Coil spring with irregular cross section

A coil spring with irregular cross section being characterized in that:

• it is a coil spring with irregular cross section, the coil spring being made by subjecting a coil wire having an irregular cross section to a fatigue-strength improving treatment including a shot peening treatment after coiling the coil wire into a spring configuration:
• when being placed in a polar coordinate system comprising a pole, and a polar axis that extends from the pole toward a coil central axis in a coil radial direction, it has a vertical cross-sectional profile that is taken along in a coil axial direction of said coil wire,
• the vertical cross-section profile makes a substantially ellipse shape in which not only said pole makes the center but also said coil radial direction makes the major-diameter direction;
• and
• when labeling the major-diameter-side maximum diameter of said vertical cross-section profile “2LR,” labeling the minor-diameter-side maximum diameter of said vertical cross-sectional profile “2SR,” labeling a central offset coefficient in said major-diameter direction “Δb,” and additionally, when labeling an inner-side x-axis coefficient “nxr” and labeling an inner-side y-axis coefficient “nyr” in an orthogonal coordinate system in which said pole makes the origin and said polar axis is set in a positive area of the x-axis,
• said vertical cross-sectional profile has a coil inner-peripheral-side section that is expressed by following Equation (1) and Equation (2):
• x=(LR−Δb)cosnxrθ+Δb (1)
• y=SRsinnyrθ (2)
• wherein θ is a deflection angle in said polar coordinate system;
• and 0°≦θ<0°, 270°≦θ<360°, 0.7≦nxr≦0.9, 0.8≦nyr≦1.0, and 0.1SR≦Δb≦0.3SR;
• in said Equation (1) and Equation (2).