Research On Control Strategy Of Rail Pressure System Of Gasoline Direct Injection Engine

Gasoline Direct Injection(GDI)engine has excellent economic,dynamic and low emission,but it has brought about the complexity of the working condition.In order to realize the pressure control of GDI engine under variable operating conditions,it is necessary to rely on the design of the application layer control software of the electronic control unit(ECU).Therefore,the control strategy of the rail pressure system is the key to realize the switching of the working condition,to realize the good atomization of the low pressure fuel spray and to prevent the overpressure under high pressure.The rail pressure system is a nonlinear dynamic system with strong disturbance,while the common rail pressure fluctuation of GDI engine will affect the change of fuel injection characteristics,resulting in a direct deviation between the actual fuel injection quantity and the expected fuel injection volume,which increases the complexity of rail pressure control.Therefore,the design of the control algorithm for the rail pressure system is the key point of eliminating the rail pressure deviation to realize the good following of the rail pressure control.This paper research and design GDI engine rail pressure control strategy and algorithm,and build control oriented GDI engine common rail pressure system mathematical model as the object to verify the control strategy and algorithm,and the establishment of rail pressure control related model using MATLAB/Simulink software,mathematical model and control strategy based on test data GDI engine common rail system is verified.The main contents are as follows:(1)Rail pressure control strategy and algorithm design.In order to prevent the engine variational condition for rail pressure,the design of rail pressure control strategy to achieve the Map selection of setting different combustion modes and rail pressure under different working conditions,get the current condition of the rail pressure setting;and for rail pressure control in the actual rail pressure and rail pressure setpoint deviation the PI control algorithm,the design of rail pressure adjustment;the static offset resulting in the simulation of rail pressure system,the rail pressure feedback control algorithm to pump oil compensation angle to offset static offset calculation.(2)The modeling of the mathematical model of the common rail system.According to the physical process of generation and transmission of fuel pressure and the oil storage characteristics of common rail,the relationship between fuel flow and pressure of high pressure solenoid valve high pressure oil pump common rail tube injector is established,and a mathematical model for control of GDI engine rail pressure system is established.On the basis of the rational and accurate mathematical model of rail pressure,it is reasonable to simplify the part that affects the smaller rail pressure.(3)The simulation of the rail pressure model and strategy.The simulation rail pressure,the target rail pressure and the actual rail pressure deviation are compared and analyzed in the idle,steady,acceleration and deceleration and addition and subtraction load conditions.The accuracy and stability of the designed rail pressure control strategy and algorithm under idle and steady state conditions,as well as the responsiveness and follower of the rail pressure step are verified.