JP3828680B2 - Hydraulic circuit for work machine and hybrid work machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic circuit for a work machine and a hybrid work machine, and more particularly to a hydraulic circuit for a work machine and a hybrid work machine that can finely operate an operation unit.
[0002]
[Prior art]
In recent years, as a hydraulic drive device including construction equipment such as hydraulic excavators and wheel loaders and hydraulic working machines such as forklifts, in addition to the engine, a generator and a battery are also used as a power source to reduce engine burden and fuel consumption rate. The so-called hybrid type that is provided is being developed.
[0003]
In such a hybrid type hydraulic drive device, instead of driving the hydraulic pump with the torque generated by the engine, the hydraulic pump is driven with the torque generated by the electric motor that uses the electric energy stored in the battery as a power source, As a result, the hydraulic cylinder can be operated.
[0004]
As described above, as a technique for controlling the speed of the hydraulic cylinder connected to the hydraulic pump driven by the electric motor, as described in JP-A-9-174300, the pressurizing pressure of the hydraulic cylinder is described. There is a technique for detecting the motor and controlling the rotational speed of the electric motor via an inverter based on the detected pressure. In this way, by controlling the rotation speed of the electric motor according to the load fluctuation to the hydraulic cylinder, the flow rate of the pressure oil discharged from the hydraulic pump can be controlled to change the speed of the hydraulic cylinder.
[0005]
[Problems to be solved by the invention]
When performing a fine operation for positioning a hydraulic cylinder connected to a hydraulic pump driven by an electric motor by the technique described in the above publication, the pressure oil supplied to the hydraulic cylinder while keeping the rotational speed of the electric motor extremely low The amount must be reduced. However, it is usually difficult to keep the rotational speed of the motor very low due to problems with the accuracy of the motor control device, problems with the lowering of the efficiency of the hydraulic pump at low speeds, and problems with friction of the rotating system. is there.
[0006]
That is, as shown in FIG. 5 which is a graph showing the relationship between the operation amount of the operation lever and the discharge amount of the hydraulic pump, the two are in a proportional relationship in a region where the operation amount of the operation lever is relatively large. In a fine operation region (region surrounded by a broken-line circle in FIG. 5), even if the lever operation amount is set to S1 or less, the pump discharge amount cannot be controlled to a minute amount less than the predetermined amount Q1 according to the lever operation. Therefore, there is a problem that the technique described in the above-mentioned publication cannot perform good fine operation of the operation unit driven by the hydraulic cylinder.
[0007]
Accordingly, a main object of the present invention is to provide a hydraulic circuit for a work machine and a hybrid work machine capable of finely manipulating an operation unit driven by a hydraulic cylinder connected to a hydraulic pump driven by an electric motor. Is to provide.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a hydraulic circuit for a work machine according to claim 1 is the hydraulic circuit for a work machine for controlling a hydraulic cylinder connected to a hydraulic pump driven by an electric motor. A pipe connecting the pressure pump and the hydraulic cylinder with a hydraulic closed circuit, a flow control valve for limiting the flow rate of the pressure liquid passing through the pipe, and an operation lever for limiting the flow rate of the pressure liquid by the flow control valve And a controller that functions in the fine operation area .
[0009]
According to a fourth aspect of the present invention, there is provided a hybrid work machine capable of storing power in the power storage means with electric power of a generator driven by an engine and operating the electric motor with at least one power of the generator and power storage means. , passing a hydraulic pump, a hydraulic cylinder operated by the hydraulic pump, a pipe connected with the hydraulic pump and said hydraulic cylinder and a hydraulic pressure closing circuit, said pipes being driven by said electric motor The flow rate control valve for restricting the flow rate of the pressure fluid to be controlled, and the controller for causing the restriction of the flow rate of the pressure fluid by the flow rate control valve to function in the fine operation region of the operation lever are provided.
[0010]
According to Claims 1 and 4, a flow rate control valve that is provided between the hydraulic pump and the hydraulic cylinder and that restricts the flow rate of the hydraulic fluid that passes through the pipe forming the hydraulic pressure closed circuit, and a controller that controls the flow rate control valve. As a result, the amount of hydraulic fluid supplied to the hydraulic cylinder when the number of revolutions of the electric motor is the same can be reduced in the fine operation region of the operation lever as compared with the conventional case. Therefore, it is possible to move the hydraulic cylinders at a very small rate, improved if fine operability of the operation unit that is driven by the hydraulic cylinder.
[0011]
The hydraulic circuit for a work machine according to claim 2 is characterized in that the flow control valve is provided in a pipe for supplying pressurized liquid from the hydraulic pump to the hydraulic cylinder . The hybrid work machine according to claim 5 is characterized in that the flow rate control valve is provided in a pipe for supplying pressurized fluid from the hydraulic pump to the hydraulic cylinder .
[0012]
According to claim 2 and 5, the flow rate control valve in the piping for supplying hydraulic fluid to the hydraulic cylinder from the hydraulic pump is provided, the flow control valve is a pressure liquid return pipe to the hydraulic pump from the hydraulic cylinder It is possible to obtain excellent fine operability with higher responsiveness than when it is provided.
[0013]
The hydraulic circuit for a work machine according to claim 3 is characterized in that the flow control valve can supply a certain amount of pressurized liquid to the hydraulic cylinder regardless of the pressure in the pipe. The hybrid work machine according to claim 6 is characterized in that the flow control valve can supply a certain amount of pressurized fluid to the hydraulic cylinder irrespective of the pressure in the pipe.
[0014]
According to claim 3 and 6, the flow rate control valve can be supplied a predetermined amount of pressurized liquid to hydraulic cylinders regardless of the pressure in the pipe, fixed to the hydraulic cylinder even if the load of the hydraulic cylinder is increased or decreased An amount of pressurized liquid can be supplied, and a constant fine operability can always be given to the operator.
[0015]
According to a seventh aspect of the present invention, there is provided a hydraulic circuit for a work machine comprising: an electric motor; a hydraulic pump driven by the electric motor; a hydraulic cylinder that operates by supplying pressurized liquid from the hydraulic pump; and the hydraulic pump And the first and second pipes connected to the hydraulic cylinder to form a hydraulic closed circuit, and the pressure fluid passing through the first pipe when the first pipe is a supply-side pipe A first flow rate control valve for limiting a flow rate, a second flow rate control valve for limiting a flow rate of pressurized liquid that passes through the second pipe when the second pipe is a supply-side pipe, and And a controller that controls the flow rate of the pressurized liquid that passes through the first and second flow rate control valves to be limited in the fine operation region of the operation lever .
[0016]
According to the seventh aspect, the controller controls the flow rate of the pressurized liquid passing through the first and second flow rate control valves to be limited in the fine operation region of the operation lever, so that the rotational speed of the electric motor can be controlled from a certain number. Even if the pressure is not lowered, the amount of hydraulic fluid supplied to the hydraulic cylinder can be greatly reduced. Therefore, the hydraulic cylinder can be moved at a very low speed, and the fine operability of the operating unit driven by the hydraulic cylinder is improved.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
[0018]
FIG. 1 is a schematic diagram showing a schematic configuration of an excavator that is a hybrid work machine according to a first embodiment of the present invention. In FIG. 1, an excavator 100 includes a lower traveling body 1, an upper swing body 2, and an excavation attachment 3.
[0019]
The lower traveling body 1 includes left and right crawler frames 4 and 5 (both shown only on one side), left and right traveling motors 7 (6) and a traveling speed reducer 36 (35) (see FIG. 1). Is shown on the left side only). The traveling speed reducers 36 and 35 decelerate the rotation of the traveling electric motors 7 and 6 and transmit it to the traveling mechanism.
[0020]
The upper swing body 2 includes a swing frame 8 and a cabin 9. The turning frame 8 includes an engine 10 as a power source, a generator 11 driven by the engine 10, a main battery 12, an auxiliary battery 42, and a turning electric motor 13 for rotating the upper turning body 3. A turning speed reducer 14 that decelerates the rotation of the turning electric motor 13 and transmits it to a turning mechanism (a turning gear), a boom electric motor 15, and a boom hydraulic pump (hereinafter referred to as “boom pump”) 16 are installed. In addition, a control unit (not shown) including an inverter 37 and a controller 43 (both see FIG. 2) is provided in the upper swing body 3.
[0021]
The excavation attachment 3 includes a boom 17, a boom cylinder 18 that extends and retracts to raise and lower the boom 17, an arm 19, an arm cylinder 20 that rotates the arm 19, a bucket 21, and a bucket cylinder that rotates the bucket 21. 22. The arm cylinder 20 is provided with an arm electric motor 23 and an arm hydraulic pump (hereinafter referred to as an “arm pump”) 24 driven by the arm electric motor 23, and the bucket cylinder 22 is provided with a bucket electric motor 25 and A bucket hydraulic pump (hereinafter referred to as “bucket pump”) 26 driven by this is attached. In the present embodiment, the arm motor 23, the arm pump 24, and the arm cylinder 20 and the bucket motor 25, the bucket pump 26, and the bucket cylinder 22 are integrated.
[0022]
Next, the drive system of the shovel 100 will be described with reference to FIG. FIG. 2 is a block diagram schematically showing the drive system of the excavator 100. As shown in FIG. 2, the generator 11 is attached to the output shaft of the engine 10. The generator 11 generates AC power from the output torque of the engine 10 and supplies it to the inverter 37. The inverter 37 connected to the generator 11 converts the AC power generated by the generator 11 into DC power and stores it in the batteries 12, 42, and the motors 15, 23, 25, 6 connected to the inverter 37. , 7, and 13, the AC power generated by the regenerative operation is converted into DC power and stored in the battery 32.
[0023]
Further, the inverter 37 converts the electric energy stored in the batteries 12 and 42 into alternating current and supplies it to the electric motors 15, 23, 25, 6, 7, and 13, and the alternating current power from the generator 11 is converted into the electric motor 15. , 23, 25, 6, 7, and 13 are performed. When performing these two actions, the inverter 37 can change the frequency of the alternating current to an arbitrary value in accordance with a command from the controller 43, whereby the motors 15, 23, 25, 6, 7, 13 The number of rotations can be controlled.
[0024]
Of the six electric motors 15, 23, 25, 6, 7, 13 connected to the inverter 37, the boom electric motor 15 operates the boom pump 16 to drive the boom cylinder 18, and the arm electric motor 23 The pump 24 is operated to drive the arm cylinder 20, and the bucket motor 25 operates the bucket pump 26 to drive the bucket cylinder 22. The turning electric motor 13 and the traveling electric motors 6 and 7 are connected to the turning speed reducer 14 and the traveling speed reducers 35 and 36, respectively. These six electric motors 15, 23, 25, 6, 7, and 13 are controlled on / off, rotational speed, and rotational direction by operating the operation lever 45 by the operator.
[0025]
The motors 15, 23, 25, 6, 7 and 13 are driven by AC power supplied from the generator 11 via the inverter 37 when the total load on these is small. At this time, surplus AC power generated by the generator 11 is converted into DC power by the inverter 37 and stored in the batteries 12 and 42. Note that the arm cylinder 20 and the boom cylinder 18 are not used, for example, when the excavator 100 is traveling, the power stored in the main battery 12 is sufficient, and the motors 15, 23, 25, 6, 7, 13 are connected. When the total load is small, the output of the engine 10 may be reduced or the engine 10 may be stopped to supply power to the motors 15, 23, 25, 6, 7, 13 only from the main battery 12. Accordingly, it is possible to prevent the engine 10 from operating wastefully, reduce noise and exhaust gas, and further reduce the fuel consumption rate.
[0026]
On the other hand, when the total load of the electric motors 15, 23, 25, 6, 7, 13 becomes larger than a predetermined value, the accumulating of the AC power generated by the generator 11 in the batteries 12, 42 is stopped, and the electric motor 15 , 23, 25, 6, 7, and 13, not only the power supplied from the generator 11, but also the power stored in the main battery 12 is used if necessary.
[0027]
Thus, the operation of the inverter 37 is switched depending on whether or not the total load of the motors 15, 23, 25, 6, 7, and 13 is larger than a predetermined value. This switching is performed by the motors 15, 23, 25, 6, 7 and 7. , 13 based on the product of the current flowing through 13 and its voltage, or manually under the control of the control unit.
[0028]
Further, during operation, the motors 15, 23, 25, 6, 7, and 13 are made to act as a generator (regenerative action) using their potential energy and kinetic energy, and the regenerative power generated thereby is transferred to the batteries 12 and 42. Can be stored. In particular, the turning electric motor 13 can store a large amount of kinetic energy at the time of turning acceleration, so that the energy regeneration effect at the time of deceleration is high.
[0029]
In the shovel 100 according to the present embodiment, two flow control valves 46a and 46b are provided in association with the pressure oil piping connecting the boom pump 16 and the boom cylinder 18. The same flow control valves 47a, 47b and 48a, 48b are also related to the pressure oil piping connecting the arm pump 24 and the arm cylinder 20 and the pressure oil piping connecting the bucket pump 26 and the bucket cylinder 22. Is provided. The flow rate control valves 46a, 46b; 47a, 47b; 48a, 48b can be controlled by the controller 43 by the operation of the operation lever 45.
[0030]
Next, the details of the drive system of the boom 17 in the excavator 100 of the present embodiment will be described with reference to FIG. FIG. 3 is a circuit diagram showing in detail a drive system related to the boom 17, and the same reference numerals are used for portions corresponding to those in FIGS. 1 and 2. Although the boom 17 will be described here, a similar drive system is configured for the arm 19 and the bucket 21 as well.
[0031]
In FIG. 3, pipes 49a and 49b are connected to the working chamber 18a on the cap side and the working chamber 18b on the head side of the boom cylinder 18, respectively. The pipes 49a and 49b are connected to the double-rotation boom pump 16 to form a hydraulic closed circuit.
[0032]
Check valves 51a and 51b are provided between the pipes 49a and 49b and the tank 53, respectively, and oil is supplied from the tank 53 into the pipes 49a and 49b when the pressure in the pipes 49a and 49b becomes negative. The As a result, cavitation is prevented from occurring in the pipes 49a and 49b. Relief valves 52 a and 52 b are provided between the pipes 49 a and 49 b and the tank 53. Thereby, when the pressure in the pipes 49a and 49b exceeds a predetermined value, the oil can be released to the tank 53, so that the hydraulic closed circuit is prevented from being damaged by the pressure increase in the pipes 49a and 49b.
[0033]
In the present embodiment, the above-described flow control valves 46a and 46b are provided in the middle of the pipes 49a and 49b, and check valves 50a and 50b are connected in parallel with the flow control valves 46a and 46b. The flow rate control valves 46a and 46b allow the pressure oil supplied from the boom pump 16 to the boom cylinder 18 to pass therethrough, and the check valves 50a and 50b allow the pressure oil returning from the boom cylinder 18 to the boom pump 16 to pass therethrough. The flow rate control valves 46 a and 46 b may be known ones such as an orifice whose opening area is variable under the control of the controller 43, and an amount of pressurized oil whose passage is restricted by the flow rate control valves 46 a and 46 b is supplied to the tank 53. It is configured to be returned.
[0034]
When the operation lever 45 is operated in the direction in which the boom cylinder 18 extends, the boom motor 15 is controlled via the controller 43 and the inverter 37, and the piping 49 b is supplied with pressure oil to the working chamber 18 a of the boom cylinder 18. The boom pump 16 is driven so that the pipe 49a becomes the return side pipe of the pressure oil from the working chamber 18b, and the boom cylinder 18 moves to the right side in the figure. That is, the pressure oil supplied from the boom pump 16 reaches the boom cylinder 18 via the flow control valve 46b, and is further returned to the boom pump 16 via the check valve 50a.
[0035]
At this time, in order to finely operate the boom 17, the operation lever 45 is moved to the fine operation region. Then, the boom motor 15 is controlled via the controller 43 and the inverter 7 in accordance with the operation amount of the operation lever 45, and the rotation speed thereof is reduced. At the same time, the flow rate of the hydraulic oil supplied to the boom cylinder 18 is limited by controlling the flow rate control valve 46 b via the controller 43.
[0036]
Therefore, as shown in FIG. 4, the discharge amount (broken line) of the boom pump 16 when the lever operation amount is reduced to the limit position S1 where flow control is possible is Q1, whereas the outlet flow rate of the flow control valve 46b. (Solid line) can be reduced to Q2 (that is, Q1-Q2 is returned from the flow control valve 46b to the tank 53). Accordingly, the flow rate of the pressure oil supplied to the boom cylinder 18 is also reduced to about Q2, and the minimum controllable flow rate to the boom cylinder 18 can be reduced by about Q1-Q2. Therefore, the boom cylinder 18 can be moved at a very low speed, and the fine operability for positioning the boom 17 in the direction in which the boom cylinder 18 is extended is improved.
[0037]
On the other hand, when the operation lever 45 is operated in the direction in which the boom cylinder 18 contracts, the boom motor 15 is controlled via the controller 43 and the inverter 37, and the piping 49 a supplies pressure oil to the working chamber 18 b of the boom cylinder 18. The boom pump 16 is driven so that the supply side piping and the piping 49b become the return side piping of the pressure oil from the working chamber 18a, and the boom cylinder 18 moves to the left in the drawing. That is, the pressure oil supplied from the boom pump 16 reaches the boom cylinder 18 through the flow control valve 46a, and is further returned to the boom pump 16 through the check valve 50b.
[0038]
At this time, in order to finely operate the boom 17, the operation lever 45 is moved to the fine operation region. Then, the boom motor 15 is controlled via the controller 43 and the inverter 7 in accordance with the operation amount of the operation lever 45, and the rotation speed thereof is reduced. At the same time, the flow rate of the pressure oil supplied to the boom cylinder 18 is limited by controlling the flow rate control valve 46 a via the controller 43.
[0039]
Therefore, as described with reference to FIG. 4, the controllable minimum flow rate to the boom cylinder 18 can be reduced by approximately Q1 -Q2, and the boom cylinder 18 is moved at a very low speed. This makes it possible to improve the fine operability for positioning the boom 17 in the direction in which the boom cylinder 18 is retracted.
[0040]
Thus, in the present embodiment, in the hydraulic closed circuit in which the boom pump 16 and the boom cylinder 18 are connected by the pipes 49a and 49b, the flow control valves 46a and 46b are provided in both the pipes 49a and 49b, and the boom cylinder 18 is provided. Since the flow rate of the pressure oil supplied to the cylinder is restricted, the minimum controllable flow rate to the boom cylinder 18 can be reduced in both cases where the boom cylinder 18 is extended and contracted. Thus, fine operability of the boom 17 can be obtained.
[0041]
In this embodiment, the flow rate control valves 46a and 46b are provided on the pressure oil supply side to the boom cylinder 18 to limit the amount of pressure oil supplied to the boom cylinder 18, but the pressure oil from the boom cylinder 18 is limited. Even if a flow control valve similar to the flow control valves 46a and 46b is provided on the discharge side to limit the amount of pressure oil discharged from the boom cylinder 18, the boom cylinder 18 can be moved at a very low speed. Thus, the fine operability of the boom 17 is improved. However, if the flow rate control valves 46a and 46b are provided on the pressure oil supply side to the boom cylinder 18 as in the present embodiment, it is possible to obtain finer operability with higher responsiveness.
[0042]
Further, as the flow control valves 46a and 46b used in the present embodiment, pressure compensated flow control valves capable of supplying a certain amount of pressurized fluid to the boom cylinder 18 regardless of the pressure in the pipes 49a and 49b are used. Is preferred. This is because when the load on the boom cylinder 18 fluctuates, the pressure in the pipes 49a and 49b fluctuates, but if a flow control valve with pressure compensation is used, the flow rate is constant regardless of the pressure fluctuations in the pipes 49a and 49b. Is supplied to the boom cylinder 18 so that a constant fine operability can always be given to the operator.
[0043]
The preferred embodiments of the present embodiment have been described above, but the present invention is not limited to the above-described embodiments, and various design changes can be made as long as they are described in the claims. Is possible. For example, in the above embodiment is provided with the flow control valve in the piping for supplying hydraulic fluid to the hydraulic cylinder from the hydraulic pump, co cement roll valve in a pipe for supplying pressurized liquid to the hydraulic cylinder from the hydraulic pump And a flow path communicating from the control valve to the tank may be provided.
[0044]
【The invention's effect】
As described above, according to claim 1, 4, it is possible to move the hydraulic cylinders at a very small rate, fine operation of the working unit is driven by the hydraulic cylinder is improved.
[0045]
According to the second and fifth aspects, it is possible to obtain fine operability with higher responsiveness than when the flow rate control valve is provided in the pipe from which the hydraulic fluid returns from the hydraulic cylinder to the hydraulic pump.
[0046]
According to the third and sixth aspects, even if the load on the hydraulic cylinder increases or decreases, a constant amount of pressurized fluid can be supplied to the hydraulic cylinder, and a constant fine operability can be always given to the operator. become able to.
[0047]
According to the seventh aspect, the controller controls the flow rate of the pressurized liquid passing through the first and second flow rate control valves to be limited in the fine operation region of the operation lever, so that the rotational speed of the electric motor can be controlled from a certain number. Even if the pressure is not lowered, the amount of hydraulic fluid supplied to the hydraulic cylinder can be greatly reduced. Therefore, the hydraulic cylinder can be moved at a very low speed, and the fine operability of the operating unit driven by the hydraulic cylinder is improved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a schematic configuration of an excavator that is a hybrid work machine according to a first embodiment of the present invention.
2 is a block diagram schematically showing a drive system of the excavator shown in FIG. 1. FIG.
FIG. 3 is a circuit diagram showing in detail a drive system related to the boom shown in FIG. 1;
FIG. 4 is a graph showing a relationship between a lever operation amount and a flow rate in a fine operation region.
FIG. 5 is a graph showing a relationship between a lever operation amount and a pump discharge amount in the conventional technique.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Lower traveling body 2 Upper revolving body 3 Excavation attachment 6, 7 Electric motor for driving 10 Engine 11 Generator 12 Main battery 13 Electric motor for turning 15 Electric motor for boom 16 Boom pump 17 Boom 18 Boom cylinder 19 Arm 20 Arm cylinder 21 Bucket 22 Bucket Cylinder 23 Electric motor for arm 24 Arm pump 25 Electric motor for bucket 26 Bucket pump 37 Inverter 42 Auxiliary battery 43 Controller 45 Operation lever 46a, 46b; 47a, 47b; 48a, 48b Flow control valve 49a, 49b Piping 50a, 50b Check valve 51a, 51b Check valve 52a, 52b Relief valve 53 Tank 100 Excavator

Claims (7)

In a hydraulic circuit for a work machine for controlling a hydraulic cylinder connected to a hydraulic pump driven by an electric motor,
A pipe connecting the hydraulic pump and the hydraulic cylinder with a hydraulic closed circuit, a flow control valve for limiting the flow rate of the pressure liquid passing through the pipe, and limiting the flow rate of the pressure liquid by the flow control valve. A hydraulic circuit for a work machine, comprising a controller that functions in a fine operation region of an operation lever . 2. The hydraulic circuit for a work machine according to claim 1, wherein the flow rate control valve is provided in a pipe for supplying pressurized liquid from the hydraulic pump to the hydraulic cylinder . 3. 3. The hydraulic circuit for a work machine according to claim 1, wherein the flow rate control valve is capable of supplying a certain amount of pressurized fluid to the hydraulic cylinder regardless of the pressure in the pipe. In the hybrid work machine that can store power in the power storage means by the power of the generator driven by the engine and operates the electric motor by power of at least one of the generator and the power storage means,
Through a hydraulic pump driven by said electric motor, a hydraulic cylinder operated by the hydraulic pump, a pipe connected with the hydraulic pump and said hydraulic cylinder and a hydraulic closed circuit, the piping A hybrid work machine comprising: a flow control valve that restricts a flow rate of pressure fluid; and a controller that causes a restriction of the flow rate of pressure fluid by the flow rate control valve to function in a fine operation region of an operation lever . 5. The hybrid work machine according to claim 4, wherein the flow rate control valve is provided in a pipe that supplies pressurized liquid from the hydraulic pump to the hydraulic cylinder . 6. 6. The hybrid work machine according to claim 4, wherein the flow control valve is capable of supplying a certain amount of pressurized liquid to the hydraulic cylinder regardless of the pressure in the pipe. An electric motor,
A hydraulic pump driven by the electric motor;
A hydraulic cylinder that operates by being supplied with hydraulic fluid from the hydraulic pump ;
First and second pipes connected to the hydraulic pump and the hydraulic cylinder to form a hydraulic closed circuit;
When the first pipe becomes the supply side pipe, the first flow rate control valve for restricting the flow rate of the pressure liquid passing through the first pipe, and the second pipe becomes the supply side pipe A second flow rate control valve for restricting the flow rate of the pressure fluid passing through the second pipe;
A hydraulic circuit for a working machine, comprising: a controller that controls the flow rate of the pressurized fluid that passes through the first and second flow control valves to be limited in a fine operation region of the operation lever .

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