Tianliang Lin

Influence of the energy regeneration unit on pressure characteristics for a proportional relief valve

Overflow loss through the relief valves is universal in hydraulic systems. To explore the feasibility to regenerate the overflow loss, an energy regeneration unit is connected to the outlet of the proportional pilot relief valve which can reduce the pressure difference and the overflow loss accordingly. The added energy regeneration unit may affect the performance of the proportional pilot relief valve. The mathematical model of the proportional pilot relief valve with the energy regeneration unit is established. And AMESim is employed to develop the simulation model of the proportional pilot relief valve to obtain the characteristics of the proportional pilot relief valve which is affected by the energy regeneration unit. The experiment is carried out to test the influence of the energy regeneration unit on the performance of the proportional pilot relief valve. The experimental results show that the inlet pressure of the proportional pilot relief valve decreases gradually with the increase in back pressure of the energy regeneration unit. The maximum pressure drop of the inlet pressure of the proportional pilot relief valve is about 0.63 MPa. Compared to the fluctuation caused by the flow rate, which is 10%–30%, the fluctuation caused by the energy regeneration unit is only 2.8% and can be neglected. This indicates that the feasibility and effectiveness to regenerate the overflow loss of the proportional pilot relief valve through connecting an energy regeneration unit to the outlet of the proportional pilot relief valve.

Characteristics of the energy regeneration and reutilization system during the acceleration stage of the swing process of a hydraulic excavator

Although the traditional energy regeneration system which uses electric or hydraulic energy recovery to regenerate part of the overflow energy loss during the acceleration and braking stages of the swing process of a hydraulic excavator, the modification cost is high and the control system is complex. To reduce the overflow energy loss of the swing process of the hydraulic excavator and to simplify the control system, a novel swing driving system based on a hydraulic accumulator to regenerate and utilize the energy automatically during the acceleration process is presented. The working mode and the assessment criteria of the swing system are analysed. The characteristics of the traditional swing system and the proposed swing system are compared. The relationships between the pressures of the two motor chambers, the pressures of the hydraulic accumulator and the motor speed of the proposed swing system in one working cycle are studied. The experimental results showed that the energy recovery efficiency of the proposed swing driving system, which can regenerate the energy automatically based on the hydraulic accumulator, was up to 80% during the acceleration stage of the swing process, and the energy consumption of the power system in one working cycle was reduced by 16.5% in comparaison with that of the traditional driving system.

Computational fluid dynamics and experimental analysis of the influence of the energy recovery unit on the proportional relief valve

The overflow energy loss in relief valve, which is one of the main reasons leading to the low efficiency of the hydraulic system, had been considered to be impossible to solve. The principle of the overflow energy loss of the relief valve is analyzed and a novel method to reduce the overflow loss using an energy recovery unit, which can improve the return line pressure of the pilot proportional relief valve, is proposed. The influence of the energy recovery unit on the pressure control characteristics and steady-state flow force of the pilot proportional relief valve are discussed. The effects of the return line pressure on the distribution of the flow field and the pressure control characteristics are analyzed through computational fluid dynamics simulation and experiment. The results show that with the increase of the return line pressure, the displacement of the main valve spool increases and the reset spring force increases accordingly. While the steady-state flow force decreases dramatically with the increase of the return line pressure, which results in a smaller pressure differential the pressure differential can be reduced from 15% to 2.5%. It is also observed that the flow rate of the pilot proportional relief valve can be maintained at a certain value with a small oscillation and that the pilot proportional relief valve can release the redundant flow of hydraulic system. This verifies that the pilot proportional relief valve with the outlet connecting to the energy recovery unit to recovery the overflow energy loss cannot reduce the pressure control characteristics, but can achieve a better pressure control accuracy of the pilot proportional relief valve.

Research on the control strategy of power train systems for hybrid hydraulic excavators

Hybrid power technology is a practicable method for construction machinery to improve fuel utilization and reduce emissions. In this article, in order to achieve the maximum degree of energy conservation for hybrid hydraulic excavator, a study on a control strategy of the hybrid power train system for a 20-t hybrid hydraulic excavator is conducted. A rule-based method which stabilizes the engine operating points in high-efficiency area and maintains the state of charge of the ultra-capacitor in a feasible operating range is presented. Meanwhile, to improve the reliability of the ultra-capacitor, a two-stage state of charge constraint is applied. To validate the effectiveness of the control strategy, a hybrid power train system simulation loading experiment platform is built. The working characteristics and the energy conservation characteristics of the hybrid power train system are explored. Actual load profiles measured from a 20-t traditional excavator are measured and applied in the system. The experimental results show that the proposed control strategy for the hybrid power train system can improve the fuel economy of the hybrid hydraulic excavator. Meanwhile, dynamic performance of the hybrid power train system is better than that of the traditional excavator.