Excavating – Miscellaneous
Reexamination Certificate
2000-01-18
2003-01-21
Novosad, Christopher J. (Department: 3671)
Excavating
Miscellaneous
C212S347000
Reexamination Certificate
active
06508019
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a boom of a bucket type excavator such as a hydraulic shovel and a method for making such boom.
BACKGROUND OF THE INVENTION
As shown in
FIG. 1
, in a hydraulic shovel of a bucket type excavator, an upper vehicle body
2
is turnably mounted on a lower running body
1
, a boom
3
is vertically swingably mounted to the upper vehicle body
2
, an arm
4
is vertically oscillatably mounted to the boom
3
, and a bucket
5
is vertically oscillatably mounted to a tip end of the arm
4
. A boom cylinder
6
is connected between the upper vehicle body
2
and the boom
3
, an arm cylinder
7
is connected between the boom
3
and the arm
4
, and a bucket cylinder
8
is connected between the arm
4
and the bucket
5
.
The hydraulic shovel vertically swings the boom
3
, the arm
4
and vertically oscillates the bucket
5
, and at the same time, laterally turns the upper vehicle body
2
, for carrying out operations such as excavation and loading to a dump truck.
As shown in
FIG. 2
, the boom
3
comprises a boom body
10
of boomerang shape as viewed from side, a vehicle body-mounting bracket
11
connected to one longitudinal end of the boom body
10
, and an arm-connection bracket
12
connected to the longitudinally other end of the boom body
10
. As shown in
FIG. 3
, the boom
10
is formed into a hollow structure of rectangular cross section in which an upper lateral plate
13
, a lower lateral plate
14
, and left and right vertical plates
15
and
15
are welded at right angles to one another so as to reduce the boom body
10
in weight.
At the time of excavation, the boom
3
is driven in the vertical direction for inserting the bucket into earth and sand, a vertical load F
1
is applied to the boom
3
as shown in FIG.
1
. When the excavator turns around the upper vehicle body
2
for loading the dipped up earth and sand onto a dump truck or the like, a lateral load F
2
, and a torsion load F
3
are applied to the boom
3
. Therefore, the boom
3
is formed such that the boom
3
can withstand the loads and is not deformed. For example, against the vertical load F
1
, a height H is increased as compared with a width W as shown in FIG.
3
. Against the lateral load F
2
and the torsion load F
3
, a partition wall
16
is connected such that an opened box-like structure is formed as shown in
FIG. 3
, and a vertical plate of a boom cylinder boss
18
is provided with a cross section restraint material such as a pipe
17
(
FIG. 4
) for dispersing the torsion force and load.
In the hydraulic shovel, a counter weight
9
is provided at a rear portion of the upper vehicle body
2
in accordance with the excavation ability of a working machine comprising the upper vehicle body
2
which is a main portion, the boom
3
, the arm
4
and the bucket
5
. If the working machine is reduced in weight, the weight of the counter weight
9
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 the boom
3
, the arm
4
and the bucket
5
is reduced in weight, it is possible to increase the volume of the bucket correspondingly and thus to increase the working load capacity.
Further, the boom
3
is vertically swung by the boom cylinder
6
, and a portion of a thrust of the boom cylinder
6
supports the weight of the boom
3
. Therefore, if the boom
3
is reduced in weight, the thrust of the boom cylinder
6
effectively can be utilized as the vertical swinging force of the boom
3
.
In general, when considering a strength of the working machine of the bucket type excavator, as the simplest method, a 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, bending stress s, and shearing stress t generating on a cross section can be obtained by the following general formulas (1) and (2):
s=M/Z
(1)
(wherein, s: bending stress generating on a cross section, M: bending moment applied to the cross section, Z: cross section coefficient)
t=T/
2
At
(2)
(wherein, t: shearing stress, 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 a stress test is carried out, the result of the test is different from a stress value calculated during the evaluation in many cases. For this reason, in recent years, simulation by a computer using finite element method (FEM) is employed as the evaluation method for enhancing the precision of the stress evaluation. If the stress is calculated using the FEM simulation, it can be found that a cross section of a working machine which was considered as beam and axis of material mechanics is changed in shape before and after the load is applied. From this fact, it can be understood that a stress calculated using the general formulas of the material mechanics derived based on a presumption that a shape of a cross section is not changed and a stress measured when a stress test is actually carried out 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 rigidity does not have sufficient strength against a load, the cross section is deformed as shown in
FIG. 5
, and an excessive load is applied to the rectangular angle portion. To prevent those, a cross section restraint material such as a partition wall is required for a portion in which its cross section is deformed, but if such material is provided, productivity of the working machine is lowered.
If the above facts are applied to the boom
3
, the boom
3
is of hollow shape of rectangular cross section as shown in
FIG. 3
, rigidity of the cross section is determined by bending rigidity of an angle portion a, bending rigidity (rigidity in the outward direction of surfaces) of the four surfaces (the upper lateral plate
13
, the lower lateral plate
14
, and the 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. For example, in
FIG. 3
, when the lower plate
14
is fixed, and a load F shown with the arrow F is applied, as shown in
FIG. 5
schematically, each of the angle portions a is bent and deformed, the upper plate
13
and the left and right vertical plates
15
and
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 these reasons, if the thickness of each plate is reduced to increase the cross section, when the lateral load F
2
and the torsion load F
3
are applied to the boom
3
, a deformation is generated in the light weight boom
3
as shown with the arrows b and c in
FIG. 3
, and the rigidity of the entire boom is largely lowered. Therefore, the above-described cross section restraint material such as the partition wall
16
and the pipe
17
must be reinforced, the weight of the boom is increased because of the reinforc
Itoh Tatsushi
Masumoto Nobuyoshi
Sasaki Hidetoshi
Tanaka Toshio
Darby & Darby
Komatsu Ltd.
Novosad Christopher J.
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