Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic compound containing boron
Reexamination Certificate
1999-08-11
2002-11-19
Medley, Margaret (Department: 1714)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic compound containing boron
C508S228000, C508S408000, C508S418000, C508S518000, C508S531000, C252S075000, C252S076000, C252S078500
Reexamination Certificate
active
06482778
ABSTRACT:
TECHNICAL FIELD
This invention relates to transmission fluid compositions comprising a zinc detergent and at least one phosphorus-containing additive having enhanced performance capabilities, including high steel-on-steel coefficients of friction, under conditions similar to those experienced by transmission systems.
BACKGROUND
There is worldwide activity by automobile manufacturers to develop continuously variable transmissions (CVT). These developments are being driven by benefits from CVTs towards Corporate Average Fuel Economy (CAFE) requirements in the U.S.A.
The advent of ECCC and continuously variable transmissions (CVT) and the manufacturing of passenger cars with smaller transmissions which tend to operate with higher energy densities and higher operating temperatures have challenged lubricant suppliers to formulate transmission fluids with new and unique performance characteristics including higher torque.
CVTs can provide improved fuel efficiency, reduced exhaust emissions and improved driving performance compared to conventional automatic transmissions. The CVT is significantly different from a conventional automatic transmission in several ways. A major feature of the CVT is the transmission of high torque between a steel belt and pulleys providing a continuously variable gear ratio between the input and output shafts. In order to realize high torque transmission between a steel belt and pulleys, high friction between metal/metal contacts is required with normal wear. Loss of transmitting torque between the belt and the pulleys leads to inefficiency and could result in damage to the CVT. A CVT fluid that can transmit high torque generates a high friction force, and, as a result, the belt and the pulleys transmit high torque efficiently. Some CVTs employ a torque converter with an electronically controlled lock-up clutch engaging at low vehicle speeds for further gains in fuel economy and drivability. Acceptable metal/clutch material frictional properties are also required of the CVT fluid when torque converters with a lock-up clutch are used with the CVT.
U.S. Pat. No. 4,897,209 discloses lubricating compositions comprising metal dihydrocarbylaromatic sulfonates and a dialkyl or trialkyl phosphite, wherein the metals are taught to be calcium, barium, sodium, magnesium and lithium. This reference fails to teach transmission fluids containing mixtures of zinc detergents and at least one phosphorus-containing compound or the increased steel-on-steel coefficients of friction obtained by using the fluids of the present invention.
SUMMARY OF THE INVENTION
In accordance with this invention there is provided, in one of its embodiments, a transmission fluid comprising a zinc detergent and at least one phosphorus-containing additive.
In another embodiment of the present invention, a method of increasing steel-on-steel friction in continuously variable transmissions is set forth. Said method comprises adding to, and operating in, a continuously variable transmission a fluid comprising (1) a major amount of a base oil and (2) a minor amount of an additive composition which comprises (A) a zinc detergent and (B) at least one phosphorus-containing additive, wherein the transmission fluid contains from about 10 to about 500 parts by weight of zinc per million parts by weight of transmission fluid (ppm w/w), preferably about 20 to 300 ppm w/w of zinc and more preferably from about 30 to about 100 ppm w/w zinc, and from about 50 to about 2000 ppm w/w, preferably 100 to 1000 ppm w/w of phosphorus, and more preferably from about 200 to 800 ppm w/w of phosphorus.
Another embodiment of the present invention is directed to an automotive transmission lubricated with the transmission fluids of the present invention.
DETAILED DESCRIPTION
The transmission fluids of the present invention comprise a major amount of a base oil and a minor amount of an additive composition which comprises (A) at least one zinc detergent and (B) at least one phosphorus-containing additive.
The zinc detergents useful in this invention are exemplified by oil-soluble neutral or overbased salts of zinc with one or more of the following acidic substances (or mixtures thereof): sulfonic acids, carboxylic acids, salicylic acids, alkyl phenols, and sulfurized alkyl phenols.
Oil-soluble neutral zinc-containing detergents are those detergents that contain stoichiometrically equivalent amounts of zinc in relation to the amount of acidic moieties present in the detergent. Thus, in general the neutral zinc detergents will have a low basicity when compared to their overbased counterparts. The neutral zinc detergents most useful in the present invention include zinc sulfonates, zinc carboxylates, zinc salicylates, zinc phenates and sulfurized zinc phenates and mixtures thereof.
Overbased zinc detergents may be formed by reaction between a neutral zinc detergent and a metal hydroxide. This reaction typically takes place using carbon dioxide in the presence of a promoter, which is generally an alcohol-type material. The promoter dissolves a small amount of metal hydroxide, which is subsequently reacted with carbon dioxide to form a metal carbonate. The amount of metal carbonate incorporated into the overbased detergents can vary depending upon the application in which the overbased detergent is used.
The preferred zinc detergents for use in the present invention include zinc sulfonates. The zinc sulfonates suitable for use in the present invention include zinc dihydrocarbyl aromatic sulfonates such as zinc dialkylnaphthalene sulfonate. The zinc dialkylnaphthalene sulfonate has a sulfonate group attached to one ring of the naphthalene nucleus and an alkyl group attached to each ring. Each alkyl group can independently contain from about six to about twenty carbon atoms, but it is preferred that they contain from about eight to twelve carbon atoms. The dialkylnaphthalene sulfonate group is attached to the zinc through the sulfonate group. A particularly preferred zinc dialkylnaphthalene sulfonate is zinc dinonylnaphthylene sulfonate available commercially as NA-SUL® ZS from King Industries, Inc.
The zinc detergents useful as component (A) in the present invention may also include mixtures of detergents such as blends of zinc sulfonates and zinc carboxylates in a ratio of zinc sulfonate to zinc carboxylate of from about 1:3 to about 3:1 parts by weight. Said blends are available commercially from King Industries, Inc. under the tradename NA-SUL® ZS-HT.
As is well known, overbased metal detergents are generally regarded as containing overbased quantitities of inorganic bases, probably in the form of micro dispersions or colloidal suspensions. Thus the term “oil soluble” as applied to the zinc detergents is intended to include zinc detergents that are not necessarily completely or truly oil-soluble, in as much as such detergents when mixed into base oils behave in much the same way as if they were fully and totally dissolved in the base oil.
In one embodiment of the present invention, component (A) is present in an amount sufficient to provide at least 10% by weight of the total zinc content of the fluid. In a preferred embodiment of the present invention, component (A) provides substantially all of the zinc to the finished fluid. The term “substantially all of the zinc to the finished fluid” herein means that greater than 50% of the total zinc, preferably greater than 75% of the total zinc, more preferably greater than 90% of the total zinc, and most preferably 100% of the total zinc content in the finished transmission fluid is provided by component (A).
Component (B) comprises at least one oil-soluble phosphorus-containing additive. Preferred phosphorus-containing additives include phosphate esters, acid phosphate esters, phosphite esters, acid phosphite esters, amine salts of the esters and phosphorus-containing ashless dispersants.
Representative phosphate esters include tributyl phosphate, trihexyl phosphate, tri-2-ethylhexyl phosphate, tridecyl phosphate, trilauryl phosphate, trimyristyl phosphate, tripalmityl phosphate, tri
Srinivasan Sanjay
Strait David L.
Tersigni Samuel H.
Ethyl Corporation
Medley Margaret
Rainear Dennis H.
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