Hydraulic system and control device

Abstract

A hydraulic system (1) includes a hydraulic actuator (5), a control valve (4) connected to the hydraulic actuator (5), and a variable displacement hydraulic pump (21) connected by a pump line (31) to the control valve (4). The minimum discharge flow rate of the hydraulic pump (21) is set to be greater than zero. The hydraulic system (1) further includes a bleed valve (34) provided in a bleed line (33), actuator pressure detectors (81, 82) for detecting the actuator pressure, and a control device (7). The control device (7) includes a processing circuit (71), and in the case of a directive to the hydraulic actuator (5) that the inflow flow rate be greater than zero and smaller than the minimum discharge flow rate, the processing circuit (71) controls the bleed valve (34) so as to establish an opening area which corresponds to the inflow flow-rate directive and the actuator pressure detected by the actuator pressure detectors (81, 82).

Description

Hydraulic Systems and Controls

[0001] The present disclosure relates to hydraulic systems including bleed valves and controls for hydraulic circuits.

[0002] Hydraulic systems that supply hydraulic oil from a hydraulic pump to a hydraulic actuator via a control valve have traditionally been used in construction machinery and industrial machinery. Some such hydraulic systems include a bleed valve that regulates the bleed flow rate that releases hydraulic oil discharged from the hydraulic pump into a tank. Bleed valves are also called unloading valves.

[0003] For example, Patent Document 1 discloses a hydraulic system including a variable displacement hydraulic pump. Specifically, in the hydraulic system of Patent Document 1, the hydraulic pump is connected to a control valve by a pump line, and the control valve is connected to a hydraulic actuator by a pair of supply and discharge lines. A bleed line branches off from the pump line and leads to a tank, and a bleed valve is provided in the bleed line.

[0004] The hydraulic system of Patent Document 1 also includes an operating device for operating the hydraulic actuator. The operating device includes an operating unit operated by an operator and outputs an operating signal corresponding to the amount of operation of the operating unit. The bleed valve is controlled so that its opening area decreases as the amount of operation of the operating unit increases. In other words, when the hydraulic actuator is stopped, the bleed valve is fully open, and the discharge pressure of the hydraulic pump becomes low.

[0005] The amount of operation of the operating unit of the operating device also serves as a speed command for the hydraulic actuator. In other words, the greater the amount of operation of the operating unit, the greater the discharge flow rate of the hydraulic pump and the opening area of ​​the control valve, and the greater the flow rate of hydraulic oil supplied to the hydraulic actuator.

[0006] Japanese Patent Application Laid-Open No. 2019-2512

[0007] In hydraulic systems, the minimum discharge flow rate of a hydraulic pump is sometimes set to be greater than zero in order to quickly raise the discharge pressure of the hydraulic pump when the hydraulic actuator begins to operate. In such hydraulic systems, when a hydraulic actuator is operated at a slow speed such that the required supply flow rate to the hydraulic actuator is smaller than the minimum discharge flow rate of the hydraulic pump, the bleed valve may be nearly fully open, causing a delay in the rise of the discharge pressure of the hydraulic pump.

[0008] Therefore, an object of the present disclosure is to provide a hydraulic system and a control device for a hydraulic circuit that can quickly increase the discharge pressure of a hydraulic pump even when a hydraulic actuator is operated at a slow speed.

[0009] From one aspect, the present disclosure provides a hydraulic system comprising: a hydraulic actuator; a control valve connected to the hydraulic actuator; a variable displacement hydraulic pump connected to the control valve by a pump line and having a minimum discharge flow rate greater than zero; a tank for storing hydraulic oil; a bleed valve provided in a bleed line branching from the pump line and leading to the tank; an actuator pressure detector for detecting an actuator pressure which is the pressure of the hydraulic oil in the hydraulic actuator; and a control device including a processing circuit for controlling the bleed valve based on an inflow flow rate command for the hydraulic actuator, wherein the processing circuit fully closes the bleed valve when the inflow flow rate command is greater than the minimum discharge flow rate, and controls the bleed valve so that the opening area corresponds to the inflow flow rate command and the actuator pressure detected by the actuator pressure detector when the inflow flow rate command is greater than zero and less than the minimum discharge flow rate.

[0010] From another aspect, the present disclosure provides a control device for a hydraulic circuit in which hydraulic oil is supplied from a hydraulic pump to a hydraulic actuator via a control valve, and a bleed flow rate at which the hydraulic oil discharged from the hydraulic pump is released to a tank is determined by a bleed valve, the control device including a processing circuit that controls the bleed valve based on an inflow flow rate command for the hydraulic actuator, and the processing circuit fully closes the bleed valve when the inflow flow rate command is greater than a minimum discharge flow rate of the hydraulic pump, and controls the bleed valve so that the opening area corresponds to the inflow flow rate command and an actuator pressure, which is the pressure of the hydraulic oil in the hydraulic actuator, when the inflow flow rate command is greater than zero and less than the minimum discharge flow rate.

[0011] According to the present disclosure, a hydraulic system and a control device for a hydraulic circuit are provided that can quickly increase the discharge pressure of a hydraulic pump even when a hydraulic actuator is operated at a slow speed.

[0012] 1 is a schematic configuration diagram of a hydraulic system according to an embodiment;

[0013] 1 shows a hydraulic system 1 according to one embodiment. The hydraulic system 1 is mounted on, for example, construction machinery such as a hydraulic excavator or a hydraulic crane, industrial machinery such as a press machine, civil engineering machinery such as a tunnel boring machine, or agricultural machinery such as a tiller.

[0014] Specifically, the hydraulic system 1 includes a hydraulic circuit 10 and a control device 7 for the hydraulic circuit 10. The hydraulic circuit 10 includes a hydraulic actuator 5, a hydraulic pump 21 that supplies hydraulic oil to the hydraulic actuator 5 via a control valve 4, a tank 20 that stores the hydraulic oil, and a bleed valve 34 that determines the bleed flow rate at which the hydraulic oil discharged from the hydraulic pump 21 is bled to the tank 20. In the illustrated example, there is one set of the hydraulic actuator 5 and the control valve 4, but multiple sets of the hydraulic actuator 5 and the control valve 4 may be provided.

[0015] In this embodiment, the hydraulic actuator 5 is a double-acting cylinder or hydraulic motor that can move in both directions when hydraulic oil is supplied. The hydraulic actuator 5 includes a first working chamber 51 for movement in a first direction X and a second working chamber 52 for movement in a second direction Y. However, the hydraulic actuator 5 may also be a single-acting cylinder that can move in one direction when hydraulic oil is supplied.

[0016] The hydraulic pump 21 is connected to the tank 20 by a suction line 30, and is connected to the control valve 4 by a pump line 31. The control valve 4 is connected to the tank 20 by a tank line 32, and is connected to a first working chamber 51 and a second working chamber 52 of the hydraulic actuator 5 by a pair of supply and discharge lines 41, 42.

[0017] The hydraulic pump 21 is a variable displacement pump with a variable tilt angle. For example, the hydraulic pump 21 is an axial piston pump such as a swash plate pump or a bent-axis pump. In this embodiment, the minimum discharge flow rate Qmin of the hydraulic pump 21 is set to be greater than zero.

[0018] The tilt angle of the hydraulic pump 21 is changed by a regulator 22. In this embodiment, the regulator 22 is electrically connected to the control device 7. The control device 7 includes a processing circuit 71, and the processing circuit 71 controls the regulator 22. For example, if the hydraulic pump 21 is a swash plate pump, the regulator 22 may electrically change the hydraulic pressure acting on a servo piston connected to the swash plate of the hydraulic pump 21, or may be an electric actuator connected to the swash plate of the hydraulic pump 21.

[0019] However, the regulator 22 does not necessarily need to be controlled by the processing circuit 71, and may be operated by the pressure of the hydraulic oil. For example, the regulator 22 may be of a negative control type or a load sensing type.

[0020] In this embodiment, the hydraulic system 1 includes an operating device 6 for operating the hydraulic actuator 5. The operating device 6 includes an operating unit operated by an operator, and outputs an operating signal corresponding to the operating direction and amount of the operating unit. The operating unit is, for example, an operating lever or a foot pedal.

[0021] In this embodiment, the operating device 6 is an electric joystick that outputs an electric signal as an operating signal, but the operating device 6 may also be a pilot operated valve that outputs a pilot pressure as an operating signal.

[0022] An operation signal output from the operating device 6 is input to the control device 7. The processing circuit 71 of the control device 7 controls the regulator 22 so that the discharge flow rate of the hydraulic pump 21 increases as the amount of operation on the operating part of the operating device 6 increases. In other words, when the operating part of the operating device 6 is not being operated, in other words, when the hydraulic actuator 5 is not moving and is stopped, the discharge flow rate of the hydraulic pump 21 is maintained at the minimum discharge flow rate Qmin.

[0023] The control valve 4 is switchable between a neutral position and a first operating position or a second operating position. In the neutral position, the control valve 4 blocks the pump line 31, the tank line 32, and the pair of supply and discharge lines 41, 42. In the first operating position, the control valve 4 connects the pump line 31 to the supply and discharge line 41 and connects the supply and discharge line 42 to the tank line 32. This allows hydraulic oil to be supplied from the hydraulic pump 21 to a first working chamber 51 of the hydraulic actuator 5, causing the hydraulic actuator 5 to move in the first direction X. In the second operating position, the control valve 4 connects the pump line 31 to the supply and discharge line 42 and connects the supply and discharge line 41 to the tank line 32. This allows hydraulic oil to be supplied from the hydraulic pump 21 to a second working chamber 52 of the hydraulic actuator 5, causing the hydraulic actuator 5 to move in the second direction Y.

[0024] In this embodiment, the control valve 4 is controlled by a processing circuit 71 of the control device 7. Note that in FIG. 1 , some signal lines are omitted for simplicity of the drawing. The control valve 4 is a spool valve including a spool and a drive unit that receives a command current to drive the spool. A command current is supplied to the drive unit from the processing circuit 71. For example, the drive unit may include a pair of electromagnetic proportional valves that output secondary pressures that act on the spool in opposite directions, or may be a linear motion mechanism that is connected to the spool and includes an electric motor, a ball screw, or the like.

[0025] When the operating portion of the operating device 6 is operated in a first direction, the processing circuit 71 switches the control valve 4 from the neutral position to the first operating position, and increases the opening areas of the meter-in and meter-out of the control valve 4 as the amount of operation of the operating portion increases. Conversely, when the operating portion of the operating device 6 is operated in a second direction, the processing circuit 71 switches the control valve 4 from the neutral position to the second operating position, and increases the opening areas of the meter-in and meter-out of the control valve 4 as the amount of operation of the operating portion increases.

[0026] However, the control valve 4 does not necessarily have to be controlled by the processing circuit 71. For example, when the operating device 6 is a pilot-operated valve as described above, the control valve 4 may include a pair of pilot ports instead of a drive unit that receives a command current, and the pilot-operated valve may be connected to the pair of pilot ports.

[0027] A bleed line 33 branches off from the pump line 31. The bleed line 33 is connected to the tank 20. The bleed line 33 is provided with the bleed valve 34 described above.

[0028] In this embodiment, the bleed valve 34 has a pilot port, and the opening area of ​​the bleed valve 34 decreases from the fully open state toward the fully closed state as the pilot pressure increases. However, the opening area of ​​the bleed valve 34 may increase from the fully closed state toward the fully open state as the pilot pressure increases. Alternatively, the bleed valve 34 does not necessarily have to be operated by the pilot pressure, and may be operated by an electric signal.

[0029] The bleed valve 34 is controlled by the processing circuit 71 of the control device 7 via the electromagnetic proportional valve 36. Specifically, the pilot port of the bleed valve 34 is connected to a secondary pressure port of the electromagnetic proportional valve 36 by a secondary pressure line 35. The primary pressure port of the electromagnetic proportional valve 36 is connected to the fixed displacement hydraulic pump 23 by a primary pressure line 37. The discharge pressure of the hydraulic pump 23 is maintained at a set pressure by a relief valve.

[0030] In this embodiment, the electromagnetic proportional valve 36 is a direct proportional valve in which a command current supplied to the electromagnetic proportional valve 36 shows a positive correlation with the secondary pressure output by the electromagnetic proportional valve 36. However, the electromagnetic proportional valve 36 may be an inverse proportional valve in which a command current supplied to the electromagnetic proportional valve 36 shows a negative correlation with the secondary pressure output by the electromagnetic proportional valve 36.

[0031] The control device 7 is electrically connected to a first actuator pressure detector 81, a second actuator pressure detector 82, and a tank pressure detector 83. The first actuator pressure detector 81 detects the pressure in the first working chamber 51 of the hydraulic actuator 5 as an actuator pressure Pa1, and the second actuator pressure detector 82 detects the pressure in the second working chamber 52 of the hydraulic actuator 5 as an actuator pressure Pa2. Both of the actuator pressures Pa1 and Pa2 are the pressures of the hydraulic oil in the hydraulic actuator 5. The tank pressure detector 83 detects the tank pressure Pt, which is the pressure in the tank 20.

[0032] In this embodiment, the first actuator pressure detector 81 and the second actuator pressure detector 82 are provided in the supply and discharge lines 41, 42, but the first actuator pressure detector 81 and the second actuator pressure detector 82 may also be provided in the hydraulic actuator 5.

[0033] With respect to the control device 7, the functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, special-purpose processors, integrated circuits, application-specific integrated circuits (ASICs), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuitry. In this disclosure, a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions. The hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the recited functions. Where hardware is a processor, which is considered a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or processor.

[0034] The processing circuit 71 of the control device 7 determines an inflow flow rate command Qi for the hydraulic actuator 5 in response to an operation signal from the operating device 6. The inflow flow rate command Qi is a supply flow rate that the hydraulic pump 21 should supply to the hydraulic actuator 5. In other words, the larger the operation amount for the operating part of the operating device 6, the larger the inflow flow rate command Qi.

[0035] The processing circuit 71 controls the bleed valve 34 based on the inflow flow rate command Qi. The processing circuit 71 fully closes the bleed valve 34 when the inflow flow rate command Qi is greater than the minimum discharge flow rate Qmin, whether the hydraulic actuator 5 is moved in the first direction X or the second direction Y. The processing circuit 71 also fully opens the bleed valve 34 when the operating section of the operating device 6 is not operated and the hydraulic actuator 5 is stopped, i.e., when the inflow flow rate command Qi is zero.

[0036] On the other hand, when the inflow flow rate command Qi is greater than zero and less than the minimum discharge flow rate Qmin, the processing circuit 71 controls the bleed valve 34 using the actuator pressure Pa1 detected by the first actuator pressure detector 81 when moving the hydraulic actuator 5 in the first direction X, and controls the bleed valve 34 using the actuator pressure Pa2 detected by the second actuator pressure detector 82 when moving the hydraulic actuator 5 in the second direction Y.

[0037] More specifically, when the hydraulic actuator 5 is moved in the first direction X, the processing circuit 71 controls the bleed valve 34 so that the opening area corresponds to the inflow flow rate command Qi and the actuator pressure Pa1 detected by the first actuator pressure detector 81. In this embodiment, the processing circuit 71 calculates the opening area A of the bleed valve 34 based on the inflow flow rate command Qi and the differential pressure ΔP between the actuator pressure Pa1 detected by the first actuator pressure detector 81 and the tank pressure Pt detected by the tank pressure detector 83, and controls the bleed valve 34 so that the calculated opening area A is achieved.

[0038] For example, the processing circuit 71 calculates the opening area A of the bleed valve 34 using the following orifice calculation formula, with the differential pressure ΔP as the target pressure. In this case, prior to calculating the opening area A, the processing circuit 71 calculates the bleed flow rate Qb passing through the bleed valve 34 by subtracting the inflow flow rate command Qi from the minimum discharge flow rate Qmin. C in the formula is a coefficient. Qb = C × A × √ΔP

[0039] Conversely, when the hydraulic actuator 5 is moved in the second direction Y, the processing circuit 71 controls the bleed valve 34 so that the opening area corresponds to the inflow flow rate command Qi and the actuator pressure Pa2 detected by the second actuator pressure detector 82. In this embodiment, the processing circuit 71 calculates the opening area A of the bleed valve 34 based on the inflow flow rate command Qi and the differential pressure ΔP between the actuator pressure Pa2 detected by the second actuator pressure detector 82 and the tank pressure Pt detected by the tank pressure detector 83, and controls the bleed valve 34 so that the calculated opening area A is achieved.

[0040] For example, the processing circuit 71 calculates the opening area A of the bleed valve 34 using the above orifice calculation formula with the differential pressure ΔP as the target pressure. In this case, as in the above, prior to calculating the opening area A, the processing circuit 71 calculates the bleed flow rate Qb passing through the bleed valve 34 by subtracting the inflow flow rate command Qi from the minimum discharge flow rate Qmin.

[0041] As described above, in the hydraulic system 1 of this embodiment, when the hydraulic actuator 5 is operated at a very slow speed such that the inflow flow rate command Qi for the hydraulic actuator 5 is smaller than the minimum discharge flow rate Qmin of the hydraulic pump 21, the bleed valve 34 has an opening area corresponding to the inflow flow rate command Qi and the actuator pressure Pa1 or Pa2, so the discharge pressure of the hydraulic pump 21 can be quickly raised to the actuator pressure Pa1 or Pa2. Moreover, the bleed flow rate Qb passing through the bleed valve 34 can also be controlled to an excess flow rate which is the difference between the minimum discharge flow rate Qmin of the hydraulic pump 21 and the inflow flow rate command Qi to the hydraulic actuator 5. Therefore, excess discharge of hydraulic oil to the tank 20 through the bleed line 33 is suppressed, resulting in good hydraulic efficiency.

[0042] <Modifications> The present disclosure is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present disclosure.

[0043] For example, one of the first actuator pressure detector 81 and the second actuator pressure detector 82 may be omitted, and the processing circuit 71 may perform the above-described control only when the hydraulic actuator 5 is moved in either the first direction X or the second direction Y. However, with the configuration as in the above embodiment, the discharge pressure of the hydraulic pump 21 can be quickly raised to the actuator pressure Pa1 or Pa2 whether the hydraulic actuator 5 is moved in the first direction X or the second direction Y.

[0044] Furthermore, the tank pressure detector 83 may be omitted, and the tank pressure Pt, which is the pressure downstream of the bleed valve 34, may be assumed to be constant at atmospheric pressure, i.e., zero Pascals, and the actuator pressure Pa1 detected by the first actuator pressure detector 81 or the actuator pressure Pa2 detected by the second actuator pressure detector 82 may be used in place of ΔP in the orifice calculation formula. However, with the configuration of the above embodiment, the bleed flow rate Qb can be controlled more accurately than when the tank pressure Pt, which is the pressure downstream of the bleed valve 34, is assumed to be constant at atmospheric pressure.

[0045] If the machine on which the hydraulic system 1 is installed is an unmanned machine, the operating device 6 may be omitted and the processing circuit 71 may determine the inflow flow rate command Qi for the hydraulic actuator 5 based on an image captured by a camera.

[0046] In addition, if multiple sets of hydraulic actuators 5 and control valves 4 are provided and the bleed line 33 also serves as a center bypass line passing through multiple control valves 4, the bleed valve 34 may be provided downstream of all of the control valves 4.

[0047] When multiple sets of hydraulic actuators 5 and control valves 4 are provided and multiple hydraulic actuators 5 are operated simultaneously, the processing circuit 71 can control the bleed valve 34 based on the maximum actuator pressure among the actuator pressures of the multiple hydraulic actuators 5.

[0048] <Summary> In a first aspect, the present disclosure provides a hydraulic system comprising: a hydraulic actuator; a control valve connected to the hydraulic actuator; a variable displacement hydraulic pump connected to the control valve by a pump line and having a minimum discharge flow rate greater than zero; a tank for storing hydraulic oil; a bleed valve provided in a bleed line branching from the pump line and leading to the tank; an actuator pressure detector for detecting an actuator pressure which is the pressure of the hydraulic oil in the hydraulic actuator; and a control device including a processing circuit for controlling the bleed valve based on an inflow flow rate command for the hydraulic actuator, wherein the processing circuit fully closes the bleed valve when the inflow flow rate command is greater than the minimum discharge flow rate, and controls the bleed valve so that the opening area corresponds to the inflow flow rate command and the actuator pressure detected by the actuator pressure detector when the inflow flow rate command is greater than zero and less than the minimum discharge flow rate.

[0049] According to the above configuration, when a hydraulic actuator is operated at a very slow speed and the inflow flow rate command for the hydraulic actuator is smaller than the minimum discharge flow rate of the hydraulic pump, the bleed valve has an opening area that corresponds to the inflow flow rate command and the actuator pressure, so the discharge pressure of the hydraulic pump can be quickly raised to the actuator pressure. Furthermore, the bleed flow rate passing through the bleed valve can be controlled to an excess flow rate, which is the difference between the minimum discharge flow rate of the hydraulic pump and the inflow flow rate command for the hydraulic actuator. This reduces excess discharge of hydraulic oil to the tank through the bleed line, resulting in good hydraulic efficiency.

[0050] In a second aspect, the first aspect may further include a tank pressure detector that detects the tank pressure, which is the pressure inside the tank, and the processing circuit may calculate the opening area of ​​the bleed valve based on the inflow flow rate command and the differential pressure between the actuator pressure detected by the actuator pressure detector and the tank pressure detected by the tank pressure detector. With this configuration, the bleed flow rate can be controlled more accurately than when the tank pressure, which is the pressure downstream of the bleed valve, is kept constant at atmospheric pressure.

[0051] As a third aspect, in the first or second aspect, the hydraulic actuator may include a first working chamber for movement in a first direction and a second working chamber for movement in a second direction, the actuator pressure detector may include a first actuator pressure detector that detects the pressure of the first working chamber as the actuator pressure, and a second actuator pressure detector that detects the pressure of the second working chamber as the actuator pressure, and the processing circuit may control the bleed valve using the actuator pressure detected by the first actuator pressure detector when moving the hydraulic actuator in the first direction, and may control the bleed valve using the actuator pressure detected by the second actuator pressure detector when moving the hydraulic actuator in the second direction. With this configuration, the discharge pressure of the hydraulic pump can be quickly raised to the actuator pressure whether the hydraulic actuator is moved in the first direction or the second direction.

[0052] As a fourth aspect, in any of the first to third aspects, for example, the above-mentioned hydraulic system may further include an operating device that outputs an operating signal according to the operating amount for the operating section, and the processing circuit may determine the inflow flow rate command according to the operating signal.

[0053] In a fifth aspect, from another aspect, the present disclosure provides a control device for a hydraulic circuit in which hydraulic oil is supplied from a hydraulic pump to a hydraulic actuator via a control valve, and a bleed flow rate at which the hydraulic oil discharged from the hydraulic pump is released to a tank is determined by a bleed valve, the control device including a processing circuit that controls the bleed valve based on an inflow flow rate command for the hydraulic actuator, and the processing circuit fully closes the bleed valve when the inflow flow rate command is greater than a minimum discharge flow rate of the hydraulic pump, and controls the bleed valve so that the opening area corresponds to the inflow flow rate command and an actuator pressure, which is the pressure of the hydraulic oil in the hydraulic actuator, when the inflow flow rate command is greater than zero and less than the minimum discharge flow rate.

[0054] According to the above configuration, when a hydraulic actuator is operated at a very slow speed and the inflow flow rate command for the hydraulic actuator is smaller than the minimum discharge flow rate of the hydraulic pump, the bleed valve has an opening area that corresponds to the inflow flow rate command and the actuator pressure, so the discharge pressure of the hydraulic pump can be quickly raised to the actuator pressure. Furthermore, the bleed flow rate passing through the bleed valve can be controlled to an excess flow rate, which is the difference between the minimum discharge flow rate of the hydraulic pump and the inflow flow rate command for the hydraulic actuator. This reduces excess discharge of hydraulic oil to the tank through the bleed line, resulting in good hydraulic efficiency.

[0055] In a sixth aspect, in the fifth aspect, the processing circuit may calculate the opening area of ​​the bleed valve based on the inflow flow rate command and the differential pressure between the actuator pressure and the tank pressure, which is the pressure inside the tank. With this configuration, the bleed flow rate can be controlled more accurately than when the tank pressure, which is the pressure downstream of the bleed valve, is kept constant at atmospheric pressure.

[0056] As a seventh aspect, in the fifth or sixth aspect, the hydraulic actuator may include a first working chamber for movement in a first direction and a second working chamber for movement in a second direction, and the processing circuit may control the bleed valve using the pressure in the first working chamber as the actuator pressure when moving the hydraulic actuator in the first direction, and control the bleed valve using the pressure in the second working chamber as the actuator pressure when moving the hydraulic actuator in the second direction. With this configuration, the discharge pressure of the hydraulic pump can be quickly raised to the actuator pressure whether the hydraulic actuator is moved in the first direction or the second direction.

[0057] As an eighth aspect, in any one of the fifth to seventh aspects, for example, the processing circuit may determine the inflow flow rate command in response to an operation signal output from an operation device.

Claims

1. A hydraulic system comprising: a hydraulic actuator; a control valve connected to said hydraulic actuator; a variable displacement hydraulic pump connected to said control valve by a pump line and having a minimum discharge flow rate greater than zero; a tank for storing hydraulic oil; a bleed valve provided in a bleed line branching from said pump line and leading to said tank; an actuator pressure detector for detecting actuator pressure, which is the pressure of the hydraulic oil in said hydraulic actuator; and a control device including a processing circuit for controlling said bleed valve based on an inflow flow rate command for said hydraulic actuator, wherein said processing circuit fully closes said bleed valve when said inflow flow rate command is greater than said minimum discharge flow rate, and controls said bleed valve so that its opening area corresponds to said inflow flow rate command and the actuator pressure detected by said actuator pressure detector when said inflow flow rate command is greater than zero but less than said minimum discharge flow rate.

2. A hydraulic system as described in claim 1, further comprising a tank pressure detector that detects the tank pressure, which is the pressure inside the tank, and wherein the processing circuit calculates the opening area of ​​the bleed valve based on the inflow flow rate command and the differential pressure between the actuator pressure detected by the actuator pressure detector and the tank pressure detected by the tank pressure detector.

3. A hydraulic system as claimed in claim 1 or 2, wherein the hydraulic actuator includes a first working chamber for movement in a first direction and a second working chamber for movement in a second direction, the actuator pressure detector includes a first actuator pressure detector that detects the pressure in the first working chamber as the actuator pressure, and a second actuator pressure detector that detects the pressure in the second working chamber as the actuator pressure, and the processing circuit controls the bleed valve using the actuator pressure detected by the first actuator pressure detector when moving the hydraulic actuator in the first direction, and controls the bleed valve using the actuator pressure detected by the second actuator pressure detector when moving the hydraulic actuator in the second direction.

4. A hydraulic system as described in claim 1 or 2, further comprising an operating device that outputs an operating signal according to an operating amount for an operating section, wherein the processing circuit determines the inflow flow rate command according to the operating signal.

5. A control device for a hydraulic circuit in which hydraulic oil is supplied from a hydraulic pump to a hydraulic actuator via a control valve and a bleed flow rate at which the hydraulic oil discharged from the hydraulic pump is released into a tank is determined by a bleed valve, the control device comprising: a processing circuit that controls the bleed valve based on an inflow flow rate command for the hydraulic actuator; and the processing circuit fully closes the bleed valve when the inflow flow rate command is greater than a minimum discharge flow rate of the hydraulic pump, and controls the bleed valve so that the opening area corresponds to the inflow flow rate command and the actuator pressure, which is the pressure of the hydraulic oil in the hydraulic actuator, when the inflow flow rate command is greater than zero and less than the minimum discharge flow rate.

6. The control device according to claim 5, wherein the processing circuit calculates the opening area of ​​the bleed valve based on the inflow flow command and the differential pressure between the actuator pressure and the tank pressure, which is the pressure inside the tank.

7. A control device as described in claim 5 or 6, wherein the hydraulic actuator includes a first working chamber for movement in a first direction and a second working chamber for movement in a second direction, and the processing circuit controls the bleed valve using the pressure in the first working chamber as the actuator pressure when moving the hydraulic actuator in the first direction, and controls the bleed valve using the pressure in the second working chamber as the actuator pressure when moving the hydraulic actuator in the second direction.

8. The control device according to claim 5 or 6, wherein the processing circuit determines the inflow flow rate command in response to an operation signal output from an operation device.

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