Development of 1520 MPa Class Lightweight Suspension Springs

The spring is an important component part of the suspension of motorcycles and automobiles. As the spring constitutes an unsprung weight, the suspension complies more quickly if the spring weighs less. Especially in off-road motorcycles, which are often subjected to extremely hard conditions such as full acceleration and braking, quick turning and jumping, a reduction of unsprung weight contributes to an enhancement of dynamic performance. As an effective means to reduce weight, use of the light-weight titanium instead of the commonly used steel is seen in some examples. However, applications of titanium are limited only to large-diameter springs because of its higher cost and challenging in coiling. To achieve a steel spring that weighs lower than a titanium counterpart, we aimed at a spring that features such a fatigue strength that allows stressing as higher as to 1520 MPa. Three technical options are used, 1) Shot peening, 2) Removal of decarburized surface on wire material, 3) Control of inclusion of impurities. As a result, we developed a steel spring with lower weight than titanium.