Research On Rail Pressure Control Strategy Of High Pressure Common Rail Diesel Engine

The fuel injection pressure of high pressure common rail diesel engine has a direct impact on the precision of fuel injected,fuel atomization and combustion process,which will affect the power,economy and emission performance of diesel engine.The deviation of fuel injection quantity was caused by fluctuating fuel supply principle of high pressure pump,Intermittent characteristics of fuel injection and frequent action of pressure control valve.In particular,the change of engine speed and fuel injection quantity results in the change of the rail pressure,which leads to the complexity and difficulty of accurate control of rail pressure.In order to ensure the stability of the injection pressure and adjustment ability,to meet the different conditions of the engine on the injection pressure requirements,rail pressure control performance is largely dependent on the electronic control unit in the application layer control software,so it is very important to design the control strategy and control algorithm.Have studied the rail pressure control strategy of high pressure common rail system of diesel,and built the oriented control model of controlled object,had established rail pressure control related model using MATLAB/Simulink software to verify the control strategy by simulation and experimental results,the main contents are as follows:(1)Modeling of control oriented common rail system.According to the physical process of high pressure common rail system of rail pressure generating and transmitting,and considering the effects of internal and external factors,a mathematical model of rail pressure based on working mechanism is established and simplified,and a rail pressure model for control is developed for the subsequent rail pressure control strategy software in the ring simulation.(2)The construction of the overall model of rail pressure control.According to the functional requirement analysis,requirement definition and requirement decomposition,the control objectives are determined,according to the principle of modularization,the overall structure of the control strategy is constructed.Based on the combination of feed forward and feedback,the rail pressure control strategy based on the fuel metering unit(MeUn),the pressure control valve(PCV)and the coupling is constructed.(3)Sub module of rail pressure control strategy.By dividing the input variables,the intermediate variables and the output variables of the model,the functional relationship of each sub module in the model is determined.Selecting the control target rail pressure by the working state,state machine transition conditions,the calculation and correction of target rail pressure,MeUn and PCV Pre-control value,calculation of MeUn and PCV regulation deviation deviation are designed.Finally,the MeUn volume and PCV pressure setting values are calculated,and the rail pressure control strategy is obtained.(4)Control strategy software in the loop simulation.By maintaining or changing the MeUn and PCV duty cycle in different ways,and then the MeUn and PCV adjustment of the PID,two methods to verify the control of the rail pressure model.Finally,to validate the control strategy of the closed-loop simulation combined with the engine steady state and transient condition,and compared with the test data of rail station.