Strength Analysis Of Engine Block Based On Coupling Of Multi-body Dynamics And Hydrodynamic Lubrication

Block, the skeleton of a diesel engine, is functioned as a complex structure and bears a heavy load, working in a bad condition. With the improvement of high-power and light-weight engines, the design and analysis of the fatigue of block structure needs higher requirements on finite element model and calculation boundary condition, which should be more accordant with the engine practical conditions. Statics method based on loading experience or partial model at special operating condition has been unable to meet the today’s requirement of the engine design and research development for a long time. Recently, the transient EHD(Elasto- hydrodynamic) lubrication has been widely used in strength calculation of crankshaft, but rarely been applied on block, because of the difficulty in mapping the main bearing oil film pressure on finite element model, lack of systematic comparative analysis about loading method, and none fixed method for reference to a complete engine model currently.In this paper, a Euro V diesel engine was set as the research objection, the strength and reliability of complete block model are calculated and analyzed based on coupling of multi-body dynamics and Hydrodynamic Lubrication. Firstly, the Reynolds equation of journal misalignment bearing is derived according to the general form of Reynolds equation. The interface to numerical solution of Reynolds equation is deduced in detail with the finite difference method, and obtained the numerical integration formula of oil film reaction force and anti-torque. Secondly, based on the lubrication theory and the theory of multi-body dynamics, the multi-body dynamics model of the diesel engine is founded with modal reduction technology. To obtain the main bearing oil film pressure, including distribution and concentrated load, and the piston thrust force for further study, the EHD bearing unit is applied to realize coupling multi-body dynamics and oil film lubrication. Thirdly, the main bearing wall(MBW) model which includes whole block and bearing caps is founded and calculated the stress and safety factor. In this chart, two different load methods were compared: one is mapping film pressure on main bearing mesh and the other one is loading on concentrated node of bearing shell. Then the engine’s complete set of finite element model is established, researched the calculation and loading method of assembly load, thermal load and dynamic load at each critical angle of crankshaft, realizing the strength and fatigue calculation of a complete set of model organism and obtaining the stress and safety factor distribution of the whole block through the simulation method. Finally, the first generation model engine’s performance and 400 h feasible is tested.The result indicates that distribution of stress and safety factors on MBW varied in different load methods, the oil film pressure mapping by shell is more accurate and can fully reflect the actual stress distribution than load on a coupling node; the simulation method, which apply engine’s complete set of finite element model based on coupling of MBD and EHD, has intuitive and global advantages in strength and fatigue calculation; thermal load, gas load and thrust force has important influence on structure between cylinder and bolt hole, but little effect on MBW, the limit value should be improved when analysis strength and safety factors of MBW on simple model; test result show that power rating, peak torque and specific fuel consumption meet the design requirement, and there is no crack or fracture on block, which verified the method is feasible and effective in this paper.