Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and...
Reexamination Certificate
1999-11-09
2002-04-16
McAvoy, Ellen M. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
C508S287000, C508S391000, C525S001001, C525S016000, C525S020000, C252S073000
Reexamination Certificate
active
06372696
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to traction fluids and their use in lubricating power transmitting equipment, especially, a traction drive, and more specifically, an automotive traction drive.
Traction drives are 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 drives can be generally used in automotive or industrial machinery for transmitting power between rotating members. They can be used as automatic transmissions and are particularly suitable as a form of continuously variable automatic transmission for use in automobile drivetrains and other applications.
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. Thus, rather than metal-to-metal rolling contact, a film of fluid is introduced into the load zone, and power is transmitted by shearing of the film, which may become very viscous due to the high pressure at the contact area. The nature and properties of the fluid, therefore, will determine to a large extent the performance and capacity of the traction drive. Traction fluids will preferably have a high shear resistance (often measured as “traction coefficient”) to maximize the power transmission performance. Low viscosity, particularly at low temperatures, is also desirable for efficient operation under cold conditions. The fluid should ideally also exhibit good lubricating properties for and compatibility with other components of the traction drive. Such fluids also serve to remove heat and prevent wear at the contact surfaces and to lubricate bearings and other moving parts associated with the drive.
Traction fluids based on a variety of base fluids are known. For example, U.S. Pat. No. 5,043,497, Muraki et al., Aug. 27, 1991, discloses a lubricating oil for a traction drive, mainly composed of a naphthenic hydrocarbon having 19 carbon atoms comprising two substituted cyclohexane rings linked by a methylene group. Additives for ordinary lubricating oils such as antioxidants, agents for increasing the viscosity index, corrosion inhibitors, detergents, defoamers, and so forth are added as necessary. Calcium sulfonate is disclosed as a detergent.
U.S. Pat. No. 3,975,278, Wygant, Aug. 17, 1976, discloses hydrogenated dimers of a-alkyl styrene, which are useful as tractive fluids. Additives such as VI improvers, antioxidants, antiwear agents, corrosion inhibitors, dispersants, and dyes can be included.
U.S. Pat. No. 3,966,624, Duling et al., Jun. 29, 1976, discloses a blended traction fluid containing hydrogenated polyolefin and an adamantane ether. The lubricant described can contain other oils and additives, e.g., a sludge dispersant. An especially useful additive, combining detergency, corrosion inhibition and friction improvement at high speeds, is a Mg, Ca or Ba salt (especially a super-based salt) of certain weak acids.
A variety of additive formulation for use in transmission fluids and other functional fluids are generally known. For instance, U.S. Pat. No. 5,858,929, Sumiejski et al., Jan. 12, 1999, equivalent to European Patent publication 747,464, published Jun. 6, 1996, discloses a composition for use in lubricants and functional fluids to provide improved anti-shudder and shudder durability properties to an automatic transmission. The composition comprises alkoxylated fatty amines as well as a mixture of other friction modifiers. Preferred compositions include alkoxylated fatty amines, other friction modifiers, antioxidants, overbased metal organic acid, dispersants, viscosity index improver and/or dispersant-viscosity modifier, extreme pressure agent, seal swell agent, and 85% phosphoric acid. The base oils of lubricating viscosity include liquid petroleum oils and solvent treated or acid treated mineral lubricating oils of the paraffinic, naphthenic or mixed naphthenic-paraffinic types.
The present invention solves the problem of providing a fluid for a traction drive with a sufficiently high traction coefficient to maintain the efficiency of the unit, while at the same time providing a low enough viscosity that the unit will operate at ambient temperatures in cold climates. Additionally, the presence of suitable additives provides lubrication and compatibility of the fluid with the operation of conventional clutches, seals, and gears which may be present in the traction drive unit. The traction fluids of the present invention can also be used in other types of power transmission devices such as continuously variable transmissions of the push-belt type. Push-belt continuously variable transmissions are described in U.S. Pat. No. 5,750,477.
SUMMARY OF THE INVENTION
The present invention provides a traction fluid useful in automotive power transmitting equipment, comprising (a) a major amount of a base fluid selected from the group consisting of polymers of at least one olefin which contains 3 to 5 carbon atoms, hydrocarbon or ester molecules containing non-aromatic cyclic moieties, and mixtures thereof; (b) a low-temperature viscosity control agent selected from the group consisting of oligomers or polymers of linear alpha olefins of at least 8 carbon atoms, naphthenic oils, synthetic ester oils, polyether oils, and mixtures thereof, in an amount sufficient to reduce the viscosity at −40° C. of said traction fluid; and (c) an additive selected from the group consisting of dispersants, detergents, and mixtures thereof, in an amount sufficient to improve the clutch friction durability performance of said traction fluid.
The present invention also provides a method of lubricating a power transmission apparatus such as a traction drive, comprising employing therein the above-described traction fluid.
DETAILED DESCRIPTION OF THE INVENTION
Various preferred features and embodiments will be described below by way of non-limiting illustration.
The first, and major component of the traction fluids of the present invention is a base fluid or base oil. Certain types of base fluids are particularly suited for use in traction fluids because of their inherently good (high) traction coefficients. Two types of base fluids which are particularly suitable are (1) polymers of at least one olefin which contains 3 to 5 carbon atoms, and (2) hydrocarbon molecules containing non-aromatic cyclic moieties. Mixtures of these types of materials can also be used. For suitable performance, the base fluid should preferably have a viscosity of greater than 2.5×10
−6
m
2
/s (2.5 cSt) at 100° C. (ASTM D-445), and more preferably a viscosity of at least 3.0×10
−6
m
2
/s (3.0 cSt) or 3.5×10
−6
m
2
/s (3.5 cSt), typically up to 8.0×10
−6
m
2
/s (8.0 cSt) or 7.0×10
−6
m
2
/s (7.0 cSt) or 6.0×10
−6
m
2
/s (6.0 cSt) at 100° C.
Suitable base fluids of type (1) include polymers of branched olefins, preferably isobutylene, particularly those having a number average molecular weight of 180 to 2000, preferably 200 to 1000 or to 700. The polymer is preferably hydrogenated to remove any residual unsaturation. Such materials and their preparation are well known and are described, for instance, in U.S. Pat. No. 3,966,624, as component A, described particularly in column 12 line 32 through column 16 line 11.
Suitable base fluids of type (2) include a wide variety of cyclic-containing hydrocarbon molecules. Examples of these include di(cyclohexyl)alkanes, cyclohexyl hydrindans and adamantane compounds, as described in U.S. Pat. No. 3,966,624; esters of cyclohexanol and cylohexanecarboxylic acid, as described in U.S. Pat. No. 4,871,476; decalin, cycohexyldecalin, alkyl-substituted decalin, alkyl-substituted cyclohexyldecalin, and mixtures thereof, as described in U.S. Pat. No. 3,803,037; various materials having two cyclohexane rings linked by a methylene group described in U.S. Pat. No. 5,043,497; various hy
Esposito Michael F.
McAvoy Ellen M.
Shold David M.
The Lubrizol Corporation
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