Le moteur électrique est l’un des organes principaux d’un véhicule électrique. Sa température, notamment celle des bobines, doit être réduite pour éviter toute dégradation. Le refroidissement par l’extérieur, comme avec une chemise d’eau dans le carter, apparait limité car les pertes générées dans les bobines doivent traverser des zones où la conduction thermique est très mauvaise. L’extraction des calories au cœur de la machine est préférable, mais les échanges thermiques avec l’air sont modérés. En application automobile, le moteur électrique est situé à proximité d’un circuit d’huile de lubrification. Le refroidissement par l'huile en contact direct avec les bobines est étudié.La thèse s’est d’abord attachée à la recherche bibliographique étendue sur les différentes solutions de refroidissement de moteur. Ensuite, les transferts thermiques à l’intérieur du moteur ont été modélisés par méthode nodale. A travers une étude de sensibilité, les principales améliorations thermiques passives ont été dégagées, puis les systèmes de refroidissement eux-mêmes ont été modélisés. Enfin, des essais ont été réalisés sur un banc spécialement conçu. Pour cette partie expérimentale, le refroidissement direct des bobines par circulation d’huile a été étudié en détail. Différents types d’injecteurs d’huile sur les têtes de bobine ont été testés dans diverses conditions de vitesse du rotor, température et débit d’huile.L’objectif de cette thèse est d’analyser l’ensemble des problématiques thermiques liées aux solutions de refroidissement à huile. Il s’agit d’une étude comparative de la performance des solutions à huile entre elles et avec celle d’un refroidissement à eau plus conventionnel. / Electric motor is one of the most important elements of an electric vehicle. Some elements, particularly the windings, can be affected by rising heat. External cooling, as water jacket in the case, appears to be limited because the losses generated in windings must pass through zones where conduction is very poor. Cooling in the core of the machine is preferable, but heat transfer with air is poor. Due to the presence of lubricating oil in the vicinity of the motor and the heat transfer enhancement that such a liquid provides, oil circulation on the windings has been considered.The research was first dedicated to an extensive bibliography on the different solutions of motor cooling. Then heat transfer within the motor was modelled by using the lumped system analysis. Thanks to a sensitivity analysis, the main parameters affecting temperature have been identified before cooling systems were modelled. Finally, tests were performed on a specially designed bench. Oil was introduced at each side of the machine to directly cool the stator coil end-windings. Several oil injection patterns were tested. The influence of the oil flow rate, rotation speed and oil temperature has been investigated.The objective of this PHD study is to analyse all the thermal issues related to the oil cooling systems. This is a comparative study of the performance of the oil cooling solutions. Comparison is also done with conventional water cooling.

This thesis describes the process of improving the engine oil cooler performance for future vehicle applications, from ideas to simulated concepts. Increasing market expectations of high engine power, low fuel consumption and high towing capabilities results in an ever rising pressure on the cooling system in modern cars. The desire to prevent a future situation where the engine oil could become too hot, formed the basis for this thesis. The thesis was performed during 10 weeks from March to June 2015, at Volvo Car Corporation in Gothenburg. The working process started with literary studies where the theory behind automotive cooling systems and heat exchangers were studied to increase the general knowledge about the theory. Studies of engine oil, heat transfer and the overall design of engine cooling systems were performed. An important part was to clarify why the oil must not exceed a certain temperature limit. This gave answers to how the oil and engine components would be affected, if the oil did exceed the set temperature limit. To get a clear target and measurable parameters, the goal of this thesis was defined by estimating what the heat transfer demands could be in the future. A competitor analysis was made to examine how and if, the competitors to VCC use a different kind of oil cooling. Generation of concept ideas were made continuously during the early stage of the work process. Concepts that proved to be interesting were analysed more deeply with performance simulations and packaging studies. Five concepts were analysed and the performance simulations indicated that all the presented concepts can reach the heat transfer goal set early in the process. They do however use different methods, and meet the goal with different levels of efficiency. All concepts are listed with their heat transfer performance results and their advantages and disadvantages. The concept that showed to be the most promising in an oil cooling perspective, was to connect an additional heat exchanger in series after the current plate heat exchanger. This is a solution which will support the current engine oil cooler by handling the additional heat produced during certain driving scenarios. The best concept reached a heat transfer rate of 40 kW at half the air flow required by the second best concept. The concepts that has been presented will implicate an alteration of the current oil cooling system design. The lack of available space in the cars will also result in some rearranging of components in order to make space for an additional heat exchanger. The purpose with the concept generation is to present a good foundation from which Volvo can base their future decisions on.

This thesis investigated the heat transfer of internally oil cooled rotors in permanent magnet electric machines which are, among other things, used in hybrid vehicles or zero emission vehicles. The magnets become sensitive and can be demagnetized at high working temperatures, hence the need of cooling. The scope of this work included CFD simulations in STAR-CCM+. Three different 3D multiphase models simulating the oil propagation in the rotor were performed. A Lagrangian multiphase model combined with a fluid film model was the most suitable model for simulating the spray of the oil and the film thickness along the inner rotor wall. It was noticed that periodic boundaries caused problems for the fluid film model, therefore a complete geometry was preferred over a truncated model. The 3D solutions provided thicker film thicknesses than the analytical solutions from the fluid film thickness theory. The maximum analytical thickness was of the same order of magnitude as the surface average film thickness provided by the multiphase models. This thickness was assumed to be constant when used as the base for the fluid region in the 2D one-phase models.The study showed that aluminum was the most suitable rotor material due to its high conductive capacity, which provided a more even distribution of the temperature in the solid and hence resulted in lower overall temperatures. The cooling power increased linearly with the volumetric flow rate, however the heat transfer coefficient decreased for the higher flow rates. A volumetric flow rate of 10dl/min was recommended. A 2D model was compared to a preliminary experiment and showed that these were not correlated. The conclusion was that more experiments and simulations are needed in order to confirm the validity of the 2D model.