【機(jī)械類(lèi)畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯】20英寸自行車(chē)輪液壓濕式制動(dòng)系統(tǒng)的優(yōu)化設(shè)計(jì)【word英文2583字7頁(yè)word中文翻譯4606字7頁(yè)】,機(jī)械類(lèi)畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯,word英文2583字7頁(yè),word中文翻譯4606字7頁(yè),機(jī)械類(lèi),畢業(yè)論文,中英文,對(duì)照,對(duì)比,比照,文獻(xiàn),翻譯,20,英寸,自行,車(chē)輪,液壓,制動(dòng),系統(tǒng),優(yōu)化,設(shè)計(jì) 20英寸自行車(chē)輪液壓濕式制動(dòng)系統(tǒng)的優(yōu)化設(shè)計(jì) 摘要 隨著氣候變化和減少使用化石燃料日益受到關(guān)注，美國(guó)環(huán)境保護(hù)署（EPA）已研發(fā)了液壓混合動(dòng)力運(yùn)輸系統(tǒng)。在7年時(shí)間中，EPA和美國(guó)密西根大學(xué)（UM）的學(xué)生組成的機(jī)械工程450團(tuán)隊(duì)（ME450）為發(fā)展自行車(chē)液壓再生制動(dòng)系統(tǒng)（HRBS）進(jìn)行了項(xiàng)目合作。一般來(lái)說(shuō)，這些系統(tǒng)節(jié)約了在摩擦制動(dòng)過(guò)程中丟失的能源。它采用了將自行車(chē)的動(dòng)能通過(guò)泵液壓油的流動(dòng)進(jìn)入蓄能器，從而制動(dòng)車(chē)輛。而此次儲(chǔ)存的能量將釋放來(lái)加速自行車(chē)向前行駛。 這學(xué)期，我們通過(guò)優(yōu)化機(jī)械系統(tǒng)和改善其安全來(lái)改進(jìn)以前HRBS設(shè)計(jì)。我們團(tuán)隊(duì)的主要目標(biāo)是建立一個(gè)正常運(yùn)作的原型20"輪，它重量更輕，并具有運(yùn)動(dòng)部件少。比前幾代，作為它部分的設(shè)計(jì)已精心研究，我們的團(tuán)隊(duì)取得了現(xiàn)存的液壓系統(tǒng)的微小變化。此次設(shè)計(jì)由我們的贊助商，大衛(wèi)環(huán)保局史懷恩先生指導(dǎo)，我們建立了一個(gè)滿足客戶的要求項(xiàng)目清單。下面的表1列出了許多我們的重點(diǎn)工程，并創(chuàng)造了滿足這些要求的規(guī)格，以及最后的樣機(jī)特征。我們的四大類(lèi)工程規(guī)格為，安全性、成本、重量和功能性。由于這些規(guī)格與其性質(zhì)的沖突，它一直難以改善自行車(chē)的許多系統(tǒng)而對(duì)他人設(shè)計(jì)產(chǎn)生不利影響。妥協(xié)以創(chuàng)造一個(gè)可行的設(shè)計(jì)是必要的途徑。 表1：重點(diǎn)工程規(guī)格概要 特征 指標(biāo) 樣機(jī) 前輪的裝配重量 ≤30磅 24.75磅 自行車(chē)額定負(fù)載（騎手體重） ≤160磅 ＞200磅 限量系統(tǒng)壓力安全閥 ≤4200psi ≤4200psi 自行車(chē)減速指標(biāo) 3.4m/s2—2.6m/s2 無(wú)法取得 自行車(chē)加速指標(biāo) 2.0m/s2—2.5m/s2 無(wú)法取得 移動(dòng)/旋轉(zhuǎn)樞紐內(nèi)部零部件數(shù)量 ＜11 7 樣機(jī)成本 ≤1400美元 1338美元 許多主要的液壓元件需要長(zhǎng)期收購(gòu)多次。為了完成我們?nèi)纹诮Y(jié)束時(shí)作出一個(gè)擁有這些功能的樣機(jī)的目標(biāo)，我們加快觀念的生成和選擇，從而以留出足夠的時(shí)間訂購(gòu)和接收這些部件?；陬A(yù)期的任務(wù)要求以及交貨時(shí)間，這學(xué)期我們創(chuàng)造了一個(gè)詳細(xì)的計(jì)劃。 與以前的設(shè)計(jì)相比，我們已經(jīng)大大降低了齒輪的數(shù)量來(lái)減輕樣機(jī)的重量，用一個(gè)輕型鋁合金發(fā)言系統(tǒng)來(lái)取代笨重的玻璃纖維樞紐的支撐系統(tǒng)，并從內(nèi)部支撐板（“superbracket”）去除多余的材料。這些修改的選擇來(lái)自于一個(gè)基于深入分析每個(gè)組件所需的力量和扭矩廣泛的概念。實(shí)現(xiàn)這些涉及公制和非公制元件之間的非標(biāo)準(zhǔn)接口這項(xiàng)主要工程的障礙進(jìn)行改進(jìn)設(shè)計(jì)，并確定液壓回路的路線選擇。 1摘要 美國(guó)環(huán)境保護(hù)署（EPA）正在努力研究液壓混合動(dòng)力運(yùn)輸系統(tǒng)以解決有關(guān)全球氣候變化和貪得無(wú)厭的化石燃料的需求得到越來(lái)越多的關(guān)注。在過(guò)去的7年里，ME450在美國(guó)密西根大學(xué)（UM）的學(xué)生為液壓混合動(dòng)力自行車(chē)系統(tǒng)設(shè)計(jì)作出發(fā)展，液壓混合動(dòng)力汽車(chē)使用再生制動(dòng)儲(chǔ)存能量加壓液體這種能量的釋放可以協(xié)助車(chē)輛加速。這學(xué)期，我們提出20英寸自行車(chē)輪內(nèi)的液壓混合動(dòng)力系統(tǒng)的設(shè)計(jì)，重點(diǎn)是降低重量，提高安全性，并減少移動(dòng)部件的數(shù)量。 2引言 本節(jié)概述了液壓混合動(dòng)力系統(tǒng)的概念、自行車(chē)環(huán)保局的起源以及其發(fā)展的原動(dòng)力。此項(xiàng)目在2009年冬季學(xué)期ME450范圍內(nèi)進(jìn)行，概要介紹如下。 2.1背景和動(dòng)機(jī) 美國(guó)環(huán)境保護(hù)局成立于1970年，是一個(gè)負(fù)責(zé)糾正損害環(huán)境和建立指引的聯(lián)邦機(jī)構(gòu)，以幫助保護(hù)美國(guó)的自然環(huán)境[1]。主要研究清潔能源，特別是運(yùn)輸是EPA的努力的幾個(gè)重點(diǎn)[2]。與伊頓公司、聯(lián)合包裹運(yùn)送服務(wù)公司、福特、國(guó)際和美國(guó)軍隊(duì)保持合作，環(huán)保局已開(kāi)發(fā)出幾種改善燃油經(jīng)濟(jì)性和減少對(duì)環(huán)境的影響為目的的液壓混合動(dòng)力汽車(chē)[3]。 液壓混合動(dòng)力車(chē)技術(shù)的主要概念是捕捉和利用，否則將失去制動(dòng)過(guò)程中用它來(lái)加快車(chē)輛的能源。作為汽車(chē)制動(dòng)器，液壓泵連接到傳動(dòng)泵的液壓油進(jìn)入高壓蓄能器。在車(chē)輛加速過(guò)程中，在蓄能器儲(chǔ)存的能量被釋放到動(dòng)力傳動(dòng)系統(tǒng)，液體流動(dòng)通過(guò)液壓馬達(dá)。這大大降低了所需的燃料，回到正常的運(yùn)行速度以加速[3]。這種再生制動(dòng)的結(jié)果是在燃油經(jīng)濟(jì)性上明顯的改善—不僅是對(duì)環(huán)境有益，也為業(yè)主降低燃料成本的特點(diǎn)。這種液壓再生制動(dòng)系統(tǒng)（HRBS）（如圖1所示）的圖表在第6頁(yè)上顯示。 圖1：液壓油在HRBS上的路徑[4] 使用自行車(chē)作為交通工具上下班，減少了化石燃料的使用、減輕了溫室氣體排放、減緩了道路擁堵，同時(shí)騎行自行車(chē)數(shù)英里還提高了用戶的身體健康[5]。環(huán)保局已經(jīng)證明在內(nèi)燃發(fā)動(dòng)機(jī)的車(chē)輛上安裝HRBS可改善20-40％的燃油經(jīng)濟(jì)值[3]。自2002年以來(lái)，環(huán)保局已與澳學(xué)生對(duì)液壓自行車(chē)實(shí)施狀況進(jìn)行合作，對(duì)其具有清潔、液壓助力式承擔(dān)的高效的運(yùn)輸可能性進(jìn)行探索。但該項(xiàng)目產(chǎn)生只有一個(gè)功能性的產(chǎn)品。 2.2工程項(xiàng)目說(shuō)明 這個(gè)項(xiàng)目是以開(kāi)發(fā)20英寸兒童式自行車(chē)液壓再生制動(dòng)系統(tǒng)為目標(biāo)。由于液壓系統(tǒng)在同比例大小進(jìn)行縮放向下的艱巨性和縮放向上較為容易性，因此選擇20英寸這個(gè)尺寸研究HRBS自行車(chē)，它在分析重量、力的大小、和固有的扭矩問(wèn)題上較為合適。 在過(guò)去的7年,環(huán)保局和機(jī)械工程學(xué)450的學(xué)生一直致力于研究HRBS自行車(chē)。以前的ME450隊(duì)一直在26英寸和20英寸自行車(chē)輪子上擬合這些系統(tǒng)。我們?cè)谘芯縃RBS方面的主要焦點(diǎn)是改善現(xiàn)有的設(shè)計(jì)，以提高它的安全性、降低重量、確保功能性和降低成本。值得注意的是，我們正在設(shè)計(jì)的20英寸輪HRBS系統(tǒng)，其主要目標(biāo)之一是在不犧牲機(jī)械強(qiáng)度或壓力容器的安全的前提下將設(shè)備的重量減少到30磅。我們的計(jì)劃是保留大部分過(guò)去設(shè)計(jì)的液壓元件，因?yàn)檫@項(xiàng)技術(shù)已由大衛(wèi)_斯溫和以前的團(tuán)隊(duì)得到了很好的研究和記錄。我們正在進(jìn)一步制定一個(gè)HRBS技術(shù)的、以減少運(yùn)動(dòng)部件、降低重量、提高安全性為重點(diǎn)的功能樣機(jī)。 3信息收集 為了更好的理解液壓混合動(dòng)力系統(tǒng)，我們團(tuán)隊(duì)調(diào)查了廣泛收集的信息，其中包括研究論文、以前ME450的報(bào)告和環(huán)保局的資源。在這部分報(bào)告所顯示的信息中我們找出了液驅(qū)混合動(dòng)力車(chē)輛技術(shù)。 液壓系統(tǒng)在如機(jī)械、制動(dòng)系統(tǒng)、儲(chǔ)能等各種應(yīng)用場(chǎng)合下受到使用。由于液壓系統(tǒng)傳輸較大的力的性質(zhì)和高效地將勢(shì)能轉(zhuǎn)換成動(dòng)力的能力而受到了大家廣泛地使用。為了安全地利用這項(xiàng)技術(shù)，我們必須采取預(yù)防措施，以防止因高壓而爆裂液壓系統(tǒng)。 4項(xiàng)目要求及工程規(guī)范 該部分概述了這個(gè)項(xiàng)目的規(guī)格，我們首先了解我們的客戶的需求。然后我們改變工程規(guī)格要求來(lái)滿足客戶的需求。這部分的報(bào)告詳細(xì)介紹了一些要求和并由此產(chǎn)生的規(guī)范。 4.1客戶要求 作為我們的提案者大衛(wèi)-斯溫在這學(xué)期為我們概述了客戶的要求，客戶的要求是，延續(xù)過(guò)去兩個(gè)學(xué)期的內(nèi)容，并補(bǔ)充強(qiáng)調(diào)了三大主題，及安全、性能、成本。通過(guò)上述要求來(lái)知道我們的工程技術(shù)規(guī)范的形成。我們對(duì)三大主題和他們的重要性進(jìn)行分組.第11頁(yè)表1顯示我們客戶要求的一個(gè)列表。 表1 按客戶要求的重要性進(jìn)行分類(lèi) 相對(duì)重要性 安全性 性能 成本 高 用戶安全 輕量級(jí) 廉價(jià)的制造工藝 自然制動(dòng)率 可靠 以A股 自行車(chē)為準(zhǔn) 使用方便 高效 材料成本 低 易于維修 足夠的啟動(dòng)速度 4.2工程規(guī)范 客戶要求的成本和安全可直接轉(zhuǎn)換成工程規(guī)格，然而，性能可分為重量和功能，我們了解兩者都具有重要性且相對(duì)獨(dú)立，而由此產(chǎn)生的規(guī)格說(shuō)明在以下列表中。這些規(guī)范以及客戶的要求可以使我們對(duì)質(zhì)量和功能設(shè)計(jì)的展開(kāi)和相互作用。 5概念生成 為了有效地創(chuàng)造廣泛收集的概念，首先，我們通過(guò)分解HRBS的主要系統(tǒng)，分解成各個(gè)子系統(tǒng)后，我們列出了其各個(gè)主要的組成部分。然后，我們每個(gè)團(tuán)隊(duì)隊(duì)員創(chuàng)建每個(gè)組件的一個(gè)概念列表，通過(guò)彼此創(chuàng)建的想法組成一個(gè)整體的概念咧表。 5.1功能分解 基于獨(dú)特的歷史和相對(duì)復(fù)雜的項(xiàng)目，以及與之前大部分團(tuán)隊(duì)相比，我們采取了稍微不同的概念生成過(guò)程。首先，我們將自行車(chē)HRBS分解成五個(gè)功能子系統(tǒng)。這些子系統(tǒng)分別為液壓系統(tǒng)、動(dòng)力系統(tǒng)、輪轂、超級(jí)支架、和用戶界面。每個(gè)子系統(tǒng)包含至少2個(gè)主要成分。圖3是一個(gè)功能分解樹(shù)，它顯示了那些組件屬于哪個(gè)子系統(tǒng)。 圖3：介紹各子系統(tǒng)的組要組成部分的功能分解數(shù) 完成功能分解后，各個(gè)系統(tǒng)產(chǎn)生了各系統(tǒng)組件的概念，作為一個(gè)團(tuán)隊(duì)，我們分別去建立概念和進(jìn)行分析，從而我們可以從多個(gè)角度入手每一個(gè)問(wèn)題。 5.2液壓系統(tǒng) 該系統(tǒng)由以前的團(tuán)隊(duì)設(shè)計(jì)，此子系統(tǒng)已經(jīng)非常完善。這項(xiàng)目也是籌備時(shí)間最長(zhǎng)的一個(gè)子系統(tǒng)。因此，我們的許多液壓元件，包括泵、電機(jī)、高壓蓄能器、管材及配件、低壓油箱，仍將以前團(tuán)隊(duì)所指定的相同。 除了前幾代所使用的系統(tǒng)，在增壓系統(tǒng)上安裝包括泄壓裝置等設(shè)備以防止過(guò)度增壓是非常重要的。如一個(gè)可變的泄壓閥或者爆裂光盤(pán)都可實(shí)現(xiàn)以上功能。 該閥的分類(lèi)是由一個(gè)防止高壓力流體進(jìn)入泵的止回閥和啟動(dòng)和停止程序啟動(dòng)的換向閥。應(yīng)用各種類(lèi)型的止回閥來(lái)更好地應(yīng)對(duì)壓力的不同。而該換向閥可以是雙向或三通電磁閥。不同類(lèi)型的閥門(mén)有不同的密封方法，其中錐閥密封性能很好，只有幾滴每分鐘，線軸閥泄漏為幾十毫升每分鐘。 5.3動(dòng)力系統(tǒng)及密封 動(dòng)力傳動(dòng)系統(tǒng)可分解成只有兩種組件的類(lèi)別，但是由于20英寸自行車(chē)車(chē)輪的約束，使得它變得非常復(fù)雜。在過(guò)去，機(jī)械式的減速裝置使用了直齒圓柱齒輪，由此我們產(chǎn)生了許多新的概念，其中包括塑料齒輪、酚醛齒輪、鏈輪及鏈條、齒形傳動(dòng)帶、電纜和滑輪、像那些用來(lái)啟動(dòng)云霄飛車(chē)的摩擦輪。 第二個(gè)動(dòng)力系統(tǒng)的組成是離合器機(jī)理。一個(gè)系統(tǒng)應(yīng)具備一個(gè)能隨時(shí)從運(yùn)行的泵和電機(jī)中脫離運(yùn)行和制動(dòng)的旋轉(zhuǎn)樞紐，而來(lái)完成這項(xiàng)任務(wù)的概念為包括機(jī)電離合器（基準(zhǔn)）、機(jī)械離合器、滾珠離合器和利用一個(gè)線性驅(qū)動(dòng)器定制的離合器。 5.4樞紐 該自行車(chē)輪轂的主要作用是支撐自行車(chē)車(chē)圈，與自行車(chē)的減速裝置連接，并在其附上該系統(tǒng)的運(yùn)動(dòng)部件。輪轂固定繞在自行車(chē)的輪軸上。以前的團(tuán)隊(duì)已經(jīng)創(chuàng)建了以碳纖維和玻璃纖維制成的輪轂，我們擴(kuò)入了以前的概念和我們自己的概念如鋁金屬板，真空成型塑料，和輪輻與薄蓋等，由此我們制定了由輪輻和真空形式設(shè)計(jì)相結(jié)合的新的概念。在本設(shè)計(jì)中，鋼性的骨骼結(jié)構(gòu)將用于支撐自行車(chē)并用塑料薄膜蓋蓋住系統(tǒng)。 5.5超級(jí)支架 該支架子系統(tǒng)由超級(jí)支架和自行車(chē)的輪轂組成，這些組件都是剛性連接在一起。該輪轂的旋轉(zhuǎn)軸和電氣線路的出入端通過(guò)軸心輪轂。Superbracket設(shè)計(jì)是材料選用以及厚度的最優(yōu)化的設(shè)計(jì)問(wèn)題。該支架需要支撐液壓和機(jī)械部件和為阻礙正在加載的徑向泵和電機(jī)的輸入\輸出軸。為了滿足這些指標(biāo)，我們創(chuàng)建了一個(gè)虛擬的材料清單，其中包括鋼鐵、鋁、玻璃纖維、工裝板、木材、碳纖維、塑料等。隨著材料的選擇完成，我們已經(jīng)討論了采用凹坑模具、加入三角撐板和增加角鋼輔助的方法來(lái)提高支架的剛度。 5.6使用者界面和控制項(xiàng) 在以往的設(shè)計(jì)中，該界面納入了一個(gè)控制啟動(dòng)和制動(dòng)功能的開(kāi)關(guān)盒，這個(gè)盒子直接安裝在座位前的自行車(chē)車(chē)架上，然而在功能上，這就迫使自行車(chē)手必須放開(kāi)至少一個(gè)把手去啟動(dòng)這些系統(tǒng)，如果系統(tǒng)發(fā)生制動(dòng)失效，騎手必須迅速調(diào)整自己手的位置去使用手剎車(chē)車(chē)把進(jìn)行制動(dòng)。這里產(chǎn)生了一個(gè)可能的概念來(lái)解決這個(gè)問(wèn)題，就是將開(kāi)關(guān)和存在的手剎車(chē)進(jìn)行集成。如可以在鋼絲繩上鉸接一個(gè)撥動(dòng)開(kāi)關(guān)，通過(guò)輕微的擠壓手剎來(lái)啟動(dòng)HRBS，而用力擠壓則足以使它摩擦制動(dòng)。另一種選擇的前提是這輛車(chē)必須配備前后手剎車(chē)，則可以脫離未修改的后手剎車(chē)，并且將前車(chē)手剎的鋼絲繩與扳鈕開(kāi)關(guān)相連，通過(guò)安裝在手把上的切換扳鈕開(kāi)關(guān)來(lái)啟動(dòng)激活系統(tǒng)，或者在每個(gè)把手上都安裝一個(gè)按鈕，而兩個(gè)開(kāi)關(guān)處于平行線狀態(tài)，就可以?xún)蓚€(gè)按鈕必須啟動(dòng)而觸發(fā)。站在安全的角度上看，這是相對(duì)有益的。 6結(jié)論 這學(xué)期，我們圍繞20英寸自行車(chē)輪設(shè)計(jì)和構(gòu)建了液壓制動(dòng)再生系統(tǒng)。通過(guò)使用環(huán)保局和以前ME450團(tuán)隊(duì)的技術(shù)，以及采用我們團(tuán)隊(duì)所具有的豐富的資源，我們?cè)谧孕熊?chē)上重新設(shè)計(jì)了機(jī)械和電氣系統(tǒng)。我們所設(shè)計(jì)的自行車(chē)，其液壓元件的規(guī)格與歷代的自行車(chē)上的規(guī)格沒(méi)有變化，而是減輕重量、提高安全性和增加其功能，并在制造和裝配過(guò)程中得到驅(qū)動(dòng)和激勵(lì)。積極采購(gòu)零部件，主動(dòng)安排任務(wù)，我們能夠在整個(gè)學(xué)期的最后期限完成這個(gè)項(xiàng)目。在這較短的設(shè)計(jì)周期中，堅(jiān)持一個(gè)以有條不紊和深思熟慮的做法是必要的，從而避免出現(xiàn)混亂和誤導(dǎo)工作，并且使得每個(gè)團(tuán)隊(duì)成員建立一個(gè)縝密的知識(shí)系統(tǒng)和它的組成，以致可以在這個(gè)項(xiàng)目上提出一些飛躍性的演化。 Optimizing a Hydraulic Regenerative Braking System for a 20" Bicycle Wheel Executive Summary With a growing concern of climate change and decreasing availability of fossil fuels, the U.S. Environmental Protection Agency (EPA) has been researching hydraulic hybrid transportation systems. For seven years, the EPA and ME450 students at The University of Michigan (U-M) have collaborated on projects developing Hydraulic Regenerative Braking Systems (HRBS) for bicycles. These systems conserve energy that is normally lost during friction braking. The bike's kinetic energy is used to drive hydraulic fluid into an accumulator via a pump, braking the vehicle. This stored energy is later released to accelerate the bike forward. This semester we have refined previous HRBS designs by optimizing the mechanical systems and improving safety. A key goal for our team was to build a functioning prototype 20" wheel that weighs less and has fewer moving parts than previous generations. Our team has made minimal changes to the extant hydraulic system, as the parts have been well-researched and recommended by our sponsor, David Swain of the EPA. Working with Mr. Swain, we created a list of customer requirements for this project. Table 1 below lists many of our key engineering specifications that were created to meet these requirements, as well as the final characteristics of the prototype. Our four categories for engineering specifications are safety, cost, weight, and functionality. Due to the conflicting nature of these specifications, it has been difficult to improve many of the bike's systems without adversely affecting others. Compromises have been necessary in order to create a feasible design. table 1：summary of key engineering specifications Characteristic Target prototype Front wheel assembly weight ≤30lbs 24.75lbs Bicycle load rating(rider weight) ≤160lbs ＞200lbs System pressure as limited by relief vale ≤4200psi ≤4200psi Bicycle deceleration target 3.4m/s2—2.6m/s2 not available Bicycle acceleration target 2.0m/s2—2.5m/s2 not available Number of moving/ rotating parts inside hub ＜11 7 Prototype cost ≤$1400 $1338 Many of the main hydraulic components have long acquisition lead times. To meet our goal of having a functional prototype by the end of the term, we expedited concept generation and selection so as to leave enough time to order and receive these parts. We created a detailed plan for the semester based on expected task requirements as well as these lead times. In reducing the weight of the prototype compared to previous designs, we have significantly reduced the number of gears, replaced the bulky fiberglass hub support system with a lightweight aluminum spoke system, and removed excess material from the internal support plate ("superbracket"). These modification choices were made from a broad number of concepts, based on a thorough analysis of the forces and torques required of each of the components. The main engineering obstacles to implementing these design improvements have been dealing with the nonstandard interface between metric and non-metric components, and determining the routing of the hydraulic circuit. 1 Abstract The U.S. Environmental Protection Agency (EPA) is researching hydraulic hybrid transportation systems in an effort to address the growing concerns about global climate change and insatiable fossil fuel demands. Hydraulic hybrid vehicles use regenerative braking to store energy in pressurized fluids. This energy is then released to assist in vehicle acceleration. For the past seven years, ME450 students at The University of Michigan (U-M) have been developing designs for hydraulic hybrid bicycle systems. This semester we refined the design of a hydraulic hybrid system enclosed in a 20" bicycle wheel, with a focus on decreasing weight, improving safety, and reducing the number of moving parts. 2 Introduction This section outlines the origins of the hydraulic hybrid bicycle system concept at the EPA as well as the driving force for its development. A brief outline of the project's scope for the Winter 2009 semester of ME450 is also presented below. 2.1 Background and Motivation Founded in 1970, the United States Environmental Protection Agency is a federal body tasked with correcting environmental damage and establishing guidelines to help protect the natural environment of the United States [1]. Research into clean energy, particularly for use in transportation, is the focus of several of the EPA's efforts [2]. In cooperation with Eaton Corporation, United Parcel Service, Ford, International, and the U.S. Army, the EPA has developed several hydraulic hybrid vehicles for the purposes of improving fuel economy and reducing environmental impact [3]. The primary concept of hydraulic hybrid technology is to capture and utilize the energy that would otherwise be lost during braking and use it to accelerate the vehicle. As the vehicle brakes, a hydraulic pump connected to the drivetrain pumps hydraulic oil into the high-pressure accumulators. During vehicle acceleration, the energy stored in the accumulators is released back into the drivetrain, as the fluid flows through a hydraulic motor. This significantly lowers the amount of fuel needed to accelerate back to normal operating speeds [3]. The result of this regenerative braking is a marked improvement in fuel economy - a feature that is not just better for the environment, but also reduces fuel costs for the owner. A diagram showing this hydraulic regenerative braking system (HRBS) is shown in Figure 1 on page 6. Figure 1: The hydraulic fluid's path in an HRBS [4] The use of bicycles for commuting reduces fossil fuel use, greenhouse gas emissions, roadway congestion, and vehicle miles traveled while increasing the user's physical health [5]. The EPA has demonstrated 20-40 percent fuel economy improvements by installing HRBS on vehicles with internal combustion engines [3]. The possibility of clean, efficient transportation with hydraulic assistance bears exploration. The EPA has been working with U-M students on hydraulic bicycle implementation since 2002, but the project has produced only one functional product. 2.2 Project Description The goal of this project is to develop a hydraulic regenerative braking system for a children's 20" bicycle. Due to the difficult nature of scaling down a hydraulic system, and the comparative ease of scaling upwards, the intent of using a 20" bicycle is to analyze the weight, force, and torque issues inherent to the HRBS on a small scale. The EPA has been working on HRBS bicycles with ME450 students for the past seven years. Previous ME450 teams have worked on fitting these systems in 26" and 20" bicycle wheels. The primary focus of our work on the HRBS is refining the existing designs by improving safety, reducing weight, ensuring functionality, and lowering cost. We are designing an HRBS for a 20" wheel. Notably, one of the main goals is to reduce the device weight to 30 lbs without sacrificing mechanical robustness or safe pressure containment. We plan to retain the majority of the hydraulic components from past designs, as this technology has been well-researched and documented by David Swain and previous teams. By focusing on reducing moving parts, decreasing weight, and improving safety, we are further developing the understanding and implementation of HRBS technology through the fabrication of a functional prototype. 3 Information Search To gain a better understanding of hydraulic hybrid systems, our team surveyed a broad collection of information including research papers, previous ME450 reports, and EPA resources. This section of the report discusses the information we found regarding hydraulic hybrid vehicle technology. Hydraulic systems are used in a variety of applications such as machinery, braking systems, and energy storage. They are often used because of their ability to transfer large forces and convert kinetic energy into potential energy efficiently. To safely utilize this technology, many precautions must be taken to prevent high-pressure systems from rupturing. The EPA, U-M, and companies such as Eaton and Ford have been developing hydraulic hybrid systems for transportation applications including cars, trucks, and bicycles. Hydraulic hybrid bicycle technology has been pioneered through a partnership between the EPA and U-M. For seven years, ME450 students at U-M have been researching, designing, and building hydraulic hybrid bicycle systems using HRBS. These systems require improvements in safety, functionality, and performance. 4 Project Requirements & Engineering Specifications To outline the specifications for this project, we began by defining our customer requirements. We then translated these requirements into engineering specifications. This section of the report details these requirements and the resulting specifications. 4.1 Customer Requirements The customer requirements for this term, as outlined by our sponsor David Swain, are continuations of the past two semesters with an added emphasis on three major underlying themes-safety, performance, and cost- to guide the formation of our engineering specifications. Table 1 on page 11 shows a listing of our customer's requirements, as grouped by the three major themes and their relative importance in each. 4.2 Engineering Specifications When translating the customer requirements into engineering specifications, cost and safety translated directly. However, performance split into weight and functionality, as we find both categories of high enough importance to be separate. The resultant engineering specifications are described in the following list. 5 Concept Generation To effectively generate a broad collection of concepts, we began by decomposing the main subsystems of the HRBS. After breaking down the subsystems, we listed the main components of each. Each team member then created a list of concepts for each of the components. We then met as a team to build on one another's ideas and we created a master concept list 5.1 Functional Decomposition Based on the unique history and relative complexity of our project, we followed a slightly different concept generation process than most teams. We began by decomposing the bicycle HRBS into five functional subsystems. These subsystems are hydraulics, powertrain, hub, superbracket, and user interface. Each of these subsystems contained at a minimum two major components. Figure 3 is a functional decomposition tree showing which components fall under which subsystem. Figure 3: Functional decomposition tree outlining main components of each subsystem After completing the functional decomposition, we generated concepts for each of the subsystem components. By individually creating concepts and analyzing them as a team, we were able to attack each design problem from multiple angles. 5.2 Hydraulics The subsystem most refined by previous teams is hydraulics. This is also the subsystem with the longest lead-time items. As a result, many of our hydraulic 5.2 Hydraulics The subsystem most refined by previous teams is hydraulics. This is also the subsystem with the longest lead-time items. As a result, many of our hydraulic components including the pump, motor, high pressure accumulator, tubing & fittings, and low pressure reservoir till remain the same as those specified by previous teams. In addition to the systems used on previous generations, it is important to include a pressure relief system to prevent over-pressurizing the system. This can be achieved by including a variable pressure relief valve or a burst disc. The valves category is made up of a check valve preventing high pressure flow from entering the pump and a directional valve to start and stop the launch process. There are various types of check valves that respond better to different pressures. The directional valve could either be a two-way or a three-way electronic valve. There are different types of each of these valves that vary in their sealing method. Poppet valves seal quite well, leaking only a few drops per minute; spool valves can leak multiple milliliters per minute. 5.3 Powertrain & Packaging Powertrain decomposes into only two component categories, but it is very complicated due to the packaging constraints of a 20" bicycle wheel. In the past, the mechanical reduction was created using steel spur gears. We generated many concepts including plastic gears, phenolic gears, sprockets & chain, cogged belts, cables & pulleys, and friction rollers like those used to launch roller coasters. The second powertrain category is clutch mechanisms. A system is needed to disengage the pump and motor from the rotating hub when braking and launching are not engaged. Concepts to complete this task included electromechanical clutches (benchmark), mechanical clutches, roller clutches, and a custom clutch utilizing a linear actuator. 5.4 Hub The hub's main roles on the bike are to support the rim, to interface with the mechanical reduction, and to enclose the system's moving components. This hub rotates around the bike's axle, which is stationary. Previous teams have created hubs made of carbon fiber and fiberglass. We included these in our concept list as well as aluminum sheet metal, vacuum formed plastic, and spokes with a thin cover. We developed another concept by combining the spoke and vacuum form designs. In this design a rigid skeletal structure would be used to support the bicycle and a thin plastic cover would enclose the system. 5.5 Superbracket The superbracket subsystem is made up of the superbracket and the bike's axle. These components are rigidly connected together. The hub rotates on the axle and electric wiring exits the hub through the center of the axle. Designing the superbracket is a material selection and thickness optimization problem. The bracket needs to support the hydraulic and mechanical components and prevent the pump and motor's output/input shafts from being loaded radially. To meet these criteria we created a list of potential materials, including steel, aluminum, fiberglass, tooling board, wood, carbon fiber, and plastic. Along with material selection we have discussed methods of increasing the bracket's stiffness by using dimple dies, adding gussets, and adding angle iron reinforcements. 5.6 User Interface and Controls Previous designs incorporated a switch box for controlling the brake and launch functions. This box was mounted on the frame of the bike directly in front of the seat. While functional, this forces the rider to let go of the handlebars with at least one hand to activate either system. In the event of a system braking failure, the rider would have to quickly adjust his hand position to activate the hand brake on the handlebar. One concept that could potentially solve this problem is to integrate the switch and the preexisting hand brake. This could be done by splicing a toggle switch into the cable. A light squeeze on the hand brake could activate the HRBS, while a hard squeeze would be enough to engage the friction brakes. Another option, provided that the bike is equipped with front and rear brakes, is to leave the rear hand brake unmodified and splice a toggle switch into the front hand brake cable. The launch activation could potentially be switched via a toggle switch mounted on the handlebars, or a pushbutton mounted on the handlebars. If two switches are wired in parallel, there is the advantage that both switches must be activated for the launch to be triggered - this could be beneficial from a safety standpoint. 6 Conclusion This semester we designed and built a hydraulic regenerative braking system enclosed in a 20" bicycle wheel. We used hydraulic hybrid technology that was proven by the EPA and previous ME450 teams. Using the vast resources available to our team, we redesigned the mechanical and electrical systems on the bike. The hydraulic component specifications did not change from previous iterations of the bicycle. We reduced weight, improved safety, and increased functionality with our design and were motivated by those driving factors during manufacturing and assembly. We were able to meet the deadlines of our project by sourcing parts aggressively and scheduling proactively throughout the semester. In such a short design cycle, adherence to a methodical and thoughtful approach was necessary to avoid confusion and misguided efforts. It also allowed for each team member to have an intimate knowledge of the system and its components, resulting directly in a significant leap forward in the evolution of this project.