The Research And Design Of Diesel Engine Rail Pressure Control System

With the increasingly stringent requirements of environmental protection and emission reduction,high pressure common rail fuel system has become the future development trend of diesel engine system.Common rail pressure control,as one of the most critical technologies in the system,will affect the dynamic performance of diesel engines,fuel economy and emissions directly.The common rail pressure control system of diesel is nonlinear,time-varying and hysteretic,and its mathematical model is difficult to be described,so this paper designs a diesel rail pressure control system based on the modeling,algorithm and strategy of common rail pressure control system at home and abroad,and this system has stronger stability,smaller overshoot and oscillation,faster response speed and so on.The main work of this paper is as follows:First of all,the main structure of BOSCH-CR common rail fuel system is studied,and the structure and working principle of high pressure oil pump,fuel injector,fuel metering proportional solenoid valve and common rail pipe assembly in the system are studied in detail to establish their mathematical models and deduce the transfer functions of system.After analyzing two kinds of rail pressure control systems with different structures,the single-loop system with the duty cycle as the control output is designed,and it is the final pattern of the rail pressure control in this paper.Secondly,the classical system control theories are studied.Combined with the strengths and weaknesses of these control theories,the fuzzy adaptive PID control algorithm is designed and optimized by feed forward control.Compared with traditional PID algorithm,it can reduce two-thirds of rail pressure control overshoot,shorten 20% of response time and nearly half of adjusting time,which shows that this new algorithm has good control effect.And then,the time sequence of sampling and control of rail pressure is determined,and the software filtering algorithm is designed.Besides,the calculation model of target value of rail pressure is derived,and finally,the overall scheme of the rail pressure control strategy is worked out.The control strategy takes into account the change of the system itself and the external disturbance,and has strong robustness.Then,the hardware circuits of the rail pressure control system are designed.Based on the main control module MC9S12XEP100,the designs of its power supply circuit,peripheral interface circuit,acquisition and processing circuit of rail pressure and temperature signal,drive circuit of proportional solenoid valve and communication module circuit are completed,and it also makes a detailed study on the generation of PWM wave of single chip microcomputer.The acquisition signals of circuits are accurate and reliable.At last,the software design of the rail pressure control system is completed.In the software development environment of CodeWarrior,some software designs of main task of system are completed,such as the initialization of main control module,communication program of main control module and the computer,switch scanning program,timed interrupt program and rail pressure acquisition and control program,and the design of fuzzy PID control algorithm and its code realization are introduced in detail.