Work machine

Abstract

To provide a work machine capable of securing continuity of a supply flow rate of work fluid to a hydraulic actuator when supply allotment of the work fluid to the hydraulic actuator by using an accumulator and a hydraulic pump is changed.SOLUTION: When a supply flow rate of an accumulator can compensate a required flow rate of a hydraulic actuator, a controller of a work machine controls a volume of a hydraulic pump to a minimum volume, controls rotating speed of a prime mover to minimum rotating speed and controls an accumulator control valve on the basis of pressure of the accumulator, pressure of the hydraulic actuator and the required flow rate of the hydraulic actuator. When the supply flow rate of the accumulator cannot compensate the required flow rate of the hydraulic actuator, the controller controls an opening area of the accumulator control valve to a maximum opening area, and controls the volume of the hydraulic pump and the rotating speed of the prime mover so that a total of the supply flow rate of the accumulator and the supply flow rate of the hydraulic pump becomes the required flow rate of the hydraulic actuator.SELECTED DRAWING: Figure 5A

Description

[Technical Field]

[0001] The present invention relates to a work machine. [Background technology]

[0002] Patent Document 1 discloses a work machine equipped with an accumulator that can store the potential energy of a load lifted by a hydraulic actuator as accumulated pressure when the load is lowered, an accumulator control valve that controls the flow of hydraulic fluid from the accumulator to the hydraulic actuator, and a control device that controls the accumulator control valve and pump power. While there is accumulated pressure in the accumulator, the control device for this work machine reduces the pump power and opens the accumulator control valve to supply hydraulic fluid from the accumulator to the hydraulic actuator. When the accumulated pressure in the accumulator is depleted, the control device for this work machine controls the pump power to supply hydraulic fluid from the pump to the hydraulic actuator. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-275771 Summary of the Invention [Problem to be solved by the invention]

[0004] In the technology described in Patent Document 1, when energy is stored in the accumulator, the required flow rate is supplied to the hydraulic actuator only from the accumulator, and the flow rate of the hydraulic pump is controlled to a minimum flow rate. Then, when the accumulator becomes empty, the required flow rate is supplied to the hydraulic actuator only from the hydraulic pump.

[0005] As described above, in the technology described in Patent Document 1, the share of hydraulic oil supplied to the hydraulic actuator by the accumulator and the hydraulic pump changes discontinuously. This causes the hydraulic actuator to operate discontinuously, which may cause discomfort to the operator of the work machine or make it difficult to accurately position the driven member driven by the hydraulic cylinder. For this reason, there is a demand for technology that can ensure continuity in the supply flow rate of hydraulic oil to the hydraulic actuator when the share of hydraulic oil supplied to the hydraulic actuator by the accumulator and the hydraulic pump changes.

[0006] An object of the present invention is to provide a work machine that can ensure continuity of the flow rate of hydraulic oil supplied to a hydraulic actuator when the share of hydraulic oil supplied to the hydraulic actuator by the accumulator and the hydraulic pump changes. [Means for solving the problem]

[0007] A working machine according to one aspect of the present invention comprises a prime mover, a hydraulic pump driven by the prime mover and discharging hydraulic oil, a hydraulic actuator driven by hydraulic oil supplied from the hydraulic pump, an actuator control valve controlling the flow of hydraulic oil supplied from the hydraulic pump to the hydraulic actuator, an accumulator that stores return oil from the hydraulic actuator, an accumulator control valve that controls the flow rate of hydraulic oil supplied from the accumulator to the hydraulic actuator, an accumulator pressure sensor that detects the pressure of the accumulator, an actuator pressure sensor that detects the pressure of the hydraulic actuator, an operating device that operates the hydraulic actuator, an operation amount sensor that detects the operation amount of the operation device, and a controller that controls the hydraulic pump, the actuator control valve, the accumulator control valve, and the prime mover, wherein the controller calculates a required flow rate of the hydraulic actuator based on the operation amount detected by the operation amount sensor, and calculates a required flow rate of the hydraulic actuator based on the pressure of the accumulator detected by the accumulator pressure sensor and the pressure of the actuator. a supply flow rate of the accumulator calculated based on the pressure of the hydraulic actuator detected by an air pressure sensor; and a determination made as to whether the supply flow rate of the accumulator can cover the required flow rate of the hydraulic actuator; and, if it is determined that the supply flow rate of the accumulator can cover the required flow rate of the hydraulic actuator, the volume of the hydraulic pump is controlled to a minimum volume and the rotational speed of the prime mover is controlled to a minimum rotational speed; and, based on the pressure of the accumulator detected by the accumulator pressure sensor, the pressure of the hydraulic actuator detected by the actuator pressure sensor, and the required flow rate of the hydraulic actuator, if it is determined that the supply flow rate of the accumulator cannot cover the required flow rate of the hydraulic actuator, the opening area of ​​the accumulator control valve is controlled to a maximum opening area; and, the volume of the hydraulic pump and the rotational speed of the prime mover are controlled so that the sum of the supply flow rate of the accumulator and the supply flow rate of the hydraulic pump becomes the required flow rate of the hydraulic actuator. [Effects of the Invention]

[0008] According to the present invention, a work machine can be provided that can ensure continuity of the flow rate of hydraulic oil supplied to a hydraulic actuator when the share of hydraulic oil supplied to the hydraulic actuator by the accumulator and the hydraulic pump changes. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a side view of a hydraulic excavator 100 according to the first embodiment. [Figure 2] FIG. 2 is a schematic diagram of the hydraulic system 106 provided in the hydraulic excavator 100. [Figure 3] FIG. 3 is a diagram showing the change over time in flow rate when control is executed by a controller according to a comparative example of this embodiment. [Figure 4] FIG. 4 is a functional block diagram of the controller 120 according to the first embodiment. [Figure 5A] FIG. 5A is a flowchart showing an example of the flow of processing executed by the controller 120 according to the first embodiment. [Figure 5B] FIG. 5B is a partial flowchart showing an example of the flow of processing that is executed when a negative determination is made in the processing of step S130 in FIG. 5A. [Figure 6] FIG. 6 is a diagram showing the change over time in the flow rate when control is executed by the controller 120 according to the first embodiment. [Figure 7] FIG. 7 is a functional block diagram of the controller 220 according to the second embodiment. [Figure 8] FIG. 8 is a flowchart showing an example of the flow of a rotation speed control process executed by the controller 220 according to the second embodiment. [Figure 9] FIG. 9 is a diagram illustrating the calculation process of the required rotation speed Nreq and the required volume qreq by the controller 220 according to the second embodiment. [Figure 10]FIG. 10 is a diagram illustrating the calculation process of the required rotation speed Nreq and the required volume qreq by the controller 220 according to the modified example of the second embodiment. [Figure 11] FIG. 11 is a functional block diagram of a controller 320 according to the third embodiment. [Figure 12] FIG. 12 is a flowchart showing an example of the processing flow of the rotation speed control (step S340) executed by the controller 320 according to the third embodiment. [Figure 13] FIG. 13 is a diagram showing the allowable torque characteristic line and the pump torque characteristic line of the hydraulic excavator 100 according to the third embodiment. [Figure 14] FIG. 14 is a flowchart showing an example of the process flow of the rotation speed control (step S440) executed by the controller 320 according to the modified example of the third embodiment. [Figure 15] FIG. 15 is a diagram showing the allowable torque characteristic line and the pump torque characteristic line of the hydraulic excavator 100 according to a modified example of the third embodiment. [Figure 16] FIG. 16 is a diagram showing an allowable torque characteristic line according to the first modification. DETAILED DESCRIPTION OF THE INVENTION

[0010] A construction machine according to an embodiment of the present invention will be described with reference to the drawings. In this embodiment, an example will be described in which the construction machine is a crawler-type hydraulic excavator. The construction machine performs work such as civil engineering work, construction work, demolition work, and dredging work at a work site.

[0011] First Embodiment - Hydraulic excavator configuration - FIG. 1 is a side view of a hydraulic excavator 100 according to the first embodiment. As shown in FIG. 1, the hydraulic excavator 100 includes a vehicle body (machine body) 105 and a working device 104 attached to the vehicle body 105. The vehicle body 105 includes a crawler-type running body 102 and a revolving body 103 that is rotatably provided on the running body 102. The running body 102 travels by driving a pair of left and right crawlers with traveling motors 102A. The revolving body 103 is connected to the running body 102 via a revolving device that has a revolving motor 103A, and is driven by the revolving motor 103A to revolve relative to the running body 102.

[0012] The rotating body 103 includes an operator's cab 118 in which an operator sits, and a machine room 119 in which a prime mover and hydraulic equipment are housed. The machine room 119 houses, for example, an engine 2 (see FIG. 2) which serves as the prime mover, and hydraulic equipment such as a hydraulic pump driven by the engine 2. Note that the prime mover may be an electric motor instead of the engine 2.

[0013] An electric operating device is provided in the operator's cab 118 for operating the hydraulic actuators (111A, 112A, 113A, 103A, 102A) of the working implement 104, the revolving body 103, and the traveling body 102. Also provided in the operator's cab 118 is a controller 120, which is a control device that controls the operation of each part of the hydraulic excavator 100.

[0014] The working device 104 is an articulated working device attached to the revolving unit 103, and includes multiple hydraulic actuators and multiple drive target members that are driven by the multiple hydraulic actuators. The working device 104 has a configuration in which three drive target members (a boom 111, an arm 112, and a bucket 113) are connected in series. The base end of the boom 111 is rotatably connected to the front of the revolving unit 103 via a boom pin. The base end of the arm 112 is rotatably connected to the tip of the boom 111 via an arm pin. The bucket 113 is rotatably connected to the tip of the arm 112 via a bucket pin.

[0015] The boom 111 is driven to rotate by the extension and retraction of a boom cylinder 111A, which is a hydraulic actuator. The arm 112 is driven to rotate by the extension and retraction of an arm cylinder 112A, which is a hydraulic actuator. The bucket 113 is driven to rotate by the extension and retraction of a bucket cylinder 113A, which is a hydraulic actuator. By operating the work device 104, the hydraulic excavator 100 can perform work such as excavating earth and sand, leveling work, and compacting the ground.

[0016] Since the boom cylinder 111A, the arm cylinder 112A, and the bucket cylinder 113A have the same configuration, they will also be collectively referred to as hydraulic cylinder 11S below.

[0017] -Hydraulic system configuration- Fig. 2 is a schematic diagram of the hydraulic system 106 provided in the hydraulic excavator 100. Of the multiple hydraulic actuators provided in the hydraulic excavator 100, Fig. 2 shows only the configuration for driving the boom cylinder 111A as a representative, and does not show the configurations for driving the other hydraulic actuators. In Fig. 2, relief valves, check valves, etc. are not shown.

[0018] As shown in FIG. 2, the hydraulic system 106 includes a hydraulic pump 1, a pilot hydraulic source 8, a hydraulic oil tank 12, a cylinder control valve (actuator control valve) 3, an accumulator control valve 5, an accumulator 6, pressure control valves 7U and 7D, and a controller 120. The controller 120 controls the operation of the hydraulic pump 1, the plurality of control valves (3, 5, 7U, and 7D), and the engine 2. The controller 120 controls the pressure control valves 7U and 7D to thereby control the cylinder control valve 3. The hydraulic oil tank 12 stores hydraulic oil. The boom cylinder 111A is provided with a piston that divides the interior of the cylinder tube into a head-side oil chamber (bottom-side oil chamber) 110a and a rod-side oil chamber 110b. The piston is provided with a piston rod. One end of the cylinder tube of the boom cylinder 111A is attached to the revolving body 103, and the piston rod protruding from the other end of the cylinder tube is attached to the boom 111. The boom cylinder 111A is driven by hydraulic oil supplied from the hydraulic pump 1.

[0019] The hydraulic pump 1 is driven by the engine 2, and sucks in hydraulic oil from a hydraulic oil tank 12 and discharges it into a discharge oil passage. The hydraulic pump 1 is a variable displacement hydraulic pump whose discharge capacity (displacement volume per rotation) can be changed. The hydraulic pump 1 is, for example, a swash plate type or bent axis type piston pump. The pilot hydraulic source 8 is driven by the engine 2, and sucks in hydraulic oil from the hydraulic oil tank 12 and discharges it into a pilot line. The pilot hydraulic source 8 is, for example, a fixed displacement hydraulic pump (pilot pump) whose discharge capacity (volume) is constant.

[0020] The volume (discharge capacity) of the hydraulic pump 1 is controlled by a regulator 1a attached to the hydraulic pump 1. The regulator 1a has a volume control valve which is a solenoid valve, a command pressure chamber to which a pump control command pressure generated by the volume control valve is input, and a volume variable mechanism which changes the volume according to the pump control command pressure input to the command pressure chamber. For example, when a pump control command is output from the controller 120 to the volume control valve, the volume control valve generates a pump control command pressure. When the pump control command pressure is input to the command pressure chamber, the volume of the hydraulic pump 1 is changed by the volume variable mechanism, and the discharge flow rate of the hydraulic pump 1 is controlled to become the pump required flow rate (target discharge flow rate).

[0021] The cylinder control valve 3 is a 4-port 3-position directional flow control valve. The cylinder control valve 3 controls the flow of hydraulic oil supplied from the hydraulic pump 1 to the boom cylinder 111A. The cylinder control valve 3 has a pump port 3a connected to the hydraulic pump 1, a tank port 3b connected to the hydraulic oil tank 12, a head-side port 3c connected to the head-side oil chamber 110a of the boom cylinder 111A, and a rod-side port 3d connected to the rod-side oil chamber 110b of the boom cylinder 111A.

[0022] Pressure receiving chambers (external input sections) 3e, 3f to which pilot pressure (external input) is input, and a centering spring are provided at each end of the cylinder control valve 3. When pilot pressure is not input to the pressure receiving chambers 3e, 3f at both ends, that is, when the pressure in the pressure receiving chambers 3e, 3f at both ends is tank pressure, the centering spring holds the cylinder control valve 3 in the neutral position. In the neutral position, the internal oil passage of the cylinder control valve 3 is closed. In other words, in the neutral position, communication between the boom cylinder 111A and the hydraulic pump 1 is blocked, and communication between the boom cylinder 111A and the hydraulic oil tank 12 is also blocked.

[0023] When pilot pressure is input to one of the pressure receiving chambers 3e, 3f at both ends, the cylinder control valve 3 moves to one side (to the left in the figure), and the boom cylinder 111A extends. This causes the boom 111 to move in the raising direction. When pilot pressure is input to the other of the pressure receiving chambers 3e, 3f at both ends, the cylinder control valve 3 moves to the other side (to the right in the figure), and the boom cylinder 111A retracts. This causes the boom 111 to move in the lowering direction.

[0024] The pressure control valves 7U, 7D are 3-port, 2-position electromagnetic proportional pressure reducing valves. The pressure control valves 7U, 7D have a pump port 7a connected to the pilot hydraulic source 8, a tank port 7b connected to the hydraulic oil tank 12, and an actuator port 7c connected to the pressure receiving chamber of the cylinder control valve 3. In response to a control command from the controller 120, the pressure control valves 7U, 7D output a secondary pressure generated by reducing the primary pressure of the pilot hydraulic source 8 as a pilot pressure (command pressure).

[0025] The cylinder control valve 3 controls the flow rate and direction of hydraulic oil supplied to the boom cylinder 111A from the hydraulic pump 1 using pilot pressure (external input) output from the pressure control valves 7U and 7D. The pilot pressure generated by the pressure control valve 7D is input to the pressure receiving chamber 3f, and the pilot pressure generated by the pressure control valve 7U is input to the pressure receiving chamber 3e.

[0026] The controller 120 controls the pressure in the head side oil chamber 110a and the rod side oil chamber 110b of the boom cylinder 111A by adjusting the magnitude of the pilot pressure supplied to the cylinder control valve 3 using the pressure control valves 7U and 7D, and thereby controls the operating speed (extension speed and retraction speed) of the boom cylinder 111A.

[0027] A branch passage 60 is connected to the oil passage connecting the head-side port 3c of the cylinder control valve 3 and the head-side oil chamber 110a of the boom cylinder 111A. The branch passage 60 is connected to the accumulator 6 via the accumulator control valve 5. The accumulator control valve 5 is a two-port, two-position flow control valve. The accumulator control valve 5 has an internal passage that connects the accumulator 6 and the boom cylinder 111A. The accumulator control valve 5 adjusts the opening area of ​​the internal passage between a fully closed position and a fully open position in accordance with the magnitude of a control command (control current) from the controller 120. In this way, the accumulator control valve 5 controls the flow rate of hydraulic oil supplied from the accumulator 6 to the boom cylinder 111A.

[0028] The accumulator 6 is a pressure accumulation device connected to the head-side oil chamber 110a of the boom cylinder 111A. When the boom 111 descends due to its own weight, the accumulator 6 accumulates return oil from the boom cylinder 111A (pressurized oil discharged from the head-side oil chamber 110a). When the boom 111 is raised, the accumulator 6 supplies the accumulated pressurized oil to the head-side oil chamber 110a of the boom cylinder 111A.

[0029] The hydraulic system 106 is equipped with a plurality of pressure sensors. The plurality of pressure sensors includes a pump pressure sensor 9 that detects the pressure of hydraulic oil in the discharge oil passage of the hydraulic pump 1 (hereinafter also referred to as pump discharge pressure), an accumulator pressure sensor 15 that detects the pressure of hydraulic oil in the accumulator 6 (hereinafter also referred to as accumulator pressure), and a cylinder pressure sensor (actuator pressure sensor) 16 that detects the pressure (load pressure) in the head-side oil chamber 110a of the boom cylinder 111A. The plurality of pressure sensors (9, 15, 16) are connected to a controller 120 and output signals representing the detected pressures to the controller 120.

[0030] An operating device 13 that operates the boom cylinder 111A is connected to the controller 120. The operating device 13 has an operating lever 13a that is operated by an operator, and an operating amount sensor 13b that detects the operating amount of the operating lever 13a. The operating amount sensor 13b outputs a signal indicating the detected operating amount to the controller 120.

[0031] The controller 120 is composed of a computer equipped with a processing device 121 such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), or DSP (Digital Signal Processor), non-volatile memory 122 such as ROM (Read Only Memory), flash memory, or hard disk drive, volatile memory 123 known as RAM (Random Access Memory), an input interface, an output interface, and other peripheral circuits. These pieces of hardware work together to run software and realize multiple functions. The controller 120 may be composed of one computer or multiple computers.

[0032] The nonvolatile memory 122 stores programs capable of executing various calculations. That is, the nonvolatile memory 122 is a storage medium (storage device) from which programs for realizing the functions of this embodiment can be read. The volatile memory 123 is a storage medium (storage device) that temporarily stores the results of calculations performed by the processing device 121 and signals input from the input interface. The processing device 121 is a device that loads the programs stored in the nonvolatile memory 122 into the volatile memory 123 and executes the calculations, and performs predetermined calculations on data taken in from the input interface, the nonvolatile memory 122, and the volatile memory 123 in accordance with the programs.

[0033] The input interface converts signals input from various devices (such as the pump pressure sensor 9, the accumulator pressure sensor 15, the cylinder pressure sensor 16, and the operation amount sensor 13b) into data that can be calculated by the processing device 121. The output interface generates an output signal according to the calculation result by the processing device 121, and outputs the signal to various devices (such as the pressure control valves 7U and 7D, the accumulator control valve 5, and the volume control valve of the regulator 1a).

[0034] -Hydraulic system operation- The operation of the hydraulic system 106 will be described with reference to Figure 2. Rotational power generated by the rotation of the engine 2 is transmitted to the hydraulic pump 1, which rotates the hydraulic pump 1. As the hydraulic pump 1 rotates, hydraulic oil is sucked into the hydraulic pump 1 from the hydraulic oil tank 12 and discharged downstream of the hydraulic pump 1.

[0035] The discharge flow rate Q of the hydraulic pump 1 is determined by the volume q of the hydraulic pump 1 (hereinafter also referred to as pump volume) and the rotation speed Np of the hydraulic pump 1. The rotation speed Np of the hydraulic pump 1 and the rotation speed N of the engine 2 are in a proportional relationship. For the sake of convenience in the following explanation, it is assumed that the rotation speed Np of the hydraulic pump 1 and the rotation speed N of the engine 2 are equal. The pump discharge pressure P P is determined by the load on the hydraulic cylinder 11S, the pressure loss in the piping downstream of the hydraulic pump 1, etc. The torque for driving the hydraulic pump 1 (hereinafter also referred to as pump torque) T P is the pump discharge pressure P P , pump volume q, and pump efficiency η. The controller 120 controls the pump torque T P Based on this, calculate the rotational power (rotational power = rotational speed N x pump torque T P The controller 120 controls the pump volume q and the rotation speed N, thereby controlling the rotational power generated by the engine 2.

[0036] The cylinder control valve 3 operates by pilot pressure generated by the pressure control valves 7U and 7D in accordance with the amount of operation of the operating device 13, and controls the direction and flow rate of the pressure oil discharged from the hydraulic pump 1.

[0037] When the boom raising operation is performed by the operation device 13, the controller 120 issues a control command (P req (up)) to the pressure control valve 7U. When the pilot pressure generated by the pressure control valve 7U is input to the pressure receiving chamber 3e, the spool of the cylinder control valve 3 moves to the left in the figure. This connects the hydraulic pump 1 to the head side oil chamber 110a of the boom cylinder 111A, and connects the rod side oil chamber 110b of the boom cylinder 111A to the hydraulic oil tank 12. Pressurized oil discharged from the hydraulic pump 1 flows into the head side oil chamber 110a of the boom cylinder 111A, and hydraulic oil in the rod side oil chamber 110b of the boom cylinder 111A flows out to the hydraulic oil tank 12. As a result, the boom cylinder 111A extends, and the boom (controlled object) 111 is raised by the boom cylinder (hydraulic cylinder) 111A.

[0038] On the other hand, when the boom lowering operation is performed by the operation device 13, the controller 120 issues a control command (P req (down)) to the pressure control valve 7D. When the pilot pressure generated by the pressure control valve 7D is input to the pressure receiving chamber 3f, the spool of the cylinder control valve 3 moves to the right in the figure. This connects the hydraulic pump 1 to the rod-side oil chamber 110b of the boom cylinder 111A, and connects the head-side oil chamber 110a of the boom cylinder 111A to the hydraulic oil tank 12. Pressurized oil discharged from the hydraulic pump 1 flows into the rod-side oil chamber 110b of the boom cylinder 111A, and the hydraulic oil in the head-side oil chamber 110a of the boom cylinder 111A flows out to the hydraulic oil tank 12. As a result, the boom cylinder 111A contracts, and the boom (controlled object) 111 is lowered by the boom cylinder (hydraulic cylinder) 111A.

[0039] When the boom 111 is lowered, the boom cylinder 111A receives a load in the contracting direction (downward direction) due to the weight of the boom (load body) 111. Therefore, when the head side oil chamber 110a of the boom cylinder 111A is in communication with the hydraulic oil tank 12, the boom cylinder 111A contracts even if hydraulic oil is not supplied from the hydraulic pump 1 to the boom cylinder 111A.

[0040] When the boom cylinder 111A is retracted, there is no need to supply hydraulic oil from the hydraulic pump 1, as described above. Therefore, when the boom 111 is lowered, the potential energy of the boom 111 is converted into hydraulic energy and stored in the accumulator 6, and when the boom 111 is raised, the pressure oil in the accumulator 6 is merged with the pressure oil in the hydraulic pump 1 and supplied to the boom cylinder 111A. This makes it possible to utilize the potential energy of the boom 111 without wasting it. As a result, the fuel consumption of the engine 2 that drives the hydraulic pump 1 can be reduced.

[0041] When the pressure accumulation condition is met, the controller 120 outputs an OFF signal (standby current) to the pressure control valves 7U and 7D and outputs an ON signal (excitation current) to the accumulator control valve 5. Because the pressure receiving chamber 3f of the cylinder control valve 3 becomes equal to the tank pressure, the spool position of the cylinder control valve 3 becomes the neutral position. When the accumulator control valve 5 opens, the head-side oil chamber 110a of the boom cylinder 111A communicates with the accumulator 6. The pressure accumulation condition is met, for example, when the boom-lowering operation amount detected by the operation amount sensor 13b is equal to or greater than the first operation threshold and the accumulator pressure detected by the accumulator pressure sensor 15 is lower than the cylinder pressure detected by the cylinder pressure sensor 16; otherwise, the pressure accumulation condition is not met. As a result, when the pressure accumulation condition is met, the potential energy of the boom 111 can increase the pressure in the accumulator 6, which has a lower pressure than the head-side oil chamber 110a.

[0042] When the assist condition is met, the controller 120 outputs an ON signal (excitation current) to the pressure control valve 7U and also outputs an ON signal (excitation current) to the accumulator control valve 5. Pilot pressure is input to the pressure receiving chamber 3e of the cylinder control valve 3, causing the spool of the cylinder control valve 3 to move leftward in the figure. As a result, the head-side oil chamber 110a of the boom cylinder 111A communicates with the hydraulic pump 1 via the cylinder control valve 3 and with the accumulator 6 via the accumulator control valve 5. The assist condition is met, for example, when the boom-raising operation amount detected by the operation amount sensor 13b is equal to or greater than the second operation threshold and the accumulator pressure detected by the accumulator pressure sensor 15 is higher than the cylinder pressure detected by the cylinder pressure sensor 16, but is not met in other cases. As a result, when the assist condition is met, the head side oil chamber 110a of the boom cylinder 111A is supplied with hydraulic oil discharged from the hydraulic pump 1, and also with hydraulic oil discharged from the accumulator 6, which has a higher pressure than the head side oil chamber 110a. In other words, the energy accumulated in the accumulator 6 can be used as energy for lifting the boom 111.

[0043] At this time, it is sufficient if the sum of the flow rate that can be supplied from the hydraulic pump 1 to the boom cylinder 111A and the flow rate that can be supplied from the accumulator 6 to the boom cylinder 111A is greater than the flow rate required to lift the boom 111 (the flow rate required by the cylinder). If the flow rate that can be supplied to the boom cylinder 111A is greater than the flow rate required by the cylinder, the flow rate actually supplied from the hydraulic pump 1 or the accumulator 6 to the boom cylinder 111A can be reduced. In this embodiment, from the viewpoint of energy efficiency, the flow rate supplied from the accumulator 6 to the boom cylinder 111A (hereinafter also referred to as the supply flow rate of the accumulator 6) is the main flow, and the flow rate supplied from the hydraulic pump 1 to the boom cylinder 111A is only used to make up for the shortfall. Specifically, by reducing the volume of the hydraulic pump 1, the energy required to drive the hydraulic pump 1 is reduced.

[0044] The amount of pressure oil stored in the accumulator 6 is VACC [m 3 ] and the supply flow rate Q of the accumulator 6 ACC [m 3 / s] and the time during which the accumulator 6 can supply pressure oil (supply time) t sup The relationship between is expressed by the following formula (1). V ACC =Q ACC ×t sup …(1) The total amount of hydraulic oil that can be supplied by the accumulator 6 is the amount of pressure oil V stored in the accumulator 6. ACC The accumulator 6 corresponds to the supply time t sup Only supply flow rate Q ACC The hydraulic oil can be supplied by

[0045] The time required to extend the boom cylinder 111A is the supplyable time t sup If the supply time t exceeds the limit, it becomes impossible to supply hydraulic oil from the accumulator 6 to the boom cylinder 111A. sup After this time has elapsed, hydraulic pump 1 supplies all of the hydraulic oil at a flow rate necessary to extend boom cylinder 111A.

[0046] -Change in supply flow rate over time when control according to the comparative example is executed- 3 is a diagram showing the change in flow rate over time when control is performed by a controller according to a comparative example of this embodiment. req As shown in FIG. 3, in a hydraulic system according to a comparative example of this embodiment, the volume q of the hydraulic pump 1 is increased after the accumulator 6 becomes empty. In the comparative example, the supply flow rate Q of the accumulator 6 ACC The supply flow rate Q of the accumulator 6 decreases suddenly. ACC The volume of hydraulic pump 1 increases after the volume of hydraulic pump 1 becomes 0. A response time is required to increase the volume of hydraulic pump 1 from the minimum value to the required volume (target value). For this reason, the supply flow rate Q of hydraulic pump 1 P is the cylinder required flow rate Q reqTherefore, when the control according to the comparative example is executed, as shown in the figure, the flow rate Q supplied to the boom cylinder 111A becomes sup This causes a temporary shortage of hydraulic oil. In other words, the hydraulic oil is not supplied continuously to the boom cylinder 111A, but is supplied discontinuously, causing the boom cylinder 111A to operate differently than expected. As a result, the operator may feel uncomfortable, and the positioning accuracy of the working device 104 may be reduced.

[0047] - Overview of control according to this embodiment - Therefore, in the hydraulic system 106 according to this embodiment, the supply flow rate Q of the accumulator 6 is ACC and the supply flow rate Q of hydraulic pump 1 P The total of the required flow rate of the hydraulic cylinder 11S (cylinder required flow rate Q req The opening area of ​​the accumulator control valve 5, the volume of the hydraulic pump 1, and the rotation speed of the engine 2 (that is, the rotation speed of the hydraulic pump 1) are controlled so that the above equation (2) is satisfied.

[0048] The controller 120 controls the supply flow rate Q of the accumulator 6. ACC Only the cylinder required flow rate Q req If the volume of hydraulic pump 1 can be increased to the minimum volume q min and the rotation speed N of the engine 2 is controlled to the minimum rotation speed N min The controller 120 controls the supply flow rate Q of the accumulator 6 to ACC Only the cylinder required flow rate Q req If this is not possible, first reduce the rotation speed N of engine 2 to the minimum rotation speed N min By adjusting the pump volume q while maintaining the required cylinder flow rate Q req Ensure that the rotation speed N of engine 2 is set to the minimum rotation speed N min When the pump volume q is set to the maximum volume q max Even if the cylinder required flow rate Q req When the pump volume q cannot be ensured, the controller 120 sets the pump volume q to the maximum volume q maxBy adjusting the rotation speed N while req However, the pump torque T P is the allowable torque T max If it is predicted that the pump torque T P is the allowable torque T max The upper limit (for example, pump torque T P =T max ) and adjust the rotation speed N of the engine 2, thereby achieving the cylinder required flow rate Q req Ensure that:

[0049] As a result, before the accumulator 6 becomes empty, specifically, the supply flow rate Q ACC The supply flow rate Q of hydraulic pump 1 starts to decrease. P can be increased (see FIG. 6). This makes it possible to prevent the occurrence of a behavior in which the flow rate supplied to boom cylinder 111A suddenly decreases and then suddenly increases (see FIG. 3). In other words, it is possible to prevent the occurrence of a discontinuous portion in which the flow rate supplied to boom cylinder 111A temporarily decreases, and it is possible to supply hydraulic oil to boom cylinder 111A continuously and stably.

[0050] -Functions and processing flow of the controller according to the first embodiment- 4 is a functional block diagram of the controller 120. By executing a program stored in the nonvolatile memory 122, the controller 120 functions as an operation determination unit 131, a valve control unit 132, a required flow rate calculation unit 133, a determination unit 134, a torque calculation unit 135, a pump control unit 136, an engine control unit 137, an accumulator control unit 138, and an accumulator flow rate calculation unit 139.

[0051] 4, a speed sensor 2a is connected to the controller 120. The speed sensor 2a detects the rotation speed of the engine 2 and outputs a signal representing the detection result to the controller 120. The controller 120 controls the fuel injection amount of the engine 2 so that the rotation speed of the engine 2 approaches a required rotation speed (target rotation speed). Note that the controller 120 may control the engine 2 via an engine controller (not shown).

[0052] Each function shown in Fig. 4 will be described in detail with reference to Fig. 5A and Fig. 5B. Fig. 5A is a flowchart showing an example of the flow of processing executed by the controller 120. Fig. 5B is a partial flowchart showing an example of the flow of processing executed when a negative determination is made in the processing of step S130 in Fig. 5A. The flowchart shown in Fig. 5A is started, for example, when the ignition switch of the hydraulic excavator 100 is turned on, and is repeatedly executed at a predetermined control period. Note that, for the sake of convenience, the flow coefficient, efficiency, and coefficients for unit conversion are omitted from the equations described below.

[0053] 5A, in step S100, operation determination unit 131 determines whether a boom-raising operation has been performed based on the detection result of operation amount sensor 13b. A boom-raising operation is an operation for extending boom cylinder 111A. If it is determined that a boom-raising operation has been performed, the process proceeds to step S105, and if it is determined that a boom-raising operation has not been performed, the process for this control cycle shown in the flowchart of FIG. 5A ends.

[0054] In step S105, the valve control unit 132 determines the control command value P to the pressure control valve 7U based on the boom-raising operation amount Command detected by the operation amount sensor 13b. req (up) (hereinafter simply P req The control command value P reqcorresponds to a current value required to generate a pilot pressure to be applied to the pressure receiving chamber 3e in order to extend the boom cylinder 111A at a cylinder speed corresponding to the boom raising operation amount Command. For example, the valve control unit 132 multiplies the operation amount Command by a conversion coefficient G to obtain the control command value P req Calculate (P req = G × Command). The conversion coefficient G is the ratio of the manipulated variable Command to the control command value P req These are conversion coefficients for converting the signal into a signal, and are stored in the nonvolatile memory 122.

[0055] The controller 120 controls the pilot pressure acting on the pressure receiving chamber 3e of the cylinder control valve 3 to be equal to a target value (external input value UP) corresponding to the operation amount Command. com. ) to the pressure control valve 7U. req The control command is output according to the

[0056] In step S105, the required flow rate calculation unit 133 calculates the cylinder required flow rate Q, which is the target value of the flow rate supplied to the boom cylinder 111A, based on the boom raising operation amount Command detected by the operation amount sensor 13b. req For example, the required flow rate calculation unit 133 multiplies the operation amount Command by a conversion coefficient G2 to calculate the required cylinder flow rate Q req Calculate (Q req = G2 × Command). The conversion coefficient G2 converts the operation amount Command into the cylinder required flow rate Q req These are conversion coefficients for converting the signal into a signal, and are stored in the nonvolatile memory 122.

[0057] In the next step S110, the accumulator flow rate calculation unit 139 calculates the accumulator pressure P detected by the accumulator pressure sensor 15. ACC and the cylinder pressure P detected by the cylinder pressure sensor 16 cyl Based on this, the maximum flow rate Q that can be supplied from the accumulator 6 is calculated using the following equation (2): ACCmax Calculate the following. Q ACCmax =f(A ACCmax ,PACC ,P cyl ) …(2) A ACCmax is the maximum value of the opening area of ​​the accumulator control valve 5 (hereinafter also referred to as the maximum opening area), and is stored in the nonvolatile memory 122. ACCmax ,P ACC ,P cyl ) is, for example, a known formula for calculating the flow rate of an orifice, and is stored in the nonvolatile memory 122. The differential pressure across the orifice (the differential pressure across the accumulator control valve 5) is calculated by multiplying the accumulator pressure P ACC Cylinder pressure P cyl It can be calculated by subtracting

[0058] In the next step S115, the determination unit 134 determines the cylinder required flow rate Q req The maximum flow rate that can be supplied from the accumulator 6 (hereinafter also referred to as the maximum supply flow rate of the accumulator 6) Q ACCmax In other words, the determination unit 134 determines whether the cylinder required flow rate Q is greater than the supply flow rate Q of the accumulator 6. req It is determined whether the required flow rate of the cylinder Q can be met. req is the maximum supply flow rate Q of accumulator 6 ACCmax If it is determined that the flow rate Q is equal to or less than the predetermined value, the process proceeds to step S120. req is the maximum supply flow rate Q of accumulator 6 ACCmax If it is determined that the flow rate of the accumulator 6 is greater than the cylinder demand flow rate Q, the process proceeds to step S125. req If it is determined that the required flow rate Q of the cylinder can be satisfied, the process proceeds to step S120, and the supply flow rate of the accumulator 6 is used to calculate the required flow rate Q of the cylinder. req If it is determined that the amount cannot be covered, the process proceeds to step S125.

[0059] In step S120, the engine control unit 137 calculates the required rotation speed N req Minimum rotation speed N min Set the required rotation speed N reqcorresponds to the target value of the rotation speed N of the engine 2. In addition, the pump control unit 136 calculates the required volume q of the hydraulic pump 1. req The minimum volume q min Set the required volume q req corresponds to the target value of the pump volume q.

[0060] Furthermore, the accumulator control unit 138 calculates the cylinder required flow rate Q req , the accumulator pressure P detected by the accumulator pressure sensor 15 ACC , and the cylinder pressure P detected by the cylinder pressure sensor 16 cyl Based on this, the required opening area A of the accumulator control valve 5 is calculated by the following equation (3): req Calculate the required opening area A req is the opening area A of the internal passage of the accumulator control valve 5 ACC This corresponds to the target value. A req =f(Q req ,P ACC ,P cyl ) …(3) The function f(Q req ,P ACC ,P cyl ) is a known orifice flow rate calculation formula similar to formula (2), for example, and is stored in the nonvolatile memory 122.

[0061] In step S125, the accumulator control unit 138 calculates the required opening area A of the accumulator control valve 5. req Maximum opening area A ACCmax Furthermore, the required flow rate calculation unit 133 sets the cylinder required flow rate Q req Maximum supply flow rate Q from accumulator 6 ACCmax Subtract the pump demand flow rate Q preq Calculate (Q Preq =Q req -Q ACCmax ) Pump required flow rate Q preq is the target value of the flow rate supplied from the hydraulic pump 1 to the boom cylinder 111A. preq is the required flow rate of the boom cylinder 111A (required flow rate of the cylinder Q req) that the accumulator 6 cannot cover, that is, the flow rate that needs to be covered by the hydraulic pump 1. In other words, the process of step S125 is ACCmax and the supply flow rate Q of hydraulic pump 1 P The total of the cylinder required flow rate Q req So, the pump demand flow rate Q preq This corresponds to the process of determining

[0062] In the next step S130, the determination unit 134 determines the pump required flow rate Q Preq But the maximum volume q max and minimum rotation speed N min The discharge flow rate (q max ×N min In other words, the determination unit 134 determines whether the rotation speed N of the engine 2 is greater than the minimum rotation speed N min The cylinder required flow rate Q req The supply flow rate Q of accumulator 6 ACC and the supply flow rate Q of hydraulic pump 1 P Determine whether the required pump flow rate Q can be met. req But the maximum volume q max and minimum rotation speed N min The discharge flow rate (q max ×N min ), the process proceeds to step S132 (see FIG. 5B). req But the maximum volume q max and minimum rotation speed N min The discharge flow rate (q max ×N min ), the process proceeds to step S140. min The cylinder required flow rate Q req The supply flow rate Q of accumulator 6 ACC and the supply flow rate Q of hydraulic pump 1 PIf it is determined that the rotation speed N of the engine 2 can be covered by the minimum rotation speed N, the process proceeds to step S132 (see FIG. 5B). min The cylinder required flow rate Q req The supply flow rate Q of accumulator 6 ACC and the supply flow rate Q of hydraulic pump 1 P If it is determined that the required amount cannot be met, the process proceeds to step S140.

[0063] As shown in FIG. 5B, in step S132, the determination unit 134 determines the minimum rotation speed N min The pump required flow rate Q Preq Torque T of hydraulic pump 1 when hydraulic oil is discharged from hydraulic pump 1 P (=Q Preq / N min ×P P ) is the allowable torque T max Determine whether the allowable torque T is greater than max is a constant value, which is determined in advance according to the specifications of the engine 2 and stored in the nonvolatile memory 122. Prior to this determination, the torque calculation unit 135 calculates the discharge pressure P P Based on this, the pump torque T P (=Q Preq / N min ×P P ) is calculated.

[0064] In step S132, the pump torque T P (=Q Preq / N min ×P P ) is the allowable torque T max If it is determined that the pump torque T P (=Q Preq / N min ×P P ) is the allowable torque T max If it is determined that the value is greater than , the process proceeds to step S180 (see FIG. 5A).

[0065] In step S135, the engine control unit 137 calculates the required rotation speed N req Minimum rotation speed N min Furthermore, the pump control unit 136 sets the pump required flow rate Q Preq to minimum rotation speed N min By dividing by , the required volume q req Calculate (q req =Q Preq / N min That is, in the process of step S135, the rotation speed N of the engine 2 is set to the minimum rotation speed N min In this state, the maximum supply flow rate Q of the accumulator 6 is ACCmax and the supply flow rate Q of hydraulic pump 1 P The total of the cylinder required flow rate Q req The required volume q of hydraulic pump 1 is req is determined.

[0066] As shown in FIG. 5A, in step S140, the controller 120 determines the maximum volume q max and minimum rotation speed N min When hydraulic pump 1 is rotated, the discharge flow rate is the pump required flow rate Q Preq This control involves controlling at least the rotation speed N of the engine 2, and is therefore hereinafter referred to as rotation speed control.

[0067] In the rotation speed control (step S140), the processes of steps S145, S150, and S180 are executed. If the determination in step S130 is affirmative, in step S145, the determination unit 134 sets the pump volume q to the maximum volume q max The torque of the hydraulic pump 1 when P (q max ) is the allowable torque T max Determine whether it is greater than

[0068] Prior to this determination, the torque calculation unit 135 calculates the discharge pressure P of the hydraulic pump 1 detected by the pump pressure sensor 9. P Based on the maximum pump torque T P (q max) is calculated. Maximum pump torque T P (q max ) is the pump discharge pressure P detected by the pump pressure sensor 9 P Maximum volume q max It can be obtained by multiplying (T P (q max )=q max ×P P ).

[0069] As shown in FIG. 5A, in step S145, the maximum pump torque T P (q max ) is the allowable torque T max If it is determined that the maximum pump torque T P (q max ) is the allowable torque T max If it is determined that the value is greater than , the process proceeds to step S180.

[0070] In step S150, the pump control unit 136 calculates the required volume q req The maximum volume q max Set to (q req =q max ) The engine control unit 137 also calculates the pump required flow rate Q Preq The maximum volume q max By dividing by N, the required rotation speed is req Calculate (N req =Q Preq / q max ) In other words, in the process of step S150, the pump volume q is set to the maximum volume q max In this state, the maximum supply flow rate Q of the accumulator 6 is ACCmax and the supply flow rate Q of hydraulic pump 1 P The total of the cylinder required flow rate Q req The required rotation speed of engine 2, N req is determined.

[0071] In step S180, the pump control unit 136 calculates the allowable torque T max to pump discharge pressure P PBy dividing by , the required volume q req Calculate (q req =T max / P P ) In other words, the pump control section 136 controls the pump torque T P is the allowable torque T max The upper limit of the pump volume q within the range not exceeding the required volume q req In other words, the pump control unit 136 calculates the pump torque T P is the allowable torque T max The required volume q is equal to req The engine control unit 137 also calculates the pump required flow rate Q Preq to the required volume q req By dividing the req Calculate (N req =Q Preq / q req That is, in the process of step S180, the pump volume q is set to the required volume q req In this state, the maximum supply flow rate Q of the accumulator 6 is ACCmax and the supply flow rate Q of hydraulic pump 1 P The total of the cylinder required flow rate Q req The required rotation speed of engine 2, N req is determined.

[0072] When the process of any one of steps S120, S135, S150, and S180 is completed, the process shown in the flowchart of FIG. 5A ends.

[0073] When the process shown in the flowchart of FIG. 5A is completed, the accumulator control unit 138 determines whether the opening area of ​​the internal passage of the accumulator control valve 5 is equal to the required opening area A req The pump control unit 136 controls the accumulator control valve 5 so that the volume q of the hydraulic pump 1 is equal to the required volume q req The engine control unit 137 controls the regulator 1a so that the rotation speed N of the hydraulic pump 1 becomes equal to the required rotation speed N reqThe rotation speed of the engine 2 is controlled so that the rotation speed of the engine 2 becomes equal to or greater than the rotation speed of the boom cylinder 111A. By repeatedly executing this process at a predetermined control cycle, the supply flow rates from the accumulator 6 and the hydraulic pump 1 to the boom cylinder 111A are adjusted.

[0074] 6 is a diagram showing the change over time in the flow rate when the controller 120 according to this embodiment executes control. As shown in FIG. 6, in this embodiment, the supply flow rate Q of the accumulator 6 decreases over time. ACC When the flow rate Q from the hydraulic pump 1 decreases, P Therefore, according to this embodiment, the cylinder required flow rate Q req The supply flow rate Q corresponds to sup This makes it possible to stably ensure the supply of hydraulic oil, and to prevent the supply of hydraulic oil from becoming discontinuous as in the comparative example (see FIG. 3).

[0075] -Effects of the first embodiment- According to the first embodiment, the following effects are achieved.

[0076] (1) A hydraulic excavator (work machine) 100 includes an engine (prime mover) 2, a hydraulic pump 1 driven by the engine 2 and discharging hydraulic oil, a boom cylinder (hydraulic actuator) 111A driven by hydraulic oil supplied from the hydraulic pump 1, a cylinder control valve (actuator control valve) 3 that controls the flow of hydraulic oil supplied from the hydraulic pump 1 to the boom cylinder 111A, an accumulator 6 that stores return oil from the boom cylinder 111A, an accumulator control valve 5 that controls the flow rate of hydraulic oil supplied from the accumulator 6 to the boom cylinder 111A, an accumulator pressure sensor 15 that detects the pressure of the accumulator 6, a cylinder pressure sensor (actuator pressure sensor) 16 that detects the pressure of the boom cylinder 111A, an operation device 13 that operates the boom cylinder 111A, an operation amount sensor 13b that detects the operation amount of the operation device 13, and a controller 120 that controls the hydraulic pump 1, the cylinder control valve 3, the accumulator control valve 5, and the engine 2.

[0077] As shown in FIG. 5A, the controller 120 determines the required flow rate Q of the boom cylinder 111A based on the operation amount Command detected by the operation amount sensor 13b. req The controller 120 calculates the pressure P of the accumulator 6 detected by the accumulator pressure sensor 15 (step S105). ACC and the pressure P of the boom cylinder 111A detected by the cylinder pressure sensor 16. cyl Based on this, the maximum flow rate that can be supplied by the accumulator 6 (the supply flow rate of the accumulator 6) Q ACCmax (Step S110). The controller 120 calculates the maximum supply flow rate Q of the accumulator 6. ACCmax The required flow rate Q of the boom cylinder 111A is req It is determined whether or not the above can be covered (step S115).

[0078] The controller 120 controls the maximum supply flow rate Q of the accumulator 6. ACCmax The required flow rate Q of the boom cylinder 111A is req If it is determined that the required capacity can be met, the volume q of the hydraulic pump 1 is set to the minimum volume q min and the rotation speed N of the engine 2 is controlled to the minimum rotation speed N min (Step S120). Furthermore, the controller 120 controls the pressure P of the accumulator 6 detected by the accumulator pressure sensor 15. ACC and the pressure P of the boom cylinder 111A detected by the cylinder pressure sensor 16. cyl and the required flow rate Q of the boom cylinder 111A. req Based on this, the accumulator control valve 5 is controlled (step S120).

[0079] The controller 120 controls the maximum supply flow rate Q of the accumulator 6. ACCmax The required flow rate Q of the boom cylinder 111A is req If it is determined that the opening area of ​​the accumulator control valve 5 cannot be covered, the opening area of ​​the accumulator control valve 5 is set to the maximum opening area A ACCmax and the maximum supply flow rate Q of the accumulator 6 ACCmax and the supply flow rate Q of hydraulic pump 1P The total of the flow rate required for the boom cylinder 111A is Q req The volume q of the hydraulic pump 1 and the rotation speed N of the engine 2 are controlled so that the above equation holds (steps S135, S150, S180).

[0080] This configuration makes it possible to provide a hydraulic excavator 100 that can ensure continuity of the flow rate of hydraulic oil supplied to the boom cylinder 111A when the share of hydraulic oil supplied to the boom cylinder 111A by the accumulator 6 and the hydraulic pump 1 changes. This prevents discontinuous supply of hydraulic oil, such as a temporary interruption in the flow rate of hydraulic oil supplied to the boom cylinder 111A, and allows hydraulic oil to be continuously supplied to the boom cylinder 111A. This prevents the operator from feeling uncomfortable and prevents a deterioration in the positioning accuracy of the work implement 104.

[0081] (2) The hydraulic excavator 100 is configured to operate at a discharge pressure P P The controller 120 is configured to detect the maximum supply flow rate Q of the accumulator 6. ACCmax The required flow rate Q of the boom cylinder 111A is req If it is determined that the required speed cannot be met, the rotation speed of the engine 2 is set to the minimum rotation speed N min The required flow rate Q of the boom cylinder 111A is maintained at req The maximum supply flow rate Q of the accumulator 6 ACCmax and the supply flow rate Q of hydraulic pump 1 P The controller 120 determines whether the rotation speed N of the engine 2 can be covered by the minimum rotation speed N min The required flow rate Q of the boom cylinder 111A is maintained at req The maximum supply flow rate Q of the accumulator 6 ACCmax and the supply flow rate Q of hydraulic pump 1 P If it is determined that the required pressure can be met by the pump pressure sensor 9, as shown in FIG. 5B, the discharge pressure P P Based on this, the rotation speed N of engine 2 is set to the minimum rotation speed N minThe required flow rate Q of the boom cylinder 111A is maintained at req Torque T of hydraulic pump 1 when discharging hydraulic oil P (=Q Preq / N min ×P P ) and calculate the calculated torque T of hydraulic pump 1. P is the allowable torque T max The controller 120 determines whether the calculated torque T of the hydraulic pump 1 is greater than or equal to the torque T P is the allowable torque T max If it is determined that the rotation speed N of the engine 2 is smaller than the minimum rotation speed N min and the maximum supply flow rate Q of the accumulator 6 ACCmax and the supply flow rate Q of hydraulic pump 1 P The total of the flow rate required for the boom cylinder 111A is Q req The controller 120 controls the volume q of the hydraulic pump 1 so that the calculated torque T P is the allowable torque T max 5A, the volume q of the hydraulic pump 1 is set to the torque T P is the allowable torque T max The upper limit (T max / P P ) and the maximum supply flow rate Q of the accumulator 6 ACCmax and the supply flow rate Q of hydraulic pump 1 P The total of the flow rate required for the boom cylinder 111A is Q req The rotation speed N of the engine 2 is controlled so that the rotation speed N of the engine 2 becomes equal to or greater than the rotation speed N of the engine 2 (step S180).

[0082] In this configuration, the rotation speed N of the engine 2 is set to the minimum rotation speed N min By controlling the volume q of the hydraulic pump 1 while maintaining the required flow rate Q of the boom cylinder 111A, req Here, between the speed control of the engine 2 and the volume control of the hydraulic pump 1, the speed control of the engine 2 has a greater contribution to fuel economy. Therefore, the flow rate of the hydraulic pump 1 is set to the required flow rate (required pump flow rate) Q PreqWhen the required flow rate Q of the boom cylinder 111A is increased to 1 / 2, the fuel consumption can be reduced by increasing the pump volume q rather than increasing the rotation speed N of the engine 2. req In order to ensure this, the displacement control of the hydraulic pump 1 is given priority over the speed control of the engine 2. This makes it possible to effectively reduce fuel consumption. min Torque T of hydraulic pump 1 while maintaining P is the allowable torque T max If it is estimated that the torque will exceed the allowable torque T max The torque of hydraulic pump 1 must not exceed T P is controlled, preventing engine 2 from lagging or stalling.

[0083] (3) The controller 120 detects the discharge pressure P of the hydraulic pump 1 detected by the pump pressure sensor 9. P Based on this, the volume q of hydraulic pump 1 is set to the maximum volume q max The maximum pump torque T is the torque of hydraulic pump 1 when P (q max ) (step S145). The controller 120 calculates the rotation speed N of the engine 2 at the minimum rotation speed N min The required flow rate Q of the boom cylinder 111A is maintained at req The maximum supply flow rate Q of the accumulator 6 ACCmax and the supply flow rate Q of hydraulic pump 1 P If it is determined that the maximum pump torque T P (q max ) is the allowable torque T max It is determined whether the value is greater than (step S145).

[0084] The controller 120 controls the maximum pump torque T P (q max ) is the allowable torque T max If it is determined that the volume q of the hydraulic pump 1 is smaller than the maximum volume q max and the maximum supply flow rate Q of the accumulator 6 ACCmaxand the supply flow rate Q of hydraulic pump 1 P The total of the flow rate required for the boom cylinder 111A is Q req The rotation speed N of the engine 2 is controlled so that the maximum pump torque T P (q max ) is the allowable torque T max If it is determined that the volume q of the hydraulic pump 1 is larger than the torque T P is the allowable torque T max The upper limit (T max / P P ) and the maximum supply flow rate Q of the accumulator 6 ACCmax and the supply flow rate Q of hydraulic pump 1 P The total of the flow rate required for the boom cylinder 111A is Q req The rotation speed N of the engine 2 is controlled so that the rotation speed N of the engine 2 becomes equal to or greater than the rotation speed N of the engine 2 (step S180).

[0085] Generally, in the variable displacement hydraulic pump 1, increasing the displacement improves the energy efficiency. In this embodiment, the rotation speed N of the engine 2 is set to the minimum rotation speed N min The required flow rate Q of the boom cylinder 111A is maintained at req The supply flow rate Q of accumulator 6 ACC and the supply flow rate Q of hydraulic pump 1 P If this is not possible, the pump torque T P is the allowable torque T max By increasing the volume q of the hydraulic pump 1 up to its upper limit within a range not exceeding q, it is possible to improve energy efficiency. Furthermore, since the rotation speed N of the engine 2 can be kept low, it is possible to effectively reduce fuel consumption. Therefore, according to this embodiment, it is possible to reduce fuel consumption without causing lug down or stalling of the engine 2.

[0086] Second Embodiment A second embodiment of the present invention will be described with reference to Figs. 7 to 9. Components that are the same as or equivalent to those described in the first embodiment are given the same reference symbols, and differences will be mainly described. In the first embodiment, it is assumed that the fluctuation range of the maximum engine torque is small within the set range of the rotation speed of the engine 2, and the allowable torque T max In contrast to this, in the second embodiment, the allowable torque T max An example of processing taking into consideration the above will be described.

[0087] -Functions and processing flow of the controller according to the second embodiment- 7 is a functional block diagram of the controller 220 according to the second embodiment. Similar to the first embodiment, the torque calculation unit 235 according to the second embodiment calculates the volume q of the hydraulic pump 1 as a predetermined volume (for example, the maximum volume q max ) and torque T of hydraulic pump 1 P (For example, maximum pump torque T P (q max )) determined by the specifications of the engine 2. req -T max (corresponding to the characteristic line) and the pump discharge pressure P detected by the pump pressure sensor 9 P and the pump required flow rate Q calculated by the required flow rate calculation unit 133. Preq and based on the pump torque T P is the allowable torque T max The rotation speed N of engine 2 and the pump volume q are calculated as follows:

[0088] The nonvolatile memory 122 stores the rotation speed N of the engine 2 and the allowable torque (maximum engine torque) T max The allowable torque characteristic line (N in Fig. 9) shows the relationship between req -T max The allowable torque characteristic line is stored in the memory. The allowable torque characteristic line is the allowable torque T max Represents the characteristics of.

[0089] FIG. 8 is a flowchart showing an example of the processing flow of the rotation speed control (step S240) executed by the controller 220 according to the second embodiment. As shown in FIG. 8, in the second embodiment, the rotation speed control of step S240 is executed instead of step S140 in the flowchart of FIG. 5A. In the second embodiment, the other processing steps (S100 to S135) of the rotation speed control are the same as those in the first embodiment, and therefore the description thereof will be omitted. Note that in the second embodiment, the allowable torque T max is the rotation speed N, the minimum rotation speed N min The maximum torque T that can be output by engine 2 when max (N min ) The torque calculation unit 235 calculates the allowable torque characteristic line (N in FIG. 9). req -T max (corresponding to the characteristic line) and the minimum rotation speed N min Allowable torque T max (N min 8, the controller 220 according to the second embodiment executes the processes of steps S245 and S280 instead of the processes of steps S145 and S180 in the flowchart of FIG. 5A.

[0090] In step S245, the determination unit 234 sets the pump volume q to the maximum volume q max The maximum pump torque T P (q max ) is the rotation speed N, the minimum rotation speed N min The maximum torque that can be output by engine 2 when max (N min 9 ) is larger than the allowable torque characteristic line (N req -T max (corresponding to the characteristic line) and the minimum rotation speed N min Allowable torque T max (N min ) is calculated.

[0091] As shown in FIG. 8, in step S245, the maximum pump torque TP (q max ) is the allowable torque T max (N min ), the process proceeds to step S150. P (q max ) is the allowable torque T max (N min ), the process proceeds to step S280.

[0092] The details of the process of step S280 will be described with reference to Fig. 9. Fig. 9 shows the required rotation speed N req and required volume q req As shown in FIG. 9, the torque calculation unit 235 calculates q req -T P Characteristic line and N req -q req Calculate the characteristic line.

[0093] N req -T max The characteristic line corresponds to the above-mentioned allowable torque characteristic line, i.e., the torque curve of the engine 2. req -T max Although the characteristic line is shown as a straight line, req -T max The characteristic line may be a curve. min to maximum rotation speed N max In the range up to, the required rotation speed N of engine 2 req The larger the allowable torque T max becomes larger. Minimum rotation speed N min corresponds to the minimum value of the rotation speed N that can be set in the engine 2, and the maximum rotation speed N max corresponds to the maximum value of the rotation speed N that can be set in the engine 2.

[0094] q req -T P The characteristic line is the pump discharge pressure P detected by the pump pressure sensor 9. PThe pump torque T P is the pump volume q and the pump discharge pressure P P Therefore, the pump discharge pressure P P When is a constant value, the pump torque T P becomes larger.

[0095] N req -q req The characteristic line is the pump required flow rate Q calculated by the required flow rate calculation unit 133. preq The supply flow rate Q of hydraulic pump 1 is calculated based on the following: P is proportional to the pump volume q multiplied by the rotational speed N. Therefore, the pump required flow rate Q Preq If is a constant value, the required volume q req The larger the required rotation speed N req becomes smaller.

[0096] The torque calculation unit 235 calculates q req -T P Characteristic line and N req -q req Based on the characteristic line, N req -T P Calculate the characteristic line. N req -T P The characteristic line is the required rotation speed N of engine 2. req The larger the pump torque T P This represents the characteristic that

[0097] The torque calculation unit 235 calculates N req -T P Characteristic line and N req -T max The torque calculation unit 235 determines the intersection point P of the characteristic line. req -T P Characteristic line and N req -T max Based on the characteristic curve, the pump torque T P is the allowable torque T max The lowest possible rotation speed (hereinafter referred to as the lower limit speed) N req1, and the largest possible required volume (hereinafter also referred to as the upper volume limit) q req1 Calculate the following.

[0098] In step S280, the pump control unit 236 calculates the required volume q req The upper volume limit q req1 Furthermore, the engine control unit 237 sets the required rotation speed N req Lower speed limit N req1 Set.

[0099] -Effects of the second embodiment- According to the second embodiment, in addition to the effects of the first embodiment, the following effects are achieved.

[0100] (4) The controller 220 according to the second embodiment includes an allowable torque T max The controller 220 stores the pressure P of the accumulator 6 detected by the accumulator pressure sensor 15. ACC and the pressure P of the boom cylinder 111A detected by the cylinder pressure sensor 16. cly Based on this, the supply flow rate (maximum supply flow rate) Q of the accumulator 6 when the opening area of ​​the accumulator control valve 5 is set to the maximum opening area is calculated. ACCmax (Step S110). The controller 220 calculates the required flow rate Q of the boom cylinder 111A. req to the supply flow rate Q of accumulator 6 ACCmax Subtract the required flow rate Q of hydraulic pump 1 Preq is calculated (step S125).

[0101] As shown in FIG. 9, the controller 220 determines the characteristics of the allowable torque and the discharge pressure P of the hydraulic pump 1 detected by the pump pressure sensor 9. P and the required flow rate Q of hydraulic pump 1 Preq and based on the pump torque T P is the allowable torque T max The required flow rate Q of hydraulic pump 1 is within the range Preq The lower limit N of the rotation speed N of engine 2 that satisfies req1and the upper limit q of the volume q of hydraulic pump 1 req1 (Step S280). The controller 220 calculates the maximum pump torque T P (q max ) is the allowable torque T max If it is determined that the rotation speed N of the engine 2 is greater than the lower limit value N req1 and the volume q of the hydraulic pump 1 is equal to or less than the volume upper limit value q req1 The rotation speed N of the engine 2 and the volume q of the hydraulic pump 1 are controlled so that

[0102] According to this configuration, the allowable torque T max changes according to the rotation speed N of engine 2, the cylinder required flow rate Q can be reduced without causing lag down or stall of engine 2 and while suppressing fuel consumption. req The supply flow rate Q of accumulator 6 ACC and the supply flow rate Q of hydraulic pump 1 P This can be covered by the following.

[0103] (5) The characteristics of the allowable torque stored in the controller 220 are the rotation speed N of the engine 2 and the allowable torque T max Allowable torque characteristic line (N req -T max 9, the controller 220 detects the discharge pressure P of the hydraulic pump 1 detected by the pump pressure sensor 9. P The pump torque T when is constant P and the volume q of hydraulic pump 1 (q req -T P characteristic line) and the relationship between the rotation speed N of the engine 2 and the volume q of the hydraulic pump 1 when the supply flow rate of the hydraulic pump 1 is constant (N req -q req Based on the characteristic line, the rotation speed N of the engine 2 and the pump torque T P The pump torque characteristic line (N req -T P The controller 220 calculates the allowable torque characteristic line (N req -T max characteristic line) and pump torque characteristic line (N req-T P Based on the information of the intersection point P with the characteristic line, the lower speed limit N req1 and upper volume limit q req1 Calculate the following.

[0104] According to this configuration, the allowable torque characteristic line (N req -T max characteristic curve) and pump torque characteristic curve (N req -T P Based on the characteristic curve, the volume q of the hydraulic pump 1 and the rotation speed N of the engine 2 can be appropriately controlled.

[0105] <Modification of the second embodiment> In the second embodiment, the allowable torque T max However, depending on the specifications of the engine 2, the allowable torque T max may become smaller.

[0106] FIG. 10 shows the required rotation speed N req and required volume q req 10 is a diagram illustrating the calculation process of the required rotation speed N req As the allowable torque T increases max becomes smallerN req -T max The characteristic line (allowable torque characteristic line) is stored.

[0107] The controller 220 according to this modification, like the second embodiment, req -T P Characteristic line and N req -q req The controller 220 calculates the characteristic line. req -T P Characteristic line and N req -q req Based on the characteristic line, N req -T P The controller 220 calculates the characteristic line. req-T P Characteristic line and N req -T max Based on the information of the intersection point P of the characteristic line, the lower speed limit N req1 and upper volume limit q req1 The controller 220 calculates the required volume q req The upper volume limit q req1 The controller 220 also sets the required rotation speed N req Lower speed limit N req1 Set.

[0108] Third Embodiment A third embodiment of the present invention will be described with reference to Figs. 11 to 13. Note that the same or corresponding components as those described in the second embodiment are designated by the same reference symbols, and differences will be mainly described. In the third embodiment, as in the second embodiment, the allowable torque T max increases as the rotation speed N of the engine 2 increases (see the dashed line in FIG. 13). In the second embodiment, the maximum pump torque T P (q max ) is the allowable torque T max If it is expected that the pump volume q will exceed the pump torque T P is the allowable torque T max However, as shown in FIG. 13, depending on the specifications of the engine 2 and the hydraulic pump 1 and the pump discharge pressure P P Depending on the minimum rotation speed N min to maximum rotation speed N max Within the range of allowable torque T max than the pump torque T P is larger and N req -T P Characteristic line and N req -T max The characteristic line may not intersect.

[0109] Therefore, in the third embodiment, N req -T P Characteristic line and N req -T max If the characteristic line does not intersect, the pump torque T PThe allowable torque T max and the required rotation speed N req Minimum rotation speed N min or maximum rotation speed N max Set to.

[0110] -Functions and processing flow of the controller according to the third embodiment- 11 is a functional block diagram of a controller 320 according to the third embodiment. The hydraulic excavator 100 according to the third embodiment includes a mode selector switch 340 provided in the operator's cab 118. The mode selector switch 340 can be switched to either an operation-oriented position or a fuel efficiency-oriented position by an operator's operation. When the mode selector switch 340 is switched to the operation-oriented position, the controller 320 sets the operation-oriented mode. When the mode selector switch 340 is switched to the fuel efficiency-oriented position, the controller 320 sets the fuel efficiency-oriented mode.

[0111] 13 is a diagram showing an allowable torque characteristic line (dotted line) and a pump torque characteristic line (solid line) of the hydraulic excavator 100 according to the third embodiment. As shown in FIG. 13, the controller 320 controls the required rotation speed N req As the allowable torque T increases max As N gets larger req -T max The characteristic line (allowable torque characteristic line) is stored.

[0112] FIG. 12 is a flowchart showing an example of the processing flow of the rotation speed control (step S340) executed by the controller 320 according to the third embodiment. As shown in FIG. 12, in the third embodiment, the processing of steps S360, S364, S370, and S375 is added to the flowchart of FIG. 8. In the third embodiment, the other processing of the rotation speed control (S100 to S135) is the same as in the second embodiment, and therefore a description thereof will be omitted. Note that in step S132 of FIG. 5B, the pump torque T P (=Q Preq / N min ×P P ) is the allowable torque T max (Nmin ), the process proceeds to step S360 in FIG.

[0113] As shown in FIG. 12, in step S245, the pump volume q is set to the maximum volume q max The maximum pump torque T P (q max ) is the rotation speed N, the minimum rotation speed N min The allowable torque T max (N min ), the process proceeds to step S360.

[0114] In step S360, the determination unit 334 determines whether the rotation speed N of the engine 2 is equal to or greater than the maximum rotation speed N max When this is the case, the flow rate that can be supplied from hydraulic pump 1 (pump supplyable flow rate) is Q P1 is the pump required flow rate Q Preq The process in step S360 determines whether the number of req -T P Characteristic line and N req -T max This corresponds to the process of determining whether or not the characteristic line intersects with the target line.

[0115] The determination unit 334 determines the pump torque T P is the allowable torque T max (N max ) required volume q req (N max ) is calculated. Allowable torque T max (N max ) is the rotation speed N to the maximum rotation speed N max The allowable torque T max and is obtained from the allowable torque characteristic line. req (N max ) maximum rotation speed N max The value multiplied by is the pump supplyable flow rate Q P1 The determining unit 334 determines the pump supplyable flow rate Q P1 is the pump required flow rate Q Preq If it is determined that the value is less than or equal to Nreq -T P Characteristic line and N req -T max If it is determined that the flow rate Q does not intersect with the characteristic line, the process proceeds to step S364. P1 is the pump required flow rate Q Preq If it is determined that the number is greater than N, req -T P Characteristic line and N req -T max If it is determined that the characteristic line is intersected, the process proceeds to step S280.

[0116] In step S364, determination unit 334 determines whether or not the performance-focused mode is set based on the operation position of mode switch 340. If mode switch 340 is operated to the operation-focused position, determination unit 334 determines that the performance-focused mode is set, and proceeds to step S375. If mode switch 340 is operated to the fuel economy-focused position, determination unit 334 determines that the fuel economy-focused mode is set, and proceeds to step S370.

[0117] In step S370, the engine control unit 137 determines the minimum rotation speed N min Request rotation speed N req Set to (N req =N min ) The pump control unit 136 also determines whether the rotation speed N is equal to or greater than the minimum rotation speed N min Allowable torque T max (N min ) is detected by the pump pressure sensor 9. P By dividing by the required volume q req Calculate (q req =T max (N min ) / P P ).

[0118] In step S375, the engine control unit 137 determines the maximum rotation speed N max Request rotation speed N req Set to (N req=N max ) The pump control unit 136 also determines whether the rotation speed N is greater than the maximum rotation speed N max Allowable torque T max (N max ) is detected by the pump pressure sensor 9. P By dividing by the required volume q req Calculate (q req =T max (N max ) / P P ).

[0119] -Effects of the third embodiment- According to the third embodiment, in addition to the effects of the second embodiment, the following effects are achieved.

[0120] (6) The controller 320 according to the third embodiment is configured to calculate the allowable torque characteristic line (N req -T max characteristic line) and pump torque characteristic line (N req -T P The controller 320 determines whether the allowable torque characteristic line (N req -T max characteristic line) and pump torque characteristic line (N req -T P If it is determined that the characteristic line does not intersect with the engine speed N, the controller 320 determines the mode that is set (step S364). If it is determined that the performance-oriented mode is set, the controller 320 sets the rotation speed N of the engine 2 to the maximum rotation speed N max The volume q of the hydraulic pump 1 is controlled to the pump torque T P is the allowable torque T max (N max ) (step S375). For example, the pump volume q is controlled to an upper limit value within a range not exceeding the pump torque T P is the allowable torque T max (N max When it is determined that the fuel economy focused mode is set, the controller 320 controls the rotation speed N of the engine 2 to be equal to the minimum rotation speed N min The volume q of the hydraulic pump 1 is controlled to the pump torque T Pis the allowable torque T max (N min ) (Step S370). For example, the pump volume q is controlled to an upper limit value within a range not exceeding the pump torque T P is the allowable torque T max (N min ) is controlled to be equal to

[0121] In this configuration, the allowable torque characteristic line (N req -T max characteristic line) and pump torque characteristic line (N req -T P characteristic line) does not intersect, that is, the cylinder demand flow Q req If the operation priority mode is set, the supply flow rate Q of the accumulator 6 is set to 0. ACC and the supply flow rate Q of hydraulic pump 1 P The sum of (Q ACC +Q P ) and cylinder required flow rate Q req In other words, the difference between the requested operation of the boom cylinder 111A and the actual operation can be minimized. As a result, the deterioration of the operability and work efficiency of the operator can be suppressed. When the fuel economy focused mode is set, the rotation speed N of the engine 2 is set to the minimum rotation speed N min This reduces fuel consumption.

[0122] The hydraulic excavator 100 is provided with a mode selector switch (mode setting device) 340 that sets either the operation-oriented mode or the fuel efficiency-oriented mode. This allows the operator to select either the operation-oriented mode or the fuel efficiency-oriented mode depending on the intended use of the hydraulic excavator 100. In other words, according to this embodiment, it is possible to provide a hydraulic excavator 100 that can perform operations in accordance with the operator's requests.

[0123] <Modification of the third embodiment> In the third embodiment, the allowable torque T maxHowever, depending on the specifications of the engine 2, as shown in FIG. 15, the allowable torque T max may become smaller.

[0124] 15 is a diagram showing an allowable torque characteristic line (dash line) and a pump torque characteristic line (solid line) of the hydraulic excavator 100 according to a modification of the third embodiment. As shown in FIG. 15, the controller 320 controls the required rotation speed N req As the allowable torque T increases max becomes smallerN req -T max The characteristic line (allowable torque characteristic line) is stored.

[0125] Fig. 14 is a flowchart showing an example of the processing flow of rotation speed control (step S440) executed by controller 320 according to the modified example of the third embodiment. As shown in Fig. 14, the modified example of the third embodiment adds processing of step S468, which is executed when a positive determination is made in step S364 of the flowchart in Fig. 12.

[0126] As shown in FIG. 14, in step S468, the determination unit 334 calculates the first flow rate Q by the following equation (4): P (N max ) and calculate the second flow rate Q using equation (5). P (N min ) is calculated. Q P (N max )=q req (N max )×N max …(4) Q P (N min )=q req (N min )×N min …(5) q req (N max ) is the pump torque T P The allowable torque T max (N max ) is the required volume when the allowable torque Tmax (N max ) to the pump discharge pressure P P It can be obtained by dividing (q req (N max )=T max (N max ) / P P ) Allowable torque T max (N max ) is the rotation speed N to the maximum rotation speed N max This is the allowable torque when the allowable torque characteristic curve is req (N min ) is the pump torque T P The allowable torque T max (N min ) is the required volume when the allowable torque T max (N min ) to the pump discharge pressure P P It can be obtained by dividing (q req (N min )=T max (N min ) / P P ) Allowable torque T max (N min ) is the rotation speed N to the minimum rotation speed N min This is the allowable torque when the above condition is met, and can be obtained from the allowable torque characteristic line.

[0127] The determination unit 334 determines the first flow rate Q P (N max ) is the second flow rate Q P (N min ) is determined to be greater than the first flow rate Q P (N max ) is the second flow rate Q P (N min If it is determined that the first flow rate Q is equal to or less than the first flow rate Q, the process proceeds to step S370. P (N max ) is the second flow rate Q P (N min ), the process proceeds to step S375.

[0128] In this way, when it is determined that the performance-oriented mode is set, the controller 320 according to the modified example of the third embodiment controls the engine 2 to rotate at the maximum rotation speed N max When rotating at a speed of 1000kJ / s, the pump torque T P is the allowable torque T max (N max ) the first flow rate Q, which is the maximum flow rate of hydraulic oil that can be discharged from the hydraulic pump 1 without exceeding P (N max ) and engine 2 is set to minimum rotation speed N min When rotating at a speed of 1000kJ / s, the pump torque T P is the allowable torque T max (N max ) the second flow rate Q, which is the maximum flow rate of hydraulic oil that can be discharged from the hydraulic pump 1 without exceeding P (N min ) is larger (step S468).

[0129] The controller 320 determines the first flow rate Q P (N max ) is the second flow rate Q P (N min ), the rotation speed N of the engine 2 is set to the maximum rotation speed N max The volume q of the hydraulic pump 1 is controlled to the pump torque T P is the allowable torque T max (N max The controller 320 controls the second flow rate Q to an upper limit value within a range not exceeding the second flow rate Q (step S375). P (N min ) is the first flow rate Q P (N max ), the rotation speed N of the engine 2 is set to the minimum rotation speed N min The volume q of the hydraulic pump 1 is controlled to the pump torque T P is the allowable torque T max (N min ) is controlled to an upper limit value that does not exceed the

[0130] In the third embodiment, the allowable torque increases as the rotation speed N of the engine 2 increases, so the second flow rate Q P (N min) is always the first flow rate Q P (N max In contrast, in the modified example of the third embodiment, the allowable torque decreases as the rotation speed N of the engine 2 increases, so the second flow rate Q P (N min ) is the first flow rate Q P (N max ) may be larger than the second flow rate Q. P (N min ) as the first flow rate Q P (N max ), the second flow rate Q P (N min ) to a pump volume q and rotation speed N that can supply the required flow rate Q of the cylinder. req can be approached as follows.

[0131] The following modified examples are also within the scope of the present invention, and it is possible to combine the configuration shown in the modified example with the configuration described in the above embodiment, to combine the configurations described in the different embodiments above, or to combine the configurations described in the different modified examples below.

[0132] <Variation 1> In the second and third embodiments, the allowable torque T max In the modified example of the second embodiment and the modified example of the third embodiment, the allowable torque T max However, depending on the specifications of the engine 2, as shown in FIG. 16, the allowable torque T max increases, and the allowable torque T increases as the rotation speed N of engine 2 increases from the medium to high rotation speed range. max may become smaller.

[0133] In the example shown in Figure 16, the allowable torque T max is the rotation speed N of engine 2 is the minimum rotation speed N min The allowable torque T max is the rotation speed from the predetermined speed Nb to the maximum rotation speed N max As the rotation speed N of the engine 2 increases, it becomes smaller.

[0134] For example, when the characteristics of the engine 2 are as shown in Fig. 16, it is determined whether the rotation speed N of the engine 2 detected by the speed sensor 2a is equal to or greater than a predetermined speed Nb. For example, when it is determined that the rotation speed N is less than the predetermined speed Nb, the control described in the second embodiment may be executed, and when it is determined that the rotation speed N is equal to or greater than the predetermined speed Nb, the control described in the modified example of the second embodiment may be executed. Also, when it is determined that the rotation speed N is less than the predetermined speed Nb, the control described in the third embodiment may be executed, and when it is determined that the rotation speed N is equal to or greater than the predetermined speed Nb, the control described in the modified example of the third embodiment may be executed.

[0135] <Variation 2> In the above embodiment, an example has been described in which the cylinder control valve 3 is driven by the pilot pressure generated by the pressure control valves 7D, 7U, but the present invention is not limited to this. Various configurations can be adopted for the actuator control valve that controls the flow of hydraulic oil supplied from the hydraulic pump 1 to the hydraulic actuator. For example, the spool of the cylinder control valve 3 may be configured to be driven by electromagnetic force. In this configuration, an electromagnetic solenoid that generates spool thrust is provided instead of the pressure receiving chambers 3e, 3f of the cylinder control valve 3. In this case, the pressure control valves 7U, 7D are omitted.

[0136] <Variation 3> In the above embodiment, the required volume q req , required rotation speed N req , and the required opening area A of the accumulator control valve reqHowever, it is also possible to use feedback control using, for example, a pump tilt angle sensor that measures the tilt angle (volume) of the hydraulic pump 1, a speed sensor 2a that measures the rotation speed of the engine 2, a stroke sensor (displacement sensor) that measures the stroke of the boom cylinder 111A, a flow meter that measures the flow rate of the hydraulic oil, etc.

[0137] <Variation 4> In the above embodiment, an example has been described in which the work machine is a crawler hydraulic excavator 100. However, the work machine is not limited to the crawler hydraulic excavator 100. The present invention can be applied to various work machines equipped with work implements, such as wheeled hydraulic excavators, crawler cranes, and wheel loaders.

[0138] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments. [Explanation of symbols]

[0139] 1...hydraulic pump, 1a...regulator, 2...engine (prime mover), 2a...speed sensor, 3...cylinder control valve (actuator control valve), 5...accumulator control valve, 6...accumulator, 7D, 7U...pressure control valve, 9...pump pressure sensor (pressure sensor), 11S...hydraulic cylinder (hydraulic actuator), 13...operation device, 13a...operation lever, 13b...operation amount sensor, 15...accumulator pressure sensor (pressure sensor), 16...cylinder pressure sensor (actuator pressure sensor, pressure sensor), 100...hydraulic excavator (work machine), 102...traveling body, 103...swinging body, 104...working device, 105...vehicle body, 106...hydraulic system, 111...boom (load body, controlled object), 111A...boom cylinder ( hydraulic cylinder, hydraulic actuator), 112... arm, 113... bucket, 118... operator's cab, 119... machine room, 120... controller, 121... processing device, 122... non-volatile memory (storage device), 123... volatile memory (storage device), 131... operation determination unit, 132... valve control unit, 133... required flow rate calculation unit, 134... determination unit, 135... torque calculation unit, 136... pump control unit, 137... engine control unit, 138... accumulator control unit, 139... accumulator flow rate calculation unit, 220... controller, 234... determination unit, 235... torque calculation unit, 236... pump control unit, 237... engine control unit, 320... controller, 334... determination unit, 340... mode changeover switch (mode setting device), P ACC …Accumulator pressure (accumulator pressure), P cly …cylinder pressure (pressure of hydraulic actuator), P P …Pump discharge pressure (hydraulic pump discharge pressure)

Claims

1. The prime mover and a hydraulic pump driven by the prime mover and discharging hydraulic oil; a hydraulic actuator driven by hydraulic oil supplied from the hydraulic pump; an actuator control valve for controlling the flow of hydraulic oil supplied from the hydraulic pump to the hydraulic actuator; an accumulator that stores return oil from the hydraulic actuator; an accumulator control valve that controls the flow rate of hydraulic oil supplied from the accumulator to the hydraulic actuator; an accumulator pressure sensor that detects the pressure of the accumulator; an actuator pressure sensor that detects the pressure of the hydraulic actuator; an operating device for operating the hydraulic actuator; an operation amount sensor that detects an operation amount of the operation device; a controller that controls the hydraulic pump, the actuator control valve, the accumulator control valve, and the prime mover, The controller calculating a required flow rate of the hydraulic actuator based on the operation amount detected by the operation amount sensor; calculating a supply flow rate of the accumulator based on the pressure of the accumulator detected by the accumulator pressure sensor and the pressure of the hydraulic actuator detected by the actuator pressure sensor; determining whether the flow rate required by the hydraulic actuator can be met by the flow rate supplied from the accumulator; when it is determined that the flow rate required by the hydraulic actuator can be satisfied by the supply flow rate of the accumulator, the volume of the hydraulic pump is controlled to a minimum volume and the rotational speed of the prime mover is controlled to a minimum rotational speed, and the accumulator control valve is controlled based on the pressure of the accumulator detected by the accumulator pressure sensor, the pressure of the hydraulic actuator detected by the actuator pressure sensor, and the flow rate required by the hydraulic actuator; When it is determined that the flow rate required by the hydraulic actuator cannot be satisfied by the supply flow rate of the accumulator, the opening area of ​​the accumulator control valve is controlled to a maximum opening area, and the volume of the hydraulic pump and the rotational speed of the prime mover are controlled so that the sum of the supply flow rate of the accumulator and the supply flow rate of the hydraulic pump becomes the flow rate required by the hydraulic actuator. A work machine characterized by:

2. 2. The work machine according to claim 1, a pump pressure sensor for detecting the discharge pressure of the hydraulic pump; The controller when it is determined that the flow rate required by the hydraulic actuator cannot be satisfied by the supply flow rate of the accumulator, determine whether the flow rate required by the hydraulic actuator can be satisfied by the supply flow rate of the accumulator and the supply flow rate of the hydraulic pump while maintaining the rotational speed of the prime mover at a minimum rotational speed; When it is determined that the required flow rate of the hydraulic actuator can be covered by the supply flow rate of the accumulator and the supply flow rate of the hydraulic pump while the rotational speed of the prime mover is maintained at a minimum rotational speed, the torque of the hydraulic pump when discharging hydraulic oil at the required flow rate of the hydraulic actuator while the rotational speed of the prime mover is maintained at a minimum rotational speed is calculated based on the discharge pressure of the hydraulic pump detected by the pump pressure sensor, and it is determined whether the calculated torque of the hydraulic pump is greater than an allowable torque; when it is determined that the torque of the hydraulic pump is smaller than the allowable torque, the rotational speed of the prime mover is controlled to a minimum rotational speed, and the displacement of the hydraulic pump is controlled so that the sum of the supply flow rate of the accumulator and the supply flow rate of the hydraulic pump becomes the required flow rate of the hydraulic actuator; When it is determined that the torque of the hydraulic pump is greater than the allowable torque, the displacement of the hydraulic pump is controlled to an upper limit value within a range in which the torque of the hydraulic pump does not exceed the allowable torque, and the rotational speed of the prime mover is controlled so that the sum of the supply flow rate of the accumulator and the supply flow rate of the hydraulic pump becomes the required flow rate of the hydraulic actuator. A work machine characterized by:

3. 3. The work machine according to claim 2, The controller calculating a maximum pump torque, which is the torque of the hydraulic pump when the volume of the hydraulic pump is set to a maximum volume, based on the discharge pressure of the hydraulic pump detected by the pump pressure sensor; when it is determined that the required flow rate of the hydraulic actuator cannot be satisfied by the supply flow rate of the accumulator and the supply flow rate of the hydraulic pump while the rotational speed of the prime mover is maintained at a minimum rotational speed, it is determined whether or not the maximum pump torque is greater than an allowable torque; when it is determined that the maximum pump torque is smaller than the allowable torque, the displacement of the hydraulic pump is controlled to the maximum displacement, and the rotational speed of the prime mover is controlled so that the sum of the supply flow rate of the accumulator and the supply flow rate of the hydraulic pump becomes the required flow rate of the hydraulic actuator; When it is determined that the maximum pump torque is greater than the allowable torque, the displacement of the hydraulic pump is controlled to an upper limit value within a range in which the torque of the hydraulic pump does not exceed the allowable torque, and the rotational speed of the prime mover is controlled so that the sum of the supply flow rate of the accumulator and the supply flow rate of the hydraulic pump becomes the required flow rate of the hydraulic actuator. A work machine characterized by:

4. 4. The work machine according to claim 3, The controller stores a characteristic of the allowable torque that changes in accordance with a change in the rotational speed of the prime mover, The controller calculating a supply flow rate of the accumulator when an opening area of ​​the accumulator control valve is set to a maximum opening area, based on the pressure of the accumulator detected by the accumulator pressure sensor and the pressure of the hydraulic actuator detected by the actuator pressure sensor; calculating a required flow rate of the hydraulic pump by subtracting the supply flow rate of the accumulator from the required flow rate of the hydraulic actuator; calculating a lower limit value of the rotational speed of the prime mover and an upper limit value of the volume of the hydraulic pump, at which the torque of the hydraulic pump satisfies the required flow rate of the hydraulic pump within the range of the allowable torque, based on the characteristics of the allowable torque, the discharge pressure of the hydraulic pump detected by the pump pressure sensor, and the required flow rate of the hydraulic pump; When it is determined that the maximum pump torque is greater than the allowable torque, the rotation speed of the prime mover and the displacement of the hydraulic pump are controlled so that the rotation speed of the prime mover becomes the speed lower limit value and the displacement of the hydraulic pump becomes the displacement upper limit value. A work machine characterized by:

5. 5. The work machine according to claim 4, the allowable torque characteristic is an allowable torque characteristic line that represents the relationship between the rotation speed of the prime mover and the allowable torque, The controller calculating a pump torque characteristic line that indicates the relationship between the rotation speed of the prime mover and the torque of the hydraulic pump based on the relationship between the torque of the hydraulic pump and the volumetric capacity of the hydraulic pump when the discharge pressure of the hydraulic pump detected by the pump pressure sensor is constant, and the relationship between the rotation speed of the prime mover and the volumetric capacity of the hydraulic pump when the supply flow rate of the hydraulic pump is set to the required flow rate of the hydraulic pump; calculating the speed lower limit value and the volume upper limit value based on information on the intersection point between the allowable torque characteristic line and the pump torque characteristic line; A work machine characterized by:

6. 6. The work machine according to claim 5, a mode setting device for setting either an operation-oriented mode or a fuel-efficiency-oriented mode; The controller determining whether the allowable torque characteristic line and the pump torque characteristic line intersect; If it is determined that the allowable torque characteristic line and the pump torque characteristic line do not intersect, the set mode is determined; When it is determined that the operation-oriented mode is set, the rotation speed of the prime mover is controlled to a maximum rotation speed, and the displacement of the hydraulic pump is controlled to an upper limit value within a range in which the torque of the hydraulic pump does not exceed the allowable torque, When it is determined that the fuel economy focused mode is set, the rotation speed of the prime mover is controlled to a minimum rotation speed, and the displacement of the hydraulic pump is controlled to an upper limit value within a range in which the torque of the hydraulic pump does not exceed the allowable torque. A work machine characterized by:

7. 7. The work machine according to claim 6, The controller When it is determined that the operation-oriented mode is set, it is determined which is larger: a first flow rate, which is the maximum flow rate of hydraulic oil that can be discharged from the hydraulic pump without the torque of the hydraulic pump exceeding the allowable torque when the prime mover is rotated at a maximum rotation speed, or a second flow rate, which is the maximum flow rate of hydraulic oil that can be discharged from the hydraulic pump without the torque of the hydraulic pump exceeding the allowable torque when the prime mover is rotated at a minimum rotation speed; When it is determined that the first flow rate is greater than the second flow rate, the rotational speed of the prime mover is controlled to a maximum rotational speed, and the displacement of the hydraulic pump is controlled to an upper limit value within a range in which the torque of the hydraulic pump does not exceed the allowable torque, When it is determined that the second flow rate is greater than the first flow rate, the rotation speed of the prime mover is controlled to a minimum rotation speed, and the displacement of the hydraulic pump is controlled to an upper limit value within a range in which the torque of the hydraulic pump does not exceed the allowable torque. A work machine characterized by:

Images