Patent ID: 8349778

Claim:
A method of reducing boundary friction and thin film friction of a lubricating fluid in an engine, said method comprising: providing to the engine a lubricating composition comprising: a major amount of a base oil; and a minor amount of an additive composition comprising (i) at least metal dihydrocarbyl dithiophosphate compound prepared by a secondary alcohol, and (ii) a phosphate salt consisting essentially of a salt of at least one hydrocarbylamine and at least one sulfur-free hydrocarbyl acid phosphate, wherein the ratio of (i) to (ii) ranges from about 90:10 to about 10:90, wherein (i) and (ii) are present in amounts sufficient to yield an engine lubricating composition having a phosphorus content ranging from about 250 ppm to about 1000 ppm, and reduced boundary friction and thin film friction compared to the same lubricating composition devoid of components (i) and (ii) in the claimed ratio.