Lubricant composition for automobile driving system

Abstract

A lubricant composition having a 40° C. dynamic viscosity of 40 mm 2 /s or less that has wear resistance equal to or better than a lubricant having a 40° C. dynamic viscosity of 76 mm 2 /s is achieved by providing a base oil with a zinc dithiophosphate and alkaline earth metal salt in an amount to provide a ratio of elemental zinc to alkaline earth metal in the oil in the range of 0.2 to 1.0.

1 . A lubricant composition for a manual speed-change gear comprising: 
 a base oil;    additives comprising    at least one alkaline earth metal salt and a zinc dithiophosphate, the amount of alkaline earth metal element based on the total weight of lubricant composition being 0.1 wt % or more,    the elemental ratio of zinc to alkaline earth metal from the additive being in the range of 0.2 to 1.0; and    wherein the dynamic viscosity at 40° C. of the lubricant is 40 mm 2 /s or less.    
   
   
       2 . The lubricant composition of  claim 1  wherein the amount of alkaline earth metal is from about 0.15 wt % to about 0.6 wt %.  
   
   
       3 . The lubricant composition of  claim 1  wherein the dynamic viscosity at 40° C. is 30 mm 2 /s or less.  
   
   
       4 . The lubricant composition of  claim 1  wherein the alkaline earth metal salt is selected from the group consisting of sulfonates, salicylates and phenolates.  
   
   
       5 . The lubricant composition of  claim 1  wherein the alkaline earth metal salt is a metal sulfonate.  
   
   
       6 . The lubricant composition of  claim 4  wherein the metal sulfonate is magnesium sulfonate.  
   
   
       7 . The lubricant composition of claims  1  and  6  wherein the ratio of zinc to alkaline earth metal is 0.3 to 0.8.  
   
   
       8 . In the method of increasing the wear resistance of manual speed-change gears by lubricating the gears, the improvement comprising: 
 lubricating the gears with a lubricant composition having a dynamic viscosity at 40° C. of 40 mm 2 /s or less and containing an additive comprising an alkaline earth metal salt and a zinc dialkylthiophosphate, the amount of alkaline earth metal element in the lubricant being 0.1 wt % or more based on the total weight of the lubricant; and    the elemental ratio of zinc to alkaline earth metal is from 0.2 to 1.0.    
   
   
       9 . The improvement of  claim 8  wherein: the alkaline earth metal salt is selected from the group consisting of sulfonates, salicylates and phenolates; 
 the amount of alkaline earth metal is from 0.15 wt % to 0.6 wt %; and    the elemental ratio of zinc to alkalinic earth metal is from 0.3 to 0.8.    
   
   
       10 . The improvement of  claim 9  wherein the alkaline earth metal salt is magnesium sulfonate.