Control Software Design Of Several Functional Modules In The ECU For The GDI Engine

With automobile emission legislation becoming more and more stringent andimplement of the fuel consumption legislation, the requirements on emission andeconomy of the engine have become increasingly demanding. The gasoline directinjection (GDI) engine, as one of the most important ways to deal with the energyand environment problems in IC engine industry, has currently become theinvestigation focus because of a serious of advantages, such as higher thermalefficiency, lower fuel consumption, better cold start performance, lower emissionand so on. As an important part of the GDI engine technology, the development ofthe electrical control unit (ECU) of the GDI engine has also become one of thekey-points in the studies.The ECU’s software is the highlight and difficult point in electronic controltechnology development of the GDI engine. According to layer model structure, theengine ECU software are divided into the application software layer, the run-timeenvironment (RTE) layer and the foundation software layer, referring to functions,strategies, algorithms, monitoring, diagnosis, communication and I/O control. Thefoundation software layer consists of the real-time operating system (RTOS), theI/O hardware abstraction layer, the microcontroller abstraction layer and thecomplex driver layer, therein the I/O hardware abstraction layer and the complexdriver layer are related to the hardware which can be achieved in the foundationsoftware layer configuration phase, according to the interface demanded by theapplication software layer and the hardware resources offered by the ECU.In the previous study, a preliminary overall design of the ECU of the GDIengine used to test in the test-bed was realized. The hardware component includesthe sensor signal processing circuit, the knock signal detection circuit, fuel injectordriver circuit, ignition driver circuit, the solenoid valve drive circuit for the VVToil pressure control and the drive circuit for the ETC module. For the software,overall structure design of the electronic control system software and thebackground calibration software design were performed. On this basis, thehardware interface circuit of an universal exhaust gas oxygen(UEGO) sensor wereadded into the ECU. The driver layer software related to the hardware and a partsof the control algorithm in several important functional modules were designed. The main research contents are as follows:(1) The design of ignition control module programsThe ignition control module is composed of the ignition advance angle controlmodule and knock detection module. Ignition advance angle includes dwell anglecontrol and advance angle control, both angles can be set by the user. The cylinderto be ignited and the compression top dead center (TDC) of this cylinder weredistinguished based on signals of the crankshaft position sensor and camshaftposition sensor, and the power-on time corresponding to the dwell angle wascalculated according to the setting values of the dwell angle and the ignitionadvance angle and the current engine speed. Then, the power-off instant wascalculated using the pulse interval of the crankshaft position sensor and thecylinder sequence control and ignition timing signal were produced.In the closed-loop control, ignition advance angle is adjusted based on theknock intensity. Microcontroller communicated with the knock signal ASIC(Application Specific Integrated Circuit, ASIC) HIP9011through the serialperipheral interface (SPI), and the knock-chip operating modes and operatingparameters which include the integration time constant, magnification, band-passfilter frequency and so on were set. According to the starting position and the widthof the knock detection window determined based on the engine speed as well as thethreshold value for knock decision, the knock intensity was judged and calculatedby the integral quantity of the knock signals within the detection window and thethreshold. Then the ignition timing was adjusted based on correction value of theignition advance angle obtained from the calculations or a lookup table. Usingvirtual knock signal produced by a signal generator, primary verification for theknock detection program was conducted. The results indicate that the signalprocessing value can be effectively extracted from different amplitudes knocksignals by the program.(2) The design of fuel control module programThe fuel control module consists of fuel rail pressure control module and fuelinjection control module. Because that fuel is injected directly into the cylinder inthe GDI engine, the injection pressure up to5~20MPa can be available to improvefuel atomization. Therefore, the accuracy of fuel metering is directly affected bythe stability of the injection pressure control. The fuel rail pressure is controlled bya fuel rail pressure control module through controlling opening time of the fuelpressure regulating valve in the high-pressure fuel pump according to the feedbacksignal of a fuel pressure sensor. The fuel rail pressure control method was determined in terms of the characteristics of high-pressure fuel pump, and a certainpoint between TDC and BDC in the rising phase of the camshaft shape-curve wasselected as the fuel-supply starting time and the TDC as the terminal time.According to the phase relationship between the fuel bump camshaft signal andcrankshaft signal, the fuel-supply signal was yielded at the right moment. The fuelrail pressure control logic was designed through dividing the rail pressure controlinto two stages—starting and after-starting phase. A look-up table was used in thestarting phase and a control method combined the pre-control with the PIDfeedback control was used in the after-starting phase. In the fuel system test-bed,fuel rail pressure control test was conducted. The results show that when the targetrail pressure is10MPa, the engine speed is503r/min and fuel injection pulse widthis3ms, the variation range of the rail pressure is less than0.04MPa.The fuel injection quantity control and injection timing control are basic tasksof the fuel injection control module. The two injecting function—one is in theintake stroke, the other in the compression stroke can be achieved by the injectordriver program. The injection pulse width was determined by looking up tableaccording to a given fuel injection quantity and fuel rail pressure. Firstly, thecylinder to be injected and its exhaust TDC were recognized based on the signals ofcrankshaft position sensor and camshaft position sensor. Then the injection timingwas determined according to the given injection advance angle and pulse interval inthe backlash of crankshaft position sensor as well as the current engine speed, andthe injection signal was produced.(3) The program design of electronic throttle control (ETC) moduleThe throttle opening is changed by the ETC module though outputting PWMpulse to control DC servo motor, and closed loop control for the throttle valve wasperformed by means of the feedback signal from a throttle position sensor. Its mainrole is to adjust the engine torque through controlling intake air quantity, and tocontrol the engine speed in cruise control mode. Through improving throttle controlalgorithm and applying a method combined closed-loop control strategy withnonlinear compensation, a fast, stabile ETC control was achieved. Meanwhile, theovershoot in control was reduced.(4) The program design of intake variable valve timing (VVT) control moduleThe camshaft phase is changed by the VVT control module by controlling oilsupply path and drainage path of the hydraulic control solenoid valve to adjust thevalve timing, to optimize the engine intake and exhaust process, to improve thevolumetric efficiency, and to enhance power output, fuel economy and idle stability. The NOXemissions can be reduced by the internal EGR. The VVT controlalgorithm was designed. According to the changes of relative position between thecrankshaft and camshaft signals, the VVT phase was distinguished. And the intakevalve phase was controlled using the segmented incremental PID control and fuzzycontrol algorithm, respectively. The control test was conducted on VVT test bench.The results show that the errors can be controlled within the range of±1°usingboth algorithms, but the fuzzy control is faster with a smaller overshoot.(5) The hardware and software design of the interface control unit for theUEGO sensorThe implement of strict automobile tail-gas emissions standards and theapplication of lean-burn technology require that air-fuel ratio is controlledaccurately within a certain range. Due to wider measurement range, the UniversalExhaust Gas Oxygen (UEGO) sensor has become an important component in theengine air-fuel ratio control system. However, the reliability and the measurementaccuracy of this sensor rely heavily on the sensor interface control unit. Therefore,the control circuit for the UEGO sensor (LSU4.2/LSU4.9) was designed based onthe CJ125interface chip. The heating control program for the UEGO sensor wasalso developed using PI control algorithm. The heating control experiment wasconducted using this PI control algorithm. The results show that the control processis more stable and the control accuracy is higher, and the sensor target temperatureof750℃is reached within13s. The sensor calibration software was developed,which was used to calibrate the LSU4.2UEGO sensor in a four-cylinder gasolineengine.