Work machine

Abstract

This work machine comprises: a first hydraulic actuator; a pressure accumulation device that accumulates oil returned from the first hydraulic actuator; a control valve that is disposed in an oil passage connecting the first hydraulic actuator and the pressure accumulation device; an operation device that operates the first hydraulic actuator; a first pressure sensor that detects the pressure in the pressure accumulation device; and a control device that controls the control valve on the basis of the operation amount of the operation device and the pressure in the pressure accumulation device detected by the first pressure sensor. When the first actuator is operated by the operation device, the control device increases the opening degree of the control valve as the differential pressure between the pressure in the pressure accumulation device and an estimated value of the load pressure of the first hydraulic actuator set as a fixed value or an estimated value of the load pressure of the first hydraulic actuator calculated on the basis of orientation information of the work device becomes smaller.

Description

Working Machine

[0001] The present invention relates to a working machine such as a hydraulic excavator.

[0002] Patent Document 1 discloses a technique for regenerating return oil from a boom cylinder into an accumulator (pressure accumulator) during a boom lowering operation to reduce fuel consumption of a working machine. In the working machine described in Patent Document 1, the flow rate of hydraulic oil from the boom cylinder regenerated into the accumulator is controlled in accordance with the differential pressure between the load pressure of the boom cylinder detected by a pressure sensor and the pressure of the accumulator detected by another pressure sensor.

[0003] International Publication No. 2021 / 256058

[0004] However, since hydraulic oil is compressible, the load pressure of the boom cylinder may vibrate due to sudden operation or sudden stop of the boom cylinder. Therefore, in the working machine described in Patent Document 1, when the load pressure of the boom cylinder detected by the pressure sensor vibrates, the control command value also vibrates, which causes a problem that it is difficult to obtain good operability.

[0005] The present invention has been made based on the above-described circumstances, and an object of the present invention is to provide a working machine having good operability in a system that regenerates return oil of an actuator into a pressure accumulator.

[0006] A working machine according to one aspect of the present invention comprises: a working device having a first hydraulic actuator; a pressure accumulator for storing return oil from the first hydraulic actuator; a control valve arranged in an oil passage connecting the first hydraulic actuator and the pressure accumulator; an operating device for operating the first hydraulic actuator; a first pressure sensor for detecting the pressure of the pressure accumulator; and a control device for controlling the control valve based on the amount of operation of the operating device and the pressure of the pressure accumulator detected by the first pressure sensor. When the first hydraulic actuator is operated by the operating device, the control device increases the opening of the control valve as the differential pressure between an estimated value of the load pressure of the first hydraulic actuator, which is set as a fixed value, or an estimated value of the load pressure of the first hydraulic actuator calculated based on the posture information of the working device, and the pressure of the pressure accumulator detected by the first pressure sensor becomes smaller.

[0007] According to the present invention, it is possible to provide a working machine with good operability in a system that regenerates the return oil of an actuator using a pressure accumulator.

[0008] Figure 1 is a side view of a hydraulic excavator according to the first embodiment. Figure 2 is a diagram showing the hydraulic system of the hydraulic excavator according to the first embodiment. Figure 3 is a hardware configuration diagram of the control device. Figure 4 is a block diagram showing the control of the pressure accumulator valve by the control device according to the first embodiment. Figure 5 is a diagram showing the hydraulic system of a hydraulic excavator according to the second embodiment. Figure 6 is a block diagram showing the control of the pressure accumulator valve by the control device according to the second embodiment. Figure 7 is a diagram showing the hydraulic system of a hydraulic excavator according to the third embodiment. Figure 8 is a block diagram showing the control of the pressure accumulator valve by the control device according to the third embodiment. Figure 9 is a diagram showing the hydraulic system of a hydraulic excavator according to the fourth embodiment. Figure 10 is a block diagram showing the control of the pressure accumulator valve by the control device according to the fourth embodiment. Figure 11 is a diagram showing the hydraulic system of a hydraulic excavator according to a comparative example.

[0009] A working machine according to an embodiment of the present invention will be described with reference to the drawings. In this embodiment, an example in which the working machine is a crawler-type hydraulic excavator will be described. In each figure, equivalent components are denoted by the same reference numerals, and redundant explanations will be omitted as appropriate.

[0010] <First Embodiment> Hereinafter, a hydraulic excavator 100 according to an embodiment of the present invention will be described with reference to Figures 1 to 4.

[0011] Figure 1 is a side view of a hydraulic excavator 100 according to the first embodiment. As shown in Figure 1, the hydraulic excavator 100 comprises a machine body 105 and a work device 104 attached to the machine body 105. The machine body 105 has a crawler-type traveling body 102 and a slewing body 103 that is rotatably mounted on the traveling body 102. The traveling body 102 moves by driving a pair of left and right crawlers with a travel motor 102A. The slewing body 103 is connected to the traveling body 102 via a slewing device having a slewing motor 103A and rotates relative to the traveling body 102 when driven by the slewing motor 103A.

[0012] The rotating body 103 comprises a driver's cab 118 where the operator sits, and an engine room 119 which houses the prime mover (not shown) and hydraulic equipment such as a hydraulic pump driven by the engine.

[0013] The operator's cab 118 is equipped with an electric control device for operating the hydraulic actuators (115, 116, 117, 103A, 102A) of the working device 104, the slewing body 103, and the traveling body 102. The operator's cab 118 is also equipped with a control device 120 for controlling the operation of various parts of the hydraulic excavator 100.

[0014] The working device 104 is a multi-jointed working device attached to the slewing body 103, and has a plurality of hydraulic actuators and a plurality of driveable members driven by the plurality of hydraulic actuators. The working device 104 has a configuration in which three driveable members (boom 111, arm 112, and bucket 113) are connected in series. The base end of the boom 111 is rotatably connected to the front of the slewing body 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 rotationally driven by the extension and retraction of the boom cylinder 115, which is a hydraulic actuator (hydraulic cylinder). The arm 112 is rotationally driven by the extension and retraction of the arm cylinder 116, which is a hydraulic actuator (hydraulic cylinder). The bucket 113 is rotationally driven by the extension and retraction of the bucket cylinder 117, which is a hydraulic actuator (hydraulic cylinder). By operating the work device 104, the hydraulic excavator 100 can perform tasks such as excavating soil, leveling, and compacting the ground.

[0016] As shown in Figure 2, the control device 120 is connected to a boom operating device 5 and an arm operating device 18. The boom operating device 5 is an operating device that instructs the raising and lowering of the boom 111 in response to operations by the operator. The boom operating device 5 has a tiltable boom operating lever 5a and a boom operating sensor 5b that outputs an operation signal to the control device 120 according to the amount of operation (operating angle) of the boom operating lever 5a. When the boom operating lever 5a is operated in the boom raising direction, the boom operating device 5 outputs a boom raising operation signal from the boom operating sensor 5b, and when the boom operating lever 5a is operated in the boom lowering direction, the boom operating sensor 5b outputs a boom lowering operation signal.

[0017] The arm operating device 18 is an operating device that instructs the arm 112 to perform an upward movement (cloud movement) and a downward movement (dump movement) in response to an operation by an operator. The arm operating device 18 includes a tiltable arm operating lever 18a and an arm operating sensor 18b that outputs an operating signal to the control device 120 according to the amount of operation (operating angle) of the arm operating lever 18a. When the arm operating lever 18a is operated in the arm upward direction, the arm operating sensor 18b outputs an arm upward operation signal (arm cloud operation signal), and when the arm operating lever 18a is operated in the arm downward direction, the arm operating sensor 18b outputs an arm downward operation signal (arm dump operation signal).

[0018] Figure 2 shows the hydraulic system 106 provided by the hydraulic excavator 100 according to the first embodiment. In Figure 2, the configuration for driving the boom cylinder 115 and arm cylinder 116, which are hydraulic actuators, is shown, but the configuration for driving other hydraulic actuators is omitted from the illustration. In this embodiment, the boom cylinder 115 corresponds to the first hydraulic actuator, and the arm cylinder 116 corresponds to the second hydraulic actuator.

[0019] The hydraulic system 106 includes a first hydraulic pump 13 and a second hydraulic pump 27, a boom cylinder 115 that is extended and driven by hydraulic fluid supplied from the first hydraulic pump 13, an arm cylinder 116 that is extended and driven by hydraulic fluid supplied from the second hydraulic pump 27, and an accumulator 4 as a pressure accumulator that stores the pressurized oil (hereinafter also referred to as return oil) discharged from the boom cylinder 115.

[0020] Furthermore, the hydraulic system 106 includes a first directional control valve 14, which is a control valve that controls the flow of hydraulic fluid supplied from the first hydraulic pump 13 to the boom cylinder 115; a pressure accumulator control valve 2, which is a control valve provided in the oil passage 40 connecting the boom cylinder 115 and the accumulator 4; a second directional control valve 28, which is a control valve that controls the flow rate of hydraulic fluid supplied from the second hydraulic pump 27 to the arm cylinder 116; and a tank 107 for storing hydraulic fluid.

[0021] The first hydraulic pump 13 and the second hydraulic pump 27 are connected to the engine. The first hydraulic pump 13 and the second hydraulic pump 27 are driven by the engine and draw hydraulic fluid from the tank 107 and discharge it as pressurized oil. The first hydraulic pump 13 and the second hydraulic pump 27 are both variable displacement hydraulic pumps. The engine is the power source for the hydraulic excavator 100 and is composed of an internal combustion engine such as a diesel engine.

[0022] The boom cylinder 115 is a hydraulic cylinder that extends and retracts using hydraulic fluid supplied to and discharged from the bottom-side oil chamber 115a and the rod-side oil chamber 115b. The base end of the cylinder tube 115c of the boom cylinder 115 is rotatably attached to the slewing body 103, and the tip of the piston rod 115d is rotatably attached to the boom 111 (see Figure 1). Therefore, the load on the boom 111, which is the object driven by the boom cylinder 115, acts on the bottom-side oil chamber 115a of the boom cylinder 115. Hereinafter, the pressure in the bottom-side oil chamber 115a of the boom cylinder 115 (bottom pressure) will also be referred to as "load pressure". Thus, in this embodiment, the bottom-side oil chamber 115a of the boom cylinder 115 corresponds to the load-side oil chamber, and the rod-side oil chamber 115b corresponds to the non-load-side oil chamber. As shown in Figure 2, the boom cylinder 115 is connected to the first hydraulic pump 13 and the tank 107 via the first directional control valve 14.

[0023] The arm cylinder 116 is a hydraulic cylinder that extends and retracts using hydraulic fluid supplied to and discharged from the bottom-side oil chamber 116a and the rod-side oil chamber 116b. The base end of the cylinder tube 116c of the arm cylinder 116 is rotatably attached to the boom 111, and the tip of the piston rod 116d is rotatably attached to the arm 112 (see Figure 1). As shown in Figure 2, the arm cylinder 116 is connected to the second hydraulic pump 27 and the tank 107 via the second directional control valve 28.

[0024] The accumulator 4 is a pressure accumulator that stores the hydraulic fluid discharged from the bottom oil chamber 115a of the boom cylinder 115 when the boom cylinder 115 is retracted and guided through the pressure accumulator control valve 2. In other words, the accumulator 4 stores the pressurized oil discharged from the boom cylinder 115. When the boom cylinder 115 is extended, the accumulator 4 supplements the hydraulic fluid guided from the first hydraulic pump 13 to the bottom oil chamber 115a and supplies the stored pressurized oil to the bottom oil chamber 115a of the boom cylinder 115 through the pressure accumulator control valve 2.

[0025] The first directional control valve 14 switches from the neutral position 14A to either the left or right position in response to a control signal from the control device 120. When the control device 120 receives a boom raising operation signal from the boom operating device 5, it switches the first directional control valve 14 to the right position 14B, and when it receives a boom lowering operation signal, it switches the first directional control valve 14 to the left position 14C.

[0026] When the first directional control valve 14 is switched to the right position 14B, the discharge port of the first hydraulic pump 13 is connected to the bottom oil chamber 115a of the boom cylinder 115, and the rod oil chamber 115b is connected to the tank 107. As a result, the discharged oil from the first hydraulic pump 13 flows into the bottom oil chamber 115a, and the hydraulic fluid from the rod oil chamber 115b is discharged into the tank 107, causing the boom cylinder 115 to extend. On the other hand, when the first directional control valve 14 is switched to the left position 14C, the discharge port of the first hydraulic pump 13 is connected to the rod oil chamber 115b, and the bottom oil chamber 115a and the tank 107 are shut off. At this time, the bottom oil chamber 115a is in communication with the accumulator 4 via the pressure accumulator control valve 2. As a result, the discharge oil from the hydraulic pump 13 flows into the rod-side oil chamber 115b, the hydraulic fluid from the bottom-side oil chamber 115a is discharged into the accumulator 4, and the boom cylinder 115 retracts.

[0027] The second directional control valve 28 switches from the neutral position 28A to either the left or right position in response to a control signal from the control device 120. When the control device 120 receives an arm cloud operation signal from the arm operating device 18, it switches the second directional control valve 28 to the right position 28B, and when it receives an arm dump operation signal, it switches the second directional control valve 28 to the left position 28C.

[0028] When the second directional control valve 28 is switched to the right position 28B, the discharge port of the second hydraulic pump 27 is connected to the bottom oil chamber 116a of the arm cylinder 116, and the rod oil chamber 115b is connected to the tank 107. As a result, the discharged oil from the second hydraulic pump 27 flows into the bottom oil chamber 116a, the hydraulic fluid from the rod oil chamber 116b is discharged into the tank 107, and the arm cylinder 116 extends. On the other hand, when the second directional control valve 28 is switched to the left position 28C, the discharge port of the second hydraulic pump 27 is connected to the rod oil chamber 116b, and the bottom oil chamber 116a is connected to the tank 107. As a result, the discharged oil from the second hydraulic pump 27 flows into the rod oil chamber 116b, the hydraulic fluid from the bottom oil chamber 116a is discharged into the tank 107, and the arm cylinder 116 retracts.

[0029] The pressure accumulator control valve 2 is located in the oil passage 40 connecting the accumulator 4 and the bottom oil chamber 115a of the boom cylinder 115. The accumulator 4 changes its opening degree in response to a control signal from the control device 120, adjusting the flow rate (regenerative flow rate) regenerated from the bottom oil chamber 115a of the boom cylinder 115 to the accumulator 4.

[0030] Furthermore, the hydraulic system 106 includes a pressure accumulator 31, which serves as a first pressure sensor for detecting the pressure of the hydraulic fluid in the accumulator 4. The pressure accumulator 31 is a pressure sensor connected to the control device 120, and outputs its detection result to the control device 120.

[0031] Figure 3 is a hardware configuration diagram of the control device 120. As shown in Figure 3, the control device 120 is composed of a computer equipped with a processor 151 such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), and DSP (Digital Signal Processor), volatile memory 152 known as RAM (Random Access Memory), non-volatile memory 153 such as ROM (Read Only Memory), flash memory, and hard disk drive, an input interface 154, an output interface 155, and other peripheral circuits. The control device 120 may be composed of one computer or multiple computers.

[0032] The non-volatile memory 153 stores a program capable of performing various calculations. In other words, the non-volatile memory 153 is a storage medium from which a program realizing the functions of this embodiment can be read. The processor 151 is a processing unit that loads the program stored in the non-volatile memory 153 into the volatile memory 152 and performs calculations, and performs predetermined calculation processing on signals taken in from the input interface 154, the volatile memory 152, and the non-volatile memory 153 according to the program.

[0033] The input interface 154 converts signals received from each sensor (5b, 18b, 31, etc.) into data that can be processed by the processor 151. The output interface 155 generates output signals according to the calculation results of the processor 151 and outputs these signals to each control valve (2, 14, 28), engine, etc.

[0034] The operation of the hydraulic system 106 will be described below with reference to Figure 2.

[0035] First, let's explain the extension operation of the boom cylinder 115 (the raising operation of the boom 111).

[0036] When the boom operation lever 5a is operated in the boom-raising direction, a boom-raising operation signal is input to the control device 120. Upon receiving the boom-raising operation signal, the control device 120 switches the first directional control valve 14 to the right position 14B. As a result, the discharged oil from the first hydraulic pump 13 flows into the bottom-side oil chamber 115a of the boom cylinder 115, and the hydraulic fluid discharged from the rod-side oil chamber 115b is returned to the tank 107, causing the boom cylinder 115 to extend.

[0037] Next, we will explain the retraction operation of the boom cylinder 115 (the lowering operation of the boom 111).

[0038] When the boom operation lever 5a is operated in the boom lowering direction, a boom lowering operation signal is input to the control device 120. Upon receiving the boom lowering operation signal, the control device 120 switches the first direction control valve 14 to the left position 14C and opens the pressure accumulator control valve 2 according to the lever operation amount. As a result, all the pressurized oil discharged from the bottom side oil chamber 115a flows into the accumulator 4, and the boom cylinder 115 retracts. At this time, pressurized oil is supplied from the first hydraulic pump 13 to the rod side oil chamber 115b of the boom cylinder 115, so that the rod side of the boom cylinder 115 does not become negative pressure. In this way, during the retraction operation of the boom cylinder 115, the load side oil chamber, the bottom side oil chamber 115a, retracts.

[0039] Next, we will explain the extension operation of the arm cylinder 116 (the clouding operation of the arm 112).

[0040] When the arm operating lever 18a is operated in the direction of the arm cloud, an arm cloud operation signal is input to the control device 120. Upon receiving the arm cloud operation signal, the control device 120 switches the second directional control valve 28 to the right position 28B. As a result, the discharged oil from the second hydraulic pump 27 flows into the bottom oil chamber 116a of the arm cylinder 116, and the hydraulic fluid discharged from the rod-side oil chamber 116b is returned to the tank 107, causing the arm cylinder 116 to extend.

[0041] Next, we will explain the contraction operation of the arm cylinder 116 (the dumping operation of the arm 112).

[0042] When the arm operation lever 18a is operated in the arm dump direction, an arm dump operation signal is input to the control device 120. The control device 120 receives the arm dump operation signal and switches the second directional control valve 28 to the left position 28C. As a result, the hydraulic fluid discharged from the second hydraulic pump 27 flows into the rod-side oil chamber 116b of the arm cylinder 116, the hydraulic fluid discharged from the bottom-side oil chamber 116a is returned to the tank 107, and the arm cylinder 116 performs a contraction operation.

[0043] Hereinafter, the processing content by the control device 120, specifically, the control method for the pressure accumulation control valve 2 will be described. The control device 120 controls the meter-out opening area of the boom lowering operation, that is, the opening area of the pressure accumulation control valve 2, according to the operation amount of the boom operation lever 5a. The control device 120 controls the pressure accumulation control valve 2 in accordance with the differential pressure between the load pressure of the boom cylinder 115 (the pressure in the bottom-side oil chamber 115a) and the pressure of the accumulator 4. More specifically, the control device 120 performs control such that the smaller the differential pressure between the load pressure of the boom cylinder 115 and the pressure of the accumulator 4, the larger the opening degree of the pressure accumulation control valve 2.

[0044] FIG. 4 is a diagram showing the processing content by the control device 120. As shown in FIG. 4, a lever operation signal is input from the boom operation sensor 5b to the control device 120 in accordance with the operation amount of the boom operation lever 5a (see FIG. 2) in the boom lowering direction.

[0045] The function generator 121 stores in advance correspondence information between the operation amount of the boom operation lever 5a and the opening area of the pressure accumulation control valve 2. When a lever operation signal is input to the function generator 121, the function generator 121 outputs the meter-out opening area for boom lowering corresponding to the operation amount, that is, the opening area of the control valve 2, to the integrator 123.

[0046] Further, a pressure sensor signal indicating the pressure of the accumulator 4 is input from the pressure accumulation sensor 31 to the function generator 122.

[0047] The function generator 122 is for correcting the meter-out opening area output from the function generator 121 in accordance with the pressure of the accumulator 4 and an estimated value of the load pressure of a boom cylinder 115, which will be described later. In the present embodiment, when the operation amount of a boom operation lever 5a is the same, the flow rate of return oil from the boom cylinder 115 during a boom lowering operation is made equal to that of a working machine not equipped with a regeneration system using the accumulator 4 (hereinafter also referred to as a "conventional machine"). For this purpose, the meter-out opening area for boom lowering is controlled in accordance with the pressure of the accumulator 4 and the estimated value of the load pressure of the boom cylinder 115.

[0048] Here, in order to facilitate understanding of the present embodiment, a comparative example of the present embodiment will be described with reference to FIG. 11. FIG. 11 is a hydraulic circuit diagram showing a hydraulic system 906 according to the comparative example.

[0049] As shown in FIG. 11, the hydraulic system 906 according to the comparative example is a so-called conventional machine, and differs from the present embodiment in that it does not include a regeneration system using the accumulator 4.

[0050] In the comparative example, return oil from a bottom-side oil chamber 115a of the boom cylinder 115 is discharged to a tank 107 through a first direction control valve 14. In the comparative example, the flow rate of return oil from the bottom-side oil chamber 115a of the boom cylinder 115 is represented by the following formula (1) based on the orifice flow rate calculation formula. Similarly, the flow rate of return oil from the bottom-side oil chamber 115a of the boom cylinder 115 in the present embodiment is represented by the following formula (2).

[0051]

[0052]

[0053] Qb_std is the flow rate of return oil from the bottom-side oil chamber 115a of the boom cylinder 115 in the comparative example, C is a flow coefficient, which is a value that also includes a unit conversion coefficient. A is the meter-out opening area of a first direction control valve 914, Pb is the bottom pressure of the boom cylinder 1151, and Pt is the tank pressure. Note that the flow coefficient C is a common value in formula (1) and formula (2), but may be different values from each other.

[0054] Qb_acc is the flow rate of return oil from the bottom oil chamber 115a of the boom cylinder 115 in this embodiment, Aacc is the opening area of ​​the pressure accumulator control valve 2 in this embodiment, and Pacc is the pressure of the accumulator 4.

[0055] When the amount of operation of the boom operation lever 5a in the boom lowering direction is the same, making the flow rate of the return oil from the bottom oil chamber 115a of the boom cylinder 115 the same in this embodiment and the comparative example means that the flow rate Qb_std and the flow rate Qb_acc are the same (Qb_stb = Qb_acc). Furthermore, since the opening area Aacc of the pressure accumulator control valve 2 is controlled by the control device 120, solving equations (1) and (2) for Aacc yields the following equation (3).

[0056]

[0057] Here, we can assume that the tank pressure Pt is approximately zero, so from equation (3) we obtain the following equation (4). If the tank pressure Pt cannot be ignored, the tank pressure Pt can be determined by measuring it or other methods, and substituted into equation (3).

[0058]

[0059] Furthermore, the opening area A included in equation (4) is determined in advance based on a comparative example (conventional machine) and is stored in the function generator 121 as correspondence information between the amount of operation of the boom operation lever 5a and the opening area of ​​the first directional control valve 14. In other words, when a lever operation signal is input to the function generator 121, it outputs a value corresponding to the opening area A in equation (4).

[0060] In the function generator 122, the portion P' obtained by removing the opening area A from the right-hand side of equation (4) is defined, and the value of P' corresponding to the input pressure sensor signal is output to the integrator 123 as a correction value.

[0061] In the integrator 123, the output of the function generator 121, which is the opening area of ​​the pressure accumulator control valve 2, is corrected by the output of the function generator 122, which corresponds to the pressure of the accumulator 4. The output of the integrator 123 is input to the output conversion unit 124, and the output conversion unit 124 outputs a solenoid valve command, which is a command to the pressure accumulator control valve 2.

[0062] The solenoid valve command is output to increase the opening degree of the pressure accumulator control valve 2 as the pressure in the accumulator 4 increases. In other words, the correspondence information between the amount operated by the boom operation lever 5a and the opening area of ​​the pressure accumulator control valve 2, stored in the function generator 121, and the correction value output by the function generator 122 are set so that the opening degree of the pressure accumulator control valve 2 increases as the pressure in the accumulator 4 increases.

[0063] Here, the bottom pressure of the boom cylinder can vibrate due to sudden movements or stops of the boom cylinder, because the hydraulic fluid is compressible rather than completely incompressible. Therefore, if the bottom pressure of the boom cylinder is sensed by a pressure sensor and used directly to control the accumulator control valve, the command value from the control device to the accumulator control valve will also become oscillating, making it difficult to ensure good operability.

[0064] Therefore, in this embodiment, the bottom pressure (load pressure) of the boom cylinder 115 used to control the pressure accumulator control valve 2 is estimated using a preset fixed value. The fixed value used as the estimated value of the bottom pressure is, for example, obtained by experimentation or simulation of the bottom pressure value of the boom cylinder when the boom is lowered in a conventional machine. For example, the average value of the bottom pressure of the boom cylinder detected by the bottom pressure sensor during the boom lowering operation in excavation and loading work is adopted as the fixed value. Alternatively, the value of the bottom pressure immediately before the boom lowering operation can also be used as the fixed value. In this way, by setting the estimated value of the bottom pressure of the boom cylinder 115 as a fixed value, it is possible to control it in a way that suppresses vibration and provides good operability. Note that the load of the boom cylinder 115 acts on the bottom side oil chamber 115a of the boom cylinder 115, and the bottom pressure is determined according to the load. Therefore, in reality, although the bottom pressure of the boom cylinder 115 changes somewhat depending on its posture, it does not usually fluctuate significantly, so it can be controlled without problems even if a fixed value is used.

[0065] Furthermore, the pressure accumulator control valve 2 is controlled so that the smaller the differential pressure (Pb - Pac) calculated by subtracting the pressure Pac of the accumulator 4 from the bottom pressure Pb of the boom cylinder 115, the larger the opening degree. In other words, normally, the pressure of the accumulator 4 is lower than the bottom pressure of the boom cylinder 115, and the bottom pressure of the boom cylinder 115 does not fluctuate significantly, so the pressure accumulator control valve 2 is controlled so that the larger the pressure Pac of the accumulator 4, the larger the opening degree. As a result, even if the pressure accumulated in the accumulator 4 increases, the opening degree of the pressure accumulator control valve 2 increases accordingly, making it easier to guide the return oil from the boom cylinder 115 to the accumulator 4. Therefore, even if the pressure in the accumulator 4 increases, the operability of the boom 111 can be ensured.

[0066] Furthermore, since the accumulator 4 is located downstream of the pressure accumulator control valve 2 relative to the boom cylinder 115, no vibration occurs in the pressure of the accumulator 4.

[0067] According to the above-described embodiment, the following effects are achieved.

[0068] (1) The hydraulic excavator 100 includes a boom cylinder 115, an accumulator 4 for storing return oil from the boom cylinder 115, a pressure accumulator control valve 2 located in an oil passage 40 connecting the boom cylinder 115 and the accumulator 4, a boom operating device 5 for operating the boom cylinder 115, a pressure accumulator sensor 31 for detecting the pressure of the accumulator 4, and a control device 120 for controlling the pressure accumulator control valve 2 based on the amount of operation of the boom operating device 5 and the pressure of the accumulator 4 detected by the pressure accumulator sensor 31. When the boom cylinder 115 is operated by the boom operating device 5, the control device 120 increases the opening of the pressure accumulator control valve 2 as the difference between the estimated load pressure of the boom cylinder 115, which is set as a fixed value, and the pressure of the accumulator 4 detected by the pressure accumulator sensor 31 becomes smaller.

[0069] With this configuration, the control of the pressure accumulator valve 2 does not directly use the detected value of the bottom pressure of the vibrating boom cylinder 115, but rather uses an estimated value of the bottom pressure of the boom cylinder 115 as the load pressure. Therefore, the effect of the vibration of the bottom pressure of the boom cylinder 115 on the operability of the hydraulic excavator 100 can be suppressed. Consequently, good operability can be obtained in a system in which the return oil of the boom cylinder 115 is regenerated by the accumulator 4.

[0070] (2) The estimated load pressure of the boom cylinder 115 is a fixed value that is pre-stored in the control device 120.

[0071] In this configuration, for example, the bottom pressure of the boom cylinder during boom lowering operations, which are frequently performed in hydraulic excavators 100, can be obtained in advance through experiments using conventional machines, and the average value can be used as an estimated value. With this configuration, it is possible to easily obtain the same level of operability as conventional machines.

[0072] <Second Embodiment> The hydraulic system 206 according to the second embodiment will be described with reference to Figures 5 and 6. Components that are the same as or equivalent to those described in the first embodiment will be given the same reference numerals, and the differences will be mainly described.

[0073] Figure 5 is a hydraulic circuit diagram showing the hydraulic system 206 of the second embodiment. As shown in Figure 5, the hydraulic system 206 of the second embodiment is equipped with a displacement sensor 33 (stroke sensor) as a displacement detection unit attached to the arm cylinder 116 to detect the displacement (stroke) of the arm cylinder 116. The displacement of the arm cylinder 116 detected by the displacement sensor 33 is input to the control device 120. The displacement of the arm cylinder 116 is one of the posture information representing the posture of the work device 104.

[0074] The control method for the pressure accumulation control valve 2 of the control device 120 according to the second embodiment will be described below. Figure 6 is a diagram showing the processing contents of the control device 120 in the second embodiment.

[0075] In the second embodiment, the load pressure of the boom cylinder 115 used to control the pressure accumulator control valve 2 is not a fixed value, but is estimated based on the state (posture information) of the work device 104, more specifically, the displacement of the arm cylinder 116.

[0076] As shown in Figure 6, the function generator 125 receives a displacement sensor signal indicating the displacement of the arm cylinder 116. The displacement of the arm cylinder 116 corresponds to the amount of movement of the piston rod 116d relative to the cylinder tube 116c, and increases as the extension amount (stroke amount) increases, with the fully retracted state being set to 0. In this embodiment, when the arm cylinder 116 is retracted and its displacement is small, the arm 112 extends, and when the arm cylinder 116 is extended and its displacement is large, the arm 112 moves closer to the boom 111 and retracts. Therefore, the smaller the displacement of the arm cylinder 116, the greater the load (load pressure) on the boom cylinder 115, and the larger the displacement of the arm cylinder 116, the smaller the load (load pressure) on the boom cylinder 115. Thus, the operating state of the arm cylinder 116 affects the load on the boom cylinder 115.

[0077] The function generator 125 is provided with a table containing information on the correspondence between the displacement of the arm cylinder 116 (the posture of the arm) and the load on the boom cylinder 115 (in other words, the load characteristics of the boom cylinder 115 in relation to the displacement of the arm cylinder 116). This allows the function generator 125 to calculate the load on the boom cylinder 115 more accurately.

[0078] The output of the function generator 125 is input to the function generator 122 as the bottom pressure Pb, which is an estimated value of the load pressure of the boom cylinder 115, and is used to correct the opening area of ​​the pressure accumulator control valve 2. In the function generator, based on equation (4), the value of P' corresponding to the input output of the function generator 125 (bottom pressure Pb) is output to the integrator 123 as a correction value.

[0079] In this second embodiment, when the boom cylinder 115 is operated by the boom operating device 5, the control device 120 increases the opening of the accumulator control valve 2 as the differential pressure between the estimated load pressure of the boom cylinder 115, calculated based on the posture information of the arm 112, and the pressure of the accumulator 4 detected by the accumulator sensor 31 decreases. According to this second embodiment, the control of the accumulator control valve 2 does not directly use the detected bottom pressure of the vibrating boom cylinder 115, but rather the bottom pressure of the boom cylinder 115 can be estimated based on the posture of the arm 112. Furthermore, by estimating the bottom pressure (load pressure) based on the posture of the arm 112, the bottom pressure (load pressure) can be estimated with greater accuracy than if the estimated load pressure were a predetermined fixed value. Therefore, good operability can be obtained in a system that regenerates the return oil of the boom cylinder 115 with the accumulator 4, and the energy regeneration efficiency can be increased.

[0080] <Third Embodiment> The hydraulic system 306 according to the third embodiment will be described with reference to Figures 7 and 8. Components that are the same as or equivalent to those described in the first embodiment will be given the same reference numerals, and the differences will be mainly described.

[0081] Figure 7 is a hydraulic circuit diagram showing a hydraulic system 306 of a third embodiment. As shown in Figure 7, the hydraulic system 306 includes a bottom pressure sensor 35 as a second pressure sensor that detects the pressure in the bottom oil chamber 115a of the boom cylinder 115. The bottom pressure sensor 35 is a pressure sensor, and the detected pressure in the bottom oil chamber 115a is input to the control device 120.

[0082] The control method for the pressure accumulation control valve 2 of the control device 120 according to the third embodiment will be described below. Figure 8 is a diagram showing the processing contents of the control device 120 in the third embodiment.

[0083] In the third embodiment, the load pressure of the boom cylinder 115 used to control the pressure accumulator control valve 2 is estimated based on the pressure in the bottom oil chamber 115a of the boom cylinder 115 before the boom lowering operation is performed. The estimated load pressure is held as a fixed value at least until the operation of the boom cylinder 115 is completed. The estimated load pressure is updated each time the boom cylinder 115 is operated.

[0084] In the hydraulic excavator 100, the bottom pressure of the boom cylinder 115 differs depending on the state immediately before the boom lowering operation is performed. For example, when moving the bucket 113 to the ground after loading the excavated material into the dump truck, the arm 112 is normally extended, and in this state, the bottom pressure of the boom cylinder 115 is relatively high (for example, around 10 [MPa]). On the other hand, when performing an operation called horizontal pulling (or horizontal pushing), where the tip of the bucket 113 is moved horizontally from a position where the arm 112 is aligned vertically (a position where the arm 112 is retracted), the bottom pressure of the boom cylinder 115 is relatively low (around 6-7 [MPa]). Thus, since the bottom pressure of the boom cylinder 115 differs depending on the position of the arm immediately before the boom lowering operation is performed, the bottom pressure can be estimated more accurately by using the pressure in the bottom side oil chamber 115a of the boom cylinder 115 immediately before the boom lowering operation is performed.

[0085] The pressure signal calculation unit 126 receives a pressure sensor signal based on the pressure in the bottom oil chamber 115a of the boom cylinder 115, as detected by the bottom pressure sensor 35. In addition to the pressure sensor signal from the bottom pressure sensor 35, the pressure signal calculation unit 126 also receives a lever operation signal. When the lever operation signal is input, the pressure signal calculation unit 126 retains the value of the pressure sensor signal immediately before the lever operation signal is input, calculates an estimated value of the bottom pressure (load pressure) of the boom cylinder 115 based on this value, and inputs it to the function generator 122. The estimated value here can be, for example, the average value of the detection results of the bottom pressure sensor 35 over a predetermined period until the lever operation signal is input.

[0086] Based on equation (4), the function generator 122 outputs a value of P' corresponding to the estimated bottom pressure of the boom cylinder 115 and the pressure of the accumulator 4 as a correction value to the integrator 123.

[0087] In this third embodiment, the control device 120 increases the opening of the pressure accumulator 2 each time the boom cylinder 115 is operated by the boom operating device 5, as the difference between the estimated load pressure of the boom cylinder 115, which is set as a fixed value, and the pressure of the accumulator 4 detected by the pressure accumulator sensor 31 decreases. The bottom pressure immediately before the boom lowering operation is performed varies depending on the state of the hydraulic excavator 100 (the posture of the work device 104). According to this third embodiment, the control of the pressure accumulator 2 does not directly use the detected value of the bottom pressure of the vibrating boom cylinder 115, but rather estimates the load pressure, which is the bottom pressure, based on the bottom pressure immediately before the boom lowering operation is performed, or more specifically, based on the average value of the bottom pressure over a predetermined period of time until the boom lowering operation is performed. By basing the estimation on the average value of the bottom pressure over a predetermined period of time until the boom lowering operation is performed, the bottom pressure corresponding to the posture of the work device 104 when the boom lowering operation is started can be estimated with high accuracy. Therefore, good operability can be obtained in a system that regenerates the return oil of the boom cylinder 115 with the accumulator 4, and the energy regeneration efficiency can be increased.

[0088] <Fourth Embodiment> The hydraulic system 406 according to the fourth embodiment will be described with reference to Figures 9 and 10. Components that are the same as or equivalent to those described in the second and third embodiments will be given the same reference numerals, and the differences will be mainly described.

[0089] Figure 9 is a hydraulic circuit diagram showing a hydraulic system 406 of the fourth embodiment. The fourth embodiment corresponds to an embodiment that combines the second and third embodiments. As shown in Figure 9, the hydraulic system 406 includes a displacement sensor 33 in the second embodiment and a bottom pressure sensor 35 in the third embodiment.

[0090] The control method for the pressure accumulation control valve 2 of the control device 120 according to the fourth embodiment will be described below. Figure 10 is a diagram showing the processing contents of the control device 120 in the fourth embodiment.

[0091] In the fourth embodiment, the load pressure of the boom cylinder 115 used to control the pressure accumulator control valve 2 is estimated based on the displacement of the arm cylinder 116 and the pressure in the bottom oil chamber 115a of the boom cylinder 115.

[0092] The function generator 122 receives a pressure sensor signal indicating the pressure of the accumulator 4, an output signal from the function generator 125 which is an estimated value of the bottom pressure of the boom cylinder 115 according to the posture of the arm 112, and an output signal from the pressure signal calculation unit 126 which is the average value of the bottom pressure of the boom cylinder 115 for a predetermined period before the input of the lever operation signal.

[0093] The function generator 122 calculates a more accurate estimated value of the load pressure of the boom cylinder 115 by correcting the bottom pressure (output signal of the function generator 125), which is estimated from the detected pressure in the bottom oil chamber 115a of the boom cylinder 115, using the posture of the arm 112 (output signal of the function generator 125). Then, based on equation (4), the function generator 122 outputs a value of P' corresponding to the bottom pressure estimated as described above and the pressure of the accumulator 4 as a corrected value to the integrator 123.

[0094] According to the fourth embodiment described above, the control of the pressure accumulator valve 2 does not directly use the detected value of the bottom pressure of the vibrating boom cylinder 115, but estimates the load pressure, which is the bottom pressure, based on the average value of the bottom pressure immediately before lowering the boom, and corrects the estimated bottom pressure according to the displacement of the arm cylinder 116. This makes it possible to estimate the bottom pressure with even greater accuracy. Therefore, good operability can be obtained in a system in which the return oil of the boom cylinder 115 is regenerated by the accumulator 4, and the energy regeneration efficiency can be increased.

[0095] The following modifications are also within the scope of the present invention, and it is possible to combine the configurations shown in the modifications with the configurations described in the embodiments described above, or to combine the configurations described in the different embodiments described above, or to combine the configurations described in the following different modifications.

[0096] <Modification 1> In the second and fourth embodiments, the bottom pressure of the boom cylinder 115 is estimated based on the posture of the arm 112 (displacement of the arm cylinder 116). In this case, the boom cylinder 115 corresponds to the first hydraulic actuator, and the arm cylinder 116 corresponds to the second hydraulic actuator that affects the load on the boom cylinder 115. In contrast, the second hydraulic actuator used to estimate the load on the first hydraulic actuator is not limited to the arm cylinder 116, as long as its operating state (displacement) affects the first hydraulic actuator.

[0097] If the boom cylinder 115 is the first actuator, the load on the boom cylinder 115 is affected by the actuators that drive the drive targets directly or indirectly connected to the boom 111, which is the drive target of the boom cylinder 115. Specifically, the arm cylinder 116 and bucket cylinder 117, which drive the arm 112 and bucket 113 connected to the boom 111, can be used as second hydraulic actuators used to estimate the load pressure of the boom cylinder 115. In other words, instead of a configuration that detects the displacement of the arm cylinder 116, a displacement sensor that detects the displacement of the bucket cylinder 117 may be provided, and the bottom pressure of the boom cylinder 115 may be estimated based on the displacement of the bucket cylinder 117 (the posture of the bucket 113).

[0098] Furthermore, the bottom pressure of the boom cylinder 115 may be estimated based on both the displacement of the arm cylinder 116 and the displacement of the bucket cylinder 117.

[0099] Furthermore, the bottom pressure of the boom cylinder 115 may be estimated based on the displacement of the boom cylinder 115 itself. In this case as well, the bottom pressure of the boom cylinder 115 may be estimated based on the displacement of the arm cylinder 116 and / or bucket cylinder 117, in addition to the displacement of the boom cylinder 115. In other words, the boom cylinder 115 may correspond to both the first hydraulic actuator and the second hydraulic actuator. In this specification, the first hydraulic actuator and the second hydraulic actuator are not limited to being different actuators, but include a configuration in which they are the same actuator.

[0100] <Modification 2> In the third and fourth embodiments, the load pressure of the boom cylinder 115 is calculated as the average value of the detected bottom pressure of the boom cylinder 115 during a predetermined period before the lever operation signal is input to the control device 120. In contrast, the bottom pressure of the boom cylinder 115 is not limited to the configuration of the above embodiments, as long as it is estimated using the detected value before the lever operation signal is input.

[0101] For example, the estimated load pressure based on the detected bottom pressure of the boom cylinder 115 may be a single value immediately before the lever operation signal is input, or it may be the minimum, maximum, or median value during a predetermined period until the lever operation signal is input. Furthermore, the predetermined period until the lever operation signal is input may be a period that is continuous in time with the timing of the lever operation signal input, or it may be a discontinuous (separated) period.

[0102] <Modification 3> In the above embodiments, the case in which the work machine is a crawler-type hydraulic excavator 100 was described as an example, but the present invention is not limited thereto. The present invention can be applied to various work machines such as wheel-type hydraulic excavators and wheel loaders.

[0103] The configuration, operation, and effects of the embodiment of the present invention configured as described above will be summarized below.

[0104] (1) The hydraulic excavator (working machine) 100 comprises a working device 104 having a boom cylinder (first hydraulic actuator) 115, an accumulator (pressure accumulation device) 4 for storing return oil from the boom cylinder 115, a pressure accumulation control valve (control valve) 2 arranged in an oil passage 40 connecting the boom cylinder 115 and the accumulator 4, a boom operating device (operating device) 5 for operating the boom cylinder 115, a pressure accumulation sensor (first pressure sensor) 31 for detecting the pressure of the accumulator 4, and a control device 120 for controlling the pressure accumulation control valve 2 based on the amount of operation of the boom operating device 5 and the pressure of the accumulator 4 detected by the pressure accumulation sensor 31. When the boom cylinder 115 is operated by the boom operating device 5, the control device 120 increases the opening of the pressure accumulator 2 as the difference between the estimated load pressure of the boom cylinder 115, which is set as a fixed value, or the estimated load pressure of the boom cylinder 115 calculated based on the posture information of the work device 104, and the pressure of the accumulator 4 detected by the pressure accumulator sensor 31 becomes smaller.

[0105] With this configuration, the control of the pressure accumulator valve 2 does not directly use the detected value of the bottom pressure of the vibrating boom cylinder 115, but rather uses an estimated value of the bottom pressure (load pressure) of the boom cylinder 115. Therefore, the effect of the vibration of the bottom pressure of the boom cylinder 115 on the operability of the hydraulic excavator 100 can be suppressed. Consequently, good operability can be obtained in a system in which the return oil of the boom cylinder 115 is regenerated by the accumulator 4.

[0106] (2) In the hydraulic excavator 100 according to the first embodiment, the estimated value of the load pressure of the boom cylinder 115 is a fixed value that is stored in advance in the control device 120.

[0107] With this configuration, the control of the pressure accumulator valve 2 does not directly use the detected value of the bottom pressure of the vibrating boom cylinder 115, but instead uses a predetermined fixed value as an estimated value of the bottom pressure, which is the load pressure of the boom cylinder 115. Therefore, the effect of the vibration of the bottom pressure of the boom cylinder 115 on the operability of the hydraulic excavator 100 can be suppressed. Accordingly, good operability can be obtained in a system in which the return oil of the boom cylinder 115 is regenerated by the accumulator 4.

[0108] (3) The working device 104 of the hydraulic excavator 100 according to the second embodiment has an arm cylinder 116 whose operating state affects the load on the boom cylinder 115. The hydraulic excavator 100 further includes a displacement sensor 33 that detects the displacement of the arm cylinder 116 as attitude information. The control device 120 stores load characteristics that define the relationship between the displacement of the arm cylinder 116 and an estimated value, and the control device 120 calculates an estimated value based on the displacement of the arm cylinder 116 and the load characteristics.

[0109] In this configuration, the control of the pressure accumulator valve 2 does not directly use the detected bottom pressure of the vibrating boom cylinder 115, but rather estimates the bottom pressure of the boom cylinder 115 based on the posture of the work device 104. By basing the estimation on the posture of the work device 104, the load pressure can be estimated with greater accuracy than if a predetermined fixed value were used. Therefore, good operability can be obtained in a system that regenerates the return oil of the boom cylinder 115 with the accumulator 4, and the energy regeneration efficiency can be increased.

[0110] (4) In the hydraulic excavator 100 according to the third embodiment, the first hydraulic actuator is a boom cylinder (hydraulic cylinder) 115 that is operated by hydraulic fluid supplied to and discharged from the bottom side oil chamber (load side oil chamber) 115a on which a load acts and the rod side oil chamber (anti-load side oil chamber) 115b. The hydraulic excavator 100 further includes a bottom pressure sensor (second pressure sensor) 35 that detects the pressure in the bottom side oil chamber 115a. When the boom operating device 5 is operated in a direction that causes the boom cylinder 115 to contract the bottom side oil chamber 115a, the control device 120 calculates an estimated value which is a fixed value based on the pressure in the bottom side oil chamber 115a before the operation is performed.

[0111] With this configuration, the load pressure used to control the pressure accumulator valve 2 can be estimated based on the bottom pressure immediately before the boom lowering operation (for example, the average value of the bottom pressure over a predetermined period of time until the boom lowering operation is performed), rather than directly using the detected bottom pressure of the vibrating boom cylinder 115. By basing the load pressure on the average value of the bottom pressure over a predetermined period of time until the boom lowering operation is performed, the load pressure can be estimated with high accuracy. Therefore, good operability can be obtained in a system that regenerates the return oil of the boom cylinder 115 with the accumulator 4, and the energy regeneration efficiency can be increased.

[0112] (5) The working device 104 of the hydraulic excavator 100 according to the fourth embodiment has an arm cylinder 116 whose operating state affects the load on the boom cylinder 115. The hydraulic excavator 100 further includes a displacement sensor 33 that detects the displacement of the arm cylinder 116 as attitude information. The control device 120 corrects the estimated value set based on the pressure in the bottom oil chamber 115a based on the displacement of the arm cylinder 116 and uses it to control the pressure accumulator control valve 2.

[0113] In this configuration, the control of the pressure accumulator valve 2 does not directly use the detected bottom pressure of the vibrating boom cylinder 115, but rather estimates the bottom pressure based on, for example, the average value of the bottom pressure immediately before lowering the boom, and corrects the estimated bottom pressure according to the displacement of the arm cylinder 116. This allows for more accurate estimation of the bottom pressure. Consequently, this provides good operability in a system that regenerates the return oil of the boom cylinder 115 with the accumulator 4, and also improves energy regeneration efficiency.

[0114] Although embodiments of the present invention have been described above, these embodiments only represent a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

[0115] 2... Pressure accumulation control valve (control valve), 4... Accumulator (pressure accumulation device), 5... Boom operating device (operating device), 31... Pressure accumulation sensor (first pressure sensor), 33... Displacement sensor, 35... Bottom pressure sensor (second pressure sensor), 40... Oil passage, 100... Hydraulic excavator, 115... Boom cylinder (first hydraulic actuator), 116... Arm cylinder (second hydraulic actuator), 120... Control device

Claims

1. A work machine comprising: a work device having a first hydraulic actuator; a pressure accumulator for storing return oil from the first hydraulic actuator; a control valve disposed in an oil passage connecting the first hydraulic actuator and the pressure accumulator; an operating device for operating the first hydraulic actuator; a first pressure sensor for detecting the pressure of the pressure accumulator; and a control device for controlling the control valve based on the amount of operation of the operating device and the pressure of the pressure accumulator detected by the first pressure sensor, wherein the control device, when the first hydraulic actuator is operated by the operating device, increases the opening of the control valve as the differential pressure between an estimated value of the load pressure of the first hydraulic actuator, which is set as a fixed value, or an estimated value of the load pressure of the first hydraulic actuator calculated based on the posture information of the work device, and the pressure of the pressure accumulator detected by the first pressure sensor becomes smaller.

2. The work machine according to claim 1, characterized in that the estimated value of the load pressure of the first hydraulic actuator is a fixed value stored in advance in the control device.

3. A work machine according to claim 1, wherein the work device has a second hydraulic actuator whose operating state affects the load of the first hydraulic actuator, the work machine further comprises a displacement sensor that detects the displacement of the second hydraulic actuator as posture information, the control device stores load characteristics that define the relationship between the displacement of the second hydraulic actuator and the estimated value, and the control device calculates the estimated value based on the displacement of the second hydraulic actuator and the load characteristics.

4. A work machine according to claim 1, wherein the first hydraulic actuator is a hydraulic cylinder operated by hydraulic fluid supplied to and discharged from a load-side oil chamber and a non-load-side oil chamber on which a load acts, the work machine further comprises a second pressure sensor for detecting the pressure in the load-side oil chamber, and the control device sets the estimated value, which is a fixed value, based on the pressure in the load-side oil chamber before the operation is performed when the operating device is operated in a direction that causes the first hydraulic actuator to move in a direction that causes the load-side oil chamber to contract.

5. A work machine according to claim 4, wherein the work device has a second hydraulic actuator whose operating state affects the load of the first hydraulic actuator, the work machine further comprises a displacement sensor that detects the displacement of the second hydraulic actuator as posture information, and the control device corrects the estimated value set based on the pressure of the load-side oil chamber based on the displacement of the second hydraulic actuator.

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