Hydraulic control device, construction machine and control method of construction machine

Abstract

To provide a hydraulic control device, a construction machine and a control method of a construction machine which improve fuel consumption in heavy load work and can secure a working amount in light load work.SOLUTION: A construction machine 1 includes a work device 4, at least one of actuator 9, 10 and 11 for operating the work device 4, a pump device 15 for supplying hydraulic oil to at least the one of actuator 9, 10 and 11, and an engine 5 for driving the pump device 15. The hydraulic control device includes operation devices 19a and 20a for receiving operation for operating the work device 4, and a controller 70. The controller 70 performs engine speed control including heavy load condition control of adjusting the engine speed to predetermined base speed N1 when the work by the construction machine 1 is predetermined heavy load work, and light load condition control of setting the engine speed to be larger than the base speed N1 when the work by the construction machine 1 is predetermined light load work.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to a hydraulic control device, a construction machine, and a method for controlling a construction machine. [Background technology]

[0002] Each of Patent Documents 1 to 3 discloses a technique for controlling the engine speed in a construction machine. In the technique described in Patent Document 1, the engine speed is increased or decreased based on the amount of operation of an operating member. In the technique described in Patent Document 2, the reduction range of the second target engine speed with respect to the first target engine speed is set according to the type of hydraulic actuator operated by the operating lever or the combination of multiple hydraulic actuators operated by the operating lever. In the technique described in Patent Document 3, when the engine torque becomes equal to or less than the first engine torque and high engine torque is not required, control is performed to reduce the engine speed.

[0003] Furthermore, Patent Document 4 discloses a technology for improving fuel efficiency. In the technology described in Patent Document 4, when the operating direction of the boom cylinder includes a directional component in which the potential energy of the boom cylinder acts, and when the regenerative condition for the arm to perform a predetermined high-load operation is satisfied, hydraulic oil is supplied from the boom cylinder to the arm cylinder. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-188827 A [Patent Document 2] International Publication No. 2011 / 096382 [Patent Document 3] International Publication No. 2009 / 104636 [Patent Document 4] JP 2010-190261 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the techniques described in Patent Documents 1 to 4 have the problem that it is not possible to simultaneously ensure the amount of work in light-load work such as leveling and soil removal, and improve fuel efficiency in heavy-load work such as excavation and lifting and turning.

[0006] In the technology described in Patent Document 1, the engine speed is increased or decreased based on the amount of operation of the operating member, so if the amount of operation of the operating member is the same in light-load work and heavy-load work, the engine speed is adjusted in the same way regardless of the work load. In this case, it may not be possible to improve fuel efficiency in heavy-load work while ensuring the amount of work in light-load work.

[0007] In the technology described in Patent Document 2, the engine speed is adjusted according to the type of actuator operated by the operating member (operating lever). However, for example, in each of leveling work (light load work) and excavation work (heavy load work), the operator applies arm pulling operation to the operating member. That is, the operating member may receive the same operation in both light load work and heavy load work. In the technology described in Patent Document 2, when the operation received by the operating member is the same (for example, when the operating member receives arm pulling operation), the engine speed is adjusted in the same way regardless of the work load, so that it may not be possible to improve fuel efficiency in heavy load work while ensuring the amount of work in light load work.

[0008] In the technology described in Patent Document 3, the engine speed is controlled so that it is high during heavy-load work such as excavation work and low during light-load work such as leveling work, so it is not possible to improve fuel efficiency during heavy-load work while ensuring the amount of work during light-load work.

[0009] The technology described in Patent Document 4 can improve fuel efficiency when the arm performs a specified high-load operation, but Patent Document 4 does not mention ensuring the amount of work during light-load work.

[0010] An object of the present disclosure is to provide a hydraulic control device, a construction machine, and a control method for a construction machine that make it possible to improve fuel efficiency in heavy-load work and ensure the amount of work in light-load work. [Means for solving the problem]

[0011] A hydraulic control device according to a first aspect is a hydraulic control device for a construction machine including a working implement, at least one actuator for operating the working implement, a pump device for supplying hydraulic oil to the at least one actuator, and an engine for driving the pump device, and includes an operation device for receiving an operation for operating the working implement, and a controller. The controller performs engine speed control including heavy-load control for adjusting the engine speed to a predetermined base speed when the work performed by the construction machine is a predetermined heavy-load work, and light-load control for making the engine speed higher than the base speed when the work performed by the construction machine is a predetermined light-load work.

[0012] In this first aspect, when the work of the construction machine is heavy-load work such as excavation work, lifting and swinging work, etc., the engine speed is adjusted to the base speed, so that fuel efficiency during heavy-load work can be improved. On the other hand, when the work of the construction machine is light-load work such as leveling work, earth removal work, etc., the engine speed is adjusted so that the engine speed is higher than the base speed, so that the amount of work during light-load work can be ensured.

[0013] In the light load control, the controller may adjust the engine speed uniformly, for example, to a constant value greater than a base speed, regardless of the amount of operation of the operation. However, it is preferable to adjust the engine speed as in the following second aspect. That is, the second aspect is preferably the hydraulic control device according to the first aspect, further comprising the following features. In the hydraulic control device according to the second aspect, it is preferable that the controller adjusts the engine speed in the light load control such that the engine speed increases from the base speed in accordance with the amount of operation of the operation. In this second aspect, the engine speed can be gradually increased in accordance with the amount of operation, compared to the case where the engine speed is adjusted uniformly to the constant value regardless of the amount of operation of the operation in the light load control. This makes it possible to suppress a sudden change in the engine speed when the light load control is started.

[0014] A third aspect may further include the following feature in the hydraulic control device according to the first or second aspect. That is, in the hydraulic control device according to the third aspect, the controller may perform the light-load control when a predetermined operation for determining whether or not the work performed by the construction machine is the light-load work is received. In other words, the controller may determine that the work performed by the construction machine is the light-load work when the operation device receives a predetermined operation. The predetermined operation may be stored in advance in the controller as an operation that the operation device receives when the light-load work is performed. Specifically, for example, when the work device includes a boom, an arm, and a bucket, the predetermined operation may include at least one of an arm pushing operation, an arm pulling operation, and a bucket soil dumping operation. In this case, the controller may perform the light-load control when the operation device receives the at least one operation (i.e., the predetermined operation).

[0015] A fourth aspect is preferably the hydraulic control device according to the third aspect, further comprising the following feature. That is, in the hydraulic control device according to the fourth aspect, it is preferable that the controller suspends execution of the light-load control when the predetermined exception condition is satisfied, even when the operating device is subjected to the predetermined operation. In this fourth aspect, not only the predetermined operation but also the predetermined exception condition is used as an index for determining whether or not the work performed by the construction machine is light-load work, so that the accuracy of determining whether or not the work performed by the construction machine is light-load work (i.e., the accuracy of determining whether or not the light-load control should be executed) is improved. In this fourth aspect, the controller may perform the heavy-load control without performing the light-load control when the predetermined exception condition is satisfied, even when the operating device is subjected to the predetermined operation.

[0016] A fifth aspect may further include the following feature in the hydraulic control device according to the fourth aspect. That is, in the hydraulic control device according to the fifth aspect, the predetermined application exclusion condition includes at least one of the following: the load acting on the at least one actuator is equal to or greater than a predetermined first set value, the pump pressure of the pump device is equal to or greater than a predetermined second set value, and horsepower control is performed, and it is preferable that the controller does not perform the light load control and performs the heavy load control when the predetermined application exclusion condition is satisfied even when the operating device is subjected to the predetermined operation. When the load acting on the at least one actuator is equal to or greater than a predetermined first set value, the pump pressure of the pump device is equal to or greater than a predetermined second set value, and horsepower control is performed, it is highly likely that the work of the construction machine is heavy load work. Therefore, in this fifth aspect, even when the operating device is subjected to the predetermined operation, when the predetermined application exclusion condition is satisfied, the heavy load control is performed instead of the light load control, thereby improving fuel efficiency in heavy load work.

[0017] A sixth aspect is preferably the hydraulic control device according to the fourth or fifth aspect, further comprising the following feature: That is, in the hydraulic control device according to the sixth aspect, the working device includes a first movable part and a second movable part, the at least one actuator includes a first actuator that operates the first movable part and a second actuator that operates the second movable part, the predetermined exemption condition includes that a predetermined regenerative control is performed, the regenerative control is a control that supplies hydraulic oil discharged from the first actuator, which has a smaller load than the second actuator, to the second actuator when the operating device simultaneously receives a predetermined first operation for operating the first movable part and a predetermined second operation for operating the second movable part, and the controller preferably does not perform the light load control but performs the heavy load control when the predetermined exemption condition is satisfied, even when the operating device receives the predetermined operation. When the regenerative control as described above is performed, the hydraulic oil discharged from the first actuator, which has a smaller load than the second actuator, is supplied to the second actuator, so that the supply amount of hydraulic oil to the second actuator can be secured even if the engine speed is low (i.e., even if the engine speed is at the base speed). Therefore, in this sixth aspect, even if the operating device is subjected to the predetermined operation, if the application exclusion condition is satisfied, the controller does not perform the light load control but performs the heavy load control, so that the supply amount of hydraulic oil can be secured while improving fuel efficiency.

[0018] A seventh aspect is preferably the hydraulic control device according to any one of the first to sixth aspects, further comprising the following feature. That is, the hydraulic control device according to the seventh aspect preferably has torque characteristics such that the torque at the base rotation speed is greater than the torque at an engine rotation speed greater than the base rotation speed. In this seventh aspect, when heavy load control is executed in which the engine rotation speed is adjusted to the base rotation speed, the horsepower control torque at the base rotation speed is greater than the horsepower control torque at an engine rotation speed greater than the base rotation speed. When the torque in the horsepower control is greater, the pump flow rate in the horsepower control range is more easily ensured. Therefore, in this seventh aspect, it is possible to ensure the amount of work in heavy load work while improving fuel efficiency in heavy load work.

[0019] An eighth aspect is preferably the hydraulic control device according to any one of the first to seventh aspects further comprising the following feature. That is, in the hydraulic control device according to the eighth aspect, it is preferable that the controller suspends execution of the engine speed control in at least one of the following cases: when the operation device receives a travel operation, when the operation device receives a predetermined option operation, when the construction machine is automatically or semi-automatically controlled, and when the engine speed is equal to or lower than a predetermined speed lower than the base speed. By suspending execution of the engine speed control, it becomes possible to control the engine speed appropriate for each of these cases without being restricted by the engine speed control.

[0020] A ninth aspect is preferably the hydraulic control device according to any one of the first to eighth aspects, further comprising the following feature. That is, in the hydraulic control device according to the ninth aspect, it is preferable that the controller performs control for suppressing an increase rate of the engine speed when switching from the heavy load control to the light load control. In this ninth aspect, it is possible to suppress the occurrence of abrupt fluctuations in the engine speed when switching from the heavy load control to the light load control. This makes it possible to suppress a decrease in operability for the operator caused by abrupt fluctuations in the engine speed, and to suppress the operator from feeling discomfort caused by abrupt fluctuations in the engine speed.

[0021] A construction machine according to a tenth aspect includes a working device, at least one actuator for operating the working device, a pump device for supplying hydraulic oil to the at least one actuator, an engine for driving the pump device, and a hydraulic control device according to any one of the first to ninth aspects.

[0022] A construction machine control method according to an eleventh aspect is a control method for controlling a construction machine including a working device, at least one actuator for operating the working device, a pump device for supplying hydraulic oil to the at least one actuator, and an engine for driving the pump device, and includes adjusting an engine speed to a predetermined base speed when the work performed by the construction machine is a predetermined heavy-load work, and making the engine speed higher than the base speed when the work performed by the construction machine is a predetermined light-load work. In this eleventh aspect, when the work performed by the construction machine is a heavy-load work such as an excavation work or a lifting and swinging work, the engine speed is adjusted to the base speed, so that fuel efficiency in the heavy-load work can be improved. On the other hand, when the work performed by the construction machine is a light-load work such as a leveling work or a soil removal work, the engine speed is adjusted so that the engine speed is higher than the base speed, so that the amount of work in the light-load work can be secured. Effect of the Invention

[0023] According to the present disclosure, a hydraulic control device, a construction machine, and a control method for a construction machine are provided that make it possible to improve fuel efficiency in heavy-load work and ensure the amount of work in light-load work. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a side view illustrating an example of a construction machine according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a diagram showing an example of a hydraulic circuit of the construction machine. [Diagram 3] 1A to 1C are diagrams illustrating the operation of the working device during excavation work. [Figure 4] 11A to 11C are diagrams illustrating the operation of the working device during horizontal pulling work. [Diagram 5] 11A and 11B are diagrams illustrating the operation of the working device in a pressing and leveling operation. [Figure 6] 4 is a flowchart illustrating an example of a calculation process performed by a controller of the hydraulic control device according to the embodiment of the present disclosure. [Figure 7] 1 is a graph showing the relationship between the operation amount and the pump capacity in a positive control. [Figure 8] 4 is a graph showing the relationship between pump pressure and pump displacement in horsepower control. [Figure 9] 4 is a graph showing an example of engine speed control performed by the controller. [Figure 10] 4 is a diagram showing an example of a map showing a relationship between an operation amount and an engine speed in light load control of the engine speed control; FIG. [Figure 11] 4 is a graph showing the relationship between engine speed and horsepower control torque (PQ control torque). [Figure 12] 4 is a graph showing torque characteristics in horsepower control and torque characteristics of the engine. [Figure 13] 11 is a graph showing an example of a change over time in the amount of arm pulling operation received by the operating device during each of a leveling operation and an excavation operation. [Figure 14]1 is a graph showing an example of changes in pump pressure over time during a leveling operation and an excavation operation. [Figure 15] 11 is a graph showing an example of a change in pump flow rate over time during a horizontal leveling operation. [Figure 16] 4 is a graph showing an example of the relationship between pump pressure and pump displacement during excavation work. [Figure 17] 1 is a graph showing an example of a change in pump capacity over time during an excavation operation. [Figure 18] 1 is a graph showing an example of a change in pump flow rate over time during excavation work. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] An embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a side view showing an example of a construction machine 1 according to this embodiment. The construction machine 1 shown in Fig. 1 is a hydraulic excavator, but the construction machine in the present disclosure is not limited to a hydraulic excavator and may be other construction machines such as a crane or a bulldozer.

[0026] The construction machine 1 includes a lower traveling body 2, an upper rotating body 3 rotatably supported on the lower traveling body 2, and a working device 4 supported on the upper rotating body 3 so as to be able to rise and fall. The lower traveling body 2 has crawlers 2a, but may have tires (not shown). The upper rotating body 3 has a rotating frame 3a supported on the lower traveling body 2, a cab arranged on the rotating frame 3a, and a counterweight. The working device 4 includes a boom 6, an arm 7 rotatably attached to the tip of the boom 6, and a bucket 8 rotatably attached to the tip of the arm 7. The boom 6 is an example of a first movable part in the present disclosure, and the arm 7 is an example of a second movable part in the present disclosure.

[0027] Fig. 2 is a diagram showing an example of a hydraulic circuit 12 of the construction machine 1. As shown in Fig. 1 and Fig. 2, the construction machine 1 includes a plurality of actuators that operate the working implement 4, an operating device that receives an operation for operating the working implement 4, a pump device 15 that supplies hydraulic oil to the plurality of actuators, an engine 5 that drives the pump device 15, a plurality of valves, and a controller 70. The hydraulic control device according to this embodiment includes the operating device and the controller 70.

[0028] In this embodiment, the multiple actuators include a boom cylinder 9, an arm cylinder 10, a bucket cylinder 11, a swing motor (not shown), and a traveling motor (not shown). The boom cylinder 9 is an example of a first actuator in the present disclosure, and the arm cylinder 10 is an example of a second actuator in the present disclosure.

[0029] The boom 6 performs a raising and lowering operation relative to the upper rotating body 3 in accordance with the extension and retraction operation of the boom cylinder 9. Specifically, when the boom cylinder 9 contracts, the boom 6 performs a boom-down operation in which the tip of the boom 6 approaches the ground. When the boom cylinder 9 extends, the boom 6 performs a boom-up operation in which the tip of the boom 6 moves away from the ground.

[0030] The arm 7 performs a rotational motion to rotate relative to the boom 6 in accordance with the extension and retraction motion of the arm cylinder 10. Specifically, when the arm cylinder 10 retracts, the arm 7 performs an arm-pushing motion in which the tip of the arm 7 moves away from the boom 6. When the arm cylinder 10 extends, the arm 7 performs an arm-pulling motion in which the tip of the arm 7 moves toward the boom 6.

[0031] The bucket 8 performs a rotational motion to rotate relative to the arm 7 in association with the extension and retraction of the bucket cylinder 11. Specifically, when the bucket cylinder 11 retracts, the bucket 8 performs a bucket earth-discharging motion (bucket pushing motion). The bucket earth-discharging motion is, for example, a motion when discharging material such as soil held in the bucket 8 to a discharge destination such as the bed of a truck. When the bucket cylinder 11 extends, the bucket 8 performs a bucket excavating motion (bucket pulling motion). The bucket excavating motion is, for example, a motion when excavating an excavation target such as the ground using the bucket 8.

[0032] The upper rotating body 3 performs a rotating motion (right-handed or left-handed) to rotate about a vertical axis relative to the lower traveling body 2 in accordance with the operation of the rotating motor. The lower traveling body 2 performs a traveling motion to travel on the ground in accordance with the operation of the traveling motor.

[0033] The operation device includes a plurality of operation members that are variously operated by an operator. Specifically, for example, the plurality of operation members may include a boom operation member 19a, an arm operation member 20a, a bucket operation member (not shown), a swing operation member (not shown), and a travel operation member (not shown). Each of the plurality of operation members may be an operation lever or an operation pedal.

[0034] The boom operation member 19a receives a boom lowering operation and a boom raising operation by the operator. The boom lowering operation is an operation for making the boom 6 perform a boom lowering operation, and the boom raising operation is an operation for making the boom 6 perform a boom raising operation. The arm operation member 20a receives an arm pushing operation and an arm pulling operation by the operator. The arm pushing operation is an operation for making the arm 7 perform an arm pushing operation, and the arm pulling operation is an operation for making the arm 7 perform an arm pulling operation. The bucket operation member receives a bucket earth discharging operation and a bucket digging operation by the operator. The bucket earth discharging operation is an operation for making the bucket 8 perform a bucket earth discharging operation, and the bucket digging operation is an operation for making the bucket 8 perform a bucket digging operation. The turning operation member receives a right turning operation and a left turning operation by the operator. The right turning operation is an operation for making the upper turning body 3 perform a right turning operation, and the left turning operation is an operation for making the upper turning body 3 perform a left turning operation. The travel operating member is operated by an operator to travel the lower travel structure 2 .

[0035] The construction machine 1 is equipped with a plurality of operation detectors. The plurality of operation detectors may include a boom operation detector, an arm operation detector, a bucket operation detector, a swing operation detector, and a travel operation detector. The boom operation detector detects the operation amount of the boom lowering operation and the operation amount of the boom raising operation received by the boom operation member 19a. The arm operation detector detects the operation amount of the arm pushing operation and the operation amount of the arm pulling operation received by the arm operation member 20a. The bucket operation detector detects the operation amount of the bucket earth dumping operation and the operation amount of the bucket excavation operation received by the bucket operation member. The swing operation detector detects the operation amount of the right swing operation and the operation amount of the left swing operation received by the swing operation member. The travel operation detector detects the operation amount of the travel operation received by the travel operation member. Each of the plurality of operation detectors inputs the detection result to the controller 70.

[0036] The construction machine 1 may be provided with a remote control valve that outputs a pilot pressure (secondary pressure) according to the amount of operation of the operation device. In this case, each of the multiple operation detectors may be a pressure sensor that detects a pilot pressure according to the amount of operation of the operation. Specifically, as shown in FIG. 2, the construction machine 1 may be provided with a remote control valve 19 that outputs a pilot pressure according to the amount of operation of the operation of the boom operation member 19a, and a remote control valve 20 that outputs a pilot pressure according to the amount of operation of the operation of the arm operation member 20a. In this case, the boom operation detector may include a pressure sensor P6 that detects the pilot pressure output from the remote control valve 19 according to the amount of operation of the boom lowering operation, and a pressure sensor P7 that detects the pilot pressure output from the remote control valve 19 according to the amount of operation of the boom raising operation. Similarly, the arm operation detector may include a pressure sensor P8 that detects the pilot pressure output from the remote control valve 20 according to the amount of operation of the arm pushing operation, and a pressure sensor P9 that detects the pilot pressure output from the remote control valve 20 according to the amount of operation of the arm pulling operation.

[0037] Although not shown, the bucket operation detector may include a pressure sensor that detects the pilot pressure output from the remote control valve in response to the operation amount of the bucket earth removal operation, and a pressure sensor that detects the pilot pressure output from the remote control valve in response to the operation amount of the bucket excavation operation. Similarly, the swing operation detector may include a pressure sensor that detects the pilot pressure output from the remote control valve in response to the operation amount of the right swing operation, and a pressure sensor that detects the pilot pressure output from the remote control valve in response to the operation amount of the left swing operation. The travel operation detector may include a pressure sensor that detects the pilot pressure output from the remote control valve in response to the operation amount of the travel operation.

[0038] The construction machine 1 does not necessarily have to include a remote control valve. In this case, the plurality of operation detectors may be configured to detect the amount of operation (e.g., the operation angle of an operation lever) of the operation received by the plurality of operation members, respectively, and input the detection results to the controller 70.

[0039] The pump device 15 includes at least one hydraulic pump that supplies hydraulic oil to at least one of the multiple actuators. The pump device may include only one hydraulic pump, or may include multiple hydraulic pumps (e.g., two hydraulic pumps). The pump device 15 discharges hydraulic oil by being driven by the engine 5. In other words, the at least one hydraulic pump of the pump device 15 discharges hydraulic oil by being driven by the engine 5.

[0040] In this embodiment, the pump device 15 is a variable displacement hydraulic pump device. In other words, the at least one hydraulic pump of the pump device 15 is a variable displacement hydraulic pump. The construction machine 1 is provided with a regulator R1 for changing the pump capacity of the pump device 15. The pump capacity of the pump device 15 is adjusted to a magnitude according to a pump capacity command input from the controller 70 to the regulator R1. When the pump device 15 includes a plurality of hydraulic pumps, the pump capacity of the pump device 15 may be the sum of the pump capacities of the plurality of hydraulic pumps. In addition, the flow rate of the hydraulic oil discharged from the pump device 15 is referred to as the pump flow rate. When the pump device 15 includes a plurality of hydraulic pumps, the pump flow rate of the pump device 15 may be the sum of the flow rates of the hydraulic oil discharged from the plurality of hydraulic pumps.

[0041] The engine 5 is configured to be able to change the engine speed in response to an engine speed command from the controller 70. For example, the engine 5 may be configured to be adjusted stepwise to a plurality of speeds in response to the engine speed command. In this embodiment, the controller 70 is configured to be able to perform control to adjust the engine speed to a plurality of predetermined levels including a base speed N1 and a standard speed N2. The base speed N1 is a speed lower than the standard speed N2.

[0042] The plurality of valves include a plurality of directional control valves. The plurality of directional control valves include a first directional control valve 17 and a second directional control valve 18. The first directional control valve 17 is interposed between the pump device 15 and the boom cylinder 9, and switches the direction in which the hydraulic oil discharged from the pump device 15 is supplied to the boom cylinder 9. The second directional control valve 18 is interposed between the pump device 15 and the arm cylinder 10, and switches the direction in which the hydraulic oil discharged from the pump device 15 is supplied to the arm cylinder 10. Specifically, the first directional control valve 17 is connected to the pump device 15 via an oil passage y1, connected to the rod side chamber of the boom cylinder 9 via an oil passage y3, and connected to the head side chamber of the boom cylinder 9 via an oil passage y4. The second directional control valve 18 is connected to the pump device 15 via an oil passage y2, connected to the rod side chamber of the arm cylinder 10 via an oil passage y5, and connected to the head side chamber of the arm cylinder 10 via an oil passage y6.

[0043] The first direction switching valve 17 is configured to be switchable among a neutral position where the pump device 15 and the tank T are blocked from the boom cylinder 9, a position (right position in FIG. 2) where the oil passage y1 is connected to the oil passage y3 and the oil passage y4 is blocked from the tank T, and a position (left position in FIG. 2) where the oil passage y1 is connected to the oil passage y4 and the tank T. The first direction switching valve 17 is switched by a pilot pressure output from the remote control valve 19 in response to the operation of the boom operation member 19a. The right position of the first direction switching valve 17 may be configured to connect the oil passage y4 to the tank T.

[0044] The second direction switching valve 18 is configured to be switchable among a neutral position where the pump device 15 and the tank T are cut off from the arm cylinder 10, a position where the oil passages y2 and y5 are connected and the oil passages y6 and the tank T are connected (right position in FIG. 2), and a position where the oil passages y2 and y6 are connected and the oil passages y5 and the tank T are connected (left position in FIG. 2). The second direction switching valve 18 is switched by a pilot pressure output from the remote control valve 20 in response to the operation of the arm operating member 20a.

[0045] The plurality of direction switching valves further include a direction switching valve (not shown) that switches the direction in which the hydraulic oil discharged from the pump device 15 is supplied to the bucket cylinder 11, a direction switching valve (not shown) that switches the direction in which the hydraulic oil discharged from the pump device 15 is supplied to the swing motor, and a direction switching valve (not shown) that switches the direction in which the hydraulic oil discharged from the pump device 15 is supplied to the travel motor. The structures and functions of these direction switching valves are similar to those of the first direction switching valve 17, so detailed explanations will be omitted.

[0046] The controller 70 has a computer including an arithmetic processing unit and a memory. The arithmetic processing unit executes a program stored in the memory, whereby the controller 70 controls the operation of the construction machine 1. The controller 70 performs engine speed control. This engine speed control includes heavy load control and light load control. The engine speed control will be described in detail later.

[0047] The construction machine 1 performs various tasks at a work site in response to operations received by the operating device. The various tasks include a predetermined heavy-load task and a predetermined light-load task. The predetermined heavy-load task includes at least one heavy-load task among various heavy-load tasks with a high load. The predetermined light-load task includes at least one light-load task among various light-load tasks with a low load. In this embodiment, the predetermined heavy-load task includes an excavation task and a lifting and turning task, and the predetermined light-load task includes a leveling task and a soil dumping task. However, the predetermined heavy-load task in this disclosure is not limited to an excavation task and a lifting and turning task, and may include other heavy-load tasks. Furthermore, the predetermined light-load task in this disclosure is not limited to a leveling task and a soil dumping task, and may include other light-load tasks.

[0048] 3 is a diagram illustrating the operation of the working device 4 during excavation work. Excavation work is work in which an excavation target, such as soil and sand in the ground, is excavated with the bucket 8. When the construction machine 1 performs excavation work, the operating device receives arm retraction operation, boom raising operation, and bucket earth discharge operation (bucket pushing operation) from the operator, and the arm 7 performs the arm retraction operation, the boom 6 performs the boom raising operation, and the bucket 8 performs the bucket earth discharge operation (bucket pushing operation). During excavation work, the arm retraction operation is performed with at least a part of the bucket 8 placed in the ground, so the load of the excavation work is high.

[0049] Lifting and swinging work is mainly performed after excavation work and before soil dumping work. Lifting and swinging work is mainly performed before soil dumping work, and involves moving the bucket 8 directly above the soil dumping destination, such as the bed of a truck, by rotating the upper rotating body 3 while raising the bucket 8. When the construction machine 1 performs lifting and swinging work, the operating device receives boom-raising and swinging operations from the operator, the boom 6 performs a boom-raising operation, and the upper rotating body 3 performs a swing operation. In lifting and swinging work, it is necessary to rotate the boom 6 in a direction against gravity and to swing the upper rotating body 3. Therefore, the load of lifting and swinging work is high.

[0050] The leveling work is a work in which a leveling target such as the surface of the ground is leveled by the bucket 8. The leveling work may be a horizontal pulling leveling work, a horizontal pushing leveling work, or a pushing leveling work.

[0051] 4 is a diagram illustrating the operation of the working device 4 during leveling work. Leveling work is a work in which the tip of the bucket 8 is moved along the ground in a direction approaching the upper rotating body 3. When the construction machine 1 performs leveling work, the operating device receives arm retraction and boom raising operations from the operator, the arm 7 performs the arm retraction operation, and the boom 6 performs the boom raising operation. During leveling work, most of the bucket 8 is positioned above the ground, and the upper rotating body 3 does not rotate. Therefore, the load during leveling work is relatively low.

[0052] When the construction machine 1 performs horizontal pushing and leveling work, the operating device receives arm pushing and boom lowering operations from the operator, and the arm 7 performs the arm pushing operation and the boom 6 performs the boom lowering operation. During horizontal pushing and leveling work, most of the bucket 8 is positioned above the ground, and the upper rotating body 3 does not rotate. Therefore, the load during horizontal pushing and leveling work is relatively low.

[0053] 5 is a diagram illustrating the operation of the working device 4 in the pressing and leveling work. The pressing and leveling work is a work in which the bucket 8 is moved along the ground while pressing the outer surface (bottom surface) of the bucket 8 against the ground. The pressing and leveling work may be a pressing and pulling leveling work or a pressing and pushing leveling work.

[0054] The pushing and leveling work is a work in which the bucket 8 is moved along the ground in a direction approaching the upper rotating body 3 while pressing the outer surface (bottom surface) of the bucket 8 against the ground. When the construction machine 1 performs the pushing and leveling work, the operating device receives the arm pulling operation, boom raising operation, and bucket earth discharge operation (bucket pushing operation) by the operator, and the arm 7 performs the arm pulling operation, the boom 6 performs the boom raising operation, and the bucket 8 performs the bucket earth discharge operation (bucket pushing operation). In the pushing and leveling work, most of the bucket 8 is positioned above the ground, and the upper rotating body 3 does not rotate. Therefore, the load during the pushing and leveling work is relatively low.

[0055] The pressing and leveling work is a work in which the bucket 8 is moved along the ground in a direction away from the upper rotating body 3 while pressing the outer surface (bottom surface) of the bucket 8 against the ground. When the construction machine 1 performs pressing and leveling work, the operating device receives arm pushing operation, boom lowering operation, and bucket digging operation (bucket pulling operation) by the operator, and the arm 7 performs the arm pushing operation, the boom 6 performs the boom lowering operation, and the bucket 8 performs the bucket digging operation (bucket pulling operation). In pressing and leveling work, most of the bucket 8 is positioned above the ground, and the upper rotating body 3 does not rotate. Therefore, the load of pressing and leveling work is relatively low.

[0056] Earth dumping work is work in which an object held in the bucket 8 is dumped at a dump destination, such as the bed of a truck, directly above the dump destination. When the construction machine 1 performs earth dumping work, the operating device receives the bucket dumping operation from the operator, and the bucket 8 performs the bucket dumping operation (bucket pushing operation). During earth dumping work, the bucket 8 is positioned above the ground, and the upper rotating body 3 does not perform a swing operation. Therefore, the load during earth dumping work is relatively low.

[0057] The controller 70 may determine the type of work performed by the construction machine 1 (i.e., the work performed by the construction machine 1) using the detection results input from the multiple operation detectors. In the controller 70, excavation work and lifting and swinging work may be preset as the predetermined heavy-load work, and leveling work and earth dumping work may be preset as the predetermined light-load work. That is, the controller 70 may be configured to be able to determine whether the work performed by the construction machine 1 is the predetermined heavy-load work, that is, whether the work performed by the construction machine 1 is excavation work or lifting and swinging work. Also, the controller 70 may be configured to be able to determine whether the work performed by the construction machine 1 is the predetermined light-load work, that is, whether the work performed by the construction machine 1 is leveling work or earth dumping work. In excavation work, the operating device receives an arm retraction operation. In lifting and swinging work, the operating device receives a boom raising operation and a swing operation. In leveling work, the operating device receives an arm retraction operation and a boom raising operation. In the pushing and leveling work, the operating device is subjected to arm pulling operation, boom raising operation, and bucket earth discharge operation. In the pushing and leveling work, the operating device is subjected to arm pushing operation, boom lowering operation, and bucket excavation operation. In the earth discharge work, the operating device is subjected to bucket earth discharge operation. In other words, the detection results input from the multiple operation detectors to the controller 70 become indicators for the controller 70 to determine the type of work.

[0058] [Engine speed control] The engine speed control performed by the controller 70 will be described below. The engine speed control includes heavy-load control for adjusting the engine speed to a predetermined base speed N1 when the work performed by the construction machine 1 is the predetermined heavy-load work, and light-load control for making the engine speed higher than the base speed N1 when the work performed by the construction machine 1 is the predetermined light-load work. By performing this engine speed control, when the work performed by the construction machine 1 is the predetermined heavy-load work, it is possible to improve fuel efficiency during the heavy-load work, and when the work performed by the construction machine 1 is the predetermined light-load work, it is possible to ensure the amount of work during the light-load work.

[0059] 6 is a flowchart showing an example of a calculation process performed by the controller 70. In step S1, the controller 70 determines whether or not the control mode is the engine speed control mode (EG speed control mode). If the control mode is the engine speed control mode (YES in step S1), the controller 70 performs the process from step S2 onwards. If the control mode is not the engine speed control mode (NO in step S1), the controller 70 performs normal control (step S6) instead of the process from step S2 onwards (engine speed control). In this embodiment, in the normal control, the controller 70 adjusts the engine speed to the standard speed N2.

[0060] In step S2, the controller 70 judges whether or not a predetermined operation is being performed based on the detection results from the multiple operation detectors. The predetermined operation is at least one operation for judging whether or not the work performed by the construction machine 1 is the predetermined light-load work. In other words, the predetermined operation is at least one operation pre-stored in the controller 70 for judging whether or not light-load control is to be performed. In this embodiment, the predetermined operations include an arm pulling operation, an arm pushing operation, and a bucket earth dumping operation. The arm pulling operation is an operation that the operating device receives in each of the horizontal pulling and leveling work and the push-pull pulling and leveling work. The arm pushing operation is an operation that the operating device receives in the push-pull and leveling work. The bucket earth dumping operation is an operation that the operating device receives in the earth dumping work.

[0061] When the operating device receives the predetermined operation (YES in step S2), specifically, when the operating device receives at least one of an arm pulling operation, an arm pushing operation, and a bucket earth removal operation, the controller 70 performs the process of step S3. On the other hand, when the operating device does not receive the predetermined operation (NO in step S2), the controller 70 performs the process of step S5.

[0062] Specifically, for example, when the operation by the construction machine 1 is the specified light-load work (leveling work or earth discharge work), the operating device receives at least one of an arm pulling operation, an arm pushing operation, and a bucket earth discharge operation (YES in step S2), so the controller 70 performs the process of step S3. When the operation by the construction machine 1 is a lifting and swinging operation (the specified heavy-load work), the operating device receives a boom raising operation and a swinging operation, but does not receive the specified operation (NO in step S2), so the controller 70 performs the process of step S5. On the other hand, when the operation by the construction machine 1 is an excavation work (the specified heavy-load work), the operating device receives an arm pulling operation, a boom raising operation, and a bucket earth discharge operation (YES in step S2), so the controller 70 performs the process of step S3.

[0063] In step S3, the controller 70 judges whether or not a predetermined application exclusion condition is satisfied. The application exclusion condition is a condition that is set in advance for judging whether or not the execution of the light-load control should be suspended even when the operation device receives the predetermined operation. If the application exclusion condition is not satisfied (NO in step S3), the controller 70 performs the light-load control (step S4). This makes it possible to secure the amount of work in the predetermined light-load work. On the other hand, if the application exclusion condition is satisfied (YES in step S3), the controller 70 does not perform the light-load control. In this embodiment, not only the type of operation received by the operation device but also the application exclusion condition is used as an index for judging whether or not the work performed by the construction machine 1 is the predetermined light-load work, so that the accuracy of judging whether or not the work performed by the construction machine 1 is the predetermined light-load work (i.e., the accuracy of judging whether or not the light-load control should be executed) is improved.

[0064] In this embodiment, the application exclusion conditions include at least one of conditions (a) to (c). Condition (a) is that the load acting on the actuator is equal to or greater than a predetermined first set value. Condition (b) is that the pump pressure of pump device 15 (pump discharge pressure of pump device 15) is equal to or greater than a predetermined second set value. Condition (c) is that horsepower control (so-called PQ control) is performed.

[0065] When at least one of the following is satisfied: the load acting on the actuator is equal to or greater than a predetermined first set value, the pump pressure is equal to or greater than a predetermined second set value (for example, equal to or greater than a set pressure Ps described below), and horsepower control is being performed, there is a high possibility that the work performed by the construction machine is heavy-load work. Therefore, in this embodiment, even when the operating device is subjected to the predetermined operation, if the application exclusion condition is satisfied by satisfying at least one of conditions (a) to (c) (YES in step S3), the heavy-load control (step S5) is performed instead of the light-load control (step S4). This improves fuel efficiency during heavy-load work.

[0066] The construction machine 1 may be equipped with a load detector for detecting the load acting on the actuator, which is a parameter included in the condition (a). In this case, the load detector inputs the detection result to the controller 70, and the controller 70 determines whether or not the load acting on the actuator is equal to or greater than a first set value based on the detection result by the load detector.

[0067] The load detector may be, for example, a pressure sensor that detects pressure acting on at least one of the plurality of actuators. Specifically, the load detector may include at least one of a pressure sensor P3 that detects pressure acting on the rod side chamber of the boom cylinder 9, a pressure sensor P4 that detects pressure acting on the head side chamber of the boom cylinder 9, a pressure sensor P5 that detects pressure acting on the rod side chamber of the arm cylinder 10, and a pressure sensor (not shown) that detects pressure acting on the head side chamber of the arm cylinder 10. The load detector may also include a pressure sensor (not shown) that detects pressure acting on at least one of the bucket cylinder 11, the swing motor, and the traveling motor.

[0068] The construction machine 1 may be equipped with a pump pressure detector for detecting the pump pressure, which is a parameter included in the condition (b). In this case, the pump pressure detector inputs the detection result to the controller 70, and the controller 70 determines whether the pump pressure is equal to or higher than a second set value based on the detection result by the pump pressure detector.

[0069] The pump pressure detector may include, for example, one or both of the pump pressure sensor P1 and the pump pressure sensor P2. When the pump device 15 includes only one hydraulic pump, the pump pressure detector may detect the pump pressure of the hydraulic pump (i.e., the pump pressure of the pump device 15) by one of the pump pressure sensor P1 and the pump pressure sensor P2. In this case, the pump pressure detector may include only one of the pump pressure sensor P1 and the pump pressure sensor P2, and the other may be omitted. When the pump device 15 includes, for example, a first hydraulic pump and a second hydraulic pump, the pump pressure sensor P1 may detect the pump pressure of the first hydraulic pump (e.g., the pressure in the oil passage y1), and the pump pressure sensor P2 may detect the pump pressure of the second hydraulic pump (e.g., the pressure in the oil passage y2). In this case, the pump pressure of the pump device 15 may be a value calculated using the pump pressure of the first hydraulic pump and the pump pressure of the second hydraulic pump. Specifically, for example, the pump pressure of the pump device 15 may be an arithmetic average of the pump pressure of the first hydraulic pump and the pump pressure of the second hydraulic pump, or a weighted average of the pump pressure of the first hydraulic pump and the pump pressure of the second hydraulic pump, or a value calculated by other calculation methods.

[0070] The controller 70 may determine whether or not horsepower control is to be performed based on, for example, the detection result by the pump pressure detector (i.e., the pump pressure of the pump device 15). However, a method other than a method based on the pump pressure may be used to determine whether or not horsepower control is to be performed.

[0071] Next, the light load control (step S4), the heavy load control (step S5), and the normal control (step S6) will be described. In the normal control, the controller 70 performs control to adjust the engine speed to a standard speed N2, which is a preset standard engine speed. In the heavy load control, the controller 70 performs control to adjust the engine speed to a base speed N1, which is lower than the standard speed N2. In the light load control, the controller 70 performs control to make the engine speed higher than the base speed N1. Specifically, in the light load control according to this embodiment, the controller 70 performs control to adjust the engine speed so that the engine speed increases from the base speed N1 in accordance with the amount of operation of the operation.

[0072] In each of the light load control, the heavy load control, and the normal control, the controller 70 performs both positive control and horsepower control (so-called PQ control) for the pump capacity of the pump device 15.

[0073] Positive control is a control for increasing the pump capacity of the pump device 15 in response to an increase in the amount of operation of the operation device received by the operating device. The controller 70 calculates the pump capacity for positive control, i.e., a pump capacity that matches the amount of operation of the operation device received by the operating device. The controller 70 is preset with, for example, a characteristic as shown in Fig. 7, i.e., a characteristic in which the pump capacity increases linearly from a minimum capacity qmin with an upper limit of a maximum capacity qmax as the amount of operation increases. The controller 70 calculates the pump capacity for positive control based on the characteristic and the amount of operation of the operation device received by the operating device.

[0074] Horsepower control is a control that limits the pump horsepower (horsepower required to drive the pump device 15), which is calculated using the pump pressure and pump capacity of the pump device 15, based on the horsepower curve of the engine 5. The controller 70 has a characteristic (horsepower control characteristic) as shown in Fig. 8, for example, preset therein. This horsepower control characteristic is a characteristic in which the pump capacity is a maximum capacity qmax in a low pressure region where the pump pressure is less than the set pressure Ps, and in a high pressure region (PQ region) where the pump pressure is equal to or greater than the set pressure Ps, the pump capacity decreases from the maximum capacity qmax as the pump pressure increases from the set pressure Ps. The controller 70 calculates the pump capacity for horsepower control based on the horsepower characteristic and the pump pressure.

[0075] The controller 70 compares the pump displacement calculated for the positive control with the pump displacement calculated for the horsepower control and selects the lower of these pump displacements (performs a low selection), and then adjusts the actual pump displacement of the pump device 15 to the pump displacement selected as above.

[0076] In this embodiment, in the predetermined light-load work, the pump pressure becomes less than the set pressure Ps, and in the predetermined heavy-load work, the pump pressure becomes equal to or greater than the set pressure Ps. Therefore, when the construction machine 1 performs the predetermined light-load work, the pump pressure becomes less than the set pressure Ps, and the pump displacement calculated for the positive control is selected to be low. On the other hand, when the construction machine 1 performs the predetermined heavy-load work and the operation amount of the operation received by the operating device is at a maximum value (so-called full lever operation), the pump displacement calculated for the horsepower control is selected to be low. Note that even when the construction machine 1 performs the predetermined heavy-load work, if the operation amount of the operation received by the operating device is small, the pump displacement calculated for the positive control may be selected to be low.

[0077] Next, the control of the rotation speed of the engine 5 in each of the light load control, the heavy load control, and the normal control will be described.

[0078] In normal control (step S6 in FIG. 6), the controller 70 adjusts the rotation speed of the engine 5 to the standard rotation speed N2. Thus, in this embodiment, the engine rotation speed in normal control is the same as the maximum value of the engine rotation speed in light load control (standard rotation speed N2), but the engine rotation speed in normal control is not limited to the standard rotation speed N2, and may be higher than the standard rotation speed N2 or may be a value between the base rotation speed N1 and the standard rotation speed N2.

[0079] Next, the light load control (step S4) and the heavy load control (step S5) in the engine speed control will be described. FIG 9 is a graph showing an example of the engine speed control performed by the controller 70.

[0080] [Light load control] First, the light load control (step S4 in FIG. 6) will be described. For example, when the construction machine 1 starts the predetermined light load operation such as leveling or earth removal, and the controller 70 determines in step S3 that the application exclusion condition is not satisfied at time t1 in FIG. 9 (NO in step S3), the controller 70 performs the light load control (step S4). In this light load control, the controller 70 adjusts the engine speed to a predetermined speed higher than the base speed N1 as shown in FIG. 9. In this light load control, the controller 70 may adjust the engine speed to the standard speed N2 uniformly regardless of the amount of operation of the operation, or may adjust the engine speed according to a map as shown in FIG. 10.

[0081] FIG. 10 is a diagram showing an example of a map showing the relationship between the lever operation amount and the engine speed in the light load control of the engine speed control. In the light load control, the controller 70 may adjust the engine speed so that the engine speed increases from the base speed N1 according to the operation amount (lever operation amount) as shown in FIG. 10. In this case, in the light load control, the engine speed can be gradually increased according to the operation amount. This makes it possible to suppress the occurrence of a sudden change in the engine speed when the light load control is started. This makes it possible to suppress the sudden operation of the working device 4 when the light load control is started. In addition, when the operating device receives an operation with a large operation amount such as a full lever operation in light load work in which work efficiency is prioritized among various light load works, the engine speed becomes a large value corresponding to the large operation amount, so that the work amount of the light load work can be secured. On the other hand, when the operating device receives an operation with a small amount of operation, such as a fine operation, in light-load work where accuracy is prioritized among various light-load works, the engine speed is suppressed to a low value corresponding to the small amount of operation, thereby ensuring the accuracy of the light-load work and improving fuel efficiency.

[0082] In this embodiment, the range in which the engine speed is adjusted in the light load control is a range from a base speed N1 as a minimum value to a standard speed N2 as a maximum value. The controller 70 adjusts the engine speed so that the engine speed increases as the amount of operation received by the operating device increases. As shown in FIG. 10, when the amount of operation received by the operating device is equal to or greater than M2, the controller 70 may adjust the engine speed to a constant value (standard speed N2). Also, as shown in FIG. 10, when the amount of operation received by the operating device is equal to or less than M1, the controller 70 may adjust the engine speed to a constant value (base speed N1).

[0083] When the engine speed is adjusted according to a map such as that shown in Fig. 10 during light load control, the "operation amount" which is the parameter on the horizontal axis in Fig. 10 is the operation amount of the operation received by the operating device during work by the construction machine 1. When the operating device receives a plurality of operations simultaneously during work by the construction machine 1, the parameter may be the operation amount of any predetermined operation among the plurality of operations, or may be the largest operation amount among the plurality of operations.

[0084] Specifically, for example, when the work performed by the construction machine 1 is a leveling work, the operating device receives an arm retraction operation and a boom raising operation, and the parameter may be the operation amount of the arm retraction operation, the operation amount of the boom raising operation, or the larger of the operation amount of the arm retraction operation and the operation amount of the boom raising operation. When the work performed by the construction machine 1 is a push-type leveling work, the operating device receives an arm retraction operation, a boom raising operation, and a bucket dumping operation (bucket pushing operation), and the parameter may be the operation amount of the arm retraction operation, the operation amount of the boom raising operation, the operation amount of the bucket dumping operation, or the largest operation amount of these operations.

[0085] When the work performed by the construction machine 1 is the predetermined light load work, the pump pressure is less than the set pressure Ps, so the pump capacity calculated for positive control is selected to be low. That is, in this case, the controller 70 performs positive control rather than horsepower control. In this case, the pump flow rate Q, which is the flow rate of hydraulic oil discharged from the pump device 15, can be expressed by the following formula (1).

[0086] Pump flow rate Q = pump capacity q × engine speed N (1)

[0087] Furthermore, when the work performed by the construction machine 1 is the above-mentioned specified light-load work such as leveling work and soil removal work, the above-mentioned exemption condition is not satisfied. Then, when the operation performed by the operating device during this light-load work is full lever operation, that is, when the amount of operation is the maximum amount of operation, the pump capacity becomes the maximum capacity qmax as shown in Figure 7, and the engine speed N increases to the standard speed N2 as shown in Figure 10, and as a result, a sufficient pump flow rate Q (= qmax × N2) is ensured. This makes it possible to ensure the amount of work during the above-mentioned specified light-load work.

[0088] [Heavy load control] Next, the heavy load control will be described. For example, when the predetermined heavy load operation such as excavation work or lifting and swinging work is started by the construction machine 1, and the controller 70 does not receive the predetermined operation in step S2 at time t1 in FIG. 9 (NO in step S2), or when the application exclusion condition is satisfied in step S3 (YES in step S3), the controller 70 performs the heavy load control (step S5). In this heavy load control, the controller 70 adjusts the engine speed to the base speed N1 as shown in FIG. 9. Note that, in the initial stage (immediately after time t1 in FIG. 9) when the heavy load control is started, the engine speed may temporarily be higher than the base speed N1. This is because the pump pressure is less than Ps in the initial stage, so the application exclusion condition may not be satisfied, and the process of step S4 may be temporarily performed in this initial stage.

[0089] When the work performed by the construction machine 1 is the above-mentioned predetermined heavy-load work such as excavation work or lifting and swinging work, and the amount of operation received by the operating device is at a maximum value (full lever operation), the application exclusion condition is satisfied by performing horsepower control (YES in step S3 in FIG. 6), and the controller 70 performs heavy-load control (step S5). In this heavy-load control, the controller 70 adjusts the engine speed N to the base speed N1.

[0090] Fig. 11 is a graph showing the relationship between engine speed and horsepower control torque (PQ control torque). As shown in Fig. 11, in this embodiment, the horsepower control torque (PQ control torque) during heavy load control, i.e., the horsepower control torque T1 at the base speed N1, is greater than the horsepower control torque T2 at the standard speed N2. In other words, the characteristics of the horsepower control torque are set so that when the engine speed decreases from the standard speed N2 to the base speed N1, the horsepower control torque increases from T2 to T1. This will be explained with reference to Fig. 12.

[0091] FIG. 12 is a graph showing the torque characteristics in horsepower control (PQ control) and the torque characteristics of the engine 5. In this embodiment, the torque characteristics of the engine 5 have a characteristic in which the torque is maximum when the engine speed is "N0" and decreases as the engine speed increases from N0. The engine speed N0 is a value smaller than the base speed N1. The torque characteristics in the horsepower control have a characteristic in which the horsepower control torque increases and decreases in response to an increase and decrease in the torque characteristics of the engine 5, and the horsepower control torque is smaller than the torque of the engine 5 when compared at the same engine speed. In this embodiment, the base speed N1 and the standard speed N2 are each set to a value larger than the speed N0, so that when the engine speed decreases from the standard speed N2 to the base speed N1, the horsepower control torque can be increased from T2 to T1.

[0092] The reason why the torque characteristics in the horsepower control are set so that the horsepower control torque is smaller than the torque of the engine 5 when compared at the same engine speed is as follows. That is, when the horsepower control is being performed, an unavoidable sudden change in the load may occur, and the pump pressure may increase suddenly accordingly. In such a case, control to reduce the pump displacement is required to keep the horsepower control torque in the horsepower control within a range smaller than the torque of the engine 5. However, if the control of the pump displacement is not completed in time, there is a possibility that the horsepower control torque may transiently exceed the torque of the engine 5, causing the engine to stall. In order to prevent such a problem from occurring, the torque characteristics in the horsepower control are set so that the horsepower control torque is smaller than the torque of the engine 5.

[0093] In this embodiment, as described above, the torque characteristics in horsepower control are such that the horsepower control torque at the base rotation speed N1 is greater than the horsepower control torque at the standard rotation speed N2, which is an engine rotation speed greater than the base rotation speed N1. When the torque in horsepower control is greater, the pump flow rate in the horsepower control range is more easily ensured. Therefore, it is possible to improve fuel efficiency in heavy-load work while ensuring the amount of work in heavy-load work.

[0094] The pump displacement for horsepower control can be determined using the following equation (2).

[0095] T = q × P / 2π (2) T: Horsepower control torque q: Pump capacity P: Pump pressure

[0096] The pump flow rate Q2 at the standard rotation speed N2 is expressed by the following equation (3).

[0097] Q2 = T2 × (2π / P) × N2 (3) Q2: Pump flow rate at standard speed N2 T2: Horsepower control torque P: Pump pressure

[0098] The pump flow rate Q1 at the base rotation speed N1 is expressed by the following equation (4).

[0099] Q1 = T1 × (2π / P) × N1 (4) Q1: Pump flow rate at base speed N1 T1: Horsepower control torque P: Pump pressure

[0100] In the heavy load control, when the engine speed is reduced from the standard speed N2 to the base speed N1 and the horsepower control torque is increased from T2 to T1, it is preferable that the following formula (5) is satisfied.

[0101] T1×N1=T2×N2 (5)

[0102] Since horsepower is proportional to the product of torque and engine speed, when the above formula (5) is satisfied, even if the engine speed is reduced from the standard speed N2 to the base speed N1 during heavy load control, the same horsepower can be obtained as before the engine speed was reduced.

[0103] Furthermore, when the above formula (5) is satisfied, the following formula (6) is also satisfied.

[0104] Q2=T2×(2π / P)×N2=T1×(2π / P)×N1 (6)

[0105] Therefore, when the load (pump pressure P) is the same, the pump flow rate Q2 is the same as the pump flow rate Q1. This makes it possible to obtain the same pump flow rate as before the engine speed reduction, even if the engine speed is reduced from the standard speed N2 to the base speed N1 under heavy load control, and improves fuel efficiency by reducing the engine speed while ensuring the amount of work during the specified heavy load work such as excavation work and lifting and swinging work.

[0106] With regard to the above embodiment, a specific example will be given in which the specified light-load work is leveling work and the specified heavy-load work is excavation work, and these specific examples will be described in further detail below with reference to Figures 13 to 18.

[0107] Fig. 13 is a graph showing an example of the change over time in the operation amount of the arm pulling operation received by the operating device in each of the leveling and leveling work and the excavation work. Fig. 14 is a graph showing an example of the change over time in the pump pressure in each of the leveling and leveling work and the excavation work. Fig. 15 is a graph showing an example of the change over time in the pump flow rate in the leveling work. Fig. 16 is a graph showing an example of the relationship between the pump pressure and the pump capacity in the excavation work. Fig. 17 is a graph showing an example of the change over time in the pump capacity in the excavation work. Fig. 18 is a graph showing an example of the change over time in the pump flow rate in the excavation work.

[0108] As shown in Fig. 13, the operation device is subjected to arm pulling operation in both cases where the construction machine 1 is performing leveling work and where it is performing excavation work. Fig. 13 illustrates a case where the operation amount of the arm pulling operation is the maximum value (full lever operation amount).

[0109] Since the leveling and smoothing work is the predetermined light-load work and the excavation work is the predetermined heavy-load work, the pump pressure is high during the excavation work and low during the leveling and smoothing work, as shown in Fig. 14. Specifically, the pump pressure during the excavation work mainly changes in a high-pressure region (PQ region) equal to or higher than the set pressure Ps, and the pump pressure during the leveling and smoothing work mainly changes in a low-pressure region below the set pressure Ps. Therefore, the controller 70 performs horsepower control (PQ control) during the excavation work and performs positive control during the leveling and smoothing work.

[0110] In the horizontal pulling and leveling work (the above-mentioned predetermined light-load work), the controller 70 performs light-load control, and increases the engine speed according to the operation amount (lever operation amount) of the arm pulling operation, for example. When the operation device receives the arm pulling operation of the full lever operation amount as shown in Fig. 13, the engine speed increases from the base speed N1 to the standard speed N2 as shown in Fig. 9. Also, in the positive control, when the operation amount is the full lever operation amount, the pump capacity becomes the maximum capacity qmax as shown in Fig. 7, so the pump flow rate Q becomes "Q = qmax x N2" as shown by the solid line in Fig. 15.

[0111] In Fig. 15, the change over time of the pump flow rate when the control according to the reference example is performed is shown by a broken line. This reference example differs from the light load control according to the above embodiment in that the engine speed before the start of the leveling work is the standard speed N2, and is maintained at the standard speed N2 even after the leveling work is started. In this reference example, when the positive control is performed in the leveling work and the operation amount of the arm pulling operation is the full lever operation amount, the pump capacity becomes the maximum capacity qmax as shown in Fig. 7, and the pump flow rate Q becomes "Q = qmax x N2" as shown by the broken line in Fig. 15.

[0112] In the light load control according to this embodiment, as shown by the solid line in FIG. 15, the pump flow rate in the initial stage when the arm pulling operation is started in the leveling work, that is, the pump flow rate in the initial stage when the engine speed increases from the base speed N1 according to the operation amount to the standard speed N2, is slightly smaller than that of the reference example. However, the pump flow rate in this embodiment is equivalent to the pump flow rate in the reference example after the engine speed reaches the standard speed N2. Therefore, when comparing the entire leveling work, the light load control according to this embodiment can obtain the same amount of work (workability) as the reference example. Note that the fuel consumption amount is relatively small in the specified light load work, so the light load control according to this embodiment prioritizes securing the amount of work over improving fuel efficiency.

[0113] Next, an excavation operation will be described. During excavation operation (the above-mentioned specified heavy load operation), the controller 70 performs heavy load control and adjusts the engine speed to the base speed N1. In the specific example of Fig. 9, since the engine speed is the base speed N1 even before time t1 when the excavation operation is started, the controller 70 performs control to maintain the engine speed at the base speed N1 when the excavation operation is started.

[0114] As shown in FIG. 14, the pump pressure immediately after the start of excavation work is smaller than the set pressure Ps, but when the pump pressure becomes equal to or greater than the set pressure Ps, the pump capacity becomes smaller than the maximum capacity qmax by the horsepower control shown in FIG. 8, even if the operating device is subjected to arm pulling operation with the full lever operation amount. On the other hand, the horsepower control torque T1 when the engine speed is the base speed N1 is larger than the horsepower control torque T2 when the engine speed is the standard speed N2 (T1>T2) as shown in FIG. 11. As shown in the above formula (2), when the horsepower control torque increases, the pump capacity also increases, so that when compared at the same pump pressure, the pump capacity in the heavy load control according to this embodiment shown by the solid line in FIG. 16 is larger than the pump capacity in the horsepower control according to the reference example shown by the dashed line in FIG. 16. As a result, as shown in FIG. 17, the pump capacity (solid line) in the heavy load control according to the embodiment is larger than the pump capacity (dashed line) in the control according to the reference example during almost the entire excavation work.

[0115] As shown in FIG. 9, the base rotation speed N1, which is the engine rotation speed in the heavy load control according to this embodiment, is lower than the standard rotation speed N2 (the engine rotation speed in the control according to the reference example), but as shown in FIG. 17, the pump capacity (solid line) in this embodiment is greater than the pump capacity (dashed line) in the reference example. As shown in the above formula (1), the pump flow rate is proportional to the product of the pump capacity and the engine rotation speed. Therefore, in the heavy load control according to this embodiment, when the engine rotation speed is reduced from the standard rotation speed N2 to the base rotation speed N1 and the horsepower control torque is increased from T2 to T1, if the torque characteristics are set so that the above formula (5) is satisfied, as shown in FIG. 18, the pump flow rate (solid line) in this embodiment becomes equal to the pump flow rate (dashed line) in the reference example. As a result, in the heavy load control according to this embodiment, it is possible to improve fuel efficiency while ensuring the pump flow rate and the amount of work.

[0116] In the above specific example described with reference to Figures 13 to 18, the specified light-load work is leveling work and the specified heavy-load work is excavation work, but the same effect as the above specific example can be obtained when the specified light-load work is other work such as soil removal work, and the same effect as the above specific example can be obtained when the specified heavy-load work is other work such as lifting and rotating work.

[0117] As described above, in the hydraulic control device, the construction machine 1, and the control method for the construction machine 1 according to this embodiment, when the work performed by the construction machine is a predetermined heavy-load work, the engine speed is adjusted to a predetermined base speed, and when the work performed by the construction machine is a predetermined light-load work, the engine speed is made higher than the base speed. This makes it possible to improve fuel efficiency during the predetermined heavy-load work, and ensure the amount of work during the predetermined light-load work.

[0118] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and includes, for example, the following modified examples.

[0119] (A) Variation 1 In the above embodiment, the application exclusion condition includes at least one of the conditions (a) to (c), but the application exclusion condition may also include the following condition (d). That is, the application exclusion condition may include at least one of the conditions (a) to (d). The condition (d) is that a predetermined regenerative control is performed.

[0120] The predetermined regenerative control may be, for example, a control to supply hydraulic oil discharged from the boom cylinder 9, which has a smaller load than the arm cylinder 10, to the arm cylinder 10 when the operating device simultaneously receives a boom lowering operation for causing the boom 6 to perform a boom lowering operation and an arm pushing operation for causing the arm 7 to perform an arm pushing operation. The boom lowering operation is an example of a first operation in the present disclosure, and the arm pushing operation is an example of a second operation in the present disclosure.

[0121] When this regenerative control is performed, hydraulic oil discharged from the boom cylinder 9, which has a smaller load than the arm cylinder 10, is supplied to the arm cylinder 10, so that even if the engine speed is low (for example, even if the engine speed is the base speed N1), the supply amount of hydraulic oil to the arm cylinder 10 can be secured. Therefore, when the operating device receives the predetermined operation (YES in step S2) and the application exclusion condition is satisfied by performing the regenerative control (YES in step S3), the controller 70 performs the heavy load control (step S5) instead of the light load control (step S4). This makes it possible to improve fuel efficiency while securing the supply amount of hydraulic oil to the arm cylinder 10.

[0122] In addition, in this modified example, the horsepower control torque T1 when the engine speed is the base speed N1 is preferably larger than the horsepower control torque T2 when the engine speed is the standard speed N2 (T1>T2), as described with reference to Fig. 11. In this case, in the heavy load control according to the modified example, it is possible to improve fuel efficiency while ensuring the pump flow rate and the workload.

[0123] The controller 70 may determine whether or not the regenerative control is performed by determining whether or not the operating device receives a boom lowering operation and an arm pushing operation simultaneously. That is, the controller 70 may determine whether or not the regenerative control is performed based on the detection results of the pressure sensors P6, P7, P8, and P9. In addition to determining whether or not the operating device receives a boom lowering operation and an arm pushing operation simultaneously, the controller 70 may determine whether or not the pressure acting on the head side chamber of the boom cylinder 9 is greater than the pressure acting on the rod side chamber of the arm cylinder 10, and determine that the regenerative control is performed when these determination conditions are satisfied.

[0124] A specific example of the work in which the operating device receives the boom lowering operation and the arm pushing operation at the same time is a return operation. The return operation is often performed after an earth dumping operation. Specifically, the construction machine 1 performs a series of operations including an excavation operation in which an excavation target such as soil and sand in the ground is excavated with the bucket 8, a lifting and swinging operation in which the bucket 8 holding the soil and sand is moved to a dumping destination such as a truck bed, an earth dumping operation in which the held object held by the bucket 8 is dumped to the dumping destination directly above the dumping destination, and a return operation in which the bucket 8 is moved from directly above the dumping destination to the excavation target. When the construction machine 1 performs a return operation, the operating device receives a boom lowering operation, an arm pushing operation, and a swinging operation by the operator, and the boom 6 performs a boom lowering operation, the arm 7 performs an arm pushing operation, and the upper swing body 3 performs a swinging operation.

[0125] An example of a hydraulic circuit 12 capable of performing the above-mentioned regenerative control (valve regenerative control) will be briefly described with reference to FIG. 2. As shown in FIG. 2, the hydraulic circuit 12 includes a regenerative oil passage y7 that connects the oil passage y4 and the oil passage y5. A regenerative valve 22 is disposed in the regenerative oil passage y7. The regenerative valve 22 is a switching valve that can be switched between a supply position (position shown in FIG. 2) that allows hydraulic oil to be supplied from the oil passage y4 to the oil passage y5, and a prohibition position (upper position in FIG. 2) that blocks the oil passage y4 from the oil passage y5. The regenerative valve 22 is normally open, and may be configured to be closed by being operated by a pilot pressure from the electromagnetic proportional valve b2. In this case, the electromagnetic proportional valve b2 operates in response to an electric signal from the amplifier a2. The amplifier a2 may be controlled by the controller 70. When the regenerative valve 22 is operated to the allowable position, the hydraulic oil led out from the head side chamber of the boom cylinder 9 can be led to the rod side chamber of the arm cylinder 10. In addition, the regenerative valve 22 may be configured to be able to adjust the flow rate of the hydraulic oil flowing through the regenerative oil passage y7 in accordance with the operation stroke between the permitted position and the prohibited position.

[0126] The exclusion condition may include, for example, that engine speed sensing control (ESS control) is performed. The ESS control is a control for adjusting the pump flow rate of the pump device 15 according to the difference between the target rotation speed and the actual rotation speed of the engine 5.

[0127] (B) Variation 2 In the construction machine 1 according to the second modification, the controller 70 suspends execution of the engine speed control in at least one of the following cases: when the operating device receives a travel operation (case 1), when the operating device receives a predetermined option operation (case 2), when the construction machine 1 is automatically or semi-automatically controlled (case 3), and when the engine speed is equal to or lower than a predetermined speed that is lower than the base speed N1 (case 4). By suspending execution of the engine speed control, it becomes possible to control the engine speed appropriate for each of these cases without being restricted by the engine speed control.

[0128] Specifically, in any of cases 1 to 4, the controller 70 may determine that the control mode is not the engine speed control mode (NO in step S1), and adjust the engine speed to the standard speed N2 in the normal control (step S6).

[0129] [Case 1] The traveling operation performed by the construction machine 1 as a result of the operation device receiving the traveling operation requires a relatively large pump flow rate. Therefore, in case 1, it is preferable that the controller 70 adjusts the engine speed to the standard speed N2, for example. This ensures the amount of work during the traveling operation.

[0130] [Case 2] An optional device (not shown) different from the bucket 8 may be attached to the tip of the arm 7. The optional device may be, for example, a tip attachment having a function of gripping an object such as a grapple or fork, a tip attachment having a function of crushing an object such as a crusher, or a tip attachment having another function. The predetermined optional operation is an operation given to the operating device to exercise the function of the optional device as described above. The optional work performed by the construction machine 1 by the operating device receiving the optional operation requires a relatively large pump flow rate. Therefore, in case 2, it is preferable that the controller 70 adjusts the engine speed to the standard speed N2, for example. This ensures the amount of work in the optional work.

[0131] [Case 3] The construction machine 1 may be machine-controlled (automatically or semi-automatically) by the controller 70. In this case, the controller 70 may be a part of the construction machine 1, or may constitute a part or all of a hydraulic control device that is located at a different place from the construction machine 1. In this case, the controller 70 sets the control mode to the machine control mode, not the engine speed control mode. In this machine control mode, there is less fluctuation in the engine speed compared to the engine speed control mode. This allows for more accurate operation in the machine control.

[0132] [Case 4] The predetermined rotation speed is a value smaller than the base rotation speed N1, and may be, for example, the rotation speed N0 in FIG. 12. Specifically, case 4 may be a case in which the standard rotation speed is set to the rotation speed N0. In such a case, the base rotation speed becomes a value even smaller than the rotation speed N0 as the standard rotation speed, and in the torque characteristic shown in FIG. 12, when the engine rotation speed decreases from the standard rotation speed N0 to the base rotation speed, the horsepower control torque also decreases. In this case, when the engine rotation speed decreases from the standard rotation speed N2 to the base rotation speed N1, the control in the above embodiment in which the horsepower control torque is increased from T2 to T1 cannot be performed. In this case, in case 4, the workload in the heavy load control may not be sufficiently secured. Therefore, in case 4, the controller 70 may determine that the control mode is not the engine rotation speed control mode (NO in step S1), and adjust the engine rotation speed to the standard rotation speed N2 in the normal control (step S6) to secure the workload. The construction machine 1 may be provided with an accelerator (not shown) that can be operated by an operator, and the standard rotation speed may be set by the operator operating the accelerator.

[0133] (C) Variation 3 When an excavation operation is being performed and the amount of penetration of the bucket 8 into the ground (penetration amount) decreases, the control may be switched from horsepower control to positive control. In such a case, the state where the application exception condition is satisfied (YES in step S3 in FIG. 6) changes to a state where the application exception condition is not satisfied (NO in step S3), and the engine speed may increase or suddenly increase from the base speed N1 toward the standard speed N2. If the pump flow rate increases suddenly due to this, the operating speed of the working implement 4 may fluctuate, which may lead to a decrease in operability for the operator.

[0134] In order to solve this problem, in the construction machine 1 according to the third modification, the controller 70 performs control to suppress the rate of increase in the engine speed when switching from the heavy load control to the light load control. In the third modification, it is possible to suppress the occurrence of abrupt fluctuations in the engine speed when switching from the heavy load control to the light load control. This makes it possible to suppress the deterioration of the operability of the operator caused by abrupt fluctuations in the engine speed, and to suppress the operator from feeling discomfort caused by abrupt fluctuations in the engine speed.

[0135] In the third modification, when switching from the heavy load control to the light load control, the controller 70 may perform a transient fluctuation suppression process such as a rate limiter for the fluctuation of the target value of the engine speed (e.g., the fluctuation from the target speed N1 to the target speed N2). This fluctuation suppression process may be, for example, adjusting the rate of change of the speed from the target speed N1 to the target speed N2 to a predetermined rate or to less than the predetermined rate. As a result, when switching from the heavy load control to the light load control, the rate of change of the engine speed decreases, so that the deterioration of the operability of the operator can be suppressed.

[0136] (D) Variation 4 The construction machine 1 may be configured to be remotely operated. In this case, the operation device may be disposed in a location (remote location) different from the construction machine 1. Furthermore, the controller 70 may be a part of the construction machine 1, may be disposed in a remote location, or may be disposed in a location different from the construction machine 1 and the operation device. [Explanation of symbols]

[0137] 1: Construction machinery 2: Lower running body 3: Upper rotating body 4: Work equipment 5: Engine 6: Boom 7: Arm 8: Bucket 9: Boom cylinder 10: Arm cylinder 11: Bucket cylinder 15: Pump equipment 19a: Boom operation member (operation device) 20a: Arm operating member (operating device) 22: Regenerative valve 70: Controller N1: Base RPM N2: Standard rotation speed

Claims

1. A hydraulic control device for a construction machine including a working device, at least one actuator that operates the working device, a pump device that supplies hydraulic oil to the at least one actuator, and an engine that drives the pump device, An operating device that receives an operation for operating the working device; and a controller that performs engine speed control including heavy load control that adjusts the engine speed to a predetermined base speed when the work performed by the construction machine is a predetermined heavy load work, and light load control that makes the engine speed higher than the base speed when the work performed by the construction machine is a predetermined light load work.

2. The hydraulic control device according to claim 1 , wherein the controller adjusts the engine speed during the light load control so that the engine speed increases from the base engine speed in accordance with an amount of the operation.

3. 2. The hydraulic control device according to claim 1, wherein the controller performs the light-load control when the operation device receives a predetermined operation for determining whether or not the work performed by the construction machine is the predetermined light-load work.

4. 4. The hydraulic control device according to claim 3, wherein the controller suspends execution of the light load control when the predetermined exemption condition is satisfied even when the operating device receives the predetermined operation.

5. the predetermined exception condition includes at least one of: a load acting on the at least one actuator is equal to or greater than a predetermined first set value; a pump pressure of the pump device is equal to or greater than a predetermined second set value; and horsepower control is being performed; 5. The hydraulic control device according to claim 4, wherein the controller does not perform the light load control and performs the heavy load control when the predetermined exemption condition is satisfied even when the operating device receives the predetermined operation.

6. The working device includes a first movable part and a second movable part, the at least one actuator includes a first actuator that actuates the first movable part and a second actuator that actuates the second movable part; the predetermined exemption condition includes a predetermined regenerative control being performed, and the regenerative control is a control for supplying hydraulic oil discharged from the first actuator, which has a smaller load than the second actuator, to the second actuator when the operating device simultaneously receives a predetermined first operation for operating the first movable part and a predetermined second operation for operating the second movable part; 5. The hydraulic control device according to claim 4, wherein the controller does not perform the light load control and performs the heavy load control when the predetermined exemption condition is satisfied even when the operating device receives the predetermined operation.

7. 2. The hydraulic control device according to claim 1, wherein the construction machine has torque characteristics such that the torque at the base rotational speed is greater than the torque at an engine rotational speed greater than the base rotational speed.

8. 2. The hydraulic control device according to claim 1, wherein the controller suspends execution of the engine speed control in at least one of the following cases: when the operating device receives a traveling operation, when the operating device receives a predetermined option operation, when the construction machine is automatically or semi-automatically controlled, and when the engine speed is equal to or lower than a predetermined speed that is lower than the base speed.

9. 2. The hydraulic control device according to claim 1, wherein the controller performs control for suppressing an increase rate of the engine speed when switching from the heavy load control to the light load control.

10. A working device; At least one actuator for actuating the working device; a pump device for supplying hydraulic fluid to the at least one actuator; an engine that drives the pump device; A construction machine comprising: a hydraulic control device according to any one of claims 1 to 9.

11. A control method for controlling a construction machine including a working device, at least one actuator that operates the working device, a pump device that supplies hydraulic oil to the at least one actuator, and an engine that drives the pump device, comprising: A method for controlling a construction machine, comprising adjusting an engine speed to a predetermined base speed when work performed by the construction machine is a predetermined heavy-load work, and making the engine speed higher than the base speed when work performed by the construction machine is a predetermined light-load work.

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