Φ Abstract – This paper investigates the effectiveness of direct oil cooling of a PMSM by modeling flows of coolant inside the machine using Computational Fluid Dynamics (CFD) software. Conjugated fluid-solid heat transfer modeling with anisotropic conductivity coefficients in solids and turbulent fluid flow was performed. The detailed flow modeling allows precise determination of possible cooling approaches and provides designers with the information required for selection of the optimal volumetric coolant flow. The CFD method is compared with a traditional LPTN approach. Index Terms—traction drive, PMSM, direct cooling. I. INTRODUCTION Advances in microprocessor technologies during the last decade have considerably increased the computational power of personal computers. This increase in computational power has enabled designers to make use of advanced simulation tools such as Finite Element Method (FEM) or Computational Fluid Dynamic (CFD) software. It has become possible to conduct numerical simulations using one modern PC, whereas 10 years ago a supercomputer or a computational cluster was required for the solution of the same model. Nevertheless, the solution process for such models, even for simplest ones, might take a couple of days or more, even for the most powerful PCs. Conjugated-fluid solid heat transfer CFD modeling for a directly-oil-cooled rotating electrical machine enables detailed analysis of coolant flow within the machine frame. Such analysis permits optimization of the coolant flow, and, consequently, enhanced thermal design, which, in turn, lead to more compact and more power- and torque- dense electrical machines - extremely important for mobile traction applications and aeronautical industry. The main interest of this work consists in CFD thermal modeling of the direct oil cooled permanent magnet synchronous machine. The simplified thermal model of the studied machine is simulated using commercial software. The temperature results are discussed and compared with temperatures obtained by the modeling based on Lumped Parameter Thermal Network (LPTN). The research introduced in this paper has been carried out as part of the EFFIMA (Energy and Life Cycle Cost Efficient Machines) - program of FIMECC (Finnish Metals and Engineering Competence Cluster). II. DIRECTLY OIL-COOLED MACHINE Figure 1 shows the cross section of the modeled machine. Fig. 1. Cut-away view of the modeled PMSM with removed end cap and shaft. The machine is targeted for use in hybrid mobile working heavy vehicles. In such environments, the hydraulic oil, normally used for the working hydraulics, might be used as coolant for electrical machines. The use of working hydraulic oil in direct cooling of electrical motors brings several benefits: • Electrical loadability of the motor can be increased by efficient cooling, which increases the torque- and power- densities • Separate cooling circuits utilizing special fluid (e.g. water/glycol) is eliminated from the system • Flow of the coolant is obtained from the working hydraulic circuit; there is no need for an additional cooling pump • Availability of a high volume of coolant allows heavy loading of the machine for a long period • Presence of oil in the machine chamber helps to dampen the noise produced by the electrical machine. The main properties of the machine under study are given in Table I. Conjugated Fluid-Solid Heat Transfer Modeling of a Directly-Oil-Cooled PMSM using CFD P. Ponomarev, M. Polikarpova, J. Pyrhönen Laboratory of Electrical Drives Technology, LUT Energy, 53850 Lappeenranta, Finland