Study On The Coupled Torsional, Axial And Bending Three-Dimensional Vibrations Of Internal Combustion Engine Shafting Basing On Exact Dynamic Stiffness Matrix Methods

Vibration problem is one of the important noise and harmful sources of internal combustion engine. To raise the reliability of internal combustion engine, reduce the work noise of internal combustion engine and improve the comfortable of internal combustion engine vehicles, NVH (Noise, Vibration & Harshness) is proposed in modern internal combustion engine design. The vibration of shafting is one of the main vibrations of internal combustion engine. It is a complex 3-D space vibration, torsional, longitudinal and lateral vibrations are coupling. Researches about vibrations, such as calculation and experiment, vibration absorber, etc., have been made significant advances. Until recently, many researches are only focus on one or two kinds of vibrations. In this thesis, 3-D coupling vibrations of internal combustion engine shafting are presented basing on dynamic stiffness matrix and precise time-integration method.Firstly, free vibration of internal combustion engine shafting is analyzed. Transfer matrix of space continuous beam is proposed. This matrix can be translated into dynamic stiffness matrix, which is applied to describe the physical model of space continuous beam correctly. Using these elements, internal combustion engine shafting can be meshed. The total stiffness matrix is also constructed by using common FE methods. Free vibration characteristics are available by applying the Wittick-Williams (W-W) algorithm. This method is able to get all natural frequencies between every frequency domain without losing any root. Using traditional vibration theory solves mode shapes. The method proposed in this dissertation can be used to correctly calculate the natural frequencies and mode shapes of 3-D space structures and crankshafts of multicylinder engine.Secondly, basing on hydrodynamic lubrication theory, dynamic characteristics of journal bearing and thrust bearing are analyzed. The calculation method for oil film load is proposed. Loaded domain of bearing is meshed by 4 nodes isoparameter elements. Gumbel condition is used as boundary conditions. Pressure distribution at circuit and longitudinal section of bearing is presented by solving Reynolds equation. Basing on these results, the dynamic characteristics coefficients, such as stiffness and damping coefficients, are calculated.Thirdly, the forced vibration calculation method for internal combustion engine shafting is developed. The dynamic stiffness matrix of every elements, construction of total dynamicstiffness matrix, total mass and stiffness matrices which are derived from total dynamic stiffness matrix at any frequency, and force resources of forced vibration are discussed at this chapter. Basing on these knowledge, the mathematic models of forced vibration of internal combustion engine can be established. Comparing vibration analysis methods in time domain, the precise time-integration method is chosen. The calculation method used in this chapter has high calculation precise and costs little computation time.Fourthly, 6110 diesel engine is analyzed by using the methods mentioned above. Free vibration of the shafting at several conditions, dynamic characteristics of oil film and its influence on natural frequencies of the shafting, and time domain response of forced vibration are presented. Torsional vibration of lump mass model and torsional vibration tests are taken into account at this thesis. They are agreement with each other. To improve the ability of VA-10 vibration analyzer, the communication program is developed, which make VA-10 communicate with computer very well. Then VA-10 can be used to measure longitudinal vibration of internal combustion engine shafting and surface vibration of engine structure.Finally, conception design of damper is discussed to reduce the vibration of internal combustion engine shafting. Combining with forced vibration characteristics of 6110 diesel engine, three mass system is used to simplify the actual shafting. The basic parameters of damper are able to be solved by using common absorber theory. This method is fit for engineering application.