Suspension spring apparatus and suspension coil spring

Abstract

A compressive residual stress portion having a compressive residual stress from a surface of a wire to a first depth is formed between end turn portions of a coil spring. The first portion of the end turn portion is always in contact with a spring seat. The second portion contacts the spring seat when the load applied to the coil spring is large, and is separated from the spring seat when the load is small. The third portion is always separated from the spring seat. In the end turn portion, in a region including the second portion, a deep residual stress portion is formed by ultrasonic shot peening. The deep residual stress portion has a compressive residual stress from a surface of the wire to a second depth deeper than the first depth.

What is claimed is: 
     
         1 . A suspension spring apparatus comprising:
 a lower spring seat;
 an upper spring seat; and 
 a coil spring which comprises a wire formed into a helical shape, and arranged in a state in which the coil spring is compressed between the lower spring seat and the upper spring seat, 
 the coil spring comprising a lower end turn portion which is less than one turn from a lower end of the wire, and an upper end turn portion which is less than one turn from an upper end of the wire, 
 at least the lower end turn portion comprising a first portion which is always in contact with the lower spring seat irrespective of magnitude of a load applied to the coil spring, a second portion which contacts the lower spring seat or is separated from the lower spring seat in accordance with the load applied to the coil spring, and a third portion which is always separated from the lower spring seat irrespective of the magnitude of the load, 
 the coil spring comprising: 
 a compressive residual stress portion between the lower end turn portion and the upper end turn portion, a compressive residual stress from a surface of the wire to a first depth being imparted to the compressive residual stress portion, and 
 a deep residual stress portion in a region including the second portion of the lower end turn portion, a compressive residual stress from a surface of the wire to a second depth deeper than the first depth being imparted to the deep residual stress portion. 
   
     
     
         2 . The apparatus of  claim 1 , wherein a maximum of an absolute value of the compressive residual stress of the deep residual stress portion is greater than a maximum of an absolute value of the compressive residual stress of the compressive residual stress portion. 
     
     
         3 . The apparatus of  claim 1 , wherein a stress transition portion in which the compressive residual stress of the deep residual stress portion gradually reduces is provided at a boundary between the deep residual stress portion and the compressive residual stress portion. 
     
     
         4 . The apparatus of  claim 2 , wherein a stress transition portion in which the compressive residual stress of the deep residual stress portion gradually reduces is provided at a boundary between the deep residual stress portion and the compressive residual stress portion. 
     
     
         5 . The apparatus of  claim 1 , wherein a first shot peening indentation is formed on a surface of the compressive residual stress portion, a second shot peening indentation is formed on a surface of the deep residual stress portion, and a size of the second shot peening indentation is larger than a size of the first shot peening indentation. 
     
     
         6 . The apparatus of  claim 2 , wherein a first shot peening indentation is formed on a surface of the compressive residual stress portion, a second shot peening indentation is formed on a surface of the deep residual stress portion, and a size of the second shot peening indentation is larger than a size of the first shot peening indentation. 
     
     
         7 . The apparatus of  claim 1 , wherein the deep residual stress portion is formed at both the lower end turn portion and the upper end turn portion. 
     
     
         8 . The apparatus of  claim 2 , wherein the deep residual stress portion is formed at both the lower end turn portion and the upper end turn portion. 
     
     
         9 . The apparatus of  claim 1 , wherein the lower spring seat comprises a bottom surface and an outer sidewall which restrain a lower surface and an outer peripheral surface of the lower end turn portion, respectively, and the deep residual stress portion is formed in a range including the lower surface and the outer peripheral surface of the lower end turn portion. 
     
     
         10 . The apparatus of  claim 2 , wherein the lower spring seat comprises a bottom surface and an outer sidewall which restrain a lower surface and an outer peripheral surface of the lower end turn portion, respectively, and the deep residual stress portion is formed in a range including the lower surface and the outer peripheral surface of the lower end turn portion. 
     
     
         11 . The apparatus of  claim 1 , wherein the lower spring seat comprises a bottom surface and an inner sidewall which restrain a lower surface and an inner peripheral surface of the lower end turn portion, respectively, and the deep residual stress portion is formed in a range including the lower surface and the inner peripheral surface of the lower end turn portion. 
     
     
         12 . The apparatus of  claim 2 , wherein the lower spring seat comprises a bottom surface and an inner sidewall which restrain a lower surface and an inner peripheral surface of the lower end turn portion, respectively, and the deep residual stress portion is formed in a range including the lower surface and the inner peripheral surface of the lower end turn portion. 
     
     
         13 . A suspension coil spring comprising:
 a lower end turn portion which is less than one turn from a lower end of a wire formed into a helical shape; and   an upper end turn portion which is less than one turn from an upper end of the wire,   at least the lower end turn portion comprising a first portion which is always in contact with a lower spring seat irrespective of magnitude of a load, a second portion which contacts the lower spring seat or is separated from the lower spring seat in accordance with the magnitude of the load, and a third portion which is always separated from the lower spring seat irrespective of the magnitude of the load,   the suspension coil spring comprising:   a compressive residual stress portion between the lower end turn portion and the upper end turn portion, a compressive residual stress from a surface of the wire to a first depth being imparted to the compressive residual stress portion; and   a deep residual stress portion in a region including the second portion of the lower end turn portion, a compressive residual stress from a surface of the wire to a second depth deeper than the first depth being imparted to the deep residual stress portion.