Patent ID: 8785359

Claim:
A lubricant oil composition comprising: a lubricant base oil whose kinematic viscosity at 100° C. is 1 to 6 mm 2 /s, % C p is not less than 70, and % C A is not more than 2; a first viscosity index improver in which a ratio A/B of a viscosity increasing effect A of a kinematic viscosity at 100° C. represented by a following equation (1) to a viscosity increasing effect B of an HTHS viscosity at 150° C. represented by a following equation (2) when added to the lubricant base oil is a value of not less than 4.5, and a PSSI is not more than 30; and a second viscosity index improver in which the ratio A/B of the viscosity increasing effect A of the kinematic viscosity at 100° C. represented by the following equation (1) to the viscosity increasing effect B of the HTHS viscosity at 150° C. represented by the following equation (2) when added to the lubricant base oil is a value less than 4.5: A=X−X 0 (1) wherein A represents a viscosity increasing effect of the kinematic viscosity at 100° C., X represents a kinematic viscosity at 100° C. [units: mm 2 /s] of a mixture of the lubricant base oil with 3% by mass of the first or second viscosity index improver, and X 0 represents a kinematic viscosity at 100° C. [units: mm 2 /s] of the lubricant base oil, B=Y−Y 0 (2) wherein B represents a viscosity increasing effect of the HTHS viscosity at 150° C., Y represents an HTHS viscosity at 150° C. [units: mPa·s] of a mixture of the lubricant base oil with 3% by mass of the first or second viscosity index improver, and Y 0 represents an HTHS viscosity at 150° C. [units: mPa·s] of the lubricant base oil.