Study On Characteristics And Control Methods Of Fuel Metering Valve In Common Rail System

As a vital component of pressure control in high pressure common rail system,the operating characteristic of fuel metering valve has an extremely important impact on the rail pressure control.The rail pressure control in high pressure common rail system is a systematic control problem,which includes research on the processing of sensor signal,the operating characteristic of actuator,the optimization of control algorithm and the response relationship between the output parameter and the actuator motion.The previous research on rail pressure control only considered few aspects,thus the ultimate control effect will be certainly influenced by other aspects.Therefore,a solution for sovling the above problems comprehensively is put forward in order to realize a better control of rail pressure.In this paper,the structures and operating principles of the main components in high pressure common rail system are analyzed.Based on the specific structure parameters,a mathematical model with flow and pressure is established.Additionally,a rail pressure state observer is designed out,which is utilized for extracting the pressure fluctuation caused by the unbalanced flow rate inside the rail pipe.The model of high pressure common rail system is set up in AMESim software,and the research on operating characteristic of fuel metering valve is conducted based on the model.The influence laws of each critical factor on operating characteristic are analyzed in detail and the influence of the operating characteristic of fuel metering valve on the establishment of rail pressure is also analyzed.During the closing process of fuel metering valve,the delay characteristic has impact on the establishment of rail pressure responsiveness,hence a bidirectional movement solenoid valve driven by electromagnetic is designed on the basis of the original fuel metering valve.Meanwhile,a drive circuit that can control the direction of the drive current inside the filed coils is developed.According to the operating characteristic of fuel metering valve and the influence on rail pressure,the whole working process can be divided into three phases: opening phase,intermediate working phase and closing phase.In accordance with the characteristics of each phase,a Peak-Hold control method for current,a driving control method for reverse current and a PI control method for synchronized control of valve opening angle and current based on fuel metering valve are proposed respectively.In the end,the bidirectional current driving function developed in this paper is validated via experiments.The control effects of different control algorithms,which are designed in Chapter 5 for each phase of fuel metering valve oriented to rail pressure control,are verified through the co-simulation process.For this model,the valve opening time can be shorten of 53 ms by utilizing Peak-Hold control method,reduced about 67.9%.Compared with the basic PI control,this PI control algorithm for synchronized control of valve opeing angle and current based on fuel metering valve can reduce both the forward overshoot and the reverse overshoot by about 60.79% and 50.95%respectively.Compared with the current unidirectional driving,the bidirectional driving can reduce the return time by about 56 ms,the decrease is around 66.3%.Besides,the rail pressure overshoot is reduced 48 bar which is around 31%.