The NVH Performance Analysis And Optimization Of The Uncertain Driveline In The Low Frequency Region

Driveline system is one of the most important sources of vibration and noise of vehicle.The driveline NVH(Noise,Vibration and Harshness)contains torsional vibration performance,judder performance,booming noise performance,rattle performance,whine performance and so on.Among them,torsional vibration,judder,and booming noise act on the range of low frequency.These NVH performance indexes have a decisive influence on the vehicle NVH performance at work conditions of starting and full throttle acceleration.The analysis and control of these indexes are of great significance to improve the NVH performance of the whole vehicle.At present,the development of driveline NVH in low frequency domain is based on uncertain parameters.However,in the practical engineering problems,the uncertainties of driveline are inevitable because of the limits of manufacturing and assembly precision,the measuring error,the change of excitations and boundary conditions,the change of environment and so on.These uncertain factors interact with each other,which can lead to a big deviation between the design performance and the practical performance.The deviation may cause a series of problems,including the inhomogeneous product performance,the difficulty of benchmarking between the simulated model and experiment results,and the less obvious effects of the optimization schemes.For the existing problems in the development of driveline NVH on the range of low frequency,the uncertain theory and algorithm are introduced to the development of driveline NVH.The development of driveline torsional vibration,judder,booming noise and the design of torsional vibration damper under uncertain conditions are studied in this paper.Firstly,the simulated models of these performance indexes are built.For the different characteristics of each model,different uncertain models,numerical methods and optimization methods are applied.The models ands methods presented in this paper are very effective to predict the fluctuation of driveline NVH performance indexes and to improve the robustness of driveline NVH performance.The main works accomplished in the paper include:(1)A new driveline and rear axle coupled torsional vibration model(DRCTVM)is built.The new model is developed by installing the input shaft of main reducer and the differential on the rear axle instead of the ground.Therefore,the couplingrelationship of the driveline and the rear axle is considered.The test results have indicated that the new model has provided much better accuracy compared with the traditional model.In addition,a new uncertain analysis and optimization method for driveline torsional vibration is presented.The frequencies of torsional modes and the peaks of the response curves are used as the response functions.A truncated normal distribution is used to describe the uncertainty of driveline torsional vibration,which considers both the probability distribution and bounds of uncertain variables.The numerical example shows that the model and method developed in this work are very effective to improve the robustness of the driveline torsional vibration.(2)A new evaluation system for driveline judder is built.The evaluation system contains the real part of judder modal eigenvalue(stability index),the moment when the clutch enters the stick state(response rate index),and the fluctuation level of the driving part of clutch(volatility index).These indexes consider the mechanism and the manifestation of the driveline judder.A hybrid uncertain model with both random and interval variables is developed.The inertia and torsional parameters are descried by the normal distribution.While the damping and friction parameters,are modelled by the interval model.The upper bounds of the expected values and the standard deviations of the judder indexes are used as objective function and boundary conditions.The results show that the model and method developed in this work are very effective to improve the robustness of the clutch judder.(3)An optimization method of TVD(Torsional Vibration Damper)considering the tolerance design is presented.Under the existing conditions,the manufacturing errors are large.Hence the real values of the TVD parameters are different from the design values.In this paper,the vibration equation of the driveline model with TVD is formulated.And the influence of torsional vibration damper on the free and forced vibration of driveline is systematically studied.The interval uncertain optimization model is introduced to the driveline vibration analysis.With the presented method,the torsional vibration damper can play its role effectively in different manufacture and use conditions with greater tolerances.(4)A new uncertain analytical method of driveline booming noise computation is presented.The exciting forces and the acoustics transfer functions at the key points are computed by the rigid-flexible coupled model of the vehicle and the acoustics-structural coupled model of the trimbody,respectively.The interior booming could be achieved by submitting the exciting forces and the acoustics transfer functions to the “Transfer Path Analysis and Synthesize” software.The stiffness of thekey bushes of the chassis and the sealant of the body are used as uncertain parameters.The upper and lower bounds of the interior booming noise can be obtained by the interval perturbation Monte Carlo method.