Research On Identification And Control Of Noise And Vibration For Internal Combustion Engines Designed For Automotive Vehicles

The vehicle NVH (Noise, Vibration and Harshness) performance is not only the index of the comfortability, but also the syntheses of the whole vehicle quality. However, there is a conflict between the need and the supply of NVH techniques in today China. Under the background, the dissertation has investigated systematically the NVH problems about vehicle and engine. The main contents, results and conclusions are as follows:(1) The theory of the BEM (Boundary Element Method)-based NAH (Near-field Acoustic Holography) method has been described in the paper. The effect aspects of reconstruction errors were analyzed in detail. The flow chart of the BEM-based NAH technique was proposed, and a speaker-louder was taken as an example to demonstrate the validity and superiority of the method. In order to reduce the reconstruction errors caused by the inverse process, the truncated singular value decomposition and the Tikhonov regularization method, which are two regularization methods, and the L-curve criterion and the generalized cross-validation method, which are two methods for choosing the regularization parameter, were analyzed and applied to create four combined regularization methods. The numerical simulation examples validate the four regularization methods.(2) The BEM-based NAH method has been investigated in the noise source identification of a passenger car diesel engine. The surface normal vibrating velocities of the engine were reconstructed successfully. And the main noise sources were identified and ranked by the panel contribution analysis of sound power level. The recalculated surface normal velocities provide an approach for the assessment of noise reduction measures and the acoustic field visual research and the inverse process of engine structure strength.(3) A six-DOF (Degree Of Freedom) rigid body dynamic model of engine mounting system has been built up. Then the mounting system design program MOUNT and the engine dynamic procedure VINO have been developed independently to evaluate the design cases of any points-supported engine mounting system and conduct the design of motion control and the dynamic response of the mounting system due to any kinds of engine disturbances. These procedures provide a useful tool for the design of engine mounting systems. The comparison of the effects of different modal parameters on vibration isolation performance of a mounting system has been made. The results demonstrate that the rigid modal frequency is the key parameter in the vibration isolation design of an engine mount system. Based on the above conclusions, the design strategy was proposed and the Multi-Objective Genetic Algorithm was implemented to solve the highly nonlinear, uncontinuous and multi-convex design optimization problem of an engine mounting system. The global Pareto solution sets were obtained. And that will provide different optimal design cases for the engineering application of an engine mount system.(4) In order to solve the lower-frequency NVH problems about a light-duty diesel passenger carriage, the vehicle interior noise and vibration were measured and analyzed under different operating conditions. The results show that the diesel engine mounting system is the key issue of the NVH control. Then the proposed optimal method was applied to the design process of the diesel engine mount system. Finally, the NVH performance of the light-duty passenger carriage with the optimized mounting system was promoted greatly.(5) To meet the NVH requirements of diesel passenger cars and passenger-car diesel engines, the near-field sound pressure scanning method and the acoustic array were used to identify the main noise sources. Based on the results, a series of noise control measures were implemented to solve the vehicle NVH problems. The experimental results demonstrate that the proposed measures are effective for the noise control of diesel passenger cars.