chpt8-Control-Components-in-Hydraulic-Systems-液压传动.ppt

,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,*,Control Components in Hydraulic Systems,8.1,Introduction,There are three basic types of control devices:,(1)directional control valves.,To determine the path through which a fluid traverses within a given circuit.,(2)pressure control valves.,To protect the system against overpressure,which may occur due to a gradual buildup as fluid demand decrease or due to a sudden surge as valves open or close.,(3)flow control valves.(Noncompensated flow control valve and compensated flow control valve),To control fluid flow rate in various lines of a hydraulic circuit.,8.2,Directional Control Valves,1.,Check Valve,(1)Simplest Check Valve:,1).Configuration:,2).Operation:,3).Symbol,(2),Pilot-operated check valve,Configuration:,Operation:,Symbol,It is frequently used for locking hydraulic cylinders,in position.,(3).,Animated demonstration,2.,Sliding valve(Most directional control valves uses a sliding spool to change the path of flow through the valve),1)Two-way and four-way valves,Two-position,spring offset,four-way valve,(2),Mechanically actuated,(3),Air or hydraulic pilot-actuated,(5),Solenoid-controlled,pilot-operated,The upper pilot stage spool(which is solenoid-actuated)controls the pilot pressure,which can be directed to either end of the main stage spool.,Unload the pump.,Keep the pressure in the hydraulic circuit.,Shift with smoothness or precision.,Start with smoothness.,The stop and“float”of hydraulic cylinder.,4.,Shuttle valve,8.3,Pressure Control Valves,Functions:a)To provide protection against any overloads experienced by the actuators in the hydraulic system(,safety valve,).b)To limit the force or torque produced by hydraulic cylinders and motors(,overflow valve,).,1.,Pressure relief valve,1),Simple pressure relief valve,2),Compound relief valve (,Click here to demonstrate,)Configuration and Operation,p,1,p,2,p,A=,p,1,A+F,s,External and Cutaway views of an actual compound relief valve.,3),Applications of pressure relief in hydraulic circuit,a.To limit the force or torque,b.To provide protection against any overloads,Pressure relief valve is normally open.,Pressure relief valve is normally closed.,c.Remote or multistage pressure setting,d.To Unload a pump.,e.To provide the back pressure for actuator.,(see item b.),Compound pressure-reducing valve,(Click here to demonstrate),p,3,p,4,P,2,A=p,3,A+F,s,Application of pressure-reducing valve in circuit,To reduce pressure in a oil line and keep it constant.,b.To remotely reduce pressure.,Unloading valve,This valve is used to permit a pump to build up to an adjustable pressure setting and then allow it to discharge to the tank at essentially zero pressure as long as pilot pressure is maintained on the valve from a remote source.,4.,The sequence valve,1),Operation,It is designed to cause a hydraulic system to operate in a pressure sequence.,Schematic of sequence valve.,b.To unload the pump,c.To keep oil pressure in hydraulic control circuit constant,Main circuit,Control circuit,5.,Counterbalance valve,1)Operation:The purpose of a counterbalance valve is to maintain control of a vertical cylinder to prevent it from descending due to gravity.,2),Application of counterbalance valve,Pressure relief valve,Pressure-reducing valve,Sequence valve,Unloading valve,A review of the symbols of these valves,8.4,Flow Control Valves,Flow control valves are used to regulate the speed of hydraulic cylinders and motors controlling the flow rate to these actuators.,There are two basic types of flow control valves:Non-pressure-compensated and pressure-compensated.,1.Throttle valves,(,节流阀),1)Operation:,Pressure vs.flow rate equation:,2),Typical orifice configurations and pressure vs.flow rate equation,Pressure vs.flow rate equation:,针式,偏心式,轴向三角槽式,周向缝隙式,轴向缝隙式,3),Throttle valves configurations and symbol,This type is used where system pressure are relatively constant and motoring speeds are not too critical.,p,3,p,2,p,1,2.,Pressure-compensated flow control valves,p,1,p,2,p,2,A,1,+,p,2,A,2,=,p,3,A+F,s,p,2,A=,p,3,A+F,s,p,=,p,2,-,p,3,=,F,s,/,A,8.7,Pressure Switches,A pressure switch is an instrument that automatically senses a change in pressure and opens or closes an electrical switching element when a predetermined pressure point is reached.,There are four different models:,1)Diaphragm,2),Bourdon tube,3),Sealed piston,4),Dia-seal piston,8.8,Shock Absorbers,A shock absorber is a device which brings a moving load to a gentle rest through the use of metered hydraulic fluid.,Application of shock absorbers,The suspension system of,automobiles,Crane,application,A B,限压式叶片泵性能实验报告,班级：学号：组别：,姓名：实验日期：指导教师：,一、实验装置液压原理图、电气控制原理图及测试仪器框图,1,液压原理图,2电气原理图,3,测试仪器框图,二、数据处理：,1,实验数据表：,p,（kgf/cm,2,）,Q,（l/min）,M,(kgfm),n,(rpm),P,入,(,KW),P,出,(,KW),总,4,10,20,30,36,38,40,42,44,46,48,50,2,绘制特性曲线：将,p,Q,、,p,P,入,、,p,总,三条特性曲线描绘在同一直角坐标系中。,三、实验结果分析与问题思考：,1结果分析：分析所得数据、曲线和计算结果是否正确？产生误差得原因？另从这些数据、曲线和计算结果中，能说明什么问题，得出什么结论？,2,问题思考：,1,）使用限压式变量叶片泵供油得液压系统有什么特点？,2）当分别调节泵得流量螺钉和压力螺钉时，,pQ,特性曲线有何变化？,3）从计算机描绘得,pQ,特性曲线看出：当泵在加载和减载时，曲线变量段是不重合。为什么？,4）当泵对外输出流量为零是，泵内定子的偏心是否为零，为什么？,5,）更换泵的限压弹簧是，即改变弹簧刚度对,p,Q,特性曲线有何影响？,