Importance

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Abstract

A coil spring with irregular cross section according to the present invention is 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, and the coil spring with irregular cross section has a vertical cross sectional profile whose coil inner-peripheral-side section is expressed by following Equation (1) and Equation (2) in a polar coordinate system and orthogonal coordinate system:

description='In-line Formulae' end='lead'x=(LR−Δb)cos^nxr θ+Δb  (1)description='In-line Formulae' end='tail'

description='In-line Formulae' end='lead'y=SR sin^nyr θ  (2)description='In-line Formulae' end='tail'

wherein θ is a deflection angle in said polar coordinate system; and 0°≦θ<90°, 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). In accordance with the present invention, it is possible to provide a coil spring with irregular cross section that exhibits more uniform and higher fatigue strength along a cross-sectional peripheral direction of the coil wire.

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First Claim