Abstract:
A knee airbag installed in a lower portion of an instrument panel has a deployed condition wherein it extends rearward and upward. The airbag has a left lobe, a right lobe, and a central portion between and joined to the left and right lobes. A vent is formed in the reaction surface of each of the lobes to allow inflation gasses to escape from the airbag when, during a crash event, an occupant force applied forwardly against the lobes is below a threshold level. When the occupant force reaches or exceeds the threshold level, the vents are urged against the instrument panel to substantially block the escape of inflation gasses. The threshold level is selected such that a child-sized occupant standing forward of a desired passenger seating position exerts less than the threshold level.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to inflatable airbags used in automotive vehicles for occupant protection, and more specifically to a knee airbag that deploys upwardly from a relatively low position on the passenger side of the vehicle. 
       BACKGROUND 
       [0002]    Most current automotive passenger vehicles include at least one inflatable airbag as part of the occupant protection system. Some proposed occupant protection systems combine an upper body airbag and a knee airbag. An upper body airbag is mounted to the instrument panel (IP) forward of a seated occupant at a relatively high position and deploys or inflates rearwardly to contact the occupant&#39;s chest or upper thorax region. A knee airbag is mounted to a lower position on the instrument panel and inflates or deploys to contact the occupant in the area of the knees and/or shins Recognized benefits of knee airbags include providing cushioning of any impact between the knees/lower legs and the lower portion of the instrument panel, as well as prevention of submarining, in which a seat occupant&#39;s hips move forwardly beneath a lap and/or chest restraint belt. 
         [0003]    Examples of such knee airbag systems include U.S. patent applications 2004/0124617 Al and U.S. 2007/0267852 Al and U.S. Pat. No. 6,712,384. The &#39;384 patent teaches that an upper body airbag and a knee airbag may be used in combination and that completing the expansion of the knee airbag earlier than the expansion of the body airbag may have benefits. 
       SUMMARY 
       [0004]    According to an embodiment of the invention disclosed herein, an occupant protection system for a vehicle comprises a knee airbag installed in a lower portion of an instrument panel and having a deployed condition wherein it extends rearward and upward to place a reaction surface of the airbag in contact with the instrument panel. The airbag comprises a left lobe, a right lobe, and a central portion disposed between and joined to the left and right lobes. At least one vent is formed in each of the lobes on the reaction surface to allow inflation gasses to escape from the airbag when, during a crash event, a forwardly-directed force applied to the airbag by the occupant against the lobes is below a threshold level. When the occupant force reaches or exceeds the threshold level, the vents are urged against the instrument panel to substantially block the escape of inflation gasses. 
         [0005]    In one disclosed embodiment of the invention, the threshold level is selected such that a child-sized occupant standing forward of a desired passenger seating position is expected to exert less than the threshold level of forward-directed occupant force. Venting of the inflation gasses prevents the airbag from inflating forcefully in order to reduce the likelihood of injury to the occupant. 
         [0006]    In another disclosed embodiment of the invention, the threshold level is selected such that an adult-sized occupant seated in the desired passenger seating position and properly restrained by a seat belt is expected to exert less than the threshold level of forward-directed occupant force. 
         [0007]    In another disclosed embodiment of the invention, an occupant protection system for a vehicle comprises a knee airbag installed in a lower portion of an instrument panel and having a deployed condition wherein it extends rearward and upward immediately adjacent to the instrument panel. The knee airbag comprises a left lobe, a right lobe, and a central portion disposed between and joined to the left and right lobes. At least one vent is formed in an instrument panel-facing surface of each lobe at positions such that the vents are urged against the instrument panel and substantially blocked when an occupant force directed forwardly against the lobes reaches a threshold level. 
         [0008]    In another disclosed embodiment of the invention, a method of protecting an occupant located forward of a desired passenger seating position (an out-of-position occupant) in an automotive, comprises inflating a knee airbag stored in a lower portion of the instrument panel to deploy upwardly between the instrument panel and the occupant. The knee airbag has a left lobe, a right lobe, and a central portion disposed between and joined to the left and right lobes, and at least one vent formed in an instrument panel-facing surface of each lobe. An occupant force directed forwardly against the knee airbag by the occupant during the crash event is below a threshold level required to substantially block the escape of inflation gasses by urging vents against the instrument panel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: 
           [0010]      FIG. 1  is a schematic view of a vehicle passenger cabin equipped with upper body airbag and knee airbag systems; 
           [0011]      FIG. 2  is a schematic view of an upper body airbag and a knee airbag in inflated conditions relative to a seat occupant; 
           [0012]      FIG. 3-A  is a cross-sectional view taken along line  3 - 3  of  FIG. 2  with the knee airbag in a venting state; 
           [0013]      FIG. 3-B  is a cross-sectional view taken along line  3 - 3  of  FIG. 2  with the knee airbag in a non-vented state; 
           [0014]      FIG. 4  is a schematic view of an out-of-position occupant with upper and knee airbags in early phases of deployment; and 
           [0015]      FIG. 5  is a downward-looking sectional view of the knee airbag and occupant of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0017]      FIG. 1  shows in schematic form the passenger cabin of an automotive vehicle  10  showing the passenger (i.e. non-driver) side of a front row seating position. A seat  12  is arranged rearward of a dashboard or instrument panel (IP)  14  in the conventionally known configuration. An occupant  16  is shown in a normal seated position in seat  12 . Seat  12  defines a desired seating position and occupant  16  is referred to as an in-position occupant when properly seated in it. 
         [0018]    An upper airbag module  18  is disposed in, on, or otherwise integrated with the IP  14  and is positioned on an upper portion of the IP so that the airbag may inflate upwardly and/or rearwardly toward the seated occupant  16 . Airbag module  18  is shown schematically to include a chest airbag  20  stored in a folded, rolled, or otherwise compacted condition, as is well known in the occupant restraints art. An inflator  22  is shown located within IP  14  a short distance away from airbag module  18  and connected with the airbag by an inflation tube  24 . Alternatively, inflator may be located immediately adjacent to airbag module  18  and discharge more directly into airbag  20 . 
         [0019]    A knee airbag module  26  is located in, on, or otherwise integrated with a lower portion of IP  14  adjacent a footwell area  28  forward of seat  12 . As is well known in the occupant restraints arts, an inflatable knee airbag  30  is stored in the module  26  in a folded, rolled, or otherwise compacted condition. Knee airbag  30  may be supplied with inflation gases by the same inflator  22  that supplies chest airbag  20 , or a separate inflator (not shown) may be provided to supply inflation gasses to the knee airbag module  26 . 
         [0020]    Chest and knee airbags  20 ,  30  may be manufactured of flexible, non-porous material(s), such as nylon. 
         [0021]    Chest and knee airbags  20 ,  30  are part of an occupant protection system that includes a restraints control module (RCM) (not shown) and one or more crash sensors and/or occupant sensors (not shown), as are well known in the vehicle safety field. Depending upon the capabilities and programming of the occupant protection system, along with the nature (severity, direction, duration, etc.) of the collision or deceleration triggering the airbag deployment, chest airbag  20  and knee airbag  30  may be commanded to deploy either simultaneously or in sequence, the timing of their deployments intended to achieve optimum occupant safety. 
         [0022]      FIG. 2  illustrates the vehicle interior configuration of  FIG. 1  except with chest airbag  20  in a partially inflated condition and knee airbag  30  in a fully (or nearly fully) inflated condition when adult-sized occupant  16  is properly belted into seat  12  (“in position”). Chest airbag  20  is shaped and otherwise adapted to inflate rearwardly toward occupant  16  to contact and restrain the upper thorax region of the occupant. Chest airbag  20  may include internal baffles, tethers, stitch lines, and/or features to achieve the desired inflated position and sequence of inflation, as is well known in the art. 
         [0023]    Knee airbag  30  is configured and oriented to inflate upwardly and rearward (relative to the front/rear directions of the vehicle), immediately adjacent to the occupant-facing surface of IP  14 . For the in-position occupant  16 , knee airbag  30  provides cushioning between the occupant&#39;s knees/shins and the adjacent portions of IP  14 . Knee airbag  30  may also prevent a condition known as submarining, wherein the occupant  16  may slide forwardly beneath a lap restraint belt (not shown) of the seatbelt system  32 . 
         [0024]    As may be seen in  FIG. 3A , knee airbag  30  comprises a left lobe  34 , a right lobe  36 , and a central portion  38  disposed between and connecting the left and right lobes. When knee airbag  30  is deployed (inflated), the surface oriented toward and contacting the surface of IP  14  is known as the reaction surface  42 , and the surface oriented toward occupant  16  is known as the primary surface  43 . Reaction surface  42  lies close to the surface of IP  14  when the airbag is inflated. Central portion  38  may be thinner than lobes  34 ,  36  thereby creating a valley  40  in the central region between the lobes  34 ,  36 . 
         [0025]    The desired inflated shape and position of knee airbag  30  is achieved by means of internal baffles, tethers, stitch lines, and/or other features, as is well known in the art. Left and right lobes  34 ,  36  may be spaced apart from one another laterally by a distance D determined by an expected spacing between the left and right knees  16   a,    16   b  consistent with normal adult knee spacing in a proper seating position of in-position occupant  16 . The distance D is preferably selected to provide a maximum amount of protection for occupants of the widest possible range of body sizes. 
         [0026]    Vent openings  44 ,  46  are formed in the reaction surface  42  of lobes  34 ,  36 . The areas of reaction surface  42  immediately surrounding vent openings  44 ,  46  (which may be referred to as vent-bearing portions) may be recessed or relieved relative to the surrounding portions of the reaction surface such that the vent openings are spaced somewhat from the surface of IP  14  when the rest of the reaction surface is in contact with the IP surface. This recessing or relief of the vent-bearing portions of reaction surface  42  allows openings  44 ,  46  to remain unblocked by contact with the IP surface unless and until airbag  30  is urged forwardly against the IP by a significant amount of forward pressure applied to the lobes by the occupant. It is also possible for the surface of IP  14  to include recesses (not shown) in positions that will be aligned with vent openings  44 ,  46  when knee airbag  30  is deployed. Such recesses may be provided instead of, or in addition to, the relieved vent-bearing portions of reaction surface  42  to ensure that vent openings  44 ,  46  are not blocked. 
         [0027]      FIG. 3-A  shows the condition in which occupant&#39;s knees  16   a,    16   b  are contacting airbag  30  but is not applying sufficient force forwardly against the airbag to urge vent openings  44 ,  46  against IP  14  and thereby close the vents. This condition may exist when occupant  16  is properly restrained in seat  12  by belt  32 . In this condition, inflation gasses entering the lobes escape relatively freely through vent openings  44 ,  46  and airbag  30  does not inflate forcefully. 
         [0028]      FIG. 3-B  shows the condition when the occupant&#39;s knees  16   a,    16   b  press forwardly against lobes  34 ,  36  with a level of force sufficient to urge the vent-bearing portions of reaction surface  42  against IP  14  so that vent openings  44 ,  46  are substantially blocked by contact with the IP. When vent opening  44 ,  46  are blocked in this manner, little venting of inflation gasses occurs so that pressure builds up rapidly within knee airbag  30  to provide firm cushioning for occupant  16 . 
         [0029]    The level of the forward-directed occupant force required to close or substantially close the vents by urging them against IP  14  is referred to as the threshold level of occupant force. The threshold level of occupant force may be exceeded if the occupant  16  is thrown forward relative to the seat so that the occupant&#39;s knees  16   a,    16   b  are forced into contact with lobes  34 ,  36 . This may occur during a severe collision or other rapid deceleration of the vehicle, and/or when the occupant is not securely/properly belted into seat  12 . The threshold force level may also be exceeded if the occupant is properly belted but knees  16   a,    16   b  are positioned so far forward (due, for example, to fore/aft adjustment of seat  12  and/or the occupant having long femurs) that when knee airbag  30  deploys the airbag contacts the occupant&#39;s knees  16   a,    16   b  with sufficient force that vent openings  44 ,  46  are urged against the surface of IP  14 . 
         [0030]    Referring now to  FIG. 4 , the same vehicle interior configuration as  FIG. 1  is shown but with an out-of-position occupant (OOPO)  50  present in the front seat area and during early phases of an airbag inflation event. OOPO  50  is shown as a small-statured and/or child-sized individual. For example, some occupant protection testing protocols used in the automotive safety industry use test dummies representative of an average-sized three year-old and an average-sized six year-old. OOPO  50  is shown standing forward of seat  12  and close to the surface of IP  14 , as this is a commonly-used test configuration. 
         [0031]    Knee airbag  30  is configured such that lobes  34 ,  36  inflate first, before central portion  38 , and primarily upwardly, remaining close to the passenger-facing surface of IP  14 . Early and rapid inflation of lobes  34 ,  36  causes the as-yet uninflated central portion  38  to be inserted between IP  14  and OOPO  50 . Inflating lobes  34 ,  36  before central portion  38  allows all of the available inflation gasses to be directed into the lobes, so that the lobes inflate as quickly as possible and thereby insert central portion  38  between OOPO  50  and IP  14 . 
         [0032]    Knee airbag  30  may be constructed with stitching, baffles, internal tethers, or other well-known features to create an internal flow path which inflation gases follow during inflation. The internal flow path is engineered so that knee airbag  30  inflates in the desired fashion as described above. For example, internal baffles  52  (shown schematically in  FIG. 5 ) may be positioned to restrict, direct, or otherwise control the flow of inflation gasses from lobes  34 ,  36  into center portion  38 . It is also possible to utilize multiple inflators (not shown) to achieve the desired inflation sequence. The manner in which knee airbag  30  is packed (by folding, rolling, compacting, etc.) for stowage inside airbag module  26  may also contribute to achieving the proper inflation sequence, as is well known in the occupant restraints arts. 
         [0033]    As seen in  FIG. 5 , OOPO  50  makes contact primarily with the central portion as opposed to lobes  34 ,  36 . Consequently, the occupant force applied to lobes  34 ,  36  by OOPO  50  does not reach the threshold level required to urge the vent openings  44 ,  46  against IP  14  and thereby close them. Because vent openings  44 ,  46  remain open, knee airbag  30  either does not fill at all, or fills relatively gradually so as to expand rearward at a rate that applies little force to OOPO  50 . 
         [0034]    The valley  40  at the center region of knee airbag  30  may be sized such that even if the OOPO  50  is somewhat offset from being centered between lobes  34 ,  36  when the inflation sequence begins, inflation of the lobes between IP  14  and the OOPO will tend to urge the OOPO toward a more centered position. If OOPO  50  is somewhat offset from being centered between lobes  34 ,  36  when the inflation sequence begins, a reduction in inflation-induced forces is provided by the venting of the unobstructed lobe. 
         [0035]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.