Lubricating oil composition

Abstract

A lubricating oil for an internal combustion engine is disclosed. The lubricating oil can provide reduced friction and can cope with environmental regulations requiring a high corrosion-preventing effect. The lubricating oil composition contains a mono or diester of glycerin and a straight-chain or branched fatty acid of C6 to 20 having a saturated hydrocarbyl group; a triazole derivative; and a mixture of primary zinc dialkyl dithiophosphate and secondary zinc dialkyl dithiophosphate.

1 . A lubricating oil composition comprising:
 as constituent (a), 0.5 to 1.5 mass % of a mono or diester of glycerin and a straight-chain or branched fatty acid of carbon number 6 to 20 having a saturated hydrocarbyl group;   as constituent (b), 0.1 to 0.5 mass % of a triazole derivative represented by general formula (1):   
       
         
           
           
               
               
           
         
       
       wherein R 1  is hydrogen or a hydrocarbyl group of carbon number 1 to 3, R 2  and R 3  are respectively independently hydrogen or a hydrocarbyl group of carbon number 1 to 20, which may contain an oxygen atom, sulphur atom or nitrogen atom; and,
 as constituent (c), 0.01 to 0.2 mass %, calculated as phosphorus, of a mixture of primary zinc dialkyl dithiophosphate whose alkyl group is a primary hydrocarbyl group and a secondary zinc dialkyl dithiophosphate whose alkyl group is a secondary hydrocarbyl group; 
 
       wherein the ratio of constituent (a)/constituent (b) is 1.5 to 8. 
     
     
         2 . A lubricating oil composition according to  claim 1 , wherein said constituent (a) is a mono or diester of glycerin and a fatty acid of straight-chain of carbon number 6 to 12 or branched saturated hydrocarbyl group of carbon number 14 to 20. 
     
     
         3 . A lubricating oil composition according to  claim 2 , wherein said constituent (a) is a mixture of glyceryl mono-isostearate or glyceryl mono-octanate and dioctanate. 
     
     
         4 . A lubricating oil composition according to  claim 1 , wherein the alkyl group of the primary zinc dialkyl dithiophosphate and of the secondary zinc dialkyl dithiophosphate of said constituent (c) is a straight-chain or branched saturated hydrocarbyl group of carbon number 3 to 20. 
     
     
         5 . A lubricating oil composition according to  claim 1 , wherein the mixing ratio of the mixture of the primary zinc dialkyl dithiophosphate and the secondary zinc dialkyl dithiophosphate of said constituent (c) is 10 to 60 mass % of the primary and 40 to 90 mass % of the secondary, referred to the phosphorus content. 
     
     
         6 . A lubricating oil composition according to  claim 1 , wherein said lubricating oil base oil contains at least 50 mass %, referred to the total amount of the composition, of a base oil belonging to group 2, group 3 or group 4 in the base oil category established by the American petroleum Institute (API), or a mixture of these. 
     
     
         7 . A lubricating oil composition according to  claim 6 , wherein said lubricating oil base oil is of Fischer-Tropsch synthetic origin, its dynamic viscosity at 100° C. being 2.5 to 8.5 mm 2 /s. 
     
     
         8 . A lubricating oil composition according to  claim 1  wherein said lubricating oil composition is employed in a lubricated mechanism wherein the lubricating oil is in contact with copper and/or lead-containing metallic material in an internal combustion engine.