Studies On The Robust Design Of Vehicle Suspension Based On Handling And Stability

Suspension system research is an important part of the vehicle chassis design and development, and also is the core technology of the automobile self-developed.In suspension development process, designers hope the vehicle have good performance. This includes two studies: first, we need to study what kind of vehicle performance is "good"; and then we should study how to design the suspension structure to achieve the "good" performance.The first aspect is about the evaluation of vehicle performance. Vehicle performance, including: handling stability, ride comfort and NVH, this paper mainly focuses on the handing stability. Handling stability evaluation can be subjective and objective. Subjective evaluation is the feeling of the real vehicle, and it can't provide help in the early days of the suspension design; Objective evaluation is testing the objective parameters which are relative to the vehicle performance and comparing to the relevant standards. Objective evaluation can be used in virtual prototyping technology in the early days of the design. In this paper, objective evaluation is used to complete the optimization of the vehicle performance. Meanwhile, the "good" also includes other meanings: robustness. As the working conditions include uncertainties (load state changes, speed changes and the changes in road surface friction coefficient, etc), the suspension structure which is optimized based on a single condition may have poor performance in other conditions. Including full consideration of the uncertain factors in the design, the robust design has good performance in most conditions.This paper used the Taguchi robust design and the dual response surface robust design to optimize the vehicle handing stability.The second aspect is about the suspension structure design. KnC means the kinematics and compliance, and is the steady-state characteristics of the suspension system. KnC includes multi-objective characteristics which may influence each other, and even conflict with each other, this make it difficult to find a solution which is suitable for all characteristics. This paper used Pareto solution, and got a series of optimization results, from which the final solution was selected by a decision-makers. In the same time, the robust design also needs to be considered. Here, we mainly study the uncertainty of the hard points and the bushing stiffness, which can lead to inconsistent performance of the suspension. Using multi-objective robust design can help us get good suspension performance even there are uncertain factors.Suspension characteristics (KnC) were associated with vehicle handling stability through CarSim model,and by optimizing vehicle handling stability,we can get the KnC targets; Suspension hard points and bushing stiffness were associated with Suspension characteristics through Adams model, and by Using multi-objective robust design, we can get hard points and bushing stiffness.The main content of this paper:1. The introduction of the concept of suspension KnC,laboratory tests,virtual simulation and the qualitative analysis of KnC;2. Using the benchmarking vehicle parameters to build the structure-based suspension model and the property-based vehicle model, and these models were verified by KnC laboratory test and vehicle handling stability experimental test,which laid the foundation of future work;3. The introduction of the robust design theory and research methods;4. Robust optimization of suspension KnC characteristics based on property-based vehicle model: vehicle handling stability was taken as the objective, working conditions was taken as the uncertainties, and Taguchi robust design and dual response surface robust design were taken as optimization method.5. Robust optimization of hard points and bushing stiffness based on structure-based suspension model: Being consistent with the KnC targets was taken as the objective, hard points error and bushing stiffness error were taken as the uncertainties, Monte Carlo was used to calculate the mean and variance, and NSGAâ…¡was used in the multi-objective robust design.6. Because there are too many parameters and the calculation is time-consuming, approximate model was used to replace the real model, which greatly improved the efficiency of the optimization without reducing the accuracy.Major Innovations of the Dissertation:(1) In-depth study on suspension characteristics (KnC), especially the study on semi-independent torsion beam suspension;(2) The robust design was introduced into Suspension system development process;(3) The approximate model instead of the real model was applied to the robust design.