Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Heavy metal or aluminum in an organic phosphorus compound...
Reexamination Certificate
2002-06-10
2004-05-04
McAvoy, Ellen M (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Heavy metal or aluminum in an organic phosphorus compound...
C508S539000, C252S074000
Reexamination Certificate
active
06730640
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to compositions useful as transmission fluids, and particularly as fluids for continuously variable transmissions, and their use in lubricating continuously variable transmissions.
Continuously variable transmissions (CVT) represent a radical departure from conventional automatic transmission. The “push belt” version of the CVT was invented by Dr. Hub Van Doorne, and since its introduction, many cars have been equipped with the push belt CVT system. CVTs are manufactured by Van Doorne's Transmissie VB of Tilburg, the Netherlands. A more detailed description of such transmissions and belts and lubricants employed therein is found in U.S. Pat. No. 5,750,477, as well as references cited therein. In brief, a belt and pulley system is central to the operation of this type of transmission. The pulley system comprises a pair of pulleys with a V-shaped cross-section, each consisting of a moveable sheave, a fixed sheave, and a hydraulic cylinder. Between the pulleys runs a belt, which consists of a set of metal elements held together by metal bands. In operation, the driving pulley pushes the belt to the driven pulley, thereby transferring power from the input to the output. The transmission drive ratio is controlled by opening or closing the moveable sheaves so that the belt rides lower or higher on the pulley faces. This manner of operation permits continuous adjustment of gear ratio between the input and output shafts. Other types of belt-driven continuously variable transmissions are also known, including “pull-belt” transmissions in which a belt transmits force in tension rather than compression.
It has become clear from commercial use of the CVT that the fluids used in the CVT are just as important as the mechanical design for satisfactory operation. The lubricant must fulfill several functions: to lubricate the metal belt in its contacts with the pulley assembly, the planetary and other gears, the wet-plate clutches, and the bearings; to cool the transmission; and to carry hydraulic signals and power. The hydraulic pressure controls the belt traction, transmission ratio, and clutch engagement. The lubricant must provide the appropriate degree of friction between the belt and pulley assembly, to avoid the problem of slippage on one hand, and binding on the other, all the while providing protection to the metal surfaces from pitting, scuffing, scratching, flaking, polishing, and other forms of wear. Accordingly, the fluid should maintain a relatively high coefficient of friction for metal/metal contact, as well as exhibiting a suitable degree of shear stability.
Traction drives can be seen as another species of continuously variable transmission. These are typically devices in which power or torque is transmitted from an input element to an output element through nominal point or line contact, typically with a rolling action, by virtue of the traction between the contacting elements. Traction fluids and traction drives in which they can be used have been described for instance, in U.S. Pat. Nos. 4,693,134 and 5,043,497. While the working elements of a traction drive are sometimes spoken of as being in contact, it is generally accepted that a fluid film must be provided therebetween. Traction fluids and traction fluid compositions are employed in this context to provide power transmission by shearing of the film.
The present invention, therefore, solves the problem of providing fluids such as fluids for push-belt type and other continuously variable transmissions, which have increased metal-on-metal coefficient of friction while exhibiting low copper corrosion, by incorporating an oil soluble zinc salt into a fluid which is substantially free from thiophosphate salts.
European Patent Application 287 618, Dec. 9, 1992, discloses functional fluid compositions which comprise metal salts of an alkyl phosphoric acid ester. The metal-containing high torque, extreme pressure agent for a lubricating composition is prepared by reacting (A) a compound of the formula ROH with (B) a sulfur-free, phosphorus-containing agent to form an intermediate, and then further reacting said intermediate with (C) an oxide or hydroxide . . . of a metal selected from . . . zinc [among others] in the presence of (D) a catalytically effective amount of a proton source. The phosphorus acid esters are usually prepared from alcohols or alkyl phenols and phosphorus pentoxide. The amount of the composition employed in a lubricant will be about 0.05% to about 20%, preferably about 0.1% to about 10%.
U.S. Pat. No. 3,803,037, Wygant, Apr. 9, 1974, discloses cyclic carbon-containing compounds suited for use as a fluid component of tractive drives. The load-bearing capability is improved by incorporating minor amounts of zinc di(neo-alkyl)phosphorodithioate. In a (comparative) example, 2% of zinc 2-ethylhexyl isopropyl phosphorodithioate was tested and the coefficient of traction was measured.
SUMMARY OF THE INVENTION
The present invention provides a method for lubricating a continuously variable transmission, comprising supplying to said transmission a composition comprising an oil of lubricating viscosity and an oil-soluble zinc salt containing at least one hydrocarbyl group of at least 4 carbon atoms, in an amount sufficient to provide an increased steel-on-steel dynamic coefficient of friction for said composition, said coefficient of friction being at least 0.125, provided that said composition is substantially free from thiophosphate salts. The resulting composition exhibits a copper corrosion rating of 1B or better as measured by the procedure of ASTM-130 at 149° C. for 3 hours.
DETAILED DESCRIPTION OF THE INVENTION
Various preferred features and embodiments will be described below by way of non-limiting illustration.
The present invention provides a method for lubricating a continuously variable transmission (CVT). CVTs include both automotive and industrial transmissions, and include transmissions of both the push-belt design and the traction drive design.
The continuously variable transmissions of the present invention are lubricated by supplying to them a fluid. The fluid serves as more than a conventional lubricant since it must provide appropriate frictional or traction performance, and it can thus also be considered to be a functional fluid. The fluid composition comprises, first, an oil of lubricating viscosity, which is generally present in a major amount (i.e. an amount greater than 50% by weight). Generally, the oil of lubricating viscosity is present in an amount of greater than 80% by weight of the composition, typically at least 85%, preferably 90 to 98%. Such oil can be derived from a variety of sources, and includes natural and synthetic lubricating oils and mixtures thereof.
The natural oils useful in making the inventive lubricants and functional fluids include animal oils and vegetable oils (e.g., lard oil, castor oil) as well as mineral lubricating oils such as liquid petroleum oils and solvent treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic or mixed paraffinic
aphthenic types which may be further refined by hydrocracking and hydrofinishing processes and are dewaxed. Oils of lubricating viscosity derived from coal or shale are also useful. Useful natural base oils may be those designated by the American Petroleum Institute (API) as Group I, II, or III oils. Group I oils contain <90% saturates and/or >0.03% sulfur and have a viscosity index (VI) of ≧80. Group II oils contain ≧90% saturates, ≦0.03% sulfur, and have a VI ≧80. Group III oils are similar to group II but have a VI ≧120.
Upon occasion, highly refined or hydrocracked natural oils have been referred to as “synthetic” oils. More commonly, however, synthetic lubricating oils are understood to include hydrocarbon oils and halo-substituted hydrocarbon oils such as polymerized and interpolymerized olefins (e.g., polybutylenes, polypropylenes, propylene-isobutylene copolymers, chlorinated polybutylenes); poly(1-hexene
Sowerby Roger L.
Sumiejski James L.
Tipton Craig D.
Esposito Michael F.
McAvoy Ellen M
Shold David M.
The Lubrizol Corporation
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