By combining an electro-hydraulic flow-on-demand system with an independent metering of the actuators in- and outlet, a higher efficiency and a better controllability compared to conventional hydraulic-mechanic load sensing systems can be reached. It also enables the integration of a hydraulic accumulator to recuperate energy due to active loads. This paper presents an alternative control strategy for this kind of hydraulic propulsion systems. Connected with the pump and during passive loads the meter-in flow controls the velocity of the actuator. Otherwise the velocity control is achieved by the meter-out flow while the oil flows into the accumulator or tank. Exemplary this system is simulated for a mobile forestry crane. Further steps are building up a test bench for optimization and validation as well as an implementation into a real machine for testing the suitability in use.
Keywords: Flow-on-demand, independent metering, control, recuperation, hybrid system