Design And Research On The Controller Of Urea-SCR For Diesel Engine

Diesel engine has many features, such as high power, low fuel consumption, good durability and so on. Therefore it is wildly used in the car. The diesel technology has become an effective way to solve the problem of resource dependence. Diesel engine can product little CO and HC emissions, but NOX emissions is much higher than the gasoline engine. So, how to reduce the diesel engine NOX emissions have been become the hot issues in recent years.SCR is an efficient technology to decrease the diesel engine NOX emission. It not only protect engine against the damage of sulfur but also can save fuel. Moreover the engine just need change little for the technology. In summary, SCR can meet the need of China’s development.SCR controller finish the control and diagnostic function of system.As the main component of SCR, controller includes many complex logic algorithms.So researching the controller has important meaning to promot the development of SCR technology.The content of paper includes three parts:the SCR controller hardware design, the software development and experimental research.In the hardware design part, First of all, analyses the main affecting factors of performance in the controller working process. Then make the solutions during the design. Secondly introduces the components and their characteristics of SCR system. Finally, designs the hardware circuit of controller. Hardware circuit includes five parts. They are microprocessor module, power module, communication module, data acquisition module and drive module.The software development start from the research of control strategy.The SCR system control strategy consists three parts:the urea injection control strategy, the pump pressure control strategy and the heating management strategy. The urea injection control strategy calculates the injection quantity. The pump pressure control strategy adjusts the pressure of the urea pump. The heating management strategy controls the heating when the urea crystallized.Paper focuses on four parts:signal acquisition and MAP search, pressure control, OBD diagnosis and the calibration drive.1) Software designed the median and mean filter to improve the accuracy of data acquisition. Using the interpolation method search the3D MAP to get the continuous control parameters.2) Pressure control function keeps the injection pressure in calibration value through the PID algorithm.3) OBD diagnosis system can finish the fault confirm, fault storage, fault repair and diagnostic communication functions. These functions can ensure the SCR systems in the stable state.4) Calibration drive can achieve the data acquisition and parameters calibration by using the CCP calibration protocol.SCR control system can complete the calibration of sensors, actuators and MAP. System uses the comparative analysis method to check the accuracy and linearity of sensors. Actuator calibration mainly completes the test of urea nozzle flow characteristics, and also analyses the affect factors. After that, we complete the measure of MAP. Paper primary introduces the procedure and method. Finally, test SCR control system performance by the ESC and ETC cycle.