Gear pumps represent the majority of the fixed displacement machines used for flow generation in fluid power systems. In this context, the paper presents a review of the different methodologies used in the last years for the simulation of the flow rates generated by gerotor, external gear and crescent pumps. As far as the lumped parameter models are concerned, different ways of selecting the control volumes into which the pump is split are analyzed and the main governing equations are presented. The principles and the applications of distributed models from 1D to 3D are reported. A specific section is dedicated to the methods for the evaluation of the necessary geometric quantities: analytic, numerical and Computer-Aided Design (CAD)-based. The more recent studies taking into account the influence on leakages of the interactions between the fluid and the mechanical parts are explained. Finally the models for the simulation of the fluid aeration are described. The review brings to evidence the increasing effort for improving the simulation models used for the design and the optimization of the gear machines.

Models for Flow Rate Simulation in Gear Pumps: A Review

In the case of internal gear pumps, the eccentricity of the outer rotor, which resembles a circular lobe, must be limited to a certain value in order to avoid the formation of cusps and loops; furthermore, the tip width of the inner rotor, which has a hypocycloid curve and an epicycloid curve, should not be allowed to exceed the limit value. In this study, we suggest that the tip width of the inner rotor be controlled by inserting a circular-arc curve between the hypocycloid and epicycloid curves. We also suggest that the outer rotor be designed using the closed-form equation for the inner rotor and the width correction coefficient. Thus, it is possible to design a gerotor for which there is no upper limit on the eccentricity, as in this case, undercut is prevented and there is no restriction on the tip width. We also develop an automated program for rotor design and calculation of the flow rate and flow rate irregularity. We demonstrate the superior performance of the gerotor developed in this study by analyzing the internal fluid flow using a commercial computational fluid dynamics (CFD)-code.

Design of Rotor for Internal Gear Pump Using Cycloid and Circular-Arc Curves

Although gerotor pumps are used in a wide range of industrial applications, higher work pressure causes shock or collision among pump components, which leads to large stress fluctuations and shortened pump life expectancy. This paper therefore proposes a novel variable clearance design that diminishes such component collisions. After a geometric mathematical model is constructed of variable clearance rotors, a fluid analysis model is developed based on a relief groove design. Applying the model to two fixed clearance and three variable clearance designs demonstrates the effects of various fixed clearance sizes on gerotor pump performance and identifies the differences between fixed and variable clearance designs. The results support the feasibility of the proposed design: the appropriate variable clearance designs maintain robust flow characteristics and effectively reduce shock and collision among pump components, thereby reducing stress level, increasing stability, and extending the life expectancy of the gerotor pumps.

Flow Characteristics of Gerotor Pumps With Novel Variable Clearance Designs

A gerotor pump, which is widely used in the automotive industry for engine oil lubrication, produces an instantaneous flow fluctuation and the estimation of this is fundamental in order to evaluate the pump quality for silent and smooth operation. The intricate aspects of the pumping process of a gerotor pump make computational fluid dynamics the appropriate tool for modelling and simulation to provide insights into its flow characteristics. Because the instantaneous flow is rather dependent on the teeth contact, a new boundary condition of a virtual wall was developed, which allows simulation of the teeth contact in the interteeth radial clearances. This new boundary condition is utilized in a three-dimensional model of the gerotor pump with mesh deformation and remeshing at every time step by means of a home-made ad-hoc code programmed by the present authors and named viscous wall cell. The code has been integrated into the computational fluid dynamics solver. The interteeth clearances are studied under the following different operating conditions (working pressures and rotational velocities): first, no contact points (no teeth contact is studied in order to prove that, even if the interteeth radial clearance is sufficiently small, the leakage cannot be negligible); second, all contact points (the ideal approach is considered with zero interteeth radial clearances used to model zero manufacturing tolerances); third, one contact point at different locations (the existence of manufacturing tolerances and the teeth contact approach make the pumpâ€™s operation and its pumping mechanism more realistic in the simulation). The numerical instantaneous flow is compared with the analytical instantaneous flow, with the instantaneous flow modelled by using the bond graph technique, and with the experimental determination of the flow ripple for a specific unit. The results obtained show the importance of simulating the teeth contact and prove to be an excellent estimation of the instantaneous flow behaviour to obtain the dynamic properties of a gerotor pump under more realistic conditions than its design.

Influence of the interteeth clearances on the flow ripple in a gerotor pump for engine lubrication

Over the years, numerous investigations have established the gerotor fundamentals. This work aims to provide a complete review of the literature from the last decade, focusing on the articles published in the past five years on gerotor technology in hydraulic machines. The report gives a catalogue of guidelines based on the trochoidal-envelope definition, a background analysis, the worldwide distribution of articles in each continent and country and the most frequently used keywords in the field. The paper identifies state-of-the-art research, and reports on current mainstream ideas. From the historical background, this literature review reports the current approaches in gerotor pumps (geometry and performance approaches, modeling and numerical simulations), orbital motors and new concepts. The report will serve as a guide and a directory for novel engineers working with gerotor technology in hydraulic machines. Another intention of this paper is to disseminate the works of the researchers who use this technology around the world, and to provide a scenario for future international collaboration. The paper gives an account of the disparity between academia and engineering applications. There is currently very little published literature on design and production methodologies for gerotor pumps and orbital motors. Hence, the future goal is to collect recommendations that combine academia and industry expertise to make better use of these extensive studies in the field.

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A Review of Gerotor Technology in Hydraulic Machines

An innovative tool for the improvement of the design methodology of a trochoidal gear, which works as a part of a hydraulic pump, is introduced. For the past few years, new, specific, and demanding applications of this type of pumps have demanded to maximize efficiency and to reduce manufacturing costs by improving its two main performance indexes: volumetric characteristics and teeth contact stress. The existing methodologies and software fail to thoroughly address the design by taking into account both performance indexes. The software presented is an integrated package system, which is composed of three basic modules: design, volumetric characteristics, and contact stress module. As a result, by consecutively following each module, this new tool allows to find the better gear set for the concrete initial required design parameters. An application using the GEROLAB package system methodology is carried out to obtain the best candidate, which is compared and contrasted with a gear set of a specific gerotor pump unit. As a conclusion, this new software aims to lead the designer to a better design by improving performance indexes of a new born gerotor pump project.

M. Khamashta

Papers

GEROLAB Package System: Innovative Tool to Design a Trochoidal-Gear Pump