Hydraulic systems are widely used in working actions of mobile machines. They offer good power to weight ratio, robustness and relatively good controllability. However, there has been growing interest on the energy efficiency of such machines during recent years. Load sensing proportional valve control is a typical solution for multi-actuator systems leaving a significant margin for improvement of energy efficiency. Digital hydraulic valve system enables independent metering and reduces losses significantly without a need of complete redesign of the hydraulic system of such machine. Digital hydraulic valve system consists of parallel connected on/off-valves and offers deterministic operation which is crucial for successful implementation of independent metering.
Four different digital hydraulic valve control approaches are analyzed in the paper: four-edge-control, four-edge control with pressurized tank line, five-edge-control and six-edge-controlled three-chamber-cylinder. The energy efficiency of digital hydraulic valve control is theoretically estimated for different operation points in steady-state conditions for single and multi-actuator systems. Another point of view is achieved by comparing measured energy consumption of the different approaches on a single-actuator test bench.
Energy recuperation becomes possible by utilizing digital hydraulic valve technology together with suitable supply system. Furthermore, the power generated by the supply unit can be better distributed among a number of active actuators through different control modes. The experimental results show that the energy losses can be decreased up to 67 % by replacing load sensing 4-way proportional valve with digital hydraulic valve system capable of independent metering.