Abstract:
An air bag unit includes a restrictive element, affixed within the air bag unit, which restricts lateral expansion of the air bag unit. The lateral restriction increases longitudinal expansion toward an occupant position.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an automotive air bag device that provides greater projection of a main bag unit using an inexpensive structure. 
     2. Description of the Related Art 
     Certain vehicles, such as automobiles, are equipped with conventional air bag devices serving as emergency safety measures. Conventional air bag devices contain a main bag unit stored in a folded state within a housing disposed inside the vehicle&#39;s instrument panel. Upon an impact at or greater than a predetermined value, the main bag unit expands and projects. This expansion is driven by pressurized gas. As a result, conventional air bag devices support and protect occupants positioned at fixed distances from the air bag device. 
     Referring to FIG. 15, a conventional two-piece air bag device includes a main bag unit, shown generally at  15 ′, formed from a pair of base fabric sections  1 ,  2 . A seam line  3  affixes base fabric sections  1 ,  2  together along a perimeter. A first side of main bag unit  15 ′ includes a gas entry opening  6  for receiving gas pressurizing main bag unit  15 ′. The first side of main bag unit  15 ′ also includes a pair of vent holes  7 , 7 , formed for adjusting the pressure inside main bag unit  15 ′. Base fabric sections  1 ,  2  are conventionally affixed together by sewing along seam line  3 . 
     Upon inflation of main bag unit  15 ′, a volume contained between base fabric sections  1 , 2  increases causing main bag unit  15 ′ to project away from an instrument panel (not shown) toward a desired contact position (not shown). The shape of base fabric sections  1 , 2  determines both the final inflated form of main bag unit  15 ′ and the amount of protection of main bag unit  15 ′ toward the desired contact position (not shown). When a manufacturer desires to change either the final inflated form or the amount of projection of conventional main bag unit  15 ′ the manufacturer must change the shape and size of base fabric sections  1 , 2 . 
     Referring to FIG. 16, a conventional three-piece air bag device includes a main bag unit, shown generally at  15 ″, formed from a pair of side fabric sections  4 ,  4  and a band-shaped base fabric section  5 . Side fabric sections  4 ,  4  are affixed to base fabric section  5  along perimeter sections by two seam lines (not shown). A gas entry opening  6 , for receiving pressurizing gas into conventional main bag unit  15 ″, is formed by side fabric sections  4 ,  4  and base fabric section  5  affixed together by seam lines (not shown). A pair of vent holes, one shown at  7 , is included in side fabric sections  4 , 4  for adjusting the pressure inside main bag unit  15 ″. Conventionally, side fabric sections  4 ,  4  are affixed to base fabric section  5  by sewing. 
     Upon inflation of main bag unit  15 ″, volume contained between side fabric sections  4 ,  4  and base fabric section  5 , increases causing main bag unit  15 ″ to project away from an instrument panel (not shown) toward a desired contact position (not shown). Conventionally, the shape of side fabric sections  4 ,  4  and base fabric section  5  determines both the final inflated form of main bag unit  15 ″ and the amount of projection toward the desired contact position (not shown). 
     Where a manufacturer desires to change either the final inflated form or the projection amount of conventional main bag unit  15 ″ the manufacturer must change the shape or size of side fabric sections  4 ,  4  and base fabric section  5 . 
     Conventional three-piece main bag unit  15 ″ provides greater projection toward the desired contact position(not shown) than conventional two-piece main bag unit  15 ′, but requires more fabric and greater labor thus adversely affecting material costs and labor costs. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to minimize the problems described above and to provide an automotive air bag device that can increase the projection distance of a main bag unit. 
     It is an object of the present invention to provide an automotive air bag device that can increase the projection of a main bag unit using an inexpensive structure. 
     The present invention relates to an air bag unit including a restrictive element, affixed within the air bag unit which restricts lateral expansion of the air bag unit. The lateral restriction increases longitudinal expansion toward an occupant position. 
     According to an embodiment of the present invention there is provided, an air bag comprising: a belt in an interior of the air bag, the air bag being of a type which expands in an expansion direction into a space in a vehicle, the belt limiting expansion of the air bag in a limiting direction, and the limiting direction being at an angle to the expansion direction, whereby expansion of the air bag in the expansion direction is increased. 
     According to another embodiment of the present invention there is provided, an air bag device comprising: an air bag unit, the air bag unit includes at least a first and a second base piece, the base pieces affixed together along a continuous seam element, a first and a second lateral position on the seam element established relative to an optimal external occupant position, the lateral positions separated by a first distance, means for restricting fixed between the lateral positions, the means has a restrictive length, the restrictive length being less than the first distance, and the restrictive means provides reduction in the first distance thereby increasing longitudinal expansion of the air bag unit into the external occupant position. 
     According to another embodiment of the present invention there is provided, an air bag device wherein: the restricting means is a belt, the belt having a first and second end and a first and second intermediate position, the first and the second ends affixed together, the first intermediate position on the belt affixed to the first lateral position, and the second intermediate position is affixed to the second lateral position. 
     According to another embodiment of the present invention there is provided, an air bag device wherein: the belt includes an intermediate section between the first and second intermediate positions, and the intermediate section overlapped and sewn thereby adjusting the restricting length. 
     According to another embodiment of the present invention there is provided, an air bag device further comprising: means for minimizing expansion failure along the perimeter seam element, and the minimizing means absorbs expansion force thereby preventing the perimeter seam element from failing when the air bag expands. 
     According to another embodiment of the present invention there is provided, an air bag device wherein: the minimizing means includes a first and a second margin extending from the base pieces, the margins extend away from the corresponding lateral positions, the restrictive means affixed between the first and the second margins along a pair of seams distinct from the continuous seam element, and the margins preferentially failing under expansion pressure thereby preventing the perimeter seam element from failing. 
     According to another embodiment of the present invention there is provided, an air bag device wherein: the minimizing means includes a first and a second weak section, the weak sections formed between the seam element and each the corresponding margin, and the weak sections preferentially failing under expansion pressure there preventing the perimeter seam element from failing. 
     According to another embodiment of the present invention there is provided, an air bag device, further comprising: a third base piece, the third base pieces fixed in two continuous seam elements to the first and second base pieces, and the third base piece provides further longitudinal expansion of the air bag unit relative to the occupant position. 
     According to another embodiment of the present invention there is an automotive air bag device equipped with a main bag unit, the main bag unit comprising: a first and a second base fabric, each of the first and second base fabrics has substantially the same shape, each of the first and second base fabrics fixed together along an outer perimeter by a seam line, the outer perimeter having a first and a second lateral side, the lateral sides positioned relative to an occupant position, the lateral sides separated by a distance, means for restricting expansion of the main bag unit during inflation, and the restrictive means provides localized reduction of the distance between the lateral sides thereby increasing projection of the main bag unit towards the occupant position. 
     According to another embodiment of the present invention there is a main bag unit, wherein: the width restricting means is a belt having a first and a second end, the belt being sewn to the base fabrics along each lateral side, and a pair of positions intermediate the ends sewn together thereby increasing projection of the main bag unit towards the occupant. 
     According to another embodiment of the present invention there is a main bag unit, wherein: each lateral side is positioned relative to an upper body portion of the occupant position. 
     According to another embodiment of the present invention there is a main bag unit, further comprising: a pair of margins extending from the base fabrics away from the outer perimeter, and the width restricting means affixed along each margin at a correspond lateral seam line adjacent to the lateral sides. 
     According to another embodiment of the present invention there is a main bag unit, further comprising: a first and a second weak section, each weak section positioned between each the corresponding margin and the seam line. 
     According to another embodiment of the present invention there is a main bag unit, wherein: the restrictive means overlapped at an intermediate section, and an intermediate seam line fixed across said intermediate section thereby reducing said distance between said lateral sides. 
     The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side-view drawing of an air bag device according to a first embodiment of the present invention. 
     FIG. 2 is an exploded perspective view of the main bag unit from FIG.  1 . 
     FIG. 3 is a perspective drawing showing a production step for the main bag unit from FIG.  2 . 
     FIG. 4 is a perspective drawing showing a production step following the steps from FIG.  3 . 
     FIG. 5 is a perspective drawing showing a production step following the steps from FIG.  4 . 
     FIG. 6 is a perspective drawing showing a production step following the steps from FIG.  5 . 
     FIG. 7 is a perspective drawing showing a production step following the steps from FIG.  6 . 
     FIG. 8 (A) is a side view drawing showing the main bag unit expanding. 
     FIG. 8 (B) is a side view drawing showing the main bag unit projecting to an occupant position. 
     FIG. 9 is a perspective drawing showing a second embodiment of the present invention. 
     FIG. 10 is a perspective drawing showing a third embodiment of the present invention. 
     FIG. 11 is a perspective drawing of a fourth embodiment of the present invention. 
     FIG. 12 is a perspective detail drawing of FIG. 11 after attachment of a belt. 
     FIG. 13 is a perspective detail drawing of a fifth embodiment of the present invention. 
     FIG. 14 is a perspective detail drawing of a belt after adjustment in any one of the embodiments of the present invention. 
     FIG. 15 is an exploded perspective drawing of a conventional two-piece bag. 
     FIG. 16 is an perspective drawing of a conventional three-piece bag. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a first embodiment of an expanded main bag unit  15  extends from a housing  13 , adjacent to a front window glass  17 , towards an occupant position  16  within a vehicle(not shown). An instrument panel  12  contains an air bag device  11  having a housing  13 . Housing  13  contains an inflator  14  for inflating main bag unit  15  and a main bag container  15   c  for containing main bag  15  prior to expansion. Main bag unit  15  is typically folded and stored in housing  13  until actuation of inflator  14 . 
     During use, inflator  14  actuates upon a sufficient impact and emits a pressurizing gas(not shown). During actuation, inflator  14  fills and extends main bag unit  15  from instrument panel  12  towards occupant position  16  until reaching a desired main bag position  15   a . A vent hole  18  is on a side of main bag unit  15 , facing away from housing  13 , and front glass window  17 . Vent hole  18 , adjusts the internal pressure in main bag unit  15 . Main bag position  15   a  is closer to occupant position  16  than a conventional main bag position  15   b.    
     Additionally referring now to FIG. 2, main bag unit  15  includes a first base fabric  21  and a second base fabric  22 , each having generally ovoid shapes, affixed together along an outer perimeter seam line  23 . First base fabric  21  includes a gas entry opening  24  positioned in a central region for receiving pressurizing gas (not shown). First base fabric  21  also includes offset vent holes  18 ,  18 , positioned near gas entry opening  24 , for adjusting the internal pressure of main bag unit  15  during use. First base fabric  21  and second base fabric  22  are typically affixed together along seam line  23  by sewing. 
     A first lateral position  25  is defined along the outer perimeter of main bag unit  15  proximal to a portion of main bag unit  15  entering occupant position  16  (not shown) upon expansion. A second lateral position  25  is defined along a complementary portion of the outer perimeter of main bag unit  15  so that a width  29  is defined across main bag unit  15  between positions  25 ,  25 . Positions  25 ,  25  correspond to an upper body or head region of an occupant (not shown) in occupant position  16  (not shown), as will be explained. 
     A belt  26 , having a first and a second end, is affixed between positions  25 ,  25  on seam line  23  along width  29 , on an outside surface of second base fabric  22 . Belt  26  extends between positions  25 ,  25  on main bag unit  15  and the first and second ends of belt  26  extend away from main bag unit  15 . Belt  26  is typically affixed along seam line  23  by sewing. Belt  26  serves as a restricting means, as will be explained. Although, the restricting means is described as a belt of flexible material or similar element, the width restricting means could also be a rigid, semi-rigid member, or hinged element performing the recited function. 
     Additionally referring now to FIG. 3, during assembly of the first embodiment of main bag unit  15 , first base fabric  21  and second base fabric  22  are affixed together along seam  23 . Next, positions  25 ,  25  are determined and belt  26  is affixed between positions  25 ,  25  having width  29 (not shown). The first and second ends of belt  26  extend away from positions  25 ,  25 . During assembly, positions  25 ,  25  and the generally ovoid shape of base fabrics  21 ,  22  of main bag unit  15 , are adjustable according to manufacturer design and need or other requirements. 
     Next during assembly, main bag unit  15  is folded along a central axis exposing a portion of gas entry opening  24  and all of vent hole  18  of first base fabric  21  and overlapping the first and second ends of belt  26 . A seam line  30  affixes the first and second ends of belt  26  together across a width of the first and second ends of belt  26 . Seam line  30  is typically created by sewing, but other methods to affix the first and second ends of belt  26  together may be used according to manufacturer design and need or other requirements. 
     Additionally referring now to FIG. 4, during assembly main bag unit  15  is partially opened ensuring access to second base fabric  22  and correct attachment of belt  26  at seam line  30 . 
     Additionally referring now to FIG. 5, next during assembly main bag unit  15  is positioned so that an outside surface of second base fabric  22  and the first and second ends of belt  26  face an operator (as shown). Main bag unit  15  is adjusted so that portions of belt  26 , affixed between seam line  30  and seam line  23 , are separated and spread apart from the center line of main bag  15 . 
     A distance  28  is the distance between corresponding seam lines  23  at positions  25 ,  25 . Distance  28  is the span of belt  26  affixed between positions  25 ,  25 , and is equal to or less than distance  29  defined between positions  25 ,  25  without belt  26 . Distance  28  may be adjusted by adjusting the position of seam line  30  relative to seam line  23 , or by changing the generally ovoid shape of base fabrics  21 ,  22 . Distance  28  is adjustable according to manufacturer design and need or other requirements. 
     Additionally referring now to FIG. 6, during assembly main bag unit  15  is turned inside-out, or reversed, generally through gas entry opening  24 . During reversal, the inside surfaces of first base fabrics  21 ,  22  are exposed and seam line  23  and belt  26 , with seam line  30 , become contained within the reversed main bag unit  15 . 
     Additionally referring now to FIG. 7, during assembly, main bag unit  15  is fully reversed and repositioned so that gas entry opening  24  and vent holes  18 ,  18  are exposed to an operator (as shown). Additionally, belt  26  with seam line  30  is evenly positioned between a pair of outside edges(not shown) of reversed main bag unit  15  so that belt  26  is centered between the outside edges of main bag unit  15  (as shown). Main bag unit  15  is then assembled within main bag canister  15   c  of air bag device  11 . 
     Additionally referring now to FIGS. 8A and 8B, as described, during operation of the first embodiment of main bag unit  15 , inflator  14  (not shown) inflates main bag unit  15 , and main bag unit  15  expands from main bag canister  15   c  (not shown) and instrument panel  12  (not shown). Main bag unit  15  expands towards an occupant  16   a  within occupant position  16 . During expansion, belt  26 , affixed between positions  25 ,  25 ,(not shown) causes positions  25 ,  25  to remain at fixed distance  28 (not shown) while allowing the main bag unit  15  to further expand. As main bag unit  15  expands, belt  26 , causes the area around positions  25 ,  25  to remain at fixed distance  28 , resulting in a partial pinching inward at positions  25 ,  25 . 
     As a result, the first embodiment of main bag unit  15  projects, longitudinally away from instrument panel  12 , and towards occupant position  16  and occupant  16   a , beyond conventional main bag position  15   b , as described above. The increased longitudinal projection of main bag unit  15 , towards main bag position  15   a , is related to a number of factors, including the length of belt  26 , positions  25 ,  25 , the position of seam line  30 , distances  28 , and  29 , and other factors. As a result, the horizontal projection of main bag unit  15  is minimized and the longitudinal projection of main bag unit  15  is increased to a position desired by a manufacturer or a customer. Adjusting the factors listed above allows a manufacture, or a customer, to direct the portions of main bag unit  15  restricted by belt  26  during expansion, and respond to needs for increased safety and reduced cost. As a result, using belt  26 , the longitudinal projection of the two-piece main bag unit  15  away from instrument panel  12  may be increased with little or no increase in capacity within main bag unit  15 . 
     Conventionally, where no belt  26  was used, expansion is controlled by the shape of base fabric pieces  21 ,  22 , inflation pressure from inflator  14 , and the positioning of air bag device  11  within instrument panel  12 . The use of the present invention allows optimization of the two-piece main bag unit  15  when corresponding to the upper body of an occupant. Thus, during expansion, main bag unit  15  is optimally placed to cushion the upper body and head of occupant  16   a  compared to conventional two-piece main bag units and injury is minimized to occupant  16   a . The first embodiment of main bag unit  15 , additionally effects passengers  16   a  not wearing seatbelts(not shown) since main air bag unit  15  contacts passenger  16   a  further from instrument panel  12 , thus improving protection for occupant  16   a.    
     Main bag unit  15 , with belt  26 , may be manufactured using simple and inexpensive structures. During manufacture, base fabrics  21 ,  22  are positioned, together with belt  26 , and sewn in a single step creating seam line  23 . Using multiple stitches to attach belt  26  to main bag unit  15  increases an attachment strength of belt  26  to main bag unit  15 . 
     The longitudinal projection of main bag unit  15  is easily adjusted since positions  25 ,  25 , at which belt  26  is sewn to base fabrics  21 ,  22 , are easily adjusted. For instance, as positions  25 ,  25  move closer together, the longitudinal projection of main bag unit  15  decreases. As positions  25 ,  25  move farther apart, the longitudinal projection of main bag unit  15  increases. Longitudinal projection may also be adjusted by adjusting the shape of base fabrics  21 ,  22 . 
     Additionally referring now to FIG. 9, a second embodiment of main bag unit  15 , includes a pair of margins  40 , 40  projecting away from base fabrics  21 ,  22  at positions  25 ,  25 . In the second embodiment, seam line  23  is positioned around a perimeter of base fabrics  21 ,  22  affixing base fabrics  21 ,  22  together. A pair of seam lines  41 ,  41  affix belt  26  to main bag unit  15  at margins  40 ,  40 , as determined by production needs. Seam lines  41 ,  41  are distinct from outer perimeter seam line  23 . Belt  26  may be affixed at seam lines  41 ,  41  individually (as shown), or may be continuous across base fabrics  21 ,  22  and affixed at seam lines  41 ,  41 (not shown). The ability of belt  26  to be affixed individually or continuous across base fabrics  21 ,  22  allows increased production flexibility concerning the length of belt  26 . 
     In the first embodiment of main bag unit  15 , expansion tension is applied to belt  26  and a pressure load(not shown) is transmitted directly through belt  26  to seam line  23 . Belt  26 , at positions  25 ,  25 , acts as a stress concentrator upon seam line  23  and fosters leakage of pressurized gas from main bag unit  15 . Thus, uneven pressure loading or extreme pressure loading may cause leakage where belt  26  is affixed to seam line  23 . Since vent holes  18 ,  18  are designed to release pressurized gas from main bag unit  15 , unexpected gas release from seam line  23  is undesirable. 
     In the second embodiment, seam lines  41 ,  41  are separated from seam line  23  by projecting margins  40 , 40 . Thus, seam lines  41 ,  41  separate the tension load of belt  26  of from seam line  23  to seam lines  41 ,  41 . As a result, the second embodiment minimizes or eliminates the risk of unexpected gas release at seam line  23 . After initial fabrication, the second embodiment of main bag unit  15  is employed similarly to the first embodiment. 
     Additionally referring now to FIG. 10, a third embodiment of main bag unit  15 , includes a pair of margins  42 ,  42  project outward from base fabrics  21 ,  22 . In the third embodiment of main bag unit  15 , seam line  23  is positioned around a perimeter of base fabrics  21 ,  22  and affixes base fabrics  21 ,  22  together. Seam lines  41 ,  41  affix belt  26  to main bag unit  15  along margins  42 ,  42  at positions  25 ,  25  as determined by production needs. As in the second embodiment, seam lines  41 ,  41  are distinct from outer perimeter seam line  23 . Belt  26  may be affixed individually at seam lines  41 ,  41  (as shown) or may be continuous across base fabrics  21 ,  22  and affixed at seam lines  41 ,  41  (not shown). Since belt  26  may be affixed individually or continuously across base fabrics  21 ,  22  increased production flexibility with the length of belt  26  exists. 
     Margins  42 ,  42  extend continuously along the full height of base fabrics  21 ,  22 , relative to the page. Margins  42 ,  42  facilitate attachment of belt  26  and allow attachment positions  25 ,  25  to be changed freely without changing the shape of base fabrics  21 ,  22 . This eliminates the need for specially formed margins  40 ,  40  and allows storage of preassembled base fabrics  21 ,  22 , thus minimizing costs while providing the same stress relieving attributes as found in the second embodiment. After initial fabrication, the third embodiment of main bag unit  15  is employed similarly to the first embodiment. 
     Additionally referring now to FIGS. 11 and 12, a fourth embodiment of main bag unit  15 , includes margins  42 ,  42  projecting inward from base fabrics  21 ,  22  along an outside width portion. In the fourth embodiment of main bag unit  15 , seam line  23  is positioned around the perimeter of base fabrics  21 ,  22  to affix base fabrics  21 ,  22  together. Seam lines  41 ,  41  affix belt  26  to main bag unit  15  along margins  42 ,  42  as determined by production needs. Seam lines  41 ,  41  are distinct from outer perimeter seam line  23 . 
     Belt  26  may be affixed individually at seam lines  41 ,  41  (as shown) or may be continuous across base fabrics  21 ,  22  and affixed at seam lines  41 ,  41  (not shown). The ability of belt  26  to be affixed individually or continuous across base fabrics  21 ,  22  allows increased production flexibility with the length of belt  26 . 
     In the fourth embodiment, an end of belt  26  may be placed on an outside portion of margins  42 ,  42  and affixed by seam line  41  (as shown) or may be placed between margins  42 ,  42  and then affixed by seam line  41 (not shown). In the fourth embodiment, the end of belt  26  is alternatively placed between or on margins  42 ,  42 . As a result, increased production flexibility is achieved and a reduction in costs. After initial fabrication, the fourth embodiment of main bag unit  15  is employed similarly to the first embodiment. 
     Referring now to FIGS. 13 and 14, a fifth embodiment of main bag unit  15  includes a pair of weak sections  43 ,  43  between margins  40 ,  40  corresponding and base fabrics  21 ,  22 . Weak sections  43 ,  43  act as stress concentrators and arc designed to preferentially fail under irregular pressure applied to belt  26  and seam lines  41 ,  41 . Under uneven or rapid expansion, irregular pressure loads may be transmitted through belt  26  and develop where margins  40 ,  40  attach to base fabrics  21 ,  22 . Where irregular pressure load transmits through margins  40 ,  40 , seam line  23  may fail and inhibit main bag unit  15  in protecting occupant  16   a . As a result, weak sections  43 ,  43  serve to protect the integrity of seam line  23  and allow main bag unit  15  to protect occupant  16   a  (not shown). 
     As previously described, a pair of seam lines  41 ,  41  affix belt  26  to main bag unit  15  along margins  40 ,  40  as determined by production needs. Belt  26  may be individually affixed at seam lines  41 ,  41  (as shown) or may be continuous across base fabrics  21 ,  22  and affixed at seam lines  41 ,  41 (not shown). 
     In the fifth embodiment, an intermediate section of belt  26  is bent into an overlapped section and sewn along a seam line  44 . The overlapping section and seam line  44  allows the length of belt  26  to be easily adjusted according to manufacturing needs. The overlapping section and seam line  44  may also be used as a stress concentrator and designed to preferentially fail under uneven or excessive pressure. For example, seam line  44  may be sewn with weaker thread than seam lines  23 ,  30 , or  41 , thus causing seam line  44  to fail under pressure load prior to seam lines  23 ,  30 , or  41  thereby maintaining safety. After initial fabrication, the fifth embodiment of main bag unit  15  is employed similarly to the first embodiment. 
     There are multiple benefits to the improved design of the automotive air bag device  11 , including the multiple embodiments. 
     First, the longitudinal projection of main bag unit  15  is increased from conventional main bag position  15   b  to main bag position  15   a , thus increasing the safety of occupant  16   a  in an accidental impact. 
     Second, where belt  26  is used, additional longitudinal projection of main bag unit  15  is achieved under similar conventional pressures. Thus, additional longitudinal projection is achieved while retaining a two-piece construction method and not substantially increasing the volume or pressure of main bag unit  15 . The improved design enables repositioning or redistribution of the inflated volume within main bag unit  15 , thus reducing manufacturing time and costs while maintaining safety. 
     Third, belt  26  has a simple and inexpensive structure and is used as a width restricting means, thus increasing projection of main bag unit  15  and minimizing manufacturing costs. Where the width restricting means serves to adjust the expansion of main bag unit  15 , alternative width restricting means may be used thus providing easy substitution and replacement under manufacturing pressures. As a result, manufacturers are not dependent upon single source suppliers and may obtain supplies easily and relatively inexpensively. For example, a three part belt, a single length of cord or rope, or an elastic or web like material may be used to replace belt  26  as a width restricting means as long as similar function is achieved. For a second example, the width restricting means may be a rigid or semi-rigid, or hinged element serving an equivalent function. 
     Fourth, the simplified design of belt  26  allows multiple embodiments to be constructed thus allowing for manufacturer adaptation to production and customer needs. For example, belt  26 , currently affixed at positions  25 ,  25  on seam line  23 , provides expansion of main bag unit  15  relative to the upper body and head regions of occupant  16   a . Alternatively, belt  26  may be adjusted in overall length and the position of seam line  30  adjusted selectively to increase or decrease the longitudinal projection of main bag unit  15 . However, where occupant&#39;s  16   a  size changes or other manufacturer or customer needs apply, positions  25 ,  25  can be selectively and quickly changed thus maximizing manufacturer speed and adaptation. 
     Fifth, the simplified design allows belt  26  to be supplied in either one or two individual parts. Where belt  26  is formed in one part, belt  26  may be continuous across base fabrics  21 ,  22 , affixed at positions  25 ,  25  and sewn at seam line  30 . Where belt  26  is formed in two parts each end may be individually affixed at positions  25 ,  25 , and sewn together at seam line  30 . Thus, belt  26  may be initially provided in variable lengths and portions but adapted during manufacturing to provide a similar result. 
     Sixth, belt  26  may be affixed to main bag unit  15  either before or after reversal of main bag unit  15 . When belt  26  is affixed to main bag unit  15  prior to reversal, an operator may affix belt  26  with minimal time and effort. However, when belt  26  is affixed to main bag unit  15  after reversal, an operator can affix belt  26  while working through gas entry opening  25  or vent holes  18 ,  18 . Thus, where main bag units  15  are produced without belt  26  by mistake or mis-design, main bag units  15  may be retroactively provided with belt  26 . As a result, time is saved and costs are minimized. Additionally, when belt  26  has been previously affixed to main bag unit  15 , later manipulation, adjustment, or correction of positions  25 ,  25  or seam lines  30 ,  41  and  44  and easily accomplished. 
     Seventh, since belt  26  is sewn to main bag unit  15 , it is possible to remove belt  26  for re-attachment or repositioning after initial manufacturer in response to a redesign or change in customer demand. Thus while sewing is a preferred method for affixing belt  26  to main bag unit, alternatively methods are easily substituted by a manufacturer. For example, belt  26  may be affixed to main bag unit by glue or grommets without effecting it&#39;s performance. 
     Eighth, despite the embodiments mentioned above, after assembly of main bag unit  15  later assembly is carried out in a generally similar manner. Thus, changes in manufacturing are minimized and costs more easily controlled. 
     Ninth, where a manufacturer desires to increase the strength of belt  26 , addition of a second belt  26 , spliced anywhere between positions  25 ,  25  in any embodiment is easily carried out. As a result, manufacturing is responsive to quickly changing customer demands or to increasing failure rates, thus minimizing down time, and maximizing customer satisfaction. 
     Tenth, where belt  26  is sewn into main bag unit  15 , the quantity of additional sewing required is minimal thus simplifying the sewing step and making the sewing operation only minimally harder for a large increase in performance. 
     Eleventh, since the use of belt  26  as a width restricting means allows a two piece main bag design to perform a similar function as a three-piece main bag design, customer and manufacturer costs are minimized. 
     Twelfth, where concerns exists regarding uneven pressure or over pressure weakening or causing seam line  23  to fail, the multiple embodiments described provide multiple responsive structures. For example, concentrating weak sections  43 ,  43 , seam lines  30 ,  41 , and  44 , margins  40 ,  40 , and margins  42 ,  42  all exist as alternative failure structures to minimize the risk of pressure failure at seam line  23 . As as result, the load on seam line  23  may be maintained and occupant  16   a  may be safely restrained. 
     Thirteenth, additional safety responsive structures can be easily incorporated into the embodiments described. For example, a secondary seam line(not shown) may be positioned on belt  26  beyond seam line  30 , to act as a back up or stress release device minimizing failure should seam line  30  fail under use. For a second example, an other secondary seam line(not shown) may be positioned on a folded portion of belt  26 , beyond seam line  44 , to act as a back up stress release device minimizing the risk of seam line  23  failure. 
     Fourteenth, the position of seam line  30  on belt  26  is easily adjusted to adjust the longitudinal projection of main bag unit  15  from instrument panel  12 . Additionally, where manufacturing defects occur causing seam line  30  to be mis-positioned, replacement is easily accomplished by first removal and then repositioning of seam line  30 . Thus, manufacturing defect rates are reduced and costs are minimized. 
     Although only a single or few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiment(s) without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Thus although a nail and screw may not be structural equivalents in that a nail relies entirely on friction between a wooden part and a cylindrical surface whereas a screw&#39;s helical surface positively engages the wooden part, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. 
     Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.