Study Of Electronic Control System With Diagnosis Function For CNG Engine On Vehicle

With the gradual shortage of oil resources and environmental issues, the alternative fuelresearch for vehicle engine is becoming the main direction of the current study. Natural gas isthe more ideal for a variety of engine alternate fuel, because of its good combustion,emissionsand economic performance, and the gradual improvement of the filling stations arranged so thatnatural gas will be a larger period of time as the main alternative fuels of the engine. However,natural gas has its unique characteristics (such as the normal state for gas, higher antiknock),what makes natural gas engines with gasoline or diesel engine is different in the mechanicalstructure and electric control system. Thus applications for natural gas engine electronic controlsystem is very necessary.In this paper, the gas supply system, ignition system, injection system, booster system andfault diagnosis system have been fully analyzed.The overall structure of the natural gas engineelectronic control system has been put forward,include intake manifold single point of injectiongas supply, air supply with turbocharged and intercooled, lean combustion and oxygen sensorclosed loop emission controlway, sequential multi-point energy ignition, automatic faultdiagnosis. Consided the principle, conditions of use, costs,we selected the sensor control chipand actuators, the Hall sensor is selected as the crankshaft and camshaft position sensor,thermal resistance type temperature sensor, high-power and high-speed switch IGBT as theignition driver chip,MOS-FET as injector driver chip, the master chip is Freescale’s16-bitmicroprocessor MC9S12XDP512which has rich internal resources. In order to save the masterchip resources, another chip is used for fault diagnosis specialy. The hardware circuit designedand debuged and considered it’s reliability, multi-functional, anti-jamming needs. The controlsoftware designed and programed, in the programming process, the underlying driver codewrittened by manually,and conditions to determine and control algorithm used the Matlab/Stateflow and Simulink model, and finally used the Matlab/Simulink automatic codegeneration feature to generate the C code, and streamlining and debug the code in Freescalecompiler environment CodeWarrior, finally, the code generated in two ways integrated as theend-use code,which is greatly improved the reliability of the code and the development speed ofthe program. The test monitoring software was programed with LabWindowsCVI software,which has the function of data collection, display and plot curves, a small amount of datacalibration and fault code reading etc.In the main control strategy, the ignition timing and ignition dwell angle control underdifferent conditions by the ignition control system. The basic ignition advance angle islookuped from the3D MAP,then plus the amount of correction of the signal generated by the water temperature, knock as the last actual ignition advance angle, close angle is lookuped fromthe table directly. The mass of the gas includ the basic the inject mass and the mass of correction,basic inject mass is carried out according to the different conditions of concentration table, themass of correction obtained by the oxygen sensor parameter,and then converted into theinjection pulse width based on the injector. On the faults diagnosis, faults detection methods,faults management and processing strategies after failure have been researched.Then some simulation experiments ware done in a homemade device “engine controlsystem on the test bench”, the experiments include the acquisition and processing of signalsfrom various quarters, the injection and ignition timing, ignition energy calibration, simulationfault diagnosis etc. The simulation experiments verified the hardware system design can beachieved, software and software development method is feasible, the entire system can meet thefunctional requirements of the natural gas engine electronic control system.Finally, the inadequacies and improved method in this paper were explained. And thefurther planning has been made.