Coil springs are the most used springs in modern cars. It has strong shock absorption capacity and good ride comfort. The disadvantage is that it is longer in length, occupies a lot of space, and the contact surface of the installation position is also larger, making it difficult to achieve a compact suspension system. Since the coil spring itself cannot bear the lateral force, a complex combination mechanism such as a four-bar coil spring has to be used in an independent suspension.

For the consideration of ride comfort, we hope that the spring can be softer for ground impact with high frequency and small amplitude, and when the impact force is large, it can show greater rigidity and reduce the impact stroke, so it is necessary The spring has two or more stiffnesses at the same time. Springs with different wire diameters or springs with different pitches can be used, and their stiffness increases with the increase of the load.