Lubricating oil composition

Abstract

The present invention provides a lubricating oil composition comprising a metal dithiophosphate and a poly(meth)acrylate containing a polar hydroxyl group in a base oil.

1 - 10 . (canceled) 
   
   
       11 . A lubricating oil composition comprising a base oil, a poly(meth)acrylate containing a hydroxyl group, and a metal dithiophosphate. 
   
   
       12 . The lubricating oil composition of  claim 11 , wherein the poly(meth)acrylate containing a hydroxyl group has an average molecular weight that is from 5,000 to 50,000. 
   
   
       13 . The lubricating oil composition of  claim 11  further comprising a poly(meth)acrylate that does not contain a hydroxyl group. 
   
   
       14 . The lubricating oil composition of  claim 13 , wherein the poly(meth)acrylate that does not contain a hydroxyl group has an average molecular weight that is from 20,000 to 100,000. 
   
   
       15 . The lubricating oil composition of  claim 13  having a weight ratio of the poly(meth)acrylate containing a hydroxyl group to the poly(meth)acrylate that does not contain a hydroxyl group in the range of 100:0 to 40:60. 
   
   
       16 . The lubricating oil composition of  claim 11  further comprising a sulphurised fat or oil and a phosphate ester. 
   
   
       17 . The lubricating oil composition of  claim 11 , wherein the base oil has a kinetic viscosity at 100° C. of at least 2 mm 2 /s and a viscosity index of at least 90. 
   
   
       18 . The lubricating oil composition of  claim 11 , wherein the metal dithiophosphate is a zinc dithiophosphate. 
   
   
       19 . A lubricating oil composition comprising:
 (a) a base oil having a kinetic viscosity at 100° C. of at least 2 mm 2 /s and no greater than 8 mm 2 /s and a viscosity index of at least 90;   (b) a poly(meth)acrylate containing a hydroxyl group, wherein the poly(meth)acrylate containing a hydroxyl group is a co-polymer that comprises (i) at least 50 weight percent of an alkyl(meth)acrylate monomer having an alkyl group of from 1 to 20 carbons and (ii) at least 5 weight percent of a vinyl monomer having an alkyl group of from 1 to 20 carbons; and   (c) one or more of zinc dithiophosphates at a combined concentration such that the total content of zinc is approximately from 0.02 to 1.0 weight percent of the lubricating oil composition.   
   
   
       20 . The lubricating oil composition of  claim 19 , wherein the alkyl group of the alkyl(meth)acrylate monomer has from 8 to 20 carbons, the vinyl monomer is a hydroxyalkyl (2-6 carbons)(meth)acrylate, and the zinc dithiophosphates are zinc dialkyl dithiophosphates having, as the alkyl groups therein, secondary alkyl groups of from 3 to 22 carbons. 
   
   
       21 . A method of lubricating an apparatus, the method comprising lubricating the apparatus with a lubricating oil composition that comprises a base oil, a poly(meth)acrylate containing a hydroxyl group, and a metal dithiophosphate. 
   
   
       22 . The method of  claim 21 , wherein the poly(meth)acrylate containing a hydroxyl group has an average molecular weight that is from 5,000 to 50,000. 
   
   
       23 . The method of  claim 21 , wherein the lubricating oil composition further comprises a poly(meth)acrylate that does not contain a hydroxyl group. 
   
   
       24 . The method of  claim 23 , wherein the poly(meth)acrylate that does not contain a hydroxyl group has an average molecular weight that is from 20,000 to 100,000. 
   
   
       25 . The method of  claim 23 , wherein the lubricating oil composition has a weight ratio of the poly(meth)acrylate containing a hydroxyl group to the poly(meth)acrylate that does not contain a hydroxyl group in the range of 100:0 to 40:60. 
   
   
       26 . The method of  claim 21 , wherein the lubricating oil composition further comprises a sulphurised fat or oil and a phosphate ester. 
   
   
       27 . The method of  claim 21 , wherein the base oil has a kinetic viscosity at 100° C. of at least 2 mm 2 /s and a viscosity index of at least 90. 
   
   
       28 . The method of  claim 21 , wherein the metal dithiophosphate is a zinc dithiophosphate.