Pressure-Drop Coefficients for Cushioning System of Hydraulic Cylinder With Grooved Piston: A Computational Fluid Dynamic Simulation

Robert Castilla,Esteban Codina,Pedro Roquet,Antonio Algar,Ignasi Alemany,Pedro Gamez-Montero

doi:10.3390/en10111704

Abstract

Cushioning is an important aspect in hydraulic cylinder performance. The piston has to be decelerated before it strikes the end cap in order to avoid stresses in the cylinder components and reduce vibration that can be transmitted to the machine. One of the least-studied methods is internal cushioning by grooves in the piston. In this method, the flow is throttled with adequately designed grooves when the piston reaches the outlet port position. The purpose of the present work is to present a method to estimate the pressure-drop coefficients for a certain design of piston grooves in order to provide a model to develop a dynamic system simulation of the cushion system. The method is based on a computational fluid dynamic simulation of flow through piston grooves to the outlet port for each piston’s static position. The results are compared with experimental measurements, and a correction, based on Reynolds number, is proposed. Good agreement, below 16%, was obtained for all the positions but particularly for the last grooves, for which the numerical result’s deviation to the experimental measurements was less than 10%. In general, the numerical simulation tended to underestimate the pressure drop for the first grooves and overestimate the calculation for the last grooves.

Highlights

End stroke cushioning in a hydraulic cylinder is important because it avoids mechanical shocks by reducing the piston velocity at the end of the cycle
The velocity has been normalized with the average velocity in the outlet port, and the pressure has been normalized with the dynamic pressure in the outlet port
Numerical CFD simulations were conducted for the analysis of the pressure drop in a groove-machined piston for the cushioning system of a hydraulic cylinder

Summary

Introduction

End stroke cushioning in a hydraulic cylinder is important because it avoids mechanical shocks by reducing the piston velocity at the end of the cycle. A proper cushioning system reduces machine noise for less downtime and lowers the machine maintenance costs [1]. Cushioning can be done with external control, but for mobile applications, this is not generally appropriate, as it requires a complex set-up of mechanical and hydraulic components [2,3]. In this case of mobile applications, internal end-stroke cushioning systems are preferably used. There are two main types of stroke-end hydraulic cylinder cushioning. It is usual to include a spear with a profile that fits conveniently in a hole drilled at the end of the cylinder

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