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• 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]

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 (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]

• 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]

• 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]

• 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]

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]

• A design parameterization of a helical/spur external gear machine was developed. • An optimization procedure was developed for design of helical and spur gear pumps. • Helical gears have more potential for better meshing stress ripple than spur. • Helical gears also have more potential for compactness and efficiency. • Spur gears offer more potential for flow ripple reduction than helical. This paper addresses the problem of determining the relative performance of spur and helical external gear pumps (EGPs) for fluid power applications. Helical EGPs are commonly considered as quieter units than spur ones; however, there is no specific study reported in literature that proves such claim. Similarly, it is hard to find data indicating which design is better in terms of compactness or energy performance. To tackle this problem, a procedure is developed for virtual design optimization of both helical and spur gear EGPs. This includes addressing the two fundamental challenges of the work, parameterizing a generic EGP design and quantifying its performance. By applying this procedure, a genetic algorithm can continue improving from generation to generation, until the pareto optimal set of designs is identified for both helical and spur units. In the comparison of these, the differences between the two configurations will be identified and the fundamental question of this work can be answered; are helical gears 'better' than spur gears? [ABSTRACT FROM AUTHOR]