Liquid pressure driving device

Abstract

To provide a liquid pressure driving device capable of suppressing an increase in the number of components.SOLUTION: A liquid pressure driving device 1 includes: a liquid pressure pump 11 connected to a pump passage 25 for discharging working liquid to the pump passage; a first liquid pressure circuit 12 connected to a first passage 26 connected to the pump passage; a second liquid pressure circuit 13 connected to a second passage 27 connected to the pump passage; and a flow control valve 14 interposed between the pump passage and the first passage for changing a first aperture, which is an aperture between the pump passage and the first passage according to a control signal. The flow control valve is further connected to a tank 28, and executes opening and closing between the pump passage and the tank according to the control signal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a hydraulic drive device that supplies hydraulic fluid to two hydraulic circuits. [Background technology]

[0002] A one-pump system in which a single pump serves as the hydraulic pressure source for the travel motor and the loading actuator of a construction machine is in practical use. As a hydraulic drive device for a one-pump system, for example, a hydraulic circuit as shown in Patent Document 1 is known. In the hydraulic circuit of Patent Document 1, a pump is connected to the travel motor and the loading 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 narrows the opening of the second pump line. This allows the pressurized oil to flow preferentially to the travel motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-026828 A Summary of the Invention [Problem to be solved by the invention]

[0004] The hydraulic circuit of Patent Document 1 further includes an unloading valve to put the pump in an unloaded state. The various valves in the hydraulic circuit, including the unloading valve, are configured, for example, by inserting a spool into an insertion hole formed in a valve block of a multi-control valve. Therefore, as the number of valves increases, the number of parts of the hydraulic drive device equipped with the hydraulic circuit also increases.

[0005] SUMMARY OF THE PRESENT DISCLOSURE In view of the above, an object of the present invention is to provide a hydraulic drive device that can suppress an increase in the number of parts. [Means for solving the problem]

[0006] The hydraulic drive device of the present invention includes a hydraulic pump connected to a pump passage and discharging hydraulic 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 and changing a first opening degree, which is the opening degree between the pump passage and the first passage, in response to a control signal, and the flow control valve is further connected to a tank and opens and closes between the pump passage and the tank in response to a control signal.

[0007] According to the present invention, the flow control valve changes the first opening, which is the opening between the pump passage and the first passage, in response to the control signal. Therefore, the flow control valve can preferentially flow the hydraulic fluid to the second hydraulic circuit by narrowing the first opening in response to the control signal. The flow control valve is further connected to the tank and opens and closes between the pump passage and the tank in response to the control signal. Therefore, the flow control valve can discharge the hydraulic fluid discharged from the hydraulic pump to the tank, that is, can put the hydraulic pump into an unloaded state. Therefore, the flow control valve can achieve both the functions of a priority valve that preferentially flows the hydraulic fluid to the second hydraulic circuit and an unloading valve that puts the hydraulic pump into an unloaded state. Therefore, an increase in the number of parts in the hydraulic drive device can be suppressed. Effect of the Invention

[0008] According to the present invention, an increase in the number of parts in a hydraulic drive device is suppressed. [Brief description of the drawings]

[0009] [Figure 1] 1 is a circuit diagram showing a configuration of a hydraulic drive device according to a first embodiment of the present invention. [Diagram 2] 4 is a graph showing changes in a first opening degree and a second opening degree with respect to a stroke amount of a control spool of a flow control valve provided in the hydraulic drive device of FIG. [Diagram 3]2 is a block diagram showing a control block of a control device provided in the hydraulic drive device of FIG. 1. [Figure 4] FIG. 4 is a circuit diagram showing the configuration of a hydraulic drive device according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, hydraulic drive devices 1, 1A according to first and second embodiments of the present invention will be described with reference to the drawings mentioned above. The concept of direction used in the following description is used for convenience in the description and does not limit the orientation of the configuration of the invention to that direction. Furthermore, the hydraulic drive devices 1, 1A described below are merely one embodiment of the present invention. Therefore, the present invention is not limited to the embodiment, and additions, deletions, and modifications are possible within the scope of the invention.

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

[0012] The vehicle body is, for example, a tracked device, and includes a pair of left and right crawlers (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 crawlers. The vehicle body may be a wheeled device, or any other device capable of travel. The travel motors 2, 3 are hydraulic motors that drive the left and right crawlers, respectively. More specifically, each of the travel motors 2, 3 has two supply and discharge ports 2a, 2b, 3a, 3b. The travel motors 2, 3 rotate in the forward direction when hydraulic fluid is supplied to one of the supply and discharge ports 2a, 3a, and rotate in the reverse direction when hydraulic fluid is supplied to the other supply and discharge port 2b, 3b.

[0013] The work machine is rotatably mounted on a vehicle body. The work machine includes a boom, an arm, a bucket (none of which are shown), and a number of hydraulic cylinders 4-6. The hydraulic cylinders 4-6, which are an example of a loading actuator, are, for example, a boom cylinder 4, an arm cylinder 5, and a bucket cylinder 6, and are mounted on the boom, arm, and bucket, respectively. The work machine moves the boom, arm, and bucket, respectively, by extending and retracting the three hydraulic cylinders 4-6. This enables the work machine to perform a variety of tasks.

[0014] <Hydraulic drive unit> The hydraulic drive system 1 includes a hydraulic pump 11, a traveling system hydraulic circuit 12, a cargo handling system hydraulic circuit 13, a flow control valve 14, a discharge pressure sensor 15, a traveling side pressure sensor 16, and a control device 20. Explaining in more detail, the hydraulic drive system 1 further includes cargo side pressure sensors 17-19, a traveling system operation device 21, and a cargo handling system operation device 22. In the hydraulic drive system 1, the traveling system hydraulic circuit 12, the cargo handling system hydraulic circuit 13, and the flow control valve 14 are configured as one multi-control valve (not shown).

[0015] The hydraulic drive unit 1 is a so-called one-pump system, and supplies hydraulic fluid from one hydraulic pump 11 to the traveling motors 2 and 3 and three hydraulic cylinders 4 to 6. The hydraulic drive unit 1 operates the crawlers corresponding to the traveling motors 2 and 3 by supplying hydraulic fluid to the first traveling motor 2 and the second traveling motor 3, respectively. In this way, the hydraulic drive unit 1 can make the hydraulic excavator travel. In addition, the hydraulic drive unit 1 supplies hydraulic fluid to the hydraulic cylinders 4 to 6 to operate the corresponding boom, arm, and bucket. In this way, the hydraulic drive unit 1 can make the hydraulic excavator perform various tasks.

[0016] <Hydraulic pump> The hydraulic pump 11 discharges hydraulic fluid. More specifically, the hydraulic pump 11 is connected to a drive source (e.g., an engine and an electric motor) not shown. The hydraulic pump 11 is connected to a pump passage 25. The hydraulic pump 11 discharges hydraulic fluid to the pump passage 25 by being rotationally driven by the drive source. The pump passage 25 is connected to a travel-side passage 26 and a loading-side passage 27. In this embodiment, the hydraulic pump 11 is a variable displacement pump.

[0017] <Drive system hydraulic circuit> The traveling hydraulic circuit 12, which is an example of a first hydraulic circuit, is connected to the traveling passage 26. The traveling passage 26, which is an example of a first passage, is connected to the pump passage 25. The traveling hydraulic circuit 12 is also connected to the two traveling motors 2 and 3. The traveling hydraulic circuit 12 controls the flow of hydraulic fluid to the traveling motors 2 and 3 by adjusting the opening between the traveling motors 2 and 3 and the hydraulic pump 11. More specifically, a traveling command signal (in this embodiment, a first traveling command signal and a second traveling command signal) which is an example of a first signal is input to the traveling hydraulic circuit 12. The traveling hydraulic circuit 12 supplies hydraulic fluid to the first traveling motor 2 and the second traveling motor 3, respectively, with a flow (flow direction and flow rate in this embodiment) according to the input first traveling command signal and second traveling command signal. The traveling hydraulic circuit 12 includes a first traveling directional control valve 31 and a second traveling directional control valve 32. The traveling system hydraulic circuit 12 further includes a first pressure compensating valve 33 and a second pressure compensating valve .

[0018] The first traveling direction control valve 31 controls the flow of hydraulic fluid to the first traveling motor 2. More specifically, the first traveling direction control valve 31 is connected to the traveling side passage 26, the tank 28, and the two supply and discharge ports 2a, 2b of the first traveling motor 2. The first traveling direction control valve 31 switches the connection destinations of the supply and discharge ports 2a, 2b to the traveling side passage 26 and the tank 28, respectively, in response to the input first traveling command signal. As a result, the first traveling direction control valve 31 rotates the first traveling motor 2 forward and backward in response to the first traveling command signal. Also, the first traveling direction control valve 31 changes its opening in response to the input first traveling command signal. Therefore, the first traveling direction control valve 31 supplies the first traveling motor 2 with hydraulic fluid in a direction and flow rate in response to the first traveling command signal. As a result, the first traveling direction control valve 31 rotates the first traveling motor 2 at a speed in response to the first traveling command signal. In this embodiment, the first traveling directional control valve 31 is an electrically controlled directional control valve, and configures a multi-control valve together with other control valves 14, 32, 41 to 43 and compensation valves 33 and , which will be described in detail later.

[0019] The second traveling direction control valve 32 controls the flow of hydraulic fluid to the second traveling motor 3. More specifically, the second traveling direction control valve 32 is connected to the traveling-side passage 26 in parallel with the first traveling direction control valve 31. Furthermore, the second traveling direction control valve 32 is connected to the tank 28 and the two supply and discharge ports 3a, 3b of the second traveling motor 3. The second traveling direction control valve 32 switches the connection destinations of the supply and discharge ports 3a, 3b to the traveling-side passage 26 and the tank 28, respectively, in response to the input second traveling command signal. As a result, the second traveling direction control valve 32 rotates the second traveling motor 3 forward and reverse in response to the second traveling command signal. Also, the second traveling direction control valve 32 changes the opening degree in response to the second traveling command signal. As a result, the second traveling direction control valve 32 rotates the second traveling motor 3 at a speed in response to the second traveling command signal. In this embodiment, the second traveling directional control valve 32 is an electrically controlled directional control valve.

[0020] The first pressure compensating valve 33 maintains the differential pressure across the first traveling direction control valve 31 at a predetermined pressure. This controls the flow rate of hydraulic fluid supplied to the first traveling motor 2 to a flow rate that corresponds to the opening degree of the first traveling direction control valve 31. In addition, the second pressure compensating valve 34 maintains the differential pressure across the second traveling direction control valve 32 at a predetermined pressure. This controls the flow rate of hydraulic fluid supplied to the second traveling motor 3 to a flow rate that corresponds to the opening degree of the second traveling direction control valve 32.

[0021] <Cargo handling hydraulic circuit> The cargo-handling hydraulic circuit 13, which is an example of a second hydraulic circuit, is connected to the cargo-handling passage 27. The cargo-handling passage 27, which is an example of a second passage, is connected to the pump passage 25. The cargo-handling hydraulic circuit 13 is also connected to the three hydraulic cylinders 4-6. The cargo-handling hydraulic circuit 13 supplies hydraulic fluid to each of the three hydraulic cylinders 4-6. The cargo-handling hydraulic circuit 13 controls the flow of hydraulic fluid to each of the hydraulic cylinders 4-6 by adjusting the opening between each of the hydraulic cylinders 4-6 and the hydraulic pump 11 in response to a cargo-handling operation signal (in this embodiment, a boom command signal, an arm command signal, and a bucket command signal, which will be described in detail later). More specifically, the cargo-handling hydraulic circuit 13 supplies hydraulic fluid to the three hydraulic cylinders 4-6 in a flow (in this embodiment, a flow direction and a flow rate) in response to the input cargo-handling operation signal. The cargo-handling hydraulic circuit 13 includes a plurality of cargo-handling directional control valves 41-43. In this embodiment, the cargo handling hydraulic circuit 13 includes three cargo handling 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 of the cargo handling directional control valves 41-43 corresponds to each of the hydraulic cylinders 4-6. Each of the cargo handling directional control valves 41-43 controls the flow rate of hydraulic fluid supplied to the hydraulic cylinders 4-6. That is, the boom handling directional control valve 41 controls the flow of hydraulic fluid to the boom cylinder 4. The arm handling directional control valve 42 controls the flow of hydraulic fluid to the arm cylinder 5. The bucket handling directional control valve 43 controls the flow of hydraulic fluid to the bucket cylinder 6. Each of the cargo handling directional control valves 41-43 is connected to the cargo handling side passage 27 so as to be in parallel with each other.

[0023] More specifically, each of the cargo handling directional control valves 41-43 is connected to the tank 28 and the rod side ports 4a, 5a, 6a and head side ports 4b, 5b, 6b of the corresponding hydraulic cylinders 4-6. Each of the cargo handling directional control valves 41-43 switches the connection destinations of the rod side ports 4a-6a and head side ports 4b-6b to the cargo handling side passage 27 and the tank 28, respectively. As a result, each of the cargo handling directional control valves 41-43 expands or contracts the corresponding hydraulic cylinders 4-6 in response to each cargo handling operation signal. Also, each of the cargo handling directional control valves 41-43 changes the opening degree in response to each cargo handling operation signal. Therefore, the corresponding hydraulic cylinders 4-6 are supplied with hydraulic fluid in a direction and at a flow rate according to each command signal from each of the cargo handling directional control valves 41-43. As a result, the cargo handling directional control valves 41-43 can extend and retract the corresponding hydraulic cylinders 4-6 at speeds according to the cargo handling command signals. Note that the cargo handling directional control valves 41-43 are also electrically controlled directional control valves in this 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 spool 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 a first opening degree, which is an opening degree between the pump passage 25 and the travel-side passage 26, in response to an input control signal. In other words, the flow control valve 14 throttles the flow rate of the hydraulic fluid flowing from the pump passage 25 to the travel-side passage 26 in response to the input control signal. As a result, the hydraulic fluid is preferentially supplied to the cargo handling hydraulic circuit 13.

[0025] The flow control valve 14 is further connected to a tank 28. The flow control valve 14 opens and closes between the pump passage 25 and the tank 28 in response to a control signal. To explain in more detail, the flow control valve 14 is connected to the tank 28 via a tank passage 29. The flow control valve 14 opens and closes between the pump passage 25 and the tank passage 29 in response to a control signal. The flow control valve 14 also changes a second opening degree, which is the opening degree between the pump passage 25 and the tank 28 (between the pump passage 25 and the tank passage 29 in this embodiment), in response to the control signal.

[0026] More specifically, the flow control valve 14 is configured as follows. That is, the flow control valve 14 has a control spool 14a. The control spool 14a is slidably inserted into an insertion hole formed in a valve block of a multi-control valve (not shown). The control spool 14a strokes in response to a control signal. More specifically, the flow control valve 14 is, for example, an electrically controlled flow control spool valve, and the control spool 14a strokes in response to a pilot pressure output by an electromagnetic proportional valve in response to a control signal. The control spool 14a strokes to switch its position between a first control position A1 and a second control position A2. In this embodiment, the control spool 14a strokes to switch its position to a third control position A3 in addition to the first control position A1 and the second control position A2. The control spool 14a is located in the first control position A1 in the neutral state, for example. The control spool 14a moves from the first control position A1 to the third control position A3 by stroking, and further moves from the third control position A3 to the second control position A2.

[0027] Each of the first to third control positions A1 to A3 will be described in detail below. In the first control position A1, the pump passage 25 and the travel-side passage 26 are opened as shown in FIG. 2. In this embodiment, the first opening degree is the maximum opening degree in the first control position A1. In addition, in the first control position A1, the pump passage 25 and the tank passage 29 are also opened. As a result, 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 11 is in an unloaded state. Furthermore, in the first control position A1, the second opening degree is narrowed according to the stroke amount of the control spool 14a. More specifically, in the first control position A1, the second opening degree is narrowed from the unloaded opening degree (the maximum opening degree of the second opening degree in this embodiment) to zero (i.e., fully closed) according to the stroke amount of the control spool 14a. By narrowing the second opening, the flow rate of the hydraulic fluid discharged to the tank 28 (bleed-off flow rate) can be adjusted, and the flow rate of the hydraulic fluid flowing through the travel-side passage 26 can be adjusted.

[0028] In the second control position A2, the pump passage 25 is closed from the tank 28. In this embodiment, in the second control position A2, the second opening is fully closed. In addition, in the second control position A2, the pump passage 25 is opened from the traveling-side passage 26. As a result, in the second control position A2, the hydraulic fluid discharged from the hydraulic pump 11 can be guided to the traveling-system hydraulic circuit 12 via the traveling-side passage 26. In addition, in the second control position A2, the first opening is narrowed according to the stroke amount of the control spool 14a. As a result, the flow control valve 14 limits the flow rate of the hydraulic fluid guided to the traveling-side passage 26, and preferentially flows the hydraulic fluid to the loading-side passage 27. That is, the flow control valve 14 preferentially flows the hydraulic fluid to the loading-system hydraulic circuit 13. In addition, the flow control valve 14 adjusts the flow rate to be flowed to the traveling-system hydraulic circuit 12 by narrowing the first opening according to the stroke amount of the control spool 14a.

[0029] In this embodiment, the first opening is narrowed down from the maximum opening to the minimum opening. That is, when the control spool 14a is at full stroke (that is, when the passage between the pump passage 25 and the tank 28 is closed), the first opening is maintained at the minimum opening. In this embodiment, the minimum opening is an opening that is not fully closed. As a result, even if the control spool 14a is stuck at full stroke, the hydraulic fluid is supplied to the traveling system hydraulic circuit 12.

[0030] In the third control position A3, the communication between the pump passage 25 and the tank 28 is closed. In this embodiment, in the third control position A3, the second opening is fully closed. In addition, in the third control position A3, the communication between the pump passage 25 and the traveling-side passage 26 is opened. As a result, in the third control position A3, the hydraulic fluid discharged from the hydraulic pump 11 can be supplied to the traveling-system hydraulic circuit 12 via the traveling-side passage 26. In this embodiment, the first opening is the maximum opening in the third control position A3, similar to the first control position A1.

[0031] <Various sensors> The discharge pressure sensor 15 detects the hydraulic pressure of the hydraulic fluid discharged from the hydraulic pump 11, i.e., the discharge pressure. To explain in more detail, the discharge pressure sensor 15 is provided in the pump passage 25. In other words, the discharge pressure sensor 15 is provided upstream of the flow control valve 14. The discharge pressure sensor 15 detects the hydraulic pressure of the hydraulic fluid flowing through the pump passage 25.

[0032] The traveling side pressure sensor 16, which is an example of a first pressure sensor, detects the traveling side supply pressure. The traveling side supply pressure, which is an example of the first supply pressure, is the hydraulic pressure of the hydraulic fluid flowing through the traveling side passage 26. In other words, the traveling side pressure sensor 16 detects the hydraulic pressure of the hydraulic fluid supplied to the traveling system hydraulic circuit 12. To explain in more detail, the traveling side pressure sensor 16 is provided in the traveling side passage 26. In other words, the traveling side pressure sensor 16 is provided downstream of the flow control valve 14.

[0033] The cargo-side pressure sensors 17-19 correspond to the hydraulic cylinders 4-6. The cargo-side pressure sensors 17-19 detect the cargo-side supply pressures, which are the supply pressures to the corresponding hydraulic cylinders 4-6. The cargo-side pressure sensors 17-19 are provided downstream of the directional control valves 41-43. In this embodiment, the cargo-side pressure sensors 17-19 are provided in the rod-side ports 4a-6a and head-side ports 4b-6b of the hydraulic cylinders 4-6, respectively. The cargo-side pressure sensors 17-19 detect the hydraulic pressure of the hydraulic fluid supplied to the rod-side ports 4a-6a and head-side ports 4b-6b of the hydraulic cylinders 4-6.

[0034] <Travel control device> The traveling system operation device 21 is a device for the driver to operate the traveling motors 2 and 3. The traveling system operation device 21 includes, for example, traveling pedals 21a and 21b which are operating tools. Each of the traveling pedals 21a and 21b can be tilted. Each of the traveling pedals 21a and 21b can be tilted, for example, in one direction and the other direction (for example, forward and backward). The traveling system operation device 21 outputs a traveling operation command according to the operation direction and operation amount (tilt direction and tilt amount in this embodiment). Note that the operating tool provided in the traveling system operation device 21 may be in another form such as an operating lever operation panel, and the form is not limited.

[0035] <Cargo handling operation device> The cargo handling operation device 22 is a device for the driver to operate an attachment (a bucket in this embodiment). More specifically, the operating tools of the cargo handling operation device 22 include cargo handling operation levers 22a, 22b. Each of the cargo handling operation levers 22a, 22b can be tilted. In this embodiment, each of the cargo handling operation levers 22a, 22b can be tilted, for example, in the front-rear and left-right directions. The cargo handling operation device 22 outputs a cargo handling operation command according to the operation direction and operation amount (tilt direction and tilt amount in this embodiment). Note that the operating tools provided in the cargo handling operation device 22 are not limited to the cargo handling operation levers 22a, 22b, and may be in other forms such as an operation panel.

[0036] <Control device> The control device 20 controls the operation of the traveling system hydraulic circuit 12. More specifically, the control device 20 acquires a traveling operation command output from the traveling system operating device 21. The control device 20 then controls the movement of each of the traveling directional control valves 31, 32 in response to the traveling operation command. In this embodiment, the control device 20 outputs each of the first and second traveling command signals in response to the traveling operation command. As a result, each of the traveling motors 2, 3 rotates in a direction and at a rotational speed in response to the traveling operation command, and the hydraulic excavator moves in a direction and at a speed in response to the traveling operation command.

[0037] The control device 20 also controls the operation of the cargo-handling hydraulic circuit 13. More specifically, the control device 20 acquires a cargo-handling operation command output from the cargo-handling operation device 22. The control device 20 then controls the movement of each of the cargo-handling directional control valves 41-43 (i.e., the position of each of the spools 41a-43a) in response to the cargo-handling operation command. In this embodiment, the control device 20 outputs a boom command signal, a boom command signal, and a bucket command signal in response to the cargo-handling operation command. The hydraulic cylinders 4-6 then expand and contract at a speed in response to the cargo-handling operation command. This allows the bucket to move in a direction and at a speed in response to the cargo-handling operation command, making it possible to cause the hydraulic excavator to perform a desired task.

[0038] Furthermore, the control device 20 controls the opening degree of the flow control valve 14 by outputting a control signal to the flow control valve 14. More specifically, the control device 20 strokes the control spool 14a by outputting a control signal in response to a traveling operation command and a cargo operation command. As a result, the control device 20 changes the position of the control spool 14a, and changes the first opening degree and the second opening degree at each of the positions A1 to A3. The control device 20 also outputs a control signal in response to the hydraulic pressure detected by each of the pressure sensors 15 to 19, thereby supplying the hydraulic fluid at a flow rate corresponding to each of the traveling operation command and the cargo operation command to each of the traveling system hydraulic circuit 12 and the cargo operation hydraulic circuit 13 with higher accuracy.

[0039] <Operation of hydraulic drive unit> In the hydraulic drive system 1, in a non-operated state, the control spool 14a of the flow control valve 14 is located in the first control position A1. The non-operated state is a state in which neither the traveling pedals 21a, 21b of the traveling system operation device 21 nor the loading operation levers 22a, 22b of the loading system operation device 22 are operated. When the control spool 14a is located in 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 hydraulic fluid discharged from the hydraulic pump 11 is discharged to the tank 28, and the hydraulic pump 11 is in an unloaded state. Note that in the first control position A1, the pump passage 25 is also connected to the traveling-side passage 26. As a result, in the unloaded state, the traveling-side passage 26 is prevented from being trapped.

[0040] In the hydraulic drive device 1, when the travel pedals 21a, 21b of the travel system operation device 21 are operated independently, a travel operation command is output from the travel system operation device 21. In this embodiment, the independent operation means that the travel pedals 21a, 21b and the load operation levers 22a, 22b are operated separately. The independent operation includes the simultaneous operation of the travel pedals 21a, 21b and the simultaneous operation of the load operation levers 22a, 22b. When the travel operation command is output, the control device 20 narrows the gap between the pump passage 25 and the tank passage 29 by the flow control valve 14 while keeping the gap between the pump passage 25 and the travel-side passage 26 open. In this embodiment, the control device 20 positions the control spool 14a of the flow control valve 14 in the first control position A1 or the third control position A3 by outputting a control signal. On the other hand, the control device 20 closes the gap between the hydraulic pump 11 and the hydraulic cylinders 4 to 6 by the load-handling hydraulic circuit 13. That is, the control device 20 closes the cargo-handling side passage 27 and the hydraulic cylinders 4-6 by the cargo-handling directional control valves 41-43. Furthermore, the control device 20 opens the travel-side passage 26 and the travel motors 2, 3 by the travel system hydraulic circuit 12.

[0041] More specifically, the control device 20 calculates the travel motor target flow rates to be supplied to each of the travel motors 2 and 3 based on the travel operation command as shown in FIG. 3. The control device 20 also calculates the second opening based on the pump discharge flow rate and the travel-side target flow rate. Here, the pump discharge flow rate is the flow rate of the hydraulic fluid discharged from the hydraulic pump 11. The pump discharge flow rate is calculated, for example, based on the driving state of the hydraulic pump 11 or based on the discharge pressure. The pump discharge flow rate may be set in advance, and the calculation method and setting method are not important. The travel-side target flow rate, which is an example of the first target flow rate, is the total flow rate of the travel motor target flow rates to be supplied to each of the travel motors 2 and 3, and is the flow rate to be flowed to the travel-side passage 26 (i.e., to be supplied to the travel system hydraulic circuit 12).

[0042] More specifically, when the pump discharge flow rate is equal to or smaller than the target travel side flow rate, the control device 20 sets the second opening to zero (i.e., fully closed). On the other hand, when the pump discharge flow rate is greater than the target travel side flow rate, the control device 20 opens the second opening to discharge a portion of the hydraulic fluid in the pump passage 25 from the flow control valve 14 to the tank 28 (i.e., bleeds off). By doing so, the control device 20 sets the actual travel side flow rate to the target travel side flow rate. The actual travel side flow rate, which is an example of the first actual flow rate, is the actual flow rate flowing in the travel side passage 26. In this embodiment, the control device 20 estimates the actual travel side flow rate based on the detected discharge pressure and travel side supply pressure. Then, the control device 20 calculates the second opening such that the actual travel side flow rate becomes the target travel side flow rate based on the discharge pressure and travel side supply pressure detected by the pressure sensors 15 and 16, the actual travel side flow rate, and the target travel side flow rate. The control device 20 changes the second opening of the flow control valve 14 by outputting a control signal according to the calculated second opening. As a result, the hydraulic fluid is supplied to the traveling system hydraulic circuit 12 at the traveling-side target flow rate.

[0043] The control device 20 also outputs first and second travel command signals corresponding to the target flow rates of the travel motors. Then, the first travel direction control valve 31 and the second travel direction control valve 32 each control the flow of hydraulic fluid to the travel motors 2, 3 to a flow (flow direction and flow rate in this embodiment) corresponding to the travel operation command. More specifically, the control device 20 calculates the opening degree of the first and second travel direction control valves 31, 32 according to the target flow rates of the travel motors 2, 3, and then outputs first and second travel command signals corresponding to the calculated opening degrees. In the travel system hydraulic circuit 12, the pressure compensation valves 33, 34 maintain the front and rear pressure differentials of each of the two travel direction control valves 31, 32. Therefore, the travel motors 2, 3 are supplied with hydraulic fluid at a flow rate corresponding to the opening degree of each travel direction control valve 31, 32. Therefore, the control device 20 can cause the hydraulic excavator to perform a traveling operation in accordance with the operation of the traveling pedals 21a, 21b.

[0044] In the hydraulic drive device 1, when the cargo handling operation levers 22a, 22b of the cargo handling system operation device 22 are operated independently, a cargo handling operation command is output from the cargo handling system operation device 22. Then, the control device 20 uses the flow control valve 14 to narrow the passage between the pump passage 25 and the travel-side passage 26, and closes the passage between the pump passage 25 and the tank passage 29. More specifically, the control device 20 moves the control spool 14a to the second control position A2 by outputting a control signal. In this embodiment, the control device 20 makes the control spool 14a move to a full stroke. As a result, the control device 20 sets the first opening to the minimum opening and the second opening to zero (i.e., fully closed). On the other hand, the control device 20 outputs the first traveling operation signal and the second traveling operation signal to block the flow of the hydraulic fluid in the traveling system hydraulic circuit 12. That is, the control device 20 closes the passage between the hydraulic pump 11 and the traveling motors 2, 3 by the traveling system hydraulic circuit 12. More specifically, the control device 20 closes the passage 26 between the travelling motors 2 and 3 using the travelling directional control valves 31 and 32. This allows the entire amount of hydraulic fluid discharged from the hydraulic pump 11 to be supplied to the cargo handling hydraulic circuit 13. Furthermore, the control device 20 opens the passage 27 between the hydraulic cylinders 4 to 6 using the cargo handling hydraulic circuit 13.

[0045] More specifically, the control device 20 calculates the target cargo handling flow rate to be supplied to each of the hydraulic cylinders 4-6 based on the cargo handling operation command as shown in FIG. 3. The control device 20 also estimates the flow rate of the hydraulic fluid to be supplied to each of the hydraulic cylinders 4-6 based on the detected discharge pressure and each cargo handling supply pressure. More specifically, the control device 20 estimates the actual cargo handling flow rate as the flow rate of the hydraulic fluid to be supplied to each of the hydraulic cylinders 4-6 based on the discharge pressure, which is the front and rear pressure of each of the cargo handling directional control valves 41-43, and each cargo handling supply pressure. The actual cargo handling flow rate is the flow rate of the hydraulic fluid flowing through each of the cargo handling directional control valves 41-43. The control device 20 calculates the opening degree of each of the cargo handling directional control valves 41-43 so that the estimated actual cargo handling flow rate becomes the target cargo handling flow rate. The control device 20 then outputs a boom command signal, a boom command signal, and a bucket command signal according to each calculated opening degree. Therefore, the flow of hydraulic fluid to the hydraulic cylinders 4-6 is controlled to a flow (flow direction and flow rate in this embodiment) according to a cargo operation command by each of the cargo handling directional control valves 41-43. This allows the control device 20 to cause the bucket to move in accordance with the operation of the cargo handling operation levers 22a, 22b.

[0046] Furthermore, when the traveling pedals 21a, 21b and the cargo handling operation levers 22a, 22b are operated simultaneously, the control device 20 operates as follows. That is, a traveling operation command is output from the traveling system operation device 21, and a cargo handling operation command is output from the cargo handling system operation device 22. Then, the control device 20 closes the passage between the pump passage 25 and the tank passage 29 by the flow control valve 14, and narrows the passage between the pump passage 25 and the traveling side passage 26. More specifically, the control device 20 moves the control spool 14a to the second position by outputting a control signal. This allows the control device 20 to supply hydraulic fluid to the traveling system hydraulic circuit 12 as well, while preferentially supplying hydraulic fluid to the cargo handling hydraulic circuit 13. Furthermore, the control device 20 opens the passage between the traveling side passage 26 and the traveling motors 2, 3 by the traveling system hydraulic circuit 12, and opens the passage between the cargo handling side passage 27 and the hydraulic cylinders 4 to 6 by the cargo handling hydraulic circuit 13.

[0047] More specifically, the control device 20 calculates the travel motor target flow rate based on the travel operation command as shown in Fig. 3. The control device 20 also estimates the travel side actual flow rate based on the detected discharge pressure and travel side supply pressure. The control device 20 then calculates a first opening degree such that the travel side actual flow rate becomes the travel side target flow rate based on the discharge pressure and travel side supply pressure detected by pressure sensors 15, 16, the travel side actual flow rate, and the travel side target flow rate.

[0048] In addition, in this embodiment, the control device 20 outputs a control signal in accordance with the target cargo handling flow rate and the actual cargo handling flow rate of each of the hydraulic cylinders 4-6 in addition to the actual cargo handling flow rate and the target cargo handling flow rate of each of the hydraulic cylinders 4-6. More specifically, the control device 20 calculates the target cargo handling flow rate of each of the hydraulic cylinders 4-6 based on the cargo handling operation command. The control device 20 also estimates the actual cargo handling flow rate of each of the hydraulic cylinders 4-6 based on the detected discharge pressure and each cargo handling supply pressure. The actual cargo handling flow rate is a flow rate actually supplied to each of the hydraulic cylinders 4-6. The control device 20 changes the first opening of the flow control valve 14 so that the actual cargo handling flow rate of the traveling side becomes the target cargo handling flow rate of the traveling side and each cargo handling target flow rate and each cargo handling actual flow rate match. In this embodiment, the total flow rate of the target cargo handling flow rate of the traveling side and each cargo handling target flow rate is discharged from the hydraulic pump 11. Therefore, the control device 20 can supply the desired flow rate with high accuracy to each hydraulic circuit 12, 13 by controlling the first opening degree of the flow control valve 14 so that the actual flow rate on the traveling side becomes the target flow rate on the traveling side and each loading target flow rate and each loading actual flow rate match.

[0049] Further, the control device 20 controls the traveling system hydraulic circuit 12 in the case of simultaneous operation as follows. That is, the control device 20 calculates the opening degree of each of the traveling direction control valves 31, 32 according to the target flow rate of each of the traveling motors 2, 3. To explain in more detail, the differential pressure across each of the traveling direction control valves 31, 32 is maintained at a predetermined pressure by each of the pressure compensation valves 33, 34 as described above. Therefore, the control device 20 controls the opening degree of each of the traveling direction control valves 31, 32 at the same ratio as the ratio of the target flow rates of each of the traveling motors 2, 3. As a result, the flow rate introduced to the traveling system hydraulic circuit 12 is supplied to each of the traveling motors 2, 3 at a distribution amount according to the target flow rate of each of the traveling motors 2, 3. Therefore, even in the case of simultaneous operation, the excavator can be made to travel in accordance with the operation of the traveling pedals 21a, 21b.

[0050] Furthermore, the control device 20 controls the cargo handling hydraulic circuit 13 in the simultaneous operation as follows. That is, the control device 20 outputs a boom command signal, a boom command signal, and a bucket command signal according to the cargo handling target flow rate of each of the hydraulic cylinders 4-6. More specifically, the control device 20 controls the opening degree of each of the cargo handling directional control valves 41-43 based on the cargo handling target flow rate and the actual flow rate of each of the hydraulic cylinders 4-6. In this embodiment, the control device 20 controls the opening degree of each of the cargo handling directional control valves 41-43 so that the actual flow rate of each of the hydraulic cylinders 4-6 becomes the cargo handling target flow rate. As a result, the control device 20 can supply the hydraulic fluid at a flow rate corresponding to the operation of the travel pedals 21a, 21b to each of the traveling motors 2, 3 with high accuracy, and supply the hydraulic fluid at a flow rate corresponding to the operation of the cargo handling operation levers 22a, 22b to each of the hydraulic cylinders 4-6 with high accuracy.

[0051] In the hydraulic drive system 1 of the first embodiment, the flow control valve 14 changes the first opening degree, which is the opening degree between the pump passage 25 and the travel-side passage 26, in response to a control signal. Therefore, the flow control valve 14 can preferentially flow the hydraulic fluid to the cargo-handling hydraulic circuit 13 by narrowing the first opening degree in response to the control signal. The flow control valve 14 is further connected to a tank 28 and opens and closes between the pump passage 25 and the tank 28 in response to a control signal. Therefore, the flow control valve 14 can discharge the hydraulic fluid discharged from the hydraulic pump 11 to the tank 28, that is, can put the hydraulic pump 11 into an unloaded state. Therefore, the flow control valve 14 can achieve both the functions of a priority valve that preferentially flows the hydraulic fluid to the cargo-handling hydraulic circuit 13, and an unloading valve that puts the hydraulic pump into an unloaded state. Therefore, an increase in the number of processing steps and parts in the hydraulic drive system 1 can be suppressed. More specifically, the number of insertion holes in the valve block of the multi-control valve into which the flow control valve 14 is inserted can be reduced, thereby suppressing an increase in the number of processing steps. Also, since it is not necessary to provide an unloading valve in the valve block of the multi-control valve, an increase in the number of parts can be suppressed.

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

[0053] Furthermore, in the hydraulic drive unit 1 of the first embodiment, the control spool 14a is switched between the first control position A1 and the second control position A2 by stroking in response to a control signal. In the first control position A1, the pump passage 25 is opened between the traveling passage 26, and the second opening degree is reduced in response to the stroke amount of the control spool 14a. In the second control position A2, the pump passage 25 is closed between the tank 28, and the first opening degree is reduced in response to the stroke amount of the control spool 14a. Therefore, the control spool 14a can function as an unloading valve in the first control position A1, and can function as a priority valve in the second control position A2. Therefore, the flow control valve 14 can function as both an unloading valve and a priority valve by stroking the control spool 14a.

[0054] Furthermore, in the hydraulic drive unit 1 of the first embodiment, in the third control position A3, the first opening degree becomes the maximum opening degree, and the connection between the pump passage 25 and the tank 28 is closed. Therefore, in the third control position A3, the control spool 14a can guide the entire amount of hydraulic fluid discharged from the hydraulic pump 11 to the traveling system hydraulic circuit 12.

[0055] Furthermore, in the hydraulic drive unit 1 of the first embodiment, the flow control valve 14 maintains the first opening at the minimum opening when the communication between the pump passage 25 and the tank 28 is closed. Therefore, even if the flow control valve 14 is stuck at the minimum opening position, the hydraulic fluid flows to the traveling-side passage 26. Therefore, even if the flow control valve 14 is stuck at the minimum opening position, the hydraulic fluid can flow to the traveling-system hydraulic circuit 12.

[0056] Furthermore, in the hydraulic drive system 1 of the first embodiment, the control device 20 outputs a control signal to reduce the first opening of the flow control valve 14 to the minimum opening, and outputs each travel operation signal to block the flow of hydraulic fluid in the travel system hydraulic circuit 12. This allows the entire amount of hydraulic fluid from the hydraulic pump 11 to flow toward the cargo system hydraulic circuit 13.

[0057] Furthermore, in the hydraulic drive device 1 of the first embodiment, the cargo handling hydraulic circuit 13 controls the flow of hydraulic fluid to each of the hydraulic cylinders 4-6 by adjusting the opening between each of the hydraulic cylinders 4-6 and the hydraulic pump 11. Therefore, the flow control valve 14 can preferentially allow the hydraulic fluid to flow to each of the hydraulic cylinders 4-6 by narrowing the first opening in response to the control signal. Moreover, the traveling hydraulic circuit 12 controls the flow of hydraulic fluid to the traveling motors 2, 3 by adjusting the opening between the traveling motors 2, 3 and the hydraulic pump 11. Therefore, the flow control valve 14 can allow the hydraulic fluid to flow to the traveling motors 2, 3 by opening the second opening in response to the control signal.

[0058] [Second embodiment] The hydraulic drive system 1A of the second embodiment shown in Fig. 4 has a configuration similar to that of the hydraulic drive system 1 of the first embodiment. Therefore, the configuration of the hydraulic drive system 1A of the second embodiment will be mainly described with respect to the differences from the hydraulic drive system 1 of the first embodiment, and the same configuration will be denoted by the same reference numerals and description thereof will be omitted.

[0059] The hydraulic drive system 1A of the second embodiment includes a hydraulic pump 11, a traveling system hydraulic circuit 12, a cargo handling system hydraulic circuit 13, a flow control valve 14A, a discharge pressure sensor 15, a traveling side pressure sensor 16, and a control device 20. More specifically, the hydraulic drive system 1 further includes cargo side pressure sensors 17-19, a traveling system operation device 21, and a cargo handling system operation device 22. In this embodiment, the cargo handling system hydraulic circuit 13 is an example of a first hydraulic circuit, and the traveling system hydraulic circuit 12 is an example of a second hydraulic circuit. That is, the cargo handling 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 spool valve. The flow control valve 14A is interposed between a loading-side passage 27, which is an example of a first passage, and a pump passage 25. In other words, the pump passage 25 is connected to the loading-side passage 27 via the flow control valve 14A. The flow control valve 14 changes a first opening in response to an input control signal. In this embodiment, the first opening is an opening between the pump passage 25 and the loading-side passage 27. Therefore, the flow control valve 14A throttles the flow rate of the hydraulic fluid flowing through the loading-side passage 27 in response to the input control signal. As a result, the hydraulic fluid is preferentially supplied to the traveling system hydraulic circuit 12.

[0061] Moreover, 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 further connected to a tank 28, and opens and closes between the pump passage 25 and the tank passage 29 in response to a control signal. Moreover, the flow control valve 14 changes the second opening in response to the control signal. Moreover, the flow control valve 14A is, for example, an electrically controlled flow control spool valve, and has a control spool 14Aa that strokes in response to the control signal. The control spool 14Aa is configured similarly to the control spool 14a of the first embodiment. That is, the control spool 14Aa is switched between the first to third control positions A1 to A3 by stroking.

[0062] Each of the first to third control positions A1 to A3 will be described in detail below. In the first control position A1, as in the first embodiment, the pump passage 25 and the loading-side passage 27 are opened. As a result, 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 addition, in the first control position, the second opening is narrowed according to the stroke amount of the control spool 14a. By narrowing the second opening, the flow rate discharged to the tank 28 (bleed-off flow rate) can be adjusted, and the flow rate of the hydraulic fluid flowing into the loading-side passage 27 can be adjusted.

[0063] In the second control position A2, as in the first embodiment, the communication between the pump passage 25 and the tank 28 is closed (fully closed in this embodiment). On the other hand, in the second control position A2, the first opening degree is narrowed according to the stroke amount of the control spool 14a. As a result, the flow control valve 14 limits the flow rate of the hydraulic fluid introduced into the loading-side passage 27, and preferentially causes the hydraulic fluid to flow into the traveling-side passage 26, which is an example of a second passage. In other words, the flow control valve 14 preferentially supplies the hydraulic fluid to the traveling system hydraulic circuit 12. Note that, as in the first embodiment, the first opening degree can be changed from the maximum opening degree to a minimum opening degree that is not fully closed.

[0064] In the third control position A3, the first opening degree is the maximum opening degree, and the second opening degree is fully closed. As a result, in the third control position A3, the hydraulic fluid discharged from the hydraulic pump 11 can be supplied to the cargo-handling hydraulic circuit 13 via the cargo-side passage 27. In this embodiment, the first opening degree is the maximum opening degree in the third control position A3, similar to the first control position A1.

[0065] <Operation of the hydraulic drive unit> In the hydraulic drive device 1, in a non-operated state, the control spool 14a is located at the first control position A1. Therefore, the hydraulic fluid discharged from the hydraulic pump 11 is discharged to the tank 28, that is, the hydraulic pump 11 can be put into an unloaded state.

[0066] In the hydraulic drive system 1A, when the travel pedals 21a, 21b of the travel system operation device 21 are operated independently, the control device 20 operates as follows based on a travel operation command. That is, the control device 20 outputs a control signal to move the control spool 14a to a full stroke and position it at the second control position A2. The control device 20 also closes the hydraulic pump 11 and the hydraulic cylinders 4-6 with the loading system hydraulic circuit 13, and opens the travel-side passage 26 and the travel motors 2, 3 with the travel system hydraulic circuit 12. At this time, the control device 20 calculates each travel motor target flow rate based on the travel operation command, and outputs first and second travel command signals according to each travel motor target flow rate. As a result, the opening degree of each of the travel direction control valves 31, 32 is controlled to an opening degree according to each travel motor target flow rate. In the hydraulic drive system 1A, the pressure compensation valves 33, 34 also maintain the front and rear pressure differentials of each of the two travel direction control valves 31, 32. Therefore, by controlling the opening degree of each of the travel direction control valves 31, 32 to an opening degree corresponding to each travel motor target flow rate, hydraulic fluid is supplied to each of the travel motors 2, 3 at a flow rate corresponding to the opening degree of each of the travel direction control valves 31, 32. Therefore, the control device 20 can cause the hydraulic excavator to perform a travel operation corresponding to the operation of the travel pedals 21a, 21b.

[0067] When the cargo handling operation levers 22a, 22b of the cargo handling system operation device 22 are operated independently, the control device 20 operates as follows based on the cargo handling operation command. That is, the control device 20 moves the control spool 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 stroking the control spool 14Aa according to the pump discharge flow rate and the cargo handling side target flow rate. As a result, even if the total flow rate of each cargo handling target flow rate is less than the pump discharge flow rate, the total flow rate can be supplied to the cargo handling system hydraulic circuit 13. Also, the control device 20 closes the passage between the hydraulic pump 11 and the traveling motors 2, 3 by the traveling system hydraulic circuit 12. As a result, the hydraulic fluid discharged from the hydraulic pump 11 is supplied to the cargo handling system hydraulic circuit 13. Furthermore, the control device 20 opens the passage between the cargo handling side passage 27 and the hydraulic cylinders 4 to 6 by the cargo handling system hydraulic circuit 13. At this time, the control device 20 calculates the target cargo handling flow rate of each hydraulic cylinder 4-6 based on the cargo handling operation command, and estimates the actual cargo handling flow rate of each hydraulic cylinder 4-6 in the same manner as in the first embodiment. The control device 20 also calculates the opening degree of each of the cargo handling directional control valves 41-43 so that each of the estimated actual cargo handling flow rates becomes the target cargo handling flow rate. The control device 20 then outputs a boom command signal, a boom command signal, and a bucket command signal according to each calculated opening degree. Then, the flow of hydraulic fluid to the hydraulic cylinders 4-6 is controlled by each of the cargo handling directional control valves 41-43 to a flow according to the cargo handling operation command. As a result, the control device 20 can make the bucket operate according to the operation of the cargo handling operation levers 22a, 22b.

[0068] Furthermore, when the traveling pedals 21a, 21b and the cargo handling operation levers 22a, 22b are operated simultaneously, the control device 20 operates as follows based on the traveling operation command and the cargo handling operation command. That is, the control device 20 moves the control spool 14a to the third control position A3 by outputting a control signal. Then, the control device 20 controls the first opening to an opening according to the cargo handling side supply pressure detected by the pressure sensors 17-19. As a result, the control device 20 supplies hydraulic fluid to the traveling system hydraulic circuit 12 with priority, while also supplying hydraulic fluid to the cargo handling system hydraulic circuit 13. Furthermore, the control device 20 opens the passage between the traveling side 26 and the traveling motors 2, 3 by the traveling system hydraulic circuit 12, and opens the passage between the cargo handling side 27 and the hydraulic cylinders 4-6 by the cargo handling system hydraulic circuit 13.

[0069] The control device 20 also controls the traveling hydraulic circuit 12 as follows. That is, the control device 20 calculates the opening degree of each traveling direction control valve 31, 32 according to the target flow rate of each traveling motor 2, 3. As described above, the front and rear differential pressures of each traveling direction control valve 31, 32 are maintained at a predetermined pressure by each pressure compensation valve 33, 34. Therefore, the control device 20 supplies the flow rate introduced to the traveling hydraulic circuit 12 to each traveling motor 2, 3 at a distribution amount according to the target flow rate of each traveling motor 2, 3 by outputting first and second traveling command signals according to the calculated opening degrees. Furthermore, the control device 20 controls the loading system hydraulic circuit 13 as follows. That is, the control device 20 calculates the opening degree of each loading direction control valve 41-43 based on the loading operation command, and outputs each loading command signal according to the calculated opening degree. As a result, the control device 20 can supply hydraulic fluid at a flow rate corresponding to the operation of the travel pedals 21a, 21b to each of the travel motors 2, 3, and can supply hydraulic fluid at a flow rate corresponding to the operation of the cargo handling operation levers 22a, 22b to each of the hydraulic cylinders 4-6. As a result, even when the travel pedals 21a, 21b are operated simultaneously, the excavator can travel in accordance with the operation of the travel pedals 21a, 21b. Also, the bucket can be moved in accordance with the operation of the cargo handling operation levers 22a, 22b.

[0070] In the hydraulic drive unit 1A of the second embodiment, the flow control valve 14A reduces the first opening in response to a control signal, thereby allowing the hydraulic fluid to flow preferentially to the travel motors 2, 3. In addition, the flow control valve 14 opens the second opening in response to a control signal, thereby allowing the hydraulic fluid to flow to each of the hydraulic cylinders 4 to 6.

[0071] In addition, the hydraulic drive system 1A of the second embodiment has the same functions and effects as the hydraulic drive system 1 of the first embodiment.

[0072] [Other embodiments] In the hydraulic drive units 1, 1A of this embodiment, the traveling motors 2, 3 supplied by the traveling hydraulic circuit 12 are two, but the number may be one, and any number is acceptable. Similarly, the number of cargo-handling actuators 4-6 supplied by the cargo-handling hydraulic circuit 13 is also acceptable. Furthermore, the cargo-handling actuators 4-6 supplied by the cargo-handling hydraulic circuit 13 are not limited to hydraulic cylinders, and may be hydraulic motors. That is, the cargo-handling hydraulic circuit 13 may include, for example, a swing motor and an optional cylinder.

[0073] Furthermore, the traveling hydraulic circuit 12 and the loading hydraulic circuit 13 in the hydraulic drive system 1, 1A of this embodiment are not limited to the structures described above. The traveling hydraulic circuit 12 and the loading hydraulic circuit 13 may be circuits capable of supplying hydraulic fluid to the traveling motors 2, 3 and the hydraulic cylinders 4-6. Furthermore, in the hydraulic drive system 1, the control device 20 may operate the traveling motors 2, 3 and the hydraulic cylinders 4-6 according to a program stored in advance. The control device 20 directly acquires hydraulic pressure from the discharge pressure sensor 15, the traveling pressure sensor 16, and the loading pressure sensors 17-19, but may acquire the hydraulic pressure indirectly, for example, via a device not shown.

[0074] In addition, in the hydraulic drive system 1, 1A of this embodiment, the travelling-side passage 26 and the loading-side passage 27 are connected to the pump passage 25 so as to branch off from each other, but they may be connected as follows. That is, the travelling-side passage 26 may be connected to the loading-side passage 27 via the flow control valve 14, and further connected to the pump passage 25 via the flow control valve 14 and the loading-side passage 27. That is, the travelling-side passage 26 and the loading-side passage 27 may be connected in series to the pump passage 25. The hydraulic drive system of such an embodiment also achieves the same effects as the hydraulic drive system 1 of this embodiment.

[0075] Furthermore, the hydraulic drive unit 1A of the second embodiment may include a pressure sensor that detects the downstream pressure of the flow control valve 14A (i.e., equivalent to the first supply pressure).The control device 20 may estimate the actual loading-side flow rate, which is the actual flow rate of the hydraulic fluid flowing through the loading-system hydraulic circuit 13, based on the pressure sensor, and output a control signal according to the loading-side target flow rate and the actual loading-side flow rate.

[0076] A hydraulic drive device in a first aspect includes a hydraulic pump connected to a pump passage and discharging hydraulic 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 and changing a first opening degree, which is an opening degree between the pump passage and the first passage, in response to a control signal, and the flow control valve is further connected to a tank and opens and closes between the pump passage and the tank in response to a control signal.

[0077] According to the above aspect, the flow control valve changes the first opening, which is the opening between the pump passage and the first passage, in response to the control signal. Therefore, the flow control valve can preferentially flow the hydraulic fluid to the second hydraulic circuit by narrowing the first opening in response to the control signal. The flow control valve is further connected to the tank and opens and closes between the pump passage and the tank in response to the control signal. Therefore, the flow control valve can discharge the hydraulic fluid discharged from the hydraulic pump to the tank, that is, can put the hydraulic pump into an unloaded state. Therefore, the flow control valve can achieve both the functions of a priority valve that preferentially flows the hydraulic fluid to the second hydraulic circuit and an unloading valve that puts the hydraulic pump into an unloaded state. Therefore, an increase in the number of parts in the hydraulic drive device can be suppressed.

[0078] In a second aspect of the hydraulic drive device, in the first aspect, the flow control valve changes a second opening degree, which is an opening degree between the pump passage and the tank, in response to a control signal.

[0079] According to the above aspect, the flow control valve changes the second opening between the pump passage and the tank in response to the control signal, thereby controlling the flow rate of the hydraulic fluid flowing from the pump passage to the tank.

[0080] In a third aspect, the hydraulic drive device is the hydraulic drive device of the second aspect, wherein the flow control valve has a control spool that is switched between a first control position and a second control position by stroking in response to a control signal, and in the first control position, communication between the pump passage and the first passage is opened and a second opening degree is reduced in response to the stroke amount of the control spool, and in the second control position, communication between the pump passage and the tank is closed and the first opening degree is reduced in response to the stroke amount of the control spool.

[0081] According to the above aspect, the control spool is switched between a first control position and a second control position by stroking in response to a control signal. In the first control position, the pump passage and the first passage are opened, and the second opening is reduced in response to the stroke amount of the control spool. In the second control position, the pump passage and the tank are closed, and the first opening is reduced in response to the stroke amount of the control spool. Therefore, the control spool can function as an unloading valve in the first control position, and can function as a priority valve in the second control position. Therefore, the flow control valve can function as both an unloading valve and a priority valve by stroking the control spool.

[0082] In a fourth aspect, in the hydraulic drive device of the third aspect, the control spool is further switched to a third control position by stroking in response to a control signal, and in the third control position, the first opening becomes a maximum opening and the connection between the pump passage and the tank is closed.

[0083] According to the above aspect, in the third control position, the first opening degree is the maximum opening degree, and the connection between the pump passage and the tank is closed, so that in the third control position, the control spool can guide the entire amount of hydraulic fluid discharged from the hydraulic pump to the first hydraulic circuit.

[0084] In a fifth aspect, in the hydraulic drive device of any one of the first to fourth aspects, the flow control valve has a first opening degree that is a minimum opening degree when communication between the pump passage and the tank is closed.

[0085] According to the above aspect, the flow control valve sets the first opening to the minimum opening when the connection between the pump passage and the tank is closed. Therefore, even if the flow control valve is stuck at the minimum opening position, the hydraulic fluid flows into the first passage. Therefore, even if the flow control valve is stuck at the minimum opening position, the hydraulic fluid can flow into the first hydraulic circuit.

[0086] In a sixth aspect, the hydraulic drive device of the fifth aspect further includes a control device that controls movement of the flow control valve by outputting a control signal, and the first hydraulic circuit blocks the flow of hydraulic fluid in response to a first signal, and the control device sets the first opening of the flow control valve to a minimum opening by outputting a control signal, and blocks the flow of hydraulic fluid in the first hydraulic circuit by outputting a first signal.

[0087] According to the above aspect, the control device outputs a control signal to set the first opening of the flow control valve to the minimum opening, and outputs the first signal to block the flow of hydraulic fluid in the first hydraulic circuit, thereby allowing the entire amount of hydraulic fluid from the hydraulic pump to flow toward the second hydraulic circuit.

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

[0089] According to the above aspect, the second hydraulic circuit is a cargo-loading hydraulic circuit that controls the flow of hydraulic fluid to the cargo-loading actuators by adjusting the opening between the cargo-loading actuators and the hydraulic pump. Therefore, the flow control valve can preferentially flow hydraulic fluid to the cargo-loading actuators by narrowing the first opening in response to the control signal. Also, the first hydraulic circuit is a travel-loading hydraulic circuit that controls the flow of hydraulic fluid to the travel motors by adjusting the opening between the travel motors and the hydraulic pump. Therefore, the flow control valve can flow hydraulic fluid to the travel motors by opening the second opening in response to the control signal.

[0090] The hydraulic drive device in an eighth aspect is the hydraulic drive device of any one of the first to sixth aspects, wherein the first hydraulic circuit is a loading system hydraulic circuit that controls the flow of hydraulic fluid to the loading actuator by adjusting the opening between the loading actuator and the hydraulic pump, and the second hydraulic circuit is a traveling system hydraulic circuit that controls the flow of hydraulic 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 traveling hydraulic circuit that controls the flow of hydraulic fluid to the traveling motor by adjusting the opening between the traveling motor and the hydraulic pump. Therefore, the flow control valve can preferentially flow hydraulic fluid to the traveling motor by narrowing the first opening in response to the control signal. Also, the first hydraulic circuit is a cargo-unloading hydraulic circuit that controls the flow of hydraulic fluid to the cargo-unloading actuator by adjusting the opening between the cargo-unloading actuator and the hydraulic pump. Therefore, the flow control valve can flow hydraulic fluid to the cargo-unloading actuator by opening the second opening in response to the control signal. [Explanation of symbols]

[0092] 1. Hydraulic drive unit 1A Hydraulic Drive Unit 2. First traction motor 3. Second traction motor 4 Boom cylinder (loading actuator) 5 Arm cylinder (loading actuator) 6 Bucket cylinder (loading actuator) 11 Hydraulic pump 12. Driving system hydraulic circuit 13 Cargo handling hydraulic circuit 14 Flow Control Valve 14a Control spool 14A Flow Control Valve 14Aa Control Spool 15 Discharge pressure sensor 16 Traveling side pressure sensor (first pressure sensor) 20 Control device 25 Pump passage 26 Traveling side aisle (1st aisle, 2nd aisle) 27 Cargo handling aisle (2nd aisle, 1st aisle) 28 Tank 31 First travel directional control valve 32 Second travel directional control valve 41 Boom directional control valve (loading directional control valve) 42 Arm directional control valve (loading directional control valve) 43 Bucket directional control valve (loading directional control valve)

Claims

1. a hydraulic pump connected to the pump passage and configured to discharge hydraulic 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; a flow control valve that is interposed between the pump passage and the first passage and changes a first opening degree, which is an opening degree between the pump passage and the first passage, in response to a control signal, The flow control valve is further connected to a tank, and is a hydraulic drive device that opens and closes between the pump passage and the tank in response to a control signal.

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

3. The flow control valve has a control spool that is switched between a first control position and a second control position by stroking in response to a control signal, In the first control position, the pump passage and the first passage are connected to each other, and a second opening degree is reduced in accordance with a stroke amount of the control spool.

3. The hydraulic drive system according to claim 2, wherein, in the second control position, communication between the pump passage and the tank is closed, and the first opening degree is reduced in accordance with a stroke amount of the control spool.

4. the control spool is further switched to a third control position by stroking in response to a control signal; 4. The hydraulic drive system according to claim 3, wherein in the third control position, the first opening degree is a maximum opening degree, and communication between the pump passage and the tank is closed.

5. 2. The hydraulic drive system according to claim 1, wherein the flow control valve has a first opening degree that is a minimum opening degree when communication between the pump passage and the tank is closed.

6. A control device that controls the movement of the flow control valve by outputting a control signal, the first hydraulic circuit cuts off the flow of hydraulic fluid in response to a first signal; 6. The hydraulic drive system according to claim 5, wherein the control device sets the first opening of the flow control valve to a minimum opening by outputting a control signal, and blocks the flow of hydraulic fluid in the first hydraulic circuit by outputting a first signal.

7. the first hydraulic circuit is a traveling system hydraulic circuit that controls a flow of hydraulic fluid to the traveling motor by adjusting an opening between the traveling motor and the hydraulic pump; 2. The hydraulic drive system according to claim 1, wherein the second hydraulic circuit is a cargo-handling system hydraulic circuit that controls a flow of hydraulic fluid to the cargo-handling actuator by adjusting an opening between the cargo-handling actuator and the hydraulic pump.

8. the first hydraulic circuit is a cargo-handling system hydraulic circuit that controls a flow of hydraulic fluid to the cargo-handling actuator by adjusting an opening between the cargo-handling actuator and the hydraulic pump; 2. The hydraulic drive system according to claim 1, wherein the second hydraulic circuit is a travel system hydraulic circuit that controls a flow of hydraulic fluid to the travel motor by adjusting an opening between the travel motor and the hydraulic pump.

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