Work machine

Abstract

This work machine is provided with: a work device; a first electric motor for driving a first hydraulic pump that supplies hydraulic oil to a high-pressure line; a second electric motor for driving a second hydraulic pump that supplies hydraulic oil to a low-pressure line; a hydraulic cylinder having four chambers, and being driven by the hydraulic oil discharged from the first hydraulic pump and the second hydraulic pump, to drive the work device; high-pressure control valves for controlling communication and interruption between the high-pressure line and the chambers; low-pressure control valves for controlling communication and interruption between the low-pressure line and the chambers; pressure sensors for detecting the pressures in the chambers; an operation amount sensor for detecting an operation amount of an operation device for operating the hydraulic cylinder; and a control device for controlling the high-pressure control valves and the low-pressure control valves on the basis of the detection results of the pressure sensors and the operation amount sensor, and controlling the rotation speed of the first electric motor on the basis of the detection result of the operation amount sensor.

Description

Work machinery

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

[0002] Multi-chamber cylinders with multiple chambers are known as hydraulic actuators for driving working equipment of work machines such as hydraulic excavators (see Patent Document 1). Patent Document 1 discloses a hydraulic drive system that includes a high-pressure accumulator connected to a high-pressure line, a low-pressure accumulator connected to a low-pressure line, and multiple control valves that control the flow of hydraulic oil supplied to the multi-chamber cylinder from each of the high-pressure line and the low-pressure line.

[0003] In this hydraulic drive system, by controlling multiple control valves to connect each of the multiple chambers to a high-pressure line or a low-pressure line, it is possible to drive the multi-chamber cylinder while suppressing pressure loss.

[0004] International Publication No. 2010 / 040890

[0005] In the hydraulic drive system described in Patent Document 1, the pressure in the high-pressure line is kept constant by the high-pressure accumulator. Therefore, there is room for improvement in terms of pressure loss that occurs in the control valve when driving the multi-chamber cylinder.

[0006] An object of the present invention is to provide a work machine that can further reduce the pressure loss that occurs when driving a hydraulic cylinder.

[0007] a control device that controls the four high-pressure control valves and the four low-pressure control valves based on detection results of the pressure sensors and the operation amount sensors; a control device that controls the four high-pressure control valves and the four low-pressure control valves based on detection results of the pressure sensors and the operation amount sensors; a hydraulic cylinder having four chambers, driven by hydraulic oil discharged from the first hydraulic pump and the second hydraulic pump to drive the working device; The control device controls the rotation speed of the electric motor, which is the first power source, based on the detection result of the operation amount sensor.

[0008] According to the present invention, a work machine can be provided that can further reduce the pressure loss that occurs when driving a hydraulic cylinder.

[0009] FIG. 1 is a side view of a hydraulic excavator 10 according to the first embodiment. FIG. 2 is a schematic diagram of a hydraulic system 106 provided in the hydraulic excavator 10. FIG. 3 is a configuration diagram of the hydraulic system 106 according to the first embodiment, showing details of the hydraulic cylinder 1, the control valve unit 150, the first hydraulic power source 101, and the second hydraulic power source 100. FIG. 4 is a hardware configuration diagram of a controller 140. FIG. 5 is an index table for explaining how 16 patterns of the hydraulic cylinder 1 are connected. FIG. 6 is a diagram showing the relationship between the load pressure and the load flow rate of the hydraulic cylinder 1. FIG. 7 is a characteristic diagram of the hydraulic cylinder 1. FIG. 8 is a functional block diagram of the controller 140 according to the first embodiment. FIG. 9 is a flowchart showing the flow of valve control processing by the valve control unit 152. FIG. 10 is a diagram explaining the calculation processing of the HP required flow rate by the required flow rate calculation unit 153. FIG. 11 is a diagram explaining the calculation processing of the target rotational speed of the first electric motor 17 by the rotational speed calculation unit 154. FIG. 12 is a diagram illustrating the calculation process of the LP required flow rate by the required flow rate calculation unit 153. FIG. 13 is a diagram illustrating the calculation process of the target rotational speed of the second electric motor 14 by the rotational speed calculation unit 154. FIG. 14 is a functional block diagram of the controller 240 according to the second embodiment. FIG. 15 is a flowchart showing the flow of the calculation process of the suction flow rate by the required flow rate calculation unit 253. FIG. 16 is a diagram illustrating the configuration of the hydraulic power source according to the third embodiment. FIG. 17 is a diagram illustrating the configuration of the hydraulic power source according to the fourth embodiment. FIG. 18 is a diagram illustrating the configuration of the hydraulic power source according to the fifth embodiment. FIG. 19 is a control block diagram of the rotational speed calculation unit 554 according to the fifth embodiment. FIG. 20 is a diagram illustrating the configuration of the hydraulic power source according to the sixth embodiment.

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

[0011] <First Embodiment> Fig. 1 is a side view of a hydraulic excavator 10 according to a first embodiment. As shown in Fig. 1, the hydraulic excavator 10 includes a vehicle body (machine body) 105 and a working device 104 attached to the vehicle body 105. The vehicle body 105 includes a crawler-type running body 102 and a rotating body 103 rotatably provided on the running body 102. The running body 102 travels by driving a pair of left and right crawlers by traveling motors 102A. The rotating body 103 is connected to the running body 102 via a swing device having a swing motor 103A, and is driven by the swing motor 103A to swing relative to the running body 102.

[0012] The rotating body 103 includes a cab 118 in which an operator sits, and a machine room 119 in which a prime mover and hydraulic equipment are housed. The machine room 119 houses, for example, an electric motor serving as the prime mover, and hydraulic equipment such as a hydraulic pump driven by the electric motor.

[0013] The operator's cab 118 is provided with an electric operating device for operating the hydraulic actuators (111A, 112A, 113A, 103A, 102A) of the work device 104, the revolving body 103, and the traveling body 102. The operator's cab 118 also provides a controller 140, which is a control device for controlling the operation of each part of the hydraulic excavator 10.

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

[0015] The boom 111 is rotationally driven by the extension and retraction of a boom cylinder 111A, which is a hydraulic actuator. The arm 112 is rotationally driven by the extension and retraction of an arm cylinder 112A, which is a hydraulic actuator. The bucket 113 is rotationally driven by the extension and retraction of a bucket cylinder 113A, which is a hydraulic actuator. By operating the work device 104, the hydraulic excavator 10 can perform work such as excavating earth and sand, leveling work, and compacting the ground.

[0016] Fig. 2 is a schematic diagram of the hydraulic system 106 provided in the hydraulic excavator 10. Note that Fig. 2 illustrates the configuration for driving the boom cylinder 111A, arm cylinder 112A, and bucket cylinder 113A, which are hydraulic actuators, and does not illustrate the configuration for driving the other hydraulic actuators. Note that the boom cylinder 111A, arm cylinder 112A, and bucket cylinder 113A each have the same configuration, and therefore will hereinafter also be referred to collectively as hydraulic cylinder 1.

[0017] 2 , the hydraulic system 106 includes a first hydraulic power source 101 that supplies hydraulic oil to a high-pressure line HL, a second hydraulic power source 100 that supplies hydraulic oil to a low-pressure line LL, and a plurality of hydraulic cylinders 1 (a boom cylinder 111A, an arm cylinder 112A, and a bucket cylinder 113A) that are driven by hydraulic oil (working fluid) discharged from the first hydraulic power source 101 and the second hydraulic power source 100. The hydraulic system 106 also includes a boom control valve unit 150A that controls the flow of hydraulic oil supplied from the first hydraulic power source 101 and the second hydraulic power source 100 to the boom cylinder 111A, an arm control valve unit 150B that controls the flow of hydraulic oil supplied from the first hydraulic power source 101 and the second hydraulic power source 100 to the arm cylinder 112A, and a bucket control valve unit 150C that controls the flow of hydraulic oil supplied from the first hydraulic power source 101 and the second hydraulic power source 100 to the bucket cylinder 113A. The boom control valve unit 150A, the arm control valve unit 150B, and the bucket control valve unit 150C each have the same configuration, and therefore will be hereinafter collectively referred to as the control valve unit 150.

[0018] Fig. 3 is a configuration diagram of the hydraulic system 106 according to the first embodiment, and shows details of the hydraulic cylinder 1, the control valve unit 150, the first hydraulic power source 101, and the second hydraulic power source 100. Fig. 3 illustrates the configuration for driving one of the multiple hydraulic cylinders 1 (for example, the boom cylinder 111A), and does not illustrate the configuration for driving the other hydraulic actuators.

[0019] As shown in Figure 3, the hydraulic cylinder 1 is a multi-chamber cylinder having four chambers (first chamber 1A, second chamber 1B, third chamber 1C, and fourth chamber 1D). When pressure increases in the first chamber 1A and third chamber 1C, a cylinder thrust is generated in a direction that extends the hydraulic cylinder 1. When pressure increases in the second chamber 1B and fourth chamber 1D, a cylinder thrust is generated in a direction that retracts the hydraulic cylinder 1.

[0020] The first hydraulic power source 101 includes a first hydraulic pump 16, a first electric motor 17 that drives the first hydraulic pump 16, and a first inverter 18 that converts DC power from the battery 12 into AC power and supplies it to the first electric motor 17. The second hydraulic power source 100 includes a second hydraulic pump 13, a second electric motor 14 that drives the second hydraulic pump 13, and a second inverter 15 that converts DC power from the battery 12 into AC power and supplies it to the second electric motor 14.

[0021] The first hydraulic pump 16 and the second hydraulic pump 13 are fixed-displacement hydraulic pumps with a fixed capacity (displacement volume). The first hydraulic pump 16 is a pump motor that has both a pump function of sucking hydraulic oil stored in a tank and discharging it to the high-pressure line HL, and a motor function of rotating in the opposite direction to the direction of discharge by the supplied hydraulic oil. The second hydraulic pump 13 only has a pump function of sucking hydraulic oil stored in a tank and discharging it to the low-pressure line LL.

[0022] The first electric motor 17 is a first power source that drives the first hydraulic pump 16, and the second electric motor 14 is a second power source that drives the second hydraulic pump 13. The first inverter 18 controls the first electric motor 17 based on a control command from the controller 140. The second inverter 15 controls the second electric motor 14 based on a control command from the controller 140. The battery 12 is an electricity storage device equipped with an electricity storage element such as a lithium ion secondary battery.

[0023] The control valve unit 150 includes four high-pressure control valves 5AH, 5BH, 5CH, and 5DH that control communication between a high-pressure line HL and the four chambers 1A, 1B, 1C, and 1D, and four low-pressure control valves 5AL, 5BL, 5CL, and 5DL that control communication between a low-pressure line LL and the four chambers 1A, 1B, 1C, and 1D. The high-pressure control valves 5AH, 5BH, 5CH, and 5DH and the low-pressure control valves 5AL, 5BL, 5CL, and 5DL are solenoid proportional valves whose opening areas are controlled by current output from a controller 140. Because the high-pressure control valves 5AH, 5BH, 5CH, and 5DH and the low-pressure control valves 5AL, 5BL, 5CL, and 5DL have similar configurations, they will hereinafter also be referred to collectively as solenoid proportional valves 5. The electromagnetic proportional valve 5 is closed when the control signal is off (when a standby current is flowing or when no current is flowing), and when the control signal is on (when a control current is flowing), the opening area is adjusted according to the magnitude of the control current. Note that the electromagnetic proportional valve 5 is not limited to a normally closed type, and may also be a normally open type.

[0024] The high-pressure control valve 5AH is provided in the oil passage connecting the first hydraulic pump 16 and the first chamber 1A, and controls the connection and disconnection of the high-pressure line HL and the first chamber 1A. The high-pressure control valve 5BH is provided in the oil passage connecting the first hydraulic pump 16 and the second chamber 1B, and controls the connection and disconnection of the high-pressure line HL and the second chamber 1B. The high-pressure control valve 5CH is provided in the oil passage connecting the first hydraulic pump 16 and the third chamber 1C, and controls the connection and disconnection of the high-pressure line HL and the third chamber 1C. The high-pressure control valve 5DH is provided in the oil passage connecting the first hydraulic pump 16 and the fourth chamber 1D, and controls the connection and disconnection of the high-pressure line HL and the fourth chamber 1D.

[0025] The low-pressure control valve 5AL is provided in the oil passage connecting the second hydraulic pump 13 and the first chamber 1A, and controls the opening and closing of the low-pressure line LL and the first chamber 1A. The low-pressure control valve 5BL is provided in the oil passage connecting the second hydraulic pump 13 and the second chamber 1B, and controls the opening and closing of the low-pressure line LL and the second chamber 1B. The low-pressure control valve 5CL is provided in the oil passage connecting the second hydraulic pump 13 and the third chamber 1C, and controls the opening and closing of the low-pressure line LL and the third chamber 1C. The low-pressure control valve 5DL is provided in the oil passage connecting the second hydraulic pump 13 and the fourth chamber 1D, and controls the opening and closing of the low-pressure line LL and the fourth chamber 1D.

[0026] The high-pressure line HL is provided with a first relief valve (pressure control valve) 35 that determines the maximum pressure of the high-pressure line HL. The low-pressure line LL is provided with a second relief valve (pressure control valve) 11 that determines the maximum pressure of the low-pressure line LL. The maximum pressure of the high-pressure line HL determined by the first relief valve 35 is higher than the maximum pressure of the low-pressure line LL determined by the second relief valve 11.

[0027] Fig. 4 is a hardware configuration diagram of the controller 140. As shown in Fig. 4, the controller 140 is configured as a computer including a processor 141 such as a CPU (Central Processing Unit) or MPU (Micro Processing Unit), a volatile memory (storage device) 142 known as RAM (Random Access Memory), a non-volatile memory (storage device) 143 such as ROM (Read Only Memory), flash memory, or a hard disk drive, an input interface 144, an output interface 145, and other peripheral circuits. The controller 140 may be configured as a single computer or as multiple computers.

[0028] The nonvolatile memory 143 stores programs capable of executing various calculations. In other words, the nonvolatile memory 143 is a storage medium from which the programs that realize the functions of this embodiment can be read. The processor 141 is a processing device that loads the programs stored in the nonvolatile memory 143 into the volatile memory 142 and executes the calculations, and performs predetermined calculations on data taken in from the input interface 144, the volatile memory 142, and the nonvolatile memory 143 in accordance with the programs.

[0029] The input interface 144 converts signals input from the sensors (36, 37, 38, 39, 40, 41, 42b) and the like into data that can be calculated by the processor 141. The output interface 145 generates an output signal according to the calculation result by the processor 141, and outputs the signal to the control valves (5AH, 5BH, 5CH, 5DH, 5AL, 5BL, 5CL, 5DL), the inverters (15, 18), and the like.

[0030] 3, an operation device 42 that operates the hydraulic cylinder 1 is connected to the controller 140. The operation device 42 is an operation device that commands the operation of a member to be driven (e.g., the boom 111), i.e., the operation of the hydraulic cylinder 1, in response to operation by an operator. The operation device 42 has an operation lever (operation member) 42a that can be tilted, and an operation amount sensor 42b that detects the operation amount (operation angle) of the operation lever 42a and outputs the detected signal to the controller 140.

[0031] The first inverter 18 and the second inverter 15 are connected to the controller 140. The first inverter 18 and the second inverter 15 control the first electric motor 17 and the second electric motor 14 so that the actual rotation speeds of the first electric motor 17 and the second electric motor 14 become the target rotation speeds set by the controller 140.

[0032] The controller 140 is connected to a first discharge pressure sensor 36, a second discharge pressure sensor 37, a first pressure sensor 38, a second pressure sensor 39, a third pressure sensor 40, and a fourth pressure sensor 41. The first discharge pressure sensor 36 detects the discharge pressure of the first hydraulic pump 16, i.e., the pressure of the hydraulic oil in the high-pressure line HL. The second discharge pressure sensor 37 detects the discharge pressure of the second hydraulic pump 13, i.e., the pressure of the hydraulic oil in the low-pressure line LL. The first pressure sensor 38 detects the pressure of the hydraulic oil in the first chamber 1A. The second pressure sensor 39 detects the pressure of the hydraulic oil in the second chamber 1B. The third pressure sensor 40 detects the pressure of the hydraulic oil in the third chamber 1C. The fourth pressure sensor 41 detects the pressure of the hydraulic oil in the fourth chamber 1D.

[0033] We will now explain the operating principle of the hydraulic cylinder (multi-chamber cylinder) 1. The thrust of the hydraulic cylinder 1 can be adjusted by changing the pressure acting on each of the chambers 1A to 1D. By connecting each of the chambers 1A to 1D to the high-pressure line HL or the low-pressure line LL, 16 patterns of cylinder thrust can be generated.

[0034] FIG. 5 is an index table illustrating 16 patterns of connection for the hydraulic cylinder (multi-chamber cylinder) 1. In the index table, A to D correspond to the chambers 1A to 1D of the hydraulic cylinder 1. The index numbers range from 1 to 16, and each indicates which chamber is connected to the high-pressure line HL or the low-pressure line LL. For example, an index number of 10 indicates that the first chamber 1A and the second chamber 1B are connected to the high-pressure line HL, and the third chamber 1C and the fourth chamber 1D are connected to the low-pressure line LL. In this way, by changing the pattern of connection between the chambers 1A to 1D and the oil passages (HL, LL), 16 patterns of cylinder thrust can be obtained. Therefore, by selecting an appropriate pattern depending on the load, desired operation can be achieved.

[0035] Next, to obtain the characteristic diagram ( FIG. 7 ) of the hydraulic cylinder (multi-chamber cylinder) 1 described later, the relationship between the load pressure and the load flow rate of the hydraulic cylinder 1 is defined as follows. FIG. 6 is a diagram showing the relationship between the load pressure and the load flow rate of the hydraulic cylinder 1. In FIG. 6 , the state of the hydraulic cylinder 1 is expressed in a four-quadrant matrix based on the operating direction of the hydraulic cylinder 1 and the direction of the load acting on it. The first quadrant represents a driving state in which the hydraulic cylinder 1 operates in the extension direction against the load, while the second quadrant represents a regenerative state in which the operating direction is the same as the direction in which the load acts. The second quadrant also represents a state in which the hydraulic cylinder 1 operates in the contraction direction. Similarly, the third quadrant represents a driving state in which the hydraulic cylinder 1 operates in the contraction direction against the load, while the fourth quadrant represents a regenerative state in which the operating direction is the same as the direction in which the load acts. The fourth quadrant also represents a state in which the hydraulic cylinder 1 operates in the extension direction.

[0036] On this four-quadrant matrix, the load pressure P Ｌ and load flow rate Q Ｌ The relationship between the load pressure P Ｌ The load pressure P of the hydraulic cylinder 1 is determined depending on the load acting on the hydraulic cylinder 1. Ｌis calculated from the relationship between the pressure in each chamber 1A to 1D and the area of ​​the pressure-receiving surface of the rod of the hydraulic cylinder 1 on which the pressure in each chamber 1A to 1D acts. Note that, hereinafter, the first chamber 1A to fourth chamber 1D will also be collectively referred to as pressure-receiving chambers.

[0037] Load pressure P Ｌ The area ratio of the pressure receiving surfaces of the pressure receiving chambers of the hydraulic cylinder 1 according to this embodiment is given by the following (Equation 1):

[0038]

[0039] Here, A Ａ is the area of ​​the pressure-receiving surface of the first chamber 1A, and A Ｂ is the area of ​​the pressure-receiving surface of the second chamber 1B, and A Ｃ is the area of ​​the pressure-receiving surface of the third chamber 1C, and A Ｄ is the area of ​​the pressure-receiving surface of the fourth chamber 1D.

[0040] Load pressure P of the hydraulic cylinder 1 in the first and second quadrants Ｌ Taking the above area ratio into consideration, the load pressure P of the hydraulic cylinder 1 in the third and fourth quadrants is expressed as follows (Equation 2). Ｌ Considering the above area ratio, is expressed as the following (Equation 3).

[0041]

[0042]

[0043] where α Ａ is the area A of the pressure-receiving surface of the first chamber 1A Ａ It is a coefficient corresponding to the value of 0.8. Ａ is the pressure of the hydraulic oil in the first chamber 1A. Ｂ is the area A of the pressure-receiving surface of the second chamber 1B Ｂ It is a coefficient corresponding to the value of 0.4. Ｂ is the pressure of the hydraulic oil in the second chamber 1B. Ｃ is the area A of the pressure-receiving surface of the third chamber 1C Ｃ It is a coefficient corresponding to the value of 0.2. Ｃis the pressure of the hydraulic oil in the third chamber 1C. Ｄ is the area A of the pressure-receiving surface of the fourth chamber 1D Ｄ It is a coefficient corresponding to the value of 0.1. Ｄ is the pressure of the hydraulic oil in the fourth chamber 1D. The coefficient α of the area ratio Ａ , α Ｂ , α Ｃ , α Ｄ are also collectively referred to as coefficient α.

[0044] For example, in the first quadrant, the pressure receiving chambers on the meter-in side are the first chamber 1A and the third chamber 1C, and the pressure receiving chambers on the meter-out side are the second chamber 1B and the fourth chamber 1D. When the pressure in the pressure receiving chamber on the meter-in side is 10 [MPa] and the pressure in the pressure receiving chamber on the meter-out side is 0 [MPa], the load pressure P Ｌ is 10 [MPa].

[0045] Load flow rate Q of hydraulic cylinder 1 in the first and second quadrants Ｌ is expressed as the following (Equation 4): The load flow rate Q of the hydraulic cylinder 1 in the third and fourth quadrants Ｌ is expressed as the following (Equation 5).

[0046]

[0047]

[0048] Load flow rate Q Ｌ Regarding v, it is defined as the meter-in side flow rate in the first and third quadrants, which are the drive side, and as the meter-out side flow rate in the second and fourth quadrants, which are the regeneration side. v is the operating speed of the hydraulic cylinder 1 (cylinder speed). The extension speed, which is the operating speed when the hydraulic cylinder 1 extends, is expressed as a positive value, and the retraction speed, which is the operating speed when the hydraulic cylinder 1 retracts, is expressed as a negative value. Therefore, the meter-in side flow rate is expressed as a positive value, and the meter-out side flow rate is expressed as a negative value. The cylinder speed v is a target speed calculated by the controller 140 based on the lever operation amount.

[0049] As shown in FIG. 6, the load pressure P Ｌ and load flow rate Q ＬWhen this is defined, the characteristic diagram of the hydraulic cylinder (multi-chamber cylinder) 1 shown in FIG. 7 is obtained. In FIG. 7, the horizontal axis represents the load flow rate Q Ｌ The vertical axis indicates the load pressure P Ｌ The characteristic diagram shown in FIG. 7 is shown as a four-quadrant matrix, similar to FIG. 6. Each of the lines numbered 1 to 16 indicates a characteristic corresponding to an index number in the index table shown in FIG. 5. According to this embodiment, 16 different cylinder thrusts can be generated by changing the pattern (hereinafter also referred to as the connection pattern) connecting each pressure-receiving chamber (1A to 1D) to the oil passages (HL, LL). The controller 140 selects the optimal connection pattern depending on the state (quadrant) and load of the hydraulic cylinder 1. This reduces the pressure loss that occurs when the hydraulic cylinder 1 is operated.

[0050] For example, the load pressure P of the hydraulic cylinder 1 Ｌ and load flow rate Q Ｌ is the OP in the first quadrant (driving state) １ , the controller 140 selects index No. 13. In other words, the controller 140 selects a characteristic line that is closest to the current state and has a higher load pressure than the current state. This makes it possible to efficiently drive the hydraulic cylinder 1 while suppressing the occurrence of pressure loss. If the controller 140 selects index No. 16, the pressure loss will increase. Furthermore, if the controller 140 selects index No. 12 or lower, the hydraulic cylinder 1 cannot be operated.

[0051] For example, the load pressure P of the hydraulic cylinder 1 Ｌ and load flow rate Q Ｌ is the OP in the second quadrant (regenerative state) ２ If so, the controller 140 selects index No. 7. In other words, the characteristic line that is closest to the current state and has a lower load pressure than the current state is selected. This allows energy to be regenerated. This is the basic operating principle of a multi-chamber cylinder.

[0052] The functions of the controller 140 will be described with reference to FIG. 8 . FIG. 8 is a functional block diagram of the controller 140. As shown in FIG. 8 , the controller 140 executes a program stored in a nonvolatile memory 143 to function as a valve index selector 151, a valve control unit 152, a required flow rate calculator 153, and a rotational speed calculator 154. The controller 140 controls the four high-pressure control valves 5AH, 5BH, 5CH, and 5DH and the four low-pressure control valves 5AL, 5BL, 5CL, and 5DL that constitute the control valve unit 150 based on the detection results of the pressure sensors 38 to 41, the operation amount sensor 42 b, and the first discharge pressure sensor 36. The controller 140 also controls the rotational speed of the first electric motor 17 based on the detection results of the pressure sensors 38 to 41 and the operation amount sensor 42 b. The controller 140 also controls the rotational speed of the second electric motor 14 based on the detection result of the second discharge pressure sensor 37.

[0053] The valve index selection unit 151 selects an index No. based on the pressure in each pressure-receiving chamber (hereinafter also referred to as actuator pressure) detected by the pressure sensors 38 to 41 and the amount of operation of the operating lever 42a (hereinafter referred to as lever operation amount) detected by the operation amount sensor 42b.

[0054] In order to identify the state of the hydraulic cylinder 1, the valve index selection unit 151 calculates the load pressure P Ｌ The valve index selection unit 151 calculates the load pressure P Ｌand the lever operation amount, the valve index selection unit 151 identifies which quadrant of the four-quadrant matrix the state of the hydraulic cylinder 1 belongs to, and outputs an actuator state signal representing the identified state (quadrant). If the load pressure is positive and the lever operation is an operation to extend the hydraulic cylinder 1, the valve index selection unit 151 determines that the state of the hydraulic cylinder 1 is in the first quadrant. If the load pressure is positive and the lever operation is an operation to retract the hydraulic cylinder 1, the valve index selection unit 151 determines that the state of the hydraulic cylinder 1 is in the second quadrant. If the load pressure is negative and the lever operation is an operation to retract the hydraulic cylinder 1, the valve index selection unit 151 determines that the state of the hydraulic cylinder 1 is in the third quadrant. If the load pressure is negative and the lever operation is an operation to extend the hydraulic cylinder 1, the valve index selection unit 151 determines that the state of the hydraulic cylinder 1 is in the fourth quadrant.

[0055] The valve index selection unit 151 selects the load pressure P corresponding to the identified state of the hydraulic cylinder 1 and the state of the hydraulic cylinder 1 described with reference to FIGS. 6 and 7. Ｌ and load flow rate Q Ｌ Based on the formula, the load pressure P of the actuator Ｌ and load flow rate Q Ｌ The valve index selection unit 151 calculates the calculated load pressure P Ｌ The valve index selection unit 151 selects the index number of the characteristic line (lines numbered 1 to 16 in FIG. 7) that is closest to the specified value. The valve index selection unit 151 selects an index number for each of the boom cylinder 111A, the arm cylinder 112A, and the bucket cylinder 113A, and outputs the selected index number.

[0056] The valve index selection unit 151 selects the load pressure P Ｌ and load flow rate Q Ｌ Output.

[0057] The valve control unit 152 shown in FIG. 8 generates a valve control command based on the index number, actuator state signal, load pressure, and load flow rate output from the valve index selection unit 151, and outputs the command to the electromagnetic proportional valve 5 to be controlled.

[0058] The flow of valve control processing by the valve control unit 152 will be described with reference to Figure 9. The processing shown in Figure 9 is started when the ignition switch (not shown) of the hydraulic excavator 10 is turned on (i.e., the key is on), and is repeatedly executed at a predetermined control cycle. Below, processing for the electromagnetic proportional valve 5 that constitutes the boom control valve unit 150A that controls the boom cylinder 111A will be described as an example, but valve control is also executed in a similar manner for the electromagnetic proportional valves 5 that constitute the arm control valve unit 150B and the bucket control valve unit 150C.

[0059] In step S105, the valve control unit 152 refers to the index table (see FIG. 5 ) and determines the electromagnetic proportional valve 5 to be controlled based on the index No. selected by the valve index selection unit 151. The electromagnetic proportional valve 5 to be controlled is controlled to be fully open or to have a predetermined target opening area, as will be described later. Meanwhile, the electromagnetic proportional valves 5 that are not to be controlled are maintained in a fully closed state.

[0060] In step S110, the valve control unit 152 selects the load pressure P Ｌ It is determined whether the load pressure P is the highest pressure among the load pressures of the hydraulic actuator. Ｌ If it is determined that the load pressure P is the highest pressure among the load pressures of the hydraulic actuators, the process proceeds to step S150, and the load pressure P Ｌ If it is determined that is not the highest pressure among the load pressures of the hydraulic actuators, the process proceeds to step S120.

[0061] In step S150, the valve control unit 152 fully opens the electromagnetic proportional valve 5 that is the control target, and ends the processing shown in the flowchart in Fig. 9 for this calculation cycle. By performing control in this manner, the hydraulic cylinder 1 with the highest load pressure can be driven while suppressing pressure loss. The flow rate supplied to the hydraulic cylinder 1 is controlled by the rotational speed of the electric motor, which will be described later.

[0062] In step S120, the valve control unit 152 determines, based on the actuator state signal, whether the state of the hydraulic cylinder 1 is in the first or second quadrant. If it is determined that the state of the hydraulic cylinder 1 is in the first or second quadrant, the process proceeds to step S140, and if it is determined that the state of the hydraulic cylinder 1 is in the third or fourth quadrant, the process proceeds to step S130.

[0063] In steps S130 and S140, flow rate control is performed to control the hydraulic cylinder 1 to a desired speed. Basically, to control the speed of the hydraulic cylinder 1, it is necessary to control the flow rate on the high-pressure side. This is because the high-pressure side controls the thrust or braking force of the hydraulic cylinder 1, and the low-pressure side has very little effect on the thrust or braking force. When the solenoid proportional valve 5 connecting the low-pressure line LL and the pressure-receiving chamber of the hydraulic cylinder 1 is selected as the control target, the solenoid proportional valve 5 is controlled to be fully open. Since it is necessary to control the flow rate on the high-pressure side to control the speed of the hydraulic cylinder 1, when the pressure-receiving chamber of the hydraulic cylinder 1 is connected to the high-pressure line HL, it is necessary to control the opening area of ​​the solenoid proportional valve 5 connected to the pressure-receiving chamber.

[0064] As described above, in the first quadrant, of the solenoid proportional valves 5 connected to the first chamber 1A and the third chamber 1C, which are meter-in flow rates, only the opening area of ​​the solenoid proportional valve 5 connected to the high-pressure line HL is controlled. In the second quadrant, of the solenoid proportional valves 5 connected to the first chamber 1A and the third chamber 1C, which are meter-out flow rates, only the opening area of ​​the solenoid proportional valve 5 connected to the high-pressure line HL is controlled. In the third quadrant, of the solenoid proportional valves 5 connected to the second chamber 1B and the fourth chamber 1D, which are meter-in flow rates, only the opening area of ​​the solenoid proportional valve 5 connected to the high-pressure line HL is controlled. In the fourth quadrant, of the solenoid proportional valves 5 connected to the second chamber 1B and the fourth chamber 1D, which are meter-out flow rates, only the opening area of ​​the solenoid proportional valve 5 connected to the high-pressure line HL is controlled. The processing contents of steps S140, S145, S130, and S135 will be specifically described below.

[0065] In step S140, the valve control unit 152 refers to the index table (see FIG. 5 ) and determines whether the oil line connecting the first chamber 1A and the third chamber 1C is the high-pressure line HL based on the index No. selected by the valve index selection unit 151. If it is determined that the oil line connected to the first chamber 1A is the high-pressure line HL, the valve control unit 152 calculates the target opening area A of the high-pressure control valve 5AH connecting the first chamber 1A and the high-pressure line HL using the following (Equation 6): ＡＨ Calculate.

[0066]

[0067] Here, c is the flow coefficient, and ΔP is the differential pressure across the high pressure control valve 5AH. The differential pressure across the high pressure control valve 5AH ΔP is obtained by subtracting the pressure in the first chamber 1A detected by the pressure sensor 38 from the pressure in the high pressure line HL detected by the first discharge pressure sensor 36. The valve control unit 152 calculates the opening area of ​​the high pressure control valve 5AH to be equal to the calculated target opening area A ＡＨIf it is determined that the oil passage connected to the first chamber 1A is the low-pressure line LL, the valve control unit 152 outputs a valve control command (control current) to the low-pressure control valve 5AL to fully open the low-pressure control valve 5AL.

[0068] Similarly, when it is determined that the oil passage connected to the third chamber 1C is the high-pressure line HL, the valve control unit 152 calculates the target opening area A of the high-pressure control valve 5CH connecting the third chamber 1C and the high-pressure line HL by the following (Equation 7): ＣＨ Calculate.

[0069]

[0070] Here, c is the flow coefficient, and ΔP is the differential pressure across the high pressure control valve 5CH. The differential pressure across the high pressure control valve 5CH ΔP is obtained by subtracting the pressure in the third chamber 1C detected by the pressure sensor 40 from the pressure in the high pressure line HL detected by the first discharge pressure sensor 36. The valve control unit 152 calculates the opening area of ​​the high pressure control valve 5CH to be equal to the calculated target opening area A ＣＨ If it is determined that the oil passage connected to the third chamber 1C is the low-pressure line LL, the valve control unit 152 outputs a valve control command (control current) to the low-pressure control valve 5CL to fully open the low-pressure control valve 5CL.

[0071] In the next step S145, the valve control unit 152 outputs a valve control command to fully open the other electromagnetic proportional valves 5 that are to be controlled. That is, the valve control unit 152 outputs a valve control command to fully open the electromagnetic proportional valve 5 selected as the controlled object from among the high pressure control valve 5BH and the low pressure control valve 5BL connected to the second chamber 1B to the electromagnetic proportional valve 5. The valve control unit 152 also outputs a valve control command to fully open the electromagnetic proportional valve 5 selected as the controlled object from among the high pressure control valve 5DH and the low pressure control valve 5DL connected to the fourth chamber 1D to the electromagnetic proportional valve 5. When the processing of step S145 ends, the processing shown in the flowchart of FIG. 9 for this calculation cycle ends.

[0072] In step S130, the valve control unit 152 refers to the index table (see FIG. 5 ) and determines whether the oil line connected to the second chamber 1B and the fourth chamber 1D is the high-pressure line HL based on the index No. selected by the valve index selection unit 151. If it is determined that the oil line connected to the second chamber 1B is the high-pressure line HL, the valve control unit 152 calculates the target opening area A of the high-pressure control valve 5BH connecting the second chamber 1B and the high-pressure line HL using the following (Equation 8): ＢＨ Calculate.

[0073]

[0074] Here, c is the flow coefficient, and ΔP is the differential pressure across the high pressure control valve 5BH. The differential pressure across the high pressure control valve 5BH ΔP is obtained by subtracting the pressure in the second chamber 1B detected by the pressure sensor 39 from the pressure in the high pressure line HL detected by the first discharge pressure sensor 36. The valve control unit 152 calculates the opening area of ​​the high pressure control valve 5BH to be equal to the calculated target opening area A ＢＨ If it is determined that the oil passage connected to the second chamber 1B is the low-pressure line LL, the valve control unit 152 outputs a valve control command (control current) to the low-pressure control valve 5BL to fully open the low-pressure control valve 5BL.

[0075] Similarly, when it is determined that the oil passage connected to the fourth chamber 1D is the high-pressure line HL, the valve control unit 152 calculates the target opening area A of the high-pressure control valve 5DH that connects the fourth chamber 1D and the high-pressure line HL using the following (Equation 9): ＤＨ Calculate.

[0076]

[0077] Here, c is the flow coefficient, and ΔP is the differential pressure across the high pressure control valve 5DH. The differential pressure across the high pressure control valve 5DH ΔP is obtained by subtracting the pressure in the fourth chamber 1D detected by the pressure sensor 41 from the pressure in the high pressure line HL detected by the first discharge pressure sensor 36. The valve control unit 152 calculates the opening area of ​​the high pressure control valve 5DH to be equal to the calculated target opening area AＤＨ If it is determined that the oil passage connected to the fourth chamber 1D is the low-pressure line LL, the valve control unit 152 outputs a valve control command (control current) to the low-pressure control valve 5DL to fully open the low-pressure control valve 5DL.

[0078] In the next step S135, the valve control unit 152 outputs a valve control command to fully open the other electromagnetic proportional valves 5 that are to be controlled. That is, the valve control unit 152 outputs a valve control command to fully open the electromagnetic proportional valve 5 selected as the controlled object from among the high pressure control valve 5AH and the low pressure control valve 5AL connected to the first chamber 1A to that electromagnetic proportional valve 5. The valve control unit 152 also outputs a valve control command to fully open the electromagnetic proportional valve 5 selected as the controlled object from among the high pressure control valve 5CH and the low pressure control valve 5CL connected to the third chamber 1C to that electromagnetic proportional valve 5. When the processing of step S135 ends, the processing shown in the flowchart of FIG. 9 for this calculation cycle ends.

[0079] 9 is performed not only for boom control valve unit 150A, but also for arm control valve unit 150B and bucket control valve unit 150C. This makes it possible to control each of boom control valve unit 150A, arm control valve unit 150B, and bucket control valve unit 150C, and to appropriately realize the operation of hydraulic cylinder 1 in response to lever operation.

[0080] 10, the calculation process of the HP required flow rate by the required flow rate calculation unit 153 in FIG. 8 will be described. The HP required flow rate is a flow rate required of the first hydraulic pump 16. When the HP required flow rate has a positive value, hydraulic oil is discharged from the first hydraulic pump 16. When the HP required flow rate has a negative value, hydraulic oil is sucked into the first hydraulic pump 16. In this case, the first hydraulic pump 16 performs regenerative operation. As shown in FIG. 10, the required flow rate calculation unit 153 calculates and outputs the sum of the load flow rate of the boom cylinder 111A, the load flow rate of the arm cylinder 112A, and the load flow rate of the bucket cylinder 113A as the HP required flow rate.

[0081] 11 , the calculation process of the target rotation speed of the first electric motor 17 by the rotation speed calculation unit 154 in FIG. 8 will be described. As shown in FIG. 11 , the rotation speed calculation unit 154 calculates the target rotation speed by multiplying the HP required flow rate calculated by the required flow rate calculation unit 153 by a gain K1. The rotation speed calculation unit 154 outputs a first motor rotation speed command, which is a command for setting the rotation speed of the first electric motor 17 to the target rotation speed. The gain K1 is a constant (conversion coefficient) that defines the relationship between the HP required flow rate of the first hydraulic pump 16 and the rotation speed of the first electric motor 17 (the rotation speed of the first hydraulic pump 16), and is determined based on the capacity (displacement volume) of the first hydraulic pump 16.

[0082] The first motor rotation speed command is input to the first inverter 18. The first inverter 18 controls the rotation speed of the first electric motor 17 based on the first motor rotation speed command so that the first electric motor 17 rotates at a target rotation speed.

[0083] 12, the calculation process of the LP required flow rate by the required flow rate calculation unit 153 of FIG. 8 will be described. The LP required flow rate is the flow rate required for the second hydraulic pump 13. As shown in FIG. 12, the required flow rate calculation unit 153 has a required flow rate table 153T that defines the relationship between the pressure in the low-pressure line LL and the LP required flow rate. The required flow rate table 153T defines the following characteristics. When the pressure in the low-pressure line LL is 0 (i.e., tank pressure), the LP required flow rate is 1, which represents the maximum flow rate. Furthermore, as the pressure in the low-pressure line LL increases, the LP required flow rate decreases. Furthermore, when the pressure in the low-pressure line LL becomes equal to or greater than a predetermined value, the LP required flow rate becomes 0, which represents the minimum flow rate. The required flow rate table 153T is pre-stored in the non-volatile memory 143.

[0084] The required flow rate calculation unit 153 refers to a required flow rate table 153T, calculates the LP required flow rate based on the pressure in the low pressure line LL detected by the second discharge pressure sensor 37, and outputs the calculated value.

[0085] 13 , the calculation process of the target rotation speed of the second electric motor 14 by the rotation speed calculation unit 154 of FIG. 8 will be described. As shown in FIG. 13 , the rotation speed calculation unit 154 calculates the target rotation speed by multiplying the LP required flow rate calculated by the required flow rate calculation unit 153 by a gain K2. The rotation speed calculation unit 154 outputs a second motor rotation speed command, which is a command for setting the rotation speed of the second electric motor 14 to the target rotation speed. The gain K2 is a constant (conversion coefficient) that defines the relationship between the LP required flow rate of the second hydraulic pump 13 and the rotation speed of the second electric motor 14 (the rotation speed of the second hydraulic pump 13), and is determined based on the capacity (displacement volume) of the second hydraulic pump 13.

[0086] The second motor rotation speed command is input to the second inverter 15. The second inverter 15 controls the rotation speed of the second electric motor 14 based on the second motor rotation speed command so that the second electric motor 14 rotates at a target rotation speed. This allows a constant pressure to be established in the low-pressure line LL, and prevents the low-pressure line LL from becoming negative pressure when the first hydraulic pump 16 draws oil in a regenerative state. Note that in this embodiment, the flow rate of the second hydraulic pump 13 is smoothly controlled in accordance with the pressure in the low-pressure line LL. Therefore, noise generation can be suppressed compared to when the second hydraulic pump 13 and the second electric motor 14 are controlled to be turned on and off at a predetermined pressure.

[0087] As described above, the controller 140 according to the first embodiment identifies the state of the hydraulic cylinder 1 according to the lever operation amount and the pressure in each pressure-receiving chamber of the hydraulic cylinder 1, and appropriately controls the control valve unit 150 according to the load on the hydraulic cylinder 1, thereby reducing pressure loss and enabling the hydraulic cylinder 1 to be driven efficiently.

[0088] According to the above-described embodiment, the following advantageous effects are achieved.

[0089] (1) A hydraulic excavator (work machine) 10 includes a vehicle body 105, a working device 104 attached to the vehicle body 105, a first hydraulic pump 16 that supplies hydraulic oil to a high-pressure line HL, a first electric motor (first power source) 17 that drives the first hydraulic pump 16, a second hydraulic pump 13 that supplies hydraulic oil to a low-pressure line LL, a second electric motor (second power source) 14 that drives the second hydraulic pump 13, a hydraulic cylinder 1 having four chambers 1A, 1B, 1C, and 1D and driven by hydraulic oil discharged from the first hydraulic pump 16 and the second hydraulic pump 13 to drive the working device 104, and four high-pressure valves that control communication and interruption between the high-pressure line HL and the four chambers 1A, 1B, 1C, and 1D of the hydraulic cylinder 1. The hydraulic cylinder 1 includes control valves 5AH, 5BH, 5CH, and 5DH, four low-pressure control valves 5AL, 5BL, 5CL, and 5DL that control communication and cutoff between the low-pressure line LL and the four chambers 1A, 1B, 1C, and 1D of the hydraulic cylinder 1, four pressure sensors 38, 39, 40, and 41 that detect the pressures of the four chambers 1A, 1B, 1C, and 1D, an operating device 42 that operates the hydraulic cylinder 1, an operation amount sensor 42b that detects the amount of operation of the operating device 42, and a controller (control device) 140 that controls the four high-pressure control valves 5AH, 5BH, 5CH, and 5DH and the four low-pressure control valves 5AL, 5BL, 5CL, and 5DL based on the detection results of the pressure sensors 38, 39, 40, and 41 and the operation amount sensor 42b. The controller 140 controls the rotation speed of the first electric motor 17 based on the detection results of the pressure sensors 38 to 41 and the operation amount sensor 42b.

[0090] Although not shown, as a first comparative example of this embodiment, in a configuration in which a high-pressure accumulator is connected to the high-pressure line HL and a low-pressure accumulator is connected to the low-pressure line LL without providing the first electric motor 17 and the second electric motor 14, the pressure in the high-pressure line HL is kept constant by the high-pressure accumulator. Therefore, a large pressure loss always occurs when the hydraulic actuator is operated. In contrast, in this embodiment, the pressure in the high-pressure line HL can be changed by controlling the rotation speed of the first electric motor 17. Therefore, when high pressure is not required in the high-pressure line HL, the pressure in the high-pressure line HL can be reduced, thereby reducing the pressure loss occurring in the control valve unit 150. In other words, according to this embodiment, the hydraulic cylinder 1 can be controlled efficiently, thereby extending the operating time of the hydraulic excavator 10.

[0091] Furthermore, in the first comparative example, a large-capacity accumulator is required to maintain constant pressures in the high-pressure line HL and the low-pressure line LL. In particular, the high-pressure accumulator requires a container with high durability, which may increase the cost of the hydraulic excavator 10. In contrast, in the present embodiment, there is no need to provide a high-pressure accumulator in the high-pressure line HL, and therefore the cost of the hydraulic excavator 10 can be kept low.

[0092] Furthermore, although not shown, in a second comparative example of this embodiment, if an engine is provided as a power source instead of an electric motor, there is a risk that the responsiveness when controlling the rotation speed of the hydraulic pump may deteriorate. Therefore, in the second comparative example, it is difficult to quickly change the pressure in the high-pressure line HL and the low-pressure line LL to the target pressure, which may deteriorate the operability of the hydraulic cylinder 1. In contrast, in this embodiment, the pressure in the high-pressure line HL and the low-pressure line LL can be quickly controlled to the target pressure by the electric motor, so the operability of the hydraulic cylinder 1 is excellent.

[0093] (2) The hydraulic excavator 10 is equipped with a second discharge pressure sensor (low-pressure line pressure sensor) 37 that detects the discharge pressure of the second hydraulic pump 32 (the pressure in the low-pressure line LL). The controller 140 controls the rotation speed of the second electric motor (second power source) 14 based on the detection result of the second discharge pressure sensor 37. This configuration makes it possible to create a constant pressure in the low-pressure line LL. As a result, it is possible to prevent the low-pressure line LL from becoming negative pressure when the first hydraulic pump 16 sucks oil in a regenerative state.

[0094] <Second embodiment> A hydraulic excavator 10 according to a second embodiment of the present invention will be described with reference to Figures 14 and 15. Note that the same reference symbols are used to designate components that are the same as or equivalent to those described in the first embodiment, and differences will be mainly described.

[0095] FIG. 14 is a functional block diagram of a controller 240 according to the second embodiment. In the second embodiment, the method of calculating the LP required flow rate by the required flow rate calculation unit 253 is different from that in the first embodiment. Note that other processes are the same as those in the first embodiment, and therefore description thereof will be omitted. As shown in FIG. 14, the required flow rate calculation unit 253 receives the index number and actuator status signal output from the valve index selection unit 151. The required flow rate calculation unit 253 calculates the index number, the actuator status signal, and the load flow rate Q Ｌ The suction flow rate is calculated based on the above.

[0096] The flow of the process of calculating the suction flow rate by the required flow rate calculator 253 will be described with reference to Figure 15. The process shown in Figure 15 is started when the ignition switch (not shown) of the hydraulic excavator 10 is turned on (i.e., key-on), and is repeatedly executed at a predetermined control period. Below, the process of calculating the suction flow rate of the boom cylinder 111A based on the connection state of the boom cylinder 111A and the low-pressure line LL will be described as an example, but the process of calculating the suction flow rate of the arm cylinder 112A based on the connection state of the arm cylinder 112A and the low-pressure line LL, and the process of calculating the suction flow rate of the bucket cylinder 113A based on the connection state of the bucket cylinder 113A and the low-pressure line LL are also executed in a similar manner.

[0097] In step S210, the required flow rate calculation unit 253 determines, based on the actuator state signal, whether the state of the hydraulic cylinder 1 is in the second quadrant. If it is determined that the state of the hydraulic cylinder 1 is in the second quadrant, the process proceeds to step S250, and if it is determined that the state of the hydraulic cylinder 1 is not in the second quadrant, the process proceeds to step S215.

[0098] In step S250, the required flow rate calculation unit 253 refers to the index table (see FIG. 5 ) and determines whether the oil line connected to the second chamber 1B is the low-pressure line LL based on the index No. selected by the valve index selection unit 151. If it is determined that the oil line connected to the second chamber 1B is the low-pressure line LL, the process proceeds to step S270, and if it is determined that the oil line connected to the second chamber 1B is the high-pressure line HL, the process proceeds to step S260.

[0099] In steps S260 and S270, the required flow rate calculation unit 253 refers to the index table (see FIG. 5 ) and determines whether the oil line connected to the fourth chamber 1D is the low-pressure line LL based on the index number selected by the valve index selection unit 151. If it is determined in step S260 that the oil line connected to the fourth chamber 1D is the low-pressure line LL, the process proceeds to step S265. If it is determined that the oil line connected to the fourth chamber 1D is the high-pressure line HL, it is determined that there is no suction flow rate, and the process shown in the flowchart in FIG. 15 for this calculation cycle ends. If it is determined in step S270 that the oil line connected to the fourth chamber 1D is the low-pressure line LL, the process proceeds to step S276. If it is determined that the oil line connected to the fourth chamber 1D is the high-pressure line HL, the process proceeds to step S273.

[0100] In step S265, the required flow rate calculation unit 253 determines the coefficient α representing the area ratio of the pressure-receiving surface of the fourth chamber 1D as the only suction-side chamber. Ｄ and load flow rate Q ＬBased on this, the suction flow rate Q of the hydraulic cylinder 1 is calculated by the following (Equation 10). ＬＰ Calculate.

[0101]

[0102] In step S273, the required flow rate calculation unit 253 determines the coefficient α representing the area ratio of the pressure-receiving surface of the second chamber 1B as the only suction-side chamber. Ｂ and load flow rate Q Ｌ Based on this, the suction flow rate Q of the hydraulic cylinder 1 is calculated by the following (Equation 11). ＬＰ Calculate.

[0103]

[0104] In step S276, the required flow rate calculation unit 253 calculates a coefficient α , which represents the area ratio of the pressure-receiving surface of the second chamber 1B, assuming that both the second chamber 1B and the fourth chamber 1D are suction-side chambers. Ｂ and a coefficient α representing the area ratio of the pressure-receiving surface of the fourth chamber 1D. Ｄ and load flow rate Q Ｌ Based on this, the suction flow rate Q of the hydraulic cylinder 1 is calculated by the following (Equation 12). ＬＰ Calculate.

[0105]

[0106] When the hydraulic cylinder 1 is in the second quadrant, as described above, it means that the hydraulic cylinder 1 is in a regenerative state where it is pushed by an external force and contracts. Therefore, when the second chamber 1B and the fourth chamber 1D are connected to the low-pressure line LL, they each need to suck in oil. Therefore, the required flow rate calculation unit 253 determines that the chamber connected to the low-pressure line LL is the suction-side chamber, and calculates the load flow rate Q Ｌ is multiplied by the area ratio coefficient α to obtain the suction flow rate Q ＬＰ Calculate.

[0107] In step S215, the required flow rate calculation unit 253 determines, based on the actuator state signal, whether the state of the hydraulic cylinder 1 is in the fourth quadrant. If it is determined that the state of the hydraulic cylinder 1 is in the fourth quadrant, the process proceeds to step S220. If it is determined that the state of the hydraulic cylinder 1 is not in the fourth quadrant, the state of the hydraulic cylinder 1 is determined to be in a driven state, and there is no suction flow rate, and the process shown in the flowchart in Fig. 15 for this calculation cycle ends.

[0108] In step S220, the required flow rate calculation unit 253 refers to the index table (see FIG. 5 ) and determines whether the oil line connected to the first chamber 1A is the low-pressure line LL based on the index No. selected by the valve index selection unit 151. If it is determined that the oil line connected to the first chamber 1A is the low-pressure line LL, the process proceeds to step S240, and if it is determined that the oil line connected to the first chamber 1A is the high-pressure line HL, the process proceeds to step S230.

[0109] In steps S230 and S240, the required flow rate calculation unit 253 refers to the index table (see FIG. 5 ) and determines whether the oil line connected to the third chamber 1C is the low-pressure line LL based on the index number selected by the valve index selection unit 151. If it is determined in step S230 that the oil line connected to the third chamber 1C is the low-pressure line LL, the process proceeds to step S235. If it is determined that the oil line connected to the third chamber 1C is the high-pressure line HL, it is assumed that there is no suction flow rate, and the process shown in the flowchart of FIG. 15 for this calculation cycle ends. If it is determined in step S240 that the oil line connected to the third chamber 1C is the low-pressure line LL, the process proceeds to step S246. If it is determined that the oil line connected to the third chamber 1C is the high-pressure line HL, the process proceeds to step S243.

[0110] In step S235, the required flow rate calculation unit 253 determines the coefficient α representing the area ratio of the pressure-receiving surface of the third chamber 1C, assuming that only the third chamber 1C is the suction-side chamber.Ｃ and load flow rate Q Ｌ Based on this, the suction flow rate Q of the hydraulic cylinder 1 is calculated by the following (Equation 13). ＬＰ Calculate.

[0111]

[0112] In step S243, the required flow rate calculation unit 253 determines the coefficient α Ａ and load flow rate Q Ｌ Based on this, the suction flow rate Q of the hydraulic cylinder 1 is calculated by the following (Equation 14). ＬＰ Calculate.

[0113]

[0114] In step S246, the required flow rate calculation unit 253 calculates a coefficient α , which represents the area ratio of the pressure-receiving surface of the first chamber 1A, assuming that both the first chamber 1A and the third chamber 1C are suction-side chambers. Ａ and a coefficient α representing the area ratio of the pressure-receiving surface of the third chamber 1C. Ｃ and load flow rate Q Ｌ Based on this, the suction flow rate Q of the hydraulic cylinder 1 is calculated by the following (Equation 15). ＬＰ Calculate.

[0115]

[0116] When the hydraulic cylinder 1 is in the fourth quadrant, as described above, it means that the hydraulic cylinder 1 is in a regenerative state where it is pulled and extended by an external force. Therefore, when the first chamber 1A and the third chamber 1C are connected to the low-pressure line LL, they each need to suck in oil. For this reason, the required flow rate calculation unit 253 determines that the chamber connected to the low-pressure line LL is the suction-side chamber, and calculates the load flow rate Q Ｌ is multiplied by the area ratio coefficient α to obtain the suction flow rate Q ＬＰ Calculate.

[0117] 14 calculates and outputs the sum of the suction flow rate of the boom cylinder 111A, the suction flow rate of the arm cylinder 112A, and the suction flow rate of the bucket cylinder 113A as the LP required flow rate. As in the first embodiment, the rotational speed calculation unit 154 calculates the target rotational speed by multiplying the LP required flow rate by a gain K2. The rotational speed calculation unit 154 outputs a second motor rotational speed command, which is a command for setting the rotational speed of the second electric motor 14 to the target rotational speed.

[0118] As described above, the controller 240 according to the second embodiment controls the rotation speed of the second electric motor 14 based on the detection results of the pressure sensors 38 to 41 and the operation amount sensor 42b. With this configuration, when the hydraulic cylinder 1 is sucking oil, the second electric motor 14 can be appropriately controlled to supply the required flow rate so as to prevent cavitation due to negative pressure or the like. Furthermore, according to the second embodiment, the installation of the second discharge pressure sensor 37 can be eliminated.

[0119] <Third Embodiment> A hydraulic excavator 10 according to a third embodiment of the present invention will be described with reference to Fig. 16. Note that components that are the same as or equivalent to those described in the first embodiment will be given the same reference symbols, and differences will be mainly described. Fig. 16 is a diagram showing the configuration of a hydraulic source according to the third embodiment.

[0120] 16, the third embodiment differs from the first embodiment in that an accumulator 19 is connected to the low-pressure line LL. The accumulator 19 is a pressure accumulator device that can store pressure oil from the second hydraulic pump 13 when the suction flow rate of the hydraulic cylinder 1 is not required.

[0121] As described above, the hydraulic excavator 10 according to the third embodiment further includes an accumulator (pressure accumulation device) 19 connected to the low-pressure line LL. This allows oil to be supplied from the accumulator 19 and the second hydraulic pump 13 when a suction flow rate for the hydraulic cylinder 1 is required. With this configuration, the capacity (size) of the second hydraulic pump 13 can be reduced.

[0122] <Fourth embodiment> A hydraulic excavator 10 according to a fourth embodiment of the present invention will be described with reference to Fig. 17. Note that components that are the same as or equivalent to those described in the first embodiment will be given the same reference symbols, and differences will be mainly described. Fig. 17 is a diagram showing the configuration of a hydraulic source according to the fourth embodiment.

[0123] As shown in Figure 17, the fourth embodiment differs from the first embodiment in the following points. (Difference 1) The second hydraulic pump 32 is a pump motor. (Difference 2) A first switching device 461 is provided so that the pressure oil discharged from the first hydraulic pump 16 can be supplied not only to the high-pressure line HL but also to the low-pressure line LL. (Difference 3) A second switching device 462 is provided so that the pressure oil discharged from the second hydraulic pump 32 can be supplied not only to the low-pressure line LL but also to the high-pressure line HL.

[0124] The first switching device 461 has an electromagnetic switching valve 23 that can be switched between a communication position that connects the first hydraulic pump 16 to the high-pressure line HL and a blocking position that blocks communication between the first hydraulic pump 16 and the high-pressure line HL, and an electromagnetic switching valve 22 that can be switched between a communication position that connects the first hydraulic pump 16 to the low-pressure line LL and a blocking position that blocks communication between the first hydraulic pump 16 and the low-pressure line LL.

[0125] The second switching device 462 has an electromagnetic switching valve 21 that can be switched between a communication position that connects the second hydraulic pump 32 to the high-pressure line HL and a blocking position that blocks communication between the second hydraulic pump 32 and the high-pressure line HL, and an electromagnetic switching valve 20 that can be switched between a communication position that connects the second hydraulic pump 32 to the low-pressure line LL and a blocking position that blocks communication between the second hydraulic pump 32 and the low-pressure line LL.

[0126] The electromagnetic switching valves 20 to 23 may be two-position switching valves or electromagnetic proportional valves whose opening area is adjusted according to the current supplied to the solenoid.

[0127] In the first embodiment, when a large flow rate is expected to be required, it was necessary to install a large-capacity hydraulic pump or hydraulic pump motor. Therefore, in the fourth embodiment, a hydraulic pump motor (first hydraulic pump 16 and second hydraulic pump 32) is installed in each of the high-pressure line HL and the low-pressure line LL, and the pressure oils from the respective lines are joined together.

[0128] As described above, the hydraulic excavator 10 according to the fourth embodiment includes a first switching device 461 that can control communication between the first hydraulic pump 16 and the high-pressure line HL and communication between the first hydraulic pump 16 and the low-pressure line LL, and a second switching device 462 that can control communication between the second hydraulic pump 32 and the low-pressure line LL and communication between the second hydraulic pump 32 and the high-pressure line HL. This configuration allows the hydraulic oil discharged from the first hydraulic pump 16 and the hydraulic oil discharged from the second hydraulic pump 32 to be combined and supplied to the hydraulic cylinder 1, thereby reducing the capacity of each hydraulic pump. Furthermore, by using pump motors for not only the first hydraulic pump 16 but also the second hydraulic pump 32, the second hydraulic pump 32 can be operated as a regenerative pump. As a result, energy can be recovered more efficiently than in the first embodiment.

[0129] Fifth Embodiment A hydraulic excavator 10 according to a fifth embodiment of the present invention will be described with reference to Figures 18 and 19. Note that components that are the same as or equivalent to those described in the fourth embodiment are given the same reference symbols, and differences will be mainly described. Figure 18 is a diagram showing the configuration of a hydraulic source according to the fifth embodiment.

[0130] 18 , the fifth embodiment has a configuration in which a third hydraulic power source 503 is added to the configuration of the fourth embodiment. The third hydraulic power source 503 includes a third hydraulic pump 24 which is a pump motor, a third electric motor 25 which drives the third hydraulic pump 24, a third inverter 26 which converts DC power from the battery 12 into AC power and supplies the AC power to the third electric motor 25, and a third switching device 563 which can connect the third hydraulic pump 24 to at least one of the high-pressure line HL and the low-pressure line LL.

[0131] The third switching device 563 has an electromagnetic switching valve 28 that can be switched between a communication position that connects the third hydraulic pump 24 to the high-pressure line HL and a blocking position that blocks communication between the third hydraulic pump 24 and the high-pressure line HL, and an electromagnetic switching valve 27 that can be switched between a communication position that connects the third hydraulic pump 24 to the low-pressure line LL and a blocking position that blocks communication between the third hydraulic pump 24 and the low-pressure line LL.

[0132] Figure 19 is a control block diagram of a rotation speed calculation unit 554 according to the fifth embodiment. As shown in Figure 19, the rotation speed calculation unit 554 generates and outputs a first electric motor rotation speed command, a second electric motor rotation speed command, and a third electric motor rotation speed command based on the HP required flow rate and the LP required flow rate. The first hydraulic pump 16, the second hydraulic pump 32, and the third hydraulic pump 24 are all pump motors with the same capacity (displacement volume).

[0133] The rotation speed calculation unit 554 has a first function generating unit 554a, a second function generating unit 554e, a third function generating unit 554d, a fourth function generating unit 554f, a first subtraction unit 554b, a second subtraction unit 554g, a third subtraction unit 554c, a fourth subtraction unit 554h, a first addition unit 554i, a second addition unit 554j, a third addition unit 554k, a first gain multiplication unit 554l, a second gain multiplication unit 554m, and a third gain multiplication unit 554n.

[0134] The first function generator 554a and the second function generator 554e store an HP pump characteristic table that defines the relationship between the required flow rate and the target flow rate of the hydraulic pump. The first function generator 554a and the second function generator 554e each calculate the flow rate that can be processed by one electric motor. The pump characteristic defined by the HP pump characteristic table has a saturation characteristic with an upper limit cut.

[0135] The first function generator 554a refers to the HP pump characteristic table and calculates the HP target flow rate of the third hydraulic pump 24 using the HP required flow rate as an input value. The first subtractor 554b subtracts the HP target flow rate of the third hydraulic pump 24 from the HP required flow rate to calculate a first HP required remaining flow rate. The second function generator 554e refers to the HP pump characteristic table and calculates the HP target flow rate of the first hydraulic pump 16 using the first HP required remaining flow rate as an input value. The second subtractor 554g subtracts the HP target flow rate of the first hydraulic pump 16 from the first HP required remaining flow rate to calculate the HP target flow rate of the second hydraulic pump 32 (second HP required remaining flow rate).

[0136] The third function generator 554d and the fourth function generator 554f store an LP pump characteristic table that defines the relationship between the required flow rate and the target flow rate of the hydraulic pump. The third function generator 554d and the fourth function generator 554f each calculate the flow rate that can be processed by one electric motor. The pump characteristics defined by the LP pump characteristic table have saturation characteristics with the upper limit cut off.

[0137] The third function generator 554d refers to the LP pump characteristic table and calculates the LP target flow rate of the second hydraulic pump 32 using the LP required flow rate as an input value. The third subtractor 554c subtracts the LP target flow rate of the second hydraulic pump 32 from the LP required flow rate to calculate the first LP required residual flow rate. The fourth function generator 554f refers to the LP pump characteristic table and calculates the LP target flow rate of the first hydraulic pump 16 using the first LP required residual flow rate as an input value. The fourth subtractor 554h subtracts the LP target flow rate of the first hydraulic pump 16 from the first LP required residual flow rate to calculate the LP target flow rate of the third hydraulic pump 24 (second LP required residual flow rate).

[0138] The first adder 554i calculates the target flow rate of the first hydraulic pump 16 by adding the HP target flow rate and the LP target flow rate of the first hydraulic pump 16. The first gain multiplier 554l calculates the target rotation speed of the first electric motor 17 by multiplying the target flow rate of the first hydraulic pump 16 by a gain K1. The rotation speed calculation unit 554 outputs a first motor rotation speed command which is a command for setting the rotation speed of the first electric motor 17 to the target rotation speed.

[0139] The second adder 554j calculates the target flow rate of the second hydraulic pump 32 by adding the HP target flow rate and the LP target flow rate of the second hydraulic pump 32. The second gain multiplier 554m calculates the target rotation speed of the second electric motor 14 by multiplying the target flow rate of the second hydraulic pump 32 by a gain K2. The rotation speed calculation unit 554 outputs a second motor rotation speed command which is a command for setting the rotation speed of the second electric motor 14 to the target rotation speed.

[0140] The third adder 554k calculates the target flow rate of the third hydraulic pump 24 by adding the HP target flow rate and the LP target flow rate of the third hydraulic pump 24. The third gain multiplier 554n calculates the target rotation speed of the third electric motor 25 by multiplying the target flow rate of the third hydraulic pump 24 by a gain K3. The rotation speed calculator 554 outputs a third motor rotation speed command which is a command for setting the rotation speed of the third electric motor 25 to the target rotation speed.

[0141] An example of the operation of this embodiment will be described below. Note that the description will be made assuming that the maximum flow rate of each hydraulic pump is 50 [L / min]. When the HP required flow rate is 50 [L / min] or less, the HP required flow rate is directly set as the HP target flow rate of the third hydraulic pump 24.

[0142] When the HP required flow rate is 120 [L / min], the upper limit of the output of the first function generator 554a is cut. As a result, the HP target flow rate of the third hydraulic pump 24 becomes 50 [L / min], which can be processed by one hydraulic pump. The first subtractor 554b calculates the remaining required flow rate of 70 [L / min] based on the HP required flow rate (120 [L / min]) and the output of the first function generator 554a (50 [L / min]). Similarly, the upper limit of the output of the second function generator 554e is cut. As a result, the HP target flow rate of the first hydraulic pump 16 becomes 50 [L / min], which can be processed by one hydraulic pump. The second subtraction unit 554g calculates the remaining required flow rate of 20 [L / min] based on the output of the first subtraction unit 554b (70 [L / min]) and the output of the second function generation unit 554e (50 [L / min]), and sets this as the HP target flow rate of the second hydraulic pump 32.

[0143] The LP target flow rate of each hydraulic pump based on the LP required flow rate is similarly calculated by a third function generating section 554d, a fourth function generating section 554f, a third subtracting section 554c, and a fourth subtracting section 554h.

[0144] The HP required flow rate can be calculated as both the required flow rate during driving, which is expressed as a positive value, and the required flow rate during regeneration, which is expressed as a negative value. On the other hand, it is necessary to prevent negative pressure from occurring in the low-pressure line LL. For this reason, the LP required flow rate takes a positive value that represents the flow rate of oil being sent.

[0145] The HP target flow rate and LP target flow rate calculated for each hydraulic pump are added together in a first adder 554i, a second adder 554j, and a third adder 554k, respectively, to calculate the final target flow rate for one hydraulic pump.

[0146] In the fifth embodiment, the third electric motor 25 and the third hydraulic pump 24 give priority to the HP required flow rate, and the second electric motor 14 and the second hydraulic pump 32 give priority to the LP required flow rate. In other words, the logic is such that one hydraulic pump is dedicated to one of the two, and flow division is avoided.

[0147] The electromagnetic directional control valves 20 to 23, 27, and 28 are electromagnetic proportional valves whose opening areas are adjusted according to the current supplied to the solenoids. The controller 140 controls the opening areas of the electromagnetic proportional valves constituting the first switching device 461, the second switching device 462, and the third switching device 563 based on the HP target flow rate and the LP target flow rate of each hydraulic pump.

[0148] The hydraulic excavator 10 according to the fifth embodiment includes a third hydraulic pump 24, a third electric motor (third power source) 25 that drives the third hydraulic pump 24, and a third switching device 563 that can control communication between the third hydraulic pump 24 and the high-pressure line HL and can control communication between the third hydraulic pump 24 and the low-pressure line LL. A controller (control device) 140 controls the rotation speeds of the first electric motor (first power source) 17, the second electric motor (second power source) 14, and the third electric motor (third power source) 25 based on the detection results of the pressure sensors 38 to 41 and the operation amount sensor 42 b. This configuration allows for fine adjustment of the flow rate of hydraulic oil flowing through the high-pressure line HL and the low-pressure line LL.

[0149] Although not shown, four or more hydraulic pumps and four or more power sources may be provided, which allows for more precise adjustment of the flow rate of hydraulic oil flowing through the high-pressure line HL and the low-pressure line LL.

[0150] <Sixth Embodiment> A hydraulic excavator 10 according to a sixth embodiment of the present invention will be described with reference to Fig. 20. Note that components that are the same as or equivalent to those described in the first embodiment will be given the same reference symbols, and differences will be mainly described. Fig. 20 is a diagram showing the configuration of a hydraulic source according to the sixth embodiment.

[0151] As shown in FIG. 20 , the sixth embodiment differs from the first embodiment in that the first hydraulic pump 34 connected to the high-pressure line HL is not a pump motor but a hydraulic pump having only a pump function, and the second hydraulic pump 33 connected to the low-pressure line LL is a pump motor having both a pump function and a motor function. By using the second hydraulic pump 33 connected to the low-pressure line LL as a pump motor in this way, it is possible to regenerate pressure oil discharged from the hydraulic cylinder 1. Furthermore, by using the first hydraulic pump 34 as a hydraulic pump having only a pump function rather than a pump motor, it is possible to simplify the configuration and reduce costs. Because high-pressure hydraulic pump motors are more expensive than low-pressure ones, this configuration can prevent an increase in the overall cost of the hydraulic excavator 10.

[0152] The following modified examples are also within the scope of the present invention, and it is also possible to combine the configuration shown in the modified example with the configuration described in the above embodiment, or to combine the configurations described in the different above-mentioned embodiments.

[0153] <Modifications> In the above embodiment, an example was described in which the work machine was a crawler-type hydraulic excavator, but the present invention is not limited to this. The work machine may also be a wheel-type hydraulic excavator. The present invention can also be applied to various work machines equipped with work implements having multiple hydraulic cylinders, such as wheel loaders and cranes.

[0154] 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.

[0155] 1... Hydraulic cylinder (multi-chamber cylinder), 1A... First chamber (pressure receiving chamber), 1B... Second chamber (pressure receiving chamber), 1C... Third chamber (pressure receiving chamber), 1D... Fourth chamber (pressure receiving chamber), 5... Electromagnetic proportional valve, 5AH, 5BH, 5CH, 5DH... High pressure control valve, 5AL, 5BL, 5CL, 5DL... Low pressure control valve, 10... Hydraulic excavator, 11... Second relief valve, 12... Battery, 13... Second hydraulic pump, 14... Second electric motor (second power source), 15... Second inverter, 16... First hydraulic pump (pump motor), 17... First electric motor (first power source), 18... First inverter, 19... Accumulator (pressure storage device), 20, 21, 22, 23... Electromagnetic switching valve, 24... Third hydraulic pump, 25... Third electric motor (third power source), 26... Third inverter, 27,28...Electromagnetic switching valve, 32...Second hydraulic pump (pump motor), 33...Second hydraulic pump (pump motor), 34...First hydraulic pump, 35...First relief valve, 36...First discharge pressure sensor (high pressure line pressure sensor), 37...Second discharge pressure sensor (low pressure line pressure sensor), 38...First pressure sensor (pressure sensor), 39...Second pressure sensor (pressure sensor), 40...Third pressure sensor (pressure sensor), 41...Fourth pressure sensor (pressure sensor), 42...Operating device, 42 a...operating lever (operating member), 42b...operated quantity sensor, 100...second hydraulic power source, 101...first hydraulic power source, 102...traveling body, 102A...traveling motor (hydraulic actuator), 103...swivel body, 103A...swivel motor (hydraulic actuator), 104...working device, 105...machine body (machine body), 106...hydraulic system, 111...boom (driven member), 111A...boom cylinder (hydraulic cylinder, hydraulic actuator), 112...arm, 112A...arm cylinder (hydraulic cylinder, hydraulic actuator), 113...bucket, 113A...bucket cylinder (hydraulic cylinder, hydraulic actuator), 118...operator's cab, 119...machine room, 140...controller (control device), 141...processor, 142...volatile memory (storage device), 143...non-volatile memory (storage device), 144...input interface, 145...output interface, 150...control valve unit, 150A...boom control valve unit, 1 50B...Arm control valve unit, 150C...Bucket control valve unit, 151...Valve index selection unit, 152...Valve control unit, 153...Required flow rate calculation unit, 153T...Required flow rate table, 154...Rotational speed calculation unit, 240...Controller (control device), 253...Required flow rate calculation unit, 461...First switching device, 462...Second switching device, 503...Third hydraulic power source, 554...Rotational speed calculation unit, 563...Third switching device, HL...High pressure line, LL...Low pressure line,

Claims

1. The car body and, A work device attached to the vehicle body, A first hydraulic pump that supplies hydraulic fluid to the high-pressure line, A first power source that drives the first hydraulic pump, A second hydraulic pump that supplies hydraulic fluid to the low-pressure line, The second power source that drives the second hydraulic pump, A hydraulic cylinder having four chambers, driven by hydraulic fluid discharged from the first and second hydraulic pumps, which drives the work device, Four high-pressure control valves that control the communication and disconnection between the high-pressure line and the four chambers of the hydraulic cylinder, Four low-pressure control valves that control the communication and disconnection between the low-pressure line and the four chambers of the hydraulic cylinder, Four pressure sensors for detecting the pressure in the four chambers, A low-pressure line pressure sensor for detecting the pressure of the low-pressure line, An operating device for operating the hydraulic cylinder, An operating amount sensor for detecting the amount of operation of the operating device, A work machine comprising a control device that controls the four high-pressure control valves and the four low-pressure control valves based on the detection results of the pressure sensor and the manipulated amount sensor, The first power source and the second power source are electric motors, The control device controls the rotational speed of the electric motor, which is the first power source, based on the detection result of the manipulated amount sensor, and controls the rotational speed of the electric motor, which is the second power source, based on the detection result of the low-pressure line pressure sensor. A work machine characterized by the following features.

2. (delete)

3. (delete)

4. In the work machine described in claim 1, The system further comprises a pressure accumulator connected to the aforementioned low-pressure line. A work machine characterized by the following features.

5. In the work machine described in claim 1, A first switching device capable of controlling the connection and disconnection between the first hydraulic pump and the high-pressure line, and capable of controlling the connection and disconnection between the first hydraulic pump and the low-pressure line, The system includes a second switching device capable of controlling the connection and disconnection between the second hydraulic pump and the low-pressure line, and also capable of controlling the connection and disconnection between the second hydraulic pump and the high-pressure line. A work machine characterized by the following features.

6. In the work machine described in claim 5, Third hydraulic pump and A third power source, which is an electric motor that drives the third hydraulic pump, The system includes a third switching device capable of controlling the connection and disconnection between the third hydraulic pump and the high-pressure line, and also capable of controlling the connection and disconnection between the third hydraulic pump and the low-pressure line, The control device controls the rotational speed of the electric motors, which are the first power source, the second power source, and the third power source, based on the detection results of the pressure sensor and the manipulated amount sensor. A work machine characterized by the following features.