Patent Publication Number: US-2005127660-A1

Title: Low friction D-ring or web guide

Description:
BACKGROUND AND SUMMARY OF THE INVENTION  
      This application claims the benefit of U.S. Provisional Application 60/529,497, filed on Dec. 15, 2003. The disclosure of the above application is incorporated herein by reference.  
      The present invention relates to D-rings or web guides for seat belt systems.  
      The typical three-point seat belt system  10  secured about an occupant  70  as shown in  FIG. 1  comprises a retractor  22  (mounted in the seat or on a vehicle pillar), a seat belt  24 , a D-ring (also referred in the art as a Web guide)  26  (often mounted on the B or C-pillar), a tongue  28  and a seat belt buckle  30  (mounted to a seat frame or to the floor). Two such web guides  26  and  26   a  are shown in  FIGS. 2 and 3 . Web guides such as  26  and  26   a  generally include a load-bearing body  32  and a load-bearing seat belt receiving surface  40  formed, for example, from a stamped plate ( FIG. 2 ) or from a wire ( FIG. 3 ). A fastener (not shown) is received through a fastener-receiving opening  42 . The seat belt receiving surface  40  is spaced apart from other portions of the D-ring thereby forming a seat belt receiving opening or slot  44 . During normal operation and as shown in  FIG. 1 , the seat belt is received through the D-ring and slides upon surface  40   
      Those familiar with the design and development of seat belt systems know the contact friction between the D-ring in the seat belt webbing (seat belt) can significantly impact the performance of the system. The friction in the seat belt system defines, in part, the spring constant of the rewind spring that acts on the spool of the retractor and which must generate a spring force sufficiently high to overcome friction in the system and pull or rewind a determinable extended length of seat belt (also referred to as webbing). As can be appreciated, the restoring force of the spring is proportional with the spring constant and as the spring constant increases (with increasing system friction) the inherent force applied by the shoulder belt upon the occupant&#39;s shoulder increases.  
      The prior art has attempted to reduce the contact friction at the D-ring by coating the D-ring with chrome, or with a synthetic or other generally low-friction or slippery material such as an electro-coat or Teflon® (PTFE). The prior art has also suggested constructing a preformed, low friction assembly and snapping this pre-form about the seat belt support surface  40  of the web guide.  
      It is an object of the present invention to provide an improved D-ring or web guide. Accordingly the invention comprises: a D-ring or web guide for a seat belt, comprising: a load-absorbing body formed with a seat belt support surface and an opening thereabove and a friction-reducing, thin, flexible synthetic tape configured to be applied to the seat belt support surface, the tape comprising a layer of low friction material with a layer of adhesive applied to a first side of the synthetic tape, the seat belt passing over a side of the tape opposite the first side of the tape, which is in contact with the adhesive.  
      Many other objects and purposes of the invention will be clear from the following detailed description of the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a conventional three-point seat belt system.  
       FIGS. 2 and 2   a  show views of a stamped D-ring or web guide.  
       FIG. 3  shows a D-ring or web guide made of bent wire.  
       FIG. 4  is a plan view of a section of tape.  
       FIG. 5  is a cross-sectional view taken through section  5 - 5  of  FIG. 4 .  
       FIGS. 6 and 6   a  show a thin film applied to the seat belt supporting surface of two different D-rings or web guides.  
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
      Reference is again briefly made to  FIGS. 2 and 2   a , which show a first type of known web guide  26  made from a one-piece steel stamping. This web guide includes a seat belt or web support surface  40  across which a seat belt slides. This web guide  26  includes a narrow opening  44  to receive the seat belt or webbing  24  (shown in phantom line).  
       FIG. 3  shows a bent wire  43  formed into a generally triangular shape. This web guide  26   a  also includes a seat belt support surface  40  across which the seat belt  24  slides. Characteristic of the bent wire type of web guide is that the web receiving opening  44  is larger than the corresponding opening shown in  FIG. 1 . As is known in the art, the web receiving opening  44  can be reduced in size by snapping an insert (not shown) to those portions of the web guide proximate the opening  44 .  
      The present invention proposes forming a flat, flexible, and generally rectangular tape (or tape segment) or applique  60  shown in  FIGS. 4 and 5  and applying this tape  62  to the support surface  40  of the D-ring. The thickness of the film  62  and the adhesive layer  64  has been exaggerated in  FIG. 5  (as well as in  FIG. 6 ). The seat belt or webbing  24  will slide over this tape or applique  60 . The tape or applique  60  comprises a low friction layer formed by a polymeric thin film  62  with an adhesive layer  64  applied to one side of the film  62 ; the other side of the film supports the seat belt. In the preferred embodiment the thin film  62  is made using a lonomer or Acetal thin film, a PTFE (Teflon or Teflon-like) film or an ultra-high molecular weight polyethylene (UHMWPE) film. The adhesive layer  64  must be able to adhere to the low friction surface of the thin film  62  as well as being able to be adhered to the metallic support surface  40  of the D-ring. In the preferred embodiment the adhesive is silicone or acrylic. Further, in the preferred embodiment of the invention the thickness of the fluoropolymer is approximately 0.13 mm while the thickness of the adhesive layer is approximately 0.04 mm. The combination of film and adhesive layer provides a 180 degree peel strength of about 0.6 lbs/in.  
      Reference is briefly made to  FIGS. 6 and 6   a , which show a web guide  100  (similar to web guide  26 ) of the present invention in which a segment  60   a  of the low friction tape  60  has been cut to length and applied to the support surface  40  of the D-ring or web guide  100 . In the cross-sectional view in  FIG. 6   a , the low friction tape  60  (or tape segment  60   a ) is shown applied to the support surface  40  of web guide  102  (similar to web guide  26 ).  
      In carrying out the preferred embodiment of the invention, it is envisioned the tape will be supplied in a roll; the tape segment  60   a  is subsequently cut to length as needed and applied to the support surface. The desired length of the tape segment  60   a  should be sufficient to cover the flat portion of the support surface  40  (and might be slightly less than the length of the support surface  40 ).  
      In an alternate embodiment of the invention the adhesive layer  64  is not used and the low friction film is transfer molded, in-line molded or insert molded to support surface  40  of the D ring.  
      Many changes and modifications in the above-described embodiment of the invention can, of course, be carried out without departing from the scope thereof. Accordingly, that scope is intended to be limited only by the scope of the appended claims.