Abstract
A two-dimensional hydraulic servo valve is an innovative servo control element that provides hydraulic systems with a high power-to-weight ratio, great anti-pollution potential, and superior static and dynamic characteristics. The spool of such a valve is subject to two degrees of freedom: rotation around and sliding along the spool axis, to accomplish both pilot control and flow amplifier functions. The structure of the spool at the main stage is similar to that of a traditional slide valve wherein the asymmetrical distribution of the oil paths manufactured in the valve body produces circumferential unevenness in the radial flow force to the spool at the annular orifice, in line with the momentum theory. Three-dimensional computational fluid dynamics analysis of the flow field revealed that the radial flow force at the annular orifice increases sharply with inlet flow velocity and decreases as the orifice opening grows, while changes in outlet pressure do not affect the levels or distribution of this force. Also, net radial force at the annular orifice increases with both inlet velocity and opening size. The paper presents results demonstrating that the net radial force from fluid flow through the orifice could increase friction resistance and cannot be safely ignored, especially under high-flow-rate conditions.
Highlights
A two-dimensional (2D) hydraulic servo valve is a control unit whose fast dynamic response and capacity for precise flow control play a critical role in determining the overall performance of the hydraulic servo system
Amirante et al [13] confirmed the necessity of full three-dimensional (3D) computational fluid dynamics (CFD) investigation of fluid flow through proportional-type hydraulic directional-control valves, which can accurately predict the flow forces acting on the spool in aims of minimising the required driving forces
Valuable results emerged from this research into 1) the radial flow force’s distribution and its effects around the annular orifice of the main stage of a 2D servo valve and 2) the net radial force acting on the spool in consequence of the fluid flows
Summary
A two-dimensional (2D) hydraulic servo valve is a control unit whose fast dynamic response and capacity for precise flow control play a critical role in determining the overall performance of the hydraulic servo system. Amirante et al [13] confirmed the necessity of full three-dimensional (3D) computational fluid dynamics (CFD) investigation of fluid flow through proportional-type hydraulic directional-control valves, which can accurately predict the flow forces acting on the spool in aims of minimising the required driving forces. They redesigned the central conical and lateral surfaces of the new spool and succeeded in reducing the actuation force by more than 10% from that of the commercial spool commonly used in four-way three-position directly operated valves at maximal opening for the given flow rate examined in the experimental verification [14]. If the spool rotates clockwise, the spool’s operation is vice versa
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