Advanced Cooling of Rotor in Electrical Motor

About one fifth of the energy used today is allocated in the transportation sector and most of the vehicles are driven by internal combustion engines. Replacing them with electrical machine would have a positive environmental impact but there is room for improvement of the electric machines.Rotors of the electrical machines in the automotive industry today are built with permanent magnets. High efficiency and high power density are two advantages with this machine design but there are a number of drawbacks as well. Temperature sensitivity and costly materials are two examples. Operation in higher temperature can lead to demagnetization of the magnets. Segmentation, leading to reduced heat generation, is used today to prevent overheating. By varying the composition of the magnet they also become more temperature resilience but this is often expensive.The goal with the thesis was to, by cooling, achieve and maintain a safe operation temperature while simultaneously allow higher performance and/or simpler magnet design alternatively lower temperature grade. The analysis is based on theoretical calculations and experimental results from a test rig that was designed and constructed within the thesis.The cooling system was designed to spray oil on the inside of the rotor of the electrical machine. Due to the high rotational speed the oil forms a thin film that absorbs the heat generated by the magnets. In the thesis a cylinder with an external heat source was used to simulate the rotor.A thermal analysis of the test setup was conducted to assess the heat transfer capability of the spraying method. Losses and operation temperature of an actual machine were estimated for different operation points and segmentation designs of the magnets. The results showed significant drop in the temperature of the magnets as well as a possibility to reduce the number of segments.Validerat; 20141031 (global_studentproject_submitter