【導(dǎo)讀】液壓挖掘機(jī)是在機(jī)械傳動挖掘機(jī)的基礎(chǔ)上發(fā)展起來的。它的工作過程是以。業(yè)的機(jī)械化施工中。據(jù)統(tǒng)計，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。整地，用于城市管道、道路、住宅建設(shè)、基礎(chǔ)工程和園林作業(yè)等。機(jī)動靈活，且可附裝各種工作裝置，屬多功能建設(shè)機(jī)械。減輕人力的勞動，縮短施工周期。證工程質(zhì)量和降低成本，采用機(jī)械化施工是根本的措施。此次對液壓挖掘機(jī)的研究具有現(xiàn)實意義。動作要產(chǎn)生很大的慣性力和沖擊載荷。1950年，德國研制出世界上第一臺全液壓挖掘。挖機(jī)行走裝置的總體設(shè)計。在工作時作場內(nèi)運行及轉(zhuǎn)移工地時作運輸性運行。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，5．挖掘機(jī)的行走裝置外形尺寸應(yīng)符合道路運輸?shù)囊?。單斗液壓挖掘機(jī)的行走裝置按照結(jié)構(gòu)的不同可分履帶式和輪胎式兩大類。履帶），張緊裝置和緩沖彈簧，行走機(jī)構(gòu)，行走架等組成。

　　

【正文】 0 ； L= BL = GT? = 所以，設(shè)計符合要求 最小離地間隙 h 也是一個重要參數(shù)。它的大小表明挖掘機(jī)通過地面障礙的能力，也會影響到整機(jī)的重心位置、穩(wěn)定性以及機(jī)械結(jié)構(gòu)等，通常取 h0． 13 31G 。 式中 h一最小離地間隙 ( 310? m)； G 一為整機(jī)質(zhì)量 (kg)。 南華大學(xué)機(jī)械工程學(xué)院畢業(yè)設(shè)計（論文） 第 38 頁 共 64 頁 參考文獻(xiàn) [1] 濮良貴 . 《機(jī)械設(shè)計（第八版）》 [M].北 京：高等教育出版社， 2020 [2] 唐增寶，常建娥 . 《機(jī)械設(shè)計課程設(shè)計（第 3版）》 [M].武漢：華中科技大學(xué)出版社， 2020 [3] 孔德文，趙克利，徐寧生 . 《液壓挖掘機(jī)》 [M].北京：化學(xué)工業(yè)出版社， 2020 [4] 張 鐵 . 《液壓挖掘機(jī)結(jié)構(gòu)、原理及使用》 [M].武漢：石油大學(xué)出版社， 2020 [5] 葉偉昌 . 《機(jī)械工程及自動化簡明設(shè)計手冊（上冊）》 [M].北京：機(jī)械工業(yè)出版社， 2020 [6] 高 衡，張全根 . 《液壓挖掘機(jī)》 [M]. 北京：中國建筑工業(yè)出版社， 1981 [7] 同濟(jì) 大學(xué)主編 . 《單斗液壓挖掘機(jī)》 [M]. 北京：中國建筑工業(yè)出版社， 1986 [8] 劉希平 . 《工程機(jī)械構(gòu)造圖冊》 [M].北京：機(jī)械工業(yè)出版社， 1990 [9] 成大先 . 《機(jī)械設(shè)計手冊》（單行本） [M]. 北京：化學(xué)工業(yè)出版社 ,2020 [10] 徐 灝 . 《機(jī)械設(shè)計手冊》 [M], 北京：機(jī)械工業(yè)出版社 ,1991 [11] 郁錄平 . 《工程機(jī)械底盤設(shè)計》 [M].上海：人民交通出版社， 2020 [12] 王之煦，許杏根 . 《簡明機(jī)械設(shè)計手冊》 [M].北京：機(jī)械工業(yè)出版社 ,1997 [13] (美 )希格利 ,米什克 .《機(jī)械設(shè)計通用手冊》 [M]. 北京：機(jī)械工業(yè)出版社 ,1993 [14] (美 )Hindhede,Zimmerman,Hopkins,et al.《 Machine Design Fundamentals— A Pratical Approach》 ,John Wiley Sons,1983 [15] Nease, .。 Alexander, ,《 Air Force construction automation/robotics. In Proc. 10th International Symposium on Automation and Robotics in Construction 》 (ISARC)。 Houston, May 1993. [16] McCloy D, 《 Discharge Characteristics of Servo Valve Orifices》 , 1968 Fluid International Conference. [17] . Binder, 《 “Fluid Mechanics”. 3rd Edition, 3rd Printing. Prent iceHall, Inc.》 , Englewood Cliffs,NJ. 1956. [18] Patton . 《 Mechanical Power Transmission》 . New Jersey: Printice— Hall, 1980 南華大學(xué)機(jī)械工程學(xué)院畢業(yè)設(shè)計（論文） 第 39 頁 共 64 頁 科技論文翻譯 Theory of fluid properties We 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/L3 ] and is expressed in kilograms per cubic meter [kg/m3 ]. 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: With 南華大學(xué)機(jī)械工程學(xué)院畢業(yè)設(shè)計（論文） 第 40 頁 共 64 頁 And This 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 1? (or m2 /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 南華大學(xué)機(jī)械工程學(xué)院畢業(yè)設(shè)計（論文） 第 41 頁 共 64 頁 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 leakage Figure 2: Air is entrained This 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。C with 0, , , 1, 10% air. The plot is obtained using the system shown. The model of the diesel fuel properties is based on accurate experimental measurements and are designed for use with injection system which are very fast acting. For this reason air is assumed to be entrained rather than dissolved. 南華大學(xué)機(jī)械工程學(xué)院畢業(yè)設(shè)計（論文） 第 42 頁 共 64 頁 Figure 3 Dissolved air Air can also be dissolved in a liquid. A certain amount of air molecule can be part of the liquid. In this case the dissolved air does not significantly change the fluid properties. 2 Air release and cavitation Air can be dissolved or entrained in liquids and it is possible for air to change from one of these two forms to the other depending on the conditions to which the fluid is subjected. Suppose the fluid is in equilibrium with a certain percentage of dissolved gas (usually air: nitrogen and oxygen). Lowering the pressure above a critical value called the saturation pressure induces aeration. This is the process where the dissolved gas forms air bubbles in the liquid until all the dissolved gases or air are free. The exact point where all the dissolved gas has e out of solution is difficult to pinpoint because it depends on the chemical position and behavior of the gas. This is a nonsymmetrical dynamic proc