A high flow fast switching valve for digital hydraulic systems
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Hydraulic systems are widely used in different industries; especially where high-magnitude forces are exerted. Traditional elector-hydraulic systems use a proportional or servo valve to control the position of hydraulic actuators. Low energy efficiency and high cost of these control valves are two important problems in these systems. Digital Hydraulics is one of the most novel methods, proposed to address these issues. Low cost, better energy efficiency, contamination insensitivity and low leakage are major advantages of Digital Hydraulics which make them popular among researchers. In this paper a Digital Hydraulic circuit is proposed, that uses a fast-switching on/off valve instead of servo valves to control the position of a hydraulic actuator. For this purpose the flow running through the fast-switching valve is controlled, employing proper PWM duty cycle. The excess flow of pump is discharged to the tank directly instead of going through the relief valve when the control valve is off. Thus the wasted energy, caused by the relief valve, is reduced significantly. A robust H∞ controller is applied to guarantee position tracking in the presence of uncertainties. The effectiveness of this method is tested after conducting experiments on a hydraulic test rig and presenting the experimental results.
Electrohydraulic servo valve
Hydraulics
Control valves
Valve actuator
Servomechanism
Electro-hydraulic actuator
Digital Control
Hydraulic circuit
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A key enabling technology to effective on/off valve based control of hydraulic systems is the high speed on/off valve. High speed valves improve system efficiency for a given PWM frequency, offer faster control bandwidth, and produce smaller output pressure ripples. Current valves rely on the linear translation of a spool or poppet to meter flow. The valve spool must reverse direction twice per PWM cycle. This constant acceleration and deceleration of the spool requires a power input proportional to the PWM frequency cubed. As a result, current linear valves are severely limited in their switching frequencies. In this paper, we present a novel fluid driven PWM on/off valve design that is based on a unidirectional rotary spool. The spool is rotated by capturing momentum from the fluid flow through the valve. The on/off functionality of our design is achieved via helical barriers that protrude from the surface of a cylindrical spool. As the spool rotates, the helical barriers selectively channel the flow to the application (on) or to tank (off). The duty ratio is controlled by altering the axial position of the spool. Since the spool no longer accelerates or decelerates during operation, the power input to drive the valve must only compensate for viscous friction, which is proportional to the PWM frequency squared. We predict that our current design, sized for a nominal flow rate of 40l/m, can achieve a PWM frequency of 84Hz. This paper presents our valve concept, design equations, and an analysis of predicted performance. A simulation of our design is also presented.
Duty cycle
Electrohydraulic servo valve
Flow control valve
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High speed on/off solenoid valves have often been used for pressure control or flow control in hydraulic servo systems for automobiles or construction machines. These systems require faster valve switching speed to improve control preciseness. The authors have designed and manufactured an electronic valve driving circuit with fast response characteristics by using a 3 power source. In experiments using a hydraulic system incorporating the new valve driving circuit, the new circuit shortened the switching delay time from 5 ms to 1.55 ms. Also, the hydraulic system with the new circuit showed excellent position tracking control performances.
Solenoid valve
Electrohydraulic servo valve
Solenoid
Hydraulic circuit
Valve actuator
Response time
Control valves
Valve timing
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In digital fluid power, fast switching valve is a potential digital hydraulic component because of less throttling loss, reliability, low price, and so on. But its outlet flow is usually small and discontinuous. In this article, a two-stage proportional flow control valve is presented, in which the main stage is a flow amplifying valve, and the pilot stage consists of several switching valves with pulse width modulation control strategy. Peak and hold technique is adopted to improve the dynamic performance of the pilot stage. Benefits of the proposed configuration are continuous outlet flow and large flow capacity. The valve performance is investigated by theoretical analysis, simulation, and test. It is shown that both poppet displacement and outlet flow fluctuate around a stable value because of the discontinuous pilot flow, but the average outlet flow as well as poppet displacement of the main stage can be approximately proportionally regulated by changing pulse width modulation duty ratio. Average outlet flow of the main stage is an amplification of that of pilot stage. Increasing the average pressure drop not only increases outlet flow but also increases the severity of flow pulsations because pressure fluctuation becomes more serious as the average pressure difference increases. In theory, higher carrier frequency leads to smoother outflow; however, tested outflow profile of the proposed valve at 50 Hz is not significantly smoother than that at 30 Hz. This phenomenon may be due to the asynchrony of the four switching valves and the pressure fluctuations during the testing process.
Bandwidth throttling
Outflow
Flow control valve
Flow Control
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Fluid power
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High-speed on-off valve has been introduced in this paper with its concept and applications in various industries.Its trend and development in the future is optimized.This technology does challenge the proportional and servo technology in hydraulic area,because the technology can be used in displacement control of hydraulic pump,proportional and servo system,valve bank shifting,digital cylinder and so on.
Electrohydraulic servo valve
Telescopic cylinder
Valve timing
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Switched-reactance hydraulics represents a radically novel approach to the control of fluid power, since the proportional metering of flow through adjustable orifices is eliminated, and the inertive properties of the fluid substituted. Potential advantages in bandwidth, linearity, and efficiency have been indicated. This paper presents the first steady-state theory and experiments with a rotary fluid switch, which accomplishes the needed pulse-width modulation at a desirably high frequency. Cavitation problems are observed, means of their partial solution are implemented, and means of a more complete solution are indicated.
Fluid power
Inertance
Hydraulics
Reactance
Electrohydraulic servo valve
Electrical reactance
Working fluid
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This paper reports on an initial investigation of a switched inertance device (‘SID’). Using this device, flow and pressure can be varied by a means that does not rely on dissipation of power. The device can provide a step-up or step-down of pressure or flowrate, analogous to a hydraulic transformer. Simulated and experimental results on a prototype device show a promising performance. The device could potentially provide very significant reduction in power consumption over conventional valve-controlled systems, provided that noise issues and some other practical problems can be overcome.
Inertance
Control valves
Pressure Control
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Digital hydraulic valve systems can offer several benefits compared to spool-type proportional valves, such as faster response, more flow capacity, better fault tolerance and individual metering. However, the digital valve systems currently available are large, heavy and slow and therefore there is a need to miniaturise them and simultaneously make them faster. This article describes the design and performance of a digital valve system which can be used to replace a proportional valve with ISO 03 (NFPA D03, CETOP 3, NG6) standard interface. The valve system consists of 32 pilot operated miniature on/off valves which form four independently controlled metering edges. The valve system has small dimensions (176 × 49 × 72 mm) even though it contains integrated control electronics, its response time is approximately 2 ms and flow capacity per metering edge is 30 l/min at Δp = 0.5 MPa. These properties are good, however, improvements are required to reduce the leakage caused by the pilot valves, which can reach 5 l/min per metering edge at 10 MPa pressure difference.
Metering mode
Control valves
Valve actuator
Leakage (economics)
Flow Control
Flow control valve
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