Lubricating oil composition

Abstract

A lubricating oil composition has excellent oxidation stability, suitable as a lubricating oil for internal combustion engines and automatic transmissions. The lubricating oil composition includes a lubricating base oil and one or more types of phosphorus compound represented by formula (1) as Component (A), the element ratio of sulfur derived from the compound of formula (1) to phosphorus in the oil (S/P molar ratio) being from 0.05 to 0.8 and the amount of phosphorus derived from Component (A) in the oil being from 0.01 to 0.5 percent by mass (in formula 1, R 1 through R 4 are each a hydrocarbon group with 1 to 30 carbon atoms or an alkylthioethyl group having an alkyl or alkenyl group with 1 to 30 carbon atoms and may be the same or different from one another, X 1 to X 4 are each independently sulfur or oxygen, and Y represents a metal element).

1 . A lubricating oil composition comprising a lubricating base oil and one or more type of phosphorus compound represented by formula (1) below as Component (A), the element ratio of sulfur derived from the compound of formula (1) to phosphorus in the oil (S/P molar ratio) being from 0.05 to 0.8 and the amount of phosphorus derived from Component (A) in the oil being from 0.01 to 0.5 percent by mass: 
       
         
           
           
               
               
           
         
       
       wherein R 1  through R 4  are each a hydrocarbon group with 1 to 30 carbon atoms or an alkylthioethyl group having an alkyl or alkenyl group with 1 to 30 carbon atoms and is the same or different from one another, X 1  to X 4  are each independently sulfur or oxygen, and Y represents a metal element. 
     
     
         2 . The lubricating oil composition according to  claim 1  wherein the metal element Y of the phosphorus compound represented by formula (1) is zinc, molybdenum or a combination of zinc and molybdenum. 
     
     
         3 . The lubricating oil composition according to  claim 1  wherein the phosphorus compounds represented by formula (1) are a compound where all of X 1  through X 4  are oxygen and a compound where at least one of X 1  through X 4  is sulfur. 
     
     
         4 . The lubricating oil composition according to  claim 1  wherein at least one type of phosphorus compound represented by formula (1) is a compound where the metal element is molybdenum and contained in an amount of 0.03 percent by mass or less on the basis of Mo. 
     
     
         5 . The lubricating oil composition according to  claim 1  further comprising (B) an ashless anti-oxidant. 
     
     
         6 . The lubricating oil composition according to  claim 5  wherein (B) the ashless anti-oxidant is an aromatic amine-based anti-oxidant.