Lubricating oil composition

Abstract

A lubricating oil composition that is free of organic friction modifiers, comprising (A) an oil of lubricating viscosity in a major proportion; (B) as an additive component in a minor proportion, a separately-prepared oil-soluble zinc salt of a dithiophosphoric acid, the dithiophosphoric acid being the reaction product of phosphorus pentasulphide with one or more alcohols, at least 50 mole % of the alcohol(s) having formula ROH where R is linear C18 to C26 saturated or double-bond unsaturated hydrocarbyl group; and (C) as an additive component in a minor proportion, a separately-prepared oil-soluble zinc salt of a dithiophosphoric acid, the dithiophosphoric acid being the reaction product of a phosphorus pentasulphide with one or more aliphatic alcohols consisting of an alcohol or alcohols each having from three to eight carbon atoms.

1 . A lubricating oil composition that is free of organic friction modifiers comprising, or made by admixing:
 (A) an oil of lubricating viscosity in a major proportion;   (B) as an additive component in a minor proportion, a separately prepared oil-soluble zinc salt of a dithiophosphoric acid, the dithiophosphoric acid being the reaction product of phosphorus pentasulphide with one or more alcohols, at least 50 mole % of the alcohol or alcohols having the formula ROH where R is a linear C18 to C26 saturated or double-bond unsaturated hydrocarbyl group; and   (C) as an additive component in a minor proportion, a separately-prepared oil-soluble zinc salt of a dithiophosphoric acid, the dithiophosphoric acid being the reaction product of phosphorus pentasulphide with one or more aliphatic alcohols consisting of an alcohol or alcohols each having from three to eight carbon atoms.   
     
     
         2 . A composition as claimed in  claim 1  wherein in (B) 70 to 100 mole % of the alcohol or alcohols have said formula ROH. 
     
     
         3 . A composition as claimed in  claim 1  or  2  wherein in (B) any alcohol or alcohols, other than those of formula ROH, have the formula R 1 OH where R 1  has 3 to 12, such as 3 to 10, such as 5 to 8, carbon atoms and is an alkyl or alkenyl, preferably alkyl, group. 
     
     
         4 . A composition as claimed in any of  claims 1  to  3  wherein in (B) R is a linear C18 to C22 saturated or unsaturated hydrocarbyl group. 
     
     
         5 . A composition as claimed in  claim 4  where R is a linear C18 saturated or unsaturated hydrocarbyl group. 
     
     
         6 . A composition as claimed in  claim 5  where R is an oleyl group. 
     
     
         7 . A composition as claimed in any of  claims 1  to  5  where, in (C), the one or more aliphatic alcohols comprise one or more secondary aliphatic alcohols such as greater than 60, such as greater than 70, such as greater than 80, such as greater than 90, such as 100, mole %. 
     
     
         8 . A composition as claimed in any of  claims 1  to  7  where, in (C), the one or more secondary aliphatic alcohols have 4 to 8 carbon atoms. 
     
     
         9 . A composition as claimed in any of  claims 1  to  8  wherein other additive components, different from (B) and from (C), are present and are selected from one or more of ashless dispersants, metal detergents, corrosion inhibitors, antioxidants, pour point depressants, antiwear agents, friction modifiers, demulsifiers, antifoam agents and viscosity modifiers. 
     
     
         10 . A composition as claimed in any of  claims 1  to  9  wherein (B) and (C) together introduce 0.02 to 0.09, such as 0.02 to 0.09, such as 0.02 to 0.08, such as 0.02 to 0.06, mass % of phosphorus, expressed as phosphorus atoms, into the composition. 
     
     
         11 . A method of improving the friction modification properties of a lubricating oil composition, which method comprises incorporating into the composition in a minor amount an additive component (B) as defined in any of  claims 1  to  6 . 
     
     
         12 . A method of lubricating surfaces of the combustion chamber of an internal combustion chamber during its operation comprising:
 (i) providing, in respective minor amounts, zinc salts (B) and (C) as defined in any of  claims 1  to  8  in a major amount of an oil of lubricating viscosity to make a lubricating oil composition, to improve the friction modification properties of the composition;   (ii) providing the lubricating oil composition in the combustion chamber;   (iii) providing a hydrocarbon fuel in the combustion chamber; and   (iv) combusting the fuel in the combustion chamber.