Calculation And Test On The Monitoring Of Diesel Engine Main Bearing Wear Using Thermoelectric Power Method

Crankshaft and main bearing are the main friction pair and key components ofthe diesel engine. Excessive inhomogeneous wear of the main bearing may enlargethe bearing clearance, which would increase the impact to the main bearing, anddirectly affect the working performance of the diesel engine. Traditional monitoringmethods can’t accurately and timely find the wear condition of the main bearing.Thermoelectric power monitoring method can realize the online monitoring of thediesel engine main bearing wear. Therefore, it has significant engineering practicalvalue to studying on the on-line monitoring of diesel engine main bearing wear byusing thermoelectric power method. The major faults caused by the main bearingexcessive wear can be avoided and the work reliability can be improved in the dieselengine. The main conclusions can be summarized as follows:Based on the analysis of the thermoelectric monitoring mechanism, FiniteElement Method (FEM) and multi-body dynamics theory analysis method areintegrated in the paper. First, a calculation model of the crankshaft and the mainbearing is established and meshed in HYPERMESH; their modal is reduced inNASTRAN. Then a2D and a3D multi-body model are built in EXCITE. The bearingload, the instantaneous friction power consumption as well as the change of the axistrajectory under the different working conditions of the diesel engine in a workingcycle are explored by analyzing the main bearing lubrication situation calculation. Itis showed that the influence factors, such as the speed, the load, and the bearingclearance have significantly effects on the lubrication performance of the mainbearing in the diesel engine. The change rule among the wear degree of the mainbearing, the instantaneous friction power consumption and the thermoelectric poweris found, which provided theoretical basis for the realization of the main bearing wearon-line monitoring using thermoelectric power method.Crankshaft free mode test and main bearing wear tests are carried out4120SGdiesel engine. The correctness of the modal reduction is checked by comparing thesetting RBE2, without setting RBE2and free test modal frequency. It is showed thatthe finite element crankshaft model after the modal reduction has the same body characteristics as the original model. Axis trajectories and thermoelectric power weremeasured under the different working conditions of the diesel engine. Tested andcalculated diesel engine axis trajectories under the different conditions have the sametrends. The friction power consumption trends of the main bearing under differentworking conditions of the diesel engine are consistent with thermoelectric powersignal change trends. Within a certain range, as the diesel engine speed increase, thethermoelectric signal decrease, and with the increase of the diesel engine load andbearing clearance, the thermoelectric signal increase accordingly. In the process frommild wear to severe wear, the bearing wear thermoelectric signal increase sharply.Thermoelectric signal amplitude are associated with the instantaneous friction powerconsumption and bearing wear degree closely, which showed that the instantaneousfriction power consumption, the thermoelectric signal and the bearing wear degreehave corresponding relationships, and it is confirmed that the main bearing wear ismonitorable and diagnosable through the thermoelectric signal test. At the same time,the main bearing wear faults could be located quickly through the firing order of thediesel engine, which showed that thermoelectric signal has good positioningcharacteristics to bearing wear.