Patent ID: 8796194

Claim:
A lubricating oil composition comprising: a lubricating base oil having a kinematic viscosity at 100° C. of 1-6 mm 2 /s, a % C p value of 70 or greater and a % C A value of no greater than 2, and a viscosity index improver which, when added to the lubricating base oil, results in an A/B ratio of less than 3.2 between the thickening effect A on the kinematic viscosity at 100° C. represented by the following formula (1) and the thickening effect B on the HTHS viscosity at 150° C. represented by the following formula (2), and a C/B ratio of less than 1.5 between the thickening effect C on the HTHS viscosity at 100° C. represented by the following formula (3) and the thickening effect B on the HTHS viscosity at 150° C. represented by the following formula (2): A=X−X 0 (1) wherein A represents the thickening effect on the kinematic viscosity at 100° C., X represents the kinematic viscosity at 100° C. by mm 2 /s of a mixture of the lubricating base oil and the viscosity index improver at 3% by mass, and X 0 represents the kinematic viscosity at 100° C. by mm 2 /s of the lubricating base oil, B=Y−Y 0 (2) wherein B represents the thickening effect on the HTHS viscosity at 150° C., Y represents the HTHS viscosity at 150° C. by mPa·s of a mixture of the lubricating base oil and the viscosity index improver at 3% by mass, and Y 0 represents the HTHS viscosity at 150° C. by mPa·s of the lubricating base oil, C=Z−Z 0 (3) wherein C represents the thickening effect on the HTHS viscosity at 100° C., Z represents the HTHS viscosity at 100° C. by mPa·s of a mixture of the lubricating base oil and the viscosity index improver at 3% by mass, and Z 0 represents the HTHS viscosity at 100° C. by mPa·s of the lubricating base oil.