ME 4232:
FLUID POWER CONTROLS LAB
Class #6
Hydraulic Pumps
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)
2
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
3
Feedback: Lab Sections
• Overall Going Well
– Helpful / Knowledgeable TAs (right amount of guidance)
• Issues:
– Some labs tight on time
– Sometimes confusion
– Lab assignments vague
4
Power Steering Valve (Lab 13)
Open center steering
Power beyond steering
5
Pumps - Introduction
6
Non-Positive Displacement Pump
7
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
8
External Gear Pump
• Driving gear and driven gear
• Fluid trapped between gear
teeth and housing
9
Gerotor pump
Inlet port
•
•
•
•
Outlet port
Internal/External Gear Pair
Inexpensive
Low-Pressure Applications
Low Flow (0.1 – 11.5 in3)
10
Vane Pump
• Vanes in slots in rotor
• Vanes loaded against
cam ring
• Eccentricity determines
displacement
• Quiet
• Limited Pressure
11
Pressure Compensated Vane Pump
12 curve
• Spring determines P-Q
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
13
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
14
Bent Axis Pump
•
•
•
•
Drive shaft coupled to cylinder block
Stationary valve plate
Low piston side load
High efficiency
15
Pumping Theory - Flow Ripple
16
Pumping Theory – Power Variable Calculations
17
Pumping Theory – Efficiency
18
19
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
20
Cavitation Video
21
http://www.youtube.com/watch?v=eMDAw0TXvUo
Hydraulic Motor / Actuator
• Hydraulic motors / actuators are basically
pumps run in reverse
• Input = hydraulic power
• Output = mechanical power
22
Hydrostatic Transmission
23
Closed Circuit Hydrostatic Trans
24
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 !
25
Hydraulic Hybrid Vehicle Circuits
Series
Parallel
Pros:
 Retains existing mechanical drive train
Cons:
 Does not allow optimal engine
management
Pros:
 Allows optimal engine management
 Four-Wheel Drive Capable
 Independent Wheel Torque Control
Cons:
 Hydraulic Efficiency Losses
 Pump/Motor Operation
26
Hydraulic Accumulators
• Energy Storage Device
• Oil Compresses a Pre-Charged Gas (Nitrogen)
27
Hydro-Mech w/ Wheel Torque Control
Accumulator
Planetary
Differential
Axle
Gearbox
Engine
Clutch
Mechanical
Transmission
• High Efficiency & Decoupling
• 2 Power Paths: Mechanical & Hydraulic
– Leverage Highly Efficient Mechanical Branch
– Infinite Speed Variability with Hydraulic Branch
• Independent Wheel Torque Control
28
Hydraulic Transformer
Q1
Q2
• 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
29
Why Are Pumps Inefficient at Low X?
 Cs
Volumetric: Q  xD 1 
x


Mechanical: T  xpD1  Cv
x

 p   p 
1  x 

   Vr 

xB
2



  
   C f 
 


p
 x 

Source:
30http://www.emeraldinsight.com/content_images/fig/0180560404021.png
Improving Pump Efficiency
• Mechanical:
– Variable Displacement Linkage
• Low Friction Pin Joints
• Volumetric:
– Rolling Diaphragm Seal
• No Leakage
• Minimal Friction
31
Source: www.diacom.com
Source: Sandor, G.N. and Erdman, A.G.,
Advanced Mechanism Design: Analysis and
Synthesis, Volume 2, Prentice-Hall, 1984.
Linkage Synthesis
• Video
Video:
http://www.youtube.com/watch?v=ovVGkjuXdvE
32
Configuration Analysis
Stroke/Footprint
Overlapped Case at R1,max
2
1.5
1
0.5
0.24
0
0.22
-0.5
-1
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
0.2
4
Optimized Solution:
•
R3 = 1.8, R4 = 1.8
•
Max Displacement = 2.11
•
Footprint = 8.38
•
•
0.18
0.16
2.5
0.14
Minimum Transmission Angle of Slider = 56°
Minimum Timing Ratio = .72
3
33
2
3
2.5
|R3| Unitless
2
1.5 1.5
|R4| Unitless
First Generation Prototype
• Variable Pump/Motor
– Design Speed: 1750 RPM
– Design Flow Rate 2.6e-4
– Design Max Pressure: 6.9 MPa (1000 psi)
34
First Generation Prototype
35
First Generation Prototype
36
Quantifying Energy Loss
• Leakage:
6
Δ
3
Δ
• Viscous Friction:
• Compressibility:
Vdead
dP
 ( P)
PV
dP
  PdV   
 ( P)
dV  
• Pin Friction:
Δ
12
Ecomp
∗
37
Energy Loss Model
Bronze Bushings
Rolling Element Bearings
System Energy Loss 1800 RPM 6.9 MPa
k = 0.173
System Energy Loss 1800 RPM 6.9MPa
18
16
Leakage
Viscous Friction
Coulomb Friction
Compressibility Losses
Total Losses
3
14
Energy Loss (J/rev)
Energy Loss (J/rev)
2.5
12
10
Leakage
Viscous Friction
Coulomb Friction
Compressibility Losses
Total Losses
8
6
4
2
1.5
1
0.5
2
0
k = .0015
3.5
0
0.1
0.2
0.3
0.4
0.5
0.6
Displacement d/dmax
0.7
0.8
0.9
0
0
1
38
0.1
0.2
0.3
0.4
0.5
0.6
Displacement d/dmax
0.7
0.8
0.9
1
Energy Loss Model
Efficiency Models at 1800 RPM and 6.9MPa
1
.0015
0.9
0.8
.173
0.7
Efficiency
0.6
0.5
0.4
0.3
0.2
Bronze Bushings
Rollerbearings
McCandlish Model
0.1
0
0.1
39
0.2
0.3
0.4
0.5
0.6
0.7
Displacement (D/Dmax )
0.8
0.9
1
Pumping Head Design
Outlet -8
Check Valve
Fittings
Inlet -12 (3/4” ID)
Leakage Port -6
40
Experimental Efficiency Testing
Optical encoder (not shown)
Torque Transducer
Accumulator to smooth
pulsating flow
Pressure Transducer
Τ
41
Flow Meter
Experimental Efficiency Testing
• Results Validate the Model
42
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
43
Linkage Preliminary Design
• Links in single shear
• Rolling element bearings
used
• Rotary input possibly
gear driven or drive shaft
can be used
Video
44
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?
45