Research On Control Strategy Of GDI Engine

Facing the intensifying energy crisis and demanding emissions regulations, GDI engine emerges at the right moment, having a notable difference in the overall structure with traditional PFI engine, and there is a huge advantage in the aspect of reducing fuel consumption and reducing emission. With national “863” project- “Development of car’s gasoline direct injection engine”, a four-cylinder gasoline direct injection(GDI) engine is taken as research object, the composition and service condition of GDI engine was studied, the structure and operating principle of the parts in the electronic control system of GDI engine which used in the experiment was analyzed, the work carried out are as follows:1. Starting with GDI engine, understand the control signal required for controlling the engine, summarize and find the corresponding sensor of the signal, analyzes the types and drive types of sensors, and logical relationship before input and output. Built engine experiment bench, design the corresponding drive circuit based on the electrical characteristics of each sensor and actuator. Install the corresponding test equipment according to the experiment’s purpose. The hardware control circuit is designed base on MC9S12XDP512 microcontroller, and μC/OS-II real-time operation system is applied in the single-chip microcomputer. According to the advantage of the GDI engine and the basic requirement of the cold start process, the cold start of engine control strategy is designed; According to the advantage of the GDI engine and the basic requirement of mode conversion process, the engine mode conversion control strategy is designed.2. Design the hardware control circuit with MC9S12XDP512 microcontroller as control core, and embed the μC/OS-II real-time operating system into microcontroller, carry out modular design based on the function of GDI engine’s electronic control system. Taking L9707 chip as the control core for injector drive circuit, design the injector driver circuit, achieve the waveform control of drive current, rapid opening of injector and accurate measurement of injecting fuel. Applying the AD signal of processor XDP512 as an input signal, the electronic throttle was controlled in close-loop, using MC33887’s current inverse feedback feature, complete the close-loop control of the throttle. Control the throttle position with the application of fuzzy PID controller, with quickly response speed adjusted to target position without overshoot, and having good robustness. Design the UEGO’s close-loop control circuit based on the UEGO processing chip CJ120 and BTS power amplifier circuit, heating the UEGO, to satisfy the rapid heating requirement for UEGO.3. According to the working characteristics of GDI engine and cold start control requirement, optimize cold start processing’s control for engine, design the cold start control strategy for engine, implementer the optimization design for control objectives of each link in the process of cold start. According to GDI engine’s advantage and the basic requirement in the mode conversion’s process, design mode transformation control strategy of engine. Through adjusting the injection timing, fuel injection, ignition timing and throttle opening, accurately control the air-fuel ration, with the control target of small change in the engine cycle and small output torque ripple, to determine the most optimal control parameters. Achieve the control function of control strategy for GDI engine, implementer the modular design for software parts, having the initialized design of main function, function design of interrupting speed handling, function design of runtime map, function design of condition management, function design of fuel injection control, function design of ignition control, function design of fuel pump control, function design of digital and analog input and function design of serial communication.4. Carry out the engine cold start research, analyzing the optimum control parameters in each stage of cold start process. Test the best fuel injection timing and ignition timing in the start-up phase of engine, under the conditions of 6% throttle opening, 0.5MPa fuel rail pressure, 0.9 excess air ration, set the fuel injection advance angle at 90°BTDC, the optimum ignition timing at 30°BTDC, at this moment, the engine starts most rapidly and with lower emissions. Test the optimum injection quantity, the optimum injection timing and optimum ignition timing in the catalyst’ ignition phase of engine, under the conditions of 6% throttle’s relative position, 5MPa fuel rail pressure, 1.1 excess air ration, the optimum control parameter is to set at two times: ration of 1:1, the fuel injection pulse width of 4ms, ignition timing of 15°BTDC, the first injection timing is 300 ° BTDC, the second injection timing is 70 ° BTDC. Test the optimum injection timing and ignition timing in the warm-up phrase of engine, under the conditions of 6% throttle opening, 1 excess air ration, set the optimum fuel injection timing at 90°BTDC, the optimum ignition timing at 32°BTDC.5. Carry out the research on the mode conversion of engine, to determine the optimum control parameter of each operating conditions in the process of mode conversion. Test the optimum ignition advance angel and optimum fuel injection advance angel of λ=1.0 and λ=1.4 under the homogeneous combustion mode of engine. Test the optimum of fuel injection ratio, the optimum injection timing and the optimum ignition timing of λ=1.4 under the stratified combustion mode of engine. Carry out “fit model method” to the optimum parameters, and optimization calibration of parameters on the basis of model, under the optimum parameters’ condition, study the mode conversion, and test the exhaust emission in each operating condition.