<p dir="ltr">In recent years increasingly stringent regulations regarding the pollution emissions and greenhouse gasses (GHG) of off-highway vehicles have emerged. However, recent studies underscores that off-highway vehicles have an average efficiency of 30%. In response, researchers are exploring the possibility of electrifying these vehicles with electric machines (EMs) potentially undertaking one, multiple, or all the vehicular functions previously reliant on internal combustion engines (ICEs).</p><p dir="ltr">Contemporary off-highway vehicle technology revolves around hydraulic systems tailored for diesel engines, tuned to specific torque characteristics and operating at a single speed. While replacing the prime mover with electric machines, the proper hydraulic supply capable of matching the same torque speed characteristics must be found. Furthermore, it must be determined whether an integration capable of reducing the mass, cost, and volume can be implemented, and if energy recuperation is possible. </p><p dir="ltr">In essence, achieving the desired transformation in off-highway vehicle technology necessitates a comprehensive reevaluation of both hydraulic systems and power sources, with electrification emerging as a promising strategy for harmonizing efficiency, emission standards, and performance expectations. </p><p><br></p><p dir="ltr">This work proposes guidelines to systematically design EMs and positive displacement hydraulic gear machines (HMs), along with their integration in an electro-hydraulic unit (EHU). To do so, three different variants of EHU are produced. The first variant features an external gear machine (EGM) integrated in a permanent magnet synchronous electric machine (PMSEM). The second and third variants integrate an internal gear machine (IGM) and a PMSEM, wherein the final variant introduces features endowing its operation at high rotational velocities.</p><p dir="ltr">The EM and HM constituting all variants of EHU are designed using a genetic algorithm-based optimization framework. This optimization framework encapsulates dedicated models for the EM and the HM that allow the calculation of the EHU performance. The first optimization objectives are the minimization of power consumption over the duty cycle of the selected reference machine, the minimization of the pressure and flow ripple, and maximization of the power density of the EHU. The optimization of the second and third variants instead only aims to maximize the total efficiency and power density of the EHU. </p><p dir="ltr">After having determined the parameters of the EHU through the optimization procedure the designs are refined with thorough simulations focusing on the fluid-dynamic features and the design of the axial balance system of the HMs. </p><p dir="ltr">The three variants present an increasing level of HM and EM integration and component reduction. While in the first variant HM and EM have a dedicated housing, and the HM is only positioned in the inert region of the EM, in the latest variants the HM and the EM also share the same casing. The first variant of EHU is air cooled by a radial fan system attached to the EM rotor and openings machined in the casing. The second variant takes advantage of the extreme integration and the differential pressure generated across the HM to liquid cooling the EM. The third variant necessitates the use of an external system to cool the EM. </p><p dir="ltr">To prove the effectiveness of the design process the first two EHU variants are prototyped and tested. The first EHU variant is tested both in a standalone configuration and on the reference machine showing total efficiency values up to 69%, proving its functionality and proving the capability of recuperating energy. The tests conducted on the second variant EHU show a volumetric efficiency that ranges between 81% and above 96% for a pinion rotation velocity of 6000 rpm proving the value of the presented design process. Despite the good quality of the volumetric efficiency values, this EHU variant present morphological limitations that negatively impact its mechanical efficiency. Finally, the third EHU concept is presented not only to remedy the morphological limitations of the second variant but also to address the challenges raised by high rotational velocity operation. </p>