Parabolic Leaf Spring Fatigue Considering Braking Windup Evaluations 2011-01-2168
Leaf springs are mainly used for absorbing energy associated with road outputs and they release energy coming from the road. If the complete leaf stiffness and each leaf stress distribution can be calculated carefully, while ensuring safety, required ride comfort will also be maintained. The desired vehicle ride height (attitude) under load must be taken into consideration during calculations of leaf spring design.
In addition to providing the loads coming from the vehicle, leaf springs are significantly controllers of windup effects. Braking windup causes rotation at the lateral axis. When vertical F jounce load and braking moment are applied to the leaf spring simultaneously, von misses stress value on leafs will increase to a higher level which is very close to and sometimes higher than the tensile strength.
The designers must ensure safety and endurance for any case during working conditions. The most critical point is front axle windup stopper position. Windup stopper position must be optimised by considering vertical movement of leaf spring due to vertical loads.
In this study, two layer parabolic leaf spring have been modelled and non linear finite element analyses have been performed according to vertical loads including F design, F jounce and Fm-m in order to see stress distributions and displacements on each leaf. Prototypes are produced and tested for endurance. Finite element analyses and physical tests are compared. Then, non linear finite element analyses have been performed for vertical load case (F jounce) with exposure windup braking moment.
This paper presents a virtual prototype process methodology considering a numerical approach correlated with vertical rig test results. Windup finite element analysis calculations have been done on the basis of material, vertical load, applied moment and windup stopper position assumptions.