Robustness Design Research Of Vehicle Wheel Alignment Parameters

Wheel alignment parameters contains kingpin inclination angle, caster angle, toe angle and camber angle, is closely related to the performance of vehicle.It is the important premise to guarantee good performance of vehicle controllability and stability, fuel economy, safety and tire wear state and so on.The kingpin inclination angle and caster angle is closely related to vehicle steering returnability,the matching between toe angle and camber angle directly affect the tire wear. At the same time, the performance of the vehicle is in the user’s main focus of attention list.On the system of vehicle chassis,wheel alignment parameters is directly related to suspension system structure,system stiffness,suspension point position and the elastic element stiffness,damping and so on. And the manufacturing error, assembly error of suspension system will lead to wheel alignment parameters exist deviation between actual and the design reference value in static. In addition, the vehicle suspension system state is affected by random load, speed operating conditions and so on,which may lead to wheel alignment parameters of dynamic fluctuation in the suspension of conventional range. For such a deviation and dynamic fluctuation caused by the uncertainty factor,can be handled by the robust design. At present, the research of robust design for wheel alignment parameters on vehicle performance, is not consider the vehicle performance and suspension factors at the same time.The robust design variables include the controllable factors and noise factors, more than the traditional optimization design variables, at the same time, the robust design is a multi-objective optimization problem, it will cost more time to solve the problem, and the actual system model of project itself is more complex. If use the original complex model for robust design, it will be difficult to guarantee the progress of engineering project. Then, in order to improve the efficiency of analysis, building the RSM model to solve the problem.For the different vehicles with the same level, the wheel alignment parameters design reference value is different by research, then it cannot simply according to the same level vehicle experience analogy, and the conventional theory design method is not very good for the design reference value with certain robustness.Then it is necessary to study the robust design on wheel alignment parameters,and establish the robust design rules of wheel alignment parameters, which can provide guidance for the similar engineering problems.Then, this paper assumes that the manufacturing and assembly process development is relatively mature, the deviation caused by the manufacturing error, assembly error and wear error of the gap is very small, and mainly considering the uncertain factors, including the random load, speed and operating conditions. Based on a B class vehicle, around the impact mechanism between wheel alignment parameters and vehicle steering return ability performance, and tire wear. Combined with the TEST, CAE and CAO analysis technology, do the following research work:(1)Based on the analysis between wheel alignment parameters and vehicle steering returnability performance, and tire wear mechanism, to determine the optimal target of robust design, the vehicle yaw rate, the residue of yaw rate, tire ground lateral slip, all of them are "small property".(2) The robust design method of this topic is identified by comparing the common robust design method (Taguchi method,6Sigma method and the method based on the response surface model), the method of robust design based on response surface model,and the improved non dominated sorting genetic algorithm (NSGA-Ⅱ) and Pareto combined to solve the problem.(3)Based on the test data,build the FVP model by ADAMS/Car, including front and rear suspension system, steering, tires, brake system, body and powertrain system. And emphasizes on the method and process of component flexible, it can make the component flexible standard. After flexible, it can get rid of the frequency making little contribution to the response of the structure,and reduce the degree of freedom of the rigid flexible coupling model, and improve the computational efficiency.(4)Based on GB/T 6323 steering returnability test and the custom condition of ups and downs,and the the sensitivity analysis of influence factors, RSM model is established between the wheel alignment parameters and response goals.Based on the Steering and Wheel travel test, RSM model is established between the suspension factors and wheel positioning parameters.In the process of building RSM model,with the iSIGHT software platform and ADAMS/Car software,the batch file calling the back orders,get the test sample points for fitting the RSM model, and it can save time,improve the efficiency of establishing RSM model.(5)Based on investigation and analysis of the wheel alignment values of 22 vehicles,which are same level as the study object vehicle. And let it as the robust desigh variable constraint interval, the load and speed of vehicles as noise factors, GB/T 6323 steering returnability test and the custom condition of ups and downs,solving the robust design problem.(6)Based on the wheel alignment parameters as target data,solve the robust design of suspension structure factors problem, get the minimum wheel alignment parameters and target data, suspension point coordinates as the design variables, the stiffness characteristics of suspension rubber bushings as noise factors, get the suspension structure of robust solution.(7) Based on the above analysis, establishing the robust design rules of wheel alignment parameters, which can provide guidance for the similar engineering problems. The innovation of subject:(1) The robust design is introduced to the study of the wheel alignment parameters, and is divided into two class of robust optimization, based on the RSM model for the first level of robust optimization, and obtain the robust solution of the wheel alignment parameters, then the robust solution as the target characteristics of the suspension structure, slove the multiobjective optimization problems between suspension structure influence factors and the wheel alignment parameters, get the influence factors of suspension structure robust solution. This method can disperse the difficulties of robust optimization analysis, which can be used to guide the vehicle and parts are collaborative development.(2) Establishing the robust design rules of wheel alignment parameters to guide the similar engineering problems, this design procedure compared to the experience analogy method and the theory of the conventional design method, it can obtain more robust wheel alignment parameters and more suitable for definite vehicle model.