JP2009067590A - Telescopic boom - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To abolish a hose guide device, to facilitate assembling work and maintenance, to reduce weight, and to prevent oil leakage. <P>SOLUTION: The telescopic boom is equipped with a boom body successively fitted with a plurality of booms so as to expand/contract, and a multi-stage cylinder 5 provided in the main body. The multi-stage cylinder comprises a hollow piston rod 11, a plurality of cylinder tubes 12, 13 successively fitted around an outer periphery of the rod coaxially so as to expand/contract, a plurality of expanding side pressure chambers 14, 15 respectively formed between a bottom portion of each cylinder tube and a cylinder tube fitted inside or a tip end surface of the piston rod, and a plurality of contracting side pressure chambers 16, 17 respectively formed between an inner peripheral surface of each cylinder tube and the cylinder tube fitted inside or an outer peripheral surface of the piston rod. To each contracting side pressure chamber, pressure oil is supplied from a contracting side pressure oil supplying port of a base end wall portion of the piston rod into the inside of each cylinder through oil passages 40, 50 independently provided in each contracting side pressure chamber. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a telescopic boom used for a crane or the like of a construction machine, and more particularly to improvement of a double-acting multistage cylinder equipped in the boom as a drive unit thereof.

  Conventionally, as this type of telescopic boom, as disclosed in, for example, Patent Document 1, a telescopic boom body is configured by sequentially fitting a plurality of booms in a telescopic manner, and double-acting in the telescopic boom body. A type in which a multi-stage cylinder is arranged and the telescopic boom body is extended and retracted by this double-acting multi-stage cylinder is known.

As a double-acting multistage cylinder, usually a two-stage telescopic cylinder is often used. This two-stage telescopic cylinder has a hollow piston rod (corresponding to the first single cylinder in Patent Document 1) and two cylinder tubes (inside and outside) that are concentrically and telescopically fitted to the outer periphery of this piston rod. Corresponding to the second and third single cylinders of Document 1) and the two expansion side pressure chambers formed between the bottom of each cylinder tube and the tip of the cylinder tube or piston rod fitted inside the cylinder tube. And two contraction-side pressure chambers formed between the inner peripheral surface of each cylinder tube and the outer peripheral surface of the cylinder tube or piston rod fitted inside thereof, and when the cylinder is extended, the piston rod The pressure oil is supplied to each of the extension-side pressure chambers through a pipe oil passage provided through the piston rod from an extension-side pressure oil supply port provided in the base end wall of the piston rod. And it is configured to at the time of reduction of the cylinder to supply pressurized oil from the contraction side pressure oil supply port provided at a base end wall of the piston rod to the respective compression-side pressure chamber through such a piston rod.
JP 2006-256828 A

  However, in the case of the conventional two-stage telescopic cylinder, since the two compression side pressure chambers are communicated with each other by a hose disposed outside the cylinder, it is necessary to provide a hose guide device for preventing wear and damage of the hose. There is. However, in this case, there is a problem that the assembly work becomes troublesome with the provision of the hose guide device and the weight of the telescopic boom increases.

  Even when a hose guide device is installed, the hose must be replaced periodically because the bending force repeatedly acts as the telescopic cylinder expands and contracts. There is also a problem that maintenance is not easy.

  The present invention has been made in view of such points, and the problem is to eliminate the hose disposed outside the cylinder as in the prior art, thereby eliminating the need for a hose guide device and facilitating assembly work and maintenance. The present invention is intended to provide a telescopic boom that can reduce the weight and prevent oil leakage.

  In order to solve the above-mentioned problem, the invention according to claim 1 is a double-acting boom provided in the telescopic boom body, wherein the telescopic boom body is constructed by sequentially fitting a plurality of booms in a telescopic manner. It is assumed that the telescopic boom body is configured to expand and contract by the multistage cylinder. The double-acting multi-stage cylinder includes a hollow piston rod, a plurality of cylinder tubes that are concentrically and telescopically fitted to the outer periphery of the piston rod, and a bottom portion and an inner side of each cylinder tube. A plurality of extension-side pressure chambers formed between the cylinder tube or piston rod end surface to be fitted, an inner circumferential surface of each cylinder tube, and an outer circumferential surface of the cylinder tube or piston rod fitted therein Pressure oil from a compression side pressure oil supply port provided on the base end wall portion of the piston rod with respect to each of the compression side pressure chambers. Are supplied through an oil passage provided separately for each of the contraction side pressure chambers inside the cylinder. Here, the oil passage provided separately for each contraction-side pressure chamber includes a case where only a part of the oil passage on the pressure chamber side is provided separately for each contraction-side pressure chamber.

  In this configuration, the pressure oil from the compression side pressure oil supply port provided in the proximal end wall portion of the piston rod is supplied to each compression side pressure chamber through an oil passage provided in the cylinder. In addition, a hose disposed outside the cylinder and a hose guide device for protecting the hose disposed outside the cylinder in order to communicate the compression side pressure chambers as in the prior art are not necessary, and these can be eliminated. In addition, since the oil passage is provided separately for each compression side pressure chamber, the oil amount and pressure of the pressure oil supplied to each compression side pressure chamber can be easily set according to the flow resistance of each oil passage. Can be adjusted.

  The invention according to claim 2 is limited to the telescopic boom according to claim 1, particularly when the double-acting multistage cylinder is constituted by a two-stage telescopic cylinder. That is, the double-acting multi-stage cylinder includes two inner and outer cylinder tubes that are concentrically and telescopically fitted to the outer periphery of the piston rod, and two inner and outer expansion side pressures corresponding to the two cylinder tubes. And a compression side pressure chamber.

  According to a third aspect of the present invention, in the telescopic boom according to the second aspect, of the two contraction-side pressure chambers, the inner peripheral surface of the outer first cylinder tube and the outer periphery of the second cylinder tube fitted inside thereof. A part of the oil passage for supplying pressure oil to the compression side pressure chamber formed between the one end and the other end is fixed to the bottom of the second cylinder tube and the other end is the tip wall of the piston rod. A first pipe that penetrates and extends into the hollow portion of the piston rod, and is disposed in the hollow portion of the piston rod, and one end is fixed to the proximal end wall portion of the piston rod in communication with the compression-side pressure oil supply port. The second pipe is configured to be telescopically fitted. In this configuration, of the two contraction-side pressure chambers of the multistage cylinder (two-stage telescopic cylinder), between the inner peripheral surface of the outer first cylinder tube and the outer peripheral surface of the second cylinder tube fitted inside thereof. The formed compression side pressure chamber moves relatively in the axial direction with the expansion and contraction operation of the multistage cylinder, and a part of the oil passage for supplying pressure oil to the compression side pressure chamber is the second cylinder tube. The first pipe fixed to the bottom portion of the piston rod and the second pipe fixed to the base end wall portion of the piston rod are telescopically fitted to each other. During relative movement, the oil passage expands and contracts between the two pipes, so that the pressure oil can be reliably supplied through the oil passage.

  According to a fourth aspect of the present invention, in the telescopic boom according to the third aspect, the first and second pipes are fitted and arranged on a substantially center line of the multistage cylinder and with the second pipe outside. A third pipe that is loosely fitted with a predetermined gap is provided on the outer periphery of the second pipe, and an extension-side oil passage is formed by the gap between the two pipes, and one end of the extension-side oil passage is connected to the piston rod. The other end of the extension side oil passage is extended to the tip wall portion of the piston rod and the communication oil passage provided on the tip wall portion is communicated with the extension side pressure oil supply port provided on the base end wall portion. It is set as the structure connected to the expansion side pressure chamber formed between the bottom part of a 2nd cylinder tube, and the front end surface of a piston rod. In this configuration, the first and second pipes constituting a part of the oil passage for supplying the pressure oil to the compression side pressure chamber are arranged on the substantially center line of the multistage cylinder. Since the extension side oil passage is formed by the gap with the third pipe loosely fitted in the multi-stage cylinder, the center of gravity of the multi-stage cylinder can be set substantially on the center line, and the outer diameter of the multi-stage cylinder can be reduced to be compact. Can be achieved.

  According to a fifth aspect of the present invention, in the telescopic boom according to any one of the second to fourth aspects, an inner peripheral surface of an inner cylinder tube and an outer peripheral surface of a piston rod, of the two contraction side pressure chambers. A part of the oil passage for supplying pressure oil to the compression side pressure chamber formed between the first and second surfaces is disposed in the hollow portion of the piston rod and one end communicated with the compression side hydraulic supply port. Consists of pipes. In this configuration, of the two contraction-side pressure chambers of the multistage cylinder (two-stage telescopic cylinder), pressure oil is applied to the contraction-side pressure chamber formed between the inner peripheral surface of the inner cylinder tube and the outer peripheral surface of the piston rod. Since the oil passage for supplying water is constituted by the fourth pipe in the hollow portion of the piston rod, it is not necessary to fill the entire hollow portion of the piston rod with pressure oil as in the prior art. The weight will be reduced.

  According to a sixth aspect of the present invention, in the telescopic boom according to the third aspect, the first and second pipes are fitted to each other with the second pipe outside and a predetermined gap therebetween. An oil passage different from the oil passage inside the first pipe is formed by the gap, and one end of this oil passage is communicated with the compression side pressure oil supply port through the second pipe, and the other end of the oil passage is connected to the piston. It is configured to communicate with a compression-side pressure chamber formed between the inner peripheral surface of the inner cylinder tube and the outer peripheral surface of the piston rod through a communication oil passage provided in the tip wall of the rod. In this configuration, the first and second pipes apply pressure to the compression side pressure chamber formed between the inner peripheral surface of the outer first cylinder tube and the outer peripheral surface of the second cylinder tube fitted inside the first cylinder tube. Not only a part of the oil passage for supplying oil is configured, but also a shrinkage formed between the inner peripheral surface of the inner second cylinder tube and the outer peripheral surface of the piston rod by the gap between these pipes Since a part of the oil passage for supplying pressure oil from the contracted side pressure oil supply port to the side pressure chamber is configured, the number of parts for constituting the oil passage can be reduced, and the piston as in the prior art It is not necessary to fill the entire hollow portion of the rod with pressure oil, and the weight of the multistage cylinder can be reduced.

  According to a seventh aspect of the present invention, in the telescopic boom according to the second aspect, of the two contraction-side pressure chambers, the inner peripheral surface of the outer first cylinder tube and the outer periphery of the second cylinder tube fitted inside thereof. A part of the oil passage for supplying pressure oil to the compression side pressure chamber formed between the one end and the other end is fixed to the bottom of the second cylinder tube and the other end is the tip wall of the piston rod. While being constituted by a pipe that penetrates and extends into the hollow portion of the piston rod, the compression side pressure oil supply port is provided to open in the hollow portion of the piston rod, and the inside of the hollow portion of the piston rod has the two compression side pressure chambers. A part of an oil passage for supplying pressure oil to each of the two is configured. In this configuration, when the oil passage is separately provided for each of the two compression side pressure chambers, the inside of the hollow portion of the piston rod is used as a part of the oil passage for supplying the pressure oil to each compression side pressure chamber. Accordingly, the passage configuration or the internal configuration of the multistage cylinder is simplified.

  As described above, according to the telescopic boom of the present invention, the pressure oil from the compression side pressure oil supply port provided in the proximal end wall portion of the hollow piston rod for each compression side pressure chamber of the double-acting multistage cylinder. Are supplied through an oil passage provided inside the cylinder, respectively, so that a hose arranged outside the cylinder to communicate the compression side pressure chambers and a hose guide device for protecting the hose are provided. Can be abolished. As a result, assembly work and maintenance can be facilitated, and weight reduction, oil leakage prevention, and cost reduction can be achieved. In addition, since the oil passage is provided separately for each compression side pressure chamber, the oil amount and pressure of the pressure oil supplied to each compression side pressure chamber can be easily set according to the flow resistance of each oil passage. This is effective in properly performing hydraulic control.

  In particular, in the invention according to claim 3, of the two contraction side pressure chambers of the two-stage telescopic cylinder as a multistage cylinder, the inner peripheral surface of the outer first cylinder tube and the second cylinder tube fitted to the inner side thereof are arranged. A part of the oil passage for supplying pressure oil to the compression side pressure chamber formed between the outer peripheral surface is a first pipe fixed to the bottom of the second cylinder tube, and a proximal end wall of the piston rod The second pipe fixed to the part is telescopically fitted, and the oil passage expands and contracts between the two pipes when the multistage cylinder is extended and retracted, so that the pressure oil is reliably supplied through the oil passage. This is effective for implementation.

  In the invention according to claim 4, the first and second pipes are arranged on substantially the center line of the multistage cylinder, and the extension side oil is formed by a gap between the second pipe and the third pipe loosely fitted to the outer periphery thereof. Since the path is formed, the center of gravity of the multistage cylinder can be set substantially on the center line, and the outer diameter of the multistage cylinder can be reduced to make it more compact. Can do.

  In the invention according to claim 5, of the two contraction-side pressure chambers of the two-stage telescopic cylinder, pressure oil is applied to the contraction-side pressure chamber formed between the inner peripheral surface of the inner cylinder tube and the outer peripheral surface of the piston rod. Since the oil passage for supplying water is constituted by the fourth pipe in the hollow portion of the piston rod, there is no need to fill the entire hollow portion of the piston rod with pressure oil as in the prior art. It is possible to further reduce the weight of the boom.

  In the invention which concerns on Claim 6, the shrink side formed by the 1st and 2nd pipe between the internal peripheral surface of an outer side 1st cylinder tube, and the outer peripheral surface of the 2nd cylinder tube fitted inside it Not only is a part of the oil passage for supplying pressure oil to the pressure chamber, but also a gap between these pipes is formed between the inner peripheral surface of the inner cylinder tube and the outer peripheral surface of the piston rod. Since a part of the oil passage for supplying pressure oil from the compression side pressure oil supply port to the compression side pressure chamber is configured, the number of parts for configuring the oil passage can be reduced, and the conventional In this way, it is not necessary to fill the entire hollow portion of the piston rod with pressure oil, and the weight reduction of the multistage cylinder and the telescopic boom can be effectively achieved.

  Furthermore, in the invention according to claim 7, when the oil passages are separately provided for each of the two contraction side pressure chambers, the inside of the hollow portion of the piston rod is used as a part of the oil passage for supplying the pressure oil to each contraction side pressure chamber. Therefore, the passage configuration or the internal configuration of the multistage cylinder can be simplified, and implementation can be facilitated.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments that are the best mode for carrying out the present invention will be described below with reference to the drawings.

(First embodiment)
1 to 4 show a three-stage telescopic boom A according to the first embodiment of the present invention. The telescopic boom A has a base boom 1, an intermediate boom 2 and a tip boom 3 in the descending order as a three-stage boom. The telescopic boom body 4 is formed by sequentially fitting the three-stage booms 1 to 3 in a telescopic manner. Is configured. The telescopic boom body 4 is provided with a two-stage telescopic cylinder 5 as a double-acting multi-stage cylinder, and the telescopic boom body 4 is configured to expand and contract by the two-stage telescopic cylinder 5.

  The two-stage telescopic cylinder 5 includes a hollow piston rod 11 and two inner and outer cylinders that are concentrically and telescopically fitted to the outer periphery of the piston rod 11, as shown in enlarged detail in FIGS. Two extension-side pressure chambers 14 formed between the tubes 12 and 13 and the bottoms 12a and 13a of the cylinder tubes 12 and 13 and the tip surfaces of the cylinder tube 12 and the piston rod 11 fitted inside thereof. , 15 and two compression-side pressure chambers 16, 17 formed between the inner peripheral surface of each of the cylinder tubes 12, 13 and the outer peripheral surface of the cylinder tube 12 or the piston rod 11 fitted inside thereof, have. Hereinafter, when the two cylinder tubes 12 and 13 are referred to separately, the outer cylinder tube 13 is referred to as a first cylinder tube, and the inner cylinder tube 12 is referred to as a second cylinder tube. When the two extension-side pressure chambers 14 and 15 are referred to separately, the extension side formed between the bottom portion 13a of the first cylinder tube 13 and the tip surface of the second cylinder tube 12 (the outer bottom surface of the bottom portion 12a). The pressure chamber 15 is referred to as a first extension side pressure chamber, and the extension side pressure chamber 14 formed between the bottom 12a of the second cylinder tube 12 and the tip surface of the piston rod 11 (the outer surface of the tip wall portion 11a). It is called a second extension side pressure chamber. Further, when the two contraction-side pressure chambers 16 and 17 are referred to separately, the contraction-side pressure chamber 17 formed between the inner peripheral surface of the first cylinder tube 13 and the outer peripheral surface of the second cylinder tube 12 is the first. The compression side pressure chamber is called a compression side pressure chamber, and the compression side pressure chamber 16 formed between the inner peripheral surface of the second cylinder tube 12 and the outer peripheral surface of the piston rod 11 is called a second compression side pressure chamber.

  The base end wall portion 11b of the piston rod 11 is connected to the base end boom 1 via a connecting pin 21 and the like, and the base end wall portion 11b of the piston rod 11 is connected to the expansion side pressure oil supply port 22 and the contraction. A side pressure oil supply port 23 is provided. Further, a ring-shaped sliding member 24 that is slidably fitted to the inner peripheral surface of the second cylinder tube 12 while maintaining an oil-tight state is mounted on the outer peripheral surface of the tip wall portion 11a of the piston rod 11. The bottom portion 12a of the second cylinder tube 12 that forms the second extension side pressure chamber 14 between the front end surface of the piston rod 11 and the second extension side pressure chamber 14 when the two-stage extension cylinder 5 is reduced. A second extension-side pressure chamber recess 25 is formed to ensure the minimum volume.

  The base end portion of the second cylinder tube 12 is connected to the intermediate boom 2 via a coupling pin 26 and the like, and the inner peripheral surface of the base end portion of the second cylinder tube 12 is connected to the piston rod 11. A ring-shaped sliding member 27 that is slidably fitted to the outer peripheral surface while maintaining an oil-tight state is mounted. A sliding member 28 is mounted on the outer peripheral surface of the bottom 12a, which is the tip of the second cylinder tube 12, so as to be slidably fitted to the inner peripheral surface of the first cylinder tube 13 while maintaining an oil-tight state. The bottom portion 13a of the first cylinder tube 13 that forms the first extension side pressure chamber 15 between the front end surface of the second cylinder tube 12 is provided on the first extension side when the two-stage expansion cylinder 5 is reduced. A first extension side pressure chamber recess 29 for securing a minimum volume of the pressure chamber 15 is formed. The opening area of the first extension-side pressure chamber recess 29 is set to be larger than the opening area of the second extension-side pressure chamber recess 25, and both the recesses 25 and 29 are extended to the first extension side. The pressure chamber 15 and the second extension side pressure chamber 14 communicate with each other so that the pressure oil can always flow regardless of the expansion / contraction state of the two-stage expansion / contraction cylinder 5 by the communication oil passage 31 provided in the bottom 12a of the second cylinder tube 12. Has been.

  The proximal end portion of the first cylinder tube 13 is connected to the distal end boom 3 via a coupling pin 32 or the like, and the second cylinder tube is disposed on the inner peripheral surface of the proximal end portion of the first cylinder tube 13. A ring-shaped sliding member 33 that fits slidably while maintaining a liquid-tight state is mounted on the outer peripheral surface of the ring 12.

  As a feature of the present invention, the pressure oil from the compression side pressure oil supply port 23 of the proximal end wall portion 11b of the piston rod 11 is applied to the first compression side pressure chamber 17 and the second compression side pressure chamber 16. Are supplied through the first contraction side oil passage 40 or the second contraction side oil passage 50 provided separately for each of the contraction side pressure chambers 17 and 16 in the two-stage expansion cylinder 5.

  The first contraction-side oil passage 40 includes a communication oil passage 41 formed at one end in the bottom portion 12 a of the second cylinder tube 12 and opened to the first contraction-side pressure chamber 17, and the other end of the communication oil passage 41. A U-shaped tube 42 connected to the bottom 12a of the second cylinder tube 12 and one end penetrates and is fixed to the bottom 12a of the second cylinder tube 12 while communicating with the other end of the U-shaped tube 42. The other end of the piston rod 11 extends through the tip wall 11a of the piston rod 11 and extends into the hollow portion of the piston rod 11, and the piston rod 11 is hollow by being fitted into the first pipe 43. And a second pipe 45 having one end fixed to the base end wall portion 11b of the piston rod 11 in a state of being connected to the contraction-side pressure oil supply port 23 via the communication oil passage 44.

  The first and second pipes 43 and 45 are arranged on the substantially center line of the two-stage telescopic cylinder 5 and slidably fitted to each other with the second pipe 45 on the outside. A third pipe 46 that is loosely fitted with a predetermined gap is provided on the outer periphery of the pipe 45, and an extension-side oil passage 47 is formed by the gap between the pipes 45 and 46. One end of the extension side oil passage 47 communicates with the extension side pressure oil supply port 22 of the base end wall portion 11 b of the piston rod 11, and the other end of the extension side oil passage 47 is the tip wall portion 11 a of the piston rod 11. And a second extension-side pressure chamber 14 formed between the bottom 12a of the second cylinder tube 12 and the tip surface of the piston rod 11 through a communication oil passage 48 provided in the tip wall portion 11a. It is communicated to. The third pipe 46 is supported by a support ring 49 that is inserted into the hollow portion of the piston rod 11.

  On the other hand, the second contraction-side oil passage 50 is connected to a communication oil passage 51 formed at one end of the tip wall portion 11a of the piston rod 11 and the sliding member 24 with the second contraction-side pressure chamber 16 opened. A fourth pipe 52 that communicates with the other end of the oil passage 51 and is disposed in the hollow portion of the piston rod 11 along the axial direction, one end of the fourth pipe 52, and a base end wall portion 11 b of the piston rod 11. In order to communicate with the contraction-side pressure oil supply port 23, a communication oil passage 53 is formed in the proximal end wall portion 11b of the piston rod 11. The communication oil passage 53 of the second contraction side oil passage 50 is integrated with the communication oil passage 44 of the first contraction side oil passage 40 at the base end wall portion 11 b of the piston rod 11 to the contraction side pressure oil supply port 23. Communicate.

  Next, the telescopic operation of the three-stage telescopic boom A will be described. Now, as shown in FIGS. 1A and 2, the telescopic boom main body 4 is in a contracted state, and the telescopic boom main body 4 The two-stage telescopic cylinder 5 is also in a contracted state.

  When the telescopic boom body 4 is extended from such a reduced state, when the pressure oil is supplied from the expansion side pressure oil supply port 22 of the two-stage expansion cylinder 5, the pressure oil is connected to the expansion side oil passage 47 and the communication oil in the cylinder 5. It flows into the second extension side pressure chamber 14 (specifically, the second extension side pressure chamber recess 25) through the passage 48, and from the second extension side pressure chamber 14 through the communication oil passage 31, the first extension side pressure chamber 15 ( Specifically, it flows into the first extension-side pressure chamber recess 29). At this time, since the opening area of the first extension-side pressure chamber recess 29 is set to be larger than that of the second extension-side pressure chamber recess 25, first, the first cylinder tube 13 is moved to the second cylinder tube 12. The distal end boom 3 of the telescopic boom body 4 extends as the first cylinder tube 13 extends (see FIGS. 1B and 3). . Subsequently, the second cylinder tube 12 extends so as to relatively move from the proximal end side to the distal end side of the piston rod 11, and the intermediate boom 2 of the telescopic boom body 4 extends as the second cylinder tube 12 extends. As a result, the telescopic boom body 4 is extended in two stages (see FIGS. 1C and 4).

  On the other hand, when the telescopic boom body 4 is contracted from the extended state, when the pressure oil is supplied from the contraction side pressure oil supply port 23 of the two-stage expansion cylinder 5, the pressure oil is supplied to the first contraction side oil passage 40 in the cylinder 5. And flows into the first contraction side pressure chamber 17 and flows into the second contraction side pressure chamber 16 through the second contraction side oil passage 50 in the cylinder 5. At this time, pressure oil remains in the first and second extension side pressure chambers 15 and 14 and acts as a load pressure. However, the load pressure of the first extension side pressure chamber 15 is that of the second extension side pressure chamber 14. Therefore, first, the second cylinder tube 12 is reduced so as to relatively move from the distal end side to the proximal end side of the piston rod 11, and as the second cylinder tube 12 is reduced, the telescopic boom body 4 The intermediate boom 2 is reduced. Subsequently, the first cylinder tube 13 is contracted so as to relatively move from the distal end side to the proximal end side of the second cylinder tube 12, and as the first cylinder tube 13 is contracted, the distal end boom 3 of the telescopic boom body 4. Is reduced and the telescopic boom body 4 is reduced to two stages.

  Accordingly, in the two-stage telescopic cylinder 5 of the telescopic boom A, the pressure oil from the contraction-side pressure oil supply port 23 of the proximal end wall portion 11b of the piston rod 11 with respect to the first and second contraction-side pressure chambers 17 and 16. Are supplied through the first contraction side oil passage 40 or the second contraction side passage 50 provided in the cylinder 5, respectively, so that the contraction side pressure chambers communicate with each other as in the prior art. The hose and the hose guide device for protecting it are not necessary and can be eliminated. As a result, the assembly work and maintenance of the telescopic boom A can be facilitated, and the telescopic boom A can be reduced in weight, oil leakage can be prevented, and the cost can be reduced.

  In addition, since the first and second contraction side oil passages 40 and 50 are provided separately for the first and second contraction side pressure chambers 17 and 16, they are supplied to the contraction side pressure chambers 17 and 16, respectively. The amount and pressure of the pressure oil can be easily adjusted according to the flow resistance of each oil passage and the like, which is effective in appropriately performing the hydraulic control.

  In particular, in the present embodiment, the first contraction-side pressure chamber 17 moves relative to the largest in the axial direction in accordance with the expansion / contraction operation of the two-stage expansion / contraction cylinder 5, but pressure oil is supplied to the first contraction-side pressure chamber 17. A part of the first contraction-side oil passage 40 to be supplied includes a first pipe 43 fixed to the bottom 12a of the second cylinder tube 12 and a second pipe fixed to the proximal end wall 11b of the piston rod 11. The pipe 45 is telescopically fitted so that the oil passage 40 extends and contracts between the pipes 43 and 45 when the two-stage expansion cylinder 5 is expanded and contracted, that is, when the first contraction side pressure chamber 17 is relatively moved. The pressure oil can be reliably supplied through the oil passage 40, which is effective for implementation.

  The first and second pipes 43 and 45 are provided substantially on the center line of the two-stage telescopic cylinder 5, and are formed by a gap between the second pipe 45 and the third pipe 46 loosely fitted on the outer periphery thereof. Since the extension side oil passage 47 is formed, the center of gravity of the two-stage telescopic cylinder 5 can be set substantially on the center line, and the outer diameter of the two-stage telescopic cylinder 5 is made as small as possible to make it compact. Therefore, implementation can be achieved more effectively.

  Furthermore, since the second contraction side oil passage 50 for supplying the pressure oil to the second contraction side pressure chamber 16 is constituted by the fourth pipe 52 in the hollow portion of the piston rod 11, the piston rod as in the prior art. 11 does not need to be filled with pressure oil, and the weight of the two-stage telescopic cylinder 5 and thus the telescopic boom A can be further reduced.

(Second Embodiment)
9 to 12 show modifications of the two-stage telescopic cylinder as the second embodiment of the present invention. In the case of the second embodiment, the basic configuration of the two-stage telescopic cylinder 60 is the same as that in the case of the first embodiment, and the same members and parts are denoted by the same reference numerals and description thereof is omitted. To do. The two-stage telescopic cylinder 60 differs from that of the first embodiment in the configuration of an oil passage for supplying pressure oil to the four pressure chambers 14 to 17 in the cylinder 60.

  That is, the base end wall portion 11 b of the piston rod 11 is provided with two extension side pressure oil supply ports 61 and 62 and one contraction side pressure oil supply port 63, and the pressure oil from the first extension side pressure oil supply port 61. The pressure oil from the second extension side pressure oil supply port 62 is supplied to the first extension side pressure chamber 15 through the first extension side oil passage 70 provided in the cylinder 60, and the second extension provided in the cylinder 60 is also provided. The pressure oil from the contraction side pressure oil supply port 63 is supplied to the second extension side pressure chamber 14 through the side pressure oil passage 80, and the first contraction side pressure chamber 17 and the second contraction side are supplied. The pressure chamber 16 is configured to be supplied through a first contraction-side oil passage 90 or a second contraction-side oil passage 100, which are partially provided inside the cylinder 60.

  One end of the first extension side oil passage 70 is fixed through the bottom 12 a of the second cylinder tube 12, and the other end passes through the tip wall 11 a of the piston rod 11 and is inside the hollow portion of the piston rod 11. A first pipe 71 that extends to the first pipe 71, and is fitted into the first pipe 71 and disposed in the hollow portion of the piston rod 11, and one end of the first pipe 71 is supplied to the base end wall portion 11b of the piston rod 11. It consists of a second pipe 73 fixed in a state where it communicates with the port 61 via a communication oil passage 72. The first and second pipes 71 and 73 are arranged on substantially the center line of the two-stage telescopic cylinder 60 and slidably fitted to each other with the second pipe 73 outside.

  The second extension-side oil passage 80 is formed by a gap between the second pipe 73 of the first extension-side oil passage 70 and a third pipe 81 loosely fitted on the outer periphery of the second pipe 73 with a predetermined gap. One end of the second extension side oil passage 80 is communicated with the second extension side pressure oil supply port 62 of the base end wall portion 11 b of the piston rod 11, and the other end of the second extension side oil passage 80 is connected to the piston rod 11. It extends to the distal end wall portion 11a and communicates with the second extension-side pressure chamber 14 via a communication oil passage 82 provided in the distal end wall portion 11a. The third pipe 81 is supported by a support ring 83 that is inserted into the hollow portion of the piston rod 11.

  The first contraction-side oil passage 90 includes a communication oil passage 91 formed at the bottom 12 a of the second cylinder tube 12 with one end opening into the first contraction-side pressure chamber 17, and one end at the other end of the communication oil passage 91. A pipe 92 that is fixed to the bottom 12a of the second cylinder tube 12 in communication with the end, and that has the other end passing through the tip wall 11a of the piston rod 11 and extending into the hollow portion of the piston rod 11. The pipe 92 is supported by the support ring 83. Further, the second contraction side oil passage 100 has one end opened in the second contraction side pressure chamber 16 and the other end opened in the hollow portion of the piston rod 11 in the tip wall portion 11a and the sliding member 24 of the piston rod 11. The communication oil path 101 is formed. On the other hand, the compression side pressure oil supply port 63 is provided to open in the hollow portion of the piston rod 11, and the inside of the hollow portion of the piston rod 11 has the first compression side oil passage 90 and the second compression side oil passage 100. A part of each oil passage 90, 100 is configured as a common part.

  Also in the second embodiment, as in the case of the first embodiment, the contraction-side pressure oil supply of the proximal end wall portion 11b of the piston rod 11 is supplied to the first and second contraction-side pressure chambers 17 and 16. Since the pressure oil from the port 63 is supplied through the first contraction side oil passage 90 or the second contraction side passage 100 provided in the cylinder 60, the contraction side pressure chambers are communicated with each other as in the prior art. Therefore, a hose arranged outside the cylinder and a hose guide device for protecting the hose are not necessary, and these can be eliminated. As a result, assembly work and maintenance of the telescopic boom A (see FIGS. 1 to 4) can be facilitated, and the telescopic boom A can be reduced in weight, oil leakage can be prevented, and costs can be reduced. Can do.

  Moreover, since the first and second contraction side oil passages 90 and 100 are provided separately for the first and second contraction side pressure chambers 17 and 16, they are supplied to the contraction side pressure chambers 17 and 16, respectively. The amount and pressure of the pressure oil can be easily adjusted according to the flow resistance of each oil passage and the like, which is effective in appropriately performing the hydraulic control. Further, the first and second extension-side oil passages 70 and 80 are provided separately for the first and second extension-side pressure chambers 15 and 14, and the extension-side pressure oil supply ports 61 and 62 are also provided separately. Therefore, the oil amount and pressure of the pressure oil supplied to each of the expansion side pressure chambers 15 and 14 can be easily adjusted, and hydraulic control can be performed more appropriately.

  In particular, in the case of the present embodiment, when the first and second contraction-side oil passages 90 and 100 are separately provided for the first and second contraction-side pressure chambers 17 and 16, the inside of the hollow portion of the piston rod 11 is on both contraction sides. Since the oil passages 90 and 100 are used as a part of the oil passages 90 and 100, the corresponding passage structure or the internal structure of the two-stage telescopic cylinder 60 can be simplified, and implementation can be facilitated.

(Third embodiment)
FIGS. 13 to 16 show another modification of the two-stage telescopic cylinder as the third embodiment of the present invention. In the case of the third embodiment, the basic configuration of the two-stage telescopic cylinder 110 is the same as that in the case of the first embodiment, and the same members / parts are denoted by the same reference numerals and description thereof is omitted. To do. The two-stage telescopic cylinder 110 is different from that of the first embodiment in the configuration of an oil passage for supplying pressure oil to the four pressure chambers 14 to 17 in the cylinder 110.

  That is, the base end wall portion 11 b of the piston rod 11 is provided with two extension side pressure oil supply ports 111 and 112 and one contraction side pressure oil supply port 113, and the pressure oil from the first extension side pressure oil supply port 111. The pressure oil from the second extension-side pressure oil supply port 112 is supplied to the first extension-side pressure chamber 15 through the first extension-side oil passage 120 provided in the cylinder 110, and the second extension-side pressure provided in the cylinder 110. The oil is supplied to the second expansion side pressure chamber 14 through the oil passage 130, and the pressure oil from the compression side pressure oil supply port 113 is supplied to the first compression side pressure chamber 17 and the second compression side pressure chamber. 16 is configured to be supplied through a first contraction-side oil passage 140 or a second contraction-side oil passage 150, which are partially provided in the cylinder 110.

  As in the case of the second embodiment, the first extension-side oil passage 120 is fixed at one end through the bottom 12a of the second cylinder tube 12, and the other end is the tip wall of the piston rod 11. A first pipe 121 that passes through 11 a and extends into the hollow portion of the piston rod 11, is fitted in the first pipe 121 and is disposed in the hollow portion of the piston rod 11, and one end is the base end of the piston rod 11 It consists of the 2nd pipe 123 fixed to the wall part 11b in the state connected to the 1st expansion | extension side pressure oil supply port 111 via the communication oil path 122. As shown in FIG. The first and second pipes 121 and 123 are arranged on substantially the center line of the two-stage telescopic cylinder 110 and slidably fitted to each other with the second pipe 123 outside.

  Similarly to the case of the second embodiment, the second extension-side oil passage 130 is also loosely fitted to the second pipe 123 of the first extension-side oil passage 120 and its outer periphery with a predetermined gap therebetween. One end of the second extension side oil passage 130 is communicated with the second extension side pressure oil supply port 112 of the base end wall portion 11b of the piston rod 11, and the second extension side oil passage 130 is connected to the second extension side oil passage 130. The other end of the oil passage 130 extends to the tip wall portion 11a of the piston rod 11 and communicates with the second extension-side pressure chamber 14 via a communication oil passage 132 provided in the tip wall portion 11a. The third pipe 131 is supported by a support ring 133 that is inserted into the hollow portion of the piston rod 11.

  On the other hand, the first contraction-side oil passage 140 has a communication oil passage 141 formed at one end in the bottom portion 12a of the second cylinder tube 12 so as to open to the first contraction-side pressure chamber 17, and one end of the communication oil passage 141 at one end. The first pipe 142 is fixed to the bottom portion 12 a of the second cylinder tube 12 in a state where it communicates with the other end of the first cylinder 142, and the other end portion extends through the tip wall portion 11 a of the piston rod 11 and into the hollow portion of the piston rod 11. And a first pipe 142 fitted into the first pipe 142 and disposed in the hollow portion of the piston rod 11 and fixed at one end thereof in communication with the contraction-side pressure oil supply port 113 of the proximal end wall portion 11b of the piston rod 11. 2 pipes 143. The first and second pipes 142 and 143 are slidably fitted with the second pipe 143 outward at a position eccentric from the center line of the two-stage telescopic cylinder 110 and with a predetermined gap therebetween, The second pipe 143 is supported by the support ring 133. The second contraction-side oil passage 150 is formed by a gap between the pipes 142 and 143, and one end of the second contraction-side oil passage 150 passes through the second pipe 143 and the contraction-side pressure oil supply port 113. As shown in an enlarged detail in FIG. 17, the other end of the second contraction side oil passage 150 is connected to the first pipe 142 in the tip wall portion 11a of the piston rod 11 from the fixed portion of the second pipe 143. The second contraction-side pressure chamber is provided through a clearance 151 between the through-hole penetrating through and the outer peripheral surface of the first pipe 142, the leading end wall portion 11 a of the piston rod 11, and the communication oil path 152 provided in the sliding member 24. 16 is communicated.

  Also in the third embodiment, as in the case of the first embodiment, the contraction side pressure oil supply of the proximal end wall portion 11b of the piston rod 11 is supplied to the first and second contraction side pressure chambers 17 and 16. Since the pressure oil from the port 113 is supplied through the first contraction-side oil passage 140 or the second contraction-side passage 150 provided in the cylinder 60, the contraction-side pressure chambers communicate with each other as in the prior art. Therefore, a hose arranged outside the cylinder and a hose guide device for protecting the hose are not necessary, and these can be eliminated. As a result, assembly work and maintenance of the telescopic boom A (see FIGS. 1 to 4) can be facilitated, and the telescopic boom A can be reduced in weight, oil leakage can be prevented, and costs can be reduced. Can do.

  Moreover, since the first and second contraction side oil passages 140 and 150 are provided separately for the first and second contraction side pressure chambers 17 and 16, they are supplied to the contraction side pressure chambers 17 and 16, respectively. The amount and pressure of the pressure oil can be easily adjusted according to the flow resistance of each oil passage and the like, which is effective in appropriately performing the hydraulic control. The first and second extension side oil passages 120 and 130 are separately provided for the first and second extension side pressure chambers 15 and 14, and the extension side pressure oil supply ports 111 and 112 are also provided separately. Therefore, the oil amount and pressure of the pressure oil supplied to each of the expansion side pressure chambers 15 and 14 can be easily adjusted, and hydraulic control can be performed more appropriately.

  In particular, in the case of the present embodiment, not only a part of the first contraction side oil passage 140 is constituted by the first pipe 142 and the second pipe 143, but also by the gap between the pipes 142 and 143. Since part of the second contraction-side oil passage 150 is also configured, the number of parts for constituting the oil passage can be reduced, and the entire hollow portion of the piston rod 11 is filled with pressure oil as in the past. There is no need to reduce the weight of the two-stage telescopic cylinder 110 and hence the telescopic boom A (see FIGS. 1 to 4).

(Fourth embodiment)
18 and 19 show a five-stage telescopic boom B according to a fourth embodiment of the present invention. The telescopic boom B includes a basic boom 161, a second-stage boom 162, a third-stage boom 163, a fourth-stage boom 164, and a fifth-stage boom 165 in the descending order as a five-stage boom. The telescopic boom main body 166 is configured by sequentially fitting ˜165 to be telescopic.

  Two-stage telescopic cylinders 170 and 180 as two double-acting multistage cylinders are arranged in the telescopic boom body 166. Each of the two-stage telescopic cylinders 170 and 180 is, like the two-stage telescopic cylinder 5 in the first embodiment, concentrically and telescopically on the outer periphery of the hollow piston rods 171 and 181 and the piston rods 171 and 181. It has two cylinder tubes 172, 173 or 182, 183 that can be fitted freely. The two two-stage telescopic cylinders 170 and 180 are disposed in a state in which the base ends 171a and 181a of the piston rods 171 and 181 are directed to the base side of the telescopic boom main body 166 in the telescopic boom main body 166, respectively. The cylinder tube 173 on the outer side of the two-stage telescopic cylinder 170 on the root side and the piston rod 181 of the two-stage telescopic cylinder 180 on the front end side are arranged in a state where the positions are shifted from each other on the side and the tip side. The telescopic boom main body 166 is disposed so as to overlap in the axial direction.

  Further, the piston rod 171 of the two-stage telescopic cylinder 170 on the base side is the basic boom 161 of the telescopic boom body 166, and the cylinder tube 172 inside the two-stage telescopic cylinder 170 on the base side is the second-stage boom of the telescopic boom body 166. 162, a cylinder tube 173 on the outer side of the two-stage telescopic cylinder 170 on the root side and a piston rod 181 of the two-stage telescopic cylinder 180 on the distal end side are connected to the third stage boom 163 of the telescopic boom body 166 and the two-stage telescopic cylinder on the distal end side. The cylinder tube 182 inside 180 is connected to the fourth-stage boom 164 of the telescopic boom body 166, and the cylinder tube 183 outside the distal-stage second-stage telescopic boom 180 is connected to the fifth-stage boom 165 of the telescopic boom body 166, respectively. (Not shown) or the like. In the figure 19 is shown by a black circle. The cylinder tube 173 on the outer side of the two-stage telescopic cylinder 170 on the root side and the piston rod 181 of the two-stage telescopic cylinder 180 on the tip side are both coupled to the third-stage boom 163 of the telescopic boom body 166. It is provided so that it cannot move relative to the other when it is expanded or contracted.

  Although both the two-stage telescopic cylinders 170 and 180 are not shown in the drawing, like the two-stage telescopic cylinder 5 in the first embodiment, two extension-side pressure chambers and two contraction-side pressure chambers are provided inside. Have. Pressure oil from an extension-side pressure oil supply port (not shown) provided in the base end wall portion of the piston rods 171 and 181 is respectively supplied to the extension-side pressure chambers of the two-stage telescopic cylinders 170 and 180. Supply through contraction side oil passages (not shown) provided inside, supply of contraction side pressure oil provided on the base end wall portions of the piston rods 171 and 181 to the contraction side pressure chambers of the two-stage expansion cylinders 170 and 180. Pressure oil from a port (not shown) is configured to be supplied through two contraction side oil passages (not shown) provided separately for each contraction side pressure chamber in the cylinder 170.180. Then, when pressure oil is supplied to the expansion side pressure chambers of both the two-stage telescopic cylinders 170 and 180, both the two-stage telescopic cylinders 170 and 180 are extended as shown in FIG. As the telescopic boom main body 166 expands with the expansion of the two, when the pressure oil is supplied to the compression chambers of the two-stage telescopic cylinders 170, 180, the two-stage telescopic cylinders 170, 180 contract as shown in FIG. As the two-stage telescopic cylinders 170 and 180 are contracted, the telescopic boom main body 166 is contracted. The expansion side pressure oil supply port and the contraction side pressure oil supply port of the proximal end wall portion of the piston rod 181 of the distal end side two-stage extension cylinder 180 are connected to the hose arranged from the root side outside the extension boom body 166. The tip is connected.

  Also in the fourth embodiment, both the two-stage telescopic cylinders 170 and 180 of the telescopic boom B are provided with two contraction-side pressure chambers as in the case of the two-stage telescopic cylinder 5 in the first embodiment. On the other hand, the pressure oil from the compression side pressure oil supply port of the base end wall portion of the piston rods 171 and 181 is supplied through two compression side oil passages provided separately for each compression side pressure chamber inside the cylinder 170.180. Therefore, the hose disposed outside the cylinder and the hose guide device for protecting the hose arranged to communicate with the contraction-side pressure chambers as in the prior art can be eliminated. Of course, there are effects such as ease of assembly work and maintenance, weight reduction of the telescopic boom B, prevention of oil leakage, and cost reduction.

  In addition, this invention is not limited to the said 1st-4th embodiment, Other various forms are included. For example, in each of the above embodiments, the case where the double-stage expansion cylinders 5, 60, 110, 170, 180 are used as double-acting multistage cylinders has been described, but the present invention is not limited to the two-stage expansion cylinders. The same applies to the case where other multistage cylinders are used.

  Further, the present invention is not limited to the three-stage telescopic boom A as in the first embodiment or the five-stage telescopic boom B as in the fourth embodiment, and a plurality of booms are sequentially fitted in a telescopic manner. Needless to say, the present invention can be widely applied to a telescopic boom body that constitutes a telescopic boom body and extends and retracts the telescopic boom body by a double-acting multistage cylinder provided in the telescopic boom body.

The appearance of the three-stage telescopic boom according to the first embodiment of the present invention is shown, (a) is a side view in a contracted state, (b) is a side view in a one-stage extended state, and (c) is a two-stage extended state. FIG. It is a cutaway side view of the contraction state of the telescopic boom. It is a cutaway side view of a 1-stage extension state similarly. It is a cutaway side view of a two-stage extension state similarly. It is a sectional side view of the two-stage telescopic cylinder of the telescopic boom. It is an enlarged view of the left side part of FIG. It is an enlarged view of the right side part of FIG. It is an expanded sectional view in the XX line of FIG. FIG. 6 is a view corresponding to FIG. 5 showing a second embodiment. It is an enlarged view of the left side part of FIG. It is an enlarged view of the right side part of FIG. It is an expanded sectional view in the YY line of FIG. FIG. 6 is a view corresponding to FIG. 5 showing a third embodiment. It is an enlarged view of the left side part of FIG. It is an enlarged view of the right side part of FIG. It is an expanded sectional view in the ZZ line of FIG. It is an enlarged view of F part of FIG. It is a cutaway side view of the extension state of the 5 step type expansion-contraction boom which concerns on 4th Embodiment. It is a cutaway side view of a contracted state.

Explanation of symbols

A, B telescopic boom 1 proximal boom 2 intermediate boom 3 distal boom 4,166 telescopic boom body 5, 60, 110, 170, 180 two-stage telescopic cylinder (double-acting multi-stage cylinder)
11, 171, 181 Piston rod 11 a Tip wall 11 b Base wall 12, 13, 172, 173, 182, 183 Cylinder tube 12 a, 13 a Bottom 14, 15 Expansion side pressure chamber 16, 17 Contraction side pressure chamber 22, 61 , 62, 111, 112 Extension side pressure oil supply port 23, 63, 113 Contraction side pressure oil supply port 40, 90, 140 First compression side oil passage 43, 142 First pipe 45, 143 Second pipe 46 Third Pipe 47 Extension side oil passage 48, 91, 141, 152 Communication oil passage 50, 100, 150 Second contraction side oil passage 52 Fourth pipe 92 Pipe 161 Basic boom 162 Second stage boom 163 Third stage boom 164 Fourth stage Eye boom 165 5th stage boom

Claims (7)

In a telescopic boom constructed such that a telescopic boom main body is configured by sequentially fitting a plurality of booms in a telescopic manner, and the telescopic boom main body is expanded and contracted by a double-acting multi-stage cylinder provided in the telescopic boom main body.
The double-acting multi-stage cylinder has a hollow piston rod, a plurality of cylinder tubes that are concentrically fitted to the outer periphery of the piston rod, and a plurality of cylinder tubes that are sequentially fitted in a telescopic manner. A plurality of extension-side pressure chambers formed between the cylinder tube or the piston rod and the inner peripheral surface of each cylinder tube and the outer peripheral surface of the cylinder tube or piston rod fitted inside thereof. A plurality of contraction-side pressure chambers formed between them,
The pressure oil from the compression side pressure oil supply port provided in the proximal end wall portion of the piston rod is supplied to each of the compression side pressure chambers through an oil passage provided separately for each compression side pressure chamber. A telescopic boom, characterized in that it is configured as described above.   The double-acting multistage cylinder has two inner and outer cylinder tubes that are concentrically and telescopically fitted to the outer periphery of the piston rod, two inner and outer expansion chambers corresponding to the two cylinder tubes, and The telescopic boom according to claim 1, further comprising a contraction side pressure chamber.   Pressure oil is supplied to the compression side pressure chamber formed between the inner peripheral surface of the outer first cylinder tube and the outer peripheral surface of the second cylinder tube fitted inside thereof, out of the two compression side pressure chambers. A part of the oil passage for the first pipe, one end is fixed to the bottom of the second cylinder tube and the other end extends through the tip wall of the piston rod into the hollow portion of the piston rod; 3. A second pipe disposed in a hollow portion of the piston rod and having one end fixed to a proximal end wall portion of the piston rod in a state communicating with the contraction-side pressure oil supply port, is telescopically fitted. The telescopic boom described.   The first and second pipes are arranged on substantially the center line of the multistage cylinder and fitted with the second pipe outside, and a predetermined gap is provided around the outer periphery of the second pipe. A third pipe that is loosely fitted is provided, and an extension side oil passage is formed by a gap between the two pipes, and one end of the extension side oil passage is supplied to the extension side pressure oil provided on the proximal end wall portion of the piston rod. The other end of the extension side oil passage is communicated with the port and extends to the tip wall portion of the piston rod, and the bottom portion of the second cylinder tube and the tip of the piston rod through the communication oil passage provided on the tip wall portion. The telescopic boom according to claim 3, wherein the telescopic boom is communicated with an expansion-side pressure chamber formed between the surface and the surface.   Of the two compression side pressure chambers, a part of the oil passage for supplying pressure oil to the compression side pressure chamber formed between the inner peripheral surface of the inner cylinder tube and the outer peripheral surface of the piston rod is: The telescopic boom according to any one of claims 2 to 4, wherein the telescopic boom is configured by a fourth pipe disposed in a hollow portion of the piston rod and having one end communicating with the contraction-side hydraulic pressure supply port.   The first and second pipes are fitted to each other with the second pipe outside and a predetermined gap therebetween, and an oil different from the oil path inside the first pipe by the gap between the two pipes. A path is formed, and one end of the oil path is communicated with the contraction-side pressure oil supply port through the second pipe, and the other end of the oil path is connected via a communication oil path provided on the tip wall portion of the piston rod. The telescopic boom according to claim 3, wherein the telescopic boom is communicated with a contraction-side pressure chamber formed between the inner peripheral surface of the inner cylinder tube and the outer peripheral surface of the piston rod.   Pressure oil is supplied to the compression side pressure chamber formed between the inner peripheral surface of the outer first cylinder tube and the outer peripheral surface of the second cylinder tube fitted inside thereof, out of the two compression side pressure chambers. A part of the oil passage is configured by a pipe having one end fixed to the bottom portion of the second cylinder tube and the other end penetrating through the tip wall of the piston rod and into the hollow portion of the piston rod. On the other hand, the compression side pressure oil supply port is provided to open in the hollow portion of the piston rod, and the inside of the hollow portion of the piston rod constitutes part of an oil passage for supplying pressure oil to the two compression side pressure chambers, respectively. The telescopic boom according to claim 2.