Trends in Digital Hydraulics

Transcription

1 Trends in Digital Hydraulics Matti Linjama Tampere University of Technology Introduction Motivation Trend I: Digital microhydraulics Trend II: Digital Hydraulic Hybrid Actuator Conclusions

2 Power flow in traditional hydraulic system Fuel 300 Diesel 100 Pump 90 Valves 45 Lines & Actuator Input = 300 kw Output = 40 kw Two ways to reduce fuel consumption 1: Reduce valve losses 2: Reduce power needed from Diesel Fuel 300 Diesel 100 Pump 90 Valves 45 Lines & Actuator

3 Digital hydraulics can reduce valve losses Digital valve system is programmable and can thus reduce valve losses by % Why digital hydraulics is not used widely? Digital hydraulics is used in Pendolino and in some paper machines Which are obstacles for wider use? General resistance to change Valve systems are big Power electronics are big

4 Trend I: Digital Microhydraulics Objectives To make digital valve systems and power electronics small To use standard CETOP interfaces To improve performance Trend I: Digital Microhydraulics Traditional digital valve 4x5 valves 40 l/min 20 ms 20 kg Microhydraulic valve 4x32 valves 48 l/min 3 ms 10 kg CETOP

5 Challenge I: How to create small enough valve? Via optimization and multifunctional parts Diameter 10 mm Maximum pressure 21 MPa Response time 3 ms 36 mm 10 mm Challenge II: How to create compact manifold? Via plate lamination (poor man s 3D printing) Cutting sheets Plating with copper Stacking on the jig Brazing in the vacuum furnace Machining threads

6 Challenge III: Integrated power electronics Via high-frequency AC technology Power Electronics for 64 valves Result: Best in the world digital servo valve 4x16 valves 3 ms full amplitude response time Zero leakage CETOP3 compliant 24 Dp = 3.5 Mpa p max = 21 MPa

7 Valve alone is nothing We need also good controller New control method has been developed Controls directly pressures and force Like electric servo system F = ma Results are VERY promising Inertia kg Almost perfect control of pressures and force Improved energy efficiency

8 Digital Microhydraulics: Conclusions 3 ms digital servo valve technology Robust on/off valves Highly fault tolerant Leak free It is estimated that the power density exceeds traditional valves in few years Trend II: Digital Hydraulic Hybrid Actuator Hybrid system has secondary power source Electric accumulator Hydraulic accumulator Flywheel Many times also energy recuperation Braking energy recuperation (kinetic energy) Potential energy recuperation

9 Digital hydraulics uses leakfree on/off valves Long term energy storing is possible Why hydraulic hybrid? Electric hybrid Big energy storing capacity More expensive Durability? Hydraulic hybrid Low-cost Robust Fully recyclable Bad efficiency?

10 Efficiency of hydraulic accumulator is good New generation accumulators are coming Heat regeneration (Prof. Pietola, Aalto university) Round trip efficiency about 97 %! Centralized Hybrid Traditional approach is centralized hybrid One big accumulator Big power are transmitted from accumulator to actuators and vice versa

11 New idea: Hybrid Actuator Actuator has integrated accumulator Big power is kept at actuator Average power only is transmitted to the actuator Power peaks from accumulator 17 kw 3 kw 20 kw Average power source

12 Excavator digging cycle: Average power is very small Power [kw] Peak power Average power Boom Arm Bucket Swing Only small e-motor and pump are needed to generate average power Small electric motor and pump

13 Power transformation is the tricky part Accumulator has e.g. 20 MPa pressure Actuator needs e.g. only 10 MPa Digital transformer is one option for power transformation Hydraulic cylinder Piston accumulator Small cylinders as pressure transformers On/Off valves for power routing [Proportional valves]

14 The idea works according to simulations m = kg Excellent controllability without proportional valves Simulated power losses are really small Energy recuperation Power loss LS Hybrid

15 First prototype is under assembly Output power 10 kw, input power 1 kw Bit bulky because traditional valves are used Acceptable in the first prototype Conclusions 1: Reduce valve losses Programmable digital valves Digital Microhydraulics 2: Reduce power needed from Diesel Hybrid systems Hybrid actuator