Hydraulic control system, method for setting target engine torque during relief in the hydraulic control system, and calibration method

Abstract

To enable software to precisely control and manage the relief pressure of a pump oil passage to which discharge oil of a hydraulic pump is supplied. [Solution] The system includes a relief time target engine torque setting and calibration unit 19 that detects engine torque while adjusting the pump flow rate so that the detected pressure value of the pump oil passage 2 during relief becomes the target relief pressure LPt, and sets and calibrates the detected engine torque as the relief time target engine torque LTt, and a relief time control unit 20 that controls the pump flow rate so that the detected value of the engine torque during relief becomes the relief time target engine torque LTt.

Description

Technical Field

[0001] The present invention relates to the technical field of a hydraulic control system in a working machine such as a hydraulic excavator.

Background Art

[0002] Generally, in a working machine such as a hydraulic excavator, a hydraulic pump driven by an engine is provided as a hydraulic supply source for a plurality of hydraulic actuators. However, the circuit pressure (maximum pressure) of the pump oil passage to which the discharged oil of the hydraulic pump is supplied is generally configured to be limited by a relief valve disposed in a relief oil passage leading from the pump oil passage to an oil tank. However, since the relief valve increases the upstream pressure (circuit pressure) of the relief valve due to the override characteristic as the flow rate passing through the relief valve increases, in order to accurately control the circuit pressure, it is necessary to adjust the set pressure of the relief valve according to the flow rate at the time of relief. However, the flow rate at the time of relief in a working machine such as a hydraulic excavator has a large individual difference due to variations in engine output, variations in pump efficiency, etc. For this reason, even if the set pressure of the relief valve is adjusted so that the circuit pressure at the time of relief becomes the target relief pressure at the time of shipment of the relief valve or the valve unit in which the relief valve is incorporated, readjustment is required when the relief valve is mounted on the working machine, which is troublesome. Therefore, an electric variable relief valve is used as a relief valve for controlling the pressure of a specific hydraulic actuator circuit, and an override pressure characteristic is corrected based on an input signal regarding the set pressure of the electric variable relief valve and the flow rate passing through the relief valve, and a control means for outputting the corrected signal to the electric variable relief valve is known (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the case of Patent Document 1, in order to correct the override pressure characteristics, a value of the flow rate passing through the relief valve is required. As the value of the flow rate passing through the relief valve, a hydraulic actuator set flow rate (attachment set flow rate) individually set according to the hydraulic actuator is used. For this reason, the device of Patent Document 1 can be adopted when it is desired to control the circuit pressure of a specific hydraulic actuator circuit in which the supply flow rate is preset. However, there is a problem that it cannot be adopted for controlling the circuit pressure of a pump oil passage of a hydraulic excavator or the like in which there are individual differences in the flow rate at the time of relief due to variations in engine output and pump efficiency. Furthermore, circuit pressure (maximum pressure) control is important from the viewpoints of protecting various hydraulic devices constituting the circuit and predicting failures, and there is a desire to perform control management over a long period of time. This is the problem to be solved by the present invention.

Means for Solving the Problems

[0005] The present invention was created for the purpose of solving these problems in view of the above circumstances. The invention according to claim 1 is a variable displacement hydraulic pump driven by an engine and serving as a hydraulic supply source for a plurality of hydraulic actuators, a relief valve disposed in a relief oil passage leading from a pump oil passage to which the discharge oil of the hydraulic pump is supplied to an oil tank, and a pump control means for outputting a control command to a capacity variable means of the hydraulic pump to control the pump flow rate. In a hydraulic control system of a work machine comprising: a relief pressure control means for controlling the pressure of the pump oil passage at the time of relief when the relief valve opens is provided in the hydraulic control system; and the relief pressure control means includes a pump pressure detection means for detecting the pressure of the pump oil passage, an engine torque detection means for detecting the engine torque, and a state in which the pump flow rate is adjusted so that the detected pressure value of the pump oil passage at the time of relief becomes a preset target relief pressure Detect the engine torque, and when the detected engine torque is within the range of a preset initial target engine torque, set the initial target engine torque as the target engine torque at the time of relief. When it is outside the range of the initial target engine torque, detect A hydraulic control system characterized by comprising a target engine torque setting means for setting the engine torque at relief as the target engine torque at relief, and a control means at relief for outputting a control command to a pump control means so that a detected value of the engine torque at relief becomes the target engine torque at relief and controlling the flow rate of a hydraulic pump. The invention according to claim 2 is a method for setting the target engine torque at relief using the target engine torque setting means at relief according to claim 1. The setting method includes a step of adjusting the pump flow rate so that a detected value of the pressure in the pump oil passage becomes a preset target relief pressure at relief, a step of detecting the engine torque when the detected value of the pressure in the pump oil passage becomes the target relief pressure, and determining whether the detected engine torque is within a range of a preset initial setting target engine torque, and a step of setting the initial setting target engine torque as the target engine torque at relief when the detected engine torque is within the range of the initial setting target engine torque, and setting the detected engine torque as the target engine torque at relief when the detected engine torque is outside the range of the initial setting target engine torque. It is a method for setting the target engine torque at relief in a hydraulic control system. The invention according to claim 3 is In a hydraulic control system of a work machine comprising a variable displacement hydraulic pump driven by an engine and serving as a hydraulic supply source for a plurality of hydraulic actuators, a relief valve disposed in a relief oil passage leading from a pump oil passage to which the discharge oil of the hydraulic pump is supplied to an oil tank, and pump control means for outputting a control command to a capacity variable means of the hydraulic pump to control the pump flow rate, a relief pressure control means for controlling the pressure of the pump oil passage at the time of relief is provided in the hydraulic control system. The relief pressure control means includes pump pressure detection means for detecting the pressure of the pump oil passage, engine torque detection means for detecting the engine torque, and relief-time target engine torque setting means for setting, as the relief-time target engine torque, the engine torque detected in a state where the pump flow rate is adjusted so that the detected pressure value of the pump oil passage at the time of relief becomes a preset target relief pressure. a calibration means for calibrating the value of the target engine torque at relief, It includes relief-time control means for outputting a control command to the pump control means to control the flow rate of the hydraulic pump so that the detected value of the engine torque at the time of relief becomes the relief-time target engine torque. and is a hydraulic control system characterized by this. The invention according to claim 4 is a method for calibrating the value of the target engine torque at relief using the calibration means according to claim 3. The calibration method includes a step of adjusting the pump flow rate so that the detected pressure value of the pump oil passage becomes a preset target relief pressure at relief, a step of detecting the engine torque when the detected pressure value of the pump oil passage becomes the target relief pressure, and determining whether or not the detected engine torque is within a preset range of the target engine torque at relief, and a step of setting the preset target engine torque at relief as the target engine torque at relief as it is when the detected engine torque is within the preset range of the target engine torque at relief, and setting the detected engine torque as a newly calibrated target engine torque at relief when it is outside the preset range of the target engine torque at relief. It is a method for calibrating the target engine torque at relief in a hydraulic control system characterized by including these steps. The invention according to claim 5 is a hydraulic control system for a working machine comprising a variable displacement hydraulic pump driven by an engine and serving as a hydraulic supply source for a plurality of hydraulic actuators, a relief valve disposed in a relief oil passage leading from a pump oil passage to which the discharge oil of the hydraulic pump is supplied to an oil tank, and pump control means for outputting a control command to a capacity variable means of the hydraulic pump to control the pump flow rate. In the hydraulic control system, relief pressure control means for controlling the pressure of the pump oil passage at the time of relief when the relief valve opens is provided. The relief pressure control means includes pump pressure detection means for detecting the pressure of the pump oil passage, and calculates the engine torque based on the pump flow rate and the detected pressure value in a state where the pump flow rate is adjusted so that the detected pressure value of the pump oil passage at the time of relief becomes a preset target relief pressure. The calculated engine torque When it is within the range of a preset initial target engine torque, set the initial target engine torque as the target engine torque at the time of relief. When it is outside the range of the initial target engine torque, calculate the engine torque is set as target engine torque at relief by target engine torque setting means at relief, and relief time control means for outputting a control command to the pump control means to control the flow rate of the hydraulic pump so that the engine torque becomes the target engine torque at relief at relief. It is a hydraulic control system characterized by comprising these means. The invention according to claim 6 is a method for setting a target engine torque at relief using the target engine torque setting means at relief according to claim 5, the setting method including: a step of adjusting the pump flow rate so that the detected pressure value of the pump oil passage becomes a preset target relief pressure at relief; a step of calculating the engine torque based on the adjusted pump flow rate and the detected pressure value, and determining whether or not the calculated engine torque is within the range of a preset initial setting target engine torque; and a step of setting the initial setting target engine torque as the target engine torque at relief when the calculated engine torque is within the range of the initial setting target engine torque, and setting the calculated engine torque as the target engine torque at relief when it is outside the range of the initial setting target engine torque. It is a method for setting a target engine torque at relief in a hydraulic control system. The invention according to claim 7 is In a hydraulic control system of a working machine comprising a variable displacement hydraulic pump driven by an engine and serving as a hydraulic supply source for a plurality of hydraulic actuators, a relief valve disposed in a relief oil passage leading from a pump oil passage to which the discharge oil of the hydraulic pump is supplied to an oil tank, and a pump control means for outputting a control command to a capacity variable means of the hydraulic pump to control the pump flow rate, a relief pressure control means for controlling the pressure of the pump oil passage at the time of relief when the relief valve opens is provided in the hydraulic control system, and the relief pressure control means includes a pump pressure detection means for detecting the pressure of the pump oil passage, and calculates the engine torque based on the pump flow rate and the detected pressure value in a state where the pump flow rate is adjusted so that the detected pressure value of the pump oil passage at the time of relief becomes a preset target relief pressure, and sets the calculated engine torque as the target engine torque at the time of relief, a target engine torque setting means at the time of relief, calibration means for calibrating the value of the target engine torque at relief, and a relief-time control means for outputting a control command to the pump control means so that the engine torque at the time of relief becomes the target engine torque at the time of relief and controlling the flow rate of the hydraulic pump a hydraulic control system characterized by this. The invention according to claim 8 is a method for calibrating the value of the target engine torque at relief using the calibration means according to claim 7, the calibration method including: a step of adjusting the pump flow rate so that the detected pressure value of the pump oil passage becomes a preset target relief pressure at relief; a step of calculating the engine torque based on the adjusted pump flow rate and the detected pressure value, and determining whether or not the calculated engine torque is within the range of a preset target engine torque at relief; and a step of setting the preset target engine torque at relief as the target engine torque at relief as it is when the calculated engine torque is within the range of the preset target engine torque at relief, and setting the calculated engine torque as a newly calibrated target engine torque at relief when it is outside the range of the preset target engine torque at relief. It is a calibration method for the target engine torque at relief in a hydraulic control system. The invention according to claim 9 is a hydraulic control system characterized in that in claim 3 or 7, monitoring means for monitoring calibration information by calibration means is provided.

Advantages of the Invention

[0006] By adopting the inventions according to claims 1 and 5, even if there are individual differences such as variations in engine output and pump efficiency among individual working machines, the relief pressure can be accurately controlled and managed, the variation in load during relief can be suppressed, and it can greatly contribute to the protection and life improvement of various hydraulic devices constituting the hydraulic system. By adopting the inventions according to claims 2 and 6, the setting of the target engine torque at relief, which is necessary for controlling the relief pressure to the target relief pressure, can be accurately and easily performed. By adopting the inventions according to claims 3 and 7, the relief pressure can be accurately controlled and managed over a long period. By adopting the inventions according to claims 4 and 8, the calibration of the target engine torque at relief can be accurately and easily performed. By adopting the invention according to claim 9, the calibration information can be effectively utilized for predicting failures of hydraulic devices and the like.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiment for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a hydraulic circuit of a working machine such as a hydraulic excavator. In FIG. 1, 1 is a variable-capacity hydraulic pump driven by the power of an engine E mounted on the working machine, 1a is a regulator for varying the capacity of the hydraulic pump 1, 2 is a pump oil passage to which the discharge oil of the hydraulic pump 1 is supplied, 3 is an oil tank, A is various hydraulic actuators such as a hydraulic cylinder and a hydraulic motor (for example, when the working machine is a hydraulic excavator, left and right travel motors, swing motor, boom cylinder, stick cylinder, bucket cylinder, etc.) driven by the hydraulic pump 1 as a hydraulic supply source, 4 is a group of spools (not shown) in which spools for oil supply / discharge control for each hydraulic actuator A are collectively arranged, 5 is a relief oil passage branched from the pump oil passage 2 and leading to the oil tank 3, 6 is a relief valve arranged in the relief oil passage 5, and 7 is a control valve unit incorporating the spool group 4, the relief valve 6, etc. Further, 8 is a pump pressure sensor (corresponding to the pump pressure detection means of the present invention) for detecting the pressure of the pump oil passage 2 (discharge pressure of the hydraulic pump 1), 9 is an engine torque detection means for detecting the engine torque, and 10 is a pump capacity control electromagnetic proportional valve that outputs a control pressure for variable capacity to the regulator 1a of the hydraulic pump 1 based on a control signal from a pump control unit 17 described later. Note that, in the present embodiment, the engine torque detection means 9 calculates the detected engine torque based on the fuel injection amount and is provided in the engine controller. Also, the regulator 1a and the pump capacity control electromagnetic proportional valve 10 correspond to the variable capacity means of the present invention.

[0009] The relief valve 6 is for limiting the maximum pressure of the pump oil passage 2. In this embodiment, a balance piston type relief valve is used. As shown by the override characteristic line R in FIG. 2, as the flow rate passing through the relief valve 6 increases, the relief pressure (the upstream pressure of the relief valve 6, i.e., the pressure of the pump oil passage 2) gradually increases from the cracking pressure CP due to the override characteristic. Thus, when the pressure (pump pressure) of the pump oil passage 2 reaches the preset target relief pressure LPt in a state where the total pump flow rate is relieved by the relief valve 6, the pump flow rate is uniquely determined by this override characteristic. Incidentally, the cracking pressure CP of the relief valve 6 is pre-adjusted to be lower than the target relief pressure LPt by a predetermined pressure.

[0010] Also, FIG. 3 is a diagram showing the output characteristics of the hydraulic pump 1. In the region where the pump pressure is medium to high pressure, as shown by the pressure-flow characteristic curves B (B1, B2, B3), the pump flow rate is controlled according to the pump pressure so as to keep the output torque (or horsepower) of the hydraulic pump 1 constant. Further, the pressure-flow characteristic curves B are controlled to shift in the arrow direction according to the increase or decrease of the preset target engine torque Tt. In FIG. 3, the pressure-flow characteristic curves B1, B2, B3 at the times of the target engine torques Tt1, Tt2, Tt3 are shown. Furthermore, in FIG. 3, R is an override characteristic line showing the override characteristic of the relief valve 6, and the intersection points C1, C2, C3 of the override characteristic line R and the pressure-flow characteristic curves B1, B2, B3 are the relief points of the relief valve 6 at the times of the target engine torques Tt1, Tt2, Tt3, and the pump pressures at these relief points C1, C2, C3 become the relief pressures LP1, LP2, LP3. That is, the relief pressure LP changes according to the value of the target engine torque Tt. For example, in FIG. 3, when the target engine torque is Tt2 (at the pressure-flow characteristic curve B2), the relief pressure is LP2.

[0011] On one hand, a controller 11 for controlling various operations of the machine body according to the operations of the operator, engine output, and the like is mounted on the working machine. The controller 11 is provided with a relief pressure control unit 15 for controlling the relief pressure (circuit maximum pressure) of the pump oil passage 2. As shown in the block diagram of FIG. 4, the relief pressure control unit 15 is connected to a pump pressure sensor 8 for detecting the pressure of the pump oil passage 2, an engine torque detection means 9 for detecting the engine torque, a monitor device 16 provided in the cab of the working machine or the like and functioning as a device for performing input operations and display outputs to the controller 11, a pump control unit 17 for outputting a control signal to the electromagnetic proportional valve 10 for pump capacity control, etc. It also includes a relief state determination unit 18, a relief-time target engine torque setting and calibration unit 19, a relief-time control unit 20, a monitoring unit 21, a memory 22, etc., which will be described later. In addition, the controller 11 is provided with various control units such as a hydraulic actuator control unit for controlling the supply flow rate to various hydraulic actuators and the pump flow rate based on the operation of the operating tool, etc., not only the relief pressure control unit 15. However, FIG. 4 only shows the part related to the relief pressure control unit 15. Further, the relief pressure control unit 15, the pump pressure sensor (pump pressure detection means) 8, and the engine torque detection means 9 constitute the relief pressure control means of the present invention. Furthermore, the pump control unit 17 corresponds to the pump control means of the present invention, the relief-time target engine torque setting and calibration unit 19 corresponds to the relief-time target engine torque setting means and calibration means of the present invention, the relief-time control unit 20 corresponds to the relief-time control means of the present invention, and the monitoring unit 21 corresponds to the monitoring means of the present invention.

[0012] Next, each part of the relief state determination unit 18, the relief-time target engine torque setting and calibration unit 19, the relief-time control unit 20, and the monitoring unit 21 provided in the relief pressure control unit 15 will be described. The relief state determination unit 18 determines whether the pump oil passage 2 is in a relief state, and outputs the determination result to the relief-time control unit 20. In the present embodiment, the determination of whether or not it is in the relief state is made when the pressure of the pump oil passage 2 detected by the pump pressure sensor 8 is a value in the vicinity of a preset target relief pressure LPt (for example, the target relief pressure ±2 Mpa) and this state continues for a certain period of time or more, it is configured to determine that it is in a relief state. Note that the target relief pressure LPt is preset as a target value of the relief pressure (circuit maximum pressure) of the pump oil passage 2 and is stored in advance in the memory 22, but it is also possible to configure it so that the target relief pressure can be arbitrarily set using the monitor device 16. In addition, the output from the relief state determination unit 18 to the relief-time control unit 20 is not performed when the setting and calibration of the target engine torque LTt at the time of relief are being executed in the target engine torque setting / calibration unit 19 at the time of relief (in the case of the "setting, calibration mode" described later). Furthermore, the determination by the relief state determination unit 18 as to whether or not it is in a relief state is not limited to being based on the pressure detection value of the pump oil passage 2 as described above. For example, a cylinder end detection means for detecting a state where a hydraulic cylinder provided in the working machine is located at the cylinder end, and an operation detection means for detecting a state where an operating tool for the hydraulic cylinder is being operated are provided, and when the detection states by both of these detection means continue for a certain period of time or more, it can also be configured to determine that it is in a relief state.

[0013] In addition, the target engine torque setting / calibration unit 19 at the time of relief executes the setting and calibration of the target engine torque LTt, which is the target value of the engine torque at the time of relief, based on an operation signal from the monitor device 16. Here, when the operator selects the "setting and calibration mode", which is a preset mode for setting and calibrating the target engine torque LTt during relief, the monitor device 16 is provided with a mode selection means 16a (such as an operation switch or an operation screen) that the operator operates. Then, when the "setting and calibration mode" is selected based on the operation of the mode selection means 16a, the control of the relief target engine torque setting and calibration unit 19 is configured to start. Further, in the "setting and calibration mode", pressure oil supply to the hydraulic actuator A is not performed, and during relief, the total amount of the pump flow rate (the discharge flow rate of the hydraulic pump 1) is controlled to pass through the relief valve 6. Furthermore, in the "setting and calibration mode", the control in the relief control unit 20 described later is not executed.

[0014] Next, the control procedure for setting and calibrating the relief target engine torque in the relief target engine torque setting and calibration unit 19 will be described based on the flowchart shown in FIG. 5. When the control starts, the relief target engine torque setting and calibration unit 19 first outputs a control command to the pump control unit 17 to increase the pump flow rate in order to start the relief of the pump oil passage 2 (step S1). Next, the pressure (pump pressure) of the pump oil passage 2 detected by the pump pressure sensor 8 is read, and a control command is output to the pump control unit 17 to adjust the pump flow rate so that the detected pump pressure is within the set range of the target relief pressure Lpt (for example, the target relief pressure Lpt ± tolerance) (step S2). In this case, as shown in FIG. 6, the pump capacity changes according to the current value output from the pump control unit 17 to the pump capacity control electromagnetic proportional valve 10, and thereby the pump flow rate is adjusted to increase or decrease. This adjustment of the pump flow rate is performed until the detected pump pressure is within the set range of the target relief pressure Lpt (step S3). When it is determined that the pump pressure is within the set range of the target relief pressure LPt, subsequently, it is determined whether the pre-set target engine torque LTt at the time of relief is stored in the memory 22 (step S4). When the pre-set target engine torque LTt at the time of relief is not stored in the memory 22, the target engine torque LTt at the time of relief is set in steps S5 to S7. When the pre-set target engine torque LTt at the time of relief is stored in the memory 22, calibration of the target engine torque LTt at the time of relief is performed in steps S8 to S10. When setting the target engine torque LTt at the time of relief (when it is determined in step S4 that the pre-set target engine torque LTt at the time of relief is not stored in the memory 22), subsequently, the value of the engine torque detected by the engine torque detection means 9 is read, and it is determined whether the detected engine torque is within the set range of the initial set target engine torque (for example, initial set target engine torque ± a predetermined variation) set in advance as the initial value of the target engine torque at the time of relief (step S5). When it is determined in the determination of step S5 that the detected engine torque is within the set range of the initial set target engine torque, the initial set target engine torque is set as the target engine torque LTt at the time of relief (step S6). On the other hand, when it is determined that the detected engine torque is not within the set range of the initial set target engine torque, the detected engine torque is set as the target engine torque LTt at the time of relief (step S7). The set target engine torque LTt at the time of relief is stored in the memory 22. Incidentally, the initial set target engine torque is stored in the memory 22 in advance, but it is also possible to configure it so that the initial set target engine torque can be arbitrarily set using the monitor device 16. On the other hand, when calibrating the target engine torque LTt at relief (when it is determined in step S4 that the pre-set target engine torque LTt at relief is stored in the memory 22), subsequently, the value of the engine torque detected by the engine torque detection means 9 is read, and it is determined whether the detected engine torque is within the set range of the pre-set target engine torque LTt at relief stored in the memory 22 (for example, the pre-set target engine torque LTt at relief ± a predetermined variation) (step S8). If it is determined in the determination of step S8 that the detected engine torque is within the set range of the pre-set target engine torque LTt at relief, the pre-set target engine torque LTt at relief is set as the target engine torque LTt at relief as it is (step S9). On the other hand, if it is determined that the detected engine torque is not within the set range of the pre-set target engine torque LTt at relief, the detected engine torque is set as the new target engine torque LTt at relief. Then, the pre-set target engine torque at relief stored in the memory 22 is rewritten with the newly set target engine torque LTt at relief.

[0015] Thus, in the target engine torque setting / calibration section 19 at relief, the detected engine torque in a state where the pump flow rate is adjusted so that the pressure in the pump oil passage 2 at relief becomes the target relief pressure LPt is set or calibrated as the target engine torque LTt at relief and stored in the memory 22. Then, the target engine torque LTt at relief stored in the memory 22 is output to the relief control section 20.

[0016] On the other hand, when the relief state determination unit 18 inputs a determination result that the pump oil passage 2 is in a relief state, the relief time control unit 20 outputs a control command to the pump control unit 17 to control the pump flow rate so that the detected engine torque detected by the engine torque detection means 9 becomes the latest target engine torque LTt at the time of relief stored in the memory 22. That is, when the detected engine torque is smaller than the target engine torque LTt at the time of relief, the pump flow rate is increased to increase the engine torque to the target engine torque LTt at the time of relief. On the other hand, when the detected engine torque is larger than the target engine torque LTt at the time of relief, feedback control is performed to decrease the pump flow rate to decrease the engine torque to the target engine torque LTt at the time of relief. In this case, since the target engine torque LTt at the time of relief is the value of the detected engine torque in a state where the pump flow rate is adjusted so that the pressure of the pump oil passage 2 at the time of relief becomes the target relief pressure LPt, by controlling the pump flow rate so as to become the target engine torque LTt at the time of relief, the pressure of the pump oil passage 2 at the time of relief is controlled to become the target relief pressure LPt.

[0017] Furthermore, the calibration information (history, data) in the target engine torque setting / calibration unit 19 at the time of relief is output to the monitoring unit 21, and is accumulated and continuously monitored (monitored) in the monitoring unit 21. Then, the result of the monitoring is output to the monitoring device 16 and is displayed, for example, as engine torque fluctuation trend data, and can be used for failure prediction and the like.

[0018] In the present embodiment configured as described above, the hydraulic control system of the working machine includes a variable displacement hydraulic pump 1 driven by an engine E and serving as a hydraulic supply source for a plurality of hydraulic actuators A, a relief valve 6 disposed in a relief oil passage 5 extending from a pump oil passage 2 to which the discharge oil of the hydraulic pump 1 is supplied to an oil tank 2, and a pump control unit 17 that outputs a control command via a pump capacity control electromagnetic proportional valve 10 to a regulator 1a of the hydraulic pump 1 to control the pump flow rate. Further, the hydraulic control system is provided with a relief pressure control unit 15 that controls the pressure of the pump oil passage 2 when the relief valve 6 opens. The relief pressure control unit 15 is connected to a pump pressure sensor 8 that detects the pressure of the pump oil passage 2 and an engine torque detection means 9 that detects the engine torque, and sets, as a target engine torque LTt at the time of relief, the engine torque detected in a state where the pump flow rate is adjusted so that the detected pressure value of the pump oil passage 2 at the time of relief becomes a preset target relief pressure LPt. The relief pressure control unit 15 includes a target engine torque setting / calibration unit 19 that sets the engine torque detected in a state where the pump flow rate is adjusted so that the detected pressure value of the pump oil passage 2 at the time of relief becomes the target relief pressure LPt as the target engine torque LTt at the time of relief, and a control unit 20 at the time of relief that outputs a control command to the pump control unit 17 so that the detected value of the engine torque at the time of relief becomes the target engine torque LTt at the time of relief to control the flow rate of the hydraulic pump 1.

[0019] Thus, when the relief valve 6 opens, the flow rate of the hydraulic pump 1 is controlled so that the detected value of the engine torque becomes the target engine torque LTt at the time of relief. Since the target engine torque LTt at the time of relief is the value of the engine torque detected in a state where the pump flow rate is adjusted so that the detected pressure value of the pump oil passage 2 at the time of relief becomes the target relief pressure LPt, by controlling the pump flow rate so as to become the target engine torque LTt at the time of relief, the pressure of the pump oil passage 2 at the time of relief is controlled to become the target relief pressure LPt.

[0020] As a result, even if there are individual differences such as variations in engine output and pump efficiency among individual work machines, by controlling the engine torque at relief so that it becomes the target engine torque LTt at relief, the relief pressure can be accurately controlled and managed to become the target relief pressure LPt. Thus, variations in the load at relief can be suppressed, greatly contributing to the protection and extended lifespan of various hydraulic devices that make up the hydraulic system. Moreover, the setting of the target engine torque LTt at relief by the target engine torque setting / calibration unit 19 at relief and the control of the engine torque by the control unit 20 at relief are performed by software with the relief valve 6 mounted on the work machine. Therefore, the control and management of the relief pressure are easy, and the adjustment work for the relief valve 6 at the time of shipment of the relief valve 6 alone or the control valve unit 7 incorporating the relief valve 6 becomes unnecessary, saving the labor of such adjustment work.

[0021] In this case, the setting of the target engine torque LTt at relief by the target engine torque setting / calibration unit 19 at relief includes a step of adjusting the pump flow rate so that the pressure detection value of the pump oil passage 2 at relief becomes the preset target relief pressure LPt (the aforementioned steps S1, S2, S3), a step of detecting the engine torque when the pressure detection value of the pump oil passage 2 has become the target relief pressure LPt, and determining whether or not the detected engine torque is within the range of the preset initial set target engine torque (the aforementioned step S5), and a step of setting the initial set target engine torque as the target engine torque LTt at relief when the detected engine torque is within the range of the initial set target engine torque, and setting the detected engine torque as the target engine torque LTt at relief when it is outside the range of the initial set target engine torque (the aforementioned steps S6, S7). These steps are sequentially executed, whereby the setting of the target engine torque LTt at relief necessary for controlling the relief pressure to become the target relief pressure LPt can be accurately and easily performed on software.

[0022] Furthermore, since the relief-time target engine torque setting / calibration unit 19 is configured to also perform control for calibrating the value of the relief-time target engine torque LTt set by the relief-time target engine torque setting / calibration unit 19, for example, by periodically calibrating the value of the relief-time target engine torque LTt before starting work or the like, it becomes possible to perform accurate control management of the relief pressure over a long period of time.

[0023] Then, the calibration of the relief-time target engine torque LTt by the relief-time target engine torque setting / calibration unit 19 includes a step of adjusting the pump flow rate so that the pressure detection value of the pump oil passage 2 becomes the preset target relief pressure LPt at the time of relief (the aforementioned steps S1, S2, S3), a step of detecting the engine torque when the pressure detection value of the pump oil passage 2 becomes the target relief pressure LPt, and determining whether or not the detected engine torque is within the range of the preset relief-time target engine torque LTt (the aforementioned step S8), and when it is within the range of the preset relief-time target engine torque LTt, the preset relief-time target engine torque LTt is used as the relief-time target engine torque LTt as it is, and when it is outside the range of the preset relief-time target engine torque LTt, the detected engine torque is set as the newly calibrated relief-time target engine torque LTt (the aforementioned steps S9, S10) are sequentially executed. Thus, the calibration of the relief-time target engine torque LTt necessary for controlling the relief pressure to become the target relief pressure LPt can be easily and accurately performed on software.

[0024] Furthermore, since the calibration information (history, data) of the relief-time target engine torque LTt by the relief-time target engine torque setting / calibration unit 19 is accumulated and monitored in the monitoring unit 21, the calibration information can be effectively used for predicting failures of hydraulic equipment and the like.

[0025] Of course, the present invention is not limited to the above-described embodiments. For example, it is also possible to configure the AI (artificial intelligence) mounted on the work machine to perform machine learning and automatically calibrate the value of the target engine torque at relief based on the engine torque at relief during excavation work. Also, in the above-described embodiment, an engine torque detection means for detecting the engine torque is provided, and the set value and calibration of the target engine torque LTt at relief are performed using the detected value (detected engine torque) of the engine torque detected by the engine torque detection means. However, the present invention is not limited to this, and the present invention can be implemented without using the detected value of the engine torque detection means. In this case, the target engine torque setting means and the calibration means are provided with an engine torque calculation means for calculating the engine torque based on the pump flow rate and the detected pressure value of the pump oil passage in a state where the pump flow rate is adjusted so that the detected pressure value of the pump oil passage at relief becomes the preset target relief pressure, and the set value and calibration of the target engine torque LTt at relief are performed using the calculated value (calculated engine torque) of the engine torque calculated by the engine torque calculation means. In this case, as described above, the engine torque calculation means calculates the engine torque based on the pump flow rate and the detected pressure value of the pump oil passage in a state where the pump flow rate is adjusted so that the detected pressure value of the pump oil passage at relief becomes the preset target relief pressure. For example, the following formula (1) is used. Tr=(P·Q) / (2π·n·ητ) ···(1) In the above formula (1), Tr is the engine torque, P is the pump pressure, Q is the pump flow rate, n is the engine speed, and ητ is the overall efficiency. By using the calculated engine torque thus calculated in place of the detected engine torque in the above embodiment, it becomes possible to set and calibrate the target engine torque at the time of relief. In this case, as shown in the flowchart of FIG. 7, after step S3 of the flowchart of FIG. 5 showing the above embodiment, a step of calculating the engine torque based on the adjusted pump flow rate value and the pressure detection value of the pump oil passage (step S11) is added, and in steps S5 to S10, the calculated engine torque is used instead of the detected engine torque. When using the calculated engine torque in this way, the engine torque detection means may not be provided. In this case, when the relief control means (relief control unit 20) receives the determination result from the relief state determination unit 18 that the pump oil passage 2 is in the relief state, it obtains the pump flow rate at which the engine torque becomes the target engine torque LTt at the time of relief based on the pump pressure, and outputs a control command to the pump control means (pump control unit 17) so as to achieve the pump flow rate. Furthermore, in the above embodiment, the configuration is such that the target engine torque at the time of relief is set and calibrated. However, the set and calibrated target engine torque at the time of relief can also be set as the target engine torque over the entire range of the pressure-flow characteristic curve B shown in FIG. 3, not only at the time of relief.

Industrial Applicability

[0026] The present invention can be used for relief pressure control of a pump oil passage to which the discharged oil of a hydraulic pump is supplied in a working machine such as a hydraulic excavator.

Claims

1. In a hydraulic control system of a working machine comprising a variable displacement hydraulic pump driven by an engine and serving as a hydraulic supply source for a plurality of hydraulic actuators, a relief valve disposed in a relief oil passage leading from a pump oil passage to which discharge oil of the hydraulic pump is supplied to an oil tank, and pump control means for outputting a control command to a capacity variable means of the hydraulic pump to control the pump flow rate, a relief pressure control means for controlling the pressure of the pump oil passage when the relief valve opens is provided in the hydraulic control system. The relief pressure control means includes a pump pressure detection means for detecting the pressure of the pump oil passage, an engine torque detection means for detecting the engine torque, detecting the engine torque in a state where the pump flow rate is adjusted so that the detected pressure value of the pump oil passage during relief becomes a preset target relief pressure, and setting the initial set target engine torque as the target engine torque during relief when the detected engine torque is within the range of the initially set target engine torque preset, and a target engine torque setting means for setting the detected engine torque as the target engine torque during relief when it is outside the range of the initially set target engine torque, and a control means during relief for outputting a control command to the pump control means so that the detected value of the engine torque during relief becomes the target engine torque during relief to control the flow rate of the hydraulic pump. A hydraulic control system characterized by comprising.

2. A method for setting a target engine torque during relief using the target engine torque setting means during relief according to claim 1, the setting method comprising: adjusting the pump flow rate so that the pressure detection value of the pump oil passage during relief becomes a preset target relief pressure; detecting the engine torque when the pressure detection value of the pump oil passage becomes the target relief pressure, and determining whether the detected engine torque is within the range of the initially set target engine torque preset; and setting the initially set target engine torque as the target engine torque during relief when the detected engine torque is within the range of the initially set target engine torque, and setting the detected engine torque as the target engine torque during relief when it is outside the range of the initially set target engine torque. A method for setting a target engine torque during relief in a hydraulic control system characterized by comprising.

3. In a hydraulic control system for a work machine comprising a variable displacement hydraulic pump driven by an engine and serving as a hydraulic supply source for a plurality of hydraulic actuators, a relief valve disposed in a relief oil passage leading from a pump oil passage to which the discharge oil of the hydraulic pump is supplied to an oil tank, and pump control means for outputting a control command to a capacity variable means of the hydraulic pump to control the pump flow rate, the hydraulic control system is provided with relief pressure control means for controlling the pressure of the pump oil passage when the relief valve opens. The relief pressure control means includes pump pressure detection means for detecting the pressure of the pump oil passage, engine torque detection means for detecting the engine torque, relief target engine torque setting means for setting, as a relief target engine torque, the engine torque detected in a state where the pump flow rate is adjusted so that the detected pressure value of the pump oil passage at the time of relief becomes a preset target relief pressure, calibration means for calibrating the value of the relief target engine torque, and relief time control means for outputting a control command to the pump control means so that the detected value of the engine torque at the time of relief becomes the relief target engine torque, thereby controlling the flow rate of the hydraulic pump. A hydraulic control system characterized by comprising the above.

4. A method for calibrating the value of the relief target engine torque using the calibration means according to claim 3, the calibration method comprising: a step of adjusting the pump flow rate so that the detected pressure value of the pump oil passage at the time of relief becomes a preset target relief pressure; a step of detecting the engine torque when the detected pressure value of the pump oil passage becomes the target relief pressure, and determining whether the detected engine torque is within a preset range of the relief target engine torque; and a step of setting the preset relief target engine torque as the relief target engine torque as it is when the detected engine torque is within the preset range of the relief target engine torque, and setting the detected engine torque as a newly calibrated relief target engine torque when the detected engine torque is outside the preset range of the relief target engine torque. A method for calibrating the relief target engine torque in a hydraulic control system characterized by comprising the above.

5. A hydraulic control system for a work machine, comprising a variable displacement hydraulic pump driven by an engine and serving as a hydraulic supply source for a plurality of hydraulic actuators, a relief valve disposed in a relief oil passage leading from a pump oil passage to which discharge oil of the hydraulic pump is supplied to an oil tank, and pump control means for outputting a control command to a capacity variable means of the hydraulic pump to control the pump flow rate. In the hydraulic control system, a relief pressure control means for controlling the pressure of the pump oil passage when the relief valve opens is provided in the hydraulic control system. The relief pressure control means includes pump pressure detection means for detecting the pressure of the pump oil passage, and calculates engine torque based on the pump flow rate and the detected pressure value in a state where the pump flow rate is adjusted so that the detected pressure value of the pump oil passage at the time of relief becomes a preset target relief pressure. When the calculated engine torque is within the range of a preset initial set target engine torque, the initial set target engine torque is set as the target engine torque at the time of relief. When it is outside the range of the initial set target engine torque, a relief time target engine torque setting means for setting the calculated engine torque as the target engine torque at the time of relief, and a relief time control means for outputting a control command to the pump control means so that the engine torque becomes the target engine torque at the time of relief at the time of relief to control the flow rate of the hydraulic pump. A hydraulic control system characterized by comprising.

6. A method for setting a target engine torque at the time of relief using the target engine torque setting means at the time of relief according to claim 5, the setting method comprising: adjusting the pump flow rate so that the pressure detection value of the pump oil passage at the time of relief becomes a preset target relief pressure; calculating engine torque based on the adjusted pump flow rate and the pressure detection value, and determining whether the calculated engine torque is within the range of a preset initial set target engine torque; and when the calculated engine torque is within the range of the initial set target engine torque, setting the initial set target engine torque as the target engine torque at the time of relief, and when it is outside the range of the initial set target engine torque, setting the calculated engine torque as the target engine torque at the time of relief. A method for setting a target engine torque at the time of relief in a hydraulic control system, characterized by including.

7. In a hydraulic control system of a work machine comprising a variable displacement hydraulic pump driven by an engine and serving as a hydraulic supply source for a plurality of hydraulic actuators, a relief valve disposed in a relief oil passage extending from a pump oil passage to which discharge oil of the hydraulic pump is supplied to an oil tank, and pump control means for outputting a control command to a capacity variable means of the hydraulic pump to control pump flow rate, a relief pressure control means for controlling the pressure of the pump oil passage when the relief valve opens is provided in the hydraulic control system, and the relief pressure control means includes pump pressure detection means for detecting the pressure of the pump oil passage, and calculates engine torque based on the pump flow rate and the detected pressure value in a state where the pump flow rate is adjusted so that the detected pressure value of the pump oil passage at the time of relief becomes a preset target relief pressure, and sets the calculated engine torque as a target engine torque at the time of relief, a calibration means for calibrating the value of the target engine torque at the time of relief, and relief time control means for outputting a control command to the pump control means so that the engine torque at the time of relief becomes the target engine torque at the time of relief to control the flow rate of the hydraulic pump. A hydraulic control system characterized by comprising.

8. A method for calibrating the value of the target engine torque at the time of relief using the calibration means according to Claim 7, the calibration method comprising: adjusting the pump flow rate so that the pressure detection value of the pump oil passage at the time of relief becomes a preset target relief pressure; calculating engine torque based on the adjusted pump flow rate and the pressure detection value; and determining whether the calculated engine torque is within a preset range of the target engine torque at the time of relief; and when the calculated engine torque is within the preset range of the target engine torque at the time of relief, setting the preset target engine torque at the time of relief as the target engine torque at the time of relief as it is, and when the calculated engine torque is outside the preset range of the target engine torque at the time of relief, setting the calculated engine torque as a newly calibrated target engine torque at the time of relief. A method for calibrating the target engine torque at the time of relief in a hydraulic control system, characterized by including.

9. The hydraulic control system according to claim 3 or 7, characterized in that monitoring means for monitoring calibration information by calibration means is provided.

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