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黃河科技學(xué)院畢業(yè)設(shè)計(jì)（文獻(xiàn)翻譯）
防抱制動系統(tǒng)
Wikipedia, the free encyclopedia
防抱死制動系統(tǒng) (ABS) 是一個安全系統(tǒng)，它允許繼續(xù) tractively 與交互指示由驅(qū)動程序轉(zhuǎn)向投入路面制動，同時防止車輪鎖起來的汽車的輪子 （即，停止旋轉(zhuǎn)）和因此避免打滑。
ABS 通常提供了改進(jìn)的車輛控制和減少停車干、 濕滑的曲面上的距離，不過，像砂礫或白雪覆蓋的路面的松散表面，ABS 可以顯著提高制動距離，雖然仍在提高車輛控制。
自從首次在生產(chǎn)的汽車中的使用以來，防抱死制動系統(tǒng)有很大變化。新版本的abs不僅防止車輪鎖制動，還以電子方式控制前向后制動偏離。此函數(shù)，取決于其特定的功能和實(shí)施，被稱為電子動力分配 (EBD)、 牽引力控制系統(tǒng)、 緊急制動輔助或電子穩(wěn)定控制 （ESC）。
1、歷史
早期系統(tǒng)
ABS 第一次飛機(jī)使用，在 1929 年由開發(fā)法國汽車和飛機(jī)先鋒，加布里埃瓦贊飛機(jī)工廠，如閾值制動在飛機(jī)上。這些系統(tǒng)中使用飛輪和附加到飼料制動缸的液壓閥門。飛輪附加到鼓輪相同的速度運(yùn)行。在正常的剎車、 鼓和飛輪應(yīng)以相同的速度旋轉(zhuǎn)。但是，如果一個輪慢下來，那么鼓也會這樣做，離開了更快的速度在旋轉(zhuǎn)的飛輪。這將導(dǎo)致的閥門打開，允許少量的制動液到水庫繞過主缸、 降低放在缸內(nèi)壓力和釋放剎車。使用鼓和飛輪意味著只打開時已開始用轉(zhuǎn)向輪的閥門。在測試中，有人指出制動性能提高 30%，因?yàn)轱w行員可以的慢慢增加壓力，以找到橇點(diǎn)而不是完全踩剎車。另一個好處是消除對燒傷或突發(fā)事故的輪胎。 1958 年，皇家恩菲爾德超級流星摩托車被用于道路研究實(shí)驗(yàn)室的測試 Maxaret 防抱死制動。 實(shí)驗(yàn)證明防抱死剎車可以在摩托車上使用，對意外中防止打滑有極大的價值。在大部分測試與鎖定的車輪制動，特別是在光滑的表面，改進(jìn)可能高達(dá) 30%相比，減少了煞車距離。恩菲爾德的技術(shù)總監(jiān)時，托尼 · 威爾遜 · 瓊斯在系統(tǒng)中，看到小小的未來，和它不投入生產(chǎn)的公司。完全機(jī)械化系統(tǒng)應(yīng)用在 1960 年代弗格森 P99 賽車、 詹森的 FF，和實(shí)驗(yàn)福特汽車，效果不明顯，所以沒有進(jìn)一步的使用 ；并且系統(tǒng)證明昂貴和不可靠。
現(xiàn)代系統(tǒng)
克萊斯勒，連同本迪克斯公司中，介紹了其 1971年帝國稱為"確保制動"的電算化、 三通道、 四傳感器全輪 ABS。它在幾年之后，發(fā)揮了預(yù)期的作用，并證明可靠。1970 年，福特添加防抱制動系統(tǒng)作為一個選項(xiàng) ； 林肯大陸的后輪稱為"當(dāng)然軌"，它成為標(biāo)準(zhǔn)在1971 年。1971 年，通用汽車公司推出了"Trackmaster"后輪 onlyABS 作為一個選項(xiàng)對他們后輪驅(qū)動凱迪拉克車型 ，日產(chǎn)提供 EAL （電防抱死系統(tǒng)） 作為對日產(chǎn)的總統(tǒng)，成為日本的第一個電子 ABS 的選項(xiàng)。
寶馬摩托車 ABS 剎車。1972 年，四輪驅(qū)動的勝利 使馬拉德電子系統(tǒng)作為標(biāo)準(zhǔn)。然而這種車非常罕見，今天很少生存。
在 1985 年，福特天蝎進(jìn)入了整個范圍的博世電子系統(tǒng)與歐洲市場，并作為標(biāo)準(zhǔn)。為此模型榮獲年度獎令人垂涎的歐洲汽車。 1986 年，贏得了駕駛記者極高的贊譽(yù)。這一成功后福特?cái)U(kuò)大他們的范圍，鼓勵其他制造商效仿，其余部分的防抱死系統(tǒng)開始研究。
1988 年，寶馬推出電子液壓 abs 的第一輛摩托車： 寶馬 K100。2007 年，鈴木推出其 GSF1200SA (土匪) 的 abs。2005 年，哈雷-戴維森開始提供 ABS 作為警察摩托的選擇。
2、 操作
防抱死制動控制器也稱為是 CAB （控制器防抱死制動）。典型的 ABS 包括中央電子控制單元 (ECU)、 4 個車輪速度傳感器和至少兩個液壓閥制動液壓系統(tǒng)。ECU 持續(xù)監(jiān)視每個車輪的轉(zhuǎn)速，如果它檢測車輪旋轉(zhuǎn)速度明顯慢于其余車輪，下達(dá)一個控制命令控制車輪鎖，它驅(qū)動受影響的方向盤，從而減少車輪滑移 ； 制動力制動減少液壓閥然后車輪變快。相反，如果 ECU 檢測車速度快得多，其他的車輪，車輪制動液壓壓力被增加因此制動力重新應(yīng)用，減慢輪子。此過程不斷重復(fù)，并且可以通過制動踏板脈動驅(qū)動程序檢測到。一些防抱死系統(tǒng)可以應(yīng)用，或釋放每秒 15 次制動壓力。因?yàn)楫?dāng)變成了車，向曲線的中心的兩個輪子轉(zhuǎn)速度慢于另外兩 個，ECU 被編程，無視輪轉(zhuǎn)速的臨界閾值以下的差異。出于同樣原因，用于幾乎所有視覺車輛差速器。
如果abs 的任何部分發(fā)生故障，通常將在汽車儀表板上, 亮起警示燈和 ABS 將被禁用，直到故障予以糾正?，F(xiàn)代 ABS 適用于通過集線器安裝傳感器和專用的微控制器的控制系統(tǒng)的所有四個輪子的個別制動壓力。ABS 提供或標(biāo)配產(chǎn)生在大多數(shù)道路車輛上，是對于 esc 鍵的系統(tǒng)，是由于大量減少價格的汽車電子產(chǎn)品多年來的基礎(chǔ)。
現(xiàn)代電子穩(wěn)定控制 （ESC 或 ESP） 系統(tǒng)是 ABS 概念的演變。在這里，將至少兩個額外的傳感器的添加來幫助系統(tǒng)工作： 這些是方向盤角度傳感器和陀螺儀的傳感器。操作理論很簡單： 當(dāng)陀螺傳感器檢測與方向盤傳感器的報(bào)告和這輛車所采取的方向不一致，ESC 軟件將控制至少三個輪剎車。方向盤傳感器還可以幫助操作的彎道制動控制 (CBC) ，因?yàn)檫@會告訴 ABS 的輪子上曲線的內(nèi)部應(yīng)該剎車還是輪子的外面，以及如何通過更多。
ABS 設(shè)備還可用于對車輛的加速實(shí)施牽引力控制系統(tǒng) (TCS)。如果加速時, 輪胎失去牽引，ABS 控制器可以檢測情況，并采取適當(dāng)行動，以便重新恢復(fù)其牽引。更復(fù)雜的版本，這還可以同時控制調(diào)節(jié)級別和剎車。
在 1989 年斯巴魯遺產(chǎn)的介紹中，斯巴魯網(wǎng)絡(luò)具有全輪驅(qū)動系統(tǒng)的四個通道防抱死剎車功能，這樣，如果汽車檢測到任何輪開始鎖定，自動變速器的車輛上安裝的所有車輪驅(qū)動系統(tǒng)會都進(jìn)行，確保所有車輪的可變協(xié)助防抱死系統(tǒng)試圖把車停下。
3、組件
ABS 有四個主要組成部分： 速度傳感器、 閥門、 泵、 和一個控制器。
速度傳感器
防抱死制動系統(tǒng)需要一些方法來了解當(dāng)輪時鎖定。速度傳感器，，位于每個車輪，或在某些情況下，提供車輪信息。
閥門
每個制動控制的 ABS 剎車中都有一個閥。在某些系統(tǒng)上，閥門具有三個位職：在第一個位置，閥門處于打開狀態(tài) ；從主缸壓力傳遞到剎車。在第兩個位置，閥門阻止線，該制動從主缸隔離。這可以防止壓力進(jìn)一步上升使驅(qū)動程序推制動踏板更難。在第三個位置上，剎車壓力從閥門的部分釋放。
泵
由于閥門是能夠釋放壓力，從踩剎車，必須有辦法使這種壓力回去。這是什么呢，泵 ；當(dāng)閥減少了在一線的壓力，泵是有辦法讓壓力減小的。
控制器
控制器是在車?yán)铮瑥拿總€個體的輪速傳感器接收信息，反過來如果輪失去牽引信號發(fā)送到控制器，控制器然后將限制動力 (EBD)，并使激活的驅(qū)動制動閥門打開和關(guān)閉。
4、應(yīng)用
ABS 有很多不同的變化和使用的控制算法，一種更簡單的系統(tǒng)工作原理如下：
（1）控制器時刻監(jiān)視速度傳感器。它在尋找在車輪的胎心。右前向上的車輪鎖，它會經(jīng)歷迅速減速。如果不加以控制，車輪會比任何一輛小汽車快得多。這可能需要一輛車五秒從 60 英里 (96.6 公里/小時）停止，在理想情況下，鎖定的車輪可以在不到一秒停止旋轉(zhuǎn)。
（2）ABS 控制器知道迅速的減速是不可能的，因此它減少了壓力制動，直到它看到加速，然后它增加壓力，直到它看到再次的減速。它可以這樣做的非?？?，實(shí)際上前輪胎可以大大改變速度。結(jié)果是的輪胎速度減慢，保持非常近的點(diǎn)，他們將開始鎖定輪胎剎車。這使系統(tǒng)有最大制動功率。
（3）ABS 系統(tǒng)操作時，驅(qū)動程序會覺得脈沖在制動踏板 ；這是來自快速打開和關(guān)閉的閥門。這個脈沖還告訴司機(jī)引發(fā)了 ABS。一些 ABS 系統(tǒng)可以每秒 16 次達(dá)循環(huán)。
5、Brake 類型
-Anti-lock 制動系統(tǒng)使用中使用不同的方案，取決于剎車的類型。他們可以用頻道數(shù)區(qū)分： 即，單獨(dú)控制閥門的多少和速度傳感器的數(shù)量。
四通道、 四傳感器 ABS
這是最佳方案。有對所有四個輪子單獨(dú)的閥門和所有輪子的轉(zhuǎn)速傳感器。在此設(shè)置，控制器監(jiān)視每個車輪單獨(dú)以確保它實(shí)現(xiàn)最大的制動力。
三通道、 四傳感器 ABS
有對所有四個輪子和單獨(dú)的前輪，每個閥但只有一個閥兩個后輪的轉(zhuǎn)速傳感器。
三通道、 三個傳感器 ABS
這項(xiàng)計(jì)劃，常見的卡車與四輪 ABS、 前輪有一個閥門和一個傳感器，兩個后輪的每個都有速度傳感器和閥門。后輪的轉(zhuǎn)速傳感器位于后橋。此系統(tǒng)提供了單個控件的鼓輪，因此他們都可以實(shí)現(xiàn)最大的制動力。，然而，一起監(jiān)視后輪 ；他們在開始鎖定之前 ABS 將背面激活。這種制度下，有可能后輪在鎖定期間停止、 減少制動效能。這個系統(tǒng)是易于識別，沒有個別的速度傳感器的后輪。
單通道、 一個傳感器 ABS
這個系統(tǒng)是常見后輪 abs 的卡車上。它有一個閥門，控制后輪和一個速度傳感器，位于后橋。此系統(tǒng)的操作與三通道系統(tǒng)的后端一樣。后輪一起進(jìn)行監(jiān)視。此系統(tǒng)中后輪的其中一個將被鎖定，減少制動效能。這個系統(tǒng)也很容易識別，沒有任何的輪子的有個別速度傳感器。
6、有效性
2003 澳大利亞莫納什大學(xué)事故研究中心發(fā)現(xiàn)，使用ABS：車輛崩潰的風(fēng)險降低 18%，減少了 35%的道路碰撞的風(fēng)險。
如瀝青或混凝土、 高牽引表面上很多 （盡管不是所有） abs 車都能夠更好地實(shí)現(xiàn)制動距離 較短，而 ABS 的好處不可能輕易地講完。在現(xiàn)實(shí)世界的條件甚至警報(bào)，熟練的驅(qū)動程序，在ABS 上不會發(fā)覺很難，還可通過閾值制動，匹配或改善性能的典型驅(qū)動程序與現(xiàn)代的 abs 的車輛技術(shù)的使用。 減少ABS崩潰的機(jī)會或減少影響的嚴(yán)重程度。使用Abs 的車，在典型的全制動緊急非專家驅(qū)動程序的推薦的技術(shù)是盡可能堅(jiān)定地踩下制動踏板，并在適當(dāng)、 規(guī)避障礙物有明顯作用。在這種情況下，ABS 將大大減少打滑的可能性，導(dǎo)致隨后失去控制。
在砂礫砂和深雪、 ABS 往往增加剎車距離。在砂礫砂和深雪、 ABS 往往增加剎車距離。ABS 防止這發(fā)生。一些 ABS 校正減緩循環(huán)的時間，因此，讓車輪一再簡要地鎖定和解鎖減少此類問題。一些汽車制造商提供"越野"按鈕關(guān)閉 ABS 功能。ABS 這種表面上的主要好處是增加保持對汽車的控制，而不是走進(jìn)打滑，驅(qū)動程序的能力，盡管失去控制還是更有可能像礫石軟表面或滑面像雪或冰上。例如冰或砂石非常光滑的表面，它是可以鎖定多個輪子一次，和這能打敗 ABS （這依賴比較所有的四個輪子和個別車輪打滑檢測）。ABS 可用性可以減輕大多數(shù)驅(qū)動程序從學(xué)習(xí)閾值制動。
1999 年 6 月國家公路交通安全管理 (NHTSA) 研究發(fā)現(xiàn) ABS 22%的平均增長松散的砂礫上停車距離。根據(jù) NHTSA，"ABS 工程與您定期的制動系統(tǒng)的自動抽他們。在沒有配備 ABS 的車輛，驅(qū)動程序必須手動泵以防止機(jī)輪抱死剎車。配備 ABS 的車輛，在你的腳下應(yīng)保持堅(jiān)定地制動踏板，同時 ABS 泵，以便您可以集中精力轉(zhuǎn)向安全剎車踏板。"
激活時，某些較早的 ABS 系統(tǒng)引起的明顯脈沖制動踏板。大多數(shù)驅(qū)動程序很少或從不剎車硬懶得看汽車的使用手冊，從而導(dǎo)致制動鎖定，并不是所有的驅(qū)動程序，這可能未被發(fā)現(xiàn)之前緊急情況。一些制造商制動輔助系統(tǒng)，用于確定驅(qū)動程序正試圖"恐慌站"，（通過檢測制動踏板消沉得非常快，與不同的正常停止，凡踏板的壓力將通常逐漸增加，因此，我們實(shí)施加速器的速率監(jiān)視另外一些系統(tǒng)發(fā)布了），系統(tǒng)將自動增加制動力，其中應(yīng)用沒有足夠的壓力。硬或恐慌制動在崎嶇不平的表面，因?yàn)橥箟K的造成，變成一個古怪的 wheel(s) 的速度也可能觸發(fā) ABS。不過，ABS 顯著提高了安全和控制在最道路情況下的驅(qū)動程序。
防抱死剎車是圍繞風(fēng)險補(bǔ)償理論，通過駕駛更積極地適應(yīng) ABS 的安全利益，驅(qū)動程序的一些實(shí)驗(yàn)的主題。在慕尼黑的研究中，半數(shù)的士車配備了防抱死剎車，而另一半則為常規(guī)制動系統(tǒng)。失事率是大致相同的兩種類型，和王爾德得出結(jié)論，這是由于 abs 出租車承擔(dān)更多的風(fēng)險，假設(shè) ABS驅(qū)動程序會照顧他們，而非 ABS 司機(jī)開車更仔細(xì)，在ABS 不會有幫助的情況下，同樣會處在一個危險的境地。類似的研究是在奧斯陸進(jìn)行的結(jié)果。
Anti-lock braking system
From Wikipedia, the free encyclopedia
An anti-lock braking system (ABS) is a safety system that allows the wheels on a motor vehicle to continue interacting tractively with the road surface as directed by driver steering inputs while braking, preventing the wheels from locking up (that is, ceasing rotation) and therefore avoiding skidding.
An ABS generally offers improved vehicle control and decreases stopping distances on dry and slippery surfaces for many drivers; however, on loose surfaces like gravel or snow-covered pavement, an ABS can significantly increase braking distance, although still improving vehicle control。
Since initial widespread use in production cars, anti-lock braking systems have evolved considerably. Recent versions not only prevent wheel lock under braking, but also electronically control the front-to-rear brake bias. This function, depending on its specific capabilities and implementation, is known as electronic brakeforce distribution (EBD), traction control system, emergency brake assist, or electronic stability control (ESC).
1、History
Early systems
The ABS was first developed for aircraft use in 1929 by the French automobile and aircraft pioneer, Gabriel Voisin, as threshold braking on airplanes is nearly impossible. These systems use a flywheel and valve attached to a hydraulic line that feeds the brake cylinders. The flywheel is attached to a drum that runs at the same speed as the wheel. In normal braking, the drum and flywheel should spin at the same speed. However, if a wheel were to slow down, then the drum would do the same, leaving the flywheel spinning at a faster rate. This causes the valve to open, allowing a small amount of brake fluid to bypass the master cylinder into a local reservoir, lowering the pressure on the cylinder and releasing the brakes. The use of the drum and flywheel meant the valve only opened when the wheel was turning. In testing, a 30% improvement in braking performance was noted, because the pilots immediately applied full brakes instead of slowly increasing pressure in order to find the skid point. An additional benefit was the elimination of burned or burst tires. (This citation has no mention of Gabriel Voisin, who was not involved in aviation at the time; neither are there patents to substantiate this claim)
In 1958, a Royal Enfield Super Meteor motorcycle was used by the Road Research Laboratory to test the Maxaret anti-lock brake.[3] The experiments demonstrated that anti-lock brakes can be of great value to motorcycles, for which skidding is involved in a high proportion of accidents. Stopping distances were reduced in most of the tests compared with locked wheel braking, particularly on slippery surfaces, in which the improvement could be as much as 30 percent. Enfield's technical director at the time, Tony Wilson-Jones, saw little future in the system, however, and it was not put into production by the company.A fully mechanical system saw limited automobile use in the 1960s in the Ferguson P99 racing car, the Jensen FF, and the experimental all wheel drive Ford Zodiac, but saw no further use; the system proved expensive and unreliable.
Modern systems
Chrysler, together with the Bendix Corporation, introduced a computerized, three-channel, four-sensor all-wheel ABS called "Sure Brake" for its 1971 Imperial.It was available for several years thereafter, functioned as intended, and proved reliable. In 1970, Ford added a antilock braking system called "Sure-track" to the rear wheels of Lincoln Continentals as an option; it became standard in 1971. In 1971, General Motors introduced the "Trackmaster" rear-wheel onlyABS as an option on their rear-wheel drive Cadillac models and the OldsmobileToronado.In the same year, Nissan offered an EAL (Electro Anti-lock System) as an option on the Nissan President, which became Japan's first electronic ABS.
ABS brakes on a BMW motorcycle
In 1972, four wheel drive Triumph 2500 Estates were fitted with Mullard electronic systems as standard. Such cars were very rare however and very few survive today.
In 1985 the Ford Scorpio was introduced to European market with a Bosch electronic system throughout the range as standard. For this the model was awarded the coveted European Car of the Year Award in 1986, with very favourable praise from motoring journalists. After this success Ford began research into Anti-Lock systems for the rest of their range, which encouraged other manufacturers to follow suit.
In 1988, BMW introduced the first motorcycle with an electronic-hydraulic ABS: the BMW K100. Honda followed suit in 1992 with the launch of its first motorcycle ABS on the ST1100 Pan European. In 2007, Suzuki launched its GSF1200SA (Bandit) with an ABS. In 2005, Harley-Davidson began offering ABS as an option for police bikes.
2、Operation
The anti-lock brake controller is also known as the CAB (Controller Anti-lock Brake).
A typical ABS includes a central electronic control unit (ECU), four wheel speed sensors, and at least two hydraulic valves within the brake hydraulics. The ECU constantly monitors the rotational speed of each wheel; if it detects a wheel rotating significantly slower than the others, a condition indicative of impending wheel lock, it actuates the valves to reduce hydraulic pressure to the brake at the affected wheel, thus reducing the braking force on that wheel; the wheel then turns faster. Conversely, if the ECU detects a wheel turning significantly faster than the others, brake hydraulic pressure to the wheel is increased so the braking force is reapplied, slowing down the wheel. This process is repeated continuously and can be detected by the driver via brake pedal pulsation. Some anti-lock systems can apply or release braking pressure 15 times per second.
The ECU is programmed to disregard differences in wheel rotative speed below a critical threshold, because when the car is turning, the two wheels towards the center of the curve turn slower than the outer two. For this same reason, a differential is used in virtually all roadgoing vehicles.
If a fault develops in any part of the ABS, a warning light will usually be illuminated on the vehicle instrument panel, and the ABS will be disabled until the fault is rectified.
The modern ABS applies individual brake pressure to all four wheels through a control system of hub-mounted sensors and a dedicated micro-controller. ABS is offered or comes standard on most road vehicles produced today and is the foundation for ESC systems, which are rapidly increasing in popularity due to the vast reduction in price of vehicle electronics over the years.
Modern electronic stability control (ESC or ESP) systems are an evolution of the ABS concept. Here, a minimum of two additional sensors are added to help the system work: these are a steering wheel angle sensor, and a gyroscopic sensor. The theory of operation is simple: when the gyroscopic sensor detects that the direction taken by the car does not coincide with what the steering wheel sensor reports, the ESC software will brake the necessary individual wheel(s) (up to three with the most sophisticated systems), so that the vehicle goes the way the driver intends. The steering wheel sensor also helps in the operation of Cornering Brake Control (CBC), since this will tell the ABS that wheels on the inside of the curve should brake more than wheels on the outside, and by how much.
The ABS equipment may also be used to implement a traction control system (TCS) on acceleration of the vehicle. If, when accelerating, the tire loses traction, the ABS controller can detect the situation and take suitable action so that traction is regained. More sophisticated versions of this can also control throttle levels and brakes simultaneously.
Upon the introduction of the Subaru Legacy in 1989, Subaru networked the four channel anti-lock brake function with the all wheel drive system so that if the car detected any wheel beginning to lock up, the variable assist all wheel drive system installed on vehicles with the automatic transmission would engage to ensure all wheels were actively gripping while the anti-lock system was attempting to stop the car.
3、Components
There are four main components to an ABS: speed sensors, valves, a pump, and a controller. -
Speed sensors
The anti-lock braking system needs some way of knowing when a wheel is about to lock up. The speed sensors, which are located at each wheel, or in some cases in the differential, provide this information.
Valves
There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions:
· In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.
· In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder.
· In position three, the valve releases some of the pressure from the brake.
Pump
Since the valve is able to release pressure from the brakes, there has to be some way to put that pressure back. That is what the pump does; when a valve reduces the pressure in a line, the pump is there to get the pressure back up.
Controller
The controller is an ECU type unit in the car which receives information from each individual wheel speed sensor, in turn if a wheel loses traction the signal is sent to the controller, the controller will then limit the brakeforce (EBD) and activate the ABS modulator which actuates the braking valves on and off.
4、Use
There are many different variations and control algorithms for use in an ABS. One of the simpler systems works as follows:
1 The controller monitors the speed sensors at all times. It is looking for decelerations in the wheel that are out of the ordinary. Right before a wheel locks up, it will experience a rapid deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It might take a car five seconds to stop from 60 mph (96.6 km/h) under ideal conditions, but a wheel that locks up could stop spinning in less than a second.
2 The ABS controller knows that such a rapid deceleration is impossible, so it reduces the pressure to that brake until it sees an acceleration, then it increases the pressure until it sees the deceleration again. It can do this very quickly, before the tire can actually significantly change speed. The result is that the tire slows down at the same rate as the car, with the brakes keeping the tires very near the point at which they will start to lock up. This gives the system maximum braking power.
3 When the ABS system is in operation the driver will feel a pulsing in the brake pedal; this comes from the rapid opening and closing of the valves. This pulsing also tells the driver that the ABS has been triggered. Some ABS systems can cycle up to 16 times per second.
5、Brake types
-Anti-lock braking systems use different schemes depending on the type of brakes in use. They can be differentiated by the number of channels: that is, how many valves that are individually controlled—and the number of speed sensors.
Four-channel, four-sensor ABS
This is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.
Three-channel, four-sensor ABS
There is a speed sensor on all four wheels and a separate valve for each of the front wheels, but only one valve for both of the rear wheels.
Three-channel, three-sensor ABS
This scheme, commonly found on pickup trucks with four-wheel ABS, has a speed sensor and a valve for each of the front wheels, with one valve and one sensor for both rear wheels. The speed sensor for the rear wheels is located in the rear axle. This sys-tem provides individual control of the front wheels, so they can both achieve maximum braking force. The rear wheels, however, are monitored together; they both have to start to lock up before the ABS will activate on the rear. With this system, it is possible that one of the rear wheels will lock during a stop, reducing brake effectiveness. This system is easy to identify, as there are no individual speed sensors for the rear wheels.
One-channel, one-sensor ABS
This system is commonly found on pickup trucks with rear-wheel ABS. It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle. This system operates the same as the rear end of a three-channel system. The rear wheels are monitored together and they both have to start to lock up before the ABS kicks in. In this system it is also possible that one of the rear wheels will lock, reducing brake effectiveness. This system is also easy to identify, as there are no individual speed sensors for any of the wheels
6、Effectiveness
A 2003 Australian study by Monash University Accident Research Centre found that ABS:
· Reduced the risk of multiple vehicle crashes by 18 percent,
· Reduced the risk of run-off-road crashes by 35 percent.
On high-traction surfaces such as bitumen, or concrete, many (though not all) ABS-equipped cars are able to attain braking distances better (i.e. shorter) than those that would be easily possible without the benefit of ABS. In real world conditions even an alert, skilled driver without ABS would find it difficult, even through the use of techniques like threshold braking, to match or improve on the performance of a typical driver with a modern ABS-equipped vehicle. ABS reduces chances of crashing, and/or the severity of impact. The recommended technique for non-expert drivers in an ABS-equipped car, in a typical full-braking emergency, is to press the brake pedal as firmly as possible and, where appropriate, to steer around obstructions. In such situations, ABS will significantly reduce the chances of a skid and subsequent loss of control.
In gravel, sand and deep snow, ABS tends to increase braking distances. On these surfaces, locked wheels dig in and stop the vehicle more quickly. ABS prevents this from occurring. Some ABS calibrations reduce this problem by slowing the cycling time, thus letting the wheels repeatedly briefly lock and unlock. Some vehicle manufacturers provide an "off-road" button to turn ABS function off. The primary benefit of ABS on such surfaces is to increase the ability of the driver to maintain control of the car rather than go into a skid, though loss of control remains more likely on soft surfaces like gravel or slippery surfaces like snow or ice. On a very slippery surface such as sheet ice or gravel, it is possible to l