Method of lubricating an internal combustion engine and improving the efficiency of the emissions control system of the engine

A method of lubricating an internal combustion engine and improving the efficiency of the emissions control system of the engine, the emissions control system being equipped with a catalyst containing exhaust gas after treatment device, the method comprising:

• (A) selecting a lubricating oil composition comprising:
• a base oil;
• an alkali or alkaline earth metal-containing detergent, the alkali or alkaline earth metal being sodium, lithium or calcium;
• a zinc salt of a phosphorus-containing compound represented by the formula
• wherein R1 and R2 independently hydrocarbyl groups, the average total number of carbon atoms per phosphorus-containing moiety being at least 10.4, wherein at least one of the R1 and R2 groups in one or more of the phosphorus-containing compounds contains 4 or fewer carbon atoms and up to about 40 percent of all the R1 and R2 groups supplied by the phosphorus-containing metal salt contain 4 or fewer carbon atoms;
• at least about 80% by weight of the phosphorus present in the lubricating oil composition being present in a compound represented by formula (II) wherein one of R1 and R2 is a hydrocarbyl group of about 6 to about 18 carbon atoms;
• and a polyisobutene substituted succinimide having a TBN of about 5 to about 30, the polyisobutene substituent having a number average molecular weight in the range of about 700 to about 3000;
• the lubricating oil composition being characterized by a phosphorus concentration of no more than about 0.12% by weight and the substantial absence of copper;
• (B) adding the lubricating oil composition to the engine;
• (C) operating the engine;
• (D) generating a lean-phosphorus containing exhaust gas;
• and (E) contacting the catalyst in the exhaust gas after treatment device with the lean-phosphorus containing exhaust gas.

A method of lubricating an internal combustion engine and improving the efficiency of the emissions control system of the engine, the emissions control system being equipped with a catalyst containing exhaust gas after treatment device, the method comprising:

• (A) selecting a lubricating oil composition comprising:
• a base oil;
• an alkali or alkaline earth metal-containing detergent;
• a metal salt of one or more phosphorus-containing compounds represented by the formula
• wherein in formula (I), X1 and X2 are independently O or S, and R1 and R2 are independently hydrocarbyl groups, the average total number of carbon atoms per phosphorus-containing moiety being at least 10.4, wherein at least one of the R1 and R2 groups in one or more of the phosphorus-containing compounds contains 4 or fewer carbon atoms and up to about 40 percent of all the R1 and R2 groups supplied by the phosphorus-containing metal salt contain 4 or fewer carbon atoms, and at least 60 mole percent of all the R1 and R2 groups supplied by the phosphorus-containing metal salts are derived from secondary alcohols;
• and an acylated nitrogen containing compound having at least about 10 aliphatic carbon atoms and a TBN of at least about 2;
• the lubricating oil composition being characterized by a phosphorus concentration of up to about 0.12% by weight and the substantial absence of copper;
• (B) adding the lubricating oil composition to the engine;
• (C) operating the engine;
• (D) generating a lean-phosphorus containing exhaust gas;
• and (E) contacting the catalyst in the exhaust gas after treatment device with the lean-phosphorus containing exhaust gas.