Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Solid hydrocarbon polymer
Reexamination Certificate
1999-06-25
2001-05-15
Johnson, Jerry D. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Solid hydrocarbon polymer
Reexamination Certificate
active
06232279
ABSTRACT:
This invention relates to a lubricant composition suitable for use in automotive engines, especially internal combustion engines.
The viscosity grade of an engine oil is a key feature when selecting a lubricant. The oil is chosen according to both the climatic temperatures to which the engine is exposed, and the temperatures and shear conditions under which the engine operates. Thus the oil must be of sufficiently low viscosity at ambient temperatures to provide adequate lubrication upon cold-starting of the engine, but must maintain sufficient viscosity to provide lubrication of the engine under full operating conditions where, for example, the temperature in the piston zone may reach 300° C. or more.
To meet both the high and low temperature viscosity requirements a multigrade engine oil is usually selected. Under the Society of Automotive Engineers classification system SAE (J 300) a passenger car multigrade engine oil is, for example, a 5W-40, 10W-40 or 15W-40 grade. The W grades are based on maximum low temperature dynamic viscosity under cold cranking conditions, as well as a minimum kinematic viscosity at 100° C. For example, a 5W grade has a maximum dynamic viscosity of 3500 mPa.s at −25° C. under a shear rate of 10
5
/s (Standard Cold Crankingr Simulator test ASTM D 2602), and a minimum kinematic viscosity at 100° C. of 3.8 mm
2
/s (ASTM D 445). A 40 grade indicates a miniiuium kinematic viscosity of 12.5 mm
2
/s at 100° C. and a maximum of less than 16.3 mm
2
/s at 100° C. To achieve multi-grade viscosity properties, the engine oil formulations contain a viscosity index (VI) improver. These are polymeric materials such as polymethylacrylic acid esters, for example polymethyl-acrylate. Whilst VI improvers have the advantage that they reduce the temperature dependency of the oil's viscosity, they have the disadvantage that they cause the oil to become non-Newtonian in behaviour, i.e. the oil tends to suffer viscosity loss under high shearing stress. This is believed to be due to the breakup of inter-molecular bonds between the polymer chains of the VI improver, and also to the breaking of the polymer chains themselves, the type and extent of the breaking depending upon the nature of the specific VI improver employed and the severity of the shearing conditions. To ensure that an engine oil has sufficient viscosity under conditions of high shear and high temperature, such as those found in today's severe engine operating conditions, particularly in the region of the crankshaft bearings, some vehicle engine manufacturers have introduced a test which specifies a minimum dynamic viscosity of the oil under specified high temperature, high shear (HTHS) conditions (ASTM D 4741). Of the standard European engine tests devised by the Association des Constructeurs Européen d'Automobiles, the tests ACEA A2-96/A3-96 /B2-96/B3-96/E2-96 and E3-96 each require a minimum HTHS viscosity of 3.5 mPa.s at 150° C. and a shear rate of 10
6
/s; and tests ACEA A1-96 and B1-96 each require a minimum HTHS of 2.9 mPa./s at 150° C. and a shear rate of 10
6
/s.
In recent years there has been an increasing concern to improve the fuel economy performance of automotive engines, particularly passenger car engines. One factor influencing fuel economy is the viscosity of the engine oil—the lower the viscosity the lower the viscous drag on the engine and hence the better the fuel economy performance. Accordingly there is beginning to be a trend towards selecting lower grade multigrade oils such as 0W-30 or 5W-30 or even 0W-20 or 5W-20. 0W and 5W grades must have respectively maximum dynamic viscosities of 3250 mPa.s at −30° C. and 3500 mPa.s at −25° C., and a minimum kinematic viscosity at 100°C. of 3.8 mm
2
/s. A 30 grade must have a minimum kinematic viscosity at 100° C. of 9.3 mm
2
/s and a maximum of less than 12.5 mm
2
/s; and a 20 grade must have a kinematic viscosity at 100° C. from 5.6 mm
2
/s to less than 9.3 mm
2
/s.
However, these lower viscosity grade oils must still meet the HTHS minimum dynamic viscosity requirements of the above-mentioned ACEA A classifications in order to provide adequate lubrication to the engine. This is the problem addressed by the present invention.
The present invention provides a lubricant composition having a kinematic viscosity at 100° C. (ASTM D 445) of less than 12.5 mm
2
/s and a high temperature, high shear dynamic viscosity at a temperature of 150° C. and a shear rate of 10
6
/s (ASTM D 4741) of at least 2.9 mpa.s, which composition comprises, or is formulated from blending:
(a) from 70 to 99.5 wt. % base oil having a kinematic viscosity at 100° C. of from 2 to 8 mm
2
/s and a viscosity index of at least 120; and
(b) from 0.5 to 3 wt. % alkenylarene-conjugated diene copolymer as a viscosity index improver,
the weight percents being based on the total weight of the composition.
Thus it has been found that by selecting a specific type of VI improver, mainly an alkenylarene-conjugated diene copolymer, and combining this with a relatively liow viscosity, high inherent VI base oil, then, for a given minimum HTHS viscosity which is sufficiently high to provide adequate lubrication of engine parts operating under conditions of high temperature and high shear, an engine oil can be formulated with lower high temperature kinematic viscosity than has previously been achievable, thereby providing fuel economy benefits.
In one specific embodiment, the invention provides a lubricant composition having a kinematic viscosity at 100° C. of less than 12.5 mm
2
/s and a HTHS viscosity of at least 3.5 mPa.s at 150° C. and a shear rate of 10
6
/s, which composition comprises, or is formulated by blending:
(a) from 70 to 99.5 wt. % base oil having a kinematic viscosity at 100° C. of from 2 to 8 mm
2
/s and a viscosity index of at least 120; and
(b) from 1 to 3 wt. % alkenylarene-conjugated diene copolymer as a viscosity index improver,
the weight percents being based on the total weight of the composition.
An engine oil according to this specific embodiment meets the SAE 30 grade. Preferably the base oil is selected so the engine oil meets the requirements of a 5W or a 0W grade as well, i.e. the engine oil is a 5W-30 or 0W-30 multigrade oil. The minimium HTHS viscosity of 3.5 mPa.s at 150° C. means that the lubricant meets the requirement of standard engine test specifications ACEA A2-96/A3-96/B2-96/B3-96/E2-96 and E3 -96. Preferably the engine oil according to this specific embodiment has a kinematic viscosity at 100° C. of no more than 11.5 mm
2
/s, more preferably no more than 11.0 mm
2
/s.
In another specific embodiment, the invention provides a lubricant composition having a kinematic viscosity at 100° C. of less than 9.3 mm
2
/s and an HTHS viscosity of at least 2.9 mPa.s at 150° C. and a shear rate of 10
6
/s, which composition comprises, or is formulated by blending:
(a) from 70 to 99.5 wt. % base oil having a kinematic viscosity at 100° C. of from 2 to 8 mm
2
/s and a viscosity index of at least 120; and
(b) from 0.5 to 0.99 wt. % alkenylarene-conjugated diene copolymer as a viscosity index improver,
the weight percents being based on the total weight of the composition.
An engine oil according to the second specific embodiment meets the SAE 20 grade. Preferably the base oil is selected so that the engine oil meets the requirements of a 5W or a 0 W grade as well, i.e. the engine oil is a 5W-20 or 0W-20 multigrade oil. The minimum HTHS viscosity of 2.9 mPa.s at 150° C. means that the lubricant meets the requirement of standard engine test specifications ACEA A1-96 and B1-96, whilst the even lower viscosity 20 grade provides enhanced fuel economy benefits.
In formulating the lubricant composition according to the invention any suitable base oil may be used provided it meets the requirements of having a kinematic viscosity at 100° C. of 2-8 mPa.s and a VI of at least 120, preferably from 120 to 160. In practice, this means the base oil is selected from one or more of synthetic oils, hydro-isomerised petroleum-derived hydrocarbons, and hydrocra
Allocca Joseph J.
Exxon Research and Engineering Company
Johnson Jerry D.
LandOfFree
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