Lubricating oil composition for internal combustion engines

1. A lubricating oil composition for internal combustion engines, which comprises the following components:

(a) a lubricant base oil having a kinematic viscosity at 100° C. of from 2 to 12mm 2 /s, which is a single API group 2 or group 3 base oil having a viscosity index of 95 or higher, a sulfur content of 0.03 mass % or lower and % CA value of 1 or lower,

(b) a nitrogen-containing ashless dispersing agent at a quantity of 0.01-0.3 mass % in terms of nitrogen content relative to the overall composition, wherein a weight average molecular weight of the nitrogen-containing ashless dispersing agent ranges between 1,000 to 20,000,

(c) a metal-containing detergent, which contains calcium as an alkaline earth metal, at a quantity of 0.05-0.3 mass % in terms of alkaline earth metal content relative to the overall composition,

(d) a zinc dialkyldithiophosphate at a quantity of 0.05-0.13 mass % in terms of phosphorus content relative to the overall composition, and

(e) an oil-soluble semi-polar organic boron glycerol ester compound represented by chemical formula 1,

at a quantity of 0.015-0.040 mass % in terms of boron content relative to the overall composition, wherein R denotes a straight chain or branched chain alkyl group or straight chain or branched chain alkenyl group having 7-20 carbon atoms; and

wherein the lubricating oil composition comprises less than a ±10% change in kinematic viscosity at 40° C., a 1.5 mg KOH/g or less increase in total acid value, and a less than 100 ppm in an eluted copper (Cu) concentration.

2. A lubricating oil composition for internal combustion engines according to claim 1 , wherein the nitrogen-containing ashless dispersing agent contains an additive selected from among the group consisting of a boronated or non-boronated alkylsuccinimide or alkenylsuccinimide, a boronated or non-boronated alkylsuccinic acid ester or alkenylsuccinic acid ester, a boronated or non-boronated alkylsuccinic acid imide or alkenylsuccinic acid imide, a boronated or non-boronated alkylsuccinic acid amide or alkenylsuccinic acid amide, or an arbitrary combination thereof.

3. A lubricating oil composition for internal combustion engines according to claim 1 , wherein the metal-containing detergent contains a salicylate, a carboxylate or a sulfonate as a primary component.

4. A lubricating oil composition for internal combustion engines according to claim 1 , wherein the zinc dialkyldithiophosphate comprises a primary or secondary alkyl group having 3-8 carbon atoms.

5. A lubricating oil composition for internal combustion engines according to claim 1 , wherein the semi-polar organic boron glycerol ester compound is glycerol monooleyl glycerol borate, as represented by chemical formula 2