Hydraulic Drive Unit

Abstract

Provided is a hydraulic drive device for individually supplying hydraulic fluid to a travel motor and a cargo handling actuator, the hydraulic drive device including: a hydraulic pump that discharges the hydraulic fluid; a travel system hydraulic pressure circuit that is connected to a first channel which branches from a pump channel connected to the hydraulic pump, and that controls the flow of the hydraulic fluid to the travel motor; a cargo handling system hydraulic pressure circuit that is connected to a second channel which branches from the pump channel, and that controls the flow of the hydraulic fluid to the cargo handling actuator; a flowrate control valve that is provided on the second channel, and that changes a degree of opening of the second channel in accordance with a degree-of-opening signal; a travel side pressure sensor that detects a travel side supply pressure that is a pressure supplied to the travel motor; and a control device that controls, by outputting the degree-of-opening signal to the flowrate control valve, the degree of opening of the second channel in accordance with the travel side supply pressure detected by the travel side pressure sensor.

Description

[Technical Field]

[0001] The present invention relates to a hydraulic drive system that supplies hydraulic fluid to a travel motor and a load-handling actuator. [Background technology]

[0002] One-pump systems using a single pump as the hydraulic pressure source for the travel motor and the load-handling actuator of a construction machine are in practical use. A hydraulic circuit such as that disclosed in Patent Document 1 is known as a hydraulic drive device for a one-pump system. In the hydraulic circuit of Patent Document 1, a pump is connected to the travel motor and the load-handling 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 pressurized oil to flow preferentially to the travel motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-026828 Summary of the Invention [Problem to be solved by the invention]

[0004] In the hydraulic circuit of Patent Document 1, the priority valve throttles the aperture of the second pump line depending on the applied supply pressure. Therefore, the priority valve determines a one-to-one relationship between the supply pressure and the aperture of the second pump line. Therefore, the priority valve has a low degree of freedom in controlling the aperture of the second pump line.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a hydraulic drive system that can improve the degree of freedom in controlling the opening degree of a passage connected to a cargo handling actuator. [Means for solving the problem]

[0006] The hydraulic drive device of the present invention supplies hydraulic fluid to a travel motor and a load-handling actuator, and includes a hydraulic pump that discharges hydraulic fluid, a travel system hydraulic circuit connected to a first passage branching from a pump passage connected to the hydraulic pump and controlling the flow of hydraulic fluid to the travel motor, a load-handling system hydraulic circuit connected to a second passage branching from the pump passage and controlling the flow of hydraulic fluid to the load-handling actuator, a flow control valve interposed in the second passage and changing the opening of the second passage in response to an opening signal, a travel-side pressure sensor that detects the travel-side supply pressure that is the supply pressure to the travel motor, and a control device that controls the opening of the second passage in response to the travel-side supply pressure detected by the travel-side pressure sensor by outputting an opening signal to the flow control valve.

[0007] According to the present invention, the control device controls the aperture of the second passage by operating the flow control valve in response to the travel-side supply pressure. Therefore, by changing the control logic of the control device, the aperture of the second passage that is opened in response to the travel-side supply pressure can be easily adjusted. This improves the degree of freedom in control of the aperture of the second passage. [Effects of the Invention]

[0008] According to the present invention, it is possible to improve the degree of freedom in controlling the opening degree of the passage leading to the cargo handling actuator.

[0009] The above and other objects, features, and advantages of the present invention will become apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a circuit diagram showing the configuration of a hydraulic drive device according to a first embodiment of the present invention. [Figure 2] FIG. 5 is a circuit diagram showing a traveling system hydraulic circuit of a hydraulic drive system according to a second embodiment of the present invention. [Figure 3]FIG. 10 is a circuit diagram showing a travel system hydraulic circuit of a hydraulic drive system according to another embodiment of the present invention. [Figure 4] FIG. 10 is a circuit diagram showing a travel system hydraulic circuit of a hydraulic drive system according to still another embodiment of the present invention. [Figure 5] FIG. 10 is a circuit diagram showing the configuration of a hydraulic drive device according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, hydraulic drive units 1, 1A according to first and second embodiments of the present invention will be described with reference to the drawings. Note that the concepts of directions used in the following description are used for the convenience of explanation and do not limit the orientation of the configuration of the invention to those directions. Furthermore, the hydraulic drive units 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.

[0012] The hydraulic drive system 1 shown in Fig. 1 is provided on a work vehicle (not shown) that includes travel motors 2 and 3 and cargo handling actuators 4 to 6. Work vehicles include, for example, construction vehicles such as hydraulic excavators and hydraulic cranes, and industrial vehicles such as lifts. In this embodiment, the hydraulic drive system 1 is provided on a hydraulic excavator, which is an example of a work vehicle. In addition to the hydraulic drive system 1, the hydraulic excavator also includes a vehicle body and a work machine.

[0013] 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 that can travel. The travel motors 2, 3 are hydraulic motors that drive the left and right crawlers, respectively. More specifically, the travel motors 2, 3 each have two supply / 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 / discharge ports 2a, 3a, and rotate in the reverse direction when hydraulic fluid is supplied to the other supply / discharge port 2b, 3b.

[0014] The work machine includes a boom, an arm, a bucket (none of which are shown), and a plurality of load-handling actuators 4-6. The work machine is rotatably mounted on the vehicle body. In this embodiment, the load-handling actuators 4-6 are hydraulic cylinders 4-6. The hydraulic cylinders 4-6 are respectively mounted on the boom, arm, and bucket. The work machine moves the boom, arm, and bucket by extending and retracting the three hydraulic cylinders 4-6. This enables the work machine to perform a variety of tasks.

[0015] <Hydraulic drive unit> The hydraulic drive unit 1 includes a hydraulic pump 11, a traveling system hydraulic circuit 12, a cargo handling system hydraulic circuit 13, a flow control valve 14, traveling side pressure sensors 15 and 16, and a control device 17. More specifically, the hydraulic drive unit 1 further includes cargo handling side pressure sensors 18-20, a traveling system operation device 21, and a cargo handling system operation device 22. The hydraulic drive unit 1 is a so-called one-pump system, in which one hydraulic pump 11 supplies hydraulic fluid to the traveling motors 2 and 3 and three hydraulic cylinders 4-6. The hydraulic drive unit 1 supplies hydraulic fluid to the first traveling motor 2 and the second traveling motor 3, respectively, thereby operating the crawlers corresponding to the traveling motors 2 and 3. This allows the hydraulic drive unit 1 to travel the hydraulic excavator. The hydraulic drive unit 1 also supplies hydraulic fluid to the hydraulic cylinders 4-6, thereby operating the corresponding boom, arm, and bucket. This allows the hydraulic drive system 1 to cause the hydraulic excavator to perform a variety of 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 is driven to rotate by the drive source, thereby discharging hydraulic fluid into the pump passage 25. The pump passage 25 branches into a first passage 26 and a second passage 27.

[0017] <Traction system hydraulic circuit> The travel system hydraulic circuit 12 includes a first travel directional control valve 31 and a second travel directional control valve 32. The travel system hydraulic circuit 12 is connected to the first passage 26 and the first and second travel motors 2 and 3. The travel system hydraulic circuit 12 supplies hydraulic fluid to each of the first and second travel motors 2 and 3. The travel system hydraulic circuit 12 controls the flow of hydraulic fluid to each of the first and second travel motors 2 and 3. More specifically, the travel system hydraulic circuit 12 supplies hydraulic fluid to the first and second travel motors 2 and 3 in a flow (flow direction and flow rate in this embodiment) that corresponds to the input first and second travel commands.

[0018] The first travel direction control valve 31 has a first travel spool 31a. The first travel direction control valve 31 controls the flow of hydraulic fluid to the first travel motor 2. More specifically, the first travel direction control valve 31 is connected to the first passage 26, the tank 28, and the two supply and discharge ports 2a and 2b of the first travel motor 2. The first travel spool 31a moves in response to an input first travel command. This switches the connection destinations of the supply and discharge ports 2a and 2b to the first passage 26 and the tank 28, respectively. The first travel spool 31a changes its opening depending on its position. Therefore, hydraulic fluid is supplied from the first travel direction control valve 31 to the first travel motor 2 in a direction and at a flow rate corresponding to the first travel command. As a result, the first travel direction control valve 31 rotates the first travel motor 2 forward and reverse in response to the first travel command, and rotates the first travel motor 2 at a speed corresponding to the first travel command. In this embodiment, the first traveling directional control valve 31 is an electrically controlled directional control valve.

[0019] The second travel direction control valve 32 has a second travel spool 32a. The second travel direction control valve 32 controls the flow of hydraulic fluid to the second travel motor 3. More specifically, the second travel direction control valve 32 is connected to the first passage 26 in parallel with the first travel direction control valve 31. The second travel direction control valve 32 is also connected to the tank 28 and two supply / discharge ports 3a and 3b of the second travel motor 3. The second travel spool 32a moves in response to an input second travel command. This switches the connection destinations of the supply / discharge ports 3a and 3b to the first passage 26 and the tank 28, respectively. The second travel spool 32a changes its opening depending on its position. Therefore, hydraulic fluid is supplied from the second travel direction control valve 32 to the second travel motor 3 in a direction and at a flow rate that corresponds to the second travel command. As a result, the second traveling direction control valve 32 rotates the second traveling motor 3 in the forward or reverse direction in response to the second traveling command, and rotates the second traveling motor 3 at a speed in accordance with the second traveling command. In this embodiment, the second traveling direction control valve 32 is an electrically controlled directional control valve.

[0020] <Cargo handling hydraulic circuit> 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 41-43. The three cargo handling directional control valves 41-43 are a boom directional control valve 41, an arm directional control valve 42, and a bucket directional control valve 43. The cargo handling hydraulic circuit 13 is connected to the second passage 27 and 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. More specifically, the cargo handling hydraulic circuit 13 supplies hydraulic fluid to the three hydraulic cylinders 4-6 in a flow (flow direction and flow rate in this embodiment) that corresponds to the input cargo handling command.

[0021] The three load-handling directional control valves 41-43 have load-handling spools 41a-43a, respectively. The three load-handling directional control valves 41-43 control the flow of hydraulic fluid to the corresponding 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. The three load-handling directional control valves 41-43 are connected to the second passage 27 in parallel with one another. Furthermore, the three load-handling directional control valves 41-43 are connected to the tank 28 and the rod-side ports 4a, 5a, 6a and head-side ports 4b, 5b, 6b of each hydraulic cylinder 4-6, respectively. The load-handling spools 41a-43a move in response to a boom command, an arm command, and a bucket command, respectively. As a result, the connections of the rod-side ports 4a-6a and the head-side ports 4b-6b are switched to the second passage 27 and the tank 28, respectively. The cargo-handling spools 41a-43a change their opening depending on their positions. Therefore, hydraulic fluid is supplied from each of the cargo-handling directional control valves 41-43 to each of the hydraulic cylinders 4-6 in a direction and at a flow rate corresponding to each command. As a result, the cargo-handling directional control valves 41-43 can extend or retract the corresponding hydraulic cylinders 4-6 at a speed corresponding to each command. In this embodiment, the cargo-handling directional control valves 41-43 are also electrically controlled directional control valves.

[0022] <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 and includes a control spool 14a. The flow control valve 14 is interposed in the second passage 27. The flow control valve 14 changes the aperture of the second passage 27 in response to an input aperture signal. More specifically, the flow control valve 14 throttles the flow rate of hydraulic fluid flowing through the second passage 27 in response to the input aperture signal. This allows hydraulic fluid to flow preferentially to the traveling system hydraulic circuit 12. In this embodiment, the hydraulic drive unit 1 is provided with one flow control valve 14 for one hydraulic pump 11. In the hydraulic drive unit 1, the single flow control valve 14 allows hydraulic fluid to flow preferentially to the traveling system hydraulic circuit 12.

[0023] The control spool 14a moves in response to the input opening signal. As a result, the control spool 14a throttles the opening of the second passage 27 in response to the input opening signal. In this embodiment, the flow control valve 14 includes an electromagnetic proportional valve 14b and a spring 14c. The electromagnetic proportional valve 14b outputs a pilot pressure to the control spool 14a in response to the opening signal. The spring 14c acts on the control spool 14a so as to resist the pilot pressure of the electromagnetic proportional valve 14b. Therefore, the control spool 14a moves to a position in response to the pilot pressure output from the electromagnetic proportional valve 14b. As a result, the control spool 14a throttles the opening of the second passage 27 to an opening in response to the opening signal.

[0024] <First driving side pressure sensor> The first traveling side pressure sensor 15 detects the first traveling side supply pressure, which is the pressure supplied to the first traveling motor 2. More specifically, the first traveling side pressure sensor 15 detects the hydraulic pressure of the hydraulic fluid supplied from the first traveling directional control valve 31 to the first traveling motor 2. In this embodiment, the first traveling side pressure sensors 15 are provided in the supply and discharge ports 2a, 2b of the first traveling motor 2. The first traveling side pressure sensor 15 outputs the hydraulic pressure detected at the supply and discharge ports 2a, 2b of the first traveling motor 2.

[0025] <Second driving side pressure sensor> Second traveling-side pressure sensor 16 is a sensor separate from first traveling-side pressure sensor 15, and detects second traveling-side supply pressure, which is the pressure supplied to second traveling motor 3. More specifically, second traveling-side pressure sensor 16 detects the hydraulic pressure of the hydraulic fluid supplied from second traveling directional control valve 32 to second traveling motor 3. In this embodiment, second traveling-side pressure sensor 16 is connected to each of supply and discharge ports 3a, 3b of second traveling motor 3. Second traveling-side pressure sensor 16 outputs the hydraulic pressure detected at supply and discharge ports 3a, 3b of second traveling motor 3.

[0026] <Loading side pressure sensor> The cargo-side pressure sensors 18-20 detect the cargo-side supply pressure, which is the pressure supplied to the hydraulic cylinders 4-6. More specifically, each of the cargo-side pressure sensors 18-20 detects the supply pressure supplied to the boom cylinder 4, the arm cylinder 5, and the bucket cylinder 6. In this embodiment, the cargo-side pressure sensors 18-20 are connected to the rod-side ports 4a-6a and the head-side ports 4b-6b of the hydraulic cylinders 4-6, respectively. The cargo-side pressure sensors 18-20 output the hydraulic pressure detected at the rod-side ports 4a-6a and the head-side ports 4b-6b of the hydraulic cylinders 4-6.

[0027] <Traveling control device> The traveling system operation device 21 is a device that allows the driver to operate the traveling motors 2, 3. The traveling system operation device 21 includes, for example, a traveling operation lever 21a, which is an operating tool. The traveling operation lever 21a can be tilted. In this embodiment, the traveling operation lever 21a can be tilted, for example, in all directions. The traveling system operation device 21 outputs a traveling operation command according to the tilt direction and tilt amount. The operating tool provided in the traveling system operation device 21 may be an operation pedal, and its form is not limited.

[0028] <Cargo handling operation device> The cargo handling system operation device 22 is a device that allows the driver to operate an attachment (a bucket in this embodiment). More specifically, the operating tools of the cargo handling system operation device 22 include a cargo handling operation lever 22a. The cargo handling operation lever 22a can be tilted. In this embodiment, the cargo handling operation lever 22a can be tilted, for example, in the forward and backward directions. The cargo handling system operation device 22 outputs a cargo handling operation command according to the tilt direction and tilt amount. Note that the operating tool provided in the cargo handling system operation device 22 is not limited to the cargo handling operation lever 22a, and may be in other forms such as an operation panel.

[0029] <Control device> The control device 17 controls the operation of the traveling system hydraulic circuit 12. More specifically, the control device 17 acquires a traveling operation command output from the traveling system operating device 21. In response to this, the control device 17 controls the movement of the first traveling direction control valve 31 and the second traveling direction control valve 32 (i.e., the positions of the spools 31a, 32a) in accordance with the traveling operation command. In this embodiment, the control device 17 outputs a first traveling command and a second traveling command in accordance with the traveling operation command. In response to this, the first traveling motor 2 and the second traveling motor 3 rotate in a direction and at a rotational speed in accordance with the traveling operation command, and the hydraulic excavator moves in a direction and at a speed in accordance with the traveling operation command.

[0030] The control device 17 also controls the operation of the cargo handling hydraulic circuit 13. More specifically, the control device 17 acquires cargo handling operation commands output from the cargo handling system operation device 22. The control device 17 then controls the movement of the cargo handling directional control valves 41-43 (i.e., the positions of the spools 41a-43a) in accordance with the cargo handling operation commands. In this embodiment, the control device 17 outputs a boom command, an arm command, and a bucket command in accordance with the cargo handling operation command. The hydraulic cylinders 4-6 then extend and retract at a speed in accordance with the cargo handling operation command. This allows the bucket to move in a direction and at a speed in accordance with the cargo handling operation command, allowing the hydraulic excavator to perform the desired work.

[0031] Furthermore, the control device 17 outputs an opening degree signal to the flow control valve 14 to control the opening degree of the second passage 27 in accordance with the travel-side supply pressure detected by the travel-side pressure sensors 15 and 16 and the loading-side supply pressure detected by the loading-side pressure sensors 18-20. More specifically, the control device 17 acquires the travel-side supply pressure and the loading-side supply pressure. In this embodiment, the control device 17 selects the first travel-side supply pressure and the second travel-side supply pressure from the hydraulic pressures detected by the travel-side pressure sensors 15 and 16. The control device 17 estimates, for example, which of the supply / discharge ports 2a, 2b, 3a, and 3b will be the supply side based on the travel operation command. The control device 17 acquires the hydraulic pressures of the supply-side ports as the first travel-side supply pressure and the second travel-side supply pressure. In a similar manner, the control device 17 selects the loading-side supply pressure for each of the hydraulic cylinders 4-6 from the hydraulic pressures detected by the loading-side pressure sensors 18-20. Furthermore, the control device 17 outputs an opening signal to the flow control valve 14 in accordance with the acquired first traveling-side supply pressure, second traveling-side supply pressure, and loading-side supply pressure for each of the hydraulic cylinders 4-6. This causes the control spool 14a to move to a position in accordance with the first traveling-side supply pressure, second traveling-side supply pressure, and loading-side supply pressure for each of the hydraulic cylinders 4-6. Therefore, the opening of the second passage 27 is controlled in accordance with the first traveling-side supply pressure, second traveling-side supply pressure, and loading-side supply pressure.

[0032] For example, when the maximum value of the two traveling-side supply pressures satisfies a predetermined condition, for example, a predetermined traveling-side threshold value or more, the control device 17 reduces the opening degree of the second passage 27. When the maximum value of the two traveling-side supply pressures is less than the traveling-side threshold value, the control device 17 opens the second passage 27. The traveling-side threshold value is set in advance in the control device 17. The traveling-side threshold value is set, for example, to be adjustable.

[0033] Furthermore, the control device 17 moves the control spool 14a in response to the first traveling-side supply pressure, the second traveling-side supply pressure, and the three loading-side supply pressures based on a preset program or the like. This controls the opening degree of the second passage 27 to a value corresponding to the first traveling-side supply pressure, the second traveling-side supply pressure, and the three loading-side supply pressures. The control device 17 can change the opening degree of the second passage 27 that is opened in response to the first traveling-side supply pressure, the second traveling-side supply pressure, and the loading-side supply pressures of the hydraulic cylinders 4-6. For example, the control device 17 adjusts the command values ​​of the commands output in response to the first traveling-side supply pressure, the second traveling-side supply pressure, and the loading-side supply pressures of the hydraulic cylinders 4-6. This allows the opening degree of the second passage 27, which is opened in response to the first traveling-side supply pressure and the second traveling-side supply pressure, to be adjusted in response to the loading-side supply pressures.

[0034] <Operation of the hydraulic drive unit> In the hydraulic drive system 1, when the travel operation lever 21a of the travel system operation device 21 is operated independently, a travel operation command is output from the travel system operation device 21. In response to this, the control device 17 actuates the travel direction control valves 31, 32 and controls the flow of hydraulic fluid to the travel motors 2, 3 to a flow (flow direction and flow rate in this embodiment) according to the travel operation command. In this way, the control device 17 can cause the hydraulic excavator to perform a travel operation according to the operation of the travel operation lever 21a. Note that when the supply of hydraulic fluid to the travel motors 2, 3 causes the maximum values ​​of the first travel-side supply pressure and the second travel-side supply pressure to exceed the travel-side threshold value, the control device 17 narrows the opening of the second passage 27.

[0035] In the hydraulic drive system 1, when the cargo handling operation lever 22a of the cargo handling system operation device 22 is operated independently, a cargo handling operation command is output from the cargo handling system operation device 22. In response, the control device 17 operates the cargo handling directional control valves 41-43 to control the flow of hydraulic fluid to the hydraulic cylinders 4-6 to a flow (flow direction and flow rate in this embodiment) according to the cargo handling operation command. This allows the control device 17 to cause the bucket to operate in accordance with the operation of the cargo handling operation lever 22a. Note that when the cargo handling operation lever 22a is operated independently, the maximum values ​​of the first traveling-side supply pressure and the second traveling-side supply pressure become less than the traveling-side threshold value, so the control device 17 opens the second passage 27.

[0036] The hydraulic drive unit 1 operates as follows when the travel operation lever 21a and the load-handling operation lever 22a are simultaneously operated. That is, the control device 17 operates the flow control valve 14 based on the acquired travel-side supply pressure and load-handling-side supply pressure. For example, when the maximum value of the two travel-side supply pressures is equal to or greater than the travel-side threshold value, the control device 17 moves the control spool 14a of the flow control valve 14 to narrow the aperture of the second passage 27. This prevents a shortage of hydraulic fluid supplied to the travel motors 2 and 3. The aperture of the second passage 27 is controlled to an aperture corresponding to the travel-side supply pressure and the load-handling-side supply pressure. This allows an appropriate amount of hydraulic fluid to flow to the load-handling system hydraulic circuit 13. On the other hand, when the maximum value of the two travel-side supply pressures is less than the travel-side threshold value, the control device 17 controls the movement of the control spool 14a of the flow control valve 14 to open the second passage 27. This prevents a shortage of hydraulic fluid supplied to the hydraulic cylinders 4 to 6.

[0037] In the hydraulic drive unit 1 of the first embodiment, the control device 17 controls the opening degree of the second passage 27 by operating the flow control valve 14 in accordance with the travel-side supply pressure. Therefore, by changing the control logic of the control device 17, the opening degree of the second passage 27 that is opened in response to the travel-side supply pressure can be easily adjusted. For example, the control device 17 can easily adjust the travel-side threshold value and the loading-side threshold value, or adjust the opening degree that should be opened in response to the travel-side supply pressure. Therefore, the degree of freedom in control of the opening degree of the second passage 27 can be improved.

[0038] In the hydraulic drive unit 1 of the first embodiment, the control device 17 controls the opening degree of the second passage 27 in accordance with the travel-side supply pressure and the cargo-side supply pressure. Therefore, the control device 17 can adjust the opening degree of the second passage 27, which is throttled down relative to the travel-side supply pressure, in accordance with the cargo-side supply pressure. This makes it possible to adjust the flow rate of hydraulic fluid flowing through the travel-system hydraulic circuit 12 in accordance with the status of the cargo-handling actuators 4 to 6.

[0039] In the hydraulic drive system 1 of the first embodiment, the control device 17 controls the opening degree of the second passage 27 in accordance with the first traveling-side supply pressure and the second traveling-side supply pressure. Therefore, even when the traveling system hydraulic circuit 12 supplies hydraulic fluid to two traveling motors 2, 3, the degree of freedom in control of the opening degree of the second passage 27 can be improved.

[0040] In the hydraulic drive system 1 of the first embodiment, the first traveling-side pressure sensor 15 detects the pressure of the hydraulic fluid supplied from the first traveling directional control valve 31 to the first traveling motor 2. The second traveling-side pressure sensor 16 detects the pressure of the hydraulic fluid supplied from the second traveling directional control valve 32 to the second traveling motor 3. Therefore, the supply pressure of the hydraulic fluid supplied to each traveling motor 2, 3 can be easily obtained.

[0041] In the hydraulic drive system 1 of the first embodiment, the control device 17 controls the aperture of the second passage 27 in accordance with the first travel-side supply pressure, the second travel-side supply pressure, and a plurality of cargo-side supply pressures. Therefore, the control device 17 controls the aperture of the second passage 27 in accordance with the first travel-side supply pressure, the second travel-side supply pressure, and three cargo-side supply pressures. Therefore, the control device 17 can adjust the aperture of the second passage 27, which is throttled back in response to the first travel-side supply pressure and the second travel-side supply pressure, in accordance with the plurality of cargo-side supply pressures. This makes it possible to adjust the flow rate of hydraulic fluid flowing through the travel-system hydraulic circuit 12 in accordance with the status of each of the cargo-side actuators 4 to 6.

[0042] In the hydraulic drive system 1 of the first embodiment, each of the multiple load-handling side pressure sensors 18-20 detects the supply pressure of the hydraulic fluid supplied from the corresponding load-handling directional control valves 41-43 to the hydraulic cylinders 4-6. Therefore, the supply pressure of the hydraulic fluid supplied to each of the hydraulic cylinders 4-6 can be easily obtained.

[0043] In the hydraulic drive system 1 of the first embodiment, the control device 17 operates the flow control valve 14 based on the maximum value of the multiple load-side supply pressures and the maximum values ​​of the first and second travel-side supply pressures. Therefore, the control device 17 can adjust the opening degree of the second passage 27 in accordance with the highest supply pressure to the travel motors 2, 3 and the hydraulic cylinders 4-6. Therefore, the control device 17 can adjust the opening degree of the second passage 27, which is throttled down relative to the travel-side supply pressure, in accordance with the maximum pressure of the three load-side supply pressures. This makes it possible to adjust the flow rate of hydraulic fluid flowing through the travel-system hydraulic circuit 12 in accordance with the largest load acting on the load actuators 4-6.

[0044] [Second embodiment] The hydraulic drive system 1A of the second embodiment is similar in configuration to the hydraulic drive system 1 of the first embodiment. Regarding the configuration of the hydraulic drive system 1A of the second embodiment, differences from the hydraulic drive system 1 of the first embodiment will be mainly described, and the same components will be assigned the same reference numerals and descriptions thereof will be omitted.

[0045] The hydraulic drive system 1A includes a hydraulic pump 11, a traveling system hydraulic circuit 12A, a cargo handling system hydraulic circuit 13, a flow control valve 14, a supply pressure selection circuit 30, a traveling side pressure sensor 15A, and a control device 17A. More specifically, the hydraulic drive system 1A further includes cargo side pressure sensors 18-20, a traveling system operating device 21, and a cargo handling system operating device 22. The traveling system hydraulic circuit 12A includes a first traveling directional control valve 31A and a second traveling directional control valve 32A.

[0046] The first traveling directional control valve 31A is connected to the first inner passage 34. The first inner passage 34 is connected to the first passage 26 via the first traveling directional control valve 31A. The first traveling directional control valve 31A controls the opening between the first inner passage 34 and the first passage 26 depending on the position of the first traveling spool 31a. Therefore, the first traveling-side supply pressure is output to the first inner passage 34. The first inner passage 34, together with the first passage 26, is connected to one of the two supply / discharge ports 2a, 2b of the first traveling motor 2. More specifically, the first inner passage 34 is connected to one of the supply / discharge ports 2a, 2b depending on the position of the first traveling spool 31a. The other of the supply / discharge ports 2a, 2b is connected to the tank 28.

[0047] The second traveling directional control valve 32A is connected to the second inner passage 35. The second inner passage 35 is connected to the first passage 26 via the second traveling directional control valve 32A. The second traveling directional control valve 32A controls the opening between the second inner passage 35 and the first passage 26 depending on the position of the second traveling spool 32a. Therefore, the second traveling-side supply pressure is output to the second inner passage 35. The second inner passage 35, together with the first passage 26, is connected to one of the two supply / discharge ports 3a, 3b of the second traveling motor 3. More specifically, the second inner passage 35 is connected to one of the supply / discharge ports 3a, 3b depending on the position of the second traveling spool 32a. The other of the supply / discharge ports 3a, 3b is connected to the tank 28.

[0048] The supply pressure selection circuit 30 has two check valves 30a, 30b. The supply pressure selection circuit 30 is connected to a first intermediate passage 34 and a second intermediate passage 35. The supply pressure selection circuit 30 acquires the first traveling side supply pressure and the second traveling side supply pressure from the intermediate passages 34, 35. The supply pressure selection circuit 30 selects and outputs the higher of the first traveling side supply pressure and the second traveling side supply pressure.

[0049] One check valve 30a is connected to the first intermediate passage 34, and the other check valve 30b is connected to the second intermediate passage 35. The two check valves 30a, 30b are connected to each other downstream. Each of the two check valves 30a, 30b allows hydraulic fluid to flow in one direction from the intermediate passages 34, 35 to the junction and prevents hydraulic fluid from flowing in the opposite direction. Therefore, the supply pressure selection circuit 30 selects and outputs the higher of the first travel-side supply pressure and the second travel-side supply pressure through the two check valves 30a, 30b.

[0050] The first running side pressure sensor 15A is connected to the supply pressure selection circuit 30. The higher of the first running side supply pressure and the second running side supply pressure is output to the first running side pressure sensor 15A from the supply pressure selection circuit 30. Therefore, the first running side pressure sensor 15A detects the higher of the first running side supply pressure and the second running side supply pressure based on the supply pressure output from the supply pressure selection circuit 30.

[0051] The control device 17A controls the operation of the traveling system hydraulic circuit 12A and the cargo handling system hydraulic circuit 13, similarly to the control device 17. The control device 17A outputs an opening signal to the flow control valve 14 in accordance with the traveling-side supply pressure detected by the traveling-side pressure sensor 15A and the cargo handling-side supply pressure detected by the cargo handling-side pressure sensors 18-20. Therefore, the control spool 14a moves to a position in accordance with the traveling-side supply pressure detected by the traveling-side pressure sensor 15A and the cargo handling-side supply pressure detected by the cargo handling-side pressure sensors 18-20.

[0052] The hydraulic drive system 1A of the second embodiment operates in the same manner as the hydraulic drive system 1 of the first embodiment.

[0053] In the hydraulic drive system 1A of the second embodiment, the supply pressure selection circuit 30 selects the higher of the first running-side supply pressure and the second running-side supply pressure and outputs it to the running-side pressure sensor 15A, which allows the number of running-side pressure sensors 15A to be reduced.

[0054] In addition, the hydraulic drive system 1A of the second embodiment has the same functions and effects as the first embodiment.

[0055] [Other embodiments] In the hydraulic drive systems 1, 1A of the first and second embodiments, the traveling system hydraulic circuit 12 supplies two traveling motors 2, 3, but the number may be one, and any number is acceptable. Similarly, the number of cargo handling actuators supplied by the cargo handling system hydraulic circuit 13 is also not important. Furthermore, the cargo handling actuators supplied by the cargo handling system hydraulic circuit 13 are not limited to hydraulic cylinders, and may be hydraulic motors.

[0056] Furthermore, the travel system hydraulic circuits 12, 12A and the cargo handling system hydraulic circuit 13 in the hydraulic drive systems 1, 1A of the first and second embodiments are not limited to the structures described above. The travel system hydraulic circuits 12, 12A and the cargo handling system hydraulic circuit 13 may be circuits that can supply hydraulic fluid to the travel motors 2, 3 and the hydraulic cylinders 4-6. Furthermore, in the hydraulic drive system 1, the control devices 17, 17A may operate the travel motors 2, 3 and the cargo handling actuators 4-6 according to a program stored in advance. The control devices 17, 17A obtain hydraulic pressure directly from the travel side pressure sensors 15, 16, 15A and the cargo handling side pressure sensors 18-20, but may also obtain hydraulic pressure indirectly, for example via a device not shown.

[0057] The hydraulic drive systems 1B and 1C may be configured as follows: That is, in the hydraulic drive system 1B, travel-side pressure sensors 15 and 16 may be connected to the middle passages 34 and 35, respectively, as shown in FIG.

[0058] 4, in the hydraulic drive unit 1C, in the traveling system hydraulic circuit 12C, supply pressure detection ports 31b, 32b may be formed in each of the first traveling directional control valve 31C and the second directional control valve 32C instead of the middle passages 34, 35. In this case, the supply pressure selection circuit 30 is connected to each of the supply pressure detection ports 31b, 32b, and acquires the first traveling-side supply pressure and the second traveling-side supply pressure from each of the supply pressure detection ports 31b, 32b. Note that in the hydraulic drive unit 1C, traveling-side pressure sensors 15, 16 may be connected to each of the supply pressure detection ports 31b, 32b.

[0059] Furthermore, in the hydraulic drive units 1, 1A to 1C of the first to fourth embodiments, the pump passage 25 branches into the first passage 26 and the second passage 27, but it may also be configured as a hydraulic drive unit 1D shown in FIG. 5. That is, the first passage 26 may be connected to the pump passage 25, and the second passage 27 may be connected to the pump passage 25 via the first passage 26. That is, the first passage 26 and the second passage 27 may be connected to the pump passage 25 in series. The hydraulic drive unit 1D of this embodiment also achieves the same effects as the first hydraulic drive unit 1.

[0060] From the above description, many modifications and other embodiments of the present invention will be apparent to those skilled in the art. Therefore, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present invention. Details of the structure and / or function thereof may be substantially changed without departing from the spirit of the present invention. [Explanation of symbols]

[0061] 1, 1A~1D Hydraulic drive unit 2. First traction motor 3. Second traction motor 4 Hydraulic cylinder (load handling actuator) 5 Hydraulic cylinder (load handling actuator) 6 Hydraulic cylinder (load handling actuator) 11 Hydraulic pump 12,12A Travel hydraulic circuit 13 Cargo handling hydraulic circuit 14 Flow control valve 15,15A First travel side pressure sensor 16 Second travel side pressure sensor 17,17A Control device 18 Loading side pressure sensor 19 Loading side pressure sensor 20 Loading side pressure sensor 25 Pump passage 26 1st aisle 27 2nd aisle 30 Supply pressure selection circuit 31, 31A, 31C First travel direction control valve 32, 32A, 31C Second travel direction control valve 41 Directional control valve for cargo handling 42 Directional control valve for cargo handling 43 Directional control valve for cargo handling

Claims

1. A hydraulic drive device that supplies hydraulic fluid to a travel motor and a cargo handling actuator, a hydraulic pump that discharges hydraulic fluid; a travel system hydraulic circuit connected to a first passage branching from a pump passage connected to the hydraulic pump, the travel system hydraulic circuit controlling the flow of hydraulic fluid to the travel motor; a cargo handling hydraulic circuit connected to a second passage branching from the pump passage and controlling the flow of hydraulic fluid to the cargo handling actuator; a flow control valve interposed in the second passage and adapted to change the degree of opening of the second passage in response to an opening degree signal; a travel-side pressure sensor that detects a travel-side supply pressure that is a supply pressure to the travel motor; a cargo-handling-side pressure sensor that detects a cargo-handling-side supply pressure that is a pressure supplied to the cargo-handling actuator; a control device that outputs an opening degree signal to the flow control valve to control the opening degree of the second passage in accordance with the traveling-side supply pressure detected by the traveling-side pressure sensor and the loading-side supply pressure detected by the loading-side pressure sensor.

2. The travel-side pressure sensors include a first travel-side pressure sensor and a second travel-side pressure sensor, the travel system hydraulic circuit supplies hydraulic fluid to the first travel motor and the second travel motor, which are the travel motors; the first travel-side pressure sensor detects a first travel-side supply pressure that is a supply pressure to the first travel motor; the second travel-side pressure sensor detects a second travel-side supply pressure that is a supply pressure to the second travel motor; 2. The hydraulic drive system according to claim 1, wherein the control device controls the opening degree of the second passage in accordance with a first traveling side supply pressure detected by the first traveling side pressure sensor and a second traveling side supply pressure detected by the second traveling side pressure sensor.

3. the traveling system hydraulic circuit includes a first traveling directional control valve that controls the flow of hydraulic fluid to the first traveling motor, and a second traveling directional control valve that controls the flow of hydraulic fluid to the second traveling motor, the first travel-side pressure sensor detects the hydraulic pressure of hydraulic fluid supplied from the first travel direction control valve to the first travel motor; 3. The hydraulic drive system according to claim 2, wherein the second travel-side pressure sensor detects the hydraulic pressure of the hydraulic fluid supplied from the second travel direction control valve to the second travel motor.

4. a supply pressure selection circuit; the travel system hydraulic circuit supplies hydraulic fluid to the first travel motor and the second travel motor, which are the travel motors; the supply pressure selection circuit outputs to the travel-side pressure sensor the higher of a first travel-side supply pressure that is the supply pressure to the first travel motor and a second travel-side supply pressure that is the supply pressure to the second travel motor; 2. The hydraulic drive system according to claim 1, wherein the control device controls the opening degree of the second passage in response to a travel-side supply pressure detected by the travel-side pressure sensor.

5. A hydraulic drive device that supplies hydraulic fluid to a travel motor and a cargo handling actuator, a hydraulic pump that discharges hydraulic fluid; a travel system hydraulic circuit connected to a first passage branching from a pump passage connected to the hydraulic pump, the travel system hydraulic circuit controlling the flow of hydraulic fluid to the travel motor; a cargo handling hydraulic circuit connected to a second passage branching from the pump passage and controlling the flow of hydraulic fluid to the cargo handling actuator; a flow control valve interposed in the second passage and adapted to change the degree of opening of the second passage in response to an opening degree signal; a travel-side pressure sensor that detects a travel-side supply pressure that is a supply pressure to the travel motor; a control device that outputs an opening degree signal to the flow control valve to control the opening degree of the second passage in accordance with the travel-side supply pressure detected by the travel-side pressure sensor; a plurality of load-side pressure sensors; the cargo handling hydraulic circuit supplies hydraulic fluid to each of a plurality of cargo handling actuators including the cargo handling actuator; each of the plurality of cargo-side pressure sensors detects a supply pressure to each of the plurality of cargo-side actuators; The control device is a hydraulic drive device that controls the opening degree of the second passage in accordance with the travel-side supply pressure detected by the travel-side pressure sensor and the plurality of loading-side supply pressures detected by the plurality of loading-side pressure sensors.

6. the cargo handling hydraulic circuit includes a plurality of cargo handling directional control valves, the plurality of cargo handling directional control valves control the flow of hydraulic fluid supplied to each of the plurality of cargo handling actuators; 6. The hydraulic drive system according to claim 5, wherein each of the plurality of cargo-side pressure sensors detects a supply pressure of hydraulic fluid supplied from a corresponding cargo-handling directional control valve to the cargo-handling actuator.

7. 7. The hydraulic drive system according to claim 4, wherein the control device operates the flow control valve based on a maximum value among a plurality of loading-side supply pressures and a maximum value among first and second traveling-side supply pressures.

8. A hydraulic drive device that supplies hydraulic fluid to a travel motor and a cargo handling actuator, a hydraulic pump that discharges hydraulic fluid; a travel system hydraulic circuit connected to a first passage leading to a pump passage connected to the hydraulic pump, and controlling the flow of hydraulic fluid to the travel motor; a cargo handling hydraulic circuit connected to a second passage connected to the pump passage via the first passage, and controlling the flow of hydraulic fluid to the cargo handling actuator; A valve is disposed in the second passage and changes the opening of the second passage in response to an opening signal. a flow control valve; detecting a travel-side supply pressure that is a supply pressure to a travel motor; a force sensor; a cargo-handling-side pressure sensor that detects a cargo-handling-side supply pressure that is a pressure supplied to the cargo-handling actuator; By outputting an opening signal to the flow control valve, a control device that controls the opening degree of the second passage in response to a travel-side supply pressure detected by a force sensor and a loading-side supply pressure detected by the loading-side pressure sensor.

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