Variable-Section Coil Spring for Lighter Nonlinear Suspension

The patent applies local quality by creating a quadrangle section portion with different cross-sectional geometry (square/rectangular) compared to the round section portion. This local geometric change reduces the polar moment of inertia in specific regions, achieving nonlinear spring characteristics without requiring extreme wire diameter reduction throughout the entire spring. The quadrangle section portion is formed by rolling the wire rod between grooved rolls, creating a localized structural modification that alters load distribution and deflection behavior.

The patent employs parameter changes by modifying the cross-sectional shape parameter from circular to square/rectangular in the quadrangle section portion. This geometric parameter change fundamentally alters the polar moment of inertia and section modulus, enabling weight reduction through optimized material distribution. The rolling process using grooved rolls transforms the wire rod cross-section in-situ, avoiding the need for post-manufacturing operations like cutting or swaging, thereby reducing manufacturing complexity while achieving the desired parameter change.

The patent implements preliminary action by pre-forming the quadrangle section portion during the wire rod rolling process before coil spring manufacturing. The grooved rolls are designed to create the square/rectangular cross-section and variable section portions in advance, integrating the geometric modification into the primary forming operation. This eliminates the need for subsequent time-consuming operations such as cutting, swaging, or plastic forming that would be required to achieve similar geometric modifications after coil formation.

The patent applies mechanics substitution by replacing traditional post-manufacturing methods (cutting, swaging, or plastic forming) with a rolling process using grooved rolls. Instead of mechanically removing material or deforming the wire after coil formation, the invention uses controlled plastic deformation during the rolling stage to create the quadrangle cross-section. This substitution simplifies the manufacturing flow by integrating the geometric modification into an existing process step, improving ease of manufacture despite the geometric complexity.