TELESCOPIC BOOM

A lightweight and high-rigidity telescopic boom in which strain during manufacturing is suppressed is disclosed. In a telescopic boom, a plurality of booms forms a telescope structure, and the telescopic boom includes a boom fixing mechanism that fixes a top boom disposed relatively inside at a predetermined position with respect to a first intermediate boom disposed relatively outside. The boom fixing mechanism includes a boom fixing pin that is provided to the top boom and advances and retreats with respect to the first intermediate boom, a fixing boss that is provided to the first intermediate boom and into which the boom fixing pin is inserted and extracted, and a gap maintaining member that is provided to the fixing boss and protrudes outward to maintain a gap between the first intermediate boom and a second intermediate boom disposed further outside.

TECHNICAL FIELD

The present invention relates to a structure of a telescopic boom mounted on a mobile crane.

BACKGROUND ART

A mobile crane such as a rough terrain crane generally includes a telescopic boom forming a telescopic structure. In the telescopic boom, a plurality of booms is assembled in a so-called nested manner, and an inner boom having a smaller outer shape is inserted into the inside of an outer boom having a larger outer shape. A predetermined gap is set between the two booms, and when the telescopic boom extends and retracts, the inner boom slides relatively with respect to the outer boom and protrudes from the outer boom.

Japanese Patent No. 4709415 discloses a coupling structure that couples the inner boom with the outer boom adjacent to the inner boom. In the coupling structure, a boom fixing pin provided to the inner boom is fitted to a fixing boss attached to the outer boom. Specifically, the boom fixing pin is inserted into a fixing hole provided to the fixing boss, thereby the inner boom and the outer boom are coupled. With this, the inner boom and the outer boom slide integrally. The boom fixing pin is extracted from the fixing hole, thereby the coupling between the inner boom and the outer boom is released.

The telescopic boom disclosed in Japanese Patent Application Laid-Open No. 2018-80020 includes a slide plate between the inner boom and the outer boom. When the inner boom is relatively displaced with respect to the outer boom, the slide plate contacts the adjacent booms. With this, the predetermined gap is maintained, and an outer surface of the inner boom and an inner surface of the outer boom are prevented from directly contacting.

Incidentally, each boom constituting the telescopic boom is obtained by forming a steel plate into a tubular shape, and is required to be lightweight and high-rigidity. Therefore, each boom is designed to have a thin thickness and a large outer size (so as to have a thin and large cross section). That is, the telescopic boom is designed compactly so that the outer size of each boom is large and the gap between the booms is small. On the other hand, the fixing boss and the slide plate are provided to each boom constituting the telescopic boom, and are generally welded from the point of view on strength and mounting method.

When the fixing boss or the like is welded to a thin steel plate, strain is likely to occur in each boom. When the strain occurs, the predetermined gap is not secured. As a result, not only it becomes difficult to assemble each boom, but also in the first place, the design of each boom does not meet the above-described requirements, and a serious problem occurs in manufacturing the telescopic boom.

SUMMARY OF THE DISCLOSURE

The present invention has been made in this background, and an object thereof is to provide a lightweight and high-rigidity telescopic boom in which strain during manufacturing is suppressed.

(1) In a telescopic boom according to the present invention, a plurality of booms forms a telescopic structure, and the telescopic boom includes a boom fixing mechanism configured to fix the boom disposed relatively inside at a predetermined position with respect to the boom disposed relatively outside. The boom fixing mechanism includes a boom fixing pin provided to the boom disposed inside and configured to advance and retreat with respect to the boom disposed outside, a fixing boss provided to the boom disposed outside and configured to allow the boom fixing pin to be inserted and extracted, and a gap maintaining member provided to the fixing boss and configured to protrude outward to maintain a gap between the boom disposed outside and the boom disposed further outside.

According to this configuration, the gap maintaining member is not directly welded to the boom, but is provided to the fixing boss. Therefore, an amount of welding to the boom is decreased, and as a result, welding strain generated at the time of manufacturing the boom is suppressed. With this, a design in which the thickness of the boom is thinner and the gap between the booms is smaller becomes possible, and a compact design and a lightweight design of the telescopic boom becomes possible. Furthermore, compared with a case in which the fixing boss and the gap maintaining member are separately welded to the boom, a space saving of the gap between the booms can be realized, and an optimal design of the boom becomes possible. Furthermore, the gap maintaining member is provided to the fixing boss, thereby the gap maintaining member is disposed in a vicinity of a portion in which the boom fixing pin is extracted and inserted. Therefore, the gap between the adjacent booms is reliably maintained in a region in which the boom fixing pin operates.

(2) The fixing boss includes a central plate portion having a rectangular shape extending in a longitudinal direction and a vertical direction of the boom, the central plate portion configured to allow the boom fixing pin to be inserted and extracted, a pair of lateral bulging portions that is respectively continuous with both sides in the longitudinal direction of the central plate portion and smoothly bulges outward, and a vertical bulging portion that smoothly bulges in a continuous manner with at least one of an upper end or a lower end of the central plate portion. The gap maintaining member is provided to the vertical bulging portion so as to protrude to a side of the boom disposed relatively outside.

In this configuration, the lateral bulging portions are smoothly continuous with the both sides of the central plate portion disposed in a relatively central portion, and the vertical bulging portion is smoothly continuous with an upper portion of the central plate portion. In other words, the fixing boss is a flat plate shaped member, and an outer peripheral edge thereof draws a smooth closed curve. Therefore, since when an external force acts on the fixing boss, stress concentration on a specific portion is relieved, the fixing boss can secure a sufficient mechanical strength, and a lightweight design is also possible.

Furthermore, the gap maintaining member is provided to the vertical bulging portion. Therefore, when the gap maintaining member contacts the adjacent boom (boom disposed further outside), an influence of an impact or the like at the time of the contact on the central plate portion or the lateral bulging portion of the fixing boss can be reduced.

(3) It is preferable that the fixing boss include a central plate portion having a rectangular shape extending in a longitudinal direction and a vertical direction of the boom, the central plate portion configured to allow the boom fixing pin to be inserted and extracted, and a pair of lateral bulging portions that is respectively continuous with both sides in the longitudinal direction of the central plate portion and symmetrically bulges outward, and the gap maintaining member is provided to the central plate portion or the lateral bulging portion and has a rectangular parallelepiped shape protruding to a side of the boom disposed relatively outside.

In this configuration, the lateral bulging portions are smoothly continuous with the both sides of the central plate portion disposed in a relatively central portion. In other words, the fixing boss is a flat plate shaped member, and an outer peripheral edge thereof draws a smooth closed curve. Therefore, since when an external force acts on the fixing boss, stress concentration on a specific portion is relieved, the fixing boss can secure a sufficient mechanical strength. In addition, the shape of the fixing boss is simple, and a further lightweight design is possible.

(4) It is preferable that the gap maintaining member be attachably and detachably provided to the fixing boss by a fastening member.

According to this configuration, the gap maintaining member is easily replaced as a consumption article.

(5) Hardness of the gap maintaining member is lower than hardness of the boom.

According to this configuration, since when the gap maintaining member contacts the boom, the gap maintaining member having lower hardness is worn, the boom is prevented from being worn.

(6) Preferably, the boom is made of steel material, and the gap maintaining member is made of copper alloy.

(7) The gap maintaining member may be welded to the fixing boss.

According to this configuration, the gap maintaining member can be strongly attached to the fixing boss.

According to the present invention, a lightweight and high-rigidity telescopic boom in which strain during manufacturing is suppressed is provided.

DETAILED DESCRIPTION

Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings as appropriate. Note that it is needless to say that the present embodiment is merely one aspect of a telescopic boom according to the present invention, and that the embodiment may be changed without departing from the gist of the present invention.

FIG.1is a left side view of a mobile crane10in which a telescopic boom13according to an embodiment of the present invention is adopted.

As shown inFIG.1, the crane10includes a carrier111, a boom device112, a cabin113, and a winch139.

The carrier111includes a vehicle body120and wheels121. The vehicle body120has axles not shown, and the axles are disposed at a front portion and a rear portion of the vehicle body120. The wheels121are provided at both ends of each axle. The axles and the wheels121are driven to rotate by an engine (not shown), thereby the carrier111travels.

The boom device112includes a slewing base11, a slewing motor (not shown), the telescopic boom13, and a derricking cylinder136.

The slewing base11is supported by the vehicle body120. The slewing base is supported so as to be rotatable around a slewing shaft extending in the vertical direction. The slewing base11is rotated by the slewing motor. The telescopic boom13is supported by the slewing base11. The telescopic boom13can slew together with the slewing base11.

The telescopic boom13stands up and lies down between a lying position and a standing position taking a derricking central shaft12as a center, by an extension and a retraction of the derricking cylinder136. The derricking central shaft12extends in a width direction102(seeFIG.2: direction orthogonal to the paper surface inFIG.1).FIG.1shows the telescopic boom13in the lying position by a solid line and shows the telescopic boom13in the standing position by a broken line.

As shown inFIG.2, the telescopic boom13includes a plurality of cylindrical booms (a base boom20, a top boom21, and intermediate booms22to25to be described later), and these booms form a telescopic structure. Each of the booms20to25is made of steel material, for example. The configuration of the telescopic boom13will be described in detail later.

The cabin113is mounted on the slewing base11. The cabin113has a seat on which an operator sits, a driving device used for driving the carrier111, and a steering device used for steering the boom device112. The crane10is a so-called rough terrain crane, and the operator performs driving of the carrier111and steering of the boom device112in one cabin113. However, the crane10may be an all-terrain crane including two cabins, that is, a cabin having the driving device and a cabin having the steering device. The driving device has a steering for steering the wheels121, an accelerator pedal, a brake pedal, a shift lever, or the like. The operator makes the carrier111travel using the driving device. The steering device has a plurality of levers or the like for driving the slewing motor, a telescopic cylinder, the derricking cylinder136, a winch motor (not shown), or the like. The operator operates the boom device112using the steering device.

The winch139includes a drum141driven to rotate, a wire rope142, and a hanging hook140. The drum141is rotatably supported by the slewing base11.

The drum141is rotated by the winch motor. The wire rope142is wound around the drum141, and is fed out from the drum141or wound around the drum141by the rotation of the drum141. The hanging hook140is connected to the wire rope142.

The wire rope142is wound from the drum141to a wire sheave144provided at a proximal end portion of the telescopic boom13, and spans along the telescopic boom13. The wire rope142is wound around a wire sheave143provided at a distal end portion of the telescopic boom13and drops down.

The hanging hook140is coupled to a distal end of the wire rope142. The hanging hook140is hanged down by the wire rope142from the distal end portion of the telescopic boom13. The hanging hook140rises and falls by the rotation of the drum141.

FIG.2is a schematic view showing a structure of the telescopic boom13.

In addition to the slewing base11, the slewing motor, the telescopic boom13, and the derricking cylinder136, the boom device112includes a telescopic cylinder14, a boom fixing mechanism15, and a cylinder boom coupling mechanism16, and a driving mechanism (not shown), as shown in the drawing.

The telescopic cylinder14makes the telescopic boom13extend and retract. The boom fixing mechanism15couples adjacent booms of the plurality of booms constituting the telescopic boom13. The cylinder boom coupling mechanism16couples the telescopic cylinder14to a predetermined portion of the telescopic boom13. The driving mechanism drives the boom fixing mechanism15and the cylinder boom coupling mechanism16. Note that since a known configuration can be adopted for the driving mechanism, detailed description thereof is omitted.

The telescopic boom13includes the base boom20, the top boom21, and the four intermediate booms22to25disposed between the base boom20and the top boom21. The intermediate booms22to25are referred to as a first intermediate boom22, a second intermediate boom23, a third intermediate boom24, and a fourth intermediate boom25in this order from the boom adjacent to the top boom21. That is, the telescopic boom13has a six-stage arrangement in the present embodiment. Each of the booms21to25is assembled so as to slide with respect to the base boom20in a longitudinal direction38.

The telescopic boom13forms a telescopic structure. That is, the fourth intermediate boom25is disposed in the base boom20and is slidable with respect to the base boom20. The third intermediate boom24is disposed in the fourth intermediate boom25and is slidable with respect to the fourth intermediate boom25. The second intermediate boom23is disposed in the third intermediate boom24and is slidable with respect to the third intermediate boom24. The first intermediate boom22is disposed in the second intermediate boom23and is slidable with respect to the second intermediate boom23. The top boom21is disposed in the first intermediate boom22and is slidable with respect to the first intermediate boom22.

Note that the telescopic boom13may not necessarily have the six-stage arrangement, and the number of the intermediate booms is not particularly limited.

The telescopic cylinder14is built in the telescopic boom13. The telescopic cylinder14is a hydraulic type double-acting cylinder. A distal end portion of a cylinder rod39is coupled to a proximal end of the base boom20. The telescopic cylinder14is disposed along the longitudinal direction38of the telescopic boom13, and a cylinder tube36is disposed inside the top boom21in the state ofFIG.2. The telescopic cylinder14performs extension and retraction operation, thereby the telescopic boom13extends and retracts as will be described later.

FIG.2shows that the telescopic boom13is in a fully retracted state. In this state, the booms adjacent to each other are always coupled by the boom fixing mechanism15.

FIGS.3and4are a longitudinal sectional view and a transverse sectional view of the telescopic boom13, respectively, andFIG.4is a sectional view taken along the IV-IV surface in FIG.3. These drawings schematically show structures of the boom fixing mechanism15and the cylinder boom coupling mechanism16. Note that inFIG.4, only the top boom21, the first intermediate boom22, and the second intermediate boom23are illustrated, and illustration of the third intermediate boom24, the fourth intermediate boom25, and the base boom20is omitted.

As shown inFIGS.2,3, and4, the boom fixing mechanism15includes five boom fixing pins (hereinafter referred to as “B pins”)26to30, a hydraulic cylinder31that drives the B pins26to30, and fixing bosses32,33. The B pins26to30penetrate the fixing bosses32,33. Note that inFIG.1, illustration of the fixing bosses32,33is omitted.

As shown inFIG.2, the B pin26is supported by the top boom21. The B pins27to30are supported by the first intermediate boom22, the second intermediate boom23, the third intermediate boom24, and the fourth intermediate boom25, respectively. Note that the base boom20located outermost does not include the B pins.

The B pin26advances and retreats with respect to the boom (boom disposed outside) adjacent to the outside of the boom (boom disposed inside) that supports the B pin26, thereby penetrating the boom disposed outside or being separated from the boom disposed outside. The same applies to the B pins27to30. The B pin26penetrates the first intermediate boom22, thereby fixing the top boom21at a predetermined position of the first intermediate boom22. Similarly, the B pins27to30respectively penetrate the boom disposed relatively outside (the second intermediate boom23, the third intermediate boom24, the fourth intermediate boom25, and the base boom20), thereby fixing the boom disposed outside at a predetermined position of the boom disposed relatively inside (the first intermediate boom22, the second intermediate boom23, the third intermediate boom24, and the fourth intermediate boom25). At all times, the B pins26to30are biased by springs (not shown) toward a side of the boom disposed relatively outside.

The B pins26to30penetrate proximal end portions and distal end portions of the booms disposed relatively outside (the first intermediate boom22, the second intermediate boom23, the third intermediate boom24, the fourth intermediate boom25, and the base boom20). The fixing bosses32,33are provided at regions through which the B pins26to30penetrate. The B pins26to30respectively penetrate the fixing bosses32,33provided to the first intermediate boom22, the fixing bosses32,33provided to the second intermediate boom23, the fixing bosses32,33provided to the third intermediate boom24, the fixing bosses32,33provided to the fourth intermediate boom25, and the fixing bosses32,33provided to the base boom20. Note that the top boom21located innermost does not include the fixing bosses32,33.

Hereinafter, a structure of the fixing boss32will be described. Note that since the fixing boss33has the same structure as that of the fixing boss32, description of the structure of the fixing boss33is omitted.

FIG.5is a perspective view of the fixing boss32.FIG.6is a perspective view of the fixing boss32viewed from a side opposite to that ofFIG.5.

As shown inFIGS.5and6, the fixing boss32is a plate shaped member having a predetermined thickness. The fixing boss32is typically made of steel material.

As shown inFIG.5, the fixing boss32includes a central plate portion51, a pair of lateral bulging portions52, and an upper bulging portion53(corresponding to a “vertical bulging portion” recited in the claims). The central plate portion51, the pair of lateral bulging portions52, and the upper bulging portion53are formed integrally, and as shown in the drawing, an outer peripheral edge of the fixing boss32draws a smooth closed curve. Although the upper bulging portion53is continuous with an upper side of the central plate portion51in the present embodiment, the upper bulging portion53may be continuous with a lower side of the central plate portion51. Furthermore, the upper bulging portion53may be continuous with the upper and lower sides of the central plate portion51. Note that inFIG.5, the central plate portion51, the pair of lateral bulging portions52, and the upper bulging portion53are separated by virtually-described broken lines.

In the following description, each direction is defined assuming that it is in a state where the fixing boss32is attached to each of the booms20,22to25. The central plate portion51has a rectangular shape extending in the longitudinal direction38and a vertical direction101. Here, the vertical direction101is a direction orthogonal to the longitudinal direction38of the boom (seeFIG.1) and the width direction102of the boom (seeFIG.2).

The pair of lateral bulging portions52is provided on both sides in the longitudinal direction38of the central plate portion51. The pair of lateral bulging portions52is located so as to sandwich the central plate portion51in the longitudinal direction38. The pair of lateral bulging portions52is respectively continuous with the both sides in the longitudinal direction38of the central plate portion51and smoothly bulges outward. An edge surface81of each lateral bulging portion52(surface forming an outer end in the longitudinal direction38of each lateral bulging portion52) is curved so as to protrude outward in the longitudinal direction38.

The upper bulging portion53protrudes upward from an upper end of the central plate portion51. The upper bulging portion53is continuous with the upper end of the central plate portion51and smoothly bulges outward (upward). An edge surface82of the upper bulging portion53is curved.

As shown inFIG.6, a thick portion84is formed on a first surface83of the fixing boss32. The first surface83bulges in the thickness direction, thereby the thick portion84is formed. Therefore, the thickness size of the thick portion84is larger than the thickness size of the remaining region. The thick portion84is formed in a portion except an edge portion85of the central plate portion51and the lateral bulging portion52, and the upper bulging portion53. A side surface86of the thick portion84is inclined. That is, a peripheral edge of the thick portion84is chamfered. With this, the thick portion84is tapered off.

As shown inFIGS.5and6, the fixing boss32has a through hole87. The through hole87penetrates the thick portion84of the fixing boss32in the thickness direction. The through hole87penetrates the fixing boss32from the first surface83to a second surface88(back surface of the first surface83). As will be described later, the B pins26to30penetrate the through holes87. Although the through hole87is provided so as to penetrate the central plate portion51and one of the pair of lateral bulging portions52in the present embodiment, the position of the through hole87is not limited to the position shown inFIGS.5and6. For example, the through hole87is not formed in the pair of lateral bulging portions52, and may be formed only in the central plate portion51. The size and the shape of the through hole87only needs to correspond to the size and the shape of the B pins26to30, and are not limited to the size and the shape shown inFIGS.5and6.

A gap maintaining member90is welded to a second surface88side of the upper bulging portion53. The gap maintaining member90has a quadrangular prism shape and protrudes from the second surface88. The cross-sectional shape of the gap maintaining member90is a trapezoid. The upper base and the lower base of the trapezoidal shape extend in the longitudinal direction38, and the upper base is shorter than the lower base.

The gap maintaining member90is configured by a material having hardness lower than those of the base boom20, the top boom21, and the intermediate booms22to25. In the present embodiment, the gap maintaining member90is configured by gunmetal (copper alloy).

Note that the fixing boss32only needs to have the through hole87and have the gap maintaining member90attached, and does not necessarily have the shape and the size shown inFIGS.5and6. The gap maintaining member90does not necessarily have the shape and the size shown inFIGS.5and6, and various shapes such as a circle, a rectangle, or an ellipse can be adopted.

FIG.7is an enlarged view of a portion surrounded by a dashed line inFIG.4.

The drawing shows a state in which the fixing boss32is attached to the first intermediate boom22. Note that since a state in which the fixing boss33is attached to the first intermediate boom22and states in which the fixing bosses32,33are attached to the second intermediate boom23, the third intermediate boom24, the fourth intermediate boom25, and the base boom20are similar to the state in which the fixing boss32is attached to the first intermediate boom22, description thereof is omitted.

As shown inFIG.2, the first intermediate boom22has through holes at a distal end portion and a rear end portion (regions through which the B pin26penetrates). As shown inFIG.7, the fixing boss32is attached to the first intermediate boom22from the outside of a proximal end portion of the first intermediate boom22. Specifically, the fixing boss32is welded to the first intermediate boom22in a state in which the thick portion84of the fixing boss32is inserted into the through hole.

Note that the second intermediate boom23and the fixing boss32attached to the second intermediate boom23are also shown inFIG.7.

In a state in which the fixing boss32is welded to the first intermediate boom22, a part of the thick portion84of the fixing boss32protrudes inward from the first intermediate boom22. However, the part of the thick portion84does not necessarily have to protrude inward from the first intermediate boom22. On the other hand, a portion of the fixing boss32other than the thick portion84abuts an outer surface72of the first intermediate boom22from the outside. At this time, the second surface88of the fixing boss32is located on the outer side (second intermediate boom23side) of the outer surface72of the first intermediate boom22. The gap maintaining member90is at a position protruding outward from the fixing boss32(second intermediate boom23side). In this case, the first intermediate boom22corresponds to a “boom disposed outside” recited in the claims, and the second intermediate boom23corresponds to a “boom disposed further outside” recited in the claims.

In the drawing, an interval between the outer surface72of the first intermediate boom22and an inner surface73of the second intermediate boom23is indicated by a reference sign L1. An interval between the second surface88of the fixing boss32welded to the first intermediate boom22and the thick portion84of the fixing boss32welded to the second intermediate boom23is indicated by a reference sign L2. An interval between the gap maintaining member90provided on a first intermediate boom22side and the inner surface73of the second intermediate boom23is indicated by a reference sign L3. The interval L3is smaller than the intervals L1, L2. With this, in such a case in which the first intermediate boom22slides with respect to the second intermediate boom23, even if the first intermediate boom22causes a mispositioning and the outer surface72of the first intermediate boom22approaches the inner surface73of the second intermediate boom23, since the gap maintaining member90abuts the inner surface73, the fixing boss32and the first intermediate boom22are prevented from contacting the second intermediate boom23. In short, the gap maintaining member90maintains a gap between the first intermediate boom22and the second intermediate boom23.

Hereinafter, advance and retreat operations of the B pin26with respect to the fixing bosses32,33will be described.

As shown inFIG.2, the B pin26penetrates the proximal end portion and the distal end portion of the first intermediate boom22. The fixing bosses32,33through which the B pin26is inserted are provided at the proximal end portion and the distal end portion. The region to which the fixing boss32is provided is a position in which the B pin26faces when the top boom21is in a fully retracted state with respect to the first intermediate boom22. The region to which the fixing boss33is provided is a position in which the B pin26faces when the top boom21is in a fully extended state with respect to the first intermediate boom22.

At all times, the B pin26is biased toward the first intermediate boom22side by the spring not shown.

As shown inFIG.7, the B pin26penetrates the through hole87of the fixing boss32, thereby the top boom21is fixedly coupled to the first intermediate boom22in the fully retracted state (seeFIG.4(B)). On the other hand, the B pin26penetrates the through hole87of the fixing boss33, thereby the top boom21is fixedly coupled to the first intermediate boom22in the fully extended state.

As shown inFIG.4(A), the B pin26is pulled out from the fixing bosses32,33provided to the first intermediate boom22, by an operation of the hydraulic cylinder31. With this, the top boom21is relatively slidable with respect to the first intermediate boom22.

In this case, the top boom21corresponds to a “boom disposed inside” recited in the claims, and the first intermediate boom22corresponds to a “boom disposed outside” recited in the claims.

Note that also regarding the B pins27to30, advance and retreat operations with respect to the fixing bosses32,33are the same as those of the B pins26.

As shown inFIGS.2,3, and4, the cylinder boom coupling mechanism16includes a cylinder coupling pin (hereinafter, referred to as a “C pin”)34and a hydraulic cylinder35that drives the same. The C pin34is provided on a cylinder tube36side of the telescopic cylinder14and is fitted to the top boom21in the state shown inFIG.2.

As shown inFIG.4, the hydraulic cylinder35includes a link mechanism40. The link mechanism40makes the C pin34slide in the width direction102by an operation of the hydraulic cylinder35.

At all time, the C pin34is biased toward a top boom21side by a spring not shown.

As shown inFIG.2, a fixing boss37is provided at a proximal end portion of the top boom21. As shown inFIGS.2and4, the C pin34is fitted to the fixing boss37. The C pin34is pulled toward a telescopic cylinder14side via the link mechanism40by an operation of the hydraulic cylinder35. When the C pin34is pulled out from the fixing boss37, the telescopic cylinder14is mechanically separated from the top boom21. At all time, the telescopic cylinder14is coupled to the top boom21, and when the hydraulic cylinder35operates, the telescopic cylinder14can slide with respect to the telescopic boom13. The fixing boss37is provided also at a proximal end portion of each of the intermediate booms22to25, and the C pin34can selectively couple to each of the intermediate booms22to25in a manner described later.

FIG.4(A)shows a state in which the B pin26is pulled out from the first intermediate boom22and the C pin34is coupled to the top boom21, andFIG.4(B)shows a state in which the B pin26is coupled to the first intermediate boom22and the C pin34is pulled out from the top boom21.

When the telescopic cylinder14is extended from the state ofFIG.4(A), the top boom21slides leftward in the longitudinal direction38with respect to the first intermediate boom22together with the cylinder tube36of the telescopic cylinder14, as shown inFIG.2. When the telescopic cylinder14is extended to a position in which the B pin26faces the fixing boss33, the operation of the hydraulic cylinder31is stopped, and the B pin26returns to the first intermediate boom22side by the above-described spring and is fitted to the fixing boss33. With this, the top boom21and the first intermediate boom22are fixed in a state in which the top boom21is fully extended with respect to the first intermediate boom22. Next, as shown inFIG.4(B), the hydraulic cylinder35operates, and the coupling between the C pin34and the top boom21is released via the link mechanism40. That is, the C pin34is pulled out from the fixing boss37of the top boom21. When the telescopic cylinder14is retracted in this state, only the cylinder tube36moves to a proximal end side of the base boom20(right side inFIG.2).

Meanwhile, the hydraulic cylinder35continues to operate, and the C pin34is kept in the state ofFIG.4(B). When the telescopic cylinder14is retracted and the C pin34moves to a position of the fixing boss37provided to the first intermediate boom22, the retraction operation of the telescopic cylinder14is stopped and the operation of the hydraulic cylinder35is stopped, and as shown inFIG.4(A), the C pin34is coupled to the fixing boss37of the first intermediate boom22. In a case in which the second intermediate boom23is extended, an operation similar to a case in which the top boom21is extended is performed, and the second intermediate boom23, the third intermediate boom24, and the fourth intermediate boom25are sequentially extended. Note that when the telescopic boom13is retracted, reverse operations described above are performed.

Actions and Effects of the Embodiment

According to the present embodiment, since the gap maintaining member90is provided to the fixing bosses32,33, the gap maintaining member90is not directly welded to the boom. In other words, among the fixing bosses32,33and the gap maintaining member90, it is only the fixing bosses32,33that are welded to the boom. Therefore, an amount of welding to the boom is decreased, and welding strain generated at the time of manufacturing the boom is reduced. As a result, further thinning of the booms and a space saving of the gaps between the booms are realized, and an optimal design of the booms becomes possible. Furthermore, the gap maintaining member90is provided to the fixing bosses32,33, thereby the gap maintaining member90is disposed near a region in which the B pins26to30are extracted and inserted. Therefore, the gap between the booms is reliably maintained at regions in which the B pins26to30operate.

According to the present embodiment, an outer edge of the fixing boss32has a smooth closed curve. In other words, since the pair of lateral bulging portions52and the upper bulging portion53are smoothly continuous with the central plate portion51, stress concentration on a specific portion is relieved. With this, the fixing boss32can secure a sufficient mechanical strength, and a lightweight design is also possible.

According to the present embodiment, the gap maintaining member90is provided to the upper bulging portion53. Therefore, when the gap maintaining member90provided to the boom disposed outside contacts the boom disposed further outside, an influence of an impact or the like at the time of the contact on the central plate portion51and the lateral bulging portions52of the fixing bosses32,33can be reduced.

According to the present embodiment, the gap maintaining member90is a quadrangular prism of which cross-sectional shape is a trapezoid. Therefore, the gap maintaining member90can be reduced in size by an amount in which the upper base is shorter than the lower base.

According to the present embodiment, since when the gap maintaining member90contacts the boom, the gap maintaining member90having low hardness is worn, the boom can be prevented from being worn.

According to the present embodiment, the gap maintaining member90is welded to the fixing bosses32,33, thereby the gap maintaining member90can be strongly attached to the fixing bosses32,33.

Modification Examples

Although the gap maintaining member90is configured by gunmetal in the above-described embodiment, the gap maintaining member90may be configured by a material other than gunmetal. In this case, although the gap maintaining member90is preferably configured by copper alloy other than gunmetal, the gap maintaining member90may be configured by a material other than copper alloy. For example, the gap maintaining member90may be of the same material as that of the fixing boss32, or resin may be adopted.

The position at which the gap maintaining member90is attached to the fixing boss32is not limited to a part of the upper bulging portion53. For example, the gap maintaining member90may be attached in the right or the left of the through hole87shown inFIG.5. A plurality of gap maintaining members90may be attached to the fixing boss32. For example, the gap maintaining member90may also be attached below the through hole87in addition to the position shown inFIG.5.

The gap maintaining member90may be attached to the fixing boss32by means other than welding, for example, by fitting or bonding. The gap maintaining member90may be provided to the fixing boss32by being formed integrally with the fixing boss32.

FIG.8is a main part enlarged cross-sectional view showing a mounting structure of the gap maintaining member90according to a modification example of the present embodiment.

As shown in the drawing, the gap maintaining member90may be attached to the fixing boss32by a bolt89(corresponding to a “fastening member” recited in the claims). In the present modification example, the gap maintaining member90is fastened to the upper bulging portion53of the fixing boss32via a seat member91. The gap maintaining member90has a stepped hole92as shown in the drawing. The bolt89is inserted into the stepped hole92and is screwed with the upper bulging portion53.

Since the gap maintaining member90is fixed by the bolt89in this manner, the gap maintaining member90is freely attachable to and detachable from the fixing boss32. Therefore, there is an advantage that the gap maintaining member90is easily replaced as a consumption article.

FIGS.9and10are perspective views showing a structure of a fixing boss60according to a modification example of the present embodiment.

The fixing boss60is different from the fixing boss32(seeFIGS.5and6) according to the above-described embodiment in that the fixing boss60does not include the upper bulging portion53that the fixing boss32includes, a central plate portion61has a rectangular shape of a substantially square shape, a lateral bulging portion62has a substantially semicircular shape, the shape of a thick portion64is also changed correspondingly, and the gap maintaining member63has a rectangular parallelepiped shape. Note that other configurations of the fixing boss60are similar to those of the fixing boss32, and the same reference signs are provided.

As shown inFIGS.9and10, the fixing boss60includes the central plate portion61and a pair of lateral bulging portions62. As with the fixing boss32, the central plate portion61and the pair of lateral bulging portions62are formed integrally. The central plate portion61has a rectangular shape extending in the longitudinal direction38and the vertical direction101. In this modification example, the central plate portion61has a square shape. However, the shape of the central plate portion61is not limited to the square, and only needs to be a rectangle.

The shape of the pair of lateral bulging portions62is a semicircular shape in the present modification example. These are continuous with both sides in the longitudinal direction38of the central plate portion61, and are disposed symmetrically. However, the shape of the lateral bulging portion62is not limited to the semicircular shape, and only needs to be a shape that smoothly bulges outward in the longitudinal direction38from the central plate portion61. The edge surface81of each lateral bulging portion62is curved so as to protrude outward in the longitudinal direction38. Note that the lateral bulging portion62may have a rectangular shape. In this case, the central plate portion61and the lateral bulging portions62have a rectangular shape as a whole.

As shown inFIG.10, the thick portion84formed on the first surface83of the fixing boss60is formed in a portion except the edge portion85of the central plate portion61and the lateral bulging portion62. The side surface86of the thick portion64is inclined in a manner similar to the thick portion84of the fixing boss32(seeFIG.6). The fixing boss60has the through hole87, which penetrates the fixing boss60from the first surface83to the second surface88(back surface of the first surface83) as with the fixing boss32. The size and the shape of the through hole87are not particularly limited, and only need to correspond to the size and the shape of the B pins26to30.

A gap maintaining member63is welded to the central plate portion61. In the present modification example, the shape of the gap maintaining member63is a rectangular parallelepiped, and the gap maintaining member63is provided on the second surface88. The gap maintaining member63is disposed at a boundary between the central plate portion61and the lateral bulging portion62. However, the gap maintaining member63may be disposed so as to extend over the central plate portion61and the lateral bulging portion63, or may be disposed in the lateral bulging portion62. The gap maintaining member63is preferably disposed in a vicinity of the through hole87, and for example, as shown inFIG.9, a distance65from an edge of the through hole87to an edge of the gap maintaining member62is preferably set to 5 mm to 20 mm.

However, the shape of the gap maintaining member63is not limited to a rectangular parallelepiped, and the cross-sectional shape thereof may be a columnar shape such as a circle, an ellipse, or a polygon. Furthermore, the shape of the gap maintaining member63may correspond to the outer shape of the fixing boss60. In other words, the outer shape of the gap maintaining member63may correspond to the central plate portion61and the lateral bulging portion62described above. In this case, a through hole similar to the through hole87is provided to the gap maintaining member63. In the present modification example, the material composing the gap maintaining member63is typically gunmetal (copper alloy), and a material having hardness lower than that of the base boom20, the top boom21, and the intermediate booms22to25can be adopted. Note that the gap maintaining member63may be composed of resin.

The fixing boss60according to the present modification example has an advantage that the shape thereof is simple, and a further lightweight design is possible compared with the fixing boss32according to the above-described embodiment.