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O+P Fluidtechnik 6/2016

O+P Fluidtechnik 6/2016


SIMULATION FORSCHUNG UND ENTWICKLUNG PEER REVIEWED 04–04 Pressure pulsation 04–05 Control deviation 80 O+P – Ölhydraulik und Pneumatik 6/2016

SIMULATION An inversely phased control variable may reduce these oscillations. Another possibility is a feedback of the actual boom velocity. This requires additional sensors in one of the boom cylinders. With fine adjustment or by proving both control strategies and analysing the cause of the oscillations on a real working machine an improvement is possible. Both control systems show similar performance. The control quality declines at the end of both cycles because of the time weighting of a deviation and the unstable characteristics. Pulsations occur in the boom rising cycle when the BERS needs support by the main hydraulic system and the boom assist valve opens. 5 SUMMARY / OUTLOOK The presented work deals with the further investigation on a boom energy recuperation system of a hybrid excavator (BERS) that was designed in former research by Doosan Infracore in collaboration with the Institute for Fluid Power Drives and Controls (IFAS) of RWTH Aachen University. A simulation of the commutation process was performed in order to optimise the efficiency of the axial piston unit that is used in the BERS. The simulation findings were validated on a test bench in the IFAS laboratory. The resulting data from the experimental study, especially the efficiency look-up table and the knowledge of the response time of control, were used for the improvement of the BERSmodel in DSHplus. Based on this model and findings of the previous research an advanced control algorithm was developed. An efficiency improvement of the BERS by optimising the control of rotational speed and swash plate angle is goal of the said algorithm. In operating points of partial load an efficiency improvement of approximately 10 % compared to the previous control system was reached. The control performance was kept, so that the BERS with advanced control algorithm is expected to find high acceptance amongst machine operators. 6 ACKNOWLEDGEMENT This project was supported by the industry convergence fundamental technology development program (Grant No. 10031841) of the Ministry of Trade, Industry and Energy, Republic of Korea Auhors: Dipl.-Ing. Markus Gärtner and Univ.-Prof. Dr.-Ing. Hubertus Murrenhoff, RWTH Aachen University, Germany, Institute for Fluid Power Drives and Controls (IFAS) Table of formulae A cyl Area of boom cylinder [mm²] I Solenoid current [A] I max Maximal solenoid current [A] n Rotational speed [rpm] n max Maximal rotational speed [rpm] n opt Optimal rotational speed [rpm] p Pressure [bar] Δp Pressure difference [bar] Δp cyl,meas Measured cylinder pressure difference [bar] Δp sim Simulated pressure difference [bar] p max Maximal power [kW] Q des Desired volume flow [l/min] Q max Maximal volume flow [l/min] t Time [s] T Torque [Nm] T max Maximal torque [Nm] ν velocity [mm/s] ν cyl,max Maximal cylinder velocity [mm/s] ν cyl Actual cylinder velocity [mm/s] ν des Desired cylinder velocity [mm/s] Δν Control deviation of cylinder velocity [mm/s] V g,max Maximal displacement [cm³] x cyl Actual cylinder position [mm] x des Desired cylinder position [mm] Δx Control deviation of cylinder position [mm] α Swash plate angle [ ° ] α opt Optimal swash plate angle [ ° ] η #1 Efficiency of unit 1 (series unit) [ - ] η #2 Efficiency of unit 2 (unit with improved valve plate [ - ] design) η el Electric efficiency [ - ] η hyd Total efficiency of the hydraulic unit [ - ] η tot,ACA Total efficiency of the advanced control algorithm [ - ] η tot,con Total efficiency of the conventional system [ - ] η vol Volumetric efficiency [ - ] Δη Difference of efficiency [ - ] Bibliography: [Bli10] Bliesener, Maurice “Optimierung der Betriebsführung mobiler Arbeitsmaschinen – Ansatz für ein Gesamtmaschinenmanagement”, Dissertation, Karlsruhe, 2010 [ISO4409] N.N. “Hydraulic fluid power – Positive displacement pumps, motors and integral transmissions – Determination of steady-state performance”, ISO4409, 2007 [Iva00] Ivantysyn J., Ivantysynova M. “Hydostatic Pumps and Motors: Principles, Design, Performance, Modelling, Analysis, Control and Testing“, 1 st edition, Akademia Books International, 2000, ISBN 81-85522-16-2 [Jan97] Jang, D. “Verlustanalyse an Axialkolbeneinheiten”, Dissertation, RWTH Aachen, 1997 [Jar97] Jarchow, M. “Maßnahmen zur Minderung hochdruckseitiger Pulsationen hydrostatischer Schrägscheibeneinheiten”, Dissertation, RWTH Aachen, 1997 [Kan10] Kang, B. Oh, S. „A study on the Boom Energy Regeneration System for a Hybrid Excavator“, 7 th International Fluid Power Conference, Aachen, 2010 [Mur12] Murrenhoff, H. „Servohydraulik – Geregelte hydraulische Antriebe“, 4. neu überarbeitete Auflage, Shaker, Aachen, 2012 [Mur14] Murrenhoff, H. „Fundamentals of Fluid Power, Part 1: Hydraulics”, Shaker, Aachen, 2014 Table of abbreviations ACA BERS ICE Advanced Control Algorithm Boom Energy Recuperation System Internal combustion engine [Pet92] Petterson, M.,Weddfelt, K. Palmberg. J.-O. “Reduction of Flow Ripple from Fluid Power Piston Machines by Means of a Precompression Filter Volume”, 10 th Aachen Colloquium on Fluid Power Technology, Aachen, Germany, 1992 [Sgr10] Sgro, Sebastian “Energierückgewinnungssysteme für Baggerausleger – Eine Systematische Übersicht der vorhandenen Lösungsmöglichkeiten”, O+P 10/2010, 2010 O+P – Ölhydraulik und Pneumatik 6/2016 81


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