Dump truck cargo box

Abstract

In a dump truck cargo box having a roughly U-shaped cross-section, the objective is to prevent cracking at the welded joints caused by defects in the welding of stiffeners on the tailgate of the cargo box, without significantly compromising the aesthetic appeal of the cargo box. [Solution] The left stiffener 33L and the right stiffener 33R are fixed to both sides of the rear surface of the panel 31, respectively, and extend in the vertical direction. The lower stiffener 34 is fixed to the lower part of the rear surface of the panel and extends in the vehicle width direction. The left diagonal stiffener 35L and the right diagonal stiffener 35R are fixed to the rear surface of the panel so as to connect the lower ends of the left and right stiffeners to both ends of the lower stiffener, respectively. The lower ends of the left and right diagonal stiffeners overlap the ends of the lower stiffener on the rear side in the vehicle longitudinal direction. The lower end faces 351 of the left and right diagonal stiffeners and the rear faces 341 on both ends of the lower stiffener are fillet welded to each other.

Description

Technical Field

[0001] The present invention relates to a cargo box of a dump truck.

Background Art

[0002] Conventionally, it has been practiced to store earth and sand, construction waste, waste, etc. in a cargo box and transport them with a dump truck. As the shape of the cargo box of such a dump truck, there is a type called a square-bottom type with a U-shaped cross-section like the cargo box described in FIGS. 1 and 2 of Patent Document 1, and a type called a round-bottom type with a U-shaped cross-section like the cargo box described in FIG. 1 of Patent Document 2. As shown in FIG. 8, the square-bottom type cargo box 9 secures the strength of the cargo box 9 by providing a large number of stiffeners 90 on the side surface and the tailgate of the cargo box. The appearance of the square-bottom type cargo box 9 gives an impression of being angular and strong. As shown in FIG. 9, the round-bottom type cargo box 91 realizes weight reduction by minimizing the stiffeners by adopting a U-shaped cross-section. It is possible to secure a larger loading weight by the amount of weight reduction. The appearance of the round-bottom type cargo box 91 gives a neater impression compared to the square-bottom type cargo box 9.

[0003] The stiffeners 90 of the square-bottom type cargo box 9 and the stiffeners 93 of the tailgate 92 of the round-bottom type cargo box 91 are welded at the connection parts between the stiffeners. Butt welding is used for the connection part 94 between the stiffeners 93 of the round-bottom type cargo box 91. By using butt welding, the stiffeners 93 can be continuously welded without a step or the like between the stiffeners 93. As a result, the appearance of the tailgate can be made neater, and a neat aesthetic impression can be given to the viewer looking at the cargo box of the dump truck.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] Incidentally, in the case of butt welding, it is necessary to weld not only the surface of the steel plate S but the entire thickness direction, as shown in the weld w in Figure 10(a). However, as shown in the weld w' in Figure 10(b), sometimes only the area near the surface of the steel plate S can be welded, leaving an unwelded portion in the thickness direction, resulting in welding defects. Furthermore, in the case of butt welding, it is difficult to confirm how far in the thickness direction the welding has been done, making it difficult to adjust the welding output so that the entire thickness direction can be welded. For example, if the welding output is increased too much during butt welding, the weld may penetrate through in the thickness direction, creating a void. Conversely, if the welding output is too low, only the area near the surface can be welded, as shown in the weld w' in Figure 10(b). If such a defect in butt welding occurs at the welded portion 94 of the stiffener 93 of the tailgate 92, the repeated impact applied to the tailgate 92 when closing it may cause cracks to form at the welded portion 94 of the stiffener 93. If cracks occur in the welded joints of the stiffener 93's connection point 94, it will affect the durability of the tailgate 92.

[0006] This invention was conceived in view of the above-mentioned problems, and aims to provide a dump truck cargo box in which the cargo box body has a substantially U-shaped cross-section, that can prevent cracking at the welded joints due to defects in the welding of the stiffeners of the tailgate without significantly impairing the aesthetic appearance of the cargo box. [Means for solving the problem]

[0007] A cargo box for a dump vehicle according to a first aspect of the present invention comprises a cargo box body having a substantially U-shaped cross-section, and a tailgate rotatably mounted downward at the rear end of the cargo box body. The tailgate has a panel, a left stiffener and a right stiffener, a lower stiffener, a left diagonal stiffener and a right diagonal stiffener. The left stiffener and the right stiffener are fixed to both sides of the rear surface of the panel, respectively, and extend in the vertical direction. The lower stiffener is fixed to the lower part of the rear surface of the panel and extends in the vehicle width direction. The left diagonal stiffener and the right diagonal stiffener are fixed to the rear surface of the panel so as to connect the lower ends of the left stiffener and the right stiffener with both ends of the lower stiffener, respectively, and each extends in a direction that slopes downward toward the vehicle center. The lower ends of the left and right diagonal stiffeners overlap the rearward side of the lower stiffener in the vehicle's longitudinal direction relative to both ends. The lower end faces of the left and right diagonal stiffeners and the rear faces of both ends of the lower stiffener are fillet welded to each other.

[0008] A second aspect of the present invention relates to a cargo box for a dump vehicle, comprising a cargo box body having a substantially U-shaped cross-section, and a tailgate attached to the rear end of the cargo box body so as to be rotatable downward. The tailgate comprises a panel, a left stiffener and a right stiffener, a lower stiffener, a left diagonal stiffener and a right diagonal stiffener. The left and right stiffeners are fixed to both sides of the rear surface of the panel, respectively, and extend in the vertical direction. The lower stiffener is fixed to the lower part of the rear surface of the panel and extends in the vehicle width direction. The left diagonal stiffener and the right diagonal stiffener are fixed to the rear surface of the panel so as to connect the lower ends of the left and right stiffeners to both ends of the lower stiffener, respectively, and each extends downward in a direction that inclins toward the vehicle center. The lower ends of the left diagonal stiffener and the right diagonal stiffener overlap the front side in the vehicle longitudinal direction with respect to both ends of the lower stiffener. The end faces of the lower stiffener and the lower rear faces of the left diagonal stiffener and the right diagonal stiffener are fillet welded to each other.

[0009] In the first or second embodiment of the dump truck cargo box, the connection between the left diagonal stiffener and the right diagonal stiffener and the lower stiffener is fillet-welded. Compared to cases where butt welding, which is more difficult to perform than fillet welding, is used at the connection point, the rate of welding defects can be suppressed. In particular, since the connection point is located at the bottom of the tailgate and receives a relatively large impact when the tailgate is closed, the dump truck cargo box with the above configuration can reduce the possibility of cracks or other defects occurring at the welded area compared to cases where the connection point is butt-welded. Furthermore, in the first or second embodiment of the dump truck cargo box, the step difference at the connection point between the left diagonal stiffener and the right diagonal stiffener and the lower stiffener is small, about the thickness of the stiffener plate, so the above effects can be obtained without significantly impairing the aesthetic appearance of the cargo box.

[0010] A third aspect of the present invention is a dump truck cargo box according to the first aspect, wherein the upper end of the left diagonal stiffener overlaps the lower end of the left stiffener on the rear side in the vehicle's longitudinal direction. The upper end of the right diagonal stiffener also overlaps the lower end of the right stiffener on the rear side in the vehicle's longitudinal direction. The upper end face of the left diagonal stiffener and the rear end of the lower end of the left stiffener are fillet welded to each other. The upper end face of the right diagonal stiffener and the rear end of the lower end of the right stiffener are fillet welded to each other.

[0011] The cargo box of a dump truck according to the fourth aspect of the present invention is the cargo box of a dump truck according to the second aspect, wherein the upper end of the left diagonal stiffener overlaps the lower end of the left stiffener on the front side in the vehicle's longitudinal direction. The upper end of the right diagonal stiffener also overlaps the lower end of the right stiffener on the front side in the vehicle's longitudinal direction. The lower end face of the left stiffener and the upper rear face of the left diagonal stiffener are fillet welded to each other. The lower end face of the right stiffener and the upper rear face of the right diagonal stiffener are fillet welded to each other. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a cargo box for a dump truck that can prevent cracking at the welded joints caused by defects in the welding of the stiffeners of the tailgate, without significantly compromising the aesthetic appeal of the cargo box. [Brief explanation of the drawing]

[0013] [Figure 1] This is a side view of a dump vehicle equipped with a cargo box according to an embodiment of the present invention. [Figure 2] This is a perspective view of the cargo box of a dump vehicle according to an embodiment of the present invention. [Figure 3] This is a rear view of the tailgate of the cargo box of a dump vehicle according to an embodiment of the present invention. [Figure 4] This is a cross-sectional view AA in Figure 3. [Figure 5] (a) is an enlarged view of section A in Figure 3, and (b) is an enlarged view of section B in Figure 3. [Figure 6] This is a rear view of the tailgate of another embodiment. [Figure 7] (a) is an enlarged view of section C in Figure 6, and (b) is an enlarged view of section D in Figure 6. [Figure 8] This is a perspective view of a conventional cargo box with a square bottom. [Figure 9] This is a perspective view of a conventional round-bottomed cargo box. [Figure 10] These are cross-sectional views of a butt weld; (a) shows a cross-sectional view when the butt weld is performed correctly, and (b) shows a cross-sectional view when a defect occurs in the butt weld. [Modes for carrying out the invention]

[0014] Hereinafter, the cargo box 1 of the dump vehicle 10 according to an embodiment of the present invention will be described with reference to the drawings. In this specification, the directions of front, rear, up, down, left, and right are defined with reference to the dump vehicle 10 to which the cargo box 1 is attached. Before describing the cargo box 1, the dump vehicle 10 equipped with the cargo box 1 will be briefly described.

[0015] As shown in Fig. 1, the dump truck 10 is composed of a round-bottom type loading box 1, a cab 11, a chassis frame 12, a sub-frame 13, and a tilting device (not shown). The loading box 1 is vertically rotatably connected to the rear part of the sub-frame 13. The loading box 1 is tilted by the tilting device from the horizontal state (the state shown by the solid line in Fig. 1) to the dump state (the state shown by the two-dot chain line in Fig. 1), or from the dump state to the horizontal state.

[0016] As shown in Figs. 1 and 2, the loading box 1 includes a loading box body 2 and a tailgate 3. The loading box body 2 has a substantially U-shaped cross section. The tailgate 3 is attached to the rear end of the loading box body 2 by a hinge mechanism 4 so as to be rotatable downward. When the loading box 1 is tilted by the tilting device, the tailgate 3 opens and the earth and sand etc. inside the loading box 1 can be discharged. The loading box 1 is provided with a locking mechanism 5 for locking the tailgate 3 to the loading box body 2.

[0017] As shown in Fig. 2, the loading box body 2 has a bottom plate 21, a pair of side plates 22 welded to both ends 21a in the vehicle width direction of the bottom plate 21, and a front plate 23 extending vertically from the front end of the bottom plate 21. The bottom plate 21 is made of, for example, a wear-resistant steel plate, and the steel plate is at least once bent at an obtuse angle into a V shape so that folds extend in the longitudinal direction. Note that the bottom plate 21 is not limited to a steel plate subjected to bending such as V bending, and a steel plate without bending may be used for the bottom plate 21.

[0018] The pair of side plates 22 are welded to the both side portions in the longitudinal direction of the bottom plate 21 with a part thereof overlapped. The side plate 22 is formed of a wear-resistant steel plate and is formed by being bent into a V shape in multiple stages at an obtuse angle by a plurality of longitudinal folds. Thus, the loading box body 2 has a substantially U-shaped cross section by the bottom plate 21 and the side plates 22 bent by the folds. By making the loading box body 2 have a substantially U-shaped cross section, when the loading box 1 is tilted to discharge earth and sand etc., the earth and sand etc. gather at the central portion in the width direction of the loading box 1, so that the distribution is not uneven and it is easy to ensure the vehicle stability during discharge.

[0019] As shown in Figures 2 and 3, the tailgate 3 includes a panel 31, an upper stiffener 32, a left stiffener 33L, a right stiffener 33R, a lower stiffener 34, a left diagonal stiffener 35L, and a right diagonal stiffener 35R.

[0020] As shown in Figure 3, the panel 31 has a hexagonal shape with the lower two corners of a rectangle cut out to match the cross-sectional shape of the cargo box body 2. The panel 31 includes a left vertical side and a right vertical side that extend vertically at both ends, an upper horizontal side that extends in the vehicle width direction at the upper end, a lower horizontal side that extends in the vehicle width direction at the lower end and is shorter than the upper horizontal side, and a right diagonal side and a left diagonal side that connect the lower ends of the left vertical side and the right vertical side to both ends of the lower horizontal side, respectively. An upper stiffener 32, a left stiffener 33L, a right stiffener 33R, a lower stiffener 34, a left diagonal stiffener 35L, and a right diagonal stiffener 35R are fixed to the rear surface of the panel 31. These stiffeners are provided to reinforce the panel 31.

[0021] The upper stiffener 32 is positioned along the upper transverse edge on the rear surface of the panel 31 and extends in the vehicle width direction. The upper stiffener 32 is fixed to the rear surface of the panel 31 by welding. As shown in Figure 4, the upper stiffener 32 has a roughly U-shaped cross-section and is welded to the panel at two locations, upper and lower. The upper welded portion of the upper stiffener 32 is a portion that is bent downward so as to overlap with the panel 31, and this welded portion is fixed to the panel 31 by a single flare weld. The lower welded portion of the upper stiffener 32 is a portion that is in contact with the panel 31 at a right angle, and this welded portion is fixed to the panel 31 by a fillet weld.

[0022] The left stiffener 33L and the right stiffener 33R are positioned along the left and right vertical edges, respectively, on the rear surface of panel 31, and extend vertically. The left stiffener 33L and the right stiffener 33R are fixed to panel 31 by welding. Together with panel 31, the left stiffener 33L and the right stiffener 33R each form a hollow trapezoidal cross-section. The lower base of the trapezoidal cross-section is formed by panel 31, and the rest of the trapezoidal cross-section is formed by the left stiffener 33L and the right stiffener 33R. The lower base of the trapezoidal cross-section and one leg of the trapezoidal cross-section (the part that forms the outer circumferential surface of the tailgate 3) are at approximately a right angle. Fillet welds are performed at the portions where the left stiffener 33L and the right stiffener 33R are in contact with panel 31. The upper end faces of the left stiffener 33L and the right stiffener 33R are fillet welded to the upper stiffener 32. As shown in Figure 3, the left and right sides of the left stiffener 33L and the right stiffener 33R have the same length, and the left and right upper and lower end faces of the left stiffener 33L and the right stiffener 33R are formed perpendicular to the vertical direction.

[0023] The lower stiffener 34 is positioned along the lower transverse edge on the rear surface of the panel 31 and extends in the vehicle width direction. The lower stiffener 34 is fixed to the panel 31 by welding. As shown in Figure 4, the lower stiffener 34, together with the panel 31, forms a hollow trapezoidal cross-section. The lower base of the trapezoidal cross-section is formed by the panel 31, and the portion of the trapezoidal cross-section other than the lower base is formed by the lower stiffener 34. The lower base of the trapezoidal cross-section and one leg of the trapezoidal cross-section (the part that forms the outer circumferential surface of the tailgate 3) are at approximately a right angle. The lower stiffener 34 is welded to the panel 31 at two points, upper and lower, where it contacts the panel 31. In Figure 4, the lower welded portion of the lower stiffener 34 is a portion that is bent upward so as to overlap with the panel 31, and this welded portion is fixed to the panel 31 by a single flare weld. The upper welded portion of the lower stiffener 34 is the part that is in diagonal contact with the panel 31, and this welded portion is fixed to the panel 31 by fillet welding. As shown in Figure 3, the length of the upper surface of the lower stiffener 34 in the vehicle width direction is the same as the length of the lower surface of the lower stiffener 34 in the vehicle width direction, and both end faces of the lower stiffener 34 are formed perpendicular to the vehicle width direction.

[0024] The left diagonal stiffener 35L and the right diagonal stiffener 35R are positioned along the left and right diagonal edges, respectively, on the rear surface of panel 31, and each extends downward in a direction that slopes toward the vehicle center. The left diagonal stiffener 35L and the right diagonal stiffener 35R are fixed to the rear surface of panel 31 by welding, connecting the lower ends of the left stiffener 33L and the right stiffener 33R to both ends of the lower stiffener 34. The left diagonal stiffener 35L and the right diagonal stiffener 35R each form a hollow trapezoidal cross-section together with panel 31. The lower base of the trapezoidal cross-section is formed by panel 31, and the parts of the trapezoidal cross-section other than the lower base are formed by the left diagonal stiffener 35L and the right diagonal stiffener 35R. The lower base of the trapezoidal cross-section and one leg of the trapezoidal cross-section (the part that forms the outer circumferential surface of the tailgate 3) are at approximately a right angle. The portions where the left-angled stiffener 35L and the right-angled stiffener 35R contact the panel 31 are fillet welded. As shown in Figure 3, the length of the side of the left-angled stiffener 35L and the right-angled stiffener 35R that faces the inside of the tailgate 3 (the length in the direction in which the left-angled stiffener 35L and the right-angled stiffener 35R extend) is shorter than the length of the side of the side facing the outside of the tailgate 3 (the length in the direction in which the left-angled stiffener 35L and the right-angled stiffener 35R extend). For this reason, both end faces of the left-angled stiffener 35L and the right-angled stiffener 35R are inclined, not perpendicular to the direction in which the left-angled stiffener 35L and the right-angled stiffener 35R extend.

[0025] As shown in Figure 5(a), the lower end of the left diagonal stiffener 35L is positioned to overlap the left end (the left end and its vicinity in this embodiment) of the lower stiffener 34 on the rear side in the front-rear direction of the dump vehicle 10. Similarly, the lower end of the right diagonal stiffener 35R is positioned to overlap the right end (the right end and its vicinity in this embodiment) of the lower stiffener 34 on the rear side in the front-rear direction of the dump vehicle 10. The lower end face 351 of the left diagonal stiffener 35L and the rear face 341 on the left end (the vicinity of the left end in this embodiment) of the lower stiffener 34 are fillet welded w1. The lower end face of the right diagonal stiffener 35R and the rear face 341 on the right end (the vicinity of the right end in this embodiment) of the lower stiffener 34 are similarly fillet welded w1 w1. Fillet welds w1 are performed over the entire area of ​​the lower end face 351 of the left diagonal stiffener 35L and the right diagonal stiffener 35R, respectively.

[0026] As shown in Figure 5(b), the upper end of the left diagonal stiffener 35L is positioned to overlap the lower end (the lower end and its vicinity in this embodiment) of the left stiffener 33L on the rear side in the front-rear direction of the dump vehicle 10. Similarly, the upper end of the right diagonal stiffener 35R is positioned to overlap the lower end (the lower end and its vicinity in this embodiment) of the right stiffener 33R on the rear side in the front-rear direction of the dump vehicle 10. The upper end face 352 of the left diagonal stiffener 35L and the rear face 331 of the lower end (the vicinity of the lower end in this embodiment) of the left stiffener 33L are fillet welded w2. The upper end face of the right diagonal stiffener 35R and the rear face of the lower end (the vicinity of the lower end in this embodiment) of the right stiffener 33R are similarly fillet welded w2 w2. Fillet welds w2 are performed over the entire upper end face 352 of the left-angled stiffener 35L and the right-angled stiffener 35R, respectively.

[0027] Compared to butt welding, which was used for the stiffeners 93 of the tailgate 92 of the conventional round-bottom type cargo box 91, fillet welding w1 and w2 allows the welding work to be performed with the end faces 351 and 352 of the left diagonal stiffener 35L and the right diagonal stiffener 35R visible, making it easier to penetrate the entire end faces 351 and 352 and reducing the likelihood of defects like those that occur with butt welding. Therefore, by performing fillet welding w1 at the connection point between the left diagonal stiffener 35L and the right diagonal stiffener 35R and the lower stiffener 34, and by performing fillet welding w2 at the connection point between the left diagonal stiffener 35L and the right diagonal stiffener 35R and the left stiffener 33L and the right stiffener 33R, the cargo box 1 of this embodiment can reduce the occurrence of cracks at the welded areas caused by defects in conventional butt welding.

[0028] Since the impact of the tailgate 3 closing is greater at the bottom of the tailgate 3, fillet welding w1 between the left diagonal stiffener 35L, the right diagonal stiffener 35R, and the lower stiffener 34 is particularly effective in preventing cracking at the welded area. However, when the tailgate 3 closes, due to variations in how the bottom plate 21 and side plates 22 contact the tailgate 3, the impact of the tailgate 3 closing may have a greater effect on the fillet weld w2 than on the fillet weld w1. This embodiment can also prevent cracking at the fillet weld w2 due to such impact effects.

[0029] For the connection between the left stiffener 33L and the left diagonal stiffener 35L, and the connection between the right stiffener 33R and the right diagonal stiffener 35R, the impact from the closing of the tailgate 3 is relatively small, so it is possible to perform conventional butt welding instead of fillet welding w1.

[0030] The hinge mechanism 4 is provided on the left and right sides of the rear of the cargo box 1. The hinge mechanism 4 has a first bracket 41, a shaft 42, and an arm 43. The first bracket 41 is fixed to the rear end of the cargo box body 2. The shaft 42 is attached to the first bracket 41. The tip of the arm 43 is fixed to the side of the tailgate 3, and the base end is rotatably attached to the first bracket 41 by the shaft 42.

[0031] The locking mechanism 5 includes a second bracket 51 provided below the tailgate 3 and a hook 52 provided at the rear of the cargo box body 2. The second bracket 51 is provided so as to protrude downward from the lower stiffener 34. When the cargo box 1 is not tilted, the hook 52 engages with the second bracket 51, locking the tailgate 3 so as not to rotate relative to the cargo box body 2. When the cargo box 1 tilts, a mechanism that operates in conjunction with the tilting of the cargo box 1 disengages the hook 52 from the second bracket 51, releasing the lock and allowing the tailgate 3 to open downward. Thus, in this embodiment, an automatic release type locking mechanism 5 is used, but a manual release type locking mechanism may also be used.

[0032] <Other Embodiments> In this embodiment, the tailgate 3 had the left diagonal stiffener 35L and the right diagonal stiffener 35R overlapping the lower stiffener 34 on the rear side. However, it is also possible to have the left diagonal stiffener 35L and the right diagonal stiffener 35R overlapping the lower stiffener 34 on the front side. This configuration will be explained using Figures 6 and 7.

[0033] As shown in Figure 6, in the tailgate 3A, the lower ends of the left diagonal stiffener 35AL and the right diagonal stiffener 35AR are positioned to overlap the front of the dump vehicle 10 in the longitudinal direction with respect to both ends of the lower stiffener 34A (both ends and their vicinity in this embodiment). Then, as shown in Figure 7(a), the left end face 342 of the lower stiffener 34A and the rear face 353 of the lower side of the left diagonal stiffener 35AL (near the lower end in this embodiment) are fillet welded w3. Similarly, the right end face of the lower stiffener 34A and the rear face of the lower side of the right diagonal stiffener 35R (near the lower end in this embodiment) are also fillet welded w3.

[0034] Furthermore, as described above, when overlapping the lower ends of the left diagonal stiffener 35AL and the right diagonal stiffener 35AR on the front sides of both ends of the lower stiffener 34A, as shown in Figure 6, the upper ends of the left diagonal stiffener 35AL and the right diagonal stiffener 35AR are overlapped on the front sides in the front-rear direction of the dump vehicle 10 with respect to the lower ends of the left stiffener 33AL and the right stiffener 33AR (in this embodiment, the lower ends and their vicinity). Then, as shown in Figure 7(b), the lower end face portion 332 of the left stiffener 33AL and the upper rear face portion 354 of the left diagonal stiffener 35AL are fillet welded w4. Similarly, the lower end face portion of the right stiffener 33AR and the upper rear face portion of the right diagonal stiffener 35AR are fillet welded w4.

[0035] Regardless of how the left-angled stiffeners 35L, 35AL and right-angled stiffeners 35R, 35AR are overlapped with the lower stiffeners 34, 34A, and the left stiffeners 33L, 33AL and right stiffeners 33R, 33AR, by fillet welding the left-angled stiffeners 35L, 35AL and right-angled stiffeners 35R, 35AR with the lower stiffeners 34, 34A, fillet welding the left-angled stiffener 35L with the left stiffener 33L, and fillet welding the right-angled stiffener 35R with the right stiffener 33R, cracks caused by defects in conventional butt welding can be prevented.

[0036] <Comparison of the tailgate in the first embodiment with that of other embodiments> In the tailgate 3 according to the first embodiment, the left diagonal stiffener 35L is overlapped with the lower stiffener 34 and the left stiffener 33L on the rear side in the vehicle's longitudinal direction, and the right diagonal stiffener 35R is overlapped with the lower stiffener 34 and the right stiffener 33R on the rear side in the vehicle's longitudinal direction. In this case, the size of the left diagonal stiffener 35L and the right diagonal stiffener 35R must be larger than in the conventional design. Therefore, the weight of the tailgate 3 increases by the amount by which the left diagonal stiffener 35L and the right diagonal stiffener 35R have been enlarged.

[0037] In the tailgate 3A of another embodiment, the left diagonal stiffener 35AL is overlapped with the lower stiffener 34A and the left stiffener 33AL on the front side in the vehicle's longitudinal direction, and the right diagonal stiffener 35AR is overlapped with the lower stiffener 34A and the right stiffener 33AR on the front side in the vehicle's longitudinal direction. In this case, the sizes of the lower stiffener 34A, the left stiffener 33AL, and the right stiffener 33AR need to be larger than in the conventional design. Therefore, the weight of the tailgate 3 increases by the amount by which the lower stiffener 34A, the left stiffener 33AL, and the right stiffener 33AR have been enlarged.

[0038] As with the tailgate 3 of the first embodiment, a tailgate 3 in which the sizes of the left diagonal stiffener 35L and the right diagonal stiffener 35R are larger than conventional models can suppress the weight increase compared to a tailgate 3A in another embodiment in which the sizes of the lower stiffener 34A, the left stiffener 33AL, and the right stiffener 33AR are larger than conventional models. Therefore, the tailgate 3 of the first embodiment can suppress the increase in impact when closing the tailgate 3 more than the tailgate 3A of the other embodiment. In particular, since the lower stiffener 34A is long in the vehicle width direction, increasing the size of the lower stiffener 34A increases the weight of the lower part of the tailgate 3A, and increases the impact when the tailgate 3A is closed. For this reason, the tailgate 3 of the first embodiment, in which the sizes of the left diagonal stiffener 35L and the right diagonal stiffener 35R are larger, is preferable to the tailgate 3A of the other embodiment in that it can minimize the weight increase of the tailgate 3 and further minimize the increase in impact on the tailgate 3. [Industrial applicability]

[0039] The present invention can be applied, for example, to the cargo box of a dump truck. [Explanation of Symbols]

[0040] 1 packing box 2. Cargo box body 21 Bottom plate 21a Both ends in the vehicle width direction 22 Side panels 23 Front panel 3, 3A Tailgate 31 panels 32 Upper Stiffuna 33L, 33AL Left-hand stiffener 33R, 34AR Right Stiffener 331 Rear section of the left stiffener 332 End face of left stiffener 34, 34A Lower stiffener 341 Rear section of the lower stiffener 342 End face of lower stiffener 35L, 35AL Left-side diagonal stiffener 35R, 35AR Right-angle stiffener 351 Left-angled end face of stiffener 352 End face of left-angle stiffener 353 Rear view of the left diagonal stiffener 354 Rear view of the left diagonal stiffener 4. Hinge mechanism 41 First bracket 42 axes 43 Arms 5. Locking mechanism 51 Second bracket 52 hooks 10 Dump trucks 11 cabins 12 Chassis Frame 13 Subframe w1, w2, w3, w4 fillet weld

Claims

1. A cargo box for a dump vehicle, comprising a cargo box body having a roughly U-shaped cross-section, and a tailgate attached to the rear end of the cargo box body so as to be rotatable downwards, The aforementioned tailgate is Panel and, The left stiffener and the right stiffener are fixed to both sides of the rear surface of the aforementioned panel, and extend in the vertical direction. A lower stiffener is fixed to the lower part of the rear surface of the aforementioned panel and extends in the vehicle width direction, A left diagonal stiffener and a right diagonal stiffener are fixed to the rear surface of the panel so as to connect the lower ends of the left and right stiffeners with both ends of the lower stiffener, respectively, and each extends in a direction that slopes downward toward the center of the vehicle. It has, The lower ends of the left diagonal stiffener and the right diagonal stiffener overlap the rearward side in the vehicle's longitudinal direction relative to both ends of the lower stiffener. The lower end faces of the left diagonal stiffener and the right diagonal stiffener, and the rear faces of both ends of the lower stiffener are fillet welded to each other. The cargo box of a dump truck.

2. A cargo box for a dump vehicle, comprising a cargo box body having a roughly U-shaped cross-section, and a tailgate attached to the rear end of the cargo box body so as to be rotatable downwards, The aforementioned tailgate is Panel and, The left stiffener and the right stiffener are fixed to both sides of the rear surface of the aforementioned panel, and extend in the vertical direction. A lower stiffener is fixed to the lower part of the rear surface of the aforementioned panel and extends in the vehicle width direction, A left diagonal stiffener and a right diagonal stiffener are fixed to the rear surface of the panel so as to connect the lower ends of the left and right stiffeners with both ends of the lower stiffener, respectively, and each extends in a direction that slopes downward toward the center of the vehicle. It has, The lower ends of the left diagonal stiffener and the right diagonal stiffener overlap the front end of the lower stiffener in the vehicle's longitudinal direction relative to both ends. The end faces of the lower stiffener and the lower rear faces of the left diagonal stiffener and the right diagonal stiffener are fillet welded to each other. The cargo box of a dump truck.

3. A cargo box for a dump truck as described in claim 1, The upper end of the left diagonal stiffener overlaps the lower end of the left stiffener on the rear side in the vehicle's longitudinal direction, and the upper end of the right diagonal stiffener also overlaps the lower end of the right stiffener on the rear side in the vehicle's longitudinal direction. The upper end face of the left diagonal stiffener and the lower rear end face of the left stiffener are fillet welded to each other, and the upper end face of the right diagonal stiffener and the lower rear end face of the right stiffener are fillet welded to each other. The cargo box of a dump truck.

4. A cargo box for a dump vehicle according to claim 2, The upper end of the left diagonal stiffener overlaps the lower end of the left stiffener on the front side in the vehicle's longitudinal direction, and the upper end of the right diagonal stiffener also overlaps the lower end of the right stiffener on the front side in the vehicle's longitudinal direction. The lower end face of the left stiffener and the upper rear face of the left diagonal stiffener are fillet welded to each other, and the lower end face of the right stiffener and the upper rear face of the right diagonal stiffener are fillet welded to each other. The cargo box of a dump truck.

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