Fluid pressure control system

Abstract

A fluid pressure control system (100) comprises: a relief valve (40); a downstream throttle (32); a pressure measurement unit (34); and a controller (50). The controller (50) sets a discharge capacity of a pump (P) and a valve opening pressure (PR) of the relief valve (40), generates a first map indicating the relationship between a flow rate (Q) of hydraulic oil passing through the downstream throttle (32) and a discharge pressure (PA) of the pump (P) when the valve opening pressure (PR) is set. The controller (50) calculates the flow rate (Q) as a calculation flow rate (QA) from a front-rear differential pressure (PB) acquired by the pressure measurement unit (34), corrects the discharge capacity of a pump (P) so that the discharge flow rate of the pump (P) decreases by the calculation flow rate (QA), calculates the discharge pressure (PA) of the pump (P) corresponding to the calculation flow rate (QA) on the basis of the first map, and corrects the valve opening pressure (PR) of the relief valve (40) to obtain the calculated discharge pressure (PA) of the pump (P).

Description

Fluid pressure control system

[0001] This invention relates to a fluid pressure control system.

[0002] JP2024-179286A discloses a fluid pressure control system used in construction machinery. The fluid pressure control system comprises a variable displacement pump that discharges working fluid through a supply passage, a control valve that controls the flow of working fluid supplied to and discharged from a fluid pressure actuator in response to operator input, a discharge passage that guides the working fluid from the supply passage to a tank, a relief valve provided in the discharge passage and configured so that its opening pressure is variable by an input electrical signal, a resistance section that provides resistance to the flow of working fluid that has been guided from the supply passage to the discharge passage and passed through the relief valve, a pressure measuring section for obtaining the differential pressure across the resistance section, and a controller that controls the pump's capacity in response to operator input for operating the fluid pressure actuator. The controller pre-stores a pressure-flow characteristic, which is the relationship between pressure loss in the resistance section and the flow rate through it, and obtains the flow rate of the working fluid passing through the resistance section based on the pressure-flow characteristic of the resistance section and the differential pressure across it obtained by the pressure measuring section, and controls the pump's discharge capacity and the relief valve's opening pressure according to the flow rate of the working fluid passing through the resistance section.

[0003] JP2024-179286A describes changing the opening pressure of the relief valve or the discharge capacity of the pump to reduce the flow rate of hydraulic fluid discharged from the pump and discharged into the tank through the discharge passage. This can reduce energy loss in a fluid pressure control system. However, Patent Document 1 does not describe a specific method for reducing energy loss in a fluid pressure control system.

[0004] The present invention aims to reduce energy loss in fluid pressure control systems.

[0005] According to one aspect of the present invention, a fluid pressure control system for controlling the operation of a fluid pressure actuator comprises: a pump that discharges working fluid through a supply passage; a control valve having a neutral position that guides the working fluid discharged from the pump to a tank when there is no operator input, and which controls the flow of working fluid supplied to and discharged from the fluid pressure actuator in response to the operator input; a discharge passage that guides the working fluid from the supply passage to the tank; a relief valve provided in the discharge passage that opens when the pressure in the discharge passage reaches a predetermined opening pressure, and which is configured such that the opening pressure is variable by an input electrical signal; a resistance unit that provides resistance to the flow of working fluid that has been guided from the supply passage to the discharge passage and passed through the relief valve; a pressure measuring unit for obtaining the differential pressure across the resistance unit; and the fluid pressure actuator. The system includes a controller that controls the discharge capacity of the pump and the opening pressure of the relief valve in response to the operation input of an operator operating the system, wherein the controller sets the discharge capacity of the pump in response to the operation input, sets the opening pressure of the relief valve in response to the operation input, generates a first map showing the relationship between the flow rate of the working fluid passing through the resistance section and the discharge pressure of the pump when the opening pressure is set, calculates the flow rate as the calculated flow rate from the differential pressure across the system obtained by the pressure measuring unit, corrects the discharge capacity of the pump so that the discharge flow rate of the pump decreases by the calculated flow rate, calculates the discharge pressure of the pump corresponding to the calculated flow rate based on the first map, and corrects the opening pressure of the relief valve so that it becomes the calculated discharge pressure of the pump.

[0006] According to another aspect of the present invention, a fluid pressure control system for controlling the operation of a fluid pressure actuator, comprising: a pump that discharges working fluid through a supply passage; a control valve having a neutral position that guides the working fluid discharged from the pump to a tank when there is no operator input, and which controls the flow of working fluid supplied to and discharged from the fluid pressure actuator in response to the operator input; a discharge passage that guides the working fluid from the supply passage to the tank; a relief valve provided in the discharge passage that opens when the pressure in the discharge passage reaches a predetermined opening pressure, and which is configured to be variable by an input electrical signal; and the supply passage to the discharge passage The device comprises a resistance unit that provides resistance to the flow of working fluid guided through a path and passing through the relief valve, a pressure measuring unit for obtaining the differential pressure across the resistance unit, and a controller that controls the discharge capacity of the pump and the opening pressure of the relief valve in accordance with the operation input of an operator operating the fluid pressure actuator. The controller sets the discharge capacity of the pump and the opening pressure of the relief valve in accordance with the operation input, and if the differential pressure across the unit obtained by the pressure measuring unit is greater than or equal to a predetermined value, it increases the opening pressure of the relief valve until the differential pressure across the unit falls below the predetermined value.

[0007] Figure 1 is a hydraulic circuit diagram of a fluid pressure control system according to an embodiment of the present invention. Figure 2 is a hydraulic circuit diagram showing the configuration of a relief valve according to an embodiment of the present invention. Figure 3 is a block diagram of a fluid pressure control system according to an embodiment of the present invention. Figure 4 is a graph showing the first target map. Figure 5 is a graph showing the second target map. Figure 6 is a graph showing the relationship between the relief valve opening pressure and the command current value. Figure 7 is a graph showing the first map. Figure 8 is a graph showing the relationship between the flow rate and discharge pressure at each opening pressure. Figure 9 is a graph showing the relationship between the opening pressure and the constants in the relationship equation between the flow rate and discharge pressure. Figure 10 is a graph showing the second map. Figure 11 is a graph showing the relationship between the differential pressure across the system and the flow rate at each opening pressure. Figure 12 is a graph showing the relationship between the opening pressure and the constants in the relationship equation between the differential pressure across the system and the flow rate. Figure 13 is a flowchart showing a control method according to an embodiment of the present invention. Figure 14 is a flowchart showing a control method according to a modified embodiment of the present invention.

[0008] Hereinafter, a fluid pressure control system 100 according to an embodiment of the present invention will be described with reference to the drawings. In the following description, a fluid pressure control system 100 used in construction machinery (for example, a hydraulic excavator) will be used as an example.

[0009] The fluid pressure control system 100 includes a lever 1 as an operating unit operated by an operator, a hydraulic cylinder 2 as a fluid pressure actuator that drives a drive target, a variable displacement pump P that discharges hydraulic oil as a working fluid, a tank T that stores the hydraulic oil, and a fluid pressure control device 10 that controls the operation of the hydraulic cylinder 2.

[0010] Lever 1 is operated by an operator to drive the hydraulic cylinder 2, and the operating input corresponding to the direction and amount of operation (operating angle) is input to the fluid pressure control device 10 as an electrical signal (operating signal). Lever 1 can be operated within a positive and negative range of the operating angle. Pilot pressure is supplied to the control valve 20 of the fluid pressure control device 10, which will be described later, according to the direction and amount of operation of lever 1.

[0011] Pump P is driven by an engine (not shown) or a motor (not shown) to discharge hydraulic fluid. Pump P is, for example, a swashplate type variable displacement piston pump, and the discharge capacity changes by changing the inclination of the swashplate with a regulator R. The regulator R controls the inclination of the swashplate of pump P based on a control signal transmitted from a controller 50, which will be described later. Specifically, the regulator R has a biasing member (not shown) that biases the swashplate to increase its tilt angle, and a solenoid unit (not shown) that generates a force that resists the biasing force of the biasing member. When the current supplied to the solenoid unit increases, the inclination of the swashplate decreases, and the discharge capacity of pump P decreases. Pump P is configured to discharge a constant flow rate even when the tilt angle of the swashplate is at its minimum. In other words, the minimum discharge capacity of pump P is a value greater than zero (hereinafter referred to as the "standby flow rate"). Since known configurations can be adopted for the pump P and regulator R, a detailed explanation is omitted. However, the pump P is not limited to this; it may also be a fixed-displacement pump driven by an electric motor. In this case, the discharge capacity and discharge pressure of the pump P are controlled by controlling the rotation of the electric motor.

[0012] The hydraulic cylinder 2 is a double-acting cylinder having a piston 4 that divides the inside of the cylinder tube 3 into a rod-side chamber 6 and a bottom-side chamber 7. A piston rod 5 is connected to the piston 4. Hydraulic fluid is supplied to and discharged from the rod-side chamber 6 of the hydraulic cylinder 2 through the rod-side passage 13. Hydraulic fluid is supplied to and discharged from the bottom-side chamber 7 of the hydraulic cylinder 2 through the bottom-side passage 14.

[0013] The hydraulic cylinder 2 extends when hydraulic fluid is supplied to the bottom chamber 7 and discharged from the rod chamber 6. Conversely, the hydraulic cylinder 2 retracts when hydraulic fluid is supplied to the rod chamber 6 and discharged from the bottom chamber 7.

[0014] The fluid pressure control device 10 controls the flow of hydraulic fluid discharged from the pump P to control the extension and retraction operation of the hydraulic cylinder 2. The hydraulic cylinder 2 extends and retracts when supplied with hydraulic fluid discharged from the pump P.

[0015] The fluid pressure control device 10 includes a control valve 20 provided in a supply passage 11 that guides the hydraulic fluid discharged from the pump P and controls the flow of hydraulic fluid supplied to and discharged from the hydraulic cylinder 2, and a safety valve 27 that opens when the pressure in the supply passage 11 reaches a predetermined opening pressure (cracking pressure) and discharges the hydraulic fluid in the supply passage 11 to the tank T.

[0016] The control valve 20 is a spool valve having a spool (not shown), and its position is switched by the movement of the spool.

[0017] The control valve 20 has a pair of pilot chambers 21a and 21b and springs 22a and 22b as biasing members, and operates according to the pressure difference between the pair of pilot chambers 21a and 21b.

[0018] The control valve 20 is connected to a supply passage 11, a tank passage 12 communicating with tank T, a branch supply passage 11a branching from supply passage 11, a branch tank passage 12a branching from tank passage 12, a rod-side passage 13, and a bottom-side passage 14. The supply passage 11 and the tank passage 12 form a center bypass passage that guides the hydraulic fluid discharged from pump P to tank T. The branch supply passage 11a is provided with a check valve 25 that allows the flow of hydraulic fluid from pump P to the control valve 20 and restricts the opposite flow.

[0019] The control valve 20 has a neutral position 20A that connects the supply passage 11 and the tank passage 12 and opens the center bypass passage; an extended position 20B as an operating position that connects the branch supply passage 11a and the bottom-side passage 14 and connects the branch tank passage 12a and the rod-side passage 13; and a retracted position 20C as an operating position that connects the branch supply passage 11a and the rod-side passage 13 and connects the branch tank passage 12a and the bottom-side passage 14.

[0020] When the lever 1 is not operated by the operator, no pilot pressure is supplied to the pair of pilot chambers 21a and 21b of the control valve 20, and the control valve 20 is held in the neutral position 20A by a pair of springs 22a and 22b. In the neutral position 20A, the rod-side passage 13, the bottom-side passage 14, the branch supply passage 11a, and the branch tank passage 12a are closed. Therefore, the hydraulic cylinder 2 does not extend or retract and is maintained in a load-holding state. In addition, the hydraulic fluid discharged from the pump P is supplied from the supply passage 11 through the control valve 20 to the tank passage 12 and then supplied to the tank T.

[0021] When the operator operates lever 1 in one direction, pilot pressure is directed to one pilot chamber 21a of the control valve 20 according to the amount of operation, and the control valve 20 switches to the extended position 20B. In the extended position 20B, communication between the supply passage 11 and the tank passage 12 is blocked, and the center bypass passage is closed. When the control valve 20 switches to the extended position 20B, the hydraulic fluid discharged from pump P is supplied to the bottom chamber 7 through the branch supply passage 11a and the bottom passage 14. The hydraulic fluid in the rod chamber 6 is discharged to the tank T through the rod passage 13 and the branch tank passage 12a. As a result, the hydraulic cylinder 2 extends.

[0022] When the operator moves lever 1 in the other direction, pilot pressure is directed to the other pilot chamber 21b of the control valve 20 according to the amount of movement, and the control valve 20 switches to the retracted position 20C. In the retracted position 20C, communication between the supply passage 11 and the tank passage 12 is blocked, and the center bypass passage is closed. When the control valve 20 switches to the retracted position 20C, the hydraulic fluid discharged from the pump P is supplied to the rod-side chamber 6 through the branch supply passage 11a and the rod-side passage 13. The hydraulic fluid in the bottom-side chamber 7 is discharged to the tank T through the bottom-side passage 14 and the branch tank passage 12a. As a result, the hydraulic cylinder 2 retracts.

[0023] The fluid pressure control device 10 includes a discharge passage 15 that guides the hydraulic fluid from the supply passage 11 to a tank T, a relief valve 40 provided in the discharge passage 15 that opens when the pressure in the discharge passage 15 reaches a predetermined opening pressure PR and the opening pressure PR is variable, a downstream throttle 32 as a resistance section that provides resistance to the flow of hydraulic fluid that has been guided from the supply passage 11 to the discharge passage 15 and passed through the relief valve 40, an upstream throttle 33 provided in the discharge passage 15 as an additional resistance section that provides resistance to the flow of hydraulic fluid that has been guided from the supply passage 11 to the relief valve 40, a pressure measuring unit 34 for obtaining the differential pressure PB across the downstream throttle 32, and a controller 50 that controls the discharge capacity of the pump P and the operation of the relief valve 40 in accordance with the operation input of the operator operating the hydraulic cylinder 2.

[0024] The relief valve 40 is an electromagnetic relief valve having a set spring 40a as a biasing member for setting the valve opening pressure PR, and a solenoid 40b that generates an electromagnetic force when energized. The valve opening pressure PR of the relief valve 40 is adjusted by the movement of a plunger (not shown) due to the electromagnetic force generated by the solenoid 40b in response to an electrical signal (valve opening pressure signal) input from the controller 50, which causes the set spring 40a to expand and contract. The valve opening pressure PR of the relief valve 40 is set to be at least greater than the tank pressure. The hydraulic fluid that has passed through the upstream throttle 33 and the hydraulic fluid that has passed through the downstream throttle 32 (tank pressure) are each led to the relief valve 40 as pilot pressure. The relief valve 40 opens when the pressure difference between the upstream throttle 33 and the relief valve 40 (the downstream pressure of the upstream throttle 33, i.e., the upstream pressure of the relief valve 40) and the tank pressure (hereinafter referred to as the "overhead pressure difference PB" of the relief valve 40) reaches the opening pressure PR, thereby opening the discharge passage 15. When the relief valve 40 is closed, the upstream pressure of the relief valve 40 is equal to the upstream pressure of the upstream throttle 33 (and thus the pressure of the supply passage 11), so the relief valve 40 essentially opens when the pressure difference between the upstream pressure of the upstream throttle 33 and the tank pressure reaches the opening pressure PR. When the relief valve 40 is open, it operates using the pressure difference between the pressure downstream of the upstream throttle 33 and upstream of the relief valve 40 and the tank pressure as the pilot pressure.

[0025] Referring to Figure 2, the configuration of the relief valve 40 will be described in detail. As shown in Figure 2, the relief valve 40 includes a housing 41, a main poppet 42 and a pilot poppet 46 provided within the housing 41, a main spring 44a as a biasing member that biases the main poppet 42 in the valve closing direction, a set spring 40a that biases the pilot poppet 46 in the valve closing direction, and a solenoid 40b that expands and contracts the set spring 40a.

[0026] The main poppet 42 partitions the housing 41 into a first upstream chamber 43a, a first downstream chamber 43b, and a first pilot chamber 43c. The first upstream chamber 43a communicates with the discharge passage 15 downstream of the upstream throttle 33, and the hydraulic fluid from the discharge passage 15 that has passed through the upstream throttle 33 is guided into it. The first downstream chamber 43b communicates with the discharge passage 15 upstream of the downstream throttle 32, and the hydraulic fluid from the first downstream chamber 43b is guided into the downstream throttle 32. When the main poppet 42 is closed, the communication between the first upstream chamber 43a and the first downstream chamber 43b is blocked by the main poppet 42, and when the main poppet 42 opens, the first upstream chamber 43a and the first downstream chamber 43b communicate. The first pilot chamber 43c is always in communication with the first upstream chamber 43a through the poppet throttle 44b. When the main poppet 42 is closed relative to the first upstream chamber 43a, the pressure-receiving area is formed to be the same as or smaller than the pressure-receiving area relative to the first pilot chamber 43c.

[0027] The pilot poppet 46 partitions the housing 41 into a second upstream chamber 47a, a second downstream chamber 47b, and a second pilot chamber 47c. The second upstream chamber 47a is in constant communication with the first pilot chamber 43c partitioned by the main poppet 42. The second downstream chamber 47b is in communication with the discharge passage 15 downstream of the downstream throttling 32 and communicates with the tank T through the discharge passage 15. When the pilot poppet 46 is closed, the communication between the second upstream chamber 47a and the second downstream chamber 47b is blocked by the pilot poppet 46, and when the pilot poppet 46 opens, the second upstream chamber 47a and the second downstream chamber 47b communicate. The second pilot chamber 47c is in constant communication with the second downstream chamber 47b. The pressure-receiving area of ​​the pilot poppet 46 with respect to the second upstream chamber 47a is smaller than the pressure-receiving area of ​​the pilot poppet 46 with respect to the second pilot chamber 47c. The second pilot chamber 47c houses a set spring 40a and a solenoid 40b. The pilot poppet 46 is biased in the closing direction by the biasing force of the set spring 40a and the thrust of the solenoid 40b.

[0028] The hydraulic fluid that has passed through the upstream throttle 33 of the discharge passage 15 is guided to the second upstream chamber 47a through the poppet throttle 44b. The second downstream chamber 47b communicates with the tank T through the discharge passage 15. If the thrust exerted on the pilot poppet 46 by the pressure guided to the second upstream chamber 47a is less than or equal to the combined force of the thrust exerted by the pressure in the second pilot chamber 47c (tank pressure) and the thrust exerted by the solenoid 40b and set spring 40a, the pilot poppet 46 closes. When the pilot poppet 46 is closed, the hydraulic fluid in the first pilot chamber 43c is not discharged to the tank T, and therefore the main poppet 42 also remains closed.

[0029] When the thrust exerted on the pilot poppet 46 by the pressure in the second upstream chamber 47a exceeds the combined force of the thrust exerted by the pressure in the second pilot chamber 47c (tank pressure) and the thrust exerted by the solenoid 40b and set spring 40a, the pilot poppet 46 opens. As a result, the hydraulic fluid in the first pilot chamber 43c is guided from the second upstream chamber 47a to the second downstream chamber 47b and discharged to the tank T through the discharge passage 15. Consequently, the main poppet 42 (and thus the relief valve 40) opens due to the pressure in the first upstream chamber 43a, and the hydraulic fluid in the discharge passage 15 is discharged to the tank T through the relief valve 40. In this way, the relief valve 40 opens when the differential pressure (front-to-back differential pressure PB) between the pressure downstream of the upstream throttle 33 and the pressure downstream of the downstream throttle 32 (tank pressure) in the discharge passage 15 reaches a predetermined opening pressure PR, and discharges the hydraulic fluid in the discharge passage 15 to the tank T.

[0030] As described above, the opening pressure PR of the relief valve 40 is determined in addition to the thrust of the set spring 40a and the solenoid 40b, according to the difference in pressure-receiving area between the first upstream chamber 43a and the first pilot chamber 43c with respect to the main poppet 42, the difference in pressure-receiving area between the second upstream chamber 47a and the second pilot chamber 47c with respect to the pilot poppet 46, the poppet throttle 44b, the main spring 44a, etc.

[0031] The configuration of the relief valve 40 is not limited to that shown in Figure 2. Any configuration that can realize the function of the relief valve 40 described herein and can be represented by a circuit symbol as shown in Figure 1 can be adopted as the relief valve 40.

[0032] The upstream throttling 33 and the downstream throttling 32 are fixed throttlings, such as orifices. The upstream throttling 33 and the downstream throttling 32 may also be flow resistance (pipe resistance) formed by the flow path (pipe) that constitutes the discharge passage 15, as fixed throttlings.

[0033] The pressure measuring unit 34 includes a pressure sensor 35a serving as an upstream pressure measuring unit that measures the pressure of hydraulic oil guided from the relief valve 40 to the downstream throttle 32, and a tank pressure sensor 35b serving as a tank pressure measuring unit that measures the pressure of the discharge passage 15 on the downstream side of the downstream throttle 32. The pressure sensor 35a measures the pressure between the relief valve 40 and the downstream throttle 32 in the discharge passage 15 (in other words, the upstream pressure of the downstream throttle 32). The measurement result of the pressure sensor 35a is input to the controller 50.

[0034] The tank pressure sensor 35b measures the pressure on the downstream side of the downstream throttle 32 guided to the relief valve 40 as pilot pressure. The measurement result of the tank pressure sensor 35b is input to the controller 50. Note that the tank pressure sensor 35b may also measure the internal pressure of the tank passage 12 or the tank T. The difference between the pressure measured by the pressure sensor 35a and the pressure measured by the tank pressure sensor 35b is the differential pressure PB across the downstream throttle 32.

[0035] Furthermore, the supply passage 11 is provided with a pressure sensor 26 that acquires the pressure of the supply passage 11. In other words, the pressure sensor 26 acquires the discharge pressure PA of the pump P. The measurement result of the pressure sensor 26 is input to the controller 50.

[0036] The controller 50 is constituted by a computer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an I / O interface (Input / Output Interface). The RAM stores data used in processing by the CPU, the ROM pre-stores control programs and the like for the CPU, and the I / O interface is used for inputting and outputting information between connected devices. The controller 50 is programmed to be able to execute at least the processing necessary for implementing the control according to the present embodiment and modified examples. Note that the controller 50 may be configured as a single device, or may be divided into a plurality of devices configured to perform distributed processing of each control among the plurality of devices. Furthermore, the controller 50 may be used in common with other controllers provided in a construction machine.

[0037] As shown in Figure 3, the controller 50 includes a storage unit 51 that stores in advance information necessary to control the discharge capacity of the pump P, and a processing unit 52 that executes a process to control the discharge capacity of the pump P.

[0038] As shown in Figure 4, the memory unit 51 pre-stores a first target map showing the relationship between the operating angle of the lever 1 and the discharge capacity of the pump P. This first target map is obtained from a map showing the current value of the regulator R with respect to the operating angle of the lever 1. Although Figure 4 only shows the positive range of the operating angle of the lever 1, the same relationship holds for the negative range of the operating angle, and the first target map is symmetrical with respect to the line where the operating angle is 0. In the first target map, when the operating input of the lever 1 is small (specifically, when the absolute value of the operating angle is Z0 or less), the discharge capacity is minimized (in other words, the standby flow rate). When the absolute value of the operating angle of the lever 1 becomes larger than Z0, the discharge capacity of the pump P increases with increasing absolute value of the operating angle.

[0039] Furthermore, the memory unit 51 pre-stores a second target map, as shown in Figure 5, which shows the relationship between the operating angle of the lever 1 and the opening pressure PR of the relief valve 40, and a map, as shown in Figure 6, which shows the relationship between the opening pressure PR of the relief valve 40 and the command current value of the solenoid 40b. Note that Figure 5 only shows the positive range of the operating angle of the lever 1, but the same relationship holds even in the negative range of the operating angle, and the second target map is symmetrical with respect to the line where the operating angle is 0. In the second target map, when the operating input of the lever 1 is small (specifically, when the absolute value of the operating angle is Z0 or less), the opening pressure PR becomes 0. When the absolute value of the operating angle of the lever 1 becomes larger than Z0, the opening pressure PR increases with increasing absolute value of the operating angle. Note that instead of the map shown in Figure 6, a mathematical formula showing the relationship between the opening pressure PR of the relief valve 40 and the command current value of the solenoid 40b may be stored in the memory unit 51.

[0040] Furthermore, as shown in FIG. 8, first data obtained experimentally in advance is stored in the storage unit 51, the first data representing the relationship between the passing flow rate Q passing through the downstream throttle 32 of the relief valve 40 and the discharge pressure PA of the pump P for each opening pressure PR of the relief valve 40. As will be described later, the first data is used to generate a first map showing the relationship between the passing flow rate Q and the discharge pressure PA of the pump P shown in FIG. 7. Furthermore, as shown in FIG. 11, second data obtained experimentally in advance is stored in the storage unit 51, the second data representing the relationship between the differential pressure PB across the downstream throttle 32 (specifically, the difference between the pressure measured by the pressure sensor 35a and the pressure measured by the tank pressure sensor 35b) and the passing flow rate Q for each opening pressure PR of the relief valve 40. As will be described later, the second data is used to generate a second map showing the relationship between the differential pressure PB across the downstream throttle 32 and the passing flow rate Q shown in FIG. 10. The first map, the first data, the second map, and the second data are used to control the discharge capacity of the pump P and the opening pressure PR of the relief valve 40, the details of which will be described later. Hereinafter, the discharge pressure PA of the pump P is also simply referred to as discharge pressure PA, the opening pressure PR of the relief valve 40 is also simply referred to as opening pressure PR, the differential pressure PB across the downstream throttle 32 is also simply referred to as differential pressure PB, and the passing flow rate Q passing through the downstream throttle 32 is also simply referred to as passing flow rate Q.

[0041] The controller 50 receives an operation signal transmitted from the lever 1 in response to an operation input to the lever 1 by an operator, and pressure signals indicating respective measured values input from the pressure sensor 35a, the tank pressure sensor 35b, and the pressure sensor 26. The processing unit 52 calculates the differential pressure PB across the throttle from the pressure signals of the pressure sensor 35a and the tank pressure sensor 35b, and calculates the discharge pressure PA from the pressure signal of the pressure sensor 26. Furthermore, the processing unit 52 controls the discharge capacity of the pump P and the opening pressure PR of the relief valve 40 based on the operation signal of the lever 1 and the pressure signals from the pressure sensor 35a, the tank pressure sensor 35b, and the pressure sensor 26.

[0042] Next, the second data and the second map will be explained. As shown in Figure 10, the second map shows the relationship between the differential pressure PB and the flow rate Q at a predetermined valve opening pressure PR, and is generated based on the second data. Figure 11 shows a part of the second data, which experimentally investigates the relationship between the differential pressure PB and the flow rate Q at valve opening pressures PR1, PR2, and PR3 (PR1 < PR2 < PR3) in the fluid pressure control system 100. As shown in Figure 11(a), the relationship between the differential pressure PB and the flow rate Q at valve opening pressure PR1 is Q = A1・PB Ｂ１ This can be expressed as (where A1 and B1 are constants). In the fluid pressure control system 100, when the valve opening pressure PR changes and the pressure of the hydraulic fluid flowing through the discharge passage 15 changes, the viscosity of the hydraulic fluid changes, and the flow of the hydraulic fluid changes. However, as shown in Figure 11(b), even when the valve opening pressure PR is PR2, the relationship between the differential pressure PB and the flow rate Q is similar, and using constants A2 and B2, Q = A2・PB Ｂ２ It can be expressed as follows. Also, as shown in Figure 11(c), when the valve opening pressure PR is PR3, the relationship between the differential pressure PB and the flow rate Q is similar, and using constants A3 and B3, Q = A3・PB Ｂ３ This can be expressed as follows. Note that the data shown in Figure 11 is an example of experimental results. In other words, even if the valve opening pressure PR changes, the relationship between the differential pressure PB and the flow rate Q is given by equation (1): Q = A・PB Ｂ (See Figure 11. A and B are constants that change according to the valve opening pressure PR.) This can be expressed as follows. If constants A and B corresponding to a predetermined valve opening pressure PR can be determined, the relationship between the differential pressure PB and the flow rate Q at the predetermined valve opening pressure PR can be shown, or in other words, a second map (Figure 10) corresponding to the predetermined valve opening pressure PR can be generated. Note that experimental data will change depending on the viscosity of the hydraulic fluid, the inner diameter of the piping of the hydraulic fluid flow path, the number of bends in the hydraulic fluid flow path, etc. For this reason, it is preferable to obtain the second data, which is experimental data, by flowing the hydraulic fluid actually used in the fluid pressure control system 100.

[0043] Figure 12 shows the constants A and B in equation (1) for each valve opening pressure PR for the three graphs shown in Figure 11. For example, at the point where the valve opening pressure PR is PR1, A1 is plotted as constant A and B1 is plotted as constant B. The data shown in Figure 12 is also stored in the storage unit 51 as second data. As shown in Figure 12, from the experimental results for each valve opening pressure PR, the constant A can be expressed as a function of the valve opening pressure PR, and in this embodiment, it is a cubic function of PR, as in equation (2): A = D1・PR ３ +E1・PR ２ It can be expressed as +F1・PR+G1 (see Figure 12; D1, E1, F1, and G1 are constants). Similarly, the constant B is a cubic function of PR, and equation (3) is: B = D2・PR ３ +E2・PR ２ It can be expressed as +F2・PR+G2 (see Figure 12; D2, E2, F2, G2 are constants). Therefore, by substituting a predetermined valve opening pressure PR value into equations (2) and (3) above, the constants A and B in equation (1) (Figure 11) can be determined, and the second map shown in Figure 10 (relationship between the differential pressure PB and the flow rate Q at a predetermined valve opening pressure PR) can be generated. The second map is used to calculate the flow rate Q at the differential pressure PB obtained from the pressure sensor 35a and the tank pressure sensor 35b as the calculated flow rate QA. In this embodiment, equations (1), (2), and (3) are stored as second data. Alternatively, only the map showing the relationship between the differential pressure PB and the flow rate Q at each valve opening pressure PR shown in Figure 11 (equation (1)) may be stored. In this case, for example, among the multiple maps shown in Figure 11, the map showing the relationship between the differential pressure PB and the flow rate Q at an opening pressure PR close to a predetermined opening pressure PR is read and generated as the second map.

[0044] Next, the first data and the first map will be described. As shown in FIG. 7, the first map shows the relationship between the passage flow rate Q at a predetermined valve opening pressure PR and the discharge pressure PA, and is generated based on the first data. FIG. 8 shows a part of the first data. In the fluid pressure control system 100, the relationship between the passage flow rate Q and the discharge pressure PA when the valve opening pressure PR is PR1, PR2, PR3 (PR1 < PR2 < PR3) is experimentally investigated. In the first data and the first map, the "discharge pressure PA" may be a difference between the discharge pressure PA (the measured value of the pressure sensor 26) and the tank pressure. That is, the "pump discharge pressure" recited in the claims also includes a difference between the discharge pressure of the pump and the tank pressure. As shown in FIG. 8(a), when the valve opening pressure PR is PR1, the relationship between the passage flow rate Q and the discharge pressure PA is PA = A1·Q ２ + B1·Q + PR (A1 and B1 are constants). As described above, in the fluid pressure control system 100, when the valve opening pressure PR changes and the pressure of the hydraulic oil flowing through the discharge passage 15 changes, the viscosity of the hydraulic oil changes and the flow of the hydraulic oil changes. However, as shown in FIG. 8(b), even when the valve opening pressure PR is PR2, the relationship between the passage flow rate Q and the discharge pressure PA can be expressed in the same form using constants A2 and B2 as PA = A2·Q ２ + B2·Q + PR. Further, as shown in FIG. 8(c), even when the valve opening pressure PR is PR3, the relationship between the passage flow rate Q and the discharge pressure PA can be expressed in the same form using constants A3 and B3 as PA = A3·Q ２ + B3·Q + PR. Note that the data shown in FIG. 8 is an example of an experimental result. That is, even if the valve opening pressure PR changes, the relationship between the passage flow rate Q and the discharge pressure PA can be expressed by Equation (4): PA = A·Q ２ + B·Q + PR (A and B are constants that change in accordance with the valve opening pressure PR). If constants A and B corresponding to a predetermined valve opening pressure PR can be obtained, the relationship between the passage flow rate Q and the discharge pressure PA at the predetermined valve opening pressure PR can be indicated; in other words, the first map (FIG. 7) corresponding to the predetermined valve opening pressure PR can be generated. It is preferable that the first data, which is experimental data, is acquired by causing the hydraulic oil to be actually used to flow in the fluid pressure control system 100, similarly to the second data.

[0045] Figure 9 shows the constants A and B in equation (4) for each valve opening pressure PR for the three graphs shown in Figure 8. For example, at the point where the valve opening pressure PR is PR1, A1 is plotted as constant A and B1 is plotted as constant B. Data like that shown in Figure 9 is also stored in the storage unit 51 as first data. As shown in Figure 9, from the experimental results for each valve opening pressure PR, the constant A can be expressed as a function of the valve opening pressure PR, and in this embodiment, it is a quadratic function of PR, as in equation (5): A = D1・PR ２ It can be expressed as +E1・PR+F1 (where D1, E1, and F1 are constants). Similarly, the constant B is a quadratic function of PR, and equation (6) is: B = D2・PR ２ It can be expressed as +E2・PR+F2 (where D2, E2, and F2 are constants). Therefore, by substituting a predetermined valve opening pressure PR value into equations (5) and (6) above, the constants A and B in equation (4) (Figure 8) can be determined, and the first map shown in Figure 7 (relationship between discharge pressure PA and flow rate Q at a predetermined valve opening pressure PR) can be generated. The first map is used to calculate the discharge pressure PA corresponding to the calculated flow rate QA calculated based on the second map (Figure 10). In this embodiment, equations (4), (5), and (6) are stored as first data. Alternatively, only a map showing the relationship between flow rate Q and discharge pressure PA at each valve opening pressure PR, as shown in Figure 8 (equation (4)), may be stored. In this case, for example, a map showing the relationship between flow rate Q and discharge pressure PA at a valve opening pressure PR close to a predetermined valve opening pressure PR is read and generated as the first map.

[0046] The following describes the method for controlling the discharge capacity and valve opening pressure PR of the pump P in this embodiment.

[0047] The control method of this embodiment will be described below with reference to the flowchart shown in Figure 13. The controller 50 executes the process shown in Figure 13 at predetermined time intervals (for example, every few milliseconds).

[0048] In step S10, the operator's operation signal for lever 1 is acquired.

[0049] In step S11, the discharge capacity of the pump P and the opening pressure PR of the relief valve 40 are set according to the acquired operating signal of the lever 1. Specifically, the discharge capacity of the pump P corresponding to the operating angle of the lever 1 is set by referring to the first target map shown in Figure 4, which shows the relationship between the operating angle of the lever 1 and the discharge capacity of the pump P, and the opening pressure PR corresponding to the operating angle of the lever 1 is set by referring to the second target map shown in Figure 5, which shows the relationship between the operating angle of the lever 1 and the opening pressure PR of the relief valve 40. In this embodiment, as shown in Figures 4 and 5, the discharge capacity of the pump P is set to the numerical value Z2 and the opening pressure PR is set to the numerical value Z3, corresponding to the operating angle Z1 of the lever 1.

[0050] In step S12, the differential pressure PB (with a value of Z4), which is the difference between the pressures of the pressure sensor 35a and the tank pressure sensor 35b, is obtained from the pressure signals, which are the measurement results of the pressure sensor 35a and the tank pressure sensor 35b.

[0051] In step S13, a second map (see Figure 10) is generated showing the relationship between the differential pressure PB across the valve opening pressure PR (numerical value Z3) and the flow rate Q. Specifically, the numerical value Z3 of the valve opening pressure PR is substituted into equations (2) and (3) shown in Figure 12, and equation (1) shown in Figures 11 and 12: Q = A・PB Ｂ The constants A and B are determined, and the second map shown in Figure 10 is generated.

[0052] In step S14, the flow rate Q at the differential pressure PB is calculated as the calculated flow rate QA based on the second map shown in Figure 10. In this embodiment, as shown in Figure 10, the calculated flow rate QA is calculated as Z5 for a value Z4 of the differential pressure PB. Thus, the calculated flow rate QA is not directly measured by a flow meter or the like, but is calculated based on the second map and the differential pressure PB.

[0053] In step S15, the discharge capacity of pump P is corrected and controlled so that the discharge flow rate of pump P decreases by the calculated flow rate QA. Specifically, the discharge flow rate of pump P is controlled by reducing the numerical value Z2 of the discharge capacity by an amount corresponding to the numerical value Z5 so that the calculated flow rate QA becomes approximately 0 (in other words, so that the flow rate Q passing through the relief valve 40 becomes approximately 0). This makes it possible to maintain the flow rate of hydraulic fluid directed to the hydraulic cylinder 2 while reducing the excess flow rate that passes through the relief valve 40 and is discharged to the tank T. Thus, energy loss in the fluid pressure control system 100 can be reduced.

[0054] In step S16, a first map (see Figure 7) is generated showing the relationship between the flow rate Q at the valve opening pressure PR (numerical value Z3) and the discharge pressure PA. Specifically, the numerical value Z3 for the valve opening pressure PR is substituted into equations (5) and (6) shown in Figure 9, and equation (4) shown in Figures 8 and 9: PA = A・Q ２ The constants A and B of +B・Q+PR are determined, and the map shown in Figure 7 is generated.

[0055] In step S17, the discharge pressure PA corresponding to the calculated flow rate QA is calculated based on the first map (Figure 7). Specifically, the numerical value of the calculated flow rate QA is substituted into the flow rate Q in the first map, and the corresponding numerical value of the discharge pressure PA is calculated. In this embodiment, as shown in Figure 7, the numerical value of the discharge pressure PA corresponding to the numerical value Z5 of the calculated flow rate QA is calculated as Z6.

[0056] In step S18, the valve opening pressure PR is corrected to match the discharge pressure PA (value Z6) calculated using the first map shown in Figure 7, and the valve opening pressure PR is controlled. In other words, the valve opening pressure PR is controlled to match the actual discharge pressure PA of the pump P. Specifically, the command current value Z7 for the solenoid 40b corresponding to the value Z6 of the valve opening pressure PR is calculated by referring to the map shown in Figure 6, and the solenoid 40b is controlled. This prevents the relief valve 40 from opening until the discharge pressure PA reaches Z6, thus maintaining the pressure of the hydraulic fluid leading to the hydraulic cylinder 2. In this way, the discharge capacity of the pump P and the valve opening pressure PR of the relief valve 40 are controlled.

[0057] Furthermore, step S15, which controls the discharge capacity of pump P, and steps S16-S18, which control the valve opening pressure PR, may be performed in reverse order or in parallel. In addition, the above control may be performed each time the lever 1 is operated or the differential pressure PB changes.

[0058] As described above, in this embodiment, the controller 50 calculates a calculated flow rate QA corresponding to the flow rate Q from the differential pressure PB acquired by the pressure measuring unit 34 (pressure sensor 35a and tank pressure sensor 35b), and controls the discharge capacity of the pump P by correcting it so that the discharge flow rate of the pump P decreases by the calculated flow rate QA. In addition, the controller 50 calculates the discharge pressure PA of the pump P corresponding to the calculated flow rate QA based on the first map, and controls the opening pressure PR of the relief valve 40 by correcting it so that it becomes the calculated discharge pressure PA of the pump P. As a result, it is possible to reduce only the flow rate passing through the downstream throttle 32 (relief valve 40) while maintaining the pressure and flow rate of the working fluid led to the hydraulic cylinder 2, thereby reducing energy loss in the fluid pressure control system 100. Furthermore, even when the above control is performed, the pressure and flow rate of the working fluid led to the hydraulic cylinder 2 are maintained, so it does not adversely affect the operation of the hydraulic cylinder 2.

[0059] Furthermore, since the controller 50 calculates a first map based on experimental data (first data) for each opening pressure PR of the relief valve 40, it is possible to improve the accuracy of the correction of the discharge capacity of the pump P and the opening pressure PR of the relief valve 40.

[0060] Furthermore, since the controller 50 calculates a second map based on experimental data (second data) for each relief valve opening pressure PR, the accuracy of the correction for the discharge capacity of the pump P and the relief valve opening pressure PR can be improved.

[0061] Furthermore, if the pressure in the supply passage 11 reaches the opening pressure of the safety valve 27, which is higher than the opening pressure PR of the relief valve 40, the safety valve 27 will open and discharge a portion of the hydraulic fluid in the supply passage 11 into the tank passage 12. This protects the entire system regardless of the opening pressure PR of the relief valve 40.

[0062] In addition to the above control, the controller 50 also performs horsepower control to control the discharge capacity of the pump P based on the pressure signal from the pressure sensor 26, so that the load on the engine driving the pump P does not exceed the permissible limit. Since the horsepower control is a known configuration, a detailed explanation will be omitted.

[0063] According to the above embodiments, the following effects and advantages are achieved.

[0064] The controller 50 calculates a calculated flow rate QA corresponding to the flow rate Q from the differential pressure PB acquired by the pressure measuring unit 34, and controls the discharge capacity of pump P by correcting it so that the discharge flow rate of pump P decreases by the calculated flow rate QA. It also calculates the discharge pressure PA of pump P corresponding to the calculated flow rate QA based on the first map, and controls the opening pressure PR of the relief valve 40 by correcting it so that it becomes the calculated discharge pressure PA of pump P. As a result, the pressure and flow rate of the working fluid led to the hydraulic cylinder 2 can be maintained, and only the flow rate passing through the downstream throttle 32 can be reduced, thereby reducing energy loss in the fluid pressure control system 100.

[0065] Next, modifications of this embodiment will be described. The following modifications are also within the scope of the present invention, and it is possible to combine the configurations shown in the modifications with the configurations described in the above embodiments, or to combine the configurations described in the following different modifications.

[0066] <Modification 1> In the above embodiment, the calculated flow rate QA is calculated as the flow rate Q corresponding to the differential pressure PB acquired by the pressure measurement unit 34 (pressure sensor 35a and tank pressure sensor 35b) based on the second map. However, the method is not limited to using the second map, as long as the flow rate Q can be calculated as the calculated flow rate QA from the differential pressure PB.

[0067] Furthermore, the discharge passage 15 and the relief valve 40 may be incorporated inside the fluid pressure control device 10, or they may be incorporated inside the pump P. Alternatively, the discharge passage 15 and the relief valve 40 may be provided separately for the fluid pressure control device 10 and the pump P, respectively.

[0068] <Modification 2> In the above embodiment, the first data and the second data are obtained from experiments. However, the first data and the second data are not limited to experiments; they can be obtained by any data that has been obtained in advance, for example, by calculation using an existing relational formula.

[0069] <Modification 3> In the above embodiment, the controller 50 calculates the flow rate Q as the calculated flow rate QA from the differential pressure PB obtained by the pressure measuring unit 34 and the second map, and corrects the discharge capacity of the pump P so that the discharge flow rate of the pump P decreases by the amount of the calculated flow rate QA. In addition, the controller 50 calculates the discharge pressure PA of the pump P corresponding to the calculated flow rate QA based on the first map, and corrects the opening pressure PR of the relief valve 40 so that it becomes the calculated discharge pressure PA of the pump P. Not limited to this, the controller 50 may not correct the discharge capacity of the pump P based on the calculated flow rate QA, and may increase the opening pressure PR of the relief valve 40 until the flow rate Q disappears when a flow rate Q is generated (in other words, until the relief valve 40 does not open). That is, if the differential pressure PB is above a predetermined value, the controller 50 may increase the opening pressure PR of the relief valve 40 until the differential pressure PB falls below a predetermined value. The "predetermined value" is set based on the minimum value of the differential pressure PB across the flow path when a flow rate Q occurs.

[0070] The control method for this modified example will be described below with reference to the flowchart shown in Figure 14. The controller 50 executes the process shown in Figure 14 at predetermined time intervals (for example, every few milliseconds).

[0071] In step S20, the operator's operation signal for lever 1 is acquired, similar to step S10. In step S21, the acquired operation signal for lever 1 is used to set the discharge capacity of pump P and the opening pressure PR of relief valve 40, similar to step S11, by referring to the first target map and the second target map. In step S22, the differential pressure PB is acquired from the pressure signals, which are the measurement results of pressure sensor 35a and tank pressure sensor 35b, similar to step S12.

[0072] In step S23, it is determined whether the differential pressure PB across the front and rear is greater than or equal to a predetermined value. If the differential pressure PB across the front and rear is greater than or equal to a predetermined value in step S23, the process proceeds to step S24, where the valve opening pressure PR is increased until the differential pressure PB across the front and rear falls below a predetermined value. In other words, in step S23, if the relief valve 40 is open, the valve opening pressure PR is increased until the relief valve 40 no longer opens, and the process ends.

[0073] On the other hand, if the differential pressure PB before and after step S23 is less than a predetermined value, the process proceeds to step S25 and ends without correcting the valve opening pressure PR. In this way, the valve opening pressure PR is controlled.

[0074] In this configuration, when the relief valve 40 is open, the opening pressure PR is increased until the relief valve 40 no longer opens. This maintains the pressure and flow rate of the hydraulic fluid supplied to the hydraulic cylinder 2, similar to the above embodiment, while reducing only the flow rate passing through the downstream throttle 32. Therefore, energy loss in the fluid pressure control system 100 can be reduced. Furthermore, since the discharge capacity of the pump P is not reduced by the correction, the flow rate of hydraulic fluid supplied to the hydraulic cylinder 2 increases, ensuring the operating speed of the hydraulic cylinder 2.

[0075] <Modification 4> In the above embodiment, the controller 50 receives an operation input as an operation signal corresponding to the operating direction and amount (operating angle) of the lever 1. However, the operation input may be determined by the pilot pressure of the control valve 20 or by an image taken of the state of the lever 1, etc.

[0076] The configuration, operation, and effects of the embodiments of the present invention will be described below.

[0077] The fluid pressure control system 100, which controls the operation of the hydraulic cylinder 2 as a fluid pressure actuator, includes a pump P that discharges hydraulic fluid through a supply passage 11, a control valve 20 that has a neutral position 20A that guides the hydraulic fluid discharged from the pump P to a tank T when there is no operator input and controls the flow of hydraulic fluid supplied to and discharged from the hydraulic cylinder 2 in response to operator input, a discharge passage 15 that guides the hydraulic fluid from the supply passage 11 to the tank T, a relief valve 40 provided in the discharge passage 15 that opens when the pressure in the discharge passage 15 reaches a predetermined opening pressure PR and is configured so that the opening pressure PR is variable by an input electrical signal, a downstream throttle 32 that acts as a resistance section that provides resistance to the flow of hydraulic fluid that has been guided from the supply passage 11 to the discharge passage 15 and passed through the relief valve 40, and a pressure measuring section for obtaining the differential pressure PB across the downstream throttle 32. The system includes 34 and a controller 50 that controls the discharge capacity of pump P and the opening pressure PR of relief valve 40 in response to the operator's input to operate the hydraulic cylinder 2. The controller 50 sets the discharge capacity of pump P in response to the operator's input, sets the opening pressure PR of relief valve 40 in response to the operator's input, generates a first map showing the relationship between the flow rate Q of the hydraulic fluid passing through the downstream throttle 32 and the discharge pressure PA of pump P when the opening pressure PR is set, calculates the flow rate Q as the calculated flow rate QA from the differential pressure PB obtained by the pressure measuring unit 34, corrects the discharge capacity of pump P so that the discharge flow rate of pump P decreases by the calculated flow rate QA, calculates the discharge pressure PA of pump P corresponding to the calculated flow rate QA based on the first map, and corrects the opening pressure PR of relief valve 40 so that it becomes the calculated discharge pressure PA of pump P.

[0078] In this configuration, the controller 50 calculates a calculated flow rate QA corresponding to the flow rate Q from the differential pressure PB acquired by the pressure measuring unit 34, and controls the discharge capacity of the pump P by correcting it so that the discharge flow rate of the pump P decreases by the calculated flow rate QA. It also calculates the discharge pressure PA of the pump P corresponding to the calculated flow rate QA based on the first map, and controls the opening pressure PR of the relief valve 40 by correcting it so that it becomes the calculated discharge pressure PA of the pump P. As a result, the pressure and flow rate of the working fluid led to the hydraulic cylinder 2 can be maintained, and only the flow rate passing through the downstream throttle 32 can be reduced, thereby reducing energy loss in the fluid pressure control system 100.

[0079] Furthermore, in the fluid pressure control system 100, the controller 50 has pre-stored first data which is the relationship between the discharge pressure PA of the pump P and the flow rate Q for each relief valve opening pressure PR, and the first map is calculated based on the first data.

[0080] In this configuration, since the first map is calculated based on pre-obtained first data, the accuracy of the correction of the discharge capacity of the pump P and the opening pressure PR of the relief valve 40 can be improved.

[0081] Furthermore, in the fluid pressure control system 100, the controller 50 generates a second map showing the relationship between the differential pressure PB across the downstream throttle 32 and the flow rate Q, and the calculated flow rate QA is calculated based on the second map as the flow rate Q corresponding to the differential pressure PB across the downstream throttle acquired by the pressure measuring unit 34.

[0082] Furthermore, in the fluid pressure control system 100, the controller 50 has pre-stored second data which is the relationship between the differential pressure PB before and after the relief valve 40 and the flow rate Q for each opening pressure PR of the relief valve 40. The second map is generated based on the second data according to the opening pressure PR of the relief valve 40.

[0083] In these configurations, the second map is calculated based on pre-obtained second data, thereby improving the accuracy of the correction of the discharge capacity of the pump P and the opening pressure PR of the relief valve 40.

[0084] The fluid pressure control system 100, which controls the operation of the hydraulic cylinder 2 as a fluid pressure actuator, includes a pump P that discharges hydraulic fluid through a supply passage 11, a control valve 20 that has a neutral position 20A that guides the hydraulic fluid discharged from the pump P to a tank T when there is no operator input and controls the flow of hydraulic fluid supplied to and discharged from the hydraulic cylinder 2 in response to operator input, a discharge passage 15 that guides the hydraulic fluid from the supply passage 11 to the tank T, a relief valve 40 provided in the discharge passage 15 that opens when the pressure in the discharge passage 15 reaches a predetermined opening pressure PR and is configured so that the opening pressure PR is variable by an input electrical signal, and a relief valve 40 that opens when the pressure in the discharge passage 15 reaches a predetermined opening pressure PR and is configured so that the opening pressure PR is variable by an input electrical signal, and discharge from the supply passage 11 The hydraulic cylinder 2 is equipped with a downstream throttle 32 as a resistance unit that provides resistance to the flow of hydraulic fluid guided to the outlet passage 15 and passing through the relief valve 40, a pressure measuring unit 34 for obtaining the differential pressure PB across the downstream throttle 32, and a controller 50 that controls the discharge capacity of the pump P and the opening pressure PR of the relief valve 40 in accordance with the operation input of the operator operating the hydraulic cylinder 2. The controller 50 sets the discharge capacity of the pump P in accordance with the operation input, sets the opening pressure PR of the relief valve 40 in accordance with the operation input, and increases the opening pressure PR of the relief valve 40 until the differential pressure PB obtained by the pressure measuring unit 34 is less than a predetermined value.

[0085] In this configuration, when the relief valve 40 is open, the opening pressure PR is increased until the relief valve 40 no longer opens, thereby maintaining the pressure and flow rate of the working fluid leading to the hydraulic cylinder 2, while only reducing the flow rate passing through the downstream throttle 32. Therefore, energy loss in the fluid pressure control system 100 can be reduced. In addition, since the discharge capacity of the pump P is not reduced by the correction, the flow rate of the working fluid supplied to the hydraulic cylinder 2 increases, ensuring the operating speed of the hydraulic cylinder 2.

[0086] Although embodiments of the present invention have been described above, these embodiments only represent a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

[0087] This application claims priority based on Japanese Patent Application No. 2025-49589, filed with the Japan Patent Office on 25 March 2025, and all contents of that application are incorporated herein by reference.

Claims

1. A fluid pressure control system for controlling the operation of a fluid pressure actuator, comprising: a pump that discharges working fluid through a supply passage; a control valve having a neutral position that guides the working fluid discharged from the pump to a tank when there is no operator input, and which controls the flow of working fluid supplied to and discharged from the fluid pressure actuator in response to the operator input; a discharge passage that guides the working fluid from the supply passage to the tank; a relief valve provided in the discharge passage that opens when the pressure in the discharge passage reaches a predetermined opening pressure, and which is configured such that the opening pressure is variable by an input electrical signal; a resistance unit that provides resistance to the flow of working fluid that has been guided from the supply passage to the discharge passage and passed through the relief valve; a pressure measuring unit for obtaining the differential pressure before and after the resistance unit; and a controller that controls the discharge capacity of the pump and the opening pressure of the relief valve in response to the operator input of the operator operating the fluid pressure actuator, wherein the controller sets the discharge capacity of the pump in response to the operator input, and sets the opening pressure of the relief valve in response to the operator input. A fluid pressure control system that generates a first map showing the relationship between the flow rate of the working fluid passing through the resistance section and the discharge pressure of the pump when the valve opening pressure is set to the aforementioned value; calculates the flow rate as the calculated flow rate from the differential pressure across the front and rear sections obtained by the pressure measuring unit; corrects the discharge capacity of the pump so that the discharge flow rate of the pump decreases by the amount of the calculated flow rate; calculates the discharge pressure of the pump corresponding to the calculated flow rate based on the first map; and corrects the valve opening pressure of the relief valve so that it becomes the calculated discharge pressure of the pump.

2. A fluid pressure control system according to claim 1, wherein the controller has in advance stored first data which is obtained by determining in advance the relationship between the flow rate through the relief valve for each opening pressure and the discharge pressure of the pump, and the first map is a fluid pressure control system calculated based on the first data.

3. A fluid pressure control system according to claim 1 or 2, wherein the controller generates a second map showing the relationship between the differential pressure across the resistance and the flow rate through the resistance, and the calculated flow rate is calculated based on the second map as the flow rate through which the differential pressure across the resistance corresponds to the differential pressure across the resistance obtained by the pressure measuring unit.

4. A fluid pressure control system according to claim 3, wherein the controller has in advance stored second data which is obtained by pre-determining the relationship between the differential pressure before and after the relief valve and the flow rate for each opening pressure of the relief valve, and the second map is a fluid pressure control system which is generated according to the opening pressure of the relief valve based on the second data.

5. A fluid pressure control system for controlling the operation of a fluid pressure actuator, comprising: a pump that discharges working fluid through a supply passage; a control valve having a neutral position that guides the working fluid discharged from the pump to a tank when there is no operator input, and which controls the flow of working fluid supplied to and discharged from the fluid pressure actuator in response to the operator input; a discharge passage that guides the working fluid from the supply passage to the tank; a relief valve provided in the discharge passage that opens when the pressure in the discharge passage reaches a predetermined opening pressure, and which is configured such that the opening pressure is variable by an input electrical signal; a resistance unit that provides resistance to the flow of working fluid that has been guided from the supply passage to the discharge passage and passed through the relief valve; a pressure measuring unit for obtaining the differential pressure across the resistance unit; and a controller that controls the discharge capacity of the pump and the opening pressure of the relief valve in response to the operator input of the operator operating the fluid pressure actuator, wherein the controller sets the discharge capacity of the pump in response to the operator input, and sets the opening pressure of the relief valve in response to the operator input. A fluid pressure control system that increases the opening pressure of the relief valve until the differential pressure across the front and rear, obtained by the pressure measuring unit, falls below a predetermined value, if the differential pressure across the front and rear is greater than or equal to a predetermined value.

Images