液壓系統的形式
液(ye)壓(ya)元(yuan)件逐步(bu)實現了(le)標準化(hua)(hua)、系列(lie)化(hua)(hua)、化(hua)(hua)，其規格、品種、質量(liang)(liang)、性能都(dou)有了(le)很大(da)提(ti)(ti)高，尤其是采用(yong)(yong)電子技(ji)(ji)術、伺服技(ji)(ji)術等新(xin)技(ji)(ji)術新(xin)工藝后(hou)，液(ye)壓(ya)系統的(de)質量(liang)(liang)得到了(le)顯著的(de)提(ti)(ti)高，其在國民(min)經(jing)濟中發(fa)揮(hui)了(le)重大(da)作(zuo)用(yong)(yong)。
從不同的角(jiao)度出發，可以把液壓系統分(fen)成不同的形(xing)式。
（1）按(an)油(you)(you)(you)(you)(you)(you)液(ye)(ye)(ye)的(de)(de)循環(huan)方式，液(ye)(ye)(ye)壓系(xi)(xi)統(tong)(tong)(tong)可分為(wei)開(kai)(kai)式系(xi)(xi)統(tong)(tong)(tong)和(he)閉式系(xi)(xi)統(tong)(tong)(tong)。開(kai)(kai)式系(xi)(xi)統(tong)(tong)(tong)是指(zhi)液(ye)(ye)(ye)壓泵(beng)從油(you)(you)(you)(you)(you)(you)箱(xiang)(xiang)(xiang)吸油(you)(you)(you)(you)(you)(you)，油(you)(you)(you)(you)(you)(you)經各種控(kong)制(zhi)閥后(hou)，驅動(dong)(dong)液(ye)(ye)(ye)壓執行(xing)元件，回油(you)(you)(you)(you)(you)(you)再(zai)經過(guo)換(huan)向(xiang)閥回油(you)(you)(you)(you)(you)(you)箱(xiang)(xiang)(xiang)。這種系(xi)(xi)統(tong)(tong)(tong)結(jie)構(gou)較為(wei)簡(jian)單(dan)，可以發揮油(you)(you)(you)(you)(you)(you)箱(xiang)(xiang)(xiang)的(de)(de)散熱、沉淀(dian)雜(za)質作用(yong)，但因油(you)(you)(you)(you)(you)(you)液(ye)(ye)(ye)常與(yu)空氣(qi)接觸(chu)，使(shi)(shi)空氣(qi)易于(yu)滲(shen)入系(xi)(xi)統(tong)(tong)(tong)，導致機構(gou)運動(dong)(dong)不平穩等后(hou)果。開(kai)(kai)式系(xi)(xi)統(tong)(tong)(tong)油(you)(you)(you)(you)(you)(you)箱(xiang)(xiang)(xiang)大(da)，油(you)(you)(you)(you)(you)(you)泵(beng)自吸性能好(hao)。閉式系(xi)(xi)統(tong)(tong)(tong)中，液(ye)(ye)(ye)壓泵(beng)的(de)(de)進(jin)油(you)(you)(you)(you)(you)(you)管直接與(yu)執行(xing)元件的(de)(de)回油(you)(you)(you)(you)(you)(you)管相連，工(gong)作液(ye)(ye)(ye)體(ti)在(zai)系(xi)(xi)統(tong)(tong)(tong)的(de)(de)管路中進(jin)行(xing)封閉循環(huan)。其(qi)結(jie)構(gou)緊湊，與(yu)空氣(qi)接觸(chu)機會(hui)少，空氣(qi)不易滲(shen)入系(xi)(xi)統(tong)(tong)(tong)，故傳動(dong)(dong)較平穩。工(gong)作機構(gou)的(de)(de)變(bian)速和(he)換(huan)向(xiang)靠調(diao)節泵(beng)或(huo)馬(ma)達的(de)(de)變(bian)量(liang)機構(gou)實(shi)現，避免(mian)了開(kai)(kai)式系(xi)(xi)統(tong)(tong)(tong)換(huan)向(xiang)過(guo)程中所(suo)出現的(de)(de)液(ye)(ye)(ye)壓沖(chong)擊和(he)能量(liang)損失。但閉式系(xi)(xi)統(tong)(tong)(tong)較開(kai)(kai)式系(xi)(xi)統(tong)(tong)(tong)復(fu)雜(za)，因無油(you)(you)(you)(you)(you)(you)箱(xiang)(xiang)(xiang)，油(you)(you)(you)(you)(you)(you)液(ye)(ye)(ye)的(de)(de)散熱和(he)過(guo)濾條件較差。為(wei)補(bu)償系(xi)(xi)統(tong)(tong)(tong)中的(de)(de)泄漏(lou)，通(tong)常需要(yao)一(yi)個小流量(liang)的(de)(de)補(bu)油(you)(you)(you)(you)(you)(you)泵(beng)和(he)油(you)(you)(you)(you)(you)(you)箱(xiang)(xiang)(xiang)。由(you)于(yu)單(dan)桿(gan)雙作用(yong)油(you)(you)(you)(you)(you)(you)缸(gang)大(da)小腔流量(liang)不等，在(zai)工(gong)作過(guo)程中會(hui)使(shi)(shi)功(gong)率利用(yong)下降，所(suo)以閉式系(xi)(xi)統(tong)(tong)(tong)中的(de)(de)執行(xing)元件一(yi)般為(wei)液(ye)(ye)(ye)壓馬(ma)達。
（2）按系(xi)統中液(ye)壓(ya)泵(beng)的數(shu)目，可(ke)分(fen)為(wei)單泵(beng)系(xi)統，雙泵(beng)系(xi)統和多泵(beng)系(xi)統。
（3）按所用液(ye)壓(ya)(ya)泵形(xing)式的不同，可分(fen)為定量(liang)泵系(xi)統(tong)(tong)和(he)變量(liang)泵系(xi)統(tong)(tong)。變量(liang)泵的優點是(shi)在調節范圍之內，可以(yi)充分(fen)利用發動機的功率，但其結構和(he)制(zhi)造工藝復雜(za)，成本高，可分(fen)為手動變量(liang)、盡可能控變量(liang)、伺服(fu)變量(liang)、壓(ya)(ya)力補償變量(liang)、恒壓(ya)(ya)變量(liang)、液(ye)壓(ya)(ya)變量(liang)等多種方式。
（4）按向執(zhi)(zhi)(zhi)行(xing)(xing)(xing)(xing)元(yuan)件(jian)(jian)供油(you)(you)方式的(de)(de)(de)(de)不同，可分為(wei)串(chuan)聯系統(tong)(tong)和并聯系統(tong)(tong)。串(chuan)聯系統(tong)(tong)中，上(shang)一(yi)(yi)個執(zhi)(zhi)(zhi)行(xing)(xing)(xing)(xing)元(yuan)件(jian)(jian)的(de)(de)(de)(de)回油(you)(you)即為(wei)下一(yi)(yi)個執(zhi)(zhi)(zhi)行(xing)(xing)(xing)(xing)元(yuan)件(jian)(jian)的(de)(de)(de)(de)進油(you)(you)，每通過一(yi)(yi)個執(zhi)(zhi)(zhi)行(xing)(xing)(xing)(xing)元(yuan)件(jian)(jian)壓力(li)就(jiu)要降低(di)一(yi)(yi)次。在串(chuan)聯系統(tong)(tong)中，當主泵向多路閥控制的(de)(de)(de)(de)各執(zhi)(zhi)(zhi)行(xing)(xing)(xing)(xing)元(yuan)件(jian)(jian)供油(you)(you)時，只要液壓泵的(de)(de)(de)(de)出(chu)口壓力(li)足夠，便可以(yi)實現各執(zhi)(zhi)(zhi)行(xing)(xing)(xing)(xing)元(yuan)件(jian)(jian)的(de)(de)(de)(de)運動的(de)(de)(de)(de)復(fu)合。但由于(yu)執(zhi)(zhi)(zhi)行(xing)(xing)(xing)(xing)元(yuan)件(jian)(jian)的(de)(de)(de)(de)壓力(li)是疊加(jia)的(de)(de)(de)(de)，所以(yi)克(ke)服(fu)外載能力(li)將(jiang)隨執(zhi)(zhi)(zhi)行(xing)(xing)(xing)(xing)元(yuan)件(jian)(jian)數量的(de)(de)(de)(de)增加(jia)而降低(di)。
并聯系統中，當一臺液壓泵向(xiang)一組執(zhi)行元(yuan)件(jian)(jian)供油(you)時，進入各(ge)(ge)執(zhi)行元(yuan)件(jian)(jian)的(de)流(liu)量只(zhi)是液壓泵輸出流(liu)量的(de)一部(bu)分(fen)。流(liu)量的(de)分(fen)配隨各(ge)(ge)件(jian)(jian)上(shang)(shang)外載(zai)荷(he)(he)的(de)不(bu)同而變(bian)化，首先進入外載(zai)荷(he)(he)較小的(de)執(zhi)行元(yuan)件(jian)(jian)，只(zhi)有當各(ge)(ge)執(zhi)行元(yuan)件(jian)(jian)上(shang)(shang)外載(zai)荷(he)(he)相等時，才能實現同時動作。
全液壓(ya)傳動(dong)機械(xie)性(xing)(xing)能(neng)的(de)優劣，主(zhu)要取決于液壓(ya)系統(tong)性(xing)(xing)能(neng)的(de)好壞，包(bao)括所用元件質量優劣，基本回(hui)路是(shi)否恰(qia)當等(deng)。系統(tong)性(xing)(xing)能(neng)的(de)好壞，除滿足(zu)使用功能(neng)要求外，應從液壓(ya)系統(tong)的(de)效率(lv)、功率(lv)利用、調速范圍和微調特性(xing)(xing)、振動(dong)和噪(zao)聲以及系統(tong)的(de)安(an)裝和調試是(shi)否方便可靠(kao)等(deng)方面進行。
現代(dai)工程機械幾乎都采用了液壓系(xi)統(tong)，并且與電子系(xi)統(tong)、計算(suan)機控制技(ji)術結合，成(cheng)為現代(dai)工程機械的(de)重要組成(cheng)部分(fen)。
