Lubricating oil composition

A method to lubricate a continuously variable transmission (CVT), comprising:

• applying a lubricating oil composition between a pulley and a belt or between a pulley and a chain of the CVT;
• wherein the lubricating oil composition comprises:
• a base oil;
• (A) an alkaline earth metal-based detergent (A) having a base number of from 10 to 500 mgKOH/g as measured according to the perchloric acid method of JIS K-2501,
• wherein the amount of the alkaline earth metal atom derived from the alkaline earth metal-based detergent (A) is from 10 to 1,500 ppm by mass;
• (B1) 0.01 to 0.5% by mass of a phosphite ester (B1) represented by the following formula (I):
• (R1O)aP(OH)3-a (I)
• wherein R1 represents a hydrocarbon group having 2 to 24 carbon atoms;
• a represents an integer of 1 to 3;
• and when a is 2 or 3, R1's may be the same as or different from each other,
• (B2) 0.01 to 0.5% by mass of a phosphate ester amine salt (B2) which is an amine salt of an acidic phosphate ester represented by the following formula (II):
• (R2O)bP(═O)(OH)3-b (II)
• wherein R2 represents a hydrocarbon group having 2 to 24 carbon atoms;
• b represents an integer of 1 or 2;
• and when b is 2, R2's may be the same as or different from each other,
• (B3) 0.01 to 0.8% by mass of an acidic phosphate ester (B3) represented by the following formula (III):
• (R3O)cP(═O)(OH)3-c (III)
• wherein R3 represents a hydrocarbon group having 2 to 24 carbon atoms;
• c represents an integer of 1 or 2;
• and when c is 2, R3's may be the same as or different from each other,
• (C1) 0.01 to 0.8% by mass of an aliphatic monoamine (C1) represented by the following formula (IV):
• NR4R5R6 (IV)
• wherein R4 represents an aliphatic hydrocarbon group having 10 to 24 carbon atoms;
• R5 and R6 each represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms;
• and R5 and R6 may be the same as or different from each other, and
• (C2) 0.05 to 0.7% by mass of an aromatic monoamine (C2) represented by the following formula (V):
• NR7R8R9 (V)
• wherein R7 represents an aromatic hydrocarbon group having 6 to 12 carbon atoms;
• R8 and R9 each represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms;
• and R8 and R9 may be the same as or different from each other;
• and further wherein
• an intermetallic friction coefficient according to ASTM D2714 of the lubricating oil is 0.114 or more, wherein the test is run under the following conditions:
• <Breaking-in conditions>
• Surface pressure:
• 0.8 GPa
• Oil temperature:
• 90° C.
• Average slipping velocity:
• 0.500 m/s
• Time:
• 30 minutes
• <Measurement conditions>
• Surface pressure:
• 0.8 GPa
• Oil temperature:
• 90° C.
• Average slipping velocity:
• 0.500 m/s
• <Material of test piece>
• Steel-steel;
• and
• a ratio of intermetallic friction-coefficient/slipping-velocity according to ASTM D2714 of the lubricating oil is 1.03 or less wherein the test is run under the following conditions:
• <Breaking-in conditions>
• Surface pressure:
• 0.8 GPa
• Oil temperature:
• 90° C.
• Average slipping velocity:
• 0.500 m/s
• Time:
• 30 minutes
• <Measurement conditions>
• Surface pressure:
• 0.8 GPa
• Oil temperature:
• 90° C.
• Average slipping velocity:
• 0.025 m/s and 0.500 m/s
• <Material of test piece>
• Steel-steel
• <Calculation method μ ratio>
• μ Ratio=(Friction coefficient at 0.025 m/s)/(Friction coefficient at 0.500 m/s).