Marine Engine Lubrication

Abstract

A two-stroke or four-stroke marine engine lubricating oil composition comprising an oil of lubricating viscosity in a major amount and (A) additives in respective minor amounts; and (B) a polymethacrylate viscosity modifier. Preferably, brightstock is completely or substantially absent from the composition.

What is claimed is: 
     
         1 . A two-stroke or four-stroke marine engine lubricating oil composition comprising an oil of lubricating viscosity in a major amount and
 (A) additives, in respective minor amounts; and   (B) a viscosity modifier in the form of a polymethacrylate in an amount in the range of 0.05-6 mass %,   wherein the composition includes less than 0.5 mass % of brightstock; and   wherein the two-stroke marine engine lubricating oil composition has a TBN of 40 to 100 mg KOH/g, as calculated using ASTM D2896, or the four-stroke marine engine lubricating oil composition has a TBN of 20 to 60 mg KOH/g, as calculated using ASTM D2896.   
     
     
         2 . The composition as claimed in  claim 1 , wherein the polymethacrylate has a weight-average molecular weight of 180,000 or more. 
     
     
         3 . The composition as claimed in  claim 1 , wherein the polymethacrylate is a polymer of
   CH 2 ═C(CH 3 )COOR 1   (I)
   
       where R 1  is a straight chain or branched alkyl group having 1-18 carbon atoms. 
     
     
         4 . The composition as claimed in  claim 3 , wherein the polymethacrylate is a copolymer of a monomer of formula (I) and a N-containing monomer selected from
   CH 2 ═C(R 2 )COO—(R 3 ) a —X 1  and CH 2 ═C(R 4 )X 2  
   
       where R 2  and R 3  are each independently, H or CH 3 ; R 3  is a straight chain or branched alkylene group having 2-18 carbon atoms; a is 0 or 1; X 1  and X 2  are each independently an amine residue or heterocyclic ring having 1 or 2 N atoms and 0-20 atoms. 
     
     
         5 . The composition as claimed in  claim 1 , in the form of a marine diesel cylinder lubricant. 
     
     
         6 . The composition as claimed in  claim 1 , in the form of a trunk piston engine oil. 
     
     
         7 . A method of lubricating a cross-head marine diesel engine comprising supplying a composition as claimed in  claim 1  to the piston/cylinder assembly of the engine. 
     
     
         8 . A method of lubricating a trunk piston marine diesel engine comprising supplying a composition as claimed in  claim 1  to the engine. 
     
     
         9 . A method of reducing the amount of brightstock in a two-stroke or four-stroke marine engine lubricating oil composition comprising an oil of lubricating viscosity in a major amount and (A) additives, in respective minor amounts; the method comprising the step of replacing, in part or in full, the brightstock with 0.05 to 6 mass % of (B) a viscosity modifier in the form of a polymethacrylate. 
     
     
         10 . The method as claimed in  claim 9 , wherein (B) substantially replaces the brightstock so that the composition includes less than 0.5 mass %. 
     
     
         11 . The method as claimed in  claim 10 , wherein the composition includes less than 0.1 mass % of brightstock. 
     
     
         12 . The method as claimed in  claim 11 , wherein the composition is completely or substantially free from brightstock. 
     
     
         13 . The method as claimed in  claim 9 , wherein the two-stroke marine engine lubricating oil composition has a TBN of 40 to 100 mg KOH/g, as calculated using ASTM D2896, or the four-stroke marine engine lubricating oil composition has a TBN of 20 to 60 mg KOH/g, as calculated using ASTM D2896.