Patent Publication Number: US-10767340-B2

Title: Reinforcement structure for boom of work machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase application of International Patent Application No. PCT/EP2016/064590 filed Jun. 23, 2016, which claims priority to Japanese Patent Application No. 2015-130123 filed Jun. 29, 2015, both of which are incorporated by reference herein in their entireties for all purposes. 
     TECHNICAL FIELD 
     The present invention relates to a reinforcement structure for a boom of a work machine, which is provided with a baffle for reinforcement in an internal space of the boom. 
     BACKGROUND ART 
     There are many types of work machines which have a front boom as a component, as exemplified by hydraulic shovels. 
     The boom is often curved in the longitudinal direction and configured with a top plate forming an upper surface, a pair of side plates forming side surfaces, a bottom plate forming a lower surface, and a baffle. The baffle is a reinforcing wall provided to partition an internal space having the top plate, side plates and bottom plate as the peripheral walls and is welded to the inner wall surfaces of the top plate, the side plates and the bottom plate. 
     Japanese Patent Application Laid-open No. 2002-348903 discloses a boom structure capable of reducing torsional stress. This boom structure simulates a reference line that connects one end portion positioned on the boom base end side in a first bracket for fitting a boom cylinder attached to the bottom surface of the boom, and the center of curvature of a middle curved portion of the boom, wherein a lower reinforcing wall that is fixed to the bottom surface at one end portion is positioned in such a manner that a flange portion of the lower reinforcing wall approaching a top surface is inclined away from the reference line at the boom base end side. In this manner, the torsional stress occurring at a tip end portion of the reinforcing wall is reduced. The disclosed boom structure serves to reduce the torsional stress that occurs in the reinforcing wall and is not designed to prevent the stress from concentrating on the rear upper portions of the side plates. 
     When longitudinal bending, lateral bending, and twisting are made multiple times in the entire boom, high stress occurs in the boom. This stress tends to concentrate on the part where the baffle in the internal space of the boom and each of the plates (the top plate, the side plates, and the bottom plate) are welded together. The stress tends to concentrate especially on the top plate side of the welded parts between the rear side baffle and side plates, i.e., the rear upper portions of the side plates. 
     Such concentration of the stress can be prevented and handled by improving the strength of the reinforcement structure by increasing the plate thickness of the side plates and/or the baffle, but it unfavorably leads to significant increases in weight and cost. 
     The present invention was contrived in view of the foregoing problems, and an object thereof is to provide a reinforcement structure for a boom of a work machine, capable of preventing the stress from concentrating on the rear upper portions of the side plates while preventing the increases in weight and cost. 
     SUMMARY OF THE INVENTION 
     (1) In order to achieve the foregoing object, a reinforcement structure for a boom of a work machine according to the present invention is a reinforcement structure for a boom of a work machine, which reinforces the boom configured with a top plate, a side plate, and a bottom plate and having an internal space and a curved portion in the middle in a longitudinal direction, wherein a baffle for reinforcement is provided further on a rear side than the curved portion in such a manner as to cut across the internal space, and the baffle is configured with a plate that curves vertically and protrudes forward. 
     (2) It is preferred that the baffle be symmetrical with respect to a centerline of the side plate. 
     According to the reinforcement structure for a boom of a work machine of the present invention, stress can be dispersed by configuring the baffle with a plate that curves vertically and protrudes forward, preventing the stress from concentrating on the rear upper portions of the side plates while preventing the increases in weight and cost. 
     The rear upper portion of the side plate described in the present invention represents a region near an upper slewing body (rear) with respect to the curved portion of the side plate, and a part of the side plate near the top plate (upper portion), the region including “a joint portion near the top plate, inside a joint portion between the side plate and the baffle at the rear of the curved portion.” 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic perspective view showing the entire configuration of a work machine according to an embodiment of the present invention. 
         FIG. 2  is a schematic diagram showing the configuration of the rear portion of a boom according to the embodiment of the present invention, without the right side panel, wherein  FIG. 2( a )  is a perspective view in which the right-hand side of the configuration is viewed obliquely downward, and  FIG. 2( b )  a right-side view. 
         FIG. 3  is a schematic side view showing a reinforcement structure for the boom, without the right side panel, wherein  FIG. 3( a )  is a diagram showing a standard structure (conventional structure),  FIG. 3( b )  a diagram showing a comparative structure  1 , and  FIG. 3( c )  a diagram showing a comparative structure  2 . 
         FIGS. 4( a ) and 4( b )  are each a schematic diagram showing the configuration of a rear portion of a boom according to a modification of the embodiment of the present invention, without the right side panel. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention are now described hereinafter with reference to the drawings. 
     Each of the embodiments illustrated below is merely an example and is not intended to exclude applications of various modifications and techniques that are not illustrated in the following embodiments. The configurations of the following embodiments can be implemented in various different ways without departing from the gist thereof, and can also be sorted out as needed or can be combined as appropriate. 
     The following embodiments each illustrate an example in which the present invention is applied to a hydraulic shovel functioning as a work machine, but the invention can be applied to various work machines across the board other than hydraulic shovels, such as hydraulic cranes. 
     In the following description, unless otherwise specified, the direction of travel of a work vehicle indicates the front, the left-hand side and the right-hand side are defined based on the front, the direction of gravity indicates the lower side, and the opposite direction indicates the upper side. In addition, in the descriptions of the devices and parts mounted in the work vehicle, unless otherwise specified, the vertical direction, the lateral direction (also referred to as “width direction,” hereinafter), and the longitudinal direction are defined based on the state in which these devices and parts are mounted in the work vehicle. 
     The configuration of a hydraulic shovel  1  according to an embodiment of the present invention is described with reference to  FIG. 1 . 
       FIG. 1  is a schematic perspective view showing the entire configuration of a work machine according to an embodiment of the present invention. This hydraulic shovel  1  is configured with a lower traveling body  2  equipped with a crawler-type traveling device, and an upper slewing body  3  mounted in a slewable manner on the lower traveling body  2 . A cabin  5  for boarding an operator and a front work device (referred to as “work device,” hereinafter) provided adjacent thereto are provided at the vehicle front side of the upper slewing body  3 . A counterweight  6  for keeping the weight balance of the machine body is disposed at the rearmost end portion of the upper slewing body  3 . 
     The work device  4  is configured with a boom  4 A, a stick  4 B, and a bucket  4 C. The boom  4 A has a curved portion  4 Aa that protrudes upward at a longitudinal middle portion of the boom  4 A in the posture shown in  FIG. 1 , and a boom foot boss  45  (see  FIGS. 2( a ) and 2( b ) ) provided at the base end portion of the boom  4 A is axially supported so as to be able to swing freely with respect to the upper slewing body  3 . Also, a boom cylinder  14 A is interposed between the boom  4 A and the upper slewing body  3 , so the boom  4 A swings in response to a telescopic motion of the boom cylinder  14 A. 
     Similarly, the stick  4 B has a base end portion thereof axially supported so as to be able to swing with respect to the end portion of the boom  4 A, and the bucket  4 C is axially supported by the end portion of the stick  4 B. A stick cylinder  14 B is interposed between the boom  4 A and the stick  4 B, and a bucket cylinder  14 C is interposed between the stick  4 B and the bucket  4 C. The stick  4 B and the bucket  4 C swing in response to telescopic motions of the stick cylinder  14 B and the bucket cylinder  14 C. 
     Various input levers and pedals, not shown, which are used for inputting the actuation amount of each of these hydraulic devices, are provided inside the cabin  5 . 
     The configuration of the boom according to the embodiment of the present invention is further described with reference to  FIGS. 2( a ) and 2( b ) . 
       FIG. 2  is a schematic diagram showing the configuration of the rear portion of the boom according to the embodiment of the present invention, without the right side panel, wherein  FIG. 2( a )  is a perspective view in which the right-hand side of the configuration is viewed obliquely downward, and  FIG. 2( b )  a right-side view. 
     The boom  4 A is configured with a top plate  41  configuring a ceiling surface, a pair of side plates  42  configuring side surfaces, and a bottom plate  43  configuring a bottom surface. Each side plate  42  is arched upward (toward the top plate  41 ) as a whole as viewed from the front, wherein the upper rim (the rim portion on the top plate  41  side) and the lower rim (the rim portion on the bottom plate  43  side) of each side plate  42  have the centers thereof in the extension direction curved upward. The top plate  41  is curved along the upper end of each side plate  42 , and the side rims of the lower surface of the top plate  41  are welded to the upper ends of the side plates. The bottom plate  43  is curved along the lower end of each side plate  42 , and the side rims of the upper surface of the bottom plate  43  are welded to the lower ends of the side plates  42 . 
     An internal space  46  surrounded by the plates  41 ,  42 ,  43  is provided with a rear baffle  44  for reinforcement, which is located further on the rear side than the curved portion  4 Aa. The rear baffle  44  is provided over the entire length of the boom  4 A in the width direction in such a manner as to cut across the internal space  46  (precisely, in such a manner as to divide the internal space  46  into a front portion and a rear portion with respect to the longitudinal direction). The rear baffle  44  has an upper end thereof welded to the lower surface of the top plate  41 , has a lower end of the same welded to the upper surface of the bottom plate  43 , and has both left and right ends of the same welded to the inner side surfaces of the left and right side plates  42 . 
     The rear baffle  44  is a plate curved vertically (in other words, bent into the opposite C shape as viewed from the right) and protruding forward. Specifically, the rear baffle  44  is a plate that has an upper inclined surface  44   a  inclining downward and forward and taking up approximately the upper half, a lower inclined surface  44   b  inclining downward and rearward and taking up approximately the lower half, and a curved portion  44   c  located in the middle in the vertical direction and connecting the upper inclined surface  44   a  and the lower inclined surface  44   b  to each other. 
     A conventional rear baffle  144  is shown with the two-dot chain line in  FIG. 2( b ) . The conventional rear baffle  144  is a flat plate that is not curved and is installed in such a manner as to be divided perpendicularly into two sections by a centerline L 0  of the side plates  42 . The centerline L 0  of the side plates  42  is defined as a line that has points C 1 , C 2 , etc. thereof dividing perpendicular lines LV 1 , LV 2  of the centerline L 0  into two sections between the top plate  41  and the bottom plate  43  (in other words, the centerline L 0  is obtained by connecting these points C 1 , C 2 , etc.). Therefore, the rear baffle  144  can also be a perpendicular line LVn of the centerline L 0 . 
     In the rear baffle  44 , the curved portion  44   c  disposed on the centerline L 0 , and each of the connecting positions between the top plate  41  and the bottom plate  43  is identical to that of the conventional baffle  144 . 
     Specifically, the rear baffle  44  is curved on the centerline L 0 , has the upper end thereof connected to the intersection point between the top plate  41  and the perpendicular line LVn described above, and has the lower end of the same connected to the intersection point between the bottom plate  43  and the perpendicular line LVn. Therefore, the upper inclined surface  44   a  and the lower inclined surface  44   b  of the rear baffle  44  are equally inclined at an angle θ 1  (30 degrees here) with respect to the conventional rear baffle  144 . 
     In other words, when viewed from a side, the rear baffle  44  resembles the two equal sides of an isosceles triangle that are symmetrical with respect to the centerline L 0 . 
     Note that the internal space  46  is provided with a front baffle, not shown, at an area in front of the curved portion  4 Aa (on the right-hand side of  FIG. 2 ). 
     The reasons why the rear baffle  44  is formed into such a shape are described with reference to  FIGS. 3( a ), 3( b ), 3( c )  in addition to  FIGS. 2( a ) and 2( b ) . 
       FIG. 3  is a schematic side view showing a reinforcement structure for the boom, without the right side panel, wherein  FIG. 3( a )  is a diagram showing a standard structure,  FIG. 3( b )  a diagram showing a comparative structure  1 , and  FIG. 3( c )  a diagram showing a comparative structure  2 . 
     First, the standard structure, the comparative structure  1 , and the comparative structure  2  are described. The standard structure is a conventional reinforcement structure configured as shown in  FIG. 3( a )  and using the conventional rear baffle  144 . As described above, the rear baffle  144  is a flat plate without a curve and installed in such a manner as to be divided perpendicularly into two sections by the centerline L 0  of the side plates  42 . 
     As with the reinforcement structure for a boom according to the present invention, this rear baffle  144  is provided over the entire width of the boom  4 A and has the entire circumference welded to the plates  41 ,  42 ,  43 . 
     The comparative structure  1  and the comparative structure  2  are configured as shown in  FIGS. 3( b ) and 3( c ) . Rear baffles  244 ,  344  according to the comparative structures  1  and  2  are the same as the conventional rear baffle  144  shown with the two-dot chain line, in that the rear baffles  244 ,  344  are each a flat plate without a bent portion, provided over the entire width of the boom  4 A, and each have the entire circumference welded to the plates  41 ,  42 ,  43 , but are different from the rear baffle  144  in terms of the installation angle. 
     Specifically, in the comparative structure  1 , the rear baffle  244  is the same as the conventional rear baffle  144  in terms of the positions thereof to be attached to the lower ends of the bottom plate  43 , but is inclined forward at a predetermined angle θ 2  (30 degrees here) from the conventional rear baffle  144 , as shown in  FIG. 3( b ) . 
     In the comparative structure  2 , the rear baffle  344  is the same as the conventional rear baffle  144  in terms of the positions thereof attached to be attached to the upper ends of the top plate  41 , but is inclined rearward at a predetermined angle θ 3  (30 degrees here) from the conventional rear baffle  144 , as shown in  FIG. 3( c ) . 
     The strengths of these reinforcement structures were evaluated. As a result of analyzing the stresses caused in the top plate  41 , the top side of each side plate  42  (near the top plate  41 ), the bottom side of each side plate  42  (near the bottom plate  43 ), and the bottom plate  43  surrounding each of the rear baffles  144 ,  244 ,  344 , the results shown in Table 1 below were obtained. 
     In the standard structure (i.e., the conventional reinforcement structure), an excessive level of stress has occurred on the top side of each side plate  42 . Therefore, for the top side of each side plate  42  in Table 1 below, “x” is entered on the assumption that there is a problem if the stress generated therein is equal to or greater than that of the standard structure, and “O” is entered on the assumption that there is an improvement if the stress generated therein is lower than that of the standard structure. 
     In the standard structure, on the other hand, the stresses that were generated in the sections other than the top side of each side plate  42 , i.e., the top plate  41 , the bottom side of each side plate  42 , and the bottom plate  43 , were comparatively small, posing no problems. Therefore, for the top plate  41 , the bottom side of each side plate  42 , and the bottom plate  43  in Table 1 below, “O” is entered on the assumption that there is no problem if the stresses generated therein are equal to or lower than those of the standard structure, and “x” is entered on the assumption that there is a problem if the stresses generated therein are significantly greater than those of the standard structure. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Stress generated on 
                   
               
               
                   
                 the rear side of 
               
               
                   
                 each side plate 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Top 
                   
                 Bottom 
                   
               
               
                   
                 plate 
                 Top side 
                 side 
                 Bottom plate 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Standard 
                 ◯ 
                 X 
                 ◯ 
                 ◯ 
               
               
                 structure 
               
               
                 (conventional 
               
               
                 structure) 
               
               
                 Comparative 
                 ◯ 
                 X 
                 ◯ 
                 ◯ 
               
               
                 structure 1 
                   
                   
                 (slightly 
                 (slightly 
               
               
                   
                   
                   
                 reduced) 
                 reduced) 
               
               
                 Comparative 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
               
               
                 structure 2 
                   
                   
                   
                 (significant 
               
               
                   
                   
                   
                   
                 increase) 
               
               
                 Present 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 invention 
               
               
                   
               
            
           
         
       
     
     In the comparative structure  1 , while a slight reduction in stress was confirmed in the bottom side of each side plate  42  and the bottom plate  43 , a reduction in stress was not confirmed in the top side of each side plate  42 , a problematic section. 
     In the comparative structure  2 , a reduction in stress was confirmed in the top side of each side plate  42  which is a problematic section. However, a significant increase in stress was confirmed in the bottom plate  43 , which is considered to make the application of this structure to an actual machine difficult. 
     In view of the results of the comparative structure  1  and the comparative structure  2 , a configuration was suggested that employs, as the shape of the rear baffle, the forward inclination of the comparative structure  1  showing an improvement on the bottom side and the rearward inclination of the comparative structure  2  showing an improvement on the top side (i.e., the shape of the rear baffle  44  shown in  FIGS. 2( a ) and 2( b ) ). As a result of analyzing the stress generated in this structure, a reduction in stress was confirmed on the rear side (back) and the top side (upper portion) of each side plate  42  that are particularly problematic, i.e., in the rear upper portion of each side plate, as shown in the “Present invention” column of Table 1. In regard to the other sections as well, the stresses were maintained at the same levels (posing no problems) as the standard structure (conventional structure). 
     Therefore, the shape of the rear baffle according to the reinforcement structure of the present invention was employed as the shape of the rear baffle  44  shown in  FIGS. 2( a ) and 2( b ) . 
     The reasons why such a shape of the rear baffle can mitigate the concentration of stress (concentration of stress particularly in the rear upper portion of each side plate  42 ) are understood as follows. 
     As described above, when longitudinal bending, lateral bending, and twisting are made multiple times in the entire boom, high stress occurs in the boom. However, forming an angle in the rear baffle  44  can retain the function of preventing the twisting, which is the original function of the rear baffle  44 , and at the same time dispersing the high stress can be understood to be able to mitigate the concentration of stress. 
     (1) According to the reinforcement structure for a boom of a work machine of an embodiment of the present invention, stress can be dispersed by simply configuring the rear baffle  44  with a plate curved vertically and protruding forward. Therefore, the plate thickness of the rear baffle  44  and the side plates  42  do not need to be increased, and concentration of stress in the rear upper portion of each side plate  42  can be prevented while preventing increases in weight and cost. 
     (2) The rear baffle  44  is curved on the centerline L 0  of the side plates  42 , has the upper end connected to the intersection point between the top plate  41  and the perpendicular line LVn of the centerline L 0 , and has the lower end connected to the intersection point between the bottom plate  43  and the perpendicular line LVn. Therefore, the rear baffle  44  is symmetrical with respect to the centerline L 0 , making it possible to attach the rear baffle  44  normally to the boom  4 A even upside down. Consequently, the rear baffle  44  can be attached to the boom  4 A without any regard to the top and the bottom. 
     In addition, the rear baffle  44  is in a vertically symmetrical, balanced shape, effectively preventing the stress from concentrating disproportionately. 
     (1) According to the foregoing embodiment, the single rear baffle  44  is provided over the entire width of the boom  4 A. However, for instance, a plurality of relatively narrow rear baffles  44  may be arranged along the width direction, with a gap therebetween or stuck close to each other. 
     (2) According to the foregoing embodiment, the inclination angles of the upper inclined surface  44   a  and the lower inclined surface  44   b  of the rear baffle  44  are equal to each other, i.e., 30 degrees. However, these inclination angles can be changed as appropriate according to the occurrence of stress and manufacturability (of each model of work machine, for example). For example, the inclination angles of the upper inclined surface  44   a  and the lower inclined surface  44   b  do not have to be equal to each other (the inclination angle of the upper inclined surface  44   a  and the inclination angle of the lower inclined surface  44   b  may be different from each other). These inclination angles do not have to be 30 degrees. In other words, the inclination angles of the upper inclined surface  44   a  and the lower inclined surface  44   b  may be set at the same angle other than 30 degrees. 
     (3) According to the foregoing embodiment, the rear baffle  44  is symmetrical with respect to the centerline L 0 ; however, the rear baffle  44  may be asymmetrical with respect to the centerline L 0  in accordance with the occurrence of stress and manufacturability (of each model of work machine, for example). 
     For example, as shown in  FIG. 4( a ) , while having the rear baffle  44  curved on the centerline L 0 , the inclination angle of the upper inclined surface  44   a  and the inclination angle of the lower inclined surface  44   b  may be set at mutually different angles of θ 1 , θ 4 . Alternatively, as shown by the solid line or the two-dot chain line in  FIG. 4( b ) , the inclination angle of the upper inclined surface  44   a  and the inclination angle of the lower inclined surface  44   b  may be the same angle of θ 1 , and the rear baffle  44  may be curved at a position away from the centerline L 0  (the position of the curved portion  44   c  may be set at a position close to the top plate  41  or a position close to the bottom plate  43 ). 
     In addition, while having the rear baffle  44  curved at the position away from the centerline L 0 , the inclination angle of the upper inclined surface  44   a  and the inclination angle of the lower inclined surface  44   b  may be set at mutually different angles.