U.S. patent application number 11/712992 was filed with the patent office on 2007-07-05 for grease composition for automobile wheel bearing.
This patent application is currently assigned to NTN CORPORATION. Invention is credited to Kazunori Kubota, Makoto Oishi.
Application Number | 20070155634 11/712992 |
Document ID | / |
Family ID | 36036402 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070155634 |
Kind Code |
A1 |
Kubota; Kazunori ; et
al. |
July 5, 2007 |
Grease composition for automobile wheel bearing
Abstract
The present invention provides a grease composition for
automobile wheel bearings, which contains (a) an urea thickener
represented by general formula (1):
R.sub.1--NHCONH--R.sub.2--NHCONH--R.sub.3 (wherein R.sub.1 and
R.sub.3 may be the same or different from each other and are each
independently an aromatic hydrocarbon group having 6 to 12 carbon
atoms, and R.sub.2 represents an aromatic hydrocarbon group having
6 to 15 carbon atoms); (b) an organic molybdenum compound; and (c)
a base oil. The composition of the present invention can extend the
flaking life and lubrication life, and reduce the fretting
wear.
Inventors: |
Kubota; Kazunori;
(Iwata-shi, JP) ; Oishi; Makoto; (Fujisawa-shi,
JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
NTN CORPORATION
Osaka
JP
KYODO YUSHI CO., LTD.
Tokyo
JP
|
Family ID: |
36036402 |
Appl. No.: |
11/712992 |
Filed: |
March 2, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP05/16401 |
Sep 7, 2005 |
|
|
|
11712992 |
Mar 2, 2007 |
|
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Current U.S.
Class: |
508/363 ;
508/528 |
Current CPC
Class: |
C10M 169/06 20130101;
C10M 2219/068 20130101; C10N 2040/02 20130101; C10M 2215/1026
20130101; C10M 2203/1006 20130101; C10M 169/00 20130101; C10N
2050/10 20130101; C10N 2030/06 20130101; C10M 2205/0285 20130101;
C10N 2030/10 20130101; C10N 2010/12 20130101; C10M 2219/068
20130101; C10N 2010/12 20130101; C10M 2219/068 20130101; C10N
2010/12 20130101 |
Class at
Publication: |
508/363 ;
508/528 |
International
Class: |
C10M 135/18 20060101
C10M135/18; C10M 173/02 20060101 C10M173/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 7, 2004 |
JP |
2004-260170 |
Claims
1. A grease composition for automobile wheel bearings, comprising:
(a) an urea thickener represented by general formula (1):
R.sub.1--NHCONH--R.sub.2--NHCONH--R.sub.3 (1) wherein R.sub.1 and
R.sub.3 may be the same or different from each other and each
independently represents an aromatic hydrocarbon group having 6 to
12 carbon atoms, and R.sub.2 represents an aromatic hydrocarbon
group having 6 to 15 carbon atoms; (b) an organic molybdenum
compound; and (c) a base oil.
2. The grease composition of claim 1, wherein the urea thickener
(a) is a compound represented by formula (1-1) or (1-2):
##STR3##
3. The grease composition of claim 1, wherein the urea thickener
(a) is contained in an amount of 2 to 35% by mass with respect to
the mass of the base oil.
4. The grease composition of claim 1, wherein the organic
molybdenum compound (b) is a molybdenum dithiocarbamate.
5. The grease composition of claim 4, wherein the organic
molybdenum compound (b) is a molybdenum dithiocarbamate represented
by formula (2):
[R.sub.4R.sub.5N--CS--S].sub.2--Mo.sub.2O.sub.mS.sub.n (2) wherein
R.sub.4 and R.sub.5, which may be the same or different and each
independently represents a straight-chain or branched alkyl group
having 1 to 24 carbon atoms; and m ranges from 0 to 3 and n ranges
from 4 to 1, provided that m+n=4.
6. The grease composition of claim 1, wherein the organic
molybdenum compound (b) is contained in an amount of 0.1 to 10% by
mass in the composition.
7. The grease composition of claim 1, wherein the organic
molybdenum compound (b) is contained in an amount of 1 to 5% by
mass in the composition.
8. The grease composition of claim 1, wherein the base oil (c) is a
mixture comprising 20 to 50% of a synthetic oil and 80 to 50% of a
mineral oil.
9. The grease composition of claim 8, wherein the synthetic oil is
a synthetic hydrocarbon oil.
10. A grease composition for automobile wheel bearings, comprising:
(a) an urea thickener represented by formula (1-1) or (1-2) in an
amount of 10 to 25% by mass with respect to the total mass of the
composition; ##STR4## (b) a molybdenum dithiocarbamate in an amount
of 1 to 5% by mass with respect to the total mass of the
composition; and (c) a mixed base oil consisting of 60% of a
mineral oil and 40% of a synthetic hydrocarbon oil.
Description
TECHNICAL FIELD
[0001] The present invention relates to a grease composition used
for automobile wheel bearings.
BACKGROUND ART
[0002] With respect to the automobile wheel bearings, the bearings
support the vehicle's weight through the tires, and at the same
time, they are operated under comparatively heavy load conditions
with the application of radial, thrust and moment loads as well as
impact loads from the contact point of the tires with ground
depending upon the running conditions of the vehicle (non-patent
document 1). This may often cause the problem of flaking as a
result of metal fatigue. To extend the flaking life (i.e., fatigue
life of the bearing material), a layer of lubricating oil is
thickened (namely, by increasing the viscosity of the oil).
However, satisfactory grease compositions have not yet been
obtained.
[0003] Further, while the vehicle carries a freight car, the
bearings are subject to slight vibration and the like and
eventually worn out to cause a phenomenon called fretting in some
cases. The solution to the fretting phenomenon conventionally lies
in improvement of the lubricating properties by choosing a grease
capable of forming a strong oil layer and showing excellent
fluidity. However, there is no grease composition that can meet
such requirements satisfactorily.
[0004] The grease composition will deteriorate due to oxidation and
cannot exhibit its desired performance as the period of service of
a car is prolonged or the mileage is accumulated. In light of this,
the grease composition is required to extend its useful oxidation
life (lubrication life).
[0005] In general, the wheel bearings for automobiles are roughly
classified into two groups according to kinds of loads to be
imposed on the bearings, that is, ball bearings (mainly used for
passenger cars) and tapered roller bearings (mainly used for
trucks). In the tapered roller bearings, when oil in the form of a
layer runs out around the periphery of the rollers, the end
portions of the rollers may be damaged while sliding. The damage
mentioned above is commonly referred to as galling at the end of
the rollers, and conventionally, some measures are taken against
this problem, for example, by increasing the amount of oil,
improving the extreme pressure performance of lubricants, and so
on.
[0006] The automobile wheel bearings have gone through some
generations in terms of their structure: bearings on their own (a
pair of bearings that match the specified standards);
first-generation bearings where two bearings are assembled into a
unit; second-generation bearings where a hub shaft or a part of
knuckle is incorporated; third-generation bearings where a hub
wheel and a knuckle are incorporated; and fourth-generation
bearings where the inner ring of a bearing and the outer ring of a
constant velocity joint are integrated. The problems mentioned
above are common to all the generations.
[0007] Non-patent Document 1: Society of Automobile Engineers of
Japan, "Jidousha no Tribology (Tribology in Automobiles)" (YOKENDO
Co., Ltd., Mar. 15, 1997): p. 270
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0008] An object of the present invention is to provide a grease
composition for wheel bearings of automobiles, which can extend the
flaking life of automobile wheel bearings and exhibit prolonged
lubrication life, with the fretting wear being reduced.
Means for Solving the Problems
[0009] Accordingly, the present invention provides a grease
composition for automobile wheel bearings, comprising:
[0010] (a) an urea thickener represented by the following general
formula (1): R.sub.1--NHCONH--R.sub.2--NHCONH--R.sub.3 (1) wherein
R.sub.1 and R.sub.3 may be the same or different from each other
and are each independently an aromatic hydrocarbon group having 6
to 12 carbon atoms, and R.sub.2 represents an aromatic hydrocarbon
group having 6 to 15 carbon atoms;
[0011] (b) an organic molybdenum compound; and
[0012] (c) a base oil.
Effects of the Invention
[0013] The grease of the present invention can significantly extend
the flaking life of the wheel bearings in the automobiles and the
lubrication life, and reduce the fretting wear. In particular, the
grease of the present invention can extend the useful life of cars
to 10 years and guarantee 1,200,000 kilometers of driving, for
example, by preventing the galling at the end of the rollers in the
tapered roller bearings.
BEST MODE FOR CARRYING OUT THE INVENTION
(a) Urea Thickener
[0014] The urea thickener usable in the present invention is a
thickener with excellent heat resistance, which is represented by
the following general formula:
R.sub.1--NHCONH--R.sub.2--NHCONH--R.sub.3 (1).
[0015] In the above formula, R.sub.1 and R.sub.3 may be the same or
different from each other and are each independently an aromatic
hydrocarbon group having 6 to 12 carbon atoms. To be more specific,
phenyl group, tolyl group, xylyl group, cumenyl group,
t-butylphenyl group, benzyl group, mesityl group and the like can
be employed. Particularly preferred is tolyl group.
[0016] In the formula, R.sub.2 represents an aromatic hydrocarbon
group having 6 to 15 carbon atoms. Representative examples of
R.sub.2 are indicated by the following structural formulas:
##STR1##
[0017] Specifically, urea compounds represented by the following
formulas (1-1) and (1-2) can be used. Particularly preferred is the
urea thickener represented by formula (1-1). ##STR2##
[0018] The content of the urea compound in the composition of the
present invention is not particularly limited, but preferably in
the range of 2 to 35% by mass with respect to the mass of the base
oil.
[0019] The urea thickener used in the present invention is
obtainable, for example, by reacting a monoamine with a
diisocyanate at 10 to 200.degree. C. The above-mentioned reaction
process is not particularly limited and any conventional methods
can be used. In the reaction, volatile solvents may be used. In
this case, the solvents can be directly incorporated into the
composition of the present invention if the solvents are usable for
the base oil.
[0020] Specific examples of the diisocyanate include aromatic
diisocyanates such as 2,4-tolylene diisocyanate, 2,6-tolylene
diisocyanate, diphenylmethane-4,4'-diisocyanate, and
naphthylene-1,5-diisocyanate, and mixtures thereof Examples of the
monoamine include aromatic amines such as aniline, benzylamine,
toluidine, chloroaniline and the like.
[0021] The urea thickener mentioned above has a film-forming
capability, so that the life of the bearings (in terms of flaking)
can be increased and the fretting can be reduced. Moreover, unlike
metallic soap thickeners, the above-mentioned urea thickener has no
promoting effect on oxidation of the base oil, with the result that
the oxidation life (i.e., lubrication life) of the grease can be
extended.
(b) Organic Molybdenum Compound
[0022] The organic molybdenum compounds herein used are generically
referred to as organic metal-containing load carrying additives
where molybdenum is used as a metal group, which are widely used as
extreme pressure additives, in general. To be more specific,
molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate and
the like can be used. In particular, MoDTC is preferred, and
preferable examples of the MoDTC are represented by the following
formula (2): [R.sub.4R.sub.5N--CS--S].sub.2--Mo.sub.2O.sub.mS.sub.n
(2) wherein R.sub.4 and R.sub.5, which may be the same or different
and each independently represents a straight-chain or branched
alkyl group having 1 to 24 carbon atoms, preferably 3 to 18 carbon
atoms; and m ranges from 0 to 3 and n ranges from 4 to 1, provided
that m+n=4.
[0023] The content of the organic molybdenum compound in the
composition of the present invention is not particularly limited,
but preferably in the range of 0.1 to 10% by mass, more preferably
1 to 5% by mass.
(c) Base Oil
[0024] The base oils usable in the present invention are those
generally serving as lubricating oils with excellent stability at
high temperatures and excellent fluidity at low temperatures.
Although mineral oils as well as synthetic oils can be used as the
base oils, preferably used is a mixed base oil where a synthetic
oil component is contained in an amount of 20 to 50% by mass and a
mineral oil component is contained in an amount of 80 to 50% by
mass. Any of the conventionally known synthetic oils are usable,
for example, poly(.alpha.-olefin) oils prepared from 1-decene as
the starting material, co-oligomer oils of .alpha.-olefin and
ethylene, phenyl ether based synthetic oils, ester based synthetic
oils, polyglycol based synthetic oils, silicone oils and the
like.
[0025] In particular, hydrocarbon oils consisting of carbon and
hydrogen atoms are especially preferred as the synthetic oils.
[0026] When the mixed base oil includes a synthetic hydrocarbon oil
as the synthetic oil component, sealing performance is not
disadvantageously affected and leakage from the bearings can
advantageously be reduced.
[0027] The grease composition of the present invention may further
comprise an antioxidant, rust preventive, anticorrosive and the
like, in addition to the above-mentioned components.
[0028] A preferable example of the composition according to the
present invention comprises;
[0029] as the component (a), an urea thickener represented by the
above-mentioned formula (1-1) or (1-2) in an amount of 10 to 25% by
mass with respect to the total mass of the composition,
[0030] as the component (b), MoDTC in an amount of 1 to 5% by mass
with respect to the total mass of the composition, and
[0031] as the component (c), a mixed base oil consisting of 60% of
a mineral oil and 40% of a synthetic hydrocarbon oil, in
particular, a poly(.alpha.-olefin) oil.
[0032] Particularly preferred is a composition wherein additives
such as an antioxidant, a rust preventive and the like are added so
that the amounts of the additives may be within the range of 1 to
10% by mass with respect to the total mass of the composition.
[0033] There is no limit to the production method for the
composition of the present invention. Any conventional methods are
usable. Specifically, the respective components may be added to a
base oil simultaneously or successively and the resultant mixture
may be kneaded using a roll mill or the like to prepare a
composition. Alternatively, a combination of additives may be
prepared so as to have a concentration of five to ten times that of
the finished composition, and thereafter the combination of
additives is mixed with a base oil to obtain a composition
according to the present invention.
EXAMPLE 1
[0034] The present invention will now be explained with reference
to the following Examples and Comparative Examples.
[0035] Grease compositions according to Examples 1 to 4 and
Comparative Examples 1 and 2 were independently prepared in such a
manner that a thickener and an organic molybdenum compound were
added to a base oil as shown in Table 1, and the resultant mixture
was kneaded using a three-roll mill. The numerical values in Table
1 indicate the contents (%) in the composition. Examples 1 to 4 and
Comparative Example 2 employed an aromatic urea compound
represented by the previously mentioned formula (1-1) as the
thickener. In each composition, an antioxidant and a rust
preventive were incorporated as auxiliary components in amounts of
3% by mass and 2% by mass, respectively. The consistency of each
grease composition was measured in accordance with JIS K2220. All
the grease compositions were adjusted to have a consistency of 300.
TABLE-US-00001 TABLE 1 Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 1
Ex. 2 (a) Thickener Aromatic Aromatic Aromatic Aromatic Complex
Aromatic diurea diurea diurea diurea lithium diurea 18 18 18 18
soap 10 18 (b) MoDTC*.sup.1 2 1 2 5 2 -- (c) Base oil Mineral oil
100 80 60 50 60 60 Synthetic 0 20 40 50 40 40 hydrocarbon oil
Flaking life .largecircle. .largecircle. .largecircle.
.largecircle. .DELTA. .largecircle. Galling at .circleincircle.
.DELTA. .circleincircle. .circleincircle. .largecircle. X end of
rollers Oxidation life .largecircle. .largecircle. .circleincircle.
.circleincircle. .largecircle. .circleincircle. (Lubrication life)
Fretting .circleincircle. .circleincircle. .circleincircle.
.circleincircle. .largecircle. .circleincircle. *.sup.1Molyvan A,
made by R.T. Vanderbilt Company, Inc.
[0036] The physical properties of the above-mentioned grease
compositions were evaluated in accordance with the test methods
shown below. The results obtained are also shown in Table 1.
[Life of Grease (in Terms of Flaking)]
[0037] The life of grease was obtained as the flaking life by a
rotational life test of a tapered roller bearing for use in large
trucks. The results are expressed in terms of lifetime (hour).
Test conditions: Fr (radial load)=62.9 kN
[0038] Fa (axial load)=25.2 kN
[0039] N (Number of revolutions of bearing)=400 r/min,
[0040] Radius of tire=517 mm
Evaluation criteria:
[0041] .circleincircle.: 700 hours or more
[0042] .largecircle.: 400 hours or more and less than 700 hours
[0043] .DELTA.: 200 hours or more and less than 400 hours
[0044] .times.: less than 200 hours
[Galling at End Portions of Rollers in Tapered Roller Bearing]
[0045] In the test machine for rotational life of a tapered roller
bearing designed for large trucks, the end portions of rollers in
the bearing were observed. The results are expressed in terms of
occurrence of galling and surface roughness. Test conditions: same
as in the above-mentioned life test.
Evaluation criteria:
[0046] .circleincircle.: Neither galling, nor surface roughness
[0047] .largecircle.: Occurrence of surface roughness
[0048] .DELTA.: Occurrence of slight galling
[0049] .times.: Occurrence of galling
[Oxidation Life (Lubrication Life)]
[0050] This item was obtained as a lubrication life of a deep
groove ball bearing. The results are expressed in terms of lifetime
(hour).
Test conditions: in accordance with ASTM D 3336
[0051] Test temperature: 150.degree. C.
[0052] Number of revolutions: 10,000 rpm
[0053] Loads: Fa=Fr=67 N
Evaluation criteria:
[0054] .circleincircle.: 2500 hours or more
[0055] .largecircle.: 1000 hours or more and less than 2500
hours
[0056] .DELTA.: 200 hours or more and less than 1000 hours
[0057] .times.: less than 200 hours
[Fretting]
[0058] The fretting wear was obtained in accordance with a Fafnir
test. The results obtained are expressed in terms of abrasion
amount.
Test conditions: in accordance with ASTM D 4170
[0059] Test bearing: 51204 J
[0060] Period of test time: 2 hours
Evaluation criteria:
[0061] .circleincircle.: 0.5 mg or less
[0062] .largecircle.: more than 0.5 mg and 1.5 mg or less
[0063] .DELTA.: more than 1.5 mg and 2.5 mg or less
[0064] .times.: more than 2.5 mg
[0065] As is apparent from the results of Table 1, the grease
compositions for automobile wheel bearings according to Examples
are superior to those of Comparative Examples in that both the
flaking life and the lubrication life are improved, the fretting
wear is reduced, and galling at the end portions of rollers in the
tapered roller bearings can be prevented.
* * * * *