Power transmission shaft

Abstract

A power transmission shaft having an improved strength and ensuring a stable torsion fatigue strength. The power transmission shaft has coupling members respectively provided on the opposite ends of an pipe part made of a steel material. The steel material includes 0.30-0.45% by weight of C, 0.05-0.35% by weight of Si, 1.0-2.0% by weight of Mn, 0.05% by weight or less of Al, 0.01% by weight or less of S, and the remainder (iron Fe and unavoidable impurities). The pipe part has an electro-unite portion that extends in the axial direction. The electro-unite portion and neighborhood thereof are hardened so as to have a Rockwell hardness HRC of 45 or more. Also, another power transmission shaft has coupling members integrally formed on opposite ends thereof. In addition, the shaft is formed from a steel element tube by a plastic working. The shaft has an inner diametrical surface which is subjected to a high-frequency induction hardening and tempering treatment to make the surface portion hardness of the inner diametrical surface to have a Rockwell hardness HRC of 35 or more.

1 . A power transmission shaft integrally with coupling members integrally formed on opposite ends thereof, which is formed from a steel element tube by a plastic working, comprising an inner diametrical surface which is subjected to a hardening treatment.  
   
   
       2 . The power transmission shaft according to  claim 1 , wherein 
 the hardening treatment is a high-frequency induction hardening and tempering treatment.    
   
   
       3 . The power transmission shaft according to  claim 1  or  2 , wherein 
 the hardened layer formed by the hardening treatment extends from an outer diametrical surface to the inner diametrical surface.    
   
   
       4 . The power transmission shaft according to  claim 3 , wherein 
 the surface portion hardness of the inner diametrical surface is a Rockwell hardness HRC of 35 or more.    
   
   
       5 . The power transmission shaft according to  claim 3 , wherein 
 a predetermined residual compression stress is applied on the outer diametrical surface.    
   
   
       6 . The power transmission shaft according to  claim 5 , wherein 
 the residual compression stress is applied by a shot peening treatment.    
   
   
       7 . The power transmission shaft according to  claim 5 , wherein the residual compression stress is 750 MPa or more.  
   
   
       8 . The power transmission shaft according to  claim 6 , wherein the residual compression stress is 750 MPa or more.