US2169231A

US2169231A - Hydraulic brake fluid

Info

Publication number: US2169231A
Application number: US152989A
Authority: US
Inventors: Harvey R Fife
Original assignee: Carbide and Carbon Chemicals Corp
Current assignee: Carbide and Carbon Chemicals Corp
Priority date: 1937-07-10
Filing date: 1937-07-10
Publication date: 1939-08-15
Anticipated expiration: 1956-08-15

Description

Patented Aug. 15, 1939 UNITED STATES PATENT OFFICE HYDRAULIC BRAKE FLUID No Drawing. Application July 10, 1937, Serial No. 152,989

6 Claims.

This invention relates to operating fluids for hydraulic brake systems and to fluid pressure operating devices generally. More particularly, it relates to the combination among themselves of certain alkyl ethers of the alkylene and polyalkylene glycols, which mixtures in turn are combined with suitable nonmineral lubricating oils, such as castor oil.

Hydraulic brake fluids generally include an oil as an essential component, and vegetable and animal oils of low solidifying point are commonly used for this purpose. These fluids must be completely miscible with other oleaginous or fatty acid-base pressure transmitting media, in order that the brake systems of automobiles may be readily-serviced. Refill solutions require miscibility with solutions already in the system in order to prevent separation of the components under conditions of use. These fluids should not corrode metal surfaces used in the hydraulic brake system. Nor should they cause deterioration or swelling of the rubber pistons or tubes which they contact in use. The rubber-swelling action of a hydraulic brake fluid is a very important factor in the efficiency of the fluid, and, in no case should the swelling action be greater than from 5% to 7% by volume of the rubber member. Again, such fluids should remain liquid over a temperature range of from at least 50 to 220 F. This is imperative if the fluids are not to congea-l at low temperatures, thereby preventing operation of the brake system, or to vaporize at high temperatures, causing a separation of the components and vapor locking, with consequent inoperativeness of the system. The solubility characteristics of a suitable fluid for use in pressure transmission devices must be such as to permit toleration of water which may be present in, or find its way into, the system. It has been found that desirable fluids should have a water tolerance up to and even greater than 15% by volume of the fluid. This is essential if separation of the components is to be avoided, particularly at low temperatures.

While many hydraulic brake fluids containing glycol alkyl ethers and castor oil meet some of these demands, no fluid at present available satisfies all of these requirements. This may poss bly be due to the failure of previous workers to recognize that the varying properties of the individual ethers are controlling factors, and the consequent failure to utilize the useful and valuable properties of each ether in mixtures of them, and in mixtures of special combinations of these ethers in definite proportions with fatty acidcontaining oils of suitable lubricating characteristics.

I have found that when certain glycol monoalkyl ethers, namely those having less than three carbon atoms in their alkyl radical, are combined 5 with other monoor dialkyl ethers having at least three carbon atoms in the alkyl substituents, the resulting mixture exhibits unexpected properties. This combination of properties, which is of paramount importance, includes a low solvent 10 action on rubber (a minimum of rubber-swelling action), and complete miscibility with castor oil. This desirable combination of properties, when the mixture is combined with castor oil, is accompanied by low corrosive action on metal sur- 1 faces, pronounced chemical stabilty, and by water tolerance well within the desired limits.

The advantages of the special combination of these particular ethers arise from two very important factors. First, those alkylene or polyal- 20 kylene glycol monoalkyl ethers which have less than three carbon atoms in their alkyl radical, while possessing exceptionally low solvent action on rubber, or rubber-swelling action, are relatively immiscible at low temperatures with castor 25 oil. As was noted above, this lack of miscibility would markedly decrease the efliciency and dependability of fluids in which such compounds were used as the sole or major diluent. The second important feature is that those alkylene and 0 polyalkylene glycol monoor dialkyl ethers having three or more carbon atoms in their alkyl radicals, while possessing excellent miscibility with castor oil, are characterized by an excessive and damaging swelling action on the rubber members 36 of the system. When two ethers of these respective classes are combined, in proportions set forth hereinafter, and this combination of ethers is admixed with castor oil, a brake fluid is obtained which more than satisfies the demands imposed 40 on such media by conditions of use. For example, with my new fluids, rubber swelling or expansion of rubber members in use, does not exceed 3.5% to 4.0%. The improved fluids are without material corrosive effect on aluminum, 45 copper or other metal surfaces which they may contact in use, My new fluids are sufliciently liquid for practical use at temperatures of from 50 F, to 220 F. Furthermore, they are completely miscible with castor oil or other oleagi- 50 nous base-containing fluids.

Broadly, the glycol ethers for use in this invention consists of mixtures of the monoand dialkyl ethers of 1.2 glycols of the ethylene, propylene, butylene and amylene series, and their 55 homologues. For example, the monomethyl or monoethyl ethers of mono-, di-, tri-, or tetraethylene glycols are admixed with the monoisopropyl. butyl, or amyl ethers, or mixtures thereoi, or, the monomethyl or monoethyl ethers of ethylene and polyethylene glycols can be admixed with the monobutyl ether of ethylene or diethylcne glycol or of tripropylene glycol, or of others of this series. In all such combinations, the glycol monomethyl or monoethyl ethers retain the greater part of their low solvent action on rubber while the miscibility of the mixture with casior oil is greatlyincreased by the effect of the glycol ether containing higher alkyl groups and which serves as a coupling agent. The glycol monoor dialkyl ethers having three or more carbon atoms in their alkyl groups retain their excellent miscibility with castor oil, and the marked tendencies of these compounds otherwise to exert high solvent action on rubber are rendered practically negligible by the presence of the compounds having less than three carbon atoms in their alkyl group.

I have found that very effective fluids are obtained when the alkylene and polyalkylene glycol monoalkyl ethers containing less than three carbon atoms in their alkyl radical are used in approximately 30% to 45% by volume, and the alkylene or polyalkylene glycol monoor dialkyl ethers containing at least three carbon atoms in the alkyl substituents are used in amounts of from about 15% to 20% by volume, together with castor oil in amounts of from 35% to 50% by volume.

A specific example of a fluid according to this invention may contain 35% of ethylene glycol monoethyl ether, 15% of diethylene glycol monobutyl ether, and 50% of castor oil, all by volume. Another fluid was formed of 40% of diethylene glycol monomethyl ether, 15% of dipropylene glycol monobutyl ether, and 45% of castor oil, all by volume. A third was composed of 30% of triethylene glycol monoethyl ether, 25% of propylene glycol monobutyl ether, and 45% of castor oil, all by volume. These three specific compositions are merely illustrative of the scope of the invention and other combinations of compounds of the classes set forth have proved to be equally effective.

The mixtures shown above in no instance caused rubber swelling of more than 5%, nor did they absorb water to the extent of more than to 11%, and in all respects these compositions manifested characteristics of highly satisfactory and dependable fluids.

It must be understood that the low rubberswelling action and complete miscibility with castor oil are two controlling features governing the composition of these fluids, and, while the percentages shown above have been found effective, it is possible that variations in these proportions may be used without departing from the spirit of this invention. For instance, the varying conditions of operation to which the fluids will be subjected might determine that more of the one and less of the othershould be employed.

If found desirable in practice, certain viscosity-reducing agents may be added to the hydraulic brake fluids. I have found that the use of most viscosity-reducing agents does not impair the efllciency of my new fluids. If such agents are desired, the ketones, such as acetone, methyl isobutyl ketone, and the like; lower fatty acid alkyl esters, such as butyl acetate and isopropyl acetate; and lower monohydric alcohols, such as ethanol and methanol, are suitable. Of course, it will be appreciated that the uses for which the fluids are intended will control the nature and quantity of the viscosity-reducing agents employed, i. e., the higher the temperature to which the fluid is to be subjected, the less volatile should be the viscosity-reducing agent. At any rate, if these agents are to be employed, it is recommended that they be used in amounts not greater than about 10% by volume. A very effective fluid employing such viscosity-reducing agents may be formed of 30% of monoethyl ether of ethylene glycol, 15% of monobutyl ether of dipropylene glycol, 45% of castor oil, and 10% of butyl acetate, all by volume.

The present invention provides compositions of matter having useful and improved operating characteristics as pressure transmission media. Specific preparations have been set forth, but the proportions shown are illustrative only, and the invention is susceptible of modification within its scope as defined by the appended claims.

I claim:

1. A hydraulic brake fluid comprising a glycol ether from the group consisting of alkylene and polyalkyiene glycol monoalkyl ethers having not more than two carbon atoms in the alkyl radical in admixture with a materially less amount of a glycol ether from the group consisting of the monoand dialkyl ethers of the monoand poly alkylene glycols having at least three carbon atoms in the alkyl radical thereof and combined with an amount of castor oil at least as great as any other ingredient, said brake fluid being characterized by a greater miscibility at low temperature with castor oil than fluids comprising the first group of the aforesaid glycol ethers and being further characterized by a lesser swelling action for rubber than fluids comprising the second group of the aforesaid glycol ethers.

2. A hydraulic brake fluid comprising a glycol ether from the group consisting of alkylene and polyalkylene glycol monoalkyl ethers having not more than two carbon atoms in the alkyl radical in admixture with a materially less amount of a glycol ether from the group consisting of the monoand dialkyl ethers of the monoand polyalkylene glycols having at least three carbon atoms in the alkyl radical thereof and combined with an amount of castor oil greater by 15% by volume than any other ingredient, said brake fluid being characterized by a greater miscibility at low temperature with castor oil than fluids comprising the first group of the aforesaid glycol ethers, and being further characterized by a lesser swelling action for rubber than fluids comprising the second group of the aforesaid glycol ethers.

3. A hydraulic brake fluid comprising about 30% to about 40% by volume of a glycol ether from the group consisting of alkylene and polyalkylene glycol monoalkyl ethers having not more than two carbon atoms in the alkyl radical, about 15% to about by volume of a glycol ether from the group consisting of the monoand dialkyl ethers of the monoand polyalkylene g1ycols having at least three carbon atoms in the alkyl radical, and the remainder an amount of castor oil at least equal to the amount of any other component present, said brake fluid being characterized by a greater miscibility at low temperature with castor oil than fluids comprising the first group of the aforesaid glycol ethers, and being further characterized by a lesser swelling action for rubber than fluids comprising the second group of the aforesaid glycol ethers.

4. A hydraulic brake fluid essentially containing about 35% by volume of ethylene glycol monoethyl ether, 15% by volume of dlethylene glycol monobutyl ether and 50% by volume of castor oil.

5. A hydraulic brake fluid essentially containing 40% by volume of dlethylene glycol monomethyl ether, 15% by volume of dlpropylene glycol monobutyl ether, and 45% by volume of castor oil.

6. A hydraulic brake fluid essentially contain- -ing 30% by volume of triethylene glycol monoethyl ether, 25% by volume of propylene glycol monobutyl ether, and 45% by volume of castor oil.

- HARVEY R. FIFE.