Hydraulic drive system and construction machinery equipped with the same

Abstract

To provide a hydraulic drive device of a construction machine which enables an actual operation speed of a hydraulic actuator to be controlled by combined control to follow a target speed even if the hydraulic actuator having a difficulty in attachment of a speed sensor is included in controlled objects by the combined control.SOLUTION: In combined control, a controller 70 of a hydraulic drive device adjusts a discharge amount of a pump device based on a first operation and a second operation to reduce an opening of a second control valve so as to bring a discharge pressure of the pump device close to a meter-in pressure of a first actuator and bring a first operation speed, which is an operation speed of the first actuator, close to a first target speed, which is a target speed of the first actuator.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a hydraulic drive system and a construction machine equipped with the same. [Background technology]

[0002] Generally, construction machinery such as hydraulic excavators includes at least one hydraulic pump that discharges hydraulic oil, multiple hydraulic actuators that operate by receiving a supply of hydraulic oil from the hydraulic pump, and multiple operating devices that are used to operate the multiple hydraulic actuators. In such construction machinery, when multiple operations are simultaneously performed to operate two or more hydraulic actuators, pressure interference can occur, resulting in a decrease in hydraulic oil supplied to a hydraulic actuator with a higher operating pressure. When this pressure interference occurs, the operation of the hydraulic actuator with the higher operating pressure can become extremely slow, significantly reducing workability. Therefore, techniques for suppressing pressure interference have been proposed (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a hydraulic control device for suppressing pressure interference between a travel motor and a work actuator. Specifically, during combined operations in which travel and work operations (such as boom-raising) are performed simultaneously, this hydraulic control device connects the pump lines of two hydraulic pumps via a communication passage and controls the opening amount of the communication passage according to the engine speed. This suppresses pressure interference during combined operations of travel and work, preventing the operation of the work actuator, which has a high operating pressure, from becoming extremely sluggish. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-218028 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the hydraulic control device described in Patent Document 1 does not take into consideration moving the travel motor and the work actuator at a target speed corresponding to the operation amount of the travel operation and the operation amount of the work operation in the combined operation, that is, making the operating speeds of the hydraulic actuators to be controlled by the combined operation each follow the target speed.

[0006] In order to adjust the operating speed of a hydraulic actuator to a target speed, for example, a speed sensor that detects the actual operating speed of the hydraulic actuator can be attached to the hydraulic actuator or near the hydraulic actuator, and the controller can control the operating speed of the hydraulic actuator based on the detection result from the speed sensor. However, the multiple hydraulic actuators equipped in a construction machine may include hydraulic actuators for which it is difficult to attach a speed sensor. When a hydraulic actuator for which it is difficult to attach a speed sensor is included in the control target for combined operation, the controller cannot control the operating speed of the hydraulic actuator based on the detection result from the speed sensor.

[0007] The present disclosure aims to provide a hydraulic drive system and a construction machine equipped with the same that are capable of causing the actual operating speeds of hydraulic actuators that are targets of control by combined operation to follow target speeds, even when the hydraulic actuators that are targets of control by combined operation include hydraulic actuators to which it is difficult to attach speed sensors. [Means for solving the problem]

[0008] What is provided is a hydraulic drive system for a construction machine, comprising a pump device that discharges hydraulic oil, a first actuator and a second actuator, a first control valve and a second control valve that control the flow rate of the hydraulic oil supplied to the first actuator and the second actuator, respectively, a first operating device to which a first operation that determines a first target speed that is a target speed of the first actuator is given, a second operating device to which a second operation is given, a first detector that detects a first operating speed that is the operating speed of the first actuator, and a controller that, during combined operation of the first operation and the second operation, adjusts the discharge volume of the pump device based on the first operation and the second operation, and gives a control command to narrow the opening of the second control valve so that the discharge pressure of the pump device approaches the meter-in pressure of the first actuator and the first operating speed approaches the first target speed.

[0009] In this hydraulic drive system, during the combined operation, the controller adjusts the pump discharge rate based on the first operation and the second operation to adjust the pump discharge rate to the total amount of hydraulic oil to be supplied to the first actuator and the second actuator. The controller also narrows the aperture of the second control valve to increase pressure loss in the second control valve and bring the discharge pressure of the pump device closer to the meter-in pressure of the first actuator, thereby suppressing pressure interference that reduces the amount of hydraulic oil supplied to the first actuator, and adjusts the first operating speed detected by the first detector to the first target speed. When the first operating speed is adjusted to the first target speed, hydraulic oil is supplied to the first actuator at a flow rate determined by the first operation, and the remaining hydraulic oil is supplied to the second actuator. Since the pump discharge rate is adjusted to the total amount of hydraulic oil to be supplied to the first actuator and the second actuator, the flow rate of the remaining hydraulic oil supplied to the second actuator necessarily becomes a flow rate determined by the second operation. This allows the pump discharge rate to be appropriately distributed to the first actuator and the second actuator. Therefore, even if it is difficult to attach a speed sensor to the second actuator or its vicinity to detect the actual operating speed of the second actuator, this hydraulic drive device can cause the actual operating speeds of the first actuator and the second actuator, which are the objects of control by combined operation, to follow the first target speed corresponding to the first operation and the second target speed corresponding to the second operation, respectively.

[0010] Preferably, the controller is configured to issue the control command when the meter-in pressure of the first actuator is greater than the meter-in pressure of the second actuator during the combined operation. In this configuration, the controller can issue a control command to throttle down the aperture of the second control valve only when necessary, that is, only when the first meter-in pressure, which is the meter-in pressure of the first actuator, is greater than the second meter-in pressure, which is the meter-in pressure of the second actuator. Specifically, by throttling the aperture of the second control valve, the controller increases the pressure loss in the second control valve and raises the discharge pressure of the pump device from the second meter-in pressure to the first meter-in pressure, thereby adjusting the first operating speed to the first target speed while suppressing pressure interference, which reduces the amount of hydraulic oil supplied to the first actuator, which has a higher operating pressure.

[0011] Preferably, the hydraulic drive system further includes a travel speed detector that detects the travel speed of the construction machine, the pump system includes a variable displacement hydraulic pump, and the second actuator is a travel motor. During the combined operation, the controller calculates a second operating speed, which is the operating speed of the second actuator, based on the detected travel speed, and controls the displacement of the hydraulic pump so that the second operating speed approaches a second target speed determined in accordance with the second operation. With this configuration, even if an error occurs between the ideal pump discharge rate corresponding to the displacement command by the controller and the actual pump discharge rate, the controller can calculate the actual operating speed (second operating speed) of the second actuator based on the detection result (i.e., the actual travel speed of the construction machine) detected by the travel speed detector, and control the displacement of the hydraulic pump so that the second operating speed approaches the second target speed, thereby reducing the error. This allows the actual operating speeds of the first and second actuators, which are controlled by the combined operation, to more accurately track the target speeds.

[0012] Preferably, during the combined operation, the controller controls the first control valve so as to bring the first operating speed closer to the first target speed. In this configuration, the controller not only controls the second control valve so as to bring the first operating speed closer to the first target speed, but also controls the first control valve so as to bring the first operating speed closer to the first target speed, so that the actual operating speeds of the first actuator and the second actuator, which are controlled by the combined operation, can be made to quickly follow the target speeds.

[0013] Preferably, the first actuator is a hydraulic cylinder, the hydraulic drive system further includes a stroke end detector that detects whether the hydraulic cylinder has reached a stroke end, and the controller adjusts the discharge rate of the pump device based on the second operation when the hydraulic cylinder has reached the stroke end. In this configuration, when the hydraulic cylinder (first actuator) has reached its stroke end and is no longer operable, the controller adjusts the discharge rate of the pump device based on the second operation, thereby adjusting the pump discharge rate to the amount of hydraulic oil to be supplied to the second actuator. This prevents the deviation between the actual operating speed of the second actuator and the target speed from becoming too large.

[0014] The provided construction machine includes the above-described hydraulic drive device, a first movable part that can be moved by the first actuator, and a second movable part that can be moved by the second actuator. With this construction machine, even if the hydraulic actuators that are the control targets of the combined operation include hydraulic actuators to which it is difficult to attach speed sensors, the actual operating speeds of the hydraulic actuators that are the control targets of the combined operation can be made to follow the target speeds. [Effects of the Invention]

[0015] According to the present disclosure, a hydraulic drive system and a construction machine equipped with the same are provided that are capable of causing the actual operating speeds of hydraulic actuators that are targets of control by combined operation to follow target speeds, even when the hydraulic actuators to which a speed sensor is difficult to attach are included in the targets of control by combined operation. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a side view showing a construction machine according to an embodiment of the present disclosure. [Figure 2] FIG. 1 illustrates a hydraulic drive system according to an embodiment of the present disclosure. [Figure 3] 4 is a map showing an example of a relationship between an operation amount applied to an operating device of the hydraulic drive system and a target speed. [Figure 4] 4 is a flowchart showing an example of calculation processing by a controller of the hydraulic drive system. [Figure 5] 4 is a flowchart illustrating an example of a calculation process performed by the controller. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, a hydraulic drive system and a construction machine equipped with the same according to an embodiment of the present disclosure will be described with reference to the drawings.

[0018] Fig. 1 is a side view showing a construction machine 100 according to an embodiment of the present disclosure, and Fig. 2 is a diagram showing a hydraulic drive system according to an embodiment of the present disclosure. The construction machine 100 according to this embodiment is a hydraulic excavator. This construction machine 100 includes a lower traveling body 1, an upper rotating body 2 supported by the lower traveling body 1 so as to be rotatable relative to the lower traveling body 1 about a Z-axis extending vertically, and an attachment 3 supported by the upper rotating body 2.

[0019] The undercarriage 1 includes a pair of left and right traveling units 1L, 1R arranged at a distance from each other on the left and right sides for traveling the construction machine 100 on the ground G, and a lower frame connecting these traveling units 1L, 1R. Each of the traveling units 1L, 1R is a crawler traveling unit having a shape extending in the front-to-rear direction. Each of the traveling units 1L, 1R includes a traveling frame 1A extending in the front-to-rear direction, wheels 1B and 1C rotatably supported at the front and rear ends of the traveling frame 1A, and a crawler belt 1D, which is an endless belt looped around the wheels 1B and 1C. In FIG. 1, the right traveling unit 1R is located behind the left traveling unit 1L.

[0020] The upper rotating body 2 includes an upper frame supported by the lower frame so as to be rotatable relative to the lower frame, and a cabin and a machinery room supported by the upper frame. The cabin contains a driver's seat where an operator sits, and the machinery room contains various devices such as an engine. The upper rotating body 2 is an example of a movable part.

[0021] The attachment 3 includes a boom 4, an arm 5, and a tip attachment. The boom 4 has a base end supported on the front of the upper frame of the upper rotating body 2 so that the boom 4 can rotate around a horizontal axis relative to the upper rotating body 2, and a tip end on the opposite side. The arm 5 has a base end attached to the tip of the boom 4 so that the arm 5 can rotate around a horizontal axis relative to the boom 4, and a tip end on the opposite side. The tip attachment may be the bucket 6 shown in FIG. 1 or another tip attachment such as a fork, a grapple, a breaker, or a crusher (crusher). The bucket 6 has a base end attached to the tip of the arm 5 so that the bucket 6 can rotate around a horizontal axis relative to the arm 5, a storage section that can store and hold earth and sand, and a tip end of the bucket 6. The tip end of the bucket 6 is formed by excavation teeth. The boom 4, the arm 5, and the tip attachment are each an example of a movable part. The boom 4 is also an example of a first movable part.

[0022] The hydraulic drive system according to this embodiment shown in FIG. 2 includes a pump device including at least one variable displacement hydraulic pump 21, a pilot pump 22, a plurality of hydraulic actuators, a plurality of control valves, a plurality of operating devices, a plurality of proportional valves, a plurality of detectors, and a controller 70.

[0023] The hydraulic pump 21 includes a pump main body that is driven by a drive source such as an engine (not shown) to discharge hydraulic oil, and a regulator. The pump main body has a variable pump capacity (displacement volume). The regulator operates the pump main body in response to a capacity command signal input from the controller 70 so that the pump capacity corresponds to the capacity command signal. The pump device may include the hydraulic pump 21 and a hydraulic pump (hereinafter sometimes referred to as a second hydraulic pump) (not shown).

[0024] The pilot pump 22 is driven by a drive source such as the engine to discharge hydraulic oil. The pilot pump 22 is driven by the engine to supply pilot pressure to each of the plurality of control valves.

[0025] Each of the hydraulic actuators is actuated by receiving a supply of hydraulic oil discharged from the pump device to move a corresponding movable part. Specifically, as shown in Figures 1 and 2, the hydraulic actuators include a boom cylinder 7, an arm cylinder 8, a bucket cylinder 9, a swing motor 11, and a pair of left and right travel motors 12.

[0026] The boom cylinder 7 receives hydraulic oil discharged from the hydraulic pump 21 of the pump device and performs an extension / retraction operation, causing the boom 4 to rise and fall relative to the upper rotating body 2 in a direction corresponding to the direction of the extension / retraction operation. The arm cylinder 8 receives hydraulic oil discharged from the pump device and performs an extension / retraction operation, causing the arm 5 to rotate relative to the boom 4 in a direction corresponding to the direction of the extension / retraction operation. The bucket cylinder 9 receives hydraulic oil discharged from the pump device and performs an extension / retraction operation, causing the bucket 6 to rotate relative to the arm 5 in a direction corresponding to the direction of the extension / retraction operation. The swing motor 11 receives hydraulic oil discharged from the pump device and rotates, causing the upper rotating body 2 to swing relative to the lower traveling body 1 in a direction corresponding to the direction of rotation.

[0027] Each of the left and right travel motors 12 has a pair of ports. Hydraulic oil is supplied to one of the pair of ports and discharged from the other of the pair of ports, thereby rotating the left and right travel motors 12. One of the left and right travel motors 12 rotates by receiving a supply of hydraulic oil discharged from the hydraulic pump 21 of the pump device, causing the wheel 1C of the travel device to rotate in a direction corresponding to the direction of rotation. The other of the left and right travel motors 12 rotates by receiving a supply of hydraulic oil discharged from the pump device (hydraulic pump 21 or the second hydraulic pump), causing the wheel 1C of the travel device to rotate in a direction corresponding to the direction of rotation. The other of the left and right travel motors 12 is not shown in FIG. 2. In this embodiment, the wheel 1C is an example of a second movable part. In this embodiment shown in FIG. 2, the boom cylinder 7 is an example of a first actuator, and one of the left and right travel motors 12 (e.g., the left travel motor 12) is an example of a second actuator.

[0028] Each of the multiple control valves is interposed between a hydraulic actuator corresponding to the control valve (hereinafter, sometimes referred to as a corresponding hydraulic actuator) and one of the hydraulic pump 21 and the second hydraulic pump of the pump device, and controls the direction and flow rate of hydraulic oil supplied to the corresponding hydraulic actuator. Specifically, the multiple control valves include a boom control valve 41, an arm control valve, a bucket control valve, a swing control valve, and left and right travel control valves 42. Of the multiple control valves, FIG. 2 illustrates the boom control valve 41 and one of the left and right travel control valves 42, while omitting to illustrate the arm control valve, the bucket control valve, the swing control valve, and the other of the left and right travel control valves 42. In this embodiment, the multiple control valves are incorporated into a common valve unit, but may be configured independently of each other.

[0029] In the present embodiment shown in FIG. 2, the boom control valve 41 is an example of a first control valve, and one of the left and right travel control valves 42 (for example, the left travel control valve 42) is an example of a second control valve. The boom control valve 41 is interposed between the hydraulic pump 21 and the boom cylinder 7, and controls the direction and flow rate of hydraulic oil supplied to the boom cylinder 7. The travel control valve 42 shown in FIG. 2 is interposed between the hydraulic pump 21 and the travel motor 12, and controls the direction and flow rate of hydraulic oil supplied to the travel motor 12. The boom control valve 41 (first control valve) and the travel control valve 42 (second control valve) are connected in parallel to the hydraulic pump 21.

[0030] Each of the control valves may be configured, for example, as a pilot-operated three-position directional control valve. In this case, each of the control valves has a pair of pilot ports that can receive pilot pressure. The configuration of each of the control valves will be specifically described below using the boom control valve 41 and the travel control valve 42 as examples.

[0031] When pilot pressure is not input to either of the pair of pilot ports, the boom control valve 41 is kept in a neutral position to block communication between the hydraulic pump 21 and the boom cylinder 7, i.e., the valve is closed to block the supply of hydraulic oil from the hydraulic pump 21 to the boom cylinder 7. Similarly, when pilot pressure is not input to either of the pair of pilot ports, the travel control valve 42 is kept in a neutral position to block communication between the hydraulic pump 21 and the travel motor 12, i.e., the valve is closed to block the supply of hydraulic oil from the hydraulic pump 21 to the travel motor 12.

[0032] When hydraulic oil is supplied to one of a pair of pilot ports, each of the boom control valve 41 and the travel control valve 42 is shifted from the neutral position in a direction corresponding to the one pilot port by a stroke corresponding to the magnitude of the pilot pressure. As a result, the boom control valve 41 forms an oil passage that allows hydraulic oil discharged from the hydraulic pump 21 to be supplied to one of the head side chamber and the rod side chamber of the boom cylinder 7, and an oil passage that allows hydraulic oil discharged from the other of the head side chamber and the rod side chamber of the boom cylinder 7 to return to the tank. Similarly, the travel control valve 42 forms an oil passage that allows hydraulic oil discharged from the hydraulic pump 21 to be supplied to one port of the travel motor 12, and an oil passage that allows hydraulic oil discharged from the other port of the travel motor 12 to return to the tank.

[0033] Each of the multiple operating devices has an operating lever or operating pedal operated by an operator to move the hydraulic actuator corresponding to that operating device, and an operating signal output unit that inputs an operating signal corresponding to the direction and amount of operation to the controller 70. The multiple operating devices include a boom operating device 51, an arm operating device, a bucket operating device, a swing operating device, and a pair of left and right traveling operating devices 52. Of the multiple operating devices, FIG. 2 illustrates the boom operating device 51 and one of the left and right traveling operating devices 52, while omitting to illustrate the arm operating device, the bucket operating device, the swing operating device, and the other of the left and right traveling operating devices 52. In the present embodiment illustrated in FIG. 2, the boom operating device 51 is an example of a first operating device, and one of the left and right traveling operating devices 52 (e.g., the left traveling operating device 52) is an example of a second operating device.

[0034] The lever structure may be such that one control lever serves the functions of multiple control levers. For example, the right control lever located on the front right side of the driver's seat where the operator sits may function as the control lever for the boom control device 51 when operated in the forward / backward direction, and as the control lever for the bucket control device when operated in the left / right direction. The left control lever located on the front left side of the driver's seat may function as the control lever for the arm control device when operated in the forward / backward direction, and as the control lever for the swing control device when operated in the left / right direction. The lever structure may be configured so that the combination of multiple control levers can be freely changed by the operator. Each of the left and right travel control devices 52 may have both a control pedal and a control lever. The configuration of each of the multiple control devices is specifically described below using the boom control device 51 and the travel control device 52 as examples.

[0035] The control lever of the boom operation device 51 is configured to be able to receive a boom-raising operation, which is an operation by the operator to move the boom 4 in the boom-raising direction, and a boom-lowering operation, which is an operation by the operator to move the boom 4 in the boom-lowering direction. When a boom-raising operation or a boom-lowering operation is applied to the control lever of the boom operation device 51, the boom operation device 51 inputs a boom operation signal corresponding to the magnitude and direction of the operation to the controller 70. The boom-raising direction is the direction in which the tip of the boom 4 moves away from the ground, and the boom-lowering direction is the direction in which the tip of the boom 4 moves towards the ground.

[0036] The operating lever or operating pedal of the traveling operation device 52 is configured to be able to receive a traveling operation by an operator for rotating the wheels 1C of the traveling device in one direction, and a traveling operation by an operator for rotating the wheels 1C of the traveling device in the other direction. In the present embodiment shown in Fig. 2, the boom-raising operation is an example of a first operation, and the traveling operation given to one of the left and right traveling operation devices 52 (for example, the left traveling operation device 52) is an example of a second operation.

[0037] The multiple proportional valves include a pair of boom electromagnetic proportional valves 81, a pair of arm electromagnetic proportional valves, a pair of bucket electromagnetic proportional valves, a pair of swing electromagnetic proportional valves, a pair of left-traveling electromagnetic proportional valves 82, and a pair of right-traveling electromagnetic proportional valves. Each of the multiple proportional valves reduces the pressure of pilot oil (hydraulic oil) discharged from the pilot pump 22 in response to a control command input from the controller 70, and operates to open and close so that the reduced pressure, i.e., pilot pressure, is supplied to the pilot port of the control valve corresponding to the proportional valve. As a result, each of the multiple control valves opens in a direction corresponding to the pilot port to which the pilot pressure is supplied, with a stroke corresponding to the magnitude of the pilot pressure. As a result, hydraulic oil from the pump device is supplied to the hydraulic actuator corresponding to the control valve at a flow rate corresponding to the stroke.

[0038] In Fig. 2, of the pair of boom electromagnetic proportional valves 81, only the boom electromagnetic proportional valve 81 that corresponds to the boom-raising operation is shown, and the boom electromagnetic proportional valve 81 that corresponds to the boom-lowering operation is omitted. Also, in Fig. 2, of the pair of left traveling electromagnetic proportional valves 82, only the left traveling electromagnetic proportional valve 82 that corresponds to the traveling operation by the operator to rotate the wheels 1C of the traveling device in one direction is shown, and the left traveling electromagnetic proportional valve 82 that corresponds to the traveling operation by the operator to rotate the wheels 1C of the traveling device in the other direction is omitted. Also, in Fig. 2, the pair of arm electromagnetic proportional valves, the pair of bucket electromagnetic proportional valves, the pair of swing electromagnetic proportional valves, and the pair of right traveling electromagnetic proportional valves are omitted.

[0039] The multiple detectors include a first pressure sensor 61, a pair of second pressure sensors 62, a discharge pressure sensor 63, and a first velocity sensor 64. Each of the multiple detectors inputs a detection signal, which is a signal corresponding to the detection result, to the controller 70. In FIG. 2, only one of the pair of second pressure sensors 62 is shown, and the other is not shown.

[0040] The first pressure sensor 61 is a pressure sensor capable of detecting a first pressure that is the meter-in pressure of the boom cylinder 7. The meter-in pressure is the pressure in a meter-in oil line that guides the hydraulic oil coming out of the boom control valve 41 to the boom cylinder 7. The meter-out pressure is the pressure in a meter-out oil line that guides the hydraulic oil discharged from the boom cylinder 7 to the boom control valve 41. In this embodiment, the first pressure sensor 61 is arranged so as to be able to detect the pressure in the oil line connected to the head side chamber of the boom cylinder 7. The pressure in the oil line connected to the head side chamber of the boom cylinder 7 corresponds to the meter-in pressure of the boom cylinder 7 when a boom-raising operation is applied to the operating lever of the boom operating device 51.

[0041] The pair of second pressure sensors 62 are pressure sensors capable of detecting the meter-in pressure and meter-out pressure of one of the left and right travel motors 12 (for example, the left travel motor 12). The meter-in pressure is a second pressure that is the pressure of a meter-in oil passage that guides hydraulic oil discharged from the travel control valve 42 to the travel motor 12. The meter-out pressure is the pressure of a meter-out oil passage that guides hydraulic oil discharged from the travel motor 12 to the travel control valve 42.

[0042] The discharge pressure sensor 63 is a pressure sensor capable of detecting the pump pressure of the hydraulic pump 21. The discharge pressure sensor 63 may be configured to detect the pressure of an oil passage through which the hydraulic oil is discharged from the hydraulic pump 21, for example.

[0043] The first speed sensor 64 is a speed sensor capable of detecting a first operating speed, which is the actual operating speed of the boom cylinder 7. The first speed sensor 64 is an example of a first detector. However, the first operating speed can be substituted with another physical quantity related to the actual operating speed of the boom cylinder 7. The other physical quantity may be, for example, an inflow amount, which is the flow rate of hydraulic oil actually flowing into the boom cylinder 7, an outflow amount, which is the flow rate of hydraulic oil actually flowing out of the boom cylinder 7, or the actual operating speed of the boom 4. Each of the inflow amount, the outflow amount, and the operating speed of the boom 4 has a high correlation with the actual operating speed of the boom cylinder 7, and therefore can be used as a physical quantity that substitutes for the actual operating speed of the boom cylinder 7.

[0044] The controller 70 includes a computer including an arithmetic processing unit such as an MPU and a memory. The controller 70 includes an operation determination unit, a pressure determination unit, a target value determination unit, a pump displacement control unit, and a valve control unit. The operation determination unit, the pressure determination unit, the target value determination unit, the pump displacement control unit, and the valve control unit are each realized by the arithmetic processing unit executing a program.

[0045] The operation determination unit determines whether a combined operation is being performed based on operation signals input from each of the multiple operation devices to the controller 70. In this embodiment, the combined operation includes both a boom-raising operation and a traveling operation. Therefore, the operation determination unit determines whether a boom-raising operation and a traveling operation are being performed simultaneously based on a boom operation signal, which is an operation signal input from the boom operation device 51 to the controller 70, and a traveling operation signal, which is an operation signal input from the traveling operation device 52 to the controller 70.

[0046] The pressure determination unit determines the maximum pressure based on the first pressure input from the first pressure sensor 61 to the controller 70 and the second pressure input from the second pressure sensor 62 to the controller 70. In this embodiment, the maximum pressure is the larger of the first pressure and the second pressure.

[0047] The target value determination unit determines a first target speed, which is a target for the operating speed of boom cylinder 7, and a second target speed, which is a target for the operating speed of traveling motor 12. The target value determination unit determines the first target speed based on the boom operation signal input from boom operation device 51 to controller 70, and determines the second target speed based on the travel operation signal input from travel operation device 52 to controller 70. Specifically, in this embodiment, the target value determination unit determines the first target speed in accordance with the operation amount of the boom raising operation. In addition, the target value determination unit determines the second target speed in accordance with the operation amount of the travel operation, specifically, the travel operation applied to left travel operation device 52, for example.

[0048] FIG. 3 is a map showing an example of the relationship between the operation amount of the operation applied to the operating device of the hydraulic drive system according to this embodiment and the target speed (target value). The memory of the controller 70 separately stores in advance a map like that of FIG. 3 for determining a first target speed and a map like that of FIG. 3 for determining a second target speed. The target determination unit determines the first target speed based on the map and information related to the operation amount of the boom-raising operation included in the boom operation signal. The target value determination unit determines the second target speed based on the map and information related to the operation amount of the traveling operation included in the traveling operation signal.

[0049] In this embodiment, the first target speed is a target speed of the boom cylinder 7 (boom cylinder target speed). However, the first target speed can be substituted for another physical quantity related to the target speed of the boom cylinder 7. The other physical quantity may be, for example, a target flow rate (target inflow rate) that is a target flow rate of hydraulic oil flowing into the boom cylinder 7, a target flow rate (target outflow rate) that is a target flow rate of hydraulic oil flowing out of the boom cylinder 7, or a target speed (boom target speed) that is a target operating speed of the boom 4. Each of the target inflow rate, the target outflow rate, and the boom target speed has a high correlation with the boom cylinder target speed, and therefore can be used as a physical quantity that substitutes for the boom cylinder target speed.

[0050] In this embodiment, the second target speed is the target speed of the travel motor 12 (travel motor target speed). However, the second target speed can be substituted with another physical quantity related to the target speed of the travel motor 12. The other physical quantity can be, for example, a target flow rate (target inflow rate) that is a target flow rate of hydraulic oil flowing into the travel motor 12, a target flow rate (target outflow rate) that is a target flow rate of hydraulic oil flowing out of the travel motor 12, or a target speed (wheel target speed) that is a target operating speed of one of the wheels 1B and 1C. The target inflow rate, the target outflow rate, and the wheel target speed each have a high correlation with the travel motor target speed, and can therefore be used as a physical quantity that substitutes for the travel motor target speed.

[0051] The pump displacement control unit inputs a displacement command signal to the regulator of the hydraulic pump 21. As a result, the pump displacement of the hydraulic pump 21 is adjusted to a displacement corresponding to the displacement command signal. In this embodiment, when the combined operation is performed and the first pressure is greater than the second pressure, the pump displacement control unit inputs to the regulator of the hydraulic pump 21 a displacement command signal such that the discharge rate of the hydraulic pump 21 is adjusted to a value corresponding to the sum of the first target speed and the second target speed, that is, a displacement command signal such that the discharge rate of the hydraulic pump 21 is adjusted to the sum of the flow rate of hydraulic oil required to operate the boom cylinder 7 at the first target speed and the flow rate of hydraulic oil required to operate the traveling motor 12 at the second target speed.

[0052] The valve control unit inputs control commands for adjusting the apertures of the respective control valves to the proportional valves corresponding to the control valves. Specifically, for example, the valve control unit inputs a control command to a traveling electromagnetic proportional valve 82 (for example, the left traveling electromagnetic proportional valve 82) for narrowing the aperture of the traveling control valve 42 so as to bring the pressure deviation, which is the deviation between the first pressure and the discharge pressure (pump pressure) of the hydraulic pump 21, closer to zero and to bring the first deviation, which is the deviation between the first target speed and the first operating speed, closer to zero.

[0053] Next, the calculation and control operations performed by the controller 70 will be described with reference to the flowcharts of FIGS.

[0054] When the operator performs an operation to start the engine, the controller 70 starts the engine (step S1). In an idling state after the engine has started, the plurality of control valves are kept in a neutral position and closed (step S2).

[0055] The operation determination unit of the controller 70 determines whether an operator has operated at least one of the multiple operating devices (step S3). If the operator has not operated the multiple operating devices (NO in step S3), the idling state is maintained (step S2). If the operator has operated the multiple operating devices (YES in step S3), the operation determination unit determines whether a predetermined specific combined operation is being performed, specifically, whether a boom-raising operation and a traveling operation are being performed simultaneously (step S4). The operation determination unit determines whether a boom-raising operation and a traveling operation are being performed simultaneously based on a boom operation signal, which is an operation signal input from the boom operating device 51 to the controller 70, and a traveling operation signal, which is an operation signal input from the traveling operating device 52 to the controller 70. If the specific combined operation is not being performed (NO in step S4), the controller 70 executes the processing of the flowchart shown in FIG. 5. FIG. 5 will be described later.

[0056] On the other hand, if the specific combined operation is being performed (YES in step S4), the target value determination unit of controller 70 determines a first target speed and a second target speed (step S5). Specifically, the target value determination unit calculates the first target speed, i.e., the target speed of boom cylinder 7, in accordance with the operation amount of the boom-raising operation applied to boom operation device 51, and calculates the second target speed, i.e., the target speed of travel motor 12, in accordance with the operation amount of the travel operation applied to travel operation device 52. Note that each of the first target speed and the second target speed may be substituted with the target flow rate described above.

[0057] The controller 70 receives an input of a detection signal related to the actual speed (first actual speed), which is the actual operating speed of the boom cylinder 7, detected by the first speed sensor 64 (step S6). Note that the detection signal related to the first actual speed may be replaced by the flow rate (actual flow rate) of hydraulic oil actually flowing into the boom cylinder 7.

[0058] The pump displacement control unit of the controller 70 calculates a feedback control value for adjusting the pump displacement of the hydraulic pump 21 so that a first deviation, which is the deviation between the first target speed and the first actual speed, approaches zero (step S7). Specifically, for example, the pump displacement control unit calculates a first displacement command value (first displacement command signal) using the following equation (1) and the first deviation. In the following equation (1), "u" is the first displacement command value, "Kp", "Ki", ​​and "Kd" are PID gains (proportional gain, integral gain, and differential gain), and "e" is the first deviation.

[0059]

number

[0060] The pump displacement control unit of the controller 70 increases or decreases the pump displacement of the hydraulic pump 21 in accordance with the operation amount of the travel operation applied to the travel operation device 52 (step S9). Specifically, for example, the pump displacement control unit determines a displacement (second displacement command value) of the pump displacement that corresponds to the operation amount of the travel operation based on a map pre-stored in the memory of the controller 70. The map represents, for example, the relationship between the operation amount of the travel operation and the displacement corresponding to the operation amount of the travel operation. The pump displacement control unit calculates a total displacement command value by summing the first displacement command value and the second displacement command value, and inputs the total displacement command value to the regulator of the hydraulic pump 21. As a result, the discharge volume of the hydraulic pump 21 is adjusted to a value corresponding to the sum of the first target speed and the second target speed, i.e., the total amount of hydraulic oil to be supplied to the boom cylinder 7 and the travel motor 12.

[0061] The controller 70 receives input of detection signals relating to the first pressure detected by the first pressure sensor 61 and the second pressure detected by the second pressure sensor 62 (step S10).

[0062] The pressure determination unit of the controller 70 determines the maximum pressure (maximum meter-in pressure value) based on the first pressure input to the controller 70 from the first pressure sensor 61 and the second pressure input to the controller 70 from the second pressure sensor 62 (step S11). In this embodiment, the maximum pressure is the larger of the first pressure and the second pressure.

[0063] If the first pressure is the maximum pressure (step S11: first pressure>second pressure), the controller 70 receives an input of a detection signal relating to the pump pressure (discharge pressure) of the hydraulic pump 21 detected by the discharge pressure sensor 63 (step S12).

[0064] The valve control section of the controller 70 reduces the opening of the travel control valve 42 so that the pressure deviation, which is the deviation between the first pressure and the pump pressure of the hydraulic pump 21, approaches zero, and the first deviation, which is the deviation between the first target speed and the first actual speed, approaches zero (steps S13 to S16).

[0065] The valve control unit calculates a pressure feedback control value, which is a feedback control value related to pressure for adjusting the opening of the travel control valve 42 so as to bring the pressure deviation closer to zero (step S13). Specifically, for example, the valve control unit calculates the pressure feedback control value using the above-mentioned equation (1) and the pressure deviation. In the above-mentioned equation (1), "u" is the pressure feedback control value, and the PID gain is a value different from the above-mentioned PID gain and is a value adjusted for the feedback control related to pressure.

[0066] Next, the valve control unit calculates a speed feedback control value, which is a feedback control value related to speed for adjusting the opening of the travel control valve 42 so as to bring the first deviation closer to zero (step S14). Specifically, for example, the valve control unit calculates the speed feedback control value using the above-mentioned equation (1) and the first deviation. In the above-mentioned equation (1), "u" is the speed feedback control value, and the PID gain is a value different from the above-mentioned PID gain and is a value adjusted for feedback control related to speed.

[0067] Next, the valve control unit calculates a second opening command value, which is the sum of the pressure feedback control value and the speed feedback control value (step S15). Then, the valve control unit outputs the calculated second opening command value (step S16). That is, the valve control unit inputs the first opening command value to the traveling electromagnetic proportional valve 82. The controller 70 repeatedly executes the processes from step S3 onwards (step S17).

[0068] The controller 70 performs the processing of steps S13 to S16 to reduce the opening of the travel control valve 42, thereby increasing the pressure loss in the travel control valve 42 and raising the discharge pressure of the hydraulic pump 21 from the second pressure to the first pressure. This reduces pressure interference, which reduces the amount of hydraulic oil supplied to the boom cylinder 7, which has a higher operating pressure. The first actual speed is adjusted to the first target speed while suppressing pressure interference. When the first actual speed is adjusted to the first target speed, hydraulic oil is supplied to the boom cylinder 7 at a flow rate determined in accordance with the amount of boom-raising operation, and the remaining hydraulic oil is supplied to the travel motor 12. Since the discharge rate of the hydraulic pump 21 is adjusted to a value corresponding to the total value, the flow rate of the remaining hydraulic oil supplied to the travel motor 12 is inevitably determined in accordance with the amount of travel operation. This allows the discharge rate of the hydraulic pump 21 to be appropriately distributed between the boom cylinder 7 and the travel motor 12. Therefore, even if it is difficult to attach a speed sensor to the traveling motor 12 or its vicinity to detect the actual operating speed of the traveling motor 12, the hydraulic drive device of this embodiment can cause the actual operating speeds of the boom cylinder 7 and traveling motor 12, which are the objects of control by combined operation, to follow a target speed (first target speed) corresponding to the operation amount of the boom-raising operation and a target speed (second target speed) corresponding to the operation amount of the traveling operation, respectively.

[0069] The reason why installing a speed sensor is difficult is as follows: For example, since the traveling motor 12 is installed close to the ground, if a speed sensor for detecting the operating speed of the traveling motor 12 is installed on or near the traveling motor 12, it is difficult to ensure that the speed sensor is waterproof.

[0070] This embodiment can also accommodate fluctuations in the load on the actuators due to the influence of external forces. An example of the external force is the increase or decrease in pressure acting on the boom cylinder 7 when the tip attachment is replaced from the bucket 6 to another tip attachment. Another example of the external force is the increase or decrease in pressure acting on the boom cylinder 7 when the tip attachment comes into contact with the ground or the like during travel. Even when such fluctuations in the load on the actuators occur due to external forces, the hydraulic drive system according to this embodiment can cause the actual operating speeds of the first actuator and the second actuator, which are the targets of control by combined operation, to follow the target speeds corresponding to the first operation and the target speeds corresponding to the second operation, respectively.

[0071] On the other hand, when the second pressure is the maximum pressure (step S11: second pressure > first pressure), the detection of the pump pressure (discharge pressure) of the hydraulic pump 21 (step S12) and the calculation of the feedback control value for adjusting the opening of the travel control valve 42 (step S13) are not performed. This is because hydraulic oil can be supplied to the boom cylinder 7 without increasing the pressure loss in the travel control valve 42 and increasing the discharge pressure of the hydraulic pump 21. Furthermore, since the calculation of the feedback control value (step S13) is not performed, the controller 70 does not perform the controls of steps S14 to S16.

[0072] In this case, the amount of hydraulic oil to be supplied to the boom cylinder 7 is regulated (managed) by the controller 70 in step S8 at the stage when the first opening command value is input to the boom electromagnetic proportional valve 81. Furthermore, the amount of hydraulic oil to be supplied to the traveling motor 12 is regulated (managed) by the controller 70 in step S9 by adjusting the discharge rate of the hydraulic pump 21 to a value corresponding to the sum of the first target speed and the second target speed, i.e., the total amount of hydraulic oil to be supplied to the boom cylinder 7 and the traveling motor 12. Therefore, even when the second pressure is the maximum pressure, the actual operating speeds of the first actuator and the second actuator, which are to be controlled by the combined operation, can be made to follow the target speed corresponding to the first operation and the target speed corresponding to the second operation, respectively.

[0073] Next, a description will be given of the flowchart shown in Fig. 5. In step S4, if the operation determination unit determines that the specific combined operation has not been performed (NO in step S4), the controller 70 executes the processing of the flowchart shown in Fig. 5.

[0074] The operation determination unit of the controller 70 determines whether or not a boom-raising operation is being performed (step S21). If a boom-raising operation is being performed (YES in step S21), the controller 70 executes the processes of steps S22 to S27, and if a boom-raising operation is not being performed (NO in step S21), the controller 70 executes the processes of steps S31 to S38.

[0075] If a boom raising operation is being performed (YES in step S21), the target value determination unit of the controller 70 determines a first target speed (step S22). Specifically, the target value determination unit calculates the first target speed, i.e., the target speed of the boom cylinder 7, according to the operation amount of the boom raising operation applied to the boom operation device 51. Note that the first target speed may be substituted by the target flow rate described above.

[0076] The controller 70 receives an input of a detection signal related to the actual speed (first actual speed), which is the actual operating speed of the boom cylinder 7, detected by the first speed sensor 64 (step S23). Note that the detection signal related to the first actual speed may be replaced by the flow rate (actual flow rate) of hydraulic oil actually flowing into the boom cylinder 7.

[0077] The pump displacement control section of the controller 70 calculates a feedback control value for adjusting the pump displacement of the hydraulic pump 21 so as to bring the first deviation, which is the deviation between the first target speed and the first actual speed, closer to zero (step S24). The processing of this step S24 is similar to the processing of step S7 described above.

[0078] The valve control section of the controller 70 calculates a feedback control value for adjusting the opening of the boom control valve 41 so as to bring the first deviation, which is the deviation between the first target speed and the first actual speed, closer to zero (step S25). Specifically, for example, the valve control section calculates a first opening command value (first opening command signal) in the same manner as the processing of step S8 described above. Then, the valve control section inputs the first opening command value to the boom electromagnetic proportional valve 81 (step S26). The controller 70 repeatedly executes the processing from step S3 described above onwards (step S27).

[0079] On the other hand, if a boom-raising operation is not being performed but a traveling operation is being performed (NO in step S21), the target value determination unit of controller 70 determines a second target speed (step S31). Specifically, the target value determination unit calculates the second target speed, i.e., the target speed of traveling motor 12, according to the amount of traveling operation applied to traveling operation device 52. The second target speed may be substituted by the target flow rate described above.

[0080] The pump displacement control unit of the controller 70 increases or decreases the pump displacement of the hydraulic pump 21 in accordance with the operation amount of the travel operation applied to the travel operation device 52 (step S32). Specifically, for example, the pump displacement control unit determines the pump displacement corresponding to the operation amount of the travel operation (second displacement command value) based on a map stored in advance in the memory of the controller 70, similar to the processing of step S9 described above. The pump displacement control unit inputs the second displacement command value to the regulator of the hydraulic pump 21. As a result, the discharge volume of the hydraulic pump 21 is adjusted to a value corresponding to the second target speed, i.e., the flow rate of hydraulic oil to be supplied to the travel motor 12.

[0081] The controller 70 receives an input of a detection signal relating to the second pressure detected by the second pressure sensor 62 (step S33).

[0082] The pressure determination unit of the controller 70 determines the maximum pressure (maximum meter-in pressure value) based on the second pressure input to the controller 70 from the second pressure sensor 62 (step S34). In this case, the maximum pressure is the second pressure.

[0083] The controller 70 receives an input of a detection signal relating to the pump pressure (discharge pressure) of the hydraulic pump 21 detected by the discharge pressure sensor 63 (step S35).

[0084] The valve control section of the controller 70 adjusts the opening of the travel control valve 42 so that the second pressure deviation, which is the deviation between the second pressure and the pump pressure of the hydraulic pump 21, approaches zero (steps S36 and S37).

[0085] The valve control unit calculates a second pressure feedback control value, which is a feedback control value for adjusting the opening of the travel control valve 42 so as to bring the second pressure deviation closer to zero (step S36). Specifically, for example, the valve control unit calculates the second pressure feedback control value using the above-mentioned equation (1) and the second pressure deviation. In the above-mentioned equation (1), "u" is the second pressure feedback control value, and the PID gain is a value different from the above-mentioned PID gain and is a value adjusted for this feedback control.

[0086] Next, the valve control unit outputs the second pressure feedback control value as a second opening command value (step S37). That is, the valve control unit inputs the second opening command value to the traveling electromagnetic proportional valve 82. The controller 70 repeatedly executes the processing from step S3 onwards described above (step S38).

[0087] The hydraulic drive system according to this embodiment may further include an unloading valve (not shown). This unloading valve is a valve provided in an unloading line that allows hydraulic oil discharged from the hydraulic pump 21 in FIG. 2 to bypass the control valves 41 and 42 and the actuators 7 and 12 and return directly to the tank. When this unloading valve is opened, it allows the hydraulic oil to flow through the unloading line at a flow rate corresponding to its opening. In the processing of step S4 in the flowchart of FIG. 4, if the specific combined operation is being performed (YES in step S4), it is preferable that the controller 70 perform control to close the unloading valve (unloading valve closing control).

[0088] [Variations] Although the hydraulic drive system according to the embodiment of the present disclosure has been described above, the present disclosure is not limited to the above embodiment and includes, for example, the following modified examples.

[0089] (A) Variation 1 The hydraulic drive system may further include a travel speed detector 65 (see FIG. 1) capable of detecting the actual travel speed of the construction machine 100. In this modified example 1, as in the above embodiment, the second actuator is the travel motor 12 used for traveling the construction machine 100. During the combined operation, the controller 70 calculates a second actual speed, which is the actual operating speed of the travel motor 12, based on the detection result detected by the travel speed detector 65. Then, the pump displacement control unit of the controller 70 controls the displacement of the hydraulic pump 21 so that a second deviation, which is the deviation between the second target speed and the second actual speed, approaches zero.

[0090] In this first modification, even if there is an error between the ideal pump discharge rate corresponding to the displacement command by the controller 70 and the actual pump discharge rate, the controller 70 calculates a second operating speed (second actual speed) which is the actual operating speed of the traveling motor 12 based on the detection result detected by the traveling speed detector 65 (i.e., the actual traveling speed of the construction machine), and controls the displacement of the hydraulic pump 21 so as to bring the second deviation between the second target speed and the second actual speed closer to zero, thereby reducing the error. This makes it possible to make the actual operating speeds of the first actuator (e.g., the boom cylinder 7) and the second actuator (traveling motor 12), which are controlled by the combined operation, more accurately follow the target speeds.

[0091] The traveling speed detector 65 is not particularly limited in its specific structure as long as it is capable of detecting the actual traveling speed of the construction machine 100. The traveling speed detector 65 may be, for example, a sensor that is capable of detecting the actual traveling speed of the construction machine 100 using a positioning system for measuring the position of the construction machine 100. An example of a positioning system is a satellite positioning system such as the GNSS (Global Navigation Satellite System), but the positioning system may be one other than a satellite positioning system. The traveling speed detector 65 is configured with a sensor that is capable of receiving signals from the positioning system. The traveling speed detector 65 may also be configured with an acceleration sensor. In this case, the controller 70 can calculate the traveling speed of the construction machine 100 by integrating the detection result (acceleration) input from the acceleration sensor over time.

[0092] (B) Variation 2 The hydraulic drive system may further include a stroke end detector 66 (see FIG. 2) that can detect whether a hydraulic cylinder serving as a first actuator has reached its stroke end. In this second modification, when a hydraulic cylinder (e.g., boom cylinder 7) reaches its stroke end during combined operation, the controller 70 adjusts the discharge rate of the hydraulic pump 21 to a value corresponding to the second target speed. In this second modification, when the hydraulic cylinder reaches its stroke end and becomes inoperable during combined operation, the discharge rate of the hydraulic pump 21 is adjusted to a value corresponding to the second target speed, thereby preventing an increase in the difference between the actual operating speed and the target speed of the second actuator (e.g., travel motor 12).

[0093] Furthermore, in this Modification 2, it is preferable that the controller 70 turns off the unloading valve closing control when the hydraulic cylinder reaches its stroke end during combined operation. In other words, it is preferable that the controller 70 performs control to open the unloading valve from its closed state when the hydraulic cylinder reaches its stroke end during combined operation.

[0094] (C) Construction machinery The construction machine according to the present disclosure is not necessarily limited to a hydraulic excavator, but may be a crane, a bulldozer, or other construction machine.

[0095] (D) Control valves The control valve according to the present disclosure is not limited to a three-position pilot operated switching valve as long as it can open in response to an operation applied to an operating device. The control valve according to the present disclosure may be, for example, a two-position switching valve or a solenoid operated switching valve.

[0096] (E) Operating Devices In the above embodiment, the circuit configuration is shown for the case where the operating device is an electric operating device. Alternatively, each operating device may be an operating device (not shown) equipped with a remote control valve. In this case, an operating signal related to the pilot pressure is input to the controller 70 from a pressure sensor that detects the secondary pressure (pilot pressure) of the remote control valve.

[0097] (F) First and second actuators In the above embodiment, the first actuator is a boom cylinder and the second actuator is a travel motor. However, the combination of the first and second actuators is not limited to the above embodiment. The first actuator may be a hydraulic actuator other than a boom cylinder, and the second actuator may be a hydraulic actuator other than a travel motor. Specifically, the second actuator may be used to move an end attachment other than the bucket 6, specifically, an optional end attachment such as a fork, a grapple, or a crusher (crusher). It is difficult to install a speed sensor on or near the actuator for moving these optional end attachments. Specifically, the reason is as follows. When the end attachment attached to the end of the arm 5 is a bucket 6, the bucket 6 only rotates within a relatively narrow angular range relative to the arm 5. Therefore, it is possible to install a speed sensor on or near the bucket 6 to detect the operating speed of the bucket cylinder 9. However, when the end attachment is, for example, a fork that can rotate around a rotation axis along the longitudinal direction of the arm 5, it is difficult to route a cable for the speed sensor to a member that rotates relatively.

[0098] (G) Composite operations involving three or more operations In the above embodiment, during a combined operation in which the first operation and the second operation are performed simultaneously, if the meter-in pressure of the first actuator is greater than the meter-in pressure of the second actuator, the controller adjusts the discharge volume of the pump device based on the first operation and the second operation, and reduces the opening of the second control valve so that the discharge pressure of the pump device approaches the meter-in pressure of the first actuator and the first actual speed approaches the first target speed. However, the combined operation may also be one in which three or more operations including the first operation and the second operation are performed simultaneously.

[0099] Below, a specific description will be given of a modified example in which the control targets of a combined operation are three hydraulic actuators. That is, this modified example is a case in which an operator simultaneously performs three operations as combined operations. Each of the three hydraulic actuators is actuated by receiving a supply of hydraulic oil discharged from the pump device, and moves a movable part corresponding to that actuator. The pump device includes at least a hydraulic pump 21, and may include the hydraulic pump 21 and the second hydraulic pump.

[0100] The three hydraulic actuators include two hydraulic actuators to which a speed sensor can be attached and one hydraulic actuator to which a speed sensor cannot be attached. Hereinafter, the hydraulic actuator to which a speed sensor can be attached is referred to as an attachable actuator, and the hydraulic actuator to which a speed sensor cannot be attached is referred to as a non-attachable actuator. One of the two attachable actuators may be, for example, the boom cylinder 7, the arm cylinder 8, the bucket cylinder 9, or the swing motor 11. The other of the two attachable actuators is an actuator different from one of the two attachable actuators and may be, for example, the boom cylinder 7, the arm cylinder 8, the bucket cylinder 9, or the swing motor 11. The non-attachable actuator may be, for example, the travel motor 12, or a hydraulic actuator for moving an end attachment other than the bucket 6 (e.g., an optional end attachment such as a fork, grapple, or crusher).

[0101] The hydraulic drive system according to this modification includes three pressure sensors and two speed sensors. The three pressure sensors include two pressure sensors that detect the meter-in pressures of the two attachable actuators and a pressure sensor that detects the meter-in pressure of the non-attachable actuator. The two speed sensors include a sensor that can detect the actual operating speed of one of the two attachable actuators and a sensor that can detect the actual operating speed of the other of the two attachable actuators.

[0102] In this modification, the pressure determination unit of the controller 70 determines the maximum pressure based on the detection results input from the three pressure sensors, as in the above embodiment. In this modification, the maximum pressure is the largest pressure among the three pressures detected by the three pressure sensors.

[0103] First, a first case will be described in which the meter-in pressure of one of the two attachable actuators is the maximum. In this first case, the attachable actuator with the maximum meter-in pressure is referred to as the maximum pressure actuator, and the actuator with the lower meter-in pressure of the two attachable actuators is referred to as the low-pressure actuator (third actuator). In this first case, the maximum pressure actuator is an actuator equivalent to the first actuator in the above embodiment (e.g., boom cylinder 7 in FIG. 2), and the non-attachable actuator is an actuator equivalent to the second actuator in the above embodiment (e.g., travel motor 12 in FIG. 2).

[0104] During combined operation in which the three operations are performed simultaneously, the pump displacement control section of the controller 70 adjusts the discharge volume of the pump device based on the three operations. That is, the pump displacement control section adjusts the discharge volume of the pump device to the total volume of hydraulic oil to be supplied to the maximum pressure actuator (first actuator), the non-installable actuator (second actuator), and the low-pressure actuator (third actuator).

[0105] 4, the valve control section of the controller 70 calculates a feedback control value for adjusting the aperture of the control valve corresponding to the maximum pressure actuator so as to bring a first deviation between a first target speed of the maximum pressure actuator (first actuator) and a first actual speed, which is the actual operating speed, closer to zero, and inputs the feedback control value to the solenoid proportional valve corresponding to the maximum pressure actuator. When the first actual speed of the maximum pressure actuator is adjusted to the first target speed, hydraulic oil is supplied to the maximum pressure actuator at a flow rate determined according to a first operation applied to its operating device, and the flow rate of the remaining hydraulic oil is equal to the sum of the flow rate of hydraulic oil supplied to the non-installable actuator (second actuator) and the flow rate of hydraulic oil supplied to the low-pressure actuator (third actuator).

[0106] Furthermore, the valve control section of the controller 70 calculates a feedback control value for adjusting the aperture of the control valve corresponding to the low-pressure actuator (third actuator) so as to bring a third deviation between a third target speed, which is a target speed of the low-pressure actuator, and a third actual speed, which is an actual operating speed, closer to zero, and inputs the feedback control value to the solenoid proportional valve corresponding to the low-pressure actuator. When the third actual speed of the low-pressure actuator is adjusted to the third target speed, hydraulic oil is supplied to the low-pressure actuator at a flow rate determined according to the operation applied to its operating device, and the remaining hydraulic oil is supplied to the non-installable actuator (second actuator). As a result, hydraulic oil is supplied to the non-installable actuator at a flow rate determined according to the operation applied to its operating device.

[0107] Next, a second case will be described in which the meter-in pressure of the non-attachable actuator (second actuator) is the maximum. In this second case, too, the pump displacement control unit of the controller 70 adjusts the discharge rate of the pump device based on the three operations during combined operation in which three operations are performed simultaneously. In other words, the pump displacement control unit adjusts the discharge rate of the pump device to the total amount of hydraulic oil to be supplied to the two attachable actuators and one non-attachable actuator.

[0108] In this second case, the valve control unit of the controller 70 performs feedback control, for example, similar to the processing of step S8 in FIG. 4, for the actuator (low-pressure actuator) having the lower meter-in pressure of the two attachable actuators, so that its operating speed (actual speed) becomes the target speed. As a result, the actual speed of the low-pressure actuator is adjusted to the target speed. Next, the valve control unit performs feedback control, for example, similar to the processing of step S8 in FIG. 4, for the actuator (high-pressure actuator) having the higher meter-in pressure of the two attachable actuators, so that its operating speed (actual speed) becomes the target speed. In a state where the operating speeds (actual speeds) of the two attachable actuators have been adjusted to their target speeds, hydraulic oil is supplied to each of the two attachable actuators at a flow rate determined according to their operation, and the remaining hydraulic oil is supplied to the non-attachable actuator (second actuator). As a result, hydraulic oil is supplied to the non-attachable actuator at a flow rate determined according to the operation applied to its operating device. [Explanation of symbols]

[0109] 7: Boom cylinder 12:Traction motor 21: Hydraulic pump 41: Boom control valve 42: Travel control valve 51: Boom operation device 52: Travel control device 61: First pressure sensor 62: Second pressure sensor 63: Discharge pressure sensor 64: First speed sensor 65: Travel speed detector 66: Stroke end detector 70: Controller 100: Construction machinery

Claims

1. a pump device that discharges hydraulic oil; a first actuator and a second actuator; a first control valve interposed between the pump device and the first actuator and configured to control the flow rate of the hydraulic oil supplied to the first actuator; a second control valve interposed between the pump device and the second actuator and configured to control the flow rate of the hydraulic oil supplied to the second actuator; a first operating device to which a first operation for determining a first target speed that is a target speed of the first actuator is applied; a second operation device to which a second operation for determining a second target speed that is a target speed of the second actuator is applied; a first detector that detects a first operating speed that is an operating speed of the first actuator; a controller that, during a combined operation of the first operation and the second operation, adjusts the discharge amount of the pump device to the total amount of the hydraulic oil to be supplied to the first actuator and the second actuator based on the first operation and the second operation, gives an opening command to adjust the opening of the first control valve so that the first operating speed approaches the first target speed, and gives a control command to reduce the opening of the second control valve so that the discharge pressure of the pump device approaches the meter-in pressure of the first actuator and the first operating speed approaches the first target speed, The first control valve and the second control valve are connected in parallel to the pump device, the opening of the first control valve is adjusted based on the opening command from the controller, and the opening of the second control valve is reduced based on the control command from the controller.

2. A pump device that discharges hydraulic oil; a first actuator and a second actuator; a first control valve and a second control valve that control the flow rates of the hydraulic oil supplied to the first actuator and the second actuator, respectively; a first operating device to which a first operation for determining a first target speed that is a target speed of the first actuator is applied; a second operating device to which a second operation is applied; a first detector that detects a first operating speed that is an operating speed of the first actuator; a controller that, during a combined operation of the first operation and the second operation, adjusts a discharge amount of the pump device based on the first operation and the second operation, and issues a control command to reduce an opening of the second control valve so that the discharge pressure of the pump device approaches a meter-in pressure of the first actuator and the first operating speed approaches the first target speed; a traveling speed detector for detecting the traveling speed of the construction machine, the pump device includes a variable displacement hydraulic pump; the second actuator is a travel motor, The controller, during the combined operation, calculates a second operating speed, which is the operating speed of the second actuator, based on the detection result of the traveling speed, and controls the capacity of the hydraulic pump so that the second operating speed approaches a second target speed determined in accordance with the second operation.

3. 3. The hydraulic drive system for a construction machine according to claim 1, wherein the controller issues the control command when the meter-in pressure of the first actuator is greater than the meter-in pressure of the second actuator during the combined operation.

4. the first actuator is a hydraulic cylinder; The hydraulic drive device further includes a stroke end detector that detects whether the hydraulic cylinder has reached a stroke end, 4. The hydraulic drive system for a construction machine according to claim 1, wherein the controller adjusts the discharge rate of the pump device based on the second operation when the hydraulic cylinder reaches the stroke end.

5. A hydraulic drive device for a construction machine as described in claim 1, 3 or 4, wherein the second actuator is a hydraulic actuator to which it is difficult to attach a speed sensor, and the hydraulic actuator is a travel motor or an actuator for moving a fork, a grapple or a crusher.

6. A construction machine comprising the hydraulic drive device according to any one of claims 1 to 5, a first movable part that can be moved by the first actuator, and a second movable part that can be moved by the second actuator.

Images