Research On Methods Of Surface Radiation Noise Prediction And Control For A Single-cylinder Gasoline Engine

The vehicle NVH performance is attracting more and more attention,as a result of rising rigorous needs from consumers and requests from laws and regulations.Levels of vibration and noise are important factors to evaluate vehicle NVH performance.While the engine surface radiation noise contributes a great part of the total engine noise.Therefore,controlling the surface radiation noise is a vital means to cut down the total engine noise.At present,researchers focus more on high-power multi-cylinder engines,especially multi-cylinder diesel engines in relevant studies.This paper studies the radiation noise for a single-cylinder gasoline engine,aiming to gain some valuable achievements.In this paper,comprehensive methods,including theoretical analysis,CAE simulation and acoustical tests,are used to achieve calculation,analysis and verification of noise radiation level of engine body.Then,it focuses on optimization design of moving parts of the engine based on their dynamic loads,aiming to provide the basis of low-noise design for the engine.In the phase of FE model preparing stage,optimal element sizes are found for each part of engine body through comparative analysis.And vibration characters of engine body are obtained by its modal analysis.In the phase of multi-body dynamics simulation,VALDYN from Ricardo Software is adopted as the modeling tool,and rigid-flexible dynamic model of engine are built.In the simulation,the crank and the connecting rod are regarded as flexible bodies,which are modally reduced to their master nodes based on the Craig-Bampton method.Then,forces on the engine body excited by moving components are calculated by running the dynamic model.The result shows that main exciting forces are from the main bearings and the valvetrain forces are next.After that,vibration parameters are computed through structural dynamics,taking exciting forces as boundary conditions.In the phase of radiation noise simulation,engine surface vibrations are set as the boundary conditions,and acoustical characters are calculated through the BEM.Further,the sound power contributions from every single part of engine body are calculated,and so are sound power contributions from each exciting force.The result shows that the problematic frequency band is 450Hz~1350Hz,the main radiation surfaces are cylinder head and valvetrain cover,the main exciting forces are crank bearing forces and cam bearing forces.Later on,acoustical bench tests are carried out,whose results are compared to those of simulations.It shows that simulation results agree reasonably well with the tests results.This proves the reliability of theoretical analysis and CAE simulations.At last,acoustical optimizations are performed based on the noise source identification results,which are mainly for reducing exciting loads and their impacts.Valve springs and cam profiles are optimized for reducing valve seating acceleration and seating force.New valve springs as well as a new camshaft are manufactured based on optimization results.Acoustical performance has been tested with all new parts installed on the engine.From test results it is concluded that total noise levels on left and right sides of the engine have been reduced respectively about 2.5dB(A)and 1.9dB(A)with new valve springs,and about 4.8(A)and 3.3dB(A)with both new valve springs and the new camshaft using new cam profiles...