JP2003269407A - Hydraulic circuit of hydraulic telescopic boom - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydraulic circuit of a hydraulic telescopic boom of high operability, in which an attachment driving hydraulic actuator is expanded and contracted by the same operation as for expanding and contracting a boom expanding and contracting cylinder by an operator without feeling the sense of discomfort. <P>SOLUTION: In this hydraulic circuit of the hydraulic telescopic boom comprising: a boom expanding and contracting hydraulic cylinder; the attachment driving hydraulic actuator for operating the attachment; an operation valve for expanding and contracting a boom; an expansion and contraction switch valve; a boom-attachment switch valve; an attachment expansion and contraction switch valve; a boom- attachment switching operation means; and an attachment expansion and contraction control means for interlocking and switching the expansion and contraction switching valve and the attachment expansion and contraction switch valve. The attachment driving hydraulic actuator is expanded when the operating valve for expanding and contracting the boom, is operated to an expansion side, and the attachment driving hydraulic actuator is contracted when the operation valve for expanding and contracting the boom is operated to a contraction side, in operating the attachment driving hydraulic actuator. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic circuit for a hydraulic telescopic boom.

[0002]

2. Description of the Related Art Conventionally, there are known crane vehicles having a telescopic jib at the tip of a telescopic boom. The telescopic boom of such a crane vehicle is telescopically extended and retracted by a hydraulic cylinder. The hydraulic circuit of such a hydraulic telescopic boom is, for example, the hydraulic circuit shown in FIG. 3 described in Japanese Utility Model Laid-Open No. 59-61188, and the telescopic boom of the boom telescopic hydraulic cylinders 2 and 3 is used. From the extension side oil passage 7 and the contraction side oil passage 10 of the boom extension hydraulic cylinder 2 attached to the tip end side, respectively, the first branch oil passage 2 is formed.
The first and second branched oil passages 22 are taken out and the first and second branched oil passages are connected to the attachment driving hydraulic actuator 1 via the electromagnetic switching valve 23. In addition, a hydraulic oil control device 25 that selectively connects the first hydraulic cylinder 2 and the attachment driving hydraulic actuator 1 to the hydraulic pressure supply source 30 at a branch point between the extension side oil passage 7 and the first branched oil passage 21, A switching valve 34 for recirculating the working oil supplied to the second oil passage 8 to the tank 29 side when the attachment driving hydraulic actuator 1 is used is attached to the second oil passage 8.

[0003]

However, such a hydraulic circuit of the hydraulic telescopic boom has the electromagnetic switching valve 2 when the hydraulic actuator 1 for driving the attachment is extended.
3 to the extension side, the manual switching valve 5 to the first position 5
When the hydraulic pressure actuator 1 for driving the attachment is set to "a", the electromagnetic switching valve 23 is switched to the compression side and the manual switching valve 5 is set to the first position 5a. In this case, the first position 5a of the manual switching valve 5 is a position where the boom extension hydraulic cylinders 2 and 3 are extended. That is, even when the attachment driving hydraulic actuator 1 is extended,
When retracting, the operator can
Since the manual switching valve 5 is operated in the same way as when the extension actuator 3 is extended, there is no discomfort when the attachment driving hydraulic actuator 1 is extended, but it is not preferable when the attachment drive hydraulic actuator 1 is contracted.

The present invention has been made in view of the above-mentioned problems, and the operator can extend and retract the attachment driving hydraulic actuator by the same operation as that by which the operator extends and retracts the boom telescopic cylinder, so that the operator does not feel uncomfortable. The purpose is to provide a hydraulic circuit for a hydraulic telescopic boom with good performance.

[0005]

In order to achieve the above object, a first invention is a hydraulic circuit of a hydraulic telescopic boom, wherein a boom telescopic hydraulic cylinder for extending and retracting the telescopic boom and a telescopic boom tip. A hydraulic actuator for driving an attachment that operates an attachment provided in, a boom expansion / contraction operation valve, an expansion / conversion switching valve, a boom / attachment switching valve, and an attachment expansion / compression switching valve,
Boom / attachment switching operation means and attachment expansion / contraction control means for switching the expansion / compression switching valve and attachment expansion / compression switching valve in tandem are provided.When operating the attachment drive hydraulic actuator, the boom expansion / contraction valve is operated to the extension side to drive the attachment. The hydraulic actuator for extension extends, and the hydraulic actuator for driving the attachment contracts when the boom expansion / contraction operation valve is operated toward the contraction side.

According to the first aspect of the invention, when extending the attachment driving hydraulic actuator, the operator can extend the attachment driving hydraulic actuator by the same operation as when extending the telescopic boom. Also,
When retracting the attachment driving hydraulic actuator, the operator can retract the attachment driving hydraulic actuator by the same operation as when retracting the telescopic boom. Therefore, the operator can operate the hydraulic actuator for driving the attachment to expand and contract without feeling uncomfortable, and a hydraulic circuit of the hydraulic telescopic boom with good operability can be realized.

According to a second aspect of the present invention, in a hydraulic circuit of a hydraulic telescopic boom, a boom telescopic hydraulic cylinder that telescopes the telescopic boom, an attachment driving hydraulic actuator that operates an attachment provided at the end of the telescopic boom, and a boom telescopic operating valve. An expansion / contraction switching valve provided between the boom expansion / contraction operation valve and the boom expansion / contraction hydraulic cylinder; a boom / attachment switching valve installed in the boom extension side oil passage between the expansion / compression switching valve and the boom expansion / contraction hydraulic cylinder;・ An oil passage connecting the attachment switching valve and the attachment driving hydraulic actuator, an oil passage connecting the attachment driving hydraulic actuator and the compression side chamber of the boom telescopic hydraulic cylinder, and a boom / attachment switching valve and the attachment driving hydraulic actuator Oil passage and attachment drive to connect with Expansion / contraction switching valve for switching the expansion / contraction of the attachment driving hydraulic actuator provided in the middle of the oil passage connecting the hydraulic actuator for boom and expansion / contraction side chamber of the boom expansion / contraction hydraulic cylinder, and boom / attachment switching operation means for switching between the boom / attachment switching valve And an attachment expansion / contraction control means for switching the expansion / contraction switching valve and the attachment expansion / contraction switching valve in an interlocking manner.

According to the second invention, similarly to the first invention, when extending the attachment driving hydraulic actuator, the operator can extend the attachment driving hydraulic actuator by the same operation as when extending the telescopic boom. . Further, when the attachment driving hydraulic actuator is contracted, the operator can contract the attachment driving hydraulic actuator by the same operation as when contracting the telescopic boom. Therefore, the operator can operate the hydraulic actuator for driving the attachment to expand and contract without feeling uncomfortable, and a hydraulic circuit of the hydraulic telescopic boom with good operability can be realized.

In a third aspect based on the first or second aspect, the compression side chamber of the boom telescopic cylinder is always in communication with the tank side when the attachment driving hydraulic actuator is activated.

According to the third aspect of the present invention, even when the attachment telescopic cylinder is telescopic, the pressure oil in the compression side chamber of the boom telescopic cylinder is drained to the hydraulic oil tank. Even if the pressure oil leaking inside the switching valve or the attachment expansion / contraction switching valve flows into the compression side chamber of the boom expansion / contraction cylinder, a reliable hydraulic circuit that does not cause a malfunction such as the boom expansion / contraction cylinder contracting does not occur.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a hydraulic circuit for a hydraulic telescopic boom according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing an appearance of a work vehicle 1 using a hydraulic circuit of a hydraulic telescopic boom of the present invention. FIG. 2 is a system configuration diagram showing the configuration of the hydraulic circuit of the hydraulic telescopic boom of the present invention.

As shown in FIG. 1, the work vehicle 51 is provided with an upper revolving structure 53 which is rotatably provided on a lower traveling structure 52 having an outrigger 52A. The upper swing body 53 is provided with a telescopic boom 54 that can be hoisted by a hoisting cylinder (not shown). At the tip of the telescopic boom 54, as an attachment,
It has a stretchable jib 55.

The telescopic boom 54 is telescopically extended by the first telescopic cylinder 61, the second telescopic cylinder 62, and the third telescopic cylinder 63, which are boom telescopic hydraulic cylinders shown in FIG. 2, and the jib 55 is driven by the attachment drive shown in FIG. It is expanded and contracted by the jib expansion and contraction cylinder 80 which is a hydraulic actuator for use.

As shown in FIG. 2, in the hydraulic circuit of the hydraulic telescopic boom according to the present invention, the discharge side of the hydraulic pump 71, which is the hydraulic source, is the boom telescopic operating valve 7 which is the pilot pressure type operating valve.
Hydraulic oil tank 72 which is a tank connected to the P port of No. 3
Is connected to the T port of the boom expansion / contraction operation valve 73.
The boom expansion / contraction operation valve 73 has a port A and a port B via oil passages 82 and 81, respectively, and is an expansion / contraction switching valve 7 which is a solenoid valve.
Connected to 4.

The B port of the expansion / conversion switching valve 74 is connected to the compression side chamber 61T of the first expansion / contraction cylinder 61 via an oil passage 83. The contraction side chamber 61T of the first retractable cylinder 61 is connected to the contraction side chamber 62T of the second retractable cylinder 62 via an oil passage 85, and the contraction side chamber 62T of the second retractable cylinder 62 is oiled to the contraction side chamber 63T of the third retractable cylinder 63. It is connected via a path 86.

The port A of the expansion / contraction switching valve 74 is connected via the oil passage 91 to a boom / attachment switching valve 78, which is an electromagnetic valve.
Connected to.

The B port of the boom / attachment switching valve 78 is connected to the boom extension / contraction sequential control valve 75 via the oil passage 92.
Connected to.

When the first telescopic cylinder 61 is fully extended, the boom telescopic sequential control valve 75 then moves to the second telescopic cylinder 62.
When oil is sent to the expansion side chamber 62N of the second expansion cylinder 62 and the second expansion cylinder 62 is fully expanded, the expansion side chamber 63 of the third expansion cylinder 63 is then expanded.
Oil is sent to N, and control is performed so that the first telescopic cylinder 61, the second telescopic cylinder 62, and the third telescopic cylinder 63 sequentially expand.

The boom expansion / contraction sequential control valve 75 is provided in the oil passage 8.
The extension side chamber 61N of the first extension cylinder 61, the extension side chamber 62N of the second extension cylinder 62, and the extension side chamber 63N of the third extension cylinder 63 are connected via 4, 88, 89, respectively.

A port of the boom / attachment switching valve 78 is connected to the hose reel 77 via the oil passage 93, and the hose reel 77 is connected to the B1 port of the attachment expansion / contraction switching valve 76 which is a solenoid valve via the oil passage 94. is doing.

The B port of the attachment expansion / contraction switching valve 76 is connected to the compression side chamber 80T of the attachment expansion / contraction cylinder 80. The port A of the attachment telescopic switching valve 76 is the extension side chamber 80N of the attachment telescopic cylinder 80.
Connected to.

The contraction side chamber 63T of the third telescopic cylinder 63 is connected to the A1 of the attachment telescopic switching valve 76 via the oil passage 87.
You are connected to a port.

The solenoid of the expansion / conversion switching valve 74 is a wiring 105.
The solenoid of the attachment expansion / contraction switching valve 76 is also connected to the controller 101 via the wiring 106. The solenoid of the boom / attachment switching valve 78 is connected to the controller 101 via the wiring 107. The power supply 108 is the input side terminal 102a of the boom / attachment changeover switch 102.
Connected to. The output side terminal 102b of the boom / attachment changeover switch 102 is connected to the controller 101.

Boom / attachment selector switch 10
2 is switched to the boom side and the boom / attachment selector switch 102 is opened, the controller 101
The electric signal from is cut off, and the boom / attachment switching valve 78 becomes the boom side position 78a. When the boom / attachment changeover switch 102 is switched to the attachment side and the boom / attachment changeover switch 102 is closed, the electric signal from the controller 101 causes the boom / attachment changeover valve 78 to move to the attachment side position 78b. Therefore, the boom / attachment changeover switch 102 constitutes the boom / attachment changeover means 200 together with the controller 101.

The expansion / contraction pilot valve 110 includes an extension side pilot pressure line 110N and a contraction side pilot pressure line 110.
The boom expansion / contraction operation valve 73 is connected via T respectively. Telescopic operating lever 111 of telescopic pilot valve 110
When the boom expansion / contraction operation valve 73 is operated to the extension side, the boom expansion / contraction operation valve 73 becomes the extension side position 73a proportional to the pilot pressure according to the operation amount of the expansion / contraction operation lever 111, and the expansion / contraction pilot valve 110
When the expansion / contraction operation lever 111 is operated toward the contraction side, the boom expansion / contraction operation valve 73 becomes the contraction side position 73b proportional to the pilot pressure according to the operation amount of the expansion / contraction operation lever 111.
The extension side pilot pressure line 110N is provided with an extension detection pressure sensor 112, and the contraction side pilot pressure line 110T is provided with a contraction detection pressure sensor 113. The extension detection pressure sensor 112 is provided with a contraction detection pressure sensor 113 via a wiring 114.
Are connected to the controller 101 via wirings 115, respectively.

When the expansion / contraction operation lever 111 of the expansion / contraction pilot valve 110 is operated to the expansion side, the expansion detection pressure sensor 112 detects the pressure in the expansion side pilot pressure line 110N and sends an expansion signal to the controller 101 to extend the expansion pilot valve. When the expansion / contraction operation lever 111 of 110 is operated toward the contraction side, the contraction detection pressure sensor 113 detects the pressure in the contraction side pilot pressure conduit 110T and sends a contraction signal to the controller 101.

Boom / attachment selector switch 10
2 is switched to the attachment side (in this state, the boom / attachment switching valve 78 is at the attachment side position 78b as described above), and when the telescopic operation lever 111 is operated to the extension side, the extension side pilot pressure pipe is The expansion detection pressure sensor 112 detects the pressure in the path 110N and sends an expansion signal to the controller 101, whereby the electric signal from the controller 101 is cut off, and the expansion / conversion switching valve 74 becomes the expansion side position 74a, and at the same time, from the controller 101. The electric expansion signal also causes the attachment expansion / contraction switching valve 76 to move to the extension side position 76a, and switches in conjunction therewith. Also, the boom / attachment selector switch 102
When the expansion / contraction operation lever 111 is operated to the contraction side in the state where is switched to the attachment side, the contraction detection pressure sensor 113 detects the pressure of the contraction side pilot pressure pipeline 110T,
The contraction signal is sent to the controller 101, and the electric signal from the controller 101 thereby causes the expansion / contraction switching valve 74.
Becomes the contraction side position 74b, and at the same time, the controller 10
The electric signal from 1 is cut off, and the attachment expansion / contraction switching valve 7
6 also becomes the contraction side position 76b, and is switched in conjunction with each other. Therefore, the controller 101 uses the elongation detection pressure sensor 11
The attachment expansion / contraction control means 300 is configured with the contraction detection pressure sensor 113.

Next, the operation of the hydraulic circuit of the hydraulic telescopic boom of the present invention will be described.

To extend the telescopic boom 54, the boom / attachment selector switch 102 is switched to the boom side. Then, the boom / attachment switching valve 78 becomes the boom side position 78a.

When the expansion / contraction operation lever 111 of the expansion / contraction pilot valve 110 is operated to the extension side so that the boom expansion / contraction operation valve 73 is set to the expansion side position 73a by the pilot pressure, the pressure oil from the hydraulic pump 71 expands / contracts the boom. From the A port of the operation valve 73 for the expansion / contraction switching valve 74, the B port of the boom / attachment switching valve 78, the boom expansion / contraction sequential control valve 75, and the expansion side chamber 61N of the first expansion / contraction cylinder 61. To be done.

The oil in the compression side chamber 61T of the first telescopic cylinder 61 is drained to the hydraulic oil tank 72 from the B port of the boom telescopic operation valve 73 via the oil passage 83, the B port of the telescopic switching valve 74. Then, when the first telescopic cylinder 61 is fully extended as described above, the boom telescopic sequential control valve 75 is actuated, and then oil is sent to the extension side chamber 62N of the second telescopic cylinder 62, and the compression side chamber of the second telescopic cylinder 62. 6
The 2T oil is drained to the hydraulic oil tank 72 from the B port of the boom telescopic operation valve 73 via the oil passage 85, the compression side chamber 61T of the first telescopic cylinder 61, the B port of the telescopic switching valve 74, and the B port of the boom telescopic operating valve 73. .

Next, when the second telescopic cylinder 62 is fully extended, the boom telescopic sequential control valve 75 is actuated to send oil to the extension side chamber 63N of the third telescopic cylinder 63, and the contraction side chamber 63T of the third telescopic cylinder 63 is moved. The oil passes through the oil passage 86,
The oil passage 8 is provided through the contraction side chamber 62T of the second telescopic cylinder 62.
5, through the contraction side chamber 61T of the first telescopic cylinder 61, the B port of the telescopic switching valve 74, and the B port of the boom telescopic operation valve 73 to the hydraulic oil tank 72.

In this way, the first telescopic cylinder 61,
The second telescopic cylinder 62 and the third telescopic cylinder 63 extend,
Therefore, the telescopic boom 54 can be extended.

To retract the telescopic boom 54, the boom / attachment changeover switch 102 is switched to the boom side. This operation is the same as the operation for extending the telescopic boom 54. Then, the boom / attachment switching valve 78 becomes the boom side position 78a.

Then, when the expansion / contraction operation lever 111 of the expansion / contraction pilot valve 110 is operated to the contraction side and the boom expansion / contraction operation valve 73 is set to the extension side position 73a by the pilot pressure, the pressure oil from the hydraulic pump 71 is transferred to the boom. From the B port of the expansion / contraction operation valve 73, through the B port of the expansion / contraction switching valve 74, through the compression side chamber 61T of the first expansion cylinder 61, and through the oil passage 85, through the compression side chamber 62T of the second expansion cylinder 62, Then, it is introduced into the compression side chamber 63T of the third telescopic cylinder 63 via the oil passage 86.

The expansion side chamber 61N of the first telescopic cylinder 61,
The oil in the expansion side chamber 62N of the second expansion / contraction cylinder 62 and the expansion side chamber 63N of the third expansion / contraction cylinder 63 is oil passages 84, 88, 89.
Through the boom expansion / contraction sequential control valve 75, through the B port of the boom / attachment switching valve 78, through the A port of the expansion / contraction switching valve 74, and from the A port of the boom expansion / contraction operation valve 73 to the hydraulic oil tank 72. It is drained.

In this way, the first telescopic cylinder 61,
The second telescopic cylinder 62 and the third telescopic cylinder 63 contract,
Therefore, the telescopic boom 54 can be contracted.

To extend the jib 55, the boom / attachment selector switch 102 is switched to the attachment side. Then, the electric signal from the controller 101 causes the boom / attachment switching valve 78 to move to the attachment side position 78b.

When the expansion / contraction operation lever 111 is operated to the expansion side, the expansion detection pressure sensor 112 detects the pressure in the expansion side pilot pressure line 110N and sends an expansion signal to the controller 101, which causes the controller 101 to operate.
The electric signal from is cut off, and the expansion / conversion switching valve 74 moves to the extension side position 7.
4a, and at the same time, the attachment expansion / contraction switching valve 76 also moves to the extension side position 76a by an electric signal from the controller 101, and switches in conjunction with each other. Further, by operating the expansion / contraction operation lever 111 to the extension side, the boom expansion / contraction operation valve 73 is set to the expansion side position 73a, so that the pressure oil from the hydraulic pump 71 is expanded / contracted from the A port of the boom expansion / contraction operation valve 73. Via port A of valve 74, via oil passage 91,
Via the port A of the boom / attachment switching valve 78,
It is introduced into the extension side chamber 80N of the attachment telescopic cylinder 80 through the oil passage 93, the hose reel 77, the oil passage 94, the B1 port of the attachment telescopic switching valve 76 and the A port.

The oil in the compression side chamber 80T of the attachment telescopic cylinder 80 passes from the B port of the attachment telescopic switching valve 76 to the A1 port, through the oil passage 87, the compression side chamber 63T of the third telescopic cylinder 63, and the oil passage 86. Through,
The oil passage 8 is provided through the contraction side chamber 62T of the second telescopic cylinder 62.
5, through the compression side chamber 61T of the first telescopic cylinder 61, through the oil passage 83, through the B port of the telescopic switching valve 74, through the oil passage 81, and from the B port of the boom telescopic operation valve 73. It is drained to the oil tank 72.

In this way, the attachment telescopic cylinder 80 can be extended and thus the jib 55 can be extended.

In this case, the operator can extend the jib 55 by operating the boom extension / contraction operation valve 73 to the extension side position 73a by the same operation as when extending the extension / contraction boom 54, and the operation can be performed without a feeling of strangeness. . That is, as described above, when the telescopic operation lever 111 is operated to the extension side, the telescopic switching valve 74 is set to the extension side position 74a at the same time as the boom extension / contraction operation valve 73 is set to the extension side position 73a. Since the attachment expansion / contraction switching valve 76 is also switched to the extension side position 76a, the jib 55 can be extended without feeling discomfort by operating the extension / contraction operation lever 111 in the extension side, as in the case of extending the extension / contraction boom 54.

When the jib 55 is contracted, the boom / attachment changeover switch 102 is changed over to the attachment side. Then, the electric signal from the controller 101 causes the boom / attachment switching valve 78 to move to the attachment side position 78b.

When the expansion / contraction operation lever 111 is operated toward the contraction side, the contraction detection pressure sensor 113 detects the pressure in the contraction side pilot pressure conduit 110T and sends a contraction signal to the controller 101, which in turn outputs an electric signal from the controller 101. As a result, the expansion / contraction switching valve 74 is moved to the contraction side position 74.
At the same time, the electric signal from the controller 101 is cut off, and the attachment expansion / contraction switching valve 76 also moves to the contraction side position 7
It becomes 6b and switches in conjunction. Further, by operating the expansion / contraction operation lever 111 to the contraction side, the boom expansion / contraction operation valve 73 becomes the contraction side position 73b, so that the hydraulic pump 7
The pressure oil from No. 1 passes through the hose reel 77 from the B port of the boom expansion / contraction operation valve 73 through the A port of the expansion / conversion switching valve 74, through the A port of the boom / attachment switching valve 78, and through the oil passage 93. , Through the oil passage 94, from the B1 port of the attachment expansion / conversion switching valve 76 to the B port,
It is introduced into the contraction side chamber 80T of the attachment telescopic cylinder 80.

The oil in the extension side chamber 80N of the attachment telescopic cylinder 80 passes through the A port of the attachment telescopic switching valve 76, the A1 port, the oil passage 87, the compression side chamber 63T of the third telescopic cylinder 63, and the oil passage 86. Through,
The oil passage 8 is provided through the contraction side chamber 62T of the second telescopic cylinder 62.
5, through the compression side chamber 61T of the first telescopic cylinder 61, through the oil passage 83, through the B port of the telescopic switching valve 74, through the oil passage 82, and from the A port of the boom telescopic operation valve 73 to the T port. It flows to the port and is drained to the hydraulic oil tank 72.

In this way, the attachment telescopic cylinder 80 contracts, and thus the jib 55 can contract.

Also in this case, the operator can
By operating the boom expansion / contraction operation valve 73 to the contraction side position 73b by the same operation as when retracting the jib 55,
Can be shortened, and it can be operated without discomfort. That is, as described above, when the telescopic operation lever 111 is operated to the retracted side, the boom telescopic operation valve 73 is moved to the retracted side position 73b.
The expansion / conversion switching valve 74 moves in the contraction side position 74
At the same time, the attachment expansion / contraction switching valve 76 is also switched to the contraction side position 76b. Therefore, as with the case of contracting the telescopic boom 54, by operating the expansion / contraction operation lever 111 to the contraction side, the jib 55 can be comfortably moved. Can be shortened.

When the jib 55 is expanded and contracted, the compression side chamber 61T of the first expansion and contraction cylinder 61, the compression side chamber 62T of the second expansion and contraction cylinder 62, and the compression side chamber 63T of the third expansion and contraction cylinder 63 are always operated. It communicates with the oil tank 72. Therefore, the pressure oil leaking inside the expansion / conversion switching valve 74 and the attachment expansion / compression switching valve 76 due to the expansion / contraction operation of the jib 55 causes the compression side chamber 61T of the first expansion / contraction cylinder 61 to move to the second side.
Even if the compression side chamber 62T of the telescopic cylinder 62 and the compression side chamber 63T of the third telescopic cylinder 63 flow into the hydraulic oil tank 72, the pressure oil is drained.
1, the second telescopic cylinder 62, the third telescopic cylinder 63
There is no malfunction that causes the contraction.

In this embodiment, the expansion / conversion switching valve 7 is used as an example.
4, the attachment expansion / contraction switching valve 76 and the boom / attachment switching valve 78 are electromagnetic valves, but may be pilot pressure type switching valves. In this case, instead of the boom / attachment changeover switch 102 and the controller 101, a changeover valve capable of changing the pilot pressure may be used as the boom / attachment changeover operation means and the expansion / contraction changeover operation means.

The boom expansion / contraction operation valve 73 may be a direct-acting type in which a spool is operated by a lever via a link or the like, or may be an electromagnetic proportional valve operated by an electric signal.

As the boom telescopic hydraulic cylinder, three cylinders of a first boom telescopic hydraulic cylinder 61, a second boom telescopic hydraulic cylinder 62, and a third boom telescopic hydraulic cylinder 63 are used. Even one is 2
It is also possible to use a book or a plurality of cylinders of four or more.

[Brief description of drawings]

FIG. 1 is a view showing an appearance of a work vehicle using a hydraulic circuit of a hydraulic telescopic boom of the present invention.

FIG. 2 is a system configuration diagram showing a configuration of a hydraulic circuit of the hydraulic telescopic boom of the present invention.

FIG. 3 is a hydraulic circuit diagram of a conventional hydraulic telescopic boom.

[Explanation of symbols]

54 ... Telescopic boom, 61 ... First boom telescopic hydraulic cylinder, 61N ... Extension side chamber, 61T ... Contraction side chamber, 62 ... Second
Boom telescopic hydraulic cylinder, 62N ... Extension side chamber, 62T ...
Contraction side chamber, 63 ... Third boom telescopic hydraulic cylinder, 63N
… Extension side chamber, 63T ... Contraction side chamber, 71 ... Hydraulic pump, 7
2 ... Hydraulic oil tank, 73 ... Boom expansion / contraction operation valve, 74 ...
Telescopic switching valve, 77 ... Hose reel, 78 ... Boom / attachment switching valve, 76 ... Attachment telescopic switching valve,
80 ... Attachment telescopic cylinder, 80N ... Extension side chamber, 80T ... Contraction side chamber, 81, 82, 83, 84, 8
5,86,87,91,92,93,94 ... Oil passage, 10
DESCRIPTION OF SYMBOLS 1 ... Controller, 102 ... Boom / attachment changeover switch, 200 ... Boom / attachment changeover operation means, 300 ... Attachment expansion / contraction control means.

Claims (3)

[Claims] 1. In a hydraulic circuit of a hydraulic telescopic boom, a boom telescopic hydraulic cylinder that telescopes the telescopic boom (54), an attachment driving hydraulic actuator that operates an attachment provided at the tip of the telescopic boom (54), and a boom telescopic operation. Valve (73), telescopic switching valve (74), boom / attachment switching valve (78), attachment telescopic switching valve (76)
And a boom / attachment switching operation means (200) and an attachment expansion / contraction control means (300) for switching the expansion / contraction switching valve (74) and the attachment expansion / compression switching valve (76) in cooperation with each other. Occasionally, operating the boom expansion / contraction valve (73) to the extension side causes the attachment drive hydraulic actuator to expand, and operating the boom expansion / contraction operation valve (73) to the contraction side causes the attachment drive hydraulic actuator to contract. Hydraulic circuit for telescopic boom. 2. In a hydraulic circuit of a hydraulic telescopic boom, a boom telescopic hydraulic cylinder that telescopes the telescopic boom, an attachment driving hydraulic actuator that operates an attachment provided at the tip of the telescopic boom (54), and a boom telescopic operating valve (73). ), A telescopic switching valve (74) provided between the boom telescopic operating valve (73) and the boom telescopic hydraulic cylinder, and the telescopic switching valve
(74) and the boom extension hydraulic cylinder, the boom attachment switching valve (78) provided in the boom extension side oil passage, and the oil passage that connects the boom attachment switching valve (78) and the attachment drive hydraulic actuator. An oil passage connecting the attachment driving hydraulic actuator and the compression side chamber of the boom telescopic hydraulic cylinder, an oil passage connecting the boom / attachment switching valve (78) and the attachment driving hydraulic actuator, and an attachment driving hydraulic actuator. Attachment expansion / contraction switching valve that switches the expansion / contraction of an attachment drive hydraulic actuator provided in the middle of the oil passage that connects the boom expansion / contraction hydraulic cylinder with the compression side chamber.
(76) and the boom / attachment switching valve (78) to switch the boom / attachment switching operation means (200), and the expansion / contraction switching valve (74) and the attachment expansion / contraction switching valve (76) in an interlocking manner. A hydraulic circuit for a hydraulic telescopic boom, which is provided with (300). 3. The hydraulic circuit for a hydraulic telescopic boom according to claim 1, wherein the compression side chamber of the boom telescopic cylinder is always communicated with the tank side when the attachment driving hydraulic actuator is activated. Hydraulic circuit.