The Frictional Characteristics Research And Optimization Of Internal Combustion Engine Main Bearing

The tribological properties of friction pairs of internal combustion engines have a great influence on the performance and reliability of the whole engine.The development and application of low friction technology is the core issue in the tribology of internal combustion engine.It is the basic premise for the development of low friction technology to clarify the lubrication characteristics and friction power consumption level of each friction pair.The internal combustion engine outputs useful work through reciprocating motion of piston and rotating motion of crankshaft through the whole crank-connecting rod mechanism.The friction loss of crank-connecting rod mechanism has become one of most important source of friction loss of internal combustion engine.The friction loss of main bearing accounts for about 10%-25% of the friction of the whole engine.The main bearing(key friction pair)is studied by simulation and experiment.At the same time,the main bearing bears the test of high load and high speed in the working process,and its lubrication performance directly affects the reliability of the internal combustion engine.Therefore,modern enhanced internal combustion engines put forward higher requirements for lubrication performance of main bearings,reliability must be ensured while reducing friction.The following research work is carried out: 1.Study on friction test of main bearingThe friction of whole internal combustion engine is easy to measure,but in the development of engine,it is necessary to know the friction proportion and friction power of each subsystem,so as to compare and optimize.There are four methods to measure friction loss: dynamometer chart method,teardown method,cylinder extinguishing method and fuel consumption line method.In the development of gasoline engine,teardown method has been widely used.In this paper,teardown method is studied and tested,and good results are obtained.2.Simulation method of friction and lubrication performance with main bearingBearing lubrication state includes fluid lubrication,mixed lubrication and boundary lubrication.With the thinning of lubricating film thickness becoming gradually thin,the state of fluid lubrication gradually transits from fluid lubrication to mixed lubrication and then into boundary lubrication.The crankshaft main bearing bears enormous alternating load,and its oil film thickness is only a few microns,so it is necessary to carry out numerical analysis of mixed lubrication and boundary lubrication.Because there are many factors affecting bearing lubrication,numerical analysis is difficult.In this paper,the load of crank pin,multi-body dynamics theory,lubricant character,oil film thickness equation and other theories are studied.Based on the teardown test method,the corresponding numerical simulation model is established,and the friction power consumption of the main bearing is obtained.Comparing the calculated value with the value of the teardown test,the difference is small.The friction calculation method of the main bearing can better reflect the actual friction power consumption,and can be applied to the friction lubrication research of the engine under the ignition conditions.In the numerical simulation model established by the teardown test method,considering the influence of cylinder pressure and reciprocating and rotating inertia force of piston and connecting rod,the numerical calculation method of the main bearing is studied.The calculation results of friction loss,oil film thickness and oil film pressure of the main bearing under the ignition conditions are obtained,which can be used to evaluate the main bearing tribological properties.3.Optimization method of numerical analysis of friction and lubrication of main bearingAccording to the characteristics of the main bearing of internal combustion engine,a friction optimization method of main bearing is proposed.Through the optimization analysis of the main bearing,the friction loss of the main bearing is reduced obviously compared with the original bearing.4.Reliability analysis method of main bearingBased on the theory of hydrodynamic lubrication,a reliability simulation model was established by using AVL EXCTTE multi-body dynamics software,and the lubrication characteristics and laws of main bearing with different working conditions were calculated.The reliability of the main bearing was evaluated from the aspects of oil film thickness,oil film pressure,shear stress and oil temperature rise.5.Determination method of the oil hole locationIn this paper,the axial position of the oil hole was determined based on the distribution law of oil pressure in the expansion plane of the bearing bush,and the best circumferential Angle of the oil hole was determined through the calculation and analysis of transient bearing lubrication characteristics which is the distribution of oil film pressure with the crank Angles.The oil film pressure and friction loss of two oil hole cases with different circumferential positions were compared.Compared with the other scheme,the oil film pressure and friction loss of the main bearing with the best circumferential position were significantly reduced.A method for determining the position of oil hole is presented and its feasibility is verified.