Research On Modeling And Rail Pressure Control Strategies For High Pressure Common Rail System

With the promulgation of the fourth stage emission regulations for off-road vehicles,the state has stricter requirements on the combustion performance and exhaust emissions of diesel engines for off-road vehicles.The electronically controlled high pressure common rail fuel injection system(HPCR)is the core of the diesel engine management system.A rapid and stable rail pressure can provide sufficient fuel injection pressure,thereby improving combustion efficiency and reducing pollutant emissions.Therefore,the research on the rail pressure tracking control algorithm of the high pressure common rail system is of great significance.Most HPCR systems currently adopt the proportional integral derivative(PID)controller,but PID controller cannot achieve satisfactory results when facing systems with nonlinearities and time-varying external disturbances.The anti-interference technology based on disturbance estimation and feed-forward compensation can effectively deal with external disturbances,among which sliding mode control has the advantages of good dynamic response and strong robustness.Therefore,this paper proposes a variety of sliding mode control algorithms based on disturbance observation compensation.The contents of this paper are as follows:Firstly,the working principle of the HPCR system is analyzed in detail,and the nonlinear models of the high pressure pump(HPP),the common rail(CR)and the injectors are established based on fluid dynamics and Newtonian mechanics.The nonlinear model of the HPCR system is analyzed,then disturbances and uncertainties are fully considered.The injection process of the injectors has a great influence on the rail pressure,and it is regarded as the external disturbance.This leads to the control objective of the system,that is,reducing the influence of disturbance on the system and reducing the fluctuation of rail pressure under steady state.Secondly,the experimental bench of the HPCR system is introduced,and the hardware design of the core components is given,including the electronic control unit(ECU),the rail pressure sensor and the current sampler.Then,the software design process and control process structure are given.The physical simulation system of HPP,CR and fuel injectors is built on AMESim simulation software,and the subsequent control algorithm is verified on this platform.Thirdly,based on the nonlinear model and a three-step analysis framework,the system is divided into three stages according to the pump pressure and the rail pressure.The fuel injection disturbance is a mismatched disturbance to the control input.Especially for the third stage,a generalized proportional integral observer based sliding mode controller(SMC+GPIO)is designed.By introducing disturbance estimation compensation in the design of the sliding mode surface,the impact of mismatched disturbances on the system is eliminated.The rail pressure tracking error converges to zero asymptotically.The effectiveness of the proposed algorithm is verified in Simulink and AMESim environment.Finally,in order to further reduce rail pressure fluctuations,a finite time disturbance observer based continuous non-singular terminal sliding mode controller(CNTSMC+FTDO)is proposed.By changing the design form of the sliding mode surface and adding disturbance estimation compensation,the rail pressure tracking error converges to zero in a finite time.With this method,the rail pressure fluctuation is smaller,and the continuous control law also avoids chattering,which is more conducive to engineering realization.The effectiveness of the proposed algorithm is verified in Simulink and AMESim environment.