Electronic Power Assist Steering Worm Gears

Abstract

Composite worm gears having little residual stress are prepared by forming a tube ( 101 ) of synthetic resin by extrusion, compression molding, or centrifugal processing, and fixing the tube thus produced or rings ( 102 ) cut therefrom onto a boss ( 103 ) or core ( 105 ), preferably of metal. The process allows high performance high molecular weight thermoplastics to be employed.

1 .- 18 . (canceled)  
     
     
         19 . A process for forming a composite gear blank, comprising a metal or a metal-containing boss, and a synthetic resin outer part, said outer part enclosing said boss in a circumferentially adjacent manner, said process comprising the steps of: 
 a) extruding, compression molding or centrifugally processing a synthetic resin tube,    b) cutting off rings from said tube, and    c) fixing said rings produced by step (b) around respective bosses    wherein residual heat from step (a) is used for fixing in step (c).    
     
     
         20 . The process of  claim 19 , wherein an annealing cycle (d) is added.  
     
     
         21 . The process of  claim 19 , wherein said boss is a metal boss.  
     
     
         22 . A process for forming a composite gear blank comprising a metal or metal-containing boss, and a synthetic resin outer part, said outer part enclosing said boss in a circumferentially adjacent manner, said process comprising the steps of: 
 (a) extruding, compression molding or centrifugally processing a synthetic resin,    (b) fixing said synthetic resin tube produced by step (a) onto a preformed metal or metal-containing core, and    (c) cutting off rings comprising a length of said synthetic resin tubes encasing a length of said preformed core.    
     
     
         23 . The process of  claim 19 , wherein said synthetic resin tube is continuously or semi-continuously extruded.  
     
     
         24 . The process of  claim 22 , wherein said synthetic resin tube is continuously or semi-continuously extruded.  
     
     
         25 . The process of  claim 22 , wherein said core is endless.  
     
     
         26 . The process of  claim 22 , wherein said core is a metal core.  
     
     
         27 . The process of  claim 19 , wherein said boss has a textured surface.  
     
     
         28 . The process of  claim 27 , wherein said textured surface is a knurled surface.  
     
     
         29 . The process of  claim 22 , wherein said core has a textured surface.  
     
     
         30 . The process of  claim 29 , wherein said textured surface is a knurled surface.  
     
     
         31 . The process of  claim 19 , wherein said tube is produced by coextruding at least two thermoplastics in concentric layers.  
     
     
         32 . The process of  claim 22 , wherein said tube is produced by coextruding at least two thermoplastics in concentric layers.  
     
     
         33 . The process of  claim 19 , further comprising induction heating the gear blank following fixing in step c) such that at least portions of the core adjacent the thermoplastic are heated to a temperature above the melt temperature of the thermoplastic.  
     
     
         34 . The process of  claim 22 , further comprising induction heating the gear blank during or following fixing in step b) such that at least portions of the core adjacent the thermoplastic are heated to a temperature above the melt temperature of the thermoplastic.  
     
     
         35 . The process of  claim 19 , wherein the tube is of semi-crystalline or crystallizable amorphous thermoplastic and extruded such that an inside diameter of the tube remains amorphous, further comprising heating the tube prior to the step of fixing (c) to just above the Tg of the thermoplastic, followed by further heating after fixing to crystallize the thermoplastic.  
     
     
         36 . The process of  claim 22 , wherein the tube is of semi-crystalline or crystallizable amorphous thermoplastic and extruded such that an inside diameter of the tube remains amorphous, further comprising heating the tube prior to the step of fixing (b) to just above the Tg of the thermoplastic, followed by further heating after fixing to crystallize the thermoplastic.  
     
     
         37 . The process of  claim 19 , wherein said tube has an inner diameter which is smaller than the outer diameter of the boss or core prior to said step of fixing (c).  
     
     
         38 . A worm gear or worm/worm gear combination, is produced by the process of  claim 19 , and wherein the synthetic resin outer part is machined into a worm gear.