JP6081288B2 - Hydraulic system for construction machinery - Google Patents

Description

  The present invention relates to a hydraulic system mounted on a construction machine.

  2. Description of the Related Art Conventionally, there is known a hydraulic circuit for a construction machine that relieves shaking of a machine body and shock to an operator when a hydraulic actuator of the construction machine is suddenly operated (see, for example, Patent Document 1).

  The hydraulic device includes a sensor that detects a hydraulic pressure downstream of a direction switching valve that controls a flow of hydraulic oil to the hydraulic actuator, a negative regulator that controls a discharge amount of the hydraulic pump according to the detected hydraulic pressure, and a negative An electromagnetic proportional pressure reducing valve that generates a secondary pressure for driving the regulator. And this hydraulic apparatus delays the response of a negative regulator by changing suitably the secondary pressure of an electromagnetic proportional pressure reducing valve based on the output of a sensor. In this way, the hydraulic device increases the discharge amount of the hydraulic pump to the discharge amount corresponding to the hydraulic pressure detected by the sensor after the hydraulic actuator has moved to some extent, and when the hydraulic actuator is suddenly operated. Relieve shaking of the aircraft and shock to the operator.

Japanese Utility Model Publication No. 5-64506

  However, the hydraulic circuit of Patent Document 1 only delays the increase in the discharge amount of the hydraulic pump when the hydraulic actuator is suddenly operated, and after a certain time has elapsed, the discharge amount corresponding to the hydraulic pressure detected by the sensor. The discharge amount is increased until. For this reason, even when the discharge pressure of the hydraulic pump reaches the relief pressure of the relief valve when the hydraulic actuator is driven, the hydraulic oil is not prevented from being discharged from the relief valve.

  In view of the above-described points, an object of the present invention is to provide a hydraulic system for a construction machine that can reduce the amount of hydraulic oil released from a relief valve when operating a hydraulic actuator.

  In order to achieve the above object, a hydraulic system for construction machinery according to an embodiment of the present invention includes a flow control valve that controls a flow of hydraulic oil discharged from a hydraulic pump to a hydraulic actuator, the flow control valve, A relief valve installed between the hydraulic actuator, an operation content detection unit for detecting an operation content of an operation lever related to the hydraulic actuator, a discharge pressure detection unit for detecting a discharge pressure of the hydraulic pump, and the operation content detection And a controller that controls the discharge amount of the hydraulic pump in response to the output of the discharge pressure detection unit, and the controller operates the operation lever, and the discharge pressure of the hydraulic pump is equal to or higher than a predetermined pressure. In this case, the discharge pressure of the hydraulic pump is higher than the cracking pressure of the relief valve and less than the relief pressure of the relief valve. While maintaining the pressure, the discharge rate of the hydraulic pump to increase up to the target pump flow rate corresponding to the operation amount of the operation lever, and controls the discharge amount of the hydraulic pump.

  With the above-described means, the present invention can provide a hydraulic system for a construction machine that can reduce the amount of hydraulic oil released from the relief valve when operating the hydraulic actuator.

It is a figure which shows the structural example of the shovel carrying the hydraulic system for construction machines which concerns on the Example of this invention. It is a circuit diagram of the hydraulic system for construction machines concerning the example of the present invention. It is a negative control chart showing the relationship between the pump flow rate and the negative control pressure. It is a horsepower control diagram (PQ diagram) showing the relationship between pump flow rate and pump discharge pressure. It is the schematic which shows the structural example of a turning hydraulic circuit. FIG. 6 is a diagram (part 1) illustrating a relationship between a swing hydraulic circuit internal pressure and a swing relief flow rate. It is a block diagram which shows the flow of turning speed control. It is a block diagram which shows the structural example of a controller. It is a flowchart which shows the flow of an electric current command output process. It is a state transition diagram between action operation | movement, transition operation | movement, and stop operation | movement. It is a flowchart which shows the flow of action operation | movement. It is a flowchart which shows the flow of transition operation | movement. It is a flowchart which shows the flow of stop operation | movement. It is a figure which shows the relationship between the excessive flow volume at the time of performing rotation relief cut control, and a pump discharge pressure. It is a figure which shows the relationship between the turning consumption flow volume and pump flow volume when the moment of inertia of an upper turning body is small. It is a figure which shows the relationship between the turning consumption flow volume and pump flow volume when the inertia moment of an upper turning body is large. FIG. 6 is a diagram (part 2) illustrating a relationship between a swing hydraulic circuit internal pressure and a swing relief flow rate.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration example of an excavator on which a construction machine hydraulic system according to an embodiment of the present invention is mounted. In FIG. 1, an excavator 1 as a construction machine has an upper swing body 3 mounted on a crawler-type lower traveling body 2 via a swing mechanism so as to be rotatable around the X axis.

  Further, the upper swing body 3 includes a drilling attachment in the front center portion. The excavation attachment includes a boom 4, an arm 5, and a bucket 6, and includes a boom cylinder 7, an arm cylinder 8, and a bucket cylinder 9 as hydraulic actuators.

  FIG. 2 is a circuit diagram of a hydraulic system for construction machines according to an embodiment of the present invention. The construction machine hydraulic system 100 is driven by a drive source such as an engine or an electric motor. The hydraulic pumps 10L and 10R (hereinafter sometimes collectively referred to as “hydraulic pump 10”. The same applies to the constituent elements of (1). The hydraulic pump 10L is a variable displacement pump that can vary the discharge amount per rotation (cc / rev). The hydraulic pump 10L circulates the hydraulic oil to the hydraulic oil tank 22 through the center bypass conduit 30L that communicates the flow control valves 11L, 12L, 13L, and 15L. Similarly, the hydraulic pump 10R circulates the hydraulic oil to the hydraulic oil tank 22 through the center bypass conduit 30R that communicates the flow control valves 12R, 13R, 14R, and 15R.

  The flow control valve 11L is a spool valve that switches the flow of hydraulic oil to supply the hydraulic oil discharged from the hydraulic pump 10L to the traveling hydraulic motor 42L as a hydraulic actuator.

  The flow control valve 12L is a spool valve that switches the flow of hydraulic oil in order to supply the hydraulic oil discharged from the hydraulic pump 10L to the turning hydraulic motor 44 as a hydraulic actuator. The flow rate control valve 12R is a spool valve that switches the flow of hydraulic oil in order to supply the hydraulic oil discharged from the hydraulic pump 10R to the traveling hydraulic motor 42R.

  The flow control valves 13L and 13R supply hydraulic oil discharged from the hydraulic pumps 10L and 10R to the boom cylinder 7 as a hydraulic actuator, and discharge the hydraulic oil in the boom cylinder 7 to the hydraulic oil tank 22, respectively. It is a spool valve that switches the flow of hydraulic oil. The flow control valve 13 </ b> R is a spool valve that supplies hydraulic oil discharged from the hydraulic pump 10 </ b> R to the boom cylinder 7 when a boom operation lever as an operation device is operated. The flow control valve 13L is a spool valve that additionally supplies hydraulic oil discharged from the hydraulic pump 10L to the boom cylinder 7 when the boom operation lever is operated at a predetermined lever operation amount or more.

  The flow rate control valve 14 </ b> R is a spool valve for supplying hydraulic oil discharged from the hydraulic pump 10 </ b> R to the bucket cylinder 9 as a hydraulic actuator and discharging hydraulic oil in the bucket cylinder 9 to the hydraulic oil tank 22.

  The flow control valves 15L and 15R supply hydraulic oil discharged from the hydraulic pumps 10L and 10R to the arm cylinder 8 as a hydraulic actuator, and discharge hydraulic oil in the arm cylinder 8 to the hydraulic oil tank 22. Therefore, it is a spool valve that switches the flow of hydraulic oil. The flow control valve 15L is a spool valve that supplies hydraulic oil discharged from the hydraulic pump 10L to the arm cylinder 8 when an arm operation lever as an operation device is operated. The flow control valve 15R is a spool valve that additionally supplies hydraulic oil discharged from the hydraulic pump 10R to the arm cylinder 8 when the arm operation lever is operated at a predetermined lever operation amount or more.

  The center bypass pipes 30L and 30R are respectively provided with negative control throttles 20L and 20R between the flow control valves 15L and 15R on the most downstream side and the hydraulic oil tank 22 (hereinafter, negative control is abbreviated as “negative control”). To do.) The negative control throttles 20L and 20R generate a negative control pressure upstream of the negative control throttles 20L and 20R by restricting the flow of hydraulic oil discharged from the hydraulic pumps 10L and 10R.

  The pressure sensors S1 and S2 detect the negative control pressure generated upstream of the negative control throttles 20L and 20R, and output the detected value to the controller 54 as an electrical negative control pressure signal. The pressure sensors S3 and S4 detect the discharge pressures of the hydraulic pumps 10L and 10R, and output the detected values to the controller 54 as electrical discharge pressure signals.

  The controller 54 is a functional element that controls the hydraulic system 100. For example, the controller 54 is a computer having a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), an NVRAM (Non Volatile RAM), and the like. is there.

  In this embodiment, the controller 54 has various operation devices based on the output of a pilot pressure sensor as an operation content detection unit that measures pilot pressure generated when various operation devices such as an arm operation lever and a boom operation lever are operated. The operation details (for example, presence or absence of lever operation, lever operation direction, lever operation amount, etc.) are electrically detected. However, the operation content detection unit may be configured using a sensor other than the pilot pressure sensor, such as an inclination sensor for detecting the inclination of various operation levers.

  Then, the controller 54 causes the CPU to execute programs corresponding to various functional elements that operate the electromagnetic valves 55L, 55R and the like according to the operation contents of the various operation devices.

  The electromagnetic valves 55L and 55R are valves that operate according to a command output from the controller 54. In the present embodiment, the electromagnetic valves 55L and 55R adjust the control pressure introduced from the control pump 52 to the pressure receiving chambers 612L and 612R of the discharge amount control units 61L and 61R in accordance with the current command output from the controller 54. It is a valve.

  The pump regulator 40L is a drive mechanism that controls the discharge amount of the hydraulic pump 10L, and mainly includes a tilt actuator 41L, a spool valve mechanism 60L, a discharge amount control unit 61L, and a feedback lever 62L.

  The tilt actuator 41L is a functional element that tilts and drives a swash plate (yoke) for changing the pump capacity of the hydraulic pump 10L. Specifically, the tilt actuator 41L includes a working piston 410L having a large diameter pressure receiving part PR1 at one end and a small diameter pressure receiving part PR2 at the other end, a pressure receiving chamber 411L corresponding to the large diameter pressure receiving part PR1, and a small diameter pressure receiving part. And a pressure receiving chamber 412L corresponding to the part PR2. The discharge pressure of the hydraulic pump 10L is introduced into the pressure receiving chamber 411L via the spool valve 600L, or the hydraulic oil is discharged from the pressure receiving chamber 411L via the spool valve 600L. Further, the discharge pressure of the hydraulic pump 10L is introduced into the pressure receiving chamber 412L. When the working oil is introduced into the pressure receiving chamber 411L and displaced toward the pressure receiving chamber 412L, the working piston 410L tilts and drives the swash plate (yoke) of the hydraulic pump 10L to the small flow rate side. Further, when the working oil is discharged from the pressure receiving chamber 411L and displaced toward the pressure receiving chamber 411L, the operating piston 410L drives the swash plate (yoke) of the hydraulic pump 10L to tilt toward the large flow rate.

  The spool valve mechanism 60L is a functional element for supplying and discharging hydraulic oil to and from the tilt actuator 41L, and includes a spool valve 600L and a spring 601L. The spool valve 600L has a first port into which the discharge pressure of the hydraulic pump 10L is introduced, a second port that communicates with the hydraulic oil tank 22, and an output port that communicates with the pressure receiving chamber 411L. The spool valve 600L has a first position where the first port communicates with the output port, a second position where the second port communicates with the output port, or both the first port and the second port serve as output ports. It is selectively switched to a neutral position that does not communicate. The spring 601L applies a force that acts in a direction to displace the spool valve 600L to the second position.

  The discharge amount control unit 61L is a functional element for displacing the spool valve 600L. Specifically, the discharge amount control unit 61L includes a servo piston 610L, a spring 611L, and a pressure receiving chamber 612L. The servo piston 610L moves in a direction to displace the spool valve 600L to the first position according to the control pressure generated by the electromagnetic valve 55L. The spring 611L applies a force acting in a direction to return the servo piston 610L against the control pressure generated by the electromagnetic valve 55L. The pressure receiving chamber 612L corresponds to the pressure receiving portion PR3 provided in the servo piston 610L, and hydraulic oil is introduced from the control pump 52 through the electromagnetic valve 55L.

  The feedback lever 62L is a link mechanism for feeding back the displacement of the tilting actuator 41L to the spool valve 600L. Specifically, when the operating piston 410L moves, the feedback lever 62L physically feeds back the movement amount to the spool valve 600L to return the spool valve 600L to the neutral position.

  The above description relates to the pump regulator 40L, but the same applies to the pump regulator 40R.

  With the above configuration, the pump regulators 40L and 40R reduce the discharge amount of the hydraulic pumps 10L and 10R as the control pressure introduced into the discharge amount control units 61L and 61R increases. The pump regulators 40L and 40R increase the discharge amounts of the hydraulic pumps 10L and 10R as the control pressure introduced into the discharge amount control units 61L and 61R is smaller.

  FIG. 2 shows a state where none of the hydraulic actuators in the excavator 1 is used. Hereinafter, this state is referred to as “standby mode”. In the standby mode, the hydraulic oil discharged from the hydraulic pumps 10L and 10R passes through the center bypass pipes 30L and 30R to the negative control throttles 20L and 20R, and increases the negative control pressure generated upstream of the negative control throttles 20L and 20R.

  As a result, the pump regulators 40L and 40R displace the spool valves 600L and 600R to the first position in accordance with a command generated by the controller 54 based on the negative control pressure signal. The spool valves 600L and 600R drive the tilting actuators 41L and 41R to reduce the discharge amounts of the hydraulic pumps 10L and 10R. As a result, pressure loss (pumping loss) when hydraulic oil discharged from the hydraulic pumps 10L and 10R passes through the center bypass pipes 30L and 30R is suppressed.

  On the other hand, when any hydraulic actuator in the excavator 1 is operated, the hydraulic oil discharged from the hydraulic pumps 10L and 10R flows into the hydraulic actuator via the flow control valve corresponding to the hydraulic actuator. Therefore, the amount reaching the negative control throttles 20L and 20R decreases or disappears, and the negative control pressure generated upstream of the negative control throttles 20L and 20R decreases.

  As a result, the pump regulators 40L and 40R increase the discharge amount of the hydraulic pumps 10L and 10R, circulate sufficient hydraulic oil to each hydraulic actuator, and ensure the driving of each actuator.

  FIG. 3 is a negative control diagram showing the relationship between the discharge amount of the hydraulic pump 10 (hereinafter referred to as “pump flow rate”) and the negative control pressure, with the pump flow rate on the vertical axis and the negative control pressure on the horizontal axis. Arrange. As described above, the pump control line represented by the solid line shows a tendency that the pump flow rate increases as the negative control pressure decreases. Note that FIG. 3 omits the illustration of the relationship between the negative control pressure and the pump flow rate in the standby mode. However, in practice, when the negative control pressure is lower than the predetermined pressure in the standby mode, the pump flow rate is limited to the minimum flow rate.

  Hereinafter, the control of the pump flow rate based on the negative control pressure as described above is referred to as “negative control”. With the negative control, the hydraulic system 100 can suppress wasteful energy consumption in the standby mode. This is because the hydraulic oil discharged from the hydraulic pumps 10L and 10R can suppress the pumping loss generated in the center bypass pipelines 30L and 30R. Further, when operating various hydraulic actuators, the hydraulic system 100 can supply necessary and sufficient hydraulic fluid from the hydraulic pumps 10L and 10R to the various hydraulic actuators.

  The hydraulic system 100 executes horsepower control in parallel with the negative control. The horsepower control is a control for reducing the pump flow rate in accordance with an increase in the discharge pressure of the hydraulic pump 10 (hereinafter referred to as “pump discharge pressure”) so that the absorption horsepower of the hydraulic pump 10 does not exceed the output horsepower of the engine. is there.

  FIG. 4 is a horsepower control diagram (PQ diagram) showing the relationship between the pump flow rate and the pump discharge pressure, where the vertical axis represents the pump flow rate and the horizontal axis represents the pump discharge pressure. The horsepower control line represented by a solid line shows a tendency that the pump flow rate increases as the pump discharge pressure decreases.

  Next, a turning hydraulic circuit 200 constituting a part of the hydraulic system 100 mounted on the excavator of FIG. 1 will be described with reference to FIG. FIG. 5 is a schematic diagram illustrating a configuration example of the swing hydraulic circuit 200.

  As shown in FIG. 5, the swing hydraulic circuit 200 mainly includes a swing hydraulic motor 44, swing relief valves 71L and 71R, and check valves 72L and 72R.

  The turning hydraulic motor 44 turns the upper turning body 3 through a turning mechanism including a mechanical brake 80 and a speed reducer 81. In the present embodiment, the output torque of the turning hydraulic motor 44 is amplified by a speed reducer 81 configured by a two-stage planetary gear mechanism. Further, the rotation of the output shaft of the turning hydraulic motor 44 is braked by a mechanical brake 80 including a plurality of brake disks and a plurality of brake plates sandwiching each brake disk.

  Further, the first port 44L of the turning hydraulic motor 44 is connected to the first port 12P1 of the flow control valve 12L via the conduit 70L, and the second port 44R of the turning hydraulic motor 44 is connected to the conduit 70R. Through the second port 12P2 of the flow control valve 12L.

  The swing relief valves 71L and 71R are valves that limit the pressure of hydraulic oil in the pipe lines 70R and 70L (hereinafter referred to as “swing hydraulic circuit internal pressure”) to a predetermined swing relief pressure or less. In this embodiment, the swing relief valves 71L and 71R are electromagnetic relief valves that can electrically adjust the swing relief pressure, and change the swing relief pressure in accordance with a control command from the controller 54. However, the swing relief valves 71L and 71R may be mechanical relief valves in which the swing relief pressure is fixedly set by a spring or the like.

  Specifically, the swing relief valve 71L is partially opened when the internal pressure of the swing hydraulic circuit in the pipe line 70L reaches the cracking pressure, and the hydraulic oil in the pipe line 70L passes through the pipe line 73. The outflow to the tank 22 is started. Further, the swing relief valve 71L is fully opened when the internal pressure of the swing hydraulic circuit in the pipe 70L reaches the swing relief pressure, and the swing relief valve 71L operates in the pipe 70L so that the internal pressure of the swing hydraulic circuit does not excessively exceed the swing relief pressure. Oil flows out to the hydraulic oil tank 22. Similarly, the swing relief valve 71R is partially opened when the internal pressure of the swing hydraulic circuit of the pipe line 70R reaches the cracking pressure, and the hydraulic oil tank 22 of the hydraulic oil in the pipe line 70R via the pipe line 73 is opened. Let the spill begin. Further, the swing relief valve 71R is fully opened when the internal pressure of the swing hydraulic circuit in the pipeline 70R reaches the swing relief pressure, and the swing relief valve 71R operates in the pipeline 70R so that the internal pressure of the swing hydraulic circuit does not excessively exceed the swing relief pressure. Oil flows out to the hydraulic oil tank 22.

  FIG. 6 is a diagram showing the relationship between the internal pressure of the swing hydraulic circuit and the flow rate of hydraulic oil that passes through the swing relief valve 71 (hereinafter referred to as “swing relief flow rate”).

  As shown in FIG. 6, the swing relief flow rate is zero when the swing hydraulic circuit internal pressure is less than the cracking pressure. Further, when the swing hydraulic circuit internal pressure is greater than or equal to the cracking pressure and less than the swing relief pressure, the swing relief flow rate increases relatively gradually as the swing hydraulic circuit internal pressure increases. Further, when the swing hydraulic circuit internal pressure is equal to or higher than the swing relief pressure, the swing relief flow rate increases relatively rapidly as the swing hydraulic circuit internal pressure increases.

  The check valves 72L and 72R are valves that prevent the pressure of the hydraulic oil in the pipelines 70L and 70R from dropping below the pressure of the hydraulic oil in the hydraulic oil tank 22 (hereinafter referred to as “tank pressure”).

  Specifically, the check valve 72L is opened when the internal pressure of the turning hydraulic circuit in the pipeline 70L becomes less than the tank pressure while prohibiting the hydraulic oil in the pipeline 70L from flowing out to the hydraulic oil tank 22. Then, the hydraulic oil in the hydraulic oil tank 22 (pipe line 73) is caused to flow into the pipe line 70L. Similarly, the check valve 72R is in an open state when the hydraulic pressure in the turning hydraulic circuit in the pipe line 70R becomes less than the tank pressure while prohibiting the hydraulic oil in the pipe line 70R from flowing out to the hydraulic oil tank 22, and the check valve 72R operates. The hydraulic oil in the oil tank 22 (pipe 73) is caused to flow into the pipe 70R.

  The main relief valve 83 is a valve that limits the pressure of the hydraulic oil in the hydraulic system 100 to a predetermined main relief pressure or less. In this embodiment, the main relief valve 83 is a mechanical relief valve whose main relief pressure is fixedly set by a spring or the like. The main relief pressure is set to be higher than the turning relief pressure.

  The controller 54 can adjust the pump flow rate of the hydraulic pump 10L and the swing relief pressures of the swing relief valves 71L and 71R based on the contents of the swing operation and the pump discharge pressure of the hydraulic pump 10L.

  In this embodiment, the contents of the turning operation including the presence / absence of the turning operation are derived based on the outputs of the pressure sensors S5 and S6. The pressure sensors S5 and S6 are pilot pressure sensors that detect a pilot pressure corresponding to the lever operation amount of the turning operation lever 82. Further, the pump discharge pressure of the hydraulic pump 10L is derived based on the output of the pressure sensor S3 as a discharge pressure sensor.

  For example, when the turning operation lever 82 is operated in the right turning direction and the pilot pressure detected by the pressure sensor S6 increases, the flow control valve 12L is moved in the left direction. At this time, the flow control valve 12L communicates the hydraulic pump 10L with the first port 44L of the turning hydraulic motor 44 through the first port 12P1, and the second port 44R of the turning hydraulic motor 44 through the second port 12P2. And the hydraulic oil tank 22 are communicated. The flow control valve 12L blocks the center bypass conduit 30L. The hydraulic pump 10L increases the pump flow rate to the maximum pump flow rate as shown in the negative control diagram of FIG. 3 because the negative control pressure is reduced to almost zero by the interruption of the center bypass pipe line 30L.

  On the other hand, the amount of hydraulic oil consumed for driving the turning hydraulic motor 44 (hereinafter referred to as “turning consumption flow rate”) gradually increases while being lower than the maximum pump flow rate of the hydraulic pump 10L. This is because the upper swing body 3 of the shovel 1 has a large moment of inertia. At this time, the hydraulic oil that causes a flow rate difference between the maximum pump flow rate and the swirling consumption flow rate is discharged to the hydraulic oil tank 22 via the swivel relief valve 71L. Therefore, a part of the hydraulic energy generated by the hydraulic pump 10L is wasted without being used.

  Therefore, the controller 54 performs control (hereinafter referred to as “swing relief cut control”) to bring the pump flow rate of the hydraulic pump 10L close to the swirling consumption flow rate in order to minimize the wasteful hydraulic energy. Run. Specifically, the controller 54 adjusts the pump flow rate of the hydraulic pump 10L, the swing relief pressures of the swing relief valves 71L and 71R, and the like based on the details of the swing operation and the pump discharge pressure of the hydraulic pump 10L. Details of the adjustment of the pump flow rate of the hydraulic pump 10L and the swing relief pressure of the swing relief valves 71L and 71R will be described later.

  Next, referring to FIG. 7, control until the rotational speed (ω) of the turning hydraulic motor 44 is determined according to the pump discharge pressure (Pd) of the hydraulic pump 10L (hereinafter referred to as “turning speed control”). ) Will be described. FIG. 7 is a block diagram showing the flow of turning speed control.

  First, the controller 54 acquires a discharge pressure signal as an electric signal representing the pump discharge pressure (Pd) of the hydraulic pump 10L detected by the discharge pressure sensor S3. The controller 54 replaces the pressure of the hydraulic oil before passing through the flow control valve 12L detected by the discharge pressure sensor S3 with the pressure of the hydraulic oil in the pipeline 70 after passing through the flow control valve 12L. You may detect as pump discharge pressure (Pd). In this case, for example, as shown in FIG. 5, the controller 54 acquires signals representing pressures detected by pressure sensors S3′L and S3′R installed in the pipe lines 70L and 70R, respectively. The controller 54 may select which signal of the discharge pressure sensors S3′L and S3′R is to be used according to the turning direction.

  Then, the controller 54 determines a current command (Is) for the electromagnetic valve 55L based on the discharge pressure (Pd). The electromagnetic valve 55L generates a control pressure (Ps) corresponding to the current command (Is) in the pressure receiving chamber 612L of the discharge amount control unit 61L.

  Thereafter, the discharge amount control unit 61L adjusts the pump flow rate (Qd) of the hydraulic pump 10L to an amount corresponding to the control pressure (Ps) via the spool valve mechanism 60L and the tilt actuator 41L. FIG. 7 shows a state in which the control pressure (Ps) is converted into the pump flow rate (Qd) of the hydraulic pump 10L via the calculation element E1 representing the first-order lag.

  Thereafter, the change in the pump flow rate (Qd) generates a pressure due to the change in the volume of the hydraulic oil in the center bypass pipe line 30L. FIG. 7 shows a state where the pump flow rate (Qd) of the hydraulic pump 10L is converted into the discharge pressure (Pd ′) via the calculation element E2 representing the compression volume. In the calculation element E2, K, V, and s represent the bulk modulus, volume, and Laplace operator, respectively. Further, the discharge pressure (Pd ′) obtained here is fed back to the controller 54 through a feedback loop. Control is performed so that the discharge pressure (Pd) detected by the discharge pressure sensor S3 is equal to the discharge pressure (Pd ′) calculated according to the current command (Is) output from the controller 54 to the electromagnetic valve 55. It is for stabilizing.

  Thereafter, the hydraulic oil having the discharge pressure (Pd ′) discharged from the pump 10L passes through the PT throttle of the flow control valve 12L corresponding to the turning hydraulic motor 44. FIG. 7 shows that the pressure obtained by subtracting the negative control pressure (Pn ′) from the pump discharge pressure (Pd ′) of the hydraulic pump 10L becomes the bleed flow rate (Qb) via the calculation element E3 representing the PT throttle of the flow control valve 12L. Represents the state of being converted. In the calculation element E3, c, A, ρ, and Δp represent a flow coefficient, an opening area, a density, and a pressure change, respectively. In this case, the pump discharge pressure (Pd ′) of the hydraulic pump 10L represents the pressure upstream of the PT throttle, and the negative control pressure (Pn ′) represents the pressure downstream of the PT throttle. The bleed flow rate (Qb) represents the flow rate of the hydraulic oil that passes through the PT throttle of the flow control valve 12L.

  The hydraulic oil having a negative control pressure (Pn ′) on the downstream side of the flow control valve is discharged to the hydraulic oil tank 22 through the negative control throttle 20L. FIG. 7 shows a state in which the negative control pressure (Pn ′) is converted into the discharge flow rate (Qe) via the calculation element E4 representing the negative control throttle 20L. In this case, the discharge flow rate (Qe) represents the flow rate of the hydraulic oil that passes through the negative control throttle 20L.

  Note that a change in the flow rate (Qb-Qe) in the negative control throttle 20L causes a pressure due to a change in the volume of the hydraulic oil. FIG. 7 shows a state in which the flow rate (Qb−Qe) is converted into the negative control pressure (Pn ′) via the calculation element E5 representing the compression volume.

  Thereafter, the flow rate of the hydraulic oil flowing through the center bypass pipe line 30 </ b> L changes when a part of the hydraulic oil flows into the turning hydraulic motor 44. Therefore, a change in the flow rate (Qd−Qb) of the hydraulic oil flowing through the center bypass pipe line 30L generates a pressure due to a change in the volume of the hydraulic oil. FIG. 7 shows a state in which the flow rate (Qd−Qb) is converted into the discharge pressure (Pd ′) via the calculation element E2 representing the compression volume.

  The hydraulic oil having a discharge pressure (Pd ′) discharged from the pump 10L passes through the PC throttle of the flow control valve 12L corresponding to the turning hydraulic motor 44. FIG. 7 shows the flow rate in the swing hydraulic circuit via the calculation element E6 in which the pressure obtained by subtracting the internal pressure (Pact) of the swing hydraulic circuit from the pump discharge pressure (Pd ′) of the hydraulic pump 10L represents the PC throttle of the flow control valve 12L. This represents a state of being converted to (Qact). In this case, the pump discharge pressure (Pd ′) of the hydraulic pump 10L represents the pressure upstream of the PC throttle, and the turning hydraulic circuit internal pressure (Pact) represents the pressure downstream of the PC throttle. Further, the flow rate (Qact) in the swing hydraulic circuit represents the flow rate of the hydraulic oil that passes through the PC throttle of the flow control valve 12L. The flow rate (Qact) in the swing hydraulic circuit is fed back to the calculation element E2. The pump discharge pressure (Pd ′) of the hydraulic pump 10L is generated by compression of hydraulic oil having a flow rate obtained by subtracting the bleed flow rate (Qb) and the turning hydraulic circuit flow rate (Qact) from the pump flow rate (Qd) of the hydraulic pump 10L. It is to be done.

  Thereafter, the change in the flow rate (Qact) in the swing hydraulic circuit generates a pressure due to the volume change of the hydraulic oil in the swing hydraulic circuit, and further generates a force (torque) for rotating the swing hydraulic motor 44. In FIG. 7, the flow rate (Qact) in the turning hydraulic circuit is converted into the turning hydraulic circuit internal pressure (Pact) via the calculation element E7 representing the compression volume, and further, the calculation element E8 representing the pressure receiving area A of the turning hydraulic motor 44. The state converted into force (torque) via is represented.

  Thereafter, the movement of the turning hydraulic motor 44 is determined according to the force (torque) generated by the turning hydraulic motor 44. FIG. 7 shows a state in which the force is converted into the rotational speed (ω) of the turning hydraulic motor 44 via the calculation element E9. In the calculation element E9, J and s represent the moment of inertia and the Laplace operator, respectively.

  Further, the turning hydraulic circuit internal pressure (Pact) output from the calculation element E7 is fed back to the calculation element E6. This is because the flow rate (Qact) in the swing hydraulic circuit is generated by the differential pressure between the pump discharge pressure (Pd ′) of the hydraulic pump 10L and the internal pressure (Pact) in the swing hydraulic circuit.

  Similarly, the rotation speed (ω) of the turning hydraulic motor 44 output by the calculation element E9 is converted into a flow (Qact ′) in the turning hydraulic circuit via the calculation element E10 that represents the pressure receiving area A of the turning hydraulic motor 44. And fed back to the calculation element E7.

  In addition, when the swing hydraulic circuit internal pressure (Pact) output by the calculation element E7 is equal to or greater than the cracking pressure of the swing relief valve 71 and less than the swing relief pressure, the swing relief valve 71 is controlled via the calculation element E11 representing the second order delay. After being converted into the passing swirl relief flow rate (Qrf), it is fed back to the calculation element E7. Note that when the swing hydraulic circuit internal pressure (Pact) is less than the cracking pressure, the swing relief flow rate is not generated, and therefore, the swing hydraulic circuit internal pressure (Pact) is not fed back to the calculation element E7 via the calculation element E11. In addition, when the swing hydraulic circuit internal pressure (Pact) is equal to or higher than the swing relief pressure, the correspondence relationship between the swing hydraulic circuit internal pressure (Pact) and the swing relief flow when the cracking pressure is higher than the swing relief pressure is different. To produce a swivel relief flow. Therefore, the swing hydraulic circuit internal pressure (Pact) is converted into a swing relief flow rate (Qrf) passing through the swing relief valve 71 via another calculation element (not shown) different from the calculation element E11. Can be fed back to the computing element E7.

  In the above-described embodiment, the calculation element represented by the first-order lag or the second-order lag may be any nonlinear element such as a third-order or higher-order lag element.

  Next, the operation of the controller 54 when driving the turning hydraulic motor 44 will be described with reference to FIG. FIG. 8 is a block diagram showing a configuration example of the controller 54.

  As shown in FIG. 8, the controller 54 mainly includes a calculation element E20, a feedback control unit E21, a minimum flow rate selection unit E22, and a reference table TB1. The reference table TB1 is stored in advance in ROM, NVRAM, or the like.

  The calculation element E20 is a functional element that converts a command value related to the pump discharge pressure into a command value related to the pump flow rate. In this embodiment, the calculation element E20 sets the deviation (P1) between the preset target pump discharge pressure (Ptgt) and the pump discharge pressure (Pd) detected by the discharge pressure sensor S3 to the pump flow rate command value Q1. Convert.

  The feedback control unit E21 is a functional element that generates and outputs a pump flow rate command value (Q2) based on a preset target pump flow rate (Qtgt) and a pump flow rate command value (Q1) output by the calculation element E20. is there. In this embodiment, the feedback control unit E21 generates a basic pump flow rate command value that increases at a predetermined increase rate based on the target pump flow rate (Qtgt), and according to the increase or decrease of the pump flow rate command value (Q1). The basic pump flow rate command value is corrected and the pump flow rate command value (Q2) is output. At this time, the feedback control unit E21 performs PID control based on the deviation between the pump discharge pressure (Pd) and the target pump discharge pressure (Ptgt) and the deviation between the pump flow rate command value (Q1) and the target pump flow rate (Qtgt). To output the pump flow rate command value (Q2). Further, the feedback control unit E21 may execute phase compensation for reducing the deviation and output the pump flow rate command value (Q2).

  The control in which the controller 54 outputs the pump flow rate command value (Q2) based on the pump discharge pressure (Pd) constitutes the above-described turning relief cut control. Therefore, hereinafter, the pump flow rate command value (Q2) is also referred to as a turning relief cut control flow rate (Q2).

  The minimum flow rate selection unit E22 selects the minimum pump flow rate command value among the pump flow rate command value (Q2) derived by the turning relief cut control and one or a plurality of pump flow rate command values derived by other control. It is a functional element. In the present embodiment, the minimum flow rate selection unit E22 uses a pump flow rate command value (Q2) derived by turning relief cut control and a pump flow rate command value derived by negative control (hereinafter, “negative control flow rate (Qn)”). .) And a pump flow rate command value derived by horsepower control (hereinafter referred to as “horsepower control flow rate (Qh)”) is selected and output as a pump flow rate command value (Q3).

  The reference table TB1 is a reference table representing a correspondence relationship between the pump flow rate command value (Q3) and the current command (Is). The controller 54 derives a current command (Is) based on the pump flow rate command value (Q3) output from the minimum flow rate selection unit E22 and the reference table TB1, and outputs the derived current command (Is) to the solenoid valve 55L. To do.

  Next, a process in which the controller 54 outputs a current command (Is) to the electromagnetic valve 55L (hereinafter referred to as “current command output process”) will be described with reference to FIG. FIG. 9 is a flowchart showing the flow of the current command output process, and the controller 54 repeatedly executes this current command output process at a predetermined control cycle.

  First, the controller 54 acquires a pilot pressure and a pump discharge pressure (step ST1). In this embodiment, the controller 54 electrically detects lever operation amounts of various operation devices based on an output of a pilot pressure sensor as an operation content detection unit that detects a pilot pressure generated when various operation devices are operated. To do. Further, the controller 54 electrically detects the pump discharge pressure of the hydraulic pump 10L based on the output of the discharge pressure sensor S3.

  Thereafter, the controller 54 determines whether or not a turning operation has been performed based on the acquired pilot pressure (step ST2). In the present embodiment, the controller 54 determines that the turning operation has been performed when the turning operation lever 82 is operated. The controller 54 can determine whether or not the turning relief valve 71 is in a relief state or a relief enabled state by determining whether or not a turning operation has been performed. This is because when the turning operation is not performed, the turning relief valve 71 does not enter a relief state or a relief ready state.

  When it is determined that the turning operation has been performed (YES in step ST2), the controller 54 determines whether or not the pump discharge pressure is equal to or higher than the threshold value TH1 (step ST3). In the present embodiment, the threshold value TH1 is the cracking pressure of the swing relief valve 71. The threshold value TH1 may be a value less than the cracking pressure.

  When it is determined that the pump discharge pressure is equal to or higher than the threshold value TH1 (YES in step ST3), the controller 54 executes an action operation (step ST4). The action operation is the smallest among a plurality of pump flow rate command values including the turning relief cut control flow rate (Q2), the negative control flow rate (Qn), and the horsepower control flow rate (Qh) after executing the turning relief cut control. This is a process of outputting a current command (Is) based on the value, details of which will be described later.

  When it is determined that the pump discharge pressure is less than the threshold TH1 (NO in step ST3), the controller 54 determines whether an operation other than the turning operation has been performed (step ST5). In this embodiment, the controller 54 determines that another operation has been performed when, for example, a boom operation lever, an arm operation lever, a bucket operation lever, or the like is operated.

  When it is determined that another operation has been performed (YES in step ST5), the controller 54 performs a transition operation (step ST6). The transition operation is a process for preparing for an action operation. Specifically, the transition operation outputs a current command (Is) based on the smallest value among a plurality of pump flow rate command values other than the turning relief cut control flow rate. In the transition operation, the pump flow rate command value selected as the minimum value is stored for feedback control in the next action operation. Details of the transition operation will be described later.

  On the other hand, when it determines with other operation not being performed (NO of step ST5), the controller 54 performs stop operation | movement (step ST7). The stop operation is a process for resetting the action operation. Specifically, the stop operation outputs a current command (Is) based on the smallest value among a plurality of pump flow rate command values other than the turning relief cut control flow rate. And a stop operation | movement resets the parameter of the feedback control part E21 for the feedback control in the next action operation | movement. Details of the stop operation will be described later.

  FIG. 10 shows a state transition diagram between the action operation, the transition operation, and the stop operation.

  As shown in FIG. 10, the controller 54 switches the stop operation to the transition operation when another operation is performed when the stop operation is periodically executed. In addition, when the turning operation is performed while the stop operation is periodically executed, the controller 54 switches the stop operation to the action operation if the pump discharge pressure (Pd) is equal to or higher than the threshold value TH1.

  Further, when the turning operation is stopped or the pump discharge pressure (Pd) becomes less than the threshold value TH1 when the action operation is periodically executed, the controller 54 performs an action if another operation is performed. The operation is switched to a transition operation. If no other operation is performed, the action operation is switched to a stop operation.

  Further, when the turning operation is performed while the transition operation is periodically executed, the controller 54 switches the transition operation to the action operation if the pump discharge pressure (Pd) is equal to or higher than the threshold value TH. In addition, the controller 54 switches the transition operation to the stop operation when another operation is stopped when the transition operation is periodically executed.

  In this way, the controller 54 periodically and continuously executes the current command (Is) while periodically and continuously executing one of the three actions of action action, transition action, and stop action. Output to the solenoid valve 55L.

  Next, details of the action operation will be described with reference to FIG. FIG. 11 is a flowchart showing an example of the flow of action operations.

  First, the controller 54 acquires a target pump discharge pressure (Ptgt), a pump discharge pressure (Pd), and a target pump flow rate (Qtgt) (step ST11).

  The target pump discharge pressure (Ptgt) is a value not less than the cracking pressure of the swing relief valve 71 and less than the swing relief pressure of the swing relief valve 71, and is stored in advance in NVRAM or the like. In the present embodiment, the target pump discharge pressure (Ptgt) is an intermediate value between the cracking pressure and the turning relief pressure. The target pump flow rate (Qtgt) is a pump flow rate of the hydraulic pump 10L required when the turning hydraulic motor 44 is rotated at a predetermined rotational speed, and is stored in advance in NVRAM or the like. In this embodiment, the target pump flow rate (Qtgt) is the pump flow rate of the hydraulic pump 10L required when the turning hydraulic motor 44 is rotated at the maximum rotational speed. The pump discharge pressure (Pd) is a value detected by the discharge pressure sensor S3.

  Further, the controller 54 may switch the work mode by changing the target pump discharge pressure (Ptgt) within a range not less than the cracking pressure and less than the turning relief pressure. For example, the controller 54 increases the swing hydraulic circuit internal pressure within a range not less than the cracking pressure and less than the swing relief pressure to generate a larger swing torque, and reduces the swing hydraulic circuit internal pressure within the range. The energy saving mode for realizing energy saving is switched by reducing the turning relief flow rate. In this way, the controller 54 can switch the work mode without interrupting the turning relief cut control.

  Thereafter, the controller 54 derives a deviation (P1) between the pump discharge pressure (Pd) and the target pump discharge pressure (Ptgt), and multiplies the deviation (P1) by a predetermined proportional gain K1 to derive a pump flow rate command value (Q1). (Step ST12).

  Thereafter, the controller 54 derives a pump flow rate command value (Q2) based on the pump flow rate command value (Q1) and the target pump flow rate (Qtgt) (step ST13). Specifically, the controller 54 performs PID control by the feedback control unit E21 to derive the pump flow rate command value (Q2). The controller 54 may derive the pump flow rate command value (Q2) by executing phase compensation by the feedback control unit E21.

  Thereafter, the controller 54 derives a negative control flow rate (Qn) and a horsepower control flow rate (Qh) (step ST14). Note that the controller 54 may execute the process of step ST14 at any timing before the process of the next step ST15 is executed. For example, the controller 54 may execute the process of step ST14 before executing the process of step ST11. Further, the controller 54 may acquire the pump flow rate command value derived by the control other than the negative control and the horsepower control in step ST14.

  Thereafter, the controller 54 uses the minimum flow rate selection unit E22 to select the smallest value among the plurality of pump flow rate command values including the turning relief cut control flow rate (Q2), the negative control flow rate (Qn), and the horsepower control flow rate (Qh). Is selected as the pump flow rate command value (Q3) (step ST15). When a turning operation is performed, the controller 54 may generate a turning operation flow rate (Qx) as a pump flow rate command value that increases at a predetermined increase rate every control cycle. In addition, the minimum flow rate selection unit E22 sets the smallest value among the plurality of pump flow rate command values including the turning operation flow rate (Qx), the negative control flow rate (Qn), and the horsepower control flow rate (Qh). Output as command value (Q3). This is because the maximum pump flow rate command value based on the negative control flow rate (Qn) is output unless the flow rate (Qx) during the turning operation is generated.

  Thereafter, the controller 54 refers to the reference table TB1, derives a current command (Is) corresponding to the pump flow rate command value (Q3), and outputs the derived current command (Is) to the solenoid valve 55L (step ST16). ).

  Next, the details of the transition operation will be described with reference to FIG. FIG. 12 is a flowchart showing an example of the flow of the transition operation.

  First, the controller 54 sets a maximum value to the pump flow rate command value (Q2) (step ST21). This is to prevent the pump flow rate command value (Q2) from being selected as the minimum value by the minimum flow rate selection unit E22.

  Thereafter, the controller 54 resets the parameters of the feedback control unit E21 (step ST22). In this embodiment, the controller 54 sets values such as proportional gain and differential gain used in PID control to zero. This is so as not to adversely affect the next action operation.

  Thereafter, the controller 54 executes the processes of steps ST23 to ST25 in the same manner as the processes of steps ST14 to ST16 in the action operation.

  Thereafter, the controller 54 stores the pump flow rate command value (Q3) in preparation for the next action operation (step ST26). In the present embodiment, the controller 54 stores the currently acquired pump flow rate command value (Q3) as an integral gain value so that the output of PID control in the next action operation does not change suddenly.

  Next, details of the stop operation will be described with reference to FIG. FIG. 13 is a flowchart showing an example of the flow of the stop operation.

  First, the controller 54 sets a maximum value to the pump flow rate command value (Q2) (step ST31). This is to prevent the pump flow rate command value (Q2) from being selected as the minimum value by the minimum flow rate selection unit E22.

  Thereafter, the controller 54 resets the parameters of the feedback control unit E21 in preparation for the next action operation (step ST32). In this embodiment, the controller 54 sets a minimum value for the integral gain used in the PID control of the next action operation. As the minimum value of the integral gain used as the pump flow rate command value, a value other than zero, for example, a value that is more than 10% of the maximum value is set. This is to prevent a sudden change in the output of the PID control in the next action operation.

  Thereafter, the controller 54 executes the processes of steps ST33 to ST35 in the same manner as the processes of steps ST14 to ST16 in the action operation.

  Next, with reference to FIG. 14, the relationship between the excessive flow volume and pump discharge pressure at the time of performing turning relief cut control is demonstrated. In FIG. 14, the vertical axis indicates the pump discharge pressure, and the horizontal axis indicates the surplus flow rate. The surplus flow rate is a flow rate obtained by subtracting the swirl consumption flow rate from the pump flow rate, and includes the swirl relief flow rate and the leakage flow rate. The pump discharge pressure (Pc) and the surplus flow rate (Qc) correspond to the pump discharge pressure and the surplus flow rate when the internal pressure of the swing hydraulic circuit reaches the cracking pressure of the swing relief valve 71, respectively, during the single swing operation. . Further, the pump discharge pressure (Pr) and the surplus flow rate (Qr) correspond to the pump discharge pressure and the surplus flow rate when the internal pressure of the swing hydraulic circuit reaches the swing relief pressure of the swing relief valve 71 in the single swing operation, respectively. To do.

  As shown in FIG. 14, when the pump discharge pressure is less than Pc, the rate of increase (gain) of the pump discharge pressure with respect to the surplus flow is significantly larger than when the pump discharge pressure is greater than Pc and less than Pr. Therefore, if the target pump discharge pressure (Ptgt) is set to a value less than Pc, the turning relief cut control loses stability, and the pump discharge pressure may be vibrated up and down.

  On the other hand, when the pump discharge pressure is greater than or equal to Pr, the rate of increase (gain) of the pump discharge pressure with respect to the surplus flow is significantly smaller than when the pump discharge pressure is greater than or equal to Pc and less than Pr. Therefore, if the target pump discharge pressure (Ptgt) is set to a value equal to or greater than Pr, the turning relief cut control will allow a relatively large fluctuation in the excess flow rate (pump flow rate), and the excess flow rate (swing relief flow rate). There is a risk of reducing the reduction effect.

  Therefore, the target pump discharge pressure (Ptgt) is set so as to have a value within the range of Pc or more and less than Pr, at which the increase rate (gain) of the pump discharge pressure with respect to the surplus flow rate is moderate.

  Next, with reference to FIG.15 and FIG.16, the effect by the turning relief cut control at the time of independent turning operation is demonstrated. FIG. 15 shows the relationship between the swirling consumption flow rate and the pump flow rate when the moment of inertia of the upper swing body 3 of the excavator 1 is small. FIG. 15A shows the relationship when the turning relief cut control is not executed, and FIG. 15B shows the relationship when the turning relief cut control is executed. Similarly, FIG. 16 shows the relationship between the swirling consumption flow rate and the pump flow rate when the moment of inertia of the upper swing body 3 of the excavator 1 is large. FIG. 16A shows the relationship when the turning relief cut control is not executed, and FIG. 16B shows the relationship when the turning relief cut control is executed.

  As shown in FIGS. 15 and 16, when the swing relief cut control is executed, the swing relief flow rate (hatched area) obtained by subtracting the swing consumption amount from the pump flow rate is conspicuous as compared with the case where the swing relief cut control is not executed. Few. This is because the pump flow rate is controlled so that the pump discharge pressure becomes the target pump discharge pressure (Ptgt), and as a result, the pump flow rate is limited to be slightly higher than the swirling consumption flow rate.

  Further, as can be seen from a comparison between FIG. 15 and FIG. 16, the greater the moment of inertia of the upper swing body 3, the greater the reduction width of the swing relief flow rate. That is, as the excavation attachment is opened and the turning radius is increased, the amount of decrease in the turning relief flow rate during the turning operation is increased.

  In this way, the controller 54 can reduce the turning relief flow rate during the turning operation and improve the energy saving by turning relief cut control.

  Note that energy saving and workability by the turning relief cut control are in a trade-off relationship. The higher the energy saving, that is, the smaller the turning relief flow rate, the smaller the turning torque that can be output.

  Therefore, the controller 54 may increase the swing relief pressure and the cracking pressure of the swing relief valve 71 in order to improve energy saving while maintaining the magnitude of the swing torque that can be output.

  However, the controller 54 can bring the turning hydraulic circuit internal pressure at the time of turning acceleration close to a predetermined value not less than the cracking pressure and less than the turning relief pressure by the turning relief cut control, but the turning hydraulic circuit internal pressure at the time of turning deceleration is set to the predetermined value. It cannot be brought close. This is because the flow rate of the hydraulic oil flowing from the turning hydraulic motor 44 to the hydraulic oil tank 22 cannot be controlled in the same manner as the pump flow rate. Therefore, when the swing relief pressure and the cracking pressure of the swing relief valve 71 are increased, the controller 54 inevitably increases the internal pressure of the swing hydraulic circuit during the swing deceleration to the increased swing relief pressure. The deceleration torque generated by the turning hydraulic circuit internal pressure equal to the increased turning relief pressure may adversely affect the structure of the turning hydraulic motor 44, the turning speed reducer, and the like. Therefore, when the swing relief pressure and cracking pressure of the swing relief valve 71 are increased during the swing acceleration, the controller 54 decreases the increased swing relief pressure and cracking pressure during the swing deceleration, and preferably before the increase. Return to the state.

  Specifically, the controller 54 determines whether turning acceleration or turning deceleration based on the outputs of the pilot pressure sensor and the discharge pressure sensor. The controller 54 increases the swing relief pressure and the cracking pressure of the swing relief valve 71 when determining that the swing is being accelerated, while turning the swing relief valve 71 when determining that the swing is being decelerated. Reduce the swing relief pressure and cracking pressure.

  With this configuration, the controller 54 can improve energy saving while maintaining the magnitude of the output turning torque during turning acceleration, while the turning hydraulic motor 44, during turning deceleration, It is possible to prevent adverse effects on the structure of the turning speed reducer and the like.

  FIG. 17 is a diagram showing the relationship between the swing hydraulic circuit internal pressure and the swing relief flow rate when the controller 54 switches the swing relief pressure and the cracking pressure of the swing relief valve 71 according to the swing state.

  As shown in FIG. 17, the controller 54 increases the swing relief pressure and cracking pressure of the swing relief valve 71 when it is determined that the swing is being accelerated, and the relationship between the swing hydraulic circuit internal pressure and the swing relief flow rate is indicated by a solid line. Make the relationship shown. Then, the controller 54 controls the pump flow rate by the swing relief cut control so that the internal pressure of the swing hydraulic circuit becomes a predetermined value between the swing relief pressure Pra and the cracking pressure Pca.

  In addition, when the controller 54 determines that the swing is being decelerated, the swing relief pressure and the cracking pressure of the swing relief valve 71 are returned to the state before the increase, and the relationship between the swing hydraulic circuit internal pressure and the swing relief flow rate is indicated by a dotted line. Make the relationship shown in. In this case, the internal pressure of the swing hydraulic circuit reaches the swing relief pressure Prd. Then, the hydraulic system 100 decelerates the upper swing body 3 while causing the hydraulic oil in the swing hydraulic circuit to flow from the swing relief valve 71 to the hydraulic oil tank 22 at a swing relief flow rate corresponding to the moment of inertia of the upper swing body 3.

  With the above configuration, the construction machine hydraulic system 100 can reduce the swing relief flow rate of the swing relief valve 71 during the swing operation by the swing relief cut control. Specifically, the hydraulic system 100 controls the pump flow rate so that the pump discharge pressure becomes the target pump discharge pressure (a value within the range of the cracking pressure of the swing relief valve 71 and less than the swing relief pressure). As a result, the hydraulic system 100 can bring the pump flow rate closer to the swirl consumption flow rate and reduce the swirl relief flow rate, which is a flow rate difference between the pump flow rate and the swirl consumption flow rate.

  Further, the hydraulic system 100 executes the turning relief cut control when the turning operation is performed and the pump discharge pressure becomes equal to or higher than the threshold value TH1. In other words, the hydraulic system 100 executes the swing relief cut control after determining that the swing relief valve 71 is in a relief state or a state in which relief is possible and that there is a possibility of a divergence between the pump flow rate and the swing consumption flow rate. To do. As a result, the hydraulic system 100 starts the control of the pump flow rate after specifying the relief valve to be controlled, so that the control accuracy can be improved.

  Further, the hydraulic system 100 can bring the pump flow rate close to the swirl consumption flow rate so that the swirl relief flow rate is maintained in a substantially constant state by swivel relief cut control. Therefore, the hydraulic system 100 can approximate the swirling consumption flow rate with the pump flow rate. As a result, the hydraulic system 100 can derive the turning angular velocity from the pump flow rate and can derive the turning torque from the pump discharge pressure. Therefore, the hydraulic system 100 can relatively accurately derive the moment of inertia of the upper-part turning body 3 that is a value obtained by dividing the turning torque by the turning angular acceleration. The moment of inertia of the upper swing body 3 is a value determined according to the attitude of the excavation attachment. Therefore, the hydraulic system 100 can estimate the attitude of the excavation attachment based on the pump discharge pressure and the pump flow rate when the turning relief cut control is being executed, and can further adjust the turning angular velocity based on the estimation result.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. Is possible.

  For example, in the above-described embodiment, the construction machine hydraulic system 100 suppresses the turning relief flow rate by making the pump flow rate of the hydraulic pump 10L close to the turning consumption flow rate by turning relief cut control while performing negative control. However, the present invention is not limited to this configuration. For example, the construction machine hydraulic system 100 may execute positive control control, load sensing control, and the like instead of the negative control.

  In the above-described embodiment, the construction machine hydraulic system 100 executes the turning relief cut control so that the turning relief flow rate of the turning relief valve 71 becomes substantially constant during the turning operation. However, the present invention is not limited to this configuration. For example, in the construction machine hydraulic system 100, when a hydraulic actuator other than the turning hydraulic motor 44 is operated, a relief flow rate of a relief valve installed between the hydraulic actuator and a flow rate control valve corresponding to the hydraulic actuator is set. The relief cut control may be executed so that is substantially constant.

  DESCRIPTION OF SYMBOLS 1 ... Excavator 2 ... Lower traveling body 3 ... Upper turning body 4 ... Boom 5 ... Arm 6 ... Bucket 7 ... Boom cylinder 8 ... Arm cylinder 9 ... Bucket cylinder 10L, 10R ... Hydraulic pump 11L, 12L, 12R, 13L, 13R, 14,15L, 15R ... Flow control valve 20L, 20R ... Negative control throttle 22 ... Hydraulic oil tank 30L, 30R .. Center bypass pipes 40L, 40R ... Pump regulators 41L, 41R ... Tilt actuators 42L, 42R ... Travel hydraulic motors 44 ... Turning hydraulic motors 52 ... Control pumps 54 ... Controller 55L, 55R ... Solenoid valve 60L, 60R ... Spool mechanism 61L, 61R ... Discharge amount Control unit 80 ... Mechanical brake 81 ... Reduction gear 82 ... Turning operation lever 83 ... Main relief valve 70, 73 ... Pipe 71 ... Turning relief valve 72 ... Check valve 100 ... Hydraulic system 200 ... Swivel hydraulic circuit S1-S6 ... Pressure sensors E1-E11, E20 ... Calculation elements E21 ... Feedback control unit E22 ... Minimum flow rate selection unit TB1 ... See table

Claims (6)

A hydraulic system for construction machinery,
A flow control valve for controlling the flow of hydraulic oil discharged from the hydraulic pump to the hydraulic actuator;
A relief valve installed between the flow control valve and the hydraulic actuator;
An operation content detection unit for detecting the operation content of the operation lever related to the hydraulic actuator;
A discharge pressure detector for detecting a discharge pressure of the hydraulic pump;
A controller that controls the discharge amount of the hydraulic pump in response to the outputs of the operation content detection unit and the discharge pressure detection unit;
The controller is configured such that when the operation lever is operated and the discharge pressure of the hydraulic pump is equal to or higher than a predetermined pressure, the discharge pressure of the hydraulic pump is not less than the cracking pressure of the relief valve and less than the relief pressure of the relief valve. Controlling the discharge amount of the hydraulic pump so as to increase the discharge amount of the hydraulic pump to the target pump flow rate corresponding to the operation amount of the operation lever, while maintaining the predetermined target pump discharge pressure of
Hydraulic system for construction machinery. The controller switches the work mode by changing the predetermined target pump discharge pressure.
The hydraulic system for construction machines according to claim 1. The predetermined pressure is a cracking pressure of the relief valve,
The hydraulic system for construction machines according to claim 1 or 2. The controller increases the cracking pressure and relief pressure of the relief valve during turning acceleration, and restores the increased cracking pressure and relief pressure during turning deceleration.
The hydraulic system for construction machines according to any one of claims 1 to 3. The hydraulic actuator is a turning hydraulic motor,
The relief valve is a swing relief valve;
The operation amount of the operation lever is the maximum operation amount of the turning operation lever.
The hydraulic system for construction machines according to any one of claims 1 to 4. The controller is configured such that when the swing operation lever is operated and the discharge pressure of the hydraulic pump is equal to or higher than the cracking pressure of the swing relief valve, the discharge pressure of the hydraulic pump is equal to or higher than the cracking pressure of the swing relief valve; The hydraulic pressure is increased so as to increase the discharge amount of the hydraulic pump to a target pump flow rate corresponding to the maximum operation amount of the swing operation lever while maintaining a predetermined target pump discharge pressure lower than the swing relief pressure of the swing relief valve. Controlling the pump discharge amount, and then estimating the moment of inertia of the swing body based on the discharge pressure of the hydraulic pump corresponding to the swing torque and the discharge amount of the hydraulic pump corresponding to the swing angular velocity,
The hydraulic system for construction machines according to claim 5.

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