Control device for work machine

Abstract

A control device for a work machine is provided with: a hydraulic pump which is rotationally driven by a prime mover and supplies hydraulic oil to a hydraulic actuator; a volume control device that controls the volume of the hydraulic pump in accordance with a control input; a volume sensor that detects a measured volume value of the hydraulic pump; and a controller that acquires a volume target value of the hydraulic pump and outputs a control input corresponding to the volume target value to the volume control device. A mathematical model for predicting the volume of the hydraulic pump is stored in the controller. The controller calculates a predicted volume value of the hydraulic pump using a mathematical model, calculates an optimal control input from the predicted volume value and a limit of the control input, calculates an evaluation value from a target volume value and a measured volume value, and changes the limit of the control input according to the evaluation value.

Description

Technical Field

[0001] The present invention relates to a control device for a working machine. Background Art

[0002] In a hydraulic excavator or other working machine, a hydraulic pump capable of changing its volume is used as a hydraulic supply source for driving a hydraulic actuator. Patent document 1 discloses a working machine including a motor driven by a fluid ejected from a swash plate type hydraulic pump, and the working machine travels using the power of the motor. The working machine described in patent document 1 sets a target position of a swash plate of a hydraulic pump according to the position of an operating member and the load of an engine, and controls a continuously variable transmission (HST) so that the swash plate position of the pump is consistent with the set target position.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2020-18171 Summary of the invention

[0006] Problems to be solved by the invention

[0007] The deviation between the actual volume and the target volume of the hydraulic pump affects the control accuracy of the hydraulic actuator, and the control accuracy of the hydraulic actuator affects the operability of the working machine. Therefore, when changing the volume of the hydraulic pump, it is desirable to make the actual volume quickly follow the target volume.

[0008] An object of the present invention is to improve the responsiveness of the displacement control of a hydraulic pump and to improve the operability of a working machine.

[0009] Means for solving problems

[0010] A control device for a working machine according to one embodiment of the present invention comprises: a hydraulic pump, which is rotationally driven by a prime mover and supplies working oil to a hydraulic actuator; a volume control device, which controls the volume of the hydraulic pump according to a control input; a volume sensor, which detects a measured volume value of the hydraulic pump; and a controller, which obtains a volume target value of the hydraulic pump and outputs the control input corresponding to the volume target value to the volume control device, wherein a mathematical model for predicting the volume of the hydraulic pump is stored in the controller, and the controller performs the following processing: using the mathematical model to calculate a predicted volume value of the hydraulic pump, calculating the optimal control input according to the predicted volume value and the restrictions of the control input, calculating an evaluation value according to the volume target value and the measured volume value, and changing the restrictions of the control input according to the evaluation value.

[0011] Effects of the Invention

[0012] According to the present invention, it is possible to improve the responsiveness of the displacement control of the hydraulic pump and to improve the workability of the working machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a diagram showing the system configuration of a working machine.

[0014] Figure 2 It is a cross-sectional view of the main pump.

[0015] Figure 3 It is a characteristic diagram of the electrical signal and output pressure of the electromagnetic proportional pressure reducing valve.

[0016] Figure 4 It is a control block diagram for controlling the control object through model predictive control.

[0017] Figure 5 This is a flowchart of the model predictive control executed by the pump controller according to the first embodiment.

[0018] Figure 6 This is a time-series waveform diagram of the control input limit set by the pump controller according to the first embodiment.

[0019] Figure 7 It is a diagram showing the time-series change in the volume of the pump system according to the first embodiment.

[0020] Figure 8 This is a flowchart of the model predictive control executed by the pump controller according to the second embodiment.

[0021] Fig. 9 This is a time-series waveform diagram of the control input limit set by the pump controller according to the second embodiment.

[0022] Fig.10 It is a diagram showing a time-series change in the volume of the pump system according to the second embodiment.

[0023] Fig.11 It is a diagram showing a time-series change in the volume of a pump system according to a modification of the second embodiment.

[0024] Fig.12 This is a flowchart of the model predictive control executed by the pump controller according to the third embodiment.

[0025] Fig.13 It is a diagram showing a time-series change in the volume of the pump system according to the third embodiment. DETAILED DESCRIPTION

[0026] Embodiments of the present invention will be described using the drawings.

[0027] <First embodiment>

[0028] -Operation machinery-

[0029] Figure 1 This is a diagram showing the system structure of the working machine. Figure 1 In the figure, one of the multiple hydraulic actuators 17 that the working machine has is representatively shown. The working machine of the present embodiment is, for example, a hydraulic excavator having the following parts: a traveling body, a rotating body rotatably mounted on the traveling body, and a working device mounted on the rotating body. The working device has a boom, an arm, a bucket, and multiple hydraulic cylinders that drive them. In addition, the working machine has: a hydraulic motor for rotating the rotating body, and a hydraulic motor for traveling that drives the traveling body. The multiple hydraulic cylinders that drive the working device, the hydraulic motor that drives the rotating body, and the hydraulic motor that drives the traveling body are hydraulic actuators 17 that are respectively provided in the working machine.

[0030] -Pump system (control device for working machinery)-

[0031] The hydraulic actuator 17 of the working machine is driven by the hydraulic oil supplied from the pump system 100. Figure 1 As shown, a control valve 16 is provided on the discharge line 15 connecting the hydraulic actuator 17 and the pump system 100. The control valve 16 is controlled according to the operation amount of the operating device of the working machine (not shown). By controlling the control valve 16, the flow rate and direction of the working oil supplied from the pump system 100 to the hydraulic actuator 17 are controlled. The hydraulic actuator 17 is driven to operate the working device, the rotating body, the traveling body and other components of the working machine. Therefore, the pump system 100 has a function as a control device of the working machine.

[0032] The pump system 100 includes: a main pump 10, which is a hydraulic pump capable of changing the volume (capacity); a volume control device 20, which controls the volume of the main pump 10 according to a control input; a vehicle body controller 40, which calculates a volume target value of the main pump 10; and a pump controller 30, which outputs a control input corresponding to the volume target value obtained from the vehicle body controller 40 to the volume control device 20. The main pump 10 is driven to rotate by the engine 19 as a prime mover, and supplies working oil (working fluid) to the hydraulic actuator 17. In addition to the variable volume main pump 10, the pump system 100 also includes a pilot pump 18 as a fixed volume hydraulic pump. The pilot pump 18 is driven to rotate by the engine 19 to generate a pilot pressure. In addition, the prime mover may be an electric motor instead of the engine 19.

[0033] - Main Pump -

[0034] Figure 2 2 is a cross-sectional view of the main pump 10. The main pump 10 is composed of the following parts: a housing 7, a cylinder 3, a plurality of pistons 4, a tilt mechanism 6, and a tilt actuator 9. Figure 2As shown, the main pump 10 of the present embodiment is a tilted-axis piston pump. However, the main pump 10 may also be a tilted-plate piston pump.

[0035] The housing 7 is composed of a main housing 7a and a head housing 7b. The main housing 7a is a cylindrical member that accommodates components of the main pump 10 such as the cylinder 3 and the rotating shaft 2. Figure 2 The right end of the housing 7 protrudes from the engine 19 (see Figure 1 ) output shaft. At the base end of the rotating shaft 2 ( Figure 2 The rotating shaft 2 is supported by a bearing so as to be rotatable relative to the main housing 7a. The head housing 7b closes the opening at the end of the main housing 7a.

[0036] The cylinder body 3 is connected to the drive plate 2a via the center shaft 5. The cylinder body 3 rotates together with the rotating shaft 2. A plurality of cylinder chambers 3a are formed in the cylinder body 3 in the axial direction. These plurality of cylinder chambers 3a are arranged in a ring shape around the rotation center line of the cylinder body 3. A piston 4 is inserted into each cylinder chamber 3a so as to be able to slide back and forth. At the base end ( Figure 2 A connecting rod 4a is provided at the right end of each connecting rod 4a. A joint ball 4b is formed at the front end of each connecting rod 4a. The plurality of pistons 4 are connected to the driving disk 2a via the joint ball 4b so as to be swingable.

[0037] The tilting mechanism 6 is a mechanism for adjusting the stroke amount (pump capacity) of the piston 4 relative to the cylinder chamber 3a. The tilting mechanism 6 is constructed to include: a valve plate 6a, which has a cylindrical lens-shaped sliding surface 6b. The center shaft 5 and the swing pin 8 are inserted into the center of the valve plate 6a from both sides. The center shaft 5 passes through the rotation center of the cylinder body 3 and is connected to the drive disk 2a. The center shaft 5 rotates integrally with the cylinder body 3. The opposing surface of the valve plate 6a and the cylinder body 3 is a rotating sliding surface, and the cylinder body 3 rotates and slides relative to the valve plate 6a with the center shaft 5 as the center. In addition, the front end ( Figure 2 The right end in FIG. 1 is a joint ball 5a, and the center shaft 5 is connected to the drive disk 2a via the joint ball 5a so as to be swingable.

[0038] The sliding surface 6b of the valve plate 6a slides on the arc-shaped guide surface formed on the head housing 7b, and the cylinder body 3 and the valve plate 6a draw an arc track and swing back and forth with the swing center line CL passing through the center of the joint ball 5a as the center. In addition, the valve plate 6a is provided with ports (discharge port 6c and suction port 6d) that are intermittently connected to each cylinder chamber 3a through the rotation of the cylinder body 3. The discharge port 6c is connected to the cylinder chamber 3a via the cylinder communication passage 3b opposite to the discharge port 6c. The suction port 6d is connected to the cylinder chamber 3a via the cylinder communication passage 3b opposite to the suction port 6d. If the inclination angle (tilting angle) of the rotation center line of the central axis 5 relative to the rotation center line of the rotation axis 2 changes, the stroke amount (pump capacity) of the piston 4 relative to the cylinder chamber 3a changes. That is, if the tilting angle changes, the supply and discharge amount of the working oil through the cylinder communication passage 3b changes.

[0039] The tilt actuator 9 is a fan-shaped variable displacement mechanism. The tilt actuator 9 includes: a cylinder chamber 9a formed in the head housing 7b, and a servo piston 9b inserted into the cylinder chamber 9a in a slidable manner. The servo piston 9b reciprocates in the cylinder chamber 9a along the axial direction of the cylinder chamber 9a (the axial direction of the servo piston 9b). A swing pin 8 is provided on the servo piston 9b. The swing pin 8 is connected to the valve plate 6a. The servo piston 9b moves in the axial direction, thereby causing the valve plate 6a to slide along the guide surface of the head housing 7b. That is, the tilt mechanism 6 is actuated and the tilt angle changes.

[0040] The interior of the cylinder chamber 9a is divided into two pressure-receiving chambers 9c and 9d by the servo piston 9b. Figure 1 As shown, the pressure receiving chamber 9d is connected to the pilot pump 18 via the electromagnetic proportional pressure reducing valve 11. The pressure receiving chamber 9c is connected to the pilot pump 18 without passing through the electromagnetic proportional pressure reducing valve 11. The pilot primary pressure generated by the pilot pump 18 acts on the pressure receiving chamber 9c. When the pressure equivalent to that of the pressure receiving chamber 9c acts on the pressure receiving chamber 9d, the servo piston 9b moves upward as shown in the figure due to the difference in the pressure receiving area. When the pressure receiving chamber 9d is depressurized, the servo piston 9b moves downward as shown in the figure.

[0041] like Figure 2 As shown, the servo piston 9b has a small diameter portion and a large diameter portion. A step portion is formed between the small diameter portion and the large diameter portion. The step portion of the servo piston 9b contacts the step of the cylinder chamber 9a, thereby determining one end (upper limit) of the movable range of the servo piston 9b. In addition, the end surface (lower end surface in the figure) of the servo piston 9b contacts the end (lower end in the figure) of the cylinder chamber 9a, thereby determining the other end (lower limit) of the movable range of the servo piston 9b.

[0042] -Main pump operation-

[0043] When the rotating shaft 2 is driven to rotate by the engine 19, the cylinder block 3 connected to the drive plate 2a is also driven to rotate. In response, each piston 4 reciprocates in each cylinder chamber 3a of the cylinder block 3. Each piston 4 repeatedly performs the suction process and the discharge process. As a result, the main pump 10 draws oil from the oil tank 12 (see Figure 1 ) The sucked working oil is ejected from the ejection port as pressurized oil.

[0044] The discharge flow rate of the main pump 10 is adjusted by changing the tilting angle. When the position of the servo piston 9b is changed, the valve plate 6a moves along the guide surface of the head housing 7b. When the position of the valve plate 6a is changed, the tilting angle changes. As a result, the displacement of each piston 4 sliding in each cylinder chamber 3a is changed. As a result, the flow rate discharged from the main pump 10 is changed. When the servo piston 9b is displaced to the pressure chamber 9c side (the upper side as shown in the figure), the tilting angle becomes smaller, and the discharge flow rate of the main pump 10 becomes smaller. On the other hand, when the servo piston 9b is displaced to the pressure chamber 9d side (the lower side as shown in the figure), the tilting angle becomes larger, and the discharge flow rate of the main pump 10 becomes larger.

[0045] -Volume Control Device-

[0046] like Figure 1 As shown, the volume control device 20 has an electromagnetic proportional pressure reducing valve 11. The electromagnetic proportional pressure reducing valve 11 has: a pump port 11a, a tank port 11b and a control pressure port 11c. The pump port 11a is connected to the discharge port of the pilot pump 18. The tank port 11b is connected to the tank 12 storing the working oil. The control pressure port 11c is connected to the pressure receiving chamber (control pressure chamber) 9d of the tilt actuator 9. The electromagnetic proportional pressure reducing valve 11 has: a solenoid 11d, a valve core 11e and a spring 11f. The spring 11f applies force to the valve core 11e in a direction opposite to the thrust generated by the solenoid 11d.

[0047] An electric signal (electrical command signal) is input as a control input from the pump controller 30 to the electromagnetic proportional pressure reducing valve 11. The electromagnetic proportional pressure reducing valve 11 generates a pilot secondary pressure to be guided to the pressure receiving chamber 9d on the large diameter side of the tilt actuator 9 using the discharge pressure (pilot primary pressure) of the pilot pump 18 as the initial pressure.

[0048] Figure 3 It is a characteristic diagram of the electrical signal and output pressure of the electromagnetic proportional pressure reducing valve 11. Figure 3 As shown, the horizontal axis represents the value of the electric signal input to the solenoid 11d of the electromagnetic proportional pressure reducing valve 11. The value of the electric signal is, for example, the value of the control current (excitation current). The vertical axis represents the pressure (pilot secondary pressure) output from the electromagnetic proportional pressure reducing valve 11 to the pressure receiving chamber (control pressure chamber) 9d.

[0049] An electric signal corresponding to the target pump volume value is input to the electromagnetic proportional pressure reducing valve 11. When the value of the electric signal increases, the valve core 11e moves to one side ( Figure 1The pressure chamber (control pressure chamber) 9d is connected to the oil tank 12. As a result, the pressure in the pressure chamber 9d decreases, and the hydraulic load acting on the large diameter part of the servo piston 9b becomes smaller than the hydraulic load acting on the small diameter part of the servo piston 9b. Therefore, the servo piston 9b moves to one side ( Figure 1 The greater the displacement of the servo piston 9b from the upper limit position to the lower direction, the greater the volume of the main pump 10. On the other hand, when the value of the electrical signal to the electromagnetic proportional pressure reducing valve 11 decreases, the valve core 11e moves to the other direction ( Figure 1 The pressure receiving chamber (control pressure chamber) 9d is connected to the pilot pump 18. As a result, the pressure in the pressure receiving chamber (control pressure chamber) 9d increases, and the hydraulic load acting on the large diameter portion of the servo piston 9b becomes larger than the hydraulic load acting on the small diameter portion of the servo piston 9b. Therefore, the servo piston 9b moves to the other side ( Figure 1 The greater the displacement of the servo piston 9b from the lower limit position to the upper direction, the smaller the capacity of the main pump 10.

[0050] like Figure 3 As shown, there is a correlation between the value of the electrical signal to the electromagnetic proportional pressure reducing valve 11 and the pilot secondary pressure output from the electromagnetic proportional pressure reducing valve 11, and there are upper and lower limits for the output pressure (control pressure of the tilt actuator 9) and the value of the electrical signal. In this embodiment, Figure 3 The value of the electric signal shown is the value of the control current (excitation current) supplied to the solenoid 11d of the electromagnetic proportional pressure reducing valve 11. Regarding the electromagnetic proportional pressure reducing valve 11 of this embodiment, the control current value is increased from the minimum current value I min The first current value I1 is a dead zone on the lower limit side of the control input. That is, the control current value is the minimum current value I min When the minimum current value I is greater than 1 and less than the first current value I1, the output pressure of the electromagnetic proportional pressure reducing valve 11 is the pilot primary pressure (the upper limit of the control pressure) Pp. min The electromagnetic proportional pressure reducing valve 11 controls the current value from the second current value I2 to the maximum current value I max is the dead zone on the upper limit side of the control input. That is, the control current value is greater than the second current value I2 and the maximum current value I max When the control current value is greater than the first current value I1 and less than the second current value I2, the output pressure of the electromagnetic proportional pressure reducing valve 11 is the tank pressure (lower limit value of the control pressure) Pt. In the range where the control current value is greater than the first current value I1 and less than the second current value I2, the output pressure decreases as the control current value increases.

[0051] -Volume Sensor-

[0052] like Figure 1 As shown, the servo piston 9b and the position of the detection servo piston 9b (displacement x from the reference position)sp ) is connected to a position sensor 13. The reference position is, for example, the position where the step portion of the servo piston 9b abuts against the step of the cylinder chamber 9a. The position sensor 13 outputs the detected position of the servo piston 9b to the pump controller 30. As described later, the position of the servo piston 9b is correlated with the actual volume of the main pump 10. That is, the position sensor 13 functions as a volume sensor that detects the actual volume (volume measurement value) of the main pump 10.

[0053] The pump controller 30 is connected to the vehicle body controller 40. The vehicle body controller 40 calculates a target value of the volume of the main pump 10 (hereinafter also referred to as a target volume value) q ref , and outputs the calculation result to the pump controller 30.

[0054] -Hardware structure of the controller-

[0055] The pump controller 30 is composed of a computer having a processing device such as a CPU (Central Processing Unit), an MPU (Micro Processing Unit), and a DSP (Digital Signal Processor), a non-volatile memory such as a ROM (Read Only Memory), a flash memory, and a hard disk drive, a volatile memory called a so-called RAM (Random Access Memory), an input / output interface, and other peripheral circuits. These hardware cooperate to make the software work and realize multiple functions. In addition, the pump controller 30 can be composed of one computer or a plurality of computers.

[0056] Programs capable of performing various operations, various threshold values, data tables, mathematical models, etc. are stored in the non-volatile memory. The non-volatile memory is a storage medium (storage device) that can read the program that implements the functions of this embodiment. The volatile memory is a storage medium (storage device) that temporarily stores the operation results of the processing device and the signals input from the input and output interface. The processing device is a device that expands the program stored in the non-volatile memory in the volatile memory and performs the operation, and performs the prescribed operation processing on the data taken from the input and output interface, the non-volatile memory and the volatile memory according to the program.

[0057] The input section of the input / output interface converts the signals input from various devices (such as the position sensor 13) into data that can be calculated by the processing device. In addition, the output section of the input / output interface generates an output signal corresponding to the calculation result in the processing device and outputs the signal to various devices (such as the electromagnetic proportional pressure reducing valve 11).

[0058] The vehicle body controller 40 , like the pump controller 30 , is constituted by a computer including a processing device, a storage device (volatile memory and nonvolatile memory), an input / output interface, and other peripheral circuits.

[0059] - Main pump control device -

[0060] The vehicle body controller 40 and the pump controller 30 of this embodiment function as a control device for the main pump 10. The control device for the main pump 10 changes the supply flow rate of the working oil from the main pump 10 to the hydraulic system for the purpose of improving the efficiency of the hydraulic system. This is achieved by changing the volume of the main pump 10 (equivalent to the discharge flow rate per rotation) according to various operating states and operating conditions of the working machine.

[0061] -Functions of the pump controller-

[0062] The position x of the servo piston 9b is stored in the pump controller 30. sp The conversion factor k converted to the actual volume of the main pump 10 is pu . Conversion factor k pu The position x of the servo piston 9b sp The geometrical relationship with the components of the main pump 10 is predetermined. pu is a fixed value. In addition, the conversion coefficient may be a variable k that changes according to the position of the servo piston 9b pu (x sp The pump controller 30 determines the position x of the servo piston 9b detected by the position sensor 13. sp and conversion factor k pu The actual volume (volume measured value) q of the main pump 10 is calculated p (q p =k pu ·x sp The pump controller 30 controls the volume target value q of the main pump 10. ref and the measured volume q p To control the electromagnetic proportional pressure reducing valve 11, so that the measured volume value q p Approaching the volume target value q ref .

[0063] The pump controller 30 can adjust the tilting angle (volume) of the main pump 10 by adjusting the value of the electrical signal to the electromagnetic proportional pressure reducing valve 11. Here, when the value of the electrical signal input to the electromagnetic proportional pressure reducing valve 11 is increased, the servo piston 9b moves in the direction in which the tilting angle becomes larger. The servo piston 9b moves until the large diameter portion of the servo piston 9b abuts against the lower end surface of the cylinder chamber 9a. On the other hand, when the value of the electrical signal input to the electromagnetic proportional pressure reducing valve 11 is reduced, the servo piston 9b moves in the direction in which the tilting angle becomes smaller. The servo piston 9b moves until the step portion of the servo piston 9b abuts against the step of the cylinder chamber 9a. Therefore, in order to move or maintain the servo piston 9b at an arbitrary position, it is necessary to gradually change the value of the electrical signal input to the electromagnetic proportional pressure reducing valve 11.

[0064] The control pressure characteristic of the tilt actuator 9 is different when the working oil flows out of the pressure chamber (control pressure chamber) 9d and when the working oil flows into the pressure chamber (control pressure chamber) 9d. Therefore, if there is a state transition between the state where the working oil flows out of the pressure chamber 9d and the state where the working oil flows into the pressure chamber 9d, the control pressure characteristic of the tilt actuator 9 switches. In this way, since the control pressure characteristic switches, when the measured volume value is near the target volume value, the control pressure characteristic of the tilt actuator 9 is a nonlinear characteristic.

[0065] The pump controller 30 calculates the volume target value q ref The measured volume q p The deviation is the volume deviation e. The volume deviation e is equivalent to the deviation from the volume target value q ref Subtract the measured volume value q p The absolute value of the value obtained (e = |q ref -q p |). The pump controller 30 inputs the volume deviation e to the control system, and outputs an electric signal to the solenoid 11d of the electromagnetic proportional pressure reducing valve 11 as a control input u for reducing the volume deviation e.

[0066] Here, the content of the volume feedback control performed by the pump controller of the comparative example of the present embodiment and the problems that may arise at this time are described. The pump controller of the comparative example performs volume feedback control using a control system that does not consider the upper and lower limits of the electrical signal value to the electromagnetic proportional pressure reducing valve 11 and the change in the control pressure characteristics of the tilting actuator 9 when the measured volume value is near the volume target value. The specific flow of the control action is as follows.

[0067] (Action 1) The pump controller of the comparative example outputs an electrical signal for increasing the volume to the electromagnetic proportional pressure reducing valve 11 for controlling the tilt actuator 9. That is, the pump controller of the comparative example increases the value of the electrical signal. (Action 2) The working oil in the cylinder chamber 9a of the tilt actuator 9 flows out, and the tilt actuator 9 moves in the direction of increasing the volume. (Action 3) When the measured volume value reaches the target volume value, the pump controller of the comparative example sets the value of the electrical signal for controlling the tilt actuator 9 to 0 (zero). (Action 4) According to the characteristics of the electrical signal to the electromagnetic proportional pressure reducing valve 11, the structural characteristics of the electromagnetic proportional pressure reducing valve 11, the structural characteristics of the tilt actuator 9, and the control pressure characteristics of the tilt actuator 9, the tilt actuator 9 does not stay at the target position corresponding to the target volume value, but stops after exceeding the target position. As a result, the measured volume value is greater than the target volume value. (Action 5) Therefore, the pump controller of the comparative example outputs an electrical signal for reducing the volume to the electromagnetic proportional pressure reducing valve 11. That is, the pump controller of the comparative example reduces the value of the electrical signal. (Action 6) The working oil flows into the cylinder chamber 9a of the tilt actuator 9, and the tilt actuator 9 moves in the direction of reducing the volume. (Action 7) As with the above (Action 3) and (Action 4), the tilt actuator 9 does not stay at the target position corresponding to the volume target value, but stops after exceeding the target position. As a result, the actual volume value is less than the volume target value. (Action 8) When the above (Action 1) to (Action 7) are repeated, the working oil in the cylinder chamber 9a of the tilt actuator 9 switches between outflow and inflow, and therefore, the control pressure characteristics of the tilt actuator 9 switch.

[0068] In the control performed by the pump controller of the comparative example, as the main reasons affecting the tracking accuracy of the measured volume value relative to the volume target value during the transient response, that is, the main reasons for the nonlinear characteristics of the pump volume, there are: the existence of a dead zone in the control input corresponding to the upper and lower limits of the control pressure, and the change in the control pressure characteristics of the tilting actuator 9 when the measured volume value is near the volume target value. The dead zone existing in the control input is the main reason for the increase in the overshoot or undershoot relative to the volume target value caused by the switching delay of the control input. In addition, the control pressure characteristics of the tilting actuator 9 switch between the characteristics when the working oil flows into the cylinder chamber 9a and the characteristics when the working oil flows out of the cylinder chamber 9a, which is the main reason for the increase in the duration and vibration amplitude of the oscillation phenomenon (vibration phenomenon) of the measured volume value relative to the volume target value.

[0069] As described above, in the method of feedback control of the measured volume value by PI control, etc., it may be impossible to obtain good tracking accuracy of the measured volume value relative to the target volume value during the transient response. Therefore, in the present embodiment, the following model predictive control is used: it is possible to reflect the restrictions of the control input (hereinafter, also referred to as the control input restrictions) when designing the control system, and it is possible to use the control input restrictions of the main pump 10 (the upper limit and lower limit of the control input) as conditions when calculating the control input. The model predictive control is performed for the purpose of reducing the volume deviation e. In addition, the control input restrictions are made variable for changes in the control pressure characteristics of the tilting actuator 9 when the measured volume value is near the target volume value. Thereby, the stabilization time during the transient response of the pump volume control is shortened. If the stabilization time can be shortened, the action delay of the hydraulic actuator can be improved, and the operability of the working machine using the hydraulic actuator can be improved. Below, the control content of the pump controller 30 of the present embodiment is described in detail.

[0070] -Model Predictive Control-

[0071] Figure 4 It is a control block diagram for controlling the control object through model predictive control. Figure 4 The control object (supporting equipment) 39 of the control system shown is the displacement from the electromagnetic proportional pressure reducing valve 11 to the servo piston 9b. When an electric signal as a control input u(k) is input to the electromagnetic proportional pressure reducing valve 11 as the control object 39, the servo piston 9b is displaced by the output pressure of the electromagnetic proportional pressure reducing valve 11. The displacement of the servo piston 9b is converted into the actual measured volume value q of the main pump 10. p .

[0072] The vehicle body controller 40 calculates a target volume value q based on the amount of operation of the operating lever of the hydraulic actuator 17 and the discharge pressure of the main pump 10. ref The operation amount of the operating lever is detected by the operation amount sensor. The discharge pressure of the main pump 10 is detected by the discharge pressure sensor. In addition, the vehicle body controller 40 can also further consider the speed of the hydraulic actuator 17, the angle and position of the parts driven by the hydraulic actuator 17, etc. to calculate the volume target value q ref The vehicle body controller 40 calculates the target volume value q ref The signal is output to the pump controller 30 .

[0073] The pump controller 30 has functions as a model predictive control unit 31, a predictor 32, and a successive least squares solver 33. The model predictive control unit 31 uses the volume target value q ref , measured volume value q p, the control input u calculated in the previous control cycle, the control input limit, and a mathematical model for predicting the volume behavior of the main pump 10 (hereinafter also referred to as a prediction model) to calculate the optimal control input u in real time.

[0074] The prediction model is a physical model for predicting the volume (future volume) after a predetermined time has passed from the current time point, and is represented by the following equation (1). The prediction model is stored in advance in the nonvolatile memory of the pump controller 30 .

[0075] [Mathematical formula 1]

[0076]

[0077] In the state equation (1), x(k) is the state vector. The structure of the state vector x(k) can be arbitrarily designed. k represents the control cycle (number of steps) of the current (operation time point), and k+1 represents the control cycle one after the current control cycle. A is the system matrix of the prediction model, B is the control input vector of the prediction model, and C is the output vector of the prediction model. The matrix A and the vectors B and C are designed to match the structure of the state vector x(k).

[0078] The parameters constituting the matrix A and the vectors B and C, i.e., the parameters of the prediction model use values ​​obtained in advance by an identification method or the like, or values ​​updated at sample time by an adaptive identification method. When the parameters are obtained in advance by an identification method, the parameters can use the average value of a plurality of parameters obtained by changing at least one of the load pressure (discharge pressure of the main pump 10) and the temperature of the working oil. Thus, even if the operating environment changes, the deviation of the characteristics can be reduced. As a result, the tilting angle of the main pump 10 can follow the target value with high accuracy.

[0079] In this embodiment, the state vector x(k) is expressed by the following equation (2).

[0080] [Mathematical formula 2]

[0081] x(k)=[q p (k) q p (k-1)] T …(2)

[0082] In formula (2), q p (k) is the measured volume value obtained in the current control cycle, q p (k-1) is the actual volume measurement value obtained in the control cycle before the current control cycle.

[0083] The model prediction control unit 31 and the predictor 32 use the control input u(k) and the volume measurement value q p(k) and the prediction model to calculate the predicted value of the volume of the main pump 10 (hereinafter also referred to as the predicted volume value) q p ^. The predictor 32 calculates the volume measured value q p (k) and volume prediction value q p The deviation of ^(k) is the prediction error ε(k)(ε(k)=q p (k)-q p ^(k)). Volume prediction value q p ^(k) is passed through θ(k) as the prediction model parameter and the regression vector It is expressed by the following equation (3): The parameter θ(k) includes the parameters of the system matrix A, the control input vector B, and the output vector C constituting the prediction model.

[0084] [Mathematical formula 3]

[0085]

[0086] Regression vector Use the measured volume q p (k) and the control input u(k) are expressed by the following equation (4). In addition, the regression vector This is a structure designed to match the structure of the state vector x(k), and the description of formula (4) is an example.

[0087] [Formula 4]

[0088]

[0089] The successive least squares solver 33 uses the measured volume value q p (k), control input u(k) and prediction error ε(k), and calculate the optimal value (prediction value) of the parameter θ(k) of the prediction model (mathematical model of the predictor), that is, the parameter prediction value θ^(k) in real time by the successive least squares method. The successive least squares solver 33 calculates the parameter prediction value θ^(k) of the prediction model so that the prediction error ε(k) calculated by the predictor 32 is close to 0 (zero). Specifically, the successive least squares solver 33 calculates the parameter prediction value θ^(k) by the following formula (5b), so that the evaluation function J represented by the following formula (5a) θ (k)Min.

[0090] [Mathematical formula 5]

[0091]

[0092] The parameter prediction value θ^(k) includes the parameters constituting the system matrix A, the control input vector B, and the output vector C. As described above, based on the volume measurement value q p (k) and control input u(k) to calculate the regression vector

[0093] The successive least squares solver 33 rewrites (overwrites) the parameters of the prediction model stored in the non-volatile memory with the parameters included in the parameter prediction value θ^(k) as the calculation result. As a result, the matrix A and vectors B and C of the prediction model used in the model prediction control unit 31 and the predictor 32 are updated by the parameter prediction value θ^(k) calculated by the successive least squares solver 33. This update process is repeatedly performed in a predetermined control cycle. That is, the prediction model is updated in real time by the successive least squares solver 33. In addition, when the prediction error ε(k) is 0, the prediction model is not substantially updated.

[0094] Furthermore, the volume of the main pump 10 can be controlled even without updating the prediction model. In this case, the parameters of the prediction model can be determined based on the test results under certain operating conditions. In addition, the average value of multiple parameters calculated based on changes in operating conditions such as load pressure and the temperature of the working oil can also be used as the parameters of the prediction model. However, during the operation of working machinery such as hydraulic excavators, the operating conditions (load pressure, temperature of the working oil), the actual volume of the main pump 10, etc. are always changing. Therefore, if the parameters of the prediction model are set to fixed values, the accuracy of the prediction control is reduced. That is, a deviation occurs between the actual value and the predicted value due to not updating the prediction model. Therefore, as in the present embodiment, it is preferred to update the parameters of the prediction model so as to be able to cope with changes in the operating conditions and the actual volume of the main pump 10. In this way, the accuracy of the prediction control can be improved.

[0095] The model prediction control unit 31 calculates the volume target value q ref The volume prediction value q calculated by the prediction model p The model prediction control unit 31 calculates the evaluation function J(k) represented by the following equation (6).

[0096] [Mathematical formula 6]

[0097]

[0098] Δu^ is the predicted change in the control input. p represents the prediction interval, H u The first term on the right side of equation (6) is: In the prediction interval of the specified time width (i = 1, ..., H p ) Volume target value q ref and volume prediction value q p The second term on the right side of equation (6) is: In the control interval of the specified time width (i = 0, ...H u-1). In addition, Q and R are design parameters of the control system used to weight the first and second terms, respectively. (k+i|k) refers to the value corresponding to each i in step k. For example, when i=2, it refers to the predicted value two steps ago when the prediction was made in step k (current time point). In addition, the volume prediction value q p The initial value of ^ is the measured volume value q p For another example, the initial value of the predicted change amount Δu^ is equivalent to the value obtained by subtracting the control input u(k-1) of the previous step (k-1) of step (k) from the control input u(k) of step (k).

[0099] The model prediction control unit 31 calculates the control input u(k) based on the control input restriction expressed by the following equation (7) so that the control input u(k) includes the volume prediction value q p The evaluation function J(k) of ^ is the minimum.

[0100] [Formula 7]

[0101]

[0102] Control input limit means: the upper limit value u of the control input max and the lower limit u min In this embodiment, the model prediction control unit 31 is based on the volume target value q ref And the measured volume value q p The volume deviation e is calculated as an evaluation value, and the control input limit is changed according to the calculated volume deviation e. The deviation threshold value e, which is a threshold value for the volume deviation e, is stored in the nonvolatile memory of the pump controller 30. th The model prediction control unit 31 calculates the volume deviation e and the deviation threshold e according to the volume deviation e. th The control input limit value is set according to the size relationship of

[0103] The volume deviation e is the deviation threshold e th In the above case, the upper limit value u of the control input max is the first upper limit u max1 , when the volume deviation e is less than the deviation threshold e th In the case of max is the second upper limit u max2 The first upper limit u max1 As long as the second current value I2 is greater than the maximum current value I max That is, the first upper limit value u is set within the following dead zone range: max1 : Even if the value of the electrical signal changes, the output pressure of the electromagnetic proportional pressure reducing valve 11 is maintained at the tank pressure Pt (fixed value). max2A value greater than the first current value I1 and smaller than the second current value I2 may be used, or a value greater than the second current value I2 may be used. max2 is greater than the first upper limit u max1 Small values ​​are fine.

[0104] The volume deviation e is the deviation threshold e th In the above case, the lower limit value u of the control input min is the first lower limit u min1 , when the volume deviation e is less than the deviation threshold e th In the case of min is the second lower limit u min2 The first lower limit u min1 As long as the minimum current value I min That is, the first lower limit value u is set within the following dead zone range: min1 : Even if the value of the electrical signal changes, the output pressure of the electromagnetic proportional pressure reducing valve 11 is maintained at the pilot primary pressure Pp (fixed value). min2 A value greater than the first current value I1 and smaller than the second current value I2 may be used, or a value less than the first current value I1 may be used. min2 is lower than the first lower limit u min1 Larger than the second upper limit u max2 In addition, the deviation threshold value e used to change the condition of control input limitation is th , you can change the upper limit value u max When and change the lower limit u min Set to different values.

[0105] In this embodiment, the change characteristics of the control input limit with respect to time have the characteristics of discretizing the first-order delay system 1 / (τs+1). s is the Laplace operator, and τ is the time constant. The time constant τ is set arbitrarily.

[0106] -Model Predictive Control Process-

[0107] Figure 5 is a flowchart of the model predictive control executed by the pump controller 30 . Figure 5 The control flow shown is started, for example, when an ignition switch of the working machine is turned on, and is repeatedly executed in a predetermined control cycle.

[0108] In step S110 , the pump controller 30 obtains the target volume value q from the vehicle body controller 40 . ref In the next step S120, the pump controller 30 obtains the position x of the servo piston 9b detected by the position sensor 13. spIn the next step S130, the pump controller 30 controls the position x of the servo piston 9b. sp Multiply by the conversion factor k pu , calculate the measured volume value q p In the next step S140, the pump controller 30 calculates the volume target value q ref The measured volume q p Volume deviation e.

[0109] In the next step S150, the pump controller 30 determines the control input limit (Formula (7)) according to the size of the volume deviation e. In the next step S160, the pump controller 30 determines the control input limit according to the prediction model of the volume of the main pump 10 (Formulas (1) and (2)) and the actual volume measurement value q calculated in step S130. p , the control input u calculated in the previous control cycle, and the control input limit determined in step S150 (formula (7)), calculate the optimal control input u so that the above-mentioned evaluation function J (formula (6)) is minimized. In the next step S170, the pump controller 30 outputs an electrical signal corresponding to the control input u calculated in step S160 to the solenoid 11d of the electromagnetic proportional pressure reducing valve 11.

[0110] When the processing of step S170 is completed, the control cycle ends. Figure 5 The pump controller 30 executes the processing shown in the flowchart shown in FIG.

[0111] -Time series variation of control input limits-

[0112] Figure 6 is the control input limit (upper limit u) set by the pump controller 30 max And the lower limit u min ) time series waveform diagram. Figure 6 In the example, the upper limit value u of the control input max And the lower limit u min The volume deviation e is represented by a thick solid line and the volume deviation e is represented by a thin solid line. ref When changing, the measured volume value q p To follow the volume target value q ref As a result, the volume deviation e becomes smaller. From time t1 to time t2, the volume deviation e is the deviation threshold value e. th Therefore, the upper limit value u of the control input max is the first upper limit u max1 , the lower limit value u of the control input min is the first lower limit u min1From time t2 to time t3, the volume deviation e is less than the deviation threshold e th Therefore, the upper limit value u of the control input max After a predetermined time has passed from time t2, the second upper limit value u max2 , the lower limit value u of the control input min After a predetermined time has passed from time t2, the second lower limit value u min2 .

[0113] After that, the volume deviation e increases, and from time t3 to time t4, it is the deviation threshold e th Therefore, the upper limit value u of the control input max After a predetermined time has passed from time t3, the first upper limit value u max1 , the lower limit value u of the control input min After a predetermined time has passed from time t3, the first lower limit value u min1 After that, the volume deviation e decreases again, and after time t4, the volume deviation e is less than the deviation threshold e th Therefore, the upper limit value u of the control input max After a predetermined time has passed from time t4, the second upper limit value u max2 , the lower limit value u of the control input min After a predetermined time has passed from time t4, the second lower limit value u min2 Furthermore, the control input limits are prevented from changing immediately by delay processing based on the first-order delay.

[0114] -Simulation results of the present embodiment and its comparative example-

[0115] Reference Figure 7 , main operations and effects of the pump system 100 of this embodiment are described. Figure 7 is a diagram showing the time series change of the volume of the pump system 100. Figure 7 The volume target value q ref The time series change of the volume in the present embodiment is indicated by a dashed line. In addition, in order to clarify the effect of the present embodiment, the time series change of the volume controlled by the pump controller of the comparative example of the present embodiment is indicated by a dotted line. The control of the pump controller of the comparative example differs from the control of the present embodiment only in that the control input limit is not changed. That is, in the comparative example, the upper limit value u of the control input is max Always the first upper limit u max1 , the lower limit value u of the control input min Always the first lower limit u min1 The horizontal axis represents time (elapsed time), and the vertical axis represents the volume of the main pump 10. The curves representing the time-series changes in the volumes of the present embodiment and the comparative example are obtained by numerical simulation.

[0116] Figure 7 Δt0 and Δt1 are the stabilization times until the volume of the main pump 10 is stabilized. The stabilization times Δt0 and Δt1 are calculated from the volume target value q ref In addition, when the volume deviation e stays within the specified error range (volume target value q ref ±De), the stabilization time is defined as the time when the volume deviation e enters the above error range (volume target value q ref ±De) within the time.

[0117] like Figure 7 As shown, if the volume target value q ref When the predetermined amount Du is reduced to the predetermined amount D1, the volume ratio target value q ref (= D1) The undershoot is reduced. In the comparative example, the undershoot amount is larger than that of the present embodiment. In addition, in the comparative example, the oscillation (vibration) of the volume continues after the undershoot occurs. In other words, in the comparative example, the vibration with a large amplitude continues for a long time.

[0118] In contrast, in the present embodiment, the undershoot amount is smaller than that of the comparative example. In addition, in the present embodiment, oscillation (vibration) of the volume after the undershoot is prevented from occurring. As a result, the stabilization time Δt1 of the present embodiment is shorter than the stabilization time Δt0 of the comparative example.

[0119] As described above, in this embodiment, the model predictive control (MPC) is used, and the nonlinearity of the upper and lower limits of the electric signal value to the electromagnetic proportional pressure reducing valve 11 can be used to limit the control input as a condition for calculating the control input. p At volume target value q ref The nonlinearity of the control pressure characteristic of the pressure receiving chamber 9d of the tilt actuator 9 when the actual volume follows the volume target value q can be reduced. ref The undershoot size (undershoot amount) generated when the main pump 10 is turned on can be reduced, and the generation of oscillation (vibration) can be prevented. As a result, the stabilization time during the transient response can be shortened. That is, according to this embodiment, the actual volume relative to the volume target value q of the main pump 10 can be improved. ref As a result, the operation delay of the hydraulic actuator 17 mounted on a working machine such as a hydraulic excavator can be improved. The improvement of the operation delay of the hydraulic actuator 17 is related to the improvement of the workability of the working machine.

[0120] -Effects of the present embodiment-

[0121] According to the above-described embodiment, the following effects are achieved.

[0122] (1) A pump system (control device for a working machine) 100 includes a main pump (hydraulic pump) 10, a displacement control device 20, a position sensor 13, and a pump controller (controller) 30. The main pump 10 is driven by an engine (prime mover) 19 to rotate and supply hydraulic oil to a hydraulic actuator 17. The displacement control device 20 controls the displacement of the main pump 10 according to a control input u. The position sensor 13 detects a measured value q of the displacement of the main pump 10. p The pump controller 30 obtains the target volume value q of the main pump 10. ref and outputs the volume target value q to the volume control device 20 ref The pump controller 30 stores a mathematical model for predicting the capacity of the main pump 10, namely, a prediction model. The pump controller 30 uses the prediction model to calculate the predicted capacity value q of the main pump 10. p ^. The pump controller 30 calculates the volume prediction value q p ^ and the limit of the control input u (upper limit u max And the lower limit u min ) to calculate the optimal control input u. The pump controller 30 calculates the optimal control input u based on the volume target value q ref And the measured volume value q p The evaluation value (the volume deviation e in the present embodiment) is calculated. The pump controller 30 changes the limit of the control input u according to the evaluation value.

[0123] According to this structure, the volume measured value q can be improved. p Relative to the target volume value q of the main pump 10 ref That is, the responsiveness of the displacement control of the main pump 10 can be improved. As a result, the control accuracy of the hydraulic actuator 17 can be improved, thereby improving the operability of the working machine.

[0124] (2) The pump controller 30 stores a threshold value (deviation threshold value e) for the evaluation value (volume deviation e). th The pump controller 30 determines the volume deviation based on the evaluation value (volume deviation e) and the threshold value (deviation threshold value e). th ) to set the limit value of the control input. The pump controller 30 sets the change characteristics of the control input limit relative to time as a first-order delay system. According to this structure, compared with the case where the control input limit is changed discontinuously, the undershoot (or overshoot) and the vibration amplitude can be reduced.

[0125] (3) The control input limit includes the upper limit value u of the control input max and the lower limit u min The pump controller 30 uses the threshold value e when the evaluation value (volume deviation e) reaches the upper limit. th When the upper limit u is maxSet as the first upper limit u max1 The pump controller 30 uses the threshold value e when the evaluation value (volume deviation e) is less than the upper limit value. th When the upper limit u max Set to be higher than the first upper limit u max1 The second small upper limit u max2 In addition, the pump controller 30 uses a threshold value e when the evaluation value (volume deviation e) is the lower limit value. th When the lower limit u is min Set as the first lower limit u min1 The pump controller 30 uses the threshold value e when the evaluation value (volume deviation e) is less than the lower limit value. th When the lower limit u min Set to be lower than the first lower limit u min1 The second lower limit u min2 In addition, in the present embodiment, the upper limit threshold and the lower limit threshold are the same value e th Although the example is described, the upper limit threshold and the lower limit threshold may be different values.

[0126] According to this configuration, when the evaluation value (volume deviation e) becomes smaller, the upper limit value u of the control input is max And the lower limit u min Both are close to the stable value (target value). max Changes, or only the lower limit u min Compared with the case where the current changes, the undershoot amount can be reduced and the vibration amplitude can be suppressed. In other words, the stabilization time can be effectively shortened.

[0127] (4) The pump controller 30 uses the volume target value q ref The measured volume q p According to this configuration, the control input limit can be appropriately changed according to the change in the volume deviation e.

[0128] In addition, as an evaluation value for changing the control input limit, the value of the evaluation function J(k) that is minimized in order to determine the control input u(k) may be used instead of the volume deviation e. The evaluation function J(k) includes the sum of squares of the deviations between the volume target value and the volume prediction value in the prediction interval of a predetermined time width. Therefore, when the control input limit is changed according to the value of the evaluation function J(k), the control input limit can be appropriately changed. In this way, the evaluation value may use the volume deviation e or the value of the evaluation function. Therefore, in this embodiment, the control system has a high degree of freedom in structure.

[0129] (5) The pump controller 30 uses the measured volume value q pAnd the prediction model (mathematical model) is updated by the control input u. In the present embodiment, when the characteristics of the prediction model change significantly, the optimal parameter prediction value is calculated in a manner that conforms to the changed characteristics, and the prediction model used for prediction is updated according to the parameter prediction value. As a result, the pump volume prediction value can be calculated with higher accuracy using a prediction model suitable for the actual characteristics. In this way, in the present embodiment, by making the limit of the control input u variable and updating the prediction model, the response time of the volume control of the main pump 10 can be reduced compared to the case where the prediction model is not updated. As a result, the operating efficiency of the operating machinery can be improved.

[0130] <Second embodiment>

[0131] Reference Figures 8 to 10 , a pump system 100 according to a second embodiment of the present invention is described. In addition, the same reference symbols are given to structures that are the same as or equivalent to those described in the first embodiment, and mainly the differences are described. In the first embodiment, an example in which only one deviation threshold value for changing the control input limit is stored in the pump controller 30 is described. In contrast, in the second embodiment, multiple deviation threshold values ​​for changing the control input limit are stored in the pump controller 30. That is, in the second embodiment, the control input limit changes in multiple stages. The following is a detailed description.

[0132] Figure 8 is with Figure 5 The same figure is a flowchart of the model predictive control executed by the pump controller 30 of the second embodiment. Figure 8 In the flowchart, replace Figure 5 The process of step S150 of the flowchart is executed, and the process of step S250 is executed. In addition, the processes of steps S110 to S140, S160, and S170 are the same as those in the first embodiment, and therefore, the description thereof is omitted.

[0133] like Figure 8 As shown, in step S250 , the pump controller 30 determines the control input limit according to the size of the volume deviation e.

[0134] In the second embodiment, the control input limitation is expressed by the following equation (8).

[0135] [Mathematical formula 8]

[0136]

[0137] The volume deviation e is the first deviation threshold e th1 In the above case, the upper limit value u of the control input max is the first upper limit u max1 , when the volume deviation e is less than the first deviation threshold e th1and is greater than the second deviation threshold e th2 In the case of max is the second upper limit u max2 The first upper limit u max1 As long as the second current value I2 is greater than the maximum current value I max That is, the first upper limit value u is set within the following dead zone range: max1 : Even if the value of the electrical signal changes, the output pressure of the electromagnetic proportional pressure reducing valve 11 is maintained at the tank pressure Pt (fixed value). max2 is higher than the first upper limit u max1 In addition, when the volume deviation e is the second deviation threshold value e th2 In the following cases, the upper limit value u of the control input max is the third upper limit u max3 The third upper limit value u max3 is less than the second upper limit u max2 The value of .

[0138] The volume deviation e is the first deviation threshold e th1 In the above case, the lower limit value u of the control input min is the first lower limit u min1 , when the volume deviation e is greater than the first deviation threshold e th1 smaller than the second deviation threshold e th2 When the control input is large, the lower limit value u min is the second lower limit u min2 The first lower limit u min1 As long as the minimum current value I min That is, the first lower limit value u is set within the following dead zone range: min1 : Even if the value of the electrical signal changes, the output pressure of the electromagnetic proportional pressure reducing valve 11 is maintained at the pilot primary pressure Pp (fixed value). min2 is lower than the first lower limit u min1 In addition, when the volume deviation e is the second deviation threshold e th2 In the following cases, the lower limit value u of the control input min is the third lower limit u min3 The third lower limit u min3 is lower than the second lower limit u min2 Large value.

[0139] In this way, the pump controller 30 of the second embodiment stores the information for changing the upper limit value u max The two deviation thresholds e th1 、e th2 The upper limit value u maxThe first upper limit value u is set according to the size of the volume deviation e. max1 , the second upper limit u max2 , the third upper limit u max3 Similarly, the pump controller 30 of the second embodiment stores a value for changing the lower limit value u min The two deviation thresholds e th1 、e th2 The lower limit value umin is set to the first lower limit value u according to the size of the volume deviation e. min1 , the second lower limit u min2 , the third lower limit u min3 One of these three values.

[0140] Fig. 9 is with Figure 6 The same figure shows the control input limit (upper limit value u) set by the pump controller 30 of the second embodiment. max And the lower limit u min ) time series waveform. When the volume target value q is changed ref When the volume is measured, the value q p To follow the volume target value q ref As a result, the volume deviation e becomes smaller. From time t21 to time t22, the volume deviation e is the first deviation threshold value e. th1 Therefore, the upper limit value u of the control input max is the first upper limit u max1 , the lower limit value u of the control input min is the first lower limit u min1 From time t22 to time t23, the volume deviation e is greater than the first deviation threshold e th1 smaller than the second deviation threshold e th2 Therefore, the upper limit value u of the control input max After a predetermined time has passed from time t22, the second upper limit value u max2 , the lower limit value u of the control input min After a predetermined time has passed from time t22, the second lower limit value u min2 From time t23 to time t24, the volume deviation e is the second deviation threshold e th2 Therefore, the upper limit value u of the control input max After a predetermined time has passed from time t23, the third upper limit value u max3 , the lower limit value u of the control input min After a predetermined time has passed from time t23, the third lower limit value u min3 .

[0141] After that, the volume deviation e increases. From time t24 to time t25, the volume deviation e is smaller than the second deviation threshold value e. th2 greater than the first deviation threshold e th1 Therefore, the upper limit value u of the control input max After a predetermined time has passed from time t24, the second upper limit value u max2 , the lower limit value u of the control input min After a predetermined time has passed from time t24, the second lower limit value u min2 From time t25 to time t26, the volume deviation e is the first deviation threshold e th1 Therefore, the upper limit value u of the control input max After a predetermined time has passed from time t25, the first upper limit value u max1 , the lower limit value u of the control input min After a predetermined time has passed from time t25, the first lower limit value u min1 .

[0142] After that, the volume deviation e decreases again. From time t26 to time t27, the volume deviation e is smaller than the first deviation threshold value e th1 smaller than the second deviation threshold e th2 Therefore, the upper limit value u of the control input max After a predetermined time has passed from time t26, the second upper limit value u max2 , the lower limit value u of the control input min After a predetermined time has passed from time t26, the second lower limit value u min2 After time t27, the volume deviation e is equal to the second deviation threshold value e th2 Therefore, the upper limit value u of the control input max After a predetermined time has passed from time t27, the third upper limit value u max3 , the lower limit value u of the control input min After a predetermined time has passed from time t27, the third lower limit value u min3 .

[0143] In addition, the first deviation threshold value e for changing the condition of the control input limitation is th1 and the second deviation threshold e th2 , you can change the upper limit value u max When and change the lower limit u min Set to different values.

[0144] In the second embodiment, as in the first embodiment, the control input limit is prevented from changing immediately by delay processing of the first-order delay. th1The time constant τa used in the first-order delay process performed at the time (time t22, t25, t26) is the same as the time constant τa used in the first-order delay process performed at the time (time t22, t25, t26) when the volume deviation e exceeds the second deviation threshold value e th2 The time constant τb used in the first-order delay processing performed at the times (time t23, t24, t27) may be the same value or different values.

[0145] Fig.10 is with Figure 7 The same figure is a diagram showing the time series change of the volume of the pump system 100 according to the second embodiment. Fig.10 In FIG. 1 , the time series change of the volume in the second embodiment is indicated by a dotted line. In addition, in order to clarify the effect of the second embodiment, the time series change of the volume in the first embodiment is indicated by a dashed line.

[0146] In the second embodiment, the undershoot amount is smaller than that in the first embodiment. In addition, the amplitude of the vibration after the undershoot is also reduced. As a result, the settling time Δt2 of the second embodiment is shorter than the settling time Δt1 of the first embodiment.

[0147] Thus, in the second embodiment, the pump controller 30 stores a plurality of threshold values ​​(deviation threshold values ​​e) for the evaluation value (volume deviation e). th1 、e th2 ). According to this structure, the responsiveness of the volume control of the main pump 10 can be further improved. Therefore, according to this second embodiment, the operability can be further improved. In addition, as in the first embodiment, the prediction model is also updated by the successive least squares method in the second embodiment, thereby further improving the accuracy of the prediction control.

[0148] -Modification of the Second Embodiment-

[0149] In the second embodiment, the second upper limit value u may be max2 and the third upper limit u max3 The magnitude relationship is opposite, and the second lower limit value u min2 and the third lower limit u min3 The size relationship is opposite (u max2 <u max3 ,u min3 <u min2 ). Fig.11 is with Fig.10 The same figure is a diagram showing the time series change of the volume of the pump system 100 according to the modification of the second embodiment. Fig.11 In FIG. 1 , the time series change of the volume of the modification of the second embodiment is indicated by a dotted line. In addition, in order to clarify the effect of the modification of the second embodiment, the time series change of the volume of the first embodiment is indicated by a dashed line.

[0150] In the modification of the second embodiment, the undershoot amount is smaller than that of the first embodiment. In addition, the amplitude of the vibration after the undershoot is also reduced. As a result, the settling time Δt2 ′ of the modification of the second embodiment is shorter than the settling time Δt1 of the first embodiment.

[0151] As described above, according to the modification of the second embodiment, the responsiveness of the displacement control of the main pump 10 can be further improved, similarly to the second embodiment.

[0152] -Other Modifications of the Second Embodiment-

[0153] The pump controller 30 of the second embodiment uses two deviation thresholds e th1 、e th2 To change the control input limit. On the other hand, the pump controller 30 may use three or more deviation thresholds to change the control input limit. In this case, three or more time constants τ in the first-order delay process may also be used.

[0154] <Third Embodiment>

[0155] Reference Fig.12 and Fig.13 , a pump system 100 according to a third embodiment of the present invention is described. In addition, the same reference symbols are given to structures that are the same as or equivalent to those described in the first embodiment, and mainly the differences are described. In the first embodiment, an example of setting the change characteristics of the control input limit with respect to time as a first-order delay system is described. In contrast, in this third embodiment, delay processing is not performed when changing the control input limit. Instead of delay processing, a restriction characteristic table is used to make the control input limit change continuously relative to the deviation threshold value.

[0156] Fig.12 is with Figure 5 The same figure is a flowchart of the model predictive control executed by the pump controller 30 of the third embodiment. Fig.12 In the flowchart, replace Figure 5 The process of step S150 of the flowchart is executed, and the process of step S350 is executed. In addition, the processes of steps S110 to S140, S160, and S170 are the same as those in the first embodiment, and therefore, the description thereof is omitted.

[0157] like Fig.12 As shown, in step S350, the pump controller 30 determines the control input limit according to the size of the volume deviation e. In the third embodiment, when determining the control input limit, the limit tables 301 and 302 defining the relationship between the volume deviation e and the control input limit are used.

[0158] The limit tables 301 and 302 are stored in the nonvolatile memory of the pump controller 30. The limit tables 301 and 302 define the upper limit value u that continuously changes with respect to the volume deviation e. max The upper limit value table (hereinafter also referred to as the upper limit value table) 301 for the characteristic of the upper limit value of the volume deviation e is defined as the lower limit value u of the continuous change of the volume deviation e. min A restriction table (hereinafter also referred to as a lower limit value table) 302 for the lower limit values ​​of the characteristics.

[0159] The volume deviation e and the upper limit value u specified in the upper limit value table 301 max The relationship is as follows. When the volume deviation e is the first deviation threshold e th1 When the upper limit value u is max is the first upper limit u max1 When the volume deviation e is the second deviation threshold e th2 When the upper limit u is below max is the second upper limit u max2 The volume deviation e is from the first deviation threshold e th1 To the second deviation threshold e th2 In the range of max Become smaller.

[0160] The volume deviation e and the lower limit value u specified in the lower limit value table 302 min The relationship is as follows. When the volume deviation e is the first deviation threshold e th1 When the lower limit value u is min is the first lower limit u min1 When the volume deviation e is the second deviation threshold e th2 When the lower limit value u is min is the second lower limit u min2 The volume deviation e is the deviation from the first deviation threshold e th1 To the second deviation threshold e th2 In the range of min Get bigger.

[0161] In addition, Fig.12 In FIG. 1 , the limit tables 301 and 302 show an example of storing characteristics in which the control input limit changes linearly according to changes in the volume deviation e. However, the characteristics stored in the limit table are not limited to linear characteristics, and may be nonlinear characteristics such as quadratic curves and cubic curves.

[0162] In step S350, the pump controller 30 refers to the upper limit value table 301 and sets the upper limit value u according to the volume deviation e. max In addition, the pump controller 30 refers to the lower limit value table 302 and sets the lower limit value u according to the volume deviation e. min .

[0163] Fig.13 is with Figure 7 The same figure is a diagram showing the time series change of the volume of the pump system 100 according to the third embodiment. Fig.13 In FIG. 1 , the time series change of the volume in the third embodiment is indicated by a dotted line. In addition, in order to clarify the effect of the third embodiment, the time series change of the volume in the first embodiment is indicated by a dashed line.

[0164] In the third embodiment, the undershoot amount is smaller than that in the first and second embodiments. In addition, the amplitude of the vibration after the undershoot is also reduced. As a result, the stabilization time Δt3 of the third embodiment is shorter than the stabilization time Δt1 of the first embodiment and the stabilization time Δt2 of the second embodiment.

[0165] Thus, in the third embodiment, the limit tables 301 and 302 defining the characteristics of the control input limit that continuously changes with respect to the evaluation value (volume deviation e) are stored in the pump controller 30. The pump controller 30 refers to the limit tables 301 and 302 and sets the limit value (upper limit value u1) of the control input according to the evaluation value (volume deviation e). max And the lower limit u min ). According to this structure, the responsiveness of the volume control of the main pump 10 can be further improved. Therefore, according to the third embodiment, the operability can be further improved. In addition, as in the first embodiment, the prediction model is also updated by the successive least squares method in the third embodiment, thereby further improving the accuracy of the prediction control.

[0166] The following modified examples are also within the scope of the present invention. The structure shown in the modified example may be combined with the structure described in the above embodiment, or the structures described in the above different embodiments may be combined with each other, or the structures described in the following different modified examples may be combined with each other.

[0167] <Variation 1>

[0168] In the above embodiment, the control input u is an example of a control current (excitation current) supplied to the solenoid 11d of the electromagnetic proportional pressure reducing valve 11. However, the control input u may be a voltage for controlling the excitation current supplied to the solenoid 11d of the electromagnetic proportional pressure reducing valve 11.

[0169] <Variation 2>

[0170] In the above embodiment, an example is described in which the pilot pump 18 is provided as a pilot hydraulic source supplied to the electromagnetic proportional pressure reducing valve 11. However, the discharge pressure of the main pump 10 may be reduced by a pressure reducing valve and supplied to the electromagnetic proportional pressure reducing valve 11. That is, the control pressure for controlling the volume of the main pump 10 may be generated by the pressure of the working oil discharged from the main pump 10 itself.

[0171] <Variation 3>

[0172] In the above embodiment, the upper limit value u of the control input is changed in the pump controller 30 according to the evaluation value. max and the lower limit u min The pump controller 30 may also change only the upper limit value u of the control input according to the evaluation value. max and the lower limit u min That is, the pump controller 30 only needs to change the upper limit value u of the control input according to the evaluation value. max and the lower limit u min At least one of the structures may be used.

[0173] <Variation 4>

[0174] In the above embodiment, an example in which the control valve 16 is provided between the main pump 10 and the hydraulic actuator 17 is described. However, the present invention can also be applied to a hydraulic system in which the main pump 10 and the hydraulic actuator 17 are connected in a closed circuit without providing the control valve 16. In this structure, the responsiveness of the volume control of the main pump 10 is more important. Therefore, the effect of the present invention is more significant.

[0175] <Variant 5>

[0176] In the above-mentioned embodiment, an example in which the working machine is a hydraulic excavator is described. However, the working machine is not limited to the hydraulic excavator, and may be a wheel loader, a road machine, or the like.

[0177] As mentioned above, although the embodiment of the present invention has been described, the above embodiment merely shows a part of application examples of the present invention, and the technical scope of the present invention is not limited to the specific structure of the above embodiment.

[0178] Explanation of symbols

[0179] 9…Tilt actuator, 9a…Cylinder chamber, 9b…Servo piston, 9c…Pressure chamber, 9d…Pressure chamber (control pressure chamber), 10…Main pump (variable displacement type hydraulic pump), 11…Solenoid proportional pressure reducing valve, 13…Position sensor (volume sensor), 17…Hydraulic actuator, 18…Pilot pump (pilot hydraulic source), 19…Engine (prime mover), 20…Volume control device, 30…Pump controller (controller), 31…Model predictive control unit, 32…Predictor, 33…Successive least squares solver, 39…Control target (supporting equipment), 40…Vehicle body controller, 100…Pump system, 301…Upper limit value table (limit table), 302…Lower limit value table (limit table), A…System matrix, B…Control input vector, C…Output vector, e…Volume deviation (deviation between volume target value and volume actual value), e th ...deviation threshold (threshold for evaluation value, threshold for lower limit value, threshold for upper limit value), e th1 ...the first deviation threshold (threshold for the evaluation value), e th2 ...the second deviation threshold (threshold for the evaluation value), q p ... measured volume, q p ^…Volume prediction value, q ref ...volume target value, u...control input, u max ...the upper limit of the control input (the limit value of the control input), u max1 ...the first upper limit, u max2 ...the second upper limit value, u max3 ...the third upper limit value, u min ...the lower limit of the control input (the limit value of the control input), u min1 ...the first lower limit, u min2 ...the second lower limit, u min3 …third lower limit value, x…state vector, Δt0~Δt3…stabilization time, ε…prediction error, θ…parameter prediction value.

Claims

1. A control device for a working machine, comprising: a hydraulic pump which is rotationally driven by the prime mover and supplies working oil to the hydraulic actuator; a volume control device for controlling the volume of the hydraulic pump according to a control input; A volume sensor, which detects the actual measured volume value of the hydraulic pump; as well as a controller that obtains a target volume value of the hydraulic pump and outputs the control input corresponding to the target volume value to the volume control device, It is characterized in that storing in the controller a mathematical model for predicting the displacement of the hydraulic pump, The controller performs the following processing: Using the mathematical model to calculate the predicted value of the volume of the hydraulic pump, calculating the optimal control input according to the volume prediction value and the control input constraint, calculating an evaluation value based on the volume target value and the volume actual measurement value, The limit of the control input is changed according to the evaluation value.

2. The control device for the working machine according to claim 1, characterized in that: storing a threshold value for the evaluation value in the controller, The controller performs the following processing: The limit value of the control input is set according to the magnitude relationship between the evaluation value and the threshold value, and the change characteristic of the limit of the control input with respect to time is set to a first-order delay system.

3. The control device for the working machine according to claim 1, characterized in that: The controller stores: a limit table that specifies the characteristics of the control input limit continuously changing relative to the evaluation value, The controller refers to the limit table and sets a limit value of the control input according to the evaluation value.

4. The control device for the working machine according to claim 1, characterized in that: The controller uses a deviation between the volume target value and the volume actual measurement value as the evaluation value.

5. The control device for a working machine according to claim 1, characterized in that: The controller performs the following processing: The control input is calculated so as to minimize an evaluation function, wherein the evaluation function includes: a sum of squares of deviations between the volume target value and the volume prediction value in a prediction interval of a predetermined time width, The value of the evaluation function is used as the evaluation value.

6. The control device for the working machine according to claim 1, characterized in that: The control input limit includes an upper limit value and a lower limit value of the control input. The controller performs the following processing: When the evaluation value is greater than or equal to the upper limit threshold, the upper limit is set as a first upper limit, When the evaluation value is smaller than the upper limit threshold, the upper limit is set to a second upper limit smaller than the first upper limit, When the evaluation value is greater than or equal to the lower limit threshold, the lower limit is set to a first lower limit. When the evaluation value is smaller than the lower limit threshold, the lower limit is set to a second lower limit greater than the first lower limit.

7. The control device for a working machine according to claim 1, characterized in that: The controller updates the mathematical model using the volume measurements and the control input.

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