Study On Control Method And System Of UEGO Sensor

Universal exhaust gas oxygen (UEGO) sensor is widely used in automobile engine control system, which allows precise measurement over a wide air/fuel ratio (AFR) range. The sensor provides accurate air/fuel ratio feedback signal to electronic control unit (ECU), which will make ECU control precision better. And then, the function of three way catalytic (TWC) is improved, the emissions of harmful gases are reduced effectively. UEGO sensor has strict requirement on the working temperature, and the measurement of air/fuel ratio by controlling the pump current. A controller must be used for UEGO senor. The performance of sensor is determined by the controller.This thesis focus on LSU4.9 type UEGO sensor, a UEGO controller based on DSP is developed, included temperature control module, pump current control module, man-machine interface module and so on. The resistance of the Nernst cell is measured by AC resistance method, which reflects the sensor’s temperature. The Nernst voltage is maintained at 450mV by driving the pump current, and then the air-fuel ratio is calculated by detecting the pump current.The model of temperature and pump current are established with system identification method, In order to shorten light off time and improve the precision of temperature control, a temperature control method combined with light off control and PI control is adopted. Considering uncertainty of the pump current model parameter, a robust PID parameter tuning method based on Hoo loop shaping is studied.The system software is designed, including the main monitoring program, the initialization module, the interrupt module, the resistance calculation module, temperature control module and so on.The results show that the Nernst cell resistance measurement accuracy is less than 1Ω, the pump current detection accuracy can reach luA. Temperature and pump current control experiments show that the sensor light off time is less than 30s, the setting time of pump control is no more than 580ms and the static error less than 0.1mV. Static and dynamic experiments have been done on a mixed gas distribution test platform, the maximum error of pump current is 0.07mA. The pump current of the controller can accurately reflect the change of the mixed gas air-fuel ratio information, and the static performance is good.