Hydraulic Drive Unit

Abstract

This hydraulic drive device supplies a working fluid to each of a travel motor and a cargo handling actuator, and comprises: a hydraulic pump that discharges the working fluid; a travel system hydraulic circuit that is connected to a first passage and controls the flow of the working fluid to the travel motor, said first passage branching from a pump passage that is connected to the hydraulic pump; a cargo handling system hydraulic circuit that is connected to a second passage and controls the flow of the working fluid to the cargo handling actuator, said second passage branching from the pump passage that is connected to the hydraulic pump; and a flow rate control valve that is interposed in the second passage and controls the openness of the second passage in accordance with the travel-side supply pressure, which is the supply pressure to the travel motor, and the cargo handling-side supply pressure, which is the supply pressure to the cargo handling actuator.

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, the 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 travel-side supply pressure, which is the supply pressure for the travel motor, acts on the priority valve. Therefore, when the travel-side supply pressure 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 opening of the second pump line in accordance with the travel-side supply pressure. On the other hand, the cargo-side supply pressure, which is the supply pressure to the cargo-handling actuators, does not act on the priority valve, and the operating status of the cargo-handling actuators is not taken into consideration.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a hydraulic drive system that can control the flow of hydraulic fluid in a cargo handling actuator in accordance with the operating status of the cargo handling actuator. [Means for solving the problem]

[0006] The hydraulic drive device of the present invention is a hydraulic drive device that 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, and a flow control valve interposed in the second passage and controlling the opening of the second passage in accordance with a travel-side supply pressure that is the supply pressure to the travel motor and a load-handling-side supply pressure that is the supply pressure to the load-handling actuator.

[0007] According to the present invention, the flow control valve controls the opening degree of the second passage in response to the travel-side supply pressure and the load-side supply pressure. Therefore, the opening degree of the second passage can be controlled taking into account not only the operating status of the travel motor but also the operating status of the load-loading actuator. This makes it possible to control the flow of hydraulic fluid to the load-loading actuator in response to the operating status of the load-loading actuator. [Effects of the Invention]

[0008] According to the present invention, the flow of hydraulic fluid to the cargo actuator can be controlled in accordance with the operating status of the cargo 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. 4 is a circuit diagram showing the configuration of a hydraulic drive system according to a second embodiment of the present invention. [Figure 3] 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 system 1 includes a hydraulic pump 11, a traveling system hydraulic circuit 12, a cargo handling system hydraulic circuit 13, a supply pressure selection circuit 14, and a flow control valve 15. The hydraulic drive system 1 also includes a traveling system operation device 16, a cargo handling system operation device 17, and a control device 18. The hydraulic drive system 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 system 1 supplies hydraulic fluid to the first traveling motor 2 and the second traveling motor 3, respectively, to operate the crawlers corresponding to the traveling motors 2 and 3. In this way, the hydraulic drive system 1 can travel the hydraulic excavator. In addition, the hydraulic drive system 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 system 1 can cause the hydraulic excavator to 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 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] <Supply pressure selection circuit> The supply pressure selection circuit 14 includes a pilot passage 51 and multiple check valves 52a-56a and 52b-56b. The supply pressure selection circuit 14 selects and outputs the maximum pressure from among the travel-side supply pressure and the load-handling-side supply pressure. More specifically, the supply pressure selection circuit 14 is connected to the travel system hydraulic circuit 12 and the load-handling-side hydraulic circuit 13. In this embodiment, the supply pressure selection circuit 14 is connected to the supply / discharge ports 2a, 2b, 3a, and 3b of the travel motors 2 and 3 and the rod-side ports 4a-6a and head-side ports 4b-6b of the load-handling actuators 4-6. The supply pressure selection circuit 14 selects and outputs the maximum pressure from among the first travel-side supply pressure, the second travel-side supply pressure, and the multiple load-handling-side supply pressures. The first travel-side supply pressure is the pressure supplied to the first travel motor 2, and the second travel-side supply pressure is the pressure supplied to the second travel motor 3. The plurality of cargo-handling-side supply pressures are supplied to the hydraulic cylinders 4 to 6, respectively.

[0023] The pilot passage 51 is connected in parallel to the traveling system hydraulic circuit 12 and the cargo handling system hydraulic circuit 13. More specifically, the pilot passage 51 has an output passage section 51a and a plurality of passage sections 51b to 51k. A plurality of passage sections (ten passage sections in this embodiment) 51b to 51k are connected in parallel to the output passage section 51a. The output passage section 51a is connected to the supply / discharge ports 2a, 2b, 3a, and 3b of the traveling motors 2 and 3 and the rod-side ports 4a to 6a and head-side ports 4b to 6b of the cargo handling actuators 4 to 6 via the passage sections 51b to 51k, respectively. The output passage section 51a is also connected to a flow control valve 15, which will be described later.

[0024] A plurality of check valves (ten check valves in this embodiment) 52a-56a and 52b-56b are interposed in each of the ten passages 51b-51k. The check valves 52a-56a and 52b-56b allow the flow of hydraulic fluid (more specifically, the flow of pilot fluid) from the ports 2a-6a and 2b-6b to the output passage 51a and prevent reverse flow. Therefore, the ten check valves 52a-56a and 52b-56b output the maximum pressure fluid among the hydraulic pressures at the ports 2a-6a and 2b-6b to the output passage 51a as the maximum pressure among the first traveling-side supply pressure, the second traveling-side supply pressure, and the multiple loading-side supply pressures.

[0025] <Flow control valve> The flow control valve 15 is, for example, a spool valve and includes a control spool 15a. The flow control valve 15 is interposed in the second passage 27. The flow control valve 15 controls the aperture of the second passage 27 in response to the travel-side supply pressure and the loading-side supply pressure. The flow control valve 15 is a hydraulic pilot-type valve. More specifically, the flow control valve 15 controls the aperture of the second passage 27 in response to the first travel-side supply pressure, the second travel-side supply pressure, and a plurality of loading-side supply pressures. In this embodiment, the flow control valve 15 receives the maximum pressure output from the supply pressure selection circuit 14 and the downstream pressure of the flow control valve 15 in opposing directions. When the maximum pressure increases, the flow control valve 15 narrows the aperture of the second passage 27. In this embodiment, one flow control valve 15 is provided for one hydraulic pump 11 in the hydraulic drive unit 1. In the hydraulic drive system 1, the single flow control valve 15 allows the hydraulic fluid to flow preferentially to the traveling system hydraulic circuit 12.

[0026] The control spool 15a receives the maximum pressure output from the supply pressure selection circuit 14 and the downstream pressure of the flow control valve 15 in opposing directions. The control spool 15a is biased by a spring 15b in a direction opposing the downstream pressure. The control spool 15a moves to a position where the maximum pressure, the downstream pressure, and the biasing force of the spring 15b are balanced. As a result, the control spool 15a controls the opening of the second passage 27 to an opening corresponding to the maximum pressure.

[0027] <Traveling system operating device> The traveling system operation device 16 is a device that allows the driver to operate the traveling motors 2 and 3. The traveling system operation device 16 includes, for example, a traveling operation lever 16a, which is an operating tool. The traveling operation lever 16a can be tilted. In this embodiment, the traveling operation lever 16a can be tilted, for example, in all directions. The traveling system operation device 16 outputs a traveling operation command according to the tilt direction and tilt amount. The operating tool provided in the traveling system operation device 16 may be an operation pedal, and its form is not limited.

[0028] <Cargo handling operation device> The cargo handling system operation device 17 is a device that allows the driver to operate an attachment (a bucket in this embodiment). More specifically, the operating tool of the cargo handling system operation device 17 includes a cargo handling operation lever 17a. The cargo handling operation lever 17a can be tilted. In this embodiment, the cargo handling operation lever 17a can be tilted, for example, in the forward and backward directions. The cargo handling system operation device 17 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 17 is not limited to the cargo handling operation lever 17a, and may be in other forms such as an operation panel.

[0029] <Control device> The control device 18 controls the operation of the traveling system hydraulic circuit 12. More specifically, the control device 18 acquires a traveling operation command output from the traveling system operating device 16. In response to this, the control device 18 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 18 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 18 also controls the operation of the cargo handling hydraulic circuit 13. More specifically, the control device 18 acquires a cargo handling operation command output from the cargo handling operation device 17. The control device 18 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 command. In this embodiment, the control device 18 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] <Operation of the hydraulic drive unit> In the hydraulic drive system 1, when the travel operation lever 16a of the travel system operation device 16 is operated independently, a travel operation command is output from the travel system operation device 16. In response, the control device 18 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 18 can cause the hydraulic excavator to perform a travel operation according to the operation of the travel operation lever 16a. Note that as hydraulic fluid is supplied to the travel motors 2, 3, either the first travel-side supply pressure or the second travel-side supply pressure is output as the maximum pressure from the supply pressure selection circuit 14 to the flow control valve 15. In response, the flow control valve 15 narrows the opening of the second passage 27.

[0032] Next, in the hydraulic drive system 1, when the cargo handling operation lever 17a of the cargo handling system operation device 17 is operated independently, a cargo handling operation command is output from the cargo handling system operation device 17. In response, the control device 18 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. In this way, the control device 18 can cause the bucket to operate in accordance with the operation of the cargo handling operation lever 17a.

[0033] Furthermore, when the cargo handling operation lever 17a is operated independently, hydraulic fluid is supplied to the hydraulic cylinders 4 to 6, and one of the three cargo handling side supply pressures is output as the maximum pressure from the supply pressure selection circuit 14 to the flow control valve 15. In response to this, the flow control valve 15 controls the opening degree of the second passage 27 in accordance with the maximum pressure output from the supply pressure selection circuit 14. More specifically, the maximum pressure of any one of the three cargo handling side supply pressures is smaller than the downstream pressure of the flow control valve 15 due to pressure loss in the second passage 27, etc. Therefore, when the cargo handling operation lever 17a is operated independently, the second passage 27 is opened by the flow control valve 15.

[0034] Furthermore, when the travel operation lever 16a and the load operation lever 17a are operated simultaneously, the hydraulic drive unit 1 operates as follows. The control device 18 operates the directional control valves 31, 32, 41-43 in response to each command, just as in the case of independent operation. This causes hydraulic fluid to be supplied to the travel motors 2, 3 and the hydraulic cylinders 4-6. The supply pressure selection circuit 14 selects the greatest pressure from the hydraulic pressures at the ports 2a-6a, 2b-6b of the travel motors 2, 3 and the hydraulic cylinders 4-6 as the maximum pressure and outputs it to the flow control valve 15.

[0035] For example, when either the first traveling-side supply pressure or the second traveling-side supply pressure is output as the maximum pressure from the supply pressure selection circuit 14 to the flow control valve 15, the following occurs. The flow control valve 15 narrows the aperture of the second passage 27 in accordance with the maximum pressure, which is either the first traveling-side supply pressure or the second traveling-side supply pressure. This causes the hydraulic fluid to flow preferentially through the first passage 26. This prevents a shortage of hydraulic fluid supplied to the traveling motors 2, 3. On the other hand, when one of the three loading-side supply pressures is output as the maximum pressure from the supply pressure selection circuit 14 to the flow control valve 15, the aperture of the second passage 27 is controlled in accordance with the maximum pressure. In this embodiment, the second passage 27 is opened.

[0036] In the hydraulic drive unit 1 of the first embodiment, the flow control valve 15 controls the opening degree of the second passage 27 in accordance with the travel-side supply pressure and the load-handling-side supply pressure. Therefore, the opening degree of the second passage 27 can be controlled taking into account not only the operating conditions of the travel motors 2, 3 but also the operating conditions of the hydraulic cylinders 4 to 6. This makes it possible to control the flow of hydraulic fluid to the hydraulic cylinders 4 to 6 in accordance with the operating conditions of the hydraulic cylinders 4 to 6.

[0037] In the hydraulic drive unit 1 of the first embodiment, the flow control valve 15 receives the maximum pressure output from the supply pressure selection circuit 14 and the downstream pressure of the flow control valve 15 in opposing directions. The flow control valve 15 narrows the opening of the second passage 27 as the maximum pressure increases. Therefore, when the travel-side supply pressure is output as the maximum pressure, the flow control valve 15 can preferentially guide the hydraulic fluid to the travel motors 2, 3 by narrowing the opening of the second passage 27. On the other hand, when the cargo-side supply pressure is output as the maximum pressure, the flow control valve 15 can supply the cargo-system hydraulic circuit 13 with a downstream pressure that keeps the differential pressure constant.

[0038] In the hydraulic drive unit 1 of the first embodiment, the cargo handling hydraulic circuit 13 includes cargo handling directional control valves 41-43 that control the flow of hydraulic fluid to the hydraulic cylinders 4-6. Therefore, when the cargo handling supply pressure is output as the maximum pressure, the differential pressure across the cargo handling directional control valves 41-43 of the hydraulic cylinders 4-6 with the greatest load can be kept constant, allowing a flow rate according to the cargo handling command to flow to the hydraulic cylinders 4-6. This allows the hydraulic cylinders 4-6 to move at a speed according to the cargo handling command.

[0039] In the hydraulic drive unit 1 of the first embodiment, the supply pressure selection circuit 14 outputs the maximum pressure among the pressures supplied to the first travel-side supply pressure, the second travel-side supply pressure, and the plurality of load-handling-side supply pressures. Therefore, when the load acting on the first travel motor 2 and the second travel motor 3 is large, the flow control valve 15 reduces the opening of the second passage 27, thereby allowing the hydraulic fluid to flow preferentially to the first passage 26. On the other hand, when the load acting on the plurality of hydraulic cylinders 4-6 is large, the flow rate of the hydraulic fluid to the hydraulic cylinders 4-6 with the large load can be ensured by keeping the front and rear pressures of the load-handling hydraulic circuit 13 constant.

[0040] [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. Therefore, the configuration of the hydraulic drive system 1A of the second embodiment will be mainly described in terms of differences from the hydraulic drive system 1 of the first embodiment, and the same components will be assigned the same reference numerals and descriptions thereof will be omitted.

[0041] 2, the hydraulic drive system 1A includes a hydraulic pump 11, a traveling system hydraulic circuit 12, a cargo handling system hydraulic circuit 13, a supply pressure selection circuit 14A, and a flow control valve 15A. The hydraulic drive system 1A also includes a traveling system operating device 16, a cargo handling system operating device 17, and a control device 18.

[0042] The supply pressure selection circuit 14A includes a travel-side circuit portion 14a and a loading-side circuit portion 14b. The supply pressure selection circuit 14A outputs a travel-side maximum pressure, which is the maximum pressure of the first travel-side supply pressure and the second travel-side supply pressure, and a loading-side maximum pressure, which is the maximum pressure of the three loading-side supply pressures.

[0043] The travel-side circuit section 14a has a first pilot passage 61 and four check valves 52a, 52b, 53a, and 53b. The travel-side circuit section 14a outputs a travel-side maximum pressure, which is the maximum pressure of the first travel-side supply pressure and the second travel-side supply pressure. The first pilot passage 61 has an output passage section 61a and four passage sections 61b to 61e. The output passage section 61a is connected to the supply and discharge ports 2a, 2b, 3a, and 3b of the travel motors 2 and 3 in parallel via the four passage sections 61b to 61e. The output passage section 61a is also connected to the flow control valve 15A. The check valves 52a, 52b, 53a, and 53b are interposed in the passage sections 61b to 61e. Therefore, the travel-side maximum pressure is output from the travel-side circuit section 14a to the flow control valve 15A.

[0044] The cargo-side circuit section 14b has a second pilot passage 62 and six check valves 54a-56b, 54b-56b. The cargo-side circuit section 14b outputs a traveling-side maximum pressure, which is the maximum pressure among multiple cargo-side supply pressures. The second pilot passage 62 has an output passage section 62a and six passage sections 62b-62g. The output passage section 62a is connected to the ports 4a-6a, 4b-6b of the cargo-side actuators 4-6 in parallel via the six passage sections 62b-62g. The output passage section 62a is also connected to the flow control valve 15A. The check valves 54a-56a, 54b-56b are interposed in the passage sections 62b-62g. Therefore, the cargo-side maximum pressure is output from the cargo-side circuit section 14b to the flow control valve 15A.

[0045] The flow control valve 15A is, for example, a spool valve and includes a control spool 15Aa. The flow control valve 15A is interposed in the second passage 27. The flow control valve 15A controls the aperture of the second passage 27 in response to the travel-side supply pressure and the loading-side supply pressure. The flow control valve 15A is a hydraulic pilot-operated valve. In this embodiment, the flow control valve 15A receives the travel-side maximum pressure and the loading-side maximum pressure in opposing directions. The flow control valve 15A narrows the aperture of the second passage 27 when the travel-side supply pressure increases. The flow control valve 15A opens the second passage 27 when the loading-side maximum pressure increases. For example, when the travel-side maximum pressure is greater than the loading-side maximum pressure, the hydraulic fluid preferentially flows to the travel system hydraulic circuit 12. On the other hand, when the travel-side maximum pressure becomes smaller than the loading-side maximum pressure, the second passage 27 opens. This allows the flow rate of the hydraulic fluid flowing through the cargo handling hydraulic circuit 13 to be increased.

[0046] The control spool 15Aa receives the traveling-side maximum pressure and the loading-side maximum pressure output from the supply pressure selection circuit 14 in opposing directions. The control spool 15Aa is also biased by a spring 15b in a direction opposing the loading-side maximum pressure. The control spool 15Aa moves to a position where the traveling-side maximum pressure, the loading-side maximum pressure, and the biasing force of the spring 15b are in balance. As a result, the control spool 15Aa controls the opening degree of the second passage 27 to an opening degree corresponding to the pressure difference between the traveling-side maximum pressure and the loading-side maximum pressure.

[0047] <Operation of the hydraulic drive unit> In the hydraulic drive unit 1A, when the travel operation lever 16a and the load-handling operation lever 17a are operated, the control device 18 operates the directional control valves 31, 32, 41-43 in response to a travel operation command and a load-handling operation command. This causes hydraulic fluid to be supplied to the travel motors 2 and 3 and the hydraulic cylinders 4-6. The supply pressure selection circuit 14A outputs the travel-side maximum pressure from the travel-side circuit section 14a to the flow control valve 15A, and also outputs the load-handling maximum pressure from the load-handling circuit section 14b to the flow control valve 15A. This causes the flow control valve 15A to throttle the second passage 27 by an opening degree corresponding to the pressure difference between the travel-side maximum pressure and the load-handling maximum pressure. By throttling the opening degree of the second passage 27, hydraulic fluid is preferentially circulated through the first passage 26, i.e., hydraulic fluid is preferentially circulated to the travel motors 2 and 3. On the other hand, when the maximum cargo handling pressure increases and the second passage 27 opens, the flow rate of the hydraulic fluid flowing through the cargo handling hydraulic circuit 13 can be increased.

[0048] In the hydraulic drive unit 1 of the second embodiment, the flow control valve 15A receives the travel-side supply pressure and the load-side supply pressure in opposing directions. The flow control valve 15A throttles the second passage 27 when the travel-side supply pressure increases. Therefore, when the travel-side supply pressure is high, the flow control valve 15A throttles the opening of the second passage 27, thereby allowing the hydraulic fluid to flow preferentially to the travel motors 2, 3. On the other hand, when the load-side supply pressure is high, the flow control valve 15A opens the second passage 27, thereby ensuring that the hydraulic fluid flows to the load-handling system hydraulic circuit 13.

[0049] Furthermore, in the hydraulic drive unit 1 of the second embodiment, the flow control valve 15A receives the maximum travel-side pressure and the maximum load-unloading pressure in opposing directions. When the maximum travel-side pressure increases, the flow control valve 15A throttles the second passage 27. Therefore, the travel-system hydraulic circuit 12 supplies hydraulic fluid to the two travel motors 2, 3, and the load-unloading hydraulic circuit 13 supplies hydraulic fluid to the multiple hydraulic cylinders 4-6. Even in such a case, hydraulic fluid is preferentially supplied to the travel motors 2, 3, and the hydraulic fluid flowing to the load-unloading hydraulic circuit 13 can be secured.

[0050] 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.

[0051] [Other embodiments] In the hydraulic drive systems 1, 1A of the first and second embodiments, the traveling system hydraulic circuit 12 supplies power to 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 limited to hydraulic cylinders and may be hydraulic motors. Furthermore, the supply pressure selection circuit 14 does not necessarily need to provide check valves for all cargo-handling actuators. In other words, the supply pressure selection circuit 14 may select the maximum pressure from some of the multiple cargo-handling actuators.

[0052] Furthermore, the travel hydraulic circuit 12 and the cargo handling 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 hydraulic circuit 12 and the cargo handling hydraulic circuit 13 may be circuits that can supply hydraulic fluid to the travel motors 2, 3 and the hydraulic cylinders 4 to 6. Furthermore, in the hydraulic drive system 1, the control device 18 may operate the travel motors 2, 3 and the cargo handling actuators 4 to 6 according to a program stored in advance.

[0053] Furthermore, in the hydraulic drive units 1, 1A of the first and second embodiments, the pump passage 25 branches into the first passage 26 and the second passage 27, but it may also be configured as in a hydraulic drive unit 1B of a third embodiment shown in Fig. 3. 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 1B also achieves the same effects as the hydraulic drive unit 1 of the first embodiment.

[0054] 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]

[0055] 1, 1A, 1B 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. Travel system hydraulic circuit 13 Cargo handling hydraulic circuit 14,14A supply pressure selection circuit 14a Running side circuit section 14b Loading side circuit section 15,15A Flow Control Valve 25 Pump passage 26 1st aisle 27 2nd aisle 31 First travel direction control valve 32 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 configured to control an opening degree of the second passage in response to a travel-side supply pressure that is a supply pressure to the travel motor and a cargo-handling-side supply pressure that is a supply pressure to the cargo-handling actuator; a supply pressure selection circuit that selects and outputs the maximum pressure from the travel-side supply pressure and the loading-side supply pressure; The flow control valve receives the maximum pressure output from the supply pressure selection circuit and the downstream pressure of the flow control valve in opposing directions, and reduces the opening of the second passage when the maximum pressure becomes large.

2. 2. The hydraulic drive system according to claim 1, wherein the cargo handling hydraulic circuit includes a cargo handling directional control valve that controls the flow of hydraulic fluid to the cargo handling actuator by changing its opening in response to an input cargo handling command.

3. the travel system hydraulic circuit supplies hydraulic fluid to the first travel motor and the second travel motor, which are the travel motors; the cargo handling hydraulic circuit supplies hydraulic fluid to a plurality of cargo handling actuators including the cargo handling actuator; 3. The hydraulic drive system according to claim 2, wherein the supply pressure selection circuit outputs a maximum pressure among the supply pressure to the first travel motor, the supply pressure to the second travel motor, and the supply pressures to each of the plurality of cargo handling actuators.

4. 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 configured to control an opening degree of the second passage in response to a travel-side supply pressure that is a supply pressure to the travel motor and a cargo-handling-side supply pressure that is a supply pressure to the cargo-handling actuator, The flow control valve receives the travel-side supply pressure and the loading-side supply pressure in opposing directions, and throttles the second passage when the travel-side supply pressure increases.

5. 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 cargo handling hydraulic circuit supplies hydraulic fluid to a plurality of cargo handling actuators including the cargo handling actuator; the supply pressure selection circuit includes a travel-side circuit section that outputs a travel-side maximum pressure that is the maximum pressure of the supply pressures to the first travel motor and the second travel motor, and a load-unloading-side circuit section that outputs a load-unloading maximum pressure that is the maximum pressure of the supply pressures to each of the plurality of load-unloading actuators, 5. The hydraulic drive system according to claim 4, wherein the flow control valve receives a traveling-side maximum pressure output from the traveling-side circuit section and a loading-side maximum pressure output from the loading-side circuit section in opposing directions, and throttles the second passage when the traveling-side maximum pressure increases.

6. 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 flow control valve interposed in the second passage and configured to control an opening degree of the second passage in response to a travel-side supply pressure that is a supply pressure to the travel motor and a cargo-handling-side supply pressure that is a supply pressure to the cargo-handling actuator; a supply pressure selection circuit that selects and outputs the maximum pressure from the travel-side supply pressure and the loading-side supply pressure; The flow control valve receives the maximum pressure output from the supply pressure selection circuit and the downstream pressure of the flow control valve in opposing directions, and reduces the opening of the second passage when the maximum pressure becomes large.

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