JP7210397B2 - construction machinery - Google Patents

Description

The present invention relates to a construction machine, and more particularly to a construction machine using a closed hydraulic circuit in which a hydraulic pump directly drives a hydraulic actuator.

In recent years, energy saving has become an important development item for construction machinery such as hydraulic excavators and wheel loaders. In order to save energy in construction machinery, it is important to save energy in the hydraulic system itself. Application of a hydraulic closed circuit system, in which a hydraulic actuator is connected in a closed circuit with a hydraulic pump and directly controlled, is being studied. This system has no pressure loss due to control valves and no flow loss because the pump delivers only the required flow rate. It is also possible to regenerate the potential energy of the actuator and the energy during deceleration. Therefore, energy saving is possible.

As a background art of construction machines combined with hydraulic closed circuits, Patent Document 1 discloses that a plurality of variable displacement hydraulic pumps are branched and connected to a plurality of hydraulic actuators via electromagnetic switching valves so as to form closed circuits. A configuration is described that enables compound motion and high-speed motion of the actuator.

JP 2015-48899 A

Construction machines such as mining shovels are required to have high availability over a long period of time as well as high reliability. For this reason, after the engine is stopped, it is necessary to release pressure from the hydraulic circuit as soon as possible to ensure safety, and to start maintenance work early, such as filter replacement, oil change, and checking for leaks in each part.

Normally, when the engine is stopped, the bucket is grounded on the ground, but if the bucket floats slightly or the vehicle body floats even slightly, residual pressure is generated in the hydraulic circuit due to its own weight. Therefore, after stopping the engine, it is necessary to move the front or body of the excavator in the direction of its own weight to bring it to the ground and release the residual pressure. Alternatively, even in the event of an emergency stop while the front is in the air, it is necessary to lower the front and ground it so that maintenance work can be started early while ensuring safety.

However, in the hydraulic circuit described in Patent Document 1, even if the hydraulic cylinder is displaced in the direction of its own weight, the make-up check valve is connected only to the charge line, so the cylinder cannot self-prime hydraulic oil. That is, even if an attempt is made to suck hydraulic oil from the tank, it cannot be sucked due to the presence of the charge pump. As a result, it takes time for the cylinder to be displaced, and there is a problem that the start of maintenance work is delayed due to the residual pressure being difficult to release. In addition, cavitation bubbles are generated because the cylinder is displaced in a state in which self-suction is not sufficiently self-priming, and these bubbles reduce the rigidity of the system, making the operation unstable. There was also a problem that there was a possibility of lowering the reliability of

Furthermore, in the hydraulic circuit described in Patent Document 1, the residual pressure on the cylinder bottom side can be released to the tank by the flow control valve, but there is also the problem that the residual pressure on the cylinder rod side cannot be released from the circuit.

The present invention has been made in view of the above problems, and an object of the present invention is to use a closed hydraulic circuit in which a hydraulic actuator is driven by a closed circuit hydraulic pump, and to quickly release the residual pressure in the closed hydraulic circuit after the engine is stopped. To provide a construction machine capable of obtaining a high operating rate by enabling maintenance work to be started early.

In order to achieve the above object, the present invention provides a closed circuit hydraulic pump having a tank for storing hydraulic oil, a prime mover, and two input/output ports capable of discharging in both directions, and driven by the prime mover, a hydraulic cylinder; a bottom side oil passage connecting one input/output port of the closed circuit hydraulic pump and a bottom side oil chamber of the hydraulic cylinder; the other input/output port of the closed circuit hydraulic pump; a rod-side oil passage connecting the rod-side oil chamber of the cylinder; an operation lever for instructing the operating direction and operating speed of the hydraulic cylinder; A construction machine comprising a controller for controlling a discharge direction and a discharge flow rate of hydraulic oil to be discharged , an open-circuit pump having a discharge port and a suction port connected to the tank, and a pump connected to the discharge port. a discharge oil passage, a bottom-side branch oil passage branched from the bottom-side oil passage and connected to the discharge oil passage, and a rod-side branch oil passage branched from the rod-side oil passage and connected to the discharge oil passage a bottom-side switching valve capable of switching between conducting and blocking of the bottom-side branched oil passage; a rod-side switching valve capable of switching between conducting and blocking of the rod-side branched oil passage; and the discharge oil passage and the tank. a connecting discharge oil passage, a bleed-off valve provided in the discharge oil passage, a bottom-side makeup oil passage connecting the bottom-side oil passage to the tank, and provided in the bottom-side makeup oil passage, A bottom-side makeup check valve that allows hydraulic fluid to be drawn from the tank to the bottom-side oil chamber, a rod-side makeup oil passage that connects the rod-side oil passage to the tank, and the rod-side makeup. A check valve for rod-side make-up is provided in the up oil passage and enables suction of hydraulic oil from the tank to the rod-side oil chamber.

According to the present invention configured as described above, when the pressure in the bottom side oil chamber of the hydraulic cylinder is high after the engine is stopped, the retraction operation of the hydraulic cylinder is instructed via the operation lever to perform the rod side make-up check. High-pressure hydraulic fluid in the bottom-side oil chamber can be discharged to the tank via the bottom-side control valve while hydraulic fluid from the tank is sucked into the rod-side oil chamber via the valve.

On the other hand, if the rod-side oil chamber of the hydraulic cylinder is at a high pressure after the engine is stopped, by instructing the extension operation of the hydraulic cylinder via the operation lever, hydraulic oil is discharged from the tank via the bottom-side make-up check valve. High-pressure hydraulic fluid in the rod-side oil chamber can be discharged to the tank via the rod-side control valve while being drawn into the bottom-side oil chamber.

As a result, the residual pressure in the closed hydraulic circuit can be released quickly after the engine is stopped, so maintenance work can be started early and the downtime of the construction equipment can be shortened, thereby improving the operation rate of the construction equipment. can be done.

According to the present invention, in a construction machine using a hydraulic closed circuit in which a hydraulic actuator is driven by a closed circuit hydraulic pump, the residual pressure in the hydraulic closed circuit can be quickly released after the engine is stopped, so maintenance work can be performed early. is started to shorten the downtime of the construction machine, the operating rate of the construction machine can be improved.

1 is a side view of a hydraulic excavator according to an embodiment of the present invention; FIG. 1 is a hydraulic circuit diagram of a hydraulic excavator according to an embodiment of the present invention; FIG. 4 is a flowchart showing processing of a control selection unit of a controller; It is a modification of the flowchart showing the processing of the control selection unit of the controller. 4 is a flowchart showing processing of a normal control section of the controller; 4 is a flow chart showing processing of a depressurization control unit of a controller; FIG. 5 is a diagram showing the operation of the hydraulic circuit when pressure is released by displacing the arm cylinder in the extension direction; FIG. 10 is a diagram showing the operation of the hydraulic circuit when pressure is released by displacing the arm cylinder in the retraction direction;

Hereinafter, a hydraulic excavator will be described as an example of a construction machine according to an embodiment of the present invention with reference to the drawings. In addition, in each figure, the same code|symbol is attached|subjected to the same member, and the overlapping description is abbreviate|omitted suitably.

FIG. 1 is a side view of a hydraulic excavator according to this embodiment.

In FIG. 1, a hydraulic excavator 100 includes a lower traveling body 101 having crawler-type traveling devices 8 on both left and right sides, and an upper revolving body 102 mounted on the lower traveling body 101 via a revolving device 7 so as to be capable of turning. It has The turning device 7 is driven by a turning hydraulic motor (not shown).

A front device 103 for performing excavation work or the like is attached to the front side of the upper revolving body 102 . The front device 103 includes a boom 2 connected to the front side of the upper swing body 102 so as to be vertically rotatable, an arm 4 connected to the tip of the boom 2 so as to be vertically rotatable, and is provided with a bucket 6 which is connected to the tip of the bucket 6 so as to be rotatable in the vertical and longitudinal directions. The boom 2, arm 4, and bucket 6 are driven by boom cylinder 1, arm cylinder 3, and bucket cylinder 5, which are single-rod hydraulic cylinders, respectively.

A cab 104 on which an operator rides is provided on the upper swing body 102 . Inside the cab 104 are a left operating lever 56a (shown in FIG. 2) for instructing the operation of the arm 4 and the upper swing body 102, and a right operating lever 56b (shown in FIG. 2) for instructing the operation of the boom 2 and the bucket 6. ), etc. are provided.

FIG. 2 is a hydraulic circuit diagram of the excavator 100. As shown in FIG. It should be noted that FIG. 2 shows only the portion related to the driving of the arm cylinder 3, and omits the portions related to the driving of the other actuators.

In FIG. 2, an engine 9 as a power source is connected to a power transmission device 10 that distributes power. A charge pump 11 , a variable displacement closed circuit pump 12 , and a variable displacement open circuit pump 13 are connected to the power transmission device 10 .

The charge pump 11 has a suction port connected to the tank 25 and a discharge port connected to the charge line 90 . A charge line 90 is connected to the tank 25 via the relief valve 20 . The relief valve 20 keeps the pressure in the charge line 90 constant.

The closed circuit pump 12 forms a hydraulic closed circuit by being connected to the arm cylinder 3 via the switching valve 43b. One input/output port of the closed circuit pump 12 is connected to the bottom side oil chamber 3a of the arm cylinder 3 via the bottom side oil passage 91a, and the other input/output port is connected to the arm cylinder 3 via the rod side oil passage 91b. It is connected to the rod side oil chamber 3b.

The open circuit pump 13 has a suction port connected to the tank 25 and a discharge port connected to the discharge oil passage 93 . The oil discharge passage 93 is connected to the tank 25 via an oil discharge passage 94 , and the oil discharge passage 94 is provided with a bleed-off valve 64 . The bleed-off valve 64 changes its opening area according to a signal from the controller 57, and is fully opened when there is no signal.

The discharge oil passage 93 is connected via a switching valve 44b to a bottom-side branching oil passage 92a branched from the bottom-side oil passage 91a, and connected via a switching valve 44e to a rod-side branching oil passage 92b branched from the rod-side oil passage 91b. connected. The switching valves 44b and 44e switch between conduction and interruption of the flow path in response to a signal from the controller 57, and are in the interruption state when there is no signal.

The bottom-side oil passage 91a and the rod-side oil passage 91b are connected to the charge line 90 via the make-up check valves 38a and 38b and the flushing valve 35, respectively. The make-up check valves 38a and 38b suck hydraulic oil from the charge pump 11 into the circuit when the pressure in the closed circuit drops, thereby preventing cavitation in the circuit. The flushing valve 35 is a low-pressure selection valve that connects the low-pressure side of the closed circuit and the charge line 90. When the hydraulic fluid in the closed circuit is excessive, it is discharged to the charge line 90, and when the hydraulic fluid is insufficient, it is charged. By sucking from the line 90, the balance of the amount of oil in the closed circuit is maintained.

Furthermore, the bottom-side oil passage 91a is connected to the tank 25 via the bottom-side makeup oil passage 95a, and the rod-side oil passage 91b is connected to the tank 25 via the rod-side makeup oil passage 95b. The bottom-side makeup oil passage 95a is provided with a bottom-side makeup check valve 80a, and the rod-side makeup oil passage 95b is provided with a rod-side makeup check valve 80b. The bottom-side make-up check valve 80a opens when the pressure in the bottom-side oil chamber 3a falls below the tank pressure, and allows hydraulic oil from the tank 25 to be drawn into the bottom-side oil chamber 3a. The rod-side make-up check valve 80b opens when the pressure in the rod-side oil chamber 3b falls below the tank pressure, and causes the hydraulic oil from the tank 25 to be sucked into the rod-side oil chamber 3b.

The controller 57 gives commands to the pumps 12, 13 and switching valves 43b, 44b, 44e according to inputs from the operation levers 56a, 56b and sensor information such as the engine speed and pressure of each part. The controller 57 includes a normal control unit 57b that performs control for performing normal operations such as excavation work while the engine is operating, a pressure release control unit 57c that performs control for releasing residual pressure in the hydraulic circuit after the engine is stopped, A control selection unit 57a for selecting these control units is provided.

FIG. 3 is a flow chart showing the processing of the control selection section 57a of the controller 57. As shown in FIG.

The control selection unit 57a first acquires a lever input (step S101).

Following step S101, it is determined whether or not the engine is in operation (step S102). Whether or not the engine 9 is operating is determined based on the engine speed detected by a speed sensor 58 (shown in FIG. 2) provided in the engine 9, for example.

When it is determined that the engine is operating (Yes) in step S102, the control mode is shifted to the normal control mode (step S103). In the normal control mode, the normal control section 57b performs control.

If it is determined in step S102 that the engine is not in operation (No), the process shifts to the depressurization control mode (step S104). In the depressurization control mode, the depressurization control section 57c performs control.

In this embodiment, when it is determined that the engine is not in operation, it is configured to shift to the pressure release control mode, but as shown in FIG. If it is determined to be normal (Yes), the process (step S105) is added, and if it is determined to be normal (Yes), the mode is shifted to the pressure release control mode (step S104). It is good also as a structure to perform. As a result, unintended operation due to depressurization control can be prevented.

FIG. 5 is a flow chart showing the processing of the normal control section 57b of the controller 57. As shown in FIG.

The normal control unit 57b first acquires a lever input from the control selection unit 57a (step S201).

Following step S201, the lever operation direction is determined based on the lever input (step S202).

If it is determined in step S202 that the lever operation direction is arm extension, when the lever operation amount exceeds the dead band, the command to the switching valves 43b and 44b is set to open, and the closed circuit pump 12 and the open circuit pump are set to the open command. 13 is increased according to the amount of lever operation (step S203).

If it is determined in step S202 that the lever operation direction is the arm retraction, when the lever operation amount exceeds the dead band, the command to the switching valves 43b and 44b is set to the open command, and the closed circuit pump 12 and the open circuit pump are set to the open command. 13 is increased according to the amount of lever operation (step S204).

Following step S203 or step S204, based on the respective pressures of the pumps 12, 13, the displacement command values of the pumps 12, 13 are limited so that the respective powers of the pumps 12, 13 are equal to or less than a predetermined value (step S205). .

Following step S205, a command is output to each switching valve and each pump (step S206).

FIG. 6 is a flow chart showing the processing of the depressurization control section 57c of the controller 57. As shown in FIG.

The depressurization control unit 57c first acquires a lever input from the control selection unit 57a (step S301).

Following step S301, the lever operation direction is determined based on the lever input (step S302).

If it is determined in step S302 that the lever operation direction is arm extension, when the lever operation amount exceeds the dead band, the command to the switching valves 43b and 44e is set to the open command, and the bleed-off valve 64 is commanded to open. The value is increased according to the lever operation amount (step S303).

If it is determined in step S302 that the lever operation direction is arm retraction, the command to the switching valves 43b and 44b is set to the open command when the lever operation amount exceeds the dead zone, and the opening command value of the bleed-off valve 64 is set. is increased according to the lever operation amount (step S304).

Following step S303 or step S304, a command is output to each switching valve (step S305).

In the above configuration, first, an example of operation in the normal control mode will be described.

In FIG. 2, when the arm cylinder 3 is to be extended, the switching valves 43b and 44b are brought into conduction, and hydraulic oil is discharged from the closed circuit pump 12 and the open circuit pump 13. As shown in FIG. As a result, the flow of two pumps flows into the bottom side oil chamber 3a of the arm cylinder 3, and the arm cylinder 3 extends. The discharged flow rate from the rod-side oil chamber 3b of the arm cylinder 3 is sucked into the closed circuit pump 12, but when the flow rate becomes excessive, it is discharged to the charge pressure line from the flushing valve 35, and when the flow rate is insufficient, it is reversed. Hydraulic oil is drawn into the closed circuit from the charge line 90 through the flushing valve 35 or the make-up check valves 38a and 38b. When the arm cylinder 3 is to be retracted, the switching valves 43b and 44b are brought into conduction, the closed circuit pump 12 is discharged in the opposite direction, and the bleed-off valve 64 is opened. As a result, hydraulic oil is discharged from the bottom side oil chamber 3a of the arm cylinder 3, and the arm cylinder 3 is retracted.

Next, an operation example of the depressurization control mode will be described.

First, as indicated by the solid line in FIG. 1, the case where the front device 103 of the excavator is extended and the engine 9 is stopped while the bucket 6 is slightly floated causes residual pressure to remain in the hydraulic circuit. After stopping the engine, the operator operates the operating levers 56a and 56b to displace any one of the boom 2, the arm 4 and the bucket 6 in the direction of its own weight and ground the bucket 6 to release the residual pressure. Although the engine 9 is stopped, the power is on when the key is ON, and the operating levers 56a, 56b, the controller 57, and the electromagnetic switching valves 43b, 44b, 44e are operable. In addition, even a large hydraulic valve whose main valve is operated by pilot pressure is provided with an accumulator (not shown) that maintains the pilot pressure, so even if it is a short-time operation such as depressurization, can drive the valve.

In the above configuration, the case where the arm 4 is moved to release the pressure will be described with reference to FIG. Since a load acts on the arm cylinder 3 in the extension direction of the cylinder due to the weight of the arm 4 and the bucket 6, the rod side has a high pressure. Therefore, it is necessary to extend the arm cylinder 3 and ground the bucket 6 by removing the high pressure on the rod side.

In FIG. 7, when the operator gives an extension command to the arm cylinder 3 with the operation lever 56a while the engine 9 is stopped, the controller 57 operates in the depressurization control mode, the switching valve 44e opens, and the lever The bleed-off valve 64 is opened according to the amount of operation. As a result, the high-pressure oil in the rod-side oil chamber 3b of the arm cylinder 3 is discharged to the tank 25 through the path indicated by the thick solid line, and the arm cylinder 3 is displaced in the extension direction. Hydraulic oil from the tank 25 is sucked into the bottom side oil chamber 3a of the arm cylinder 3 via the bottom side make-up check valve 80a. As a result, the arm cylinder 3 can be quickly displaced without causing cavitation.

Next, referring to FIG. 8, the front device 103 of the excavator is folded as shown by the dotted line in FIG. If there is Since the weight of the arm 4 and the bucket 6 acts on the arm cylinder 3 in the cylinder retraction direction, the pressure on the bottom side is high. Therefore, it is necessary to retract the arm cylinder 3 and ground the bucket 6 by releasing the high pressure on the bottom side.

In FIG. 8, when the operator gives a pull-in command to the arm cylinder 3 with the operation lever 56a with the engine 9 stopped, the controller 57 operates in the depressurization control mode, the switching valve 44b opens, and the lever The bleed-off valve 64 is opened according to the amount of operation. As a result, the high-pressure oil in the bottom-side oil chamber 3a of the arm cylinder 3 is discharged to the tank 25 through the path indicated by the thick solid line, and the arm cylinder 3 is displaced in the retraction direction. Hydraulic oil from the tank 25 is sucked into the rod-side oil chamber 3b of the arm cylinder 3 via the rod-side make-up check valve 80b.

In this manner, in the depressurization control mode, even if the hydraulic pumps 12 and 13 are not operating, the arm cylinder 3 can be moved in either the extension direction or the retraction direction by simply opening and closing the switching valves 43b, 44b and 44e. can also be displaced to release the pressure.

Although only the case of moving the arm 4 has been described above, the boom 2 and the bucket 6 can be similarly operated by connecting make-up check valves to the rod side and bottom side of each cylinder and operating them in the depressurization control mode. It is possible to release the pressure by displacing it in the direction of its own weight.

In this embodiment, a closed circuit hydraulic pump 12 having a tank 25 for storing hydraulic oil, a prime mover 9, two input/output ports capable of discharging in both directions, and driven by the prime mover 9, and a hydraulic cylinder 3 , a bottom side oil passage 91a connecting one input/output port of the closed circuit hydraulic pump 12 and the bottom side oil chamber 3a of the hydraulic cylinder 3, the other input/output port of the closed circuit hydraulic pump 12, and the hydraulic cylinder 3, an operating lever 56a for instructing the operating direction and operating speed of the hydraulic cylinder 3, and the closed circuit hydraulic pressure in response to input from the operating lever 56a. In a construction machine 100 equipped with a controller 57 for controlling the discharge direction and discharge flow rate of hydraulic oil discharged from a pump 12, bottom side discharge oil passages 92a, 93, 94 connecting a bottom side oil passage 91a to a tank 25; , a bleed-off valve 64 as a bottom-side control valve provided in the bottom-side discharge oil passages 92a, 93, 94 and capable of adjusting the flow rate of hydraulic oil discharged from the bottom-side oil chamber 3a to the tank 25; Rod-side discharge oil passages 92b, 93, and 94 connecting the passage 91b to the tank 25, and the flow rate of hydraulic oil provided in the rod-side discharge oil passages 92b, 93, and 94 and discharged from the rod-side oil chamber 3b to the tank 25 a bleed-off valve 64 as a rod-side control valve capable of adjusting a bottom-side makeup oil passage 95a that connects the bottom-side oil passage 91a to the tank 25; A bottom-side makeup check valve 80a that allows hydraulic oil to be sucked into the bottom-side oil chamber 3a, a rod-side makeup oil passage 95b that connects the rod-side oil passage 90b to the tank 25, and a rod-side makeup oil. A rod-side make-up check valve 80b is provided in the passage 95b and enables the intake of hydraulic oil from the tank 25 to the rod-side oil chamber 3b.

Further, construction machine 100 according to the present embodiment includes rotation speed sensor 58 that detects the rotation speed of prime mover 9 , and controller 57 detects the rotation speed of prime mover 9 detected by rotation speed sensor 58 . When it is determined that the prime mover 9 is not in operation and the extension operation of the hydraulic cylinder 3 is instructed via the operation lever 56a, the rod side is extended according to the amount of operation of the operation lever 56a. When the bleed-off valve 64 as a control valve is opened, it is determined that the prime mover 9 is not in operation, and the retraction operation of the hydraulic cylinder 3 is instructed via the operation lever 56a, the operation amount of the operation lever 56a is controlled. to open the bleed-off valve 64 as the bottom side control valve. In this embodiment, the bottom side control valve and the rod side control valve are configured by the single bleed-off valve 64, but the bottom side control valve and the rod side control valve may be provided independently.

According to the construction machine 100 according to the present embodiment configured as described above, when the pressure in the bottom side oil chamber 3a of the hydraulic cylinder 3 is high after the engine is stopped, the retraction operation of the hydraulic cylinder 3 is performed via the operation lever 56a. By instructing, the hydraulic oil from the tank 25 is sucked into the rod-side oil chamber 3b via the rod-side make-up check valve 80b, and the high-pressure hydraulic oil in the bottom-side oil chamber 3a is operated as the bottom-side control valve. It can be discharged to tank 25 via bleed-off valve 64 .

On the other hand, when the rod-side oil chamber 3b of the hydraulic cylinder 3 is at a high pressure after the engine is stopped, by instructing the retraction operation of the hydraulic cylinder 3 via the operation lever 56a, the tank pressure is increased via the bottom-side make-up check valve 80a. 25 is sucked into the bottom-side oil chamber 3a, high-pressure hydraulic oil in the rod-side oil chamber 3b can be discharged to the tank 25 via the bleed-off valve 64 as a rod-side control valve.

As a result, the residual pressure in the closed hydraulic circuit can be quickly released after the engine is stopped, so maintenance work can be started early to shorten the downtime of the construction machine 100, thereby improving the operation rate of the construction machine 100. can do.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the described configurations.

DESCRIPTION OF SYMBOLS 1... Boom cylinder (hydraulic cylinder), 2... Boom, 3... Arm cylinder (hydraulic cylinder), 3a... Bottom side oil chamber, 3b... Rod side oil chamber, 4... Arm, 5... Bucket cylinder (hydraulic cylinder), 6 Bucket 7 Slewing device 8 Traveling device 9 Engine (motor) 10 Power transmission device 11 Charge pump 12 Closed circuit pump (hydraulic pump for closed circuit) 13 Open circuit pump 20... Relief valve, 25... Tank, 35... Flushing valve, 38a, 38b... Make-up check valve, 43b, 44b, 44e... Switching valve, 56a... Left operating lever (operating lever), 56b... Right operating lever (operating lever), 57 controller, 57a control selection unit, 57b normal control unit, 57c depressurization control unit, 58 rotation speed sensor, 64 bleed off valve (bottom side control valve, rod side control valve), 80a Bottom side make-up check valve 80b Rod side make-up check valve 90 Charge line 91a Bottom side oil passage 91b Rod side oil passage 92a Bottom side branch oil passage (bottom side discharge oil 92b... Rod side branch oil passage (rod side discharge oil passage) 93... Discharge oil passage (bottom side discharge oil passage, rod side discharge oil passage) 94... Discharge oil passage (bottom side discharge oil passage, rod side discharge passage) side discharge oil passage), 95a Bottom side makeup oil passage 95b Rod side makeup oil passage 100 Hydraulic excavator (construction machine) 101 Lower running body 102 Upper revolving body 103 Front device 104... A cab.

Claims (2)

a tank that stores hydraulic oil;
a prime mover;
a closed-circuit hydraulic pump having two input/output ports capable of discharging in both directions and driven by the prime mover;
a hydraulic cylinder;
a bottom side oil passage connecting one input/output port of the closed circuit hydraulic pump and a bottom side oil chamber of the hydraulic cylinder;
a rod-side oil passage connecting the other input/output port of the closed-circuit hydraulic pump and the rod-side oil chamber of the hydraulic cylinder;
an operating lever for indicating the operating direction and operating speed of the hydraulic cylinder;
A construction machine comprising a controller for controlling a discharge direction and a discharge flow rate of hydraulic oil discharged from the closed-circuit hydraulic pump according to an input from the operation lever,
an open circuit pump having a discharge port and a suction port connected to the tank;
a discharge oil passage connected to the discharge port;
a bottom-side branch oil passage that branches from the bottom-side oil passage and connects to the discharge oil passage;
a rod-side branch oil passage that branches from the rod-side oil passage and connects to the discharge oil passage;
a bottom side switching valve capable of switching conduction and blocking of the bottom side branched oil passage;
a rod-side switching valve capable of switching between conduction and interruption of the rod-side branch oil passage;
a discharge oil passage connecting the discharge oil passage and the tank;
a bleed-off valve provided in the drain oil passage;
a bottom-side makeup oil passage connecting the bottom-side oil passage to the tank;
a bottom-side make-up check valve provided in the bottom-side make-up oil passage and enabling suction of hydraulic oil from the tank to the bottom-side oil chamber;
a rod-side makeup oil passage connecting the rod-side oil passage to the tank;
A construction machine comprising: a rod-side make-up check valve provided in the rod-side make-up oil passage and allowing hydraulic oil to be sucked from the tank into the rod-side oil chamber. In the construction machine according to claim 1,
A rotation speed sensor that detects the rotation speed of the prime mover,
The controller is
determining whether or not the prime mover is operating based on the revolution speed of the prime mover detected by the revolution speed sensor;
When it is determined that the prime mover is not in operation and an extension operation of the hydraulic cylinder is instructed via the operation lever, the rod-side control valve is opened , and the operation amount of the operation lever is adjusted. to open the bleed-off valve ,
When it is determined that the prime mover is not in operation and the retraction operation of the hydraulic cylinder is instructed via the operation lever, the bottom side control valve is opened , and according to the operation amount of the operation lever. opening the bleed-off valve
A construction machine characterized by:

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