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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]

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: 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 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]

• 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, a novel approach for the simulation of cavitation and aeration in hydraulic systems using the lumped parameter method is presented. The presented approach called the Hybrid Rayleigh–Plesset Equation model is derived from the Rayleigh–Plesset Equation representative of bubble dynamics and overcomes several shortcomings present in existing lumped parameter based cavitation modeling approaches. Models based on static approximations do not consider the non-equilibrium effects of phase change on the system and incorrectly predict the system dynamics. On the other hand, the existing dynamic cavitation modeling strategies account for the non-equilibrium effects of phase change but express the evolution of phases through approximations of the Rayleigh–Plesset Equation (such as exclusion of nonlinear interactions in bubble dynamics), which often lead to physically unrealistic time-scales of bubble growth or dissolution. This paper presents a dynamic model for cavitation which is capable of predicting cavitation in hydraulic systems while preserving the nonlinear dynamics arising from the Rayleigh–Plesset Equation. The derived model determines the evolution of phases in terms of physically realizable parameters such as the bubble radius and the nuclei density, which can be estimated or determined experimentally. The paper demonstrates the effectiveness of the derived modeling approach with the help of numerical simulations of an External Gear Machine. Results from the simulations employing the proposed model are compared with an existing dynamic cavitation modeling approach and validated with experimental results over a range of dynamic parameters. [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]

In the context of improving energy efficiency and fuel consumption of mobile hydraulic equipment, it is important to analyze all the sources of power loss occurring within the hydraulic systems. While plenty of analyses have been performed on the working implements and the main transmission systems, very little attention has been paid to low-pressure (LP) systems until recently. LP systems are required on closed-circuit hydraulic systems to replenish losses, provide cooling flow, and maintain a pilot pressure necessary to operate hydraulic control valves and variable displacement units. It is shown that these circuits, which are often thought to have minimal impact on power consumption, actually cause significant, continuous power loss. A new method of power savings in these circuits is investigated through management of charge pump flow by application of an accumulator-sense pump-unloading (ASPU) valve. This work further proposes the combination of a split LP architecture with an ASPU valve. Three systems are simulated using Simcenter Amesim® and MATLAB/Simulink®. Using realistic duty cycles and unit loss models on a circuit for mobile off-road hydraulic equipment, it is shown that a standard LP system can consume about 5 kW of power. Power savings of up to 65% over a standard LP system are demonstrated by the proposed architecture. [ABSTRACT FROM AUTHOR]