A Study on Design Methodologies for Compact Electric Machines Used in Electrified Mobile Hydraulics

Electric Machines (EMs) have gained increasing importance in the mobile hydraulic industry as prime movers for hydraulic actuation systems. There-fore, their design and sizing are important aspects for any system layout architecture. The on-road vehicle industry has exploited EM versatility by proposing different sizes for various applications. However, off-road vehicles cannot borrow designs from on-road applications directly due to their unique challenges pertaining to drive cycle dynamics and limited space availability. Furthermore, considerations of the thermal limitations of EM and their cooling must also be studied to devise an effective methodology for designing prime movers suitable for mobile hydraulic applications. This paper proposes EM operational sizing strategies based on corner point operation, flux weakening and transient operation that can downsize EMs by carefully selecting sizing points from the operating domain. These strategies can leverage the operational capabilities of EMs and involve trade-offs in terms of EM compactness and efficiency. Therefore, based on a specific requirement, a given strategy can have certain benefits explored in this paper. The paper also examines two other downsizing methods based on switching the ePump architecture to variable displacement pump operation and improving the cooling performance. The paper considers a 5-tonmini excavator's arm actuator as a reference application. The resulting EMs are compared in terms of size and efficiency to study the effectiveness of each operational sizing strategy. This paper uses a well-established genetic algorithm-based multi-objective algorithm to design a Permanent Magnet Synchronous Machine (PMSM) for each sizing strategy. The effect of cooling technology is considered in terms of limiting winding current density for the EMs, and the impact of cooling technology on the size and efficiency of the EM is also demonstrated. Finally, the effectiveness of the proposed operational sizing strategies in downsizing EMs is combined with, and compared to other methods like variable displacement operation and aggressive cooling to identify the best ways to obtain the most compact EMs for any hydraulic application.