Introduction to Hydraulic Systems Part 2. Timothy Kerrigan Fluid Power Institute

Transcription

1 Introduction to Hydraulic Systems Part 2 Timothy Kerrigan Fluid Power Institute

2 Cylinder Types

3 Linear Motion: Hydraulic Cylinders Single acting o o Gravity return Spring return

4 Linear Motion: Hydraulic Cylinders Double acting o Differential area o Most common configuration

5 Single Acting Cylinder Circuit

6 Linear Motion: Hydraulic Cylinders Double rod Same area One rod working

7 Double Rod Annular areas are equal Cylinder has equal maximum force capability and same speed in both directions.

8 Rotary Loads Hydraulic motor has continuous rotation Rotary actuator refers to device with limited rotation - also known as oscillating motor or torque generator.

9 Motor Calculations Theoretical Flowrate: Q th gpm = DxN/231 o Where D is the displacement in in 3 /rev, N is speed in rpm, 231 converts in 3 into gallons Actual Flowrate: Q act gpm is measured using a flowmeter when the motor is being tested

10 Motor Calculations Theoretical Torque: T th in-lbs = DxΔP/2π o Where D is displacement in in 3 /rev, ΔP is differential pressure in psid Actual Torque: T act in-lbs is measured using a torque shaft when the motor is being tested

11 Motor Calculations Output Horsepower: o {(T act in-lbs)x(n rpm)}/63025 Input Horsepower: o {(Q act gpm)x(δp psid)}/1714

12 Motor Efficiencies Volumetric Efficiency: Indicates the amount of leakage that takes place inside the motor due to manufacturing tolerances and imperfect sealing surfaces It is expressed as a ratio of theoretical flow to actual flow: o E v = (Q th )/(Q act )

13 Motor Efficiencies Mechanical Efficiency: Indicates the amount of energy losses that occur for reasons other than leakage. This includes friction between mating surfaces as well as fluid turbulence It is expressed as a ratio of actual torque to theoretical torque: o E m = (T act )/(T th )

14 Motor Efficiencies Overall Efficiency: Indicates the amount of all energy losses in the motor It is expressed as a ratio of output horsepower to input horsepower: o E o = (HP o )/(HP i ) o E o is also = (E v )x(e m )

15 i i i i s p s p s p s p , 0 0 5, 0 0 0, m p r - n lb -. T in Typical Catalog Data for a Hydraulic Motor 0 2 m p g 0 3 m p g 0 1 m p g Displacement = 4.0 in 3 /revolution

16 Example Using Catalog Graph from Preceding Slide Determine the performance when the motor is receiving 20 gpm and the load dictates an operating pressure differential of 2,000 psid. The motor will be operating at a speed of 1,100 rpm and producing a torque of 1,200 in-lbs.

17 Example using catalog graph from preceding slide Output horsepower = T x N/63025 (1,200 in-lbs x 1,100 rpm)/63025 = 20.9 HP Input horsepower = ΔP x Q/1714 (2,000 psid x 20 gpm)/1714 = 23.3 HP

18 Example using catalog graph from preceding slide Theoretical speed = Q x 231/D (20 gpm x 231)/(4 in 3 /rev) = 1,155rpm Theoretical torque = ΔP x D/2π (2,000 psid x 4in 3 /rev)/2π = 1,274 in-lbs

19 Example using catalog graph from preceding slide Volumetric efficiency = Q th /Q act or N act /N th E v = 1,100/1,155 = 95.2% Mechanical efficiency = T act /T th or ΔP th / ΔP act E m = 1,200/1,274 = 94.2%

20 Example using catalog graph from preceding slide Overall efficiency = HP o /HP i E o = 20.9/23.3 = 89.7% Overall efficiency = E v x E m E o = x = 89.7%

21 Motor Sizing Example Determine the required load torque o This includes starting torque as well as running torque o If the load has large inertia and fast acceleration, then the starting torque could be significantly higher than the running torque Determine the required load speed Select a target differential pressure

22 Motor Sizing Example Calculate the minimum required displacement as follows: D in 3 /rev = (T x 2π)/(ΔP x E m ). Calculate the minimum flow rate required as follows: Q = (D x N)/(231 x E v ). Allowances for starting torque may be required based upon the following: o o Load requirements Motor starting torque efficiency

23 Motor Sizing Example Either the displacement or the available differential pressure must be increased to account for motor starting torque efficiency and load starting requirements On some motor designs, the starting torque at a given differential pressure can be as low as 70% of the running torque at the same differential pressure

24 Motor Sizing Example Example T = 2,000 in-lbs, N = 1,800 rpm, E m = 93%, E v = 95%, Starting Torque Eff. = 80%, Target Differential Pressure = 3,000 psid Initial sizing D = (2,000 x 2π)/(3,000 x 0.93) o D = 4.5 in 3 /rev Allowance for starting torque efficiency by increasing D. D! = D x 1.20 D! = 4.5 in 3 /rev x 1.2 = 5.4 in 3 /rev

25 Motor Sizing Example Allowance for starting torque efficiency by increasing differential pressure ΔP! = ΔP target x 1.20 = 3,000 x 1.2 o ΔP! = 3,600 psid Required flowrate based upon original value of D: Q = (4.5 x 1,800)/(231 x 0.95) o Q = 36.9 gpm

26 Motor Sizing Example Required flowrate based upon D!: Q = (5.4 x 1800)/(231 x 0.95) o Q! = 44.3 gpm

27 Hydraulic Motor Shaft Seal Hydraulic motors are apt to provide an external case drain in order to use a lowpressure shaft seal for installations which require bi-directional operation or braked stopping in only one direction Some manufacturers have hydraulic motor designs which eliminate the case drain by using a high-pressure mechanical shaft seal

28 Function o o Rotary Actuators The rotary actuator rotates an output shaft through a limited arc, which may be more or less than 360 deg It produces high torque at relatively low speed

29 Terminology o o Rotary Actuators The name causes some confusion because it contradicts the classification of hydraulic actuators Several other names have been suggested for the device described in this chapter: Oscillating motor Rotary cylinder

30 Types of Construction The external appearance of the vane type has the general configuration of a hydraulic motor The other types look rather like a hydraulic cylinder with a shaft that rotates instead of extending

31 VANE TYPE PORT PORT PORT PORT

32 RACK-AND-PINION

33 HELICAL SPLINE

34 HELICAL SPINE - more Within a cylindrical bore there is a short piston with a high helical angle internal thread which meshes with the central helical drive shaft Guide rods prevent the piston from rotating as it extends and rotates the drive shaft The rotation can exceed 360 deg

35 HELICAL SPLINE - more This design is used where a long, slim envelope is desired It offers the advantage of load locking, because the helix angle is designed to resist rotation by external loads

36 Applications Axes of hydraulic robots Welding fixtures to turn over the workpiece Indexing work tables Clamping Dipping the workpiece in a tank of liquid Material mixing processes Roll-over devices such as metal coil upenders

37 Rotary Actuator Definitions D v = displacement, in 3 /rev F = load force, lb. r = load radius, in. n = rotational speed, rpm v = load velocity, ft/sec Q = hydraulic fluid flow rate from pump, gpm n r F v

38 M Rotary Actuator Circuit

39 Basic Hydraulic Circuits

40 M Double Acting Cylinder Circuit With Tandem Center Valve

41 Cylinder Circuit with Pilot Operated Check Valves M

42 Cylinder Counterbalance Circuit with Overrunning Load

43 Cylinder Circuit with Mobile Valve and Load-Port Reliefs

44 Cylinder Circuit with Mobile Valve and Work-port Anti-Cavitation Checks

45 Parallel Stack Valve with Joy Stick A B J A B

46 Cylinder Circuit with Load- Sensing Relief Valve 3000psi 100psi

47 M

48 Pressure Compensated Pump to load Schematic

49 Cylinder Circuit with Load-Sensing Pump

50 Cylinder Regeneration Circuit Self Shift M

51 Cylinder Regeneration Fourth Position on Valve Spool M

52 M Rotary Actuator Circuit

53 Bi-Directional Motor Free Wheeling Stop M

54 Bi-Directional Motor Braked Stop M

55 Uni-Directional Motor with Brake Valve M

56 M Parallel Hydraulic Motors

57 M Series Hydraulic Motors

58 Hydrostatic Transmission Basic Circuit Variable Pump Fixed Motor

59 M High Low Pump Circuit

60 Accumulator Circuit M

61 Multiple Actuators with Gear Type Flow Divider M

62 M Meter-In Flow Control

63 M Meter-Out Flow Control

64 Multiple Actuators With Flow Divider Valve M

65 Illustrations Courtesy of: Skid Steers

66 Illustrations Courtesy of: Scissor Lift

67 Any Questions? Thank You