JP6723839B2 - Hydraulic system of work machine - Google Patents

Description

The present invention relates to, for example, a hydraulic system of a work machine in which a front loader is attached to a tractor.

BACKGROUND ART Conventionally, as a working machine in which a front loader is attached to a tractor, one shown in Patent Document 1 is known.
The working machine disclosed in Patent Document 1 includes a boom, a bucket, a boom hydraulic cylinder, a bucket hydraulic cylinder, a boom control valve that controls the boom hydraulic cylinder, and a bucket control valve that controls the bucket hydraulic cylinder. ing. The boom control valve and the bucket control valve are three-position switching valves. Therefore, the boom can be swung up or down by switching the boom control valve to a predetermined position, and the bucket can be scooped or dumped by switching the bucket control valve to a predetermined position.

JP, 2009-052287, A

Now, in addition to the bucket, various front attachments can be attached to the front loader. The preliminary attachment is operated by, for example, a hydraulic cylinder (referred to as a preliminary hydraulic cylinder). The control of the auxiliary hydraulic cylinder is performed by the auxiliary control valve of the three-position switching valve. As described above, various hydraulic actuators such as the boom hydraulic cylinder, the bucket hydraulic cylinder, and the standby hydraulic cylinder are controlled by the control valve corresponding to the hydraulic actuator. The hydraulic cylinder controlled by the control valve may have to hold the same attitude for a long time.

The present invention has been made to solve the above-described problems of the conventional technology, and an object of the present invention is to provide a hydraulic system for a working machine that can maintain the posture of the hydraulic actuator for a long time. ..

The technical means of the present invention for solving this technical problem are as follows.
The hydraulic system of the working machine is capable of switching between a first hydraulic actuator, a first connecting oil passage connected to the first hydraulic actuator, and a first position and a second position. A first port that is connected, a second port that is connected to the first connection oil passage at a position different from the first port, and a first flow path that connects the first port and the second port A second flow path different from the first flow path; and a second flow path, which is provided in the second flow path and blocks the flow of hydraulic oil from the second port to the first port, and from the first port to the second port. A switching valve having a shut-off portion for shutting off the flow of hydraulic oil to the oil, a discharge oil passage for discharging hydraulic oil, a fifth port and a sixth port, and hydraulic oil at the sixth port. When the hydraulic fluid is supplied to the fifth port, the third hydraulic actuator that contracts when hydraulic oil is supplied to the fifth port, the first supply/discharge passage connected to the fifth port, and the sixth hydraulic actuator. A second connection oil passage having a second supply/discharge passage connected to the port, and the hydraulic oil supplied to the sixth port when the third hydraulic actuator expands escapes to the second connection oil passage. And prevents the hydraulic oil supplied to the sixth port from escaping to the second connection oil passage when the third hydraulic actuator contracts, and connects to the second supply/discharge passage. A first bypass oil passage that bypasses the relief valve by connecting the relief valve upstream of the relief valve and the downstream of the relief valve in the second supply/discharge passage with the relief valve capable of reducing the set pressure during the contraction. And a fifth check valve that is provided in the first bypass oil passage and that prevents the hydraulic oil from flowing from downstream to upstream which is the sixth port side and allows the hydraulic oil to flow from upstream to downstream. And a float part that is connected to the second supply/discharge path and the first supply/discharge path and discharges the hydraulic oil of the fifth port and the sixth port to the discharge oil path. A second bypass oil passage that bypasses the first bypass oil passage by connecting an upstream side of the first bypass oil passage and a downstream side of the first bypass oil passage in the second supply/discharge passage; A third switching valve which is provided in the bypass oil passage, connects the second bypass oil passage when the float portion is operating, and shuts off the second bypass oil passage when the float portion is not operating. ing.

The blocking part includes a first check valve for blocking the flow of hydraulic oil from and the second port provided in the second flow path to the first port and the second is provided in the second flow path and a second check valve for blocking the flow of hydraulic fluid to the second port from the first port.
The hydraulic system of the working machine is capable of switching between a first hydraulic actuator, a first connecting oil passage connected to the first hydraulic actuator, and a first position and a second position. A first port that is connected, a second port that is connected to the first connection oil passage at a position different from the first port, and a first flow path that connects the first port and the second port A second flow path different from the first flow path; and a second flow path, which is provided in the second flow path and blocks the flow of hydraulic oil from the second port to the first port, and from the first port to the second port. Block the flow of hydraulic oil to
A plurality of first switching valves each having a first shutoff portion for disconnecting; a discharge oil passage for discharging hydraulic oil; a fifth port and a sixth port; A third hydraulic actuator that expands when supplied, and contracts when hydraulic oil is supplied to the fifth port, a first supply/discharge path connected to the fifth port, and the sixth port A second connection oil passage having a second supply/discharge passage connected to the second connection passage, and the hydraulic oil supplied to the sixth port when the third hydraulic actuator extends to the second connection oil passage. And allows the hydraulic oil supplied to the sixth port to escape to the second connection oil passage when the third hydraulic actuator contracts, and is connected to the second supply/discharge passage. And a first bypass oil passage for bypassing the relief valve by connecting the upstream side of the relief valve and the downstream side of the relief valve in the second supply/discharge passage with the relief valve capable of reducing the set pressure during the contraction. A fifth check valve that is provided in the first bypass oil passage and that prevents the hydraulic oil from flowing from downstream to upstream, which is the sixth port side, and allows the hydraulic oil to flow from upstream to downstream, And a float part connected to the second supply/discharge path and the first supply/discharge path, for discharging the hydraulic oil of the fifth port and the sixth port to the discharge oil path, A second bypass oil passage that bypasses the first bypass oil passage by connecting an upstream side of the first bypass oil passage and a downstream side of the first bypass oil passage in the second supply/discharge passage, and the second bypass oil passage. A third switching valve that is provided in the oil passage, connects the second bypass oil passage when the float portion is operating, and shuts off the second bypass oil passage when the float portion is not operating. There is.

It said first blocking portion includes a first check valve for blocking the flow of hydraulic oil from and the second port provided in the second flow path to the first port, and provided in the second flow path and a second check valve for blocking the flow of hydraulic fluid to the second port from the first port.
Said plurality of first switching valve is the first position and the switchable electromagnetic switching valve to the second position, it switched simultaneously to one of said first position and said second position.

The hydraulic system of the working machine is provided in a branch oil passage branched from the first connection oil passage, a second hydraulic actuator connected to the branch oil passage, the branch oil passage, and a third position and a third position. A plurality of second switching valves capable of switching to four positions, wherein the plurality of second switching valves are provided at a position different from the third port connected to the branch oil passage and the third port. a fourth port connected to the branch oil passage, a third flow path for communicating the third port and the fourth port, and a different fourth flow path and the third flow path, the fourth flow path are provided and a second blocking portion for blocking the flow of hydraulic fluid to the fourth port from the flow cut off and the third port of the hydraulic oil to the fourth from said port third port ..

Said second blocking portion has a third check valve for blocking the flow of hydraulic fluid of the and is provided with a fourth flow path from the fourth port to the third port, and provided in the fourth channel and a fourth check valve for blocking the flow of hydraulic fluid to the fourth port from the third port.
Said plurality of second switching valve, the third is the position and the fourth switchable electromagnetic switching valve to a position, switched simultaneously to one of said third position and said fourth position.

It said plurality of second switching valve is switched to the fourth position when said plurality of first switching valve is switched to the first position, when the plurality of first switching valve is switched to the second position To the third position.
A hydraulic system of the working machine is provided in a spare hydraulic cylinder for operating a spare attachment mounted on a boom, a first connecting oil passage connected to the spare hydraulic cylinder, and a first connecting oil passage, and A plurality of first switching valves capable of switching between a first position and a second position, a branch oil passage branched from the first connecting oil passage, and a bucket connected to the branch oil passage and attached to the boom. A bucket hydraulic cylinder to be moved, a plurality of second switching valves provided in the branch oil passage and switchable between a third position and a fourth position, a fifth port and a sixth port, and A third hydraulic actuator that expands when hydraulic oil is supplied to the sixth port and contracts when hydraulic oil is supplied to the fifth port, and the fifth port and the third hydraulic actuator of the third hydraulic actuator. The second connection oil passage connected to the 6th port and the hydraulic oil supplied to the sixth port when the third hydraulic actuator is extended are prevented from flowing out to the second connection oil passage, and When the third hydraulic actuator contracts, an operating portion that allows the hydraulic oil supplied to the sixth port to escape to the second connecting oil passage, a discharge oil passage that discharges the hydraulic oil, and the fifth hydraulic fluid And a second bypass oil passage, and a third switching valve, wherein the plurality of first switching valves have the first connection. A first port connected to an oil passage, a second port connected to the first connection oil passage at a position different from the first port, and the first port and the first port when the second position A first flow path that is a flow path that connects two ports and a flow path that is different from the first flow path, and that is connected to the first port and the second port when in the first position Two flow paths and a second flow path are provided to block the flow of hydraulic oil from the second port to the first port and block the flow of hydraulic oil from the first port to the second port. A plurality of second switching valves connected to the branched oil passage, and a plurality of second switching valves connected to the branched oil passage at positions different from the third port. 4 ports, a third flow path that is a flow path that communicates the third port and the fourth port when in the fourth position, and a flow path that is different from the third flow path. And a fourth flow path connected to the third port and the fourth port when in the position, and blocking the flow of hydraulic oil from the fourth port to the third port provided in the fourth flow path. And the above A second shut-off portion for shutting off the flow of hydraulic oil from a third port to the fourth port, wherein the plurality of first switching valves are electromagnetic switches capable of switching between the first position and the second position. Is a switching valve, is switched to any one of the first position and the second position at the same time, and the plurality of second switching valves is an electromagnetic switching valve capable of switching to the third position and the fourth position, The plurality of second switching valves are switched to the third position and the fourth position at the same time, the plurality of first switching valves are switched to the first position, and the first shut-off portion is the standby unit. When the hydraulic oil is blocked from flowing to the hydraulic cylinder, switching to the fourth position allows the third flow path to allow hydraulic oil to flow to the bucket hydraulic cylinder, and the plurality of first switching When the valve switches to the second position and the first flow path allows hydraulic oil to flow to the preliminary hydraulic cylinder, switching to the third position causes the second cutoff portion to move to the bucket. A first check valve that blocks flow to a hydraulic cylinder, and the first block part is provided in the second flow path and blocks a flow of hydraulic oil from the second port to the first port; A second check valve that is provided in the second flow passage and shuts off the flow of the hydraulic oil from the first port to the second port, and the second shutoff portion is provided in the fourth flow passage. And a third check valve for blocking the flow of hydraulic oil from the fourth port to the third port, and a third check valve provided in the fourth flow path for hydraulic oil from the third port to the fourth port. A fourth check valve for shutting off the flow, and the second connection oil passage includes a first supply/discharge passage connected to the fifth port and a second supply/discharge passage connected to the sixth port. And a relief valve connected to the second supply/discharge path and capable of lowering a set pressure during the contraction, and an upstream side of the relief valve and a relief valve of the relief valve in the second supply/discharge path. A first bypass oil passage that connects the downstream side to bypass the relief valve, and a first bypass oil passage, which is provided in the first bypass oil passage and prevents the hydraulic oil from flowing from the sixth port side downstream to upstream. A fifth check valve that allows hydraulic oil to flow from upstream to downstream; the float portion is connected to the second supply/discharge path and the first supply/discharge path, and the fifth port and The hydraulic oil of the sixth port is discharged to the discharge oil passage, and the second bypass oil passage connects the upstream of the first bypass oil passage and the downstream of the first bypass oil passage in the second supply/ discharge passage. By connecting the first bypass oil passage, The third bypass valve is provided in the second bypass oil passage, and the third bypass valve communicates with the second bypass oil passage when the float portion is operating and the second bypass oil passage is not operating. Shut off the oil passage .

The hydraulic system of the working machine is connected to the discharge oil passage for discharging the hydraulic oil, the second supply/discharge passage and the first supply/discharge passage, and the hydraulic oil of the fifth port and the sixth port is connected to the discharge oil passage. A second bypass that bypasses the first bypass oil passage by connecting a float portion discharging to the passage and an upstream side of the first bypass oil passage and a downstream side of the first bypass oil passage in the second supply/discharge passage. An oil passage and a second bypass oil passage, which communicate with the second bypass oil passage when the float portion is in operation and shut off the second bypass oil passage when the float portion is not in operation; And 3 switching valves.

According to the present invention, the posture of the hydraulic actuator can be maintained for a long time.

It is a schematic diagram of a hydraulic system of a work machine. It is an enlarged view of an operation part. It is a side view of the working machine.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 3 shows a side view of the working machine according to the present invention. In FIG. 3, the working device 3 mounted on the tractor 2 is shown as an example of the working machine 1. However, the working machine 1 according to the present invention is not limited to the working device 3 mounted on the tractor 2, and may be, for example, another loader working machine or an agricultural machine.

As shown in FIG. 3, the tractor 2 includes a traveling vehicle body (hereinafter referred to as a vehicle body) 4, a prime mover 5, a transmission device 6, and a traveling device 7. The vehicle body 2 is provided with a driver's seat 8. In the embodiment of the present invention, the front side (left side of FIG. 3) of the driver seated in the driver's seat 8 of the work machine 1 is forward, the rear side of the driver (right side of FIG. 3) is rear, and the left side of the driver (FIG. 3 will be described as the left side and the driver's right side (the back side in FIG. 3) as the right side. Further, the horizontal direction, which is a direction orthogonal to the front-back direction, will be described as the width direction. The direction from the central portion of the vehicle body 4 toward the right portion or the left portion will be described as the vehicle outer side. In other words, the outside of the vehicle body is the width direction and the direction away from the central portion of the vehicle body 4. The direction opposite to the outside of the vehicle body will be described as the inside of the vehicle body. In other words, the inside of the machine body is the width direction of the vehicle body and is the direction toward the central portion of the vehicle body 4.

The vehicle body 4 includes a front axle frame 10, a first frame (first support member) 11 projecting outward from the front axle frame 10, and a pair of second frames (second support member) standing upright from the first frame 11. ) 12a, 12b. The prime mover 5 is a diesel engine, a gasoline engine, an electric motor, or the like. In this embodiment, the prime mover 5 is a diesel engine (hereinafter referred to as an engine). The traveling device 7 is a wheel type device having front wheels and rear wheels. The traveling device 7 may be a crawler type (including a semi-crawler type) device.

The work device 3 is a front loader mounted on the second frames 12a and 12b. The front loader 3 includes booms 15a and 15b that are swingably supported by the second frames 12a and 12b, a bucket 16 that is swingably supported by the booms 15a and 15b, and booms 15a and 15b that are extended and retracted to support the booms 15a and 15b. It has a boom hydraulic cylinder 17 for rocking and a bucket hydraulic cylinder 18 for rocking the bucket 16 by expansion and contraction. Therefore, by expanding and contracting the boom hydraulic cylinder 17, the booms 15a and 15b can be swung upward or downward. Further, by expanding and contracting the bucket hydraulic cylinder 18, the bucket 16 can be scooped or dumped. Various preliminary attachments such as a pallet fork, a sweeper, and a mower can be attached to the tips of the booms 15a and 15b. The preliminary attachment is operated by a preliminary hydraulic cylinder 19 (see FIG. 1) provided in the preliminary attachment.

Next, the hydraulic system of the working machine will be described.
FIG. 1 is an overall view of a hydraulic system (hydraulic circuit) of a working machine. As shown in FIG. 1, the hydraulic system of the working machine includes a hydraulic pump P1 and a plurality of control valves 20.
The hydraulic pump P1 is a pump that discharges the hydraulic oil stored in the hydraulic oil tank, and is, for example, a constant capacity type gear pump. The hydraulic pump P1 may be a variable displacement pump. An oil passage 25 is connected to the discharge side of the hydraulic pump P1, and a plurality of control valves 20 are connected to the oil passage 25.

Each of the plurality of control valves 20 is a valve capable of switching the direction in which hydraulic oil flows. Also. Each of the plurality of control valves 20 is a valve that controls a plurality of hydraulic actuators provided in the work machine 1. The hydraulic actuator is a hydraulic cylinder, a hydraulic motor, or the like. In this embodiment, the plurality of hydraulic actuators are hydraulic cylinders, which are a boom hydraulic cylinder 17, a bucket hydraulic cylinder 18, and a preliminary hydraulic cylinder 19.

Hereinafter, for convenience of explanation, the spare hydraulic cylinder 19 is referred to as a “first hydraulic actuator 19,” the bucket hydraulic cylinder 18 is referred to as a “second hydraulic actuator 18,” and the boom hydraulic cylinder 17 is referred to as a “third hydraulic actuator 17.” There is a thing.
As shown in FIG. 1, the plurality of control valves 20 are a first control valve 20A and a second control valve 20B. The first control valve 20A is a valve that controls both the first hydraulic actuator (preliminary hydraulic cylinder) 19 and the second hydraulic actuator (bucket hydraulic cylinder) 18. Second control valve 20
B is a valve that controls the boom hydraulic cylinder (third hydraulic actuator) 17.

The first control valve 20A is a manual direct acting spool type three-position switching valve. The first control valve 20A can be switched to the first position 20a1, the second position 20a2, and the neutral position 20a3 by an operation lever (operation member) provided near the driver's seat 8.
The first control valve 20A and the auxiliary hydraulic cylinder 19 are connected by a first connecting oil passage 31. Specifically, the preliminary hydraulic cylinder 19 includes a tubular body 19a, a rod 19b movably provided on the tubular body 19a, and a piston 19c provided on the rod 19b. A port 19d for supplying/discharging hydraulic oil is provided at the base end portion of the cylindrical body 19a (the side opposite to the rod 19b side). A port 19e for supplying and discharging hydraulic oil is provided at the tip (on the side of the rod 19b) of the cylindrical body 19a.

The first connection oil passage 31 includes a first supply/discharge passage 31a that connects the port 21 and the port 19e of the first control valve 20A, and a second supply/discharge passage that connects the port 22 and the port 19d of the first control valve 20A. And a path 31b.
Therefore, when the first control valve 20A is set to the first position 20a1, the hydraulic oil can be supplied from the second supply/discharge passage 31b to the port 19d of the auxiliary hydraulic cylinder 19, and the port 19e of the auxiliary hydraulic cylinder 19 can be supplied to the first position. The hydraulic oil can be discharged to the first supply/discharge passage 31a. Further, if the first control valve 20A is set to the second position 20a2, the hydraulic oil can be supplied from the first supply/discharge passage 31a to the port 19e of the auxiliary hydraulic cylinder 19 and the port 19d of the auxiliary hydraulic cylinder 19 can be supplied to the first position. 2 The hydraulic oil can be discharged to the supply/discharge passage 31b. Thereby, the preliminary hydraulic cylinder 19 can be expanded and contracted, that is, the preliminary hydraulic cylinder 19 can be operated.

The first control valve 20A and the bucket hydraulic cylinder 18 are connected to each other through a branch oil passage 33 that branches from a midway portion of the first connection oil passage 31. Specifically, the bucket hydraulic cylinder 18 includes a tubular body 18a, a rod 18b movably provided on the tubular body 18a, and a piston 18c provided on the rod 18b. A port 18d for supplying/discharging hydraulic oil is provided at the base end portion (the side opposite to the rod 18b side) of the cylindrical body 18a. A port 18e for supplying and discharging hydraulic oil is provided at the tip (on the side of the rod 18b) of the cylindrical body 18a.

The branch oil passage 33 has a first branch passage 33a connecting the first supply/discharge passage 31a and the port 18e, and a second branch passage 33b connecting the second supply/discharge passage 31b and the port 18d. ..
Therefore, if the first control valve 20A is set to the first position 20a1, the working oil can be supplied from the second supply/discharge passage 31b to the port 18d of the bucket hydraulic cylinder 18 via the second branch passage 33b, and the bucket oil can be supplied. The hydraulic oil can be discharged from the port 18e of the hydraulic cylinder 18 to the first supply/discharge passage 31a via the first branch passage 33a. Further, if the first control valve 20A is set to the second position 20a2, the hydraulic oil can be supplied from the first supply/discharge passage 31a to the port 18e of the bucket hydraulic cylinder 18 via the first branch passage 33a, and the bucket oil can be supplied. The hydraulic oil can be discharged from the port 18d of the hydraulic cylinder 18 to the second supply/discharge passage 31b via the second branch passage 33b. Thereby, the bucket hydraulic cylinder 18 can be expanded and contracted, that is, the bucket hydraulic cylinder 18 can be operated.

The second control valve 20B is a manual direct acting spool type 4-position switching valve. The second control valve 20B can be switched to the first position 20b1, the second position 20b2, the third position 20b3, and the neutral position 20b4 by an operation lever (operation member) provided near the driver's seat 8.
The second control valve 20B and the boom hydraulic cylinder 17 are connected by the second connecting oil passage 32. Specifically, the boom hydraulic cylinder 17 includes a cylindrical body 17a, a rod 17b movably provided on the cylindrical body 17a, and a piston 17c provided on the rod 17b. A port 17d for supplying and discharging hydraulic oil is provided at the base end portion of the cylindrical body 17a (the side opposite to the rod 17b side). A port 17e for supplying/discharging hydraulic oil is provided at the tip (on the rod 17b side) of the cylinder 17a. For convenience of description, the port 17e may be referred to as a "fifth port 17e" and the port 17d may be referred to as a "sixth port 17d".

The second connection oil passage 32 connects the first supply/discharge passage 32a that connects the port 23 of the second control valve 20B and the fifth port 17e, and the port 24 of the second control valve 20B and the sixth port 17d. It has a second supply/discharge path 32b.
Therefore, if the second control valve 20B is set to the first position 20b1, the hydraulic oil can be supplied from the second supply/discharge passage 31b to the sixth port 17d of the boom hydraulic cylinder 17 and the fifth hydraulic cylinder 17 can be supplied. The hydraulic oil can be discharged from the port 17e to the first supply/discharge passage 32a. When the second control valve 20B is set to the second position 20b2, the hydraulic oil can be supplied from the first supply/discharge passage 32a to the fifth port 17e of the boom hydraulic cylinder 17, and the sixth hydraulic pressure of the boom hydraulic cylinder 17 can be increased. The hydraulic oil can be discharged from the port 17d to the second supply/discharge passage 32b. As a result, the boom hydraulic cylinder 17 can be expanded and contracted, that is, the boom hydraulic cylinder 17 can be operated.

The second control valve 20B also has a float portion 34. The float part 34 discharges hydraulic oil from the fifth port 17e (first supply/discharge passage 32a) and the sixth port 17e (second supply/discharge passage 32b) when the second control valve 20 is in the third position 20b3. The oil is discharged to the oil passage 26. That is, the float portion 34 connects the port 23 and the port 24 of the second control valve 20B to the port 27 to which the discharge oil passage 26 is connected, when the float portion 34 is in the third position 20b3. As a result, the hydraulic oil of the fifth port 17e (first supply/discharge passage 32a) and the sixth port 17e (second supply/discharge passage 32b) is discharged to the discharge oil passage 26. The discharge oil passage 26 is connected to the hydraulic oil tank. The connection destination of the discharge oil passage 26 is not limited to this, and may be connected, for example, in the vicinity of the suction port of the hydraulic pump, or may be connected to another place. In this embodiment, the float portion 34 is provided in the second control valve 20B, but it may be provided in another place. In the hydraulic system of this embodiment, the control valve (spill guard valve) 28 is provided in the middle of the first connection oil passage 31 (first supply/discharge passage 32a, second supply/discharge passage 32b). The control valve 28 may not be provided. Further, although the control valve (horizontal control valve) 29 that keeps the bucket 16 horizontal is provided, the horizontal control valve 29 may not be provided. That is, the present invention can be applied to a hydraulic system in which the control valve 28 and the control valve 29 are not provided.

A plurality of switching valves 41 are provided in the section between the first control valve 20A and the first hydraulic actuator (preliminary hydraulic cylinder) 19, that is, in the first connection oil passage 31. A plurality of switching valves 42 are also provided in the section between the first control valve 20A and the second hydraulic actuator (bucket hydraulic cylinder) 18, that is, in the branch oil passage 33. The plurality of switching valves 41 are valves corresponding to the auxiliary hydraulic cylinder 19, and the plurality of switching valves 42 are valves corresponding to the bucket hydraulic cylinder 18. Hereinafter, for convenience of description, the switching valve 41 may be referred to as a “first switching valve 41”, and the switching valve 42 may be referred to as a “second switching valve 42”.

Next, details of the plurality of first switching valves 41 will be described.
As shown in FIGS. 1 and 2, the plurality of first switching valves 41 are a first switching valve 41A and a first switching valve 41B. The first switching valve 41A is a valve provided in the middle of the first supply/discharge passage 31a, and the first switching valve 41B is a valve provided in the middle of the second supply/discharge passage 31b. The first switching valve 41A is a two-position switching valve capable of switching between a first position 41a1 and a second position 41a2. The first switching valve 41 is an electromagnetic switching valve and is switched by the control device 50. Further, the first switching valve 41B is also a two-position switching valve like the first switching valve 41A, and can switch between the first position 41b1 and the second position 41b2. The controller 50 also switches the first switching valve 41B.

41 A of 1st switching valves have the 1st port 51, the 2nd port 52, the 1st flow path 53, the 2nd flow path 54, and the 1st cutoff part 55. The first port 51 is connected to the oil passage 31a1 downstream of the first switching valve 41A in the first supply/discharge passage 31a. That is, the first port 51 is connected to the oil passage 31a1 on the auxiliary hydraulic cylinder 19 side of the first supply/discharge passage 31a. Further, the second port 52 is connected to the oil passage 31a2 upstream of the first switching valve 41A in the first supply/discharge passage 31a. That is, the second port 52 is connected to the oil passage 31a2 on the first control valve 20A side of the first supply/discharge passage 31a.

The first flow path 53 is a flow path that connects the first port 51 and the second port 52 when the first switching valve 41A is in the second position 41a2. In the first flow path 53, hydraulic oil passes from the first port 51 to the second port 52, or hydraulic oil passes from the second port 52 to the first port 51. The second flow path 54 is a flow path different from the first flow path 53. The second flow path 54 is an oil path that blocks the flow of hydraulic oil via the first blocking section 55.

The first cutoff portion 55 is provided in the second flow path 54, cuts off the flow of the hydraulic oil from the second port 52 to the first port 51, and moves from the first port 51 to the second port 52. It is a part that shuts off the flow of hydraulic oil. The first cutoff portion 55 includes a first check valve 55A and a second check valve 55B. Each of the first check valve 55A and the second check valve 55B is provided on the same straight line of the second flow path 54, and the valve portions that prevent the backflow of the hydraulic oil face each other (opposite each other). Exist). That is, the first check valve 55A blocks (blocks) the hydraulic oil that has flowed into the second flow path 54 from the second port 52 from flowing into the first port 51. The second check valve 55B shuts off (blocks) the hydraulic oil flowing from the first port 51 into the second flow path 54 to the second port 52.

The 1st switching valve 41B has the 1st port 51, the 2nd port 52, the 1st flow path 53, the 2nd flow path 54, and the 1st cutoff part 55 similarly to the 1st switching valve 41A. doing. The first switching valve 41B is different in connection destination from the first switching valve 41A, but has the same structure, and thus the description of the structure will be omitted.
The first port 51 of the first switching valve 41B is connected to the oil passage 31b1 downstream of the first switching valve 41B in the second supply/discharge passage 31b. That is, the first port 51 is connected to the oil passage 31b1 on the auxiliary hydraulic cylinder 19 side of the second supply/discharge passage 31b. Further, the second port 52 is connected to the oil passage 31b2 upstream from the first switching valve 41B in the second supply/discharge passage 31b. That is, the second port 52 is connected to the oil passage 31b2 on the first control valve 20A side of the second supply/discharge passage 31b.

The control device 50 simultaneously switches the plurality of first switching valves 41 (first switching valves 41A and 41B). Specifically, the controller 50 is connected to a switch 56 that selects the first hydraulic actuator (preliminary hydraulic cylinder 19) 19 or the second hydraulic actuator (bucket hydraulic cylinder) 18. When the auxiliary actuator 19 (preliminary attachment) is selected by the switch 56, the control device 50 simultaneously excites the solenoid of the first switching valve 41A and the solenoid of the first control valve 41B. On the other hand, when the bucket hydraulic cylinder 18 (bucket 16) is selected by the switch 56, the control device 50 simultaneously demagnetizes the solenoid of the first switching valve 41A and the solenoid of the first control valve 41B.

As described above, according to the first switching valve 41, if the first switching valve 41A is switched to the first position 41a1 and the first switching valve 41B is switched to the first position 41b1, the first check valve 55A and the second check valve. The valve 55B can reliably block the communication between the first port 51 and the second port 52 (the second flow path 54). That is, by setting the first switching valve 41A to the first position 41a1 and the first switching valve 41B to the first position 41b2, the oil passage 31a1 of the first supply/discharge passage 31a (the first switching valve 41A and the backup hydraulic cylinder 19 It is possible to suppress the discharge of the hydraulic oil in the section (1) to the first switching valve 41A. Further, it is possible to suppress the discharge of the hydraulic oil in the oil passage 31b1 (the section between the first switching valve 41B and the preliminary hydraulic cylinder 19) of the second supply/discharge passage 31b to the first switching valve 41B.

Conventionally, the outer peripheral surface of the spool blocks communication between the first port and the second port. Therefore, the hydraulic oil that slightly leaks from the gap between the outer peripheral surface of the spool and the inner wall of the valve element causes the posture of the preliminary hydraulic cylinder 19 to slightly change, and the posture of the preliminary hydraulic cylinder 19 can be maintained for a long time. Is difficult. On the other hand, in the present invention, since the communication between the first port 51 and the second port 52 is blocked by the first blocking portion 55 (the first check valve 55A and the second check valve 55B), the conventional problem It is possible to prevent the hydraulic oil from leaking. As a result, the posture of the preliminary hydraulic cylinder 19 can be maintained for a long time.

Next, details of the plurality of second switching valves 42 will be described.
The plurality of second switching valves 42 are a second switching valve 42A and a second switching valve 42B. The second switching valve 42A is a valve provided in the middle of the first branch passage 33a, and the second switching valve 42B is a valve provided in the middle of the second branch passage 33b. The second switching valve 42A is a two-position switching valve capable of switching between the third position 42a1 and the fourth position 42a2. The second switching valve 42A and the second switching valve 42B are electromagnetic switching valves. The switching of the second switching valve 42A is performed by the second switching valve 42A.
This can be done by exciting or demagnetizing the solenoid of. The control device 50 excites or demagnetizes the solenoid of the second switching valve 42A. The second switching valve 42B is also a two-position switching valve, like the second switching valve 42A, and can switch between the third position 42b1 and the fourth position 42b2. The switching of the second switching valve 42B can be performed by exciting or demagnetizing the solenoid of the second switching valve 42B. The control device 50 excites or demagnetizes the solenoid of the second switching valve 42B.

The second switching valve 42A has a third port 61, a fourth port 62, a third flow passage 63, a fourth flow passage 64, and a second cutoff portion 65. The third port 61 is connected to the oil passage 33a1 downstream of the second switching valve 42A in the first branch passage 33a. That is, the third port 61 is connected to the oil passage 33a1 on the bucket hydraulic cylinder 18 side of the first branch passage 33a. The fourth port 62 is connected to the oil passage 33a2 upstream of the second switching valve 42A in the first branch passage 33a. That is, the fourth port 62 is connected to the oil passage 33a2 on the first control valve 20A side of the first branch passage 33a.

The third flow passage 63 is a flow passage that connects the third port 61 and the fourth port 62 when the second switching valve 42A is in the fourth position 42a2. In the third flow passage 63, hydraulic oil passes from the third port 61 to the fourth port 62, or hydraulic oil passes from the fourth port 62 to the third port 61. The fourth flow path 64 is a flow path different from the third flow path 63. The fourth flow path 64 is an oil path that blocks the flow of hydraulic oil via the second blocking section 56.

The second cutoff portion 65 is provided in the fourth flow path 64, cuts off the flow of the hydraulic oil from the fourth port 62 to the third port 61, and moves from the third port 61 to the fourth port 62. It is a part that shuts off the flow of hydraulic oil. The second cutoff portion 65 includes a third check valve 65A and a fourth check valve 65B. Each of the third check valve 65A and the fourth check valve 65B is provided on the same straight line of the fourth flow path 64, and the valve portions that prevent the reverse flow of the hydraulic oil face each other (opposite each other). Exist). That is, the third check valve 65</b>A blocks (blocks) the hydraulic oil flowing from the fourth port 62 into the fourth flow path 64 from flowing into the third port 61. The fourth check valve 65</b>B blocks (blocks) the hydraulic oil flowing from the third port 61 into the fourth flow path 64 from flowing into the fourth port 62.

Like the second switching valve 42A, the second switching valve 42B has a third port 61, a fourth port 62, a third flow passage 63, a fourth flow passage 64, and a second cutoff portion 65. doing. The second switching valve 42B is different in connection destination from the second switching valve 42A, but has the same structure, and thus the description of the structure will be omitted.
The third port 61 of the second switching valve 42B is connected to the oil passage 33b1 downstream of the second switching valve 42B in the second branch passage 33b. That is, the third port 61 is connected to the oil passage 33b1 on the bucket hydraulic cylinder 18 side of the second branch passage 33b. Further, the fourth port 62 is connected to the oil passage 33b2 upstream of the second switching valve 42B in the second branch passage 33b. That is, the fourth port 62 is connected to the oil passage 33b2 on the first control valve 20A side of the second branch passage 33b.

The control device 50 simultaneously switches the plurality of second switching valves 42 (second switching valves 42A and 42B). Specifically, when the preliminary actuator 19 is selected by the switch 56, the control device 50 simultaneously energizes the solenoid of the second switching valve 42A and the solenoid of the second control valve 42B. On the other hand, when the bucket hydraulic cylinder 18 (bucket 16) is selected by the switch 56, the control device 50 simultaneously demagnetizes the solenoid of the second switching valve 42A and the solenoid of the second control valve 42B. That is, the plurality of second switching valves 42 switch to the fourth positions 42a2 and 42b2 when the plurality of first switching valves 41 switch to the first positions 41a1 and 41b1. The plurality of second switching valves 42 switch to the third positions 42a1 and 42b1 when the plurality of first switching valves 41 switch to the second positions 41a2 and 41b2. Therefore, the plurality of first switching valves 41 and the plurality of second switching valves 42 are switched in the opposite directions. Therefore, the preliminary hydraulic cylinder 19 and the bucket hydraulic cylinder 18 can be stably and independently operated by the plurality of first switching valves 41, the plurality of second switching valves 42, and the first control valve 20A.

According to the second switching valve 42 described above, the branch oil passage 33 can be shut off by switching the second switching valve 42A to the third position 42a1 and switching the second switching valve 42B to the third position 42b1. .. That is, it is possible to prevent the hydraulic oil in the oil passage 33a1 (the section between the second switching valve 42A and the bucket hydraulic cylinder 18) of the first branch passage 33a from being discharged to the second switching valve 42A. Further, it is possible to suppress the hydraulic oil in the oil passage 33b1 (the section between the second switching valve 42B and the bucket hydraulic cylinder 18) of the second branch passage 33b from being discharged to the second switching valve 42B. That is, also in the second switching valve 42A, the second shutoff portion 65 (the first check valve 55A and the second check valve 55B) shuts off the communication between the third port and the fourth port. It is possible to prevent the hydraulic oil from leaking like a problem. As a result, the attitude of the bucket hydraulic cylinder 18 can be maintained for a long time.

In particular, the working machine 1 in this embodiment includes the first switching valve 41 and the second switching valve 42. Therefore, in various operations, the posture of the preliminary attachment (preliminary hydraulic cylinder 19) or the bucket 16 (bucket hydraulic cylinder 18) can be supported for a long time while the heavy weight is supported by the preliminary attachment and the bucket 16.
Next, the boom hydraulic cylinder (third hydraulic actuator) 17 and the second connecting oil passage 32 will be described. The second connecting oil passage 32 is provided with an operating portion 70. When the boom hydraulic cylinder 17 is extended and stopped (when the booms 15a and 15b are lifted and stopped), the operating portion 70 transfers the hydraulic oil of the boom hydraulic cylinder 17 from the sixth port 17d to the second connection oil passage. Prevents you from exiting to 32. That is, the operating unit 70 holds the booms 15a and 15b in a raised state. Further, when the boom hydraulic cylinder 17 is contracted (when the booms 15a and 15b are lowered), the operating unit 70 controls that the hydraulic oil of the boom hydraulic cylinder 17 flows from the sixth port 17d to the second connection oil passage 32. Tolerate. That is, when lowering the booms 15a and 15b, the operating unit 70 can release the holding of the booms 15a and 15b and lower the booms 15a and 15b.

Specifically, the operating unit 70 has a relief valve 71, a first bypass oil passage 72, and a fifth check valve 73. The relief valve 71 is a valve whose set pressure can be changed, and is connected to a middle portion of the second supply/discharge passage 32b. An oil passage 76 is connected to the pressure receiving portion 71a of the relief valve 71, and the oil passage 76 is connected to the first supply/discharge passage 32a. Therefore, when the pressure of the hydraulic oil acts on the first supply/discharge passage 32a, the pressure acting on the first supply/discharge passage 32a acts on the pressure receiving portion 71a, and the set pressure of the relief valve 71 can be lowered. On the other hand, when the pressure of the hydraulic oil does not act on the first supply/discharge passage 32a, the pressure does not act on the pressure receiving portion 71a, so that the set pressure of the relief valve 71 can be increased.

The first bypass oil passage 72 is an oil passage connected to the second supply/discharge passage 32b, and bypasses the relief valve 71 by connecting the upstream side of the relief valve 71 and the downstream side of the relief valve 71. That is, the first bypass oil passage 7 2, in the second supply and discharge passage 32 b, (upstream of the section of the relief valve 71) section that connects the port 71 b1 and the port 24 of the second control valve 20B of the relief valve 71 32b1 and , A section that connects the port 71b 2 of the leaf valve 71 and the sixth port 17d of the boom hydraulic cylinder 17 (section downstream of the relief valve 71) 32b2.

The fifth check valve 73 is provided in the middle of the first bypass oil passage 72. The fifth check valve 73 prevents the hydraulic oil from flowing from the downstream to the upstream and allows the hydraulic oil to flow from the upstream to the downstream.
Therefore, when the booms 15a and 15b are raised (when the second control valve 20B is set to the first position 20b1), the pressure of the hydraulic oil acting on the pressure receiving portion 71a of the relief valve 71 rises, and the operation is performed. The set pressure of the relief valve 71 rises due to the oil pressure. Therefore, when the booms 15a and 15b are stopped at the raised position, the hydraulic oil in the second supply/discharge passage 32b passes through the relief valve 71 and the fifth check valve 73 and then escapes to the second control valve 20B. Can be prevented. That is, the booms 15a and 15b can be held in the raised posture (raised posture). On the other hand, when the booms 15a and 15b are lowered, the pressure of the hydraulic oil that has acted on the pressure receiving portion 71a of the relief valve 71 decreases, so the set pressure of the relief valve 71 decreases. Therefore, when the booms 15a and 15b are lowered (when the second control valve 20B is set to the second position 20b2), the hydraulic oil in the second supply/discharge passage 32b passes through the relief valve 71 and the second control is performed. The booms 15a and 15b can be lowered because they escape to the valve 20B.

The hydraulic system also includes a second bypass oil passage 74 and a third switching valve 75.
The second bypass oil passage 74 connects the upstream side of the first bypass oil passage 72 and the downstream side of the first bypass oil passage 72 in the second supply/discharge passage 32b. Specifically, the second bypass oil passage 74 is connected to the section 32b1 on the upstream side of the connecting portion 72a that connects the section 32b1 of the second supply/discharge passage 32b and the first bypass oil passage 72. The second bypass oil passage 74 is connected to the section 32b2 on the downstream side of the connecting portion 72b that connects the section 32b2 of the second supply/discharge passage 32b and the first bypass oil passage 72.

The third switching valve 75 is provided in the middle of the second bypass oil passage 74. The third switching valve 75 is a two-position switching valve that can switch between the first position 75a and the second position 75b. The switching of the third switching valve 75 can be performed by exciting or demagnetizing the solenoid of the third switching valve 75. The third switching valve 75 communicates with the second bypass oil passage 74 by switching to the second position 75b when the float portion 34 operates. The third switching valve 75 shuts off the second bypass oil passage 74 when the float portion 34 is not operating. The structure of the third switching valve 75 is the same as that of the first switching valve 41 and the second switching valve 42, and the description thereof will be omitted.

Therefore, although the boom 15a, 15b can be held in the raised posture by the operating portion 70, if the third switching valve 75 is switched to the second position 75b, the hydraulic oil in the sixth port 17d of the boom hydraulic cylinder 17 is discharged. Then, the booms 15a and 15b can be floated.
The embodiments disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

1 Working machine 31 First connection oil passage 41, 41A, 41B Switching valve (first switching valve)
42, 42A, 42B switching valve (second switching valve)
41a1 1st position 41a2 2nd position 41b1 1st position 41b2 2nd position 42a1 3rd position 42a2 4th position 42b1 3rd position 42b2 4th position 51 1st port 52 2nd port 53 1st flow path 54 2nd flow path 55 1st cutoff part 55A 1st check valve 55B 2nd check valve 61 3rd port 62 4th port 63 3rd flow path 64 4th flow path 65 2nd cutoff part 65A 3rd check valve 65B 4th check Stop valve 70 Actuator 71 Relief valve 72 First bypass oil passage 73 Fifth check valve 74 Second bypass oil passage 75 Third switching valve 76 Oil passage

Claims (10)

A first hydraulic actuator,
A first connection oil passage connected to the first hydraulic actuator;
Switchable between a first position and a second position,
A first port connected to the first connection oil passage, a second port connected to the first connection oil passage at a position different from the first port, and the first port and the second port are communicated with each other. A first flow path that is different from the first flow path, a second flow path different from the first flow path, and a second flow path that blocks the flow of hydraulic oil from the second port to the first port and A switching valve having a shutoff unit for shutting off the flow of hydraulic oil from one port to the second port;
A discharge oil passage for discharging hydraulic oil,
A third hydraulic actuator having a fifth port and a sixth port, which expands when hydraulic oil is supplied to the sixth port and contracts when hydraulic oil is supplied to the fifth port;
A second connection oil passage having a first supply/discharge passage connected to the fifth port and a second supply/discharge passage connected to the sixth port;
When the third hydraulic actuator expands, the hydraulic oil supplied to the sixth port is prevented from flowing out to the second connection oil passage, and the sixth hydraulic actuator contracts when the third hydraulic actuator contracts. Allowing the hydraulic oil supplied to the port to escape to the second connecting oil passage,
A relief valve connected to the second supply/discharge path and capable of reducing the set pressure during the contraction, and a relief valve by connecting the upstream side of the relief valve and the downstream side of the relief valve in the second supply/discharge path. And a first bypass oil passage that bypasses the first bypass oil passage and that prevents the working oil from flowing from the downstream side to the upstream side that is the sixth port side and that the working oil flows from the upstream side to the downstream side. An actuating portion having a fifth check valve for allowing;
A float part which is connected to the second supply/discharge path and the first supply/discharge path and discharges the hydraulic oil of the fifth port and the sixth port to the discharge oil path;
A second bypass oil passage that bypasses the first bypass oil passage by connecting an upstream side of the first bypass oil passage and a downstream side of the first bypass oil passage in the second supply/discharge passage;
A third switching valve that is provided in the second bypass oil passage, connects the second bypass oil passage when the float portion is operating, and shuts off the second bypass oil passage when the float portion is not operating; ,
Is equipped with a hydraulic system of the working machine. The shut-off portion is provided in the second flow passage and is provided in the second flow passage, and a first check valve that shuts off a flow of hydraulic oil from the second port to the first port. The hydraulic system for a working machine according to claim 1, further comprising a second check valve that shuts off a flow of hydraulic oil from one port to the second port. A first hydraulic actuator,
A first connection oil passage connected to the first hydraulic actuator;
Switchable between a first position and a second position,
A first port connected to the first connection oil passage, a second port connected to the first connection oil passage at a position different from the first port, and the first port and the second port are communicated with each other. A first flow path that is different from the first flow path, a second flow path different from the first flow path, and a second flow path that blocks the flow of hydraulic oil from the second port to the first port and A plurality of first switching valves having a first cutoff portion for cutting off the flow of hydraulic oil from one port to the second port;
A discharge oil passage for discharging hydraulic oil,
A third hydraulic actuator having a fifth port and a sixth port, which expands when hydraulic oil is supplied to the sixth port and contracts when hydraulic oil is supplied to the fifth port;
A second connection oil passage having a first supply/discharge passage connected to the fifth port and a second supply/discharge passage connected to the sixth port;
When the third hydraulic actuator expands, the hydraulic oil supplied to the sixth port is prevented from flowing out to the second connection oil passage, and the sixth hydraulic actuator contracts when the third hydraulic actuator contracts. Allowing the hydraulic oil supplied to the port to escape to the second connecting oil passage,
A relief valve connected to the second supply/discharge path and capable of lowering the set pressure during the contraction, and the relief valve by connecting the upstream side of the relief valve and the downstream side of the relief valve in the second supply/discharge path. And a first bypass oil passage that bypasses the first bypass oil passage and that prevents the working oil from flowing from the downstream side to the upstream side that is the sixth port side and that the working oil flows from the upstream side to the downstream side. An actuating part having a fifth check valve to allow,
A float part which is connected to the second supply/discharge path and the first supply/discharge path and discharges the hydraulic oil of the fifth port and the sixth port to the discharge oil path;
A second bypass oil passage that bypasses the first bypass oil passage by connecting an upstream side of the first bypass oil passage and a downstream side of the first bypass oil passage in the second supply/discharge passage;
A third switching valve that is provided in the second bypass oil passage, connects the second bypass oil passage when the float portion is operating, and shuts off the second bypass oil passage when the float portion is not operating; ,
Is equipped with a hydraulic system of the working machine. The first cutoff portion is provided in the second flow passage, and is provided in the second flow passage, and a first check valve that shuts off a flow of hydraulic oil from the second port to the first port. The hydraulic system for a working machine according to claim 3, further comprising a second check valve that shuts off a flow of hydraulic oil from the first port to the second port. The said several 1st switching valve is an electromagnetic switching valve which can switch to said 1st position and said 2nd position, and it switches to either of said 1st position and said 2nd position simultaneously. Hydraulic system for the described work machine. A branched oil passage branched from the first connection oil passage,
A second hydraulic actuator connected to the branch oil passage,
A plurality of second switching valves provided on the branch oil passage and switchable between a third position and a fourth position;
Equipped with
The plurality of second switching valves,
A third port connected to the branch oil passage,
A fourth port connected to the branch oil passage at a position different from the third port,
A third flow path connecting the third port and the fourth port,
A fourth flow path different from the third flow path,
A second shut-off portion provided in the fourth flow passage for shutting off the flow of hydraulic oil from the fourth port to the third port and shutting off the flow of hydraulic oil from the third port to the fourth port; ,
The hydraulic system for a working machine according to any one of claims 3 to 5, further comprising: The second cutoff portion is provided in the fourth flow passage, and is provided in the fourth flow passage, and a third check valve that shuts off the flow of the hydraulic oil from the fourth port to the third port. The hydraulic system for a working machine according to claim 6, further comprising a fourth check valve that shuts off a flow of hydraulic oil from the third port to the fourth port. The said 2nd switching valve is an electromagnetic switching valve which can be switched to said 3rd position and said 4th position, It switches to either of said 3rd position and said 4th position at the same time to Claim 6 or 7. Hydraulic system for the described work machine. The plurality of second switching valves switch to the fourth position when the plurality of first switching valves switch to the first position, and the plurality of first switching valves switch to the second position The hydraulic system for a working machine according to claim 6, wherein the hydraulic system is switched to the third position. A spare hydraulic cylinder that operates a spare attachment mounted on the boom,
A first connecting oil passage connected to the preliminary hydraulic cylinder;
A plurality of first switching valves provided in the first connection oil passage and switchable between a first position and a second position;
A branched oil passage branched from the first connection oil passage,
A bucket hydraulic cylinder that is connected to the branch oil passage and swings a bucket attached to the boom;
A plurality of second switching valves provided on the branch oil passage and switchable between a third position and a fourth position;
A third hydraulic actuator having a fifth port and a sixth port, which expands when hydraulic oil is supplied to the sixth port and contracts when hydraulic oil is supplied to the fifth port;
A second connection oil passage connected to the fifth port and the sixth port of the third hydraulic actuator;
When the third hydraulic actuator expands, the hydraulic oil supplied to the sixth port is prevented from flowing out to the second connection oil passage, and the sixth hydraulic actuator contracts when the third hydraulic actuator contracts. An operating portion that allows the hydraulic oil supplied to the port to escape to the second connecting oil passage;
A discharge oil passage for discharging hydraulic oil,
A float part for discharging the hydraulic oil of the fifth port and the sixth port to the discharge oil passage,
A second bypass oil passage,
A third switching valve,
Equipped with
The plurality of first switching valves,
A first port connected to the first connection oil passage,
A second port connected to the first connection oil passage at a position different from the first port;
A first flow path that is a flow path that communicates the first port and the second port when in the second position;
A second flow path that is different from the first flow path and that is connected to the first port and the second port when in the first position;
A first cutoff portion provided in the second flow passage, for cutting off a flow of the hydraulic oil from the second port to the first port and for cutting a flow of the hydraulic oil from the first port to the second port; ,
Have
The plurality of second switching valves,
A third port connected to the branch oil passage,
A fourth port connected to the branch oil passage at a position different from the third port,
A third flow path that is a flow path that communicates the third port and the fourth port when in the fourth position,
A fourth flow path which is a flow path different from the third flow path, and which is connected to the third port and the fourth port when in the third position;
A second shut-off portion provided in the fourth flow passage for shutting off the flow of hydraulic oil from the fourth port to the third port and shutting off the flow of hydraulic oil from the third port to the fourth port; ,
Have
The plurality of first switching valves are electromagnetic switching valves capable of switching to the first position and the second position, and are switched to either the first position or the second position at the same time,
The plurality of second switching valves are electromagnetic switching valves capable of switching to the third position and the fourth position, and simultaneously switch to any one of the third position and the fourth position,
The plurality of second switching valves,
By switching to the fourth position when the plurality of first switching valves switch to the first position and the first cutoff portion blocks the hydraulic oil from flowing to the auxiliary hydraulic cylinder, the first switching valve switches to the fourth position. 3 passages allow hydraulic oil to flow to the bucket hydraulic cylinder,
By switching to the third position when the plurality of first switching valves switch to the second position and the first flow passage allows hydraulic oil to flow to the preliminary hydraulic cylinder, 2 cut off the flow to the bucket hydraulic cylinder,
The first cutoff portion is provided in the second flow passage, and is provided in the second flow passage, and a first check valve that shuts off a flow of hydraulic oil from the second port to the first port. A second check valve for shutting off the flow of hydraulic oil from the first port to the second port,
The second cutoff portion is provided in the fourth flow passage, and is provided in the fourth flow passage, and a third check valve that shuts off the flow of the hydraulic oil from the fourth port to the third port. A fourth check valve for shutting off the flow of hydraulic oil from the third port to the fourth port,
The second connection oil passage has a first supply/discharge passage connected to the fifth port and a second supply/discharge passage connected to the sixth port,
The operating unit is
A relief valve connected to the second supply/discharge path and capable of reducing the set pressure during the contraction;
A first bypass oil passage that bypasses the relief valve by connecting the upstream side of the relief valve and the downstream side of the relief valve in the second supply/discharge path;
A fifth check valve provided in the first bypass oil passage, which prevents the hydraulic oil from flowing from the downstream side to the upstream side which is the sixth port side and allows the hydraulic oil to flow from the upstream side to the downstream side;
Have
The float portion is connected to the second supply/discharge path and the first supply/discharge path, and discharges the hydraulic oil of the fifth port and the sixth port to the discharge oil path ,
The second bypass oil passage bypasses the first bypass oil passage by connecting an upstream side of the first bypass oil passage and a downstream side of the first bypass oil passage in the second supply/discharge passage,
The third switching valve is provided in the second bypass oil passage, connects the second bypass oil passage when the float portion is operating, and opens the second bypass oil passage when the float portion is not operating. Hydraulic system of work machine to shut off .

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