| With the continuous increasing of quantity of motors,cities’ pressure of environmental protection rises unceasingly.While SCR technology firstly lets diesel oil in engine burn completely by increasing temperature and pressure,which would improve the economics of fuel,reduce the emission of PM.It uses NH3 to reduce NOx in emission afterwards.SCR technology is the main direction of upgrading and alteration of engines.In the process of catalytic reduction,the amount of urea must be matched with the density of NOx,therefore high metering precision of electromagnetic pump is required.Limited to capacity of soft magnetic materials,precision of machining and assembly and delayed response of single-directed valve,metering precision of electromagnetic pump is comparatively low.This article develops electromagnetic metering pump closed-loop control system based on detecting of flow,its metering precision can meet the demand of SCR system.The main content of this article is as follows:Based on studying internal and international ways of controlling electromagnetic metering pump,this article comprehends the structure,philosophy and control way of electromagnetic metering pump,analyses low metering precision of open-loop electromagnetic metering pump,puts forward the design thinking of electromagnetic metering pump closed-loop control system.Electromagnetic metering pump conveys liquid by the movement of moving iron core,electromagnetic metering pump output high frequency pulsating flow,which means pump outputs large flow when electromagnetic coil is electrified and outputs little flow when electromagnetic coil is not electrified,which can’t be detected precisely by ordinary flow meter.This article decreases pulsating flow by setting up buffer at the exit of electromagnetic metering pump,prolongs time of continuous flow and makes flow convenient for flow meter to detect.This article adopts sensitive responding electromagnetic flow meter to gather flow data intensively and makes it easy to control electromagnetic metering pump flow.The electromagnetic metering pump driven by PFM signal is simple in structure,reliable for operating,but its low metering precision can’t meet the demand of SCR system on cars.This article establishes electromagnetic metering pump closed-loop control system based on detecting flow,which is able to improve the metering precision of electromagnetic metering pump by detecting the difference between detected flow and theory flow and compensating flow of electromagnetic metering pump.This article accomplishes the design of hardware and software of electromagnetic metering pump closed-loop control system.The hardware design includes keyboard control unit,LCD displaying unit,driving unit,discharge protection unit and flow detecting element.This article solves the problem that MOSFET gets heated and capability of electromagnetic metering pump attenuates at high frequency by optimizing releasing resistance.The software design includes main program,driving program,keyboard management program,displaying program,data detecting program and serial ports communicating program.The programs are designed in modules and written in language C.This article establishes Simulink simulation model of electromagnetic metering pump closed-loop control system,the simulation result indicates that the electromagnetic metering pump closed-loop control system has a higher metering precision than open-loop electromagnetic metering pump.This article establishes experiment system of electromagnetic metering pump,and uses experiment device to measure the induction voltage of electromagnetic coil,the additional temperature of MOSFET and the output flow of electromagnetic metering pump.The result of experiment indicates that the induction voltage of electromagnetic coil and the additional temperature of MOSFET are both lower than permitted value.The metering precision of electromagnetic metering pump closed-loop control system is obviously higher than open-loop electromagnetic metering pump.Electromagnetic metering pump control system has advantages of high capability,good stability,high metering precision and can satisfy the demand of project. |
