The Control Unit Design And Studies For SCR System Of Diesel Engine

The diesel engine is the primary power source of the transporter and government vehicles because of its high compression ratio, power and heat efficiency. Compared to the gasoline engine, the NO_X emission of diesel engine was higher, with the regulations of National IV and V promoting, diesel engine cannot meet the more and more stringent emission standards just using the interior purification, matching the after treatment system to reduce NO_X has become an important research direction. Because diesel engine with the selective catalytic reduction(SCR) technology has the advantages of high efficiency, low emissions and less engine changes, etc.SCR system has been recognized as the mainstream method to reduce the NO_X emission. According to the shortage of petrol resource, higher sulfur content and other issues of my country, it is one of the best way to install the SCR system for the diesel vehicles.Referring to advanced SCR technology of other countries and combing with the demand of domestic, the control unit of SCR system was designed independently. The main content of the paper were divided into four parts, such as the hardware circuits design, the board support package set, the detection platform design and test analysis.The concept of “module” was used in the designing of hardware system. The control unit hardware circuits contained microcontroller unit(MCU) control module, power management module, input adjustment module, output driver module and controller area network(CAN) communication module. In this part, the selection of the chip, the circuit filter, peak-hold and electromagnetic susceptibility were analyzed.The Freescales’ microcontroller MC9S12XS128 board support packages were designed based on MATLAB/Simulink. The methods and principles of S function, TLC function and drive block packages were stated detailedly. According to the requirements of SCR system, the board support packages of analog to digital conversion module(ADC), digital input and output module(DI/DO), the pulse width modulation module(PWM), input capture module(IC), real time interrupt module(RTI) and CAN module were set. In order to facilitate the upper users, the script function was written to transplant the board support packages into the Matlab/Simulink library, which could improve the efficiency of designing the system.The detection platform was built composed by the upper computer, signal generator, the data acquisition card, CAN card and stepper motor, the login and monitor interface of upper computer were designed by Labview. The function experiment was performed using the independently developed SCR control unit, including the sensor signal acquisition, digital signal processing, pulse width modulation signal capturing, motor driving and CAN communication. The results showed that the hardware circuits of the control unit were stable, the board support packages of MC9S12XS128 were reliable and the detection platform met the requirements of SCR system. Therefore, the studies about the control unit for SCR system have practical value.