Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic compound containing boron
Reexamination Certificate
1997-03-07
2003-09-02
McAvoy, Ellen M. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic compound containing boron
C508S291000, C508S434000, C508S436000, C508S441000, C508S442000, C508S554000, C508S562000
Reexamination Certificate
active
06613722
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a composition and a method for lubricating a steel belt continuously variable transmission (CVT).
BACKGROUND OF THE INVENTION
The continuing pursuit of more fuel efficient motor vehicles has led to the development of continuously variable transmissions by a number of manufacturers. The major difference between a continuously variable transmission and a conventional automatic transmission is that automatic transmissions use planetary gear sets to accomplish speed changes, whereas a continuously variable transmission uses pulleys and a belt to change speed. A conventional automatic transmission normally has 3, 4 or 5 fixed reduction ratios or “speeds”, e.g., a 5-speed automatic transmission. The operating system of the transmission selects the appropriate reduction ratio, or speed, based on engine rpm, ground speed and throttle position. In a continuously variable transmission an almost infinite number of reduction ratios, within fixed limits, can be achieved by changing the relative radius of travel of the driving belt on the driving and driven pulleys.
The critical mechanism in the CVT is the variator. The variator is composed of two steel pulleys and a steel belt. The pulleys can be opened and closed thereby allowing the belt to travel at different radiuses. When the driving pulley is fully opened (small radius of belt travel) and the driven pulley is fully closed (large radius of belt travel) very high reduction ratios are achieved (yielding low ground speeds). Conversely when the driving pulley is fully closed (large radius of belt travel) and the driven pulley is fully opened (small radius of belt travel) increases in output speed over input speed are achieved. (yielding high ground speeds).
The novelty of this design is that the belt is made of steel. Two types of CVT transmissions exist. In one design, the belt is “pushed” or compressed to transmit power, and in the other the belt is pulled, as is more common with a V-belt. Since steel belts are used in contact with steel pulleys, the lubrication requirements are identical for both design types.
There are two critical requirements for the lubricants used in CVT transmissions: (1) control of wear and (2) control of friction. Since steel-on-steel coefficients of friction tend to be very low, e.g., 0.03 to 0.2, extremely high closing forces are applied to the pulley sides to keep the belt from slipping. Any slippage of the belt causes catastrophic wear which quickly leads to failure. The pulleys are made to exacting limits and have a precise surface finish to allow optimum operation. No wear of these surfaces can be allowed. Therefore, an appropriate lubricant must have excellent wear control. The frictional characteristics of the belt-pulley. interface are also critical. The friction must be very high to prevent slippage of the belt during transmission of high torque from the engine to the drive wheels. Too high a static coefficient of friction, however, can cause “sticking” of the belt which will lead to oscillation and audible noise in the passenger compartment of the vehicle. This “whistling” of the belt is highly undesirable.
We have now found a unique combination of antiwear additives and friction modifiers that solve the difficult lubrication problems created by the steel-on-steel pulley system used in a continuously variable transmission.
SUMMARY OF THE INVENTION
This invention relates to a composition and a method of lubricating a continuously variable transmission comprising:
(1) a major amount of a lubricating oil; and
(2) an effective amount of a performance enhancing additive combination comprising:
(a) an organic phosphite;
(b) an amine salt of an organic phosphate; and
(c) one or more friction modifiers chosen from:
(1) selected amides,
(2) succinimides, and
(3) ethoxylated amines.
DETAILED DESCRIPTION OF THE INVENTION
Lubricating the variator system of a CVT is not a simple matter. It presents a unique problem of controlling wear and friction to very exacting limits. The antiwear agents must be carefully selected to provide excellent wear control and yet not interfere with the friction modifiers. The friction modifiers must be selected so as to provide very precise control of the steel-on-steel friction and not interfere with the control of wear.
1. Lubricating Oils
Lubricating oils useful in this invention are derived from natural lubricating oils, synthetic lubricating oils, and mixtures thereof. In general, both the natural and synthetic lubricating oil will each have a kinematic viscosity ranging from about 1 to about 100 mm
2
/s (cSt) at 100° C., although typical applications will require the lubricating oil or lubricating oil mixture to have a viscosity ranging from about 2 to about 8 mm
2
/s (cSt) at 100° C.
Natural lubricating oils include animal oils, vegetable oils (e.g., castor oil and lard oil), petroleum oils, mineral oils, and oils derived from coal or shale. The preferred natural lubricating oil is mineral oil.
Suitable mineral oils include all common mineral oil basestocks. This includes oils that are naphthenic or paraffinic in chemical structure. Oils that are refined by conventional methodology using acid, alkali, and clay or other agents such as aluminum chloride, or they may be extracted oils produced, for example, by solvent extraction with solvents such as phenol, sulfur dioxide, furfural, dichlorodiethyl ether, etc. They may be hydrotreated or hydrofined, dewaxed by chilling or catalytic dewaxing processes, or hydrocracked. The mineral oil may be produced from natural crude sources or be composed of isomerized wax materials or residues of other refining processes.
Typically the mineral oils will have kinematic viscosities of from 2.0 mm
2
/s (cSt) to 8.0 mm
2
/s (cSt) at 100° C. The preferred mineral oils have kinematic viscosities of from 2 to 6 mm
2
/s (cSt), and most preferred are those mineral oils with viscosities of 3 to 5 mm
2
/s (cSt) at 100° C.
Synthetic lubricating oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as oligomerized, polymerized, and interpolymerized olefins [e.g., polybutylenes, polypropylenes, propylene, isobutylene copolymers, chlorinated polylactenes, poly(1-hexenes), poly(1-octenes), poly-(1-decenes), etc., and mixtures thereof]; alkylbenzenes [e.g., dodecyl-benzenes, tetradecylbenzenes, dinonyl-benzenes, di(2-ethylhexyl)benzene, etc.]; polyphenyls [e.g., biphenyls, terphenyls, alkylated polyphenyls, etc.]; and alkylated diphenyl ethers, alkylated diphenyl sulfides, as well as their derivatives, analogs, and homologs thereof, and the like. The preferred oils from this class of synthetic oils are oligomers of &agr;-olefins, particularly oligomers of 1-decene.
Synthetic lubricating oils also include alkylene oxide polymers, interpolymers, copolymers, and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification, etc. This class of synthetic oils is exemplified by: polyoxyalkylene polymers prepared by polymerization of ethylene oxide or propylene oxide; the alkyl and aryl ethers of these polyoxyalkylene polymers (e.g., methyl-polyisopropylene glycol ether having an average molecular weight of 1000, diphenyl ether of polypropylene glycol having a molecular weight of 1000 to 1500); and mono- and poly-carboxylic esters thereof (e.g., the acetic acid esters, mixed C
3
-C
8
fatty acid esters, and C
12
oxo acid diester of tetraethylene glycol).
Another suitable class of synthetic lubricating oils comprises the esters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebasic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkylmalonic acids, alkenyl malonic acids, etc.) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoethers, propylene glycol, etc.). Specific examples of these esters include dibutyl adipat
Reeve Philip
Watts Raymond F.
Exxon Chemical Patents Inc.
McAvoy Ellen M.
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