Long Quan

Characteristics of delivery pressure in the axial piston pump with combination of variable displacement and variable speed

In recent years, a trend toward the combination of variable displacement and speed-variable pump drive is becoming apparent. Combination of variable displacement and speed-variable pump drive has been revealed to be more efficient than speed-variable pump drive or variable displacement pump drive. However, few research works have dealt with the pumping performance of combination of variable displacement and speed-variable pump. This study aims to investigate the characteristics of pressure pulsations of combination of variable displacement and speed-variable pump. A simulation model is developed by means of software package ITI-SimulationX®. The model is used to predict the pressure pulsations under different operating conditions. Experiments are also carried out to verify theoretical results. From these results, it can be drawn that the pumping dynamics of combination of variable displacement and speed-variable pump is not the best in the view of pressure pulsation, and it is slightly inferior to that of variable displacement pump drive. For required delivery volumetric flow and load pressure, delivery pressure pulsations’ amplitude of combination of variable displacement and speed-variable pump slightly increases with an increase in swash plate angle and adapted rotational speed. However, test results also show that lower rotational speed and adapted swash plate angle working condition can effectively reduce total noise level of the system. Consequently, lower rotational speed and higher swash plate angle working condition are suggested for the design of combination of variable displacement and speed-variable pump drive controller.

Research on the performance of hydraulic excavator with pump and valve combined separate meter in and meter out circuits

Conventional hydraulic actuator is controlled by mechanically connected orifices valve. The controllability of this method is poor and the energy consumption is huge especially under the over-running condition. So a novel system configuration of the hydraulic excavator is presented to improve the problem mentioned above, in which boom cylinder, stick cylinder and swing motor are controlled with separate meter in and meter out technology, bucket cylinder and travel motors are controlled with conventional valves. Firstly, the paper provides a comprehensive review on the development of the separate meter in and meter out technology. Then the principles of load sensing system and SMISMO system applied on the excavator are illustrated though two diagram to show the difference of the two systems. And then a virtual prototype based on the real physical structures is established, which consists of the hydraulic excavator mechanical structure with multi-body dynamics and electro-hydraulic system. The model is verified by the statics and dynamics experiments. Then the dynamic, static performances as well as the energy consumption characteristics of the boom, arm and swing actuators are investigated under the condition of load sensing hydraulic system and the proposed system using the virtual prototype. The control strategy of the actuators is formulated according to their load condition and operation characteristics also based on the detailed analysis. After that, the physical prototype based on the proposed configuration system is established and its performance is tested. The experimental results show that the accuracy of the virtual prototype is validated; the proposed configuration system can significantly decreases the pressure losses through the valve and improve the energy efficiency of the machine; the pressure shocks within hydraulic actuators is decreased as well, thus the stationarity of the whole machine is improved accordingly.

Research on the performance of electro-hydraulic proportional flow valve controlled by pilot pump

Cartridge flow valves, widely applied in heavy machine and equipment, have the advantages of low leakage, large flow capacity, and simple structure. However, in the existence technologies, in order to reduce the influence of load variety on valve flow, a pressure differential compensator or a cartridge type flow sensor should be added to proportional throttle valve. This method reduces valve flow capacity and increases system throttling loss. In large flow occasion, flow only can be indirectly controlled by changing valve opening area for the limitation of the structure. So a low energy consumption, high controllable electro-hydraulic proportional valve which is structured by a hydraulic transistor (Valvistor) and a small displacement hydraulic pump driven by a servo motor is introduced. Based on the Valvistor valve flow amplification principle, main valve flow is controlled by pilot pump flow which is controlled by changing rotation speed without the influence of load variety. In the research, its known from the analysis of the new principle valve steady flow characteristics that feedback throttle slot pre-opening will cause the decrease of the main valve flow as pressure drop increases. Soa method of pressure differential-pilot pump rotation speed compensation is put forward and it can obtain ideal flow characteristic. Then the dynamic mathematical model is established and the main valve stability criterion is derived. The influence of the valve parameters on main valve performance is analyzed and simulated. The results provide a new method for the large flow electro-hydraulic proportional control system.

The distributed parameter model of hydraulic axial piston motor and its application in hydraulic excavator swing system

Hydraulic axial piston motor is one of the fundamental components in hydraulic systems; it is widely used in engineered machine, especially in high-power drive or reciprocating motion, such as hydraulic excavator. For hydraulic axial piston motor efficient planning, in addition designing and controlling are required for system operating safety and efficiency. Simulation delivers an advantage over analytical approaches and allows better understanding of the motor performance. For multi-piston hydraulic motor, one of the simulation methods, distributed parameter model, could analyze the detailed performance in each piston chamber. Therefore, in this study, we investigate the characteristics of hydraulic axial piston motor by setting up a distributed parameter model based on physical prototype, which includes mechanical–hydraulics coupling process. The effects of the dynamic pressure inside the piston chamber, the fluidic compressibility and other related parameters are considered in the coupling process. At the same time, the distributed parameter model of hydraulic axial piston motor was used in the simulation model of hydraulic excavator. The results indicate that in two-way hydraulic axial piston motor, the valve plane should adopt symmetrical structure, and silencing groove set should be put on both ends of the valve plane slots, which could reduce pressure ripple and overshoot in the piston chamber. Furthermore, the torque characteristics are highly affected by the clearance between the piston and the cylinder bore. Through this research, we may have a better understanding about the mechanism of output torque fluctuation in hydraulic axial piston motor, and the pressure ripple and overshoot in the piston chamber due to through-flow area discontinuity between the silencing groove and the ends of the valve plane slots. The model is verified using a nine-piston hydraulic motor in hydraulic excavator.

Reduction of steady flow torques in a single-stage rotary servo valve

In this paper, geometry optimization of spool is proposed to reduce the steady flow torques in a single-stage rotary servo valve. The steady flow torques under different spool structures are studied by computational fluid dynamics simulation and experimental test and the most effective spool structure is found out. Then, the effects of geometry parameters on the steady flow torques are studied and an optimized solution for reduction of the steady flow torques is suggested by considering the optimization qualities and production costs. The results show that modification of the geometry of spool can make the jet angle at the orifices much closer to 90°, with almost no effect on the flow rate. Processing annular groove in the spool land with increased number of grooves on one side of the spool land is an effective way to reduce the steady flow torques. The maximum value of steady flow torques reduces with a gradual decrease in reduction as the external diameter of annular groove and the number of grooves increase. With the optimized spool structure, the maximum value of steady flow torques can be reduced significantly.

Flow matching with combined control of the pump and the valves for the independent metering swing system of a hydraulic excavator

Because of the throttling loss of the control valves and the overflow loss in the frequently accelerating and decelerating motion with a large inertia, the swing system of a hydraulic excavator has a high energy consumption; also, it has a poor controllability. To solve these problems, this paper proposes flow matching with combined control of the pump and the valves and an independent metering method for the swing system of the hydraulic excavator. The inlet pressure and the outlet pressure of the hydraulic motor can be controlled independently. With combined control of the pump and the valves, the flow rate can match the rotational speed of the hydraulic motor so that the overflow loss is avoided. Furthermore, we also develop a simulation model consisting of the mechanical structure of the hydraulic excavator with multi-body dynamics and an electrohydraulic system for analysing the feasibility of this swing system, and the simulation results demonstrate that this system works smoothly. After using the presented control strategies, the results of experiments show that the energy efficiency is improved and that the system can reduce the throttling loss and can obviously suppress the swing vibrations.

Research on the performance of electro-hydraulic proportional flow valve controlled by active pilot pump

The cartridge flow valves, used in heavy machine and equipment, have the advantages of low leakage, large flow capacity, simple structure, and ease of modulation. However, in order to reduce the influence of load variety on the flow through valve, a pressure differential compensator or a cartridge type flow sensor should be added to the proportional throttle valve. These methods have disadvantages of reducing the flow capacity of valve and increasing the throttling loss. To overcome these disadvantages, a low energy consumption, high controllable electro-hydraulic proportional flow valve which consists of a hydraulic transistor (Valvistor) and a small displacement hydraulic pump driven by a servo motor is proposed firstly in the world. As the pump flow is basically proportional to the pump speed and little influenced by load variety, the flow through main valve is proportional to pilot pump speed. In the research, it’s known that feedback throttle slot pre-opening will cause the decrease of the main valve flow as pressure drop increases. So, small orifices are used instead of the pre-opening of feedback throttle slot to reduce the influence of load variety on the flow through valve. Furthermore, a method of pressure differential changing with pilot pump rotational speed calibration is introduced to further mitigate the influence of pressure difference. In this paper, the mathematical dynamic model of the valve is also established and the stability criterion of valve is derived. The influence of valve parameters and the flow pulsation of pilot pump on valve flow performance is analyzed and simulated. In view of the pilot pump flow pulsation frequency being much higher than the valve natural frequency, the research shows that the influence of flow pulsation of pilot pump on valve flow performance is very little. The research work provides a new method for the large flow electro-hydraulic proportional control system.

Characteristics of a piloted digital flow valve based on flow amplifier

Hydraulic switching techniques which have less throttling losses, good repeatability and can be controlled intelligently have been largely developed. The biggest challenge is the hydraulic fluctuation. It is generated in the process of opening and closing the valve. A two-stage digital flow valve operated by Pulse Width Modulation (PWM) signal is studied in this paper. The main stage is cartridge valve based on flow amplifying principle; the pilot stage is high-speed on/off valve. The fluctuation characteristic of the digital flow valve is investigated using theoretical derivation and simulation analysis. The results show that the outlet flow fluctuation is influenced by many parameters such as the frequency and duty ratio of PWM signal, the volume of control chamber, etc. It can be weakened through the proper design of these parameters. Although the fluctuation exists, the mean outlet flow can be proportionally controlled by adjustment of the duty ratio of the control signal.