摘 要： 設(shè)計(jì)了一種基于CAN總線的自動(dòng)離合器控制器，采用高性能微處理器XC878完成離合器控制器軟硬件開(kāi)發(fā),。設(shè)計(jì)了離合器執(zhí)行電機(jī)的驅(qū)動(dòng)電路及自動(dòng)離合器控制程序,。針對(duì)離合器與發(fā)動(dòng)機(jī)協(xié)調(diào)控制的需要，設(shè)計(jì)了CAN總線節(jié)點(diǎn)接口電路及一套簡(jiǎn)單,、實(shí)用,、高效的CAN總線通信協(xié)議。試驗(yàn)表明,所設(shè)計(jì)的自動(dòng)離合器控制器在功能上滿(mǎn)足實(shí)際應(yīng)用的需要,，CAN通信模塊能夠準(zhǔn)確無(wú)誤地收發(fā)數(shù)據(jù),，可靠性高。
關(guān)鍵詞： CAN總線,； ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" 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title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" 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title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS" title="ACS">ACS,； XC878單片機(jī)
隨著社會(huì)的發(fā)展，人們對(duì)汽車(chē)的舒適性和安全性要求越來(lái)越高,，而手動(dòng)檔汽車(chē)因其繁重的選換檔及離合器操作增加了駕駛難度,。對(duì)于駕駛新手而言，又會(huì)產(chǎn)生坡道起步易熄火,、油耗大,、離合器磨損嚴(yán)重等問(wèn)題[1]。自動(dòng)檔汽車(chē)雖然駕駛操作簡(jiǎn)單,，但其造價(jià)高,，開(kāi)發(fā)難度大。本文設(shè)計(jì)的電控自動(dòng)離合器ACS(Automatic Clutch System)是在手動(dòng)變速箱基礎(chǔ)上安裝電控系統(tǒng),，取消離合踏板,，實(shí)現(xiàn)自動(dòng)離合。ACS的優(yōu)勢(shì)十分明顯：與手動(dòng)擋相比,，其駕駛操控更為簡(jiǎn)單,，具有加速快、駕駛舒適的特點(diǎn),；與自動(dòng)變速器汽車(chē)相比,，ACS具有造價(jià)便宜、維修方便,、經(jīng)濟(jì),、省油。
1 系統(tǒng)功能
ACS將現(xiàn)代電子控制技術(shù)用于控制干式摩擦離合器,，模擬優(yōu)秀駕駛員的操縱動(dòng)作和感覺(jué),，實(shí)現(xiàn)最佳的離合器結(jié)合規(guī)律,，其實(shí)質(zhì)是為汽車(chē)駕駛員配備一個(gè)操縱離合器的機(jī)械人，實(shí)現(xiàn)自動(dòng)離合器的功能,。本文設(shè)計(jì)的ACS控制器主要實(shí)現(xiàn)了如下幾大功能,。
(1)換檔離合：控制器接收到換檔信號(hào)后，離合器迅速自動(dòng)分離,，換檔到位后離合器自動(dòng)結(jié)合,，結(jié)合規(guī)律由電控單元依據(jù)汽車(chē)行駛工況確定。
(2)坡道起步：駕駛員踩制動(dòng)踏板,，啟動(dòng)發(fā)動(dòng)機(jī),，將換檔手柄置于一檔或倒檔，松開(kāi)手制動(dòng)器,，解除制動(dòng)后不踩油門(mén)踏板汽車(chē)能夠自動(dòng)慢速行駛,，起步平穩(wěn)，沖擊小,，不熄火,。
(3)熄火保護(hù)：汽車(chē)行駛過(guò)程中，車(chē)速和發(fā)動(dòng)機(jī)轉(zhuǎn)速低于設(shè)定值后離合器自動(dòng)分離,，車(chē)速和發(fā)動(dòng)機(jī)轉(zhuǎn)速高于設(shè)定值后離合器再自動(dòng)結(jié)合,。
(4)CAN通信：ACS控制器通過(guò)CAN總線接口與發(fā)動(dòng)機(jī)控制器實(shí)現(xiàn)數(shù)據(jù)通信，為離合器與發(fā)動(dòng)機(jī)的協(xié)調(diào)控制提供數(shù)據(jù)支持,。
2 系統(tǒng)的硬件設(shè)計(jì)
2.1 控制器組成
自動(dòng)離合器控制器原理框圖如圖1所示,。本系統(tǒng)的微處理器選用英飛凌高性能的8位微處理器XC878CM，工作頻率最高可達(dá)27 MHz,其片內(nèi)硬件資源十分豐富,，片內(nèi)集成了MultiCAN控制器,、捕獲/比較單元6(CCU6)、高性能ADC模塊等,。XC878CM出色的性能完全滿(mǎn)足本系統(tǒng)的設(shè)計(jì)需要,。本系統(tǒng)的硬件部分主要包括電源模塊、數(shù)據(jù)采集模塊,、CAN通信模塊,、執(zhí)行電機(jī)驅(qū)動(dòng)模塊等,。
(1)電源模塊 整車(chē)低壓控制系統(tǒng)通過(guò)12 V電池供電,，8位MCU采用5 V供電。所以本系統(tǒng)需要采用電源芯片進(jìn)行電壓的轉(zhuǎn)換和隔離,。本系統(tǒng)選用英飛凌電源芯片TLE4290,，該芯片可提供穩(wěn)定的5 V電壓，誤差在2%以?xún)?nèi),，輸入電壓最高可達(dá)42 V,。經(jīng)測(cè)試,，其工作可靠，滿(mǎn)足系統(tǒng)要求,。
(2)CAN通信模塊 CAN通信模塊使用XC878CM片內(nèi)MultiCAN控制器和英飛凌高速CAN收發(fā)器IFX1050G作為CAN通信的硬件組成,。CAN模塊負(fù)責(zé)離合器控制器和發(fā)動(dòng)機(jī)控制器之間的數(shù)據(jù)交換和共享，為發(fā)動(dòng)機(jī)與離合器的協(xié)調(diào)控制提供數(shù)據(jù)通信支持,。
(3)執(zhí)行電機(jī)驅(qū)動(dòng)模塊 本系統(tǒng)使用的執(zhí)行電機(jī)為額定電壓為12V的直流電機(jī),。單片機(jī)使用一個(gè)IO口控制執(zhí)行電機(jī)的轉(zhuǎn)動(dòng)方向,一路PWM輸出控制電機(jī)的轉(zhuǎn)速。PWM波由單片機(jī)內(nèi)含的CCU6模塊配置為比較模式產(chǎn)生,。單片機(jī)通過(guò)英飛凌電機(jī)驅(qū)動(dòng)芯片BTS7810K實(shí)現(xiàn)對(duì)執(zhí)行電機(jī)的控制,。
(4)數(shù)據(jù)采集模塊 本系統(tǒng)采集的數(shù)據(jù)主要有三種類(lèi)型：開(kāi)關(guān)量、模擬量,、頻率量,。開(kāi)關(guān)量主要是指點(diǎn)火信號(hào)和駕駛員的掛檔信號(hào)等,通過(guò)單片機(jī)的I/O口采集。XC878CM單片機(jī)片內(nèi)集成一個(gè)帶有8路模擬輸入選擇的高性能10 bit模數(shù)轉(zhuǎn)換器,可方便地用于模擬量的采集,。XC878CM內(nèi)含的CCU6模塊可配置工作在捕獲模式,，用于采集車(chē)速傳感器發(fā)送來(lái)的頻率量信號(hào)。由于汽車(chē)環(huán)境干擾較大,，信號(hào)采集電路需添加濾波,、電壓調(diào)理等電路。此外,，對(duì)于頻率量采集,，由于接收的是脈沖信號(hào)，還需要使用施密特觸發(fā)器進(jìn)行脈沖信號(hào)的整形,。
2.2 電機(jī)驅(qū)動(dòng)電路設(shè)計(jì)
離合器執(zhí)行機(jī)構(gòu)采用12 V直流電機(jī)驅(qū)動(dòng),，單片機(jī)采用脈寬調(diào)制PWM技術(shù)控制電機(jī)轉(zhuǎn)速。PWM調(diào)速方法以控制簡(jiǎn)單,、動(dòng)態(tài)響應(yīng)效果好,、調(diào)速范圍寬等優(yōu)點(diǎn)成為應(yīng)用十分廣泛的調(diào)速方法[2]。對(duì)直流電機(jī)轉(zhuǎn)動(dòng)方向的控制需要通過(guò)搭建H橋電路實(shí)現(xiàn),，由于自行搭建的H橋電路及柵極驅(qū)動(dòng)電路往往在可靠性方面很難保證,。因此，本文選擇了集成的電機(jī)驅(qū)動(dòng)芯片BTS7810K來(lái)驅(qū)動(dòng)離合器執(zhí)行電機(jī),。芯片BTS7810K是一款全橋電機(jī)驅(qū)動(dòng)芯片,，其內(nèi)部集成了H橋電機(jī)驅(qū)動(dòng)電路及柵極驅(qū)動(dòng)電路，其工作頻率高達(dá)1 kHz以上,，可方便可靠地實(shí)現(xiàn)對(duì)直流電機(jī)的控制,。BTS7810K正常工作模式的輸入輸出特性如表1所示。
電機(jī)驅(qū)動(dòng)電路如圖2所示，單片機(jī)使用一個(gè)I/O口輸出控制電機(jī)轉(zhuǎn)向,，一路PWM輸出控制電機(jī)轉(zhuǎn)速,。兩路控制信號(hào)通過(guò)一個(gè)與門(mén)和兩個(gè)非門(mén)組成的接口電路連接到驅(qū)動(dòng)芯片的輸入端IH1、IH2,。這樣做是為了保證兩個(gè)輸入端不同時(shí)為高電平,，防止橋臂直通問(wèn)題的出現(xiàn)，提高系統(tǒng)的安全性和可靠性,。
2.3 CAN節(jié)點(diǎn)接口設(shè)計(jì)
CAN總線是德國(guó)Bosch公司20世紀(jì)90年代初為解決現(xiàn)代汽車(chē)中眾多控制與測(cè)試儀器之間的信息交換而開(kāi)發(fā)的一種串行通信協(xié)議網(wǎng)絡(luò)[3],。它具有傳輸速率高、可靠性強(qiáng)和實(shí)時(shí)性好等特點(diǎn),正好符合ACS與發(fā)動(dòng)機(jī)協(xié)調(diào)控制的通信需要,。對(duì)發(fā)動(dòng)機(jī)和離合器進(jìn)行綜合控制,充分利用發(fā)動(dòng)機(jī)電子控制系統(tǒng)控制發(fā)動(dòng)機(jī)轉(zhuǎn)速及時(shí),、準(zhǔn)確的特點(diǎn), 使之與離合器相互協(xié)調(diào)配合,將有利于離合器取得更好的控制效果，進(jìn)而提高換擋品質(zhì)[4],。
CAN節(jié)點(diǎn)硬件電路主要包括：帶有 CAN 控制器的微控制器和用于數(shù)據(jù)收發(fā)的CAN 收發(fā)器,。本文選用的微處理器XC878CM帶有片內(nèi)的CAN控制器，主要負(fù)責(zé)CAN的初始化和數(shù)據(jù)處理,。MultiCAN模塊集成了除收發(fā)器外CAN總線控制器的所有功能,。此外，MultiCAN還具有先進(jìn)的驗(yàn)收濾波功能,、先進(jìn)的數(shù)據(jù)管理,、先進(jìn)的中斷管理等優(yōu)良特性。CAN 的收發(fā)器種類(lèi)很多,，本設(shè)計(jì)中選用英飛凌公司的高速收發(fā)器IFX1050G,。CAN節(jié)點(diǎn)的接口電路圖如圖3所示。
3 軟件設(shè)計(jì)
電控單元ECU的控制軟件主要由離合器控制程序和CAN總線通信程序組成,。
3.1 離合器控制軟件設(shè)計(jì)
離合器的控制程序包括三個(gè)部分：離合器分離控制程序,、起步結(jié)合控制程序、換擋結(jié)合控制程序,。其中分離控制程序比較簡(jiǎn)單,，ECU得到分離指令后，離合器全速分離,，并且準(zhǔn)確地在完全分離點(diǎn)停止即可,。離合器的控制難點(diǎn)在于起步結(jié)合控制。離合器的起步結(jié)合過(guò)程既要保證車(chē)輛起步的平穩(wěn)性,、舒適性,、起步不熄火，又要保證起步的快速性,，減少滑摩功的產(chǎn)生,，延長(zhǎng)離合器使用壽命。因此,，要取得較好的控制效果除了對(duì)離合器的結(jié)合量進(jìn)行控制外,，還要對(duì)離合器的結(jié)合速度進(jìn)行控制，并通過(guò)與發(fā)動(dòng)機(jī)的協(xié)調(diào)控制,，提高控制效果,。圖4為起步結(jié)合控制軟件流程圖。換擋過(guò)程中離合器的結(jié)合控制與起步控制在控制策略上類(lèi)似,在此不再贅述,。
3.2 CAN通信協(xié)議設(shè)計(jì)
CAN通信協(xié)議包括物理層,、數(shù)據(jù)鏈路層和應(yīng)用層。物理層和數(shù)據(jù)鏈路層是通過(guò)硬件實(shí)現(xiàn)的,，在使用CAN通信時(shí),，需要開(kāi)發(fā)者自行定義應(yīng)用層協(xié)議。構(gòu)造應(yīng)用層協(xié)議的主要任務(wù)是ID分配,、定義消息周期,、確定信號(hào)與消息的映射關(guān)系。設(shè)計(jì)要考慮的主要因素有數(shù)據(jù)傳輸?shù)膶?shí)時(shí)性要求,、數(shù)據(jù)的相對(duì)重要程度,、與數(shù)據(jù)相關(guān)的應(yīng)用控制算法對(duì)數(shù)據(jù)的時(shí)間要求等。國(guó)際上存在一些現(xiàn)有的標(biāo)準(zhǔn),，如CANopen,、SAE J1939等。在一些利用簡(jiǎn)單的通信協(xié)議就可以滿(mǎn)足要求的情況下,，采用復(fù)雜的協(xié)議會(huì)造成資源浪費(fèi),，用戶(hù)在應(yīng)用時(shí)也會(huì)覺(jué)得諸多不便，反而限制了靈活性,。本文設(shè)計(jì)的CAN總線網(wǎng)絡(luò)中僅有離合器控制器和發(fā)動(dòng)機(jī)控制器兩個(gè)節(jié)點(diǎn),。針對(duì)僅有兩個(gè)節(jié)點(diǎn)的實(shí)驗(yàn)平臺(tái)，本文從協(xié)議實(shí)現(xiàn)的代碼量,、目標(biāo)系統(tǒng)的信息量,、軟件的開(kāi)發(fā)成本等角度出發(fā)，定義一種簡(jiǎn)單可靠的CAN協(xié)議,。具體的通信協(xié)議定義如表2所示,，標(biāo)識(shí)符用來(lái)表示信息的優(yōu)先級(jí)，標(biāo)識(shí)符越小優(yōu)先級(jí)越高,。
4 CAN通信測(cè)試實(shí)驗(yàn)
本文實(shí)驗(yàn)是在自行搭建的離合器模擬實(shí)驗(yàn)平臺(tái)上進(jìn)行的,。本實(shí)驗(yàn)平臺(tái)是由離合器控制板、加速踏板,、剎車(chē)踏板,、相關(guān)傳感器、離合器執(zhí)行機(jī)構(gòu)及發(fā)動(dòng)機(jī)模擬控制板組成。離合器控制板與發(fā)動(dòng)機(jī)模擬控制板之間通過(guò)CAN總線通信,。圖5為實(shí)驗(yàn)過(guò)程中通過(guò)CAN總線傳送的檔位變化信息,，圖6為通過(guò)CAN總線傳遞的加速踏板開(kāi)度信號(hào)。
本文提出了一套電控自動(dòng)離合器的控制器方案,，并進(jìn)行了系統(tǒng)的軟硬件開(kāi)發(fā),，初步實(shí)現(xiàn)了自動(dòng)離合器的基本功能，設(shè)計(jì)了CAN總線接口,。在實(shí)驗(yàn)平臺(tái)上驗(yàn)證了控制器方案及CAN通信模塊的可行性和可靠性,，為實(shí)車(chē)試驗(yàn)打下基礎(chǔ)。
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