Investigation On Powertrain Structure's Vibration And Noise Performance Based On Virtual Forecast Technology

Numeric simulation technology and experimental identification method are two effective ways for analyzing vibration and noise of vehicles and engine systems. With the processes of virtual forcasting, this paper analyzes dynamic characteristics of the important motion sub-system of the powertrain, consist of engine and gearbox, crank-connecting rod mechanism and gear transmission system. Furthermore, research topics are worked on the strength, vibration and noise characteristics of important structural motion parts and fixing parts.By comparing simulated and tested results of torsional vibration response of the crankshaft system, an elastical dynamic model, which is built by coupling the crankshaft system and cylinder system, is verified valid. Main bearing dynamic loads has taken the effects of journal tilt and elastic coupling into account, and the effects of elastic coupling and bearing clearance on the vibration and noise behavior of cylinder body are discussed. Based on the shaft coupling dynamics, dynamic strength of the crankshaft system is analyzed both by direct transient method and modal stress synthesization method. With the fine FEM in the displacement-stress field, the dynamic strength of the crankshaft oil orifices is researched. Meanwhile the dynamic fatigue safety of the crankshaft fillets is checked under the high-cycle fatigue designing principle. The R-K numeric integration method is used to solve the dynamics equation for the secondary motion of the piston. The time-domain characteristic of the secondary motion, dynamic slap force of the piston on the cylinder liner, and the influence of the sensitive parameter are discussed as well. With experiments results, the vibration characteristic of the cylinder surface is identified, in order to verify the accuracy of the simulation model.Measurement has been made on the surface vibration of the gear box and oil pan on a vehicle roller testbed, calculating out the structural noise radiation power and analyzing the variant contribution of each side plate vibration to the whole radiated noise. A multi-body dynamic model is built for the gear train, to study the dynamical characteristics of the gear train by the perspectives of both the internal and external excitations. Dynamic response and radiated noise characteristics are analyzed for the gearbox shell structure. The vibration response of a full elastic model built for the power train agrees well with the experiments within 800 Hz. Meanwhile, to shorten modeling and analyzing time, a double-mass vibration model has been developed for the power train. Compared with the full elastic model, the double-mass model is validated, providing a new calculation model for the power train vibration analysis. The magnesium alloy AZ91D is used to design out a lighter oil pan and gearbox shell structure. And an analyzing method for the noise-vibration characteristic and structural strength is presented for the magnesium structure, and for the optimization of its noise-vibration characteristic.The paper promotes the application of the numeric simulation technology in the domain of powertrain, by a way of engineering design and analysis, and developed the related new method and technical process. It has gained a series of results with practical engineering value for the vehicle and engine companies.