Hydraulic system and spool position calibration method thereof

Abstract

The purpose of this invention is to provide a hydraulic system applicable to both centralized and individual pressure relief types, and a valve core position calibration method thereof, comprising: a central bypass passage; a parallel passage arranged in parallel with the central bypass passage; a directional control valve group having multiple directional control valves arranged in series with the central bypass passage and connected in parallel with the parallel passage; and a pressure relief valve arranged on the central bypass passage downstream of the directional control valve group; each directional control valve is connected to an actuator, and the flow of working fluid from the parallel passage to the actuator is controlled according to the position of the valve core, and the pressure relief valve controls the pressure relief flow rate discharged from the central bypass passage by changing the opening area of ​​the central bypass passage.

Description

Technical Field

[0001] This invention relates to a hydraulic system for controlling the flow of working fluid and a method for calibrating the position of the valve core. Background Technology

[0002] In construction machinery, hydraulic systems are used to control the flow of working fluid to multiple actuators. As an example of a hydraulic system, the hydraulic circuit of Patent Document 1 is known. In the hydraulic system of Patent Document 1, multiple directional control valves are arranged in series in a center bypass passage. Furthermore, a bleed-off valve is arranged further downstream of the multiple directional control valves in the center bypass passage.

[0003] Existing technical documents:

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-001768. Summary of the Invention

[0006] The problem the invention aims to solve:

[0007] Hydraulic systems used in construction machinery include centralized pressure relief systems (like the hydraulic circuit in Patent Document 1) and individual pressure relief systems. In an individual pressure relief system, directional control valves connected in series in a central bypass passage regulate the opening of the central bypass passage. Centralized pressure relief systems and individual pressure relief systems are formed with different passage structures. Therefore, it is preferable to form centralized pressure relief systems and individual pressure relief systems with a common passage structure.

[0008] Therefore, the purpose of this invention is to provide a method for calibrating the valve core position of a hydraulic system applicable to both centralized and individual pressure relief types.

[0009] Solution methods:

[0010] The hydraulic system of the present invention comprises: a central bypass passage for supplying working fluid from a hydraulic pump; a parallel passage for supplying working fluid from the hydraulic pump and arranged in parallel with the central bypass passage; a directional control valve group having a plurality of directional control valves arranged in series with the central bypass passage and connected in parallel with the parallel passage; and a pressure relief valve disposed on the central bypass passage downstream of the directional control valve group; each of the directional control valves is connected to an actuator, and controls the flow of working fluid from the parallel passage to the actuator according to the position of the valve core, and the pressure relief valve controls the pressure relief flow rate discharged from the central bypass passage by changing the opening area of ​​the central bypass passage.

[0011] According to the present invention, a pressure relief valve is provided on the downstream side of the central bypass passage. Therefore, a centralized pressure relief passage structure can be formed in the hydraulic system. Furthermore, each directional control valve is connected in parallel with the parallel passage. Therefore, the directional control valves are configured to throttle the central bypass passage according to the position of the valve core, thereby forming an individual pressure relief passage structure in the hydraulic system.

[0012] The method for calibrating the valve spool position in a hydraulic system according to the present invention is a method for a hydraulic system comprising: a central bypass passage supplying working fluid from a hydraulic pump; a parallel passage supplying working fluid from the hydraulic pump and arranged in parallel with the central bypass passage; a directional control valve group comprising multiple directional control valves arranged in series with the central bypass passage and connected in parallel with the parallel passage and respectively connected to actuators, and controlling the flow of working fluid from the parallel passage to the actuators according to the position of the valve spool; a pressure relief valve disposed downstream of the directional control valve group in the central bypass passage and controlling the pressure relief flow rate discharged from the central bypass passage by changing the opening area of ​​the central bypass passage according to the position of the valve body; and a discharge valve for detecting the discharge pressure of the hydraulic pump. The device includes: a pressure sensor; and a control device for controlling the movement of the valve core and the valve body; comprising: an unloading step for adjusting the movement of the valve body in such a way that the opening area of ​​the central bypass passage in the pressure relief valve is greater than the opening area of ​​the central bypass passage in the directional control valve; a valve core movement step for outputting a control signal from the control device to the directional control valve and moving the valve core according to the control signal; a position estimation step for estimating the position of the valve core based on the detected discharge pressure when the valve core is moved, as detected by the discharge pressure sensor; and a calibration step for comparing the control signal output to the directional control valve with the estimated position of the valve core and adjusting the relationship between the control signal and the position of the valve core.

[0013] According to the present invention, in hydraulic systems applicable to both centralized and individual pressure relief types, the deviation between the control signal and the valve spool position can be adjusted. Thus, for example, when the control signal is output according to the operating amount, inconsistencies in the valve spool position relative to the operating amount can be suppressed within each system. That is, inconsistencies in operability are suppressed.

[0014] Invention effects:

[0015] According to the present invention, it can be applied to any type, including centralized pressure relief type and individual pressure relief type. Attached Figure Description

[0016] Figure 1 This is a circuit diagram showing the hydraulic circuit when centralized bleed control is performed in a hydraulic system according to a first embodiment of the present invention;

[0017] Figure 2 It is shown in Figure 1 The circuit diagram of the hydraulic circuit when performing individual bleed control in a hydraulic system;

[0018] Figure 3 It is shown Figure 1 A circuit diagram showing the flow of pressurized fluid in a hydraulic system during operation;

[0019] Figure 4 It is shown in Figure 1 A graph showing the variation of valve core opening area applicable to each control valve in a hydraulic system for performing calibration valve core stroke.

[0020] Figure 5 It is shown in Figure 1 A flowchart illustrating the sequence of calibrations performed in the hydraulic system;

[0021] Figure 6 This is a circuit diagram showing the hydraulic circuit of a hydraulic system according to a second embodiment of the present invention;

[0022] Explanation of symbols:

[0023] 1.1A Hydraulic System

[0024] 3. Hydraulic pump

[0025] 4-6 Actuators

[0026] 11. Central bypass passage

[0027] 12 Parallel Pathways

[0028] 13-way control valve group

[0029] 14 Pressure relief valve

[0030] 14a Valve body

[0031] 15. Exhaust pressure sensor

[0032] 18. Control device

[0033] 21 Directional control valve

[0034] 21a, 21b valve cores

[0035] 22 Directional control valve

[0036] 22a, 22b valve cores

[0037] 23 Directional control valve

[0038] 23a, 23b valve cores

[0039] 31 Throttling section

[0040] 32 Safety valve

[0041] 33 Negative control pathway. Detailed Implementation

[0042] Hereinafter, hydraulic systems 1 and 1A according to the first and second embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, the concept of direction used in the following description is for ease of explanation and is not intended to limit the structural direction of the invention to these directions. Also, the hydraulic systems 1 and 1A described below are only one embodiment of the present invention. Therefore, the present invention is not limited to any particular embodiment, and additions, deletions, and modifications can be made without departing from the purpose of the present invention.

[0043] (First implementation form)

[0044] <Hydraulic drive unit>

[0045] Figure 1 The hydraulic drive unit 2 shown is mounted on hydraulic vehicles such as construction vehicles and industrial vehicles. The hydraulic drive unit 2 drives various devices (such as excavating devices, lifting devices, and traveling devices) of the hydraulic vehicle. More specifically, each device of the hydraulic vehicle includes actuators 4 to 6, such as a hydraulic motor 4, a first cylinder 5, and a second cylinder 6. Furthermore, the hydraulic drive unit 2 includes a hydraulic pump 3 and a hydraulic system 1. Moreover, the hydraulic drive unit 2 supplies working fluid from the hydraulic pump 3 to the hydraulic motor 4, the first cylinder 5, and the second cylinder 6 via the hydraulic system 1. As a result, the actuators 4 to 6 operate to drive each device. The structure of the hydraulic system 1 will be described in more detail below.

[0046] [Hydraulic pump]

[0047] Hydraulic pump 3 discharges working fluid. More specifically, hydraulic pump 3 is connected to a drive source (e.g., an engine or electric motor) not shown. Then, hydraulic pump 3 is driven by the drive source to discharge working fluid. Furthermore, hydraulic pump 3 is a variable-capacity pump; in this embodiment, it is a variable-capacity swashplate pump. That is, hydraulic pump 3 is equipped with a regulator 8. Moreover, regulator 8 changes the discharge flow rate of hydraulic pump 3 according to the input pump signal. Thus, hydraulic pump 3 discharges working fluid at a discharge flow rate corresponding to the pump signal. Alternatively, hydraulic pump 3 can be a fixed-capacity pump or a variable-capacity axle pump.

[0048] Hydraulic system

[0049] Hydraulic system 1 is connected to hydraulic pump 3. Hydraulic system 1 then controls the flow of working fluid from hydraulic pump 3 to actuators 4-6, driving various devices. More specifically, hydraulic system 1 includes: a central bypass passage 11, a parallel passage 12, a directional control valve group 13, a pressure relief valve 14, a discharge pressure sensor 15, load pressure sensors 16a-16c, an operating device 17, and a control device 18.

[0050] [Central Bypass Path]

[0051] The central bypass passage 11 is connected to the hydraulic pump 3. Working fluid from the hydraulic pump 3 is then supplied into the central bypass passage 11. Furthermore, the downstream side of the central bypass passage 11 is connected to the tank 7.

[0052] [Parallel Pathway]

[0053] The parallel passage 12 is arranged in parallel with the central bypass passage 11. Then, working fluid is supplied from the hydraulic pump 3 into the parallel passage 12. More specifically, the parallel passage 12 branches at the branch point 11a of the central bypass passage 11 and is arranged in parallel with the central bypass passage 11.

[0054] [Directional control valve group]

[0055] The directional control valve group 13 includes multiple directional control valves 21 to 23. These multiple directional control valves 21 to 23 are then connected in series with the central bypass passage 11 and in parallel with the parallel passage 12. More specifically, the multiple directional control valves 21 to 23 are respectively provided with each actuator 4 to 6. In this embodiment, the directional control valve group 13 includes the same number of directional control valves 21 to 23 as the number of actuators, i.e., three directional control valves 21 to 23. However, the number of directional control valves in the directional control valve group 13 is not limited to three; it can be two or more. Furthermore, the number of directional control valves does not necessarily have to be the same as the number of actuators.

[0056] Each directional control valve 21-23 is connected to a corresponding actuator 4-6 and controls the flow of working fluid to the corresponding actuator 4-6. In this embodiment, the first directional control valve 21 controls the flow of working fluid to the hydraulic motor 4, the second directional control valve 22 controls the flow of working fluid to the first cylinder 5, and the third directional control valve 23 controls the flow of working fluid to the second cylinder 6. More specifically, each of the directional control valves 21-23 has a valve core 21a-23a. Furthermore, each of the directional control valves 21-23 controls the flow of working fluid from the parallel passage 12 to the corresponding actuator 4-6 (i.e., the flow direction and flow rate of the working oil) according to the position of the valve cores 21a-23a. Also, when performing the centralized pressure relief control described later, the central bypass passage remains open regardless of the position of the valve cores 21a-23a. On the other hand, when performing the individual pressure relief control described later, such as... Figure 2 As shown, the directional control valves 21 to 23 each change the opening area of ​​the central bypass passage according to the position of the valve cores 21a to 23a.

[0057] Furthermore, in this embodiment, directional control valves 21-23 are center-open type electromagnetic pilot-operated spool valves. That is, directional control valves 21-23 output pilot pressure corresponding to the input control signal to valve cores 21a-23a (or 21b-23b), causing valve cores 21a-23a (or 21b-23b) to move to a position corresponding to the input control signal. Thus, each directional control valve 21-23 controls the flow of working fluid to actuators 4-6 (i.e., the flow direction and flow rate of the working oil) according to the input control signal. Additionally, directional control valves 21-23 are not limited to electromagnetic pilot-operated spool valves; they can also be electrically driven spool valves or pilot-operated spool valves driven by an electric motor or the like.

[0058] [Pressure relief valve]

[0059] The pressure relief valve 14 is disposed on the downstream side of the directional control valve group 13 on the central bypass passage 11. Furthermore, the pressure relief valve 14 controls the pressure relief flow rate from the central bypass passage 11 to the tank 7 by changing the opening area of ​​the central bypass passage 11. More specifically, the pressure relief valve 14 has a valve body 14a (a valve core in this embodiment). Moreover, the pressure relief valve 14 changes the position of the valve body 14a according to the input pressure relief signal. Furthermore, the pressure relief valve 14 changes the opening area of ​​the central bypass passage 11 according to the position of the valve body 14a. Thus, the pressure relief valve 14 controls the pressure relief flow rate. In this embodiment, the pressure relief valve 14 is an inverse proportional solenoid valve. Alternatively, the pressure relief valve 14 could also be a direct proportional solenoid valve.

[0060] [Output pressure sensor]

[0061] The discharge pressure sensor 15 detects the discharge pressure of the hydraulic pump 3. More specifically, the discharge pressure sensor 15 is connected to the discharge port 3a of the hydraulic pump 3. In this embodiment, the discharge pressure sensor 15 is connected to the discharge port 3a via a central bypass passage 11. The discharge pressure sensor 15 outputs a signal corresponding to the detected discharge pressure.

[0062] [Load pressure sensor]

[0063] Load pressure sensors 16a-16c detect the load pressure of the working fluid supplied to the corresponding actuators 4-6. More specifically, load pressure sensors 16a-16c are connected to each port of the corresponding actuators 4-6 and the passageway of directional control valves 21-23, respectively. Furthermore, load pressure sensors 16a-16c detect the load pressure of the hydraulic fluid flowing through the actuators 4-6. Also, load pressure sensors 16a-16c output a signal corresponding to the detected load pressure.

[0064] [Operating Device]

[0065] The operating device 17 outputs operating commands for operating actuators 4 to 6. More specifically, the operating device 17 has a corresponding number of operating levers 17a to 17c for each of the actuators 4 to 6. In this embodiment, the operating device 17 has one operating lever 17a to 17c for each of the actuators 4 to 6. Furthermore, the first operating lever 17a corresponds to the hydraulic motor 4, the second operating lever 17b corresponds to the first cylinder 5, and the third operating lever 17c corresponds to the second cylinder 6. The number of operating levers is not limited to the stated number; the operating lever provided relative to the actuators 5 and 6 can be a single lever capable of omnidirectional operation. The operating device 17 outputs operating commands corresponding to the operating direction and amount of operation of the operating levers 17a to 17c.

[0066] [Control Device]

[0067] The control device 18 controls the movement of the valve cores 21a-23a (or 21b-23b) of the directional control valves 21-23 and the valve body 14a of the pressure relief valve 14. Furthermore, the control device 18 controls the discharge flow rate of the hydraulic pump 3. Moreover, the control device 18 calibrates the valve cores 21a-23a (or 21b-23b) based on signals from the discharge pressure sensor 15. More specifically, the control device 18 outputs control signals to each directional control valve 21-23 according to the operation command from the operating device 17. This controls the position of the valve cores 21a-23a (or 21b-23b) of the directional control valves 21-23. Furthermore, the control device 18 outputs a pressure relief signal to the pressure relief valve 14 according to the operation command from the operating device 17. This causes the valve body 14a to move. Finally, the control device 18 outputs a pump signal to the regulator 8 corresponding to the operation command from the operating device 17. Therefore, the control device 18 can make the hydraulic pump 3 discharge working fluid at a discharge flow rate corresponding to the operating amount.

[0068] <Driving Operation of Hydraulic Systems>

[0069] In the hydraulic drive unit 2, when the operating levers 17a to 17c of the operating device 17 are operated, a pump signal corresponding to the operation amount of the operating levers 17a to 17c is output from the control device 18 to the regulator 8. As a result, the hydraulic pump 3 discharges working fluid corresponding to the discharge flow rate corresponding to the operation amount. That is, in the hydraulic drive unit 2, positive control is implemented corresponding to the discharge flow rate of the hydraulic pump 3. Furthermore, in the hydraulic system 1, when the operating levers 17a to 17c of the operating device 17 are operated, the following actions are performed.

[0070] Centralized pressure relief control

[0071] In hydraulic system 1, when performing centralized pressure relief control, directional control valves 21-23 are suitable for use as follows: Figure 1 The valve cores 21a to 23a are shown. Here, as previously described, valve cores 21a to 23a open the central bypass passage regardless of their position. Furthermore, when at least one of the operating levers 17a to 17c of the operating device 17, for example the second operating lever 17b, is operated, the control device 18 operates as follows.

[0072] When the second operating lever 17b is operated, the control device 18 moves the valve core 22a of the second direction control valve 22 according to its operating direction and operating amount (see reference). Figure 3 Furthermore, the control device 18 activates the regulator 8 based on the operation amount of the second operating lever 17b, thereby controlling the output flow rate of the hydraulic pump 3. Additionally, the control device 18 moves the valve body 14a of the pressure relief valve 14 based on the operation amount of the second operating lever 17b, thereby controlling the opening area of ​​the central bypass passage 11. Thus, the pressure relief flow rate in the hydraulic system 1 is controlled (see reference...). Figure 3 The working fluid, at a flow rate corresponding to the operating volume (medium thickness line), is supplied to the first cylinder 5 (refer to...). Figure 3 (thick lines in the middle).

[0073] On the other hand, the same applies when operating levers 17a and 17c are operated in hydraulic system 1, and when at least two of operating levers 17a to 17c are operated simultaneously. That is, operating device 17 controls the position of valve cores 21a to 23a according to the operating direction and amount of the operated levers 17a to 17c. Furthermore, control device 18 controls the discharge flow rate of hydraulic pump 3 and moves valve body 14a according to the amount of operation of operating levers 17a to 17c. As a result, the pressure relief flow rate in hydraulic system 1 is controlled, and the working fluid with a flow rate corresponding to the operating amount is supplied to actuators 4 to 6. In such hydraulic system 1, centralized pressure relief control can be achieved by using valve cores 21a to 23a.

[0074] [Individual pressure relief control]

[0075] In hydraulic system 1, when performing individual pressure relief control, directional control valves 21-23 are suitable as follows: Figure 2 The valve cores 21b to 23b are shown. Here, as previously described, the valve cores 21b to 23b change the opening area of ​​the central bypass passage 11 according to their position. More specifically, the valve cores 21b to 23b reduce the opening area of ​​the central bypass passage 11 according to the amount of movement from the neutral position. Furthermore, when at least one of the operating levers 17a to 17c of the operating device 17, for example, the second operating lever 17b, is operated, the control device 18 operates as follows.

[0076] The control device 18 increases the opening area of ​​the central bypass passage 11 at the pressure relief valve 14 regardless of the amount of operation of the second operating lever 17b. In this embodiment, the control device 18 fully opens the opening area of ​​the central bypass passage at the pressure relief valve 14. Furthermore, when, for example, the second operating lever 17b is operated, the control device 18 activates the regulator 8 according to its operation amount, thereby controlling the output flow rate of the hydraulic pump 3. Moreover, the control device 18 moves the valve core 22b of the second direction control valve 22 according to the operation direction and operation amount of the second operating lever 17b. As a result, the opening area of ​​the central bypass passage 11 changes according to the position of the valve core 22b, that is, according to the operation amount of the second operating lever 17b. As a result, the pressure relief flow rate in the hydraulic system 1 is controlled by the valve core 21b (see reference). Figure 2 The medium-thickness line in the middle), the working fluid at a flow rate corresponding to the operating volume is supplied to the first cylinder 5 (refer to...). Figure 2 (thick lines in the middle).

[0077] Furthermore, in hydraulic system 1, the same applies when operating levers 17a and 17c are operated, and when at least two of operating levers 17a to 17c are operated simultaneously. That is, operating device 17 fully opens the central bypass passage 11 at the vent valve 14, and controls the discharge flow rate of the hydraulic pump according to the operation amount of operating levers 17a to 17c. Moreover, control device 18 controls the position of valve cores 21b to 23b according to the operating direction and operation amount of the operated levers 17a to 17c. Thus, the pressure relief flow rate in hydraulic system 1 is controlled, and working fluid with a flow rate corresponding to the operation amount is supplied to actuators 4 to 6. In such a hydraulic system 1, individual pressure relief control can be achieved by using valve cores 21b to 23b.

[0078] In the hydraulic system 1 of this embodiment, a pressure relief valve 14 is arranged downstream of the central bypass passage 11. Therefore, a centralized pressure relief passage structure can be formed in the hydraulic system 1. Thus, centralized pressure relief control is achieved by using valve cores 21a to 23a. Furthermore, each directional control valve 21 to 23 is connected in parallel with the parallel passage 12. Therefore, the directional control valves 21 to 23, depending on the position of the valve cores 21b to 23b, can throttle the central bypass passage 11, thereby forming an individual pressure relief passage structure in the hydraulic system 1. Thus, individual pressure relief control is achieved by using valve cores 21b to 23b.

[0079] <Calibration procedures for hydraulic systems>

[0080] In hydraulic system 1, to move valve cores 21a-23a (or 21b-23b) to a predetermined position, control device 18 outputs control signals (current or voltage) to directional control valves 21-23. However, directional control valves 21-23 may deviate from the predetermined position relative to the control signal, causing valve cores 21a-23a (or 21b-23b) to move. Therefore, hydraulic system 1 can calibrate directional control valves 21-23 by using valve cores 21a-23a (or 21b-23b) with the following characteristics: That is, valve cores 21a-23a (or 21b-23b) have the following characteristics: Figure 4 The opening characteristics are shown. The opening area of ​​valve cores 21a to 23a (or 21b to 23b) changes slope before and after the specified stroke s1 (inflection point) (refer to...). Figure 4 (The dotted line L1). Furthermore, in the hydraulic system 1, the control device 18 performs the following actions to calibrate the valve cores 21a to 23a: Figure 5 The calibration process is shown below. Additionally, the calibration process for the valve core 21a of the first directional control valve 21 will be described below. Furthermore, regarding the calibration process for the valve cores 22a and 23a of the other directional control valves 22 and 23, which are performed in the same manner, the description of the calibration process for valve core 21a is provided, and details are omitted. After performing the calibration process, proceed to step S1.

[0081] In step S1, which is an unloading process, the opening area of ​​the central bypass passage 11 at the pressure relief valve 14 is adjusted (refer to...). Figure 4 The movement of valve body 14a is adjusted by the solid line L2 being greater than the opening area of ​​the central bypass passage 11 at directional control valves 21-23. In this embodiment, control device 18 puts hydraulic system 1 into an unloaded state. More specifically, control device 18 outputs a pressure relief signal to pressure relief valve 14, increasing the opening area of ​​the central bypass passage 11 at pressure relief valve 14. In this embodiment, control device 18 makes the opening area of ​​the central bypass passage 11 at pressure relief valve 14 fully open. Then, proceed to step S2.

[0082] In step S2, which is the valve core movement process, the control device 18 outputs a control signal to the first directional control valve 21. As a result, the first directional control valve 21 moves the valve core 21a according to the input control signal. When the valve core 21a moves, the opening area of ​​the central bypass passage 11 at the first directional control valve 21 is changed. After the position of the valve core 21a changes, the process proceeds to step S3.

[0083] In step S3, which is a position estimation process, the change in discharge pressure is detected by the discharge pressure sensor 15. Furthermore, the control device 18 estimates the position of the valve core 21a based on the detected discharge pressure. More specifically, when the control device 18 moves the valve core 21a in step S2, it acquires the discharge pressure at each position and the load pressure of the hydraulic motor 4 based on signals from the discharge pressure sensor 15 and the load pressure sensor 16a. The control device 18 stores the acquired discharge pressure and load pressure in correspondence with the position of the valve core 21a, i.e., the stroke amount. Moreover, the control device 18 calculates the opening area for each stroke amount based on the corresponding stored discharge pressure and load pressure, and obtains the opening characteristics based on the calculated opening area. Then, the control device 18 estimates the position of the valve core 21a relative to the output control signal based on the inflection point of the obtained opening characteristics. After estimating the position of the valve core 21a, the process proceeds to step S4.

[0084] In step S4, which is part of the calibration process, the control signal output to the directional control valve 21 is compared with the estimated position of the valve core 21a, and the relationship between the control signal and the position of the valve core 21a is adjusted. More specifically, when the position that the control signal should move to deviate from the estimated position of the valve core 21a, the control device 18 adjusts the relationship between the control signal and the position of the valve core 21a. Therefore, the control device 18 compares the control signal with the estimated position (stroke) of the valve core 21a. Then, the control device 18 obtains the control signal when the valve core 21a reaches the inflection point. Then, the control device 18 adjusts the relationship between the control signal and the position of the valve core 21a so that the obtained control signal is in the form of a value indicating the position reached at the inflection point. After adjusting the relationship between the control signal and the valve core position in this way, the calibration is completed.

[0085] In the hydraulic system 1 of this embodiment, by using valve cores 21a to 23a suitable for centralized pressure relief control as described above, both centralized pressure relief control and position calibration of valve cores 21a to 23a can be achieved in a centralized pressure relief type passage structure. That is, in centralized pressure relief control, such as Figure 5 As shown, in the central bypass passage 11, the opening area of ​​the pressure relief valve 14 is increased (refer to...). Figure 4 The solid line L2 is always larger than the opening area of ​​the directional control valves 21-23, thereby achieving both centralized pressure relief control of the hydraulic system 1 and position calibration of the valve cores 21a-23a. Furthermore, in the hydraulic system 1, by using valve cores 21b-23b suitable for individual pressure relief control, position calibration of valve cores 21b-23b can be achieved in an individual pressure relief type passage structure. Therefore, in the hydraulic system 1, valve core position calibration can be achieved in either a centralized pressure relief type passage structure or an individual pressure relief type passage structure.

[0086] Furthermore, in hydraulic system 1, the deviation between the control signal and the position of valve cores 21a-23a (or 21b-23b) can be adjusted. Therefore, when outputting a control signal corresponding to the operating amount, inconsistencies in the position of valve cores 21a-23a (or 21b-23b) relative to the operating amount can be suppressed in each system. Thus, inconsistencies in the action of actuators 4-6 relative to the operating amount can be suppressed in each system, i.e., operational inconsistencies can be suppressed.

[0087] (Second implementation form)

[0088] The hydraulic system 1A of the second embodiment has a similar structure to the hydraulic system 1 of the first embodiment. Therefore, regarding the structure of the hydraulic system 1A of the second embodiment, the differences from those of the hydraulic system 1 of the first embodiment will be mainly explained, and the same structures will be marked with the same symbols and the descriptions will be omitted.

[0089] The second embodiment of the hydraulic system 1A is equipped with a hydraulic drive unit 2A. Furthermore, the hydraulic drive unit 2A uses the hydraulic system 1A to perform negative control on the output flow of the hydraulic pump 3. More specifically, in addition to the directional control valve group 13, the pressure relief valve 14, the output pressure sensor 15, the load pressure sensors 16a-16c, the operating device 17, and the control device 18, the hydraulic system 1A also includes a throttling section 31, a relief valve 32, and a negative control passage 33.

[0090] Throttling section 31 is disposed on the downstream side of pressure relief valve 14 in central bypass passage 11. Thus, hydraulic pressure corresponding to the flow rate of the working pressure flowing through it can be generated on the upstream side of central bypass passage 11.

[0091] Safety valve 32 is disposed on the central bypass passage 11 near the downstream side of pressure relief valve 14 and is arranged in parallel with throttling section 31. Thus, when the pressure of the working fluid flowing in the upstream side of throttling section 31 of central bypass passage 11 exceeds the specified safety pressure, the working fluid flowing through the upstream side of throttling section 31 is discharged to tank 7.

[0092] The negative control passage 33 is connected to the pressure relief valve 14 and the safety valve 32. Furthermore, the negative control passage 33 is connected to the regulator 8. The negative control passage 33 supplies the hydraulic pressure, i.e., the negative control pressure (hereinafter referred to as "negative control pressure") upstream of the throttling section 31, to the regulator 8.

[0093] In the hydraulic system 1 constructed in this way, the negative control pressure corresponding to the pressure relief flow is input to the regulator 8 as a pump signal. Therefore, the output flow of the hydraulic pump 3 is controlled according to the negative control pressure. That is, by implementing negative control on the output flow of the hydraulic pump 3, a negative control loop can be realized in the hydraulic system 1.

[0094] Furthermore, the hydraulic system 1A in the second embodiment has the same effect as the hydraulic system 1 in the first embodiment.

[0095] (Other implementation forms)

[0096] In the hydraulic systems 1 and 1A of the first and second embodiments, by applying a component having such Figure 4 Centralized pressure relief control is implemented using valve cores 21a to 23a with the shown opening characteristics, but it is not always necessary to use valve cores 21a to 23a with such opening characteristics. For example, valve cores 21a to 23a can always be fully open in the central bypass passage 11, or they can have no inflection point in their opening characteristics. That is, valve cores 21a to 23a only need to make the opening area of ​​the control valves 21 to 23 in each direction larger than the opening area of ​​the valve body 14a at the central bypass passage 11 during the implementation of centralized pressure relief control.

Claims

1. A hydraulic system, characterized in that, It features: a central bypass passage for supplying working fluid from the hydraulic pump; The working fluid is supplied from the hydraulic pump, and a parallel passage is configured alongside the central bypass passage; A directional control valve group having multiple directional control valves configured in series with the central bypass passage and connected in parallel with the parallel passage; and A pressure relief valve is configured on the downstream side of the directional control valve group on the central bypass passage; Each of the directional control valves is connected to the actuator. The opening area of ​​the central bypass passage is changed according to the position of the valve core. The flow of working fluid from the parallel passage to the actuator is controlled by changing the opening area. The pressure relief valve controls the pressure relief flow rate from the central bypass passage by changing the opening area of ​​the central bypass passage according to the position of the valve body. The valve core has a larger opening area at each position compared to the valve body of the pressure relief valve.

2. The hydraulic system according to claim 1, characterized in that, It also includes: a discharge pressure sensor for detecting the discharge pressure of the hydraulic pump; and A control device for controlling the movement of the valve core and the valve body; The control device adjusts the movement of the valve body by making the opening area of ​​the central bypass passage at the pressure relief valve larger than the opening area of ​​the central bypass passage at the directional control valve, and moves the valve core, so that the change in discharge pressure is detected by the discharge pressure sensor, and the position of the valve core is estimated based on the detected discharge pressure.

3. The hydraulic system according to claim 2, characterized in that, The directional control valve changes the position of the valve core according to the input control signal. The control device compares the control signal output from the directional control valve with the estimated position of the valve core, and adjusts the relationship between the control signal and the position of the valve core.

4. The hydraulic system according to any one of claims 1 to 3, characterized in that, It also includes: a throttling section disposed on the central bypass passage closer to the downstream side than the pressure relief valve; A safety valve is arranged in the central bypass passage, parallel to the throttling section, closer to the downstream side than the pressure relief valve; and A negative control passage connecting the pressure relief valve and the safety valve on the central bypass passage.

5. A method for calibrating the position of a valve core in a hydraulic system, characterized in that, This is a method for calibrating the valve spool position in a hydraulic system, which includes: a central bypass passage supplying working fluid from a hydraulic pump; a parallel passage supplying working fluid from the hydraulic pump and arranged in parallel with the central bypass passage; a directional control valve group having multiple directional control valves arranged in series with the central bypass passage and connected in parallel with the parallel passage and connected to actuators respectively, and controlling the flow of working fluid from the parallel passage to the actuators according to the position of the valve spool; a pressure relief valve disposed in the central bypass passage downstream of the directional control valve group, and controlling the pressure relief flow rate from the central bypass passage by changing the opening area of ​​the central bypass passage according to the position of the valve body; a discharge pressure sensor for detecting the discharge pressure of the hydraulic pump; and a control device for controlling the movement of the valve spool and the valve body. It includes an unloading process that adjusts the movement of the valve body in such a way that the opening area of ​​the central bypass passage in the pressure relief valve is greater than the opening area of ​​the central bypass passage in the directional control valve. The valve core moving process involves the control device outputting a control signal to the directional control valve and moving the valve core according to the control signal. The valve core is moved, the discharge pressure sensor detects the change in discharge pressure, and a position estimation process is performed to estimate the position of the valve core based on the detected discharge pressure; and A calibration process involves comparing the control signal output to the directional control valve with the estimated position of the valve core and adjusting the relationship between the control signal and the position of the valve core.

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