Study On Development Of High Pressure Common Rail Diesel Engine Fuel Injection Control System And Consistency Of Injection

The new generation of combustion theory characterized by'homogeneous compression ignition, low-temperature combustion'is an effective way to achieve clean and high-efficiency combustion, while the electronic control technology is a just means of carrying out those combustion theories. Therefore, this thesis adopted the heavy-duty diesel as the control object and developed the control system in view of the fuel injection strategy control and in-cylinder condition (temperature, pressure and oxygen concentration) control. The emphasis of this thesis is to deal with the technology problems of the response characteristics of the injection driving circuit, consistency of each cylinder's injection, engine control of each system and coordinated control of those systems.The thesis develops the control unit based on 32-bit microprocessor MCF5235. In order to reduce the burden of CPU, the logical signal circuit is designed based on the processor of CPLD to synthesize the driving pulses, which can achieve control algorithm tasks of processor and digital logic tasks to concurrently process. For the sake of meeting the response characteristics of the injector solenoid valve and improving control precision, the high-low voltage time-sharing driving circuit is designed to drive injectors based on bootstrap circuit. The EGR valve, variable intake valve close timing and intake pressure regulating valve control circuit are designed to achieve the effective control of the state in cylinder.In order to improve the injection consistency of the control channels, driving response characteristics of the injection solenoid valve are analyzed. The factors that affect the opening process of the solenoid are the power up voltage and the circuit resistance, while the factors in the closing process are the discharge feedback voltage, discharge circuit resistance and the holding current. According to the factors, both the driving circuit and the parameters of the driving pulse are optimized. The test results show that the current turn-off time is reduced from 0.066ms to 0.022ms through optimization.In order to improve the reliability of the driving circuit, the fault diagnosis and compensation handling system based on characteristic value of driving current is designed to diagnose the faults of the injection driving circuit real-time and dispose and compensate according to different faults. The experiments show that this system can detect the faults of solenoid valve driving circuit in real time and the fault of overload of the circuit within 0.005ms, and take appropriate self-protection measures. Regarding the other faults, the compensation handling system can automatically adjust the injection timing and the parameters of driving pulse to ensure that the fault cylinder and the normal cylinder have the same injection timing and injection quantity.The control software is developed based on CodeWarrior IDE development environment. The injection timing control algorithm is designed based on eTPU and the instantaneous speed, and the multi-pulse control algorithm is also designed based on the array of structure. The adjustment range of injection timing is from -68°CA ATDC to 30°CA ATDC to meet the demand of pre-injection and post-injection. The control algorithm is designed to realize the common rail pressure closed-loop control and other controls. The control system can flexibly control injection pressure, injection timing and injection quantity, and it can also realize the flexibly modulating of injection mode and freely switch between different modes. The control programs of the engine systems are designed, and priority is assigned to the control tasks according to the level of the real-time. The systems of the engine can be coordinately controlled according to the scheduling mechanism of preemptive based on the priority. The start, idle and speed control routines are designed and the control strategies are preliminary studied.