WO2022270176A1

WO2022270176A1 - Hydraulic drive device

Info

Publication number: WO2022270176A1
Application number: PCT/JP2022/020227
Authority: WO
Inventors: 純一白尾; 英紀田中; 康弘藤原
Original assignee: 川崎重工業株式会社
Priority date: 2021-06-25
Filing date: 2022-05-13
Publication date: 2022-12-29
Also published as: JP2023004125A

Abstract

This hydraulic drive device drives a hydraulic cylinder by supplying and discharging a hydraulic fluid and comprises: a main pump which has first and the second pump ports and which suctions the hydraulic fluid from one pump port of the first and the second pump port and discharges the hydraulic fluid from the other pump port; a hydraulic circuit that forms a closed circuit by connecting a rod-side port of the hydraulic cylinder and the first pump port to each other and connecting a head-side port of the hydraulic cylinder and the second pump port to each other; and a charge pump that replenishes the one pump port with the hydraulic fluid. The hydraulic circuit is interposed in a rod-side passage connecting the rod-side port and the first pump port to each other and has a control valve capable of controlling the opening degree.

Description

hydraulic drive

The present invention relates to a hydraulic drive device that drives a hydraulic cylinder by supplying and discharging hydraulic fluid.

　Hydraulic drive devices that drive hydraulic cylinders by supplying and discharging hydraulic fluid have been put into practical use. 2. Description of the Related Art As an example of a hydraulic drive system, for example, a hydraulic closed circuit disclosed in Patent Document 1 is known. The hydraulic closed circuit of Patent Document 1 forms a closed circuit together with a hydraulic cylinder and a variable displacement pump. The hydraulic closed circuit also includes a charge pump. The charge pump replenishes the shortage of working oil when introducing the working oil from the rod-side port of the hydraulic cylinder to the head-side port.

JP-A-59-133804

In the closed hydraulic circuit of Patent Document 1, when switching the direction of hydraulic fluid flowing from the hydraulic pump to the hydraulic cylinder from the head side port to the rod side port, both the head side port and the rod side port may become high pressure. Then, the suction side port (for example, the first pump port) of the hydraulic pump becomes high pressure. The discharge pressure of the charge pump is set to a low pressure. Therefore, when the first pump port becomes high pressure, hydraulic oil cannot be supplied to the hydraulic pump. As a result, the flow rate of the hydraulic oil supplied from the hydraulic pump to the head-side port becomes insufficient, so that the hydraulic cylinder cannot be operated smoothly.

Accordingly, an object of the present invention is to provide a hydraulic drive device capable of more reliably replenishing hydraulic fluid from a charge pump to a first pump port.

A hydraulic drive device according to the present invention is a hydraulic drive device for driving a hydraulic cylinder by supplying and discharging hydraulic fluid, the hydraulic drive device having first and second pump ports, wherein the first and second pump ports are connecting a main pump that sucks hydraulic fluid from one of the pump ports and discharges hydraulic fluid from the other pump port, the rod side port of the hydraulic cylinder, and the first pump port; a hydraulic circuit forming a closed circuit by connecting the head-side port of the hydraulic cylinder and the second pump port; and a charge pump for supplying hydraulic fluid to the one pump port. The pressure circuit is interposed in the rod-side passage connecting the rod-side port and the first pump port, and has a control valve whose opening degree can be adjusted.

According to the present invention, when hydraulic fluid is supplied to the head side port and hydraulic fluid is sucked from the rod side port to the first pump port, by adjusting the opening degree of the control valve, Hydraulic pressure can be adjusted. As a result, for example, the hydraulic pressure on the first pump port side can be suppressed below the discharge pressure of the charge pump. Therefore, it is possible to more reliably replenish the hydraulic fluid from the charge pump to the first pump port.

According to the present invention, it is possible to more reliably replenish the hydraulic fluid from the charge pump to the first pump port.

The above object, other objects, features, and advantages of the present invention will be made clear from the following detailed description of preferred embodiments with reference to the accompanying drawings.

1 is a circuit diagram showing the configuration of a hydraulic drive device of the present invention; FIG. FIG. 2 is a graph showing changes over time in pressure at each port in the hydraulic drive device of FIG. 1; FIG. FIG. 2 is a flow chart showing the procedure of opening degree control processing in the hydraulic drive system of FIG. 1 ; FIG.

A hydraulic drive device 1 according to an embodiment of the present invention will be described below with reference to the above-described drawings. It should be noted that the concept of direction used in the following description is used for convenience of explanation, and does not limit the orientation of the configuration of the invention to that direction. Moreover, the hydraulic drive device 1 described below is merely an embodiment of the present invention. Therefore, the present invention is not limited to the embodiments, and additions, deletions, and modifications can be made without departing from the spirit of the invention.

<Hydraulic equipment>
Hydraulic equipment 2 mounted on construction machinery and industrial machinery includes a hydraulic cylinder 3 and a hydraulic drive device 1 as shown in FIG. The hydraulic device 2 operates the hydraulic cylinder 3 by means of the hydraulic drive device 1 . As a result, various components (not shown) of the hydraulic device 2 are moved.

<Hydraulic cylinder>
The hydraulic cylinder 3 expands and contracts by supplying hydraulic fluid (for example, oil or liquid such as water). Also, the hydraulic cylinder 3 can be switched between extension and contraction by switching the direction of flow of the hydraulic fluid. More specifically, the hydraulic cylinder 3 has a cylinder tube 11 and a rod 12 . The cylinder tube 11 has a rod side port 11a and a head side port 11b. The rod 12 is slidably inserted through the cylinder tube 11 . The rod 12 partitions the inside of the cylinder tube 11 into two chambers, a rod chamber 11c and a head chamber 11d. Each

chamber

11c, 11d is connected to the rod side port 11a and the head side port 11b, respectively.

Also, the hydraulic cylinder 3 is a single-rod cylinder. That is, in the hydraulic cylinder 3, the areas of the pressure-receiving surfaces of the rod 12 facing the

chambers

11c and 11d are different. Therefore, when the hydraulic cylinder 3 expands and contracts, the flow rate of the hydraulic fluid supplied to and discharged from the

chambers

11c and 11d differs. In the present embodiment, in the hydraulic cylinder 3, the flow rate supplied to and discharged from the rod chamber 11c is smaller than the flow rate supplied to and discharged from the head chamber 11d.

<Hydraulic drive device>
The hydraulic drive device 1 supplies and discharges hydraulic fluid to and from the hydraulic cylinder 3 . The hydraulic drive device 1 expands and contracts the hydraulic cylinder 3 by supplying and discharging hydraulic fluid. More specifically, the hydraulic drive device 1 includes a main pump 21, an electric motor 22, a hydraulic circuit 23, a charge pump 24, a pump pressure sensor 25, a rod pressure sensor 26, and a head pressure sensor 27. , a position sensor 28 and a controller 29 .

<Main pump>
The main pump 21 sucks and discharges working fluid. More specifically, the main pump 21 has a shaft 21a, a first pump port 21b and a second pump port 21c. The main pump 21 sucks hydraulic fluid from one of the two

pump ports

21b and 21c according to the rotation direction (forward direction and reverse direction) of the shaft 21a. Then, the main pump 21 discharges the hydraulic fluid from the

other pump ports

21c, 21b (that is, discharge side ports). In this embodiment, the main pump 21 is a variable displacement swash plate pump. However, instead of the swash plate pump, the main pump 21 may be another pump such as an inclined shaft pump, or may be a fixed displacement pump.

<Electric motor>
The electric motor 22 rotationally drives the main pump 21 . More specifically, the electric motor 22 is connected to the shaft 21 a of the main pump 21 . The electric motor 22 rotates the main pump 21 forward or backward through the shaft 21a. In this embodiment, the electric motor 22 is a servomotor. That is, the electric motor 22 can control the amount of rotation. The electric motor 22 may be rotatable only in one direction. In this case, the main pump 21 employs, for example, a double tilt type swash plate pump.

<Hydraulic circuit>
The hydraulic circuit 23 connects the rod side port 11 a of the hydraulic cylinder 3 and the first pump port 21 b of the main pump 21 . Also, the hydraulic circuit 23 connects the head-side port 11 b of the hydraulic cylinder 3 and the second pump port 21 c of the main pump 21 . Thereby, the hydraulic circuit 23 constitutes a closed circuit. More specifically, the hydraulic circuit 23 includes a rod-side passage 31, a head-side passage 32, a supply passage 33, two

check valves

34 and 35, a relief valve 36, and a rod-side control valve 37. , and a head-side on-off valve 38 .

The rod-side passage 31 connects the rod-side port 11a and the first pump port 21b. The head-side passage 32 connects the head-side port 11b and the second pump port 21c. A replenishment passage 33 is connected to a tank 39 and each of the two

passages

31 and 32 . More specifically, one end of the supply passage 33 is bifurcated. In the replenishment passage 33 , the bifurcated portion is connected to the

passages

31 and 32 via

check valves

34 and 35 . The

check valves

34, 35 allow the flow in the replenishment passage 33 toward the

passages

31, 32 and block the flow in the opposite direction. The other end of the replenishment passage 33 is connected to a tank 39 via a relief valve 36 .

[Rod side control valve]
The rod side control valve 37 is interposed in the rod side passage 31 . More specifically, the rod-side control valve 37 is interposed in the rod-side passage 31 on the hydraulic cylinder 3 side (that is, on the rod-side port 11a side) from the point g1 where the supply passages 33 join. Moreover, the rod side control valve 37 is configured to be able to open and close the opening. Furthermore, the rod side control valve 37 functions as a holding valve in this embodiment.

In more detail, the rod side control valve 37 is configured as follows. That is, the rod side control valve 37 blocks communication between the rod side port 11a and the first pump port 21b in the closed state. Further, the rod side control valve 37 communicates the rod side port 11a and the first pump port 21b in the open state. More specifically, the rod-side control valve 37 is configured so that the degree of opening can be adjusted. The rod-side control valve 37 can adjust the hydraulic pressure on both sides of the rod-side passage 31 by changing the degree of opening. That is, by adjusting the degree of opening of the rod-side control valve 37, the rod-side passage 31 flows from the rod-side control valve 37 to the first pump port 21b side and from the rod-side control valve 37 to the rod-side port 11a side, respectively. Adjust hydraulic fluid pressure. In addition, the rod side control valve 37 is a proportional control valve in this embodiment. However, the rod-side control valve 37 is not limited to a proportional control valve, and may be an inverse proportional control valve.

[Head side open/close valve]
The head side on-off valve 38 is interposed in the head side passage 32 . More specifically, the head-side on-off valve 38 is interposed in the head-side passage 32 on the side of the hydraulic cylinder 3 (that is, on the side of the head-side port 11b) from the point g2 where the supply passage 33 joins. Further, the head side opening/closing valve 38 is configured so that the opening can be adjusted. The head side on-off valve 38 is a holding valve in this embodiment. That is, the head side opening/closing valve 38 blocks communication between the head side port 11b and the second pump port 21c in the closed state. Further, the head side on-off valve 38 communicates the head side port 11b and the second pump port 21c in the open state.

<Charge pump>
The charge pump 24 supplies hydraulic fluid to one of the first pump port 21b and the

second pump port

21c, 21b and 21c. More specifically, the charge pump 24 is connected in the make-up passage 33 of the hydraulic circuit 23 between the branch point and the relief valve 36 . The charge pump 24 discharges working fluid to the supply passage 33 . The discharged hydraulic fluid is supplied to one of the

pump ports

21b, 21c through one of the

check valves

34, 35. As shown in FIG. In this embodiment, the charge pump 24 is a fixed displacement pump, and discharges working fluid at a constant pressure. Also, the charge pump 24 is driven by a prime mover (not shown) such as an engine and an electric motor.

<Pump pressure sensor>
A pump pressure sensor 25, which is an example of a pump-side hydraulic pressure detector, detects the hydraulic pressure on the first pump port 21b side from the rod-side control valve 37. As shown in FIG. More specifically, the pump pressure sensor 25 is provided in the rod-side passage 31 closer to the first pump port 21 b than the rod-side control valve 37 . The pump pressure sensor 25 detects the hydraulic pressure of the hydraulic fluid flowing therethrough, that is, the hydraulic pressure of the first pump port 21b (pump-side pressure, which corresponds to the suction pressure or discharge pressure of the main pump 21).

<Rod pressure sensor>
A rod pressure sensor 26 , which is an example of a cylinder-side hydraulic pressure detector, detects the hydraulic pressure on the rod-side port 11 a side from the rod-side control valve 37 . More specifically, the rod pressure sensor 26 is provided in the rod-side passage 31 closer to the rod-side port 11 a than the rod-side control valve 37 . The rod pressure sensor 26 detects the hydraulic pressure of the hydraulic fluid flowing therethrough, that is, the hydraulic pressure of the rod-side port 11a (the cylinder-side pressure, which corresponds to the rod pressure).

<Head pressure sensor>
The head pressure sensor 27 detects the hydraulic pressure on the side of the head side port 11b from the head side on-off valve 38 . More specifically, the head pressure sensor 27 is provided in the head-side passage 32 closer to the head-side port 11b than the head-side on-off valve 38 is. The head pressure sensor 27 detects the fluid pressure flowing therethrough, that is, the fluid pressure of the head-side port 11b (corresponding to the head pressure).

<Position sensor>
A position sensor 28 detects the position of the rod 12 of the hydraulic cylinder 3 . More specifically, position sensor 28 detects the stroke amount of rod 12 .

<Control device>
The control device 29 acquires detection results from each of the pump pressure sensor 25 , rod pressure sensor 26 , head pressure sensor 27 and position sensor 28 . Further, the control device 29 controls the operations of the main pump 21 and the electric motor 22 based on a pre-stored operation plan (program) or operation of an operation device (not shown) and the above-described detection results. That is, the control device 29 controls the discharge flow rate of the main pump 21 , that is, the meter-in flow rate of the hydraulic cylinder 3 based on the stroke amount detected by the position sensor 28 . Thereby, the position of the rod 12 of the hydraulic cylinder 3 is controlled by the control device 29 .

The control device 29 also controls the opening of the rod-side control valve 37 based on the pump-side pressure detected by the pump pressure sensor 25 . More specifically, the control device 29 controls the opening of the rod-side control valve 37 so that the hydraulic pressure of the first pump port 21b is equal to or lower than the discharge pressure of the charge pump 24. As shown in FIG. Further, the control device 29 controls the opening degree of the rod side control valve 37 based on the pressure difference between the rod pressure and the pump side pressure, which is the detection result of the rod pressure sensor 26 . Furthermore, the control device 29 opens and closes the rod-side control valve 37 based on the comparison result between the rod pressure and the head pressure. Furthermore, the control device 29 also controls the operation of the head side on-off valve 38 .

<Operation of hydraulic drive device>
In the hydraulic drive system 1, the rod side control valve 37 and the head side opening/closing valve 38 serve as holding valves as described above. Therefore, the hydraulic drive device 1 closes the openings of the rod-side control valve 37 and the head-side on-off valve 38 in the stopped state. Then, supply and discharge of hydraulic fluid to and from the

chambers

11c and 11d of the hydraulic cylinder 3 are stopped. Thereby, the rod 12 of the hydraulic cylinder 3 is held at that position.

Next, the hydraulic drive device 1 operates as follows when the hydraulic cylinder 3 is contracted based on the operation plan or operation of the operation device (that is, when hydraulic fluid is supplied to the rod side port 11a). That is, in the hydraulic drive system 1, the controller 29 causes the electric motor 22 to rotate the shaft 21a of the main pump 21 in the reverse direction. As a result, the main pump 21 sucks the hydraulic fluid from the second pump port 21c. The main pump 21 then discharges the hydraulic fluid from the first pump port 21b.

The control device 29 also controls the movement of the electric motor 22 and opens the rod-side control valve 37 and the head-side on-off valve 38 . In this embodiment, the control device 29 fully opens the rod side control valve 37 and the head side on-off valve 38 . However, the rod side control valve 37 and the head side on-off valve 38 do not necessarily have to be fully opened. By opening the rod-side control valve 37 and the head-side on-off valve 38, the hydraulic fluid sucked from the second pump port 21c is discharged from the first pump port 21b. Hydraulic fluid is supplied to the rod chamber 11c through the rod-side port 11a. This causes the hydraulic cylinder 3 to contract. Further, the control device 29 controls the meter-in flow rate to the rod side port 11 a by controlling the discharge capacity of the main pump 21 and the output of the electric motor 22 . Thereby, the control device 29 can move the rod 12 to a position according to the operation plan or the operation of the operating device. That is, the control device 29 contracts the hydraulic cylinder 3 and controls the position of the rod 12 . In the hydraulic drive system 1, since the head chamber 11d is larger than the rod chamber 11c, the working fluid is discharged to the tank 39 by a throttle valve (not shown) at a flow rate corresponding to the difference in volume between the head chambers 11d.

Next, in the hydraulic drive device 1, the case where the operation of the hydraulic cylinder 3 is switched from the contraction operation to the extension operation based on the operation plan or the operation of the operating device will be explained. When the operation is switched, the supply destination of the hydraulic fluid from the main pump 21 is switched from the rod-side port 11a to the head-side port 11b. More specifically, in the hydraulic drive system 1 , the controller 29 switches the direction of rotation of the electric motor 22 . As a result, the rotation direction of the shaft 21a of the main pump 21 is switched from the reverse direction to the forward direction. Then, in the hydraulic drive device 1, the main pump 21 sucks the hydraulic fluid from the first pump port 21b. The main pump 21 then discharges the hydraulic fluid from the second pump port 21c.

The control device 29 also controls the movement of the electric motor 22 and opens the head side on-off valve 38 (fully open in this embodiment). As a result, the hydraulic fluid is sucked from the first pump port 21b and the hydraulic fluid discharged from the second pump port 21c is supplied to the head chamber 11d through the head-side port 11b. The controller 29 controls the discharge capacity of the main pump 21 and the output of the electric motor 22 to control the meter-in flow rate to the head-side port 11b. Thereby, the rod 12 can be moved to a position according to the operation plan or the operation of the operating device. That is, the control device 29 extends the hydraulic cylinder 3 and controls the position of the rod 12 .

Also, after the hydraulic fluid is supplied to the head-side port 11b, the hydraulic fluid in the rod chamber 11c is pushed out by the rod 12 from the rod-side port 11a into the rod-side passage 31. Therefore, the rod side port 11a as well as the head side port 11b are maintained at high pressure. Therefore, the control device 29 controls the opening degree of the rod-side control valve 37 as follows.

That is, based on the pump-side pressure acquired from the pump pressure sensor 25, the control device 29 determines that the pump-side pressure (see the solid line in FIG. 2) is the discharge pressure of the charge pump 24 (that is, the boost pressure, see the chain line in FIG. 2). ) The opening degree of the rod-side control valve 37 is controlled so as to be as follows (see after time t1 in FIG. 2). More specifically, the controller 29 controls the opening of the rod-side control valve 37 based on the pressure difference between the pump-side pressure and the rod pressure. In this embodiment, the control device 29 generates a predetermined pressure difference between the pump-side pressure and the rod pressure (see the two-dot chain line in FIG. 2). As a result, the pump-side pressure is kept below the discharge pressure of the charge pump 24 . Furthermore, the control device 29 controls the opening degree of the rod-side control valve 37 so that the pressure difference falls within a predetermined range equal to or less than the upper limit threshold and equal to or more than the lower limit threshold.

More specifically, the control device 29 executes the opening degree control process shown in FIG. 3 in order to control the opening degree of the rod side control valve 37 . When the opening degree control process is started, the process proceeds to step S1. In step S1, which is a pressure difference calculation step, the control device 29 calculates the pressure difference. More specifically, the control device 29 acquires the pump-side pressure from the pump pressure sensor 25 and the rod pressure from the rod pressure sensor 26 . The controller 29 then calculates the pressure difference between the pump-side pressure and the rod pressure. After calculating the pressure difference, the process proceeds to step S2.

In step S2, which is a pressure difference determination step, the control device 29 determines whether the pressure difference is within a predetermined range. Then, when the control device 29 determines that the pressure difference is within the predetermined range, the opening degree of the rod-side control valve 37 is maintained. Then, the process returns to step S1. On the other hand, when the control device 29 determines that the pressure difference exceeds the upper limit threshold value, the process proceeds to step S3. Moreover, when the control device 29 determines that the pressure difference is less than the lower limit threshold value, the process proceeds to step S4.

In step S3, which is the first degree-of-opening adjustment step, the control device 29 increases the degree of opening of the rod-side control valve 37 . As a result, the rod pressure is lowered, so the pressure difference can be reduced. If the pressure difference is reduced, the process returns to step S1.

In step S4, which is the second degree-of-opening request step, the control device 29 reduces the degree of opening of the rod-side control valve 37 . As a result, the rod pressure rises, so the pressure difference can be increased. When the pressure difference is increased, the process returns to step S1.

In this way, the control device 29 maintains the pressure difference within a predetermined range by executing the opening degree control process. As a result, the pump-side pressure can be suppressed below the boost pressure. Also, the rod side control valve 37 can prevent the rod pressure from becoming too high. Therefore, when the hydraulic cylinder 3 is extended, it is possible to prevent the back pressure in the hydraulic cylinder 3 from increasing.

Also, the control device 29 acquires the head pressure from the head pressure sensor 27 (see the dashed-dotted line in FIG. 2). The controller 29 then compares the head pressure and the rod pressure. If the comparison result shows that the head pressure is lower than the rod pressure, the control device 29 continues control of the opening degree of the rod-side control valve 37 . On the other hand, when the head pressure is higher than the rod pressure in the comparison result, the control device 29 stops controlling the opening of the rod-side control valve 37 . The controller 29 then widens the opening of the rod-side control valve 37 (see time t2 in FIG. 2). Then, since the rod pressure can be lowered, the back pressure generated when the rod 12 moves can be further reduced. As a result, deterioration in energy efficiency when extending the hydraulic cylinder 3 is suppressed.

In the hydraulic drive device 1 of this embodiment, the control device 29 operates as follows. That is, the control device 29 controls the opening degree of the rod side control valve 37 when supplying the hydraulic fluid to the head side port 11b and sucking the hydraulic fluid from the rod side port 11a to the first pump port 21b. Then, the pump-side pressure on the first pump port 21b side can be adjusted. In this embodiment, the pump-side pressure on the side of the first pump port 21b can be suppressed below the boost pressure. Therefore, it is possible to reliably replenish the first pump port 21b from the charge pump 24 with the working fluid. As a result, it is possible to prevent a shortage of the discharge flow rate of the main pump 21 when supplying the hydraulic fluid to the second pump port 21c.

In addition, in the hydraulic drive system 1 of the present embodiment, the control device 29 feedback-controls the rod side control valve 37 so that the hydraulic pressure on the first pump port 21b side is suppressed below the boost pressure. Therefore, it is possible to reliably replenish the first pump port 21b from the charge pump 24 with the working fluid.

Furthermore, in the hydraulic drive system 1 of this embodiment, the control device 29 controls the opening degree of the rod side control valve 37 based on the pressure difference. As a result, it is possible to prevent the hydraulic pressure in the rod-side port 11a from remaining at a high level. As a result, the back pressure in the hydraulic cylinder 3 can be prevented from remaining at a high level. Therefore, the discharge pressure of the main pump 21 can be kept low. That is, energy loss in the hydraulic drive system 1 is suppressed.

Furthermore, in the hydraulic drive device 1 of the present embodiment, the control device 29 narrows the opening when the pressure difference is less than the lower limit threshold, and opens the opening when the pressure difference exceeds the upper limit threshold. Then, the control device 29 maintains the opening degree of the rod-side control valve 37 when the pressure difference is within a predetermined range. In this way, the control device 29 provides hysteresis characteristics to the relationship between the opening of the rod-side control valve 37 and the pressure difference, so that pressure hunting occurs in the rod pressure due to fluctuations in the opening of the rod-side control valve 37. can be suppressed.

Furthermore, in the hydraulic drive device 1 of this embodiment, the rod side control valve 37 functions as a holding valve. Therefore, in the hydraulic drive device 1, the number of parts can be reduced.

[About other embodiments]
In the hydraulic drive device 1 of this embodiment, the head side on-off valve 38 is an on-off valve that can be switched between opening and closing. may Also, although the rod-side control valve 37 and the head-side opening/closing valve 38 function as holding valves, they do not necessarily have such a function. Further, a holding valve may be separately provided in the hydraulic drive device 1 .

In addition, in the hydraulic drive system 1 of this embodiment, the control device 29 controls the opening degree of the rod side control valve 37 according to the pressure difference. The degree of opening of the rod-side control valve 37 may be controlled only in accordance with the pressure.

From the above description, many modifications and other embodiments of the invention will be apparent to those skilled in the art. Accordingly, the above description is to be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. Substantial details of construction and/or function may be changed without departing from the spirit of the invention.

Claims

A hydraulic drive device that drives a hydraulic cylinder by supplying and discharging hydraulic fluid,
a main pump having first and second pump ports, sucking hydraulic fluid from one of the first and second pump ports and discharging hydraulic fluid from the other pump port;
a hydraulic circuit forming a closed circuit by connecting the rod side port of the hydraulic cylinder and the first pump port and connecting the head side port of the hydraulic cylinder and the second pump port;
a charge pump that supplies hydraulic fluid to the one pump port,
The hydraulic drive device, wherein the hydraulic circuit includes a control valve that is interposed in a rod-side passage that connects the rod-side port and the first pump port and that is adjustable in opening degree.
a pump-side hydraulic pressure detector that detects the hydraulic pressure on the first pump port side of the control valve in the rod-side passage;
a control device that controls the opening of the control valve based on the detection result of the pump-side hydraulic pressure detector,
2. The hydraulic drive device according to claim 1, wherein said control device controls the degree of opening of said control valve so that the hydraulic pressure of said first pump port is equal to or less than the discharge pressure of said charge pump.
further comprising a cylinder-side hydraulic pressure detector that detects the hydraulic pressure on the rod-side port side of the control valve in the rod-side passage,
The control device determines the degree of opening of the control valve based on the pressure difference between the pump-side pressure, which is the detection result of the pump-side hydraulic pressure detector, and the cylinder-side pressure, which is the detection result of the cylinder-side hydraulic pressure detector. 3. The hydraulic drive according to claim 2, which controls the
4. The control device according to claim 3, wherein the control device reduces the degree of opening of the control valve when the pressure difference becomes less than a predetermined lower threshold, and opens the degree of opening of the control valve when the pressure difference exceeds a predetermined upper threshold. hydraulic drive.
The hydraulic drive device according to any one of claims 1 to 4, wherein the control valve is a holding valve that holds the hydraulic pressure of the rod side port.