Leaf springs are used as the suspension elements for the front and rear axles of light and heavy commercial vehicles in the automotive key industry. While the vehicle is running empty or with a load under on-road or off-road conditions, it catches the loads transmitted from the wheels i.e., the loads from the ground to the hub axle, and working together with the damper it helps absorption of such loads and prevents them from being transmitted to the chassis. As a result, vehicle comfort is achieved. In addition to this function, leaf springs act as a safety part that continuously hold the chassis and axle together under static and dynamic loads.
While the vehicle is runs under rough road conditions, the impact loads from the road not only cause negative impacts on the vehicle but also damage the drivetrain. Such impact loads substantially disturb both the vehicle and the passengers. The main target of the vehicle manufacturers is to eliminate the fatigue caused by impact effects created at high amplitudes (strokes) under rough road conditions, in order to achieve vehicle comfort.
In this study, a progressive lead spring consisting of a main spring and a helper spring, which operates at high displacement and tensile values under bad road conditions and consists of a main spring and a helper spring with two different spring constants for different loading conditions is taken as reference.
During final decision of virtual optimized design, leaf spring design attributes, different load conditions, rig test results and real-life fatigue test conditions were taken into consideration with leaf spring safety and driving comfort conditions in mind. A finite element model under different load conditions, the reaction forces on leaf spring, suspension controlled & load controlled rig tests, real-life test results on rough road, and the correlation of real-life and virtual optimized design have been presented.