Coil Spring Tapered Ends for Link-Motion Suspension Bowing

The patent applies local quality by creating a taper portion only at the end turn portions of the coil spring, while the effective portion maintains uniform wire diameter. This localized modification reduces stress concentration at the ends without affecting the spring's overall functionality, thereby reducing stress amplitude while maintaining suspension performance.

The taper portion is formed in advance during the hot forming coiling process before the coil spring is assembled into the suspension. This preliminary action of creating the tapered geometry prevents stress concentration from occurring during suspension operation, rather than attempting to mitigate it after the fact.

Instead of uniformly increasing the wire diameter throughout the coil spring, the patent applies a taper portion only at the end turn portions where stress concentration occurs. This localized approach provides the necessary strength at critical areas while maintaining lighter weight in the effective portion, thus resolving the contradiction between strength and weight.

The patent changes the wire diameter parameter locally at the end turn portions by creating a taper geometry, rather than maintaining a constant diameter. This parameter change allows the wire diameter to vary from larger at the ends (for strength) to smaller in the effective portion (for weight reduction), optimizing both strength and weight simultaneously.

The taper portion is formed as a preliminary action during the wire preparation stage before the coiling process begins. By pre-forming the tapered geometry on the wire, the subsequent coiling operation can proceed efficiently without requiring complex tooling or processes to create the taper during winding, thus maintaining high productivity.

The patent utilizes the plasticity of heated wire to change its cross-sectional geometry from circular to tapered shape before coiling. This parameter change in wire geometry is achieved while the wire is in a softened state, making it easy to form the taper portion using simple rolling or shaping operations prior to the coiling process.