Bearings – Rotary bearing – Plain bearing
Reexamination Certificate
2001-12-21
2004-03-02
Hannon, Thomas R. (Department: 3682)
Bearings
Rotary bearing
Plain bearing
C384S296000, C384S297000
Reexamination Certificate
active
06698932
ABSTRACT:
TECHNICAL FIELD
This invention relates to a bearing assembly for a work implement of a construction machine.
BACKGROUND OF THE INVENTION
A rotational member for a work implement on a construction machine that includes a bearing assembly. The bearing assembly can include a boss portion of a first member (hereinafter referred to as “boss”) that is positioned and pivotally connected by a pin. The pin is arranged between a pair of bracket portions of a bifurcated member.
FIG. 7
shows an example of a work implement on a excavator. The work implement has a boom
11
that is pivoted vertically in the front portion of the body frame
4
, an arm
13
that is articulately connected at the end portion thereof, and a bucket
15
that is pivotally connected to the arm
13
. The connections between the pivoting members of the work implement are provided with a bearing assembly at each pin joint.
Japanese patent application 1995-354061, filed on Dec. 28, 1995 and assigned to Hitachi Construction Machinery shows a known bearing assembly.
FIGS. 8 and 9
show a cross sectional view of the bearing assembly described in the above-mentioned Japanese application, which is seen along line M—M in FIG.
7
. As shown in
FIG. 8
, the arm
13
has a boss
13
a
at the end portion thereof. A pair of bushings
61
,
61
are fixed on opposing sides of a bore defined within the boss
13
a
, so that a pin
27
can slide axially in the bore of the boss
13
a
. A pair of bosses
15
b
,
15
b
are formed on a pair of bifurcated flanges or a pair of brackets
15
a
,
15
a
, which are positioned on the opposing sides of the end portion of the bucket
15
. The pin
27
is inserted through the bore defined within the brackets
15
a
,
15
a
and the bushing
61
,
61
.
In the description of the aforesaid Japanese application, it is explained that the use of a heavy lubricant will prevent the bushing
61
from overheating while sliding around the pin
27
, when the bushing is subjected to a heavy radial load. The use of a heavy lubricant also prevents vibration and frictional wear. Sintered hard alloy metals or ceramics such as tungsten carbide and the like are disposed on both of the end surfaces
13
b
,
13
b
of the boss
13
a
, as well as the opposing inner surfaces
15
c
,
15
c
of the bosses
15
b
that extends inward towards the brackets
15
a
,
15
a
. The brackets
15
a
,
15
a
face the end surface
13
b
,
13
b
and form anti-wear layers
71
and
72
respectively. The Japanese patent application explains that the anti-wear layers
71
and
72
have a hardness equal to earth and sand, so that the bushing surfaces are difficult to scratch, when earth, sand and the like get between the sliding surfaces of the bushings
61
,
61
. The anti-wear layers prevent the deleterious scouring action of the sand on the sliding surfaces of the bushing flange, which would result in abrasive wear.
FIG. 9
shows also another embodiment of the above-mentioned Japanese application. In the drawing, both end surfaces
13
b
,
13
b
of the bosses
13
a
and opposing inner sides
15
c
,
15
c
of the bosses
15
b
,
15
b
, which extend inward toward the brackets
15
a
,
15
a
, define a pair of annular grooves
81
,
82
, where a pair of rings
83
,
84
are respectively installed. The rings
83
,
84
are fixed by a number of screws
85
. A pair of anti-wear layers
86
,
87
, which are formed by a spray coating process with sintered hard alloy metal or ceramics such as tungsten carbide prior to its installation, are positioned on the facing sliding surfaces of the rings
83
,
84
.
The following are drawbacks associated with the conventional technology described in the above-referenced Japanese patent application.
(1) Since the anti-wear layers
71
,
72
and
86
,
87
are bonded directly to the sliding surface of the annular rings by the spray deposit of the sintered hard alloy metal such as tungsten carbide; they can be equal in hardness to earth and sand containing aluminum, silica, quartz and feldspar, but not significantly harder. This results in quick degradation of the anti-wear layers
71
,
72
. In addition, the anti-wear layer made by spray forming is extremely thin, ranging from tens to hundreds of microns, resulting in a relatively short wear life. Furthermore, when hard gravel and the like as small as several millimeters get into the space between the rings
83
and
84
and a strong force is being applied, impressions that are created by the gravel reach the base metals through the relatively thin anti-wear layers
71
and
72
or
86
and
87
disposed thereon. This can increase the possibility of cracks and peeling of the anti-wear layers starting from the impressed portions.
(2) When the anti-wear layers
71
,
72
or
86
,
87
are worn out and damaged as described in (1), it very difficult to repair these parts with this particular type of bearing assembly on site. This leads to poor machine maintenance.
(3) With this type of bearing assembly, the ring shaped members
83
,
84
and the anti wear layers
86
,
87
are fastened by a number of screws
85
to both end surfaces
13
b
,
13
b
of the boss
13
a
and the opposing inner sides
15
c
of the bracket bosses
15
b
(FIG.
9
). The ring shaped members
83
,
84
repeat a reverse turn with the bucket
15
pivoted about the pin
27
with respect to the arm
13
. This causes the screws
85
to be repeatedly subjected to lateral forces in opposite directions, which reduces the tightening force or axial tension of the screws
85
and raises the possibility that screws will loosen and fall free whenever the rings
83
,
84
are subject to an additional thrust force. Thus, the described bearing assembly can suffer from the drawback of poor durability.
The present invention is directed to overcoming the problems described above. It is the object of the present invention to provide a bearing assembly for a work implement on a construction machine that has a significant bearing performance, excellent durability, and easy maintenance.
REFERENCES:
patent: 1439297 (1922-12-01), De Coninck
patent: 1868687 (1932-07-01), Bijur
patent: 4203684 (1980-05-01), Stecklein
patent: 4400898 (1983-08-01), Christensen et al.
patent: 4607977 (1986-08-01), Varnelis et al.
patent: 4917509 (1990-04-01), Takano
patent: 4932795 (1990-06-01), Guinn
patent: 5509738 (1996-04-01), Haynes et al.
Hamaguchi Masahiko
Kondou Monta
Shimada Yoshiaki
Hannon Thomas R.
Komatsu Ltd.
Varndell & Varndell PLLC
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