Energy efficiency improvement of battery powered wheel loader with an electric-hydrostatic hybrid powertrain

An electric-hydrostatic hybrid powertrain is proposed for the wheel loader propulsion system. The powertrain is constituted from an electric hydrostatic powertrain by adding a hydraulic accumulator as the second power source. It not only reduces energy consumption through regenerative braking, but also improves the power performance of the machine. A thermostat control strategy is developed for electric hydrostatic hybrid wheel loader and a speed-displacement compound control is developed for the electric hydrostatic wheel loader. The energy flow, losses analysis, and energy efficiency in the two powertrains are studied. The energy consumption reduction of the electric hydrostatic hybrid powertrain over the electric hydrostatic powertrain is identified in the wheel loader loading cycle. Results show the hydraulic accumulator in the hybrid powertrain increases the hydrostatic transmission efficiency and overall system efficiency. The energy efficiency in the electric hydrostatic powertrain is 45.64% and 51.66% in the electric hydrostatic hybrid powertrain. The total battery energy consumption is 14.20 kWh in the EH wheel loader and 12.48 kWh in the EH-hybrid wheel loader (50 cycles). The total energy consumption saving by using hybrid powertrain is 12.11%.