Chapter-6-The-Source-of-Hydraulic-Power-Pumps-液压传动

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Chapter 6 The Source of Hydraulic Power:Pumps,6.1,Introduction,1.A pump,which is the heart of a hydraulic system,converts mechanical energy into hydraulic energy.,2.Pump classification,1)Nonpositive displacement pumps:,low-pressure,high-volume flow.To be Used for transporting fluids.Examples of this type are the centrifugal and axial pumps,2),Positive displacement pumps:,I.High-pressure capability,small and compact size,high volumetric efficiency,small changes in efficiency throughout the design pressure range,great flexibility of performance.To be used for fluid power systems.,II.There are three main types:,a.,Gear pumps,(fixed displacement only by geometrical necessity):External gear pumps,Internal gear pumps,Lobe pumps,Screw pumps.,b.,Vane pumps,:Unbalanced vane pumps(fixed or variable displacementpressure compensation capability),Balanced vane pumps(fixed displacement only).,c.,Piston pumps,(fixed or variable displacement):Axial design,Radial design.,III.Pumps produce fluid flow instead of pressure.,6.2,Pump Theory,The volume of oil displaced by the piston per rev is called,the displacement volume of the pump.,2),Pump flow rate:,I.Theoretical flow rate,Q,t,(neglecting the internal leakage):,II.Actual flow rate,Q,a,:,III.Rated flow rate,Q,r,:,Q,a,at rated pressure and speed,3.Power and efficiency:,1)Theoretical power,P,t,(neglecting energy loss):,Input power:P,t,=T,t,=T,t,2,N,Output power:P,t,=,p,Q,t,T,t,2,N=,p,Q,t,=,p,q,p,N,T,t,=,p,q,p,/(,2,),Q,t,=q,p,n,2),Volumetric efficiency(,v,):indicated the amount of leakage which takes place within the pump.,3)Mechanical efficiency(,m,):indicated the amount of energy losses that occur due to reasons other than leakage.This includes friction and fluid turbulence.,=,Q,a,/Q,t,100%,m,=,Theoretical power required to operate pump,Actual power delivered to pump,100%,v,=,Actual flow rate produced by pump,Theoretical flow rate pump should produce,100%,or,m,=,Pump output power assuming no leakage,Input power delivered to pump,100%,m,=,Theoretical torque required to operate pump,Actual torque supplied to pump,100%,or,=,T,t,T,a,100%,4)Overall efficiency(,o,):considers all energy losses and is defined mathematically as follows.,=,v,m,o,o,=,Pump output power,Pump input power,100%,4.,Pump performance curves,See fig.6-31.,5.,Noise:,It is a significant parameter used to determine the performance of a pump and measured in units of decibels db(A).,There are three main factors in noise:,1.Pump speed has a strong effect on noise.,2.Another cause of noise is entrained air bubbles in the hydraulic fluid.,3.Cavitation contributes to noise.,Cavitation,6.4,Symbolic representation of Pump,The following rules will control or eliminate cavitation of a pump.(1)Keep suction line velocities below 0.51.5 m/s.(2)Keep pump inlet lines as short as possible.(3)Minimize the number of fittings in the inlet line.(4)Mount the pump as close as possible to the reservoir.(5)Use low-pressure drop inlet filters or strainers.(6)Use the proper oil.,Example 6-4,A pump has displacement volume of 5 in.,3,It delivers 20 gpm(0.001264 m,3,/s)at 1000 rpm and 1000 psi.(68.9655 2bar)If the prime mover input torque is 900 in.,lb(101.523 N,m),a.what is the overall efficiency of the pump?,b.what is the theoretical torque required to operate the pump?,Solution:,a.Q,t,=q,p,N,v,=Q,a,/Q,t,m,=T,t,/T,a,T,t,=,p,q,p,/,(2,),o,=,v,m,b.T,t,=,p,q,p,/(,2,),6.5,Gear Pumps,External gear pump operation:,Its detailed features see fig.6-6,It consists of gears,pump housing,and the side wear plates.,特点,结构简单，抗污染能力强，耐冲击负载，价格最便宜。,容积效率较低，轴承上不平衡力大，工作压力不高。齿轮泵的另一个重要缺点是流量脉动大，运行时噪声水平较高，在高压下运行时尤为突出。,齿轮泵主要用于低压或噪声水平限制不严的场合。通常,p10MPa,，如工程机械、建筑机械、农用机械等。一般机械的润滑泵以及非自吸式泵的辅助泵都采用齿轮泵。,存在的三大问题,:,1.,泄漏,2.,不平衡径向力,3.,困油,2.,Internal gear pump:,1),Operation of involute(,渐开线),gear pump:,2),Operation,of gerotor（,摆线或转子）,pump:,3),Variable displacement pressure-compensated vane pump:,i.Configuration:Vanes,rotor,cam ring,pressure compensator adjustment,maximum displacement adjustment,cover plate,valve plate.,ii.Operation:,The initial spring force:,F,s,=k,x,0,The horizontal force produced by pressure:,F,x,=,p,A,x,If F,x,F,s,the compensator spring is compressed until zero eccentricity.,iii.Pressure versus flow rate curve for pressure-compensated vane pump.,Q,e=e,MAX,p,p,deadhead,e=0,A,B,C,p,cutoff,a.When we adjust the pressure compensator,line BC moves right and left.,b.When we change the initial eccentricity,line AB moves up and down.,6.7,Piston Pumps,1.,Axial piston pumps:(the swash plate type),The valve plate,Fixed displacement Piston Pumps,1,2,Q=（number of pistons,）,x（piston area,）,x（piston stroke,）,x（rpm of pump,）,One cycle,Q,Variable,displacement Piston Pumps,Q=（number of pistons,）,x（piston area,）,x（piston stroke,）,x（rpm of pump,）,One cycle,Q,Variable displacement Piston Pumps,Q=（number of pistons,）,x（piston area,）,x（piston stroke,）,x（rpm of pump,）,Q,One Cycle,Variable displacement Piston Pumps,Q=（number of pistons,）,x（piston