5. Hydraulic Pumps. Positive & non-positive displacement pumps Pumping action of pumps Fixed & variable displacement pumps

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1 5. Hydraulic Pumps Positive & non-positive displacement pumps Pumping action of pumps p Fixed & variable displacement pumps Operation of gear, vane, piston pumps Flow rate delivered by pumps Operation of pressure-compensated pumps Efficiency: volumetric, mechanical, overall Pump cavitation Pump noise: sound intensity levels Selection of a pump for a given application -1-

2 유압파워유닛 -2-

3 5.1 Introduction Hydraulic Pump the heart of a hydraulic system converts mechanical energy into hydraulic energy 유압공학에서다루는펌프는 hydrostatic pump 밀어내기식, 용적식 (positive displacement) 펌프 작동 cycle 흡입 ( 빨아들임 ), 공간차단, 압축및토출 ( 밀어냄 ), 공간차단 Displacement ( 배제용적 ) the amount of fluid ejected per revolution unit: cm 3 /rev, cc/rev, cm 3 /rad, cc/rad 정수압적유압기기 파스칼의원리를기초로하는유압기기 기기내부에서정압적 (static) 특성이지배 -3-

4 5.2 Pumping action of a pump Piston Pump 의작업 Cycle 흡입 빨아들임피스톤의후진에의하여만들어지는공간으로대기압상태의탱크에서작동유가빨려들어가거나, 선행부스터펌프에의하여가압된유량이공급된다. 유로전환흡입유로차단및토출유로연결 흡입구와압축실사이의유로를차단하고토출구와압축실사이의유로를연결한다. P S P D P D P D V 0 V CYL V P V P 압축및토출 밀어냄피스톤의전진 ( 밀어내기운동 ) 에의하여압축실내의유압유가토출구로밀려나간다. 유로전환토출유로차단및흡입유로연결토출구와압축실사이의유로를차단하고흡입구와압축실사이의유로를연결한다. ΔP W D W P P S V0 VCYL V -4-

5 Pumping Theory: piston pump Principle a partial vacuum is created at the pump inlet due to internal operation of the pump. -5-

6 5.3 Non-positive Displacement Pumps Hydrodynamic pump: 유체의 velocity energy 이용 용도 : low-pressure, high-volume flow application Max. pressure capacity: 250~300psi 종류 : Centrifugal (impeller) pump, axial flow (propeller) pump -6-

7 Centrifugal Pump -7-

8 Centrifugal Pumps Flow output is reduced as circuit resistance is increased. centrifugal pump can operate even when there is no demand for fluid. no need for a pressure relief valve to prevent pump p damage. 용도 : to deliver water to homes and factories Although dynamic pumps provided d smooth continuous flow, their output flow rate is reduced as resistance to flow is increased. -8-

9 Positive Displacement Pumps Hydrostatic pump: 유체의 pressure energy 이용 ejects a fixed amount of fluid into the hydraulic system per revolution of pump shaft rotation pump output flow is constant and not dependent on system pressure. Notice! Pumps produce fluid flow. Pumps do not pump pressure. The pressure is determined by the resistance to this flow. The pressure will rise until some component breaks unless pressure relief is provided. pumps must be protected against overpressure pressure relief valve -9-

10 Positive Displacement Pumps Advantages over non-positive displacement pumps High-pressure capability: up to 12,000psi (800bar) Small, compact size High volumetric efficiency Small changes in efficiency throughout the design pressure range Great flexibility of performance: wide range of pressure & speed Gear pumps External gear pumps Internal gear pumps Lobe pumps Screw pumps Vane pumps Unbalanced vane pumps Balanced vane pumps Piston pumps Axial piston pumps Radial piston pumps -10-

11 Fixed & Variable Displacement Pumps Fixed displacement pumps the amount of fluid ejected per revolution cannot be varied. Variable displacement pumps the displacement can be varied by changing the physical relationships of various pump elements. this change in pump displacement produces a change in pump flow output even though pump speed remains constant. vane pump, piston pump gear pump: fixed displacement only by geometrical necessity. -11-

12 5.4 Gear Pumps External Gear Pump fixed displacement pump uses spur gear (teeth are parallel to the axis of the gear) are noisy at relatively high speeds -12-

13 External Gear Pump EXTERNAL GEAR PUMP EXTERNAL GEAR PUMP End Pause / Restart Esc S -13-

14 Theoretical Flow Rate Volumetric displacement π V = D D L ( 2 2 ) 4 D o i Theoretical flow rate Q m V m rev N rev 3 3 T ( /min) = D ( / ) ( /min) Volumetric efficiency QA η v = 100 Q T -14-

15 Internal Gear Pump Crescent Seal Type Internal gear pump with built-in safety relief valve -15-

16 Internal Gear Pump INTERNAL GEAR PUMP INTERNAL GEAR PUMP End Pause / Restart Esc S -16-

17 Internal Gear Pump Gerotor Pump -17-

18 Internal Gear Pump Lobe Pump -18-

19 Screw Pump Screw Pump -19-

20 기어펌프, 나사펌프특징 External gear pump 구동기어와종동기어가서로외접인벌류트치형의기어사용보통 100bar 이내의압력에서사용 210bar까지도사용가능진동, 소음이발생하기쉬움압력분포의불균형문제발생정용량형만가능고부하, 고회전수, 고온에서는사용불가용량증대를위해서는치폭을증가. 대신베어링부하가커짐 Internal gear pump 외접형에비해흐름의맥동이적음 내외의양기어의상대속도가작으므로고속회전에용이 140bar 이하에서사용 210bar 까지도사용가능 Screw pump 구조상송출류가완전한 smooth flow 를이룸 진동이나소음이적음 마찰력이크고, 비교적효율이낮다. 정용량형펌프만가능 70bar 이내의압력에서사용 -20-

21 5.5 Vane Pumps Vane pump operation -21-

22 Simple Vane Pump SIMPLE VANE PUMP SIMPLE VANE PUMP End Pause / Restart Esc S -22-

23 Analysis of Volumetric Displacement D C : diameter of cam ring (in, m) D R : diameter of rotor (in, m) L: width of rotor (in, m) V D : pump volumetric displacement (in 3, m 3 ) e: eccentricity (in, m) e max : max. possible eccentricity (in, m) V Dmax : max. possible volumetric displacement (in 3, m 3 ) e max = D C D 2 R 2 2 ( ) ( )( ) ( )( 2 max ) π π π VD = D max C DR L= DC + DR DC DR L= DC + DR e L π VD = ( DC + DR) el 2-23-

24 Pressure-Compensated Vane Pump -24-

25 Vane Pump Balanced vane pump principles -25-

26 Balanced Vane Pump BALANCED VANE PUMP BALANCED VANE PUMP End Pause / Restart Esc S -26-

27 베인펌프의특징 Vane pump 장점 Vane pump 단점 송출압력의맥동이적음 vane 의마모에의한압력저하가발생하지않음 펌프의유동력에비해형상치수가작음고장이적고보수가용이 제작시정밀도가요구됨유압유의점도에제한일반적으로 38 o C에서 150~300 SUS 오일의보수에주의가필요 -27-

28 5.6 Piston Pumps Axial Piston Pump Swash plate design ( 사판식 ): 사판의각도 ( 사판각 ) 에의하여피스톤을축방향으로구동 Bent axis design ( 사축식 ) : 2 축의기울어진각도 ( 사축각 ) 에의하여피스톤을축방향으로구동 사판식 사축식 -28-

29 Swash Plate Type Piston Pump -29-

30 Operation of Swash Plate Type Piston Pump 축, CYLINDER BLOCK, PISTON 등이회전 밸브판 (VALVE PLATE), 사판 (SWASH PLATE) 은고정 SHOE PLATE 에의해 PISTON SHOE 는사판에밀착 축이회전하게되면 PISTON 은사판위를따라미끄러지며, 실린더블록의실린더내에서축방향으로왕복운동을한다. -30-

31 Piston Pump Principle PISTON PUMP PRINCIPLE PISTON PUMP PRINCIPLE End Pause / Restart Esc S -31-

32 펌프토출량 (Fixed Displacement Pump) -32-

33 Displacement of Swash Plate Type Piston Pump 펌프의배제용적 (displacement) 이란? - 단위회전당토출하는체적 ( 이론 ) - 토출량 / 회전속도 ( 실험 ): 최소토출압력, 정격회전속도조건 V P = 1 π D 2 P 4 D CYL tanαz P V P D D :1회전당토출유량( cm 3 / rev) P : piston직경( cm) CYL : cylinder block piston 직경( cm) α : 사판경사각 Z P : piston it 수량 -33-

34 Variable Displacement Version of Piston Pump -34-

35 Operation of Variable Displacement Piston Pump 가변용량펌프 (Variable displacement pump) 사판또는사축의기울어진각도를제어 정용량펌프 (Fixed displacement pump) 사판또는사축의기울어진각도가고정 -35-

36 Pressure-Compensated Piston Pump -36-

37 Operation of Pressure Compensated Pump Maximum Flow Zero Flow -37-

38 Pressure Compensation -38-

39 Bent-Axis Type Piston Pump 축, CYLINDER BLOCK, PISTON 등이회전 밸브판 (VALVE PLATE) 은고정 축의단부에 PISTON 의구면부가물려동시에회전 축이회전하게되면 PISTON은같이따라돌며실린더내에서축방향으로왕복운동을한다 -39-

40 Variable Displacement Bent-Axis Piston Pump -40-

41 Variable Displacement Piston Pump with Handwheel -41-

42 Radial Piston Pump 실린더블록의회전여부에따라, 회전실린더형과고정실린더형으로구분가변용량형이가능 20bar 이상의고압용에주로사용항공기, 산업용으로널리사용 -42-

43 Radial Piston Pump -43-

44 Volumetric Displacement & Theoretical Flow Rate θ: offset angle ( o ) S: piston stroke (in, m) D: piston circle diameter (in, m) Y: number of pistons A: piston area (in 2, m 2 ) N: pump speed (rpm) Q T : theoretical flow-rate (gpm, m 3 /min) S tan( θ ) = S = D tan( θ ) D V = YAS = YAD tan( θ ) D Q m DANY θ 3 T ( /min) = tan( ) -44-

45 피스톤펌프특징 특징 사판식 가변용량이가능효율이높다용적효율 : 97% 전효율 : 90% 고압용 : 200bar 베인펌프보다소음이심하다항공기, 산업용가격이비싸다 비교적고속회전에적합마력당중량이작다사축식에비해구조가간단사축식제작비용이많이든다누설손실이적다사판식보다효율이조금좋다 -45-

46 5.7 Pump Performance 배제용적 Displacement 단위회전당토출하는체적 ( 이론 ) 토출량 / 회전속도 ( 실험 ) 최소토출압력, 정격회전속도조건 3 사용단위 : m / rad, cc / rev 정격압력 : 설계상의기준치 정격회전속도 : 정격압력으로연속운전가능한설계상의기준이되는회전속도 무부하토출압력 : 시험설비가허용하는토출압력의최소치 -46-

47 Pump 구동에필요한 Torque Mechanical power supplied to pump H m = Tω Hydraulic power delivered by pump H p = 두관계식으로부터 PQ P : pressure rise across the pump Q : delivery rate T ω = PQ = P ω D T th th p th = PD 여기서D p : 펌프배제용적[ m3/ rad] p -47-

48 Torque 손실 Viscous Damping Torque: Fluid shear 에의한손실 Td = Bmω = CdDmμω B = C D μ : Damping coefficient C m d m d : 무차원 Damping coefficient μ : 절대점도 Coulumb Friction Torque: 작용력 - 마찰력에의한손실 Tf = ω CfDm P + P ω C f ( ) 1 2 : 내부마찰계수 Seal Friction Torque: shaft seal 에서발생 ω T c ω -48-

49 Pump Efficiency Measurement Volumetric efficiency (η v ): 누설과관련 압력이낮을수록, 속도가빠를수록용적효율좋다. 일반적으로용적효율은 90% 실제유량 ( Q OUT ) ηv = 이론유량( Qth ) Qth ΔQ ΔQ = = 1 Q Q = where, C th P μω d 1 S P ΔQ = δ C μ = D th 3 d d s P P ;( 누설유량 ) μ T ω Pd Qin Qout η v Qdrain μ : 점도, δ : 누설틈새, C S : 무차원의누설계수 -49-

50 Pump Efficiency Mechanical efficiency (η m ): 마찰과관련 압력이높을수록, 속도가느릴수록기계효율좋다 마찰과관련 η m 이론수요토크 (T Tth ) = 실제수요토크 ( T ) Tth = = Tth + ΔT 1 = 1 + C + C where, f d 1 Δ T 1 + T μω P DP ΔT = ( C d μω + C f Pd ) 2π C C d : 무차원의마찰계수, f d th T ω Pd Qin Qout Qdrain -50-

51 Pump Efficiency Overall efficiency (η o ) 에너지절약을위해서는전효율이가장좋은압력과속도에서주로작동하는것이좋다. η o = 실제출력유체동력(H H ) 공급된기계동력( H ) m PQ = Tω PDP Q = T T D ω = η v η m P ω Pd Qin Qout Qdrain -51-

52 Pump Efficiency Measurement Terms involving pump mechanical efficiency -52-

53 Performance Curves of Piston Pump 6-in 3 variable displacement pump Pressure Level 3,000psi 5,000psi -53-

54 Performance Curves of Radial Piston Pumps PR24: 2.40-in 3 displacement PR30: 3.00-in 3 displacement PR40: 4.00-in 3 displacement -54-

55 Performance Curves for Vane Pump Performance curves for variable displacement pressure-compensated vane pump at 1200rpm -55-

56 Comparison of various performance factors -56-

57 5.8 Pump Noise: Common Sound Levels [unit: db] Threshold of Pain 140 Jet Takeoff at Close Range 130 Hydraulic Press 120 Nearby Riveter Deafening 110 Amplified Rock Band 100 Noisy City Traffic Very Loud Noisy Factory, Gear Pump Vacuum Cleaner, Vane Pump Loud Moderate Noise Office, Piston Pump Average Factory, Screw Pump Average Office Private Office Faint 30 Quiet Conversation 20 Rustle of Leaves Very Faint 10 0 Whisper Threshold of Hearing -57-

58 Pump Noise as a Performance Parameter Data showing effect of changing size, pressure, and speed -58-

59 Preferred Range of Oil Viscosities & Temperatures Noise levels for various pump design Pump Noise Level Design (db-a) Gear Vane Piston Screw

60 5.9 Pump Selection 기본사양 펌프크기즉배제영적 : 출력장치의속도정격압력 : 출력장치가발생하는최대힘, 부하저항사이클원동기속도 : 펌프의토출유량 펌프수명 : 펌프내베어링의 B-10 정격수명, 내구시험에의한마모특성설치와포트연결문제 : 다른부품과의조합성, O-ring, 테이퍼나사크기와중량효율 : 용적효율, 기계효율, 전효율초기가격 수리문제 : 써비스부품의구입, 교환의용이성납기문제수요자선택 : 수요자요구, 경쟁기종실적 -60-

61 Pump Selection 부하율 간헐부하 ( 그림 a) 연속부하 ( 그림 b) 경부하 (light duty) : 부하계수 (load factor) 가정격최대용량의 25% 이내 중간부하 (medium duty) : 부하계수가 25% 이상 75% 이내 중부하 (heavy duty) : 부하계수가 75% 이상 0 Work Dwell Time 0 Work Dwell Time Cycle (a) Cycle (b) -61-

62 Pump Selection 가격요인 시스템필요조건의관리 ( 계획 ) 유체의종류 (fluid type) 사용정격압력작동교체모드여유율과수명시스템의교체 펌프의특성정용량형펌프 : 통상적으로가격이저렴하나제어에필요한여러가지부품의가격이고려되어야한다. 가변용량형펌프 : 가격은고가이나필요한제어장치가적다. 시스템의배치는펌프타입의선택에영향을미치고, 펌프의종류에따라필요한공간이달라진다. (ex. 원심펌프 < 왕복펌프, 수직펌프 < 수평펌프 ) 대체로같은용량에서는기어펌프가가장싸고피스톤펌프가가장비싸다. 베인펌프는중간정도의가격이다. -62-

63 펌프선정지표 펌프종류시스템압력, 작동유고려기어펌프, 베인펌프, 피스톤펌프사용압력 : rated pressure 펌프제조사는통상전효율이가장좋은압력또는베어링수명과효율을동시에고려하여사용압력을제시최대압력 : max. pressure 펌프가견딜수있는최대압력흡입압력 : suction pressure 낮을수록좋다. 흡입압력이높아야할경우에는탱크가압배제용적 : volumetric displacement 1회전당토출하는작동유의부피 (cc/rev) 시스템유량과원동기의회전속도에따라결정배제용적 = 필요유량 / 원동기회전속도 최대속도 : max. speed 펌프의기계적특성으로최대회전속도가제한점도범위 : viscosity it range 작동유종류, 선정온도범위 seal, 작동부의열팽창고려유압유청정도용량가변여부회전방향설치방법원동기와의설치방법과형상에따라축형상축연결방법연결구배관설계고려 기타 부속부품외관크기 -63-

64 참고 : 펌프의설계 - 기어펌프 (1) 작동원리및분류외접기어펌프 내접기어펌프 (2) 체적유량및유량의맥동 (3) 작용력과모멘트치차의작용력해석 펌프케이스의부하 (4) 축방향과반경방향의간극보상 (5) 주요치수의결정 (6) 펌프설계의예 -64-

65 Report Text Problems Due date: 2 주후 -65-

Lecture Note 8-1 Hydraulic Systems. System Analysis Spring

Lecture Note 8-1 Hydraulic Systems 1 Vehicle Model - Brake Model Brake Model Font Wheel Brake Pedal Vacuum Booster Master Cylinder Proportionnig Valve Vacuum Booster Rear Wheel Master Cylinder Proportioning