CASAPPALVP负载敏感泵工作原理.ppt

PLATA Series,variable displacement axial piston pumps,Working Principle and Hydraulic Controls,PLATA features,Designed for open circuit Suitable for medium and high pressure,for both mobile and industrial applications Low noise emission Energy savings thanks to the variable displacement High operational flexibility thanks to the wide range of control options:pressure controlflow controlpower(torque)control Short response time Drive shaft bearing suitable for both radial and axial loads Pump supports full torque transmission in multiple body configurations,PLATA technical data,*With an inlet pressure of 1 bar abs,With HL or HLP mineral oil,TORQUE LIMITER,Pump assembly,PRESSURE LIMITER,FLOW REGULATOR,Connection between flow regulator and torque limiter(LS signal),OUTLET PORT,INLET PORT,Pump components,Axial piston pumps convert rotary motion of an input shaft to an axial reciprocating motion of the pistons.During one half of the circle rotation,the piston moves out of the cylinder barrel and generates an increasing volume.In the other half of the rotation,the piston moves into the cylinder barrel and generates a decreasing volume.This reciprocating motion draws fluid in and pumps it out.,Working principle,The reciprocating motion is due to the angle between swash plate and shaft axis.This angle is variable(variable displacement pump).,Working principle,The reciprocating motion is due to the angle between swash plate and shaft axis.This angle is variable(variable displacement pump).,The delivery pressure and a spring act in the counterbalancing piston,keeping the swashplate to maximum displacement at pump starting up.,Pump displacement is regulated by the control valves,that decide the pressure in the pilot piston.When pilot pressure grows,swashplate angle decreases,leading to a shorter piston stroke and a reduced pump displacement.,Working principle,Working principle,Pump efficiency experimental tests,Q=FlowrateT=TorqueV=Displacementp=Pressuren=Speed,Volumetric efficiency,Mechanical-hydraulic efficiency,Pump LVP 48(46 cm3/rev)50 C mineral oil arnica 46,Pump efficiency experimental tests,Pin=Absorbed mechanical powerPout=Hydraulic power available on the outlet linehv=Volumetric efficiencyhmh=Mechanical-hydraulic efficiency,Overall efficiency,Pump LVP 48(46 cm3/rev)50 C mineral oil arnica 46,The portplate provides the connection between the piston(variable volume chambers)and the pump inlet and outlet ports.,Pump delivery,The grooves and the slots on the portplate are optimized in order to reduce pump noise,Connections inside the cover,The channels inside the pump end cover connect the regulation valves toP-the pressure source(outlet port)T-the return line(pump case)A the regulation chamber(pilot piston),P,T,A,A,P,P,Pressure control(RP),The pressure control regulates the pump displacement to equal system flow requirement,in order to maintain the pre-adjusted pressure,Maximum pump flowrate is provided if pressure is lower than the setting value Pump is protected without any external component Energy saving is guaranteed,because no exceeding flow is laminated through valves,S1,The pressure limiter regulates the pilot pressure keeping:,Pressure control(RP),T,A,P,Dynamic restrictor(=0.5 mm):it damps pressure oscillations and stabilizes the system,Acting on the spring preload,thepre-adjusted pressure p*PC can be set.,S1,Pressure control(RP),p*PC,The pump working conditions lie on two lines in the V-p diagram:the pump displacement is maximum if pressure is lower then the control pre-adjusted value p*PC(line not exactly horizontal due to the volumetric efficiency)if pressure tends to increase,the pump displacement adapts to system flow requirement,so that the maximum pressure is limited to p*PC(line not exactly vertical due to the springs stiffness),The pressure control is usually set to:p*PC=280 bar(maximum continuous pump outlet pressure),Flow control(LS),The flow control regulates the pump displacement in order to maintain a constant pressure drop across a flow metering device(LS principle),The LS signal must be connected to the port X of the flow regulator pX=pLS The LS signal provides the load information:thus at any value of pressure the pump flowrate equals the system flow requirement Energy saving is guaranteed,because no exceeding flow is laminated through valves,LS,X,LS principle,LOAD SENSING system:,(Variable displacement)Pump with LS regulator,LS control valve,Remote control for user command:user command u decides valve opening,X,LS principle,LOAD SENSING system:,The LS signal continuously provides information about the load pressure,The control system keeps a constant pressure drop across a flow metering device(control valve),directly acting on pump displacement,The control valve works as a restrictor:with a constant pressure drop the flowrate depends only on the valve opening,p,Q(to the circuit),X,LS principle,LOAD SENSING system:,The flow to the circuit depends on the user command and not on the load controllability The pressure drop p*FC is a pre-adjustable value p*FC is set to a low value(about 14 bar),then only a little power(Q x p*FC)is wasted through the control valve,Flow to the circuit is directly proportional to the user command u,p,Q(to the circuit),X,LS principle,LOAD SENSING system:,p,Null user command stand-by condition:The LS control valve completely closes and connects the LS signal to the discharge line The control system keeps p=p*FC(14 bar):the pump displacement becomes nearly null(only regulation flowrate is provided)and the outlet pressure is very low Energy saving,T,X,LS principle,LS advantages:CONTROLLABILITY pump always supplies the system with the required flowrate(under max available value),even with variable load the flowrate to the system is directly proportional to the user command,and not dependent on the load POWER SAVING the pressure on pump delivery depends on the actual load condition,through the Load Sensing signal no exceeding flowrate is provided by the pump if no flowrate is needed,the pump displacement is(nearly)null no lamination through relief valves(pump regulators act on pilot signals,so a very little amount of oil is wasted),The flow regulator regulates the pilot pressure keeping:,Acting on the spring preload,the pre-adjusted pressure drop p*FC can be set.,Flow control(LS),LS,T,A,P,Flow control(LS),LS,LS0 configurationDynamic restrictor(=0.4 mm):it damps LS pressure oscillations and stabilizes the system,T,A,P,LS2 configurationA plug takes the place of the dynamic restrictorSome applications do not need stabilization:the plug leads to a faster response of the flow control,S2,Flow control(LS),The spring preload is usually set to:p*FC=14 bar,Qmax,p*PC,The pump working conditions lie on a quadrangle in the V-p diagram:the pump displacement adapts to system flow requirement,at any value of pressure:with a constant opening of the control valve,the flowrate is constant even with a variable loadthe maximum pressure is still limited to p*PC by the pressure control,Torque control,The torque limiter regulates the pump displacement to maintain the pre-adjusted torque,according to the system pressure,The prime mover is protected from overload The prime mover can work always in maximum efficiency conditions If torque limit is not reached,the flow control is provided The pressure control limits the system maximum pressure,Torque control,The restrictor S3 is needed on the LS signal pX pLS S3 is functional:the torque control cannot work without it The dynamic restrictor in the flow regulator must be closed for a correct torque control working(LS2)A pipe connects the LS ports of the flow regulator and the torque limiter,connection pipe,LS,X,X,S3,Plug(LS2),The torque limiter puts a limit on the signal X:,1)if pLS p*TC:px=p*TCp=p*TC+p*FC Limit on the outlet pressure,Torque control,T,The flow regulator keeps:p-px=p*FC,X,Torque control,p*TC,swashplate stem,rear spring,swashplate,sleeve,X,Torque control,swashplate stem,rear spring,p*TC,sleeve,X,swashplate,The torque setting is a customer requestThe minimum torque limiter working pressure pTC should be at least 80 bar,Torque control,Qmax,p*PC,The pump working conditions lie on a quadrangle,the up right corner excluded:the pump displacement adapts to system flow requirement,at any value of pressureif the absorbed torque tends to increase,the pump displacement is reduced,so that the maximum absorbed torque is limited to Tmax(and the power to Pmax at constant speed)the maximum pressure is still limited to p*PC by the pressure control,Pmax,pTC,Torque control,The theorical operation at constant power(torque)is a hyperbola in the V-p diagram The real pump operation is a straight line(linear characteristics of the springs)In order to approximate the theorical operation two different working conditions are provided,corresponding to the two different springs in the torque limiter.The sleeve moving against the springs first compresses only the external one(higher pump displacement),and then the internal too(lower pump displacement),external spring,internal spring,Diapositive,