Efficiency improvement and evaluation of electric hydraulic excavator with speed and displacement variable pump

Hydraulic excavator driven by an internal-combustion engine is widely used in the construction field. However, some problems, such as high pollutant emissions, noise and low efficiency, exist universally. To address these problems, an electric hydraulic excavator configuration combining with an independent metering in and metering out system is proposed to improve the overall energy efficiency. In this paper, a displacement variable pump driven by a speed variable electric motor is used as power source, and a matching method based on the segmented speed and continuous displacement control of the pump is proposed to meet the requirements of high dynamic, high energy efficiency and zero emission of hydraulic excavator under different working conditions. Then, an independent metering in and metering out system is employed to reduce throttling loss. A test rig with a 6-ton hydraulic excavator was built up and used to validate the proposed scheme. The energy consumption characteristics of the electro-hydraulic power source under different rotational speeds and different loads are further investigated to provide analytical and experimental references for control strategy designing. Furthermore, the working performance and energy distributions of the excavator with the pure displacement variable concept, and speed and displacement variable concept are studied comparatively. Results show that, compared with pure displacement variable concept, the electric power consumption during the idle period can be reduced from 2.05 kW to 0.7 kW, the energy saving ratio under partial load condition can be up to 33%, while it is 28.5% under digging condition.