Investigations of the micro surface shape for the gear-shaft/journal-bearing interface in water hydraulic internal gear pumps

Hua Zhou,Ruilong Du,Huayong Yang,Anhuan Xie

doi:10.1177/1687814017742577

Abstract

This article presents an approach for improving the water film’s carrying capacity in the gear-shaft/journal-bearing interface in water hydraulic internal gear pumps by applying micro shapes to the gear shaft’s surface. The micro shapes are in the shape of sinusoidal waves that can be determined by three design parameters in terms of the wave number, the wave amplitude, and the convex ratio. An elasto-hydrodynamic model, which involves the evaluations of the film height, the film pressure, and the bearing deformation, is proposed to analyze the performance of the micro shapes, and the model is validated by comparison with the results from other research groups. By observing the performance of the micro shapes, it is seen that the convex shape has a positive effect while the concave shape has a negative effect on the film’s carrying capacity, and the carrying capacity decreases as the wave number increases. Additionally, further discussions are performed with respect to the design parameters of the convex shape under different operating conditions, suggesting that the wave amplitude should be maintained 0.8–0.9 times the maximum deformation of the bearing and the convex ratio should be 1/3.

Highlights

Water hydraulics is becoming more and more popular in many occasions, especially in pollution-free occasions such as food and drug processing facilities and nuclear industries, due to its advantages over traditional oil hydraulics in terms of environmental friendliness, nontoxicity, and non-flammability.[1,2] Water hydraulic internal gear pumps (WHIGPs) represent a promising power unit in water hydraulics due to their advantages of compactness, low noise level, and low flow ripple.[3]
The gear-shaft/journal-bearing interface represents one of the key design elements of WHIGPs, and this article is focused on the micro shapes applied to the gear shaft’s surface for the purpose of improving the carrying capacity of the water film in the gearshaft/journal-bearing interface
It can be seen that the gear shaft is subjected to a radial force caused by the circumferential fluid pressure and the meshing force, which needs to be balanced by the water film in the gear-shaft/journal-bearing interface

Summary

Introduction

Water hydraulics is becoming more and more popular in many occasions, especially in pollution-free occasions such as food and drug processing facilities and nuclear industries, due to its advantages over traditional oil hydraulics in terms of environmental friendliness, nontoxicity, and non-flammability.[1,2] Water hydraulic internal gear pumps (WHIGPs) represent a promising power unit in water hydraulics due to their advantages of compactness, low noise level, and low flow ripple.[3]. It is worth noting that the aforementioned works concerning micro surface shapes on the lubricating interfaces, including the bearing surface and the interface in hydraulic units, are conducted using the mineral oil as the working medium, and the works are mainly focused on the decrease of the power loss caused by the viscous friction. This article makes an attempt to investigate the potentials of the micro shapes on the gear shaft’s surface to improve the water film’s carrying capacity in the gear-shaft/journal-bearing interface by analyzing four different micro surface shapes using an EHD model. It can be seen that the film height is contributed by three parts: the eccentric position of the gear shaft (h0), the bearing deformation (hp), and the micro surface shape (Dh), as expressed in equation (4). In equations (9) and (10), ‘‘ + ’’ corresponds to the convex shape while ‘‘–’’ corresponds to the concave shape

Simulation procedure

Results and discussion

Design parameters of the convex shape