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 highspeed, 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.

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.

This work presents a model-based study of crescent-type internal gear pump total efficiency, the measure between the output and input energy of the machine. The proposed numerical approach couples a lumped parameter simulation of the fluid pressure within the inter-teeth volumes, a CFD simulation of the lubricating interfaces, and a simulation of the micromotions of the pressure-compensating components. This paper’s simulation tool developed in C++ constitutes the software Multics’ simulation core for internal gear pumps. The total efficiency predictions from the model show consistency with the measurements performed on a reference commercial unit. Minor discrepancies can be explained with an underprediction of the contact friction within the lateral films. The study also provides a breakdown of the sources of energy loss within the reference internal gear pump, from where the lateral lubricating films exhibit the most power losses. The ring gear bearing film also presents substantial mechanical losses, and the volumetric losses become increasingly important with a higher temperature.

Lumped parameter approaches for the description of the flow displaced by hydrostatic pumps and motors have proven to be very effective for both analysis and design purposes. However, while these methods are relatively easy to implement for most of the existing design architectures for positive displacement machines, the case of a crescent-type internal gear machine (CIGM) presents clear challenges as it pertains to the definition of lumped control volumes within the machine. This paper proposes an original scheme for defining lumped control volumes within a CIGM with involute teeth profiles, which is suitable for developing fluid dynamic simulation models for CIGMs. The proposed method strictly obeys fundamental rules on continuous volumes required by lumped parameters models. This is achieved by defining not only multiple control volumes for each displacement chamber but also two variable porting volumes to respect the volume conservation. To prove the validity of the proposed numerical method, the paper provides comparisons between the displaced volume found by the proposed lumped parameter approach and the theoretical kinematic flow ripple provided by an analytical formula available from literature. The results show how the method can be used as a design tool for CIGMs, and particularly to further develop lumped parameter simulation models for detailed fluid dynamic analysis of CIGMs.