When hydraulic excavators lower their boom or brake the rotating upper structure, recoverable potential or kinetic energy is available. In recent years electric and hydraulic hybrid excavators have been developed to recover this energy that is lost through usually the throttle or relief valve. Although boom lowering motion occurs frequently, most commercial hybrid excavators only recover the swing braking energy. Some hybrid architectures to recover the boom potential energy have also been introduced, however, much of this energy is still lost as throttling losses when they save the energy into a storage device by using a recuperation scheme or they need many additional electric components.
This paper introduces a new regeneration scheme to recover the boom potential energy for hydraulic excavators. By directly connecting the head chambers of the boom cylinders to a variable displacement hydraulic motor installed on the engine shaft, the boom potential energy could be used to support the torque required to be delivered by the engine. The speed of boom lowering is controlled by adjusting the motor displacement. Also bypass into a tank is implemented to limit the size of the recovery motor. The simulation results show the average fuel consumption in leveling and 90deg truck loading tasks can be reduced by 10% and 7%, respectively.