EP0092946B1

EP0092946B1 - Glycerol esters with oil-soluble copper compounds as fuel economy additives

Info

Publication number: EP0092946B1
Application number: EP83302155A
Authority: EP
Inventors: Phillip William Brewster; Clinton Richard Smith
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1982-04-22
Filing date: 1983-04-15
Publication date: 1988-03-16
Also published as: EP0092946A3; JPH0377837B2; DE3376016D1; CA1205451A; JPS58191795A; EP0092946A2

Description

This invention relates to lubricating oil compositions which exhibit marked improvements in fuel economy. More particularly, this invention relates to lubricating oil compositions which contain very minor proportions of a glycerol fatty acid ester fuel economy additive in combination with an oil-soluble organic copper compound.
It is a current objective of the industry to provide lubricating oil compositions which exhibit improvements in fuel savings in gasoline and diesel engine vehicles. To meet that current goal, a new category of additives commonly referred to as fuel economy additives are being developed which function primarily to increase the miles or kilometers obtained per unit volume of fuel. Since modern day lubricating oil compositions are complex formulations, such additives must be compatible with the other components of such compositions and should not adversely affect the numerous other functions of conventional lubricant additives such as dispersancy, viscosity stability, corrosion and oxidation inhibition, and the like.
Illustrative of recent patents reflecting developments in this field are U.S. Patents 4,201,684 and 4,208,293. These patents show the use of fatty acid amides and sulfurized amides as additives which have fuel economy benefits as demonstrated by friction reducing data.
The present invention concerns the use of glycerol fatty acid esters as such fuel economy additives, specifically glycerol esters of C_16-C₁₈ fatty acids in combination with oil-soluble copper organic compounds. There is prior art disclosing the use of each of these materials in lubricating oil compositions which is discussed hereinbelow.
British Application 2097813A, published November 10, 1982, discloses the use of 0.05 to 0.2 wt.% glycerol partial esters of C16-C18 fatty acids as fuel economy additives. The present invention is an improvement over said British application.
West German Application P-2949940 and P-2949910 of Chevron Research Company, both published July 3,1980, disclose the use of glycerol fatty esters as fuel economy additives. These references state that the addition of 0.25 to 2 weight percent, preferably 0.40 to 1.25 weight percent, of a fatty acid ester will offer a fuel economy credit of 2-3 percent in both gasoline and diesel engines. Glycerol oleic acid esters are preferred. West German Application P-2949940 illustrates the preferred embodiment showing the use of the glycerol ester at the same treat level in combination with zinc dihydrocarbyl dithiophosphate additives. Similarly U.S. Patent 4,304,678 discloses hydroxyl-containing esters including glycerol oleates as being effective friction modifiers only at levels of 1-4 wt.% with no benefit observed at levels less than 1 % by wt. in oil.
In contrast to the teachings of these references, the present invention is based upon the discovery that very low levels of glycerol esters; that is, up to about 0.2 percent by weight, in combination with certain amounts of oil-soluble organic copper compounds, provide enhanced performance of these fuel economy lubricating oils. No benefit is obtainable in using relatively higher amounts and in some cases substantial debits in terms of formulation stability or adverse performance may occur.
Another reference disclosing the use of polyolcarboxylic acid esters in lubricating oil compositions is U.S. Patent 3,933,659, which shows a multi-component functional fluid, one component of which can be a polyol ester friction modifier or a fatty acid amide friction modifier. The primary use disclosed in that reference is for automatic transmission fluids. U.S. Patent 3,273,981 discloses anti-wear additives comprising a mixture of dimer acids and a partial ester of a polyhydric alcohol, the additive being noted as improving lubricity as well as functioning in the anti-wear category. U.S. Patent 3,112,271 discloses glycerol mono-oleate as an extreme pressure additive as does U.S. 3,112,269 and U.S. 3,041,284. U.S. 2,493,483 discloses marine engine lubricants which contain a partial ester of glycerol or other polyol fatty acid esters in amounts of from 0.05 to 1 percent.
Other references disclosing polyol esters of fatty acids are U.S. 2,788,326, which discloses these compounds in extreme pressure lubricants, U.S. 2,527,889, which shows polyol esters, such as glycerol monooleate, as anti-corrosion agents in turbine oils and diesel fuels, and U.S. 2,911,367 which shows polyol esters as preventing rusting and corrosion of metal surfaces exposed to moisture.
The use of oil-soluble copper compounds at levels of about 5 to 500 parts per million (ppm) of copper by weight, based on the total weight of lubricating oil composition, as a highly effective antioxidant is a relatively recent development of additive technology and is disclosed in European Published Application No. 0024146, published on February 25, 1981.
The present invention is based on the discovery that these copper compounds, when used in an oil in combination with glycerol esters, e.g. oleates, act cooperatively with the glycerol ester in substantially increasing the fuel economy of the formulated oil. The cumulative effect observed would not be expected by adding the fuel economy credit obtained in oils which contain one or the other of the glycerol ester or copper compound. Data obtained therefore provide the basis for an unexpected additive effect upon fuel economy due to more effective lubrication of an internal combustion engine operated using the oils of the present invention.
The prior art also recognizes that copper components per se can be favorable friction reducing agents in certain circumstances. German Democratic Republic Patents 145,469 and 145,470 disclose the reduction of wear and friction in iron/iron and iron/bronze friction interfaces using polyol or mineral oil lubricants containing copper compounds such as copper naphthenate, copper octoate, copper stearate and reaction products of lubricants themselves with copper, copper oxide and copper salts of inorganic acids. These references indicate that the friction reduction is achieved by deposition on the substrate being lubricated of a film reaction layer of copper with adequate adhesion properties. It is recommended in these references that the concentration of the copper compound in the lubricant provide a copper content of 0.001 to 5 volume % relative to the lubricant. These references however did not evaluate lubricating oil compositions for internal combustion engines.
In accordance with the present invention, there are provided fuel economy improving lubricating oil compositions for internal combustion engines which comprise an oil of lubricating viscosity and, as the fuel economy additive, a combination from 0.05 to 0.20 weight percent of a glycerol partial ester of a C₁₆―C₁₈ fatty acid with from 5 to 500 ppm (parts per million) copper present in the form of an oil-soluble copper compound, preferably 60 to 200 ppm copper being present, based upon the weight of the total composition, the copper compound also functioning as an antioxidant.
The lubricating oil compositions of the present invention comprise both straight grade and multigrade lubricating oil formulations for both gasoline and diesel (compression ignition) engines. Thus, in the practice of the present invention the lubricating oil compositions will contain those additive systems formulated to meet the viscosity requirements or other specifications as required for qualification as a gasoline engine or diesel lubricating oil. A straight grade lubricating oil formulation will normally contain conventional amounts of an ashless dispersant, a normal or basic metal detergent, an anti-wear additive and an antioxidant and a multi-grade oil will contain, in addition to the foregoing, a viscosity index improver or viscosity modifier. In addition to these principal additives, very small proportions of other special purpose additives, such as pour depressants, rust inhibitors, anti-foamants and the like are conventionally blended into lubricating oil compositions.
The ester component of the fuel economy additive of the present invention is preferably a glycerol mono- or diester of a saturated or unsaturated C₁₆―C₁₈ fatty acid, such as oleic or linoleic acid. Optimum efficiency has been found to be at about the 0.1 to 0.2 weight percent level and use in the excess of this amount may even be detrimental to the overall performance of the lubricating oil composition.
Oil-soluble copper components useful herein include both cuprous or cupric compounds which are oil-soluble under normal blending conditions in the oil additive package. Particularly preferred are the copper salts of C,_o-C₂₂ fatty acids, such as stearic or palmitic acid, but copper salts of unsaturated acids, such as oleic acid, linoleic acid, naphthenic acid of 200―500 molecular weight or synthetic carboxylic acids are preferred. The particularly preferred embodiment is copper (cupric) oleate when present in an amount to provide about 100 to 150 ppm copper in the lubricating oil composition.
Other suitable copper compounds include the same as those disclosed in said European Published Application 0024146 and these include copper dithiocarbamates of the formula (RR'NCSS)_nCU where n is 1 or 2 and R and R' are the same or different C₁-C₁₈ hydrocarbyl radicals, preferably C2-C,, alkyl, copper sulphonates, copper phenates and acetyl acetonates as well as copper dihydrocarbyl dithiophosphate, the hydrocarbyl being C₁-C₁₈ and preferably C₂-C_B alkyl, such as a hexyl or isooctyl.
Crankcase oil formulations to which the present invention relates are those which contain a major amount of lubricating oil and effective amounts of conventional additives in addition to the aforesaid fuel economy additive, the copper compound serving the dual function of being both an antioxidant and, in combination with the glycerol oleate, a fuel economy additive. Percentages of additives as described herein are by weight based on the total weight of lubricating oil formulation unless otherwise indicated.
These conventional additives comprise ashless dispersants typically nitrogen-containing dispersant, additives which are oil-soluble salts, amides, imides and esters made from high molecular weight mono- or di-carboxylic acids and various amines having an amino or heterocyclic nitrogen with at least one amido or hydroxy group capable of salt, amide or ester formation. Preferred are the reaction products of polyolefin (C₂-C_S olefin), such as polyisobutenyl, succinic anhydride with an alkylene polyamine such as tetraethylenepentamine. The polyisobutenyl portion has between 50 and 250 carbon atoms. The alkylene polyamines are those represented by the formula:
where n is 2 to 3 and m is a number from 0 to 10. Mixtures of alkylene polyamines which approximate tetraethylenepentamine are commercially available materials. Dispersants are used generally in amounts of from 0.1 to 10 wt.%, preferably in the range of 0.5 to 5 wt.%, based on the weight of the lubricating oil composition.
Detergents useful in the formulations include the normal, basic or overbased metal, that is, calcium, magnesium and so forth, salts of petroleum naphthenic acids, petroleum sulfonic acids, alkyl benzene sulfonic acids, alkyl phenols, alkylene-bis-phenol, oil-soluble fatty acids and the like. The preferred materials are the normal or overbased calcium or magnesium phenates, sulfurized phenates and/or sulfonates, and these metal-containing detergent additives are typically used in amounts of from 1 to 3 wt.% based on the total weight of lubricating oil compositions.
Suitable pour point depressants, which are usually present in amounts of 0.01 to 1 wt.%, include wax alkylated aromatic hydrocarbons, olefin polymers and copolymers, acrylate and methacrylate polymers and copolymers.
Anti-wear additives generally are the oil-soluble zinc dihydrocarbyl dithiophosphates having a least a total of 5 carbon atoms, the alkyl group being preferably C₂-C₈. These are typically present in amounts of from 0.01 to 5 wt.%, preferably 0.5 to 1.5 wt.%, in the lubricating oil.
Suitable conventional viscosity index improvers, or viscosity modifiers, are the olefin polymers such as polybutene, ethylene-propylene copolymers, hydrogenated polymers and copolymers and terpolymers of styrene with isoprene and/or butadiene, polymers of alkyl acrylates or alkyl methacrylates, copolymers of alkyl methacrylates with N-vinyl pyrrolidone or dimethylaminoalkyl methacrylate, post-grafted polymers of ethylene-propylene with an active monomer, such as maleic anhydride, which may be further reacted with an alcohol or an alkylene polyamine, styrene-maleic anhydride polymers post-reacted with alcohols and amines and the like. These additives are used in amounts of 1.5% to 15% by wt., depending on the exact viscosity specifications desired.
Conventionally used antioxidants include phenols, hindered phenols, bis-phenols, sulfurized phenols, catechol, alkylated and sulfurized alkylated catechols, diphenylamine, alkylated diphenylamines and phenyl-1-naphthylamines, alkyl and aryl borates, phosphites and phosphates, trialkyl and triaryl dithiophosphates and the like.
Suitable hydrocarbon base stocks are those mineral oils of lubricating viscosity as measured by ASTM D-455 of from 2 to 40, preferably 5 to 20 centistokes at 99°C.
These conventional additives are used in amounts normally necessary to provide their attendant functions in a formulated crankcase lubricating oil composition. Very small proportions of additional special purpose additives, such as anti-foam agents or rust inhibitors, may also be present in a fully formulated lubricating oil composition.
The invention is further illustrated by the following Examples.

Example 1

The reference oil used in this example was a formulated straight grade 20W30 crankcase mineral lubricating oil (corresponding to ASTM "HR" oil) to which was added 0.2 weight percent of a glycerol monooleate (GMO) fuel economy additive or 0.2 weight percent of a fuel economy additive being a mixture (GMO/GDO) of glycerol monooleate and glycerol dioleate in a weight ratio of 3 parts of GMO to 2 parts of GDO in said mixture. The reference oil contained 2.10 wt.% dispersant, 1.10 wt.% antioxidant, 1.00 wt.% basic metal detergent, 1.95 wt.% anti-wear additive, 0.21 wt.% pour depressant and 0.001 wt.% anti-foam agent. This type of reference oil, which is generally accepted by the industry for establishing fuel economy data, provides a reproducible baseline against which fuel economy credits may be measured and is considered to provide test results which accurately reflect the effect of a given fuel economy additive.
Fuel economy was evaluated using the Laboratory Engine Fuel Economy Test (LEFET) summarized below:

The fuel economy test used is a fired engine procedure. The engine is a 5.0 liter, V₌8 Chevrolet engine coupled to a water cooled electric dynamometer. The engine is run with a dry sump by the use of external oil pumps. One pump supplies oil to the oil gallery from an external sump and a second pump scavenges the sump and returns the oil to the external sump. The conditions that the engine runs at are as follows:
The results are expressed as a percentage fuel economy credit with respect to the referenced oil, as are all fuel economy credit results reported in the Examples. Results at the 0.2 wt.% treat level for both GMO and the GMO/GDO mixture are set forth in Table I.

Example 2

(a) Comparative evaluations utilizing increased amounts of the GMO/GDO mixture, that is, at the 0.3 weight percent and 0.5 weight percent levels showed no increase in fuel economy credit for treatment at these levels and in some cases, an adverse effect on fuel economy credits or other lubricating oil performance criteria, such as increased piston deposit formation tendencies or poor results in bearing corrosion tests.
(b) Coefficient of friction (CF) testing using a Roxana Four-ball wear tester in accordance with the procedure described in ASTM D2266-67 at 110°C, 2.5 RPM at both 15 kg and 3 kg was carried out with a formulated mineral oil (Base oil) containing conventional amounts of dispersant (2.12%), basic metal sulfonate (1.02%), antioxidant (0.72%), anti-wear additive (1.96%) and viscosity index improver (only present at 8.7 wt.% in test oils 5 and 6 to evaluate compatibility) to which was added varying amounts of the GDO/GMO mixture. The results in Table II below show essentially no additional friction reducing benefit at levels in excess of 0.2 wt.% and, at 0.9 wt.% in the test, potential instability or incompatibility was observed since the samples appeared hazy.

Example 3

(a) The Laboratory Fuel Economy Test of Example 1 was repeated utilizing a 10W40 multigrade mineral oil containing 0.09 wt.% of the GMO/GDO mixture as the fuel economy additive. The oil contained about 14% by wt. of a multifunctional dispersant viscosity index improver (acryloid 1155), 0.5% dispersant, 1.85% of basic metal detergent, 0.75 wt.% of anti-wear additive and 0.75% antioxidant.
Table III shows the fuel economy credits over the oil used as the reference in Example 1.

(b) Utilizing the same oil as Example 3(a) the Laboratory Fuel Economy results were confirmed in the Proposed ASTM 5 Car Interim Fuel Economy Procedure which utilized the EPA car certification cycle in 5 automobiles having engine sizes of 2.3 liter, 2.8 liter, 3.7 liter, 3.8 liter and 5.0 liter. Five Car average fuel economy credit of 1.64% was obtained in one series of fuel economy tests.

Based upon these results one would expect that the fuel economy credits attributed to a glycerol mono-oleate to be non-cumulative when the treatment level is increased above the range of about 0.1 wt.% to 0.2 wt.% and the inventors hereof have found this principle is generally true in fuel economy additives technology, i.e., increasing the amount of friction modifier additive does not result in a concomitant straight line proportional increase in the observed fuel economy. For example, combining the glycerol oleate mixed esters described above with a known fuel economy additive such as a dimerized linoleic acid ester as described in U.S. Patent 4,105,571 has been found to offer no better fuel economy than when either compound is used alone. This will be demonstrated in Example 6. Thus, as a general rule increasing the treat level of the friction modifier itself or increasing the treat level by adding another friction modifier known to have fuel economy benefits has not heretofore been found to offer a fuel economy improvement. Examples 1-4 and 6 are presented here to illustrate these principles.

Example 4

Evaluation of copper compounds for fuel economy

The LEFET test was carried out using an Oil^* equivalent to the HR straight grade oil of Example 1 except that 0.3 wt.% of a 40 wt.% solution of copper oleate in mineral oil, which is equivalent to 120 ppm copper was used in place of the anti-oxidant reported in Example 1. The LEFET results for this test are below in Table IV:
This example establishes that copper does provide a significant fuel economy credit in addition to its antioxidant effectiveness.
The foregoing examples, carried out in fired engine tests using a 5.0 liter 8-cylinder engine demonstrate that the oil-soluble organic copper compounds offer a beneficial fuel economy credit and that the glycerol ester offers a fuel economy credit which does not increase to any significant degree above the 0.2 wt.% treat level.

Example 5

Evaluation of combination of copper compound and glycerol ester

To determine if oils containing both the oil-soluble organic copper compound and glycerol ester friction modifier would exhibit any complementary effect, different oils were formulated and tested in Ford 2.3 liter 4-cylinder engine. The purpose of these tests was to evaluate the increase in fuel economy credits when the copper compound and the glycerol ester were combined over the credits obtained with these additives separately in the same engine. Fuel economy credit values will vary among engines of differing sizes. This is due to the inherent differences in engine design and operating conditions. It is known therefore that the values for a 2.3 liter 4-cylinder engine will be lower than fuel economy credit values for a 5 liter 8-cylinder used in these examples.
The additive content in weight percent of the oils evaluated is given below, balance is basestock mineral oil.
Fuel economy results for these oils are given in Table V below. Percentage credits are calculated again with respect to the same reference oil used in Example 1.
Oil D represents the advantage of this invention. Oils B, C, E show the maximum values one can expect to obtain based on the credits due only to the copper compound. Oil D, however, achieves a value of 0.9%. This result is not expected because it is known, as a general principle, that merely increasing the treatment level of a given fuel economy additive does not increase the credit obtained.

Example 6

To demonstrate the principle that fuel economy additives, when combined together, cannot be expected to have a combined effect. The following oils G, H, I and J were evaluated for fuel economy in the 5.0 L engine using the same LEFET procedure of Example I. Oil G was a formulated lubricating oil having 4 wt.% dispersant, 1 wt.% overbased metal sulfonate, 1.5 wt.% antioxidant and 2 wt.% anti-wear additive. Oil H was the same as Oil G, except for the inclusion of 0.1 wt.% dimerized linoleic acid ester of diethylene glycol as disclosed in U.S. Patent 4,105,571. Oil I was the same as Oil G except 0.2 wt.% of the GMO/GDO ester was added. Oil J was the same as Oil G except both 0.1 wt.% of the dimerized linoleic acid ester and 0.2 wt.% of the GMO/GDO were added. Fuel economy results for these four oils are shown below in Table VI.

Example 7

The positive effect on fuel economy attributable to use of the two component fuel economy additive of this invention is further demonstrated by LEFET results in the 5.0 L engine and these data confirm the results shown above in Example 5. Here Oil K contained 5.5 wt.% dispersant, 1 wt.% overbased metal sulfonate, 1.4 wt.% anti-wear additive and 1 wt.% anti-oxidant. Oil L was the same as Oil K with 0.3 wt.% of a 40 wt.% solution of copper oleate (120 ppm copper) included and Oil M was the same as Oil L except 0.1 wt.% of the GMO/GDO glycerol oleate was included. Fuel economy credits are in Table VII below.

Claims

1. A lubricating oil composition for improving the fuel economy of an internal combustion engine comprising a major amount of an oil of a lubricating viscosity which has incorporated therein (a) from 0.05 to 0.20 weight percent of a glycerol partial ester or mixtures thereof of a C₁₆-C₁₈ fatty acid, and (b) 5 to 500 ppm of copper in the form of an oil-soluble organic copper compound.

2. The composition of claim 1 wherein the fatty acid is oleic acid.

3. The composition of claim 1 wherein said partial ester is a mixture of glycerol monooleate and glycerol dioleate.

4. The composition of claims 1-3 wherein there is present 0.1 to 0.2 weight percent of said partial ester.

5. The composition of claims 1-4 wherein said lubricating oil composition contains an ashless dispersant, a metal detergent additive and a zinc dihydrocarbyl dithiophosphate anti-wear additive in conventional amounts to provide their normal attendant functions.

6. The composition of claim 5 wherein said lubricating oil composition contains a viscosity index improver.

7. The composition of claims 1-6 where said copper compound is copper oleate.

8. The composition of claims 1-7 where there is present 60 to 200 ppm of copper.

9. A method of improving the fuel economy of an internal combustion engine by lubricating the internal portion thereof with a lubricating oil composition containing (a) 0.05 to 0.2 wt.% of a glycerol partial ester of a C16-C18 fatty acid or mixtures thereof and (b) 5 to 500 ppm of copper in the form of an oil-soluble organic copper compound.

10. The method of claim 9 wherein said (a) component is a mixture of glycerol monoleate and glycerol dioleate present in an amount of from 0.1 to 0.2 wt.%, and said (b) component is copper oleate present in an amount to provide 60 to 200 ppm copper.

11. The use as an additive for lubricating oil of a mixture of (A) a glycerol partial ester or mixtures thereof of a C₁₅―C₁₈ fatty acid, and (B) an oil-soluble organic copper compound.