Research On Vibration And Acoustic Radiation Of Silent Chain Drive System

Silent chain drive, a kind of dynamic and motion transmission device which is widelyused in the field of mechanical drive, with the characteristics of high efficiency, little noise,high reliability, high kinematic accuracy and so on, is widely applied to the drivingconditions of high speed, heavy load, low noise and big center distance. As silent chain drivedevelops towards high speed, heavy load and variable speed and load, with the increasedrequirement for higher transmission power of the drive system, the vibration and noiseproblem of silent chain drive system has become especially predominant. Such vibration andnoise problem which objectively reflect the working condition of drive system and influenceits reliability and stability, to some extent, have limited the extension and application of thesilent chain. Therefore, it is extremely important to study vibration and noise of the silentchain drive system.In this paper, vibration and noise of a certain silent chain drive system that is light8×8wheeled all-terrain vehicle is studied, and the excitation of meshing impact and polygoneffect of vibration and noise produced in the meshing process of silent chain and sprocketare analyzed. The acoustic shock model of silent chain drive system is established, andimpulsive noise of the silent chain drive system is calculated quantitatively. The research ofdynamic incentive simulation of multibody dynamics, finite element modal analysis,experimental modal analysis, dynamic response analysis, noise radiation analysis of acousticboundary element, sound intensity testing and noise source identification of silent chaindrive system are described. The main research contents in this paper are as follows:(1) The two main dynamic incentives, namely, meshing impact excitation and thepolygon effect, which produce vibration and noise in silent chain drive system, are analyzed.The biggest impact speed, generated in the meshing process of sprocket and chain plate at arelative speed when chain link and sprocket mesh instantly, is calculated. And starting fromthe polygon effect of silent chain drive itself, the change law of silent chain linear velocity,driven sprocket angular speed and additional dynamic load are analyzed, thus, from theperspective of kinematics, the causes of the unstable running, vibration and noise of thesilent chain are obtained.(2) Based on the analysis of the relevant standards of silent chain and sprocket, from therespective of two cylindrical shock theory and acoustic theory, research on vibration andnoise of the silent chain drive system is carried out. The acoustic impact model of the silentchain drive system is established, and impact force, impact acceleration, impact time and impact velocity produced by elastic deformation when link and sprocket mesh are analyzed.The wave equation for small amplitude wave propagation with velocity potential parameterin cylindrical coordinate is deduced. The calculation expressions of sound pressure andsound power generated when link and sprocket impact are obtained, and an instance ofimpact noise of the silent chain drive system is calculated.(3) Based on multi-body dynamics theory and the contact analysis theory, the theoreticalmodel of multi-rigid-body dynamics of silent chain drive system is established. And basedon the analysis of the structural style of the silent chain and sprocket and the architecturalfeature of the silent chain drive system assembly, the virtual prototype model of silent chaindrive system is established. Through simulation analysis of the meshing contact force ofsilent chain and sprocket, the torsional vibration of sprockets and the characteristics oftransverse and longitudinal vibration under the influence of the meshing impact and polygoneffect, the simulation data of the meshing contact force of the silent chain is obtained, whichprovides accurate and reliable incentive load for the dynamic response analysis of the silentchain drive system.(4) From the structural dynamics and modal analysis theory, the finite element model ofthe silent chain drive system assembly is established. The modal analysis of the silent chaindrive system at a free state and finite element modal analysis of the prestressed assembly arecarried out. Then, the intrinsic characteristic of the silent chain drive system is analyzed, andthe effect of the prestress on the stress distribution, strength, stiffness inherent frequency andinherent vibration mode of the system are discussed. And experiment modal test and analysisis carried out by hammering method. The modal parameter of silent chain drive system isobtained. The correctness of finite element modal analysis and calculation is verified and itis discussed that whether the inherent characteristic of system structure can be reflected.(5) Based on the analysis of harmonic response analysis theory and its solving method,the meshing contact force obtained by mesh dynamic simulation of the silent chaintransmission system is transformed to frequency domain load by FFT(fast fourier transform).The frequency domain load is used as incentive boundary load for the prestress finiteelement harmonic response analysis. And through four node interpolation method, thevibration information of displacement response node in the grid structure obtained byharmonic response analysis is transferred into the acoustic surface mesh. And define thevibration displacement as the boundary condition to carry out the acoustic boundary elementcalculation. The acoustic quantity of field point in the outer sound field is obtained, thus, theanalysis about the acoustic characteristic of the sound field is conducted.(6) Sound intensity measurement technology is adopted to measure the sound intensityand identify the noise source of the silent chain drive system. Through the processing and analysis of the data of sound intensity, the distribution diagrams of the sound powerspectrum and isacoustic line are obtained. From the diagrams above, the main noise sourceof the silent chain drive system is analyzed and identified, and the location of noise sourceand the main noise frequency components are obtained, which provide a basis for modifyingthe structure of the silent chain drive system, improving the analysis model and reducing thenoise.