Modal Test And Analysis Of Automobile Engine Structure

With the rapidly development of automobile industry, the controlling of vibrationand noise on the automobile engine has become increasingly demanded and moreattention is drawn to analysis its dynamic characteristics. Experimental modal analysisis proved to be a proper method because of its effective identification for the dynamiccharacteristics. Considering oil pan and the belt as research object, the identification ofdynamic characteristics for linear system (cover, oil pan) and non-linear systems (belt)are investigated using experimental modal method, which can aided to reduce noise, tosuppress the vibration and to carry out the structural performance optimization. Theresearch can enrich the applications field.The modal experiment and analysis of linear system, such as cover and oil pan, isperformed. Firstly, the modal test is verified according to the modal test, finite elementanalysis, and theoretical arithmetic for the aluminum plate. The frequency responsefunction can be recorded by hammer method, then the modal parameter will identifiedbased on the least-squares complex frequency domain method with poly-reference(PolyMax). As a result, the natural frequencies, damping ratio and vibration mode offirst seven-order for the cover and oil pan are obtained.Modal parameters of belt in longitudinal vibration are measured by different shockmethods-hammer and shaker. The FRF and natural frequency are compared, and theyturn out to be in good agreement. Damping ratio is measured by half-power of spectrumzoom method and logarithmic decrement method, as well as the longitudinal stiffnessand damping coefficient is carried out. The influences of the belt length on the beltnatural frequency, damping ratio, longitudinal stiffness and damping coefficients areinvestigated. The longitudinal natural frequency and damping ratio are decreased;dynamic stiffness and damping coefficient are increased with the increase of belt length.Theoretical model of the belt considering bending stiffness is established and itscalculate formula is deduced. Natural frequency and damping ratio of traverse vibrationare identified by multi-DOF method and single-DOF method. The free response intraverse vibration is measured in different length (l=1.0m, l=0.9m) and longitudinalforce. The natural frequency and damping ratio are identified as well. The bendingstiffness of the belt is obtained by least-squares method. The influences of thelongitudinal force on the belt natural frequency and the influences of the belt length on the bending stiffness are investigated. The longitudinal natural frequency is increasedwith the decrease of longitudinal force. And bending stiffness is decreased with theincrease of belt length.