Research On Hydrodynamic Lubrication Of Crank Assembly In Diesel Engine

At present, the diesel engine develops toward high intensity, high-speed and high torque development. It makes the in-cylinder pressure rise so rapidly that the demands of the various diesel engine components increase higher and higher. Crank assembly is a critical lubrication component in diesel engine, so it'a very useful to do research on hydrodynamic lubrication of crank assembly. The research achievement of the thesis provides foundation to understand the friction and wear state of diesel engine. Besides it's a necessary step to build the dynamic environment of diesel engine.First of all, the present status of the multi-body dynamical theory is reviewed. The crankshaft mode is calculated using finite element method, and theoretical calculation results compare with the actual experimental dates. The multi-body dynamic simulation model of 6BT5.9 Cummins diesel engine is established making use of ADAMS. The main bearing loads are calculated.Secondly, on the basis of the hydrodynamic lubrication theory on sliding bearing, the Reynolds equation and the corresponding boundary condition, that are applicable to crankshaft bearings of diesel engine, are put forward. The Reynolds equation is calculated in use of the finite difference method for programming. The oil film pressure on the bearing and bearing load are analyzed. The Holland method is improved combined with diesel engine crankshaft dynamical characteristics.Third, the relation of the oil viscosity and temperature is analyzed, and the equation of viscosity-temperature is set up. Through analyzing and calculating the bearing wasting power and oil flux, the calculation process of bearing temperature is put forward. The factors affecting bearing temperature are analyzed.Fourth, under some work conditions, the lubrication characteristics of sliding bearing are studied in the use of sliding bearing test-bed. The friction characteristic, oil film pressure and bearing capacity of sliding bearing are measured and analyzed. It's shown that the experimental results are coincident with the theoretical analysis.Fifth, with the study of dynamic environment of piston in diesel engine, the hydrodynamic lubrication model of piston is founded. The oil film bearing capacity and oil film course of the piston skirt are discussed.Finally, based on the lubrication model and simulation method presented above, the tribological behaviors of 6BT5.9 Cummins diesel engine are analyzed under rated work condition. The journal center locus, minimum oil film thickness, oil film force, maximal oil pressure and oil film temperature of seven main bearings are calculated in a work cycle of diesel engine, as also the oil film bearing capacity and oil film course of six piston skirts are calculated. It's shown that friction performance of crank assembly in diesel engine have direct effect on the reliability and durability of diesel engine.