Experimental study on energy efficiency of two-cylinder direct driven hydraulic system in a large-scale test bench

Robert Hermansson, Ville Närvänen, Jyrki Kajaste, Olof Calonius, Matti Pietola, Petri Kuosmanen

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

1 Citation (Scopus)


In this research the energy efficiency of a pump controlled direct driven hydraulic (DDH) system is experimentally tested and analyzed. The test bench uses two cylinderś crossconnection to rotate the middle joint of the 5-meter-long pivot arm which is loaded with unequal load of maximum 1685 kg. Originally the test bench is designed to study the application of DDH in the case of an articulated steering system, but in this research the system is treated as load lifting and load lowering application. The power pack of the test bench features a permanent magnet servo motor and a bent-axis, fixed-displacement hydraulic motor-pump unit. A separate charge pump circuit is attached, which also controls the servo motor and pump case temperature and takes care of fluid heat management as well as filtering. An extensive CAN-network is utilized for measurement and control. The motion of the test bench is driven with position control to give reproducible lifting and lowering cycles with different loads and velocities. Three motion cycles are executed involving three different loads, nine combinations in total, to study their effect on energy efficiency in load lifting and load lowering situations. Mechanical input power is measured between the electric motor and pump, hydraulic power is measured at the pump outlet and at the cylinder ports, and finally the mechanical output power is calculated for the cylinder-to-mechanical interface. Energy losses are determined as well as the overall energy efficiency of the hydraulic system. The research focuses on the hydraulic system and therefore the electric input power to the system and the regenerated electric power in load lowering is left out of the study. However, the regeneration potential in load lowering part of the cycles is measured as the available electric motor shaft power. In load lifting, the total energy efficiency of the hydraulic system was at its best at 82% when using the maximum additional load of 1685 kg and the lowest lifting velocity of 0.1 rad/s. Energy efficiency of load lowering was at its best in the same cycle with 77% of the energy recovered from the pumpmotor's shaft. High dependency on load and velocity was detected, because the total efficiency in lifting decreased to 44% with highest velocity (0.3 rad/s) and lowest load (445 kg). In lowering, during the same cycle, the total efficiency was -17%, meaning that gravity loading alone could not produce fast enough motion and that active input power was needed. In conclusion, very good energy efficiency could be achieved when operating against high enough loading. Operating at partial loads and with higher velocities will clearly reduce energy efficiency, emphasizing the need for careful dimensioning of all the power train components.

Original languageEnglish
Title of host publicationProceedings of ASME/BATH 2021 Symposium on Fluid Power and Motion Control, FPMC 2021
PublisherAmerican Society of Mechanical Engineers
Number of pages12
ISBN (Electronic)978-0-7918-8523-9
Publication statusPublished - 19 Oct 2021
MoE publication typeA4 Conference publication
EventASME/BATH Symposium on Fluid Power and Motion Control - Virtual Conference, Online, Virtual, Online, United States
Duration: 19 Dec 202121 Dec 2021


ConferenceASME/BATH Symposium on Fluid Power and Motion Control
Abbreviated titleFPMC
Country/TerritoryUnited States
CityVirtual, Online
Internet address


  • energy efficiency
  • direct drive hydraulics
  • electro-hydraulic actuators
  • boom operations
  • large-scale test rig


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  • EZE: Easy zonal hydraulics

    Pietola, M., Hermansson, R., Lehto, J., Närvänen, V., Heikkinen, J., Calonius, O. & Korhonen, A.


    Project: Business Finland: Other research funding

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