Low phosphorus lubricating oil composition having lead corrosion control

Abstract

The present invention provides a low phosphorus lubricating oil composition containing a mixture of zinc dithiophosphates in a certain ratio surprisingly yields improved lead corrosion. The synergistic combination of mixed zinc dithiophosphates containing a zinc primary dialkyl dithiophosphate, zinc secondary dialkyl dithiophosphate and zinc diaryl dithiophosphate in a respective ratio, based on the phosphorus content, of the zinc primary dialkyl dithiphosphate to zinc secondary dialkyl dithiophosphate from about 2:1 to about 1:2 and the ratio of the mixture of zinc primary dialkyl dithiophosphate and zinc secondary dialkyl dithiophosphate to zinc diaryl dithiophosphate from about 6:1 to about 1:1. When used in a lubricating oil composition having a total phosphorus content less than about 0.06 wt %, based on the total weight of the lubricating oil composition to lubricate internal combustion engines. The mixture of zinc dithiophosphates greatly reduces lead corrosion.

Description

[0001]The present invention is related, in part, to a lubricating oil composition. More particularly, the present invention relates to a low phosphorus lubricating oil composition employing a mixture of zinc dithiophosphates and wherein the lubricating oil composition has less than about 0.06 wt % total phosphorus content based on the total weight of the lubricating oil composition. The low phosphorus lubricating oil composition of the present invention is effective in lead corrosion control when used as a lubricating oil composition in internal combustion engines.BACKGROUND OF THE INVENTION[0002]Emissions arising from automotive exhaust has been a problem for several decades and approaches for addressing this problem have included the use of unleaded fuel (to deal, in part, with lead pollution arising from leaded fuels), oxygenated fuel (to reduce hydrocarbon emissions), the use of catalytic converters (also to reduce hydrocarbon emissions), etc.[0003]Catalytic converters are now u...

AI Technical Summary

Benefits of technology

[0009]As previously mentioned, the present invention is related, in part, to a lubricating oil composition. More particularly, the present invention relates to a low phosphorus lubricating oil composition employing a mixture of zinc dithiophosphates in a certain ratio and wherein the lubricating oil composition has less than about 0.06 wt % total phosphorus content, based on the total weight of the lubricating oil composition. The low phosphorus lubricating oil composition of the present invention is effective in lead corrosion control when used as a lubricating oil composition in internal combustion engines.

[0022]Among other factors, the present invention provides a low phosphorus lubricating oil composition containing a mixture of zinc dithiophosphates in a certain ratio surprisingly yields improved lead corrosion. The mixture of zinc dithiophosphates contains a zinc primary dialkyl dithiophosphate, a zinc secondary dialkyl dithiophosphate and a zinc diaryl dithiophosphate. The synergistic combination of mixed zinc dithiophosphates wherein the respective ratio, based on the phosphorus content, of the zinc primary dialkyl dithiophosphate to zinc secondary dialkyl dithiophosphate is from about 2:1 to about 1:2 and the ratio of the mixture of zinc primary dialkyl dithiophosphate and zinc secondary dialkyl dithiophosphate to zinc diaryl dithiophosphate is from about 6:1 to about 1:1 when used in a lubricating oil composition having a total phosphorus content less than about 0.06 wt %, based on the total weight of the lubricating oil composition, greatly reduces lead corrosion when used to lubricate internal combustion engines.

Problems solved by technology

One problem arising with the use of such converters is poisoning of the catalyst resulting in reduced catalyst efficiency.

Since catalytic converters are intended for extended use, catalyst poisoning results in higher levels of atmospheric discharges of pollutants from internal combustion engines over prolonged periods of time.

In any event, the phosphorus is known to accumulate in the catalytic converter, at active metal sites; thus reducing catalyst efficiency and effectively over time, poisoning the catalyst.

A problem arises when the level of phosphorus is reduced in a lubricant composition containing an oil-soluble, phosphorus-containing, anti-wear compound in that there is a significant reduction in anti-wear performance arising from the diminution in phosphorus content.

At lower levels, it is not found to be an effective antiwear additive.

For instance, as exemplified in U.S. Pat. No. 6,696,393, issued Feb. 24, 2004, lowering the level of phosphorus glue to the presence of a metal dithiophosphate additive in a lubricant composition by one-half from 0.095 weight percent to 0.048 weight percent phosphorus results in about a seven-fold increase in engine wear.

Images