Hydraulic control circuit

Abstract

[Problem] In order to achieve improved operability and reduced energy loss, in a hydraulic control circuit having a bypass valve for controlling a bypass amount from a hydraulic pump to a tank, at the time of control, the upper limit pressure of a discharge line is made to correspond to the pressure of an operation tool operation amount by controlling the increase or decrease of the bypass amount. [Solution] By using a bypass valve control map (25) indicating the relationship between the operation tool operation amount and the spool stroke, the spool stroke of the bypass valve (19) is controlled, and the upper limit pressure of the discharge line (2) is set so that the operation amount at which the opening area of the bypass valve (19) is completely closed is greater than the operation tool operation amount at which the maximum pressure of the discharge line (2) is reached.

Description

Technical Field

[0001] This invention relates to the technical field of hydraulic control circuits for operating machines such as hydraulic excavators. Background Technology

[0002] Typically, the hydraulic control circuit of a working machine such as a hydraulic excavator is configured to include a hydraulic pump; a hydraulic actuator from which pressurized oil is supplied; an operating tool operated to actuate the hydraulic actuator; a control valve connected to the discharge line of the hydraulic pump and configured to control the supply of oil to and discharge from the hydraulic actuator according to the operation of the operating tool; and a main relief valve configured to set the maximum pressure of the discharge line; and so on. Furthermore, some hydraulic control circuits include a bypass oil passage (drainage oil passage) that branches off from the discharge line and reaches the oil tank to regulate the pressure of the hydraulic pump's discharge line; and a bypass valve (discharge valve) located in the bypass oil passage and controlling the bypass flow (drainage amount) from the hydraulic pump to the oil tank in response to a control signal output from a control device (see, for example, Patent Documents 1, 2, and 3).

[0003] Controlling such bypass valves reduces the opening area, meaning the bypass flow decreases as the amount of operation increases. In this case, the hydraulic control circuit disclosed in Patent Document 1 is configured such that the opening area of ​​the bypass valve is controlled to follow a pre-set flow rate curve that varies with the stroke of the control valve (operating valve). Furthermore, the hydraulic control circuit disclosed in Patent Document 2 is configured to control the stroke of the bypass valve using a table representing the relationship between the operating signal of the operating tool and the stroke of the bypass valve's slide. Moreover, the hydraulic control circuit disclosed in Patent Document 3 is configured such that the opening area of ​​the bypass valve decreases proportionally as the amount of operation increases.

[0004] Existing technical documents

[0005] [Patent Literature]

[0006] [Patent Document 1] Japanese Utility Model Application Publication No. 2-88005

[0007] [Patent Document 2] Japanese Patent Application Publication No. 2017-20604

[0008] [Patent Document 3] Japanese Patent Application Publication No. 2019-94973 Summary of the Invention

[0009] [The problem solved by this invention]

[0010] Meanwhile, in such hydraulic control circuits as described above, the maximum pressure of the hydraulic pump's discharge line is set by the main relief valve, while the upper limit pressure of the discharge line is adjusted by controlling the increase and decrease of the opening area of ​​the bypass valve corresponding to the operating amount of the tool. Therefore, when controlling the opening area of ​​the bypass valve, the relationship between the maximum pressure of the discharge line set by the main relief valve and the upper limit pressure of the discharge line adjusted by the bypass valve needs to be considered. However, none of the hydraulic control circuits disclosed in Patent Documents 1 to 3 mentioned above considers the above relationship. Therefore, the operating range of the tool may be narrowed, in which the upper limit pressure can be adjusted by the bypass valve, resulting in impaired operability, and even after the discharge line reaches its maximum pressure, oil may continue to flow from the bypass valve to the tank, resulting in energy loss.

[0011] Furthermore, for spool-type bypass valves, when the pressure in the hydraulic pump's discharge line is high, even when the bypass valve is fully closed, oil may leak from the bypass valve depending on the overlap length between the shoulder portion of the bypass valve's spool and the sliding contact portion of the housing (the shoulder portion and the sliding contact portion of the housing are in sliding contact). These are the problems that this invention aims to solve.

[0012] [Problem-solving methods]

[0013] In view of the above-mentioned actual situation, the object of the present invention is to solve these problems. The hydraulic control circuit for a working machine of the present invention includes: a hydraulic pump; a hydraulic actuator, from which pressurized oil is supplied from the hydraulic pump to the hydraulic actuator; an operating tool operated to actuate the hydraulic actuator; a control valve connected to the discharge line of the hydraulic pump and configured to control the supply of oil to and discharge from the hydraulic actuator according to the operation of the operating tool; a main relief valve configured to set the maximum pressure of the discharge line; a bypass oil passage branching from the discharge line to a tank; and a spool-type bypass valve disposed on the bypass oil passage and configured to control the bypass flow from the hydraulic pump to the tank in response to a control signal output from a control device.

[0014] The bypass valve is configured such that its opening area increases or decreases with the displacement of the slide. During control, the bypass volume is increased or decreased according to the amount of operation of the operating tool, so that the upper limit pressure of the discharge line becomes a pressure corresponding to the amount of operation of the operating tool. On the other hand, the control device is provided with a mapping representing the relationship between the amount of operation of the operating tool and the amount of slide displacement, and the slide displacement of the bypass valve, which changes with the amount of operation of the operating tool, is controlled based on the mapping. The mapping is set such that the upper limit pressure of the discharge line is a pressure corresponding to the amount of slide displacement, such that the amount of operation that completely closes the opening area of ​​the bypass valve is greater than the amount of operation of the operating tool when the maximum pressure of the discharge line is reached.

[0015] According to one embodiment of the invention, the hydraulic control circuit is configured to control the displacement of the slide rod as the amount of operation of the operating tool changes, even when the bypass valve is fully closed, by using the mapping, so as to control the overlap length between the shoulder portion of the slide rod of the bypass valve and the sliding contact portion of the housing, the shoulder portion slidingly contacting the sliding contact portion of the housing, when the bypass valve is fully closed.

[0016] According to one embodiment of the present invention, the control device is configured to input a signal from a pressure detection device for detecting the pressure of the discharge line of the hydraulic pump and to change the mapping according to the input pressure of the discharge line, thereby changing the overlap length between the shoulder portion of the slide and the sliding contact portion of the housing in the fully closed state of the bypass valve according to the pressure of the discharge line.

[0017] [Beneficial effects of the present invention]

[0018] According to the present invention, the operating area of ​​the hydraulic actuator operating tool can be manufactured to be as wide as possible, wherein the increase or decrease of the upper limit pressure can be controlled by a bypass valve, which can help improve operability and reduce energy loss.

[0019] According to the present invention, the overlap length between the shoulder portion of the slide column and the sliding contact portion of the housing can be controlled in the fully closed state, wherein the shoulder portion slides in contact with the sliding contact portion of the housing.

[0020] According to the present invention, even when the discharge line is high, oil leakage from the bypass valve can be prevented by increasing the overlap length. Attached Figure Description

[0021] Figure 1 This is the hydraulic control circuit diagram of the first embodiment.

[0022] Figure 2 This is a graph showing the relationship between the slide stroke and the bypass valve opening area in the first embodiment.

[0023] Figure 3 This is a block diagram illustrating the inputs / outputs of the controller in the first embodiment.

[0024] Figure 4 (A) is a diagram showing the bypass valve control mapping of the first embodiment, and (B) is a diagram showing the relationship between the operating amount of the operating tool and the upper limit pump pressure.

[0025] Figure 5 This is a diagram illustrating the changes in the bypass valve control mapping in the first embodiment.

[0026] Figure 6 This is the hydraulic control circuit diagram of the second embodiment.

[0027] Figure 7 This is a graph showing the relationship between the slide stroke and the bypass valve opening area in the second embodiment.

[0028] Figure 8 This is a diagram illustrating the bypass valve control mapping of the second embodiment.

[0029] Figure 9 This is a diagram illustrating the changes in the bypass valve control mapping in the second embodiment. Detailed Implementation

[0030] In the following description, embodiments of the invention will be described with reference to the accompanying drawings.

[0031] First, refer to Figures 1 to 5 The first embodiment of the present invention is described. Figure 1 This is a schematic diagram of the hydraulic control circuit of a hydraulic excavator, used as an example of a working machine. Figure 1 In the figure, reference numeral 1 indicates a variable capacity hydraulic pump driven by engine E; reference numeral 1a indicates a capacity changing device for hydraulic pump 1; reference numeral 2 indicates a discharge line for hydraulic pump 1; reference numeral 3 indicates an oil tank; reference numeral 4 indicates a hydraulic actuator that operates by using hydraulic pump 1 as a hydraulic pressure supply source; reference numeral 5 indicates a pilot-operated control valve that controls the supply of oil to and from hydraulic actuator 4; reference numerals 6A and 6B indicate a first electromagnetic proportional pressure reducing valve and a second electromagnetic proportional pressure reducing valve that output pilot pressure to operate control valve 5.

[0032] Hydraulic excavators are equipped with various types of hydraulic actuators, such as boom cylinders, stick cylinders, bucket cylinders, travel motors, and swing motors, and various control valves associated with each hydraulic actuator. Additionally, they are equipped with electromagnetic proportional pressure reducing valves, which output pilot pressure to operate the various control valves. However, in Figure 1 In the diagram, these hydraulic actuators, control valves, and electromagnetic proportional pressure reducing valves are represented. Only one hydraulic actuator (hydraulic cylinder) 4 and the control valve 5 corresponding to the hydraulic actuator 4, the first electromagnetic proportional pressure reducing valve 6A and the second electromagnetic proportional pressure reducing valve 6B corresponding to the control valve 5, and two other control valves 5 corresponding to two other hydraulic actuators (not shown) are shown.

[0033] The control valve 5 is a center-closed spool valve, including a first pilot port 5a and a second pilot port 5b respectively connected to the first electromagnetic proportional pressure reducing valve 6A and the second electromagnetic proportional pressure reducing valve 6B; a pump port 5c connected to the discharge line 2 of the hydraulic pump 1; an oil tank port 5d connected to the oil tank 3; and a pair of actuator ports 5e and 5f respectively connected to the corresponding ports 4a and 4b of the hydraulic actuator 4. Furthermore, the control valve 5 is configured such that when no pilot pressure is input to the first pilot port 5a and the second pilot port 5b, the slide is in the intermediate position N, with the pump port 5c, the tank port 5d, and the pair of actuator ports 5e and 5f closed; however, when pilot pressure is input from the first electromagnetic proportional pressure reducing valve 6A or the second electromagnetic proportional pressure reducing valve 6B to the first pilot port 5a or the second pilot port 5b, the slide switches to the first operating position X or the second operating position Y. At the first operating position X or the second operating position Y, the supply flow passage 5g extends from the pump port 5c to one actuator port 5e or 5f, and the discharge flow passage 5h extends from the other actuator port 5f or 5e to the tank port 5d, to perform supply flow rate control to the hydraulic actuator 4 and discharge flow rate control from the hydraulic actuator 4.

[0034] In this embodiment, each control valve 5 is connected in parallel with respect to the hydraulic pump 1, and a check valve 9 is provided in the oil passage upstream of the pump port 5c of each control valve 5 to maintain the load pressure of the hydraulic actuator 4.

[0035] In addition, Figure 1In the attached drawing, reference numeral 10 indicates a pilot primary side oil passage for supplying pilot primary pressure to the first electromagnetic proportional pressure reducing valve 6A and the second electromagnetic proportional pressure reducing valve 6B, and the pilot primary side oil passage 10 is formed as a branch from the discharge line 2 of the hydraulic pump 1 via the pressure reducing valve 11. That is, the pressure reducing valve 11 reduces the pressure of the hydraulic pump 1, which is a shared oil pressure supply source with the hydraulic actuator 4, to generate a predetermined pilot primary pressure Pp, and is designed to supply the pilot primary pressure Pp to the first electromagnetic proportional pressure reducing valve 6A and the second electromagnetic proportional pressure reducing valve 6B via the pilot primary side oil passage 10. However, in the pilot primary side oil passage 10, a check valve 12 for maintaining the pilot primary pressure Pp and an accumulator 13 for smoothing the pilot primary pressure are sequentially arranged from the upstream side (pressure reducing valve 11 side). The first electromagnetic proportional pressure reducing valve 6A and the second electromagnetic proportional pressure reducing valve 6B do not output pilot pressure in the non-operating state. Instead, they operate in response to a control signal output from the controller 15 to reduce the input pilot primary pressure Pp and output it to the first pilot port 5a and the second pilot port 5b of the control valve 5, which will be described below. Then, as described above, the control valve 5 is designed to switch from the intermediate position N to the first operating position X or the second operating position Y by the pilot pressure output from the first electromagnetic proportional pressure reducing valve 6A and the second electromagnetic proportional pressure reducing valve 6B, and to perform flow control for supplying flow to the hydraulic actuator 4 and flow control for discharging flow from the hydraulic actuator 4. In this case, the pilot pressure output from the first electromagnetic proportional pressure reducing valve 6A and the second electromagnetic proportional pressure reducing valve 6B is controlled by the controller 15 to increase or decrease according to the amount of operation of the hydraulic actuator operating tool (corresponding to the operating tool of the present invention) 21. The displacement of the slide of the control valve 5 increases or decreases according to the increase or decrease of the pilot pressure, thereby controlling the increase or decrease of the opening area of ​​the supply flow channel 5g and the discharge flow channel 5h, and thus controlling the increase or decrease of the supply flow rate and the discharge flow rate.

[0036] The hydraulic actuator operating tool 21 and the operation detection device 22 for detecting the operation (operation amount and operation direction) of the hydraulic actuator operating tool 21 are respectively associated with the corresponding hydraulic actuator, but Figure 1 Only the operating tool 21 and the operating detection device 22 corresponding to one hydraulic actuator 4 are shown.

[0037] In addition, Figure 1 In the figure, reference numeral 16 indicates the main relief oil passage, which is formed by branching from the discharge line 2 of the hydraulic pump 1 and reaching the oil tank 3, and the main relief oil passage 16 is provided with a main relief valve 17, which is configured to set the maximum pressure (system pressure) of the discharge line 2.

[0038] In addition, Figure 1In the attached drawing, reference numeral 18 indicates a bypass oil passage that branches off from the discharge line 2 of the hydraulic pump 1 and leads to the oil tank 3. A bypass valve (relief valve) 19 is arranged in the bypass oil passage 18, configured to control the bypass flow (relief) from the hydraulic pump 1 through the bypass oil passage 18 to the oil tank 3. The bypass valve 19 includes: an inlet port 19a connected to the hydraulic pump 1; an outlet port 19b connected to the oil tank 3; a housing (not shown) having these inlet ports 19a and outlet ports 19b; a slide 19c inserted into the housing to allow free movement in the axial direction; a spring 19d disposed at one end of the slide 19c and pushing the slide 19c to its initial position; and a proportional solenoid 19e disposed at the other end of the slide 19c, causing the slide 19c to move against the force of the spring 19d; and so on. Furthermore, the bypass valve 19 is configured to allow the pilot primary pressure Pp to act on the other end of the slide 19c via the inlet oil passage 20, which is branched from the pilot primary side oil passage 10. Then, by controlling the increase or decrease of the current value applied to the proportional solenoid 19e as a control signal from the controller 15, the stroke (displacement from the initial position) of the slide 19c is controlled to increase or decrease, and the bypass amount flowing from the hydraulic pump 1 to the oil tank 3 via the bypass oil passage 18 is controlled according to the opening area of ​​the bypass valve 19 corresponding to this stroke.

[0039] At the same time, it will refer to Figure 2Describe the relationship between the stroke of the spool 19c of the bypass valve 19 and the opening area. In a state where no current is applied to the proportional solenoid 19e, the spool 19c is located at the initial position (stroke "0") by the thrust of the spring 19d. However, at the initial position, the opening area of the bypass valve 19 is set to an initial opening area Af that is smaller than the set opening area As, which will be described below. Then, the current applied to the proportional solenoid 19e causes the spool 19c to shift from the initial position, and the stroke of the spool 19c increases as the current value applied to the proportional solenoid 19e increases. In this case, the opening area remains at the initial opening area Af until the stroke reaches the first stroke S1 from the initial position, and the opening area decreases as the stroke increases until it reaches the second stroke S2 (S1 < S2). When the second stroke S2 is reached, the opening area of the bypass valve 19 is set to "0", that is, it is completely closed. Then, after the stroke increases from the second stroke S2 to the third stroke S3 (S2 < S3), this completely closed state (opening area A = 0) is maintained. In addition, when the stroke of the spool 19c increases from the third stroke S3, the bypass valve 19 opens. However, in this case, when the stroke reaches the fourth stroke S4 (S3 < S4) before reaching the maximum stroke Sm, the opening area also increases as the stroke increases, and the opening area reaches the set opening area As, which is larger than the initial opening area Af and slightly smaller than the maximum opening area Am. In addition, when the stroke reaches the fifth stroke S5 (S4 < S5) that is slightly shifted from the fourth stroke S4, the opening area reaches the maximum opening area Am, and the maximum opening area Am is maintained until the maximum stroke Sm is reached from the fifth stroke S5 (S5 < Sm). In Figure 2 , the sixth stroke S6 is a stroke between the second stroke S2 and the third stroke S3 (S2 < S6 < S3), in which the opening area remains at "0". The stroke S6 will be described below.

[0040] On the other hand, as shown in the block diagram of Figure 3 , the controller (which corresponds to the control device of the present invention) 15 is configured to input signals from the operation detection device 22 and the pump pressure sensor (which corresponds to the pressure detection device of the present invention) 23. The operation detection device 22 is used to detect the operations of the respective hydraulic actuator operation tools 21, and the pump pressure sensor 23 is used to detect the pressure (pump pressure) of the discharge line 2 of the hydraulic pump 1, the engine controller 24, etc. Then, in response to these input signals, the controller outputs control signals to the first electromagnetic proportional pressure reducing valve 6A, the second electromagnetic proportional pressure reducing valve 6B, the proportional solenoid 19e of the bypass valve 19, the capacity changing device 1a of the hydraulic pump 1, etc., and is provided with a bypass valve control map (which corresponds to the map of the present invention) 25, as described below.

[0041] As described above, the stroke of the spool 19c of the bypass valve 19 is controlled according to the current value applied from the controller 15 to the proportional solenoid 19e. However, the control of the stroke of the bypass valve 19 by the controller 15 will be described. First, before the engine E is started, no current is applied from the controller 15 to the proportional solenoid 19e, and the bypass valve 19 is located at the initial position by the driving force of the spring 19d. In addition, the opening area of the bypass valve 19 at the initial position is set to the initial opening area Af as described above. The initial opening area Af is set to be smaller than the opening area (Af < As) of the set opening area as described above, which is the minimum opening area required to immediately escape the discharged oil of the hydraulic pump 1 to the oil tank 3 after the engine is started, to prevent the pump pressure from rising rapidly immediately after the start of driving of the hydraulic pump 1 related to the engine start, and to prevent an excessive load from being applied to the engine E.

[0042] On the other hand, when the engine E is started and the hydraulic pump 1 accordingly starts to operate, no current is applied from the controller 15 to the proportional solenoid 19e of the bypass valve 19, and the spool 19c remains at the initial position, that is, the opening area of the bypass valve 19 remains at the initial opening area Af until the pump pressure detected by the pump pressure sensor 23 reaches the required pressure Po. Compared with the case where the opening area of the bypass valve is set to the maximum opening area when the engine is started (for example, similar to the case of the bypass valve 33 in the following second embodiment), this will be able to prevent the pump pressure from rising rapidly immediately after the start of engine driving, and will be able to make the pump pressure rise faster until it reaches the required pressure Po. The required pressure Po is a value greater than the pilot primary pressure Pp, so that a predetermined pilot primary pressure Pp can be supplied from the hydraulic pump 1 to the pilot primary side oil passage 10, and from the viewpoint of energy saving, a small value, such as about 4 Mpa, is desirable.

[0043] Then, after the pump pressure reaches the required pressure Po, without inputting an operation signal from the operation detection device 22, i.e., without operating the hydraulic actuator operating tool 21 (the operating tool is in the intermediate position), the controller 15 applies current to the proportional solenoid 19e, causing the stroke of the slide 19c to reach the fourth stroke S4. This causes the opening area of ​​the bypass valve 19 to reach the set opening area As. However, when the discharge volume of the hydraulic pump 1 is at a predetermined level, and as described above, when the engine speed E is at a predetermined speed (e.g., rated speed), the set opening area As is the opening area at which the pressure of the discharge line 2 is maintained at the required pressure Po level, and is greater than the initial opening area Af. Furthermore, from the start of the engine E until the pump pressure reaches the required pressure Po, even if the hydraulic actuator operating tool 21 is operated, the controller 15 will not output an actuation control signal to the first electromagnetic proportional pressure reducing valve 6A and the second electromagnetic proportional pressure reducing valve 6B, so that the control valve 5 remains in the neutral position N, in which pressure oil is not supplied to the hydraulic actuator 4. Furthermore, when no operation signal is input from the operation detection device 22 for a predetermined time or longer, the controller 15 applies current to the proportional solenoid 19e, causing the stroke of the slide 19c to become the fifth stroke S5, and setting the opening area of ​​the bypass valve 19 to the maximum opening area Am. This will reduce the pressure loss in the bypass oil circuit 18 when the hydraulic actuator operating tool 21 is not operated for a predetermined time or longer.

[0044] Simultaneously, as described above, the pilot primary pressure Pp acts on the other end (opposite side of 19d) of the slide 19c of the bypass valve 19 via the inlet oil passage 20 formed by branching from the pilot primary side oil passage 10. Therefore, when the pressure in the discharge line 2 decreases below the desired pressure Po and becomes less than the pilot primary pressure Pp, without operating the hydraulic actuator operating tool 21, the pilot pressure acting on the other end of the slide 19c of the bypass valve 19 decreases, and the slide 19c moves in the direction of decreasing stroke from the fourth stroke S4 or the fifth stroke S5. This allows adjustment to reduce the opening area of ​​the bypass valve 19 and to bring the pressure in the discharge line 2 to the desired pressure Po.

[0045] Furthermore, as described above, when no current is applied from the controller 15 to the proportional solenoid 19e, the bypass valve 19 is in its initial position by the pushing force of the spring 19d, and the opening area of ​​the bypass valve 19 in the initial position is set to the initial opening area Af. As a result, even assuming a failure in the bypass valve 19 due to some defect in the electrical system extending from the controller 15 to the proportional solenoid 19e, the bypass oil passage 18 will be opened by the bypass valve 19, and the rapid rise in pump pressure during engine start-up or the inability to start when the engine is not started can be avoided. Since the initial opening area Af (in this case, the opening area of ​​the bypass valve 19) is smaller than the set opening area As, which is the opening area of ​​the bypass valve 19 when the operating tool is in the intermediate position, the pressure in the discharge line 2 will also rise above the required pressure Po when the operating tool is in the intermediate position, and even if the bypass valve 19 stops operating, the minimum operation required for emergency venting of the working machine can be performed, and so on.

[0046] Next, the control of the bypass valve 19 will be described when the hydraulic actuator operating tool 21 is operated after the engine E is started and the pump pressure reaches the required pressure Po. In this case, the controller 15 controls the stroke of the slide 19c by using the bypass valve control map 25, which will be described below.

[0047] like Figure 4 As shown in (A), the bypass valve control mapping 25 is a mapping that represents the relationship between the operating amount (operating tool operating amount) of the hydraulic actuator operating tool 21 input from the operation detection device 22 and the stroke of the slide 19c set for each hydraulic actuator 4. For example, in a hydraulic excavator, a corresponding bypass valve control mapping 25 is set individually for the corresponding hydraulic actuator, such as the extension and retraction sides of the boom cylinder, the extension and retraction sides of the stick cylinder, the extension and retraction sides of the bucket cylinder, and the travel motor and swing motor. By determining the opening area of ​​the bypass valve 19 used to set the upper limit pressure of the discharge line 2 to correspond to the upper limit pressure of the operating tool's operating amount, and further by determining the stroke of the slide 19c that reaches the relevant opening area, the bypass valve control mapping 25 is created as a mapping representing the relationship between the operating tool's operating amount and the stroke of the slide 19c, such that the relationship between the operating tool's operating amount and the upper limit pressure of the discharge line 2 (e.g., the pressure of the discharge line 2 when pressure oil is not supplied to the hydraulic actuator 4 because the piston is located at the cylinder end) becomes a predetermined pressure characteristic relationship. In this case, as... Figure 4As shown in (B), a pre-set pressure characteristic relationship is established such that when the operating tool's operating amount is the first operating amount L1, the upper limit pump pressure (the upper limit pressure of discharge line 2) reaches the system pressure (the maximum pressure of discharge line 2 set by the main relief valve 17, for example, 35 MPa); and in the bypass valve control mapping 25, as shown... Figure 4 As shown in (A), when the opening area of ​​the bypass valve 19 becomes "0" at the second operating amount L2, the preset pressure characteristic relationship is set to reach the third stroke S3, where the second operating amount is slightly increased to be greater than the first operating amount L1. In this case, the stroke of the slide 19c is controlled so that, during the time from when the upper limit pump pressure reaches the system pressure until the opening area of ​​the bypass valve 19 becomes "0", the change in opening area is smoothly correlated with the increase in the operating amount of the operating tool from the first operating amount L1 to the second operating amount L2.

[0048] In some cases, it may be better to implement special controls, such as controlling the upper limit pump pressure to be lower than the system pressure when the boom of a hydraulic excavator is lowered. In this case, the opening area of ​​the bypass valve 19 is set to avoid being "0" even when the operating tool is operating at its maximum capacity.

[0049] When reference Figure 4 (A) When the controller 15 controls the bypass valve 19 using the bypass valve control mapping 25, in the state where the hydraulic actuator operating tool 21 is not operated (the operating tool operation amount is "0", and the operating tool is in the intermediate position), as described above, the slide 19c is controlled to remain in the fourth stroke S4. Then, when the hydraulic actuator operating tool 21 is operated, the slide 19c is controlled to move in the direction of decreasing stroke as the operating tool operation amount increases, that is, in the direction of decreasing opening area of ​​the bypass valve 19; and when the operating tool operation amount is operated to the second operation amount L2, the slide 19c is controlled to reach the third stroke S3, at which the opening area of ​​the bypass valve 19 becomes "0". Furthermore, even after the opening area of ​​the bypass valve 19 becomes "0", the controller 15 controls the stroke of the slide 19c according to the increase of the operating tool operation amount.

[0050] When the opening area of ​​the bypass valve 19 becomes “0”, it is desirable to correct the stroke of the slide 19c by calibration, that is, the current value applied to the proportional solenoid 19e corresponding to the position of the third stroke S3.

[0051] Furthermore, in the interlocked operation where multiple hydraulic actuators 4 operate simultaneously, the stroke of the slide 19c of the bypass valve 19 is calculated based on the operation amount of the operating tool 21 of each hydraulic actuator input from the operation detection device 22 and the bypass valve control mapping 25 for each hydraulic actuator.

[0052] At the same time, it will refer to Figure 5 The partially enlarged view of the bypass valve control mapping 25 illustrates the control of the stroke of slide 19c after the opening area of ​​bypass valve 19 becomes "0". After the opening area of ​​bypass valve 19 becomes "0", controller 15 changes the bypass valve control mapping 25 in response to the current pump pressure of discharge line 2 input from pump pressure sensor 23. In this case, when the pump pressure input from pump pressure sensor 23 is higher than a preset set pressure (e.g., 35 MPa), even after the stroke of slide 19c reaches the third stroke S3 where the opening area of ​​bypass valve 19 becomes "0", as Figure 5 As shown by the solid line, the stroke of the slide 19c is set to decrease as the operating tool's operating amount increases, i.e., it shifts towards the second stroke S2. When the operating tool's operating amount reaches its maximum value (maximum operating amount Lm), the slide 19c is controlled to remain in the sixth stroke S6, which is an intermediate stroke between the third stroke S3 and the second stroke S2. The sixth stroke S6 is located between the third stroke S3 and the second stroke S2. In the third stroke, the opening area of ​​the bypass valve 19 remains at "0". In the second stroke, the overlap length between the shoulder portion of the slide 19c and the sliding contact portion of the housing is at its longest, with the sliding contact portion of the housing sliding in contact with the shoulder portion. Even when the pump pressure is high, the slide 19c remaining in the sixth stroke S6 can reliably prevent oil leakage from the bypass valve 19.

[0053] On the other hand, when the pump pressure input from the pump pressure sensor 23 becomes lower than the set pressure, the bypass valve control mapping 25 is changed so that the displacement 19 in the direction from the third stroke S3 to the second stroke S2 ​​after the opening area of ​​the bypass valve 19 becomes "0", decreasing as the pump pressure decreases, and is set so that when the pump pressure is sufficiently low (e.g., 5 MPa), even when the operating tool operation amount reaches the maximum operation amount Lm, the slide 19c is located in the third stroke S3, as... Figure 5 As shown by the dashed line. As a result, when the pump pressure is low enough to prevent the danger of leakage of the slide 19c, the slide 19c will immediately move in the direction of the fourth stroke S4 to open the opening of the bypass valve 19 as the amount of operation of the operating tool decreases, so that the bypass valve 19 has good responsiveness to the operation of the operating tool.

[0054] In this embodiment configured as described above, the hydraulic control circuit of the hydraulic excavator is configured to include: a hydraulic pump 1; a hydraulic actuator 4, from which pressurized oil is supplied from the hydraulic pump 1 to the hydraulic actuator 4; a hydraulic actuator operating tool 21, which is operated to actuate the hydraulic actuator 4; a control valve 5, which is connected to the discharge line 2 of the hydraulic pump 1 and is configured to control the supply of oil to / from the hydraulic actuator 4 according to the operation of the hydraulic actuator operating tool 21; a main relief valve 17, which is configured to set the maximum pressure of the discharge line 2; a bypass oil passage 18, which is formed to branch from the discharge line 2 and reach the oil tank 3; and a spool-type bypass valve 19, which is disposed on the bypass oil passage 18 and is configured to control the bypass flow from the hydraulic pump 1 to the oil tank 3 in response to a control signal output from the controller 15, etc. In this hydraulic control circuit, the bypass valve 19 is configured such that its opening area increases or decreases with the displacement of the slide 19c. In the control, by controlling the increase or decrease of the bypass amount that varies with the operation amount of the hydraulic actuator operating tool 21, the upper limit pressure of the discharge line 2 becomes a pressure corresponding to the operation amount of the operating tool. On the other hand, the controller 15 has a bypass valve control map 25, which represents the relationship between the operation amount of the operating tool and the slide stroke (the displacement amount of the slide 19c), and controls the slide stroke of the bypass valve 19 that varies with the operation amount of the operating tool according to the bypass valve control map 25. In the bypass valve control map 25, the upper limit pressure of the discharge line 2 is set to the pressure corresponding to the slide stroke (the third stroke S3 in the first embodiment) where the opening area of ​​the bypass valve 19 is completely closed by the second operation amount L2, which is an operation amount greater than the first operation amount L1, at which the maximum pressure of the discharge line 2 is reached.

[0055] Therefore, by using the bypass valve control mapping 25, the displacement of the slide 19c of the bypass valve 19 is controlled according to the operating amount of the operating tool. Based on the increase or decrease of the opening area of ​​the bypass valve 19 associated with the displacement of the slide 19c, the upper limit pressure of the discharge line 2 is controlled to correspond to the operating amount of the hydraulic actuator operating tool 21. In this case, however, the upper limit pressure of the discharge line 2 is controlled such that the opening area of ​​the bypass valve 19 is completely closed at the second operating amount L2, which is greater than the first operating amount L1, at which the maximum pressure of the discharge line 2 is reached. As a result, until the upper limit pressure of the discharge line 2 reaches its maximum pressure, by controlling the increase / decrease of the opening area of ​​the bypass valve 19, the upper limit pressure of the discharge line 2 can be controlled to correspond to the operating amount of the operating tool, and the operating area of ​​the hydraulic actuator operating tool 21 can be made as wide as possible, where the increase or decrease of the upper limit pressure can be controlled by the bypass valve 19, which can greatly improve operability. On the other hand, by controlling the upper limit pressure of discharge line 2, the bypass valve is completely closed when the operating amount becomes greater than the maximum pressure of discharge line 2, thereby reducing energy loss.

[0056] Furthermore, in this hydraulic control circuit, even with the bypass valve 19 fully closed, the stroke of the slide 19c relative to the operating tool is controlled by the bypass valve control mapping 25. This allows control over the overlap length between the shoulder portion of the slide 19c (when the bypass valve 19 is fully closed) and the sliding contact portion of the housing, where the shoulder portion slides into contact with the housing. In this configuration, a signal from the pump pressure sensor 23, which detects the pressure of the discharge line 2 of the hydraulic pump 1, is input to the controller 15. The overlap length is changed according to the pressure of the discharge line 2 by altering the bypass valve control mapping 25 based on the input pressure of the discharge line 2. Even when the discharge line 2 has high pressure, increasing the overlap length helps prevent oil leakage from the bypass valve 19, thereby reducing energy loss.

[0057] Next, we will refer to Figures 6 to 9 A second embodiment of the present invention will be described. Elements identical to those in the first embodiment are denoted by the same reference numerals, and therefore their description will be omitted.

[0058] Figure 6 This is a diagram illustrating a schematic of the hydraulic control circuit of the second embodiment. Figure 6In the attached drawing, reference numeral 30 denotes a pilot pump driven by engine E. The pilot primary pressure generated by pilot pump 30 is supplied to a first electromagnetic proportional pressure reducing valve 6A and a second electromagnetic proportional pressure reducing valve 6B. The first electromagnetic proportional pressure reducing valve 6A and the second electromagnetic proportional pressure reducing valve 6B output the pilot pressure to control valve 5 through a pilot primary side oil passage 31 connected to pilot pump 30. In other words, in the second embodiment, a hydraulic pump serving as the oil pressure supply source for hydraulic actuator 4 and a pilot pump 30 supplying pilot primary pressure to the first electromagnetic proportional pressure reducing valve 6A and the second electromagnetic proportional pressure reducing valve 6B are respectively provided. Figure 6 In the figure, reference numeral 32 indicates a pilot pressure reducing valve, which is used to set the circuit pressure of the pilot primary side oil circuit 31.

[0059] In addition, Figure 6 In the figure, reference numeral 33 indicates a bypass valve according to the second embodiment. The bypass valve 33 is disposed in a bypass oil passage 18, which is formed to branch from the discharge line 2 of the hydraulic pump 1 and reach the oil tank 3, similar to the first embodiment. The bypass valve 33 then controls the bypass flow from the hydraulic pump 1 to the oil tank 3 via the bypass oil passage 18. The bypass valve 33 includes an inlet side port 33a connected to the hydraulic pump 1, an outlet side port 33b connected to the oil tank 3, a housing (not shown) having these inlet side 33a and outlet side ports 33b, a slide 33c that is axially movable and inserted into the housing, a spring 33d disposed on one end of the slide 33c and pushing the slide 33c to an initial position, a proportional solenoid 33e disposed on the other end of the slide 33c and moving the slide 33c against the thrust of the spring, etc., and so on. Then, based on the increase or decrease of the current value applied from the controller 15 to the proportional solenoid 33e, the stroke (displacement from the initial position) of the slide 33c is controlled to increase or decrease. Based on the opening area of ​​the bypass valve 33 corresponding to the stroke, the bypass flow from the hydraulic pump 1 to the oil tank 3 via the bypass oil passage 18 is controlled.

[0060] Meanwhile, in the second embodiment, reference will be made to Figure 7Describe the relationship between the stroke of the spool 33c of the bypass valve 33 and the opening area. When no current is applied to the proportional solenoid 33e, the spool 33c is located at the initial position by the thrust of the spring. However, at the initial position, the opening area of the bypass valve 33 is set to the maximum opening area Am. Then, since current is applied to the proportional solenoid 33e, the spool 33c is displaced from the initial position, and the stroke of the spool 33c increases as the current value applied to the proportional solenoid 33e increases. However, in this case, the opening area remains at the maximum opening area Am until the stroke reaches the first stroke S1 from the initial position, and the opening area is set to decrease as the stroke increases from the first stroke S1. When the stroke reaches the second stroke S2 (S1 < S2), the opening area A of the bypass valve 33 is set to "0", that is, it is fully closed. Then, this fully closed state (opening area A = 0) will be maintained until the stroke further increases from the second stroke S2 and reaches the maximum stroke SM (S2 < Sm).

[0061] Control the stroke of the spool 33c of the bypass valve 33 according to the current value applied from the controller 15 to the proportional solenoid 33e. However, the control of the stroke of the bypass valve 33 by the controller 15 will be described. First, before the engine E is started, no current is applied from the controller 15 to the proportional solenoid 33e, and the bypass valve 33 is positioned at the initial position by the thrust of the spring 33d. Moreover, as described above, the opening area of the bypass valve 33 at the initial position is set to the maximum opening area Am.

[0062] In addition, when the hydraulic actuator operating tool 21 is not operated, after the engine E is started, no current is applied from the controller 15 to the proportional solenoid 33e, and the bypass valve 33 is held at the initial position, that is, the maximum opening area Am, by the thrust of the spring 33d. On the other hand, when the hydraulic actuator operating tool 21 is operated, the controller 15 controls the stroke of the spool 33c of the bypass valve 33 by using the bypass control map 34 of the second embodiment.

[0063] As Figure 8 shown, the bypass valve control map 34 shows the relationship between the operation amount of the hydraulic actuator operating tool 21 (operation tool operation amount) input from the operation detection device 22 and the stroke of the spool 33c, and is set for each hydraulic actuator and generated in the same manner as in the first embodiment. However, in this case, when the operation tool operation amount is maintained at the first operation amount L1, the upper limit pump pressure (the pump pressure in the state where pressure oil is not supplied to the hydraulic actuator 4) is set to reach the system pressure (the maximum pressure of the discharge line 2 set by the main relief valve 17 (see Figure 4(B) When the operating tool operation amount is maintained at a second operating amount L2 that is slightly greater than the first operating amount L1, the stroke is set to a second stroke S2 ​​where the opening area of ​​the bypass valve 33 becomes “0”. In this case, the stroke of the slide 33c is controlled such that after the pump pressure reaches the system pressure, during the time until the opening area of ​​the bypass valve 33 becomes “0”, the change in opening area is smoothly performed in relation to the increase in the operating tool operation amount from the first operating amount L1 to the second operating amount L2, similar to the first embodiment.

[0064] Reference Figure 8 The controller 15 controls the bypass valve 33 using the bypass valve control mapping 34. In the state where the hydraulic actuator operating tool 21 is not operated (operating tool operation amount "0", controlling the operating tool in the intermediate position), the slide 33c is controlled to remain in the initial position, where the opening area becomes the maximum opening area Am, as described above. Then, when the hydraulic actuator operating tool 21 is operated, the slide 33c is controlled to shift in the direction that increases with the operating tool operation amount, i.e., in the direction that decreases the opening area of ​​the bypass valve 33; and when the operating tool operation amount is operated to the second operation amount L2, the slide 33c is controlled to reach the second stroke S2, where the opening area of ​​the bypass valve 33 becomes "0". Furthermore, similar to the first embodiment, even after the opening area of ​​the bypass valve 33 becomes "0", the controller 15 controls the stroke of the slide 33c according to the increase in the operating tool operation amount.

[0065] Simultaneously, after the opening area of ​​the bypass valve 33 becomes "0", the stroke of the control slide 33c is controlled; the reference... Figure 9 The bypass valve control mapping 34 is shown in a partially enlarged view. Even in the second embodiment, after the opening area of ​​the bypass valve 33 becomes “0”, the controller 15 changes the bypass valve control mapping 34 in response to the pump pressure of the discharge line 2 input from the pump pressure sensor 23. In this case, when the pump pressure (e.g., 35 MPa) input from the pump pressure sensor 23 is higher than a preset set pressure, even after the stroke of the slide reaches the second stroke where the opening area of ​​the bypass valve becomes “0”, as... Figure 9 As shown by the solid line, the stroke of the slide column 33c increases with the increase of the operating tool's operating amount. That is, the slide column 33c is set to displace along the direction of the maximum stroke Sm, and when the operating tool's operating amount becomes the maximum (maximum operating amount Lm), the slide column 33c is set to reach the maximum stroke Sm. At the maximum stroke Sm, the overlap length between the slide column's shoulder and the sliding contact portion of the housing is formed to be at its longest, and the shoulder and the sliding contact portion of the housing slide in contact. Therefore, even under high pump pressure, oil leakage from the bypass valve can be reliably prevented.

[0066] On the other hand, when the pump pressure input from the pump pressure sensor 23 becomes lower than the set pressure, the bypass valve control mapping 34 is changed, so that after the opening area of ​​the bypass valve 33 becomes "0", the displacement in the direction from the second stroke S2 ​​to the maximum stroke Sm becomes "0", decreasing as the pump pressure decreases, and is set so that when the pump pressure is sufficiently low (e.g., 5 MPa), even when the operating tool operation amount reaches the maximum operation amount Lm, the slide 33c is located in the second stroke S2, as... Figure 9 As shown by the dashed line. As a result, when the pump pressure is low enough to prevent the risk of leakage of the slide 33c, the slide 33c will immediately move in the direction of the first stroke S1 to open the opening of the bypass valve 33 as the amount of operation of the operating tool decreases, so that the bypass valve 33 has good responsiveness to the operation of the operating tool.

[0067] Therefore, the bypass valve 33 of the second embodiment adopts a configuration in which the opening area decreases as the stroke of the slide 33c increases, and the slide stroke of the bypass valve 33 increases as the operating amount of the hydraulic actuator operating tool 21 increases. Although the slide stroke is configured to increase, even in the second embodiment using the bypass valve 33 with such a configuration, controlling the upper limit pressure of the discharge line 2 such that the opening area of ​​the bypass valve 19 is completely closed, at the second operating amount L2, which is larger than the first operating amount L1 when the discharge line 2 reaches its maximum pressure, it exhibits the same function and effect as the first embodiment, thereby helping to improve operability and reduce energy loss.

[0068] Industrial applicability

[0069] This invention can be used to control bypass valves installed in the hydraulic control circuit of working machines such as hydraulic excavators.

Claims

1. A hydraulic control circuit for a working machine, the hydraulic control circuit comprising: Hydraulic pump; A hydraulic actuator, to which pressurized oil is supplied from the hydraulic pump; an operating tool, which is operated to actuate the hydraulic actuator; A control valve, connected to the discharge line of the hydraulic pump, is configured to control the supply of oil to and discharge from the hydraulic actuator according to the operation of the operating tool; a main relief valve is configured to set the maximum pressure of the discharge line; A bypass oil passage, which branches off from the discharge line and leads to the oil tank; and a spool-type bypass valve, disposed on the bypass oil passage and configured to control the bypass flow from the hydraulic pump to the oil tank in response to a control signal output from a control device. The bypass valve is configured such that its opening area increases or decreases with the displacement of the slide. During control, the bypass flow is increased or decreased based on the amount of operation of the operating tool, causing the upper limit pressure of the discharge line to become a pressure corresponding to the amount of operation. The control device has a mapping representing the relationship between the amount of operation and the slide displacement, and controls the slide displacement of the bypass valve as it changes with the amount of operation based on this mapping. Furthermore, the mapping is set such that the upper limit pressure of the discharge line is a pressure corresponding to the amount of slide displacement, where the amount of operation required to completely close the opening area of ​​the bypass valve is greater than the amount of operation required to reach the maximum pressure of the discharge line. The control device is configured to input a signal from a pressure detection device, which detects the pressure of the discharge line of the hydraulic pump and changes the mapping according to the input pressure of the discharge line. The overlap length between the shoulder portion of the slide of the bypass valve and the sliding contact portion of the housing is changed according to the pressure of the discharge line when the bypass valve is fully closed.

2. The hydraulic control circuit for a working machine according to claim 1, configured to control the amount of slide displacement as the amount of operation of the working tool changes, even when the bypass valve is fully closed, by using the mapping, so as to control the overlap length between the shoulder portion of the slide of the bypass valve and the sliding contact portion of the housing, the shoulder portion slidingly contacting the sliding contact portion of the housing, when the bypass valve is fully closed.

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