Optimization Research On Vehicle Suspension NVH Performance Based On Virtual Prototype Model

With the great improvement of economics and people’s living standard, the number of retained vehicles is becoming more and more huge.In this situation, the vehicle NVH performance(NVH, just the three initial characters of noise, vibration and harshness)is drawing more and more concerns, and it is also considered as one important index for judging the level of the modern vehicle industry.Because the performance is closely related to the physical and metal health of human beings, many international organizations have established according laws and regulations to confirm the requirements of the vehicle NVH performance.In the meanwhile,the academia and industria have invested a lot of money, materials and manpower for the vehicle NVH researches.At present, the vehicle NVH researches are centered on the vehicle power assembly, intake and exhaust system, and transmission assembly. This dissertation aims at studying the suspension NVH performances under different road conditions, and carries out theoretical analyses, simulation and tests of the effects of the key suspension parameters on the NVH performance.Firstly, the dissertation reviews the vehicle NVH technology development and research status on the basis of looking up many papers.After that, this dissertation uses the finite element theory and method for the modal analyses and flexible treatments of some suspension parts.The dissertation analyses the path of the road irregularity vertical excitations transferred to the vehicle body, establishes the vehicle NVH performance index and builds up the rigid-flexible coupling vehicle dynamical model.Under different work conditions,the effects of the suspension stiffness and damping on the vehicle NVH performance are studied.The DOE(Design of Experiments) method is applied for improving the vehicle NVH performance by fitness-optimization.dissertation analyzes the structural and material properties of the suspension rubber bushings.The flexible deformations in every direction are analyzed, and compared with the test data supplied by the manufacturers.The vehicle NVH performance are compared, before and after the suspension bushings are installed.Then the sensitivities of different suspension bushing stiffness on the NVH index are studied.Some rather sensitive parameters are choosed for the DOE,in order to improve the vehicle NVH performance.The dissertation establishes up the half vehicle model including the bushing effects, and compares the simulation results with those of the half vehicle model without the bushing effects and rigid-flexible coupling model.The dissertation analyzes the structural and material properties of the vehicle tires in theory, and builds up the three-dimensional(3D) finite element method(FEM) model for the analysis of the radial tire roll. In the FEM model,the complexity of the tire materials and structures are taken into account adequately, and the contact frictions among the tires,rim and ground are also studied.The dissertation studies the effects of different vehicle speeds and steering angle on the tire deformations and ground area stress distribution.The relations between the tire pneumatic stress and radial stiffness are studied.The tire radial stiffness would affect the suspension stiffness furthermore.and the mathematical relations between it and the suspension stiffness are also built up.By comparing the full vehicle simulation response curves of different tire stiffness, the vehicle NVH performance is studied.And then, the dissertation analyzes the effects of semi-active suspensions on the vehicle NVH performance,as compared to traditional passive suspensions.On those vehicle NVH time-domain indices,frequency weightings are carried out.When taking into account of the different sensitivities of diverse frequency bands towards the NVH performance indices,the driving safety is also considered in the control method design. Through simulation,the effects of the semi-active suspension on the vehicle NVH improvement are verified.Many tests are carried out in the dissertation, and by testing the vehicle NVH performances under different work conditions,the exactness of simulation models are verified.The semi-active suspensions are installed on the test vehicle,through rig and real vehicle road tests,those suspension effects on the vehicle NVH performance improvements are verified.