Lubricating oil composition for internal combustion engine

Abstract

A lubricating oil composition for an internal combustion engine, which includes a base oil, (A) at least one member selected from the group consisting of disulfide compounds represented by the general formula (I): R 1 OOC-A 1 -S—S-A 2 -COOR 2   (I) and disulfide compounds represented by the general formula (II): R 7 OOC—CR 9 R 10 —CR 11 (COOR 8 )—S—S—CR 16 (COOR 13 )—CR 14 R 15 —COOR 12   (II), and (B) at least one member selected from the group consisting of alkali metal-based detergents and alkaline earth metal-based detergents, the component (B) being present in an amount of 10 to 2,000 ppm by mass in terms of metal content. The lubricating oil composition has a low ash content, a low phosphorous content and a low sulfur content. But, Nonetheless, it can maintain wear resistance, has excellent heat resistance, can extend the lubricating oil change interval and has a long service life.

1 . A lubricating oil composition for an internal combustion engine, includes a base oil; (A) at least one member selected from the group consisting of disulfide compounds represented by the general formula (I):
   R 1 OOC-A 1 -S—S-A 2 -COOR 2   (I)   
     (wherein R 1  and R 2  each independently represent a C 1  to C 30  hydrocarbyl group which may contain an oxygen atom, a sulfur atom or a nitrogen atom, and A 1  and A 2  each independently represent a group expressed by CR 3 R 4  or CR 3 R 4 —CR 5 R 6  where R 3  to R 6  each independently represent a hydrogen atom or C 1  to C 20  hydrocarbyl group), and disulfide compounds represented by the general formula (II):
   R 7 OOC—CR 9 R 10 —CR 11 (COOR 8 )—S—S—CR 16 (COOR 13 )—CR 14 R 15 —COOR 12   (II) 
 
     (wherein R 7 , R 8 , R 12  and R 13  each independently represent a C 1  to C 30  hydrocarbyl group which may contain an oxygen atom, a sulfur atom or a nitrogen atom and R 9  to R 11  and R 14  to R 16  each independently represent a hydrogen atom or C 1  to C 5  hydrocarbyl group), and (B) at least one member selected from the group consisting of alkali metal-based detergents and alkaline earth metal-based detergents, the component (B) being present in an amount of 10 to 2,000 ppm by mass in terms of metal content. 
   
   
       2 . The lubricating oil composition for an internal combustion engine as defined in  claim 1 , wherein the component (A) being at least one member selected from the disulfide compounds is present in an amount of 0.01 to 0.50% by mass in terms of sulfur content. 
   
   
       3 . The lubricating oil composition for an internal combustion engine as defined in  claim 1 , wherein the alkali metal-based or alkaline earth metal-based detergent of the component (B) is a salicylate and/or a sulfonate. 
   
   
       4 . The lubricating oil composition for an internal combustion engine as defined in  claim 1 , wherein the metal of the component (B) is Ca or Mg.