Liquid pressure driving device

Abstract

To provide a liquid pressure driving device capable of suppressing deterioration in an operation speed of loading actuators when operating travelling motors and the loading actuators simultaneously.SOLUTION: A liquid pressure driving device 1 for supplying working liquid to travelling motors 2 and 3, and loading actuators 4, 5, and 6 includes: a liquid pressure pump 11 connected to a pump passage 25 for discharging working liquid to the pump passage; a travelling system liquid pressure circuit 12 connected to a first passage 26 connected to the pump passage for controlling the flow of the working liquid to the travelling motors; a loading system liquid pressure circuit 13 connected to a second passage 27 connected to the pump passage for controlling the flow of the working liquid to the loading actuators; a flow control valve 14 interposed in the first passage for changing an aperture according to an aperture signal; and a control device 20 for controlling the aperture of the flow control valve by outputting the aperture signal to the flow control valve.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

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

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

[0004] In the hydraulic circuit of Patent Document 1, when the traveling motor and the cargo actuator are operated simultaneously, the priority valve is narrowed to allow the hydraulic fluid to flow preferentially to the traveling motor, thereby ensuring the amount of hydraulic fluid supplied to the traveling motor. On the other hand, the flow rate of the hydraulic fluid flowing to the cargo actuator is reduced. This may result in a decrease in the operating speed of the cargo actuator.

[0005] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a hydraulic drive device capable of suppressing a decrease in the operating speed of a load actuator when a travel motor and a load actuator are operated simultaneously. [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 traveling motor and a loading actuator, and includes a hydraulic pump connected to a pump passage and discharging hydraulic fluid into the pump passage, a traveling system hydraulic circuit connected to a first passage connected to the pump passage and controlling the flow of hydraulic fluid to the traveling motor, a loading system hydraulic circuit connected to a second passage connected to the pump passage and controlling the flow of hydraulic fluid to the loading actuator, a flow control valve interposed in the first passage and changing its opening degree in response to an opening signal, and a control device that controls the opening degree of the flow control valve by outputting an opening degree signal to the flow control valve.

[0007] According to the present invention, the control device controls the opening of the flow control valve by outputting an opening signal to the flow control valve. Therefore, the control device can preferentially flow the hydraulic fluid to the cargo-handling hydraulic circuit by outputting an opening signal to the flow control valve to reduce the opening of the flow control valve. This makes it possible to suppress a decrease in the operating speed of the cargo-handling actuator. Effect of the Invention

[0008] According to the present invention, it is possible to suppress a decrease in the operating speed of the cargo actuator when the travel motor and the cargo actuator are operated simultaneously. [Brief description of the drawings]

[0009] [Figure 1] 1 is a circuit diagram showing a configuration of a hydraulic drive device according to an embodiment of the present invention. [Diagram 2] 2 is a block diagram showing a control block of a control device for the hydraulic drive device of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, a hydraulic drive device 1 according to an embodiment of the present invention will be described with reference to the drawings mentioned above. Note that the concept of directions used in the following description is used for convenience in the description and does not limit the orientation of the configuration of the invention to those directions. Furthermore, the hydraulic drive device 1 described below is 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 spirit of the invention.

[0011] The hydraulic drive system 1 shown in Fig. 1 is provided in a work vehicle (not shown) including travel motors 2, 3 and loading actuators 4-6. Work vehicles are, for example, construction vehicles such as hydraulic shovels and hydraulic cranes, and industrial vehicles such as lifts. In this embodiment, the hydraulic drive system 1 is provided in a hydraulic shovel, which is an example of a work vehicle. In addition to the hydraulic drive system 1, the hydraulic shovel is provided with a vehicle body and a work machine.

[0012] The vehicle body is, for example, a tracked device, and includes a pair of left and right crawlers (not shown) and a pair of left and right travel motors 2, 3. The vehicle body travels by operating the pair of left and right crawlers. The vehicle body may be a wheeled device, or any other device capable of travel. The travel motors 2, 3 are hydraulic motors that drive the left and right crawlers, respectively. More specifically, each of the travel motors 2, 3 has two supply and discharge ports 2a, 2b, 3a, 3b. The travel motors 2, 3 rotate in the forward direction when hydraulic fluid is supplied to one of the supply and discharge ports 2a, 3a, and rotate in the reverse direction when hydraulic fluid is supplied to the other supply and discharge port 2b, 3b.

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

[0014] <Hydraulic drive unit> The hydraulic drive system 1 includes a hydraulic pump 11, a traveling system hydraulic circuit 12, a cargo handling system hydraulic circuit 13, a flow control valve 14, a discharge pressure sensor 15, a traveling side pressure sensor 16, and a control device 20. More specifically, the hydraulic drive system 1 further includes cargo side pressure sensors 17-19, a traveling system operation device 21, and a cargo handling system operation device 22.

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

[0016] <Hydraulic pump> The hydraulic pump 11 discharges hydraulic fluid. More specifically, the hydraulic pump 11 is connected to a drive source (e.g., an engine and an electric motor) not shown. The hydraulic pump 11 is connected to a pump passage 25. The hydraulic pump 11 is rotationally driven by the drive source to discharge hydraulic fluid to the pump passage 25. The pump passage 25 is connected to a first passage 26 and a second passage 27, respectively.

[0017] <Drive system hydraulic circuit> The traveling system hydraulic circuit 12 is connected to the first passage 26. The traveling system hydraulic circuit 12 is also connected to the two traveling motors 2, 3. The traveling system hydraulic circuit 12 controls the flow of hydraulic fluid to the traveling motors 2, 3. More specifically, the traveling system hydraulic circuit 12 supplies the first traveling motor 2 and the second traveling motor 3 with hydraulic fluid that flows (in this embodiment, the flow direction and the flow rate) according to the input first traveling command signal and second traveling command signal. The traveling system hydraulic circuit 12 includes a first traveling directional control valve 31 and a second traveling directional control valve 32. The traveling system hydraulic circuit 12 further includes a first pressure compensating valve 33 and a second pressure compensating valve 34.

[0018] The first traveling direction control valve 31 has a first traveling spool 31a. The first traveling direction control valve 31 controls the flow of hydraulic fluid to the first traveling motor 2. More specifically, the first traveling direction control valve 31 is connected to the first passage 26, the tank 28, and the two supply and discharge ports 2a and 2b of the first traveling motor 2. The first traveling spool 31a strokes in response to the input first traveling command signal. 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 traveling spool 31a changes its opening degree by stroking. That is, the first traveling spool 31a changes its opening degree in response to the first traveling command signal. Therefore, hydraulic fluid is supplied from the first traveling direction control valve 31 to the first traveling motor 2 in a direction and at a flow rate in response to the first traveling command signal. As a result, the first traveling directional control valve 31 rotates the first traveling motor 2 in the forward and reverse directions in response to the first traveling command signal, and rotates the first traveling motor 2 at a speed in response to the first traveling command signal. In this embodiment, the first traveling directional control valve 31 is an electrically controlled directional control valve.

[0019] The second traveling direction control valve 32 has a second traveling spool 32a. The second traveling direction control valve 32 controls the flow of hydraulic fluid to the second traveling motor 3. More specifically, the second traveling direction control valve 32 is connected to the first passage 26 in parallel with the first traveling direction control valve 31. Furthermore, the second traveling direction control valve 32 is connected to the tank 28 and two supply and discharge ports 3a, 3b of the second traveling motor 3. The second traveling spool 32a strokes in response to the input second traveling operation command signal. This switches the connection destinations of the supply and discharge ports 3a, 3b to the first passage 26 and the tank 28, respectively. The second traveling spool 32a changes its opening degree by stroking. That is, the second traveling spool 32a changes its opening degree in response to the second traveling command signal. Therefore, hydraulic fluid is supplied from the second traveling direction control valve 32 to the second traveling motor 3 in a direction and flow rate corresponding to the second traveling command signal. As a result, the second traveling direction control valve 32 rotates the second traveling motor 3 in the forward and reverse directions in response to the second traveling command signal, and rotates the second traveling motor 3 at a speed corresponding to the second traveling command signal. In this embodiment, the second traveling direction control valve 32 is an electrically controlled directional control valve.

[0020] The first pressure compensating valve 33 maintains the differential pressure across the first travel direction control valve 31 at a predetermined pressure. The first pressure compensating valve 33 has a spool 33a and a spring 33b. The spool 33a changes its opening depending on its position. The first upstream pressure and the first downstream pressure of the first travel direction control valve 31 act in opposing directions. The first upstream pressure is the hydraulic pressure of the hydraulic fluid guided from the first passage 26 to the first travel direction control valve 31, and the first downstream pressure is the hydraulic pressure of the hydraulic fluid supplied from the first travel direction control valve 31 to the first travel motor 2. The spring 33b biases the spool 33a in a direction against the first upstream pressure. Therefore, the first travel direction control valve 31 moves the spool 33a so that the differential pressure across the first travel direction control valve 31 becomes a predetermined pressure according to the biasing force of the spring 33b. As a result, the pressure difference between the front and rear of the first traveling direction control valve 31 becomes a predetermined pressure according to the biasing force of the spring 33b. Therefore, the flow rate of the hydraulic fluid supplied to the first traveling motor 2 is controlled to a flow rate according to the opening degree of the first traveling direction control valve 31.

[0021] The second pressure compensating valve 34 maintains the differential pressure across the second travel direction control valve 32 at a predetermined pressure. The second pressure compensating valve 34 has a spool 34a and a spring 34b. The spool 34a adjusts the opening depending on its position. The second upstream pressure and the second downstream pressure of the second travel direction control valve 32 act in opposing directions. The second upstream pressure is the hydraulic pressure of the hydraulic fluid guided from the first passage 26 to the second travel direction control valve 32, and the second downstream pressure is the hydraulic pressure of the hydraulic fluid supplied from the second travel direction control valve 32 to the second travel motor 3. The spring 34b biases the spool 34a in a direction against the second upstream pressure. Therefore, the second travel direction control valve 32 moves the spool 34a so that the differential pressure across the second travel direction control valve 32 becomes a predetermined pressure according to the biasing force of the spring 34b. As a result, the differential pressure across the second traveling directional control valve 32 becomes a predetermined pressure. Therefore, the flow rate of the hydraulic fluid supplied to the second traveling motor 3 is controlled to a flow rate according to the opening degree of the second traveling directional control valve 32.

[0022] <Cargo handling hydraulic circuit> 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 in response to cargo handling operation signals (in this embodiment, a boom command signal, an arm command signal, and a bucket command signal, which will be described in detail later). More specifically, the cargo handling hydraulic circuit 13 supplies hydraulic fluid to the three hydraulic cylinders 4-6 in a flow (in this embodiment, a flow direction and a flow rate) in response to the input cargo handling operation signal. The cargo handling hydraulic circuit 13 includes a plurality of cargo handling directional control valves 41-43. In this embodiment, the cargo handling hydraulic circuit 13 includes three cargo handling directional control valves 41-43, for example, a boom directional control valve 41, an arm directional control valve 42, and a bucket directional control valve 43.

[0023] The cargo handling directional control valves 41-43 correspond to the hydraulic cylinders 4-6, respectively. The cargo handling directional control valves 41-43 control the flow rate of hydraulic fluid supplied to the corresponding hydraulic cylinders 4-6 by changing the opening degree. That is, the boom directional control valve 41 controls the flow of hydraulic fluid to the boom cylinder 4. The arm directional control valve 42 controls the flow of hydraulic fluid to the arm cylinder 5. The bucket directional control valve 43 controls the flow of hydraulic fluid to the bucket cylinder 6. The cargo handling directional control valves 41-43 are connected to the second passage 27 in parallel with each other. Furthermore, the cargo 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 the corresponding hydraulic cylinders 4-6, respectively.

[0024] More specifically, each of the cargo handling directional control valves 41-43 has a cargo handling spool 41a-43a. Each of the cargo handling spools 41a-43a strokes in response to a boom command signal, an arm command signal, and a bucket command signal, which are examples of cargo handling operation signals. As a result, the connection destinations 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. Also, each of the cargo handling spools 41a-43a changes its opening degree by stroking. That is, the cargo handling spools 41a-43a change their opening degree in response to each of the cargo handling operation signals. Therefore, the cargo handling directional control valves 41-43 supply the hydraulic fluid to the corresponding hydraulic cylinders 4-6 in a direction and at a flow rate in response to each command signal. As a result, the cargo handling directional control valves 41-43 can extend and retract the corresponding hydraulic cylinders 4-6 at a speed in response to each command signal. In this embodiment, the cargo handling directional control valves 41 to 43 are also electrically controlled directional control valves.

[0025] <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 between the pump passage 25 and the first passage 26. In other words, the pump passage 25 is connected to the first passage 26 via the flow control valve 14. The flow control valve 14 changes the opening degree in response to an input opening degree signal. More specifically, the flow control valve 14 throttles the flow rate of the hydraulic fluid flowing through the first passage 26 in response to the input opening degree signal. This allows the hydraulic fluid to flow preferentially to the cargo handling hydraulic circuit 13.

[0026] <Discharge pressure sensor> The discharge pressure sensor 15 detects the hydraulic pressure of the hydraulic fluid discharged from the hydraulic pump 11, i.e., the discharge pressure. To explain in more detail, the discharge pressure sensor 15 is provided in the pump passage 25. In other words, the discharge pressure sensor 15 is provided upstream of the flow control valve 14. The discharge pressure sensor 15 detects the hydraulic pressure of the hydraulic fluid flowing through the pump passage 25.

[0027] <Drive side pressure sensor> The driving side pressure sensor 16 detects the driving side supply pressure, which is the hydraulic pressure of the hydraulic fluid flowing through the first passage 26. In other words, the driving side pressure sensor 16 detects the hydraulic pressure of the hydraulic fluid supplied to the driving system hydraulic circuit 12. To explain in more detail, the driving side pressure sensor 16 is provided in the first passage 26. In other words, the driving side pressure sensor 16 is provided downstream of the flow control valve 14.

[0028] <Loading side pressure sensor> The cargo-side pressure sensors 17-19 correspond to the hydraulic cylinders 4-6. The cargo-side pressure sensors 17-19 detect the cargo-side supply pressures, which are the supply pressures to the corresponding hydraulic cylinders 4-6. More specifically, the cargo-side pressure sensors 17-19 are, for example, a boom pressure sensor 17, an arm pressure sensor 18, and a bucket pressure sensor 19, and detect the supply pressures supplied to the boom cylinder 4, the arm cylinder 5, and the bucket cylinder 6, respectively. The cargo-side pressure sensors 17-19 are provided downstream of the directional control valves 41-43. In this embodiment, the cargo-side pressure sensors 17-19 are 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 17-19 detect the hydraulic pressures of the hydraulic fluid supplied to the rod-side ports 4a-6a and the head-side ports 4b-6b of the hydraulic cylinders 4-6.

[0029] <Travel control device> The traveling system operation device 21 is a device for the driver to operate the traveling motors 2 and 3. The traveling system operation device 21 includes, for example, traveling pedals 21a and 21b which are operating tools. Each of the traveling pedals 21a and 21b can be tilted. Each of the traveling pedals 21a and 21b can be tilted, for example, in one direction and the other direction (for example, forward and backward). The traveling system operation device 21 outputs a traveling operation command according to the operation direction and operation amount (tilt direction and tilt amount in this embodiment). Note that the operating tool provided in the traveling system operation device 21 may be in another form such as an operating lever operation panel, and the form is not limited.

[0030] <Cargo handling operation device> The cargo handling operation device 22 is a device for the driver to operate an attachment (a bucket in this embodiment). More specifically, the operating tools of the cargo handling operation device 22 include cargo handling operation levers 22a, 22b. Each of the cargo handling operation levers 22a, 22b can be tilted. In this embodiment, each of the cargo handling operation levers 22a, 22b can be tilted, for example, in the front-rear and left-right directions. The cargo handling operation device 22 outputs a cargo handling operation command according to the operation direction and operation amount (tilt direction and tilt amount in this embodiment). Note that the operating tools provided in the cargo handling operation device 22 are not limited to the cargo handling operation levers 22a, 22b, and may be in other forms such as an operation panel.

[0031] <Control device> The control device 20 controls the operation of the traveling system hydraulic circuit 12 in response to the traveling operation command. More specifically, the control device 20 acquires the traveling operation command output from the traveling system operation device 21. Then, the control device 20 controls the movement of each of the traveling directional control valves 31, 32 (i.e., the position of each of the spools 31a, 32a) in response to the traveling operation command. In this embodiment, the control device 20 outputs each of the first and second traveling command signals in response to the traveling operation command. Then, each of the traveling motors 2, 3 rotates in a direction and at a rotational speed in response to the traveling operation command, so that the hydraulic excavator moves in a direction and at a speed in response to the traveling operation command.

[0032] The control device 20 also controls the operation of the loading / unloading hydraulic circuit 13 in response to a loading / unloading operation command. More specifically, the control device 20 acquires a loading / unloading operation command output from the loading / unloading operation device 22. The control device 20 then controls the movement of each of the loading / unloading directional control valves 41-43 (i.e., the position of each of the spools 41a-43a) in response to the loading / unloading operation command. In this embodiment, the control device 20 outputs a boom command signal, a boom command signal, and a bucket command signal in response to the loading / unloading operation command. The hydraulic cylinders 4-6 then expand and contract at a speed in response to the loading / unloading operation command. This allows the bucket to move in a direction and at a speed in response to the loading / unloading operation command, allowing the hydraulic excavator to perform a desired task.

[0033] Furthermore, the control device 20 controls the opening of the flow control valve 14 by outputting an opening signal to the flow control valve 14. More specifically, the control device 20 controls the opening of the first passage 26 by outputting an opening signal according to the travel operation command and the cargo operation command. The control device 20 also outputs an opening signal according to the hydraulic pressure detected by each of the pressure sensors 15-19, thereby supplying hydraulic fluid at a flow rate according to each of the travel operation command and the cargo operation command to each of the travel system hydraulic circuit 12 and the cargo operation hydraulic circuit 13 with higher accuracy.

[0034] <Operation of the hydraulic drive unit> In the hydraulic drive device 1, when the travel pedals 21a, 21b of the travel system operation device 21 are operated independently, a travel operation command is output from the travel system operation device 21. The independent operation means that the travel pedals 21a, 21b and the loading operation levers 22a, 22b are operated separately. The independent operation includes the simultaneous operation of the travel pedals 21a, 21b and the simultaneous operation of the loading operation levers 22a, 22b, respectively. When the travel operation command is output, the control device 20 opens the flow control valve 14. In this embodiment, the control device 20 outputs an opening signal to maximize the opening of the flow control valve 14. On the other hand, the control device 20 closes the passage between the hydraulic pump 11 and the hydraulic cylinders 4-6 by the loading system hydraulic circuit 13. That is, the control device 20 closes the passage between the first passage 26 and the hydraulic cylinders 4-6 by the loading directional control valves 41-43. In addition, the control device 20 opens communication between the hydraulic pump 11 and the traveling motors 2, 3 via the traveling system hydraulic circuit 12.

[0035] More specifically, the control device 20 calculates a target travel motor flow rate to be supplied to each of the travel motors 2 and 3 based on a travel operation command as shown in Fig. 2. The control device 20 then outputs first and second travel command signals corresponding to the respective travel motor target flow rates. As a result, each of the first travel direction control valve 31 and the second travel direction control valve 32 controls the flow of hydraulic fluid to the travel motors 2 and 3 to a flow (flow direction and flow rate in this embodiment) corresponding to the travel operation command.

[0036] Specifically, the differential pressures before and after each of the two travel direction control valves 31, 32 are made the same by the pressure compensation valves 33, 34. Therefore, the flow rate of the hydraulic fluid supplied to each of the travel motors 2, 3 corresponds to the opening degree of each travel direction control valve 31, 32. Therefore, the control device 20 calculates the opening degree of the first and second travel direction control valves 31, 32 according to the target flow rate of each travel motor 2, 3, and outputs first and second travel command signals according to each calculated opening degree. This makes it possible to supply hydraulic fluid to the travel motors 2, 3 at a flow rate according to the travel operation command (more specifically, the operation amount of the travel pedals 21a, 21b). Therefore, the control device 20 can cause the hydraulic excavator to perform a travel operation according to the operation of the travel pedals 21a, 21b.

[0037] In the hydraulic drive system 1, when the cargo handling operation levers 22a, 22b of the cargo handling system operation device 22 are operated independently, a cargo handling operation command is output from the cargo handling system operation device 22. In response, the control device 20 throttles the flow control valve 14. More specifically, the control device 20 sets the opening of the flow control valve 14 to the minimum opening by outputting an opening signal. In addition, the control device 20 calculates the target cargo handling flow rates to be supplied to each of the hydraulic cylinders 4-6 based on the cargo handling operation command as shown in FIG. 2. In addition, the control device 20 estimates the flow rates (actual flow rates) of the hydraulic fluid supplied to each of the hydraulic cylinders 4-6 based on the detected discharge pressures and each cargo handling side supply pressure. More specifically, the control device 20 estimates the flow rate of the hydraulic fluid flowing through each of the loading and unloading directional control valves 41-43 based on the discharge pressure, which is the pressure in front of and behind each of the loading and unloading directional control valves 41-43, and each loading-side supply pressure, as the flow rate of the hydraulic fluid supplied to each hydraulic cylinder 4-6. The control device 20 calculates the opening degree of each of the loading and unloading directional control valves 41-43 so that the estimated actual flow rate becomes the loading and unloading target flow rate. Then, the control device 20 outputs a boom command signal, an arm command signal, and a bucket command signal according to each calculated opening degree. Therefore, the flow of the hydraulic fluid to the hydraulic cylinders 4-6 is controlled by each of the loading and unloading directional control valves 41-43 to a flow (flow direction and flow rate in this embodiment) according to the loading and unloading operation command. As a result, the control device 20 can make the bucket operate according to the operation of the loading and unloading operation levers 22a, 22b.

[0038] The hydraulic drive device 1 operates as follows when the traveling pedals 21a, 21b and the loading / unloading operation levers 22a, 22b are operated simultaneously. That is, a traveling operation command is output from the traveling system operation device 21, and a loading / unloading operation command is output from the loading / unloading system operation device 22. The control device 20 calculates the traveling motor target flow rate based on the traveling operation command as shown in FIG. 2. The control device 20 also estimates the traveling side actual flow rate (i.e., equivalent to the total flow rate of the hydraulic fluid supplied to the two traveling motors 2, 3), which is the flow rate of the hydraulic fluid supplied to the traveling system hydraulic circuit 12, based on the detected discharge pressure and traveling side supply pressure. Then, the control device 20 controls the opening degree of the flow control valve 14 so that the traveling side actual flow rate becomes the traveling side target flow rate. The traveling side target flow rate is the total flow rate of the traveling motor target flow rates of the two traveling motors 2, 3, and is the flow rate to be supplied to the traveling system hydraulic circuit 12.

[0039] In this embodiment, the control device 20 outputs an opening signal in accordance with the target cargo handling flow rate and actual cargo handling flow rate of each of the hydraulic cylinders 4-6 in addition to the actual cargo handling flow rate and the target cargo handling flow rate of each of the hydraulic cylinders 4-6. More specifically, the control device 20 calculates the target cargo handling flow rate of each of the hydraulic cylinders 4-6 based on the cargo handling operation command. The control device 20 also estimates the actual cargo handling flow rate of each of the hydraulic cylinders 4-6 based on the detected discharge pressure and each of the cargo handling supply pressures. The control device 20 then controls the opening of the flow control valve 14 so that the actual cargo handling flow rate becomes the target cargo handling flow rate of the hydraulic cylinders 4-6 and each of the target cargo handling flow rates and the actual cargo handling flow rates match each other.

[0040] Furthermore, when the motors 2 and 3 are operated simultaneously, the control device 20 controls the traveling hydraulic circuit 12 as follows. That is, the control device 20 calculates the opening degree of each traveling direction control valve 31, 32 according to the target flow rate of each traveling motor 2, 3. To explain in more detail, the differential pressure across each traveling direction control valve 31, 32 is maintained at a predetermined pressure by each pressure compensation valve 33, 34 as described above. Therefore, the control device 20 can supply the flow rate introduced to the traveling hydraulic circuit 12 to each traveling motor 2, 3 at a distribution amount according to the target flow rate of each traveling motor 2, 3 by controlling the opening degree of each traveling direction control valve 31, 32 at the same ratio as the ratio of the target flow rates of each traveling motor 2, 3. Therefore, when the target flow rates of each traveling motor 2, 3 are the same, for example, the control device 20 sets the opening degree of each traveling direction control valve 31, 32 to the same opening degree (both are maximum opening degrees in this embodiment). On the other hand, when the target flow rate of the first traveling motor 2 is half the target flow rate of the second traveling motor 3, the control device 20 sets the opening degree of the first traveling direction control valve 31 to half the opening degree of the second traveling direction control valve 32 (maximum opening degree in this embodiment). The control device 20 controls the opening degree of each traveling direction control valve 31, 32 by outputting first and second traveling command signals according to the calculated opening degrees. As a result, the flow rate guided to the traveling system hydraulic circuit 12 can be supplied to each traveling motor 2, 3 at a distribution amount according to the target flow rate of each traveling motor 2, 3. As a result, the excavator can be traveled in accordance with the operation of the traveling pedals 21a, 21b even when the traveling motors are operated simultaneously.

[0041] Furthermore, the control device 20 controls the cargo handling hydraulic circuit 13 in the simultaneous operation as follows. That is, the control device 20 outputs a boom command signal, an arm command signal, and a bucket command signal according to the cargo handling target flow rate of each of the hydraulic cylinders 4-6. More specifically, the control device 20 controls the opening degree of each of the cargo handling directional control valves 41-43 based on the cargo handling target flow rate and the actual flow rate of each of the hydraulic cylinders 4-6. In this embodiment, the control device 20 controls the opening degree of each of the cargo handling directional control valves 41-43 so that the actual flow rate of each of the hydraulic cylinders 4-6 becomes the cargo handling target flow rate. As a result, the control device 20 can supply the hydraulic fluid at a flow rate corresponding to the operation of the travel pedals 21a, 21b to each of the traveling motors 2, 3 with high accuracy, and supply the hydraulic fluid at a flow rate corresponding to the operation of the cargo handling operation levers 22a, 22b to each of the hydraulic cylinders 4-6 with high accuracy.

[0042] In the hydraulic drive unit 1 of this embodiment, the control device 20 controls the opening of the flow control valve 14 by outputting an opening signal to the flow control valve 14. Therefore, the control device 20 can preferentially allow the hydraulic fluid to flow to the cargo-handling hydraulic circuit 13 by outputting an opening signal to the flow control valve 14 to reduce the opening of the flow control valve 14. This can prevent the operating speed of the hydraulic cylinders 4 to 6 from decreasing.

[0043] In the hydraulic drive unit 1 of this embodiment, the control device 20 outputs an opening signal to the flow control valve 14 in accordance with the target traveling flow rate and the actual traveling flow rate to be flowed through the traveling system hydraulic circuit 12. Therefore, it is possible to control the opening of the flow control valve 14 so that the actual traveling flow rate becomes the target traveling flow rate. This makes it possible to flow hydraulic fluid preferentially to the loading system hydraulic circuit 13 while flowing hydraulic fluid at a flow rate in accordance with the target traveling flow rate to the traveling system hydraulic circuit 12. This makes it possible to operate the traveling motors 2, 3 at a desired operating speed.

[0044] In the hydraulic drive unit 1 of this embodiment, the control device 20 closes the connection between the hydraulic pump 11 and the hydraulic cylinders 4 to 6 by the loading system hydraulic circuit 13, and opens the connection between the hydraulic pump 11 and the traveling motors 2, 3 by the traveling system hydraulic circuit 12. This allows the entire amount of working fluid discharged from the hydraulic pump 11 to be guided to the traveling motors 2, 3 via the traveling system hydraulic circuit 12. This allows only the traveling motors 2, 3 to be driven.

[0045] In the hydraulic drive system 1 of this embodiment, the first pressure compensating valve 33 maintains the differential pressure across the first traveling direction control valve 31, and the second pressure compensating valve 34 maintains the differential pressure across the second traveling direction control valve 32. The control device 20 outputs a first traveling command signal to the first traveling direction control valve 31, which changes its opening in response to the first traveling command signal, and outputs a second traveling command signal to the second traveling direction control valve 32, which changes its opening in response to the second traveling command signal. Therefore, the control device 20 can supply the first traveling motor 2 with a flow rate of hydraulic fluid corresponding to the first traveling command signal, and supply the second traveling motor 3 with a flow rate of hydraulic fluid corresponding to the second traveling command signal. This allows the control device 20 to control the distribution amount of the flow rate guided to the traveling system hydraulic circuit 12 to each traveling motor 2, 3 by each traveling command signal. Therefore, each traveling motor 2, 3 can be operated at a desired operating speed.

[0046] In the hydraulic drive unit 1 of this embodiment, the control device 20 outputs an opening signal to the flow control valve 14 that corresponds to the target cargo handling flow rate to be flowed to each of the hydraulic cylinders 4 to 6. Therefore, by narrowing the opening of the flow control valve 14, it is possible to flow the hydraulic fluid at the cargo handling target flow rate to each of the hydraulic cylinders 4 to 6. This allows each hydraulic cylinder to move at a desired speed.

[0047] In the hydraulic drive unit 1 of this embodiment, the control device 20 estimates each actual cargo handling flow rate based on the discharge pressure and each cargo handling supply pressure, and outputs an opening signal to the flow control valve according to each cargo handling target flow rate and each cargo handling flow rate. The control device 20 can flow the hydraulic fluid at the traveling system target flow rate with high accuracy through the traveling system hydraulic circuit 12, and therefore can also flow the hydraulic fluid at the cargo handling system target flow rate with high accuracy through each hydraulic cylinder 4-6. This allows each of the hydraulic cylinders 4-6 to move at a desired speed.

[0048] [Other embodiments] In the hydraulic drive device 1 of this embodiment, the traveling system hydraulic circuit 12 supplies two traveling motors 2, 3, but the number may be one, and the number is not limited. Similarly, the number of cargo-handling actuators 4-6 supplied by the cargo-handling system hydraulic circuit 13 is not limited. Furthermore, the cargo-handling actuators 4-6 supplied by the cargo-handling system hydraulic circuit 13 are not limited to hydraulic cylinders, and may be hydraulic motors. That is, the cargo-handling system hydraulic circuit 13 may include, for example, a swing motor and an optional cylinder. Also, the spools 31a, 32a, 41a-43a included in each of the control valves 31, 32, 41-43 do not necessarily have to be one. Each of the control valves 31, 32, 41-43 may include, for example, two spools to independently control the meter-in flow rate and the meter-out flow rate.

[0049] Furthermore, the traveling hydraulic circuit 12 and the loading hydraulic circuit 13 in the hydraulic drive device 1 of this embodiment are not limited to the structures described above. The traveling hydraulic circuit 12 and the loading hydraulic circuit 13 may be circuits that can supply hydraulic fluid to the traveling motors 2, 3 and the hydraulic cylinders 4-6. Furthermore, in the hydraulic drive device 1, the control device 20 may operate the traveling motors 2, 3 and the hydraulic cylinders 4-6 according to a program stored in advance. The control device 20 directly acquires hydraulic pressures from the discharge pressure sensor 15, the traveling pressure sensor 16, and the loading pressure sensors 17-19, but may also acquire the hydraulic pressures indirectly, for example, via a device not shown.

[0050] Furthermore, in the hydraulic drive device 1 of this embodiment, the first passage 26 and the second passage 27 are connected to the pump passage 25 so as to branch off from each other, but they may be connected as follows. That is, the first passage 26 may be connected to the second passage 27 via the flow control valve 14, and further connected to the pump passage 25 via the flow control valve 14 and the second passage 27. That is, the first passage 26 and the second passage 27 may be connected in series to the pump passage 25. The hydraulic drive device of this embodiment also achieves the same effects as the hydraulic drive device 1 of this embodiment.

[0051] In the hydraulic drive device 1 of this embodiment, the control device 20 outputs an opening signal corresponding to the estimated actual travel flow rate and the target travel flow rate to the flow control valve 14, but may output an opening signal corresponding to a travel operation command and a cargo operation command to the flow control valve 14. In more detail, the control device 20 acquires an operation pattern for the travel pedals 21a, 21b and the cargo operation levers 22a, 22b based on the acquired travel operation command and the cargo operation command. Here, the operation pattern is a combination of the operation direction and operation amount when the travel pedals 21a, 21b and the cargo operation levers 22a, 22b are operated. The control device 20 stores the relationship between the operation pattern and the opening signal, for example, in a map. The control device 20 selects an opening signal based on the acquired operation pattern and the map, and outputs the selected opening signal to the flow control valve 14.

[0052] In this way, the control device 20 outputs an opening signal corresponding to the travel operation command and the cargo handling operation command to the flow control valve 14. Therefore, it is possible to control the opening of the flow control valve so that the actual travel side flow rate becomes the flow rate corresponding to the travel operation command. This makes it possible to flow hydraulic fluid preferentially to the cargo handling system hydraulic circuit, while flowing hydraulic fluid at a flow rate corresponding to the travel side target flow rate to the travel system hydraulic circuit. This makes it possible to operate the travel motor at a desired operating speed.

[0053] A hydraulic drive device in a first aspect is a hydraulic drive device that supplies hydraulic fluid to a traveling motor and a loading actuator, and includes a hydraulic pump connected to a pump passage and discharging hydraulic fluid into the pump passage, a traveling system hydraulic circuit connected to a first passage connected to the pump passage and controlling the flow of hydraulic fluid to the traveling motor, a loading system hydraulic circuit connected to a second passage connected to the pump passage and controlling the flow of hydraulic fluid to the loading actuator, a flow control valve interposed in the first passage and changing its opening degree in response to an opening signal, and a control device that controls the opening degree of the flow control valve by outputting an opening degree signal to the flow control valve.

[0054] According to the above aspect, the control device controls the opening of the flow control valve by outputting an opening signal to the flow control valve. Therefore, the control device can preferentially flow the hydraulic fluid to the cargo-handling hydraulic circuit by outputting an opening signal to the flow control valve to reduce the opening of the flow control valve. This makes it possible to suppress a decrease in the operating speed of the cargo-handling actuator.

[0055] The hydraulic drive device of a second aspect is the hydraulic drive device of the first aspect, further comprising a discharge pressure sensor that detects a discharge pressure of the hydraulic pump, and a driving side pressure sensor that detects a driving side supply pressure, which is the hydraulic pressure of hydraulic fluid flowing through the first passage, and the control device estimates an actual driving side flow rate flowing to the driving system hydraulic circuit based on the discharge pressure and the driving side supply pressure, and outputs an opening signal to the flow control valve according to the driving side target flow rate and the actual driving side flow rate to be flowed through the driving system hydraulic circuit.

[0056] According to the above aspect, the control device outputs an opening signal to the flow control valve according to the target travel-side flow rate and the actual travel-side flow rate to be flowed through the travel system hydraulic circuit. Therefore, the opening of the flow control valve can be controlled so that the actual travel-side flow rate becomes the target travel-side flow rate. This makes it possible to flow hydraulic fluid preferentially through the loading system hydraulic circuit, while flowing hydraulic fluid at a flow rate according to the target travel-side flow rate through the travel system hydraulic circuit. This makes it possible to operate the travel motor at a desired operating speed.

[0057] A hydraulic drive device in a third aspect is the hydraulic drive device of the second aspect, wherein the cargo-unloading hydraulic circuit controls the flow of hydraulic fluid to the cargo-unloading actuator by adjusting the opening between the hydraulic pump and the cargo-unloading actuator, the traveling system hydraulic circuit controls the flow of hydraulic fluid to the traveling motor by adjusting the opening between the hydraulic pump and the traveling motor, and the control device closes the gap between the hydraulic pump and the cargo-unloading actuator using the cargo-unloading hydraulic circuit and opens the gap between the hydraulic pump and the traveling motor using the traveling system hydraulic circuit.

[0058] According to the above aspect, the control device closes the connection between the hydraulic pump and the load actuator by the load-handling hydraulic circuit, and opens the connection between the hydraulic pump and the traveling motor by the travelling hydraulic circuit. This allows the entire amount of hydraulic fluid discharged from the hydraulic pump to be guided to the traveling motor via the travelling hydraulic circuit, thereby allowing only the traveling motor to be operated.

[0059] A hydraulic drive device in a fourth aspect is the hydraulic drive device of any of the first to third aspects, wherein the control device controls the operation of the traveling system hydraulic circuit based on a traveling operation command, and controls the operation of the loading system hydraulic circuit based on a loading operation command, and outputs an opening signal to the flow control valve according to the traveling operation command and the loading operation command.

[0060] According to the above aspect, the control device outputs an opening signal corresponding to the travel operation command and the cargo operation command to the flow control valve. Therefore, the opening of the flow control valve can be controlled so that the actual travel-side flow rate becomes the flow rate corresponding to the travel operation command. This makes it possible to flow hydraulic fluid preferentially to the cargo-handling hydraulic circuit while flowing hydraulic fluid at a flow rate corresponding to the travel-side target flow rate to the travel hydraulic circuit. This makes it possible to operate the travel motor at a desired operating speed.

[0061] The hydraulic drive device of a fifth aspect is the hydraulic drive device of any of the first to fourth aspects, wherein the traveling system hydraulic circuit includes a first traveling direction control valve connected to a first traveling motor which is the traveling motor and to the first passage, a second traveling direction control valve connected to a second traveling motor and to the first passage, a first pressure compensating valve which maintains a differential pressure across the first traveling direction control valve, and a second pressure compensating valve which maintains a differential pressure across the second traveling direction control valve.

[0062] According to the above aspect, the first pressure compensating valve maintains the differential pressure across the first travel direction control valve, and the second pressure compensating valve maintains the differential pressure across the second travel direction control valve. Therefore, it is possible to supply the first travel motor with a flow rate of hydraulic fluid corresponding to the opening degree of the first travel direction control valve, and to supply the second travel motor with a flow rate of hydraulic fluid corresponding to the opening degree of the second travel direction control valve. This allows the control device to adjust the distribution amount of the flow rate guided to the travel system hydraulic circuit to each travel motor by the opening degree of each directional control valve. Therefore, it is possible to operate each travel motor at a desired operating speed.

[0063] In a sixth aspect, the hydraulic drive device of the second aspect further includes a plurality of cargo-side pressure sensors, and the cargo-unloading hydraulic circuit includes a plurality of cargo-unloading directional control valves each corresponding to a plurality of cargo-unloading actuators including the cargo-unloading actuator and controlling the flow rate of hydraulic fluid supplied to the corresponding cargo-unloading actuator by changing the opening degree, and each of the cargo-unloading pressure sensors corresponds to each of the cargo-unloading actuators and detects the cargo-unloading supply pressure to the corresponding cargo-unloading actuator, and the control device estimates each of the actual cargo-unloading flow rates flowing to each of the cargo-unloading actuators based on the discharge pressure and each of the cargo-unloading supply pressures, and outputs an opening degree signal to the flow control valve in accordance with each of the target cargo-unloading flow rates and each of the actual cargo-unloading flow rates to be flowed to each of the cargo-unloading actuators.

[0064] According to the above aspect, the control device estimates each of the cargo handling flow rates based on the discharge pressure and each of the cargo handling side supply pressures, and outputs an opening signal to the flow control valve in accordance with each of the cargo handling target flow rates and each of the cargo handling flow rates. Since the control device can cause the hydraulic fluid at the traveling side target flow rate to flow with high accuracy through the traveling system hydraulic circuit, the control device can also cause the hydraulic fluid at the cargo handling target flow rate to flow with high accuracy through each of the cargo handling actuators. This allows each of the cargo handling actuators to be operated at a desired speed. [Explanation of symbols]

[0065] 1. Hydraulic drive unit 2. First driving motor (driving motor) 3. Second drive motor (drive motor) 4 Boom cylinder (loading actuator) 5 Arm cylinder (loading actuator) 6 Bucket cylinder (loading actuator) 11 Hydraulic pump 12. Driving system hydraulic circuit 13 Cargo handling hydraulic circuit 14 Flow Control Valve 15 Discharge pressure sensor 16 Traveling side pressure sensor 17 Boom pressure sensor (loading side pressure sensor) 18 Arm pressure sensor (loading side pressure sensor) 19 Bucket pressure sensor (loading side pressure sensor) 20 Control device 25 Pump passage 26 1st aisle 27 2nd aisle 31 First travel directional control valve 32 Second travel directional control valve 33 First pressure compensation valve 34 Second pressure compensation valve 41 Boom directional control valve (loading directional control valve) 42 Arm directional control valve (loading directional control valve) 43 Bucket directional control valve (loading directional control valve)

Claims

1. A hydraulic drive device that supplies hydraulic fluid to a travel motor and a load actuator, a hydraulic pump connected to the pump passage and configured to discharge hydraulic fluid into the pump passage; a travel system hydraulic circuit connected to a first passage connected to the pump passage and controlling a flow of hydraulic fluid to the travel motor; a cargo handling hydraulic circuit connected to a second passage connected to the pump passage and controlling a flow of hydraulic fluid to the cargo handling actuator; a flow control valve that is interposed in the first passage and changes its opening in response to an opening signal; a control device that outputs an opening signal to the flow control valve to control the opening of the flow control valve.

2. a discharge pressure sensor for detecting a discharge pressure of the hydraulic pump; a travel-side pressure sensor that detects a travel-side supply pressure, which is a hydraulic pressure of the hydraulic fluid flowing through the first passage; 2. The hydraulic drive system according to claim 1, wherein the control device estimates an actual driving side flow rate flowing through the driving system hydraulic circuit based on the discharge pressure and the driving side supply pressure, and outputs an opening signal to the flow control valve according to the driving side target flow rate and the actual driving side flow rate to be flowed through the driving system hydraulic circuit.

3. the cargo-handling hydraulic circuit controls the flow of hydraulic fluid to the cargo-handling actuator by adjusting an opening between the hydraulic pump and the cargo-handling actuator; the traveling system hydraulic circuit controls the flow of hydraulic fluid to the traveling motor by adjusting an opening between the hydraulic pump and the traveling motor, 3. The hydraulic drive system according to claim 2, wherein the control device closes communication between the hydraulic pump and the lifting actuator by the load-handling hydraulic circuit, and opens communication between the hydraulic pump and the drive motor by the travelling hydraulic circuit.

4. 2. The hydraulic drive system according to claim 1, wherein the control device controls operation of the traveling system hydraulic circuit based on a traveling operation command, controls operation of the loading system hydraulic circuit based on a loading operation command, and outputs an opening signal to the flow control valve in accordance with the traveling operation command and the loading operation command.

5. 2. The hydraulic drive device according to claim 1, wherein the traveling system hydraulic circuit includes: a first traveling direction control valve connected to a first traveling motor that is the traveling motor and to the first passage; a second traveling direction control valve connected to a second traveling motor and to the first passage; a first pressure compensating valve that maintains a pressure difference between before and after the first traveling direction control valve; and a second pressure compensating valve that maintains a pressure difference between before and after the second traveling direction control valve.

6. Further comprising a plurality of load-side pressure sensors; the cargo-handling hydraulic circuit includes a plurality of cargo-handling directional control valves each corresponding to a plurality of cargo-handling actuators including the cargo-handling actuator, and each controlling a flow rate of hydraulic fluid supplied to the corresponding cargo-handling actuator by changing an opening degree of the respective directional control valves; Each of the cargo-side pressure sensors corresponds to each of the cargo-side actuators and detects a cargo-side supply pressure to the corresponding cargo-side actuator; 3. The hydraulic drive system according to claim 2, wherein the control device estimates an actual loading flow rate flowing to each of the loading actuators based on the discharge pressure and each loading side supply pressure, and outputs an opening signal to the flow control valve in accordance with each of the target loading flow rates and each of the actual loading flow rates to be flowed to each of the loading actuators.

Images