Theoretical analysis of tapered pistons in high speed hydraulic actuators
TL;DR: In this article, an attempt is made to analyse systematically the three types of profiles commonly considered for high speed actuators, using Reynolds' differential equation, and analyses are made using an analytical method for one-dimensional flow and using the finite element method for twodimensional flow.
Abstract: In a high speed hydraulic actuator the usage of seals on the piston surface causes excessive wear on the seals and positional inaccuracies owing to coulomb friction. Hence sealless pistons with sloping surfaces have been tried by some manufacturers of such actuators. Here an attempt is made to analyse systematically the three types of profiles commonly considered for high speed actuators, using Reynolds' differential equation. Analyses are made using an analytical method for one-dimensional flow and using the finite element method for two-dimensional flow. The analyses reveal that single tapered pistons have certain limitations and that double tapered pistons can function successfully under different conditions in hydraulic actuators. It is also shown that friction in these types of pistons is much less than in conventional pistons with seals.
TL;DR: In this article, the fluid-structure interaction between the piston and the fluid cavities at the piston end was modeled with special purpose hydrostatic fluid elements while the piston is modeled with brick elements.
Abstract: This paper gives a new approach for modeling the fluid-structure interaction of servovalve component-actuator. The analyzed valve is a precision flow control valve-jet pipe electrohydraulic servovalve. The positioning of an actuator depends upon the flow rate from control ports, in turn depends on the spool position. Theoretical investigation is made for No-load condition and Load condition for an actuator. These are used in finite element modeling of an actuator. The fluid-structure-interaction (FSI) is established between the piston and the fluid cavities at the piston end. The fluid cavities were modeled with special purpose hydrostatic fluid elements while the piston is modeled with brick elements. The finite element method is used to simulate the variation of cavity pressure, cavity volume, mass flow rate, and the actuator velocity. The finite element analysis is extended to study the system's linearized response to harmonic excitation using direct solution steady-state dynamics. It was observed from the analysis that the natural frequency of the actuator depends upon the position of the piston in the cylinder. This is a close match with theoretical and simulation results. The effect of bulk modulus is also presented in the paper.
TL;DR: In this paper, a commercial computational fluid dynamics (CFD) code, FLUENT, is used to investigate the effects of groove sectional shapes and its sizes on the flow and lubrication characteristics of single grooved hydraulic spool valve.
Abstract: The spools in most all the hydraulic spool type control valve have several circumferential grooves to prevent well known hydraulic locking problems which result in high friction force and excessive wear. In this paper, a commercial computational fluid dynamics (CFD) code, FLUENT is used to investigate the effects of groove sectional shapes and its sizes on the flow and lubrication characteristics of single grooved hydraulic spool valve. The streamlines, velocity and pressure distributions in the groove, and leakage flow through the clearance are obtained for various groove depths and sectional shapes. For shallow groove, the streamlines and leakages are highly affected by groove shapes and depths. However, for relatively deep groove, the pressure distribution and leakage are nearly uninfluenced by groove depth. It is newly found that there occurred vortices inside groove beyond a certain ratio of groove depth to width. The vortex can play as contaminants collector so contribute to reduce abrasive wear. The numerical method adopted in this paper and results can be used in optimum design of spool valves.
TL;DR: In this paper, the authors analyzed the speed characteristics of the water hydraulic axial piston motor and found that the clearance of friction pairs is the key factor in the hydraulic piston motor's speed.
Abstract: Purpose The purpose of this study is to analyze the speed characteristics of the water hydraulic axial piston motor. The speed performance of water hydraulic piston motor which uses water as medium is different from that mineral oil one. Design/methodology/approach To analyze the speed characteristics of the water hydraulic motor, the speed model of a swash plate water hydraulic piston motor is developed theoretically and a simulation model with AMESim is built. Findings The effects of clearance between friction pairs and input pressure on the speed are analyzed and compared between the theoretical and numerical models. Originality/value The results of the theoretical and simulation models both verify that the clearance of friction pairs is the key factor in the hydraulic piston motor’s speed.
TL;DR: In this paper , the authors proposed an accurate mathematical model with rectangular grooves to investigate the effect of uneven pressure distribution in the clearance film between the sleeve and the spool, and compared the results obtained by the Reynolds equation and the Navier-Stokes equation.
Abstract: As an actuator control element of the electrohydraulic system in aerospace, airplanes, and other equipment, the spool valve is prone to the “hydraulic lock” problem, which may cause major accidents of these electrohydraulic systems. The grooves engraved on the spool can effectively eliminate this problem by migrating the uneven pressure distribution in the clearance film between the sleeve and the spool. The effect of migrating uneven pressure distribution depends on the groove parameters. This paper proposed an accurate mathematical model with rectangular grooves to investigate the effect. Unlike previous mathematical models based on the Reynolds equation, the proposed model is based on the Navier–Stokes equation, which is more valid in the range where the clearance film thickness is much less than the groove depth. Meanwhile, the mathematical model takes the distributions, width, depth, and the number of grooves into consideration. Then, the proposed mathematical model was used to investigate the effects of mitigating the uneven pressure distribution under various parameters of grooves. To verify the accuracy of the mathematical model, the volume flow leakage in the clearance film obtained by the proposed model and the Reynolds equation, respectively, is compared with that obtained by the experimental test. The comparison results indicate that the results obtained by the Reynolds equation could reach a maximum of 14.75% different from the experimental results, while the results obtained by the NS equation are only 5.57% different under the same conditions, implying that the mathematical model derived from the NS equation is more accurate.
01 Mar 2013
01 Jan 1975
TL;DR: The Finite Element Method as discussed by the authors is a method to meet the Finite Elements Method of Linear Elasticity Theory (LETI) and is used in many of the problems of mesh generation.
Abstract: PART I. Meet the Finite Element Method. The Direct Approach: A Physical Interpretation. The Mathematical Approach: A Variational Interpretation. The Mathematical Approach: A Generalized Interpretation. Elements and Interpolation Functions. PART II. Elasticity Problems. General Field Problems. Heat Transfer Problems. Fluid Mechanics Problems. Boundary Conditions, Mesh Generation, and Other Practical Considerations. Appendix A: Matrices. Appendix B: Variational Calculus. Appendix C: Basic Equations from Linear Elasticity Theory. Appendix D: Basic Equations from Fluid Mechanics. Appendix E: Basic Equations from Heat Transfer. References. Index.
01 Jan 1961
01 Jan 1949
01 Jan 1969
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