汽車電動(dòng)轉(zhuǎn)向器動(dòng)力學(xué)建模與控制仿真研究,汽車,電動(dòng),轉(zhuǎn)向器,動(dòng)力學(xué),建模,控制,節(jié)制,仿真,研究,鉆研 Ks=115; Rs=0.0078; G=7.225; Jm=0.0004704; Km=125; bm=0.003399; KT=91859; br=653; m=32; Jh=0.0459; bh=0.361; >> Ke=0.04; >> R=0.1; >> L=0.00015; >> Td=10; >> Kp=0.1; >> N=10; >> Kv=0.02; 中文譯文 汽車電動(dòng)助力轉(zhuǎn)向系統(tǒng)的研究 隨著汽車電子技術(shù)的迅猛發(fā)展,人們對汽車轉(zhuǎn)向操縱性能的要求也日益提高。汽車轉(zhuǎn)向系統(tǒng)已從傳統(tǒng)機(jī)械轉(zhuǎn)向、液壓助力轉(zhuǎn)向(Hydraulic Power Steering ,簡稱HPS) 電控液壓助力轉(zhuǎn)向( Electric Hydraulic Power Steering , 簡稱EHPS) , 發(fā)展到電動(dòng)助力轉(zhuǎn)向系統(tǒng)(Electric Power Steering ,簡稱EPS) ,最終還將過渡到線控轉(zhuǎn)向系統(tǒng)(Steer By Wire ,簡稱SBW)。 機(jī)械轉(zhuǎn)向系統(tǒng)是指以駕駛員的體力作為轉(zhuǎn)向能源,其中所有傳力件都是機(jī)械的,汽車的轉(zhuǎn)向運(yùn)動(dòng)是由駕駛員操縱方向盤,通過轉(zhuǎn)向器和一系列的桿件傳遞到轉(zhuǎn)向車輪而實(shí)現(xiàn)的。機(jī)械轉(zhuǎn)向系由轉(zhuǎn)向操縱機(jī)構(gòu)、轉(zhuǎn)向器和轉(zhuǎn)向傳動(dòng)機(jī)械3大部分組成。 通常根據(jù)機(jī)械式轉(zhuǎn)向器形式可以分為:齒輪齒條式、循環(huán)球式、蝸桿滾輪式、蝸桿指銷式。應(yīng)用最廣的兩種是齒輪齒條式和循環(huán)球式(用于需要較大的轉(zhuǎn)向力時(shí)) 。在循環(huán)球式轉(zhuǎn)向器中,輸入轉(zhuǎn)向圈與輸出的轉(zhuǎn)向搖臂擺角是成正比的;在齒輪齒條式轉(zhuǎn)向器中,輸入轉(zhuǎn)向圈數(shù)與輸出的齒條位移是成正比的。循環(huán)球式轉(zhuǎn)向器由于是滾動(dòng)摩擦形式,因而正傳動(dòng)效率很高,操作方便且使用壽命長,而且承載能力強(qiáng),故廣泛應(yīng)用于載貨汽車上。齒輪齒條式轉(zhuǎn)向器與循環(huán)球式相比,最大特點(diǎn)是剛性大,結(jié)構(gòu)緊湊重量輕,且成本低。由于這種方式容易由車輪將反作用力傳至轉(zhuǎn)向盤,所以具有對路面狀態(tài)反應(yīng)靈敏的優(yōu)點(diǎn),但同時(shí)也容易產(chǎn)生打手和擺振等現(xiàn)象,且其承載效率相對較弱,故主要應(yīng)用于小汽車及輕型貨車上,目前大部分低端轎車采用的就是齒輪齒條式機(jī)械轉(zhuǎn)向系統(tǒng)。 隨著車輛載重的增加以及人們對車輛操縱性能要求的提高,簡單的機(jī)械式轉(zhuǎn)向系統(tǒng)已經(jīng)無法滿足需要,動(dòng)力轉(zhuǎn)向系統(tǒng)應(yīng)運(yùn)而生,它能在駕駛員轉(zhuǎn)動(dòng)方向盤的同時(shí)提供助力,動(dòng)力轉(zhuǎn)向系統(tǒng)分為液壓轉(zhuǎn)向系統(tǒng)和電動(dòng)轉(zhuǎn)向系統(tǒng)2種。其中液壓轉(zhuǎn)向系統(tǒng)是目前使用最為廣泛的轉(zhuǎn)向系統(tǒng)。 液壓轉(zhuǎn)向系統(tǒng)在機(jī)械系統(tǒng)的基礎(chǔ)上增加了液壓系統(tǒng),包括液壓泵、V 形帶輪、油管、供油裝置、助力裝置和控制閥。它借助于汽車發(fā)動(dòng)機(jī)的動(dòng)力驅(qū)動(dòng)液壓泵、空氣壓縮機(jī)和發(fā)電機(jī)等,以液力、氣力或電力增大駕駛員操縱前輪轉(zhuǎn)向的力量,使駕駛員可以輕便靈活地操縱汽車轉(zhuǎn)向,減輕了勞動(dòng)強(qiáng)度,提高了行駛安全性。 液壓助力轉(zhuǎn)向系統(tǒng)從發(fā)明到現(xiàn)在已經(jīng)有了大約半個(gè)世紀(jì)的歷史,可以說是一種較為完善的系統(tǒng),由于其工作可靠、技術(shù)成熟至今仍被廣泛應(yīng)用。它由液壓泵作為動(dòng)力源,經(jīng)油管道控制閥向動(dòng)力液壓缸供油,通過活塞桿帶動(dòng)轉(zhuǎn)向機(jī)構(gòu)動(dòng)作,可通過改變缸徑及油壓的大小來改變助力的大小,由此達(dá)到轉(zhuǎn)向助力的作用。傳統(tǒng)液壓式動(dòng)力轉(zhuǎn)向系統(tǒng)一般按液流的形式可以分為:常流式和常壓式2 種類型,也可根據(jù)控制閥形式分為轉(zhuǎn)閥式和滑閥式。 隨著液壓動(dòng)力轉(zhuǎn)向系統(tǒng)在汽車上的日益普及,人們對操作時(shí)的輕便性和路感的要求也日益提高,然而液壓動(dòng)力轉(zhuǎn)向系統(tǒng)卻存在許多的缺點(diǎn): ①由于其本身的結(jié)構(gòu)決定了其無法保證車輛在任何工況下轉(zhuǎn)動(dòng)轉(zhuǎn)向盤時(shí),都有較理想的操縱穩(wěn)定性,即無法同時(shí)保證低速時(shí)的轉(zhuǎn)向輕便性和高速時(shí)的操縱穩(wěn)定性; ②汽車的轉(zhuǎn)向特性受駕駛員駕駛技術(shù)的影響嚴(yán)重; ③轉(zhuǎn)向傳動(dòng)比固定,使汽車轉(zhuǎn)向響應(yīng)特性隨車速、側(cè)向加速度等變化而變化,駕駛員必須提前針對汽車轉(zhuǎn)向特性幅值和相位的變化進(jìn)行一定的操作補(bǔ)償,從而控制汽車按其意愿行駛。這樣增加了駕駛員的操縱負(fù)擔(dān),也使汽車轉(zhuǎn)向行駛中存在不安全隱患;而此后出現(xiàn)了電控液壓助力系統(tǒng),它在傳統(tǒng)的液壓動(dòng)力轉(zhuǎn)向系統(tǒng)的基礎(chǔ)上增加速度傳感器,使汽車能夠隨著車速的變化自動(dòng)調(diào)節(jié)操縱力的大小,在一定程度上緩和了傳統(tǒng)的液壓轉(zhuǎn)向系統(tǒng)存在的問題。 目前我國生產(chǎn)的商用車和轎車上采用的大多是電控液壓助力轉(zhuǎn)向系統(tǒng),它是比較成熟和應(yīng)用廣泛的轉(zhuǎn)向系統(tǒng)。盡管電控液壓助力裝置從一定程度上緩解了傳統(tǒng)的液壓轉(zhuǎn)向中輕便性和路感之間的矛盾,然而它還是沒有從根本上解決HPS 系統(tǒng)存在的不足,隨著汽車微電子技術(shù)的發(fā)展,汽車燃油節(jié)能的要求以及全球性倡導(dǎo)環(huán)保,其在布置、安裝、密封性、操縱靈敏度、能量消耗、磨損與噪聲等方面的不足已越來越明顯,轉(zhuǎn)向系統(tǒng)向著電動(dòng)助力轉(zhuǎn)向系統(tǒng)發(fā)展。 電動(dòng)助力轉(zhuǎn)向系統(tǒng)是現(xiàn)在汽車轉(zhuǎn)向系統(tǒng)的發(fā)展方向,其工作原理是:EPS 系統(tǒng)的ECU 對來自轉(zhuǎn)向盤轉(zhuǎn)矩傳感器和車速傳感器的信號進(jìn)行分析處理后,控制電機(jī)產(chǎn)生適當(dāng)?shù)闹D(zhuǎn)矩,協(xié)助駕駛員完成轉(zhuǎn)向操作。近幾年來,隨著電子技術(shù)的發(fā)展,大幅度降低EPS的成本已成為可能,日本的大發(fā)汽車公司、三菱汽車公司、本田汽車公司、美國的Delphi 汽車系統(tǒng)公司、TRW公司及德國的ZF 公司都相繼研制出EPS。Mercedes2Benz 和Siemens Automotive 兩大公司共同投資6500萬英鎊用于開發(fā)EPS ,目標(biāo)是到2002 年裝車,年產(chǎn)300 萬套,成為全球EPS 制造商。到目前為止,EPS 系統(tǒng)在輕微型轎車、廂式車上得到廣泛的應(yīng)用,并且每年以300 萬臺的速度發(fā)展。 .轉(zhuǎn)向是一個(gè)專業(yè)術(shù)語,適用于采集部件,聯(lián)系等,其中允許一艘(艦船)或汽車(轎車)按照預(yù)期的方向行駛. 一個(gè)例外的情況是鐵路運(yùn)輸由路軌組合在一起鐵路道岔提供轉(zhuǎn)向功能。 許多現(xiàn)代轎車使用齒輪齒條式轉(zhuǎn)向器,在方向盤末端有轉(zhuǎn)動(dòng)齒輪;該齒輪帶動(dòng)齒條移動(dòng),它是一種線性的齒輪緊密配合,從一邊到一邊。這種運(yùn)動(dòng)把轉(zhuǎn)矩通過轉(zhuǎn)向橫拉桿和一種叫做轉(zhuǎn)向節(jié)臂的短形臂傳遞給轉(zhuǎn)向輪的主銷。 以前的設(shè)計(jì)往往采用循環(huán)球式轉(zhuǎn)向器,而這種轉(zhuǎn)向器仍然應(yīng)用在卡車和多用途車輛。這是一種老式的螺母和齒扇設(shè)計(jì)，該轉(zhuǎn)向管柱轉(zhuǎn)動(dòng)大螺絲("蝸輪"),它與一個(gè)齒扇齒輪嚙合,當(dāng)蝸輪轉(zhuǎn)動(dòng)時(shí)，齒扇也隨之轉(zhuǎn)動(dòng)，一個(gè)安裝在齒扇軸上且與轉(zhuǎn)向聯(lián)動(dòng)有關(guān)的搖臂帶動(dòng)轉(zhuǎn)向節(jié)臂 ,從而使車輪轉(zhuǎn)動(dòng). 循環(huán)球式轉(zhuǎn)向器通過安裝滾珠減少螺母和螺桿之間的摩擦;兩根導(dǎo)管和螺母內(nèi)的螺旋管狀通道組合成兩條各自獨(dú)立的封閉的鋼球“流到”。 齒輪齒條式轉(zhuǎn)向器設(shè)計(jì)具有很大程度的反饋和直接轉(zhuǎn)向"路感";它也通常不會(huì)有任何反彈,或呆滯。缺點(diǎn)是,它是不可調(diào)的,因此當(dāng)它磨損唯一的解決辦法更換。 循環(huán)球式轉(zhuǎn)向器的優(yōu)點(diǎn)是機(jī)械優(yōu)勢,因此,它被使用在較大較重的車輛,而齒輪齒條式原本僅限于較小和較輕;由于幾乎普遍采用動(dòng)力轉(zhuǎn)向系統(tǒng),不過,這已不再是一個(gè)重要的優(yōu)勢,導(dǎo)致越來越多地在新型汽車應(yīng)用齒輪齒條式轉(zhuǎn)向器。 循環(huán)球式轉(zhuǎn)向器設(shè)計(jì)在中心也有明顯的沖擊,或"死點(diǎn)"。凡一分鐘交替方向盤出不來并不移動(dòng)轉(zhuǎn)向機(jī)構(gòu);這是很容易可調(diào)螺桿的端部來減少磨損,但它并不能完全消除或機(jī)制開始磨損很快。 這項(xiàng)設(shè)計(jì)目前仍在使用中,在卡車和其他大型車輛,也應(yīng)用于迅速轉(zhuǎn)向,路感與穩(wěn)健性,可維護(hù)性,和機(jī)械的優(yōu)勢相比不太重要的場合。 較小程度的反饋,這樣的設(shè)計(jì)也有時(shí)是一種優(yōu)點(diǎn);當(dāng)前輪碰撞時(shí)，使用齒輪齒條轉(zhuǎn)向的司機(jī)只有自己的大拇指受傷,造成方向盤揭開一邊突然(因?yàn)轳{駛教練告訴學(xué)生把自己的大拇指在前面的方向盤,而非放在左右的內(nèi)邊緣).這種效果在像卡車一樣的重型汽車更為明顯;循環(huán)球式轉(zhuǎn)向防止這種程度的反饋,只是因?yàn)樗梢栽谡Ｇ闆r下防止可取反饋。 轉(zhuǎn)向連鎖連接轉(zhuǎn)向器和車輪通常符合一個(gè)阿克曼轉(zhuǎn)向幾何的變化,它交代了一個(gè)事實(shí):當(dāng)轉(zhuǎn)向是,內(nèi)輪轉(zhuǎn)過的半徑比外輪小得多，因此適合駕駛的直路,是不適合曲折。 由于車輛已成為較重而改用前輪驅(qū)動(dòng),為了扭轉(zhuǎn)方向盤，通常的,主要的是體力。為了解決這一問題,汽車業(yè)發(fā)展的動(dòng)力轉(zhuǎn)向系統(tǒng)。 有兩種類型的助力轉(zhuǎn)向系統(tǒng)-液壓和電氣/電子。 T還有一種液壓-電動(dòng)混合系統(tǒng)。 液壓助力轉(zhuǎn)向系統(tǒng)(hps)利用油壓供應(yīng)的一個(gè)發(fā)動(dòng)機(jī)驅(qū)動(dòng)泵,以協(xié)助將方向盤轉(zhuǎn)轉(zhuǎn)動(dòng)。 電動(dòng)助力轉(zhuǎn)向系統(tǒng)(EPS)方式,是較有效率的液壓助力轉(zhuǎn)向系統(tǒng),由于電動(dòng)助力轉(zhuǎn)向汽車只需要提供協(xié)助時(shí),方向盤被轉(zhuǎn)動(dòng),而液壓泵必須不斷運(yùn)行。 在EPS的幫助下是很容易調(diào)節(jié)車型,最高車速,甚至駕駛的喜好。 另外一個(gè)好處是,通過泄漏和處置動(dòng)力轉(zhuǎn)向液消除對環(huán)境構(gòu)成危險(xiǎn) 。 A動(dòng)力轉(zhuǎn)向的分支是速度可調(diào)轉(zhuǎn)向而轉(zhuǎn)向是大量輔助以低速行駛,稍微協(xié)助高速。 汽車制造商認(rèn)為,當(dāng)要停車時(shí)駕駛?cè)丝赡苄枰龀龃罅哭D(zhuǎn)向投入，但當(dāng)時(shí)高速行駛時(shí)則不然。第一輛有這特點(diǎn)的汽車,是雪鐵龍與其diravi，雖然改變了現(xiàn)代汽車轉(zhuǎn)向系統(tǒng)資金的投入，但它改變了定心凸輪的壓力，使得方向盤盡力去回到原來的位置?，F(xiàn)代速度可調(diào)式動(dòng)力轉(zhuǎn)向系統(tǒng),當(dāng)速度增長時(shí)減少了活塞的壓力 ,給予更直接的感受。這一特點(diǎn)在所有新車正逐漸成為司空見慣。 四輪轉(zhuǎn)向(或全輪轉(zhuǎn)向)是一種系統(tǒng),當(dāng)高速行駛時(shí)能增加車輛穩(wěn)定型，而在低速行駛時(shí)可以減小轉(zhuǎn)彎半徑。 大多數(shù)的四輪轉(zhuǎn)向系統(tǒng),后輪轉(zhuǎn)向通過單片機(jī)和驅(qū)動(dòng)器實(shí)現(xiàn)。 后輪一般不能反過來,有幾個(gè)系統(tǒng),包括Delphi的quadrasteer，該系統(tǒng)在本田的生產(chǎn)前線，當(dāng)前輪低速時(shí)，允許后輪在相反方向轉(zhuǎn)向。這使得車輛轉(zhuǎn)彎半徑較小,有時(shí)應(yīng)用于大型卡車車輛及掛車。 電子動(dòng)力轉(zhuǎn)向系統(tǒng) 圖1 電子動(dòng)力轉(zhuǎn)向系統(tǒng)的工作原理 電子動(dòng)力轉(zhuǎn)向系統(tǒng)是通過一個(gè)電動(dòng)機(jī)來驅(qū)動(dòng)動(dòng)力方向盤液壓泵或直接驅(qū)動(dòng)轉(zhuǎn)向聯(lián)動(dòng)裝置。 電子動(dòng)力轉(zhuǎn)向的功能由于不依賴于發(fā)動(dòng)機(jī)轉(zhuǎn)速，所以能節(jié)省能源 電子動(dòng)力轉(zhuǎn)向系統(tǒng)是這樣運(yùn)行的 傳統(tǒng)的動(dòng)力方向盤系統(tǒng)使用一條引擎輔助傳送帶駕駛泵浦，提供操作在動(dòng)力方向盤齒輪或作動(dòng)器的一個(gè)活塞協(xié)助司機(jī)的被加壓的流體。在電動(dòng)液壓的指點(diǎn)，一個(gè)電子動(dòng)力方向盤概念使用一臺電動(dòng)機(jī)駕駛的一個(gè)高效率泵浦。 泵浦速度是由一個(gè)電控制器調(diào)控的變化泵浦壓力和流程，提供被剪裁的指點(diǎn)努力為不同的駕駛的情況。 泵浦可以跑在低速或關(guān)閉提供節(jié)能在大多時(shí)間在多數(shù)世界市場上)直向前的駕駛期間(直接電指點(diǎn)使用一臺電動(dòng)機(jī)附加指點(diǎn)機(jī)架通過齒輪機(jī)構(gòu)(沒有泵浦或流體)。 各種各樣的馬達(dá)類型和齒輪驅(qū)動(dòng)是可能的。 微處理器控制指點(diǎn)動(dòng)力學(xué)和司機(jī)努力。 輸入包括車速和指點(diǎn)、輪子扭矩，角位和轉(zhuǎn)動(dòng)率。 工作運(yùn)行時(shí)的具體細(xì)節(jié)： A “指點(diǎn)傳感器”位于它進(jìn)入傳動(dòng)箱住房的輸入軸。 指點(diǎn)傳感器實(shí)際上是在一個(gè)的二個(gè)傳感器： 那“扭矩的傳感器”轉(zhuǎn)換指點(diǎn)扭矩輸入和它的方向成電壓信號，并且那“自轉(zhuǎn)的傳感器”轉(zhuǎn)換轉(zhuǎn)動(dòng)速度和方向成電壓信號。 分享同一套住房的“接口”電路轉(zhuǎn)換從扭矩傳感器和自轉(zhuǎn)傳感器的信號成控制電子學(xué)可能處理的信號。從指點(diǎn)傳感器的輸入由那微處理器的控制單元消化也監(jiān)測從車速傳感器的輸入。 傳感器輸入然后被比較確定多少機(jī)械化根據(jù)一張被預(yù)編程序的“力量地圖”需要在控制單元的記憶。 控制單元然后派出適當(dāng)?shù)拿顚θ缓蠊┙o電動(dòng)機(jī)以潮流的“電源裝置”。 馬達(dá)推擠機(jī)架在右邊或左根據(jù)哪個(gè)方式電壓流動(dòng)(扭轉(zhuǎn)潮流扭轉(zhuǎn)方向馬達(dá)旋轉(zhuǎn))。 增加潮流對馬達(dá)增加功率協(xié)助。系統(tǒng)有三種操作方式： 左邊或右邊機(jī)械化提供以回應(yīng)從指點(diǎn)扭矩和自轉(zhuǎn)傳感器的輸入的輸入的“正?！笨刂品绞? 被用于在完成輪以后協(xié)助指點(diǎn)回歸的“回歸”控制方式; 并且改變與車速改進(jìn)路感受和挫傷傭金的“更加潮濕的”控制方式。如果方向盤被轉(zhuǎn)動(dòng)，并且舉行在充分鎖位置和指點(diǎn)協(xié)助到達(dá)最大值，控制單元使潮流降低到電動(dòng)機(jī)防止也許損壞馬達(dá)的超載情況。 控制單元也被設(shè)計(jì)保護(hù)馬達(dá)以防止電壓浪涌免受一個(gè)有毛病的交流發(fā)電機(jī)或充電的問題。 電子轉(zhuǎn)向控制單位有能力在自我診斷的缺點(diǎn)通過監(jiān)測系統(tǒng)輸入和產(chǎn)品和電動(dòng)機(jī)的激勵(lì)電流上。 如果問題發(fā)生，控制單元通過開動(dòng)在電源裝置的一個(gè)故障自動(dòng)保險(xiǎn)的中轉(zhuǎn)關(guān)閉系統(tǒng)。 這消滅所有機(jī)械化，造成系統(tǒng)恢復(fù)回到手工指點(diǎn)。 破折號EPS警告燈也被闡明警告司機(jī)。 要診斷問題，技術(shù)員跳服務(wù)檢查連接器的終端并且讀出問題代碼。 圖 2 電子動(dòng)力方向盤機(jī)制 當(dāng)前發(fā)明與提供的供給動(dòng)力的援助一電子功率驅(qū)動(dòng)器馬達(dá)關(guān)連給車操縱機(jī)構(gòu)。根據(jù)當(dāng)前發(fā)明的一個(gè)方面，那里為提供供給動(dòng)力的援助提供一個(gè)電子功率驅(qū)動(dòng)器機(jī)制給有車的操縱機(jī)構(gòu)一名手動(dòng)地可旋轉(zhuǎn)的成員為操作操縱機(jī)構(gòu)、傳動(dòng)機(jī)構(gòu)包括可行扭矩的傳感器感覺手動(dòng)地被申請于可旋轉(zhuǎn)的成員的扭矩，一個(gè)電子功率驅(qū)動(dòng)器馬達(dá)操縱著被連接到可旋轉(zhuǎn)的成員和安排控制主驅(qū)動(dòng)電動(dòng)機(jī)自轉(zhuǎn)速度和方向以回應(yīng)從扭矩傳感器收到的信號的控制器，扭矩傳感器包括為與可旋轉(zhuǎn)的成員的連接適應(yīng)的傳感器軸形成引伸因此，以便扭矩通過前述傳感器軸被傳送，當(dāng)時(shí) 可旋轉(zhuǎn)的成員被轉(zhuǎn)動(dòng)，并且應(yīng)變儀在導(dǎo)致的信號傳感器軸手動(dòng)地登上表示通過前述軸被傳送的相當(dāng)數(shù)量扭矩。 圖3 傳感器軸不旋轉(zhuǎn)更好地登上在一個(gè)軸向末端在第一名聯(lián)結(jié)成員和不旋轉(zhuǎn)地登上在它的相反軸向末端在第二名聯(lián)結(jié)成員，第一和第二名聯(lián)結(jié)成員相互允諾允許有限的自轉(zhuǎn)之間連接，以便在一個(gè)被預(yù)先決定的極限之下的扭矩由僅傳感器軸傳送，并且，以便在前述被預(yù)先決定的極限之上的扭矩通過第一和第二名聯(lián)結(jié)成員被傳送。 更適宜地安排第一和第二名聯(lián)結(jié)成員作為操縱的連接的第一和第二個(gè)部分的一座橋梁互相的旋轉(zhuǎn)式成員。合適的傳感器軸是通常在多數(shù)的長方形橫斷面它的長度中。應(yīng)變儀包括一個(gè)或更多的適應(yīng)地看見了諧振器綁到傳感器軸上。好的馬達(dá)操縱的被連接到可旋轉(zhuǎn)的成員通過傳動(dòng)器。馬達(dá)更好地包括一個(gè)工具箱和同心地被安排相對可旋轉(zhuǎn)的成員。當(dāng)前發(fā)明的Various方面此后將描述，關(guān)于伴隨的圖畫， ：圖1是一個(gè)車操縱機(jī)構(gòu)的一個(gè)圖表看法包括一個(gè)電子功率驅(qū)動(dòng)器機(jī)制根據(jù)當(dāng)前發(fā)明，圖 2是說明在圖顯示的傳動(dòng)機(jī)構(gòu)的各種各樣的組分的之間流程圖互作用1上，圖 3是一個(gè)軸截面通過在圖顯示的傳動(dòng)機(jī)構(gòu)1，圖4上是一張截面圖被采取沿著線IV-IV在表3，圖5是在圖顯示的輸入推進(jìn)聯(lián)結(jié)的一張更加詳細(xì)的分解圖3上，和圖 6是顯示在表3.的傳動(dòng)器的一張更加詳細(xì)的分解圖。 圖1的最初Referring，那里顯示一個(gè)車操縱機(jī)構(gòu)10操縱的被連接到一個(gè)對易操縱的路輪子12。這個(gè)顯示的操縱機(jī)構(gòu)包括一個(gè)齒條和齒輪匯編14被連接到路輪子12通過聯(lián)接15。 鳥翼末端(沒顯示)匯編14可旋轉(zhuǎn)地駕駛一名手動(dòng)地可旋轉(zhuǎn)的成員以駕駛桿18的形式哪些由方向盤19手動(dòng)地轉(zhuǎn)動(dòng)。這個(gè)駕駛桿18包括包括一臺電主驅(qū)動(dòng)電動(dòng)機(jī)的一個(gè)電力的傳動(dòng)機(jī)構(gòu)30 (沒顯示在駕駛的鳥翼末端圖1)上以回應(yīng)在駕駛桿18的扭矩裝貨為了為機(jī)械人員提供力量援助，當(dāng)轉(zhuǎn)動(dòng)方向盤19時(shí)。如概要地被說明在表2，電力的傳動(dòng)機(jī)構(gòu)包括測量駕駛桿申請的扭矩18，當(dāng)駕駛鳥翼末端時(shí)并且提供信號給控制器40的扭矩傳感器20。 控制器40被連接到主驅(qū)動(dòng)電動(dòng)機(jī)50并且控制電流被提供給馬達(dá)50控制馬達(dá)50和它的自轉(zhuǎn)的方向扭矩引起的相當(dāng)數(shù)量。馬達(dá)50 操縱的更適宜地被連接到駕駛桿18通過工具箱60，更適宜地一個(gè)周轉(zhuǎn)齒輪箱子和傳動(dòng)器70。 在一定條件下傳動(dòng)器70在正常運(yùn)行時(shí)更適宜地永久地接合并且是有效的隔絕從馬達(dá)50的驅(qū)動(dòng)使鳥翼末端通過傳動(dòng)機(jī)構(gòu)30手動(dòng)地被駕駛。 這是使機(jī)制的安全特點(diǎn)起作用在試圖的馬達(dá)50情形下駕駛太快速的駕駛桿并且/或者在錯(cuò)誤的方向或在案件 電動(dòng)機(jī)和工具箱占領(lǐng)了。 扭矩傳感器20更適宜地是一個(gè)匯編包括在扭矩應(yīng)用達(dá)到的傳感器軸登上應(yīng)變儀能夠準(zhǔn)確測量張力在一個(gè)被預(yù)先決定的范圍之內(nèi)的一個(gè)短的傳感器軸。被測量扭矩的被預(yù)先決定的范圍是0-lONm; 更好是關(guān)于l-5Nm。被測量的扭矩的范圍更好地對應(yīng)于大約0-1000微指令，并且傳感器軸的建筑更好被選擇這樣5Nm扭矩比在軸的2°導(dǎo)致較少的轉(zhuǎn)彎，少于1 °。好的應(yīng)變儀是鋸諧振器，在WO91/13832被描述的一臺適當(dāng)?shù)匿徶C振器。 類似在圖顯示的那WO91/13832 3上更好地運(yùn)用配置，二看見諧振器被安排在對軸軸的45°和在90°對互相。諧振器經(jīng)營與在200-400 MHz之間共鳴頻率和被安排導(dǎo)致信號到控制器1 MHz 40 ± 500 KHz根據(jù)傳感器軸的自轉(zhuǎn)方向的自我調(diào)節(jié)。 因此，當(dāng)傳感器軸不被扭轉(zhuǎn)的歸結(jié)于缺乏扭矩時(shí)，它導(dǎo)致一個(gè)1 MHz信號。當(dāng)它導(dǎo)致在1.0到1.5 MHz之間的一個(gè)信號的傳感器軸在一個(gè)方向被扭轉(zhuǎn)。 當(dāng)傳感器軸在相反方向時(shí)被扭轉(zhuǎn)它導(dǎo)致在1.0到0.5 MHz之間的一個(gè)信號。 因而同樣傳感器能導(dǎo)致信號表示程度扭矩并且傳感器軸的自轉(zhuǎn)的方向。好的馬達(dá)扭矩引起的相當(dāng)數(shù)量以回應(yīng)在0-10Nm之間被測量的扭矩是0-40Nm，并且為在l-5Nm之間被測量的扭矩是0-25Nm。反饋電路提供自我調(diào)節(jié)，借以馬達(dá)使用的電流由控制器40測量并且比較保證馬達(dá)在正確方向運(yùn)行并且提供期望功率協(xié)助。 控制器更好地行動(dòng)使被測量的扭矩降低到零和如此控制馬達(dá)增加它的扭矩產(chǎn)品減少被測量的扭矩。 (沒顯示)更適宜地提供車速傳感器哪些寄發(fā)一個(gè)信號表示車速到控制器。 控制器使用這個(gè)信號修改程度力量協(xié)助提供以回應(yīng)被測量的扭矩。將提供在低車速最大力量協(xié)助的，因而，并且將提供高車速極小的力量協(xié)助。更適宜地是邏輯順序器有一個(gè)現(xiàn)場可編程序的門數(shù)組例如XC 4005如Xilinx供應(yīng)這個(gè)控制器。 這樣控制器不依靠軟件和，因此能更起作用可靠地在汽車車環(huán)境里。 被想象也許使用有邏輯的序列一個(gè)現(xiàn)場可編程序的列陣。 一個(gè)電力傳動(dòng)機(jī)構(gòu)10的A具體建筑在表3.被說明。 電子動(dòng)力轉(zhuǎn)向系統(tǒng)（英文簡稱EPS）， 與液壓動(dòng)力轉(zhuǎn)向系統(tǒng)（HPS）相比，EPS具有很多優(yōu)點(diǎn)。即EPS的優(yōu)勢在于： 1）效率高。HPS效率很低，一般為60%~70%；而EPS與電機(jī)連接，效率高，有的可高達(dá)90%以上。 2）耗能少。汽車在實(shí)際行駛過程中，處于轉(zhuǎn)向的時(shí)間約占行駛時(shí)間的5%，對于HPS系統(tǒng)，發(fā)動(dòng)機(jī)運(yùn)轉(zhuǎn)時(shí)，油泵始終處于工作狀態(tài)，油液一直在管路中循環(huán)，從而使汽車燃油消耗率增加4%~6%；而EPS僅在需要時(shí)供能，使汽車的燃油消耗率僅增加0.5%左右。 3）“路感“好。由于EPS內(nèi)部采用剛性連接，系統(tǒng)的滯后特性可以通過軟件加以控制，且可以根據(jù)駕駛員的操作習(xí)慣進(jìn)行調(diào)整。 4）回正性好。EPS結(jié)構(gòu)簡單內(nèi)部阻力小，回正性好，從而可得到最佳的轉(zhuǎn)向回正特性，改善汽車操縱穩(wěn)定性。 5）對環(huán)境污染少。HPS液壓回路中有液壓軟管和接頭，存在油液泄露問題，而且液壓軟管不可回收，對環(huán)境有有一定污染；而EPS對環(huán)境幾乎沒有污染。 6）可以獨(dú)立于發(fā)動(dòng)機(jī)工作。EPS以電池為動(dòng)力元件，只要電池電量充足，不論發(fā)動(dòng)機(jī)出于何種狀態(tài)，都可以產(chǎn)生助力作用。 7）應(yīng)有范圍廣。 8）裝配性好易于布置。 現(xiàn)在，動(dòng)力轉(zhuǎn)向系統(tǒng)已成為一些轎車的標(biāo)準(zhǔn)設(shè)置，全世界約有一半的轎車采用動(dòng)力轉(zhuǎn)向。隨著汽車電子技術(shù)的發(fā)展，目前一些轎車已經(jīng)使用電動(dòng)助力轉(zhuǎn)向器，使汽車的經(jīng)濟(jì)性、動(dòng)力性和機(jī)動(dòng)性都有所提高。電動(dòng)助力轉(zhuǎn)向裝置是汽車上一種新的助力轉(zhuǎn)向系統(tǒng)裝置,近年來在國內(nèi)外發(fā)展迅速,由于它采用了可編程電子控制裝置,在帶來靈活性的同時(shí)也存在著安全隱患.在分析這種產(chǎn)品特殊性的基礎(chǔ)上,筆者結(jié)合電子控制裝置的特點(diǎn),指出了事關(guān)安全性的因素,提出了處理安全性的措施,并討論了幾個(gè)事關(guān)安全性的具體問題.研究結(jié)果表明:現(xiàn)有標(biāo)準(zhǔn)不能夠滿足電動(dòng)助力轉(zhuǎn)向裝置安全性的需要;并提出了對電動(dòng)助力轉(zhuǎn)向裝置進(jìn)行安全性測評的思想.研究工作對電動(dòng)助力轉(zhuǎn)向裝置的開發(fā)以及評價(jià)具有參考意義。 編號 無錫太湖學(xué)院 畢業(yè)設(shè)計(jì)（論文） 相關(guān)資料 題目： 汽車電動(dòng)轉(zhuǎn)向器動(dòng)力學(xué)建模與 控制仿真研究 信機(jī) 系 機(jī)械工程及自動(dòng)化專業(yè) 學(xué) 號： 　　　 0923217　　　　 學(xué)生姓名： 鮑 維 俊 指導(dǎo)教師： 　 陳炎冬 （職稱：講 師） （職稱： ） 2013年5月25日 無錫太湖學(xué)院 畢業(yè)設(shè)計(jì)（論文） 開題報(bào)告 題目： 汽車電動(dòng)轉(zhuǎn)向器動(dòng)力學(xué)建模與控制仿真研究 信機(jī) 系 機(jī)械工程及自動(dòng)化 專業(yè) 學(xué) 號： 0923217 學(xué)生姓名： 鮑 維 俊 指導(dǎo)教師： 陳炎冬 （職稱：講 師） （職稱： ） 2012年11月28日 課題來源 生產(chǎn)實(shí)踐 科學(xué)依據(jù)（包括課題的科學(xué)意義；國內(nèi)外研究概況、水平和發(fā)展趨勢；應(yīng)用前景等） （1）課題科學(xué)意義 目前汽車已經(jīng)走入尋常百姓家中，人們對汽車需求逐建增大，對它的技術(shù)要求也越來越高。隨著現(xiàn)代汽車技術(shù)的迅猛發(fā)展，人們對汽車操縱性能的要求也日益提高。為了保證車輛在停車或低速泊車情況下轉(zhuǎn)動(dòng)方向盤也能夠輕松自如，在高速行駛時(shí)又不會(huì)感到輕飄不穩(wěn)，汽車轉(zhuǎn)向系統(tǒng)不斷地發(fā)展，從簡單的純機(jī)械式轉(zhuǎn)向系統(tǒng)，發(fā)展到機(jī)械液壓動(dòng)力轉(zhuǎn)向系統(tǒng)，到電控液壓助力轉(zhuǎn)向系統(tǒng)，直至如今的更為節(jié)能，操縱性能更優(yōu)的電子控制式EPS 階段?，F(xiàn)代汽車技術(shù)追求高效節(jié)能、高舒適性和高安全性等三大目標(biāo)。高效節(jié)能與環(huán)境保護(hù)密切相關(guān),是當(dāng)今全球性最熱門和最受關(guān)注的話題之一。后兩項(xiàng)目標(biāo)是汽車朝著高性能化方向發(fā)展要研究和解決的重要課題。電動(dòng)助力轉(zhuǎn)向系統(tǒng)(EPS)由于具備環(huán)保性能好、能耗低、重量輕、體積小、空間省等性能而應(yīng)運(yùn)而生。 （2）電動(dòng)轉(zhuǎn)向器的研究狀況及其發(fā)展前景 電動(dòng)轉(zhuǎn)向器電動(dòng)轉(zhuǎn)向器是一種新型的汽車轉(zhuǎn)向系統(tǒng),該系統(tǒng)能根據(jù)車輛的運(yùn)動(dòng)狀況和駕駛員的要求實(shí)行多目標(biāo)控制,以獲得較強(qiáng)的路感、較輕的操縱力、較好的回正穩(wěn)定性和回正速度、較強(qiáng)的抗干擾能力和較快地響應(yīng)轉(zhuǎn)向輸入,而且這些控制是在基本上不改變硬件的條件下通過軟件即可實(shí)現(xiàn)。比傳統(tǒng)液壓動(dòng)力轉(zhuǎn)向系統(tǒng)相比電動(dòng)助力轉(zhuǎn)向系統(tǒng)的優(yōu)勢體現(xiàn)在下面幾個(gè)方面： 1　 采用電能做能源,有利于環(huán)保。 2　 與液壓助力系統(tǒng)相比,降低了燃油消耗。 3　 改善了車輛的回正特性。 4　 提高了車輛的操縱穩(wěn)定性。 5　 減小了轉(zhuǎn)向遲滯效應(yīng),增強(qiáng)了轉(zhuǎn)向跟隨性。 6　 系統(tǒng)結(jié)構(gòu)簡單,占用空間小,布置方便,性能優(yōu)越。 EPS己在轎車土得到應(yīng)用，其優(yōu)良的性能己得到認(rèn)可。隨著直流電動(dòng)機(jī)性能的改進(jìn)，EPS助力能力的提高，其應(yīng)用范圍將進(jìn)一步拓寬。EPS代表未來動(dòng)力轉(zhuǎn)向技術(shù)的發(fā)展方向,將作為標(biāo)準(zhǔn)件裝置在汽車上，并將在動(dòng)力轉(zhuǎn)向領(lǐng)域中占據(jù)主導(dǎo)地位。四大“EV”車將構(gòu)成未來汽車發(fā)展的主體,這給EPS帶來了廣闊的應(yīng)用前景。 研究內(nèi)容 ① 熟悉汽車電動(dòng)助力轉(zhuǎn)向器的工作原理及各部分組成； ② 對電動(dòng)助力轉(zhuǎn)向器進(jìn)行分析并建立動(dòng)力學(xué)模型； ③ 對電動(dòng)助力轉(zhuǎn)向器進(jìn)行控制分析，確定控制方式； ④ 能夠熟練使用MATLAB/Simulink，搭建框圖并進(jìn)行仿真。通過調(diào)整參數(shù)，對系統(tǒng)進(jìn)行分析； ⑤ 比較不同控制方式系統(tǒng)的穩(wěn)定性、快速性和準(zhǔn)確性。 擬采取的研究方法、技術(shù)路線、實(shí)驗(yàn)方案及可行性分析 （1）實(shí)驗(yàn)方案 對電動(dòng)轉(zhuǎn)向器進(jìn)行動(dòng)力學(xué)分析，建立動(dòng)力學(xué)模型，列出相應(yīng)的動(dòng)力學(xué)方程。根據(jù)動(dòng)力學(xué)方程，用MATLAB/Simulink，搭建框圖并進(jìn)行仿真。通過調(diào)整參數(shù)，對系統(tǒng)進(jìn)行分析，著重研究基于PID控制下的EPS系統(tǒng)的性能的改變。最后比較三種轉(zhuǎn)向系統(tǒng)的穩(wěn)定性、快速性和準(zhǔn)確性。 （2）研究方法 1在同種轉(zhuǎn)向控制系統(tǒng)下，改變參數(shù)，分析對系統(tǒng)的影響。 2 在不同的轉(zhuǎn)向控制系統(tǒng)下，對同一個(gè)參數(shù)，分析對不同系統(tǒng)的影響，改變同一個(gè)參數(shù)，分析對轉(zhuǎn)向系統(tǒng)的影響。 研究計(jì)劃及預(yù)期成果 研究計(jì)劃： 2012年11月12日-2012年12月2日：初步閱讀資料，完成畢業(yè)設(shè)計(jì)開題報(bào)告。 2012年12月3日-2013年1月20日：專業(yè)實(shí)訓(xùn)。 2013年1月21日-2013年3月1日 ：畢業(yè)實(shí)習(xí)。 2013年3月2日-2013年3月8日：學(xué)習(xí)并翻譯一篇與畢業(yè)設(shè)計(jì)相關(guān)的英文材料。 2013年3月9日-2013年3月29日：EPS動(dòng)力學(xué)建模和分析。 2013年3月30日-2013年4月26日：用MATLAB/Simulink，搭建框圖并進(jìn)行仿真。 2013年4月27日-2013年5月25日：畢業(yè)論文撰寫和修改工作。 預(yù)期成果： 基于PID控制下的EPS系統(tǒng)相對純機(jī)械轉(zhuǎn)向系統(tǒng)和無PID控制下的EPS系統(tǒng)，能提高EPS系統(tǒng)的快速性、穩(wěn)定性和準(zhǔn)確性。 特色或創(chuàng)新之處 ① 使用MATLAB對EPS系統(tǒng)進(jìn)行仿真，方便改變參量，能夠直觀判斷實(shí)驗(yàn)結(jié)果。 ② 采用固定某些參數(shù)、改變某些參數(shù)來研究問題的方法，思路清晰，簡潔明了，行之有效。 已具備的條件和尚需解決的問題 ① 實(shí)驗(yàn)方案思路已經(jīng)非常明確，已經(jīng)具備使用仿真的能力MATLAB/Simulink等方面的知識。 ② 使用MATLAB編程的能力尚需加強(qiáng)。 指導(dǎo)教師意見 指導(dǎo)教師簽名： 年 月 日 教研室（學(xué)科組、研究所）意見 教研室主任簽名： 年 月 日 系意見 主管領(lǐng)導(dǎo)簽名： 年 月 日 目 錄 一、畢業(yè)設(shè)計(jì)（論文）開題報(bào)告 二、畢業(yè)設(shè)計(jì)（論文）外文資料翻譯及原文 三、學(xué)生“畢業(yè)論文（論文）計(jì)劃、進(jìn)度、檢查及落實(shí)表” 四、實(shí)習(xí)鑒定表 英文原文 The auto electric power steering system research Along with automobile electronic technology swift and violent development, the people also day by day enhance to the motor turning handling quality request. The motor turning system hanged, the hydraulic pressure boost from the traditional machinery changes (Hydraulic Power Steering, is called HPS), the electrically controlled hydraulic pressure boost changes (Electronic Hydraulic Power Steering, is called EHPS), develops the electrically operated boost steering system (Electronic Power Steering, is called EPS), finally also will transit to the line controls the steering system (Steer By Wire, will be called SBW). The machinery steering system is refers by pilot's physical strength achievement changes the energy, in which all power transmission all is mechanical, the automobile changes the movement is operates the steering wheel by the pilot, transmits through the diverter and a series of members changes the wheel to realize. The mechanical steering system by changes the control mechanism, the diverter and major part changes the gearing 3 to be composed. Usually may divide into according to the mechanical diverter form: The gear rack type, follows round the world -like, the worm bearing adjuster hoop type, the worm bearing adjuster refers sells the type. Is the gear rack type and follows using the broadest two kinds round the world -like (uses in needing time big steering force).In follows round the world -like in the diverter, the input changes the circle and the output steering arm pivot angle is proportional; In the gear rack type diverter, the input changes the turn and the output rack displacement is proportional. Follows round the world -like the diverter because is the rolling friction form, thus the transmission efficiency is very high, the ease of operation also the service life are long, moreover bearing capacity, therefore widely applies on the truck. The gear rack type diverter with follows round the world -like compares, the most major characteristic is the rigidity is big, the structure compact weight is light, also the cost is low. Because this way passes on easily by the wheel the reacting force to the steering wheel, therefore has to the pavement behavior response keen merit, but simultaneously also easy to have phenomena and so on goon and oscillation, also its load bearing efficiency relative weak, therefore mainly applies on the compact car and the pickup truck, at present the majority of low end passenger vehicle uses is the gear rack type machinery steering system. Along with the vehicles carrying capacity increase as well as the people to the vehicles handling quality request enhancement, the simple mechanical type steering system were already unable to meet the needs, the power steering system arise at the historic moment, it could rotate the steering wheel while the pilot to provide the boost, the power steering system divides into the hydraulic pressure steering system and the electrically operated steering system 2kinds.Hydraulic pressure steering system is at present uses the most widespread steering system. The hydraulic pressure steering system increased the hydraulic system in the mechanical system foundation, including hydraulic pump, V shape band pulley, drill tubing, feed installment, boost installment and control valve. It with the aid of in the motor car engine power actuation hydraulic pump, the air compressor and the generator and so on, by the fluid strength, the physical strength or the electric power increases the pilot to operate the strength which the front wheel changes, enables the pilot to be possible nimbly to operate motor turning facilely, reduced the labor intensity, enhanced the travel security. The hydraulic pressure boost steering system from invented already had about half century history to the present, might say was one kind of more perfect system, because its work reliable, the technology mature still widely is applied until now. It takes the power supply by the hydraulic pump, after oil pipe-line control valves to power hydraulic cylinder feed, through the connecting rod impetus rotation gear movement, may changes the boost through the change cylinder bore and the flowing tubing head pressure size the size, from this achieved changes the boost the function. The traditional hydraulic pressure type power steering system may divide into generally according to the liquid flow form: Ordinary flow type and atmospheric pressure type 2 kind of types, also may divide into according to the control valve form transfers the valve type and the slide-valve type. Along with hydraulic pressure power steering system on automobile daily popularization, the people to operates when the portability and the road feeling request also day by day enhance, however the hydraulic pressure power steering system has many shortcomings actually: ①Because its itself structure had decided it is unable to guarantee vehicles rotates the steering wheel when any operating mode, all has the ideal operation stability, namely is unable simultaneously to guarantee time the low speed changes the portability and the high speed time operation stability;②The automobile changes the characteristic to drive the pilot technical the influence to be serious; ③The steering ratio is fixed, causes the motor turning response characteristic along with changes and so on vehicle speed, transverse acceleration to change, the pilot must aim at the motor turning characteristic peak-to-peak value and the phase change ahead of time carries on certain operation compensation, thus controls the automobile according to its wish travel. Like this increased pilot's operation burden, also causes in the motor turning travel not to have the security hidden danger; But hereafter appeared the electrically controlled hydraulic booster system, it increases the velocity generator in the traditional hydraulic pressure power steering system foundation, enables the automobile along with the vehicle speed change automatic control force size, has to a certain extent relaxed the traditional hydraulic pressure steering system existence question. At present our country produces on the commercial vehicle and the passenger vehicle uses mostly is the electrically controlled hydraulic pressure boost steering system, it is quite mature and the application widespread steering system. Although the electrically controlled hydraulic servo alleviated the traditional hydraulic pressure from certain degree to change between the portability and the road feeling contradiction, however it did not have fundamentally to solve the HPS system existence insufficiency, along with automobile microelectronic technology development, automobile fuel oil energy conservation request as well as global initiative environmental protection, it in aspect and so on arrangement, installment, leak-proof quality, control sensitivity, energy consumption, attrition and noise insufficiencies already more and more obvious, the steering system turned towards the electrically operated boost steering system development. The electrically operated boost steering system is the present motor turning system development direction, its principle of work is: EPS system ECU after comes from the steering wheel torque sensor and the vehicle speed sensor signal carries on analysis processing, controls the electrical machinery to have the suitable boost torque, assists the pilot to complete changes the operation. In the last few years, along with the electronic technology development, reduces EPS the cost to become large scale possibly, Japan sends the car company, Mitsubishi Car company, this field car company, US's Delphi automobile system company, TRW Corporation and Germany's ZF Corporation greatly all one after another develops EPS.Mercedes2Benz Siemens Automotive Two big companies invested 65,000,000 pounds to use in developing EPS, the goal are together load a car to 2002, yearly produce 300 ten thousand sets, became the global EPS manufacturer. So far, the EPS system in the slight passenger vehicle, on the theater box type vehicle obtains the widespread application, and every year by 300 ten thousand speed development. Steering is the term applied to the collection of components, linkages, etc. which allow for a vessel (ship, boat) or vehicle (car) to follow the desired course. An exception is the case of rail transport by which rail tracks combined together with railroad switches provide the steering function. The most conventional steering arrangement is to turn the front wheels using a hand–operated steering wheel which is positioned in front of the driver, via the steering column, which may contain universal joints to allow it to deviate somewhat from a straight line. Other arrangements are sometimes found on different types of vehicles, for example, a tiller or rear–wheel steering. Tracked vehicles such as tanks usually employ differential steering — that is, the tracks are made to move at different speeds or even in opposite directions to bring about a change of course. Many modern cars use rack and pinion steering mechanisms, where the steering wheel turns the pinion gear; the pinion moves the rack, which is a sort of linear gear which meshes with the pinion, from side to side. This motion applies steering torque to the kingpins of the steered wheels via tie rods and a short lever arm called the steering arm. Older designs often use the recirculating ball mechanism, which is still found on trucks and utility vehicles. This is a variation on the older worm and sector design; the steering column turns a large screw (the "worm gear") which meshes with a sector of a gear, causing it to rotate about its axis as the worm gear is turned; an arm attached to the axis of the sector moves the pitman arm, which is connected to the steering linkage and thus steers the wheels. The recirculating ball version of this apparatus reduces the considerable friction by placing large ball bearings between the teeth of the worm and those of the screw; at either end of the apparatus the balls exit from between the two pieces into a channel internal to the box which connects them with the other end of the apparatus, thus they are "recirculated". The rack and pinion design has the advantages of a large degree of feedback and direct steering "feel"; it also does not normally have any backlash, or slack. A disadvantage is that it is not adjustable, so that when it does wear and develop lash, the only cure is replacement. The recirculating ball mechanism has the advantage of a much greater mechanical advantage, so that it was found on larger, heavier vehicles while the rack and pinion was originally limited to smaller and lighter ones; due to the almost universal adoption of power steering, however, this is no longer an important advantage, leading to the increasing use of rack and pinion on newer cars. The recirculating ball design also has a perceptible lash, or "dead spot" on center, where a minute turn of the steering wheel in either direction does not move the steering apparatus; this is easily adjustable via a screw on the end of the steering box to account for wear, but it cannot be entirely eliminated or the mechanism begins to wear very rapidly. This design is still in use in trucks and other large vehicles, where rapidity of steering and direct feel are less important than robustness, maintainability, and mechanical advantage. The much smaller degree of feedback with this design can also sometimes be an advantage; drivers of vehicles with rack and pinion steering can have their thumbs broken when a front wheel hits a bump, causing the steering wheel to kick to one side suddenly (leading to driving instructors telling students to keep their thumbs on the front of the steering wheel, rather than wrapping around the inside of the rim). This effect is even stronger with a heavy vehicle like a truck; recirculating ball steering prevents this degree of feedback, just as it prevents desirable feedback under normal circumstances. The steering linkage connecting the steering box and the wheels usually conforms to a variation of Ackermann steering geometry, to account for the fact that in a turn, the inner wheel is actually traveling a path of smaller radius than the outer wheel, so that the degree of toe suitable for driving in a straight path is not suitable for turns. As vehicles have become heavier and switched to front wheel drive, the effort to turn the steering wheel manually has increased - often to the point where major physical exertion is required. To alleviate this, auto makers have developed power steering systems. There are two types of power steering systems—hydraulic and electric/electronic. There is also a hydraulic-electric hybrid system possible. A hydraulic power steering (HPS) uses hydraulic pressure supplied by an engine-driven pump to assist the motion of turning the steering wheel. Electric power steering (EPS) is more efficient than the hydraulic power steering, since the electric power steering motor only needs to provide assist when the steering wheel is turned, whereas the hydraulic pump must run constantly. In EPS the assist level is easily tunable to the vehicle type, road speed, and even driver preference. An added benefit is the elimination of environmental hazard posed by leakage and disposal of hydraulic power steering fluid. An outgrowth of power steering is speed adjustable steering, where the steering is heavily assisted at low speed and lightly assisted at high speed. The auto makers perceive that motorists might need to make large steering inputs while manoeuvering for parking, but not while traveling at high speed. The first vehicle with this feature was the Citro?n SM with its Diravi layout, although rather than altering the amount of assistance as in modern power steering systems, it altered the pressure on a centring cam which made the steering wheel try to "spring" back to the straight-ahead position. Modern speed-adjustable power steering systems reduce the pressure fed to the ram as the speed increases, giving a more direct feel. This feature is gradually becoming commonplace across all new vehicles. Four-wheel steering (or all wheel steering) is a system employed by some vehicles to increase vehicle stability while maneuvering at high speed, or to decrease turning radius at low speed. In most four-wheel steering systems, the rear wheels are steered by a computer and actuators. The rear wheels generally cannot turn as far as the Alternatively, several systems, including Delphi's Quadrasteer and the system in Honda's Prelude line, allow for the rear wheels to be steered in the opposite direction as the front wheels during low speeds. This allows the vehicle to turn in a significantly smaller radius — sometimes critical for large trucks or vehicles with trailers. An exception is the case of rail transport by which rail tracks combined together with railroad switches provide the steering function.Many modern cars use steering mechanisms, where the steering wheel turns the pinion gear; the pinion moves the rack, which is a sort of linear gear which meshes with the pinion, from side to side.mechanism, which is still found on trucks and utility vehicles.This is a variation on the older and thus steers the wheels.The recirculating ball version of this apparatus reduces the considerable friction by placing large ball bearings between the teeth of the worm and those of the screw; at either end of the apparatus the balls exit from between the two pieces into a channel internal to the box which connects them with the other end of the apparatus, thus they are "recirThe rack and pinion design has the advantages of a large degree of feedback and direct steering "feel"; it also does not normally have any , or slack.culated".A disadvantage is that it is not adjustable, so that when it does wear and develop lash, the only cure is replacement.The recirculating ball mechanism has the advantage of a much greater , however, this is no longer an important advantage, leading to the increasing use of rack and pinion on newer cars.to account for wear, but it cannot be entirely eliminated or the mechanism begins to wear very rapidly.This design is still in use in trucks and other large vehicles, where rapidity of steering and direct feel are less important than robustness, maintainability, and mechanical advantage.The much smaller degree of feedback with this design can also sometimes be an advantage; drivers of vehicles with rack and pinion steering can have their thumbs broken when a front wheel hits a bump, causing the steering wheel to kick to one side suddenly (leading to driving instructors telling students to keep their thumbs on the front of the steering wheel, rather than wrapping around the inside of the rim). This effect is even stronger with a heavy vehicle like a truck; recirculating ball steering prevents this degree of feedback, just as it prevents desirable feedback under normal circumstances.As vehicles have become heavier and switched to front wheel drive , the effort to turn the steering wheel manually has increased - often to the point where major physical exertion is required.There are two types of power steering systems—hydraulic and electric/electronic.here is also a hydraulic-electric hybrid system possible.A hydraulic power steering (HPS) uses hydraulic pressure supplied by an engine-driven pump to assist the motion of turning the stElectric power steering (EPS) is more efficient than the hydraulic power steering, since the electric power steering motor only needs to provide assist when the steering wheel is turned, whereas the hydraulic pump must run constantly.eering wheel.In EPS the assist level is easily tunable to the vehicle type, road speed, and even driver preference.An added benefit is the elimination of environmental hazard posed by leakage and disposal of hydraulic power steering fluid.n outgrowth of power steering is speed adjustable steering, where the steering is heavily assisted at low speed and lightly assisted at high speed.The auto makers perceive that motorists might need to make large steering inputs while manoeuvering for parking, but not while traveling at high speed.The first vehicle with this feature was the Citro?n SM with its Diravi layout, although rather than altering the amount of assistance as in modern power steering systems, it altered the pressure on a centring cam which made the steering wheel try to "spring" back to the straight-ahead position.Modern speed-adjustable power steering systems reduce the pressure fed to the ram as the speed increases, The rear wheels giving a more direct feel.This feature is gradually becoming commonplace across all new vehicles.In most four-wheel steering systems, the rear wheels are steered by a computer and actuators.generally cannot turn as far as the Alternatively, several systems, including Delphi's Quadrasteer and the system in Honda's Prelude line, allow for the rear wheels to be steered in the opposite direction as the front wheels during low speeds.This allows the vehicle to turn in a significantly smaller radius — sometimes critical for large trucks or vehicles with trailers. Electronic power steering system What it is Electrically powered steering uses an electric motor to drive either the power steering hydraulic pump or the steering linkage directly. The power steering function is therefore independent of engine speed, resulting in significant energy savings. How it works : Conventional power steering systems use an engine accessory belt to drive the pump, providing pressurized fluid that operates a piston in the power steering gear or actuator to assist the driver. In electro-hydraulic steering, one electrically powered steering concept uses a high efficiency