JPH0160684B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a hydraulic circuit that has a switching valve between a variable displacement pump and an actuator and controls the speed of the actuator in accordance with the discharge flow rate of the pump.

FIG. 1 is a circuit diagram showing the basic configuration of a control device for a hydraulic circuit of this type, and FIG. 2 is a block diagram showing an example of control means included in the control device shown in FIG. In Fig. 1, 1 is a variable displacement pump;
a is a discharge amount control device that controls the discharge flow rate of the variable displacement pump 1; 2 is an actuator, such as a cylinder, driven by pressure oil supplied from the variable displacement pump 1; and 3 is the variable displacement pump 1 and the cylinder 2.
This is an on/off switching valve that is interposed between the variable displacement pump and the cylinder 2 and connects and disconnects the flow of pressure oil supplied to the cylinder 2 from the variable displacement pump. Reference numeral 4 indicates an operating device, that is, an operating lever, which commands the discharge flow rate of the variable displacement pump 1 and also switches the on/off switching valve 3. Reference numeral 5 indicates an operation for turning the on/off switching valve 3 ON in accordance with the operating amount X _L of the operating lever 4. It is a control means that outputs a signal or an OFF signal and also outputs a command signal having a discharge amount command value X to the discharge amount control device 1a. Note 6
7 indicates a load driven by the cylinder 2, and 7 indicates a relief valve interposed between the variable displacement pump 1 and the on/off switching valve 3.

As shown in FIG. 2, the above-mentioned control means 5 is composed of, for example, a digital arithmetic unit, and includes an A/D converter 5 that converts an analog signal into a digital signal.
a, a central processing unit (CPU) 5b that performs various controls and arithmetic processing, a memory 5c in which control procedure programs and predetermined functional relationships are set, and a driver circuit that outputs control contents to the discharge amount control device 1a. 5d. In the conventional hydraulic circuit control device, the functional relationship between the operation amount X _L of the operation lever 4 and the discharge amount command value X is set in the memory 5c constituting the control means 5. Also, 8,
Lines 9 and 10 are respectively connected to the operating lever 4, the switching valve 3, and the discharge amount control device 1a.

In the case of conventional hydraulic circuit control devices,
This is carried out according to the procedure shown in the flowchart of FIG. That is, first, as shown in step 30,
The operation amount X _L of the operation lever 4 is read into the central processing unit 5b via the A/D converter 5a of the control means 5. Next, as shown in step 31, the central processing unit 5b determines whether the operating lever 4 is being operated, that is, whether the operating amount _XL is zero. At this time, if it is determined that the operating lever 4 is not operated, the process moves to step 32, and the switching valve 3 is transferred from the central processing unit 5b to the driver circuit 5d.
An OFF signal is output, thereby keeping the switching valve in the closed state shown in FIG. Next, as shown in step 33, the memory 5c performs a process of setting the discharge amount command value X to 0 according to a command from the central processing unit 5b. In addition, if it is determined in step 31 that the operating lever 4 is being operated, step 3
4, from the central processing unit 5b to the driver circuit 5
d, an ON signal is output to the switching valve 3, thereby switching the switching valve 3 from the state shown in FIG. 1 to the right and into the open state. Next, as shown in step 35, the central processing unit 5b calculates the operating amount X _L of the operating lever 4 and the discharge amount command value X stored in the memory 5c.
A process is performed to select a specific value X _O corresponding to the manipulated variable X _L based on the functional relationship with the operation amount X L, and this X=X _O is set in the memory 5c. After steps 33 and 35, the process moves to step 36, where the central processing unit 5
b to the discharge amount control device 1 via the driver circuit 5d.
A command signal having a discharge amount command value X is output to a. The discharge amount control device 1a controls the discharge flow rate of the variable displacement pump 1 according to this discharge amount command value X.

Conventionally, the hydraulic circuit control device configured as described above has had the following problems. That is, the variable displacement pump 1 generally has a
There is a flow rate qlt that leaks from the discharge port (not shown) into the tank, and a flow rate qli that leaks from the discharge port to the suction port as shown by arrow 12 in the figure.
Therefore, if this hydraulic circuit is applied to a circuit that operates the boom of a hydraulic excavator (corresponding to load 6), the pressure in the circuit will increase due to the boom load being applied to cylinder 2, and the leakage flow rate will increase.
Both qlt and qli will increase. In such a situation, when attempting to slightly operate the operating lever 4 to slightly move the cylinder 2, conventionally the switching valve 3 would close, as is clear from steps 31 and 34 in the flowchart of FIG. state to open state. As a result, cylinder 2 and variable displacement pump 1 communicate with each other, and cylinder 2 switches to a control mode based on the discharge amount of pump 1, and even if the discharge amount of pump 1 is almost 0, cylinder 2 is activated by the leakage flow rate qlt + qli. Resulting in.

For this reason, even though the operating lever 4 is moved to raise the cylinder 2 slightly, the cylinder 2 may drop down, or even if the cylinder 2 is lowered only slightly, the leakage flow rate qlt + qli In other words, the speed of the cylinder 2 could not be controlled below the speed corresponding to the leakage flow rate, resulting in poor fine controllability. Such defects in fine operability are also a problem from the standpoint of protecting the safety of workers working on various hydraulic machines to which the above-mentioned hydraulic circuit control device is applied.

The present invention has been made in view of the actual situation in the prior art, and its purpose is to provide a hydraulic circuit control device that can control the speed of the actuator below the speed of the actuator corresponding to the leakage flow rate of a variable displacement pump. It's about doing.

To achieve this objective, the present invention provides a variable displacement pump, an actuator that is driven and loaded by the variable displacement pump, and an actuator that is interposed between the variable displacement pump and the actuator, and that is connected to the variable displacement pump. A hydraulic circuit having a switching valve that connects and disconnects the flow of pressure oil supplied to the actuator, the hydraulic circuit including an operating device that commands the discharge flow rate of the variable displacement pump and switches the switching valve. In a circuit control device, a variable capacity that exceeds the leakage flow rate and reaches a preset pressure setting value when a command amount within a predetermined range within the dead zone is output from the operating device. a first calculation means for calculating a first calculation value which is a discharge amount command value for determining the discharge flow rate of the pump; and a variable displacement pump corresponding to the first calculation value and a signal output from the operation device. a second calculation means for calculating a second calculation value that determines the discharge flow rate of the variable displacement pump by adding the discharge amount command value of the variable displacement pump; and a valve opening control hand that outputs a control signal for opening the valve, and is configured to control the discharge flow rate of the variable displacement pump in accordance with the second calculated value.

The hydraulic circuit control device of the present invention will be described below.

Figure 4 is a characteristic diagram commonly seen in this type of hydraulic circuit, with the upper part showing the relationship between the pump tilting angle and the pressure in the circuit, and the lower part showing the relationship between the pump tilting angle and the pressure in the circuit. A tilt angle-cylinder speed characteristic diagram showing the relationship with cylinder speed is drawn. Note that 13 in the tilt angle-pressure characteristic diagram indicates relief pressure. In addition, in the tilting angle-cylinder speed characteristic diagram, + and - on the horizontal axis indicating the pump tilting angle indicate the tilting direction of the variable displacement pump, and + and - on the vertical axis indicating the cylinder speed indicate the operating direction of cylinder 2. It shows. As can be seen from the dashed line 14 in FIG. 4, the pump tilt angle at which the cylinder speed is zero is the angle at which the pressure in the circuit increases. The present invention focuses on the relationship between the pump tilt angle, that is, the discharge amount of the variable displacement pump and the circuit pressure. In FIG. This is a preset pressure setting value that will be passed when the pressure is exceeded.

FIG. 5 is a circuit diagram showing a schematic configuration of a first embodiment of a control device for a hydraulic circuit of the present invention, and FIG. 6 is an explanatory diagram showing the basic principle of control performed by the control device of the present invention. FIG. 7 is a flowchart illustrating the control procedure in the first embodiment shown in FIG.

In FIG. 5, reference numeral 15 denotes a pressure detector for detecting the pressure in the circuit on the head side of the cylinder 2. Other basic configurations are the same as those shown in FIGS. 1 and 2 described above. That is, the control means 5 is, for example, an A/D
It is constituted by a digital arithmetic unit having a converter 5a, a central processing unit (CPU) 5b, a memory 5c, and a driver circuit 5d. The central processing unit 5b and the memory 5c of this control means 5 operate within a predetermined range a (a') within a dead zone F shown in FIG. When a certain command amount, _that is, a manipulated amount a first calculation means for calculating a first calculation value X ₁ which is a discharge amount command value for the discharge amount of the variable displacement pump 1 corresponding to the first calculation value X ₁ and the operation amount X _L of the operation lever 4; A second calculation value (discharge amount command value) X, which is a new discharge flow rate of the variable displacement pump 1, is calculated by adding the specific value X ₀ of the flow rate.
and outputs a control signal to open the switching valve 3 when the operation amount X _L of the operating lever exceeds a dead zone set value A (A') that specifies the range of the dead zone F in FIG. 6, which will be described later. It constitutes a valve opening control means.

FIG. 6 is an explanatory diagram showing the basic principle of control carried out by the control device of the present invention, in which the horizontal axis represents the operation amount X _L of the operating lever 4, and the vertical axis represents the cylinder speed. In this Figure 6, F is the operating lever 4.
A and A' are the dead zone setting values that specify the range of the dead zone F, and B and B' are the above-mentioned first dead zone.
The calculation start values a and _a ' corresponding to the point in time when the calculation to obtain the calculation value A range forming a preparation area immediately before speed control of the cylinder 2 is performed;
b and b' are ranges in which the discharge amount of the variable displacement pump 1 is always zero. In the control device of the present invention, the operation amount X _L of the operation lever 4 is the calculation start value B,
When the temperature reaches B', with the switching valve 3 kept closed,
Calculation by the first calculation means is _started to obtain a _first calculation value , a specific value of the discharge amount command value X of the variable displacement pump 1 corresponding to the operation amount X _L of the operation lever 4
X ₀ and the calculated value X ₁ obtained by the first calculation means
The discharge amount control device 1a controls the discharge flow rate of the variable displacement pump 1 and operates the cylinder 2 in accordance with the discharge amount command value X obtained thereby. It's like this.

The correlation between the above-mentioned dead band set values A, A', calculation start values B, B', pressure C, and the operation amount X _L of the operating lever 4 to give the specific value X ₀ and the discharge amount command value is as follows. It is set in advance in the memory 5c of the control means 5.

In the first embodiment configured in this way, control is performed, for example, according to the procedure shown in the flowchart of FIG. In this flowchart, it is assumed that the head side circuit of the cylinder 2 in which the pressure detector 15 is provided is at high pressure, and that pressure oil is flowing through the head side circuit.
Further, in this flowchart, ΔX indicates an increment corresponding to the amount of change in the discharge flow rate of the variable displacement pump 1, and P _L indicates a pressure value detected by the pressure detector 15.

First, as shown in step 40, the central processing unit 5
The operating amount X _L of the operating lever 4 is read into b. Next, as shown in step 41, this central processing unit 5
At step b, it is determined whether the manipulated variable X _L is greater than or equal to the calculation start value B. At this time, if the manipulated variable X _L is smaller than the calculation start value B, that is, if it is determined that it is within the range b in FIG. An OFF signal is output to keep the switching valve 3 in the closed state shown in FIG. Next, as shown in step 43, the memory 5c sets the discharge amount command value X to 0 according to a command from the central processing unit 5b. Next, in step 44, the current discharge amount command value X is set in the memory 5c as the calculated value _X1 . In this case, since X=0, X ₁ =0. Then, proceeding to step 45, the discharge amount control device 1 passes through the central processing unit 5b of this control means 5 and the driver circuit 5d.
A command signal of the discharge amount command value X (=X ₁ =0) is output to a.

In addition, in step 41 described above, the amount of operation of the operating lever 4 is
If it is determined that X _L is greater than or equal to the calculation start value B, the process moves to step 46, where the central processing unit 5b calculates the operation amount.
It is determined whether _XL is greater than or equal to the dead zone setting value A. At this time, if the operation _amount
OFF signal is output. Next, the process moves to step 48, and the pressure value P _L of the pressure detector 15 is determined by the A/D converter 5a.
is read into the central processing unit 5b via step 49.
Move to. In this step 49, the magnitude relationship between the pressure C stored in the memory 5c and the above-mentioned pressure value P _L is determined. At this time, if it is determined that the pressure value P _L is smaller than the pressure C, the process moves to step 50, and the central processing unit 5b performs a first calculation of adding an increment ΔX to the calculation value _X1 . Next, in step 44, the current discharge amount command value X is set as a new calculated value _X1 , and in step 45, a command signal of the discharge amount command value X (= _X1 ) is output to the discharge amount control device 1a. be done. Further, when it is determined in step 49 that the pressure value P _L is equal to or higher than the pressure C, the process moves to step 51, and the discharge amount command value X is set to the calculated value X ₁ in the memory 5c.
Next, proceed to step 44 to set the current discharge amount command value X as a new calculated value X ₁ , and then proceed to step 45.
Inputs the discharge amount command value X (=X ₁ ) to the discharge amount control device 1a.
A command signal is output.

In addition, if it is determined in step 46 that the manipulated variable X _L is equal to or greater than the dead band setting value A, the operation of cylinder 2 is to be started or continued, and the process moves to step 52, where the central processing Turns ON from the device 5b to the switching valve 3 via the driver circuit 5d.
A signal is output, whereby the switching valve 3 is switched to the right position in FIG. 5, and becomes open. Next, the process moves to step 53, and the central processing unit 5b determines a specific value X 0 corresponding to the operation amount X _L from the functional relationship between the operation amount X _L of the operating lever 4 and the discharge amount command value X set in the memory _5c. At the same time, the calculated value previously set in the memory 5c is
Read X ₁ and calculate X ₀ +X ₁ to obtain a second calculated value. Then, the process moves to step 45, and a command signal of the discharge amount command value X (=X ₀ +X ₁ . . . second calculated value) is output to the discharge amount control device 1a. Discharge amount control device 1a
is the variable displacement pump 1 according to this discharge amount command value
control the discharge flow rate.

In the first embodiment configured in this way, with the switching valve 3 in the closed state, the pressure is approximately the same as the pressure in the head side circuit which is the high pressure side (equal to the first calculated value X ₁ ). (pressure corresponding to discharge amount command value X)
, the pressure in the discharge side circuit of the variable displacement pump 1 is increased, and then the switching valve 3 is opened, and the first calculated _value
and the specific value X ₀ corresponding to the operation amount X _L of the operating lever 4
Since the control is performed using a command signal having a discharge amount command value X equal to the second calculated value obtained by the sum of , therefore, the cylinder 2 according to the operation amount X _L of the operation lever 4
speed control can be achieved.

FIG. 8 is a circuit diagram showing a schematic configuration of a second embodiment of the present invention, and FIG. 9 is a flowchart illustrating a control procedure in the second embodiment shown in FIG.

In FIG. 8, numeral 15 is a pressure detector for detecting the pressure in the circuit on the head side of the cylinder 2, and numeral 16 is a pressure detector for detecting the pressure in the circuit on the head side of the cylinder 2, as shown in the first embodiment described above.
A pressure detector that detects the pressure in the circuit on the rod side of the
Reference numeral 17 denotes a shuttle that moves in the left-right direction in the figure depending on the level of pressure in the head side circuit and rod side circuit of the cylinder 2. Reference numerals 18 and 19 denote switches that output signals in accordance with the movement of the shuttle 17, such as proximity switches. It is. Note that the pressure detectors 15 and 16 and the proximity switches 18 and 19 are connected to the control means 5. Further, the proximity switch 19 of the cylinder 2 is
High level (signal value 1) when the head side is high voltage
On the other hand, the proximity switch 18 outputs a signal L of low level (signal value 0) at this time,
Further, when the rod side of the cylinder 2 is under high pressure, the proximity switch 18 outputs a high level signal L, and the proximity switch 19 outputs a low level signal R.
Note that when both the head side and rod side of the cylinder 2 are at the same pressure, the proximity switches 18 and 19 both output low level signals L and R.

The control in this second embodiment is basically the same as that in the first embodiment, but unlike the first embodiment, control is performed according to the pressure in the circuit on the head side of the cylinder 2. On the other hand, in this second embodiment, control can be performed in accordance with the pressures of both the head side circuit and the rod side circuit of the cylinder 2.

Control in the second embodiment configured as described above is performed, for example, according to the procedure shown in the flowchart of FIG. In this flowchart, P _L indicates a pressure value detected by the pressure detector 15, and P _R indicates a pressure value detected by the pressure detector 16.

First, as shown in step 60, the A/D of the control means 5
The operating amount X _L of the operating lever 4 and the pressure signals R and L of the proximity switches 18 and 19 are read into the central processing unit 5b via the converter 5a. Next, as shown in step 61, the central processing unit 5b determines whether the manipulated variable X _L is greater than or equal to the calculation start value B. At this time, if the manipulated variable X _L is smaller than the calculation start value B, that is, if it is determined that it is within the range b shown in FIG. to valve 3
An OFF signal is output, thereby keeping the switching valve 3 in the closed state shown in FIG. Then step 63
In step 64, the memory 5c is set to set the discharge amount command value X to 0, and in step 64, the current discharge amount command value X (=0) is changed to the calculated value X ₁ (=0).
A command signal of a discharge amount command value X (=X ₁ =0) is outputted to the discharge amount control device 1a via the central processing unit 5b of the control means 5 and the driver circuit 5d in step 65.

Further, if it is determined in step 61 that the manipulated variable X _L is greater than or equal to the calculation start value B, the process moves to step 66, and the central processing unit 5b determines that the manipulated variable X _L is the dead zone setting value shown in FIG. It is determined whether it is A or higher. At this time, if the manipulated variable X _L is smaller than the dead band setting value A, that is, if it is determined that it is within the range a in FIG. The process then moves to step 68, where it is determined whether the L signal of the proximity switch 18 has a signal value of one. At this time, if the relevant L signal does not have a signal value of 1, the process moves to step 69, and in this step 69, the R signal of the proximity switch 19 is
It is determined whether the At this time, if the R signal does not have a signal value of 1, the L signal and R
The signal values of both signals are 0, and the pressure on the head side and rod side of the cylinder 2 is approximately the same, and the shuttle 17 is held in a neutral state. Therefore, the process moves to step 63, and the setting to set the discharge amount command value X to 0 is made in the memory 5c.
In step 64, the current discharge amount command value
(=0) is set as the calculated value X ₁ (=0), and in step 65 a command signal of the discharge amount command value X (=X ₁ =0) is output to the discharge amount control device 1a.

Also, in step 69 described above, the proximity switch 19 is set to R.
If the signal is determined to have a signal value of 1, then
The circuit on the head side of the cylinder 2 is at high pressure, and the shuttle 17 is in a state of being moved to the right in FIG. Therefore, proceeding to step 70, the pressure value P _L of the pressure detector 15 that detects the pressure in the circuit on the head side of the cylinder 2 is read into the central processing unit 5b via the A/D converter 5a of the control means 5, Next, as shown in step 71, a predetermined pressure C preset in the memory 5c is read out to the central processing unit 5b.
The magnitude relationship between this pressure C and the above-mentioned pressure value P _L is determined. At this time, if it is determined that the pressure value P _L is smaller than the pressure C, the process moves to step 72, and the central processing unit 5b performs a first calculation of adding an increment ΔX to the calculation value _X1 . Next, the process moves to step 64, where the current discharge amount command value X is calculated as a new calculated value _X1 , and in step 65, a command signal of the discharge amount command value X (= _X1 ) is output to the discharge amount control device 1a. be done. In addition, in step 71 described above, the pressure value P _L is changed to the pressure C
If it is determined that the above is the case, the process moves to step 73, and a setting is made in the memory 5c to set the discharge amount command value X to the calculated value _X1 . Next, in step 64, the current discharge amount command value X is set as a new calculated value _X1 , and in step 65, a command signal of the discharge amount command value X (= _X1 ) is output to the discharge amount control device 1a. be done.

Further, in the above-described step 68, if it is determined that the L signal of the proximity switch 18 has a signal value of 1,
The circuit on the rod side of the cylinder 2 becomes high pressure, and the shuttle 17 moves to the left in FIG. Therefore, the process moves to step 74, where the pressure value P _R of the pressure detector 16 that detects the pressure in the circuit on the rod side is read into the central processing unit 5b via the A/D converter 5a of the control means 5, and in step 75, As shown, a predetermined pressure C preset in the memory 5c is read out by the central processing unit 5b, and the magnitude relationship between this pressure and the above-mentioned pressure value _PR is determined. At this time, if it is determined that the pressure value P _R is smaller than the pressure C, the process moves to step 76, and the central processing unit 5b calculates the calculated value.
A first operation is performed that subtracts the increment ΔX from X ₁ . Next, in step 64, the current discharge amount command value X is set as a new calculated value _X1 , and in step 65, the discharge amount command value
(=X ₁ ) command signal is output. Further, if it is determined in step 75 that the pressure value P _R is equal to or higher than the pressure C, the process moves to step 73 described above, and the discharge amount command value X is set to be the calculated value _X1 in the memory 5c. Next, in step 64, the current discharge amount command value X is set to a new calculated value _X1 , and in step 65, a command signal of the discharge amount command value X (= _X1 ) is sent to the discharge amount control device 1a Output.

If it is determined in step 66 that the operation _amount Turns ON from the device 5b to the switching valve 3 via the driver circuit 5d.
A signal is output, whereby the switching valve 3 is switched to the right position in FIG. 8 and becomes open. Next, the process moves to step 78, and the central processing unit 5b determines a specific value X ₀ corresponding to the operation amount X _L based on the functional relationship between the operation amount X _L of the operating lever 4 and the discharge amount command value X set in the memory 5c. At the same time, the calculated value previously set in the memory 5c is
Read X ₁ and calculate X ₀ +X ₁ to obtain a second calculated value. Then, the process moves to step 65, and a command signal of the discharge amount command value X (=X ₀ +X ₁ . . . second calculated value) is output to the discharge amount control device 1a. Discharge amount control device 1a
is the variable displacement pump 1 according to this discharge amount command value
control the discharge flow rate.

Even in the second embodiment configured in this way, the pressure in the discharge side circuit of the variable displacement pump 1 is increased to approximately the same pressure as the head side circuit or rod side circuit of the cylinder 2 forming the high pressure side. let me,
In this state, the switching valve 3 is opened and controlled by a command signal having a discharge amount command value X equal to the second calculated value (=X ₀ +X ₁ ). Similarly, the speed of the cylinder 2 can be controlled according to the operation amount X _L of the operation lever 4.

In addition, in the first and second embodiments described above, in view of the tilting direction of the variable displacement pump 1, the control related to the calculation start value B, the dead zone setting value A, and the ranges a and b in FIG. 6 will be described. However, if the tilting direction of the variable displacement pump 1 is reversed, the calculation start value shown in Fig. 6
B', dead zone setting value A', and ranges a' and b' may be controlled.

Since the hydraulic circuit control device of the present invention is configured as described above, it is possible to perform speed control below the actuator speed corresponding to the leakage flow rate of the variable displacement pump, and has the effect of improving fine operability. There is. Therefore, it is possible to prevent the actuator from operating unintentionally by the worker who operates the actuator, contributing to the safety of the worker.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram illustrating a conventional hydraulic circuit control device, and FIG. 2 is a block diagram showing an example of a control means constituting the hydraulic circuit control device shown in FIG.
FIG. 3 is a flowchart illustrating a control procedure in a conventional hydraulic circuit control means, and FIG. 4 is a pump tilting angle-pressure characteristic and pump tilting angle-cylinder generally seen in a hydraulic circuit to which the present invention is applied. A characteristic diagram showing the speed characteristics, FIG. 5 is a circuit diagram showing a schematic configuration of the first embodiment of the control device for a hydraulic circuit of the present invention, and FIG. 6 shows the control performed by the control device of the present invention. Explanatory diagram showing the basic principle of
The figure is a flowchart illustrating the control means in the first embodiment shown in FIG. 5, FIG. 8 is a circuit diagram showing a schematic configuration of the second embodiment of the present invention, and FIG. 9 is shown in FIG. 7 is a flowchart illustrating a control procedure in a second embodiment. 1... Variable displacement pump, 1a... Discharge amount control device, 2... Cylinder (actuator), 3...
On/off switching valve, 4... Operating lever, 5... Control means, 5a... A/D converter, 5b... Central processing unit (CPU), 5c... Memory, 5d... Driver circuit, 7... Relief Valve, 15, 16...Pressure detector, 17...Shuttle, 18, 19...Proximity switch.

Claims (1)

[Claims] 1 A variable displacement pump, an actuator that is driven by the variable displacement pump and subjected to a load, and an actuator that is interposed between the variable displacement pump and the actuator to control the flow of pressure oil supplied from the variable displacement pump to the actuator. In a hydraulic circuit having a switching valve that connects and disconnects, the control device for the hydraulic circuit is equipped with an operating device that commands the discharge flow rate of the variable displacement pump and commands switching of the switching valve, wherein: When a command amount within a predetermined range within the dead band is output, the discharge flow is set to exceed the leakage flow rate and reach the preset pressure setting value of the variable displacement pump. a first calculation means for calculating a first calculation value that is a quantity command value; a second calculation means for calculating a second calculation value that determines the discharge flow rate of the variable displacement pump; and a valve opening unit that outputs a control signal to open the switching valve when the command amount of the operating device exceeds the dead zone. A control device for a hydraulic circuit, comprising a control means, and controlling a discharge flow rate of a variable displacement pump according to the second calculated value.