Research On OBD System Of Engine ECU

With the growth of car ownership, vehicle security has increasingly become the focus ofattention. The public environmental voice becomes increasingly strong and environmentalregulations get increasingly stringent, equipping a car with the OBD system has becomeinevitable, at the meantime the system for the automotive repair and maintenance help a greatdeal. Foreign OBD system is relatively mature, and occupies the domestic market monopolyof OBD. They extensively use of dedicated chips in the system, and have developed a set ofstandards. Domestic OBD research is still in its infancy, hardly a practical product comes out.China to develop the automotive technology of independent intellectual property rights, onthe one hand, we need to explore ways and means of fault diagnosis, the other hand, subject tothe cumbersome foreign standards.In this paper, a relative comprehensive study has been carried out on the problems andmethods of the OBD system based on a diesel engine electronic control system developed byan enterprise. Based on the target of independently developing a low-cost, high reliability,practicality and as much as possible with independent intellectual property OBD products, thefocus of research is designing our own economic and reliable diagnostic signal acquisition,processing, and failure dealing strategy and supporting the design of diagnostic equipment,the difficulty lies in the R&D results to comply with cumbersome foreign standards withoutlosing the independent intellectual property rights.First, the paper studies the general content of the existing diagnostic criteria explicitlydiesel engine fault diagnosis, the general methods of diagnosis and treatment and the generalrequirements of the service interface of fault diagnosis, Combines with the thesis of the dieselengine system characteristics and determine the overall program for the fault diagnosis system.The overall program including the selection of diagnostic agreement; fault diagnosisinformation, the general strategy to deal with; determined on the basis of the J1939protocolas the communication protocol between the various ECU, using the ISO15765communication protocol between the ECU and the external diagnostic apparatus and anagreement to do a brief introduction; discussion focused on the design of the system faultinformation processing strategy, including the confirmation of the fault path, informationstorage and removal of the fault, the fault light lit and extinguished, etc.. Second, the paperselected for the coolant temperature sensor, the rail pressure sensor and the cam angle sensoras typical sensors, select a high-speed injector solenoid valve as a typical actuator,respectively, their design specific diagnostic features of the interface circuit and faultprocessing strategy. And use of Matlab Simulink to create a diagnostic model for simulationand theoretical studies, and automatic generation of software programs on this basis. Again,the actual bench test and a separate circuit experiment to prove the correctness and feasibilityof the design experience, but also for other more complex OBD system. Finally, as an integralpart of the diagnostic system,design fault diagnostic apparatus. At the end of the thesis, thisstudy and further work is prospected.The test proves that the diagnostic program presented in the paper is correct and feasible, it provides a general method for diesel engine fault diagnosis, and provides experience forother more complex OBD system.