液壓油泵的功耗占整個液壓機的97%以上，降低其功耗是液壓機節能的關鍵。液壓機所需的壓力和流量在快速下降、慢速下降、保壓、泄壓和回壓、活塞頂出、活塞后退、緩沖缸頂出等階段發生變化。當液壓機的用油量發生變化時，油泵出口的溢流閥調節負載壓力和流量，而電機的輸出功率不變，造成能量浪費。

四柱液壓機的(de)電(dian)能耗費首要表(biao)現在液壓體(ti)系油泵的(de)電(dian)能耗費。

變頻調(diao)速設備由整(zheng)流電(dian)(dian)路、濾波(bo)電(dian)(dian)路、逆(ni)變電(dian)(dian)路和控(kong)制電(dian)(dian)路組(zu)成(cheng)，其(qi)功用是經(jing)過(guo)整(zheng)流環(huan)節將溝通電(dian)(dian)能經(jing)過(guo)整(zheng)流、濾波(bo)為直(zhi)流電(dian)(dian)能，又經(jing)過(guo)逆(ni)變環(huan)節轉變成(cheng)不同頻率(lv)的(de)(de)溝通電(dian)(dian)能輸(shu)出給電(dian)(dian)機(ji)。所以可讓液(ye)壓(ya)油泵電(dian)(dian)機(ji)在(zai)不同的(de)(de)轉速下作業。別的(de)(de)，依據油泵的(de)(de)理論，油泵的(de)(de)輸(shu)出流量Q的(de)(de)計(ji)算公式為：

　　Q=2[π（R2-r2）-（R-r）S×Z/COSθ]B×N10-6

　　式中：R-葉片的半徑r-定子的短半徑

　　S-葉片(pian)的(de)(de)厚度(du)B-轉子的(de)(de)軸向寬(kuan)度(du)

　　Z-葉片數目θ-葉片相對半徑方向的傾角

由(you)上(shang)式公式中可得出改動(dong)油(you)泵(beng)電(dian)(dian)(dian)(dian)(dian)機(ji)(ji)轉(zhuan)(zhuan)子的(de)(de)轉(zhuan)(zhuan)速N也就改動(dong)輸出流量(liang)(liang)(liang)Q，即(ji)油(you)泵(beng)      油(you)流量(liang)(liang)(liang)與(yu)油(you)泵(beng)電(dian)(dian)(dian)(dian)(dian)機(ji)(ji)的(de)(de)轉(zhuan)(zhuan)速成(cheng)正(zheng)比，而改動(dong)油(you)泵(beng)電(dian)(dian)(dian)(dian)(dian)機(ji)(ji)轉(zhuan)(zhuan)子的(de)(de)轉(zhuan)(zhuan)速N是經過液壓機(ji)(ji)的(de)(de)同(tong)步信號自動(dong)控制(zhi)變頻(pin)節能調速設(she)備的(de)(de)輸出頻(pin)率(lv)來實現，油(you)泵(beng)電(dian)(dian)(dian)(dian)(dian)機(ji)(ji)的(de)(de)耗(hao)電(dian)(dian)(dian)(dian)(dian)與(yu)其轉(zhuan)(zhuan)速近似成(cheng)三次方聯(lian)系，即(ji)油(you)泵(beng)電(dian)(dian)(dian)(dian)(dian)機(ji)(ji)的(de)(de)耗(hao)電(dian)(dian)(dian)(dian)(dian)功(gong)(gong)率(lv)P=P｀（N｀/N）3，若液壓機(ji)(ji)油(you)泵(beng)電(dian)(dian)(dian)(dian)(dian)機(ji)(ji)額定功(gong)(gong)率(lv)為55KW，則當轉(zhuan)(zhuan)速下降(jiang)到原轉(zhuan)(zhuan)速的(de)(de)4/5時，其耗(hao)電(dian)(dian)(dian)(dian)(dian)量(liang)(liang)(liang)用(yong)28.16KW，省電(dian)(dian)(dian)(dian)(dian)48.8%；當轉(zhuan)(zhuan)速下降(jiang)到原轉(zhuan)(zhuan)速的(de)(de)1/2時，其耗(hao)電(dian)(dian)(dian)(dian)(dian)量(liang)(liang)(liang)僅用(yong)6.875KW，省電(dian)(dian)(dian)(dian)(dian)87.5%,從而使油(you)泵(beng)負載具有顯(xian)著的(de)(de)節電(dian)(dian)(dian)(dian)(dian)作用(yong)（其中：P｀=55KW，N｀/N=4/5和N｀/N=1/2）。