Work machine

Abstract

Provided is a work machine that improves the fuel economy of the work machine while suppressing reduction in productivity at a work site.　The work machine comprises: a work device that operates by a hydraulic actuator; a variable displacement hydraulic pump that supplies hydraulic oil to the hydraulic actuator; and a controller that controls pump output of the hydraulic pump. The work machine sequentially performs loading work on a first transport vehicle that stops at a loading site and a second transport vehicle that arrives at the loading site after the first transport vehicle. The controller predicts a predicted arrival time that is a time until the second transport vehicle arrives at the loading site during work on the first transport vehicle, and executes a pump output control process for reducing the pump output if the predicted arrival time is later than a predetermined target arrival time.

Description

Work machinery

[0001] The present invention relates to a work machine that performs work on a circulating transport vehicle.

[0002] Conventionally, there have been known construction machines (e.g., hydraulic excavators and wheel loaders) that perform work on transport vehicles (e.g., dump trucks) that circulate between loading and dumping sites. For construction machines used at such sites, there is a technique for switching to energy-saving operation by reducing the operating speed when the actual fuel consumption of the construction machine falls below a target fuel consumption (see, for example, Patent Document 1).

[0003] Patent No. 6872510

[0004] However, with the method of Patent Document 1, the operating speed of the work machine is reduced, which means that excavation and loading operations take longer, and transport vehicles end up lining up in front of the energy-saving operating work machine, resulting in a new problem of reduced productivity across the entire work site.

[0005] The present invention has been made in consideration of the above-described circumstances, and its object is to provide a technology for improving the fuel efficiency of a work machine that performs work on a circulating transport vehicle while suppressing a decrease in productivity at the work site.

[0006] In order to achieve the above object, the present invention provides a work machine that includes a work implement operated by a hydraulic actuator, a variable capacity hydraulic pump that supplies hydraulic oil to the hydraulic actuator, and a controller that controls the pump output of the hydraulic pump, and that sequentially loads a first transport vehicle parked at a loading point and a second transport vehicle that arrives at the loading point after the first transport vehicle.The controller is characterized in that, when working on the first transport vehicle, it predicts a predicted arrival time, which is the time it will take for the second transport vehicle to arrive at the loading point, and if the predicted arrival time is later than a predetermined target arrival time, it executes a pump output control process that reduces the pump output.

[0007] According to the present invention, in a work machine that performs work on a patrolling dump truck, it is possible to improve the fuel efficiency of the work machine while suppressing a decrease in productivity at the work site. Note that problems, configurations, and effects other than those described above will become clear from the description of the embodiment below.

[0008] It is a schematic diagram of a system according to the present embodiment. It is a side view of a hydraulic excavator. It is a diagram showing a drive circuit of a hydraulic excavator. It is a control block diagram of a hydraulic excavator. It is a flowchart of a pump output control process. It is a conceptual diagram for calculating a predicted arrival time. It is a table for determining a coefficient.

[0009] An embodiment of a system 100 according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of the system 100 according to this embodiment. The system 100 shown in FIG. 1 includes a plurality of dump trucks 101, 102, and 103 that patrol (return) between a loading site A and an earth dumping site B at a work site such as a mine. The system 100 also includes a hydraulic excavator 104 that loads earth (cargo) onto the bed of the dump truck 101 parked at the loading site A. The system 100 also includes a wheel loader 105 that transports the earth dumped by the dump truck 102 at the earth dumping site B to a predetermined position.

[0010] The loading site A and the dump site B are examples of destinations for the dump trucks 101 to 103. The dump trucks 101 to 103 are also examples of transport vehicles. The hydraulic excavator 104 and wheel loader 105 are also examples of work machines that perform work on the dump trucks 101 to 103. However, the number and types of destinations, transport vehicles, and work machines are not limited to the example in FIG. 1 .

[0011] Fig. 2 is a side view of the hydraulic excavator 104. As shown in Fig. 2, the hydraulic excavator 104 includes a lower traveling body 2 and an upper rotating body 3 supported by the lower traveling body 2. The lower traveling body 2 and the upper rotating body 3 are an example of a vehicle body.

[0012] The lower traveling body 2 is equipped with a pair of left and right crawlers 4, which are endless tracks. The pair of left and right crawlers 4 are rotated independently by driving a traveling motor 5. As a result, the hydraulic excavator 104 travels. However, the lower traveling body 2 may be of a wheeled type instead of the crawlers 4.

[0013] The upper rotating body 3 is supported on the lower traveling body 2 so as to be rotatable by a swing motor 6. That is, rotation of the swing motor 6 causes the upper rotating body 3 to swing relative to the lower traveling body 2. The upper rotating body 3 mainly includes a swing frame 7 serving as a base, a counterweight 9 disposed at the rear of the swing frame 7, a front working implement 10 attached to the front center of the swing frame 7 so as to be rotatable in the vertical direction, and a cab (driver's seat) 20 disposed on the front left side of the swing frame 7.

[0014] The front work implement 10 includes a boom 11 supported on the upper rotating body 3 so that it can be raised and lowered, an arm 12 supported at the tip of the boom 11 so that it can be rotated (crowd, dump), a bucket 13 (attachment) supported at the tip of the arm 12 so that it can be rotated (crowd, dump), a boom cylinder 14 that drives the boom 11, an arm cylinder 15 that drives the arm 12, and a bucket cylinder 16 that drives the bucket 13. Note that specific examples of the attachment are not limited to the bucket 13, and may include a grapple, cutter, crusher, breaker, etc. The counterweight 9 is a heavy object that has an arc shape when viewed from above and is used to balance the weight of the front work implement 10.

[0015] The cab 20 is disposed adjacent to the front working implement 10 in the left-right direction (the width direction of the vehicle body). More specifically, the cab 20 is disposed to the left of the front working implement 10 (on one side in the left-right direction). However, the location of the cab 20 is not limited to the example described above, and the cab 20 may be disposed on one side of the front working implement 10 in the left-right direction. Inside the cab 20, there are provided a seat on which an operator sits, an operating device 21 (see FIG. 4) that is operated by the operator seated in the seat, and a changeover switch 22 (see FIG. 4) that switches whether or not to execute the pump output control process described below.

[0016] The operation device 21 receives an operation from the operator to operate the hydraulic excavator 104, and outputs an operation signal corresponding to the received operation to the controller 50 (see FIG. 4 ). When the operator operates the operation device 21, the lower traveling body 2 travels, the upper rotating body 3 rotates, and the front working implement 10 operates. Specific examples of the operation device include a lever, a steering wheel, a pedal, a switch, etc.

[0017] The changeover switch 22 (switching operation device) receives an operator's operation to switch whether or not to execute the pump output control process (see FIG. 5 ), and outputs a switching signal corresponding to the received operation to the controller 50. The changeover switch 22 is configured to be switchable between an ON state indicating that the pump output control process is to be executed, and an OFF state indicating that the pump output control process is not to be executed. However, the changeover switch 22 is not limited to a physical switch, and may be in the form of an icon displayed on a display.

[0018] The lower traveling body 2, the upper revolving body 3, and the front working implement 10 are examples of working implements operated by hydraulic actuators (5, 6, 14-16). However, specific examples of working implements are not limited to the above-mentioned examples. That is, in the wheel loader 105, the vehicle body that is turned by a steering cylinder (hydraulic actuator), and the front working implement that is operated by a lift arm cylinder and a bucket cylinder (hydraulic actuator) are other examples of working implements.

[0019] Fig. 3 is a diagram showing a drive circuit of the hydraulic excavator 104. As shown in Fig. 3, the hydraulic excavator 104 mainly includes an engine 31, a hydraulic oil tank 32, a main pump 33 (hydraulic pump), a pilot pump 34, directional control valves 35, 36, 37, and 38, and pilot control valves 40a, 40b, 41a, 41b, 42a, 42b, 43a, and 43b.

[0020] The engine 31 is a prime mover that consumes fuel (e.g., diesel or gasoline) and generates driving force for driving the hydraulic excavator 104. The hydraulic oil tank 32 stores hydraulic oil. The main pump 33 is rotated by the driving force of the engine 31 and pressure-feeds the hydraulic oil stored in the hydraulic oil tank 32 to the hydraulic oil supply flow path L1. The main pump 33 is a variable displacement hydraulic pump whose pump displacement can be changed by a regulator (not shown) being controlled by the controller 50. The pilot pump 34 is rotated by the power of the engine 31 and pressure-feeds the hydraulic oil stored in the hydraulic oil tank 32 to the pilot supply flow path L3 as pilot pressure oil.

[0021] The hydraulic oil supply flow path L1 is a flow path for hydraulic oil that runs from the hydraulic oil tank 32 to the hydraulic actuators (6, 14-16) via the main pump 33 and the directional control valves 35-38. That is, the hydraulic oil supply flow path L1 supplies the hydraulic oil pressure-fed by the main pump 33 to the hydraulic actuators (6, 14-16). Note that the travel motor 5 is not shown in Figure 3.

[0022] The hydraulic actuators (6, 14-16) are connected to the hydraulic oil tank 32 through a hydraulic oil return flow path L2. The hydraulic oil return flow path L2 is a flow path that runs from the hydraulic actuators (6, 14-16) to the hydraulic oil tank 32 via the directional control valves 35-38. That is, the hydraulic oil return flow path L2 returns the hydraulic oil discharged from the hydraulic actuators (6, 14-16) to the hydraulic oil tank 32.

[0023] The pilot supply flow path L3 is a flow path for pilot pressure oil that runs from the hydraulic oil tank 32 via the pilot pump 34 and the pilot control valves 40a to 43b to the pilot ports 35a to 38b of the directional control valves 35 to 38. That is, the pilot supply flow path L3 supplies the pilot pressure oil pressure-fed by the pilot pump 34 to the pilot ports 35a to 38b.

[0024] Furthermore, the pilot ports 35a to 38b are connected to the hydraulic oil tank 32 through a pilot return flow path L4. The pilot return flow path L4 is a flow path that runs from the pilot ports 35a to 38b via the pilot control valves 40a to 43b to the hydraulic oil tank 32. In other words, the pilot return flow path L4 returns the pilot pressure oil discharged from the pilot ports 35a to 38b to the hydraulic oil tank 32.

[0025] The directional control valves 35 to 38 are disposed on the hydraulic oil supply passage L1 and the hydraulic oil return passage L2. The directional control valves 35 to 38 control the amount and direction of hydraulic oil supplied to the hydraulic actuators (6, 14 to 16) through the hydraulic oil supply passage L1, and the amount of hydraulic oil discharged from the hydraulic actuators (6, 14 to 16) through the hydraulic oil return passage L2.

[0026] More specifically, the directional control valve 35 controls the supply and discharge of hydraulic oil to the swing motor 6, the directional control valve 36 controls the supply and discharge of hydraulic oil to the boom cylinder 14, the directional control valve 37 controls the supply and discharge of hydraulic oil to the arm cylinder 15, and the directional control valve 38 controls the supply and discharge of hydraulic oil to the bucket cylinder 16.

[0027] The pilot control valves 40a to 43b are arranged on the pilot supply passage L3 and the pilot return passage L4. The pilot control valves 40a to 43b control the amount of hydraulic oil supplied to the pilot ports 35a to 38b through the pilot supply passage L3 and the amount of hydraulic oil discharged from the pilot ports 35a to 38b through the pilot return passage L4. The pilot control valves 40a to 43b are electromagnetic switching valves that control the amount of hydraulic oil supplied under the control of the controller 50.

[0028] The specific configuration of the drive circuit is not limited to the example shown in Fig. 3. As another example, the pilot pump 34 and the pilot control valves 40a to 43b may be omitted, and the directional control valves 35 to 38 may be electromagnetic changeover valves. The controller 50 may then output control signals to the directional control valves 35 to 38 to change the positions of the spools.

[0029] Fig. 4 is a control block diagram of the hydraulic excavator 104. As shown in Fig. 4, the hydraulic excavator 104 includes a controller 50 having a central processing unit (CPU) 51 and a memory 52. ​​The memory 52 is configured, for example, by a read-only memory (ROM), a random access memory (RAM), a hard disk drive (HDD), or a combination of these. The controller 50 realizes the processing described below by having the CPU 51 read and execute program code stored in the memory 52.

[0030] However, the specific configuration of the controller 50 is not limited to this, and may be realized by hardware such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array).

[0031] The hydraulic excavator 104 also includes a pressure sensor 53 and a communication I / F (Interface) 54. The pressure sensor 53 detects the pressure of the hydraulic oil (hereinafter referred to as "pump pressure P") output from the main pump 33 (in other words, passing through the hydraulic oil supply flow path L1), and outputs a pressure signal indicating the detected pump pressure P to the controller 50. The communication I / F 54 is a communication interface that transmits and receives data to and from external devices (e.g., dump trucks 101 to 103, server) via a communication network (e.g., the Internet, a mobile communication system, Wi-Fi (registered trademark)).

[0032] The controller 50 controls the overall operation of the hydraulic excavator 104. For example, the controller 50 rotates the engine 31, the main pump 33, and the pilot pump 34 and opens and closes (outputs control signals for) the pilot control valves 40a to 43b based on an operation signal output from the operation device 21. Furthermore, when the selector switch 22 is switched to the ON state, the controller 50 executes the pump output control process shown in FIG. 5 based on a pressure signal output from the pressure sensor 53 and information received from the dump trucks 101 to 103 via the communication I / F 54.

[0033] [Pump Output Control Process] Fig. 5 is a flowchart of the pump output control process. Fig. 6 is a conceptual diagram for calculating the predicted arrival time Te. Fig. 7 is a table for determining the coefficient K. As one example, the controller 50 may start the pump output control process shown in Fig. 5 at the timing when the dump truck 101 arrives at the loading site A. As another example, the controller 50 may start the pump output control process shown in Fig. 5 at the timing when information indicating that the dump truck 102 has departed from the discharge site B is received via the communication I / F 54.

[0034] At the work site shown in Figure 1, dump trucks 101 to 103 circulate between a loading site A and a dump site B according to a predetermined operation schedule. However, if the arrival of the dump trucks 101 to 103 at the loading site A or the dump site B is delayed for some reason, the hydraulic excavator 104 and the wheel loader 105 will have to wait. Meanwhile, the dump trucks 101 to 103 will try to make up for the delay in arrival time by increasing their travel speed. However, because the dump trucks 101 to 103 cannot exceed the speed limit set by the work site, the delay in arrival time will gradually be reduced in the process of traveling back and forth between the loading site A and the dump site B.

[0035] Therefore, the hydraulic excavator 104 executes the pump output control process to control the pump output of the main pump 33 in accordance with the degree of delay in the arrival of the dump truck 102 at the loading site A, thereby adjusting the speed at which earth and sand is loaded onto the dump truck 101. This reduces the waiting time of the hydraulic excavator 104, which is expected to have the effect of suppressing a decrease in productivity at the work site and improving the fuel efficiency of the hydraulic excavator 104.

[0036] Hereinafter, the pump output control process will be described assuming that the hydraulic excavator 104 is loading earth and sand onto the dump truck 101 parked at the loading site A, while the dump truck 102 that has departed from the soil discharge site B is moving (traveling) toward the loading site A. That is, the loading site A is an example of a destination, the dump truck 101 is an example of a first transport vehicle that is parked at the loading site A, the dump truck 102 is an example of a second transport vehicle that arrives at the loading site A after the dump truck 101, and the hydraulic excavator 104 is an example of a work machine that sequentially loads the dump trucks 101 and 102. However, the pump output control process can also be performed in a case where the soil discharge site B is the destination, the dump truck 103 is the first transport vehicle, the dump truck 101 is the second transport vehicle, and the wheel loader 105 is the work machine, and the pump output of the wheel loader 105 is controlled.

[0037] First, the controller 50 calculates a delay rate D of the dump truck 102 to the loading site A (S11). The delay rate D is the ratio (=Te / Tg) of the predicted arrival time Te to the target arrival time Tg. As shown in FIG. 6 , the target arrival time Tg is the time obtained by subtracting the current time tc from the target arrival time tg at which the dump truck 102 will arrive at the loading site A. The predicted arrival time Te is the time required for the dump truck 102 to arrive at the loading site A. The predicted arrival time Te is predicted by dividing the remaining distance L between the loading position Xg at the loading site A and the current position Xc of the dump truck 102 by the traveling speed V of the dump truck 102.

[0038] The controller 50 receives, for example, a current location Xc detected by a GPS (Global Positioning System) of the dump truck 102 and a traveling speed V detected by a speed sensor of the dump truck 102 from the dump truck 102 via the communication I / F 54 (or via a relay server not shown). On the other hand, the loading position Xg and the target arrival time tg may be set in advance in the controller 50, or may be received from a management server or the like via the communication I / F 54.

[0039] Next, the controller 50 determines a coefficient K (0<K≦1) according to the operation of the hydraulic excavator 104 (S12). The operation of the hydraulic excavator 104 includes, for example, an excavation operation for digging the ground, a loading operation for moving the excavated earth and sand above the dump truck 101, an earth-discharging operation for discharging the earth and sand in the bucket 13 onto the loading platform, and a return operation for returning the discharged bucket to the excavation position. The operation of the hydraulic excavator 104 can be specified by the amount of operation of the operating device 21, for example, as shown in FIG. 7 .

[0040] The load on the hydraulic excavator 104 (in other words, the pump pressure P) is in the order of excavation operation > loading operation > dumping operation > return operation. The coefficient K is set to a lower value as the load on the hydraulic excavator 104 (in other words, the pump pressure P) is higher. That is, K1 < K2 < K3 < K4. As one example, the controller 50 may determine the coefficient K in accordance with the operation specified by the operation signal output from the operation device 21. As another example, the controller 50 may determine the coefficient K in accordance with the pump pressure specified by the pressure signal output from the pressure sensor 53.

[0041] Next, the controller 50 corrects the pump output E0 corresponding to the amount of operation of the operating device 21 based on the delay rate D calculated in step S11 and the coefficient K determined in step S12 (S13). The controller 50 specifies the pump displacement C0 corresponding to the amount of operation of the operating device 21 according to a predetermined characteristic line (for example, a characteristic in which the pump pressure and the pump displacement are inversely proportional). The controller 50 then calculates the pump output E0 corresponding to the amount of operation of the operating device 21 by substituting the pump pressure P detected by the pressure sensor 53, the pump displacement C0 corresponding to the amount of operation of the operating device 21, and the rotation speed N0 of the engine 31 into the following equation 1: E0 = P × C0 × N0 (Equation 1)

[0042] Next, the controller 50 calculates the corrected pump output E1 by substituting the pump output E0, delay rate D, and coefficient K into the following equation 2. That is, the controller 50 increases the amount of reduction in the pump output (E0-E1) the higher the pressure of the hydraulic oil supplied from the main pump 33 to the hydraulic actuator. Also, the controller increases the amount of reduction in the pump output E (E0-E1) the longer the predicted arrival time Te is relative to the target arrival time Tg. E1 = E0 × K / D (Equation 2)

[0043] The controller 50 then controls at least one of the rotation speed N0 of the engine 31 and the pump capacity C0 of the main pump 33 so that the pump output becomes equal to the corrected pump output E1. On the other hand, when the selector switch 22 is in the OFF state, the controller 50 rotates the engine 31 at the rotation speed N0 and adjusts the pump capacity of the main pump 33 to C0 so that the pump output becomes equal to the pre-correction pump output E0.

[0044] As one example, the controller 50 may reduce the rotation speed of the engine 31 from the rotation speed N0 before correction to the rotation speed N1 after correction (Equation 3). As another example, the controller 50 may reduce the pump displacement of the main pump 33 from the pump displacement C0 before correction to the pump displacement C1 after correction (Equation 4). As yet another example, the controller 50 may correct both the rotation speed N0 of the engine 31 and the pump displacement C0 of the main pump 33 to achieve the corrected pump output E1. N1 = N0 × K / D (Equation 3) C1 = C0 × K / D (Equation 4)

[0045] Furthermore, the controller 50 controls the pilot control valves 40a to 43b in accordance with an operation signal output from the operation device 21. Therefore, assuming that the operation amount of the operation device 21 is the same, when the selector switch 22 is in the ON state, the operating speed of the hydraulic excavator 104 becomes slower than when the selector switch 22 is in the OFF state. Furthermore, the operating speed of the hydraulic excavator 104 becomes slower as the pump pressure P becomes larger (i.e., the coefficient K becomes smaller), and as the predicted arrival time Te is longer relative to the target arrival time Tg (i.e., the delay rate D becomes larger).

[0046] When the hydraulic excavator 104 is operated at the corrected pump output E1, the operator in the cab 20 may feel that the responsiveness (follow-up ability) of the hydraulic excavator 104 to the amount of operation of the operation device 21 has decreased. Therefore, the controller 50 may notify the operator that the hydraulic excavator 104 is being operated at the corrected pump output E1 through an alarm device (for example, a display or an LED lamp) provided in the cab 20.

[0047] Next, the controller 50 repeatedly executes the processing of steps S12 to S13 (i.e., corrects the pump output E0 in accordance with changes in the operation amount of the operation device 21) until the loading of earth and sand into the bed of the dump truck 101 is completed (S15: No). Furthermore, if a predetermined update period has elapsed before the loading of earth and sand is completed (S14: Yes), the controller 50 executes the processing of step S11 (i.e., recalculate the delay rate D).

[0048] In other words, the controller 50 fixes the delay rate D until the update period has elapsed (S14: No), updates the coefficient K according to the amount of operation of the operation device 21 (S12), and corrects the pump output E0 (S13). Furthermore, the controller 50 updates the delay rate D every time the update period has elapsed (S14: Yes), in other words, every time the dump truck 102 travels a predetermined distance (S11). Furthermore, the controller 50 repeatedly recalculates the delay rate D (in other words, predicts the predicted arrival time Te) until loading of earth and sand into the dump truck 101 is completed.

[0049] According to the above embodiment, when the arrival of the dump truck 102 at the loading site A is significantly delayed (the predicted arrival time Te is later than the target arrival time Tg), the pump output of the main pump 33 is reduced to slow down the working speed of the hydraulic excavator 104. This makes it possible to improve the fuel efficiency of the hydraulic excavator 104 while suppressing a decrease in productivity at the work site.

[0050] Furthermore, according to the above embodiment, the reduction amount (E0-E1) of the pump output E increases as the pump pressure P increases (in other words, the greater the fuel consumption of the work), thereby further improving the fuel efficiency of the hydraulic excavator 104. However, the processing of step S12 may be omitted, and the pump output E0 may be corrected based only on the delay rate D.

[0051] Furthermore, according to the above embodiment, by providing the changeover switch 22 that switches whether or not to execute the pump output control process, the operator in the cab 20 can select between improving fuel efficiency or maintaining responsiveness to the operation of the operating device 21. However, the changeover switch 22 may be omitted and the pump output control process may always be executed.

[0052] Furthermore, according to the above embodiment, by executing step S11 every time an update period elapses, it is possible to correct the pump output E0 based on the latest predicted arrival time Te of the dump truck 102 that is trying to make up for the delay in arrival time. Note that the update period is not limited to a fixed period, and may be an irregular period, such as when the traveling speed V of the dump truck 102 changes significantly. Furthermore, the processing of step S14 may be omitted, and the delay rate D may be calculated only once at any timing.

[0053] Furthermore, the applicability of the pump output control process is not limited to work machines that are operated by an operator in the cab 20 operating the operation device 21. As another example, the pump output control process can also be applied to work machines that are automatically operated according to a predetermined schedule. In this case, the pump output E0 is determined based on a predetermined schedule, instead of the amount of operation of the operation device 21, so that the loading of earth and sand will be completed in time for the departure time of the dump truck 101 from loading site A.

[0054] The above-described embodiments are merely illustrative examples of the present invention, and are not intended to limit the scope of the present invention to these embodiments. Those skilled in the art can implement the present invention in various other forms without departing from the spirit of the present invention.

[0055] DESCRIPTION OF SYMBOLS 2: Lower traveling body 3: Upper rotating body 4: Crawler 5: Travel motor 6: Swing motor 7: Swing frame 9: Counterweight 10: Front working implement 11: Boom 12: Arm 13: Bucket 14: Boom cylinder 15: Arm cylinder 16: Bucket cylinder 20: Cab 21: Operating device 22: Changeover switch 31: Engine 32: Hydraulic oil tank 33: Main pump (hydraulic pump) 34: Pilot pump 35: Directional switching valve 50: Controller 51: CPU 52: Memory 53: Pressure sensor 54: Communication I / F 100: System 101-103: Dump truck 104: Hydraulic excavator (working machine) 105: Wheel loader (working machine)

Claims

1. A work machine comprising: a work implement operated by a hydraulic actuator; a variable capacity hydraulic pump that supplies hydraulic oil to the hydraulic actuator; and a controller that controls the pump output of the hydraulic pump, which sequentially loads a first transport vehicle parked at a loading point and a second transport vehicle that arrives at the loading point after the first transport vehicle, wherein the controller, when working on the first transport vehicle, predicts a predicted arrival time, which is the time it will take for the second transport vehicle to arrive at the loading point, and executes pump output control processing to reduce the pump output if the predicted arrival time is later than a predetermined target arrival time.

2. A work machine according to claim 1, wherein the controller, in the pump output control process, increases the amount of reduction in the pump output the higher the pressure of the hydraulic oil supplied from the hydraulic pump to the hydraulic actuator.

3. A work machine according to claim 1, characterized in that the controller increases the amount of reduction in the pump output as the ratio of the predicted arrival time to the target arrival time increases.

4. A work machine according to claim 1, characterized in that it is provided with a changeover switch for switching whether or not the pump output control process is executed.

5. A work machine according to claim 1, wherein the controller acquires the current location and traveling speed of the second transport vehicle, and predicts the predicted arrival time by dividing the remaining distance from the current location to the loading site by the traveling speed.

6. A work machine according to claim 5, wherein the controller repeatedly predicts the predicted arrival time until work on the first transport vehicle is completed.

7. A work machine as claimed in claim 1, further comprising a prime mover that generates a driving force to rotate the hydraulic pump, and wherein the controller reduces the pump output by reducing at least one of the displacement of the hydraulic pump and the rotational speed of the prime mover.