Study & Application Of Multi-objective Optimization Methodology In The Car Chassis Platform Development

Chassis is the platform of a car development, and it is the foundation of the car to guarantee a good handling, ride comfort and NVH performance. Both handling and ride comfort play an important role in the performance of a vehicle, usually influencing the customers'to purchase a car. It's necessary to optimize the above multi-performances of a car chassis system, but there are difficulties in the application of multi-objective optimization theory and method to the car chassis design. This thesis focuses on the study & application of multi-objective optimization to the engineering practice, which mainly deals with:1. The typical problems and analysis methods of vehicle system dynamics which related with car chassis are introduced, and the idea of cooperative optimization among handling, ride and cabin noise level is presented.2. The definition of multi-objective optimization and the character of its solution are explained and the concept of Pareto solution set of the multi-objective optimization problem is the emphasized. Meanwhile the theory of multi-objective optimization problem is researched, and the algorithm of multi-objective optimization problem is analyzed, such as the linear weighting factor method and genetic algorithm of multi-objective problem.3. Based on the owned-brand passenger car development project of an enterprise, modeling of multi-body system is used to simulate the handling and ride performance, and the FEM model of acoustic-structure is built to calculate the cabin noise of the car. Further more, the multi-objective optimization tool is utilized to integrate the above multi-body software and FEM solver for cooperative optimization of chassis multi-objective optimization problem, for improving handling, ride comfort and minimize the cabin noise, according to the double lane change maneuver and riding on a random road. In the optimization process the chassis elastic element characteristics such as spring, shock absorber and anti-roll bar are set as the design variables. The optimization results indicate that the chassis performance has an obvious improvement in handling and ride comfort, even the cabin noise level.4. For the complex optimization problem, the conventional optimization method is not feasible due to huge number of iterations and time consumption. Accordingly, in this thesis, a methodology is investigated to build an approximation model based on a vehicle multi-body model by response surface method (RSM) for optimizing the vehicle's handling and ride comfort. The results indicate that the approximation methodology is efficient to the multi-objective trade-offs in vehicle development.