Note: Descriptions are shown in the official language in which they were submitted.
1
AUTOMOTIVE TRANSMISSION FLUID COMPOSITIONS FOR IMPROVED
ENERGY EFFICIENCY
The present invention provides automotive transmission fluid compositions
having
improved power transmission properties through the presence therein of certain
defined
additives. In particular, the invention provides transmission fluid
compositions for automotive
vehicles, the use of which increase the fuel efficiency of the vehicle during
operation. The
invention further provides a process for the manufacture of such transmission
fluid
compositions, a method of improving the energy efficiency of a transmission,
and an additive
concentrate for a transmission fluid, and other aspects as hereinafter
described.
Political, regulatory and consumer pressures abound to increase the energy
efficiency
of the modern world. Machines for many applications rely on co-operation
between moving
parts to transmit power from drive units to driven units, and the efficiency
of this power
transmission contributes to the overall energy efficiency of the machine. The
pursuit of ever
more energy-efficient machines has become a constant goal in many industry
sectors.
In the automotive sector, power transmission occurs primarily through the
drive-train
components of the vehicle. The crankshaft of the engine is typically coupled
to the transmission
through some form of clutch, with power transmission occurring across the
clutch to drive the
transmission and ultimately the road wheels. Further clutches may be present
within the
transmission depending upon the design of the vehicle and its transmission
type. An essential
characteristic of such clutches is their ability to efficiently transmit power
across the contact
between the clutch plates. Any losses in power transmission between the engine
and roads
wheels result in reduced energy efficiency for the vehicle, as demonstrated
for example by
poorer fuel efficiency.
Improving the energy efficiency of automotive transmissions via the automotive
transmission fluid presents challenges different to improving the energy
efficiency of an engine.
In general terms, energy losses occur in moving engine parts due to friction.
A common goal in
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the lubrication of engines is therefore to reduce friction and, in so doing,
reduce attendant
energy losses. In contrast, transmissions function by transmitting power
across moving surfaces
via high friction. Therefore, creating an environment of low friction between
these surfaces
would lead to a loss of energy transfer between the surfaces and attendant
loss in power
transmission. At the same time, however, wear must be controlled. Thus, the
formulation of
effective transmission fluids having a beneficial balance of clutch friction,
wear, fatigue
prevention and energy efficiency is a complex task, and not one that readily
lends itself to
routine analysis.
There remains in the art a need for improved automotive transmission fluids
which, in
use, lead to increased energy efficiency of the transmission and, in
particular, there remains a
need in the art for automotive transmission fluids which lead to increased
fuel efficiency for the
vehicle during operation.
An approach to this problem described in the art concerns the modification of
transmission fluid viscosity through the use of viscosity modifiers. By
altering the viscometric
properties of the fluid, i.e. lowering the fluid viscosity, some benefits in
fuel efficiency have
been seen in given cases. However, this effect has been attributed to the
physical impact of
altered bulk liquid viscometrics, and has been associated with a number of
disadvantages such
as durability of mechanical parts and reliability of operation.
The present invention concerns automotive transmission fluid compositions
having
improved power transmission properties through the presence therein of certain
defined
additives. In particular, the invention provides transmission fluids for
automotive vehicles, the
use of which demonstrably increase the fuel efficiency of the vehicle during
operation.
In particular, the present invention has determined that a class of
polyalphaolefin
polymer made by a particular form of polymerisation reaction has utility as a
performance-
enhancing additive for transmission fluids, when present in conjunction with
one or more
detergent additives and specific viscosity modifiers, wherein the combination
functions to
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improve the power transmission properties of the fluid. This combination of
additives enables
the transmission to operate with greater energy efficiency, as demonstrated
for example by an
increase in the fuel efficiency of the vehicle during operation. The
polyalphaolefin shows
advantageous performance as an additive for this purpose when used in an
amount that does
not exceed 4 percent by weight of the total transmission fluid composition,
and optimal
performance when used in an amount in the range of 1 to 3 percent by weight of
the total
transmission fluid composition.
As the examples hereafter demonstrate, the energy efficiency benefit arising
from the
combination of polyalphaolefin, specific viscosity modifier and detergent
additive is manifest
even under conditions in which the main viseometric properties of the fluids
under comparison
(kinematic viscosity and viscosity index) have been controlled to remain
essentially constant.
Thus, the fundamental effect of the additive combination is seen to operate
independent of fluid
viscosity per se. The improvement in energy efficiency attributable to the
combination of
additives essential to the invention is thus attributed to a mechanism
different from simply
lowering the fluid viscosity by the approach known in the art.
US-A-2010/0035778 provides a composition for a power transmitting fluid that
has
inter alia improved fuel economy which preferably comprises an additive and a
base stock
having a polyalphaolefin blend. The additive preferably includes inter alia a
viscosity index
improver. This teaching reports the use of a basestock that includes a
polyalphaolefin (PAO) or
PAO blend that has an unconventional viscosity profile, and recites a fluid
composition having
from about 8% to about 90% by weight of the PAO blend. The worked example of
the
composition contains 77.4% by weight of the PAO blend, being comprised of PAO
2cSt and
PAO 6 cSt in proportions of 9.4% and 68.0% by weight respectively, along with
a viscosity
modifier and detergent additive. This teaching reports that any number of PAOs
may be
employed so long as the PAO blend is selected such that the base viscosity of
the fluid is greater
than or equal to 4.0cSt at 100 C. This teaching fails to conceptually
recognise the benefit arising
from use of a specific polyalphaolefin at additive treat levels within the
transmission fluid, and
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again focusses on altered bulk viscometrics as the means by which fluid
performance is
enhanced.
US-A-2007/000807 provides an industrial lubricant and grease composition
containing
high viscosity index polyalphaolefins (HVI-PAO) characterised by having a high
viscosity
index of preferably 130 or greater and certain other define characteristics.
Such HV1-PAOs may
be prepared by a variety of routes, including activated metallocene catalysts.
The document
teaches in paragraph 0016 that a particular advantage of its HVI-PAO
formulations is that
certain conventional additives are not required, particularly polymeric
thickeners or other
thickening fluids, eg. viscosity index (VI) improvers, although they may be
included as an
optional element.
The present invention has found that the nature of the viscosity modifier used
in
combination with the defined polyalphaolefin influences the degree of
improvement in energy
efficiency achieved through use of the resulting transition fluid composition,
and in particular
the degree of improvement in fuel efficiency of the vehicle. As described
hereinafter, different
viscosity modifiers demonstrate differential improvements in combination with
the
polyalphaolefin when compared in formulated oils having equivalent viscometric
properties.
This improvement in efficiency is therefore attributable to the nature of the
viscosity modifier
per se rather than to differential viscosity modification effects.
In addition, the present invention has found that the presence of at least one
detergent
additive increases the improvement in energy efficiency achieved through use
of the resulting
transition fluid composition, and in particular optimises the fuel efficiency
of the vehicle.
Preferably, for improving energy efficiency, at least one detergent additive
(iv) comprises one
or more alkaline earth metal detergent compounds, wherein at least one
alkaline earth metal
detergent compound is an alkaline earth metal salicylate or sulphonate
compound. More
preferably, each alkaline earth metal detergent compound present in the
transmission fluid
composition is a neutral or overbased calcium salicylate compound, and more
preferably the
total amount of these calcium salicylate compound(s) is such as to provide the
transmission
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fluid composition with a calcium content of between 50 and 250 parts per
million by weight,
per weight of the transmission fluid composition.
In a first aspect therefore, the present invention provides a transmission
fluid
composition consisting of:
(i) a lubricating oil, or blend of lubricating oils;
(ii) a viscosity modifier additive or blend of viscosity modifier
additives;
(iii) a polyalphaolefin compound or compounds; and
(iv) one or more detergent additives,
wherein the or each polyalphaolefin compound (iii) is made by the metallocene-
catalysed polymerisation of an alphaolefin feedstock, and wherein the total
amount of the
polyalphaolefin compound(s) (iii) in the transmission fluid composition does
not exceed 4
percent by weight of the composition; and wherein at least one viscosity
modifier additive (ii)
contains a polymer or blend of polymers selected from one or more of the
following groups:
(ii)(a) random or block poly-alkylacrylates or poly-alkylmethacrylates, or
copolymers
thereof;
(ii)(b) star polymers comprising a polyvalent core of polyalkylacrylate or
polyalkylmethacrylate from which a plurality or arms depend, the arms being
polymer chains
containing alkylacrylate or alkylmethacrylate monomer units; or
(ii)(c) comb polymers prepared by the copolymerisation of one or more
alkylacrylate
or alkylmethacrylate monomers with one or more olefin or polyolefin monomers.
The, or each, polyalphaolefin compound (iii) is made by a polymerisation
reaction in
which the corresponding alphaolefin feedstock is polymerised through the
action of a
metallocene catalyst. Such polyalphaolefins are known per se, and are
sometimes referred to in
the polymer art as "mPAO". They possess a structure different from
polyalphaolefins derived
from other catalytic processes. In particular, the action of the metallocene
catalyst is such as to
cause the formation of a polymer product having a narrow molecular weight
distribution, and a
structure that embodies a high proportion of head-to-tail monomer unit
additions, i.e. can be
regarded as an essentially ideal polymer. The literature for such materials
also reports a more
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ordered pattern of hydrocarbon side chains with fewer short side chains than
other processes.
The result is a polymer with a more "perfect" structure and different
properties.
The present invention has determined that such polyalphaolefins show a
particular
benefit when used as performance-enhancing additives in transmission fluid
compositions. As
illustrated in the examples which follow, the additive benefit from such
polyalphaolefins is seen
at a treat rate of not more than 4 percent by weight of the total transmission
fluid composition,
preferably between I and 3 percent by weight, and optimally between 2 and 3
percent by weight.
Such treat rates correspond to typical additive treat rates in such fluids,
and are not to be
confused with the use of synthetic polymers as lubricating oils per se
(sometimes called
"basestocks") or as basestock blending components, which involve the
incorporation of larger
relative quantities of polymer for constituting the bulk volume of base
lubricating oil.
In a second aspect, the present invention provides a process for the
manufacture of a
transmission fluid composition, the composition consisting of:
(i) a lubricating oil, or blend of lubricating oils;
(ii) a viscosity modifier additive or blend of viscosity modifier additives
containing a
polymer or blend of polymers selected from one or more of the following
groups:
(ii)(a) random or block poly-alkylacrylates or poly-alkylmethacrylates, or
copolymers
thereof;
(ii)(b) star polymers comprising a polyvalent core of polyalkylacrylate or
polyalkylmethaerylate from which a plurality or arms depend, the arms being
polymer
chains containing alkylacrylate or alkylmethacrylate monomer units; or
(ii)(e) comb polymers prepared by the copolymerisation of one or more
alkylacrylate or
alkylmethacrylate monomers with one or more olefin or polyolefin monomers;
(iii) a polyalphaolefin compound or compounds, each made by the metallocene-
catalysed
polymerisation of an alphaolefin feedstock; and
(iv) one or more detergent additives;
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the process comprising the following steps:
a) obtaining (by manufacture or otherwise) a lubricating oil or blend of
lubricating oils
containing no polyalphaolefin compound(s) made by the metallocene-catalysed
polymerisation
of an alphaolefin feedstock; and
b) mixing with this lubricating oil or blend of lubricating oils the
following:
(b)(1) the viscosity modifier additive or blend of viscosity modifier
additives (ii),
(b)(2) the polyalphaolefin compound(s) (iii) in a total amount not exceeding 4
percent
by weight of the transmission fluid composition, and
(b)(3) one or more detergent additives (iv);
to provide the transmission fluid composition.
In particular, the process of the present invention is employed to manufacture
an
automotive transmission fluid, wherein the additions in step b) improve the
efficiency of power
transmission provided by the resulting composition when used in the vehicle,
as demonstrated
by an increase in the fuel efficiency of the vehicle during operation.
In a third aspect, the present invention provides a method of improving the
energy
efficiency of an automotive transmission, comprising the use therein of the
transmission fluid
composition defined in the first aspect or of the transmission fluid
composition obtained by the
process of the second aspect. In this aspect of the invention, the
transmission is a transmission
for an automotive vehicle, and the improvement in energy efficiency is
preferably an increase
in fuel economy of the vehicle during operation.
In a fourth aspect, the invention provides an additive concentrate for an
automotive
transmission fluid, the concentrate consisting of a suitable carrier liquid,
and (ii) a viscosity
modifier or blend of viscosity modifiers, (iii) a polyalphaolefin compound or
mixture of
polyalphaolefin compounds made by the metallocene-catalysed polymerisation of
an
alphaolefin feedstock, and (iv) one or more detergent additives, all as
defined in relation to the
first aspect. Preferably at least one of the detergent aditives comprises one
or more alkaline
earth metal detergent compounds wherein at least one alkaline earth metal
detergent compound
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is an alkaline earth metal salicylate or sulphonate compound. Alternatively,
or in addition, the
total amount of polyalphaolefin compound(s) (iii) present in the concentrate
is preferably such
that, after addition of the concentrate at its specified treat rate to the
transmission fluid, said
compounds (iii) constitute no more than 4 percent by weight of the resulting
transmission fluid
composition.
The present invention is hereinafter described in more detail.
The transmission fluid composition consists of four essential elements (i),
(ii), (iii) and
(iv). The components are:
(i) a lubricating oil, or blend of lubricating oils;
(ii) a viscosity modifier additive or blend of viscosity modifier additives
as
hereinafter described;
(iii) a polyalphaolefin compound or compounds made by the metallocene-
catalysed polymerisation of an alphaolefin feedstock; and
(iv) one or more detergent additives.
It is essential that the total amount of the polyalphaolefin compound(s) (iii)
in the
transmission fluid composition does not exceed 4 percent by weight of the
composition,
regardless of the means of incorporation. Thus, in principle, it is possible
in the practice of this
invention that some, or all, of the small amount of polyalphaolefin(s) (iii)
in the composition of
the first aspect may be introduced to the composition via incorporation in the
lubricating oil or
oil blend (i). However, it is preferred that the lubricating oil or oil blend
component (i) per se
contains no such polyalphaolefins (iii), and that these essential compounds
(iii) are instead
incorporated into the composition by direct addition as a discrete additive in
the process of
manufacture of the composition, or are mixed with the viscosity modifier
additive or blend of
viscosity modifier additives (ii) to form a single additive concentrate prior
to their addition to
the lubricating oil or blend of oils. Alternatively, the polyalphaolefin
compound(s) (iii) may be
mixed with one or more of the detergent additive (iv) to form a single
additive concentrate prior
to addition to the lubricating oil or blend of oils.
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The most additive benefit from such polyalphaolefins (iii) when used in
accordance with
the invention is seen at a treat rate of below 4 percent by weight of the
total transmission fluid
composition, more preferably between 1 and 3 percent by weight, and optimally
between 2 and
3 percent by weight of the total transmission fluid composition.
The lubricating oil or oil blend (i) constitutes the bulk of the fluid
composition. Oils
useful in this invention as the lubricating oil, or for constituting the oil
blend, 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 mm2/s (cSt) at 100 C depending on the specification or quality of
transmission
fluid sought, although typical applications will require each oil to have a
viscosity ranging from
about 2 to about 8 mm2/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, dichlordiethyl 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 mm2/s
(cSt) to
10.0 mm2/s (cSt) at 100 C. The preferred mineral oils have kinematic
viscosities of from 2 to
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8 mm2/s (cSt), and most preferred are those mineral oils with viscosities of 3
to 6 mm2/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-octencs), 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 Group IV basestocks,
i.e.
polyalphaolefins (PAO), including hydrogenated oligomers of an alpha-olefin,
particularly
oligomers of 1-decene, especially those produced by free radical processes,
Ziegler catalysis,
or cationic, Friedel-Crafts catalysis.
The polyalphaolefins typically have viscosities in the range of 2 to 20 cSt at
100 C,
preferably 4 to 8 cSt at 100 C. They may, for example, be oligomers of
branched or straight
chain alpha-olefins having from 2 to 16 carbon atoms, specific examples being
polypropenes,
polyisobutenes, poly-l-butenes, poly- 1 -hexenes, poly-l-octenes and poly-l-
decene. Included
are homopolymers, interpolymers and mixtures.
As explained earlier however, in the context of the present invention, should
the
lubricating oil or lubricating oil blend (i) be additionally constituted from
any polyalphaolefin
(iii), i.e. mPAO made by the metallocene-catalysed polymerisation of an
alphaolefin feedstock,
it is important that such polyalphaolefins (iii) do not collectively
contribute more than 4% by
weight of the total transmission fluid composition.
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Preferably, any and all polyalphaolefin(s) constituting the lubricating oil or
lubricating
oil blend (i) are not made by the metallocene-catalysed polymerisation of an
alphaolefin
feedstock.
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 - 1500); and mono- and poly-
carboxylic esters thereof
(e.g., the acetic acid esters, mixed C3-C8 fatty acid esters, and C12 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
adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate,
diisooctyl azelate,
diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate,
the 2-ethylhexyl
diester of linoleic acid dimer, and the complex ester formed by reacting one
mole of sebasic
acid with two moles of tetraethylene glycol and two moles of 2-ethyl-hexanoic
acid, and the
like. A preferred type of oil from this class of synthetic oils is adipates of
C4 to C12 alcohols.
Esters useful as synthetic lubricating oils also include those made from C5 to
C12
monocarboxylic acids and polyols and polyol ethers such as neopentyl glycol,
trimethylolpropane pentaerythritol, dipentaerythritol, tripentaerythritol, and
the like.
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The lubricating oils may be derived from refined, rerefined oils, or mixtures
thereof.
Unrefined oils are obtained directly from a natural source or synthetic source
(e.g., coal, shale,
or tar sands bitumen) without further purification or treatment. Examples of
unrefined oils
include a shale oil obtained directly from a retorting operation, a petroleum
oil obtained directly
from distillation, or an ester oil obtained directly from an esterification
process, each of which
is then used without further treatment. Refined oils are similar to the
unrefined oils except that
refined oils have been treated in one or more purification steps to improve
one or more
properties. Suitable purification techniques include distillation,
hydrotreating, dewaxing,
solvent extraction, acid or base extraction, filtration, and percolation, all
of which are known to
those skilled in the art. Rerefined oils are obtained by treating used oils in
processes similar to
those used to obtain the refined oils. These rerefined oils are also known as
reclaimed or
reprocessed oils and are often additionally processed by techniques for
removal of spent
additives and oil breakdown products.
Another class of suitable lubricating oils are those basestocks produced from
oligomerization of natural gas feed stocks or isomerization of waxes. These
basestocks can be
referred to in any number of ways but commonly they are known as Gas-to-Liquid
(GTL) or
Fischer-Tropsch base stocks.
The lubricating oil (i) may be a blend of one or more of the above described
oils, and a
blend of natural and synthetic lubricating oils (i.e., partially synthetic) is
expressly
contemplated under this invention.
The viscosity modifier or blend of viscosity modifiers (ii) may be a single
compound or
a blend of compounds capable of modifying the viscosity of lubricating oil
when added thereto,
so as to make its viscosity profile more advantageous for lubricant function.
Typically,
lubricating oils experience a range of operating temperatures within the
device being lubricated
and, as viscosity is a temperature-dependent characteristic, must therefore
maintain an
appropriate viscosity throughout the range of operating temperatures, such
that the oil neither
becomes too viscous (`thick') at lower temperatures to cause viscous drag in
the device, nor too
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thin to provide adequate lubrication at higher temperatures. Viscosity
modifiers typically have
the property of increasing the viscosity of the oil at higher temperatures, so
offsetting the natural
thinning of the lubricant base-stock, whilst having lesser (or no) thickening
effect at lower
temperatures, so as to not contribute substantially to viscous drag. In
addition, preferred
viscosity modifiers show a greater resistance to loss of activity over time,
when exposed to the
shear forces and other degrading effects that an automotive lubricant
experiences during the
rigours of operation.
In the practice of this invention, certain defined classes of viscosity
modifier are used
in combination with components (i), (iii) and (iv) to provide transmission
fluid compositions
with the advantages of the present invention.
Thus, the viscosity modifier or blend of viscosity modifiers (ii) is a polymer
or blend of
polymers derived from one or more olefin or unsaturated ester monomers; and
more preferably
a polymer or blend of polymers derived from one or more olefin monomers, or
from one or
more a,I3-unsaturated ester monomers such as alkyl acrylates and alkyl
methacrylates, or from
one or more olefins and one or more ad3-unsaturated ester monomers such as
alkyl acrylates
and alkyl methacrylates.
Most preferably, the viscosity modifier or blend of viscosity modifiers (ii)
is a polymer
or blend of polymers selected from one or more of the following groups:
(ii)(a) random or block poly-alkylacrylates or poly-alkylmethacrylates, or
copolymers
thereof;
(ii)(b) star polymers comprising a polyvalent core of polyalkylacrylate or
polyalkylmethacrylate from which a plurality or arms depend, the arms being
polymer chains
containing alkylacrylate or alkylmethacrylate monomer units; or
(ii)(c) comb polymers prepared by the copolymerisation of one or more
alkylacrylate
or alkylmethacrylate monomers with one or more olefin or polyolefin monomers.
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Materials in group (ii)(a) arc prepared by the polymerisation of one or more
alkylacrylate or alkylmethacrylate monomers, wherein the alkyl groups
preferably contain from
1 to 20, more preferably 1 to 10 carbon atoms, using techniques known in the
art, such as radical
polymerisation. Such materials are known in the art and are commercially
available, an example
being VISCOPLEX 12-075 supplied by Evonik Rohmax USA, Inc.
Materials in the group (ii)(b) are prepared by the stepwise polymerisation of
a core
portion from one or more alkylacrylate or alkylmethacrylate monomers, wherein
the alkyl
groups preferably contain from 1 to 30, more preferably 1 to 20 carbon atoms,
followed by
further polymerisation with such monomers to form the pendant arms. Suitable
processes
include atom transfer radical polymerisation (ATRP) and reversible addition-
fragmentation
chain transfer (RAFT) polymerisation. Alternatively the arms can be separately
formed and
attached to the core via reaction at the linking groups. Such materials are
known in the art.
Materials in the group (ii)(c) are most conveniently prepared by radical
polymerisation.
The term "comb" is known in the polymer art, and refers to the comb-like
architecture of the
polymer which possesses a series of side-chains depending from the main
backbone chain, these
side-chains being formed either from the alkyl substituents of the alkyl
acrylate or methacrylate
monomer units, or from the residues of the olefin monomers, or both.
Preferably, where the comb polymer (ii)(c) is prepared from one or more
alkylacrylate
or alkylmethacrylate monomers, it is formed by the polymerisation of one or
more alkylacrylate
or alkylmethacrylate monomers wherein the alkyl chains contain between 4 and
20, such as 8
to 18, carbon atoms, preferably by radical polymerisation.
Preferably, where the comb polymer (ii)(c) is prepared from one or more olefin
or
polyolefin monomers, it is formed by the polymerisation of one or more olefin
monomers
containing between 4 and 20, such as 4 to 12, carbon atoms. Alternatively, it
may be prepared
from one or more polyolefin macromonomers providing alkyl or alkenyl groups of
considerable
size, which form the side-chains of the resulting comb polymer structure.
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More preferably, the comb polymer (ii)(c) is prepared by the copolymerisation
of one
or more alkylacrylate or alkylmethacrylate monomers with one or more olefin or
polyolefin
monomers. In such polymers, the backbone is formed by the co-polymerising
(meth)acrylate
and olefin or polyolefin monomer units, with the alkyl ester groups of the
(meth)acrylate units
and the residues of the olefin or polyolefin depending from the resulting
backbone to form the
comb structure. In such structures, the alkyl groups of the alkylacrylate or
alkylmethacrylate
monomers preferably contain between 4 and 20, such as 8 to 18, carbon atoms;
whilst the co-
monomer is preferably an olefin or polyolefin providing a longer dependant
chain to the
resulting copolymer, such as a long chain alpha-olefin or a polyolefin
macromonomer such as
poly(isobutylene) or hydrogenated poly(butadiene). When present in the
lubricating oil, such
polymers are capable of significant expansion when energy is applied (such as
occurs when the
oil heats up during operation), and this thermal expansion behaviour enables
them to entrain
more of the bulk oil within a fluid network of expanded comb structures, and
so oppose the
thinning in oil viscosity that otherwise typically occurs with increasing
temperature. . Such
materials are described, for example, in the SAE paper entitled "A New
Generation of High
Performance Viscosity Modifiers Based on Comb Polymers" by Stoehr, Eisenberg
and Mueller,
published in SAE Int. J. Fuels Lubr., Volume I, Issue 1, 1511 and numbered as
2008-0102462
and in US-A-2010/0190671 which describes their nature and preparation.
Whilst polymer(s) from the above groups (ii)(a), (ii)(b) and (ii)(c) are all
favoured for
the practice of this invention, differentiation in the magnitude of that
effect is seen between the
three classes, whilst maintaining the overall viscometrics of the oils as
equal as practically
possible, to confirm that such differential effects are not accounted for by
the conventional
approach of variation in bulk oil viscosity. Thus, polymers from the class
(ii)(c) were most
effective in combination with the other essential elements (i), (iii) and (iv)
for increasing fuel
economy, and are most preferred for the practice of this invention. Class
(ii)(a) is least preferred.
The polyalphaolefin compound or compounds (iii) are those by the metallocene-
catalysed polymerisation of an alphaolefin feedstock. Such "mPAO" materials
are known in
the art per se and are described, for example, in US-A-2007/145924 along with
their method of
CA 2859438 2019-07-29
16
manufacture via metallocene catalysis. In this reference they are described as
a lubricant base-
stock component and used primarily to make high viscosity basestock blends.
They are for
example available to the skilled person as items of commerce under the name
"Spectrosyn
EliteTM from ExxonMobil Chemical Company and its regional sales affiliates,
under the
description of "Advanced synthetic basestock". The performance advantages of
Spectrosyn
Elite' as a lubricant basestock are described in that reference as shear
stability, viscosity index
for high and low temperature performance, and increased flow in cold
environments. The
reference also explains that the use of metallocene catalysis in the
manufacture of the mPAO
results in a particular molecular structure in the polymer product.
In the present invention, the polyalphaolefin compound(s) (iii) are used in
additive
quantities in the transmission fluid composition in combination with a
viscosity modifier
additive or blend of viscosity modifier additives (ii) and specific detergent
additives(s) (iv) to
improve the energy efficiency of a transmission utilising said fluid.
Metallocene-made
polyalphaolefins (iii) having characteristics particularly suitable for the
practice of this
invention can be produced from a feedstock containing one or more, preferably
two or more,
linear C6 to CI8 alphaolefins. Preferred polyalphaolefins (iii) are those made
from a feedstock
mixture of C6 and C18 linear alphaolefins or a mixture of C6 and C12
alphaolefins. The
feedstock is typically contacted with an activated metallocene catalyst under
polymerisation
conditions known in the art, to give the compounds (iii).
In the preferred embodiment of the invention, and the examples which follow
hereafter,
the invention employs Spectrosyn EliteTM 150 as the polyalphaolefin (iii).
This material is
available as an item of commerce through the above source according to a
published
specification, and has a typical kinematic viscosity at 100 C of 156 mm2/s as
measured by
ASTM D445, and a typical viscosity index of 206 as measured by ASTM D2270,
together with
a pour point of minus 33 C as measured by ASTM D5950/D97.
=
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In addition to the essential metallocene-derived polyalphaolefin (iii) in the
requisite
amount, the compositions of the invention may, via additive (iv), additionally
contain other
non-essential polyalphaolefins.
The present invention concerns automotive transmission fluid compositions
having
improved power transmission properties, in particular those which demonstrably
increase the
fuel efficiency of the vehicle during operation. Thus, the transmission fluid
composition of the
invention is an automotive transmission fluid, such as an automatic
transmission fluid
(hereinafter referred to as "ATF"), continuously variable transmission fluid
("CVTFs"), or
double clutch transmission fluid ("DCTFs").
Such fluids are formulated with a detergent additive (iv) to meet the various
performance requirements and/or specifications of a given application,
especially automotive
application. Within this specification, the term "detergent additive" is used
to denote an additive
comprising one or more detergent compounds, and optionally other compounds
('components')
which function as performance-enhancing additives for transmission fluids. In
the art, such
detergent additives are sometimes generally known as detergent packages or
detergent-inhibitor
packages, and may contain a variety of other components and a mutually-
compatible solvent or
dispersion medium.
These other components include dispersants, antiwear agents, friction
modifiers,
corrosion inhibitors, extreme pressure additives, and the like. They are
typically disclosed in,
for example, "Lubricant Additives" by C. V. Smallheer and R. Kennedy Smith,
1967, pp. 1-11
and U.S. Patent 4,105,571.
Representative amounts of typical components of additive (iv) in an automotive
transmission fluid are summarized as follows:
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Additive (Broad) Wt.% (Preferred) Wt.%
Dispersants 0.10 - 10 2 - 5
Antiwear Agents 0.005 - 5 0.5 - 3
Friction modifiers 0.05 - 5 0.5 ¨3.0
Corrosion Inhibitor 0.01 - 3 0.02 - 1
Antifoaming Agents 0.001 - 5 0.001 - 0.5
Pour Point Depressants 0.01 - 2 0.01 -1.5
Seal Swellants 0.1- 8 0.5 - 5
Diluent Balance Balance
It is preferred that at least one additive (iv) comprises one or more alkaline
earth metal
detergent compounds wherein at least one alkaline earth metal detergent
compound is an
alkaline earth metal salicylate or sulphonate compound, leading to further
improvement of the
energy efficiency of the resulting fluid, as hereinbefore described.
The preferred detergents that are generally employed in the invention are
exemplified
by oil-soluble neutral or overbased salts of alkaline earth metals with one or
more hydrocarbyl-
substituted sulfonic acids or salicylic acids. The preferred salts of such
acids from the cost-
effectiveness, toxicological, and environmental standpoints are the salts of
calcium and
magnesium. The more preferred salts useful with this invention are either
neutral or overbased
salicylate salts of calcium or magnesium.
Oil-soluble neutral metal-containing detergents are those detergents that
contain
stoichiometrically equivalent amounts of metal in relation to the amount of
acidic moieties
present in the detergent. Thus, in general the neutral detergents will have a
low basicity when
compared to their overbased counterparts.
The term "overbased" in connection with metallic detergents is used to
designate metal
salts wherein the metal is present in stoichiometrically larger amounts than
the organic radical.
The commonly employed methods for preparing the over-based salts involve
heating a mineral
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oil solution of an acid with a stoichiometric excess of a metal neutralizing
agent such as the
metal oxide, hydroxide, carbonate, bicarbonate, of sulfide at a temperature of
about 50 C, and
filtering the resultant product. The use of a "promoter" in the neutralization
step to aid the
incorporation of a large excess of metal likewise is known. Examples of
compounds useful as
the promoter include phenolic substances such as phenol, naphthol, alkyl
phenol, thiophenol,
sulfurized alkylphenol, and condensation products of formaldehyde with a
phenolic substance;
alcohols such as methanol, 2-propanol, octanol, CellosolveTM alcohol,
CarbitolTM alcohol,
ethylene glycol, stearyl alcohol, and cyclohexyl alcohol; and amines such as
aniline, phenylene
diamine, phenothiazine, phenyl-beta-naphthylamine, and dodecylamine. A
particularly
effective method for preparing the basic salts comprises mixing an acid with
an excess of a
basic alkaline earth metal neutralizing agent and at least one alcohol
promoter, and carbonating
the mixture at an elevated temperature such as 60 to 200 C.
Examples of suitable metal-containing detergents are neutral and overbased
salts of
calcium sulfonates and magnesium sulfonates wherein each sulfonic acid moiety
is attached to
an aromatic nucleus which in turn usually contains one or more aliphatic
substituents to impart
hydrocarbon solubility, and calcium salicylates and magnesium salicylates
wherein the
aromatic moiety is usually substituted by one or more aliphatic substituents
to impart
hydrocarbon solubility. Mixtures of neutral or over-based salts of two or more
different alkaline
earth metals can be used. Likewise, neutral and/or overbased salts of mixtures
of two or more
different acids (e.g. one or more overbased calcium salicylates with one or
more overbased
calcium sulfonates) can also be used.
As is well known, overbased metal detergents are generally regarded as
containing
overbasing quantities of inorganic bases, probably in the form of micro
dispersions or colloidal
suspensions. Thus the term "oil soluble" as applied to metallic detergents is
intended to include
metal detergents wherein inorganic bases are present that are not necessarily
completely or truly
oil-soluble in the strict sense of the term, inasmuch as such detergents when
mixed into base
oils behave much the same way as if they were fully and totally dissolved in
the oil.
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Methods for the production of these oil-soluble neutral and overbased alkaline
earth
metal-containing detergents are well known to those skilled in the art, and
extensively reported
in the patent literature.
The metallic detergents utilized in this invention can, if desired, be oil-
soluble boronated
neutral and/or overbased alkali of alkaline earth metal-containing detergents.
Methods for
preparing boronated metallic detergents are described in, for example, U.S.
Pat. Nos. 3,480,548;
3,679,584; 3,829,381; 3,909,691; 4,965,003; 4,965,004.
Most preferred metallic detergents for use with this invention are calcium
sulfonates
and/or magnesium sulfonates, and calcium and/or magnesium salicylates.
Preferably at least
one such alkaline earth metal detergent compound is a calcium salicylate or
calcium sulphonate
compound. Preferably, the total amount of the alkaline earth metal detergent
compound(s)
present in the transmission fluid composition is such as to provide the
transmission fluid
composition with a an alkaline earth metal content of between 50 and 250 parts
per million by
weight, per weight of the transmission fluid composition.
More preferably, each alkaline earth metal detergent compound present in the
transmission fluid composition is a neutral or overbased calcium salicylate
compound.
Salicylate compounds have been found to be particularly advantageous in
combination with the
additives (ii) and (iii) described herein and contribute to the fuel
efficiency advantage of the
present invention.
Most preferably each alkaline earth metal detergent compound present in the
transmission fluid composition is a neutral or overbased calcium salicylate
compound, and
wherein the total amount of the calcium salicylate compound(s) present is such
as to provide
the transmission fluid composition with a calcium content of between 50 and
250 parts per
million by weight, per weight of the transmission fluid composition, this
amount having been
found to provide optimal efficiency gains.
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Dispersants, specifically those characterised as ashless dispersants, are also
useful in
this invention as components of additive (iv). Suitable dispersants include
long chain (i.e.
greater than forty carbon atoms) substituted hydrocarbyl succinimides and
hydrocarbyl
succinamides, mixed ester/amides of long chain (i.e. greater than forty carbon
atoms)
hydrocarbyl-substituted succinic acid, hydroxyesters of such hydrocarbyl-
substituted succinic
acid, and Mannich condensation products of long chain (i.e. greater than forty
carbon atoms)
hydrocarbyl-substituted phenols, formaldehyde and polyamines. Mixtures of such
dispersants
can also be used.
The preferred dispersants are the long chain alkenyl succinimides. These
include
acyclic hydrocarbyl substituted succinimides formed with various amines or
amine derivatives
such as are widely disclosed in the patent literature. Use of alkenyl
succinimides which have
been treated with an inorganic acid of phosphorus (or an anhydride thereof)
and a boronating
agent are also suitable for use in the compositions of this invention as they
are much more
compatible with elastomeric seals made from such substances as fluoro-
elastomers and silicon-
containing elastomers. Polyisobutenyl succinimides formed from polyisobutenyl
succinic
anhydride and an alkylene polyamine such as triethylene tetramine or
tetraethylene pentamine
wherein the polyisobutenyl substituent is derived from polyisobutene having a
number average
molecular weight in the range of 500 to 5000 (preferably 800 to 2500) are
particularly suitable.
Dispersants may be post-treated with many reagents known to those skilled in
the art. (see, e.g.,
U.S. Pat. Nos. 3,254,025, 3,502,677 and 4,857,214).
Anti-wear additives useful in this invention as components in additive (iv)
are typically
oil-soluble phosphorus-containing compounds that, in the context of this
invention, may vary
widely and are not limited by chemical type. The only limitation is that the
material be oil
soluble so as to permit the dispersion and transport of phosphorus-containing
compound within
the lubricating oil system to its site of action. Examples of suitable
phosphorus compounds are:
phosphites and thiophosphites (mono-alkyl, di-alkyl, tri-alkyl and partially
hydrolyzed analogs
thereof); phosphates and thiophosphates; amines treated with inorganic
phosphorus such as
phosphorous acid, phosphoric acid or their thio analogs; zinc
dithiodiphosphates; amine
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phosphates. Examples of particularly suitable phosphorus compounds include:
mono-n-butyl-
hydrogen-acid-phosphite; di-n-butyl-hydrogen phosphite; triphenyl phosphite;
triphenyl
thiophosphite; tri-n-butylphosphate; dimethyl octadecenyl phosphonate, 900MW
polyisobutenyl succinic anhydride (PIBSA) polyamine dispersant post treated
with H3P03 and
H3B03 (see e.g., U.S. 4,857,214); zinc (di-2-ethylhexyldithiophosphate).
The preferred oil soluble phosphorus compounds are the esters of phosphoric
and
phosphorous acid. These materials would include the di-alkyl, tri-alkyl and
tri-aryl phosphites
and phosphates. A preferred oil soluble phosphorus compound is the mixed
thioalkyl phosphite
esters, for example as produced in U.S. 5,314,633.
The phosphorus compounds of the invention can be used in the oil in any
effective
amount. However, a typical effective concentration of such compounds would be
that
delivering from about 5 to about 5000 ppm phosphorus into the oil. A preferred
concentration
range is from about 10 to about 1000 ppm of phosphorus in the finished oil and
the most
preferred concentration range is from about 50 to about 500 ppm.
Preferred friction modifiers useful as components in additive (iv) comprise a
reaction
product of an isomerized alkenyl substituted succinic anhydride and a
polyamine characterized
by structure (1), where structure (I) is:
CH3 CH3
(CH2)x (CH2)x
0 0
HC CH (I)
CH N -(CH2CH2N-)- CH2CH2N CI I
II H zII
CH3 - (CI-19)y -CH
0 0 HC- (CH2)y -CH3
where x and y are independent integers whose sum is from 1 to 30, and z is an
integer from 1
to 10.
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The starting components for forming the structure (I) compounds are isomerized
alkenyl
succinic anhydrides which are prepared from maleic anhydride and internal
olefins i.e., olefins
which are not terminally unsaturated and therefore do not contain the
H2 C=C )-
1
moiety. These internal olefins can be introduced into the reaction mixture as
such, or they can
be produced in situ by exposing alpha-olefins to isomerization catalysts at
high temperatures.
A process for producing such materials is described in U.S. 3,382,172. The
isomerized alkenyl
substituted succinic anhydrides have the structure shown as structure (II),
where structure (II)
is represented by:
CH3
(CH2)x
0
0 CH (II), where x and y are independent integer:
HA
whose sum is from 1 to 30.
C/ 0
(CH2)y
CH3
The preferred succinic anhydrides are produced from isomerization of linear
alpha-
olefins with an acidic catalyst followed by reaction with maleic anhydride.
The preferred alpha-
olefins are 1-octene, 1-decene, 1-dodecene, 1- tetradecene, 1-hexadecene, 1-
octadecene, 1-
eicosane, or mixtures of these materials. The products described can also be
produced from
internal olefins of the same carbon numbers, 8 to 20. The preferred materials
for this invention
are those made from 1-tetradecene (x + y = 9), 1-hexadecene (x + y = 11) and 1-
octadecene (x
+ y = 13), or mixtures thereof.
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24
The isomerized alkenyl succinic anhydrides are then further reacted with
polyamines of
structure (III), where structure (III) is represented by:
H2N CH2CH2N __________________ CH2CH2NH2 (III),
H z
where z is an integer from 1 to 10, preferably from 1 to 3.
These are common polyethylene amines. When z = 1 the material is diethylene
triamine,
when z = 2 the material is triethylene tetramine, when z = 3 the material is
tetraethylene
pentamine, for products where z> 3 the products are commonly referred to as
'polyamine or
PAM. The preferred products of this invention employ diethylene triamine,
triethylene
tetramine, tetraethylene pentamine or mixtures thereof.
The isomerized alkenyl succinic anhydrides (II) are typically reacted with the
amines in
a 2:1 molar ratio so that both primary amines are converted to succinimides.
Sometimes a slight
excess of isomerized alkenyl succinic anhydride (II) is used to insure that
all primary amines
have reacted. The products of the reaction are shown as structure (I).
The di-succinimides of structure (I) may be further post-treated by any number
of
techniques known in the art. These techniques would include, but not be
limited to: boration,
maleation, acid treating with inorganic acids such as phosphoric, phosphorous,
and sulfuric.
Descriptions of these processes can be found in, for example, U.S. 3,254,025;
U.S. 3,502,677;
U.S. 4,686,054; and U.S. 4,857,214.
Other useful derivatives of these preferred friction modifiers are where the
isomerized
alkenyl groups of structures (I) and (II) have been hydrogenated to form their
saturated alkyl
analogs. These saturated versions of structures (I) and (II) may likewise be
post-treated as
previously described.
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25
While any effective amount of the compounds of structure (I) and its
derivatives may
be used in additive (iv) of this invention, typically these effective amounts
will range from 0.5
to 10, preferably from 2 to 7, most preferably from 3 to 6 weight percent of
the finished fluid.
The various chosen components of additive (iv) of this invention may be
combined in
the form of a concentrate. Typically the active ingredient (a.i.) level of the
concentrate will
range from 20 to 90%, preferably from 25 to 80%, most preferably from 35 to 75
weight percent
of the concentrate. The balance of the concentrate is a diluent typically
comprised of a diluent
or solvent.
The process of the present invention provides for the manufacture of an
automotive
transmission fluid composition, the composition consisting of:
(v) a lubricating oil, or blend of lubricating oils;
(vi) a viscosity modifier additive or blend of viscosity modifier additives
as defined above
in relation to the first aspect of the invention;
(vii) a polyalphaolefin compound or compounds, each made by the metallocene-
catalysed
polymerisation of an alphaolefin feedstock; and
(viii) one or more detergent additives;
the process comprising the following steps:
a) obtaining (by manufacture or otherwise) a lubricating oil or blend of
lubricating oils
containing no polyalphaolefin compound(s) made by the metallocene-catalysed
polymerisation
of an alphaolefin feedstock; and
b) mixing with this lubricating oil or blend of lubricating oils the
following:
(b)(1) the viscosity modifier additive or blend of viscosity modifier
additives (ii),
(b)(2) the polyalphaolefin compound(s) (iii) in a total amount not exceeding 4
percent
by weight of the transmission fluid composition, and
(b)(3) one or more detergent additives (iv);
to provide the transmission fluid composition.
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Preferably, the additions in step b) improve the efficiency of power
transmission
provided by the composition in use, as demonstrated by an increase in the fuel
efficiency of the
vehicle during operation.
In the process, the polyalphaolefin compound(s) (iii) are preferably mixed
with one or
more of the detergent additives (iv) to form a single additive concentrate
prior to addition to the
lubricating oil or blend of oils.
Preferably, in the process, the total amount of the polyalphaolefin compound
or
compounds (iii) mixed with the lubricating oil or blend of lubricating oils is
in the range of 2
to 3 percent by weight of the transmission fluid composition.
Also preferably in the process, at least one of the detergent additives (iv)
comprises one
or more alkaline earth metal detergent compounds wherein at least one alkaline
earth metal
detergent compound is an alkaline earth metal salicylate or sulphonate
compound. More
preferably, each alkaline earth metal detergent compound mixed with the
transmission fluid
composition is a neutral or overbased calcium salicylate compound. Most
preferably, when
each alkaline earth metal detergent compound mixed with the transmission fluid
composition
is a neutral or overbascd calcium salicylate compound, the total amount of
calcium salicylate
compound(s) mixed with the lubricating oil or blend of lubricating is such as
to provide the
transmission fluid composition with a calcium content of between 50 and 250
parts per million
by weight, per weight of the transmission fluid composition.
The invention further provides a method of improving the energy efficiency of
an
automotive transmission, comprising the use therein of the transmission fluid
composition
defined in the first aspect, or of the transmission fluid composition obtained
by the process of
the second aspect.
Preferably, in this method, the improvement in energy efficiency is an
increase in fuel
economy of the vehicle during operation.
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The invention further provides an additive concentrate for an automotive
transmission
fluid, the concentrate consisting of a suitable carrier liquid, and (ii) a
viscosity modifier or blend
of viscosity modifiers, (iii) a polyalphaolefin compound or mixture of
polyalphaolefin
compounds made by the metallocene-catalysed polymerisation of an alphaolefin
feedstock, and
(iv) one or more detergent additives, all as defined above in relation to the
first aspect.
Preferably, the total amount of polyalphaolefin compound(s) (iii) present in
the
concentrate is such that, after addition of the concentrate at its specified
treat rate to the
transmission fluid, said compounds (iii) constitute no more than 4 percent by
weight of the
resulting transmission fluid composition.
Preferably, in the additive concentrate, the total amount of the
polyalphaolefin compound or
compounds (iii) in the composition is in the range of 2 to 3 percent by weight
of the
composition.
Also preferably, in the additive concentrate at least one of the detergent
additives (iv)
comprises one or more alkaline earth metal detergent compounds wherein at
least one alkaline
earth metal detergent compound is an alkaline earth metal salicylate or
sulphonate compound,
which compound is preferably a neutral or overbased calcium salicylate
compound.
In the process, method and concentrate aspects of the invention, the other
preferments
for each of the components (i), (ii), (iii) and (iv) are as stated previously
in relation to the
composition of the first aspect.
Examples:
The following examples are given as specific illustrations of the claimed
invention. It
should be understood, however, that the invention is not limited to the
specific details set forth
in the examples. All parts and percentages are by weight per weight of the
resulting
transmission fluid composition, unless otherwise specified.
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Worked example 1 - benefit of additive treat levels of the polyalphaolefin
(iii)
The essentiality of the defined metallocene-derived polyalphaolefin in the
invention is
demonstrated by back-to-back tests conducted on transmission fluids with and
without this
material present.
Four automotive transmission fluids were prepared according to the process
aspect of
the invention, by blending together the components shown in Table 1. In each
case the
components (i), (ii), (iv) were the same, and the fluids differ chemically
only in the presence or
absence of the polyalphaolefin (iii).
Table 1
Component Composition Composition Composition Composition
(% by weight, per weight of 1 1C 2 2C
finished composition) (comparative) (comparative)
Base lubricating oil 83.7 86.3 83.3 85.1
Viscosity modifier 3.0 3.0 2.0 4.2
Pour point depressant 0.3 0.2 0.2 0.2
mPolyalphaolefin 2.5 4.0
Detergent additive:
- Overbased calcium 0.08 0.08 0.08 0.08
salicylate
- Overbased calcium
sulphonate
- Other components 10.42 10.42 10.42 10.42
KV 40 C 19.84 17.73 19.23 18.69
KV 100 C 4.77 4.37 4.63 4.69
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In these compositions, the base lubricating oil, viscosity modifier, pour
point depressant
and detergent additive were the same in each case, and the blends differed
only in the relative
proportions of these constituents and, in the case of Compositions 1C and 2C,
in the absence of
the mPAO.
The mPolyalphaolefin was Spectrosyn EliteTM 150, an item of commerce from
Exxonmobil Chemical Company. The detergent additive contained overbased
calcium
salicylate and additionally contained other components being dispersant, anti-
wear, and other
minor active components typical of a detergent additive package, combined with
a small
amount of base oil and diluent. These other components of the detergent
additive were the same
in each case. The viscosity modifier was VISCOPLEX 12-199, available as an
item of
commerce from Evonik Rohmax USA, Inc and falling within the class (ii)(c)
described earlier
in relation to suitable viscosity modifiers. The pour point depressant was a
typical commercially
available material and the same in each case.
The performance of these compositions were tested in the following two
experiments.
A bench-test experiment called the "FE-8" test measures the torque required to
rotate a
radial thrust roller bearing assembly lubricated by the transmission fluid in
question. The
efficiency of the formulations was tested by measuring torque to rotate the
cylindrical roller
bearings at various conditions using an FE-8 radial thrust roller bearing
tester. The bearings
used are 15 roller FAG/NA 81212 bearings. The bearings were installed in the
test rig and
then pre-loaded to 60 kN. The bearings are run-in for 20 hours at 500 rpm at
100 C prior to
taking any measurement.
For each test fluid, the test head is heated until the bearing temperature
reaches
40 C. While maintaining this temperature, bearings are rotated at 10 rpm for
10mins then at
100rpm and 500rpm for 5 mins each. The reported torque at each condition is
calculated by
averaging the torque reading during the last 1 minute of the condition.
Temperature is then
increased to 80 C and then finally to 120 C and torque is measured with the
same procedure at
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the three speeds. After this, the rig is cooled down to room temperature and
the whole process
is repeated. Final test results are the average of two repeats at each
temperature and speed.
The FE-8 test thus compares the energy requirements needed to achieve defined
bearing
rotation with different fluids. Achieving the defined rotations with lower
applied torque
indicates greater energy efficiency within the mechanical system.
A vehicle test experiment was conducted according to the standard US Federal
Test
Procedure 75 ("FTP 75"). A commercially-available SUV with six speed automatic
transmission was repeatedly run on a vehicle dynamometer according to the
operating cycle
specified in FTP 75, and in each case the improvement in fuel economy observed
for the
transmission fluid employed in the test is reported (as % improvement) over a
reference fluid.
The FTP 75 provides a direct measure of fuel economy observed in vehicle
operation.
A positive percentage indicates greater fuel efficiency compared to reference.
In an FE-8 test, fluid compositions 1, 1C and 2C were compared for energy
efficiency.
The results are shown in Table 2 below. As can be seen, composition 1
consistently required
lower applied torque to achieve rotations of 100 and 500 rpm in the FE-8 test,
indicating
improved energy efficiency for composition 1 (with polyalphaolefin (iii) at
2.5%) as compared
to compositions 1C (and 2C) (no polyalphaolefin (iii)). In this screener test,
the presence of
polyalphaolefin (iii) shows an overall benefit for energy efficiency.
Table 2
FE-8 Torque, NM Composition 1 Composition 1C
Composition 2C
40 C, 100rpm 26.3 27.0 27.1
40 C, 50Orpm 21.2 21.7 21.9
80 C, 100rpm 30.2 31.2 30.9
80 C, 500rpm 23.3 24.4 24.1
120 C, 100rpm 30.1 30.6 30.9
120 C, 500rpm 23.1 23.9 24.2
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In particular, the compared samples were blended to have similar kinematic
viscosity
behaviour, thus eliminating the possibility of viscosity differences
accounting for the
differences in measured torque. Comparing the results for compositions 1C and
2C further
demonstrates that the small residual differences in the KV values of these
samples do not
account for the differences in torque seen between composition 1 and
composition 1C, which
must therefore be attributable to the effect of polyalphaolefin (iii). For
example, composition
2C had a KV 100 of 4.69, almost identical to that of composition 1 (4.77), yet
at 120 C the
torque results for composition 2C are even higher than those for composition
IC, indicating
that the better results obtained for composition I cannot be explained by
reference to viscosity
behaviour per se.
In FTP 75 vehicle tests, composition 1 (polyalphaolefin (iii) at 2.5%) was
compared to
the test reference fluid (contains no polyalphaolefin (iii)) and to
composition 2
((polyalphaolefin (iii) at the higher treat rate of 4%). The percentage
improvement in fuel
economy over the whole test was 0.86% for composition 1, compared to only
0.42% for
composition 2. Thus the fuel efficiency benefit of polyalphaolefin (iii) in
the composition
showed an optimum at the treat rate of 2.5%, and at a higher treat rate of 4%
the fuel efficiency
benefit had dropped off considerably, confirming the benefit seen is one
attributable to additive-
level proportions of polyalphaolefin (iii).
Worked example 2 ¨ benefit of the specific viscosity modifiers (ii)
The fuel efficiency effect of the defined viscosity modifiers (ii) in the
invention is
demonstrated by further comparative tests.
Two further automotive transmission fluids were prepared according to the
process
aspect of the invention, by blending together the components shown in Table 3.
These fluids
were tested alongside composition 1 from Table 1 in the FTP 75 vehicle test to
compare the
effect of changing viscosity modifier chemistry on fuel efficiency in the
formulations of the
invention.
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The vehicle test experiment was again conducted according to the standard US
Federal
Test Procedure 75 ("FTP 75"), using the same commercially-available SUV with
six speed
automatic transmission on a vehicle dynamometer. In each case the improvement
in fuel
economy observed for the transmission fluid employed in the test is again
reported (as %
improvement) over reference fluid.
Table 3
Component Composition 3 Composition 4
(% by weight, per weight of
finished composition)
Base lubricating oil 83.0 84.7
Viscosity modifier 1
Pour point depressant
Viscosity modifier 2 4.0
Viscosity modifier 3 2.8
mPolyalphaolefin 2.5 2.0
Detergent additive :
- Overbased calcium 0.08 0.08
salicylate
- Other components 10.42 10.42
KV 40 C 20.74 20.47
KV 100 C 4.72 4.76
Viscosity modifier 2 was VISCOPLEX012-075, available as an item of commerce
from
Fvonik Rohmax Additives GmbH and being a solution of polyalkyl methacrylate in
diluent oil,
ie a viscosity modifier of class (ii) (a) as described herein. Viscosity
modifier 3 was
LUBRIZOL 87725, also available as an item of commerce from Lubrizol
Corporation and
being a viscosity modifier of class (ii)(b) as defined herein.
Composition 1 (from Example 1 above, containing Viscosity modifier 1) showed a
fuel
economy improvement over the total FTP 75 test of 0.86%. Composition 3
(Viscosity modifier
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2 ¨ VISCOPLEXO 12-075) showed a lesser improvement of 0.37%, whilst
Composition 4
(Lubrizol 87725) showed an intel mediate fuel economy result of 0.54%.
In each case, the level of viscosity modifier in the composition was chosen
having
regard to maintaining the viscosity behavior of the transmission fluid as
consistent as practically
possible between compositions, so as to exclude conventional bulk viscosity
effects from the
equation and demonstrate the particular advantages of specific viscosity
modifiers in the present
invention.
Worked example 3 ¨ comparison with existing base-stock approach in the art
The ability of the present invention to achieve fuel efficiency improvements
through
additive-level quantities of the specific polyalphaolefin (iii), detergent
additive (iv) and
viscosity modifier (ii) was compared to the prior art PAO basestock approach
described in US-
A-2010/0035778 referred to above.
US-A-2010/0035778 (to GM global technology operations Inc.) exemplifies a
composition comprising 9.4% (by weight, per total weight of fluid) of a first
polyalphaolefin
(PAO 2cSt) and 68.0% of a second polyalphaolefin (PAO 6cSt), together with
proprietary
additives comprising the additive package Hitec 3491 plus viscosity index
improver and ester
to a total of 22.6% by weight of the composition. The reference claims a fuel
economy benefit
for such compositions.
The performance of Composition 1 of the present invention was compared to a
commercially-obtained GM automatic transmission fluid (GM ATF 212-B), having a
reported
PAO composition the same as that of the example from US-A-2010/0035778, and
likewise a
total additive content of 22.6% (Hitec 3941A). The applicant therefore regards
this as
illustrative of the invention exemplified in US-A-2010/0035778.
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The performance of Composition 1 in the FTP 75 test has been noted as 0.86%
fuel
economy improvement over the whole test. In contrast, the GM ATF 212-B sample
gave a
result in the same test of 0.12% improvement in fuel economy over reference
fuel. Thus,
Composition 1 showed substantially better fuel economy than the invention
described in US-
A-2010/0035778.
US-A-2010/0035778 teaches a solution for fuel economy that requires the blend
of two
PAOs of differing viscosities as the basestock for the transmission fluid. As
shown by the above
results, a greater improvement in fuel economy is surprisingly obtained from
the composition
of the present invention.
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