Research On The Electronic Control Unit Of Nitrogen Oxygen Sensor

With the increasing of heavy duty diesel emission standard,NOx emissions from5.0g·?kW·h?^-1in stage III emission regulation gradually dropped to2.0g·?kW·h?^-1in stage?,which also requires more strict NOx post-processing SCR system.Automotive NOX sensors play an important role in this system.By means of measuring the NOx gas concentration in exhaust and sending the signal to engine control unit in real time,SCR system control the reduction of NOx gas through this feedback signal,thus realizing closed loop control of NOx concentration in exhaust effectively.Domestic automobile NO_X sensors are basically used of foreign products at present,because both the research and design are mature in NO_X sensors in foreign,however domestic main research pay more attention to SCR control system than nitrogen oxygen sensor itself,not to mention the electronic control unit of NO_X sensors.Therefore,this paper takes the current model of nitrogen oxygen sensors as the research object.For the electronic control unit,following is the main work of the research:?1?Owing to the NOX sensors detect NOX concentration by measuring the O2concentration which is reducted of NOx gas.Conducted a deep resesrch on the working principle of NO_X sensor and the ZrO₂ pump oxygen properties as well as electrical characteristics of this sensor firstly,on the basis of above all,put forward the control strategies of the main pump,auxiliary pump and measurement of pump,including the strategies of nernst voltage and pump current fixed value feedback.Due to the sensitive element only in the best high temperature can produce electrical characteristics,heating of the sensor control method is put forward.?2?On account of the mathematically model of the control unit,established dynamic equilibrium oxygen concentration of the first chamber and then made the PI control simulation of the pump circuit,established the sensor heating control algorithms and conducted PID heating control simulation analysis,therefore the optimum PID control parameters have found.?3?The controller unit hardware circuit is designed,including the master control circuit based in Freescale chip MC69HC908AZ60A,PI drive and control circuit of pump circuit,instrument amplifier of pump circuit,heating circuit with PWM control MOSFET,power circuit and CAN bus communication circuit.?4?According to the functional requirements of the controller unit,software is programmed,including the design of the process framework,main program,A/D acquisition,PID heating control as well as CAN bus communication program.