CA2168915A1 - Lubricating oil compositions for internal combustion engines having silver bearing parts - Google Patents

Abstract

Lubrication of internal combustion engines having silver bearing parts with essentially chlorine-free and zinc dithiophosphate-free lubricating compositions having a TBN
of about 5 to 30 certain silver bearing protecting acyloxy polyalkoxy alcohols. An additive concentrate for the lubricating compositions is also disclosed.

Description

216~

01BUBRICATING OI~ COMPOSITIONS FOR INTERNAL
02CO~US'1'10N ENGINES HAVING SILVER BEARING PARTS

04BACKGROUND OF THE INV~N'1'10N

06 This invention relates to lubricating oil compositions for 07 use in engines having silver bearings. In a further aspect, 08 the invention relates to the protection of silver bearing 09 parts in internal combustion engines.
11 AS is well known, lubricating oils for heavy duty diesel 12 engines require crankcase lubricating oils which are 13 stabilized against oxidation and which limit the formation 14 of engine deposits. In addition, these crankcase lubricating oils must also have a high alkalinity to 16 neutralize acids formed during fuel combustion.

18 Many heavy duty railroad and tugboat diesel engines in use 19 in the United States and certain other countries pose an additional lubrication problem, because they have silver-21 surfaced engine parts, such as silver or silver-plated 22 bearings. While the foregoing properties of oxidation 23 stability, deposit control and alkalinity can be achieved by 24 the use of lubricating oil additives known in the art, many of the resulting oils cause unacceptable corrosion and wear 26 to silver-surfaced diesel engine parts. Silver, or silver-27 surfaced bearing parts, pose a special problem since many of 28 the bearing protection additives which are effective to 29 protect bearings surfaced with other materials, e.g., brass, copper-lead, bronze, aluminum, are ineffective to protect 31 silver bearing parts or, for example as in the case of 32 materials such as zinc dithiophosphates (commonly used in 33 lubricants to provide lead bearing protection) are 34 deleterious to silver bearings.

216891~

01 Typically, lubricating oil compositions for such engines 02 have a TBN of from 5 to 30. This alkalinity is typically 03 achieved by inclusion of a requisite amount of a calcium 04 overbased sulfurized alkylphenate in the composition.
05 However, the overbased alkylphenate is also detrimental 06 because it imparts undesirable wear to the silver coating on 07 the silver wrist-pin bearings.

09 At present silver protection is largely provided by the use of lubricants containing chlorinated paraffins or other 11 chlorinated additives. Examples of halogenated additives 12 used to provide silver protection are, for example, 13 described in U.S. Patent Nos. 4,131, 551; 4,169,799;
14 4,171,269; 4,320,016; 4,428,850; and 4,464,276. However, a problem has arisen with respect to the use of halogenated 16 additives in that they are perceived as presenting 17 environmental problems. Thus, there is a need for 18 lubricants which provide silver protection without the 19 inclusion of halogenated additives.
21 In view of this need the art has already developed certain 22 halogen-free or reduced halogen silver corrosion inhibitor-23 containing lubricants. For example, U.S. Patent 24 Nos. 4,764,296 and 4,734,211 disclose a marine and railway diesel engine lubricating oil composition containing certain 26 polyhydroxy esters as silver wear inhibitors. These patents 27 also disclose lubricating oil compositions containing a 28 mixture of these polyhydroxy esters and chlorinated 29 paraffins. U.S. Patent No. 4,820,431 discloses a method for reducing silver wear in marine and railway diesel engines 31 using similar lubricating oil compositions. U.S. Patent 32 No. 4,171,270 discloses lubricating oil compositions 33 containing a sulfurized overbased calcium alkylphenolate and 34 a sulfurized naphthenic base oil-containing composition 01 having a sulfur content of from 1 percent to 6 percent by 02 weight. These compositions are also thought to have silver 03 protective properties. U.S. Patent 4,871,465 discloses 04 lubricating oils containing as a silver protectant (a) a 05 sulfurized olefin, sulfurized fatty acid, sulfurized 06 hydroxyaromatic, sulfur cont~;n;ng heterocyclic compounds, 07 organic sulfide or dithiocarbamate and (b) the reaction 08 product of a saturated aliphatic dicarboxylic acid with an 09 optionally substituted aminoguanidine. U.S. Patent No. 2,795,548 teaches that certain borate-glycol complexes 11 were found to give effective lubrication over long periods 12 with very low weight loss of silver bearings. U.S. Patent 13 No. 4,278,553 discloses a railway diesel engine lubricant 14 containing a silver corrosion inhibitor comprising a benzotriazole compound present in concentrations from about 16 0.5 to 2.0 wt~ and U.S. Patent No. 4,285,823 discloses a 17 diesel lubricant composition containing a silver 18 corrosion-inhibiting amount of an N-substituted 19 5-amino-lH-tetrazole. Commonly assigned U.S. Patent No.
5,244,591 teaches that certain unsaturated carboxylic acid, 21 e.g., oleic acid, provides silver bearing protection 22 particularly when used in combination with a small amount of 23 a sulfurized olefin.

A continuing need exists for additives which provide silver 26 protection without presenting potential environmental 27 problems and preferably, which are readily available. As 28 before mentioned, a significant problem in meeting this need 29 is the unpredictability of additive response with respect to silver bearing systems. One simply cannot predict whether a 31 given additive will provide silver bearing protection based 32 on its properties in lubricants for non-silver bearing 33 engines or a general characterization of the additives' 34 properties or function. Thus, for example as previously 01 mentioned, zinc dithiophosphates which are widely used to 02 provide wear and oxidation protection, are recognized to be 03 deleterious to the silver bearing parts of engines; see, for 04 example, U.S. Patent No. 4,849,118. It is also well 05 recognized that providing silver bearing protection is not 06 merely a matter of neutralizing engine acid; see, for 07 example, U.S. Patent No. 3,779,920, column 1, lines 20-30 08 and U.S. Patent No. 4,849,118, column 2, lines 24-35. U.S.
09 Patent No. 3,933,662 is directed to lubricating compositions which are described as having improved neutralization 11 capacity and rust inhibition by virtue of the incorporation 12 therein of the combination of a polyoxylated compound and an 13 alkaline earth metal carbonate. The '662 patent is more 14 specifically concerned with providing rust protection for ferrous metals; see column 2, lines 43-45, and all of the 16 lubricating compositions described in the examples contain a 17 zinc alkyldithiophosphate.

19 Polyoxyalkylene compounds have been used as lubricating oil additives in compositions for use in the upper cylinder 21 chamber of marine diesel cylinder engines of the crosshead 22 type. For example, U.S. Patent No. 4,402,845 discloses 23 lubricant compositions having a TBN of from 50 to 100 which 24 are used in marine diesel cylinder engines of the crosshead type and which contain a polyethylene glycol compound of the 26 formula:

28 R-CH2O-(cH2cH2O)nH

wherein n ranges from 7 to 40 and R is an alkyl group 31 containing from 11 to 15 carbon atoms. These compounds are 32 disclosed as improving the spreadability of marine diesel 33 engine cylinder oils after injection of the oil into the 34 interior of the cylinder chamber. In column 2, line 40 of 2168~15 01 the patent, TERGITOL~ 15-S-20 is cited as a particularly 02 preferred compound. Similarly, U.S. Patent No. 4,479,882 03 discloses a process for improving the spreadability of a 04 lubricating oil composition having a TBN of from 50 to 100 05 for use in a marine diesel engine of the crosshead type by 06 incorporating therein a polyalkoxylated phenoxy compound of 07 the formula:

R ~ O-(cH2cH2o)nH

13 wherein R is an aliphatic hydrocarbyl group having from 5 to 14 70 carbon atoms and n ranges from 14 to 30.

16 Two cycle railroad diesel engines and the similar type 17 engines used in some tugboats should also be contrasted with 18 the large marine diesel engines used in freighters or other 19 large ships. ~oth railroad type diesel engines and the large marine diesel engines are heavy duty diesel engines, 21 the internal components and operating conditions of these 22 engines are quite different. Two cycle railroad diesel 23 engines are characterized by and distinguished from large 24 marine diesel engines by many factors including silver wrist-pin bearings. Silver coatings are used in the wrist-26 pin bearings because this metal imparts superior advantages 27 in wear resistance to the bearing when operated under such 28 extreme conditions. In contrast, large marine engines do 29 not require silver coating of any of their internal parts.

31 My co-pending commonly assigned Application Serial 32 No. 08/099,632 filed July 30, 1993, hereby incorporated by 33 reference in its entirety, teaches that compound having the 34 formulas:

216891a 02 l l 03 R-X-[(RlO-)nH]m; R-X-CH2CHCH2OH; or R-X-CH
04 (A) (B) (C) CH2OH

06 wherein R iS a hydrocarbyl radical having from about 4 to 07 about 50 carbon atoms; Rl is independently an alkylene group 08 of from about 2 to about 6 carbon atoms; X is selected from og the group consisting of oxygen, sulfur and nitrogen, preferably oxygen; n is an integer from 1 to about 30, 11 preferably 10 to 20; m is 1 when X is oxygen or sulfur and 12 iS 1 or 2 when X is nitrogen; with the proviso that when R
13 iS ethylene, the lubricating oil should be a single grade 14 oil and adducts of the compounds of formula B or C with alkylene oxide of from 2 to 6 carbon atoms or glycidol 16 provide silver bearing protection in lubricating oils 17 containing the requisite amount of an overbased calcium 18 sulfurized alkylphenate to provide a TBN of about 5 to about 19 30.

23 I have now discovered that certain acyloxy derivatives of 24 certain of the compounds described in my previous application Serial No. 08/099,632, are effective to provide 26 silver bearing protection in lubricating oil.

28 In one embodiment the present invention provides an 29 essentially chlorine-~ree and zinc dithiophosphate-free lubricating composition having a TBN of about 5 to 30 31 comprising a major amount of an oil of lubricating viscosity 32 and an amount of a silver protectant which is effective to 33 inhibit or reduce silver wear or deterioration in internal 34 combustion engines having silver bearing parts and wherein 216~915 01 said silver protectant is selected from the group of 02 compounds having the formula I herein below and mixtures 03 thereof:

R-CO~R O)nH (I) wherein R is a hydrocarbyl radical having about from 4 to 50 carbon atoms; R1 is independently selected from alkylenes 11 having 2 to 8 carbon atoms; and n is a whole integer of 12 about from 1 to 30, preferably 8 to 20 and more preferably 10 to 20.

In a further embodiment, the invention provides a method for reducing silver bearing wear in internal combustion engines 17 having silver bearing parts via the use of the present 18 lubricating composition.

In another embodiment, the invention provides an additive 21 package or concentrate having a TBN of 90 to 120 containing 22 a small amount, generally under 20~ by wt., of a diluent oil 23 and a silver protectant selected from the group of the 24 compounds of formula I and mixtures thereof, and wherein said silver protectant and the additive providing the TBN
26 are in a relative weight ratio such that the additive 27 package may be admixed with an oil of lubricating viscosity 28 to provide a lubricant having a TBN of 5 to 30 and an amount of said silver protectant effective to provide silver bearing protection.

2168~15 01 DETAI~ED DESCRIPTION OF THE INVENTION

03 As above noted the compositions of the present invention 04 contain an amount of a compound or mixture of compounds, 05 according to Formula I effective to provide silver 06 protection for engines having silver bearings. In general, 07 two theories are advanced as to why a material provides 08 silver protection; i.e., the material may act as a lubricity 09 agent or it may act as a silver pacifier (i.e., provides protection by entering into a chemical reaction with silver 11 to form a bearing surface less susceptible to wear).
12 However one cannot predict that a material which provides 13 protection as a lubricating agent or pacifier with some 14 other bearing material will provide protection for silver bearings. The term silver protectant is intended to refer 16 to a material which provides silver bearing protection 17 regardless of the particular mechanism involved. As well as 18 providing silver wear protection the compounds of formula I
19 also have excellent oil solubility which readily facilitates their use in lubricating oil compositions.

22 Preferably, R is a saturated or unsaturated aliphatic 23 radical having at least eight carbon atoms more preferably 24 an alkyl or alkenyl. Preferably, the R1 substituent has 2 to 6 carbon atoms and more preferably has 2 to 4 carbons 26 The preferred compounds of formula I have at least one 27 preferred substituent and more preferably have a combination 28 of preferred substituents; Iypically best results in terms 29 of silver protection are obtained using the compounds of formula I wherein R is an aliphatic hydrocarbon having 14 to 31 30 carbon atoms, R1 is an alkylene having 2 to 4 carbon 32 atoms and n is 2 to 20. In general, the compounds of 33 formula I, wherein the RC(O)O- moiety is a fatty acid 216891~

01 radical, provide excellent silver weàr protection and 02 readily provided commercially in large quantities.

04 The compounds of formula I are generally known compounds and 05 can be prepared by using or adapting known procedures. In 06 many instances, the compounds of formula I can be readily 07 obtained in large quantities from commercial sources. In 08 many instances, it will be more convenient to use a mixture 09 of compounds in the present invention because the compounds or starting materials therefor, are more economically 11 provided as mixtures. For example, commercial oleic acid, 12 used to prepare the oleate of formula I, will also typically 13 contain minor amounts of other fatty acids. In general, the 14 compounds of formula I can be obtained by reacting the desired R carboxylic acid (i.e. RCOOH) with an alkali metal 16 hydroxide (e.g., sodium hydroxide) and the desired alkylene 17 oxide. The n values can be controlled by adjusting the 18 ratio of alkylene oxide to acid. In general, it is 19 preferred to conduct the reaction step wise and remove the byproduct glycol-water by distillation after each step or 21 conduct the reaction as a continuous process with continuous 22 distillation off of the byproduct.

24 The compounds of formula I can also be prepared by reacting the corresponding poly(oxyalkylene)diol, having terminal 26 hydroxy groups, e.g., HO-(RlO)nH, with the desired RCOOH
27 acid. The diols can be produced using similar procedure as 28 used to produce hydrocarbyl poly(oxyalkylene) alcohols, for 29 example the addition of lower alkylene oxides, such as oxirane, ethylene oxide, propylene oxide, the butylene 31 oxides, or the pentylene oxides to the hydroxy compound 32 under polymerization conditions, and adjusting the ratio of 33 reactants to provide the diol as the primary product.
34 Additional information regarding the production and 2168~1~

01 properties of these polymers are for example disclosed in 02 U.S. Patent Nos. 2,841,479 and 2,782,240, and Kirk-Othmerls 03 "Encyclopedia of Chemical Technology", vol. 19, p. 507, and 04 my co-pending application Serial No. 08/099,632, all of 05 which are hereby incorporated by reference in their 06 entirety.

08 In order to be useful as a lubricating oil additive, the 09 additive must be sufficiently lubricating oil soluble and compatible in the fully formulated composition. That is to 11 say that the compound I shall be sufficiently soluble in a 12 formulated lubricating oil composition to provide a wear-13 inhibiting amount of the compound in the oil which amount 14 does not precipitate or cause other components in the composition to precipitate from the composition under 16 ambient conditions (i.e., about 20C). Preferably, the 17 silver protectant is soluble and compatible to a level of at 18 least 0.1 weight percent in the formulated composition and 19 more preferably to a level of at least 0.3 weight percent for a period of at least about one month and preferably for 21 a period of at least about six months. As noted above, one 22 of the advantages of the compounds of formula I is that in 23 general such compounds have excellent oil solubility. Thus, 24 this will generally not be a concern however, in any event methods for determ;n;ng oil solubility and compatibility for 26 these compositions are well known in the art and can be 27 determined by the exercise of routine skill. For example, 28 precipitation from a formulated lubricating oil composition 29 at ambient conditions can be measured by either actual precipitation from the oil composition or the formation of a 31 "cloudy" solution which evidences formation of insoluble wax 32 particles. As noted above, the compounds of formula I are 33 oil soluble single grade and multi-grade oils. It has been 34 further found that the solubility of such compounds are 01 further enhanced when the R hydrocarbyl radical is attached 02 to the carboxy group by a branched carbon atom.

04 Definitions 06 As used herein the following terms have the following 07 m.o~n;ngs unless expressly stated to the contrary:

09 The term "essentially chlorine-free" refers to the absence 10 of chlorinated compounds to provide silver protection and 11 the absence of any amounts of chlorinated compounds which 12 could be considered to have an adverse effect on the 13 environment.

15 The term "zinc dithiophosphate-free" refers to the absence 16 of zinc dithiophosphates such as are conventionally used to 17 provide wear protection for other bearing materials, notably 18 lead, but are deleterious to silver bearing materials. The 19 term "TBN" refers to total base number and is a measure of 20 the ability of the lubricant to neutralize acid as 21 determined by the procedure described in ASTM D2896-85, and 22 in general terms, is the neutralization capacity of one gram 23 of the lubricating composition expressed as a number equal 24 to the mg of potassium hydroxide providing the equivalent 25 neutralization. Thus, a TBN of 10 means that one gram of 26 the composition has a neutralization capacity equal to 10 mg 27 of potassium hydroxide.

29 The term "hydrocarbyl" refers to an organic radical composed 30 of carbon and hydrogen which may be aliphatic, alicyclic, 31 aromatic or combinations thereof, i.e., aralkyl. The 32 hydrocarbyl radical may have a straight- or branched- chain 33 of carbon atoms and may be saturated or unsaturated.

01 Preferably the hydrocarbyl radical is free of acetylenic 02 unsaturation.

04 Lubricating Compositions 06 The lubricating compositions can be conveniently prepared by 07 simple blending or m; ~r; ng of the compounds of formula I with 08 an oil of lubricating viscosity. The compounds of formula I
09 may also be preblended as a concentrate or package with various other additives in the appropriate ratios to 11 facilitate blending of a lubricating composition cont~;n;ng 12 the desired concentration of additives. Typically the 13 lubricating composition of the invention contains about from 14 0.8 to 3 wt~, preferably about from 0.85 to 2 wt~ based on the total weight of the composition, of a silver protectant 16 selected from the lubricating oil soluble compounds of 17 formula I and mixtures thereof. More preferably, the 18 lubricating composition contains about from 0.9 to 1.5 wt~
19 of the said silver protectant.
21 The lubricating composition has a TBN of about 5 to 30, 22 preferably 15 to 25. This is a measure of the alkalinity or 23 neutralizing capacity and is typically provided by the 24 addition of basic detergents or overbased materials. The 25 function of the basic component is to neutralize acid 26 oxidation products, such as sulfuric acid in the case of 27 diesel fuels. Various ty~?es of overbased materials can be 28 used, such as, for example, sulfurized and/or carbonated 29 phenates, salicylates, and sulfonates. Various overbased phenates are described in U.S. Patent Nos. 2,680,096;
31 3,036,971; 3,336,224; 3,437,595; 3,801,507; and 4,251,379.
32 Various overbased sulfonates are described in U.S. Patent 33 Nos. 2,616,904; 2,626,207; 2,767,209; 3,126,340; 3,524,814;
34 and 3,609,076.

01 The present lubricating oil compositions will also typically 02 contain, in addition to the silver protectant, various 03 other additives used to impart desirable properties to 04 lubricating oil compositions used for internal combustion 05 engines having silver bearing parts. Thus, the lubricating 06 composition will typically contain one or more of the 07 following additives: detergents or detergent-dispersant, 08 dispersants, ashless dispersants, overbased detergents, 09 oxidation inhibitors and most preferably will contain a 10 combination of such additives and may contain other 11 additives designed to improve the properties of lubricating 12 oil compositions. Such additives are generally commercially 13 available and can be made by known procedures; however, if 14 desired, additional details regarding the manufacture of, 15 for example, overbased calcium sulfurized alkylphenate 16 detergents and succinimate dispersants can be had by 17 references to my co-pending application 08/099,632, hereby 18 incorporated by reference in its entirety and the references 19 cited therein.
21 The base oil can be a mineral, synthetic or natural oil 22 (vegetable or ~n~m~l-derived oils), but from an economic 23 standpoint, is preferably a mineral oil. Solvent refined 24 and hydrorefined base oils may also be used. Frequently a mixture of different oils is used as the base oil. The 26 individual oils typically have viscosities of about from 27 4 centistokes to 40 centistokes at 100C, and preferably 8 28 to 14 centistokes at 100C. The base oil or mixture of base 29 oils are typically preselected so that the final lubricating oil, containing the various additives, including the silver 31 protectant, has a viscosity at 100C of 4 to 22 centistokes, 32 preferably 10 to 17 centistokes and more preferably 13 to 17 33 centistokes.

216~15 01 Detergent-dispersant additives are designed to keep sludge, 02 carbon and products derived from the partial oxidation of 03 the diesel fuel or base oil, suspended in the base oil.
04 Suitable detergent-dispersants include phenate and sulfonate 05 metallic detergents, for example, calcium phenate or 06 sulfonate. Various ashless dispersants are described in 07 U.S. Patent Nos. 3,172,892; 3,219,666; 3,282,955; and 08 3,361,673. Succinimide and succinate ester ashless 09 dispersants are typically prepared by the reaction of polyisobutenyl succinic anhydride with a polyalkylene 11 polyamine or polyol, respectively.

13 The lubricating composition may also optionally contain 14 viscosity index improvers ("VI improvers") to regulate viscosity, i.e., reduce viscosity changes produced by 16 temperature changes, e.g., multi-grade oils. However, care 17 must be taken in using VI improvers because the VI improver 18 may be deleterious to silver bearings. Thus, it may be 19 desirable to increase the amount of silver protectant or add additional corrosion inhibitors where VI improvers are used.
21 The VI improver may be a non-dispersant viscosity improver 22 or a dispersant viscosity improver, which acts as a 23 dispersant as well as regulating viscosity. Examples of 24 non-dispersant VI improvers include various oil-soluble polymers typically having molecular weights in the range of 26 20,000 to 1,000,000 and include alkyl methacrylate polymers, 27 ethylene-propylene copolymers, mixed alkylmethylacrylate-28 ethylene-propylene polymers, isobutylene polymers, 29 hydrogenated styrene-diene polymers, and the like.
Dispersant VI improvers are also typically polymers, but 31 which incorporate some degree of nitrogen functionality 32 which imparts dispersancy to the molecular, in addition to 33 the viscosity, regulating effect. Examples of dispersant VI
34 improvers include styrene-based polyesters incorporating a 216891~

01 succinimide or substituted succinimide [e.g., 02 N-(3'-morpholin-4-ylpropyl) succinimide] unit; mixed alkyl 03 methacrylate-vinyl pyrrolidone polymers, aminated ethylene-04 propylene polymers; and the like. Compatible mixtures of VI
05 improvers can also be used. Where a VI improver is used, it 06 may be desirable to separately blend the VI improver with 07 the base oil rather than part of a package with-other 08 additives. The newer synthetic or poly alpha olefin base 09 oils may also afford multigrade performance or reduce the 10 amount of VI improver required.

12 With the possible exception of the inclusion of a viscosity 13 index improver, typically, best overall results in terms of 14 affording the properties desired in a modern lubricating oil 15 composition for internal combustion engines having silver 16 bearings are obtained wherein the lubricating composition 17 contains a compatible combination of additives representing 18 one or more and preferably each of the above classes of 19 additives in effective amounts as well as the silver 20 protectant of the present invention and a sufficient amount 21 of a neutral and/or overbased detergent, preferable both, 22 sufficient to provide the desired neutralization capacity 23 (typically expressed as TBN).

25 The lubricating composition may also contain small amounts 26 of supplemental corrosion inhibitors without harming the 27 properties of the composition and perhaps providing some 28 additional benefit and as above noted, may be desirable when 29 VI improvers are used. The corrosion inhibitor should not, 30 of course, be a corrosion inhibitor such as, for example, 31 zinc dithiophosphate which is itself corrosive to silver 32 bearings. Where supplemental corrosion inhibitors are used, 33 they are generally used in amounts of about from 0.02 to 34 1 wt% of the lubricating composition. Additional amounts of 2168~1~

01 supplemental corrosion inhibitor may not be harmful but 02 generally are not beneficial. Thus, for example, the 03 composition may contain, based on the total weight of 04 lubricating composition, about 0.02 to 0.08 wt~ of a 05 sulfurized olefin corrosion inhibitor (for example, 06 cosulfurized alkenyl ester/alpha olefins) and/or up to about 07 1~ by wt., preferably about from 0.5 to 0.8 wt~ of 08 terephthalic acid or a salt or derivative thereof. A
09 variety of sulfurized olefin corrosion inhibitors, as well as other corrosion inhibitors, are described in the 11 published literature and are available commercially. The 12 cosulfurized alkenyl ester/alpha olefin additives, for 13 example, typically prepared by reacting a mixture of the 14 desired olefins, typically C12-C20 linear olefins, and unsaturated esters, e.g., oleate, linoleate, with sulfur at 16 moderate to elevated temperatures via known procedures.
17 Various sulfurized olefin corrosion inhibitors or wear 18 inhibitors are described in U.S. Patent Nos. 4,053,427;
19 4,119,549 and 4,240,549. In the case of terephthalic acid corrosion inhibitors, either a solubilized form of the acid 21 is used, or more conveniently, when the additive package 22 includes a succinimide dispersant, the acid is simply 23 solubilized by reaction with the succinimide dispersant to 24 form an oil-soluble salt of terephthalic acid.
26 As above noted, the present invention also provides an 27 additive package or concentrate which may be added to an oil 28 of lubricating viscosity either as the sole additive or in 29 combination with other additives. (Generally, the additive package will not contain a viscosity index improver because 31 even where desired the viscosity index improver is generally 32 added to the base oil by the lubricant formulator.) Thus, a 33 preferred additive concentrate contains about from 5 to 34 14 wt~ more preferably 6 to 10 wt~ of the silver protectant 2168~1~

01 and sufficient basic material (typically overbased 02 detergents) to provide the concentrate with a TBN of about 03 from 60 to 180 preferably 60 to 120; and about 1 to 10 wt~
04 preferably 2 to 6 wt~ of a diluent oil. With the general 05 exception of the VI improver, the concentrate will 06 frequently also contain various other additives considered 07 desirable for the intended use and generally will contain 08 about from 30 to 60 wt~ of an ashless dispersant and 09 frequently will also contain neutral or slightly alkaline detergent in addition to the overbased detergent. The 11 amount of overbased detergent needed to provide the 12 requisite TBN will, of course, vary with the TBN of the 13 overbased detergent but typically will be 20 to 80 wt~ of 14 the concentrate.
16 The various additive materials or classes of materials 17 described above are known materials and can be prepared by 18 known procedures or obvious modifications thereof and 19 frequently are readily available from commercial sources.
21 A further understanding of the invention can be had from the 22 following nonlimiting examples.

SILVER WEAR EVALUATION

27 The lubricating oil compositions identified in Table 1 28 hereinbelow were evaluated for silver wear protection by the 29 standard silver bearing wear test EMD 2-567, also commonly known as the "2-Holer Test" used to assess the distress 31 rating of a silver-plated wrist pin after 25 hours of 32 operation.

216~91~

01 A test formulation was prepared by blending 0.6 wt~ of an 02 ethoxylated oleate ester having an average of about ten 03 exthoxy units per molecule, e.g.
04 CH3(CH2)7CH=CH(CH2)7C(O)O~CH2O)IoH, (sold under the tradename 05 Ethofat 10/20~ by AKZO Chemical Co. Inc. of McCook, 06 Illinois, USA) with a formulated 20W40 lubricating oil 07 containing 4.0 wt~ of a viscosity index improver and the 08 requisite amount of a sulfurized overbased calcium phenate 09 needed to provide a TBN of 17 and small amounts of other additives for example as ashless dispersant. The comparison 11 formulation was the identical to the test formulation but 12 without the ethoxylated oleate ester silver protectant.

14 In the 2-holer test, the normally protected silver bushing of the wrist pin bushing assembly is replaced with an 16 unprotected silver bushing. (Normally, the bushing is 17 protected with a thin lead flashing to protect the silver 18 surface from corrosion and high friction during break in.) 19 Removal of the lead flashing greatly increases the test severity. The test engine used in this evaluation had a D-1 21 type assembly. (The D-1 configuration uses three chrome-22 plated and one ferrite-filled cast iron compression rings 23 above the piston pin with one hooked scraper-type oil 24 control ring and one ventilated cast iron ring below the pin. The nominal compression ratio was 20:1.) 27 The engine is kept in newly built condition by periodic 28 replacement of the liners, pistons, rings, carriers, thrust 29 washers, cam bearings, rods, rod bearings, main bearings, and reconditioned heads with new valves and rebuilt 31 injectors.

33 For each silver wear test, the engine is thoroughly cleaned 34 with a commercial petroleum-based solvent and the wrist pin 2168~1~

01 replaced with a new piston pin and unprotected (i.e., 02 unleaded) silver-plated pin bearings. Prior to conducting 03 the silver wear test, the engine is given a full 9-hour and 04 20-minute EMD-type break-in. Following the break-in, the 05 crankcase and air boxes are inspected for signs of bearing 06 failure before the test phase is initiated. While under 07 test, the engine is held at 835 rpm, 91 i 1.0 lbs./hr. fuel 08 rate and 6.8 inches of Hg air box pressure by a distributed 09 digital process control computer. The water and oil inlet temperatures are controlled at 180 + 2F and 210 + 2F, 11 respectively. The crankcase and all oil lines are flushed 12 with test oil, and the crankcase is charged to its full 13 capacity of 45 U.S. gallons. The fuel for these tests 14 contained 0.1~ sulfur and the cetane number is a nom; n~l 47-50 No. 2 diesel. Each test is conducted using identical 16 test conditions. The pin bearings were weighed before and 17 after the test. The piston pin diameters and in-carrier 18 clearances were taken before and after the test.

At the conclusion of the test, the pin bearings were removed 21 and rated according to the EMD distress demerit procedure 22 which measures and assigns demerits based on the amount of 23 silver which has been displaced from the bearings into the 24 oil grooves. An average of 30 or less demerits with neither of the two bearings having 40 or more demerits is considered 26 a passing result. The engine using the comparison 27 lubricating oil composition had a right bearing demerit 28 rating of 8 and a left bearing demerit rating of 440 and 29 actually failed before completion of the test. In contrast to this engine using the lubricating oil formulation 31 containing the compound of formula I had a bearing demerit 32 rating of 9 for both the right and left bearings and passed 33 the test.

2168gl~

01 Obviously, many modifications of the invention described 02 hereinabove and below can be made without departing from the 03 essence and scope thereof.

Claims (11)

1. A method for reducing silver bearing wear in internal combustion engines having silver bearings which comprises lubricating said engines with an essentially chlorine-free and zinc dithiophosphate-free lubricating composition having a TBN of about from 5 to 30, consisting essentially of a major amount of an oil or mixture of oils of lubricating viscosity and an amount effective to inhibit or reduce wear or deterioration of said silver bearings of a silver protectant selected from the group of oil soluble compounds having the formula:

(I) (I) wherein R is a hydrocarbyl radical having about from 4 to 50 carbon atoms; R1 is independently selected from the group of alkylenes having 2 to 8 carbon atoms, and n is a whole integer of from 1 to about 30;

and mixtures thereof.

2. The method of Claim 1 wherein R is an aliphatic radical having at least 8 carbon atoms.

3. The method of Claim 2 wherein R has from 14 to 30 carbon atoms.

4. The method of Claim 1 wherein said composition has a TBN
of about from 10 through 25.

5. The method of Claim 1 wherein R is alkyl or alkenyl having 8 through 50 carbon atoms.

6. The method of Claim 5 wherein R has 14 to 30 carbon atoms.

7. The method of Claim 1 wherein n is a whole integer of from 8 to 20.

8. The method of Claim 1 wherein R1 has 2 through 4 carbon atoms.

9. The method of Claim 8 wherein R is alkyl or alkenyl having 14 to 30 carbon atoms.

10. The method of Claim 9 wherein RC(O)O- is oleoyloxy.

11. The method of Claim 10 wherein R1 has 2 through 4 carbon atoms and n is a whole integer of from 8 to 20.