Work Machine

Abstract

This work machine comprises a flow rate control valve as a flow rate control mechanism that controls the flow rate of pressure oil from a hydraulic pump to a hydraulic actuator via a first control valve. When pressure oil is supplied to the hydraulic actuator only from an accumulator, a control device for the work machine drives a second control valve so as to connect the meter-in side of the hydraulic actuator to the accumulator, drives the first control valve so as to connect the meter-out side of the hydraulic actuator to a tank, and drives the flow rate control mechanism so as to block the flow of pressure oil from the hydraulic pump to the hydraulic actuator via the first control valve.

Description

[Technical field]

[0001] The present invention relates to a work machine, and more particularly to a work machine that is provided with an accumulator in addition to a hydraulic pump as a hydraulic source that supplies pressure oil to a hydraulic actuator. [Background technology]

[0002] In some working machines such as hydraulic excavators and cranes, in order to reduce losses in the hydraulic pump, an accumulator is provided that stores the pressurized oil discharged from the hydraulic pump, and an actuator that operates with the pressurized oil from the hydraulic pump and the accumulator. When the power required to drive the actuator is small, a part of the pressurized oil discharged from the hydraulic pump is stored in the accumulator, and when the power required to drive the actuator is large, the pressurized oil stored in the accumulator is supplied to the actuator. As such a working machine, for example, one equipped with a hydraulic drive unit described in Patent Document 1 is known. The hydraulic drive unit of the working machine described in Patent Document 1 is equipped with one circuit that supplies pressurized oil directly from the hydraulic pump to the hydraulic actuator via a valve (flow control valve), and another circuit that supplies the pressurized oil stored in the accumulator to the hydraulic actuator via another valve (flow control valve), and it is possible to supply pressurized oil to the hydraulic actuator from a more efficient circuit (one circuit or another circuit) depending on the operation of the working machine. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 061165 Summary of the Invention [Problem to be solved by the invention]

[0004] In the hydraulic drive system of the working machine described in Patent Document 1, in addition to a valve for one circuit that directly supplies pressure oil from a hydraulic pump to a hydraulic actuator, another valve for another circuit that supplies pressure oil stored in an accumulator to a hydraulic actuator is added. In addition to a return oil passage (a line connecting flow control valves 8 and 9 and a tank in FIG. 4 of Patent Document 1) for returning return oil discharged from the hydraulic actuator to a tank via a valve (flow control valve) of one circuit, a return oil passage (a line connecting flow control valve 20 and a tank in FIG. 4) for returning the return oil to a tank via another valve (flow control valve) of the other circuit is also added. In this configuration, if it is necessary to control the meter-out flow rate when pressure oil is supplied from the accumulator to the hydraulic actuator via another valve of the other circuit, it is necessary to further add a flow control valve to the return oil passage connected to the other valve. In this way, when an accumulator is added as a hydraulic source that supplies pressurized oil to the hydraulic actuator, a problem occurs in that the configuration of the hydraulic system becomes complicated by the need to provide a return oil passage and a flow control valve (meter-out side circuit) for the valve (flow control valve) that supplies pressurized oil from the accumulator to the hydraulic actuator.

[0005] The present invention has been made to solve the above problems, and an object of the present invention is to provide a work machine that can suppress the complexity of the configuration in a hydraulic system that is capable of supplying pressurized oil to a hydraulic actuator from an accumulator other than a hydraulic pump. [Means for solving the problem]

[0006] The present application includes a plurality of means for solving the above-mentioned problems. As one example, in a work machine including a hydraulic pump that discharges pressure oil, a hydraulic actuator driven by the pressure oil discharged from the hydraulic pump, a tank that stores return oil discharged from the hydraulic actuator, an accumulator that stores the pressure oil discharged from the hydraulic pump and supplies the stored pressure oil to the hydraulic actuator, a first control valve that controls the connection between a meter-in side of the hydraulic actuator and the hydraulic pump and also controls the connection between a meter-out side of the hydraulic actuator and the tank, and a second control valve that controls the connection between the meter-in side of the hydraulic actuator and the accumulator, and a control device which controls the first control valve, the second control valve, and the flow control mechanism, wherein when pressure oil is supplied to the hydraulic actuator only from the accumulator, the control device drives the second control valve to connect a meter-in side of the hydraulic actuator to the accumulator, drives the first control valve to connect a meter-out side of the hydraulic actuator to the tank, and drives the flow control mechanism to block the flow of pressure oil from the hydraulic pump to the hydraulic actuator via the first control valve. Effect of the Invention

[0007] According to the present invention, when pressure oil is supplied to the hydraulic actuator only from the accumulator, the meter-out side of the hydraulic actuator is connected to the tank by driving the first control valve, and the flow of pressure oil from the hydraulic pump to the hydraulic actuator via the first control valve is blocked by driving the flow control mechanism, so that even when pressure oil is supplied to the hydraulic actuator from the accumulator, the return oil of the hydraulic actuator can be discharged to the tank via the first control valve. In other words, the control of the flow on the meter-out side of the hydraulic actuator can be realized only by the first control valve. Therefore, there is no need to provide a meter-out circuit such as a return oil path or a flow control valve for the second control valve, and the configuration can be prevented from becoming complicated in a hydraulic system that can supply pressure oil from the accumulator to the hydraulic actuator other than the hydraulic pump. Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is an external view showing a hydraulic excavator as a work machine according to a first embodiment of the present invention. [Diagram 2] 1 is a hydraulic circuit diagram showing the configuration of a hydraulic system provided in a work machine according to a first embodiment. [Diagram 3] 3 is a diagram showing a part of the hydraulic system (a circuit for driving a boom) of the work machine according to the first embodiment shown in FIG. 2, together with a control device. [Figure 4] 3 is an opening area diagram of a directional control valve for a pump in the hydraulic system according to the first embodiment shown in FIG. 2. [Diagram 5] 3 is an opening area diagram of a pump flow control valve of the hydraulic system according to the first embodiment shown in FIG. 2. [Figure 6] 4 is a block diagram showing a control logic in the control device for the work machine according to the first embodiment shown in FIG. 3. [Figure 7] 7 is a table used by an operation pattern calculation unit of the control device according to the first embodiment shown in FIG. 6. [Figure 8]FIG. 5 is a hydraulic circuit diagram showing the configuration of a hydraulic system provided in a work machine according to a second embodiment of the present invention. [Figure 9] FIG. 9 is an opening area diagram of a directional control valve for a pump in the hydraulic system according to the second embodiment shown in FIG. 8. [Figure 10] 9 is a block diagram showing a control logic of a control device for the hydraulic system according to the second embodiment shown in FIG. 8. [Figure 11] FIG. 11 is a hydraulic circuit diagram showing the configuration of a hydraulic system provided in a work machine according to a third embodiment of the present invention. [Figure 12] 12 is an opening area diagram of a directional control valve for a pump in the hydraulic system according to the third embodiment shown in FIG. [Figure 13] 12 is a block diagram showing a control logic of a control device for the hydraulic system according to the third embodiment shown in FIG. 11. FIG. [Figure 14] FIG. 14 is a characteristic diagram used by a function generator of the control device according to the third embodiment shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a work machine according to the present invention will be described with reference to the drawings. In this embodiment, a hydraulic excavator will be described as an example of a work machine.

[0010] [First embodiment] First, a schematic configuration of a hydraulic excavator as a work machine according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is an external view showing a hydraulic excavator as a work machine according to a first embodiment of the present invention. Here, the description will be given using the direction as seen by an operator seated in the driver's seat.

[0011] 1, a hydraulic excavator as a work machine includes a self-propelled lower traveling body 1, an upper rotating body 2 rotatably mounted on the lower traveling body 1, and a front working device 3 provided at the front of the upper rotating body 2 so as to be capable of ascending and descending. The upper rotating body 2 is configured to be rotated relative to the lower traveling body 1 by a swing hydraulic motor 5 which is a hydraulic actuator.

[0012] The lower traveling body 1 has, for example, crawler-type traveling devices 11 (only the left one is shown in FIG. 1) on both the left and right sides. The left and right traveling devices 11 are each operated to travel by a traveling hydraulic motor 11a which is a hydraulic actuator.

[0013] The upper rotating body 2 includes a rotating frame 13 as a support structure rotatably mounted on the lower traveling body 1, a cab 14 installed on the left front side of the rotating frame 13, a counterweight 15 provided at the rear end of the rotating frame 13, and a machine room 16 provided between the cab 14 and the counterweight 15. Inside the cab 14, a driver's seat (not shown) where an operator sits, an operating device 7 (see FIG. 3 described later), and the like are arranged. The counterweight 15 is for achieving weight balance with the front working mechanism 3. The machine room 16 houses various devices such as hydraulic pumps 31, 32, a prime mover 33, and control valve units 40, 80 (see FIG. 2 described later), which will be described later.

[0014] The front working mechanism 3 is for performing various operations such as excavation work, and is, for example, an articulated working mechanism configured by connecting a plurality of driven members so that they can rotate vertically. The plurality of driven members are, for example, configured with a boom 18, an arm 19, and a bucket 20 as a working tool. The base end of the boom 18 is supported on the front part of the revolving frame 13 of the upper revolving body 2 so that it can rotate vertically. The base end of the arm 19 is supported on the tip of the boom 18 so that it can rotate vertically. The base end of the bucket 20 is supported on the tip of the arm 19 so that it can rotate vertically. The boom 18, the arm 19, and the bucket 20 are operated by driving a boom cylinder 21, an arm cylinder 22, and a bucket cylinder 23, which are hydraulic actuators, respectively.

[0015] Next, the configuration of a hydraulic system provided in the work machine according to the first embodiment will be described with reference to Fig. 2. Fig. 2 is a hydraulic circuit diagram showing the configuration of the hydraulic system provided in the work machine according to the first embodiment.

[0016] In Fig. 2, the hydraulic excavator includes a hydraulic system 30 that hydraulically operates a lower traveling body 1, an upper rotating body 2, and a front working device 3 (see Fig. 1 for all). The hydraulic system 30 includes a first hydraulic pump 31 (hereinafter referred to as the first pump) and a second hydraulic pump 32 (hereinafter referred to as the second pump) that discharge pressure oil, a boom cylinder 21, an arm cylinder 22, a bucket cylinder 23, and a swing hydraulic motor 5 as hydraulic actuators driven by pressure oil supplied from the first pump 31 and the second pump 32, and a tank 34 that stores return oil discharged from the hydraulic actuators 21, 22, 23, and 5. A prime mover 33 is mechanically connected to the first pump 31 and the second pump 32, and the first pump 31 and the second pump 32 are driven by the power of the prime mover 33. The first pump 31 and the second pump 32 are, for example, variable displacement pumps, and have a regulator that adjusts the pump volume. The prime mover 33 is, for example, an engine or an electric motor.

[0017] The first pump 31 and the boom cylinder 21 are connected via a first boom direction control valve 41, and the second pump 32 and the boom cylinder 21 are connected via a second boom direction control valve 42. The first pump 31 and the arm cylinder 22 are connected via a first arm direction control valve 43, and the second pump 32 and the arm cylinder 22 are connected via a second arm direction control valve 44. The first pump 31 and the bucket cylinder 23 are connected via a bucket direction control valve 45. The second pump 32 and the swing hydraulic motor 5 are connected via a swing direction control valve 46.

[0018] The first boom direction control valve 41 controls the flow of pressure oil supplied from the first pump 31 to the boom cylinder 21, and also controls the flow of return oil discharged from the boom cylinder 21. The second boom direction control valve 42 controls the flow of pressure oil supplied from the second pump 32 to the boom cylinder 21, and also controls the flow of return oil of the boom cylinder 21. The first arm direction control valve 43 controls the flow of pressure oil supplied from the first pump 31 to the arm cylinder 22, and also controls the flow of return oil discharged from the arm cylinder 22. The second arm direction control valve 44 controls the flow of pressure oil supplied from the second pump 32 to the arm cylinder 22, and also controls the flow of return oil of the arm cylinder 22. The bucket direction control valve 45 controls the flow of pressure oil supplied from the first pump 31 to the bucket cylinder 23, and also controls the flow of return oil discharged from the bucket cylinder 23. The swing directional control valve 46 controls the flow of pressure oil supplied from the second pump 32 to the swing hydraulic motor 5 , and also controls the flow of return oil discharged from the swing hydraulic motor 5 .

[0019] In other words, the first boom direction control valve 41 controls the connection between the meter-in side of the boom cylinder 21 and the first pump 31, and also controls the connection between the meter-out side of the boom cylinder 21 and the tank 34. The second boom direction control valve 42 controls the connection between the meter-in side of the boom cylinder 21 and the second pump 32, and also controls the connection between the meter-out side of the boom cylinder 21 and the tank 34. The first arm direction control valve 43 controls the connection between the meter-in side of the arm cylinder 22 and the first pump 31, and also controls the connection between the meter-out side of the arm cylinder 22 and the tank 34. The second arm direction control valve 44 controls the connection between the meter-in side of the arm cylinder 22 and the second pump 32, and also controls the connection between the meter-out side of the arm cylinder 22 and the tank 34. The bucket direction control valve 45 controls the connection between the meter-in side of the bucket cylinder 23 and the first pump 31, and also controls the connection between the meter-out side of the bucket cylinder 23 and the tank 34. The swing directional control valve 46 controls the connection between the meter-in side of the swing hydraulic motor 5 and the second pump 32 , and also controls the connection between the meter-out side of the swing hydraulic motor 5 and the tank 34 .

[0020] Each of the directional control valves 41 to 46 is, for example, an open center type control valve that discharges pressure oil from the first pump 31 or the second pump 32 to the tank 34 when pressure oil is not supplied to the hydraulic actuators 21, 22, 23, 5. Specifically, each of the directional control valves 41 to 46 is, for example, a 6-port 3-position spool valve (6 ports: a pump port, a tank port, a pair of actuator ports, and a pair of center bypass ports).

[0021] The first boom directional control valve 41, the first arm directional control valve 43, and the bucket directional control valve 45 are provided in this order from the upstream side on a first center bypass line 37 connected to the first pump 31 via a first discharge line 35, for example, and are connected in tandem. The first center bypass line 37 connects the first pump 31 and the tank 34. A first center bypass cut valve 47 (hereinafter referred to as a first CB cut valve) is provided at the most downstream position of the first center bypass line 37. The first CB cut valve 47 controls the flow of pressure oil flowing from the first pump 31 to the tank 34 via the first center bypass line 37.

[0022] The second boom directional control valve 42, the second arm directional control valve 44, and the swing directional control valve 46 are provided, for example, in this order from the upstream side on a second center bypass line 38 connected to the second pump 32 via the second discharge line 36, and are connected in tandem. The second center bypass line 38 connects the second pump 32 and the tank 34. A second center bypass cut valve 48 (hereinafter referred to as a second CB cut valve) is provided at the most downstream position on the second center bypass line 38. The second CB cut valve 48 controls the flow of pressure oil flowing from the second pump 32 to the tank 34 via the second center bypass line 38.

[0023] A first boom flow control valve 51 is provided upstream of the meter-in side (pump port side) of the first boom directional control valve 41. The first boom flow control valve 51 controls the flow rate of pressurized oil supplied from the first pump 31 to the boom cylinder 21 via the first boom directional control valve 41. A second boom flow control valve 52 is provided upstream of the meter-in side (pump port side) of the second boom directional control valve 42. The second boom flow control valve 52 controls the flow rate of pressurized oil supplied from the second pump 32 to the boom cylinder 21 via the second boom directional control valve 42.

[0024] A first arm flow control valve 53 is provided upstream of the meter-in side (pump port side) of the first arm directional control valve 43. The first arm flow control valve 53 controls the flow rate of pressure oil supplied from the first pump 31 to the arm cylinder 22 via the first arm directional control valve 43. A second arm flow control valve 54 is provided upstream of the meter-in side (pump port side) of the second arm directional control valve 44. The second arm flow control valve 54 controls the flow rate of pressure oil supplied from the second pump 32 to the arm cylinder 22 via the second arm directional control valve 44.

[0025] A bucket flow rate control valve 55 is provided upstream of the meter-in side (pump port side) of the bucket directional control valve 45. The bucket flow rate control valve 55 controls the flow rate of pressure oil supplied from the first pump 31 to the bucket cylinder 23 via the bucket directional control valve 45.

[0026] A swing flow control valve 56 is provided upstream of the meter-in side (pump port side) of the swing directional control valve 46. The swing flow control valve 56 controls the flow rate of pressure oil supplied from the second pump 32 to the swing hydraulic motor 5 via the swing directional control valve 46.

[0027] The first boom direction control valve 41 is connected to the bottom side and rod side of the boom cylinder 21 via first boom actuator lines 61, 61, and the second boom direction control valve 42 is connected to the bottom side and rod side of the boom cylinder 21 via second boom actuator lines 62, 62. The first arm direction control valve 43 is connected to the bottom side and rod side of the arm cylinder 22 via first arm actuator lines 63, 63, and the second arm direction control valve 44 is connected to the bottom side and rod side of the arm cylinder 22 via second arm actuator lines 64, 64. The bucket direction control valve 45 is connected to the bottom side and rod side of the bucket cylinder 23 via first bucket actuator lines 65, 65. The swing direction control valve 46 is connected to the first port side and the second port side of the swing hydraulic motor 5 via first swing actuator lines 66, 66.

[0028] The meter-out side (tank port side) of the first boom direction control valve 41 is connected to the tank 34 via a first boom return line 71, and the meter-out side (tank port side) of the second boom direction control valve 42 is connected to the tank 34 via a second boom return line 72. The meter-out side (tank port side) of the first arm direction control valve 43 is connected to the tank 34 via a first arm return line 73, and the meter-out side (tank port side) of the second arm direction control valve 44 is connected to the tank 34 via a second arm return line 74. The meter-out side (tank port side) of the bucket direction control valve 45 is connected to the tank 34 via a bucket return line 75. The meter-out side (tank port side) of the swing direction control valve 46 is connected to the tank 34 via a swing return line 76.

[0029] The above-mentioned directional control valves 41 to 46, flow rate control valves 51 to 56, and CB cut valves 47, 48 constitute a first control valve unit 40 as an assembly of a plurality of control valves.

[0030] The first pump 31 and the second pump 32 are connected to the tank 34 via a relief valve 57. The relief valve 57 opens when the pressure in the hydraulic circuit reaches or exceeds a set pressure, and has a function of preventing damage to hydraulic equipment due to an excessive pressure rise. The relief valve 57 is connected to the first discharge line 35 via a first check valve 58, and is connected to the second discharge line 36 via a second check valve 59. The first check valve 58 and the second check valve 59 allow flow from the first pump 31 and the second pump 32 side to the relief valve 57 side, while preventing flow from the relief valve 57 side to the first discharge line 35 and the second discharge line 36.

[0031] The hydraulic system 30 further includes an accumulator 78. The accumulator 78 accumulates and pressurizes the pressure oil supplied from the first pump 31 and the second pump 32, and supplies the accumulated pressure oil to the hydraulic actuators 21, 22, 23, and 5.

[0032] The accumulator 78 is connected to the first pump 31 via a first accumulator flow control valve 81 (hereinafter referred to as the first ACC flow control valve), and is connected to the second pump 32 via a second accumulator flow control valve 82 (hereinafter referred to as the second ACC flow control valve). The first ACC flow control valve 81 is connected to the first pump 31 via a first supply line 88, and the second ACC flow control valve 82 is connected to the second pump 32 via a second supply line 89.

[0033] The accumulator 78 is connected to the boom cylinder 21 via a first accumulator directional control valve 83 (hereinafter referred to as the first ACC directional control valve), to the arm cylinder 22 via a second accumulator directional control valve 84 (hereinafter referred to as the second ACC directional control valve), to the bucket cylinder 23 via a third accumulator directional control valve 85 (hereinafter referred to as the third ACC directional control valve), and to the swing hydraulic motor 5 via a fourth accumulator directional control valve 86 (hereinafter referred to as the fourth ACC directional control valve). The first ACC directional control valve 83 controls the flow (direction and flow rate) of pressure oil supplied from the accumulator 78 to the boom cylinder 21. The second ACC directional control valve 84 controls the flow (direction and flow rate) of pressure oil supplied from the accumulator 78 to the arm cylinder 22. The ACC third directional control valve 85 controls the flow (direction and flow rate) of pressure oil supplied from the accumulator 78 to the bucket cylinder 23. The ACC fourth directional control valve 86 controls the flow (direction and flow rate) of pressure oil supplied from the accumulator 78 to the swing hydraulic motor 5.

[0034] The first ACC directional control valve 83 is connected to the accumulator 78 via a boom accumulator line 91, and is connected to the bottom side and rod side of the boom cylinder 21 via third boom actuator lines 96, 96. The second ACC directional control valve 84 is connected to the accumulator 78 via an arm accumulator line 92, and is connected to the bottom side and rod side of the arm cylinder 22 via third arm actuator lines 97, 97. The third ACC directional control valve 85 is connected to the accumulator 78 via a bucket accumulator line 93, and is connected to the bottom side and rod side of the bucket cylinder 23 via second bucket actuator lines 98, 98. The fourth ACC directional control valve 86 is connected to the accumulator 78 via a swing accumulator line 94, and is connected to the first port side and the second port side of the swing hydraulic motor 5 via second swing actuator lines 99, 99.

[0035] The ACC directional control valves 83-86 are configured, for example, by a 3-port 3-position spool valve. The three ports are an accumulator port connected to the accumulator 78, and a pair of actuator ports connected to the bottom and rod sides of the hydraulic cylinders 21, 22, 23 or the first and second port sides of the hydraulic motor 5. In other words, the ACC directional control valves 83-86 are configured without a tank port. That is, the ACC directional control valves 83-86 control the connection between the meter-in sides of the hydraulic actuators 21, 22, 23, 5 and the accumulator 78.

[0036] The above-mentioned ACC flow rate control valves 81, 82 and ACC directional control valves 83 to 86 configure a second control valve unit 80 as an assembly of a plurality of control valves.

[0037] In the hydraulic system 30 of the present embodiment, the ACC directional control valves 83-86 are configured without a return line for connecting to the tank 34 or a meter-out circuit such as a flow control valve for controlling the flow of return oil.

[0038] Next, the controlled object of the control device and the characteristics of the controlled object (control valve) in the hydraulic system of the work machine according to the first embodiment will be described with reference to Figures 3 to 5. Figure 3 is an excerpt of the hydraulic circuit for a boom cylinder from the hydraulic system shown in Figure 2, and is a diagram showing the controlled object of the control device.

[0039] The hydraulic system 30 is configured to be controlled by commands from the control device 100. Here, in order to simplify the explanation of the control of the hydraulic system 30 by the control device 100, only the hydraulic circuit for driving the boom cylinder 21 of the hydraulic system 30 will be explained. However, the control of the hydraulic circuits for driving the arm cylinder 22, bucket cylinder 23, and swing hydraulic motor 5 in the hydraulic system 30 is also similar to the explanation below.

[0040] 3, an operation signal from an operating device 7 is input to a control device 100. The operating device 7 issues instructions for the movement of the boom 18, arm 19, and bucket 20 of the front working mechanism 3 and the rotation operation of the upper rotating body 2. The operating device 7 outputs operation signals (electrical signals) for boom operation, arm operation, bucket operation, and rotation operation to the control device 100 according to the direction and amount of operation operated by the operator.

[0041] The control device 100 controls the driving of each control valve of the hydraulic system 30 described above, namely, the first boom directional control valve 41, the second boom directional control valve 42, the first boom flow control valve 51, the second boom flow control valve 52, the first CB cut valve 47, the second CB cut valve 48, the first ACC flow control valve 81, the second ACC flow control valve 82, and the first ACC directional control valve 83, in response to an operation signal for boom operation from the operation device 7. The same applies when each operation signal (electrical signal) for arm operation, bucket operation, and swing operation other than boom operation is input.

[0042] The first boom direction control valve 41 and the second boom direction control valve 42 are configured to switch a spool position (spool stroke) in response to a command (e.g., an electromagnetic command) from the control device 100, for example. The first boom direction control valve 41 and the second boom direction control valve 42 have a meter-in passage, a meter-out passage, and a center bypass passage. The meter-in passage is a passage for connecting the first discharge line 35 (first pump 31) or the second discharge line 36 (second pump 32) to the meter-in side of the boom cylinder 21. The meter-out passage is a passage for connecting the meter-out side of the boom cylinder 21 to the tank 34. The center bypass passage is a passage for connecting the first discharge line 35 (first pump 31) or the second discharge line 36 (second pump 32) to the first center bypass line 37 or the second center bypass line 38 (tank 34). In the first boom directional control valve 41 and the second boom directional control valve 42, the ratio of the opening area of ​​the meter-in passage, the opening area of ​​the meter-out passage, and the opening area of ​​the center bypass passage changes when the spool position is switched.

[0043] The first boom direction control valve 41 and the second boom direction control valve 42 of this embodiment have opening characteristics, for example, as shown in Fig. 4. Fig. 4 is an opening area diagram of the first boom direction control valve and the second boom direction control valve. In Fig. 4, the horizontal axis S1 represents the spool stroke, and the vertical axis A1 represents the opening area of ​​each of the meter-in passage, the meter-out passage, and the center bypass passage. The solid line represents a characteristic diagram of the meter-in passage, the dashed line represents a characteristic diagram of the meter-out passage, and the dashed line represents a characteristic diagram of the center bypass passage. In the present invention, the stroke is synonymous with the stroke amount.

[0044] The spool stroke (spool position) of the first boom direction control valve 41 and the second boom direction control valve 42 has a characteristic that increases in proportion to the amount of operation of the operating device 7. The center bypass passage is configured so that the opening area is narrowed as the spool stroke increases. On the other hand, the meter-in passage and the meter-out passage are configured in advance so that they start to open simultaneously at a predetermined spool stroke (predetermined spool position) and the opening area gradually increases as the spool stroke increases from there. In the case of such opening characteristics, as the spool stroke increases, the flow rate of pressure oil flowing out from the first pump 31 or the second pump 32 shown in FIG. 3 through the first boom direction control valve 41 or the second boom direction control valve 42 (center bypass passage) to the tank 34 is narrowed. Meanwhile, pressurized oil from the first pump 31 or the second pump 32 is supplied to the boom cylinder 21 via the first boom directional control valve 41 or the second boom directional control valve 42 (meter-in passage), and return oil discharged from the boom cylinder 21 is discharged from the first boom actuator line 61, 61 or the second boom actuator line 62, 62 and the first boom directional control valve 41 or the second boom directional control valve 42 (meter-out passage) via the first boom return line 71 or the second boom return line 72 to the tank 34.

[0045] The first boom flow control valve 51 and the second boom flow control valve 52 are configured so that the stroke (spool position) can be switched in response to a command (e.g., an electromagnetic command) from the control device 100. The first boom flow control valve 51 and the second boom flow control valve 52 have, for example, opening characteristics shown in Fig. 5. Fig. 5 is an opening area diagram of the first boom flow control valve and the second boom flow control valve. In Fig. 5, the horizontal axis S2 indicates the stroke, and the vertical axis A2 indicates the opening area.

[0046] The opening areas of the first boom flow control valve 51 and the second boom flow control valve 52 have a normally open characteristic. That is, when the spool is not displaced, the opening area is maximum, and as the stroke increases, the opening area gradually decreases and closes. Unlike the first boom directional control valve 41 and the second boom directional control valve 42, the strokes of the first boom flow control valve 51 and the second boom flow control valve 52 are controlled according to the situation without corresponding to the amount of operation of the operating device 7.

[0047] The first CB cut valve 47 and the second CB cut valve 48 are configured so that the stroke (spool position) can be switched in response to a command (e.g., an electromagnetic command) from the control device 100, and are, for example, control valves having a normally open characteristic. The first ACC flow control valve 81 and the second ACC flow control valve 82 are configured so that the stroke (spool position) can be switched in response to a command (e.g., an electromagnetic command) from the control device 100, and are, for example, control valves having a normally closed characteristic. The first ACC directional control valve 83 is configured so that the spool stroke (spool position) can be switched in response to a command (e.g., an electromagnetic command) from the control device 100, and is, for example, a control valve having a characteristic in which the opening area increases as the spool stroke increases.

[0048] Next, the control of the control device for the work machine according to the first embodiment will be described with reference to Fig. 2 to Fig. 7. Fig. 6 is a block diagram showing the control logic in the control device for the work machine according to the first embodiment shown in Fig. 3. Fig. 7 is a table used by the operation pattern calculation unit of the control device according to the first embodiment shown in Fig. 6.

[0049] 3, the control device 100 includes, as a hardware configuration, a storage device 100a including a RAM, a ROM, etc., and a processing device 100b including a CPU, an MPU, etc. The storage device 100a stores in advance programs and various information required for controlling the operation of the directional control valves 41-46, the flow control valves 51-56, and the CB cut valves 47-48 for the pumps 31 and 32 in the hydraulic system 30, and the flow control valves 81 and 82 and the directional control valves 83-86 for the accumulator 78. The processing device 100b appropriately reads the programs and various information from the storage device 100a, and executes processing according to the programs to realize various functions.

[0050] Here, we will explain the control for driving the boom cylinder 21 by the supply of pressure oil from the first pump 31, the second pump 32, and the accumulator 78. The control for driving the arm cylinder 22, the bucket cylinder 23, and the swing hydraulic motor 5 by the supply of pressure oil from the first pump 31, the second pump 32, and the accumulator 78 is similar to that for the boom cylinder 21, so the explanation of those controls will be omitted.

[0051] The control device 100 of this embodiment generally executes the following controls. When the control device 100 supplies pressure oil from the first pump 31 to the boom cylinder 21, it controls the drive of the first boom direction control valve 41 to control the flow of pressure oil supplied from the first pump 31 to the boom cylinder 21, and controls the return oil discharged from the boom cylinder 21 to be discharged via the first boom direction control valve 41 to the tank 34. When the control device 100 supplies pressure oil from the second pump 32 to the boom cylinder 21, it controls the drive of the second boom direction control valve 42 to control the flow of pressure oil supplied from the second pump 32 to the boom cylinder 21, and controls the return oil from the boom cylinder 21 to be discharged via the second boom direction control valve 42 to the tank 34. In addition, when the pressurized oil stored in the accumulator 78 is supplied to the boom cylinder 21, the operation of the first directional control valve for ACC 83 is controlled to control the flow of pressurized oil supplied from the accumulator 78 to the boom cylinder 21, and the operation of the first directional control valve for boom 41 is controlled to discharge the return oil of the boom cylinder 21 to the tank 34 via the first directional control valve for boom 41, while the operation of the first flow control valve for boom 51 is controlled to finally cut off the pressurized oil supplied from the first pump 31 to the boom cylinder 21 via the first directional control valve for boom 41.

[0052] In order to achieve the above-mentioned control, the control device 100 executes a control logic shown in FIG. 6, for example, in response to input of operation amounts (operation signals) for each operation (boom operation, arm operation, bucket operation, swing operation) of the operating device 7, and outputs a boom first spool control command C1 that commands the drive of the boom first directional control valve 41, a boom second spool control command C2 that commands the drive of the boom second directional control valve 42, a boom first flow rate control command C3 that commands the drive of the boom first flow control valve 51, a boom second flow rate control command C4 that commands the drive of the boom second flow control valve 52, and a boom ACC flow rate control command C5 that commands the drive of the ACC first directional control valve 83.

[0053] Specifically, in FIG. 6, the control logic of the control device 100 has an operation pattern calculation unit 101 that determines the operation pattern of the hydraulic excavator based on the operation amount (operation signal) of each operation from the operating device 7, integrators 103, 104, 105 corresponding to the first boom directional control valve 41, the second boom directional control valve 42, and the first ACC directional control valve 83 among the multiple control valves 41, 42, 51, 52, 83 that are the control objects, and function generators 111, 112, 113, 114, 115 and output conversion units 121, 122, 123, 124, 125 corresponding to each of the control valves 41, 42, 51, 52, 83 that are the control objects.

[0054] The operation pattern calculation unit 101 determines an operation pattern to be performed by the hydraulic excavator based on the operation amount (operation signal) of each operation from the operating device 7, and sets the drive state of each of the control valves 41, 42, 51, 52, 83 to be controlled so as to optimally operate the hydraulic system 30 for each determined operation pattern. That is, it determines which hydraulic actuators 21, 22, 23, 5 should be connected to each of the hydraulic sources of the first pump 31, the second pump 32, and the accumulator 78 in accordance with each operation pattern, and sets the drive state of each of the control valves 41, 42, 51, 52, 83 to be controlled so that pressure oil can be supplied to the connection destinations of the determined hydraulic sources 31, 32, 78. Specifically, the operation pattern calculation unit 101 sets the drive state of each of the control valves 41, 42, 51, 52, 83 to be controlled by referring to information (table) shown in FIG. 7, for example.

[0055] In the table shown in FIG. 7, the operation patterns include an excavation operation, a swing boom raising operation, and an independent boom raising operation, which are typical operations of a hydraulic excavator. The excavation operation is a three-combined operation that combines the operations of three link members, the boom 18, the arm 19, and the bucket 20 that configure the front working mechanism 3. That is, the excavation operation is an operation in which the boom cylinder 21, the arm cylinder 22, and the bucket cylinder 23 are driven simultaneously. The swing boom raising operation is a two-combined operation that combines the swing operation of the upper swing body 2 and the operation of the boom 18. That is, it is an operation in which the swing hydraulic motor 5 and the boom cylinder 21 are driven simultaneously. The independent boom raising operation is an independent operation in which only the boom 18 operates by driving only the boom cylinder 21 in the extension direction.

[0056] The table shown in Fig. 7 indicates the connection destinations (destinations of pressure oil) of each hydraulic source 31, 32, 78 for optimal operation of the hydraulic system 30 for each operation pattern. In Fig. 7, pump 1 indicates the first pump 31, pump 2 indicates the second pump, and ACC indicates the accumulator 78. BM indicates the boom cylinder 21, AM indicates the arm cylinder 22, BK indicates the bucket cylinder 23, and SW indicates the swing hydraulic motor 5.

[0057] When the determination result of the operation pattern is an excavation operation, the first pump 31 is connected to the boom cylinder 21 and the bucket cylinder 23. This means that the first boom directional control valve 41 and the bucket directional control valve 45 shown in FIG. 2 are driven. In addition, the second pump 32 is connected to the arm cylinder 22. This means that the second arm directional control valve 44 shown in FIG. 2 is driven. The accumulator 78 is not connected to any of the hydraulic actuators 21, 22, 23, 5.

[0058] In the case of a swing boom raising operation, the second pump 32 is connected to the swing hydraulic motor 5. This means that the swing directional control valve 46 shown in FIG. 2 is driven. In addition, the accumulator 78 is connected to the boom cylinder 21. This means that the ACC first directional control valve 83 shown in FIG. 2 is driven. However, when pressure oil is supplied from the accumulator 78 to the boom cylinder 21 via the ACC first directional control valve 83, due to the configuration of the hydraulic system 30, the return oil discharged from the boom cylinder 21 cannot be discharged to the tank 34 via the ACC first directional control valve 83.

[0059] Therefore, in this embodiment, the meter-out side of the boom cylinder 21 is connected to the tank 34 via the first boom direction control valve 41 by driving the first boom direction control valve 41, which is unrelated to the pressure oil supply from the second pump 32. However, when the first boom direction control valve 41 is driven, the meter-in passage is opened at the same time as the meter-out passage is opened as shown in FIG. 4, so that the meter-in side of the boom cylinder 21 is connected to the first pump 31 via the first boom direction control valve 41. This means that the pressure oil of the first pump 31 is unintentionally supplied to the boom cylinder 21. Therefore, in this embodiment, the supply of pressure oil from the first pump 31 to the boom cylinder 21 via the first boom direction control valve 41 is blocked by driving the first boom flow control valve 51 shown in FIG. 2. As a result, pressure oil is supplied to the boom cylinder 21 only from the accumulator 78. That is, in the table shown in FIG. 7, the entry of (BM) as the connection destination of pump 1 during the swing boom raising operation indicates that the meter-out side of boom cylinder 21 is connected to tank 34 by driving the first boom directional control valve 41 for connecting first pump 31 to boom cylinder 21, and also indicates that the supply of pressurized oil from the first pump 31 to boom cylinder 21 via the first boom directional control valve 41 is cut off by driving the first boom flow control valve 51.

[0060] In addition, in the case of a boom raising operation alone, the three hydraulic power sources, the first pump 31, the second pump 32, and the accumulator 78, are simultaneously connected to the boom cylinder 21. This means that the first boom directional control valve 41, the second boom directional control valve 42, and the first ACC directional control valve 83 are simultaneously driven.

[0061] The operation pattern calculation unit 101 sets the drive state of each of the above-mentioned control valves 41, 42, 51, 52, 83 to be controlled in accordance with the operation pattern discrimination result. The drive state setting result for each of the control valves 41, 42, 51, 52, 83 is output to the corresponding integrators 103, 104, 105 or function generators 113, 114.

[0062] Specifically, the operation pattern calculation unit 101 outputs a setting result of "1" when driven or "0" when not driven as the drive state of the first boom direction control valve 41 to an integrator 103. Also, as the drive state of the second boom direction control valve 42, it outputs a setting result of "1" when driven or "0" when not driven to an integrator 104. Also, as the drive state of the first ACC direction control valve 83, it outputs a setting result of "1" when driven or "0" when not driven to an integrator 105. Such outputs from the operation pattern calculation unit 101 make it possible to control whether or not to drive the first boom direction control valve 41, the second boom direction control valve 42, and the first ACC direction control valve 83.

[0063] Furthermore, the operation pattern calculation unit 101 outputs to the function generator 113 a setting result for increasing the opening area when the first pump 31 is connected to the meter-in side of the boom cylinder 21 via the first boom directional control valve 41 (in the case of an excavation operation or an independent boom raising operation) as the driving state of the first boom flow control valve 51. Furthermore, the operation pattern calculation unit 101 outputs to the function generator 113 a setting result for closing the opening when the meter-out side of the boom cylinder 21 is connected to the tank 34 via the first boom directional control valve 41 (in the case of a swing boom raising operation) as the driving state of the first boom flow control valve 51.

[0064] Furthermore, the operation pattern calculation unit 101 outputs to the function generator 114 a setting result for increasing the opening area as the drive state of the second boom flow control valve 52 when the second pump 32 is connected to the meter-in side of the boom cylinder 21 via the second boom directional control valve 42 (in the case of independent boom raising operation). Furthermore, the operation pattern calculation unit 101 outputs to the function generator 114 a setting result for closing the opening as the drive state of the second boom flow control valve 52 when the meter-out side of the boom cylinder 21 is connected to the tank 34 via the second boom directional control valve 42.

[0065] The integrator 103 for the first boom direction control valve 41 integrates the operation amount (operation signal) of the boom operation of the operation device 7 and the setting result of the drive state of the first boom direction control valve 41 of the operation pattern calculation unit 101. The integration result is output to a function generator 111 for the first boom direction control valve 41. The operation signal of the boom operation of the operation device 7 is a signal corresponding to the operation amount of the boom operation, and is, for example, a value of 0 to 100 [%]. As described above, the setting result of the drive state of the first boom direction control valve 41 of the operation pattern calculation unit 101 is "0" when not driven or "1" when driven. That is, the integrator 103 outputs to the function generator 111 a value equal to the operation signal of the boom operation of the operation device 7 when the first boom direction control valve 41 is driven, and a value (signal) of "0" when the first boom direction control valve 41 is not driven.

[0066] The function generator 111 calculates the opening area of ​​the first boom direction control valve 41 according to the output (integration result) of the integrator 103. The calculation result is output to an output conversion unit 121 for the first boom direction control valve 41.

[0067] The output conversion unit 121 is a calculation unit that converts the opening area of ​​the first boom direction control valve 41, which is the output (calculation result) of the function generator 111, into a displacement amount (stroke) of the spool. The calculation result is output to the first boom direction control valve 41 as a boom first spool control command C1. This controls the first boom direction control valve 41 to a desired stroke and opening area.

[0068] The integrator 104, function generator 112, and output conversion unit 122 for the second boom direction control valve 42 are similar to those for the first boom direction control valve 41 described above. That is, the integrator 104 integrates the operation signal (0 to 100) for boom operation of the operation device 7 and the setting result of the drive state for the second boom direction control valve 42 by the operation pattern calculation unit 101 ("0" when not driven or "1" when driven), and outputs the integration result to the function generator 112. The function generator 112 calculates the opening area of ​​the second boom direction control valve 42 according to the output of the integrator 104, and outputs the calculation result to the output conversion unit 122. The output conversion unit 122 converts the opening area of ​​the second boom direction control valve 42, which is the output of the function generator 112, into the displacement amount of the spool, and outputs the calculation result to the second boom direction control valve 42 as a boom second spool control command C2. This allows the second boom directional control valve 42 to be controlled to a desired stroke and opening area.

[0069] The integrator 105, function generator 115, and output conversion unit 125 for the first ACC directional control valve 83 are similar to those for the first boom directional control valve 41 described above. That is, the integrator 105 integrates the operation signal (0 to 100) for boom operation of the operation device 7 and the setting result of the drive state for the first ACC directional control valve 83 from the operation pattern calculation unit 101 ("0" when not driven or "1" when driven), and outputs the integration result to the function generator 115. The function generator 115 calculates the opening area of ​​the first ACC directional control valve 83 according to the output of the integrator 105, and outputs the calculation result to the output conversion unit 125. The output conversion unit 125 converts the opening area of ​​the ACC first directional control valve 83, which is the output of the function generator 115, into the displacement amount of the spool of the ACC first directional control valve 83, and outputs the calculation result as a boom ACC flow rate control command C5 to the ACC first directional control valve 83. This controls the ACC first directional control valve 83 to the desired stroke and opening area.

[0070] The function generator 113 for the first boom flow control valve 51 performs calculations to control the opening area of ​​the first boom flow control valve 51 in accordance with the setting results (signals) for the drive state of the first boom flow control valve 51 from the operation pattern calculation unit 101. The calculation results are output to an output conversion unit 123 for the first boom flow control valve 51.

[0071] When the first pump 31 is connected to the boom cylinder 21 (in the case of excavation operation or single boom raising operation in FIG. 7), the function generator 113 outputs a calculation result to increase the opening area (reduce the stroke) in accordance with the output of the operation pattern calculation unit 101. On the other hand, when the boom cylinder 21 is not driven or the meter-in side of the boom cylinder 21 is connected only to the accumulator 78 (in the case of swing boom raising operation in FIG. 7), the function generator 113 outputs a calculation result to close the opening (increase the stroke) in accordance with the output of the operation pattern calculation unit 101.

[0072] The output conversion unit 123 calculates the boom first flow control command C3 based on the output of the function generator 113 and outputs it to the first boom flow control valve 51. This controls the first boom flow control valve 51 to a desired stroke and opening area. When only the accumulator 78 is connected to the meter-in side of the boom cylinder 21 (in the case of the swing boom raising operation in FIG. 7), the first boom flow control valve 51 is controlled to close the opening, but if the stroke is changed suddenly, a shock occurs. Therefore, the first boom flow control valve 51 is controlled not to be switched ON / OFF, but to be gradually changed in stroke and finally closed. In other words, the drive of the first boom flow control valve 51 is controlled so that the flow of pressure oil from the first pump 31 to the boom cylinder 21 via the first boom directional control valve 41 is gradually narrowed and then finally cut off.

[0073] The function generator 114 and output conversion section 124 for the second boom flow control valve 52 are similar to those for the first boom flow control valve 51 described above. The function generator 114 performs calculations for controlling the opening area of ​​the second boom flow control valve 52 in accordance with the setting results (signals) for the drive state of the second boom flow control valve 52 from the operation pattern calculation section 101, and outputs the calculation results to the output conversion section 124. The output conversion section 124 calculates a second boom flow control command C4 based on the output of the function generator 114, and outputs it to the second boom flow control valve 52. This controls the second boom flow control valve 52 to the desired stroke and opening area. Next, the operation of the work machine according to the first embodiment will be described with reference to FIGS.

[0074] When the control device 100 shown in FIG. 6 determines that the operation is an “excavation operation” based on the operation signals of each operation of the operating device 7, it controls the first boom direction control valve 41 and the bucket direction control valve 45 to be driven in order to connect the first pump 31 shown in FIG. 2 to the boom cylinder 21 and the bucket cylinder 23, and also controls the second arm direction control valve 44 to be driven in order to connect the second pump 32 to the arm cylinder 22.

[0075] As a result, the pressure oil of the first pump 31 is supplied to the boom cylinder 21 via the first boom flow control valve 51 and the first boom direction control valve 41. At this time, the return oil discharged from the boom cylinder 21 is guided from the first boom direction control valve 41 to the tank 34 via the first boom return line 71. Similarly, the pressure oil of the first pump 31 is supplied to the bucket cylinder 23 via the bucket flow control valve 55 and the bucket direction control valve 45. At this time, the return oil discharged from the bucket cylinder 23 is guided from the bucket direction control valve 45 to the bucket return line 75 to the tank 34. In addition, the pressure oil of the second pump 32 is supplied to the arm cylinder 22 via the second arm flow control valve 54 and the second arm direction control valve 44. At this time, the return oil discharged from the arm cylinder 22 is guided from the second arm direction control valve 44 to the tank 34 via the second arm return line 74.

[0076] Furthermore, when the control device 100 determines that the operation is a "swing boom raising operation", it controls to drive the swing directional control valve 46 to connect the second pump 32 to the swing hydraulic motor 5, and controls to drive the ACC first directional control valve 83 to connect the accumulator 78 to the boom cylinder 21. In this case, the control device 100 further controls to drive the boom first directional control valve 41 to connect the meter-out side of the boom cylinder 21 to the tank 34, and controls to gradually narrow the opening of the boom first flow control valve 51 and then finally close it.

[0077] As a result, the pressure oil of the second pump 32 is supplied to the swing hydraulic motor 5 via the swing flow control valve 56 and the swing directional control valve 46. At this time, the return oil discharged from the swing hydraulic motor 5 is guided to the tank 34 by the swing return line 76 via the swing directional control valve 46. In addition, the pressure oil of the accumulator 78 is supplied to the boom cylinder 21 via the ACC first directional control valve 83. At this time, the return oil of the boom cylinder 21 is guided to the tank 34 by the boom first return line 71 from the boom first actuator line 61 via the boom first directional control valve 41. At this time, the flow of pressure oil from the first pump 31 to the boom cylinder 21 via the boom first directional control valve 41 due to the drive of the boom first directional control valve 41 is gradually throttled by the drive of the boom first flow control valve 51 and then finally shut off.

[0078] Furthermore, if the pressure in the hydraulic circuit of the first pump 31 exceeds a set value due to the operation of the first boom directional control valve 41 and the first boom flow control valve 51, the relief valve 57 opens to prevent damage to the hydraulic equipment.

[0079] Furthermore, when the control device 100 determines that the operation is “boom raising alone,” it controls the first boom directional control valve 41, the second boom directional control valve 42, and the first ACC directional control valve 83 to be driven in order to connect the three hydraulic power sources, the first pump 31, the second pump 32, and the accumulator 78, to the boom cylinder 21.

[0080] As a result, pressure oil from the first pump 31 is supplied to the boom cylinder 21 via the first boom flow control valve 51 and the first boom directional control valve 41. Similarly, pressure oil from the second pump 32 is supplied to the boom cylinder 21 via the second boom flow control valve 52 and the second boom directional control valve 42. Also, pressure oil from the accumulator 78 is supplied to the boom cylinder 21 via the first ACC directional control valve 83. At this time, the return oil from the boom cylinder 21 is guided from the first boom directional control valve 41 to the tank 34 via the first boom return line 71, and is also guided from the second boom directional control valve 42 to the tank 34 via the second boom return line 72.

[0081] In this way, when pressure oil is supplied to each of the hydraulic actuators 21, 22, 23, 5 only from the hydraulic source of the accumulator 78, the control device 100 according to this embodiment drives the ACC directional control valves 83, 84, 85, 86 corresponding to each of the hydraulic actuators 21, 22, 23, 5, and controls the driving of each of the directional control valves 41-46 and the flow control valves 51-56 corresponding to each of the hydraulic actuators 21, 22, 23, 5. As a result, while the supply of pressure oil from the first pump 31 or the second pump 32 to each of the hydraulic actuators 21, 22, 23, 5 via each of the directional control valves 41-46 is cut off, each of the hydraulic actuators 21, 22, 23, 5 can be driven only by pressure oil from the accumulator 78 while the meter-out sides of each of the hydraulic actuators 21, 22, 23, 5 are connected to the tank 34. By such control, it is possible to realize a hydraulic circuit that does not require meter-out circuits such as return lines and flow control valves on the return lines for each ACC directional control valve 83, 84, 85, 86 that control the flow of pressurized oil from the accumulator 78 to each hydraulic actuator 21, 22, 23, 5.

[0082] Furthermore, by processing by the operation pattern calculation unit 101 of the control device 100, it is possible to supply pressure oil to each of the hydraulic actuators 21, 22, 23, and 5 from the most efficient hydraulic source among the three hydraulic sources, the first pump 31, the second pump 32, and the accumulator 78. Furthermore, it is also possible to supply pressure oil to each of the hydraulic actuators 21, 22, 23, and 5 simultaneously from the three hydraulic sources, the first pump 31, the second pump 32, and the accumulator 78.

[0083] In addition, in the hydraulic system 30 of this embodiment, when pressurized oil from the first pump 31 and the second pump 32 is supplied to the accumulator 78, control is performed to drive the first CB cut valve 47 and the second CB cut valve 48 so that their openings are throttled or closed.

[0084] The hydraulic excavator (work machine) according to the first embodiment described above includes a first pump 31 and a second pump 32 (hydraulic pumps) that discharge pressure oil, hydraulic actuators 21, 22, 23, 5 that are driven by the pressure oil discharged from the first pump 31 and the second pump 32 (hydraulic pumps), a tank 34 that stores return oil discharged from the hydraulic actuators 21, 22, 23, 5, and a storage tank 35 that stores the pressure oil discharged from the first pump 31 and the second pump 32 (hydraulic pumps) and supplies the stored pressure oil to the hydraulic actuators. The hydraulic actuator 21, 22, 23, 5 is provided with an accumulator 78 that supplies hydraulic fluid to the first pump 31 or the second pump 32 (hydraulic pump), directional control valves 41-46 (first control valves) that control the connection between the meter-in sides of the hydraulic actuators 21, 22, 23, 5 and the tank 34, and directional control valves 83-86 (second control valves) that control the connection between the meter-in sides of the hydraulic actuators 21, 22, 23, 5 and the accumulator 78. Furthermore, the hydraulic system is provided with flow control valves 51-56 as a flow control mechanism that controls the flow rate of pressurized oil from the first pump 31 or the second pump 32 (hydraulic pump) to the hydraulic actuators 21, 22, 23, 5 via directional control valves 41-46 (first control valves), and a control device 100 that controls the directional control valves 41-46 (first control valves), directional control valves 83-86 (second control valves), and the flow control valves 51-56 (flow control mechanism). When pressure oil is supplied to the hydraulic actuators 21, 22, 23, 5 only from the accumulator 78, the control device 100 is configured to drive the directional control valves 83-86 (second control valves) to connect the meter-in sides of the hydraulic actuators 21, 22, 23, 5 to the accumulator 78, drive the directional control valves 41-46 (first control valves) to connect the meter-out sides of the hydraulic actuators 21, 22, 23, 5 to the tank 34, and drive the flow control valves 51-56 (flow control mechanism) to finally cut off the flow of pressure oil from the first pump 31 or the second pump 32 (hydraulic pump) to the hydraulic actuators 21, 22, 23, 5 via the directional control valves 41-46 (first control valves).

[0085] According to this configuration, when pressure oil is supplied to the hydraulic actuators 21, 22, 23, 5 only from the accumulator 78, the meter-out sides of the hydraulic actuators 21, 22, 23, 5 are connected to the tank 34 by driving the directional control valves 41-46 (first control valves), and the flow of pressure oil from the first pump 31 or the second pump 32 (hydraulic pump) to the hydraulic actuators 21, 22, 23, 5 via the directional control valves 41-46 (first control valves) is blocked by driving the flow control valves 51-56 (flow control mechanism). Therefore, even when pressure oil is supplied to the hydraulic actuators 21, 22, 23, 5 from the accumulator 78, the return oil of the hydraulic actuators 21, 22, 23, 5 can be discharged to the tank 34 via the directional control valves 41-46 (first control valves). That is, the control of the flow on the meter-out side of the hydraulic actuators 21, 22, 23, 5 can be realized only by the directional control valves 41-46 (first control valves). Therefore, there is no need to provide meter-out circuits such as return oil lines or flow control valves for the directional control valves 83-86 (second control valves), and the configuration of the hydraulic system 30, which is capable of supplying pressurized oil from the accumulator 78 to the hydraulic actuators 21, 22, 23, and 5 in addition to the first pump 31 and the second pump 32 (hydraulic pumps), can be made less complicated.

[0086] In this embodiment, the directional control valves 41-46 (first control valves) have opening characteristics in which both passages, a meter-in passage for connecting the first pump 31 or the second pump 32 (hydraulic pump) to the hydraulic actuators 21, 22, 23, 5 and a meter-out passage for connecting the tank 34 to the hydraulic actuators 21, 22, 23, 5, begin to open and communicate simultaneously at a preset predetermined stroke, and both passages are in an open state at a stroke larger than the predetermined stroke. In addition, the flow control mechanism is composed of flow control valves 51-56 different from the directional control valves 41-46 (first control valves).

[0087] According to this configuration, the control device 100 individually controls the directional control valves 41-46 (first control valves) and the flow control valves 51-56 to ensure the connection between the meter-out side of the hydraulic actuators 21, 22, 23, 5 and the tank 34, and to cut off the connection between the first pump 31 or the second pump 32 (hydraulic pump) and the hydraulic actuators 21, 22, 23, 5, thereby making it easy to control the directional control valves 41-46 (first control valves) and the flow control valves 51-56. [Second embodiment] Next, a second embodiment of a work machine of the present invention will be described with reference to Figures 8 to 10. In Figures 8 to 10, the same reference numerals as those shown in Figures 1 to 7 denote similar parts, and detailed description thereof will be omitted. Figure 8 is a hydraulic circuit diagram showing the configuration of a hydraulic system provided in a work machine according to a second embodiment of the present invention.

[0088] The second embodiment of the work machine of the present invention differs from the first embodiment in that the opening characteristics of each of the directional control valves 41A, 42A, 43A, 44A, 45A, and 46A of the hydraulic system 30A shown in FIG. 8 are different, and the control method of the control device 100A shown in FIG. 10 for the hydraulic system 30A differs depending on the difference in the opening characteristics of each of the directional control valves 41A to 46A.

[0089] Specifically, the directional control valves 41A to 46A have a characteristic that the center bypass passage does not close even if the position of the spool is switched. The directional control valves 41A to 46A have, for example, the opening characteristic shown in Fig. 9. Fig. 9 is an opening area diagram of each of the directional control valves 41A to 46A of the hydraulic system 30A shown in Fig. 8. In Fig. 9, the horizontal axis S3 indicates the spool stroke, and the vertical axis A3 indicates the opening area of ​​each of the meter-in passage, the meter-out passage, and the center bypass passage. The solid line indicates the characteristic diagram of the meter-in passage, the dashed line indicates the characteristic diagram of the meter-out passage, and the dashed line indicates the characteristic diagram of the center bypass passage.

[0090] The spool strokes (spool positions) of the directional control valves 41A to 46A have a characteristic that increases in proportion to the amount of operation of each operation of the operating device 7, similar to the directional control valves 41 to 46 of the first embodiment. The meter-in passage and the meter-out passage are configured in advance to start opening simultaneously at a predetermined spool stroke (predetermined spool position) and gradually increase in opening area as the spool stroke increases from there, similar to the first embodiment. On the other hand, the center bypass passage has a constant opening area regardless of the increase or decrease in the spool stroke, unlike the first embodiment. That is, the directional control valves 41A to 46A have an opening characteristic in which the opening amount (opening area of ​​the center bypass passage) to the first center bypass line 37 or the second center bypass line 38 is constant over the entire stroke.

[0091] Next, the control logic of the control device for the work machine according to the second embodiment will be described with reference to Fig. 10. Fig. 10 is a block diagram showing the control logic of the control device for the hydraulic system shown in Fig. 8.

[0092] In response to the fact that the opening areas of the center bypass passages of the directional control valves 41A to 46A are constant over the entire spool stroke, the control device 100A controls the flow of pressure oil in the first center bypass line 37 connecting the first pump 31 and the tank 34 only by the first CB cut valve 47, and controls the flow of pressure oil in the second center bypass line 38 connecting the second pump 32 and the tank 34 only by the second CB cut valve 48. In the control device 100A shown in FIG. 10, the first CB cut valve 47 and the second CB cut valve 48 are added to the control valves 41, 42, 51, 52, and 83 in the first embodiment as the control target. That is, the control device 100A outputs a first cut control command C6 for commanding the operation of the first CB cut valve 47 and a second cut control command C7 for commanding the operation of the second CB cut valve 48 in addition to the control commands C1 to C5 in the first embodiment. The control logic of the control valves 41, 42, 51, 52, and 83 that are the objects of control in the first embodiment of the control device 100A is the same as that in the first embodiment, and therefore a description thereof will be omitted.

[0093] In the first embodiment, when the hydraulic actuators 21, 22, 23, 5 are driven only by the pressure oil from the accumulator 78, the directional control valves 41-46 are driven so as to connect the meter-out sides of the hydraulic actuators 21, 22, 23, 5 to the tank 34, thereby guiding the return oil of the hydraulic actuators 21, 22, 23, 5 to the tank 34 via the directional control valves 41-46, while the flow control valves 51-56 corresponding to the driven directional control valves 41-46 are also driven and controlled to be finally closed, thereby blocking the supply of pressure oil from the first pump 31 or the second pump 32 to the hydraulic actuators 21, 22, 23, 5 via the directional control valves 41-46. At this time, the opening area of ​​the center bypass passages of the directional control valves 41-46 in the first embodiment is reduced in response to the drive (the magnitude of the spool stroke) (see FIG. 4), which may cause an unintended increase in pressure in the first pump 31 or the second pump 32, resulting in an excessive pressure loss.

[0094] In contrast, in this embodiment, as shown in Fig. 9, the opening area of ​​the center bypass passage of the directional control valves 41A to 46A is constant over the entire spool stroke. Therefore, even if the directional control valves 41A to 46A are driven so as to connect the meter-out sides of the hydraulic actuators 21, 22, 23, 5 to the tank 34 when the hydraulic actuators 21, 22, 23, 5 are driven only by the pressure oil of the accumulator 78 (even if the meter-out passages of the directional control valves 41A to 46A are controlled to be open), the first CB cut valve 47 and the second CB cut valve 48 are controlled to be open, so that the connection between the first pump 31 or the second pump 32 and the tank 34 via the first center bypass line 37 or the second center bypass line 38 can be secured. This makes it possible to suppress excess pressure loss due to an unintended pressure rise in the first pump 31 or the second pump 32 when the hydraulic actuators 21, 22, 23, 5 are driven only by the pressure oil of the accumulator 78.

[0095] Furthermore, when the hydraulic actuators 21, 22, 23, 5 are driven by the pressure oil of the first pump 31 or the second pump 32, even if the directional control valves 41A-46A are driven so as to connect the meter-in side of the hydraulic actuators 21, 22, 23, 5 to the first pump 31 or the second pump 32 (even if the directional control valves 41A-46A are controlled so as to open the meter-in passages), the connection between the first pump 31 or the second pump 32 and the tank 34 via the directional control valves 41A-46A is maintained. Therefore, by controlling the first CB cut valve 47 and the second CB cut valve 48 to close, the connection between the first pump 31 or the second pump 32 and the tank 34 is interrupted, and the pressure oil from the first pump 31 or the second pump 32 can be supplied to the hydraulic actuators 21, 22, 23, 5 via the directional control valves 41A-46A.

[0096] Specifically, as shown in Fig. 10, the control logic of the control device 100A includes integrators 106, 107, function generators 116, 117, and output conversion units 126, 127 for the first CB cut valve 47 and the second CB cut valve 48 in addition to the integrators 103-105, function generators 111-115, and output conversion units 121-125 in the first embodiment. Also, the operation pattern calculation unit 101A of the control device 100A sets the drive states of the control valves 41, 42, 51, 52, and 83 that are the control targets of the first embodiment in accordance with the operation pattern determined based on the operation signals of each operation from the operation device 7, and also sets the drive states of the first CB cut valve 47 and the second CB cut valve 48. The operation pattern calculation unit 101A outputs the setting results of the drive states of the first CB cut valve 47 and the second CB cut valve 48 to the integrators 106 and 107, either "1" when the valves are driven or "0" when the valves are not driven.

[0097] When the motion pattern determination result is an excavation motion, the motion pattern calculation unit 101A sets the first CB cut valve 47 to a drive state in which the opening is narrowed in order to supply pressure oil from the first pump 31 to the boom cylinder 21 and the bucket cylinder 23. Similarly, the motion pattern calculation unit 101A sets the second CB cut valve 48 to a drive state in which the opening is narrowed in order to supply pressure oil from the second pump 32 to the arm cylinder 22. In other words, the motion pattern calculation unit 101A outputs "1" to the integrators 106, 107 when driving.

[0098] In the case of a swing boom raising operation, the operation pattern calculation unit 101A sets a drive state such that the opening of the second CB cut valve 48 is narrowed in order to supply pressure oil from the second pump 32 to the swing hydraulic motor 5. On the other hand, since the pressure oil from the first pump 31 is not used to drive the hydraulic actuator, it is necessary to ensure the connection between the first pump 31 and the tank 34 via the first center bypass line 37. Therefore, a drive state is set such that the opening of the first CB cut valve 47 is maintained. In other words, the operation pattern calculation unit 101A outputs "0" to the integrator 106 when the valve is not driven, and "1" to the integrator 107 when the valve is driven.

[0099] In the case of boom raising alone, the operation pattern calculation unit 101A sets a drive state in which the openings of the first CB cut valve 47 and the second CB cut valve 48 are narrowed in order to supply pressure oil from the first pump 31 and the second pump 32 to the boom cylinder 21. In other words, the operation pattern calculation unit 101A outputs "1" to the integrators 106, 107 when driving.

[0100] The integrators 106 and 107 for the first CB cut valve 47 and the second CB cut valve 48 respectively integrate the operation signal of the boom operation of the operation device 7 and the setting result of the drive state for the first CB cut valve 47 and the second CB cut valve 48 by the operation pattern calculation unit 101A. The integration results are output to the function generators 116 and 117 for the first CB cut valve 47 and the second CB cut valve 48. In other words, the integrators 106 and 107 output to the function generators 116 and 117 a value equal to the operation signal of the boom operation of the operation device 7 when the first CB cut valve 47 and the second CB cut valve 48 are driven, and output a value (signal) of "0" when the first CB cut valve 47 and the second CB cut valve 48 are not driven.

[0101] The function generators 116 and 117 calculate the opening areas of the first CB cut valve 47 and the second CB cut valve 48 according to the outputs (integration results) of the integrators 106 and 107. The calculation results are output to the output conversion units 126 and 127 for the first CB cut valve 47 and the second CB cut valve 48. The first CB cut valve 47 and the second CB cut valve 48 are controlled so that the opening areas become smaller as the operation amount of the boom operation becomes larger.

[0102] The output conversion unit 126 and the output conversion unit 127 are calculation units that convert the opening areas of the first CB cut valve 47 and the second CB cut valve 48, which are the outputs (calculation results) of the function generators 116 and 117, into displacement amounts (strokes). The calculation results are output to the first CB cut valve 47 and the second CB cut valve 48 as a first cut control command C6 and a second cut control command C7. This controls the first CB cut valve 47 and the second CB cut valve 48 to the desired stroke and opening area.

[0103] Next, the operation of the work machine according to the second embodiment will be described with reference to FIGS.

[0104] When the control device 100A shown in Fig. 10 determines that the operation is an "excavation operation" based on the operation signals of each operation of the operating device 7, it controls so as to drive the first boom direction control valve 41 and the bucket direction control valve 45 shown in Fig. 8, as in the first embodiment, and controls so as to drive the second arm direction control valve 44. In the case of this embodiment, at the same time, it controls so as to drive the first CB cut valve 47 and the second CB cut valve 48, thereby narrowing the openings of the first CB cut valve 47 and the second CB cut valve 48.

[0105] As a result, the outflow of pressurized oil from the first pump 31 to the tank 34 is restricted by the first CB cut valve 47, so that the pressurized oil of the first pump 31 is supplied to the boom cylinder 21 via the first boom flow control valve 51 and the first boom direction control valve 41, and is also supplied to the bucket cylinder 23 via the bucket flow control valve 55 and the bucket direction control valve 45. In addition, the outflow of pressurized oil from the second pump 32 to the tank 34 is restricted by the second CB cut valve 48, so that the pressurized oil of the second pump 32 is supplied to the arm cylinder 22 via the second arm flow control valve 54 and the second arm direction control valve 44.

[0106] Furthermore, when it is determined that the operation is a "swing boom raising operation", similarly to the first embodiment, the swing directional control valve 46 is controlled to be driven, and the first directional control valve for ACC 83 is controlled to be driven. Furthermore, the first directional control valve for boom 41 is controlled to be driven, and the first flow control valve for boom 51 is controlled to be driven (to close the opening). In the case of this embodiment, at the same time, the second CB cut valve 48 is controlled to be driven to narrow the opening of the second CB cut valve 48, while the first CB cut valve 47 is not driven to maintain the opening of the first CB cut valve 47.

[0107] As a result, the outflow of pressure oil from the second pump 32 to the tank 34 is restricted by the second CB cut valve 48, and the pressure oil of the second pump 32 is supplied to the swing hydraulic motor 5 via the swing flow control valve 56 and the swing direction control valve 46. In addition, the pressure oil of the accumulator 78 is supplied to the boom cylinder 21 via the ACC first direction control valve 83, while the return oil of the boom cylinder 21 is led from the boom first actuator line 61 to the tank 34 via the boom first direction control valve 41 by the boom first return line 71. At this time, the flow of pressure oil from the first pump 31 to the boom cylinder 21 via the boom first direction control valve 41 is finally blocked by the boom first flow control valve 51, while the flow of pressure oil from the first pump 31 to the tank 34 via the boom first direction control valve 41 is hardly restricted by the first CB cut valve 47. For this reason, it is possible to suppress pressure loss due to an increase in the discharge pressure of the first pump 31 as in the first embodiment.

[0108] Furthermore, when it is determined that the operation is a "boom raising only operation", similarly to the first embodiment, the first boom directional control valve 41, the second boom directional control valve 42, and the first ACC directional control valve 83 are controlled to be driven. In the case of this embodiment, at the same time, the first CB cut valve 47 and the second CB cut valve 48 are controlled to be driven, thereby narrowing the openings of the first CB cut valve 47 and the second CB cut valve 48.

[0109] As a result, the outflow of pressurized oil from the first pump 31 and the second pump 32 to the tank 34 is restricted by the first CB cut valve 47 and the second CB cut valve 48, so that the pressurized oil from the first pump 31 and the second pump 32 is supplied to the boom cylinder 21 via the first boom direction control valve 41 and the second boom direction control valve 42. In addition, the pressurized oil from the accumulator 78 is supplied to the boom cylinder 21 via the first ACC direction control valve 83.

[0110] According to the second embodiment of the work machine of the present invention described above, similarly to the first embodiment, when pressure oil is supplied to the hydraulic actuators 21, 22, 23, 5 only from the accumulator 78, the meter-out sides of the hydraulic actuators 21, 22, 23, 5 are connected to the tank 34 by driving the directional control valves 41A-46A (first control valves), and the flow of pressure oil from the first pump 31 and the second pump 32 (hydraulic pumps) to the hydraulic actuators 21, 22, 23, 5 via the directional control valves 41A-46A (first control valves) is blocked by driving the flow control valves 51-56 (flow control mechanisms). Therefore, even when pressure oil is supplied to the hydraulic actuators 21, 22, 23, 5 from the accumulator 78, the return oil from the hydraulic actuators 21, 22, 23, 5 can be discharged to the tank 34 via the directional control valves 41A-46A (first control valves). That is, the control of the flow on the meter-out side of the hydraulic actuators 21, 22, 23, and 5 can be realized only by the directional control valves 41A-46A (first control valves). Therefore, there is no need to provide a meter-out circuit such as a return oil path or a flow control valve for the directional control valves 83-86 (second control valves), and it is possible to suppress the complexity of the configuration of the hydraulic system 30A that can supply pressure oil from the accumulator 78 to the hydraulic actuators 21, 22, 23, and 5 in addition to the first pump 31 and the second pump 32 (hydraulic pumps).

[0111] In the present embodiment, the directional control valves 41A to 46A (first control valves) are control valves provided on a first center bypass line 37 and a second center bypass line 38 (center bypass line) that connect the first pump 31 and the second pump 32 (hydraulic pump) to the tank 34, and have opening characteristics in which the opening amount to the first center bypass line 37 and the second center bypass line 38 (center bypass line) is constant over the entire stroke. The hydraulic excavator (work machine) is provided with a first CB cut valve 47 and a second CB cut valve 48 (center bypass cut valves) that are provided downstream of the directional control valves 41A to 46A (first control valves) on the first center bypass line 37 and the second center bypass line 38 (center bypass line) and control the flow rate of pressure oil flowing through the first center bypass line 37 and the second center bypass line 38. Furthermore, when pressure oil is supplied from the accumulator 78 to the hydraulic actuators 21, 22, 23, 5, the control device 100A is configured to drive the first CB cut valve 47 and the second CB cut valve 48 (center bypass cut valves) to maintain the flow of pressure oil in the first center bypass line 37 and the second center bypass line 38 as is, and when pressure oil is supplied from the first pump 31 and the second pump 32 (hydraulic pump) to the hydraulic actuators 21, 22, 23, 5, the control device 100A is configured to drive the directional control valves 41A to 46A (first control valves) to connect the meter-in sides of the hydraulic actuators 21, 22, 23, 5 to the first pump 31 and the second pump 32 (hydraulic pump), and to drive the first CB cut valve 47 and the second CB cut valve 48 (center bypass cut valves) to throttle the flow of pressure oil in the first center bypass line 37 and the second center bypass line 38 (center bypass line).

[0112] According to this configuration, when the directional control valves 41A-46A are driven to connect the meter-out sides of the hydraulic actuators 21, 22, 23, 5 to the tank 34, the first CB cut valve 47 and the second CB cut valve 48 are controlled to be opened, thereby ensuring connection between the first pump 31 or the second pump 32 and the tank 34 via the directional control valves 41A-46A. This makes it possible to suppress pressure loss due to an unintended pressure rise in the first pump 31 or the second pump 32 when the hydraulic actuators 21, 22, 23, 5 are driven only by the pressure oil in the accumulator 78. [Third embodiment] Next, a third embodiment of a work machine of the present invention will be described with reference to Figures 11 to 14. In Figures 11 to 14, the same reference numerals as those in Figures 1 to 10 denote similar parts, and detailed descriptions thereof will be omitted. Figure 11 is a hydraulic circuit diagram showing the configuration of a hydraulic system provided in a work machine according to a third embodiment of the present invention.

[0113] The third embodiment of the work machine of the present invention differs from the first embodiment mainly in the following three points. First, in the hydraulic system 30B shown in Fig. 11, the opening characteristics (opening characteristics of the meter-in passage, the meter-out passage, and the center bypass passage) of the directional control valves 41B, 42B, 43B, 44B, 45B, and 46B are different. Second, in the hydraulic system 30B shown in Fig. 11, the flow control valves 51, 52, 53, 54, 55, and 56 (see Fig. 2) of the first embodiment are replaced with load check valves 51B, 52B, 53B, 54B, 55B, and 56B that block the flow of pressure oil from the hydraulic actuators 21, 22, 23, and 5 to the first pump 31 or the second pump 32. Thirdly, the control of the hydraulic system 30B of the control device 100B shown in FIG. 13 is changed in accordance with the difference in the opening characteristics of the directional control valves 41B to 46B and the replacement with the load check valves 51B to 56B.

[0114] Specifically, the directional control valves 41-46 of the first embodiment have opening characteristics in which the position (stroke) at which the meter-in passage starts to open is the same as the position (stroke) at which the meter-out passage starts to open (see FIG. 4). In contrast, the directional control valves 41B-46B in the hydraulic system 30B of the present embodiment have opening characteristics in which the meter-out passage opens widely before the meter-in passage opens.

[0115] Each of the directional control valves 41B to 46B has, for example, the opening characteristics shown in Fig. 12. Fig. 12 is an opening area diagram of the directional control valves 41B to 46B of the hydraulic system 30B shown in Fig. 11. In Fig. 12, the horizontal axis S4 represents the spool stroke, and the vertical axis A4 represents the opening area of ​​each of the meter-in passage, the meter-out passage, and the center bypass passage. The solid line represents the characteristics of the meter-in passage, the dashed line represents the characteristics of the meter-out passage, and the dashed line represents the characteristics of the center bypass passage.

[0116] The spool stroke (spool position) of the directional control valves 41B to 46B has a characteristic of increasing in proportion to the amount of operation of each operation of the operating device 7, similar to the case of each directional control valve 41 to 46 of the first embodiment. The center bypass passage is configured so that the opening area is narrowed as the spool stroke increases, similar to the case of the first embodiment. The meter-in passage is configured in advance so that it starts to open at a predetermined spool stroke (predetermined spool position) and the opening area gradually increases as the spool stroke increases from there, similar to the case of the first embodiment. Unlike the case of the first embodiment, the meter-out passage is set to a predetermined spool stroke different from the above-mentioned predetermined spool stroke so that it starts to open before the meter-in passage opens as the spool stroke increases, and the opening area increases sharply with respect to the increase in the spool stroke. The meter-out passage is configured so that the opening area is maintained constant at a maximum value at the stroke in which the meter-in passage is open. That is, the opening characteristics of the directional control valves 41B to 46B are such that, when the stroke is within a predetermined range ΔSto, the meter-out passage is in an open state, while the meter-out passage is in a closed state. Furthermore, when the stroke is larger than the predetermined range ΔSto, both the meter-in passage and the meter-out passage are in an open state.

[0117] In the directional control valves 41B to 46B having such opening characteristics, when the stroke is within a predetermined range ΔSto, it is possible to connect only the meter-out sides of the hydraulic actuators 21, 22, 23, 5 to the tank 34 without connecting the meter-in sides of the hydraulic actuators 21, 22, 23, 5 to the first pump 31 or the second pump 32. Therefore, in the case where only the pressure oil of the accumulator 78 is supplied to the hydraulic actuators 21, 22, 23, 5, even if the directional control valves 41B to 46B are driven to connect the meter-out sides of the hydraulic actuators 21, 22, 23, 5 to the tank 34, it is possible to cut off the supply of pressure oil from the first pump 31 or the second pump 32 to the hydraulic actuators 21, 22, 23, 5 via the directional control valves 41B to 46B without using the flow rate control valves 51 to 56 of the first embodiment.

[0118] Next, the control logic of the control device for the work machine according to the third embodiment will be described with reference to Fig. 13 and Fig. 14. Fig. 13 is a block diagram showing the control logic of the control device for the hydraulic system according to the third embodiment shown in Fig. 11.

[0119] The control logic of the control device 100B according to the third embodiment shown in FIG. 13 differs from that of the first embodiment in the following points. First, the control logic of the control device 100B is such that the flow control valves 51, 52 (see FIG. 3) of the first embodiment are replaced with the load check valves 51B, 52B, making it unnecessary to control the flow control valves 51, 52. That is, the control logic of the control device 100B shown in FIG. 13 is configured such that the function generators 113, 114 and the output conversion units 123, 124 for the flow control valves 51, 52 in the control logic of the control device 100 shown in FIG. 6 are deleted. Second, the drive of the directional control valves 41B, 42B for each operation pattern of the hydraulic excavator is changed in accordance with the above-mentioned opening characteristic. In detail, in the control logic of the control device 100B shown in Fig. 13, the integrators 103 and 104 for the directional control valves 41 and 42 in the control logic of the control device 100 shown in Fig. 6 are deleted, and the function generators 111 and 112 for the directional control valves 41 and 42 are changed to function generators 111B and 112B having different characteristics. Thirdly, the output of the operation pattern calculation unit 101B is changed in accordance with the deletion of the integrators 103 and 104 and the function generators 113 and 114 in the first embodiment shown in Fig. 6 and the change of the function generators 111 and 112 to function generators 111B and 112B. The integrator 105, the function generator 115, and the output conversion unit 125 for the ACC first directional control valve 83 are the same as those in the first embodiment.

[0120] The motion pattern calculation unit 101B outputs a setting result of the hydraulic source of the hydraulic actuator (boom cylinder 21) corresponding to the directional control valves 41B, 42B according to the determined motion pattern, instead of outputting a setting of whether or not to drive the directional control valves 41B, 42B to the function generators 111B, 112B for the directional control valves 41B, 42B ("1" for driving or "0" for not driving). That is, when the determined motion pattern is an excavation motion, the motion pattern calculation unit 101B sets only the first pump 31 as the hydraulic source of the boom cylinder 21. When the motion pattern is a swing boom raising motion, the motion pattern calculation unit 101B sets only the accumulator 78 as the hydraulic source of the boom cylinder 21. When the boom raising motion is the only boom raising motion, the first pump 31, the second pump 32, and the accumulator 78 are set as the hydraulic source of the boom cylinder 21. The setting result of the hydraulic source output from the motion pattern calculation unit 101B is used to switch between two characteristics of the function generators 111B, 112B, which will be described later.

[0121] The function generators 111B and 112B have, for example, the characteristics shown in Fig. 14. Fig. 14 is a characteristic diagram used by the function generators 111B and 112B of the control device 100B shown in Fig. 13. In Fig. 14, the horizontal axis L represents the operation amount (%) of the operation device, and the vertical axis S5 represents the spool stroke of the directional control valves 41B and 42B.

[0122] The function generators 111B and 112B have two different characteristics, and are configured to switch to one of the two characteristics depending on the setting result of the hydraulic source of the hydraulic actuator (boom cylinder 21), which is the output of the operation pattern calculation unit 101B. The characteristic diagram of the solid line is used when the first pump 31 or the second pump 32 is set as the hydraulic source of the hydraulic actuators 21, 22, 23, and 5. In this characteristic diagram, the spool stroke increases in proportion to the increase in the operation amount of the operating device 7. The characteristic diagram of the broken line is used when only the accumulator 78 is set as the hydraulic source of the hydraulic actuators 21, 22, 23, and 5. In this characteristic diagram, when the operation amount of the operating device 7 increases, the spool stroke increases up to a predetermined spool stroke, but thereafter, the spool stroke is limited and remains constant. This limiting of the spool stroke means that the directional control valves 41B and 42B are driven with a spool stroke up to a predetermined range ΔSto in the opening characteristic of the directional control valves 41B and 42B shown in FIG. 12. This is for controlling the directional control valves 41B, 42B so that the meter-in passages of the directional control valves 41B, 42B remain closed and only the meter-out passages are open.

[0123] Function generators 111B, 112B select a characteristic diagram according to the output of operation pattern calculation unit 101B (the setting result of the hydraulic source of hydraulic actuator 21), and use the selected characteristic diagram to calculate the spool stroke of directional control valves 41B, 42B based on the operation amount of boom operation output from the operation device 7. The calculated spool stroke is output to output conversion units 121B, 122B.

[0124] The output conversion units 121B, 122B are calculation units that convert the spool strokes (spool displacement amounts) of the directional control valves 41B, 42B, which are the outputs (calculation results) of the function generators 111B, 112B, into command values ​​(for example, current values) for the directional control valves 41B, 42B. The calculation results are output to the first boom direction control valve 41B and the second boom direction control valve 42B as a first boom direction control command C1B and a second boom direction control command C2B. This makes it possible to control the first boom direction control valve 41B and the second boom direction control valve 42B to the desired stroke and opening area.

[0125] Next, the operation of the work machine according to the third embodiment will be described with reference to Figs.

[0126] When the operation pattern calculation unit 101B of the control device 100B shown in Fig. 13 determines that the operation is an "excavation operation" based on the operation signals of each operation of the operating device 7, it sets the first pump 31 as the hydraulic source of the boom cylinder 21. The function generator 111B selects a pump characteristic diagram (characteristic diagram indicated by a solid line) from the two characteristic diagrams shown in Fig. 14 based on the setting result of the first pump 31 as the hydraulic source of the boom cylinder 21 by the operation pattern calculation unit 101B, and calculates a spool stroke corresponding to the boom operation amount using the selected characteristic diagram. The first boom directional control command C1B corresponding to the spool stroke calculated by the function generator 111B is output to control the driving of the first boom directional control valve 41B.

[0127] In this case, in the first boom direction control valve 41B having the opening characteristic shown in Fig. 12, the meter-in passage has an opening area corresponding to the boom operation amount, while the meter-out passage opens widely (the opening area becomes maximum). The center bypass passage is narrowed as in the first embodiment. As a result, pressure oil of the first pump 31 shown in Fig. 11 is supplied to the boom cylinder 21 via the load check valve 51B and the first boom direction control valve 41B (meter-in passage). At the same time, return oil of the boom cylinder 21 is led from the first boom direction control valve 41B (meter-out passage) to the tank 34 via the first boom return line 71.

[0128] When it is determined that the operation is a "swing boom raising operation", the control device 100B sets only the accumulator 78 as the hydraulic source for the boom cylinder 21. In this case, the function generator 111B selects a characteristic diagram for the accumulator shown in Fig. 14 (characteristic diagram indicated by a broken line) based on the result of the setting of the hydraulic source for only the accumulator 78 by the operation pattern calculation unit 101B, and calculates a spool stroke corresponding to the amount of boom operation using the selected characteristic diagram. The first boom directional control command C1B corresponding to the spool stroke calculated by the function generator 111B is output to control the driving of the first boom directional control valve 41B.

[0129] In this case, the drive of the first boom direction control valve 41B is limited to a spool stroke within a predetermined range ΔSto in the opening characteristic shown in Fig. 12 by limiting the spool stroke according to the characteristic diagram of the dashed line shown in Fig. 14. That is, the first boom direction control valve 41B is driven so that the meter-in passage is closed and the meter-out passage is open.

[0130] 11 is supplied to the boom cylinder 21 via the first ACC directional control valve 83, the return oil of the boom cylinder 21 is guided from the first boom actuator line 61 through the first boom directional control valve 41 (meter-out passage) by the first boom return line 71 to the tank 34. At the same time, the supply of pressure oil from the first pump 31 to the boom cylinder 21 is blocked by the first boom directional control valve 41 with the meter-in passage closed. This makes it possible to prevent unintended supply of pressure oil from the first pump 31 to the boom cylinder 21.

[0131] Furthermore, when it is determined that the operation is a "boom raising operation alone", the operation pattern calculation unit 101B sets the first pump 31, the second pump 32, and the accumulator 78 as the hydraulic source of the boom cylinder 21. The function generators 111B and 112B select a characteristic diagram for the pump (characteristic diagram indicated by a solid line) based on the setting result of the first pump 31 and the second pump 32 as the hydraulic source of the boom cylinder 21 by the operation pattern calculation unit 101B, and calculate a spool stroke corresponding to the boom operation amount using the selected characteristic diagram. The first boom directional control command C1B and the second boom directional control command C2B corresponding to the calculated spool stroke by the function generators 111B and 112B are output to control the driving of the first boom directional control valve 41B and the second boom directional control valve 42B.

[0132] In this case, in the first boom direction control valve 41B and the second boom direction control valve 42 having the opening characteristic shown in Fig. 12, the meter-in passage has an opening area according to the boom operation amount, while the meter-out passage opens widely (the opening area becomes maximum). As a result, the pressure oil of the first pump 31 is supplied to the boom cylinder 21 via the load check valve 51B and the first boom direction control valve 41B (meter-in passage). In addition, the pressure oil of the second pump 32 is supplied to the boom cylinder 21 via the load check valve 52B and the second boom direction control valve 42B (meter-in passage). In addition, the pressure oil of the accumulator 78 is supplied to the boom cylinder 21 via the first ACC direction control valve 83. At the same time, the return oil of the boom cylinder 21 is led from the first boom direction control valve 41B (meter-out passage) via the first boom return line 71 to the tank 34, and is also led from the second boom direction control valve 42B (meter-out passage) via the second boom return line 72 to the tank 34. In this way, pressure oil can be supplied to the boom cylinder 21 from three hydraulic sources, namely, the first pump 31, the second pump 32, and the accumulator 78.

[0133] According to the third embodiment of the work machine of the present invention described above, similarly to the first embodiment, when pressure oil is supplied to the hydraulic actuators 21, 22, 23, 5 only from the accumulator 78, the meter-out sides of the hydraulic actuators 21, 22, 23, 5 are connected to the tank 34 by driving the directional control valves 41B-46B (first control valves), and the flow of pressure oil from the first pump 31 and the second pump 32 (hydraulic pumps) to the hydraulic actuators 21, 22, 23, 5 via the directional control valves 41B-46B (first control valves) is blocked by driving the directional control valves 41B-46B (flow rate control mechanism). Therefore, even when pressure oil is supplied to the hydraulic actuators 21, 22, 23, 5 from the accumulator 78, the return oil from the hydraulic actuators 21, 22, 23, 5 can be discharged to the tank 34 via the directional control valves 41B-46B (first control valves). That is, the control of the flow on the meter-out side of the hydraulic actuators 21, 22, 23, and 5 can be realized only by the directional control valves 41B-46B (first control valves). Therefore, there is no need to provide a meter-out circuit such as a return oil path or a flow control valve for the directional control valves 83-86 (second control valves), and it is possible to suppress the complexity of the configuration in the hydraulic system 30B that can supply pressure oil from the accumulator 78 to the hydraulic actuators 21, 22, 23, and 5 in addition to the first pump 31 and the second pump 32 (hydraulic pumps).

[0134] In the present embodiment, the directional control valves 41B to 46B (first control valves) are configured to include a flow control mechanism by having specific opening characteristics in the meter-in passages for connecting the first pump 31 and the second pump 32 (hydraulic pumps) to the hydraulic actuators 21, 22, 23, and 5 and the meter-out passages for connecting the tank 34 to the hydraulic actuators 21, 22, 23, and 5. The specific opening characteristics of the directional control valves 41B to 46B (first control valves) are such that, when the stroke is within a predetermined range, the meter-in passage is in an open state, while the meter-out passage is in a closed state, and when the stroke is larger than the predetermined range, both the meter-in passage and the meter-out passage are in an open state.

[0135] According to this configuration, when pressurized oil is supplied to the hydraulic actuators 21, 22, 23, and 5 only from the accumulator 78, the return oil from the hydraulic actuators 21, 22, 23, and 5 can be discharged to the tank 34 and the flow of pressurized oil from the first pump 31 and the second pump 32 (hydraulic pumps) to the hydraulic actuators 21, 22, 23, and 5 can be blocked by controlling only the directional control valves 41B to 46B.

[0136] In addition, in this embodiment, when pressure oil is supplied to the hydraulic actuators 21, 22, 23, 5 only from the accumulator 78, the control device 100B is configured to control the directional control valves 41B to 46B (first control valves) so that the strokes of the directional control valves 41B to 46B (first control valves) are within a predetermined range ΔSto.

[0137] According to this configuration, when only the accumulator 78 is used as the hydraulic source, by controlling only the directional control valves 41B to 46B, it is possible to discharge the return oil from the hydraulic actuators 21, 22, 23, 5 to the tank 34 and to cut off the flow of pressurized oil from the first pump 31 and the second pump 32 (hydraulic pumps) to the hydraulic actuators 21, 22, 23, 5, thereby making it possible to simplify the configuration of the hydraulic system 30B compared to the first embodiment.

[0138] [Other embodiments] In the above-described first to third embodiments, an example has been shown in which the present invention is applied to a hydraulic excavator, but the present invention can be widely applied to various types of work machines equipped with hydraulic systems 30, 30A, 30B that can supply pressurized oil from accumulator 78 to hydraulic actuators 21, 22, 23, 5 in addition to hydraulic pumps 31, 32.

[0139] Furthermore, the present invention is not limited to the above-described embodiment, and various modified examples are included. The above-described embodiment has been described in detail to easily explain the present invention, and is not necessarily limited to those having all of the configurations described. For example, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

[0140] In addition, each function of the control devices 100, 100A, and 100B in the above-described embodiments may be realized in hardware by designing a part or all of them as an integrated circuit. In addition, information such as programs, tables, and files that realize each function can be stored in a recording device such as a hard disk or SSD (Solid State Drive), or a recording medium such as an IC card, SD card, or DVD, in addition to the storage device 100a. [Explanation of symbols]

[0141] 5...swing hydraulic motor (hydraulic actuator), 21...boom cylinder (hydraulic actuator), 22...arm cylinder (hydraulic actuator), 23...bucket cylinder (hydraulic actuator), 31...first hydraulic pump (hydraulic pump), 32...second hydraulic pump (hydraulic pump), 34...tank, 37...first center bypass line (center bypass line), 38...second center bypass line (center bypass line), 41-46, 41A-46A, 41B-46B...directional control valve (first control valve, flow control mechanism), 47...first center bypass cut valve (center bypass cut valve), 48...second center bypass cut valve (center bypass cut valve), 51-56...flow control valve (flow control mechanism), 83-86...accumulator directional control valve (second control valve), 78...accumulator, 100, 100A, 100B...Control device

Claims

1. A hydraulic pump that discharges pressure oil; a hydraulic actuator driven by pressure oil discharged from the hydraulic pump; A tank for storing return oil discharged from the hydraulic actuator; an accumulator that accumulates pressure oil discharged from the hydraulic pump and supplies the accumulated pressure oil to the hydraulic actuator; a first control valve that controls a connection between a meter-in side of the hydraulic actuator and the hydraulic pump and also controls a connection between a meter-out side of the hydraulic actuator and the tank; a second control valve that controls a connection between a meter-in side of the hydraulic actuator and the accumulator, a flow rate control mechanism for controlling a flow rate of pressure oil from the hydraulic pump to the hydraulic actuator via the first control valve; a control device that controls the first control valve, the second control valve, and the flow rate control mechanism, When pressure oil is supplied to the hydraulic actuator only from the accumulator, Driving the second control valve to connect a meter-in side of the hydraulic actuator and the accumulator; Driving the first control valve to connect a meter-out side of the hydraulic actuator to the tank; The flow rate control mechanism is driven to block the flow of pressure oil from the hydraulic pump to the hydraulic actuator via the first control valve. A working machine characterized by:

2. 2. The work machine according to claim 1, the first control valve has an opening characteristic in which a predetermined stroke is set at which a meter-in passage for connecting the hydraulic pump to the hydraulic actuator and a meter-out passage for connecting the tank to the hydraulic actuator begin to communicate with each other, The flow rate control mechanism is configured with a control valve different from the first control valve. A working machine characterized by:

3. 3. The work machine according to claim 2, the first control valve is a control valve provided on a center bypass line that connects the hydraulic pump and the tank, the first control valve has an opening characteristic in which an opening amount to the center bypass line is constant over an entire stroke, a center bypass cut valve that is provided on the center bypass line downstream of the first control valve and controls a flow rate of pressure oil flowing through the center bypass line, The control device includes: When pressure oil is supplied from the accumulator to the hydraulic actuator, the center bypass cut valve is driven to maintain the flow of pressure oil in the center bypass line as it is, When pressure oil is supplied from the hydraulic pump to the hydraulic actuator, the first control valve is driven to connect the meter-in side of the hydraulic actuator to the hydraulic pump, and the center bypass cut valve is driven to throttle the flow of pressure oil in the center bypass line. A working machine characterized by:

4. 2. The work machine according to claim 1, the first control valve is configured to include the flow rate control mechanism by having a meter-in passage for connecting the hydraulic pump to the hydraulic actuator and a meter-out passage for connecting the tank to the hydraulic actuator each have a specific opening characteristic; The particular opening characteristic of the first control valve is When the stroke is within a predetermined range, the meter-out passage is in an open state, while the meter-in passage is in a closed state, When the stroke is larger than the predetermined range, both the meter-in passage and the meter-out passage are in an open state. A working machine characterized by:

5. 5. The working machine according to claim 4, When pressure oil is supplied to the hydraulic actuator only from the accumulator, the control device controls the first control valve so that a stroke of the first control valve is within the predetermined range. A working machine characterized by:

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