Work machine

Abstract

This work machine comprises: a prime mover; a hydraulic pump; a hydraulic actuator; a pressure accumulation device; an assist flow rate control valve for controlling the flow rate of hydraulic oil supplied from the pressure accumulation device to the hydraulic actuator; an operation device; an operation amount sensor; a pressure accumulation sensor; and a control device. The control device calculates the target flow rate of the hydraulic oil supplied to the hydraulic actuator on the basis of the operation amount, calculates an assist flow rate that is the flow rate of the hydraulic oil supplied from the pressure accumulation device to the hydraulic actuator through the assist flow rate control valve on the basis of the amount of change per unit time of the pressure detected by the pressure accumulation sensor, calculates the target discharge flow rate of the hydraulic pump by subtracting the assist flow rate from the target flow rate, and controls the rotation speed of the prime mover and / or the volume of the hydraulic pump so that the flow rate of the hydraulic oil discharged from the hydraulic pump becomes equal to the target discharge flow rate.

Description

Work machinery

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

[0002] Some work machines, such as hydraulic excavators, are equipped with a system that uses energy stored in an accumulator to drive a hydraulic actuator. In this system, an assist flow control valve is provided between the accumulator and the hydraulic actuator. By opening the assist flow control valve and sending pressure oil from the accumulator to the hydraulic actuator, the discharge flow rate of the hydraulic pump can be reduced accordingly. Reducing the discharge flow rate of the hydraulic pump reduces the pump output, leading to energy savings.

[0003] In the above system, the flow rate of hydraulic oil supplied to the hydraulic actuator is the sum of the flow rate of hydraulic oil supplied from the hydraulic pump to the hydraulic actuator (pump supply flow rate) and the flow rate of hydraulic oil supplied from the accumulator through the assist flow control valve to the hydraulic actuator (assist flow rate). Therefore, if the assist flow rate fluctuates, the flow rate of hydraulic oil supplied to the hydraulic actuator will fluctuate unless the pump supply flow rate is changed accordingly. Therefore, in order to maintain the operability of the hydraulic actuator, it is necessary to estimate the assist flow rate (the flow rate passing through the assist flow control valve) and control the pump supply flow rate using the estimated result.

[0004] A known technique for estimating the flow rate through a valve is to measure the differential pressure across the valve and estimate the flow rate based on an orifice equation. Patent Document 1 describes a technique for deriving an estimated value for the flow rate of hydraulic oil passing through a control valve based on the flow coefficient, the opening area of ​​the control valve, the density of the hydraulic oil, and the differential pressure across the control valve.

[0005] JP 2018-159210 A

[0006] However, when calculating the flow rate through a valve using the orifice equation, the flow coefficient changes depending on the hydraulic fluid flow conditions (such as the temperature and viscosity of the hydraulic fluid), the opening area changes due to fluid forces, and parameters (such as the opening area of ​​the valve, the density of the hydraulic fluid, and the differential pressure across the valve) change depending on various conditions. Furthermore, even if pressure sensors are installed before and after the valve, the calculated flow rate through the valve changes due to pressure losses in the oil passages inside the valve and in the fittings used to connect the pressure sensors. Therefore, to improve the accuracy of the flow rate calculated using the orifice equation, it is necessary to investigate the characteristics of each variable parameter under various conditions, which requires a huge amount of development time and therefore requires huge development costs. Therefore, a low-cost technology for estimating the flow rate through an assist flow control valve was needed.

[0007] An object of the present invention is to provide a work machine that is capable of supplying energy stored in a pressure accumulator to a hydraulic actuator, and that is capable of accurately estimating, at low cost, the flow rate through an assist flow control valve that controls the flow rate of hydraulic oil supplied from the pressure accumulator to the hydraulic actuator.

[0008] A work machine according to one aspect of the present invention comprises a prime mover, a hydraulic pump driven by the prime mover, a hydraulic actuator driven by hydraulic oil discharged from the hydraulic pump, an accumulator that accumulates hydraulic oil, a pump flow control valve that controls the flow rate of hydraulic oil supplied from the hydraulic pump to the hydraulic actuator, an assist flow control valve that controls the flow rate of hydraulic oil supplied from the accumulator to the hydraulic actuator, an operating device that operates the hydraulic actuator, an operation amount sensor that detects the operation amount of the operating device, an accumulator sensor that detects the pressure of hydraulic oil in the accumulator, and a control device that controls at least one of the prime mover and the hydraulic pump based on the operation amount detected by the operation amount sensor and the pressure detected by the accumulator sensor. The control device calculates a target flow rate, which is a target value for the flow rate of hydraulic oil supplied to the hydraulic actuator, based on the operation amount detected by the operation amount sensor, calculates an assist flow rate, which is the flow rate of hydraulic oil supplied from the accumulator to the hydraulic actuator through the assist flow control valve, based on the amount of change per unit time of pressure detected by the pressure accumulator sensor, calculates a target discharge flow rate, which is a target value for the discharge flow rate of the hydraulic pump, by subtracting the assist flow rate from the target flow rate, and controls at least one of the rotational speed of the prime mover and the volume of the hydraulic pump so that the flow rate of hydraulic oil discharged from the hydraulic pump is equal to the target discharge flow rate.

[0009] According to the present invention, it is possible to provide a work machine that is capable of supplying energy stored in a pressure accumulator to a hydraulic actuator, and that is capable of accurately estimating, at low cost, the flow rate through an assist flow control valve that controls the flow rate of hydraulic oil supplied from the pressure accumulator to the hydraulic actuator.

[0010] Fig. 1 is a perspective view of a hydraulic excavator shown as an example of a work machine according to an embodiment of the present invention. Fig. 2 is a schematic diagram of a hydraulic drive unit mounted on the hydraulic excavator. Fig. 3 is a diagram showing a drive control system mounted on the hydraulic excavator. Fig. 4 is a block diagram showing the functions of a control device.

[0011] A work machine according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a hydraulic excavator 1 shown as an example of a work machine according to an embodiment of the present invention. As shown in FIG. 1, the hydraulic excavator 1 includes a vehicle body 52 and an articulated work device 51 attached to the vehicle body 52. ​​The work device 51 has a boom 1a, an arm 1b, and a bucket 1c. The work device 51 also includes a boom cylinder 3a that drives the boom 1a, an arm cylinder 3b that drives the arm 1b, and a bucket cylinder 3c that drives the bucket 1c. The vehicle body 52 includes a lower traveling body 1e and an upper rotating body 1d attached to the lower traveling body 1e. The upper rotating body 1d rotates relative to the lower traveling body 1e by a swing motor 4 (see FIG. 2). The lower traveling body 1e travels by left and right traveling motors 3e.

[0012] The boom 1a is rotatably attached to the upper rotating body 1d and driven by a boom cylinder 3a. The arm 1b is rotatably attached to the boom 1a and driven by an arm cylinder 3b. The bucket 1c is rotatably attached to the arm 1b and driven by a bucket cylinder 3c. The bucket 1c is a work tool used for excavation work and for loading excavated soil and other materials into a dump truck or the like.

[0013] FIG. 2 is a schematic diagram of a hydraulic drive system mounted on the hydraulic excavator 1. As shown in FIG. 2, the hydraulic drive system of the hydraulic excavator 1 includes an engine 5, a first hydraulic pump 6, a second hydraulic pump 7, multiple hydraulic actuators (3a, 3b, 3c, 4), multiple flow control valves (8, 13-22), and an accumulator 9. The multiple hydraulic actuators include a boom cylinder 3a, an arm cylinder 3b, a bucket cylinder 3c, and a swing motor 4. The boom cylinder 3a, the arm cylinder 3b, and the bucket cylinder 3c are hydraulic cylinders each having a cylinder tube, a disc-shaped piston that divides the interior of the cylindrical cylinder tube into a bottom chamber 301 and a rod chamber 302, and a piston rod connected to the piston. The swing motor 4 is a hydraulic motor. The multiple flow control valves (8, 13-22) are driven by commands from a control device 100 (see FIG. 3), which will be described later. The flow control valve (8, 13 to 22) adjusts the area of ​​the opening by changing the position of the internal spool, thereby controlling the flow rate of the hydraulic oil passing through the opening.

[0014] The engine 5, which is a prime mover, is an internal combustion engine such as a diesel engine, etc. The engine 5 is provided with a fuel injection device 5a that injects fuel into a combustion chamber.

[0015] The first hydraulic pump 6 and the second hydraulic pump 7 are mechanically linked to the engine 5 and driven by the power of the engine 5 to discharge hydraulic oil (pressure oil). The first hydraulic pump 6 and the second hydraulic pump 7 are variable displacement hydraulic pumps that can change their discharge capacity (displacement volume). The first hydraulic pump 6 and the second hydraulic pump 7 are, for example, well-known bent-axis or swash plate hydraulic pumps, and their discharge capacity (volume) is adjusted by changing the tilt angle. The volume (tilting angle) of the first hydraulic pump 6 is controlled by a regulator 23 attached to the first hydraulic pump 6. The volume (tilting angle) of the second hydraulic pump 7 is controlled by a regulator 24 attached to the second hydraulic pump 7.

[0016] The first hydraulic pump 6 and the second hydraulic pump 7 are connected to a plurality of hydraulic actuators via respective pipelines. The plurality of hydraulic actuators are driven by pressurized oil discharged from the first hydraulic pump 6 and the second hydraulic pump 7. The accumulator 9 is a pressure accumulator device that accumulates pressurized oil supplied from the bottom chamber 301 of the boom cylinder 3a, which contracts due to the weight of the working device 51 during a boom lowering operation. The accumulator 9 has a liquid chamber and a gas chamber separated by a diaphragm. Nitrogen gas is sealed in the gas chamber. Hydraulic oil is accumulated in the liquid chamber.

[0017] A first boom control valve 14, which is a flow control valve (pump flow control valve) that controls the flow rate of hydraulic oil supplied from the first hydraulic pump 6 to the boom cylinder 3a, is provided in the pipe connecting the first hydraulic pump 6 and the boom cylinder 3a. The first boom control valve 14 also controls the flow rate of hydraulic oil discharged from the boom cylinder 3a to the tank 12. A second boom control valve 15, which is a flow control valve (pump flow control valve) that controls the flow rate of hydraulic oil supplied from the second hydraulic pump 7 to the boom cylinder 3a, is provided in the pipe connecting the second hydraulic pump 7 and the boom cylinder 3a. The second boom control valve 15 also controls the flow rate of hydraulic oil discharged from the boom cylinder 3a to the tank 12.

[0018] A first arm control valve 16, which is a flow control valve (pump flow control valve) that controls the flow rate of hydraulic oil supplied from the first hydraulic pump 6 to the arm cylinder 3b, is provided in the pipe connecting the first hydraulic pump 6 and the arm cylinder 3b. The first arm control valve 16 also controls the flow rate of hydraulic oil discharged from the arm cylinder 3b to the tank 12. A second arm control valve 17, which is a flow control valve (pump flow control valve) that controls the flow rate of hydraulic oil supplied from the second hydraulic pump 7 to the arm cylinder 3b, is provided in the pipe connecting the second hydraulic pump 7 and the arm cylinder 3b. The second arm control valve 17 also controls the flow rate of hydraulic oil discharged from the arm cylinder 3b to the tank 12.

[0019] A bucket control valve 18, which is a flow control valve (pump flow control valve) that controls the flow rate of hydraulic oil supplied from the first hydraulic pump 6 to the bucket cylinder 3c, is provided in the pipe connecting the first hydraulic pump 6 and the bucket cylinder 3c. The bucket control valve 18 also controls the flow rate of hydraulic oil discharged from the bucket cylinder 3c to the tank 12. A swing control valve 13, which is a flow control valve (pump flow control valve) that controls the flow rate of hydraulic oil supplied from the second hydraulic pump 7 to the swing motor 4, is provided in the pipe connecting the second hydraulic pump 7 and the swing motor 4. The swing control valve 13 also controls the flow rate of hydraulic oil discharged from the swing motor 4 to the tank 12.

[0020] The above-mentioned flow control valves (13 to 18) are center bypass type control valves. The flow control valves (14, 16, 18) have a center bypass passage that communicates between the first hydraulic pump 6 and the tank 12 when in the neutral position, and discharge hydraulic oil discharged from the first hydraulic pump 6 to the tank 12 through the center bypass passage when in the neutral position. The flow control valves (13, 15, 17) have a center bypass passage that communicates between the second hydraulic pump 7 and the tank 12 when in the neutral position, and discharge hydraulic oil discharged from the second hydraulic pump 7 to the tank 12 through the center bypass passage when in the neutral position.

[0021] A make-up device is provided between the conduit 10 connecting the swing control valve 13 and the right swing port of the swing motor 4, and the conduit 11 connecting the swing control valve 13 and the left swing port of the swing motor 4. The make-up device has mutually opposite check valves 25, 26 and relief valves 27, 28. A conduit 29 is provided between these check valves 25, 26 and relief valves 27, 28 to return oil discharged from the swing motor 4 to the tank 12. The conduit 29 functions as a make-up conduit that can replenish hydraulic oil to the swing motor 4.

[0022] A conduit 38 is connected to the accumulator 9, and pressure oil discharged from the accumulator 9 is supplied to each hydraulic actuator through the conduit 38. The bottom chamber 301 of the boom cylinder 3a and the conduit 38 are connected by a conduit (hereinafter also referred to as the bottom-side conduit) 32. The bottom-side conduit 32 is provided with a regenerative valve 8 that regenerates pressure oil in the bottom chamber 301 of the boom cylinder 3a and sends it to the accumulator 9 when the boom is lowered. The regenerative valve 8 is a regenerative flow control valve (flow control valve) that adjusts the opening area to control the regenerative flow rate, which is the flow rate of hydraulic oil that flows from the bottom chamber 301 side of the boom cylinder 3a to the accumulator 9 side.

[0023] A plurality of branch pipelines 39, 40, 41, and 42 are connected to the pipeline 38. The branch pipeline 39 is connected to the boom cylinder 3a. The branch pipeline 40 is connected to the arm cylinder 3b. The branch pipeline 41 is connected to the bucket cylinder 3c. The branch pipeline 42 is connected to the swing motor 4.

[0024] The branch pipe 39 is provided with a boom assist valve 19, which is a flow control valve (assist flow control valve) that controls the flow rate of hydraulic oil supplied from the accumulator 9 to the boom cylinder 3 a. The branch pipe 40 is provided with an arm assist valve 20, which is a flow control valve (assist flow control valve) that controls the flow rate of hydraulic oil supplied from the accumulator 9 to the arm cylinder 3 b. The branch pipe 41 is provided with a bucket assist valve 21, which is a flow control valve (assist flow control valve) that controls the flow rate of hydraulic oil supplied from the accumulator 9 to the bucket cylinder 3 c. The branch pipe 42 is provided with a swing assist valve 22, which is a flow control valve (assist flow control valve) that controls the flow rate of hydraulic oil supplied from the accumulator 9 to the swing motor 4.

[0025] In this way, the accumulator 9 is connected to each hydraulic actuator via a respective pipe line. The energy stored in the accumulator 9 is used to drive each hydraulic actuator.

[0026] Figure 3 is a diagram showing a drive control system mounted on the hydraulic excavator 1. Note that the operator's cab of the hydraulic excavator 1 is provided with actuator operating devices for operating each hydraulic actuator, but Figure 3 shows only a boom operating lever (cylinder operating device) 30 that operates the boom cylinder 3a and a bucket operating lever (cylinder operating device) 44 that operates the bucket cylinder 3c, which is a hydraulic actuator different from the boom cylinder 3a, and omits illustration of the other actuator operating devices and operation amount sensors that detect the operation amounts of the other actuator operating devices. Also omitted from Figure 3 are the arm cylinder 3b, the swing motor 4, and the flow control valves (13, 16, 17, 20, 22) used to control these hydraulic actuators.

[0027] As shown in Fig. 3, the drive control system includes a plurality of sensors that detect the state of the hydraulic drive unit, and a control device 100 that controls the flow control valve, engine 5, and hydraulic pump (6, 7) of the hydraulic drive unit based on the detection results of the plurality of sensors. The plurality of sensors includes a rotational speed sensor 5b of the engine 5, a pressure accumulation sensor 43, and a plurality of operation amount sensors. The rotational speed sensor 5b detects the rotational speed of the engine 5 and outputs a signal representing the detected rotational speed (actual rotational speed) to the control device 100. The pressure accumulation sensor 43 is provided in the conduit 38 and detects the pressure of the hydraulic oil in the accumulator 9 (hereinafter also referred to as accumulator pressure). The pressure accumulation sensor 43, which is a pressure sensor, outputs a signal representing the detected pressure to the control device 100. The plurality of operation amount sensors includes a boom operation amount sensor 31 and a bucket operation amount sensor 45.

[0028] The boom operation amount sensor 31 is an operation amount sensor that detects the operation amount of the boom operation lever 30 (hereinafter also referred to as the boom operation amount) and outputs a signal representing the detected operation amount to the control device 100. The bucket operation amount sensor 45 is an operation amount sensor that detects the operation amount of the bucket operation lever 44 (hereinafter also referred to as the bucket operation amount) and outputs a signal representing the detected operation amount to the control device 100. The boom operation amount detected by the boom operation amount sensor 31 includes a boom-raising operation amount for operating the boom 1a in the raising direction and a boom-lowering operation amount for operating the boom 1a in the lowering direction. The bucket operation amount detected by the bucket operation amount sensor 45 includes a bucket crowding operation amount for operating the bucket 1c in the crowding direction and a bucket dumping operation amount for operating the bucket 1c in the dumping direction.

[0029] The first boom control valve 14 is a three-position closed center directional control valve and is provided at both ends with operating terminals 14a, 14b that receive electromagnetic commands from the control device 100. The first boom control valve 14 switches its spool position in response to the electromagnetic command from the control device 100 sent to its operating terminal. When a boom-raising operation is performed, an electromagnetic command is sent to the operating terminal 14b, and pressure oil from the first hydraulic pump 6 is supplied to the bottom chamber 301 of the boom cylinder 3a through the first boom control valve 14, and hydraulic oil in the rod chamber 302 of the boom cylinder 3a is discharged to the tank 12 through the first boom control valve 14. When a boom-lowering operation is performed, an electromagnetic command is sent to the operating terminal 14a, and the first hydraulic pump 6 and the rod chamber 302 of the boom cylinder 3a are connected via the first boom control valve 14. When the boom is raised, the rod chamber 302 of the boom cylinder 3a and the tank 12 are connected via the first boom control valve 14, whereas when the boom is lowered, the bottom chamber 301 of the boom cylinder 3a and the tank 12 are not connected via the first boom control valve 14. Therefore, when the boom is lowered, hydraulic oil is not discharged from the bottom chamber 301 of the boom cylinder 3a to the tank 12 via the first boom control valve 14.

[0030] The second boom control valve 15 is a three-position closed-center directional control valve having operating terminals 15a, 15b at both ends that receive electromagnetic commands from the control device 100. The second boom control valve 15 switches its spool position in response to the electromagnetic command from the control device 100 sent to its operating terminal. When a boom-raising operation is performed, an electromagnetic command is sent to the operating terminal 15b, and pressure oil from the second hydraulic pump 7 is supplied to the bottom chamber 301 of the boom cylinder 3a through the second boom control valve 15, and hydraulic oil in the rod chamber 302 of the boom cylinder 3a is discharged to the tank 12 through the second boom control valve 15. When a boom-lowering operation is performed, an electromagnetic command is sent to the operating terminal 15a. As a result, the second hydraulic pump 7 and the rod chamber 302 of the boom cylinder 3a are communicated via the second boom control valve 15, and the bottom chamber 301 of the boom cylinder 3a is communicated with the tank 12 via the second boom control valve 15.

[0031] The bucket control valve 18 is a three-position closed-center directional control valve, and is provided at both ends with operating terminals 18a, 18b that receive electromagnetic commands from the control device 100. The bucket control valve 18 switches its spool position in response to electromagnetic commands from the control device 100 sent to its operating terminals. When a bucket dump operation is performed, an electromagnetic command is sent to the operating terminal 18a, and pressure oil from the first hydraulic pump 6 is supplied to the rod chamber 302 of the bucket cylinder 3c through the bucket control valve 18, and hydraulic oil in the bottom chamber 301 of the bucket cylinder 3c is discharged to the tank 12 through the bucket control valve 18. When a bucket crowd operation is performed, an electromagnetic command is sent to the operating terminal 18b, and pressure oil from the first hydraulic pump 6 is supplied to the bottom chamber 301 of the bucket cylinder 3c through the bucket control valve 18, and hydraulic oil in the rod chamber 302 of the bucket cylinder 3c is discharged to the tank 12 through the bucket control valve 18.

[0032] Although omitted in FIG. 3, the driving of the arm cylinder 3b by the first hydraulic pump 6 and the second hydraulic pump 7 and the driving of the swing motor 4 by the second hydraulic pump 7 are similar to the driving of the bucket cylinder 3c described above.

[0033] The hydraulic drive system of the hydraulic excavator 1 according to this embodiment is equipped with an assist system capable of driving the hydraulic actuator by utilizing the energy of the accumulator 9. In such a hydraulic drive system, by accurately estimating the assist flow rate, which is the flow rate of hydraulic oil supplied from the accumulator 9 to the hydraulic actuator via the assist flow control valve, it is possible to maintain the operability of the hydraulic actuator even if the assist flow rate fluctuates. Therefore, the control device 100 according to this embodiment estimates the assist flow rate based on the amount of change per unit time in the pressure of the accumulator 9. This will be explained in detail below.

[0034] The control device 100 is composed of a computer equipped with a processing device 100a such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), or DSP (Digital Signal Processor), a non-volatile memory 100b such as a ROM (Read Only Memory), flash memory, or hard disk drive, a volatile memory 100c called RAM (Random Access Memory), an input / output interface, and other peripheral circuits. These pieces of hardware work together to run software and realize multiple functions. The control device 100 may be composed of a single computer or multiple computers.

[0035] The nonvolatile memory 100b stores programs capable of executing various calculations. In other words, the nonvolatile memory 100b is a storage medium (storage device) from which the programs that realize the functions of this embodiment can be read. The volatile memory 100c is a storage medium (storage device) that temporarily stores the results of calculations performed by the processing device 100a and signals input from the input / output interface. The processing device 100a is a device that loads the programs stored in the nonvolatile memory 100b into the volatile memory 100c and executes the calculations, and performs predetermined calculations on data taken from the input / output interface, the nonvolatile memory 100b, and the volatile memory 100c in accordance with the programs.

[0036] The input section of the input / output interface converts signals input from various devices (sensors, etc.) into data that can be calculated by the processing device 100a. The output section of the input / output interface generates an output signal according to the calculation result by the processing device 100a and outputs the signal to various devices (flow control valve, regulators 23, 24, fuel injection device 5a, etc.).

[0037] The control device 100 according to this embodiment outputs a pump control command to the regulator 23, which controls the displacement of the first hydraulic pump 6. The control device 100 also outputs a pump control command to the regulator 24, which controls the displacement of the second hydraulic pump 7.

[0038] Based on the operation amount detected by the boom operation amount sensor 31, the control device 100 outputs an electromagnetic command to the operation end of the flow control valve to be driven, for driving at least one of the first boom control valve 14, the second boom control valve 15, the regenerative valve 8, and the boom assist valve 19. For example, if a boom-raising operation is performed when the pressure in the accumulator 9 is equal to or higher than a threshold, the control device 100 controls each of the first boom control valve 14, the second boom control valve 15, and the boom assist valve 19 to have an opening area corresponding to the boom-raising operation amount. As a result, the hydraulic oil discharged from the first hydraulic pump 6 and the second hydraulic pump 7 and the hydraulic oil discharged from the accumulator 9 are supplied to the bottom chamber 301 of the boom cylinder 3c, and the boom cylinder 3a is driven in the extension direction. Furthermore, for example, if a boom lowering operation is performed when the pressure in the accumulator 9 is below the threshold value, the control device 100 controls each of the first boom control valve 14, the second boom control valve 15, and the regenerative valve 8 to have an opening area that corresponds to the amount of boom lowering operation. As a result, hydraulic oil is supplied to the accumulator 9 from the bottom chamber 301 of the boom cylinder 3c, which contracts due to the weight of the working device 51, and pressure is accumulated in the accumulator 9.

[0039] The control device 100 outputs an electromagnetic command to the operation end of the flow control valve to be driven, for driving at least one of the bucket control valve 18 and the bucket assist valve 21, based on the operation amount detected by the bucket operation amount sensor 45. For example, if a bucket crowding operation is performed when the pressure in the accumulator 9 is equal to or higher than a threshold value, the control device 100 controls each of the bucket control valve 18 and the bucket assist valve 21 to have an opening area that corresponds to the bucket crowding operation amount. As a result, the hydraulic oil discharged from the first hydraulic pump 6 and the hydraulic oil discharged from the accumulator 9 are supplied to the bottom chamber 301 of the bucket cylinder 3c, and the bucket cylinder 3c is driven in the extension direction.

[0040] The control device 100 controls the engine rotation speed by adjusting the amount of fuel injected by the fuel injection device 5 a. The control device 100 calculates a target rotation speed of the engine 5 and controls the fuel injection device 5 a so that the rotation speed (actual rotation speed) of the engine 5 detected by the rotation speed sensor 5 b becomes the target rotation speed.

[0041] FIG. 4 is a block diagram showing the functions of the control device 100. The processing performed by the control device 100 will be described in detail using FIG. 4. The control device 100 controls the discharge flow rates of the first hydraulic pump 6 and the second hydraulic pump 7 based on the operation amount of the hydraulic actuator and the pressure of the accumulator 9. FIG. 4 shows the contents of various arithmetic processing performed when the bucket cylinder 3c is operated, by supplying hydraulic oil from the first hydraulic pump 6 to the bucket cylinder 3c via the bucket control valve 18 and supplying hydraulic oil from the accumulator 9 to the bucket cylinder 3c via the bucket assist valve 21, thereby driving the bucket cylinder 3c. Although not shown, the various arithmetic processing performed when assisting the drive of the boom cylinder 3a, the arm cylinder 3b, and the swing motor 4 is similar to the various arithmetic processing performed when assisting the drive of the bucket cylinder 3c shown in FIG. 4, and therefore will not be described here.

[0042] 4, the control device 100 includes a target flow rate calculation unit 101, a discharge flow rate calculation unit 102, a first filter 103, a volume calculation unit 104, a differential calculator 105, a second filter 106, a discharge flow rate control unit 107, an engine command unit 108, a pump command unit 109, a code conversion unit 110, and an assist flow rate determination unit 111. The control device 100 realizes these functions by executing programs stored in the nonvolatile memory 100b.

[0043] The target flow rate calculation unit 101 receives the bucket manipulation amount Lb detected by the bucket manipulation amount sensor 45. The target flow rate calculation unit 101 references a target flow rate table and calculates a target flow rate Qb, which is a target value for the flow rate of hydraulic oil supplied to the bucket cylinder 3c, based on the bucket manipulation amount Lb. The target flow rate table is a data table (characteristic data) that defines the relationship between the target flow rate Qb of the bucket cylinder 3c and the bucket manipulation amount Lb. The target flow rate table defines a characteristic that the target flow rate Qb increases as the bucket manipulation amount Lb increases. The target flow rate table is determined in advance through experiments or the like and stored in the non-volatile memory 100b. Note that the characteristic data of the target flow rate Qb corresponding to the bucket manipulation amount Lb is not limited to a table format and may be defined in a functional format (mathematical formula). The target flow rate Qb calculated by the target flow rate calculation unit 101 is output to the discharge flow rate calculation unit 102.

[0044] The first filter 103 detects the accumulator pressure p Ａ The first filter 103 performs filtering to attenuate the amplitude of noise contained in the detection result (pressure signal) of the pressure accumulation sensor 43, and outputs the filtered accumulator pressure p Ａ is output to the volume calculation unit 104.

[0045] The volume calculation unit 104 calculates the filtered accumulator pressure p Ａ The volume calculation unit 104 inputs the filtered accumulator pressure p Ａ The volume calculation unit 104 calculates the volume of the pressure oil in the accumulator 9 using the following equations (1) to (3).

[0046] Assuming that the pressure and volume of the nitrogen gas in the accumulator 9 change through reversible adiabatic change, the following basic equation (1) of the accumulator 9 holds true.

[0047]

[0048] In the thermodynamic adiabatic change equation (1), p Ａ０ is the pressure of the nitrogen gas when the nitrogen gas is sealed in the accumulator 9. That is, p Ａ０ is the pressure of the nitrogen gas when there is no oil in the accumulator 9, and will hereinafter also be referred to as the reference pressure. Ａ０ is the volume of nitrogen gas sealed in the accumulator 9. That is, V Ａ０ is the volume of nitrogen gas when there is no oil in the accumulator 9, and will hereinafter also be referred to as the reference volume. Ａ is the pressure of the nitrogen gas when oil is in the accumulator 9. Ａ is the pressure of nitrogen gas p Ａ Here, since the pressure of the nitrogen gas in the accumulator 9 and the pressure of the pressure oil in the accumulator 9 are approximately equal, the value of the accumulator pressure after filtering is p Ａ That is, p Ａ is the pressure of the pressure oil in the accumulator 9 at the current time. κ is the adiabatic index (polytropic index). The adiabatic index κ is a value that changes depending on the pressure inside the accumulator 9 and the inflow and outflow times of the accumulator 9. Note that the usage time of the accumulator 9 used to assist the hydraulic actuator of the hydraulic excavator 1 is short (for example, about 6 to 7 seconds at most). Therefore, the influence of the inflow and outflow times can be ignored.

[0049] The volume V of nitrogen gas when pressure oil flows into the accumulator 9 Ａ can be calculated by the following formula (2).

[0050]

[0051] In formula (2), Q Ａ is the flow rate of pressure oil flowing into the accumulator 9. Q Ａis integrated over time t to obtain the volume of pressure oil that has flowed into the accumulator 9. Ａ０ As described above, V is the volume of nitrogen gas when there is no oil in the accumulator 9. As expressed by equation (2), the volume V of nitrogen gas Ａ is the reference volume V Ａ０ The value is obtained by subtracting the volume of pressure oil that has flowed into the accumulator 9 from the above.

[0052] Substituting equation (2) into equation (1) and transforming it, the following equation (3) is obtained: The value of equation (3) is the volume of pressure oil in the accumulator 9 at the current time.

[0053]

[0054] The volume calculation unit 104 calculates the accumulator pressure p Ａ , reference volume V Ａ０ , reference pressure p Ａ０ , and the adiabatic index κ, the volume ∫Q of the pressure oil flowing into the accumulator 9 is calculated using equation (3) derived from the thermodynamic adiabatic change equation (1). Ａ dt (the value of the left side of equation (3)) is calculated. Ａ As described above, the reference volume V is input to the volume calculation unit 104. Ａ０ and reference pressure p Ａ０ is determined in advance through experiments or the like and stored in the nonvolatile memory 100b.

[0055] The nonvolatile memory 100b also stores the adiabatic index κ and the accumulator pressure p Ａ The index table is a data table that defines the relationship between the accumulator pressure p Ａ The larger the accumulator pressure p, the larger the adiabatic index κ. Ａ The characteristic data of the insulation index κ according to the accumulator pressure p is not limited to a table format, but may be specified in a function format (mathematical formula). Ａ The adiabatic index κ is calculated based on the above.

[0056] The volume calculation unit 104 outputs the calculated volume of the pressure oil in the accumulator 9 to the differential calculator 105 .

[0057] The differential calculator 105 calculates the amount of change in volume per unit time by differentiating the value of the volume of the pressure oil in the accumulator 9 with respect to time. When the value of the volume of the pressure oil in the accumulator 9 is differentiated with respect to time, the following equation (4) is obtained. Q calculated by equation (4) Ａ is output to the second filter 106 as the inflow flow rate of hydraulic oil into the accumulator 9. For example, the differential calculator 105 calculates the inflow flow rate Q of hydraulic oil into the accumulator 9 by dividing the value obtained by subtracting the volume of hydraulic oil calculated by equation (3) in the control cycle one step before from the volume of hydraulic oil calculated by equation (3) in the current control cycle by the time of the control cycle. Ａ is obtained.

[0058]

[0059] The adiabatic index κ varies depending on the conditions of use of the accumulator 9, but if the conditions of use are known in advance, it can be easily obtained by conducting an experiment. One method of obtaining the characteristics of κ is to measure the inflow flow rate while the accumulator 9 is being pressurized using a flow meter or the like, and adjust κ based on the measurement results. Another method of obtaining the characteristics of κ is to measure the flow rate discharged from the accumulator 9 using a flow meter or the like, and adjust κ based on the measurement results. Q calculated by equation (4) Ａ The characteristics of κ can be obtained by selecting a value of κ such that is equal to the measured flow rate value of the accumulator 9. For example, in an actual machine, hydraulic oil is supplied to the bucket cylinder 3c from the first hydraulic pump 6 and the accumulator 9, and the value obtained by subtracting the measured flow rate value of the hydraulic oil discharged from the first hydraulic pump 6 from the measured flow rate value of the hydraulic oil supplied to the bucket cylinder 3c is the flow rate Q calculated using equation (4). ＡThe adiabatic index κ is determined so as to coincide with the pressure condition and inflow / outflow time of the accumulator 9 when the hydraulic drive system according to this embodiment is actually driven. As described above, the accumulator 9 used to assist the hydraulic actuator of the hydraulic excavator 1 is used for a short period of time. Therefore, the influence of the inflow / outflow time can be ignored. In other words, it is sufficient to determine the adiabatic index κ that changes only in response to the pressure of the accumulator 9.

[0060] The second filter 106 is a differential calculator 105 that calculates the inflow rate Q Ａ The second filter 106 performs filtering to attenuate the amplitude of noise contained in the calculation result of the differential calculator 105, and outputs the inflow flow rate Q Ａ to the code conversion unit 110.

[0061] The code conversion unit 110 converts the inflow rate Q Ａ The code conversion unit 110 inputs the filtered inflow rate Q Ａ The value obtained by multiplying this by -1 is the assist flow rate Q, which is the discharge flow rate of the accumulator 9. ＡＳ and outputs it to the assist flow rate determining unit 111.

[0062] The assist flow rate determination unit 111 determines the assist flow rate Q ＡＳ The assist flow rate determination unit 111 inputs the assist flow rate Q ＡＳ The assist flow rate determining unit 111 determines whether the assist flow rate Q is equal to or greater than 0. ＡＳ If is 0 or more, the input assist flow rate Q ＡＳ The assist flow rate determination unit 111 outputs the assist flow rate Q ＡＳ When is less than 0, the assist flow rate Q ＡＳ is set to 0 and output to the discharge flow rate calculation unit 102. Therefore, when hydraulic oil is flowing into the accumulator 9, the assist flow rate Q ＡＳ is output as 0.

[0063] The first filter 103, the volume calculation unit 104, the differential calculation unit 105, the second filter 106, the sign conversion unit 110, and the assist flow rate determination unit 111 calculate the assist flow rate Q ＡＳ As described above, the assist flow rate calculation unit 112 calculates the accumulator pressure p Ａ Based on this, the volume ∫Q of the hydraulic oil in the accumulator 9 Ａ The assist flow rate calculation unit 112 calculates the volume ∫Q of the hydraulic oil in the accumulator 9. Ａ Based on the change in dt per unit time, the assist flow rate Q ＡＳ (differential calculator 105, second filter 106, sign converter 110, assist flow rate determiner 111). Ａ The amount of change in dt per unit time is determined by the accumulator pressure p Ａ That is, the assist flow rate calculation unit 112 calculates the assist flow rate by calculating the amount of change per unit time of the accumulator pressure p Ａ Based on the change per unit time, the assist flow rate Q ＡＳ is calculated.

[0064] The discharge flow rate calculation unit 102 calculates the target flow rate Qb of the bucket cylinder 3c and the assist flow rate Q ＡＳ The discharge flow rate calculation unit 102 calculates the assist flow rate Q from the target flow rate Qb. ＡＳ By subtracting Qb from Qb, the target discharge flow rate Qp, which is the target value of the discharge flow rate of the first hydraulic pump 6, is calculated (Qp=Qb−Q ＡＳ The target discharge flow rate Qp calculated by the discharge flow rate calculation unit 102 is output to the discharge flow rate control unit 107.

[0065] The discharge flow rate control unit 107 receives the target discharge flow rate Qp as an input. The discharge flow rate control unit 107 calculates a target rotation speed Nt of the engine 5 (target value of engine rotation speed) and a target volume qt of the first hydraulic pump 6 (target value of displacement volume) in order to achieve the target discharge flow rate Qp. The calculated target rotation speed Nt of the engine 5 is output to the engine command unit 108. The calculated target volume qt of the first hydraulic pump 6 is also output to the pump command unit 109.

[0066] The engine command unit 108 receives a target rotation speed Nt of the engine 5. The engine command unit 108 calculates a control command value for the fuel injection device 5a according to the target rotation speed Nt. The engine command unit 108 outputs an engine control command (electrical signal) according to the calculated control command value to the fuel injection device 5a of the engine 5. In this way, the engine 5 is controlled so that the actual rotation speed of the engine 5 becomes equal to the target rotation speed Nt.

[0067] The pump command unit 109 receives the target volume qt of the first hydraulic pump 6. The pump command unit 109 calculates a control command value to the regulator 23 according to the target volume qt. The pump command unit 109 outputs a pump control command (electrical signal) according to the calculated control command value to the regulator 23 of the first hydraulic pump 6. As a result, the first hydraulic pump 6 is controlled so that the actual displacement volume of the first hydraulic pump 6 becomes equal to the target volume qt.

[0068] The discharge flow rate of the hydraulic pump is determined by multiplying the rotational speed of the engine 5, the displacement volume of the hydraulic pump (corresponding to the flow rate discharged per rotation), and the pump volumetric efficiency. In this embodiment, the discharge flow rate control unit 107 controls the discharge flow rate of the hydraulic pump by adjusting the target volume qt while setting the target rotational speed Nt of the engine 5 to a constant value. Note that the method of controlling the discharge flow rate is not limited to this. The method of controlling the discharge flow rate may be a method of adjusting the target rotational speed Nt of the engine 5 while setting the target volume qt to a constant value. Alternatively, the method of controlling the discharge flow rate may be a method of adjusting both the target volume qt and the target rotational speed Nt. In other words, the engine command unit 108 and the pump command unit 109 may be configured to control at least one of the rotational speed of the engine 5 and the volume of the first hydraulic pump 6 so that the flow rate of hydraulic oil discharged from the first hydraulic pump 6 is equal to the target discharge flow rate Qp. Furthermore, the discharge flow rate control unit 107 may change the method of controlling the discharge flow rate depending on the operating conditions of the hydraulic excavator 1.

[0069] As described above, in this embodiment, when the hydraulic actuator is driven, the flow rate (assist flow rate) of hydraulic oil supplied from the accumulator 9 to the hydraulic actuator (e.g., bucket cylinder 3 c) can be estimated based on the pressure of the accumulator 9. By reducing the discharge flow rate of the hydraulic pump (e.g., the first hydraulic pump 6) by the estimated assist flow rate, it is possible to reduce the output of the hydraulic pump while maintaining operability. Reducing the output of the hydraulic pump improves energy efficiency and leads to reduced fuel consumption.

[0070] When estimating the flow rate through a valve based on the orifice equation from the differential pressure across the valve as in the prior art, multiple parameters (valve opening area, hydraulic oil density, differential pressure across the valve) fluctuate under various conditions, so it is necessary to investigate the characteristics of each fluctuating parameter through a large number of pre-tests. In contrast, the adiabatic index κ used in the flow rate estimation method according to this embodiment is calculated by multiplying the pressure p of the accumulator 9 by the adiabatic index κ. Ａ In other words, according to the flow rate estimation method of this embodiment, the fluctuation parameter is determined only by the pressure p Ａ In addition, the pressure p of the accumulator 9 can be reduced by simply operating the accumulator 9 under the conditions for actually using the accumulator 9. Ａ Since the characteristics of the insulation index κ according to the temperature can be obtained, the number of trials of the preliminary test can be reduced.

[0071] According to the above-described embodiment, the following advantageous effects are achieved.

[0072] (1) A hydraulic excavator (work machine) 1 includes an engine (prime mover) 5, hydraulic pumps (first hydraulic pump 6 and second hydraulic pump 7) driven by the engine 5, a bucket cylinder (hydraulic actuator) 3 c driven by hydraulic oil discharged from the first hydraulic pump 6, an accumulator (pressure accumulator) 9 that accumulates the hydraulic oil, a bucket control valve (pump flow rate control valve) 18 that controls the flow rate of the hydraulic oil supplied from the first hydraulic pump 6 to the bucket cylinder 3 c, a bucket assist valve (assist flow rate control valve) 21 that controls the flow rate of the hydraulic oil supplied from the accumulator 9 to the bucket cylinder 3 c, a bucket operation lever (operation device) 44 that operates the bucket cylinder 3 c, a bucket operation amount sensor (operation amount sensor) 45 that detects the operation amount of the bucket operation lever 44, a pressure accumulation sensor 43 that detects the pressure of the hydraulic oil in the accumulator 9, and a control device 100 that controls at least one of the engine 5 and the first hydraulic pump 6 based on the operation amount detected by the bucket operation amount sensor 45 and the pressure detected by the pressure accumulation sensor 43.

[0073] The control device 100 calculates a target flow rate Qb, which is a target value of the flow rate of hydraulic oil supplied to the bucket cylinder 3c, based on the operation amount detected by the bucket operation amount sensor 45. The control device 100 calculates a target flow rate Qb, which is a target value of the flow rate of hydraulic oil supplied to the bucket cylinder 3c, based on the pressure detected by the pressure accumulation sensor 43 (accumulator pressure p Ａ ) per unit time, the assist flow rate Q ＡＳ The control device 100 calculates the assist flow rate Q from the target flow rate Qb. ＡＳ By subtracting Qb from Qb, the target discharge flow rate Qp, which is the target value of the discharge flow rate of the first hydraulic pump 6, is calculated (Qp=Qb−Q ＡＳ The control device 100 controls at least one of the rotation speed of the engine 5 and the displacement of the first hydraulic pump 6 so that the flow rate of the hydraulic oil discharged from the first hydraulic pump 6 becomes equal to the target discharge flow rate Qp.

[0074] In this configuration, the state quantity of the accumulator 9 (pressure p Ａ ) per unit time, the assist flow rate QＡＳ Therefore, the assist flow rate Q is calculated without being affected by the piping connected to the accumulator 9, the configuration of the bucket assist valve 21, etc. ＡＳ Therefore, according to this embodiment, the assist flow rate Q can be calculated using the orifice equation based on the differential pressure before and after the bucket assist valve 21. ＡＳ Compared to estimating the assist flow rate Q ＡＳ As a result, the discharge flow rate of the hydraulic pump can be appropriately controlled, and therefore the operability of the hydraulic actuator can be maintained even if the assist flow rate fluctuates.

[0075] (2) The control device 100 detects the pressure (accumulator pressure) p Ａ Based on this, the volume ∫Q of the hydraulic oil (pressure oil) in the accumulator 9 Ａ The control device 100 calculates the assist flow rate Q based on the amount of change per unit time of the volume of hydraulic oil in the accumulator 9. ＡＳ The change in the volume of hydraulic oil in the accumulator 9 per unit time is calculated using the change in the pressure of the hydraulic oil in the accumulator 9 per unit time (the pressure difference between the pressure at a certain point in time and the pressure after a predetermined time has elapsed). In this way, by calculating the change in the volume of hydraulic oil in the accumulator 9 per unit time, the assist flow rate Q, which is the flow rate of hydraulic oil discharged from the accumulator 9, can be calculated. ＡＳ can be estimated with high accuracy.

[0076] (3) The control device 100 calculates the adiabatic index κ based on the pressure detected by the pressure accumulation sensor 43. The control device 100 according to this embodiment refers to an index table stored in the nonvolatile memory 100b and calculates the adiabatic index κ based on the accumulator pressure p Ａ The control device 100 calculates the insulation index κ based on the insulation index κ and the accumulator pressure p detected by the pressure accumulation sensor 43. Ａ Based on this, the volume ∫Q of the hydraulic oil in the accumulator 9 is calculated using the thermodynamic adiabatic change equation (see equation (1)). ＡSpecifically, the volume V of the gas (nitrogen gas) sealed in the accumulator 9 is calculated using equation (1). Ａ Calculate the calculated volume V Ａ and reference volume V Ａ０ Based on this, the volume ∫Q of the hydraulic oil in the accumulator 9 is calculated. Ａ In this way, by focusing on the fact that the pressure accumulation characteristic of the accumulator 9 is an adiabatic change, the adiabatic change equation (Poisson's equation: p Ａ V Ａ κ = constant) to obtain the assist flow rate Q ＡＳ can be estimated with high accuracy.

[0077] Furthermore, since the adiabatic index κ can be easily obtained as described above, the development man-hours and development costs can be reduced compared to when an orifice equation is used. Furthermore, the flow coefficient c used in the orifice equation varies depending on the valve configuration, the circuit configuration related to the valve (the degree of curvature and length of the piping connected to the valve), environmental conditions, and the like. For this reason, it is difficult to use the same flow coefficient c for various models of hydraulic excavators 1. In contrast, in this embodiment, the same index table can be used for different models of hydraulic excavators 1 as long as the same accumulator 9 is installed, even if the valve configuration, circuit configuration, and operating conditions are different, making the system highly versatile.

[0078] (4) The hydraulic excavator 1 includes a boom cylinder (second hydraulic actuator) 3a, which is a hydraulic actuator different from the bucket cylinder (first hydraulic actuator) 3c, and a regenerative valve 8 that controls the flow rate of hydraulic oil flowing from the boom cylinder 3a to the accumulator 9. With this configuration, when the boom cylinder 3a is lowered, the accumulator 9 can be pressurized by pressurized oil from the bottom chamber 301 of the boom cylinder 3a, which contracts due to the weight of the work device 51 including the boom 1a. This eliminates the need to provide a dedicated hydraulic pump or the like for supplying hydraulic oil to the accumulator 9, thereby improving energy efficiency. As a result, fuel efficiency can be improved.

[0079] (5) The hydraulic excavator 1 includes a boom assist valve (second assist flow control valve) 19, which is an assist control valve that controls the flow rate of hydraulic oil supplied from the accumulator 9 to the boom cylinder 3a, in addition to the bucket assist valve (first assist flow control valve) 21. According to this configuration, regenerative energy generated when the boom is lowered can be stored in the accumulator 9 and used when the boom is raised.

[0080] As described above, according to this embodiment, it is possible to provide a hydraulic excavator 1 that is capable of supplying energy accumulated in the accumulator 9 to a hydraulic actuator, and that is capable of accurately estimating, at low cost, the flow rate through the assist flow control valve that controls the flow rate of hydraulic oil supplied from the accumulator 9 to the hydraulic actuator.

[0081] The following modifications are also within the scope of the present invention, and one or more of the modifications may be combined with the above-described embodiment.

[0082] (Modification 1) In the above embodiment, an example has been described in which the return oil from the boom cylinder 3a is regenerated by the accumulator 9, but the return oil from another hydraulic actuator may also be regenerated by the accumulator 9.

[0083] (Variation 2) The work machine is not limited to the crawler-type hydraulic excavator 1. The present invention may be applied to a wheel-type hydraulic excavator. Furthermore, the work implement may be a grapple, a breaker, a lifting magnet, or the like, instead of a bucket.

[0084] (Modification 3) Two or more accumulators may be provided. The hydraulic pump that supplies hydraulic oil to the hydraulic actuator may be configured to be provided with only one or three or more.

[0085] (Modification 4) The prime mover that drives the hydraulic pumps (6, 7) is not limited to the engine 5. The prime mover may be an electric motor.

[0086] 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.

[0087] 1...hydraulic excavator (work machine), 1a...boom, 1b...arm, 1c...bucket, 1d...upper swing body, 1e...lower traveling body, 3a...boom cylinder (hydraulic actuator, an example of a second hydraulic actuator), 3b...arm cylinder (hydraulic actuator), 3c...bucket cylinder (hydraulic actuator, an example of a first hydraulic actuator), 3e...travel motor (hydraulic actuator), 4...swing motor (hydraulic actuator), 5...engine (prime mover), 5a...fuel injection device, 5b...rotation Rotation speed sensor, 6...first hydraulic pump (hydraulic pump), 7...second hydraulic pump (hydraulic pump), 8...regenerative valve (flow control valve), 9...accumulator (pressure storage device), 12...tank, 13...swing control valve (flow control valve), 14...first boom control valve (flow control valve), 15...second boom control valve (flow control valve), 16...first arm control valve (flow control valve), 17...second arm control valve (flow control valve), 18...bucket control valve (flow control valve, an example of a pump flow control valve), 19...boom assist valve (flow control valve, 2 assist flow control valve), 20...arm assist valve (assist flow control valve), 21...bucket assist valve (assist flow control valve, an example of a first assist flow control valve), 22...swing assist valve (assist flow control valve), 23, 24...regulator, 30...boom operation lever, boom operation amount sensor, 43...accumulator sensor (pressure sensor), 44...bucket operation lever (operation device), 45...bucket operation amount sensor (operation amount sensor), 51...work device, 52...vehicle body, 100...control device, 100 a...processing device, 100b...non-volatile memory (storage device), 100c...volatile memory (storage device), 101...target flow rate calculation unit, 102...discharge flow rate calculation unit, 103...first filter, 104...volume calculation unit, 105...differential calculator, 106...second filter, 107...discharge flow rate control unit, 108...engine command unit, 109...pump command unit, 110...sign conversion unit, 111...assist flow rate determination unit, 112...assist flow rate calculation unit, Lb...bucket operation amount, Nt...target rotational speed (target value of engine rotational speed), p Ａ...Accumulator pressure (pressure of hydraulic oil in the accumulator, pressure of nitrogen gas sealed in the accumulator), p Ａ０ …reference pressure of nitrogen gas sealed in the accumulator, Q Ａ ... inflow flow rate (flow rate of hydraulic oil flowing into the accumulator), Q ＡＳ ... Assist flow rate (flow rate of hydraulic oil supplied from the accumulator to the bucket cylinder), Qb... Target flow rate (target value of the flow rate of hydraulic oil supplied to the bucket cylinder), Qp... Target discharge flow rate (target value of the discharge flow rate of the first hydraulic pump), qt... Target volume (target value of the displacement volume of the first hydraulic pump), V Ａ ...volume of gas sealed in the accumulator, V Ａ０ …reference volume of gas sealed in the accumulator, κ…adiabatic index

Claims

1. A work machine comprising: a prime mover; a hydraulic pump driven by the prime mover; a hydraulic actuator driven by hydraulic oil discharged from the hydraulic pump; an accumulator that accumulates hydraulic oil; a pump flow control valve that controls the flow rate of hydraulic oil supplied from the hydraulic pump to the hydraulic actuator; an assist flow control valve that controls the flow rate of hydraulic oil supplied from the accumulator to the hydraulic actuator; an operating device that operates the hydraulic actuator; an operation amount sensor that detects the operation amount of the operating device; an accumulator sensor that detects the pressure of hydraulic oil in the accumulator; and a control device that controls at least one of the prime mover and the hydraulic pump based on the operation amount detected by the operation amount sensor and the pressure detected by the accumulator sensor, wherein the control device calculates a target flow rate that is a target value for the flow rate of hydraulic oil supplied to the hydraulic actuator based on the operation amount detected by the operation amount sensor, and calculates an assist flow rate that is the flow rate of hydraulic oil supplied from the accumulator to the hydraulic actuator through the assist flow control valve based on the amount of change per unit time of the pressure detected by the accumulator sensor, a target discharge flow rate, which is a target value for the discharge flow rate of the hydraulic pump, is calculated by subtracting the assist flow rate from the target flow rate, and at least one of the rotation speed of the prime mover and the displacement of the hydraulic pump is controlled so that the flow rate of hydraulic oil discharged from the hydraulic pump becomes equal to the target discharge flow rate.

2. A work machine according to claim 1, wherein the control device calculates the volume of hydraulic oil in the pressure accumulator based on the pressure detected by the pressure accumulator sensor, and calculates the assist flow rate based on the amount of change per unit time in the volume of hydraulic oil in the pressure accumulator.

3. A work machine according to claim 2, wherein the control device calculates an adiabatic index based on the pressure detected by the pressure accumulator sensor, and calculates the volume of hydraulic oil in the pressure accumulator device using the thermodynamic adiabatic change equation based on the adiabatic index and the pressure detected by the pressure accumulator sensor.

4. A work machine according to claim 1, comprising: a second hydraulic actuator different from the first hydraulic actuator, which is the hydraulic actuator; and a regenerative valve that controls the flow rate of hydraulic oil flowing from the second hydraulic actuator to the pressure accumulator.

5. A work machine according to claim 4, characterized in that it is provided with a second assist flow control valve that controls the flow rate of hydraulic oil supplied from the pressure accumulator to the second hydraulic actuator, separate from the first assist flow control valve that is the assist flow control valve.

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