Work machine

Abstract

Provided is a work machine capable of increasing the speed of a hydraulic actuator while suppressing the flow rate of a hydraulic oil supplied from a regeneration device to the hydraulic actuator.　A controller in the work machine measures the operation amount of an operation device with respect to a predetermined hydraulic actuator, determines whether a predetermined movable member is in a power running state or a self-weight falling state, and outputs, when the predetermined movable member is determined to be in the power running state, a control signal to an assist control valve so as to increase the opening amount of the assist control valve as the operation amount increases and to increase the opening amount of the assist control valve as the pressure detected by a first pressure detector decreases.

Description

Work machinery

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

[0002] Hydraulic excavators, which are one type of work machine, are used for a variety of tasks, including excavation, loading dump trucks, and leveling. In light of environmental issues and running costs, there is a strong demand for reduced fuel consumption in work machines, including hydraulic excavators. While fuel economy can be reduced by, for example, reducing engine load and reducing fuel consumption per short period of time, it can also be achieved by increasing the amount of work done per unit of fuel consumption. Furthermore, from the perspectives of workability and operability, it is important to increase the actuator drive speed to approach the work speed intended by the operator as closely as possible. Patent Document 1, for example, is a prior art document disclosing such a work machine.

[0003] The hydraulic drive system for a work machine described in Patent Document 1 is equipped with a mechanism that can assist the operation of the engine through the hydraulic motor using an accumulator, and by calculating the assistable torque based on the amount of pressure stored in the accumulator and increasing the capacity of the hydraulic motor, it is possible to operate so that the absorption torque of the main pump exceeds the upper limit torque of the engine, thereby making it possible to bring the working speed of the hydraulic actuator closer to the speed required by the operator.

[0004] Patent No. 6987611

[0005] To ensure stable operation of the actuator while it is accelerated, it is necessary to secure a large amount of energy that can be used for assisting by storing pressure in a large-capacity accumulator to a high pressure. One method of storing pressure in an accumulator is to reuse (regenerate) the energy of the pressurized oil discharged from the actuator, but there is a limit to the amount of energy that can be regenerated. It is also possible to store pressure by sending pressurized oil from a hydraulic pump to the accumulator, but this requires a major review of the installation layout to install an additional pump. Furthermore, there is an upper limit to the accumulator capacity when considering installation on the work machine and the strength of the structure. For this reason, it is important to increase the speed of the actuator while minimizing the amount of assistance provided by the accumulator as much as possible.

[0006] The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a work machine that is capable of increasing the speed of a hydraulic actuator while suppressing the flow rate of pressurized oil supplied from a regenerative device to the hydraulic actuator.

[0007] In order to achieve the above object, the present invention provides a front device including a vehicle body, a front device having a plurality of movable members attached to the vehicle body, a plurality of hydraulic actuators for driving the vehicle body and the plurality of movable members, a hydraulic pump for supplying pressure oil to the plurality of hydraulic actuators, an operating device for instructing operation of the plurality of hydraulic actuators, a plurality of directional control valves for controlling the flow rate of pressure oil supplied from the hydraulic pump to the plurality of hydraulic actuators, a regenerative device capable of regenerating energy of pressure oil, an assist oil passage connecting a predetermined hydraulic actuator for driving a predetermined movable member of the plurality of movable members to the regenerative device, an assist control valve provided in the assist oil passage, a first pressure detector for detecting the pressure of pressure oil discharged from the regenerative device, and a control device for controlling the operation device and the a controller that receives a signal from a first pressure detector and outputs control signals to the plurality of directional control valves and the assist control valve, wherein the controller measures the amount of operation of the operating device for the predetermined hydraulic actuator, controls the opening amount of a predetermined directional control valve among the plurality of directional control valves that corresponds to the predetermined hydraulic actuator in accordance with the amount of operation, determines whether the predetermined movable member is in a powering state or a gravity-falling state, and, when it is determined that the predetermined movable member is in the powering state, outputs a control signal to the assist control valve so that the opening amount of the assist control valve increases as the amount of operation increases and the opening amount of the assist control valve increases as the pressure detected by the first pressure detector decreases.

[0008] According to the present invention, in a work machine, it is possible to increase the speed of a hydraulic actuator while suppressing the flow rate of pressure oil supplied from a regenerative device to the hydraulic actuator.

[0009] Fig. 1 is a side view of a hydraulic excavator according to a first embodiment of the present invention. Fig. 2 is a hydraulic circuit diagram of a hydraulic drive system according to a first embodiment of the present invention. Fig. 3 is a functional block diagram of a controller according to a first embodiment of the present invention. Fig. 4 is a diagram showing the opening characteristics of an assist control valve realized by an assist control valve opening control section according to the first embodiment of the present invention. Fig. 5 is a diagram showing the opening characteristics of an arm direction switching valve realized by an arm direction switching valve opening control section according to the first embodiment of the present invention. Fig. 6 is a hydraulic circuit diagram of a hydraulic drive system according to a second embodiment of the present invention. Fig. 7 is a functional block diagram of a controller according to the second embodiment of the present invention. Fig. 8 is a hydraulic circuit diagram of a hydraulic drive system according to a third embodiment of the present invention.

[0010] Hereinafter, an embodiment of a work machine according to the present invention will be described with reference to the drawings. In each drawing, the same components are designated by the same reference numerals, and duplicated explanations will be omitted where appropriate. Furthermore, although a hydraulic excavator will be used as an example in this embodiment, the present invention can also be applied to other work machines such as wheel loaders, dump trucks, and hydraulic cranes.

[0011] 1 is a side view of a hydraulic excavator 100 according to a first embodiment of the present invention. The hydraulic excavator 100 includes a traveling body 3 having a pair of left and right traveling devices 1, 2, a revolving body 4 (vehicle body) mounted on the traveling body 3, a boom 5 (movable member) having one end rotatably connected to the revolving body 4 by a pin, an arm 6 (movable member) having one end rotatably connected to the boom 5 by a pin, and a bucket 7 (movable member) having one end rotatably connected to the arm 6 by a pin. The boom 5, arm 6, and bucket 7 form a front device 101. A cab 8, a machine room 9 for accommodating an engine and a hydraulic pump, a counterweight 10, etc. are provided on the revolving body 4.

[0012] The traveling devices 1 and 2 are driven by traveling motors 11 and 12, and the rotating body 4 is driven by a swing motor 13. The boom 5 is driven by boom cylinders 14 and 15 (hydraulic actuators), the arm 6 is driven by an arm cylinder 16 (hydraulic actuator), and the bucket 7 is driven by a bucket cylinder 17 (hydraulic actuator). The attitudes of the boom 5, arm 6, and bucket 7 are determined by the amount of movement of the boom cylinders 14 and 15, arm cylinder 16, and bucket cylinder 17 in the extension / retraction direction.

[0013] Fig. 2 is a hydraulic circuit diagram of a hydraulic drive system 200 mounted on the hydraulic excavator 100. Note that Fig. 2 only shows the parts related to the drive of the boom cylinder 14 and the arm cylinder 16, and omits the parts related to the drive of the other hydraulic actuators.

[0014] In FIG. 2 , the hydraulic drive system 200 includes a boom cylinder 14, an arm cylinder 16, hydraulic pumps 18, 24, a boom direction switching valve 19, an arm direction switching valve 25, a regenerative control valve 30, an accumulator 32 (regenerative device), an assist control valve 34, a boom operation device 20, an arm operation device 26, and a controller 38.

[0015] The boom direction switching valve 19 controls the flow rate of pressurized oil supplied from the hydraulic pump 18 to one side (bottom side or rod side) of the boom cylinder 14, and also controls the flow rate of pressurized oil discharged from the other side (rod side or bottom side) of the boom cylinder 14 to the tank 23, thereby driving the boom cylinder 14. The boom direction switching valve 19 switches to either position 19a or 19b in response to a control signal from a controller 38. The controller 38 outputs a control signal for the boom direction switching valve 19 in response to an operation signal input from the boom operation device 20. This allows the operator of the hydraulic excavator 100 to instruct the operation of the boom cylinder 14 by operating the boom operation device 20.

[0016] When the boom cylinder 14 is extended (boom-raising operation), the boom direction switching valve 19 is switched to position 19a, so that the pressurized oil discharged from the hydraulic pump 18 flows into the bottom side of the boom cylinder 14 through oil passage 21, and the pressurized oil discharged from the rod side of the boom cylinder 14 is returned to the tank 23 through oil passage 22. When the boom cylinder 14 is retracted (boom-lowering operation), the boom direction switching valve 19 is switched to position 19b, so that the pressurized oil discharged from the hydraulic pump 18 flows into the rod side of the boom cylinder 14 through oil passage 22, and the pressurized oil discharged from the bottom side of the boom cylinder 14 is returned to the tank 23 through oil passage 21.

[0017] The arm direction switching valve 25 controls the flow rate of pressure oil supplied from the hydraulic pump 24 to one side (bottom side or rod side) of the arm cylinder 16, and also controls the flow rate of pressure oil discharged from the other side (rod side or bottom side) of the arm cylinder 16 to the tank 23, thereby driving the arm cylinder 16. The arm direction switching valve 25 receives a control signal from a controller 38 and switches to either position 25a or 25b. The controller 38 outputs a control signal for the arm direction switching valve 25 in accordance with an operation signal input from the arm operating device 26. This allows the operator of the hydraulic excavator 100 to instruct the operation of the arm cylinder 16 by operating the arm operating device 26.

[0018] When performing an extension operation (arm pulling operation) of the arm cylinder 16, the arm direction switching valve 25 is switched to the position 25a side, so that the pressure oil discharged from the hydraulic pump 24 flows into the bottom side of the arm cylinder 16 through the oil passage 27, and the pressure oil discharged from the rod side of the arm cylinder 16 is returned to the tank 23 through the oil passage 28. When performing a retraction operation (arm pushing operation) of the arm cylinder 16, the arm direction switching valve 25 is switched to the position 25b side, so that the pressure oil discharged from the hydraulic pump 24 flows into the rod side of the arm cylinder 16 through the oil passage 28, and the pressure oil discharged from the bottom side of the arm cylinder 16 is returned to the tank 23 through the oil passage 27.

[0019] Oil line 21 connected to the bottom side of boom cylinder 14 is connected to one port of regenerative control valve 30 via regenerative oil line 29. The other port of regenerative control valve 30 is connected to accumulator 32 via oil line 31. By switching regenerative control valve 30 to position 30a during the boom lowering operation, pressurized oil discharged from the bottom side of boom cylinder 14 can be stored in accumulator 32.

[0020] The oil passage 28 connected to the rod side of the arm cylinder 16 is connected to one port of the assist control valve 34 via an assist oil passage 33. The other port of the assist control valve 34 is connected to an accumulator 32 via an oil passage 31. By switching the assist control valve 34 to the position 34a side during the arm pushing operation, the pressurized oil discharged from the accumulator 32 can be sent to the rod side of the arm cylinder 16.

[0021] The oil passage 31 is provided with a pressure detector 35 (first pressure detector) that detects the pressure of the accumulator 32. The oil passage 27 is provided with a pressure detector 36 (second pressure detector) that detects the pressure on the bottom side of the arm cylinder 16. The oil passage 28 is provided with a pressure detector 37 (second pressure detector) that detects the pressure on the rod side of the arm cylinder 16.

[0022] 3 is a functional block diagram of the controller 38. The controller 38 has a pressure measurement unit 39, an operation state determination unit 40, an operation amount measurement unit 41, an assist control valve opening control unit 42, and an arm directional control valve opening control unit 43. The controller 38 is equipped with a calculation unit such as a CPU, storage devices such as a ROM and RAM, an input / output interface for inputting and outputting signals to and from external devices, and realizes the functions of each unit by loading a program stored in the ROM or the like onto the RAM and executing it.

[0023] The pressure measuring unit 39 measures the pressure of the accumulator 32 and the pressures on the bottom side and rod side of the arm cylinder 16 based on the signals input from the pressure detectors 35 to 37 .

[0024] The motion state determination unit 40 determines whether the motion of the front device 101 is an arm pushing motion based on a signal input from the arm operating device 26, and also determines whether the arm 6 is in a powering state or a gravity-falling state during the arm pushing motion based on the pressures on the bottom side and rod side of the arm cylinder 16 measured by the pressure measurement unit 39. Specifically, when the determination formula expressed by the following formula (1) is positive, it is determined to be in a powering state, and when it is negative it is determined to be in a gravity-falling state. The powering state is a state in which the arm moves in a direction against gravity, and the gravity-falling state is a state in which the arm moves in a direction following gravity.

[0025] Determination formula=rod side pressure×rod side pressure receiving area−bottom side pressure×bottom side pressure receiving area (1) The operation amount measuring unit 41 measures the operation amount of the arm pushing operation from the signal detected by the arm operating device 26.

[0026] When the operation state determination unit 40 determines that the arm 6 is in a powering state, the assist control valve opening control unit 42 controls the opening amount of the assist control valve 34 in accordance with the opening characteristics shown in Fig. 4. By increasing the opening amount of the assist control valve 34 as the arm pushing operation amount increases, the flow rate required to accelerate the arm pushing operation is secured from the accumulator 32. When the pressure in the accumulator 32 is low and the difference with the pressure on the rod side of the arm cylinder 16 is small, the flow rate is secured by increasing the opening amount of the assist control valve 34. Furthermore, when the speed-up ratio is large, the flow rate required for acceleration also increases, so the assist control valve opening amount is further increased. The speed-up ratio is stored in advance in the controller 38 and is expressed by the following equation (2).

[0027] Speed-up ratio = arm pushing speed with speed-up control / arm pushing speed without speed-up control (2) Figure 5 is a diagram showing the opening characteristics of the arm direction switching valve 25 realized by the arm direction switching valve opening control unit 43. As the arm pushing operation amount increases, the opening amount of the arm direction switching valve 25 is increased, and the flow rate of pressure oil supplied from the hydraulic pump 24 to the rod side of the arm cylinder 16 or the flow rate of pressure oil discharged from the bottom side of the arm cylinder 16 to the tank 23 is increased. In a state of falling due to gravity during an arm pushing operation, the speed of the arm 6 is affected by the amount of throttling in the oil path from where the pressure oil discharged from the bottom side of the arm cylinder 16 flows to the tank 23. Therefore, the speed of the arm cylinder 16 can be increased by increasing the opening amount of the arm direction switching valve 25 (reducing the amount of throttling) according to the speed-up ratio.

[0028] Here, if the opening amount of the arm directional control valve 25 is increased to increase the speed in a state where the arm 6 is falling under its own weight, the hydraulic pump 24 alone cannot provide the flow rate of pressurized oil flowing into the rod side of the arm cylinder 16, and there is a risk that negative pressure will be created on the rod side of the arm cylinder 16. Therefore, when the operation state determination unit 40 determines that the arm 6 is in a state where the arm 6 is falling under its own weight, the assist control valve opening control unit 42 slightly opens the assist control valve 34 to allow the pressurized oil stored in the accumulator 32 to flow to the bottom side of the arm cylinder 16. Specifically, the opening amount of the assist control valve 34 is increased to an extent that the pressure on the rod side of the arm cylinder 16 detected by the pressure detector 37 does not fall below a predetermined threshold value (for example, a value obtained by adding a margin to atmospheric pressure). This makes it possible to increase the speed of the arm cylinder 16 while preventing negative pressure from being created on the rod side of the arm cylinder 16 when the arm 6 is in a state where the arm 6 is falling under its own weight.

[0029] (Summary) In the first embodiment, the vehicle includes a vehicle body 4, a front device 101 having a plurality of movable members 5 to 7 attached to the vehicle body 4, a plurality of hydraulic actuators 13 to 17 that drive the vehicle body 4 and the plurality of movable members 5 to 7, hydraulic pumps 18, 24 that supply pressure oil to the plurality of hydraulic actuators 13 to 17, operation devices 20, 26 that instruct the operation of the plurality of hydraulic actuators 13 to 17, a plurality of directional control valves 19, 25 that control the flow rate of pressure oil supplied from the hydraulic pumps 18, 24 to the plurality of hydraulic actuators 13 to 17, a regenerative device 32 that can regenerate energy of the pressure oil, an assist oil passage 33 that connects the regenerative device 32 to a predetermined hydraulic actuator 16 that drives a predetermined movable member 6 of the plurality of movable members 5 to 7, an assist control valve 34 provided in the assist oil passage 33, and a first pressure detector 31 that detects the pressure of the pressure oil released from the regenerative device 32. and a controller 38 that receives signals from the operating device 26 and the first pressure detector 35 and outputs control signals to the plurality of directional control valves 19, 25 and the assist control valve 34. The controller 38 measures the amount of operation of the operating device 26 for a predetermined hydraulic actuator 16, controls the amount of opening of a predetermined directional control valve 19 of the plurality of directional control valves 19, 25 that corresponds to the predetermined hydraulic actuator 16 in accordance with the amount of operation, determines whether a predetermined movable member 6 is in a powering state or a state of falling under its own weight, and, when it is determined that the predetermined movable member 6 is in the powering state, outputs a control signal to the assist control valve 34 so that the amount of opening of the assist control valve 34 increases as the amount of operation increases and the opening of the assist control valve 34 increases as the pressure detected by the first pressure detector 35 decreases.

[0030] According to the first embodiment configured as described above, when the movable member 6 is in a powering state, pressure oil is supplied from the regenerative device 32 to the hydraulic actuator 16 at a flow rate corresponding to the amount of operation of the operating device 26 on the hydraulic actuator 16 that drives the movable member 6, regardless of pressure fluctuations in the pressure oil released from the regenerative device 32. This makes it possible in the hydraulic excavator 100 to increase the speed of the hydraulic actuator 16 while suppressing the flow rate of pressure oil supplied from the regenerative device 32 to the hydraulic actuator 16.

[0031] Moreover, in the first embodiment, the predetermined hydraulic actuator 16 is a hydraulic cylinder 16, the hydraulic excavator 100 (work machine) is further provided with second pressure detectors 36, 37 that detect the pressures on the discharge and inlet sides of the hydraulic cylinder 16, and the controller 38 determines that the predetermined movable member 6 is in the powering state when the product of the pressure and the pressure on the inlet side of the hydraulic cylinder 16 is greater than the product of the pressure and the pressure on the discharge side of the hydraulic cylinder 16, and determines that the predetermined movable member 6 is in the gravity-falling state when the product of the pressure and the pressure on the inlet side of the hydraulic cylinder 16 is less than the product of the pressure and the pressure on the discharge side of the hydraulic cylinder 16. This makes it possible to determine whether the predetermined movable member 6 is in the powering state or the gravity-falling state based on the pressures on the discharge and inlet sides of the hydraulic cylinder 16.

[0032] In the first embodiment, the regenerative device 32 has an accumulator 32 that stores pressurized oil discharged from the boom cylinder 14 (at least one of the hydraulic actuators 13 to 17). This makes it possible to efficiently regenerate the energy of the pressurized oil discharged from the boom cylinder 14. The accumulator 32 may store pressurized oil discharged from another hydraulic actuator (for example, the swing motor 13), or may store pressurized oil discharged from the hydraulic pumps 18 and 24.

[0033] In the first embodiment, the controller 38 stores the speed increase ratio of the predetermined hydraulic actuator 16, outputs a control signal to the assist control valve 34 so as to increase the opening of the assist control valve 34 as the speed increase ratio increases, and outputs a control signal to the predetermined directional control valve 25 so as to increase the opening of the predetermined directional control valve 25 as the speed increase ratio increases. This makes it possible to increase the speed of the hydraulic cylinder 16 in accordance with the speed increase ratio.

[0034] Moreover, in the first embodiment, the hydraulic excavator 100 (work machine) further includes a second pressure detector 37 that detects the pressure on the inlet side of the predetermined hydraulic actuator 16, and when it is determined that the predetermined movable member 6 is in the gravity-falling state, the controller 38 outputs a control signal to the assist control valve 34 so that the assist control valve 34 opens and pressure oil is supplied from the regenerative device 32 to the predetermined hydraulic actuator 16 so that the pressure detected by the second pressure detector 37 does not fall below a predetermined threshold. As a result, when the predetermined movable member 6 is in the gravity-falling state, it is possible to increase the speed of the predetermined hydraulic actuator 16 while minimizing consumption of pressure oil stored in the accumulator 32.

[0035] The second embodiment of the present invention will be described, focusing on the differences from the first embodiment.

[0036] 6 is a hydraulic circuit diagram of a hydraulic drive system 200 according to the second embodiment. The hydraulic drive system 200 according to the present embodiment includes a stroke amount detector 44 that detects the stroke amount of the arm cylinder 16, instead of the pressure detectors 37 and 36 (shown in FIG. 2). A signal from the stroke amount detector 44 is input to the controller 38.

[0037] 7 is a functional block diagram of the controller 38 in the second embodiment. The controller 38 in this embodiment further includes a stroke amount measuring unit 45.

[0038] The stroke amount measuring unit 45 measures the stroke amount of the arm cylinder 16 based on the signal from the stroke amount detector 44 .

[0039] The operation state determination unit 40 determines whether the operation of the front device 101 is an arm pushing operation based on a signal input from the arm operating device 26, and also determines whether the arm 6 is in a powered state or a gravity-falling state during the arm pushing operation based on the stroke amount of the arm cylinder 16 measured by the stroke amount measurement unit 45. In the arm pushing operation, a small stroke amount indicates a powered state, and a large stroke amount indicates a gravity-falling state. Therefore, a threshold value is set for the stroke amount, and a stroke amount smaller than the threshold is determined to be a powered state, and a stroke amount larger than the threshold is determined to be a gravity-falling state. Note that, depending on how the stroke amount detector 44 is attached, the smaller the detected stroke amount, the more extended the arm cylinder 16 may be. In that case, a stroke amount larger than the threshold is determined to be a powered state, and a stroke amount smaller than the threshold is determined to be a gravity-falling state.

[0040] (Summary) In the second embodiment, the multiple movable members 5 to 7 possessed by the front device 101 include a boom 5 rotatably attached to the vehicle body 4, and an arm 6 rotatably attached to the tip of the boom 5, the hydraulic cylinder 16 that drives a predetermined movable member 6 of the multiple movable members 5 to 7 is the arm cylinder 16 that drives the arm 6, the hydraulic excavator 100 (work machine) further includes a stroke amount detector 44 that detects the stroke amount of the arm cylinder 16, and when a retraction operation of the arm cylinder 16 is instructed via the operation device 26, the controller 38 determines whether the arm 6 is in a powered state or a gravity falling state based on the magnitude relationship between the stroke amount and a predetermined threshold value.

[0041] In the second embodiment configured as described above, the same effects as those of the first embodiment can be obtained. Furthermore, it is possible to determine whether the arm 6 is in a powered state or a gravity falling state based on the stroke amount of the arm cylinder 16.

[0042] The third embodiment of the present invention will be described, focusing on the differences from the first embodiment.

[0043] 8 is a hydraulic circuit diagram of a hydraulic drive system 200 according to a third embodiment. The hydraulic drive system 200 according to this embodiment includes an electric storage device 46, a generator 47, and a hydraulic motor 48 instead of the accumulator 32 (shown in FIG. 2).

[0044] By switching the regenerative control valve 30 to position 30a during the boom lowering operation, the hydraulic motor 48 is driven by the pressurized oil discharged from the bottom side of the boom cylinder 14. The rotational force of the hydraulic motor 48 drives the generator 47, and the electricity generated by the generator 47 is stored in the power storage device 46 as electrical energy.

[0045] If the operation state determination unit 40 determines that the arm 6 is in a powering state during the arm pushing operation, the assist control valve 34 opens and the hydraulic motor 48 is driven as a pump by the electrical energy stored in the power storage device 46. As a result, pressure oil is sent from the hydraulic motor 48 to the arm cylinder 16, and the speed of the arm cylinder 16 increases.

[0046] (Summary) In the third embodiment, the regenerative device capable of regenerating the energy of pressurized oil includes a hydraulic motor 48 driven by pressurized oil discharged from the boom cylinder 14 (at least one hydraulic actuator among the plurality of hydraulic actuators 11 to 17), a generator 47 driven by the hydraulic motor 48, and a power storage device 46 that stores the electricity generated by the generator 47.

[0047] The third embodiment configured as described above also provides the same effects as the first embodiment. Furthermore, it is possible to convert the energy of the pressure oil discharged from the boom cylinder 14 into electrical energy and store it.

[0048] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments are presented to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0049] DESCRIPTION OF SYMBOLS 1, 2...Traveling device, 3...Travel body, 4...Swing body (vehicle body), 5...Boom (movable member), 6...Arm (movable member), 7...Bucket (movable member), 8...Driver's cab, 9...Machine room, 10...Counterweight, 11, 12...Travel motor (hydraulic actuator), 13...Swing motor (hydraulic actuator), 14...Boom cylinder (hydraulic actuator), 15...Boom cylinder (hydraulic actuator), 16...Arm cylinder (hydraulic actuator, hydraulic cylinder), 17...Bucket cylinder (hydraulic actuator), 18...Hydraulic pump, 19...Boom direction switching valve, 19a, 19b...Position, 20...Boom operation device, 21, 22...Oil line, 23...Tank, 24...Hydraulic pump, 25...Arm direction switching valve, 25a, 25b... Position, 26...arm operating device, 27, 28...oil passage, 29...regenerative oil passage, 30...regenerative control valve, 30a...position, 31...oil passage, 32...accumulator (regenerative device), 33...assist oil passage, 34...assist control valve, 34a...position, 35...pressure detector (first pressure detector), 36...pressure detector (second pressure detector), 37...pressure detector (second pressure detector), 38...controller, 39...pressure measurement unit, 40...operation state determination unit, 41...operation amount measurement unit, 42...assist control valve opening control unit, 43...arm directional switching valve opening control unit, 44...stroke amount detector, 45...stroke amount measurement unit, 46...electricity storage device, 47...generator, 48...hydraulic motor, 100...hydraulic excavator (work machine), 101...front device, 200...hydraulic drive device.

Claims

a front device attached to the vehicle body and having a plurality of movable members; a plurality of hydraulic actuators for driving the vehicle body and the plurality of movable members; a hydraulic pump for supplying pressurized oil to the plurality of hydraulic actuators; an operating device for instructing the operation of the plurality of hydraulic actuators; a plurality of directional control valves for controlling the flow rate of pressurized oil supplied from the hydraulic pump to the plurality of hydraulic actuators; a regenerative device capable of regenerating energy of the pressurized oil; an assist oil line connecting a predetermined hydraulic actuator for driving a predetermined movable member of the plurality of movable members to the regenerative device; an assist control valve provided in the assist oil line; a first pressure detector for detecting the pressure of the pressurized oil released from the regenerative device; and a controller which receives signals from the operating device and the first pressure detector and outputs control signals to the plurality of directional control valves and the assist control valve, wherein the controller measures the amount of operation of the operating device for the predetermined hydraulic actuator, and controls the opening amount of a predetermined directional control valve of the plurality of directional control valves corresponding to the predetermined hydraulic actuator in accordance with the amount of operation, a control signal output to the assist control valve so that the opening amount of the assist control valve increases as the operation amount increases and the opening amount of the assist control valve increases as the pressure detected by the first pressure detector decreases, when the predetermined movable member is determined to be in the powering state.

2. A work machine as claimed in claim 1, wherein the predetermined hydraulic actuator is a hydraulic cylinder, and the work machine further comprises a second pressure detector for detecting the pressure on the inlet and outlet sides of the hydraulic cylinder, and the controller determines that the predetermined movable member is in the powering state when the product of the pressure-receiving area and pressure on the inlet side of the hydraulic cylinder is greater than the product of the pressure-receiving area and pressure on the outlet side of the hydraulic cylinder, and determines that the predetermined movable member is in the gravity-falling state when the product of the pressure-receiving area and pressure on the inlet side of the hydraulic cylinder is less than the product of the pressure-receiving area and pressure on the outlet side of the hydraulic cylinder.

3. A work machine as claimed in claim 1, wherein the plurality of movable members include a boom rotatably attached to the vehicle body and an arm rotatably attached to the tip of the boom, the predetermined hydraulic actuator is an arm cylinder that drives the arm, the work machine further comprises a stroke amount detector that detects the stroke amount of the arm cylinder, and the controller, when instructed to retract the arm cylinder via the operating device, determines whether the arm is in the powered state or the gravity-falling state based on the magnitude relationship between the stroke amount and a predetermined threshold value.

4. A work machine according to claim 1, wherein the regenerative device has an accumulator that stores pressurized oil discharged from at least one hydraulic actuator among the plurality of hydraulic actuators.

5. A work machine according to claim 1, characterized in that the regenerative device comprises a hydraulic motor driven by pressurized oil discharged from at least one of the plurality of hydraulic actuators, a generator driven by the hydraulic motor, and an electricity storage device that stores the electricity generated by the generator.

6. A work machine according to claim 1, wherein the controller stores the speed increase ratio of the specified hydraulic actuator, outputs a control signal to the assist control valve so as to increase the opening of the assist control valve as the speed increase ratio increases, and outputs a control signal to the specified directional control valve so as to increase the opening of the specified directional control valve as the speed increase ratio increases.

7. A work machine as claimed in claim 1, further comprising a second pressure detector for detecting the pressure on the inlet side of the specified hydraulic actuator, wherein when it is determined that the specified movable member is in the gravity falling state, the controller outputs a control signal to the assist control valve so that the assist control valve opens and pressure oil is supplied from the regenerative device to the specified hydraulic actuator so that the pressure detected by the second pressure detector does not fall below a specified threshold.

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