Method of Viscosity Control

Abstract

This invention relates to a method of lubricating an internal combustion engine comprising at least one of a crankcase, a gear and a wet-clutch, said method comprising supplying to said crankcase, gear and wet-clutch a lubricating composition comprising: (a) an oil of lubricating viscosity; and (b) a viscosity modifier with a number average molecular weight from 1000 to 75,000, wherein the lubricating composition has a SAE viscosity grade from XW-Y, wherein X is from 0 to 20 and Y is from 20 to 50; and wherein the lubricating composition has a phosphorus content from a metal hydrocarbyl dithiophosphate of 0.12 wt % or less.

Description

FIELD OF INVENTION[0001]The present invention relates to a method of viscosity control by lubricating an internal combustion engine comprising at least one of a crankcase, a gear, and a wet-clutch with a lubricating composition.BACKGROUND OF THE INVENTION[0002]It is well known for lubricating oils to contain a number of additives used to protect the engine from wear and provide viscosity control. Common additives for engine lubricating oils include zinc dialkyldithiophosphate (ZDDP) an antiwear additive. It is believed that ZDDP antiwear additives protect the engine by forming a protective film on metal surfaces. Viscosity modifiers with a number average molecular weight above 100,000 are known in crankcase applications as viscosity modifiers because they help control high temperature viscometrics in multi-grade lubricants. Viscosity modifiers in various applications are known from, e.g., U.S. Pat. No. 5,112,509.[0003]Current and future government legislation regulating exhaust emis...

AI Technical Summary

Benefits of technology

The solution effectively controls wear, maintains acceptable fuel economy, and extends lubricant oil service life while adhering to emission regulations by stabilizing the lubricating film and reducing phosphorus content, thus preventing surface film breakdown.

Problems solved by technology

This reduction in the phosphorus and metal content of engine oils is being implemented because it is thought that they can adversely affect the performance of exhaust treatment devices.

However, any reduction in the performance of catalytic converters caused by phosphorus poisoning tends to result in increased amounts of greenhouse gases such as nitric oxide and / or ash formation.

Furthermore, reducing the amount of ZDDP will increase the amount of wear in an engine crankcase.

However, as the internal combustion engine has a common oil reservoir, the oil must be suitable for a crankcase application and a gear, a transmission system or a clutch mechanism which all have higher operating conditions resulting in a severe wear environment.

Therefore removing antiwear chemistry, such as, a phosphorus containing compound will tend to increase the amount of wear in the gear, transmission or clutch.

If a conventional crankcase viscosity modifier (with a number average molecular weight of 100,000 or more) is employed in combination with reduced amounts of antiwear chemistry, it is believed that surface film break down due to the viscosity modifier shear will give rise to increased wear.

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