Method of lubricating an internal combustion engine

Abstract

The invention provides a method of lubricating an internal combustion engine equipped with a centrifugal oil mist separator, wherein the lubricant contains 0.1 wt % to 8 wt % soot resulting from operation of the engine, and wherein the lubricant composition comprises an oil of lubricating viscosity, and 0.2 wt % to 3 wt % of a soot dispersing additive having a shear stability index of 0 to 25, wherein the soot dispersing additive comprises a block copolymer comprising (i) a vinyl aromatic monomer block and (ii), a conjugated diene olefin monomer block.

1 - 33 . (canceled) 
     
     
         34 . A method of lubricating an internal combustion engine equipped with a centrifugal oil mist separator, wherein the lubricant contains 0.1 wt % to 8 wt % soot resulting from operation of the engine, and wherein the lubricant composition comprises an oil of lubricating viscosity, and 0.2 wt % to 3 wt % of a soot dispersing additive having a shear stability index of 0 to 25, wherein the soot dispersing additive comprises a block copolymer comprising (i) a vinyl aromatic monomer block and (ii), a conjugated diene olefin monomer block. 
     
     
         35 . The method of  claim 34 , wherein the lubricating composition is characterized as having (i) a sulfur content of 0.5 wt % or less, (ii) a phosphorus content of 0.15 wt % or less, and (iii) a sulfated ash content of 0.5 wt % to 1.5 wt %. 
     
     
         36 . The method of  claim 35 , wherein the lubricating composition is characterized as having a sulfated ash content of 0.5 wt % to 1.2 wt %. 
     
     
         37 . The method of  claim 34 , wherein the lubricating composition is characterized as having at least one of (i) a sulfur content of 0.2 wt % to 0.4 wt %, (ii) a phosphorus content of 0.08 wt % to 0.15 wt %, and (iii) a sulfated ash content of 0.5 wt % to 1.5 wt %. 
     
     
         38 . The method of  claim 34 , wherein the lubricating composition is characterized as having a total base number (TBN) content of at least 5 mg KOH/g. 
     
     
         39 . The method of  claim 38 , wherein the lubricating composition is characterized as having a total base number (TBN) content of 6 to 13 mg KOH/g. 
     
     
         40 . The method of  claim 34 , wherein the vehicle powered by a compression-ignition internal combustion engine has a maximum laden mass over 3,500 kg. 
     
     
         41 . The method of  claim 34 , wherein the soot dispersing additive has a shear stability index of 0 to 20 as measured by the Orbahn shear test (ASTM D6278). 
     
     
         42 . The method of  claim 41 , wherein the soot dispersing additive is present at 0.3 wt % to 1.4 wt % of the lubricating composition. 
     
     
         43 . The method of  claim 34 , wherein the soot dispersing additive is present at 0.2 wt % to 2.5 wt % of the lubricating composition. 
     
     
         44 . The method of  claim 43 , wherein the soot dispersing additive has a shear stability index of 5 to 15. 
     
     
         45 . The method of  claim 34 , wherein the block copolymer comprises a hydrogenated styrene-butadiene copolymer. 
     
     
         46 . The method of  claim 34 , wherein the block copolymer comprises a hydrogenated styrene-isoprene copolymer. 
     
     
         47 . The method of  claim 34 , wherein the soot dispersing additive is prepared by a process comprising:
 1) reacting an alpha-beta unsaturated carboxylic acid or active derivative thereof with a selectively hydrogenated star-shaped polymer comprising a polyvinylaromatic nucleus and at least 4 polymeric arms linked to said nucleus wherein said polymeric arms are chosen from:
 (i) hydrogenated homopolymers and hydrogenated copolymers of conjugated dienes; 
 (ii) hydrogenated copolymers of conjugated dienes and monoalkenyl arenes (typically a vinyl aromatic monomer such as styrene); and 
 (iii) mixtures thereof; 
   
       and wherein at least 80% of the aliphatic unsaturation of the star-shaped polymer has been reduced by hydrogenation while less than 20% of the aromatic unsaturation has been reduced; and
 2) reacting the activated star polymer thus formed with:
 (a) at least one compound of general formula RO(AO) n H, 
 
 wherein R is a C 4-20  alkyl group, any A moiety is independently an ethylene or propylene moiety, and n is 0 to 5, optionally followed by reaction with (b) a long chain alkane-substituted carboxylic acid or active derivative thereof, and/or (c) a C 1  to C 8  amine containing 1 to 8 nitrogen atoms and/or an alkane polyol having at least two hydroxy groups; or with (d) the pre-formed product of reactants (b) and (c), optionally followed by esterifying any residual acid groups with a C 1-6  alkanol. 
 
     
     
         48 . The method of  claim 34 , wherein the lubricating composition comprises less than 0.1 wt % of olefin copolymer soot dispersing additives having a number average molecular weight above 20,000. 
     
     
         49 . The method of  claim 34 , wherein the lubricating composition comprises less than 0.1 wt % of olefin copolymer soot dispersing additives. 
     
     
         50 . The method of  claim 34 , wherein the lubricating composition further comprises an antioxidant selected from the group consisting of a phenolic antioxidant, an aminic antioxidant, and mixtures thereof, and wherein the antioxidant is present at 0.1 wt % to 3 wt %. 
     
     
         51 . The method of  claim 34 , wherein the lubricating composition further comprises an overbased sulfonate detergent present at 0.01 wt % to 0.9 wt %. 
     
     
         52 . The method of  claim 51 , wherein the overbased sulfonate detergent has a metal ratio of 12 to less than 20. 
     
     
         53 . The method of  claim 51 , wherein the overbased sulfonate detergent comprises a calcium sulfonate detergent having a metal ratio of 18 to 40 and having a TBN of 300 to 500. 
     
     
         54 . The method of  claim 51 , wherein the lubricating composition further comprises 0.01 wt % to 2 wt % of a further detergent different from the overbased sulfonate detergent, wherein the further detergent is selected from the group consisting of borated and non-borated non-sulfur containing phenates, borated and non-borated sulfur containing phenates, borated and non-borated sulfonates, borated and non-borated salixarates, borated and non-borated salicylates, and mixtures thereof. 
     
     
         55 . The method of  claim 34 , wherein the lubricating composition further comprises a “hybrid” detergent formed with mixed surfactant systems selected from the group consisting of phenate/salicylates, sulfonate/phenates, sulfonate/salicylates, sulfonates/phenates/salicylates and mixtures thereof. 
     
     
         56 . The method of  claim 34 , wherein the lubricating composition further comprises a phosphorus-containing antiwear agent, typically zinc dialkyldithiophosphate. 
     
     
         57 . The method of  claim 34 , wherein the lubricating composition further comprises an ashless dispersant comprising a succinimide dispersant different from the soot-dispersing additive of the invention, wherein the succinimide dispersant has a TBN of at least 40 mg KOH/g, and is present at 1.2 wt % to 5 wt % of the lubricating composition. 
     
     
         58 . The method of  claim 57 , wherein the succinimide dispersant comprises a polyisobutylene succinimide, wherein the polyisobutylene from which polyisobutylene succinimide is derived has a number average molecular weight of 350 to 5000. 
     
     
         59 . The method of  claim 34 , wherein the internal combustion engine comprises a steel surface on at least one of a cylinder bore, cylinder block, or piston ring. 
     
     
         60 . The method of  claim 34 , wherein the centrifugal oil mist separator rotates at 2500 to 10000 rpm. 
     
     
         61 . The method of  claim 60 , wherein the internal combustion engine has a closed crankcase ventilation.