# Patent

## Title
Construction machine

## Abstract

A construction machine where an operating load is transferred to a location having good rigidity, thereby ensuring the strength of a vehicle body and increasing the load-withstanding strength in relation to running loads. The frame of the lower traveling body of the construction machine comprising a hollow center frame having an upper plate with an attachment ring, a lower plate, and side plates that surrounding sides of the frame and that jut out from the attachment ring, and reinforcing ribs which connect the upper plate to the lower plate in the interior of the center frame beneath the attachment ring.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a construction machine such as a hydraulic shovel, and more particularly to a frame constitution of a lower traveling body in a construction machine.
2. Description of the Related Art
A conventional hydraulic shovel 100 disclosed in “Crawler-type Vehicle” (Japanese Unexamined Patent Application Publication 2002-178960) comprises a traveling body 101 to enable movement, and a slewing body 102 which is mounted slewably above the traveling body 101, as shown in FIG. 9.
The slewing body 102 comprises a slewing frame 103, and the stewing frame 103 is provided with a body cover 104 accommodating a motor and the like, a cab 105 which defines the operating cabin, a counterweight 106, and so on, for example.
A working device 107 is provided elevatably at the front portion of the slewing body 102.
A truck frame 108 constituting the main body part of the traveling body 101 is constituted by a center frame 109 positioned in the center by means of steel plate welding or the like, and side frames 112 provided on both the left and right sides of the center frame 109 and extending to the front and rear, as shown in FIGS. 10A, 10B, and 10C.
Here, the center frame 109 is constituted by a central circular core 110, and leg parts 111 extending in a front/rear direction and a left/right direction from the outer periphery of the circular core 110 to form an overall H shape.
The leg parts 111 are formed as canning structures by an upper plate portion 111A, a lower plate portion 111B, side plate portions 111C which connect the plate portions 111A, 111B in a vertical direction, and so on.
112, 112 are left and right side frames provided on the tip end side of the leg portions 111 of the center frame 109 by welding. The side frames 112 are formed as frame bodies in a substantially reverse C shape extending in a front/rear direction.
Left and right mudguard covers 125, 125 are disposed respectively on the side frames 112, 112 of the truck frame 108.
The hydraulic shovel 100 described above travels over various types of ground surface by driving crawler belts 117 disposed on the traveling body 101 to rotate. As a result, earth, mud, and so on are churned up by the crawler belts 117.
Here, the mudguard covers 125, 125 provided in the vicinity of the crawler belts 117, 117 are constituted so as to extend in a horizontal direction, and hence the earth, mud, and so on that are churned up by the crawler belts 117 may accumulate on top of the mudguard covers 125, 125.
In this case, a worker must remove the accumulated earth, mud, and so on, and if the earth, mud, and so on are left to accumulate, they cause running resistance when the hydraulic shovel 100 is operated.
To improve earth removal, a constitution has been considered in which the frame of the lower traveling body is divided into a central box-shaped rotary case portion and the pair of truck frame portions, on which the crawler belts are provided, on the two sides of the rotary case portion, whereby the truck frames are connected to the rotary case portion via a pair of leg-shaped connecting members.
According to this constitution, the rotary case portion and the truck frame portions are connected via a pair of connecting members, and hence an open space is formed between the pair of connecting members through which the earth that is churned up by the crawler belt passes and falls to the ground. Thus earth removal can be precipitated favorably.
Incidentally, various loads act on the slewing body 102 of the hydraulic shovel 100, on which the working device 107 is provided, during an operation.
However, the conventional truck frames 108 are constituted by sheet metal, as shown in FIG. 10C, and hence a vertical plate may be provided below the circular core 110 to which the slewing body 102 is connected, and a vertical plate 120 is provided between the upper plate portion 111A and lower plate portion 111B.
Hence stress that is generated by a load transmitted to the circular core 110 which supports the slewing body 102 is transferred smoothly to the vertical plate 120 from the circular core 110, thus eliminating problems relating to strength.
When the truck frame portions and central rotary case portion are constituted separately and joined via connecting members, however, the length of the connecting members is preferably set at no more than a predetermined length from the point of view of problems regarding the strength of the connecting members and the prevention of increases in the moment of loads generated during travel. To shorten the connecting members, a side plate of the rotary case portion to which the connecting members are joined must be formed so as to jut out from the connecting member side.
In this case, the side plate of the rotary case portion is provided at a remove from the location of the upper plate of the rotary case portion on which the slewing body is mounted, and as a result, loads transmitted from the slewing body are transferred to the upper plate having low load-withstanding strength, leading to possible breakage of the rotary case portion depending on the structure thereof.
SUMMARY OF THE INVENTION
The present invention has been designed in consideration of this situation, and it is an object thereof to provide a construction machine in which a load that is transmitted during an operation is transferred to a location having good rigidity, thereby securing the strength of a vehicle body, and which is also capable of realizing an increase in the load-withstanding strength in relation to a load that is applied during travel, thereby improving reliability.
A construction machine according to a first invention comprises a lower traveling body having a frame and an upper slewing body which slews freely about the lower traveling body, the frame of the lower traveling body comprising a hollow center frame having an upper plate, a lower plate, and side plates surrounding sides thereof, the upper plate being formed with an attachment ring on which a slewing bearing of the upper slewing body is mounted; a pair of truck frames disposed on outside of two side portions of the center frame; and connecting members for connecting the center frame to the truck frames, center joining portions of the connecting members being welded to the side plates of the center frame, wherein the center frame comprises the side plates positioned so as to jut out from the attachment ring, and reinforcing ribs which connect the upper plate to the lower plate in an interior of the center frame beneath the attachment ring.
According to this constitution, the reinforcing rib is provided in the interior of the center frame beneath the attachment ring for connecting the upper plate to the lower plate, and hence an operating load from the upper slewing body that is transmitted to the attachment ring is transferred to the highly rigid reinforcing rib and dispersed over the center frame.
Hence the load-withstanding strength of the center frame to operating loads is secured, leading to an improvement in the reliability of the vehicle body.
Moreover, the center frame comprises the side plate which are positioned so as to jut out from the attachment ring, and hence the length of the connecting member which connects the center frame to the truck frames can be reduced. As a result, increases in the moment of a load that is generated during traveling and transmitted to the connecting member can be prevented, and such loads can be received in the strong center frame.
Hence the load-withstanding strength of the center frame to running loads is secured, leading to an improvement in the reliability of the vehicle body.
In a construction machine according to a second invention, pertaining to the construction machine according to the first invention, the reinforcing rib has a U-shaped form when seen from above.
According to this constitution, the reinforcing rib has a U-shaped form when seen from above, and hence rigidity is high in relation to compressive loads, tensile loads, bending moments, and so on which act on the center frame. Thus the load-withstanding strength of the center frame can be improved.
In a construction machine according to a third or a fourth invention, pertaining to the construction machine according to the first or second invention, the reinforcing rib is provided on inside of the center frame and inside of the joining portion of the connecting member, or extending along a line of extension of a vertical plate of the connecting member.
According to this constitution, the reinforcing rib is provided on the inside of the center frame and the inside of the joining portion of the connecting member, or extending along the line of extension of a vertical plate of the connecting member, and hence a load from the connecting member can be received in the reinforcing rib which is disposed along the transmission direction, and can thus be dispersed smoothly to the center frame.
A construction machine according to a fifth invention comprises a lower traveling body having a frame and an upper stewing body which slews freely about the lower traveling body, the frame of the lower traveling body comprising a hollow center frame having an upper plate, a lower plate, and side plates surrounding sides thereof, the upper plate being formed with an attachment ring on which a slewing bearing of the upper slewing body is mounted; a pair of truck frames disposed on outside of two side portions of the center frame; and connecting members for connecting the center frame to the truck frames, the center joining portions of the connecting members being welded to the side plates of the center frame, wherein the side plate of the center frame is formed in a position jutting out from the attachment ring, and comprises a reinforcing plate portion which recedes inward below the attachment ring at an intermediate portion of locations at which the center joining portion of the connecting member is joined.
According to this constitution, the side plate of the center frame comprises a reinforcing plate portion which recedes inward below the attachment ring at an intermediate portion of the locations at which the center joining portion of the connecting member is joined, and hence an operating load from the upper slewing body that is transmitted to the attachment ring is transferred to the side plate provided with the highly rigid reinforcing plate portion, and dispersed over the center frame.
Hence the load-withstanding strength of the center frame to operating loads is secured, leading to an improvement in the reliability of the vehicle body.
Further, the side plate of the center frame is formed in a position jutting out from the attachment ring, and hence the length of the connecting member which connects the center frame to the truck frames can be reduced. As a result, increases in the moment of a load that is generated during traveling and transmitted to the connecting member can be prevented, and such loads can be received in the strong center frame.
Hence the load-withstanding strength of the center frame to running loads is secured, leading to an improvement in the reliability of the vehicle body. In a construction machine according to a sixth invention, pertaining to the construction machine according to the fifth invention, the reinforcing plate portion is provided on inside of the center frame and inside of the joining portion of the connecting member, or extending along a line of extension of a vertical plate of the connecting member.
According to this constitution, the reinforcing plate portion is provided on inside of the center frame and inside of the joining portion of the connecting member, or extending along the line of extension of a vertical plate of the connecting member, and hence a transfer load from the connecting member can be received in the reinforcing plate portion which is disposed along the transmission direction, and can thus be dispersed smoothly to the center frame.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view showing a hydraulic shovel of an embodiment according to the present invention;
FIG. 2 is a perspective view of the frame of a lower traveling body in the hydraulic shovel of a first embodiment according to the present invention;
FIG. 3 is a top view of the frame of the lower traveling body in the hydraulic shovel of the first embodiment according to the present invention;
FIGS. 4A, 4B, and 4C are a perspective view, a partially cut-away top view, and a bottom view showing a center frame of the hydraulic shovel of the first embodiment according to the present invention;
FIGS. 5A and 5B are perspective views of a connecting member of the hydraulic shovel of the first embodiment according to the present invention;
FIGS. 6A and 6B are a conceptual top view of a first modified example and a conceptual top view of a second modified example of a joining portion between the center frame and connecting member in the first embodiment according to the present invention;
FIG. 7 is a top view of a frame of a lower traveling body in a hydraulic shovel of a second embodiment according to the present invention;
FIG. 8 is a conceptual top view of a modified example of a joining portion between a center frame and a connecting member in the second embodiment according to the present invention;
FIG. 9 is a side view showing a conventional hydraulic shovel; and
FIGS. 10A, 10B, and 10C are a plan view, a perspective view, and a sectional view along an I—I line of FIG. 10A showing a truck frame, a mudguard cover, and so on of a conventional hydraulic shovel.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described in detail below on the basis of the drawings illustrating embodiments thereof.
As shown in FIG. 1, a hydraulic shovel 1 according to a first embodiment of the present invention comprises a lower traveling body 2 provided with a crawler belt r to enable motion, and an upper slewing body 3 which is attached slewably to the top of the lower traveling body 2 via a slewing bearing J, and which is mounted by an operator to perform an operation.
An operating seat 3a on which the operator sits to perform an operation is provided on the upper slewing body 3, and a working machine 10 comprising a boom 10a, an arm 10b, and an excavating bucket 10c attached to the tip end of the arm 10b, which are hydraulically driven, is axially supported in a vertical direction to the front of the operating seat 3a so as to swing freely.
As a result of this constitution, various loads act on the upper slewing body 3, to which the working device 10 comprising the bucket 10c is attached, during an operation.
In the lower traveling body 2, a drive shaft 5 and a pivot 6 are attached respectively to the two end portions of truck frames 4l, 4r, and the crawler belt r is wrapped around the drive shaft 5 and pivot 6.
The hydraulic shovel 1 is driven by starting a traction motor such that the power thereof is transmitted to the drive shaft 5. This causes the drive shaft 5 to rotate, which drives the crawler belt r to rotate, and as a result, traveling is performed.
An outer ring (not shown) of the slewing bearing J is attached to the upper slewing body 3, and an inner ring (not shown) of the slewing bearing J is fastened to an attachment ring 7r (to be described below, see FIGS. 2, 3) of a center frame 7 by bolts. An internal gear is formed on the inner peripheral face of the inner ring of the slewing bearing J, this internal gear meshing with a pinion gear (not shown) that is driven by a slewing motor (not shown) attached to the upper stewing body 3.
By driving the slewing motor, the inner ring is caused to rotate relative to the outer ring, and hence the upper slewing body 3 is driven to slew relative to the lower traveling body 2.
As shown in FIG. 2 and the top view of FIG. 3, the center frame 7 formed with the attachment ring 7r, on which the slewing bearing J is mounted, is disposed in the central portion of a frame 2F of the lower traveling body, and the truck frames 4r, 4l are disposed on the two side portions thereof. The truck frame 4r is connected to the center frame 7 by two leg-shaped connecting members 8r, 9r, and the truck frame 4l is connected to the center frame 7 by two leg-shaped connecting members 8l, 9l. 
These members are joined to each other by welding.
Here, reinforcing ribs 7kr, 7kl for smoothly dispersing stress generated by a load that is transmitted from the upper slewing body 3 to the attachment ring 7r over the center frame 7 are disposed directly beneath or approximately beneath the attachment ring 7r in the interior of the center frame 7 along the load transmission direction so as to connect an upper plate 7u and a lower plate 7s. 
Note that as shown in FIG. 3, the truck frame 4r and the pair of connecting members 8r, 9r, and the truck frame 4l and the pair of connecting members 8l, 9l are constituted in plane symmetry about a central face (the center line of the vertical direction of the center frame 7 in FIG. 3) of the center frame 7 in the direction of width (the vertical direction in FIG. 3).
More specifically, in FIG. 3, the connecting member 8r and connecting member 8l take a symmetrical form about the central face of the center frame 7 in the direction of width, and the connecting member 9r and connecting member 9l take a symmetrical form about the central face of the center frame 7 in the direction of width.
The center frame 7 is manufactured as a cast using cast steel, and as shown in FIG. 4A, the top view in FIG. 4B, and the bottom view in FIG. 4C, is constituted in a hollow box form comprising a front side plate 7sm, a rear side plate 7su, a right side plate 7sr to which the connecting members 8r, 9r are joined, a left side plate 7sl to which the connecting members 8l, 9l are joined, the upper plate 7u in which the attachment ring 7r is formed, and the lower plate 7s. 
Note that the lower plate 7s is welded from below, and improves the strength of the center frame 7 by blocking the internal space of the center frame 7.
The attachment ring 7r, to which the inner ring of the stewing bearing J that is fixed to the upper slewing body 3 is attached by bolts, is formed in the upper plate 7u of the center frame 7, and comprises an opening in its central portion.
In the interior of the center frame 7 directly beneath or approximately beneath the attachment ring 7r, the reinforcing rib 7kr is formed inward in continuation from the right side plate 7sr so as to connect the upper plate 7u and lower plate 7s, and the reinforcing rib 7kl is formed inward in continuation from the left side plate 7sl so as to connect the upper plate 7u and lower plate 7s, as shown in FIGS. 3, 4A, 4B, and 4C.
The reinforcing rib 7kr and the reinforcing rib 7kl are also formed along the transmission direction of a load that is transmitted from the upper slewing body 3 to the attachment ring 7r. 
Hence, a load from the upper stewing body 3 that is generated by the working device 10 and transmitted to the attachment ring 7r is transferred to the center frame 7 via the reinforcing ribs 7kr, 7kl which are formed along the load transmission direction and have better load-withstanding strength and rigidity than the upper plate 7u which is flat, formed perpendicular to the load transmission direction, and cannot be the to have good strength in relation to loads.
By forming the reinforcing ribs 7kr, 7kl in a U-shaped form when seen from above in this manner, the load-withstanding strength of the center frame 7 can be improved in relation to compressive loads, tensile loads, bending moments, and so on that are transmitted to the attachment ring 7r. 
Note that an example was described in which the reinforcing ribs 7kr, 7kl are formed in continuation from the right side plate 7sr and left side plate 7sl respectively, but the reinforcing ribs 7kr, 7kl need not be formed in continuation from the right side plate 7sr and left side plate 7sl. 
Further, the reinforcing ribs 7kr, 7kl need not be formed integrally with the center frame 7 by casting, but may be formed by bending sheet metal in advance to produce members corresponding to the U-shaped reinforcing ribs 7kr, 7kl, and welding these members to predetermined locations within the center frame 7.
The front side plate 7sm and rear side plate 7su are formed directly beneath or approximately beneath the attachment ring 7r and extend in a vertical direction along the direction in which a load from the upper slewing body 3 is transmitted to the attachment ring 7r. 
By forming the front side plate 7sm and rear side plate 7su along the transmission direction of a load from the upper slewing body 3 that is transmitted to the attachment ring 7r in this manner, loads transmitted to the attachment ring 7r are transferred smoothly to the front side plate 7sm and rear side plate 7su and dispersed over the center frame 7.
As shown in FIGS. 4A, 4B, 4C, the right side plate 7sr and left side plate 7sl are formed in positions jutting out from the attachment ring 7r of the center frame 7, and are formed in a flat plate form along a vertical direction which appears rectilinear when seen from above (see FIG. 3).
The connecting member 8r is manufactured as a cast using cast steel, and as shown in FIG. 5A (which is a perspective view of the connecting member 8r alone seen from the side of the center frame 7 shown in FIG. 3), is constituted in a hollow form comprising a core portion 8r1 having a substantially pentagonal cross section and provided with an angled portion at the upper portion thereof at which a ridge is formed in the longitudinal direction of the upper face, a center joining portion 8r2 having a quadrilateral cross section and formed with an opening 8r0, and a truck joining portion 8r3 formed with an opening.
The center joining portion 8r2 of the connecting member 8r comprises a joining face 8rb which is joined to the right side plate 7sr of the center frame 7, and as shown in FIG. 3, this joining face 8rb is formed in planar form to appear rectilinear when seen from above, and is thus non-perpendicular to the axis which runs along the direction in which the connecting member 8r extends.
Further, a height dimension hr1 between an upper face 8ru and a lower face 8rs of the center joining portion 8r2 having the joining face 8rb is set to be slightly shorter than the dimension between the upper and lower faces (the dimension between the upper face of the upper plate 7u and the lower face of the lower plate 7s) of the center frame 7 (see FIG. 2).
The connecting member 8l shown in FIGS. 2, 3 is manufactured as a cast using cast steel and, as described above, is constituted in plane symmetry with the connecting member 8r about the central face of the center frame 7 in the direction of width.
Similarly to the connecting member 8r, the connecting member 8l is constituted as a pipe-form hollow member extending in a longitudinal direction having a closed transverse section. Since the connecting member 8l is constituted similarly to the connecting member 8r, detailed description thereof has been omitted.
The connecting member 9r is manufactured as a cast using cast steel, and as shown in FIG. 5B (which is a perspective view of the connecting member 9r alone seen from the center frame side in FIG. 3), is constituted in a hollow form comprising a tapered core portion 9r1 having a substantially pentagonal cross section and provided with an angled portion at the upper portion thereof at which a ridge is formed in the longitudinal direction of the upper face, a center joining portion 9r2 having a quadrilateral cross section and formed with an opening 9r0, and a truck joining portion 9r3 formed with an opening.
The center joining portion 9r2 of the connecting member 9r comprises a joining face 9rb which is joined to the right side plate 7sr of the center frame 7, and as shown in FIG. 3, this joining face 9rb is formed in planar form to form a straight line when seen from above, and is thus non-perpendicular to the axis which runs along the direction in which the connecting member 9r extends.
Further, a height dimension hr2 between an upper face 9ru and a lower face 9rs of the center joining portion 9r2 having the joining face 9rb is set to be slightly shorter than the dimension between the upper and lower faces (the dimension between the upper face of the upper plate 7u and the lower face of the lower plate 7s) of the center frame 7 (see FIG. 2).
The connecting member 9l shown in FIGS. 2, 3 is manufactured as a cast using cast steel and, as described above, is constituted in plane symmetry with the connecting member 9r about the central face of the center frame 7 in the direction of width.
Similarly to the connecting member 9r, the connecting member 9l is constituted as a tapered, pipe-form hollow member extending in a longitudinal direction having a closed transverse section. Since the connecting member 9l is constituted similarly to the connecting member 9r, detailed description thereof has been omitted.
As described above, the connecting members 8r, 8l, 9r, 9l are constituted in a form having a ridge with an angled portion on the upper face thereof, and hence earth that is churned up by the crawler belt r during traveling slides down the inclined surface of the upper face of the connecting members 8r, 8l, 9r, 9l and falls to the ground, thus prevented the accumulation thereof on top of the connecting members 8r, 8l, 9r, 9l. 
The truck frames 4r, 4l extend in a front-rear direction (the left/right direction in FIGS. 1, 2, and 3) and have a quadrilateral cross section. As shown in FIG. 2, the upper face portion thereof is constituted with an inclined face plate 4a forming a singly tapered face which inclines downward toward the outside of the vehicle body. An earth removing hole 4ah is pierced through the inclined face plate 4a of the truck frames 4 near the center thereof.
Next, a method of joining the center frame 7 to the connecting members 8r, 8l, 9r, 9l will be described.
As shown in FIGS. 2 and 3, when the center frame 7 is joined to the connecting member 8r, the center joining portion 8r2 on the connecting member 8r is disposed in an intermediate position in the vertical direction of the right side plate 7sr of the center frame 7, whereupon welding is performed at a welding location y1 between the right side plate 7sr of the center frame 7 and the center joining portion 8r2 of the connecting member 8r. 
Welding between the center frame 7 and the connecting member 8l is performed similarly to the welding described above between the center frame 7 and connecting member 8r. 
Further, as shown in FIGS. 2 and 3, when the center frame 7 is joined to the connecting member 9r, the center joining portion 9r2 on the connecting member 9r is disposed in an intermediate position in the vertical direction of the right side plate 7sr of the center frame 7, whereupon welding is performed at a welding location y2 between the right side plate 7sr of the center frame 7 and the center joining portion 9r2 of the connecting member 9r. 
Welding between the center frame 7 and the connecting member 9l is performed similarly to the welding described above between the center frame 7 and connecting member 9r. 
Note that in this embodiment, an example was described in which the connecting members 8r, 8l, 9r, 9l are manufactured as casts, but the connecting members 8r, 8l, 9r, 9l are not limited to casts, and may be manufactured from sheet metal.
According to the constitution described above, various loads act on the upper slewing body 3 provided with the working device 10 during an operation of the bucket 10c, and these loads are transmitted to the attachment ring 7r of the center frame 7 which is connected to the upper stewing body 3 via the slewing bearing J.
However, the reinforcing ribs 7kr, 7kl which connect the upper plate 7u and lower plate 7s are formed directly beneath or approximately beneath the attachment ring 7r in the interior of the center frame 7, and these reinforcing ribs 7kr, 7kl extend in the direction in which the aforementioned loads are transmitted.
Hence the loads are transferred to the reinforcing ribs 7kr, 7kl, which have good rigidity in relation to loads, and then dispersed over the center frame 7 via the reinforcing ribs 7kr, 7kl, and thus the load-withstanding strength of the center frame 7 to operating loads is improved, leading to an improvement in the reliability of the vehicle body.
Since a load that is transmitted to the attachment ring 7r from the upper slewing body 3 is dispersed smoothly over the center frame 7 via the reinforcing ribs 7kr, 7kl, the strength required by the right side plate 7sr and left side plate 7sl to transmit the load to the center frame 7 decreases relatively.
As a result, design freedom regarding the positioning of the right side plate 7sr and left side plate 7sl is increased.
Thus, in the design process, the right side plate 7sr and left side plate 7sl may be formed in positions removed and jutting out from the attachment ring 7r, enabling the length of the connecting members 8r, 9r connecting the center frame 7 to the truck frame 4r and the connecting members 8l, 9l connecting the center frame 7 to the truck frame 4l to be shortened as required.
Here, the hydraulic shovel 1 travels over various ground surfaces by driving the crawler belts r, r to rotate, and hence loads of varying magnitudes act on the respective truck frames 4r, 4l. 
These loads are transmitted respectively to the connecting members 8r, 9r that are connected to the truck frame 4r and the connecting members 8l, 9l that are connected to the truck frame 4l. 
By forming the connecting members 8r, 8l, 9r, 9l to be as short as possible, the length of the moment lever caused by a load generated during traveling can be shortened, thereby preventing increases in the moment.
Moreover, since the connecting members 8r, 8l, 9r, 9l are formed as pipe-form hollow members due to weight considerations and therefore have low load-withstanding strength, in this regard also it is advantageous to be able to shorten the connecting members 8r, 8l, 9r, 9l. 
As a result, loads generated during traveling can be received in the strong center frame 7 through the short connecting members 8r, 8l, 9r, 9l. 
Thus the load-withstanding strength of the vehicle body to loads generated during traveling is ensured, and reliability is improved.
Next, first and second modified examples of the reinforcing ribs 7kr, 7kl of the center frame 7 in the first embodiment will be described using FIGS. 6A, 6B.
Note that since the reinforcing rib 7kl on the side of the connecting members 8l, 9l and the reinforcing rib 7kr on the side of the connecting members 8r, 9r are symmetrical about the central face of the center frame 7 in the direction of width and have similar constitutions, only the reinforcing rib 7kr is described, and description of the reinforcing rib 7kl is omitted.
FIG. 6A is a conceptual top view of the vicinity of the joining portion between a center frame 7a and connecting members 8ra, 9ra, illustrating the first modified example.
In the first modified example, a reinforcing rib 7kra extends inward when seen from above from the inside of a joining portion 7sra1 between a right side plate 7sra of the center frame 7a and the connecting member 8ra, passes through the interior of the center frame 7a below the attachment ring 7ra or in the vicinity thereof, and connects to the right side plate 7sra along the line of extension of a front vertical plate 9ra1 of the connecting member 9ra. 
Simultaneously, the reinforcing rib 7kra is formed integrally with an upper plate 7ua of the center frame 7a and extends to a lower plate 7sa in a vertical direction (a perpendicular direction to the paper surface in FIG. 6A).
According to the first modified example, the reinforcing rib 7kra extends inward from the inside of the joining portion 7sra1 between the right side plate 7sra of the center frame 7a and the connecting member 8ra, and hence a load that is transmitted to the center frame 7a from the connecting member 8ra can be received in the reinforcing rib 7kra along the line of extension of the connecting member 8ra, which is the load transmission direction.
Running loads from the truck frame 4r are transmitted to the connecting member 9ra, and these loads are transferred to the right side plate 7sra of the center frame 7a via the front vertical plate 9ra1, rear vertical plate 9ra2, and so on forming the connecting member 9ra. However, by forming the reinforcing rib 7kra along the line of extension of the front vertical plate 9ra1 of the connecting member 9ra, these loads can be received in the reinforcing rib 7kra extending along the transmission direction.
Hence a transfer load from the connecting member 8ra and connecting member 9ra can be dispersed smoothly over the center frame 7a without applying an excessive structural load thereto.
Note that in the first modified example, an example was described in which the reinforcing rib 7kra is formed on the line of extension of the front vertical plate 9ra1 of the connecting member 9ra, but the reinforcing rib 7kra may be provided on the line of extension of the front vertical plate 8ra1 and rear vertical plate 8ra2 of the connecting member 8ra, or on the line of extension of the rear vertical plate 9ra2 of the connecting member 9ra. 
FIG. 6B is a conceptual top view of the vicinity of the joining portion between a center frame 7b and connecting members 8rb, 9rb, illustrating the second modified example.
In the second modified example, a reinforcing rib 7krb extends inward when seen from above from the inside of a joining portion 7srb1 between a right side plate 7srb of the center frame 7b and the connecting member 8rb, passes through the interior of the center frame 7b below the attachment ring 7rb or in the vicinity thereof, and connects to the inside of a joining portion 7srb2 between the right side plate 7srb and the connecting member 9rb. 
Simultaneously, the reinforcing rib 7krb is formed integrally with an upper plate 7ub of the center frame 7b and extends to a lower plate 7sb in a vertical direction (a perpendicular direction to the paper surface in FIG. 6B).
According to the second modified example, the reinforcing rib 7krb extends inward from the inside of the joining portions 7srb1, 7srb2 between the right side plate 7srb of the center frame 7b and the connecting members 8rb, 9rb, and hence a load that is transmitted to the center frame 7b from the connecting members 8rb, 9rb can be received in the reinforcing rib 7krb which exists on the line of extension of the connecting members 8rb, 9rb, or in other words along the load transmission direction. Hence this load can be dispersed smoothly over the center frame 7b without applying an excessive structural load thereto.
Note that in both the first and second modified examples, the reinforcing ribs are molded into a U-shaped form when seen from above, and hence the reinforcing ribs are firmly supported in relation to compressive loads, tensile loads, bending moments, and so on that are transmitted to the attachment ring, thus enabling improvements in the load-withstanding strength of the center frame.
Thus the reinforcing ribs are able to improve the load-withstanding strength of the center frame in relation to loads that are transmitted to the center frame from the connecting members as well as loads that are transmitted to the attachment ring.
Note that the reinforcing ribs need not be formed integrally with the center frame by casting, but may also be formed by bending sheet metal in advance to produce members corresponding to the U-shaped reinforcing ribs, and welding these members to predetermined locations within the center frame.
In the first and second modified examples, a description was provided in which the reinforcing ribs 7kra, 7krb take a continuous U-shaped form, but the reinforcing ribs 7kra, 7krb may take an interrupted U-shaped form instead of a continuous form.
Further, as long as the reinforcing ribs 7kra, 7krb take a U-shaped form, this may be a substantially U-shaped form or the like, and need not be a strictly U-shaped form.
Next, a second embodiment will be described.
In the second embodiment, the reinforcing ribs 7kr, 7kl of the first embodiment are not provided below the attachment ring 7r in the interior of the center frame 7, but are substituted for the right side plate 7sr and left side plate 7sl. 
All other constitutions are identical to those of the first embodiment. Hence identical constitutional elements to those of the first embodiment are illustrated by adding to the same reference symbol, and detailed description of these elements is omitted.
As shown in the top view in FIG. 7, a center frame 27 is disposed in the central portion of a frame 21F of the lower traveling body, and truck frames 4r′, 4l′ are disposed on the two side portions thereof. The truck frame 4r′ is connected to the center frame 27 by two leg-shaped connecting members 8r′, 9r′, and the truck frame 4l′ is connected to the center frame 27 by two leg-shaped connecting members 8l′, 9l′. 
These members are joined to each other by welding.
The center frame 27 is manufactured as a cast using cast steel, and is constituted in a hollow box form comprising an upper plate 27u formed with an attachment ring 27r on which a stewing bearing J′ is mounted, a lower plate, a front side plate 27sm, a rear side plate 27su, a right side plate 27sr to which the connecting members 8r′, 9r′ are joined, and a left side plate 27sl to which the connecting members 8l′, 9l′ are joined.
The right side plate 27sr of the center frame 27 is formed in a position jutting out from the side portion of the attachment ring 27r, and the left side plate 27sl is formed in a position jutting out from the side portion of the attachment ring 27r. 
A reinforcing plate portion 27sr1 which recedes inward below the attachment ring 27r between the locations at which the connecting members 8r′, 9r′ are joined is formed on the right side plate 27sr of the center frame 27.
The reinforcing plate portion 27sr1 is formed extending in a vertical direction along the transmission direction of a load from the upper slewing body 3′ that is transmitted to the attachment ring 27r. 
Thus an operating load from the upper stewing body 3′ that is transmitted to the attachment ring 27r is transferred to the reinforcing plate portion 27sr1 and dispersed over the center frame 27, enabling an improvement in the load-withstanding strength of the center frame 27 in relation to operating loads.
Likewise, a reinforcing plate portion 27sl1 which recedes inward below the attachment ring 27r between the locations at which the connecting members 8l′, 9l′ are joined is formed on the left side plate 27sl of the center frame 27.
The reinforcing plate portion 27sl1 is formed extending in a vertical direction along the transmission direction of a load from the upper slewing body 3′ that is transmitted to the attachment ring 27r. 
Thus an operating load from the upper slewing body 3′ that is transmitted to the attachment ring 27r is transferred to the reinforcing plate portion 27sl1 and dispersed over the center frame 27, enabling an improvement in the load-withstanding strength of the center frame 27 in relation to operating loads.
Further, the right side plate 27sr and left side plate 27sl are formed respectively in positions jutting out from the side portion of the attachment ring 27r, thus reducing the length of the connecting members 8r′, 9r′ that are joined to the right side plate 27sr and the length of the connecting members 8l′, 9l′ that are joined to the left side plate 27sl. 
Moreover, the front side plate 27sm and rear side plate 27su are formed directly beneath or approximately beneath the attachment ring 27r, and hence a load from the upper slewing body 3′ that is transmitted to the attachment ring 27r is transferred smoothly to the front side plate 27sm and rear side plate 27su which are formed in a vertical direction along the transmission direction of the load, and have good strength in relation to the load, whereupon the load is dispersed over the center frame 27.
According to this constitution, the reinforcing plate portion 27sr1 of the right side plate 27sr and the reinforcing plate portion 27sl1 of the left side plate 27sl are formed beneath the attachment ring 27r in the center frame 27, and hence a load from the upper slewing body 3′ that is transmitted to the attachment ring 27r is transferred smoothly to the right side plate 27sr and left side plate 27sl which, comprising the reinforcing plate portion 27sr1 and the reinforcing plate portion 27sl1 respectively, have improved strength and rigidity in relation to the load. The load is thus dispersed over the center frame 27.
As a result, similarly to the first embodiment, the load-withstanding strength of the center frame 27 to operating loads is improved, leading to an improvement in the reliability of the vehicle body.
Thus the reinforcing plate portion 27sr1 of the right side plate 27sr is formed so as to recede inward below the attachment ring 27r, the reinforcing plate portion 27sl of the left side plate 27sl is formed so as to recede inward below the attachment ring 27r, and the right side plate 27sr and left side plate 27sl are formed in positions jutting out from the attachment ring 27r. 
As a result, the length of the connecting members 8r′, 9r′ connecting the center frame 27 to the truck frame 4r′ can be shortened, and similarly, the length of the connecting members 8l′, 9l′ connecting the center frame 27 to the truck frame 4l′ can be shortened.
Hence, similarly to the first embodiment, a load generated during traveling can be received in the strong center frame 27 through the short connecting members 8r′, 9r′, 8l′, 9l′. 
Thus the load-withstanding strength of the vehicle body to loads generated during traveling is ensured, and reliability is improved.
In this manner, similar effects to those of the first embodiment can be achieved in the second embodiment.
Next, a modified example of the second embodiment will be described using FIG. 8 (which is a conceptual top view of the vicinity of the joining portion between a center frame 27a and connecting members 8ra′, 9ra′).
Note that the constitution of the vicinity of the joining portion between the center frame 27a and connecting members 8la′, 9la′ is identical to the constitution of the vicinity of the joining portion between the center frame 27a and the connecting members 8ra′, 9ra′, and is symmetrical thereto about the central face of the center frame 27a in the direction of width. Accordingly, description will only be provided regarding the constitution of the vicinity of the joining portion between the center frame 27a and the connecting members 8ra′, 9ra′. 
A right side plate 27sra of the center frame 27a is formed in a position jutting out from the side portion of an attachment ring 27ra when seen from above, and a reinforcing plate portion 27sra1 which recedes inward beneath the attachment ring 27ra between the locations at which the connecting members 8ra′, 9ra′ are joined is formed on the right side plate 27sra. 
The reinforcing plate portion 27sra1 extends inward from the inside of a joining portion 27sra2 between the right side plate 27sra and the connecting member 8ra′, passes beneath the attachment ring 27ra or the vicinity thereof, and then extends along the line of extension of a front vertical plate 9ra1′ of the connecting member 9ra′. 
Here, running loads that are transmitted to the connecting members 8ra′, 9ra′ from a truck frame 4r′ are transferred to the right side plate 27sra of the center frame 27a via the connecting member 8ra′ formed from the front vertical plate 8ra1′, rear vertical plate 8ra2′, and so on, and the connecting member 9ra′ formed from the front vertical plate 9ra1′, rear vertical plate 9ra2′, and so on.
However, according to the constitution of this modified example, the reinforcing plate portion 27sra1 extends inward from the inside of the joining portion 27sra2 between the right side plate 27sra and the connecting member 8ra′, and hence a transfer load from the connecting member 8ra′ can be received along the line of extension of the connecting member 8ra′, or in other words in the reinforcing plate portion 27sra1 which is disposed along the load transmission direction.
Further, since the reinforcing plate portion 27sra1 extends along the line of extension of the front vertical plate 9ra1′ of the connecting member 9ra′, loads are transferred smoothly to the reinforcing plate portion 27sra1 which is disposed along the load transmission direction.
Hence a transfer load from the connecting members 8ra′, 9ra′ can be dispersed over the center frame 27a without applying any structurally excessive loads thereto.
Thus the reinforcing plate portion 27sra1 enables improvements in the load-withstanding strength of the center frame 27a not only to loads transmitted to the attachment ring 27ra, but also to loads that are transmitted to the center frame 27a from the connecting members 8ra′, 9ra′. 
It goes without saying that similar effects to those of the second embodiment described above are also achieved in this modified example.
Note that in this modified example, a description was provided in which the reinforcing plate portion 27sra1 is formed on the line of extension of the front vertical plate 9ra1′ of the connecting member 9ra′, but the reinforcing plate portion 27sra1 may be provided on the line of extension of the front vertical plate 8ra1′ or rear vertical plate 8ra2′ of the connecting member 8ra′, or on the line of extension of the rear vertical plate 9ra2′ of the connecting member 9ra′. 
Note that in the embodiment described above, an example was provided in which a hydraulic shovel is used as the construction machine, but the construction machine according to the present invention may of course be applied effectively to a construction machine other than a hydraulic shovel having a similar constitution.
For example, the present invention may be applied effectively to a machine other than a hydraulic shovel which has a base carrier constitution, such as a crawler dump, a bulldozer, or an agricultural machine.

## Claims

1. A construction machine comprising a lower traveling body having a frame and an upper slewing body which slews freely about the lower traveling body,
the frame of the lower traveling body comprising a hollow center frame having an upper plate, a lower plate, and side plates surrounding sides thereof, the upper plate being formed with an attachment ring on which a slewing bearing of the upper slewing body is mounted; a pair of truck frames disposed on outside of two side portions of the center frame; and connecting members for connecting the center frame to the truck frames, center joining portions of the connecting members being welded to the side plates of the center frame,
wherein the center frame comprises the side plates positioned so as to jut out from the attachment ring, and reinforcing ribs which connect the upper plate to the lower plate in an interior of the center frame beneath the attachment ring, and
the reinforcing ribs expand from the side plates to the interior of the center frame beneath the attachment ring.

2. The construction machine according to claim 1, wherein the reinforcing ribs have a U-shape when viewed from above the frame, where tops of the U-shape are joined to the side walls.

3. The construction machine according to claim 2, wherein the reinforcing rib is provided on an inside of the center frame and inside of the joining portion of the connecting member, or extending along a line of extension of a vertical plate of the connecting member.

4. The construction machine according to claim 1, wherein the reinforcing rib is provided on an inside of the center frame and inside of the joining portion of the connecting member, or extending along a line of extension of a vertical plate of the connecting member.

5. A construction machine comprising a lower traveling body having a frame and an upper slewing body which slews freely about the lower traveling body,
the frame of the lower traveling body comprising a hollow center frame having an upper plate, a lower plate, and side plates surrounding sides thereof, the upper plate being formed with an attachment ring on which a slewing bearing of the upper slewing body is mounted; a pair of truck frames disposed on outside of two side portions of the center frame; and connecting members for connecting the center frame to the truck frames, the center joining portions of the connecting members being welded to the side plates of the center frame,
wherein the side plate of the center frame is formed in a position jutting out from the attachment ring, and comprises a reinforcing plate portion which recedes inward below the attachment ring at an intermediate portion of locations at which the center joining portion of the connecting member is joined.

6. The construction machine according to claim 5, wherein the reinforcing plate portion is provided on an inside of the center frame and inside of the joining portion of the connecting member, or extending along a line of extension of a vertical plate of the connecting member.