solutions. Many of these proposed solutions address a “depowered” airbag, which will deploy with less velocity. This approach can reduce the incidence and severity of airbag induced injuries in minor crashes, but may also compromise the performance of the airbag system in severe crashes. 
     In proper system operation, the airbag inflates before the occupant enters the area that will be occupied by the airbag. A design rule of thumb, that has appeared in the literature over the years, is that the airbag must be fully deployed before the occupant has moved forward (due to crash acceleration) more than 5 inches from the normal sitting position. Some crash sensors perform this calculation and do not fire the inflator if the criterion is not met. While this prevents possible airbag induced injury, it follows that any benefit that might have been provided by the airbag has also been defeated. 
     Other proposals include a great variety of sensors intended to detect the size and position of seat occupants (especially the passenger) and microprocessor circuitry programmed with appropriate logic to control airbag deployment. Depending on the specific crash situation, these “smart airbag systems” may deploy using the full power of dual inflators, deploy with less force by using only one inflator, or not deploy at all. Again, if the system does not deploy, any possible benefit during a crash event has been forfeited. 
     Considerable research on improving the efficiency of cargo drop airbag systems has been conducted or sponsored by U.S. Army Soldier Systems Command, Natick, Mass. Numerous studies have been conducted with airbags having fixed exhaust vents. Studies have been conducted with various auxiliary devices. One such system involved injecting compressed air into an airbag while the airbag was being compressed. Another system, described in ASME Paper No. 091-WA-DE-1, uses a servo-controlled, mechanical sliding vent closure to affect greater system efficiency. A recent research program conducted by Warrick and Associates Inc. (ref. U.S. Army Soldier Systems Command, Natick, Mass., Contract No. DAAK-97-C-9204) has also demonstrated the efficiency advantages of maintaining a constant “ride-down” pressure in a cargo-drop airbag system. That system utilizes a pneumatic pilot-pressure feed back loop with flexible diaphragm valving. Although the size and complexity of such systems are not appropriate for personnel protection in passenger vehicles, the concept of using venting control to improve airbag efficiency has been clearly validated. 
     SAE Technical Paper Series Number 980646, “An Innovative Approach to Adaptive Airbag Modules” by Ryan, describes a valve developed to control the gas going into the airbag rather than controlling the gas exiting the airbag. Depending upon crash severity determinations made by the crash sensor, some gas may be diverted at the time of airbag inflation. 
     U.S. Pat. No. 5,219,179 to Eyrainer describes airbag valves which are essentially burst discs. These valves simply open at a pressure which is selected at the time of design. After opening, these valves function as fixed vents much the same as conventional airbags. 
     U.S. Pat. No. 5,310,215 to Walner shows conventional fixed vents overlying deflectors to minimize injury to the occupant. There is no provision for maintaining constant pressure. 
     U.S. Pat. No. 5,489,117 to Huber shows reed valves designed to operate at a very low pressure, and these valves are used to allow aspiration of ambient air during the inflation process. Although vent control is disclosed, the vent valves are designed to provide only two levels of fixed vent area and have no provision for maintaining a constant pressure. 
     U.S. Pat. No. 5,505,485 to Breed shows a spring-biased cover as “ . . . vent means . . . for deflating said airbag”. There is no mention of the cover&#39;s purpose being other than a means of quickly venting the “excess” gases. There is no specific mention of controlled venting, and indeed, it seems obvious that the cover could not serve such a purpose. The spring tabs shown would have a spring constant much too high. It appears that the cover simply remains closed, until the selected pressure is reached, and then, swings open, bending the “spring” tabs with it. Also of importance is the fixed nature of the cover. The cover is not adjustable in any way to vary the pressure for different occupant sizes. 
     U.S. Pat. No. 5,538,279 to Link et al shows a fixed vent (or vents) initially closed by a cover flap. The text repeatedly states that the cover will only open the vent port(s) after a pre-determined pressure is reached, but there is no attempt to explain how that occurs. It appears that the cover flap does little more than aerially distribute and re-direct the exhaust gases. 
     U.S. Pat. No. 5,603,526 to Buchanan shows fixed vents in the bag fabric, which are initially closed by frangible coverings. Functionally, this is very similar to the Eyrainer patent, previously referenced, and is apparently unique only in detail construction. 
     U.S. Pat. No. 5,695,214 to Faigle et al shows various methods of pre-selecting different fixed vent openings. Several devices are shown, including hinged doors, deformable doors, and explosive rivets or bolt releases. In all cases, once a vent-area setting has been selected, the vent area remains constant throughout system operation regardless of pressure. 
     U.S. Pat. No. 5,707,078 to Swanberg et al shows a mechanical valving system that pre-selects exhaust vent area, and simultaneously selects flow area from the inflator into the bag. As with the Faigle patent above, once the vent area is selected, the vent area remains constant throughout system operation. 
     U.S. Pat. No. 5,709,405 to Saderholm et al shows another mechanical means of pre-selecting flow area to control mass flow into the bag. 
     U.S. Pat. No. 5,853,192 to Silkorski et al shows yet another means of pre-selecting vent area with hinged doors and latches. 
     Although their purposes are stated somewhat differently, these last four patents, to Faigle, Swanberg, Saderholm and Silkorski, all do essentially the same thing. Their pre-set vents act as proportioning devices, wherein a portion of the inflation gases is directed toward the airbag while the remainder is directed to atmosphere. In all of these cases, where vent area is pre-selected as a result of various sensors, the areas selected are based on a presumed or anticipated inflator output. Even if it were possible to perfectly measure the critical variables and correctly discriminate the crash conditions, system performance would be vulnerable to inflator variations because no means of actual pressure control is provided. Elimination of inflator-specific variations is virtually impossible because of manufacturing tolerances and the effects of variable environmental conditions. 
     SUMMARY OF THE INVENTION 
     The present invention is a flat cantilever vent valve system for significantly improving airbag performance. Individual vent valve units, located on the outside of an airbag module, provide the necessary total vent area to controllably release inflation gases following deployment of the airbag. The vent valves are normally closed, and are preset to open only at a pre-determined pressure (a venting pressure). Preferably, this preset venting pressure is adjustable and is preset according to the occupant size. In a crash event, a crash sensor triggers ignition of the inflator; the airbag module cover is forced open; and the airbag inflates. During this process, the vent valves retain inflation gases until the airbag fully inflates. Impact of the occupant into the airbag (due to crash acceleration) compresses the airbag causing the internal airbag pressure to rise. As the pressure of the gases within the airbag exceeds the preset venting pressure value of the vent valves, the vent valves open to release the inflation gases. Conversely, as the forward motion of the occupant slows, due to deceleration, the displacement rate slows and the vent valves close as the decreasing pressure of the gases within the airbag approaches the preset venting pressure value of the vent valves. 
     There are two primary advantages to the operation just described. First, the ability of the vent valves to relieve pressure within an airbag above a preset limit protects the occupant from excessive and potentially injurious deceleration during a crash. Secondly, maintaining a relatively constant pressure throughout ride-down provides a higher degree of energy absorption efficiency than with a conventional airbag system. This higher efficiency results in a shorter ride-down distance to absorb the energy of a given crash event. Therefore, for a given degree of protection, a smaller airbag can be used with the system of the present invention than would be required for a conventional airbag system or, in other words, with this higher efficiency, the use of a conventional size airbag in the system of the present invention would provide protection in more severe crashes than with present airbag systems. 
     Another advantage of the preferred vent valve system of the present invention is its adjustability for occupant size. For any given airbag system and crash situation, it takes more force (and therefore higher pressure) to stop a large occupant at an acceptable level of deceleration than it does for a small occupant. The adjustment feature of the present preferred vent valve system allows the airbag to function at similar efficiencies in both cases. 
     A further significant advantage of the vent valve system of the present invention is the ability of the vent valve system to protect the occupant during an OOPS. As mentioned above, the vent valves open when subjected to inflation gas pressures above the vent valves&#39; preset venting pressure value. Since the vent valves are located in the airbag housing near the inflator, the vent valves are available for venting immediately in the inflation cycle. This is especially advantageous in the case of a severe OOPS (occupant very close to the airbag module). Whatever the position of the occupant, if the airbag attempts to deploy but strikes the occupant, the resulting resistance will cause the inflation pressure to rise to the preset valve venting pressure level. The vent valves will open and vent the excess gases, thus, minimizing the force on the occupant. 
     A further advantage of the vent valve system of the present invention is its simplicity and flexibility. In the preferred embodiment of the invention, individual valve assemblies can be attached to the outside of various sizes and shapes of airbag modules. The parts themselves, utilize common materials, and can be easily produced using conventional manufacturing equipment and processes. Vent valve size can be easily adapted to a particular airbag application. Depending on the physical limitations of an installation, a small number of larger vent valves could be used, or conversely, a larger number of smaller vent valves could be used. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is an isometric view of a generic airbag module having a plurality of simple, flat cantilever vent valves, wherein the valves are not adjustable. The module cover is partially cut away to show a stowed airbag. 
     FIG. 1B is a partial cross-section view of the module of FIG. 1A, and shows a single flat cantilever vent valve mounted on the module housing. The airbag and module cover are not shown. 
     FIG. 2 is an exploded view of an adjustable flat cantilever vent valve. 
     FIG. 3 is an exploded view of an adjustable flat cantilever vent valve that also includes an intermediate member to enhance preset venting pressure accuracy. 
     FIG. 4A is a partial cutaway view of an adjustment mechanism for adjusting the preset venting pressure of a flat cantilever vent valve that can be used on round airbag modules. The adjustment mechanism is shown in its lowest pressure setting position. 
     FIG. 4B shows the adjustment mechanism of FIG. 4A in its highest pressure setting position. 
     FIG. 4C is a partial isometric view of an airbag module, shown to further illustrate the function of the cam ring shown in FIGS. 4A and 4B. The vent valves, as well as other details are not shown. 
     FIG. 5A shows an adjustment mechanism, for adjusting the preset venting pressure, which may be used when the vent valves are installed on a square or rectangular airbag module. The adjustment mechanism is shown in its lowest pressure setting position. 
     FIG. 5B is the adjustment mechanism of FIG. 5A, shown in its highest pressure setting position. 
     FIG. 5C shows a rotating fulcrum adjustment mechanism for adjusting the preset venting pressure. The fulcrum mechanism is shown applied to a fixed vent valve, such as illustrated in FIG. 1, but can also be applied to adjustable valves such as those illustrated in FIGS. 2 and 3. 
     FIG. 6A shows an alternate preferred embodiment of the flat cantilever vent valve, wherein the components can be pre-assembled, calibrated, and furnished as a kit for installation on various airbag modules. 
     FIG. 6B is an exploded view further illustrating part of the valve shown in FIG. 6A and, specifically, showing the assembly of the actuating cam, which adjusts the preset venting pressure, to the valve base. 
     FIG. 7 shows a mechanism for blocking the vent ports during the initial pressure spike phase of airbag deployment. 
     FIG. 8A is a schematic diagram representing a system using a manual adjustment. 
     FIG. 8B is a schematic diagram of a system having an automatic (sensor controlled) adjustment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the figures, FIG. 1A illustrates a generic airbag module, having a plurality of flat cantilever vent valves  10  mounted on a housing  12 . Other module components shown in this view include an airbag  14  and a partially cut away cover  16 . 
     FIG. 1B is a partial cross section view of the module in FIG. 1A, and is taken through the centerline of a single vent valve  10  (the airbag  14  and the cover  16  are omitted from this view). The flat cantilever spring  18  of the vent valve  10  is secured to a mounting block  20  by screws  22  and a backing plate  24 . The cantilever spring/mounting block assembly is attached to the airbag housing  12  with machine screws  26 . A conventional airbag inflator  28  is shown installed in the housing  12  for reference purposes. The vent valve  10  is positioned such that, when the vent valve is closed, the cantilever spring  18  of the vent valve completely covers and seals a vent port  30 . 
     The preferred material for the cantilever spring  18  is 17-7 Precipitation Hardening Stainless steel, heat-treated to a tensile strength of approximately 300,000 pounds per square inch. Although other materials can be used for the cantilever spring  18 , 17-7 was chosen for its high strength, excellent spring properties (its flexibility and resilience or its ability to undergo flexure when subjected to a force and recover its original shape when released from the force), and corrosion resistance. The specific material used to make the mounting block  20  is not critical. However, in the interest of maintaining a reasonably low weight for the overall valve assembly, an aluminum alloy is preferred. If the mounting block  20  is made from aluminum, the surfaces of the aluminum must be anodized, or otherwise treated, to prevent galvanic corrosion between the mounting block  20  and the cantilever spring  18 . 
     In principle, the airbag system could use one of several types of relief valves, for example, a spring loaded poppet valve. However, an important advantage of the present invention is the fast response time of the vent valve  10  due to the cantilever spring&#39;s relatively low mass, flexibility and resilience. The total airbag ride-down time during a crash is typically less than 100 milliseconds. A spring-loaded poppet valve or similar valve, in combination with the relatively low pressures involved, would take far too long to respond to pressure changes because of its mass and the associated acceleration time to open or close. Mathematical approximation and test verification with the cantilever spring  18  of the vent valve  10  has indicated that the response time of the vent valve  10 , with a differential of one pound per square inch, is less than 5 milliseconds. 
     As manufactured, cantilever spring  18  of the vent valve  10  is a flat part having a width greater than the width of the vent port  30  and a length which enables the cantilever spring  18  to be secured to and extend from the mounting block  20  to a location is beyond the vent port  30 . The surface  32  surrounding the outer end of the vent port  30 , with which the underside of the free end portion  34  of the cantilever spring  18  forms a seal when the vent valve  10  is closed, is flat or planar to conform the underside of the cantilever spring  18 . The spring mounting surface  36  of the mounting block  20  is angled with respect to the flat or planar surface  32  adjacent the vent port  30  at an acute angle “a” to orient the underside of the cantilever spring  18 , where the cantilever spring  18  extends beyond the mounting surface  36 , at the desired acute angle “a” to the flat or planar surface  32  surrounding the vent port  30 . The spring mounting surface  36  of the mounting block  20  is of a proper height and spacing from the vent port  30  to cause, with the angle “a” of orientation of the underside of the cantilever spring  18 , the desired deflection of the cantilever spring  18  at the vent port  30  to set the venting pressure of the vent valve  10  at a desired preset pressure level or value. In other words, the desired deflection of the cantilever spring  18  at the vent port  30  is a function of the required preset venting pressure for a given airbag system. Although there are many permutations of the possible variables (e.g., spring length, spring thickness, vent port diameter, preset venting pressure, etc.) a simplified example follows for illustration purposes. 
     In establishing a venting pressure setting for the vent valve  10  and the other vent valve embodiments of the present invention, it is first necessary to define the circumstances for which the setting is to be used. In general, effective body mass and airbag configuration are the two main factors to be considered. For an occupant wearing a seat belt, it is common practice to assume that the effective weight (upper torso weight), to be decelerated by the airbag  14 , is approximately 30% of the total occupant weight. It is also common practice to assume an effective airbag area to be approximately 200 square inches. A 16-inch diameter airbag is approximately this size. Typically, conventional airbags have an overall diameter larger than 16 inches, and are internally tethered to form a somewhat flattened pillow. However, studies have shown that the average effective area of the occupant contacting the bag is also approximately 200 square inches. If a diameter smaller than 16 inches were to be used for the airbag, the area would have to be calculated for that diameter. Otherwise, an effective area of 200 square inches is used. Also, numerous studies have been conducted to determine injury criteria due to acceleration (or deceleration) on the human body. Even though the apparent limits of such studies may vary due to variable circumstances, it is commonly known that deceleration in the 10 G to 15 G range, in an airbag system, are well within the limits of human tolerance. Therefore, assuming a nominal weight of 60 pounds (the effective weight of an upper torso for a 180 pound adult wearing a seat belt), and a desired deceleration of 15 G provided by the airbag, it follows that the airbag must provide 900 pounds of resistance during ride-down. Further assuming that the effective area of the occupant displacing the airbag is 200 square inches, the internal airbag pressure must be 4.5 pounds per square inch (psi) to create the 900 pounds of ride-down resistance. Therefore, the desired preset venting pressure for the vent valve  10  and other embodiments of the vent valve of the present invention, for a seat belted adult weighing about 180 pounds, is approximately 4.5 psi. 
     To determine the load and deflection characteristics of the cantilever spring  18 , it is necessary to consider the area of the cantilever spring  18  that is exposed to the desired preset venting pressure. Again referring to FIG. 1B, if the vent port  30  is assumed to have a diameter of 1¼ inches, its equivalent area is 1.227 square inches. A desired preset venting pressure of 4.5 psi, acting on an area of 1.227 square inches, creates a load of approximately 5½ pounds. Preferably, the cantilever spring  18  is of a constant width and thickness, and acts as a simple cantilever beam. The cantilever spring mounting surface  36  of the mounting block  20  is then established at a height and angle “a” such that, with a 5½ pound load, the surface surrounding the vent port  30  (the vent port surface) becomes tangent to the natural curvature of the underside of the cantilever spring  18  slightly short of the edge of the vent port  30  nearest the mounting block  20 . The remaining free portion  34  of the cantilever spring  18  (from the tangent point to its free end) lies flat on the vent port surface  32  and extends beyond the lateral edges and the far edge of the vent port  30  to seal the vent port  30  until the preset venting pressure is reached. Once the pressure within the airbag  14  reaches or exceeds the preset venting pressure, the free end portion  34  of the cantilever spring  18  lifts off of the vent port surface  32  (the vent valve  10  opens) and allows the inflation gases to escape through the vent port  30  from the airbag  14  until the pressure within the airbag  14  again drops below the preset venting pressure whereupon the free end portion  34  of the cantilever spring  18  returns to rest on the vent port surface  32  to again seal the vent port  30 . For the parameters just described, a 17-7 Stainless Steel flat cantilever spring  18  having a width of 1½ inches, an operating length (from the edge of the mounting block mounting surface  36  to the center of the vent port  30 ) of 2½ inches, and a thickness of 0.025 inches, can serve the intended purpose. Even though there are many detail configurations possible, the engineering calculations required are straightforward in accordance with common practice, and can be performed by anyone of ordinary skill in the art. 
     In actual practice, the total vent area required for any particular airbag system is a function of the airbag size, inflator output, and the resulting worst-case mass flow required of the system. That total area is achieved by using a plurality of vent valves  10 . In the case of a round airbag housing (a housing having a circular transverse cross section such as the housing  12  of FIG. 1) the vent valves  10  are typically spaced equally around the periphery of the housing if the physical limitations of the installation permit. In the case of a multi-sided airbag housing having four or more sides (a housing having a transverse cross section such as but not limited to a square, rectangular or hexagonal cross section), the vent valves  10  would be placed on one or more of the housing&#39;s flat side surfaces. 
     During a crash event, a crash sensor triggers the airbag inflation process. The vent valves  10  remain closed, retaining the inflation gases, until the airbag  14  fully inflates. As the occupant starts to compress the airbag  14  (due to forward acceleration), the vent valves  10  open when the pressure within the airbag reaches or exceeds the preset venting pressure. If the occupant&#39;s forward rate of displacement is great enough to cause a significant pressure increase, the vent valves  10  will open wider venting the gases from within the airbag  14  faster, and still maintain a relatively constant pressure. Conversely, as the occupant decelerates, the rate of forward displacement diminishes, the pressure within the airbag  14  drops and the vent valve  10  will become less open and the gases from within the airbag  14  will vent less quickly. As the pressure within the airbag  14  once again drops below the vent valves&#39; preset venting pressure, the vent valves  10  close and continue to maintain a relatively constant pressure within the airbag  14 . 
     In the case of an OOPS, the pressure within an airbag  14  will rise rapidly when the occupant blocks the deployment of the airbag. The vent valves  10  will immediately open to release the excess inflation gases from the airbag  14  and drop the internal pressure of the airbag  14 , thus minimizing potential injury to the occupant. 
     FIG. 2 shows an embodiment  40  of the vent valve of the present invention which is an independent, adjustable subassembly. As shown, a flat cantilever spring  42  of the vent valve  40  is a formed stamping having a flat free end portion  44  (like the free end portion  34  of cantilever spring  18 ) for overlaying, completely covering, and sealing a vent port  46  in a valve base  48  of the subassembly and a pair of lateral arms  50  depending from either side of the flat cantilever spring  42  for mounting the cantilever spring  42  on the valve base  48 . As with the cantilever spring  18 , the free end portion  44  of the cantilever spring  42  extends from where the vent port surface  51  surrounding the vent port  46  in the valve base  48  becomes tangent to the underside of the cantilever spring  42  to the free end of the cantilever spring. The lateral arms  50  extend parallel or generally parallel to a longitudinal centerline  52  of the cantilever spring  42  from an opposite end or adjacent an opposite end  54  of the cantilever spring  42  toward the free end portion  44  of the cantilever spring  42 . Aligned holes  56  in the free ends of the arms  50  and the lugs  58  of the valve base  48  accept a pivot pin  60  for mounting the cantilever spring  42  on the valve base  48  so that the cantilever spring  42  pivots about an axis: a) oriented perpendicular to the longitudinal centerline  52  of the cantilever spring  42  and parallel to planes containing the major upper and lower surfaces of the cantilever spring, and b) located intermediate the free end portion  44  and the opposite end  54  of the cantilever spring  42 . The pivot pin  60  is held in place by flattening the ends of the pin after assembly, or by any other acceptable retention means. 
     As with the flat-form cantilever spring  18  of FIG. 1B, the preferred material for the formed spring  42  is 17-7 Precipitation Hardening Stainless Steel, heat-treated to a tensile strength of approximately 300.000 psi. The material of the valve base  48  is not critical, but in the interest of minimal weight and reasonable strength, machine-grade aluminum such as 6061-T6 is preferred. The pivot pin  60  should be a high strength stainless or alloy steel. Whatever the materials, appropriate surface treatments must be applied to prevent galvanic corrosion. The valve base  48  is shown with countersunk holes  62  for assembly to an airbag housing with flat head screws. When mounted on an airbag housing, the vent port  46  in valve base  48  is centered over the vent port in the airbag housing, such as the vent port  30  in the airbag housing  12 , and becomes outer or external end of airbag housing vent port. Various attachment methods, other than screws, could be used equally as well to attach the valve base to an airbag housing, such as but not limited to riveting, clamping, welding, etc. 
     During inflation, the tip of the valve spring  42  will start to rise slightly, allowing some leakage before the vent valve  40  actually opens at its preset venting pressure. In use, where the airbag is filled with a high volumetric rate of flow produced by the inflator, a perfect seal is not essential for proper system performance. However, minimizing leakage in the pre-loaded position will minimize inflator performance requirements and thereby contribute to reductions in size and weight. FIG. 3 shows a method of preventing this initial leakage, thus improving the efficiency of the basic vent valve  40  of FIG.  2 . The vent valve subassembly  40  shown in FIG. 3 is much the same as that illustrated in FIG. 2, except, an intermediate valve seal  64  has been added between the cantilever spring  42  and the vent port  46  in the valve base  48  to serve as the primary valve closure. The intermediate valve seal  64  overlays, completely covers, and seals the vent port  46  when the vent valve is closed. The cantilever spring  42  of FIG. 3 is the same as the cantilever spring  42  of FIG. 2, except, with the intermediate valve seal  64 , a full radius end is no longer required and the cantilever spring need only be long enough to engage a dimple-like projection  66  on the valve seal  64 . A tubular section  68  is formed on one end of the valve seal  64  to provide an attachment to the pivot pin  60 . The dimple-like projection  66  of the valve seal  64  is centered with respect to the vent port  46  and projects toward the underside of the free end portion  44  of the cantilever spring  42 . The projection  66  provides a central, constant pressure point so that the valve seal  64  will always lie flat. Now during airbag inflation, the valve seal  64  remains flat and keeps the vent port  46  closed until the load, due to the inflation pressure on the valve seal  64 , overcomes the preset venting pressure or load of the cantilever spring  42 . The valve seal  64  is also a stainless steel part, but need not have the high strength or spring characteristics of the cantilever spring  42 . Therefore, a 300 Series Stainless Steel will suffice. 
     FIGS. 4A-4C show a mechanism  72  for preset venting pressure adjustment that can be applied to the vent valve  40  of FIGS. 2 and 3, if the airbag housing is a round housing, such as the airbag housing  12  of FIG.  1 . FIG. 4A shows the adjustment mechanism  72  in the lowest preset venting pressure setting, while FIG. 4B shows the adjustment mechanism  72  in the highest preset venting pressure setting. The adjustment mechanism  72  includes a cam ring  74  which is slip-fitted to the housing  12  and held in position by a plurality of guide pins  76  located in angled slots  78 . The guide pins  76  are permanently affixed to the cam ring  74 , but are free to move in the slots  78 . As shown by the arrow in FIG. 4C, a pulling action applied to a control cable  80  which is attached to a lug  82  of the cam ring  74 , rotates cam ring  74  in a counterclockwise direction and causes axial translation of the cam ring  74  toward the vent valves  40  mounted on the airbag housing  12  as the cam ring follows the slots  78 . As shown in FIGS. 4A and 4B, a surface  84  of the cam ring  74  is engaged with and maintains contact with inclined edges  86  of the mounting arms  50  of the cantilever spring  42  of each vent valve  40  intermediate the axis of the pivot pin  60  and the end  54  of the cantilever spring. As the cam ring  74  is rotated counterclockwise and moves toward the vent valve  40 , the cam ring  74 , through its contact with the inclined edges  86  of the mounting arms  50 , forces the end  54  of the cantilever spring  42  of the vent valve upward and increases the deflection of the cantilever spring  42  from the deflection shown in FIG.  4 A. This increases the pre-load force or preset force on the cantilever spring  42  of the vent valve  40  and raises the pressure required to open the vent valve  40  (raises the preset venting pressure). Conversely, when the cam ring  74  is rotated clockwise and moves away from the vent valves  40 , the movement of the cam ring  74  away from the vent valves  40  permits the end  54  of the resilient cantilever spring  42  of each vent valve to move downward toward the position shown in FIG.  4 A and decreases the deflection of the cantilever spring  42 . This decreases the pre-load force or preset force on the cantilever spring  42  and lowers the pressure required to open the vent valve  40  (lowers the preset venting pressure). 
     Although FIGS. 4A-4C illustrate a control cable  80  for the actuation means, many methods are possible depending upon the requirements of a specific installation. For example, in general aviation aircraft, a manual control can be mounted on the instrument panel and connected to the airbag module  12  by way of a rod, simple linkage or lever mechanism. A weight scale beside the control lever would indicate approximate occupant weight ranges. Making the proper setting can be an item on the pilot&#39;s pre-flight checklist. In the much less disciplined automotive operating environment, automatic adjustment would be almost mandatory. In that application, the adjustment mechanism would be servo-driven and controlled by a sensor device similar to those used in some current airbag systems. 
     FIGS. 5A and 5B show an alternate adjustment mechanism  90  that can be used on a square or rectangular airbag housing to adjust the preset venting pressures of the valves  40  of FIGS. 2 and 3. The adjustment mechanism  90  performs the same function as the adjustment mechanism  72  shown in FIGS. 4A-4C, except, this adjustment mechanism  90  uses a plurality of cams  92  mounted on a camshaft  94  to adjust the preset venting pressure of each vent valve  40 . FIG. 5A illustrates the adjustment mechanism  90  at its the lowest venting pressure setting while FIG. 5B illustrates the adjustment mechanism  90  at its highest venting pressure setting. As shown in FIGS. 5A and 5B, each cam  92  engages an underside of the cantilever spring  42  of a vent valve  40  intermediate the axis of the pivot pin  60  and the end  54  of the cantilever spring. As the cam  92  is rotated counterclockwise, the free end of the cam  92  moves upward and, through its contact with the underside of the cantilever spring  42 , forces the end  54  of the cantilever spring  42  upward thereby increasing the deflection of the cantilever spring  42  from the deflection shown in FIG.  5 A. This increases the pre-load force or preset force on the cantilever spring  42  of each vent valve and raises the pressure required to open the vent valve  40  (raises the preset venting pressure). Conversely, when the cam  92  is rotated clockwise and the free end of the cam moves downward, the downward movement of the cam  92  permits the end  54  of the resilient cantilever spring  42  of each vent valve  40  to move downward toward the position shown in FIG.  5 A and decreases the deflection of the cantilever spring  42 . This decreases the pre-load force or preset force on the cantilever spring  42  and lowers the pressure required to open the vent valve  40  (lowers the preset venting pressure). Typically, a plurality of vent valves  40  are placed on one or more flat surfaces of an airbag housing. Individual cams  92  on a common camshaft  94  would operate all of the vent valves mounted on a common surface. Control considerations discussed above in connection with the adjustment mechanism  72  of FIGS. 4A-4C also apply to adjustment mechanism  90 . 
     FIG. 5C shows an adjustment mechanism  100  for adjusting the preset venting pressure of the vent valves of FIG. 1A,  1 B,  2  or  3 . While the adjustment mechanism  100  can be used with the vent valves  40  of FIGS. 2 and 3, the adjustment mechanism is shown in use with the vent valve  10  of FIGS. 1A and 1B. The adjustment mechanism  100  includes an adjustable fulcrum device  102  which acts as a cam to press down on the upper surface of the cantilever spring  18  intermediate the cantilever spring mounting surface  36  of the mounting block  20  and the free end portion  34  of the cantilever spring  18 . As the fulcrum device  102  is rotated to press downward on the upper surface of the cantilever spring  18  with more force, the preset venting pressure of the vent valve  10  is increased due to greater cantilever spring deflection. As the fulcrum device  102  is rotated to press downward on the upper surface of the cantilever spring  18  with less force, the preset venting pressure of the vent valve  10  is decreased due to lower cantilever spring deflection. The fulcrum device  102  can also be used on the vent valves  40  by locating the fulcrum device  102  to press down on the upper surface of the cantilever spring  42  intermediate the axis of the pivot pin  60  and the free end portion  44  of the cantilever spring  42 . As the fulcrum device  102  is rotated to press downward on the upper surface of the cantilever spring  42  with more force, the preset venting pressure of the vent valve  40  is increased due to greater cantilever spring deflection. As the fulcrum device  102  is rotated to press downward on the upper surface of the cantilever spring  42  with less force, the preset venting pressure of the vent valve  40  is decreased due to lower cantilever spring deflection. 
     The fulcrum device  102  is mounted on a shaft  104 , which is in turn suspended in a bracket or pair of brackets  106  mounted on the module housing. The fulcrum device  102  itself can be of various shapes such as but not limited to triangular, as shown, an elliptical cam, or any other shape that will provide the desired deflection in the cantilever spring  18  or  42 . 
     The above adjustment mechanisms are a few examples of the adjustment mechanisms that can be used to control the preset venting pressures of the vent valves of the present invention. The actual adjustment mechanisms used for a particular application is dependent on the requirements of the particular installation. The cantilever springs themselves can be of various shapes, and can be adjusted in various ways. There may also be circumstances where it is desirable to use the adjustable fulcrum in FIG. 5C in combination with the formed valve spring and adjustment systems in either FIGS. 4A and 4B or  5 A and  5 B. Once this specification has been read, other devices or combinations of devices might easily be created by anyone of ordinary skill in the art. Of primary importance with regard to the preferred embodiments of the present invention is that the vent valve must be adjustable to provide the proper preset venting pressure for different size occupants. 
     FIG. 6A shows another variation  108  of the vent valve of the present invention wherein the vent valve  108  can be pre-assembled, calibrated, and furnished as a kit for installation on various airbag modules. The cantilever spring  110  of the vent valve  108  and the mounting of the cantilver spring on the valve base  112  of the vent valve  108  is like the vent valve  40  of FIG.  2 . The valve base  112  is like to the valve base  48 , shown in FIGS. 2 and 3, of the vent valve  40 , except for an extension  114  which has an integral pair of lugs  116  for mounting an actuating cam  118 . This arrangement is further clarified by the exploded view in FIG. 6B, which shows the relationship and method of mounting the actuating cam  118  the valve base  112 . A cam shaft  120  passes through a tubular section  121  of the actuating cam  118  and aligned holes  122  in the mounting lugs  116  to pivotally secure the actuating cam  118  to the valve base  112 . The cam shaft  120  has a small flattened portion  124  which, when assembled, matches the location of a threaded hole  126  in the actuating cam  118 . At assembly, a set screw  128  is tightened firmly against the flat area  124 , so that input torque from the actuating mechanism or arm  130  will reliably rotate the cam  118 . 
     The vent valves of the present invention, as previously described, can either be manufactured and assembled to airbag modules, or furnished as kits independent of airbag systems and module design and manufacture. Depending on the airbag system manufacturer&#39;s requirements, kit parts can be identified and furnished as a bag of loose parts or pre-assembled, as discussed above. Numerous variables may be considered and incorporated into the kits depending on the user&#39;s needs. For example, vent valves may be designed for bolting, riveting, crimping, clamping, or welding to the airbag module. Actuating methods and mechanisms may vary also depending on specific intended installations. Pre-set venting pressure ranges, and even vent port sizes, may also vary depending on specific system requirements. 
     FIG. 7 shows another mechanism  140  to increase the efficiency of the vent valve system of the present invention. When an airbag deploys, an initial pressure spike occurs. This is caused by a resisting force imposed by the module cover, by the inertia of the airbag fabric, and by any resistance to unfolding. Some locking of the folds also occurs as parts of the airbag inflate (gas fails to pass through the folds and pressure in the inflated section of the airbag pinches the folds tighter). Since the vent valves of the present invention have a very short response time, the vent valves will briefly open as this pressure pulse occurs. This brief opening and associated leakage is acceptable for most applications, but an optimum design would minimize or eliminate this opening. Doing so will conserve gas, and minimize the required size and weight of the inflator. The mechanism  140  includes a sleeve  142 , a tubular part with a circular or generally circular transverse cross section, which is permanently attached to an airbag retainer  144  to form a sliding canister  146 . The sliding canister  146  holds a portion of the airbag fabric which is folded and packed within the sliding canister  146 . The remainder of the airbag (not shown) is packed in an extended portion of the housing  148 , and is held in place by the module cover (not shown). The sliding canister  146  is shown in its pre-inflated position with the sleeve  142  completely covering a vent port  150 . The airbag retainer  144  of the sliding canister is located a short distance from the inflator  152  to prevent intimate contact between the airbag fabric and the inflator  152 , and to provide some initial volume for the gases from the inflator. During the inflation cycle, initial pressure is confined to the initial volume surrounding the inflator  152 . This pressure acts upon the entire cross section area of the sliding canister  146  (and the packed airbag), and forces everything toward the exit of the airbag module (toward the left as shown in FIG.  7 ). As this motion proceeds, the airbag fabric will be compressed slightly, and the cover will be forced open. Then, as the initial pressure spike subsides, further movement of the sliding canister  146  uncovers vent ports  150 , allowing the vent valves of the present invention, such as but not limited to the vent valve  40  shown in FIG. 7, to control vent flow of inflation gases. When the vent ports  150  are fully open, the canister  146  stops against shoulder  154 , and the airbag continues to deploy. Even though the vent ports  150  are initially closed, the vent valves  40  can still protect against a severe OOPS (occupant very close to the airbag module) because the canister motion required to open the vent valves is very short. Also, if the airbag were to strike an occupant during the very early stage of deployment, the inflation gases only act on an effective area equal to the cross section of the housing bore. The resulting force is much less than if the airbag were partially inflated, thus minimizing potential injury to the occupant. Even though this pressure blocking arrangement is described relative to a round airbag housing, the same principle may be applied to square or rectangular modules. All that is necessary is to provide a sliding canister, similar to the canister  146 , just inside the module housing that conforms to the interior transverse cross section of the module housing. 
     FIGS. 8A and 8B are schematic diagrams to illustrate possible system arrangements, the first with a manual control, the latter with a sensor/servo control. Even though round airbag modules with cam rings are indicated, there are many other possible system arrangements and variations that could be designed by anyone of ordinary skill in the art once that person has read this specification. 
     In describing the invention, certain embodiments have been used to illustrate the invention and the practices thereof. However, the invention is not limited to these specific embodiments as other embodiments and modifications within the spirit of the invention will readily occur to those skilled in the art on reading this specification. Thus, the invention is not intended to be limited to the specific embodiments disclosed, but is to be limited only by the claims appended hereto.