Composition and Method for Lubricating Automotive Gears, Axles and Bearings

#The disclosed technology relates to a lubricant composition for automotive gears, axles, and bearings, the lubricant composition containing an oil of lubricating viscosity and a metal thiophosphate compound, such as zinc dialkyldithiophosphate, as well as a method of obtaining extreme pressure performance in automotive gears, axles, and bearings at lower sulfur content than is typical, by lubricating such automotive gears, axles, and bearings with a lubricant composition containing a metal thiophosphate compound, such as zinc dialkyldithiophosphate.

#Driveline power transmitting devices (such as gears or transmissions) present highly challenging technological problems and solutions for satisfying the multiple and often conflicting lubricating requirements, while providing durability and cleanliness. Fluids for lubricating automotive gears in particular can be defined by adherence to the American Petroleum Institute (“API”) category GL-5 ratings, which denotes lubricants intended for gears, particularly hypoid gears, in axles operating under various combinations of high-speed/shock load and low-speed/high-torque conditions, and specifically tests such as ASTM D7452 (former L-42). Manual transmission fluids can be evaluated for hardware protection by FZG gear scuffing, pitting and wear procedures such as FZG A10/16.6R/90, FZG A10/16.6R/120, further defined by the Coordinating European Council (“CEC”) standards, such as the CEC L-84-02 FZG gear scuffing load carrying test. While these tests will determine if a suitable level of gear durability has been met, in neither case do these tests alone determine it to be suitable for use as considerations of friction, cleanliness, bearing life, seals and other performance parameters need to be considered.

#For decades sulfurized olefins have been the main extreme pressure additive to actively control gear break in and shock loading, particularly for hypoid gear break in and shock loading to prevent adhesive wear under high contact pressures and temperatures. Sulfurized olefins can react in asperity contact to minimize adhesion through forming iron sulfides that have a lower shear stress than the parent steel that wear preferentially. However, high levels of active sulfur in sulfurized olefin can lead to corrosion of yellow metals that may be present in a driveline device, as well as to reduced thermal/oxidative stability of the gear lubricant composition, and contribute to the formation of thiol by-products, which raise odor issues.

#Various preferred features and embodiments will be described below by way of non-limiting illustration. One aspect of the invention is a lubricant composition for automotive gears, axles, and bearings containing (a) an oil of lubricating viscosity, (b) a metal thiophosphate, (c) a non-metal phosphorous containing compound.

#One component of the disclosed technology is an oil of lubricating viscosity, also referred to as a base oil. The base oil may be selected from any of the base oils in Groups I-V of the American Petroleum Institute (API) Base Oil Interchangeability Guide-lines (2011), namely

#Viscosity Index Base Oil Category Sulfur (%) Saturates (%) Viscosity Index Group I >0.03 and/or <90 80 to less than 120 Group II ≤0.03 and >90 80 to less than 120 Group III ≤0.03 and >90 ≥120 Group IV All polyalphaolefins (PAOs) Group V All others not included in Groups I, II, III or IV