DK162656B - APPLICATION OF A LUBRICANE OIL COMPOSITION CONTAINING A BORATED GLYCEROL FAT ACID ESTATE FOR REDUCING BRAKE NOISE FROM OIL SUBMITTED DISC BRAKES - Google Patents

Description

DK 162656 B

This invention relates to the use of lubricating oil compositions for reducing brake noise from oil-immersed disc brakes.

The use of heavy machinery, such as drive machines, has increased the demand for high-performance lubricating compositions. Modern powertrain features many servo components, such as power steering and servo brakes. Servo brakes are preferably disc type as they have greater braking capacity. The preferred 10 disc brakes are the wet type brake which is immersed in a lubricant and therefore insulated from dirt and grime.

Such brakes suffer from a problem, namely the brake clamp or brake pipe. This phenomenon consists in a very unpleasant noise that occurs when applying the brake. So far, brake lubricant compositions have been added to friction modifiers, such as dioleyl hydrogen phosphite, to reduce noise. Lubricating compositions containing this additive tend to suffer from very high wear rates, especially at high temperature.

A further complication in removing brake noise is the desire to use the same working fluid, not only for brake lubrication, but also for lubrication of other drive parts, such as the hydraulic 25 and mechanical power take-offs, the drive transmission, gears and bearings, etc. The working fluid should act as a lubricant, a power transfer agent and as a heat transfer medium. Obtaining a composite fluid to meet all these requirements without brake noise is difficult.

30 U.S. Patent No. 3,151,077 discloses the use of borated monoacylated trimethylol in alkanes as engine fuel and lubricating oil additives.

The additives are said to reduce the appearance of surface ignition in an internal combustion engine and inhibit the build-up of carburetor deposits.

U.S. Patent No. 2,795,548 discloses the use of lubricating oil compositions containing borated glycerol monooleate. The oil compositions apply 2

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is turned in the crankcase of an internal combustion engine to reduce the oxidation of the oil and corrosion of the metal parts of the engine.

It has now been found that oil-soluble borated glycerol fatty acid esters act as a suitable friction modifier which, when added to a lubricating oil, has good anti-noise properties.

Accordingly, the invention relates to the use of a composition comprising a lubricating oil, containing 0.1-5% by weight of a borated fatty acid ester of glycerol, for reducing brake noise from oil-immersed disc brakes by lubricating the contact surfaces of the oil-immersed disc brakes with the composition.

The borated fatty acid glycerol esters are prepared by borating a fatty acid glycerol ester with boric acid while removing the reaction water. Preferably, sufficient boron is present so that each boron atom will react with from 1.5 to 2.5 hydroxy groups present in the reaction mixture.

The reaction can be carried out at a temperature in the range of 60 to 135 ° C, with or without any suitable organic solvent such as methanol, benzene, xylenes, toluene, neutral oil and the like.

Fatty acid glycerol esters can be prepared by a variety of known methods. Many of these esters such as glycerol monooleate and glycerol thalloate are commercially produced. The esters useful for this invention are oil soluble and are preferably prepared from Cg to C22 fatty acids or mixtures thereof, such as those found in natural products. The fatty acid may be saturated or unsaturated. -Some compounds found in acids from natural sources may include lactic acid containing a keto group. The most preferred C 6 to C 22 fatty acids are those of the formula R-COOH, wherein r is alkyl or alkenyl.

The fatty acid monoester of glycerol is preferred, however, mixtures of mono- and diesters can be used. It is preferred that any mixture of mono- 3

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and diesters contain at least 40% of the monoester.

Preferably, mixtures of mono- and diesters of glycerol contain from 40 to 60% by weight of monoester. Eg. commercial glycerol monooleate contains a mixture of 5 from 45 to 55% by weight of monoester and from 55 to 45% diester.

Preferred fatty acids are oil, stearin, palmitin, myristin, palmitol, linoleic, lauric, linolenic and eleostearic acids, as well as the acids from the natural products tallow, palm oil, olive oil, peanut oil, corn oil, clove oil beer.

A particularly preferred acid is oleic acid.

The lubricating compositions used according to the invention contain a substantial portion of lubricating oil and from about 15% to about 15%. 0.1 to 5.0% by weight borated fatty acid glycerol ester, preferably from 0.5 to 2% by weight, based on the weight of the total composition.

The optimal amount of borated fatty acid ester of glycerol within these ranges will vary slightly depending on the base oil and other additives present.

Additive concentrates are also relevant for the purposes of the present application. In the concentrated additive form, the borated fatty acid glycerol ester is present at a concentration ranging from 5 to 50% by weight.

The lubricating compositions are prepared by admixture using conventional techniques of the appropriate amount of the desired borated fatty acid glycerol ester in the lubricating oil. In preparing concentrates, the amount of lubricating oil is limited but sufficient to dissolve the required amount of borated fatty acid glycerol ester. In general, the concentrate will contain enough borated fatty acid ester of glycerol to allow a subsequent dilution of 1 to 10 times more lubricating oil.

The lubricating oil which may be used in the practice of the invention includes a wide variety of hydrocarbon oils 4

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from synthetic or natural sources, such as naphthenic, paraffinic, and mixed base oils, obtained by refining crude oil. Other lubricating oils from shale oil, tar sands or coal are also applicable. The lubricating oils 5 can be used individually or in combinations where they are miscible. The lubricating oils generally have a viscosity ranging from 7.4-1079 cSt. and generally from 20.5 to 324 cSt at 37.8 ° c. The preferred oils have a "SAE rating" ranging from 10 to 40 and are paraffinic 10 in structure.

In some powertrain systems in which the brake fluid is kept in a separate sump, the hydrocarbon oil: borated fatty acid glycerol ester composition of the invention is a sufficient lubricant and can be used as such. In the more common powertrain systems, where there is a common sump for all the working fluids, e.g. transmission oil, hydraulic fluid and the like, the lubricating oil is compounded with a variety of additives. These additives include antioxidants, detergents, dispersants, rust inhibitors, foam inhibitors, corrosion inhibitors, anti-abrasives, viscosity index (VI) - enhancers, friction regulators, elastomeric swelling agents, extreme pressure (EP) agents, "and metal-deak-25 tivants. All of these additives are well known in the art of lubricating oil.

The preferred additives which can be added to the lubricating oils to which the borated fatty acid glycerol esters are added are the oil-soluble detergents such as alkali or alkaline earth metal hydrocarbons. sulfonates or alkali or alkaline earth metal metal phenates or mixtures thereof, extreme pressure additives such as group II metal salts of dicarboxylic hydrophosphoric acids and dispersants such as alkenyl succinimides or suicides.

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cinates or mixtures thereof.

The alkali or alkaline earth metal hydrocarbon sulfonates may be either petroleum sulfonate, synthetic alkylated aromatic sulfonates or aliphatic sulfonates such as those obtained from polyisobutylene. One of the more important functions of the sulfonates is to act as a detergent and dispersant. These sulfonates are well known.

The hydrocarbon group must have a sufficient number of carbon atoms to make the sulfonate molecule oil soluble.

The hydrocarbon moiety preferably contains at least 20 carbon atoms and may be aromatic or aliphatic, but is generally alkyl aromatic. The most preferred for use are calcium, magnesium or barium sulfonates which are aromatic in character.

Certain sulfonates are typically prepared by sulfone ringing an oil fraction with aromatic groups, generally mono- or dialkylbenzene groups, and subsequent formation of the metal salt of the sulfonic acid material.

Other starting materials for use in the preparation of these sulfonates include synthetically alkylated benzenes and aliphatic hydrocarbons prepared by polymerization of a mono- or diolefin, e.g. a polyisobutenyl group, prepared by polymerization of isobutene. The metal salts are formed directly or by metathesis using well-known procedures.

The sulfonates may be neutral or overbased with base numbers up to ca. 400 or more. Carbon dioxide is the most widely used material in the production of basic or overbased sulfonates. Mixtures of neutral and overbased sulfonates may be used. The neutral sulfonates are generally used so as to obtain from 5 to 25 millimoles of sulfonate per day. kg of total composition. Preferably, the neutral sulfonates are present at from 10 to 20 millimoles per minute. kg of total composition and the basic sulfonates are present at from 50 to 200 millimoles per minute. kg of total composition.

The phenates used in the invention are the common products which are alkali or alkaline earth

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number salts of alkylated phenols. One of the functions of the phenates is thought to act as a detergent and dispersant. The phenols may be mono- or polyalkylated.

The alkyl portion of the phenylphenate is present to render the phenate oil soluble. The alkyl moiety can be obtained from naturally occurring or synthetic sources. Naturally occurring sources include mineral turpentine and wax. As obtained from the oils, the hydrocarbon moiety is a mixture of different hydrocarbon groups, the specific composition of which depends on the particular oil fraction used as the starting material. Suitable synthetic sources include various commercially available alkenes and alkane derivatives which, when reacted with the phenol, give an alkyl phenol. Suitable groups obtained include butyl, hexyl, octyl, decyl, dodecyl, hexadecyl, eicosyl, tricontyl and the like. Other suitable synthetic sources for the alkyl group include olefin polymers such as polypropylene, polybutylene, polyisobutylene and the like.

The alkyl group may be straight chain or branched, saturated or unsaturated (if unsaturated it preferably contains no more than 2 and generally no more than 1 position with olefinic unsaturation). The alkyl groups will generally contain from 4 to 30 carbon atoms. When the phenol 25 is monoalkyl-substituted, the alkyl group should generally contain at least 8 carbon atoms. The phenate may be sulfurized if desired. It can be either neutral or overbased and should, if overbased, have a base number of up to 200 to 300 or more. Mixtures of 30 neutral and overbased phenates may be used.

The phenates are generally present in the oil to obtain from 10 to 60 millimoles of phenate per day. kg of total composition. The neutral phenates are preferably present at from 20 to 50 millimoles per minute. and the overbased phenates are present at from 50 to 200 millimoles per kilogram. kg of total composition. Preferred metals are calcium, magnesium, strontium or barium.

Sulfurized alkaline earth metal alkyl phenates may and 7

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then applied.

These salts are obtained by a variety of methods such as treating a neutralization product of an alkaline earth metal base and an alkyl phenol with sulfur. Conveniently, sulfur in its elemental form is added to the neutralization product and reacted at elevated temperature to produce the sulfurized alkaline earth metal alkyl phenate.

If during the neutralization reaction more alkaline earth metal base is added than is necessary for neutralization of the phenol, a basic sulfurized alkaline earth metal alkyl phenate is obtained. See, for example, the method disclosed by Walker et al., U.S. Patent No. 2,680,096. Further basicity can be obtained by adding carbon dioxide to the basic sulfurized alkaline earth metal alkyl phenate. The excess alkaline earth metal base can be added after the sulfurization step, but conveniently added at the same time as the alkaline earth metal base is added to neutralize the phenol.

Carbon dioxide is the most commonly used material to produce the basic or "overbased" phenates.

A process in which basic sulfurized alkaline earth metal alkyl phenates are prepared by the addition of carbon dioxide is disclosed by Hanneman in U.S. Patent No. 3,178,3,6 8.

Group II metal salts of dicarbohydride dithiophosphoric acid have wear, antioxidant and thermal stability properties. Group II metal salts of phosphorus dithio acids have been described previously. See e.g. U.S. Patent No. 3,390,080, columns 6 and 7, wherein these compounds and their preparation are described generally. Group II metal salts of dicarbohydride dithiophosphoric acids useful in lubricating oil compositions used according to the invention suitably contain from ca. 4 to 12 carbon atoms in each of the hydrocarbon groups, and may be the same or different and may be aromatic, alkyl or cycloalkyl. Preferred hydrocarbon groups are alkyl groups having from 4 to 8 carbon atoms and are represented by butyl, isobutyl, sec.-butyl, hexyl, isohexyl, octyl, 2-ethylhexyl and the like. The metals suitable for forming these salts, 8

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includes barium, calcium, strontium, zinc and cadmium, among which zinc is preferred.

Group II metal salts of dicarbohydride dithiophosphoric acid preferably have the following formula:

Ro - M1

io L J

wherein R 2 and R 2 are each independently hydrocarbon groups as described above and M1 is a group II metal cation as described above.

The dithiophosphoric acid salts are present in the lubricating oil composition in an amount effective to inhibit wear and oxidation of the lubricating oil. The preferred amount is from 3 to 30 millimoles of dithiophosphoric acid salt per liter. kg of total composition. The salt is best present in an amount of 20 from ca. 15 to 20 millimoles per kg of total lubricating oil composition.

Alkenyl succinimides or succinates or mixtures thereof are present, inter alia, to act as dispersing agents and prevent the formation of deposits. Alkenyl succinimides and succinates are well known. Alkenyl succinimides are a reaction product of a polyolefin polymer-substituted succinic anhydride with an amine, preferably a polyalkylene polyamine, and the alkenyl succinates are a reaction product of a polyolefin polymer-substituted succinic anhydride with mono- and polyhydric alcohols, polyhydric alcohols and polyhydric alcohols. naphtholes, preferably a polyhydric alcohol having at least three hydroxy groups. The polyolefin polymer-substituted succinic anhydrides are obtained by reacting a polyolefin polymer or a derivative thereof with maleic anhydride. The succinic anhydride thus obtained is reacted with an amine or hydroxy compound. Preparation of alkenylsuccinimides has been described many times in the art. See, e.g., U.S. Patent 9

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Written Nos. 3 * 390,082, 3,219,666 and 3,172,892. Preparation of alkenyl succinates is also described in the literature. See, for example, U.S. Patent Nos. 3,381,022 and 3,522,179.

Particularly good results can be obtained with the lubricating oil compositions used according to the invention, if the alkenyl succinimide or succinate is a polyisobutene-substituted succinic anhydride of a polyalkylene polyamine or polyhydric alcohol respectively.

The polyisobutene, of which the polyisobutene-substituted succinic anhydride is obtained by polymerization of the isobutene, may vary widely in its composition. The average number of carbon atoms can range from 30 or less to 250 or more, with a resultant number average molecular weight of approx. 400 or less to 3,000 or more.

Preferably, the number of carbon atoms per polyisobutylene molecule range from approx. 50 to approx. 100, the polyisobutylene having a number average molecular weight of approx. 600 to approx.

1500. It is preferred that the average number of carbon atoms per polyisobutene molecule is from ca. 60 to approx. 90, and that the number average molecular weight is from approx. 800 to 1,300. The polyisobutene is reacted with maleic anhydride according to well-known techniques to obtain the polyisobutene-substituted succinic anhydride.

In preparing the alkenyl succinimide, the substituted succinic anhydride is reacted with a polyalkylene polyamine to give the corresponding succinimide.

Each alkylene group of the polyalkylene-polyamine generally has up to approx. 8 carbon atoms. The number of alkylene groups may go up to approx. 8. The alkylene group is, for example, ethylene, propylene, butylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, octamethylene, etc. The number of amino groups is generally, but not necessarily, one greater than the number of alkylene groups present in the amine, i.e. if a polyalkylene polyamine contains 3 alkylene groups, it will generally contain 4 amino groups. The number of amino groups can go up to approx. 9. Preferably, the alkylene group contains from 10

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ca. 2 to approx. 4 carbon atoms and all the amine groups are primary or secondary. In this case, the number of amine groups exceeds the number of alkylene groups by 1. The polyalkylene polyamine preferably contains from 3 to 5 amine groups. Specific examples of the polyalkylene polymers include ethylenediamine, diethylenetriamine, triethylene tetramine, propylenediamine, tripropylenetetramine, tetraethylene pentamine, trimethylenediamine, pentaethylene-hexamine, di- (tri-methylene) triamine, tri (hexamethylene) tetramine, and the like.

Other amines suitable for preparing the alkenylsuccinimide useful in the compositions of this invention include cyclic amines such as piperazine, morpholine and dipiperizines.

The alkenylsuccinimides which may be included in the compositions used according to the invention preferably have the following formula:

R1-CH-C

20 N-N-alkylene-N 2 H I

ch9-c ^ I

\ A

is an alkenyl group, preferably a substantially saturated hydrocarbon, prepared by polymerization of aliphatic monoolefins. Preferably R 1 is prepared from isobutene and has an average number of carbon atoms and number average molecular weight, as described above; b. "Alkylene" is essentially a hydrocarbon group containing up to approx. 8 carbon atoms and preferably containing from 2 to 4 carbon atoms as described above; C. A is a hydrocarbon group, an amine-substituted hydrocarbon group or hydrogen. The hydrocarbon group and the amine-substituted hydrocarbyl groups are generally the alkyl and amino-substituted alkyl analogs of the above.

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11 for described alkylene groups. It is preferred that A is hydrogen; and d. n is an integer from ca. 1 to 10 and preferably from ca. 3 to 5.

The alkenyl succinimide can be reacted with boric acid or a corresponding boron containing compound to form borated dispersants which can be used in the compositions used in the invention. The borated succinimides are encompassed by the term "alkenylsuccinimide".

The alkenyl succinates are those of the above-described succinic anhydride having hydroxy compounds which may be aliphatic compounds such as mono- and polyhydric alcohols or aromatic compounds such as phenols and naphtols. The aromatic hydroxy compounds of which the esters are obtainable are illustrated by the following specific examples: Phenol, β-naphtol, α-naphtol, cresol, resorcinol, catechol, ρ, ρ'-dihydroxybiphenyl, 2-chlorophenol, 2,4-dibutylphenol, propylene tetra-substituted phenol, didodecylphenol, 4,4'-methylene-bis-phenol, α-decyl-β-ρο-20-isobutene (molecular weight of 1000) -substituted phenol, a condensation product of heptylphenol with 0.5 mole of formaldehyde, a condensation product of octylphenol with acetone, di (hydroxyphenyloxide, di (hydroxyphenyl) sulfide, di- (hydroxyphenyl) disulfide and 4-cyclohexylphenol. Phenol and 25 alkylated phenols with up to three alkyl substituents are preferred. Each of the alkyl substituents may contain 100 or more carbonates.

The alcohols from which the esters can be obtained preferably contain up to 40 aliphatic carbon atoms. They can be monovalent alcohols such as methanol, ethanol, isooctanol, dodecanol, cyclohexanol, cyclopentanol, behenyl, alcohol, hexatriacontanol, neopentyl alcohol, iso-butyl alcohol, benzyl alcohol, β-phenylethyl alcohol, 2-methylcyclohexanol, -35 methyl ether, ethylene glycol monobuthyl ether, diethylene glycol monopropyl ether, triethylene glycol monododecyl ether, ethylene glycol monooleate, diethylene glycol monostearate, 12

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sec.-pentyl alcohol, tert-butyl alcohol, 5-bromo dodecanol, nitrooctadecanol and glycerol dioleate. The polyhydric alcohols preferably contain from 2 to 10 hydroxy groups. They are, for example, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, dibutylene glycol, tributylene glycol and other alkylene glycols wherein the alkylene group contains from 2 to about 8 carbon atoms. Other polyhydric alcohols used include glycerol, monooleate of glycerol, monomethyl ether of glycerol, pentaerythritol, 9,10-dihydroxystearic acid, 9,10-dihydroxystearic acid methyl ester, 1,2-butanediol, 2,3-hexanediol, 2,4-hexanediol, pinacol , erythritol, arabitol, sorbitol, mannitol, 1,2-cyclohexanediol and xylene glycol. Carbohydrates such as sugars, starches, cellulose, etc. can also give esters. The carbohydrates can be, for example, glucose, fructose, sucrose, rhamnose, mannose, glyceraldehyde and galactose.

A particularly preferred group of polyhydric alcohols are those having at least three hydroxy groups, some of which have been esterified with a monocarboxylic acid having from about

8 to approx. Carbon atoms such as octanoic, oleic, stearic, linoleic, dodecanoic or tallowic acid. Examples of such partially esterified polyhydric alcohols are sorbitol monooleate, sorbitol distearate, glycerol monooleate, glycerol monostearate and erythritol diode canoate.

The esters can also be obtained from unsaturated alcohols such as allyl alcohol, cinnamyl alcohol, propargyl alcohol, 1-cyclohexen-3-ol, an oleyl alcohol. Other groups of alcohols capable of providing the esters of the invention include ether alcohols and amino alcohols including f e.g., oxyalkylene, oxyarylene, aminoalkylene and amino-arylene substituted alcohols with one or more oxyalkylene, aminoalkylene, amino-arylene or oxyarylene groups. The 35 are e.g. Cellosolve, carbitol, phenoxy-ethanol, heptyl-phenyl (oxypropylene) gH, octyl (oxyethylene / 1H, phenyl (oxyoctylene) H, mono (heptylphenyloxypropylene) -substituted glycerol, poly (styrene oxide, aminoethanol) - (hydroxyethyl) - 13

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-amine, p-aminophenol, tri (hydroxypropyl) amine, N-hydroxyethylethylenediamine, Ν, Ν, Ν1, N'-tetrahydroxytrimethylene diamine and the like. For the most part, ether alcohols of up to approx. 150 oxyalkylene groups, wherein the alkylene groups contain from 1 to ca. 8 carbon atoms.

The esters may be di-esters of succinic acid esteric esters, i.e. partially esterified succinic acids, as well as partially esterified polyhydric alcohols or phenols, i.e. esters with free alcohol or phenolic hydroxy groups. Mixtures of the above esters are also within the scope of the invention.

The alkenyl succinates may be reacted with boric acid or a corresponding boron-containing compound to form borated dispersants useful in the invention. Such borated succinates are described in U.S. Patent No. 3,533,945. The borated succinates are understood to be within the term "alkenyl succinate".

Alkenyl succinimide and succinates are present in the lubricating oil compositions in an amount effective to act as a dispersant and prevent the deposition of contaminants formed in the oil. The amount of alkenylsuccinimide and succinates may range from approx. 0.5 to approx. 20% by weight of the entire lubricating oil composition. Preferably, the amount of alkenyl succinimide or succinate which may be present in the lubricating oil composition is from about 1 2 to approx. 5% by weight of the entire composition.

The finished lubricating oil can be single or multigrade. Multigrade lubricating oils are prepared by adding 30 viscosity index (VI) enhancers. Typical viscosity index enhancers are polyalkyl methacrylates, ethylene-propylene copolymers, styrene-diene copolymers, and the like. So-called decorated VI enhancers with both viscosity index and dispersion properties are also suitable for use in the compositions of the invention.

The following examples are given to illustrate the invention.

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14

Example 1

Preparation of Borated Glycerol Monooleate.

To a mixture containing 125.23 g of glycerol monooleate (45 to 55% by weight) and glycerol dioleate (55 to 545% by weight) was added. 30.92 g of boric acid and 250 N of L. xylene. The reaction mixture was heated at 99 ° to 141 ° C for approx. 9§ hours under nitrogen and azeotropic conditions. 17.6 ml of water was collected with a Dean Stark trap. The reaction product was filtered and stripped on a rotary evaporator 10 in vacuo to 135 ° C to give 128.35 g. Analysis:

Boron 2.42% and 2.52%, hydroxyl number 32 mg KOH / g. IR analysis of the product showed no free hydroxyl stretch fluctuations of the glycerol type but has a strong BO-E bond and substantially no B-O-B type absorption.

15

Example 2

The present compositions were tested in a laboratory test. The test was performed on a SAE No. 2 friction machine modified by the addition of a moderate speed 20-speed hydraulic motor drive. The sample was a sandwich by a General Metals Powder Co. 1500 mix sintered bronze plate between two steel spacer plates, mounted in the above apparatus. The test liquid, approx. 300 g, then placed in the sample oil sump. The hydraulic drive rotated the samples at 100 rpm. A piston-like brake was applied with an overpressure of 517 kPa. SAE No. 2 load cell measured the braking torque and an electric tachometer measured rpm. An x-y plotter was used to generate a torque curve to rpm, adjusting the hydraulic drive slowly ΟΛ J to lower the speed to 0 rpm. The braking noise effect of a liquid is associated with the slope of friction against the velocity curve. The slope of the curve is found by measuring the slope of a line drawn through 50 o; m point on the drawn curve and the highest point on the drawn curve below 50 rpm. As the slope of this curve becomes more and more negative, the braking noise becomes more and more high. This trend is consistent with full-scale drivetrain brake noise studies.

Claims (4)

20 B - base oil + 1 wt% -, 0092 borated red glycerol oleate from Example 1 C - Commercial formulation - 0143 25 Use of a composition comprising a lubricating oil containing 0.1-5% by weight of a borated fatty acid ester of glycerol for reducing brake noise from 30 oil-immersed disc brakes by lubricating the contact surfaces. Use according to claim 1, characterized in that the borated fatty acid ester of glycerol is a borated glycerol oleate. Use according to claim 2, characterized in that the borated fatty acid ester of glycerol is a mixture containing 45-55% by weight borated glycerol monoleate and 55-45% by weight borated glycerol dioleate. DK 162656 B Use according to claim 2, characterized in that the borated fatty acid ester of glycerol is borated glycerol monooleate.