Abstract:
An in-line seat belt pretensioner is provided that includes a frame containing a first guide member and a second guide member for tensioning of seat belt webbing upon pretensioner activation. As the pretensioner is activated, the seat belt is tensioned by activation of an actuator operably coupled to the second guide. The second guide is then routed over a vertically stationary first guide that is slidably engaged within a slot within the frame, thereby contributing to reducing the load on the occupant. A low-friction material employed in the manufacture of the guide member(s), contributes to a smoother and less abrupt tensioning of the seat belt upon activation of the pretensioner.

Description:
BACKGROUND OF THE INVENTION 
   Safety belt pretensioners remove slack from a safety belt in the event of a collision in order to minimize forward movement of the passenger. It is known to use pyrotechnic gas generators to operate pretensioner mechanisms that wind up or otherwise pull in slack in the safety belt during a collision. Such pyrotechnic gas generators are often disposed internally of a safety belt retractor. High-temperature gases tend to abrade interior metal surfaces and produce ash and clinkers that bind up the retraction mechanism. Thus, the vehicle owner is faced with a significant cost penalty in that the entire pretensioner and retractor assembly must be replaced after activation because of the inability to prevent degradation of the retractor. 
   Further, where pyrotechnic gas generators are used to supply the rapidly increasing gas pressure for the pretensioner, the gas pressurization rate and the resultant initial driving force or acceleration of the piston can exceed the structural capability of the driven components. As a result, the entire pretensioner assembly can malfunction due to fracturing of a given part. If damaged due to application of excessive forces, the retractor will not retract and function as a load limiter during a second impact. Thus, the retractor must be replaced. 
   In addition, many existing retractor designs incorporate the pretensioner into the retractor assembly. In these designs, the retractor tends to occupy valuable space in the retractor assembly that could be used for other useful mechanisms, such as load-limiting devices. 
   SUMMARY OF THE INVENTION 
   The present invention provides a safety belt pretensioner that works independently of the safety belt retractor. Prior to function, it remains operatively independent from safety belt or retractor operations. During a collision, and when the retractor locks up the safety spool during impact, the pretensioner assembly pulls in safety belt webbing from the shoulder loop direction. After the collision, the safety belt is free to slide through the pretensioner assembly for load-limiting webbing payout, or post-impact belt take-up by the retractor. 
   The pretensioner assembly embodiments disclosed herein obviate damage to the retractor due to chemical abrasion and application of excessive forces. Also, as the pretensioner assembly disclosed herein is positioned separate from the retractor, it does not occupy space in the retractor assembly, thereby permitting a corresponding reduction in the size of the retractor assembly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of a first embodiment of an in-line safety belt pretensioner assembly in accordance with the present invention; 
       FIG. 2  is a partially cross-sectioned edge view of the pretensioner assembly of  FIG. 1 ; 
       FIGS. 3 and 4  are edge views of the first embodiment of the pretensioner assembly shown in  FIG. 1 , showing operation of the first embodiment; 
       FIGS. 5A-5C  are edge views of a second embodiment of the pretensioner assembly, showing construction and operation of the second embodiment; 
       FIG. 6  is an edge view of a third embodiment of an in-line safety belt pretensioner assembly in accordance with the present invention wherein a roller is slidably engaged within a slot formed in the activation mechanism; 
       FIG. 7A-7D  are edge views of the third embodiment of the pretensioner assembly shown in  FIG. 6 , showing operation of the third embodiment; and 
       FIG. 8  is a schematic representation of an exemplary vehicle occupant restraint system incorporating a pretensioner assembly in accordance with the present invention. 
   

   DETAILED DESCRIPTION 
     FIGS. 1 and 2  show a pretensioner assembly  10  in accordance with a first embodiment of the present invention. Pretensioner assembly  10  may be used to pretension a safety belt  12  wound about a webbing reel  14  of a conventional safety belt retractor mechanism  16 . “Pretensioning” is generally defined as tightening the slack in a safety belt in the event of sudden deceleration or a collision. 
   During safety belt use, the belt is typically anchored to the interior of a vehicle by retractor mechanism  16  at one end of the belt and by a safety belt buckle mechanism (not shown) at an opposite end of the belt. Safety belt  12  may also pass through an intermediate guiding member, such as a shoulder loop (not shown) positioned between pretensioner assembly  10  and the buckle mechanism. 
   Pretensioner assembly  10  may be characterized as an “in-line” assembly because it is positioned and acts along a portion of safety belt  12  extending between retractor  16  and the buckle mechanism, rather than being incorporated into the retractor mechanism as in previous designs. For example, pretensioner assembly may be located in the vehicle B pillar between the retractor and the shoulder loop. 
   Typical safety belt retractor mechanisms which may be used in conjunction with the pretensioner assembly of the present invention are described in U.S. Pat. Nos. 5,743,480, 5,553,803, 5,667,161, 5,451,008, 4,558,832 and 4,597,546, each incorporated herein by reference. 
   Referring again to  FIGS. 1 and 2 , pretensioner assembly  10  includes a pretensioner mechanism, generally designated  18 , and an activation mechanism  20  operably coupled to pretensioner mechanism  18  for actuating the pretensioner mechanism. Pretensioner mechanism  18  includes a frame  22 , a first guide member  24  secured to frame  22 , and a second guide member  26  operably coupled to the frame so as to enable movement of the second guide member  26  with respect to first guide member  24 . In the embodiment shown in  FIGS. 1 and 2 , frame  22  is a unitary block  16  formed from steel, aluminum, metal alloys, plastic and/or other known materials suitable for use in a pretensioner and for attachment of the components described below. Frame  22  will generally (but not exclusively) be secured to an interior portion of the vehicle. 
   Either (or both) of guide members  24 ,  26  may be statically mounted or rotatably mounted to respective portions of pretensioner assembly  10 . In the embodiment shown in  FIGS. 1 and 2 , guide members  24 ,  26  each comprise a roller rotatably secured to frame  22  or another portion of pretensioner assembly  10 . Alternatively, either of guide members  24 ,  26  may comprise a statically mounted bushing. Generally, portions of guide members  24 ,  26  in contact with safety belt  12  are formed from a relatively low-friction material, for example, a polymer compound. In contrast to comparable pretensioners, therefore, the present pretensioner is designed to operate with less friction about the guide member/seat belt interface thereby improving the gradual tensioning of the seat belt as opposed to an abrupt tensioning upon pretensioner activation. 
   In the embodiment shown in  FIG. 1 , second guide member  26  is operably coupled to frame  22  through activation mechanism  20 , in a manner described in more detail below. In alternative embodiments, second guide member  26  may be coupled to frame  22  using one of many other alternative methods (not shown). For example, second guide member  26  may be attached by a hinge to frame  22 . Or, as shown in  FIG. 6 , guide member  26  may be slidably positioned in a slot formed in frame  22  thereby providing a packaging advantage in that the unit is relatively smaller than comparable pretensioners. The slot also may function to permit a load-limiting function of guide member  26 , whereby when weight is exerted on the belt, guide member  26  retracts in the slotted position to release a small amount of belt webbing thereby partially absorbing the impact force on the occupant. 
   A first portion  12   a  of safety belt  12  is coiled about first guide member  24  and extends between a first safety belt securement (for example, a retractor mechanism in the embodiment shown) and second guide member  26 . Similarly, a second portion  12   b  of safety belt  12  is coiled about second guide member  26  and extends between a first guide member  24  and a second safety belt securement (for example, a safety belt buckle mechanism, not shown). 
   A detent mechanism, generally designated  46 , is provided for releasably securing second guide member  26  in a first position with respect to first guide member  24  prior to pretensioner activation. Detent mechanism  46  may comprise, for example, a shear pin in engagement with second guide member  26  and with another member (for example, frame  22  or an interior portion of the vehicle) that is mounted in a fixed spatial relationship with first guide member  24 . In another example, detent mechanism  46  comprises a deformation (for example, a crimp) in a surface of second guide member  26  in engagement with a corresponding deformation in a surface of another member mounted in a fixed spatial relationship with first guide member  24 . 
   Referring again to  FIGS. 1 and 2 , activation mechanism  20  includes a longitudinal housing  28  with at least one cylindrical passage  30  formed therein. Passage  30  has a first end  32  and a second end  34 . In the embodiment shown, housing  28  is secured to pretensioner mechanism frame  22 . However, housing  28  may alternatively be secured to another suitable portion of the vehicle interior. Housing  28  is may be formed from steel, aluminum, metal alloys, and/or other known materials suitable for use in a pressure resistant vessel or piston housing. 
   An actuator or piston  36  is movable in housing passage  30  and has a pressure surface  38  formed thereon. In the embodiment shown, actuator  36  is essentially cylindrical and is slidingly received in cylindrical passage  30  in housing  28 . Actuator  36  may be die cast, molded, or otherwise formed from metal, plastics, other suitably rigid materials, and combinations thereof. Actuator  36  might be constructed as a single piece or, alternatively, as a plurality of pieces or segments. 
   It should be appreciated that neither actuator  36  nor housing passage  28  need be cylindrical, and various deviations from the design of the disclosed embodiments might be made without departing from the scope of the present invention. For instance, actuator  36  and passage  30  might be flat-sided, or even rectangular in cross section. 
   Referring to  FIGS. 1 ,  2 , and  4 , activation mechanism  20  is operably coupled to pretensioner mechanism  10  via a connecting member  44  connecting actuator  36  to second guide member  26  such that the second guide member moves in correspondence with actuator  36  upon activation of the pretensioner assembly. In the embodiment shown, the connecting member operates in tension. Thus, the connecting member may be formed from steel, aluminum, or other metals or alloys into a relatively rigid member, such as a rod, or into a relatively pliable member, such as a length of cable. In an alternative embodiment, activation mechanism  20  may be arranged on a side of frame  22  opposite that shown in  FIGS. 1 and 2 . In this arrangement, activation mechanism  20  is configured to push, rather than pull, on second guide member  26  upon actuation, in the direction indicated by arrow A ( FIG. 4 ). In this case, connecting member  44  is a substantially rigid member. 
   A gas generator  40  is provided in fluid communication with first end  32  of housing passage  30  and adjacent actuator pressure surface  38  for providing a gas pressure to actuator pressure surface  38 . As is known in the art, gas generator  40  includes an initiator (not shown) and a quantity of a suitable gas generant composition (also not shown) in fluid communication with the initiator. Gas generator  40  may (but not necessarily) be formed as a “micro” gas generator as disclosed in U.S. Pat. No. 6,789,485, incorporated herein by reference. Gas generants useful in conjunction with the present invention are gas generants well known to those of ordinary skill in the art including cellulose-based compositions. Other examples include those described in U.S. Pat. Nos. 5,035,757, 5,460,668, 5,756,929, and 5,872,329, each herein incorporated by reference. These compositions exemplify, but do not limit, useful gas generant compositions. A gas port  42  is formed in housing  28  to enable fluid communication between housing passage  30  and gas generator  40 . Gas generator  40  may be secured to housing  28 , to frame  22 , or to some other suitable portion of the vehicle interior. 
   In operation, and referring to  FIGS. 3 and 4 , when activation of pretensioner assembly  10  is desired, for example in the event of a crash, a sensor (not shown) communicates electrical current via electrical contacts (not shown) to the initiator in gas generator  40 . Energizing of the initiator causes the combustion of the gas generant composition in gas generator  40 . The resulting pressurized gas enters housing passage  30  wherein the gas pressure in passage  30  begins to rise extremely rapidly, as does the pressure acting on actuator pressure surface  38 . When a sufficient level of gas pressure is reached, actuator  36  begins to move through passage  30  from first end  32  toward second end  34 , in the direction indicated by arrow A. 
   As actuator  36  moves toward housing passage second end  34 , force is generated on detent mechanism  46  sufficient to disengage the detent mechanism, thereby releasing second guide member  26  from securement. For example, if detent mechanism  46  comprises a shear pin, sufficient force is generated by pressure of inflation gas on pressure surface  38  to cause shearing of the pin, thereby releasing second guide member  26 . The shear pin may be selected to shear at a predetermined pressure in accordance with design requirements. 
   Thus, as actuator  36  moves toward housing passage second end  34 , second guide member  26  is pulled in the direction of arrow A via attached connecting member  44 . At this time, one end of belt  12  is immobilized by retractor mechanism  16 . Also, an opposite end of belt  12  is immobilized by the belt buckle mechanism, and slack exists in the portion of the belt residing between the buckle mechanism and second guide portion  26 . Movement of second guide member  26  with respect to first guide member  24  effectively increases a length of a portion of the safety belt extending between second guide member  26  and the buckle mechanism, thereby removing slack from the safety belt. At the end of travel of actuator  36  within housing passage  30 , second guide member  26  has also reached its limit of downward travel and, having removed the slack from belt  12 , becomes an additional, temporary anchor for the safety belt. 
   Pretensioner assembly  20  also serves a load-limiting function. As the vehicle occupant is thrown forward into safety belt  12 , a tension force is exerted on the belt, causing second guide member  26  to retract, in the direction indicated by arrow B. This causes, via connecting member  44 , a movement of actuator  36  and a corresponding compression of the gas contained in housing passage  30 . This motion of second guide member  26  releases a slight amount of belt webbing, helping to absorb the impact force on the occupant and to aid in minimizing belt-inflicted injury. 
   In another embodiment, shown in  FIGS. 5A-5C , second guide member  26  is attached to connecting member  44  via a hinge  60 . In yet another embodiment, shown in  FIGS. 6-7D , first guide member  24  is slidingly secured to frame  22  so as to be slidable between a first end position C and a second end position D. Movement of second guide member  26  with respect to first guide member  24  upon pretensioner actuation causes movement of first guide member  24  between first end position C and second end position D. The embodiments of the present invention shown in  FIGS. 5A-5C  and  FIGS. 6-7D  function in much the same manner as the embodiments shown in  FIGS. 1-4 . However, the different geometry illustrates how a varying design accomplishes the same goal without departing from the present invention&#39;s scope. In these embodiments, safety belt  12  is out of contact with guide members  24 ,  26  prior to pretensioner activation, and movement of second guide member  26  with respect to first guide member  24  upon pretensioner actuation produces coiling of the first portion of the safety belt about first guide member  24  and coiling of the second portion of the safety belt about second guide member  24 . 
   Referring to  FIG. 8 , any of the pretensioner assembly embodiments described above may also be incorporated into a safety belt assembly  150 . Safety belt assembly  150  includes a safety belt housing  152 , a safety belt  151 , a pretensioner assembly  20  in accordance with the present invention, and a retractor mechanism  154 . Safety belt system  150  may be in communication with a crash event sensor  158  (for example, an inertia sensor or an accelerometer) including a known crash sensor algorithm that signals actuation of belt pretensioner  156  via, for example, activation of a the initiator in a gas generator (not shown). U.S. Pat. Nos. 6,505,790 and 6,419,177, previously incorporated herein by reference, provide illustrative examples of pretensioners actuated in such a manner. 
   Referring again to  FIG. 8 , safety belt assembly  150  may also be incorporated into a broader, more comprehensive vehicle occupant restraint system  180  including additional elements such as an airbag system  200 .  FIG. 8  shows a schematic diagram of one exemplary embodiment of such a restraint system. Airbag system  200  includes at least one airbag  202  and an inflator  204  coupled to airbag  202  so as to enable fluid communication with an interior of the airbag. Inflator  204  contains a combustible gas generant composition for generating inflation gas for inflating airbag  202 , and at least one igniter for igniting the gas generant composition in the inflator. Examples of inflators which may be incorporated into airbag system  200  are described in U.S. Pat. Nos. 6,752,421, 5,806,888, and 6,341,799, all incorporated herein by reference. Airbag system  200  may also be in communication with a crash event sensor  210  including a known crash sensor algorithm that signals actuation of airbag system  200  via, for example, activation of airbag inflator  204  in the event of a collision. 
   It should be understood that the preceding is merely a detailed description of various embodiments of this invention and that numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit or scope of the invention. The preceding description, therefore, is not meant to limit the scope of the invention.