Class #6Hydraulic Pumps

ME 4232:FLUID POWER CONTROLS LAB

2

Notes• Next Friday:

– Van de Ven Traveling– Servo Hydraulic Overview & System Dynamics Review

• Upcoming Labs:– Lab 11/12: Synchronous / Asynchronous &

Tandem / Parallel Connections– Lab 13: Power Steering

– Lab 14: Integrated Lab (Part I)

3

Agenda• Feedback: Lab Sections• Power Steering Valve• Pump Classification

– Positive Displacement Types

• Pump Theory– Flow Ripple– Inefficiencies– Aeration/Cavitation

• Hydrostatic Transmissions– Types / Characteristics– Hybrid Vehicle Architectures

4

Feedback: Lab Sections

• Overall Going Well– Helpful / Knowledgeable TAs (right amount of guidance)

• Issues:– Some labs tight on time– Sometimes confusion– Lab assignments vague

5

Power Steering Valve (Lab 13)

Open center steering Power beyond steering

6

Pumps - Introduction

7

Non-Positive Displacement Pump

8

Types of Positive Displacement Pumps• Gear pump (fixed displacement)

– internal gear (gerotor)– external gear

• Vane pump – fixed or variable displacement– pressure compensated

• Piston pump– axial design– radial design– bent-axis design

9

External Gear Pump

• Driving gear and driven gear• Fluid trapped between gear

teeth and housing

10

Gerotor pump

• Internal/External Gear Pair• Inexpensive• Low-Pressure Applications• Low Flow (0.1 – 11.5 in3)

Inlet portOutlet port

11

Vane Pump

• Vanes in slots in rotor• Vanes loaded against

cam ring• Eccentricity determines

displacement• Quiet• Limited Pressure

12

Pressure Compensated Vane Pump

• Spring determines P-Q curve

13

Axial Piston Pump• Pistons rotate with cylinder

block• Pistons translate against swash

plate• Displacement determined by

swash plate angle• Fluid enters/exits through valve

plate

14

Radial Piston Pump

• Cam moves pistons radially• Displacement determined by

cam profile• Displacement variation can be

achieved by moving the cam (not common)

• High pressure capable, and efficient

• Pancake profile

15

Bent Axis Pump

• Drive shaft coupled to cylinder block• Stationary valve plate• Low piston side load• High efficiency

16

Pumping Theory - Flow Ripple

17

Pumping Theory – Power Variable Calculations

18

Pumping Theory – Efficiency

19

20

Aeration and Cavitation• Disastrous Events • Aeration

– air bubbles enter pump at low pressure side

• Cavitation– Dissolved air cavitation– Vapor cavitation

• Bubbles expand in low pressure• Bubbles collapse in high

pressure– Micro-jets formed Rapid

Erosion

21

Cavitation Video

http://www.youtube.com/watch?v=eMDAw0TXvUo

22

Hydraulic Motor / Actuator

• Hydraulic motors / actuators are basically pumps run in reverse

• Input = hydraulic power• Output = mechanical power

23

Hydrostatic Transmission

24

Closed Circuit Hydrostatic Trans

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General Consideration - Hydrostats• Advantages:

– Wide range of operating speeds/torque– Infinite gear ratios - continuous variable transmission (CVT)– High power, low inertia (relative to mechanical transmission)– Dynamic braking via relief valve– Engine does not stall– No interruption to power when shifting gear

• Disadvantage:– Lower energy efficiency (80% versus 92%+ for mechanical

transmission)– Leaks !

26

Hydraulic Hybrid Vehicle CircuitsParallel Series

Pros: Retains existing mechanical drive trainCons: Does not allow optimal engine

management

Pros: Allows optimal engine management Four-Wheel Drive Capable Independent Wheel Torque ControlCons: Hydraulic Efficiency Losses Pump/Motor Operation

27

Hydraulic Accumulators

• Energy Storage Device• Oil Compresses a Pre-Charged Gas (Nitrogen)

28

Hydro-Mech w/ Wheel Torque Control

• High Efficiency & Decoupling• 2 Power Paths: Mechanical & Hydraulic

– Leverage Highly Efficient Mechanical Branch– Infinite Speed Variability with Hydraulic Branch

• Independent Wheel Torque Control

Engine

Clutch

Accumulator

Axle Gearbox

MechanicalTransmission

Planetary Differential

29

Hydraulic Transformer

• Used to change pressure in a power conservative way

• Pressure boost or buck is accompanied by proportionate flow decrease and increase

• Note: Hydrostatic transmission can be thought of as a mechanical transformer

Q1 Q2

30

Why Are Pumps Inefficient at Low X?

Volumetric:

Mechanical:

211 xV

xBpp

xC

DxQ rs

xC

pxC

xpDT fv 1

Source: http://www.emeraldinsight.com/content_images/fig/0180560404021.png

31

Improving Pump Efficiency• Mechanical:

– Variable Displacement Linkage• Low Friction Pin Joints

• Volumetric:– Rolling Diaphragm Seal

• No Leakage• Minimal Friction

Source: www.diacom.com

Source: Sandor, G.N. and Erdman, A.G., Advanced Mechanism Design: Analysis and Synthesis, Volume 2, Prentice-Hall, 1984.

32

Linkage Synthesis

• Video Video: http://www.youtube.com/watch?v=ovVGkjuXdvE

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Configuration Analysis

Optimized Solution:

• R3 = 1.8, R4 = 1.8

• Max Displacement = 2.11

• Footprint = 8.38

• Minimum Transmission Angle of Slider = 56°

• Minimum Timing Ratio = .72

Overlapped Case at R1,max

1.5

2

2.5

3

1.52

2.53

0.14

0.16

0.18

0.2

0.22

0.24

|R4| Unitless

Stroke/Footprint

|R3| Unitless

-1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4-1.5

-1

-0.5

0

0.5

1

1.5

2

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First Generation Prototype• Variable Pump/Motor

– Design Speed: 1750 RPM

– Design Flow Rate 2.6e-4

– Design Max Pressure: 6.9 MPa (1000 psi)

35

First Generation Prototype

36

First Generation Prototype

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Quantifying Energy Loss• Leakage:

• Viscous Friction:

• Compressibility:

• Pin Friction:

6 Δ 3

12

Δ

Δ

∗

( )compPVE PdV dP

P

( )deadVdV dPP

38

Energy Loss Model

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

2

4

6

8

10

12

14

16

18

Displacement d/dmax

Ene

rgy

Loss

(J/re

v)

System Energy Loss 1800 RPM 6.9 MPa k = 0.173

LeakageViscous FrictionCoulomb FrictionCompressibility LossesTotal Losses

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.5

1

1.5

2

2.5

3

3.5

Displacement d/dmaxE

nerg

y Lo

ss (J

/rev)

System Energy Loss 1800 RPM 6.9MPa k = .0015

LeakageViscous FrictionCoulomb FrictionCompressibility LossesTotal Losses

Bronze Bushings Rolling Element Bearings

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Energy Loss Model

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Displacement (D/Dmax)

Effi

cien

cy

Efficiency Models at 1800 RPM and 6.9MPa

Bronze BushingsRollerbearingsMcCandlish Model

.173

.0015

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Pumping Head DesignCheck Valve

Fittings

Inlet -12 (3/4” ID)

Outlet -8

Leakage Port -6

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Experimental Efficiency Testing

Pressure Transducer Flow Meter

Optical encoder (not shown)

Τ

Accumulator to smooth pulsating flow

Torque Transducer

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Experimental Efficiency Testing

• Results Validate the Model

43

2nd Generation Prototype

• 10kW power output• Three cylinder design• Linkage Balancing• Incorporate roller bearings into design• Multi-parameter re-optimization

– Include both mechanical and fluid dynamics simultaneously

44

Linkage Preliminary Design

• Links in single shear• Rolling element bearings

used• Rotary input possibly

gear driven or drive shaft can be used

Video

45

2 Minute Writing

• ½ Sheet of Paper• No Names

1. What do you like most about the way the course is going?

2. What do you like least about the way the course is going?

3. Suggestions for improvement?