Hydraulic drive system
Patent Information
- Application Number
- JP2025569402
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Filing Date
- 2025-10-29
- Publication Date
- 2026-09-07
Abstract
Description
Hydraulic Drive System
[0001] The present invention relates to a hydraulic drive system that drives a hydraulic actuator.
[0002] BACKGROUND ART Conventionally, work machines such as hydraulic excavators, dump trucks, and wheel loaders are equipped with hydraulic drive systems that include a hydraulic actuator, a hydraulic pump that discharges hydraulic oil, and a plurality of valves that control the supply direction and supply amount of the hydraulic oil discharged from the hydraulic pump.
[0003] As an example of such a hydraulic drive system, Patent Document 1 discloses a configuration including a directional control valve that is arranged in a supply line from a hydraulic pump to a hydraulic actuator and controls the supply direction of hydraulic oil to the hydraulic actuator, a flow control valve that is arranged upstream of the directional control valve in the supply line in the flow of hydraulic oil and controls the flow rate of hydraulic oil supplied from the hydraulic pump to the directional control valve, and a solenoid valve that opens and closes the flow control valve.
[0004] Patent No. 7193446
[0005] In the hydraulic drive system configured as described above, the opening of the flow control valve in response to a command current output to the solenoid valve may vary due to manufacturing errors, etc. Therefore, calibration is required to adjust the magnitude of the command current and the opening of the flow control valve.
[0006] One possible method is to attach a pressure sensor to the output side of a solenoid valve to measure the output characteristics of the pilot pressure. However, if the solenoid valve is built into and integrated with a flow control valve, it is difficult to attach a pressure sensor to the output side of the solenoid valve. Another possible method is to measure the pressure between the flow control valve and the directional control valve and perform calibration. However, when the work machine is actually operating, there is little need to attach a pressure sensor between the flow control valve and the directional control valve. Therefore, attaching and detaching the pressure sensor each time calibration is performed requires a great deal of work.
[0007] The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a hydraulic drive system that can be calibrated without the need to attach dedicated parts.
[0008] In order to achieve the above object, the present invention provides a hydraulic drive system including a hydraulic pump that discharges hydraulic oil stored in a hydraulic oil tank, a hydraulic actuator that is driven by the hydraulic oil discharged from the hydraulic pump, a directional control valve that is arranged in a supply line from the hydraulic pump to the hydraulic actuator and controls the supply direction of the hydraulic oil to the hydraulic actuator, a flow control valve that is arranged in the supply line upstream of the directional control valve in the flow of hydraulic oil and controls the flow rate of the hydraulic oil supplied from the hydraulic pump to the directional control valve, a pressure sensor that detects the pressure of the hydraulic oil supplied to the hydraulic actuator, a solenoid valve that opens and closes the flow control valve by supplying a pilot pressure to a pilot port of the flow control valve, and a controller that executes a calibration process to adjust a command current to be output to the solenoid valve, wherein the controller, in the calibration process, changes the command current to be output to the solenoid valve in a direction that opens the flow control valve while keeping the flow control valve closed and the directional control valve open, and identifies the command current at the time when the pressure detected by the pressure sensor changes as an opening start current at which the flow control valve starts to open.
[0009] According to the present invention, it is possible to obtain a hydraulic drive system that can be calibrated without installing dedicated parts. Note that problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments.
[0010] FIG. 1 is a side view of a hydraulic excavator. FIG. 2 is a part of a circuit diagram of a hydraulic drive system. FIG. 3 is another part of the circuit diagram of a hydraulic drive system. FIG. 4 is a cross-sectional view of a flow control valve. FIG. 5 is an opening area diagram of a flow control valve. FIG. 6 is a functional block diagram of a controller. FIG. 7 is an explanatory diagram of performance errors of a solenoid valve. FIG. 8 is a flowchart of a calibration process. FIG. 9 is a diagram showing changes in command current over time and changes in load pressure relative to the command current in the calibration process.
[0011] [Configuration of Hydraulic Excavator 200] An embodiment of a hydraulic excavator 200 (work machine) according to the present invention will be described with reference to the drawings. However, specific examples of the work machine are not limited to the hydraulic excavator 200, and include any device equipped with a hydraulic actuator, such as a wheel loader, a dump truck, or a crane truck. Furthermore, unless otherwise specified, the terms front, back, left, and right in this specification are based on the viewpoint of an operator who is on board and operating the hydraulic excavator 200.
[0012] Fig. 1 is a side view of a hydraulic excavator 200. As shown in Fig. 1, the hydraulic excavator 200 includes a lower traveling body 201 and an upper rotating body 202 supported by the lower traveling body 201. The lower traveling body 201 and the upper rotating body 202 are examples of a vehicle body.
[0013] The lower traveling structure 201 is equipped with a pair of left and right crawlers 204, which are endless tracks. The pair of left and right crawlers 204 rotate independently when driven by a traveling motor 205. As a result, the hydraulic excavator 200 travels. However, the lower traveling structure 201 may be wheeled instead of the crawlers 204.
[0014] The upper rotating body 202 is supported on the lower traveling body 201 so as to be rotatable by a swing motor 206. That is, rotation of the swing motor 206 causes the upper rotating body 202 to swing relative to the lower traveling body 201. The upper rotating body 202 mainly includes a swing frame 207 serving as a base, a cab (operator's seat) 208 disposed on the front left side of the swing frame 207, a counterweight 209 disposed at the rear of the swing frame 207, and a front work machine 210 (work device) attached to the front center of the swing frame 207 so as to be rotatable in the vertical direction.
[0015] The cab 208 is disposed adjacent to the front working implement 210 in the left-right direction (the width direction of the vehicle body). More specifically, the cab 208 is disposed to the left (one side in the left-right direction) of the front working implement 210. However, the location of the cab 208 is not limited to the example described above, and the cab 208 may be disposed on one side of the front working implement 210 in the left-right direction.
[0016] The cab 208 is formed with a space for an operator to ride in and operate the hydraulic excavator 200. Inside the cab 208, a seat for the operator and an operating device operated by the operator seated in the seat are arranged. The operating device accepts operations by the operator to operate the hydraulic excavator 200. When the operator operates the operating device, the lower traveling body 201 travels, the upper rotating body 202 rotates, and the front working implement 210 operates. The operating device includes at least the operating levers 115a and 115b shown in FIG. 3. Specific examples of the operating device include a lever, a steering wheel, a pedal, a switch, etc.
[0017] The front working implement 210 includes a boom 211 supported on the upper rotating body 202 so that it can be raised and lowered, an arm 212 supported at the tip of the boom 211 so that it can be rotated (crowd, dump), a bucket 213 (attachment) supported at the tip of the arm 212 so that it can be rotated (crowd, dump), a boom cylinder 214 that drives the boom 211, an arm cylinder 215 that drives the arm 212, and a bucket cylinder 216 that drives the bucket 213. Note that specific examples of the attachment are not limited to the bucket 213, and may include a grapple, cutter, crusher, breaker, etc. The counterweight 209 is a heavy object that has an arc shape when viewed from above and is used to balance the weight of the front working implement 210.
[0018] The travel motor 205, the swing motor 206, the boom cylinder 214, the arm cylinder 215, and the bucket cylinder 216 are examples of hydraulic actuators. That is, a hydraulic actuator includes one or both of a hydraulic motor that rotates when hydraulic oil is supplied thereto and a hydraulic cylinder that expands and contracts when hydraulic oil is supplied or discharged therefrom. However, specific examples of hydraulic actuators are not limited to the above examples.
[0019] [Configuration of Hydraulic Drive System 100] Fig. 2 is a part of a circuit diagram of the hydraulic drive system 100. Fig. 3 is another part of the circuit diagram of the hydraulic drive system 100. The hydraulic excavator 200 is equipped with the hydraulic drive system 100 shown in Figs. 2 and 3. The hydraulic drive system 100 is a system for driving hydraulic actuators (for example, a travel motor 205, a swing motor 206, a boom cylinder 214, an arm cylinder 215, and a bucket cylinder 216).
[0020] As shown in Fig. 2, the hydraulic drive system 100 includes three hydraulic pumps 1, 2, and 3, and a hydraulic oil tank 4 that stores the hydraulic oil discharged by the hydraulic pumps 1 to 3. The hydraulic pumps 1 to 3 are driven by an engine (not shown), and discharge the hydraulic oil stored in the hydraulic oil tank 4 toward the hydraulic actuator. The hydraulic pumps 1 to 3 are variable displacement hydraulic pumps that are capable of changing the discharge capacity (for example, the tilting angle). The discharge capacity (tilting angle) of the hydraulic pumps 1 to 3 is controlled by a regulator attached to each of the hydraulic pumps 1 to 3. The regulators of the hydraulic pumps 1 to 3 each include a flow control command pressure port 1a, 2a, and 3a.
[0021] The hydraulic drive system 100 includes a right traveling directional control valve 6, a bucket directional control valve 7, a second arm directional control valve 8, a first boom directional control valve 9, a second boom directional control valve 10, a first arm directional control valve 11, a first attachment directional control valve 12, a left traveling directional control valve 13, a swing directional control valve 14, a third boom directional control valve 15, and a second attachment directional control valve 16. The directional control valves 6 to 16 are arranged in supply lines (oil passages 44 to 49, 54 to 59, 65 to 70) extending from the hydraulic pumps 1 to 3 to the hydraulic actuators. The directional control valves 6 to 16 control the supply direction of hydraulic oil discharged from the hydraulic pumps 1 to 3 to the corresponding hydraulic actuators.
[0022] A discharge line 41 of the hydraulic pump 1 is connected to the hydraulic oil tank 4 via a center bypass line 42. In the center bypass line 42, there are arranged, in order from the upstream side of the hydraulic oil flow, a right traveling directional control valve 6 that controls the right traveling motor 205, a bucket directional control valve 7 that controls the flow of pressure oil supplied to the bucket cylinder 216, a second arm directional control valve 8 that controls the flow of pressure oil supplied to the arm cylinder 215, and a first boom directional control valve 9 that controls the flow of pressure oil supplied to the boom cylinder 214.
[0023] The supply ports of bucket directional control valve 7, second arm directional control valve 8, and first boom directional control valve 9 are connected in parallel to a parallel line 43 branching off from a center bypass line 42 connecting right travel directional control valve 6 and bucket directional control valve 7, via oil passages 44, 45, oil passages 46, 47, and oil passages 48, 49, respectively. In addition, a bleed-off valve 34 is disposed at the most downstream side of center bypass line 42, controlling the flow of pressure oil discharged from center bypass line 42 to hydraulic oil tank 4. Furthermore, discharge line 41 is connected to hydraulic oil tank 4 via oil passage 50, in which relief valve 31 is provided to protect the circuit from excessive pressure buildup.
[0024] The discharge line 51 of the hydraulic pump 2 is connected to the hydraulic oil tank 4 via a center bypass line 52. Arranged in the center bypass line 52, in this order from the upstream side of the hydraulic oil flow, are: a second boom directional control valve 10 that controls the flow of pressurized oil supplied to the boom cylinder 214; a first arm directional control valve 11 that controls the flow of pressurized oil supplied to the arm cylinder 215; a first attachment directional control valve 12 that controls the flow of pressurized oil supplied to a first actuator (not shown) that drives a first special attachment such as a chopper that is provided in place of the bucket 213; and a left traveling directional control valve 13 that controls the drive of the left traveling motor 205.
[0025] The supply ports of the second boom directional control valve 10, the first arm directional control valve 11, the first attachment directional control valve 12, and the left travel directional control valve 13 are connected in parallel to a parallel line 53 branching off from a discharge line 51 via oil passages 54, 55, oil passages 56, 57, oil passages 58, 59, and oil passage 60, respectively. A bleed-off valve 35 is disposed at the most downstream end of the center bypass line 52, controlling the flow of pressurized oil discharged from the center bypass line 52 to the hydraulic oil tank 4. Lines 41, 53 are connected via an oil passage 69 in which a junction valve 37 is installed, and check valves 38, 39 are installed in the lines 41, 53 to prevent backflow from the lines 41, 53. The parallel line 53 is connected to the hydraulic oil tank 4 via an oil passage 61 in which a relief valve 32 is installed to protect the circuit from excessive pressure buildup.
[0026] The discharge line 62 of the hydraulic pump 3 is connected to the hydraulic oil tank 4 via a center bypass line 63. Arranged in the center bypass line 63, in this order from the upstream side of the hydraulic oil flow, are a swing directional control valve 14 that controls the flow of pressure oil supplied to the swing motor 206 that drives the upper swing body 202, a third boom directional control valve 15 that controls the flow of pressure oil supplied to the boom cylinder 214, and a second attachment directional control valve 16. The second attachment directional control valve 16 is used to control the flow of pressure oil supplied to the second actuator when a second special attachment equipped with a second actuator is attached in addition to the first special attachment, or when a second special attachment equipped with two actuators, a first actuator and a second actuator, is attached instead of the first special actuator.
[0027] The supply ports of the swing directional control valve 14, the third boom directional control valve 15, and the second attachment directional control valve 16 are connected in parallel to a parallel line 64 branching off from a discharge line 62 via oil passages 65, 66, oil passages 67, 68, and oil passages 69, 70, respectively. In addition, a bleed-off valve 36 that controls the flow of pressure oil discharged from the center bypass line 63 to the hydraulic oil tank 4 is disposed at the most downstream side of the center bypass line 63. Furthermore, the parallel line 64 is connected to the hydraulic oil tank 4 via an oil passage 71 that is provided with a relief valve 33 that is provided to protect the circuit from excessive pressure buildup.
[0028] The oil passages 44 to 49, 54 to 59, and 65 to 70 are examples of supply lines extending from the hydraulic pumps 1 to 3 to the hydraulic actuators. The bleed-off valves 34, 35, and 36 are examples of opening and closing devices that open and close center bypass lines 42, 52, and 63 that extend from the hydraulic pumps 1 to 3 via the directional control valves 6 to 16 to the hydraulic oil tank 4.
[0029] The hydraulic drive system 100 includes flow control valves 21, 22, 23, 24, 25, 26, 27, 28, and 29. The flow control valves 21 to 29 are arranged upstream of the directional control valves 6 to 16 in the flow of hydraulic oil in the supply lines (oil passages 44 to 49, 54 to 59, 65 to 70). The flow control valves 21 to 29 control the flow rate of hydraulic oil supplied from the hydraulic pumps 1 to 3 to the directional control valves 6 to 16. Details of the flow control valves 21 to 29 will be described later with reference to FIG. 4.
[0030] Bucket flow control valve 21 is provided in oil passages 44, 45 connected to the supply port of bucket directional control valve 7. Second arm flow control valve 22 is provided in oil passages 46, 47 connected to the supply port of second arm directional control valve 8. First boom flow control valve 23 is provided in oil passages 48, 49 connected to the supply port of first boom directional control valve 9.
[0031] The second boom flow control valve 24 is provided in oil passages 54, 55 connected to the supply port of the second boom directional control valve 10. The first arm flow control valve 25 is provided in oil passages 56, 57 connected to the supply port of the first arm directional control valve 11. The first attachment flow control valve 26 is provided in oil passages 58, 59 connected to the supply port of the first attachment directional control valve 12.
[0032] The swing flow control valve 27 is provided in oil passages 65, 66 connected to the supply port of the swing directional control valve 14. The third boom flow control valve 28 is provided in oil passages 67, 68 connected to the supply port of the third boom directional control valve 15. The second attachment flow control valve 29 is provided in oil passages 69, 70 connected to the supply port of the second attachment directional control valve 16.
[0033] 3, the hydraulic drive system 100 includes a pilot pump 111, a pilot relief valve 112, and a solenoid valve unit 113. The pilot pump 111 is connected to the hydraulic oil tank 4 via the pilot relief valve 112 for generating pilot primary pressure. The pilot pump 111 is also connected to the solenoid valve unit 113 via an oil passage 121. The pilot pump 111 compresses the hydraulic oil stored in the hydraulic oil tank 4 and outputs pilot pressure to the solenoid valve unit 113.
[0034] The solenoid valve unit 113 includes a plurality of solenoid valves 113a, 113b, 113c, 113d, and 113e. The solenoid valve 113a is connected to a flow control command pressure port 2a of the regulator of the hydraulic pump 2 via a pilot line 123. The solenoid valves 113b and 113c are connected to command pressure ports 11a and 11b of the first arm directional control valve 11 via pilot lines 124 and 125. The solenoid valve 113d is connected to a command pressure port 25j of the first arm flow control valve 25 via a pilot line 126. The solenoid valve 113e is connected to a command pressure port 35a of the bleed-off valve 35 via a pilot line 127. Furthermore, the solenoid valves 113a to 113e are connected to the hydraulic oil tank 4 via an oil passage 122.
[0035] The solenoid valve 113d is a proportional solenoid valve whose opening is adjusted in accordance with a command current output from the controller 114. The solenoid valve 113d supplies pilot pressure to a command pressure port 25j (pilot port) of the first-arm flow control valve 25 under the control of the controller 114. More specifically, the pilot pressure supplied by the solenoid valve 113d increases as the command current increases. This opens and closes the first-arm flow control valve 25. The same applies to the other solenoid valves 113a to 113c and 113e.
[0036] To avoid complicating the explanation, solenoid valves for hydraulic pump 1, hydraulic pump 3, right travel directional control valve 6, bucket directional control valve 7, second arm directional control valve 8, first boom directional control valve 9, second boom directional control valve 10, first attachment directional control valve 12, left travel directional control valve 13, swing directional control valve 14, third boom directional control valve 15, second attachment directional control valve 16, bucket flow control valve 21, second arm flow control valve 22, first boom flow control valve 23, second boom flow control valve 24, first attachment flow control valve 26, swing flow control valve 27, third boom flow control valve 28, second attachment flow control valve 29, bleed-off valve 34, bleed-off valve 36, and junction valve 37 are not shown in the figures.
[0037] 2 and 3, the hydraulic drive system 100 includes pressure sensors 84, 85, 86, 87a, 87b, 88a, 88b, 89a, 89b, 90a, 90b, 133, 134, 135, 136, and 137. The pressure sensors 84 to 90 and 133 to 137 detect the pressures (e.g., discharge pressure, actuator pressure, load pressure, flow control command pressure, command pressure) of the hydraulic oil flowing through the flow paths, and output pressure signals indicative of the detected pressures to the controller 114.
[0038] Pressure sensor 84 detects the discharge pressure of hydraulic pump 1 on discharge line 41. Pressure sensor 85 detects the discharge pressure of hydraulic pump 2 on discharge line 51. Pressure sensor 86 detects the discharge pressure of hydraulic pump 3 on discharge line 62. Pressure sensors 87a, 87b detect the actuator pressure on actuator lines 72a, 72b connected to boom cylinder 214. Pressure sensors 88a, 88b detect the actuator pressure on actuator lines 73a, 73b connected to arm cylinder 215. Pressure sensors 89a, 89b detect the actuator pressure on actuator lines 74a, 74b connected to bucket cylinder 216. Pressure sensors 90a, 90b detect the actuator pressure on actuator lines 75a, 75b connected to swing motor 206. To avoid complicating the explanation, the left traveling motor (not shown), the right traveling motor (not shown), and pressure sensors for detecting actuator pressures of the attachments (not shown) are omitted from the illustration.
[0039] Pressure sensor 133 detects, on pilot line 123, the flow control command pressure output from solenoid valve 113a to flow control command pressure port 2a. Pressure sensors 134 and 135 detect, on pilot lines 124 and 125, the command pressure output from solenoid valves 113b and 113c to command pressure ports 11a and 11b. Pressure sensor 136 detects, on pilot line 126, the command pressure output from solenoid valve 113d to command pressure port 25j. Pressure sensor 137 detects, on pilot line 127, the command pressure output from solenoid valve 113e to command pressure port 35a.
[0040] To avoid complicating the explanation, the following will be mentioned: hydraulic pump 1, hydraulic pump 3, right travel directional control valve 6, bucket directional control valve 7, second arm directional control valve 8, first boom directional control valve 9, second boom directional control valve 10, first attachment directional control valve 12, left travel directional control valve 13, swing directional control valve 14, third boom directional control valve 15, second attachment directional control valve 16, bucket Pressure sensors that detect the command pressures of the solenoid valves for the first boom flow control valve 21, the second arm flow control valve 22, the first boom flow control valve 23, the second boom flow control valve 24, the first attachment flow control valve 26, the swing flow control valve 27, the third boom flow control valve 28, the second attachment flow control valve 29, the bleed-off valve 34, the bleed-off valve 36, and the junction valve 37 are not shown in the figure.
[0041] The hydraulic drive system 100 includes temperature sensors 91 and 92. The temperature sensors 91 and 92 detect the temperature of the hydraulic oil and output a temperature signal indicating the detected temperature to the controller 114. The temperature sensor 91 detects the temperature of the hydraulic oil stored in the hydraulic oil tank 4. The temperature sensor 92 detects the temperature of the hydraulic oil flowing through the oil passage 121.
[0042] The hydraulic drive system 100 includes attitude sensors 222, 223, 224, 225, and 226. The attitude sensors 222 to 226 detect the attitude of the hydraulic excavator 200 or the hydraulic actuators, and output attitude signals indicating the detected attitudes to the controller 114. The attitude sensors 222 to 224 are, for example, stroke sensors that detect the attitudes (amount of extension and contraction) of the boom cylinder 214, arm cylinder 215, and bucket cylinder 216. The attitude sensor 225 is, for example, an inclination sensor that detects the attitude of the hydraulic excavator 200 (vehicle body). The attitude sensor 226 is, for example, a rotation angle sensor that detects the rotation angle (swing angle) of the swing motor 206.
[0043] The hydraulic drive system 100 includes current sensors 143, 144, 145, 146, and 147. The current sensors 143 to 147 detect the magnitude of the command current output from the controller 114 to the solenoid valves 113a to 113e, and output a current signal indicating the magnitude of the detected command current to the controller 114.
[0044] To avoid complicating the explanation, the following will be used: hydraulic pump 1, hydraulic pump 3, right travel directional control valve 6, bucket directional control valve 7, second arm directional control valve 8, first boom directional control valve 9, second boom directional control valve 10, first attachment directional control valve 12, left travel directional control valve 13, swing directional control valve 14, third boom directional control valve 15, second attachment directional control valve 16, bucket flow rate Current sensors that detect the control current output to the solenoid valves for control valve 21, second arm flow control valve 22, first boom flow control valve 23, second boom flow control valve 24, first attachment flow control valve 26, swing flow control valve 27, third boom flow control valve 28, second attachment flow control valve 29, bleed-off valve 34, bleed-off valve 36, and junction valve 37 are not shown in the illustration.
[0045] The hydraulic drive system 100 includes an operation lever 115a that can switch between the first boom directional control valve 9, the second boom directional control valve 10, and the third boom directional control valve 15, and an operation lever 115b that can switch between the first arm directional control valve 11 and the second arm directional control valve 8. The operation levers 115a and 115b are examples of operation devices. The operation levers 115a and 115b output operation signals that indicate the operation direction (lowering direction) and operation amount (lowering amount) by the operator to the controller 114.
[0046] To simplify the explanation, the right traveling operation lever that switches the right traveling directional control valve 6, the bucket operation lever that switches the bucket directional control valve 7, the first attachment operation lever that switches the first attachment directional control valve 12, the left traveling operation lever that switches the left traveling directional control valve 13, the swing operation lever that switches the swing directional control valve 14, and the second attachment operation lever that switches the second attachment directional control valve 16 are not shown in the illustration.
[0047] The controller 114 includes a central processing unit (CPU) and a memory. The memory may be, for example, a read-only memory (ROM), a random access memory (RAM), a hard disk drive (HDD), or a combination of these. The controller 114 performs the processes described below by having the CPU read and execute program code stored in the ROM or HDD. The RAM is used as a work area when the CPU executes the program.
[0048] However, the specific configuration of the controller 114 is not limited to this, and may be realized by hardware such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array).
[0049] The controller 114 is mounted on the hydraulic excavator 200 (vehicle body). The controller 114 adjusts (increases or decreases) command currents output to the solenoid valves 113a to 113e included in the solenoid valve unit 113, based on operation signals output from the operation levers 115a and 115b, pressure signals output from the pressure sensors 84 to 90 and 133 to 137, temperature signals output from the temperature sensors 91 and 92, current signals output from the current sensors 143 to 147, and attitude signals output from the attitude sensors 221 to 226.
[0050] The solenoid valves 113a to 113e (and solenoid valves not shown) reduce the pilot primary pressure and output it as a command pressure based on a command current output from the controller 114. In this embodiment, the larger the command current output from the controller 114, the larger the pilot pressure output through the solenoid valves 113a to 113e. Also, the smaller the command current output from the controller 114, the smaller the pilot pressure output through the solenoid valves 113a to 113e. However, the relationship between the command current and the pilot pressure is not limited to the example described above.
[0051] The hydraulic drive system 100 includes a calibration instruction device 116 (instruction device). The calibration instruction device 116 receives an instruction to execute a calibration process ( FIG. 8 ) from an operator and inputs the received instruction to the controller 114. As an example, the calibration instruction device 116 may be part of an operating device installed inside the cab 208 (for example, a push button or an icon displayed on a touch panel display).
[0052] As another example, the calibration instruction device 116 may be configured as a portable device (e.g., a tablet terminal, a smartphone, a feature phone, or a laptop computer) that is detachable from the controller 114 (first controller) mounted on the hydraulic excavator 200. Such a portable device includes at least a second controller and a user interface (e.g., a display, an operation panel). The configuration of the second controller is similar to that of the controller 114. The second controller may instruct the controller 114 to perform calibration processing in accordance with instructions from an operator via the user interface. Furthermore, the first and second controllers may share the responsibility of performing the calibration processing, which will be described later with reference to FIG. 8 .
[0053] [Configuration of Flow Control Valve 25] Figure 4 is a cross-sectional view of the flow control valve 25. As shown in Figure 4, the first-arm flow control valve 25 mainly includes a main housing 151, a pilot housing 152, a main poppet 153 (main valve), a pilot spool 154, coil springs 155, 158, 159, and a ball check 156. The main housing 151 and the pilot housing 152 are examples of housings. Note that the flow control valves 21 to 29 have a common configuration, so the configuration of the first-arm flow control valve 25 will be described below. Furthermore, the configuration of the flow control valves 21 to 29 mounted in the hydraulic drive system 100 is not limited to the example shown in Figure 4.
[0054] A first pressure chamber 161, a second pressure chamber 173, and a third pressure chamber 166 are formed inside the main housing 151. The first pressure chamber 161, the second pressure chamber 173, and the third pressure chamber 166 are spaces through which hydraulic oil can pass. The first pressure chamber 161 is connected to the oil passage 56 (the supply line on the hydraulic pump 2 side). The second pressure chamber 173 is connected to the oil passage 57 (the supply line on the first arm directional control valve 11 side). The third pressure chamber 166 is disposed opposite the first pressure chamber 161 in the direction of movement of the main poppet 153.
[0055] Pilot pressure chambers 168, 170, pilot oil passages 167, 171, 172, and pilot ports 174, 175 are formed inside the pilot housing 152. The pilot pressure chambers 168, 170, the pilot oil passages 167, 171, 172, and the pilot ports 174, 175 are spaces through which hydraulic oil can pass.
[0056] The pilot pressure chambers 168, 170 are spaces that accommodate the pilot spool 154. The pilot oil passage 167 is an oil passage that connects the third pressure chamber 166 and the pilot pressure chambers 168, 170. The pilot oil passages 171, 172 are oil passages that connect the pilot pressure chambers 168, 170 and the second pressure chamber 173. The pilot pressure chambers 168, 170 and the pilot oil passages 167, 171, 172 are examples of pilot lines. The pilot port 174 is connected to the hydraulic oil tank 4. The pilot port 175 is connected to the oil passage 121 of the pilot pump 111 via the solenoid valve 113d.
[0057] The main poppet 153 moves within the main housing 151 in a direction that connects or blocks communication between the first pressure chamber 161 and the second pressure chamber 173 depending on the pressure difference between the first pressure chamber 161 and the third pressure chamber 166. More specifically, as the pressure in the first pressure chamber 161 becomes greater than that of the third pressure chamber 166, the main poppet 153 moves in a direction that connects the first pressure chamber 161 and the second pressure chamber 173. On the other hand, as the pressure in the third pressure chamber 166 becomes greater than that of the first pressure chamber 161, the main poppet 153 moves in a direction that blocks communication between the first pressure chamber 161 and the second pressure chamber 173.
[0058] The first pressure chamber 161 and the second pressure chamber 173 communicate with each other via a variable throttle formed in the main housing 151. The main poppet 153 is seated on the main housing 151 (i.e., blocks the first pressure chamber 161 and the second pressure chamber 173) by a coil spring 155 set in the third pressure chamber 166. The main poppet 153 also constantly blocks communication between the second pressure chamber 173 and the third pressure chamber 166. The main poppet 153 also communicates between the first pressure chamber 161 and the third pressure chamber 166 via communication passages 163, 164 and the controllable throttle 165.
[0059] The main poppet 153 is also formed with communication passages 163 and 164 and a control variable throttle 165. The communication passages 163 and 164 and the control variable throttle 165 are spaces through which hydraulic oil can pass. The communication passages 163 and 164 pass through the interior of the main poppet 153, connecting the first pressure chamber 161 and the third pressure chamber 166. The control variable throttle 165 is formed at the end of the communication passage 164 on the third pressure chamber 166 side (i.e., at a position facing the third pressure chamber 166 and the inner wall of the main housing 151). The opening area of the control variable throttle 165 varies in conjunction with the movement of the main poppet 153. More specifically, the opening area of the control variable throttle 165 increases as the pressure in the third pressure chamber 166 decreases. Conversely, the opening area of the control variable throttle 165 decreases as the pressure in the third pressure chamber 166 increases.
[0060] A ball check 156 and a coil spring 158 are housed in the communication passage 163. The ball check 156 is biased by the coil spring 158 in a direction that closes the communication passage 163. When the pressure in the first pressure chamber 161 is greater than that in the third pressure chamber 166, the ball check 156 opens the communication passage 163. On the other hand, when the pressure in the third pressure chamber 166 is greater than that in the first pressure chamber 161, the ball check 156 closes the communication passage 163.
[0061] The pilot spool 154 opens and closes the pilot pressure chambers 168, 170 (i.e., the pilot line) using the pilot pressure supplied through the solenoid valve 113d. More specifically, the pilot spool 154 reduces the opening amount of the pilot pressure chambers 168, 170 as the pilot pressure supplied to the pilot port 175 increases. On the other hand, the pilot spool 154 increases the opening amount of the pilot pressure chambers 168, 170 as the pilot pressure supplied to the pilot port 175 decreases. Furthermore, the pilot spool 154 is biased by a coil spring 159 in a direction that opens the pilot pressure chambers 168, 170.
[0062] The first pressure chamber 161 and the second pressure chamber 173 communicate with each other via a variable throttle formed in the main housing 151. The main poppet 153 is provided with a notch 162 that defines the opening characteristics of the variable throttle. The opening characteristics of the pilot line are adjusted by a throttle provided between the pilot pressure chambers 168, 170 and a notch 169 provided in the pilot spool 154. Furthermore, the notches 162, 169 and the control variable throttle 165 can adopt various combinations of shapes other than those shown in the drawings in order to obtain the opening characteristics desired by the designer.
[0063] Fig. 5 is an opening area diagram of the flow control valve 25. More specifically, Fig. 5 shows changes in the opening areas of the pilot spool 154, the control variable throttle 165, and the main poppet 153 relative to the command pressure Pi_fcv of the first-arm flow control valve 25. Note that the other flow control valves have a similar configuration.
[0064] The opening area aPS of the pilot spool 154 and the opening area aFB of the control variable throttle 165 have an opening control range in which the command pressure Pi_fcv ranges from Pi_fcv1 to Pi_fcv4. On the other hand, the opening area aMP of the main poppet 153 has an opening control range in which the command pressure Pi_fcv ranges from Pi_fcv2 (>Pi_fcv1) to Pi_fcv3 (<Pi_fcv4). The maximum opening area aMP1 of the main poppet 153 is set sufficiently large relative to the opening area aPS of the pilot spool 154 and the opening area aFB of the control variable throttle 165. That is, the opening amount of the first-arm flow control valve 25 decreases as the command pressure Pi_fcv increases and increases as the command pressure Pi_fcv decreases. However, the relationship between the command pressure Pi_fcv and the opening amount of the first-arm flow control valve 25 is not limited to the example described above.
[0065] When the command pressure Pi_fcv is between Pi_fcv2 and Pi_fcv3, the opening amount of the first-arm flow control valve 25 is equal to the sum of the opening area aMP of the main poppet 153 and the opening area aPS of the pilot spool 154. That is, when the opening amount of the pilot pressure chambers 168, 170 by the pilot spool 154 is equal to or greater than the threshold value S, the first-arm flow control valve 25 supplies hydraulic oil to the first-arm directional control valve 11 through the first pressure chamber 161 and the second pressure chamber 173 communicated by the main poppet 153, the first pressure chamber 161, the communicating passages 163, 164, the third pressure chamber 166, and the pilot lines (167, 168, 170, 171, 172).
[0066] On the other hand, when the command pressure Pi_fcv is between Pi_fcv3 and Pi_fcv4, the opening area aMP of the main poppet 153 is zero. Therefore, the opening amount of the first-arm flow control valve 25 is equal to the opening area aPS of the pilot spool 154. That is, when the opening amount of the pilot pressure chambers 168, 170 by the pilot spool 154 is less than the threshold value S, the main poppet 153 blocks the first pressure chamber 161 and the second pressure chamber 173, and the first-arm flow control valve 25 supplies hydraulic oil to the first-arm directional control valve 11 through the first pressure chamber 161, the communicating passages 163, 164, the third pressure chamber 166, and the pilot lines (167, 168, 170, 171, 172).
[0067] In this way, the first arm flow control valve 25 has a region where the opening amount is controlled by the sum of the opening area aMP of the main poppet 153 and the opening area aPS of the pilot spool 154 in response to the command pressure Pi_fcv, and a region where the opening amount is controlled by only the opening area aPS of the pilot spool 154, and these regions switch at a predetermined command pressure Pi_fcv3.
[0068] [Functional Blocks of Controller 114] Fig. 6 is a functional block diagram of the controller 114. As shown in Fig. 6, the controller 114 includes an actuator target speed calculation unit 114a, an actuator target flow rate calculation unit 114b, a pump target flow rate calculation unit 114c, a pump control command calculation unit 114d, a directional control valve target opening calculation unit 114e, a directional control valve control command calculation unit 114f, a flow control valve target opening calculation unit 114g, a flow control valve control command calculation unit 114h, and a calibration processing unit 114i.
[0069] Below, an example will be described in which the hydraulic pump 2, the first arm directional control valve 11 (hereinafter simply referred to as the "directional control valve 11"), the first arm flow control valve 25 (hereinafter simply referred to as the "flow control valve 25"), and the arm cylinder 215 are controlled, but other hydraulic pumps, directional control valves, flow control valves, and hydraulic actuators are controlled in the same manner.
[0070] The actuator target speed calculation unit 114a calculates a target speed of the arm cylinder 215 based on an operation signal output from the operation lever 115b. The actuator target flow rate calculation unit 114b calculates a target flow rate of hydraulic oil to be supplied to the arm cylinder 215 based on the actuator target speed calculated by the actuator target speed calculation unit 114a. The pump target flow rate calculation unit 114c calculates a pump target flow rate of hydraulic oil to be discharged from the hydraulic pump 2 based on the actuator target flow rate calculated by the actuator target flow rate calculation unit 114b. The pump control command calculation unit 114d calculates a pump command current based on the pump target flow rate calculated by the pump target flow rate calculation unit 114c, and outputs the pump command current to the solenoid valve 113a that supplies pilot pressure to the flow control command pressure port 2a. As a result, the discharge capacity of the hydraulic pump 2 is set according to the operation amount of the operation lever 115b. Note that the greater the operation amount of the operation lever 115b, the greater the discharge capacity of the hydraulic pump 2.
[0071] The directional control valve target opening calculation unit 114e calculates the directional control valve target opening based on the operation signal output from the operation lever 115b and the pressure signals output from the pressure sensors 84 to 90, 133 to 137. The directional control valve control command calculation unit 114f calculates a directional control valve command current based on the directional control valve target opening calculated by the directional control valve target opening calculation unit 114e, and outputs the calculated directional control valve command current to the solenoid valves 113b, 113c. In this way, the supply direction of hydraulic oil from the directional control valve 11 to the arm cylinder 215 is set according to the operation direction of the operation lever 115b.
[0072] The flow control valve target opening calculation unit 114g calculates a final target opening that ensures flow control accuracy based on the actuator target flow rate calculated by the actuator target flow rate calculation unit 114b, the pressure signals output from the pressure sensors 84-90, 133-137, and a predetermined limit opening area. The flow control valve control command calculation unit 114h calculates a flow control valve command current based on the flow control valve target opening calculated by the flow control valve target opening calculation unit 114g, and outputs the calculated flow control valve command current to the solenoid valve 113d. This sets the flow rate of hydraulic oil supplied from the flow control valve 25 to the directional control valve 11 according to the amount of operation of the operating lever 115b. Note that the greater the amount of operation of the operating lever 115b, the greater the flow rate of hydraulic oil supplied from the flow control valve 25 to the directional control valve 11.
[0073] The calibration processing unit 114i outputs target control commands for executing the calibration process to the pump control command calculation unit 114d, the directional control valve control command calculation unit 114f, and the flow control valve control command calculation unit 114h, based on a calibration execution command output from the calibration instruction device 116. Furthermore, the calibration processing unit 114i adjusts (calibrates) the opening start current at which the flow control valve 25 starts opening, based on the pressure signals output from the pressure sensors 84-90 and 133-137 and the current signals output from the current sensors 143-147.
[0074] [Performance Error of Solenoid Valve 113d] Figure 7 is an explanatory diagram of the performance error of the solenoid valve 113d. More specifically, the left diagram in Figure 7 is a diagram showing the correspondence relationship between the target opening Atgt of the flow control valve 25 and the command current I to the solenoid valve 113d. The center diagram in Figure 7 is a diagram showing the correspondence relationship between the command current I to the solenoid valve 113d and the command pressure Pi of the solenoid valve 113d. The right diagram in Figure 7 is a diagram showing the relationship between the command pressure Pi of the solenoid valve 113d and the opening area A of the flow control valve 25.
[0075] The controller 114 calculates a command current I corresponding to the target opening Atgt based on a predetermined correspondence relationship (left diagram in FIG. 7) between the target opening Atgt and the command current I, and outputs the calculated command current I to the solenoid valve 113d. Here, due to manufacturing variations in the controller 114, a current error CUerror may occur between the command current I calculated based on the correspondence relationship in the left diagram in FIG. 7 and the command current I that is actually output.
[0076] 7, the solenoid valve 113d outputs a command pressure Pi corresponding to a command current I output from the controller 114. Here, a command pressure error Pierror may occur between the command current I and the command pressure Pi due to manufacturing variations in the solenoid valve 113d, etc. Furthermore, as shown in the right diagram in FIG. 7, the flow control valve 25 is set to an opening area A corresponding to the command pressure Pi output from the solenoid valve 113d. Here, an opening area error Aerror may occur between the command pressure Pi and the opening area A due to manufacturing variations in the flow control valve 25, etc.
[0077] That is, an error that is the sum of the current error CUerror, the command pressure error Pierror, and the opening area error Aerror may occur between the target opening Atgt calculated by the controller 114 and the actual opening area A. Therefore, the controller 114 needs to execute the calibration process shown in FIG.
[0078] [Calibration Process] Fig. 8 is a flowchart of the calibration process. Fig. 9 is a diagram showing the change in command current over time in the calibration process and the change in load pressure relative to the command current. The operator may execute the calibration process, for example, when the assembly of the hydraulic excavator 200 is completed, during regular maintenance, or when parts are replaced. Below, the calibration process for the flow control valve 25 will be described, but the same applies to the other flow control valves 21 to 24 and 26 to 29.
[0079] First, the calibration instruction device 116 displays a list of the flow control valves 21 to 29 on a display and allows the operator to select a calibration target via an operation panel (S11). Here, it is assumed that the flow control valve 25 has been selected. The calibration instruction device 116 then specifies the flow control valve 25 selected by the operator and outputs an instruction to execute calibration to the controller 114. As another example, the calibration instruction device 116 may automatically select the plurality of flow control valves 21 to 29 in a predetermined order and output an instruction to execute calibration.
[0080] Next, the controller 114 outputs a pump command current to the solenoid valve 113a so that the discharge capacity of the hydraulic pump 2 is reduced to a predetermined value or less (S12). In step S12, it is desirable to reduce the discharge capacity of the hydraulic pump 2 as much as possible within the range in which the arm cylinder 215 can be driven (i.e., the calibration process can be executed).
[0081] Next, the controller 114 controls the hydraulic pump 2, the directional control valve 11, and the flow control valve 25 to change the position of the arm cylinder 215 to a predetermined position (S13). This process may be automatically performed by the controller 114, or the operator in the cab 208 may be prompted to operate the operating device via a display.
[0082] As one example, the predetermined posture is a posture in which the arm cylinder 215 does not move under its own weight even if the meter-out side of the directional control valve 11 is connected to the tank line during the calibration process. As another example, the predetermined posture is a posture in which the operating range of the arm cylinder 215 is limited during the calibration process, and more specifically, a position where the arm cylinder 215 is returned a predetermined amount from the stroke end on the cloud side toward the dump truck side. That is, the controller 114 executes an operation of extending (moving) the arm cylinder 215 to the stroke end and then slightly returning (retracting) it to a predetermined position away from the stroke end.
[0083] In the case of the boom cylinder 214, this is a position returned a predetermined amount from the boom-raising stroke end. In the case of the bucket cylinder 216, this is a position returned a predetermined amount from the crowd stroke end. In the case of the travel motor 205 or the swing motor 206, it is assumed that the actuator will be installed on a horizontal location where it will not move under its own weight even if the operator connects the meter-out side of the directional control valve to the tank line before performing the calibration process, so there is no need to change it to the predetermined attitude in this step. In addition, the predetermined amount is a stroke amount that is sufficient and necessary to return the load pressure, which has been increased to the relief pressure set by a relief valve installed in the pump line when moved to the cylinder stroke end, to the actuator holding pressure.
[0084] Next, the controller 114 maximizes the command current output to the solenoid valve 113d (i.e., Pi_fcv4) to close the flow control valve 25 (S14). This blocks communication between the oil passages 56 and 57, and the hydraulic oil discharged from the hydraulic pump 2 is no longer supplied to the directional control valve 11 through the flow control valve 25.
[0085] Next, the controller 114 outputs a command current to the solenoid valves 113b and 113c to open the directional control valve 11 so that the hydraulic oil is supplied in the direction that extends the arm cylinder 215 (S15). Next, the controller 114 cuts off the center bypass line 52 (S16). As a result, the pressure in the parallel line 53 is increased to the relief pressure of the relief valve 32.
[0086] As one example, the controller 114 may close the bleed-off valve 35 by outputting a command current to the solenoid valve 113e. As another example, the directional control valve 11 may be configured to cut off the center bypass line 52 when switched to supply hydraulic oil to the arm cylinder 215. In this case, the directional control valve 11 is another example of an opening and closing device. In this case, switching of the bleed-off valve 35 is not necessary.
[0087] Next, the controller 114 gradually changes the command current output to the solenoid valve 113d in a direction that opens the flow control valve 25 (S17). In this embodiment, the command current is gradually reduced. More specifically, the controller 114 gradually reduces the command current within a range in which the first pressure chamber 161 and the second pressure chamber 173 are blocked by the main poppet 153 and the oil passages 56, 57 remain blocked (i.e., from Pi_fcv4 to Pi_fcv3).
[0088] Next, the controller 114 monitors fluctuations in the load pressure indicated by the pressure signal from the pressure sensor 88a (S18). In other words, the controller 114 gradually reduces the command current (upper diagram in FIG. 9) until the load pressure detected by the pressure sensor 88a changes (lower diagram in FIG. 9). Then, the controller 114 identifies the command current at the time when the load pressure detected by the pressure sensor 88a changes (increases) as the opening start current at which the flow control valve 25 starts opening (S18: Yes→S19).
[0089] Then, the controller 114 performs calibration using the opening start current identified in step S19 (S20). The controller 114 adjusts the correspondence relationship between the target opening Atgt and the command current I shown in the left diagram in Fig. 7, for example, using the opening start current. More specifically, the controller 114 translates the solid line in the left diagram in Fig. 7 so that the intercept of the command current I coincides with the opening start current.
[0090] Next, the controller 114 determines whether any other flow control valves 21 to 29 remain to be calibrated (S21). If the controller 114 determines that any other flow control valves 21 to 29 remain to be calibrated (S21: No), it executes the processing from step S11 onwards again. On the other hand, if the controller 114 determines that calibration has been executed for all of the flow control valves 21 to 29 (S21: Yes), it ends the calibration processing.
[0091] According to the above embodiment, for example, the following advantageous effects are achieved.
[0092] According to the above embodiment, the pressure sensors 88a, 88b are used to detect the pressure of the hydraulic oil supplied to the arm cylinder 215, so the calibration process can be performed without attaching dedicated parts to the hydraulic excavator 200.
[0093] Furthermore, according to the above embodiment, when the discharge capacity of the hydraulic pump 2 is at its minimum and the parallel line 53 is pressurized to the relief pressure, the command current to the solenoid valve 113d is gradually reduced, thereby gradually displacing the pilot spool 154 and eventually opening (communicating) the pilot pressure chambers 168, 170. At this time, the discharge capacity of the hydraulic pump 2 is kept to the minimum necessary, and the oil passages 56, 57 are communicated only by the pilot lines (167, 168, 170, 171, 172) of the flow control valve 25. This suppresses vibration of the vehicle body due to abrupt operation of the arm cylinder 215, and makes it possible to accurately measure changes in the load pressure of the arm cylinder 215.
[0094] Furthermore, according to the above embodiment, the arm cylinder 215 reaches the stroke end from a predetermined position with the minimum necessary stroke, and therefore, after the flow control valve 25 opens, the pressure is immediately increased from the holding pressure to the relief pressure in a short time, making it easy to measure fluctuations in the load pressure.
[0095] Furthermore, according to the above embodiment, the amount of movement of the hydraulic excavator 200 during the calibration process is minimized by minimizing the flow rate of hydraulic oil supplied to the arm cylinder 215 and the stroke amount of the arm cylinder 215. As a result, it is possible to reduce the impact on the surroundings when the calibration process is being performed.
[0096] Furthermore, according to the above embodiment, by performing calibration in a state in which the arm cylinder 215 has been changed to a position in which it does not move under its own weight, it is possible to prevent the arm cylinder 215 from moving when the directional control valve 11 is opened.
[0097] The above-described embodiments are merely illustrative examples of the present invention, and are not intended to limit the scope of the present invention to these embodiments. Those skilled in the art can implement the present invention in various other forms without departing from the spirit of the present invention.
[0098] 1, 2, 3: Hydraulic pump 1a, 2a, 3a: Flow control command pressure port 6-16: Directional control valve 11a, 11b, 35a: Command pressure port 21-29: Flow control valve 31-33: Relief valve 34, 35, 36: Bleed-off valve 37: Merging valve 38, 39: Check valve 41, 51, 62: Discharge line 42, 52, 63: Center bypass line 43, 53, 64: Parallel line 72-75: Actuator line 84-90, 133-137: Pressure sensor 91-92: Temperature sensor 100: Hydraulic drive system 111: Pilot pump 112: Pilot relief valve 113: Solenoid valve unit 113a-113e: Solenoid valve 114: Controller 114a: Actuator target speed calculation unit 114b: Actuator target flow rate calculation unit 114c: Pump target flow rate calculation unit 114d: Pump control command calculation unit 114e: Directional control valve target opening calculation unit 114f: Directional control valve control command calculation unit 114g: Flow control valve target opening calculation unit 114h: Flow control valve control command calculation unit 114i: Calibration processing unit 115a, 115b: Operating lever 116: Calibration instruction device 123-127: Pilot line 143-147: Current sensor 151: Main housing 152: Pilot housing 153: Main poppet 154: Pilot spool 155, 158, 159: Coil spring 156: Ball check 161: First pressure chamber 162,169: Notch 163, 164: Communication passage 165: Control variable throttle 166: Third pressure chamber 167, 171, 172: Pilot oil passage 168, 170: Pilot pressure chamber 173: Second pressure chamber 174, 175: Pilot port 200: Hydraulic excavator 201: Lower traveling body 202: Upper rotating body 204: Crawler 205: Travel motor 206: Swing motor 207: Swing frame 208: Cab 209: Counterweight 210: Front working machine 211: Boom 212: Arm 213: Bucket 214: Boom cylinder 215: Arm cylinder 216: Bucket cylinder 221, 226: Attitude sensor
Claims
1. A hydraulic pump that discharges the hydraulic fluid stored in the hydraulic fluid tank, A hydraulic actuator driven by the hydraulic fluid discharged from the aforementioned hydraulic pump, A directional control valve is positioned in the supply line from the hydraulic pump to the hydraulic actuator to control the direction of hydraulic fluid supply to the hydraulic actuator, A flow control valve is positioned upstream of the directional control valve in the supply line and controls the flow rate of the hydraulic fluid supplied from the hydraulic pump to the directional control valve, A pressure sensor for detecting the pressure of the hydraulic fluid supplied to the hydraulic actuator, A solenoid valve that opens and closes the flow control valve by supplying pilot pressure to the pilot port of the flow control valve, A controller that performs a calibration process to adjust the command current output to the solenoid valve, In a hydraulic drive system equipped with, The hydraulic actuator is a hydraulic cylinder that extends and retracts by supplying and discharging hydraulic fluid, The aforementioned controller, In the calibration process, Controlling the flow control valve and the directional control valve to move the hydraulic cylinder to the stroke end and return it to a predetermined position a predetermined distance away from the stroke end, closing the flow control valve and opening the directional control valve so that the hydraulic cylinder moves a predetermined distance from the predetermined position toward the stroke end, the command current output to the solenoid valve is varied in the direction that opens the flow control valve. The command current at the time when the pressure detected by the pressure sensor changes is identified as the opening start current at which the flow control valve begins to open. A hydraulic drive system characterized by the following features.
2. In the hydraulic drive system according to claim 1, The system includes an opening / closing device that opens and closes a bypass line from the hydraulic pump through the directional control valve to the hydraulic fluid tank, The aforementioned controller, In the calibration process, With the flow control valve closed, the directional control valve open, and the switching device closed, the command current output to the solenoid valve is varied in a direction that opens the flow control valve. A hydraulic drive system characterized by the following features.
3. In the hydraulic drive system according to claim 1, The aforementioned controller, In the calibration process, With the hydraulic actuator changed to a predetermined position in which it does not operate under its own weight, the command current output to the solenoid valve is varied in a direction that causes the flow control valve to open. A hydraulic drive system characterized by the following features.
4. In the hydraulic drive system according to claim 3, The aforementioned hydraulic pump is of variable capacity type, The aforementioned controller, In the calibration process, Prior to changing the position of the hydraulic actuator to the predetermined position, the discharge capacity of the hydraulic pump is reduced to a predetermined value or less. A hydraulic drive system characterized by the following features.
5. (delete)
6. In the hydraulic drive system according to claim 1, The device further includes an instruction device that instructs the execution of the calibration process, The aforementioned controller, Based on the instruction to execute the calibration process by the instruction device, the calibration process is executed. A hydraulic drive system characterized by the following features.
7. In the hydraulic drive system according to claim 1, The flow control valve is A housing having a first pressure chamber connected to the supply line on the hydraulic pump side, a second pressure chamber connected to the supply line on the directional control valve side, a third pressure chamber positioned opposite the first pressure chamber, and a pilot line connecting the third pressure chamber and the second pressure chamber, A main valve that moves in a direction that connects or disconnects the first and second pressure chambers depending on the pressure difference between the first and third pressure chambers, A pilot spool opens and closes the pilot line by the pilot pressure supplied through the solenoid valve, Equipped with, The main valve has, A connecting passage that connects the first pressure chamber and the third pressure chamber, A controllable throttling is formed at the end of the communication passage on the third pressure chamber side, wherein the opening area increases as the pressure inside the third pressure chamber decreases. The flow control valve is When the opening amount of the pilot line by the pilot spool is less than a threshold, the main valve blocks the passage between the first pressure chamber and the second pressure chamber, and hydraulic fluid is supplied to the directional control valve through the first pressure chamber, the communication passage, the third pressure chamber, and the pilot line. When the opening of the pilot line by the pilot spool is greater than or equal to the threshold, hydraulic fluid is supplied to the directional control valve through the first pressure chamber and the second pressure chamber, which are connected by the main valve, the first pressure chamber, the communication passage, the third pressure chamber, and the pilot line. A hydraulic drive system characterized by the following features.
8. In the hydraulic drive system according to claim 7, The aforementioned controller, In the calibration process, The command current is varied within a range where the opening of the pilot line is less than the threshold. A hydraulic drive system characterized by the following features.
9. In the hydraulic drive system according to claim 1, The aforementioned controller, The first controller mounted on the vehicle body, A second controller is provided in a portable device separate from the vehicle body and instructs the first controller to perform the calibration process, including A hydraulic drive system characterized by the following features.
10. In the hydraulic drive system according to claim 1, The aforementioned controller is mounted on the vehicle body. A hydraulic drive system characterized by the following features.