Title of Invention

A SLIDE BEARING ASSEMBLY

Abstract The invention relates to a slide bearing assembly comprising a slide bearing (16) formed of a porous sintered alloy-made bushing having pores (30) impregnated with a lubricating material (31); a shaft (22) inserted in said slide bearing (16) and supported to be slidingly rotatable in the circumferential direction; and slide bearing grease (24) supplied between the slide bearing (16) and the shaft (22), wherein the slide bearing grease (24) contains a base oil having a dynamic viscosity lower than that of the lubricating material, and when the relative sliding between the slide bearing (16) and the shaft (22) is stopped, the base oil of the slide bearing grease (24) exudes under a load of said shaft (22) to form an oil film between said slide bearing (16) and said shaft (22).
Full Text DESCRIPTION
GREASE FOR SLIDE BEARING
Technical Field
The present invention relates to grease for a slide
bearing which is formed of a porous sintered alloy-made
bushing having pores impregnated with lubricating oil.
Background Art
Many of various machines, such as construction machines,
civil engineering machines, carrying machines, jacking
machines, machine tools, and automobiles, employ slide
bearing assemblies each comprising a slide bearing and a
shaft which is inserted in the slide bearing and is
supported to be slidingly rotatable in the circumferential
direction. For example, an excavation mechanism of a
hydraulic excavator as a representative of construction
machines has a boom coupled to an upper swing body installed
on a track body, an arm coupled to a fore end of the boom,
and a bucket coupled to a fore end of the arm. At each of
articulated portions of the boom, the arm and the bucket, a
slide bearing assembly is generally employed which includes
a slide bearing for supporting a pivot shaft.
In that type of slide bearing assembly, a bearing is
often formed of an oil-impregnated and sintered alloy-made
bushing which is obtained by impregnating highly-viscous
lubricating oil in a porous bushing made of an iron-base


sintered alloy. The oil-impregnated and sintered alloy-made
bushing operates such that the impregnated oil swells and
reduces its own viscosity due to frictional heat generated
when the shaft slides relative to the bushing, whereby the
lubricating oil exudes to form a thin oil film on a sliding
surface. Therefore, the oil-impregnated and sintered alloy-
made bushing exhibits the superior self-lubricating function
(see, e.g., Patent Document 1)
Patent Document 1: JP,A 8-105444
Disclosure of the Invention
Problems to be Solved by the Invention
For example, when the excavation mechanism of the
hydraulic excavator at a standstill is left in a condition
where the bucket is held above the ground surface, a moment
acts about the shaft of the slide bearing assembly due to
the dead load of the excavation mechanism. The excavation
mechanism tries to maintain its posture with the aid of
holding forces of hydraulic cylinders used for driving the
respective articulated portions. In some cases, however, a
slip may occur between the shaft and the bearing because
pressures in the hydraulic cylinders are lowered with slight
leaks of a hydraulic fluid and the force against a downward
moment of the excavation mechanism is gradually reduced with
the lapse of time.
On that occasion, because two contact surfaces, i.e.,
the surface of the oil-impregnated and sintered alloy-made
bushing and the surface of the counterpart shaft, are


generally in an "intimately adapted state", an actual
contact area between the shaft and the bearing is much
larger than that in the case of using an ordinary iron
bushing. With an increase of the contact area between two
solid members, an adhesion force acting between the two
solid members is also increased and therefore an apparent
frictional force acting between the oil-impregnated and
sintered alloy-made bushing and the shaft tends to increase
in a not-lubricated state (i.e., in a stationary state). As
a result, when the oil-impregnated and sintered alloy-made
bushing is employed, energy released upon the occurrence of
a slip is increased and vibrations generated in the slide
bearing assembly are also increased. This results in a fear
that, looking at the above-described example, the generated
vibrations resonate with other parts of the excavation
mechanism, thus causing larger unusual noise correspondingly.
Such unusual noise is not related to machine's reliability,
but it may give undesired psychological influences and an
unpleasant feeling to workers and inhabitants.
An object of the present invention is to provide grease
for a slide bearing, which can suppress unusual noise
attributable to a slip caused between a shaft and a bearing
when a machine is stopped.
Means for Solving the Problems
(1) To achieve the above object, the present invention
provides slide bearing grease supplied to between a slide
bearing formed of a porous sintered alloy-made bushing


having pores impregnated with a lubricating material and a
shaft inserted in the slide bearing and supported to be
slidingly rotatable in the circumferential direction,
wherein the slide bearing grease contains base oil having
dynamic viscosity of 10 - 70 mm2/s at 40 °C and exuding under
a load of the shaft to form an oil film between the slide
bearing and the shaft.
(2) Also, to achieve the above object, the present
invention provides slide bearing grease supplied to between
a slide bearing formed of a porous sintered alloy-made
bushing having pores impregnated with a lubricating material,
in which a solid lubricant is mixed, and a shaft inserted in
the slide bearing and supported to be slidingly rotatable in
the circumferential direction, wherein the slide bearing
grease contains base oil having dynamic viscosity of 10 - 70
mm2/s at 40 °C and exuding under a load of the shaft to form
an oil film between the slide bearing and the shaft.
(3) Further, to achieve the above object, the present
invention provides slide bearing grease supplied to between
a slide bearing formed of a porous sintered alloy-made
bushing having pores impregnated with a lubricating material
and a shaft inserted in the slide bearing and supported to
be slidingly rotatable in the circumferential direction,
wherein the slide bearing grease contains base oil having
dynamic viscosity lower than that of the lubricating oil and
exuding under a load of the shaft to form an oil film
between the slide bearing and the shaft.
(4) Still further, to achieve the above object, the present


invention provides slide bearing grease supplied to between
a slide bearing formed of a porous sintered alloy-made
bushing having pores impregnated with lubricating oil and a
shaft inserted in the slide bearing and supported to be
slidingly rotatable in the circumferential direction,
wherein the slide bearing grease contains base oil having
dynamic viscosity of 10 - 70 mm2/s at 40°C and exuding under
a load of the shaft to form an oil film between the slide
bearing and the shaft, the slide bearing grease being added
with at least a solid lubricant.
(5) Still further, to achieve the above object, the present
invention provides slide bearing grease supplied to between
a slide bearing formed of a porous sintered alloy-made
bushing having pores impregnated with lubricating oil and a
shaft inserted in the slide bearing and supported to be
slidingly rotatable in the circumferential direction,
wherein the slide bearing grease contains base oil having
dynamic viscosity lower than that of the lubricating oil and
exuding under a load of the shaft to form an oil film
between the slide bearing and the shaft, the slide bearing
grease being added with at least a solid lubricant.
(6) In above (2), (4) or (5), preferably, the solid
lubricant contains at least one selected from among organic
molybdenum, molybdenum disulfide, tungsten disulfide, boron
nitride, graphite, nylon, polyethylene, polyimide,
polyacetal, polytetrafluoroethylene, and polyphenylene
sulfide.
(7) In any one of above (1) to (5), preferably, an extreme-

pressure agent and a greasy agent are added in the slide
bearing grease.
Advantages of the Invention
According to the present invention, even when the slide
bearing and the shaft are in a relatively stopped state, the
oil film is formed between the slide bearing and the shaft
by the base oil having a low viscosity and exuding from the
slide bearing grease. Since the thus-formed oil film serves
as a lubricating film to reduce a frictional force between
the slide bearing and the shaft, it is possible to suppress
the generation of unusual noise or to reduce the generated
unusual noise.
Brief Description of the Drawings
Fig. 1 is a side view showing an overall structure of a
hydraulic excavator as one example of machines to which is
applied slide bearing grease according to the present
invention.
Fig. 2 is a sectional view showing an internal
structure of a slide bearing assembly to which is applied
slide bearing grease according to a first embodiment of the
present invention.
Fig. 3 is a partial sectional view illustratively
showing, in enlarged scale, the proximity of an interface
between a slide bearing and a shaft to which is applied the
slide bearing grease according to the first embodiment of
the present invention.


Fig. 4 is a sectional view of the slide bearing and the
shaft, the view illustratively showing a state of an oil
film exuding from the slide bearing grease according to the
present invention.
Fig. 5 is a side view showing an overall structure of
the hydraulic excavator as one example of machines to which
is applied the slide bearing grease according to the present
invention, the view showing a condition where a bucket is
floated above the ground surface.
Fig. 6 is a partial sectional view illustratively
showing, in enlarged scale, the proximity of the interface
between the slide bearing and the shaft to which is applied
slide bearing grease according to a second embodiment of the
present invention.
Fig. 7 is a table showing compositions of the slide
bearing grease according to the present invention and
commercially sold greases and comparison results of
performance tests.
Fig. 8 is a graph showing the results of measuring the
coefficients of friction of the slide bearing grease
according to the present invention and the commercially sold
greases.
Reference Numerals
16 slide bearing
22 shaft
24 grease for slide bearing
30 pore

31 lubricating oil
33 solid lubricant
35 oil film
Best Mode for Carrying Out the Invention
Embodiments of the present invention will be described
below with reference to the drawings.
Fig. 1 is a side view showing an overall structure of a
hydraulic excavator as one example of machines to which is
applied slide bearing grease according to the present
invention.
The hydraulic excavator shown in Fig. 1 comprises a
lower travel structure 1, an upper swing body 2 installed on
the lower travel structure 1 to be able to swing, a cab 3
disposed at one side (left side in Fig. 1) on the upper
swing body 2, an engine room 4 disposed at the other side
(right side in Fig. 1) on the upper swing body 2, and an
excavation mechanism 5 disposed on the upper swing body 2 at
the same side as the cab 3.
The excavation mechanism 5 comprises a boom 6 supported
by the upper swing body 2 to be able to pivotally move up
and down, a boom hydraulic cylinder 7 for pivotally moving
the boom 6 up and down, an arm 8 rotatably supported to a
fore end of the boom 6, an arm hydraulic cylinder 9 for
rotating the arm 8, a bucket 10 rotatably supported to a
fore end of the arm 8, and a bucket hydraulic cylinder 11
for rotating the bucket 10.
Those components of the excavation mechanism 5, i.e.,

the boom 6, the arm 8, the bucket 10, and the associated
hydraulic cylinders 7, 9 and 11 are connected to respective
counterparts through slide bearing assemblies 12 in a
mutually rotatable manner. Although the slide bearing
assemblies used in the excavation mechanism 5 differ in fact
in size, shape, etc. depending on places where they are
mounted, all the slide bearing assemblies have basically the
same structure.
Fig. 2 is a sectional view showing an internal
structure of a slide bearing assembly to which is applied
slide bearing grease according to a first embodiment of the
present invention.
A slide bearing assembly 12 shown in Fig. 2 comprises a
boss 15, a slide bearing 16 formed of a porous sintered
alloy-made bushing which is fixedly fitted to an inner
periphery of the boss 15 by a shrinkage fit, such as a
heating or cooling shrinkage fit, and a shaft 22 inserted in
and supported by the slide bearing 16 to be slidingly
rotatable in the circumferential direction.
Dust seals 18, 18 are disposed on both sides of the
slide bearing 16 to face opposite end surfaces of the slide
bearing 16 and are press-fitted to the inner periphery of
the boss 15. Also, on both sides of the boss 15, brackets
19, 19 are disposed with shims 20, 20 held between opposite
end surfaces of the boss 15 and the brackets 19, 19. Gaps
between the brackets 19, 19 and the boss 15 are sealed by 0-
rings 21, 21 fitted at the outer peripheral sides of the
gaps. The shaft 22 penetrates through the brackets 19, the


shims 20, the dust seals 18 and the slide bearing 16, and is
locked to one bracket 19 by a rotation check bolt 23.
A grease supply hole 25 is formed in the shaft 22 to
supply slide bearing grease 24 to a substantially central
portion of the slide bearing 16 from the side opposed to the
side where the rotation check bolt 23 is mounted. A sealing
plug 26 is screwed to one end of the grease supply hole 25
so that the slide bearing grease 24 filled in the grease
supply hole 25 is sealed off by the sealing plug 26. With
such an arrangement, the slide bearing grease 24 filled in
the grease supply hole 25 is supplied to between the slide
bearing 16 and the shaft 22.
The slide bearing 16 is formed using a porous composite
sintered alloy made of copper powder and iron powder, for
example, and it has a large number of pores. Highly-viscous
lubricating oil is impregnated in the pores such that, when
the slide bearing 16 and the shaft 22 are in relative
sliding motion, the slide bearing 16 exhibits a sufficient
lubrication effect relative to the shaft 22 even when the
slide bearing grease 24 is not supplied. The porosity of
the slide bearing 16 is preferably in the range of, e.g.,
about 5-30 [vol%]. If the porosity is less than 5 [vol%],
there is a risk that a sufficient amount of lubricating oil
is not impregnated and the function as the bearing of the
type supplied with no grease becomes insufficient. On the
other hand, if the porosity is more than 30 [vol%], the
mechanical strength of the slide bearing 16 is reduced.
Additionally, any suitable composite sintered alloy made of


other materials than copper powder and iron powder can also
be used as a material of the slide bearing 16.
Highly-viscous oil having a comparatively high dynamic
viscosity is used as the lubricating oil to be impregnated
in the slide bearing 16. The lubricating oil swells and
reduces its own viscosity due to frictional heat generated
when the shaft 22 slides relative to the slide bushing 16,
whereby the lubricating oil exudes to a sliding interface
between the shaft 22 and the slide bushing 16 and forms a
thin oil film. After the use, the lubricating oil shrinks
with lowering of temperature and is returned back into the
pores of the slide bearing 16 by capillarity. Based on
those behaviors of the lubricating oil, the slide bearing 16
exhibits the superior self-lubricating function. The
dynamic viscosity of the impregnated lubricating oil is not
necessarily limited, but it is required, on an assumption of
being impregnated in the slide bearing 16, to fall in such a
range that the oil can be held inside the pores in an
ordinary state after being impregnated, can exude to the
sliding interface during use due to frictional heat
generated between the shaft 22 and the slide bearing 16, and
thereafter can be returned back to the slide bearing 16 with
lowering of temperature. As a practical range of the
dynamic viscosity of the lubricating oil, by way of example,
it is confirmed that the oil is able to exhibit the above-
mentioned behaviors when the dynamic viscosity at 25.5 [°C] ,
for example, has a value of about 56 - 1500 [mm2/s]. However,
if the dynamic viscosity at 25.5 [°C], for example, is a


value of not higher than 220 [mm2/s], seizure of the slide
bearing 16 has been confirmed in some cases when contact
pressure is 40 [Mpa] that is lower than standard contact
pressure acting on bearings of construction machines, i.e.,
70 [Mpa]. In view of such a result, when the present
invention is practiced, it is more preferable to employ
lubricating oil having a value of the dynamic viscosity at
25.5 [°C] in the range of about 220 - 1500 [mm2/s].
As the lubricating oil impregnated in the slide bearing
16, most of various lubricating oils generally commercially
available, including mineral oil, synthetic oil, etc., can
be used and the composition of the lubricating oil is not
limited to particular one so long as the oil has the dynamic
viscosity capable of exhibiting the above-mentioned
behaviors. Note that grease containing a fibrous thickener
or the like is excluded from the selection target because
such grease cannot be impregnated in the slide bearing 16.
Further, in this embodiment, a solid lubricant is
contained in the lubricating oil impregnated in the slide
bearing 16. The solid lubricant contained in the
lubricating oil has a layered structure and exhibits a
superior lubrication effect with sliding of individual
layers in the layer extending direction. The solid
lubricant includes at least one selected from among, for
example, organic molybdenum, molybdenum disulfide, tungsten
disulfide, boron nitride, graphite, nylon, polyethylene,
polyimide, polyacetal, polytetrafluoroethylene, and
polyphenylene sulfide. The content of the solid lubricant


in the lubricating oil is in the range of, e.g., about 2.0 -
30 [% by weight], and the particle size of solid lubricating
fine particles is selected to be sufficiently small (e.g.,
about 0.1 µm - 100 µm) such that the fine particles are able
to freely move out of and into the pores of the slide
bearing 16 without being clogged in the pores.
The lubricating oil containing the solid lubricant is
impregnated in the slide bearing 16 through the steps of
sufficiently agitating the solid lubricant in the form of
fine particles and the lubricating oil to uniformly disperse
the solid lubricant in the lubricating oil, and then heating
the lubricating oil so as to reduce the oil viscosity for
liquefaction. The slide bearing 16 is immersed in the
liquefied lubricating oil and is left to stand in a vacuum
atmosphere. As a result, air in the pores of the slide
bearing 16 is sucked out, and the lubricating oil containing
the solid lubricant is sucked into the pores. After
impregnating the lubricating oil in the pores in such a
manner, the slide bearing 16 is taken out into air and is
naturally cooled to room temperature, whereby the
lubricating oil restores the original viscosity again and
loses fluidity while residing in the pores of the slide
bearing 16. Thus, the lubricating oil containing the solid
lubricant is impregnated and held in the pores of the slide
bearing 16.
The heating temperature of the lubricating oil when the
lubricating oil is impregnated in the slide bearing 16 is
not limited to a particular value, but the heating


temperature is changed depending on the viscosity of the
lubricating oil used. In other words, it is just required
that the lubricating oil be heated to temperature enough for
liquefaction of the lubricating oil. However, when resin-
base materials, such as polyethylene, polyimide, polyacetal,
and PTFE (polytetrafluoroethylene), are used as the solid
lubricant, the heating temperature has to be set lower than
the heat-resistant temperature of the resin used. Also, the
immersion time and the vacuum pressure during and under
which the slide bearing 16 is immersed in the lubricating
oil are not limited to particular values, but they are set
depending on the viscosity of the lubricating oil used. In
other words, it is just required that the slide bearing 16
is impregnated until the pores of the slide bearing 16 are
saturated with the lubricating oil. Assuming, for example,
that lubricating oil having the dynamic viscosity of 460
[mm2/s] is heated to temperature of 60 - 80 [°C] and the
slide bearing 16 is immersed in the heated lubricating oil
under a vacuum of 2 x 10~2 [mmHg], the pores of the slide
bearing 16 are usually saturated with the lubricating oil in
about 1 hour.
The shaft 22 is made of a steel material or the like.
Preferably, after performing treatment, such as carburizing,
high-frequency induction quenching, laser quenching, or
nitriding, on a shaft surface (outer peripheral surface),
the shaft surface is subjected to surface reforming
treatment by transformation (to, e.g., zinc phosphate or
manganese phosphate) or sulphurizing. By thus performing


the surface reforming treatment of the shaft 22 with the use
of an extreme-pressure applying material, such as Zn (zinc),
Mn (manganese) and S (sulfur), "wetness" between the shaft
and the lubricating oil impregnated in the slide bearing 16
is improved, whereby the lubrication effect and tribology
characteristics are enhanced. From a similar point of view,
it is more preferable that, like the surface of the shaft 22,
the sliding surface (inner peripheral surface) of the slide
bearing 16 coming into contact with the shaft 22 is also
subjected to the surface reforming treatment, such as
carburizing, quenching, nitriding, or sulphurizing.
Abrasion resistance of the slide bearing 16 is further
increased by forming a carburizing-hardened layer with a
thickness of about 1 [mm] - 3 [mm], preferably 2 [mm], on
the sliding surface of the slide bearing 16 in contact with
the shaft 22.
Fig. 3 is a partial sectional view illustratively
showing, in enlarged scale, the proximity of the interface
between the slide bearing and the shaft to which is applied
the slide bearing grease according to the first embodiment
of the present invention.
As shown in Fig. 3, when the slide bearing 16 and the
shaft 22 slide relative to each other, highly-viscous
lubricating oil 31 impregnated in pores 30 of the slide
bearing 16 is caused to exude onto the inner peripheral
surface of the slide bearing 16 together with a solid
lubricant 33 in the form of fine particles due to frictional
heat generated by the relative sliding, thereby forming a
15

thin oil film 32. Because the oil film 32 formed by the
lubricating oil 31 containing the solid lubricant 33 serves
as a sliding interface between the slide bearing 16 and the
shaft 22, fine layers of the solid lubricant 33 slide in the
layer extending direction, thus resulting in an excellent
lubrication effect and superior tribology characteristics.
The lubricating oil 31 impregnated in the pores 30 has very
low fluidity and is therefore hardly lost even when the
relative sliding of the slide bearing 16 and the shaft 22 is
repeated. As a result, the oil film 32 can be continuously
supplied with stability for a very long term. The so-called
"scoring phenomenon" occurred between the shaft 22 and the
slide bearing 16, which are angularly movable relative to
each other, is caused by microscopic metal contact between
them. However, that phenomenon is prevented by the presence
of a microscopic "oil pool" (i.e., the oil film 32) shown in
Fig. 3.
Returning to Fig. 2, the above-described slide bearing
grease 24 in the grease supply hole 25 is made of base oil
having lower dynamic viscosity than the lubricating oil 31,
more particularly base oil that has the dynamic viscosity of
10 - 70 [mm2/s] (preferably 30 - 70 [mm2/s] ) at 40 [°C] and
is capable of exuding due to the load of the shaft 22 to
form an oil film (described later) between the slide bearing
16 and the shaft 22. Such base oil is obtained as low-
viscous base oil of hydrocarbon-base synthetic oil, low-
viscous mineral oil, or the like. The slide bearing grease
24 is prepared by adding, to the low-viscous base oil, not


only at least one selected from among metallic soap,
polyurea resin, organic bentonite, silica, and a fluorine-
contained resin as a thickner compatible with the base oil,
but also an antioxidant, an extreme-pressure agent, a greasy
agent serving as a lubrication aid, or a viscosity improver,
if necessary. Furthermore, the solid lubricant contained in
the lubricating oil impregnated in the slide bearing 16 may
also be added to the slide bearing grease 24.
By selecting the base oil having the dynamic viscosity
of 10 - 70 [mm2/s] at 40 [°C], the slide bearing grease 24
having the above-described composition exhibits the
functions of ensuring lubrication between the slide bearing
16 and the shaft 22 during a certain time or longer in which
the relative sliding between them is stopped. The grounds
why the dynamic viscosity of the base oil used in the slide
bearing grease 24 should be limited to the above range will
be described later.
A description is now made of the operation and action
of the slide bearing assembly to which is applied the grease
according to the first embodiment of the present invention.
As described above with reference to Fig. 3, when the
slide bearing 16 and the shaft 22 slide relative to each
other, the lubricating oil 31 impregnated in the pores 30 of
the slide bearing 16 is caused to exude onto the inner
peripheral surface of the slide bearing 16 together with the
solid lubricant 33, thereby forming the thin oil film 32.
Stated another way, because the solid lubricant 33 enters
the sliding interface between the slide bearing 16 and the


shaft 22 along with the lubricating oil 31, the thin oil
film 32 made of the lubricating oil 31 and the solid
lubricant 33 is formed at the sliding interface between the
slide bearing 16 and the shaft 22, and an excellent
lubrication effect is obtained between the slide bearing 16
and the shaft 22, which are slidingly movable relative to
each other, regardless of the sliding speed.
On the other hand, when the relative sliding of the
slide bearing 16 and the shaft 22 is stopped with, e.g.,
cease of the machine's operation, the lubricating oil 31
forming the oil film 32 at the sliding interface is sucked
into the numerous pores 30 of the slide bearing 16 together
with the solid lubricant 33 by capillarity with lowering of
temperature. On that occasion, the lubricating oil 31 is
returned back into the slide bearing 16, thus resulting in a
condition where the lubricating oil 31 hardly exudes to
between the slide bearing 16 and the shaft 22. As shown in
Fig. 4, however, the low-viscous base oil exuding from the
slide bearing grease 24 due to the load of the shaft 22
forms an oil film 35 between the slide bearing 16 and the
shaft 22. This is because the base oil of the slide bearing
grease 24 has a low dynamic viscosity of 10 - 70 [mm2/s] and
has superior "wetness". Fig. 4 is a sectional view of the
slide bearing 16 and the shaft 22, the view illustratively
showing a state of the oil film 35.
In general, since grease used in slide bearings of
construction machines is usually prepared such that base
oils has viscosity set to a comparatively high value for the


purpose of increasing the lubrication effect under high
contact pressure, a lubrication film formed between the
slide bearing and the shaft is lost while the construction
machine is stopped.
Here, when the hydraulic excavator is stopped longer
than a certain time, it is generally brought into such a
posture that the bucket 10 of the excavation mechanism 5 is
contacted with the ground as shown in Fig. 1. However, if
the bucket 10 is left in a state of being floated above the
ground surface as shown in Fig. 5, a moment attributable to
the dead load of the excavation mechanism 5 acts on the
slide bearing assembly 12. Although the excavation
mechanism 5 tries to maintain its current posture with the
aid of holding forces given by a hydraulic fluid supplied to
the hydraulic cylinders 7, 9 and 11, the force against a
downward moment of the excavation mechanism 5 is gradually
reduced with the lapse of time if pressures in the hydraulic
cylinders are lowered with slight leaks of the hydraulic
fluid in a hydraulic drive system. Consequently, in spite
of the hydraulic excavator being in the completely stopped
state, there generates a force acting to slide the slide
bearing 16 and the shaft 22 relative to each other.
In this connection, assuming the case of not supplying
the slide bearing grease 24, the oil film is hardly present
between the slide bearing 16 and the shaft 22 when those two
members are held in a relatively stationary state for a
period longer than the certain time. Because the contact
surface of the slide bearing 16, i.e., the oil-impregnated




and sintered alloy-made bushing, and the contact surface of
the shaft 22 are in a smooth state containing less
unevenness, which is called an "intimately adapted state",
an actual contact area between the slide bearing and the
shaft is much larger than that in the case of a bearing
assembly using a simple iron bushing. In general, with an
increase of the actual contact area between two solid
members, an adhesion force acting between the two solid
members is also increased. In other words, when the two
solid members start relative sliding again, energy required
to shear the adhered portion between the two solid members
is increased and an apparent frictional force is also
increased correspondingly.
Accordingly, when the moment acting on the slide
bearing assembly 12 exceeds the maximum static frictional
force acting between the slide bearing 16 and the shaft 22,
the energy accumulated so far is released at a stroke and
the two members slide relative to each other by a
predetermined distance. If vibrations generated in the
slide bearing 16 due to a fretting phenomenon, which is
caused as described above, resonate with the excavation
mechanism 5, large unusual noise may occur unexpectedly.
Such unusual noise attributable to the fretting phenomenon
is repeated until the bucket 10 reached the ground surface.
In contrast, according to this embodiment, even when
the slide bearing 16 and the shaft 22 are in the relatively
stopped state, the oil film 35 is formed between the slide
bearing 16 and the shaft 22 by the low-viscous base oil


having superior "wetness" and exuding from the slide bearing
grease 24 as described above with reference to Fig. 4. The
thus-formed oil film 35 serves as a lubricating film to
reduce the frictional force between the slide bearing 16 and
the shaft 22, thereby suppressing the generation of unusual
noise or reducing the generated unusual noise.
Fig. 6 is a partial sectional view illustratively
showing, in enlarged scale, the proximity of the interface
between the slide bearing and the shaft to which is applied
slide bearing grease according to a second embodiment of the
present invention. Similar components in Fig. 6 to those
shown in the above-described drawings are denoted by the
same numerals as those in the above description and they are
not described here.
The slide bearing 16 in this second embodiment is also
formed of a porous sintered alloy-made bushing as in the
foregoing embodiment, but highly-viscous lubricating oil
containing no solid lubricant is impregnated in the pores of
the slide bearing 16. In this second embodiment, the
lubricating oil can be impregnated in the slide bearing 16
in the same manner as in the foregoing embodiment by
replacing the lubricating oil containing the solid lubricant
in the foregoing embodiment with the lubricating oil
containing no solid lubricant in this second embodiment.
In this second embodiment, as shown in Fig. 6, when the
slide bearing 16 and the shaft 22 slide relative to each
other, highly-viscous lubricating oil 31 impregnated in
pores 30 of the slide bearing 16 is caused to exude onto the


inner peripheral surface of the slide bearing 16 due to
frictional heat generated by the relative sliding, thereby
forming a thin oil film 32. Because the oil film 32 serves
as a sliding interface between the slide bearing 16 and the
shaft 22, an excellent lubrication effect is developed and
superior tribology characteristics are obtained. The
lubricating oil 31 impregnated in the pores 30 has very low
fluidity and is therefore hardly lost even when the relative
sliding of the slide bearing 16 and the shaft 22 is repeated.
As a result, the oil film 32 can be continuously supplied
with stability for a very long term. The so-called "scoring
phenomenon" occurred between the shaft 22 and the slide
bearing 16, which are angularly movable relative to each
other, is caused by microscopic metal contact between them.
However, that phenomenon is prevented by the presence of a
microscopic "oil pool" (i.e., the oil film 32) shown in Fig.
6.
Further, in this second embodiment, the slide bearing
grease 24 filled in the grease supply hole 25 (see Fig. 2)
is prepared by adding a solid lubricant similar to that used
in the first embodiment to base oil similar to that used in
the first embodiment. Stated another way, while the
lubricating oil 31 impregnated in the slide bearing 16
contains the solid lubricant in the first embodiment, the
slide bearing grease 24 filled in the grease supply hole 25
contains the solid lubricant in this second embodiment.
By employing the base oil having the dynamic viscosity
of 10 - 70 [mm2/s] at 40 [°C], the slide bearing grease 24 in


this second embodiment, which has the above-described
composition, ensures lubrication between the slide bearing
16 and the shaft 22 during a certain time or longer in which
the relative sliding between them is stopped. Moreover,
addition of the solid lubricant develops the function of
ensuring lubrication between the slide bearing 16 and the
shaft 22 when they undergo fine pivotal motion.
Also in this second embodiment, when the slide bearing
16 and the shaft 22 slide relative to each other, the
lubricating oil 31 impregnated in the pores 30 of the slide
bearing 16 is caused to exude onto the inner peripheral
surface of the slide bearing 16, thereby forming the thin
oil film 32. On that occasion, because the slide bearing
grease 24 filled in the grease supply hole 25 is supplied to
the interface between the slide bearing 16 and the shaft 22,
the solid lubricant being in the form of fine particles and
mixed in the slide bearing grease 24 enter between the slide
bearing 16 and the shaft 22. Thus, the solid lubricant
enters the sliding interface between the slide bearing 16
and the shaft 22 together with the lubricating oil 31,
whereby fine layers made up of the lubricating oil 31 and
the slide bearing grease 24 containing the solid lubricant
are formed between the slide bearing 16 and the shaft 22 so
as to develop an excellent lubrication effect between the
slide bearing 16 and the shaft 22 which are slidingly
movable relative to each other.
The other construction and operation of this second
embodiment are the same as those in the first embodiment and,


the second embodiment can also provide similar advantages to
those obtained with the first embodiment.
In the operation accompanying with fine pivotal motion
or extremely low-speed sliding in which the slide bearing 16
and the shaft 22 slide just slightly, contact pressure is
produced at a level higher than that in the stopped state,
and the oil film 35 formed by only the base oil of the slide
bearing grease 24 can not provide a film thickness enough
for lubrication of the sliding. Furthermore, because the
frictional heat generated in such a situation is very small,
the lubricating oil 31 does not exude in sufficient amount
sometimes. This results in a risk of producing local
contact pressure that may cause local abrasion or damage,
such as "scoring", on the surface of the shaft 22 or the
inner peripheral surface of the slide bearing 16, and may
give rise to incidental unusual noise.
In contrast, according to this embodiment, because the
solid lubricant contained in the slide bearing grease 24
promptly enters between the slide bearing 16 and the shaft
22, a sufficient lubrication effect can be ensured even when
the excavation mechanism 5 is driven at a comparatively low
speed. As a matter of course, when the excavation mechanism
5 is driven at a higher speed, the frictional heat is
generated in sufficient mount, whereby the lubricating oil
31 exudes in necessary and sufficient amount and the
superior lubrication effect specific to the oil-impregnated
and sintered alloy-made bushing is developed.
In spite of the slide bearing 16 and the shaft 22 being


apparently stationary relative to each other, when an engine
is driven, engine vibrations are transmitted to the slide
bearing assembly 12 and high contact pressure is momentarily
generated between the slide bearing 16 and the shaft 22.
Further, looking from a microscopic point of view, a slip
occurs, though slightly, between the slide bearing 16 and
the shaft 22. Thus, even with the excavation mechanism 5
itself being not operated, when the engine is driven, the
slide bearing 16 and the shaft 22 are not in the relatively
stationary state, and the above-described adhesion force is
hardly generated. Therefore, when the fine pivotal motion
of the excavation mechanism 5 is started from the engine
driven state, the fretting phenomenon is hard to occur.
Also, in such a case, the sliding operation of the slide
bearing assembly 12 is lubricated additionally with the
action of the solid lubricant contained in the slide bearing
16. Even if the fretting phenomenon occurs, the above-
described adhesion force is small and the generated unusual
noise is so small as to be almost inaudible.
Fig. 7 is a table showing compositions of the slide
bearing grease according to the present invention and
commercially sold greases and comparison results of
performance tests.
The inventors have studied the mechanism of generation
of the fretting phenomenon and the relationship between that
mechanism and the kinds of greases, and have made the
performance tests. Based on the test results, the range of
the dynamic viscosity of the base oil used in the slide


bearing grease according to the present invention is limited
to the range described above.
In the tests, samples 1-5 of the slide bearing grease
according to the present invention were prepared through the
steps of producing base grease in the same manner as that
generally used in producing lithium grease, mixing additives
in the produced grease, kneading the mixture by using a 3-
roll mill, and adjusting the consistency of the mixture to
NLGI (National Lubricating Grease Institute) No. 2 grade
(consistency: 265-295). The performances of the samples 1-5
were compared with those of commercially sold greases 1-3.
Any of the samples 1-5 contained mineral oil as the
base oil, Li as a thickener, and an extreme-pressure agent,
a rust inhibitor, an organic Mo (solid lubricant), and a
greasy agent were as additives. However, the base oils used
in the samples 1-5 differed in dynamic viscosity from one
another, and the dynamic viscosities of the base oils used
in the samples 1-5 at 40 [°C] had values [mm2/s] of 10, 22,
32, 46 and 68, respectively.
On the other hand, the commercially sold greases 1 and
2 tested for comparison were ones very commonly supplied to
the slide bearing assembly in the excavation mechanism of
the hydraulic excavator shown in Fig. 1. The commercially
sold grease 3 was one in which base oil had higher viscosity
to increase the extreme-pressure performance. While the
consistency of each of the commercially sold greases 1-3 was
set to NLGI No. 2 grade, the dynamic viscosities of the base
oils (mineral oils) used in the commercially sold greases 1-


3 had values [mm2/s] of 143, 93 and 430, respectively.
The samples 1-5 and the commercially sold greases 1-3,
prepared as described above, were tested for load-bearing
performance and abrasion resistance performance. As a
result of the tests, any of the samples 1-5 showed a value
comparable to those of the commercially sold greases 1 and 2
in the abrasion resistance performance, and showed a value
comparable to or better than those of the commercially sold
greases 1 and 2 in the load-bearing performance. In
particular, the samples 4 and 5 showed a high value of 3090
[N] in the load-bearing performance. The load-bearing
performance test was conducted in accordance with a high-
speed 4-ball test (1770 [rpm] x 10 [sec]), and the abrasion
resistance performance test was conducted in accordance with
a high-speed 4-ball test (1220 [rpm] x 40 [kgf] x 75 [°C] x 1
[hr]).
Also, the samples 1-5 and the commercially sold greases
1-3 were evaluated for the coefficient of friction. The
coefficient of friction was evaluated by a method of
preparing a disk made of an oil-impregnated alloy and having
a diameter of 60 [mm] and a pin having dimensions of Φ 4
[mm] x 6 [mm] (disk contact surface: R = 2 [mm]) with its
surface subjected to high-frequency induction quenching, and
then determining changes in the coefficient of friction
measured when the pin was moved to reciprocally slide on the
disk with each kind of grease interposed between them. Test
conditions were set to the sliding speed: 180 [mm/min], the
sliding width: 10 [mm], the pressing load of the pin against

the disk: 1 [kg], and the grease film thickness: 0.2 [mm].
The coefficient of friction at a certain point in time
(corresponding to 5000 reciprocal sliding motions) was
measured after the lapse of a predetermined time from the
start of the sliding. Fig. 8 is a graph showing the
measured results.
Based on the graph of Fig. 8, the inventors evaluated
the coefficient of friction in three grades as follows. The
grease having the coefficient of friction being constantly
low with stability was evaluated as "O", the grease having
the coefficient of friction being low at the beginning, but
increasing from in intermediate point in time was evaluated
as "A", and the grease having the coefficient of friction
being constantly high was evaluated as "x". As a result,
the commercially sold grease 3 in which the base oil had a
very high viscosity was evaluated as "x", and the samples 1,
2 and the commercially sold grease 1, 2 were evaluated as
"A". The sample 5 was evaluated as "A - O", and the samples
3, 4 were evaluated as "O".
The effect in an actual machine was confirmed by a
method of supplying each of the samples 1-5 and the
commercially sold greases 1-3 to the slide bearing
assemblies in the excavation mechanism of the hydraulic
excavator, stopping the bucket 10 in a state floated (e.g.,
about 1 [m]) above the ground surface as shown in Fig. 5,
and measuring how many times unusual noise generated due to
slips in the slide bearing assemblies 12 between the boom 6
and the arm 8 and between the arm 8 and the bucket 10 for 30


minutes. In such tests, a weight of about 1 t was attached
to the bucket 10 in order to make a larger moment acting on
the slide bearing assemblies 12.
As a result of conducting the tests as described above,
the inventors evaluated the case generating unusual noise in
number of times of not larger than 30 (not larger than 1 in
average /minute) to be "©", the case generating unusual
noise in number of times of not larger than 60 (not larger
than 2 in average /minute) to be "O", the case generating
unusual noise in number of times of not larger than 90 (not
larger than 3 in average /minute) to be "A", the case
generating unusual noise in number of times of not larger
than 120 (not larger than 4 in average /minute) to be "x",
and the case generating unusual noise in number of times of
larger than 120 (larger than 4 in average /minute) to be
"xx". As seen from the results, any of the commercially
sold greases 1-3 was evaluated as "x" or inferior. In
particular, the commercially sold grease 3 in which the base
oil had a very high dynamic viscosity showed the test result
inferior to those of the commercially sold greases 1 and 2.
On the other hand, when the samples 1-5 were used, the
number of times of unusual noise generated was apparently
reduced from that when the commercially sold greases 1-3
were used.
From the results of the above performance tests, it was
found that, by using the grease containing the base oil with
the dynamic viscosity being not higher than 70 [mm2/s] at 40
[°C], the occurrence of unusual noise can be suppressed in


comparison with the case of using the commercially sold
greases. Meanwhile, oil having the dynamic viscosity of
lower than 10 [mm2/s] at 40 [°C] is special and not general.
Although being present as a part of synthetic oils, such
special oil is hardly known in mineral oils and is not
adeguate as the base oil of the grease because of having a
low ignition point. For that reason, a lower limit value of
the base oil viscosity is just reguired to be set to 10
[mm2/s]. Thus, it has been found that the occurrence of
unusual noise can be suppressed by using the grease
containing the base oil with the dynamic viscosity of 10 -
70 [mm2/s] at 40 [°C]. In particular, a satisfactory effect
of suppressing the unusual noise is confirmed for the
samples 3-5. Therefore, the grease containing the base oil
with the dynamic viscosity of 30 - 70 [mm2/s] at 40 [°C] is
especially preferable from the viewpoint of obtaining the
satisfactory effect of suppressing the unusual noise.
In the above-described performance tests, the various
kinds of greases were supplied to the slide bearing
assemblies from the beginning. Additionally, another test
was performed, by holding the slide bearing assemblies in a
solid lubricated state in an initial stage, to determine
whether the unusual noise could be suppressed when the
greases were supplied after the occurrence of the unusual
noise. As a result, it was confirmed that while no effect
was found with the supply of the commercially sold greases,
the occurrence of the unusual noise was promptly suppressed
when the samples of the grease according to the present


invention were supplied.
The present invention is intended to limit the dynamic
viscosity of the base oil exuding from the grease, whereas
the viscosity of the grease itself is not limited to
particular one. Accordingly, the grease according to the
present invention may be prepared in the form of a paste
with adjustment of composition and coated by using, e.g., a
spatula or poured through, e.g., a tube. As an alternative,
the grease may be diluted with a solvent and sprayed by
using, e.g., a spray.
While the first embodiment has been described in
connection with the oil-impregnated and sintered alloy-made
bushing in which the lubricating oil to be impregnated
contains the solid lubricant, as one application example of
the slide bearing grease according to the first embodiment,
the slide bearing grease according to the first embodiment
can also be applied to the oil-impregnated and sintered
alloy-made bushing in which lubricating oil containing no
solid lubricant is impregnated.
Further, while the above description has been made in
connection with the case where the grease according to the
present invention is applied to slide bearings disposed in
the articulated portions of the excavation mechanism in the
hydraulic excavator, the present invention can also be
applied to similar articulated portions in other various
machines, such as construction machines, civil engineering
machines, carrying machines, jacking machines, machine tools,
and automobiles.


We Claim:
1. A slide bearing assembly comprising:
a slide bearing (16) formed of a porous sintered alloy-made bushing
having pores (30) impregnated with a lubricating material (31);
a shaft (22) inserted in said slide bearing (16) and supported to be
slidingly rotatable in the circumferential direction; and
slide bearing grease (24) supplied between the slide bearing (16) and
the shaft (22),
wherein the slide bearing grease (24) contains a base oil having a
dynamic viscosity lower than that of the lubricating material, and
when the relative sliding between the slide bearing (16) and the shaft (22) is
stopped, the base oil of the slide bearing grease (24) exudes under a load of
said shaft (22) to form an oil film between said slide bearing (16) and said
shaft (22).


2. The slide bearing assembly as claimed in claim 1, wherein the lubricating
material (31) is optionally mixed with a solid lubricant (33).
3. The slide bearing assembly as claimed in claim 1 or 2, wherein the
dynamic viscosity of the base oil is between 10 to 70mm2/sec at 40° C.
4. The slide bearing assembly as claimed in any of the preceeding claims,
said solid lubricant (33) contains at least one selected from among organic
molybdenum, molybdenum disulfide, tungsten disulfide, boron nitride,
graphite, nylon, polyethylene, polyimide, polyacetal,
polytetrafluoroethylene, and polyphenylene sulfide.
5. The slide bearing assembly as claimed in any of the preceding claims,
wherein the slide bearing grease (24) is optionally mixed with a solid
lubricant.


6. The slide bearing assembly as claimed in any of the preceding claims,
wherein an extreme-pressure agent and a greasy agent are added in the
slide bearing grease (24).


The invention relates to a slide bearing assembly comprising a slide bearing (16)
formed of a porous sintered alloy-made bushing having pores (30) impregnated
with a lubricating material (31); a shaft (22) inserted in said slide bearing (16)
and supported to be slidingly rotatable in the circumferential direction; and slide
bearing grease (24) supplied between the slide bearing (16) and the shaft (22),
wherein the slide bearing grease (24) contains a base oil having a dynamic
viscosity lower than that of the lubricating material, and when the relative
sliding between the slide bearing (16) and the shaft (22) is stopped, the base oil
of the slide bearing grease (24) exudes under a load of said shaft (22) to form
an oil film between said slide bearing (16) and said shaft (22).

Documents:

03057-kolnp-2006-abstract.pdf

03057-kolnp-2006-claims.pdf

03057-kolnp-2006-correspondence others-1.1.pdf

03057-kolnp-2006-correspondence others.pdf

03057-kolnp-2006-description(complete).pdf

03057-kolnp-2006-drawings.pdf

03057-kolnp-2006-form-26.pdf

03057-kolnp-2006-form1.pdf

03057-kolnp-2006-form2.pdf

03057-kolnp-2006-form3.pdf

03057-kolnp-2006-form5.pdf

03057-kolnp-2006-international publication.pdf

03057-kolnp-2006-international search authority report.pdf

03057-kolnp-2006-pct others.pdf

03057-kolnp-2006-priority document-1.1.pdf

03057-kolnp-2006-priority document.pdf

3057-KOLNP-2006-ABSTRACT 1.1.pdf

3057-KOLNP-2006-ABSTRACT.pdf

3057-KOLNP-2006-CANCELLED PAGES.pdf

3057-KOLNP-2006-CLAIMS 1.1.pdf

3057-KOLNP-2006-CLAIMS.pdf

3057-kolnp-2006-correspondence-1.1.pdf

3057-KOLNP-2006-CORRESPONDENCE.pdf

3057-KOLNP-2006-DESCRIPTION (COMPLETE) 1.1.pdf

3057-KOLNP-2006-DESCRIPTION (COMPLETE).pdf

3057-kolnp-2006-examination report.pdf

3057-KOLNP-2006-FORM 1.1.pdf

3057-KOLNP-2006-FORM 1.pdf

3057-kolnp-2006-form 18.pdf

3057-KOLNP-2006-FORM 2.1.pdf

3057-KOLNP-2006-FORM 2.pdf

3057-kolnp-2006-form 26.pdf

3057-kolnp-2006-form 3-1.1.pdf

3057-KOLNP-2006-FORM 3.pdf

3057-kolnp-2006-form 5.pdf

3057-KOLNP-2006-FORM-27.pdf

3057-kolnp-2006-granted-abstract.pdf

3057-kolnp-2006-granted-claims.pdf

3057-kolnp-2006-granted-description (complete).pdf

3057-kolnp-2006-granted-drawings.pdf

3057-kolnp-2006-granted-form 1.pdf

3057-kolnp-2006-granted-form 2.pdf

3057-kolnp-2006-granted-specification.pdf

3057-KOLNP-2006-INTERNATIONAL SEARCH REPORT 1.1.pdf

3057-kolnp-2006-others.pdf

3057-KOLNP-2006-PETITION UNDER RULE 137-1.1.pdf

3057-KOLNP-2006-PETITION UNDER RULE 137.pdf

3057-KOLNP-2006-PRIORITY DOCUMENT.pdf

3057-KOLNP-2006-REPLY TO EXAMINATION REPORT 1.1.pdf

3057-kolnp-2006-reply to examination report-1.2.pdf

3057-KOLNP-2006-REPLY TO EXAMINATION REPORT.pdf

abstract-03057-kolnp-2006.jpg


Patent Number 246794
Indian Patent Application Number 3057/KOLNP/2006
PG Journal Number 11/2011
Publication Date 18-Mar-2011
Grant Date 16-Mar-2011
Date of Filing 23-Oct-2006
Name of Patentee HITACHI CONSTRUCTION MACHINERY CO. LTD.
Applicant Address 5-1, KORAKI 2-CHOME, BUNKYO-KI, TOKYO 112-0004
Inventors:
# Inventor's Name Inventor's Address
1 HIDEKI AKITA C/O HITACHI CONSTRUCTION MACHINERY CO., LTD., TSUCHIURA WORKS, INTELLECTUAL PROPERTY DEPARTMENT, 650, KANDATSUMACHI, TSUCHIURA-SHI, IBARAKI 300-0013
2 MINORU FUJISAKI C/O HITACHI CONSTRUCTION MACHINERY CO., LTD., TSUCHIURA WORKS, INTELLECTUAL PROPERTY DEPARTMENT, 650, KANDATSUMACHI, TSUCHIURA-SHI, IBARAKI 300-0013
3 HAJIME MAEZAWA C/O HITACHI CONSTRUCTION MACHINERY CO., LTD., TSUCHIURA WORKS, INTELLECTUAL PROPERTY DEPARTMENT, 650, KANDATSUMACHI, TSUCHIURA-SHI, IBARAKI 300-0013
4 NOBUO YANAKA 1-2-603, HIKARIGAOKA 6-CHOME, NERIMA-KU, TOKYO 179-0072
5 HIROSHI NISHIMURA 44-22, SUGITA 8-CHOME, ISOGO-KU, YOKOHAMA-SHI, KANAGAWA 235-0033
6 HIDEYUKI FUJIYA 22-11-301, NISHIROKUGOU 3-CHOME, OTA-KU, TOKYO 144-0056
7 OSAMU GOKITA C/O HITACHI CONSTRUCTION MACHINERY CO., LTD., TSUCHIURA WORKS, INTELLECTUAL PROPERTY DEPARTMENT, 650, KANDATSUMACHI, TSUCHIURA-SHI, IBARAKI 300-0013
PCT International Classification Number F16C 33/10
PCT International Application Number PCT/JP2005/019623
PCT International Filing date 2005-10-25
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2004-316745 2004-10-28 Japan
2 2004-316755 2004-10-29 Japan