JPH0316523B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic circuit for driving an inertial mass that is equipped with an actuator that drives a large inertial mass, such as a hydraulic motor that drives a revolving body of a hydraulic excavator. .

[Conventional technology]

In FIG. 1, which shows an example of a conventional hydraulic circuit for driving an inertial mass, 1 is an actuator that drives a large inertial mass, such as a hydraulic motor that drives a rotating body of a hydraulic excavator, and 2 is a hydraulic motor that supplies pressure oil to this hydraulic motor 1. A hydraulic pump 3 is a prime mover that drives this hydraulic pump 2. 4 is a closed center type three-position switching valve; 5 is a pipe connected to the discharge side of the hydraulic pump 2; the discharge side is connected to the neutral position N of the switching valve 4;
The switching valve 4 is connected to the tank communication pipe 6 via the tank port T. 7 is a pipe branched from the pipe 5 and communicates with one input port a of the switching valve 4; 8 is a check valve installed in the pipe 7 to prevent backflow; 9 is a pipe of the switching valve 4; This is a conduit that connects the other input port b and the tank communication conduit 6. 1
0 is a relief valve that sets the maximum pressure of pipe line 5,
Pipe line 1 that communicates pipe line 5 and tank communication pipe line 6
1 is interposed. 12 is a conduit that communicates the first port of the hydraulic motor 1, that is, one suction/discharge port, and one output port c of the switching valve 4; and 13 is the second port of the hydraulic motor 1, that is, the other suction/discharge port, and the switching valve. This is a conduit that communicates with the other output port d of No. 4. 14 is a differential pressure type relief valve, ie, a brake valve, which sets the maximum pressure of the pipe line 12;
It is interposed in a pipe line 15 that communicates the pipe line 13 with the pipe line 13. Reference numeral 16 denotes a differential pressure type relief valve, ie, a brake valve, which sets the maximum pressure of the pipe line 13, and is interposed in the pipe line 17 that connects the pipe line 12 and the pipe line 13.
Reference numerals 18 and 19 indicate check valves, which are interposed in a pipe line 21 and a pipe line 22 branched from a pipe line 20 communicating with the pipe line 6, respectively, and supply oil from a tank 23 to the pipe line 12 and the pipe line 13. .

FIG. 2 is a sectional view showing the structure of the three-position switching valve 4 described above, and this figure shows the neutral state. The pipe line 24 shown in FIG. 2 is connected to the above-mentioned pipe line 5, and thus communicates with the hydraulic pump 2. Conduit 2
5 is connected to the tank communication pipe 6 mentioned above and communicates with the tank 23. The pipe line 26 communicates with one output port c of the switching valve 4, and communicates with one intake/discharge port of the hydraulic motor 1 via the pipe line 12. The pipe line 27 communicates with the other output port d of the switching valve 4 , and communicates with the other intake/discharge port of the hydraulic motor 1 via the pipe line 13 .
28 is a spool which, when moved in the x direction in FIG. 2, is switched to position B in FIG. 1. In addition, 29
is a first opening/closing part formed between the main body of the switching valve 4 and the spool 28, which connects the pipe line 24 and the pipe line 26, that is, one intake/discharge port of the hydraulic motor 1 and the hydraulic pump. Open and close the conduit connecting 2. Reference numerals 30 and 31 are second opening/closing parts formed between the main body of the switching valve 4 and the spool 28;
4 and the pipe line 25, that is, the pipe line that communicates the hydraulic pump 2 and the tank 23. Further, 32 is a third opening/closing part formed between the main body of the switching valve 4 and the spool 28, and is connected to a pipe line that communicates the pipe line 27 and the pipe line 25, that is, the other suction/discharge port of the hydraulic motor 1. The pipe line communicating with the tank 23 is opened and closed. In addition, 33 is a check valve provided in the middle of the pipe line which communicates the pipe line 24 and the pipe line 26.

In a conventional hydraulic circuit for driving an inertial mass having such a three-position switching valve 4, when the switching valve 4 is switched to the B position by the operation lever in order to drive the inertial mass, the hydraulic pump 2 is turned off. Discharge side pipe line 5
communicates with the pipe line 12 via the pipe line 7 and the input port a and output port c of the switching valve 4, and communication between the hydraulic pump 2 and the tank communication pipe line 6 is cut off by the switching valve 4. As a result, the pressure oil of the hydraulic pump 2 is guided to the hydraulic motor 1 and attempts to operate the inertial mass via the hydraulic motor 1. However, since the inertial force due to the inertial mass acts on the hydraulic motor 1, the rotational speed of the hydraulic motor 1 does not suddenly increase, and high pressure is generated in the pipe line 12. When this high pressure exceeds the set value of the brake valve 14, it is relieved to the conduit 13 via the brake valve 14 and the conduit 15. When the acceleration state ends, the hydraulic motor 1 enters a steady speed state and operates at a constant speed. From this state, when the switching valve 4 is returned to the neutral position N, which is the state shown in FIG.
2 and the pipe line 13 are closed by the switching valve 4. At this time, the hydraulic motor 1 continues to operate due to the inertial force of the inertial mass, and discharges the oil sucked in from the pipe line 12 to the pipe line 13. For this purpose, conduit 13
becomes high pressure, and when this high pressure exceeds the set value of the relief valve 16, the relief valve 16 and the pipe line 17
Pressure oil is relieved into the conduit 12 through the pipe. Further, the hydraulic motor 1 is gradually decelerated due to the high pressure in the conduit 13.

Next, the above-mentioned operating state will be explained based on FIGS. 2 and 3 and FIG. 1, which are sectional views showing the structure of the three-position switching valve 4. Note that FIG. 2 shows the neutral state as described above, and FIG. 3 shows the state switched to the B position.

When the switching valve 4 is switched to the B position as shown in FIG. 3, the pipe line 24 communicating with the discharge side pipe line 5 of the hydraulic pump 2 shown in FIG. It communicates with the conduit 26 via the opening/closing part 29 of 1. Note that the pipe line 26 communicates with the above-mentioned pipe line 12. Further, the pipe line 27 communicating with the above-mentioned pipe line 13 communicates with the pipe line 25 via the third opening/closing part 32 and the pipe line 34 which are in an open state. Note that this pipe line 25 communicates with the tank communication pipe line 6.
On the other hand, a pipe line 24 and a pipe line 2 communicating with the hydraulic pump 2
5 is blocked by the second opening/closing parts 30, 31 in the closed state.

When the switching valve 4 is returned to the neutral position N and the brake is applied while the hydraulic motor 1 is in operation, the switching valve 4 will be in the state shown in FIG. 2. That is, conduit 1
2 and 13 are a first opening/closing part 29 and a third opening/closing part 32
The pipe line 24 and the pipe line 25 are communicated with each other by opening the second opening/closing parts 30 and 31, and the pressure oil discharged from the hydraulic pump 2 flows into the tank 23.

Note that such an operation is the same when decelerating when the switching valve 4 is switched to the A position shown in FIG. 1 and the hydraulic motor 1 is rotated in the opposite direction.

FIG. 4 shows the amount of movement of the spool 28 of the switching valve 4 accompanying the operation of the switching valve 4, the first opening/closing part 29, the second opening/closing part 30, 31, and the third opening/closing part 3.
FIG. 2 is a diagram showing the relationship between No. 2 and the opening area. Note that α on the horizontal axis in FIG. 4 indicates the amount of movement of the spool 28, and the amount of movement increases toward the x direction in FIG. Further, β on the vertical axis indicates the opening area, and the opening area increases in the y direction. 35 is a characteristic line in the third opening/closing part 32, 36 is a characteristic line in the first opening/closing part 29, 37 is a characteristic line in the second opening/closing part 30,
31 is shown.

When attempting to return the spool 28 to neutral in order to apply a brake to the hydraulic motor 1 in operation (when attempting to move it in the opposite direction to the x direction), as shown by characteristic lines 35 and 36 in FIG. Third opening/closing part 3
2 and the opening area of the first opening/closing part 29 decrease, and then, as shown by a characteristic line 37, the opening area of the second opening/closing part 30, 31 starts to increase. Note that the second opening/closing parts 30 and 31 are opened to a sufficiently large opening area before the third opening/closing part 32 and the first opening/closing part 29 complete closing. Furthermore, the third opening/closing section 32 and the first opening/closing section 29 are configured to complete closing at the same time.

[Problem to be solved by the invention]

By the way, in the conventional inertial mass drive hydraulic circuit configured as described above, as shown by the characteristic lines 35 and 36 in FIG.
The conduit 12 and the conduit 13 are closed at the γ point where the opening area of the first switching section 2 and the opening area of the first opening/closing section 29 become zero, but at that time, as shown by the characteristic line 37 in FIG. The opening/closing parts 30 and 31 are opened to a sufficiently large opening area, so that the pressure in the pipe line 5 communicating with the hydraulic pump 2 becomes the tank pressure. Therefore, when the pipe line 12 and the pipe line 13 are closed and the brake is applied to the hydraulic motor 1, the pressure in the pipe line 12 becomes the tank pressure, and the pressure in the pipe line 13 at this time is equal to the tank pressure and the relief valve. 16 set pressures are added.
Note that when the circuit constituted by the hydraulic motor 1 and the pipes 12 and 13 is closed, oil leakage to the outside of the circuit is generally prevented due to the functionality of the hydraulic motor 1 etc. It definitely happens. For example, in the hydraulic motor 1, leaks occur between the cylinder and the valve plate, and between the piston shoe and the swash plate, and in the switching valve 4, leaks occur from the annular gap in the spool 28.
Therefore, the amount of oil in the circuit becomes insufficient, the amount of suction into the hydraulic motor 1 becomes insufficient, and cavitation will occur if this state continues.

In the conventional hydraulic circuit described above, in order to prevent such cavitation, as shown in FIG.
8 and 19 are provided so that oil from the tank 23 can be replenished via pipes 21 and 22 via check valves 18 and 19. In other words, as described above, when the amount of oil in the pipe line 12 is insufficient and the pressure in the pipe line 12 becomes equal to or lower than the tank pressure, the insufficient amount of oil is caused by the check valve 18.
It is supplied to the conduit 12 via. But in general,
In many cases, the tank pressure can only be made slightly higher than atmospheric pressure, and the pressure difference between the conduit 12 and the tank pressure cannot be made large. For this reason, in the past, due to the pressure loss of the check valve 18, etc., it may not be possible to sufficiently replenish the insufficient amount of oil, resulting in the problem that it is not always possible to adequately prevent cavitation. be.

The present invention has been made in view of the actual situation in the prior art, and its purpose is to apply relief pressure of a hydraulic pump in a pipe line connected to the actuator that drives an inertial mass when decelerating the actuator that drives the inertial mass. It is an object of the present invention to provide a hydraulic circuit for driving an inertial mass that can be enclosed and does not require replenishment of oil.

[Means to solve the problem]

In order to achieve this object, the present invention includes a hydraulic pump driven by a prime mover, and a rotating swing equipped in a hydraulic excavator that is operated by pressure oil supplied from the hydraulic pump and drives a large inertial mass. an actuator such as a hydraulic motor, a tank connected to the hydraulic pump, and a first conduit interposed between the tank and the hydraulic pump that opens and closes the pipe connecting the hydraulic pump and the first port of the actuator. a second opening/closing part for opening/closing a pipeline connecting the hydraulic pump and the tank; and a third opening/closing part for opening/closing a pipeline connecting the second port of the actuator and the tank. A valve, a brake valve that sets the maximum pressure in the pipeline between the switching valve and the actuator, and a relief valve that sets the maximum pressure in the pipeline between the hydraulic pump and the switching valve, When the actuator is decelerated, the switching valve described above closes the third opening/closing part with priority over the first opening/closing part, or closes the third opening/closing part with priority over the first opening/closing part. is brought into a nearly closed state in which The structure includes a means for opening the second opening/closing part which is in a closed state or a nearly closed state so as to enlarge the opening area.

[Effect]

In the present invention configured as described above, the third opening/closing part that opens and closes the pipe connecting the second port of the actuator and the tank is connected to the pipe connecting the hydraulic pump and the first port of the actuator. By closing or nearly closing the first opening/closing part with priority over the first opening/closing part, the communication between the second port of the actuator and the tank is cut off, and the pressure generated on the second port side A brake is applied to the actuator. In addition, the second opening/closing part of the switching valve that connects the hydraulic pump and the tank,
Since the third opening/closing part and the first opening/closing part are closed or opened after close operation, the hydraulic pump and switching valve generated due to the above-mentioned brake operation must be removed before the second opening/closing part is opened. The maximum pressure set in the line between the lines can be supplied to the line connecting the hydraulic pump and the first port of the actuator via the first opening/closing part in the open state, whereby the line and The set maximum pressure described above can be confined in both of the pipe lines connected to the second port of the actuator. It takes some time, for example several seconds, for the pressure in these pipes to fall from the maximum pressure to the tank pressure, within which time the inertial mass stopping operation can be completed, and therefore,
Until the inertial mass stops, the pressure in each of the above lines is maintained higher than the tank pressure, so that cavitation does not occur and no oil replenishment is required to prevent such cavitation. .

〔Example〕

Hereinafter, a hydraulic circuit for driving an inertial mass according to the present invention will be explained based on the drawings.

FIG. 5 is a partial sectional view of a three-position switching valve constituting a main part of an embodiment of the present invention, showing a neutral state. In this figure and later-described FIGS. 7a and 7b, the same parts as those shown in FIGS. 2 and 3 described above are designated by the same reference numerals. The basic configuration of the hydraulic circuit in which the switching valve shown in FIG. 5 is disposed is substantially the same as the hydraulic circuit shown in FIG. 1 described above. However, the pipes 20 and 2 shown in FIG.
1, 22, and check valves 18, 19 are not necessary for the technology targeted by the present invention, so they are omitted, for example.

In FIG. 5, 40 is the main body of the switching valve, 41 is the spool, and 42 is the first switch when switching the spool 41.
This reference line 42 is a reference line temporarily set to explain the opening/closing timing of the opening/closing part 29, the second opening/closing part 30, 31, and the third opening/closing part 32.In the neutral state shown in FIG. It passes through the center of the spool 41 and the main body 40.

In this embodiment, the main body 40 of the switching valve 4
and spool 41 are provided as described below.

For now, the main body 40 constituting the third opening/closing section 32
The distance between the end face 43 of the spool 41 and the reference line 42 is x ₁ , and the distance between the end face 44 of the spool 41 constituting the third opening/closing portion 32 and the reference line 42 is y ₁ . Furthermore, the distance between the end surface 45 of the main body 40 constituting the first opening/closing section 29 and the reference line 42 is _x2 , and the distance between the end surface 46 of the spool 41 constituting the first opening/closing section 29 and the reference line 42 is x2. Let y be ₂ . Also, among the second opening/closing parts 30 and 31, the distance x ₃ between the end surface 47 of the main body 40 constituting the second opening/closing part 31 and the reference line 42,
1 and the reference line 4 of the spool 41
₂ , and the distance between the end surface 49 of the main body 40 constituting the second opening/closing part 30 and the reference line 42.
x ₄ , spool 41 that constitutes the second opening/closing section 30
Let the distance between the end face 50 and the reference line 42 be _y4 . Then, the third opening/closing part 32, the first opening/closing part 29, the second opening/closing part 32,
If the lengths of the outer peripheries of the end surfaces 44, 46, 50, 48 of the spool 41 constituting each of the opening/closing parts 30, 31 are all πd, then these third opening/closing part 32, first opening/closing part 29, Second opening/closing part 3
The opening areas of 0 and 31 are (y ₁ −x ₁ )πd, respectively.
They are expressed as (x ₂ −y ₂ )πd, (y ₄ −x ₄ )πd, and (x ₃ −y ₃ )πd. Therefore, the area of these openings is linearly proportional to the distance traveled by the spool 41. For this reason, in this embodiment, the above x ₁ ~
x ₄ , y ₁ to _{y 4} , when y ₁ < x ₁ , y ₂ > x ₂ , y ₄ >
When x ₄ , y ₃ < x ₃ and y 1 ≧ x ₁ , _{x 2 >} y ₂ and x ₂ − y ₂ > y ₁ − x ₁ , and x ₂ ≧ y ₂ , x ₄ > y ₄ , y ₃ > x ₃ , and |y ₄ −x ₄ |+|x ₃ −
It is set so that y ₃ |>|x ₂ −y ₂ | is satisfied.

These relationships are expressed as the amount of movement of the spool 41 and the first
When expressed in relation to the opening area of the opening/closing part 29, the second opening/closing part 30, 31, and the third opening/closing part 32, the sixth
The result will be as shown in the figure. Note that α on the horizontal axis of FIG. 6 indicates the amount of movement of the spool 41, and β on the vertical axis indicates the opening area. Further, 51 is the third opening/closing part 3
2, 52 is a characteristic line in the first opening/closing part 29, and 53 is a characteristic line in the second opening/closing part 30, 31.

As is clear from FIG. 6, in this embodiment, the main body 40 and spool 41 of the switching valve 4 constitute means for realizing the operations described below. That is, when decelerating, first, as shown by the characteristic lines 51 and 52, the opening area of the third opening/closing part 32 is smaller than the opening area of the first opening/closing part 29, that is, the third opening/closing part 32 is The first
After the opening area of the third opening/closing part 32 and the first opening/closing part 29 becomes zero, that is, the third opening/closing part 32
After the closing operation of the first opening/closing part 29 is completed, the second opening/closing parts 30 and 31, which are in the closed state with an opening area of zero as shown by the characteristic line 53, are opened so as to enlarge the opening area. .

Next, the operation of the hydraulic motor of the embodiment configured as described above during deceleration will be explained based on FIGS. 7a and 7b and FIG. 1. Note that FIGS. 7a and 7b are partial sectional views illustrating the operation of the switching valve 4.

When trying to switch the switching valve 4 from the B position shown in FIG. 1 to the neutral position in order to apply a brake to the hydraulic motor 1 in operation, first, as shown in FIGS. 7a and 7b, the third opening/closing part 32 is closed and the first
The pipeline 27 communicating with the pipeline 13 shown in the figure and the pipeline 54 communicating with the tank communication pipeline 6 via the aforementioned pipeline 25 are cut off. At this time, the first opening/closing part 29 is in an open state, and therefore the pipe line 26 communicating with the pipe line 12 shown in FIG.
It communicates with a conduit 24 which is connected to a conduit 5 which communicates with the conduit 5 . Note that the second opening/closing parts 30 and 31 are in a closed state, so that the conduit 24 and the aforementioned conduit 25 are closed.
The conduit 55 communicating with is cut off. the result,
The pressure of the hydraulic pump 2 is transmitted from the pipe line 5 to the pipe line 13 via the pipe line 12 and the hydraulic motor 1. However, since the third opening/closing part 32 is in the closed state, the pressure of the hydraulic pump 2 is transmitted to the pipe line 13 via the pipe line 12 and the hydraulic motor 1. The pressure increases to the relief pressure of .

Then, when the spool 41 continues to move,
As shown in FIG. 7b, the second opening/closing parts 30, 3
1 and the third opening/closing part 32, the first opening/closing part 29 is in a closed state, and the relief pressure of the hydraulic pump 2 is applied to the pipe lines 12, 1 of both ports of the hydraulic motor 1.
be trapped in 3. In addition, since the brake pressure of the hydraulic motor 1 is determined by the pressure difference between the pipes 12 and 13, the brake pressure is ensured.

Furthermore, when the neutral state is reached, as shown in FIG.
0 and 31 are in an open state, and the pipe line 24 communicating with the pipe line 5 and the pipe line 55 communicating with the pipe line 25, that is, the tank communication pipe line 6, communicate with each other.

The time required for the relief pressure of the hydraulic pump 2 trapped in both ports of the hydraulic motor 1 to drop to the tank pressure due to leakage, etc. as described above is as follows:
When considering the normal manufacturing accuracy of the hydraulic motor 1 and the normal manufacturing accuracy of the switching valve 4, for example, if the relief pressure is 350 Kg/cm ² , it takes a relatively long time of 3 to 4 seconds.
On the other hand, the time from when the inertial mass, for example, the rotating body is fully accelerated and rotated through an angle of 90° and when the switching valve 4 is returned to neutral with the intention of stopping the rotating body until the rotating body actually stops, is determined empirically. It is around 1.8 seconds. Therefore, in this embodiment, the pressure trapped in both ports of the hydraulic motor 1 decreases to the tank pressure within the time from when the switching valve 4 is switched to neutral until the rotating structure stops. As a result, cavitation does not occur until the rotating body comes to a stop, and there is no need to replenish oil to prevent such cavitation.

The above-described operation is the same when decelerating when the switching valve 4 is switched to the A position shown in FIG. 1 and the hydraulic motor 1 is rotated in the opposite direction.

FIG. 8 shows the amount of movement of the spool 41 of the switching valve 4, the first opening/closing part 29, the second opening/closing part 30, 31, and the third opening/closing part 3 for explaining another embodiment of the present invention.
FIG. 2 is a diagram showing the relationship between No. 2 and the opening area.

What is shown in FIG. 8 shows the characteristics (characteristic line 5
2, 53) are set to be equivalent to the characteristics shown in FIG. 5 described above, but the pipe line 1 shown in FIG.
2, 13 are provided with a small opening area sufficient to confine the relief pressure of the hydraulic pump 2, that is, a notch capable of forming an approximately closed state.
Only the characteristics of the opening/closing part 32 differ from the previous embodiment. In addition, 56 shown in FIG. 8 indicates a characteristic line in the third opening/closing part 32, and 56
7 indicates the range in which the opening area changes due to the notch provided on the end surface 44 of the spool 41.

In a hydraulic circuit equipped with a switching valve 4 having a spool and a main body each having the characteristics shown in FIG. 3
0 and 31 can be brought into a close approximate state sufficient to confine the relief pressure of the hydraulic pump 2 in the conduits 12 and 13, and therefore, the braking operation of the hydraulic motor 1 can be made similar to the above-mentioned embodiment. There will be no shortage of oil and no need to replenish oil.

In addition, in the case of a hydraulic circuit equipped with the switching valve 4 illustrated in FIG. End face 4 of spool 41
Since the notches 8 and 50 are provided, a smooth switching operation of the switching valve 4 can be realized, and the impact at the time of switching can be reduced.

〔Effect of the invention〕

Since the inertial mass drive hydraulic circuit of the present invention is configured as described above, when decelerating the actuator that drives the inertial mass, the relief pressure of the hydraulic pump is closed in the pipe connected to the actuator. Therefore, there is no need for oil replenishment, which has the effect of reliably preventing cavitation.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional hydraulic circuit for driving an inertial mass, and FIGS. 2 and 3 are explanatory diagrams showing the structure of a three-position switching valve provided in the hydraulic circuit shown in FIG. The figure is a cross-sectional view showing the neutral state, and Figure 3 is B
FIG. 4 is a sectional view showing the state in which the three-position switching valve is switched to the position shown in FIG. FIG. 5 is a partial cross-sectional view of a three-position switching valve that constitutes a main part of an embodiment of the inertial mass drive hydraulic circuit of the present invention; Figure 6 shows the amount of movement of the spool of the three-position switching valve shown in Figure 5 as it operates, and the opening areas of the first opening/closing part, the second opening/closing part, and the third opening/closing part. A diagram showing the relationship between, Figure 7a,
b is a partial sectional view illustrating the operation of the three-position switching valve shown in FIG. 5, and FIG. 8 is a diagram showing the amount of movement of the spool of the three-position switching valve for explaining another embodiment of the present invention;
It is a figure which shows the opening area of a 1st opening/closing part, a 2nd opening/closing part, and a 3rd opening/closing part. 1... Hydraulic motor (actuator), 2...
Hydraulic pump, 3... Prime mover, 4... Three-position switching valve, 5, 7, 9, 11, 12, 13, 15, 1
7, 24, 25, 26, 27, 34, 54, 55
...Pipeline, 6...Tank connection pipeway, 8,33...
Check valve, 10... Relief valve, 14, 16... Brake valve, 23... Tank, 28... Spool,
29... First opening/closing part, 30, 31... Second opening/closing part, 32... Third opening/closing part, 40... Main body, 4
1...Spool, 43, 44, 45, 46, 4
7, 48, 49, 50...end surface.

Claims (1)

[Claims] 1. A hydraulic pump driven by a prime mover, an actuator that is operated by pressure oil supplied from the hydraulic pump and drives a large inertial mass, a tank connected to the hydraulic pump, and a tank connected to the hydraulic pump. A first opening/closing part that is interposed between the hydraulic pump and opens and closes a conduit connecting the hydraulic pump and a first port of the actuator, and a conduit connecting the hydraulic pump and the tank. A switching valve having a second opening/closing part that opens and closes, and a third opening/closing part that opens and closes a pipe connecting a second port of the actuator and the tank, and a pipe between the switching valve and the actuator. In an inertial mass drive hydraulic circuit comprising a brake valve that sets a maximum pressure in a pipeline, and a relief valve that sets a maximum pressure in a pipeline between the hydraulic pump and the switching valve, the switching valve When decelerating the actuator, the third opening/closing part is closed with priority over the first opening/closing part, or the third opening/closing part is prioritized over the first opening/closing part so that the opening area is sufficiently closed. After the closing operation of the third opening/closing part and the first opening/closing part is completed, or after the closing operation of the third opening/closing part and the first opening/closing part, the closed state or A hydraulic circuit for driving an inertial mass, comprising means for opening the second opening/closing section which is in an approximately closed state so as to enlarge the opening area.