Work machine

Abstract

This work machine is provided with: a direction control valve that controls the flow of pressure oil to a hydraulic actuator; a flow rate control valve that is disposed upstream of the direction control valve and controls the flow rate of pressure oil to the hydraulic actuator; and a control device that controls the direction control valve and the flow rate control valve on the basis of instruction information, which is an operation instruction to the driven body that is driven by the hydraulic actuator. The control device determines whether a differential pressure across the flow rate control valve obtained from the detection value of the pressure sensor is within a predetermined range. If the differential pressure across the flow rate control valve is outside the predetermined range, the control device controls the direction control valve by using a final target opening, which is calculated by adjusting the target opening of the direction control valve calculated on the basis of the instruction information so that the differential pressure across the flow rate control valve falls within the predetermined range.

Description

Work machinery

[0001] The present invention relates to a work machine, and more particularly to a work machine that drives a driven body such as a work implement or a rotating body by a hydraulic actuator.

[0002] A work machine such as a hydraulic excavator includes a vehicle body including a revolving body and a work device attached to the revolving body. Driven bodies such as the revolving body and the work device are driven by hydraulic actuators such as hydraulic motors and hydraulic cylinders. The work device is an articulated device configured by rotatably connecting multiple link members, and may include, for example, a boom connected to the revolving body so as to be rotatable in the vertical direction, an arm connected to the tip of the boom so as to be rotatable in the vertical direction, and a bucket connected to the tip of the arm so as to be rotatable in the vertical direction. The boom, arm, and bucket are driven by a boom cylinder, an arm cylinder, and a bucket cylinder, respectively. It is not easy to manually operate the multiple link members that make up the work device to excavate a predetermined area using an operating device, and an operator must be highly skilled in operating the device.

[0003] One example of a method for facilitating such work is the technology described in Patent Document 1. The area-limiting excavation control device for a construction machine described in Patent Document 1 performs control (direction change control) to slow down the movement of the front equipment in a direction approaching the boundary of the set area by correcting the operation signal of an operating lever device related to the front equipment (working equipment) using a first signal correction means. When the front equipment approaches the boundary of the set area, the movement in the direction approaching the boundary is slowed down, making it possible to move the front equipment along the boundary of the set area. This allows the operator to perform work with high precision and stability, regardless of their level of proficiency in operating techniques.

[0004] However, the technology described in Patent Document 1 has the following problem. When semi-automatically controlling a front device (working device) in response to a command from a control device that corrects the operation signal of a control lever device, it is important that the tip of the front device accurately move along a target trajectory. To achieve this, it is necessary to match the flow rate of pressure oil supplied to the hydraulic actuator that drives the front device with the target flow rate. In the area-limiting excavation control device described in Patent Document 1, the opening of the flow control valve is adjusted by controlling the control pressure (pilot pressure) that drives the flow control valve, thereby controlling the flow rate supplied to the hydraulic actuator. However, even if the opening of the flow control valve can be accurately controlled, if the differential pressure across the flow control valve fluctuates due to load fluctuations in the front device (fluctuations in the load pressure of the hydraulic actuator), the flow rate of pressure oil supplied to the hydraulic actuator via the flow control valve may fluctuate and become unstable.

[0005] As means for solving such problems, for example, the techniques described in Patent Document 2 and Patent Document 3 have been proposed.

[0006] In the hydraulic control valve device described in Patent Document 2, a seat valve cooperating with a pilot control valve is arranged in series upstream of a directional control valve. The seat valve and pilot control valve function as auxiliary flow control means that auxiliary control the flow rate of pressure oil supplied to the directional control valve in accordance with the differential pressure across the directional control valve. The seat valve and pilot control valve control the differential pressure across the directional control valve so that it is maintained at a predetermined value regardless of fluctuations in the load pressure of the hydraulic actuator or the supply pressure of the hydraulic pump. In other words, the seat valve cooperates with the pilot control valve to provide pressure compensation for the directional control valve. Therefore, even if the load pressure of the hydraulic actuator or the supply pressure of the hydraulic pump fluctuates, the seat valve and pilot control valve maintain the differential pressure across the directional control valve at a predetermined value, making it possible to accurately control the flow rate of pressure oil supplied to the hydraulic actuator via the directional control valve.

[0007] In the hydrostatic drive system described in Patent Document 3, the flow rate of pressure medium (pressure oil) supplied to a consumer (hydraulic actuator) is controlled by a regulating valve (flow control valve) with a throttling action. The opening of the regulating valve is adjusted according to the pressure drop (differential pressure before and after the regulating valve) detected by a pressure sensor so that the volumetric flow rate required by a setting device is supplied to the consumer. This makes it possible to accurately control the flow rate of pressure medium supplied to the consumer without an additional pressure compensator, even if the load pressure of the consumer or the supply pressure of the hydraulic pump fluctuates.

[0008] International Publication No. 1995 / 030059 Japanese Patent Application Laid-Open No. 6-137304 Japanese Patent Application Laid-Open No. 2014-98487

[0009] When the restriction of a flow control valve that controls a flow rate, such as the seat valve described in Patent Document 2 or the regulating valve described in Patent Document 3, is defined as an orifice restriction, the flow rate Q passing through the flow control valve is expressed by the following equation (1).

[0010] Q = a × √(2 × ΔP / ρ) × Cd ... Equation (1) where a is the opening area of ​​the flow control valve, ΔP is the differential pressure across the flow control valve, ρ is the density of the hydraulic oil, and Cd is the flow coefficient of the flow control valve.

[0011] In the hydraulic control valve device described in Patent Document 2, the seat valve functioning as a flow control valve has a poppet-type valve structure. The valve displacement of a poppet valve is determined by the balance of forces generated by three pressures: the pressure on the primary side (pump side), the pressure on the secondary side (the inlet side of the directional control valve), and the pressure on the back pressure side (pilot passage side). For this reason, poppet valves are susceptible to fluid forces, pressure pulsations, and load fluctuations, which can lead to unstable behavior and reduced flow control accuracy. In particular, under conditions where the target flow rate is low and the differential pressure across the valve is high, the accuracy of flow control by a poppet valve can be reduced. This is because, under these conditions (where Q is small and ΔP is large), as is clear from Equation (1), the opening area (a) of the poppet valve must be controlled within a small range. However, with a poppet valve, the change in opening area relative to valve displacement is relatively larger than with a spool valve, and therefore the change in opening area relative to valve displacement errors caused by disturbances such as fluctuations in the load pressure of the hydraulic actuator is relatively large. Therefore, when the opening area needs to be controlled in a small area, the effect on the flow rate of the passage caused by the change in opening area due to disturbances becomes relatively large, and there is a concern that the accuracy of the flow rate control will decrease.

[0012] Furthermore, in the drive system described in Patent Document 3, the opening amount of the regulating valve is adjusted according to the pressure drop (differential pressure across the regulating valve) detected by a pressure sensor. Therefore, measurement errors of the pressure sensor can affect the accuracy of flow control by the regulating valve (flow control valve). Particularly under conditions where the target flow rate is high and the differential pressure across the valve is low, as is clear from Equation (1), the opening area (a) of the regulating valve needs to be set large. In this case, deviations in the differential pressure across the valve due to measurement errors of the pressure sensor significantly affect the flow rate through the regulating valve, which may reduce the accuracy of flow control.

[0013] The present invention has been made to solve the above problems, and its object is to provide a work machine that can prevent a decrease in the accuracy of flow rate control for a hydraulic actuator, both when the flow rate through the flow control valve and the differential pressure before and after the valve are under conditions of a small flow rate and a high pressure difference, and when they are under conditions of a large flow rate and a low pressure difference.

[0014] The present application includes a plurality of means for solving the above-mentioned problems. One example of the present application is a work machine including a hydraulic actuator that drives a driven body, a hydraulic pump that supplies pressure oil to the hydraulic actuator, a directional control valve that controls a flow of pressure oil supplied from the hydraulic pump to the hydraulic actuator, a flow rate control valve that is arranged upstream of the directional control valve and controls a flow rate of pressure oil supplied from the hydraulic pump to the hydraulic actuator via the directional control valve, and a control device that controls the directional control valve and the flow rate control valve based on instruction information that instructs an operation of the driven body, the work machine including a pressure sensor that detects a differential pressure across the flow rate control valve, the control device determining whether the differential pressure across the flow rate control valve obtained from a detection value of the pressure sensor is within a predetermined range, and, if it is determined that the differential pressure across the flow rate control valve is outside the predetermined range, controlling the directional control valve using a final target opening obtained by adjusting a target opening of the directional control valve calculated based on the instruction information so that the differential pressure across the flow rate control valve is within the predetermined range.

[0015] According to one example of the present application, when the differential pressure across the flow control valve falls outside a predetermined range, the opening of the directional control valve is adjusted so that the differential pressure across the flow control valve falls within the predetermined range, making it possible to operate the flow control valve under a differential pressure across the flow control valve that provides flow control accuracy above the allowable accuracy. Therefore, it is possible to prevent a decrease in the accuracy of flow control for the hydraulic actuator both when the flow rate through the flow control valve and the differential pressure across the flow control valve are low and have a high pressure difference, and when they are high and have a low pressure difference. Other problems, configurations, and effects will become clear from the description of the embodiments below.

[0016] FIG. 1 is a side view showing a hydraulic excavator as an example of a work machine according to an embodiment of the present invention. FIG. 2 is a hydraulic circuit diagram showing a main configuration (main circuit) of a hydraulic system equipped in the work machine according to the embodiment shown in FIG. 1. FIG. 3 is a hydraulic circuit diagram showing a pilot circuit of the hydraulic system equipped in the work machine according to the embodiment shown in FIG. 1. FIG. 4 is a block diagram showing the hardware and functional configuration of a control device in the work machine according to an embodiment. FIG. 5 is a characteristics diagram showing the relationship between the differential pressure across a flow control valve, which is a component of the hydraulic system of the work machine according to the embodiment shown in FIG. 2, and the accuracy of flow control. FIG. 6 is a flowchart showing an example of a control procedure for a hydraulic pump by the control device for the work machine according to the embodiment shown in FIG. 4. FIG. 7 is a flowchart showing an example of a control procedure for a flow control valve by the control device for the work machine according to the embodiment shown in FIG. 4.

[0017] Hereinafter, an embodiment of a work machine of 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. Note that the front, rear, left, and right directions referred to in this specification refer to directions as seen by an operator riding on the work machine.

[0018] [One embodiment] First, the configuration of a hydraulic excavator as a work machine according to one embodiment will be described with reference to Fig. 1. Fig. 1 is a side view showing a hydraulic excavator as an example of a work machine according to one embodiment.

[0019] 1, the hydraulic excavator 1 is generally composed of a self-propelled running body 2, a rotating body 3 rotatably mounted on the running body 2, and a working device 4 attached to the rotating body 3 so as to be rotatable in the vertical direction. The rotating body 3 is configured to rotate relative to the running body 2 by a rotating device including a swing motor 6 (see also FIG. 2 described later) as a hydraulic actuator.

[0020] The traveling body 2 is provided with left and right (only one is shown) crawler-type traveling devices 8. The left and right traveling devices 8 are each driven by a traveling motor (only the left traveling motor 9 is shown) serving as a hydraulic actuator.

[0021] The revolving unit 3 includes a revolving frame 11 as a support structure rotatably mounted on the running unit 2, a cab 12 installed on the left front side of the revolving frame 11, a counterweight 13 provided at the rear end of the revolving frame 11, and a machinery room 14 provided between the cab 12 and the counterweight 13. The cab 12 is equipped with a driver's seat (not shown) where an operator sits, and operation devices 141 and 142 (see FIG. 3 described below) described below. The counterweight 13 is used to balance the weight of the work device 4. The machinery room 14 houses various devices such as a prime mover (not shown), hydraulic pumps 31, 32, and 33 (see FIG. 2 described below), a pilot pump 111 (see FIG. 3 described below), and a control valve block 15 as an assembly of multiple control valves.

[0022] The working device 4 is an articulated operating mechanism for performing excavation work and the like, and includes, for example, three link members: a boom 21, an arm 22, and a bucket 23 as an attachment. The base end of the boom 21 is rotatably attached to the front of the revolving unit 3. The base end of an arm 22 is rotatably attached to the tip of the boom 21. The base end of the bucket 23 is rotatably attached to the tip of the arm 22. The boom 21, arm 22, and bucket 23 as driven bodies are driven by a pair of hydraulic actuators: a boom cylinder 25, an arm cylinder 26, and a bucket cylinder 27 (see also FIG. 2 , which will be described later).

[0023] Next, the configuration of a hydraulic system provided in a work machine according to one embodiment will be described with reference to Figures 2 and 3. Figure 2 is a hydraulic circuit diagram showing the main configuration (main circuit) of the hydraulic system provided in the work machine according to the embodiment shown in Figure 1. Figure 3 is a hydraulic circuit diagram showing the configuration of a pilot circuit of the hydraulic system provided in the work machine according to the embodiment shown in Figure 1.

[0024] 2, the hydraulic excavator 1 is equipped with a hydraulic system 30 that hydraulically drives the driven bodies of the traveling body 2, the rotating body 3, and the work device 4 (see FIG. 1). The hydraulic system 30 is equipped with three main pumps, namely, a first hydraulic pump 31, a second hydraulic pump 32, and a third hydraulic pump 33, and a hydraulic oil tank 34 that stores hydraulic oil.

[0025] The three main pumps 31, 32, and 33 are driven by a prime mover (not shown). The first hydraulic pump 31, the second hydraulic pump 32, and the third hydraulic pump 33 are, for example, variable displacement hydraulic pumps, and each includes a first regulator, a second regulator, and a third regulator that adjust the tilt angle of the swash plate or the inclined axis. The first regulator includes a first command pressure port 31a to which a command pressure PiP1 is input from a pilot circuit 110 (described later), a first pump self-pressure port 31b to which the pressure on the discharge side of the first hydraulic pump 31 is input, and a second pump self-pressure port 31c to which the pressure on the discharge side of the second hydraulic pump 32 is input. The second regulator includes a second command pressure port 32a to which a command pressure PiP2 is input from the pilot circuit 110, a second pump self-pressure port 32b to which the pressure on the discharge side of the second hydraulic pump 32 is input, and a first pump self-pressure port 32c to which the pressure on the discharge side of the first hydraulic pump 31 is input. The third regulator includes a third command pressure port 33a to which the command pressure PiP3 is input from the pilot circuit 110, and a third pump self-pressure port 33b to which the pressure on the discharge side of the third hydraulic pump 33 is input.

[0026] A first discharge line 71 of the first hydraulic pump 31 is connected to the hydraulic oil tank 34 via a first center bypass line 72, and is also connected to the hydraulic oil tank 34 via a main relief valve 48 to protect the hydraulic circuit from an excessive pressure increase. Arranged on the first center bypass line 72, in this order from upstream, are the right travel direction control valve 36, the bucket direction control valve 37, the second arm direction control valve 38, and the first boom direction control valve 39. The bucket direction control valve 37, the second arm direction control valve 38, and the first boom direction control valve 39 are connected in parallel to a first parallel line 73 branching off from a portion of the first center bypass line 72 connecting the right travel direction control valve 36 and the bucket direction control valve 37, via first oil passages 74 and 75, second oil passages 76 and 77, and third oil passages 78 and 79, respectively.

[0027] The right traveling directional control valve 36 controls the flow of pressure oil supplied from the first hydraulic pump 31 to the right traveling motor of the pair of traveling motors. The bucket directional control valve 37 controls the flow of pressure oil supplied from the first hydraulic pump 31 to the bucket cylinder 27. The second arm directional control valve 38 controls the flow of pressure oil supplied from the first hydraulic pump 31 to the arm cylinder 26. The first boom directional control valve 39 controls the flow of pressure oil supplied from the first hydraulic pump 31 to the boom cylinder 25.

[0028] A second discharge line 81 of the second hydraulic pump 32 is connected to the hydraulic oil tank 34 via a second center bypass line 82, and is also connected to the hydraulic oil tank 34 via a main relief valve 49 to protect the hydraulic circuit from excessive pressure buildup. Arranged on the second center bypass line 82, in this order from upstream, are the second boom directional control valve 40, the first arm directional control valve 41, the first attachment directional control valve 42, and the left travel directional control valve 43. The second boom directional control valve 40, the first arm directional control valve 41, the first attachment directional control valve 42, and the left travel directional control valve 43 are connected in parallel to a second parallel line 83 connected to the second discharge line 81 via first oil passages 84 and 85, second oil passages 86 and 87, third oil passages 88 and 89, and fourth oil passage 90, respectively.

[0029] The second boom directional control valve 40 controls the flow of pressure oil supplied from the second hydraulic pump 32 to the boom cylinder 25. The first arm directional control valve 41 controls the flow of pressure oil supplied from the second hydraulic pump 32 to the arm cylinder 26. The first attachment directional control valve 42 controls the flow of pressure oil supplied to a first special-purpose hydraulic actuator (not shown) that drives a first special attachment (not shown), such as a chopper or grapple, when the first special attachment is attached instead of or in addition to the bucket 23 (see FIG. 1 ). The left travel directional control valve 43 controls the flow of pressure oil supplied from the second hydraulic pump 32 to the left travel motor 9 (see FIG. 1 ) of the pair of travel motors.

[0030] The fourth oil passage 90 is connected to the first discharge line 71 of the first hydraulic pump 31 via a connection line 80. A merging valve 65 is arranged on the connection line 80. The merging valve 65 controls the supply of pressure oil from the first hydraulic pump 31 from the connection line 80 to the fourth oil passage 90, and enables the pressure oil from the first hydraulic pump 31 to be merged with the pressure oil from the second hydraulic pump 32 and supplied to the left traveling motor 9.

[0031] A check valve 67 is disposed in the second parallel line 83 downstream of the connection point with the third oil line 88. The check valve 67 allows flow from the second parallel line 83 to the fourth oil line 90, while blocking flow from the connection line 80 to the directional control valves 40, 41, 42 other than the left traveling directional control valve 43.

[0032] A third discharge line 91 of the third hydraulic pump 33 is connected to the hydraulic oil tank 34 via a third center bypass line 92, and is also connected to the hydraulic oil tank 34 via a main relief valve 50 to protect the hydraulic circuit from excessive pressure buildup. On the third center bypass line 92, in this order from upstream, are arranged a swing directional control valve 44, a third boom directional control valve 45, and a second attachment directional control valve 46. The swing directional control valve 44, the third boom directional control valve 45, and the second attachment directional control valve 46 are connected in parallel to a third parallel line 93 connected to the third discharge line 91 via first oil passages 94 and 95, second oil passages 96 and 97, and third oil passages 98 and 99, respectively.

[0033] The swing directional control valve 44 controls the flow of pressure oil supplied from the third hydraulic pump 33 to the swing motor 6. The third boom directional control valve 45 controls the flow of pressure oil supplied from the third hydraulic pump 33 to the boom cylinder 25. The second attachment directional control valve 46 controls the flow of pressure oil supplied to the second special hydraulic actuator that drives the second special attachment when a second special attachment (not shown) equipped with a second special actuator (not shown) is attached in addition to the first special attachment instead of or in addition to the bucket 23, or when a second special attachment equipped with two special actuators, first and second, is attached instead of the first special attachment.

[0034] Furthermore, first oil lines 74, 75, second oil lines 76, 77, and third oil lines 78, 79, which connect the bucket directional control valve 37, the second arm directional control valve 38, and the first boom directional control valve 39 to the first parallel line 73, respectively, are provided with a bucket flow control valve 51, a second arm flow control valve 52, and a first boom flow control valve 53. The bucket flow control valve 51 controls the flow rate of pressure oil supplied from the first hydraulic pump 31 to the bucket cylinder 27 via the bucket directional control valve 37 (pump port). The second arm flow control valve 52 controls the flow rate of pressure oil supplied from the first hydraulic pump 31 to the arm cylinder 26 via the second arm directional control valve 38. The first boom flow control valve 53 controls the flow rate of pressure oil supplied from the first hydraulic pump 31 to the boom cylinder 25 via the first boom directional control valve 39.

[0035] First oil lines 84, 85, second oil lines 86, 87, and third oil lines 88, 89 connect the second boom directional control valve 40, the first arm directional control valve 41, and the first attachment directional control valve 42 to the second parallel line 83, respectively, and are provided with a second boom flow control valve 54, a first arm flow control valve 55, and a first attachment flow control valve 56. The second boom flow control valve 54 controls the flow rate of pressure oil supplied from the second hydraulic pump 32 to the boom cylinder 25 via the second boom directional control valve 40 (pump port). The first arm flow control valve 55 controls the flow rate of pressure oil supplied from the second hydraulic pump 32 to the arm cylinder 26 via the first arm directional control valve 41. The first attachment flow control valve 56 controls the flow rate of pressure oil supplied from the second hydraulic pump 32 to the first special actuator (not shown) via the first attachment directional control valve 42.

[0036] A swing flow control valve 57, a third boom flow control valve 58, and a second attachment flow control valve 59 are provided in first oil lines 94, 95, second oil lines 96, 97, and third oil lines 98, 99, which connect the swing directional control valve 44, the third boom directional control valve 45, and the second attachment directional control valve 46 to the third parallel line 93, respectively. The swing flow control valve 57 controls the flow rate of pressure oil supplied from the third hydraulic pump 33 to the swing motor 6 via the swing directional control valve 44 (pump port). The third boom flow control valve 58 controls the flow rate of pressure oil supplied from the third hydraulic pump 33 to the boom cylinder 25 via the third boom directional control valve 45. The second attachment flow control valve 59 controls the flow rate of pressure oil supplied from the third hydraulic pump 33 to a second special actuator (not shown) via the second attachment directional control valve 46.

[0037] All of the flow control valves 51 to 59 have the same configuration. In Figure 2, only the configurations of the second boom flow control valve 54 and the first arm flow control valve 55 are shown, and the configurations of the other flow control valves 51 to 53 and 55 to 59 are omitted. The components of the first arm flow control valve 55 shown in Figure 2 are the same as those of the second boom flow control valve 54, but only the reference numerals have been changed to those for the first arm. Here, only the configuration of the second boom flow control valve 54 will be described.

[0038] The second boom flow control valve 54 is, for example, a seat-type flow control valve, and has superior responsiveness characteristics to a spool-type flow control valve. The flow control valve 54 has a seat-type valve element 541 that forms a variable throttle between the first oil passage 84 on the primary side and the first oil passage 85 on the secondary side, a control variable throttle 542 that is provided on the valve element 541 so as to communicate with the primary side (first oil passage 84) of the valve element 541, a pilot line 543 that communicates between the downstream side of the control variable throttle 542 and the secondary side (first oil passage 85) of the valve element 541, and a pilot variable throttle 544 that is arranged on the pilot line 543. The housing incorporating the valve element 541 has a first pressure chamber 545 formed at a connection portion with the first oil passage 84, which is the primary side of the valve element 541 (variable throttle), a second pressure chamber 546 formed at a connection portion with the first oil passage 85, which is the secondary side of the valve element 541 (variable throttle), and a third pressure chamber 547 formed to communicate with the first pressure chamber 545 via the control variable throttle 542. The control variable throttle 542 is connected to the first pressure chamber 545 via an oil passage 548 formed inside the valve element 541, and is configured so that the opening area to the third pressure chamber 547 changes depending on the amount of movement of the valve element 541. The pilot variable throttle 544 has a pilot port 544p to which a command pressure (pilot pressure) generated in response to a command from the control device 200, which will be described later, is input, and the opening amount is adjusted depending on the pilot pressure input to the pilot port 544p.

[0039] In the flow control valve 54, the movement amount of the valve element 541 is determined by the action of the control variable throttle 542 in accordance with the pilot flow rate passing through the pilot line 543. The pilot flow rate in the pilot line 543 is controlled by the opening amount of the pilot variable throttle 544. Therefore, the movement amount of the valve element 541 can be controlled via the opening amount of the pilot variable throttle 544, which can control the pilot flow rate in the pilot line 543. In other words, the flow control valve 54 is configured to control the flow rate of pressure oil supplied to the second boom directional control valve 40 via the first oil passages 84, 85 in accordance with the opening amount of the pilot variable throttle 544.

[0040] 3, the hydraulic system 30 includes a pilot circuit 110 that controls the operation of the hydraulic pilot-type directional control valves 36-46 and the flow control valves 51-59 (see FIG. 2) and also controls the pump capacity of the hydraulic pumps 31-33 (see FIG. 2). The pilot circuit 110 includes a pilot pump 111 that serves as a pilot hydraulic source. The pilot pump 111 is connected to the hydraulic oil tank 34 via a pilot relief valve 112 that generates pilot primary pressure, and is also connected via a pilot line 114 to electromagnetic proportional pressure reducing valves 113a, 113b, 113c, 113d, 113e, 113f, and 113g that constitute a solenoid valve unit 113.

[0041] The electromagnetic proportional pressure reducing valve 113a is connected to the second command pressure port 32a of the second regulator of the second hydraulic pump 32, and reduces the discharge pressure (pilot primary pressure) of the pilot pump 111 in response to a command from the control device 200 (described later) to generate pilot secondary pressure PiP2 as a command pressure. The electromagnetic proportional pressure reducing valves 113b, 113c are connected to a pilot port (not shown) of the second boom direction control valve 40, and reduce the discharge pressure of the pilot pump 111 in response to a command from the control device 200 to generate pilot secondary pressures PiBm2R, PiBm2L as command pressures. The electromagnetic proportional pressure reducing valves 113d, 113e are connected to a pilot port (not shown) of the first arm direction control valve 41, and reduce the discharge pressure of the pilot pump 111 in response to a command from the control device 200 to generate pilot secondary pressures PiAm1C, PiAm1D as command pressures. The electromagnetic proportional pressure reducing valve 113f is connected to a pilot port 544p of the pilot variable throttle 544 of the second boom flow control valve 54, and reduces the discharge pressure of the pilot pump 111 in accordance with a command from the control device 200 to generate a pilot secondary pressure as a command pressure. The electromagnetic proportional pressure reducing valve 113g is connected to a pilot port 554p of the pilot variable throttle 554 of the first arm flow control valve 55, and reduces the discharge pressure of the pilot pump 111 in accordance with a command from the control device 200 to generate a pilot secondary pressure as a command pressure.

[0042] To avoid complicating the explanation, the electromagnetic proportional pressure reducing valves for the command pressure ports 31a, 33a of the regulators of the first hydraulic pump 31 and the third hydraulic pump 33 are not shown in the figure. Also, the electromagnetic proportional pressure reducing valves for the directional control valves 36 to 39 and 42 to 46 other than the second boom directional control valve 40 and the first arm directional control valve 41 are not shown in the figure. Furthermore, the electromagnetic proportional pressure reducing valves for the flow control valves 51 to 53 and 56 to 59 other than the second boom flow control valve 54 and the first arm flow control valve 55 are also not shown in the figure.

[0043] 2 and 3 , a pressure sensor 121 is provided in the second discharge line 81 of the second hydraulic pump 32. The pressure sensor 121 detects the discharge pressure of the second hydraulic pump 32 (the pressure on the upstream side of the flow control valves 54 to 56). The pressure sensor 121 outputs a detection signal PsP2 corresponding to the detected pressure value to a control device 200, which will be described later. A pressure sensor 122 is provided in a first oil passage 85 that connects the second boom direction control valve 40 and the corresponding flow control valve 54. The pressure sensor 122 detects the pressure on the downstream side of the flow control valve 54. The pressure sensor 122 outputs a detection signal PyBm2 corresponding to the detected pressure value to a control device 200, which will be described later. The pressure sensors 121 and 122 together constitute a pressure sensor that detects a differential pressure across the flow control valve 54. A pressure sensor 123 is provided in a second oil passage 87 that connects the first arm direction control valve 41 and the corresponding flow control valve 55. The pressure sensor 123 detects the pressure downstream of the flow control valve 55. The pressure sensor 123 outputs a detection signal PyAm1 corresponding to the detected pressure value to the control device 200 described below. The pressure sensors 121 and 123 constitute a pressure sensor that detects the differential pressure before and after the flow control valve 55.

[0044] Although not shown in the drawings for the sake of simplicity, similar pressure sensors are provided for the flow control valves 51 to 53 and 55 to 59 other than the flow control valves 54 and 55. These pressure sensors and the pressure sensor 121 constitute pressure sensors that detect the differential pressure before and after the flow control valves 51 to 53 and 55 to 59.

[0045] The boom cylinder 25, arm cylinder 26, and bucket cylinder 27 are respectively provided with a stroke sensor 131 that detects the stroke amount of the boom cylinder 25, a stroke sensor 132 that detects the stroke amount of the arm cylinder 26, and a stroke sensor 133 that detects the stroke amount of the bucket cylinder 27. Each of the stroke sensors 131, 132, and 133 outputs detection signals SBm, SAm, and SBk corresponding to the detected stroke value to the control device 200, which will be described later. These stroke sensors 131, 132, and 133 can detect, for example, the operating state and posture of the working device 4. Note that in place of the stroke sensors 131, 132, and 133, an inclination sensor, a rotation angle sensor, an IMU, or the like can also be used to detect the operating state and posture of the working device 4.

[0046] The hydraulic system 30 is equipped with operating devices including a boom operating lever 141 and an arm operating lever 142 that respectively instruct the operation of the boom 21 and arm 22 as driven bodies. The boom operating lever 141 is capable of switching between the first boom directional control valve 39, the second boom directional control valve 40, and the third boom directional control valve 45, and outputs an operating signal (electrical signal) as instruction information instructing the operation of the boom 21 to the control device 200 described below. The arm operating lever 142 is capable of switching between the first arm directional control valve 41 and the second arm directional control valve 38, and outputs an operating signal (electrical signal) as instruction information instructing the operation of the arm 22 to the control device 200 described below.

[0047] In order to avoid complicating the explanation of the operating devices, the right traveling operation lever that switches the right traveling direction control valve 36, the bucket operation lever that switches the bucket direction control valve 37, the first attachment operation lever that switches the first attachment direction control valve 42, the left traveling operation lever that switches the left traveling direction control valve 43, the swing operation lever that switches the swing direction control valve 44, and the second attachment operation lever that switches the second attachment direction control valve 46 are not shown in the figures.

[0048] The control device 200 controls the hydraulic system 30. The control device 200 is electrically connected to an operation device including the boom operation lever 141 and the arm operation lever 142, and operation signals of the operation levers 141, 142 of the operation device are input to the control device 200. The control device 200 is also electrically connected to the pressure sensors 121, 122, and 123, and detection signals PsP2, PyBm2, and PyAm1 of the pressure sensors 121, 122, and 123 are input to the control device 200.

[0049] The control device 200 controls the pump volume of the second hydraulic pump 32 via the second regulator of the second hydraulic pump 32 by controlling the electromagnetic proportional pressure reducing valve 113a of the pilot circuit 110 in accordance with the operation amounts (instruction information) of the operation devices 141, 142. Similarly, the control device 200 also controls the pump volumes of the first hydraulic pump 31 and the third hydraulic pump 33.

[0050] Furthermore, the control device 200 controls the hydraulic pilot type second boom directional control valve 40 and flow control valve 54 by controlling the electromagnetic proportional pressure reducing valves 113b, 113c and electromagnetic proportional pressure reducing valve 113f of the pilot circuit 110. Similarly, the control device 200 controls the hydraulic pilot type first arm directional control valve 41 and flow control valve 55 by controlling the electromagnetic proportional pressure reducing valves 113d, 113e and electromagnetic proportional pressure reducing valve 113g. The other directional control valves 37 to 39, 42, 44 to 46 and their corresponding flow control valves 51 to 53 and 56 to 59 are controlled in a similar manner.

[0051] Next, the hardware and functional configuration of the control device in the work machine according to one embodiment will be described using Figures 4 and 5. Figure 4 is a block diagram showing the hardware and functional configuration of the control device in the work machine according to one embodiment. Figure 5 is a characteristics diagram showing the relationship between the differential pressure across the flow control valve, which is a component of the hydraulic system of the work machine according to the embodiment shown in Figure 2, and the accuracy of flow control.

[0052] 4, the control device 200 basically controls the flow direction of the pressure oil supplied to each of the hydraulic actuators 6, 25 to 27 using each of the directional control valves 36 to 46, and also controls the flow rate (meter-in flow rate) of the pressure oil supplied to each of the hydraulic actuators 6, 25 to 27 using each of the flow control valves 51 to 59. However, in order to accurately control the meter-in flow rates of the hydraulic actuators 6, 25 to 27, when a pressure difference across the hydraulic fluid causes the accuracy of flow control by each of the flow control valves 51 to 59 to fall below an allowable accuracy, the control device 200 according to this embodiment is characterized in that, by adjusting the opening amount of the corresponding directional control valves 37 to 42, 44 to 46, the pressure difference across the hydraulic fluid supply valves 51 to 59 is adjusted so that the accuracy of flow control is equal to or higher than the allowable accuracy.

[0053] The control device 200 is configured, for example, by a computer including a storage device 201 including RAM, ROM, etc., and a processing device 202 including a CPU, MPU, etc. The storage device 201 pre-stores programs and various information necessary for controlling the discharge flow rates of the directional control valves 36-46 and the flow control valves 51-59, which are used to control the drive of the hydraulic actuators 6, 25-27, as well as the hydraulic pumps 31-33. The processing device 202 reads the programs and various information from the storage device 201 as appropriate, and executes processing in accordance with the programs to realize various functions. The control device 200 may be configured by one computer or by multiple computers.

[0054] The control device 200 has, as functional units for executing flow control of the meter-in flow rates of the hydraulic actuators 6, 25 to 27 with an allowable accuracy or higher, an actuator target flow rate calculation unit 211, a pump target flow rate calculation unit 212, a flow control valve target opening calculation unit 213, a flow control valve auxiliary target opening calculation unit 214, an upstream / downstream pressure difference determination unit 215, a flow control valve target opening determination unit 216, a directional control valve target opening calculation unit 217, and a directional control valve target opening adjustment unit 218.

[0055] The actuator target flow rate calculation unit 211 calculates the target flow rate to be supplied to each of the hydraulic actuators 6, 25 to 27 based on the operation signals (input values ​​of instruction information) of each of the operation levers 141, 142 of the operation device. The target flow rates of each of the hydraulic actuators 6, 25 to 27 as a result of the calculation are output to the pump target flow rate calculation unit 212 and the flow control valve target opening calculation unit 213.

[0056] The pump target flow rate calculation unit 212 calculates the pump target flow rate from the target flow rates of the hydraulic actuators 6, 25 to 27, which are the calculation results of the actuator target flow rate calculation unit 211. Furthermore, it generates a pump flow rate command (electrical signal) according to the pump target flow rate as a result of the calculation, and outputs it to the pump electromagnetic proportional pressure reducing valve 113a.

[0057] The flow control valve target opening calculation unit 213 calculates the target opening of each of the flow control valves 51 to 59 based on the target flow rates of each of the hydraulic actuators 6, 25 to 27, which are the calculation results of the actuator target flow rate calculation unit 211, and the detection values ​​of the pressure sensors 121 to 123 of the corresponding flow control valves 51 to 59. For this calculation, for example, an orifice restriction flow rate calculation formula or a preset map is used. That is, the target opening of each of the flow control valves 51 to 59 can be calculated based on the differential pressure across each of the flow control valves 51 to 59, which is obtained from the detection values ​​of the pressure sensors 121 to 123, and the target flow rates of each of the hydraulic actuators 6, 25 to 27 as the flow rates passing through each of the flow control valves 51 to 59. The calculated target opening of each of the flow control valves 51 to 59 is output to a flow control valve target opening determination unit 216.

[0058] The flow control valve auxiliary target opening calculation unit 214 uses a map in which the relationship between the operation amount (instruction information) of each operating lever 141, 142 of the operating device and the opening amount of each flow control valve 51 to 59 is predefined, and calculates the auxiliary target opening amount of each flow control valve 51 to 59 from the input operation signal (instruction information) of each operating lever 141, 142 of the operating device. The map is predefined in the storage device 201. The calculated auxiliary target opening amount of each flow control valve 51 to 59 is output to a flow control valve target opening determination unit 216. Note that the calculation of the auxiliary target opening amount may be performed by any method that uses control information in which the relationship between the operation amount (instruction information) of each operating lever 141, 142 of the operating device and the opening amount of each flow control valve 51 to 59 is predefined.

[0059] The upstream-to-downstream differential pressure determination unit 215 determines whether the upstream-to-downstream differential pressure of each of the flow control valves 51 to 59, obtained based on the detection values ​​(pressure values) of the pressure sensors 121 to 123, satisfies predetermined conditions. The determination result is output to the flow control valve target opening determination unit 216 and the directional control valve target opening adjustment unit 218.

[0060] This predetermined condition is set as a range of the upstream-to-downstream differential pressure within which the accuracy of flow control by each of the flow control valves 51 to 59 can be maintained at or above the allowable accuracy. Specifically, the relationship between the upstream-to-downstream differential pressure and the accuracy of flow control for each of the flow control valves 51 to 59 is as shown in the characteristic diagram in FIG. 5 . That is, the accuracy of flow control reaches an extreme value at a certain upstream-to-downstream differential pressure, and decreases as the upstream-to-downstream differential pressure decreases or increases from that extreme value. A tolerance is set for the control accuracy of the meter-in flow rate of each of the hydraulic actuators 6, 25 to 27, and it is desirable that the accuracy of flow control by the flow control valves 51 to 59 be at or above the allowable accuracy. Therefore, the intersection points between the curve showing the characteristics of the flow control accuracy versus the upstream-to-downstream differential pressure for each of the flow control valves 51 to 59 and the allowable accuracy are defined as the lower limit threshold ΔPlow and the upper limit threshold ΔPhigh of the upstream-to-downstream differential pressure. In this case, the condition of the upstream-to-downstream differential pressure ΔP within which the flow control by the flow control valves 51 to 59 can be maintained at or above the allowable accuracy is expressed by the following equation (2):

[0061] ΔPlow < ΔP < ΔPhigh Equation (2) The determination by the upstream / downstream differential pressure determination unit 215 is made, for example, using a condition using the two threshold values ​​ΔPlow and ΔPhigh in the above equation (2). The determination is made, for example, based on whether the upstream / downstream differential pressure of each of the flow control valves 51 to 59 is lower than the lower threshold value ΔPlow. The lower threshold value ΔPlow and the upper threshold value ΔPhigh are stored in advance in the storage device 201.

[0062] The flow control valve target opening determination unit 216 determines whether to use the target opening calculated by the flow control valve target opening calculation unit 213 or the auxiliary target opening calculated by the flow control valve auxiliary target opening calculation unit 214 as the final target opening of each of the flow control valves 51 to 59, based on the determination result of the upstream / downstream pressure difference determination unit 215. Furthermore, it generates a flow control valve command (electrical signal) according to the determined final target opening of each of the flow control valves 51 to 59, and outputs it to each of the electromagnetic proportional pressure reducing valves 113f, 113g for the flow control valves.

[0063] The directional control valve target opening calculation unit 217 uses a map in which the relationship between the operation amount (instruction information) of each operating lever 141, 142 of the operating device and the opening amount of each directional control valve 36 to 46 is defined in advance, and calculates the target opening amount of each directional control valve 36 to 46 from the input operation signal (instruction information) of each operating lever 141, 142 of the operating device. The map is stored in advance in the storage device 201. The calculated target opening amount of each directional control valve 36 to 46 is output to a directional control valve target opening adjustment unit 218.

[0064] The directional control valve target opening adjustment unit 218 adjusts the final target opening of each directional control valve 36-46 so that the differential pressure across each flow control valve 51-59 falls within the predetermined range shown in the above-mentioned formula (2), based on the determination result of the upstream / downstream pressure difference determination unit 215, the detection values ​​(pressure values) of the pressure sensors 121-123, and the calculation result of the directional control valve target opening calculation unit 217. Furthermore, a directional control valve command (electrical signal) corresponding to the adjusted final target opening of each directional control valve 36-46 is generated and output to each electromagnetic proportional pressure reducing valve 113b-113e for the directional control valve.

[0065] Next, the control procedure for the hydraulic pump by the control device for the work machine according to one embodiment will be described with reference to Fig. 6. Fig. 6 is a flowchart showing an example of the control procedure for the hydraulic pump by the control device for the work machine according to one embodiment shown in Fig. 4.

[0066] 6, the control device 200 shown in FIG. 4 first determines whether or not an operation signal has been input from the operation devices 141, 142 (step S10). If it is determined in step S10 that an operation signal has not been input (NO), the control device 200 terminates the calculation process related to the control of the hydraulic pumps 31-33. On the other hand, if it is determined that an operation signal has been input (YES), the actuator target flow rate calculation unit 211 of the control device 200 calculates the target flow rates QactA, QactB, ... of each actuator A, B, ... in accordance with the operation signal from each control lever of the operation device (step S20). The calculation of the target flow rates QactA, QactB, ... of each actuator A, B, ... may be performed in parallel or sequentially.

[0067] Next, the pump target flow rate calculation unit 212 of the control device 200 calculates the pump target flow rate Qpmp by adding up the target flow rates QactA, QactB, ... of the actuators A, B, ... (step S30). Here, the target pump flow rate Qpmp is not limited to just the sum of the target flow rates QactA, QactB, ... of the actuators A, B, ..., but may be set appropriately taking into account the bleed-off flow rate, drain flow rate, etc.

[0068] Next, the control device 200 outputs a pump flow rate command (electrical signal) corresponding to the target pump flow rate Qpmp to the electromagnetic proportional pressure reducing valve 113a for the second hydraulic pump 32 (step S40). As a result, the electromagnetic proportional pressure reducing valve 113a for the second hydraulic pump 32 shown in FIG. 3 generates a command pressure PiP2 (pilot secondary pressure) corresponding to the pump flow rate command (electrical signal) and inputs it to the second command pressure port 32a of the second regulator of the second hydraulic pump 32 shown in FIG. 2. As a result, the tilt of the second hydraulic pump 32 changes, thereby controlling the flow rate of pressure oil discharged from the second hydraulic pump 32. Note that in this description, only the second hydraulic pump 32 and the electromagnetic proportional pressure reducing valve 113a for the second hydraulic pump 32 are taken up as specific controlled objects. However, the control device 200 similarly controls the other hydraulic pumps 31, 33 and the corresponding electromagnetic proportional pressure reducing valves (not shown).

[0069] When the control device 200 outputs the pump flow rate command, the control device 200 ends the calculation process for the control cycle. When the next control cycle starts, the control device 200 repeats the calculation process of steps S10 to S40 described above.

[0070] Next, a control procedure for the flow control valve by the control device for a work machine according to one embodiment will be described with reference to Fig. 7. Fig. 7 is a flowchart showing an example of a control procedure for the flow control valve by the control device for a work machine according to one embodiment shown in Fig. 4.

[0071] 7, the control device 200 shown in FIG. 4 first determines whether or not an operation signal has been input from the operating device (step S110). If it is determined in step S110 that an operation signal has not been input (NO), the calculation process related to the control of the flow control valves 51 to 59 is terminated. On the other hand, if it is determined that an operation signal has been input (YES), the actuator target flow rate calculation unit 211 of the control device 200 calculates a target flow rate QactA for hydraulic actuator A in accordance with the operation signal (instruction information) from the operating device (step S120). This calculation is performed for all of the multiple hydraulic actuators 6, 25 to 27, although a detailed description thereof will be omitted here.

[0072] Next, a flow control valve target opening calculation unit 213 of the control device 200 calculates a target opening Afv of the flow control valve corresponding to hydraulic actuator A based on the target flow rate QactA calculated in step S120 and the differential pressure ΔP across the flow control valve obtained from the detected value of the pressure sensor (step S130). At the same time, a flow control valve auxiliary target opening calculation unit 214 of the control device 200 calculates an auxiliary target opening Afv_aux of the flow control valve corresponding to actuator A from the input operation signal (command information) of the operation device based on a map in which the relationship between the operation amount (command information) of the operation device and the opening of the flow control valve is predefined (step S140). These calculations are not described here, but are performed for all of the plurality of flow control valves 51 to 59.

[0073] Next, the upstream-to-downstream pressure differential determination unit 215 of the control device 200 determines whether the upstream-to-downstream pressure differential ΔP of the flow control valve, obtained from the detected value of the pressure sensor, is smaller than a preset lower threshold ΔPlow (ΔP<ΔPlow) (step S150). If it is determined in step S150 that the upstream-to-downstream pressure differential ΔP is equal to or greater than the lower threshold ΔPlow (NO), the flow control valve target opening determination unit 216 of the control device 200 sets the target opening Afv, which is the result of the calculation in step S130, as the final target opening Afv_ref of the flow control valve (step S160). On the other hand, if it is determined that the upstream-to-downstream pressure differential ΔP is smaller than the lower threshold ΔPlow (YES), the flow control valve target opening determination unit 216 of the control device 200 sets the auxiliary target opening Afv_aux, which is the result of the calculation in step S140, as the final target opening Afv_ref of the flow control valve (step S170).

[0074] Next, the control device 200 outputs a flow control valve command (electrical signal) corresponding to the final target opening Afv_ref to the electromagnetic proportional pressure reducing valve 113f for the second boom flow control valve 54 (step S180). As a result, the electromagnetic proportional pressure reducing valve 113f for the second boom flow control valve 54 shown in FIG. 3 reduces the discharge pressure of the pilot pump 111 to generate a command pressure (pilot secondary pressure) corresponding to the flow control valve command (electrical signal), and inputs this to the pilot port 544p of the pilot variable throttle 544 of the second boom flow control valve 54 shown in FIG. 2. As a result, the opening area of ​​the valve body 541 of the second boom flow control valve 54 changes, thereby controlling the flow rate of pressure oil supplied from the second boom flow control valve 54 to the second boom directional control valve 40. Note that in this description, only the second boom flow control valve 54 and the electromagnetic proportional pressure reducing valve 113f for the second boom flow control valve 54 have been taken up as specific controlled objects. However, the other flow control valves 51 to 53, 55 to 59 and the corresponding electromagnetic proportional pressure reducing valves 113g (including pressure reducing valves not shown) are also controlled by the control device 200 in the same manner.

[0075] When the control device 200 outputs the flow control valve command (electrical signal), it ends the calculation process for the control cycle. When the next control cycle starts, the control device 200 repeats the calculation process of steps S110 to S180 described above.

[0076] Next, the control procedure for the directional control valve by the control device for a work machine according to one embodiment will be described with reference to Fig. 8. Fig. 8 is a flowchart showing an example of the control procedure for the directional control valve by the control device for a work machine according to one embodiment shown in Fig. 4.

[0077] 8, the control device 200 shown in FIG. 4 first determines whether or not an operation signal has been input from an operating device (step S210). If it is determined in step S210 that an operation signal has not been input (NO), the calculation process for controlling the directional control valves 36-46 is terminated. On the other hand, if it is determined that an operation signal has been input (YES), the directional control valve target opening calculation unit 217 of the control device 200 calculates the target opening Ams of the directional control valve from the input operation signal (instruction information) of the operating device using a map in which the relationship between the operation amount (instruction information) of the operating device and the opening amount of the directional control valve is predefined (step S220). This calculation is performed for all of the multiple directional control valves 36-46, although a detailed description thereof will be omitted here.

[0078] Next, the upstream-to-downstream pressure differential determination unit 215 of the control device 200 determines whether the upstream-to-downstream pressure differential ΔP of the flow control valve obtained from the detection value of the pressure sensor is within a predetermined range from a preset lower threshold ΔPlow to an upper threshold ΔPhigh (ΔPlow<ΔP<ΔPhigh) (step S230). If it is determined in step S230 that the upstream-to-downstream pressure differential ΔP is outside the predetermined range (NO), the directional control valve target opening adjustment unit 218 of the control device 200 adjusts the target opening Ams, which is the calculation result of step S220, so that the upstream-to-downstream pressure differential of the flow control valve is within the above-mentioned predetermined range, and sets the adjusted target opening Ams_ref as the directional control valve (step S240). On the other hand, if it is determined that the front-to-rear differential pressure ΔP is within a predetermined range (YES), the directional control valve target opening adjustment unit 218 of the control device 200 sets the target opening Ams, which is the calculation result of step S220, as the final target opening Ams_ref of the directional control valve (step S250).

[0079] Next, the control device 200 outputs a directional control valve command (electrical signal) corresponding to the final target opening Ams_ref to the electromagnetic proportional pressure reducing valves 113b, 113c for the second boom direction control valve 40 (step S260). As a result, one of the electromagnetic proportional pressure reducing valves 113b, 113c for the second boom direction control valve 40 shown in FIG. 3 reduces the discharge pressure of the pilot pump 111 to generate command pressures PiBm2R, PiBm2L (pilot secondary pressures) corresponding to the directional control valve command (electrical signal), and inputs these to the pilot port (not shown) of the second boom direction control valve 40 shown in FIG. 2. As a result, the switching position and opening amount of the second boom direction control valve 40 change, thereby controlling the flow direction of pressure oil from the second boom direction control valve 40 to the boom cylinder 25 and controlling the differential pressure before and after the second boom flow control valve 54 to be within a predetermined range. In this description, only the second boom direction control valve 40 and the electromagnetic proportional pressure reducing valves 113b, 113c for the second boom direction control valve 40 are taken up as specific objects of control. However, control by the control device 200 is also similarly performed on the first arm direction control valve 41 and the electromagnetic proportional pressure reducing valves 113d, 113e for the first arm direction control valve 41, the other directional control valves 37 to 39, 42 to 46, and the corresponding electromagnetic proportional pressure reducing valves (not shown).

[0080] When the control device 200 outputs the directional control valve command (electrical signal), the calculation process for the control cycle ends. When the next control cycle starts, the control device 200 repeats the calculation process of steps S210 to S260 described above.

[0081] Here, with regard to the control of the flow control valve and the directional control valve by the control device 200, it is desirable that the update period (control period) Tfv when the control device 200 outputs a flow control valve command to the electromagnetic proportional pressure reducing valve 113f for the second boom flow control valve 54, and the update period (control period) Tms when the control device 200 outputs a directional control valve command to the electromagnetic proportional pressure reducing valves 113b, 113c for the second boom direction control valve 40 have the relationship shown in the following formula (3).

[0082] Tms > Tfv ... Equation (3) This is intended to give priority to flow control over pressure control by making the flow control valve move faster than the directional control valve. This makes it possible to suppress instability caused by mutual interference between the flow control of the flow control valve and the pressure control of the directional control valve.

[0083] Next, the operation of a work machine according to one embodiment will be described with reference to Figures 1 to 3 and 6 to 8. As a first example, the operation of the hydraulic system during combined aerial operation of the boom and arm will be described. As a second example, the operation of the hydraulic system during combined excavation operation of the boom and arm will be described.

[0084] 1, when the boom 21 and arm 22 are operated in combination in the air, the load pressure of the boom cylinder 25 shown in Fig. 2 becomes high, while the load pressure of the arm cylinder 26 becomes relatively low. Therefore, the differential pressure across the flow control valves 52, 55 corresponding to the arm cylinder 26 (the pressure difference between the discharge pressure of the first hydraulic pump 31 or the second hydraulic pump 32 and the load pressure of the arm cylinder 26) becomes high. When fine manipulation is performed on the arm 22 in this situation, the operating conditions of the flow control valves 52, 55 corresponding to the arm cylinder 26 become a small flow rate and a high differential pressure.

[0085] 2 and 3 operates as follows under the control of the control device 200 under these operating conditions of the flow control valves 52, 55. To simplify the explanation, only the components related to the flow of pressure oil supplied from the second hydraulic pump 32 to the arm cylinder 26, i.e., the second hydraulic pump 32, the first arm directional control valve 41, and the first arm flow control valve 55, will be extracted and explained here.

[0086] When the arm operation lever 142 is "finely operated," the second hydraulic pump 32 is controlled as follows. The control device 200 outputs a pump flow rate command (electrical signal) to the electromagnetic proportional pressure reducing valve 113a so that the discharge flow rate of the second hydraulic pump 32 becomes the pump target flow rate Qpmp corresponding to the operation amount (input value) of the arm operation lever 142 (step S40 shown in FIG. 6 ). As a result, the electromagnetic proportional pressure reducing valve 113a reduces the discharge pressure of the pilot pump 111 to generate a command pressure PiP2 corresponding to the pump flow rate command. The command pressure PiP2 generated by the electromagnetic proportional pressure reducing valve 113a is input to the second command pressure port 32a of the second regulator of the second hydraulic pump 32, and the tilt of the second hydraulic pump 32 changes. As a result, the flow rate of pressure oil discharged from the second hydraulic pump 32 is controlled to become the pump target flow rate Qpmp.

[0087] Furthermore, under the above-described conditions of small flow rate and high differential pressure, the first-arm flow control valve 55 is controlled as follows: The control device 200 determines that the differential pressure ΔP across the first-arm flow control valve 55 obtained from the detection values ​​of the pressure sensors 121, 123 is equal to or greater than the lower threshold value ΔPlow (NO) (step S150 shown in FIG. 7 ). In this case, the control device 200 determines the target opening Afv calculated from the actuator target flow rate corresponding to the operation amount (input value) of the arm control lever 142 and the differential pressure ΔP across the first-arm flow control valve 55 as the final target opening Afv_ref of the first-arm flow control valve 55 (step S160 shown in FIG. 7 ), and outputs a flow control valve command (electrical signal) corresponding to the final target opening Afv_ref to the electromagnetic proportional pressure reducing valve 113g for the first-arm flow control valve 55 (step S180 shown in FIG. 7 ).

[0088] As a result, the electromagnetic proportional pressure reducing valve 113g reduces the discharge pressure of the pilot pump 111 to generate a command pressure according to the flow control valve command (electrical signal). The command pressure generated by the electromagnetic proportional pressure reducing valve 113g is input to the pilot port 554p of the pilot variable throttle 554 of the first-arm flow control valve 55, and the pilot flow rate passing through the pilot line 553 is controlled. As a result, the opening area of ​​the variable throttle changes due to the displacement of the valve body 551, and the flow rate of pressure oil supplied from the first-arm flow control valve 55 to the first-arm directional control valve 41 is controlled.

[0089] Furthermore, under the above-described conditions of small flow rate and high differential pressure, the first-arm directional control valve 41 is controlled as follows: The control device 200 determines whether the differential pressure ΔP across the first-arm flow control valve 55 obtained from the detection values ​​of the pressure sensors 121, 123 is within a predetermined range from a lower threshold value ΔPlow to an upper threshold value ΔPhigh (ΔPlow<ΔP<ΔPhigh) (step S230 shown in FIG. 8 ). If it is determined that the front-to-rear differential pressure ΔP is within a predetermined range (YES), the control device 200 determines the target opening Ams corresponding to the operation amount (input value) of the arm operating lever 142 as the final target opening Ams_ref of the first-arm directional control valve 41 (step S250 shown in FIG. 8), and outputs a directional control valve command (electrical signal) corresponding to the final target opening Ams_ref to the electromagnetic proportional pressure reducing valves 113d, 113e for the first-arm directional control valve 41 (step S260 shown in FIG. 8).

[0090] As a result, one of the electromagnetic proportional pressure reducing valves 113d, 113e reduces the discharge pressure of the pilot pump 111 to generate command pressures PiAm1C, PiAm1D according to the directional control valve command (electrical signal). The command pressures PiAm1C, PiAm1D generated by one of the electromagnetic proportional pressure reducing valves 113d, 113e are input to a pilot port (not shown) of the first arm directional control valve 41. As a result, the switching position and opening of the first arm directional control valve 41 change, thereby controlling the flow direction of pressure oil from the first arm directional control valve 41 to the arm cylinder 26. At this time, the first arm directional control valve 41 has an opening that does not affect the flow rate control by the flow control valve 55.

[0091] On the other hand, if it is determined that the pressure difference between before and after ΔP is equal to or greater than the upper threshold value ΔPhigh (outside the predetermined range) (NO), the control device 200 adjusts the final target opening Ams_ref of the first-arm directional control valve 41 so that the pressure difference between before and after the first-arm flow control valve 55 falls within the above-mentioned predetermined range that is smaller than the upper threshold value ΔPhigh (step S240 shown in FIG. 8), and outputs a directional control valve command (electrical signal) corresponding to the adjusted final target opening Ams_ref to the electromagnetic proportional pressure reducing valves 113d, 113e (step S260 shown in FIG. 8).

[0092] In this case, command pressures PiAm1C, PiAm1D corresponding to the final target opening Ams_ref such that the differential pressure across the first-arm flow control valve 55 falls within the above-mentioned predetermined range are input to the first-arm directional control valve 41. Therefore, the opening of the first-arm directional control valve 41 is controlled so that the differential pressure across the first-arm flow control valve 55 is smaller than the upper limit threshold ΔPhigh and falls within the above-mentioned predetermined range. This makes it possible to maintain the accuracy of flow control by the flow control valve 55 at or above the allowable accuracy.

[0093] In this manner, in this embodiment, when the operating conditions of the flow control valve are a small flow rate and a high differential pressure, the opening of the directional control valve that controls the flow direction of pressure oil from the hydraulic pump to the hydraulic actuator is adjusted to control the differential pressure across the flow control valve that controls the flow rate of pressure oil from the hydraulic pump to the hydraulic actuator within the above-mentioned predetermined range. This makes it possible to maintain the accuracy of flow control at or above the allowable accuracy under operating conditions of a small flow rate and a high differential pressure, where the accuracy of flow control by the flow control valve is likely to decrease.

[0094] Second, during combined excavation operation of the boom 21 and arm 22 shown in Figure 1, the load pressure of the arm cylinder 26 increases due to the application of an excavation load compared to combined aerial operation. As a result, the load pressure of the arm cylinder 26 and the load pressure of the boom cylinder 25 may become approximately the same. In this state, if the amount of operation of the operating device is increased, the operating conditions of the flow control valve become a large flow rate and a low pressure difference.

[0095] Under these operating conditions of the flow control valve, the hydraulic system 30 shown in Figures 2 and 3 operates as follows under the control of the control device 200. Again, for the sake of simplicity, only the second hydraulic pump 32, the first arm directional control valve 41, and the first arm flow control valve 55 will be extracted and explained.

[0096] As in the first example, the control device 200 outputs a pump flow rate command (electrical signal) to the electromagnetic proportional pressure reducing valve 113a so that the flow rate of the second hydraulic pump 32 becomes the pump target flow rate Qpmp corresponding to the operation amount (input value) of the arm operating lever 142 (step S40 shown in FIG. 6). As a result, the electromagnetic proportional pressure reducing valve 113a generates a command pressure PiP2 corresponding to the pump flow rate command and inputs it to the second command pressure port 32a of the second regulator of the second hydraulic pump 32. As a result, the flow rate of pressure oil discharged from the second hydraulic pump 32 is controlled.

[0097] Furthermore, under the conditions of the large flow rate and low pressure difference described above, the first-arm flow control valve 55 is controlled as follows: The control device 200 determines whether the pressure difference ΔP across the valve 55 obtained from the detection values ​​of the pressure sensors 121, 123 is smaller than the lower threshold value ΔPlow (ΔP<ΔPlow) (step S150 shown in FIG. 7 ). If it is determined that the pressure difference ΔP across the valve 55 is equal to or greater than the lower threshold value ΔPlow (NO), the control and operation are the same as in the first example, and therefore a description thereof will be omitted.

[0098] On the other hand, if it is determined that the front-to-rear differential pressure ΔP is smaller than the lower limit threshold ΔPlow (YES), the control device 200 determines the auxiliary target opening Afv_aux calculated based on the operation amount (input value) of the arm operating lever 142 as the final target opening Afv_ref of the first arm flow control valve 55 (step S170 shown in Figure 7), and outputs a flow control valve command (electrical signal) corresponding to the final target opening Afv_ref to the electromagnetic proportional pressure reducing valve 113g for the first arm flow control valve 55 (step S180).

[0099] As a result, the electromagnetic proportional pressure reducing valve 113g generates a command pressure according to the auxiliary target opening Afv_aux serving as the final target opening Afv_ref, and inputs this command pressure to the pilot port 554p of the pilot variable throttle 554 of the first-arm flow control valve 55. The first-arm flow control valve 55 changes the opening area of ​​the valve body 551 serving as a variable throttle, thereby controlling the flow rate of pressure oil flowing from the first-arm flow control valve 55 to the first-arm directional control valve 41.

[0100] In the present embodiment, when the differential pressure ΔP across the first-arm flow control valve 55 is smaller than the lower threshold ΔPlow, the opening area of ​​the first-arm flow control valve 55 is controlled in accordance with the amount of operation of the arm operating lever 142 without using the detection values ​​of the pressure sensors 121, 123. Therefore, compared to when the opening area of ​​the first-arm flow control valve 55 is controlled using the differential pressure across the arm obtained from the detection values ​​of the pressure sensors 121, 123, there is no influence from detection errors of the pressure sensors 121, 123. Therefore, there is no need to worry about a decrease in the accuracy of flow control due to detection errors of the pressure sensors 121, 123.

[0101] Furthermore, under the conditions of the large flow rate and the low pressure difference described above, the first-arm directional control valve 41 is controlled as follows: The control device 200 determines whether the pressure difference ΔP across the first arm obtained from the detection values ​​of the pressure sensors 121, 123 is within a predetermined range from a lower threshold value ΔPlow to an upper threshold value ΔPhigh (ΔPlow<ΔP<ΔPhigh) (step S230 shown in FIG. 8 ). If it is determined that the pressure difference ΔP across the first arm is within the predetermined range (YES), the control and operation are similar to those in the first example, and therefore a description thereof will be omitted.

[0102] On the other hand, if it is determined that the pressure difference between before and after ΔP is equal to or less than the lower threshold value ΔPlow (outside the predetermined range) (NO), the control device 200 adjusts the final target opening Ams_ref of the first-arm directional control valve 41 so that the pressure difference between before and after the first-arm flow control valve 55 is greater than the lower threshold value ΔPlow and falls within the predetermined range (step S240 shown in FIG. 8), and outputs a directional control valve command corresponding to the adjusted final target opening Ams_ref to the electromagnetic proportional pressure reducing valves 113d, 113e (step S260 shown in FIG. 8).

[0103] In this case, command pressures PiAm1C, PiAm1D corresponding to the final target opening Ams_ref adjusted so that the differential pressure across the first-arm flow control valve 55 falls within the above-mentioned predetermined range are input to the first-arm directional control valve 41. Therefore, the opening amount of the first-arm directional control valve 41 is controlled so that the differential pressure across the first-arm flow control valve 55 falls within the above-mentioned predetermined range that is greater than the lower limit threshold ΔPlow. This makes it possible to maintain the accuracy of flow control by the flow control valve 55 at or above the allowable accuracy.

[0104] In this manner, in the present embodiment, when the operating conditions of the flow control valve are a high flow rate and a low differential pressure, the opening amount of the directional control valve that controls the flow direction of pressure oil from the hydraulic pump to the hydraulic actuator can be controlled to adjust the differential pressure across the flow control valve that controls the flow rate of pressure oil from the hydraulic pump to the hydraulic actuator within the above-mentioned predetermined range. Therefore, under operating conditions of a high flow rate and a low differential pressure, where the accuracy of flow control by the flow control valve is likely to decrease, the accuracy of flow control can be maintained at or above the allowable accuracy.

[0105] As described above, the hydraulic excavator 1 (work machine) according to one embodiment comprises the hydraulic motor 6 and hydraulic cylinders 25, 26, 27 as hydraulic actuators for driving the revolving body 3 and work devices 21, 22, 23, which are driven bodies; hydraulic pumps 31, 32, 33 for supplying pressure oil to the hydraulic actuators 6, 25 to 27; directional control valves 37, 38, 39, 40, 41, 42, 44, 45, 46 for controlling the flow of pressure oil supplied from the hydraulic pumps 31 to 33 to the hydraulic actuators 6, 25 to 27; and directional control valves 37, 38, 39, 40, 41, 42, 44, 45, 46 for controlling the flow of pressure oil supplied from the hydraulic pumps 31 to 33 to the hydraulic actuators 6, 25 to 27. , 44-46 and are arranged upstream of the hydraulic actuators 6, 25-27. The hydraulic actuators 6, 25-27 are provided with flow control valves 51, 52, 53, 54, 55, 56, 57, 58, 59 that control the flow rate of pressurized oil supplied from the hydraulic pumps 31-33 to the hydraulic actuators 6, 25-27 via the directional control valves 37-42, 44-46, and a control device 200 that controls the directional control valves 37-42, 44-46 and the flow control valves 51-59 based on instruction information that instructs the operation of the driven bodies 3, 21-23. The hydraulic actuators 6, 25-27 are also provided with pressure sensors 121, 122, 123 that detect differential pressures before and after the flow control valves 51-59. The control device 200 determines whether the differential pressure before and after obtained from the detection values ​​of the pressure sensors 121 to 123 falls within a predetermined range, and if it determines that the differential pressure before and after is outside the predetermined range, it is configured to control the directional control valves 37 to 42, 44 to 46 using the final target opening obtained by adjusting the target opening of the directional control valves 37 to 42, 44 to 46 calculated based on the instruction information so that the differential pressure before and after the flow control valves 51 to 59 falls within the predetermined range.

[0106] According to this configuration, when the differential pressure across the flow control valves 51 to 59 is outside a predetermined range, the openings of the directional control valves 37 to 42, 44 to 46 are adjusted so that the differential pressure across the flow control valves 51 to 59 is within the predetermined range, so that the flow control valves 51 to 59 can be driven under a differential pressure across the valves that provides flow control accuracy equal to or greater than the allowable accuracy. Therefore, whether the flow rate through the flow control valves 51 to 59 and the differential pressure across the valves are low and have a high pressure difference, or high and have a low pressure difference, a decrease in the accuracy of flow control for the hydraulic actuators 6, 25 to 27 can be prevented.

[0107] Furthermore, the control device 200 of the hydraulic excavator 1 (work machine) according to this embodiment is configured so that the first control period, which is the period for executing control over the flow control valves 51 to 59, is shorter than the second control period, which is the period for executing control over the directional control valves 37 to 42 and 44 to 46.

[0108] According to this configuration, flow control to the hydraulic actuators 6, 25 to 27 by the flow control valves 51 to 59 takes priority over pressure control of the front and rear differential pressure by the directional control valves 37 to 42, 44 to 46, so it is possible to suppress system instability due to mutual interference between flow control by the flow control valves 51 to 59 and pressure control by the directional control valves 37 to 42, 44 to 46.

[0109] Furthermore, the control device 200 of the hydraulic excavator 1 (work machine) according to this embodiment calculates target openings of the flow control valves 51 to 59 based on the target flow rates of the hydraulic actuators 6, 25 to 27 calculated in response to command information from the operating levers 141, 142 of the operating device and the front-to-back differential pressure obtained from the detection values ​​of the pressure sensors 121 to 123, calculates auxiliary target openings of the flow control valves 51 to 59 based on a map (control information) in which the relationship between the command information and the opening area of ​​the flow control valve is defined in advance, and controls the flow control valves 51 to 59 using the target openings of the flow control valves 51 to 59 when it is determined that the front-to-back differential pressure obtained from the detection values ​​of the pressure sensors 121 to 123 is equal to or greater than the lower limit ΔPlow of a predetermined range, and controls the flow control valves 51 to 59 using the auxiliary target openings of the flow control valves 51 to 59 when it is determined that the front-to-back differential pressure obtained from the detection values ​​of the pressure sensors 121 to 123 is smaller than the lower limit ΔPlow of the predetermined range.

[0110] According to this configuration, when the differential pressure across the flow control valves 51 to 59 is smaller than the lower limit ΔPlow, the openings of the flow control valves 51 to 59 are controlled in accordance with the amounts of operation (instruction information) of the operating levers 141, 142 of the operating device without using the detection values ​​of the pressure sensors 121 to 123, and therefore are not affected by detection errors of the pressure sensors 121 to 123, as compared to when the flow control valves 51 to 59 are controlled using the detection values ​​of the pressure sensors 121 to 123. Therefore, there is no need to worry about a decrease in the accuracy of flow control due to detection errors of the pressure sensors 121 to 123.

[0111] Furthermore, the flow control valves 51 to 59 in this embodiment have seat-type valve elements 541, 551 that form variable throttles, control variable throttles 542, 552 that are provided on the valve elements 541, 551 so as to communicate with the primary sides of the valve elements 541, 551 and whose opening area changes according to the amount of movement of the valve elements 541, 551, pilot lines 543, 553 that communicate the control variable throttles 542, 552 with the secondary sides of the valve elements 541, 551 and determine the amount of movement of the valve elements 541, 551 according to the flow rate passing through, and pilot variable throttles 544, 554 that are arranged on the pilot lines 543, 553 and whose opening amount is controlled based on commands from the control device 200.

[0112] According to this configuration, the flow control valves 51 to 59 have seat-type valve elements 541, 551, which provide better response characteristics than flow control valves with spool-type valve elements. Therefore, by using the flow control valves 51 to 59 that include seat-type valve elements 541, 551, the control device 200 can more easily perform pressure feedback control.

[0113] [Other Embodiments] The present invention is not limited to the above-described embodiment, but includes various modifications. The above-described embodiment has been described in detail to clearly explain the present invention, and is not necessarily limited to an embodiment having all of the described configurations. It is also possible to add, delete, or replace part of the configuration of this embodiment with other configurations.

[0114] For example, in the above-described embodiment, an example of a configuration has been shown in which the control device 200 controls the openings of the directional control valves 37-42, 44-46 and the flow control valves 51-59 and the flow rates of the hydraulic pumps 31-33 based on instruction information as the operation amounts of the operating levers 141, 142 of the operating device that instructs the operation of the driven bodies such as the revolving body 3 and the work devices 21, 22, 23. However, the control device 200 can also be configured to control the openings of the directional control valves 37-42, 44-46 and the flow control valves 51-59 and the flow rates of the hydraulic pumps 31-33 based on instruction information as the operation amounts of a remote control device that remotely instructs the operation of the driven bodies 2, 3, 21, 22, 23. In addition, the control device 200 can also be configured to control the opening of the directional control valves 37-42, 44-46 and the flow control valves 51-59 and the flow rate of the hydraulic pumps 31-33 based on instruction information, which is an operation instruction for the driven bodies 2, 3, 21, 22, 23 that the control device 200 itself generates to automatically control the driven bodies 2, 3, 21, 22, 23 to perform operations that satisfy specified conditions.

[0115] REFERENCE SIGNS LIST 1...hydraulic excavator (work machine), 3...swing body (driven body), 6...swing motor (hydraulic actuator), 21...boom (driven body), 22...arm (driven body), 23...bucket (driven body), 25...boom cylinder (hydraulic actuator), 26...arm cylinder (hydraulic actuator), 27...bucket cylinder (hydraulic actuator), 31...first hydraulic pump (hydraulic pump), 32...second hydraulic pump (hydraulic pump), 33...third hydraulic pump (hydraulic pump), 37, 38, 39, 40, 41, 42, 44, 45, 46...directional control valve, 51, 52, 53, 54, 55, 56, 57, 58, 59...flow control valve, 541, 551...valve body, 542, 552...control variable throttle, 543, 553...pilot line, 544, 554...pilot variable throttle, 121, 122, 123...pressure sensors, 200...control device

Claims

1. A work machine comprising: a hydraulic actuator for driving a driven body; a hydraulic pump for supplying pressurized oil to said hydraulic actuator; a directional control valve for controlling the flow of pressurized oil supplied from said hydraulic pump to said hydraulic actuator; a flow control valve arranged upstream of said directional control valve for controlling the flow rate of pressurized oil supplied from said hydraulic pump to said hydraulic actuator via said directional control valve; and a control device for controlling said directional control valve and said flow control valve based on instruction information for instructing the operation of said driven body, wherein said work machine is further provided with a pressure sensor for detecting a differential pressure before and after said flow control valve, and said control device determines whether the differential pressure before and after obtained from the detection value of said pressure sensor is within a predetermined range, and when it is determined that the differential pressure before and after is outside the predetermined range, controls said directional control valve using a final target opening obtained by adjusting a target opening of said directional control valve calculated based on the instruction information so that the differential pressure before and after of said flow control valve is within said predetermined range.

2. A work machine as described in claim 1, characterized in that the control device is configured so that a first control period, which is the execution period of control for the flow control valve, is shorter than a second control period, which is the execution period of control for the directional control valve.

3. A work machine as described in claim 1, wherein the control device calculates a target opening of the flow control valve based on the target flow rate of the hydraulic actuator calculated in response to the command information and the front-to-back differential pressure obtained from the detection value of the pressure sensor, calculates an auxiliary target opening of the flow control valve based on control information in which the relationship of the opening area of ​​the flow control valve to the command information is predefined, controls the flow control valve using the target opening of the flow control valve when it is determined that the front-to-back differential pressure obtained from the detection value of the pressure sensor is equal to or greater than the lower limit of the predetermined range, and controls the flow control valve using the auxiliary target opening of the flow control valve when it is determined that the front-to-back differential pressure obtained from the detection value of the pressure sensor is smaller than the lower limit of the predetermined range.

4. A work machine as claimed in claim 1, characterized in that the flow control valve comprises: a seat-type valve element forming a variable throttle; a control variable throttle provided on the valve element so as to communicate with the primary side of the valve element and whose opening area changes according to the amount of movement of the valve element; a pilot line which communicates between the control variable throttle and the secondary side of the valve element and determines the amount of movement of the valve element according to the flow rate passing through; and a pilot variable throttle which is arranged on the pilot line and whose opening amount is controlled based on commands from the control device.

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