Abstract:
A slider bar for use with two-door style motor vehicles for anchoring the lap belt for front seat occupants. The slider bar allows the lower anchorage point of the lap belt to freely move in the fore and aft direction to enhance rear seat compartment passenger ingress and egress. The slider bar further incorporates a pyrotechnic lap pretensioner (PLP) function for exerting pretensioning motion of the lap belt in response to a vehicle impact. The slider bar incorporates an internal piston which acts on the belt webbing position on the outside of the slider bar tube. Various embodiments are described incorporating alternate means of mounting the lap belt lower end to the slider bar, as well as various configurations for transferring the motion of the internal piston to the lap belt lower anchorage.

Description:
FIELD OF THE INVENTION 
     This invention is related to an automotive seat belt restraint safety device and particularly to a pyrotechnic lap belt pretensioner which also functions as a slider bar for the lower anchorage end of a seat belt system lap belt. 
     BACKGROUND OF THE INVENTION 
     Seatbelt restraint systems for restraining an occupant in a vehicle seat play an important role in reducing occupant injury in vehicle crash situations. Seatbelt restraint systems of the conventional so-called “3-point” variety commonly have a lap belt section extending across the seat occupant&#39;s pelvis and a shoulder belt section crossing the upper torso, which are fastened together or are formed by a continuous length of seatbelt webbing. The lap and shoulder belt sections are connected to the vehicle structure by anchorages. A belt retractor is typically provided to store belt webbing and may further act to manage belt tension loads in a crash situation. 
     Seatbelt restraint systems which are manually deployed by the occupant (so-called “active” types) also typically include a buckle attached to the vehicle body structure by an anchorage. A latch plate attached to the belt webbing is received by the buckle to allow the belt system to be fastened for enabling restraint, and unfastened to allow entrance and egress from the vehicle. Seatbelt systems, when deployed, effectively restrain the occupant during a collision. 
     One type of pretensioning device is a pyrotechnic lap pretensioner (PLP). PLPs are attached to a webbing guide loop or a seatbelt anchorage. Typical PLPs having included a pyrotechnic charge that is fired when a collision occurs, producing expanding gas which pressurizes a gas chamber within a tube, which forces a piston down the tube. The piston is connected with the belt system by a cable or strap. Stroking of the piston tightens or “pretensions” the belt against the occupant. 
     In order to provide enhanced occupant ingress and egress in two-door style vehicles, the lower anchorage end of the lap belt portion of the seat belt can be attached to a slider bar. The slider bar is mounted to the vehicle floor pan at the rear outboard corners of the front occupant seats. The slider bar allows the lower anchorage end of the seat belt webbing that is normally anchored solidly to the vehicle floor pan or sill plate to slide backwards to allow ingress and egress to and from the rear seat area of the vehicle. When the front seat occupant dons the seat belt, the lower anchorage end of the seat belt slides forward and is solidly anchored at the front end of the slider bar. One drawback to this type of hardware is that it cannot be easily used in conjunction with a pyrotechnic lap pretensioner (PLP) being used today in the automotive industry. 
     Another design constraint in the design of PLP&#39;s is attributed to the fact that normally a piston sliding within the gas cylinder of the PLP includes a cable (or rod) which is pulled through the cylinder when the pyrotechnic charge is ignited. As the piston is moved along the tube, it pulls the cable through the gas cylinder of the PLP. A seal is required where the cable passes out of the gas cylinder where it is anchored to a belt system component. The presence of the cable in the gas cylinder results in a gas leakage path created where the cable passes through the gas chamber. This increases the complexity of the PLP and increases the gas production capacity required for the gas generator. It is a desirable design feature to eliminate the cable or other mechanism present within the gas cylinder of the PLP to thereby provide a completely sealed gas chamber. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a slider bar PLP is provided which provides the function of a slider bar used to enhance egress and ingress to and from the rear seat area of a two-door vehicle, and also acts as a PLP in the event of a vehicle impact. The PLP slider bar utilizes an internal piston driven under the influence of a micropyrotechnic gas generator to move within a sealed gas cylinder section of the bar tube. Such movement is transferred to the outside of the tube and engages the lap belt lower anchorage end. This movement draws the belt anchorage end in the rearward direction to exert pretensioning tightening of the lap belt. Various additional features of this device are disclosed including designs which engage the seat belt lower anchorage end in various manners, as well as clutch mechanisms to maintain the PLP and its desired rearward pretensioned position after firing of the gas generator. 
     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a representative two-door motor vehicle incorporating the PLP slider bar in accordance with the present invention; 
         FIG. 2  is pictorial view of the PLP slider bar in accordance with a first embodiment of the invention shown with seat belt webbing attached in a normal non-deployed condition; 
         FIG. 3  shows the PLP slider bar of  FIG. 2  shown in a pretensioning deployed condition; 
         FIG. 4  is an exploded view of the PLP slider bar shown in  FIGS. 2 and 3 ; 
         FIG. 5  is an elevational view of a PLP slider bar in accordance with the second embodiment of this invention utilizing a winged driver element for engaging the webbing loop forming the sliding webbing anchor; 
         FIG. 6  is an exploded pictorial view of the PLP slider bar shown in  FIG. 5 ; 
         FIG. 7  is a pictorial view of a PLP slider bar in accordance with a third embodiment of this invention; 
         FIG. 8  is a longitudinal sectional view of a PLP slider bar shown in  FIG. 7 ; 
         FIG. 9  is an enlarged cross-sectional view of the internal clutch mechanism of the PLP shown in  FIG. 8 ; and 
         FIG. 10  is a partial cross-section view of the PLP slider bar of  FIG. 9  having an alternate design of a one-way ball-ramp clutch. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a representative motor vehicle  10  of the two-door variety which includes driver side doors  12 , and passenger side doors  14 . Seat belt system  16  is used to provide occupant restraint for an occupant in one of front seats  18  and  20 . Seat belt system  16  includes an upper torso shoulder belt section  22  and a lap belt section  24  which extends across the pelvic area of the seat occupant. A buckle and attachment plate of conventional design (not shown) is used for attaching the lap and shoulder belt sections  22  and  24  at the inboard position of the front seats  18  and  20 . In one popular configuration as shown, shoulder belt section  22  is anchored at its upper location directly to the seat backs of front seats  18  and  20 . 
     The present invention utilizes a PLP slider bar  26  mechanism for allowing the lower anchorage end  30  of lap belt section  24  to be moved in the fore and aft direction to allow enhanced ingress and egress to and from the rear passenger compartment area  28 . For that purpose, PLP slider bar  26  allows the lower anchorage end  30  of lap belt section  24  to freely move in the fore and aft direction. Donning of the seat belt by the vehicle occupant applies enough tension on lap belt section  24  to cause lower anchorage end  30  to move to its forward-most position. Although not shown in  FIG. 1 , an identical PLP slider bar  26  would be provided for the passenger side front seat  20 . The PLP slider bar  26  in accordance with the present invention also provides a seat belt pretensioning function. In the event of a vehicle impact, PLP slider bar  26  is actuated to pull the lower anchorage end  30  of lap belt  24  in the rearward direction, thereby exerting pretensioning force on the lap belt. The details on the construction of various embodiments of PLP slider bars in accordance with this invention are illustrated in the remaining figures and discussed in the following description. 
     A first embodiment of a PLP slider bar  26  in accordance with this invention is illustrated in  FIGS. 2 through 4 . PLP slider bar  26  includes main tube  32  extending along longitudinal axis  37  and is a hollow cylinder with an external surface  33  and a hollow interior  35 . Tube  32  has two sections, including a closed gas cylinder section  34  extending from a first end of the tube, and a webbing sliding section  36  extending to an opposite second end. One or more attachment clips  38  are provided for attachment of main tube  32  to a structural component of the motor vehicle. As shown, attachment clip  38  includes a bolt-type fastener  40 . Collar  42 , at the opposite second end of main tube  32 , also provides a means for mounting PLP slider bar to the motor vehicle using another bolt-type fastener  44 . Sliding collar  46  is moveable along exterior surface  33  of main tube webbing sliding section  36  in a manner which will be described in more detail as follows. The lower anchorage end  30  of lap belt section  24  is affixed to slider  49  which forms a sliding webbing anchor  48 . In normal use of PLP slider bar  26  when it is in the normal condition shown in  FIG. 1 , slider  49  is freely able to slide between positions adjacent to sliding collar  46  and fixed collar  42 . As described previously, this is desirable for facilitating ingress and egress for occupants of rear passenger compartment  28 . 
     Internal components of PLP slider bar  26  are illustrated in  FIG. 4 . Internally positioned within gas cylinder section  34  is an elongated first piston section  50  which may be formed of a plastic material which butts against second piston section  52 , preferably made of metal. Micropryotechnic gas generator  54  is positioned at the end of gas cylinder section  34  and is fixed and sealed in position, for example by rolling a shoulder  62  around tube  32 . Firing line  56  provides electrical impulses to activate gas generator  54  when it is desired to provide the pretensioning function. 
     In a normal operating condition, first and second piston sections  50  and  52  are positioned in gas cylinder section  34  such that the bore  56  through the second piston section is positioned at the left-hand end of tube slot  58 . In that position, fastener  60  passing through sliding collar bore  64  and into piston bore  56  is positioned against the left-hand end of tube slot  58 . Slider  49  is designed to be freely movable along webbing sliding section  36  as mentioned previously, and acts as a sliding webbing anchor  48  in this design. 
     When it is desired to engage pretensioning functions, mircopyrotechnic gas generator  54  is activated which generates gas in main tube gas cylinder section  34 . Gas pressure causes first and second piston sections  50  and  52  to be forcibly moved in the right-hand direction, as the components are shown in  FIGS. 2 through 4 . This action drives sliding collar  46  in the right-hand direction until it reaches the pretensioning position shown in  FIG. 3 . Fixed collar  42  and its fastener  44  prevent sliding collar  46  from coming off the main tube  32 . Piston section  50  is long enough to prevent gas from gas generator  54  from escaping through slot  58  when the pretensioning operation occurs. This motion provides a rearward pretensioning retraction of the lap belt webbing section  24  for enhancing occupant restraint. PLP slider bar  26  provides a fully enclosed gas cylinder section within which the pistons  50  and  52  move which does not require a seal for a cable or other element which passes through the gas chamber. 
     In many designs of PLP slider bar  26 , it would be desirable to incorporate a clutch mechanism to prevent sliding collar  46  from returning to its pre-deployment normal condition shown in  FIG. 2  after firing of gas generator  54 . Such a clutch mechanism can be provided by the design of first or second piston section  50  and  52  which could include barbs or ramped surfaces to prevent back-driving after actuation. Ball ramp-type clutch mechanisms, as described below, can also be provided for piston section  52 . 
     It should be noted that it is not necessary for tube slot  58  to be formed through both sides of tube webbing sliding section  36 . Bolt fastener  60  can enter into a blind threaded bore  56  in piston section  52 , or it could pass completely through the piston to the opposite side of main tube  32 , passing through an aligned hole in sliding collar  46 . However, it may be more efficient to provide only a single tube slot  58  in the main tube  32 . 
     Various approaches toward allowing sliding webbing anchor  48  of lap belt lower anchorage end  30  to freely side along webbing sliding section  36  can be provided. For example, as an alternative to using slider  49 , the webbing end  30  could simply be sewn into a loop and directly wrapped around webbing sliding section  36 . Such an approach could be implemented with a plastic or metal collar which may provide a bearing surface to allow free sliding motion of the webbing end. 
       FIGS. 5 and 6  illustrate PLP slider bar  70  in accordance with a second embodiment of this invention. Slider bar  70  has some components identical to that of the first embodiment which are identified by like reference numbers. This embodiment of slider bar  70  differs from slider bar  26  in several ways. First, sliding webbing anchor  48  for anchorage end  30  of the lap belt is formed by directly wrapping the webbing around webbing sliding section  36  into loop  82 , as suggested previously. This design avoids the use of a separate slider  49  component. As mentioned previously, the lower loop  82  can be reinforced or provided with an internal collar  66  fitted between the webbing and the outer diameter of tube  32 , and can be added to enhance the ease of sliding motion and avoid rattle problems. In this embodiment, a winged driver  72  is affixed to second piston section  74  by a screw fastener  76  installed into threaded bore  80 . Winged driver  72  has a pair of winged projections  76  which extend out of a pair of diametrically opposed tube slots  58 . Winged projections  76  extend through tube slot  58  far enough to directly engage with lap belt loop  82  to drive it in the manner described in the first embodiment from the left-hand edge of tube slots  58  toward the right-hand end of the tube slots. 
     A further embodiment of slider bar  70  incorporates winged driver  78  having a single winged projection  76 . Such a design would preferably be used with a main tube  32  featuring a single tube slot  58 , but would otherwise operate in a manner identical to the prior embodiment in that projection  76  would directly engage lap belt loop  82  to drive it a previously described. PLP slider bar  70  does not use fixed collar  42 . Instead, bolt  44  is installed directly through tube  32 . 
       FIGS. 7 ,  8 , and  9  illustrate a PLP slider bar  90  in accordance with a further alternate embodiment of the present invention which includes elements previously described which are identified by like reference numbers. PLP slider bar  90  differs from the prior embodiments in that it utilizes an internal ball-ramp type clutch mechanism associated with the piston to prevent back-driving of the piston after actuation. In this embodiment, piston  92  is shown as a single element as opposed to the prior embodiments which incorporated a sectioned piston. Piston  92  includes a cross bore  94  which allows attachment of sliding collar  95  using attachment bolt  97 . The end of piston  92  closest to gas generator  54  has a projecting post  96  with collar  98  installed over it. Collar  98  includes an external ramp or conical ramp surface  100  which interacts with a series of metal balls  102 . Flange  104  of collar  98  traps balls  102  to move along the conical surface. 
     When PLP slider bar  90  is actuated by firing gas generator  54 , piston  92  is driven in the right-hand direction to provide the pretensioning motion previously described. In this motion, balls  92  tend to move, due to frictional interaction of the inside of tube  32 , to the left-hand position along ramp surface  100 . If a force acts on piston  92  urging it to move in the left-hand direction after actuation, however, balls  102  become jammed between the conical surface  100  and the inside surface of tube  32 , thus acting as a one-way ball-ramp type clutch to prevent back-driving of the piston.  FIG. 8  illustrates PLP slider bar  88  in an activated extended position which provides pretensioning motion. 
       FIG. 10  illustrates PLP slider bar  70  having a modified form of a back-driving prevention clutch of the ball-ramp variety. Rather than having an internal clutch, collar  95  uses ball elements  102  engaging the exterior surface  33  of tube  32 . Collar  95  has an internal bushing  106  forming conical surface  108  which cooperates with the balls to prevent back-driving of collar  95  once it is stroked to the pretensioning position. 
     While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation, and change without departing from the proper scope and fair meaning of the accompanying claims.