Generation Mechanism Of Interior Noise Induced By Torsional Vibration And Design Method Of Multi-DOF Damper

Mini-car is favored by consumers for its own advantages, such as small volume, flexible handling, low price, high practicability and low energy consumption. The vibration and noise problem of Mini-car draws more public attention, according to the facts as follows, the characteristics of Mini-car, speeding lightweight trend, increasing demand of NVH and strict laws & regulations. Issue, such as the ubiquitous inner booming noise problem on FR cars with unknown mechanism, seriously impacts NVH performance of vehicle, on which the related mechanism and control method need to be researched urgently.In this thesis, in-depth research has been done for a FR mini-car, on its generating reason of inner booming noise and design methods of Multi-DOF damper.For the quantitive computation problem of torsional vibration measurement error caused by sensor work space variations, unified voltage signal and instantaneous speed expressions considering the influence of sensor work space are firstly derived. Then, the mechanism of instantaneous speed measurement error caused by sensor work space variations is clarified. And the influence law and features of instantaneous speed measurement error are concluded. Studies show that the error and its frequency characteristics can be calculated by the instantaneous speed expression, and also show that the quantitive computation problem of torsional vibration measurement error is successfully resolved. Finally, methods to eliminate the instantaneous speed measurement amplitude modulation error based on the optimal reference voltage are proposed, and related simulations to verify the correctness are carried out.The mechanism of inner booming noise is analyzed using experiment, theory and simulation method. Firstly, vehicle NVH experiments, including driveline torsional vibration, vehicle body vibration and inner booming noise, are carried out. The exciting forces, transmission path and reasons of vibration peaks related to the inner booming noise, are analyzed using Transfer Path Analysis (TPA) and experimental modal methods. The time-frequency coherent analysis method is introduced into interior noise analysis, to quantitatively evaluate the degree of correlation between driveline torsional vibration and interior noise, and to verify the TPA of exciting forces, further. Then, new coupling mechanism through the engagement reaction force of final reduction gear is revealed. Finally, and the fact that driveline torsional force could be loaded on linear vibration system by the engagement reaction force of final reduction gear and the new coupling mechanism is demonstrated to be dominant are proved, using coupled Multi-body dynamic mode between driveline and whole body.For vibration problem caused by resonance of signal mode, the motion equation and dimensionless power amplification factor of parallel and series Multi-DOF damper system installed on equivalent single mode primary system (ESM_PS) are derived, at first beginning. Instructive conclusions for analyzing the engineering problem are obtained by studying influence laws of damper parameters amplitude and distribution on dynamic magnification factor. Then, the optimal parameters including stage number of Multi-DOF dampers are obtained by optimizing with sequential quadratic programming (SQP) and artificial selection method. At the same time, correctness of the derivation is verified by comparing optimal solution got from Multi-DOF damper expression with optimal solution got from dynamic amplification factor analytic expression, when the damper just has one DOF. Finally, forced vibration responses of systems installed the optimal damper are calculated. The results show that Multi-DOF damper designed by the method in terms of single mode has better damping effect.For the interior noise problem with wide-band and multi-objective characteristics, a new idea for controlling interior noise realized by installing driveline torsional vibration damper is proposed. At the same time, experimental analysis is done. The results show that the idea is feasible. The motion equation and dimensionless power amplification factor based on the real response of the system with Multi-DOF damper system installed on any DOF of primary system are derived. Then, optimal parameters including stage number of Multi DOF dampers are obtained through optimizing with sequential quadratic programming (SQP) and artificial selection method. At the same time, the effective frequency range of multi DOF dampers designed using different methods. The results show that method based on real response can be used to solve the wide-band vibration problem. Finally, multi-objective optimization model is established, and optimal parameters are obtained by Multi-Objective Genetic Algorithm (GA), and good control effect on each goals are achieved.Through above studies, the quantitive computation method of torsional vibration measure error provides a theoretical basis for evaluating testing accuracy and setting standards. The found coupling mechanism through the engagement reaction force of final reduction gear between torsional vibration and vehicle vibration explains the generating reason of inner booming noise and provides a basis for establishing the control scheme. The research further improves the theory system of Multi-DOF damper. The proposed design method of Multi-DOF damper based on real response can solve the wide-band vibration problem.