JP2013040641A - Hydraulic circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve regeneration efficiency even when controlling supply of oil to a hydraulic cylinder of requiring quick operation.SOLUTION: A regeneration directional control valve 60 for switching a communicating state between a head side oil passage 42 and a bottom side oil passage 41, is constituted so as to cut off a regeneration oil passage 45 in an ordinary state and to also communicate the regeneration oil passage 45 only when pressure between a head chamber 10b and a variable throttle valve 50 becomes higher by exceeding a set value than pressure between the variable throttle valve 50 and directional control valve 30. The variable throttle valve 50 arranged up to the directional control valve 30 from a connecting point with the regeneration oil passage 45 in the head side oil passage 42, is constituted so as to maintain the opening area of an orifice in a minimum value in the ordinary state and to also increase the opening area of the orifice in response to the size of differential pressure when the pressure between the head chamber 10b and the variable throttle valve 50 becomes higher by exceeding the set value than the pressure between the variable throttle value 50 and the directional control valve 30.

Description

  The present invention relates to a hydraulic circuit, and more specifically, between a head-side oil passage that circulates oil to a head chamber of a hydraulic cylinder and a bottom-side oil passage that circulates oil to a bottom chamber of the hydraulic cylinder. And a regeneration switching valve that switches between a state where the head side oil passage and the bottom side oil passage are communicated with the regeneration oil passage and a state where it is shut off.

  A construction machine in which a work machine is operated by a hydraulic cylinder is provided with a hydraulic circuit including a regenerative oil passage and a regenerative switching valve. In this hydraulic circuit, a regenerative oil passage connects between a head-side oil passage that circulates oil to the head chamber of the hydraulic cylinder and a bottom-side oil passage that circulates oil to the bottom chamber of the hydraulic cylinder. In addition, a regeneration switching valve is disposed in the regeneration oil passage. When in the normal state, the regeneration switching valve is maintained in a state where the regeneration oil passage is shut off. On the other hand, when the hydraulic cylinder is extended, a part of the pilot pressure output from the operation valve to the direction switching valve is applied to the regeneration switching valve, and the regeneration switching valve opens to open the regeneration oil passage. Is done.

  Therefore, according to this hydraulic circuit, a part of the oil discharged from the head chamber of the hydraulic cylinder can be supplied to the bottom chamber without returning to the oil tank, and the hydraulic cylinder can be quickly extended. Moreover, since the switching valve for regeneration is switched by the pilot pressure output from the operation valve, the oil always passes through the regeneration oil passage when the hydraulic cylinder is extended regardless of the operation amount of the operation valve. Is regenerated, which is advantageous in terms of oil regeneration efficiency (see, for example, Patent Document 1).

  The technique disclosed in Patent Document 1 focuses on a hydraulic cylinder for an arm of a hydraulic excavator. Patent Document 1 does not disclose the position where the regeneration switching valve is installed, but the regeneration switching valve is located near the direction switching valve in order to avoid lengthening the pipe for applying the pilot pressure to the regeneration switching valve. It is preferable to install in. However, when it is arranged in the vicinity of the direction switching valve, the distance from the hydraulic cylinder to the regeneration switching valve becomes long, and the pressure loss also increases.

  The hydraulic cylinder for an arm of a hydraulic excavator to which Patent Document 1 is applied is driven while controlling the movement of the arm, and thus does not require a quick operation such as a natural fall. For this reason, since the meter-out opening area can be set small and the upstream pressure can be increased, the effective differential pressure between the bottom chamber and the head chamber is set relatively large, and the pressure loss described above However, it does not significantly affect the oil regeneration efficiency.

  However, for example, in a hydraulic cylinder that lifts and lowers a bulldozer blade, there are some that require a quick operation for a driven object such as a natural drop of the blade. In a hydraulic circuit including such a hydraulic cylinder, the meter-out opening area cannot be set small, and it is difficult to increase the effective differential pressure between the bottom chamber and the head chamber. For this reason, when the position where the switching valve for regeneration is provided is away from the hydraulic cylinder, the oil regeneration efficiency may be significantly lowered due to the effect of pressure loss. In order to reduce the pressure loss and increase the regeneration efficiency, it is effective to arrange the regeneration switching valve in the vicinity of the hydraulic cylinder and shorten the pipe length between the regeneration switching valve and the hydraulic cylinder. However, in this case, as described above, there is a problem that the piping for applying the pilot pressure to the regeneration switching valve becomes long.

  On the other hand, a hydraulic circuit provided with a regeneration oil passage and a regeneration switching valve is provided in which the regeneration switching valve is switched without depending on the pilot pressure from the operation valve. For example, in the hydraulic circuit shown in FIGS. 5 and 6, the throttle 5 is arranged between the connection point of the regenerative oil passage 3 and the direction switching valve 4 in the head side oil passage 2 connected to the head chamber 1 a of the hydraulic cylinder 1. The regeneration switching valve 6 is switched by the differential pressure across the throttle 5.

  In this hydraulic circuit, when the pressure on the upstream side of the throttle 5 becomes larger than the pressure set on the downstream side, the state shown in FIG. 5 is switched to the state shown in FIG. 6, and the regenerated oil passage 3 is opened. Therefore, the head side oil passage 2 and the bottom side oil passage 7 are communicated with each other, and a part of the oil discharged from the head chamber 1a of the hydraulic cylinder 1 is supplied to the bottom chamber 1b without passing through the direction switching valve 4. Therefore, the extension operation of the hydraulic cylinder 1 can be performed quickly. In addition, since the piping for applying the pilot pressure to the regeneration switching valve 6 is not required, the regeneration switching valve 6 can be disposed in the vicinity of the hydraulic cylinder 1, and the blade can be quickly dropped. Even when applied to a hydraulic cylinder 1 that requires operation, there is no risk of impairing the oil regeneration efficiency.

JP-A-11-230107

  Incidentally, in a hydraulic circuit applied to a construction machine, a meter-out opening area 4a is set in the direction switching valve 4 in order to suppress the influence on the hydraulic cylinder 1 when a load change occurs. In the conventional hydraulic circuit shown in FIGS. 5 and 6, the opening area of the above-described throttle 5 cannot be set smaller than the meter-out opening area 4a. For this reason, the operation amount of the operation valve (not shown) is small, and it is difficult to switch the regeneration switching valve 6 only by passing a small amount of oil through the head side oil passage 2, and a relatively large amount of oil is generated. It is not necessarily preferable in terms of regeneration efficiency, for example, oil regeneration can be performed only when it passes.

  In view of the above circumstances, an object of the present invention is to provide a hydraulic circuit that can improve regeneration efficiency even when oil supply control is performed on a hydraulic cylinder that requires quick operation.

  In order to achieve the above object, a hydraulic circuit according to the present invention includes a head-side oil passage that circulates oil to a head chamber of a hydraulic cylinder, and a bottom-side oil passage that circulates oil to a bottom chamber of the hydraulic cylinder. Directional switching for controlling the drive of the hydraulic cylinder by switching the connection mode of the oil supply passage with respect to the head side oil passage and the bottom side oil passage, and an oil supply passage for supplying oil discharged from the hydraulic pump A valve, a reclaimed oil passage connecting between the head side oil passage and the bottom side oil passage, and a state in which the head side oil passage and the bottom side oil passage are communicated with each other. A regenerative switching valve that switches to a shut-off state, and a variable throttle valve that is disposed in the head side oil passage between a connection point with the regenerative oil passage and the direction switching valve, The normal switching valve shuts off the regenerated oil passage in a normal state, while the pressure between the head chamber and the variable throttle valve is higher than the pressure between the variable throttle valve and the direction switching valve. The regenerative oil passage is configured to communicate only when the value exceeds a set value, and the variable throttle valve maintains a throttle opening area at a minimum value in a normal state, while the head chamber and When the pressure between the variable throttle valve and the pressure between the variable throttle valve and the direction switching valve is higher than a set value, the opening area of the throttle according to the magnitude of the differential pressure It is characterized by having become large.

  In the hydraulic circuit described above, the present invention provides a check valve for providing a bypass oil passage to the variable throttle valve and preventing passage of oil from the head chamber toward the direction switching valve in the bypass oil passage. Is provided.

  The hydraulic circuit according to the present invention includes a head-side oil passage that circulates oil to the head chamber of the hydraulic cylinder, a bottom-side oil passage that circulates oil to the bottom chamber of the hydraulic cylinder, and a hydraulic pump. An oil supply passage for supplying discharged oil, a direction switching valve for controlling driving of the hydraulic cylinder by switching a connection mode of the oil supply passage with respect to the head side oil passage and the bottom side oil passage, and the head A reclaimed oil passage connecting the side oil passage and the bottom oil passage, and a state of being disposed in the reclaimed oil passage and communicating between the head side oil passage and the bottom side oil passage A regenerative switching valve that switches between the connection point of the head side oil passage and the regenerative oil passage to the direction switching valve, and a front side of the head side oil passage. A bypass oil passage that bypasses the variable throttle valve from the connection point with the regenerative oil passage and connects to the direction switching valve, and is disposed in the bypass oil passage, and is directed from the head chamber to the direction switching valve. A check valve for blocking the passage of oil, and the regeneration switching valve shuts off the regeneration oil passage in a normal state, while the pressure between the head chamber and the variable throttle valve is variable. The regenerative oil passage is configured to communicate only when the pressure between the throttle valve and the direction switching valve exceeds a set value, and the variable throttle valve is configured to restrict the throttle in a normal state. While maintaining the opening area at a minimum value, the pressure between the head chamber and the variable throttle valve is higher than the set value than the pressure between the variable throttle valve and the direction switching valve. In case before the differential pressure according to the magnitude Characterized by being configured so that the opening area of the throttle is large.

  According to the present invention, the variable throttle valve is disposed in the head side oil passage between the connection point with the regenerative oil passage and the direction switching valve, and the variable throttle valve minimizes the opening area of the throttle in the normal state. If the pressure between the head chamber and the variable throttle valve becomes higher than the value set between the variable throttle valve and the direction switching valve, the pressure difference is maintained. Since the aperture area of the diaphragm is large, the amount of operation is small, and even when a relatively small amount of oil is passed through, the oil can be regenerated and the regeneration efficiency can be improved. It becomes. In addition, when a large amount of oil is allowed to pass, the opening area of the throttle also increases, so that the operation of the hydraulic cylinder can be controlled by operating the operation valve.

FIG. 1 is a diagram showing a hydraulic circuit according to an embodiment of the present invention. FIG. 2 is a diagram showing a state in which the regeneration switching valve is operated in the hydraulic circuit shown in FIG. FIG. 3 is a diagram showing a state where the variable throttle valve is operated in the hydraulic circuit shown in FIG. FIG. 4 is a perspective view conceptually showing a construction machine to which the hydraulic circuit shown in FIG. 1 is applied. FIG. 5 is a diagram showing a conventional hydraulic circuit. 6 is a diagram showing a state in which the regeneration switching valve is operated in the hydraulic circuit shown in FIG.

  Hereinafter, preferred embodiments of a hydraulic circuit according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a diagram showing a hydraulic circuit according to an embodiment of the present invention. The hydraulic circuit exemplified here includes a hydraulic cylinder 10 and a direction switching valve 30 that switches a supply direction of oil from the hydraulic pump 20 to the hydraulic cylinder 10, and the direction switching valve 30 via an operation valve (not shown). The drive of the hydraulic cylinder 10 is controlled by operating. In the present embodiment, in particular, a hydraulic circuit for driving the hydraulic cylinder 10 that raises and lowers the blade (drive target) B in the bulldozer shown in FIG. 4 is illustrated. In the hydraulic cylinder 10, the piston rod 12 extends / retracts with respect to the cylinder tube 11, the cylinder tube 11 is attached to the vehicle body V, and the tip of the piston rod 12 is attached to the blade B.

  As shown in FIG. 1, the direction switching valve 30 of the hydraulic circuit is operated by a pilot pressure output from an operation valve (not shown), and an oil supply port cp and a drain port dp for the two input / output ports ap and bp The connection mode is selectively switched. Specifically, when pilot pressure is not supplied from an operation valve (not shown), the directional control valve 30 is in the neutral position shown in FIG. 1 by the neutral springs 31 at both ends, and the two input / output ports ap and bp And the oil supply port cp and the drain port dp are maintained in a disconnected state. From this state, when the pilot pressure is supplied to the pressure chamber 32a located on the left side in FIG. 1, as shown in FIG. 2, the direction switching valve 30 is switched to the extended position, and the first input / output port ap and The oil supply port cp is connected, and the second input / output port bp and the drain port dp are connected. On the other hand, when the pilot pressure is supplied from the neutral position shown in FIG. 1 to the pressure chamber 32b located on the right side in FIG. 1, the direction switching valve 30 is switched to the retracted position (not shown), and the first The input / output port ap and the drain port dp are connected, and the second input / output port bp and the oil supply port cp are connected. As shown in FIG. 2, the meter-out opening area 33a of the valve passage 33 from the second input / output port bp to the drain port dp at the extended position of the direction switching valve 30 is the magnitude of the pilot pressure supplied to the pressure chamber 32a. It changes according to.

  The first input / output port ap of the direction switching valve 30 is connected to the bottom chamber 10a of the hydraulic cylinder 10 through the bottom side oil passage 41, and the second input / output port bp is connected to the hydraulic cylinder 10 through the head side oil passage 42. It is connected to the head chamber 10b. The oil supply port cp of the direction switching valve 30 is connected to a supply oil passage 43 that connects the discharge port 21 of the hydraulic pump 20, and the drain port dp of the direction switching valve 30 is connected to the oil tank T. A drain oil passage 44 is connected between the two.

  Accordingly, when the direction switching valve 30 is switched to the extended position, the bottom side oil passage 41 connected to the bottom chamber 10a of the hydraulic cylinder 10 is connected to the first input / output port ap of the direction switching valve 30 as shown in FIG. And the head side oil passage 42 connected to the head chamber 10b of the hydraulic cylinder 10 connects the second input / output port bp and the drain port dp of the direction switching valve 30 to the supply oil passage 43 through the oil supply port cp. To the drain oil passage 44. On the contrary, when the direction switching valve 30 is switched to the retracted position (not shown), the bottom side oil passage 41 connected to the bottom chamber 10a of the hydraulic cylinder 10 becomes the first input / output port of the direction switching valve 30. The head-side oil passage 42 connected to the drain oil passage 44 via the ap and the drain port dp and supplied to the head chamber 10b is supplied via the second input / output port bp and the oil supply port cp of the direction switching valve 30. The oil passage 43 is connected.

  Further, as is apparent from FIG. 1, the hydraulic circuit is provided with a regeneration valve unit 100 including a regeneration oil passage 45, a variable throttle valve 50, a regeneration switching valve 60 and a bypass oil passage 70.

  The regeneration oil passage 45 is an oil passage that connects between the bottom side oil passage 41 and the head side oil passage 42, and includes a regeneration switching valve 60 that will be described later.

  The variable throttle valve 50 is disposed in the head side oil passage 42 between the connection point with the regenerative oil passage 45 and the direction switching valve 30, and maintains the aperture area of the throttle at a minimum value in a normal state. In addition, the opening area of the throttle is changed according to the pressure difference between the pressure between the head chamber 10 b and the variable throttle valve 50 and the pressure between the variable throttle valve 50 and the direction switching valve 30. More specifically, one end of the variable throttle valve 50 is provided with a decreasing-side pressure chamber 51 and a throttle spring 52 that press in a direction that minimizes the aperture area of the throttle, and the other end. The part is provided with an increasing-side pressure chamber 53 that presses in the direction in which the aperture area of the diaphragm increases. A first pressure oil passage 54 for applying a pressure between the variable throttle valve 50 and the direction switching valve 30 is connected to the decrease side pressure chamber 51, and a head side oil passage 42 is connected to the increase side pressure chamber 53. And a second pressure oil passage 55 for applying a pressure at a connection point between the regeneration oil passage 45 and the regenerated oil passage 45 is connected. The maximum opening area of the diaphragm is set to be equal to or larger than the maximum value of the meter-out opening area 33a of the direction switching valve 30.

  The regeneration switching valve 60 opens and closes the regeneration oil passage 45 in accordance with the differential pressure between the pressure between the head chamber 10 b and the variable throttle valve 50 and the pressure between the variable throttle valve 50 and the direction switching valve 30. The head-side oil passage 42 and the bottom-side oil passage 41 are switched between a state where the head-side oil passage 42 and the bottom-side oil passage 41 are communicated with each other. More specifically, at one end of the regeneration switching valve 60, there is provided a shut-off pressure chamber 61 and a shut-off spring 62 that press in the direction of shutting off the regeneration oil passage 45, and the other end. The part is provided with a communication side pressure chamber 63 that presses in the direction in which the regenerated oil passage 45 is communicated. A third pressure oil passage 64 for applying a pressure between the variable throttle valve 50 and the direction switching valve 30 is connected to the cutoff side pressure chamber 61, and the head side oil passage 42 is connected to the communication side pressure chamber 63. And a fourth pressure oil passage 65 for applying the pressure at the connection point between the regenerated oil passage 45 and the regenerated oil passage 45 is connected.

  The bypass oil passage 70 is a bypass passage from the connection point with the regenerative oil passage 45 in the head side oil passage 42 to a portion located between the variable throttle valve 50 and the direction switching valve 30 without passing through the variable throttle valve 50. is there. The bypass oil passage 70 is provided with a check valve 71 that prevents passage of oil from the head chamber 10 b toward the direction switching valve 30.

  In the hydraulic circuit configured as described above, when the direction switching valve 30 is switched from the neutral position shown in FIG. 1 to the retracted position, the bottom side oil passage 41 connects the first input / output port ap and the drain port dp of the direction switching valve 30. The head side oil passage 42 is connected to the supply oil passage 43 through the second input / output port bp and the oil supply port cp of the direction switching valve 30. Accordingly, when the hydraulic pump 20 is driven, oil is supplied to the head chamber 10b of the hydraulic cylinder 10, and the oil in the bottom chamber 10a is discharged to the oil tank T. The hydraulic cylinder 10 is degenerated and the bulldozer Blade B rises. In this case, the variable throttle valve 50 is provided in the head side oil passage 42, but the bypass oil passage 70 is provided for the variable throttle valve 50. Therefore, the oil discharged from the direction switching valve 30 to the head side oil passage 42 is supplied to the head chamber 10b via the bypass oil passage 70, and the variable throttle valve 50 is maintained at the minimum value. Even in this case, there is no possibility that the degeneration operation of the hydraulic cylinder 10 is delayed or that unnecessary pressure loss is caused.

  On the other hand, when the direction switching valve 30 is switched to the extended position shown in FIG. 2 from the state where the blade B is raised, the bottom side oil passage 41 is supplied oil via the first input / output port ap and the oil supply port cp of the direction switching valve 30. The head side oil passage 42 is connected to the drain oil passage 44 through the second input / output port bp and the drain port dp of the direction switching valve 30 while being connected to the passage 43. Accordingly, when the hydraulic pump 20 is driven, oil is supplied to the bottom chamber 10a of the hydraulic cylinder 10, and the oil in the head chamber 10b is discharged to the oil tank T. Blade B descends.

  Here, immediately after the directional control valve 30 is switched from the neutral position shown in FIG. 1 to the extended position, the aperture area of the throttle of the variable throttle valve 50 is kept to a minimum. For this reason, even when a small amount of oil discharged from the head chamber 10b of the hydraulic cylinder 10 passes, a differential pressure is generated before and after the variable throttle valve 50, and as shown in FIG. The load becomes equal to or greater than the set load of the cutoff spring 62, and the regeneration switching valve 60 is switched so that the regeneration oil passage 45 is communicated. As a result, the head side oil passage 42 and the bottom side oil passage 41 communicate with each other, and a part of the oil discharged from the head chamber 10b of the hydraulic cylinder 10 is supplied to the bottom chamber 10a without being drained to the oil tank T. Thus, the extension operation of the hydraulic cylinder 10 can be quickly performed, that is, the blade B can be quickly lowered. In addition, since piping for applying a pilot pressure from an operation valve (not shown) to the regeneration switching valve 60 is not required, the regeneration switching valve 60 is connected to the hydraulic cylinder 10 while simplifying the hydraulic piping. The oil can be disposed in the vicinity, and the oil regeneration efficiency can be improved while minimizing the pressure loss.

  Further, even if the operation amount of the operation valve (not shown) is small and a small amount of oil passes through the head side oil passage 42, the operation amount of the operation valve (not shown) is large and the head side oil passage. Even when a large amount of oil passes through 42, the change in the differential pressure generated before and after the variable throttle valve 50 is reduced. Therefore, even if the direction switching valve 30 is suddenly operated in a direction in which the meter-out opening area 33a is reduced through an operation valve (not shown), the flow rate of oil passing through the regeneration switching valve 60 is suddenly increased. It does not affect the operation of the hydraulic cylinder 10 and the blade B can be lowered smoothly continuously.

  On the other hand, when the direction switching valve 30 is instantaneously switched to the extended position by operating an operation valve (not shown), the flow rate of oil discharged from the head chamber 10b of the hydraulic cylinder 10 becomes large. The differential pressure generated before and after the variable throttle valve 50 also increases. When the differential pressure across the variable throttle valve 50 exceeds the set load of the throttle spring 52, as shown in FIG. 3, the opening area of the throttle of the variable throttle valve 50 increases according to the differential pressure. The maximum value of the opening area of the throttle of the variable throttle valve 50 is set to be larger than the maximum value of the meter-out opening area 33 a of the direction switching valve 30. Therefore, according to the above-described hydraulic circuit, even when the operation valve (not shown) is largely operated, the extension operation speed of the hydraulic cylinder 10, that is, the lowering speed of the blade B is set to the meter-out opening of the direction switching valve 30. The area 33a can be controlled, and the workability of the blade B is not affected.

  In the above-described embodiment, the hydraulic circuit for raising and lowering the blade B in the bulldozer is illustrated. However, the invention is not necessarily limited to this, and for example, the hydraulic circuit for driving the hydraulic cylinder for the arm of the hydraulic excavator is used. Can also be applied.

  In addition, a bypass oil passage 70 is provided for the variable throttle valve 50, and a check valve for preventing passage of oil from the head chamber 10b toward the direction switching valve 30 is provided in the bypass oil passage 70. When the hydraulic cylinder 10 is retracted, there is no risk of delay or unnecessary pressure loss, but if only the regeneration efficiency is improved, the bypass oil passage 70 with respect to the variable throttle valve 50 is not necessarily required. Etc. need not be provided.

DESCRIPTION OF SYMBOLS 10 Hydraulic cylinder 10b Head chamber 20 Hydraulic pump 30 Direction switching valve 33a Meter-out opening area 41 Bottom side oil passage 42 Head side oil passage 43 Supply oil passage 44 Drain oil passage 45 Regeneration oil passage 50 Variable throttle valve 54 First pressure oil passage 55 Second pressure oil passage 60 Regenerative switching valve 61 Blocking side pressure chamber 62 Blocking spring 63 Communication side pressure chamber 64 Third pressure oil passage 65 Fourth pressure oil passage 70 Bypass oil passage 71 Check valve 100 Regeneration valve unit B Blade

Claims (3)

A head-side oil passage for distributing oil to the head chamber of the hydraulic cylinder;
A bottom-side oil passage for circulating oil to the bottom chamber of the hydraulic cylinder;
An oil supply passage for supplying oil discharged from the hydraulic pump;
A direction switching valve that controls the drive of the hydraulic cylinder by switching the connection mode of the oil supply passage with respect to the head side oil passage and the bottom side oil passage;
A regenerated oil passage connecting between the head side oil passage and the bottom side oil passage;
A regeneration switching valve that is disposed in the regeneration oil passage and switches between a state in which the head-side oil passage and the bottom-side oil passage are communicated with each other, and a state in which the state is shut off;
A variable throttle valve disposed in the head-side oil passage between a connection point with the regeneration oil passage and the direction switching valve, and the regeneration switching valve shuts off the regeneration oil passage in a normal state. On the other hand, only when the pressure between the head chamber and the variable throttle valve becomes higher than the pressure set between the variable throttle valve and the direction switching valve, the regenerated oil passage Configured to communicate,
The variable throttle valve maintains the aperture area of the throttle at a minimum value in a normal state, while the pressure between the head chamber and the variable throttle valve is between the variable throttle valve and the direction switching valve. A hydraulic circuit characterized in that when the pressure exceeds a set value, the opening area of the throttle increases according to the magnitude of the differential pressure.   2. A bypass oil passage is provided for the variable throttle valve, and a check valve for preventing passage of oil from the head chamber toward the direction switching valve is provided in the bypass oil passage. Hydraulic circuit as described in. A head-side oil passage for distributing oil to the head chamber of the hydraulic cylinder;
A bottom-side oil passage for circulating oil to the bottom chamber of the hydraulic cylinder;
An oil supply passage for supplying oil discharged from the hydraulic pump;
A direction switching valve that controls the drive of the hydraulic cylinder by switching the connection mode of the oil supply passage with respect to the head side oil passage and the bottom side oil passage;
A regenerated oil passage connecting between the head side oil passage and the bottom side oil passage;
A regeneration switching valve that is disposed in the regeneration oil passage and switches between a state in which the head-side oil passage and the bottom-side oil passage are communicated with each other, and a state in which the state is shut off;
A variable throttle valve disposed between a connection point with the regenerated oil passage and the direction switching valve in the head side oil passage;
A bypass oil passage that bypasses the variable throttle valve from the connection point with the regenerated oil passage in the head side oil passage and connects to the direction switching valve;
A check valve disposed in the bypass oil passage and blocking passage of oil from the head chamber toward the direction switching valve, and the regeneration switching valve shuts off the regeneration oil passage in a normal state. On the other hand, only when the pressure between the head chamber and the variable throttle valve becomes higher than the value set between the variable throttle valve and the direction switching valve, the regenerated oil passage is opened. Configured to communicate,
The variable throttle valve maintains the aperture area of the throttle at a minimum value in a normal state, while the pressure between the head chamber and the variable throttle valve is between the variable throttle valve and the direction switching valve. A hydraulic circuit characterized in that when the pressure exceeds a set value, the opening area of the throttle increases according to the magnitude of the differential pressure.

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