Boom for construction machine

Abstract

To provide a boom for a construction machine that can ensure sufficient strength against torsional load applied to an end of the boom.SOLUTION: In a boom 5 for a construction machine which has a boom body part 100 equipped with an upper plate 110, a lower plate 111, and left and right side plates 112 and 113, a boom top 200, and a boom foot 300, at least one of the boom body part 100 and the boom foot 300 is made of a cast steel body formed into a hollow box-shaped structure that opens toward the boom body part 100 and is welded to the boom body part 100. The cast steel body has a thick-walled portion 211 formed with a thickness t1, a thin-walled portion 212 formed with a thickness t2 that is thinner than t1, and a thickness-changing portion 213 whose thickness changes from t1 to t2 along the extension direction of the boom body part 100. The upper plate 110, the lower plate 111, and the left and right side plates 112 and 113 of the boom body part 100 are welded to an outer surface of the thick-walled portion 211.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a boom for use in a construction machine. [Background technology]

[0002] Patent Document 1 discloses a boom structure in which the boom is formed with left and right side plates and an upper and lower plate having a substantially rectangular cross section, a thick bracket plate extending in a bifurcated shape from the tips of the left and right side plates, a tip closure plate is provided at the rear between the bracket plates, the tip closure plate is welded to the upper and lower plates, and the outer edges of both sides of the tip closure plate are welded to the corners of the inner surfaces of the bracket plates, and the upper and lower rear edges of the tip closure plate are butt-welded to the front edges of the upper and lower plates, respectively. In this boom structure, the upper and lower plates of the boom are butt-welded to the tip closure plate at the boom top, and the welded portions between the boom top and the upper and lower plates are offset from the welded portions between the boom top and the left and right side plates, thereby increasing the strength of the welded structure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 5-10541 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned Patent Document 1, the reinforcing plate located inside the boom top to reinforce the strength of the boom top is far from the two welded portions, and the reinforcing plate does not contribute sufficiently to improving the strength of the welded portions, resulting in a problem in that the boom top is not strong enough to withstand the torsional load applied to it.

[0005] The present invention has been made in view of the above circumstances, and its object is to provide a boom for a construction machine that can ensure sufficient strength against torsional loads applied to the end of the boom. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides a boom for a construction machine having a boom main body with an upper plate, a lower plate, and left and right side plates, a boom top fixed to one end of the boom main body, and a boom foot fixed to the other end of the boom main body, wherein at least one of the boom top or the boom foot is fixed to the boom main body by welding and is made of a cast steel body formed into a hollow box-like structure that opens toward the boom main body, and the cast steel body has: a thick-walled section located on the boom main body side and having a predetermined first thickness, which is the dimension in the thickness direction between its inner surface and outer surface; a thin-walled section located on the opposite side of the boom main body and having a second thickness thinner than the first thickness; and a thickness-changing section that connects the thick-walled section and the thin-walled section, where the thickness changes from the first thickness to the second thickness along the extension direction of the boom main body, and the upper plate, the lower plate, and the side plates of the boom main body are welded to the outer surfaces of the thick-walled section. [Effects of the Invention]

[0007] According to the present invention, it is possible to ensure sufficient strength against the torsional load applied to the end of the boom. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a left side view showing the overall external structure of a hydraulic excavator, which is an example of a construction machine to which an embodiment of the present invention is applied. [Figure 2] 1 is a perspective view showing the overall external structure of a boom for a construction machine according to an embodiment of the present invention. [Figure 3] FIG. 1 is a perspective view showing the overall structure of a boom top provided on a boom for a construction machine. [Figure 4]FIG. 4 is a perspective view of the interior of the boom top shown in FIG. 3. [Figure 5] FIG. 4 is a side view of the boom top as viewed from the direction of the arrow A in FIG. 3. [Figure 6] FIG. 4 is a side cross-sectional view taken along the line BB in FIG. 3. [Figure 7] 6 is a top view taken along the arrow C in FIG. 5. [Figure 8] FIG. 7 is a cross-sectional view taken along the line DD in FIG. 6. [Figure 9] 6A and 6B are a cross-sectional view taken along the line EE in FIG. 5, a cross-sectional view taken along the line FF in FIG. 5, and a cross-sectional view taken along the line GG in FIG. [Figure 10] 1 is a side view of a boom foot provided on a boom for a construction machine according to an embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] <Overview of hydraulic excavator> FIG. 1 shows the overall external structure of a hydraulic excavator 1, which is an example of a construction machine to which a construction machine boom according to this embodiment can be applied. In FIG. 1, the hydraulic excavator 1 is a construction machine used for excavation work, for example. Note that the present invention may also be applied to other construction machines besides the hydraulic excavator 1, which are equipped with a working device, as described below. In the following description of the present application, the case where the present invention is applied to the hydraulic excavator 1 will be described as an example.

[0011] In this example, the hydraulic excavator 1 is a small hydraulic excavator (mini-excavator) used in relatively narrow work sites such as urban areas. The body of the hydraulic excavator 1 is mainly composed of a self-propelled crawler-type lower traveling body 2 and an upper rotating body 3 that is rotatably mounted on the lower traveling body 2. In this example, the turning radius of the upper rotating body 3 is configured to be approximately within the vehicle width of the lower traveling body 2.

[0012] A working device 4 is provided on the front side of the upper rotating body 3 via a swing post 51. The working device 4 has an articulated structure and is supported via the swing post 51 so that it can swing left and right and move up and down, and is equipped with a boom 5 (a boom for construction machinery) driven by a boom cylinder 52, an arm 6 rotatably connected to the tip of the boom 5 and driven by an arm cylinder 53, and a bucket 7 rotatably connected to the tip of the arm 6 and driven by a bucket cylinder 54.

[0013] The upper rotating body 3 is equipped with a rotating frame 55 that serves as a frame for the upper rotating body 3, a cab 56, and a counterweight 57. In the following description, the up-down direction, the front-rear direction, and the left-right direction correspond to the directions of arrows appropriately shown in each drawing such as FIG. 1. In other words, the illustrated "up," "down," "front," "rear," "left," and "right" correspond to the up-down, left-right, and front-rear directions as seen by an operator seated in the cab 56.

[0014] <Overall boom structure> The overall external structure of the boom 5 according to this embodiment is shown in Fig. 2. In Fig. 2 and Fig. 1, the boom 5 includes a boom main body 100, a boom top 200 fixed to one end of the boom main body 100 and used for rotatably connecting to the arm 6, and a boom foot 300 fixed to the other end of the boom main body 100 and used for rotatably connecting to the swing post 51.

[0015] <Boom body> The boom main body 100 includes an upper plate 110 welded to the upper sides of the boom top 200 and the boom foot 300, a lower plate 111 welded to the lower sides of the boom top 200 and the boom foot 300, a left side plate 112 welded to the left side of the boom top 200 and the boom foot 300, a right side plate 113 welded to the right side of the boom top 200 and the boom foot 300, an arm cylinder bracket 114 welded to the upper side of the upper plate 110, and a boom cylinder bracket 115 welded to the lower side of the lower plate 111. As shown in FIG. 1 , the rod side of a boom cylinder 52 is connected to the boom cylinder bracket 115, and the bottom side of the boom cylinder 52 is connected to the swing post 51. In addition, the bottom side of an arm cylinder 53 is connected to the arm cylinder bracket 114.

[0016] <Boom Top> This embodiment is characterized by the structures of the boom top 200 and boom foot 300. First, the boom top 200 will be described with reference to Figs. 3 to 9. Fig. 3 shows a perspective view illustrating the overall structure of the boom top 200, and Fig. 4 shows a perspective view of the interior thereof. Fig. 5 shows a side view of the boom top 200 as viewed from the direction A in Fig. 3, and Fig. 6 shows a side cross-sectional view taken along the line BB in Fig. 3. Fig. 7 shows a top view as viewed from the direction C in Fig. 5, and Fig. 8 shows a cross-sectional view taken along the line DD in Fig. 6.

[0017] 3 to 8, boom top 200 has a generally U-shape that is similar to a Y-shape. Boom top 200 is made of a cast steel body formed into a hollow box-like structure that opens toward boom main body 100, and that integrates base 210, which is fixed to boom main body 100 by welding, and bracket portion 220, which is bifurcated and provided on the side of base 210 opposite boom main body 100. The bracket part 220 has a connecting hole 221 for connecting to the arm 6 on the side opposite to the boom body 100 .

[0018] <Thick base structure> Base 210, which forms part of the cast steel body, has a thick-walled portion 211 located on the boom main body 100 side, a thin-walled portion 212 located on the opposite side of thick portion 211 from boom main body 100, a thickness-changing portion 213 provided to connect thick portion 211 and thin portion 212, and a rear wall portion 214 located on the opposite side of thin portion 212 from boom main body 100. The thick-walled portion 211 has a thickness t1 (first thickness), which is the dimension in the thickness direction between the inner surface and the outer surface. The thin-walled portion 212 has a thickness t2 (second thickness), which is thinner than the thickness t1. The thickness-varying portion 213 has a thickness, which is the dimension in the thickness direction between the inner surface and the outer surface, that varies from a value equal to the thickness t1 to a value equal to the thickness t2 along the extension direction of the boom body 100. Hereinafter, thickness t1 will be simply referred to as "thickness t1," and thickness t2 will be simply referred to as "thickness t2." Furthermore, an opening 217 is provided at the end of the base 210 opposite the bracket portion 220 to remove a core during casting.

[0019] The thickness t2 is achieved by forming recesses 212A on the left and right outer surfaces of the thin-walled portion 212. The thickness-varying portion 213 has a stepped portion 213a, which is a machined surface that is machined to be recessed more than other portions, on the outer surface on the thick-walled portion 211 side.

[0020] The thickness t1 of the thick-walled portion 211 and the thickness t2 of the thin-walled portion 212 do not necessarily have to be uniform across the entire cross section. For example, within the range shown in FIG. 6, the thicknesses t1 and t2 may vary within a certain range. The values ​​of the thicknesses t1 and t2 shown in FIG. 8 may differ from those shown in FIG. 6. Similarly, the thicknesses t1 and t2 may vary within a certain range, for example, within the range shown in FIG. 8. In any case, even taking into account the above-mentioned variation range, it is sufficient that the relationship t1 > t2 is always true, in other words, that the minimum value of t1 is always greater than the maximum value of t2. The thickness of the varying thickness portion 213, for example, in a specific cross section, varies continuously to smoothly connect the thicknesses t1 and t2 in that cross section.

[0021] <Welded structure> Next, we will explain the welding structure of the base 210 and the boom main body 100. The base 210 is welded and fixed to the lower plate 111, left plate 112, and right plate 113 of the boom main body 100 so as to be in contact with the inside of the plate, and the welded portions are near an opening 217 of the base 210 inside the boom main body 100. The base 210 is fillet welded to the upper plate 110 and the lower plate 111 at weld portions M1 and M2, respectively.

[0022] 5 and 7, a welded portion M1 between the upper plate 110 and the base portion 210, a welded portion M2 between the lower plate 111 and the base portion 210, a welded portion M3 between the left side plate 112 and the base portion 210, and a welded portion M4 between the right side plate 113 and the base portion 210 are all located in the thick portion 211. In other words, the upper plate 110, the lower plate 111, the left side plate 112, and the right side plate 113 of the boom main body 100 are welded to the outer surface of the thick portion 211. Note that, of the outer surface of the thick portion 211, at least the portions to which the upper plate 110, the lower plate 111, the left side plate 112, and the right side plate 113 are welded are machined surfaces. In addition, at this time, the welded portions M1 and M2 between the upper plate 110 and the lower plate 111 and the base portion 210, and the welded portions M3 and M4 between the left and right plates 112 and 113 and the base portion 210 in the thick-walled portion 211 are spaced apart along the extension direction of the boom body 100. That is, the welded portions M1 and M2 are closer to the bracket portion 220 than the welded portions M3 and M4, and the welded portions M1 to M4 are not all at the same axial position, thereby increasing the strength of each weld. In addition, the welded portions M3 and M4 are equidistant from each other in the axial direction to the connecting hole 221 of the bracket portion 220.

[0023] <Cross-sectional shape of hollow space> The cross-sectional structure of the base 210 and the boom main body 100 in the vicinity of the base 210, which is realized by the thick-wall structure and welding structure described above, is shown in Figure 9(a) by the cross section EE in Figure 5, Figure 9(b) by the cross section FF in Figure 5, and Figure 9(c) by the cross section GG in Figure 5.

[0024] As shown in Figures 9(a) to 9(c), the shape of the internal space R (see Figures 6 and 8) of the base 210 gradually changes from the rear wall 214 toward the opening 217, and the cross-sectional area of ​​the internal space R becomes smaller as it approaches the opening 217.

[0025] In particular, as shown in Figure 9(a), the cross-sectional shape of the inner surface of the thin-walled portion 212 that constitutes the outline of the internal space R in the thin-walled portion 212, as taken perpendicular to the extension direction of the boom main body 100, is approximately rectangular, and the thin-walled portion 212 includes four corners 212a that have rounded cross-sectional shapes. That is, the four corners 212a with large rounding radii are formed near the welded portions M1, M2 between the upper plate 110 and the base 210, and the lower plate 111 and these four corners 212a are connected by plate-like portions 212b. Furthermore, as shown in Figure 9(b), the cross-sectional shape of the inner surface of the thin-walled portion 212 that constitutes the outline of the internal space R in the thick-walled portion 211, as taken perpendicular to the extension direction of the boom main body 100, is approximately elliptical, thereby increasing the rigidity of the thick-walled portion 211 against torsional loads.

[0026] <Effects at the top of the boom> As described above, the boom top 200 provided on the boom 5 of this embodiment is formed of a cast steel body. This eliminates the need for welding, which would be required if the boom top 200 itself were a welded assembly structure, thereby improving production efficiency. In this embodiment, instead of a bulkhead in a welded structure, a thick-walled portion 211 with a large thickness t1 is provided in the base 210 as a strength reinforcement for the cast steel body. The upper plate 110, lower plate 111, left plate 112, and right plate 113 of the boom body 100 are welded to the outer surface of the thick-walled portion 211. This allows the strength reinforcement and the welded portions to be closer together, unlike conventional structures in which the strength reinforcement and the welded portions are spaced apart. As a result, sufficient strength against torsional loads applied to the end of the boom 5 can be ensured.

[0027] Furthermore, in particular with the boom top 200 of this embodiment, the welded regions M1 and M2 in the thick-walled portion 211 between the upper plate 110 and the lower plate 111 of the boom main body 100 and the base 210, and the welded regions M3 and M4 between the left and right plates 112 and 113 of the boom main body 100 and the base 210 are spaced apart along the extension direction of the boom main body 100. This makes it possible to reliably ensure sufficient strength compared to when these welded positions are the same in the axial direction.

[0028] Furthermore, in particular, in the boom top 200 of this embodiment, the cross-sectional shape of the inner surface of the thin-walled portion 212 that forms the outer contour of the internal space R of the thick-walled portion 211, as measured perpendicular to the extension direction of the boom main body 100, is approximately elliptical, and the cross-sectional shape of the inner surface of the thin-walled portion 212 that forms the outer contour of the internal space R of the thin-walled portion 212, as measured perpendicular to the extension direction of the boom main body 100, is approximately rectangular. This makes it possible to smoothly realize the large thickness t1 of the thick portion 211 and the small thickness t2 of the thin portion 212 in the base 210, in which the thick portion 211, the thickness-changing portion 213, and the thin portion 212 are continuously and integrally formed.

[0029] In particular, in the boom top 200 of this embodiment, the thin-walled portion 212 has recesses 212A formed on the left and right outer surfaces. This allows the thin-walled portion 212 to have a small thickness t2 with a simple structure, and also makes it easy to reduce the weight of the entire cast steel body.

[0030] Furthermore, in particular, in the boom top 200 of this embodiment, in order to facilitate the process of welding the thick-walled portion 211 so as to be in contact with the inner surfaces of the upper plate 110, the lower plate 111, and the left and right plates 112, 113 of the boom main body 100, a stepped portion 213a, which is a machined surface, is provided on the outer surface of the thickness-changing portion 213 located on the side of the thick-walled portion 211 opposite to the boom main body 100. Since the stepped portion 213a is formed by machining, it can be finished with high dimensional accuracy, and therefore high-quality welding and fixing can be easily achieved.

[0031] <Boom Hoot> Next, the boom foot 300 will be described with reference to Figure 10. Illustrations and descriptions of parts similar to those of the boom top 200 will be omitted or simplified as appropriate. Figure 10 is a side view of the boom foot 300 provided on the boom 5 of this embodiment, corresponding to Figure 5 described above.

[0032] 10 and the above-mentioned Fig. 2, boom foot 300, like boom top 200, is formed from a hollow cast steel body that integrates base 310, which is fixed to boom main body 100 by welding, and bracket portion 320, which is provided on the opposite side of base 310 from boom main body 100. Bracket portion 320 has connecting hole 321, for connecting to upper rotating body 3, on the opposite side from boom main body 100.

[0033] Similar to base 210, base 310 has a thick portion (not shown) located on the boom main body 100 side and having a first thickness, a thin portion (not shown) located on the opposite side of the thick portion from boom main body 100 and having a second thickness smaller than the first thickness, and a thickness-changing portion (not shown) that is provided to connect thick portion 211 and thin portion 212 and changes from the first thickness to the second thickness along the extension direction of boom main body 100. In addition, an opening (not shown) is provided at the end of base 310 opposite bracket portion 320 for removing a core during casting.

[0034] Similar to the base 210, the base 310 is welded and fixed to the lower plate 111, left side plate 112, and right side plate 113 of the boom body 100 so as to be in contact with the inside of the plate, and the base 310 is fillet welded to the upper plate 110 and the lower plate 111 at weld locations M11 and M12, respectively.

[0035] At this time, the welded portion M11 between the upper plate 110 and the base portion 310, the welded portion M12 between the lower plate 111 and the base portion 310, the welded portion M13 between the left side plate 112 and the base portion 310, and the welded portion M14 (not shown) between the right side plate 113 and the base portion 310 are all located in the thick-walled portion. At this time, the welded portions M11, M12 between the upper plate 110 and the lower plate 111 and the base portion 310, and the welded portions M13, M14 between the left and right side plates 112, 113 and the base portion 310 in the thick-walled portion are spaced apart along the extension direction of the boom main body 100. In other words, the welded portions M11, M12 are closer to the bracket portion 320 than the welded portions M13, M14, and the welded portions M11 to M14 are not all located in the same axial position, thereby increasing the strength of each weld. Furthermore, the distances to the connecting hole 321 of the bracket portion 320 of the welded portion M13 and the welded portion M14 are equal to each other.

[0036] Furthermore, due to the thick-walled structure and welded structure described above, similar to the aforementioned base 210, the cross-sectional shape of the inner surface of base 310 that forms the outline of its internal space, perpendicular to the extension direction of boom body 100, gradually changes from the back wall toward the opening, with the cross-sectional area decreasing as it approaches the opening. In particular, although not shown, similar to base 210, the cross-sectional shape of the inner surface of the thick-walled portion of base 310 is generally elliptical, and the cross-sectional shape of the inner surface of the thin-walled portion is generally rectangular.

[0037] <Effects on boom foot> As described above, the boom foot 300 provided on the boom 5 of this embodiment is formed of a cast steel body. This eliminates the need for welding, which would be required if the boom foot 300 itself were a welded assembly structure, thereby improving production efficiency. In this embodiment, instead of a bulkhead in a welded structure, a thick-walled portion having a large first thickness is provided in the base 310 as a strength reinforcement in the cast steel body. The upper plate 110, the lower plate 111, and the left and right plates 112, 113 of the boom body 100 are welded to the outer surface of the thick-walled portion. This allows the strength reinforcement and the welded portions to be closer together, unlike the conventional structure in which the strength reinforcement and the welded portions are separated, as in the boom top 200 described above. As a result, sufficient strength against torsional loads applied to the end of the boom 5 can be ensured.

[0038] Furthermore, in the boom foot 300 of this embodiment in particular, the welded regions M11, M12 in the thick-walled portion between the upper plate 110 and the lower plate 111 of the boom main body 100 and the base 310, and the welded regions M13, M14 between the left and right plates 112, 113 of the boom main body 100 and the base 310 are spaced apart along the extension direction of the boom main body 100. This makes it possible to reliably ensure sufficient strength compared to when these welded positions are the same in the axial direction.

[0039] Furthermore, in particular with the boom foot 300 of this embodiment, the cross-sectional shape of the inner surface of the thick portion perpendicular to the extension direction of the boom body 100 is approximately elliptical, and the cross-sectional shape of the inner surface of the thin portion perpendicular to the extension direction of the boom body 100 is approximately rectangular. This allows the thick portion, the thickness-changing portion, and the thin portion to be continuously and integrally formed in the base 310, making it possible to smoothly achieve a large first thickness in the thick portion and a small second thickness in the thin portion.

[0040] <Other> In the above description, the boom 5 is provided with the boom top 200 and the boom foot 300 having the above-described structure, but this is not limited to this. In other words, the boom 5 may be provided with either the boom top or the boom foot having a conventional structure instead of the above-described structure.

[0041] <About the problem to be solved and the effects of the invention> The problems to be solved by the invention and the effects of the invention are not limited to those described above. That is, the present invention may solve problems or achieve effects not described above, or may solve only some of the problems or achieve only some of the effects described above.

[0042] In addition to the above, the methods according to the above embodiments and modifications may be used in appropriate combination.

[0043] Although not specifically illustrated, the present invention can be implemented with various modifications within the scope of the invention. [Explanation of symbols]

[0044] 1. Hydraulic excavator (construction machinery) 5. Boom 100 Boom body 110 Upper Plate 111 Lower plate 112 Left side plate 113 Right side plate 200 Boom Top 210 base 211 Thick wall part 212 Thin-walled section 212A Recess 212a Four corners 213 Thickness change area 213a Stepped section 217 Opening 220 Bracket part 300 Boomfoot 310 base 311 Thick wall part 320 Bracket part M1 Welded part M2 welding area M3 welding area M4 welding area M11 welding area M12 welded part M13 welding area M14 welding area R interior space t1 wall thickness t2 wall thickness

Claims

1. A boom body equipped with an upper plate, a lower plate, and left and right side plates; a boom top fixed to one end side of the boom body; a boom foot fixed to the other end of the boom body; In a construction machine boom having At least one of the boom top and the boom foot is fixed to the boom main body by welding and is made of a cast steel body formed into a hollow box-like structure that opens toward the boom main body, The cast steel body is a thick-walled portion located on the boom main body side and having a thickness, which is a dimension in a thickness direction between an inner surface and an outer surface, formed to a predetermined first thickness; a thin-walled portion located on the opposite side of the boom body, the thin-walled portion having a second thickness thinner than the first thickness; a thickness changing portion that is provided so as to connect the thick portion and the thin portion, and in which the thickness changes from the first thickness to the second thickness along the extension direction of the boom main body; and The upper plate, the lower plate, and the side plates of the boom body are welded to the outer surface of the thick-walled portion. A boom for construction machinery.

2. 2. The construction machine boom according to claim 1, The welded portions between the upper plate and the lower plate and the thick portion and the welded portions between the side plates and the thick portion are spaced apart along the extension direction of the boom body. A boom for construction machinery.

3. 2. The construction machine boom according to claim 1, a cross-sectional shape of an inner surface of the thick-walled portion perpendicular to the extension direction of the boom body is substantially elliptical, The cross-sectional shape of the inner surface of the thin-walled portion perpendicular to the extending direction of the boom body is substantially rectangular. A boom for construction machinery.

4. The construction machine boom according to any one of claims 1 to 3, The outer surface of the thin-walled portion has A recess is formed A boom for construction machinery.

5. The construction machine boom according to any one of claims 1 to 3, The outer surfaces of the thickness changing portion and the thick portion are It has a machined surface, The boom body is welded to the machined surface. A boom for construction machinery.

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