ERC C&E Fluid Power 1
ROTARY SELF-SPINNING HIGH SPEED ON-OFF VALVE
Center for Compact and Efficient Fluid Power
Department of Mechanical Engineering
University of Minnesota
Dr. Perry Li
Dr. Tom Chase
Dr. Jim Van de Ven
Haink Tu Rachel Wang Mike Rannow
ERC C&E Fluid Power 2
Throttle-less Control
Valve control wastes energy
Heat loss through throttle valve
Generate excess flow
Direct pump control
Produces energy only when needed
ERC C&E Fluid Power 3
Drawbacks of Direct Pump Control
Currently available variable displacement pumps tend to be ~3 times heavier than a fixed displacement pump
Variable displacement pumps are more expensive than fixed displacement pumps
A valve controls a piston which controls a swash plate which controls the flow• Complex control• Slow response times
Goal: Design a compact, efficient, and responsive method of control
ERC C&E Fluid Power 4
Concept
• Use switching to eliminate throttling losses• Create the hydraulic analog of a DC-DC Boost
Converter• Controlled using Pulse-Width-Modulation (PWM)• Same concept can be applied to motor, hydrostats,
hydraulic transformer
ERC C&E Fluid Power 5
Operation of a PWM Pump
2 States of Operation
Open State
• Pump flow is diverted through the On/Off valve to tank
• Energy is stored in the flywheel
• The load is driven by the accumulator
Closed State
• Energy is pumped into the accumulator
• Energy is withdrawn from the flywheel
Low PQ loss through the valve in both states
Switching leads to a ripple on the output to the load
ERC C&E Fluid Power 6
Ideal Model
)(2
)(0
/10
)/11(
tQD
tuVP
PP out
outout
)(2
)( tPD
tuJ outf
u(t)=1 when the valve is closed
u(t)=0 when the valve is open
Controlled using PWM
• s(t) is the duty ratio
Adiabatic accumulator operation
•
Use state-space averaging
• u(t) becomes s(t)
2
)()(
DtstQout
outPDts
t2
)()(
In steady-state:
00VPVPout
1mod)/()( if 0
1mod)/()( if 1)(
Ttts
Tttstu
ERC C&E Fluid Power 7
Experimental Results: Power Loss
Results show significant improvement over valve control
Switching effects cause energy loss to increase with frequency
• Compressibility• Valve transition
Slight increase in power loss as more flow is diverted
• Full open throttling
Experimental Apparatus: 5.7 l/m flow rate, 4.8 MPa load pressure, 10 Hz max frequency, 40 ml inlet volume, 0.4 MPa drop across the valve
ERC C&E Fluid Power 8
s=0 (Flow fully diverted)
s=.25
s=.5 (50% flow to application)
s=.75
s=1 (100% flow to application)
To Tank
To Application
Decrease s (more flow to tank)
Increase s (more flow to application)
Tangential rhombus inlet nozzle
Helical barriers/inlet turbine blades
Outlet turbine blades
Spool Functionality
• No spool acceleration /deceleration
• Rotary actuation power PWM frequency^2
• Linear actuation power PWM frequency^3
• Use helical profile to apportion flow between application (on) or tank (off) as the spool rotates
• Move the spool axially to determine duty ratio
• Utilize fluid to spin spool• Transition time scales with
spool speed
ERC C&E Fluid Power 9
Valve Packaging
Integrated Design• Mounts directly onto existing fixed displacement pumps• Reduces inlet volume and losses due to fluid compressibility
ERC C&E Fluid Power 10
Prototype Parts
ERC C&E Fluid Power 11
x
y
Ain
Rin
ω
Inlet turbine stage Outlet turbine stage
cout
Rout
ω
Control Volumes (for 1 of N sections)
Vout=Q/Aaxial k
Vin=Q/(N·Ain) j
Vin=Q/Aaxial k
Vout=-Q/(N·cout·Le) j
ω
Spool Velocity Analysis
2QAN
R
in
ininlet
QRQAN
Rout
out
outoutlet
22
2Rc
Asurffriction
Inlet Turbine:
Outlet Turbine:
Friction (Petroff’s Law):
Design Consideration: Minimize bearing area while maximizing momentum capture
ERC C&E Fluid Power 12
Throttling Loss Analysis
Conclusions• Majority of losses occur during valve transition• Relief valve contributes significantly to losses
Replace relief valve with check valve parallel to load branch
4 Transition Events per Cycle:1. Closing to Tank2. Opening to Load3. Closing to Load4. Opening to Tank
)(1, openreliefopenreliefopenw
lost PPPPPR
RQE
12
12,
open
loadreliefopenloadrelief
loadrelief
openwlost P
PPPPP
PP
P
R
RQE
ERC C&E Fluid Power 13
Throttling Loss Analysis
Fully open throttling loss
wD
PPower pwmopenfull 2
Full Open
Transition
ERC C&E Fluid Power 14
Fluid Compressibility
dV
dPVP )(
β(P): Yu Model
Definition of Bulk Modulus:
high
low
P
P
comp dPP
PVE
)(
ERC C&E Fluid Power 15
Linear Actuation
Actuation and Sensing• Linear position actuated hydraulically• Sensing achieved using non-contact optical method
ERC C&E Fluid Power 16
System Simulation
Simulation Results• Predict 28Hz spool/84Hz PWM
frequency• Transition time from full on to full
off in 3.2ms• Step change in pressure from
200psi-800psi achieved in .19sec• Average Pressure Ripple = 6.7%
ERC C&E Fluid Power 17
System setup
ERC C&E Fluid Power 18
Experimental Results
Motor Driven Spool• Actuated with electric motor• Achieve PWM frequency of 500Hz
1st Generation Self-spinning Spool• Achieve maximum 27Hz Spool
/54Hz PWM frequency
ERC C&E Fluid Power 19
Current System Work
Pload
Ps
Use a conventional (linear spool) valve to study the effect of on/off control in typical applications
• Experiment 1: Use a throttling valve to cancel the output ripple Load sensing approach Achieve precise position control Use minimal throttling to eliminate the ripple
• Experiment 2: Simulate regenerative braking with an on/off valve Use an accumulator to spin a flywheel Slow the flywheel by pumping to high pressure Demonstrate an on/off pump motor
ERC C&E Fluid Power 20
Future Work
• Test and Improve Rotary Self-Spinning valve• Investigate efficiency of a high speed system• Develop control algorithms for PWM hydraulic
systems• Apply switching strategy to other applications
(variable motor, regeneration, etc.)• Perform CFD analysis to determine interaction
between spool and sleeve, and to improve turbine design