Research On Modeling And Rail Pressure Control Strategies For High Pressure Common Rail System Of One-Cylinder Diesel Engine

With the increasing of energy consumption in China,energy shortage,environmental pollution and corresponding issues are becoming more and more serious.Meanwhile,new emission standards with higher requirements are on the way.Thus,it's urgent to upgrade the electronic control technology of diesel engines.Compared with electronic controlled VE pump,by introducing the common rail,the high pressure common rail injection system can obtain higher injection precision,improve fuel efficiency and system dynamics,and reduce emissions as well.Rail pressure control is the precondition to achieve high performance of common rail system.The basic principle of common rail system which uses the fuel metering unit as the actuator can be descripted as below: effective voltage acting on the actuator drives the actuator open at a certain opening degree.During fuel feed stroke,the oil in the tank is transferred to high pressure pump by electronic controlled oil pump;then in the following pump stroke,the oil is compressed by the camshaft and is pumped to the common rail which can cause the change of the rail pressure.The common rail system contains various kinds of internal and external disturbances such as input voltage fluctuations,system parameter perturbations,etc.The system also includes nonlinear characteristics caused by the pump process and fuel injection process.These existing disturbances and nonlinearities make it difficult for the system to achieve a satisfactory closed-loop control performance.In this paper,the nonlinear model of the common rail system is established and various advanced control schemes are put forward to improve the system performance.The operating principle and structural characteristics of common rail system are introduced in this paper,and then a mechanism model of the main components including fuel metering unit,high pressure pump and common rail is established.Cascade control scheme is proposed according to the fixed hardware condition,in which the outer loop model is simplified based on the mechanism analysis.Firstly,a rail pressure control scheme based on linear feedback control is investigated.However,the analysis and simulations indicate that the presented scheme can not achieve satisfactory performance in the existence of nonlinearities and disturbances.On this occasion,a compound control scheme based on the disturbance estimation technology is proposed: a disturbance observer is adopted in the current loop to estimate the coil parameter perturbations and input voltage fluctuations,which is then compensated in the controller.Active disturbance rejection control is developed in the rail pressure loop,by introducing tracking differentiator and extended state observer and employing the general state error for controller design.The dynamics and anti-disturbance abilities of the system are enhanced.The application of general proportional integral observer based backstepping control scheme in the common rail system is studied.The mismatched time-varying disturbances caused by injection dynamics and parameter perturbations are considered here,which can be estimated efficiently by the designed general proportional integral observer.The antidisturbance abilities of the system can be improved by introducing the estimations of the disturbances in the backstepping control design.The effectiveness of the proposed algorithm is validated by the simulation results.