Abstract: To address the stringent lubrication requirements for gears and bearings in electric vehicle (EV) transmissions under high-frequency and high-load conditions, while mitigating the energy loss caused by traditional high-viscosity lubricants, this study enhances the micropitting resistance of low-viscosity lubricants by incorporating ultra-high base number calcium alkylsalicylate detergent. The micropitting initiation and evolution on roller surfaces were observed by using an MPR micropitting tester under simulated operating conditions. The impact of the detergent on surface fatigue damage was evaluated through indicators such as friction coefficient, vibration signals, roller width, and weight changes. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were employed to analyze the film-forming mechanism and elemental distribution on metal surfaces. The results demonstrate that adding 0.3% ultra-high base number calcium alkylsalicylate detergent reduces micropitting damage by nearly 40%. The core mechanism involves the formation of a physical deposition film on the metal surface, which delays the initiation of microscopic fatigue cracks. However, a "competitive failure" relationship between wear and micropitting was identified: while increasing detergent content improves micropitting resistance, it also elevates the friction coefficient and wear rate. Additionally, the detergent synergizes with anti-wear agents to form a Ca- and P-rich composite friction film on the roller surface. Notably, the elemental content in micropits is significantly lower than that on worn surfaces due to material spalling, which hinders friction film regeneration.

Key words: micropitting, detergent, deposition film, chemical reaction film, e-transmission fluid