Proportional Directional Valve Research Articles

A model-based sliding mode control with intelligent distribution for a proportional valve driven by digital valve arrays

Parallel-connected digital valve arrays are commonly utilized in the pilot stage of the proportional directional valve to enhance dynamic performance and reliability. However, when the digital valve array is driven by a digital signal, it is difficult to optimally assign the signal pulses to each valve. If the assignment is not well executed, it can significantly reduce the switching uniformity of the digital valves or lead to performance degradation of the system. In this paper, a model-based sliding mode control strategy based on the intelligent distribution of control law is proposed and successfully applied to a proportional valve driven by digital valve arrays. The intelligent distribution strategy encompasses a logic distribution algorithm and a circular sliding distribution algorithm that automatically assigns control laws to different valves based on the rolling of the PWM signal cycle. Experimental results confirm that the proposed strategy not only simultaneously reduces the total number of valve switches and enhances the switching uniformity among the valves, but also adapts to the variation in the number of valves. The proposed strategy is not limited to the application of digital valve arrays, it is also applicable in other fields of multi-actuators driven by digital signals, and can simultaneously improve the control accuracy, lifetime, and maintenance friendliness.

Recent advances in control strategies and algorithms for pilot-operated electro-hydraulic proportional directional valves

Pilot-operated electro-hydraulic proportional directional valve is a key hydraulic component to control the motion of large power equipment such as construction machinery and agricultural equipment. The control accuracy and response speed of the valve control element are very important to the performance of the hydraulic system. In this paper, control strategies for dead-zone control and valve control systems are reviewed. In order to eliminate the dead-zone of pilot-operated proportional valve control, the current control schemes for dead-zone detection and dead-zone compensation are summarized, and the control schemes are evaluated. The proportional–integral–derivative-related control, nonlinear control, and robust control of the pilot-operated electro-hydraulic proportional directional valve control system are reviewed, the relationship between the control strategies is analyzed, and the different control algorithms are evaluated. The shortcomings of the research program are analyzed, and the corresponding solutions are proposed. Based on the current research, future research progresses for eliminating the control dead-zone and optimizing control strategies are presented.

Optimization of the Control Performance of a Novel 3/2 Water Proportional Directional Valve With a Special Position Following Servo Mechanism

Optimization of the Control Performance of a Novel 3/2 Water Proportional Directional Valve With a Special Position Following Servo Mechanism

Experimental and Numerical Analysis of Flow Force Acting on the Spool of Proportional Directional Valve

This paper deals with the experimental and numerical analysis of the flow force acting on the spool of a proportional directional valve. The flow force arises due to the fluid flow through the flow path of the proportional directional valve and significantly influences the dynamics of the valve spool. The valve under investigation is a three-position four-way proportional directional valve with zero spool lap and feedback from the spool position. The dependence of the valve spool flow force on the volumetric flow rate is measured as part of the experiment. The measurements are performed for different spool displacements. The measured data will be used to verify the numerical simulations. The proportional directional valve was modified so that a force sensor could be included on the spool axis to realize the experiment. Firstly, the flow force is measured as the fluid passes through the two flow paths of the valve (PB and AT). Subsequently, the experimental setup is modified to determine the flow force when the fluid passes through each flow path separately. The measurements are compared. Simulations of the flow through the proportional directional valve are performed using Ansys Fluent 2022 R2 software to determine the flow forces acting on the valve spool. Simulations are performed for the selected spool positions of the proportional directional valve. Finally, the results of the simulation and the experiment are compared. The contribution of this study is a CFD model of the flow paths of the proportional directional valve verified by experiment. The CFD model will allow the flow force analysis for different flow path geometries of the investigated valve. Experimental analysis of flow force is performed over the entire spool stroke at different volumetric flow rates. The flow forces are measured for each flow path separately and for both flow paths simultaneously.

Simulation and experimental research on steady flow force compensation for a servo proportional valve

In the development of high-performance directly driven proportional directional valves, reducing the flow force of the spool is a crucial aspect due to its significant influence on the dynamic characteristics and power consumption of these valves. This paper presents a study on the steady-state flow force of a servo-proportional valve spool by employing a combined approach of numerical simulations and experiments. Additionally, a method is proposed to compensate for the steady-state flow force by modifying the shoulder inclination of the spool. The results demonstrate that modifying the shoulder angle of the spool alters the emergence angle, leading to a substantial reduction in the steady-state flow force acting on the spool. Notably, the compensation method has negligible impact on the through-flow capability of the servo-proportional valve.

MODELLING AND SIMULATION OF ELECTROPNEUMATIC POSITIONING SYSTEM INCLUDING THE LENGTH OF PNEUMATIC LINES

This paper presents a mathematical model of electropneumatic positioning system including the length of pneumatic lines for the determination of flow and pressure in unsteady operating modes. A simulation model is developed to study the dynamic processes in an electropneumatic positioning system. Simulation of the mathematical models of the screw compressor, proportional directional valve, pneumatic lines, pneumatic cylinder and PID controller were designed in “MatLab Simulink”. The simulation models of the transients in the electropneumatic positioning system at different line lengths from 1m and 10m with stepwise variation of the input setpoint are simulated developed. Graphical comparison is made of the obtained experimental results and simulation model influence of the pneumatic line length on the dynamics of the electropneumatic positioning system are made.

A composite adaptive robust control for pneumatic servo systems with time-varying inertia

This article proposes a composite adaptive robust control for a pneumatic servo system with time-varying inertia to achieve a good tracking performance. The proposed design not only preserves the merits of both direct adaptive robust control and indirect adaptive robust control but also obtains a better performance of the working condition with time-varying inertias. Firstly, prescribed tracking performance is guaranteed without knowing the bounds of parametric and non-parametric uncertainties by leveraging a discontinuous projection and deterministic robust control technique. And a nonlinear tracking differentiator is used to obviate differential signal in backstepping. Secondly, the online parametric estimation algorithm is developed by intelligently integrating tracking error dynamics and physical plant dynamics. By effectively using the information of both tracking error and prediction error, a high adaptation gain can be used for achieving a faster parameter convergence and smaller tracking error. Moreover, exponential convergence of both tracking error and prediction error can be obtained under certain conditions. Lastly, comparative experiments on different conditions are carried out for a single-rod pneumatic cylinder driven by a proportional directional valve to demonstrate the superiority of the proposed method.

Research on Dynamic Performance of Independent Metering Valves Controlling Concrete-Placing Booms Based on Fuzzy-LADRC Controller

Motion control of truck-mounted concrete pump booms is an important part of concrete construction work. The quality of the boom movement will affect the efficiency and safety of construction operations. To make the boom move quickly and steadily, its hydraulic control system needs to be improved. In this article, we firstly combine independent metering control (IMC) and active disturbance rejection control (ADRC). The hydraulic system that controls the boom is meliorated by replacing the traditional proportional directional spool valve with four cartridge flow control valves to realize IMC. Meanwhile, a fuzzy linear ADRC algorithm is proposed for a new IMC hydraulic system where ADRC is linearized and combined with fuzzy logic to achieve better motion control performance of boom sections. According to the results of experiments conducted using all six boom sections, compared with the PID control algorithm, the fuzzy linear active disturbance rejection control (FLADRC) proposed in this article can improve the stability and rapidity of valves controlled by hydraulic cylinders by 10.0% to 66.7% in different working conditions.

Leakage Characteristics of Proportional Directional Valve

This paper deals with the analysis of leakage characteristics of the proportional directional valve. These characteristics distinguish a real directional valve from an ideal one. The ideal directional valve is characterized by zero leakage due to its perfect geometry. The investigated element is the three-position four-way proportional directional valve with zero spool lap and feedback from the spool position. The spool position is measured by the inductive position sensor and processed by external electronics. Internal leakage occurs due to axial and radial clearances between the spool and the sleeve. The magnitude of axial clearances that occur at throttle edges and their effect on the directional valve leakage is the subject of research. The blocked-line pressure sensitivity curve, the leakage flow curve and the center flow curve are determined by experiment. Individual characteristics are determined for different working fluid temperatures and different supply pressures. The flow through internal leaks in the center position of the valve spool is determined by analytical calculations. The flow through internal leaks is also simulated using the Ansys Fluent software. Subsequently, the geometry of the flow simulation model is modified to take into account manufacturing tolerances. From simulation results, the effect of the manufacturing tolerance magnitude on the internal leakage of the directional valve is evaluated. Finally, simulated dependencies are compared with experimentally determined characteristics.

Research of Vibration Effects on a Hydraulic Valve in the Pressure Pulsation Spectrum Analysis

This paper identifies mechanical vibrations occurring in the operating environment of hydraulic systems used in marine engineering. Particular attention was paid to the influence of periodic vibrations on changes in the amplitude-frequency spectrum in a marine hydraulic system. For the case of analysing the effect of vibration on changes in the pressure pulsation spectrum with a proportional directional valve, a modified mathematical model was used. Experimental results were presented and compared with the results obtained from the mathematical model. A way of limiting the transmission of vibrations to the directional control valve body was proposed.

Characteristics Analysis of the Pilot-Operated Proportional Directional Valve by Experimental and Numerical Investigation

The main valve spool structure of the pilot-operated proportional directional valve is diverse and has a direct impact on the flow field. To improve the valve’s performance, this work studied the characteristics of four types of spool structures with the following throttling groove arrangements: no throttling groove, a U-shaped groove, a triangle groove, and a combined groove. This study analyzed the flow field simulation of four spool structures under the same opening degree and different pressures to study the flow field cavitation characteristics and pressure distribution in the valve. According to the simulation results, the necessity of opening throttling grooves for the pilot proportional directional valve and the advantages of combined grooves over U-shaped and triangular grooves were verified. Then, the proportional valve with a combined groove structure was simulated and analyzed to study its throttling characteristics, steady flow characteristics, and flow and load differential pressure characteristics, and further explore the advantages of a combined groove. Finally, the experimental results are compared with the simulation results, which can provide a theoretical reference for the selection of the throttle groove of the proportional valve and the structural design of the slide valve.

A new compressible flow model for pneumatic directional control valves

In this study, a new compressible flow model for small orifice openings in pneumatic proportional directional control valves has been proposed. It is crucial to precisely control pneumatic valves over all control ranges; yet, conventional flow models fail around the closed position of the valve. The main deficit of the existing studies in the literature is to assume constant values for the parameters of the flow model over changing operating conditions. It has been demonstrated that these rough assumptions are insufficient in precisely predicting the mass flow rate, particularly for small orifice openings. An enhanced experimental setup has been introduced to improve the effectiveness of the proposed model. The cracking pressure ratio and parameters of the model have been identified with experimental method. In the proposed model, new empirical coefficients have been established after a thorough investigation of the impact of supply pressure on the flow behavior of the valve. Validation studies of the model in both the filling and exhausting states of the valve have been carried out at various supply pressures and orifice openings, yielding rather promising modeling performances. In validation tests, the real pressure and the pressure produced by new model have been compared, and good agreement has been achieved with 0.0039% absolute error. According to the findings, the proposed improved flow model can be selected in precision pneumatic control applications.

Power control of a wind turbine using an electrohydraulically controlled active pitch control mechanism

The paper presents the numerical simulation of a horizontal axis wind turbine and the electrohydraulic system that maintains the constant frequency of the alternating current generator regardless of its load or the variation of the wind speed. As a starting point, the turbine parameters such as speed, torque and power were determined in relation to the angle of attack of the blades. In order to keep the frequency of the alternating current generator constant, the solution that adjusts the angle of attack of the blades was chosen using the active pitch control mechanism. This mechanism is controlled by a PID type controller, by controlling a proportional directional control valve that feeds the 3 orbital hydraulic motors, which are coupled in series so that the angle of the three blades is identical.

Pneumatic cylinder speed and force control using controlled pulsating flow

An application for accurate and low-cost force and velocity control of a pneumatic actuator, which can be used in any pneumatic circuit, is described in this paper. Control of a pneumatic cylinder is proposed via a pulsating flow technique. The technique uses on/off solenoid coils in the direction control valves in lieu of expensive servo controllers, such as proportional directional control valves. Pulsating air frequencies of 1.5, 3, and 4.5 Hz are applied by the designed circuit to investigate inlet constant pressures ranging from 1.72 to 5.17 × 105 Pa. The speed and force of a pneumatic cylinder rod are controlled using the generated pulsating flow and the results show success of idea of ​​controlling the speed and force of the pneumatic cylinder rod using the pulse flow technique. Empirical correlations suitable for later use in automatic control circuits are derived and are shown to exhibit an accuracy of up to ∼ 90–95.5% in predicting output force and velocity. It is also used to select the required frequency to obtain the speed and force required for the cylinder. To validate the pneumatic cylinder speed and force control using pulse flow technique, simulations are carried out using the Automation Studio program. The results show an improvement in control of the pneumatic cylinder mechanical performance and demonstrate that improvements are a function of the frequency of compressed air source pulses and pressure. An empirical correlation is also derived for predicting the cylinder rod speed and force at any source pressure and pulse frequency.

Coincidence of pressure pulsations with excitation of mechanical vibrations of hydraulic system components: An experimental study

This paper discusses certain excitations that affect the components of hydraulic systems: pipes and valves. The negative effects of low-frequency noise and vibration on humans were also pointed out. Particular attention is given to the effect of pulsatile flow on the structure of hydraulic components. Pressure pulsations in a hydraulic system have been shown to generate and transmit mechanical vibrations across a wide spectrum of frequencies, and the negative consequences of this phenomenon have been pointed out. Based on the latest generation of proportional directional control valve, a special stand was built to generate pressure pulsations over a wide frequency range (up to 350 Hz). Amplitude-frequency spectra of mechanical vibrations and pressure pulsations were used instead of time courses in the considerations. The paper concludes that effort must be made to reduce the amplitudes of pressure pulsations in hydraulic systems, particularly in the low-frequency spectrum.

Harmonic control of a dual‐valve hydraulic servo system with dynamically allocated flows

AbstractModern industries face increasing demands to improve the precision and workability of equipment, leading to stringent requirements for hydraulic servo systems in terms of flow, accuracy, and output power. High‐flow servo valves and multi‐valve synchronous control methods have seen more applications in the industry to meet these demands. However, high‐flow servo valves are expensive and have unsatisfactory performance, and synchronous control methods require servo valves to have the same hydraulic characteristics, resulting in higher cost and lower accuracy of high‐flow hydraulic servo systems. Also, very little has been conducted on controlling single actuators using multiple valves. In this study, we design a novel dual‐valve hydraulic servo system structure with a high‐flow proportional directional valve that is connected in parallel with a low‐flow servo valve and further develop the mathematical model of this dual‐valve system. Next, a harmonic control scheme was proposed, which included a flow allocation layer and trajectory tracking layer. Thereby, we achieved optimal control of two valves, and robust performance was guaranteed. Finally, we investigate the relationships between the flows of two valves, the deadband of the proportional directional valve, and trajectory tracking errors. Experimental results show that the proposed control scheme can effectively adjust the output flow of each valve dynamically according to the tracking trajectory and the hydraulic characteristics of the two valves, and the tracking performance of the servo system is significantly improved. This method is promised to enable the realization of an economical, high‐flow, high‐precision hydraulic servo system that can be generally used in various fields, such as marine engineering and construction.

A Case Study of Open- and Closed-Loop Control of Hydrostatic Transmission with Proportional Valve Start-Up Process

This paper concerns the start-up process of a hydrostatic transmission with a fixed displacement pump, with particular emphasis on dynamic surplus pressure. A numerically controlled transmission using a proportional directional valve was analysed by simulation and experimental verification. The transmission is controlled by the throttle method, and the variable resistance is the throttling gap of the proportional spool valve. A mathematical description of the gear start-up process was obtained using a lumped-parameters model based on ordinary differential equations. The proportional spool valve was described using a modified model, which significantly improved the performance of the model in the closed-loop control process. After assuming the initial conditions and parameterization of the equation coefficients, a simulation of the transition start-up was performed in the MATLAB–Simulink environment. Simulations and experimental studies were carried out for control signals of various shapes and for various feedback from the hydraulic system. The pressure at the pump discharge port and the inlet port of the hydraulic motor, as well as the rotational speed of the hydraulic motor, were analysed in detail as functions of time. In the experimental verification, complete measuring lines for pressure, speed of the hydraulic motor, flow rate, and temperature of the working liquid were used.

Development of a new high-precision friction test platform and experimental study of friction characteristics for pneumatic cylinders

In order to achieve high-precision pneumatic cylinder friction test, this paper proposes a new direct measurement method based on electric cylinder in which the axially acting forces from the compressed air in the two facing pneumatic cylinders cancel each other out and the detected value of the force transducer is just friction. For the sake of the implementation of the method, a new low-cost test method for identifying deadband of proportional directional valve was proposed, and a set of fuzzy PI constant pressure control system was designed to cope with a certain degree of leakage in the chamber. Based on the above, a friction test platform with two pneumatic cylinders facing each other was eventually built to study the influence of pressure, pressure difference, and piston speed on the friction of two commonly used different types of pneumatic cylinders. Through multiple sets of tests, it is found that when the lip seals are used in pairs between the piston and the inner wall of the cylinder, the friction between the piston and the cylinder is only related to the sum of the two chamber pressures, but not to the pressure difference between the two chambers. When the O-ring seal is used between the piston and the inner wall of the cylinder, the friction between the piston and the cylinder is related not only to the pressure of the two chambers, but also to the pressure difference between the two chambers. In addition, a series of comparative tests with the traditional single-cylinder friction test method directly demonstrate the effectiveness of the proposed new method.

Validation of a Simulink Model for Simulating the Two Typical Controlled Ventilation Modes of Intensive Care Units Mechanical Ventilators

Mechanical ventilators are vital components of critical care services for patients with severe acute respiratory failure. In particular, pressure- and volume-controlled mechanical ventilation systems are the typical modes used in intensive care units (ICUs) to ventilate patients who cannot breathe adequately on their own. In this paper, a Simulink model is proposed to simulate these two typical modes employed in intensive care lung ventilators. Firstly, these two modes of ventilation are described in detail in the present paper. Secondly, the suggested Simulink model is analysed: it consists of using well-established subroutines already present in Simulink through the Simscape Fluids (gas) library, to simulate all the pneumatic components employed in some commercial ICU ventilators, such as pressure reducing valves, pressure relief valves, check valves, tanks, ON\OFF and proportional directional valves, etc. Finally, the simulation results of both modes in terms of pressure, tidal volume, and inspired/expired flow are compared with the real-life quantitative trends taken from previously recorded real-life experiments in order to validate the Simulink model. The accuracy of the model is high, as the numerical predictions are in good agreement with the real-life data, the percentage error being less than 10% in most comparisons. In this way, the model can easily be used by manufacturers and start-ups in order to produce new mechanical ventilators in the shortest time possible. Moreover, it can also be used by doctors and trainees to evaluate how the mechanical ventilator responds to different patients.

Establishment and Experimental Verification of a Nonlinear Position Servo System Model for a Magnetically Coupled Rodless Cylinder

The nonlinear characteristics of the pneumatic servo system are the main factors limiting its control accuracy. A new mathematical model of the nonlinear system of the valve control cylinder is proposed in order to improve the control accuracy of the pneumatic servo system. Firstly, the mass flow equation of the gas flowing through each port is established by analyzing the physical structure of the proportional directional control valve. Then, the dynamic equation of the system is set up by applying the Stribeck friction model for the friction model of the valve control cylinder and building a pneumatic circuit experiment to identify the friction model parameters. Finally, the correctness of the mathematical model is verified by the inflation and deflation experiment of the fixed capacitive chamber and the servo controls experiment based on PID position. The Simulink simulation of the mathematical model better reflects the characteristics of the pneumatic position servo system.