Lubrication Challenges in Deep-Sea Gear Transmissions: A Review of High-Pressure and Low-Temperature Effects

The extremely high pressure and low temperature inherent to deep-sea environments pose significant challenges for the lubrication performance of gear transmission systems. The synergistic effects of high pressure and low temperature not only cause an exponential increase in lubricant viscosity, leading to reduced fluidity, startup difficulties, and lubrication starvation, but also allow seawater intrusion, which may induce lubricant emulsification, additive failure, and tooth surface corrosion, further exacerbating the risk of lubrication failure. This article reviews recent research progress in gear lubrication under deep-sea high-pressure and low-temperature conditions, with a specific focus on Elasto-Hydrodynamic Lubrication (EHL) theory and gear interface texturing. By thoroughly analyzing deep-sea environmental characteristics and their influence on lubricant properties, this article explores the applicability of Thermal Elasto-Hydrodynamic Lubrication (TEHL) theory in extreme environments. The discussion covers advancements in numerical simulations as well as key challenges. Additionally, the paper elaborates on the anti-friction and wear-resistance mechanisms of interface texturing, emphasizing its ability to improve gear lubrication states and boost tribological performance. Consequently, this study summarizes the limitations of existing research. It proposes future development directions, including multiphysics coupling modeling, synergistic texture and coating design, experimental validation, and engineering applications. Ultimately, this review aims to provide theoretical support and technical references for the reliable design and long-term stable operation of gear transmission systems in deep-sea equipment.