Engine oil compositions

Abstract

A low phosphorous or phosphorous-free sulfur lubricating oil composition and / or low phosphorous or phosphorous-free and low sulfur or sulfur-free lubricating oil composition for internal combustion engines comprising (a) a major amount of a base oil of lubricating viscosity and (b) a minor deposit-inhibiting effective amount of at least one polyol ester of the general formula wherein R1, R2 and R3 are independently aliphatic hydrocarbyl moieties having from 4 to about 24 carbon atoms, R4 is hydrogen or an aliphatic hydrocarbyl moiety having 1 to 10 carbon atoms and x, y and z are the same or different and are integers from 1 to 6, and additive compositions and additive packages containing the foregoing polyol ester are provided.

Description

BACKGROUND OF THE INVENTION 1. Technical Field The present invention generally relates to improved lubricating oils containing additives and additive mixtures for use in internal combustion engines. More particularly, the present invention is directed to low phosphorous lubricating oils and to low phosphorous and low sulfur lubricating oils compositions containing at least a base oil and a polyol ester. 2. Description of the Related Art Automobile spark ignition and diesel engines have valve train systems, including valves, cams and rocker arms which present special lubrication concerns. It is extremely important that the lubricant, i.e., the engine oil, protects these parts from wear. It is also important for engine oils to suppress the production of deposits in the engines. Such deposits are produced from non-combustibles and incomplete combustion of hydrocarbon fuels (e.g., gasoline, diesel fuel oil) and by the deterioration of the engine oil employed. Engine oils typically ...

AI Technical Summary

Benefits of technology

The present invention advantageously provides lubricating oil compositions which provide high antiwear, oxidation-corrosion and deposit protection in an engine, but which have only low levels of phosphorous, i.e., less than 0.1%, preferably not exceeding 0.08% and more preferably not exceeding 0.05% by weight and low levels of sulfur, i.e., not exceeding 0.2% by weight. Accordingly, the lubricating oil compositions of the present invention are more environmentally desirable than the higher phosphorous and sulfur lubricating oil compositions generally used in internal combustion engines because they facilitate longer catalytic converter life and activity while also providing the desired high wear and deposit protection and oxidation-corrosion inhibition. This is due to the decreased levels of additives containing phosphorus and sulfur compounds in these lubricating oil compositions. Conventional lubricating oil compositions, on the other hand, typically contain relatively high concentrations of such additives.

Problems solved by technology

However, simple base oils alone do not provide the necessary properties to provide adequate wear protection, deposit control, etc. required to protect internal combustion engines.

However, a problem has arisen with respect to the use of zinc dialkyldithiophosphate, because phosphorous and sulfur derivatives poison catalyst components of catalytic converters.

As previously mentioned, these catalyst components are poisoned by the phosphorous and sulfur components, or the phosphorous and sulfur decomposition product of the zinc dialkyldithiophosphate; and accordingly, the use of engine oils containing phosphorous and sulfur additives may substantially reduce the life and effectiveness of catalytic converters.

However, simply decreasing the amount of zinc dialkyldithiophosphate presents problems because this necessarily lowers the antiwear properties and oxidation inhibition properties of the lubricating oil.

However, the use of such known oxidation inhibitors in place of zinc dialkyldithiophosphate at best only marginally satisfies the required levels of antiwear, oxidation inhibition and deposit control.

However, detergents may impart undesirable properties.

For example, overbased sulfonates such as magnesium sulfonate detergents are also effective to enhance the antiwear properties in valve train systems, but have drawbacks in that crystalline precipitates are sometimes produced when these engine oils are stored under humid or variable temperature conditions for a long period of time.

Such precipitates may cause plugging of the filter which is installed in the engine oil circulating system.

Accordingly, as demand for further decrease of the phosphorous content and a limit on the sulfur content of lubricating oils is very high, this reduction cannot be satisfied by the present measures in practice and still meet the severe antiwear and oxidation-corrosion inhibiting properties, as well as cleanliness (i.e., deposit protection) required of today's engine oils.

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