For decades zinc dialkyldithiophosphates (ZDDPs) have been used as extreme pressure (EP) and antiwear additives in engine oils. A problem with the use of these compounds, however, is that phosphorus contaminates catalysts used in exhaust gas after treatment devices and thereby reduces their effectiveness. In response to this problem, the phosphorus concentration has been reduced for some Society of Automotive Engineers (SAE) passenger car engine oil classifications. With the introduction of ILSAC GF-1, phosphorus levels were limited to no more than 1200 parts per million (ppm) and with GF-3 to 1000 ppm. Even at these levels of phosphorus, however, catalyst contamination is still an issue. The problem therefore is to provide adequate engine lubrication and at the same time reduce catalyst contamination. The disclosed invention, in at least one embodiment, provides a solution to this problem.
USPTO Backgrounds
USPTO Backgrounds