An Investigation on the Leakage Flow and Instantaneous Tooth Space Pressure in External Gear Machines

Abstract

External gear machines (EGMs) are used in a variety of industries ranging from fluid power machinery to fluid transport system and fuel injection applications. To gain understanding of the performance and dynamic characteristics of operation of these units, several simulation tools have been developed in past. Some of these tools are based on lumped parameter approaches, which are useful for fast design studies and optimizations. However, most of these models are based on “a priori” assumptions, particularly as concerns the flow regime of the leakage flows. Internal leakages not only determine the volumetric efficiency of an EGM, they also affect the actual pressure loading on the gears. A simple Iaminar flow assumption is usually considered for the leakage flow at the tooth tip of the gears, but as this paper will show, for certain EGMs this hypothesis is not valid, and effects of turbulence at the tooth tip are observed. The goal of this paper is to propose a methodology for fast lumped parameter approaches to model the tooth tip leakage flow in EGMs, applicable for a broad range of operating conditions. The proposed model considers the occurrence of turbulent flow conditions as well as the entrance pressure drop, with considerations based on existing published work and CFD simulations. In order to show realistic simulation, the proposed model is implemented within the HYdraulic GEar machines Simulator (HYGESim), developed by the authors’ team over the past years. The proposed model is then used to study the tooth space volume pressurization and leakage flow on a reference pump working with Jet A-l fuel, showing the importance of the proposed modeling approach.