Abstract:
A soft-surface inflatable knee bolster airbag system which provides a soft surface to impact the vehicle occupant&#39;s legs and knees, uses a fixed load distribution panel to provide the necessary support to prevent sliding, is simple, easy to fabricate, and offers flexibility in the design of vehicle interiors. The soft-surface inflatable knee bolster airbag system includes a load distribution panel, an airbag curtain, an inflator configured to inflate the airbag curtain, and a housing for storage of the airbag curtain and the inflator. The airbag curtain configured such that upon inflation the airbag curtain is oriented parallel to the load distribution panel. This positioning utilizes the load distribution panel as support for the inflated airbag curtain which is absorbing the impact force imposed by the vehicle occupant&#39;s lower extremities.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. The Field of the Invention  
           [0002]    The present invention relates to airbag inflation systems in motor vehicles. More specifically, the invention relates to a soft-surface airbag for closing the space between an vehicle occupant&#39;s knees and the load distribution panel of a knee bolster.  
           [0003]    2. Technical Background  
           [0004]    Inflatable airbags are well accepted for use in motor vehicles and have been credited with preventing numerous deaths and accidents. Some statistics estimate that frontal airbags reduce the fatalities in head-on collisions by 25% among drivers using seat belts and by more than 30% among unbelted drivers. Statistics further suggest that with use of a combination of seat belt and airbag, serious chest injuries in frontal collisions can be reduced by 65% and serious head injuries by up to 75%. Airbag use presents clear benefits and vehicle owners are frequently willing to pay the added expense for airbags.  
           [0005]    A modem airbag apparatus may include an electronic control unit (‘ECU’) and one or more airbag modules. The ECU is usually installed in the middle of an automobile, between the passenger and engine compartments. If the vehicle has a driver airbag only, the ECU may be mounted in the steering wheel. The ECU includes a sensor which continuously monitors the acceleration and deceleration of the vehicle and sends this information to a processor which processes an algorithm to determine if the vehicle is in an accident situation.  
           [0006]    When the processor determines that there is an accident situation, the ECU transmits an electrical current to an initiator in the airbag module. The initiator triggers operation of the inflator or gas generator which, in some embodiments, uses a combination of compressed gas and solid fuel. The inflator inflates a textile airbag to impact a passenger and prevent injury to the passenger. In some airbag apparatuses, the airbag may be fully inflated within 50 thousandths of a second and deflated within two tenths of a second.  
           [0007]    An airbag cover, also called a trim cover panel, covers a compartment containing the airbag module and may reside on a steering wheel, instrument panel, vehicle door, vehicle wall, or beneath the dash board. The airbag cover is typically made of a rigid plastic and may be forced open by the pressure from the deploying airbag. In deploying the airbag, it is preferable to retain the airbag cover to prevent the airbag cover from flying loose in the passenger compartment. If the airbag cover freely moves into the passenger compartment, it may injure a passenger.  
           [0008]    Airbag apparatuses have been primarily designed for deployment in front of the torso of an occupant between the upper torso of an occupant and the windshield or instrument panel. Conventional airbags, such as driver&#39;s or passenger airbags (hereinafter referenced as the “primary airbag”), protect the occupant&#39;s upper torso and head from colliding with a windshield or instrument panel.  
           [0009]    Airbag apparatuses are generally designed under the assumption that the occupant is riding in the vehicle in a forward facing, seated position with both feet on the vehicle floor. When an occupant is not in this position, the occupant or occupant&#39;s body part is said to be ‘out of position.’ As an occupant occasionally is ‘out of position’, airbag apparatuses which effectively restrain the occupant regardless of the occupant&#39;s position are advantageous.  
           [0010]    During a front end collision, if the occupant is restrained by a seat belt, the occupant&#39;s upper torso bends at the waist and hits the primary airbag. However, depending on the design of the vehicle seat and force of the collision, there is a tendency for an occupant to slide forward along the seat and slip below the primary airbag, falling to the feet and leg compartment of the vehicle. Alternatively, the legs and knees of the occupant may slide or shift to one side of the seat or the other. The tendency is pronounced when the occupant is not properly restrained by a seat belt. This tendency may be referred to as “sliding”. Sliding often causes the occupant&#39;s upper torso to bend at the waist but not in a direction perpendicular to the primary airbag. When the occupant slides, the primary airbag is less effective in protecting the occupant.  
           [0011]    Sliding is more prevalent in vehicles which have large leg room compartments. Vehicles which have restricted leg room, such as sports cars, have a lower sliding tendency. In vehicles like sports cars, the distance between the legs and knees of the occupant and the instrument panel is shorter than the distance in vehicles like sport utility vehicles or trucks. In an accident in a sports car, the knees of the occupant often strike the instrument panel. The instrument panel prevents sliding. Generally, the material of the sports car instrument panel defonns to some degree to help protect the legs and knees of the occupant. The area of the instrument panel which is impacted is called the knee bolster.  
           [0012]    In order to prevent sliding in vehicles with large leg room compartments, a knee airbag system has been developed. A knee airbag system is generally positioned in the lower portion of the instrument panel. Knee airbag systems allow vehicle manufacturers to design vehicles with more leg room and still have safety comparable to that of vehicles with less leg room.  
           [0013]    The knee airbag system includes an inflator, a housing, an airbag, and a trim cover panel. The housing is a conventional enclosure for securing the knee airbag components to the vehicle. The housing stores the knee airbag system components while the airbag is deflated and not in use.  
           [0014]    The airbag provides the main structure for protecting the occupant. The bag is generally made of flexible fabric material. The material is generally a weave of nylon and/or polyester. Generally, multiple pieces of fabric are sewn together to form an airbag. Alternatively, the material may be woven to create a one piece airbag.  
           [0015]    The trim cover panel is a panel which covers the airbag and inflator within the housing and presents an aesthetic trim surface to the vehicle occupant. The trim cover panel is connected to the housing such that the pressure of the inflating airbag pushes the trim cover panel out of the way. Often, the trim cover panel is attached by a hinge on one side and a fastener on the other.  
           [0016]    The inflator, once triggered, uses compressed gas, solid fuel, or their combination to produce rapidly expanding gas to inflate the airbag. As with conventional airbag systems, a knee airbag is a large textile bag which the gas inflates like a balloon. The inflated knee airbag occupies a generally rectangular volume of the vehicle leg compartment. The knee airbag system may also include a fixed panel, called a load distribution panel (‘LDP’) or knee bolster panel. The LDP is generally made of foam and hard plastic surrounding a metal substrate. The LDP provides support to prevent sliding.  
           [0017]    Generally, two designs are used in knee airbag systems. The first design concentrates on moving a piece of rigid material or LDP, similar to the material of the instrument panel in a sports car, close to the occupant&#39;s knees and legs creating leg and knee support (‘LDP designs’.) The second design does not use an LDP. This design  19  relies on the knee airbag to provide the necessary knee and leg support. (‘Non-LDP design’)  
           [0018]    LDP designs are configured to rapidly move the LDP from a resting pre-accident position in the instrument panel to a position immediately in front of the occupant&#39;s knees and legs during an accident. These systems secure the housing behind the LDP in the instrument panel. The inflator and airbag are secured within the housing Generally, the LDP is secured to the airbag. The LDP may serve both as an LDP and a trim cover panel. Alternatively, a separate trim cover panel may be attached to the front of the LDP. Once the airbag is triggered, the inflator fills the airbag with gas. The inflating airbag pushes the LDP forward and closer to the knees and legs of the occupant. Once the airbag is fully inflated, the LDP is only a few inches from the knees and legs of the occupant.  
           [0019]    The non-LDP design relies primarily on the airbag to provide the necessary support to prevent sliding. There is no LDP between the airbag and the occupant. The knee airbag system is mounted in the instrument panel as in the previous design. Just as with a primary airbag, the inflated knee airbag comes in direct contact with the occupant. The volume of gas within the knee airbag and the attachment of the knee airbag to the housing provide the needed support. The non-LDP design is simpler but provides minimal protection from sliding.  
           [0020]    The non-LDP design is not generally as effective as the LDP design. This is because of the difficulty in using a flexible gas filled airbag to stop moving rigid legs and knees. When an inflated knee airbag, without rigid support, contacts the legs, the flexible airbag material wraps around each leg. This deformation allows each leg to travel some distance into the airbag before the volume of gas within the bag effectively stops the forward travel. This distance may be great enough that the legs of the occupant slide off the knee airbag and sliding results. If the occupant&#39;s legs are ‘out of position’ then the risk of sliding with this design is even greater. Additionally, knee airbags which present a curved surface once inflated increase the likelihood the knees and legs will slide off the airbag resulting in sliding. The flexible knee airbag lacks the rigid support necessary to prevent sliding.  
           [0021]    An improvement to the non-LDP design is to add some form of rigid support. One technique is to use rigid slats. Slats are long rectangular pieces of rigid material such as plastic, aluminum, hard rubber, and the like. The slats are sewn, woven or otherwise attached to the surface of the airbag. Once the airbag is inflated, the slats act together to present a more rigid structure similar to a LDP. The slats evenly distribute the load of the impacting legs across the whole surface of the airbag. Even distribution of the load causes less deformation of the rectangular shape of the knee airbag. The legs and knees travel less distance into the airbag. The surface of the inflated knee airbag using slats functions as a rigid structure.  
           [0022]    These designs have significant limitations. LDP designs involve complicated systems for attaching the LDP to the knee airbag. Attachment of the LDP is important because the design requires that a stable LDP be presented to the occupant&#39;s legs. Failure to do so creates the same limitations as those in non-LDP designs. LDP designs also require more parts and more skill in assembly than non-LDP designs. The attached LDP also limits the flexibility vehicle manufacturers have in designing the instrument panel. Generally, the knee airbag system must have a surface area at least the size of the LDP. But, one of the more significant limitations of LDP designs is that, although the LDP deforms on impact to some degree, the rigid LDP could cause some injury to the occupant&#39;s legs and fragile knee joints.  
           [0023]    Non-LDP designs suffer from the inefficiencies discussed above. In addition, non-LDP designs using slats present a more rigid structure but likewise may result in a more significant injury to occupant&#39;s legs and knees. The slats make the design more complicated. Non-LDP designs require more materials, and more skilled workers to assemble the knee airbag systems. Generally, each rigid slat extends the length of the surface of the inflated airbag. To accommodate the lengths of these slats the housing must be at least as long as the slats which are attached to the folded airbag stored in the housing. A dimension requirement of the housing interferes with the flexibility an instrument panel designer has in positioning the knee airbag system.  
           [0024]    Accordingly, it would be an advancement in the art to provide a soft-surface inflatable knee bolster airbag system which prevents sliding while providing a soft surface for contacting a vehicle occupant&#39;s legs and knees. A further advancement in the art would be to provide a soft-surface inflatable knee bolster airbag system which provides an even distribution of the impact force of the occupant&#39;s knees and legs by using a fixed LDP and a knee airbag. It would be another advancement in the art to provide a soft-surface inflatable knee bolster airbag system which functions even though the occupant&#39;s legs and knees are ‘out of position’. A further advancement in the art would be to provide a soft-surface inflatable knee bolster airbag system which is compact, simple, and has fewer parts. The present invention provides these advancements in a novel and useful way.  
         BRIEF SUMMARY OF THE INVENTION  
         [0025]    The apparatus of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available soft-surface inflatable knee bolster airbags. Thus, the present invention provides a soft-surface inflatable knee bolster airbag system which provides a soft surface to impact the vehicle occupant&#39;s legs and knees, uses a fixed LDP to provide the necessary support, is simple, easy to fabricate, and offers flexibility in the design of vehicle interiors.  
           [0026]    In one embodiment of the present invention, the soft-surface inflatable knee bolster airbag system includes an airbag. The airbag may take various forms, each of which provide a soft surface to engage the knees and legs of a vehicle occupant. The airbag is configured in the shape of a curtain. The inflated airbag is generally rectangular in shape and includes a plurality of long rectangular channels formed inside the airbag. Alternatively, the inflated airbag may be of a circular or polygonal shape. The channels may be formed by sewing dividing walls within the airbag. The dividing walls may be made of the same textile material as the airbag. Alternatively, the channels may be formed by weaving or welding the airbag such that a portion of the front surface is connected to a back or side surface of the airbag.  
           [0027]    The channels within the airbag may also be arranged in various configurations. For example, the channels may be in parallel horizontally or vertically or the channels may form a star shaped design inside the airbag. Alternatively, the channels may take various other shapes depending on how the interior of the airbag is divided.  
           [0028]    Alternatively, the airbag interior may be divided into a plurality of chambers formed in the same manner as the channels. The chambers may be of varied configurations while still presenting a generally flat rectangular front surface when the airbag is inflated. The airbag may be configured with chambers such that openings and holes between sealed chambers of the airbag exist. These openings and holes allow the airbag to present a soft front surface close to the occupant&#39;s legs and knees. But, the openings and holes allow the airbag to perform the soft surface presentation function using less inflator gas than without openings.  
           [0029]    The various configurations of the airbag within the scope of the present invention provide flexibility in the design of the remaining soft-surface inflatable knee bolster airbag system components. The soft-surface inflatable knee bolster airbag system further includes an inflator, a trim cover panel, and a housing. The housing stores the airbag and inflator and connects the airbag to the instrument panel of the vehicle. The trim cover panel, as described above, closes the housing and protects the soft-surface inflatable knee bolster airbag system components while in storage. The inflator is configured to quickly inflate the airbag with gas. The design of the airbag influences the design of the inflator and housing and the location of the housing within the instrument panel. Airbags with chambers and openings, as discussed above, may use smaller inflators and housings because they use less gas and take up less space in the housing. This allows the whole soft-surface inflatable knee bolster airbag system to be smaller.  
           [0030]    In the preferred embodiment, the airbag is configured such that, upon inflation, the airbag cooperates with a fixed load distribution panel (‘LDP’) to restrain the legs and knees of the occupant. The housing containing the soft-surface inflatable knee bolster airbag is located above the LDP within the lower portion of the instrument panel. Once the inflator is triggered, the inflating airbag forces open the trim cover panel and descends into the space between the occupant&#39;s lower extremities and the fixed LDP. The airbag inflates from the top side of the rectangular airbag rather than the middle of the airbag as in conventional airbag systems. Once inflated, the airbag occupies the majority of the rectangular space of the leg compartment of a vehicle and is aligned in parallel with the LDP. The rear surface of the airbag abuts the LDP and the front surface is a few inches from the occupant&#39;s knees and legs. Because the whole rectangular rear surface contacts the LDP, the soft-surface inflatable knee bolster airbag system presents a soft front surface which has substantially the same support characteristics as inflatable knee bolster airbag designs which position the airbag behind the LDP (LDP-designs). The channels within the airbag ensure that a generally planar front surface is presented to ensure the knees and legs do not slide off the knee airbag. Alternatively, the channels in the airbag may be designed to form ‘T’ shaped sections in the front surface. The channels guide the knees and legs of the occupant towards the ‘T’ shaped sections which are centrally located in the airbag.  
           [0031]    These and other features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    In order that the manner in which the above-recited and other advantages of the invention are obtained and be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention, and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:  
         [0033]    [0033]FIG. 1 is a perspective view of a vehicle instrument panel illustrating possible locations of the soft-surface inflatable knee bolster airbag system once installed within the instrument panel.  
         [0034]    [0034]FIG. 2 is a perspective view of a vehicle instrument panel illustrating a driver&#39;s side soft-surface inflatable knee bolster airbag system and a passenger&#39;s side soft-surface inflatable knee bolster airbag system following deployment.  
         [0035]    [0035]FIG. 3 is a perspective view of a vehicle instrument panel illustrating a driver&#39;s side soft-surface inflatable knee bolster airbag system and a passenger&#39;s side soft-surface inflatable knee bolster airbag system each illustrating a different knee airbag channel configuration.  
         [0036]    [0036]FIG. 4 is a cut away side elevation view of a preferred embodiment of the present invention in various stages of operation.  
         [0037]    [0037]FIG. 4A illustrates the soft-surface inflatable knee bolster airbag system prior to deployment.  
         [0038]    [0038]FIG. 4B illustrates the soft-surface inflatable knee bolster airbag system during initial stages of deployment.  
         [0039]    [0039]FIG. 4C illustrates the soft-surface inflatable knee bolster airbag system during a middle stage of deployment.  
         [0040]    [0040]FIG. 4D illustrates the soft-surface inflatable knee bolster airbag system with the airbag fully inflated and positioned.  
         [0041]    [0041]FIG. 5 is a cross-sectional view of alternative embodiments of the present invention illustrating several configurations of internal airbag chambers.  
         [0042]    [0042]FIG. 5A illustrates the alternative embodiment with internal chambers prior to deployment.  
         [0043]    [0043]FIG. 5B illustrates the alternative embodiment with internal chambers after deployment.  
         [0044]    [0044]FIG. 5C illustrates yet another alternative embodiment after deployment with internal chambers which are secured to each other to form a hole behind the front portion of the inflated airbag.  
         [0045]    [0045]FIG. 6 is a rear elevation view illustrating alternative embodiments of the present invention illustrating several configurations of airbag chambers which provide holes and/or openings behind the front surface of the airbag.  
         [0046]    [0046]FIG. 6A illustrates an alternative embodiment with openings between two chambers of the airbag.  
         [0047]    [0047]FIG. 6B illustrates an alternative inflator orientation for the embodiment of FIG. 6A.  
         [0048]    [0048]FIG. 6C illustrates an alternative embodiment with openings and holes between two chambers of the airbag. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0049]    The present invention can be better understood with reference to the drawings where like parts are designated with like numerals throughout.  
         [0050]    Reference is now made to FIG. 1 which illustrates a vehicle instrument panel  11  with indicators for the different locations of soft-surface inflatable knee bolster airbag systems  10 . A soft-surface inflatable knee bolster airbag system  10  is generally located towards the bottom portion of the vehicle instrument panel  11 . The system  10  may be installed on the driver&#39;s side to protect a driver, on the passenger&#39;s side to protect a passenger, or on both sides.  
         [0051]    Preferably, a soft-surface inflatable knee bolster airbag system  10  is compact in design and space requirements such that the system  10  fits behind a trim cover panel  12  as illustrated. Alternatively, the system  10  may also be positioned in the instrument panel  11  at a point central to a load distribution panel (‘LDP’)  14 . FIG. 1 illustrates the size of the soft-surface inflatable knee bolster airbag system  10  in relation to the other components positioned in the instrument panel  11 .  
         [0052]    Generally, it is desired that instrument panel&#39;s  11  component occupant facing surfaces  13  be as compact as possible. The vehicle design generally provides sufficient space between the front of the instrument panel  11  and the vehicle firewall (not shown) that depth of instrument panel  11  components is not an issue. Compact occupant facing surfaces  13  allow vehicle instrument panel  11  designers more flexibility in arranging the instrument panel  11  layout than they would have otherwise.  
         [0053]    The present invention has dimension requirements which offer flexibility and fit well into instrument panel  11  designs. A trim cover panel  12  conceals the main system  10  components from the occupant. The length and height dimensions of the trim cover panel  12  are representative of the front dimensions of the main components of the soft-surface inflatable knee bolster airbag system  10 . In the preferred embodiment, the trim cover panel  12  has a high length to height ratio. This means the length is considerably greater than the height. Specifically, the length is in the range of 18 to 36 inches while the height is in the range of 4 to 6 inches. These ranges result in the trim cover panel  12  of the soft-surface inflatable knee bolster airbag system  10  occupying a narrow rectangular area. Alternatively, the soft-surface inflatable knee bolster airbag system  10  may occupy various other circular and polygon shapes. Trim cover panels  12  which have dimensions meeting these ranges tend to have lengths which are about five times their respective heights.  
         [0054]    [0054]FIG. 2 illustrates the importance of the location of the soft-surface inflatable knee bolster airbag system  10 . The location of the soft-surface inflatable knee bolster airbag system  10  is directly related to the location of the LDP  14 . Preferably, the soft-surface inflatable knee bolster airbag system  10  is located directly above the LDP  14 . At this location, the airbag  16  descends under the force of gravity and the inflation force created by the inflator (not shown) such that the inflated airbag  16  is positioned directly in front of the LDP  14 . In this manner, the soft-surface inflatable knee bolster airbag system  10  utilizes the LDP  14  for structural support.  
         [0055]    Referring still to FIG. 2, the soft-surface inflatable knee bolster airbag system may be configured such that one or more chambers  18  are formed inside the airbag  16 . The chambers  18  are formed by securing the front surface  20  of the airbag  16  to the rear surface  22 . Alternatively, the front surface  20  may be secured to an interior divider which is then attached to the rear surface  22  of the airbag  16 . Securement is accomplished by common techniques in the industry including glueing, sewing, welding, and the like. As a result of securement techniques creating the chambers  18 , T-shaped depressions  26  may be formed. The securement techniques allow that the depressions  26  may have alternative shapes such as ‘L’, ‘U’, ‘H’, ‘O’, and the like. Preferably, the depressions  26  are sized to retain a proportional letter shape and extend substantially to the height of an LDP  14 .  
         [0056]    The depressions  26  cooperate with the chambers  18  to serve two purposes. First, they guide the occupant&#39;s legs and knees such that on impact the legs and knees remain in contact with the airbag  16  rather than sliding off to one side. The depressions  26  and chambers  18  aide in moving knees and legs of an occupant who is ‘out of position’ such that the knees and legs are in position at the time of impact with the airbag  16 .  
         [0057]    Second, these components reduce the volume of space between the occupant and the LDP  14  which the airbag  16  must occupy to function properly. By reducing the volume, less inflation gas is required. Therefore, the inflator  34  (See FIG. 4) may be smaller. A smaller inflator  34  allows the housing  32  (See FIG. 4) to be smaller. A smaller housing  32  means the whole soft-surface inflatable knee bolster airbag system  10  is smaller. A smaller system  10  allows more flexibility in vehicle instrument panel  11  design.  
         [0058]    [0058]FIG. 3 illustrates airbags  16  having tubes  28  formed therein. Tubes  28  are generally small long rectangular enclosures within the airbag  16 . Tubes  28  may be divisions formed within chambers  18 . Gas inflating the chamber  18  inflates all the tubes  28  through tube openings  30 . Alternatively, a first tube  28  is connected to an inflator  34  and the remaining tubes  28  are connected to each other such that gas inflating the first tube  28  inflates all the tubes  28  formed in the airbag  16 .  
         [0059]    Generally, tubes  28  are made from the same material as the airbag  16 . The tubes  28  may be formed using similar techniques to techniques used to form chambers  18 . Preferably, the tubes  28  are formed by welding or sewing two pieces of textile airbag material together. The pattern of welding or sewing is such that a compartment is formed between the two pieces of material and the perimeter of the compartment forms tubes  28  once the airbag  16  is inflated. Alternatively, the tubes  28  may be formed by weaving the tubes  28  into the airbag  16 . Upon inflation, the gas leaves the inflator  34  and enters the chambers  18 . From the chambers  18 , the gas passes through the tube openings  30  to fill each individual tube  28 .  
         [0060]    The different embodiments on the driver&#39;s and passenger&#39;s side of the vehicle instrument panel  11  in FIG. 3 illustrate airbags  16  having one or more tubes  28 . The tubes  28  may be organized in various configurations. In the inflated airbag  16  on the driver&#39;s side, the tubes  28  are aligned horizontally one above the other. Each tube  28  includes at least one tube opening  30 . A tube opening  30  is a hole in the tube  28 . Tube openings  30  may be formed when the tube  28  is formed. Alternatively, the tube opening  30  may be formed by cutting a hole in the tube  28  once the tube  28  is formed. The tube opening  30  may be located at any point along the tube  28  so long as the tube opening  30  provides fluid communication between a chamber  18  receiving inflation gas and the inside of the tube  28 .  
         [0061]    In the embodiment illustrated on the passenger&#39;s side, the tubes  28  are configured in the shape of a star. The opening  30  is positioned on the end of one of the tubes  28 . The tubes  28  interconnect at a point central to the star shape to allow inflation gas to fully inflate each tube  28 . Alternatively, the tubes  28  do not interconnect at a central point but instead have tube openings  30  on an end in fluid communication with a chamber  18 .  
         [0062]    Referring still to FIG. 3, chambers  18  cooperate with tubes  28  to provide a generally flat front surface  20  and rear surface  22  for the airbag  16 . Due to the flexible material used to make airbags  12  a conventional airbag  16  inflates to present a surface with a high degree of curve, much like the surface of a balloon. Such a high degree of curve in a knee bolster airbag context is undesirable. It is desirable to present a flat surface to accommodate different sized occupants and positions of knees and legs.  
         [0063]    A flat front surface  20  of a knee bolster engages most of the knee and lower leg at nearly the same time during impact. The tubes  28  and chambers  18  cooperate to restrain the front surface  20  and rear surface  22  of the airbag  16  upon inflation. A generally flat rear surface  22  allows the present invention to leverage the advantages of rigid LDPs  14 . The flexibility of the airbag  16  material and the interconnected tubes  28  forms an inflated airbag  16  which is flat on two sides much like a curtain.  
         [0064]    Reference is now made to FIG. 4, wherein FIGS. 4A, 4B,  4 C, and  4 D illustrate cut away side elevation views of the various stages of deployment for a soft-surface inflatable knee bolster airbag system  10 . The system  10  includes a housing  32 , an inflator  34 , an airbag  16 , a trim cover panel  12 , and a load distribution panel  14  (‘LDP’).  
         [0065]    As seen in FIG. 4A, an inflator  34  is attached to a housing  32 . The housing  32 , in cooperation with the trim cover panel  12 , stores the inflator  34  and airbag  16  until the system  10  is initiated by the electronic control unit (‘ECU’), as discussed above. The housing  32  secures a majority of the members of the system  10  to the vehicle. Housings  32  are common in the industry. A housing  32  allows the main members of the system  10  to be assembled at one location and installed in the vehicle at second location. Housings  32  may be of a generic shape, or may be designed specifically to fit the design of the lower instrument panel  11  of a particular type of vehicle. The location of the housing  32  and the functional requirements of the system  10  allow for the housing  32  to be in the shape of a long thin rectangle. Two opposing sides of the housing  32  are substantially shorter than the other two opposing sides. A long thin rectangular shape is optimal because this allows more instrument panel front surface area for other vehicle components. Alternatively, the shape may be circular or polygonal.  
         [0066]    [0066]FIG. 4A also illustrates a trim cover panel  12 . The trim cover panel  12  conceals the airbag  16  and other internal components. The trim cover panel  12  also provides a decorative appearance for the installed airbag system  10 . Generally, the trim cover panel  12  is made of pre-formed hard plastic. The trim cover panel  12  may be made of wood, metal, foam, or like materials common in the industry. The shape and size of the trim cover panel  12  generally depends on the size of the assembled airbag module and the size of the surface area within the lower portion of the instrument panel, which the housing  32  occupies. In one embodiment, the trim cover panel  12  is of a thin rectangular shape. For each vehicle model the shape, size and decor of the trim cover panel  12  may vary.  
         [0067]    The trim cover panel  12  is attached to the housing  32  by a trim cover panel fastener  36 . Alternatively, the trim cover panel  12  may be attached to the housing  32  by various fastening techniques common in the industry. Such techniques include tree clips, snaps, rivets, or the like. The trim cover panel fastener  36  must allow trim cover panel  12  to easily be moved to open the housing  32 . The housing  32  must easily open to allow the inflating airbag  16  to obtain its optimal position in the lower leg compartment of the vehicle. Preferably, the trim cover panel fastener  36  cooperates with structure for tethering the trim cover panel  12  to the housing  32  when the airbag inflates  12 . In the preferred embodiment, a trim cover panel fastener  36  configured as a hinge serves the tethering and fastening functions needed for the trim cover panel  12 .  
         [0068]    [0068]FIG. 4A illustrates the system  10  fully assembled and installed in an optimal position inside the instrument panel of a vehicle. The airbag  16  is connected to the inflator  34  which is connected to the housing  32 . These connections are made by conventional means including clamps, screws, nuts and bolts, welding, and the like. The trim cover panel  12  is fastened to the housing  32  by the trim cover panel fastener  36  embodied as a hinge. Preferably, the airbag  16  is then rolled from the unattached end toward the attached end and placed in the opening between the inflator  34  and the trim cover panel  12 . Alternatively, the airbag  16  may be folded and placed into the housing  32 . The trim cover panel  12  is then closed to keep the airbag  16  within the housing  32 . Opposite the trim cover panel fastener  36  the trim cover panel  12  may be secured to the housing  32  by wedging a lip  37  (see FIGS. 4B, 4C, and  4 D) of the trim cover panel  12  between the LDP  14  and the body (not shown) of the instrument panel  11 . The aforementioned members make up a knee airbag module  38 . The knee airbag module  38  is then installed into an instrument panel  11  as illustrated.  
         [0069]    [0069]FIG. 4B illustrates the soft-surface inflatable knee bolster airbag system  10  and its members at a beginning phase of deployment of the airbag  16 . The electronic control unit (‘ECU’ not shown) has signaled the inflator  34  to inflate the airbag  16 . The inflator  34  is injecting gas into the airbag  16  at a very high velocity. As illustrated in FIG. 4B, the force F of the gas inflating airbag  16  has moved the trim cover panel  12  on its hinge, trim cover panel fastener  36 , such that the housing  32  is now open. The force F of the gas inflating airbag  16  and gravity begin to unroll the airbag  16  into the lower leg compartment.  
         [0070]    In FIG. 4C, the inflating airbag  16  is almost completely unrolled. The housing  32  is kept open by the inflating airbag  16  biasing the trim cover panel  12 . Next, the airbag  16  begins to fill with gas (not shown).  
         [0071]    [0071]FIG. 4D illustrates the position of members of the soft-surface inflatable knee bolster airbag system  10  prior to and including the point when the airbag  16  is completely inflated. The inflated airbag  16  is positioned in front of a LDP  14 . The generally flat front surface  20  and rear surface  22  of the inflated airbag  16  utilize the characteristics of the LDP  14 .  
         [0072]    An LDP  14  provides a large rigid surface to distribute and absorb the force of the legs and knees. The large rigid surface allows less travel of the legs and knees in an accident which prevents sliding. The LDP  14  is preferably a rectangular shaped panel. Alternatively, the LDP  14  may be a thin rigid rectangular plate, a rod having a polygonal cross-section, or other similarly shaped material. To conserve space and reduce weight, the rigid LDP  14  is preferably made as strong and as light as possible. Typically, the LDP  14  is made from wood, metal, Styrofoam®, hard plastic, or the like surrounding a metal or hard plastic substrate.  
         [0073]    The inflated airbag  16  forms a curtain or wall between the occupant and the LDP  14 . Once the occupant impacts the airbag  16 , the generally flat rear surface  22  of the airbag  16  provided by the tubes  28  and chambers  18  (See FIG. 3) contacts the LDP  14 . The generally flat rear surface  22  allows the impact force of the occupant&#39;s knees and legs on the airbag  16  to be evenly distributed across the surface of the rigid LDP  14 . An even distribution of the impact forces on the rigid LDP  14  results in less impact stress on the legs and knees of the occupant. In this way, the soft-surface inflatable knee bolster airbag system  10  provides a soft surface to impact the knees and lower legs of the occupant and evenly distributes the impact force to reduce the likelihood of injury.  
         [0074]    [0074]FIG. 5 is a cross-sectional view of alternative embodiments of the a knee airbag module  38  for use in a soft-surface inflatable knee bolster airbag system  10 . In these embodiments, the housing  32  and inflator  34  are positioned such that they are behind and central to the inflated airbag  16 . The knee airbag module  38  is preferably located substantially in the middle of an LDP  14  positioned in the lower portion of the instrument panel  11 . FIGS. 5A and 5B are, respectively, illustrate of one embodiment of a knee airbag module  38  before and after inflation of the airbag  16 . FIG. 5C illustrates an alternative embodiment of the invention.  
         [0075]    [0075]FIG. 5A illustrates a knee airbag module  38  prior to inflation of the airbag  16 . The housing  32  is connected to the inflator  34  which is connected to the airbag  16 . These connections are all of the same nature as those in FIG. 4. The airbag  16  is rolled or folded from the outer edge of the airbag  16  towards the middle of the airbag  16 .  
         [0076]    [0076]FIG. 5B illustrates the knee airbag module  38  once it is fully inflated. In this embodiment, chambers  18  are formed within the airbag  16  in the same manner as the chambers  18  described above. These chambers  18  serve to provide a generally flat front surface  20  for impacting the legs and knees of the occupant.  
         [0077]    Preferably, the knee airbag module  38  of FIG. 5B is secured inside a cavity (not shown) of an LDP  14  such that the trim cover panel  12  front surface is flush with the front surface of the LDP  14 . With the knee airbag module  38  in the preferred position, the rear surface  22  of the inflated airbag  16  will impact the LDP  14  once the occupant impacts the airbag  16 . The chambers  18  within the airbag  16  provide a generally flat rear surface  22 . The generally flat rear surface  22  allows the knee airbag module  38  to leverage the characteristics of the LDP  14  just as in the embodiment of FIG. 4.  
         [0078]    [0078]FIG. 5C illustrates an alternative embodiment wherein the airbag  16  is fully inflated. FIG. 5C has a different configuration of chambers  18  within the airbag  16  from FIGS. 5A and 5B. The inflator  34 , housing  32  and airbag  16  are connected as discussed above. The knee airbag module  38  includes a hole  40 . The hole  40  is formed by securing the front surface  20  of the airbag  16  to the inflator  34 . Securing the front surface  20  of the airbag  16  to the inflator  34  creates two chambers  18  which are connected to the inflator  34  such that gas escaping the inflator  34  fills the two chambers  18 . The two chambers  18  are then secured to each other at chamber connection  42 . Preferably, chamber connection  42  is formed by stitching an end of a first chamber  18  to an end of a second chamber  18 . Alternatively, the two chambers  18  may form a chamber connection  42  by other techniques common in the industry. These techniques include welding, glueing, and the like.  
         [0079]    The knee airbag module  38  illustrated in FIG. 5C requires less gas to inflate than conventional knee airbag modules  38 . The knee airbag module  38  still provides protection comparable to conventional knee airbag modules  38 . Knee airbag modules  38  which require less gas allow for smaller inflators  34 . This allows for smaller knee airbag modules  38  with the accompanying advantages in instrument panel  11  design flexibility as discussed above.  
         [0080]    [0080]FIG. 6 is a rear elevation view illustrating alternative designs of the airbag  16 . FIGS. 6A and 6C show alternative chamber  18  designs. FIG. 6B illustrates a different orientation of the inflator  34 .  
         [0081]    In FIG. 6A, an airbag  16  is illustrated having two chambers  18  connected by a chamber passage  44 . A chamber passage  44  is a portion of the airbag  16  between two chambers  18  which allows inflation gas to easily pass from one chamber  18  to the other. The chamber passage  44  is sized to allow unimpeded flow of gas between the two connected chambers  18 .  
         [0082]    Preferably, the two chambers  18  and chamber passage  44  are formed by welding two pieces of airbag material together along an ‘H’ shaped perimeter. The material between the legs and arms of the ‘H’ is then cut away. Alternatively, the material may be left between the arms and legs of the ‘H’. The cut away portions of the airbag form openings  46  on both sides of the chamber passage  44 . The openings  46  and chamber passage  44  together allow the airbag  16  to protect the occupant in the same space as the preferred embodiment yet require less inflation gas. The advantages of using less inflation gas are described above. Alternatively, the chamber passages  44  may be formed within the airbag  16  in a manner similar to that used to form chambers  18 , as discussed above.  
         [0083]    To achieve the orientation of the airbag  16  illustrated in FIG. 6A, the ‘H’ is turned 90 degrees. Next, a first chamber  18  of the ‘H’ is fitted to an inflator  34  such that inflation gas flows easily from the inflator  34  into the first chamber  18 . Preferably, the first chamber  18  is the bottom chamber  18 . Alternatively, the first chamber  18  may be the top chamber  18 . The chamber passage  44  allows gas to flow from the first chamber  18  into the second chamber  18 .  
         [0084]    [0084]FIG. 6B illustrates the same airbag  16  design as in FIG. 6A. In FIG. 6B, the inflator  34  is in alignment with the cross-bar of the ‘H’ rather than one side. In this embodiment, the inflator  34  is connected to both chambers  18  and the chamber passage  44 . Alternatively, the inflator  34  is connected to one chamber  18  or the other. In another alternative, the inflator  34  may be connected to a chamber passage  44  and one chamber  18 .  
         [0085]    Referring now to FIG. 6C, the idea of a chamber passage  44  is expanded to include a plurality of chamber passages  44  which form holes  48  between the outside chamber passages  44  and one or more internal chamber passages  44 . FIG. 6C illustrates three chamber passages  44 . Alternatively, there may be one or more chamber passages  44  connecting one or more chambers  18 .  
         [0086]    As in FIGS. 6A and 6B, the holes  48  serve the same purpose as the openings  46 , discussed above. Alternatively, the holes  48  may be sized and configured such that they receive the knees of an average size occupant. The holes  48  may be sized and shaped such that the knees of an average size occupant are restrained within the holes  48 . Such a configuration may prevent the knees from contacting an LDP  14  positioned behind the airbag  16 . This would further help to protect the knees of the occupant.  
         [0087]    Referring now to FIGS.  1 - 6  generally, the components described above comprise the soft-surface inflatable knee bolster airbag system  10 . In order to practice the present invention, a housing  32 , an inflator  34 , a load distribution panel (‘LDP’)  14 , and an airbag  16  are provided. The airbag  16  is a textile bag common in the industry. The airbag  16  is sized and shaped to operably position itself between the LDP  14  and an occupant&#39;s legs once inflated. The inflator  34  is secured within the housing  32 . The airbag  16  is secured to the inflator  34  or housing  32  such that the airbag  16  is in fluid communication with the inflator  34 . The airbag  16  is rolled up or folded and placed inside the housing  32 . The housing  32  is closed by a trim cover panel  12 . The LDP  14  is installed in an instrument panel  11  of a vehicle. Next, the housing  32  is secured to the instrument panel  11  directly above the LDP  14 .  
         [0088]    Operation of the soft-surface inflatable knee bolster airbag system  10  is as follows. First, a vehicle with the system  10  installed is involved in an accident. Next, the ECU signals the inflator  34  to inflate the airbag  16 . The inflator  34  begins to fill the airbag  16 . The inflating airbag  16  forces open the trim cover panel  12 . The airbag  16  fills in the space in the leg compartment of the vehicle between a LDP  14  and the occupant&#39;s lower legs and knees. Once inflated, the airbag  16  is aligned in parallel with and rests against the LDP  14 . The front surface  20  of the airbag  16  is within a few inches of the occupant&#39;s knees and lower legs. The sudden deceleration of the vehicle causes the occupant to begin to slide. The legs and knees contact the front surface  20  of the airbag  16 . The airbag  16  is pressed against the entire surface of the LDP  14 . The LDP  14  and airbag  16  cooperate to prevent the knees and legs from impacting the LDP  14 . The occupant is restrained from sliding and minimal damage to the occupant&#39;s knees and lower legs results.  
         [0089]    The soft-surface inflatable knee bolster airbag system  10  provides a soft front surface  20  for impacting the knees and legs of an occupant. Additionally, the airbag  16  occupies the space in the lower leg compartment such that the impact load is substantially evenly distributed across the LDP  14 . Furthermore, the soft-surface inflatable knee bolster airbag system  10  requires minimal front surface space in the instrument panel  11  of a vehicle.  
         [0090]    The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.