WO2008053779A1 - Boom and front attachment for working machine - Google Patents

Abstract

A boom for a working machine having enhanced working ability achieved without an increase in the size of a split boom. The boom has a first boom (6a), a second boom (6b), and a second boom cylinder (12). The first boom (6a) is supported at its base end by a working machine body. An arm or a working device is connected to the forward end of the second boom (6b). The first and second booms (6a, 6b) are connected together so as to be rotatable about a horizontal axis (6c). The second boom cylinder (12) rotates the second boom (6b). A rod connection section (61) to which a piston rod (12b) of the second boom cylinder (12) is connected is formed on the second boom (6b) at its end on the side where the first boom is connected. The rear end (12a) of the second boom cylinder (12) connected to the rod connection section (61) is supported by the first boom (6a).

Description

 Technical field

 [0001] The present invention relates to a boom provided in a working machine such as a hydraulic excavator or a building demolition machine, and a front attachment using the boom.

 Background art

 [0002] Generally, a boom of a hydraulic excavator is composed of a single member provided with a folding angle in the shape of a "<", but the first boom supported by the hydraulic excavator body, There is also a split boom that has a second boom pivotably connected to the tip of the first boom about a horizontal axis, and the folding angle of both booms can be freely changed by a hydraulic cylinder. It has been.

 FIG. 15 shows a configuration of a front attachment having the split boom.

 In the front attachment 50 shown in the figure, an arm 52 is connected to the tip of a split boom 51, and a bucket 53 is provided at the tip of the arm 52. 51a is a boom cylinder, 52a is an arm cylinder, and 53a is a bucket cylinder.

 [0005] The split boom 51 includes a first boom 51b whose proximal end is supported by a hydraulic excavator body (upper swing body), and a second boom 51c connected to the distal end side of the first boom 51b. Both the booms 51b and 51c are connected via a connecting pin 51d.

 [0006] A second boom cylinder 51e is installed at the center of each lower surface of the first boom 51b and the second boom 51c. By extending and retracting the piston rod 51f of the second boom cylinder 51e, both booms 51b And 51c bend angle Θ can be changed.

 [0007] According to the front attachment 50 including the split-type boom 51, the arm 52 can be pulled closer to the foot side, so that the working range can be expanded compared to a boom constituted by a single member. There is an advantage that can be.

 [0008] However, in the above-described front attachment 50, when excavation work is performed, if the ground to be excavated is hard, the arm 53 is pulled in a state where the bucket 53 is not easily inserted into the ground, and the upward movement with respect to the split boom 51 is performed. The tensile force of

[0009] At this time, since the first boom 51b is held by the two boom cylinders 51a, the first boom 51b is changed. However, the second boom 51c may float in the direction of arrow X with the connecting pin 51d as a fulcrum due to insufficient thrust of the second boom cylinder 51e. If the piston rod 51f of the second boom cylinder 51e extends in this way, the digging force is inevitably reduced.

 [0010] In order to compensate for the above-described decrease in excavation force, it is possible to consider a method of enlarging the second boom cylinder 51e to prevent the piston rod 51f from extending. In that case, the front attachment 50 also has its enlarged second boom. It must be reinforced to a structure suitable for the cylinder 51e, which increases the weight. In addition, if the weight of the front attachment 50 increases, the counterweight for balancing the weight must also be increased.

 [0011] The present invention has been made in consideration of the problems in the conventional split-type boom as described above, and a boom and a front attachment for a working machine that can increase work capacity without increasing the size of the split-type boom. Is to provide.

 Disclosure of the invention

 [0012] In the present invention, a first boom having a base end supported by a work machine main body and a second boom to which an arm or a work device is connected at a distal end are swingable about a horizontal axis. A boom which is connected and includes a second boom cylinder for swinging the second boom,

 A rod connecting portion for connecting the piston rod of the second boom cylinder is formed at the first boom connecting side end portion of the second boom, and the second boom cylinder connected to the rod connecting portion is formed. This is a boom for a working machine having a rear end pivotally supported by the first boom.

 [0013] According to the present invention, the undulation force can be applied to the second boom from the rear side of the horizontal axis that is the swing center of the second boom, so that the first boom and the second boom Compared with the conventional configuration in which the second boom cylinder is installed approximately in the middle, the force S that effectively uses the capacity of the second boom cylinder is reduced.

 [0014] In the present invention, a boss is formed on the upper side of the first boom connection side end to allow the connection pin as the horizontal shaft to pass therethrough, and is formed below the first boom connection side end. It is preferable that a bracket as the rod connecting portion is extended from the side toward the work machine main body.

[0015] Thereby, the distance between the horizontal axis that is the swing center of the second boom and the rod connecting portion is increased. And the undulation force on the second boom can be increased.

In the present invention, in order to effectively utilize the capability of the second boom cylinder, the connection point between the first boom and the second boom is A, and the rear end of the second boom cylinder in the first boom When the connecting point of the second boom cylinder is B and the connecting point of the rod of the second boom cylinder in the second boom is C, the connecting point C is less than the connecting point A in the contracted state of the second boom cylinder. It is preferable to arrange each connection point so that it is located on the work machine body side.

 [0017] Further, it is preferable that the connection points are arranged so that an angle formed by the connection point A, the connection point C, and the connection point B forms approximately 90 ° during or during extension of the second boom cylinder. Good.

 [0018] In the state in which the second boom cylinder is contracted, the boom of the present invention is bent into the first boom and the second boom force S, and the second boom cylinder is extended to the maximum. If it does, the said 2nd boom of the shape of a dogleg will be constituted so that it may warp in the direction opposite to a bending direction.

 [0019] In the present invention, a pair of boom cylinders for raising and lowering the first boom is provided on both side surfaces of the first boom. In the configuration of! /, The second boom cylinder is connected to the first boom. When housed inside, work visibility is improved, and the ability to operate the boom without any discomfort. In addition, contact with the second boom cylinder can be eliminated when the tip attachment such as a packet or a crusher is operated.

 In the present invention, if a partition plate is provided along the second boom cylinder above the second boom cylinder in the first boom, the second boom is placed in the first boom by the partition plate. A storage chamber for storing the cylinder can be formed.

 [0021] In the present invention, in the configuration in which the boom cylinder for raising and lowering the first boom is provided on the front surface of the first boom, a pair of the second booms are provided on both side surfaces of the first boom. A cylinder can be provided. According to this configuration, the boom of the present invention can be applied to a small work machine.

[0022] The present invention provides a boom having the above-described configuration and a gear connected to the tip of the second boom. And a work machine front attachment comprising a work device coupled to the tip of the arm.

 [0023] The present invention is a front attachment for a working machine including a boom having the above-described configuration and a work device coupled to a distal end portion of the second boom.

 [0024] According to the present invention, the force S can be increased to increase the working ability such as arm pulling without increasing the size of the split boom.

 Brief Description of Drawings

 FIG. 1 is a working range diagram of a hydraulic excavator having a front attachment constituted by a boom according to the present invention.

 2 is an enlarged cross-sectional view of a main part of the boom shown in FIG.

 FIG. 3 is a plan view of the boom shown in FIG.

 4 is a cross-sectional view taken from the direction of arrows WW shown in FIG.

 FIG. 5 is an explanatory diagram of a front attachment operation as a comparative example.

 FIG. 6 is an explanatory diagram of a front attachment operation as a comparative example.

 FIG. 7 is an explanatory diagram of a front attachment operation according to the present invention.

 FIG. 8 is an explanatory diagram of a front attachment operation according to the present invention.

 FIG. 9 (a) is an explanatory view showing the swing range of the boom according to the present invention, and FIG. 9 (b) is a conventional boom shown for comparison.

 FIG. 10 (a) is an explanatory view showing the forward turning radius of a construction machine equipped with the boom of the present invention, and FIG. 10 (b) is an explanatory view showing the forward turning radius of a conventional construction machine. .

 FIG. 11 is an explanatory view showing a pin arrangement of a boom according to the present invention.

 FIG. 12 is an explanatory diagram showing a configuration when the boom of the present invention is applied to a small hydraulic excavator.

 FIG. 13 is an enlarged view of the boom shown in FIG.

 FIG. 14 is an explanatory diagram showing a configuration when a crusher and a breaker are attached to the boom of the present invention.

FIG. 15 is a side view showing a configuration of a conventional split boom.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

 [0027] Fig. 1 shows a hydraulic excavator as a work machine and its work range.

 H

 The position of the front attachment at the work site, P is the front attachment at the excavation work

 L

 The other postures indicate the work postures between the aerial work and the excavation work.

[0028] In the figure, reference numeral 1 denotes a hydraulic excavator, and an upper swing body 4 is pivotably mounted on a lower traveling body 3 fitted with crawlers 2 on the left and right sides. A working front attachment 5 is attached!

[0029] 1. Configuration of front attachment

 The front attachment 5 includes a boom 6, an arm 7 connected to the tip of the boom 6, and a bucket (working device) 8 connected to the tip of the arm 7. 6 is configured to undulate by expanding and contracting the boom cylinder 9, and the arm 7 is configured to swing around the horizontal axis (in the direction of arrow U) by expanding and contracting the arm cylinder 10. It is also configured to swing around the horizontal axis (in the direction of arrow V) by extending and retracting the bucket cylinder 11! /.

[0030] The boom 6 further includes a first boom 6a supported on the front portion of the upper swing body (work machine main body) 4, and a second boom 6b connected to the tip of the first boom 6a. Both booms 6a and 6b are connected to be swingable about a horizontal axis via a second boom foot pin 6c. The second boom 6b is configured to be raised and lowered by extending and contracting the second boom cylinder 12.

 In the figure, reference numeral 13 denotes a counterweight attached to the rear part of the upper swing body 4.

[0032] 2. Boom configuration

 FIG. 2 is an enlarged side cross-sectional view showing the main part of the boom 6, and FIG. 3 is a plan view of the boom 6.

 [0033] In both figures, the first boom 6a is made of a box-shaped member formed in an arc shape that protrudes upward, and is connected to the base end portion via an upper swing body 4 and a boom foot pin (not shown). A boss 6d is formed, and a pair of support portions 6e, 6e for connecting the second boom 6b via the second boom foot pin 6c is formed at the tip.

[0034] Further, bosses 6f, 6f are formed near the tip of the first boom 6a, and the bosses 6f, 6f are passed through the shaft. The opposite ends of the pin 6g are connected to the rods of the boom cylinders 9 and 9.

[0035] A partition plate 6h is formed in an L shape inside the first boom 6a so as to bypass the lower side of the boss 6f, and the second boom cylinder 12 is accommodated below the partition plate 6h. A storage chamber S is provided for this purpose. The portion of the partition plate 6h that is close to the boss 6f is formed in the rounded portion 6h ′, and the rear side of the rounded portion 6h ′ is formed in a straight line along the second boom cylinder 12.

 [0036] The rear end portion 12a of the second boom cylinder 12 is supported via a connecting pin 14 with respect to the side wall 6i of the first boom 6a (showing a cross section taken along the line WW in FIG. 2). The rod tip 12c of the piston head 12b is connected to a bracket (described later) 61 of the second boom 6b.

 [0037] Further, on the upper side of the rear end portion (first boom connection side end portion) of the second boom 6b, the support portion 6e and the second boom foot pin 6c that passes through the support portion 6e are supported. A supported portion 6k is formed. On the other hand, on the lower side of the rear end part ¾, a bracket (rod connecting part) 61 for connecting the piston rod 12b is obliquely downward (in the posture of the second boom 6b indicated by a two-dot chain line! /, E) It extends like a tongue!

 [0038] Further, on the upper surface of the bracket 61, a collar portion 61 'is formed corresponding to the rounded portion 6h' of the partition plate 6h.

 [0039] When the second boom cylinder 12 is extended and retracted in a state where the second boom foot pin 6c is mounted through the supported portion 6k and the pair of supporting portions 6e, the second boom foot pin 6c is centered. The second boom 6b can be swung vertically.

 [0040] When the piston rod 12b of the second boom cylinder 12 is returned to the contracted state, the bracket 61 stops in a state where the rounded portion 61 'of the bracket 61 is close to the rounded portion 6h' of the partition plate 6h. The second boom cylinder 12 is stored in the storage chamber S of the first boom 6a. At this time, the rod tip 12c of the second boom cylinder 12 is positioned rearward of the second boom foot pin 6c, that is, on the hydraulic excavator body side.

 [0041] On the other hand, when the piston rod 12b of the second boom cylinder 12 is extended, the second boom foot pin is extended.

The second boom 6b rotates upward about 6c, and the bracket 61 is indicated by a two-dot chain line in the figure. Displace to the position.

 [0042] In this case, the first boom 6a and the second boom 6b are substantially in a straight line, and are in a posture suitable for distal work.

 [0043] When two boom cylinders 9 having an inner diameter of φ120 mm, for example, are used as the boom cylinder 9, for example, as the second boom cylinder 12, a hydraulic cylinder for 35 MPa and having an inner diameter of φ190 mm can be used.

 [0044] 3. Operation comparison of front attachment

 Next, the conventional front attachment shown in FIGS. 5 and 6 and the front attachment equipped with the boom of the present embodiment shown in FIGS. 7 and 8 are compared in terms of operation.

[0045] 3-1 Operation of conventional split boom

 3-1-1 When the second boom cylinder is reduced

 In FIG. 5, when excavation by arm pulling is performed, the arm 52 rotates around the arm foot pin 52a and moves to the boom 51 side. At this time, the length of the arm 52 does not change when the bucket 53 ahead of the arm 52 does not sink into the ground. Converted to lifting the boom 51c.

 [0046] At this time, the first boom 51b is held by two boom cylinders (not shown), so that the second boom cylinder 51e has a weaker holding force than those boom cylinders that cannot be displaced. The second boom 51c held by the lever will be lifted. As a result, a phenomenon occurs in which the second boom cylinder 51e extends.

 [0047] 3-1-2 Force and stress applied to the second boom cylinder 51e

 The force F1 for pulling the second boom cylinder 51e is constituted by a line segment K M passing through the point K and the point M, and a cylinder thrust P Q pushing it. However, it is more efficient to push the cylinder thrust from the line segment N-O side perpendicular to the line segment R-S! Therefore, the angle formed by the line segment P-Q with respect to the line segment N-O Z OMP The thrust is reduced by that amount.

 [0048] That is, in the conventional split-type boom,

Since the angle of Z OMP is 63 ° and cos63 ° is 0.454, the second boom cylinder 5 About 100% of the thrust of le is about 45%, and it is not used.

[0049] 3-1-3 When the second boom cylinder is extended

 In FIG. 6, when the second boom cylinder 51e is extended to the middle point and the stress applied to the cylinder is obtained in the same manner as described above,

 The force that makes the Z OMP angle 69 ° means that only 36% of the capacity is used for the thrust 100 of the second boom cylinder 51e.

[0050] Thus, the second boom cylinder 51e in the conventional split boom is less than half.

V, ability, power, used!

[0051] 3-2 Boom operation of this embodiment

 3-2-1 When the second boom cylinder is reduced

 In Fig. 7, the force and stress applied to the second boom cylinder 12 of the front attachment 5 are examined.

 [0052] The force F2 for pulling the second boom cylinder 12 is constituted by a line segment A-C passing through the points A and C and a cylinder thrust F-G pushing the same. In this case, the thrust is reduced by the angle ZFCH formed by the line segment FG with respect to the line segment HJ.

 [0053] However, the angle of ZFCH is as small as 38 °, and cos38 ° can be used up to 79% of the thrust of 100 of the second boom cylinder 12 with a force of 0.888. .

 [0054] 3-2-2 When the second boom cylinder is extended

 In FIG. 8, when the second boom cylinder 12 is extended to the middle point, the stress applied to the cylinder is obtained in the same manner as above.

 Since the angle of ZFCH is further reduced to 3 ° (compared to ZFCH), it becomes possible to use up to 99% of the second boom cylinder 12 with a thrust of 100.

[0055] That is, according to the boom 6 according to the present embodiment, the capacity of the second boom cylinder 12 can be increased to 79/45 = 1.76 times when the second boom cylinder is reduced compared to the conventional one. Also, when the second boom cylinder is extended, 99/36 = 2.75 times higher.

Thus, according to the boom 6 of the present embodiment, the second boom cylinder 12 can be extended. Starting with a cylinder holding force of about 80%, the cylinder holding force can be increased to approximately 100%, so that it is possible to reliably prevent the second boom from being lifted due to insufficient thrust of the second boom cylinder.

[0057] 4. Features of boom according to this embodiment

 According to the boom of the present embodiment described above, the second boom cylinder 1 is used during excavation work.

There are the following advantages in addition to preventing 2 from stretching.

[0058] (a) It becomes possible to warp the second boom 6b.

 [0059] Fig. 9 (a) shows the swing range of the second boom 6b. The posture shown by the solid line corresponds to Fig. 8, and the posture shown by the two-dot chain line corresponds to Fig. 7. Yes.

[0060] Fig. 9 (b) shows a conventional boom 60 having a single configuration bent into a square shape. When the boom 60 having the conventional configuration is overlapped with Fig. 9 (a), Boom 60 is shown as a broken line.

 [0061] As can be seen from FIG. 9 (a), the second boom 6b of the present invention is further warped in the T direction (opposite to the folding direction) from 42 to 43 ° from the conventional boom 60 folded into a square shape. It is possible to return.

[0062] Such warping operation is impossible even with a conventional split boom (see Fig. 5). This is because the second boom cylinder 51e with a limited cylinder stroke is installed on the first boom 51b and the second boom 51c.

[0063] As described above, when the second boom 6b can be warped, there is an advantage that the forward turning radius is reduced.

 FIG. 10 shows the difference in the forward turning radius. FIG. 10 (a) shows a hydraulic excavator 1 having a front attachment constituted by the boom of the present invention, and FIG. This is a hydraulic excavator 60 with a front attachment composed of a boom.

 [0065] As shown in Fig. 10 (b), in the conventional front attachment 61, even when the boom 62 is rotated rearward to the maximum and the arm 63 is folded, it is between the wall 64. If the distance X is not secured, turning is not possible. In the figure, 65 is a bucket.

[0066] On the other hand, in the hydraulic excavator 1 having the front attachment of the present invention shown in FIG. 10 (a), the balance of the front attachment 5 is lost by turning the second boom 6b back. The second boom 6b can be displaced rearward, thereby making it possible to reduce the forward turning radius.

 Therefore, in the hydraulic excavator 1 of the present invention, even if the wall surface 64 is present in the front, it is possible to turn as long as the distance X ′ is about ½ of the distance X.

 (B) As shown in FIG. 2, since the second boom cylinder 12 is housed in the first boom 6a, the operator's work field of view is improved compared to the conventional split boom, Even an operator who is unfamiliar with the split boom can operate the boom without any discomfort. Further, for example, even when the arm pull is performed and the tip attachment such as a packet approaches the driver's seat side, the tip attachment does not contact the second boom cylinder.

 [0069] (c) Boom 6 can be shaped substantially the same as a single boom and does not require significant design changes.

 [0070] (d) The conventional split-type boom is configured so that the capacity of the second boom cylinder cannot be fully utilized. Since the cylinder holding force of the boom cylinder can be increased, a long boom can be manufactured.

 [0071] (e) In the conventional split-type boom, since the second boom cylinder is installed at a substantially intermediate position between the first boom and the second boom, the cylinder length must be increased. The form boom can be configured compactly with a short cylinder.

 [0072] (f) In the conventional split-type boom, the force required to design the rod diameter of the second boom cylinder to be thin because the pulling side thrust is required as the cylinder holding force. A force that could not be realized. On the other hand, the boom of this embodiment is the first

2Since the boom cylinder can be short, it is possible to obtain sufficient pulling side thrust without the risk of buckling even if the rod diameter is designed to be thin.

[0073] 5. Advantages of pin arrangement in the boom of this embodiment

 Next, advantages provided by the unique pin arrangement in the boom of this embodiment will be described with reference to FIG.

[0074] The cylinder pin position (rod side pin position) of the second boom cylinder 12 for raising and lowering the second boom 6b is a position for raising and lowering the second boom 6b more efficiently without damaging the boom shape. Is arranged.

 [0075] Specifically, the undulation force of the second boom 6b depends on the distance L1 between points A and C.

 If the boom shape is not changed from the original boom shape, the cylinder pin position is at the virtual point V, so the distance between points A and V is L2.

 [0076] Comparing the lengths of the points A—C and A—V, which are the distances between the pins, the force of LI> L2 and the placement of the pin position at the dots indicate that the second boom 6b It is advantageous in increasing power. The distance between point A-C and point A-V is specifically 842mm and 566mm, which is about 1.5 times increase in undulation force.

 [0077] 6. Application example of boom according to the present invention

 FIG. 12 shows an example in which the boom of the present invention is applied to a small hydraulic excavator.

 As shown in the figure, in the so-called rear small turning type small hydraulic excavator 67 in which the turning radius of the rear end 66 of the upper turning body 65 is shortened, a boom cylinder 69 for raising and lowering the boom 68 is used as the boom 68. It is provided on the front side of!!

 [0079] When the boom of the present invention is mounted on the small hydraulic excavator having such a configuration, the second boom cylinder 70 is provided on the left and right sides of the first boom 68a, specifically on the part that does not interfere with the boom cylinder 69. Just place a pair! /

 In this case, as shown in the enlarged view of FIG. 13, a pair of brackets 68c, 68d (only the front bracket 68c is shown) are extended in parallel from the rear end of the second boom 68b, The bracket 68c and the boss 68e provided on one side of the first boom 68a are connected by a first second cylinder 70 via a pin, and the other bracket 68d and the other side of the first boom 68a are connected to the other side of the first boom 68a. The provided boss 68f (not shown) is connected to the second boom cylinder 71 (not shown) via a pin.

 [0081] Even if the second boom cylinders 70 and 71 are arranged as described above, they are outside the turning radius, and therefore do not interfere with the cabin when the boom 68 is raised and lowered.

[0082] 7. Example of combination of boom and work equipment

FIG. 14 shows a configuration when a working device such as a crusher or a breaker is mounted on the boom of the present invention. For simplicity of explanation, the crusher installation example and the breaker installation example are shown together on the same drawing. In the same figure, 80 is a crusher mounted on the tip of the boom 6, and 81 is a breaker.

 [0084] When the crusher 80 is mounted, the bracket 80a of the crusher 80 is attached to the tip of the second boom 6b, and the optional hydraulic piping routed to the second boom 6b is built into the crusher 80. It is connected to the hydraulic cylinder for driving the crusher.

 [0085] In this configuration, the second boom 6b can function as an arm, so that the arm is not required and the front attachment can be made compact. In addition, since the second boom 6b is warped, the working range can be increased while being compact, so that the working environment in which the height direction is restricted as in the case where there is a ceiling above, for example, underground or tunnel. As described above, there is an advantage that the work can be performed efficiently even in an environment where the work cannot be performed with a normal front attachment.

 [0086] When installing the breaker 81, the bracket 81a of the breaker 81 is attached to the tip of the second boom 6b, and the optional hydraulic piping routed to the second breaker 6b is attached to the breaker 81. Connect to the built-in chisel driving striking cylinder.

 [0087] In this configuration as well, the second boom 6b can function as an arm, so that the front attachment can be made compact. In addition, since the work range can be expanded by turning the second boom 6b in the same manner as described above, work in a narrow space can be performed efficiently.

 As described above, in the combination of the boom and the working device shown in FIG. 14, the length of the front attachment can be shortened and a large working device with high ability can be mounted. For example, while disassembling the foot It is also suitable for dismantling work that moves the work place downstairs.

 [0089] Further, since the boom of the present invention has a feature that the work range is wide while being compact, the work device can be mounted without exchanging with a special boom.

 [0090] It should be noted that the above-described crusher can be replaced with a reinforcing bar cutter used for dismantling a reinforcing bar or a steel structure.

 Industrial applicability

[0091] The boom of the working machine according to the present invention is a front end of a hydraulic excavator for general civil engineering. It can be applied not only to tachment, but also to dedicated construction machines such as building demolition machines and crushers that crush reinforced concrete.Furthermore, front attachments such as dedicated cargo handling machines and dedicated forestry machines equipped with grapples It can also be applied widely.

Claims

The scope of the claims  [1] A first boom whose base end is supported by the work machine main body and a second boom whose arm or work device is connected to the tip are connected to be swingable about a horizontal axis. A boom provided with a second boom cylinder for swinging the second boom,  A rod connecting portion for connecting the piston rod of the second boom cylinder is formed at the first boom connecting side end portion of the second boom, and the second boom cylinder connected to the rod connecting portion is formed. A boom for a working machine, wherein a rear end portion is pivotally supported by the first boom. [2] A boss is formed on the upper side of the first boom connection side end to allow the connection pin as the horizontal shaft to pass therethrough, and from the lower side of the first boom connection side end, The work machine boom according to claim 1, wherein the bracket extends toward the work machine main body.  [3] The connection point of the first boom and the second boom is A, the connection point of the rear end of the second boom cylinder in the first boom is B, and the second boom cylinder of the second boom is connected to the second boom cylinder. When the connecting point of the rod is C, the connecting points are arranged so that the connecting point C is located closer to the work machine body than the connecting point A in the contracted state of the second boom cylinder! A boom for a working machine according to claim 2.  [4] The connecting points are arranged so that an angle formed by the connecting point A, the connecting point, and the connecting point B forms approximately 90 ° when the second boom cylinder is extended or extended. The boom of the described work machine.  [5] With the second boom cylinder contracted, the first boom and the second boom are folded into a U-shape, and the second boom cylinder is extended to the maximum, so that the The work machine boom according to any one of claims 1 to 4, wherein the second boom in a posture is configured to warp in a direction opposite to a bending direction. [6] A pair of boom cylinders for raising and lowering the first boom are provided on both side surfaces of the first boom, and the second boom cylinder is accommodated in the first boom. 5. Any force of 5, the boom of work machine described in 1. [7] A partition plate is provided along the second boom cylinder above the second boom cylinder in the first boom, and the partition plate is used to house the second boom cylinder in the first boom. The work machine boom according to claim 6, wherein a storage chamber is formed.  [8] The boom cylinder for raising and lowering the first boom is provided on the front surface of the first boom, and the pair of second boom cylinders are provided on both side surfaces of the first boom. The power of any one of 1 to 5, the boom of the work machine according to 1.  [9] The force according to any one of claims 1 to 8, comprising the boom according to item 1, an arm connected to the tip of the second boom, and a work device connected to the tip of the arm. A front attachment of a work machine characterized by being made.  [10] A front attachment for a working machine comprising any one of the above-mentioned claims 1 to 8, the boom according to claim 1, and a work device connected to a tip of the second boom. Yes