Design Difficulties of Torsion Springs

Unlike the shear stress of tension/compression springs, torsion spring coils bear bending stress during operation, and the stress concentration point is located on the inner side of the coil. The calculation requires additional consideration of the curvature correction factor and material bending allowable stress, with more complex formulas. In high-torque scenarios, the inner side stress is very likely to exceed the limit, which is a high-incidence area of fatigue fracture.

Theoretically, torsion angle is proportional to torque. However, in actual large-angle torsion, the spring coil diameter will shrink and the number of effective coils will change, causing the torque to deviate from the theoretical value. For high-precision scenarios such as precision instruments and regulating valves, repeated iterative correction of wire diameter and coil parameters is required, resulting in high debugging costs.

Torsion springs are divided into left-hand and right-hand types. The working torsion direction must be consistent with the spring helix hand (when the torsion direction matches the helix hand, the spring hugs the mandrel and the torque is stable). Incorrect helix hand design will directly cause the coil diameter to expand, the torque to drop sharply, and even cause the torsion arm to fall off and fail.

The root connecting the torsion arm and the coil is the second major stress concentration area, which is prone to fracture under long-term repeated torsion. It is necessary to optimize the transition fillet, torsion arm length and support angle to balance force transmission efficiency and fatigue life. The stress simulation and verification cost of special-shaped torsion arms is higher.

Most application scenarios have limited installation space. It is necessary to meet the requirements of torque, torsion angle and service life at the same time within the limited inner diameter, outer diameter and axial length. It often requires multiple iterations of wire diameter, coil number and coil diameter parameters to balance performance and installation dimensions.