1 ABE 223 ABE Principles – Machine systems ABE 223 ABE Principles – Machine systems Pumps and Actuators Tony Grift Dept. of Agricultural & Biological Engineering University of Illinois

2 Agenda Units, Pumps, Pressure Relief Valve Cylinders Double acting/ Single acting Single rod, Double rod Cylinder construction Pressure, Flow, Work and Power in cylinders Pressure, Flow, Torque and Power in pump/motors Volumetric and Torque efficiency of pump/motors Pump implementations

3 Hydraulic Units (SI) Pascal Newton Watt

4 Hydraulic drive unit

5 A Pressure Relief Valve (PRV) provides overload protection In the symbol there are Main pressure lines (solid) Sense lines (dashed) Spring return Adjust arrow Direction arrow Pressure and Tank connections

6 Some questions about a PRV Is this valve normal open or normal closed Closed / open, think of a door Where is the pressure sensed, upstream or downstream and why ? What is the pressure at the tank port ? Why is a PRV adjustable ?

7 Cylinders

8 Video 9: Hydraulic actuators (6:58) Cylinders convert hydraulic energy into linear motion Motors generate rotary motion Single acting cylinder: One working port Can do work in only one direction (extension) External force retracts the cylinder No perfect seal, over time oil passes on to unpressurized side: need for drain Good for high load single lift (scissor platform) Return stroke through gravity or spring return Plunger (ram) cylinders: Cap end only, very powerful and stiff Double acting cylinder: Two working ports Pressure advances and retracts the cylinder: push and pull Cylinder retracts faster than it extends due to different areas of cap end and rod end side

9 Video 9: Hydraulic actuators (6:58) cont. Example: ratio of cap and rod end side area is 2:1. Assume During extension rod end pressure =0 During retraction cap end pressure =0

10 Video 9: Hydraulic actuators (6:58) cont. Example: ratio of cap and rod end side area is 2:1. Linear Power:

11 Hydraulic Cylinder

12 Cylinder construction

13 1.Tie rod ( keeps cylinder assembly together ) 2.Rod end head( mounting point ) 3.Rod end port ( fluid entrance/exit point ) 4.Piston seals ( dynamic, seals cap end from rod end pressure) 5.Cap end head ( mounting point) 6.Cap end port ( fluid entrance/exit point ) 7.Rod bearing ( lateral support of the rod ) 8.Rod wiper ( keeps dirt out ) 9.Rod seal (dynamic, seals fluid from environment ) 10.Barrel ( cylinder ) 11.Piston rod ( mechanical force output ) 12.Piston ( pressure to force converter ) 13.Static seal ( seals fluid from environment )

14 Tie rod cylinder versus a welded body cylinder

15

16 Cylinders are perfect for linear motion Single rod (most common) Dual rod (power steering)

17 Telescopic cylinder

Long stroke telescoping cylinder: avoiding buckling is a major design criterion 18

Cylinder cushioning is used to slowly decelerate the cylinder when it reaches the fully retracted/extended position 19

Cylinder cushioning is used to slowly decelerate the cylinder when it reaches the fully retracted/extended position cont. 20 Cylinders with large piston rods leave little room for a rod end cushion

Cylinder mounting options 21 Head flange mount Double spherical eye mount Clevis mount

22 Basic Circuit with Double Acting CylinderPump Actuator OverloadProtection Reservoir Pressuregage Electric Motor

23 Question: Can the cylinder be moved ? 1)Cylinder: Double acting, differential area 2)Fluid is incompressible 3)Rod and cap end connected Check in FluidSim

24 Hydraulic Work (rod end pressure = 0)

25 Differential area cylinder: Flow and displacement

26 Differential area cylinder: Force equilibrium

27 Differential area cylinder: Work

28 Differential area cylinder: Power

29 Dual rod cylinder: Power

30 Power if (as in motors and pumps)

31 Question: Will the cylinder extend ? Check in FluidSim

32 Video 5: Pressure transmission (0:53) Pressure intensification in hydraulic systems: Differential area cylinders cause this effect Max pressure in the system is NOT PRV setting ! Check in FluidSim

33 Pumps and Motors

34 Hydraulic motors perform rotary operations Variable speed, bidirectional

35 Hydraulic Motor

36 Basic Circuit with hydraulic motorPump Actuator OverloadProtection(PRV) Reservoir Pressuregage Electric Motor

37 In case of a motor shaft, the Work can be found by multiplying a force through a distance. Suppose we assume a force at a distance. The total work per radian of the shaft is now equal to Mechanical Torque in a pump/motor

38 Mechanical Power in a pump/motor The power is now equal to this value divided by the time per radian. If the shaft is turning at it takes seconds per radian. Since for Power we have to divide the Work by time, this leads to:

39 Hydraulic Power in pump/motor ( )

40 Hydraulic Motor Displacement Motor displacement D is a volume per angular displacement (revolution or radian). Assuming the volumetric efficiency is 1.0 Common are the CCR (Cubic Centimeter per Revolution) and the CIR (Cubic Inch per Revolution)

41 Torque in a Motor is proportional to Pressure Here we assumed no losses, all the hydraulic energy is converted into mechanical energy.

42 Pump Displacement Pump displacement is a volume per angular displacement (radian). Assuming the volumetric efficiency is 1.0 (no leakage) More realistic, with Volumetric Efficiency (why in numerator?)

43 Torque Required to drive a pump is proportional to Pressure More realistic, with Torque Efficiency (why in the denominator?) (No losses here).

44 Power Efficiency of Pumps From before: And Power Efficiency: Without loss Efficiencies

45 Data sheet Data sheet Eaton MHT vane pump

46 Question in ‘Customary Units’ Given PRV Setting 15 MPa pump displacement of cm 3 /rev the speed of the pump is 1800 rpm Required Torque needed to drive the pump Power needed to drive the pump Neglect friction

47 Answer in ‘Customary Units’

48 Question in ‘Customary Units’ Given PRV Setting pump displacement of the speed of the pump Required Torque needed to drive the pump Power needed to drive the pump. Neglect friction

49 Answer in SI Units

50 Types of Pumps and Motors External Gear Internal Gear Vane Axial Piston Radial Piston

51 External Gear Fixed Displacement

52 Video 8: Power units (3:26) Power supply unit Converts Mechanical energy into hydraulic energy Hydraulic Fluid is conditioned (cooled, cleaned) Components Drive motor Safety valve Oil reservoir Pump External Gear pump function (constant delivery) Where teeth unmesh, volume increases, oil enters Where teeth mesh, volume decreases, oil leaves Pressure only builds when there is a resistance (load) Safety valve needed to prevent failure when cylinder stalls Pressure Relief Valve diverts flow back to tank when cylinders are stalled Reservoir Cools oil Cleans oil from suspended particles, water and air which takes time (Capacity) Filters trap impurities 70% of all malfunctions are due to impurities

53 Internal Gear Fixed Displacement

54 Vane pump Fixed or Variable Displacement

55 Axial Piston Fixed or Variable DisplacementFixed or Variable Displacement Displacement depends on size and number of pistonsDisplacement depends on size and number of pistons

56 Radial Piston Fixed or VariableFixed or VariableDisplacement Displacement dependsDisplacement depends on size and number of pistons

57 Pump ‘family tree’

58 Pumps and Actuators: The End