Hydraulic drive system

Abstract

When performing calibration of a flow control valve, the operator prevents unintended operation of the hydraulic actuator. The hydraulic drive system of the present invention comprises a first valve (5a) provided between a hydraulic pump and a hydraulic actuator, a second valve (5b) provided between a hydraulic actuator and the first valve, a control device, a pressure sensor for detecting pressure in a flow path, and an input device. When a signal requesting calibration is input by the input device, the control device closes the valve to be calibrated and opens the valve not to be calibrated so that the flow path is maintained at a predetermined pressure, then closes the valve not to be calibrated, increases the opening degree command value of the valve to be calibrated to open it, records the opening degree command value when the amount of change in pressure in the flow path detected by the pressure sensor exceeds a predetermined value, and controls the valve to be calibrated based on the recorded opening degree command value.

Description

Technology Field

[0001] The present invention relates to a hydraulic drive system suitable for work machines, such as hydraulic shovels, for example. Background Technology

[0002] The performance (characteristics) of control valves used in hydraulic drive systems may vary due to manufacturing reasons. For this reason, it is common practice to perform calibration for each control valve. For example, Patent Document 1 discloses a calibration device for calibrating the stroke characteristics of an electronically controlled valve unit. The calibration device described in Patent Document 1 comprises a pump, a measuring passage connecting the discharge port of the pump to a tank, a sub-valve body (spool) connected to the valve body so as to stroke in conjunction with the valve body (spool) of the valve unit provided in the middle of the measuring passage, an interlocking opening / closing valve that opens and closes the measuring passage according to the stroke of the sub-valve body, a downstream opening / closing valve provided on the downstream side of the interlocking opening / closing valve, a pressure detector that detects pressure in the area between the opening / closing valves, and a relief valve that maintains the pressure on the upstream side of the interlocking opening / closing valve at a predetermined relief pressure. Prior art literature

[0003] Japanese Patent Publication No. 6554346 The problem to be solved

[0004] In the prior art described in Patent Document 1, when correcting the stroke characteristics of a valve unit, it is necessary to stroke the spool of the interlocking opening and closing valve, but since the spool of the flow control valve also strokes in conjunction with the stroke of the spool of the interlocking opening and closing valve, there is a possibility that the hydraulic actuator connected to the flow control valve may perform an unintended operation by the operator.

[0005] The object of the present invention is to provide a hydraulic drive system capable of preventing unintended operation of a hydraulic actuator by an operator when performing calibration of a flow control valve (valve). means of solving the problem

[0006] To achieve the above objective, one aspect of the present invention is a hydraulic drive system of a work machine comprising: a hydraulic pump; a hydraulic actuator operated by hydraulic fluid discharged from the hydraulic pump; a first valve provided between the hydraulic pump and the hydraulic actuator and controlling the flow rate of hydraulic fluid supplied from the hydraulic pump to the hydraulic actuator; a second valve provided between the hydraulic actuator and the first valve and controlling the flow rate of hydraulic fluid supplied from the first valve to the hydraulic actuator; and a control device that controls the first valve and the second valve by an opening degree command value; wherein the control device comprises a pressure sensor that detects the pressure of the fluid path between the first valve and the second valve and an input device, and when a signal requesting calibration of the first valve or the second valve is input by the input device, the control device closes the valve to be calibrated among the first valve or the second valve and opens the valve not to be calibrated so that the fluid path is maintained at a predetermined pressure, and then calibrate The method is characterized by closing a valve that is not the target, increasing the opening degree command value of the valve to be calibrated to open it, recording the opening degree command value when the amount of change in the pressure of the flow path detected by the pressure sensor exceeds a predetermined value, and setting the valve to be calibrated to be controlled based on the recorded opening degree command value. Effects of the invention

[0007] According to the present invention, when performing calibration of a flow control valve (valve), unintended operation of a hydraulic actuator by an operator can be prevented. Furthermore, problems, configurations, and effects other than those described above will become clear from the description of the following embodiments. Brief explanation of the drawing

[0008] Figure 1 is a side view of a hydraulic shovel. FIG. 2 is a circuit diagram of a hydraulic drive system according to a first embodiment. FIG. 3 is a flowchart showing the calibration procedure of the first flow control valve according to the first embodiment. FIG. 4 is a flowchart showing the calibration procedure of the second flow control valve according to the first embodiment. FIG. 5 is a circuit diagram of a hydraulic drive system according to a second embodiment. FIG. 6 is a flowchart showing the calibration procedure of the first flow control valve according to the second embodiment. FIG. 7 is a flowchart showing the calibration procedure of the second flow control valve according to the second embodiment. Specific details for implementing the invention

[0009] First, a work machine equipped with a hydraulic drive system according to the present invention will be described. Hereinafter, a crawler-type hydraulic shovel (100) will be described as an example of one embodiment of the work machine, but the work machine to which the present invention is applied is not limited to a hydraulic shovel. It goes without saying that the present invention can be applied to all work machines such as wheel loaders and cranes.

[0010] FIG. 1 is a side view of a hydraulic shovel (100). As shown in FIG. 1, the hydraulic shovel (100) is equipped with a crawler-type lower driving body (1) that forms the vehicle body, an upper turning body (2) that forms the vehicle body and is pivotably provided above the lower driving body (1), and a hydraulically driven work device (3) that is installed on the upper turning body (2) to perform various tasks.

[0011] The upper slewing body (2) is driven to slewing relative to the lower driving body (1) by the driving force of the slewing device (5). The upper slewing body (2) mainly comprises a slewing frame (2a) which is a base frame, a cab (7) where an operator sits and performs various operations, and a machine room (2b) in which an engine or hydraulic pump (9) (not shown) is housed (see FIG. 2).

[0012] The working device (33) is equipped with a boom (3a) which is rotatably installed on a pivoting frame (2a) at its base, an arm (3b) which is rotatably installed at the tip of the boom (3a), and a bucket (3c) which is rotatably installed at the tip of the arm (3b).

[0013] The boom (3a) is driven by a boom cylinder (4a). Specifically, the boom cylinder (4a) is connected at one end to the pivot frame (2a) and at the other end to the boom (31), and the boom (3a) is rotated (elevated) in the up and down direction relative to the upper pivot body (2) by extending and retracting the rod through the supply and discharge of hydraulic fluid.

[0014] The arm (3b) is driven by an arm cylinder (4b). Specifically, the arm cylinder (4b) is connected at one end to the boom (3a) and at the other end to the arm (3b), and the arm (3b) is rotated in the forward and backward direction relative to the boom (3a) by extending and retracting the rod through the supply and discharge of hydraulic fluid.

[0015] The bucket (3c) is driven by a bucket cylinder (4c). Specifically, the bucket cylinder (4c) is connected at one end to the arm (3b) and at the other end to the bucket (3c), and the bucket (3c) is rotated in the forward and backward directions relative to the arm (3b) by extending and retracting the rod through the supply and discharge of hydraulic fluid.

[0016] The bucket (3c) is a work tool used for tasks such as scooping up cargo such as soil or minerals and lowering the cargo to a designated location or leveling the ground. Additionally, this bucket (3c) can be replaced with various attachments, such as a grapple for gripping wood, rocks, or waste, or a breaker for crushing rocks.

[0017] <First Embodiment>

[0018] Next, a hydraulic drive system according to the first embodiment of the present invention will be described. FIG. 2 is a circuit diagram of a hydraulic drive system according to the first embodiment, illustrating the hydraulic circuit of a boom cylinder (4a). Here, since the hydraulic circuit of the boom cylinder (4a) and the hydraulic circuit of other hydraulic actuators (arm cylinder (4b), bucket cylinder (4c), etc.) have basically the same configuration, the hydraulic circuit of the boom cylinder (4a) will be described mainly below, and the illustration and description of the hydraulic circuit of other hydraulic actuators will be omitted.

[0019] As illustrated in FIG. 2, the hydraulic drive system according to the first embodiment comprises a hydraulic pump (9), a boom cylinder (4a), a first flow control valve (5a) (first valve) and a second flow control valve (5b) (second valve), a vehicle-mounted controller (first controller) (15), and a pressure sensor (8). The boom cylinder (4a) has a bottom seal (4a1) and a rod seal (4a2).

[0020] The hydraulic pump (9) is, for example, a variable displacement piston pump and is driven by an engine (12) which is the driving source. The hydraulic pump (9) sucks in the hydraulic fluid stored in the hydraulic fluid tank (10) and discharges it toward the boom cylinder (4a).

[0021] The first flow control valve (5a) and the second flow control valve (5b) are arranged in the order of the first flow control valve (5a) and the second flow control valve (5b) from upstream in the flow path (6) between the boom cylinder (4a) and the hydraulic pump (9). Here, the flow path (6) is described in detail. Among the flow paths (6b) between the hydraulic pump (9) and the first flow control valve (5a) and the first flow control valve (5a) and the first flow control valve (5a) that are paired, the flow path (6a) connecting the bottom chamber (4a1) of the boom cylinder (4a) and the first flow control valve (5a), and the flow path (6c) connecting the first flow control valve (5a) or the hydraulic pump (9) and the tank are mainly used in the following description.

[0022] The first flow control valve (5a) is a directional control valve (first valve) having an electronic proportional 3-position 6-port with a built-in spool, and by switching the flow direction of the hydraulic fluid from the hydraulic pump (9) according to the position of the spool, the boom cylinder (4a) is extended or shortened. Depending on the spool position of the first flow control valve (5a), the hydraulic fluid from the hydraulic pump (9) is supplied to one side of the bottom chamber and the rod chamber of the boom cylinder (4a) and discharged from the other side. The hydraulic fluid discharged from the other side of the bottom chamber and the rod chamber of the boom cylinder (4a) is returned to the hydraulic fluid tank (10) through the first flow control valve (5a).

[0023] The second flow control valve (5b) is positioned upstream of the flow of the operating fluid compared to the first flow control valve (5a) and has the function of maintaining the load of the boom cylinder (4a) when the hydraulic hose forming the flow path (6) is damaged, etc. That is, the second flow control valve (5b) (second valve) is a load maintaining valve.

[0024] The pressure sensor (8) detects the pressure of the flow path (6a) between the first flow control valve (5a) and the second flow control valve (5b). The pressure sensor (8) is connected to the vehicle controller (15) via electrical wiring, and the pressure data of the flow path (6a) detected by the pressure sensor (8) is input to the vehicle controller (15).

[0025] In addition to adjusting the opening degree of the first flow control valve (5a) and the second flow control valve (5b), the vehicle controller (15) performs calibration of the first flow control valve (5a) and the second flow control valve (5b), which will be described later, based on pressure data from the pressure sensor (8). The vehicle controller (15) is positioned inside the cap (7).

[0026] The vehicle controller (15) is configured such that the CPU, RAM, ROM, HDD, input I / F, and output I / F are connected to each other via a bus. In this hardware configuration, the CPU reads a control program (software) stored on a recording medium such as a ROM, HDD, or optical disc, deploys it onto the RAM, and executes the deployed control program, thereby enabling the control program and hardware to cooperate to realize the function of the vehicle-mounted controller (15).

[0027] The vehicle-mounted controller (15) is connected to an external device (second controller) (16) via a communication line (20). The external device (16) is, for example, a smartphone or a tablet. Additionally, the external device (16) may be a PC installed in a control room. Furthermore, in this embodiment, wireless is exemplified as the communication line (20), but it may also be wired. Although not related to the implementation of the calibration of the present invention, the vehicle-mounted controller (15) is configured to receive an input signal of an operating lever for operating various actuators.

[0028] When the vehicle-mounted controller (15) receives a calibration execution command from an external device (16), it performs calibration of the first flow control valve (5a) and the second flow control valve (5b) described below.

[0029] (Calibration of the first flow control valve (5a))

[0030] FIG. 3 is a flowchart showing the calibration procedure of the first flow control valve (5a) (first valve) according to the first embodiment. When the calibration process of the first flow control valve (5a) is initiated, first, the vehicle-mounted controller (15) outputs an opening degree indicator value to close the first flow control valve (5a) by displacement (maintaining) it to position A, thereby blocking the flow path (6) (more specifically, the flow path (6b) and the flow path (6a)) (step S11). Next, the vehicle-mounted controller (15) outputs an opening degree indicator value to open the second flow control valve (5b) to open the flow path (6a) (step S12). When the second flow control valve (5b) is opened and the flow path (6a) is opened, the bottom pressure of the boom cylinder (4a) acts on the flow path (6a). Next, the vehicle-mounted controller (15) outputs an opening degree indicator value to close the second flow control valve (5b) to block the flow path (6a) (step S13). When the second flow control valve (5b) is closed and the flow path (6a) is blocked, the flow path (6a) is maintained at the bottom pressure of the boom cylinder (4a).

[0031] With the bottom pressure of the boom cylinder (4a) maintained in Euro (6a), the vehicle-mounted controller (15) records the value P(n) input from the pressure sensor (8) in RAM (step S14). Next, the vehicle-mounted controller (15) adds a step increment s to the opening degree indicator value Sa output to the first flow control valve (5a) (step S15). Next, the vehicle-mounted controller (15) records the value P(n+1) input from the pressure sensor (8) after the opening degree indicator value of the first flow control valve (5a) has increased (step S16).

[0032] Next, the vehicle-mounted controller (15) calculates the absolute value D of the difference between P(n) and P(n+1) and compares it with a first threshold (a predetermined value) (step S17). If D ≥ the first threshold, it can be determined that the first flow control valve (5a) is open and the working fluid in the flow path (6a) has flowed into the working fluid tank (10), so the vehicle-mounted controller (15) records the opening degree indicator value Sa (step S18) and terminates the calibration. On the other hand, if D < the first threshold, it can be determined that the first flow control valve (5a) is still closed, so the vehicle-mounted controller (15) returns to step S14. Additionally, the first threshold is pre-set to a value corresponding to the difference between the bottom pressure of the boom cylinder (4a) and the pressure of the working fluid tank (10) (i.e., atmospheric pressure).

[0033] In this way, in step S17, the vehicle-mounted controller (15) monitors the pressure change (in this case, pressure drop) of the flow path (6a), thereby allowing the opening characteristics of the first flow control valve (5a) to be determined with high precision. Therefore, even if there is a change in the performance of the first flow control valve (5a) during the manufacturing process, the change can be corrected by performing the calibration shown in FIG. 3. Furthermore, since the second flow control valve (5b) is closed while the calibration of the first flow control valve (5a) is being performed, the bottom pressure of the boom cylinder (4a) does not fluctuate before or after the calibration. Therefore, during the calibration, the boom cylinder (4a) does not operate against the operator's intention. In other words, there is no concern that the boom (3a) will rotate arbitrarily during the calibration.

[0034] (Calibration of the second flow control valve (5b))

[0035] FIG. 4 is a flowchart showing the calibration procedure of the second flow control valve (5b) (second valve) according to the first embodiment. When the calibration process of the second flow control valve (5b) is initiated, first, the vehicle-mounted controller (15) outputs an opening degree indicator value to close the second flow control valve (5b) and block the flow path (6) (Step S21). Next, the vehicle-mounted controller (15) outputs an opening degree indicator value to open the flow path (6) by displacement of the first flow control valve (5a) to position B (Step S22). When the first flow control valve (5a) is opened and the flow path (6) is opened, the flow path (6a) becomes tank pressure. Next, the vehicle-mounted controller (15) outputs an opening degree indicator value to close the flow path (6) by displacement of the first flow control valve (5a) to position A and block the flow path (6) (Step S23). When the first flow control valve (5a) is closed and the flow path (6) is blocked, the flow path (6a) is maintained at tank pressure.

[0036] With Euro (6a) maintained at tank pressure, the vehicle-mounted controller (15) records the value P(n) input from the pressure sensor (8) in RAM (step S24). Next, the vehicle-mounted controller (15) adds s, a step increment, to the opening degree indicator value Sb output to the second flow control valve (5b) (step S25). Next, the vehicle-mounted controller (15) records the value P(n+1) input from the pressure sensor (8) after the opening degree indicator value of the second flow control valve (5b) has increased (step S26).

[0037] Next, the vehicle-mounted controller (15) calculates the absolute value D of the difference between P(n) and P(n+1) and compares it with a second threshold (a predetermined value) (step S27). If D ≥ the second threshold, it can be determined that the second flow control valve (5b) is open and the bottom pressure of the boom cylinder (4a) is applied to the flow path (6a), so the vehicle-mounted controller (15) records the opening degree indicator value Sb (step S28) and terminates the calibration. On the other hand, if D < the second threshold, it can be determined that the second flow control valve (5b) is still closed, so the vehicle-mounted controller (15) returns to step S24. Additionally, the second threshold is pre-set to a value corresponding to the difference between the bottom pressure of the boom cylinder (4a) and the pressure of the hydraulic fluid tank (10) (i.e., atmospheric pressure). Here, the first and second thresholds may be the same value or different values. These values ​​can be appropriately determined based on the leakage flow rate of each flow control valve, the elasticity of the working fluid, the volume of the flow path, etc.

[0038] In this way, in step S27, the vehicle-mounted controller (15) monitors the pressure change (in this case, pressure increase) of the flow path (6a), thereby allowing the opening characteristics of the second flow control valve (5b) to be determined with high precision. Therefore, even if there is a change in the performance of the second flow control valve (5b) during the manufacturing process, the change can be corrected by performing the calibration shown in FIG. 4. Furthermore, since the first flow control valve (5a) is closed while the calibration of the second flow control valve (5b) is being performed, the bottom pressure of the boom cylinder (4a) does not fluctuate before or after the calibration. Therefore, during the calibration, the boom cylinder (4a) does not operate against the operator's intention. In other words, there is no concern that the boom (3a) will rotate arbitrarily during the calibration.

[0039] According to the hydraulic drive system of the first embodiment configured as described above, the following operational effects can be exhibited.

[0040] By executing the calibration procedure shown in FIGS. 3 and FIGS. 4, the opening characteristics of the first flow control valve (5a) and the second flow control valve (5b) can be adjusted. Specifically, the vehicle-mounted controller (15) can correct for variations in the opening characteristics of the first flow control valve (5a) caused by manufacturing by controlling the opening and closing of the first flow control valve (5a) based on the opening degree indicator value Sa recorded in step S18 of FIG. 3. Likewise, for the second flow control valve (5b), variations in the opening characteristics can be corrected by controlling it based on the opening degree indicator value Sb. In addition, since the flow control valves (5a, 5b) can be calibrated with high precision, deterioration of operability of the boom cylinder (4a) or occurrence of shock can be prevented.

[0041] In addition, since no fluctuation occurs in the bottom pressure of the boom cylinder (4a) even during the calibration of the first flow control valve (5a) and the second flow control valve (5b), the boom (3a) does not move contrary to the operator's intention.

[0042] Of course, it goes without saying that other hydraulic actuators (arm cylinder (4b), bucket cylinder (4c), etc.) can also exhibit the same operating effect.

[0043] <Second Embodiment>

[0044] Next, a hydraulic drive system according to a second embodiment of the present invention will be described. FIG. 5 is a circuit diagram of a hydraulic drive system according to a second embodiment, illustrating the hydraulic circuit of a boom cylinder (4a). In addition, parts common to the first embodiment in the second embodiment are given the same reference numerals and their descriptions are omitted. Furthermore, in the second embodiment, the hydraulic circuit of other hydraulic actuators (arm cylinder (4b), bucket cylinder (4c), etc.) is the same as that in FIG. 5, which is the same as in the first embodiment.

[0045] As illustrated in FIG. 5, the hydraulic drive system according to the second embodiment differs from the first embodiment in that it has a third flow control valve (flow control valve) (5c) and a fourth flow control valve (5d) instead of the second flow control valve (load holding valve) (5b) of the first embodiment. Specifically, the third flow control valve (5c) (first valve) is provided in the flow path (6b) between the hydraulic pump (9) and the first flow control valve (5a) (second valve), and the fourth flow control valve (5d) is provided in the flow path (6c) between the first flow control valve (5a) and the hydraulic fluid tank (10). Additionally, the installation location of the pressure sensor (8a) in the second embodiment differs from the first embodiment in that it is provided in the flow path (6b) between the first flow control valve (5a) and the third flow control valve (5c).

[0046] In the second embodiment configured with such a hydraulic circuit, the calibration of the first flow control valve (5a) and the third flow control valve (5c) can be performed in the order of FIGS. 6 and FIGS. 7. As described below, the pressure state of the flow path (6) (flow path (6a, 6b, 6c)) is different from that of the first embodiment.

[0047] (Calibration of the first flow control valve (5a))

[0048] FIG. 6 is a flowchart showing the calibration procedure of the first flow control valve (5a) (second valve) according to the second embodiment. When the calibration process of the first flow control valve (5a) is initiated, first, the vehicle-mounted controller (15) outputs an opening degree indicator value to close the first flow control valve (5a) and the fourth flow control valve (5d) to block the passage between the passage (6a) and the passage (6b) (Step S31). Next, the vehicle-mounted controller (15) outputs an opening degree indicator value to open the third flow control valve (5c) to open the passage (6b) (Step S32). At this time, the set pressure of the relief valve (11) is applied to the passage (6b). Next, the vehicle-mounted controller (15) outputs an opening degree indicator value to close the third flow control valve (5c) to block the passage (6c) (Step S33). When the third flow control valve (5c) is closed and the flow path (6b) is blocked, the flow path (6b) is maintained at the set pressure of the relief valve (11).

[0049] With Euro (6b) maintained at the set pressure of the relief valve (11), the vehicle-mounted controller (15) records the value P(n) input from the pressure sensor (8) in RAM (step S34). Next, the vehicle-mounted controller (15) adds a step increment s to the opening degree indicator value Sa output to the first flow control valve (5a) (step S35). Next, the vehicle-mounted controller (15) records the value P(n+1) input from the pressure sensor (8) after the opening degree indicator value of the first flow control valve (5a) has increased (step S36).

[0050] Next, the vehicle-mounted controller (15) calculates the absolute value D of the difference between P(n) and P(n+1) and compares it with a third threshold (a predetermined value) (step S17). If D ≥ the third threshold, it can be determined that the first flow control valve (5a) is open and the working fluid in the flow path (6b) has flowed into the working fluid tank (10), so the vehicle-mounted controller (15) records the opening degree indicator value Sa (step S38) and terminates the calibration. On the other hand, if D < the first threshold, it can be determined that the first flow control valve (5a) is still closed, so the vehicle-mounted controller (15) returns to step S34. Additionally, the third threshold is pre-set to a value corresponding to the difference between the set pressure of the relief valve (11) and the pressure of the working fluid tank (10) (i.e., atmospheric pressure).

[0051] (Calibration of the third flow control valve (5c))

[0052] FIG. 7 is a flowchart showing the calibration procedure of the third flow control valve (5c) (first valve) according to the second embodiment. When the calibration process of the third flow control valve (5c) is initiated, first, the vehicle-mounted controller (15) outputs an opening degree indicator value to close the third flow control valve (5c) to block the flow path (6a) and the flow path (6b) (step S41). Next, the vehicle-mounted controller (15) outputs an opening degree indicator value to open the first flow control valve (direction control valve) (5a) by displacement to position B to open the flow path (6a) and the flow path (6b) (step S42). When the first flow control valve (5a) is opened and the flow path (6a) and the flow path (6b) are opened, the flow path (6a), the flow path (6b), and the flow path (6c) become tank pressure. Next, the vehicle-mounted controller (15) outputs an opening degree indicator value to close the first flow control valve (5a) to block the passage (6a) and the passage (6b) (step S43). When the first flow control valve (5a) is closed and the passage (6a) and the passage (6b) are blocked, the passage (6a) and the passage (6c) are maintained at tank pressure.

[0053] With Euro (6a) and Euro (6c) maintained at tank pressure, the vehicle-mounted controller (15) records the value P(n) input from the pressure sensor (8) in RAM (step S44). Next, the vehicle-mounted controller (15) adds a step increment s to the opening degree indicator value Sb output to the third flow control valve (5c) (step S45). Next, the vehicle-mounted controller (15) records the value P(n+1) input from the pressure sensor (8) after the opening degree indicator value of the third flow control valve (5c) has increased (step S46).

[0054] Next, the vehicle-mounted controller (15) calculates the absolute value D of the difference between P(n) and P(n+1) and compares it with the fourth threshold (a predetermined value) (step S47). If D ≥ the fourth threshold, it can be determined that the third flow control valve (5c) is open and the set pressure of the relief valve (11) is applied to the flow path (6b), so the vehicle-mounted controller (15) records the opening degree indicator value Sb (step S48) and terminates the calibration. On the other hand, if D < the fourth threshold, it can be determined that the third flow control valve (5c) is still in a closed state, so the vehicle-mounted controller (15) returns to step S44. In addition, the fourth threshold is pre-set to a value corresponding to the difference between the set pressure of the relief valve (11) and the pressure of the hydraulic fluid tank (10) (i.e., atmospheric pressure). Here, the third threshold and the fourth threshold may be the same value or different values.

[0055] According to the hydraulic drive system of the second embodiment configured in this manner, it can exhibit the same operational effects as the first embodiment.

[0056] The embodiments and variations of the present invention have been described above. Furthermore, the present invention is not limited to the embodiments or variations described above and includes various other variations. For example, the embodiments and variations described above are described in detail to facilitate understanding of the present invention and are not limited to having all the configurations described. Additionally, it is possible to substitute some of the configurations of the present embodiment with configurations of other embodiments, and it is also possible to add configurations of other embodiments to the configurations of the present embodiment. Furthermore, it is possible to add, delete, or substitute other configurations for some of the configurations of the present embodiment.

[0057] For example, although an embodiment in which the external device (16) is configured separately from the vehicle-mounted controller (15) has been described, a configuration in which the functions of the external device (16) are integrated into the vehicle-mounted controller (15) may also be adopted. Explanation of the symbols

[0058] 1: Underbody 2: Upper pivot body 3: Working device 3a: Boom 3b: female 3c: Bucket 4a: Boom cylinder (hydraulic actuator) 4b: Arm cylinder (hydraulic actuator) 4c: Bucket cylinder (hydraulic actuator) 5a: First flow control valve (direction control valve / first valve / second valve) 5b: Second flow control valve (load holding valve / second valve) 5c: Third flow control valve (flow control valve / first valve) 5d: 4th flow control valve 6, 6a, 6b, 6c: Euro 8: Pressure sensor 9: Hydraulic pump 10: Hydraulic fluid tank 11: Relief valve 12: Engine 15: Vehicle-mounted controller (control unit / first controller) 16: External device (second controller) 20: Communication line 100: Hydraulic Shovel

Claims

Claim 1 A hydraulic drive system of a work machine comprising: a hydraulic pump; a hydraulic actuator operated by hydraulic fluid discharged from the hydraulic pump; a first valve provided between the hydraulic pump and the hydraulic actuator to control the flow rate of hydraulic fluid supplied from the hydraulic pump to the hydraulic actuator; a second valve provided between the hydraulic actuator and the first valve to control the flow rate of hydraulic fluid supplied from the first valve to the hydraulic actuator; and a control device that controls the first valve and the second valve by an opening degree command value; wherein the control device comprises a pressure sensor that detects the pressure of the fluid path between the first valve and the second valve and an input device; and wherein, when a signal requesting calibration of the first valve or the second valve is input by the input device, the control device closes the valve to be calibrated among the first valve or the second valve and opens the valve not to be calibrated so that the fluid path is maintained at a predetermined pressure, and then closes the valve not to be calibrated, and the valve to be calibrated A hydraulic drive system characterized by increasing the opening degree command value of the valve to open it, recording the opening degree command value when the amount of change in the pressure of the fluid path detected by the pressure sensor exceeds a predetermined value, and setting the valve to be calibrated to be controlled based on the recorded opening degree command value. Claim 2 A hydraulic drive system according to claim 1, wherein the first valve is a direction control valve that controls the operating direction of the hydraulic actuator, and the second valve is a load maintaining valve that maintains the load of the hydraulic actuator. Claim 3 A hydraulic drive system according to paragraph 2, wherein the control device comprises a first controller provided in the work machine and a second controller provided in an external device separate from the work machine, which instructs the first controller to perform calibration processing of the direction control valve and the load holding valve. Claim 4 A hydraulic drive system according to claim 1, wherein the first valve is a flow control valve that controls the flow rate of hydraulic fluid, and the second valve is a direction control valve that controls the operating direction of the hydraulic actuator. Claim 5 A hydraulic drive system according to claim 4, wherein the control device comprises a first controller provided in the work machine and a second controller provided in an external device separate from the work machine, which instructs the first controller to perform calibration processing of the flow control valve and the direction control valve.

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