Control and Energy Efficiency of a Multi-pressure System – An Excavator Study

Hydraulic powered systems in mobile machines suffer from low operating efficiency during multiple actuator operation owed to large throttling losses when metering the flow to low pressure actuators. State of the art throttling based systems suffer from these losses, demand higher engine power to supply for peaks, couple the prime mover to the dynamic nature of the load and offer no energy recuperation or regeneration. Significant improvement in energy efficiency of mobile machines can be achieved by addressing these drawbacks. This paper presents a novel multi-pressure system aiming to reduce throttling losses, handles power peaks locally, regenerates and stores energy and decouples the supply system from load dynamics. In the multi-pressure system, Proportional bidirectional poppet type 2/2 valves are used to select the best possible pressure line from four levels maintained by integrated hydraulic accumulators while simultaneously adjusting the flow for the actuators’ piston and rod sides. A controller is studied and presented for the novel system and the challenges are also discussed. Additionally, possibilities to improve the energy efficiency is also illustrated. Simulation results from a 20-ton wheeled excavator work functions show good controllability and tracking performance as well as regeneration of energy during lowering of the boom. Reduction in energy consumption compared to a traditional load sensing system is also realizable although difficulties defining the novel system’s saving abilities is present.