CA1159436A

CA1159436A - Lubricant composition with improved friction reducing properties

Info

Publication number: CA1159436A
Application number: CA000388821A
Authority: CA
Inventors: Harold Shaub
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1980-11-10
Filing date: 1981-10-27
Publication date: 1983-12-27
Also published as: JPS57108194A; DE3169874D1; EP0051998B1; EP0051998A1

Abstract

ABSTRACT OF THE DISCLOSURE
A storage stable lubricating composition with improved friction reducing properties is provided by a lubricating oil which includes an additive combination of (1) an ester of a polycarboxylic acid with a glycol or glycerol, (2) a zinc dihydrocarbyl dithiophosphate and (3) an ashless dis-persant containing a high molecular weight aliphatic hydro-carbon oil solubilizing group attached thereto and a selec-ted amount of free hydroxyl groups.

Description

BAC~CGROUMD OF THE INVE~ITIO~I

2 This invention relates to a storage stable lu-

3 bricating oil composition having particularly improved

4 anti-friction properties.
There has been considerable effort in recent 6 years to develop lubricating oil compositions which will 7 reduce friction in engines and particularly automotive 8 engines. This effort is based on the need to improve the 9 fuel economy of such engines which operate on petroleum fuel, a product having a declining source of supply and 11 an escalating price. It is known that high engine fric-12 tion causes significant energy loss and thus one way to 13 improve fuel economy is to reduce such friction.
14 Xnown ways to solve the problem of energy losses due to high friction e.g., in crackcase motor oils in-16 clude the use of synthetic ester base oils which are ex- -17 pensive and ~the use of insoluble molybdenum sulfides 18 which have the disadvantage of giving the oil composition 19 a black or hazy appearance.
Another approach to reduce energy losses by the 21 use of a lubricating oil composition involves a composi-22 ticn containing an additive combination of an oil soluble 23 friction reducing ester component derived from esterifi-24 cation of a polycarboxylic acid wi'h a glycol and a zinc dihydrocarbyl dithiophosphate. This type of composition 26 is disclosed in U.S. Patent 4,105,571 which notes that 27 while a lubricating composition containing the additive 28 package of such ester and zinc thiophosphate components 29 provides excellent anti-friction and anti-wear properties, it presents compatability and stability problems. The 31 problem is solved by adding a selected ashless dispersant 32 containing a high molecular weight aliphatic hydrocarbon 33 oil solubilizing group attached thereto to the composi-34 tion, and preferably predispersing either the ester and/
or zinc thiophosphate components prior to their addition ~._.

- 2 _ 1 to the remainder of the composition. Such ashless dis-2 persants may contain hydroxyl groups as noted in tne 3 patent.
4 r~rnile the above approaches all provide reduced engine friction and consequently improved fuel economy, 6 there is always the need and desire for further reductions 7 in energy losses due to friction or otherwise since even 8 small reductions per engine can result in a rather large 9- savings in fuel, particularly when considering the total number of engines in use.
11 SU~ RY OF THE INV~NTIOM
_ .
12 It has now surprisingly been discovered that 13 lubricating oil compositions containing an additive combi-14 nation of an ester of a polycarboxylic acid and a glycol or glycerol plus zinc dihydrocarbyl dithiophosphate can be made storage stable and have particularly improved 17 friction reducing properties when an ashless dispersant 18 containing a selected amount of free hydroxyl is used.
19 ~ore particularly a storage stable lubricating oil compo-sition with improved friction reducing properties is 21 provided by the composition of this invention which in-22 cludes an additive combination of (1) an ester of a 3 polycarboxylic acid with a glycol or glycerol, (2) a 24 zinc dihvdrocarbyl dithiophosphate and (3) an ashless dispersant containing a high molecular weight aliphatic 26 hydrocarbon oil solubilizing group attached thereto and 27. a selected amount of free hydroxyl groups.
28 In accordance with the present invention a 29 storage stable lubricating oil composition with improved friction reducing properties is provided by a composition 31 comprising a major portion of lubricating oil, from about 32 0.01 to 1.0 parts by weight of an es.er of a polycarboxylic 33 acid with a glycol or glycerol, from about 0.01 to about 34 5.0 parts by weight of zinc dihydrocarbyl dithiophosphate and from about 0.1 to about 20 parts by weight of an 36 hydroxyl containing ashless dispersant having a high molecular weight aliphatic hydrocarbon oil solubilizing group attached thereto, said dispersant containing from about 0.35 to about 1.8 millimoles (mM) of free hydroxyl per gram of dispersant, all weights based on 100 parts by weight of said lubricating oil composition.
In another aspect, the invention provides a method of re-ducing friction in an internal combustion engine comprising lubri-cating the engine using a lubricating oil composition as just described.
DETAILED DESCRIPTION OF THE INVENTION
As previously indicated the present invention relates to a storage stable lubricating oil composition having particularly im-proved friction reducing properties comprising an additive combina-tion of an ester of a polycarboxylic acid and a glycol or glycerol, zinc dihydrocarbyl dithiophosphate and an ashless dispersant con-taining a selected amount of free hydroxyl groups.
The oil soluble friction reducing ester component used in the composition of this invention generally, can be any hdyroxy substituted oil soluble ester of a polycarboxylic acid.
Best results are, however, obtained when such compounds are derived from the esterification of a polycarboxylic acid with a glycol or glycerol, preferably glycol. Such an ester may be a par-tial, di- or polyester with typical formulas of the ester repre-sented by the following general formulas when using a glycol:
(1) HO-R-OOC-R"-COOH
(2) HO-R-OOC-R"-COOR'-OH
(3) HO-R-OOC-R"-COOR-OOC-R"-COOR'-OH
wherein R" is the hydrocarbon radical of said acid and each R and R' may be the same or different hydrocarbon radicals associated with a glycol or diol as hereinafter defined. It will, of course, be appreciated that esters of the type illustrated by the fore-going formulas can be obtained by esterifying a polycarboxyli.c acid, or a mix-ture of such acids, with a diol or mixture of such diols.
The polycarboxylic acid used in preparing the ester may be an aliphatic saturated or unsaturated acid - 3a -1 and will generally have a total of about 24 to about 90, 2 pref2rably about 24 to about 60 carbon atoms and about 2 3 to about 4, re~erably about 2 to about 3 and more pref-4 erably about 2 carboxyiic acid groups witn at least about 9 up to about 42 carbon atoms, preferably about 12 to 6 about 42 and more preferably about 16 to about 22 carbon 7 atoms between the carboxylic acid groups.
8 The oil insoluble glycol which is reacted with 9 the polycarboxylic acid may be an alkane diol, i.e.
alkylene glycol or an oxa-alkane diol, i.e. polyalkylene 11 glycol, straight chain or branched. The alkane diol may 12 have from about 2 to about 12 carbon atoms and preferably 13 about 2 to about 5 car~on atoms in the molecule and the 14- oxa-alkane diol will, generally, have from about 4 to about 200, preferably about 4 to about 100 carbon atoms.
16 The oxa-alkane diol (polyal]sylene glycol) will, of course, 17 contain periodically repeating groups of the formula:
18 _ _ H H
21 x 22 wherein R may be H, CH3, C2H5 or C3H7, and x is 2 to 100, 23 preferably 2 to 25. The preferr2d alkane diol or alkylene 24 glycol is ethylene glycol and the preferred oxa-alkane diol or polyalkylene glycol is diethylene glycol. As 26 indicated previously, glycerol may also be used in pre-27 paring the ester of polycarboxylic acid and it is con-28 templated that such component will also include its higher29 molecular weight analogues.
~rnile any of the esters as set forth above can 31 be effectively used, best results are, however, obtained 32 wit'n such compounds wherein the carboxyl groups of tne 33 polycarboxylic acid are separated from each other by from 34 about 16 to aoout 22 carbon atoms and wllerein the hydroxy groups are separated from the closest carboxyl group by 36 from about 2 to about 12 carbon atoms. Particularly 1 desirable results have been obtained with additives pre-2 ~ared by esterifying a dimer of a fatty acid particularly 3 those containing conjugated unsaturation with a poly-4 hydroxy compound. Such dimers are, of course, clearly taught in U.S. Patent 3,180,832 which was granted on 6 April 27, 1965 and U.S. Patent 3,429,817 which was granted 7 on February 25, 1969, and as there indicated, the hydro-8 carbon portion of the dimer or dicarboxylic acid thus 9 obtained may contain a six member ring. ~he formation of the dimer from linoleic acid, oleic acid and mixtures of 11 these acids is illustrated by the following:
12 A. CH3(cH2)4cH=cHcH2cH=cH(cH2)7coo~ ~ 30005 13 9, 12 Linoleic ~cid 14 2 molecules CH3(CH2)5CH=CHCH=CH(CH2)7COOH 9-11 acid 16 3iels-Alder 17 9,11 Linoleic Acid A
18( 2~7 ~ (CH2)5CH3 19;~OOC(CH2) ~ ~CH2)5CH3 20Linoleic Acid Dimer (dilinoleic acid) 212 mole~ules 23 3 2 72 7 Diels Alder 24 Oleic Acid ~
CH3(CH2)7CH 5~(Cil2)7 26 CH3(CH~)7CH2CH(CH2)7COOH
27 Oleic Acid Dimer (Dioleic Acid) 28 C. 9,11 Linoleic Acid + Olei~ Acid 29 CH3(CH2)6CHCH=CH(cH2)7cooH
CH3(cH2)4cHcH=cHcH=cH(cH2)7cooH
31 ~i~ed Dimer 32 It will, of course, be appreciated that while the reac-33 tions illustrated produce the dimers, commercial applica-34 tion of the reactions will, generally, lead to trimer 1 formation and in some cases the pxoduct thus obtained will 2 contain minor amounts of unreacted monomer or monomers.
3 As a result, commercially available dimer acids may con-4 tain as much as 25% trimer and the use of such mixtures is within the scope of the present invention.
6 The preferred hydroxy-substituted ester lubri-7 city additives useful in the present invention will be 3 the reaction product of a dimerized fatty acid, such as 9 those illustrated, and an oil insoluble glycol and may be produced by various techniques. As praviously pointed 11 out, the preferred acid dimers are the dimers of linoleic 12 acid, oleic acid or the mixed dimer of linoleic and oleic 13 acids, which may also contain some monomer as well as 14 trimer. Other specifically satisfactory glycols in addi-lS tion to ethylene glycol and polyethylene glycol are, for 16 example, propylene glycol, polypropylene glycol, butylene 17 glycol, polybutylene glycol and the like.
18 The zinc dihydrocarbyl dithiophosphates useful 19 in the present invention are salts of dihydrocarbyl esters of dithiophosphoric acids and may be represented by the 21 following formula: _ _ 24 RO - P - S Zn 26 OR' 2 27 wherein R and R' may be the same or different hydrocarbyl 28 radicals containing from 1 to 18 and preferably 2 to 12 29 carbon atoms and including radicals such as alkyl, alkenyl, aryl, aralkyl, alkaryl and cycloaliphatic radicals. Par-31 ticularly preferred as R and R' groups are alkyl groups of 32 2 to 8 carbon atoms. Thus, the radicals may, for example, 33 be ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl, 34 tert-butyl, amyl, n-hexyl, i-hexyl, n-heptyl, n-octyl, decyl, dodecyl, octadecyl, 2-ethylhexyl, phenyl, butyl-36 phenyl, cyclohexyl, methylcyclopentyl, propenyl, butenyl, c~

1 etc. In order to obtain oil solubility, the total number 2 of carbon atoms in the dithiophosphoric acid will average 3 about S or greater.
4 The zinc dihydrocarbyl dlthiophosphates which are useful in the compositions of the present invention 6 may be prepared in accordance ~ith known techniques by 7 first esterifying a dithiophosphoric acid usually by 8 reaction of an alcohol or phenol with P2S5 and then neu-9 tralizing the dithiophosphoric acid ester with a suitable zinc compound such as zinc oxide. In general, the alcohol 11 or mixtures of alcohols containing from 1 to 13 carbon 12 atoms may be used to effect the esterification. The 13 hydrocarbon portion of the alcohol may, for example, be 14 a straight or branched chain alkyl or al~enyl group, or a cycloaliphatic or aromatic group. ~mong the alcohols which are generally preferred for use as starting mate-17 rials in the preparation of the esters may be mentioned 18 ethyl, isopropyl, amyl, 2-ethylhexyl, lauryl, stearyl and 19 methyl cyclohexyl alcohols as well as commercial mixtures o~ alcohols, such as the mixture of alcohols derived from 21 coconut oil and known as "Lorol B" alcohol, which mixture 22 consists essentially of alcohols in the C10 to C18 range.
23 Other natural products containing alcohols such as the 24 alcohols derived from wool fat, natural waxes and the li~e may be used. ;qoreover, alcohols produced by the oxidation 26 of petroleum hydrocarbon products as well as the Oxo-27 alcohols produced from olefins, carbon monoxide and 28 hydrogen may be employed. Further aromatic compounds such 29 as alkylated phenols of the type n-butyl phenol, tertiary-amyl phenol, diamyl phenol, tertiary octyl phenol, cetyl 31 phenol, petroleum phenol and the like as well as the 32 corresponding naphthols may be employed in like manner.
33 Following the esterification, the diester is 34 then neutralized with a suitable basic zinc compound or a mixture of such compounds. In general, any compound 36 could be used but the oxides, hydroxides and carbonates 1 are most generally employed.
2 Generally, any lubricating oil ashless disper-3 sant containing a high ~olecular weight aliphatic hydro-4 carbon oil solubilizing group attached thereto and the selected amount of free hydroxyl groups can be used in 6 the composition of this invention. More particularly, 7 said dispersant will contain from a~out 0.35 to about 1.8 8 millimoles of free hydroxyl per gram of dispersant, pref-9 erably from about 0.5 to about 1.5 and more preferably about 0.7 to about 1.3 millimoles of free hydroxyl per 11 gram of dispersant. In referring to dispersant in the 12 context of free hydroxyl groups, the gram weight is of 13 active dispersant, i.e. it does not include the carrier 14 or lubricating oil in which the dispersant is diluted or otherwise dispersed.
16 The significance of the hydroxyl content in the 17 dispersant is the essential feature of this invention 18 since it has surprisingly been found that controlling 19 hydroxyl content per gram of active dispersant results in significantly lower engine friction. Additionally, there 21 is a minimum amount of hydroxyl content which must be 22 maintained in the dispersant in order to retain composi-23 tion stability. Accordingly, it is essential that the 24 dispersant contain a selected amount of free hydroxyl content as described herein to provide a lubricating 26 composition with improved friction reducing properties 27 while retaining its stability.
28 A variety of compounds may be used as the ash-29 less dispersant in the composition of this invention provided they have a suitable high molecular weight ali-31 phatic hydrocarbon oil solubilizing group attached thereto 32 and most important a selected amount of free hydroxyl 33 groups. 3ispersant compounds of this type include esters 34 of mono and polycarboxylic acids witll polyhydric alcohols, p~enols and naphthols as well as nitrogen containing 36 compounds containing the necessary hydroxyl content as l previously noted. It is contemplated that mixtures and 2 a wlde variety of compounds may be utilized as the ash-3 less dispersant or ashless dispersant system in this in-4 vention provided the necessary functionality is available, S particularly the selected amount of free hydroxyl content.
6 Thus, the ashless dispersant of this invention may comprise 7 a mixture of a hydroxylated and non-hydroxylated compound 8 provided the necessary functionality as defined herein is 9 satisfied. Accordingly, the term ashless dispersant as used throughout this application is intended to include ll such mixtures and combination of compounds thereof.
12 The different dispersants which can be used in 13 this invention are characterized by a long chain hydro-14 carbon group or groups, which may be attached, e.g. to the acid, so the acid contains a total of about 50 to 16 about 400 carbon atoms, said acid being attached, e.g.
17 to an amine and/or ester group or both.
18 Ester containing ashless dispersants of this19 invention can be derived from polyhydric aliphatic alcohols or polyhydric aromatic hydroxyl containing com-21 pounds such as phenols and naphthols. The polyhydric 22 alcohols and aromatic compounds used will preferably 23 contain from 2 to about 10 nydroxy radicals and are 24 illustrated by ethylene glycol, diethylene glycol, tri-25 ethylene glycol, tetraethylene glycol, dipropylene glycol, 2~ tripropylene glycol, dibutylene glycol, tributylene 27 glycol, and other alkylene glycols in which the alkylene 28 radicals contain from about 2 to about 8 carbon atoms.
29 Also, resorcinol, catechol, p,p'-dihydroxybiphenyl, 4,4'-methylene bis-phenol, di (nydroxyphenyl) oxide, 31 and di (hydroxyphenyl) sulfide. Other useful polyhy-7ric 32 compounds include glycerol, mono-oleate of glycerol, 33 pentaerythritol, trimethylol propane, 9,10-dihydroxy-34 stearic acid, 1,2-butanediol, 2,3-hexanediol, 2,4 hexane-35 diol, ?inacol, erythritol, arabitol, sorbitol, mannitol, 36 and 1,2-cyclohexanediol. Carbohydrates such as sugars, 37 starches, cellulose, etc., likewise may yield appropriate 3'~

1 esters as exempllfied by flucose, fructose, sucrose, 2 rhamnose, mannose, glyceraldehyde, and galactose.
3 An especially preferred class of polyhydric 4 alcohols are those having at least three hydroxy radicals,

5 some o~ which have been esterified with a monocarboxylic

6 acid having from about 8 to about 30 carbon atoms such as

7 octanoic acid, oleic acid, stearic acid, linoleic acid, ~ dodecanoic acid or tall oil acid. Examples of such g partially esterified polyhydric alcohols are the mono-10 oleate of glycerol, monosterate of glycerol, di-dodecanote 11 of erythritol.
12 T~e ester dispersant of this invention may also 13 be derived from unsaturated alcohols, ether-alcohols, and 14 amino alcohols including for example: oxy-alkylene, lS oxy-arylene, amino-alkylene, and amino-arylene substituted 16 alcohols. Such compounds include di (hydroxyethyl~ amine, 17 tri (hydroxypropyl) amine, N,~,~FN-tetrahydroxytrimethyl-18 enediamine, 2-amino-2-methyl-1,3 propanediol, 2-amino-2-19 ethyl-1,3-oropanediol, tris (hydroxymethyl) amino-methane, 20 etc.
21 As indicated earlier, the particular dispersants 22 used in this invention contain a long chain hydrocarbon 23 group which will generally have about 50 to about 400 24 carbon atoms and oreferably will be derived from an alkenyl succinic acid/anhydride where the alkenyl radical will 26 have a molecular weight of at least about 900 and pref-27 erably at least about 1200 and more preferably at least 28 about 1300.
29 A large number of dispersants having the above identified characteristics can be used in this invention 31 some of which are disclosed in U.S. Patents 4,105,571;
32 3,542,678; 3,522,179; 3,542,680i 3,632,511; and 3,804,763.
33 Methods for preparing such dispersants are generally well 34 known and are also disclosed in the noted patents. Some particularly preferred dispersant combinations include 36 1) a combination of a polyisobutenyl succinic anhydride, 37 a hydroxy compound e.g. pentaerythritol and a polyoxy-1 alkylene ~olyamine e.g. ~olyoxypropylenediamine and a 2 2olyalkylene ~ol~amine e.g. polyet!lylenediamine and 3 .etraet'lylene pentamine and ~) a combination of polyiso-4 butenyl succinic anhydride, polyal~ylene polyamine e.g., tetraethylene 2entamine and a polyhydric alcohol or poly-6 hydroxy-substituted aliphatic pri~ary amine e.g. ~enta-7 erythritol or trismethylolaminomethane.

8 In general, the zinc dihydrocarbyl dithiophos-

9 phate will be used in the lubricating composition at a

10 concentration within the range of about 0.01 to about 5

11 parts by weight per 100 parts of lubricating oil composi-

12 tion and preferably from about 0.5 to about 1.5. The

13 polycarboxylic acid/glycol or glycerol ester will be used

14 at a concentration of about 0.01 to about 2.0, preferably

15 about 0.05 to about 1.0 and more preferably 0.05 to 0.5

16 parts by weight per 100 parts of lubricating oil composi-

17 tion and the ashless dispersant will be employed at a

18 concentration of about 0.1 to about 20 and preferably

19 about 0.5 to about 10 parts by weight per 100 parts of

20 lubricating oil composition.

21 The lubricating oil liquid hydrocarbons which

22 may be used include the mineral lubricating oils and the

23 synthetic lubricating oils and mixtures thereof. The

24 synthetic oils will include diester oils such as di (2-ethylhexyl) sebacate, azelate and adipate; complex 26 ester oils such as those formed from dicarboxylic acids, 27 glycols and either monobasic acids or monohydric alcohols;
23 silicone oils; sulfide esters; organic carbonates; and 29 other synthetic oils known to the art.
Other additives, of course, may be added to t,he 31 oil compositions of the ~resent invention to form a 32 finisned oil. Such additives may be the conventionally 33 used additives including oxidation inhibitors such as 34 phenothiazine or phenyl C7~naphthylamine; rust inhibitors 35 such as lecithin or sorbitan monoleate; detergents such 36 as barium phenates; pour point depressants such as co-~olymers of vinyl ace~ate with fumaric acid esters of 1 ~oconut oil alcoholsi viscosity index improvers such as 2 ole~in co?olymers, pol~methacrylates; etc. I~ particularly 3 useful additive i5 the basic alkaline earth metal salts ~ of an organic sulfonic acid, generally a ~etroleum sulfonic acid or a synthetically prepared alkaryl sulfonic 6 acid. Among the ~etroleum sulfonates, the most useful 7 products are those prepared by the sulfonation of suitable 8 petroleum fractions with subsequent removal of acid sludge g and purification. Synthetic alkaryl sulfonic acids are usually prepared from alkylated benzenes such as the 11 Friedel-Crafts reaction product of benzene and a polymer 12 such as tetrapropylene. Suitable acids may also be 13 obtained by sulfonation of alkylated derivatives of such 14 compounds as diphenylene oxide thianthrene, phenolthioxine, diphenylene sulfide, phenothiazine, diphenyl oxide, di-16 phenyl sulfide, diphenylamine, cyclohexane, decahydro 17 naphthalene and tlle like.
18 Basic alkaline earth metal sulfonates are gener-19 ally prepared by reacting an alkaline earth metal base, e.g. lime, magnesium oxide, magnesium alcoholate with CO2 21 in the presence of sulfonic acid or neutral metal sulfo-22 nates, ordinarily the calcium, Magnesium or barium salts.
23 These neutral salts in turn may be prepared from the free 24 acids by reaction with the suitable alkaline earth metal base, or by double decomposition of an alkali metal 26 sulfonate, which methods are well known in the art.
27 Further details are described in U.S. Patent No. 3,562,159.
28 The composition of this invention is particularly 29 useful when metal containing additives such as the normal and basic metal phenates, sulfonates or sulfurized 31 phenates are used since such components have been known 32 to cause compatability problems in more conventional type 33 lubricant compositions.

34 The above described additive package may be used in conventional base oils with other conventional addi-36 tives. While tlle components can generallv be added in 37 their normal and conventional manner, it is a preferred 1 2~L,odimer.t of t:nis invention to .~eep ~he zinc dihydrocarbyl 2 ~ aiophosphate and polycarboxylic acid/glycol or glycerol 3 ester components apart from one another until at least 4 one of SUCL1 components has been predis?ersed as described 5 in U.S. 4,105,571. This will help to maintain a storage 6 stable and compatible composition. By predispersed it 7 is meant that the ester component or the zinc component 8 or both separately are mixed with the ashless dispersant, 9 which may be in oil solution, until the solution is lO generally clear.
ll The following examples are further illustrative 12 of this invention and are not intended to be construed as 13 limitations thereof.
14 E~A~lPLE 1 Formulations were prepared using a lOW-40SE
16 quality automotive engine oil containing 1.5% by weight, 17 based on the total lubric~ting oil weight, of zinc dialkyl 18 dithiophosphate (80% active ingredient in diluent mineral 19 oil) in which the al]~yl groups were a mixture of such 20 groups having ~etween 4 and 5 carbon atoms and made by 21 reacting P2S5 with a mixture of about 65% isobutyl alco-22 l~ol and 35% of amyl alcohol; 0.1% by weight, based on the 23 total lubricating oil weight of an ester formed by esteri-24 fication of a dimer acid of linoleic acid and diethylene

25 glycol and having the formula:

2276 HocH2cE~2ociH2cH2oc (CH2)7CH=CH (CH2)5CH3 29 H0CH2CH20cH2cH20~l(cH2)7 ~ (CH2)5CH3 This additive is actually a mixture of the 31 structure shown plus ~igher molecular weight repeating 32 units (polymers) of this material.
33 Dispersants containing different amounts of free 34 hydroxyl contents were used in the different lubricating formulations as described ~elow:

3~

1 A) 5.25% by wt. of dispersant (mixture of 46.5%
2 by weignt active ingredient in mineral lubricating oil) 3 was used, said dispersant prepared by reacting polyiso-4 butenyl succinic anhydride (pIssA)~ the polyisobutenyl radical (PIB) having an average molecular weight (.`~n) of 6 about 900 with an equal molar amount of pentaerythritol 7 and a minor amount of a polyamine mixture comprising 8 polyoxypropylene amine and polyethylene amines to form a 9 a product having a nitrogen content of about 0.35% by weight and having a millimole (m.~) hydroxyl per gram of 11 active ingredient of 2.00. ~aterials of this type are 12 described in U.S. Patent 3,804,763 and sold by Lubrizol 13 Corporation under the tradename ~ubrizol 6431;
14 B) A dispersant similar to A described above but having about 75~ of the pentaerythritol added was 16 prepared and llad a nitrogen content of 0.27% and 1.55 m~
17 of hydroxyl per gram of active ingredient;
18 C) ~nother dispersant similar to A described 19 above but using about 50% of the pentaerythritol was pre-pared and had a nitrogen content of 0.44~ and 1.25 m,~ of 21 hydroxyl per gram of active ingredient;
22 3) Another dispersant similar to A described 23 above was prepared using 10% of pentaerythritol and had 24 a nitrogen content of 1.05% and 0.75 ~`~ of hydroxyl per gram of active ingredient.

26 The dispersants noted above were added to the

27 lOW-40SE crankcase oil along with the other additives and

28 a rust inhibitor, i.e. overbased magnesium sulfonate, a

29 detergent and a VI improver, i.e. an ethylene-propylene copolymer.
31 The above noted compositions all exhibited 32 storage stability and compatibility over an extended period 33 and were further tested for relative friction using a ball 34 on cylinder test.
The apparatus used in the ball on cylinder test 36 is described in the Journal of the American Society of 1 Lubrication Engineers, entitled i'ASLE Transactions", 2 Vol. 4 pages 1-11, 1961. In essence, the apparatus con-3 sists basically of a fixed metal ball loaded against a 4 rotating cylinder. The weight on the ball and the rota-tion of the cylinder can be varied during any given test 6 or from test to test. Also, the time of any given test 7 can be varied. Generally, however, steel on steel is 8 used at a constant load, a constant rpm and a fi~ed time 9 and in each of the tests of this example, a 4Xg load, 0.26 rpm and 70 minutes was used. The actual friction was 11 determined from the power actually required to effect 12 rotation and the relative friction determined by ratioing 13 the actual load to that of a standard. The apparatus and 14 method used is more fully described in U.S. Patent No.
3,129,580 which was issued ~ay 21, 1964 to Furey et al 16 and which is entitled "Apparatus for ~leasuring Friction 17 and Contacts Between Sliding Lubricating Surfaces".
1~ The results of ball on cylinder test are given 19 below:
~ OH per gram Coeff of Frict.
21Composition of Active Dispersant @70 ~lin.
22 A 2.0 .135 23 B 1.55 .095 24 C 1.25 .~75 D 0.75 .055 26 ~hile noting in the above composition that the 27 amount of friction was significantly reduced by decreasing 28 the hydroxyl content, it was ascertained that a level of 29 about 0.35 mM OE/gram of active dispersant was needed to have a compatible system. Thus, the surprising friction 31 effects of using the composition of this invention where-32 in a dispersant having selected hydroxyl content is used 33 is readily shown by the results.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a storage stable lubricating oil composi-tion with friction reducing properties comprising a major portion of lubricating oil, from about 0.01 to about 2.0 parts by weight of an ester of a polycarboxylic acid with a glycol or glycerol, from about 0.01 to about 5.0 parts by weight of zinc dihydrocarbyl dithiophosphate and from about 0.1 to about 20 parts by weight of a hydroxyl con-taining ashless dispersant having a high molecular weight aliphatic oil solubilizing group attached thereto, all weights based on 100 parts by weight of lubricating oil composition, the improvement comprising said disper-sant containing from about 0.35 to about 1.8 millimoles of free hydroxyl groups per gram of dispersant.

2. The composition of claim 1 wherein said dispersant is derived from an alkenyl succinic acid or anhydride with said alkenyl group having a molecular weight of at least about 900.

3. The composition of claim 2 wherein said dispersant contains from about 0.5 to about 1.5 millimoles of free hydroxyl groups per gram of dispersant.

4. The composition of claim 3 wherein said dispersant is an ester or nitrogen containing alkenyl succinic acid or anhydride derived from polyhydric alcohols, phenols and naphthols.

5. The composition of claim 4 wherein said polycarboxylic acid ester is formed from a dicarboxylic acid having from about 9 to about 42 carbon atoms between carboxylic acid groups and a glycol which is selected from the group consisting of alkane diols having from about 2 to about 12 carbon atoms or an oxa-alkane diol having from about 4 to about 200 carbon atoms.

6. The composition of claim 5 wherein the di-hydrocarbyl groups of said zinc compound are alkyl groups of from about 2 to about 8 carbon atoms.

7. The composition of claim 6 which contains a metal containing additive comprising a normal or basic metal phenate, sulfonate or sulfurized phenate.

8. The composition of claim 6 wherein said polycarboxylic acid ester is formed from a dimer acid of a conjugated fatty acid having from about 16 to about 22 carbon atoms between carboxylic acid groups.

9. The composition of claim 8 wherein said polycarboxylic acid ester is formed by the esterification of a dimer acid of linoleic acid and diethylene glycol.

10. The composition of claim 1 which is prepared by predispersing either said zinc dihydrocarbyl dithio-phosphate or said ester of polycarboxylic acid or both separately in said dispersant prior to combining them in the lubricating oil composition.

11. A method of reducing friction in an internal combustion engine comprising lubricating said engine using a lubricating oil composition as claimed in claim 1.

12. The method of claim 11 wherein said dispersant is derived from an alkenyl succinic acid or anhydride with said alkenyl group having a molecular weight of at least about 900.

13. The method of claim 12 wherein said dispersant contains from about 0.5 to about 1.5 millimoles of free hydroxyl groups per gram of dispersant.

14. The method of claim 13 wherein said dispersant is an ester containing derivative of alkenyl succinic acid or anhydride derived from polyhydric alcohols, phenols and naphthols.

15. The method of claim 14 wherein from about 0.01 to about 2.0 parts by weight of said polycarboxylic acid ester is used and said composition also contains from about 0.01 to about 5.0 parts by weight of zinc dihydrocarbyl dithiophosphate, said weights based on 100 parts by weight of lubricating oil composition.

16. The method of claim 15 wherein said polycarboxy-lic acid is formed from a dicarboxylic acid having from about 9 to about 42 carbon atoms between carboxylic acid groups and a glycol which is selected from the group consisting of alkane diols having from about 2 to about 12 carbon atoms or an oxa-alkane diol having from about 4 to about 200 carbon atoms.

17. The method of claim 16 wherein said polycarboxy-lic acid ester is formed from a dimer acid of a conjugated fatty acid having from about 16 to about 22 carbon atoms between carboxylic acid groups.

18. The method of claim 17 wherein said dispersant contains from about 0.7 to about 1.3 millimoles of free hydroxyl groups per gram of dispersant.