Experimental Reseach On Monitoring Method Of Bearing Wear Based On Thermoelectricity For Diesel Engine

As main frication parts of marine diesel engines,bearing's severe wear conditions lead to crankshaft embrace molten,the piston crankshaft connecting rod failure,such malignant accident seriously affect the safe operation of the ship,and bring huge economic losses.Therefore,on-line monitoring technology research of diesel engine bearing wear,can prevent bearing abnormal wear malignant accidents,improve the reliability of bearing,has very important scientific significance and practical value in engineering.Based on the analysis of the domestic and international journal bearing wear monitoring technology,a new monitoring method for diesel engine bearing wear based on thermoelectricity technology has been made a test research.Through the diesel engine fault simulation test of bearing wear,analyzed the relationship between diesel engine bearing wear and the amplitude variation of thermoelectric signal.The main research contents and conclusions are as follows:1.According to the basic theory of thermoelectric effect,the calculating method of thermoelectric potential of closed loop consist of two different conductors,analyzed the mechanism and influence factors of thermoelectric potential.Combined the characteristics of diesel engine structure with lubrication theory of dynamic pressure journal bearing,analyzed the producing mechanism and the influence factors of thermoelectric signal between diesel engine body and crankshaft.On the bearing fatigue test machine,bearing wear thermoelectric monitoring experiment was conducted the bearing clearance,bearing load on the influence of the thermal signal,and the reliability of the measurement system was tested.2.On 4120 SG diesel engine test bench,respectively,the fault simulation test reseach of the main bearing and big end bearing wear was carryed,the results showed that:(1)On the idle speed condition,bearing oil film has not yet formed,with the increase of diesel engine speed,oil film gradually was developed,thermoelectric signal amplitude decrease rapidly after a weak increase;Under the rated speed,full oil film formed,speed had no obvious effect on thermoelectric signal.(2)Bearing clearance increases,the oil film thickness increases,but their bearing capacity decreases,bearing wear,thermal signal amplitude rise;Diesel engine load rises,journal eccentricity and bearing clearance decrease,then thermoelectric amplitude decrease.The influence of bearing clearance on thermoelectric signal amplitude is greater than the diesel engine load.(3)There is a difference characteristic of wear thermoelectric signal between the big end bearing and the main bearing,the former thermoelectric signal rise at the moment when corresponding cylinder ignite,the latter rise when the adjacent two cylinder ignite.(4)Thermoelectric signal amplitude increased at a sudden reduction of diesel engine load.(5)The material properties has a huge influence on contact potential.All other conditions being the same,the thermoelectric signal amplitude of AlSn alloy is greater than the CuPb.3.Designed a kind of journal bearing wear monitoring test bench,combinated static load with dynamic load to simulation the diesel engine bearing load.Through ultrasonic oil film thickness monitoring technology,match thermoelectric signal with thermal bearings wear conditions to realize the separation of its characteristics.