Pump/valves coordinate control of the independent metering system for mobile machinery

Abstract The independent metering system is an alternative to the conventional valve control system by decoupling the meter-in and meter-out orifices. With a number of features such as flow recuperation or regeneration, and simultaneous control of speed and pressure, the energy saving performance can be improved. Nevertheless, independent metering systems make the control more complex. The current control design focused on the two-level controller: mode switch in upper level, and velocity and pressure control in lower level. However, pump control is seldom considered and the coordinate control of pump and valves briefly couples electronic load sensing (ELS) with the two-level controller. The contribution of this paper is to design a three-level controller to improve the energy efficiency. The upper level determines the operating mode in terms of the current system states and desired motion trajectory. The lower level contains the meter-out flow/pressure valve control and the open-loop displacement pump control. A coordinate level is added to incorporate the pump control into the valve control. By the coordinate control of the pump and valves, the meter-in valve opens maximally and the pressure losses across the valves can be minimized. The problems caused by the maximal opening of the meter-in valve are described and then solved by three parts: pressure matching, configuration of flow/pressure valve control and damping compensator. The proposed controller is applied to a mini-excavator. The experimental results of boom and arm motions show that the three-level controller is able to address dual objectives of energy saving and control performance improvement.