【正文】 初步確定L／B的比值后，可通過(guò)原地轉(zhuǎn)彎能力的理論分析進(jìn)行核算來(lái)選定. S=式中一履帶板修正系數(shù)，=(，b為履帶板寬度(m)；G一整機(jī)機(jī)重(N)；T一行走最大牽引力(N)。則X[Pmin +(PmaxPmin)]dx=G（+e） (2)則由（1）得到Pmax Pmin=由（2）得到3Pmax +Pmin =（1+）則得到：=(） 如果偏心距e＝0，比壓呈矩形分布；如果e＝，則比壓呈三角形分布，此時(shí)履帶兩端的比壓值為：最小比壓=0最大比壓== （）符合設(shè)計(jì)要求。是增根，校核地面附著力與牽引力的關(guān)系。 支重輪的摩擦阻力，這部分阻力主要由支重輪沿履帶板的滾動(dòng)阻力及軸頸的摩擦阻力組成 w39。土壤受到的比壓與受壓表面的下陷深度有下面的關(guān)系P=P0h（KPa） （）式中 P—為土壤的比壓（KPa） h—受壓表面下陷的深度（cm） P0—使受壓表面下陷1cm的比壓,此值與土壤的種類有關(guān)，表示土壤的承載能力，單位為。為了提高履帶行走裝置的越過(guò)障礙的能力，行走裝置應(yīng)有合適的接近角1，和離去角2。目前在液壓挖掘機(jī)中廣泛采用液壓張緊裝置，這種帶有輔助液壓缸的彈簧張緊裝置()借助潤(rùn)滑用的黃油槍將黃油壓注入液壓缸，使活塞外伸，一端移動(dòng)導(dǎo)向輪，另一端壓縮彈簧使之預(yù)緊。拖鏈輪的結(jié)構(gòu)與支重輪類似，但其所受載荷要比支重輪小得多，工作時(shí)少受泥水侵蝕，因此尺寸可較小。軸兩端裝有浮動(dòng)油封。驅(qū)動(dòng)輪節(jié)圓半徑 （） ——取自《工程機(jī)械底盤(pán)構(gòu)造與設(shè)計(jì)》P316驅(qū)動(dòng)輪的節(jié)圓直徑為 履帶銷(xiāo)套直徑：則驅(qū)動(dòng)輪齒根圓直徑為：驅(qū)動(dòng)輪齒頂圓直徑：（～）d 齒谷半徑為： 谷齒距離為： c) 驅(qū)動(dòng)輪的強(qiáng)度計(jì)算驅(qū)動(dòng)輪需要校核其彎曲強(qiáng)度和擠壓強(qiáng)度。 ——需用拉伸應(yīng)力，所以σp== ≤所以，履帶的抗拉強(qiáng)度滿足要求。 式中KL為履帶長(zhǎng)度經(jīng)驗(yàn)系數(shù)。支重輪直徑較小，在行走裝置的長(zhǎng)度內(nèi)，每邊可裝5—9個(gè)支重輪。履帶呈抱死循環(huán)繞過(guò)驅(qū)動(dòng)輪5和導(dǎo)向輪1，為了減少上分支撓度，履帶由l一2個(gè)托鏈輪4支持。 2．在不增高行走裝置總高度的前提下應(yīng)使行走裝置具有較大的離地間隙，使挖掘機(jī)在不平地面上行走具有良好的通過(guò)性能。（3）不斷提高可靠性和使用壽命。第一臺(tái)有確切記載的挖掘機(jī)械是1796年英國(guó)人發(fā)明的蒸汽“挖泥鏟”。而對(duì)于還在學(xué)習(xí)當(dāng)中的我來(lái)說(shuō)，這個(gè)課題能讓我更深入地鞏固和學(xué)習(xí)液壓、機(jī)械原理、機(jī)械設(shè)計(jì)、機(jī)械繪圖等方面的知識(shí)。據(jù)統(tǒng)計(jì)，一般工程施工中約有60%的土石方量、露天礦山中80%的剝離量和采掘量是用挖掘機(jī)完成的。而液壓挖掘機(jī)則具有下列主要特點(diǎn)：1　 大大改善了挖掘機(jī)的技術(shù)性能，挖掘力大、牽引力大，傳動(dòng)平穩(wěn)，作用效率高，結(jié)構(gòu)緊湊。 國(guó)內(nèi)液壓挖掘機(jī)發(fā)展概況及趨勢(shì)我國(guó)己經(jīng)形成了挖掘機(jī)的系列化生產(chǎn)，近年來(lái)還開(kāi)發(fā)了許多新產(chǎn)品，引進(jìn)了國(guó)外的一些先進(jìn)的生產(chǎn)率較高的挖掘機(jī)型號(hào)。(2) 行走裝置四輪一帶的結(jié)構(gòu)設(shè)計(jì)與布置。盡管履帶式行走裝置存在一些，但在單斗液壓挖掘機(jī)中使用較為廣泛，而且本機(jī)主要用于城市道路建設(shè)或者狹窄空間內(nèi)作業(yè)。底架連接轉(zhuǎn)臺(tái)，承受上部的載荷，并通過(guò)橫梁傳給履帶架行走架按結(jié)構(gòu)的不同分組合式和整體式兩種。 目前液壓挖掘機(jī)中廣泛采用工業(yè)拖拉機(jī)型式的組合式履帶。 c）履帶節(jié)距 節(jié)距越小，履帶鏈軌運(yùn)轉(zhuǎn)在驅(qū)動(dòng)輪、導(dǎo)向輪上沖擊越小，運(yùn)轉(zhuǎn)越均勻，有利于減少磨損，提高效率，但最小節(jié)距值受到鏈軌結(jié)構(gòu)尺寸的限制。 本設(shè)計(jì)采用典型的“三圓弧一直線”型齒形。支重輪輪體常用35Mn或者50Mn制造。因?yàn)槁膸У闹蚊鎸挾萀0=2500綜合考慮以上因素，取支重輪的數(shù)量為6個(gè)。根據(jù)前述相關(guān)尺寸，： 導(dǎo)向輪的聯(lián)系尺寸/mm安裝尺寸外形尺寸配合尺寸特性尺寸ABDEF335300590160556555082b）導(dǎo)向輪軸的強(qiáng)度計(jì)算 導(dǎo)向輪的材料一般是40或45鑄鋼，輪緣通常不加工，表面淬火硬度HRC45以上。由《機(jī)械設(shè)計(jì)》P386表166常用旋繞比C值，在此取，根據(jù)《機(jī)械設(shè)計(jì)手冊(cè)》第三卷彈簧常用材料選取熱軋鋼，牌號(hào)為。為了不和它們的運(yùn)動(dòng)發(fā)生干涉，支重輪的位置應(yīng)保證當(dāng)導(dǎo)向輪在緩沖彈簧達(dá)到最大變形時(shí)相互不發(fā)生干涉，后支重輪的輪緣外徑與驅(qū)動(dòng)輪齒頂圓之間應(yīng)保留一定的間隙。 履帶轉(zhuǎn)彎阻力履帶寬為b，長(zhǎng)為L(zhǎng)，且=5則一條履帶的微面積bdx繞履帶中心點(diǎn)o轉(zhuǎn)動(dòng)時(shí)的力矩可表示為。 目前大多數(shù)履帶式液壓挖掘機(jī)的行走牽引力T與機(jī)重G取下列比例，即T=(~)G （）初步取T==48000N履帶行走裝置一個(gè)顯著特點(diǎn)就是爬坡能力大，一般為50%~80%。原地轉(zhuǎn)彎的行走阻力可用下式計(jì)算：W=（—）μG+ =6000+6000 =27783N （）式中——轉(zhuǎn)彎阻力系數(shù)，取=挖掘機(jī)的牽引力TW 故在一般路面能實(shí)現(xiàn)原地轉(zhuǎn)彎，滿足設(shè)計(jì)要求。 接地長(zhǎng)度、軌距校核以及最小離地間隙的確定 挖掘機(jī)行走裝置的接近角和離開(kāi)角一般較小，可近似認(rèn)為導(dǎo)向輪與驅(qū)動(dòng)輪中心距離即軸距A等于履帶接地長(zhǎng)度L。 Houston, May 1993.[16] McCloy D, 《Discharge Characteristics of Servo Valve Orifices》, 1968 Fluid International Conference.[17] . Binder, 《“Fluid Mechanics”. 3rd Edition, 3rd Printing. PrenticeHall, Inc.》, Englewood Cliffs,NJ. 1956.[18] Patton . 《Mechanical Power Transmission》. New Jersey: Printice—Hall, 1980科技論文翻譯Theory of fluid propertiesWe will concentrate mainly on three fluid properties in this chapter: ? The density which leads to mass and hence to hydraulic inertia effects.? The viscosity which leads to the hydraulic friction effects.? The pressibility and thus the bulk modulus which leads to the hydraulic system stiffness. Notice that the pressibility effect can be modified by air release, cavitation phenomena and by expansion of a pipe, hose or chamber containing the hydraulic fluid.1 Density and pressibility coefficient The density is the mass of a substance per unit volume:Density has dimensions of [M/L] and is expressed in kilograms per cubic meter [kg/m]. As mentioned previously the density is a function of the pressure and the temperature:This function can be approximated by the first three terms of a Taylor series:This can also be expressed as:WithAndThis equation is the linearized state equation for a liquid. Using the definition of the density, the two coefficients α and B can also be expressed as:B is known as the isothermal bulk modulus or for simplicity the bulk modulus and α is known as the cubical expansion coefficient. Since fluid density varies with the applied pressure, this implies that a given mass of fluid submitted to a pressure change changes its volume. This phenomenon leads to the definition of the pressibility coefficient β: where β is expressed in units Pa (or m/N). Considering the relation for a closed hydraulic circuit the mass is constant, and hence: it follows that Using the definition of the pressibility coefficient β we obtain: More usually we use the bulk modulus B also known as the volumetric elasticity modulus: The relation between ρ and B implies mass conservation. This relation must be RIGOROUSLY RESPECTED in the calculations. In the modeling and simulation context of fluid energy systems, disregarding the relation between ρ and B leads to abnormal evolutions of pressure in the closed circuit submitted to pression and expansion cycles. This phenomenon is strongly accentuated if aeration occurs in the circuit (when dissolved air in the fluid reappears in the form of bubbles). We shall approach this point by examining the phenomena of aeration and cavitation. The air can also have adverse consequences on a fluid pressibility. In liquid air can be present in two forms: entrapped and dissolved. Entrapped air When the return pipe is not submersed in the tank the liquid jet can entrain some air bubbles in the tank. Another phenomenon that affects the quantity of air in liquid is the leakage. Figure 1: Liquid leakageFigure 2: Air is entrainedThis air stays in the liquid as cavities and can modify the fluid pressibility. In this context we talk about effective bulk modulus. Figure 3 shows the bulk modulus of a diesel fuel at 40 176。=式中一馬達(dá)轉(zhuǎn)速(r／min)。=176。驅(qū)動(dòng)輪的摩擦阻力 一般根據(jù)經(jīng)驗(yàn)公式，履帶的內(nèi)阻力 =（~）G(N) () 以上四種運(yùn)行阻力中，以坡度阻力和轉(zhuǎn)彎阻力為最大。因此履帶上比壓基本上可寫(xiě)作均勻分布。~3176。緩沖彈簧工作行程終了時(shí)的壓縮力：40=(60~80)KN緩沖彈簧工作行程需考慮履帶和驅(qū)動(dòng)輪卡入石塊時(shí)能脫離嚙合，即工作行程為： （） ——取自《工程機(jī)械底盤(pán)構(gòu)造與設(shè)計(jì)》P320式中：驅(qū)動(dòng)輪齒頂圓直徑，； 驅(qū)動(dòng)輪齒根圓直徑。導(dǎo)向輪的中間擋肩環(huán)應(yīng)有足夠的高度，兩側(cè)邊的斜度要小。