Work Machine

Abstract

To provide a work machine capable of preventing runaway of a hydraulic actuator, capable of smoothly stopping the driving of the hydraulic actuator, and capable of improving control accuracy of the hydraulic actuator.SOLUTION: A controller calculates thrust F of hydraulic actuators 204a, 205a, 206a, 211 on the basis of an output value of first pressure sensors 84-91, and controls directional control valves 7-12, 14, 15 on the basis of a front-and-back differential pressure ΔP of flow control valves 21-29 detected by second pressure sensors 81-83 and the thrust F of the hydraulic actuators 204a, 205a, 206a, 211.SELECTED DRAWING: Figure 2A

Description

[Technical field]

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

[0002] Generally, a work machine such as a hydraulic excavator is provided with a plurality of hydraulic actuators. Conventionally, as a control circuit for controlling the supply and discharge of hydraulic oil to these hydraulic actuators, a control circuit that simultaneously performs a direction switching control for switching the supply and discharge direction of hydraulic oil to the hydraulic actuators using a single spool valve, a supply flow control for controlling the supply flow rate from the hydraulic pump to the hydraulic actuator, and a discharge flow control for controlling the discharge flow rate from the hydraulic actuator to a hydraulic oil tank is widely known. However, when the supply flow control and the discharge flow control are performed using a single spool valve, the relationship between the opening area on the supply flow control side and the opening area on the discharge flow control side with respect to the moving position of the spool valve is uniquely determined. Therefore, it is not possible to change the relationship between the supply flow rate and the discharge flow rate according to different work conditions such as a single operation in which only one hydraulic actuator is driven, a composite operation in which multiple hydraulic actuators are driven simultaneously, or a light load work in which the load on the hydraulic actuator is light and a heavy load work in which the load is heavy, which leads to a decrease in operability.

[0003] In view of this, a hydraulic actuator control circuit that can individually and precisely control the supply flow rate and discharge flow rate for a hydraulic actuator has been proposed as a conventional technique (Patent Document 1). In this conventional technique, the oil supply / discharge control circuit is composed of a flow control valve and a spool valve, and the flow control valve controls the supply flow rate for the hydraulic actuator, and the spool valve controls the direction switching and the discharge flow rate for the hydraulic actuator, thereby enabling individual and precise control of the supply flow rate and discharge flow rate of hydraulic oil for the hydraulic actuator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-20604 A Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned conventional technology has the following problems. In the above-mentioned conventional technology, the drive speed of the hydraulic actuator can be determined by controlling the supply flow rate and discharge flow rate to the hydraulic actuator, but the pressure (back pressure) of the discharge port of the hydraulic actuator is not controlled, so the hydraulic actuator cannot be decelerated with high precision. Therefore, when stopping the drive of the hydraulic actuator, the hydraulic actuator may run away, and the operator may not be able to stop it at the target position.

[0006] In addition, since only the supply and discharge flow rate to the hydraulic actuator is controlled, if a small flow rate is to be supplied to the hydraulic actuator, a small difference in the opening of the flow control valve will cause a large fluctuation in the supply flow rate if the differential pressure between the upstream and downstream of the flow control valve is large, which may cause a control problem in that excessive flow control accuracy is required for the flow control valve.

[0007] The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a work machine that can prevent a hydraulic actuator from running away, smoothly stop the drive of the hydraulic actuator, and improve the control accuracy of the hydraulic actuator. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a work machine including a hydraulic pump, a hydraulic actuator, a directional control valve that controls the flow direction of pressure oil supplied from the hydraulic pump to the hydraulic actuator, a flow control valve that controls the flow rate of pressure oil supplied from the hydraulic pump to the hydraulic actuator, an operating device for instructing the operation of the hydraulic actuator, and a controller that controls the directional control valve and the flow control valve in accordance with an input value of the operating device, the work machine including a first pressure sensor that detects the pressure of the hydraulic actuator, and a second pressure sensor that detects a differential pressure before and after the flow control valve, and the controller includes: a first target meter-out opening amount, which is a target value of the meter-out opening amount of the directional control valve, is calculated based on an input value of the operating device, and if the differential pressure before and after the flow control valve detected by the second pressure sensor falls within a predetermined range set based on a flow control accuracy of the flow control valve, the first target meter-out opening amount is set to a provisional target meter-out opening amount, and if the differential pressure before and after the flow control valve detected by the second pressure sensor exceeds the predetermined range, a meter-out opening amount of the directional control valve that puts the differential pressure before and after the flow control valve within the predetermined range is set to the provisional target meter-out opening amount, and a second target meter-out opening amount, which is a target value of the meter-out opening amount of the directional control valve, is calculated based on a thrust of the hydraulic actuator calculated based on an output value of the first pressure sensor, and the meter-out opening amount of the directional control valve is adjusted so that it coincides with the smaller value of the provisional target meter-out opening amount and the second target meter-out opening amount. The directional control valve is to be controlled.

[0009] According to the present invention configured as described above, by adjusting the back pressure of the hydraulic actuator by controlling the directional control valve, it is possible to prevent runaway of the hydraulic actuator and smoothly stop the operation of the hydraulic actuator. In addition, by adjusting the differential pressure before and after the flow control valve by controlling the directional control valve, it is possible to operate the flow control valve under differential pressure conditions with high flow control accuracy. As a result, even under small flow rate / high pressure difference or large flow rate / low pressure difference conditions that require high control accuracy of the hydraulic actuator, it is possible to drive the hydraulic actuator more accurately by accurately supplying the target flow rate without causing a decrease in the flow control accuracy of the flow control valve. Effect of the Invention

[0010] According to the work machine of the present invention, runaway of the hydraulic actuator can be prevented, the drive of the hydraulic actuator can be stopped smoothly, and the control accuracy of the hydraulic actuator can be improved. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a side view of a hydraulic excavator according to an embodiment of the present invention. [Figure 2A] FIG. 1 is a circuit diagram (1 / 2) of a hydraulic drive system according to a first embodiment of the present invention. [Figure 2B]FIG. 2 is a circuit diagram (2 / 2) of a hydraulic drive system according to a first embodiment of the present invention. [Diagram 3] FIG. 2 is a functional block diagram of a controller according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing the relationship between the differential pressure across the flow control valve and the flow control accuracy. [Diagram 5] FIG. 11 is a diagram showing a correspondence map between the thrust of the hydraulic actuator and a target meter-out opening amount. [Figure 6] FIG. 4 is a diagram showing a correspondence map between an operation lever input value and a target meter-in opening amount of a directional control valve. [Figure 7] FIG. 4 is a diagram showing a correspondence map between an operation lever input value and a target meter-out opening amount of a directional control valve. [Figure 8] 4 is a flowchart showing a process related to pump flow rate control by a controller in the first embodiment of the present invention. [Figure 9] 5 is a flowchart showing processing relating to flow rate control valve opening control by a controller in the first embodiment of the present invention. [Figure 10] 5 is a flowchart showing a process related to a directional control valve opening control by a controller in the first embodiment of the present invention. [Figure 11] FIG. 11 is a functional block diagram of a controller according to a second embodiment of the present invention. [Figure 12] 10 is a flowchart showing a process related to the directional control valve opening control of a controller in a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a hydraulic excavator will be described as an example of a work machine according to an embodiment of the present invention with reference to the drawings. In each drawing, the same reference numerals are used to designate the same members, and duplicated descriptions will be omitted as appropriate.

[0013] Fig. 1 is a side view of a hydraulic excavator according to this embodiment. As shown in Fig. 1, a hydraulic excavator 901 includes a traveling body 201, a rotating body 202 arranged so as to be able to rotate on the traveling body 201, and a working device 203 attached to the rotating body 202 so as to be able to rotate in the vertical direction and for performing work such as excavating earth and sand. The rotating body 202 is driven by a swing motor 211.

[0014] The working device 203 has a boom 204 attached to the rotating body 202 so as to be rotatable in the vertical direction, an arm 205 attached to the end of the boom 204 so as to be rotatable in the vertical direction, a bucket 206 attached to the end of the arm 205 so as to be rotatable in the vertical direction, a boom cylinder 204a which is an actuator that drives the boom 204, an arm cylinder 205a which is an actuator that drives the arm 205, and a bucket cylinder 206a which is an actuator that drives the bucket 206.

[0015] A cab 207 is provided at the front position on the rotating body 202, and a counterweight 209 for ensuring weight balance is attached at the rear position. A machine room 208 is provided between the cab 207 and the counterweight 209, and the machine room 208 houses an engine (not shown), hydraulic pumps 1 to 3 (shown in FIG. 2A), a control valve 210, etc. The control valve 210 controls the flow of hydraulic oil from the hydraulic pumps to each actuator.

[0016] A hydraulic excavator 901 according to this embodiment is equipped with a hydraulic drive system which will be described in each of the following embodiments. EXAMPLES

[0017] 2A and 2B are circuit diagrams of a hydraulic drive system according to a first embodiment of the present invention.

[0018] 2A, the hydraulic drive system 902 in the first embodiment includes three main hydraulic pumps driven by an engine (not shown), for example, a first hydraulic pump 1, a second hydraulic pump 2, and a third hydraulic pump 3, each of which is a variable displacement hydraulic pump. The hydraulic drive system 902 also includes a pilot pump 4 driven by an engine (not shown) (see FIG. 2B), and a hydraulic oil tank 5 that supplies oil to the hydraulic pumps 1 to 3 and the pilot pump 4.

[0019] The tilt angle of the first hydraulic pump 1 is controlled by a regulator attached to the first hydraulic pump 1. The regulator of the first hydraulic pump 1 includes a flow control command pressure port 1a, a first hydraulic pump self-pressure port 1b, and a second hydraulic pump self-pressure port 1c. The tilt angle of the second hydraulic pump 2 is controlled by a regulator attached to the second hydraulic pump 2. The regulator of the second hydraulic pump 2 includes a flow control command pressure port 2a, a second hydraulic pump self-pressure port 2b, and a first hydraulic pump self-pressure port 2c. The tilt angle of the third hydraulic pump 3 is controlled by a regulator attached to the third hydraulic pump 3. The regulator of the third hydraulic pump 3 includes a flow control command pressure port 3a and a third hydraulic pump self-pressure port 3b.

[0020] A discharge line 40 of the first hydraulic pump 1 is connected to the hydraulic oil tank 5 via a center bypass line 41, and is also connected to the hydraulic oil tank 5 via a main relief valve 18 to protect the circuit from an excessive pressure rise. In the center bypass line 41, in order from the upstream side, a right traveling directional control valve 6, a bucket directional control valve 7, a second arm directional control valve 8, and a first boom directional control valve 9 are arranged. The supply ports of the directional control valves 7 to 9 are connected in parallel to a part of the center bypass line 41 that connects the right traveling directional control valve 6 and the bucket directional control valve 7, via oil passages 42, 43, oil passages 44, 45, and oil passages 46, 47, respectively.

[0021] The right traveling directional control valve 6 controls the flow of pressure oil supplied from the first hydraulic pump 1 to a right traveling motor (not shown) of a pair of traveling motors that drive the traveling body 201. The bucket directional control valve 7 controls the flow of pressure oil supplied from the first hydraulic pump 1 to the bucket cylinder 206a. The second arm directional control valve 8 controls the flow of pressure oil supplied from the first hydraulic pump 1 to the arm cylinder 205a. The first boom directional control valve 9 controls the flow of pressure oil supplied from the first hydraulic pump 1 to the boom cylinder 204a.

[0022] A discharge line 50 of the second hydraulic pump 2 is connected to the hydraulic oil tank 5 via a center bypass line 51, and is also connected to the hydraulic oil tank 5 via a main relief valve 19 to protect the circuit from an excessive pressure rise. In the center bypass line 51, in order from the upstream side, a second boom directional control valve 10, a first arm directional control valve 11, a first attachment directional control valve 12, and a left traveling directional control valve 13 are arranged. The supply ports of the directional control valves 10 to 13 are connected in parallel to the discharge line 50 via oil passages 52, 53, oil passages 54, 55, oil passages 56, 57, and an oil passage 58, respectively.

[0023] An oil passage 58 connected to a supply port of the left-traveling directional control valve 13 is connected to the discharge line 40 of the first hydraulic pump 1 via the junction valve 17 in order to merge the discharge oil of the first hydraulic pump 1. A check valve 30 is provided between the discharge line 50 and the oil passage 58. The check valve 30 prevents the pressure oil that merges from the discharge line 40 of the first hydraulic pump 1 to the oil passage 58 via the junction valve 17 from flowing into the directional control valves 10 to 12 other than the left-traveling directional control valve 13.

[0024] The second boom directional control valve 10 controls the flow of pressure oil supplied from the second hydraulic pump 2 to the boom cylinder 204a. The first arm directional control valve 11 controls the flow of pressure oil supplied from the second hydraulic pump 2 to the arm cylinder 205a. The first attachment directional control valve 12 controls the flow of pressure oil supplied from the second hydraulic pump 2 to a first actuator (not shown) that drives a first special attachment such as a small chopper provided in place of the bucket 206. The left traveling directional control valve 13 controls the flow of pressure oil supplied from the second hydraulic pump 2 to a left traveling motor (not shown) of a pair of traveling motors that drive the traveling body 201.

[0025] A discharge line 60 of the third hydraulic pump 3 is connected to the hydraulic oil tank 5 via a center bypass line 61, and is connected to the hydraulic oil tank 5 via a main relief valve 20 to protect the circuit from an excessive pressure rise. In the center bypass line 61, in order from the upstream side, a swing directional control valve 14, a third boom directional control valve 15, and a second attachment directional control valve 16 are arranged. The supply ports of the directional control valves 14 to 16 are connected in parallel to the discharge line 60 via oil passages 62, 63, oil passages 64, 65, and oil passages 66, 67, respectively.

[0026] The swing directional control valve 14 controls the flow of pressurized oil supplied from the third hydraulic pump 3 to the swing motor 211. The third boom directional control valve 15 controls the flow of pressurized oil supplied from the third hydraulic pump 3 to the boom cylinder 204a. The second attachment directional control valve 16 controls the flow of pressurized oil supplied to the second actuator when a second special attachment equipped with a second actuator is attached in addition to the first special attachment, or when a second special attachment equipped with two actuators, the first actuator and the second actuator, is attached instead of the first special actuator.

[0027] Flow control valves 21-23 that control the flow rate of pressurized oil supplied from first hydraulic pump 1 to each directional control valve during combined operation are provided in oil passages 42, 43 connected to the supply port of directional control valve 7 for the bucket, oil passages 44, 45 connected to the supply port of directional control valve 8 for the second arm, and oil passages 46, 47 connected to the supply port of directional control valve 9 for the first boom, respectively.

[0028] Flow control valves 24-26 that control the flow rate of pressurized oil supplied from the second hydraulic pump 2 to each directional control valve during combined operation are provided in oil passages 52, 53 connected to the supply port of the second boom directional control valve 10, oil passages 54, 55 connected to the supply port of the first arm directional control valve 11, and oil passages 56, 57 connected to the supply port of the first attachment directional control valve 12, respectively.

[0029] Flow control valves 27-29 are provided in oil passages 62, 63 connected to the supply port of the swing directional control valve 14, in oil passages 64, 65 connected to the supply port of the third boom directional control valve 15, and in oil passages 66, 67 connected to the supply port of the second attachment directional control valve 16, respectively, for controlling the flow rate of pressurized oil supplied from the third hydraulic pump 3 to each directional control valve during combined operation.

[0030] The discharge port of the pilot pump 4 is connected to the hydraulic oil tank 5 via a pilot relief valve 92 for generating pilot primary pressure, and is also connected to a solenoid valve unit 93 via an oil passage 73. The solenoid valve unit 93 has built-in electromagnetic proportional pressure reducing valves 93a to 93g. One input port of each of the electromagnetic proportional pressure reducing valves 93a to 93g is connected to the oil passage 73, and the other input port is connected to the hydraulic oil tank 5. The output port of the electromagnetic proportional pressure reducing valve 93a is connected to a flow control command pressure port 2a of the regulator of the second hydraulic pump 2, the output ports of the electromagnetic proportional pressure reducing valves 93b, 93c are connected to a pilot port of the second boom directional control valve 10, the output ports of the electromagnetic proportional pressure reducing valves 93d, 93e are connected to a pilot port of the first arm directional control valve 11, the output port of the electromagnetic proportional pressure reducing valve 93f is connected to a pilot port 32a of a pilot variable throttle valve 32 of a second boom flow control valve 24 described later, and the output port of the electromagnetic proportional pressure reducing valve 93g is connected to a pilot port 34a of a pilot variable throttle 34 of a first arm flow control valve 25 described later. The electromagnetic proportional pressure reducing valves 93a to 93g reduce the pilot primary pressure in response to a command signal from a controller 94, and output it as a pilot command pressure.

[0031] In order to simplify the explanation, the electromagnetic proportional pressure reducing valves for the flow control command pressure ports 1a, 3a of the regulators of the first hydraulic pump 1 and the third hydraulic pump 3, the electromagnetic proportional pressure reducing valve for the right traveling directional control valve 6, the electromagnetic proportional pressure reducing valve for the bucket directional control valve 7, the electromagnetic proportional pressure reducing valve for the second arm directional control valve 8, the electromagnetic proportional pressure reducing valve for the first boom directional control valve 9, the electromagnetic proportional pressure reducing valve for the first attachment directional control valve 12, the electromagnetic proportional pressure reducing valve for the left traveling directional control valve 13, the electromagnetic proportional pressure reducing valve for the swing directional control valve 14, the electromagnetic proportional pressure reducing valve for the third boom directional control valve 15, the electromagnetic proportional pressure reducing valve for the second attachment directional control valve 16, and the electromagnetic proportional pressure reducing valves for the flow control valves 21-23, 26-29 are not shown in the illustration.

[0032] The flow control valve 24 is composed of a seat-type main valve 31 forming an auxiliary variable throttle, a control variable throttle 31b provided on a valve body 31a of the main valve 31 and changing an opening area according to the amount of movement of the valve body 31a, and a pilot variable throttle valve 32 as a pilot variable throttle. The housing in which the main valve 31 is built has a first pressure chamber 31c formed at a connection part between the main valve 31 and an oil passage 52, a second pressure chamber 31d formed at a connection part between the main valve 31 and an oil passage 53, and a third pressure chamber 31e formed to communicate with the first pressure chamber 31c via the control variable throttle 31b. The third pressure chamber 31e and the pilot variable throttle valve 32 are connected by an oil passage 68a, and the pilot variable throttle valve 32 and the oil passage 53 are connected by an oil passage 68b, and the oil passages 68a, 68b form a pilot line 68.

[0033] A pressure sensor 81 is provided in the discharge line 50 of the second hydraulic pump 2, a pressure sensor 82 is provided in the oil passage 53 connecting the supply port of the second boom directional control valve 10 and the second boom flow control valve 24, and pressure sensors 84, 85 are provided in the oil passages 48, 49 connecting the boom cylinder 204a and the boom directional control valves 9, 10, 15. Note that, although some parts are omitted from the illustration for ease of explanation, the flow control valves 21-29 and the peripheral devices, piping, and wiring all have the same configuration.

[0034] 2B, the hydraulic drive unit 902 includes a boom operation lever 95a which is an operation device capable of switching the first boom directional control valve 9, the second boom directional control valve 10, and the third boom directional control valve 15, and an arm operation lever 95b which is an operation device capable of switching the first arm directional control valve 11 and the second arm directional control valve 8. In order to simplify the explanation, the illustration does not include a right traveling operation lever for switching the right traveling directional control valve 6, a bucket operation lever for switching the bucket directional control valve 7, a first attachment operation lever for switching the first attachment directional control valve 12, a left traveling operation lever for switching the left traveling directional control valve 13, a swing operation lever for switching the swing directional control valve 14, and a second attachment operation lever for switching the second attachment directional control valve 16.

[0035] The hydraulic drive device 902 includes a controller 94 having a calculation function. The controller 94 outputs command signals to electromagnetic proportional pressure reducing valves 93a to 93g (including electromagnetic proportional pressure reducing valves not shown) in response to signals input from operation levers 95a, 95b and pressure sensors 81 to 85.

[0036] Fig. 3 is a functional block diagram of the controller 94. In Fig. 3, the controller 94 has an actuator target flow rate calculation unit 94a, a pump target flow rate calculation unit 94b, a flow control valve target opening calculation unit 94c, a flow control valve auxiliary target opening calculation unit 94d, a pressure state determination unit 94e, a flow control valve target opening determination unit 94f, a first directional control valve target meter-out opening calculation unit 94g, a directional control valve target meter-out opening adjustment unit 94h, a thrust calculation unit 94i, a second directional control valve target meter-out opening calculation unit 94j, and a directional control valve target meter-out opening determination unit 94k.

[0037] The actuator target flow rate calculation unit 94a calculates a target value of the flow rate supplied to the actuators (actuator target flow rate) based on the operation lever input value. The pump target flow rate calculation unit 94b calculates a target value of the discharge flow rate of the hydraulic pumps 1 to 3 (pump target flow rate) based on the calculation result (actuator target flow rate) of the actuator target flow rate calculation unit 94a. The controller 94 outputs a command signal (pump flow rate control command signal) according to the pump target flow rate to the solenoid valve unit 93.

[0038] The flow control valve target opening calculation unit 94c calculates a target value of the opening of the flow control valve (flow control valve target opening) based on the calculation result (actuator target flow rate) of the actuator target flow rate calculation unit 94a and the pressure sensor output value. The flow control valve auxiliary target opening calculation unit 94d refers to a correspondence map between a preset operation lever input value and the opening of the flow control valve, and calculates an auxiliary target value of the opening of the flow control valve (flow control valve auxiliary target opening) based on the operation lever input value. The pressure state determination unit 94e determines whether the differential pressure across the flow control valves 21-29 calculated based on the pressure sensor output value is larger than a preset threshold value.

[0039] A flow control valve target opening determination unit 94f adopts either the calculation result (target opening) of the flow control valve target opening calculation unit 94c or the calculation result (auxiliary target opening) of the flow control valve auxiliary target opening calculation unit 94d as the final target opening based on the judgment result of the pressure state judgment unit 94e. The controller 94 outputs a command signal (flow control valve control command signal) according to the final target opening to the solenoid valve unit 93.

[0040] The first directional control valve target meter-out opening calculation unit 94g refers to a preset correspondence map between the operation lever input value and the meter-out opening of the directional control valves 7-12, 14, 15, and calculates a target value (first target meter-out opening) of the directional control valves 7-12, 14, 15 based on the operation lever input value. The directional control valve target meter-out opening adjustment unit 94h adjusts the first target meter-out opening based on the determination result of the pressure state determination unit 94e and the pressure sensor output value so that the differential pressure before and after the flow control valves 21-29 falls within a predetermined range.

[0041] FIG. 4 is a diagram showing the relationship between the upstream and downstream differential pressure of the flow control valves 21-29 and the flow control accuracy. As shown in FIG. 4, the flow control accuracy of the flow control valves 21-29 is maximum at a certain upstream and downstream differential pressure ΔP (for example, the median value between ΔPlow and ΔPhigh), and the flow control accuracy decreases when the upstream and downstream differential pressure ΔP decreases or increases from that point. For the flow control accuracy, a permissible value (allowable accuracy) of the control accuracy of the flow supplied to the hydraulic actuator is set. Here, the upstream and downstream differential pressure ΔP at the intersection of the curve showing the characteristics of the flow control accuracy with respect to the upstream and downstream differential pressure ΔP and the allowable accuracy is defined as a lower threshold ΔPlow and an upper threshold ΔPhigh, from the lower side. If the upstream and downstream differential pressure ΔP is in the range from the lower threshold ΔPlow to the upper threshold ΔPhigh (predetermined range), the flow control accuracy of the flow control valves 21-29 is equal to or higher than the allowable accuracy.

[0042] The thrust calculation unit 94i calculates the thrust of the hydraulic actuator based on the pressure sensor output value. The method of calculating the thrust when the hydraulic actuator is a hydraulic cylinder and the hydraulic cylinder is driven in the extension direction will be described. If the rod side pressure receiving area of ​​the hydraulic cylinder is Ar, the bottom side pressure receiving area is Ab, the rod side pressure is Pr, and the bottom side pressure is Pb, the thrust F is expressed by the following formula.

[0043]

number

[0044] Here, if the hydraulic actuator is moved in the same direction as the driving direction due to the weight of the working device 203 or the inertial force of the rotating body 202, the thrust F will be a negative value.

[0045] A second directional control valve target meter-out opening calculation unit 94j calculates a directional control valve target meter-out opening (second target meter-out opening) based on the calculation result (thrust F) of the thrust calculation unit 94i. A directional control valve target meter-out opening determination unit 94k determines the ratio of the calculation result (first target meter-out opening) of the directional control valve target meter-out opening adjustment unit 94h and the calculation result (second target meter-out opening) of the second directional control valve target meter-out opening calculation unit 94j. The smaller value is adopted as the final target meter-out opening. The controller 94 outputs a command signal (directional control valve control command signal) to the solenoid valve unit 93 according to the final target meter-out opening.

[0046] 5 is a correspondence map between the thrust F of the hydraulic actuator and the target meter-out opening amount, which is referred to by the second directional control valve target meter-out opening calculation unit 94j. As shown in FIG. 5, the target meter-out opening amount becomes smaller as the negative thrust of the hydraulic actuator increases. As a result, the back pressure of the hydraulic actuator increases according to the negative thrust of the hydraulic actuator.

[0047] Fig. 6 is a diagram showing a correspondence map between the operation lever input value and the target meter-in opening of the directional control valve. As shown in Fig. 6, the target meter-in opening increases steeply from zero to the maximum opening according to the operation lever input value. As a result, when the hydraulic actuator is driven, the meter-in opening becomes the maximum opening, and the flow rate supplied from the flow control valve to the directional control valve flows directly into the hydraulic actuator. In other words, the flow rate supplied to the hydraulic actuator is controlled only by the flow control valves 21-29.

[0048] Fig. 7 is a diagram showing a correspondence map between the operation lever input value and the target meter-out opening of the directional control valve. As shown in Fig. 7, the target meter-out opening gradually increases from zero to the maximum opening according to the operation lever input value. This makes it possible to adjust the meter-out opening between zero and the maximum opening by operating the lever.

[0049] 8 is a flowchart showing the process related to the pump flow rate control of the controller 94. Only the process related to the flow rate control of the second hydraulic pump 2 will be described below, but the process related to the flow rate control of the other hydraulic pumps is similar to this.

[0050] The controller 94 first determines whether or not there is an input to the operation levers 95a, 95b (step S101). If it is determined in step S101 that there is no input to the operation levers 95a, 95b (YES), the flow ends.

[0051] If it is determined in step S101 that there is an input to the operation levers 95a, 95b (NO), the actuator target flow rate calculation unit 94a calculates actuator target flow rates QactA, QactB, ... based on the operation lever input values ​​(steps S102A, S102B, ...). Here, the actuator target flow rate QactA is a target value of the flow rate supplied from the hydraulic pump 2 to actuator A (e.g., boom cylinder 204a), and the actuator target flow rate QactB is a target value of the flow rate supplied from the hydraulic pump 2 to actuator B (e.g., arm cylinder 205a).

[0052] Following steps S102A, S102B, ..., the pump target flow rate calculation unit 94b calculates the sum of the actuator target flow rates QactA, QactB, ... as the target pump flow rate Qpmp (step S103). Here, the target pump flow rate Qpmp is appropriately set by the designer and does not need to strictly match the sum of the actuator target flow rates QactA, QactB, ..., and a bleed-off flow rate, a drain flow rate, etc. may be added.

[0053] Following step S103, the controller 94 outputs a command signal corresponding to the target pump flow rate Qpmp to the electromagnetic proportional pressure reducing valve 93a for controlling the pump flow rate of the hydraulic pump 2 (S104), causes the electromagnetic proportional pressure reducing valve 93a to generate a pump flow rate control command pressure PiP2 for the hydraulic pump 2 (S105), changes the tilt of the second hydraulic pump 2 in accordance with the pump flow rate control command pressure PiP2 (S106), and then ends the flow.

[0054] 9 is a flowchart showing the process related to the flow control valve opening control of the controller. In the following, only the process related to the flow control of the second boom flow control valve 24 will be described, but the process related to the flow control of the other flow control valves is similar to this.

[0055] The controller 94 first determines whether or not there is an input to the boom operation lever 95a (step S201). If it is determined in step S201 that there is no input to the boom operation lever 95a (YES), the flow ends.

[0056] If it is determined in step S201 that there is an input from the boom operation lever 95a (NO), the actuator target flow rate calculation unit 94a calculates the actuator target flow rate Qact based on the operation lever input value (step S202).

[0057] Following step S202, the flow control valve target opening calculation unit 94c calculates a target opening Afcv of the second boom flow control valve 24 based on the actuator target flow rate Qact and the front-to-rear differential pressure ΔP of the second boom flow control valve 24 obtained by the pressure sensors 81, 82 (step S203). If the throttle portions of the flow control valves 21-29 are defined as orifice throttles, the target opening Afcv can be calculated using the following formula.

[0058]

number

[0059] Here, Cd is the flow coefficient and ρ is the fluid density.

[0060] In parallel with steps S202 and S203, the flow control valve auxiliary target opening calculation unit 94d refers to a correspondence map between a preset operating lever input value and a flow control valve opening amount, and calculates the auxiliary target opening amount Afcv_aux of the second boom flow control valve 24 based on the operating lever input value (step S204).

[0061] Following steps S203 and S204, the pressure state determination unit 94e determines whether the differential pressure ΔP across the second boom flow control valve 24 is smaller than the threshold value ΔPlow (step S205).

[0062] If it is determined in step S205 that the pressure difference ΔP across the flow control valve is equal to or greater than the threshold ΔPlow (NO), the flow control valve target opening determination unit 94f adopts the target opening Afcv calculated by the flow control valve target opening calculation unit 94c as the final target opening Afcv_ref (step S206).

[0063] If it is determined in step S205 that the pressure difference between the front and rear ΔP is smaller than the threshold value ΔPlow (YES), the flow control valve target opening determination unit 94f adopts the auxiliary target opening Afcv_aux calculated by the flow control valve auxiliary target opening calculation unit 94d as the final target opening Afcv_ref (step S207). The reason for this is that when the pressure difference between the front and rear of the flow control valves 21 to 29 is small, the target opening Afcv changes significantly in response to a slight fluctuation in the pressure difference between the front and rear ΔP, and calculating the target opening Afcv based on the pressure difference between the front and rear ΔP would instead reduce the accuracy of flow control.

[0064] Following step S206 or step S207, the controller 94 outputs a command signal corresponding to the final target opening amount Afcv_ref to the electromagnetic proportional pressure reducing valve 93f for the second boom flow control valve 24 (S208), causes the electromagnetic proportional pressure reducing valve 93f to generate a command pressure for the second boom flow control valve 24 (S209), opens the second boom flow control valve 24 in accordance with the command pressure (S210), and ends this flow.

[0065] 10 is a flowchart showing processing related to the directional control valve opening control of the controller 94. Only the processing related to the opening control of the second boom directional control valve 10 will be described below, but the processing related to the opening control of the other directional control valves is similar to this.

[0066] The controller 94 first determines whether or not there is an input to the boom operation lever 95a (step S301). If it is determined in step S301 that there is no input to the boom operation lever 95a (YES), the flow ends.

[0067] If it is determined in step S301 that there is an input to the boom operation lever 95a (NO), the first directional control valve target meter-out opening calculation unit 94g refers to a correspondence map (shown in FIG. 7) between a preset operation lever input value and a target meter-out opening amount of the directional control valve, and calculates a first target meter-out opening amount Ams of the second boom directional control valve 10 based on the operation lever input value (step S302).

[0068] Following step S302, the pressure state determination unit 94e determines whether or not the pressure difference ΔP across the second boom flow control valve 24 is within a predetermined range ΔPlow to ΔPhigh, based on the pressure sensor output value (step S303).

[0069] If it is determined in step S303 that the upstream / downstream differential pressure ΔP is not within the predetermined range ΔPlow to ΔPhigh (NO), the directional control valve target meter-out opening adjustment unit 94h calculates a provisional target meter-out opening Ams_adj that causes the upstream / downstream differential pressure ΔP to fall within the predetermined range ΔPlow to ΔPhigh (step S304).

[0070] If it is determined in step S303 that the front-rear differential pressure ΔP is within the predetermined range ΔPlow to ΔPhigh (YES), the directional control valve target meter-out opening adjustment unit 94h adopts the first target meter-out opening Ams calculated by the first directional control valve target meter-out opening calculation unit 94g as a provisional target meter-out opening Ams_adj (step S305).

[0071] In parallel with steps S302 to S305, the thrust calculation unit 94i calculates the thrust F of the boom cylinder 204a based on the pressure sensor output value (step S306).

[0072] Following step S306, the second directional control valve target meter-out opening calculation unit 94j refers to a correspondence map (shown in FIG. 5) between a preset negative thrust F and a target opening of the flow control valve, and calculates a second target meter-out opening Ams_thr of the second boom directional control valve 10 based on the thrust F calculated in step S306 (step S307).

[0073] Following steps S304, S305, and S307, the directional control valve target meter-out opening determination unit 94k determines whether the provisional target meter-out opening Ams_adj calculated in step S304 or step S305 is greater than or equal to the second target meter-out opening Ams_thr calculated in step S307 (step S308).

[0074] If it is determined in step S308 that the provisional target meter-out opening Ams_adj is less than the second target meter-out opening Ams_thr (NO), the provisional target meter-out opening Ams_adj is adopted as the final target meter-out opening Ams_ref (step S309).

[0075] If it is determined in step S308 that the provisional target meter-out opening Ams_adj is equal to or greater than the second target meter-out opening Ams_thr (YES), the second target meter-out opening Ams_thr is adopted as the final target meter-out opening Ams_ref (step S310).

[0076] Following step S309 or step S310, the controller 94 outputs a command signal corresponding to the final target meter-out opening amount Ams_ref to the electromagnetic proportional pressure reducing valves 93b, 93c for the second boom directional control valve 10 (step S311), causes the electromagnetic proportional pressure reducing valves 93b, 93c to generate a command pressure for the second boom directional control valve 10 (step S312), and opens the second boom directional control valve 10 in accordance with the command pressure (step S313), thereby ending this flow.

[0077] It is preferable that the update period Tfcv of the command signal output by the controller 94 to the solenoid valve unit 93 to generate pilot pressures for the flow control valves 21-29 is shorter than the update period Tms of the command signal output to the solenoid valve unit 93 to generate pilot pressures for the directional control valves 7-12, 14, and 15. This makes it possible to improve the control accuracy of the flow control valves 21-29.

[0078] (summary) In this embodiment, there are hydraulic pumps 1 to 3, hydraulic actuators 204a, 205a, 206a, 211, directional control valves 7 to 12, 14, 15 for controlling the flow direction of pressure oil supplied from the hydraulic pumps 1 to 3 to the hydraulic actuators 204a, 205a, 206a, 211, flow control valves 21 to 29 for controlling the flow rate of pressure oil supplied from the hydraulic pumps 1 to 3 to the hydraulic actuators 204a, 205a, 206a, 211, operating devices 95a, 95b for instructing the operation of the hydraulic actuators 204a, 205a, 206a, 211, and a control system for controlling the directional control valves 7 to 12, 14, 15 and the flow control valves 21 to 29 in accordance with input values ​​of the operating devices 95a, 95b. A work machine 901 equipped with a controller 94 is equipped with first pressure sensors 84-91 that detect the pressure of the hydraulic actuators 204a, 205a, 206a, 211, and second pressure sensors 81-83 that detect the pressure difference ΔP across the flow control valves 21-29. The controller 94 calculates the thrust F of the hydraulic actuators 204a, 205a, 206a, 211 based on the output values ​​of the first pressure sensors 84-91, and controls the directional control valves 7-12, 14, 15 based on the pressure difference ΔP across the flow control valves 21-29 detected by the second pressure sensors 81-83, the thrust F of the hydraulic actuators 204a, 205a, 206a, 211, and input values ​​of the operating devices 95a, 95b.

[0079] Further, as an example of a method of controlling the directional control valves 7 to 12, 14, 15, the controller 94 in this embodiment calculates a first target meter-out opening Ams, which is a target value of the meter-out opening of the directional control valves 7 to 12, 14, 15, based on the input values ​​of the operating devices 95a, 95b, and sets the first target meter-out opening Ams to a provisional target meter-out opening Ams_adj when the upstream / downstream differential pressure ΔP of the flow control valves 21 to 29 detected by the second pressure sensors 81 to 83 falls within a predetermined range ΔPlow to ΔPhigh set based on the flow control accuracy of the flow control valves 21 to 29, and sets the first target meter-out opening Ams to a provisional target meter-out opening Ams_adj when the upstream / downstream differential pressure ΔP of the flow control valves 21 to 29 detected by the second pressure sensors 81 to 83 exceeds the predetermined range ΔPlow to ΔPhigh. The meter-out openings of the directional control valves 7 to 12, 14, 15 that bring the pressure difference ΔP across the flow control valves 21 to 29 into a predetermined range ΔPlow to ΔPhigh are set as provisional target meter-out openings Ams_adj, the thrust F of the hydraulic actuators 204a, 205a, 206a, 211 is calculated based on the output values ​​of the second pressure sensors 84 to 91, a second target meter-out opening Ams_thr that is a target value of the meter-out openings of the directional control valves 7 to 12, 14, 15 is calculated based on the thrust F of the hydraulic actuators 204a, 205a, 206a, 211, and the meter-out openings of the directional control valves 7 to 12, 14, 15 are set to the provisional target meter-out openings Ams_adj and the second target meter-out opening Ams_thr. The smaller value The directional control valves 7 to 12, 14, and 15 are controlled so as to coincide with the above.

[0080] According to the present embodiment configured as described above, the back pressure of the hydraulic actuators 204a, 205a, 206a, 211 is adjusted by controlling the directional control valves 7-12, 14, 15, thereby preventing the hydraulic actuators 204a, 205a, 206a, 211 from running away, and the drive of the hydraulic actuators 204a, 205a, 206a, 211 can be stopped smoothly. In addition, the differential pressure across the flow control valves 21-29 is adjusted by controlling the directional control valves 7-12, 14, 15, thereby allowing the flow control valves 21-29 to be operated under differential pressure conditions with high flow control accuracy. As a result, even under low flow rate, high pressure difference or high flow rate, low pressure difference conditions requiring high control accuracy of the hydraulic actuators 204a, 205a, 206a, 211, the target flow can be accurately supplied without causing a decrease in the flow control accuracy of the flow control valves 21-29, thereby allowing the hydraulic actuators 204a, 205a, 206a, 211 to be driven more accurately. EXAMPLES

[0081] A second embodiment of the present invention will be described, focusing on the differences from the first embodiment.

[0082] Fig. 11 is a functional block diagram of a controller in a second embodiment of the present invention. The controller 94 in this embodiment includes a control switch determination unit 94l in addition to the configuration of the first embodiment (see Fig. 3). The control switch determination unit 94l determines whether or not the operation of the corresponding actuator is an operation that does not require meter-out opening control based on the operation lever input value and the pressure sensor output value, and outputs the determination result to a directional control valve target meter-out opening determination unit 94k. The directional control valve target meter-out opening determination unit 94k performs the meter-out opening control described in the first embodiment only for operations that do not require meter-out opening control.

[0083] 12 is a flowchart showing the process related to the opening control of the directional control valve by the controller in this embodiment. In the following, only the process related to the opening control of the second boom direction control valve 10 will be explained, but the process related to the opening control of the other directional control valves is similar to this.

[0084] Following step S302, the control switching determination unit 94l determines whether or not the operation of the boom cylinder 204a is an operation that does not require meter-out opening control based on the operation lever input value and the pressure sensor output value (step S314). Here, an operation that does not require meter-out opening control is an operation in which a decrease in the flow control accuracy of the flow control valves 21-29 is permitted, and corresponds to an operation such as compacting the ground. The operation of compacting the ground can be determined by whether or not the boom operation lever 95a is operated to the boom lowering side and the thrust F in the boom lowering direction calculated from the output values ​​of the pressure sensors 84, 85 and Equation 3 is greater than a predetermined threshold value.

[0085] If it is determined in step S314 that the operation requires meter-out opening control (NO), the process proceeds to step S303, and if it is determined that the operation of the boom cylinder 204a does not require meter-out opening control (NO), the target meter-out opening Ams calculated in step S302 is adopted as the final target meter-out opening Ams_ref (step S315), and the process proceeds to step S311. As a result, the meter-out opening control is disabled when an operation that does not require high flow control accuracy is performed, and the back pressure of the hydraulic actuators 204a, 205a, 206a, 211 is reduced, so that the thrust F of the hydraulic actuators 204a, 205a, 206a, 211 can be increased.

[0086] (summary) The controller 94 in this embodiment determines whether the operation of the hydraulic actuators 204a, 205a, 206a, 211 is an operation in which a decrease in the flow control accuracy of the flow control valves 21-29 is acceptable based on the input values ​​of the operating devices 95a, 95b and the output values ​​of the first pressure sensors 84-91, and if it is determined that the operation of the hydraulic actuators 204a, 205a, 206a, 211 is an operation in which a decrease in the flow control accuracy of the flow control valves 21-29 is acceptable, the controller 94 controls the directional control valves 7-12, 14, 15 so that the meter-out opening amounts of the directional control valves 7-12, 14, 15 match the first target meter-out opening amount Ams calculated based on the input values ​​of the operating devices 95a, 95b.

[0087] According to this embodiment configured as described above, by disabling the meter-out opening control for operations in which a decrease in the flow control accuracy of the flow control valves 21 to 29 is permitted, the thrust F of the hydraulic actuators 204a, 205a, 206a, and 211 can be increased, thereby making it possible to improve work efficiency.

[0088] Although the embodiments of the present invention have been described above in detail, the present invention is not limited to the above-mentioned embodiments and includes various modified examples. For example, the above-mentioned embodiments have been described in detail to easily explain the present invention, and the present invention is not necessarily limited to those having all of the configurations described. In addition, it is possible to add a part of the configuration of one embodiment to the configuration of another embodiment, and it is also possible to delete a part of the configuration of one embodiment or replace it with a part of another embodiment. [Explanation of symbols]

[0089] 1...First hydraulic pump, 1a...Flow control command pressure port, 1b...First hydraulic pump self-pressure port, 1c...Second hydraulic pump self-pressure port, 2...Second hydraulic pump, 2a...Flow control command pressure port, 2b...Second hydraulic pump self-pressure port, 2c...First hydraulic pump self-pressure port, 3...Third hydraulic pump, 3a...Flow control command pressure port, 3b...Third hydraulic pump self-pressure port, 4...Pilot pump, 5...Hydraulic oil tank, 6...Directional control valve for right travel, 7...Directional control valve for bucket direction control valve, 8...direction control valve for second arm, 9...directional control valve for first boom, 10...directional control valve for second boom, 11...directional control valve for first arm, 12...directional control valve for first attachment, 13...directional control valve for left travel, 14...directional control valve for turning, 15...directional control valve for third boom, 16...directional control valve for second attachment, 17...junction valve, 18~20...main relief valve, 21...flow control valve for bucket, 22...flow control valve for second arm, 23...first Boom flow control valve, 24... second boom flow control valve, 25... first arm flow control valve, 26... first attachment flow control valve, 27... rotation flow control valve, 28... third boom flow control valve, 29... second attachment flow control valve, 30... check valve, 31... main valve, 31a... valve body, 31b... control variable throttle, 31c... first pressure chamber, 31d... second pressure chamber, 31e... third pressure chamber, 32... pilot variable throttle valve, 32a... pilot port, 32 b...drain port, 33...main valve, 33a...valve body, 33b...control variable throttle, 33c...first pressure chamber, 33d...second pressure chamber, 33e...third pressure chamber, 34...pilot variable throttle valve, 34a...pilot port, 34b...drain port, 40...discharge line, 41...center bypass line, 42-49...oil passage, 50...discharge line, 51...center bypass line, 52-58...oil passage, 60...discharge line, 61...center bypass line, 62-67,71 to 73... oil passages, 81 to 83... pressure sensors (second pressure sensors), 84 to 91... pressure sensors (first pressure sensors), 92... pilot relief valve, 93... solenoid valve unit, 93a to 93g... solenoid proportional pressure reducing valve, 94... controller, 94a... actuator target flow rate calculation unit, 94b... pump target flow rate calculation unit, 94c... flow control valve target opening calculation unit, 94d... flow control valve auxiliary target opening calculation unit, 94e... pressure state determination unit, 94f... flow control valve target opening determination unit, 94g... first directional control valve target meter-out opening calculation unit, 94h... directional control valve target meter-out opening adjustment unit, 94i... thrust calculation unit, 94j... second directional control valve target meter Out opening calculation unit, 94l...control switching determination unit, 95a...boom operation lever (operation device), 95b...arm operation lever (operation device), 201...traveling body, 202...rotating body, 203...working device, 204...boom, 204a...boom cylinder (hydraulic actuator), 205...arm, 205a...arm cylinder (hydraulic actuator), 206...bucket, 206a...bucket cylinder (hydraulic actuator), 207...operator's cab, 208...machine room, 209...counterweight, 210...control valve, 211...swing motor (hydraulic actuator), 901...hydraulic excavator (working machine), 902...hydraulic drive unit.

Claims

1. A hydraulic pump; A hydraulic actuator; a directional control valve for controlling a flow direction of pressure oil supplied from the hydraulic pump to the hydraulic actuator; a flow control valve for controlling a flow rate of pressure oil supplied from the hydraulic pump to the hydraulic actuator; an operating device for instructing an operation of the hydraulic actuator; A working machine including a controller for controlling the directional control valve and the flow rate control valve in response to an input value of the operating device, A first pressure sensor for detecting a pressure of the hydraulic actuator; a second pressure sensor for detecting a pressure difference before and after the flow control valve; The controller: calculating a first target meter-out opening amount, which is a target value of a meter-out opening amount of the directional control valve, based on an input value of the operating device; When the differential pressure across the flow control valve detected by the second pressure sensor falls within a predetermined range that is set based on the flow control accuracy of the flow control valve, the first target meter-out opening is set as a provisional target meter-out opening, When the differential pressure across the flow control valve detected by the second pressure sensor exceeds the predetermined range, a meter-out opening amount of the directional control valve that brings the differential pressure across the flow control valve within the predetermined range is set to the provisional target meter-out opening amount, calculating a second target meter-out opening amount, which is a target value of a meter-out opening amount of the directional control valve, based on a thrust of the hydraulic actuator calculated based on an output value of the first pressure sensor; The directional control valve is controlled so that a meter-out opening amount of the directional control valve coincides with a smaller value of the provisional target meter-out opening amount and the second target meter-out opening amount. A working machine characterized by:

2. 2. The work machine according to claim 1, The controller: determining whether or not an operation of the hydraulic actuator is an operation in which a decrease in flow control accuracy of the flow control valve is permitted based on an input value of the operating device and an output value of the first pressure sensor; When it is determined that the operation of the hydraulic actuator is an operation in which a decrease in flow control accuracy of the flow control valve is permitted, the directional control valve is controlled so that a meter-out opening amount of the directional control valve coincides with the first target meter-out opening amount calculated based on an input value of the operating device. A working machine characterized by:

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