Generic Knuckle Concept Model for Wheel Suspension Performance

Abstract

The knuckle is a wheel suspension component that transfers the forces acting upon the tires through the linkages to the vehicle’s sub-frame. The coordinates, or joints, where the knuckle and linkages connect are the outer hardpoints and the joints where the linkages and vehicle’s sub-frame connect are the inner hardpoints. The position of hardpoints in 3D space will determine the motion of the wheels during different maneuvers. In the concept phase of the suspension system development, the hardpoints are computed and analyzed iteratively for optimum kinematics and compliance behavior. The suspension knuckle is developed based on the hardpoints. However, optimizing the knuckle design based on stiffness and weight targets for different test cases is time-consuming. Therefore, a quick computation of the knuckle’s approximate stiffness right after the iteration of hardpoints in the concept phase will speed up the suspension development process. This quick approximation of the stiffness, using the concept of 3D-frame analysis, is computed using the Direct Stiffness Method. The frame structure is formed by joining the outer hardpoints using 3D beam elements of uniform and linearly varying cross-sections. The four-link suspension system is mathematically modeled to compute the reaction forces at the outer hardpoints for the applied force at the tire contact patch. The deformation of the nodes at each knuckle hardpoint is calculated based on the reaction forces and appropriate constraints. This mathematical model is validated using NX Finite Element software using 1D elements of uniform and varying cross-sections. Upon validation, the mathematical model is compared against the finite element model of the knuckle for camber and aligning torque stiffness.