The powertrain electrification is an effective solution to emission reduction of mobile machines. To overcome the low power density of electric drive, a hydraulic accumulator is introduced as a supplementary power source. In this paper an electric-hydraulic hybrid powertrain solution is studied for wheel loader propulsion system, where it combines the energy density of electric drive and high power density of hydraulic drive. The energy management strategy is essential for hybrid powertrain since it determines how efficiently the power is transferred between different energy sources. In this paper a mode-driven control strategy for electric-hydraulic hybrid wheel loader is proposed to achieve electric power reduction over power follower strategy (baseline strategy), without sacrificing electric energy use and vehicle operation hours. In the strategy four modes are defined and the expected hydraulic SOC (system pressure) profile in each mode is scheduled to provide supplementary power assist and capture regenerative braking energy. By setting the pressure profile, the hydraulic charge sustaining is guaranteed. The system operation with mode-driven strategy is compared with power follower strategy through simulation studies. Results show that peak powers of battery and electric motor with mode-driven strategy are reduced by nearly 30% compared to power follower strategy. Results also show that the vehicle operation hour has been slightly increased by 3% by using mode-driven strategy. These results verify the effectiveness of proposed strategy for electric-hydraulic hybrid wheel loader.

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