Performance Comparison between Single and Double Pump Controlled Asymmetric Cylinder under Four-quadrant Operation

Since the single pump controlled asymmetric cylinder closed circuit demands extra flow compensating unit and its velocity fluctuates during the changes of load directions, an innovative double pump controlled asymmetric cylinder closed circuit system and its control strategy were proposed. The cylinder was directly controlled by double variable speed pumps driven by a servo motor and a low-pressure hydraulic accumulator was adopted as the tank. The operating principles of the single pump and double pump controlled cylinder closed circuit under a four-quadrant operation were analyzed. The mechanical model of the front attachment of a micro-excavator was built, as well as the pump controlled cylinder closed circuit system and the velocity feed-forward open loop and closed loop control strategies. Furthermore, the built hydraulic system of the double pump controlled cylinder was partially validated. The simulation was performed by using this partially validated model, a velocity reference for the stick cylinder and a zero load for the bucket of the front attachment. After the analyses and comparisons of the operating behavior and energy consumption, the results magnified that compared with the single pump controlled cylinder system, although the energy efficiency of the proposed double pump controlled cylinder system was decreased by 4 percentage points, the velocity fluctuation problem caused by the four-quadrant operation was eliminated and the maximum position error of running 0.8m was only 4mm. Therefore, the proposed system and its control strategies were effective and feasible for the four-quadrant operation of the asymmetric cylinder.