轎車液壓制動系統(tǒng)設(shè)計(jì)含仿真
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汽車制動系統(tǒng)
制動系統(tǒng)是汽車中最重要的系統(tǒng)。 如果制動失靈，結(jié)果可能是損失慘重的。制動器實(shí)際就是能量轉(zhuǎn)換裝置，它將汽車的動能（動量）轉(zhuǎn)化成熱能（熱量）。當(dāng)駕駛員踩下制動踏板，所產(chǎn)生的制動力是汽車運(yùn)動時動力的10倍。制動系統(tǒng)能對四個剎車系統(tǒng)中的每個施加數(shù)千磅的力。
每輛汽車上使用兩個完全獨(dú)立的制動系統(tǒng)，即行車制動器和駐車制動器。
行車制動器起到減速、停車、或保持車輛正常行駛。制動器是由司機(jī)用腳踩、松制動器踏板來控制的。駐車制動器的主要作用就是當(dāng)車內(nèi)無人的時候，汽車能夠保持靜止。當(dāng)獨(dú)立的駐車制動器—踏板或手桿，被安裝時，駐車制動器就會被機(jī)械地操作。
制動系統(tǒng)是由下列基本的成分組成:位于發(fā)動機(jī)罩下方，而且直接地被連接到制動踏板的“制動主缸”把駕駛員腳的機(jī)械力轉(zhuǎn)變?yōu)橐簤毫Αｄ撝频摹爸苿庸苈贰焙陀腥嵝缘摹爸苿榆浌堋卑阎苿又鞲走B接到每個輪子的“制動輪缸”上。 制動液, 特別地設(shè)計(jì)為的是工作在極端的情況，填充在系統(tǒng)中?！爸苿颖P”和“襯塊”是被制動輪缸推動接觸“圓盤”和“回轉(zhuǎn)體”如此引起緩慢的拖拉運(yùn)動, 使汽車減慢速度。
典型的制動系統(tǒng)布置有前后盤式，前盤后鼓式，各個車輪上的制動器通過一套管路系統(tǒng)連接到制動主缸上。
基本上講，所有的汽車制動器都是摩擦制動器。當(dāng)司機(jī)剎車時，控制裝置會迫使制動蹄，或制動襯片與車輪處的旋轉(zhuǎn)的制動鼓或制動盤接觸。接觸后產(chǎn)生的摩擦使車輪轉(zhuǎn)動減慢或停止，這就是汽車的制動。
在最基本的制動系統(tǒng)中，有一個制動主缸，這個主缸內(nèi)部填充制動液，并包含兩個部分，每個部分里都有一個活塞，兩個活塞都連接駕駛室里的制動踏板。當(dāng)制動踏板被踩下時，制動液會從制動主缸流入輪缸。在輪缸中，制動液推動制動蹄或制動襯片與旋轉(zhuǎn)的制動鼓或制動盤接觸。靜止的制動蹄或制動襯片與旋轉(zhuǎn)的制動鼓或制動盤之間產(chǎn)生摩擦力使汽車的運(yùn)動逐漸減緩或停止。
制動液的裝置位于主缸的頂部。目前大多數(shù)的車都有一個容易看見的裝制動液的裝置，為的是不用打開蓋子就可以看得見制動液的油面。隨著制動踏板的運(yùn)動制動液就會緩慢的下降，正常情況下是這樣的。如果制動液在很短的時間內(nèi)下降得明顯或者下降了三分之二，那么就要盡快的檢查你的制動系統(tǒng)了。保持制動液裝置充滿制動液除非你需要維修它，制動液必須保持很高的沸點(diǎn)。位于在空氣中的制動液就會吸收空氣中的潮氣引起制動液低于沸點(diǎn)。
制動液通過一系列的管路從主缸到達(dá)各車輪。橡膠軟管只用在需要彈力的地方，比如應(yīng)用在前輪。在車的行進(jìn)中上下來回運(yùn)動。系統(tǒng)的其它部分在所有的連接點(diǎn)上都應(yīng)用了無腐蝕性的無縫鋼管。如果鋼線需要修理的話，最好的方法就是代替這條線。如果這不符合實(shí)際，那么為了制動系統(tǒng)可以用特殊的裝置修理它。你不可以用銅管來修理制動系。它們是危險也是不正確的。
鼓式制動器包括制動鼓，一個輪缸，回拉彈簧，一個制動底版，兩個帶摩擦層的制動蹄。制動底版固定在輪軸外部的法蘭或轉(zhuǎn)向節(jié)。制動鼓固定在輪轂上。制動鼓的內(nèi)部表面與制動蹄的內(nèi)層之間有空隙。要使用制動器時，司機(jī)就要踩下踏板，這時輪缸擴(kuò)大制動片，對其施加壓力，是制動蹄觸碰制動鼓。制動鼓與摩擦片之間產(chǎn)生的摩擦制動了車輪，從而使汽車停止。要釋放制動器時，司機(jī)松開踏板，回拉彈簧拉回制動片，這樣車輪會自由轉(zhuǎn)動。
盤式制動器包括制動盤而不是鼓，在它的兩面上各有一個薄的制動片或叫盤式制動器的制動片。制動片是靠擠住旋轉(zhuǎn)的制動盤來停住汽車。制動主缸里流出的制動液迫使活塞向里部的金屬盤移動，這便使摩擦片緊緊地貼住制動盤。這時制動片與制動盤產(chǎn)生的摩擦使汽車減速、停止，出現(xiàn)了制動行為?；钊纸饘倩蛩芰稀１P式制動器主要有三種，即：浮動卡鉗型、固定卡鉗型和滑動卡鉗型。浮動卡鉗型和滑動卡鉗型盤式制動器使用單活塞。固定卡鉗型盤式制動器既可以使用兩個活塞有可以使用四個活塞。
制動系統(tǒng)是由機(jī)械能，液壓能或氣壓能裝置驅(qū)動的。在機(jī)械杠桿適合所有的汽車的駐車制動器中使用。當(dāng)踩下制動踏板時，杠桿就會推動制動器主缸的活塞給制動液施加壓力，制動液通過油管流入輪缸。制動液的壓力施加到輪缸活塞以使制動片被壓到制動鼓或制動盤上。如果松開踏板，活塞回到原來的位置上，回拉彈簧拉回制動片，制動液返回制動主缸，這樣制動停止。
駐動制動器的主要作用是車內(nèi)無人時，使汽車靜止不動。如果車內(nèi)安裝的是獨(dú)立的駐車制動器，那么駐車制動器是由司機(jī)手動的控制。駐車制動器正常是當(dāng)車已經(jīng)停止時使用的。向后拉手閘，并把手柄卡在正確的位置上?，F(xiàn)在，即使離開汽車也不用害怕它會自己滑走。如果司機(jī)要再次啟車時，他必須在松開手桿之前按下按鈕。在行車制動器失靈的情況下，手閘必須能停住車。正因?yàn)檫@樣，手閘與腳閘分開，手閘使用的是繩索或杠桿而不是液壓系統(tǒng)。
防抱死制動系統(tǒng)是使汽車制動更安全、更方便的制動裝置，它既有調(diào)節(jié)制動系統(tǒng)的壓力來防止車輪被完全抱死的功能，又有防止輪胎在滑的路面上行駛或緊急停車時的滑動。
防抱死制動系統(tǒng)最早應(yīng)用在航空飛行器上，而且在二十世紀(jì) 90年代一些國內(nèi)的汽車內(nèi)也安裝了這種系統(tǒng)。近來，幾個汽車制造商引進(jìn)了更為復(fù)雜的防抱死系統(tǒng)。歐洲使用這種系統(tǒng)已有幾十年的時間，通過對其的調(diào)查，一位汽車制造商坦言，如果所有的汽車都安裝上防抱死制動系統(tǒng)，那么交通事故的發(fā)生率會降低7.5%。同時，一些權(quán)威人士預(yù)測這種系統(tǒng)會提高汽車的安全性。
防抱死制動系統(tǒng)可以在一秒鐘內(nèi)調(diào)節(jié)幾次制動時車輪上的受力，使車輪的滑移受到控制，而且所有的系統(tǒng)基本上都以相同的方式完成。每個車輪都會有一個傳感器，電子控制裝置能連續(xù)檢測來自車輪傳感器傳來的脈沖電信號，并將它們處理轉(zhuǎn)換成和輪速成正比的數(shù)值；如果其中一個傳感器的信號不斷下降，那么這就表明了相應(yīng)的輪胎趨于抱死，這時電子控制裝置向該車輪的制動器發(fā)出降低壓力的指令。當(dāng)信號顯示車輪轉(zhuǎn)速恢復(fù)正常時，電子控制裝置會增加制動器的液壓。這種循環(huán)像司機(jī)一樣調(diào)節(jié)制動器，但它的速度更快，達(dá)到了每秒循環(huán)數(shù)次。
防抱死制動系統(tǒng)除了上面基本操作，還有兩個特點(diǎn)。首先，當(dāng)制動系統(tǒng)的壓力上升到使輪胎抱死或即將抱死的時候，防抱死制動系統(tǒng)才會啟動；當(dāng)制動系統(tǒng)在正常情況下，防抱死制動系統(tǒng)停止運(yùn)作。其次，如果防抱死制動系統(tǒng)有問題時，制動器會獨(dú)立地繼續(xù)運(yùn)行。但控制板上的指示燈亮起提醒司機(jī)系統(tǒng)出現(xiàn)問題。
目前歐洲汽車生產(chǎn)商，如：寶馬、奔馳、寶時捷等廣泛使用的是波許（Bosch）防抱死制動系統(tǒng)。這種系統(tǒng)基本組成包括車輪轉(zhuǎn)速傳感器，電子控制裝置和調(diào)節(jié)裝置。
每個有一個向電子控制裝置發(fā)出車輪轉(zhuǎn)動情況的信號的傳感器，它一般由磁感應(yīng)傳感頭和齒圈組成。前面的傳感器安在輪轂上，齒圈安在輪網(wǎng)上。后面的傳感器安在后部的監(jiān)測系統(tǒng)上，齒圈安在輪軸上。傳感器本身是纏繞電磁核的電線圈，電磁核才線圈的周圍產(chǎn)生磁場。當(dāng)齒圈的齒移動到磁場時，就會改變線圈的電流。電子控制裝置會監(jiān)測這種變化，然后判斷車輪是否即將抱死。
電子控制裝置有三個作用，即：信號的處理，編輯和安全防護(hù)。信號的處理起到轉(zhuǎn)換器的作用，它是將接受的脈沖電信號處理轉(zhuǎn)換成數(shù)值，為編輯做準(zhǔn)備。編輯就是分析這些數(shù)值，計(jì)算出需要制動壓力。如果檢測出車輪即將抱死，電控裝置就會計(jì)算出數(shù)值向調(diào)節(jié)裝置發(fā)出指令。
調(diào)節(jié)裝置
當(dāng)接受到電子控制裝置的指令后，液壓執(zhí)行裝置會調(diào)節(jié)制動輪缸的液壓的大小。調(diào)節(jié)裝置能保持或減小來自制動主缸的液壓，而裝置本身是不能啟用制動器的。這種裝置有三個高速率的電磁閥，兩個油液存儲器和一個帶有內(nèi)外檢測閥的傳動泵。調(diào)節(jié)裝置中的電子連接器隱藏在塑料蓋下。
每個電磁閥都是其獨(dú)立控制的，并作用于前輪。后部的制動輪缸受到一個電磁閥控制，并依照------的原理進(jìn)行調(diào)節(jié)。當(dāng)防抱死制動系統(tǒng)運(yùn)行時，電子控制裝置會使電磁閥循環(huán)運(yùn)作，這樣既能收回又能釋放制動器的壓力。當(dāng)壓力釋放時，它會釋放到液壓單元。前部的制動器電路有一個單元。存儲器低壓存儲器，它在低壓下存儲油液，直到回流泵打開，油液流經(jīng)制動輪缸進(jìn)入制動主缸。
制動器：它們的作用？
簡單的說：它會使你的汽車慢下來。
復(fù)雜的說：制動器被用來讓你的車減速，但可能不是你所想的意思。普遍的誤解是，制動器擠壓制動鼓或制動片，擠壓的壓力的作用使你的車慢下來。但這只是制動的一部分。制動系統(tǒng)本質(zhì)上是改變能量的類型。當(dāng)你在全速行駛時，你的汽車獲得動能。當(dāng)你踩下剎車，墊子或鞋子對制動鼓和轉(zhuǎn)子的作用轉(zhuǎn)化為摩擦熱能。剎車的冷卻使車的熱能消散，減慢車速。這是熱力學(xué)第一定律，有時被視為能量守恒定律。也是就說：能量不能被創(chuàng)造也不能被消滅，只能由一種形式轉(zhuǎn)換成另一種。制動情況下，它是動能轉(zhuǎn)化為熱能。
角向力。 因?yàn)樵诒P式制動器的剎車片和轉(zhuǎn)子的位置，摩擦產(chǎn)生的接觸點(diǎn)的位置也產(chǎn)生了一個機(jī)械的抵御轉(zhuǎn)子的回轉(zhuǎn)運(yùn)動。熱力學(xué)，制動失效，鉆孔轉(zhuǎn)子。
如果你騎摩托車或駕駛一輛賽車，你或許熟悉制動失效，描述當(dāng)制動器太熱，他發(fā)生了什么。一個很好的例子就是從山上下來使用剎車制動,而不是你的引擎使你減速。當(dāng)汽車開始滑動下來時，剎車使汽車產(chǎn)生熱能,使你減速。但是如果你持續(xù)使用他們， 轉(zhuǎn)子或鼓留熱并沒有機(jī)會冷卻。從某種意義上說他們不能吸收更多的熱量，使剎車墊熱了起來。在每一個墊子的摩擦材料有某種共同的樹脂一旦開始變得太熱，該樹脂開始蒸發(fā)，形成氣。由于氣體之間不能待在墊層及轉(zhuǎn)子，而是形成薄薄的一層在兩個之間準(zhǔn)備排走。墊失去與轉(zhuǎn)子的接觸，減少摩擦和熱量。這是完全的制動失效。
典型的補(bǔ)救辦法，將車停了下來，等待幾分鐘。由于制動部件降溫，吸收熱量的原因，下一次您使用剎車的能力，似乎會好一點(diǎn)。這種類型的制動失效在舊車輛更常見。新的車輛往往從剎車墊中減少排氣，但他們?nèi)杂兄苿邮?。為什么呢？它仍然因?yàn)閯x車墊太熱。猶由于新的剎車墊合成，襯墊的熱傳遞到卡鉗一旦轉(zhuǎn)子太熱了，制動液開始沸騰冒泡。因?yàn)榭諝馐强蓧嚎s的(制動液不是)當(dāng)你踩剎車，氣泡的壓縮代替了流體轉(zhuǎn)移到制動卡鉗。這就是現(xiàn)代制動失效。
工程師們是怎樣設(shè)計(jì)減少或消除剎車制動失效的? 年長的車輛，是使氣化的氣體有地方排掉。新的車輛，找到一些方式來冷卻轉(zhuǎn)子更為有效。無論如何你最終獲得交叉鉆孔或溝槽剎車盤。當(dāng)槽表面是可以減少比熱容量的轉(zhuǎn)子，其效果可以忽略不計(jì)的。然而當(dāng)大力剎車時一旦一切都是熱和樹脂材料蒸發(fā)，槽讓氣體排去， 所以墊可以繼續(xù)接觸轉(zhuǎn)子，讓車減速停下來。
整個的理解能量轉(zhuǎn)換的關(guān)鍵是，剎車他們該做什么,以及為什么它們設(shè)計(jì)成這樣。如果你曾看過一級方程式賽車，你就可以看到向前的前輪里面有很大的洞（如上圖所示）。這是管道空氣剎車部件，以幫助他們冷卻下來，因?yàn)樵贔1賽車中，剎車每隔幾秒鐘頻繁使用，花很多時間預(yù)留熱量。如果沒有某種冷卻協(xié)助，剎車就可能在最開始的幾個轉(zhuǎn)角失靈，最后剎車失效賽車在一半路程出局。
轉(zhuǎn)子技術(shù)。
如果制動轉(zhuǎn)子是一個單一的鋼鐵鑄塊，這將有嚴(yán)重的散熱性能和氣化氣無法排去。因此，剎車盤通常使用各種額外的設(shè)計(jì)特點(diǎn)的方式來改進(jìn)幫助他們冷卻下來，盡快使墊和轉(zhuǎn)子之間的任何氣體排走。 這里的圖表顯示了轉(zhuǎn)子類型的各種修改，可以改進(jìn)幫助他們創(chuàng)造更多的摩擦力，更迅速地驅(qū)散更多的熱量，通風(fēng)氣體的一些例子。 從左至右。
1：基本制動轉(zhuǎn)子。
2：溝槽轉(zhuǎn)子-溝槽給予更多口，他們之間產(chǎn)生更多的摩擦，還允許氣體從墊和轉(zhuǎn)子之間的排走。
3：溝槽鉆孔轉(zhuǎn)子-再給多一點(diǎn)口，但也讓氣流(渦旋)通過制動盤協(xié)助冷卻和通風(fēng)。
4：雙通風(fēng)轉(zhuǎn)子-以前一樣，然而現(xiàn)在有了兩個轉(zhuǎn)子而不是一個，和他們之間葉片產(chǎn)生渦流將進(jìn)一步冷卻轉(zhuǎn)子同時試圖實(shí)際上從襯墊中排掉任何氣體。
重要的一點(diǎn)：鉆孔轉(zhuǎn)子通常只使用于賽車。鉆孔使得轉(zhuǎn)子變?nèi)酰ǔ?dǎo)致轉(zhuǎn)子產(chǎn)生各類裂縫。在賽車中這不是一個問題——在每場比賽或者每周都會更換剎車盤。但在路上的車，最終會導(dǎo)致剎車轉(zhuǎn)子失靈的，不是你能想象的。我只提這件事，因?yàn)橛性S多供應(yīng)商將為您提供鉆孔轉(zhuǎn)子，沒有直接提到這個事實(shí)。
這是如何適用于更大的剎車轉(zhuǎn)子-一種普遍的跑車升級？汽車和自行車運(yùn)動比賽通常有比一般的家庭汽車更大的盤或轉(zhuǎn)子。一個更大的轉(zhuǎn)子有更多的材料在里面，因此它可以吸收更多的熱量。更多的物質(zhì)也意味著更大的表面積，墊片產(chǎn)生摩擦,和更好的散熱。較大的角度也將轉(zhuǎn)子接觸墊進(jìn)一步遠(yuǎn)離軸旋轉(zhuǎn)。這提供了一個更大的機(jī)械優(yōu)勢抵抗旋轉(zhuǎn)的轉(zhuǎn)子本身。這個工作最好的說明，設(shè)想一種紡紗鋼軸上的閥瓣在你的面前。如果你夾緊你的大拇指任何一方的閥瓣靠近中間，你的大拇指將熱得非?？欤銜枰苿酉喈?dāng)大的摩擦力使閥瓣慢下來?，F(xiàn)在想象做同樣的事情，但是你的大拇指夾在一起接近外緣的閥瓣。閥瓣將停止旋轉(zhuǎn)得特別快，你的大拇指也不會很熱。簡單地說解釋整個原理就是更大轉(zhuǎn)子=更好的制動原則。
不同類型的制動器。
所有制動器都產(chǎn)生摩擦力。摩擦力是熱的一部分動能轉(zhuǎn)換過程。他們是如何不同的設(shè)計(jì)產(chǎn)生了摩擦的。
我想我覆蓋這些，因?yàn)樗鼈兪亲罨绢愋偷闹苿臃绞?，你可以看到，看工作了解。設(shè)計(jì)非常簡單，在外部。一雙橡膠塊連接到一雙卡鉗，能在機(jī)架上旋轉(zhuǎn)。當(dāng)你拉剎車線，剎車墊壓向一側(cè)或自行車輪輞的內(nèi)側(cè)邊緣。 橡膠產(chǎn)生摩擦，產(chǎn)生熱量，這是動能轉(zhuǎn)移使車慢下來。 自行車制動實(shí)際上只有兩個類型 - 自行車剎車制動蹄上有相同的摩擦點(diǎn)，并有兩個摩擦點(diǎn)。 如果你可以看了自行車制動，不明白發(fā)生了什么事情，本頁面的其余部分你理解起來有麻煩了。
鼓式制動器-單前沿
下一個，更加復(fù)雜的類型的制動是鼓式制動器。這是簡單的概念。兩個半圓形的剎車片裝在里面連接一個旋轉(zhuǎn)的車輪的鼓。當(dāng)你踩下剎車,剎車片向外擴(kuò)大擠壓內(nèi)側(cè)的鼓。這造成了摩擦，產(chǎn)生熱量，轉(zhuǎn)移動能，這將使車減速。下面的例子顯示了一個簡單的模型。制動器在這種情況下是藍(lán)色橢圓形的對象。因?yàn)檫@是扭曲的，它的力使剎車片迫使他們向外擴(kuò)張。當(dāng)松開剎車，回位彈簧從制動鼓的表面拉回剎車片。看到章節(jié)后面更多信息。
"單前沿"是指實(shí)際接觸的旋轉(zhuǎn)鼓輪制動蹄部件的數(shù)量。因?yàn)橹苿犹闫谝欢?，簡單的幾何意味著整個剎車片無法都接觸到制動鼓。單前沿就是部分剎車片的術(shù)語，那些接觸制動鼓，在單一制動情況下的方法，在最接近制動器的襯墊。此圖 （右側(cè)） 顯示當(dāng)剎車時，會發(fā)生什么情況。這剎車片向外壓和制動襯墊的最初接觸制動鼓的部分剎車片就是前沿。制動鼓旋轉(zhuǎn)實(shí)際上有助于制動片向外加壓，因?yàn)閯x車片向口子的摩擦力。后沿的制動蹄片與制動鼓幾乎沒有接觸。這個簡單的幾何解釋了，為什么汽車是很難停止向后滾動，如果它只配單前緣沿鼓式制動器。由于制動鼓向后旋轉(zhuǎn)，前沿的剎車片成為了后沿，因?yàn)橹苿硬粫Ш稀?
鼓剎車-雙前沿
可以通過添加回位彈簧和旋轉(zhuǎn)第二個制動器中心點(diǎn)來消除鼓式制動器的單個前沿的缺點(diǎn)。踩下剎車時，剎車片在兩個點(diǎn)向外壓。所以每個剎車片現(xiàn)在有一個前沿的和一個后沿。因?yàn)橛袃蓚€剎車蹄，那里有兩個剎車片，這意味著有兩個邊沿。因此名稱雙前沿。
盤式制動器一些背景。
盤式制動器在 1902 年被發(fā)明，伯明翰汽車制造商檢基威廉 · 蘭徹斯特的專利。他原先的設(shè)計(jì)了兩個光盤，緊貼彼此產(chǎn)生摩擦來使車減速。直到 1949 盤式制動器的量產(chǎn)車上使用。在美國汽車創(chuàng)始人克羅斯利發(fā)明了我們目前熟知和喜愛的快車，就是使用了很多類似的盤動制動器和卡鉗。他原先的設(shè)計(jì)雖然有點(diǎn)缺陷-制動器持續(xù)不到一年。終于在 1954 年雪鐵龍推出先進(jìn)的DS，成就了像自流平懸浮、 半自動變速箱、 活動前燈和復(fù)合車身盤式制動器的第一次現(xiàn)代化身。（所有事情，在 90 年代的汽車制造商都重新作為"新型"）。
盤式制動器比鼓式制動器好了一個數(shù)量級來使車輛制動，這就是為什么你會發(fā)現(xiàn)的現(xiàn)代幾乎所以汽車和摩托車都使用的是盤式制動器。運(yùn)動型車輛具有更高的速度需要更好的制動減速，所以您會明白盤式制動器在這些車上的使用。
附錄B
外文翻譯
Automobile Brake System
The braking system is the most important system in cars. If the brakes fail, the result can be disastrous. Brakes are actually energy conversion devices, which convert the kinetic energy (momentum) of the vehicle into thermal energy (heat).When stepping on the brakes, the driver commands a stopping force ten times as powerful as the force that puts the car in motion. The braking system can exert thousands of pounds of pressure on each of the four brakes.
Two complete independent braking systems are used on the car. They are the service brake and the parking brake.
The service brake acts to slow, stop, or hold the vehicle during normal driving. They are foot-operated by the driver depressing and releasing the brake pedal. The primary purpose of the brake is to hold the vehicle stationary while it is unattended. The parking brake is mechanically operated by when a separate parking brake foot pedal or hand lever is set.
The brake system is composed of the following basic components: the “master cylinder” which is located under the hood, and is directly connected to the brake pedal, converts driver foot’s mechanical pressure into hydraulic pressure. Steel “brake lines” and flexible “brake hoses” connect the master cylinder to the “slave cylinders” located at each wheel. Brake fluid, specially designed to work in extreme conditions, fills the system. “Shoes” and “pads” are pushed by the slave cylinders to contact the “drums” and “rotors” thus causing drag, which (hopefully) slows the car.
The typical brake system consists of disk brakes in front and either disk or drum brakes in the rear connected by a system of tubes and hoses that link the brake at each wheel to the master cylinder (Figure).
Basically, all car brakes are friction brakes. When the driver applies the brake, the control device forces brake shoes, or pads, against the rotating brake drum or disks at wheel. Friction between the shoes or pads and the drums or disks then slows or stops the wheel so that the car is braked.
In most modern brake systems (see Figure 15.1), there is a fluid-filled cylinder, called master cylinder, which contains two separate sections, there is a piston in each section and both pistons are connected to a brake pedal in the driver’s compartment. When the brake is pushed down, brake fluid is sent from the master cylinder to the wheels. At the wheels, the fluid pushes shoes, or pads, against revolving drums or disks. The friction between the stationary shoes, or pads, and the revolving drums or disks slows and stops them. This slows or stops the revolving wheels, which, in turn, slow or stop the car.
The brake fluid travels from the master cylinder to the wheels through a series of steel tubes and reinforced rubber hoses. Rubber hoses are only used in places that require flexibility, such as at the front wheels, which move up and down as well as steer. The rest of the system uses non-corrosive seamless steel tubing with special fittings at all attachment points. If a steel line requires a repair, the best procedure is to replace the compete line. If this is not practical, a line can be repaired using special splice fittings that are made for brake system repair. You must never use copper tubing to repair a brake system. They are dangerous and illegal.
With the parameter change, the change situation which in the template characteristic possibly appears.the characteristic maintenance is invariable, is only the size reproduce by pantograph.the structure.characteristic changes.Above two kind of change situation, in actual operation, because selects the template with the simulated target size difference which must design is not very big, therefore mainly has the first kind of situation, the size changes in the characteristic maintenance scope. when the parameter change quite fierce , is the second kind of situation, this request establishment template must describe the model comprehensively. Certainly, if a template closer model, the characteristic which must increase manual are less, but this template has representative and typical nature bad somewhat; The template with awaits construction the model to have certain disparity, needs to increase manually the characteristic are many,but its representation and typical nature are good somewhat. This is a pair of contradictory, in the construct
Drum brakes, it consists of the brake drum, an expander, pull back springs, a stationary back plate, two shoes with friction linings, and anchor pins. The stationary back plate is secured to the flange of the axle housing or to the steering knuckle. The brake drum is mounted on the wheel hub. There is a clearance between the inner surface of the drum and the shoe lining. To apply brakes, the driver pushes pedal, the expander expands the shoes and presses them to the drum. Friction between the brake drum and the friction linings brakes the wheels and the vehicle stops. To release brakes, the driver release the pedal, the pull back spring retracts the shoes thus permitting free rotation of the wheels.
Disk brakes, it has a metal disk instead of a drum. A flat shoe, or disk-brake pad, is located on each side of the disk. The shoes squeeze the rotating disk to stop the car. Fluid from the master cylinder forces the pistons to move in, toward the disk. This action pushes the friction pads tightly against the disk. The friction between the shoes and disk slows and stops it. This provides the braking action. Pistons are made of either plastic or metal. There are three general types of disk brakes. They are the floating-caliper type, the fixed-caliper type, and the sliding-caliper type. Floating-caliper and sliding-caliper disk brakes use a single piston. Fixed-caliper disk brakes have either two or four pistons.
The brake system assemblies are actuated by mechanical, hydraulic or pneumatic devices. The mechanical leverage is used in the parking brakes fitted in all automobile. When the brake pedal is depressed, the rod pushes the piston of brake master cylinder which presses the fluid. The fluid flows through the pipelines to the power brake unit and then to the wheel cylinder. The fluid pressure expands the cylinder pistons thus pressing the shoes to the drum or disk. If the pedal is released, the piston returns to the initial position, the pull back springs retract the shoes, the fluid is forced back to the master cylinder and braking ceases.
The primary purpose of the parking brake is to hold the vehicle stationary while it is unattended. The parking brake is mechanically operated by the driver when a separate parking braking hand lever is set. The hand brake is normally used when the car has already stopped. A lever is pulled and the rear brakes are approached and locked in the “on” position. The car may now be left without fear of its rolling away. When the driver wants to move the car again, he must press a button before the lever can be released. The hand brake must also be able to stop the car in the event of the foot brake failing. For this reason, it is separate from the foot brake uses cable or rods instead of the hydraulic system.
Anti-lock Brake System
Anti-lock brake systems make braking safer and more convenient, Anti-lock brake systems modulate brake system hydraulic pressure to prevent the brakes from locking and the tires from skidding on slippery pavement or during a panic stop.
Anti-lock brake systems have been used on aircraft for years, and some domestic car were offered with an early form of anti-lock braking in late 1990’s. Recently, several automakers have introduced more sophisticated anti-lock system. Investigations in Europe, where anti-lock braking systems have been available for a decade, have led one manufacture to state that the number of traffic accidents could be reduced by seven and a half percent if all cars had anti-lock brakes. So some sources predict that all cars will offer anti-lock brakes to improve the safety of the car. In order to describe the relation among characteristic, may apply the concept of characteristic class, the characteristic example. The characteristic class is the description about the characteristic type, is summary of all same information characteristic. The characteristic example is specific characteristic after the characteristic attribute evaluation, is the member of characteristic class. Among the characteristic class, the characteristic example, the characteristic class and the characteristic example has relation as follows.Inherits relates level relation among the characteristic, which is located the level higher authority to be called the ultra kind of characteristic, is located the level lower level to be called the subgroup characteristic. The subgroup characteristic may inherit the ultra kind of characteristic the attribute and the method, this kind of inheritance relation is called the relation. Another kind of inheritance relation is the relation between characteristic cl ass and this kind of characteristic example, this kind of relation is called the relation. For example, some concrete circular cylinder is a example that circular cylinder characteristic class, among themselves has reflected the relation.
Adjacent relation. Reflected the mutual position relations among the shape characteristic, indicated with CONT. Among the constitution adjacency relation shape characteristic adjacency condition may share.For example, a steps and ladders axis, between each neighboring two axis section's relations are the syntopy, in which each adjacency surface condition may share. Hypotaxis.the description about shape characteristic compliance or the attached relations. The subordinate shape characteristic relies on in the shape characteristic which is subordinated is existed, like bevel edge attached in circular cylinder. Quote relation. describing characteristic class as the connection attribute which the quotes mutually, indicated with RE. The quotation relation mainly exists in the quotation that the shape characteristic to the precision characteristic, the material characteristic.
Anti-lock systems modulate brake application force several times per second to hold the tires at a controlled amount of slip; all systems accomplish this in basically the same way. One or more speed sensors generate alternating current signal whose frequency increases with the wheel rotational speed. An electronic control unit continuously monitors these signals and if the frequency of a signal drops too rapidly indicating that a wheel is about to lock, the control unit instructs a modulating device to reduce hydraulic pressure to the brake at the affected wheel. When sensor signals indicate the wheel is again rotating normally, the control unit allows increased hydraulic pressure to the brake. This release-apply cycle occurs several time per second to “pump” the brakes like a driver might but at a much faster rate.
In addition to their basic operation, anti-lock systems have two other things in common. First, they do not operate until the brakes are applied with enough force to lock or nearly lock a wheel. At all other times, the system stands ready to function but does not interfere with normal braking. Second, if the anti-lock system fail in any way, the brakes continue to operate without anti-lock capability. A warning light on the instrument panel alerts the driver when a problem exists in the anti-lock system.
The current Bosch component Anti-lock Braking System (ABSⅡ), is a second generation design wildly used by European automakers such as BWM, Mercedes-Benz and Porsche. ABSⅡ system consists of : four wheel speed sensor, electronic control unit and modulator assembly.
A speed sensor is fitted at each wheel sends signals about wheel rotation to control unit. Each speed sensor consists of a sensor unit and a gear wheel. The front sensor mounts to the steering knuckle and its gear wheel is pressed onto the stub axle that rotates with the wheel. The rear sensor mounts the rear suspension member and its gear wheel is pressed onto the axle. The sensor itself is a winding with a magnetic core. The core creates a magnetic field around the winding, and as the teeth of the gear wheel move through this field, an alternating current is induced in the winding. The control unit monitors the rate o change in this frequency to determine impending brake lockup.
The control unit’s function can be divided into three parts: signal processing, logic and safety circuitry. The signal processing section is the converter that receives the alternating current signals form the speed sensors and converts them into digital form for the logic section. The logic section then analyzes the digitized signals to calculate any brake pressure changes needed. If impending lockup is sensed, the logic section sends commands to the modulator assembly.
Modulator assembly
The hydraulic modulator assembly regulates pressure to the wheel brakes when it receives commands from the control utuit. The modulator assembly can maintain or reduce pressure over the level it receives from the master cylinder, it also can never apply the brakes by itself. The modulator assembly consists of three high-speed electric solenoid valves, two fluid reservoirs and a turn delivery pump equipped with inlet and outlet check valves. The modulator electrical connector and controlling relays are concealed under a plastic cover of the assembly.
Each front wheel is served by electric soleno
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