Patent Publication Number: US-2020291600-A1

Title: Box-shaped structure for work machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National stage application of International Application No. PCT/JP2017/035316, filed on Sep. 28, 2017. This U.S. National stage application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2016-193969, filed in Japan on Sep. 30, 2016, the entire contents of which are hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention relates to a box-shaped structure for a work machine. 
     A work vehicle, such as a hydraulic excavator, includes a work machine that has a box-shaped structure formed of, for example, a boom and an arm. In Japanese Unexamined Patent application publication No. H6-220880, there is proposed a method of forming a box-shaped structure with two separate bodies welded together along a neutral axis, and expanding the width of the box-shaped structure at an end portion thereof. The method disclosed in Japanese Unexamined Patent application publication No. H6-220880 describes that it can reduce a cross-section of the box-shaped structure along a longitudinal direction thereof to provide a lighter structure, while also preventing a decrease in strength of the end portion that is mounted to another structure. 
     SUMMARY 
     In the box-shaped structure of Japanese Unexamined Patent application publication No. H6-220880A, each side plate of the box-shaped structure is bent at a plurality of positions in order to increase the width at an end portion thereof. Because of this, stress concentrates at the bent portions of each side plate. In particular, in the box-shaped structure of Japanese Unexamined Patent application publication No. H6-220880 that has been made with a smaller cross-section, more stress is generated at the bent portions of each side plate due to the bending of the box-shaped structure. 
     The present invention has been made in light of the above-described problem, and it is an object of the present invention to provide a box-shaped structure for a work machine that can have improved durability. 
     A box-shaped structure for a work machine according to a first aspect of the present invention includes a body that extends in a longitudinal direction and a bracket that is connected to one end of the body. The body including a straight section having a substantially constant width when viewed from above, and a wide section that is connected to the bracket and has a width that increases toward the bracket when viewed from above, and the straight section and the wide section are smoothly continuous to each other. 
     According to the box-shaped structure for a work machine according to the first aspect of the present invention, the wide section has a width that increases toward the bracket, and hence the cross-sectional area of the body can be increased on the bracket side. With this configuration, strength of the body can be enhanced. In addition, because the straight section and the wide section are smoothly continuous to each other, it is possible to reduce locally concentrating stresses in the body. 
     A box-shaped structure for a work machine according to a second aspect of the present invention is the box-shaped structure for a work machine according to the first aspect, in which the body is formed of a top plate, a bottom plate, a first side plate and a second side plate. The bracket includes a first abutment surface that abuts against the first side plate and a second abutment surface that abuts against the second side plate, and each of the first abutment surface and the second abutment surface are angled with respect to the longitudinal direction of the body. 
     A box-shaped structure for a work machine according to a third aspect of the present invention is the box-shaped structure for a work machine according to the first or second aspect, in which the body has a center boss centrally located in the longitudinal direction, and the bracket has an end boss. The straight section is smoothly continuous to the wide section at a predetermined position between the center boss and the end boss. A ratio of a first interval between a center axis of the center boss and the predetermined position to a second interval between a center axis of the end boss and the predetermined position is from 1:1 to 4:1. 
     A method of manufacturing a box-shaped structure for a work machine according to a fourth aspect of the present invention including the steps of: placing a first side plate and a second side plate on a bottom plate; pushing one end portion of the first side plate and one end portion of the second side plate outward using a lining; sandwiching and fixing a bracket between the end portions of the first side plate and the second side plate; and fixing a top plate on the first side plate and the second side plate. 
     According to the present invention, there can be provided a box-shaped structure for a work machine that can have improved durability. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of a hydraulic excavator. 
         FIG. 2  is a side view of a boom of the hydraulic excavator of  FIG. 1 . 
         FIG. 3  is a plan view of the boom of  FIG. 2 . 
         FIG. 4  is a cross-sectional view taken along the line A-A of the boom in  FIG. 2 . 
         FIG. 5  is a partially expanded view of the boom of  FIG. 4 . 
         FIGS. 6A-6D  are schematic diagrams illustrating a method of manufacturing the boom. 
         FIG. 7  is a schematic diagram illustrating the method of manufacturing the boom including a pressing tool and a lining tool. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Configuration of Hydraulic Excavator  1   
       FIG. 1  is a side view for illustrating a hydraulic excavator  1 . Herein, “up,” “down,” “front,” “rear,” “left” and “right” are directions from the point of view of an operator sitting in a driver&#39;s seat. 
     The hydraulic excavator  1  includes a traveling body  10 , a turning body  11 , a counterweight  12 , an engine compartment  13 , a device compartment  14 , a cab  15  and a work machine  16 . 
     The traveling body  10  has a pair of track pads that are rotatable independently of each other. The turning body  11  is turnably disposed on the traveling body  10 . The turning body  11  provides a vehicle body frame of the hydraulic excavator  1 . 
     The counterweight  12  is disposed on a rear end portion of the turning body  11 . The engine compartment  13  is disposed on the turning body  11 . The engine compartment  13  is disposed on the turning body  11  in front of the counterweight  12 . The engine compartment  13  houses an engine, an exhaust gas processing device and other components. The device compartment  14  is disposed on the turning body  11  in front of the engine compartment  13 . The device compartment  14  houses a hydraulic pump, a fuel tank, a working fluid tank and other components. The cab  15  is disposed on the turning body  11  in front of the device compartment  14 . The cab  15  is provided with a driver&#39;s seat where an operator sits. 
     The work machine  16  is mounted in a vertically swingable manner on the turning body  11  in front of the device compartment  14  and to the right of the cab  15 . The work machine  16  includes a boom  17 , an arm  18 , a bucket  19 , a pair of boom cylinders  20 , an arm cylinder  21  and a bucket cylinder  22 . The boom  17  is an example of the “box-shaped structure for a work machine.” 
     A base end portion of the boom  17  is swingably mounted to the turning body  11 . A tip end portion of the boom  17  is swingably mounted to a base end side bracket  18   b . A base end portion of the arm  18  is mounted to the base end side bracket  18   b . The bucket  19  is swingably mounted to a bucket bracket  18   a  that is provided on a tip end portion of the arm  18 . 
     Both boom cylinders  20  drive the boom  17 . The boom cylinders  20  are linked to the turning body  11  and a center boss CB of the boom  17 . The arm cylinder  21  drives the arm  18 . The bucket cylinder  22  drives the bucket  19 . 
     Configuration of Boom  17   
     A configuration of the boom  17  according to this embodiment is described with reference to the figures.  FIG. 2  is a side view for illustrating the boom  17 .  FIG. 3  is a plan view for illustrating the boom  17 . 
     The boom  17  includes a body  30 , a base end bracket  31  and an arm bracket  32 . The base end bracket  31  is an example of a “bracket” in this embodiment. 
     The body  30  extends in a longitudinal direction. The body  30  has a boomerang-like shape when viewed from the side. The body  30  is a hollow tube. The body  30  forms a box shape with a top plate  33 , a bottom plate  34 , a first side plate  35  and a second side plate  36 . 
     The first side plate  35  and the second side plate  36  are disposed with a predetermined clearance therebetween. A rear end portion of the first side plate  35  is deformed so as to expand outward. Similarly, a rear end portion of the second side plate  36  is deformed so as to expand outward. A center boss CB that extends in a width direction is attached to the first side plate  35  and the second side plate  36 . The center boss CB is located substantially at the center of the body  30 . 
     The top plate  33  is disposed so as to cover a top opening of a space formed between the first side plate  35  and the second side plate  36 . The bottom plate  34  is disposed so as to cover a bottom opening of the space formed between the first side plate  35  and the second side plate  36 . 
     The base end bracket  31  is connected to a rear end of the body  30 . The base end bracket  31  is provided with an end boss EB that extends in the width direction. The base end bracket  31  may be an ingot that is formed by casting a metal material. 
     The arm bracket  32  is connected to a front end of the body  30 . The arm bracket  32  is provided with an arm mounting hole  32   a . The arm  18  (see  FIG. 1 ) is mounted in the arm mounting hole  32   a . The arm bracket  32  may be an ingot that is formed by casting a metal material. 
     Configuration of Body  30   
     A configuration of the body  30  is described with reference to  FIGS. 2 and 3 . 
     The body  30  includes a straight section  30   a  and a wide section  30   b . The straight section  30   a  is formed of front side portions of each of the top plate  33 , the bottom plate  34 , the first side plate  35  and the second side plate  36 . The wide section  30   b  is formed of rear side portions of each of the top plate  33 , the bottom plate  34 , the first side plate  35  and the second side plate  36 . 
     The straight section  30   a  is continuous to the wide section  30   b  at a predetermined position LP between the center boss CB and the end boss EB. The straight section  30   a  is smoothly continuous to the wide section  30   b  at the predetermined position LP. In this embodiment, “smoothly continuous” means that there is no point of inflection in any of the top plate  33 , the bottom plate  34 , the first side plate  35  and the second side plate  36  at the predetermined position LP. None of the top plate  33 , the bottom plate  34 , the first side plate  35  and the second side plate  36  are bent at the predetermined position LP. Therefore, a drastic change in the cross-sectional area of the body  30  at the predetermined position LP is eliminated. 
     In this embodiment, as illustrated in  FIG. 2 , the predetermined position LP at which the straight section  30   a  is smoothly continuous to the wide section  30   b  is located substantially center between the center boss CB and the end boss EB. On an imaginary line that connects the center boss CB and the end boss EB to each other, an interval L 1  between a center axis AX 1  of the center boss CB and the predetermined position LP is substantially equal to an interval L 2  between a center axis AX 2  of the end boss EB and the predetermined position LP. In this embodiment, a ratio of the interval L 1  to the interval L 2  is approximately 1:1. However, the predetermined position LP may be anywhere as long as the wide section  30   b  does not interfere with the pair of boom cylinders  20  (see  FIG. 1 ). For example, the ratio of the interval L 1  to the interval L 2  can be set between 1:1 to 4:1. 
     The straight section  30   a  is connected to the front of the wide section  30   b . As illustrated in  FIG. 3 , when viewed from above, the straight section  30   a  has a width Wa of that is substantially constant in the longitudinal direction. In this embodiment, the width Wa of the straight section  30   a  is 450 mm. 
     The wide section  30   b  is connected to the rear of the straight section  30   a . As illustrated in  FIG. 3 , when viewed from above, the wide section  30   b  has a width Wb that increases toward the base end bracket  31 . The width Wb of the wide section  30   b  is not constant across the entire wide section  30   b  and continues to increase from the predetermined position LP, at which the straight section  30   a  and the wide section  30   b  are smoothly continuous to each other, to the base end bracket  31 . In this embodiment, the width Wb of the wide section  30   b  has a maximum value of 570 mm. In this embodiment, a ratio of the width Wa of the straight section  30   a  to the wide section  30   b  is 15:19. 
     As illustrated in  FIG. 3 , when viewed from above, a first side surface S 1  of the wide section  30   b  is convexly curved toward the inner side of the body  30 . Similarly, a second side surface S 2  of the wide section  30   b  is convexly curved toward the inner side of the body  30 . The first side surface S 1  is a part of a surface of the first side plate  35  and the second side surface S 2  is a part of a surface of the second side plate  36 . 
     In this embodiment, the wide section  30   b  has a height that becomes smaller toward the base end bracket  31  from the straight section  30   a . On the other hand, as described above, the width of the wide section  30   b  increase from the predetermined position LP, at which the straight section  30   a  and the wide section  30   b  are smoothly continuous to each other, to the base end bracket  31 . With this configuration, the wide section  30   b , which is most likely subject to load, is able to have improved bending strength at the sides. 
     Configuration of Base End Bracket  31   
       FIG. 4  is a cross-sectional view taken along the line A-A in  FIG. 2 .  FIG. 5  is a partially expanded view of  FIG. 4 . 
     The base end bracket  31  is formed in a shape that is entirely tapered toward the body  30 . The base end bracket  31  includes a first abutment surface S 3 , a second abutment surface S 4 , and a front end surface S 5 . 
     The first side plate  35  of the body  30  abuts against the first abutment surface S 3 . The first abutment surface S 3  is formed so as to be angled with respect to the longitudinal direction of the body  30  such that the first abutment surface S 3  follows the first side plate  35  that expands outward. The first abutment surface S 3  is a part of a left side surface of the base end bracket  31 . 
     The second side plate  36  of the body  30  abuts against the second abutment surface S 4 . The second abutment surface S 4  is formed so as to be angled with respect to the longitudinal direction of the body  30  such that the second abutment surface S 4  follows the second side plate  36  that expands outward. The second abutment surface S 4  is a part of a right side surface of the base end bracket  31 . 
     The front end surface S 5  is continued to the first abutment surface S 3  and the second abutment surface S 4 . In this embodiment, the front end surface S 5  is formed into a flat plate, but the front end surface S 5  is not limited to this shape. 
     Method of Manufacturing Boom  17   
       FIGS. 6A to 6E  and  FIG. 7  are schematic diagrams for showing a method of manufacturing the boom  17 . 
     First, as illustrated in  FIG. 6A , the bottom plate  34  having a rear end portion that flares toward the bottom is prepared. 
     Next, as illustrated in  FIG. 6B , the first side plate  35  and the second side plate  36  are placed in parallel on the bottom plate  34  with a predetermined clearance therebetween. 
     Next, as illustrated in  FIG. 6C , with the first side plate  35  and the second side plate  36  being fixed at the predetermined positions LP, rear end portions of the first side plate  35  and the second side plate  36  are pushed outward using a lining. More specifically, as illustrated in  FIG. 7 , with a pair of pressing tools  40  abutting against the predetermined positions LP on outer surfaces of the first side plate  35  and the second side plate  36 , a lining tool  41  applies outward pressure to inner surfaces of the rear end portions of the first side plate  35  and the second side plate  36 . At this time, the lining is adjusted to cause elastic deformation within a range that does not plastically deform the first side plate  35  and the second side plate  36 . 
     Next, as illustrated in  FIG. 6D , the base end bracket  31  is inserted between the respective rear end portions of the first side plate  35  and the second side plate  36  that have elastically deformed outward, and then the lining is removed, to thereby sandwich and fix the base end bracket  31  between the respective rear end portions of the first side plate  35  and the second side plate  36 . Then, the bottom plate  34  and the first side plate  35  are welded together and the bottom plate  34  and the second side plate  36  are welded together. In addition, the base end bracket  31  is temporarily mounted to the first side plate  35  from the inner side, and the base end bracket  31  is temporarily mounted to and the second side plate  36  from the inner side. 
     Next, as illustrated in  FIG. 6E , the top plate  33  is placed on top of the first side plate  35  and the second side plate  36 . Then, the top plate  33  and the first side plate  35  are welded together and the top plate  33  and the second side plate  36  are welded together, to thereby fix the top plate  33 . 
     The boom  17  includes the body  30  and the base end bracket  31 . The body  30  includes the straight section  30   a  and the wide section  30   b . When viewed from above, the width Wa of the straight section  30   a  is substantially constant. When viewed from above, the width Wb of the wide section  30   b  increases toward the base end bracket  31 . The straight section  30   a  and the wide section  30   b  are smoothly continuous to each other. 
     As described above, because the wide section  30   b  is configured to increase in the width Wb toward the base end bracket  31 , the bending strength of the wide section  30   b  at the sides can be improved. In addition, because the straight section  30   a  and the wide section  30   b  are smoothly continuous to each other, it is possible to reduce locally concentrating stresses in the body  30 . 
     In the above-described embodiment, a case has been described in which a “box-shaped structure for a work machine” according to the present invention is applied to the boom  17 , but the present invention is not limited thereto. The “box-shaped structure for a work machine” according to the present invention can also be applied to the arm  18 . Even in this case, durability of the arm  18  can be improved with the body of the arm  18  having a width that increases toward the base end side bracket  18   b.    
     In the above-described embodiment, as illustrated in  FIG. 6C , the first side plate  35  and the second side plate  36  are pushed outward using a lining, but the first side plate  35  and the second side plate  36  may be pushed outward by pushing the base end bracket  31  in between the first side plate  35  and the second side plate  36 . 
     In the above-described example, the end boss EB that extends in the width direction is separately provided on the base end bracket  31 , but the base end bracket  31  and the end boss EB may be formed integrally. 
     In the above-described example, an ingot formed by casting a metal material is used for the base end bracket  31 , but the base end bracket  31  may be formed by forging or be formed of a metal plate.