Power transmission shaft

Abstract

A power transmission shaft which can be evaluated on torsional fatigue strength based on a management indicator different from compressive residual stress in an outer surface. In a power transmission shaft having outer circumferential serrations 1 a, 1 b , torsional fatigue strength is evaluated by using compressive residual stress at a depth of 30 μm (and 50 μm) from an outer surface of a rising portion of each concave of the outer circumferential serrations 1 a, 1 b as a management indicator. A high torsional fatigue strength can be secured by having a compressive residual stress of 1150 MPa or more at a depth of 30 μm (and 50 μm) from the outer surface.

1 . A power transmission shaft having an axial notch on its outer circumferential surface, 
 said axial notch having an axial end having a compressive residual stress of 1150 MPa or more at a depth of 30 μm from an outer surface.    
   
   
       2 . The power transmission shaft according to  claim 1 , wherein said axial end has a compressive residual stress of 1150 MPa or more at a depth of 50 μm from the outer surface.  
   
   
       3 . The power transmission shaft according to  claim 1 , wherein said compressive residual stress is imparted by shot peening comprising pelting said axial end at a speed of 55 to 90 m/sec with shots having an average particle radius of one-third to two-thirds of a minimum curvature radius of said axial end and a higher hardness than a surface hardness of said axial end before shot peening by 50 to 300 Hv.  
   
   
       4 . The power transmission shaft according to  claim 3 , wherein thermal treatment is applied to said axial end before said shot peening.  
   
   
       5 . The power transmission shaft according to  claim 2 , wherein said compressive residual stress is imparted by shot peening comprising pelting said axial end at a speed of 55 to 90 m/sec with shots having an average particle radius of one-third to two-thirds of a minimum curvature radius of said axial end and a higher hardness than a surface hardness of said axial end before shot peening by 50 to 300 Hv.  
   
   
       6 . The power transmission shaft according to  claim 5 , wherein thermal treatment is applied to said axial end before said shot peening.  
   
   
       7 . The power transmission shaft according to  claim 1 , wherein said axial notch is a serration.  
   
   
       8 . The power transmission shaft according to  claim 1 , wherein said power transmission shaft is a power transmission shaft for an automobile to be connected to a universal coupling, and 
 said axial notch is a part to be connected to said universal coupling.