Research On Acoustic Performance And Structure Design Of The Intake System Of Automobile Engine

The control and research of vehicle noise is the main content of NVH and the inlet noise is one of the sources of car noise.Because the speed and load of the engine are instantaneous,the direction of the intake air flow and the direction of propagation of the intake noise are opposite,as well as the characteristics of the plastic components of the intake system and the coupling of the sound field and flow field inside the intake system,the accurate simulation of the acoustic performance of the air intake system and the efficient development and design of the system have been difficult to solve.Based on the above problems,this thesis starts with the simulation accuracy of the air intake system and divides the air intake system noise into the intake nozzle noise and the housing radiation noise.Through the simulation analysis of the transmission loss of the air intake system's silencing element,the simulation design method of the silencing element was proposed based on the experiment.At the same time,the sound source characteristics of the air intake system were extracted by the four-load test as the acoustic simulation boundary conditions.Through the analysis of the structure and acoustic-structure coupling of the air intake system,the radiated noise of the air intake system is controlled.Based on the test results,a new type of micro-perforated silencer is designed to reduce the noise in the intake system.The main research work of this thesis includes:1 Determine the method of simulation analysis.Through the analysis of the evaluation index of the sound attenuation performance,the test results are used to analyze the simulation accuracy of the calculation of the transmission loss of the air intake system noise attenuation components by different transmission loss calculation methods,to find the optimal simulation method,and to guide the design of the sound attenuation components.2 In order to avoid the influence of the error of the one-dimensional modeling accuracy of the engine on the intake nozzle noise,the four-pole parameters of the load and the test test results are used to calculate the characteristics of the engine throttle sound source as the sound source input conditions of the air intake system.Experiments and simulations comparing the sound source impedance and intensity of the engine at multiple speeds and different loads demonstrate the effectiveness of the sound source characteristics extraction test results.3 Based on the finite element simulation and modal test results of the typical intake system structure,the coupling relationship between the acoustic modal frequency and the structural modal frequency is analyzed,and the intake radiated noise is predicted and analyzed to find out the main participate in the order modes of radiation noise,and propose the radiation noise control measures of the air intake system.4 The main contribution frequency of the intake noise was analyzed through the acoustic test of the vehicle's semi-anechoic chamber,and the control measures of high-frequency and wide-band noise in the noise were studied.A new broadband micro-perforated muffler was designed.Through the acoustic modal calculation of the air intake pipeline,a reasonable arrangement of sound-absorbing components,and sample processing and actual vehicle test of the air intake system,it was found that it effectively reduces the intake noise.Based on the improvement of the acoustic simulation accuracy of the air intake system,this thesis accurately predicts the intake nozzle noise and radiation noise through engine noise separation test and simulation analysis.Using the transmission loss as an indicator,a new type of micro-perforated muffler was designed for high-frequency and wide-band noise,which reduced the noise value of the intake system by 7dB and the maximum value by 13 dB.