U.S. patent application number 11/885228 was filed with the patent office on 2008-06-19 for outdoor unit for air conditioner.
Invention is credited to Jihong Liu, Mikayo Yamanaka.
Application Number | 20080141710 11/885228 |
Document ID | / |
Family ID | 37396615 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080141710 |
Kind Code |
A1 |
Liu; Jihong ; et
al. |
June 19, 2008 |
Outdoor Unit for Air Conditioner
Abstract
An air conditioner outdoor unit including a box-shaped casing
for accommodating at least a heat exchanger, an air blower, and a
compressor. The casing has a front wall with an opening. A
reinforcement rib is arranged near the opening of the front wall to
increase compressive strength in the vicinity of the opening.
Inventors: |
Liu; Jihong; (Sakai-shi,
JP) ; Yamanaka; Mikayo; (Sakai-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
37396615 |
Appl. No.: |
11/885228 |
Filed: |
May 11, 2006 |
PCT Filed: |
May 11, 2006 |
PCT NO: |
PCT/JP2006/009465 |
371 Date: |
August 28, 2007 |
Current U.S.
Class: |
62/515 ;
312/100 |
Current CPC
Class: |
F24F 1/56 20130101; F24F
1/54 20130101; F24F 1/38 20130101 |
Class at
Publication: |
62/515 ;
312/100 |
International
Class: |
F24F 5/00 20060101
F24F005/00; A47B 81/00 20060101 A47B081/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 11, 2005 |
JP |
2005-138160 |
Claims
1. An air conditioner outdoor unit including a box-shaped casing
(1) for accommodating at least a heat exchanger (5), an air blower
(6), and a compressor (3), wherein the casing (1) has a front wall
(11F) with an opening (9), the outdoor unit being characterized by:
a reinforcement rib (10), (10a), (10b) arranged near the opening
(9) of the front wall (11F) to increase compressive strength in the
vicinity of the opening (9).
2. The air conditioner outdoor unit according to claim 1,
characterized in that the reinforcement rib (10), (10a), (10b)
extends in a vertical direction.
3. The air conditioner outdoor unit according to claim 1 or 2,
characterized in that the reinforcement rib (10), (10a), (10b)
extends upward from a side of the opening (9) and along an edge of
the opening (9).
4. The air conditioner outdoor unit according to claim 2,
characterized in that the reinforcement rib (10), (10a), (10b) has
a length set in accordance with height of the opening (9).
5. The air conditioner outdoor unit according to claim 1,
characterized by: a plurality of reinforcement ribs (10a, 10b)
arranged parallel to each other.
6. The air conditioner outdoor unit according to claim 1,
characterized in that the reinforcement rib (10), (10a), (10b ) is
formed by pressing part of the front wall (11F) so as to have a
U-shaped cross-section.
Description
TECHNICAL FIELD
[0001] The present invention relates to a casing structure for an
outdoor unit for an air conditioner.
BACKGROUND ART
[0002] An air conditioner generally includes an indoor unit
arranged inside a dwelling unit and an outdoor unit arranged
outside the dwelling unit. As shown in FIGS. 15 and 16, the outdoor
unit includes a box-shaped casing 1. A partition plate 2 partitions
the space in the casing 1 into a machine compartment 1A and a fan
compartment 1B. A compressor 3 and a receiver 4 are arranged in the
machine compartment 1A, and a heat exchanger 5 and an air blower 6
are arranged in the fan compartment 1B.
[0003] Air inlets 7 are formed in the front and side surfaces of
the casing 1. Air outlets 8 are formed in the rear surface of the
casing 1. An opening 9 used for maintenance is formed in the lower
end of the casing 1, and a cover 9a is attached to the casing 1 to
cover the opening 9 (refer to, for example, patent document 1).
[Patent Document 1] Japanese Laid-Open Patent Publication No.
2003-106565
DISCLOSURE OF THE INVENTION
[0004] Prior to shipment, the outdoor unit is stored in a warehouse
in a stacked state. Thus, impacts produced when stacking the
outdoor units and the weight of the outdoor units result in a
tendency of load being concentrated on the front wall 11F near the
opening 9 (portion X shown in FIG. 15). As a result, buckling
deformation may occur near the opening 9 of the front wall 11F when
stacking outdoor units.
[0005] The front wall 11F is a component that is separate from a
frame body 11R, which forms the rear surface of the casing 1, and a
frame plate 11Y, which is arranged near the air inlets 7. The front
wall 11F has an L-shaped cross-section and is partially narrowed
near the opening 9. Thus, the rigidity of the front wall 11F is
partially low near the opening 9. As a result, compressive load
that is produced during stacking tends to cause buckling
deformation occurring near the opening 9 of the front wall 11F. For
the above reasons, it is required that compression rigidity be
increased near the opening 9 of the front wall 11F so that buckling
deformation does not occur when stacking the outdoor units.
[0006] However, patent document 1 only disclosed a structure for
increasing the strength of a curved portion of the partition plate
and does not disclose a structure for increasing the strength of
the front wall of the casing.
[0007] It is an object of the present invention to provide an
outdoor unit for air conditioner that increases the compression
rigidity near the opening in the front wall with a reinforcement
rib and minimizing buckling deformation caused by compressive
load.
[0008] In order to solve the above problems, a first aspect of the
present invention provides an air conditioner outdoor unit
including a box-shaped casing for accommodating at least a heat
exchanger, an air blower, and a compressor. The casing has a front
wall with an opening. A reinforcement rib is arranged near the
opening of the front wall to increase compressive strength in the
vicinity of the opening.
[0009] With such a structure, the reinforcement rib increases the
compression rigidity of the front wall near the opening. Thus,
deformation caused by compressive load is less likely to occur near
the opening of the front wall when stacking outdoor units.
[0010] In the air conditioner outdoor unit, it is preferred that
the reinforcement rib extend in the vertical direction. In this
case, the reinforcement rib increases the compression rigidity of a
thin plate that forms the casing. This effectively suppresses
deformation caused by a compressive load.
[0011] In the air conditioner outdoor unit, it is preferred that
the reinforcement rib extends upward from the side of the opening
and along the edge of the opening. This entirely and effectively
reinforces the vicinity of the opening. Thus, the compression
rigidity near the opening of the front wall increases, and
deformation caused by compressive load is further suppressed.
[0012] In the air conditioner outdoor unit, it is preferred that
the length of the reinforcement rib be set in accordance with the
height of the opening. In this case, the reinforcement rib moves
the area in which buckling stress concentrates to above the opening
of the front wall. Thus, concentration of buckling stress in the
front wall at the vicinity of the opening is avoided, and
deformation caused by compressive load is further suppressed.
[0013] In the air conditioner outdoor unit, it is preferred that a
plurality of reinforcement ribs are arranged parallel to each
other. In this case, each reinforcement rib increases the
reinforcement effect near the opening of the front wall. Thus,
compression rigidity of the front wall near the opening further
increases, and deformation caused by compressive load is further
suppressed.
[0014] In the air conditioner outdoor unit, it is preferred that
the reinforcement rib is formed by pressing part of the front wall
so as to have a U-shaped cross-section. This simultaneously and
easily forms the reinforcement rib with the front wall when
manufacturing the casing. This lowers the manufacturing cost of the
product.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a perspective view showing the entire structure of
an air conditioner outdoor unit according to a first
embodiment;
[0016] FIG. 2 is a perspective view showing a front wall of a
casing;
[0017] FIG. 3 is a cross-sectional view taken along line 3-3 in
FIG. 2;
[0018] FIG. 4 is a partial plan view showing the vicinity of an
opening in the front wall;
[0019] FIG. 5 is a front view showing the front wall;
[0020] FIG. 6 is a front view showing the front wall with a
plurality of reinforcement ribs;
[0021] FIG. 7 is a front view showing a front wall for an air
conditioner outdoor unit according to a second embodiment;
[0022] FIG. 8 is a front view showing a modification of the
reinforcement rib;
[0023] FIG. 9 is a front view showing a first sample (first
analysis example) of the front wall;
[0024] FIG. 10 is a front view showing a second sample (second
analysis example) of the front wall;
[0025] FIG. 11 is a front view showing a third sample (third
analysis example) of the front wall;
[0026] FIG. 12 is a factor effect diagram for analyzing the
reinforcement effects of the reinforcement ribs in the first and
the second embodiments;
[0027] FIG. 13 is a graph showing the relationship between the rib
length and the buckling load;
[0028] FIG. 14 is a graph showing the relationship between the rib
position and the buckling value;
[0029] FIG. 15 is a perspective view showing the entire structure
of an outdoor unit for an air conditioner in the prior art; and
[0030] FIG. 16 is a cross-sectional view showing the internal
structure of the outdoor unit.
BEST MODE FOR CARRYING OUT THE INVENTION
FIRST EMBODIMENT
[0031] An air conditioner outdoor unit according to a first
embodiment of the present invention will now be described with
reference to FIGS. 1 to 6.
[0032] As shown in FIG. 1, the air conditioner outdoor unit
includes a generally box-shaped casing 1. A pair of air inlets 7
are formed in the front surface of the casing 1, and air outlets
(not shown) are formed in the rear surface. The inlets 7 are
respectively formed at an upper part and a lower part of the casing
1.
[0033] The front surface of the casing 1 includes a frame plate 11Y
arranged near the air inlets 7, and a front wall 11F having an
L-shaped cross-section. A frame body 11R having a U-shaped
cross-section and forming the rear surface of the casing 1 is
attached to the rear part of the frame plate 11Y and the front wall
11F. An opening 9 used for maintenance is formed at the lower end
of the casing 1, and a cover 9a is attached to the casing 1 so as
to cover the opening 9. The opening 9 is formed by cutting out a
corner of the front wall 11F and the frame body 11R. Thus, the
front wall 11F is defined into a lower part P1 and an upper part
P2, which is wider than the lower part P1, as shown in FIG. 2. In
the following description, the lower part P1 has a width of G2, and
the upper part P2 has a width of G1, as shown in FIG. 4.
[0034] The lower part P1 of the front wall 11F is narrow and
planar. Thus, the strength (compressive strength) is low against
compressive load. Thus, buckling deformation is likely to occur
near the opening 9 of the lower part P1 of the front wall 11F, in
particular, at portion X shown in FIG. 15 due to the impact
produced during stacking and the weight of the outdoor unit (about
90 kg in a case of trunk type).
[0035] In the present invention, a reinforcement rib 10 for
increasing the compressive strength is arranged at the lower part
P1 of the front wall 11F. The reinforcement rib 10 is extending
linearly in the vertical direction along the side edge of the
opening 9. As shown in FIGS. 3 and 4, the reinforcement rib 10 has
a U-shaped cross-section and projects toward the front from the
front wall 11F. The reinforcement rib 10 increases the bending
rigidity of the front wall 11F near the opening 9. In the following
description, the reinforcement rib 10 has a width of A, a depth of
B, and a length of C.
[0036] The reinforcement rib 10 is spaced laterally from the side
edge of the opening 9 by distance D. The length C of the
reinforcement rib 10 corresponds to the height H of the opening 9.
The length C, which corresponds to the height H of the opening 9,
is a value obtained by adding the length of distance E from the
upper end of the opening 9 to the length from a position separated
upward by distance F from the lower end of the opening 9 to the
upper end of the opening 9. The length C corresponding to the
height H of the opening 9 may be the length from a position
separated upward by distance F to the upper end of the opening
9.
[0037] The reinforcement rib 10 moves the region of stress
concentration, which results from compressive load, from the lower
part P1 to the upper part P2 of the front wall 11F. Thus, the
concentration of stress at the vicinity of the opening 9 of the
front wall 11F is avoided. As a result, buckling deformation caused
by compressive load is less likely to occur near the opening 9 of
the front wall 11F even when stacking outdoor units.
[0038] As shown in FIG. 5, it is preferred that the distance E from
the upper end of the opening 9 to the upper end of the
reinforcement rib 10 be set to be longer than as shown in FIG. 4.
In this case, the compressive strength is increased not only at
location X (see FIG. 15) at which buckling deformation is likely to
occur but also in a wide range near the opening 9 of the front wall
11F.
[0039] The reinforcement rib 10 is formed to have a U-shaped
cross-section by pressing part of the front wall 11F of the casing
1. In this case, the reinforcement rib 10 is easily formed at the
same time as when forming the front wall 11F when manufacturing the
casing 1.
[0040] The first embodiment has the advantages described below.
[0041] (1) The compressive strength near the opening 9 of the front
wall 11F is greatly increased.
[0042] (2) Since the compressive strength near the opening 9 of the
front wall 11F is increased, more products may be stacked together
for storage. This increases the efficiency of a warehouse. Further,
buckling deformation resulting from compressive load is less likely
to occur near the opening 9 of the casing 1 when delivering the
products.
[0043] (3) The compressive strength near the opening 9 of the front
wall 11F is increased. Thus, the plate thickness of the front wall
11F may be decreased to 0.7 mm to 0.6 mm. This reduces the used
material and lowers the material cost reduces. Furthermore, the
formation quality of the product may be improved.
[0044] (4) Since the compressive strength near the opening 9 of the
front wall 11F is increased, the used amount of material for
packaging the product may be reduced.
SECOND EMBODIMENT
[0045] An air conditioner outdoor unit according to a second
embodiment of the present invention will now be described with
reference to FIG. 7 and FIG. 8. Detailed description of portions in
the second embodiment that are similar to the first embodiment will
be omitted.
[0046] As shown in FIGS. 7 and 8, a reinforcement rib 10, which
extends along the side edge of the opening 9, includes an upper end
portion extending along the corner of the opening 9. The
reinforcement rib 10 increases the bending rigidity of the front
wall 11F near the opening 9.
[0047] Unlike the first embodiment, in the reinforcement rib 10
shown in FIG. 7, the upper end portion of the reinforcement rib 10
is curved along the corner of the opening 9. In the reinforcement
rib 10 shown in FIG. 8, the upper end portion of the curved
reinforcement rib 10 extends laterally along the upper side edge of
the opening 9. The reinforcement rib 10 reinforces most of the
opening 9 in the front wall 11F.
[0048] The reinforcement effect in the case of FIG. 7 is assumed to
be the same as the first embodiment, and the reinforcement effect
in the case of FIG. 8 is assumed to be higher than in the case of
FIG. 7.
(Study of Reinforcement Effect)
[0049] In relation to the reinforcement rib 10 of the first
embodiment (see FIGS. 1 to 6) and the reinforcement rib 10 of the
second embodiment (see FIGS. 7 and 8), an arcuate reinforcement rib
10 arranged only at the corner of the opening 9 as shown in FIG. 9
was used as a first sample. That in which the upper end of A
reinforcement rib 10 that laterally extends the upper end of the
reinforcement rib 10 of FIG. 9 along the upper side edge of the
opening 9 as shown in FIG. 10 used as a second sample. Furthermore,
a reinforcement rib 10 (lateral rib) extending in the lateral
direction along the upper side edge of the opening 9 as shown in
FIG. 11 was used as a third sample. The reinforcement effects by
the reinforcement rib 10 of the first and the second embodiments
were studied from the standpoint of quality engineering including
comparison among first to third samples.
(Influence of Dimension and Position of the Reinforcement Rib 10 on
the Compressive Strength)
[0050] First, the reinforcement effect of the reinforcement rib 10
of the first embodiment was studied.
[0051] During the study, the dimensions (width A, depth B, length C
of FIG. 3 and FIG. 4) and the position (distance D in FIG. 4) of
the reinforcement rib 10 were assumed as design variables
(evaluation parameters), and three patterns (standard values 1 to
3) were set for standard values of each design variable. The design
variable and each standard value are shown in table 1. The standard
values 1, 2, 3 of each design variable A to D were allocated to an
L9 orthogonal experiment table of table 2. The buckling load (kgf)
for when stacking the outdoor units were obtained for analyses No.
1 to No. 9 in which the standard values were combined. The results
are shown in table 2.
TABLE-US-00001 TABLE 1 Rib Dimension and Standard value Position
(mm) 1 2 3 A (Width) 4.0 5.0 6.0 B (Depth) 1.0 1.5 2.0 C (Length)
100.0 142.0 184.0 D (Distance) 48.0 33.0 18.0
TABLE-US-00002 TABLE 2 Analysis Combination of Standards Buckling
No. A B C D Load (kgf) 1 1 1 1 1 545.3 2 1 2 2 2 616.0 3 1 3 3 3
721.2 4 2 1 2 3 595.9 5 2 2 3 1 642.4 6 2 3 1 2 624.1 7 3 1 3 2
621.3 8 3 2 1 3 624.1 9 3 3 2 1 703.6 No Ribs 524.2
[0052] Table 3 is a dispersion analysis table for the calculation
results of table 2. Table 4 is a dispersion analysis table for a
residual group.
TABLE-US-00003 TABLE 3 Source S f V F0 S' P (%) A 0.2678 2 0.1339
0.2678 6.38 B 2.5585 2 1.2793 2.5585 60.92 C 1.1931 2 0.5966 1.1931
28.41 D 0.1805 2 0.0903 0.1805 4.30 e 0 0 0 -- 0 0 T 4.1999 8
4.1999 100.00
TABLE-US-00004 TABLE 4 Source S f V F0 S' P (%) A 0.2678 2 0.1339
1.48 0.0873 2.08 B 2.5585 2 1.2793 14.17 2.378 56.62 C 1.1931 2
0.5966 6.61 1.0126 24.11 e 0.1805 2 0.0903 -- 0.722 17.19 T 4.1999
8 4.1999 100.00
[0053] FIG. 12 is a factor effect diagram of each design variable A
to D. In FIG. 12, the vertical axis indicates the SN ratio, and the
horizontal axis indicates the design variable (A(width), B(depth),
C(length), D(distance) from the left). In the factor effect
diagram, the reinforcement effect increases as the SN ratio
increases, and the degree of contribution to the reinforcement
effect increases as the inclination of the design variable
increases. Table 5 shows the SN ratio corresponding to each
standard value (1-3) of each design variable.
TABLE-US-00005 TABLE 5 Design Variable Standard value (Factor)
Title 1 2 3 A (Width) 55.8956 55.8548 56.2394 B (Depth) 55.3576
55.9510 56.6712 C (Length) 55.5146 56.0808 56.3945 D (Distance)
55.9454 55.8546 56.1899
[0054] From the factor effect diagram of FIG. 12, the predicted
value of the SN ratio is 57.5051 dB, or 749.9 kgf when converted to
the buckling load value, under the optimum condition in which the
standard values of each design variable at which the SN ratio
becomes maximum are combined. The calculated value (analytic value)
of the buckling load when the optimum standard values are combined
is 741.3 kgf, which is substantially the same as the predicted
value of the SN ratio. According to this result, the result
obtained using the orthogonal table was verified as being correct
and reliable. The predicted value and the analytic value are shown
in table 6.
TABLE-US-00006 TABLE 6 Analytic Value Predicted value (Study) SN
Ratio (dB) Load Value (kgf) Load Value (kgf) 57.5051 749.9
741.3
[0055] The followings are apparent from the above result.
[0056] (1) A large reinforcement effect is obtained by the
reinforcement rib (vertical rib) extending in the vertical
direction.
[0057] (2) The depth B of the reinforcement rib 10 contributes the
most, and the length C of the reinforcement rib 10 contributes the
next most to the reinforcement effect. The contribution to the
reinforcement strength of the width A and the spaced distance D of
the reinforcement rib 10 are both small. However, if the
reinforcement rib 10 is too deep, the formation quality and the
outer appearance quality of the product may be decreased. Due to
such reasons, the depth B of the reinforcement rib 10 is preferably
between 1.0 mm and 3.0 mm, and the width A of the reinforcement rib
10 is preferably between 4.0 mm and 6.0 mm.
[0058] (3) Since the length C of the reinforcement rib 10 also
greatly contributes to the reinforcement effect, a large
reinforcement effect is obtained by elongating the reinforcement
rib 10.
[0059] According to such results, the reinforcement rib 10 shown in
FIGS. 1 to 4 of the first embodiment is effective in increasing the
compressive strength, and the reinforcement rib 10 shown in FIG. 5
is further effective in increasing the compressive strength.
Furthermore, it can be easily assumed that a greater reinforcement
effect is obtained by arranging two reinforcement ribs 10 in
parallel as shown in FIG. 6.
[0060] The reinforcement effect of one vertical rib and the
reinforcement effect of two vertical ribs were then compared. A
case in which there was only one vertical rib is represented by
(S1) (see FIG. 1 to FIG. 5), a case in which there are two vertical
ribs is represented by (S2) (see FIG. 6), and a case in which there
is only the horizontal rib is represented by (S3) (see FIG. 11).
The buckling load (kgf) of when the length C of each reinforcement
rib 10 was 0 mm, 100 mm, 142 mm, 184 mm, 226 mm, and 268 mm was
respectively obtained for (S1) to (S3). The results are shown in
table 7.
TABLE-US-00007 TABLE 7 Length of rib (mm) 0.0 100.0 142.0 184.0
226.0 268.0 Buckling S1 524.2 618.9 675.0 741.0 848.8 852.6 Load S2
524.2 -- -- -- 1002.4 -- (kgf) S3 524.2 542.0 580.0 634.5 672.2
--
[0061] The relationship between the length of the rib and the
buckling load was respectively obtained for (S1) and (S3). The
results are shown in the graph of FIG. 13.
[0062] From the graph of FIG. 13, the reinforcement effect of the
vertical rib was found to be higher than the reinforcement effect
of the horizontal rib. Furthermore, the reinforcement effect of two
vertical ribs was found to be higher than the reinforcement effect
of one vertical rib from the result of table 7. Moreover, the
reinforcement effect was found to increase as the length of the rib
increases in the case of the vertical rib. The reinforcement effect
of the horizontal rib was found to be higher, although slightly,
when the rib length became greater than or equal to a predetermined
dimension.
[0063] Similar effects are obtained by the reinforcement rib 10 of
FIG. 9 and the reinforcement rib 10 of FIG. 10. In the case of the
reinforcement rib 10 of FIG. 11, the reinforcement effect was found
to become higher as the rib became longer, or the rib portion
corresponding to the lower part P1 of the front wall 11F became
longer.
[0064] From the above results, the bending rigidity in the vertical
direction and the horizontal direction are both increased, and thus
the compressive strength is further effectively increased by the
reinforcement rib 10 of FIG. 7 that combines the reinforcement rib
10 of FIG. 1 to FIG. 5 and the reinforcement rib 10 of FIG. 9 or
the reinforcement rib 10 of FIG. 8 that combines the reinforcement
rib 10 of FIGS. 1 to 5 and the reinforcement rib 10 of FIG. 10.
[0065] The reinforcement rib 10 of FIG. 7 shown in the second
embodiment is represented by (S4), the reinforcement rib 10 of FIG.
8 is represented by (S5), the reinforcement rib 10 of FIG. 9 is
represented by (S6), and the reinforcement rib 10 of FIG. 10 is
represented by (S7). The buckling loads (kgf) for (S4) to (S7) were
respectively obtained. The results are shown in table 8 along with
the case for no ribs.
TABLE-US-00008 TABLE 8 Rib Arrangement None S6 S4 S7 S5 Buckling
524.2 543.6 706.7 562.9 831.7 Load (kgf)
[0066] From the results of table 8, a large reinforcement effect
was obtained for (S4) and (S5). Although small, a reinforcement
effect was obtained for (S7). However, sufficient reinforcement
effect was not obtained for (S6).
[0067] With regarding to the reinforcement ribs 10, 10a, 10b of
FIG. 1 to FIG. 6 and the reinforcement rib 10 of FIG. 7 and FIG. 8,
the distance D from the opening 9 is set to an appropriate
dimension from the ratio with respect to the width G2 of the lower
part P1 of the front wall 11F so as to obtain compressive strength
that is greater than or equal to a predetermined value.
[0068] FIG. 14 is a graph showing a relationship between the width
G2 of the lower part P1 of the front wall 11F and the spaced
distance D from the opening 9 of the reinforcement rib. From the
graph of FIG. 14, sufficient compressive strength was found to be
obtained by setting the distance D in the range of 5% to 40% of the
width G2 of the lower part P1 of the front wall 11F.
[0069] Furthermore, when the width G2 of the lower part P1 of the
front wall 11F is narrower than the width A of the opening 9 (black
circle in FIG. 14), the range of the ratio (D/G2) of the width G2
and the distance D at which the reinforcement effect is sufficient
was found to be narrower than when the width G2 is the same or
greater than the width W of the opening 9 (square or triangle of
FIG. 14). The reinforcement effect was also found to significantly
lower when the width G2 is constant and the spaced distance D is
reduced.
[0070] If the reinforcement effect is small, the buckling position
exists at the lower part P1 of the front wall 11F adjacent to the
opening 9 in the same manner as the case of no rib shown in FIG.
15. However, if the reinforcement effect is large, the buckling
position moves above the reinforcement rib 10, that is, to the
upper part P2 of the front wall 11F having a width that is wider
than the lower part P1.
(General Overview of the Results of the Study)
[0071] (1) The reinforcement effect of the horizontal rib is
extremely limited compared to the reinforcement effect of the
vertical rib in the reinforcement ribs 10, 10a, and 10b. Thus, the
reinforcement effect further increases by combining the horizontal
rib and the vertical rib.
[0072] (2) When the length of the vertical rib is greater than or
equal to the height H of the opening 9, deformation due to the
compressive load is effectively suppressed compared to when the
length is less than the height H of the opening 9. Therefore, it is
preferable that the length of the vertical rib be longer than the
height H of the opening 9.
[0073] (3) The reinforcement effect is barely obtained when the
length of the horizontal rib is the same as the width W of the
opening 9. However, the reinforcement effect further increases if
the length of the horizontal rib is longer than the width W of the
opening 9. Thus, the length of the horizontal rib is preferably
longer than the width W of the opening 9.
[0074] (4) The reinforcement effect is barely obtained even if an
arcuate reinforcement rib is arranged at the corner of the opening
9. However, the reinforcement effect further increases by combining
the reinforcement rib and the vertical rib.
[0075] (5) The compressive strength during stacking is greatly
increased when a plurality of vertical ribs are arranged under the
above conditions.
* * * * *