Abstract: To reduce the no-load losses in the gearbox of new energy vehicles under low-temperature and high-speed operating conditions, a drag-reduction strategy based on nano-composite ceramic coatings is proposed. A low-temperature oil churning flow visualization test bench is established to compare and analyze the flow field and oil churning losses of coated and uncoated rotating components at different speeds under -20°C conditions. An analysis is conducted using the mobile particle semi-implicit(MPS) method to investigate the effects of rotational speed and temperature on oil churning losses, and to explore the mechanisms for suppressing churning losses. Further numerical simulations are performed to validate the drag-reducing effects of the coating in the complex flow environment of a gearbox in a specific type of new energy vehicle. The results indicate that the surface contact angle increases from 7.8° to 52.7° after coating application, and the coating exhibits excellent wear resistance；at -20°C, the reduction rate of oil churning loss on the disk remained between 31.7% and 48.5%, with decreases in viscous resistance, pressure drop resistance, and turbulent resistance；in the gearbox of a new energy vehicle, the drag reduction effect remained between 11.0% and 17.3%. The research findings will provide technical support for enhancing the efficiency of gear transmission through the application of nano-composite ceramic coating.

Key words: low temperature, nano-composite ceramic coating, churning loss, drag reduction, gearbox, MPS