Hydraulic drive device for construction machine

Abstract

A hydraulic drive device (101) for a construction machine (100) includes a hydraulic pump (22) that discharges hydraulic fluid, a hydraulic cylinder (8) that includes 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 regeneration control valve (53) arranged in the third passage (33). The regeneration control valve (53) includes a spool capable of being switched between a regeneration position for allowing hydraulic fluid released from the rod side chamber (8R) to flow from the second passage (32) into the first passage (31) and return to the head side chamber (8H), and a meter-in position for allowing hydraulic fluid 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).

Description

Technical Field

[0001] The present disclosure relates to a hydraulic drive device for a construction machine.Background Art

[0002] Patent Literature 1 discloses a pressurized 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 that is provided between the hydraulic pump and the hydraulic actuator and controls a meter-in flow rate according to differential pressure between pump pressure and load pressure. In this pressurized oil supply device, a meter-out switching valve that controls 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 Literature 2 discloses a hydraulic regeneration device of a hydraulic machine including a direction switching valve that controls a flow of pressurized oil supplied from a hydraulic pump to a hydraulic cylinder, a variable throttle valve that is provided in a return pipeline and controls a flow rate of pressurized oil guided to a tank, a check valve that is provided in a merging pipeline that communicates a supply pipeline and the return pipeline and allows supply of pressurized oil from the return pipeline to the supply pipeline, a pressure detector that detects pilot pressure applied to a drive unit of the direction switching valve, an on-off valve that selectively communicates or blocks the merging pipeline, a mode switch that operates the on-off valve, and a control device that controls a throttle amount of the variable throttle valve according to magnitude of a value of a signal output from the pressure detector.

[0004] In the technique described in Patent Literature 1, the meter-in switching valve for a function of controlling a meter-in opening and the meter-out switching valve for a function of controlling a meter-out opening are mounted. In the technique described in Patent Literature 2, the variable throttle valve for a function of controlling a flow rate of pressure oil guided to the tank and the on-off valve for a function of selectively communicating or blocking the merging pipeline are mounted. That is, in each of these techniques, since a valve (spool) is provided for each function, the number of spools increases and a circuit configuration becomes complicated in order to realize a plurality of functions. The same applies to the techniques described in Patent Literatures 3 to 5.Citation List Patent Literature

[0005] Patent Literature 1: JP H11-303814 A Patent Literature 2: JP H7-35110 A Patent Literature 3: JP H8-132218 A Patent Literature 4: JP 5004641 B2 Patent Literature 5: JP 3675703 B2 Summary of Invention

[0006] An object of the present disclosure is to provide a hydraulic drive device of a construction machine capable of suppressing complication of a configuration of a hydraulic circuit.

[0007] A hydraulic drive device for a construction machine according to a first aspect includes a hydraulic pump that discharges hydraulic fluid, a hydraulic cylinder having a head side chamber and a rod side chamber, a first passage that connects the hydraulic pump and the head side chamber, a second passage connected to the rod side chamber, a third passage that connects the first passage and the second passage, and a regeneration control valve arranged in the third passage, in which the regeneration control valve includes a spool capable of being switched between a regeneration position for allowing hydraulic fluid released 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 for allowing hydraulic fluid discharged from the hydraulic pump to flow from the first passage into the second passage and be supplied to the rod side chamber.Brief Description of Drawings

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

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

[0010] FIG. 1 is a side view illustrating a construction machine 100 according to the embodiment. The construction machine 100 illustrated in FIG. 1 is a hydraulic excavator. The construction machine 100 includes a self-propelled lower travelling body 1, an upper slewing body 2 supported by the lower travelling body 1 so as to be capable of slewing around a Z axis in a vertical direction with respect to the lower travelling body 1, a work device 3, and a plurality of hydraulic actuators.

[0011] The lower travelling body 1 includes left and right crawler travelling devices and a lower frame supported by the crawler travelling devices. The upper slewing body 2 includes a slewing frame slewably supported by the lower frame of the lower travelling body 1, and a cab supported by the slewing frame. The work device 3 includes a boom 4 supported by the slewing frame so as to be raised and lowered, an arm 5 rotatably supported by a tip portion of the boom 4, and a bucket 6 as a tip attachment rotatably supported by a tip portion 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 a fork. A plurality of hydraulic actuators include a boom cylinder 7, an arm cylinder 8, a bucket cylinder 9, a slewing motor 11, and a travel motor 12.[First embodiment]

[0012] FIG. 2 is a diagram illustrating an example of a hydraulic circuit of the construction machine 100. In the hydraulic circuit illustrated in FIG. 2, only a portion related to the arm cylinder 8 is illustrated, and illustration of other configurations is omitted.

[0013] The construction machine 100 includes a hydraulic drive device 101. The hydraulic drive device 101 includes a hydraulic pump 22, the arm cylinder 8, a first passage 31, a second passage 32, a third passage 33, and a direction switching valve 53. The direction switching 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, for example, to discharge hydraulic fluid. In the present embodiment, the hydraulic pump 22 is a hydraulic pump of a variable displacement type. Pump capacity of the hydraulic pump 22 is adjusted based on a command output from a controller 80. Information (rotational speed detection signal) related to a rotational speed of a power source 91 that drives the hydraulic pump 22 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 operates when hydraulic fluid is supplied from the hydraulic pump 22. As illustrated in FIG. 1, the arm cylinder 8 has a base end portion connected to the boom 4 and a tip portion connected to the arm 5. The arm cylinder 8 extends when hydraulic fluid is supplied to the head side chamber 8H and released from the rod side chamber 8R, and contracts when hydraulic fluid is supplied to the rod side chamber 8R and released from the head side chamber 8H.

[0016] The arm 5 performs an arm pulling operation as the arm cylinder 8 extends, and performs an arm pushing operation as the arm cylinder 8 contracts. The arm pulling operation is an operation in which a tip portion of the arm 5 approaches the boom 4, and the arm pushing operation is an operation in which the tip portion 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 direction switching valve 53 is arranged in the third passage 33.

[0018] The direction switching valve 53 has not only a function as a regeneration control valve but also a function as a meter-in control valve.

[0019] The direction switching valve 53 is configured to be switchable between a regeneration position and a meter-in position. Specifically, the direction switching valve 53 has a spool that can be displaced between a neutral position and the regeneration position and between the neutral position and the meter-in position. The neutral position is a position for preventing hydraulic fluid discharged from the hydraulic pump 22 from being supplied to the rod side chamber 8R of the arm cylinder 8, and preventing hydraulic fluid released 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 is a position for allowing hydraulic fluid released 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 is a position for allowing hydraulic fluid 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 the hydraulic drive device 101, the direction switching valve 53 shifts from the neutral position to the regeneration position and functions as a regeneration control valve for returning hydraulic fluid, released from the rod side chamber 8R, to the head side chamber 8H when there is an operation (arm pulling operation) for extending the arm cylinder 8, and shifts from the neutral position to the meter-in position and functions as a meter-in control valve for supplying hydraulic fluid, discharged from the hydraulic pump 22, to the rod side chamber 8R when there is an operation (arm pushing operation) for contracting the arm cylinder 8. That is, in the hydraulic drive device 101, since the direction switching valve 53 has not only a function as a regeneration control valve but also a function as a meter-in control valve, it is possible to realize these functions while suppressing a configuration of a hydraulic circuit from becoming complicated as compared with a case where the regeneration control valve and the meter-in control valve are individually provided.

[0021] In the first embodiment, the direction switching valve 53 may function as a regeneration control valve for returning hydraulic fluid, released from the rod side chamber 8R, to the head side chamber 8H when an operation member 15A of an operation device 15 receives only the arm pulling operation (that is, at the time of arm pulling independent operation), or may function as a meter-in control valve for supplying hydraulic fluid, discharged from the hydraulic pump 22, to the rod side chamber 8R when the operation member 15A of the operation device 15 receives only the arm pushing operation (that is, at the time of arm pushing independent operation).

[0022] A main feature of the hydraulic drive device 101 according to the first embodiment is as described above. Hereinafter, the hydraulic drive device 101 according to the first embodiment will be described more specifically.

[0023] The direction switching valve 53 may be, for example, a three-position direction switching valve as illustrated in FIG. 2. The direction switching valve 53 may be, for example, an electromagnetic valve having a pair of solenoids 53a and 53b as illustrated in FIG. 2. The direction switching valve 53 includes a spool that can be switched between a neutral position (intermediate position in FIG. 2), the regeneration position (right position in FIG. 2), and the meter-in position (left position in FIG. 2) according to a valve command (command signal) input to the direction switching valve 53. The direction switching valve 53 has a plurality of ports, and a plurality of the ports includes 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 the first port of the direction switching valve 53. The second portion 33B of the third passage 33 connects the second passage 32 and the second port of the direction switching valve 53. The third portion 33C of the third passage 33 connects the first passage 31 and the third port of the direction switching valve 53.

[0025] In a case where all command values of valve commands input to the solenoids 53a and 53b are 0 or minute, the spool of the direction switching valve 53 is kept at the neutral position (intermediate position in FIG. 2). When the spool of the direction switching valve 53 is arranged at the neutral position, the first port, the second port, and the third port are closed. By this, the first passage 31 and the second passage 32 are blocked by the direction switching valve 53. That is, when the spool of the direction switching valve 53 is arranged at the neutral position, hydraulic fluid discharged from the hydraulic pump 22 is prevented from being supplied to the rod side chamber 8R of the arm cylinder 8, and hydraulic fluid released 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. In a case where the spool of the direction switching valve 53 is kept at the neutral position, a meter-in opening and a regeneration opening of the direction switching valve 53 are in a "fully closed" state in which the openings are completely blocked.

[0026] In a case where a command value of a valve command input to the solenoid 53b is equal to or more than a certain value, the spool of the direction switching valve 53 shifts from the neutral position to the regeneration position (right position in FIG. 2) with a stroke corresponding to magnitude of the command value. When the spool of the direction switching valve 53 is arranged at the regeneration position, the second port and the third port are in a state of being connected to each other, and the first port is in a state of being closed. That is, when the spool of the direction switching valve 53 is arranged at the regeneration position, hydraulic fluid released 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. In a case where the spool of the direction switching valve 53 completely shifts to the regeneration position, the regeneration opening of the direction switching valve 53 has a maximum opening degree, that is, is in a "fully open" state.

[0027] In a case where a command value of a valve command input to the solenoid 53a is equal to or more than a certain value, the spool of the direction switching valve 53 shifts from the neutral position to the meter-in position (left position in FIG. 2) with a stroke corresponding to magnitude of the command value. When the spool of the direction switching valve 53 is arranged at the meter-in position, the first port and the second port are in a state of being connected to each other, and the third port is in a state of being closed. That is, when the spool of the direction switching valve 53 is arranged at the meter-in position, hydraulic fluid 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. In a case where the spool of the direction switching valve 53 completely shifts to the meter-in position, the meter-in opening of a direction switching valve 51 has a maximum opening degree, that is, is in a "fully open" state.

[0028] As illustrated in FIG. 2, the hydraulic drive device 101 further includes a check valve 71, a check valve 72, a pilot check valve 73, the direction switching valve 51, a plurality of the operation devices 15, and the controller 80. In FIG. 2, only one of the operation devices 15 is illustrated, and illustration of the other operation devices 15 is omitted.

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

[0030] The check valve 72 is arranged in the third portion 33C of the third passage 33. The check valve 72 allows hydraulic fluid to flow from the third port of the direction switching valve 53 toward the first passage 31, while preventing hydraulic fluid from flowing from the first passage 31 toward the third port of the direction switching valve 53.

[0031] The pilot check valve 73 is arranged 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 hydraulic fluid to flow from the second port of the direction switching valve 53 toward the rod side chamber 8R of the arm cylinder 8, while preventing hydraulic fluid from flowing in the opposite direction. Further, the pilot check valve 73 allows hydraulic fluid to flow in the opposite direction, that is, allows hydraulic fluid to flow from the rod side chamber 8R of the arm cylinder 8 to the second port of the direction switching valve 53 in a state where pilot pressure is applied. A state of the pilot check valve 73 is switched based on a command output from the controller 80.

[0032] The direction switching valve 51 has both a function as a meter-in control valve and a function as a meter-out control valve. The direction switching valve 51 may be, for example, a three-position direction switching valve as illustrated in FIG. 2. The direction switching valve 51 may be, for example, an electromagnetic valve having a pair of solenoids as illustrated in FIG. 2.

[0033] The direction switching valve 51 is arranged 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 direction switching valve 51 includes a spool that can be switched between a meter-in position (right position in FIG. 2) and a meter-out position (left position in FIG. 2) according to a valve command input to a pair of solenoids of the direction switching valve 51. The meter-in position is a position for allowing hydraulic fluid 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 for allowing hydraulic fluid released from the head side chamber 8H of the arm cylinder 8 to return to a tank 92. In a case where the direction switching valve 51 is a three-position direction switching valve as illustrated in FIG. 2, the spool of the direction switching valve 51 can be switched to a neutral position (intermediate position). When the spool of the direction switching valve 51 is arranged at the neutral position, the first passage 31 is blocked by the direction switching valve 51.

[0034] Specifically, in a case where all command values of valve commands input to the pair of solenoids of the direction switching valve 51 are 0 or minute, the spool of the direction switching valve 51 is kept at the neutral position. In a case where a command value of a valve command input to the solenoid on the right side of the direction switching valve 51 illustrated in FIG. 2 is equal to or more than a certain value, the spool of the direction switching valve 51 shifts from the neutral position to the meter-in position with a stroke corresponding to magnitude of the command value. In a case where a command value of a valve command input to the solenoid on the left side of the direction switching valve 51 illustrated in FIG. 2 is equal to or more than a certain value, the spool of the direction switching valve 51 shifts from the neutral position to the meter-out position with a stroke corresponding to magnitude of the command value. In a case where the spool of the direction switching valve 51 is kept at the neutral position, a meter-in opening and a meter-out opening of the direction switching valve 51 are in a "fully closed" state in which the openings are completely blocked. In a case where the spool of the direction switching valve 51 completely shifts to the meter-in position, the meter-in opening of the direction switching valve 51 has a maximum opening degree, that is, is in a "fully open" state. In a case where the spool of the direction switching valve 51 completely shifts to the meter-out position, the meter-out opening of the direction switching valve 51 has a maximum opening degree, that is, is in a "fully open" state.

[0035] Each of a plurality of the operation devices 15 includes the operation member 15A such as an operation lever and an operation pedal, and an output device 15B. The operation member 15A receives an operation by an operator. Examples of operation by an operator include an arm pulling operation, an arm pushing operation, a boom raising operation, a boom lowering operation, and a slewing operation. The output device 15B outputs an operation command corresponding to an operation by an 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 contraction operation in the present disclosure.

[0036] FIG. 3 is a graph illustrating an example of a relationship between an operation input to the operation device 15 of the construction machine 100 and output of the operation device 15. When an operator gives a lever operation such as the arm pulling operation to the operation member 15A of the operation device 15, the output device 15B outputs an operation command corresponding to an operation amount (for example, an operation angle of the operation member 15A) of the lever operation to the controller 80. The horizontal axis of the graph of FIG. 3 illustrates a region of a half lever operation and a region of a full lever operation. In the region of the full lever operation, that is, in the region where an operation amount of a lever operation is equal to or more than a predetermined value, an operation command output from the output device 15B has a constant maximum value. On the other hand, in the region of the half lever operation, an operation command output from the output device 15B gradually increases to the maximum value according to an operation amount of a lever operation.

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

[0038] In a case where the operation member 15A of the operation device 15 receives the arm pulling operation, the controller 80 may input a valve command to the direction switching valve 53 so that the spool of the direction switching valve 53 is arranged at the regeneration position (right position in FIG. 2), and may input a valve command to the direction switching valve 51 so that the spool of the direction switching valve 51 is arranged at the meter-in position (right position in FIG. 2). In this case, the controller 80 may output a command so that a state in which pilot pressure is applied to the pilot check valve 73, that is, a state in which hydraulic fluid is allowed to flow from the rod side chamber 8R of the arm cylinder 8 toward the second port of the direction switching valve 53 is obtained. The command may be input to, for example, a proportional valve (not illustrated). By this, hydraulic fluid discharged from the hydraulic pump 22 is supplied to the head side chamber 8H of the arm cylinder 8, hydraulic fluid is released from the rod side chamber 8R of the arm cylinder 8, and the released hydraulic fluid merges with hydraulic fluid flowing through the first passage 31 via the direction switching valve 53 and the third portion 33C of the third passage 33. In the present embodiment, supplying hydraulic fluid, released from the rod side chamber 8R of the arm cylinder 8, to the head side chamber 8H of the arm cylinder 8 again is referred to as "regenerating hydraulic fluid". Further, a flow rate of hydraulic fluid released from the rod side chamber 8R and supplied again to the head side chamber 8H is referred to as a "regeneration amount". In the present embodiment, at the time of the arm pulling operation, hydraulic fluid is regenerated and a regeneration amount is secured, so that an operating speed of the arm cylinder 8 can be increased.

[0039] Further, in a case where the operation member 15A of the operation device 15 receives the arm pushing operation, the controller 80 may input a valve command to the direction switching valve 53 so that the spool of the direction switching valve 53 is arranged at the meter-in position (left position in FIG. 2), and may input a valve command to the direction switching valve 51 so that the spool of the direction switching valve 51 is arranged at the meter-out position (left position in FIG. 2). By this, hydraulic fluid discharged from the hydraulic pump 22 is supplied to the rod side chamber 8R of the arm cylinder 8, hydraulic fluid is released from the head side chamber 8H of the arm cylinder 8, and the released hydraulic fluid returns to the tank 92 via the direction switching valve 51.[Second embodiment]

[0040] FIG. 4 is a diagram illustrating a hydraulic circuit of the construction machine 100 according to a second embodiment. The construction machine 100 according to the second embodiment includes the hydraulic drive device 101. A basic structure of the hydraulic drive device 101 in the second embodiment is similar to that of the hydraulic drive device 101 in the first embodiment.

[0041] That is, the hydraulic drive device 101 according to the second embodiment includes the hydraulic pump 22, the arm cylinder 8, the first passage 31, the second passage 32, the third passage 33, the direction switching valve 53, the check valve 71, the check valve 72, the pilot check valve 73, the direction switching valve 51, a plurality of the operation devices 15, and the controller 80. 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, and the third passage 33 connects the first passage 31 and the second passage 32. The direction switching valve 51 is arranged 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 direction switching valve 53 is arranged in the third passage 33.

[0042] The hydraulic drive device 101 according to 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 is referred to as the first hydraulic pump 21, and the hydraulic pump 22 is referred to as the second hydraulic pump 22. Further, the direction switching valve 51 is referred to as the first direction switching valve 51, the direction switching valve 52 is referred to as the second direction switching valve 52, the direction switching valve 53 is referred to as the third direction switching valve 53, and the direction switching valve 54 is 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 the present embodiment, the first hydraulic pump 21 is a hydraulic pump of a variable displacement type. Pump capacity of the first hydraulic pump 21 is adjusted based on a command output from the controller 80.

[0044] The first pressure sensor 41 detects a first pump pressure that is a discharge pressure of the first hydraulic pump 21, and inputs a pump pressure detection signal that is a detection signal corresponding to the first pump pressure to the controller 80. The second pressure sensor 42 detects a second pump pressure that is a discharge pressure of the second hydraulic pump 22, and inputs a pump pressure detection signal that 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 is a passage branched 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 connected to the fourth direction switching valve 54. The sixth passage 36 is a passage branched from the fourth passage 34 and 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 arranged in a portion of the fourth passage 34 between a portion to which the sixth passage 36 is connected and the first hydraulic pump 21. The check valve 74 allows hydraulic fluid discharged from the first hydraulic pump 21 to flow toward the second direction switching valve 52 and allows hydraulic fluid discharged from the first hydraulic pump 21 to flow toward the fourth direction switching valve 54, while preventing hydraulic fluid from flowing from the second direction switching valve 52 to the first hydraulic pump 21 and preventing hydraulic fluid from flowing from the fourth direction switching valve 54 to the first hydraulic pump 21.

[0047] In the second embodiment, as in the first embodiment, the first direction switching valve 51 has both the function as the meter-in control valve and the function as the meter-out control valve, and the third direction switching valve 53 has both the function as the regeneration control valve and the function as the meter-in control valve. In the first direction switching valve 51, size of the meter-in opening or size of the meter-out opening is adjusted according to a valve command input from the controller 80. In the third direction switching valve 53, size of the regeneration opening or size of the meter-in opening is adjusted according to a valve command input from the controller 80.

[0048] The second direction switching valve 52 has both a function as a meter-in control valve and a function as a meter-out control valve. The second direction switching valve 52 may be, for example, a three-position direction switching valve as illustrated in FIG. 4. The second direction switching valve 52 may be, for example, an electromagnetic valve having a pair of solenoids as illustrated in FIG. 4. The second direction switching valve 52 includes a spool that can be switched to a neutral position (intermediate position) illustrated in FIG. 4, a meter-out position (right position in FIG. 4), and a meter-in position (left position in FIG. 4) according to a valve command input to a pair of the solenoids of the second direction switching valve 52. In the second direction switching valve 52, size of a meter-in opening or size of a meter-out opening is adjusted according to a valve command input from the controller 80.

[0049] Specifically, in a case where all command values of valve commands input to the pair of solenoids of the second direction switching valve 52 are 0 or minute, the spool of the second direction switching valve 52 is kept at the neutral position. In a case where a command value of a valve command input to the solenoid on the right side of the second direction switching valve 52 illustrated in FIG. 4 is equal to or more than a certain value, the spool of the second direction switching valve 52 shifts from the neutral position to the meter-out position with a stroke corresponding to magnitude of the command value. In a case where a command value of a valve command input to the solenoid on the left side of the second direction switching valve 52 illustrated in FIG. 4 is equal to or more than a certain value, the spool of the second direction switching valve 52 shifts from the neutral position to the meter-in position with a stroke corresponding to magnitude of the command value. In a case where the spool of the second direction switching valve 52 is kept at the neutral position, the meter-in opening and the meter-out opening of the second direction switching valve 52 are in a "fully closed" state in which the openings are completely blocked. In a case where the spool of the second direction switching valve 52 completely shifts to the meter-out position, the meter-out opening of the second direction switching valve 52 has a maximum opening degree, that is, is in a "fully open" state. In a case where the spool of the second direction switching valve 52 completely shifts to the meter-in position, the meter-in opening of the second direction switching valve 52 has a maximum opening degree, that is, is in a "fully open" state.

[0050] The fourth direction switching valve 54 has both a function as a meter-in control valve and a function as a meter-out control valve. The fourth direction switching valve 54 may be, for example, a three-position direction switching valve as illustrated in FIG. 4. The fourth direction switching valve 54 may be, for example, an electromagnetic valve having a pair of solenoids as illustrated in FIG. 4. The fourth direction switching valve 54 includes a spool that can be switched to a neutral position (intermediate position) illustrated in FIG. 4, a meter-in position (right position in FIG. 4), and a meter-out position (left position in FIG. 4) according to a valve command input to the pair of the solenoids of the fourth direction switching valve 54. In the fourth direction switching valve 54, size of a meter-in opening or size of a meter-out opening is adjusted according to a valve command input from the controller 80.

[0051] Specifically, in a case where all command values of valve commands input to the pair of solenoids of the fourth direction switching valve 54 are 0 or minute, the spool of the fourth direction switching valve 54 is kept at the neutral position. In a case where a command value of a valve command input to the solenoid on the right side of the fourth direction switching valve 54 illustrated in FIG. 4 is equal to or more than a certain value, the spool of the fourth direction switching valve 54 shifts from the neutral position to the meter-in position with a stroke corresponding to magnitude of the command value. In a case where a command value of a valve command input to the solenoid on the left side of the fourth direction switching valve 54 illustrated in FIG. 4 is equal to or more than a certain value, the spool of the fourth direction switching valve 54 shifts from the neutral position to the meter-out position with a stroke corresponding to magnitude of the command value. In a case where the spool of the fourth direction switching valve 54 is kept at the neutral position, the meter-in opening and the meter-out opening of the fourth direction switching valve 54 are in a "fully closed" state in which the openings are completely blocked. In a case where the spool of the fourth direction switching valve 54 completely shifts to the meter-in position, the meter-in opening of the fourth direction switching valve 54 has a maximum opening degree, that is, is in a "fully open" state. In a case where the spool of the fourth direction switching valve 54 completely shifts to the meter-out position, the meter-out opening of the fourth direction switching valve 54 has a maximum opening degree, that is, is in a "fully open" state.

[0052] In a case where the operation member 15A of the operation device 15 receives the arm pulling operation, the controller 80 controls opening degrees of the meter-in openings of the first direction switching valve 51 and the fourth direction switching valve 54 according to an operation amount (arm pulling operation amount) of the arm pulling operation. Specifically, as illustrated in FIG. 5(A), in a case where an arm pulling operation amount is smaller than a first operation amount A1, the meter-in opening of the first direction switching valve 51 is in a blocked state, that is, a fully closed state. When an arm pulling operation amount is larger than the first operation amount A1, the meter-in opening of the first direction switching valve 51 is in a state of being open from the fully closed state, and has an opening degree corresponding to the arm pulling operation amount. In a case where an arm pulling operation amount is smaller than a 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, that is, a fully closed state. When an arm pulling operation amount is larger than the second operation amount A2, the meter-in opening of the fourth direction switching valve 54 is in a state of being open from the fully closed state, and has an opening degree corresponding to the arm pulling operation amount. In a case where an arm pulling operation amount is larger than the second operation amount A2, hydraulic fluid supplied from the first hydraulic pump 21 merges, via the fourth direction switching valve 54, with hydraulic fluid supplied from the second hydraulic pump 22 to the head side chamber 8H of the arm cylinder 8. Therefore, in this case, an operation speed (speed of an arm pulling operation) of the arm cylinder 8 can be improved (increased) as compared with a case where only hydraulic fluid from the second hydraulic pump 22 is supplied to the head side chamber 8H of the arm cylinder 8.

[0053] In a case where the operation member 15A of the operation device 15 receives the arm pushing operation, the controller 80 controls opening degrees of the meter-in openings of the third direction switching valve 53 and the second direction switching valve 52 according to an operation amount (arm pushing operation amount) of the arm pushing operation. Specifically, as illustrated in FIG. 5(B), in a case where an arm pushing operation amount is smaller than a first operation amount B1, the meter-in opening of the third direction switching valve 53 is in a blocked state, that is, a fully closed state. When an arm pushing operation amount is larger than the first operation amount B1, the meter-in opening of the third direction switching valve 53 is in a state of being open from the fully closed state, and has an opening degree corresponding to the arm pushing operation amount. In a case where an arm pushing operation amount is smaller than a 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, that is, a fully closed state. When an arm pushing operation amount is larger than the second operation amount B2, the meter-in opening of the second direction switching valve 52 is in a state of being open from the fully closed state, and has an opening degree corresponding to the arm pushing operation amount. In a case where an arm pushing operation amount is larger than the second operation amount B2, hydraulic fluid supplied from the first hydraulic pump 21 merges, via the second direction switching valve 52, with hydraulic fluid supplied from the second hydraulic pump 22 to the rod side chamber 8R of the arm cylinder 8. Therefore, in this case, an operation speed (speed of an arm pushing operation) of the arm cylinder 8 can be improved (increased) as compared with a case where only hydraulic fluid from the second hydraulic pump 22 is supplied to the rod side chamber 8R of the arm cylinder 8.

[0054] In a case where the operation member 15A of the operation device 15 receives the arm pushing operation, the controller 80 controls opening degrees of the meter-out openings of the first direction switching valve 51 and the fourth direction switching valve 54 according to an arm pushing operation amount. Specifically, as illustrated in FIG. 5(C), in a case where an arm pushing operation amount is smaller than a first operation amount C1, the meter-out opening of the first direction switching valve 51 is in a blocked state, that is, a fully closed state. When an arm pushing operation amount is larger than the first operation amount C1, the meter-out opening of the first direction switching valve 51 is in a state of being open from the fully closed state, and has an opening degree corresponding to the arm pushing operation amount. In a case where the arm pushing operation amount is smaller than a second operation amount C2, which is an operation amount larger than the first operation amount C1, the meter-out opening of the fourth direction switching valve 54 is in a blocked state, that is, a fully closed state. When an arm pushing operation amount is larger than the second operation amount C2, the meter-out opening of the fourth direction switching valve 54 is in a state of being open from the fully closed state, and has an opening degree corresponding to the arm pushing operation amount. The first operation amount B1 and the first operation amount C1 may be operation amounts of the same magnitude or different magnitudes. The second operation amount B2 and the second operation amount C2 may be operation amounts of the same magnitude or different magnitudes. In the present embodiment, the first operation amount B1 and the first operation amount C1 are set to the same magnitude, and the second operation amount B2 and the second operation amount C2 are set to the same magnitude.

[0055] FIG. 6 is a table summarizing content of operation received by the operation member 15A of the operation device 15, a condition, and a state of each direction switching valve in the construction machine 100 according to the second embodiment. In the second embodiment, the controller 80 performs any of a plurality of controls as illustrated in FIG. 6 according to content of operation received by the operation member 15A of the operation device 15 and a condition. Note that "*" in the table of FIG. 6 means that an opening area (opening degree) increases to fully open according to an operation amount.[First control]

[0056] The controller 80 determines whether or not the operation member 15A of the operation device 15 receives an arm pulling operation based on an operation command input from the output device 15B of the operation device 15 to the controller 80. In a case where the determination result is positive (when it is determined that the operation device 15 receives an arm pulling operation), the controller 80 controls each of the first to fourth direction switching valves 51, 52, 53, and 54 as described in a first row in the table of FIG. 6 (first control).

[0057] In the first control, as illustrated in FIG. 5(A), when an arm pulling operation amount becomes an operation amount 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 in a state of being open at an opening degree according to the arm pulling operation amount, and when the arm pulling operation amount becomes an operation amount 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 in a state of being open at an opening degree according to the arm pulling operation amount. When the arm pulling operation amount increases to reach a maximum operation amount, the meter-in opening of the first direction switching valve 51 becomes "fully open", and the meter-in opening of the fourth direction switching valve 54 becomes "fully open". Further, in the first control, valve commands are input to the second direction switching valve 52 and the third direction switching valve 53, respectively, so that the meter-out opening of the second direction switching valve 52 becomes "fully closed" and the regeneration opening of the third direction switching valve 53 becomes "fully open".

[0058] In the first control, the meter-out opening of the second direction switching valve 52 is "fully closed", so that an entire amount of hydraulic fluid released from the rod side chamber 8R of the arm cylinder 8 flows into the first passage 31 from the second passage 32 through the third passage 33 and is supplied to the head side chamber 8H of the arm cylinder 8. At the time of the arm pulling independent operation, an operation speed of the arm cylinder 8 can be increased as a regeneration amount of hydraulic fluid is secured. This first control is effective, for example, in a case of causing the arm 5 to perform an arm pulling operation without bringing the work device 3 (boom 4, arm 5, and tip attachment) into contact with another object, and increasing an operation speed of the arm pulling operation by increasing an arm pulling operation amount. The first control is an example of regeneration control in the present disclosure.

[0059] In the first control, an operation speed of the arm cylinder 8 can be increased also from the following viewpoint. In the second embodiment, a length of a passage connecting the third direction switching valve 53 and the arm cylinder 8 is shorter than a length of a passage connecting the second direction switching valve 52 and the arm cylinder 8, and shorter than a length of a passage connecting the fourth direction switching valve 54 and the arm cylinder 8. This enables reduction in pressure loss when hydraulic fluid is regenerated via the third direction switching valve 53. By this, operating pressures including pump pressure, pressure of the rod side chamber 8R, and pressure of the head side chamber 8H are reduced. When the operating pressures are reduced, leakage of hydraulic fluid is reduced in a hydraulic circuit, and decrease in a flow rate of hydraulic fluid flowing to the arm cylinder 8 is suppressed. By this, an operation speed of the arm cylinder 8 can be increased. Further, in a case where a hydraulic circuit operates under horsepower control, pump capacity can be increased by reduction in the operating pressures. By this, a flow rate of hydraulic fluid supplied to the arm cylinder 8 is also increased, so that an operation speed of the arm cylinder 8 can be increased.[Second control]

[0060] The controller 80 determines whether or not the operation member 15A of the operation device 15 receives an arm pulling operation and a regeneration cut-off condition is satisfied based on an operation command input from the output device 15B of the operation device 15 to the controller 80 and a pump pressure detection signal input from the second pressure sensor 42. The regeneration cut-off condition includes a condition that a discharge pressure of the second hydraulic pump 22 exceeds a reference pressure set in advance. The regeneration cut-off condition may include a condition that a discharge pressure of the first hydraulic pump 21 exceeds a reference pressure set in advance for the first hydraulic pump 21 or a condition that a discharge pressure of the second hydraulic pump 22 exceeds a reference pressure set in advance for the second hydraulic pump 22. In a case where the determination result is positive (in a case where it is determined that the operation device 15 receives the arm pulling operation and the regeneration cut-off condition is satisfied), the controller 80 controls each of the first to fourth direction switching valves 51, 52, 53, and 54 as described in a second row of the table of FIG. 6 (second control).

[0061] In the second control, similarly to the first control, as illustrated in FIG. 5(A), when an arm pulling operation amount becomes an operation amount 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 in a state of being open at an opening degree according to the arm pulling operation amount, and when the arm pulling operation amount becomes an operation amount 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 in a state of being open at an opening degree according to the arm pulling operation amount. When the arm pulling operation amount increases to reach a maximum operation amount, the meter-in opening of the first direction switching valve 51 becomes "fully open", and the meter-in opening of the fourth direction switching valve 54 becomes "fully open". Furthermore, in the second control, in a case where the regeneration cut-off condition is satisfied, valve commands are input to the second direction switching valve 52 and the third direction switching valve 53, respectively, so that the meter-out opening of the second direction switching valve 52 becomes "fully open" and the regeneration opening of the third direction switching valve 53 becomes "fully closed". The second control is an example of regeneration cut-off control in the present disclosure. In the regeneration cut-off control, the spool of the third direction switching valve 53 (regeneration control valve) may be arranged at the 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 fluid released 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, and it is possible to reduce operating pressure of the rod side chamber 8R of the arm cylinder 8 and increase differential pressure between the head side chamber 8H and the rod side chamber 8R of the arm cylinder 8. By this, it is possible to suppress generation of back pressure in the second passage 32 during heavy load work (for example, at the time of excavation work) in which a discharge pressure of the second hydraulic pump 22 is higher than the reference pressure, and to secure driving force (excavation force) of an arm pulling operation. In the second control, a regeneration amount is zero. The second control is an example of regeneration cut-off control in the present disclosure.

[0063] During light load work (for example, an arm pulling operation in the air) in which a discharge pressure of the second hydraulic pump 22 is lower than the reference pressure, the first control is executed, and return oil from the rod side chamber 8R of the arm cylinder 8 is regenerated to the head side chamber 8H, so that increase in speed of an arm pulling operation can be achieved.[Third control]

[0064] The controller 80 determines whether or not the operation member 15A of the operation device 15 receives an arm pulling operation and a cavitation prevention condition is satisfied based on an operation command input from the output device 15B of the operation device 15 to the controller 80 and an operation state of the power source 91. The cavitation prevention condition may include, for example, a condition that a rotational speed of the second hydraulic pump 22 driven by the power source 91 is equal to or less than a reference rotational speed set in advance. A rotational speed to be compared with the reference rotational speed may be a rotational speed of the second hydraulic pump 22 itself as described above, or may be a rotational speed of an engine or an electric motor constituting the power source 91. In a case where the determination result is positive (in a case where it is determined that the operation device 15 receives an arm pulling operation and the cavitation prevention condition is satisfied), the controller 80 controls each of the first to fourth direction switching valves 51, 52, 53, and 54 as described in a third row of the table of FIG. 6 (third control).

[0065] In the third control, similarly to the first control, as illustrated in FIG. 5(A), when an arm pulling operation amount becomes an operation amount 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 in a state of being open at an opening degree according to the arm pulling operation amount, and when the arm pulling operation amount becomes an operation amount 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 in a state of being open at an opening degree according to the arm pulling operation amount. When the arm pulling operation amount increases to reach a maximum operation amount, the meter-in opening of the first direction switching valve 51 becomes "fully open", and the meter-in opening of the fourth direction switching valve 54 becomes "fully open". Furthermore, in the third control, valve commands are input to the second direction switching valve 52 and the third direction switching valve 53, respectively, 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 "half open". The "half open" of the regeneration opening means that an opening degree of the regeneration opening of the third direction switching valve 53 is between fully closed and fully open, that is, the regeneration opening of the third direction switching valve 53 is in a state of being narrowed as compared with fully open and of being open.

[0066] In the third control, the meter-out opening of the second direction switching valve 52 is "fully closed", so that an entire amount of hydraulic fluid released from the rod side chamber 8R of the arm cylinder 8 flows into the first passage 31 from the second passage 32 through the third passage 33 and is supplied to the head side chamber 8H of the arm cylinder 8. Further, in the third control, since the third direction switching valve 53 is "half open", it is possible to increase pressure of the rod side chamber 8R of the arm cylinder 8 and reduce an operation speed of an arm pulling operation of the arm cylinder 8 as compared with a case of "fully open". By this, even in a case where a rotational speed of the second hydraulic pump 22 becomes equal to or less than the reference rotational speed set in advance and hydraulic fluid supplied from the second hydraulic pump 22 to the head side chamber 8H of the arm cylinder 8 is reduced, pressure of the head side chamber 8H is prevented from becoming excessively low, and occurrence of cavitation in the head side chamber 8H is prevented. That is, in the third control, it is possible to achieve both regeneration of hydraulic fluid and prevention of occurrence of cavitation. The third control is an example of regeneration control in the present disclosure.

[0067] When the third control is executed, in the present embodiment, the first direction switching valve 51 and the fourth direction switching valve 54 can be caused to function as meter-in control valves, and the third direction switching valve 53 can be caused to function as a regeneration control valve. Since the meter-in control valve and the regeneration control valve are caused to function by separate control valves, in the third control, a regeneration opening can be variably set according to an engine rotational speed without being affected by a meter-in opening.

[0068] Note that, in a case where a rotational speed of the second hydraulic pump 22 exceeds the reference rotational speed set in advance, the first control is executed, and return oil from the rod side chamber 8R of the arm cylinder 8 is regenerated to the head side chamber 8H, so that increase in speed of an arm pulling operation can be achieved. Further, in a case where capacity of the second hydraulic pump 22 is increased in accordance with decrease in a rotational speed of the second hydraulic pump 22, the reference rotational speed may be set in consideration of the increase in the pump capacity.[Fourth control]

[0069] The controller 80 determines whether or not the operation member 15A of the operation device 15 receives an arm pushing operation based on an operation command input from the output device 15B of the operation device 15 to the controller 80. In a case where the determination result is positive (when it is determined that the operation device 15 receives an arm pushing operation), the controller 80 controls each of the first to fourth direction switching valves 51, 52, 53, and 54 as described in a fourth row in the table of FIG. 6 (fourth control).

[0070] In the fourth control, as illustrated in FIG. 5(B), when an arm pushing operation amount becomes an operation amount 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 in a state of being open at an opening degree according to the arm pushing operation amount, and when the arm pushing operation amount becomes an operation amount 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 in a state of being open at an opening degree according to the arm pushing operation amount. When the arm pushing operation amount increases to reach a maximum operation amount, the meter-in opening of the third direction switching valve 53 becomes "fully open", and the meter-in opening of the second direction switching valve 52 becomes "fully open". Further, in the fourth control, as illustrated in FIG. 5(C), when an arm pushing operation amount becomes an operation amount 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 in a state of being open at an opening degree according to the arm pushing operation amount, and when the arm pushing operation amount becomes an operation amount 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 in a state of being open at an opening degree according to the arm pushing operation amount. When the arm pushing operation amount increases to reach a maximum operation amount, the meter-out opening of the first direction switching valve 51 becomes "fully open", and the meter-out opening of the fourth direction switching valve 54 becomes "fully open".

[0071] In the fourth control, the meter-in opening of the third direction switching valve 53 is opened at an opening degree according to an arm pushing operation amount, so that hydraulic fluid supplied from the first hydraulic pump 21 (specifically, hydraulic fluid supplied from the second hydraulic pump 22 by opening of the meter-in opening of the second direction switching valve 52 at an opening degree corresponding to the arm pushing operation amount) merges with hydraulic fluid supplied from the second hydraulic pump 22 to the rod side chamber 8R of the arm cylinder 8 via the second direction switching valve 52 and is supplied to the rod side chamber 8R of the arm cylinder 8. Further, hydraulic fluid released from the head side chamber 8H of the arm cylinder 8 is guided to the tank 92 through the meter-out opening of the first direction switching valve 51 and the meter-out opening of the fourth direction switching valve 54. By this, operating pressure of the rod side chamber 8R of the arm cylinder 8 is reduced, and differential pressure between the head side chamber 8H and the rod side chamber 8R of the arm cylinder 8 is increased, so that an arm pushing operation of the arm 5 can be performed at a sufficient speed.[Fifth control]

[0072] The controller 80 determines whether or not the operation member 15A of the operation device 15 receives an arm pushing operation and a cavitation prevention condition is satisfied based on an operation command input from the output device 15B of the operation device 15 to the controller 80 and an operation state of the power source 91. The cavitation prevention condition is similar to that in the third control, and may include, for example, a condition that a rotational speed of the second hydraulic pump 22 driven by the power source 91 is equal to or less than a reference rotational speed set in advance. A rotational speed to be compared with the reference rotational speed may be a rotational speed of the second hydraulic pump 22 itself as described above, or may be a rotational speed of an engine or an electric motor constituting the power source 91. In a case where the determination result is positive (in a case where it is determined that the operation device 15 receives an arm pushing operation and the cavitation prevention condition is satisfied), the controller 80 controls each of the first to fourth direction switching valves 51, 52, 53, and 54 as described in a fifth row of the table of FIG. 6 (fifth control).

[0073] In the fifth control, as in the fourth control, as illustrated in FIG. 5(B), when an arm pushing operation amount becomes an operation amount 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 in a state of being open at an opening degree according to the arm pushing operation amount, and when the arm pushing operation amount becomes an operation amount 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 in a state of being open at an opening degree according to the arm pushing operation amount. When the arm pushing operation amount increases to reach a maximum operation amount, the meter-in opening of the third direction switching valve 53 becomes "fully open", and the meter-in opening of the second direction switching valve 52 becomes "fully open". As illustrated in FIG. 5(C), when an arm pushing operation amount becomes an operation amount 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 in a state of being open at an opening degree according to the arm pushing operation amount, and when the arm pushing operation amount becomes an operation amount 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 in a state of being open at an opening degree according to the arm pushing operation amount. When the arm pushing operation amount increases to reach a maximum operation amount, the meter-out opening of the first direction switching valve 51 becomes "fully open", and the meter-out opening of the fourth direction switching valve 54 becomes "fully open". Furthermore, in the fifth control, in a case where 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 becomes "fully closed".

[0074] In the fifth control, the meter-out opening of the fourth direction switching valve 54 is "fully closed", so that pressure of the head side chamber 8H of the arm cylinder 8 can be increased and an operation speed of an arm pushing operation of the arm cylinder 8 can be reduced as compared with a case where the meter-out opening of the fourth direction switching valve 54 is "half open" or "fully open". By this, even in a case where a rotational speed of the second hydraulic pump 22 becomes equal to or less than the reference rotational speed set in advance and hydraulic fluid supplied from the second hydraulic pump 22 to the rod side chamber 8R of the arm cylinder 8 is reduced, pressure of the rod side chamber 8R is prevented from becoming excessively low, and occurrence of cavitation in the rod side chamber 8R is prevented.

[0075] When the fourth control and the fifth control are executed, 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. Further, when the fifth control is executed, the meter-out opening of the fourth direction switching valve 54 is narrowed, and the meter-out opening becomes "fully closed". In the present embodiment, since a meter-in control valve and a meter-out control valve are caused to function by separate control valves, it is possible to individually set each of a meter-in opening and a meter-out opening.

[0076] Note that FIG. 4 illustrates the boom cylinder 7, direction switching valves 55 and 56, a relief valve 78, and a back pressure valve 79. These will be briefly described. When the operation member 15A of the operation device 15 receives a boom raising operation, a spool of the direction switching valve 55 is arranged at a meter-in position (left position in FIG. 4) from a neutral position (intermediate position in FIG. 4), and a spool of the direction switching valve 56 is arranged at a meter-out position (left position in FIG. 4). By this, hydraulic fluid discharged from the first hydraulic pump 21 is supplied to a head side chamber of the boom cylinder 7 via the direction switching valve 56, and hydraulic fluid in a rod side chamber of the boom cylinder 7 is released to the tank 92 via the direction switching valve 56. By this, the boom cylinder 7 extends and the boom 4 performs a boom raising operation. When the operation member 15A of the operation device 15 receives a boom lowering operation, the spool of the direction switching valve 55 is arranged at a meter-out position (right position in FIG. 4) from the neutral position, and the spool of the direction switching valve 56 is arranged at a meter-in position (right position in FIG. 4) from the neutral position. By this, hydraulic fluid discharged from the first hydraulic pump 21 is supplied to the rod side chamber of the boom cylinder 7 via the direction switching valve 56, and hydraulic fluid in the head side chamber of the boom cylinder 7 is released to the tank 92 via the direction switching valve 55. By this, the boom cylinder 7 contracts, and the boom 4 performs a boom lowering operation. The relief valve 78 is opened when a pump pressure of at least one of the first hydraulic pump 21 and the second hydraulic pump 22 reaches a predetermined relief pressure. The back pressure valve 79 is provided in a return passage for returning hydraulic fluid to the tank 92, and generates back pressure in the return passage. In a hydraulic circuit illustrated in FIG. 4, only portions related to the arm cylinder 8 and the boom cylinder 7 are illustrated, and illustration of other configurations is omitted.[Modification]

[0077] The embodiment of the present disclosure is described above, but the present disclosure is not limited to the embodiment, and includes a modification below, for example.(A) Regarding direction switching valve

[0078] In the above embodiment, the direction switching valve 53 is an electromagnetic valve having a solenoid, but the direction switching valve in the present disclosure is not limited to an electromagnetic valve, and may be a direction switching valve having a pilot port to which pilot pressure is input.(B) Regarding operation device

[0079] In the above embodiment, the operation device 15 includes the operation member 15A such as an operation lever and the output device 15B, and the output device 15B inputs an operation command according to an operation given to the operation member 15A to the controller 80, however, the operation device in the present disclosure is not limited to the specific example of the above embodiment. The operation device may include an operation member such as an operation lever and a remote control valve as an output device. In this case, the remote control valve may output secondary pressure (pilot pressure) corresponding to an operation applied to the operation member, and the pilot pressure may be input to a pilot port of the direction switching valve 53.(C) Regarding construction machine

[0080] Although the construction machine 100 according to the above embodiment is a hydraulic excavator, the construction machine in the present disclosure is not limited to a hydraulic excavator, and may be another construction machine such as a crane or a bulldozer.

[0081] As described above, according to the present disclosure, there is provided a hydraulic drive device for a construction machine capable of suppressing complication of a configuration of a hydraulic circuit.

[0082] A hydraulic drive device for a construction machine according to a first aspect includes a hydraulic pump that discharges hydraulic fluid, a hydraulic cylinder having a head side chamber and a rod side chamber, a first passage that connects the hydraulic pump and the head side chamber, a second passage connected to the rod side chamber, a third passage that connects the first passage and the second passage, and a regeneration control valve arranged in the third passage, in which the regeneration control valve includes a spool capable of being switched between a regeneration position for allowing hydraulic fluid released 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 for allowing hydraulic fluid 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 the first aspect, the direction switching valve functions as a regeneration control valve for returning hydraulic fluid, released from the rod side chamber, to the head side chamber when the hydraulic cylinder extends, and functions as a meter-in control valve for supplying hydraulic fluid, discharged from the hydraulic pump, to the rod side chamber when the hydraulic cylinder contracts. That is, in the first aspect, since the regeneration control valve also has a function as a meter-in control valve, it is possible to realize these functions while suppressing complication of a configuration of a hydraulic circuit as compared with a case where the regeneration control valve and the meter-in control valve are individually provided.

[0084] According to a second aspect, the hydraulic drive device according to the first aspect preferably further includes the following configuration. That is, the hydraulic drive device according to the second aspect preferably further includes a first direction switching valve arranged in the first passage, in which the first direction switching valve is preferably configured to adjust a meter-in opening for supplying hydraulic fluid to the head side chamber of the hydraulic cylinder when the hydraulic cylinder extends, and adjust a meter-out opening for releasing hydraulic fluid from the head side chamber of the hydraulic cylinder when the hydraulic cylinder contracts. In the second aspect, since the first direction switching valve has both a function as a meter-in control valve and a function as a meter-out control valve, it is possible to further suppress complication of a configuration of a hydraulic circuit.

[0085] According to a third aspect, the hydraulic drive device according to the second aspect preferably further includes the following configuration. That is, the hydraulic drive device according to the third aspect preferably further includes a second direction switching valve arranged in the second passage, and a controller, in which the controller preferably performs regeneration control such that when the hydraulic cylinder extends, the spool of the regeneration control valve is arranged at the regeneration position, and a meter-out opening of the second direction switching valve is narrowed, so that hydraulic fluid released from the rod side chamber of the hydraulic cylinder is supplied to the head side chamber via the regeneration control valve. In the third aspect, the regeneration control is appropriately performed by the regeneration control valve and the second direction switching valve.

[0086] According to a fourth aspect, the hydraulic drive device according to the third aspect preferably further includes the following configuration. That is, in the hydraulic drive device according to the fourth aspect, in a case where a regeneration cut-off condition is satisfied when the hydraulic cylinder extends, the controller preferably performs regeneration cut-off control such that a regeneration opening of the regeneration control valve is narrowed and the meter-out opening of the second direction switching valve becomes larger than that in the regeneration control, so that hydraulic fluid released from the rod side chamber of the hydraulic cylinder is released to a tank. In the fourth aspect, the regeneration control valve and the second direction switching valve appropriately perform regeneration cut-off control. Note that, in the regeneration cut-off control, the spool of the regeneration control valve may be arranged at a neutral position.

[0087] According to a fifth aspect, the hydraulic drive device according to any of the second to fourth aspects preferably further includes the following configuration. That is, in the hydraulic drive device according the fifth aspect, the hydraulic pump is preferably a second hydraulic pump, and the regeneration control valve is preferably a third direction switching valve, the hydraulic drive device preferably further includes a first hydraulic pump that is a hydraulic pump provided separately from the second hydraulic pump, and a fourth direction switching valve arranged in a passage between the first hydraulic pump and the head side chamber, the fourth direction switching valve is preferably configured to adjust a meter-in opening for supplying hydraulic fluid, discharged from the first hydraulic pump, to the head side chamber of the hydraulic cylinder when the hydraulic cylinder extends, and adjust a meter-out opening for releasing hydraulic fluid from the head side chamber of the hydraulic cylinder when the hydraulic cylinder contracts. In the fifth aspect, since the fourth direction switching valve has both a function as a meter-in control valve and a function as a meter-out control valve, it is possible to further suppress complication of a configuration of a hydraulic circuit.

[0088] According to a sixth aspect, the hydraulic drive device according to any of the first to fifth aspects preferably further includes the following configuration. That is, in the hydraulic drive device 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. hydraulic drive device for a construction machine comprising: a hydraulic pump that discharges hydraulic fluid; a hydraulic cylinder having a head side chamber and a rod side chamber; a first passage that connects the hydraulic pump and the head side chamber; a second passage connected to the rod side chamber; a third passage that connects the first passage and the second passage; and a regeneration control valve arranged in the third passage, wherein the regeneration control valve includes a spool capable of being switched between a regeneration position for allowing hydraulic fluid released 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 for allowing hydraulic fluid 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 device according to claim 1, further comprising a first direction switching valve arranged in the first passage, wherein the first direction switching valve is configured to adjust a meter-in opening for supplying hydraulic fluid to the head side chamber of the hydraulic cylinder when the hydraulic cylinder extends, and adjust a meter-out opening for releasing hydraulic fluid from the head side chamber of the hydraulic cylinder when the hydraulic cylinder contracts.

3. The hydraulic drive device according to claim 2, further comprising: a second direction switching valve arranged in the second passage; and a controller, wherein the controller performs regeneration control such that when the hydraulic cylinder extends, the spool of the regeneration control valve is arranged at the regeneration position, and a meter-out opening of the second direction switching valve is narrowed, so that hydraulic fluid released from the rod side chamber of the hydraulic cylinder is supplied to the head side chamber via the regeneration control valve.

4. The hydraulic drive device according to claim 3, wherein in a case where a regeneration cut-off condition is satisfied when the hydraulic cylinder extends, the controller performs regeneration cut-off control such that a regeneration opening of the regeneration control valve is narrowed and the meter-out opening of the second direction switching valve becomes larger than that in the regeneration control, so that hydraulic fluid released from the rod side chamber of the hydraulic cylinder is released to a tank.

5. The hydraulic drive device according to any one of claims 2 to 4, wherein the hydraulic pump is a second hydraulic pump, and the regeneration control valve is a third direction switching valve, the hydraulic drive device further comprises: a first hydraulic pump that is a hydraulic pump provided separately from the second hydraulic pump; and a fourth direction switching valve arranged in a passage between the first hydraulic pump and the head side chamber, the fourth direction switching valve is configured to adjust a meter-in opening for supplying hydraulic fluid, discharged from the first hydraulic pump, to the head side chamber of the hydraulic cylinder when the hydraulic cylinder extends, and adjust a meter-out opening for releasing hydraulic fluid from the head side chamber of the hydraulic cylinder when the hydraulic cylinder contracts.

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

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