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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]

This paper presents a numerical modeling approach for investigating crescent‐type internal gear pumps (CIGPs) considering radial micromotions of both gears. The modeling approach couples a lumped parameter pressure solver on the bulk fluid domain, with a transient computational fluid dynamics film simulator based on transient gap geometries solved from the gear loading forces. Simulation results on a commercial unit shows that for a wide range of operating conditions, the model gives volumetric efficiency predictions with errors less than 2 % comparing to measurements. To highlight the importance of considering radial micromotions, the paper also provides the results achieved assuming nominal position for both gears. [ABSTRACT FROM AUTHOR]

The stability conditions of a two-dimensional gravity-driven flow of a thin layer of a power-law fluid flowing over a heated, uneven, inclined porous surface are investigated. A two-sided model is employed to account for the bottom filtration in the porous layer. The governing equations are reduced under the long-wave approximation and the cross-stream dependence is eliminated by means of the Integral Boundary Layer technique. Floquet–Bloch theory is used to investigate at linear level how the porous bottom waviness influences the thermocapillarity stability of the flow in a shear-thinning fluid. Differently from the even case, the linear stability analysis suggests that for flow over sufficiently wavy undulations the thermocapillarity may stabilize the equilibrium flow, depending on the values of dimensionless governing numbers and parameters. This stabilizing phenomenon is enhanced by the shear-thinning rheology of the fluid while it is reduced by the permeability of the layer. Numerical simulations, performed solving the reduced nonlinear model through a second order Finite Volume scheme, confirm the results of the linear stability analysis. • An investigation of instability of heated flow down an uneven porous incline. • A power-law rheological model is implemented. • Film flow is coupled with the filtration ow through the porous medium. • Combined effects of thermocapillarity, rheology and properties of substrate determined. [ABSTRACT FROM AUTHOR]

This paper presents a model formulation for balanced twin lip vane pumps and an experimental activity to validate the model. The simulation model begins with a geometrical module that preprocesses the CAD drawings of a given unit. The model then performs a fluid dynamic analysis using a lumped-parameter formulation to solve for the pressures inside properly defined control volumes within the unit. The fluid dynamic model is solved simultaneously with a motion module that evaluates the planar motions of the vanes using Newton's law of motion and with a lubricating interface solver based on the Reynolds equation. Contact dynamics formulations and elastohydrodynamic relations are applied at the vane locations in contact with the cam ring. The comparison with experimental results highlights a good match in volumetric and hydromechanical efficiencies. The measured outlet pressure ripple matches the simulated one for all tested speeds and pressures. The paper also shows a breakdown of the distribution of volumetric and power losses arising from various components of the machine. The proposed methodology is computationally inexpensive, so it can be used in future design and optimization studies aimed at improving the performance of such units. • A novel simulation approach for high-pressure pressure balanced vane pumps. • Multiphysics approach coupling mixed lubrication, vane motions, and fluid dynamics. • Capturing details in cam ring profile, fluid properties, clearances, vane designs. • Experimental activity performed to validate the modeling approach. • Good accuracy for pressure pulsations, volumetric and hydromechanical performance. [ABSTRACT FROM AUTHOR]

This paper presents the formulation of a variable load sense control strategy suitable to achieve power savings in hydraulic systems using postcompensated load sensing (LS) hydraulic control architectures. Such architecture is typical in off-road construction machinery. The paper also describes the application of the proposed control strategy referred to as variable load sensing margin (VLM) on a full-size wheel loader. The paper first presents the rationale for the proposed strategy, showing how the state-of-the-art LS architecture present in commercial machines has a margin for lowering the throttling losses present at the control valves. A feedforward controller, derived from an empirical study on a reference vehicle, is used to control the flow to the front-end loader functions. Test results show improvements of the hydraulic power consumption up to 45%, based on the commanded speed of each front-end loader actuator. The paper also describes a gain scheduling pressure feedback control strategy, which is used to allow controlling also functions that include priority. For the case of off-road vehicles, this is typically the steering function. The experimental results show good performances with an error in controlled velocity below 5%, which is achieved when the front-end loader functions are used concurrently with the steering. [ABSTRACT FROM AUTHOR]

Counterbalance valves (CBVs) are widely used in hydraulic machines handling gravitational loads. They are usually adopted in hydraulic circuits that set the flow to the actuator with either metering control strategies or primary control strategies. In these circuits, the CBV does not determine the actuator velocity, but it establishes a proper counterpressure that balances the actuator during overrunning loads. A well-known problem of CBVs is the excessive power consumption introduced into the circuit, which is due to an excessive pressurization of the flow supply. This paper presents a solution for using CBVs to control the actuator velocity while also reducing energy consumption. The method consists in controlling the pilot port of the CBV through an external pressure source (adjustable pilot). The solution is first studied analytically, considering all the possible loading conditions at the actuator. Two different control strategies are presented: the "Smart CBV," where the CBV does not control the actuator velocity but it minimizes the system pressure; and the "Smart System" that uses the CBV to efficiently control the actuator velocity during overrunning load conditions. An experimental validation of the proposed solutions is also provided, taking as reference a truck-mounted hydraulic crane. The results of the proposed solutions are compared to those achieved by the traditional circuit of the reference hydraulic crane which uses standard CBVs. For both cases of smart CBV and smart system, a remarkable power saving, respectively, up to 75% and up to 90% is observed. [ABSTRACT FROM AUTHOR]

This paper proposes a novel hybrid power-split transmission to drive hydraulic implements in construction machinery. The highly efficient power-split hybrid transmission is combined with displacement-controlled (DC) actuators to eliminate throttling losses within the hydraulic system and achieve higher fuel savings. The architecture design, sizing, and power-management are addressed. Simulation results considering a realistic truck-loading cycle on a mini-excavator demonstrate the feasibility of the idea. A systematic comparison between the proposed system and the previously developed series-parallel hybrid is also carried out. The paper compares engine operation and fuel consumption of the previously mentioned hybrid system with the original nonhybrid load-sensing (LS) machine. It is shown that by implementing an efficient engine operation control, the proposed system can achieve up to 60.2% improvement in fuel consumption when compared to the original machine and consume 11.8% less than the previously developed series-parallel hybrid with DC actuation. Other advantages of the proposed solution include a much steadier engine operation, which open to the possibility of designing an engine for optimal consumption and emissions at a single operating point as well as greatly reduce pollutant emissions. A steadier prime mover operation should also benefit fully electric machines, as the battery would not be stressed with heavy transients. [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]

• A numerical model for the analysis of the compensation mechanism of an aerospace fuel delivery pump is presented. • Coupled fluid and structural effects in lubricating gaps are considered in the analysis. • Effect of frictional forces is shown to create a hysteresis effect on the bearing motion. • Experimental measurements are performed to validate the findings of the numerical model. External gear pumps (EGPs) are one of the most common choices in aerospace engines as a fuel delivery pump. These units usually include a pressure compensation system that defines the lubricating gap at the lateral side of the gears. This lubricating interface is a critical design aspect, which strongly affects the reliability as well as the mechanical and volumetric efficiencies of the pump. Major challenges in designing these lubricating gaps in aero engine fuel pumps, include high operating speeds, delivery pressures and low viscosity of the working fluids. Virtual prototyping methods present a fast and efficient design tool and have the potential to improve the EGP's reliability and efficiency. This paper presents a study on the pressure compensation system of a fuel delivery EGP and shows how the presence of frictional forces opposing the motion of the compensating element significantly affect the lubricating performance of the unit. The presence of these frictional forces produces an effect of hysteresis on the axial balance system, so that the lubricating gaps that develop within the pump at a certain operating condition depend on the previous operating state. This effect was captured in an experimental setup purposely developed for this study at Rolls-Royce. Within this work, this behavior was also reproduced numerically, through a coupled fluid structure interaction – elastohydrodynamic (EHD) model that includes the modeling of these frictional forces. After detailing the implementation of the lateral gap model, this paper presents measurements from carefully conducted experiments which correlate with the simulated predictions of the influence of frictional forces on the performance of a reference EGP design under study. [ABSTRACT FROM AUTHOR]

Environmental concerns have pushed toward electrified technologies for off‐road vehicle actuations that can lower greenhouse gas emissions and reduce energy consumption. Replacing a central diesel engine with a dedicated electric machine (EM) as a prime mover for the hydraulic supply offers several opportunities for so‐called ePumps (aka electric‐driven pumps) to maximize energy efficiency and limit the usage of electric materials. This paper discusses the impact of different choices for the ePumps architecture (i.e., fixed vs. variable displacement pump; variable speed vs. fixed speed electrical machine), and on their main design parameters in terms of size and efficiency. Although the procedure followed in the study could be extended to different types of electric and hydraulic units, the paper particularly considers ePumps based on permanent magnet synchronous machines combined with axial piston machines. The importance of properly considering the ePump drive cycle and its cooling requirements is taken into account while addressing energy efficiency, mass, and overall compactness of the solution. The results show that an ePump based on a variable displacement pump, when compared to fixed displacement ePumps, reduces the electrical machine size both in volume and mass up to 40%, when the high‐pressure demand is not combined with high flow rate demand, thus decreasing the cost of the EM. In all drive cycles, the variable speed EM–fixed displacement pump architecture has a higher efficiency, ranging from 1% to 5%, compared to the case of fixed speed EM–variable displacement pump. Finally, the paper compares the advantages and shortcomings of each ePump architecture presented, based on representative drive cycles. [ABSTRACT FROM AUTHOR]

This paper describes a unique design concept that is capable of electronically controlling the flow delivered by an external gear pump (EGP). The principle used for varying the flow relies on the variable timing concept which has been previously demonstrated by the author's research team for EGP's operating at high pressures (HPs) (p > 100 bar). This principle permits to vary the flow within a certain range, without introducing additional sources of power loss. In this paper, the above concept has been applied to formulate a design for a variable delivery EGP for low pressure (LP) applications (p < 30 bar), suitable for direct electric actuation. Specific design principles for the gear and the flow variation mechanisms are introduced to limit the force required by the electric actuation, and for maximizing the flow variation range. Also, the low target pressure allows the variable timing principle to be realized with an asymmetric solution, with only one variable timing element present at one side of the gears. A detailed analysis concerning the relationship between the electrically commanded position of the flow varying element and the theoretical flow delivered by the pump is also presented. This analysis is used to formulate analytical expressions for the instantaneous flow rate and the flow nonuniformity of the pump. The paper details the design principle of the proposed variable flow pump and describes the multi-objective optimization approach used for sizing the gears and flow variation mechanism. The paper also discusses the experimental activity performed on a prototype of the proposed unit, able to achieve a flow variation of 31%. [ABSTRACT FROM AUTHOR]

Highlights • Four objective functions are defined to minimize pump size, flow ripple, and wear. • Constraints are given to guarantee a feasible geometry. • Circular-toothed gerotor geometry was optimized by the NSGA-II genetic algorithm. • An optimized design is found that could be an improvement over existing designs. • Methodology presented here can be applied to novel gear forms. Abstract A multi-objective optimization of circular-toothed gerotor gear geometry by genetic algorithm is presented that minimizes the size, flow ripple, adhesive wear, and subsurface fatigue wear (pitting) of the pump, insofar as the geometry is concerned, subject to the constraints to guarantee a feasible profile. Three pump geometries available to the authors used in automotive applications were compared to the optimization results. A clear Pareto front was established that gives insight into the design space of circular-toothed gerotors. The optimization identified that the industry reference pumps were very near to or on the Pareto front, so this work demonstrates mathematically that some circular-toothed gerotors in industry have reached an optimal solution. Another pump geometry is also identified that could be a better compromise between the objective functions than the reference pumps. The methodology presented here can be readily extended to other profile types and the results can serve as a benchmark for comparison. [ABSTRACT FROM AUTHOR]

External gear pumps are one of the most commonly used types of positive displacement machines in high pressure hydraulic control systems, fuel-injection and fuel transport systems. Despite many merits of the traditional external gear pump design with involute teeth, the significant flow non-uniformity intrinsic of such design is considered to be a detrimental aspect, since it causes undesired noise emissions and mechanical vibrations. A disruptive concept of continuous-contact helical gear pumps (CCHGP) was proposed and successfully commercialized in the recent past. Such concept was proven to have clear advantages in terms of noise emissions. However, a clear interpretation of the displacing action and the transient features of the delivery flow was never addressed in past literature. This paper addresses this gap by first discussing the family of gear profiles suitable for implementing the CCHGP design. Subsequently, an analysis on the kinematic flow ripple is given, showing how such design concept can reduce or even eliminate the kinematic flow pulsations. The paper also presents a numerical approach for modelling the operation of CCHGPs, starting from the modeling of the geometric features necessary for a fluid dynamic analysis based on a lumped parameter approach. For model validation purposes, a commercial CCHGP was tested at the authors’ research center, and the simulation results were compared against the experiments, to show the level of accuracy of the model, as well as it potentials for future design studies. [ABSTRACT FROM AUTHOR]

External Gear Pumps are used in various industries to pump non-Newtonian viscoelastic fluids like plastics, paints, inks, etc. For both design and analysis purposes, it is often a matter of interest to understand the features of the displacing action realized by meshing of the gears and the description of the behavior of the leakages for this kind of pumps. However, very limited work can be found in literature about methodologies suitable to model such phenomena. This article describes the technique of modelling external gear pumps that operate with non-Newtonian fluids. In particular, it explains how the displacing action of the unit can be modelled using a lumped parameter approach which involves dividing fluid domain into several control volumes and internal flow connections. This work is built upon the HYGESim simulation tool, conceived by the authors’ research team in the last decade, which is for the first time extended for the simulation of non-Newtonian fluids. The article also describes several comparisons between simulation results and experimental data obtained from numerous experiments performed for validation of the presented methodology. Finally, operation of external gear pump with fluids having different viscosity characteristics is discussed. [ABSTRACT FROM AUTHOR]

External gear pumps (EGPs) have gained popularity among applications in many fields like fluid power transmissions and systems, automotive, aerospace thanks to their advantage of simplicity, robustness and low cost. Several studies were performed to analyze and innovate the gear profiles of EGPs to achieve better performance, in terms of flow smoothness power to weight ratio. Asymmetric gears represent one of the possible choices. This paper is aimed at developing a methodology of designing asymmetric involute gear, and formulate analytical expression for the instantaneous flowrate and flow non-uniformity given by asymmetric, non-standard involute gear pumps. These analytical expressions are then used within a multi-objective numerical optimization algorithm aimed at minimizing both the flow non-uniformity and the pump size to achieve a specific displacement. The results illustrate the highly constrained nature of the optimization problem, and the relevant impact of certain parameters of the tooth profile. It is shown how gears obtained with the proposed procedure can have significantly higher performance of standard gears, and in particular how the parameters affecting tooth profile asymmetry can further improve the EGP flow irregularity and size. [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]

This article presents a novel mixed-thermoelastohydrodynamic (TEHD) model for the lateral lubricating interfaces which exist between floating lateral bushings and gears in external gear machines (EGMs). The proposed model integrates the influence of surface asperities along with the fluid structure and thermal interaction in the interface, especially in the regions of very low film thicknesses by following a stochastic approach in modelling the mixed lubrication regime. Furthermore, the current work includes validation of the predictions of the mixed-TEHD model against experimentally measured leakages from the lateral gap and compares the performance of this model with a previously developed full film TEHD model for the lateral gaps in EGMs. [ABSTRACT FROM AUTHOR]

• Integrating hydraulic and electric machines leads to greater power density. • Electrification allows novel throttle less actuator control strategies. • Electro-hydraulic drives allow energy recovery. • The hydraulic gear machine optimal rotation speed needs to be increased. This paper presents an innovative design of an integrated electro-hydraulic (EH) flow generation unit able to operate in multiple quadrants. The proposed unit is composed of a hydraulic machine which can operate in either pumping or motoring mode, and an electric machine, which can operate as electric motor or generator. The adopted morphological integration of the two unit fulfills the goals of maximizing compactness, power to weight ratio, energy efficiency and quietness. The design results from a numerical optimization procedure that includes detailed simulation of both the electric machine and the hydraulic machine, using simulation tools previously developed by the authors, but combined for the first time in this work. After describing the optimization procedure, the paper focuses on the design integration aspects of the novel unit. A 9 kW prototype of the integrated unit was also fabricated and tested to verify its performance. Tests results show a measured overall energy efficiency up to 69%, demonstrating the potentials of the proposed concept, despite some limitations present in the first prototypes which could be addressed in future design refinements. [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]

This paper presents an experimental and numerical modal analysis for an external gear pump considering its mounting on a test rig in a laboratory setting. Most of the previous studies on experimental modal analysis (EMA) of hydraulic pumps focused on the modal frequencies to allow model validation. However, the mode shapes of pump bodies have not extensively been discussed. Furthermore, the nature of the pump components assembly and mounting poses some modeling challenges, such as the uncertain material properties of each component, the behavior of the bolted joints, and some critical modeling boundary conditions related to pump mounting. In this regard, the experimentally obtained vibration modes of a reference pump using the least-square complex exponential (LSCE) method are analyzed with an emphasis on the characteristics of the mode shapes. Then, simple modeling strategies are proposed and validated by performing the analysis from the component level to the full assembly. As a result, the mode shapes are categorized depending on the type of motions that the modes exhibit. It is observed that the pump casing does not show any substantial deformation but is close to the rigid body motion. Moreover, without considerably increasing model complexities, the proposed numerical approach provides reasonable accuracy with average errors in modal frequencies of 6%, as well as good agreement in terms of mode shapes. The vibration reduction strategy is briefly discussed based on the measured mode shapes, and the proposed modeling approaches can be useful to study external gear pumps with minimal model complexities yet allowing reasonable result accuracy. [ABSTRACT FROM AUTHOR]

Highlights: [•] A model to evaluate fluid properties considering the dynamic features of cavitation is presented. [•] The new model for the evaluation of fluid properties is suitable for lumped parameters models. [•] The paper studies the operation of gear pumps under cavitating conditions. [•] Experimental activity on a gear pump was performed to validate the modelling approach. [Copyright &y& Elsevier]

Highlights: [•] A graphical method to study the operation of counterbalance valves is presented. [•] The method is suitable to study the impact of valve settings on energy consumption. [•] Energetic considerations on a hydraulic crane were performed through numerical simulations. [•] Test were performed to validate the model on steady-state and transient conditions. [•] Energy consumption reduction potentials in current applications were discussed. [ABSTRACT FROM AUTHOR]

Abstract: In this paper an innovative procedure for determining the optimal design of an external spur gear pump for a particular emission reduction application in automobiles has been proposed. The pump forms the main part of a mechatronic system that controls the flow rate of a mixture of urea in water to catalytically reduce emissions in diesel engines. The proposed research proves to be an advance in gear machine design by using a multi-objective based genetic algorithm, to determine the optimal design of the gears and the casing by maximizing the volumetric efficiency, minimizing pressure overshoots, localized cavitation and noise emissions. The research uses HYGESim (HYdraulic GEar machines Simulator) simulation tool, which is being developed by the authors’ research group, for calculating the important performance features of the machine. The best designs for the machine based on enhancement in performance are presented. Results in terms of simulations and tests which validate the effectiveness of the proposed novel design methodology are also presented. [Copyright &y& Elsevier]

• A fully coupled multi-domain multi-physics dynamic system is presented. • Three components of the loadings are explained and analyzed in detail. • The patterns of 3D transient loadings and dynamics are discussed with simulation results. • A design routine for the axial balancing mechanism of helical gear pumps is provided. • The pattern of wear seen from experiments can be replicated by the wear model. This paper presents a multi-domain dynamic simulation model for continuous-contact helical gear pumps, which is an unconventional hydraulic pump design that is capable of canceling its kinematic flowrate variation. In this model, the fluid dynamics (in its lumped-element representation) are fully coupled in a closed feedback loop with other physical domains, including critical tribological interfaces, 3D dynamic loadings on the solid parts, dynamics, and micro-vibrations of the rotors. The model is compared to the analytical derivation and experimental measurements to prove its validity. The model can be used to provide predictive simulations for existing designs, or as a tool to optimize the design to provide better hydrostatic balancing for future iterations of hydraulic pump designs. [ABSTRACT FROM AUTHOR]

We investigate the stability of a fluid film with power-law rheology flowing down a porous nonplanar incline with periodic undulations. A model is implemented which accounts for filtration flow through the substrate. A reduction in dimensionality in the model is achieved by exploiting the assumed thinness of the liquid film relative to the wavelength of the bottom undulations. A steady flow is obtained and its linear stability determined through the application of Floquet–Bloch theory. A nonlinear stability analysis is also carried out by calculating the evolution of the perturbed steady flow by means of numerical simulations. • An investigation of instability of film flow down an uneven porous incline. • A power-law rheological model is implemented. • Film flow is coupled with the filtration flow through the porous medium. • Combined effects of surface tension, rheology and properties of substrate determined. [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]

Abstract: The properties of seven ferruginous paleosols, formed in alluvial continental deposits of Upper Cretaceous-Paleocene age in central-southern Sardinia (Italy), were examined to understand their genesis. Particular attention has been addressed to their paleoenvironmental and paleogeographic significance, also in comparison with similar paleosols in southern France, and to their potential to represent good pedostratigraphic markers for a larger area. The paleosols are characterized by petroplinthic, pisoplinthic, plinthic or pisolithic horizons. Their genesis started under a warm and humid tropical climate, with distinct wet and dry seasons, of the Latest Maastrichtian-Lower Paleocene and continued, under increasingly dry conditions, during the Middle to Upper Paleocene. The major differences that occur among the paleosols can be related to differences in geomorphic position, parent material characteristics and drainage conditions. The pisolithic paleosols of central-southern Sardinia show a structure and composition comparable to those of the coeval ones in southern France, which were formed under similar climatic conditions. On the basis of the constant stratigraphic position, the large geographic extent and the supposed former lateral continuity, the studied ferruginous paleosols can be considered to be a good pedostratigraphic marker in central-southern Sardinia and in southern France and are informally named as the “Monte Maraconis geosol”. This allows extensive chronostratigraphic correlations as well as regional-scale morphostratigraphic correlations and represents, with its typical pedofacies, a pedostratigraphic unit worthy of consideration in future regional geological mapping. [Copyright &y& Elsevier]

The present work describes the modeling of a proportional relief valve actuated by an electromagnet. Two models were developed and compared each other: a detailed nonlinear model and its linearized version. The modeling approach presented has a general nature and can be applied to various types of electrohydraulic proportional valves (EHPV). The comparison between nonlinear and linear model results shows the limits of the linear approximation to study the real component. Substantially, the nonlinear model is composed by three submodels: the fluid-dynamic model (for the evaluation of the main flow features), the mechanical model (which solves the mobile body motion), and the electromagnetic model (which evaluates the magnetic forces and the electric transient). All submodels are based on a lumped parameter (LP) approach and they implement a specific set of nonlinear equations. However, to carefully model the main electromagnetic phenomena that characterize the proportional electromagnet behavior (including: magnetic losses, fringing effects, and magnetic saturation), a finite element analysis (FEA) 3D model was developed by the authors. The LP electromagnetic model is based on a particular use of the FEA 3D model steady state results. A series of transient simulations were performed through the FEA 3D model in order to quantify the effect of the eddy currents and to determine a second order transfer function used in the linear model to describe the electromagnet dynamics. The remaining parts of the linear model are obtained by linearizing the nonlinear model equations. The FEA 3D model was experimentally validated in steady-state conditions, while the results of the overall model of the valve were verified in both steady-state and dynamic conditions. [ABSTRACT FROM AUTHOR]

Abstract: The modelling of positive displacement machines has to deal with the complexity of solving the flow through the unit in presence of simultaneous macro and micro-motions of the moving parts. In this paper, the main phenomena characterizing the operation of the spur external gear units are successfully analyzed by means of a numerical model developed by the authors. The model, here referred as HYdraulic GEar machines Simulator (HYGESim), consists of different modules: a fluid dynamic model, a model for the evaluation of the movements of the gears’ axes of rotation and a geometrical model. When performing a HYGESim simulation, these models are executed in a co-operative simulation. Starting directly from the CAD drawing of the unit as input, the simulation tool permits to describe the main features of the flow though the machine and to evaluate the possible wear of the casing wear accounting for a detailed description of the geometry of the internal components (i.e. teeth’s profile, design of lateral bushes). The paper describes the modelling approach and the main potentials of the simulation tool, pointing out how it can be utilized for design purposes. As a matter of fact, HYGESim permits to analyse the effects of the main design parameters on important aspects like efficiency, internal pressure peaks, local cavitation and fluctuations of flow at unit’s ports (associated with fluid borne noise). The presented tool also allows the evaluation of the radial movements of the gears’ axes of rotation resulting from the forces exerted on both gears, thus permitting to study the balancing feature related to a certain design. The paper also presents several comparisons between simulation results and experimental data coming from an experimental activity specifically performed for validation of the presented tool. [Copyright &y& Elsevier]

Abstract: This paper describes a numerical procedure for the prediction of the homogenizing performance of high pressure homogenizing valves used in diary plants. The method is based on a strict interaction between a complex CFD code and a simple homogenizing simulation code developed by the authors. This latter implements a mathematical model for the evaluation of droplets break-up, that needs an accurate evaluation of few significant fluid dynamic parameters in the whole fluid dynamic domain inside the valve. Due to the relevant pressure gradients within the flow and to the possibility of cavitation, particular attention has been paid in defining the fluid model, the mesh and the parameters required for CFD simulations. Notwithstanding the quite simple model of the homogenizing process, comparatively with the complexity of phenomena involved, the first results obtained are in general agreement with the experimental data available. These results point out the potential of the procedure proposed as a starting point for further implementation of more complex effects. [Copyright &y& Elsevier]

Abstract: This paper presents a numerical model for the simulation of a swash-plate axial piston pump, focusing on the characterization of fluid properties. As it is well known, the reduction of flow oscillations (which generates pressure ripples and produces vibration and noise in the entire circuit) and the avoidance of cavitation are the major problems in the design of these pumps. Developing a simulation code can be very useful for component optimisation in order to predict and reduce the undesired phenomena. The paper first gives a quick overview on a previously developed pump model; afterwards four different models of the fluid are presented: they take into account cavitation in different ways. Their aim at characterizing as well as possible the unsteady and erratic cavitation features in a simplified manner, in order to apply the models to the simulation of hydraulic components. In the second part of the paper an application is shown of these models to an axial piston pump: a few results are presented and compared with available test data. The effects of the fluid models on the predicted pump performance are shown and commented. [Copyright &y& Elsevier]

The paper describes the effects of forced harmonic oscillations of fixed frequency and amplitudes in the range Λ = Um/Ub =1-11 on the characteristics of a turbulent pipe flow with a bulk Reynolds number of 5900. The resulting Stokes layer δ is a fraction of the pipe radius (Χ =R/δ=53) so that the vorticity associated to the oscillating motion is generated in a small near wall region. The analysis is carried out processing a set of statistically independent samples obtained from wall-resolved large eddy simulations (LES); time and space averaged global quantities, extracted for the sake of comparison with recent experimental data, confirm the presence of a non-negligible drag reduction phenomenon. Phase averaged profiles of the Reynolds stress tensor components provide valuable material for the comprehension of the effects of the time varying mean shear upon the near wall turbulent flow structures. The large scales of motion are directly computed through numerical integration of the space filtered three-dimensional Navier-Stokes equations with a spectrally accurate code; the subgrid scale terms are parametrized with a dynamic procedure. [ABSTRACT FROM AUTHOR]

In this paper we present a preconditioned multi-domain algorithm applied to the elliptic kernels arising from the spectral collocation of the incompressible Navier–Stokes equations in three space dimensions with one homogeneous direction. The technique, based on the iterative solution of the Schur complement matrix, allows for efficient numerical solution of the operators in complex geometries consisting of a collection of non-overlapping rectangular subdomains. The method is shown to be nearly optimal in terms of condition number behavior in a double path of refinement strategy, i.e. whenever both the number of Legendre modes and the number of subdomains are significantly increased. It is thus well suited for engineering applications in the fields of direct numerical simulation and large eddy simulation of turbulence. [Copyright &y& Elsevier]

• The paper presents a methodology for modeling hydro-mechanical losses in external gear machines. • Friction at the gears' tooth tips, lateral surfaces, shafts and meshing interfaces is considered. • The gear meshing friction is found to be the major contributor to the torque losses. • The simulated hydro-mechanical efficiency trends match the experimental data. During the operation of external gear machines (EGMs), the friction between the internal components results in the loss of hydro-mechanical (or torque) performance of these units. However, current EGM simulation models either do not consider these losses or have significant limitations in their approach. This paper presents a novel methodology for modeling the hydro-mechanical losses in EGMs. The sources of torque losses considered are the friction at the gears' tooth tips, lateral surfaces, shafts, and meshing interfaces. The friction models are developed for each of these sources considering the effects of micromotion of the gears and bushings. Further, the effects of elastohydrodynamic lubrication (EHL) are considered in the modeling of meshing friction. The friction models are integrated in a lumped parameter simulation tool, and the operation of a commercial gear pump is simulated. From the simulation results, the meshing friction is determined to be the dominant source of torque losses. Further, the hydro-mechanical efficiencies predicted by the model are found to match those observed in the experiments indicating the validity of the model developed in this work. [ABSTRACT FROM AUTHOR]

• A novel model for curve-constricted leakage flows in hydraulic gear pumps is presented. • The flow model is applicable over a wide range of flow regimes including localized cavitation. • The model is developed in dimensionless form based on sets of CFD simulations. • Model validation is achieved through experiments conducted on a custom test apparatus. The internal leakage flows in external gear and gerotor pumps are often represented by flow through curved constrictions. The nature of this flow can vary from laminar to turbulent and the flow can experience localized cavitation too. In the current literature, there is a scarcity of techniques for accurately modelling such curve-constricted flows which limits the accuracy of the current simulation tools for gear pumps. This paper presents a novel flow model for curve-constricted geometries that is applicable over a wide range of flow regimes including localized cavitation. Using a dimensionless form, the proposed model characterizes the constriction flow velocity as the function of the constriction shape, the pressure difference, and a properly defined cavitation indicator. The functional relationships between these dimensionless parameters are developed based on CFD simulations. The flow model is validated by the means of several experiments conducted on a custom test apparatus. The model presented in this paper can be incorporated in the lumped parameter simulation tools widely used for modelling gear pumps, improving their accuracy in predicting the internal leakages. Consequently, this model will also aid the development of novel energy efficient gear pump designs, where such leakages are kept to a minimum. [ABSTRACT FROM AUTHOR]

Axial piston machines of swash plate design rely on three main lubricating interfaces to support the load on their slippers, pistons, and cylinder block. The respective loads on these parts are carried by the fluid pressure in these interfaces— pressure from hydrostatic sources (from the inlet and outlet ports of the pump), as well as hydrodynamic pressure, generated by the relative motion of the surfaces that border a fluid film. The present work investigates how the hydrostatic and hydrodynamic components of fluid pressure compare in terms of their importance to load support in the three interfaces. A methodology is proposed to calculate these two fluid pressure components, and their contributions to load support, for each interface in a given unit, at a given operating condition. Separating the interface's fluid pressure fields, and the forces they generate, into their hydrostatic and hydrodynamic components offers a novel view into the load-support mechanism of the interfaces, and how they compare to each other. Moreover, the proposed methodology can easily be adapted to bent axis machines. Through a case study involving a 75 cc commercial unit, the proposed methodology shows that the hydrodynamic contribution to load support in two of the interfaces of axial piston machines of swash plate design can significantly exceed the estimates typically provided in literature, and that in the third interface, the force from hydrostatic fluid pressure can be so large that less than 60% of it is required to balance the load, and over 40% of it is excess— i.e. it becomes the load force. • Study of importance of hydrodynamic pressure in axial piston pump lubricating gaps. • Hydrostatic pressure force on piston can exceed load. • Hydrodynamic pressure force required to counter the excess can exceed original load. [ABSTRACT FROM AUTHOR]

This paper presents a solution for reducing energy loss in the hydraulic control system of agricultural tractors and their implements. The solution is referred to as a multi-pressure rail (MPR) and provides power to the hydraulic functions following a pressure control logic, as opposed to the traditional flow control logic typical of hydraulic systems used in off-road vehicles. The proposed hydraulic control system allows for elimination of redundant flow control valves in the state-of-the-art system, which cause excessive throttling losses leading to poor overall energy efficiency. Related work on MPR technology targets construction vehicles, where the MPR solution can allow energy recovery during overrunning loads and better engine management. This paper alternatively addresses the case of agricultural applications where functions mostly operate under resistive load conditions with slow dynamics, which offers an opportunity to target throttle losses. For this purpose, the paper introduces a variable pressure control strategy to handle the instantaneous pressure at each rail. To develop both the controller and the hydraulic system architecture, a stationary test rig is conceived and used to validate a numerical simulation model of the MPR system and its control strategy. Particular focus is given to the dynamic behavior of the system during the switches of a function between different pressure rails, which needs to ensure reduced oscillations of the flow provided to each hydraulic function. Once validated, the simulation model is used to predict the energy savings of the MPR solution in an actual application: a 435 hp hydraulic tractor powering a 16-row planter, for which operating features during typical drive cycles were available to the authors. The results show up to 59% total power reduction at the pump shaft, corresponding to 89.8% system efficiency gain. [ABSTRACT FROM AUTHOR]

• 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]

• The proposed simulation model evaluates torque efficiency of hydraulic orbit motors. • The model considers deformation effects and frictional losses of the hydraulic motor. • Both the torque pulsation and the mechanical efficiency are experimentally validated. • The simulated torque agrees with the measurements. • The micro-motion of rotor, subjective to forces, is evaluated numerically. This article presents a method for evaluating the torque output of orbit type displacement machines. Orbit machines are commonly used as hydraulic motors, for applications involving low speed and high torque output. The evaluation of the actual shaft torque as well as the hydro-mechanical efficiency in positive displacement machines is a topic that still presents challenges related to the evaluation of the torque losses associated with the functioning of the unit. This paper proposes a method of evaluating the torque efficiency starting from the evaluation of the instantaneous pressurization of each displacement chamber through a lumped parameter approach. From the instantaneous pressure in each chamber of the orbit motor, the contact forces normal to the rotor profiles are evaluated using a contact mechanics formulation accounting for the energy dissipation. The proposed algorithm computes the friction losses at the contact points to evaluate the net torque output of the orbit motor. Besides accounting for the frictional losses, the main elements of novelty of this approach also include the evaluation of the component deformation, instead of making rigid body assumptions. Experiments are performed on a set of reference orbit motor units to evaluate the torque output at different operating conditions. A good agreement between the simulated output torque and the one measured from experiments was observed, in terms of both instantaneous and mean values. The corresponding comparison of mechanical efficiency map is also presented. This shows the potential of the proposed method, which can potentially be extended to other types of gear machines, to evaluate the net shaft torque. [ABSTRACT FROM AUTHOR]

This paper presents the experimental characterization of the vibroacoustic fields and the evaluation of noise performances of hydraulic pumps. Research on hydraulic pump noise has traditionally focused on the fluid-borne noise sources, and very often the analyses of vibration and noise have been performed focusing on a few local points. This trend results in the lack of investigation on the overall behaviors of vibroacoustic fields of hydraulic pumps, and it has been one of the obstacles to understand the complete mechanisms of noise generation. Moreover, despite the existence of the ISO standards for the determination of noise levels, diverse metrics have been used for the evaluation of noise performances of the pumps, but the adequacy of these metrics has not been carefully examined. In this respect, this paper aims at introducing a way to characterize and interpret the measured vibroacoustic field and providing proper methods which are also capable of applying the ISO standards for the fair assessment of pump noise performances. For the characterization of the vibroacoustic field, operational deflection shapes (ODS) and corresponding radiated sound fields are visualized at harmonics of the pumping frequency by using a spectral analysis. Observations are made regarding the motions of the pump and its mounting plate and the resultant radiated noise, depending on the frequency, as well as their correlation. A numerical analysis using the Rayleigh integral equation is also performed to further investigate the contribution of the mounting plate motion on the noise radiation. For the evaluation of noise performance, two different units are tested at multiple operating conditions, and comparisons are made based on their measured sound power levels (SWLs) and sound pressure levels (SPLs). The results emphasize the importance of SWL measurement for the fair noise performance evaluation, and the two methods are proposed as practices to determine the minimum number of measurement points for practicability and to have reliable sound power determination for hydraulic pumps. [ABSTRACT FROM AUTHOR]

A novel virtual prototyping algorithm has been developed to design one of the most critical lubricating interfaces in axial piston machines of the swash plate type—the piston–cylinder interface—for operation with water as the working fluid. Due to its low viscosity, the use of water as a lubricant can cause solid friction and wear in these machines at challenging operating conditions. The prototyping algorithm compensates for this by tailoring the shape of the bore surface that guides the motion of each piston in this type of positive displacement machine to conform with the piston surface, taking into account both the piston's tilt and its deformation. Shaping these surfaces in this manner can render the interface more conducive to generating hydrodynamic pressure buildup that raises its load-carrying capacity. The present work first outlines the structure of the proposed algorithm, then presents a case study in which it is employed to design a bore surface shape for use with two prototypes, one virtual and one physical—both modified versions of a 444 cc commercial axial piston pump. Experimental testing of the physical prototype shows it to achieve a significantly higher maximum total efficiency than the stock unit. [ABSTRACT FROM AUTHOR]

A novel virtual prototyping algorithm has been developed to design one of the most critical lubricating interfaces in axial piston machines of the swash plate type—the piston–cylinder interface—for operation with water as the working fluid. Due to its low viscosity, the use of water as a lubricant can cause solid friction and wear in these machines at challenging operating conditions. The prototyping algorithm compensates for this by tailoring the shape of the bore surface that guides the motion of each piston in this type of positive displacement machine to conform with the piston surface, taking into account both the piston's tilt and its deformation. Shaping these surfaces in this manner can render the interface more conducive to generating hydrodynamic pressure buildup that raises its load-carrying capacity. The present work first outlines the structure of the proposed algorithm, then presents a case study in which it is employed to design a bore surface shape for use with two prototypes, one virtual and one physical—both modified versions of a 444 cc commercial axial piston pump. Experimental testing of the physical prototype shows it to achieve a significantly higher maximum total efficiency than the stock unit. [ABSTRACT FROM AUTHOR]

This article presents a novel passive fluid borne noise source reduction strategy, based on tandem axial-piston unit indexing with the usage of symmetric lines. The strategy consists of setting the phase between the two synchronous units to accomplish destructive interference in targeted unit harmonics. A strategy capable of achieving destructive interference in all odd harmonics is investigated first analytically and then confirmed by a simulation study. Experiments on the proposed strategy confirmed its effectiveness at the first and third pump fundamental harmonics, and pressure ripple reduction was accomplished. The fluid borne noise source reduction in the first and third harmonic is verified to be propagated to pipe vibration and sound power. Regarding the first harmonic, pressure ripple was reduced by up to 18 dB; while for third harmonic, pressure ripple was reduced by up to 11 dB. In the experiment, however, noise cancellation is not achieved for the higher odd harmonics, as is instead found in the simulation. Conversely, transfer functions form pressure ripple to pipe wall acceleration are obtained experimentally, and a critical vibration band from 2000 Hz to 3000 Hz is identified as being crucial for effective overall sound power reduction. [ABSTRACT FROM AUTHOR]

• A strongly coupled model of the displacement chambers and lubricating interfaces of external gear machines is presented. • The impedance tensor of the Reynolds equation was derived to support asynchronous time stepping of the coupled simulation. • The model considers the transient deformation and inertia of all bodies, aeration and cavitation, and mixed-lubrication. • Experimental testing of a reference machine was performed for model validation. • The journal bearings contribute an average of 20% of the overall opposition to tilting of the lateral bushing compensation. This paper presents a strongly coupled simulation model, Multics HYGESim, for the displacing action of external gear machines coupled with a detailed simulation of the main lubricating interfaces (i.e. the gaps at the gear tooth tips, at the gear lateral side, and at the journal bearings). In order to allow this strong coupling, the solution of the main displacing action realized by the tooth space volumes is tied with the solution of the lubricating gaps through asynchronous time stepping. This approach is made possible by the introduction of the numerical impedance of the floating films, and by considering the dynamic fluid-structure interaction and boundary friction of the bodies with both the film and displacement chamber pressures. The resulting floating body dynamics are solved to inform the solution of both the displacing action and the lubricating films of the machine. This model is then used to simulate a reference reversible pressure-compensated external gear machine. An experimental activity is performed for preliminary validation of the model. Notable results for this reference machine are then discussed to demonstrate model potentials. [ABSTRACT FROM AUTHOR]

In this paper, External Gear Machine (EGM) torque losses arising from friction at lubricating interfaces are modeled by considering mixed lubrication conditions. A novel contribution of this paper is to consider mixed elastohydrodynamic lubrication contact conditions along with the effect of gear flank surface roughness to determine the meshing losses, which are also the major contributors towards the EGM torque loss. These hydromechanical loss models are integrated in a multibody, multi-physics simulation tool Multics-HYGESim developed at the authors' research center. Experimental activity is performed on two EGM units using different surface finish for gears. Simulated hydromechanical efficiencies match the experimental trends with average deviation of 2.5%. Most importantly, the results capture effects of different gear flank roughness on the torque efficiency. An average increase of 0.9% in the efficiency value is predicted by the simulation model for the EGM with lower teeth roughness, as compared to 1.1% rise obtained via experiments. The proposed torque loss evaluation methodology shows high potential in assisting designers and manufacturers of EGMs to choose the suitable surface finishing for achieving desired hydromechanical performance. • Torque efficiency of external gear machines has been determined via simulation. • Mixed Elasto hydrodynamic lubrication model is used to evaluate meshing frictional loss. • Experimental tests show rise in torque efficiency for lower gear surface roughness. • Computational analysis of lubricating interfaces predicts leakage and friction loss. • Proposed model exhibits potential for virtual prototyping of new gear pump designs. [ABSTRACT FROM AUTHOR]

The flow of energy within external gear machines (EGMs) leads to the variation of fluid temperature in the EGMs, which affects their performance. However, the common approaches for the simulation of EGMs assume isothermal conditions. This isothermal assumption negatively impacts their modelling accuracy in terms of the internal flows which are dependent on the fluid temperature (via fluid properties). This paper presents a lumped parameter based thermal model of EGMs where the fluid temperature in the EGM is evaluated considering the effects of compression/expansion, internal flows, and power losses. Further, numerical techniques are developed to model each of these three aspects. The thermal model is validated via the outlet temperature and volumetric efficiency measurements obtained from experiments conducted on six units of an EGM taken as a reference with different internal clearances. The results from the model show that the fluid temperature increases as it is carried from the inlet side to the outlet side during the pumping operation. However, the fluid at the ends of the shafts has the highest temperature. By comparing the isothermal simulation results with the proposed thermal model, the results also point out how the isothermal assumption becomes inaccurate, particularly in conditions of low volumetric efficiency. [ABSTRACT FROM AUTHOR]