The Analysis Study Of Counterweight Configuration Of High Power Diesel Engine On Main Bearing Lubrication And Crankshaft Vibration Characteristics

The future development direction of diesel engine is higher power,higher speed,smaller size,low energy consumption and environmentally friendly as possible.As the design capability of diesel engine is improved continually,the impact loads,such as cylinder explosion pressure and inertia force,are further intensified,which will deteriorate the lubrication performance of the main bearings.In this paper,through theoretical analysis,simulation,optimization analysis and other means,the dynamical and tribological model of crankshaft bearing system of 12V150 diesel engine is established,and the influence of Counterweight Configuration on Main Bearing Lubrication and Crankshaft Vibration Characteristics were analyzed.Based on the kinematics and dynamics theory of the crankshaft bearing system,the internal and external balances of the diesel engine were analyzed,and it was found that the rotational and reciprocating inertia force and torque of the 12V150 diesel engine reached naturally balanced.Since the 12V flexible crankshaft still has the problems of increased vibration and poor lubrication caused by high speed,the counterweight configuration method of flexible crankshaft for high speed diesel engine is proposed.The dynamic models of crankshaft with 6 counterweights,8 counterweights,and 12 counterweights were established,and the main bearing loads in four balance states including underbalance,critical balance,50%overbalance and 100%overbalance were analyzed.After comparing the maximum and average main bearing loads of each main bearing,it is found that the crankshaft with 12counterweights is better than 6 and 8 counterweights.The analyses can provide useful guidance for the design of main bearing at the development stage of the engine.The influence of the balance rate of flexible crankshaft on the lubrication and vibration characteristics was studied by using 12 counterweights.The existing literature on the influence analysis of bearing lubrication and vibration characteristics of crankshaft focused on the bearing width,bearing clearance,oil viscosity and other factors.In this thesis,the effects of different balance rates on bearing lubrication and crankshaft vibration were analyzed in which the characteristics of system dynamics,elastic vibration of moving parts and dynamic lubrication were considered.It is found that the influence of crankshaft balance rate on lubrication and vibration characteristics is significant and cannot be ignored.For the 10 factors including the balance rate,the2_Ⅳ^10-5factorial experiment with resolution IV,factor effect diagram,statistical analysis,residual probability diagram and other methods are used to screen and verify the significant factors that influence the lubrication characteristics of crankshaft are the balance rate,bearing width,radial clearance,bearing crown height and oil viscosity.Then,orthogonal simulation design of these five factors was established,and the influence weight of balance rate on bearing lubrication and crankshaft vibration characteristics is determined by range analysis method.It is found that the crankshaft balance rate has the greatest influence on the minimum oil film thickness,peak asperity contact pressure,average friction power loss,axial vibration and free end torsional vibration,while the influence weight of the maximum oil film pressure is lower than that of the bearing width and bearing crown height,and the influence weight of the horizontal and vertical bending vibration are lower than that of the radial clearance.The improved neural network nonlinear relationship between the significant influence factors（balance rate,bearing width,radial clearance,bearing crown height,oil viscosity）and responses（average friction power loss,free end torsional vibration）was established using the data of orthogonal experiments.Then,comparing the simulation results and the prediction,it is found that the genetic algorithm optimized neural network model has higher prediction accuracy.Furthermore,taking the non-linear relationship as the fitness function,the multi-objective optimization model was established based on the NSGA-Ⅱgenetic algorithm.Finally,the Pareto optimal solution set was obtained.The multi-objective optimization results were compared with the simulation results based on AVL software,showing that this optimization method has significantly improved the lubrication and vibration characteristics of the crankshaft.The research results have important theoretical significance and engineering use value for the counterweight design of diesel engines after its power output was enhanced.