The Pipeline Simulation Study On Active Exhaust Noise Control Of Vehicle Engine

Automobile has become the representative of modern human civilization,it was noted that as motor vehicles contribute to the rapid development of modern society,they also brought the more serious urban pollution.Vehicle noise will inevitably become the object of controlled and the engine exhaust noise is the main source of vehicle pass-by noise.Vehicle engine exhaust noise is aerodynamic noise and take a high proportion in the whole noise of engine,so it is the largest noise source.and the exhaust muffler is used to reduce noise,The exhaust mufflers are divided into the passive mufflers and active mufflers. Usually according mechanism,the passive mufflers are divided into three kinds:resistant muffler,dissipative muffler and impedance compound muffler.The methods of muffler design has sub-experimental design and software simulation design,the test was muffler design and verification of the basic method,static bench test is a muffler design and research infrastructure.In the domestic leading research units are based on muffler GB T4760-1995 Test Principles to construct the test bench.of muffler,the theoretical study of the muffler is earlier,the method of automobile muffler commonly used can be divided into:four-terminal network method,characteristic method,finite volume method,boundary element method. finite element method.With the development of computer technology to enable rapid development of numerical simulation,especially the full-featured commercial software continue to emerge,so that the use of computer design has become an indispensable design step,simulation of vehicle muffler design can be divided into one-dimensional and three-dimensional approach,the software simulation in three-dimensional sound field within the muffler flow field studies show an irreplaceable role.At present,it is through testing and simulation complementary manner vehicle muffler design,by designing the accumulation of experience,a great Simulation designers can design to meet the minimum consumption of time and money,can be expected in the future will play a simulation designed to the absolute role.Passive muffler in the elimination of engine exhaust noise during low-frequency noise in frequency reveals the limitations of bulky and so on.The Active muffler main effect is to eliminate low-frequency noise,and aerodynamic drag is small,reducing the engine power loss.After nearly eight decades development of active noise elimination technology,pipeline active noise control technology from theory to practice,have made significant achievements, and now in the research phase of practical use,but the active muffler has not commercialization,Note engine exhaust active noise control technology has not yet fully mature.China's active control study of active compared with other countries there is a difference,basically,in the right engine exhaust active noise control technology and application of the gradual absorption of the active pipeline of exploration-related research stage.Therefore for the vehicle engine exhaust noise;active control study is very necessary. While it is not a new technology,but by its spin-off is very broad,the impact will be far-reaching:in projects that can contribute to the practical application of this technology driven bv related technology;in theory,it is helpful to acoustic theory research.There is no direct application of a suitable device corresponding to the engine's exhaust system,but we should not be enabled the research in this area lags behind the practical application. Therefore,the papers will combine the practical use of pipe-type active noise control, simulation active control of engine exhaust noise.verify the new algorithm,and the algorithm is to explore the details of specific aspects,in the space hardware systems,to select and optimize active control system structural arrangement of research,for the real vehicle, providing helpful theoretical and experimental experienceThis paper under the Lighthill acoustic analogy theory,a more detailed analysis of the jet engine exhaust space generated noise situation,clearly pointed out the different that the base-band noise and jet noise,so that clearly delineate the basic composition of exhaust noise sound.According channel noise active control to low-frequency noise,targeted analysis of the plane wave and the speed of the sound source,and based on sound principle of superposition that the active control of space sound pressure level is less than to be controlled to limit the acoustic pressure,which in the actual process design and analysis of the problem time is very important.The Paper specifically articulated the engine exhaust noise signals are included periodic,quasi-periodic signals and a certain random signals broadband noise can be referred to as colored noise signal,adaptive active noise control concept can be referred to as active control muffler.At the same time pointed out that the vehicle engines exhaust piping active noise control systems are time-varying systems. Planning vehicle engine exhaust active noise control system,the main concepts,you can clearly find relevant to theory,facilitate its research.The steepest descent gradient algorithm is a long history of classical iterative algorithm. its physical properties is clear and rigorous mathematical ceremony,comprehensive. geometric analysis is clear,while the physical meaning of the LMS algorithm is rather obvious,and mathematical statement is simply.This Paper adetailed analysis the intrinsic link between the steepest descent gradient method ans the LMS algorithm,the exact description the statistical properties consistency of them,for completely use the mathematical statement of gradient algorithms holds for the nature of the LMS algorithm,for a more intuitive and rigorous mathematical meaning of display LMS algorithm.Paper analyzes the ideal assumptions of the LMS algorithm,and the small step length theory. pointed out that the application of LMS adaptive system to handle colored signal input is reasonable.Specificity for the exhaust noise signal,through the Matlab math test and mathematical statement holds for the derivation of gradient algorithms,discussed the characteristics of adaptive filter tap weights,as well as the reference input from the relevant and reference input and expectations of the relevance of the LMS adaptive system the impact of highlighting the impact that the latter is much greater than the former effects.The paper also discussed the impact of the lengths of filter and the initial value of tap weight settings to adaptive systems.That should take advantage of the apriority of vehicle engine exhaust noise signal,repeatability and other conditions,according to the actual tests to set these parameters. The direct impact of input signal sampling and quantify,mainly reflected in the iterative algorithm for tap weight,there should be attention to the selection and reasonable sampling frequency.In addition,the colored input signal with the statistical mean and sampling frequency of periodic input have a very close relationship,in practical applications it requires zero or tends to zero,it is very difficult and not practical.All of the above analysis shows that.The LMS algorithm,without strict requirements input is not related to the signal,and without input value is zero-mean signals,in order to applications LMS algorithm for exhaust active noise control to provide a reliable theoretical support,rather than the hard to use rigidly.Mathematical simulation test is a common method of digital signal processing.The paper according to vehicle engine exhaust active noise control systems are time-varying systems,proposed adaptive variable step the mathematical basis,given the mathematical model framework,design a normalized,variable step-size filter-XLMS with leakage formula.The formula referred to as aNFxLMS algorithm, and application of Matlab M-function.S-function and the Simulink simulation programs were designed accordingly,proved to be effective of the algorithm,for the next step the actual hardware and software design to provide support.Through mathematics test results show that the adaptive filter length of the choice is not arbitrary,there is the best range,the small values in the range can improve the convergence speed.The main frequency noise of Engine exhaust noise belong to a constant rate of monopole sound source, during vehicle exhaust pipe active noise control simulation,it can bring the speed dishware loudspeaker design equation speed sound source,to simulate sound source.Before the test.we should demarcate system hardware:presented the demarcate method in the paper,and effective in the experiment.Finite element simulation of acoustic field in the acoustic theory and experiment for the adaptive active control of structures to provide effective support.In the pipeline test.The design of DSP board hardware such as sound sources and the microphone is test the key to success,the right choice of the sound source and the location of microphone are test for a guarantee of success.Through the DSP target boards carried out the different angles between two sound source.0°,30°,45°,90°,150°,180°and different spacing of the active control muffler test.The results showed that:0°state is ineffective and difficult to control,if we want to obtain satisfactory results need a long stable region sound field,not suitable for real vehicle applications. 90°belonging to the sound source energy absorption and energy structural reflection format,regardless of silencer performance and installation are relatively reasonable and suitable for real vehicle in the form of installation,in order to reduce the impact of air may be appropriate to increase the angle.180°obtain more wide-band noise elimination,but the two sound sources directly each other,especially when the directly inhibit to the engine exhaust valve with each other,it will also be a small value and the substantial value of airflow pulsation impact,it can arose a big damage for the active control of sound.It should be noted in paper tests,the position of microphone is fixed,the specific data obtained from the experiments,targeted towards bench test,but according to the condition of this bench test to horizontal comparison,also can explain issue and guide practice.