Hydraulic drive device for construction machine

Abstract

A hydraulic drive device (101) for a construction machine (100) comprises: a hydraulic pump (22) that discharges a hydraulic fluid; a hydraulic cylinder (8) that has a head side chamber (8H) and a rod side chamber (8R); a first passage (31) that connects the hydraulic pump (22) and the head side chamber (8H); a second passage (32) that is connected to the rod side chamber (8R); a third passage (33) that connects the first passage (31) and the second passage (32); and a recycle control valve (53) that is disposed in the third passage (33). The recycle control valve (53) has a spool that can be switched between a recycle position at which the spool allows the hydraulic fluid released from the rod side chamber (8R) to flow into the first passage (31) from the second passage (32) and return to the head side chamber (8H) and a meter-in position at which the spool allows the hydraulic fluid discharged from the hydraulic pump (22) to flow into the second passage (32) from the first passage (31) and be supplied to the rod side chamber (8R).

Description

Hydraulic drive systems for construction machinery

[0001] The present disclosure relates to a hydraulic drive system for a construction machine.

[0002] Patent Document 1 discloses a pressure oil supply device including a hydraulic pump, a hydraulic actuator provided in a discharge circuit of the hydraulic pump, and a meter-in switching valve provided between the hydraulic pump and the hydraulic actuator for controlling a meter-in flow rate in accordance with a differential pressure between the pump pressure and the load pressure. In this pressure oil supply device, a meter-out switching valve for controlling a meter-out flow rate independent of the meter-in switching valve is provided in a return circuit from the hydraulic actuator to a tank.

[0003] Patent Document 2 discloses a hydraulic regeneration device for a hydraulic machine, which includes a directional control valve that controls the flow of pressurized oil supplied from a hydraulic pump to a hydraulic cylinder, a variable throttle valve that is provided in a return line and controls the flow rate of pressurized oil led to a tank, a check valve that is provided in a junction line that connects the supply line and the return line and allows the supply of pressurized oil from the return line to the supply line, a pressure detector that detects pilot pressure applied to a drive unit of the directional control valve, an on-off valve that selectively connects or disconnects the junction line, a mode switch that operates this on-off valve, and a control device that controls the amount of throttling of the variable throttle valve in accordance with the magnitude of the value of the signal output from the pressure detector.

[0004] The technology described in Patent Document 1 includes a meter-in switching valve for controlling the meter-in opening and a meter-out switching valve for controlling the meter-out opening. The technology described in Patent Document 2 includes a variable throttle valve for controlling the flow rate of pressure oil introduced to a tank and an on-off valve for selectively connecting or disconnecting a junction pipeline. That is, each of these technologies requires a valve (spool) for each function, and therefore, in order to achieve multiple functions, the number of spools increases, resulting in a complex circuit configuration. The same is true for the technologies described in Patent Documents 3 to 5.

[0005] JP 11-303814 JP 7-35110 JP 8-132218 Patent No. 5004641 Patent No. 3675703

[0006] An object of the present disclosure is to provide a hydraulic drive system for a construction machine that can prevent the configuration of the hydraulic circuit from becoming complicated.

[0007] A hydraulic drive system for a construction machine according to a first aspect includes a hydraulic pump that discharges hydraulic oil, a hydraulic cylinder having a head side chamber and a rod side chamber, a first passage connecting the hydraulic pump and the head side chamber, a second passage connected to the rod side chamber, a third passage connecting the first passage and the second passage, and a regeneration control valve arranged in the third passage, wherein the regeneration control valve has a spool that can be switched between a regeneration position that allows hydraulic oil discharged from the rod side chamber to flow from the second passage into the first passage and return to the head side chamber, and a meter-in position that allows hydraulic oil discharged from the hydraulic pump to flow from the first passage into the second passage and be supplied to the rod side chamber.

[0008] FIG. 1 is a side view showing an example of a construction machine. FIG. 2 is a diagram showing a hydraulic circuit of the construction machine according to the first embodiment. FIG. 3 is a graph showing an example of the relationship between an operation input to a controller of the construction machine and the output of the controller. FIG. 4 is a diagram showing a hydraulic circuit of the construction machine according to the second embodiment. FIG. 5 is a graph showing the relationship between an operation input to a controller of the construction machine according to the second embodiment and the opening degree of a switching valve. FIG. 6 is a table summarizing the content and conditions of operations, and the state of each directional switching valve in the construction machine according to the second embodiment.

[0009] Embodiments of the present disclosure will be described with reference to the drawings.

[0010] Fig. 1 is a side view showing a construction machine 100 according to an embodiment. The construction machine 100 shown in Fig. 1 is a hydraulic excavator. The construction machine 100 includes a self-propelled undercarriage 1, an upper rotating body 2 supported by the undercarriage 1 so as to be able to rotate about a Z-axis in the up-down direction relative to the undercarriage 1, a working device 3, and a plurality of hydraulic actuators.

[0011] The undercarriage 1 includes left and right crawler travelling devices and a lower frame supported by the crawler travelling devices. The upper revolving body 2 includes a revolving frame that is revolvably supported on the lower frame of the undercarriage 1, and a cab that is supported on the revolving frame. The working device 3 includes a boom 4 that is supported on the revolving frame so that it can be raised and lowered, an arm 5 that is rotatably supported at the tip of the boom 4, and a bucket 6 that serves as a tip attachment that is rotatably supported at the tip of the arm 5. The tip attachment is not limited to the bucket 6 and may be, for example, another tip attachment such as a breaker or fork. The multiple hydraulic actuators include a boom cylinder 7, an arm cylinder 8, a bucket cylinder 9, a revolving motor 11, and a travel motor 12.

[0012] [First embodiment] Fig. 2 is a diagram showing an example of a hydraulic circuit of a construction machine 100. In the hydraulic circuit shown in Fig. 2, only the parts related to the arm cylinder 8 are shown, and other components are not shown.

[0013] The construction machine 100 includes a hydraulic drive system 101. The hydraulic drive system 101 includes a hydraulic pump 22, an arm cylinder 8, a first passage 31, a second passage 32, a third passage 33, and a directional control valve 53. The directional control valve 53 is an example of a regeneration control valve in the present disclosure.

[0014] The hydraulic pump 22 is driven by a power source 91 such as an engine or an electric motor to discharge hydraulic oil. In this embodiment, the hydraulic pump 22 is a variable displacement hydraulic pump. The pump displacement of the hydraulic pump 22 is adjusted based on a command output from a controller 80. Information regarding the rotation speed of the power source 91 that drives the hydraulic pump 22 (a rotation speed detection signal) is input to the controller 80.

[0015] The arm cylinder 8 is a hydraulic cylinder having a head-side chamber 8H and a rod-side chamber 8R. The arm cylinder 8 is actuated by the supply of hydraulic oil from the hydraulic pump 22. As shown in FIG. 1 , the arm cylinder 8 has a base end connected to the boom 4 and a tip end connected to the arm 5. The arm cylinder 8 extends when hydraulic oil is supplied to the head-side chamber 8H and discharged from the rod-side chamber 8R, and contracts when hydraulic oil is supplied to the rod-side chamber 8R and discharged from the head-side chamber 8H.

[0016] The arm 5 performs an arm pulling operation by extending the arm cylinder 8, and performs an arm pushing operation by retracting the arm cylinder 8. The arm pulling operation is an operation in which the tip of the arm 5 approaches the boom 4, and the arm pushing operation is an operation in which the tip of the arm 5 moves away from the boom 4.

[0017] The first passage 31 connects the hydraulic pump 22 and the head side chamber 8H of the arm cylinder 8. The second passage 32 is a passage connected to the rod side chamber 8R of the arm cylinder 8. The third passage 33 connects the first passage 31 and the second passage 32. The directional control valve 53 is disposed in the third passage 33.

[0018] The directional control valve 53 not only functions as a regeneration control valve but also functions as a meter-in control valve.

[0019] The directional control valve 53 is configured to be switchable between a regeneration position and a meter-in position. Specifically, the directional control valve 53 has a spool that is displaceable between a neutral position and a regeneration position and between the neutral position and the meter-in position. The neutral position prevents hydraulic oil discharged from the hydraulic pump 22 from being supplied to the rod side chamber 8R of the arm cylinder 8 and prevents hydraulic oil discharged from the rod side chamber 8R of the arm cylinder 8 to the second passage 32 from returning to the head side chamber 8H of the arm cylinder 8. The regeneration position allows hydraulic oil discharged from the rod side chamber 8R of the arm cylinder 8 to the second passage 32 to flow from the second passage 32 into the first passage 31 and return to the head side chamber 8H of the arm cylinder 8. The meter-in position allows hydraulic oil discharged from the hydraulic pump 22 to flow from the first passage 31 into the second passage 32 and be supplied to the rod side chamber 8R of the arm cylinder 8.

[0020] In this hydraulic drive system 101, when there is an operation to extend the arm cylinder 8 (arm pulling operation), the direction switching valve 53 shifts from the neutral position to the regeneration position and functions as a regeneration control valve for returning the hydraulic oil discharged from the rod side chamber 8R to the head side chamber 8H, and when there is an operation to retract the arm cylinder 8 (arm pushing operation), the direction switching valve 53 shifts from the neutral position to the meter-in position and functions as a meter-in control valve for supplying the hydraulic oil discharged from the hydraulic pump 22 to the rod side chamber 8R. That is, in this hydraulic drive system 101, the direction switching valve 53 functions not only as a regeneration control valve but also as a meter-in control valve, so that these functions can be achieved while preventing the configuration of the hydraulic circuit from becoming complicated compared to when a regeneration control valve and a meter-in control valve are provided separately.

[0021] In the first embodiment, the directional control valve 53 may function as a regeneration control valve for returning hydraulic oil discharged from the rod side chamber 8R to the head side chamber 8H when the operating member 15A of the controller 15 is subjected to only the arm-pushing operation (i.e., during the arm-pushing operation alone), or may function as a meter-in control valve for supplying hydraulic oil discharged from the hydraulic pump 22 to the rod side chamber 8R when the operating member 15A of the controller 15 is subjected to only the arm-pushing operation (i.e., during the arm-pushing operation alone).

[0022] The above are the main features of the hydraulic drive system 101 according to the first embodiment. The hydraulic drive system 101 according to the first embodiment will be described in more detail below.

[0023] The directional control valve 53 may be, for example, a three-position directional control valve as shown in Fig. 2. The directional control valve 53 may be, for example, a solenoid valve having a pair of solenoids 53a and 53b as shown in Fig. 2. The directional control valve 53 has a spool that can be switched among a neutral position (middle position in Fig. 2), the regeneration position (right position in Fig. 2), and the meter-in position (left position in Fig. 2) in accordance with a valve command (command signal) input to the directional control valve 53. The directional control valve 53 has a plurality of ports, including a first port, a second port, and a third port.

[0024] The third passage 33 includes a first portion 33A, a second portion 33B, and a third portion 33C. The first portion 33A of the third passage 33 connects the first passage 31 and a first port of the directional control valve 53. The second portion 33B of the third passage 33 connects the second passage 32 and a second port of the directional control valve 53. The third portion 33C of the third passage 33 connects the first passage 31 and a third port of the directional control valve 53.

[0025] When the command values ​​of the valve commands input to the solenoids 53a, 53b are both 0 or very small, the spool of the directional control valve 53 is maintained in a neutral position (the intermediate position in FIG. 2 ). When the spool of the directional control valve 53 is disposed in the neutral position, the first port, the second port, and the third port are sealed. As a result, the first passage 31 and the second passage 32 are blocked in the directional control valve 53. That is, when the spool of the directional control valve 53 is disposed in the neutral position, the hydraulic oil discharged from the hydraulic pump 22 is prevented from being supplied to the rod side chamber 8R of the arm cylinder 8, and the hydraulic oil discharged from the rod side chamber 8R of the arm cylinder 8 to the second passage 32 is prevented from returning to the head side chamber 8H of the arm cylinder 8. When the spool of the directional control valve 53 is maintained in the neutral position, the meter-in opening and the regeneration opening of the directional control valve 53 are completely blocked, that is, they are in a "fully closed" state.

[0026] When the command value of the valve command input to the solenoid 53b is equal to or greater than a certain value, the spool of the directional control valve 53 shifts from the neutral position to the regeneration position (the right-hand position in FIG. 2 ) by a stroke corresponding to the magnitude of the command value. When the spool of the directional control valve 53 is positioned in the regeneration position, the second port and the third port are connected, and the first port is sealed. That is, when the spool of the directional control valve 53 is positioned in the regeneration position, hydraulic oil discharged from the rod-side chamber 8R of the arm cylinder 8 to the second passage 32 is allowed to flow from the second passage 32 into the first passage 31 and return to the head-side chamber 8H of the arm cylinder 8. When the spool of the directional control valve 53 is completely shifted to the regeneration position, the regeneration opening of the directional control valve 53 is at its maximum opening, i.e., is in a "fully open" state.

[0027] When the command value of the valve command input to the solenoid 53a is equal to or greater than a certain value, the spool of the directional switching valve 53 shifts from the neutral position to the meter-in position (the left position in FIG. 2 ) by a stroke corresponding to the magnitude of the command value. When the spool of the directional switching valve 53 is positioned in the meter-in position, the first port and the second port are connected, and the third port is sealed. In other words, when the spool of the directional switching valve 53 is positioned in the meter-in position, hydraulic oil discharged from the hydraulic pump 22 is allowed to flow from the first passage 31 into the second passage 32 and be supplied to the rod-side chamber 8R of the arm cylinder 8. When the spool of the directional switching valve 53 is completely shifted to the meter-in position, the meter-in opening of the directional switching valve 53 reaches its maximum opening, i.e., is in a "fully open" state.

[0028] 2, the hydraulic drive system 101 further includes a check valve 71, a check valve 72, a pilot check valve 73, a directional control valve 51, a plurality of actuators 15, and a controller 80. In FIG. 2, only one actuator 15 is shown, and the other actuators 15 are not shown.

[0029] The check valve 71 is disposed in a portion of the first passage 31 between the hydraulic pump 22 and a portion to which the first portion 33A of the third passage 33 is connected. The check valve 71 allows the hydraulic oil discharged from the hydraulic pump 22 to flow toward the direction switching valve 53 and the hydraulic oil discharged from the hydraulic pump 22 to flow toward the direction switching valve 51, while preventing the hydraulic oil from flowing from the direction switching valve 53 toward the hydraulic pump 22 and from the direction switching valve 51 toward the hydraulic pump 22.

[0030] The check valve 72 is disposed in the third portion 33C of the third passage 33. The check valve 72 allows the hydraulic oil to flow from the third port of the directional control valve 53 to the first passage 31, while preventing the hydraulic oil from flowing from the first passage 31 to the third port of the directional control valve 53.

[0031] The pilot check valve 73 is disposed in a portion of the second passage 32 between a portion to which the second portion 33B of the third passage 33 is connected and the rod side chamber 8R of the arm cylinder 8. In a normal state, the pilot check valve 73 allows the hydraulic oil to flow from the second port of the directional control valve 53 to the rod side chamber 8R of the arm cylinder 8, but prevents the hydraulic oil from flowing in the opposite direction. Furthermore, when pilot pressure is applied, the pilot check valve 73 allows the hydraulic oil to flow in the opposite direction, that is, the hydraulic oil to flow from the rod side chamber 8R of the arm cylinder 8 to the second port of the directional control valve 53. The state of the pilot check valve 73 is switched based on a command output from the controller 80.

[0032] The directional control valve 51 functions as both a meter-in control valve and a meter-out control valve. The directional control valve 51 may be, for example, a three-position directional control valve as shown in Fig. 2. The directional control valve 51 may be, for example, an electromagnetic valve having a pair of solenoids as shown in Fig. 2.

[0033] The directional control valve 51 is disposed in a portion of the first passage 31 between a portion to which the third portion 33C of the third passage 33 is connected and the head side chamber 8H of the arm cylinder 8. The directional control valve 51 has a spool that can be switched between a meter-in position (right-hand position in FIG. 2 ) and a meter-out position (left-hand position in FIG. 2 ) in response to a valve command input to a pair of solenoids of the directional control valve 51. The meter-in position is a position that allows hydraulic oil discharged from the hydraulic pump 22 to be supplied to the head side chamber 8H of the arm cylinder 8. The meter-out position is a position that allows hydraulic oil discharged from the head side chamber 8H of the arm cylinder 8 to return to the tank 92. When the directional control valve 51 is a three-position directional control valve as shown in FIG. 2 , the spool of the directional control valve 51 can also be switched to a neutral position (intermediate position). When the spool of the directional control valve 51 is placed in the neutral position, the first passage 31 is blocked in the directional control valve 51 .

[0034] Specifically, when the command values ​​of the valve commands input to the pair of solenoids of the directional control valve 51 are both zero or a small value, the spool of the directional control valve 51 is maintained in a neutral position. When the command value of the valve command input to the right solenoid of the directional control valve 51 shown in FIG. 2 is equal to or greater than a certain value, the spool of the directional control valve 51 shifts from the neutral position to the meter-in position by a stroke corresponding to the magnitude of the command value. When the command value of the valve command input to the left solenoid of the directional control valve 51 shown in FIG. 2 is equal to or greater than a certain value, the spool of the directional control valve 51 shifts from the neutral position to the meter-out position by a stroke corresponding to the magnitude of the command value. When the spool of the directional control valve 51 is maintained in the neutral position, the meter-in opening and the meter-out opening of the directional control valve 51 are completely blocked and are in a "fully closed" state. When the spool of the directional control valve 51 is completely shifted to the meter-in position, the meter-in opening of the directional control valve 51 is at its maximum opening, i.e., is in a "fully open" state. When the spool of the directional control valve 51 is completely shifted to the meter-out position, the meter-out opening of the directional control valve 51 reaches the maximum opening degree, that is, is in a "fully open" state.

[0035] Each of the multiple operating devices 15 has an operating member 15A such as an operating lever or an operating pedal, and an output device 15B. The operating member 15A is operated by an operator. Examples of the operations by the operator include an arm pulling operation, an arm pushing operation, a boom raising operation, a boom lowering operation, and a swinging operation. The output device 15B outputs an operation command corresponding to the operation by the operator to the controller 80. The arm pulling operation is an example of an extension operation in the present disclosure, and the arm pushing operation is an example of a retraction operation in the present disclosure.

[0036] Figure 3 is a graph showing an example of the relationship between the operation input to the controller 15 of the construction machine 100 and the output of the controller 15. When the operator applies a lever operation, such as an arm pull operation, to the operating member 15A of the controller 15, the output device 15B outputs an operation command to the controller 80 according to the amount of lever operation (for example, the operating angle of the operating member 15A). The horizontal axis of the graph in Figure 3 shows the half-lever operation region and the full-lever operation region. In the full-lever operation region, i.e., the region where the amount of lever operation is equal to or greater than a predetermined value, the operation command output from the output device 15B is a constant maximum value. On the other hand, in the half-lever operation region, the operation command output from the output device 15B gradually increases up to the maximum value according to the amount of lever operation.

[0037] The controller 80 inputs valve commands to the directional control valves 53 and 51 based on the operation commands output from the output device 15B. The magnitude of the command value of the valve command is determined according to the magnitude of the operation command. The controller 80 is equipped with a computer having an arithmetic processing unit and a memory, and controls various operations of the construction machine 100 by the arithmetic processing unit executing programs stored in the memory. The controller 80 may perform the following control, for example.

[0038] When the operating member 15A of the controller 15 is subjected to an arm-pulling operation, the controller 80 may input a valve command to the directional switching valve 53 such that the spool of the directional switching valve 53 is positioned at the regeneration position (the right-hand position in FIG. 2 ), and may input a valve command to the directional switching valve 51 such that the spool of the directional switching valve 51 is positioned at the meter-in position (the right-hand position in FIG. 2 ). In this case, the controller 80 may output a command to place the pilot check valve 73 in a state in which pilot pressure is applied, that is, a state in which hydraulic oil is permitted to flow from the rod-side chamber 8R of the arm cylinder 8 to the second port of the directional switching valve 53. This command may be input to, for example, a proportional valve (not shown). As a result, hydraulic oil discharged from the hydraulic pump 22 is supplied to the head-side chamber 8H of the arm cylinder 8, and is discharged from the rod-side chamber 8R of the arm cylinder 8. The discharged hydraulic oil passes through the directional switching valve 53 and the third portion 33C of the third passage 33 to join the hydraulic oil flowing through the first passage 31. In this embodiment, the act of hydraulic oil being discharged from the rod side chamber 8R of the arm cylinder 8 being supplied again to the head side chamber 8H of the arm cylinder 8 is referred to as "hydraulic oil being recycled." Additionally, the flow rate of hydraulic oil being discharged from the rod side chamber 8R and supplied again to the head side chamber 8H is referred to as the "recycled amount." In this embodiment, during the arm pulling operation, the hydraulic oil is recycled and the recycled amount is ensured, thereby making it possible to increase the operating speed of the arm cylinder 8.

[0039] Furthermore, when the operating member 15A of the controller 15 is subjected to an arm pushing operation, the controller 80 may input a valve command to the direction switching valve 53 such that the spool of the directional switching valve 53 is positioned in the meter-in position (the left position in FIG. 2), and may input a valve command to the direction switching valve 51 such that the spool of the directional switching valve 51 is positioned in the meter-out position (the left position in FIG. 2). As a result, the hydraulic oil discharged from the hydraulic pump 22 is supplied to the rod side chamber 8R of the arm cylinder 8, and the hydraulic oil is discharged from the head side chamber 8H of the arm cylinder 8. The discharged hydraulic oil returns to the tank 92 via the directional switching valve 51.

[0040] Second Embodiment Fig. 4 is a diagram showing a hydraulic circuit of a construction machine 100 according to a second embodiment. The construction machine 100 according to the second embodiment is equipped with a hydraulic drive system 101. The basic structure of the hydraulic drive system 101 in the second embodiment is similar to that of the hydraulic drive system 101 in the first embodiment.

[0041] That is, the hydraulic drive system 101 in the second embodiment includes a hydraulic pump 22, an arm cylinder 8, a first passage 31, a second passage 32, a third passage 33, a directional control valve 53, a check valve 71, a check valve 72, a pilot check valve 73, a directional control valve 51, a plurality of operators 15, and a controller 80. The first passage 31 connects the hydraulic pump 22 to the head side chamber 8H of the arm cylinder 8, the second passage 32 is a passage connected to the rod side chamber 8R of the arm cylinder 8, and the third passage 33 connects the first passage 31 and the second passage 32. The directional control valve 51 is disposed in a portion of the first passage 31 between a portion of the first passage 31 to which the third portion 33C of the third passage 33 is connected and the head side chamber 8H of the arm cylinder 8. The directional control valve 53 is disposed in the third passage 33.

[0042] The hydraulic drive system 101 in the second embodiment further includes a hydraulic pump 21, a first pressure sensor 41, a second pressure sensor 42, a direction switching valve 52, a direction switching valve 54, a fourth passage 34, a fifth passage 35, a sixth passage 36, a seventh passage 37, and a check valve 74. Hereinafter, the hydraulic pump 21 will be referred to as the first hydraulic pump 21, and the hydraulic pump 22 will be referred to as the second hydraulic pump 22. In addition, the direction switching valve 51 will be referred to as the first direction switching valve 51, the direction switching valve 52 will be referred to as the second direction switching valve 52, the direction switching valve 53 will be referred to as the third direction switching valve 53, and the direction switching valve 54 will be referred to as the fourth direction switching valve 54. The third direction switching valve 53 is an example of a regeneration control valve in the present disclosure.

[0043] In this embodiment, the first hydraulic pump 21 is a variable displacement hydraulic pump. The pump displacement of the first hydraulic pump 21 is adjusted based on a command output from the controller 80.

[0044] The first pressure sensor 41 detects the first pump pressure, which is the discharge pressure of the first hydraulic pump 21, and inputs a pump pressure detection signal, which is a detection signal corresponding to the first pump pressure, to the controller 80. The second pressure sensor 42 detects the second pump pressure, which is the discharge pressure of the second hydraulic pump 22, and inputs a pump pressure detection signal, which is a detection signal corresponding to the second pump pressure, to the controller 80.

[0045] The fourth passage 34 connects the first hydraulic pump 21 and the second direction switching valve 52. The fifth passage 35 branches off from a portion of the first passage 31 between the first direction switching valve 51 and the head side chamber 8H of the arm cylinder 8 and is connected to the fourth direction switching valve 54. The sixth passage 36 branches off from the fourth passage 34 and is connected to the fourth direction switching valve 54. The seventh passage 37 connects the fourth direction switching valve 54 and the tank 92.

[0046] The check valve 74 is disposed in a portion of the fourth passage 34 between the portion to which the sixth passage 36 is connected and the first hydraulic pump 21. The check valve 74 allows the hydraulic oil discharged from the first hydraulic pump 21 to flow toward the second direction switching valve 52 and the hydraulic oil discharged from the first hydraulic pump 21 to flow toward the fourth direction switching valve 54, while preventing the hydraulic oil from flowing from the second direction switching valve 52 to the first hydraulic pump 21 and the hydraulic oil from flowing from the fourth direction switching valve 54 to the first hydraulic pump 21.

[0047] In the second embodiment, similarly to the first embodiment, the first directional control valve 51 functions as both a meter-in control valve and a meter-out control valve, and the third directional control valve 53 functions as both a regeneration control valve and a meter-in control valve. The first directional control valve 51 adjusts the size of the meter-in opening or the size of the meter-out opening in accordance with a valve command input from the controller 80. The third directional control valve 53 adjusts the size of the regeneration opening or the size of the meter-in opening in accordance with a valve command input from the controller 80.

[0048] The second direction switching valve 52 functions as both a meter-in control valve and a meter-out control valve. The second direction switching valve 52 may be, for example, a three-position directional control valve as shown in FIG. 4 . The second direction switching valve 52 may be, for example, a solenoid valve having a pair of solenoids as shown in FIG. 4 . The second direction switching valve 52 has a spool that can be switched between a neutral position (middle position) shown in FIG. 4 , a meter-out position (right position in FIG. 4 ), and a meter-in position (left position in FIG. 4 ) in accordance with a valve command input to the pair of solenoids of the second direction switching valve 52. In the second direction switching valve 52, the size of the meter-in opening or the size of the meter-out opening is adjusted in accordance with a valve command input from the controller 80.

[0049] Specifically, when the command values ​​of the valve commands input to the pair of solenoids of the second direction switching valve 52 are both zero or a small value, the spool of the second direction switching valve 52 is maintained in a neutral position. When the command value of the valve command input to the right solenoid of the second direction switching valve 52 shown in Fig. 4 is equal to or greater than a certain value, the spool of the second direction switching valve 52 shifts from the neutral position to the meter-out position by a stroke corresponding to the magnitude of the command value. When the command value of the valve command input to the left solenoid of the second direction switching valve 52 shown in Fig. 4 is equal to or greater than a certain value, the spool of the second direction switching valve 52 shifts from the neutral position to the meter-in position by a stroke corresponding to the magnitude of the command value. When the spool of the second direction switching valve 52 is maintained in the neutral position, the meter-in opening and the meter-out opening of the second direction switching valve 52 are completely blocked and are in a "fully closed" state. When the spool of the second direction switching valve 52 is completely shifted to the meter-out position, the meter-out opening of the second direction switching valve 52 is at its maximum opening degree, i.e., is in a "fully open" state. When the spool of the second direction switching valve 52 is completely shifted to the meter-in position, the meter-in opening of the second direction switching valve 52 is at its maximum opening degree, i.e., is in a "fully open" state.

[0050] The fourth directional control valve 54 functions as both a meter-in control valve and a meter-out control valve. The fourth directional control valve 54 may be, for example, a three-position directional control valve as shown in FIG. 4 . The fourth directional control valve 54 may be, for example, a solenoid valve having a pair of solenoids as shown in FIG. 4 . The fourth directional control valve 54 has a spool that can be switched between a neutral position (middle position) shown in FIG. 4 , a meter-in position (right position in FIG. 4 ), and a meter-out position (left position in FIG. 4 ) in accordance with a valve command input to the pair of solenoids of the fourth directional control valve 54. In the fourth directional control valve 54, the size of the meter-in opening or the size of the meter-out opening is adjusted in accordance with a valve command input from the controller 80.

[0051] Specifically, when the command values ​​of the valve commands input to the pair of solenoids of the fourth direction switching valve 54 are both 0 or a small value, the spool of the fourth direction switching valve 54 is maintained in a neutral position. When the command value of the valve command input to the right solenoid of the fourth direction switching valve 54 shown in FIG. 4 is equal to or greater than a certain value, the spool of the fourth direction switching valve 54 shifts from the neutral position to the meter-in position by a stroke corresponding to the magnitude of the command value. When the command value of the valve command input to the left solenoid of the fourth direction switching valve 54 shown in FIG. 4 is equal to or greater than a certain value, the spool of the fourth direction switching valve 54 shifts from the neutral position to the meter-out position by a stroke corresponding to the magnitude of the command value. When the spool of the fourth direction switching valve 54 is maintained in the neutral position, the meter-in opening and the meter-out opening of the fourth direction switching valve 54 are completely blocked and are in a "fully closed" state. When the spool of the fourth direction switching valve 54 is completely shifted to the meter-in position, the meter-in opening of the fourth direction switching valve 54 is at its maximum opening degree, i.e., is in a "fully open" state. When the spool of the fourth direction switching valve 54 is completely shifted to the meter-out position, the meter-out opening of the fourth direction switching valve 54 is at its maximum opening degree, i.e., is in a "fully open" state.

[0052] When the operating member 15A of the controller 15 is subjected to an arm pull operation, the controller 80 controls the opening degrees of the meter-in openings of the first direction switching valve 51 and the fourth direction switching valve 54 in accordance with the operation amount of the arm pull operation (arm pull operation amount). Specifically, as shown in FIG. 5A , when the arm pull operation amount is smaller than the first operation amount A1, the meter-in opening of the first direction switching valve 51 is in a blocked state, i.e., fully closed state. When the arm pull operation amount becomes larger than the first operation amount A1, the meter-in opening of the first direction switching valve 51 changes from a fully closed state to an open state, and its opening degree corresponds to the arm pull operation amount. When the arm pull operation amount is smaller than the second operation amount A2, which is an operation amount larger than the first operation amount A1, the meter-in opening of the fourth direction switching valve 54 is in a blocked state, i.e., fully closed state. When the arm pull operation amount becomes larger than the second operation amount A2, the meter-in opening of the fourth direction switching valve 54 changes from a fully closed state to an open state, and the opening degree corresponds to the arm pull operation amount. When the arm pull operation amount is larger than the second operation amount A2, the hydraulic oil supplied from the first hydraulic pump 21 joins the hydraulic oil supplied from the second hydraulic pump 22 to the head side chamber 8H of the arm cylinder 8 via the fourth direction switching valve 54. Therefore, in this case, the operating speed of the arm cylinder 8 (the speed of the arm pull operation) can be improved (accelerated) compared to the case where only the hydraulic oil from the second hydraulic pump 22 is supplied to the head side chamber 8H of the arm cylinder 8.

[0053] When the operating member 15A of the controller 15 is subjected to an arm pushing operation, the controller 80 controls the opening degrees of the meter-in openings of the third direction switching valve 53 and the second direction switching valve 52 in accordance with the amount of arm pushing operation (arm pushing operation amount). Specifically, as shown in FIG. 5B , when the arm pushing operation amount is smaller than the first operation amount B1, the meter-in opening of the third direction switching valve 53 is in a blocked state, i.e., fully closed state. When the arm pushing operation amount becomes larger than the first operation amount B1, the meter-in opening of the third direction switching valve 53 changes from a fully closed state to an open state, and its opening degree corresponds to the arm pushing operation amount. When the arm pushing operation amount is smaller than the second operation amount B2, which is an operation amount larger than the first operation amount B1, the meter-in opening of the second direction switching valve 52 is in a blocked state, i.e., fully closed state. When the arm pushing operation amount becomes larger than the second operation amount B2, the meter-in opening of the second direction switching valve 52 changes from a fully closed state to an open state, and the opening degree corresponds to the arm pushing operation amount. When the arm pushing operation amount is larger than the second operation amount B2, the hydraulic oil supplied from the first hydraulic pump 21 joins via the second direction switching valve 52 with the hydraulic oil supplied from the second hydraulic pump 22 to the rod side chamber 8R of the arm cylinder 8. Therefore, in this case, the operating speed of the arm cylinder 8 (the speed of the arm pushing operation) can be improved (accelerated) compared to the case where only the hydraulic oil from the second hydraulic pump 22 is supplied to the rod side chamber 8R of the arm cylinder 8.

[0054] Furthermore, when the operating member 15A of the controller 15 is subjected to an arm pushing operation, the controller 80 controls the opening degrees of the meter-out openings of the first direction switching valve 51 and the fourth direction switching valve 54 in accordance with the amount of arm pushing operation. Specifically, as shown in FIG. 5C , when the amount of arm pushing operation is smaller than the first amount of operation C1, the meter-out opening of the first direction switching valve 51 is in a blocked state, i.e., a fully closed state. When the amount of arm pushing operation becomes larger than the first amount of operation C1, the meter-out opening of the first direction switching valve 51 changes from a fully closed state to an open state, and its opening degree corresponds to the amount of arm pushing operation. When the amount of arm pushing operation is smaller than the second amount of operation C2, which is an operation amount larger than the first amount of operation C1, the meter-out opening of the fourth direction switching valve 54 is in a blocked state, i.e., a fully closed state. When the arm pushing operation amount becomes larger than the second operation amount C2, the meter-out opening of the fourth direction switching valve 54 changes from a fully closed state to an open state, and the opening degree corresponds to the arm pushing operation amount. The first operation amount B1 and the first operation amount C1 may be the same in magnitude or may be different in magnitude. The second operation amount B2 and the second operation amount C2 may be the same in magnitude or may be different in magnitude. In this embodiment, the first operation amount B1 and the first operation amount C1 are set to the same in magnitude, and the second operation amount B2 and the second operation amount C2 are set to the same in magnitude.

[0055] Figure 6 is a table summarizing the operation content and conditions of the operation received by the operating member 15A of the controller 15, and the state of each directional control valve in the construction machine 100 according to the second embodiment. In the second embodiment, the controller 80 performs one of a plurality of controls as shown in Figure 6 depending on the operation content and conditions of the operating member 15A of the controller 15. Note that the "*" in the table of Figure 6 means that the opening area (opening degree) increases to the fully open position depending on the amount of operation.

[0056] [First Control] The controller 80 determines whether or not the operating member 15A of the controller 15 is subjected to an arm pull operation, based on an operation command input to the controller 80 from the output device 15B of the controller 15. If the determination result is positive (if it is determined that the controller 15 is subjected to an arm pull operation), the controller 80 controls each of the first to fourth directional control valves 51, 52, 53, 54 as shown in the first row of the table in FIG. 6 (first control).

[0057] 5A , in the first control, when the arm pull operation amount becomes larger than the first operation amount A1, a valve command is input to the first direction switching valve 51 so that the meter-in opening of the first direction switching valve 51 is opened at an opening degree corresponding to the arm pull operation amount, and when the arm pull operation amount becomes larger than the second operation amount A2, a valve command is input to the fourth direction switching valve 54 so that the meter-in opening of the fourth direction switching valve 54 is opened at an opening degree corresponding to the arm pull operation amount. When the arm pull operation amount increases to its maximum operation amount, the meter-in opening of the first direction switching valve 51 is fully open, and the meter-in opening of the fourth direction switching valve 54 is fully open. Also, in the first control, valve commands are input to the second direction switching valve 52 and the third direction switching valve 53 so that the meter-out opening of the second direction switching valve 52 is fully closed, and the regeneration opening of the third direction switching valve 53 is fully open.

[0058] In the first control, the meter-out opening of the second directional control valve 52 is "fully closed," causing the entire amount of hydraulic oil discharged from the rod side chamber 8R of the arm cylinder 8 to flow from the second passage 32 through the third passage 33 into the first passage 31 and be supplied to the head side chamber 8H of the arm cylinder 8. During a single arm retraction operation, the regeneration amount of hydraulic oil is ensured, making it possible to increase the operating speed of the arm cylinder 8. This first control is effective, for example, when the arm 5 is to be retracted without the working device 3 (boom 4, arm 5, and tip attachment) hitting another object, and when the arm retraction operation amount is increased to increase the operating speed of the arm retraction operation. The first control is an example of regeneration control in the present disclosure.

[0059] In the first control, the operating speed of the arm cylinder 8 can be increased from the following perspective as well. In the second embodiment, the length of the passage connecting the third directional control valve 53 and the arm cylinder 8 is shorter than the length of the passage connecting the second directional control valve 52 and the arm cylinder 8, and shorter than the length of the passage connecting the fourth directional control valve 54 and the arm cylinder 8. This makes it possible to reduce pressure loss when the hydraulic oil is regenerated via the third directional control valve 53. As a result, the operating pressure, including the pump pressure, the pressure in the rod side chamber 8R, and the pressure in the head side chamber 8H, is reduced. When the operating pressure is reduced, leakage of hydraulic oil in the hydraulic circuit is reduced, and a decrease in the flow rate of hydraulic oil flowing to the arm cylinder 8 is suppressed. This makes it possible to increase the operating speed of the arm cylinder 8. Furthermore, when the hydraulic circuit is operating under horsepower control, the pump capacity can be increased by reducing the operating pressure, which increases the flow rate of hydraulic oil supplied to the arm cylinder 8, thereby increasing the operating speed of the arm cylinder 8.

[0060] [Second Control] The controller 80 determines whether the operating member 15A of the controller 15 has received an arm pull operation and whether a regeneration cut-off condition is satisfied, based on an operation command input to the controller 80 from the output device 15B of the controller 15 and a pump pressure detection signal input from the second pressure sensor 42. The regeneration cut-off condition includes a condition that the discharge pressure of the second hydraulic pump 22 exceeds a predetermined reference pressure. The regeneration cut-off condition may also include a condition that the discharge pressure of the first hydraulic pump 21 exceeds a predetermined reference pressure for the first hydraulic pump 21 or that the discharge pressure of the second hydraulic pump 22 exceeds a predetermined reference pressure for the second hydraulic pump 22. If the determination result is positive (if it is determined that the controller 15 has received an arm pull operation and the regeneration cut-off condition is satisfied), the controller 80 controls each of the first to fourth directional control valves 51, 52, 53, and 54 as shown in the second row of the table in FIG. 6 (second control).

[0061] 5(A), in the same way as in the first control, when the arm pull operation amount becomes larger than the first operation amount A1, a valve command is input to the first direction switching valve 51 so that the meter-in opening of the first direction switching valve 51 is opened at an opening degree corresponding to the arm pull operation amount, and when the arm pull operation amount becomes larger than the second operation amount A2, a valve command is input to the fourth direction switching valve 54 so that the meter-in opening of the fourth direction switching valve 54 is opened at an opening degree corresponding to the arm pull operation amount. When the arm pull operation amount increases and reaches its maximum operation amount, the meter-in opening of the first direction switching valve 51 is "fully open," and the meter-in opening of the fourth direction switching valve 54 is "fully open." Furthermore, in the second control, when the regeneration cut condition is satisfied, valve commands are input to the second directional control valve 52 and the third directional control valve 53 so that the meter-out opening of the second directional control valve 52 is "fully open" and the regeneration opening of the third directional control valve 53 is "fully closed." The second control is an example of the regeneration cut control in the present disclosure. In this regeneration cut control, the spool of the third directional control valve 53 (regeneration control valve) may be placed in a neutral position.

[0062] In the second control, the meter-out opening of the second direction switching valve 52 is fully opened and the regeneration opening of the third direction switching valve 53 is fully closed, so that the entire amount of hydraulic oil discharged from the rod side chamber 8R of the arm cylinder 8 is guided to the tank 92 via the meter-out opening of the second direction switching valve 52. This reduces the operating pressure in the rod side chamber 8R of the arm cylinder 8 and increases the pressure difference between the head side chamber 8H and the rod side chamber 8R of the arm cylinder 8. This suppresses back pressure from occurring in the second passage 32 during heavy-load operation (e.g., excavation operation) in which the discharge pressure of the second hydraulic pump 22 is higher than the reference pressure, thereby ensuring the driving force (excavation force) for the arm pulling operation. In this second control, the regeneration amount is zero. The second control is an example of the regeneration cut control in the present disclosure.

[0063] During light-load work (for example, when pulling the arm in the air) in which the discharge pressure of the second hydraulic pump 22 is lower than the reference pressure, the first control is executed, and the return oil from the rod side chamber 8R of the arm cylinder 8 is regenerated into the head side chamber 8H, thereby speeding up the arm pulling operation.

[0064] [Third Control] The controller 80 determines whether the operating member 15A of the controller 15 has undergone an arm-pull operation and whether the cavitation prevention condition is satisfied, based on an operation command input to the controller 80 from the output device 15B of the controller 15 and the operating state of the power source 91. The cavitation prevention condition may include, for example, a condition that the rotational speed of the second hydraulic pump 22 driven by the power source 91 is equal to or less than a predetermined reference rotational speed. The rotational speed compared with the reference rotational speed may be the rotational speed of the second hydraulic pump 22 itself, as described above, or the rotational speed of the engine or electric motor constituting the power source 91. If the determination result is positive (if it is determined that the controller 15 has undergone an arm-pull operation and the cavitation prevention condition is satisfied), the controller 80 controls each of the first to fourth directional control valves 51, 52, 53, and 54 as shown in the third row of the table in FIG. 6 (third control).

[0065] 5(A), in the same way as in the first control, when the arm pull operation amount becomes larger than the first operation amount A1, a valve command is input to the first direction switching valve 51 so that the meter-in opening of the first direction switching valve 51 is opened at an opening degree corresponding to the arm pull operation amount, and when the arm pull operation amount becomes larger than the second operation amount A2, a valve command is input to the fourth direction switching valve 54 so that the meter-in opening of the fourth direction switching valve 54 is opened at an opening degree corresponding to the arm pull operation amount. When the arm pull operation amount increases and reaches its maximum operation amount, the meter-in opening of the first direction switching valve 51 is "fully open," and the meter-in opening of the fourth direction switching valve 54 is "fully open." Furthermore, in the third control, valve commands are input to the second directional control valve 52 and the third directional control valve 53 so that the meter-out opening of the second directional control valve 52 is "fully closed" and the regeneration opening of the third directional control valve 53 is "half open." "Half open" of the regeneration opening means that the opening degree of the regeneration opening of the third directional control valve 53 is between fully closed and fully open, that is, the regeneration opening of the third directional control valve 53 is in a state that is both narrowed and open compared to when it is fully open.

[0066] In the third control, the meter-out opening of the second directional control valve 52 is fully closed, causing all of the hydraulic oil discharged from the rod side chamber 8R of the arm cylinder 8 to flow from the second passage 32 through the third passage 33 into the first passage 31 and be supplied to the head side chamber 8H of the arm cylinder 8. Furthermore, in the third control, the third directional control valve 53 is half-opened, thereby increasing the pressure in the rod side chamber 8R of the arm cylinder 8 and reducing the operating speed of the arm-pulling operation of the arm cylinder 8 compared to when the third directional control valve 53 is fully open. This prevents the pressure in the head side chamber 8H from becoming excessively low, thereby preventing cavitation from occurring in the head side chamber 8H, even when the rotation speed of the second hydraulic pump 22 falls below a predetermined reference rotation speed and the amount of hydraulic oil supplied from the second hydraulic pump 22 to the head side chamber 8H of the arm cylinder 8 decreases. In other words, the third control can regenerate hydraulic oil and prevent cavitation from occurring at the same time. The third control is an example of a regeneration control in the present disclosure.

[0067] When the third control is performed, in this embodiment, the first directional control valve 51 and the fourth directional control valve 54 function as meter-in control valves, and the third directional control valve 53 functions as a regeneration control valve. Because the meter-in control valve and the regeneration control valve function as separate control valves, the third control makes it possible to variably set the regeneration opening according to the engine speed without being affected by the meter-in opening.

[0068] If the rotation speed of the second hydraulic pump 22 exceeds a preset reference rotation speed, the first control is executed, and the return oil from the rod side chamber 8R of the arm cylinder 8 is regenerated into the head side chamber 8H, thereby speeding up the arm retraction operation. Furthermore, if the capacity of the second hydraulic pump 22 is increased in response to a decrease in the rotation speed of the second hydraulic pump 22, the reference rotation speed may be set taking into account the increase in pump capacity.

[0069] [Fourth Control] The controller 80 determines whether or not the operating member 15A of the controller 15 is subjected to an arm pushing operation, based on an operation command input to the controller 80 from the output device 15B of the controller 15. If the determination result is positive (if it is determined that the controller 15 is subjected to an arm pushing operation), the controller 80 controls each of the first to fourth directional control valves 51, 52, 53, 54 as shown in the fourth row of the table in FIG. 6 (fourth control).

[0070] 5(B), in the fourth control, when the arm pushing operation amount becomes larger than the first operation amount B1, a valve command is input to the third direction switching valve 53 so that the meter-in opening of the third direction switching valve 53 is opened at an opening degree corresponding to the arm pushing operation amount, and when the arm pushing operation amount becomes larger than the second operation amount B2, a valve command is input to the second direction switching valve 52 so that the meter-in opening of the second direction switching valve 52 is opened at an opening degree corresponding to the arm pushing operation amount. When the arm pushing operation amount increases and reaches its maximum operation amount, the meter-in opening of the third direction switching valve 53 is "fully open," and the meter-in opening of the second direction switching valve 52 is "fully open." 5(C), when the arm pushing operation amount becomes larger than the first operation amount C1, a valve command is input to the first direction switching valve 51 so that the meter-out opening of the first direction switching valve 51 is opened at an opening degree corresponding to the arm pushing operation amount, and when the arm pushing operation amount becomes larger than the second operation amount C2, a valve command is input to the fourth direction switching valve 54 so that the meter-in opening of the fourth direction switching valve 54 is opened at an opening degree corresponding to the arm pushing operation amount. When the arm pushing operation amount increases and reaches its maximum operation amount, the meter-out opening of the first direction switching valve 51 is "fully open," and the meter-out opening of the fourth direction switching valve 54 is "fully open."

[0071] In the fourth control, the meter-in opening of the third direction switching valve 53 is opened at an opening degree corresponding to the amount of arm pushing operation, and thereby the hydraulic oil supplied from the second hydraulic pump 22 to the rod side chamber 8R of the arm cylinder 8 is joined via the second direction switching valve 52 with the hydraulic oil supplied from the first hydraulic pump 21 (specifically, the meter-in opening of the second direction switching valve 52 is opened at an opening degree corresponding to the amount of arm pushing operation) and supplied to the rod side chamber 8R of the arm cylinder 8. In addition, the hydraulic oil discharged from the head side chamber 8H of the arm cylinder 8 is led to the tank 92 via the meter-out opening of the first direction switching valve 51 and the meter-out opening of the fourth direction switching valve 54. This reduces the operating pressure in the rod side chamber 8R of the arm cylinder 8 and increases the pressure difference between the head side chamber 8H and rod side chamber 8R of the arm cylinder 8, making it possible to perform the arm pushing operation of the arm 5 at a sufficient speed.

[0072] [Fifth Control] The controller 80 determines whether the operating member 15A of the controller 15 has undergone an arm-pushing operation and whether the cavitation prevention condition is satisfied, based on an operation command input to the controller 80 from the output device 15B of the controller 15 and the operating state of the power source 91. The cavitation prevention condition is similar to that of the third control and may include, for example, a condition that the rotational speed of the second hydraulic pump 22 driven by the power source 91 is equal to or less than a predetermined reference rotational speed. The rotational speed compared with the reference rotational speed may be the rotational speed of the second hydraulic pump 22 itself, as described above, or the rotational speed of the engine or electric motor constituting the power source 91. If the determination result is positive (if it is determined that the controller 15 has undergone an arm-pushing operation and the cavitation prevention condition is satisfied), the controller 80 controls each of the first to fourth directional control valves 51, 52, 53, and 54 as shown in the fifth row of the table in FIG. 6 (fifth control).

[0073] 5(B), in the same way as in the fourth control, when the arm pushing operation amount becomes larger than the first operation amount B1, a valve command is input to the third direction switching valve 53 so that the meter-in opening of the third direction switching valve 53 is opened at an opening degree corresponding to the arm pushing operation amount, and when the arm pushing operation amount becomes larger than the second operation amount B2, a valve command is input to the second direction switching valve 52 so that the meter-in opening of the second direction switching valve 52 is opened at an opening degree corresponding to the arm pushing operation amount. When the arm pushing operation amount increases and reaches its maximum operation amount, the meter-in opening of the third direction switching valve 53 is "fully open," and the meter-in opening of the second direction switching valve 52 is "fully open." 5(C), when the arm pushing operation amount becomes larger than the first operation amount C1, a valve command is input to the first direction switching valve 51 so that the meter-out opening of the first direction switching valve 51 is opened at an opening degree corresponding to the arm pushing operation amount, and when the arm pushing operation amount becomes larger than the second operation amount C2, a valve command is input to the fourth direction switching valve 54 so that the meter-in opening of the fourth direction switching valve 54 is opened at an opening degree corresponding to the arm pushing operation amount. When the arm pushing operation amount increases to the maximum operation amount, the meter-out opening of the first direction switching valve 51 is "fully open," and the meter-out opening of the fourth direction switching valve 54 is "fully open." Furthermore, in the fifth control, when the cavitation prevention condition is satisfied, a valve command is input to the fourth direction switching valve 54 so that the meter-out opening of the fourth direction switching valve 54 is "fully closed."

[0074] In the fifth control, the meter-out opening of the fourth direction switching valve 54 is "fully closed," thereby increasing the pressure in the head side chamber 8H of the arm cylinder 8 and reducing the operating speed of the arm pushing operation of the arm cylinder 8, compared to when the meter-out opening of the fourth direction switching valve 54 is "half open" or "fully open." As a result, even when the rotation speed of the second hydraulic pump 22 becomes equal to or lower than a preset reference rotation speed and the amount of hydraulic oil supplied from the second hydraulic pump 22 to the rod side chamber 8R of the arm cylinder 8 decreases, the pressure in the rod side chamber 8R is prevented from becoming excessively low, and the occurrence of cavitation in the rod side chamber 8R is prevented.

[0075] When the fourth control and the fifth control are performed, the third direction switching valve 53 and the second direction switching valve 52 function as meter-in control valves, and the first direction switching valve 51 and the fourth direction switching valve 54 function as meter-out control valves. Furthermore, when the fifth control is performed, the meter-out opening of the fourth direction switching valve 54 is throttled and becomes "fully closed." In this embodiment, the meter-in control valve and the meter-out control valve function as separate control valves, so that the meter-in opening and the meter-out opening can be set independently.

[0076] 4 also illustrates the boom cylinder 7, directional control valves 55, 56, relief valve 78, and back pressure valve 79. These will be briefly described. When the operating member 15A of the controller 15 is operated to raise the boom, the spool of the directional control valve 55 is moved from the neutral position (the middle position in FIG. 4) to the meter-in position (the left position in FIG. 4), and the spool of the directional control valve 56 is moved to the meter-out position (the left position in FIG. 4). As a result, hydraulic oil discharged from the first hydraulic pump 21 is supplied to the head-side chamber of the boom cylinder 7 via the directional control valve 56, and hydraulic oil in the rod-side chamber of the boom cylinder 7 is discharged to the tank 92 via the directional control valve 56. As a result, the boom cylinder 7 extends, and the boom 4 performs a boom-raising operation. When the operating member 15A of the controller 15 is operated to lower the boom, the spool of the directional control valve 55 moves from the neutral position to the meter-out position (the right-hand position in FIG. 4 ), and the spool of the directional control valve 56 moves from the neutral position to the meter-in position (the right-hand position in FIG. 4 ). As a result, hydraulic oil discharged from the first hydraulic pump 21 is supplied to the rod-side chamber of the boom cylinder 7 via the directional control valve 56, and hydraulic oil in the head-side chamber of the boom cylinder 7 is discharged to the tank 92 via the directional control valve 55. This causes the boom cylinder 7 to contract, and the boom 4 performs a boom-lowering operation. The relief valve 78 opens when the pump pressure of at least one of the first hydraulic pump 21 and the second hydraulic pump 22 reaches a predetermined relief pressure. The backpressure valve 79 is provided in a return passage that returns hydraulic oil to the tank 92 and generates back pressure in this return passage. In the hydraulic circuit shown in FIG. 4 , only parts related to the arm cylinder 8 and the boom cylinder 7 are shown, and other components are omitted.

[0077] [Modifications] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and includes, for example, the following modifications.

[0078] (A) Regarding the Directional Switching Valve In the above embodiment, the directional switching valve 53 is a solenoid valve having a solenoid. However, the directional switching valve in the present disclosure is not limited to a solenoid valve, and may be a directional switching valve having a pilot port to which a pilot pressure is input.

[0079] (B) Regarding the Controller In the above embodiment, the controller 15 includes an operating member 15A such as a control lever and an output device 15B, and the output device 15B inputs an operation command to the controller 80 in response to an operation applied to the operating member 15A. However, the controller in the present disclosure is not limited to the specific example of the above embodiment. The controller may include an operating member such as a control lever and a remote control valve as an output device. In this case, the remote control valve outputs a secondary pressure (pilot pressure) in response to an operation applied to the operating member, and this pilot pressure may be input to a pilot port of the directional control valve 53.

[0080] (C) Regarding the Construction Machine The construction machine 100 according to the embodiment is a hydraulic excavator, but the construction machine in the present disclosure is not limited to a hydraulic excavator and may be other construction machines such as a crane or a bulldozer.

[0081] As described above, the present disclosure provides a hydraulic drive system for a construction machine that can prevent the hydraulic circuit configuration from becoming complicated.

[0082] A hydraulic drive system for a construction machine according to a first aspect includes a hydraulic pump that discharges hydraulic oil, a hydraulic cylinder having a head side chamber and a rod side chamber, a first passage connecting the hydraulic pump and the head side chamber, a second passage connected to the rod side chamber, a third passage connecting the first passage and the second passage, and a regeneration control valve arranged in the third passage, wherein the regeneration control valve has a spool that can be switched between a regeneration position that allows hydraulic oil discharged from the rod side chamber to flow from the second passage into the first passage and return to the head side chamber, and a meter-in position that allows hydraulic oil discharged from the hydraulic pump to flow from the first passage into the second passage and be supplied to the rod side chamber.

[0083] In this first aspect, the directional control valve functions as a regeneration control valve for returning hydraulic oil discharged from the rod-side chamber to the head-side chamber when the hydraulic cylinder is extended, and functions as a meter-in control valve for supplying hydraulic oil discharged from the hydraulic pump to the rod-side chamber when the hydraulic cylinder is contracted. That is, in this first aspect, since the regeneration control valve also functions as a meter-in control valve, these functions can be achieved while preventing the configuration of the hydraulic circuit from becoming complicated compared to when a regeneration control valve and a meter-in control valve are provided separately.

[0084] A second aspect is preferably the hydraulic drive system according to the first aspect, further comprising the following configuration. That is, the hydraulic drive system according to the second aspect further comprises a first directional control valve disposed in the first passage, and the first directional control valve is preferably configured to adjust a meter-in opening that supplies hydraulic oil to the head-side chamber of the hydraulic cylinder when the hydraulic cylinder extends, and to adjust a meter-out opening that discharges hydraulic oil from the head-side chamber of the hydraulic cylinder when the hydraulic cylinder contracts. In this second aspect, the first directional control valve functions as both a meter-in control valve and a meter-out control valve, which further prevents the configuration of the hydraulic circuit from becoming complicated.

[0085] A third aspect is preferably the hydraulic drive system according to the second aspect, further comprising the following configuration. That is, the hydraulic drive system according to the third aspect further comprises a second directional control valve arranged in the second passage, and a controller, and the controller preferably performs regeneration control such that, when the hydraulic cylinder extends, the spool of the regeneration control valve is arranged in the regeneration position and a meter-out opening of the second directional control valve is throttled, thereby supplying hydraulic oil discharged from the rod-side chamber of the hydraulic cylinder to the head-side chamber via the regeneration control valve. In this third aspect, regeneration control is appropriately performed by the regeneration control valve and the second directional control valve.

[0086] A fourth aspect is preferably the hydraulic drive system according to the third aspect, further comprising the following configuration. That is, in the hydraulic drive system according to the fourth aspect, when a regeneration cut condition is satisfied during extension of the hydraulic cylinder, the controller preferably performs regeneration cut control such that the regeneration opening of the regeneration control valve is narrowed and the meter-out opening of the second directional control valve is made larger than during the regeneration control, thereby causing the hydraulic oil discharged from the rod side chamber of the hydraulic cylinder to be discharged to a tank. In this fourth aspect, the regeneration cut control is appropriately performed by the regeneration control valve and the second directional control valve. Note that during regeneration cut control, the spool of the regeneration control valve may be positioned in a neutral position.

[0087] A fifth aspect is preferably the hydraulic drive system according to any one of the second to fourth aspects, further comprising the following configuration. That is, in the hydraulic drive system according to the fifth aspect, the hydraulic pump is a second hydraulic pump, the regeneration control valve is a third direction switching valve, and the hydraulic drive system further comprises a first hydraulic pump that is a hydraulic pump provided separately from the second hydraulic pump, and a fourth direction switching valve disposed in a passage between the first hydraulic pump and the head side chamber, wherein the fourth direction switching valve is preferably configured to adjust a meter-in opening through which hydraulic oil discharged by the first hydraulic pump is supplied to the head side chamber of the hydraulic cylinder when the hydraulic cylinder extends, and to adjust a meter-out opening through which hydraulic oil is discharged from the head side chamber of the hydraulic cylinder when the hydraulic cylinder retracts. In this fifth aspect, since the fourth direction switching valve functions as both a meter-in control valve and a meter-out control valve, the configuration of the hydraulic circuit can be further prevented from becoming complicated.

[0088] A sixth aspect is preferably the hydraulic drive system according to any one of the first to fifth aspects, further comprising the following configuration: That is, in the hydraulic drive system according to the sixth aspect, the construction machine may include a boom and an arm, and the hydraulic cylinder may be an arm cylinder for moving the arm.

Claims

1. A hydraulic drive device for a construction machine comprising: a hydraulic pump that discharges hydraulic oil; a hydraulic cylinder having a head side chamber and a rod side chamber; a first passage connecting the hydraulic pump to the head side chamber; a second passage connected to the rod side chamber; a third passage connecting the first passage to the second passage; and a regeneration control valve arranged in the third passage, wherein the regeneration control valve has a spool that can be switched between a regeneration position that allows hydraulic oil discharged from the rod side chamber to flow from the second passage into the first passage and return to the head side chamber, and a meter-in position that allows hydraulic oil discharged from the hydraulic pump to flow from the first passage into the second passage and be supplied to the rod side chamber.

2. The hydraulic drive system according to claim 1, further comprising a first directional control valve disposed in the first passage, the first directional control valve being configured to adjust a meter-in opening that supplies hydraulic oil to the head side chamber of the hydraulic cylinder when the hydraulic cylinder is extended, and to adjust a meter-out opening that discharges hydraulic oil from the head side chamber of the hydraulic cylinder when the hydraulic cylinder is contracted.

3. The hydraulic drive system according to claim 2, further comprising: a second directional control valve arranged in the second passage; and a controller, wherein the controller performs regeneration control such that, when the hydraulic cylinder is extended, the spool of the regeneration control valve is arranged in the regeneration position and a meter-out opening of the second directional control valve is narrowed, thereby causing hydraulic oil discharged from the rod side chamber of the hydraulic cylinder to be supplied to the head side chamber via the regeneration control valve.

4. A hydraulic drive system as described in claim 3, wherein when a regeneration cut condition is satisfied during extension of the hydraulic cylinder, the controller performs regeneration cut control such that the regeneration opening of the regeneration control valve is narrowed and the meter-out opening of the second directional control valve becomes larger than during the regeneration control, thereby causing the hydraulic oil discharged from the rod side chamber of the hydraulic cylinder to be discharged into a tank.

5. The hydraulic drive system according to any one of claims 2 to 4, wherein the hydraulic pump is a second hydraulic pump, the regeneration control valve is a third directional control valve, and the hydraulic drive system further comprises a first hydraulic pump which is a hydraulic pump provided separately from the second hydraulic pump, and a fourth directional control valve arranged in a passage between the first hydraulic pump and the head side chamber, and the fourth directional control valve is configured to adjust a meter-in opening through which hydraulic oil discharged by the first hydraulic pump is supplied to the head side chamber of the hydraulic cylinder when the hydraulic cylinder is extended, and to adjust a meter-out opening through which hydraulic oil is discharged from the head side chamber of the hydraulic cylinder when the hydraulic cylinder is contracted.

6. The hydraulic drive system according to any one of claims 1 to 5, wherein the construction machine comprises a boom and an arm, and the hydraulic cylinder is an arm cylinder for moving the arm.

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