Direct Driven Hydraulics: What can possibly go wrong? -A thermal analysis

This paper focuses on a thermal analysis of Direct Driven Hydraulics (DDH). DDH combines the benefits of electric and hydraulic technologies in a compact package with high power density, superior performance and increased controllability. It enables a reduction of hydraulic losses therefore achieves better fuel efficiency. The main advantages of the presented architecture compared to a conventional valve-controlled system are the reduced hydraulic tubing and the amount of potential leakage points. DDH however represents a challenge for the prediction of the thermal behavior and its management as the temperature is a determining parameter of performance, lifespan, and safety of the system. Therefore, the electro-hydraulic model of a DDH involving a variable motor speed, two fixed-displacement internal gear pump/motors was developed at a system level for thermal analysis. In addition, losses dependent on temperature were validated by measurements under various operating conditions set by a cold chamber to 20, 10, and -5 °C. A model investigation predict heat dissipation from the electrical machine to the rest of the system. The electric machine heat dissipation plays an important role in the system temperature balance while the DDH is operated in extreme continuous operating condition. Furthermore, expected challenges for the future development of DDH concept are discussed.