Bio-inspired shaft seal in coolant pump for electric vehicles

Abstract

Electric vehicles require a high-power device, such as a semiconductor power device, for their power control. Power devices have the drawback of high heat-generation. Water-cooling is an effective method for cooling these power devices. Their durability is affected by the performance of the shaft seal in the coolant pump. The shaft seal, in which a rotating shaft passes between liquid phase and gas phase, plays an important role in the separation of the two phases. For cooling power devices, a specifically designed shaft seal is required, as it is subjected to the high pressure and temperature of the coolant and the high-speed rotation of the shaft. A new-type of shaft seal has been developed using a biomimetic mechanism in which the lubrication mechanism found in natural synovial joints is adopted. A fibre-reinforced PVF (polyvinyl formal) was adopted as the hydrated seal-lip material. The hydrated seal-lip was attached to the shaft. The shaft was rotated by a servomotor at a speed of 5,000 min−1 (rpm). A LLC (long life coolant) was used as the coolant, which was diluted with distilled water at a concentration of 50%, heated to 75 °C, and pressurized to 0.3 MPa. A low leakage flow rate (less than 0.15 ml/h) was continuous and damage to the hydrated seal lip was not obvious after undergoing testing for a duration of 4,500 h. The frictional torque of the bio-inspired shaft seal was lower than that of the conventional oil seal. These results suggest that the bio-inspired shaft seal is a useful component for the water-cooling system of high-power devices.