CA1169046A - Aviation motor oil - Google Patents

Abstract

Abstract of the Disclosure A multigrade lubricating oil composition for airplane engines containing 0.7 to 3 volume percent of a specific butadiene-styrene copolymer and 0.05 to 1.0 volume percent of an ashless pour point depressant. The preferred aviation lubricating oil contains in addition an ashless dispersant additive package.

Description

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AVIATION MOTOR OIL
This invention relates to an aviation motor oil process for operating an aviation piston engine.
Background_of the Invention Multlgrade lubricating oils have been known for use in automobile engines for some time. A multitude of additives for lubricating oils have been developed to produce lubricating oils for automobiles useful in varying conditions. Some multigrade oils for aircraft piston engines such as SAE lOW-30 and SAE 20W-40 oils have been developed, but they were recommended for use in lighter, smaller engines in winter and not recommended for high performance radial or opposed piston engines. The ; ~ oils were not suitable for high temperature summer operation.
A variety of polymeric additives have been employed as viscosity index improvers and pour point depressants for lubricating oils used in automobile engines. However most were sub~ect to shear degradation in air cooled aircraft engines. Cylinder head temperatures in aircraft piston ; engines may average 460F. It~is well known that the air cooled aircraft piston engines operate at higher cylinder temperatures than water cooled automobile engines.
Therefore, aircraft service stations had to maintain a supply of several single weight grades of aviation lubricating oils to accomodate different piston engine needs~at different weather and season conditions.
: An aviation oil with~good low temperature flow and high viscosity properties at~higll temperatures would thus be;very desirable. Starting at low temperature with too viscous an oil results in excessive engine wear due to poor oil circulation immediately after start. ~This made it necessary ae times to heat the very cold engines externally before starting, at increased expense and inconvenience.
Statement o~ the Invention :, ~
; It is one object~of this invention to provide a multigrade aviation lubricating oil having a relatively low viscosity at low temperatures : : : :

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-2- 28106 and a sufficiently high viscosity at higher temperatures.
Another object of this invention is to provide a process for operating an airplane engine avoiding the necessity of having to change oils when rapid temperature changes are caused by the weather.
These and other objects, advantages, details, and embodiments of this invention will become apparent to those skilled in the art from the following description thereof and the appended claims.
In accordance with this invention it has surprisingly been found that a lubricating oil composition to be defined showed excellent viscosity behavior at a wide range of temperatures so that it could be used as a multigrade lubricating oil and that this lubricating oil was capable of sustaining the extreme temperature conditions at which an air-; plane engine is operated for extended periods of time. The lubricating oil composition of this invention therefore is capable of being used as an airplane engine lubricating oil.
In accordance with one embodiment of this invention a lubricatingoil composition useful for airplane piston engine lubrication is provided which consists essentially of a multigrade lubricating oil basestock, 0.7 to 3 volume percent of an oil soluble butadiene-styrene copolymer defined in more detail in the following and 0.05 to 1 volume percent of a ; pour point depressant.
According to the present invention a multiviscosity aircraft piston engine lubricating oil composition is provided which, due to a unique combination of additives has shear stability at high operating temperatures. It has been found that incorporation of a pour point depressant,and a unique viscosity index improver with a blend of suitable lubricating oil base stocks, provides a multiviscosity, nondispersant mineral oil suitable for aircraft engine use.
For a more general purpose aviation oilj the addition of an ashless dispersant, oxidation inhibitor additive package pr~vides a multi-viscosity oil suitable for both low temperature aircraft piston engine start-up, at 0F, and high temperature operating conditions of aircraft piston engines. This is surprising since earlier attempts by aviation oil ~ manufacturers to formulate multiviscosity aviation oil spanning 3 grades, ; such as SAE 20W-50 have resulted in insufficient shear stability for ~; operation of air cooled aircraft engines.
Oil In the preparation of lubricating compositions of this invention various mineral oils can be employed. Generally these are of petroleum - ' ' :

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-3- 2~106 origin. Preferably, the mineral oils are reEined products as obtained by well-known reEining processes. The oils have a Saybolt viscosity at 100F
in the range of about 60-5000 and a Saybolt viscosity at 210F of about 30~250. Paraffinic, naphthenic or aromatic oils, as well as mixtures of these oils can be used. Preferred oils are paraffinic oils which are obtained by solvent extraction.
A particularly suitable and preferred oil base stock is a blend of SAE 20 and SAE 50 stock lubricating oils. Preferably, the lubricating oil composition of this invention should have a viscosity index of at least 10 about 140.
Copolymer The copolymer employed in the lubricating oil compositi~n of this invention is an oil additive which is known as such. The copolymer functions as a viscosity index improver and is an oil soluble hydrogenated butadiene-styrene copolymer having a butadiene content of 33-44 weight persent and the remainder being styr~ne and having a molecular weight ranging from 25,000 to 125,000. Further details concerning this copolymer are disclosed in U.S. Patent 3,554,911. A particularly suitable butadiene-styrene copolymer viscosity index improver is commercially available from Phillips Petroleum Co. as Phil ~d VII ~trademark).
The butadiene-styrene viscosity index improver is present in an amount from 0.7 to 3.0 volume percent (active ingredient), and most preferably is present in an amount of about 0.9-1.4 volume percent in the presence of the ashless dispersant additive package described later.
However, in the absence of this ashless dispersant additive package the butadiene-styrene copolymer is most preferably present in an amount of about 1.6 to 2.6 volume percent.
` Ashless Dispersant :;~
It is an important feature of the lubricating oil composition of ~; 30 this invention that the composition is essentially free of metal containing ash forming additives. Typical ash forming additives which are not present in the lubricating oil composition of this invention are calcium petroleum sulfonates, magnesium petroleum sulfonates, and zinc dialk~l-dithiophosphates. Thus, whereas no ash forming metal containing additives are present in the lubricating oil composition of this invention, an ashless dispersant additive package may be and preferably is present in the lubricating oil composition of this inven~ion. This ashless dispersant : ~ '~, ;'' : . . . ,:

:: , ~ ~ 690'16 _~_ 2~106 additive package can be added to the composition to meet Military Speci~ication MlL-L-22851C for type I ashless dispersant, aircraft piston engine lubricating oil, as well as Teledyne Continental Motors specification MHS-24B and Avco Lycoming specification 301F. Any such ashless dispersant additive package that meets the above specificatlons is suitable. This additive package also contains an ashless oxidation inhibitor. An especially suitable ashless dispersant additive package is disclosed in U.S. Patent 3,206,403. Such an ~dditive package is available from Shell Oil Co. as Shell Concentrate A. (trademark).
The ashless dispersant additive package can be present in an amount from 8 to 12 volume percent arld most preferably is present in an amount of about 9.8 to l0.2 volume percent, based on the total volume of the lubricating oil composition.
Pour Point Depressant The lubricating oil composition of this invention also contains a pour point depressant. The nature of the pour point depressant is not critical and any suitable commercial ashless product manufactured for this purpose and compatible with the other components of this invention can be used. In the preseDce of the ashless dispersant additive package described the additionally used pour point depressant is used in an amount from 0 - l.0 volume percent most preferably in an amount of about 0.05 to 0.3 volume percent active ingredient based on the total lubricating oil composition. In the absence of the ashless dispersant additive package, the pour point depressant is used in the lubricating oil composition in an amount of 0.05 to l.0 volume percent active ingredient, and most preferably in an amount of about l.0 to 0.4 volume percent active ingredient.
~ The following examples illustrate the invention but are intended `~ not to unduly limit the scope thereof.
EXAMPL~ I
The properties provided by the lubricating oil of this invention are illustrated in the following formulation and certification evaluation ~est. The test was made by Teledyne Continental Motors on a SAE 20~-50 formulation. The formulation is shown in the Table I below.
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Table I
SAE 20W-50 Dispersant Aviation Oil Composition Vol. %
Mid Continent SAE 20 stock 58.1 Mid Con-tinent SAE 50~1~tock 19.4 Copo:Lymer additive 2)12.3 (1.1 vol. % copolymer) Pour point depressant( (3)0.2 (.1 vol. % active ingredient) Ashless dispersant package10.0 Properties Viscosity: cSt at 104F140.4 cSt at 212E 17.9 SUS at 0F (Cold crank) 39,300 Pour Poin-t F ma~. -25 Viscosity Index 142 (1) Commercially available viscosity index improver, Phil-Ad VII~, PhiIlips Petroleum Company, containing 90 weight percent SAE 10 oil, 10 weight percent copoly~er of 41 weight percent butadiene and 59 weight percent stryene, having less than 1% olefinic unsaturation and a weight average molecular weight of 60,000.
(2) Commercial product ECA 5118 (trademark) manufactured and sold by Exxon Corp.
(3) Commercially available as Shell Concentrate A (-trademark) from Shell Oil Co. and containing 67% carrier oil, 3% of an ashless antioxidant, 30/0 of an ashless dispersant.
The certification test of the above formulation was performed by Teledyne Continental Motors as a 201 hour endurance test on a TSIO-520-WB (trademark) aircraft piston engine at 325 BHP/2700 RPM nominal power rating. The test schedule and temperatures appear in the following Tables II and III.
Table II
Teledyne Continental 201 Hour Test Schedule Test Condition Hours Cruise Power 31.5 100% Power 82.5 ~ (333 CBHP at 2700 RPM) :~ Endurance Time 114.0 Power Calibration~ 87.5 Total Time 201.5 ~A carburator was tested for its fuel flow characteristics using the same engine and oil as during the first 114 hour test. During the power calibra-tion the throttle was wide open about 1/3 of the time, the engine was run at 75% power for about 1/3 of the time and at 50-60% for the rest of the time.

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Table III
201 Hour Schedule Test Temperature Cruise - Lean out fuel mixture to peak turbocharger inlet temperature -(1650F max.) Normal Operational Limits:
~il-in temp. 180-200F
CHT* average 400-420F
(460F max~
10 "Hot" Operational Limits:
Oil-in temp. 230-240F
CHT* max. cyl. only 460~465F
CHT~; all other cyls. 410-460F
*CHT, cylinder head top The 20W-50 oil was used throughout the above -test with complete oil changes at 50 hours and 200 hours endurance time. Chevron 100 LL (trademark) grade fuel conforming to Spec. ASTM D910-76 was used throughout the test. After - completion of the test, the engine was disassembled for inspection and post-test measurement of principal parts. '!

Results of test: Engine performance was fully satisfactory.
Engine average oil consumption was 2.72 hrs/qt. Post test visual and dimensional inspection indicated the engine to be in excellent condition.
All parts were suitable for further service without reconditioning. All wear or working contact suraces were found in excellent condition and none displayed any scoring scuffing or abnormal wear.
, EXAMPLE II
~' A similar certification program was carried out on an Avco-Lycoming H-360-FIAD ~trademark) aviation engine with a maximum continuous rating of 225 BHP at 3050 RPM equipeed with an Engstrom Turbo Charger (trademark). 87.5 hours of the 150 test hours were run at 100%
power or~with wide open throttle. The oil described in Table I passed this certification test.
The figure shows the viscosity of the oil composition of this ~ invention compared to the viscosity behavior of Aviation Type A 65 grade, :; :
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_7_ 28106 80 grade and 100 grade oils. It is qulte apparent that in this logarithmic viscosity graph, the lubricating oil composition of this invention has a significantly lower viscosity at 0 F and a viscosity equivalent to 100 : grade oil at a high temperature such as 350F.
Reasonable variations and modification which will become apparent to those skilled in the art can be made in this invention without departing from the spirit and scope thereof.

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Claims (8)

The embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An airplane engine lubricating oil composition consisting essentially of a) a multigrade lubricating oil basestock, b) 0.7 to 3 volume percent of an oil soluble butadiene-styrene copolymer being hydrogenated to remove essentially all of the olefinic unsaturation while leaving the aromatic unsaturation essentially unchanged, said polymer having a butadiene content of 33 to 44 weight percent and a styrene content of 67 to 56 weight percent and having a weight average molecular weight in the range of 25,000 to 125,000.
c) 0.05 to 1 volume percent of a pour point depressant, said composition being essentially free of metal containing and ash forming additives.

2. Composition in accordance with claim 1 containing 8 to 12 volume percent of an ashless dispersant additive package.

3. A composition in accordance with claim 2 containing 0.9 to 1.4 volume percent of said butadiene-styrene copolymer.

4. A composition in accordance with claim 1 wherein said oil base stock is a multiviscosity oil SAE 20W-50 having a viscosity index of at least 140.

5. In a process for operating an air cooled airplane piston internal combustion engine, by combusting and igniting a fuel and free oxygen containing mixture in said engine and lubricating the engine with a lubricating oil composition containing a hydrocarbon oil as the main ingredient, the improvement which comprises using a lubricating oil composition as defined in claim 1 for said lubricating.

6. A process in accordance with claim 5 wherein said lubricating oil composition comprises 8 to 12 volume percent of an ashless dispersant additive package.

7. A process in accordance with claim 6 wherein said lubricating oil composition contains 0.9 to 1.4 volume percent of said butadiene-styrene copolymer.

8. A process in accordance with claim 5 wherein said piston engine is operated at a cylinder head top temperature of 420 to 490°F.