U.S. patent application number 12/974706 was filed with the patent office on 2012-06-21 for lubricating oil with improved wear properties.
This patent application is currently assigned to Chevron U.S.A. Inc.. Invention is credited to James BOOTH, Jim MCGEEHAN, Trevor MILLER, Willem VAN DAM.
Application Number | 20120157359 12/974706 |
Document ID | / |
Family ID | 46235153 |
Filed Date | 2012-06-21 |
United States Patent
Application |
20120157359 |
Kind Code |
A1 |
VAN DAM; Willem ; et
al. |
June 21, 2012 |
LUBRICATING OIL WITH IMPROVED WEAR PROPERTIES
Abstract
Provided is a lubricating oil composition for internal
combustion engines comprising at least one hydrocarbon base stock
which is determined to exhibit a 40.degree. C. PVC/100.degree. C.
PVC ratio approaching one or greater, and one or more lubricating
additives. Also provided is a method for preparing such a
composition, which includes determining the 40.degree. C.
PVC/100.degree. C. PVC ratio of a hydrocarbon base stock oil, and
selecting a hydrocarbon base stock oil which exhibits a 40.degree.
C. PVC/100.degree. C. PVC ratio approaching one. One or more
lubricating additives is then added to the selected base stock
oil.
Inventors: |
VAN DAM; Willem; (Novato,
CA) ; MCGEEHAN; Jim; (San Rafael, CA) ;
MILLER; Trevor; (Dublin, CA) ; BOOTH; James;
(Napa, CA) |
Assignee: |
Chevron U.S.A. Inc.
San Ramon
CA
|
Family ID: |
46235153 |
Appl. No.: |
12/974706 |
Filed: |
December 21, 2010 |
Current U.S.
Class: |
508/110 |
Current CPC
Class: |
C10N 2040/25 20130101;
C10N 2030/06 20130101; C10N 2040/255 20200501; C10M 2205/173
20130101; C10M 2203/1025 20130101; C10M 171/00 20130101; C10N
2040/252 20200501; C10M 171/02 20130101; C10N 2030/02 20130101;
C10N 2070/00 20130101 |
Class at
Publication: |
508/110 |
International
Class: |
C10M 169/04 20060101
C10M169/04 |
Claims
1. A lubricating oil composition for internal combustion engines
comprising: a) at least one hydrocarbon base stock which is
selected once it is determined to exhibit a 40.degree. C.
PVC/100.degree. C. PVC ratio approaching one or greater; and b) one
or more lubricating additives.
2. The composition of claim 1, wherein the at least one hydrocarbon
base stock is blended with a minor amount of a different base
stock.
3. The composition of claim 2, wherein the different base stock is
a Fischer-Tropsch derived base oil.
4. The composition of claim 1, wherein the at least one hydrocarbon
base stock which is selected because it exhibits a 40.degree. C.
PVC/100.degree. C. PVC ratio is a Fischer-Tropsch derived base
oil.
5. The composition of claim 1, wherein the ratio is at least
0.85.
6. The composition of claim 1, wherein the ratio is at least
0.90.
7. The composition of claim 1, wherein the ratio is at least
0.95.
8. The composition of claim 3, wherein the Fischer-Tropsch derived
base oil blended with the hydrocarbon base stock exhibits a
kinematic viscosity at 100.degree. C. of at least 7
mm.sup.2/sec.
9. The composition of claim 3, wherein the Fischer-Tropsch derived
base oil blended with the hydrocarbon base stock exhibits a
kinematic viscosity at 100.degree. C. of at least 10 mm2/sec.
10. The composition of claim 1, wherein the at least one
hydrocarbon base stock exhibits a kinematic viscosity at
100.degree. C. in the range of from 3 to 12 mm.sup.2/sec.
11. The composition of claim 1, wherein the at least one
hydrocarbon base stock exhibits a kinematic viscosity at
100.degree. C. in the range of from 4 to 10 mm.sup.2/sec.
12. The composition of claim 1, wherein the composition contains no
viscosity modifier.
13. The composition of claim 1, wherein the composition contains
one or more detergents.
14. The composition of claim 1, wherein the composition contains
one or more dispersants.
15. The composition of claim 1, wherein the composition contains
one or more anti-oxidants.
16. The lubricating oil composition of claim 1, wherein the
composition further comprises one or more conventional base oils,
and wherein the conventional base oil is a maximum of 30 weight
percent based on the total weight of the lubricating oil
composition.
17. A method for lubricating an internal combustion engine and
reducing the wear comprising lubricating the internal combustion
engine with the lubricating oil composition of claim 1.
18. A method for lubricating an internal combustion engine and
reducing the wear comprising lubricating the internal combustion
engine with the lubricating oil composition of claim 3.
19. A method for preparing the lubricating oil composition of claim
1, comprising: a) determining the 40.degree. C. PVC/100.degree. C.
PVC ratio of a hydrocarbon base stock oil; b) selecting a
hydrocarbon base stock oil once it is determined to have a
40.degree. C. PVC/100.degree. C. PVC ratio approaching one; and c)
adding one or more lubricating additives.
20. The method of claim 19, further comprising blending the
hydrocarbon base stock oil of b) with a Fischer-Tropsch derived
base oil.
21. The method of claim 19, wherein the hydrocarbon base stock oil
is a Fischer-Tropsch derived base oil.
22. The method of claim 19, wherein the hydrocarbon base stock oil
has a ratio of at least 0.85.
23. The method of claim 19, wherein the hydrocarbon base stock oil
has a ratio of at least 0.90.
24. The method of claim 19, wherein the hydrocarbon base stock oil
has a ratio of at least 0.95.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a lubricating oil
composition having improved wear properties, and in particular
valve train wear properties. More particularly, the present
invention employs base stocks exhibiting low temperature
sensitivity of the Pressure-Viscosity-Coefficient (PVC) to obtain
improved wear properties.
BACKGROUND OF THE INVENTION
[0002] Lubricating oils for internal combustion engines contain one
or more additives in addition to at least one base lubricating oil.
Lubricating oils are used to perform the critical function of
lubricating moving parts in the internal combustion engine.
Lubricating oils perform this function by maintaining a
sufficiently high lubricating film thickness on metal surfaces in
order to maintain low friction and reduce wear of the metal parts.
Reduction in friction ultimately results in improved fuel economy
and enhanced mechanical efficiency.
[0003] Reduction in friction can be accomplished by reducing the
viscosity of the lubricating oil. While this approach works well at
higher contact speeds, it may increase wear at lower contact speeds
if a sufficiently thick lubricating oil cannot be maintained.
Conventional lubricating oils rely on friction reducing agents,
such as surface active friction modifiers, for protecting the metal
surfaces at these lower contact speeds.
[0004] Fischer-Tropsch derived base oils have been blended to make
lubricating oils. See, US 2008/0128322; US 2006/0027486; US
2006/0070914; US 2006/0076266; US 2006/0076227; US 2007/0049507; US
2006/0172898; US 2004/0235682; and U.S. Pat. Nos. 7,195,706 and
7,141,157. Some of the blends comprise two or more Fischer-Tropsch
derived base oils. Additives have also been used in the blends to
enhance certain targeted properties. Specifications throughout the
world are continually getting more stringent, making it more
difficult to meet the specification.
[0005] In evaluation, lubricants for internal combustion engines
have to deal with many contradicting requirements. Those
requirements come in the form of limits for performance parameters
measured in engine and bench tests as well as physical and chemical
requirements. Typically included in those lubricant specifications
are engine tests evaluating the lubricant's capability in
protecting the engine's valve train from wear. Wear protection is
traditionally obtained from anti-wear additives, such as ZnDTP and
other surface active materials. Another approach used to obtain
wear protection is to increase the viscosity of the lubricant by
going to higher viscosity grade lubricants, which increases the
separation between the valve train components. The industry is
constantly searching, however, for improved ways to obtain wear
protection for internal combustion engines. Improved wear
protection in a more economic and simple manner would be of great
benefit of the industry.
SUMMARY OF THE INVENTION
[0006] Provided is a lubricating oil composition for internal
combustion engines which provides improved wear protection for
valve train components through the selection of a base stock having
specific temperature sensitivity characteristics. The lubricating
oil composition comprises at least one hydrocarbon base stock which
is selected due to it exhibiting a 40.degree. C. PVC/100.degree. C.
PVC ratio approaching one or greater, and one or more lubricating
additives. Also provided is a method for preparing such a
composition, which includes determining the 40.degree. C.
PVC/100.degree. C. PVC ratio of a hydrocarbon base stock oil, and
selecting a hydrocarbon base stock oil which exhibits a 40.degree.
C. PVC/100.degree. C. PVC ratio approaching one. One or more
lubricating additives is then added to the selected base stock
oil.
[0007] Among other factors, the present lubricating oil composition
and method for preparing same is based on the discovery of a
relationship between temperature sensitivity of the
Pressure-Viscosity-Coefficient (PVC) of a base stock and the wear
properties exhibited by that base stock. Thus, by determining the
temperature sensitivity of the PVC of a base stock and selecting
the correct base stock for a lubricating oil composition, the wear
properties of the lubricating oil composition are improved
immediately. The need for additional additives is reduced and the
need for higher viscosity grade lubricants is avoided. A lower
viscosity oil can be used in the present composition, while still
exhibiting excellent cam wear properties.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0008] The present lubricant composition provides greatly improved
valve train wear control due to the selection of base stocks with
specific temperature sensitivity characteristics. The base stocks
of choice exhibit less temperature sensitivity of the
Pressure-Viscosity-Coefficient (PVC) than conventionally used base
stocks, thus minimizing the reduction of contact film thickness
with increasing temperature, relative to `typical` base oils. Such
base stocks have been found to exhibit higher PVC at the
temperature levels experienced in the valve train's wear contacts
of an internal combustion engine. As a result of this higher PVC,
these base stocks behave more solid-like under extremely high
contact pressures, greater than 0.5 GPa. By measuring the PVC of a
base oil at 40.degree. C. and 100.degree. C., the temperature
sensitivity of the PVC can be determined by the ratio of 40.degree.
C. PVC/100.degree. C. PVC. As this ratio approaches 1.00, the base
stock PVC is less sensitive to the temperature. Base stocks showing
this behavior have been found to provide improved wear protection.
Such base stocks surprisingly cover a broad range of viscosity
indices (VI), indicating that the characteristic of interest is not
necessarily correlated with VI or any of its associated parameters
such as the VII content or the lubricant's VII dosage related shear
behavior.
[0009] The PVC of a base stock can be determined using a
calculation procedure as follows: [0010] Measure the EHL film
thickness of the samples and the reference oil, e.g., Squalane, at
desired temperatures, i.e., 40.degree. C. and 100.degree. C. [0011]
Calculate the PVC values by applying the following equation:
[0011] .alpha.S=.alpha.R[(hS/hR) (.eta.S/.eta.R)-0.67]1/0.53
[0012] The subscripts S and R refer to the samples and the
reference oil, respectively; .alpha. is the PVC value; h the film
thickness, and .eta. the dynamic viscosity.
[0013] The h values are measured on an EHL system, the viscosity
.eta. data can be measured or obtained by a provider of the base
stock. The parameter values .alpha. and .eta. of the reference oil,
Squalane, are available in the literature.
[0014] The EHL film thickness is measured on an EHL Ultra Thin Film
Measurement System, a computer controlled instrument for measuring
the film thickness and traction coefficient (friction coefficient)
of lubricants in the elastohydrodynamic (EHL) lubricating regime.
The instrument can measure lubricant film thickness down to 1 nm
with a precision of +/-1 nm. Traction coefficient can be measured
at any slide/roll ratio from pure rolling up to 100%. The
instrument measures these lubricant properties in the contact
formed between a steel ball and a rotating glass or steel disk. The
contact pressures and shear rates in this contact are similar to
those found in for example, gears, rolling element bearings and
cams.
[0015] Once the PVC ratio is determined, a base stock oil having a
ratio approaching one or greater is selected. The 40.degree. C.
PVC/100.degree. C. PVC ratio is generally at least 0.85, e.g., in
the range of from 0.85 to 1.05. In another embodiment, the ratio is
at least 0.90, e.g., in the range of from 0.09 to 1.05; and the
ratio in another embodiment is at least 0.95, e.g., in the range of
from 0.95 to 1.05. The measurements can be at 20 N or 50N, which
values have not generally been found to change the results of the
determination. Suitable additives can then be added to the selected
base stock oil to obtain the lubricating oil composition.
[0016] The base stock oil can be any suitable base stock oil as
long as it exhibits a 40.degree. C. PVC/100.degree. C. PVC ratio
approaching one, e.g., at least 0.85. The base stock oil can be any
base stock oil, conventional or FTBO, but the use of an FTBO has
been found quite advantageous. The viscosity of the base stock oil
also can vary greatly, as long as the ratio is met, e.g., a
kinematic viscosity at 100.degree. C. of 7 mm.sup.2/sec or higher
can be used. The selected base stock oil can be used alone, or in a
mixture with other base stock oils meeting the PVC ratio
requirement.
[0017] The selected base stock oil or oils can be used alone to
formulate the lubricating oil composition, or can be blended with a
minor amount, i.e., less than 50 wt %, of another base stock oil
not meeting the PVC ratio requirement. The blending component can
comprise any suitable base stock oil, with good results being
achieved with Fischer-Tropsch derived base oils. The mixing
component can have any suitable viscosity as well, e.g., at least 7
mm.sup.2/sec, or at least 10 mm.sup.2/sec. When conventional base
oils are mixed with the selected base stock oil, the amount blended
will generally be a maximum of 30 wt %, or even 10 wt %, based on
the total weight of the lubricating oil composition. Conventional
base oils include any hydrocarbon base stocks, conventional mineral
oil derived base oils as well as synthetic oils, including
synthetic esters.
[0018] The base stock or blend of base stocks used in the
lubricating oil composition will generally have a kinematic
viscosity at 100.degree. C. in the range of from 3 to 12
mm.sup.2/sec, and more likely in the range of from 4 to 10
mm.sup.2/sec. Various additives can be added to adjust the
viscosity if desired.
[0019] In preparing the present lubricating oil composition,
therefore, one first determines the 40.degree. C. PVC/100.degree.
C. PVC ratio of a hydrocarbon base stock. Then a hydrocarbon base
stock is selected which has been determined to have a 40.degree. C.
PVC/100.degree. C. PVC ratio approaching one, e.g., at least 0.85.
This can be mixed with other such base stock oils, or blended with
a minor amount, i.e., less than 50 wt %, of base stock oil,
conventional, FTBO, etc., which does not meet the PVC ratio.
Suitable lubricating additives can be added to prepare the final
lubricating oil composition.
[0020] Fischer-Tropsch derived base oils are well known. In Fischer
Tropsch chemistry, syngas is converted to liquid hydrocarbons by
contact with a Fischer Tropsch catalyst under reactive conditions.
Typically, methane and optionally heavier hydrocarbons (ethane and
heavier) can be sent through a conventional syngas generator to
provide synthesis gas. Generally, synthesis gas contains hydrogen
and carbon monoxide, and may include minor amounts of carbon
dioxide and/or water. The presence of sulfur, nitrogen, halogen,
selenium, phosphorus and arsenic contaminants in the syngas is
undesirable. For this reason and depending on the quality of the
syngas, it is preferred to remove sulfur and other contaminants
from the feed before performing the Fischer-Tropsch chemistry.
Means for removing these contaminants are well known to those of
skill in the art.
[0021] In the Fischer-Tropsch process, contacting a synthesis gas
comprising a mixture of H.sub.2 and CO with a Fischer-Tropsch
catalyst under suitable temperature and pressure reactive
conditions forms liquid and gaseous hydrocarbons. Examples of
conditions for performing Fischer-Tropsch type reactions are well
known to those of skill in the art.
[0022] The fractions of the Fischer-Tropsch synthesis process may
range from C.sub.1 to C.sub.200+ with a majority in the C.sub.5 to
C.sub.100+ range. The reaction can be conducted in a variety of
reactor types, such as fixed bed reactors containing one or more
catalyst beds, slurry reactors, fluidized bed reactors, or a
combination of different type reactors. Such reaction processes and
reactors are well known and documented in the literature.
[0023] The slurry Fischer-Tropsch process, which is preferred in
the practice of the invention, utilizes superior heat (and mass)
transfer characteristics for the strongly exothermic synthesis
reaction and is able to produce relatively high molecular weight,
paraffinic hydrocarbons when using a cobalt catalyst. A
particularly preferred Fischer-Tropsch process is taught in
European Patent Application No. 9400600.7 (Publication No. EP 060
9079 B1).
[0024] In general, Fischer Tropsch catalysts contain a Group VII
transition metal on a metal oxide support. The catalysts may also
contain a noble metal promoter(s) and/or crystalline molecular
sieves. Suitable Fischer-Tropsch catalysts comprise one or more of
Fe, Ni, Co, Ru and Re, with cobalt being preferred. A preferred
Fischer-Tropsch catalyst comprises effective amounts of cobalt and
one or more of Re, Ru, Pt, Fe, Ni, Th, Zr, Hf, U, Mg and La on a
suitable inorganic support material, preferably one which comprises
one or more refractory metal oxides. Useful catalysts and their
preparation are known and illustrated in U.S. Pat. No. 4,568,663,
which is intended to be illustrative but not limiting the selection
of the catalyst.
[0025] A particularly preferred Fischer-Tropsch process is taught
in European Patent Application No. 9400600.7 (Publication No. EP
060 9079 B1). Examples of processes producing waxes of higher
carbon number distribution are taught in PCT International
Application PCT/98EP/08545 (Publication No. WO9934917 A1).
[0026] The fractions from Fischer-Tropsch reactions generally
include a light reaction fraction and a waxy reaction fraction,
which typically contain predominantly paraffins. It is the waxy
reaction fraction (i.e., the wax fraction) that is used as a
feedstock to the process for providing the Fischer-Tropsch derived
lubricating base oil used in the blended lubricants and blended
finished lubricants of the present invention.
[0027] Isomerized Fischer-Tropsch distillate fractions are prepared
from the waxy fractions of the Fischer-Tropsch syncrude by a
process including hydroisomerization. Preferably, the
Fischer-Tropsch lubricant base oils are made by a process as
described in U.S. Pat. No. 7,083,713, herein incorporated by
reference in its entirety.
[0028] Hydroisomerization is intended to improve the cold flow
properties of the lubricating base oil by the selective addition of
branching into the molecular structure. Hydroisomerization ideally
will achieve high conversion levels of the Fischer-Tropsch wax to
non-waxy iso-paraffins while at the same time minimizing the
conversion by cracking.
[0029] Hydroisomerization catalysts useful in the present invention
comprise a shape selective intermediate pore size molecular sieve
and optionally a catalytically active metal hydrogenation component
on a refractory oxide support. Preferred shape selective
intermediate pore size molecular sieves used for hydroisomerization
are based upon aluminum phosphates, with SAPO-11 being preferred.
SM-3 is a particularly preferred shape selective intermediate pore
size SAPO, which has a crystalline structure falling within that of
the SAPO-11 molecular sieves. The preparation of SM-3 and its
unique characteristics are described in U.S. Pat. Nos. 4,943,424
and 5,158,665. Other shape selective intermediate pore size
molecular sieves used for hydroisomerization are zeolites, and
SSZ-32 and ZSM-23 are preferred.
[0030] A particularly preferred intermediate pore size molecular
sieve, which is useful in the present process, is described in U.S.
Pat. Nos. 5,135,638 and 5,282,958, the contents of which are hereby
incorporated by reference in their entirety.
[0031] Hydroisomerization catalysts useful in the present invention
comprise a catalytically active hydrogenation metal. The presence
of a catalytically active hydrogenation metal leads to fraction
improvement, especially VI and stability. Typically catalytically
active hydrogenation metals include chromium, molybdenum, nickel,
vanadium, cobalt, tungsten, zinc, platinum, and palladium. The
metals platinum and palladium are especially preferred, with
platinum most especially preferred.
[0032] The refractory oxide support may be selected from those
oxide supports, which are conventionally used for catalysts,
including silica, alumina, silica-alumina, magnesia, titania and
combinations thereof.
[0033] Suitable conditions for performing hydroisomerization are
described in U.S. Pat. Nos. 5,282,958 and 5,135,638, the contents
of which are incorporated by reference in their entirety.
[0034] Hydrogen is present in the reaction zone during the
hydroisomerization process. Hydrogen may be separated from the
fraction and recycled to the reaction zone.
[0035] A waxy feed to the hydroisomerization process may be
hydrotreated prior to hydroisomerization dewaxing. Hydrotreating
refers to a catalytic process, usually carried out in the presence
of free hydrogen, in which the primary purpose is the removal of
various metal contaminants, such as arsenic, aluminum, and cobalt;
heteroatoms, such as sulfur and nitrogen; oxygenates; or aromatics
from the feed stock.
[0036] Catalysts used in carrying out hydrotreating operations are
well known in the art, for example, U.S. Pat. Nos. 4,347,121 and
4,810,357, the contents of which are hereby incorporated by
reference in their entirety. Other suitable catalysts are
described, for example, in U.S. Pat. Nos. 4,157,294 and 3,904,513.
The non-noble hydrogenation metals, such as nickel-molybdenum, are
usually present in the final catalyst composition as oxides.
[0037] Typical hydrotreating conditions vary over a wide range.
[0038] Hydrofinishing is a hydrotreating process that may be used
as a step following hydroisomerization to provide the
Fischer-Tropsch lubricating base oil. Hydrofinishing is intended to
improve oxidation stability. UV stability, and appearance of the
Fischer-Tropsch lubricating base oil fraction by removing traces of
aromatics, olefins, color bodies, and solvents. A general
description of hydrofinishing may be found in U.S. Pat. Nos.
3,852,207 and 4,673,487.
[0039] The conditions for hydrofinishing will be tailored to
achieve an isomerized Fischer-Tropsch derived distillate fraction
comprising weight percent aromatics less than 0.30.
[0040] Suitable hydrofinishing catalysts include noble metals from
Group VIIIA, such as platinum or palladium or an alumina or
siliceous matrix, and unsulfided Group VIIIA and Group VIB, such as
nickel-molybdenum or nickel-tin on an alumina or silica matrix.
U.S. Pat. No. 3,852,207 describes a suitable noble metal catalyst
and mild conditions. Other suitable catalysts are described in U.S.
Pat. Nos. 4,157,294 and 3,904,513.
[0041] Clay treating to remove impurities is an alternative final
process step to provide an isomerized Fischer-Tropsch derived
distillate fraction.
[0042] The separation of Fischer-Tropsch derived fractions and
petroleum derived fractions into various fractions having
characteristic boiling ranges in generally accomplished by either
atmospheric or vacuum distillation or by a combination of
atmospheric and vacuum distillation. Fractionating the lubricating
base oil into different boiling range cuts enables the lubricating
base oil manufacturing plant to produce more than one grade, or
viscosity, or lubricating base oil.
[0043] The process to make an isomerized Fischer-Tropsch derived
distillate fraction may also include a solvent dewaxing step
following the hydroisomerization process. Solvent dewaxing
optionally may be used to remove small amounts of remaining waxy
molecules from the lubricating base oil after hydroisomerization
dewaxing. Solvent dewaxing is done by dissolving the lubricating
base oil in a solvent, such as methyl ethyl ketone, methyl
iso-butyl ketone, or toluene, and precipitating the wax molecules.
Solvent dewaxing is described in U.S. Pat. Nos. 4,477,333,
3,773,650 and 3,775,288 and 7,018,525.
[0044] Conventional synthetic oils include hydrocarbon synthetic
oils and synthetic esters. Useful synthetic hydrocarbon oils
include liquid polymers of alpha-olefins having the proper
viscosity. Especially useful are the hydrogenated liquid oligomers
of C.sub.6 to C.sub.12 alpha-olefins such as 1-decene trimer.
Similarly, alkyl benzenes of proper viscosity, such as didodecyl
benzene, may be used. Useful synthetic esters include the esters of
mono-carboxylic acids and polycarboxylic acids as well as
mono-hydroxy alkanols and polyols. Typical examples are didodecyl
adipate, pentaerthritol tetracapoate, di-2-ethylhexyl adipate,
di-laurylsebacate and the like. Complex esters prepared from
mixtures of mono- and di-carboxylic acid and mono- and di-hydroxy
alkanols can also be used.
[0045] Below are listed the American Petroleum Institute's (API)
base oil categories, Groups I-V. Preferred are base oils in Groups
II-V. Any suitable base stock oil, conventional or FTBO can be used
as the selected base stock long as the PVC ratio requirement is
met.
TABLE-US-00001 API Base Oil Categories Base Oil Saturates Viscosity
Category Sulfur (%) (%) Index Group I >0.03 and/or <90 80 to
120 Group II <0.03 and >90 80 to 120 Group III <0.03 and
>90 >120 Group IV PAO synthetic lubricants Group V All other
base oils not included in Group I, II, III, IV
[0046] If desired, any of the conventional lubricating additives
can be added to fine tune the characteristics and properties of the
final lubricating oil composition. Below is described a number of
such exemplary lubricating additives.
Dispersants
[0047] The lubricating oil composition of the present invention can
contain dispersants. Typically, the ashless dispersants are
nitrogen-containing dispersants formed by reacting alkenyl succinic
acid anhydride with an amine Examples of such dispersants are
alkenyl succinimides and succinamides. These dispersants can be
further modified by reaction with, for example, boron or ethylene
carbonate. Ester-based ashless dispersants derived from long chain
hydrocarbon-substituted carboxylic acids and hydroxy compounds may
also be employed. Preferred ashless dispersants are those derived
from polyisobutenyl succinic anhydride. A large number of
dispersants are commercially available.
Anti-Wear Agents
[0048] Traditional wear inhibitors may be employed in the
lubricating oil compositions of this invention. As their name
implies, these agents reduce wear of moving metallic parts.
Examples of such anti-wear agents include, but are not limited to
phosphates, phosphites, carbamates, esters, sulfur containing
compounds, and molybdenum complexes. The lubricating oil
composition of this invention may comprise one or more anti-wear
agents, such as metal di-thio di-phosphates and metal
di-thiocarbamates or mixtures thereof. A preferred anti-wear agent
for use in this invention comprises zinc di-thio di-phosphate.
Anti-Oxidants
[0049] Anti-oxidants are used in lubricating oils for inhibition of
decomposition processes that occur naturally in lubricating oils as
they age or oxidize in the presence of air. These oxidation
processes may cause formation of gums, lacquers and sludge
resulting in an increase in acidity and viscosity. Examples of
useful anti-oxidants are hindered phenol oxidation inhibitors, such
as 4,4'-methylene-bis(2,6-di-tert-butylphenol),
4,4'-bis(2,6-di-tert-butylphenol),
4,4'-bis(2-methyl-6-tert-butylphenol),
2,2'-methylene-bis(4-methyl-6-tert-butylphenol),
4,4'-butylidene-bis(3-methyl-6-tert-butylphenol),
4,4'-isopropylidene-bis(2,6-di-tert-butylphenol),
2,2'-methylene-bis(4-methyl-6-nonylphenol),
2,2'-isobutylidene-bis(4,6-dimethylphenol),
2,2'-5-methylene-bis(4-methyl-6-cyclohexylphenol),
2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol,
2,4-dimethyl-6-tert-butyl-phenol,
2,6-di-tert-1-dimethylamino-p-cresol,
2,6-di-tert-4-(N,N'-di-methylaminomethylphenol),
4,4'-thiobis(2-methyl-6-tert-butylphenol),
2,2'-thiobis(4-methyl-6-tert-butylphenol),
bis(3-methyl-4-hydroxy-5-tert-10-butylbenzyl)-sulfide, and
bis(3,5-di-tert-butyl-4-hydroxybenzyl). Examples of alkylated and
non-alkylated aromatic amines are alkylated diphenylamine,
phenyl-alpha-naphthylamine, and alkylated-alpha-naphthylamine Other
classes of anti-oxidants are esters of thiodicarboxylic acids,
salts of di-thiophosphoric acids, alkyl or aryl phosphates and
molybdenum compounds, such as amine-molybdenum complex compound and
molybdenum di-thiocarbamates may also be used as anti-oxidants,
provided the molybdenum compounds do not include tri-nuclear
molybdenum. However, their addition will contribute to the
phosphorus, sulfur and sulfated ash content of the lubricating
oil.
Low, Medium and High Overbased Metal Detergents
[0050] Examples of the low and medium overbased metal detergents
employed in the lubricating oil composition of the present
invention are low, medium or high overbased sulfonates,
salicylates, phenates or Mannich condensation products of
alkylphenols, aldehydes and amines These detergents may be alkali
metal detergents or alkaline earth metal detergents. Preferably
they are alkaline earth metal detergents and more preferably they
are calcium detergents. The TBN of these detergents is greater than
1 and about 500, or more. These detergents are well known in the
art and are commercially available.
Other Additives
[0051] The lubricating oil composition of the present invention may
also contain, in addition to the additives discussed above, other
additives used to impart desirable properties to the lubricating
oil composition of the present invention. Thus, the lubricating oil
may contain one or more of additives, such as viscosity index
improvers, pour point depressants, demulsifiers, extreme pressure
agents and foam inhibitors. These additional additives are
described in more detail below.
Viscosity Index Improvers
[0052] Viscosity index improvers are added to lubricating oil to
regulate viscosity changes due to the change in temperature. Some
commercially available examples of viscosity index improvers are
olefin copolymers, such as ethylene-propylene copolymers,
styrene-isoprene copolymers, hydrated styrene-isoprene copolymers,
polybutene, polyisobutylene, polymethacrylates, vinylpyrrolidone
and methacrylate copolymers and dispersant type viscosity index
improvers.
Extreme Pressure Agents
[0053] Extreme pressure agents that may be used in the lubricating
oil composition of the present invention include alkaline earth
metal borated extreme pressure agents and alkali metal borated
extreme pressure agents. Extreme pressure agents containing
molybdenum may also be employed in the lubricating oil composition
of the present invention, provided the molybdenum compounds do not
include tri-nuclear molybdenum. Sulfurized olefins, zinc
dialky-1-dithiophosphate (primary alkyl, secondary alkyl, and aryl
type), di-phenyl sulfide, methyl tri-chlorostearate, chlorinated
naphthalene, fluoroalkylpolysiloxane, lead naphthenate, neutralized
or partially neutralized phosphates, di-thiophosphates, and
sulfur-free phosphates. The preferred extreme pressure agents are
those that will not contribute to the phosphorous content of the
lubricating oil.
Pour Point Depressants
[0054] Pour point depressants are additives that optimize the low
temperatures fluidity of the lubricating oil. Examples are various
copolymers.
Rust Inhibitors
[0055] Rust inhibitors include nonionic polyoxyethylene surface
active agents, such as polyoxyethylene lauryl ether,
polyoxyethylene higher alcohol ether, polyoxyethylene nonyl phenyl
ether, polyoxyethylene octyl phenyl ether, polyoxyethylene octyl
stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene
sorbitol monostearate, polyoxyethylene sorbitol mono-oleate, and
polyethylene glycol mono-oleate. Other compounds that may also be
employed as rust inhibitors include stearic acid and other fatty
acids, di-carboxylic acids, metal soaps, fatty acid amine salts,
metal salts of heavy sulfonic acid, partial carboxylic acid ester
of polyhydric alcohol, and phosphoric ester. However, preferred
rust inhibitors are those that do not contribute to the phosphorus
or sulfur content of the lubricating oil. Some of the above listed
rust inhibitors may have friction modifying properties. However,
these could be added in quantities sufficient for rust inhibition,
but not high enough to provide their friction modifying
property.
Corrosion Inhibitors
[0056] Corrosion inhibitors are included in lubricating oils to
protect vulnerable metal surfaces. Such corrosion inhibitors are
generally used in very small amounts in the range of from about
0.02 weight percent to about 1.0 weight percent. Examples of
corrosion inhibitors that may be used are sulfurized olefin
corrosion inhibitor and the co-sulfurized alkenyl ester/alpha
olefin corrosion inhibitor.
Metal Deactivators
[0057] Metal deactivators that may be employed in the lubricating
oil composition of the present invention include but are not
limited to di-salicylidene propylenediamine, triazole derivatives,
mercaptobenzothiazoles, thiodiazole derivatives, and
mercaptobenzimidazoles.
Demulsifiers
[0058] Addition product of alkylphenol and ethylene oxide,
polyoxyethylene alkyl ether, and polyoxyethylene sorbitan ester may
be employed in the lubricating oil composition of the present
invention.
Foam Inhibitors
[0059] Useful foam inhibitors for the present invention are alkyl
methacrylate polymers, dimethyl silicone polymers and polysiloxane
type foam inhibitors.
[0060] For best overall results in terms of affording the
properties desired in a conventional lubricating oil composition
for lubricating diesel engines, gasoline engines and natural gas
engines, the lubricating oil may contain a compatible combination
of additives of each of the above classes of additives in effective
amounts.
[0061] The various additive materials or classes of materials
herein described are well known materials and can be readily
purchased commercially or prepared by known procedures or obvious
modification thereof.
EXAMPLE 1
[0062] The following runs were made to demonstrate the superior
wear characteristics of the lubricating oils of the present
invention. Five separate comparative lubricating oils were made
using SAE 15W-40 formulation with an additive package, using Group
II base stocks. The lubricant of the present invention used a
Fischer Tropsch base oil, also known as Gas-to-Liquid base oil
(FTBO or GTL), and was blended with another FTBO (FTBO 14). The
actual viscosity of the base oils was different depending on the
viscosity grade of the lubricant. The FTBO used for the lubricant
of the present invention (FTBO 7) had a Kinematic Viscosity at
100.degree. C. of 7 mm.sup.2/sec.
[0063] The PVC ratio for each of the lubricating base stocks used
was determined as follows: [0064] Pressure viscosity coefficient
(PVC) calculation procedures: [0065] Measure the EHL film thickness
of the samples and the reference oil, Squalane, at desired
temperatures, i.e., 40.degree. C. and 100.degree. C. [0066]
Calculate the PVC values by applying the following equation:
[0066] .alpha.S=.alpha.R[(hS/hR) (.eta.S/.eta.R)-0.67]1/0.53
[0067] The subscripts S and R refer to the samples and the
reference oil, respectively; .alpha. is the PVC value; h the film
thickness, and .eta. the dynamic viscosity.
[0068] The h values are measured on an EHL system, the viscosity
.eta. data can be measured or obtained by a provider of the base
stock. The parameter values .alpha. and .eta. of the reference oil,
Squalane, are available in the literature.
[0069] The EHL film thickness was measured on an EHL Ultra Thin
Film Measurement System, a computer controlled instrument for
measuring the film thickness and traction coefficient (friction
coefficient) of lubricants in the elastohydrodynamic (EHL)
lubricating regime.
[0070] The FTBO 7 had a 40.degree. C. PVC/100.degree. C. PVC ratio
of about 0.88, while the base stock with which it was blended, FTBO
14, had a 40.degree. C. PVC/100.degree. C. PVC ratio of about 0.97.
In the comparative lubricating oils, the Motiva Star 5 and Motiva
Star 8 had a 40.degree. C. PVC/100.degree. C. PVC ratio of less
than 0.80, as did the EHC 110 and EHC 60 lubricating oils.
[0071] The following results were obtained by running the oils with
the same additive package, but differing base oils through the
Daimler OM611 test, which evaluates engine crankcase lubricants
with respect to wear under severe operating conditions.
TABLE-US-00002 Exam- Comparatives ple Viscosity Grade 15W-40 15W-40
15W-40 15W-40 15W-40 10W-40 Inlet 78 117 60 132 131 38 Camshaft
wear [.mu.m] Outlet 166 174 139 183 188 58 Camshaft wear [.mu.m]
Base oil % Motiva Star 5 19 21 -- -- -- -- Motiva Star 8 81 79 --
-- -- -- EHC 110 -- -- 29 36 36 -- EHC 60 -- -- 71 64 64 -- Chevron
-- -- -- -- -- 68 FTBO 7 Chevron -- -- -- -- -- 32 FTBO 14
Viscosity 6 7 6.7 6.1 6.5 0.95 modifier
[0072] The results show that the present formulation exhibited cam
wear that was excellent, as it was 37.9/57.6 .mu.m (inlet/outlet
valve), far lower than any of the other 5 runs.
EXAMPLE 2
[0073] The following results were obtained by running oils with the
same additive package, but differing base oils through the Cummins
ISB valve-train wear test (ASTM D7484). The PVC ratio for each
lubricating oil was determined in Example 1, and is the same as
noted in Example 1.
TABLE-US-00003 Comparative Example A Example B Viscosity Grade
15W-40 10W-40 5W-30 Camshaft wear [.mu.m] 49 15 37 Tappet weight
loss 91 36 47 [mg] Base oil % Motiva Star 5 21 -- -- Motiva Star 8
79 -- -- Chevron FTBO 7 -- 69 100 Chevron FTBO 14 -- 31 --
Viscosity modifier 7 1.65 0.8
[0074] The overall performance demonstrated in the OM 611 Engine
Test and in the Cummins ISB Engine Test (ASTM D7484) clearly
demonstrates the improved wear performance of the present
lubricating compositions. In both tests/examples, the comparatives
were blended to a higher viscosity grade than the lubricant of the
present invention, yet the lower viscosity grade lubricant of the
present invention provided significant and surprising wear
benefits. In all cases, the comparative and the present lubricant
differ only in the base stock selection, with no differences in
surface active additives.
[0075] The determination and selection of a base stock oil having a
40.degree. C. PVC/100.degree. C. PVC ratio approaching one provided
for superior wear properties, even at lower viscosity grades.
[0076] Various modifications and alterations of this invention will
become apparent to those skilled in the art without departing from
the scope and spirit of the invention. Other objects and advantages
will become apparent to those skilled in the art from a review of
the preceeding description.
* * * * *