Study On Air Flow Meter For Automobile Engineair Intake

Being an important part of electronic fuel injection system,the air-flow meter matters much to the electronic fuel injection system.The air-flow meter measures air mass flow that goes into engines and sends air mass flow signal to the automotive electronic control unit.Basing on engine intake parameters,the electronic control unit adjusts fuel injection quantity and igniting time to keep air-fuel ratio at best range.And the preciseness of the measurement of the air-flow meter will affect air-fuel ratio of engines,owing to that,it will further affect the dynamic performance,exhaust emission of engine and other indexes.The thermal mass flow meter measures directly air mass flow and do not need pressure or temperature adjustment.It also has the following advantages: high preciseness,quick response,small volume,small mass and so on,which make it widely applied in engines.By studying the principles of thermal mass flow meter and after referring to related national and international papers and documents,this thesis intends to design a new air-flow meter for vehicles.Contents of this thesis include: an analysis of theories related to air-flow meter,such as flow states in sampling channel,heat transfer in sensing cell and air mass flow measurement method;the design of heating control circuit and signal processing circuit of which the core lies in Kinetis series of microcontroller with 32-bit ARM Cortex M0+ core newly launched by Freescale in hardware circuit;microchip programming and Host computer designing by VC++ in system softwares.This thesis also comprises an improvement on traditional air-flow meters used on vehicles that neglect self-heating effect resulting from ambient temperature compensating resistance to reduce the influence of self-heating effect on air mass flow measurement;the application of digital filtering by making use of grubbs criterion for an improvement on the preciseness of signal collection;the attempt to solve the problem that traditional air-flow meters do not have many calibrating offset values by adding calibrating offset values to improve calibrating results and storing all calibrating offset values in MKE02Z32VLC2 for the purpose of avoiding extra eternal memories;a new design of air flow meter that can export both analog signal and pulse singal to make up for traditional air flow meters which can only export analog signal or digital signal.In the final part of this thesis includes a simple test bed for the calibration,so,the calibration tests of the new air-flow meter can be conducted on host computer.The tests show that the preciseness of the air-flow meter design qualifies for engines and the air-flow meter exhibits high stability.