Coil Spring Flat Face Design for Stress Distribution

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Solution Overview

Problem

There are limitations in designing coil springs with a non-circular sectional outer shape, particularly in achieving better stress distribution and design compared to coil springs with a circular cross section.

Innovation Solution

A coil spring with a circular sectional outer shape and contact faces between the inner and outer diameter sections, where the flattening ratio (T/W) is set to be equal to or lower than that of a circular cross section, stabilizing adjacent coil portions and reducing stress, thereby improving design and stress distribution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If flat faces are formed on the spring wire to stabilize adjacent coil portions, then slippage in coil diameter direction is suppressed, but stress concentration occurs on the inner diameter side

Engineering Contradiction:

Improvestability of adjacent coil portionsVSAvoidstress on inner diameter side

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The patent applies local quality by creating flat faces only at specific locations on the spring wire cross-section (inner diameter side and outer diameter side) rather than uniformly modifying the entire cross-section. This localized flattening stabilizes adjacent coil portions at contact points while preserving the circular cross-section geometry in other areas, thereby reducing overall stress concentration compared to conventional approaches that flatten the entire cross-section.

Inventive Principle:

Principle #3Local quality

2Length of moving object

If the spring wire cross-section is flattened to form contact faces, then the solid length is shortened for long stroke design, but the stress distribution becomes uneven

Engineering Contradiction:

Improvesolid length in coil axis directionVSAvoidstress distribution in sectional circumferential direction

Core Design Contradiction:

Length of moving objectVSStress or pressure

Solution Approach 1:

The patent applies partial action by forming flat faces only on the inner and outer diameter sides of the spring wire cross-section while leaving the top and bottom surfaces circular. This partial flattening achieves the necessary contact face geometry for stable coil compression and reduced solid length, while minimizing the disruption to stress distribution compared to complete cross-sectional flattening.

Inventive Principle:

Principle #16Partial or excessive action

3Stress or pressure

If a circular cross-section is used, then stress distribution is relatively uniform, but the solid length is longer limiting stroke capability

Engineering Contradiction:

Improvestress distribution uniformityVSAvoidsolid length in coil axis direction

Core Design Contradiction:

Stress or pressureVSLength of moving object

Solution Approach 1:

The patent reconciles this contradiction by applying local quality - maintaining a predominantly circular cross-section for uniform stress distribution while creating localized flat faces at the inner and outer diameter sides. These localized flat faces provide the necessary contact surfaces for stable coil compression and reduced solid length, achieving both uniform stress distribution and compact solid height.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS8876095B2Coil spring

Publication Date: 2014.11.04 NHK SPRING CO LTD

AI summary

A coil spring has a spring wire that is wound in a coil shape and whose sectional outer basic shape is circular and flat faces are formed between coil inner and outer diameter sections of a sectional outer shape of the spring wire, wherein a flattening T/W of the sectional outer shape with the flat faces in the coil axis direction is set so that a stress ratio is equal to or lower than a stress ratio of a coil spring whose sectional outer shape is circular.