Study On Rail Pressure Control Based On PID Of The Diesel ECU

The ECU is an important component of diesel engine.It is generally responsible for the management of common rail pressure, injection volume and timing. Common rail pressure affects not only the injection pressure but also the injection metering. Its stability and transient response directly influence the engine starting,idle and acceleration performance. Therefore,it is a crucial and difficult part to control the rail pressure in the ECU.Open-loop control is adopted in the stage of start and afterrun. Volume flow rate of metering unit is got through looking up the MAP with engine speed and temperature in start.And in the afterrun,the volume flow rate is set as a constant.PID control based on the expert system is adopted in normal state, and the volume flow rate is got through PID control algorithm by target and actual rail pressure difference value. And the duty of solenoid valve is obtained according to the volume flow rate.In addition,the PID parameters will adapt for different speed and temperature. Integral separation and incomplete differential methods have been used in practical applications to reduce the system overshoot and high frequency interference.According to the minimum system functional requirements, the outflow rate of the pump at the pressure of OMPa,20MPa,30MPa,50MPa,80MPa under different speeds has been measured. The character data of pressure sensor between OMPa to 120MPa has been got too.Besides, the oil outflow and return rate of the injectors at the pressure of 30MPa,50MPa,70MPa,90MPa with different pulse width has been measured.Around the rail pressure control strategy, the rail pressure control driver, the application software and the lookup algorithms software have been designed used modular method. The driver include AD,PWM and speed acquisition. The application software is based on start,normal and afterrun.2D and 3D lookup algorithms have been completed used linear interpolation method. Tests of start, idle, acceleration and small load working condition have been done with DK4A on 32 bit ECU. Rail pressure can be stable around the set value with 1-2MPa fluctuation. Some dynamic rail pressure tests have been done with DV6 system on the injection test bench. The dynamic response time of the rail pressure is less than 20ms with 1-2MPa fluctuation.The test results show that the present control methods and software are reliable and effective. The results of rail pressure control have reached the desired effect and have high practical value.