| Vehicle lightweight is a well-known strategy to achieve energy conservation and emission reduction. The lightweight design of car suspension components plays an important role in full vehicle lightweight. However, fatigue failure of these components always occurs due to being subjected to complicated load, while lightweight design may make this situation much worse. Meanwhile, suspension system is closely related to vehicle performance, including ride comfort and handling stability. It is necessary to take the effect that the changes of suspension parameters have on vehicle performance into consideration, during the lightweight design of car suspension components. Therefore, fatigue life prediction of car suspension components, and suspension system optimization in the term of vehicle performance during lightweight design are the key technologies of vehicle chassis design and development, and the research focus of suspension development as well.The car equipped with Mac Pherson front suspension and twist beam rear suspension has been studied in this paper. The rigid-flexible coupled virtual prototype model of this car is built based on multi-body dynamics and finite element theories. The fatigue life of lower control arm in front suspension and twist beam in rear suspension is predicted. And an investigation of the effect that the changes of suspension parameters have on vehicle performance is conducted. On this basis, this paper presents a multi-objective optimization method of performance matching and lightweight design of car suspension components including lower control arm and twist beam, by taking the mass, fatigue life, stiffness and modal frequency of lower control arm and twist beam, and ride comfort and handling stability of full vehicle into consideration. It provides some reference for independent design and development of vehicle chasiss.Firstly, the full vehicle rigid-flexible coupling model with flexible lower control arm and twist beam is established using Adams/Car software. The test data of suspension K&C is used to check the accuracy of the front and rear suspension models. The full vehicle model is also validated by the road test data of ride comfort and handling stability. The verification results indicate that this model has a good accuracy, which lays a foundation for further study of lightweight design of lower control arm and twist beam.Secondly, several typically proving ground road surfaces including cobblestone road, washboard road surface and Belgian block type track are modeled according to durability road parameters of proving ground. This virtual proving ground road model is integrated with the full vehicle model to perform vehicle durability simulations. Since the lower control arm and twist beam have different structural characteristics, the dynamic stress time histories of the lower control arm are obtained through quasi-static method, while the dynamic stress time histories of twist beam are calculated by modal stress recovery method. On this basis, the fatigue life of lower control arm and twist beam is estimated using S-N methodThe contribution degree for each structure parameter of lower control arm and twist beam to different suspension performance index is different, which makes it difficult to determine its degree of influence on the suspension performance. Thus, this paper proposes the calculation method of integrated contribution coefficient based on the technique for ordering preferences by similarity to ideal solution(TOPSIS) method coupled with entropy measurement. In this calculation, design of experiment(DOE) method is employed to obtain the contribution degree for each structure parameter of lower control arm and twist beam to all the suspension performance indexes. The structure parameters with high integrated contribution coefficient are then determined as design variables. The approximation model and NSGA-II algorithm are used to optimize the ride comfort and handling stability. The optimization results are validated by ride comfort and handling stability simulations, which indicate that the vehicle performance gets a considerable improvement.Subsequently, the topology optimization of lower control arm in front suspension and twist beam in rear suspension is carried out by means of variable density method. The optimal configuration of lower control arm and twist beam are obtained based on the topology optimization results. After that, the parameterized model of the lower control arm and twist beam, in which a total of 16 geometric parameters are defined as design variables, are developed by using free form morphing and control block morphing techniques. The Kriging model and NSGA-II are employed for size and shape optimization of lower control arm and twist beam. This multi-objective optimization is performed to further minimize the mass while meeting the fatigue life, stiffness and natural frequency targets of lower control arm and twist beam, as well as the ride comfort and handling stability targets of the full vehicle. Accordingly, a set of Pareto-optimal solutions are obtained from the optimization process and one of them having a smaller mass is determined as the optimization solution of this multi-objective optimization problem. The comparisons between the baseline design and optimum solution in aspects of structural performance of lower control arm and twist beam, and ride comfort and handling stability of full vehicle are conducted. The results show that the presented optimization approach can achieve a substantial weight reduction with all the targets meeting their requirements. In order to evaluate the effectiveness of lightweight design for suspension components much more objectively and reasonably, a calculation method of lightweight coefficient of lower control arm and twist beam is proposed in this paper by considering mass, structural performance and vehicle parameters. Through the comparison of lightweight coefficients of the optimum solution and the baseline design, it indicates that the lightweight level of lower control arm and twist beam could be evaluated by using this lightweight coefficient.Finally, according to the optimum solution, new twist beams are produced for modal, torsional stiffness, strength and fatigue test validation. The verification results show that, the twist beam achieves a significant mass reduction through lightweight design, while the structural performance meet the requirement. It also could demonstrate that the optimization method proposed by this paper is an effective technique for the lightweight design of car suspension components. |
PDF Full Text Request