JP2023123027A - Work machine - Google Patents

Abstract

To provide a work machine capable of suppressing deterioration of a closed circuit pump.SOLUTION: A work machine includes a hydraulic actuator, a closed circuit pump connected to the hydraulic actuator by a closed circuit and supplying and discharging working fluid to and from the hydraulic actuator, an opened circuit pump connected to the hydraulic actuator by an opened circuit and supplying the working fluid to the hydraulic actuator, a charge pump, a charge flow channel for guiding the working fluid discharged from the charge pump to the closed circuit, a pressure sensor for detecting a pressure of the charge flow channel, a surplus oil discharge device for discharging the surplus working fluid in the closed circuit to the charge flow channel, and a controller for controlling discharge capacity of the closed circuit pump and the opened circuit pump. The controller determines whether or not the pressure of the charge flow channel detected by the pressure sensor is less than a pressure threshold value, and increases the discharge capacity of the opened circuit pump when the pressure of the charge flow channel detected by the pressure sensor is decreased from the pressure threshold value or more to less than the pressure threshold value.SELECTED DRAWING: Figure 6

Description

The present invention relates to work machines.

In order to make up for the shortage of hydraulic fluid in the closed circuit due to the difference in pressure receiving area between the hydraulic fluid flow path that forms a closed circuit between the hydraulic pump and the hydraulic cylinder and the rod side oil chamber and the bottom side oil chamber of the hydraulic cylinder, A working machine including a charge circuit connected to an oil flow path is known (see Patent Document 1). The charge circuit described in Patent Document 1 has a charge flow path connected to a hydraulic fluid flow path, and a charge pump that discharges hydraulic fluid to the charge flow path. When the pressure becomes lower than the pressure of

JP 2013-174325 A

In the work machine described in Patent Document 1, when the bucket hits hard soil or the like during excavation and the operation of the hydraulic cylinder is restricted, the amount of return oil from the hydraulic cylinder decreases, and the pressure in the hydraulic oil flow path decreases. When the pressure in the hydraulic fluid passage becomes lower than the pressure in the charge passage, the hydraulic fluid is replenished from the charge circuit to the hydraulic fluid passage. There may be cases where the required flow rate is not reached. In this case, the charge channel and the hydraulic fluid channel are put into a negative pressure state, and cavitation is likely to occur. Further, if this is repeated many times, there is a risk that the closed circuit pump will deteriorate over time.

An object of the present invention is to provide a working machine capable of suppressing deterioration of a closed circuit pump.

A work machine according to an aspect of the present invention includes a hydraulic actuator, a closed circuit pump connected to the hydraulic actuator in a closed circuit to supply and discharge working oil to and from the hydraulic actuator, and a closed circuit connected to the hydraulic actuator in an open circuit. an open circuit pump that supplies hydraulic fluid to the hydraulic actuator, a charge pump, a charge flow path that guides the hydraulic fluid discharged from the charge pump to the closed circuit, and a pressure that detects the pressure in the charge flow path. A sensor, a surplus oil discharge device for discharging surplus hydraulic oil in the closed circuit to the charge flow path, and a controller for controlling discharge volumes of the closed circuit pump and the open circuit pump. The controller determines whether the pressure in the charge flow path detected by the pressure sensor is less than a pressure threshold, and determines whether the pressure in the charge flow path detected by the pressure sensor is equal to or higher than the pressure threshold. If the pressure drops below the threshold, the displacement of the open circuit pump is increased.

ADVANTAGE OF THE INVENTION According to this invention, the working machine which can suppress deterioration of a closed-circuit pump can be provided.

FIG. 1 is a side view of a hydraulic excavator shown as an example of a working machine according to a first embodiment of the present invention. FIG. 2 is a diagram showing a hydraulic system mounted on a hydraulic excavator. FIG. 3 is a hardware configuration diagram of the controller. FIG. 4 is a functional block diagram of the controller. FIG. 5 is a diagram showing a first discharge flow rate table and a second discharge flow rate table stored in the nonvolatile memory. FIG. 6 is a flowchart showing an example of flow rate control executed by the controller according to the first embodiment; FIG. 7 is a flowchart showing an example of flow rate control executed by the controller according to the second embodiment. FIG. 8 is a flow chart showing an example of flow rate control executed by a controller according to the third embodiment.

A working machine according to an embodiment of the present invention will be described with reference to the drawings.

<First embodiment>
FIG. 1 is a side view of a hydraulic excavator 100 shown as an example of a working machine according to the first embodiment of the invention. As shown in FIG. 1 , the hydraulic excavator 100 includes a crawler type traveling body 30 , a revolving body (vehicle body) 40 provided to be able to turn relative to the traveling body 30 , and a front working device (hereinafter referred to as a front working device) attached to the revolving body 40 . , working device) 20. In addition to the hydraulic excavator 100, the present invention can be applied to construction machines such as wheel loaders, and various work machines that perform excavation work at construction sites, mining sites, and the like using work devices.

The traveling body 30 is provided with a pair of left and right traveling hydraulic motors (hereinafter referred to as travel motors) 31 . The left and right crawlers are independently driven to rotate by the left and right traveling motors 31 . As a result, the traveling body 30 travels forward or backward.

The revolving body 40 is provided with an operating device for performing various operations of the hydraulic excavator 100 and an operator's cab 41 in which an operator's seat and the like are arranged. The operating devices include an operating device for operating the work device 20 , an operating device for operating the traveling body 30 , and an operating device for operating the revolving body 40 .

In addition, the revolving body 40 is equipped with a prime mover such as an engine, a hydraulic pump driven by the engine, a revolving hydraulic motor (hereinafter referred to as a revolving motor) 42, and the like. The revolving body 40 is revolved rightward or leftward with respect to the traveling body 30 by a revolving motor 42 .

The work device 20 is a multi-joint type work device attached to the revolving structure 40, and includes a plurality of hydraulic actuators (hydraulic cylinders) and a plurality of (three in this embodiment) driven actuators driven by the plurality of hydraulic actuators. It has a target member. The boom 24, the arm 23, and the bucket 22, which are members to be driven, are connected in series. The base end of the boom 24 is rotatably connected to the front part of the revolving body 40 via a boom pin. The base end of the arm 23 is rotatably connected to the tip of the boom 24 via an arm pin. The bucket 22 is rotatably connected to the tip of the arm 23 via a bucket pin.

The boom 24 is rotationally driven by the telescopic motion of a boom cylinder 27, which is a hydraulic cylinder. The arm 23 is rotationally driven by an extension and contraction operation of an arm cylinder 26, which is a hydraulic cylinder. The bucket 22 is rotatably driven by an expansion and contraction operation of a bucket cylinder 25, which is a hydraulic cylinder. The boom cylinder 27 has one end connected to the boom 24 and the other end connected to the frame of the revolving body 40 . The arm cylinder 26 has one end connected to the arm 23 and the other end connected to the boom 24 . The bucket cylinder 25 has one end connected to the bucket 22 via a bucket link and the other end connected to the arm 23 .

FIG. 2 is a diagram showing a hydraulic system 60 mounted on the hydraulic excavator 100. As shown in FIG. The hydraulic system 60 comprises a plurality of hydraulic circuits for driving a plurality of hydraulic actuators (25-27, 31, 42).

In FIG. 2, the hydraulic circuit for driving the arm cylinder 26 is shown, and the hydraulic circuit for driving the other hydraulic actuators (25, 27, 31, 42) is omitted.

The arm cylinder 26 includes a bottomed cylindrical cylinder tube with one end closed, a head cover closing the opening at the other end of the cylinder tube, a cylinder rod 26r passing through the head cover and inserted into the cylinder tube, and the cylinder rod 26r. and a piston 26p that is provided at the tip of the cylinder tube and divides the inside of the cylinder tube into a rod-side oil chamber 26b and a bottom-side oil chamber 26a.

As shown in FIG. 2, the hydraulic system 60 includes a closed circuit pump 1 connected to the arm cylinder 26 via a closed circuit Cc to supply and discharge working oil to and from the arm cylinder 26, and an open circuit Oc to the arm cylinder 26. The open circuit pump 3 connected to supply hydraulic oil to the arm cylinder 26, the operating device 8 instructing the operation of the arm cylinder 26, and the discharge capacity (displacement capacity) of the closed circuit pump 1 and the open circuit pump 3 are controlled. a controller 7;

The operating device 8 is one of operating devices for operating the working device 20 . The discharge capacity is the discharge amount per pump rotation. The closed circuit Cc is a circuit for returning the return oil from the hydraulic actuator to the pump. The open circuit Oc is a circuit that does not return oil from the hydraulic actuator to the pump. For example, the open circuit Oc is a circuit that returns oil from the hydraulic actuator to a tank (not shown).

The hydraulic system 60 includes a first switching valve 15a, a second switching valve 15b, a first relief valve 19a, a second relief valve 19b, a flushing valve 16, a charge circuit 63, a tank 17, an engine 5 and .

The closed circuit pump 1 and the open circuit pump 3 are rotationally driven by the engine 5 and discharge working oil. The engine 5 is a power source of the hydraulic excavator 100, and is configured by an internal combustion engine such as a diesel engine, for example. Hydraulic oil is stored in the tank 17 .

The closed circuit pump 1 is a variable displacement hydraulic pump whose discharge capacity (displacement volume) can be changed. The closed circuit pump 1 is, for example, a swash plate hydraulic pump or a swash shaft hydraulic pump.

The discharge capacity of the closed circuit pump 1 is controlled by a regulator (hereinafter referred to as a first regulator) 2 for the closed circuit pump. The first regulator 2 controls the displacement of the closed circuit pump 1 by controlling the tilting angle of the swash plate or the swash shaft of the closed circuit pump 1 based on the control signal from the controller 7 . The discharge flow rate of the closed circuit pump 1 is determined according to the discharge capacity of the closed circuit pump 1 and the rotational speed of the engine 5 .

The closed circuit pump 1 is a bi-tilting hydraulic pump capable of discharging hydraulic oil in two directions. The closed circuit pump 1 has a first pump port 1a and a second pump port 1b. The closed circuit pump 1 can be switched between a first discharge state and a second discharge state. In the first discharge state, the closed circuit pump 1 sucks working oil from the second pump port 1b and discharges working oil from the first pump port 1a. In the second discharge state, the closed circuit pump 1 sucks working oil from the first pump port 1a and discharges working oil from the second pump port 1b.

The first pump port 1 a of the closed circuit pump 1 and the bottom side oil chamber 26 a of the arm cylinder 26 are connected by a first flow path 61 . A second flow path 62 connects the second pump port 1 b of the closed circuit pump 1 and the rod side oil chamber 26 b of the arm cylinder 26 . In this embodiment, the closed circuit Cc is formed by connecting the closed circuit pump 1 and the arm cylinder 26 by the first flow path 61 and the second flow path 62 .

The open circuit pump 3 is a variable displacement hydraulic pump whose discharge capacity (displacement volume) can be changed. The open circuit pump 3 is, for example, a swash plate hydraulic pump or a swash shaft hydraulic pump.

The discharge capacity of the open circuit pump 3 is controlled by a regulator (hereinafter referred to as a second regulator) 4 for the open circuit pump. The second regulator 4 controls the displacement of the open circuit pump 3 by controlling the tilt angle of the swash plate or the swash shaft of the open circuit pump 3 based on the control signal from the controller 7 . The discharge flow rate of the open circuit pump 3 is determined according to the discharge capacity of the open circuit pump 3 and the rotation speed of the engine 5 .

The open circuit pump 3 is a unidirectional hydraulic pump capable of discharging hydraulic oil in one direction. The open circuit pump 3 has a pump port 3a and a suction port 3b. The open circuit pump 3 sucks the hydraulic oil in the tank 17 from the suction port 3b and discharges it from the pump port 3a.

The pump port 3a of the open circuit pump 3 is connected to the first flow path 61 via the first switching valve 15a. Also, the pump port 3a of the open circuit pump 3 is connected to the second flow path 62 via the second switching valve 15b.

The first switching valve 15a and the second switching valve 15b are, for example, 2-port 2-position electromagnetic switching valves. The first switching valve 15a and the second switching valve 15b are switched between the open position and the closed position based on the control signal from the controller 7. FIG. The first switching valve 15a and the second switching valve 15b are switched to the closed position by the urging force of the spring when not energized.

When the first switching valve 15a is switched to the open position, the discharge flow path of the open circuit pump 3 and the first flow path 61 communicate with each other via the first switching valve 15a. When the first switching valve 15a is switched to the closed position, communication between the discharge flow path of the open circuit pump 3 and the first flow path 61 is blocked by the first switching valve 15a.

When the second switching valve 15b is switched to the open position, the discharge flow path of the open circuit pump 3 and the second flow path 62 communicate with each other via the second switching valve 15b. When the second switching valve 15b is switched to the closed position, communication between the discharge flow path of the open circuit pump 3 and the second flow path 62 is blocked by the second switching valve 15b.

The first relief valve 19 a is connected to the first flow path 61 and regulates the maximum pressure of the first flow path 61 . The second relief valve 19 b is connected to the second flow path 62 and regulates the maximum pressure of the second flow path 62 .

The charge circuit 63 includes the charge pump 9, a charge flow path 11 that guides the hydraulic oil discharged from the charge pump 9 to the closed circuit Cc through the first makeup valve 66a or the second makeup valve 66b, and the charge flow path 11. and a charge relief valve 65 that defines a maximum pressure.

The charge pump 9 is a fixed displacement hydraulic pump having a constant discharge displacement. Charge pump 9 is, for example, a gear pump. The charge pump 9 is driven by the engine 5 and sucks and discharges hydraulic oil in the tank 17 .

The set pressure of the charge relief valve 65 is set to approximately 2 MPa, for example. The charge relief valve 65 discharges the surplus hydraulic oil discharged from the charge pump 9 to the tank 17 and maintains the pressure of the charge flow path 11 at 2 MPa.

A pump port 9 a of the charge pump 9 is connected to the charge flow path 11 , and a suction port 9 b of the charge pump 9 is connected to the tank 17 .

The charge flow path 11 is connected to the first flow path 61 via a first make-up valve 66a. The first make-up valve 66 a is a check valve that allows hydraulic fluid to flow from the charge flow path 11 to the first flow path 61 and prohibits hydraulic fluid to flow from the first flow path 61 to the charge flow path 11 . be.

Also, the charge flow path 11 is connected to the second flow path 62 via the second make-up valve 66b. The second make-up valve 66b is a check valve that allows hydraulic fluid to flow from the charge flow path 11 to the second flow path 62 and prohibits hydraulic fluid to flow from the second flow path 62 to the charge flow path 11. be.

The charge pump 9 sucks hydraulic oil from the tank 17 and discharges the hydraulic oil to the charge flow path 11 . Hydraulic oil discharged from the charge pump 9 to the charge flow path 11 replenishes the closed circuit Cc through the first makeup valve 66a or the second makeup valve 66b.

The flushing valve 16 is connected to the first flow path 61, the second flow path 62, and the charge flow path 11, and discharges surplus hydraulic fluid (hereinafter also referred to as surplus oil) in the closed circuit Cc to the charge flow path 11. Excess oil discharge device.

The flushing valve 16 communicates the high-pressure side of the first flow path 61 and the second flow path 62 with the charge flow path 11 . When the pressure in the first flow path 61 is higher than the pressure in the second flow path 62, the flushing valve 16 moves in the first direction D1, and the first flow path 61 and the charge flow path 11 are in contact with the flushing valve 16. Communicate via. When the pressure in the second flow path 62 is higher than the pressure in the first flow path 61, the flushing valve 16 moves in the second direction D2, and the second flow path 62 and the charge flow path 11 are in contact with the flushing valve 16. Communicate via.

The operation device 8 has a tiltable operation lever 8b and an operation amount sensor 8a that detects the operation amount (tilt angle) of the operation lever 8b. The manipulated variable sensor 8 a is electrically connected to the controller 7 . The operation amount sensor 8a detects the amount of operation of the operation lever 8b and outputs a signal representing the detection result to the controller 7. FIG.

A pressure sensor 10 , a first regulator 2 , a second regulator 4 , a first switching valve 15 a and a second switching valve 15 b are electrically connected to the controller 7 . The pressure sensor 10 detects the pressure (hereinafter also referred to as charge pressure) Pc of the charge flow path 11 and outputs a signal representing the detection result to the controller 7 . The controller 7 outputs control signals to the first regulator 2 and the second regulator 4 as well as the first switching valve 15a and the second switching valve 15b based on the detection results of the operation amount sensor 8a and the pressure sensor 10 .

FIG. 3 is a hardware configuration diagram of the controller 7. As shown in FIG. As shown in FIG. 3, the controller 7 includes a processing device 71 such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), DSP (Digital Signal Processor), ROM (Read Only Memory), flash memory, hard disk drive, etc. A non-volatile memory 72, a volatile memory 73 called RAM (Random Access Memory), an input interface 74, an output interface 75, and a computer equipped with other peripheral circuits. Note that the controller 7 may be composed of one computer, or may be composed of a plurality of computers. As the processing device 71, an ASIC (application specific integrated circuit), an FPGA (Field Programmable Gate Array), or the like can be used.

The nonvolatile memory 72 stores programs capable of executing various calculations. In other words, the non-volatile memory 72 is a storage medium that can read a program that implements the functions of this embodiment.

The processing device 71 develops the program stored in the nonvolatile memory 72 in the volatile memory 73 and executes calculations. The processing unit 71 performs predetermined arithmetic processing on signals received from the input interface 74, the nonvolatile memory 72 and the volatile memory 73 according to a program.

The input interface 74 converts signals input from various devices (manipulated variable sensor 8a, pressure sensor 10, etc.) into data that can be calculated by the processing device 71 . In addition, the output interface 75 generates a signal for output according to the calculation result of the processing device 71, and outputs the signal to various devices (first switching valve 15a, second switching valve 15b, first regulator 2, second switching valve 15b). regulator 4, etc.).

FIG. 4 is a functional block diagram of the controller 7. As shown in FIG. As shown in FIG. 4, the controller 7 executes a program stored in the nonvolatile memory 72 to perform a target supply flow rate calculation section 101, a target discharge flow rate calculation section 102, a valve control section 103, a determination section 104, It functions as a correction unit 105 and a pump control unit 106 .

In addition, below, for convenience of explanation, the case where the rotational speed of the engine 5 is a constant value will be explained. As described above, the discharge flow rates of the closed circuit pump 1 and the open circuit pump 3 are determined by the discharge capacity and the rotation speed of the engine 5 . The controller 7 controls the discharge flow rate of the closed circuit pump 1 and the open circuit pump 3 by controlling the discharge capacity of the closed circuit pump 1 and the open circuit pump 3 .

The target supply flow rate calculation unit 101 calculates a target value for the flow rate of hydraulic oil to be supplied to the arm cylinder 26 (hereinafter referred to as target supply flow rate) based on the manipulated variable detected by the manipulated variable sensor 8a.

The nonvolatile memory 72 stores a supply flow rate table that defines the relationship between the manipulated variable and the target supply flow rate. The supply flow rate table defines supply flow rate characteristics in which the target supply flow rate increases as the manipulated variable increases.

The target supply flow rate calculator 101 refers to the supply flow rate table stored in the nonvolatile memory 72 and calculates the target supply flow rate based on the manipulated variable detected by the manipulated variable sensor 8a.

The target discharge flow rate calculation unit 102 calculates a target flow rate Q1, which is the target value of the discharge flow rate of the closed circuit pump 1, and the discharge flow rate of the open circuit pump 3, based on the target supply flow rate calculated by the target supply flow rate calculation unit 101. A target flow rate Q2 which is a target value of is calculated.

The nonvolatile memory 72 stores a first discharge flow rate table and a second discharge flow rate table shown in FIG. The first discharge flow rate table defines the relationship between the target supply flow rate and the target flow rate Q1. The second discharge flow rate table defines the relationship between the target supply flow rate and the target flow rate Q2.

The first discharge flow rate table defines discharge flow rate characteristics in which the target flow rate Q1 increases as the target supply flow rate increases in the range of the target supply flow rate from 0 to a predetermined value Ft. In the second discharge flow rate table, the target flow rate Q2 is 0 when the target supply flow rate is less than the predetermined value Ft, and when the target supply flow rate is equal to or higher than the predetermined value Ft, the target flow rate Q2 increases as the target supply flow rate increases. stipulates. That is, the arm cylinder 26 (hydraulic actuator to be operated) is driven by the hydraulic fluid discharged from the closed circuit pump 1 when the target supply flow rate is in the range from 0 to the predetermined value Ft. On the other hand, when the target supply flow rate is equal to or greater than the predetermined value Ft, the arm cylinder 26 is driven by hydraulic fluid (total flow rate) discharged from both the closed circuit pump 1 and the open circuit pump 3 .

The target discharge flow rate calculation unit 102 refers to the first discharge flow rate table stored in the nonvolatile memory 72, and calculates the target flow rate of the closed circuit pump 1 based on the target supply flow rate calculated by the target supply flow rate calculation unit 101. Compute Q1. The target discharge flow rate calculation unit 102 refers to the second discharge flow rate table stored in the nonvolatile memory 72, and calculates the target flow rate of the open circuit pump 3 based on the target supply flow rate calculated by the target supply flow rate calculation unit 101. Compute Q2.

As shown in FIG. 4, the valve control unit 103 identifies the operating direction of the operating lever 8b based on the detection result of the operating amount sensor 8a.

The valve control unit 103 outputs an ON signal to the first switching valve 15a and an OFF signal to the second switching valve 15b when the operating direction of the control lever 8b is the arm cloud direction. As a result, the first switching valve 15a is positioned at the open position, and the second switching valve 15b is positioned at the closed position.

When the operating direction of the operating lever 8b is the arm dumping direction, the valve control unit 103 outputs an ON signal to the second switching valve 15b and an OFF signal to the first switching valve 15a. As a result, the second switching valve 15b is positioned at the open position, and the first switching valve 15a is positioned at the closed position.

The ON signal corresponds to a control signal (control current) for energizing the solenoids of the first switching valve 15a and the second switching valve 15b to switch to the open position. The off signal is a control signal (control current) corresponding to standby current.

The determination unit 104 determines whether or not the charge pressure Pc detected by the pressure sensor 10 is less than the pressure threshold value Pc0. The pressure threshold Pc0 is, for example, equal to or lower than the set pressure of the charge relief valve 65, and is set to an arbitrary value equal to or higher than the pressure at which cavitation does not occur in the closed circuit pump 1.

The charge pressure Pc drops when the closed circuit cannot be replenished with hydraulic oil from the charge circuit 63 . The determination unit 104 monitors the detection result of the pressure sensor 10 and detects that the charge pressure Pc has decreased from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0. That is, the determination unit 104 has a function of detecting, based on the detection result of the pressure sensor 10, that the closed circuit cannot be replenished with hydraulic oil from the charge circuit 63.

When the determination unit 104 determines that the charge pressure Pc is less than the pressure threshold value Pc0, the correction unit 105 adjusts the corrected target flow rate Q2c based on the target flow rate Q1 of the closed circuit pump 1 and the discharge flow rate Q3 of the charge pump 9. Calculate.

In this embodiment, the corrected target flow rate Q2c is calculated by the following equation (1).
Q2c=Q1-Q3 (1)
Q1 is the target flow rate of the closed circuit pump 1 calculated by the target discharge flow rate calculator 102, and Q3 is the discharge flow rate of the charge pump 9. As shown in FIG. The discharge flow rate Q3 of the charge pump 9 is stored in the nonvolatile memory 72. FIG.

The pump control unit 106 outputs to the first regulator 2 a control signal for setting the discharge flow rate of the closed circuit pump 1 to the target flow rate Q1 calculated by the target discharge flow rate calculation unit 102 . That is, the pump control unit 106 controls the discharge capacity of the closed circuit pump 1 via the first regulator 2 so that the discharge flow rate of the closed circuit pump 1 becomes the target flow rate Q1.

When the determination unit 104 determines that the charge pressure Pc is equal to or higher than the pressure threshold value Pc0, the pump control unit 106 sets the discharge flow rate of the open circuit pump 3 to the target flow rate Q2 calculated by the target discharge flow rate calculation unit 102. to the second regulator 4 . That is, the pump control unit 106 controls the discharge capacity of the open circuit pump 3 via the second regulator 4 so that the discharge flow rate of the open circuit pump 3 becomes the target flow rate Q2.

When the determination unit 104 determines that the charge pressure Pc is less than the pressure threshold value Pc0, the pump control unit 106 controls the discharge flow rate of the open circuit pump 3 to the corrected target flow rate Q2c calculated by the correction unit 105. A signal is output to the second regulator 4 . That is, the pump control unit 106 controls the discharge capacity of the open circuit pump 3 via the second regulator 4 so that the discharge flow rate of the open circuit pump 3 becomes the corrected target flow rate Q2c.

When the charge pressure Pc drops from the pressure threshold Pc0 or higher to less than the pressure threshold Pc0, the pump control unit 106 increases the discharge capacity of the open circuit pump 3 compared to before the charge pressure Pc drops below the pressure threshold Pc0. As a result, the discharge flow rate of the open circuit pump 3 increases.

When the charge pressure Pc rises from less than the pressure threshold Pc0 to the pressure threshold Pc0 or more, the pump control unit 106 reduces the discharge capacity of the open circuit pump 3 compared to before the charge pressure Pc rises to the pressure threshold Pc0 or more. . As a result, the discharge flow rate of the open circuit pump 3 is reduced.

An example of flow rate control performed by the controller 7 will be described with reference to FIG. The process shown in the flowchart of FIG. 6 is started when an ignition switch (not shown) is turned on, and after initial setting (not shown) is performed, it is repeatedly executed at a predetermined control cycle.

As shown in FIG. 6, in step S110, the target supply flow rate calculation unit 101 calculates the target supply flow rate to the arm cylinder 26 based on the operation amount detected by the operation amount sensor 8a, and operates the operation lever 8b. After specifying the direction, the process proceeds to step S115.

In step S115, the target discharge flow rate calculation unit 102 calculates the target flow rate Q1 of the closed circuit pump 1 and the target flow rate Q2 of the open circuit pump 3 based on the target supply flow rate calculated in step S110, and the process proceeds to step S120. move on.

In step S120, the determination unit 104 determines whether or not the charge pressure Pc detected by the pressure sensor 10 is less than the pressure threshold value Pc0. If it is determined in step S120 that the charge pressure Pc is equal to or higher than the pressure threshold value Pc0, the process proceeds to step S125, and if it is determined that the charge pressure Pc is less than the pressure threshold value Pc0, the process proceeds to step S130.

In step S<b>125 , the pump control unit 106 outputs a control signal corresponding to the target flow rate Q<b>2 calculated in step S<b>115 to the second regulator 4 of the open circuit pump 3 .

Also, although not shown, in step S125, the valve control unit 103 outputs a control signal corresponding to the operation direction specified in step S110 to the first switching valve 15a and the second switching valve 15b. After completing the process of step S125, the controller 7 proceeds to step S140.

In step S130, the correction unit 105 subtracts the discharge flow rate Q3 of the charge pump 9 stored in the nonvolatile memory 72 from the target flow rate Q1 of the closed circuit pump 1 calculated in step S115. It is calculated as the corrected target flow rate Q2c, and the process proceeds to step S135.

In step S<b>135 , the pump control unit 106 outputs a control signal corresponding to the corrected target flow rate Q<b>2 c calculated in step S<b>130 to the second regulator 4 of the open circuit pump 3 .

Further, although not shown, in step S135, the valve control unit 103 outputs a control signal corresponding to the operation direction specified in step S110 to the first switching valve 15a and the second switching valve 15b. After completing the process of step S135, the controller 7 proceeds to step S140.

In step S140, the pump control unit 106 outputs a control signal corresponding to the target flow rate Q1 calculated in step S115 to the first regulator 2 of the closed circuit pump 1, and performs the processing shown in the flowchart of FIG. 6 in this control cycle. finish. That is, when the process of step S140 ends, the process of step S110 in the next control cycle is executed.

An example of the operation of the hydraulic excavator 100 according to this embodiment will be described. For convenience of explanation, specific numerical values are described and explained, but these numerical values are only examples. The discharge flow rate of the charge pump 9 is 30 [L/min]. 0 [MPa].

When the operator operates the operating device 8 of the arm 23 toward the arm cloud side in order to excavate with the excavator 100, the controller 7 calculates the target supply flow rate.

The controller 7 calculates a target flow rate Q1 for the closed circuit pump 1 and a target flow rate Q2 for the open circuit pump 3 based on the target supply flow rate. The controller 7 outputs control signals corresponding to the calculation results to the first regulator 2 and the second regulator 4 .

The controller 7 also outputs an ON signal to the first switching valve 15a to switch the first switching valve 15a to the open position. The controller 7 outputs an OFF signal to the second switching valve 15b to hold the second switching valve 15b at the closed position.

Here, for example, when the target supply flow rate is 100 [L/min], the target flow rate Q1 of the closed circuit pump 1 is 80 [L/min], and the target flow rate Q2 of the open circuit pump 3 is 20 [L/min] will be explained. When the charge pressure Pc detected by the pressure sensor 10 is equal to or higher than the pressure threshold value Pc0, the controller 7 sets the discharge flow rate of the closed circuit pump 1 to 80 [L/min] and the discharge flow rate of the open circuit pump 3 to 20 [L/min]. min], the first regulator 2 and the second regulator 4 are controlled.

When the flow rate of the hydraulic oil supplied to the bottom side oil chamber 26a of the arm cylinder 26 is 100 [L/min], the pressure receiving area difference between the bottom side oil chamber 26a and the rod side oil chamber 26b causes the rod side oil chamber 26b to The flow rate of hydraulic oil discharged from is 70 [L/min]. Note that the flow rate of hydraulic oil supplied to the charge flow path 11 from the closed circuit Cc through the flushing valve 16 is 0 [L/min].

The required flow rate of hydraulic oil returning to the closed circuit pump 1 is 80 [L/min], which is the same as the discharge flow rate. Therefore, of the hydraulic fluid discharged from the charge pump 9, 10 [L/min] of hydraulic fluid is supplied from the charge flow path 11 to the second flow path 62 through the second make-up valve 66b. Of the hydraulic fluid discharged from the charge pump 9 , the remaining 20 [L/min] of hydraulic fluid that is not refilled into the second flow path 62 is discharged from the charge relief valve 65 to the tank 17 .

Hydraulic oil is supplied to the bottom side oil chamber 26a of the arm cylinder 26 and is discharged from the rod side oil chamber 26b, whereby the arm cylinder 26 extends. The extension speed of the arm cylinder 26 is determined by the flow rate of hydraulic oil supplied to the bottom side oil chamber 26a and the pressure receiving area of the bottom side oil chamber 26a. As the arm cylinder 26 extends, the arm 23 moves to the arm cloud side, and the bucket 22 excavates the earth and sand.

During excavation, if the bucket 22 contacts hard soil, the crowding motion of the arm 23 is restricted. For example, the crowding motion of the arm 23 slows down or stops. When the extension operation of the arm cylinder 26 is restricted, the flow rate of hydraulic fluid discharged from the rod-side oil chamber 26b to the second flow path 62 is reduced.

For example, when the crowding operation of the arm 23 stops, the flow rate of hydraulic oil discharged from the rod-side oil chamber 26b to the second flow path 62 becomes 0 [L/min]. The discharge flow rate of the charge pump 9 is 30 [L/min]. Note that in the present embodiment, hydraulic fluid discharged from the open circuit pump 3 to the first flow path 61 is guided to the charge flow path 11 through the flushing valve 16 .

However, if the discharge flow rate of the open circuit pump 3 remains at 20 [L/min], the return oil to the closed circuit pump 1 will be the discharge flow rate of 30 [L/min] of the charge pump 9 and the Combined with the discharge flow rate of 20 [L/min], the result is 50 [L/min], which is less than the required flow rate of return oil to the closed circuit pump 1 of 80 [L/min].

If the return oil to the closed circuit pump 1 is insufficient, the pressure on the return side of the closed circuit pump 1 temporarily becomes negative, causing cavitation, which may deteriorate the closed circuit pump 1 . In addition, if the return oil to the closed circuit pump 1 is insufficient, there is a possibility that the flow rate necessary for lubricating the movable parts such as the gears and bearings of the closed circuit pump 1 cannot be secured temporarily. As a result, the movable portion may be dented and deteriorated.

When the pressure in the charge flow path 11 and the second flow path 62 decreases due to insufficient return oil to the closed circuit pump 1, the pressure difference between the bottom side oil chamber 26a and the rod side oil chamber 26b of the arm cylinder 26 increases. . As a result, the cylinder thrust force of the arm cylinder 26 increases and the operation feeling changes.

Furthermore, when the cylinder thrust increases, the load acting on the connecting portion between the members to be driven of the working device 20 also increases. For this reason, the stress generated in the welded portion or the like of the connection portion between the members to be driven of the working device 20 increases, and the life of the connection portion may be shortened.

Therefore, in order to prevent these problems from occurring, the controller 7 according to the present embodiment increases the discharge flow rate of the open circuit pump 3 to compensate for the shortage of return oil to the closed circuit pump 1 . Specifically, when the charge pressure Pc drops from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0 due to the restricted operation of the arm cylinder 26, the controller 7 reduces the discharge flow rate of the open circuit pump 3. increase.

When the operation of the arm cylinder 26 is forcibly stopped due to the bucket 22 coming into contact with hard soil, the pressure difference between the bottom side oil chamber 26a and the rod side oil chamber 26b causes the flushing valve 16 to open. is switched to the first direction D1. As a result, the first flow path 61 and the charge flow path 11 communicate with each other via the flushing valve 16 . Therefore, the hydraulic oil discharged from the open circuit pump 3 is led to the charge flow path 11 through the flushing valve 16 as surplus oil.

The flow rate of the hydraulic oil guided from the charge flow path 11 to the second flow path 62 through the second make-up valve 66b is 30 [L/min] discharged from the charge pump 9 and 20 [L/min] discharged from the open circuit pump 3. min] is added to 50 [L/min]. Therefore, the shortage of return oil to the closed circuit pump 1 is 30 [L/min] (=80 [L/min]-50 [L/min]). The controller 7 increases the discharge flow rate of the open circuit pump 3 by 30 [L/min], which is the shortage, in order to equalize the flow rate on the discharge side and the suction side of the closed circuit pump 1 .

Specifically, the controller 7 subtracts the discharge flow rate Q3=30 [L/min] of the charge pump 9 from the target flow rate Q1=80 [L/min] of the closed circuit pump 1, and sets the corrected target flow rate Q2c=50. Calculate as [L/min]. The corrected target flow rate Q2c is a value obtained by adding the insufficient hydraulic oil flow rate of 30 [L/min] (=Q1-(Q2+Q3)) to the target flow rate of the open circuit pump 3 of 20 [L/min] (=Q2). It corresponds to 50 [L/min] (=Q2c).

The controller 7 controls the second regulator 4 so that the discharge flow rate of the open circuit pump 3 becomes the corrected target flow rate Q2c=50 [L/min]. In other words, the controller 7 increases the discharge flow rate of the open circuit pump 3 by the amount of the insufficient hydraulic oil flow rate.

As a result, the flow rate of the hydraulic oil guided from the charge flow path 11 to the second flow path 62 through the second make-up valve 66b is 30 [L/min] of the discharge flow rate of the charge pump 9 and 50 [L/min] of the discharge flow rate of the open circuit pump 3. [L/min] is added to 80 [L/min]. As a result, the required flow rate of the return oil of the closed circuit pump 1 is ensured. As the discharge flow rate of the open circuit pump 3 increases, the pressure in the charge flow path 11 recovers to the set pressure.

According to the embodiment described above, the following effects are obtained.

(1) A hydraulic excavator (working machine) 100 includes an arm cylinder (hydraulic actuator) 26 and a closed circuit pump 1 connected to the arm cylinder 26 via a closed circuit Cc to supply and discharge hydraulic oil to and from the arm cylinder 26. , an open circuit pump 3 which is connected to the arm cylinder 26 by an open circuit Oc to supply hydraulic oil to the arm cylinder 26, a charge pump 9, and a charge flow path which guides the hydraulic oil discharged from the charge pump 9 to the closed circuit Cc. 11, a pressure sensor 10 that detects a charge pressure Pc that is the pressure in the charge passage 11, a flushing valve (excess oil discharge device) 16 that discharges excess hydraulic oil in the closed circuit Cc to the charge passage 11, and a closed valve. and a controller 7 for controlling the discharge volumes of the circuit pump 1 and the open circuit pump 3 .

The controller 7 determines whether or not the charge pressure Pc detected by the pressure sensor 10 is less than the pressure threshold value Pc0 (step S120 in FIG. 6). The controller 7 repeats the determination process (step S120) at a predetermined control cycle, and detects that the charge pressure Pc has decreased from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0 when the negative determination changes to the positive determination. do. The controller 7 increases the discharge capacity of the open circuit pump 3 when the charge pressure Pc detected by the pressure sensor 10 drops from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0 (steps S130 and S135 in FIG. 6). As a result, the flow rate of hydraulic oil discharged from the open circuit pump 3 increases.

In this configuration, when the movement of the arm cylinder 26 is restricted due to the bucket 22 contacting hard soil during excavation, the discharge flow rate of the open circuit pump 3 is increased, and the return oil of the closed circuit pump 1 is insufficient. can be prevented. As a result, it is possible to prevent cavitation and galling due to insufficient return oil of the closed circuit pump 1 .

Therefore, according to the present embodiment, it is possible to provide the hydraulic excavator (working machine) 100 capable of suppressing deterioration of the closed circuit pump 1 due to cavitation and erosion.

(2) Further, according to the present embodiment, it is possible to prevent a change in the cylinder thrust of the arm cylinder 26 due to insufficient return oil of the closed circuit pump 1 . As a result, it is possible to prevent a change in operation feeling.

(3) Furthermore, according to the present embodiment, by preventing an increase in the cylinder thrust of the arm cylinder 26 due to the shortage of the return oil of the closed circuit pump 1, the connection between the members to be driven of the working device 20, etc. It is possible to suppress an increase in the load on As a result, it is possible to prevent the life of the work device 20 from being shortened.

(4) When the charge pressure Pc detected by the pressure sensor 10 decreases from the pressure threshold value Pc0 or more to less than the pressure threshold value, the controller 7 maintains the discharge flow rate of the closed circuit pump 1 and increases the discharge capacity of the open circuit pump 3. to increase With this configuration, the arm cylinder 26 can be driven at the operating speed required by the operator immediately after excavating hard soil.

(5) When the charge pressure Pc detected by the pressure sensor 10 decreases from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0, the controller 7 changes the discharge flow rate of the closed circuit pump 1 from the target value (target flow rate) Q1 to the charge pump The target value (corrected target flow rate) Q2c of the discharge flow rate of the open circuit pump 3 is calculated by subtracting the discharge flow rate Q3 from 9 (step S130 in FIG. 6). The controller 7 controls the discharge capacity of the open circuit pump 3 based on the calculated target value (corrected target flow rate) Q2c of the discharge flow rate of the open circuit pump 3 (step S135 in FIG. 6). As a result, the required flow rate of the return oil to the closed circuit pump 1 can be appropriately ensured, so deterioration of the closed circuit pump 1 can be effectively suppressed.

(6) By the way, the charge circuit 63 may leak hydraulic oil due to aged deterioration. In this case, since the pressure in the charge flow path 11 decreases, there is a risk that the replenishment flow rate of hydraulic oil from the charge flow path 11 to the closed circuit Cc will be insufficient. In this embodiment, when the pressure in the charge flow path 11 is lowered, the return oil can be replenished to the closed circuit Cc by increasing the discharge flow rate of the open circuit pump 3 .

Therefore, according to the present embodiment, even if hydraulic oil leaks from the charge circuit 63 due to deterioration over time, it is possible to properly replenish the closed circuit Cc with return oil. As a result, similar to (1) above, deterioration of the closed circuit pump 1 due to cavitation and erosion can be suppressed. Also, as in the case of (2) above, it is possible to prevent changes in the operational feeling. Furthermore, similarly to (3) above, the reduction in the life of the working device 20 can be suppressed.

<Second embodiment>
A hydraulic excavator 100 according to a second embodiment of the present invention will be described with reference to FIG. The same reference numerals are given to the same or corresponding configurations as those described in the first embodiment, and the differences will be mainly described.

In the first embodiment, when the charge pressure Pc decreases from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0, the controller 7 maintains the discharge capacity (tilt angle) of the closed circuit pump 1 and causes the open circuit pump 3 to discharge. Increase capacity (tilt angle).

In contrast, in the second embodiment, when the charge pressure Pc drops from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0, the controller 7 increases the discharge capacity (tilt angle) of the open circuit pump 3 and closes the circuit. Decrease the discharge capacity (tilt angle) of the pump 1 . Details of control by the controller 7 according to the second embodiment will be described below.

FIG. 7 is similar to FIG. 6 and is a flow chart showing an example of flow rate control executed by the controller 7 according to the second embodiment. In the flowchart of FIG. 7, the processes of steps S223 to S246 are executed instead of the processes of steps S125 to S140 of the flowchart of FIG.

As shown in FIG. 7, in step S120, the determination unit 104 determines whether or not the charge pressure Pc detected by the pressure sensor 10 is less than the pressure threshold value Pc0. If it is determined in step S120 that the charge pressure Pc is equal to or higher than the pressure threshold value Pc0, the process proceeds to step S223, and if it is determined that the charge pressure Pc is less than the pressure threshold value Pc0, the process proceeds to step S233.

In step S223, the pump control unit 106 outputs a control signal corresponding to the target flow rate Q1 calculated in step S115 to the first regulator 2 of the closed circuit pump 1, and proceeds to step S226.

In step S<b>226 , the pump control unit 106 outputs a control signal corresponding to the target flow rate Q<b>2 calculated in step S<b>115 to the second regulator 4 of the open circuit pump 3 .

Also, although not shown, in step S226, the valve control unit 103 outputs a control signal corresponding to the operation direction specified in step S110 to the first switching valve 15a and the second switching valve 15b.

After finishing the process of step S226, the controller 7 finishes the process shown in the flowchart of FIG. 7 in this control cycle.

In step S233, the correction unit 105 calculates the adjustment flow rate Qa based on the target flow rate Q1 and the target flow rate Q2 calculated in step S115 and the discharge flow rate Q3 of the charge pump 9. FIG. The adjusted flow rate Qa is calculated by the following equation (2).
Qa=[Q1-(Q2+Q3)]/2 (2)
After the adjustment flow rate Qa is calculated, the process proceeds to step S236.

In step S236, the correction unit 105 calculates a corrected target flow rate Q1c based on the target flow rate Q1 calculated in step S115 and the adjusted flow rate Qa calculated in step S233. The corrected target flow rate Q1c is calculated by the following equation (3).
Q1c=Q1-Qa (3)
After the corrected target flow rate Q1c is calculated, the process proceeds to step S239.

In step S239, the correction unit 105 calculates a corrected target flow rate Q2c based on the target flow rate Q2 calculated in step S115 and the adjusted flow rate Qa calculated in step S233. The corrected target flow rate Q2c is calculated by the following equation (4).
Q2c=Q2+Qa (4)
After the corrected target flow rate Q2c is calculated, the process proceeds to step S243.

In step S243, the pump control unit 106 outputs a control signal corresponding to the corrected target flow rate Q1c calculated in step S236 to the first regulator 2 of the closed circuit pump 1, and proceeds to step S246.

In step S<b>246 , the pump control unit 106 outputs a control signal corresponding to the corrected target flow rate Q<b>2 c calculated in step S<b>236 to the second regulator 4 of the open circuit pump 3 .

Also, although not shown, in step S246, the valve control unit 103 outputs a control signal corresponding to the operation direction specified in step S110 to the first switching valve 15a and the second switching valve 15b.

After finishing the process of step S246, the controller 7 finishes the process shown in the flowchart of FIG. 7 in this control cycle.

An example of the operation of the hydraulic excavator 100 according to this embodiment will be described. For convenience of explanation, specific numerical values are described and explained, but these numerical values are only examples. As in the first embodiment, the discharge flow rate of the charge pump 9 is 30 [L/min], the pressure receiving area ratio of the bottom side oil chamber 26a and the rod side oil chamber 26b of the arm cylinder 26 is 1:0.7, and the charge relief valve The set pressure of 65 is assumed to be 2.0 [MPa]. Further, as in the first embodiment, when the target supply flow rate is calculated to be 100 [L/min], the target flow rate Q1 to be 80 [L/min], and the target flow rate Q2 to be 20 [L/min] during excavation. Next, the operation when the bucket 22 comes into contact with hard soil will be described.

When the charge pressure Pc drops from the pressure threshold Pc0 to less than the pressure threshold Pc0, the controller 7 according to the first embodiment increases the discharge capacity of the open circuit pump 3 while maintaining the discharge capacity of the closed circuit pump 1. Let On the other hand, the controller 7 according to the second embodiment increases the discharge capacity of the open circuit pump 3 and increases the discharge capacity of the closed circuit pump 1 when the charge pressure Pc decreases from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0. Decrease capacity.

When the operation of the arm cylinder 26 is forcibly stopped due to the bucket 22 coming into contact with hard soil, the pressure difference between the bottom side oil chamber 26a and the rod side oil chamber 26b causes the flushing valve 16 to open. is switched to the first direction D1. As a result, the first flow path 61 and the charge flow path 11 communicate with each other via the flushing valve 16 . Therefore, the hydraulic oil discharged from the open circuit pump 3 is led to the charge flow path 11 through the flushing valve 16 as surplus oil.

The flow rate of the hydraulic oil guided from the charge flow path 11 to the second flow path 62 through the second make-up valve 66b is 30 [L/min] discharged from the charge pump 9 and 20 [L/min] discharged from the open circuit pump 3. min] is added to 50 [L/min]. Therefore, the shortage of return oil to the closed circuit pump 1 is 30 [L/min] (=80 [L/min]-50 [L/min]). The controller 7 increases the discharge flow rate of the open circuit pump 3 by 15 [L/min] (=30 [L/min]/2) in order to equalize the discharge rate and suction rate of the closed circuit pump 1. At the same time, the discharge flow rate of the closed circuit pump 1 is decreased by 15 [L/min] (=30 [L/min]/2).

Specifically, the controller 7 calculates half of the insufficient flow rate of hydraulic fluid 30 [L/min] as the adjusted flow rate Qa. The controller 7 calculates a value obtained by adding the adjusted flow rate Qa=15 [L/min] to the target flow rate Q2=20 [L/min] of the open circuit pump 3 as the corrected target flow rate Q2c=35 [L/min]. In addition, the controller 7 calculates a value obtained by subtracting the adjusted flow rate Qa=15 [L/min] from the target flow rate Q1=80 [L/min] of the closed circuit pump 1 as the corrected target flow rate Q1c=65 [L/min]. do.

The controller 7 controls the first regulator 2 so that the discharge flow rate of the closed circuit pump 1 becomes the corrected target flow rate Q1c=65 [L/min]. The controller 7 controls the second regulator 4 so that the discharge flow rate of the open circuit pump 3 becomes the corrected target flow rate Q2c=35 [L/min].

As a result, the flow rate of the hydraulic oil guided from the charge flow path 11 to the second flow path 62 through the second make-up valve 66b is 30 [L/min] of the discharge flow rate of the charge pump 9 and 35 [L/min] of the discharge flow rate of the open circuit pump 3. [L/min] is added to 65 [L/min]. Since the discharge flow rate of the closed circuit pump 1 is reduced to 65 [L/min], the required flow rate of the return oil of the closed circuit pump 1 is ensured.

As described above, the controller 7 according to the second embodiment increases the discharge capacity of the open circuit pump 3 and closes it when the charge pressure Pc detected by the pressure sensor 10 decreases from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0. The discharge capacity of the circuit pump 1 is decreased (steps S233, S236, S239, S243, S246 in FIG. 7).

According to such a second embodiment, the same effects as (1) to (3) and (6) described in the first embodiment can be obtained. Furthermore, according to the second embodiment, the following effect (7) can be obtained.

(7) When the charge pressure Pc detected by the pressure sensor 10 decreases from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0, the controller 7 controls the sum of the discharge flow rate of the closed circuit pump 1 and the discharge flow rate of the open circuit pump 3. is maintained, the discharge capacity of the open circuit pump 3 is increased and the discharge capacity of the closed circuit pump 1 is decreased (steps S233, S236, S239, S243, S246 in FIG. 7).

In the first embodiment, the total value (100 [L/min]) of the discharge flow rate (80 [L/min]) of the closed circuit pump 1 and the discharge flow rate (20 [L/min]) of the open circuit pump 3 before the above determination ]), and the total value (130 [L/min]) of the discharge flow rate of the closed circuit pump 1 (80 [L / min]) and the discharge flow rate of the open circuit pump 3 (50 [L / min]) after the above determination was different. Therefore, in the first embodiment, there is a risk that a shock will occur in the operation of the work device 20 after excavating hard soil.

On the other hand, according to the second embodiment, the sum of the discharge flow rate of the closed circuit pump 1 (80 [L/min]) and the discharge flow rate of the open circuit pump 3 (20 [L/min]) before the determination value (100 [L/min]) and the sum of the discharge flow rate of the closed circuit pump 1 (65 [L/min]) and the discharge flow rate of the open circuit pump 3 (35 [L/min]) after the above determination ( 100 [L/min]). Therefore, it is possible to prevent a shock from occurring in the operation of the work device 20 after excavating hard soil.

<Third Embodiment>
A hydraulic excavator 100 according to a third embodiment of the present invention will be described with reference to FIG. The same reference numerals are given to the same or corresponding configurations as those described in the first embodiment, and the differences will be mainly described.

In the first embodiment, when the charge pressure Pc decreases from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0, the controller 7 maintains the discharge capacity (tilt angle) of the closed circuit pump 1 and causes the open circuit pump 3 to discharge. Increase capacity (tilt angle).

In contrast, in the third embodiment, when the charge pressure Pc drops from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0, the controller 7 maintains the discharge capacity (tilt angle) of the open circuit pump 3 and closes it. The discharge capacity (tilting angle) of the circuit pump 1 is decreased. Details of control by the controller 7 according to the third embodiment will be described below.

FIG. 8 is similar to FIG. 6 and is a flow chart showing an example of flow rate control executed by the controller 7 according to the third embodiment. In the flowchart of FIG. 8, the processes of steps S325 to S340 are executed instead of the processes of steps S125 to S140 of the flowchart of FIG.

As shown in FIG. 8, in step S120, the determination unit 104 determines whether or not the charge pressure Pc detected by the pressure sensor 10 is less than the pressure threshold value Pc0. If it is determined in step S120 that the charge pressure Pc is equal to or greater than the pressure threshold value Pc0, the process proceeds to step S325, and if it is determined that the charge pressure Pc is less than the pressure threshold value Pc0, the process proceeds to step S330.

In step S325, the pump control unit 106 outputs a control signal corresponding to the target flow rate Q1 calculated in step S115 to the first regulator 2 of the closed circuit pump 1, and proceeds to step S340.

In step S330, the correction unit 105 adds the discharge flow rate Q3 of the charge pump 9 stored in the nonvolatile memory 72 to the target flow rate Q2 of the open circuit pump 3 calculated in step S115. It is calculated as the corrected target flow rate Q1c, and the process proceeds to step S335.

In step S335, the pump control unit 106 outputs a control signal corresponding to the corrected target flow rate Q1c calculated in step S330 to the first regulator 2 of the closed circuit pump 1, and proceeds to step S340.

In step S<b>340 , the pump control unit 106 outputs a control signal corresponding to the target flow rate Q<b>2 calculated in step S<b>115 to the second regulator 4 of the open circuit pump 3 .

Further, although not shown, in step S340, the valve control unit 103 outputs a control signal corresponding to the operation direction specified in step S110 to the first switching valve 15a and the second switching valve 15b.

After finishing the process of step S340, the controller 7 finishes the process shown in the flowchart of FIG. 8 in this control cycle.

An example of the operation of the hydraulic excavator 100 according to this embodiment will be described. For convenience of explanation, specific numerical values are described and explained, but these numerical values are only examples. As in the first embodiment, the discharge flow rate of the charge pump 9 is 30 [L/min], the pressure receiving area ratio of the bottom side oil chamber 26a and the rod side oil chamber 26b of the arm cylinder 26 is 1:0.7, and the charge relief valve The set pressure of 65 is assumed to be 2.0 [MPa]. Further, as in the first embodiment, when the target supply flow rate is calculated to be 100 [L/min], the target flow rate Q1 to be 80 [L/min], and the target flow rate Q2 to be 20 [L/min] during excavation. Next, the operation when the bucket 22 comes into contact with hard soil will be described.

The controller 7 adds the target flow rate Q2=20 [L/min] of the open circuit pump 3 and the target flow rate Q3=30 [L/min] of the charge pump 9 to the corrected target flow rate Q1c=50 [L/min]. ]. The corrected target flow rate Q1c is a value obtained by subtracting the insufficient hydraulic oil flow rate of 30 [L/min] (=Q1-(Q2+Q3)) from the target flow rate of the closed circuit pump 1 of 80 [L/min] (=Q1). It corresponds to 50 [L/min] (=Q1c).

The controller 7 controls the first regulator 2 so that the discharge flow rate of the closed circuit pump 1 becomes the corrected target flow rate Q1c=50 [L/min]. That is, the controller 7 reduces the discharge flow rate of the closed circuit pump 1 by the shortage of the flow rate of the hydraulic fluid. As a result, the flow rate of the return oil of the closed circuit pump 1, which is the total value of the discharge flow rate of the open circuit pump 3 and the discharge flow rate of the charge pump 9, and the discharge flow rate of the closed circuit pump 1 are matched. no more shortage of return oil.

As described above, the controller 7 according to the third embodiment reduces the displacement of the closed circuit pump 1 when the charge pressure Pc detected by the pressure sensor 10 decreases from the pressure threshold Pc0 or more to less than the pressure threshold Pc0.

According to such a third embodiment, the same effects as (1) to (3) and (6) described in the first embodiment can be obtained. Furthermore, according to the third embodiment, the following effect (8) can be obtained.

(8) When the charge pressure Pc detected by the pressure sensor 10 decreases from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0, the controller 7 sets the discharge flow rate of the open circuit pump 3 to a target value (target flow rate) Q2. 9 is calculated as a target value (correction target flow rate) Q1c of the discharge flow rate of the closed circuit pump 1. The controller 7 controls the discharge capacity of the closed circuit pump 1 based on the calculated target value (correction target flow rate) Q1c of the discharge flow rate of the closed circuit pump 1 . As a result, the required flow rate of the return oil to the closed circuit pump 1 can be appropriately ensured, so deterioration of the closed circuit pump 1 can be effectively suppressed.

The following modifications are also within the scope of the invention.

<Modification 1>
In the first embodiment, when it is determined that the charge pressure Pc detected by the pressure sensor 10 is less than the pressure threshold value Pc0, the controller 7 subtracts the discharge flow rate of the charge pump 9 from the target flow rate of the closed circuit pump 1. Although an example in which the value is calculated as the target flow rate of the open circuit pump 3 has been described, the present invention is not limited to this.

The target flow rate of the open circuit pump 3 may be set to a lower value than in the first embodiment within a range in which deterioration due to insufficient return oil of the closed circuit pump 1 is unlikely to occur. Also, in the first embodiment, the controller 7 may slightly decrease the discharge flow rate of the closed circuit pump 1 .

<Modification 2>
In the second embodiment, the amount of increase in the target flow rate of the open circuit pump 3 when the charge pressure Pc detected by the pressure sensor 10 decreases from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0, and the target flow rate of the closed circuit pump 1 Although the example in which the amount of decrease in is the same has been described, the present invention is not limited to this. Within a range in which deterioration caused by insufficient return oil of the closed circuit pump 1 is unlikely to occur, the amount of increase in the target flow rate of the open circuit pump 3 and the amount of decrease in the target flow rate of the closed circuit pump 1 must match. good too.

<Modification 3>
In the third embodiment, when the charge pressure Pc detected by the pressure sensor 10 drops from the pressure threshold value Pc0 or more to less than the pressure threshold value Pc0, a value obtained by adding the discharge flow rate of the charge pump 9 to the target flow rate of the open circuit pump 3 is Although an example of calculating the target flow rate of the closed circuit pump 1 has been described, the present invention is not limited to this.

The target flow rate of the closed circuit pump 1 may be set to a higher value than in the third embodiment within a range in which deterioration due to insufficient return oil of the closed circuit pump 1 is unlikely to occur. Also, in the third embodiment, the controller 7 may slightly increase the discharge flow rate of the open circuit pump 3 .

<Modification 4>
In the first embodiment, the correction unit 105 calculates the corrected target flow rate Q2c when the determination unit 104 determines that the charge pressure Pc is less than the pressure threshold value Pc0. However, the present invention is limited to this. not. For example, the process of step S130 in FIG. 6 may be performed between steps S115 and S120. That is, the correction unit 105 may always calculate the corrected target flow rate Q2c.

<Modification 5>
In the second embodiment, the correction unit 105 calculates the corrected target flow rates Q1c and Q2c when the determination unit 104 determines that the charge pressure Pc is less than the pressure threshold value Pc0. is not limited to For example, the processing of steps S233, S236, and S239 in FIG. 7 may be performed between steps S115 and S120. That is, the correction unit 105 may always calculate the corrected target flow rates Q1c and Q2c.

<Modification 6>
In the third embodiment, the correction unit 105 calculates the corrected target flow rate Q1c when the determination unit 104 determines that the charge pressure Pc is less than the pressure threshold value Pc0. However, the present invention is limited to this. not. For example, the process of step S330 in FIG. 8 may be performed between steps S115 and S120. That is, the correction unit 105 may always calculate the corrected target flow rate Q1c.

<Modification 7>
In the above embodiment, an example in which the first switching valve 15a and the second switching valve 15b are electromagnetic switching valves has been described, but the present invention is not limited to this. The hydraulic system 60 includes a first electromagnetic proportional valve capable of adjusting the flow rate of hydraulic oil discharged from the open circuit pump 3 and guiding it to the closed circuit Cc instead of the first switching valve 15a and the second switching valve 15b. and a second electromagnetic proportional valve.

<Modification 8>
In the above embodiment, an example in which the first switching valve 15a and the second switching valve 15b are separately provided has been described, but the present invention is not limited to this. The hydraulic system 60 may include one spool valve having the functions of the first switching valve 15a and the second switching valve 15b instead of the first switching valve 15a and the second switching valve 15b.

<Modification 9>
In the above-described embodiment, the flow rate control when the operation of the arm cylinder 26 is restricted has been described, but the present invention is not limited to this. The hydraulic circuits of the boom cylinder 27 and the bucket cylinder 25 are configured in the same manner as the hydraulic circuit of the arm cylinder 26, and the controller 7 controls the flow rate in the hydraulic circuits of the boom cylinder 27 and the bucket cylinder 25 in the same manner as in the above embodiment. may

Also, the hydraulic actuator is not limited to a hydraulic cylinder. For example, the controller 7 may perform the same flow rate control as in the above embodiment when the charge pressure is reduced due to the restricted operation of a hydraulic motor such as the turning motor 42 .

Although the embodiments of the present invention have been described above, the above embodiments merely show a part of application examples of the present invention, and the technical scope of the present invention is not limited to the specific configurations of the above embodiments. do not have.

The above-described embodiments and modifications are exemplified for easy understanding and description of the present invention, and are not necessarily limited to those having all the described configurations. Also, part of the configuration of one embodiment or modification can be replaced with the configuration of another embodiment or modification, and the configuration of one embodiment or modification can be replaced with another embodiment or modification. Additional configuration is also possible. It should be noted that the control lines and information lines shown in the drawings are those considered to be necessary for explanation, and do not necessarily show all the control lines and information lines necessary on the product. In fact, it may be considered that almost all configurations are interconnected.

REFERENCE SIGNS LIST 1 closed circuit pump 2 first regulator 3 open circuit pump 4 second regulator 5 engine 7 controller 8 operation device 8a operation amount sensor 8b operation lever 9 Charge pump 10 Pressure sensor 11 Charge flow path 15a First switching valve 15b Second switching valve 16 Flushing valve (excess oil discharge device) 17 Tank 20 Working device 22 Bucket 23 arm 24 boom 25 bucket cylinder (hydraulic actuator) 26 arm cylinder (hydraulic actuator) 26a bottom side oil chamber 26b rod side oil chamber 27 boom cylinder (hydraulic actuator) , 30... Traveling body 31... Traveling motor (hydraulic actuator) 40... Revolving body (vehicle body) 42... Revolving motor (hydraulic actuator) 60... Hydraulic system 61... First flow path 62... Second flow path , 63... Charge circuit, 65... Charge relief valve, 66a... First make-up valve, 66b... Second make-up valve, 71... Processing unit, 72... Non-volatile memory, 73... Volatile memory, 74... Input interface, 75... Output interface 100... Hydraulic excavator (working machine) 101... Target supply flow rate calculation unit 102... Target discharge flow rate calculation unit 103... Valve control unit 104... Judgment unit 105... Correction unit 106... Pump control part, Cc... Closed circuit, Oc... Open circuit

Claims (7)

a hydraulic actuator, a closed circuit pump connected to the hydraulic actuator in a closed circuit to supply and discharge working oil to and from the hydraulic actuator, and a closed circuit pump connected to the hydraulic actuator in an open circuit to supply working oil to the hydraulic actuator. an open circuit pump, a charge pump, a charge flow path that guides hydraulic oil discharged from the charge pump to the closed circuit, and a controller that controls the discharge volumes of the closed circuit pump and the open circuit pump. in the working machine,
a pressure sensor that detects the pressure in the charge channel;
a surplus oil discharge device for discharging surplus hydraulic oil in the closed circuit to the charge flow path,
The controller is
determining whether the pressure in the charge flow path detected by the pressure sensor is less than a pressure threshold;
A working machine, wherein the discharge capacity of the open circuit pump is increased when the pressure in the charge flow path detected by the pressure sensor drops from the pressure threshold value or more to less than the pressure threshold value. The work machine according to claim 1,
The controller discharges the open circuit pump while maintaining the discharge capacity of the closed circuit pump when the pressure in the charge flow path detected by the pressure sensor decreases from the pressure threshold value or more to less than the pressure threshold value. A work machine characterized by increasing capacity. The work machine according to claim 1,
The controller is
When the pressure in the charge flow path detected by the pressure sensor decreases from the pressure threshold value or more to less than the pressure threshold value, a value obtained by subtracting the discharge flow rate of the charge pump from the target value of the discharge flow rate of the closed circuit pump is calculated. Calculate as a target value of the discharge flow rate of the open circuit pump,
A working machine, wherein the discharge capacity of the open circuit pump is controlled based on the calculated target value of the discharge flow rate of the open circuit pump. The work machine according to claim 1,
The controller increases the discharge capacity of the open circuit pump and increases the discharge capacity of the closed circuit pump when the pressure in the charge flow path detected by the pressure sensor decreases from the pressure threshold value or more to less than the pressure threshold value. A working machine characterized by reducing In the working machine according to claim 4,
When the pressure in the charge flow path detected by the pressure sensor decreases from the pressure threshold value or more to less than the pressure threshold value, the controller controls the total value of the discharge flow rate of the closed circuit pump and the discharge flow rate of the open circuit pump. A working machine, wherein the displacement of the open circuit pump is increased and the displacement of the closed circuit pump is decreased so as to maintain the a hydraulic actuator, a closed circuit pump connected to the hydraulic actuator in a closed circuit to supply and discharge working oil to and from the hydraulic actuator, and a closed circuit pump connected to the hydraulic actuator in an open circuit to supply working oil to the hydraulic actuator. an open circuit pump, a charge pump, a charge flow path that guides hydraulic oil discharged from the charge pump to the closed circuit, and a controller that controls the discharge volumes of the closed circuit pump and the open circuit pump. in the working machine,
a pressure sensor that detects the pressure in the charge channel;
a surplus oil discharge device for discharging surplus hydraulic oil in the closed circuit to the charge flow path,
The controller is
determining whether the pressure in the charge flow path detected by the pressure sensor is less than a pressure threshold;
A working machine, wherein the discharge capacity of the closed circuit pump is reduced when the pressure in the charge flow path detected by the pressure sensor drops from the pressure threshold value or more to less than the pressure threshold value. The work machine according to claim 6,
The controller is
When the pressure in the charge flow path detected by the pressure sensor drops from the pressure threshold value or more to less than the pressure threshold value, a value obtained by adding the discharge flow rate of the charge pump to the target value of the discharge flow rate of the open circuit pump is calculated. Calculate as a target value of the discharge flow rate of the closed circuit pump,
A working machine, wherein the discharge capacity of the closed circuit pump is controlled based on the calculated target value of the discharge flow rate of the closed circuit pump.

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