Independent metering valve (IMV) control of working hydraulic systems in mobile machines has been studied for more than two decades and during the past few years it has also been adopted to commercial excavators. The main advantages of the IMV systems, compared to load sensing and open centre systems are the possibility of optimizing the ressure losses of the metering edges and the possibility of re-routing the hydraulic energy between actuators. Energy re-routing can be realized without storing the energy to accumulators and thus avoiding the losses of additional routing valves and energy conversions. IMV combined with a hybrid system allows even more improved energy efficiency. igital hydraulic IMV (D-IMV) allows additional benefits to the IMV systems with more fault-tolerant operation with robust components, faster and more precise control and leak-free valves.
The purpose of this study is to apply a D-IMV system to a midsize (20t) excavator and to study the differences in energy consumption of the working hydraulic system with four actuators. This paper presents the controller designed for the D-IMV and a simulation model for analysing the system. The energy consumption of the D-IMV is compared to the measured energy consumption of a state-of-the-art excavator with a load-sensing hydraulic system.
The Controller of the D-IMV system is realized with a sub-optimal mode control, so that instead of calculating and optimizing the total energy consumption of all possible mode combinations, simpler control logic is defined to remove the complex structure of the controller and ease the computational burden. Simulation study shows that the hydraulic input energy can be reduced 28-42% compared to a standard LS-controlled excavator. Detailed analysis of where the reduction emerges is presented.
Keywords: Digital hydraulics, Independent metering valve, mobile hydraulics, excavator