Abstract: In response to the new requirements for the electrical performance of the transmission fluid of electric vehicle motor, reducer, and controller "three-in-one" integrated drive system, the influence of lube base oil and additives on the conductivity of electric vehicle transmission fluid at different temperatures was systematically studied according to the conductivity measurement method of liquid hydrocarbons (ASTM D4308). The results show that with the temperature increases, the conductivity of all test samples increases due to the decrease of oil viscosity and the increase of carrier migration rate; and the influence of lube base oil, anti-wear, anti-oxygen and anti-corrosion additives on the conductivity of transmission fluid is negligible. Detergents play the dominate role on the conductivity of lubricants. Among them, detergents with high total base number (TBN) have significantly greater influence on conductivity than that of medium and low TBN detergents. The dispersant is another key ingredients influence factor on the oil conductivity, and the conductivity of the lubricating oil with dispersant treated by boron and phosphate is the highest than that of others.

Key words: electric vehicle, transmission fluid, lube base oil, additives, electrical conductivity