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汽車防抱死制動(dòng)系統(tǒng)（ABS）
摘要：本文簡要介紹了汽車防抱死制動(dòng)系統(tǒng)（Anti-lock Braking System，簡稱ABS）的控制原理，對目前汽車防抱死制動(dòng)系統(tǒng)所采用的控制技術(shù)進(jìn)行了綜述，并對其發(fā)展趨勢進(jìn)行了預(yù)測。
關(guān)鍵詞：汽車；防抱死制動(dòng)系統(tǒng)；控制技術(shù)
1.概述
隨著汽車工業(yè)的迅猛發(fā)展和高速公路的不斷修建，汽車的行駛安全性越來越為人們重視。為了全面滿足制動(dòng)過程中汽車對制動(dòng)的要求，使制動(dòng)器制動(dòng)力分配更趨合理。汽車防抱死制動(dòng)系統(tǒng)（簡稱ABS）已越來越多地應(yīng)用在汽車上。
“ABS”中文譯為“防鎖死剎車系統(tǒng)”.它是一種具有防滑、防鎖死等優(yōu)點(diǎn)的汽車安全控制系統(tǒng)。ABS是常規(guī)剎車裝置基礎(chǔ)上的改進(jìn)型技術(shù)，可分機(jī)械式和電子式兩種。
現(xiàn)代汽車上大量安裝防抱死制動(dòng)系統(tǒng)，ABS既有普通制動(dòng)系統(tǒng)的制動(dòng)功能，又能防止車輪鎖死，使汽車在制動(dòng)狀態(tài)下仍能轉(zhuǎn)向，保證汽車的制動(dòng)方向穩(wěn)定性，防止產(chǎn)生側(cè)滑和跑偏，是目前汽車上最先進(jìn)、制動(dòng)效果最佳的制動(dòng)裝置。
普通制動(dòng)系統(tǒng)在濕滑路面上制動(dòng)，或在緊急制動(dòng)的時(shí)候，車輪容易因制動(dòng)力超過輪胎與地面的摩擦力而安全抱死。
汽車防抱死制動(dòng)系統(tǒng)是指汽車在制動(dòng)過程中能實(shí)時(shí)判定車輪的滑動(dòng)率，自動(dòng)調(diào)節(jié)作用在車輪上的制動(dòng)力矩，防止車輪抱死。從而獲得最佳制動(dòng)效能的電子裝置。它能把車輪的滑動(dòng)率控制在一定的范圍之內(nèi)，充分地利用輪胎與路面之間的附著力，有效地縮短制動(dòng)距離，顯著地提高車輛制動(dòng)時(shí)的可操縱性和穩(wěn)定性，從而避免了車輪抱死時(shí)易出現(xiàn)的各種交通事故。
隨著制動(dòng)強(qiáng)度的增加，車輪滾動(dòng)成分越來越少，而滑動(dòng)成分越來越多，一般用滑動(dòng)率S 來說明制動(dòng)過程中滑動(dòng)成分的多少?；瑒?dòng)率越大，滑動(dòng)成分越少。
S=1-
其中： u——車輪中心的速度；
r——沒有地面制動(dòng)力時(shí)的車輪滾動(dòng)半徑；
w——車輪的角速度。
縱向和側(cè)向附著系數(shù)可表達(dá)為車輪滑動(dòng)率的函數(shù)（如圖1）。最大縱向附著系數(shù)所對應(yīng)的滑動(dòng)率稱為臨界穩(wěn)定點(diǎn)SK。根據(jù)控制理論把滑動(dòng)率小于SK 的區(qū)域稱為穩(wěn)定制動(dòng)區(qū)，SK 以后的為非穩(wěn)定制動(dòng)區(qū)。ABS 正是利用道路與輪胎之間的關(guān)系，強(qiáng)制性地把車輪滑動(dòng)率控制在臨界穩(wěn)定點(diǎn)SK 附近，使路面附著性能得到最充分的發(fā)揮，從而達(dá)到最佳的制動(dòng)效果。
圖1 附著系數(shù)-滑動(dòng)率曲線
目前所采用的ABS 主要由輪速傳感器，電子控制單元，壓力控制閥和線束、管路等附件組成。ABS 的開發(fā)主要是研究設(shè)計(jì)優(yōu)化運(yùn)算和控制程序軟件，實(shí)現(xiàn)實(shí)時(shí)精確制動(dòng)調(diào)節(jié)的技術(shù)，同時(shí)提高硬件的水平。
2.目前ABS 所采用的控制技術(shù)
ABS 的控制效果很大程度上取決于系統(tǒng)所采用的控制技術(shù)[4]。目前所采用的主要是邏輯門限值控制技術(shù)。為進(jìn)一步提高ABS 的性能，還提出了一些基于滑動(dòng)率的控制技術(shù)，如PID 控制，滑動(dòng)模態(tài)變結(jié)構(gòu)控制，模糊控制等。每種控制均以不同的控制規(guī)律逼近期望的點(diǎn)。
2.1 PID 控制
定義期望滑動(dòng)率S0 與實(shí)際滑動(dòng)率S 之差為控制誤差e=S-S0，則PID 的控制規(guī)律可表示為：
因此，ABS 控制器的設(shè)計(jì)最后就歸結(jié)為，根據(jù)ABS 動(dòng)態(tài)系統(tǒng)，確定出一組最佳的參數(shù)Kp、Ki 和Kd，使車輪的滑動(dòng)率以最快的方式逼近設(shè)定目標(biāo)S0。
2.2 滑動(dòng)模態(tài)變結(jié)構(gòu)控制
由汽車防抱死制動(dòng)的基本原理可知，其制動(dòng)過程的本質(zhì)問題是把車輪的滑動(dòng)率控制在附著系數(shù)的峰值點(diǎn)Sk，則滑動(dòng)模態(tài)變結(jié)構(gòu)根據(jù)系統(tǒng)當(dāng)時(shí)的狀態(tài)、偏差及其導(dǎo)數(shù)值，在不同的控制區(qū)域，以理想開關(guān)的方式切換控制量的大小和符號，以保證系統(tǒng)在滑動(dòng)區(qū)域很小的范圍內(nèi)，狀態(tài)軌跡（S，×S）沿滑動(dòng)換節(jié)曲線滑向控制目標(biāo)（Sk，0）。
通常取制動(dòng)力矩為控制變量U，切換條件為：
其中 Mb- 、Mb+分別代表由調(diào)節(jié)系統(tǒng)所決定的制動(dòng)力矩減少、增加兩種不同的狀態(tài)。
為切換函數(shù)，e=S－Sk 為實(shí)際滑動(dòng)率相對目標(biāo)點(diǎn)的偏差。
2.3 模糊控制
對于以滑動(dòng)率為控制對象的防抱死制動(dòng)系統(tǒng)，其輸入量取期望滑動(dòng)率與車輪實(shí)際滑動(dòng)率的偏差E 以及偏差的變化率EC，輸出量為制動(dòng)管路油壓。采用帶修正因子的模糊控制器，把用模糊推理算法形成的控制表概括為一個(gè)解析式：
U =α × E + (1-α)EC
其中α為修正因子，α值的大小直接反映了對偏差及偏差變化率的加權(quán)程度。通過調(diào)整修正因子α，就可以改變控制規(guī)則。當(dāng)α較大時(shí)，表明對偏差的加權(quán)大，階躍響應(yīng)快，控制能量主要用于減少偏差，但易出現(xiàn)超調(diào)；當(dāng)α較小時(shí)，控制目的是減少超調(diào)，但響應(yīng)過程較慢。通常采用帶兩個(gè)α值的修正因子表達(dá)式就可滿足性能要求，即：
其中，修正因子α1 、α2∈(0，1)且α1<α2 ，控制系統(tǒng)在判斷E 值的大小之后，選擇控制規(guī)則表達(dá)式。
2.4 邏輯門限值控制
此方法預(yù)先對若干個(gè)控制參數(shù)設(shè)定一些控制極限（門限）值，制動(dòng)時(shí)，根據(jù)計(jì)算的實(shí)時(shí)參數(shù)值與對應(yīng)門限值的大小關(guān)系，來判定車輪的運(yùn)動(dòng)狀態(tài)，從而控制調(diào)節(jié)制動(dòng)壓力，以獲取足夠大的制動(dòng)強(qiáng)度和良好的方向穩(wěn)定性。常作為ABS 控制參數(shù)的有：車輪滑移率S，車輪轉(zhuǎn)動(dòng)的角加（減）速度ω及其變化率.ω等三種描述車輪運(yùn)動(dòng)情況或動(dòng)力學(xué)狀態(tài)的參數(shù)。由于僅用一個(gè)控制參數(shù)難于保證ABS 在各種行駛條件下都具有良好的性能，因此，目前邏輯門限值控制方法通常將車輪轉(zhuǎn)動(dòng)的角加（減）速度作為主要控制參數(shù)，而將車輪的滑動(dòng)率S 作為輔助控制參數(shù)。其中滑動(dòng)率是從各輪速信號按一定邏輯確定汽車的參考速度后，計(jì)算出的參考滑動(dòng)率，與實(shí)際滑動(dòng)率存在著差異。
2．5雙參數(shù)控制
雙參數(shù)控制的 ABS ，由車速傳感器 ( 測速雷達(dá) ) 、輪速傳感器、控制裝置 ( 電腦 ) 和執(zhí)行機(jī)構(gòu)組成。
其工作原理是車速傳感器和輪速傳感器，分別將車速和輪速信號輸入電腦，由電腦計(jì)算出實(shí)際滑移率，并與理想滑移率 15 ％一 20 ％作比較，再通過電磁閥增減制動(dòng)器的制動(dòng)力。
這種曳速傳感器常用多普勒測速雷達(dá)。當(dāng)汽車行駛時(shí)，多普勒雷達(dá)天線以一定頻率不斷向地面發(fā)射電磁波，同時(shí)又接收反射回來的電磁波，測量汽車?yán)走_(dá)發(fā)射與接收的差值，便可以準(zhǔn)確計(jì)算出汽車車速。而輪速傳感器裝在變速器外殼，由變速器輸出軸驅(qū)動(dòng)，它是一個(gè)脈沖電機(jī)，所產(chǎn)生的頻率與輪速成正比。 執(zhí)行機(jī)構(gòu)由電磁閥及繼電器等組成。電磁閥調(diào)整制動(dòng)力，以便保持理想的滑移率。 這種 ABS 可保證滑移率的理想控制，防抱制動(dòng)性能好，但由于增加了一個(gè)測速雷達(dá)，因此結(jié)構(gòu)較復(fù)雜，成本也較高。
2．6單參數(shù)控制
它以控制車輪的角減速度為對象，控制車輪的制動(dòng)力，實(shí)現(xiàn)防抱死制動(dòng)，其結(jié)構(gòu)主要由輪速傳感器、控制器 ( 電腦 ) 及電磁閥組成。 為了準(zhǔn)確無誤地測量輪速，傳感頭與車輪齒圈間應(yīng)留有 1mm 間隙。為避免水、泥、灰塵對傳感器的影響，安裝前應(yīng)將傳感器加注黃油。電磁閥用于車輪制動(dòng)器的壓力調(diào)節(jié)。對于四通道制動(dòng)系統(tǒng)，一個(gè)車輪圈有一個(gè)電磁閥；三通道制動(dòng)系統(tǒng)，每個(gè)前輪擁有一個(gè)，兩個(gè)后輪共用一個(gè)。電磁閥有三個(gè)液壓孔，分別與制動(dòng)主缸與車輪制動(dòng)分缸相連，并能實(shí)現(xiàn)壓力升高、壓力保持、壓力降低的調(diào)壓功能。工作原理如下:
1) 升壓 在電磁閥不工作時(shí)，制動(dòng)主缸接口和各制動(dòng)分缸接口直通。由于主彈簧強(qiáng)度大，使進(jìn)油閥開啟，制動(dòng)器壓力增加。
2) 壓力保持 當(dāng)車輪的制動(dòng)分缸中的壓力增長到一定值時(shí)，進(jìn)油閥切斷關(guān)閉。支架就保持在中間狀態(tài)，三個(gè)孔間相互密封，保持制動(dòng)壓力。
3) 降壓 當(dāng)電磁閥工作時(shí)，支架克服兩個(gè)彈簧的彈力，打開卸荷肉使制動(dòng)分缸壓力降低。壓力一旦降低，電磁閥就轉(zhuǎn)換到壓力保持狀態(tài)，或升壓的準(zhǔn)備狀態(tài)。
控制裝置 ECU 的主要任務(wù)是把各車輪的傳感器傳回來的信號進(jìn)行計(jì)算、分析、放大和判別，再由輸出級將指令信號輸出到電磁閥，去執(zhí)行制動(dòng)壓力調(diào)節(jié)任務(wù)。電子控制裝置，由四大部分組成，輸入級 A 、控制器 B 、輸出級 C ，穩(wěn)壓與保護(hù)裝置 D 。 電子控制器以 4 一 101tz 的頻率驅(qū)動(dòng)電磁閥，這是駕駛員無法做到的。 這種單參數(shù)控制方式的 ABS ，由于結(jié)構(gòu)簡單、成本低，故目前使用較廣。
在美國克萊斯勒型高級轎車中大多配備了這種單參數(shù)控制方式的 ABS 。它在轎車的四個(gè)輪上都裝有輪速傳感器。 在車輪軸上安裝有 45 齒或 100 齒的齒圈，輪速傳感器的傳感頭裝在齒圈的頂上。當(dāng)車輪轉(zhuǎn)動(dòng)時(shí)，使傳感器不斷產(chǎn)生電壓信號，并輸入電腦，與 RoM 中理想速度比較，算出車輪的增速或減速，向電磁閥發(fā)出升壓或卸壓的指令，以控制制動(dòng)分缸制動(dòng)力。
3. ABS 使用中注意的問題
1) 更換制動(dòng)器或更換液壓制動(dòng)系部件后，應(yīng)排凈制動(dòng)管路中的空氣，以免影響制動(dòng)系統(tǒng)的正常工作。
2) 裝有 ABS 的汽車，每年應(yīng)更換一次制動(dòng)液。否則，制動(dòng)液吸濕性很強(qiáng)，含水后不僅會(huì)降低沸點(diǎn)，產(chǎn)生腐蝕，而且還會(huì)造成制動(dòng)效能衰退。
3) 檢查 ABS 防抱死制動(dòng)系統(tǒng)前應(yīng)先拔去電源。
4. 發(fā)展趨勢
采用邏輯門限值控制算法，可避免一系列繁雜的理論分析和對一些不確定因素的定量計(jì)量。簡化了控制器的設(shè)計(jì)，而且因僅需測定車輪的角速度，便于實(shí)現(xiàn)，所以裝車成本低。該算法現(xiàn)已趨近成熟，為當(dāng)前汽車ABS 系統(tǒng)所普遍采用，但它并非最佳的控制算法。由于不同路況下各種門限值及保壓時(shí)間都是經(jīng)過反復(fù)試驗(yàn)得出的經(jīng)驗(yàn)數(shù)值，沒有十分明確的理論依據(jù)，故ABS 開發(fā)的周期長，且控制品質(zhì)難以保證。
基于滑動(dòng)率的控制算法容易實(shí)現(xiàn)連續(xù)控制，且有十分明確的理論加以指導(dǎo)，但目前制約其發(fā)展的瓶頸主要是實(shí)現(xiàn)的成本問題，根據(jù)我們的研究認(rèn)為，今后ABS 控制算法的發(fā)展方向?qū)⒃谝韵聨追矫妗?
(1) 針對當(dāng)前廣泛采用的邏輯門限值控制算法所存在的缺點(diǎn)，研究能跟蹤路面特性變化，使ABS 各項(xiàng)性能指標(biāo)始終處于最佳狀態(tài)的控制算法。其中預(yù)測控制技術(shù)值得重視。由于在制動(dòng)過程中，輪胎與路面間的摩擦特性導(dǎo)致防抱死制動(dòng)系統(tǒng)具有非常明顯的非線性、時(shí)變性和不確定性。因而難于建立其精確的數(shù)學(xué)模型，而預(yù)測控制具有預(yù)測模型、滾動(dòng)優(yōu)化和反饋校正的基本特性，可根據(jù)某一優(yōu)化指標(biāo)設(shè)計(jì)控制系統(tǒng)，確定一個(gè)控制量的時(shí)間序列，使未來一段時(shí)間內(nèi)被調(diào)量與經(jīng)過柔化后的期望軌跡之間的誤差為最小。由于該算法采用的是不斷在線滾動(dòng)優(yōu)化，且在優(yōu)化過程中不斷通過實(shí)測系統(tǒng)輸出與預(yù)測模型輸出的誤差來進(jìn)行反饋校正，所以能在一定程度上克服由于預(yù)測模型誤差和某些不確定性干擾等的影響，使系統(tǒng)的魯棒性得到增強(qiáng)。
(2) 隨著體積更小，價(jià)格更便宜，可靠性更高的車速傳感器的出現(xiàn)，ABS 系統(tǒng)中增加車速傳感器成為可能，確定車輪滑動(dòng)率將變得準(zhǔn)確而快速。其中非接觸式的車速傳感器（如光電式、多譜勒儀等）今后最有可能應(yīng)用于汽車ABS 系統(tǒng)中。此時(shí)基于滑動(dòng)率的控制算法就可被重視。其中模糊控制將以其不依賴對象的數(shù)學(xué)模型，便于利用人的經(jīng)驗(yàn)知識(shí)，魯棒性好，簡單實(shí)用等特點(diǎn)而會(huì)被廣泛采用。
(3) 由單一的ABS 控制目標(biāo)轉(zhuǎn)向多目標(biāo)的綜合控制[10]，其中已出現(xiàn)的牽引力控制系統(tǒng)（TCS）不僅能夠在制動(dòng)過程中防止車輪發(fā)生抱死，而且能夠在驅(qū)動(dòng)過程中（特別是在起步、加速、轉(zhuǎn)彎等過程中）防止驅(qū)動(dòng)輪發(fā)生滑轉(zhuǎn)，使汽車在驅(qū)動(dòng)過程中的方向穩(wěn)定性、轉(zhuǎn)向操縱能力和加速性能等也都得到提高。未來汽車電子控制系統(tǒng)將朝著從多電子控制單元（ECU）的分散的獨(dú)立控制向單一ECU 的整車控制，以網(wǎng)絡(luò)的方式實(shí)現(xiàn)數(shù)據(jù)共享和綜合控制的方向發(fā)展；或者向動(dòng)態(tài)遞階控制方向發(fā)展，即各分散控制系統(tǒng)的ECU 不僅是各自獨(dú)立地構(gòu)造自己的動(dòng)態(tài)補(bǔ)償器，而且要再統(tǒng)一地建立一個(gè)高層的動(dòng)態(tài)協(xié)調(diào)器來幫助確定各ECU 的控制策略，以增強(qiáng)各ECU 的控制能力，解決分散控制系統(tǒng)存在不穩(wěn)定模時(shí)不能用動(dòng)態(tài)分散控制鎮(zhèn)定的問題[11]，使整車綜合性能得到保證。
5. 總結(jié)
汽車防抱死制動(dòng)系統(tǒng)（ABS）能提高汽車在低附著系數(shù)或變附著系數(shù)路面條件下的制動(dòng)性能。目前ABS 的控制技術(shù)主要采用邏輯門限值控制方法，但隨著車速傳感器技術(shù)的發(fā)展，基于車輪滑動(dòng)率的各種控制算法將被廣泛的重視和采用。另外。未來汽車電子控制技術(shù)與裝置將以網(wǎng)絡(luò)的方式實(shí)現(xiàn)資源共享和綜合控制，并朝著多目標(biāo)綜合控制，以提高系統(tǒng)性能成本比的方向發(fā)展。
附錄1外文翻譯
Automobile anti-lock braking system (ABS)
Abstract: This article introduced briefly the automobile anti-lock braking system (Anti-lock Braking System, is called ABS) the control principle, the control technology which used in the present automobile anti-lock braking system has carried on the summary, and has carried on the forecast to its trend of development.
Key word: Automobile anti-lock braking system control technology
1. outline
Along with automobile industry's rapid development and highway's unceasing construction, automobile's travel security more and more takes seriously for the people. To satisfy in comprehensively the brake process the automobile to the brake request, causes the brake braking force assignment to hasten reasonably. The automobile anti-lock braking system (i.e. ABS) more and more has applied on the automobile.
“ABS” Chinese translates is “against deadlocks the brake system”. It is one kind has the skid prevention, against to deadlock and so on merit auto safety control systems. ABS is in the convention brake system foundation advanced version technology, separable mechanical and electronic formula two kinds.
On the modern automobile installs the anti-lock braking system massively, ABS both has the ordinary braking system's brake function, and could prevent the wheel to deadlock, enables the automobile still to change under the stopping, guaranteed that automobile's brake yawing stability, prevented to have the side-slipping and to run, was on the present automobile is most advanced, the brake effect best arresting gear.
The ordinary braking system applies the brake in the slippery road surface, or in emergency brake, because the wheel is easy the braking force to surpass the tire and the ground friction force hugs safely dies.
The automobile anti-lock braking system is refers to the automobile in the brake process to be able the real-time determination wheel's glide rate, the automatic control function on wheel's braking moment, prevents the wheel to hug dies. Thus obtains the best brake potency the electronic installation. It can wheel's glide rate control in certain scope, use fully between the tire and the road surface adhesion, reduces the stopping distance effectively, obviously enhances when the car braking controllability and stability, when each kind of traffic accident which has avoided the wheel hugs dies easy to appear. along with brake intensity's increase, the wheel rolling ingredient are getting fewer and fewer, but skids the ingredient to be getting more and more, generally explains in the brake process with glide rate S to skid ingredient how many. The glide rate is bigger, the glide ingredient are less.
S=1-
And: u-- wheel center speed; r-- does not have time the ground braking force wheel rolling radius; w-- wheel's angular speed.
Longitudinal and the lateral adhesion coefficient may express for the wheel slip rate function (e.g. Figure 1). The most greatly longitudinal coefficient of adhesion corresponds the glide rate is called critical point of fixity SK. Grips fast the pace according to the control theory is smaller than the SK region is called the stable brake area, what SK later has custom-made unstable moves the area. ABS is precisely uses between the path and tire's relations, compulsory wheel slip rate control nearby critical point of fixity SK, enables the road surface adhesion property to obtain the fullest display, thus achieves the best brake effect.
Figure 1 coefficient of adhesion - glide rate curve
At present uses ABS mainly by a round fast sensor, the electronic control unit, appendices and so on pressure control valve and group of lines, pipeline is composed. The ABS development is mainly studies the design optimization operation and the control procedure software, realizes the real-time precise brake adjustment technology, simultaneously raises hardware's level.
2. Control technology used by ABS now
The ABS control effect is decided control technology [4] which to a great extent uses in the system. At present uses is mainly the logical threshold value control technology. To further enhance ABS the performance, but also proposed some based on the glide rate control technology, like the PID control, the glide modality change the structure controls, fuzzy control and so on. Each kind of control approaches the expectation by the different control rule the spot.
2.1 PID controls
The definition expects glide rate S0 and difference of the actual glide rate S for ning error e=S-S0, then the PID control rule may be represented as:
Therefore, the ABS controller's design sums up finally as, according to the ABS dynamic system, determined group of best parameter Kp, Ki and Kd, enable wheel's glide rate to approach hypothesis goal S0 by the quickest way.
2.2 The glide modality changes the structure control
Against holds the dead brake by the automobile the basic principle to be possible to know, its brake process's essential question is wheel's glide rate control in coefficient of adhesion peak point Sk, then the glide modality changed structure basis system condition, the deviation and the derivative value then, in the different controlled area, by perfect switch's way hand-off control quantity's size and the mark, the guarantee system in the glide region very small scope, the state point locus (S,×S) along moved the festival curve to slide slippery to the control objective (Sk,0). usually takes the braking moment for controlled variable U, the cut condition is:
And Mb-, Mb+ represent the braking moment which decided by the governing system to reduce, to increase two different conditions separately.
For the cut function, e=S-Sk is the actual glide rate relative target point deviation.
2.3 Fuzzy control
Regarding take the glide rate as controlled member's anti-lock braking system, its input value takes the expectation glide rate and wheel actual glide rate deviation E as well as deviation's rate of change EC, the output for the brake line flowing tubing head pressure. Uses the belt modification factor the fuzzy controller, uses the control list summary which the fuzzy reasoning algorithm forms is an analysis formula:
U =α × E + (1-α)EC
And Alpha is the modification factor, Alpha the value size has reflected directly to the deviation and the deviation rate of change weighting degree. Through the adjustment modification factor Alpha, may change the control rule. When Alpha is big, indicated that is big to deviation's weighting, the step response is quick, the control energy mainly uses in reducing the deviation, but easy to present the over modulation; When Alpha is small, the control goal reduces the over modulation, but the response process is slow. Usually uses the belt two Alpha values the modification factor expressions to be able to request on the satisfiability, namely:
And, modification factor α1, α2∈ (0,1), and α1
2.4 Logical threshold value control
This method establishes some control limit in advance to certain controlled variable (threshold) the value, when applies the brake, according to the computation real-time parameter value and the corresponding threshold value's size relations, determines wheel's state of motion, thus the control adjustment brake pressure, gains enough big brake intensity and the good yawing stability. Often includes as the ABS controlled variable: Wheel skidding rate S, the wheel rotates the angle adds (reduces) the speed Omega and the rate of change .
2.5 Double parameter control
Double parameter control's ABS, by the vehicle speed sensor (velocity radar), a round fast sensor, the control device (computer) and the implementing agency is composed.
Its principle of work is the vehicle speed sensor and a round fast sensor, separately signal input the vehicle speed and round fast the computer, calculates the actual slipping rate based on the computer, and 15% one 20% does with the ideal slipping rate compares, fluctuates brake's braking force again through the solenoid valve. this kind tows the fast sensor commonly used Doppler velocity radar. When the which unceasingly reflects, surveys the automobile radar launch and the receive differential value, then may calculate the automobile vehicle speed accurately. But turns the fast sensor to install in the transmission gearbox outer covering, actuates by the transmission gearbox output shaft, it is a pulse electrical machinery, produces frequency and round intensive direct proportion. The implementing agency and so on is composed of the solenoid valve and the relay. Solenoid valve adjustment braking force, with the aim of maintaining the ideal slipping rate. This kind of ABS may guarantee that the slipping rate ideal control, against holds the braking quality to be good, but because increased a velocity radar, therefore the structure is complex, the cost is also high.
2.6 Single parameter control
It take controls wheel's angle retarded velocity as the object, controls wheel's braking force, realizes against holds the dead brake, its structure mainly by a round fast sensor, the controller (computer) and the solenoid valve is composed. For accurate meter wheel fast, the sensing and between the wheel tooth ring should leave leeway the 1mm gap. In order to avoid the water, the putty, the dust to the sensor the influence, before the installment, should the sensor replenishment butter. The solenoid valve uses in wheel brake's pressure control. Regarding four channel braking system, a vehicle rim has a solenoid valve; Three channel braking system, each front wheel has one, two trailing wheels use in common one. The solenoid valve has three hydraulic pressure holes, separately applies the brake with the brake master cylinder and the wheel to divide the cylinder to be connected, and can realize pressure lifting, pressure maintenance, the pressure drop accent to press the function. The principle of work is as follows:
1) Pressure-rise when the solenoid valve does not work, the brake master cylinder connection and applies the brake to divide the cylinder connection respectively to go nonstop. Because the main spring intensity is big, makes charging valve opening, the brake pressure to increase.
2) pressure maintenance, when wheel's brake divides in cylinder's pressure grows to certain value, charging valve cut-off closure. The support maintains at the compound state, three panels seal, maintain the brake pressures mutually.
3) voltage dropping, when the solenoid valve works, the support overcomes two spring's tension, opens the discharge meat to cause to apply the brake to divide cylinder pressure drop. Once the pressure reduces, the solenoid valve transforms to the pressure maintenance condition, or pressure-rise ready condition.
The control device ECU primary mission is the signal which passes on various wheels' sensor carries on the computation, the analysis, the enlargement and the distinction, outputs again from the output stage the command signal the solenoid valve, carries out the brake pressure adjustment task. The electronic control, by four major part is composed, input level A, controller B, output stage C, constant voltage and protective device D. Electronic controller by 4 101tz frequency actuation solenoid valves, this is the pilot is unable to achieve. This kind of single parameter control mode ABS, because the structure is simple, the cost is low, therefore the present use is broad.
Mostly has provided this kind of single parameter control mode ABS in the American Chrysler custom car. It is loaded with a round fast sensor on passenger vehicle's four wheels. The installment has 45 teeth or 100 tooth's tooth rings on the axle tree, turns a fast sensor's sensing attire to go against in the tooth ring. When the wheel rotates, causes the sensor to produce the voltage signal unceasingly, and inputs the computer, the ideal speed compares with RoM, figures out wheel's speed-up or the deceleration, issues pressure-rise or the release of pressure instruction to the solenoid valve, controls applies the brake to divide the cylinder braking force.
3. The problems by used the ABS system
(1) replaces the brake or the replacement hydraulic pressure braking system part, should arrange only in brake line's air, in order to avoid influence braking system's normal work.
(2) is loaded with the ABS automobile, every year should replace a brake fluid. Otherwise, the brake fluid water absorbability is very strong, after the watery, not only will reduce the boiling point, will have the corrosion, will also create the brake potency decline.
(3) inspects the ABS anti-lock braking system, to cramp out the power source first.
4. Trend of development
Uses the logical threshold value control algorithm, may avoid a series of numerous and diverse theoretical analysis and to some element of certainty quota measurement. Simplified controller's design, because moreover only need determine wheel's angular speed, is advantageous realizes, therefore the load cost is low. This algorithm already drew close maturely, for current automobile ABS system universal use, but it by no means best control algorithm. Because under the different state of roads each kind of threshold value and guarantees presses the time is the empirical value which obtains after the repeated test, does not have the very explicit theory basis, therefore the ABS development's cycle is long, and the control quality guaranteed with difficulty.
Easy to realize the stepless control based on the glide rate control algorithm, and has the very explicit theory to instruct, but present restricts the cost question which its development the bottleneck is mainly realizes, believed according to ours research, from now on ABS control algorithm development direction in the following several aspects.
(1) aims at current widely uses the logical threshold value control algorithm which exists, the research can track the road surface characteristic change, causes the ABS each performance index to be at the optimum condition throughout the control algorithm. And the predictive control technology is worth taking seriously. Because when the brake process, friction characteristic between the tire and the road surface causes the anti-lock braking system has the very obvious misalignment, the denaturation and the uncertainty. Therefore difficulty with establishes its precise mathematical model, but the predictive control has the basic characteristic which the forecast model, the trundle optimize and feed back adjust, may act according to some optimized target design control system, determined that a control quantity the time series, after causing in period of time to move the quantity and the process will soften between the expectation