Hydraulic and pneumatic pressure transmissionChapter 4 Hydraulic Actuators Chapter 4 Hydraulic Actuators24.1HydraulicMotors 4.2Cylinders Thefunctionofhydraulicactuators is to translate hydraulic energy of fluid into energy of the machine. They will drive themechanism motion path like a straight, swingorrotation. Thestraightorswingarereferredashydraulicactuatororswingmotionactuator,andtherotationalmotioniscalledhydraulicmotor.Theoutputparametersareforceandspeedortorqueandrotatingspeed. Chapter 4 Hydraulic Actuators34.14.1HydraulicMotors 4.1.1 4.1.1 Introduction The popular concept of a hydraulic motor is that it is nothing but a pump run backwards. 1.Characteristicparameters （1）Powerandoverallefficiencies The input power of motor is:(4-1) The output power of the motor is: (4-2) The overall efficiency of the motor is the ratio of to ,(4-3) Chapter 4 Hydraulic Actuators4（2）Torquesandmechanicalefficiencies（a）Thetheoretictorque Oralso（b）Startuptorque (4-4)(4-5)Chapter 4 Hydraulic Actuators5（c） Mechanicalefficienciesthus (4-6) (4-7) （3）Flowrateandvolumetricefficiency (4-8) Chapter 4 Hydraulic Actuators6 (3-9)（4）Deliveryandrotatingspeed (3-10)（5）Workingandratedpressures Chapter 4 Hydraulic Actuators7 2.Motorclassification Motors may be classified based upon their working performances:(1) High-speedhydraulic motors whose ratedrotatingspeedisbeyond500r/min; (2) Low-speedhydraulic motors whose ratedrotatingspeedisbelow500r/min. High-speedhydraulic motors may be further divided into gear motors, vane motors, axial piston motors, screw motors, etc. Low-speed hydraulic motors include single-acting connecting rod type radial piston motors and incurve multiple-acting radial piston motors. Motors can also be classified as fixed delivery and variable delivery according to their delivery types.Fig.4-1Graphicssymbolsofmotor3.The graphicsymbols of motor Chapter 4 Hydraulic Actuators84.1.2 4.1.2 Hydraulicmotorsoperation 1.AxialpistonmotorsFig.4-2Axialpistonmotorsoperation Chapter 4 Hydraulic Actuators92.Vanemotors 3. Double-acting vane motors are generally used in industrial hydraulic systems, here a double-acting design operation is illustrated as follows:Fig.4-3Balancedvanemotoroperation Chapter 4 Hydraulic Actuators10Structure features The vanes in a vane motor are positioned radially with a zero vane angle (=0). A shuttle valve is set at the path between high/low pressure oil chambers and the vane bottom to ensure high pressure oil at the vane bottom. To ensure a normal startup, a spring with preload is mounted at the vane bottom to prevent the connection of high and low pressure chambers when high pressure oil enters into the vane motor. Vane type motors are small in size and thus the moment of inertia, making a short reaction time and applicable to frequent direction-changing occasions. However vane type motors find more applications in small torque, high speed, low mechanical performance request occasions due to its large leakage and inadequate stabilization at low speed.Chapter 4 Hydraulic Actuators113.Gearmotors Fig.4-4ExternalgearmotoroperationChapter 4 Hydraulic Actuators12Structure features Chapter 4 Hydraulic Actuators134.1.3 4.1.3 Low-speedmotors Low-speed motors are usually radial piston motors. They possess high pressure and large delivery to meet the needs of low speed rotation and large torque. Because of their large size and large moment of inertia, they are not suitable for the applications which require rapid response and frequent direction changing. Low-speed motors may be further classified based on how they function: (1)single-acting motors which provide a push in one direction; (2)double-acting motors which provide push in both directions; (3)multiple-acting motors which provide push in many directions.Chapter 4 Hydraulic Actuators141.Single-actingconnectingrodtyperadialpistonmotors Fig.4-5Crankandconnectingrodtyperadical-plungermotoroperation Chapter 4 Hydraulic Actuators15 The delivery for single acting radical-plunger type motors is expressed by:(4-11)(4-11)where d is the diameter of the plunger,e is the eccentric distance of the crankshaft and z is the plunger number. Structurefeatures Chapter 4 Hydraulic Actuators162. 2. Incurve multiple-acting radial piston motors Fig.4-6Incurvemultiple-actingradialpistonmotors Chapter 4 Hydraulic Actuators17 The delivery of this type is expressed by: (4-12)(4-12) where d is the piston diameter, s is the piston stroke, x is the action times, y is the number of the piston rows, z is the number of pistons in each row. StructurefeaturesChapter 4 Hydraulic Actuators184.2 4.2 Cylinders 4.2.1 4.2.1 Classificationandspeed-thrustcharacteristic Cylinders may be further divided into piston type, plunger type and swing type based on their constructions or single-acting, double-acting according to how they function. Some typical cylinders are described as follows.1.Pistoncylinder2.2.(1(1）Double-rod3.pistoncylinders a)Fig.4-7Double-rodpistoncylinder b)Chapter 4 Hydraulic Actuators19 The two piston rods in the two sides of the double rod piston cylinder are equal in diameters. When input flow rates and pressures are constant, the output thrust F and speed v are equal in the two opposite directions. F and v can be calculated as follows: (4-13)(4-13) (4-14) (4-14) Chapter 4 Hydraulic Actuators20（2 2）Single-rodpistoncylinders a)b)c)Fig.4-8Single-rodpistoncylinder Chapter 4 Hydraulic Actuators213 3. . Plungercylinders Fig.4-9Plungercylinder Chapter 4 Hydraulic Actuators22 Note the plunger diameter as d, the input hydraulic oil flow rate as q, then the thrust F on the plunger and its speed v are:(4-23)(4-23) (4-24)(4-24) Chapter 4 Hydraulic Actuators233 3. . Cylindersofothertypes （1）Telescopiccylinders The cylinders shown in Fig. 4-10 and 4-11 are single-acting and doubleacting telescoping cylinders respectively. Their principal difference lies in: single-acting type needs outside force (such as gravity) to return to its home position, while the double type accomplishes this by the hydraulic oil.Chapter 4 Hydraulic Actuators24Fig.4-11Single-actingtelescopingcylinder Fig.4-10Double-actingtelescopingcylinder Chapter 4 Hydraulic Actuators25Fig.4-12Rack-pistoncylinder 2.Rack-pistoncylinderChapter 4 Hydraulic Actuators26（3 3）Superchargecylinders Fig.4-13Superchargecylinder Chapter 4 Hydraulic Actuators274.2.2 4.2.2 Typicalconstructionsandmakeups 1. 1. Typicalconstructions Fig.4-14Single-rodcylinderconstruction 1-Cylinderbottom(缸底缸底)2-Cushionpiston(缓冲柱塞缓冲柱塞)3-Clipkey(卡键卡键)4、6、10、12-Seal(密封圈密封圈)5-Piston(活塞活塞)7-Cylinderbarrel(缸筒缸筒)8-Pistonrod（活塞杆）（活塞杆）9-Guidesleeve（导向套）（导向套）11-Cylinderlid(缸盖缸盖)13-Dustproofring（防尘圈）（防尘圈）14-Trunnion（耳轴）（耳轴） Chapter 4 Hydraulic Actuators282. 2. Makeups Cylinders can be further divided into cylinder block assembly, piston assembly, sealing device, cushion device and venting device. （1）Cylinderblockassembly Fig.4-15Cylinderbarrelandcylindercoverconnection Chapter 4 Hydraulic Actuators29（2 2） Pistonassembly Fig.4-16Pistonsandrodsconnection Chapter 4 Hydraulic Actuators30（3 3）Cushiondevices Fig.4-17Cylindercushiondevice a)Circularcylindricalvoidb)Circularconevoidb)c)Variablethrottlegrooved)AdjustablethrottleorificeChapter 4 Hydraulic Actuators31（4) 4) Ventingdevices Fig.4-18Ventingdevices Chapter 4 Hydraulic Actuators324.2.3Maindimensioncalculation The cylinder structure dimension has a direct relationship with the working mechanism of the mainframe. 1. 1. Problems for attention (1) On the precondition of proper speed and suitable thrust, each part of the cylinder must be designed according to related standards. The cylinders should be as compact as possible and convenient to machine, install and maintain. (2)The piston rod is in tension under the heaviest load. If the piston rod is in compression, it should possess a good longitudinal stability. When long stroke piston rod extends out, auxiliary support is needed to prevent the piston rod from drooping. (3) Only one end of the cylinder can be fixed for position for installation or fastness to ensure non-obstruction for cylinders expanding with heat and contracting with cold. (4)Whether the cylinder system needs cushions, venting and dustproof devices or not must be determined based on the concrete working conditions.Chapter 4 Hydraulic Actuators332. 2. Maindimensioncalculation （1 1）InnerdiameterDofthecylindertube （2 2）Thediameterdofthepistonrod （3 3）Cylindertubelengths （4 4）TheshortestguidelengthHChapter 4 Hydraulic Actuators343. 3. Intensitychecking （1 1）Wallthicknessofthecylindertube When D/10, is checked according to the thin-tube formula: (4-29)(4-29)When D/10, is calculated according to the formula for the thick wall of the cylinder tube: (4-30)(4-30) Chapter 4 Hydraulic Actuators35（2 2）Diameterdofthepistonrodchecking The piston rod is mainly in tension or compression, and its checking formula is:(4-31)(4-31) If the length of the piston calculated 10d, and suppose the piston is in compression and the load on it surpasses the critical value, the piston will lose its stability. So stability checking according to the related formulae in material mechanics is necessary.（3 3）Checkingofthediameteroftheconnectingboltsinthecylinder When the cylinder tube and the cylinder cap are connected by a bolt, the bolt is both in tension and under torsion stress. The outer force on the bolt should be amplified by 1.3 times. The bolt must be checked according to the related formulae in the material mechanics.Chapter 4 Hydraulic Actuators364.2.44.2.4Swingcylinders A swing cylinder show as Fig.4-20 Fig.4-20Rotarycylinder Chapter 4 Hydraulic Actuators37Ifthemechanicalefficiencyisconsidered,theoutputtorqueoftheswingshaftinthesinglevanecylindercanbeexpressedas:(4-32)(4-32)Fromtheaboveformulaandtheenergyconservativeprinciple,theoutputangularspeedis:(4-33)(4-33)Chapter 4 Hydraulic Actuators38your suggestions are welcome!The EndChapter 4 Hydraulic Actuators39Fig.4-4ExternalgearmotoroperationChapter 4 Hydraulic Actuators40Fig.4-3BalancedvanemotoroperationChapter 4 Hydraulic Actuators41Fig.4-7aDouble-rodpistoncylinderChapter 4 Hydraulic Actuators42Fig.4-7bDouble-rodpistoncylinderChapter 4 Hydraulic Actuators43Fig.4-8aSingle-rodpistoncylinderChapter 4 Hydraulic Actuators44Fig.4-8bSingle-rodpistoncylinderChapter 4 Hydraulic Actuators45Fig.4-8cSingle-rodpistoncylinderChapter 4 Hydraulic Actuators46Fig.4-9aPlungercylinderChapter 4 Hydraulic Actuators47Fig.4-9bPlungercylinderChapter 4 Hydraulic Actuators48Fig.4-10Double-actingtelescopingcylinderChapter 4 Hydraulic Actuators49Fig.4-11Single-actingtelescopingcylinder Chapter 4 Hydraulic Actuators50Fig.4-12Rack-pistoncylinderChapter 4 Hydraulic Actuators51Fig.4-13SuperchargecylinderChapter 4 Hydraulic Actuators52Fig.4-19Shortestguidelengthofcylinder