Research On The Condition Monitoring And Diagnosis Method Of Main Bearing Of Internal Combustion Engine

Since the creation of Internal Combustion Engine (I.C.E.) about one hundred ago, it has been the "drive heart" for a great deal of machine, such as automobile, construction machinery, shipping, locomotive and power unit. These kinds of equipment takes important tasks in our live. Some technical specific on I..C.E., such as reliability, economic viability and working life, has been grown up, which compared with the lower developing of technology, condition monitoring and predictive maintenance based on vibration analysis, on I.C.E. This is because of the complexity of vibration signal from I.C.E.Working as a reciprocating engine, I.C.E. generates wild vibration signal and often changes its operate speed. So it's difficult to get clear spectrum unlike a rotary machine. The signals that indicate the fault of I.C.E. usually being concealed by the normal working signal. The key work should be finding out the feature parameter from vibration signal for detecting engine defect.Taking a 2100-BI diesel as example, this paper analyzed its dynamical principle, and calculated the moving track of main shaft. It is presented that the main reason of force change in main bearing is the change of oil film force. When the minimum thickness of oil film decreasing, the rotated oil film force will decrease and the press oil film force will increase. The direct influence on minimum thickness of oil film from lube oil viscosity and main bearing gap has been proved.Based on the results of above, this paper presents one suppose about oil film breach. That is, when the minimum thickness of oil film decreasing to a dead line, the film would break and shaft would directly impact to the bearing. Its force wave would be very sharp while the total force energy is not obviously changed. According to this suppose, the vibration signal had been emulated. More energyfrom high frequency have been found to this kind of sharp force wave. This is the base of theory, which can be used to monitor the condition of main bearing.Author built an I.C.E. experiment equipment to simulate the change of main bearing gap for above theory analysis and suppose. Using own collecting program, perfect vibration data ware taken under various tests. Using the methods of Wavelet Filtering Envelop spectrum and Spike Energy spectrum, the test data ware analyzed, and the results indicate that both methods can detect the main bearing wear. The magnitude of 0.5x speed frequency in both spectrums can be take as the feature parameter for monitoring main bearing condition.Many factors to influence the monitoring results also ware discussed in this paper, such as the operating condition of I.C.E., detecting position, selecting transducer, etc. It can be said that the vibration signal taken from bearing stand can be used to monitor main bearing condition, while the signal from side face of engine is not obvious to the condition.