| Oxygen sensors used for determination of oxygen concentration of the annual demand accounted for 40% of all gas sensor demand,especially in the field of automobile manufacturing and exhaust gas detection,oxygen sensor used in vehicle demand up to tens of millions every year;at the same time,air-fuel ratio(A/F)analysis method and device have important value for automobile engine control system development and exhaust gas treatment based on the measurement of the oxygen concentration of the automobile exhaust.New generation of wide range oxygen sensor(UEGO)has been widely used in the engine A/F control system and vehicle exhaust purification system.High precision and fast determination of oxygen concentration and A/F are the key problems in the process of automobile exhaust detection under medium high temperature environment.In this thesis,the characteristics of the sensor,control algorithm design,modeling and simulation,controller,and other aspects are researched,a domestic leading A/F measurement instrument is developed.First of all,this thesis makes a detailed analysis on the structure,working principle and the inherent characteristics of the oxygen sensor with heater and the planar-type wide range oxygen sensor,according to the technical development of automobile oxygen sensor.At the same time,it also analyzes the advantages of UEGO in the measuring accuracy and speed.This thesis further analyzes the research significance of the A/F measurement device that used to the development of the engine control system in the Automobile manufacturing field,based on oxygen concentration accurate acquisition with UEGO.The performance of A/F measurement instrument requires high precision and rapidity.There are some key problems such as the complex electrochemical characteristics of the sensor,the temperature can not be measured directly,the control is complex,and the output signal of the sensor is weak when we develop the A/F measurement instrument.At present,thereare some technology challenge to develop the A/F measurement instrument based on UEGO,including the internal resistance measurement,temperature control,pump unit control and weak signal detection.Secondly,a hardware in loop simulation platform of A/F measurement instrument is built based on dSAPCE real-time simulation system combined with UEGO.The characteristics of the sensor are studied on the platform,and the object model of the sensor is established by experiment.At the same time,establishing A/F measurement instrument control model in MATLAB Simulink,designing the algorithm of temperature control and pump unit control,implementing online simulation combined with sensor entity,and tuning PID control parameters with ZN critical proportioning method.So we verify the feasibility of the control scheme and optimize the control performance.Then,hardware,the control software and the software are developed,the function requirements of A/F measurement instrument are realized,based on the simulation results.Finally,the dynamic and static performance analysis of the A/F measurement instrument is carried out on the synchronous atmosphere configuration instrument and the engine bench,the performance indexes are verified,and the control algorithm and the control parameters are optimized based on the test results.its precision and rapidity reach the performance of the same kind of equipment.At the same time,combined the self-developed A/F measurement instrument with domestic oxygen sensor,the output characteristic curve of the domestic oxygen sensor was established based on the test experiment. |
