Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic compound containing boron
Reexamination Certificate
2000-03-21
2002-09-17
Howard, Jacqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic compound containing boron
C508S186000, C508S189000
Reexamination Certificate
active
06451745
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to high-boron formulations suitable for use as fluids for continuously variable transmissions.
Continuously variable transmissions (CVT) represent a radical departure from conventional automatic transmissions. 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. CVT push belts 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 European Patent Application 753 564, published Jan. 15, 1997, 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.
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.
U.S. Pat. No. 5,759,964, Sumiejski, Jun. 2, 1998 discloses an antiwear enhancing composition for lubricants and functional fluids such as automatic transmission fluids. It comprises a boron-containing overbased material; a phosphorus acid, ester, or derivative thereof, and a borated epoxide or borated fatty acid ester of glycerol.
U.S. Pat. No. 4,948,522, Dunn et al., Aug. 14, 1990, discloses a dispersant additive package for marine diesel engines comprising an oil of lubricating viscosity, a borated ashless dispersant, and one or more overbased metal compounds.
U.S. Pat. No. 5,750,477, Sumiejski et al., May 12, 1998, which is equivalent to EP 0 753 564 referred to above, discloses a shear stable lubricating/functional fluid composition, comprising an oil of lubricating viscosity, 1-15% by weight of the metal salt of an organic acid, and 1-25% viscosity modifier, wherein the composition has certain defined viscosity. Other components in the additive package include a metal dialkyl dithiophosphate, sulfur containing friction modifiers, dialkyl phosphites, and fatty amides.
European Application 761 805, Mar. 12, 1997, discloses a lubricating/functional fluid which comprises an oil of lubricating viscosity, 2,5dimercapto-1,3,4-thiadiazole or a derivative thereof and an antifoam agent. The composition may include phosphoric acid. Friction modifiers are included in the compositions in the amounts of 0.1-10 weight percent and may be a single friction modifier or mixtures of two or more. Friction modifiers also include metal salts of fatty acids. Preferred cations are zinc, magnesium, calcium, and sodium and any other alkali, or alkaline earth metals may be used. The salts may be overbased by including an excess of cations per equivalent of amine [sic; acid?]. Zinc salts are added in amounts of 0.1-5 weight percent to provide antiwear protection. The zinc salts are normally added as zinc salts of phosphorodithioic acids.
U.S. Pat. No. 4,792,410, Dec. 20, 1988, Schwind et al., discloses a lubricant mixture suitable for a manual transmission fluid, comprising a boronated overbased alkali metal or alkaline earth metal salt, a friction modifier or mixture of friction modifiers such as e.g. fatty acid amides and borated derivatives, and an oil of lubricating viscosity. Other typical ingredients may be included.
The metal-metal coefficient of friction and the antiseizure properties of CVT fluids are important performance parameters for the effective application of continuously variable transmissions. It is generally known that formulations containing zinc salts such as primary zinc dihydrocarbyl dithiophosphates resist metal-metal seizure and maintain high metal-metal coefficients of friction at the CVT belt-pulley interface. It is, however, desirable to formulate CVT fluids with compositions similar to automatic transmission fluids (ATFs). ATFs are generally not formulated with zinc dihydrocarbyl dithiophosphates because of their low thermal and oxidative stability and their known problems with clutch incompatibility.
The present invention, therefore, solves the problem of providing a suitable CVT fluid with exceptional metal-metal friction and good antiseizure properties, preferably free from primary zinc dihydrocarbyl dithiophosphates, by means of including boronated detergents and/or dispersants. The amount of zinc dihydrocarbyl dithiophosphates in the fully formulated CVT fluid is therefore preferably less than 1 percent, more preferably less than 0.5 percent, 0.1 percent, or 0.05%. The most preferred compositions are substantially free from zinc dihydrocarbyl dithiophosphates, e.g, less than 0.01 percent.
The compositions of the present invention can be used as lubricating oils and greases useful in industrial applications and in automotive engines, transmissions and axles. These compositions are effective in a variety of applications including crankcase lubricating oils for spark-ignited and compression-ignited internal combustion engines, including automobile and truck engines, two-cycle engines, aviation piston engines, marine and low-load diesel engines, and the like. They are also useful as additives for traction fluids. Also, automatic transmission fluids, manual transmission fluids, transaxle lubricants, gear lubricants, metalworking lubricants, hydraulic fluids, and other lubricating oil and grease compositions can benefit from the incorporation of the compositions of this invention. The inventive functional fluids are particularly effective as automatic transmission fluids, particularly fluids for continuously variable transmissions, including push-belt type and toroidal traction drive transmissions.
SUMMARY OF THE INVENTION
The present invention provides formulations suitable for use as fluids for continuously variable transmissions, comprising:
(a) an oil of lubricating viscosity; and
(b) a dispersant; or
(c) a detergent; or mixtures of (b) and (c);
wherein at least one of the dispersant (b) and the detergent (c) is a borated species and wherein the amount of boron supplied to the formulation is sufficient to impart improved friction and anti-seizure properties to said formulation.
The present invention further provides a method for lubricating a continuously variable transmission, comprising imparting to said transmission the aforedescribed formulation.
DETAILED DESCRIPTION OF THE INVENTION
Various preferred features and embodiments will be described below by way of non-limiting illustration.
The first component of the present invention is an oil of lubricating viscosity which is generally present in a major amount (i.e. an amount greater than 50% by weigh
Esposito Michael F.
Howard Jacqueline V.
Shold David M.
The Lubrizol Corporation
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