Performance Analysis And Optimization Design For Suspension System Based Virtual Prototype Technology

In the design of vehicle suspension system, the characteristics and their matching of important components, such as spring and damper, have crucial effects on suspension and vehicle behaviors. Due to their complicated relationships and influences with each other and the complexity of suspension system structure, variable loads and work conditions, the conventional physical-prototype-based design approaches has become difficult to accommodate with stricter design requirements. With the rapid developments of CAD/CAM/CAE technology, the validity and efficiency of virtual-prototype-based design approaches have been utilized in the design for more and more new CAR products. Therefore, taking widely used Macpherson suspension system as example, this dissertation performs the study on"Performance Analysis and Optimization Design for Suspension System Based on Virtual Prototype Technology", which is sponsored by SAIC Technology Fund.Taking Santana2000 car model as example and sufficiently considering the nonlinear characteristics of springs, dampers, rubber bushings and bumper blocks, a detailed dynamics model for MacPherson suspension system is built using Multi-body system dynamics software, i.e. ADAMS, at first to perform kinematics and dynamics simulations. The simulation results are compared with experimental data for validating of the established suspension model. Then the side load of MacPherson suspension system is analyzed and the optimization target is proposed accordingly.Base on the established suspension model, the whole vehicle model is built to perform ride comfort analysis in sine sweep and random road surface imputs respectively, which is validated by body acceleration PSD test data. The effects of elastic and nonlinear component characteristics (including spring stiffness, shock absorber damper coefficient, bushing stiffness, etc.) and suspension linkage on suspension performances are studied to determine the requirements for individual system component design. Based on theoretical study of the curve spring, a virtual-prototype-based approach, combining vehicle system dynamics simulation with the Finite Element Analysis, is proposed and validated for the optimal design of suspension system with these complicated structure springs. Adopting top-down design philosophy, the designers decide suspension performances according to the requirements of vehicle ride comfort, shock absorber service life and spring manufacture cost, etc. Then the characteristic requirements for each component are obtained according to suspension performance requirements. Taking spring component as example, a coil spring with curved centerline is substituted for original conventional spring and the structure parameters and desired centerline function for the complicated structure spring are optimized. Then the spring samples are produced and tested accordingly so that spring stiffness characteristics can be introduced into system dynamics model. The simulation results show significant reduction in shock absorber's side load, while the experimental data of vehicle body acceleration also indicate the improvement in ride comfort.It has been proved that this curve coil spring can reduce MacPherson suspension side load efficiently. However, due to its complicated compression process, the distortion mechanism and stiffness characteristics of this complicated spring need comprehensively studies. Therefore, base on FEA software ANSYS, a software package for coil spring characteristic analysis and structure design is developed. Using this design package, the effects of main structure parameters of the complicated spring, including wire diameter, mean diameter, available coils number, free length and slender ratio, can be investigated. Accordingly, the design principals for the springs with curve centerline are discussed. Five groups of the spring samples with different structure parameters are experimented on ZwickZ050 test rig. The vertical and lateral stiffness experimental data match well with the FEA simulation results and the comparisons between force incline angles validate the conclusions on the design principals of this complicated structure spring as well.