JP3511500B2 - Hydraulic circuit of construction machinery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic circuit for a construction machine having an independent attachment circuit.

[0002]

2. Description of the Related Art As in the hydraulic circuit of a construction machine disclosed in Japanese Patent Laid-Open No. 2000-73409, between a first hydraulic pump and a second hydraulic pump and a left traveling circuit, a right traveling circuit and an independent attachment circuit. Some have a pressure-compensated shunt valve.

This pressure compensating type shunt valve includes a shunt control valve for controlling a flow rate diverted to an independent attachment circuit with respect to a traveling circuit, and a pressure for maintaining a constant differential pressure across a variable throttle of the shunt control valve. Compensation valve and built-in.

The diversion control valve is an internal oil having an opening characteristic in which the flow rate of hydraulic oil diverted from the first hydraulic pump to the left traveling circuit is equal to the flow rate of hydraulic oil diverted from the second hydraulic pump to the right traveling circuit at the same time. Of the hydraulic oil that has a passage and that divides from these internal oil passages into the independent attachment circuit from the first hydraulic pump and the hydraulic oil that divides from the second hydraulic pump into the independent attachment circuit at the same time. It has the opening characteristic that the flow rate becomes equal.

The pressure compensating valve controls the variable throttle by maintaining the constant differential pressure across the variable throttle of the shunt control valve regardless of the circuit pressures of the left traveling circuit, the right traveling circuit and the independent attachment circuit. The flow rate according to the opening degree of is supplied to the independent attachment circuit.

In a hydraulic pump mounted on such a construction machine, as shown in FIG. 3, a limit diagram (hereinafter referred to as PQ diagram) of pump discharge flow rate and pump discharge pressure determined by engine horsepower. ), The pump discharge flow rate is set to decrease as the pump discharge pressure increases.

[0007]

In the independent attachment circuit of this prior art, the function of the pressure compensating valve allows the independent attachment circuit to operate regardless of the circuit pressure of the independent attachment circuit.
Since the hydraulic oil of the flow rate according to the opening amount of the variable throttle of the diversion control valve is supplied to the independent attachment circuit, the circuit pressure of the independent attachment circuit becomes a high pressure near the relief pressure,
As shown in the P-Q diagram of FIG. 3, even when the pump discharge flow rate decreases, if the opening amount of the variable throttle of the diversion control valve is considerably open, most of the pump discharge flow rate is an independent attachment circuit. Flows to.

At this time, the permanent compensating actuator of the main body side working device, that is, the hydraulic oil for traveling and turning, and the hydraulic cylinders for the front working machine such as the boom, arm and bucket are suppressed by the pressure compensating valve. Therefore, in the interlocking operation of the attachment and the main body side working device, the speed of the main body side working device becomes slow as soon as the independent attachment circuit becomes close to the relief pressure.

The present invention has been made in view of the above circumstances, and a part of the amount of hydraulic oil supplied to a permanent actuator circuit is diverted by a pressure-compensated shunt control valve to be supplied to an independent attachment circuit. In this case, it is an object of the present invention to be able to supply the required amount of hydraulic oil to the permanent actuator circuit even if the circuit pressure of the independent attachment circuit rises excessively.

[0010]

The invention according to claim 1 is
The permanent actuator circuit that controls the hydraulic oil supplied from the hydraulic pump to drive the permanent actuator of the construction machine, and the attachment of the construction machine to the permanent actuator circuit by controlling part of the hydraulic oil supplied to the permanent actuator circuit. Is an independent attachment circuit that drives independently, and a part of the hydraulic oil supplied from the hydraulic pump to the permanent actuator circuit is diverted to the independent attachment circuit and the flow rate of the diverted hydraulic oil is adjusted according to the stroke. Control valve, a pressure compensation valve that controls the differential pressure across the variable throttle of the shunt control valve to keep it constant, a pressure sensor that detects the circuit pressure of the independent attachment circuit, and a shunt control valve that uses the pilot pressure. Solenoid proportional valve with stroke control and independent attachment circuit detected by pressure sensor In the area where the circuit pressure is not excessive, the solenoid proportional valve is controlled according to the operation signal for attachment to control the opening area of the variable throttle of the diversion control valve, and the circuit pressure of the independent attachment circuit detected by the pressure sensor is excessive. The hydraulic circuit of the construction machine is provided with a controller that controls the solenoid proportional valve to control the opening area of the variable throttle of the shunt control valve in a direction to reduce the opening regardless of the operation signal for attachment when it rises to the state.

When an excessive circuit pressure is not generated in the independent attachment circuit, the controller which receives the operation signal for attachment outputs an electric signal proportional to the operation signal for attachment to the solenoid proportional valve, and the electromagnetic proportional valve. The diversion control valve is stroke-controlled via the valve. on the other hand,
If an excessive circuit pressure is generated in the independent attachment circuit, the controller that detects the state via the pressure sensor controls the solenoid proportional valve regardless of the attachment operation signal to open the variable throttle of the diversion control valve. By controlling the area to a small value, the amount of oil supplied to the independent attachment circuit is controlled to be reduced. As a result, the amount of hydraulic oil supplied to the permanent actuator circuit is recovered by the amount of oil supplied to the independent attachment circuit, and the attachment and the permanent actuator are smoothly interlocked.

According to a second aspect of the present invention, in the hydraulic circuit of the construction machine according to the first aspect, when the circuit pressure of the independent attachment circuit is excessive, the circuit pressure close to the relief pressure is generated in the independent attachment circuit. And the fact that the circuit pressure of the independent attachment circuit is close to the relief pressure means that the attachment is near the stall state, and a small amount of oil to hold the circuit pressure is enough. And it makes sense.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to the embodiment shown in FIG.

FIG. 1 shows an example of an independent attachment circuit using a pressure compensation type flow dividing valve in a two-pump hydraulic excavator.

In FIG. 1, the discharge ports of a first hydraulic pump 2 and a second hydraulic pump 3 driven by an engine 1 mounted on a hydraulic excavator as a construction machine are connected via a pressure compensation type shunt valve 4. The permanent actuator circuit 5 of the left traveling system group, the permanent actuator circuit 6 of the right traveling system group, and an independent attachment circuit 7 that is controlled independently of the permanent actuator circuits 5 and 6.

The permanent actuator circuits 5 and 6 supply the operating oil supplied from the first hydraulic pump 2 and the second hydraulic pump 3 through the pressure compensating type diversion valve 4 by various control spools (not shown) of the main control valve. It controls to drive the hydraulic motors of the traveling system and the swing system, which are the permanent actuators of the hydraulic excavator, and the hydraulic cylinders (boom cylinder, arm cylinder, bucket cylinder) of the front working machine.

One of the permanent actuator circuits 5 has a first
A left traveling system group that controls the hydraulic oil supplied from the hydraulic pump 2 and controls at least the left traveling hydraulic motor that drives the left crawler belt by the left traveling spool, and the other permanent actuator circuit 6 is 2 is a right traveling system group that controls hydraulic oil supplied from the hydraulic pump 3 and controls at least the right traveling hydraulic motor that drives the right crawler belt with the right traveling spool.

The independent attachment circuit 7 controls the hydraulic oil divided by the pressure compensating flow dividing valve 4 from the hydraulic oil supplied from the first hydraulic pump 2 and the second hydraulic pump 3 to the permanent actuator circuits 5 and 6. Control spool for attachment (not shown) that controls the hydraulic fluid controlled by this control spool for attachment, such as a hydraulic breaker or a crusher attached to the tip of the front working machine of the hydraulic excavator in place of a bucket. The attachment is driven independently of the permanent actuator circuits 5,6.

The independent attachment circuit 7 is provided with a relief valve 8 for attachment, and the relief valve 8 for attachment allows the independent attachment circuit 7 to operate.
Set the relief pressure of.

The pressure compensating type shunt valve 4 includes a shunt control spool 10 as one shunt control valve, and a pressure compensating valve for compensating the flow rate of the working oil diverted to the independent attachment circuit 7 by the shunt control spool 10. Pair of pressure compensating spools 11 and 12 and these pressure compensating spools 1
It incorporates check valves 13 and 14 provided in the output circuit from 1 and 12 to the independent attachment circuit 7.

The diversion control spool 10 is the first hydraulic pump 2
From a part of the hydraulic oil supplied to the permanent actuator circuit 5 of the left traveling system group is supplied to the independent attachment circuit 7 and the flow rate of the divided hydraulic oil is controlled by the variable throttle 39 according to the stroke. At the same time, a part of the hydraulic oil supplied from the second hydraulic pump 3 to the permanent actuator circuit 6 of the right traveling system group is diverted to be supplied to the independent attachment circuit 7 and the flow rate of the diverted hydraulic oil is adjusted according to the stroke. It is controlled by the variable aperture 40.

Further, one of the pressure compensating spools 11 has oil pressure from the A1 port and the B1 port of the diversion control spool 10 through oil passages 17 and 18 at both ends of the spool biased by the spring 16 on one side. When the differential pressure (PB1-PA1) at the B1 port and A1 port of the diversion control spool 10 becomes a constant differential pressure ΔP, the spring 16
It is set to switch from the position 21 to the position 22 against the biasing force of and to switch to the position 23 when the differential pressure increases.

Then, the pressure compensating spool 11 for one side is provided.
Is pressure-compensated and controlled so as to maintain the differential pressure (PB1-PA1), that is, the differential pressure across the variable throttle 39 at a constant value, and the other pressure-compensated spool 12 is likewise a shunt control spool.
Differential pressure (PB2−
PA2), that is, pressure compensation control is performed so that the differential pressure across the variable throttle 40 is maintained at a constant value.

The A1 'port of the pressure compensation spool 11 and the A2' port of the pressure compensation spool 12 are connected to the check valves 13, 1
4 is connected to the independent attachment circuit 7 by a single independent attachment line 31, and the B1 'port is connected to the permanent actuator circuit 5 of the left traveling system group via the left traveling system line 32 and the B2' port. Is
It is connected to the permanent actuator circuit 6 of the right traveling system group via the right traveling system line 33.

The diversion control spool 10 will be described in more detail. On the diversion control spool 10, the left traveling system line 32 from the first hydraulic pump 2 to the permanent actuator circuit 5 is provided.
Internal oil passage 35 of the hydraulic oil that is diverted to and the internal oil passage 36 of the hydraulic oil that is diverted to the independent attachment line 31 of the independent attachment circuit 7, and the right traveling system line 33 of the permanent actuator circuit 6 from the second hydraulic pump 3. Internal oil passage 37 for the hydraulic oil that is diverted to and the internal oil passage for the hydraulic oil that is diverted to the independent attachment line 31 of the independent attachment circuit 7.
38 and are formed.

The internal oil passages 35, 37 of the flow dividing control spool 10
Is an opening characteristic in which the flow rate of the hydraulic oil diverted from the first hydraulic pump 2 to the left traveling system line 32 is equal to the flow rate of the hydraulic oil diverted from the second hydraulic pump 3 to the right traveling system line 33 at the same time. The internal oil passages 36 and 38 have the flow rates of the hydraulic oil that is split from the first hydraulic pump 2 to the independent attachment line 31, and the flow rates of the hydraulic oil that is split from the second hydraulic pump 3 to the independent attachment line 31 at the same time. And have the same opening characteristic.

The variable throttles 39 and 40 are provided in the internal oil passages 36 and 38 of the hydraulic oil that is diverted to the independent attachment circuit 7. These variable throttles 39 and 40 change the opening area according to the valve stroke of the diversion control spool 10 as shown in FIG. 2. The diversion control spool 10 receives the biasing force of the spring 41 on one side, and , Pi port from the pilot pressure introducing path 42 is received on the other side, and the spool valve stroke is controlled at the equilibrium point between the pressing force by the pilot pressure and the repulsive force of the spring 41.

That is, the smaller the pilot pressure at the Pi port, the closer the shunt control spool 10 is to the position 43,
As the pilot pressure of the i port increases, the diversion control spool 10 shifts from position 44 to position 45, and the variable throttles 39, 40
The opening degree of changes. The drain oil passage 46 drawn out from the diversion control spool 10 is connected to the tank 47.

Since the operating principle of the right traveling portion of the diversion control spool 10 and the pressure compensating spool 12 is the same as that of the left traveling portion of the diversion control spool 10 and the pressure compensating spool 11, the P1 port is referred to as the P2 port. , A1 port to A2 port, B1 port to B2 port, and A1 port
The description of the “port” is replaced with the A2 ′ port and the B1 ′ port is replaced with the B2 ′ port, and the description thereof is omitted.

Next, as shown in FIG. 1, a pressure sensor 51 for detecting the circuit pressure of the independent attachment circuit 7 is provided in an independent attachment line 31 connecting the pressure compensation type shunt valve 4 to the independent attachment circuit 7. The signal detection line 52 of the pressure sensor 51 is connected to the signal input unit of the controller 53.

Further, an operation lever 54, which is an electric joystick for operating an attachment, is connected to an input section of the controller 53 by an input signal line 55.

The output section of the controller 53 is connected to the solenoid 58 of the solenoid proportional valve 57 by the output signal line 56.

This solenoid proportional valve 57 is a solenoid valve which operates proportionally according to the control current value to the solenoid 58 output from the controller 53 and stroke-controls the shunt control spool 10 by pilot pressure, and its primary port. Is connected to the pilot hydraulic power source 59, and the secondary port is connected to the Pi port for inputting the switching signal pressure to the diversion control spool 10.

The solenoid proportional valve 57 is a pilot that proportionally changes the constant pilot primary pressure supplied from the pilot hydraulic pressure source 59 according to the control current value to the solenoid 58 output from the controller 53. The secondary pressure is converted and output to the Pi port, and the stroke of the flow dividing control spool 10 is controlled against the spring 41.

In the controller 53, the circuit pressure of the independent attachment circuit 7 detected by the pressure sensor 51 does not reach a region which is not excessive, that is, near the relief pressure set by the relief valve 8. Upon receiving an operation signal for attachment which is an electric signal proportional to the lever operation amount output from the operation lever 54, an electric signal (current) corresponding to the operation signal for attachment is output to the solenoid 58 of the solenoid proportional valve 57, By controlling the solenoid proportional valve 57, the diversion control spool 10 is stroke-controlled to control the opening areas of the variable throttles 39, 40. However, when the circuit pressure of the independent attachment circuit 7 rises to an excessive state, That is, when the circuit pressure close to the relief pressure set by the relief valve 8 rises, it is detected by the pressure sensor 51, Control so that the current value to the solenoid 58 of the solenoid proportional valve 57 is reduced regardless of the operation signal for the attachment, and the shunt control valve switching pressure output from the solenoid proportional valve 57 is automatically reduced. so,
The opening areas of the variable throttles 39, 40 of the diversion control spool 10 are controlled so as to be reduced.

Next, the operation of the embodiment shown in FIG.
Description will be made with reference to FIG.

The discharge oil discharged from the first hydraulic pump 2 and the second hydraulic pump 3 driven by the vehicle-mounted engine 1 is passed through the pressure compensation type shunt valve 4 to two permanent actuator circuits 5 and 6, and It is separately supplied to the independent attachment circuit 7.

One permanent actuator circuit 5 controls at least the left traveling hydraulic motor for driving the left crawler belt by the left traveling spool, and the other permanent actuator circuit 6 includes at least the right traveling spool. Controls a right-side running hydraulic motor for driving the right-side crawler belt.

Further, the independent attachment circuit 7 controls the hydraulic oil supplied to the attachment such as a hydraulic breaker or a crusher attached to the front end of the front working machine in place of the bucket by the attachment spool.

The pressure compensating type shunt valve 4 supplies the hydraulic oil discharged from each of the pumps 2 and 3 to the permanent actuator circuit 5 or 6 via the shunt control spool 10 and the pressure compensating spool 11 or 12, and , Shunt control spool
Flow control is performed at 10, the pressure is compensated at the pressure compensating spools 11 and 12, the flow is merged through the check valves 13 and 14, and then supplied to the independent attachment circuit 7.

The diversion control spool 10 is stroke-displaced by the pilot pressure from the Pi port against the biasing force of the spring 41, and the opening characteristics of the variable throttles 39 and 40 as shown in FIG. The flow rate of hydraulic oil from the P1 port connected to the pump 2 to the A1 port, and the second hydraulic pump 3
It freely controls the flow rate of hydraulic oil from the P2 port connected to the A2 port.

When the pilot pressure is not loaded on the Pi port, the total pump flow rate flows from the P1 port to the B1 port, from the P2 port to the B2 port, and further through the position 23 of the pressure compensation spools 11 and 12, to the left and right. It is supplied to various control spools of the permanent actuator circuits 5 and 6.

Now, the hydraulic pressures of the A1 port and the B1 port are set to PA1 and PB1, respectively, and the variable throttle 39 of the diversion control spool 10 is set.
Let Ax be the opening (Fig. 2) and QA1 be the flow rate of the hydraulic oil flowing from the P1 port to the A1 port.

QA1 = K · Ax · (PB1-PA1) ^1/2 (1) (where K is a constant) By the way, the pressure compensating spool 11 has a differential pressure (PB1-PA1).
Exceeds the constant differential pressure ΔP set by the spring 16, the spring 16
The position is switched from position 21 to position 22 against the urging force of No. 2 and when the differential pressure is further increased, position 23 is switched.

Therefore, when the diversion control spool 10 is at the position 43, (PB1-PA1) >> ΔP, the pressure compensation spool 11 is at the position 23, and the total flow rate flows to the B1 'port side.

On the other hand, when the diversion control spool 10 is at the position 44 or the position 45, (B1 'port pressure PB1')>
In case of (A1 'port pressure PA1'), a large amount of oil tries to flow to the A1 'port side, but at this time, the differential pressure (PB1-P
When A1) becomes larger than ΔP, the pressure compensation spool 11 becomes
It shifts to the position 23, that is, in the direction in which the flow rate of the hydraulic oil to the A1 'port side is regulated.

On the contrary, when PB1 '<PA1', the oil is B1 '
Attempts to flow a large amount to the port side, but at this time the differential pressure (P
When B1-PA1) becomes smaller than ΔP, the pressure compensation spool
11 is shifted toward the position 21 by the urging force of the spring 16, that is, in the direction of restricting the flow rate of hydraulic oil toward the B1 'port side.

That is, the pressure compensating spool 11 is A1 '.
Regardless of the port pressure PA1 'and B1' port pressure PB1 ', the differential pressure across the variable throttle 39 (PB1-PA
1) operates so as to maintain a constant value (ΔP), the flow rate QA1 according to the opening Ax of the variable throttle 39 is calculated from the equation (1).
Are supplied to the independent attachment circuit 7 from the A1 'port.

Similarly, the pressure compensation spool 12 for right running
Also, pressure compensation is performed on the shunt by the variable throttle 40 of the shunt control spool 10 according to the same operating principle as the pressure compensating spool 11 for left traveling.

In addition, the diversion control spool 10 has the same opening characteristic that communicates with the A1 port from the P1 port through the internal oil passage 36 and with the A2 port that communicates with the A2 port through the P2 port through the internal oil passage 38. Therefore, the equally divided flow rates of the hydraulic oil are always supplied to the A1 ′ port and the A2 ′ port, and at the same time, the equally divided flow rates of the hydraulic oil are also supplied to the B1 ′ port and the B2 ′ port. For this reason,
Since the flow rates of the hydraulic oil supplied to the left and right permanent actuator circuits 5 and 6 are always the same, the flow rates of the hydraulic oil supplied to the left traveling motor and the right traveling motor are always the same, and traveling bending does not occur.

When no excessive circuit pressure is generated in the independent attachment line 31, the controller 53 which receives an electric signal from the operation lever 54 for attachment
Outputs an electric signal proportional to the lever operation amount to the solenoid 58 of the solenoid proportional valve 57, and the stroke of the flow dividing control spool 10 is controlled via the solenoid proportional valve 57.

On the other hand, when an excessive pressure close to the relief pressure set by the relief valve 8 rises on the independent attachment line 31, a pressure sensor 51 that detects the pressure sends a signal of an overload condition to the controller 53. Therefore, the controller 53 reduces the current value actually output to the solenoid proportional valve 57 regardless of the current value to the solenoid proportional valve 57 instructed from the operation lever 54, and performs the shunt control from the solenoid proportional valve 57. The independent attachment circuit 7 is provided by automatically lowering the switching pressure output to the spool 10 and reducing the opening areas of the variable throttles 39 and 40 of the diversion control spool 10 as shown in FIG.
Control to reduce the amount of oil supplied to.

In this way, the independent attachment line 31
When a pressure close to the relief pressure rises, the amount of oil supplied to the independent attachment circuit 7 is automatically reduced. Therefore, the permanent actuator of the main body side working device, that is,
A large amount of oil will flow through the hydraulic motors for traveling and turning, and the hydraulic cylinders of the front work equipment such as booms, arms, and buckets, as compared to the conventional technology, and the attachment and the work device on the main body side will work together. In operation, as soon as the attachment became close to the relief pressure,
The speed of the body side work device does not slow down.

The fact that the circuit pressure of the independent attachment circuit 7 becomes close to the relief pressure means that the attachment is close to the stall state (overload stop state), and a small amount of oil that can hold the circuit pressure is required. It suffices and makes sense.

[0055]

According to the invention of claim 1, when an excessive circuit pressure is not generated in the independent attachment circuit,
The controller outputs an electric signal proportional to the operation signal for attachment to the solenoid proportional valve, and the stroke control of the diversion control valve can be performed via this solenoid proportional valve.On the other hand, if excessive circuit pressure is generated in the independent attachment circuit, The controller that detects this state via the pressure sensor controls the solenoid proportional valve regardless of the operation signal for attachment, and reduces the opening area of the variable throttle of the diversion control valve to supply to the independent attachment circuit. It can be controlled to reduce the amount of oil, and as a result, the amount of hydraulic oil supplied to the permanent actuator circuit can be restored as much as the amount of oil supplied to the independent attachment circuit has decreased, allowing smooth operation of the attachment and permanent actuator. , The workability of construction machinery can be improved.

According to the second aspect of the present invention, the state in which the circuit pressure of the independent attachment circuit is excessive is a state in which the circuit pressure close to the relief pressure is generated in the independent attachment circuit, so that the attachment is stalled. When it is close to, it is sufficient to have a small amount of oil to hold the circuit pressure, so that the circuit pressure of the independent attachment circuit can be reasonably dealt with in an excessive state.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of a hydraulic circuit of a construction machine according to the present invention.

FIG. 2 is a characteristic diagram showing an opening characteristic of a diversion control valve in the hydraulic circuit.

FIG. 3 is a PQ diagram showing the pressure-flow rate characteristic of the hydraulic pump in the hydraulic circuit.

[Explanation of symbols]

A few hydraulic pumps 5,6 Permanent actuator circuit 7 Independent attachment circuit 10 Flow control spool as flow control valve 11, 12 Pressure compensating spool as pressure compensating valve 39, 40 variable aperture 51 Pressure sensor 53 Controller 57 Solenoid proportional valve

Continuation of the front page (56) References JP 2000-73409 (JP, A) JP 53-41681 (JP, A) JP 56-90107 (JP, A) JP 60-137201 (JP, A) JP 5-172115 (JP, A) JP 64-93605 (JP, A) JP 7-190006 (JP, A) Special table 8-509054 (JP, A) (58) Survey Fields (Int.Cl. ⁷ , DB name) F15B 11/00 E02F 9/22

Claims (2)

(57) [Claims] 1. A permanent actuator circuit for controlling hydraulic oil supplied from a hydraulic pump to drive a permanent actuator of a construction machine, and an attachment of a construction machine by controlling a part of hydraulic oil supplied to the permanent actuator circuit. And an independent attachment circuit that drives independently of the permanent actuator circuit, and part of the hydraulic oil supplied from the hydraulic pump to the permanent actuator circuit is diverted to the independent attachment circuit and the flow rate of the diverted hydraulic oil is stroked. Flow control valve that controls the variable throttle according to the pressure control valve, a pressure compensation valve that controls the differential pressure across the variable throttle of the flow control valve to keep it constant, a pressure sensor that detects the circuit pressure of the independent attachment circuit, An electromagnetic proportional valve that controls the stroke of the control valve with pilot pressure and an independent valve detected by a pressure sensor. In the area where the circuit pressure of the attachment circuit is not too large, the solenoid proportional valve is controlled according to the operation signal for attachment to control the opening area of the variable throttle of the diversion control valve and the circuit of the independent attachment circuit detected by the pressure sensor. When the pressure rises to an excessive state, it is equipped with a controller that controls the solenoid proportional valve regardless of the operation signal for attachment to control the opening area of the variable throttle of the diversion control valve. The hydraulic circuit of the machine. 2. The hydraulic circuit for a construction machine according to claim 1, wherein the state in which the circuit pressure of the independent attachment circuit is excessive is a state in which a circuit pressure close to the relief pressure is generated in the independent attachment circuit.