Research On Control Strategy Of Ultra Low Emission Vehicle Exhaust Sensor And Development Of Control Unit

In recent years,air quality problems have become increasingly prominent in China,and people are paying more and more attention to the pollution caused by automobile exhaust emissions.In 2019,some provinces and cities took the lead in implementing the national VI emission standards,in which the NO_X emission limit was reduced to 35mg/km,which put forward higher requirements for automotive NO_X sensor assemblies.The NO_X sensor assembly is mainly composed of a NO_X sensor and its control unit,which is widely used in the determination of NO_X content in various types of automobiles.However,this field has been monopolized by foreign countries for a long time.In order to break the monopoly,this thesis takes the NO_X sensor of Japan NGK company as the research object and develops a control unit matching it.Based on the structure of the NO_X sensor,this thesis proposes an improved Ip1 constant value feedback control strategy based on the principle of limit current,which makes the control process of the NO_X sensor simpler and more reliable,and the measurement more accurate.This thesis focuses on the design of the improved Ip1 fixed-value feedback control strategy to develop hardware and software.The pump current drive circuit,pump current sampling circuit,temperature control circuit and other hardware circuits combined with fuzzy PID control,average filtering,IIR digital filtering and other software algorithms,thereby achieving closed-loop control of the sensor.In addition,an experimental gas distribution platform was set up in this thesis to calibrate the concentration of the NO_X sensor control unit,establish a function relationship between pump current and concentration,and solve the pain points of O₂ concentration affecting NO_X measurement through mathematical means.This thesis writes the fitted formula into the microcontroller program,and performs static test,dynamic test,interference test and comparison test on the control unit.Experiments show that the control unit of the NO_X sensor in this thesis has high measurement accuracy,excellent dynamic response and strong anti-interference ability.