Construction machinery control device and construction machinery

Abstract

To provide a construction machinery control device and construction machinery that can improve engine fuel efficiency while ensuring the workability of construction machinery. [Solution] When a predetermined condition is met for determining whether or not to reduce the rotational speed Ne of the engine 5 during the operation of the construction machine 1, the rotational speed Ne of the engine 5 is controlled to a specific rotational speed N2 which is lower than the base rotational speed N1 which is the rotational speed when the predetermined condition is not met, and the pump capacity q of the hydraulic pump 15 is increased to a size that ensures the flow rate of the hydraulic pump 15 when the rotational speed of the engine 5 is the base rotational speed N1.

Description

Technical Field

[0001] The present disclosure relates to a construction machine control device and a construction machine for a construction machine powered by an engine.

Background Art

[0002] Patent Document 1 discloses a control device for a hydraulic construction machine including a prime mover, at least one variable displacement hydraulic pump driven by the prime mover, at least one hydraulic actuator driven by the pressure oil of the hydraulic pump, and a rotational speed control means for controlling the rotational speed of the prime mover. This control device includes a mode selection means for selecting a control mode related to the prime mover, a load pressure detection means for detecting the load pressure of the hydraulic pump, and a prime mover rotational speed for reducing the rotational speed of the prime mover in response to an increase in the load pressure of the hydraulic pump is preset. When a specific mode is selected by the mode selection means, a corresponding prime mover rotational speed is obtained by referring to the load pressure of the hydraulic pump detected by the load pressure detection means to the preset prime mover rotational speed, and a target rotational speed setting means for setting the target rotational speed of the rotational speed control means based on this prime mover rotational speed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the technology of Patent Document 1, in a range where the pump pressure (load) of the hydraulic pump is high, the rotational speed of the engine is controlled low, so the flow rate of the hydraulic pump decreases, and the workability of the construction machine may deteriorate. Also, in a range where the pump pressure of the hydraulic pump is low, the rotational speed of the engine does not decrease, so the fuel consumption improvement effect of the engine cannot be sufficiently obtained.

[0005] This disclosure was made to resolve the above-mentioned problems, and its purpose is to provide a construction machine control device and a construction machine that can improve the fuel efficiency of the engine while ensuring the workability of the construction machine. [Means for solving the problem]

[0006] A construction machine control device according to a first embodiment is a construction machine control device for a construction machine comprising an engine, a variable displacement hydraulic pump driven by the engine, and at least one hydraulic actuator that operates when hydraulic fluid discharged from the hydraulic pump is supplied, the control device comprising a controller that controls the rotational speed of the engine and the pump capacity of the hydraulic pump, wherein, when a predetermined condition for determining whether or not to reduce the rotational speed of the engine during the operation of the construction machine is met, the controller controls the rotational speed of the engine to a specific rotational speed lower than the base rotational speed which is the rotational speed when the predetermined condition is not met, and increases the pump capacity to a size that ensures the flow rate of the hydraulic pump when the rotational speed of the engine is the base rotational speed.

[0007] According to the first embodiment, when predetermined conditions for determining whether or not to reduce the engine speed are met, fuel efficiency can be improved by reducing the engine speed. At this time, the pump capacity of the hydraulic pump is increased to a size that ensures the flow rate of the hydraulic pump when the engine speed is the base speed, thereby ensuring the flow rate of the hydraulic pump and ensuring the workability of the construction machine.

[0008] A construction machinery control device according to a second embodiment preferably has the following additional features compared to a construction machinery control device according to a first embodiment. That is, in a construction machinery control device according to a second embodiment, the predetermined conditions include a heavy load condition for determining whether or not to reduce the rotational speed of the engine during a predetermined heavy load operation, and a light load condition for determining whether or not to reduce the rotational speed of the engine during a predetermined light load operation.

[0009] According to the second embodiment, the engine speed can be reduced during predetermined heavy load operations and predetermined light load operations, and the engine's fuel efficiency can be improved during predetermined heavy load operations and predetermined light load operations.

[0010] A construction machinery control device according to the third embodiment preferably further comprises the following features in addition to the construction machinery control device according to the second embodiment. In other words, in the construction machinery control device according to the third embodiment, the heavy load condition is met when PQ control is being executed, the pump capacity of the hydraulic pump is below a predetermined first threshold, and the construction machinery is in a predetermined operating state, or when PQ control is being executed, the pump pressure of the hydraulic pump is above a predetermined second threshold, and the construction machinery is in a predetermined operating state, and when the heavy load condition is met, the controller controls the rotational speed of the engine to the specific rotational speed, and increases the torque setting value of the PQ control to a second PQ control torque which is a higher torque than the first PQ control torque when the rotational speed of the engine is at the base rotational speed, the second PQ control torque is a torque that ensures the output of the hydraulic pump even when the rotational speed of the engine decreases from the base rotational speed to the specific rotational speed, and the PQ control is a control that reduces the pump capacity of the hydraulic pump in accordance with the pump pressure when the pump pressure of the hydraulic pump becomes above a predetermined pressure.

[0011] According to the third embodiment, when heavy load conditions are met, the engine speed decreases, thus improving the engine's fuel efficiency. At this time, the torque setting value for PQ control increases to a second PQ control torque, which is higher than the first PQ control torque, thus ensuring the output of the hydraulic pump and the workability of the construction machinery.

[0012] A construction machinery control device according to a fourth embodiment preferably further comprises the following features in addition to the construction machinery control device according to a second embodiment. That is, in a construction machinery control device according to a fourth embodiment, the heavy load condition is met when PQ control is being executed and the construction machinery is in a predetermined operating state, and when the heavy load condition is met, the controller controls the rotational speed of the engine to continuously decrease from the base rotational speed to the specific rotational speed until the pump capacity of the hydraulic pump decreases to a predetermined first threshold, and continuously increases the torque setting value of the PQ control to a second PQ control torque which is higher than the first PQ control torque when the rotational speed of the engine is at the base rotational speed, the second PQ control torque is a torque that ensures the output of the hydraulic pump even when the rotational speed of the engine decreases from the base rotational speed to the specific rotational speed, and the PQ control is a control that reduces the pump capacity of the hydraulic pump in accordance with the pump pressure when the pump pressure of the hydraulic pump exceeds a predetermined pressure.

[0013] According to the fourth embodiment, when heavy load conditions are met, the engine speed decreases continuously, thereby improving the engine's fuel efficiency. At this time, the torque setting value of the PQ control increases continuously to a second PQ control torque, which is higher than the first PQ control torque. As a result, the output of the hydraulic pump is maintained even while the engine speed is decreasing, ensuring the workability of the construction machinery.

[0014] A construction machine control device according to the fifth embodiment preferably has the following additional features compared to a construction machine control device according to the third or fourth embodiment. That is, in a construction machine control device according to the fifth embodiment, the construction machine includes a work device mounted on the upper slewing body of the construction machine, the work device includes a boom rotatably attached to the upper slewing body, an arm rotatably attached to the tip of the boom, and a bucket rotatably attached to the tip of the arm, the hydraulic actuator includes a first hydraulic actuator for rotating the boom, a second hydraulic actuator for rotating the arm, a third hydraulic actuator for rotating the bucket, and a fourth actuator for rotating the upper slewing body, and the predetermined operating state is a state in which at least one of a boom raising operation and a bucket digging operation is performed simultaneously with an arm pulling operation.

[0015] According to the fifth embodiment, when at least one of the boom raising operation and the bucket digging operation is performed simultaneously with the arm pulling operation (for example, digging operation), the workability of the construction machine can be ensured while improving fuel efficiency by reducing the engine speed.

[0016] A construction machine control device according to the sixth embodiment preferably has the following additional features in addition to the construction machine control device according to the third or fourth embodiment. That is, in the construction machine control device according to the sixth embodiment, the construction machine includes a work device mounted on the upper slewing body of the construction machine, the work device includes a boom rotatably attached to the upper slewing body, an arm rotatably attached to the tip of the boom, and a bucket rotatably attached to the tip of the arm, the hydraulic actuator includes a first hydraulic actuator for rotating the boom, a second hydraulic actuator for rotating the arm, a third hydraulic actuator for rotating the bucket, and a fourth actuator for rotating the upper slewing body, and the predetermined operating state is a state in which a boom raising operation and a slewing operation for rotating the upper slewing body are performed simultaneously.

[0017] According to the sixth embodiment, when the boom raising operation and the slewing operation for rotating the upper slewing body are performed simultaneously, the engine speed can be reduced to improve fuel efficiency while ensuring the workability of the construction machinery.

[0018] A construction machine control device according to the seventh embodiment is preferably a construction machine control device according to any of the second to sixth embodiments, further comprising the following features. That is, in the construction machine control device according to the seventh embodiment, the construction machine comprises a work device mounted on the upper slewing body of the construction machine, the work device includes a boom rotatably attached to the upper slewing body, an arm rotatably attached to the tip of the boom, and a bucket rotatably attached to the tip of the arm, the hydraulic actuator includes a first hydraulic actuator for rotating the boom, a second hydraulic actuator for rotating the arm, a third hydraulic actuator for rotating the bucket, and a fourth actuator for rotating the upper slewing body, the light load condition is met when a rapid slewing operation is performed to rapidly rotate the upper slewing body and the pump capacity of the hydraulic pump is less than or equal to a predetermined third threshold, or when the rapid slewing operation is performed and the slewing speed of the upper slewing body is less than or equal to a predetermined fourth threshold.

[0019] According to the seventh embodiment, when a rapid rotation operation is performed to rapidly rotate the upper rotating body, the engine speed can be reduced to improve fuel efficiency while ensuring the workability of the construction machine.

[0020] The construction machine control device according to the eighth embodiment preferably further comprises the following features in a construction machine control device according to any of the second to seventh embodiments. That is, in the construction machine control device according to the eighth embodiment, the construction machine includes a work device mounted on the upper slewing body of the construction machine, the work device includes a boom rotatably attached to the upper slewing body, an arm rotatably attached to the tip of the boom, and a bucket rotatably attached to the tip of the arm, the hydraulic actuator includes a first hydraulic actuator for rotating the boom, a second hydraulic actuator for rotating the arm, a third hydraulic actuator for rotating the bucket, and a fourth actuator for rotating the upper slewing body, and the light load condition is met when the boom lowering operation is performed.

[0021] According to the eighth aspect, when the boom is lowered, the workability of the construction machine can be ensured while improving fuel efficiency by reducing the engine speed.

[0022] A construction machinery control device according to the ninth embodiment preferably further comprises the following features in addition to a construction machinery control device according to any of the first to eighth embodiments. That is, in a construction machinery control device according to the ninth embodiment, the controller does not reduce the rotational speed of the engine even if the predetermined conditions are met when at least one of the following is met: when abnormal processing of the engine is being performed; when a condition for a decrease in the output of the engine is met; when the oil temperature of the hydraulic fluid supplied to the hydraulic actuator is above a predetermined fifth threshold; when the water temperature of the cooling water of the construction machinery is above a predetermined sixth threshold; when an operation requiring a large flow rate is performed on the hydraulic actuator; when an operation for precise operation of the construction machinery is performed; and when a mode for precise operation of the construction machinery is selected.

[0023] According to the ninth aspect, when there is a risk of causing engine stall by changing the engine speed, when there is a possibility of causing engine overheat, when there is a possibility of a decrease in the flow rate of the hydraulic oil supplied to the hydraulic actuator, or when the operability of the construction machine may deteriorate, these can be avoided by not reducing the engine speed.

[0024] The construction machine according to the tenth aspect includes a boom rotatably attached to the upper slewing body, an arm rotatably attached to the tip of the boom, a bucket rotatably attached to the tip of the arm, at least one hydraulic actuator for operating the boom, the arm, and the bucket, a hydraulic pump for supplying hydraulic oil to the hydraulic actuator, and a construction machine control device according to any one of the first to ninth aspects.

[0025] According to the tenth aspect, when a predetermined condition for determining whether to reduce the engine speed is satisfied, it is possible to provide a construction machine that can improve fuel efficiency by reducing the engine speed while ensuring the workability of the construction machine.

Effect of the Invention

[0026] According to the present disclosure, it is possible to provide a construction machine control device and a construction machine that can improve the fuel efficiency of the engine while ensuring the workability of the construction machine.

Brief Description of the Drawings

[0027] [Figure 1] It is a side view showing an example of a construction machine according to an embodiment of the present disclosure. [Figure 2] It is a diagram showing an example of the hydraulic circuit of the construction machine. [Figure 3] It is a time chart showing an operation pattern during the excavation and loading work mainly performed by the construction machine and the control state of the engine corresponding to the above operation pattern. [Figure 4] It is a diagram for explaining the operation of the working device in the excavation work. [Figure 5] This flowchart shows an example of the calculation process performed by the controller during excavation and loading operations. [Figure 6] This is an example of a map used when determining whether an engine speed reduction operation has occurred. [Figure 7] This is a map showing the relationship between pump pressure and pump capacity, used when calculating the pump capacity for PQ control. [Figure 8] This map shows the relationship between manipulated variables and pump capacity, and is used when calculating pump capacity for positive control. [Figure 9] This is an example of a map used when determining whether an engine speed reduction operation has occurred. [Figure 10] This diagram shows the switching operation of the rotation reduction operation judgment when PQ control is turned ON during excavation work and lifting and rotating work (i.e., during heavy load operation). [Figure 11] This is a simplified hydraulic circuit diagram showing the path through which the hydraulic fluid discharged from the hydraulic pump is supplied to the swing motor. [Figure 12] This is a time chart showing the changes in pump flow rate and motor flow rate when the upper rotating body is rapidly rotated. [Figure 13] This is an example of a correspondence table used when determining whether an engine speed reduction operation has occurred. [Figure 14] This is a time chart explaining the operation of the upper rotating body during rotation. [Figure 15] This is an example of a correspondence table used when determining whether an engine speed reduction operation has occurred. [Figure 16] This figure shows the switching operation of the rotation reduction operation determination when PQ control is turned ON during excavation work and lifting and rotating work (i.e., during heavy load operation), corresponding to the second embodiment of this disclosure. [Figure 17] This diagram shows the relationship between engine torque and PQ torque. [Figure 18] This figure illustrates the change in engine speed, corresponding to the third embodiment of this disclosure. [Modes for carrying out the invention]

[0028] [First Embodiment] Embodiments of this disclosure will be described in detail below with reference to the drawings. Figure 1 is a side view showing an example of a construction machine 1 according to this embodiment. The construction machine 1 shown in Figure 1 is a hydraulic excavator, but the construction machine in this disclosure is not limited to a hydraulic excavator and may be other construction machines such as cranes or bulldozers.

[0029] The construction machine 1 comprises a lower traveling body 2, an upper slewing body 3 rotatably supported on the lower traveling body 2, and a work device 4 that is rotatably mounted on the upper slewing body 3. The lower traveling body 2 has crawler tracks 2a, but may also have tires as shown in the figure. The upper slewing body 3 has a slewing frame 3a supported on the lower traveling body 2, a cab positioned on the slewing frame 3a, and a counterweight. The work device 4 comprises 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.

[0030] Figure 2 shows an example of a hydraulic circuit 12 of a construction machine 1. As shown in Figures 1 and 2, the construction machine 1 includes a plurality of hydraulic actuators for operating a work device 4, an operating device for receiving operations to operate the work device 4, a hydraulic pump 15 for supplying hydraulic fluid to the plurality of hydraulic actuators, an engine 5 for driving the hydraulic pump 15, a plurality of valves, and a construction machine control device. The construction machine control device includes a controller 70.

[0031] In this embodiment, the plurality of hydraulic actuators include a boom cylinder 9 for rotating the boom 6, an arm cylinder 10 for rotating the arm 7, a bucket cylinder 11 for rotating the bucket 8, a slewing motor 22 (see Figure 11) for slewing the upper slewing body 3, and a travel motor (not shown). The plurality of hydraulic actuators are operated by the supply of hydraulic fluid discharged from a hydraulic pump 15. The boom cylinder 9 is an example of the first hydraulic actuator of this disclosure, the arm cylinder 10 is an example of the second hydraulic actuator of this disclosure, the bucket cylinder 11 is an example of the third hydraulic actuator of this disclosure, and the slewing motor 22 is an example of the fourth hydraulic actuator of this disclosure.

[0032] The boom 6 is rotatably attached to the upper slewing body 3 and performs a luffing motion relative to the upper slewing body 3 in conjunction with the extension and retraction of the boom cylinder 9. Specifically, when the boom cylinder 9 is retracted, the boom 6 performs a boom-lowering motion, bringing its tip closer to the ground. When the boom cylinder 9 is extended, the boom 6 performs a boom-raising motion, bringing its tip further away from the ground.

[0033] The arm 7 is rotatably attached to the tip of the boom 6 and rotates relative to the boom 6 in conjunction with the extension and retraction of the arm cylinder 10. Specifically, when the arm cylinder 10 is retracted, the arm 7 performs an arm-pushing motion, moving its tip away from the boom 6. When the arm cylinder 10 is extended, the arm 7 performs an arm-pulling motion, moving its tip closer to the boom 6.

[0034] Bucket 8 is rotatably attached to the tip of arm 7 and rotates relative to arm 7 in conjunction with the extension and retraction of bucket cylinder 11. Specifically, when bucket cylinder 11 is retracted, bucket 8 performs a bucket soil discharge operation (bucket pushing operation). Bucket soil discharge operation is the operation of discharging held material such as soil held in bucket 8 to a destination such as the bed of a truck. When bucket cylinder 11 is extended, bucket 8 performs a bucket digging operation (bucket pulling operation). Bucket digging operation is the operation of excavating an object to be excavated, such as ground, using bucket 8.

[0035] The upper rotating body 3 performs a rotational movement (right rotation or left rotation) around a vertical axis relative to the lower traveling body 2 in accordance with the operation of the rotation motor 22. The lower traveling body 2 performs a traveling movement along the ground in accordance with the operation of the traveling motor.

[0036] The operating device includes a plurality of operating members that receive various operations from an operator. Specifically, for example, the plurality of operating members may include a boom operating member 19a, an arm operating member 20a, a bucket operating member (not shown), a slewing operating member (not shown), and a travel operating member (not shown). Each of the plurality of operating members may be an operating lever or an operating pedal.

[0037] The boom operating member 19a receives boom lowering and boom raising operations by the operator. The boom lowering operation is an operation to cause the boom 6 to perform a boom lowering movement, and the boom raising operation is an operation to cause the boom 6 to perform a boom raising movement. The arm operating member 20a receives arm pushing and arm pulling operations by the operator. The arm pushing operation is an operation to cause the arm 7 to perform an arm pushing movement, and the arm pulling operation is an operation to cause the arm 7 to perform an arm pulling movement. The bucket operating member receives bucket soil removal operations (bucket pushing operation) and bucket excavation operations (bucket pulling operation) by the operator. The bucket soil removal operation is an operation to cause the bucket 8 to perform a bucket soil removal movement, and the bucket excavation operation is an operation to cause the bucket 8 to perform a bucket excavation movement. The slewing operating member receives right slewing and left slewing operations by the operator. The right turn operation is an operation to cause the upper rotating body 3 to perform a right turn, and the left turn operation is an operation to cause the upper rotating body 3 to perform a left turn. The travel operation member receives travel operations from an operator to move the lower traveling body 2.

[0038] The construction machine 1 is equipped with a plurality of operation sensors. The plurality of operation sensors may include a boom operation sensor, an arm operation sensor, a bucket operation sensor, a slewing operation sensor, and a travel operation sensor. The boom operation sensor detects the amount of boom lowering operation and boom raising operation received by the boom operating member 19a. The arm operation sensor detects the amount of arm pushing operation and arm pulling operation received by the arm operating member 20a. The bucket operation sensor detects the amount of bucket soil removal operation and bucket excavation operation received by the bucket operating member. The slewing operation sensor detects the amount of right slewing operation and left slewing operation received by the slewing operating member. The travel operation sensor detects the amount of travel operation received by the travel operating member. Each of the plurality of operation sensors inputs its detection result to the controller 70.

[0039] The construction machine 1 may be equipped with a remote control valve that outputs pilot pressure (secondary pressure) corresponding to the amount of operation received by the operating device. In this case, each of the multiple operation detectors may be a pressure sensor that detects the pilot pressure corresponding to the amount of operation. Specifically, as shown in Figure 2, the construction machine 1 may be equipped with a remote control valve 19 that outputs pilot pressure corresponding to the amount of operation received by the boom operating member 19a, and a remote control valve 20 that outputs pilot pressure corresponding to the amount of operation received by the arm operating 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 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 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 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 arm pulling operation.

[0040] Although not shown in the diagram, the bucket operation detector may include a pressure sensor that detects the pilot pressure output from the remote control valve according to the amount of operation of the bucket excavation operation, and a pressure sensor that detects the pilot pressure output from the remote control valve according to the amount of operation 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 according to the amount of operation of the right swing operation, and a pressure sensor that detects the pilot pressure output from the remote control valve according to the amount of operation 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 according to the amount of operation of the travel operation.

[0041] Note that the construction machine 1 does not necessarily have to be equipped with a remote control valve. In this case, the plurality of operation detectors may be configured to each detect the amount of operation (for example, the operating angle of the operating lever) received by the plurality of operating members and to input the detection results to the controller 70.

[0042] The hydraulic pump 15 supplies hydraulic fluid to the plurality of hydraulic actuators. The hydraulic pump may include only one hydraulic pump, or it may include multiple hydraulic pumps (for example, two hydraulic pumps). The hydraulic pump 15 discharges hydraulic fluid when driven by the engine 5.

[0043] In this embodiment, the hydraulic pump 15 is a variable displacement hydraulic pump. The construction machine 1 is equipped with a regulator R1 for changing the pump capacity q of the hydraulic pump 15. The pump capacity q of the hydraulic pump 15 is adjusted to a size corresponding to the pump capacity command input from the controller 70 to the regulator R1. If the construction machine 1 is equipped with a pump system that includes multiple hydraulic pumps 15, the pump capacity q of the pump system may be the sum of the pump capacities of the multiple hydraulic pumps 15. Furthermore, the pump flow rate Q of the hydraulic fluid discharged from the hydraulic pump 15 is calculated from the product of the pump capacity q and the pump rotation speed of the hydraulic pump 15 (i.e., engine rotation speed Ne) (Q = q × Ne), or by multiplying the said product by a predetermined coefficient. If the construction machine 1 is equipped with a pump system that includes multiple hydraulic pumps 15, the pump flow rate Q of the pump system may be the sum of the flow rates of the hydraulic fluid discharged from the multiple hydraulic pumps 15.

[0044] The engine 5 is configured to change its rotational speed Ne in response to an engine rotational speed command from the controller 70. For example, the engine 5 may be configured to adjust in stages to a plurality of rotational speeds Ne in response to the engine rotational speed command. In this embodiment, the controller 70 is configured to control the engine rotational speed Ne to a predetermined plurality of levels, including a base rotational speed N1 and a specific rotational speed N2, which will be described later.

[0045] 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 hydraulic pump 15 and the boom cylinder 9 and switches the direction in which the hydraulic fluid discharged from the hydraulic pump 15 is supplied to the boom cylinder 9. The second directional control valve 18 is interposed between the hydraulic pump 15 and the arm cylinder 10 and switches the direction in which the hydraulic fluid discharged from the hydraulic pump 15 is supplied to the arm cylinder 10. Specifically, the first directional control valve 17 is connected to the hydraulic pump 15 via an oil passage y1, to the rod side chamber of the boom cylinder 9 via an oil passage y3, and 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 hydraulic pump 15 via an oil passage y2, to the rod side chamber of the arm cylinder 10 via an oil passage y5, and to the head side chamber of the arm cylinder 10 via an oil passage y6.

[0046] The first directional control valve 17 is configured to be switchable between a neutral position that shuts off the hydraulic pump 15 and tank T and the boom cylinder 9, a position that connects oil passage y1 and oil passage y3 and shuts off oil passage y4 and tank T (right position in Figure 2), and a position that connects oil passage y1 and oil passage y4 and connects oil passage y3 and tank T (left position in Figure 2). The first directional control valve 17 is switched by pilot pressure output from the remote control valve 19 in response to the operation received by the boom operating member 19a. The right position of the first directional control valve 17 may be configured to connect oil passage y4 and tank T.

[0047] The second directional control valve 18 is configured to be switchable between a neutral position that shuts off the hydraulic pump 15 and tank T and the arm cylinder 10, a position that connects oil passage y2 and oil passage y5 and connects oil passage y6 and tank T (right position in Figure 2), and a position that connects oil passage y2 and oil passage y6 and connects oil passage y5 and tank T (left position in Figure 2). The second directional control valve 18 is switched by pilot pressure output from the remote control valve 20 in response to an operation received by the arm operating member 20a.

[0048] The aforementioned plurality of directional control valves further include a directional control valve (not shown) that switches the direction in which the hydraulic fluid discharged from the hydraulic pump 15 is supplied to the bucket cylinder 11, a directional control valve 14 (see Figure 11) that switches the direction in which the hydraulic fluid discharged from the hydraulic pump 15 is supplied to the swing motor, and a directional control valve (not shown) that switches the direction in which the hydraulic fluid discharged from the hydraulic pump 15 is supplied to the travel motor. The structure and function of these directional control valves are the same as those of the first directional control valve 17 or the second directional control valve 18, so a detailed explanation is omitted.

[0049] The controller 70 has a computer including an arithmetic processing unit and memory. The controller 70 controls the operation of the construction machine 1 by having the arithmetic processing unit execute a program stored in memory. The controller 70 performs various controls, including, for example, controlling the rotational speed Ne of the engine 5 (engine speed control) and controlling the pump capacity q of the hydraulic pump 15 (pump capacity control). The engine speed control and pump capacity control will be described later.

[0050] Construction machine 1 performs various tasks at a work site in response to operations received by its operating device. These various tasks include predetermined heavy-load tasks and predetermined light-load tasks. The predetermined heavy-load tasks include at least one heavy-load task from among various heavy-load tasks with high loads. The predetermined light-load tasks include at least one light-load task from among various light-load tasks with low loads. In this embodiment, the predetermined heavy-load tasks include excavation work and lifting and rotating work, which will be described later, and the predetermined light-load tasks include soil removal work and return work, which will be described later. However, the predetermined heavy-load tasks in this disclosure are not limited to excavation work and lifting and rotating work, but may include other heavy-load tasks. Also, the predetermined light-load tasks in this disclosure are not limited to soil removal work and return work, but may include other light-load tasks.

[0051] Figure 3 is a time chart showing the operation patterns of each operating member during the excavation and loading work mainly performed by construction machine 1, and the control state of engine 5 corresponding to the above operation patterns. In Figure 3, the upper section shows the amount of operation of the boom operating member 19a, the arm operating member 20a, the bucket operating member, and the slewing operating member during the excavation and loading work. Note that "FULL" in Figure 3 indicates the maximum amount of operation of each operating member. In Figure 3, the lower section shows the PQ control determination for determining whether or not to activate the PQ control described later, the engine speed reduction possible operation determination for determining whether or not to reduce the engine speed Ne, and the engine speed Ne, respectively.

[0052] When construction machine 1 performs excavation and loading operations, which involve excavating soil and other materials from the ground with its bucket 8 and loading them onto a truck or other cargo bed, it repeatedly performs a series of operations: excavation, lifting and rotating, soil removal, and return to the starting position. In Figure 3, the time period from t1 to t2 is when excavation is performed, the time period from t2 to t3 is when lifting and rotating is performed, the time period from t3 to t4 is when soil removal is performed, and the time period from t4 to t5 is when return to the starting position is performed.

[0053] Excavation work is the process of excavating the target material, such as soil and sand, from the ground using the bucket 8. Figure 4 is a diagram illustrating the operation of the work device 4 during excavation work. When the construction machine 1 performs excavation work, the operating device receives arm pulling operations, boom raising operations, and bucket excavation operations (bucket pulling operations) from the operator. The arm 7 performs the arm pulling operation, the boom 6 performs the boom raising operation, and the bucket 8 performs the bucket excavation operation (bucket pulling operation). During excavation work, the bucket 8 is subjected to resistance from the soil placed in the ground, so the excavation operations performed by the operator during excavation work are usually heavy load operations.

[0054] The lifting and rotating operation is performed after the excavation work but before the soil removal work. The lifting and rotating operation involves raising the bucket 8 while rotating the upper rotating body 3 to move the bucket 8 directly above the soil removal destination, such as the bed of a truck. When the construction machine 1 performs the lifting and rotating operation, the control device simultaneously receives boom raising and rotating operations from the operator, with the boom 6 performing the boom raising operation and the upper rotating body 3 performing the rotating operation. In the lifting and rotating operation, the load becomes large because the boom 6 is rotated in a direction against gravity and the upper rotating body 3 is rotated. Therefore, the lifting and rotating operation performed by the operator during the lifting and rotating operation is usually a heavy load operation.

[0055] Soil removal is performed after the lifting and rotating operation. Soil removal involves removing the object held by the bucket 8 directly above the destination, such as the bed of a truck. When the construction machine 1 performs soil removal, the control device receives the bucket soil removal operation from the operator, and the bucket 8 performs the bucket soil removal operation (bucket pushing operation). During soil removal, the bucket 8 is positioned above the ground, and the upper rotating body 3 does not rotate. Therefore, the soil removal operation performed by the operator during soil removal is usually a light load operation.

[0056] The return operation is performed after the soil removal operation. The return operation is the process of returning construction machine 1 to the state it was in immediately before the excavation work. When construction machine 1 performs the return operation, the control device receives a rapid rotation operation by the operator in the first half of the return operation, which is a rotation operation that quickly rotates the upper slewing body 3, and simultaneously receives a boom lowering operation and an arm pushing operation in the second half of the return operation. In response to these operations, the upper slewing body 3 performs a rapid rotation movement toward the position where the excavation work will be performed, and then the boom 6 performs a boom lowering operation while the arm 7 performs an arm pushing operation. The rapid rotation movement of the upper slewing body 3 performed in the first half of the return operation is performed alone, so the workload is relatively small. Also, the boom lowering operation performed in the second half of the return operation is less of a workload because the weight of the boom 6 contributes to it, and the workload is essentially only from the arm pushing operation. Therefore, the return operation performed by the operator during the return operation is usually a light-load operation.

[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 plurality of operation detectors. The controller 70 may have pre-set heavy-load operations such as excavation and lifting / slewing, and pre-set light-load operations such as soil removal and return operations. In other words, the controller 70 may be configured to determine whether the operation performed by the operator is a heavy-load operation, i.e., whether it is an excavation operation or a lifting / slewing operation. The controller 70 may also be configured to determine whether the operation performed by the operator is a light-load operation, i.e., whether it is a soil removal operation or a return operation. In an excavation operation, the operating device receives arm pulling operation, boom raising operation, and bucket excavation operation. In a lifting / slewing operation, the operating device receives boom raising operation and slewing operation. In a soil removal operation, the operating device receives bucket soil removal operation. In a return operation, the operating device receives rapid slewing operation, boom lowering operation, and arm pushing operation. In other words, the detection results input to the controller 70 from the multiple operation detectors serve as an indicator for the controller 70 to determine the type of work.

[0058] [Engine speed control and pump capacity control] The following describes the control of the engine speed Ne of the engine 5 (engine speed control) and the control of the pump capacity q of the hydraulic pump 15 (pump capacity control) performed by the controller 70 during the excavation and loading operation.

[0059] The controller 70 performs engine speed control, which controls the engine speed Ne to a specific rotational speed N2 that is lower than the base rotational speed N1, which is the rotational speed when the predetermined conditions are not met, when predetermined conditions for determining whether or not to reduce the engine speed Ne during the operation of the construction machine 1 are met. The predetermined conditions include heavy load conditions for determining whether or not to reduce the engine speed Ne during predetermined heavy load operations, and light load conditions for determining whether or not to reduce the engine speed Ne during predetermined light load operations. Fuel efficiency can be improved by reducing the engine speed Ne during predetermined heavy load operations and predetermined light load operations during the operation of the construction machine 1.

[0060] Figure 5 is a flowchart showing an example of the calculation process performed by the controller 70 during excavation and loading operations. This flowchart is repeated during the operation of the construction machine 1.

[0061] The controller 70 acquires various information such as the amount of operation of various operating members and flag information for various judgments such as PQ control judgment described later (step S10). The amount of operation of the various operating members includes the amount of operation for boom lowering, boom raising, arm pulling, arm pushing, bucket soil removal, bucket excavation, right rotation, left rotation, and travel operation.

[0062] The above PQ control is a control that reduces the pump capacity q of the hydraulic pump 15 in accordance with the pump pressure Ppump of the hydraulic fluid discharged from the hydraulic pump 15 when the pump pressure Ppump exceeds a predetermined pressure Ps. When the pump pressure Ppump becomes high, the load on the engine 5 that drives the hydraulic pump 15 increases, and there is a risk that the engine 5 will stop (engine stall). In response to this, the controller 70 prevents engine stall by reducing the load on the engine 5 as the pump pressure Ppump increases in the region where the pump pressure Ppump is above the predetermined pressure Ps. On the other hand, in the region where the pump pressure Ppump is below the predetermined pressure Ps, the load on the engine 5 is relatively small, so the controller 70 suppresses a decrease in workability by controlling the pump capacity q to the maximum pump capacity qmax. The maximum pump capacity qmax is the maximum value of the pump capacity determined by the characteristics of the hydraulic pump 15 used.

[0063] Next, the controller 70 determines whether or not to reduce the engine speed Ne of the engine 5 based on the various information acquired in step S10 (step S20). In other words, it determines whether or not one of the predetermined heavy load conditions and light load conditions has been met. The specific method for determining whether or not one of the above heavy load conditions and light load conditions has been met will be described later. If the engine speed Ne is to be reduced (YES in step S20), the controller 70 controls the engine speed Ne to a specific rotational speed N2 that is lower than the base rotational speed N1 (step S30). The base rotational speed N1 is the rotational speed set when the engine speed Ne is not to be reduced. The specific rotational speed N2 is a rotational speed lower than the base rotational speed N1 that is set when the engine speed Ne is to be reduced. Next, the controller 70 executes control so that the speed of the hydraulic actuator does not decrease even when the engine speed Ne is reduced (step S40). The control so that the speed of the hydraulic actuator does not decrease will be described later. In step S20, if it is determined that the engine speed Ne should not be reduced (NO in step S20), the controller 70 controls the engine speed Ne to the base speed N1 (step S50).

[0064] The control modes of the controller 70 during excavation and loading operations will be described in detail below for each of the following operations: excavation, lifting and rotating, soil removal, and return.

[0065] [Excavation work] In excavation work, as described above, the main operation is the arm pulling operation, and the boom raising operation and bucket excavation operation are performed simultaneously (or nearly simultaneously) in conjunction with it. Therefore, the controller 70 determines that an excavation operation is occurring if the amount of arm pulling operation is equal to or greater than a predetermined amount, and the amount of bucket excavation operation is equal to or greater than a predetermined amount. The controller 70 also determines that an excavation operation is occurring if the amount of arm pulling operation is equal to or greater than a predetermined amount, and the amount of boom raising operation is equal to or greater than a predetermined amount. Specifically, the controller 70 determines whether or not an excavation operation is occurring by referring to a pre-stored correspondence table as shown in Figure 6.

[0066] In the correspondence table in Figure 6, the arm pulling operation determination is set to "ON" when the amount of arm pulling operation is equal to or greater than a predetermined amount. The bucket digging operation determination is set to "ON" when the amount of bucket digging operation is equal to or greater than a predetermined amount. The boom raising operation determination is set to "ON" when the amount of boom raising operation is equal to or greater than a predetermined amount. The controller 70 determines that an digging operation is taking place when both the arm pulling operation determination and the bucket digging operation determination are set to ON. The controller 70 also determines that an digging operation is taking place when both the arm pulling operation determination and the boom raising operation determination are set to ON. Note that the state in which the boom raising operation is performed simultaneously with the arm pulling operation, and the state in which the bucket digging operation is performed simultaneously with the arm pulling operation are examples of predetermined operation states in this disclosure.

[0067] During this excavation operation, the bucket 8 encounters excavation resistance from the soil, causing the pump pressure (Ppump) of the hydraulic pump 15 to increase. This creates a possibility of engine stall, hence the PQ control described above is implemented.

[0068] Whether or not the above PQ control is performed is determined by the smaller of the following two values: pump capacity q1, which is determined based on a map described later that is pre-set for PQ control, and pump capacity q2, which is determined based on a map described later that is pre-set for positive control control. Positive control control is a control method that increases the pump capacity q2 according to the amount of operation of the operating device.

[0069] Figure 7 is a map showing the relationship between pump pressure Ppump [Pa] and pump capacity q1, which is used to determine the pump capacity q1 for PQ control. As shown in Figure 7, when the pump pressure Ppump is below a predetermined pressure Ps, the pump capacity q1 becomes the maximum pump capacity qmax determined by the characteristics of the hydraulic pump 15. When the pump pressure Ppump exceeds the predetermined pressure Ps, the pump capacity q1 decreases as the pump pressure Ppump increases. In the region where the pump pressure Ppump exceeds the predetermined pressure Ps (the curved portion in Figure 7), the torque, which is the product of the pump pressure Ppump and the pump capacity q, remains constant. The controller 70 determines the pump capacity q1 for PQ control by applying the pump pressure Ppump to the map in Figure 7.

[0070] Figure 8 is a map showing the relationship between the operating amount L of an operating member and the pump capacity q2, which is used to determine the pump capacity q2 for positive control. The map in Figure 8 may be set for each of multiple operating members. As shown in Figure 8, in positive control, the pump capacity q2 increases as the operating amount L of the operating member increases. The controller 70 determines the pump capacity q2 by applying the operating amount of the operated operating member to the map in Figure 8.

[0071] The controller 70 selects the smaller of the determined pump capacities q1 and q2 (lower selection) and performs control using the selected pump capacity q. During excavation work, the pump pressure Ppump increases, so the pump capacity q1 decreases according to the relationship in Figure 7. Also, because the amount of operation of the operating member is large, the pump capacity q2 increases according to the relationship in Figure 8. As a result, during excavation work, the pump capacity q1 becomes smaller than the pump capacity q2, so PQ control is selected. At this time, the PQ control determination shown in Figure 6, which determines whether or not to perform PQ control, becomes "ON".

[0072] Here, if the PQ control is detected during excavation, the engine speed reduction operation detection (hereinafter referred to as the speed reduction operation detection) shown in Figure 6 becomes "ON". Specifically, if the arm pull operation detection is "ON", at least one of the bucket excavation operation detection and the boom lifting operation detection is "ON", and the PQ control is detected is "ON", then the speed reduction operation detection becomes "ON". The controller 70 performs engine speed control to reduce the engine speed Ne from the base speed N1 to a specific speed N2 that is lower than the base speed N1, provided that the speed reduction operation detection is detected during excavation. Fuel efficiency is improved by controlling the engine speed Ne to a specific speed N2 that is lower than the base speed N1. The reason why fuel efficiency is improved when the engine speed Ne is reduced is that as the engine speed Ne decreases, the engine 5 operates in a region with high torque and good fuel efficiency characteristics. In addition, fuel efficiency is also improved as the losses due to the rotation of auxiliary equipment decrease as the engine speed Ne decreases.

[0073] [Lifting and rotating operations] In lifting and slewing operations, the slewing operation of the upper slewing body 3 and the boom raising operation are performed simultaneously. The controller 70 determines that a lifting and slewing operation is being performed when, according to the correspondence table shown in Figure 9, the boom raising operation determination is "ON" and the slewing operation determination is "ON". In the correspondence table in Figure 9, the boom raising operation determination is "ON" when the amount of operation for the boom raising operation exceeds a predetermined amount, and the slewing operation determination is "ON" when the amount of operation for the left slewing operation or the right slewing operation exceeds a predetermined amount. Note that the state in which a slewing operation is performed to rotate the upper slewing body 3 simultaneously with the boom raising operation is an example of a predetermined operation state in this disclosure.

[0074] The lifting and slewing operation involves simultaneously raising the boom 6 and slewing the upper slewing body 3. Therefore, the lifting and slewing operations performed by the operator during this operation are heavy-load operations that result in high pump pressure (Ppump). Consequently, in the lifting and slewing operation, just like in the excavation operation, the pump capacity q1 determined for PQ control becomes smaller than the pump capacity q2 determined for positive control control. As a result, the PQ control corresponding to pump capacity q1 is selected. At this time, the PQ control detection shown in Figure 9 becomes "ON".

[0075] During a lift-and-slewing operation, if the PQ control is turned ON, the rotation reduction operation determination shown in Figure 9 becomes "ON". Specifically, if the boom lift operation determination is "ON", the slewing operation determination is "ON", and the PQ control determination is "ON", the rotation reduction operation determination becomes "ON". The controller 70, on the condition that the rotation reduction operation determination is turned ON during the lift-and-slewing operation, executes engine speed control to reduce the engine speed Ne from the base speed N1 to a specific speed N2. As a result, fuel efficiency is improved by controlling the engine speed Ne to a specific speed N2 that is lower than the base speed N1.

[0076] [Pump capacity control] Furthermore, during excavation and lifting / swinging operations, if the engine speed Ne decreases, the pump flow rate Q discharged from the hydraulic pump 15 may decrease. In this case, insufficient flow rate of hydraulic fluid supplied to the hydraulic actuator may cause a decrease in the workability of the hydraulic actuator. To address this, the controller 70 controls the pump capacity q of the hydraulic pump 15 to increase. Specifically, the controller 70 controls the pump capacity q of the hydraulic pump 15 to a size that ensures the pump flow rate Q of the hydraulic pump 15 when the engine speed Ne is the base speed N1. The control of the pump capacity q of the hydraulic pump 15 will be described below.

[0077] Figure 10 shows the switching operation of the rotation speed reduction operation determination when PQ control is turned ON during excavation work or lifting and rotating work (i.e., during a predetermined heavy load operation). In Figure 10, the solid line shows the operation of this embodiment, and the dashed line shows the operation when the engine speed Ne is not reduced, i.e., when the engine speed Ne is controlled to the base speed N1.

[0078] In Figure 10, the horizontal axis represents the pump pressure Ppump [Pa] of the hydraulic pump 15, and the pump pressure Ppump increases with heavy load operation. The PQ torque T_PQ is the load torque of the hydraulic pump 15 set when PQ control is executed. The PQ torque T_PQ is set to a value lower than the engine torque Te by a predetermined margin in order to prevent engine stall. When the pump pressure Ppump is less than the predetermined pressure Ps, the engine speed Ne is controlled to the base speed N1, and the pump capacity q is set to the maximum pump capacity qmax. In connection with this, when the pump pressure Ppump is less than the predetermined pressure Ps, the pump flow rate Q of the hydraulic pump 15 is calculated as the product of the maximum pump capacity qmax and the base speed N1 (Q = qmax × N1). Also, the PQ torque T_PQ becomes the first PQ torque T_PQ1 set at the base speed N1.

[0079] When the engine speed Ne is controlled to the base speed N1, the pump capacity q_N1 is determined by the following equation (1). Here, the pump capacity q cannot exceed the maximum pump capacity qmax determined by the characteristics of the hydraulic pump 15, so even if the pump capacity q calculated from equation (1) is greater than the maximum pump capacity qmax, it will be the maximum pump capacity qmax (a constant value). On the other hand, when the pump pressure Ppump exceeds a predetermined pressure Ps, the pump capacity q decreases according to equation (1).

[0080] q_N1=T_PQ1×(2π) / Ppump ···(1)

[0081] Furthermore, when the pump capacity q decreases to a predetermined first threshold q_c1, the rotational speed reduction operation determination is turned ON, and the engine speed Ne decreases to a specific rotational speed N2. Here, when the controller 70 reduces the engine speed Ne to a specific rotational speed N2, it increases the PQ torque T_PQ based on the following equation (2). In equation (2), T_PQ2 is the PQ torque T_PQ when the engine speed Ne is reduced to a specific rotational speed N2, i.e., the second PQ torque T_PQ2 after the torque increase. Equation (2) is used in the region where the pump pressure Ppump in Figure 10 is above a predetermined second threshold P1. The second threshold P1 is set to the value at which the pump capacity q becomes the maximum pump capacity qmax when the engine speed Ne is reduced to a specific rotational speed N2 and the PQ torque T_PQ becomes the second PQ torque T_PQ2.

[0082] T_PQ2=(N1 / N2)×T_PQ1 ···(2)

[0083] Here, the output of the hydraulic pump 15 is the product of the rotational speed of the hydraulic pump 15, i.e., the engine rotational speed Ne, and the torque T_PQ (output = Ne × T_PQ). Therefore, the pump output Po_N1 [kW] before the decrease in engine rotational speed Ne is calculated from equation (3) below. The pump output Po_N2 after the decrease in engine rotational speed Ne is calculated from equation (4) below.

[0084] Po_N1 = N1 × T_PQ1 ... (3) Po_N2=N2×T_PQ2=N2×(N1 / N2)×T_PQ1=N1×T_PQ1 ···(4)

[0085] From equation (4), if the PQ torque T_PQ is increased after the engine speed Ne decreases as in equation (2), the pump output Po will be the same before and after the decrease in engine speed Ne. That is, the second PQ torque T_PQ2 is the torque that ensures the output of the hydraulic pump 15 even when the engine speed Ne decreases to a specific speed N2. If the pump output Po is the same, the relationship in equation (5) below holds, so if the pump pressure Ppump is the same (i.e., the load on the hydraulic actuator is the same), the pump flow rate Q will also be the same. As a result, the pump flow rate Q does not change before and after the decrease in engine speed Ne, so the operating speed of the hydraulic actuator does not decrease, and the same level of workability (working speed) as when the engine speed Ne is not decreased can be obtained.

[0086] Po = Pump × Q ···(5)

[0087] Specifically, as shown in Figure 10, when the pump capacity q decreases to the first threshold q_c1, the engine speed Ne decreases to a specific speed N2, while the PQ torque T_PQ increases to the second PQ torque T_PQ2. As a result, even after the engine speed Ne decreases, the pump flow rate Q of the hydraulic pump 15 becomes the same as the pump flow rate Q when the engine speed Ne is not reduced (shown by the dashed line), and the same level of workability (working speed) as when the engine speed Ne is not reduced is obtained.

[0088] Equation (6) below shows the relationship between pump capacity q_N2 after a decrease in engine speed Ne. Furthermore, under the same conditions for pump pressure Ppump, the relationship between pump capacity q_N1 when engine speed Ne is the base speed N1 and pump capacity q_N2 when engine speed Ne is a specific speed N2 is as shown in equation (7) below, and the pump capacity q increases as engine speed Ne decreases.

[0089] q_N2 = T_PQ2 × (2π) / P ... (6) q_N2 = q_N1 × (N1 / N2) ... (7)

[0090] Here, the pump flow rate Q of the hydraulic pump 15 is determined by the product of the engine speed Ne and the pump capacity q. Therefore, the pump flow rate Q1 before the decrease in engine speed Ne is calculated from equation (8) below. Also, the pump flow rate Q2 after the decrease in engine speed Ne is calculated from equation (9) below. From equations (8) and (9), the pump flow rate Q2 after the engine speed Ne is reduced to a specific speed N2 is equal to the pump flow rate Q1 before the decrease in engine speed Ne.

[0091] Q1 = q_N1 × N1 ... (8) Q2=q_N2×N2=q_N1×(N1 / N2)×N2=q_N1×N1 ···(9)

[0092] The above relationship holds true in the region where the pump pressure Ppump is equal to or greater than the second threshold P1. In the region where the pump pressure Ppumu is less than the second threshold P1, the pump capacity q cannot be made greater than or equal to the maximum pump capacity qmax, and therefore the torque increase shown in equation (2) is not possible. In other words, the torque increase shown in equation (2) becomes possible when the pump pressure Ppump becomes equal to or greater than the second threshold P1. Therefore, as shown in Figure 10, when the pump pressure Ppump becomes equal to or greater than the second threshold P1, the controller 70 switches the rotation reduction operation judgment ON, reduces the engine speed Ne from the base speed N1 to a specific speed N2, and increases the PQ torque T_PQ from the first PQ torque T_PQ1 to the second PQ torque T_PQ2. Thus, when the construction machine 1 is performing an excavation operation or a lifting and rotating operation, and PQ control is being executed, and the pump pressure Ppump of the hydraulic pump 15 becomes equal to or greater than the second threshold P1, the rotation reduction operation judgment is turned ON, i.e., the heavy load condition is met.

[0093] Furthermore, if the pump capacity q falls below the first threshold q_c1, the controller 70 may switch the rotation reduction operation determination ON, reduce the engine speed Ne from the base speed N1 to a specific speed N2, and increase the PQ torque T_PQ from the first PQ torque T_PQ1 to the second PQ torque T_PQ2. In other words, when the construction machine 1 is performing an excavation operation or a lifting and rotating operation, and PQ control is being executed, if the pump capacity q of the hydraulic pump 15 falls below the first threshold q_c1, the rotation reduction operation determination is turned ON, meaning the heavy load condition is met.

[0094] The first threshold q_c1 is calculated from equations (10) to (12) below. That is, the relationship shown in equation (11) from equation (10) holds. Furthermore, since the relationship in equation (12) holds, the first threshold q_c1 can be calculated by applying the relationship in equation (11) to equation (12). Therefore, when the pump capacity q falls below the first threshold q_c1 calculated from equation (12), the controller 70 switches the rotation reduction operation judgment ON.

[0095] qmax=T_PQ2×(2π) / P1 ···(10) P1=T_PQ2×(2π) / qmax=(N1 / N2)×T_PQ1×(2π) / qmax (11) q_c1=T_PQ1×(2π) / P1=(N2 / N1)×qmax ···(12)

[0096] As described above, when PQ control is selected during a specified heavy load operation (excavation operation, lifting and rotating operation), if the pump capacity q is less than or equal to the first threshold q_c1, or if the pump pressure Ppump is greater than or equal to the second threshold P1, the engine speed Ne is reduced from the base speed N1 to a specific speed N2, and the PQ torque T_PQ is increased, thereby increasing the pump capacity q, and the pump flow rate Q becomes the same before and after the reduction in engine speed Ne. As a result, fuel efficiency is improved by reducing the engine speed Ne, and the same working speed as before is obtained by increasing the pump capacity q. In addition, the pump efficiency of the hydraulic pump 15 is improved by increasing the pump capacity q.

[0097] Furthermore, in order to prevent frequent switching of the rotation speed reduction operation judgment when the pump pressure Ppump fluctuates near the second threshold P1, or when the pump capacity q fluctuates near the first threshold q_c1, vibration prevention measures may be taken, such as by applying hysteresis to the rotation speed reduction operation judgment.

[0098] [Soil removal work] Since the soil removal operation is performed with a relatively low pump pressure, the soil removal operation performed by the operator during the operation is a light-load operation. The controller 70 can determine that a soil removal operation is occurring if the amount of soil removal operation exceeds a predetermined amount. At this time, the pump capacity q1 determined for PQ control becomes larger than the pump capacity q2 determined for positive control control, so the pump capacity q2 is selected (lower selection) and positive control control is performed.

[0099] If a soil removal operation is detected, the rotation speed reduction operation detection is turned OFF. During soil removal operations, it is necessary to operate the bucket cylinder 11 quickly and to ensure the flow rate of hydraulic fluid supplied to the bucket cylinder 11. In such cases, the engine speed Ne is controlled to the base speed N1, that is, the operating speed of the bucket cylinder 11 is ensured by not reducing the engine speed Ne.

[0100] [Recovery process] In the return operation, the upper slewing body 3 is rapidly rotated in the first half, and the boom lowering operation and arm pushing operation are performed simultaneously in the second half. The controller 70 may determine that the upper slewing body 3 has rapidly rotated if the relief cutoff control described later is performed. During the return operation, the pump pressure Ppump does not become high, and the return operation performed by the operator during the return operation is a light load operation. Therefore, even during the return operation, the pump capacity q2 is selected (low selection) and positive control control is performed.

[0101] The rapid rotation operation, which is performed in the first half of the return operation to quickly rotate the upper rotating body 3, will now be described. Even when a rapid rotation operation is performed, the rotation motor 22 (see Figure 11) does not accelerate immediately due to its large inertia, and the speed of the rotation motor 22 gradually increases over time. Accordingly, the flow rate of the hydraulic fluid supplied to the rotation motor 22 also gradually increases. On the other hand, in positive control, the pump flow rate Q increases rapidly with the rapid operation of the rotation operating member, so the pump flow rate Q becomes larger than the flow rate required for the rotation motor 22, resulting in a surplus of hydraulic fluid. This surplus is discharged into the tank via the relief valve 24 (see Figure 11).

[0102] Figure 11 is a simplified hydraulic circuit diagram showing the path through which the hydraulic fluid discharged from the hydraulic pump 15 is supplied to the swing motor 22. As shown in Figure 11, a relief valve 24 is connected to the oil passage connecting the hydraulic pump 15 and a directional control valve 14 that switches the direction of the hydraulic fluid supplied to the swing motor 22. Any excess hydraulic fluid is discharged to the tank via the relief valve 24. Since this excess fluid is wasted, it is preferable for the controller 70 to perform relief cutoff control to reduce the excess fluid. Relief cutoff control estimates the motor flow rate Qmotor of the hydraulic fluid required for the swing motor 22 from the rotational speed of the swing motor 22, and adjusts the pump flow rate Q so that the minimum amount of hydraulic fluid is discharged from the relief valve 24 while ensuring the estimated motor flow rate Qmotor.

[0103] Figure 12 is a time chart showing the changes in pump flow rate Q and motor flow rate Qmotor when the upper slewing body 3 is rapidly rotated. When the slewing control member is rapidly rotated at time t1, the pump flow rate Q increases from time t1 onward. In Figure 12, the solid line shows the pump flow rate Q1 when relief cutoff control is not performed, and the dashed line shows the pump flow rate Q2 when relief cutoff control is performed. The dashed line shows the motor flow rate Qmotor of the slewing motor 22 required to rotate the upper slewing body 3.

[0104] In Figure 12, when relief cutoff control is not performed, the pump flow rate Q1 increases rapidly, as shown by the solid line, and the difference with the motor flow rate Qmotor becomes large. This difference becomes the excess hydraulic fluid. On the other hand, when relief cutoff control is performed, as shown by the dashed line, the pump flow rate Q2 increases in accordance with the increase in the motor flow rate Qmotor, thus reducing the excess hydraulic fluid. Also, when relief cutoff control is performed, as shown in Figure 12, the pump flow rate is low in the initial and middle stages of the turning operation, so the required horsepower (output) is also small. For this reason, in this embodiment, rapid turning operations are classified as light-load operations.

[0105] The controller 70 determines that a swing operation is being performed if the relief cutoff control determination is "ON" in the correspondence table shown in Figure 13. The relief cutoff control determination shown in Figure 13 is "ON" if, for example, the sum of the flow rate calculated from the rotational speed of the swing motor 22 and the preset additional flow rate is smaller than the pump flow rate Q calculated in positive control control. Also, the relief cutoff control capacity setting value or less determination shown in Figure 13 is "ON" if, for example, the pump capacity q is less than or equal to the preset third threshold q3. Alternatively, the relief cutoff control capacity setting value or less determination may be "ON" if the swing speed of the swing motor 22 is less than or equal to the preset fourth threshold V4. Both the third threshold q3 and the fourth threshold V4 are set to values ​​that ensure the pump flow rate Q even if the engine speed Ne decreases. In other words, the relief cutoff control capacity setting value or less determination is "ON" if the pump flow rate Q is ensured even if the engine speed Ne decreases. When both the relief cutoff control determination and the determination below the relief cutoff control capacity setting value are ON, the engine speed Ne can be reduced, and the rotation speed reduction operation determination in Figure 13 becomes "ON". When the rotation speed reduction operation determination in Figure 13 becomes ON, the controller 70 reduces the engine speed Ne to a specific rotation speed N2. As a result, the fuel efficiency of the engine 5 is improved. The light load condition is met when the upper slewing body 3 is rapidly rotated and the pump capacity q is below the third threshold q3, or when the rapid rotation is performed and the rotation speed of the upper slewing body 3 is below the fourth threshold V4.

[0106] Furthermore, during turning operations, as shown in the time chart of Figure 14, the controller 70 may increase the pump capacity q by the amount of the decrease in engine speed Ne. When the rotation speed reduction operation judgment is turned ON at time t1 in Figure 14 and the engine speed Ne decreases, the pump capacity q is increased by the amount of the decrease in engine speed Ne, as shown by the solid line. The pump capacity q shown by the dashed line corresponds to the pump capacity q when the engine speed Ne is controlled at the base rotation speed N1. The amount of increase in pump capacity q when the engine speed Ne is reduced is set so that the pump flow rate Q is maintained when the engine speed Ne is controlled at the base rotation speed N1. As a result, the pump flow rate Q when the engine speed Ne shown by the solid line in Figure 14 is reduced to a specific rotation speed N2 becomes equal to the pump flow rate Q when the engine speed Ne is controlled at the base rotation speed N1, as shown by the dashed line. As a result, the turning acceleration performance during turning becomes the same as when the engine speed Ne is controlled at the base rotation speed N1.

[0107] In the time chart of Figure 14, the engine speed Ne and pump capacity q changed abruptly at time t1 and t2, respectively. However, the engine speed Ne and pump capacity q may be changed more gradually. Furthermore, control to increase the pump capacity q is not necessarily required. As long as hydraulic fluid is discharged from the relief valve 24, the hydraulic pressure of the hydraulic fluid supplied to the swing motor 22 will be the relief pressure defined by the relief valve 24, and the swing acceleration will hardly change.

[0108] Next, the operation of the second half of the recovery operation will be explained. In the second half of the recovery operation, the boom lowering operation and the arm pushing operation are performed simultaneously. The controller 70 determines whether or not to reduce the engine speed Ne by referring to the correspondence table shown in Figure 15, for example. In Figure 15, the boom lowering operation determination is turned "ON" when the amount of operation of the boom operating member 19a exceeds a predetermined amount. Also, the rotation reduction operation determination shown in Figure 15 is turned "ON" when the boom lowering operation determination is turned ON. When the rotation reduction operation determination is turned ON in Figure 15, the controller 70 reduces the engine speed Ne. Note that the light load condition is met when the boom lowering operation is performed.

[0109] During boom lowering, the boom 6 lowers under its own weight, so the boom lowering speed can be maintained even if the discharge volume (flow rate) of hydraulic fluid from the hydraulic pump 15 is low. In other words, during boom lowering operations, the boom lowering speed of the boom 6 can be maintained even if the engine speed Ne is reduced. Therefore, the controller 70 can improve fuel efficiency by reducing the engine speed Ne during boom lowering operations while maintaining the same level of workability as when the engine speed Ne is not reduced.

[0110] Here, during the return operation, the boom lowering operation and the arm pushing operation are performed simultaneously, so hydraulic fluid is required for the arm cylinder 10. In contrast, in the construction machine 1 of this embodiment, regenerative control is performed so that the hydraulic fluid discharged from the boom cylinder 9 when the boom is lowered is supplied to the arm cylinder 10, so the pump flow rate Q of the hydraulic pump 15 can be kept low. Specifically, as shown in the hydraulic circuit 12 of Figure 2, when the boom is lowered, the hydraulic fluid discharged from the boom cylinder 9 is supplied to the arm cylinder 10 via the oil passage y7, the switching valve 26, and the oil passage y5. Therefore, even if the engine speed Ne is reduced, there will be no shortage of hydraulic fluid.

[0111] As described above, during excavation and loading operations, fuel efficiency is improved by reducing the engine speed Ne during bucket excavation and lifting / swinging operations, which are predetermined heavy load operations, and work efficiency is ensured by increasing the pump capacity q of the hydraulic pump 15. Also, during return operations, which are predetermined light load operations, fuel efficiency is improved by reducing the engine speed Ne, and work efficiency is ensured by increasing the pump capacity q as needed.

[0112] Furthermore, the controller 70 may perform control that prevents a decrease in engine speed Ne, even during bucket digging operations, lifting and slewing operations, and return operations, under the following predetermined conditions. Examples of these predetermined conditions include when the engine ECU controlling the engine 5 is performing abnormal processing on the engine 5, when conditions that reduce the output of the engine 5, such as high altitude, are met, when the oil temperature of the hydraulic fluid supplied to each cylinder is above a predetermined fifth threshold, and when the water temperature of the cooling water of the construction machine 1 is above a predetermined sixth threshold. In these cases, preventing a decrease in engine speed Ne can reduce the possibility of engine stall or overheating. Additionally, the predetermined conditions may include when an operation requiring a large flow rate is performed on a specific cylinder, when an operation that requires precise operation of the construction machine 1 is performed, and when a mode for precise operation of the construction machine 1 is selected. In these cases as well, preventing a decrease in engine speed Ne can reduce the possibility of a decrease in the operational accuracy of the construction machine 1 due to changes in engine speed Ne.

[0113] [Second Embodiment] Figure 16 shows the switching operation of the rotation reduction operation determination when PQ control is turned ON during excavation work and lifting and rotating work, corresponding to the second embodiment of the present disclosure. In this embodiment, the controller 70 continuously (for example linearly) reduces the engine speed Ne from the base speed N1 to a specific speed N2 when the pump pressure Ppump is between a predetermined pressure Ps and a second threshold P1, and continuously (for example linearly) increases the PQ torque T_PQ from the first PQ torque T_PQ1 to the second PQ torque T_PQ2.

[0114] The pump output Po of the hydraulic pump 15 is calculated as the product of the pump speed (i.e., engine speed Ne) and the PQ torque T_PQ. Therefore, even if the engine speed Ne is continuously decreased and the PQ torque T_PQ is continuously increased between a predetermined pressure Ps and a second threshold P1, the product remains constant, and the pump output Po does not change between the predetermined pressure Ps and the second threshold P1. As a result, the pump flow rate Q is ensured, the operating speed of each cylinder does not change, and the same level of workability as before the engine speed Ne was reduced is obtained. Furthermore, in this embodiment, since the engine speed Ne is continuously decreased, the amount of reduction in engine speed Ne is greater than when the engine speed Ne is reduced in steps, resulting in a higher fuel efficiency improvement effect than in the first embodiment described above.

[0115] [Third Embodiment] In the above-described embodiment, the engine speed Ne was controlled to the same specific speed N2 during both predetermined heavy-load and light-load operations. In contrast, in this embodiment, the controller 70 controls the engine speed Ne to different speeds during heavy-load and light-load operations.

[0116] Figure 17 shows the relationship between engine torque Te and PQ torque T_PQ. The PQ torque T_PQ, which is set during PQ control, is set to a lower value than the engine torque Te in order to prevent engine stall due to excessive load on the engine 5. Furthermore, as mentioned above, when the engine speed Ne is reduced to a specific speed N2 during heavy load operation, the PQ torque T_PQ2 is set to a higher value than the PQ torque T_PQ1 before the engine speed reduction.

[0117] Here, if the torque characteristic of engine 5 is torque Te_A, shown by the solid line in Figure 17, then even if the engine speed Ne is reduced to a specific speed N2, the difference between torque Te_A and the second PQ torque T_PQ2, i.e., the margin torque, is large, so engine stall can be prevented. On the other hand, if the torque characteristic of engine 5 is torque Te_B, shown by the dashed line in Figure 17, then when the engine speed Ne is reduced to a specific speed N2, the margin torque, which is the difference between torque Te_B and the second PQ torque T_PQ2, becomes smaller. In this case, when the load on engine 5 increases, engine stall may occur.

[0118] In contrast, in this embodiment, as shown in Figure 18, the controller 70 controls the engine speed Ne when heavy load conditions are met to a heavy load specific rotation speed N3 that is higher than the specific rotation speed N2. The heavy load specific rotation speed N3 is lower than the base rotation speed N1. In this third embodiment, the engine speed Ne when light load conditions are met is controlled to a light load specific rotation speed N2. This light load specific rotation speed N2 may be the same value as the specific rotation speed N2 in the first embodiment. In this third embodiment, as shown in Figure 17, the PQ torque T_PQ becomes the third PQ torque T_PQ3, which is lower than the second PQ torque T_PQ2, so engine stall can be suppressed even if the torque characteristic of the engine 5 is torque Te_B.

[0119] [Differentiation] In the above embodiment, positive control was performed during light-load operations such as soil removal and return operations, but this disclosure is not limited thereto. For example, during light-load operations, control other than PQ control, such as load sensing control or negative control, may be performed.

[0120] In the first embodiment described above, the controller 70 changed the engine speed Ne in steps from the base speed N1 to a specific speed N2. However, in order to suppress the discomfort such as auditory disturbance caused by rapid fluctuations in the engine speed Ne, rate limiter processing may be performed to limit the amount of change in the engine speed Ne per unit time. This suppresses rapid fluctuations in the engine speed Ne and improves the discomfort such as auditory disturbance.

[0121] In the above embodiment, positive control and PQ control are selected as the lower priority, but instead of positive control, for example, load sensing control or negative control may be used.

[0122] In the above embodiment, the construction machine control device is provided on the construction machine 1, but the construction machine control device in this disclosure does not necessarily have to be provided on the construction machine and may be located at a location away from the construction machine. In this case, the construction machine control device and the construction machine are configured to be able to send and receive information via a network such as the Internet or a mobile phone network. [Explanation of symbols]

[0123] 1: Construction machinery 3: Upper rotating body 5: Engine 6: Boom 7: Arm 8: Bucket 9: Boom cylinder (first hydraulic actuator, hydraulic actuator) 10: Arm cylinder (second hydraulic actuator, hydraulic actuator) 11: Bucket cylinder (third hydraulic actuator, hydraulic actuator) 15: Hydraulic pump 22: Swivel motor (4th hydraulic actuator, hydraulic actuator) 70: Controller

Claims

1. A construction machine control device for a construction machine comprising an engine, a variable displacement hydraulic pump driven by the engine, and at least one hydraulic actuator that is operated by the supply of hydraulic fluid discharged from the hydraulic pump, The system includes a controller that controls the rotational speed of the engine and the pump capacity of the hydraulic pump, The controller, when a predetermined condition for determining whether or not to reduce the engine speed during the operation of the construction machine is met, controls the engine speed to a specific speed lower than the base speed, which is the speed when the predetermined condition is not met, and increases the pump capacity to a size that ensures the flow rate of the hydraulic pump when the engine speed is the base speed.

2. The construction machinery control device according to claim 1, wherein the predetermined conditions include a heavy load condition for determining whether or not to reduce the rotational speed of the engine during a predetermined heavy load operation, and a light load condition for determining whether or not to reduce the rotational speed of the engine during a predetermined light load operation.

3. The heavy load condition is met when PQ control is being executed, the pump capacity of the hydraulic pump is below a predetermined first threshold, and the construction machine is in a predetermined operating state, or when PQ control is being executed, the pump pressure of the hydraulic pump is above a predetermined second threshold, and the construction machine is in a predetermined operating state. When the heavy load condition is met, the controller controls the engine speed to the specified speed and increases the torque setting value for the PQ control to a second PQ control torque which is higher than the first PQ control torque when the engine speed is the base speed. The second PQ control torque is a torque that ensures the output of the hydraulic pump even when the engine speed decreases from the base speed to the specific speed. The construction machinery control device according to claim 2, wherein the PQ control is a control that reduces the pump capacity of the hydraulic pump in accordance with the pump pressure when the pump pressure of the hydraulic pump exceeds a predetermined pressure.

4. The aforementioned heavy load condition is met when PQ control is being executed and the construction machine is in a predetermined operating state. The aforementioned controller, When the heavy load condition is met, the engine speed is controlled to continuously decrease from the base speed to the specific speed until the pump capacity of the hydraulic pump decreases to a predetermined first threshold, The torque setting value of the PQ control is continuously increased to a second PQ control torque that is higher than the first PQ control torque controlled when the engine speed is the base speed. The second PQ control torque is a torque that ensures the output of the hydraulic pump even when the engine speed decreases from the base speed to the specific speed. The construction machinery control device according to claim 2, wherein the PQ control is a control that reduces the pump capacity of the hydraulic pump in accordance with the pump pressure when the pump pressure of the hydraulic pump exceeds a predetermined pressure.

5. The aforementioned construction machine is equipped with a work device mounted on the upper rotating body of the construction machine, The work apparatus includes a boom rotatably attached to the upper rotating body, an arm rotatably attached to the tip of the boom, and a bucket rotatably attached to the tip of the arm. The hydraulic actuator includes a first hydraulic actuator for rotating the boom, a second hydraulic actuator for rotating the arm, a third hydraulic actuator for rotating the bucket, and a fourth actuator for rotating the upper rotating body. The construction machinery control device according to claim 3 or 4, wherein the predetermined operating state is a state in which at least one of the boom raising operation and the bucket digging operation is performed simultaneously with the arm pulling operation.

6. The aforementioned construction machine is equipped with a work device mounted on the upper rotating body of the construction machine, The work apparatus includes a boom rotatably attached to the upper rotating body, an arm rotatably attached to the tip of the boom, and a bucket rotatably attached to the tip of the arm. The hydraulic actuator includes a first hydraulic actuator for rotating the boom, a second hydraulic actuator for rotating the arm, a third hydraulic actuator for rotating the bucket, and a fourth actuator for rotating the upper rotating body. The construction machinery control device according to claim 3 or 4, wherein the predetermined operating state is a state in which a boom raising operation and a slewing operation for slewing the upper slewing body are performed simultaneously.

7. The aforementioned construction machine is equipped with a work device mounted on the upper rotating body of the construction machine, The work apparatus includes a boom rotatably attached to the upper rotating body, an arm rotatably attached to the tip of the boom, and a bucket rotatably attached to the tip of the arm. The hydraulic actuator includes a first hydraulic actuator for rotating the boom, a second hydraulic actuator for rotating the arm, a third hydraulic actuator for rotating the bucket, and a fourth actuator for rotating the upper rotating body. The construction machinery control device according to claim 2, wherein the light load condition is met when a rapid turning operation is performed to rapidly turn the upper rotating body and the pump capacity of the hydraulic pump is less than or equal to a predetermined third threshold, or when the rapid turning operation is performed and the turning speed of the upper rotating body is less than or equal to a predetermined fourth threshold.

8. The aforementioned construction machine is equipped with a work device mounted on the upper rotating body of the construction machine, The work apparatus includes a boom rotatably attached to the upper rotating body, an arm rotatably attached to the tip of the boom, and a bucket rotatably attached to the tip of the arm. The hydraulic actuator includes a first hydraulic actuator for rotating the boom, a second hydraulic actuator for rotating the arm, a third hydraulic actuator for rotating the bucket, and a fourth actuator for rotating the upper rotating body. The construction machinery control device according to claim 2, wherein the aforementioned light load condition is met when the boom lowering operation is performed.

9. The construction machine control device according to claim 1, wherein the controller does not reduce the rotational speed of the engine even if the predetermined conditions are met when abnormal processing of the engine is being performed, when a condition for a decrease in the output of the engine is met, when the oil temperature of the hydraulic fluid supplied to the hydraulic actuator is above a predetermined fifth threshold, when the water temperature of the cooling water of the construction machine is above a predetermined sixth threshold, when an operation requiring a large flow rate is performed on the hydraulic actuator, when an operation for precise operation of the construction machine is performed, and when a mode for precise operation of the construction machine is selected.

10. A boom that is rotatably attached to the upper rotating body, An arm rotatably attached to the tip of the boom, A bucket is rotatably attached to the tip of the aforementioned arm, At least one hydraulic actuator for operating the boom, the arm, and the bucket, A hydraulic pump that supplies hydraulic fluid to the hydraulic actuator, A construction machine comprising the construction machine control device described in claim 1.

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