(a)主缸的流量
快速下行时q1 = A1v1 = 804×6 = 120600px3/s = 289.4 L/min
工作行程时q2 = A2v2 = 804×0.6 = 12050px3/s = 28.9 L/min
快速回程时q3 = A3v3 = 183.5×5.3 = 24975px3/s = 59.9 L/min
(b)主缸的功率计算
快速下行时(起动):P1 = p1q1 = 12533×4824×10-6 = 60.46 W
工作行程初压阶段末:P2 = p2q2 = 2.46×106×482×10-6 = 1186 W
终压阶段:此过程中压力和流量都在变化,情况比较复杂。压力p在最后20 mm行程内由2.46 MPa增加到24.6 MPa,其变化规律为
p = 2.46+20(24.6-2.46)S = 2.46+1.11S(MPa)
式中S——行程(mm),由压头开始进入终压阶段算起。
流量q在20 mm内由482 cm3/s降到零,其变化规律为q = 482(1-20(S))(cm3/s)
功率为P = pq = 482×(2.46+1.11S)×(1-20(S))
求其极值,?S(?P) = 0得S = 8.9(mm)此时功率P最大
Pmax = 482×(2.46+1.11×8.9)×(1-20(8.9))= 3300.8 W = 3.3 kW
快速回程时;等速阶段P = pq = 1.75×106×999×10-6 = 1.748 kW
起动阶段:此过程中压力和流量都在变化,情况也比较复杂。设启动时间0.2秒内作等加速运动,起动阶段活塞行程为
S = 0.5vt = 0.5×5.3×0.2 = 5.3mm
在这段行程中压力和流量均是线性变化,压力p由21 MPa降为1.75 MPa。其变化规律为
p = 21–5.3(21-1.75)S = 21–3.6S(MPa)
式中 S——行程(mm),由压头开始回程时算起。流量q由零增为999 cm3/s,其变化规律为
q = 5.3(999)S = 188S(cm3/s)
功率为P = pq = 188S(21–3.6S)
求其极值,?S(?P) = 0得S = 2.9(mm),此时功率P最大
Pmax = 188×2.9×(21–3.6×2.9) = 5755 W = 5.76 kW
由以上数据可画出主液压缸的工况图(压力循环图、流量循环图和功率循环图)见图1.3。
(c)顶出缸的内径Dd
Dd = ηcmπp(4Fd)= 0.91×π×25×106(4×3.6×106)= 1419 m = 142 mm
按标准取Dd = 150 mm