Hydraulic drive device

Abstract

Provided is a hydraulic drive device capable of suppressing an increase in the number of components. A hydraulic drive device is provided with: a hydraulic pump that is connected to a pump passage and discharges a working fluid to the pump passage; a first hydraulic circuit connected to a first passage connected to the pump passage; a second hydraulic circuit connected to a second passage connected to the pump passage; and a flow control valve interposed between the pump passage and the first passage, the flow control valve changing a first opening degree, which is an opening degree between the pump passage and the first passage, in accordance with a control signal. The flow control valve is further connected with the tank and opens and closes the pump passage and the tank according to a control signal.

Description

Technical Field

[0001] The invention relates to a hydraulic drive device for supplying working fluid to two hydraulic circuits. Background Art

[0002] In practice, a single pump system is provided in which the hydraulic source of the travel motor and the loading and unloading actuator of the construction machinery is a single pump. As a hydraulic drive device of the single pump system, for example, a hydraulic circuit such as Patent Document 1 is known. In the hydraulic circuit of Patent Document 1, the pump is connected to the travel motor and the loading and unloading actuator via a first pump line and a second pump line, respectively. A priority valve is provided on the second pump line. The supply pressure of the travel motor acts on the priority valve. Therefore, when the supply pressure of the travel motor increases, the priority valve reduces the opening of the second pump line. As a result, the pressure oil flows to the travel motor preferentially.

[0003] Prior art literature: Patent Literature: Patent document 1: Japanese Patent Application Publication No. 2020-026828. Summary of the invention

[0004] Problems to be solved by the invention: The hydraulic circuit of Patent Document 1 is also provided with an unloading valve to put the pump into an unloading state. Various valves of the hydraulic circuit including the unloading valve are formed by inserting a valve core into an insertion hole formed on a valve block of a multi-control valve, for example. Therefore, as the number of valves increases, the number of components of the hydraulic drive device provided in the hydraulic circuit increases.

[0005] Therefore, an object of the present invention is to provide a hydraulic drive device that can suppress an increase in the number of components.

[0006] Means of solving the problem: The hydraulic drive device of the present invention comprises: a hydraulic pump connected to a pump passage to discharge working fluid into the pump passage; a first hydraulic circuit connected to a first passage connected to the pump passage; a second hydraulic circuit connected to a second passage connected to the pump passage; and a flow control valve disposed between the pump passage and the first passage to change the opening between the pump passage and the first passage, i.e., the first opening, according to a control signal; the flow control valve is also connected to a tank to open and close the pump passage and the tank according to a control signal.

[0007] According to the present invention, the flow control valve changes the first opening degree, which is the opening degree between the pump passage and the first passage, according to the control signal. Therefore, the flow control valve can make the working fluid flow into the second hydraulic circuit preferentially by reducing the first opening degree according to the control signal. In addition, the flow control valve is also connected to the tank, and opens and closes the pump passage and the tank according to the control signal. Therefore, the flow control valve can discharge the working fluid discharged from the hydraulic pump into the tank, that is, can put the hydraulic pump into an unloading state. Therefore, the flow control valve can realize both the functions of a priority valve that makes the working fluid flow into the second hydraulic circuit preferentially and an unloading valve that puts the hydraulic pump into an unloading state. Therefore, the increase in the number of components in the hydraulic drive device can be suppressed.

[0008] Effect of the invention: According to the present invention, an increase in the number of components in the hydraulic drive device can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a circuit diagram showing the structure of a hydraulic drive device according to a first embodiment of the present invention; Figure 2 The first opening and the second opening are shown relative to Figure 1 A graph showing a change in the stroke amount of a control valve core of a flow control valve provided in a hydraulic drive device; Figure 3 It is shown Figure 1 A block diagram of a control block of a control device provided in a hydraulic drive device; Figure 4 is a circuit diagram showing the structure of a hydraulic drive device according to a second embodiment of the present invention; Explanation of symbols: 1Hydraulic drive device 1A Hydraulic drive unit 2First travel motor 3 Second travel motor 4 Boom cylinder (loading and unloading actuator) 5 Stick cylinder (loading and unloading actuator) 6 Bucket cylinder (loading and unloading actuator) 11Hydraulic pump 12 Travel system hydraulic circuit 13Hydraulic circuit of loading and unloading system 14Flow control valve 14a control valve core 14A flow control valve 14Aa control valve core 15 Discharge pressure sensor 16 Driving side pressure sensor (first pressure sensor) 20 Control device 25 Pump access 26 Driving side passage (first passage, second passage) 27 Loading and unloading side passage (second passage, first passage) 28 cans 31 First travel directional control valve 32 Second travel directional control valve 41 Directional control valve for boom (direction control valve for loading and unloading) 42 Directional control valve for bucket arm (direction control valve for loading and unloading) 43 Directional control valve for bucket (directional control valve for loading and unloading). DETAILED DESCRIPTION

[0010] Hereinafter, the hydraulic drive device 1, 1A of the first and second embodiments of the present invention will be described with reference to the above-mentioned drawings. In addition, the directional concept used in the following description is used only for the convenience of description, and does not limit the structural orientation of the invention to the direction. In addition, the hydraulic drive device 1, 1A described below is only an embodiment of the present invention. Therefore, the present invention is not limited to the embodiment, and additions, deletions, and changes can be made within the scope of the main purpose of the invention.

[0011] [First embodiment] Figure 1 The hydraulic drive device 1 of the first embodiment shown is equipped in a work vehicle (not shown) including travel motors 2, 3 and loading and unloading actuators 4 to 6. The work vehicle is, for example, a construction vehicle such as a hydraulic excavator and a hydraulic crane, and an industrial vehicle such as a lift. In this embodiment, the hydraulic drive device 1 is equipped in a hydraulic excavator as an example of a work vehicle. The same is true for the hydraulic drive device 1A of the second embodiment. The hydraulic excavator is equipped with a vehicle body and a work machine in addition to the hydraulic drive device 1.

[0012] The vehicle body is, for example, a track-type device, including a pair of left and right tracks (not shown) and a pair of left and right travel motors 2, 3. The vehicle body travels by operating the pair of left and right tracks. In addition, the vehicle body can also be a wheeled device, as long as it is a travelable device. The travel motors 2, 3 are hydraulic motors and drive the left and right tracks respectively. In more detail, the travel motors 2, 3 have two supply and discharge ports 2a, 2b, 3a, 3b respectively. The travel motors 2, 3 rotate forward when the working fluid is supplied to the supply and discharge ports 2a, 3a on one side, and reverse when the working fluid is supplied to the supply and discharge ports 2b, 3b on the other side.

[0013] The working machine is rotatably mounted on the vehicle body. The working machine includes a boom, an arm, a bucket (none of which is shown in the figure) and a plurality of hydraulic cylinders 4 to 6. The hydraulic cylinders 4 to 6 as an example of a loading and unloading actuator are, for example, a boom cylinder 4, an arm cylinder 5 and a bucket cylinder 6, which are respectively mounted on the boom, the arm and the bucket. The working machine moves the boom, the arm and the bucket respectively by extending and retracting the three hydraulic cylinders 4 to 6. Thus, the working machine can perform various operations.

[0014] <Hydraulic drive unit> The hydraulic drive device 1 includes a hydraulic pump 11, a travel system hydraulic circuit 12, a loading and unloading system hydraulic circuit 13, a flow control valve 14, a discharge pressure sensor 15, a travel side pressure sensor 16, and a control device 20. In more detail, the hydraulic drive device 1 also includes loading and unloading side pressure sensors 17 to 19, a travel system operating device 21, and a loading and unloading system operating device 22. In addition, in the hydraulic drive device 1, the travel system hydraulic circuit 12, the loading and unloading system hydraulic circuit 13, and the flow control valve 14 constitute a multi-control valve (not shown).

[0015] The hydraulic drive device 1 is a so-called single pump system, and a hydraulic pump 11 supplies working fluid to the travel motors 2, 3 and three hydraulic cylinders 4 to 6. The hydraulic drive device 1 supplies working fluid to the first travel motor 2 and the second travel motor 3, respectively, to operate the crawlers corresponding to the travel motors 2 and 3. Thus, the hydraulic drive device 1 can drive the hydraulic excavator. Furthermore, the hydraulic drive device 1 supplies working fluid to the hydraulic cylinders 4 to 6, thereby operating the corresponding booms, arms and buckets. Thus, the hydraulic drive device 1 can enable the hydraulic excavator to perform various operations.

[0016] <Hydraulic pump> The hydraulic pump 11 discharges working fluid. To explain in more detail, the hydraulic pump 11 is connected to a driving source (such as an engine and a motor) not shown in the figure. The hydraulic pump 11 is connected to a pump passage 25. The hydraulic pump 11 is driven to rotate by the driving source, thereby discharging working fluid to the pump passage 25. The pump passage 25 is connected to a travel side passage 26 and a loading and unloading side passage 27, respectively. In the present embodiment, the hydraulic pump 11 is a variable capacity pump.

[0017] <Travel system hydraulic circuit> The travel hydraulic circuit 12 as an example of the first hydraulic circuit is connected to the travel side passage 26. The travel side passage 26 as an example of the first passage is connected to the pump passage 25. In addition, the travel hydraulic circuit 12 is connected to the two travel motors 2 and 3. The travel hydraulic circuit 12 controls the flow of the hydraulic fluid to the travel motors 2 and 3 by adjusting the opening between the travel motors 2 and 3 and the hydraulic pump 11. In more detail, a travel command signal (in this embodiment, the first travel command signal and the second travel command signal) as an example of the first signal is input to the travel hydraulic circuit 12. And the travel hydraulic circuit 12 supplies the hydraulic fluid that flows (in this embodiment, the flow direction and flow rate) according to the input first travel command signal and second travel command signal to the first travel motor 2 and the second travel motor 3, respectively. The travel hydraulic circuit 12 includes a first travel directional control valve 31 and a second travel directional control valve 32. In addition, the travel hydraulic circuit 12 also includes a first pressure compensation valve 33 and a second pressure compensation valve 34.

[0018] The first travel directional control valve 31 controls the flow of the working fluid to the first travel motor 2. To explain in more detail, the first travel directional control valve 31 is connected to the travel side passage 26, the tank 28, and the two supply and discharge ports 2a and 2b of the first travel motor 2. The first travel directional control valve 31 switches the connection destinations of the supply and discharge ports 2a and 2b to the travel side passage 26 and the tank 28, respectively, according to the input first travel command signal. Thus, the first travel directional control valve 31 rotates the first travel motor 2 forward and reverse according to the first travel command signal. In addition, the first travel directional control valve 31 changes the opening according to the input first travel command signal. Therefore, the working fluid of the direction and flow rate corresponding to the first travel command signal is supplied from the first travel directional control valve 31 to the first travel motor 2. Thus, the first travel directional control valve 31 rotates the first travel motor 2 at a speed corresponding to the first travel command signal. In the present embodiment, the first travel directional control valve 31 is an electrically controlled directional control valve, and constitutes a multi-control valve together with other control valves 14 , 32 , 41 to 43 and compensation valves 33 and 34 described in detail later.

[0019] The second travel directional control valve 32 controls the flow of the working fluid to the second travel motor 3. To explain in more detail, the second travel directional control valve 32 is connected to the travel side passage 26 in parallel with the first travel directional control valve 31. In addition, the second travel directional control valve 32 is connected to the tank 28 and the two supply and discharge ports 3a and 3b of the second travel motor 3. The second travel directional control valve 32 switches the connection destinations of the supply and discharge ports 3a and 3b to the travel side passage 26 and the tank 28, respectively, according to the input second travel command signal. Thus, the second travel directional control valve 32 rotates the second travel motor 3 forward and reverse according to the second travel command signal. In addition, the second travel directional control valve 32 changes the opening according to the second travel command signal. Thus, the second travel directional control valve 32 rotates the second travel motor 3 at a speed corresponding to the second travel command signal. In the present embodiment, the second travel directional control valve 32 is an electrically controlled directional control valve.

[0020] The first pressure compensation valve 33 maintains the pressure difference between the front and rear of the first travel directional control valve 31 at a predetermined pressure. Thus, the flow rate of the hydraulic fluid supplied to the first travel motor 2 is controlled to a flow rate corresponding to the opening of the first travel directional control valve 31. In addition, the second pressure compensation valve 34 maintains the pressure difference between the front and rear of the second travel directional control valve 32 at a predetermined pressure. Thus, the flow rate of the hydraulic fluid supplied to the second travel motor 3 is controlled to a flow rate corresponding to the opening of the second travel directional control valve 32.

[0021] <Hydraulic circuit of loading and unloading system> The loading and unloading system hydraulic circuit 13, which is an example of a second hydraulic circuit, is connected to the loading and unloading side passage 27. The loading and unloading side passage 27, which is an example of a second passage, is connected to the pump passage 25. In addition, the loading and unloading system hydraulic circuit 13 is connected to three hydraulic cylinders 4 to 6. The loading and unloading system hydraulic circuit 13 supplies working fluid to the three hydraulic cylinders 4 to 6, respectively. The loading and unloading system hydraulic circuit 13 controls the flow of working fluid to each hydraulic cylinder 4 to 6 by adjusting the opening between each hydraulic cylinder 4 to 6 and the hydraulic pump 11 according to the loading and unloading operation signal (in this embodiment, the boom command signal, the dipper arm command signal, and the bucket command signal described in detail later). In more detail, the loading and unloading system hydraulic circuit 13 supplies working fluid that flows (in this embodiment, the flow direction and flow rate) in accordance with the input loading and unloading operation signal to the three hydraulic cylinders 4 to 6. The loading and unloading system hydraulic circuit 13 includes a plurality of loading and unloading directional control valves 41 to 43. In the present embodiment, the loading and unloading system hydraulic circuit 13 includes three loading and unloading directional control valves 41 to 43 , for example, a boom directional control valve 41 , an arm directional control valve 42 , and a bucket directional control valve 43 .

[0022] Each loading and unloading directional control valve 41 to 43 corresponds to each hydraulic cylinder 4 to 6. Moreover, each loading and unloading directional control valve 41 to 43 controls the flow rate of the working fluid supplied to the hydraulic cylinder 4 to 6. That is, the boom directional control valve 41 controls the flow of the working fluid to the boom cylinder 4. The arm directional control valve 42 controls the flow of the working fluid to the arm cylinder 5. The bucket directional control valve 43 controls the flow of the working fluid to the bucket cylinder 6. Each loading and unloading directional control valve 41 to 43 is connected to the loading and unloading side passage 27 in parallel with each other.

[0023] To explain in more detail, each loading and unloading directional control valve 41-43 is connected to the tank 28, the rod side ports 4a, 5a, 6a and the head side ports 4b, 5b, 6b of the corresponding hydraulic cylinders 4-6. Each loading and unloading directional control valve 41-43 switches the connection destinations of the rod side ports 4a-6a and the head side ports 4b-6b to the loading and unloading side passage 27 and the tank 28. Thus, each loading and unloading directional control valve 41-43 causes the corresponding hydraulic cylinder 4-6 to expand and contract according to each loading and unloading operation signal. In addition, each loading and unloading directional control valve 41-43 changes the opening degree according to the loading and unloading operation signal. Therefore, the working fluid of the direction and flow rate corresponding to each command signal is supplied from each loading and unloading directional control valve 41-43 to the corresponding hydraulic cylinder 4-6. Thus, the loading and unloading directional control valve 41-43 can cause the corresponding hydraulic cylinder 4-6 to expand and contract at a speed corresponding to each loading and unloading command signal. In addition, the loading and unloading directional control valves 41 to 43 are also electrically controlled directional control valves in the present embodiment.

[0024] <Flow Control Valve> The flow control valve 14 is an electrically controlled valve. The flow control valve 14 is, for example, an electrically controlled slide valve. The flow control valve 14 is interposed between the pump passage 25 and the travel side passage 26. In other words, the pump passage 25 is connected to the travel side passage 26 via the flow control valve 14. The flow control valve 14 changes the opening between the pump passage 25 and the travel side passage 26, i.e., the first opening, according to the input control signal. That is, the flow control valve 14 throttles the flow of the working fluid flowing from the pump passage 25 to the travel side passage 26 according to the input control signal. As a result, the working fluid is preferentially supplied to the loading and unloading system hydraulic circuit 13.

[0025] The flow control valve 14 is also connected to the tank 28. The flow control valve 14 opens and closes between the pump passage 25 and the tank 28 according to the control signal. In more detail, the flow control valve 14 is connected to the tank 28 via the tank passage 29. Moreover, the flow control valve 14 opens and closes between the pump passage 25 and the tank passage 29 according to the control signal. Furthermore, the flow control valve 14 changes the opening degree between the pump passage 25 and the tank 28 (in the present embodiment, between the pump passage 25 and the tank passage 29), that is, the second opening degree, according to the control signal.

[0026] To further explain in detail, the flow control valve 14 is constructed as follows. That is, the flow control valve 14 has a control valve core 14a. The control valve core 14a is slidably inserted into the insertion hole formed on the valve block of the multi-control valve not shown. Moreover, the control valve core 14a is stroked according to the control signal. To explain in more detail, the flow control valve 14 is, for example, an electrically controlled flow control slide valve, and the control valve core 14a is stroked according to the pilot pressure output by the electromagnetic proportional valve according to the control signal. Moreover, the control valve core 14a switches the position to the first control position A1 and the second control position A2 through the stroke. In this embodiment, the control valve core 14a switches the position to the third control position A3 in addition to the first control position A1 and the second control position A2 through the stroke. In addition, the control valve core 14a is located at the first control position A1, for example, in the neutral state. Moreover, the control valve core 14a moves from the first control position A1 to the third control position A3 through the stroke, and then moves from the third control position A3 to the second control position A2.

[0027] The first to third control positions A1 to A3 are described in detail below. In the first control position A1, Figure 2 As shown, the pump passage 25 and the travel side passage 26 are opened. In the present embodiment, the first opening is the maximum opening at the first control position A1. Moreover, at the first control position A1, the pump passage 25 and the tank passage 29 are also opened. Thus, at the first control position A1, the working fluid ejected from the hydraulic pump 11 is discharged to the tank 28, and the hydraulic pump 11 is in an unloaded state. In addition, at the first control position A1, the second opening is reduced according to the stroke amount of the control valve core 14a. To explain in more detail, at the first control position A1, the second opening is reduced from the unloading opening (in the present embodiment, the maximum opening under the second opening) to zero (i.e., fully closed) according to the stroke amount of the control valve core 14a. By reducing the second opening to adjust the flow rate (bleed-off flow; bleed flow) discharged to the tank 28, the flow rate of the working fluid flowing in the travel side passage 26 can be adjusted.

[0028] In the second control position A2, the pump passage 25 and the tank 28 are closed. In the present embodiment, in the second control position A2, the second opening is fully closed. Also, in the second control position A2, the pump passage 25 and the travel side passage 26 are opened. Thus, in the second control position A2, the working fluid discharged from the hydraulic pump 11 can be introduced into the travel system hydraulic circuit 12 via the travel side passage 26. Also, in the second control position A2, the first opening is reduced according to the stroke amount of the control valve core 14a. Thus, the flow control valve 14 limits the flow rate of the working fluid introduced into the travel side passage 26, and the working fluid preferentially flows into the loading and unloading side passage 27. That is, the flow control valve 14 allows the working fluid to preferentially flow into the loading and unloading system hydraulic circuit 13. Also, the flow control valve 14 reduces the first opening according to the stroke amount of the control valve core 14a, thereby adjusting the flow rate flowing through the travel system hydraulic circuit 12.

[0029] In addition, in the present embodiment, the first opening is reduced from the maximum opening to the minimum opening. That is, when the control valve core 14a is in full stroke (that is, when the pump passage 25 and the tank 28 are closed), the first opening is maintained at the minimum opening. In the present embodiment, the minimum opening is a non-fully closed opening. Thus, even if the control valve core 14a is stuck in the full stroke state, the working fluid is supplied to the travel system hydraulic circuit 12.

[0030] In the third control position A3, the pump passage 25 and the tank 28 are closed. In the present embodiment, in the third control position A3, the second opening is fully closed. In addition, in the third control position A3, the pump passage 25 and the travel side passage 26 are opened. Thus, in the third control position A3, the hydraulic fluid discharged from the hydraulic pump 11 can be supplied to the travel system hydraulic circuit 12 via the travel side passage 26. In the present embodiment, the first opening is the maximum opening in the third control position A3, similarly to the first control position A1.

[0031] <Various sensors> The discharge pressure sensor 15 detects the hydraulic pressure of the working fluid discharged from the hydraulic pump 11, that is, the discharge pressure. In more detail, the discharge pressure sensor 15 is provided in the pump passage 25. That is, the discharge pressure sensor 15 is provided on the upstream side of the flow control valve 14. And the discharge pressure sensor 15 detects the hydraulic pressure of the working fluid flowing in the pump passage 25.

[0032] The travel side pressure sensor 16 as an example of the first pressure sensor detects the travel side supply pressure. The travel side supply pressure as an example of the first supply pressure is the hydraulic pressure of the working fluid flowing in the travel side passage 26. That is, the travel side pressure sensor 16 detects the hydraulic pressure of the working fluid supplied to the travel system hydraulic circuit 12. To explain in more detail, the travel side pressure sensor 16 is provided in the travel side passage 26. That is, the travel side pressure sensor 16 is provided on the downstream side of the flow control valve 14.

[0033] The loading and unloading side pressure sensors 17 to 19 correspond to the hydraulic cylinders 4 to 6. Moreover, the loading and unloading side pressure sensors 17 to 19 respectively detect the supply pressure to the corresponding hydraulic cylinders 4 to 6, that is, the loading and unloading side supply pressure. The loading and unloading side pressure sensors 17 to 19 are provided on the downstream side of each directional control valve 41 to 43. In the present embodiment, the loading and unloading side pressure sensors 17 to 19 are provided on the rod side ports 4a to 6a and the head side ports 4b to 6b of the hydraulic cylinders 4 to 6, respectively. Moreover, the loading and unloading side pressure sensors 17 to 19 detect the hydraulic pressure of the working fluid supplied to the rod side ports 4a to 6a and the head side ports 4b to 6b of the hydraulic cylinders 4 to 6.

[0034] <Travel system operating device> The travel system operating device 21 is a device used by the driver to operate the travel motors 2 and 3. The travel system operating device 21 includes, for example, travel pedals 21a and 21b as operating tools. The travel pedals 21a and 21b can be tilted respectively. The travel pedals 21a and 21b can be tilted in one direction and the other direction (for example, forward and backward) in a predetermined direction, for example. The travel system operating device 21 outputs a travel operation instruction corresponding to the operation direction and the operation amount (the tilting direction and the tilting amount in this embodiment). In addition, the operating tool provided by the travel system operating device 21 can be in other forms such as an operating lever, an operating panel, etc., and its form does not matter.

[0035] <Loading and unloading system operating device> The loading and unloading system operating device 22 is a device used by the driver to operate the accessory (in this embodiment, the bucket). To explain in more detail, the operating tools of the loading and unloading system operating device 22 include loading and unloading operating levers 22a and 22b. The loading and unloading operating levers 22a and 22b can be tilted respectively. In the present embodiment, the loading and unloading operating levers 22a and 22b can be tilted in the forward, backward, left and right directions, for example. The loading and unloading system operating device 22 outputs loading and unloading operation instructions corresponding to the operation direction and operation amount (the tilting direction and tilting amount in this embodiment). In addition, the operating tools of the loading and unloading system operating device 22 are not limited to the loading and unloading operating levers 22a and 22b, but can also be other forms such as an operating panel.

[0036] <Control device> The control device 20 controls the operation of the travel system hydraulic circuit 12. In more detail, the control device 20 obtains the travel operation command output from the travel system operating device 21. Then, the control device 20 controls the movement of each of the travel direction control valves 31 and 32 according to the travel operation command. In this embodiment, the control device 20 outputs the first and second travel command signals respectively according to the travel operation command. Then, the travel motors 2 and 3 rotate in the direction and rotation speed corresponding to the travel operation command, so that the hydraulic excavator moves in the direction and speed corresponding to the travel operation command.

[0037] Furthermore, the control device 20 controls the operation of the loading and unloading system hydraulic circuit 13. To explain in more detail, the control device 20 obtains the loading and unloading operation instructions output from the loading and unloading system operating device 22. Then, the control device 20 controls the movement of each of the loading and unloading directional control valves 41 to 43 (i.e., the position of each valve core 41a to 43a) according to the loading and unloading operation instructions. In the present embodiment, the control device 20 outputs a boom command signal, a dipper arm command signal, and a bucket command signal according to the loading and unloading operation instructions. Then, the hydraulic cylinders 4 to 6 extend and retract at a speed corresponding to the loading and unloading operation instructions. Thus, the bucket can be moved in a direction and at a speed corresponding to the loading and unloading operation instructions, so that the hydraulic excavator can perform the desired operation.

[0038] In addition, the control device 20 controls the opening of the flow control valve 14 by outputting a control signal to the flow control valve 14. In more detail, the control device 20 outputs a control signal according to the travel operation command and the loading and unloading operation command to make the control valve core 14a stroke. As a result, the control device 20 changes the position of the control valve core 14a, and changes the first opening and the second opening at each position A1 to A3. In addition, the control device 20 also outputs a control signal according to the hydraulic pressure detected by each pressure sensor 15 to 19, so that the working fluid of the flow rate corresponding to the travel operation command and the loading and unloading operation command is supplied to the travel system hydraulic circuit 12 and the loading and unloading system hydraulic circuit 13 with higher accuracy.

[0039] <About the operation of the hydraulic drive unit> In the hydraulic drive device 1, in the non-operation state, the control valve core 14a of the flow control valve 14 is located at the first control position A1. The non-operation state refers to a state in which the travel pedals 21a, 21b of the travel system operating device 21 and the loading and unloading operating levers 22a, 22b of the loading and unloading system operating device 22 are not operated. By the control valve core 14a being located at the first control position A1, the pump passage 25 is connected to the tank passage 29. That is, the pump passage 25 is connected to the tank 28. As a result, the working fluid ejected from the hydraulic pump 11 is discharged to the tank 28, and the hydraulic pump 11 is in the unloading state. In addition, in the first control position A1, the pump passage 25 is also connected to the travel side passage 26. As a result, in the unloading state, the pressure increase in the travel side passage 26 is suppressed.

[0040] In the hydraulic drive device 1, when the travel pedals 21a and 21b of the travel system operating device 21 are operated individually, the travel operation command is output from the travel system operating device 21. In the present embodiment, the individual operation means that the travel pedals 21a and 21b and the loading and unloading operating levers 22a and 22b are operated independently. In addition, the individual operation includes operating the travel pedals 21a and 21b and operating the loading and unloading operating levers 22a and 22b simultaneously. When the travel operation command is output, the control device 20 throttles the flow between the pump passage 25 and the tank passage 29 through the flow control valve 14 while opening the flow between the pump passage 25 and the travel side passage 26. In the present embodiment, the control device 20 outputs a control signal to make the control valve core 14a of the flow control valve 14 located at the first control position A1 or the third control position A3. On the other hand, the control device 20 closes the flow between the hydraulic pump 11 and the hydraulic cylinders 4 to 6 through the loading and unloading system hydraulic circuit 13. That is, the control device 20 closes the connection between the loading and unloading passage 27 and the hydraulic cylinders 4 to 6 via the loading and unloading directional control valves 41 to 43. In addition, the control device 20 opens the connection between the traveling passage 26 and the traveling motors 2 and 3 via the traveling hydraulic circuit 12.

[0041] More specifically, the control device 20 is as follows: Figure 3 As shown, the target flow of the travel motor supplied to each travel motor 2, 3 is calculated based on the travel operation instruction. Furthermore, the control device 20 calculates the second opening based on the pump discharge flow and the travel side target flow. Here, the pump discharge flow is the flow of the working fluid discharged from the hydraulic pump 11. The pump discharge flow is calculated based on the driving state of the hydraulic pump 11 or based on the discharge pressure. The pump discharge flow can be set in advance, and its calculation method and setting method are irrelevant. Furthermore, the travel side target flow, which is an example of the first target flow, is the total flow of the travel motor target flow supplied to each travel motor 2, 3, and is the flow that should flow into the travel side passage 26 (that is, should be supplied to the travel system hydraulic circuit 12).

[0042] To explain in more detail, the control device 20 makes the second opening zero (i.e., fully closed) when the pump discharge flow rate is the same as or smaller than the driving side target flow rate. On the other hand, when the pump discharge flow rate is larger than the driving side target flow rate, the control device 20 opens the second opening and discharges a portion of the working fluid in the pump passage 25 from the flow control valve 14 to the tank 28 (i.e., bleeds). In this way, the control device 20 makes the driving side actual flow rate the driving side target flow rate. The driving side actual flow rate, which is an example of the first actual flow rate, is the actual flow rate flowing in the driving side passage 26. In this embodiment, the control device 20 estimates the driving side actual flow rate based on the detected discharge pressure and the driving side supply pressure. Moreover, the control device 20 calculates the second opening degree so that the driving side actual flow rate becomes the driving side target flow rate based on the discharge pressure and the driving side supply pressure detected by the pressure sensors 15 and 16, the driving side actual flow rate, and the driving side target flow rate. The control device 20 changes the second opening degree of the flow control valve 14 by outputting a control signal corresponding to the calculated second opening degree. As a result, the hydraulic fluid is supplied to the travel-side target flow rate to the travel-system hydraulic circuit 12 .

[0043] Furthermore, the control device 20 outputs the first and second travel command signals corresponding to the target flow rates of the travel motors, respectively. Then, the first travel directional control valve 31 and the second travel directional control valve 32 control the flow of the hydraulic fluid relative to the travel motors 2 and 3 to the flow (flow direction and flow rate in this embodiment) corresponding to the travel operation command, respectively. In more detail, the control device 20 calculates the openings of the first and second travel directional control valves 31 and 32 according to the target flow rates of the travel motors 2 and 3, and the control device 20 outputs the first and second travel command signals corresponding to the calculated openings, respectively. In the travel system hydraulic circuit 12, the pressure difference between the front and rear of the two travel directional control valves 31 and 32 is maintained by the pressure compensation valves 33 and 34. Therefore, the hydraulic fluid of the flow rate corresponding to the opening of each travel directional control valve 31 and 32 is supplied to each travel motor 2 and 3. Therefore, the control device 20 can make the hydraulic excavator perform a travel action corresponding to the operation of the travel pedals 21a and 21b.

[0044] In the hydraulic drive device 1, when the loading and unloading operating levers 22a and 22b of the loading and unloading system operating device 22 are operated individually, the loading and unloading operation command is output from the loading and unloading system operating device 22. Then, the control device 20 throttles the flow between the pump passage 25 and the travel side passage 26 through the flow control valve 14, and closes the flow between the pump passage 25 and the tank passage 29. In more detail, the control device 20 moves the control valve core 14a to the second control position A2 by outputting a control signal. In the present embodiment, the control device 20 makes the control valve core 14a full stroke. Thus, the control device 20 makes the first opening degree the minimum opening degree, and makes the second opening degree zero (that is, fully closed). On the other hand, the control device 20 cuts off the flow of the working fluid in the travel system hydraulic circuit 12 by outputting the first travel operation signal and the second travel operation signal. That is, the control device 20 closes the flow between the hydraulic pump 11 and the travel motors 2 and 3 through the travel system hydraulic circuit 12. To explain in more detail, the control device 20 closes the travel side passage 26 and the travel motors 2 and 3 through the travel directional control valves 31 and 32. As a result, the total amount of the working fluid discharged from the hydraulic pump 11 can be supplied to the loading and unloading system hydraulic circuit 13. In addition, the control device 20 opens the loading and unloading side passage 27 and the hydraulic cylinders 4 to 6 through the loading and unloading system hydraulic circuit 13.

[0045] More specifically, the control device 20 is as follows: Figure 3 As shown, the target flow rate of loading and unloading supplied to each hydraulic cylinder 4 to 6 is calculated based on the loading and unloading operation command. In addition, the control device 20 estimates the flow rate of the working fluid supplied to each hydraulic cylinder 4 to 6 based on the detected discharge pressure and the supply pressure on each loading and unloading side. In more detail, the control device 20 estimates the actual flow rate on the loading and unloading side based on the front and rear pressures of each loading and unloading directional control valve 41 to 43, that is, the discharge pressure and the supply pressure on each loading and unloading side, as the flow rate of the working fluid supplied to each hydraulic cylinder 4 to 6. The actual flow rate on the loading and unloading side is the flow rate of the working fluid flowing in each loading and unloading directional control valve 41 to 43. The control device 20 calculates the opening of each loading and unloading directional control valve 41 to 43 in such a way that the estimated actual flow rate on the loading and unloading side becomes the target flow rate on loading and unloading. Moreover, the control device 20 outputs the boom command signal, the dipper arm command signal and the bucket command signal corresponding to each calculated opening. Therefore, the flow of the working fluid relative to the hydraulic cylinders 4 to 6 is controlled to flow (flow direction and flow rate in this embodiment) in accordance with the loading and unloading operation instructions by the loading and unloading directional control valves 41 to 43. Thus, the control device 20 can make the bucket perform actions in accordance with the operation of the loading and unloading operating levers 22a and 22b.

[0046] Furthermore, when the travel pedals 21a, 21b and the loading and unloading operating levers 22a, 22b are operated simultaneously, the control device 20 operates as follows. That is, the travel operation command is output from the travel system operating device 21, and the loading and unloading operation command is output from the loading and unloading system operating device 22. Then, the control device 20 closes the flow between the pump passage 25 and the tank passage 29 through the flow control valve 14, and also throttles the flow between the pump passage 25 and the travel side passage 26. In more detail, the control device 20 outputs a control signal to move the control valve core 14a to the second position. Thus, the control device 20 can supply the working fluid to the travel system hydraulic circuit 12 while preferentially supplying the working fluid to the loading and unloading system hydraulic circuit 13. Furthermore, the control device 20 opens the flow between the travel side passage 26 and the travel motors 2, 3 through the travel system hydraulic circuit 12, and also opens the flow between the loading and unloading side passage 27 and the hydraulic cylinders 4 to 6 through the loading and unloading system hydraulic circuit 13.

[0047] More specifically, the control device 20 is as follows: Figure 3 The control device 20 calculates the target flow rate of the travel motor based on the travel operation command. The control device 20 estimates the actual flow rate on the travel side based on the detected discharge pressure and the travel side supply pressure. The control device 20 calculates the first opening degree so that the actual flow rate on the travel side becomes the target flow rate on the travel side based on the discharge pressure and the travel side supply pressure detected by the pressure sensors 15 and 16, the actual flow rate on the travel side, and the target flow rate on the travel side.

[0048] Furthermore, in the present embodiment, the control device 20 outputs a control signal based on the loading and unloading target flow and the actual loading and unloading flow of each hydraulic cylinder 4 to 6 in addition to the actual flow rate on the driving side and the target flow rate on the driving side. To explain in more detail, the control device 20 calculates the loading and unloading target flow of each hydraulic cylinder 4 to 6 based on the loading and unloading operation instructions. Furthermore, the control device 20 estimates the actual loading and unloading flow of each hydraulic cylinder 4 to 6 based on the detected discharge pressure and the supply pressure on each loading and unloading side. In addition, the actual loading and unloading flow is the flow actually supplied to each hydraulic cylinder 4 to 6. The control device 20 changes the first opening of the flow control valve 14 in such a manner that the actual flow rate on the driving side becomes the target flow rate on the driving side, and each loading and unloading target flow rate is consistent with each loading and unloading actual flow rate. In the present embodiment, the total flow of the driving side target flow and each loading and unloading target flow rate is discharged from the hydraulic pump 11. Therefore, the control device 20 controls the first opening of the flow control valve 14 so that the actual flow rate on the travel side becomes the target flow rate on the travel side and each loading and unloading target flow rate coincides with each loading and unloading actual flow rate, thereby supplying the desired flow rate to each hydraulic circuit 12, 13 with higher accuracy.

[0049] Furthermore, the control device 20 controls the travel system hydraulic circuit 12 as follows when the travel motors 2 and 3 are operated simultaneously. That is, the control device 20 calculates the opening of each travel directional control valve 31 and 32 based on the target flow rate of each travel motor 2 and 3. To explain in more detail, the front and rear pressure differences of each travel directional control valve 31 and 32 are maintained at a predetermined pressure by the pressure compensation valves 33 and 34, respectively, as described above. Therefore, the control device 20 controls the opening of each travel directional control valve 31 and 32 at the same ratio as the ratio of the target flow rate of each travel motor 2 and 3. As a result, the flow rate introduced into the travel system hydraulic circuit 12 is supplied to each travel motor 2 and 3 in a distribution amount corresponding to the target flow rate of each travel motor 2 and 3. Therefore, even when the travel motors 2 and 3 are operated simultaneously, the excavator can be driven in accordance with the operation of the travel pedals 21a and 21b.

[0050] In addition, when the control device 20 is operated simultaneously, the hydraulic circuit 13 of the loading and unloading system is controlled as follows. That is, the control device 20 outputs a boom command signal, a dipper arm command signal, and a bucket command signal corresponding to the loading and unloading target flow rate of each hydraulic cylinder 4 to 6, respectively. In more detail, the control device 20 controls the opening of each loading and unloading directional control valve 41 to 43 based on the loading and unloading target flow rate and the actual flow rate of each hydraulic cylinder 4 to 6. In the present embodiment, the control device 20 controls the opening of each loading and unloading directional control valve 41 to 43 in a form that the actual flow rate of each hydraulic cylinder 4 to 6 becomes each loading and unloading target flow rate. As a result, the control device 20 can supply the working fluid of the flow rate corresponding to the operation of the travel pedals 21a and 21b to each travel motor 2 and 3 with higher accuracy, and can supply the working fluid of the flow rate corresponding to the operation of the loading and unloading operating levers 22a and 22b to each hydraulic cylinder 4 to 6 with higher accuracy.

[0051] In the hydraulic drive device 1 of the first embodiment, the flow control valve 14 changes the opening between the pump passage 25 and the travel side passage 26, that is, the first opening, according to the control signal. Therefore, the flow control valve 14 can make the working fluid flow preferentially into the loading and unloading system hydraulic circuit 13 by reducing the first opening according to the control signal. In addition, the flow control valve 14 is also connected to the tank 28, and opens and closes between the pump passage 25 and the tank 28 according to the control signal. Therefore, the flow control valve 14 can discharge the working fluid discharged from the hydraulic pump 11 to the tank 28, that is, can make the hydraulic pump 11 unloaded. Therefore, the flow control valve 14 can realize both the functions of a priority valve that makes the working fluid flow preferentially into the loading and unloading system hydraulic circuit 13 and an unloading valve that makes the hydraulic pump unloaded. Therefore, the increase in the amount of processing work and the number of parts in the hydraulic drive device 1 can be suppressed. In more detail, the number of insertion holes can be reduced in the valve block of the multi-control valve inserted by the flow control valve 14, so the increase in the amount of processing work can be suppressed. Furthermore, since it is not necessary to provide an unloading valve on the valve block of the multi-control valve, it is possible to suppress an increase in the number of components.

[0052] In the hydraulic drive device 1 of the first embodiment, the flow control valve 14 changes the second opening between the pump passage 25 and the tank 28 according to the control signal. Therefore, the flow control valve 14 can control the flow rate of the working fluid flowing from the pump passage 25 to the tank 28 .

[0053] In addition, in the hydraulic drive device 1 of the first embodiment, the control valve core 14a is stroked according to the control signal to switch to the first control position A1 and the second control position A2. In the first control position A1, the pump passage 25 and the travel side passage 26 are opened, and the second opening is reduced according to the stroke amount of the control valve core 14a. In the second control position A2, the pump passage 25 and the tank 28 are closed, and the first opening is reduced according to the stroke amount of the control valve core 14a. Therefore, the control valve core 14a can realize the function of the unloading valve in the first control position A1, and realize the function of the priority valve in the second control position A2. Therefore, the flow control valve 14 realizes the functions of both the unloading valve and the priority valve by making the control valve core 14a.

[0054] In the hydraulic drive device 1 of the first embodiment, the first opening is set to the maximum opening in the third control position A3, and the pump passage 25 and the tank 28 are closed. Therefore, the control valve element 14a can introduce the total amount of the working fluid discharged by the hydraulic pump 11 into the travel system hydraulic circuit 12 in the third control position A3.

[0055] Furthermore, in the hydraulic drive device 1 of the first embodiment, the flow control valve 14 maintains the first opening at the minimum opening in a state of closing the pump passage 25 and the tank 28. Therefore, even if the flow control valve 14 is stuck at the minimum opening position, the working fluid flows into the travel side passage 26. Therefore, even if the flow control valve 14 is stuck at the minimum opening position, the working fluid can flow into the travel system hydraulic circuit 12.

[0056] Furthermore, in the hydraulic drive device 1 of the first embodiment, the control device 20 reduces the first opening of the flow control valve 14 to the minimum opening by outputting a control signal, and cuts off the flow of the working fluid in the travel system hydraulic circuit 12 by outputting each travel operation signal. Thus, the total amount of the working fluid from the hydraulic pump 11 can flow in the direction of the loading and unloading system hydraulic circuit 13.

[0057] In addition, in the hydraulic drive device 1 of the first embodiment, the loading and unloading system hydraulic circuit 13 controls the flow of the working fluid to each hydraulic cylinder 4 to 6 by adjusting the opening between each hydraulic cylinder 4 to 6 and the hydraulic pump 11. Therefore, the flow control valve 14 can make the working fluid flow into each hydraulic cylinder 4 to 6 preferentially by reducing the first opening according to the control signal. In addition, the travel system hydraulic circuit 12 controls the flow of the working fluid to the travel motors 2 and 3 by adjusting the opening between the travel motors 2 and 3 and the hydraulic pump 11. Therefore, the flow control valve 14 can make the working fluid flow into the travel motors 2 and 3 by opening the second opening according to the control signal.

[0058] [Second Embodiment] Figure 4 The hydraulic drive device 1A of the second embodiment shown has a similar structure to the hydraulic drive device 1 of the first embodiment. Therefore, the structure of the hydraulic drive device 1A of the second embodiment will mainly be described with respect to the differences from the hydraulic drive device 1 of the first embodiment, and the same structures are given the same reference numerals and description thereof will be omitted.

[0059] The hydraulic drive device 1A of the second embodiment includes a hydraulic pump 11, a travel system hydraulic circuit 12, a loading and unloading system hydraulic circuit 13, a flow control valve 14A, a discharge pressure sensor 15, a travel side pressure sensor 16, and a control device 20. In further detail, the hydraulic drive device 1 also includes loading and unloading side pressure sensors 17 to 19, a travel system operating device 21, and a loading and unloading system operating device 22. In addition, in this embodiment, the loading and unloading system hydraulic circuit 13 is an example of a first hydraulic circuit, and the travel system hydraulic circuit 12 is an example of a second hydraulic circuit. That is, the loading and unloading operation signal corresponds to the first signal.

[0060] <Flow Control Valve> The flow control valve 14A is an electrically controlled valve. The flow control valve 14 is, for example, an electrically controlled slide valve. The flow control valve 14A is interposed between the loading and unloading side passage 27 and the pump passage 25, which are an example of a first passage. In other words, the pump passage 25 is connected to the loading and unloading side passage 27 via the flow control valve 14A. The flow control valve 14 changes the first opening according to an input control signal. In the present embodiment, the first opening is the opening between the pump passage 25 and the loading and unloading side passage 27. Therefore, the flow control valve 14A throttles the flow of the working fluid flowing in the loading and unloading side passage 27 according to the input control signal. As a result, the working fluid is preferentially supplied to the travel system hydraulic circuit 12.

[0061] The flow control valve 14A is configured similarly to the flow control valve 14 of the first embodiment. That is, the flow control valve 14A is also connected to the tank 28, and opens and closes between the pump passage 25 and the tank passage 29 according to the control signal. The flow control valve 14 changes the second opening according to the control signal. The flow control valve 14A is, for example, an electrically controlled flow control slide valve, and has a control valve core 14Aa that has a stroke according to the control signal. The control valve core 14Aa is configured similarly to the control valve core 14a of the first embodiment. That is, the control valve core 14Aa switches the position to the first to third control positions A1 to A3 respectively by the stroke.

[0062] The first to third control positions A1 to A3 are described in detail below. In the first control position A1, the pump passage 25 and the loading and unloading passage 27 are opened in the same manner as in the first embodiment. Thus, in the first control position A1, the hydraulic fluid discharged from the hydraulic pump 11 is discharged to the tank 28, and the hydraulic pump is in an unloaded state. In the first control position, the second opening is reduced according to the stroke amount of the control valve core 14a. By reducing the second opening, the flow rate (drainage flow rate) discharged to the tank 28 can be adjusted, and the flow rate of the hydraulic fluid flowing in the loading and unloading passage 27 can be adjusted.

[0063] In the second control position A2, the pump passage 25 and the tank 28 are closed as in the first embodiment (fully closed in the present embodiment). On the other hand, in the second control position A2, the first opening is reduced according to the stroke amount of the control valve core 14a. As a result, the flow control valve 14 limits the flow rate of the working fluid introduced into the loading and unloading side passage 27, and the working fluid preferentially flows into the travel side passage 26 as an example of the second passage. That is, the flow control valve 14 preferentially supplies the working fluid to the travel system hydraulic circuit 12. In addition, the first opening is changed from the maximum opening to the minimum opening which is not fully closed as in the first embodiment.

[0064] In the third control position A3, the first opening is the maximum opening, and the second opening is fully closed. Thus, in the third control position A3, the hydraulic fluid discharged from the hydraulic pump 11 can be supplied to the loading and unloading system hydraulic circuit 13 via the loading and unloading side passage 27. In this embodiment, the first opening is the maximum opening in the third control position A3, similar to the first control position A1.

[0065] <About the operation of the hydraulic drive unit> In the hydraulic drive device 1 , the control valve element 14 a is located at the first control position A1 in the non-operation state. Therefore, the hydraulic fluid discharged from the hydraulic pump 11 can be discharged to the tank 28 , that is, the hydraulic pump 11 can be placed in the unloaded state.

[0066] In the hydraulic drive device 1A, when the travel pedals 21a and 21b of the travel system operating device 21 are operated individually, the control device 20 operates as follows based on the travel operation command. That is, the control device 20 outputs a control signal to make the control valve core 14a full stroke and located at the second control position A2. In addition, the control device 20 closes the connection between the hydraulic pump 11 and the hydraulic cylinders 4 to 6 through the loading and unloading system hydraulic circuit 13, and opens the connection between the travel side passage 26 and the travel motors 2 and 3 according to the travel system hydraulic circuit 12. At this time, the control device 20 calculates the target flow rate of each travel motor based on the travel operation command, and outputs the first and second travel command signals corresponding to the target flow rate of each travel motor. As a result, the opening of each travel directional control valve 31 and 32 is controlled to an opening corresponding to the target flow rate of each travel motor. The hydraulic drive device 1A also maintains the front and rear pressure difference of each of the two travel directional control valves 31 and 32 through the pressure compensation valves 33 and 34. Therefore, by controlling the opening of each of the travel directional control valves 31 and 32 to an opening corresponding to the target flow rate of each travel motor, the hydraulic fluid of the flow rate corresponding to the opening of each travel directional control valve 31 and 32 is supplied to each travel motor 2 and 3. Therefore, the control device 20 can make the hydraulic excavator perform a travel action corresponding to the operation of the travel pedals 21a and 21b.

[0067] Furthermore, when the loading and unloading operating levers 22a and 22b of the loading and unloading system operating device 22 are operated individually, the control device 20 operates as follows based on the loading and unloading operation instructions. That is, the control device 20 moves the control valve core 14Aa to the first control position A1 or the third control position A3 by outputting a control signal. That is, the control device 20 controls the second opening by causing the control valve core 14Aa to stroke according to the pump discharge flow rate and the loading and unloading side target flow rate. Thus, the total flow rate can be supplied to the loading and unloading system hydraulic circuit 13 even when the total flow rate of each loading and unloading target flow rate is less than the pump discharge flow rate. Furthermore, the control device 20 closes the connection between the hydraulic pump 11 and the travel motors 2 and 3 through the travel system hydraulic circuit 12. Thus, the working fluid discharged from the hydraulic pump 11 is supplied to the loading and unloading system hydraulic circuit 13. In addition, the control device 20 opens the connection between the loading and unloading side passage 27 and the hydraulic cylinders 4 to 6 through the loading and unloading system hydraulic circuit 13. At this time, the control device 20 calculates the target flow rate of loading and unloading of each hydraulic cylinder 4 to 6 based on the loading and unloading operation command, and estimates the actual flow rate on the loading and unloading side of each hydraulic cylinder 4 to 6 in the same way as in the first embodiment. In addition, the control device 20 calculates the opening of each loading and unloading directional control valve 41 to 43 in such a way that the estimated actual flow rate on each loading and unloading side becomes the target flow rate of loading and unloading. Moreover, the control device 20 outputs the boom command signal, the dipper arm command signal and the bucket command signal corresponding to each calculated opening. Then, the flow of the working fluid relative to the hydraulic cylinder 4 to 6 is controlled to a flow corresponding to the loading and unloading operation command through each loading and unloading directional control valve 41 to 43. As a result, the control device 20 can make the bucket perform an action corresponding to the operation of the loading and unloading operating levers 22a and 22b.

[0068] In addition, when the travel pedals 21a, 21b and the loading and unloading operating levers 22a, 22b are operated simultaneously, the control device 20 operates as follows based on the travel operation command and the loading and unloading operation command. That is, the control device 20 moves the control valve core 14a to the third control position A3 by outputting a control signal. Moreover, the control device 20 controls the first opening to an opening corresponding to the loading and unloading side supply pressure detected by the pressure sensors 17 to 19. Thus, the control device 20 supplies working fluid to the loading and unloading system hydraulic circuit 13 while preferentially supplying working fluid to the travel system hydraulic circuit 12. In addition, the control device 20 opens the travel side passage 26 and the travel motors 2 and 3 through the travel system hydraulic circuit 12, and also opens the loading and unloading side passage 27 and the hydraulic cylinders 4 to 6 through the loading and unloading system hydraulic circuit 13.

[0069] Furthermore, the control device 20 controls the travel system hydraulic circuit 12 as follows. That is, the control device 20 calculates the opening of each travel directional control valve 31, 32 based on the target flow rate of each travel motor 2, 3. As described above, the front and rear pressure differences of each travel directional control valve 31, 32 are respectively maintained at a specified pressure by the pressure compensation valves 33, 34. Therefore, the control device 20 supplies the flow introduced into the travel system hydraulic circuit 12 to each travel motor 2, 3 in a distribution amount corresponding to the target flow rate of each travel motor 2, 3 by outputting the first and second travel command signals corresponding to the calculated openings respectively. In addition, the control device 20 controls the loading and unloading system hydraulic circuit 13 as follows. That is, the control device 20 calculates the opening of each loading and unloading directional control valve 41~43 based on the loading and unloading operation command, and outputs each loading and unloading command signal according to the calculated opening. Thus, the control device 20 can supply the hydraulic fluid at a flow rate corresponding to the operation of the travel pedals 21a and 21b to each travel motor 2 and 3, and can supply the hydraulic fluid at a flow rate corresponding to the operation of the loading and unloading operating levers 22a and 22b to each hydraulic cylinder 4 to 6. Thus, even when the operation is performed simultaneously, the excavator can be driven in accordance with the operation of the travel pedals 21a and 21b. In addition, the bucket can be moved in accordance with the operation of the loading and unloading operating levers 22a and 22b.

[0070] In the hydraulic drive system 1A of the second embodiment, the flow control valve 14A reduces the first opening according to the control signal to allow the hydraulic fluid to flow preferentially into the travel motors 2 and 3. The flow control valve 14 opens the second opening according to the control signal to allow the hydraulic fluid to flow into the hydraulic cylinders 4 to 6.

[0071] Otherwise, the hydraulic drive system 1A according to the second embodiment exerts the same operational effects as those of the hydraulic drive system 1 according to the first embodiment.

[0072] [Other embodiments] In the hydraulic drive device 1, 1A of the present embodiment, the number of travel motors 2, 3 supplied by the travel system hydraulic circuit 12 is two, but it may be one, and the number is not important. Moreover, the number of loading and unloading actuators 4-6 supplied by the loading and unloading system hydraulic circuit 13 is also not important. In addition, the loading and unloading actuators 4-6 supplied by the loading and unloading system hydraulic circuit 13 are not limited to hydraulic cylinders, but may also be hydraulic motors. That is, the loading and unloading system hydraulic circuit 13 may also include, for example, a rotary motor and an optional cylinder.

[0073] Furthermore, the travel system hydraulic circuit 12 and the loading and unloading system hydraulic circuit 13 in the hydraulic drive device 1, 1A of the present embodiment are not limited to the aforementioned structure. The travel system hydraulic circuit 12 and the loading and unloading system hydraulic circuit 13 can be circuits that can supply working fluid to the travel motors 2, 3 and the hydraulic cylinders 4 to 6. In addition, in the hydraulic drive device 1, the control device 20 can also operate the travel motors 2, 3 and the hydraulic cylinders 4 to 6 according to a pre-stored program. The control device 20 directly obtains the hydraulic pressure from the discharge pressure sensor 15, the travel side pressure sensor 16 and the loading and unloading side pressure sensors 17 to 19, but can also obtain it indirectly through a device not shown in the figure.

[0074] In addition, in the hydraulic drive device 1, 1A of the present embodiment, the travel side passage 26 and the loading and unloading side passage 27 are connected to the pump passage 25 in a mutually divergent form, but they may be connected as follows. That is, the travel side passage 26 may be connected to the loading and unloading side passage 27 via the flow control valve 14, and may be connected to the pump passage 25 via the flow control valve 14 and the loading and unloading side passage 27. That is, the travel side passage 26 and the loading and unloading side passage 27 may be connected in series with the pump passage 25. The hydraulic drive device of such an embodiment also exerts the same effects as the hydraulic drive device 1 of the present embodiment.

[0075] In addition, the hydraulic drive device 1A of the second embodiment may be provided with a pressure sensor for detecting the downstream pressure (i.e., equivalent to the first supply pressure) of the flow control valve 14A. Furthermore, the control device 20 may also estimate the actual flow rate of the working fluid flowing in the loading and unloading system hydraulic circuit 13, i.e., the loading and unloading side actual flow rate, based on the pressure sensor, and output a control signal according to the loading and unloading side target flow rate and the loading and unloading side actual flow rate.

[0076] The hydraulic drive device of the first aspect comprises: a hydraulic pump connected to a pump passage to discharge working fluid into the pump passage; a first hydraulic circuit connected to a first passage connected to the pump passage; a second hydraulic circuit connected to a second passage connected to the pump passage; and a flow control valve disposed between the pump passage and the first passage to change a first opening as an opening between the pump passage and the first passage according to a control signal; the flow control valve is also connected to a tank to open and close between the pump passage and the tank according to a control signal.

[0077] According to the above aspect, the flow control valve changes the first opening degree, which is the opening degree between the pump passage and the first passage, according to the control signal. Therefore, the flow control valve can make the working fluid flow into the second hydraulic circuit preferentially by reducing the first opening degree according to the control signal. In addition, the flow control valve is also connected to the tank, and opens and closes the pump passage and the tank according to the control signal. Therefore, the flow control valve can discharge the working fluid discharged from the hydraulic pump into the tank, that is, can make the hydraulic pump in an unloading state. Therefore, the flow control valve can realize both the functions of a priority valve that makes the working fluid flow into the second hydraulic circuit preferentially and an unloading valve that makes the hydraulic pump in an unloading state. Therefore, the increase in the number of components in the hydraulic drive device can be suppressed.

[0078] The hydraulic drive device according to a second aspect is the hydraulic drive device according to the first aspect, wherein the flow control valve changes a second opening degree that is an opening degree between the pump passage and the tank in accordance with a control signal.

[0079] According to the above aspect, the flow control valve changes the second opening degree, which is the opening degree between the pump passage and the tank, according to the control signal. Therefore, the flow control valve can control the flow rate of the working fluid flowing from the pump passage to the tank.

[0080] In the hydraulic drive device of the third aspect, in the hydraulic drive device of the second aspect, the flow control valve has a control valve core, and the control valve core performs a stroke according to a control signal, thereby switching to a first control position and a second control position. In the first control position, the pump passage and the first passage are opened, and the second opening is reduced according to the stroke amount of the control valve core. In the second control position, the pump passage and the tank are closed, and the first opening is reduced according to the stroke amount of the control valve core.

[0081] According to the above aspect, the control valve core performs a stroke according to the control signal to switch to the first control position and the second control position. In the first control position, the pump passage and the first passage are opened, and the second opening is reduced according to the stroke amount of the control valve core. In the second control position, the pump passage and the tank are closed, and the first opening is reduced according to the stroke amount of the control valve core. Therefore, the control valve core can realize the function of the unloading valve in the first control position and the function of the priority valve in the second control position. Therefore, the flow control valve can realize the functions of both the unloading valve and the priority valve by causing the control valve core to stroke.

[0082] The hydraulic drive device of the fourth aspect is the hydraulic drive device of the third aspect, wherein the control valve core is stroked according to the control signal and is also switched to a third control position, in which the first opening is the maximum opening and the pump passage and the tank are closed.

[0083] According to the above aspect, in the third control position, the first opening is the maximum opening and the pump passage and the tank are closed. Therefore, in the third control position, the control valve element can introduce the total amount of the hydraulic fluid discharged from the hydraulic pump into the first hydraulic circuit.

[0084] A hydraulic drive device according to a fifth aspect is the hydraulic drive device according to any one of the first to fourth aspects, wherein the flow control valve has the first opening degree at a minimum opening degree in a state where the flow control valve closes a portion between the pump passage and the tank.

[0085] According to the above aspect, the flow control valve makes the first opening degree the minimum opening degree in the state of closing the pump passage and the tank. Therefore, even if the flow control valve is stuck at the minimum opening position, the working fluid can flow into the first passage. Therefore, even if the flow control valve is stuck at the minimum opening position, the working fluid can flow into the first hydraulic circuit.

[0086] The hydraulic drive device of the sixth aspect is in the hydraulic drive device of the fifth aspect, and further includes a control device for controlling the movement of the flow control valve by outputting a control signal, the first hydraulic circuit cuts off the flow of the working fluid according to the first signal, the control device makes the first opening of the flow control valve the minimum opening by outputting a control signal, and cuts off the flow of the working fluid in the first hydraulic circuit by outputting the first signal.

[0087] According to the above aspect, the control device outputs a control signal to make the first opening of the flow control valve the minimum opening and outputs a first signal to cut off the flow of the working fluid in the first hydraulic circuit. Thus, the total amount of working fluid from the hydraulic pump can flow toward the second hydraulic circuit.

[0088] The hydraulic drive device of the seventh aspect is a hydraulic drive device of any one of the first to sixth aspects, wherein the first hydraulic circuit is a travel system hydraulic circuit that controls the flow of working fluid to the travel motor by adjusting the opening between the travel motor and the hydraulic pump, and the second hydraulic circuit is a loading and unloading system hydraulic circuit that controls the flow of working fluid to the loading and unloading actuator by adjusting the opening between the loading and unloading actuator and the hydraulic pump.

[0089] According to the above aspect, the second hydraulic circuit is a hydraulic circuit of a loading and unloading system that controls the flow of working fluid to the loading and unloading actuator by adjusting the opening between the loading and unloading actuator and the hydraulic pump. Therefore, the flow control valve reduces the first opening according to the control signal, so that the working fluid can flow into the loading and unloading actuator preferentially. In addition, the first hydraulic circuit is a hydraulic circuit of a traveling system that controls the flow of working fluid to the traveling motor by adjusting the opening between the traveling motor and the hydraulic pump. Therefore, the flow control valve opens the second opening according to the control signal, so that the working fluid can flow into the traveling motor.

[0090] In the hydraulic drive device of the eighth aspect, in the hydraulic drive device of any one of the first to sixth aspects, the first hydraulic circuit is a loading and unloading system hydraulic circuit that controls the flow of working fluid to the loading and unloading actuator by adjusting the opening between the loading and unloading actuator and the hydraulic pump, and the second hydraulic circuit is a traveling system hydraulic circuit that controls the flow of working fluid to the traveling motor by adjusting the opening between the traveling motor and the hydraulic pump.

[0091] According to the above aspect, the second hydraulic circuit is a travel system hydraulic circuit that controls the flow of working fluid to the travel motor by adjusting the opening between the travel motor and the hydraulic pump. Therefore, the flow control valve reduces the first opening according to the control signal, so that the working fluid can flow into the travel motor preferentially. In addition, the first hydraulic circuit is a loading and unloading system hydraulic circuit that controls the flow of working fluid to the loading and unloading actuator by adjusting the opening between the loading and unloading actuator and the hydraulic pump. Therefore, the flow control valve opens the second opening according to the control signal, so that the working fluid can flow into the loading and unloading actuator.

Claims

1. A hydraulic drive device, characterized in that: have: a hydraulic pump connected to the pump passage and discharging working fluid into the pump passage; a first hydraulic circuit connected to a first passage connected to the pump passage; a second hydraulic circuit connected to a second passage connected to the pump passage; as well as a flow control valve interposed between the pump passage and the first passage, the flow control valve changing a first opening degree as an opening degree between the pump passage and the first passage according to a control signal; The flow control valve is also connected to the tank, and opens and closes the passage between the pump and the tank according to a control signal.

2. The hydraulic drive device according to claim 1, characterized in that: The flow control valve changes a second opening degree, which is an opening degree between the pump passage and the tank, according to a control signal.

3. The hydraulic drive device according to claim 2, characterized in that: The flow control valve has a control valve core, which performs a stroke according to a control signal to switch to a first control position and a second control position; In the first control position, the pump passage and the first passage are opened, and the second opening is reduced according to the stroke amount of the control valve core; In the second control position, the pump passage and the tank are closed, and the first opening is reduced according to the stroke amount of the control valve element.

4. The hydraulic drive device according to claim 3, characterized in that: The control valve core performs a stroke according to the control signal so as to switch to a third control position; In the third control position, the first opening is the maximum opening, and the pump passage and the tank are closed.

5. The hydraulic drive device according to claim 1, characterized in that: The flow control valve sets the first opening degree to a minimum opening degree in a state where the flow control valve closes the pump passage and the tank.

6. The hydraulic drive device according to claim 5, characterized in that: Also provided is a control device for controlling the movement of the flow control valve by outputting a control signal; The first hydraulic circuit cuts off the flow of the working fluid according to the first signal; The control device sets the first opening of the flow control valve to a minimum opening by outputting a control signal, and cuts off the flow of the working fluid in the first hydraulic circuit by outputting a first signal.

7. The hydraulic drive device according to claim 1, characterized in that: The first hydraulic circuit is a travel system hydraulic circuit that controls the flow of working fluid to the travel motor by adjusting the opening between the travel motor and the hydraulic pump; The second hydraulic circuit is a loading and unloading system hydraulic circuit that controls the flow of the hydraulic fluid to the loading and unloading actuator by adjusting the opening between the loading and unloading actuator and the hydraulic pump.

8. The hydraulic drive device according to claim 1, characterized in that: The first hydraulic circuit is a loading and unloading system hydraulic circuit that controls the flow of working fluid to the loading and unloading actuator by adjusting the opening between the loading and unloading actuator and the hydraulic pump; The second hydraulic circuit is a travel system hydraulic circuit that controls the flow of hydraulic fluid to the travel motor by adjusting the opening between the travel motor and the hydraulic pump.

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