Research And Application Of Fault Diagnosis Technology Of Common Rail Diesel Engine

Diesel engine is indispensable in industry and daily life.In order to improve the performance of diesel engine and reduce its emissions,high pressure common rail technology is widely used.As a result of that,modern diesel engine is becoming more and more complex,and the difficulty of fault diagnosis is increasing.In order to diagnose the fault in time,some fault diagnostic technologies are studied and they are applied in specific objects.After the survey of fault diagnosis technologies of diesel engine,the OBD is studied by considering the cost and practicality,and the specific work is carried out in the light of the technical requirements and the shortcomings of the OBD system.The generalized OBD system includes the online diagnosis of ECU and the external diagnostic instrument.The corresponding design is carried out respectively.The ECU diagnostic module is subdivided into data acquisition module,fault monitoring module,fault management module and diagnostic communication module.And the diagnosis strategies of key components including accelerator pedal sensor,coolant temperature sensor,fuel rail pressure sensor,speed sensor are studied.Finally,the design is realized in the ECU of the fuel system of a single cylinder common rail diesel engine.In the design of the diagnostic instrument,the basic functions including reading the data flow,reading the fault code,reading the freeze frame,clearing the diagnosis information are realized.In order to make up the shortcomings of OBD system in diagnosing mechanical and gas related faults and locating the specific cause,some other methods are discussed and used to find the cause of the misfire fault.Through the analysis of the relationship between the instantaneous speed and the misfire fault,the characteristic parameters which can be used to determine the failure of the combustion are extracted.The cause of the failure is divided into the primary cause and the specific cause.The primary cause can be determined by the extracted characteristic parameters with the ART2 neural network.Due to the use of ART2 neural network,the system has a strong ability to learn new faults.The further searching of the cause is regarded as a multi-objective decision-making problem and AHP is used then.The above fault diagnosis methods are realized as an extension module of the diagnostic instrument.Finally,the functions of the diagnosis system composed of the ECU diagnosis module and the external diagnostic instrument are verified respectively.The test results show that all functions work well.The system can find out the electrical faults quickly and accurately,and it can give the specific cause of misfire at low speed.