Dissertation
Dissertation > Industrial Technology > Energy and Power Engineering > Internal combustion engine > General issues > Theory

Lubrication Characteristics Analysis of the Main Bearing Using Multi-body Dynamics

Author WangHuiHui
Tutor LiGuoXiang
School Shandong University
Course Power Machinery and Engineering
Keywords Elasto-hydrodynamic lubrication thermal-elasto-hydrodynamic mainbearing multi-body dynamics
CLC TK401
Type Master's thesis
Year 2012
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The main bearing is one of the most important components of internal combustion engine, which has a crucial influence on reliability, durability and the overall life-span of engine. With the enhancement of engine intensity index, the main bearing will endure more instantaneous load. Thus the research of lubrication on the main bearing is a vital factor for engine development. Taking a marine diesel engine with six cylinders in line as a research object, this paper carried out calculations of the elasto-hydrodynamic lubrication referring to cavitation, surface topography effect and elastic deformation and the calculations considering thermal-elasto-hydrodynamic and above three effects. Besides various influencing factors on bearing lubrication performance are investigated on the basis of the thermal-elasto-hydrodynamic lubrication calculation.Elasto-hydrodynamic theory and thermal-elasto-hydrodynamic theory are discussed in detail. This paper introduces Ptair and Cheng Average Reynolds Equation and the Expansion Reynolds Equation, both including the term of lubricant fill ratio. Further this paper presents the oil Film Thickness Equation, Elastic Deformation Equation, Energy Equation and Heat Conduction Equations and boundary conditions of each equation. This research also illustrates the meaning of the parameters of each equation. According to these equations, the formation mechanism of oil film is described, especially during the operation of the main bearing of the internal combustion engine.The relevant dynamics theory regarding to the multi-body dynamics software AVL/EXCITE is studied in three aspects, including kinematics parameters’ representation of flexible body, unification form of multi-body differential dynamic equation, reduction method for the DOF (Degrees Of Freedom) of system and the classification of the block units and link units with similar properties. Besides, the state of bearing lubrication is analysed combining the multi-body dynamic equation with lubrication control equation based on the multi-body dynamics. The Maine engine is modeled in the AVL/EXCITE software based on above theories. In the multi-body dynamics model, EHD and TEHD bearing components are applied to calculate and analyse performances of the main journal bearings. Comparing the TEHD results with the EHD results, it can be demonstrated that thermal effect has great influence on the bearing lubrication performance, and different parameters are sensitive to thermal effect for each bearing. Hence it is of great significance to adopt thermal-elasto-hydrodynamic method to calculate bearing lubrication.Bearing lubrication performance is affected by load, bearing material, manufacturing factors, operating conditions, etc. The influence of three key factors, including bearing clearance, position of oil holes and off-firing cylinder, is investigated on the basis of thermal-elasto-hydrodynamic lubrication method. Some valuable conclusions are illuminated, which provides more suitable foundation for bearing optimum design.

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