US2768953A - Hydraulic transmission fluid - Google Patents

Description

United States Patent amass HYDRAULIC TRANSMISSION FLUID William C. Howell, Jr., and Jones I. Wasson, Union, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware 3. Claims. (Cl. 252-425) This application is a division of copending application Serial No. 306,500, filed August 26, 1952, now Patent No. 2,731,418.

The present invention relates to improvements in hydraulic transmission fluids and more generally to lubricating compositions having superior anti-friction properties. The invention relates particularly to power transmitting and lubricating compositions designed for use in hydraulic transmissions of modern automotive vehicles.

In the prior art numerous compositions have been proposed for use in torque converters, fluid clutches, semiautomatic and fully automatic automotive transmissions and the like and in some cases difliculty has been encountered in meeting certain specific requirements. This is not surprising when it is considered that for many types of such automatic transmissions the fluid must act not only as a power transmission medium but in addition must provide satisfactory lubrication, act as a hydraulic control fluid, and perform as a heat transfer medium. The fluid must also be free from corrosive eflects and objectionable odors. Moreover, the fluid must be so designed as to function properly over a wide temperature range and it must possess a high level of oxidation resistance and a good degree of detergency. The latter properties are extremely important, since even small quantities of sludge and other oxidation products, if allowed to settle out, can easily clog the very small orifices in the hydraulic control system and cause serious malfunctioning and damage to the transmission.

Although many of the numerous compositions of hydraulic transmission fluids hereinbefore referred to have been satisfactory with regard to most of the requirements as set forth above, to date no product has been found that is entirely satisfactory with respect to its anti-friction properties. In one popular type of torque converter transmission, for example, under certain operating conditions there is sliding contact between certain elements and a tendency for them to alternately seize and separate with stick-slip or chattering action. Ordinary lubricants such as straight mineral oil and a number of products especially compounded for the purpose do not prevent this objectionable type of operation. For example, the lubricants specifically recommended by the manufacturer of this transmission, known as Automatic Transmission Fluids, Type A, are completely inadequate for preventing this chattering action. This is true despite the fact that these approved fluids vary widely in their compositions and contain a wide variety of detergent inhibitor additives, anti-friction additives, and other materials. However, when the fluids described in this invention are used, the objectionable chatter, particularly common when certain transmissions are operated in reverse, is almost completely eliminated.

As has been previously mentioned, lubricants for use in automatic hydraulic transmissions must, in addition to other important properties, possess a high degree of detergency, freedom from corrosion, and good odor. According to the present invention, it has been discovered 2,768,953 Patented Oct. 30, 1956 ice that a particular combination of detergent inhibitors and acidic type materials, when combined in the correct proportions, give a fluid that has these desirable properties in optimum combination. The specific acidic materials to be employed in a given fluid depend upon the exact detergent-inhibitor used and the detailed fluid properties desired. Oleic acid or similar unsaturated long chain fatty acids, or natural fats containing acids of this type (such as lard oil), may be used as anti-friction agents where detergent-inhibitors such as P2S5 treated barium salt of diisobutyl phenol sulfide are employed.

Even better anti-friction properties can be obtained by the inclusion of certain phosphoric acid esters, especially triphosphate esters such as tricresyl phosphate, along with the acid type anti-friction agent. Saturated long chain fatty acids such as stearic acid or alkyl mercapto acids such as lauryl mercaptoacetic acid cannot be employed with detergent-inhibitors of this type. By substituting an unsaturated acid such as oleic acid, or lard oil, H25 evolution is reduced, probably by being. taken up at the unsaturated bonds. When saturated acids are employed, H28 evolution occurs, resulting in objectionable odor and corrosion properties despite the fact that good anti-friction action is obtained. Also, substitution of a non-P285 treated detergent-inhibitor such as the barium salt of diisobutyl phenol sulfide for the P2S5-treated detergent material would reduce H2S evolution. However, such substitution cannot be made Without destroying the effectiveness of the anti-friction agent. Neither can detergent-inhibitors containing petroleum sulfonates be employed for the same reason.

For improved anti-corrosion properties, combined withv better detergency and better odor than is obtained with oleic acid-Pzss-treated detergent type blends, it is preferred to use non-PzSs-treated detergent inhibitors. However, neither the saturated or unsaturated fatty acids nor the mercapto acids are effective anti-friction agents in the presence of these non-PzSs-treated detergent-inhibitors. It has been discovered, and is another feature of this invention, that if certain concentrations of fatty acid and alkylmercapto acid are employed jointly, excellent antifriction properties result even in the presence of the non-P2S5-treated detergent-inhibitors. Also, very good odor and corrosion properties are observed for blends of this type because of absence of free H28. Sulfonatecontaining detergent-inhibitors cannot be used, however, without destroying the anti-friction properties.

The invention will be more fully understood by specific reference to a series of blends which have been made in the study of the anti-friction problem. In general, two types of detergents were employed. One of these was a highly successful commercial product obtained by treating the barium and/or calcium salt of diisobutyl phenol sulfide with a phosphorus sulfide such as P255. The other consists of the untreated barium or mixed bariumcalcium salt of diisobutyl phenol sulfide. The former gives superior anti-friction properties in combination with fatty acids but has an objectionable tendency to evolve HzS gas under certain conditions. The untreated salt, on the other hand, is free from .the objectionable H28 evolution but is somewhat deficient alone or in combination with fatty acids, as an anti-friction agent in mineral base lubricating oil.

Byv combining certain concentrations of fatty acid of the C12 to C22 range with a C8 to C24 alkyl mercapto acid, specifically lauryl mercapto acetic acid, the combination is found to possess all the desired properties to an excellent degree. In the mercapto acids, instead of lauryl the alkyl group obviously may be octyl, Z-ethyl hexyl, decyl, tetradecyl, etc. Among the C12 to C22 fatty acids that may be used are myristic, palmitic, stearic, erucic, brassidic, etc. In either case the addition of a small Concen- Anti-Friction Agents tration, Detergcnt- Other Wt. Inhibitor Additives Percent Pour depres- Stcaric Acid 0. 3-0. 4 sant, V. I. 1 Lauryl Mercapto Acetic Aei 0. 2-0. 3 A Improver, (Tricresyl Phosphate) 1 0. 5-1. 0 Anti-foam 01 A d 7 1 Agent eic ci 0. 0 i (or No. 1 Lard on 2.0 i B May be omitted at the expense of a slight impairment of antitriction properties.

A series of tests was made of various compositions in an actual hydraulic transmission of the torque converter type where a strong tendency to chatter was found in reverse gear operation. In the particular transmission used, there is a large steel bearing surface in the reverse planetary gear set which rotates against a bronze bushing when the unit is put into reverse. This bearing is lubricated by the transmission fluid. As will be seen by reference to the data in Table I, when either straight mineral oil or the fluids presently approved by the manufacturer of this transmission are used, stick-slip occurs in this bearing, and undesirable chatter is obtained. When the fluids described in this invention are used, the chatter is almost entirely eliminated.

acetic acid. 10. 0.3% Stearic acid, 0.2% Lauryl mercapto acetic acid. 11. No. 10+0.5% Tricresyl Very It. to Light.

Very Light. phosphate. 12. 0.4% Stearic acid, 0.5% 2.0% Detergent A.-. Medium to Heavy Trieresyl phosphate. 13. 0.3% Lauryl mercapto do Do.

acetic acid, 0.5% Tricresyl phosphate. 14. 0.2% Lauryl mercapto acetic acid, 0.3% Stearic acid. 16. 2.0% No. 1 Lard oil 2.0% Detergent A,

1.2% Calcium sulfonate concentrate.

2.0% Detergent 13...

Light to Medium.

Light.

1 Recommended by manufacturer for use in this transmission.

The concentration of the fattyacid and mercapto acid to be employed will depend upon the nature of the other ingredients present and the required anti-friction prop erties. In general, the best concentration range for the fatty acids is from about 0.2 to 1.0% by weight, and for the mercapto acetic acid about 0.2 to 0.4%. Lower concentrations result in decreased efiectiveness while higher concentrations are objectionable from the standpoint of oxidation stability and corrosion. If tricresyl phosphate 4 is also employed, a concentration of about 0.5% by weight has been found to be efiective. Of those listed above in Table I, compositions Nos. 6, 10, 11 and 15 are most satisfactory over all.

In general, the invention contemplates the use of a lubricating oil as a major component. This is preferably a mineral base lubricating oil, although synthetic oils such as dibasic acid esters, complex esters, polyglycols, and the like may be used so long as they are compatible with the additives. The preferred viscosity range is between 35 and S. S. U. at 210 F., particularly between 45 and 55 for the average transmission unit.

This lubricating oil base should contain about 1 to 6% by weight, based on the total composition, of an alkaline earth metal salt of alkyl phenol sulfide as a detergent, which is free from HzS evolution together with 0.2 to 1% by weight of fatty acid of the C12 to C22 range, 0.2 to 0.5 by weight of Cu to C18 alkyl mercapto acid, preferably an alkyl mercapto acetic acid, and 0 to 1% by weight, preferably at least 0.2%, of a tri-ester of phosphoric acid, e. g. tricresyl phosphate, as an oiliness agent. When mineral oil is used as the fluid base it preferably has a viscosity between 35 and 65 S. S. U. at 210 F. and is of reasonably high viscosity index. A preferred composition comprises 93.7 to 97.4% of such a mineral base oil with 2 to 6% of the alkaline earth salt of non-P285- treated alkyl phenol sulfide as detergent, 0.3 to 1% of a fatty acid, preferably a C18 acid, stearic acid being first choice, 0.1 to 0.3% of lauryl mercapto acetic acid although other alkyl derivatives may be used, and 0.2 to 1% of tri-cresyl phosphate.

It is to be noted that the invention as described contemplates the use of alkaline earth metal salts derived from the alkyl phenol sulfides as the preferred detergents, and that the exact detergent-inhibitor to be employed will depend upon the nature of the acidic type anti-friction additive to be used. It is also to be noted, however, that other detergent-inhibitors may also be used provided they do not interfere with the activity of the anti-friction agents employed or do not result in objectionable corrosion or odor properties. Various other additives may also be included as required to impart specific properties to the blend such as conventional antioxidants, pour depressants, viscosity index improvers, anti-foam agents, and the like.

What is claimed is:

1. A lubricant composition of high detergency and superior anti-friction properties, consisting essentially of a major proportion of a lubricating oil of low viscosity, 1 to 6% by weight based on the total composition of a P255 treated alkaline earth metal salt of alkyl phenol sulfide as a detergent, and 0.2 to 1% of oleic acid.

2. Composition according to claim 1 wherein a small amount of a triester of phosphoric acid is added.

3. A composition having substantially the following components:

92 to 98.8% by weight of mineral lubricating oil base of 35 to 65 S. S. U. viscosity at 210 F.

1 to 6% P255 treated alkaline earth metal salt of diisobutyl phenol sulfide.

0.2 to 1% oleic acid 0.0 to 1% tricresyl phosphate.

References Cited in the file of this patent UNITED STATES PATENTS 1,319,129 Wells Oct. 21, 1919 2,203,102 Powers June 4, 1940 2,237,336 Caprio Apr. 8, 1941 2,451,345 McNab et al. Oct. 12, 1948

Claims (1)

1. A LUBRICAN COMPOSITON OF HIGH DETERGENCY AND SUPERIOR ANTI-FRICTION PROPERTIES, CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OF A LUBRICATING OIL OF LOW VISCOSITY, 1 TO 6% BY WEIGHT BASED ON THE TOTAL COMPOSITION OF A P2S5 TREATED ALKALINE EARTH METAL SALT ALKYL PHENOL SULFIDE AS A DETERGEN, AND 0.2 TO 1% OF OLEIC ACID.