JP2023066210A - boom head and mobile crane - Google Patents

Abstract

To provide a mobile crane having visibility to a lower part of a boom from a driver seat during traveling in which the visibility from the driver seat is improved during traveling.SOLUTION: A boom head mounted on a tip of a boom in a mobile crane includes: a boom head fixing part fixed to the tip of the boom; and a boom head movable part pivotally supported to the boom head fixing part and having a sheave. The boom head movable part extends from a pivotally supported position and is bent in a reverse direction of the boom so as to be shifted to an extended state in which the boom head movable part extends from the boom head fixing part and a folded state in which the boom head movable part overlaps with the boom head fixing part in a bending direction.SELECTED DRAWING: Figure 4

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile crane that has a view from the driver's seat below the boom during travel.

A mobile crane as shown in Patent Documents 1 and 2 has a boom attached to a revolving body provided at the rear of a vehicle. At the work site, the hook is suspended from the tip of the boom while the boom is lifted from the revolving structure. FIG. 1 shows the vicinity of a boom head 9 in a conventional mobile crane 8 with the boom 11 raised. In FIG. 1, the main hook 31 is suspended by the main wire 41 via the upper sheave 212 and the main sheave 222, and the sub hook 32 is suspended by the sub wire 42 via the upper sheave 212 and the single top sheave 223 which is a sub sheave. . When using the main hook 31 and the sub-hook 32 with the boom 11 erected for work as shown in FIG. For this reason, the main sheave 222 and the single top sheave 223 are provided at positions shifted forward as indicated by arrows from the tip of the boom 11 as shown in FIG. The boom head 9 holding the main sheave 222 and the single top sheave 223 also protrudes forward from the top of the boom 11 . Even in a mobile crane with only one hook, such as without the single top sheave 223, the sub wire 42, and the sub hook 32, the sheave is similarly provided at a position shifted forward from the tip of the boom 11, and the boom The head protrudes forward from the tip of the boom 11 .

JP 2018-203434 A JP 2014-125350 A

The mobile crane travels with the boom tilted toward the front of the mobile crane. When the boom is reclined, the sheave protrudes below the boom. Therefore, in a mobile crane that has a view from the driver's seat below the boom with the boom folded down during travel, the forward view from the driver's seat is partially blocked by the boom head and sheave that protrude downward during travel. The operator must pay sufficient attention when traveling such a mobile crane.

The above points will be explained with reference to the drawings. FIG. 2 shows the state when the mobile crane 8 of FIG. 1 travels. When traveling, the boom 11 is tilted forward from the revolving body 12 . The main hook 31 and the sub-hook 32 are locked to the front of the vehicle body 13, and the connected wire 4 passes through the main sheave, the single top sheave 223, and the upper sheave 212 to a winch (not shown) provided on the revolving body 12. ).

When the mobile crane 8 is traveling, the boom head 9 protrudes into a protruding area P surrounded by a dotted line below the boom 11 in FIG. The tip of the boom 11 is positioned in front of the driver's seat 14 while the vehicle is running. Therefore, the boom head 9 , the main sheave 222 and the single top sheave 223 protrude downward from the boom 11 in front of the driver's seat 14 . The mobile crane 8 shown in FIG. 2 has an operator's cab having an operator's seat 14 on the right side of the boom 11 . Therefore, the front left side viewed from the driver's seat 14 is difficult to see due to the boom head 9 projecting downward from the boom 11, the main sheave 222, and the single top sheave 223. In such a state, the operator drives the mobile crane 8 while paying sufficient attention.

Such obscurity also occurs in mobile cranes with a single hook. However, in the mobile crane 8 having the main hook 31 and the sub hook 32 as shown in FIG. 1, the single top sheave 223 is positioned further below the main sheave 222 when the boom 11 is collapsed. Therefore, the blocking range is larger than with a single hook.

Note that unlike the mobile crane 8 in FIG. 2, even in a mobile crane that tilts the boom over the operator's cab when moving, the boom head and sheave that hang down from the boom make it difficult to see diagonally forward from the driver's seat. Become.

In order to eliminate such difficulty in seeing, it is possible to install a camera facing forward on the left front of the mobile crane so that the left front can be confirmed on the display provided in the driver's seat. However, there are problems such as the cost of installing cameras and the like, and difficulty in checking the left front in the event of equipment failure.

An object of the present invention is to improve the visibility from the driver's seat during travel in a mobile crane having a visibility from the driver's seat below the boom during travel.

A boom head according to one embodiment of the present invention is a boom head attached to the tip of a boom in a mobile crane, and comprises a boom head fixing part fixed to the tip of the boom, and a boom head fixing part pivotally supported. a boom head movable part having a sheave, wherein the front surface of the boom head movable part is bent in the opposite direction of the boom, and the boom head movable part is extended from the boom head fixed part; It is characterized in that the boom head movable part can shift to a folded state in which it overlaps with the boom head fixed part in a bent direction.

According to the present invention, the visibility can be improved by reducing the downward protrusion of the boom while suppressing the overall length and height of the mobile crane.

The boom head and hook of a conventional mobile crane with the boom raised. The left side view of the conventional mobile crane when traveling. Fig. 3 is a left side view of the mobile crane of the embodiment with the boom lowered; The left view of the mobile crane of embodiment at the time of driving|running|working. (a) is a left side view of the boom head fixed part in embodiment, (b) is a left side view of the boom head movable part. (a) is a front view of the boom head fixed part in embodiment, (b) is a front view of a boom head movable part. (a) is a left side view of the boom head in the extended state in the embodiment, and (b) is a right side view of the boom head in the extended state in the embodiment. (a) is a left side view of the boom head in the folded state in the embodiment, and (b) is a right side view of the boom head in the folded state in the embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent constituent elements, members, and processes shown in each drawing are denoted by the same reference numerals, and duplication of description will be omitted as appropriate. Also, in the figure, a portion of the hidden configuration is indicated by a dotted line.

A mobile crane 1 of an embodiment according to the invention is shown in FIG. The boom 11 is attached to the vehicle body 13 via the revolving body 12 . A driver's cab having a driver's seat 14 is provided on the right side of the boom 11 above the vehicle body 13 . The mobile crane 1 in FIG. 3 is in a state where the boom 11 is lowered. A boom head 2 is provided at the tip of the boom 11 . As in the conventional mobile crane 8 of FIG. 2, the boom head 2 has a main sheave 222 and a sub-sheave single top sheave 223 protruding below the boom 11 . Note that FIG. 3 omits the description of the pressed arm 23, the pressing device 5, and the sensor 6, which will be described later.

In FIG. 3 , the boom head 2 is divided into two parts, a boom head fixed part 21 and a boom head movable part 22 . The boom head movable portion 22 is pivotally supported by the boom head fixed portion 21 and is foldable. The boom head 2 in FIG. 3 is in an extended state in which the boom head movable portion 22 is extended from the boom head fixed portion 21 . An upper sheave 212 is pivotally supported above the boom head fixing portion 21 . A main sheave 222 is pivotally supported on the boom head movable portion 22 on the side closer to the boom 11 , and a single top sheave 223 is pivotally supported on the distal end side of the boom head movable portion 22 .

The mobile crane 1 of the embodiment also has two hooks 3 . Two wires 4 extending along the boom 11 from a winch (not shown) provided on the revolving body 12 are hung on the upper sheave 212 . The main wire 41 is connected from the upper sheave 212 to the main hook 31 via the main sheave 222 , and the sub wire 42 is connected from the upper sheave 212 to the sub hook 32 via the single top sheave 223 . In FIG. 3, the main hook 31 and the sub hook 32 are engaged with the vehicle body 13 .

When the boom 11 is lowered during traveling, the left area of the mobile crane 1 can be viewed from the driver's seat 14 through the boom 11 . However, when the boom 11 is lowered as shown in FIG. 3, the boom head 2 protrudes into the projecting area P, and the amount of downward projection of the boom 11 is large as in the conventional example of FIG. Therefore, it is difficult to see the left front area of the mobile crane 1 from the driver's seat 14 .

In this embodiment, before traveling, the boom head movable part 22 is rotated and lifted forward to overlap with the boom head fixed part 21 as shown in FIG. 4 to fold the boom head 2 . In the folded state shown in FIG. 4, the boom head 2 does not protrude into the projecting area P below the boom 11 . In this way, since the amount of downward protrusion of the boom head 2 from the boom 11 can be reduced, the visibility from the driver's seat 14 can be improved when the mobile crane 1 is traveling.

Next, the boom head 2 of this embodiment will be described in detail. FIG. 5 shows a left side view of parts constituting the boom head 2. As shown in FIG. In FIG. 5, the boom head 2 in FIGS. 3 and 4 is enlarged. FIG. 5(a) shows the boom head fixing portion 21, which is fixed to the tip of the boom 11. FIG. FIG. 5(b) shows a boom head movable portion 22, which is pivotally supported by the boom head fixed portion 21 and rotatably attached.

The boom head fixing portion 21 shown in FIG. 5A is sandwiched between the inner upper portion of the fixing portion main body 211 and rotatably supports the upper sheave 212 . A head tilt shaft 213 is provided at the bottom, and a head tilt fixing pin 214 is provided beside it. Furthermore, a contact portion 215 is provided below the head tilt shaft 213 inside the fixed portion main body 211 . A thick side plate 216 is provided at the lower portion of the fixing portion main body 211 where the head tilt shaft 213 and the head tilt fixing pin 214 are provided. The head tilt fixing pin 214 is electrically protruded or returned to its original position by an actuator.

The boom head movable portion 22 shown in FIG. 5B is rotatably supported by a movable portion main body 221 with a main sheave 222 and a single top sheave 223 interposed therebetween. A head tilt hole 224 supported through a head tilt shaft 213 is provided in the upper part of the movable part main body 221, and a first fixing hole 225 is provided on the side of the head tilt hole 224 in FIG. is provided with a second fixing hole 226 . In addition, in the movable portion main body 221, the surface on the boom 11 side between the head tilt hole 224 and the second fixing hole 226 is a contact portion 227, and the contact portion 215 of the boom head fixing portion 21 in the extended state. abut. The movable portion main body 221 has a thick side plate 228 extending from the head tilt hole 224 and the first fixing hole 225 in the upper portion to the shaft supporting portion of the main sheave 222 in the middle.

Further, the movable portion main body 221 is provided with a pressed arm 23 projecting leftward. The pressed arm 23 includes a protruding tube 231 protruding leftward from the main body 221 of the movable part, a side plate 232 provided on the end surface of the protruding tube 231, and a semi-cylindrical pressed recess protruding leftward from the side plate 232. 233, and a small side plate 234 provided on the end surface of the recess to be pressed. The front surface of the movable portion main body 221 is indicated by a dashed line in FIG. 5B as an upper front surface A and a lower front surface B. As shown in FIG. The lower anterior surface B is bent at 68° from the upper anterior surface A, and the internal angle between the upper anterior surface A and the lower anterior surface B is 112°.

FIG. 6 shows a front view of parts constituting the boom head 2. As shown in FIG. 3 and 5 are views viewed from the left front. 6(a) shows a boom head fixing portion 21 fixed to the tip of the boom 11, and FIG. 6(b) shows a boom head movable portion 22 rotatably attached to the boom head fixing portion 21. FIG. Two sheaves are provided for the main wire 41 and the sub wire 42 as the upper sheave 212 . Thick side plates 216 are provided on both sides of substantially the lower half of the fixing portion main body 211 , and a head tilt shaft 213 is provided between the two thick side plates 216 . In addition, the front surface of approximately the lower half of the fixing portion main body 211 has an opening 217 into which a part of the boom head movable portion 22 enters when folded. The upper part of the opening 217 is the front plate 218 of the fixed part main body 211 . Further, although not shown in FIG. 6A, the thick side plate 216 is provided with a head tilt fixing pin 214 .

In the boom head movable portion 22 of FIG. 6B, a head tilt hole 224 is provided in the upper portion of the thick side plate 228 in the movable portion main body 221 . The boom head movable part 22 is rotatably supported by the boom head fixing part 21 by the head tilt shaft 213 of the boom head fixing part 21 passing through the head tilt hole 224 . A main sheave 222 is provided between the two thick side plates 228 . The main sheave 222 consists of four sheaves. A movable pulley is provided on the main hook 31, and the main wire 41 is wound multiple times between the movable pulley and the four sheaves. A single top sheave 223 is provided at the lower portion of the movable portion main body 221 . The single top sheave 223 is composed of one sheave. Furthermore, although not shown in FIG. 6B, the thick side plate 228 is also provided with a first fixing hole 225 and a second fixing hole 226 .

A pressed arm 23 is provided on the left side (right side in FIG. 6B) of the movable portion main body 221 . One end of the projecting tube 231 of the pressed arm 23 is connected to the movable portion main body 221 and extends leftward from the one end. The other end of the projecting tube 231 is connected to one end of the side plate 232 . The side plate 232 extends in the direction of the boom 11 as shown in FIG. 5(b), and connects one end of the pressed concave portion 233 to the left side of the other end. The recessed portion 233 to be pressed extends leftward while directing the recessed portion in the direction of the boom 11 , and the other end is closed by a small side plate 234 having a semi-disc shape.

FIG. 7 is a side view of the vicinity of the boom head 2 composed of the boom head fixed portion 21 and the boom head movable portion 22 in the extended state. The boom head movable part 22 is pivotally supported by the boom head fixed part 21 shown in FIGS. 5 and 6, and corresponds to a partially enlarged view of the boom head 2 shown in FIG. FIG. 7(a) shows the left side, and FIG. 7(b) shows the right side. In the extended state of the boom head 2 in FIG. 7, the boom head movable portion 22 is in the working position, and the boom 11 can be raised to lift a load with the hook 3 as shown in FIG.

The head tilt shaft 213 passes through the head tilt hole 224 and pivotally supports the boom head movable portion 22 . The center position of the head tilt shaft 213 and the head tilt hole 224 is the head tilt rotation center. 7A, the first fixing hole 225 is locked by the head tilt fixing pin 214, and the boom head movable portion 22 is fixed to the boom head fixing portion 21. As shown in FIG. The fixing by the head tilt fixing pin 214 is for preventing rotation of the boom head movable portion 22, not for receiving a load. The contact portion 215 of the boom head fixing portion 21 contacts the contact portion 227 of the boom head movable portion 22 in the extended state where the boom head movable portion 22 is in the working position. A load when suspending the hook 3 to which a load is attached by the wire 4 acts on the movable part main body 221 via the main sheave 222 or the single top sheave 223 . The head tilt shaft 213 passes through the head tilt hole 224 and is supported by the contact between the contact portion 215 and the contact portion 227 .

The head tilt shaft 213 is provided between the thick side plates 216 , and the boom head 2 has a structure capable of withstanding the load when the hook 3 on which the load is attached is suspended by the wire 4 . Further, the main sheave 222 is provided at a position closer to the head tilt hole 224 and the contact portion 227 than the single top sheave 223 is, and a shaft is provided between the thick side plates 228 . This allows the structure to withstand heavy loads.

As shown in FIG. 7A, a pressing device 5 is provided at the lower left near the tip of the boom 11 when the boom 11 is laid down. In the mobile crane 1 , the pressing device 5 is provided on the side opposite to the driver's seat 14 with respect to the boom 11 . A tilt cylinder 51 of the pressing device 5 has one end supported by a shaft support portion 52 and a middle portion supported by a support spring 53 so as to be suspended. A shaft 54 that is pushed out by hydraulic pressure is provided inside the tilt cylinder 51 , and a shaft tip 55 protruding in a semi-cylindrical shape is provided at the tip of the shaft 54 . The tip end 55 of the shaft is fitted into the pressed concave portion 233 of the pressed arm 23 fixed to the boom head movable portion 22 . The recessed portion 233 to be pressed is recessed in a semi-cylindrical shape and substantially matches the shape of the tip end 55 of the shaft. Both ends of the pressed recess 233 are closed by the side plate 232 and the small side plate 234, and the shaft tip 55 is surrounded by the pressed recess 233, the side plate 232, and the small side plate 234. . A pressed recess 233 formed at the end of the pressed arm 23 is a pressed portion.

FIG. 8 is a side view of the vicinity of the boom head 2 composed of the boom head fixing portion 21 and the boom head movable portion 22 in the folded state. This corresponds to a partially enlarged view of the boom head 2 in FIG. FIG. 8(a) shows the left side, and FIG. 8(b) shows the right side. In the folded state of the boom head 2 in FIG. 8, the boom head movable portion 22 is in the traveling position. In the folded state, the front surface of the thick side plate 228 shown in FIG. 6(b), which is the upper front surface A of the movable portion main body 221 shown in FIG. 5(b), faces the fixed portion main body 211 shown in FIG. It enters the provided opening 217 . Then, the lower front surface B of the movable portion main body 221 shown in FIG. 5(a) is folded so as to be positioned in front of the front surface C of the fixed portion main body 211 shown in FIG. state.

As described above, the boom head movable portion 22 can shift between the extended state in which the boom head movable portion 22 extends from the boom head fixed portion 21 and the folded state in which the boom head movable portion 22 overlaps the boom head fixed portion 21 in the bent direction. As shown in FIG. 4, in the folded state, the boom head movable part 22 does not protrude into the protruding area P, and the mobile crane 1 can be driven with a good field of view from the driver's seat 14 to the left front.

A sensor 6 is provided in the mobile crane 1 in order to detect the state of transition between the extended state and the folded state of the boom head 2 . As shown in FIGS. 6(a), 7(b), and 8(b), the boom head fixing portion 21 is provided with a working position detection switch 61 and a travel position detection switch 62. As shown in FIGS. In the extended state, which is the working position, as shown in FIG. 7B, the movable part main body 221 contacts the working position detection switch 61 to detect that the boom head movable part 22 is in the working position. In the folded state, which is the running position, as shown in FIG. 8B, the movable part main body 221 contacts the running position detection switch 62 to detect that the boom head movable part 22 is in the running position. The pressing device 5 is provided with a length detector 63 that detects the amount of protrusion of the shaft 54 from the tilt cylinder 51 .

After the work at the site is completed, the mobile crane 1 lowers the boom 11 and shifts the boom head 2 from the extended state shown in FIG. 3 to the folded state shown in FIG. When shifting from the extended state of FIG. 7 to the folded state of FIG. 8, the head tilt fixing pin 214 is pulled out from the first fixing hole 225 by an actuator (not shown). After that, hydraulic pressure is applied to the tilt cylinder 51 to push out the shaft 54 . A shaft tip 55 provided at the tip of the extruded shaft 54 pushes the pressed recess 233 , thereby rotating the pressed arm 23 and the boom head movable portion 22 around the head tilt shaft 213 .

At that time, the shaft tip 55 moves leftward in FIG. As a result, the position of the depression 233 to be pressed is temporarily lowered, but the support spring 53 suspending the tilt cylinder 51 is stretched, so that the tip end 55 of the shaft does not come off the depression 233 to be pressed. Further, the pressing device 5 has a stopper bolt 56 on the upper portion of the tilt cylinder 51 to prevent the tip end 55 of the shaft from being lifted too much and coming off the depressed recess 233 .

When the boom head movable portion 22 is folded into the boom head fixed portion 21 in the state shown in FIG. 8, the second fixing hole 226 overlaps the position of the head tilt fixing pin 214, and the traveling position detection switch 62 is turned on. . When the traveling position detection switch 62 is turned on, an actuator (not shown) inserts the head tilt fixing pin 214 into the second fixing hole 226 to fix the boom head movable portion 22 in the folded state.

When the mobile crane 1 traveling with the boom head 2 folded as shown in FIG. 4 arrives at the work site, the boom head 2 is shifted to the extended state shown in FIG. At that time, the head tilt fixing pin 214 is first pulled out from the second fixing hole 226 by an actuator (not shown). The pressing device 5 comprises a hydraulic system with an overload relief valve. With the sub hook 32 fixed to the front of the mobile crane 1, when the sub wire 42 is hoisted by a winch (not shown) provided on the revolving body 12, the tip of the boom head movable portion 22 is pulled downward. Due to this force and the weight of the boom head movable portion 22, the shaft 54 is pushed into the tilt cylinder 51 via the pressed arm 23, the pressure of the hydraulic system increases, and the overload relief valve opens. Then, the boom head 2 is in the extended state shown in FIGS. When the boom head movable portion 22 is lowered as shown in FIG. 7, the first fixing hole 225 is aligned with the position of the head tilt fixing pin 214, and the working position detection switch 61 is turned on. When the working position detection switch 61 is turned on, the actuator (not shown) inserts the head tilt fixing pin 214 into the first fixing hole 225 to lock the boom head movable portion 22 .

The boom head movable part 22 extends from the pivotally supported position and is bent in the opposite direction of the boom. Overlap. With such a configuration, as shown in FIG. 4, in the folded state in which the mobile crane 1 travels, visibility can be secured in the protruding region P, and the forward protrusion of the mobile crane 1 can be reduced. can. In addition, the amount of upward protrusion in the folded state can be reduced, and the height of the mobile crane 1 during travel can be suppressed. By utilizing the bending of the boom head movable portion 22 due to the attachment positions of the main sheave 222 and the single top sheave 223, the amount of forward protrusion and height during travel of the mobile crane can be suppressed.

In the embodiment, the boom head movable portion 22 is bent forward at 68°. The bending angle is not limited to this, but the boom head movable part bends forward in the range of 45° to 90° (the internal angle between the upper front surface A and the lower front surface B of the movable part main body 221 is 135° to 90°). is preferred.

In the embodiment, the position of the head tilt fixing pin 214 is electrically operated by an actuator to insert/remove the head tilt fixing pin 214 into/from the first fixing hole 225 and the second fixing hole 226, but the operator manually inserts/removes the head tilt fixing pin 214. You may do so. Further, in the embodiment, when the boom head 2 is shifted from the folded state to the extended state, a winch is used to apply force to the boom head movable portion 22, and the overload relief valve causes the shaft 54 of the pressing device 5 to move to the tilt cylinder 51. housed in However, the shaft 54 of the pressing device 5 may be accommodated in the tilt cylinder 51 by lowering the hydraulic pressure of the pressing device 5 . After the boom head 2 is fixed in the folded state by the head tilt fixing pin 214 , the hydraulic pressure of the pressing device 5 can be lowered to accommodate the shaft 54 of the pressing device 5 in the tilt cylinder 51 . The pressed arm is separated from the pressing device 5 when the pressing device 5 is retracted. The mobile crane 1 may be made to travel in such a state.

In addition, the specific configuration is not limited to the embodiment, and even if there is a change in design within the scope of the present invention, it is included in the present invention. In addition, each of the above-described embodiments can be combined by utilizing each other's techniques unless there is a particular contradiction or problem in the purpose, configuration, or the like.

1 mobile crane 11 boom 12 rotating body 13 vehicle body 14 driver's seat 2 boom head 21 boom head fixing part 211 fixing part main body 212 upper sheave 213 head tilt shaft 214 head tilt fixing pin 215 contact part 216 thick side plate 217 opening 218 front plate 22 boom head movable part 221 movable part body 222 main sheave 223 single top sheave 224 head tilt hole 225 first fixing hole 226 second fixing hole 227 contact part 228 thick side plate 23 pressed arm 231 projecting tube 232 side Side plate 233 Pressed concave portion 234 Small side plate 3 Hook 31 Main hook 32 Sub hook 4 Wire 41 Main wire 42 Sub wire 5 Pressing device 51 Tilt cylinder 52 Axle 53 Support spring 54 Shaft 55 Shaft tip 56 Stopper bolt 6 Sensor 61 Work Position detection switch 62 Traveling position detection switch 63 Length detector 8 Mobile crane 9 Boom head P Projection area A Upper front surface B of movable part main body 221 Lower front surface of movable part main body 221

Claims (10)

A boom head attached to the tip of a boom in a mobile crane,
a boom head fixing portion fixed to the tip of the boom;
Having a boom head movable part pivotally supported by the boom head fixed part and having a sheave,
a front surface of the boom head movable portion is bent in a direction opposite to the boom;
A boom head that can shift between an extended state in which the boom head movable portion extends from the boom head fixed portion and a folded state in which the boom head movable portion overlaps the boom head fixed portion in a bent direction. . 2. The boom head of claim 1, wherein said sheaves are a main sheave and a sub sheave. A mobile crane having a view from the driver's seat below the boom when traveling,
A mobile crane, wherein the boom head according to claim 1 or 2 is provided at the tip of the boom. 4. The mobile crane according to claim 3, wherein the extension of the pushing device rotates the movable portion of the boom head to shift from the extended state to the folded state. The pressing device has a tilt cylinder,
5. The mobile crane according to claim 4, wherein said tilt cylinder is rotatably pivoted and supported by a support spring. A mobile crane according to claim 4 or 5, characterized in that said pressing device is a hydraulic device with an overload relief valve. The boom head movable part has a pressed arm projecting laterally,
7. The mobile crane according to any one of claims 4 to 6, wherein the pushed arm is pushed by the pushing device to shift from the extended state to the folded state. 8. The mobile crane according to claim 7, wherein the pressed arm is separated from the pressing device when the pressing device is retracted. The mobile crane according to any one of claims 4 to 8, wherein the pressing device is provided on the opposite side of the operator's seat with respect to the boom. The boom head movable part has a contact part below a pivot supported by the boom head fixed part,
10. The mobile crane according to any one of claims 3 to 9, wherein in the extended state, the boom head movable part is supported by the pivot part and the contact part.

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