Abstract:
In a vehicle occupant restraint system provided in association with a vehicle seat for preventing a vehicle occupant from slipping forward under a seat belt in an impact situation such as a vehicle crash, a pair of casings are provided on either side of the seat frame, and pivotally support a pair of arms across which a cross member extends A power unit pivotally incorporated in at east one of the casings raises the arms and cross member in an impact situation. The casing is formed by a main member having a vertical section and a pair of Ranges extending from upper and lower ends of the vertical section, and a lid member attached to the free ends of the flanges. The hollow structure of the casing provides a high level of mechanical strength, and the two piece structure of the casing allows the assembly work to be performed in a simple manner because the components can be installed from sideways one after another in a relatively simple manner.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to a vehicle occupant restraint system that is provided in a vehicle seat, and in particular to a vehicle occupant restraint system for preventing the submarining or slipping forward of the vehicle occupant under the seat belt in an impact situation such as a vehicle crash.  
         BACKGROUND OF THE INVENTION  
         [0002]    The term “submarining” means the slipping forward of a vehicle occupant under the scat belt in an impact situation such as a vehicle crash in case the lap belt fails to restrain the pelvis of the vehicle occupant. This occurs most frequently when the vehicle occupant is sitting on an edge of the seat and/or the seat back is significantly reclined, and could impair the restraining capability of the seat belt because the seat belt fails to restrain the proper part of the vehicle occupant.  
           [0003]    A copending U.S. patent application No. 09/526,405 filed Mar. 15, 2000 discloses a vehicle occupant restraint system in which a forward slip preventing member is moveably supported by a pair of casings fixedly attached to either side of a seat frame at a front part of a seat bottom so as to selectively project upward. The front end of the seat is raised only in case of an impact situation such a vehicle crash by actuating this forward slip preventing member with a power unit. The contents of this copending application are hereby incorporated in this application by reference.  
           [0004]    Because the power unit produces a significant force at the time of its activation, the structural members of the system are required to withstand the resulting reaction force. However, the system is required to be compact enough to be installed in a limited space of a vehicle seat. The system is also desired to be inexpensive for the system to be accepted by the consumers.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    In view of such problems of the prior art, a primary object of the present invention is to provide an anti-submarine vehicle occupant restraint system which is compact and light-weight.  
           [0006]    A second object of the present invention is to provide an anti-submarine vehicle occupant restraint system which is easy and economical to manufacture.  
           [0007]    According to the present invention, such objects can be accomplished by providing a vehicle occupant restraint system provided in association with a vehicle scat for preventing a vehicle occupant from slipping forward under a seat belt in an impact situation such as a vehicle crash, comprising: a pair of fixed support members attached to either side of a seat frame at a front part of a seat bottom; an arm pivotally attached to a front end of each of the fixed support members; a cross member extending between free ends of the arms; and a power unit provided in association with at least one of the support members for actuating the arms and cross member upward so as to selectively raise a front part of the seat bottom in an impact situation such as a vehicle crash; at least one of the support members comprising a main member having a vertically extending section which is elongated in a fore-and-aft direction, an upper flange extending laterally from an upper end of the vertically extending section, and a lower flange extending laterally in a same direction as the upper flange from a lower end of the vertically extending section, and a lid member which is attached to free ends of the upper and lower flanges to form a closed profiled casing in cooperation with the main member.  
           [0008]    The hollow structure of the casing provides a high level of mechanical strength, and the two piece structure of the casing allows the assembly work to be performed in a simple manner because the components can be installed from sideways one after another in a relatively simple manner. Likewise, each of the arms may comprise a substantially horizontal web and a pair of arm flanges depending from either side of the web. Preferably, both the casing and arm are formed by stamp forming sheet metal. The pivot shaft for the arm may be passed through the vertically extending section of the main member, the lid member, and the arm flanges. According to a preferred embodiment, the pivot shaft consists of a hollow collar through which one of the mounting bolts for the casing is passed. The other mounting bolt may be passed through a suitable part of the casing. The side flanges of the arm extend along either outer or inner surfaces of the vertically extending section of the main member and the lid member.  
           [0009]    Preferably, the power unit comprises a pyrotechnic cylinder unit which is received in the closed profiled casing and extends in the fore-and-aft direction, and a piston rod which is adapted to be actuated by the cylinder unit and engages a point of the corresponding arm offset from a pivot point at which the arm is attached to the casing. The pyrotechnic cylinder unit may be engaged by a pair of shoulders formed in the casing which, for instance, may be defined by edges of openings formed in the casing.  
           [0010]    To simplify the arrangement, the lid part of the support member may comprise a part of the seat frame.  
           [0011]    For the restraint system to be effective in use, the system may comprise a lock mechanism for retaining a corresponding one of the arms in the upwardly actuated state. It may be provided in each of the casings while the power unit is provided only in one of the casing. The casing typically receives therein a rod which extends in the fore-and-aft direction and engages a point of the corresponding arm offset from a pivot point at which the arm is attached to the support member, and the lock mechanism receives the rod so as to permit a sliding motion of the rod in a direction corresponding to a rising motion of the arm but prevent a sliding motion of the rod in an opposite direction. The rod may extend either rearward or forward from the point of engagement to the arm. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    Now the present invention is described in the following with reference to the appended drawings, in which:  
         [0013]    [0013]FIG. 1 is a transparent perspective view of a vehicle seat embodying the present invention;  
         [0014]    [0014]FIG. 2 is an exploded perspective view of the subassembly provided on the right had side of the seat frame;  
         [0015]    [0015]FIG. 3 is a side view of the subassembly on the right as seen from the right side;  
         [0016]    [0016]FIG. 4 is a cross sectional view taken along line IV-IV of FIG. 3;  
         [0017]    [0017]FIG. 5 is a perspective view of the subassembly provided on the left had side of the seat frame;  
         [0018]    [0018]FIG. 6 is a side view of the subassembly on the left as seen from the left side;  
         [0019]    [0019]FIG. 7 is a sectional view of the power unit including a cylinder unit and a piston rod;  
         [0020]    [0020]FIG. 8 is a side view an alternate embodiment;  
         [0021]    [0021]FIG. 9 is a view similar to FIG. 2 showing another embodiment of the present invention; and  
         [0022]    [0022]FIG. 10 is a view similar to FIG. 2 showing yet another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    [0023]FIG. 1 is a perspective view of a vehicle seat  1  embodying the present invention. The vehicle seat  1  comprises a seat bottom  1   a  and a seat back  1   b  which is typically adapted to be reclined to a desired angle by an adjustable pivot mechanism not shown in the drawing. The seat bottom  1   a  comprises a seat frame  4  which in this case consists of a rectangular frame having a pair of longitudinal side members and a pair of cross members joining the front and rear ends of the side members with each other, and a cushion member  5  which covers the seat frame  4 . The cushion member  5  may be simply made of foamed plastic material or consist of any known composite structure. A pair of subassemblies  2  and  3  forming a vehicle occupant restraint system according to the present invention are attached to the inner sides of the side members of the seat frame  4 . The seat frame  4  may be supported by a seat rail assembly fixedly attached to the vehicle body via sliders in a slidable manner, and adapted to be fixed at a desired position with a seat adjust mechanism not shown in the drawing.  
         [0024]    FIGS.  2  to  4  show the structure of the subassembly  2  on the right hand side of the vehicle occupant restraint system. The subassembly  2  comprises a tubular casing  6  having a rectangular cross section and elongated in the fore-and-aft direction of the vehicle body. The casing  6  is comprised of a main member  7  and a lid member  8  both of which are formed by stamp forming sheet metal. The main member  7  comprises a vertically extending section  7   a  and a pair of flanges  7   b  extending from upper and lower ends of the vertically extending section  7   a  toward the lid member  8 . In this embodiment the upper and lower flanges  7   a  are smoothly connected to each other at the front end of the casing  6 . Free ends of the upper and lower flanges  7   b  are provided with projecting tabs  9  which are fitted into corresponding openings  10  provided in the lid member  8 , and crimped on the lid member  8 .  
         [0025]    An arm  11  is pivotally attached to the front end of the casing  6 . The arm  11  comprises a laterally extending web  11   a  and a pair of arm flanges  11   b  depending from either side of the web  11   a . The upper front parts of the main member  7  and lid member  8  are provided with mutually aligned openings  12  and  13 , and a corresponding opening  19  is passed through the arm flanges  11   b . A collar  25  is passed through these openings  12 ,  13  and  19  to pivotally support the arm  11  with respect to the casing  6 .  
         [0026]    A power unit comprising a cylinder unit  22  extending in a fore-and-aft direction and a piston rod  23  extending from a front end of the cylinder unit  22  is received in the casing  6 . The front end of the piston rod  23  is provided with a ring  23   a . The outer circumferential surface of the piston rod  23  is provided with annular or spiral grooves. The lower front parts of the main member  7  and lid member  8  are provided with slots  14  and  15  elongated in the fore-and-aft direction, and a corresponding oblique slot  18  which is only slightly elongated and offset from the opening  19  is passed through the arm flanges  11   b . A pin  30  is passed through these slots  14 ,  18  and  15  and the ring  23   a , and is retained therein by a retaining ring  31 .  
         [0027]    As best shown in FIG. 4, the vertically extending section  7   a  of the main member  7  and lid member  8  are profiled so as to conform to or wrap around the cylindrical contour of the cylinder unit  22 . Rectangular openings  16  and  17  are formed in intermediate parts of the main member  7  and lid member  8 , and jointly retain therein a radial flange  22   a  formed in the front end of the cylinder unit  22  as well as a lock mechanism  24  provided on the front end of the radial flange  22   a . Thus, the front facing edges of the rectangular openings  16  and  17  are adapted to support the reaction of the cylinder unit  22  at the time of its activation via the back surface of the radial flange  22   a . These edges are also contoured around the cylinder unit  22  as a result of the fact that the vertically extending section  7   a  of the main member  7  and lid member  8  are contoured around the cylinder unit  22 , and are therefore allowed to abut the back surface of the radial flange  22   a  over a relatively large support surface. These rectangular openings  16  and  17  are each closed on all sides so that a high mechanical strength can be achieved with respect to the impact which is generated at the time of the activation of the vehicle occupant restraint system.  
         [0028]    This subassembly  2  is attached to the side member of the seat frame  4  by passing a pair of threaded bolts  26  and  29  through the collar  25  pivotally supporting the arm  11  and a hole  28  formed in a tab-like extension of the lid member  8  at an upper rear end thereof from inside the seat frame  4  and fastening nuts from the outside of the seat frame  4 . The collar  25  is provided with an adequate length to support the axial force of the threaded bolt  26  without preventing the pivoting movement of the arm  11 . Therefore, there is a play that permits a slight lateral movement of the arm  11  along the collar  25 , and a rubber ring  27  interposed between a head of the collar  25  and a side of the arm  11  prevents any rattling of the arm  11  during use.  
         [0029]    [0029]FIGS. 5 and 6 show the structure of the subassembly  3  on the left hand side of the vehicle occupant restraint system. The subassembly  3  comprises a tubular casing  36  having a rectangular cross section and elongated in the fore-and-aft direction of the vehicle body. The casing  36  is comprised of a main member  37  and a lid member  38  both of which are formed by stamp forming sheet metal. The main member  37  comprises a vertically extending section  37   a  and a pair of flanges  37   b  extending from upper and lower ends of the vertically extending section  37   a  toward the lid member  38 . Free ends of the upper and lower flanges  37   b  are provided with projecting tabs  39  which are fitted into corresponding openings  40  provided in the lid member  38 , and crimped on the lid member  38 .  
         [0030]    An arm  41  is pivotally attached to the front end of the casing  36 . The arm  41  comprises a laterally extending web  41   a  and a pair of arm flanges  41   b  depending from either side of the web  41   a . The upper front parts of the main member  37  and lid member  38  are provided with mutually aligned opening  42  and  43 , and a corresponding opening  49  is passed through the arm flanges  41   b . A collar  55  is passed through these openings  42 ,  43  and  49  to pivotally support the arm  41  with respect to the casing  36 .  
         [0031]    A rod  53  extending in a fore-and-aft direction is received in the casing  36 . The front end of the rod  53  is provided with a ring  53   a . The outer circumferential surface of the rod  53  is provided with annular or spiral grooves. The lower front parts of the main member  37  and lid member  38  are provided with slots  44  and  45  elongated in the fore-and-aft direction, and a corresponding oblique slot  48  which is only slightly elongated and offset from the opening  49  is passed through the arm flanges  41   b . A pin  60  is passed through those slots  44 ,  48  and  45  and the ring  53   a , and is retained therein by a retaining ring  61 .  
         [0032]    Rectangular openings  46  and  47  are formed in intermediate parts of the main member  37  and lid member  38 , and jointly retain therein a lock mechanism  54  and the rod  53  is passed through this lock mechanism  54 .  
         [0033]    This subassembly  3  is attached to the side member of the seat frame  4  by passing a pair of threaded bolts  56  and  59  through the collar  55  pivotally supporting the arm  41  and a hole  59  formed in a tab-like extension of the lid member  38  at an upper rear end thereof from inside the seat frame  4  and fastening nuts from the outside of the seat frame  4 . The collar  55  is provided with an adequate length to support the axial force of the threaded bolt  56  without preventing the pivoting movement of the arm  41 . Therefore, there is a play that permits a slight lateral movement of the arm along the collar, and a rubber ring  57  interposed between a head of the collar  55  and a side of the arm  41  prevents any rattling of the arm  41  during use.  
         [0034]    A cross member consisting of a pipe member  32  and serving as a forward slip preventing member extends across the free end  20  of the arm  11  of the subassembly  2  and the free end  50  of the arm  41  of the subassembly  3 . Because the pipe member  32  must not extend beyond the side profile of the subassembly  2  or  3 , the free end  20  or  50  of each arm  11  or  41  consisting of the arm flanges are made narrower in width by bending the flanges  11   b  and  41   b  inwardly about vertical folding lines as indicated by numeral  21  and  51 .  
         [0035]    Referring to FIG. 7, the cylinder unit  22  comprises a cylindrical cylinder member  72 , a piston member  71  slidably received in the cylinder member  72  and a propellant module  73  received in an end of the cylinder member  72  remote from the flange  22   a . The propellant module  73  is provided with a small diameter portion facing the piston member  71 , and an annular seal member  74  is fitted on the small diameter portion so as to abut an annular shoulder defined at the base of the small diameter portion and the inner circumferential surface of the cylinder member  72  to seal off the gas that is produced from the small diameter portion when the propellant module  73  is activated. The end of the cylinder member  72  adjacent to the rear end of the propellant module  73  is crimped on the propellant module  73 , and the annular seal  74  resiliently supports the propellant module  73  against the force of crimping. A compression coil spring  75  is interposed between the piston member  71  and the annular seal  74 . The inner end of the piston rod  23  is provided with a spherical shape, and is received in a complementary spherical recess formed in the piston member  71 .  
         [0036]    The lock mechanism  24  is provided with a casing  76  which internally defines a sloping surface  77 . An engagement piece  78  is resiliently urged against this sloping surface  77  by a compression coil spring  79 , and the slopping surface  77  is oriented in such a manner that the engagement piece  78  is resiliently urged also against the outer surface of the piston rod  23  under the spring force of the compression coil spring  79 . The engagement piece  78  is provided with teeth  80  which mesh with the grooved surface of the piston rod  23 . Because of the orientation of the sloping surface  77 , the engagement piece  78  would not prevent the outward movement of the piston rod  23  by being pushed away from the sloping surface  77  against the spring force of the compression coil spring  79 , but prevents the inward movement of the piston rod  23  by wedging in between the sloping surface  77  and the outer circumferential surface of the piston red  23 .  
         [0037]    Only one engagement piece  78  was used in the above described embodiment to engage a part of the outer circumferential surface of the piston rod  23 , but a plurality of engagement pieces may be used for engaging the outer circumferential surface of the piston rod  23  from a plurality of directions. The other lock mechanism  54  may be similar to the lock mechanism  24 .  
         [0038]    The vehicle occupant restraint systems is thus formed by the right and left subassemblies  2  and  3 , and the pipe member  32 . An impact detecting sensor consisting of an acceleration sensor or the like not shown in the drawing, and a control unit may be provided for activating the restraint system when appropriate.  
         [0039]    The mode of operation of this embodiment is described in the following. When an impact of a vehicle crash is detected, gas is produced in the cylinder unit  22 , and the resulting rapid rise in the internal pressure inside the cylinder member  72  produces a thrust which pushes the piston member  71  out of the cylinder member  72  causing the free end of the piston rod  23  to project rapidly. As a result, the arm  11  connected to the free end of the piston rod  23  rotates in counterclockwise direction as indicated by the imaginary lines in FIG. 3, and the pipe member  32  moves upward causing the seat cushion member  5  to bulge out and prevent the submarining of the vehicle occupant. The annular shoulder formed in the inner circumferential surface of the cylinder member  72  at the flanged end of the cylinder unit  22  prevents the piston member  71  from being thrown forward out of the cylinder unit  22 . When the gas has ceased to be produced from the propellant module  73 , and the drive force of the cylinder unit  22  has been lost, the one-way lock mechanisms  24  and  54  prevent the pipe member  32  from coming down, and continues to prevent the submarining.  
         [0040]    The cylinder unit  22  was provided only on the right hand side of the seat, but may also be provided on each side of the seat. If two cylinder units are used, each of them can be made smaller. Although not shown in the drawings, the one-way lock mechanism may also consist of a ball type one-way lock mechanism which can prevent the reverse rotation in a continuous manner, a ratchet mechanism or the like.  
         [0041]    [0041]FIG. 8 shows a modified embodiment of the subassembly  3  which is not provided with a power unit. The parts corresponding to those of the previous embodiments are denoted with like numerals. According to this structure, the casing  70  has a smaller length than the corresponding casing of the previous embodiment. A lock mechanism  54  which is substantially identical to the lock mechanism  54  of the previous embodiment is received in the casing  70 , and is fixedly secured therein by means which is not shown in the drawing. A rod  53  passes through the lock mechanism  54 . The rear end of the rod  53  is provided with a ring  53   a  through which a pin  60  is passed. The pin  60  is also passed through the flanges of the arm  41  and is guided by slots provided in the arm and the casing in a similar manner as in the previous embodiment. The mode of operation of this embodiment is similar to that of the previous embodiment, This embodiment allows the structure to be highly compact and light weight.  
         [0042]    This embodiment can be also applied to the subassembly incorporated with a power unit. In this case, the piston rod is provided with a ring for passing a pin in an intermediate part of the rod, and the rear end thereof is received in the cylinder unit while the front end is received in the lock mechanism.  
         [0043]    [0043]FIG. 9 is a view similar to FIG. 2 showing another embodiment of the subassembly which is provided with a power unit. The parts corresponding to those of the previous embodiments are denoted with like numerals. In this embodiment, the arm  11  has a relatively small width, and is interposed between the vertical section  7   a  of the main member  7  and the lid member  8 . This can be applied equally to the subassembly which is not provided with a power unit. This embodiment allows the overall lateral width of the subassembly to be reduced  
         [0044]    [0044]FIG. 10 is a view similar to FIG. 2 showing yet another embodiment of the subassembly which is provided with a power unit. The parts corresponding to those of the previous embodiments are denoted with like numerals. In this embodiment, the lid member  68  of the casing  66  consists of a part of the seat frame  4 . The main member  67  of the casing  66  is similar to that of the previous embodiment. According to this embodiment the number of component parts is reduced, and the weight of the device is reduced. Similarly as the previous embodiment, the arm  11  is interposed between the vertical section of the main member  67  and the lid member  68 , instead of being arranged on the exterior of the casing  66 . This can be applied to the subassembly which is not provided with a power unit. This embodiment allows the overall lateral width of the subassembly to be reduced.  
         [0045]    Although the present invention has been described in terms of preferred embodiments thereof, it is obvious to a person skilled in the art that various alterations and modifications are possible without departing from the scope of the present invention which is set forth in the appended claims.