Combinations of phosphorous-containing compounds for use as anti-wear additives in lubricant compositions

A lubricant composition comprising:

• (a) a first phosphorus compound formed by:
• (i) reacting an O,O-dihydrocarbyl phosphorodithioic acid with an epoxide to form a product;
• (ii) reacting the product with phosphorus pentoxide to produce an acid phosphate intermediate;
• and
• (iii) neutralizing at least a major portion of the intermediate with at least one first amine;
• (b) a second phosphorus compound formed by reacting a sulfur source with a dihydrocarbyl phosphite;
• (c) a third phosphorus compound formed by reacting an acid phosphate with at least one second amine;
• and
• (d) a base fluid in a major amount, the base fluid comprising a base oil and a sulfurized isobutylene extreme pressure additive;
• wherein the first and second amine are the same or different,
• wherein the first phosphorus compound is present in the lubricant composition to provide between about 120 and about 350 ppm phosphorus to the lubricant composition,
• wherein the second phosphorus compound is present in the lubricant composition to provide between about 400 and about 500 ppm phosphorus to the lubricant composition,
• wherein the third phosphorus compound is present in the lubricant composition to provide up to 525 ppm phosphorus to the lubricant composition,
• wherein the total amount of phosphorus present in the lubricant composition is between about 820 and about 1375 ppm,
• wherein the lubricant composition lasts at least 300 hours without failure when subjected to the FZG Pitting Test, and
• wherein the lubricant composition maintains an iron level at or below 320 ppm when subjected to a High Temperature L-37 Test according to ASTM D-6121.