Traction fluids

Details Traction fluids Traction fluids

2001-12-28

2003-09-23

Dawson, Robert (Department: 1712)

Friction gear transmission systems or components

With friction enhancing fluid

C252S078300, C192S021500, C508S208000, C475S125000, C475S087000, C475S159000, C476S011000, C476S008000, C528S010000

Reexamination Certificate

active

06623399

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to siloxane compositions which are useful as traction fluids in traction drive systems subject to varied operating temperature and pressure conditions.
BACKGROUND OF THE INVENTION
Certain hydrocarbon oils and organosilicone compounds have been found to be useful in a variety of engineering applications, including traction fluids for traction drive systems. Most current toroidal—continuously variable transmission (T-CVT) traction fluids are hydrocarbon molecules based primarily on dimers of the same or two different monomers. They possess saturated rings structures such as cyclohexane, alkylcyclohexane, bicycloheptane or bicyclooctane. Traction is broadly defined as the adhesive friction of a body on a surface on which it moves. A traction drive is a device in which 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.
While traction elements are commonly spoken of as being in contact, it is generally accepted that a fluid film is present therebetween. Almost all traction drives require these fluids to remove heat, to prevent wear at the contact surfaces and to lubricate bearings and other moving parts associated with the drive. Thus, instead of metal to metal rolling contact there is a film of fluid introduced into the contact zone and interposed between the metal elements. High pressures and high shear conditions are found in this area of contact between the roller elements and so the nature of this fluid determines to a large extent the limits of performance and the capacity of the drive. It is through the traction fluid's resistance to shear that the torque transmitting ability of a given fluid arises. The torque transmitting ability of a fluid, and thus its suitability as a traction fluid, is measured by and is directly related to its traction coefficient at varying temperatures. In addition to a fluid's torque transmitting ability, its ability to protect against wear is also important.
The inventors have now determined that certain siloxane compositions have traction coefficients and anti-wear properties that make them useful as traction fluids at varied temperatures. An object of the invention is to provide traction fluids useful for low temperature applications. Another object of the invention is to provide traction fluids useful for high temperature applications. Another object of the invention is to provide traction fluids having improved anti-wear properties.
SUMMARY OF THE INVENTION
This invention relates to siloxane compositions which are useful as traction fluids in traction drive systems which are subject to varied operating temperature conditions. Specific siloxane compositions included contain units of formulae
(I) (R
3
SiO
1/2
)(RSiO
3/2
)(SiO
4/2
),
(II) (R
3
SiO
1/2
)(RSiO
3/2
),
(III) (R
3
SiO
1/2
)(SiO
4/2
),
(IV) (R
3
SiO
1/2
)(R
2
SiO
2/2
)(RSiO
3/2
),
(V) (R
3
SiO
1/2
)(R
2
SiO
2/2
), and
(VI) (R
2
SiO
2/2
)
a
in varying mole percents, where a is an integer ranging from 3 to 20 and each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms.
DETAILED DESCRIPTION OF THE INVENTION
A method for transmitting torque in a traction drive system having at least two relatively rotatable members in a torque transmitting relationship comprising disposing on the tractive surfaces of the members a traction fluid comprising at least one siloxane composition chosen from
(I) 33 to 80 mole percent units of formula (R
3
SiO
1/2
), 0.2 to 66.8 mole percent units of formula (RSiO
3/2
), and 66.8 to 0.2 mole percent units of formula (SiO
4/2
) having a viscosity of from 1.0 to 50,000 mPa·s at 40° C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl;
(II) 33 to 75 mole percent units of formula (R
3
SiO
1/2
) and 67 to 25 mole percent units of formula (RSiO
3/2
) having a viscosity of from 2.0 to 20,000 mPa·s at 40° C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl;
(III) 33 to 80 mole percent units of formula (R
3
SiO
1/2
) and 67 to 20 mole percent units of formula (SiO
4/2
) having a viscosity of from 1.0 to 70,000 mPa·s at 40° C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl;
(IV) 0 to 28 mole percent units of formula (R
3
SiO
1/2
), 37 to 93 mole percent units of formula (R
2
SiO
2/2
), and 6 to 56 mole percent units of formula (RSiO
3/2
) having a viscosity of from 5.0 to 10,000 mPa·s at 40° C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl and provided further that at least one of the R groups which is not methyl is chosen from alkyl groups comprising 7 to 18 carbon atoms and aryl groups comprising 7 to 18 carbon atoms;
(V) 1 to 100 mole percent units of formula (R
3
SiO
1/2
) and 99 to 0 mole percent units of formula (R
2
SiO
2/2
) having a viscosity of from 1.0 to 50,000 mPa·s at 40° C., where each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl and provided further that at least one of the R groups which is not methyl is chosen from alkyl groups comprising 7 to 18 carbon atoms and aryl groups comprising 7 to 18 carbon atoms; and
(VI) cyclosiloxanes of formula (R
2
SiO
2/2
)
a
having a viscosity of from 2.0 to 50,000 mPa·s at 40° C., where a is an integer ranging from 3 to 20, each R is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms provided from 10 to 70 mole percent of R groups are not methyl.
The traction fluids useful in the present method comprise at least one siloxane composition chosen from (I)-(VI) described above, preferably chosen from (II), (III), (IV), (V), and (VI), and more preferably chosen from (II), (III), and (VI). The siloxane compositions described above may contain monofunctional siloxane units (M units) represented by formula (R
3
SiO
1/2
), difunctional siloxane units (D units) represented by formula (R
2
SiO
2/2
), trifunctional siloxane units (T units) represented by formula (RSiO
3/2
), and tetrafunctional siloxane units (Q units) represented by formula (SiO
4/2
).
Each R in siloxane compositions (I)-(VI) is independently selected from alkyl groups comprising 1 to 18 carbon atoms and aryl groups comprising 6 to 18 carbon atoms. The alkyl groups of R can be linear, branched and cyclic. Examples of linear alkyl groups include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, decyl, and octadecyl. Examples of branched alkyl groups include isobutyl, tertiary butyl, 2-ethylhexyl, 2,4,4,6,6-pentarnethylheptyl and 2,4,4-trimethylpentyl. The cyclic groups may be attached directly to the silicon atom or attached through a divalent hydrocarbon group. Preferably, the divalent hydrocarbon group is an alkylene group. In addition, the cyclic groups may have hydrocarbon groups attached to the ring. Examples of cyclic alkyl groups include cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, dimethylcyclohexyl, 2-cyclohexylethyl, 2-cyclohexylpropyl, cyclooctyl, bicyclo (2.2.1) heptyl, bicyclo (2.2.2) octyl, methylnorbornyl, ethylnorbornyl, trimethylnorbornyl, 2-norbornylethyl, and decanyl.
The aryl groups of R may be attached directly to the silicon atom or attached through a divalent hydrocarbon group. Preferably, the divalent hydrocarbon group is an alkylene group. In

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