This paper is to study on a novel recovery and release hydraulic hybrid system for excavators (HHE). The HHE uses hydraulic accumulators to recover the potential energy of the boom, the kinetic energy of the swing motor and the overflow hydraulic energy of the excavator’s main relief. The recovered energy is then utilized through a variable hydraulic motor as assistant power of the engine. The key issue of the HHE is that the operation of the boom must be similar to the conventional one about the sensing of the driver and the system must achieve higher efficiency and save more energy when comparing with the conventional system. In order to improve the recovery efficiency and while controlling the boom velocity with the similar operation, one design concept named “microcut” is proposed. When the boom drops down fast, a proportional valve is used to control the boom. While the boom goes down slowly, the recovery system is cut off. Then, the multi-way valve of the original system works to ensure good handling. An experimental prototype is designed and built in a 21-tons excavator. A 16% fuel-saving effect is obtained by weighing engine’s fuel consumption with the same amount of work, under conditions of the similar operation and higher efficiency compared with the conventional excavator.

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