Abstract:
A flexible shaft having square or helical square tips with thermoplastic felt covering and adherent to the tips including the tip ends. The felt has fused bulges adjacent the ends. When the tips are inserted into mating recesses of driving and driven members, the felt is deformed to improve the fit between the tips and the recesses and reduce noise and vibration when the driving member is rotated.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/366,737 filed Jul. 22, 2010 and entitled Low Noise and Vibration Flexible Shaft Assembly. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a rotatable flexible shaft transmitting torque with reduced noise and vibration. 
     Such shafts normally have ends of square cross-section which are adapted to engage square recesses in mating torque transmitting and receiving members. When such a shaft is rotated, noise is generated due to movement of the shaft ends within the mating recesses. It is not possible to provide an exact fit between the shaft ends and the recesses, since manufacturing tolerances must be maintained to insure the ends can be inserted into the recesses when the associated devices, such as motor vehicle seats, are assembled. 
     Prior art efforts to reduce such noise and vibration include applying flocked yarn or flock fibers, grease, or heat shrink tubing such as polytetrafluoroethylene to the lateral surfaces of the shaft ends. See, for example, U.S. Pat. No. 7,717,795 to Mellor. 
     Such prior art constructions have various disadvantages such as significant manufacturing expense, fabrication difficulty, limited durability, limited useful life, and/or a performance level less than that desired. 
     Patent Application Publication No. US 2008/0220883 of Yuen shows a noise and vibration reducing construction wherein felt or a material having similar mechanical characteristics is wrapped around a major part of the shaft to reduce noise and vibration due to contact with the surrounding casing. U.S. Pat. No. 5,558,578 to Uryu et al. discloses compressed felt coaxial sheaths which surround spaced portions of the shaft. However, further reduction of noise and vibration is generally desired. 
     Patent Application Publication No. US 2010/0252359 of Yuen shows a noise reducing construction wherein the shaft ends have raised portions of compressible material such as flocked yarn covered with plastic tubing. This construction also fails to provide the desired level of durability, useful life, and noise and vibration reduction. 
     Accordingly, an object of the present invention is to provide an improved reduced noise and vibration flexible shaft which can readily be manufactured at reasonable cost and which exhibits improved durability and useful life. 
     SUMMARY OF THE INVENTION 
     According to the invention, a torque transmitting wire wound flexible shaft has noncircular end portions, preferably having a square or helical square shape and chamfered end portions. Felt strips are wrapped around and adhered to all or part of the end portions including the distal end surfaces thereof, and may be wrapped around all or part of the chamfered parts of those end portions. Overlapping parts of the felt strips are preferably fused together, in which case they are made of thermoplastic material. 
    
    
     
       IN THE DRAWING 
         FIG. 1  is an isometric view of a flexible shaft according to a first embodiment of the invention. 
         FIG. 2   a  is an isometric view of one tip of the shaft shown in  FIG. 1 . 
         FIG. 2   b  is a front elevation view of the shaft tip shown in  FIG. 2   a.    
         FIG. 2   c  is a front cross-sectional view of the shaft tip shown in  FIG. 2   b , taken along the cutting plane A-A. 
         FIG. 3   a  is an isometric view of a flexible shaft tip according to a second embodiment of the invention. 
         FIG. 3   b  is a front elevation view of the shaft tip shown in  FIG. 3   a.    
         FIG. 3   c  is a front cross-sectional view of the shaft tip shown in  FIG. 3   b , taken along the cutting plane A-A. 
         FIG. 4   a  is an isometric view of a flexible shaft tip according to a third embodiment of the invention. 
         FIG. 4   b  is a front elevation view of the shaft tip shown in  FIG. 4   a.    
         FIG. 4   c  is a front cross-sectional view of the shaft tip shown in  FIG. 4   b , taken along the cutting plane A-A. 
         FIG. 5   a  is an isometric view of a flexible shaft tip according to a fourth embodiment of the invention. 
         FIG. 5   b  is a front elevation view of the shaft tip shown in  FIG. 5   a.    
         FIG. 5   c  is a front cross-sectional view of the shaft tip shown in  FIG. 5   b , taken along the cutting plane A-A. 
         FIG. 6   a  is an isometric view of a flexible shaft tip according to a fifth and preferred embodiment of the invention. 
         FIG. 6   b  is a front elevation view of the shaft tip shown in  FIG. 6   a.    
         FIG. 6   c  is a front cross-sectional view of the shaft tip shown in  FIG. 6   b , taken along the cutting plane A-A. 
         FIG. 6   d  is a left side cross-sectional view of the shaft tip shown in  FIG. 6   b , taken along the cutting plane B-B. 
     
    
    
     DETAILED DESCRIPTION 
     The wire wound flexible shaft  10  shown in  FIGS. 1 to 2   c  has a central generally cylindrical major portion  1   a  with noncircular end portions  11   a  and  11   b  which have tips  1   b  and  1   c  respectively of square cross-section and chamfered transition parts  12   a  and  12   b  between the tips and the major portion of the shaft. 
     The shaft tips may if desired have a helical square end shape such as that shown in U.S. Pat. No. 6,464,588 to Rupp. Both the square and helical square tip shapes have a square cross-section. 
     Alternatively, the tips may have other geometries such as generally conical, dome-shaped, or of complex shape, so long as they have a noncircular cross-section. 
     As best seen in  FIGS. 2   a  and  2   c , a single felt strip  2   a  covers part of the front and rear surfaces  13   a  and  13   b  of tip  1   b  as well as the tip end surface  13   c.    
     The felt strip  2   a  preferably comprises a thermoplastic felt and is glues to the adjacent parts of the tip  1   b . Alternatively, wool, a rayon-wool composite, or another felt material may be used. 
     The felt strip  2   a  should have a thickness and compressibility consistent with the manufacturing tolerance between the shaft tip and the mating recess of a driving or driven member into which the tip is to be inserted. When so inserted, the felt is compressed to accommodate, that is, partially fill the space between the tip and mating recess, resulting in reduced noise and vibration when the shaft is rotated. 
     While only one shaft tip is shown and described in detail, the opposite shaft tip of each embodiment is covered with felt to a similar extent and in a similar manner. 
     In the first embodiment the upper and lower surfaces of the shaft tips are not covered; while in the other embodiments all four tip lateral surfaces are covered with felt. In the fourth embodiment ( FIGS. 5   a - 5   c ) the ends of the shaft tips are only partially covered with felt, while in the other embodiments the ends are substantially fully covered. 
     In the second embodiment ( FIGS. 3   a - 3   c ) two felt strips  3   a  and  3   a ′ cover the tip  1   b . Strip  3   a  covers part of the front and rear surfaces  13   a  and  13   b  of tip  1   b  as well as the tip end surface  13   c ; while strip  3   a ′ covers part of the upper and lower surfaces  13   d  and  13   e  of tip  1   b  as well as the tip end surface  13   c , where strip  3   a ′ overlaps strip  3   a.    
     Felt strips  3   a  and  3   a ′ comprise a thermoplastic material and are glued to the adjacent surfaces of the tip  1   b . After they are applied, a hot anvil is used to contact the overlapping parts of the strips at the tip end  13   c , to cause those parts to fuse together. 
     Instead of using two strips to cover the tip end in the second embodiment, a single piece of felt having the shape of a cross can be used, with the center of the cross shape being applied to the tip end  13   c  and the arms covering the adjacent lateral surfaces  13   a ,  13   b ,  13   d  and  13   e  of the tip  1   b.    
     In the third embodiment ( FIGS. 4   a - 4   c ) thermoplastic felt tape  4   a  is helically wrapped around and glued to the end of the tip  1   b  in such a manner that adjacent turns are close to each other but do not overlap. The tape is overwound at the tip end  13   c  so that a small part of the tape extends beyond the tip end. The extending part of the tape is then contacted with a hot anvil to cause the extending part to fuse so as to form a fused felt bulge  4   b  on the tip end  13   c.    
     The fourth embodiment ( FIGS. 5   a - 5   c ) is the same as the fourth embodiment, except that the tape  4   a  is overwound by a smaller amount so that after fusing of its extending part, the resulting bulge  4   c  covers only a peripheral portion of the tip end, leaving a central part of the end exposed. 
     In the fifth and preferred embodiment ( FIGS. 6   a - 6   d ) a single piece of thermoplastic felt  6   a  is wrapped around the tip  1   b  and overwound at the tip end  13   c  so that a small part of the tape extends beyond the tip end. The extending part of the tape is then contacted with a hot anvil to cause the extending part to fuse so as to form a fused felt bulge  6   b  on the tip end  13   c.    
     The distal ends (not shown) are chamfered to facilitate insertion into mating recesses of driving and driven members of an associated device. 
     The felt strips or tape are secured to the adjacent surfaces of the shaft end portions by glue suitable for adhering the particular felt being used to the tip metal without saturating the felt. 
     If desired, the felt strips or tape may extend so far along the tips that part or all of the chamfered portions  12   a  are covered. Instead of felt, a similar compressible, vibration damping material may be used. The felt or similar material prevents rattle by filling the space between the shaft end portion and mating hole with compressible, vibration damping material which deforms upon engagement of the shaft end portion and hole to conform itself to that space.