The design and analysis of a hydro-pneumatic energy storage closed-circuit pump control system with a four-chamber cylinder

A decentralized variable electric motor and fixed pump (VMFP) system with a four-chamber cylinder is proposed for mobile machinery, such that the energy efficiency can be improved by hydro-pneumatic energy storage, and problems of closed-circuit pump-controlled systems including asymmetrical flow and speed limitation are addressed. One of the chambers is arranged to the energy storage accumulator to increase energy efficiency, while the other chambers are flexibly connected to the pump ports to achieve variable transmission ratios. The piston areas of the multiple chambers are designed at first to permit a symmetric single-rod cylinder, and secondly a switching system with three operating modes is presented to expand force-velocity capabilities. Then, the four-chamber cylinder system with three solenoid valves is designed to substitute for the traditional two-chamber boom cylinder in a 6-ton excavator. A valve switching logic, as well as a feedforward and feedback compound speed controller, are presented. Simulations conducted in a 6-ton excavator model show that the maximum velocity increases by 66 %, together with asymmetrical flows to diminish the low-pressure charging accumulator. Peak power and energy consumption are both reduced by more than 20 % compared with the VMFP using the two-chamber cylinder. The energy-saving characteristics of the 6-ton excavator are emphatically analyzed considering energy storage and re-utilization. At last, experiment verifications are conducted in a lifting mechanism to verify the proposed energy-storage system.