【正文】 nal, and sends it to the engine ECU (electronic control unit). Electric signal of intake air used to calculate the basic fuel injection duration and basic ignition advance angle. The task of the project is to design a concise signal acquisition system for automotive engine air flow meter so that people can clearly be acquainted with Air flow meter working process. This design describes the air flow meter works and work. And in accordance with the principles of air flow meter and hardware architecture, use the appropriate software to do system programming, and make simulations. Software programming is divided into two parts: A / D converter, SCI munication. In addition,we also need write a interface with labview software. The A / D conversion of the air flow convert a voltage signal into a digital identification signal ,and the SCI munication pass data to the puter. Then the interface piled with labview will display the change of the data. Via Simulation experiment , giving SCM a varying voltage signal to make the chang of air flow meter in the voltage displayed in the interface . Key words: air flow meter A/D conversion SCI munication1 目錄 摘 要 ................................................................................................................................. I ABSTRACT......................................................................................................................... II 1 緒論 ................................................................................................................................ 1 前言 ...........................................................................................................................1 空氣流量計(jì)系統(tǒng)介紹 ................................................................................................1 空氣流量計(jì)國(guó)內(nèi)外的現(xiàn)狀和趨勢(shì) ...............................................................................2 2 硬件設(shè)計(jì) ........................................................................................................................ 4 空氣流量計(jì)的基本組成 ..............................................................................................4 、質(zhì)量型空氣流量計(jì)： .......................................................................................4 體積型空氣流量計(jì) .............................................................................................6 MC9S12XS128 內(nèi)部結(jié)構(gòu)、主要特性 ...........................................................................7 MAX232....................................................................................................................8 3 軟件設(shè)計(jì) ...................................................................................................................... 11 CodeWarrior 軟件簡(jiǎn)介 ............................................................................................. 11 項(xiàng)目調(diào)試場(chǎng)景 ................................................................................................. 11 CodeWarrior 中項(xiàng)目的基本管理和設(shè)定 ............................................................ 12 系統(tǒng)流程 ................................................................................................................. 14 A／Ｄ轉(zhuǎn)換模塊設(shè)計(jì) ................................................................................................ 16 SCI 模塊設(shè)計(jì) ............................................................................................................. 23 labview 軟件設(shè)計(jì) ...................................................................................................... 27 labview 軟件簡(jiǎn)介 ............................................................................................. 27 labview 應(yīng)用程序構(gòu)成 ...................................................................................... 27 前面板 ........................................................................................................... 27 流程圖 ........................................................................................................... 27 圖標(biāo)連接器 ................................................................................................... 28 4 調(diào)試過(guò)程 ........................................................................................................................ 30 調(diào)試過(guò)程 .................................................................................................................. 30 調(diào)試中出現(xiàn)的問(wèn)題 ................................................................................................... 31 調(diào)試結(jié)果 .................................................................................................................. 31 總結(jié) .................................................................................................................................... 33 參考文獻(xiàn) ............................................................................................................................ 34 致謝 .................................................................................................................................... 35 附錄 .................................................................................................................................... 36 1 1 緒論 前言 空氣流量計(jì) 傳感器向電子控制器提供反映進(jìn)氣流量的電信號(hào)，在電子控制汽油噴射系統(tǒng)中是電子控制器計(jì)算噴有時(shí)間的重要參數(shù)，而在微機(jī)控制點(diǎn)火時(shí)刻系統(tǒng)中則是作為發(fā)動(dòng)機(jī)負(fù)荷的間接參數(shù)，用于確定最佳的基本點(diǎn)火提前角。由于機(jī)械式的空氣流量計(jì)是體積流量型；所以測(cè)量范圍大；進(jìn)氣量增大測(cè)量精度降低；電位計(jì)滑動(dòng)觸頭影響精度；而且體積大，響應(yīng)慢。所以現(xiàn)在的汽車上都采用電子式的空氣流量計(jì)，其特點(diǎn)是：發(fā)熱體不直接承受空氣流動(dòng)所產(chǎn)生的作用力，增加了發(fā)熱體的強(qiáng)度，提高了可靠性，誤差較小，而且減低了成本。 空氣流量計(jì)系統(tǒng)介紹 空氣流量計(jì)是將進(jìn)入到汽車發(fā)動(dòng)機(jī)內(nèi)的空氣流量生成電壓信號(hào)，電壓信號(hào)通過(guò)A/D 轉(zhuǎn)換之后傳送給 CPU，進(jìn)而通過(guò) CPU 來(lái)控制節(jié)氣門的開度大小。其工作原理是：在空氣通道中放置一電熱體，通電后使電熱體保持一定的溫度，空氣通過(guò)時(shí)，空氣將會(huì)帶走熱量而使電熱體溫度下降，電熱體的電阻下降?？刂齐娐纷詣?dòng)增大電流，增大帕熱絲電阻使電橋重新恢復(fù)平衡。該電位與進(jìn)氣量成正比，作為進(jìn)氣量信 號(hào)電壓傳輸給發(fā)動(dòng)機(jī) ECU,如圖 12。進(jìn)入 60 年代后，國(guó)外汽車流量計(jì)檢測(cè)技術(shù)發(fā)展很快，并且大量的應(yīng)用電子技術(shù)。隨著電子與計(jì)算機(jī)技術(shù)，特別是軟件工程的進(jìn)一步發(fā)展，到了本世紀(jì)末，國(guó)外發(fā)達(dá)國(guó)家的流量計(jì)檢測(cè)都具備了單機(jī)采集多種數(shù)據(jù)，同時(shí)處理多種數(shù)據(jù)的功能，如電壓、流量等。進(jìn)入到 21 世紀(jì)，國(guó)外比較先進(jìn)的流量檢測(cè)臺(tái)具有自診斷技術(shù)，并且其流量傳感器在結(jié)構(gòu)設(shè)計(jì)上遵循集成更多功能的理念。隨著科學(xué)技術(shù)在各個(gè)領(lǐng)域都有了較快的發(fā)展， 特別是中國(guó)汽摩配行業(yè)的快速發(fā)展，使得汽車零部件的檢測(cè)技術(shù)也逐漸發(fā)展起來(lái)，汽車流量計(jì)的檢測(cè)也不例外。但上述的工具軟件并沒(méi)有