Lubricating Oil Compositions

Abstract

An internal combustion engine crankcase lubricating oil composition has a phosphorus content of not greater than 0.09 mass % a metal detergent additive system comprising one or more metal salts of organic carboxylic acids, and a viscosity index improver comprising a linear diblock copolymer, one block being derived from a vinyl aromatic hydrocarbon monomer and one block being derived from a diene monomer.

1 . An internal combustion engine crankcase lubricating oil composition having a phosphorus concentration expressed as atoms of phosphorus, of not greater than 0.09 mass % based on the mass of the oil composition, which composition comprises or is made by admixing: 
 (A) an oil of lubricating viscosity, in a major amount;    (B) a metal detergent system, as an additive in a minor amount, comprising one or more metal salts of organic carboxylic acids; and    (C) a viscosity index improver comprising a linear diblock copolymer comprising at least one block derived primarily from a vinyl aromatic hydrocarbon monomer and at least one block derived primarily from a diene monomer.    
   
   
       2 . An oil composition as claimed in  claim 1  wherein the linear diblock copolymer is at least one diblock copolymer comprising at least a polystyrene block and a block derived from isoprene, butadiene or a mixture thereof.  
   
   
       3 . An oil composition as claimed in  claim 2  wherein the linear diblock copolymer is at least one diblock copolymer selected from the group consisting of hydrogenated styrene/butadiene diblock copolymers and hydrogenated styrene/isoprene diblock copolymers.  
   
   
       4 . An oil composition as claimed in  claim 2  wherein the diblock copolymer has a Shear Stability Index value of from 2 to 50% (30 cycles) and the polydiene block of the diblock copolymer comprises from 40 to 90 mass % derived from isoprene and from 10 to 60 mass % derived from butadiene.  
   
   
       5 . An oil composition as claimed in  claim 3  wherein the diblock copolymer has a Shear Stability Index value of from 2 to 50% (30 cycles) and the polydiene block of the diblock copolymer comprises from 40 to 90 mass % derived from isoprene and from 10 to 60 mass % derived from butadiene.  
   
   
       6 . An oil composition as claimed in  claim 1  wherein the diblock copolymer has a Shear Stability Index value of from 5 to 25% (30 cycles).  
   
   
       7 . An oil composition as claimed in  claim 1  having a sulphated ash concentration of not greater than 1.0 mass %.  
   
   
       8 . An oil composition as claimed in  claim 1  having a sulphur concentration, expressed as atoms of sulphur, of not greater than 0.3 mass %.  
   
   
       9 . An oil composition as claimed in  claim 8  having a sulphur concentration, expressed as atoms of sulphur, of not greater than 0.2, mass %.  
   
   
       10 . An oil composition as claimed in  claim 1  wherein the metal salts of organic carboxylic acids are overbased alkaline earth metal salicylates.  
   
   
       11 . An oil composition as claimed in  claim 2  wherein the metal salts of organic carboxylic acids are overbased alkaline earth metal salicylates.  
   
   
       12 . An oil composition as claimed in  claim 3  wherein the metal salts of organic carboxylic acids are overbased alkaline earth metal salicylates.  
   
   
       13 . An oil composition as claimed in  claim 4  wherein the metal salts of organic carboxylic acids are overbased alkaline earth metal salicylates.  
   
   
       14 . An oil composition as claimed in  claim 1  further including one or more additives, other than (B) and (C), selected from dispersants, detergents, antioxidants, antiwear agents, friction modifiers, corrosion inhibitors, pour point depressants, demulsifiers and anti-foaming agents.  
   
   
       15 . An oil composition as claimed in  claim 2  further including one or more additives, other than (B) and (C), selected from dispersants, detergents, antioxidants, antiwear agents, friction modifiers, corrosion inhibitors, pour point depressants, demulsifiers and anti-foaming agents.  
   
   
       16 . An oil composition as claimed in  claim 3  further including one or more additives, other than (B) and (C), selected from dispersants, detergents, antioxidants, antiwear agents, friction modifiers, corrosion inhibitors, pour point depressants, demulsifiers and anti-foaming agents.  
   
   
       17 . An oil composition as claimed in  claim 4  further including one or more additives, other than (B) and (C), selected from dispersants, detergents, antioxidants, antiwear agents, friction modifiers, corrosion inhibitors, pour point depressants, demulsifiers and anti-foaming agents.  
   
   
       18 . A method of lubricating a compression-ignited or spark-ignited internal combustion engine which comprises supplying, to the engine a lubricating oil composition as claimed in  claim 1 .  
   
   
       19 . A method of lubricating a compression-ignited or spark-ignited internal combustion engine which comprises supplying to the engine a lubricating oil composition as claimed in  claim 2 .  
   
   
       20 . A method of lubricating a compression-ignited or spark-ignited internal combustion engine which comprises supplying to the engine a lubricating oil composition as claimed in  claim 3.