Investigation on the influence of oil ratio coefficient on temperature rise in UUV propulsion motors

Permanent magnet synchronous motors (PMSMs) demonstrate significant advantages in enhancing propulsion efficiency and system compactness for unmanned underwater vehicles (UUVs), yet their operational reliability is constrained by winding insulation degradation and permanent magnet demagnetization caused by accumulated heat in sealed and narrow space,and traditional oil-cooled systems require extra cooling equipment, which can take up more space and make it difficult to fit into the tight layout of UUVs. Aiming at this challenge, an oil cooling system without extra cooling equipment utilizing oil churning effect is proposed in this paper to address the thermal management limitations of UUV propulsion systems. An electromagnetic-thermal-fluid multi-physics coupling model is established for UUV propulsion motor thermal management system. The oil ratio coefficient (ORC), the UUV's different speeds, type of cooling oil, and different motor working conditions as input parameters are used to analyzes the influence on the motor's cooling conditions. The result shows that oil cooling have excellent thermal management performance compared with natural cooling, achieving a temperature reduction of 80 K at 150kW. The type of oil shows a relatively small impact on motor components temperature. Satisfyingly, the cooling efficiency of the oil churning system increases with the increase of UUV speed. Besides, a dimensionless power density enhancement factor is proposed firstly to evaluate the cooling system comprehensive performance. The cooling system shows the best performance at an ORC of 0.6. The power density reaches 3.067 kW/kg, which is 43% higher than that of natural cooling. Therefore, in the design of oil cooling systems for UUV motors, the ORC is a crucial parameter for effective temperature control.