Long life lubricating oil composition using particular antioxidant components

Abstract

A natural gas engine oil composition with enhanced resistance to oxidation, nitration and viscosity increase comprising: an oil basestock; neutral and overbased metallic detergents; an antioxidant comprising an alkylthiocarbamoyl compound or a mixture of an alkylthiocarbamoyl compound and an ashless, non-sulfur containing, hindered phenol; and a zinc dihydrocarbyl dithiophosphate in an amount sufficient to provide the composition with from 250 to 450 wppm phosphorus.

1 . A natural gas engine lubricating oil composition having enhanced resistance to oxidation, nitration and viscosity increase comprising: 
 a major amount of an oil of lubricating viscosity;    a minor amount of a detergent mixture comprising low/neutral TBN and over based metallic detergents selected from the group consisting of alkali and alkaline earth sulphonates, phenates, and salicylates;    a minor amount of an antioxidant comprising an alkylthiocarbamoyl compound or a mixture of an alkylthiocarbamoyl compound and an ashless, non-sulfur containing hindered phenol; and    a zinc dihydrocarbyl dithiophosphate in an amount sufficient to provide the composition with from 250 to 450 wppm phosphorus.    
     
     
         2 . The composition of  claim 1  wherein the oil basestock has a kinematic viscosity at 100° C. of about 5 to about 16 cSt.  
     
     
         3 . The composition of  claim 2  wherein, based on the total volume of the composition the detergents comprise from about 0.5 volume % to about 10 volume %.  
     
     
         4 . The composition of  claim 3  wherein the antioxidant is an alkylthiocarbamoyl compound which comprises about 0.25 volume % to about 2.0 volume % of the composition.  
     
     
         5 . The composition of  claim 3  wherein the antioxidant is a mixture of an alkylthiocarbamoyl compound and an ashless, non-sulfur containing hindered phenol, wherein the alkylthiocarbamoyl compound comprises 0.25 volume % to 1.5 volume % of the composition and the phenol, 0.25 volume % to 1.5 volume % of the composition.  
     
     
         6 . The composition of  claim 4  or  5  wherein the alkylthiocarbamoyl compound is represented by the formula  
       
         
           
           
               
               
           
         
       
       where R 1 , R 2 , R 3  and R 4  are the same or different linear and branched alkyl groups of from 1 to 18 carbon atoms, X is S, S—S, S—(CH 2 ) y —S, S—CH 2 —CH(R 5 )—S; y is an integer of 1 to 4, and R 5  is an alkyl group of 1 to 2 carbons. Preferably R 1 , R 2 , R 3  and R 4  are C 4  alkyl, X is S(CH 2 ) y S, Y is 1-3.  
     
     
         7 . The composition of  claim 5  wherein the ashless, non-sulfur containing, hindered phenol is represented by the formulae:  
       
         
           
           
               
               
           
         
       
       where R 1 , R 2  and R 3  are the same or different alkyl groups of 1 to 18 carbon atoms.