ROTARY SELF-SPINNING HIGH SPEED ON-OFF VALVE

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


Throttle-less Control

Valve control wastes energy

Heat loss through throttle valve

Generate excess flow

Direct pump control

Produces energy only when needed


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


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


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• Energy is withdrawn from the flywheel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


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


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


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


Valve Packaging

Integrated Design• Mounts directly onto existing fixed displacement pumps• Reduces inlet volume and losses due to fluid compressibility


Prototype Parts


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


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


Throttling Loss Analysis

Fully open throttling loss

wD

PPower pwmopenfull 2

Full Open

Transition


Fluid Compressibility

dV

dPVP )(

β(P): Yu Model

Definition of Bulk Modulus:

high

low

P

P

comp dPP

PVE

)(


Linear Actuation

Actuation and Sensing• Linear position actuated hydraulically• Sensing achieved using non-contact optical method


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%


System setup


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


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


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

Documents

ROTARY SELF-SPINNING HIGH SPEED ON-OFF VALVE