Abstract: When the hydraulic excavator works, its boom lifts and lowers frequently. During the lowering process, a large amount of working device's gravitational potential energy accumulated during the lifting process is converted into heat energy and dissipated through the control valve. That not only causes large energy loss, but also causes the oil temperature to rise rapidly. The temperature rising of the oil often causes hydraulic system failure and additional cooling equipment is required for heat dissipation. To solve the above issues, a hydraulic-electric combined driving scheme for boom is proposed. In the scheme, electric cylinder is set as main driving unit and hydraulic cylinder-accumulator combination is set as auxiliary driving unit. When the boom lowers, the gravitational potential energy of the working device is converted into the hydraulic energy and stored in the accumulator. When the boom lifts, the hydraulic energy stored in the accumulator can be directly used to drive the hydraulic cylinder to assist to drive the boom, and the electric cylinder only needs to drive the inertial load and the load of goods. In this paper, a test prototype of the hydraulic-electric combined driving system was established, and the operating characteristics and energy efficiency of the system were tested. The test results show that, compared with the independent meter-in and meter-out control system without potential energy recovery function, the hydraulic-electric combined driving system reduces the energy consumption by 72.7% under the same working conditions and the energy efficiency of excavator boom system is significantly improved.

Key words: electric cylinder, energy saving, hydraulic excavator, hydraulic-electric combined driving