Research On Thermoelectricity Monitoring Method Of Main Bearing Wear Based On Tribology Characterstics For Diesel Engine

The diesel engine is the heart of a Marine power system,accounting for more than 82% of the market.With the increase of marine diesel loading,at the moment of ignition of the diesel engine,contact pressure of the main bearing increases vastly,which substantially increases the difficulty of establishing the lubricating oil film of the main bearing.It makes the main bearing in a worse condition and causes wear failure of the main bearing.Serious wear failure of main bearing will lead to high oil mist concentration in crankcase and increase the possibility of crankcase explosion,which lead to huge economic losses.Therefore,research on thermoelectricity monitoring method of main bearing wear based on tribology characterstics for diesel engine has certain theoretical significance and engineering application value.In this paper,the domestic and international development present situation of the friction and wear,the lubrication characteristics of main bearing,the intelligent diagnosis technology and the online monitoring technology of main bearing has been analyzed.The lubrication characteristics and fatigue tests of aluminum and copper alloy bearing have been carried out on the bearing fatigue wear test bench.The relationship between thermoelectricity and wear quantity is put forward.Experimental research was carried out on 4120 SG and TBD234 diesel engines to verify the effectiveness of feature extraction and fault location method for main bearing wear of Marine diesel engines.An intelligent diagnosis model based on thermoelectric method was established to improve the fault identification rate and genericity.A calculation method of thermoelectric potential for main bearing based on thermoelastic-flowtheory is proposed,which provides a method to determine fault location for the engine which is difficult to conduct fault simulation test.The main contents and conclusions of this paper are as follows:Based on the basic principle of thermoelectric effect and the mechanism of thermoelectric potential in a closed circuit,the generation and influencing factors of thermoelectric potential had been analyzed.Combined with the structural characteristics and stress of main bearing for diesel engine,the feasibility of main bearing wear monitoring method based on thermoelectric has been analyzed.A test bench of wear measurement system based on thermoelectric method has been built.Then the wear fault tests of different speeds and different location were completed on the test bench to verify the measurability and localization of the method.The basic theory of fluid dynamic pressure lubrication and tribology is elaborated.Considering the micro convex contact between crankshaft and bearing,the Reynolds equation was derived.The multibody dynamic model of bearing fatigue test bed was established.Then orthogonal analysis of different parameters was carried out on the multibody dynamic model.It is concluded that bearing load,clearance and roughness have great influence on bearing lubrication condition.The test of different loads and different oil inlet temperatures for aluminum alloy and copper alloy bearing have been tested on the bearing fatigue test bench.The characteristic of temperature,torque and minimum oil film thickness of aluminum alloy and copper alloy bearing under different lubrication conditions were obtained.Taking the boundary lubrication points as the fatigue wear test conditions,which is obtained from the lubrication characteristics test,the fatigue wear test was carried out for 20 h.The influence of different materials on the thermoelectric characteristics of bearing was analyzed.The tests found that the thermoelectric signals were more sensitive to the bearing wear than the temperature and torque signals.And the relationship between thermoelectric and wear quantity was established.The thermoelectric potential of main bearing under different working conditions is calculated for 4120 SG diesel engine Then the wear fault simulation test of different clearance,roughness and gear bearing have been carried out The results show that:(1)the thermoelectric characteristic values of each gear main bearings increase with the increase of diesel engine load.(2)When a main bearing wear,the thermoelectric characteristic value of the bearing is the largest,and the thermoelectric peak value increases at the firing time of the corresponding cylinder.(3)The more serious the wear degree of a main bearing is,the greater its thermoelectric characteristic value is.(4)The crank angle corresponding to the peak load of the main bearing is extracted as the thermoelectric characteristic value angle.The main bearing wear fault location can be realized by the thermoelectric characteristic value angle.(5)The thermoelectric data have been analyzed by five supervised learning algorithms such as decision tree,random forest,support vector machine,XGBOOST algorithm and KNN algorithm.the results show that KNN algorithm and SVM algorithm have better generalization ability and higher accuracy of new sample recognition,which could up to 98%.From the basic principle of modal reduction and multi-body dynamics,the thermal elastic fluid dynamics model of TBD234 diesel engine have been set up.The accuracy of the model is verified by instantaneous speed data.Based on thermoelectric effect,the calculation method of thermoelectric potential for main bearing is proposed.The effects of diesel load,bearing clearance and bearing roughness on thermoelectric potential are analyzed.Then the difference of thermoelectric potential between in-line and V type diesel engines is analyzed.