Structure for working unit for bucket excavators and method...

Metal fusion bonding – Process – With shaping

Reexamination Certificate

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C037S443000

Reexamination Certificate

active

06536652

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a structure for a working machine of a bucket type excavator such as a hydraulic shovel. The present invention also includes a method for producing an arm of a bucket type excavator and the structure for the working machine of the bucket type excavator.
FIG. 1
depicts a hydraulic shovel which is a bucket type excavator. The bucket type excavation machine includes: an upper vehicle body
2
turnably mounted on a lower running body
1
, a boom
3
vertically swingably mounted to the upper vehicle body
2
, an arm
4
vertically oscillatably mounted to boom
3
, and a bucket
5
vertically oscillatably mounted to a tip end of arm
4
. A boom cylinder
6
is connected between the upper vehicle body
2
and boom
3
. An arm cylinder
7
is connected between boom
3
and arm
4
. A bucket cylinder
8
is connected between arm
4
and bucket
5
.
During operation of the hydraulic shovel, boom
3
swings vertically, arm
4
and bucket
5
oscillate vertically. Upper vehicle body
2
turns laterally simultaneous with the bucket oscillation, thereby carrying out operations such as excavation and loading to a dump truck.
As shown in
FIG. 2
, arm
4
includes an arm body
10
, an arm cylinder-mounting bracket
11
jointed to one longitudinal end of arm body
10
, and a bucket-connection bracket
12
jointed to another longitudinal end of arm body
10
.
As shown in
FIG. 3
, arm body
10
has a hollow and rectangular cross-section comprising an upper lateral plate
13
, a lower lateral plate
14
and left and right vertical plates
15
,
15
.
As shown in
FIG. 1
, during operation of the excavation machine a vertical load F
1
, a lateral load F
2
, a torsion load F
3
and the like are applied to arm
4
. Durability against these loads is secured by choosing proper dimensional constraints on arm body
10
. For example, referring to
FIG. 3
, load F
1
can be stabilized by appropriately choosing dimensions for the arm body cross-sectional width W, cross-sectional height H, as well as appropriately choosing the thicknesses of upper lateral plate
13
, lower lateral plate
14
and left and right vertical plates
15
,
15
. These dimensions and thicknesses are appropriately set in accordance with the magnitude of the loads shown in FIG.
3
. In addition, lateral load F
2
and torsional load F
3
can be compensated for by adding a cross-section restraint member such as a rib
16
shown in FIG.
2
.
In hydraulic shovel excavation machines including an upper vehicle body
2
main portion, a boom
3
, an arm
4
and a bucket
5
, a counter weight
9
is provided at a rear portion of upper vehicle body
2
. The amount of counter weight required for the excavation machine depends upon the weight of the machine. For Example, if the working machine is reduced in weight, the weight of the counter weight
9
mounted to the rear portion of the upper vehicle body
2
can be reduced, the rearward projecting amount of the upper vehicle body
2
can be reduced and therefore, a turning radius of the rear end of the upper vehicle body
2
can be reduced.
If the working machine comprising boom
3
, arm
4
and bucket
5
is reduced in weight, it is possible to increase the volume of the bucket correspondingly instead of reducing the weight of the counter weight
9
and thus increasing the working amount of the machine.
Further, arm
4
is vertically swung by arm cylinder
7
, and a portion of a thrust of arm cylinder
7
supports the weight of arm
4
. Therefore, if arm
4
is reduced in weight, the thrust of arm cylinder
7
is effectively utilized as the vertical swinging force of arm
4
. Similarly, the weight of arm
4
is applied to boom cylinder
6
. Thus, if arm
4
is reduced in weight, the thrust of boom cylinder
6
is effectively utilized.
In generally, when considering the strength of a working machine of the bucket type excavator, as the simplest method, the working machine is replaced with a beam or a thin pipe which is discussed in material mechanics and a strength with respect to the bending and torsion can be evaluated.
That is, the bending stress and shearing stress applied to a cross-section can be obtained by the following general formulas (1) and (2):
&sgr;=
M/Z
  (1)
(wherein, &sgr;: bending stress on a cross-section, is determined from M; bending moment of a cross-sectional area subject to bending stress, and Z is a cross-section coefficient)
&tgr;=
T
/(2
·A·t
)  (2)
(wherein, &tgr;: shearing stress, is determined from T: torsion torque, A: projection area of neutral line of cross-section plate thickness, t: thickness of cross-section plate)
An appropriate shape of the cross-section can be determined from the results of the above calculation and permissible stress of the material to be used. Similarly, deflection of the beam and torsion of the axis can be calculated using general formula of the material mechanics, and such calculation, rigidity of the working machine can also be evaluated.
However, if a working machine designed in accordance with the above evaluation method is actually produced and stress tests are carried out, in many cases the results of the tests are different from the calculated stress values. For this reason, in recent years, stress is evaluated by a computer simulation using finite element method (FEM). Computer simulations result in enhancing the precision in stress evaluations. When stress is calculated using an FEM simulation, it can be found that a cross-sectional area of a working machine, which was previously considered as a beam and axis of material mechanics, is actually changed in shape before and after the load is applied. As a result of this, it is understood that a stress calculated using the general formulas of material mechanics based on the presumption that the shape of a cross-sectional material is not changed and a stress measured during an actual stress test do not coincide with each other.
In the case of a conventionally used working machine having a rectangular cross-section, there are two factors for determining a deformation strength of the cross-section, i.e., rigidity of a rectangular angle portion and rigidity of a rectangular side portion in the outward direction of a surface. When each of the two rigidities do not have sufficient strength, an excessive load applied to the rectangular angle portion causes the cross-section to deform as shown in FIG.
5
. To prevent deformation, a cross-section restraint material such as a partition wall is required for a portion in which the cross-section deforms. However, when a cross-section restraint material is provided the productivity of the working machine is lowered.
Referring now to
FIG. 3
, if the above facts are applied to arm
4
which has a hollow rectangular cross-section, rigidity of the cross-section is determined by bending rigidity of an angle portion (a) and bending rigidity (rigidity in the outward direction of surfaces) of the four surfaces (upper lateral plate
13
, lower lateral plate
14
, and left and right vertical plates
15
and
15
).
That is, influence of the bending rigidity of the surfaces and the bending rigidity of the angle portion is great with respect to the deformation of the cross-section. As shown in
FIGS. 3 and 4
, when lower plate
14
is fixed and a load F (shown with arrow F) is applied, each of the angled portions (a) are bent and deformed. Upper plate
13
, left vertical plate
15
and right vertical plate
15
are bent and deformed in the outward direction of the surfaces (thickness direction). When the thickness of the plate is reduced, reduction of rigidity in the outward direction of the surface is proportional to the third power of a ratio of reduction of the plate thickness.
For the above discussed reasons, if the thickness of each plate is reduced to increase the cross-section of arm
4
, the rigidity of the entire boom is largely lowered. As depicted in
FIG. 3
with arrows b and c, lateral load F
2
and torsion load F
3
apply force to arm
4
causing ligh

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