Power devices used for power control in electric vehicles have the drawback of high heat-generation, which can be effectively addressed by water-cooling. Their durability is affected by the performance of the seal lip in the coolant pump. The seal lip, in which a rotating shaft passes between liquid and gas phases, plays an important role in the separation of the two phases. To cool power devices, a specifically designed seal lip is required, as the seal lip is subjected to high pressure and temperatures of the water-based coolant and high-speed shaft rotation. A new type of seal lip has been developed by employing a biomimetic mechanism in which the hydrated lubrication mechanism found in natural articular cartilage is adopted. A fiber-reinforced PVF (polyvinyl formal) was employed as the hydrated and biomimetic seal lip material. The bio-inspired seal lip was attached to the shaft. Shaft rotation was controlled by a servomotor, which generated a speed of 5,000 rpm (revolutions per minute). An 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. Although the continuous leakage of LLC was observed, it was estimated that the bio-inspired seal lip might prevent the abrupt function failure in air-LLC separation. The frictional torque of the bio-inspired seal lip was lower than that of the conventional oil seal. These results suggest that the bio-inspired seal lip is a useful component in the water-cooling systems of high-power devices.
An all-new sealing system for a rotating shaft, which specializes in excellent separation between water and air, has been developed for installation in an ocean current or tidal power generator. Two seal lips made of a polyvinyl formal (PVF) were attached to a rotating shaft, and an aqueous solution of 3.0 wt% polyethylene glycol (PEG), a non-Newtonian fluid with a molecular weight of 2.0 million, was supplied between two lips for lubrication. Expected lubrication modes between the dynamic seal surfaces were hydration lubrication, softelastohydrodynamic lubrication, and weeping lubrication, similar to that observed in a natural synovial joint. Using PVF with a small porous diameter of 8 m and continuously porous structure promoted hydration lubrication between seal surfaces at the molecular level, and low leakage of water, less than 0.05 ml/h, throughout the experiment. Mean frictional torque was lower than that found in the mechanical and oil seals that are generally used for industrial components. Frictional torque had been stable; the friction was independent of the shaft rotational speed, and the stick-slip friction that might lead to leakage of water was moderated in comparison with the conventional sealing systems.
Shaft seals with a seal lip are used in various applications to separate gases and fluids, but their sealing function and durability are affected by the extent of lubrication at the dynamic seal faces between a rotating shaft and the seal lip. A new sealing system consisting of two hydrated seal rings and non-Newtonian lubricants was designed by a biomimetic approach to minimise frictional loss and provide high waterproof function when separating air and water. This system demonstrates significant superiority in low-speed rotation, conditions under which the lubrication mechanism of an oil seal or mechanical seal does not generally work well. Fibre reinforcement of the seal ring material was performed to prevent the deformation of the soft seal rings because of the frictional force in the tangential direction of the shaft and water pressure. This reinforcement enabled the new sealing system to obtain both high waterproof performance and low frictional characteristics in the speed range of 20–100 r/min.
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