Comparative Analysis of External Gear Machine Performance Considering Deformation and Thermal Effects

Abstract

The energy efficiency of external gear pumps (EGPs), as in other positive displacement machines for high-pressure applications, is significantly influenced by the power losses occurring in the lubricating interfaces that seal the internal displacement chambers. Therefore, it is crucial to account for these interfaces accurately when developing predictive simulation tools. However, in literature various modeling approaches can be found that consider different assumptions regarding the analysis of these interfaces. This makes it challenging for a designer to determine which physical domains needed to be modelled accurately in order to assess the EGP performance.

This paper addresses the above research question by leveraging a comprehensive simulation tool (Multics-HYGESim) developed at the authors’ research team which includes thermal-tribological considerations pertaining to the meshing of the gears, the lubricating films at the tooth tip interfaces, at the journal bearings, and at the lateral interfaces. The tool considers realistic fluid properties, including the effects of cavitation and aeration, mixed lubrication effects, as well as material deformation effects for the gears, lateral bushings and the EGP housing. Additionally, recent advancements to the model, presented for the first time in this work, include coupled thermal analysis of the EGP, including fluid domain, lubricating interface domain and solid domain. The heat transfer evaluation in the solid domain allows predicting the body temperatures along with their thermal deformation. Material deformation effects strongly affect the internal balancing features of an EGP as well as its internal pressurization. All the mutual interaction between the geometrical domain, the body motions and their deformation, the fluid dynamic and the thermal domains make a realistic quantification of these effects difficult in simulation.

Using a commercial EGP as a reference, for which experimental results are available concerning volumetric and hydromechanical efficiency, this paper demonstrates how predictions can vary based on different simulation assumptions regarding body and lubricating film behavior. The paper will present simulated predictions starting from a basic rigid body assumption that considers only body motion and analytical formulations of lubricating interfaces, to simulation model cases of progressively increasing in complexity to account for deformations different bodies i.e. the gears, bushings and the housing. The most complex case would include evaluation of thermal behavior along with deformation effects. A detailed distribution of power loss and leakages arising from different sources of hydromechanical and volumetric losses is presented for all cases under consideration. The results will offer valuable insights to EGP designers, enabling them to understand the strengths and limitations of different modeling assumptions on the prediction of EGP behavior, especially regarding the effects of body deformation.