ROTARY SELF-SPINNING HIGH SPEED ON-OFF VALVE

1. Dr. Perry Li Center for Compact and Efficient Fluid Power Department of Mechanical Engineering University of Minnesota ROTARY SELF-SPINNING HIGH SPEED ON-OFF VALVE Dr. Tom Chase Dr. Jim Van de Ven Mike Rannow Haink Tu Rachel Wang

2. Throttle-less Control Valve control wastes energy Heat loss through throttle valve Generate excess flow Direct pump control Produces energy only when needed

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

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

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in the flywheel The load is driven by the accumulator Closed State Energy is pumped into the accumulator Energy is withdrawn from the flywheel Low PQ loss through the valve in both states Switching leads to a ripple on the output to the load

6. Ideal Model • 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) In steady-state:

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, 0.4MPa drop across the valve

8. Decrease s (more flow to tank) Outlet turbine blades To Application s=1 (100% flow to application) Tangential rhombus inlet nozzle s=.75 s=.5 (50% flow to application) s=.25 s=0 (Flow fully diverted) Helical barriers/ inlet turbine blades To Tank Increase s (more flow to application) Spool Functionality • No spool acceleration/deceleration • Rotary actuation power  PWM frequency^2 • Linear actuation power  PWM frequency^3 • Use helical profile to apportion flowbetween 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

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

10. Prototype Parts

11. Spool Velocity Analysis Inlet Turbine: Outlet Turbine: Friction (Petroff’s Law): y x Inlet turbine stage Outlet turbine stage Rout ω cout Rin ω Control Volumes (for 1 of N sections) ω • Design Consideration: Minimize bearing area while maximizing momentum capture Vout=Q/Aaxialk Vin=Q/Aaxialk Vout=-Q/(N·cout·Le) j Ain Vin=Q/(N·Ain) j

12. Throttling Loss Analysis • 4 Transition Events per Cycle: • Closing to Tank • Opening to Load • Closing to Load • Opening to Tank • Conclusions • Majority of losses occur during valve transition • Relief valve contributes significantly to losses • Replace relief valve with check valve parallel to load branch

13. Throttling Loss Analysis Transition Full Open Fully open throttling loss

14. Fluid Compressibility Definition of Bulk Modulus: β(P): Yu Model

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

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%

17. System setup

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

19. Current System Work Ps Pload • 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

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