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Lumped parameter modeling is a consolidated technique for analyzing the fluid dynamic behavior of positive displacement machines, owing to their computational swiftness and the ease of integrating other physical domains affecting the operation of the machine. With some very limited exceptions, this modeling technique typically neglects fluid inertia and momentum effects. This paper proposes an approach to study the effects of fluid inertia affecting the pressurization and depressurization of the tooth space volumes of an external gear pump. The approach is based on considering the fluid inertia in the pressurization grooves and inside the control volumes with a peculiar subdivision. Further, frequency-dependent friction is also modeled to provide realistic damping of the fluid inside these channels. Validation of the model has been performed by comparing the lumped parameter model with a full three-dimensional Navier-Stokes solver. The quantities compared, such as tooth space volume pressures and outlet volumetric flow rate, show a good match between the two approaches for varying operating speeds. A comparison with the experiments supports the modeling approach as well. The paper finally, also discusses which operating conditions and geometries play a significant role that governs the necessity to model such fluid inertia effects in the first place. [ABSTRACT FROM AUTHOR]

• An approach for modeling of manufacturing errors in gear machines is presented. • The proposed model incorporates both conicity and concentricity errors. • The model is validated against experiments conducted on six gearsets. • Volumetric efficiency decreases with an increase of the conicity error. • Volumetric efficiency increases with concentricity error in absence of case wear. Manufacturing errors are always unavoidable in actual machines. In external gear machines (EGMs), some of the manufacturing errors are typically on the same scale as the nominal clearances between the internal parts. These clearances are responsible for leakage flows that reduce the volumetric efficiency of EGMs and impact their overall performance. Current approaches of modeling the operation of EGMs neglect the manufacturing errors which limits their accuracy. This paper proposes a technique to study the operation of EGMs accounting for two common gear manufacturing errors: conicity and concentricity. Furthermore, an alternate technique to model these errors is proposed by defining an "effective gap height". This latter technique can be used in any existing lumped parameter model as well as for quick estimations. To validate the approach, experiments are performed with gearsets exhibiting varying amounts of conicity and concentricity errors. The results from both the simulations and the experiments show that the volumetric efficiency decreases with an increase of the conicity error. Instead, by increasing the concentricity error, an increase in the volumetric efficiency is found, at least until the conditions of contact between the gears and the casing's internal surface are avoided. [ABSTRACT FROM AUTHOR]

With their advantages of low-cost, high-reliability and simplicity, external gear machines (EGMs) are among the most common pumps or motors in high pressure applications. As all positive displacement machines, EGMs are characterized by a substantial flow non-uniformity, which is given by the gear meshing and results in vibrations and noises. Several analytical methods are available but require the knowledge of the tooth profile, involute or cycloidal, and are not directly applicable to unconventional gears. This paper presents a numerical approach for the analysis of the theoretical flow through spur gear EGMs which does not require a-priori knowledge of the gear profile. Starting from a CAD input, the proposed approach automatically determines control volumes for every angular position of the gears to describe the displacing action realized by the unit. After describing the method, the paper shows its application to different geometric morphologies for the gear profiles to calculate the theoretical flow rate. The verification of the numerical model is demonstrated by comparing its results with those provided by the analytical methods available in literature for the case of involute gears. [ABSTRACT FROM AUTHOR]

This paper presents an analytical approach for the analysis of a new working concept for variable delivery external gear machines. The proposed design principle encompasses all the advantages of conventional fixed displacement external gear machines, along with a simple mechanism to change the displaced flow per shaft revolution. The variation in the displaced flow is achieved by realizing a variable timing for the connections of each tooth space volume (volume between two adjacent teeth of the gears) with the inlet and outlet. This is achieved through a movable slider placed at the gear lateral sides. The position of the slider determines the amount of flow displaced by the unit per revolution. Analytical expressions which define the range of percentage variation in flow displacement that can be achieved based on a generic asymmetric design of the gears are presented. The paper presents a detailed analytical derivation for geometric displacement, flow delivered at the outlet and shaft torque required during operation as well as flow non-uniformity/pulsation. The analytical expressions were compared with proof of concept test. Experimental results were in line with the analytical prediction and show a 32% variation in displacement. These positive results show promising potentials for the working of a new concept for variable delivery external gear machine. [ABSTRACT FROM AUTHOR]

A novel fluid–structure interaction–thermal coupled model for the lateral lubricating gaps between gears and lateral bushes in external gear machines (EGM) is presented in this study. The model is the first of the lateral lubricating interface in EGMs capable of considering heat transfer, thermal effects in the fluid film and solid components as well as thermo-elastic deformation of the solids enabling prediction of the film thickness in EGM lateral gaps considering thermoelastohydrodynamic lubrication. Model validation is performed using lateral gap leakage measurement which is dependent on absolute film thickness. A novel relative lubricant film thickness measurement method in gear machines using capacitive sensors is also presented, and used to validate the spatial film thickness predictions from the model. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a fluid structure interaction (FSI) model for the simulation of the flow in the lubricating gaps between gears and lateral bushes in external gear machines (EGMs). The proposed model is capable of accounting for elasto-hydrodynamic effects in the lubricant film, and can predict the lubricant film thickness. Three different constraint methods are considered as concerns the structural problem: “ideally supported”, “inertia relief” and a “low pressure” constraint specifically formulated for EGMs. The proposed model is validated against measurements performed on an experimental prototype. Detailed formulation of the FSI model as well as significant simulation results are presented for a wide range of operating conditions along with comparison to experimental results. [Copyright &y& Elsevier]

Abstract: This paper presents a novel modeling approach for studying the lateral lubricating gap between sliding lateral bushes and spur gears in external gear machines. Pressure compensated lateral bushings are important design elements for efficient operation of an external gear pump or motor, being responsible for functions such as sealing the displacement chambers, guaranteeing a proper timing for the connections with outlet and inlet port limiting pressure peaks and cavitation. As regards the sealing function, they must be designed with the two main goals of reducing power losses due to leakages and of maintaining full film lubrication in the gap, to minimize shear stress and prevent wear in the elements. Because of the complexity of the simultaneous processes that characterize the operation of this kind of units, only limited research has been performed on modeling the lubricating gap in the past. The model presented in this paper is the first tool that can predict the lateral lubricating gap features, accounting for the main features of machine operation. A Computational Fluid Dynamics solver that solves for the flow field in the lubricating gap is coupled with a model of the axial motion of the lateral bushes to determine the lubricating gap heights. The model also interacts closely with a lumped parameter model as well as a geometric model of gear teeth control volumes, and therefore provides a tool for a “complete simulation” of the unit. The forces acting on the lateral bushing are seen to lead to an axially balanced condition. An original method of decomposition of forces was developed to perform an analysis of the effect of the hydrodynamic as well as hydrostatic forces acting on the bushing. It was found that the hydrodynamic generation of pressure from the “wedge” mechanism determines the orientation of the lateral bushing at axial balance. Gap heights and the resulting power losses from the lubricating gap are also calculated for a range of operating conditions. Using the proposed methodology, competing designs of lateral bushes can be evaluated and optimized for low chances of wear, as well as low losses. The tool developed has the potential to be used to drive design of gear machines with greater efficiency and reliability. [Copyright &y& Elsevier]

• Summary of common gerotor gear profiles (epitrochoidal, hypotrochoidal, cycloidal). • Optimization presented to identify the optimal design space for each profile type. • Optimal design space of each profile type is compared. • No profile type is universally superior to the others. Gerotors are positive displacement machines known for being cost-effective, durable, compact, and quiet and are used in many low-pressure applications. Nearly any smooth curve can define a gerotor gearset, yet three conventional profile types that are based on either epitrochoids, hypotrochoids, or cycloids are used almost exclusively in industry. Although each of the profile types has been known since the early 20th century, no extensive comparison has been made between them. In the present work a multi-objective optimization strategy using a genetic algorithm is used to find the Pareto front for each profile type when considering seven performance goals. The optimal designs of each profile type were combined, and a new set of Pareto designs was identified. The results showed that no single profile type can be considered universally better than the others. However, some observations about the general trade-offs for each profile type are presented, and the work serves as a baseline for development of novel gerotor profiles. [ABSTRACT FROM AUTHOR]

• Electrification to increase off-highway vehicles efficiency. • Electro-hydraulic unit as a prime mover of off-highway vehicles. • Integrated hydraulic gear machine and permanent magnet synchronous electric machine. • Electric and hydraulic machines integration to increase compactness. • High rotational velocity operation to increase efficiency. In recent years, increasingly stringent emission regulations have spurred an electrification trend in off-highway vehicle technology. To address challenges such as the high cost of power electronics components, limited battery capacity, and the substantial modifications required for the vehicles, there is a pressing need to develop high-speed, cost-effective, compact, and efficient electro-hydraulic units capable of powering vehicle functions. In response to these demands, this paper introduces an innovative morphology for an electro-hydraulic unit and outlines the integration method for a crescent-type internal gear machine with a permanent magnet synchronous electric machine. The proposed morphology aims to minimize component count through a shaftless solution while incorporating a cooling system that utilizes the same working fluid as the hydraulic machine. The design approach utilizes a genetic algorithm optimization process to maximize overall energy efficiency and compactness. Insights gained from the optimization results shed light on the relationship between key design parameters and unit performance, enhancing the understanding of this electro-hydraulic unit. A prototype of the unit was manufactured and tested, demonstrating a volumetric efficiency ranging from 81 % to 97 % at a maximum rotational velocity of the pinion of 6000 rpm. These results validate both the morphology and the design approach, indicating the feasibility of designing compact electro-hydraulic units that leverage hydraulic machines with higher maximum rotational velocities than commercially available counterparts as a mean to enhance efficiency and compactness. [ABSTRACT FROM AUTHOR]