Lubricating compositions

Abstract

A method of reducing low-speed pre-ignition (LSPI) in a direct-injected spark-ignited internal combustion engine comprising lubricating the crankcase of the engine with a composition comprising a combination of a molybdenum-containing additive and a boron-containing additive. Preferably, the composition comprises a calcium detergent providing a calcium content of at least 0.08 wt %, based on the weight of the lubricating oil composition.

What is claimed is: 
     
         1 . A method of reducing low-speed pre-ignition (LSPI) events in a direct-injection spark-ignition internal combustion engine comprising lubricating the crankcase of the engine with a lubricating oil composition, the lubricating oil composition comprising a boron-containing additive and a molybdenum-containing additive, said lubricating oil composition having a molybdenum content of at least 150 ppm by weight, based on the weight of the lubricating oil composition, and having a boron content of at least 150 ppm by weight, based on the weight of the lubricating oil composition. 
     
     
         2 . A method according to  claim 1 , wherein, in operation, the engine generates a brake mean effective pressure level of greater than 1,500 kPa, at engine speeds of from 1,000 to 2,500 rotations per minute (rpm). 
     
     
         3 . A method according to  claim 1 , wherein the lubricating oil composition has a molybdenum content of from 150 ppm to 1500 ppm by weight, based on the weight of the lubricating oil composition. 
     
     
         4 . A method according to  claim 2 , wherein the lubricating oil composition has a molybdenum content of from 150 ppm to 1500 ppm by weight, based on the weight of the lubricating oil composition. 
     
     
         5 . A method according to  claim 1 , wherein the lubricating oil composition has a boron content of from 150 to 1500 ppm, based on the weight of the lubricating oil composition. 
     
     
         6 . A method according to  claim 2 , wherein the lubricating oil composition has a boron content of from 150 to 1500 ppm, based on the weight of the lubricating oil composition. 
     
     
         7 . A method according to  claim 3 , wherein the lubricating oil composition has a boron content of from 150 to 1500 ppm, based on the weight of the lubricating oil composition. 
     
     
         8 . A method according to  claim 4 , wherein the lubricating oil composition has a boron content of from 150 to 1500 ppm, based on the weight of the lubricating oil composition. 
     
     
         9 . A method according to  claim 1 , wherein the lubricating oil composition comprises a calcium detergent providing the lubricating oil composition with a calcium content of from 0.08 to 0.5 wt. %, based on the weight of the lubricating oil composition. 
     
     
         10 . A method according to  claim 7 , wherein the lubricating oil composition comprises a calcium detergent providing the lubricating oil composition with a calcium content of from 0.08 to 0.5 wt. %, based on the weight of the lubricating oil composition. 
     
     
         11 . A method according to  claim 1 , wherein the lubricating oil composition has a magnesium content of no more than 0.12 wt. %, based on the weight of the lubricating oil composition. 
     
     
         12 . A method according to  claim 10 , wherein the lubricating oil composition has a magnesium content of no more than 0.12 wt. %, based on the weight of the lubricating oil composition. 
     
     
         13 . A method according to  claim 11 , wherein the lubricating oil composition has a magnesium content of less than 0.05 wt. %, based on the weight of the lubricating oil composition. 
     
     
         14 . A method according to  claim 12 , wherein the lubricating oil composition has a magnesium content of less than 0.05 wt. %, based on the weight of the lubricating oil composition. 
     
     
         15 . A method according to  claim 1 , wherein the boron-containing additive Is one or more of: a borated dispersant, a borated dispersant viscosity index improver, an alkali metal or an alkaline earth metal borate, a borated overbased metal detergent, a borated epoxide, a borate ester, a sulfurised borate ester, or a borate amide; optionally wherein the boron-containing additive is one or more of a borated dispersant, a borate ester or a borated overbased metal detergent. 
     
     
         16 . A method according to  claim 1 , wherein the molybdenum-containing additive is an oil-soluble or oil-dispersible organo-molybdenum compound, optionally wherein the molybdenum-containing additive is one or more of a molybdenum dithiocarbamate, a molybdenum dithiophosphate, a molybdenum dithiophosphinate, a molybdenum xanthate, a molybdenum thioxanthate, or a molybdenum sulfide. 
     
     
         17 . A method according to  claim 1 , wherein the lubricating oil composition has a phosphorus content of no more than 0.12 wt. %, based on the weight of the lubricating oil composition. 
     
     
         18 . A method according to  claim 17 , wherein the lubricating oil composition has a phosphorus content of no more than 0.08 wt. %, based on the weight of the lubricating oil composition. 
     
     
         19 . A method according to  claim 13 , wherein the lubricating oil composition has a phosphorus content of no more than 0.08 wt. %, based on the weight of the lubricating oil composition. 
     
     
         20 . A method according to  claim 18 , wherein the lubricating oil composition has a phosphorus content of no more than 0.06 wt. %, based on the weight of the lubricating oil composition, 
     
     
         21 . A method according to  claim 19 , wherein the lubricating oil composition has a phosphorus content of no more than 0.06 wt. %, based on the weight of the lubricating oil composition.