Lubricant Compositions For Direct Injection Engines

Abstract

The invention is directed to a method for reducing low speed pre-ignition events in a spark-ignited direct injection internal combustion engine by supplying to the sump a lubricant composition which contains an oil of lubricating viscosity and a metal overbased detergent. The metal overbased detergent may be selected from sulfonate detergents, phenate detergents, and salicylate detergents, especially sulfonate detergents with a metal ratio of at least 5.

What is claimed: 
     
         1 . A lubricant composition comprising:
 (a) a base oil of lubricating viscosity;   (b) at least one magnesium salicylate overbased detergent in an amount to provide at least 450 ppm magnesium from the magnesium overbased detergent to the lubricating composition;   (c) at least one calcium salicylate overbased detergent in an amount to provide at least 1,000 ppm calcium to the lubricating composition; and   (d) 0.5 to 0.9 wt.% of a zinc dialkyldithiophosphate anti-wear additive, 
 wherein the magnesium salicylate overbased detergent and the calcium salicylate overbased detergent collectively contribute up to about 0.9 weight percent of sulfated ash to the lubricating composition and wherein the lubricating composition has a phosphorus content of 0.12 wt.% or less and total sulfated ash of 1.1% or less. 
     
     
         2 . The composition of  claim 1 , further comprising one or more additional additives is selected from an ashless dispersant, an ashless antioxidant, a friction modifier, and a polymeric viscosity modifier. 
     
     
         3 . The composition of  claim 1 , wherein the magnesium overbased detergent has a metal ratio of 5 to 30. 
     
     
         4 . The composition of  claim 2 , wherein the one or more additional additives includes a polyalkenyl succinimide dispersant in an amount from 0.5 to 4 weight % of the lubricating composition. 
     
     
         5 . The composition of  claim 2 , wherein the one or more additional additives includes a boron post-treated polyalkenyl succinimide dispersant. 
     
     
         6 . The composition of  claim 2 , wherein the one or more additional additives includes a molybdenum compound in an amount to deliver 20 to 750 ppm molybdenum. 
     
     
         7 . The method of  claim 1 , wherein the base oil comprises at least 50 weight % of a Group II base oil, a Group III base oil, or mixtures thereof. 
     
     
         8 . The composition of  claim 1 , wherein the one or more additional additives includes an ashless antioxidant present in the lubricating composition in an amount of from 0.3 weight % to 5 weight %. 
     
     
         9 . The composition of  claim 8 , wherein the ashless antioxidant is selected from one or more of arylamines, diarylamines, alkylated arylamines, alkylated diaryl amines, phenols, hindered phenols, sulfurized olefins, or mixtures thereof. 
     
     
         10 . A lubricant composition comprising:
 (a) a base oil of lubricating viscosity;   (b) at least one magnesium salicylate overbased detergent in an amount to provide at least 450 ppm magnesium from the magnesium overbased detergent to the lubricating composition;   (c) at least one calcium salicylate overbased detergent in an amount to provide at least 1,000 ppm calcium to the lubricating composition; and   (d) 0.5 to 0.9 wt.% of a zinc dialkyldithiophosphate anti-wear additive, 
 wherein the magnesium salicylate overbased detergent and the calcium salicylate overbased detergent collectively contribute up to about 0.9 weight percent of sulfated ash to the lubricating composition and wherein the lubricating composition has a phosphorus content of 0.12 wt.% or less and total sulfated ash of 1.1% or less, where the lubricant composition is capable of reducing low speed pre-ignition events in a spark-ignited direct injection internal combustion engine equipped with a turbocharger and operated under a load with a brake mean effective pressure (BMEP) of greater than or equal to 12 bars at speeds less than or equal to 3,000 rpm.